CA1301396C - High green strength induction curable adhesives - Google Patents
High green strength induction curable adhesivesInfo
- Publication number
- CA1301396C CA1301396C CA000536251A CA536251A CA1301396C CA 1301396 C CA1301396 C CA 1301396C CA 000536251 A CA000536251 A CA 000536251A CA 536251 A CA536251 A CA 536251A CA 1301396 C CA1301396 C CA 1301396C
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- Prior art keywords
- curing agent
- component
- green strength
- adhesive composition
- induction
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
A new and improved one part, induction curable epoxy adhesive composition exhibiting storage stability at temperatures of a least 41°C for about two weeks, induction curable at temperatures of less than about 185°C in 6 seconds or less to a green strength of at least 200 psi, and exhibiting excellent full-cured physical and environmental properties is disclosed. The adhesive compositions are rendered induction curable by a combination curing agent comprising:
(i) a latent high temperature curing agent, such as dicyandiamide;
(ii) a latent intermediate temperature curing agent, such as HY940 or ANCAMINE ? 2041A; and (iii) a green strength enhancing agent comprising a finely divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl meth-acrylate), NYLON-12, hot melt polyester resins and mixtures of any of the foregoing resins.
The compositions are especially suited for fixturing oily galvanized metal parts in accordance with contemporary automobile manufacturing methods.
A new and improved one part, induction curable epoxy adhesive composition exhibiting storage stability at temperatures of a least 41°C for about two weeks, induction curable at temperatures of less than about 185°C in 6 seconds or less to a green strength of at least 200 psi, and exhibiting excellent full-cured physical and environmental properties is disclosed. The adhesive compositions are rendered induction curable by a combination curing agent comprising:
(i) a latent high temperature curing agent, such as dicyandiamide;
(ii) a latent intermediate temperature curing agent, such as HY940 or ANCAMINE ? 2041A; and (iii) a green strength enhancing agent comprising a finely divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl meth-acrylate), NYLON-12, hot melt polyester resins and mixtures of any of the foregoing resins.
The compositions are especially suited for fixturing oily galvanized metal parts in accordance with contemporary automobile manufacturing methods.
Description
3L~013~
30, 076 HIGH GREEN STRENGTH
.. . .. ..
INDUCTION CURABLE ADHESIVES
Background of the Invention , . .
The present invention relates to storage stable, one-part, epoxy adhesives that cure rapidly at elevated temperatures. More psrticularly, the invention relates to induction curable adhesives which develop minimum inter-mediate-cure or green strengths of 200 psi in six seconds or less upon induction heating to temperatures of 185Corles.s.
One part epoxy adhesive compositions containing at least one latent curing agent, alone or in comL~ination with a co-c~lring agent or cure accelerator, and containing other modifiers and/or fillers are known.
U.S. 2, 915, 490; U.S. 2, 986, 546; and U.S. 3, 098, 054 disclose the combination of epoxy, polyvinyl formai and fillers in adhesive compositions.
U.S. 3, 635, 87S discloses an adhesive composition c~ntaining epoxy resins derived from bisphenol-A, polyglycol diepoxide, dicyandiamide, silica and glycidoxypropyltri-methoxysilane.
U.S. 3, 639, 657 discloses the reaction product of phthalic anyhydride and diethylenetriamine. U.S. 3, 48~, 742 describes hardenable compositions comprising: a 1, 2-epoxy compound having a 1, 2-epoxy equivalency greater than 1; a curing agent comprising dicyandiamide and as a curing accelerator, the condensation product obtained by reacting equimolar proportions of phthalic anhydride and diethylene-triamine.
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Of particular interest are the disclosures of U.S.
4,2~3,706 and U.S. 4,459,398. In U.S. 4,243,706 a one part adhesive composition useful in the automobile manufacturing for bonding metal substrates is described. This adhesive contains a minor proportion of epoxy resin; a plasticizer, such as alkyl benzyl phthalate; a latent curing agent com-prising Ciba-Geigy's HY940~; and a major proportion of carboxy-functional polyvinyl chloride polymer.
In U.S. 4,459,398, another adhesive for use in bonding metal and polymeric parts in automobile manufac-turing is disclosed. This adhesive comprises an epoxy com-ponent and a triple curing agent combination comprising:
dicyandiamide; a complex of an imidaæole with a nickel or copper metal salt; and a ]atent curing agent complex that liberates diethylenetriamine at elevated cure temperatures, i.e. HY9~0~.
Current automotive designs incorporate both steel and molded polymeric component parts. In the case of metal to metal parts, for example, oily metal hemflanges must be bonded to automotive doors, hoods and deck lids. Welding has been the traditional method for providing fixture strength to these parts. Currently, however, there is a need to use galvanized metal parts and components. Although galvanized metal can be welded, it is susceptible to the formation of weld marks. Moreover, during welding, the galvanic coating is burned off, leaving sites for corrosion to start.
These shortcomings have caused automobile manu-facturers to consider alternative bonding methods and pri-marily one component heat curable epoxy adhesives are currently being considered for this purpose. The criteria which an epoxy adhesive must meet to satisfy automobile manufacturers needs are highly specialized.
A conventional one part epoxy adhesive containing a latent curing agent reactive only at elevated temperatures is unsatisfactory because prior to curing, the uncured adhesive acts as a lubricant, permittirlg slippage and misalignment of parts during shipment from the stamping plant ~ 3 ~ 6 to the assembly plant. In addition, after assembly, the bonded parts and more particularly the adhesive must be able to withstand the extremely high temperatures of the paint ovens, usually at least about 180C and higher when final paint coats are applied, without losing post-cure physical properties.
Current requirements dictate that the adhesive composition must be capable of developing an intermediate cure strength sufficient to provide a fixture strength comparable to prior art welding methods. This intermediate cure strength is referred to herein as green streng~h. The bonded parts must survive trans-shipment and handling in a useable condition. The adhesive must also develop final cure properties, including physical and environmental properties and be able to withstand the temperatures and conditions of subsequent processing, e.g. the paint ovens.
Induction heating of these parts is of considerable interest to automobile manufacturers. In in-duction curing methods, low frequency electromagnetic radiation is used to provide very fast localized heating in the metal parts as a meclns for partially curing the adhesive.
Energy requirements for induction heating are fairly low compared to other methods of heating. Moreover, the speed with which heating is accomplished, e.g. 2 seconds or less to reach 200C metal temperature, makes the concept particu-larly desirable in automotive stamping plant processes which are required to produce about 300 parts per hour.
Induction curing processes raise special problems for epoxy adhesives. It is known, for example, from oven cured systems, that porosity in the bond line has an adverse effect on environmental properties. Induction heating causes bondline porosity to develop in response to the rapid applications of heat. Moist~re, volatiles, trapped air and exotherm in the adhesive can all cause porosity in the bondline. An induction curable adhesive should not be overly sensitive to these problems.
Furthermore, the localized heating of metal parts ~30~13~
by induction is not as precise as may be desired. Induction heating responses can vary and the process may be greatly affected by such varlables as coil distance from the part, metal thickness, heating time and the configuration of the part. Therefore, an induction curable adhesive should develop acceptable green strength over a broad temperature range of at least about +25C, to accommodate variations inherent in an induction heating process, and the broader the cure range the better.
Accordingly, it is an object of the present invention to provide an induction curable one-part epoxy adhesive composition whicll develops high green strength for use in modern automobile manufacturing processes.
It is another object oE the present invention to provide an lnduction curable epoxy adhesive composition capable oE bonding oily galvanized metal parts together and provide structural strength.
It is a further object of the present lnvention to provide an induction curable epoxy adhesive composition capable of developing a minimum green strength of 200 psi in six seconds or less by induction heating to 185C or less.
It is still another object of the present invention to provide a high green strength induction-curable epoxy adhesive which is storage stable and remains pumpable after aging for a period of at least about two weeks at 41C.
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4~a) 61109-7529 Summary of Invention The present invention provides a curing agent additive for induction curing of epoxy-based adhesive compositions; said curing agent comprising:
(i) a latent high temperature curing agent;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl Eormal, polyvinyl butyral, poly(methyl methacrylate) NYLON-12 and hot melt polyester resins and mixtures o.E any of the Eoregoing resins wherein component (i) comprises from about 7 to about 12% by weight, component (ii) comprises :Erom about 35 to about 65% by weight; and component (iii) comprises about 26 to about 53% by weight, based upon the total weight of said curing agent additive.
The present invention also provides an induction curable adhesive composition comprising:
(a) an epoxy resin comprising a polyepoxide or mixture of polyepoxides; and (b) an effective amount of a combination curing agent therefor comprising:
a~
, 4(b) 61109-7529 (i) a latent high temperature curing agent, which remains relatively inert up to about 149C, but above 149C is capable of rapidly catalyzing the crosslinking of the epoxy resin;
: (ii) a latent intermediate temperature curing agent;
and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures thereof, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185C or less.
:~3-~1396 In preferred embodiments, the epoxy resin component (a) comprises:
(i) a polyfunctional aromatic epoxy resin;
(ii) a polyfunctional aliphatic epoxy resin; and (iii) glycidoxypropyltrimethoxysilane The latent high temperature curing agent comprises a latent epoxide curing agent which remains relatively inert up to temperatures of about 1~9C but at temperatures above about 149C is capable of rapidly catalyzing the crosslinking of the epoxy resin component. Illustrative latent high temperature curing agents may include dicyandiamide and diaminodiphenyl sulfone, for example. The preferred latent high temperature curing agent for use herein as component (b) (i) is dicyandiamide (DICY).
The latent intermediate temperature curing agents for use as component (b)(ii) herein are generally unreactive up to temperatures o~ between about 100C and 150C and are present in an amount eEfective to partially cure the adhesive in combination with component (b)(iii) to provide a green strength of at least about 200 psi in six seconds or less upon induction heating to temperatures of about 185C or less.
Illustrative latent intermediate temperature curing agents include HY939 ~ , HY9~0 ~ available from Ciba-Geigy and ANCAMINE ~201~A a modified polyamine available from Anchor Chemical Corporation.
The thermoplastic powders for use as green strength enhancing agent (b)(iii) will generally have a particle size of between about 5 to about 500 microns and ~\
~3UD~ 3 ~ ~
exhibit a glass transition temperature or crystalline melt temperature in the range oE between about 50C to about 160C.
It is important to note that only the thermoplastic powders recited, enhanced green strength properties out of several polymers evaluated. The green strength enhancing agent must contribute to handling strength upon induction heating.
In preferred embodiments, a new and improved com-bination curing agent additive for epoxy resins is provided, said additive comprising components (b)(i) to (b)(ii) in the following proportions: from about 7 to about 12~/, by weight (b)(i); from about 35 to about 65% by weight of (bO(ii); and from about 26 to abut 53% by weight of (b)(iii), based upon the total weight of said additive.
Ihe new and improved induction curable adhesives of the present invention generally comprise about 100 parts of epoxy resin component (a) and from about 30 to about 50 parts by weight of combination curing agent component (b), based on the total weight of the adhesive compositions, wherein in component (b), component (b)(i) is present in an amount of from about 2 to about ~ phr; component (b)(ii) is present in an amount oE from about 12 to about 30 phr; and component (b)(iii) i9 present in an amount of from about 12 to about 28 phr. In especially preferred embodiments, induction curable adhesives for bonding oily metal sub-strates are provided which additionally comprise as com-ponent (c) on metal adhesion promoter comprising a finely-divided mineral filler selected from the group consisting of talc, calcium carbonate, fumed silica and mixtures of any of the foregoing fillers. In accordance with these embodiments,-the adhesive compositions for oil metal substrates comprise 100 parts by weight of epoxy component (a), from about 30 to about 50 parts by weight of combination curing agent (b) and from about 27 to about 100 parts by weight of metal adhesion promoter component (c), based on the total weight of the composition. The compositions of this invention may also comprise other additives conventional for epoxy adhesives ~3C~39t~
and pastes, such as fillers, thixotropic agents, dyes, pig-ments and the like.
The new and improved induction curable adhesive compositions oE the present invention are characterized by a storage stability of at least about 2 weeks at 41C (105F) without premature crosslinking or loss in pumpability. The compositions are induction curable to provide green strength bonding of metal parts of at least about 200 psi in six seconds or less upon induction heating to 185C or less. The new and improved adhesives in final cured state exhibit good physical properties and good environmental properties such as for example high impact strength, good high tempera-ture/humidity resistance, good salt spray resistance and good scab corrosion resistance. In accordance with the pre-sent invention, a satisfactory one-part, induction curable epoxy adhesive for bonding oily galvanized metal parts during automobile assembly proced~lres is provided.
Other objects and advantages of the present inven-tion wi]l become apparent from the fol]owing detailed description and illustrative working ~xamples.
~ 39 Detailed Description of the Invention In general, the induction-curable adhesive com-positions of the present invention are prepared by mixing the epoxide prepolymers or mixtures of prepolymers (a) with the unique induction curing agent combination, components (b)~ (b)(iii) above in carefully specified amounts, to provide induction curable epoxy adhesives exhibiting ex-cellent storage stability, improved green strength adhesion and toughness and excellent environmental and final cure properties.
The epoxy resins suitable for use in component (a) in the present invention are compounds having more than one epoxide group per molecule available for reaction with the combination curing agents of the present invention. Such epoxy prepolymers include but are not limited to polyglycidyl ethers of polyvalent phenols, for example pyrocatechol;
resorcinol, hydroquinone; 4,4'-dihydroxydiphenyl methane;
4,4'-dihydro~y-3,3'-dimethyldiphenyl methane; 4,4'-dihy-droxydiphenyl dimethyl methane; 4,4'-dihydroxydiphenyl methyl methane; 4,4'-dihydroxydiphenyl cyclohexane; 4,4'-dihydroxy-3,3'-dimethyldiphenyl propane; 4,~'-dihydroxydi-phenyl sulEone; or tris-(4-hydroxyphenyl)methane; poly-glycidyl ethers of the chlorination and bromination products of the above-mentioned diphenols; polyglycidyl ethers of novolacs (i.e., reaction products of monohydric or poly hydric phenols with aldehydes, formaldehyde in particular, in the presence of acid catalysts); polyglycidyl ethers of diphenols obtained by esterifying 2 mols of the sodium salt of an aromatic hydrocarboxylic acid with 1 mol of a dihaloalkane or dihalogen dialkyl ether (U.K. 1,017,612);
and polyglycidyl ethers of polyphenols obtained by con-densing phenols and long-chain halogen paraffins containing at least two halogen atoms (U.K. 1,024,288).
Other suitable compounds include polyepoxy com-pounds based on aromatic amines and epichlorohydrin, for example N,N'-diglycidyl-aniline; N,N'-dimethyl-N,N'-digly-cidyl-4,4'-diaminodiphenyl methane; N,N,N',N'-tetra-' . ~, .
, . , .
~3(~1396 glycidyl-4,4'-diaminodiphenyl methane; and N-diglycidyl-4-aminophenyl glycidyl ether. Special mention is made of N,N,N',N'-tetraglycidyl~1,3-propylene-bis(4-aminobenzoate) Glycidyl esters and/or epoxycyclohexyl esters of aromatic, aliphatic and cycloaliphatic polycarboxylic acids, for example phthalic acid diglycidyl esters and adipic diglycidyl ester and glycidyl esters of reaction products of I mol. of an aromatic or cycloaliphatic dicarboxylic acid anhydride and 1/2 mole of a diol or l/n mol of a polyol wi~h n hydroxyl groups, of hexahydrophthalic acid diglycidyl esters, optionally substituted by methyl groups, are also suitable.
Glycidyl ethers of polyhydric alcohols, for example oE 1,4-butanediol; 1,4-butenediol; glycerol;
l,l,l-trimethylol propane; pentaerythritol and polyethylene glycols may also be used. Triglycidyl isocyanurate; and poly-glycidyl thioethers of polyva]ent thiols, for example of bis-mercaptomethylbenzene; and diglycidyltrimethylene sulfone, are also suitable.
Preferably the epoxy prepolymer component will be selected Erom compounds having the idealized formula:
c and halogen and alkyl substituted derivatives of such com-pounds, wherein c is 2,3 or 4 and equal to the valence of Q;
Q is a divalent, trivalent or tetravalent radical; G is -O-3~t~
NR' or -N-;Rl is hydrogen or alkyl; and d is 1 or 2 depend-ing on the valence of G.
Useful epoxy compounds will include the following:
( ~ ~ ~ ~ ~ 2 wherein x is an integer from 1 to 4, available commercially (where x=l) as ARALDITE~ MY-720 (Ciba-Geigy);
HC -~ o ~~ ~3 available commercially as XD 7342 (Dow Chemica].).
Preferred epoxy compounds are of the Eormula ~ CH O--CH -- CH --CH~
CE~3 n ~0 ~ I ~ O'~\C
CH
wherein n is a whole number of from about 1 to about 10. Such compounds are availaable commercially as DER 331 (Dow Chem-ical), average molecular weight 350-400, or EPON~ 828 (Shell).
Also useful are compounds of the formula 0~ o ~,~
O ~ ~ ~o o~ ~o, available commercially as EPON~ 1031 (Shell): and compounds oE the Eormula X ~ X X
~ C112~ R3 .
1~U~ 3 wherein Y is 1 or 2, X is -0- or -NH, R3 is H or CH3 and n is 2 to 8.
Compounds in which X is -0- are available as a mixture under the tradename D~N-438 ~rom Dow Chemical Company.
Useful in addition are triglycidyl ethers of meta-and para-hydroxyaniline, e.g., represented by the formula:
0~ ~ ~0) lS
These are available under the tradename ARALDITE~ 0500, 0510 Erom Ciba-Geigy.
In especia]ly preEerred embodiments component (a) comprises a mixture of epoxy prepolymers comprising:
(i) d;glycidyl ether of bisphenol-A (DGEBA~:
(ii) neopentylglycol diglycidyl ether; and (iii) glycidoxypropyltrimethoxy silane In accordance with these preEerred embodiments, the DGEBA resin component (a)(i) is present in an amount of from about 33% to about 43% by weight, the neopentylglycol diglycidyl ether component (a)(ii) is present in an amount of from about 3 to about 7% by weight and the glycidoxypro-pyltrimethoxysilane component (a)(iii) is present in an amount of from about 1 to about 6% by weight, based on 100%
by weight of the overall adhesive composition.
In accordance with the present invention, new and improved induction curable adhesive compositions, stable for a period of two weeks at temperatures of about 41C, capable of achieving minimum green strength of 200 psi in six seconds or less by induction heating to 185 or less, are provided by incorporation of an effective amount of a unique multi-component curing agent combination comprising:
13~139~
(b) (i~ a latent high-temperature curing agent;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent, in care-fully specified relative proportions, set forth above.
The new and improved adhesives of the present invention are especially adapted for modern automobile fabrication and manufactur;ng by virtue of their unique combination curing agent system. The stable latent high temperature curing agent provides high crosslinking of the epoxy components for full cure during the paint bake oven cycles. The stable latent intermediate temperature curing agent reacts very quickly with a portion of the epoxide components during the very short induction heating portion of the cure cycle, giving cufficient handling strength for fixturing purposes. The green strength enhancing agent comprises a member of certain thermoplastic powders dis-persed in the adhesive paste as an enhancin~ agent to melt or fuse within the adhesive during the induction heating cycle to provide additional green strength to the induction cured or partially cured adhesive.
In greater detail, the latent high temperature curing agents for use as component (b)(ii) of the induction curing agent combination of this invention comprise any latent high temperature curing a8ent for epoxy resins which beco~e effective crosslinking agents at temperatures of above about 149C, but which are ~table and inert to epo~ide groups at temperatures of 149C or less. The pre-ferred latent high temperature curing agent for use as component (b)(i) herein is dicyandiamide (DICY).
Dicyandiamide is employed to provide full cured properties by catalyzing crosslinking in the high temperature paint bake ovens. DICY is the preferred latent high temperature curing agent because it is inexpensive, exhibits excellent latency at ~emperatures below 149C and exceptional catalyt-ic ,~
activity at higher temperatures to provide excellent final cure properties. DICY is abundantly commercially available.
Other known latent high temperature curing agents such as diaminodiphenylsulfone or DICY analogs might also be used in 5 - coMponent (b)(i).
The latent high temperature curing agent remains essentially unreacted during the induction heat cycle.
Accelerators commonly employed with DICY as co-catalysts are not generally necessary for the high temperature curing of the paint bake ovens. Accelerators may be added together with the DICY, if oven cure temperatures are expected ~o be less than 149C. Careful selection of a high temperature curing agent accelerator must be made because, addition of accelerators to lower cure temperature for the DICY may also disadvantageously shorten shelf life stability of the ad-hesive. One particular curing accelerator for the DICY
component which has unexpectedly been discovered not to adversely affect stability of the adhesive compositions is CA301~ available from American Cyanamid Company. CA301~ is the reaction product of 1,4-phenylenediisocyanate and dimethylamine having the formula:
H3C \ 0 H H ,CH3 N-C-N - ~ \ CH3 CA301 provides good final oven cured properties at 135C or less, without shortening shelf life. Moreover, the handling strength after the induction heating cycles is not adversely af~ected by the addition of CA301 with the latent high temperature curing agent component (b)(i). For compositions which are to be final cured in ~aint bake ovens or the like at temperatures below about 149C, a minor effective amount of CA301 or accelerator may be used, e.g., in an amount of from about 0.01% to abo~t 3.0% by weight of the overall adhesive 130~396 composition.
The latent intermediate temperature curing agents for use herein as component (b)(ii) comprise latent curing agents which are unreactive at temperatures of about 100C or less, but which effectively cure epoxide prepolymers at temperatures of between about 100C and 175C. Suitable intermediate temperature curing agents include the reaction product of diethylene triamine and phthalic anhydride sold under the trade names HY940 and ~Y939 by Ciba-Geigy and a modified polyamine sold under the tradename ANCAMINE 2014~ by Anchor Chemical Corporation.
HY940~ has an idea]ized structure as follows:
O O
C-NH-C~I2-CH2-N~-CH~-CH2-NH-C
O O
The latent intermediate temperature curing agent component (b)(ii) is used in an amount which is less than a stoichiometric amount necessary for full cure. The rapid reaction times oE these curing agents are generally better than can be achieved with DICY. Stability of the adhesive is an important consideration for the automobile manufacturers.
Earlier eEforts at achieving a high green strength adhesive employing DICY combined with accelerator to lower activation temperatures generally have provided relatively unstable compositions~ The intermediate temperature curing agents for use herein exhibit excellent stability and provide the new and improved combination curing agent oE this invention with the necessary crosslinking upon induction heating to provide sufficient green strength for fixturing of parts for shipment, storage, assembly and coating/finishing operations prior to final curing. The high cost and ultimately poor final-cure properties obtained with using the intermediate :~3n~L39 temperature curing agents as the sole curative in the com-positions indicates the need for a combination of both intermediate temperature and high temperature curing agents as taught herein.
The combination curing agent of the present in-vention also includes, as component (b)(iii), a green strength enhancing agent comprising a finely divided thermo-plastic powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate copolymer, polystyrene polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), Nylon-12 and hot melt polyester resins and mixtures of these resins.
The green strength enhancing agent must provide toughness in the partially cured adhesive. HY940, if used alone as the curing agent, yields a very brittle partially cured adhesive. &enerally, the overall adhesive composition, does not require the addition of the thermoplastic green strength enhancing agent to enhance its fully cured proper-ties. A careful selection of enhancing agent, however, may increase toughness and adhesion of the fully cured adhesive to oily galvanized substrates.
The green strellgth enhancing agent contributes to the handling strength of the adhesive after induction heat-ing. The reasons Eor this and for the fact that only some of the thermoplastic powders tested improved green strength is uncertain at this time. The enhancing agents which do work are observed to increase the viscosity of the adhesive paste through the melt;ng and/or fusing of polymer particles. In the case of one enhancing agent, for example, FORMVAR 15/95E~, a polyvinyl formal resin available from Monsanto Company, the thermoolastic green strength enhancing agent contributed approximately 25 psi of bonding strength to an induction heated partially-cured adhesive sample which did not contain the intermediate temperature curing agent HY9~0.
Of the thermoplastic powders tested which provided a green strength enhancing effect, all exhibited a glass L3~39~ ~
transition temperature between about 50 and 160C, and more particularly between about 65 and 130C. However, this property is not determinative because a number of thermo-plastic powders evaluated which exhibited a glass transition temperature within this range did not enhance the green strength of an inductive cured adhesive formulation.
The green strength enhancing agent is a thermo-plastic powder in a finely divided form and generally a particle size of between about 5 to about 500 microns i5 satisfactory. Many of the polymers identified as green strength enhancing agents are commercially available in finely divided form or they may be size reduced by con-ventional methods, such as by cryogenic grinding, but care should be taken in the size reduction method employed not to degrade the polymers.
The green strength enhancing agents for use as component (b)(iii) herein are generally commercially avail-able materials.
I]lustrative low density polyethylene polymers for use herein as component (b)(iii) include MICROTE~ENE FN510 from USI. MICROTHENE FN510 polymers have a melt index of about 5 g/10 min.; a density of 0.924 g/cc; a spherical particle shape oE an average particle size oE less than about ~0 microns; and a Vicat soEtening point of about 9~C. An ethylene vinyl acetate polymer sold under the trade desig-nation MICROTHENE FE 532 also from USI may also be used.
MICROTHENE FE532 has a melt index of 9 g/10 min; a density of 0.928 g/cc; a spherical shape of average particle size of less than 20 microns; and a Vicat softening point of about 75C.
A suitable polystyrene polymer is HOSTYREN~ 57 available from American Hoechst Corporation. HOSTYREN~ 57 has a melt flow rate of 2 g/10 min; gravity of 1.05; and a Vicat softening point of 107C. A suitable poly(methyl methacrylate) polymer is EI.VA~ITE~ 2021 from Rohm and Haas Company. ELVACITE~ 2021 is a high molecular weight resin having a density of 1196 kg/m3; a specific gravity of 1.20 and a glass transition ~~ ~3~ 35H6 temperature of 98C. A suitable polyvinyl formal resin is FORMVAR~ 15/95E, available from Monsanto Company. FORMVAR~
15/95E has an average molecular weight of between about 24,000-40,000; a flow temperature at 1000 psi of 160-170C;
and an apparent glass transition temperature of about 103-113C. A suitable polyvinyl butyral resin is BUTVAR~ B-7B
Resin also available from Monsanto. BUTVAR~ B-7B resins have an average molecular weight of between about 50,000-80,000;
a flow temperature at 1000 psi of 125-130C; and an apparent glass transition temperature of 62-68C. A suitable hot meltpolyester resin is VESTAMELT~ X4053, available from ~UELS Corporation. VESTAMELT~ X4053 has a melt flow index of about 10.0 g/10 min., a melt viscosity at 140C or 950 Pas;
and a capillary method melting point of about 123C. Other suitable thermoplastic powders are illustrated in the Exam-ples which follow.
The new and improved induction curable adhesive compositions of this invention may also contain other additives such as fillers, pigments and dyes or the like added to make a paste of desired properties. Suitable fillers for use in the compositions of this invention are mineral fil-lers. Illustrative examples include: talc, mica, titanium dioxide, lithopone, zinc oxide, zirconium silica, silica aerogel, iron dioxide, diatomaceous earth, calcium carbonate, fumed silica, silazane treated silica, precipitated silica, glass Eibers, magnesium oxide, chromic oxide, æirconium oxide, aluminum oxide, crushed quartz, calcined clay, asbestos, carbon, graphite, cork, cotton, synthetic fibers, to name but a few. Preferred fillers for use herein include: talc, hydrophobic fumed silica such as CABO-SIL~ N707SD from Cabot Corporation and titanium di-oxide. Generally, the other additives such as fillers, dyes, pigments, thioxotropic agents and the like will be added in conventional amounts.
Other objects and advantages of the present in-vention will become apparent from the following working Examples:
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Detailed Description of the Preferred Embodiments In the following Examples a number of adhesive compositions were prepared and tested for shelf stability at 41C; induction cure response and green strength; and final cure physical and environmental properties.
The adhesive compositions were each prepared by adding the components to a Ross Planetary Mixer, liquids then powders, and the compositions were blended under a vacuum for a time sufficient to insure thorough mixing and de-aeration of the compositions. The test formulations were s~ored in closed containers at temperatures of less than 49C until use. Care should be taken to ensure that the compositions are de-aerated and stored in air-tight containers because several of the components are hygroscopic. The presence of lS additional or excess moisture in the compositions is un-desirable because it may cause foaming o~ the compositions during cure which may adversely effect intermediate and final cured properties.
The compositions were prepared from commerc`ially available products, identified as follows:
,.
30, 076 HIGH GREEN STRENGTH
.. . .. ..
INDUCTION CURABLE ADHESIVES
Background of the Invention , . .
The present invention relates to storage stable, one-part, epoxy adhesives that cure rapidly at elevated temperatures. More psrticularly, the invention relates to induction curable adhesives which develop minimum inter-mediate-cure or green strengths of 200 psi in six seconds or less upon induction heating to temperatures of 185Corles.s.
One part epoxy adhesive compositions containing at least one latent curing agent, alone or in comL~ination with a co-c~lring agent or cure accelerator, and containing other modifiers and/or fillers are known.
U.S. 2, 915, 490; U.S. 2, 986, 546; and U.S. 3, 098, 054 disclose the combination of epoxy, polyvinyl formai and fillers in adhesive compositions.
U.S. 3, 635, 87S discloses an adhesive composition c~ntaining epoxy resins derived from bisphenol-A, polyglycol diepoxide, dicyandiamide, silica and glycidoxypropyltri-methoxysilane.
U.S. 3, 639, 657 discloses the reaction product of phthalic anyhydride and diethylenetriamine. U.S. 3, 48~, 742 describes hardenable compositions comprising: a 1, 2-epoxy compound having a 1, 2-epoxy equivalency greater than 1; a curing agent comprising dicyandiamide and as a curing accelerator, the condensation product obtained by reacting equimolar proportions of phthalic anhydride and diethylene-triamine.
~J :~
" ~ 3-~1 3 ~ ~
Of particular interest are the disclosures of U.S.
4,2~3,706 and U.S. 4,459,398. In U.S. 4,243,706 a one part adhesive composition useful in the automobile manufacturing for bonding metal substrates is described. This adhesive contains a minor proportion of epoxy resin; a plasticizer, such as alkyl benzyl phthalate; a latent curing agent com-prising Ciba-Geigy's HY940~; and a major proportion of carboxy-functional polyvinyl chloride polymer.
In U.S. 4,459,398, another adhesive for use in bonding metal and polymeric parts in automobile manufac-turing is disclosed. This adhesive comprises an epoxy com-ponent and a triple curing agent combination comprising:
dicyandiamide; a complex of an imidaæole with a nickel or copper metal salt; and a ]atent curing agent complex that liberates diethylenetriamine at elevated cure temperatures, i.e. HY9~0~.
Current automotive designs incorporate both steel and molded polymeric component parts. In the case of metal to metal parts, for example, oily metal hemflanges must be bonded to automotive doors, hoods and deck lids. Welding has been the traditional method for providing fixture strength to these parts. Currently, however, there is a need to use galvanized metal parts and components. Although galvanized metal can be welded, it is susceptible to the formation of weld marks. Moreover, during welding, the galvanic coating is burned off, leaving sites for corrosion to start.
These shortcomings have caused automobile manu-facturers to consider alternative bonding methods and pri-marily one component heat curable epoxy adhesives are currently being considered for this purpose. The criteria which an epoxy adhesive must meet to satisfy automobile manufacturers needs are highly specialized.
A conventional one part epoxy adhesive containing a latent curing agent reactive only at elevated temperatures is unsatisfactory because prior to curing, the uncured adhesive acts as a lubricant, permittirlg slippage and misalignment of parts during shipment from the stamping plant ~ 3 ~ 6 to the assembly plant. In addition, after assembly, the bonded parts and more particularly the adhesive must be able to withstand the extremely high temperatures of the paint ovens, usually at least about 180C and higher when final paint coats are applied, without losing post-cure physical properties.
Current requirements dictate that the adhesive composition must be capable of developing an intermediate cure strength sufficient to provide a fixture strength comparable to prior art welding methods. This intermediate cure strength is referred to herein as green streng~h. The bonded parts must survive trans-shipment and handling in a useable condition. The adhesive must also develop final cure properties, including physical and environmental properties and be able to withstand the temperatures and conditions of subsequent processing, e.g. the paint ovens.
Induction heating of these parts is of considerable interest to automobile manufacturers. In in-duction curing methods, low frequency electromagnetic radiation is used to provide very fast localized heating in the metal parts as a meclns for partially curing the adhesive.
Energy requirements for induction heating are fairly low compared to other methods of heating. Moreover, the speed with which heating is accomplished, e.g. 2 seconds or less to reach 200C metal temperature, makes the concept particu-larly desirable in automotive stamping plant processes which are required to produce about 300 parts per hour.
Induction curing processes raise special problems for epoxy adhesives. It is known, for example, from oven cured systems, that porosity in the bond line has an adverse effect on environmental properties. Induction heating causes bondline porosity to develop in response to the rapid applications of heat. Moist~re, volatiles, trapped air and exotherm in the adhesive can all cause porosity in the bondline. An induction curable adhesive should not be overly sensitive to these problems.
Furthermore, the localized heating of metal parts ~30~13~
by induction is not as precise as may be desired. Induction heating responses can vary and the process may be greatly affected by such varlables as coil distance from the part, metal thickness, heating time and the configuration of the part. Therefore, an induction curable adhesive should develop acceptable green strength over a broad temperature range of at least about +25C, to accommodate variations inherent in an induction heating process, and the broader the cure range the better.
Accordingly, it is an object of the present invention to provide an induction curable one-part epoxy adhesive composition whicll develops high green strength for use in modern automobile manufacturing processes.
It is another object oE the present invention to provide an lnduction curable epoxy adhesive composition capable oE bonding oily galvanized metal parts together and provide structural strength.
It is a further object of the present lnvention to provide an induction curable epoxy adhesive composition capable of developing a minimum green strength of 200 psi in six seconds or less by induction heating to 185C or less.
It is still another object of the present invention to provide a high green strength induction-curable epoxy adhesive which is storage stable and remains pumpable after aging for a period of at least about two weeks at 41C.
~L3C~39~
,, ~
4~a) 61109-7529 Summary of Invention The present invention provides a curing agent additive for induction curing of epoxy-based adhesive compositions; said curing agent comprising:
(i) a latent high temperature curing agent;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl Eormal, polyvinyl butyral, poly(methyl methacrylate) NYLON-12 and hot melt polyester resins and mixtures o.E any of the Eoregoing resins wherein component (i) comprises from about 7 to about 12% by weight, component (ii) comprises :Erom about 35 to about 65% by weight; and component (iii) comprises about 26 to about 53% by weight, based upon the total weight of said curing agent additive.
The present invention also provides an induction curable adhesive composition comprising:
(a) an epoxy resin comprising a polyepoxide or mixture of polyepoxides; and (b) an effective amount of a combination curing agent therefor comprising:
a~
, 4(b) 61109-7529 (i) a latent high temperature curing agent, which remains relatively inert up to about 149C, but above 149C is capable of rapidly catalyzing the crosslinking of the epoxy resin;
: (ii) a latent intermediate temperature curing agent;
and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures thereof, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185C or less.
:~3-~1396 In preferred embodiments, the epoxy resin component (a) comprises:
(i) a polyfunctional aromatic epoxy resin;
(ii) a polyfunctional aliphatic epoxy resin; and (iii) glycidoxypropyltrimethoxysilane The latent high temperature curing agent comprises a latent epoxide curing agent which remains relatively inert up to temperatures of about 1~9C but at temperatures above about 149C is capable of rapidly catalyzing the crosslinking of the epoxy resin component. Illustrative latent high temperature curing agents may include dicyandiamide and diaminodiphenyl sulfone, for example. The preferred latent high temperature curing agent for use herein as component (b) (i) is dicyandiamide (DICY).
The latent intermediate temperature curing agents for use as component (b)(ii) herein are generally unreactive up to temperatures o~ between about 100C and 150C and are present in an amount eEfective to partially cure the adhesive in combination with component (b)(iii) to provide a green strength of at least about 200 psi in six seconds or less upon induction heating to temperatures of about 185C or less.
Illustrative latent intermediate temperature curing agents include HY939 ~ , HY9~0 ~ available from Ciba-Geigy and ANCAMINE ~201~A a modified polyamine available from Anchor Chemical Corporation.
The thermoplastic powders for use as green strength enhancing agent (b)(iii) will generally have a particle size of between about 5 to about 500 microns and ~\
~3UD~ 3 ~ ~
exhibit a glass transition temperature or crystalline melt temperature in the range oE between about 50C to about 160C.
It is important to note that only the thermoplastic powders recited, enhanced green strength properties out of several polymers evaluated. The green strength enhancing agent must contribute to handling strength upon induction heating.
In preferred embodiments, a new and improved com-bination curing agent additive for epoxy resins is provided, said additive comprising components (b)(i) to (b)(ii) in the following proportions: from about 7 to about 12~/, by weight (b)(i); from about 35 to about 65% by weight of (bO(ii); and from about 26 to abut 53% by weight of (b)(iii), based upon the total weight of said additive.
Ihe new and improved induction curable adhesives of the present invention generally comprise about 100 parts of epoxy resin component (a) and from about 30 to about 50 parts by weight of combination curing agent component (b), based on the total weight of the adhesive compositions, wherein in component (b), component (b)(i) is present in an amount of from about 2 to about ~ phr; component (b)(ii) is present in an amount oE from about 12 to about 30 phr; and component (b)(iii) i9 present in an amount of from about 12 to about 28 phr. In especially preferred embodiments, induction curable adhesives for bonding oily metal sub-strates are provided which additionally comprise as com-ponent (c) on metal adhesion promoter comprising a finely-divided mineral filler selected from the group consisting of talc, calcium carbonate, fumed silica and mixtures of any of the foregoing fillers. In accordance with these embodiments,-the adhesive compositions for oil metal substrates comprise 100 parts by weight of epoxy component (a), from about 30 to about 50 parts by weight of combination curing agent (b) and from about 27 to about 100 parts by weight of metal adhesion promoter component (c), based on the total weight of the composition. The compositions of this invention may also comprise other additives conventional for epoxy adhesives ~3C~39t~
and pastes, such as fillers, thixotropic agents, dyes, pig-ments and the like.
The new and improved induction curable adhesive compositions oE the present invention are characterized by a storage stability of at least about 2 weeks at 41C (105F) without premature crosslinking or loss in pumpability. The compositions are induction curable to provide green strength bonding of metal parts of at least about 200 psi in six seconds or less upon induction heating to 185C or less. The new and improved adhesives in final cured state exhibit good physical properties and good environmental properties such as for example high impact strength, good high tempera-ture/humidity resistance, good salt spray resistance and good scab corrosion resistance. In accordance with the pre-sent invention, a satisfactory one-part, induction curable epoxy adhesive for bonding oily galvanized metal parts during automobile assembly proced~lres is provided.
Other objects and advantages of the present inven-tion wi]l become apparent from the fol]owing detailed description and illustrative working ~xamples.
~ 39 Detailed Description of the Invention In general, the induction-curable adhesive com-positions of the present invention are prepared by mixing the epoxide prepolymers or mixtures of prepolymers (a) with the unique induction curing agent combination, components (b)~ (b)(iii) above in carefully specified amounts, to provide induction curable epoxy adhesives exhibiting ex-cellent storage stability, improved green strength adhesion and toughness and excellent environmental and final cure properties.
The epoxy resins suitable for use in component (a) in the present invention are compounds having more than one epoxide group per molecule available for reaction with the combination curing agents of the present invention. Such epoxy prepolymers include but are not limited to polyglycidyl ethers of polyvalent phenols, for example pyrocatechol;
resorcinol, hydroquinone; 4,4'-dihydroxydiphenyl methane;
4,4'-dihydro~y-3,3'-dimethyldiphenyl methane; 4,4'-dihy-droxydiphenyl dimethyl methane; 4,4'-dihydroxydiphenyl methyl methane; 4,4'-dihydroxydiphenyl cyclohexane; 4,4'-dihydroxy-3,3'-dimethyldiphenyl propane; 4,~'-dihydroxydi-phenyl sulEone; or tris-(4-hydroxyphenyl)methane; poly-glycidyl ethers of the chlorination and bromination products of the above-mentioned diphenols; polyglycidyl ethers of novolacs (i.e., reaction products of monohydric or poly hydric phenols with aldehydes, formaldehyde in particular, in the presence of acid catalysts); polyglycidyl ethers of diphenols obtained by esterifying 2 mols of the sodium salt of an aromatic hydrocarboxylic acid with 1 mol of a dihaloalkane or dihalogen dialkyl ether (U.K. 1,017,612);
and polyglycidyl ethers of polyphenols obtained by con-densing phenols and long-chain halogen paraffins containing at least two halogen atoms (U.K. 1,024,288).
Other suitable compounds include polyepoxy com-pounds based on aromatic amines and epichlorohydrin, for example N,N'-diglycidyl-aniline; N,N'-dimethyl-N,N'-digly-cidyl-4,4'-diaminodiphenyl methane; N,N,N',N'-tetra-' . ~, .
, . , .
~3(~1396 glycidyl-4,4'-diaminodiphenyl methane; and N-diglycidyl-4-aminophenyl glycidyl ether. Special mention is made of N,N,N',N'-tetraglycidyl~1,3-propylene-bis(4-aminobenzoate) Glycidyl esters and/or epoxycyclohexyl esters of aromatic, aliphatic and cycloaliphatic polycarboxylic acids, for example phthalic acid diglycidyl esters and adipic diglycidyl ester and glycidyl esters of reaction products of I mol. of an aromatic or cycloaliphatic dicarboxylic acid anhydride and 1/2 mole of a diol or l/n mol of a polyol wi~h n hydroxyl groups, of hexahydrophthalic acid diglycidyl esters, optionally substituted by methyl groups, are also suitable.
Glycidyl ethers of polyhydric alcohols, for example oE 1,4-butanediol; 1,4-butenediol; glycerol;
l,l,l-trimethylol propane; pentaerythritol and polyethylene glycols may also be used. Triglycidyl isocyanurate; and poly-glycidyl thioethers of polyva]ent thiols, for example of bis-mercaptomethylbenzene; and diglycidyltrimethylene sulfone, are also suitable.
Preferably the epoxy prepolymer component will be selected Erom compounds having the idealized formula:
c and halogen and alkyl substituted derivatives of such com-pounds, wherein c is 2,3 or 4 and equal to the valence of Q;
Q is a divalent, trivalent or tetravalent radical; G is -O-3~t~
NR' or -N-;Rl is hydrogen or alkyl; and d is 1 or 2 depend-ing on the valence of G.
Useful epoxy compounds will include the following:
( ~ ~ ~ ~ ~ 2 wherein x is an integer from 1 to 4, available commercially (where x=l) as ARALDITE~ MY-720 (Ciba-Geigy);
HC -~ o ~~ ~3 available commercially as XD 7342 (Dow Chemica].).
Preferred epoxy compounds are of the Eormula ~ CH O--CH -- CH --CH~
CE~3 n ~0 ~ I ~ O'~\C
CH
wherein n is a whole number of from about 1 to about 10. Such compounds are availaable commercially as DER 331 (Dow Chem-ical), average molecular weight 350-400, or EPON~ 828 (Shell).
Also useful are compounds of the formula 0~ o ~,~
O ~ ~ ~o o~ ~o, available commercially as EPON~ 1031 (Shell): and compounds oE the Eormula X ~ X X
~ C112~ R3 .
1~U~ 3 wherein Y is 1 or 2, X is -0- or -NH, R3 is H or CH3 and n is 2 to 8.
Compounds in which X is -0- are available as a mixture under the tradename D~N-438 ~rom Dow Chemical Company.
Useful in addition are triglycidyl ethers of meta-and para-hydroxyaniline, e.g., represented by the formula:
0~ ~ ~0) lS
These are available under the tradename ARALDITE~ 0500, 0510 Erom Ciba-Geigy.
In especia]ly preEerred embodiments component (a) comprises a mixture of epoxy prepolymers comprising:
(i) d;glycidyl ether of bisphenol-A (DGEBA~:
(ii) neopentylglycol diglycidyl ether; and (iii) glycidoxypropyltrimethoxy silane In accordance with these preEerred embodiments, the DGEBA resin component (a)(i) is present in an amount of from about 33% to about 43% by weight, the neopentylglycol diglycidyl ether component (a)(ii) is present in an amount of from about 3 to about 7% by weight and the glycidoxypro-pyltrimethoxysilane component (a)(iii) is present in an amount of from about 1 to about 6% by weight, based on 100%
by weight of the overall adhesive composition.
In accordance with the present invention, new and improved induction curable adhesive compositions, stable for a period of two weeks at temperatures of about 41C, capable of achieving minimum green strength of 200 psi in six seconds or less by induction heating to 185 or less, are provided by incorporation of an effective amount of a unique multi-component curing agent combination comprising:
13~139~
(b) (i~ a latent high-temperature curing agent;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent, in care-fully specified relative proportions, set forth above.
The new and improved adhesives of the present invention are especially adapted for modern automobile fabrication and manufactur;ng by virtue of their unique combination curing agent system. The stable latent high temperature curing agent provides high crosslinking of the epoxy components for full cure during the paint bake oven cycles. The stable latent intermediate temperature curing agent reacts very quickly with a portion of the epoxide components during the very short induction heating portion of the cure cycle, giving cufficient handling strength for fixturing purposes. The green strength enhancing agent comprises a member of certain thermoplastic powders dis-persed in the adhesive paste as an enhancin~ agent to melt or fuse within the adhesive during the induction heating cycle to provide additional green strength to the induction cured or partially cured adhesive.
In greater detail, the latent high temperature curing agents for use as component (b)(ii) of the induction curing agent combination of this invention comprise any latent high temperature curing a8ent for epoxy resins which beco~e effective crosslinking agents at temperatures of above about 149C, but which are ~table and inert to epo~ide groups at temperatures of 149C or less. The pre-ferred latent high temperature curing agent for use as component (b)(i) herein is dicyandiamide (DICY).
Dicyandiamide is employed to provide full cured properties by catalyzing crosslinking in the high temperature paint bake ovens. DICY is the preferred latent high temperature curing agent because it is inexpensive, exhibits excellent latency at ~emperatures below 149C and exceptional catalyt-ic ,~
activity at higher temperatures to provide excellent final cure properties. DICY is abundantly commercially available.
Other known latent high temperature curing agents such as diaminodiphenylsulfone or DICY analogs might also be used in 5 - coMponent (b)(i).
The latent high temperature curing agent remains essentially unreacted during the induction heat cycle.
Accelerators commonly employed with DICY as co-catalysts are not generally necessary for the high temperature curing of the paint bake ovens. Accelerators may be added together with the DICY, if oven cure temperatures are expected ~o be less than 149C. Careful selection of a high temperature curing agent accelerator must be made because, addition of accelerators to lower cure temperature for the DICY may also disadvantageously shorten shelf life stability of the ad-hesive. One particular curing accelerator for the DICY
component which has unexpectedly been discovered not to adversely affect stability of the adhesive compositions is CA301~ available from American Cyanamid Company. CA301~ is the reaction product of 1,4-phenylenediisocyanate and dimethylamine having the formula:
H3C \ 0 H H ,CH3 N-C-N - ~ \ CH3 CA301 provides good final oven cured properties at 135C or less, without shortening shelf life. Moreover, the handling strength after the induction heating cycles is not adversely af~ected by the addition of CA301 with the latent high temperature curing agent component (b)(i). For compositions which are to be final cured in ~aint bake ovens or the like at temperatures below about 149C, a minor effective amount of CA301 or accelerator may be used, e.g., in an amount of from about 0.01% to abo~t 3.0% by weight of the overall adhesive 130~396 composition.
The latent intermediate temperature curing agents for use herein as component (b)(ii) comprise latent curing agents which are unreactive at temperatures of about 100C or less, but which effectively cure epoxide prepolymers at temperatures of between about 100C and 175C. Suitable intermediate temperature curing agents include the reaction product of diethylene triamine and phthalic anhydride sold under the trade names HY940 and ~Y939 by Ciba-Geigy and a modified polyamine sold under the tradename ANCAMINE 2014~ by Anchor Chemical Corporation.
HY940~ has an idea]ized structure as follows:
O O
C-NH-C~I2-CH2-N~-CH~-CH2-NH-C
O O
The latent intermediate temperature curing agent component (b)(ii) is used in an amount which is less than a stoichiometric amount necessary for full cure. The rapid reaction times oE these curing agents are generally better than can be achieved with DICY. Stability of the adhesive is an important consideration for the automobile manufacturers.
Earlier eEforts at achieving a high green strength adhesive employing DICY combined with accelerator to lower activation temperatures generally have provided relatively unstable compositions~ The intermediate temperature curing agents for use herein exhibit excellent stability and provide the new and improved combination curing agent oE this invention with the necessary crosslinking upon induction heating to provide sufficient green strength for fixturing of parts for shipment, storage, assembly and coating/finishing operations prior to final curing. The high cost and ultimately poor final-cure properties obtained with using the intermediate :~3n~L39 temperature curing agents as the sole curative in the com-positions indicates the need for a combination of both intermediate temperature and high temperature curing agents as taught herein.
The combination curing agent of the present in-vention also includes, as component (b)(iii), a green strength enhancing agent comprising a finely divided thermo-plastic powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate copolymer, polystyrene polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), Nylon-12 and hot melt polyester resins and mixtures of these resins.
The green strength enhancing agent must provide toughness in the partially cured adhesive. HY940, if used alone as the curing agent, yields a very brittle partially cured adhesive. &enerally, the overall adhesive composition, does not require the addition of the thermoplastic green strength enhancing agent to enhance its fully cured proper-ties. A careful selection of enhancing agent, however, may increase toughness and adhesion of the fully cured adhesive to oily galvanized substrates.
The green strellgth enhancing agent contributes to the handling strength of the adhesive after induction heat-ing. The reasons Eor this and for the fact that only some of the thermoplastic powders tested improved green strength is uncertain at this time. The enhancing agents which do work are observed to increase the viscosity of the adhesive paste through the melt;ng and/or fusing of polymer particles. In the case of one enhancing agent, for example, FORMVAR 15/95E~, a polyvinyl formal resin available from Monsanto Company, the thermoolastic green strength enhancing agent contributed approximately 25 psi of bonding strength to an induction heated partially-cured adhesive sample which did not contain the intermediate temperature curing agent HY9~0.
Of the thermoplastic powders tested which provided a green strength enhancing effect, all exhibited a glass L3~39~ ~
transition temperature between about 50 and 160C, and more particularly between about 65 and 130C. However, this property is not determinative because a number of thermo-plastic powders evaluated which exhibited a glass transition temperature within this range did not enhance the green strength of an inductive cured adhesive formulation.
The green strength enhancing agent is a thermo-plastic powder in a finely divided form and generally a particle size of between about 5 to about 500 microns i5 satisfactory. Many of the polymers identified as green strength enhancing agents are commercially available in finely divided form or they may be size reduced by con-ventional methods, such as by cryogenic grinding, but care should be taken in the size reduction method employed not to degrade the polymers.
The green strength enhancing agents for use as component (b)(iii) herein are generally commercially avail-able materials.
I]lustrative low density polyethylene polymers for use herein as component (b)(iii) include MICROTE~ENE FN510 from USI. MICROTHENE FN510 polymers have a melt index of about 5 g/10 min.; a density of 0.924 g/cc; a spherical particle shape oE an average particle size oE less than about ~0 microns; and a Vicat soEtening point of about 9~C. An ethylene vinyl acetate polymer sold under the trade desig-nation MICROTHENE FE 532 also from USI may also be used.
MICROTHENE FE532 has a melt index of 9 g/10 min; a density of 0.928 g/cc; a spherical shape of average particle size of less than 20 microns; and a Vicat softening point of about 75C.
A suitable polystyrene polymer is HOSTYREN~ 57 available from American Hoechst Corporation. HOSTYREN~ 57 has a melt flow rate of 2 g/10 min; gravity of 1.05; and a Vicat softening point of 107C. A suitable poly(methyl methacrylate) polymer is EI.VA~ITE~ 2021 from Rohm and Haas Company. ELVACITE~ 2021 is a high molecular weight resin having a density of 1196 kg/m3; a specific gravity of 1.20 and a glass transition ~~ ~3~ 35H6 temperature of 98C. A suitable polyvinyl formal resin is FORMVAR~ 15/95E, available from Monsanto Company. FORMVAR~
15/95E has an average molecular weight of between about 24,000-40,000; a flow temperature at 1000 psi of 160-170C;
and an apparent glass transition temperature of about 103-113C. A suitable polyvinyl butyral resin is BUTVAR~ B-7B
Resin also available from Monsanto. BUTVAR~ B-7B resins have an average molecular weight of between about 50,000-80,000;
a flow temperature at 1000 psi of 125-130C; and an apparent glass transition temperature of 62-68C. A suitable hot meltpolyester resin is VESTAMELT~ X4053, available from ~UELS Corporation. VESTAMELT~ X4053 has a melt flow index of about 10.0 g/10 min., a melt viscosity at 140C or 950 Pas;
and a capillary method melting point of about 123C. Other suitable thermoplastic powders are illustrated in the Exam-ples which follow.
The new and improved induction curable adhesive compositions of this invention may also contain other additives such as fillers, pigments and dyes or the like added to make a paste of desired properties. Suitable fillers for use in the compositions of this invention are mineral fil-lers. Illustrative examples include: talc, mica, titanium dioxide, lithopone, zinc oxide, zirconium silica, silica aerogel, iron dioxide, diatomaceous earth, calcium carbonate, fumed silica, silazane treated silica, precipitated silica, glass Eibers, magnesium oxide, chromic oxide, æirconium oxide, aluminum oxide, crushed quartz, calcined clay, asbestos, carbon, graphite, cork, cotton, synthetic fibers, to name but a few. Preferred fillers for use herein include: talc, hydrophobic fumed silica such as CABO-SIL~ N707SD from Cabot Corporation and titanium di-oxide. Generally, the other additives such as fillers, dyes, pigments, thioxotropic agents and the like will be added in conventional amounts.
Other objects and advantages of the present in-vention will become apparent from the following working Examples:
?13~
Detailed Description of the Preferred Embodiments In the following Examples a number of adhesive compositions were prepared and tested for shelf stability at 41C; induction cure response and green strength; and final cure physical and environmental properties.
The adhesive compositions were each prepared by adding the components to a Ross Planetary Mixer, liquids then powders, and the compositions were blended under a vacuum for a time sufficient to insure thorough mixing and de-aeration of the compositions. The test formulations were s~ored in closed containers at temperatures of less than 49C until use. Care should be taken to ensure that the compositions are de-aerated and stored in air-tight containers because several of the components are hygroscopic. The presence of lS additional or excess moisture in the compositions is un-desirable because it may cause foaming o~ the compositions during cure which may adversely effect intermediate and final cured properties.
The compositions were prepared from commerc`ially available products, identified as follows:
,.
3~13~
Tradename Description Commercial Source DER 331~ Diglycidyl Ether Dow Chemical of Bisphenol-A
DER 736~ a polyglycol Dow Chemical diepoxide Kelpoxy 293-100~ rubber-modified Spencer-Kellogg - epoxy WC-6~ Neopentyl glycol Wilmington Chemical diglycidyl ether Z-6040~ glycidoxypropyl- Dow Corning trimethoxy silane CA 150~ l,l'-(4-methyl-m- American Cyanamid -phenylene)bis (3,3-dimethylurea) CA 152~ l,l-(methylene di- American Cyanamid phenyl)bis(4,4-di-methyl urea) HY940~ 100 pbw Araldite~ Ciba-Geigy 6010 epoxy and 70 pbw HT939 Formvar~ 15/95E po:lyvinyl Eormal Monsanto resin Acryloid~ Kl20N acrylate/methyl Rohm ~ Haas methacrylate resin The adhesive formulations were teste~ for shelf stability by placing 200g portions of the compositions in one-pint sealed containers and placing them in an oven at 105~. Visual inspections of the cornpositions for a clear increase in viscosity were conducted regularly over a three week period. Time until a marked viscosity increase was noted.
The compositions were tested for induction cure response and green strength properties by first preparing test coupons.
The test coupons were cut from one side-galvanized cold rolled steel measuring 0.03 inch thick and rrlill oil ~L~1 3 coated, into 1 inch by 4 inch strips. The strips were conditioned for 24 hours at 23+2C and 50% +5% relative humidity. The adhesive was applied to the galvanized surface and a 1 inch overlap lap joint was prepared between test strips having a bondline thickness of between a minimum of .005 inch and a maximum of 0.01 inch. 5 mil glass beads were added to the adhesive compositions to insure minimum bondline thickness. Excess adhesive squeeze-out was removed after the coupons had been assembled, prior to clamping on the in-duction curing apparatus.
~or some of the samples, test panels measuring 4 inches by 12 inches oE cold rolled 3 mil, mill oil treated, galvanized steel and adhesive were assembled into lap joints with a 0.5 inch overlap and cured as indicated. Thereafter, test strips measuring 1 inch by 6 inches are cut from the panel and tested for lap shear pull strength as described below. The green strengths for these test strips are reported in lbs, whereas test coupon results are reported in psi below.
The test coupons and test panels were induction cured on low frequency lOKHz Robotron equipment equipped with aver and under coils. Temperature measurements were con-ducted with an I~CON infra-red pyrometer with a capability of 23-300C temperature range and -~ 3C accuracy. The mounted test coupons were subjected to induction heating using a 4 second heating cycle and induction heating to a metal tem-perature of between 176C and 185C.
Some oE the induction heated test coupons were conditioned to 23 ~ 2C and lap shear pull tests were performed on standard Instron equipment at a shear pull test rate of 13 mm per minute. The tensile shear pull strength of the induction cured samples, referred to herein as green strength was noted, recording the peak load and type of separation, i.e. "adhesive failure" wherein adhesive separated from substrate, or "cohesive failure" wherein there was a separation within the adhesives.
Some of the test coupons were fully cured by .. :
. ~ .
~113~
.
heating in a forced air oven at 204C for 30 minutes. Shear pull strength of the fully cured adhesive was determined on Instron equipment as outlined above.
The compositions prepared and tested and the results obtained are set forth in Table 1 as foliows:
:~3~13~
TABLE 1: INDUCTION CURABLE ADHESIVE COMPOSITIONS
Composition: A B C D 1 2 3 4 _ A. Epoxides (pbw) DER 331 48.5 37.9 49.637.9 42.4 45.5 45.6 38.5 DER 736 - 8.0 - - - - - -Kelpoxy 293-100 - 5.0 WC-68 5 3 ~ 5 7 ~ ~ 9 5 3 5 3 5'3 Z-6040 0.4 O.~ 0.4 0.4 0.3 0,4 0,4 0,4 B. Curing Agents (pbw) Dicyandiamide 2.3 2.3 2.5 2.1 2.1 2.4 2.4 2.3 CA 150 - 0.4 0.8 2.1 0.7 0.7 CA 152 - - - - - - 0.7 Ciba-Geigy HY940 20.0 - - 4.2 10.0 11.0 11.0 20.0 Formvar 15/95E - 20.020.5 - 17.5 10.0 10.0 10.0 Acryloid K120N - - - 2.0 C. Other Additives (pbw) Talc 20.4 - 20.548.4 17.5 21.2 21.1 20.5 Calcium Carbonate - 26.0 Cab-o-sil N707SD 2.0 - - - - 2.0 2.0 2.0 5 mil glass beads 1.0 1 0 - 2.9 5 0 1.5 1.5 1.5 99.9 101.0 100 100 99.7 100 100 100 Properties:
Stability @ 41 C >3 wks <1 wk <1 wk tl wk <1 wk <1 wk <2 wkS >3 wks Induction cure 4s@ 6s @ 6.s@ 6s@ 6s @ 6s @ estimated 4s @
182-C 160-C 138C 163-c154-c 193-C 181-C
Green Strength, 301bs. 30 85 300 460 375 20 20 3751bs.
pSi Full Cure Strength, 2100 1600 2000 1900 2100 1700 2300 2100 pSl foaming foaming 20 mil bondline .
~3~3~36 Table 1 shows the results of some formulations testing which had target criteria of providing an induction curable adhesive composition which is stable for at least two weeks at 41 C; is induction curable to a green strength of at least 200 psi in 6 seconds or less when induction heated to 185C or less and which provides good final cure adhesive properties to oily galvanized metal substrates on the order of about 2000 psi.
Example A shows a composition containing a curing agent comprising DICY and HY940. Although stability and full cure criteria were met, the induction cured green strength of Example A was well below the 200 psi criteria.
Examples B and C show a combination of a thermo-plastic polyvinyl formal powder and DICY with a curing accelerator. The samples foamed considerably and failed to satisfy all three criteria. Examples B and C indicated that at 20% use levels foaming under humid summer conditions would be a major problem and also that use of a thermoplastic alone would not satisfy green strength criteria.
Example D shows that a combination of DICY, HY940 and a thermoplastic powder provide good green strength results but stability was very poor.
Example 1 demonstrates that good results are achieved by combining polyvinyl formal powder and HY940 together with ~ICY. Stability is still too poor and foaming at higher levels of thermoplastic may be a problem. Examples 2 and 3 show the results obtained using lower levels of polyvinyl formal. Stability for compositions containing an accelerator for the DICY were all genera]ly poor. Green strength was undesirably low.
Example 4 shows preferred embodiment of this in-vention wherein the concentration of HY940 was increased while the lower level of thermoplastic was retained. Cure accelerator for DICY was deleted. The results show that the composition of Example 4 was the best formulation tested. All three criteria were met.
~30:139~
The data of Table 1 demonstrate that an effective curing agent for an induction cured epoxy adhesive requires a combination of DICY, HY940 and a suitable green strength enhancing thermoplastic powder, in this case, a polyvinyl formal powder.
Following the lessons learned in Example 4, another adhesive composition comprising a combined curing agent comprising DICY, HY940 and polyvinyl formal was pre-pared and more thoroughly investigated for stability, green strength and final cure properties.
The composition prepared is set forth in Table 2.
... .. ~
~ ~ .
.. , : ~ ~ ...... ...
~;~13~
TABTE 2: INDUCTION CURABLE ADHESIVE COMPOSITION
Composition, pbw A. Epoxides:
DER 331 38.5 WC-6~ 5 3 Z-6040 0.4 B. Curing Agent:
DICY 2.3 HY940 20.0 FORMVAR 15/95E 10.0 C. Other Additives:
Talc 21.4 Cab-o-sil N70TSD 2.0 TiO2 .08 CALCO BLUE ZV BASE _ .02 100 parts Physical Properties:
Color - Green Press Flow Viscosity, seconds (80 psi, 0.104 inch orifice, 20 gms) Initial - 17-20 3 weeks at 41C - 19-22 6 weeks at 41C ~ 46-50 4 weeks at 35C - 18-22 Density, lbs/gal - . 11.0 .~
3~31~39~
Test coupons were prepared, induction cured and tested in accordance with the methods of Examples 1-4 using the composition of Example 5. The induction cured coupons were also subjected to special conditioning tests to deter-mine environmental green strength properties. Where in-dicated, some of the induction cured test coupons were subjected to Environmental Exposure, whlch consisted of consecutively storing induction heat cured coupons 1 week at -29c, 1 week at 38C and 100% relative humidity and l week at 41C. This was done to simulate possible part shipping and storage conditions prior to final curing. Some of the test coupons were subjected to thermal cycling tests wherein induction cured coupons were subjected to repeated thermal cycles wherein one thermal cycle consisted of conditioning 4 hours at 88C ~ followed by 4 hours at 38C and 100% relative humidity followed by 16 hours at -29C. Some of the test coupons were subjected to salt spray resistance tests in accordance with ASTM D-117 wherein the test coupon was suspended in a saturated 5% salt ~ater atmosphere for the times and temperatures indicated.
Some samples were subjected to scab corosion test-ing in accordance with Fisher Body Test ~ethod, FBTM 54-26.
In accordance with this testing procedure on a Monday, cured samples are conditioned by oven heating for 1 hour at 60C
followed by 30 minutes in a -10C cold cabinet followed by 15 minutes of immersion in a 5% salt solution followed by conditioning for 21 hours of humidity exposure at 60C and 85% relative humidity. From Tuesday through Friday, the samples are re-immersed in salt solution, drained and re-turned to humidity conditioning. On Saturday and Sunday the samples remain under humidity conditioning. This weekly cycle is repeated for a period of four weeks before testing.
Some cured samples were also tested for tortional shear strength in accordance with the Pendulum-Shear Impact test, Fisher Body Test Method, FBTM 45-76. In accordance with this method a mounted sample is impacted broadside at 90 angle with a weighted pendulum. The number of ft-lbs of C
energy absorbed by the sample in producing failure is noted as is the percentage and type of failure, e.g. cohesive or adhesive.
Results of the green strength stress conditioning studies are set forth in Table 3, as follows:
13~)1396 TABLE 3: Environmental Green Strength Properties Example 5 LAP SHEAR Results, psi, % and type of failure CONDITIONING:
1. Initial Green Strength 370 psi 2. Green Strength after 720 p8 i Environmental Exposure 3. Postcured 25 minutes at 171C 1340 psi, 100% Cohesive 4. Postcured 25 minutes at 171C 1310 psi, After Environmental Exposure 100% Cohesive 5. 500 Hours Salt Spray at 35C 1325 psi, After Post cure 25 minutes at 171C 100% Cohesive After Environmental Exposure 6. 10 Thermal Cycles, After Postcure 1260 psi, of 25 minutes at 171C. After 100% Cohesive Environmental Exposure 7. 500 Hours Salt Spray at35-C 9 1300 psi, After Postcure 25 minutes at 100% Cohesive 8. 10 Thermal Cycles, After Postcure 1250 psi, 25 minutes at171C 100% Cohesive 9. 1000 Hours Salt Spray at 35-C, after 1200 psi, post cure 25 minutes at171C 100% Cohesive 10. 1000 Hours Salt Spray at35C, after 1200 psi, post cure 25 minutes at 171C 100~/o Cohesive After Environmental Exposure 139~i , Test coupons prepared with the adhesive compo-sition of Example 5 were also simply oven cured for 30 minutes at 204C and subjected to conditioning to determine full-cure physical and environmental properties the results are reported in Table 4, below:
~3~ 39S~
, .
TABLE 4: OVEN CURED PROPERTIES OF EXAMPLE 5 Test Results - Oven Cured Only Cold Rolled Steel (DQSAK/DQSAK) .03 inch thick, mill oil coated, .5 inch over lap, .005 inch bond line thickness, cured 30 minutes at 204oC
Tensile Lap Shear Pull strength, psi Initial 2080 psi, 100% Cohesive 250 Hours S~lt Spray 2030 psi, 100% Cohesive at 35C
2 Weeks at 38C and 2130 psi, 100% Cohesive 100% RH
4 Weeks Scab Corrosion 1600 psi, 80% Cohesive (Painted Coupons) Torosional Impact 44 in. lb., 100CL Cohesive Galvanizedt G90, .035 inch thick, mill oil coated, .5 inch overlap, .005 inch bond line thickness, cured 30 minutes at 204C
Tensile Lap Shear Pull strength, psi Initial 2900 p5i, 100% Cohesive 2 Weeks 38C and 100% R.H. 2400 psi, 100% Cohesive 100% R.H.
250 Hours Salt Spray 2500 psi, 100% Cohesive at 35C
3 Weeks 38C and 100% R.H. 2450 psi, 90% Cohesive (Cured 20 minutes at 177C
plus 30 minutes at 121C
C
9~;
The data of Tables 3 and ~ indicate that the composition of Example 5 provides an excellent induction curable adhesive for oily galvanized metal parts especially adapted for use ;n modern automobile manufacturing methods.
In the following Examples, a number of different thermoplastic powders were evaluated for suitablility as green strength enhancing agents in the combined induction curing agent of this invention.
The thermoplastic powders were preliminarily evaluated for stability in epoxy resins and for gel behavior in epoxies to pre-screen suitable candidates prior to working up to a complete formulation. The thermoplastic powders were tested by first hand mixing a 70/30 blend of DER
lS 331/thermoplastic powder. Portions of the blendswere placed in sealed containers and stored in a 41C oven for a period of three weeks. The stability samples were regularly checked throughout the period until a marked increase in vi 5COS ity of the blend was noted. In addition, portions of the blend were baked at 149C for 10 minutes and were visually observed to determine whether the thermoplastic showed some gel effect, either by melting or melting and fusing within the epoxy resin. For purposes of this inspection some physical change in the thermoplastic powder was required.
Test samples of the 70/30 blends which exhibited a gel effect ;n epoxy and were stable for a two week period at 41C were considered candidates for further formulation studies.
The thermoplastic powders evaluated and the re-sults obtained are set forth in Table 5 as follows:
L3013~6 TABLE 5: 70/30 Blends of DER 331/Thermoplastic Thermoplastic Name Gels in Epoxy Stability Chemical Name Yes/No Polyvinyl Alcohol - DuPont No Yes Acryloid K120N - Rohm & Haas Yes No Acrylic Polymer of Methyl Methacrylate Acryloid A-30 Rohm & HaasYes No Acryloid A-ll Methyl Methacrylate Polymers Yes Yes (Poor) Blendex 311 Borg Warner No Yes Blendex 386 No Yes Blendex 131 Yes No ~lendex 586 Yes Yes (Poor) Hostyren 57 - American Yes Yes Polystyrene Hoecht Phenoxy PKHH - Union Carbide Yes (Excellent) No Polyhydroxyether Polyox WSR-1105 Ethylene Oxide - Union Carbide Yes Yes Effect is too weak Nylon 12 - Huels Polyamide polymer Yes Yes Vestamelt X4053A - Huels Yes Yes Hot Melt Polyester Elvacite - DuPont 2013 Yes No 2021 Yes Yes (Workable Formula) 2045 Yes No FPC-9275 Occidental No Yes polyvinyl chloride polymer FN 510 USI . Yes Yes Polyethylene Powder FE 532 USI Yes Yes Ethylene Vinyl Acetate Formvar 15/95E Monsanto Yes Yes Polyvinyl Formal !.
'' " ~ .
~30:~39~;
- 3~ -TABLE 5 (cont'd.) Thermoplastic NameGels in Epoxy Stability Chemical Name Yes/No .
Butvar - Monsanto Yes Yes Polyvinyl Butyral Chemigum P83 Goodyear Yes No Nitrile Rubber Dylark 232 - ARCO Yes No Styrene/Maleic Anhydride BaylithT Mobay No Yes .
From the foregoing screen testing it was determined that the following thermoplastic powders provided satisfactory properties for induction heat curing:
Formvar 15/95E Polyvinyl Formal FN 510 Low density polyethylene Vestamelt X4053A Polyester Elvacite 2021 Acrylic Resin, Methyl methacrylate Butvar Polyvinyl butyral Hostyren 57 Polystyrene FE 532 Ethylene vinyl acetate Nylon-12 Polyamide Several of the thermoplastic powders evaluated in Example 6, some of which passed the pre-screen testing and some of which did not, were formulated with or without curing agents into adhesive compositions which were tested for stability at 4~C in accordance with the methods of Examples 1-5. Lap shear coupons were prepared, some of them for induction curing on Robotron equipment as in Examples 1-5 above, for other coupons a simulated intermediate cure was achieved by oven heating the lap shear coupons atl35-149C
for 5 to 10 minutes, to provide a green strength value without activating the high temperature cure reaction of the DICY
component. The samples were fully cured by heating lap shear coupons at 191C for 60 minutes.
The compositions prepared and the results obtained are set forth in Table 6 as follows:
3~;
6l109-7529 TABLE 6: Adhesive Compositions COMPOSITIO_ A. EPOXIDES
r:ER 331 32.32 32.32 32.32 32.32 32.32 32.32 WC-68 5.0 5.0 5.0 5.0 5.0 5.0 Z-6040 0.4 0.4 0.4 0.4 0.4 0.4 B. OTHER ADDITIVES
TALC 16.0 16.0 16.0 16.0 16.0 16.0 CAB-O-SIL 2.0 2.0 2.0 2.0 2.0 2.0 DYES 0.08 - 0.08 0.08 0.08 0.08 5 mil. GLASS BEADS
ALUMINUM M0201 6.0 6.0 6.0 6.0 6.0 6.0 C. CURING AGENT
DICY 2.2 2.2 2.2 2.0 2.0 2.0 HY940 25.0 25.0 25.0 25.0 25.0 25.0 FN 510 11.0 - ~ - ~ ~
FN 532 - 11.0 X4053APl - - 11.0 - - -ELVACITE~ 2013 - - - 11.0 ELVACITE~ 2021 - - - - 11.0 ELVACITE~ 2041 - - - - - 11.0 BUTVAR B72 - - - - - ~
PROPERTIES:
Stability at 4lC>3 >2 >2 <1 >2 <1 weeks Green Strength, psi 325 325 325 - 300 (Robotron, cure (1 77C/~s. ) ( 1 77y4s. ) ( 1 ~C/4s. ) ( 1 ~y45- ) conditions) Full cure Pull 2000 1600 1500 2000 1700 1700 Shear Strength, pSi f~
13~)13~j TABLE 6 (cont'd.): Adhesive Compositions EXAMPLE G H I J K
COMPOSITION
A. EPOXIDES
DER 331 45.5 45.5 45.4 52.5 52.5 WC-68 5.; 5.3 5.3 5.3 5.3 Z-6040 0.4 0.4 G.4 0.4 0.4 B. OTHER ADDITIVES
TALC 20.h 20.4 20.4 20.4 20.4 CAB-O-SIL 3.0 3.0 2.0 2.0 2.0 DYES - _ _ _ _ 5 mil. GLASS BEADS 1.0 l.O - - -C. CURING AGENT
DICY - 2.4 2.4 2.4 2.4 HY940 - - 6.1 X4053APl ELVACITE~ 2013 ELVACITE~ 2021 ELVACITE~ 2041 NYLON-12 22.0 22.0 FORMVAR 15/95E - - 10.0 10.0 10.0 HQSTYREN 57 - - 6.0 BUTVAR B72 - - - 6.0 ACRYLOID A-30 - - - - 6.0 PROPERTIES:
Stability at 41C,~3 ~3 >3 ~3 <1 weeks Green Strength, psi 66 - 5Q 65 36 (Robotron, cure conditions) Full cure Pull - 1800 2100 2000 2000 Shear Strength, psi 13~1396 . ~
The results of Table 6 verify the accuracy of the pre-screening methods employed in Example 6. The compo-sitions of Examples 6-8 all subtantially met the stability green strength and final cure criteria. The compositions of Examples E, 9, and F show that of the polyacrylic resins tested only the Elvacite 2021 provided acceptable results.
Examples G and H were formulated without HY940. Example G
demonstrates that the NYLON 12 does contribute to green strength and does not adversely effect final cure properties, as shown in the DICY containing formulation of Example H.
Similarly, the compositions of Examples I and J show that a combination of FORMVAR~ and HOSTYREN~ and FORMVAR~ and BUTVAR~ resins contributed to green strength enhancement, respectively, even though the compositions did not contain a sufficient amount of HY940. In contrast, the composition of Example K, containing AC~YLOID A-30~ resin did not enhance green strength and had poor stability.
In the following Examples, test panels were pre-pared and tested in accordance with E~amples 1-4, with the exception that, instead oE employing HY940 as the inter-mediate temperat~lre curing agent, a modified polyamine, ANCAMINE 2014A~ ~rom Anchor Chemical Corporation was used.
The compositions prepared and the results obtained are set Eorth in Table 7 as follows:
TABI.E 7: Induction Curable Adhesives Comprising ANCAMINE 2014A~
Composition, pbw A. Epoxides:
DER 331 47.5 47.5 WC-68 8.0 8.0 B. Curing Agent:
DICY 2.0 2.0 FORMVAR 15/95E 4.0 4.0 FN 510 3.4 3.4 CIBA HT939 12.7 ANCAMINE 2041 - 12.8 C. Other Additives:
Talc 19.~ 19.9 Cab-o-sil N70TSD 3.0 3.0 Dyes 0.08 0.08 PROPEP~TIES
Stability at 41C, weeks >2 >2 Green Strength, lbs. 350 450 Final Cure strength, psi 2200 2100 C
3~i As shown by the data of Table 7, the composition of Example 11 containing ANCAMINE 2041A~ provided a satis-factory induction curable adhesive for bonding oily gal-vanized metallic parts having properties as good as the same formulation prepared with HY939, the active ingredient in HY9~0.
Although the present invention has been described with reference to certain preferred embodiments, modifi-cation or changes may be made therein by those skilled in this art. For example, a different mixture of polyepoxides may be used as the epoxy component. For end use applications where the adhesive is used to bond non-oily metals, some or all of the mineral filler adhesion promoters may be omitted. All such obvious modifications may be made without departing from the scope and spirit of the present invention as defined by the appended Claims.
Tradename Description Commercial Source DER 331~ Diglycidyl Ether Dow Chemical of Bisphenol-A
DER 736~ a polyglycol Dow Chemical diepoxide Kelpoxy 293-100~ rubber-modified Spencer-Kellogg - epoxy WC-6~ Neopentyl glycol Wilmington Chemical diglycidyl ether Z-6040~ glycidoxypropyl- Dow Corning trimethoxy silane CA 150~ l,l'-(4-methyl-m- American Cyanamid -phenylene)bis (3,3-dimethylurea) CA 152~ l,l-(methylene di- American Cyanamid phenyl)bis(4,4-di-methyl urea) HY940~ 100 pbw Araldite~ Ciba-Geigy 6010 epoxy and 70 pbw HT939 Formvar~ 15/95E po:lyvinyl Eormal Monsanto resin Acryloid~ Kl20N acrylate/methyl Rohm ~ Haas methacrylate resin The adhesive formulations were teste~ for shelf stability by placing 200g portions of the compositions in one-pint sealed containers and placing them in an oven at 105~. Visual inspections of the cornpositions for a clear increase in viscosity were conducted regularly over a three week period. Time until a marked viscosity increase was noted.
The compositions were tested for induction cure response and green strength properties by first preparing test coupons.
The test coupons were cut from one side-galvanized cold rolled steel measuring 0.03 inch thick and rrlill oil ~L~1 3 coated, into 1 inch by 4 inch strips. The strips were conditioned for 24 hours at 23+2C and 50% +5% relative humidity. The adhesive was applied to the galvanized surface and a 1 inch overlap lap joint was prepared between test strips having a bondline thickness of between a minimum of .005 inch and a maximum of 0.01 inch. 5 mil glass beads were added to the adhesive compositions to insure minimum bondline thickness. Excess adhesive squeeze-out was removed after the coupons had been assembled, prior to clamping on the in-duction curing apparatus.
~or some of the samples, test panels measuring 4 inches by 12 inches oE cold rolled 3 mil, mill oil treated, galvanized steel and adhesive were assembled into lap joints with a 0.5 inch overlap and cured as indicated. Thereafter, test strips measuring 1 inch by 6 inches are cut from the panel and tested for lap shear pull strength as described below. The green strengths for these test strips are reported in lbs, whereas test coupon results are reported in psi below.
The test coupons and test panels were induction cured on low frequency lOKHz Robotron equipment equipped with aver and under coils. Temperature measurements were con-ducted with an I~CON infra-red pyrometer with a capability of 23-300C temperature range and -~ 3C accuracy. The mounted test coupons were subjected to induction heating using a 4 second heating cycle and induction heating to a metal tem-perature of between 176C and 185C.
Some oE the induction heated test coupons were conditioned to 23 ~ 2C and lap shear pull tests were performed on standard Instron equipment at a shear pull test rate of 13 mm per minute. The tensile shear pull strength of the induction cured samples, referred to herein as green strength was noted, recording the peak load and type of separation, i.e. "adhesive failure" wherein adhesive separated from substrate, or "cohesive failure" wherein there was a separation within the adhesives.
Some of the test coupons were fully cured by .. :
. ~ .
~113~
.
heating in a forced air oven at 204C for 30 minutes. Shear pull strength of the fully cured adhesive was determined on Instron equipment as outlined above.
The compositions prepared and tested and the results obtained are set forth in Table 1 as foliows:
:~3~13~
TABLE 1: INDUCTION CURABLE ADHESIVE COMPOSITIONS
Composition: A B C D 1 2 3 4 _ A. Epoxides (pbw) DER 331 48.5 37.9 49.637.9 42.4 45.5 45.6 38.5 DER 736 - 8.0 - - - - - -Kelpoxy 293-100 - 5.0 WC-68 5 3 ~ 5 7 ~ ~ 9 5 3 5 3 5'3 Z-6040 0.4 O.~ 0.4 0.4 0.3 0,4 0,4 0,4 B. Curing Agents (pbw) Dicyandiamide 2.3 2.3 2.5 2.1 2.1 2.4 2.4 2.3 CA 150 - 0.4 0.8 2.1 0.7 0.7 CA 152 - - - - - - 0.7 Ciba-Geigy HY940 20.0 - - 4.2 10.0 11.0 11.0 20.0 Formvar 15/95E - 20.020.5 - 17.5 10.0 10.0 10.0 Acryloid K120N - - - 2.0 C. Other Additives (pbw) Talc 20.4 - 20.548.4 17.5 21.2 21.1 20.5 Calcium Carbonate - 26.0 Cab-o-sil N707SD 2.0 - - - - 2.0 2.0 2.0 5 mil glass beads 1.0 1 0 - 2.9 5 0 1.5 1.5 1.5 99.9 101.0 100 100 99.7 100 100 100 Properties:
Stability @ 41 C >3 wks <1 wk <1 wk tl wk <1 wk <1 wk <2 wkS >3 wks Induction cure 4s@ 6s @ 6.s@ 6s@ 6s @ 6s @ estimated 4s @
182-C 160-C 138C 163-c154-c 193-C 181-C
Green Strength, 301bs. 30 85 300 460 375 20 20 3751bs.
pSi Full Cure Strength, 2100 1600 2000 1900 2100 1700 2300 2100 pSl foaming foaming 20 mil bondline .
~3~3~36 Table 1 shows the results of some formulations testing which had target criteria of providing an induction curable adhesive composition which is stable for at least two weeks at 41 C; is induction curable to a green strength of at least 200 psi in 6 seconds or less when induction heated to 185C or less and which provides good final cure adhesive properties to oily galvanized metal substrates on the order of about 2000 psi.
Example A shows a composition containing a curing agent comprising DICY and HY940. Although stability and full cure criteria were met, the induction cured green strength of Example A was well below the 200 psi criteria.
Examples B and C show a combination of a thermo-plastic polyvinyl formal powder and DICY with a curing accelerator. The samples foamed considerably and failed to satisfy all three criteria. Examples B and C indicated that at 20% use levels foaming under humid summer conditions would be a major problem and also that use of a thermoplastic alone would not satisfy green strength criteria.
Example D shows that a combination of DICY, HY940 and a thermoplastic powder provide good green strength results but stability was very poor.
Example 1 demonstrates that good results are achieved by combining polyvinyl formal powder and HY940 together with ~ICY. Stability is still too poor and foaming at higher levels of thermoplastic may be a problem. Examples 2 and 3 show the results obtained using lower levels of polyvinyl formal. Stability for compositions containing an accelerator for the DICY were all genera]ly poor. Green strength was undesirably low.
Example 4 shows preferred embodiment of this in-vention wherein the concentration of HY940 was increased while the lower level of thermoplastic was retained. Cure accelerator for DICY was deleted. The results show that the composition of Example 4 was the best formulation tested. All three criteria were met.
~30:139~
The data of Table 1 demonstrate that an effective curing agent for an induction cured epoxy adhesive requires a combination of DICY, HY940 and a suitable green strength enhancing thermoplastic powder, in this case, a polyvinyl formal powder.
Following the lessons learned in Example 4, another adhesive composition comprising a combined curing agent comprising DICY, HY940 and polyvinyl formal was pre-pared and more thoroughly investigated for stability, green strength and final cure properties.
The composition prepared is set forth in Table 2.
... .. ~
~ ~ .
.. , : ~ ~ ...... ...
~;~13~
TABTE 2: INDUCTION CURABLE ADHESIVE COMPOSITION
Composition, pbw A. Epoxides:
DER 331 38.5 WC-6~ 5 3 Z-6040 0.4 B. Curing Agent:
DICY 2.3 HY940 20.0 FORMVAR 15/95E 10.0 C. Other Additives:
Talc 21.4 Cab-o-sil N70TSD 2.0 TiO2 .08 CALCO BLUE ZV BASE _ .02 100 parts Physical Properties:
Color - Green Press Flow Viscosity, seconds (80 psi, 0.104 inch orifice, 20 gms) Initial - 17-20 3 weeks at 41C - 19-22 6 weeks at 41C ~ 46-50 4 weeks at 35C - 18-22 Density, lbs/gal - . 11.0 .~
3~31~39~
Test coupons were prepared, induction cured and tested in accordance with the methods of Examples 1-4 using the composition of Example 5. The induction cured coupons were also subjected to special conditioning tests to deter-mine environmental green strength properties. Where in-dicated, some of the induction cured test coupons were subjected to Environmental Exposure, whlch consisted of consecutively storing induction heat cured coupons 1 week at -29c, 1 week at 38C and 100% relative humidity and l week at 41C. This was done to simulate possible part shipping and storage conditions prior to final curing. Some of the test coupons were subjected to thermal cycling tests wherein induction cured coupons were subjected to repeated thermal cycles wherein one thermal cycle consisted of conditioning 4 hours at 88C ~ followed by 4 hours at 38C and 100% relative humidity followed by 16 hours at -29C. Some of the test coupons were subjected to salt spray resistance tests in accordance with ASTM D-117 wherein the test coupon was suspended in a saturated 5% salt ~ater atmosphere for the times and temperatures indicated.
Some samples were subjected to scab corosion test-ing in accordance with Fisher Body Test ~ethod, FBTM 54-26.
In accordance with this testing procedure on a Monday, cured samples are conditioned by oven heating for 1 hour at 60C
followed by 30 minutes in a -10C cold cabinet followed by 15 minutes of immersion in a 5% salt solution followed by conditioning for 21 hours of humidity exposure at 60C and 85% relative humidity. From Tuesday through Friday, the samples are re-immersed in salt solution, drained and re-turned to humidity conditioning. On Saturday and Sunday the samples remain under humidity conditioning. This weekly cycle is repeated for a period of four weeks before testing.
Some cured samples were also tested for tortional shear strength in accordance with the Pendulum-Shear Impact test, Fisher Body Test Method, FBTM 45-76. In accordance with this method a mounted sample is impacted broadside at 90 angle with a weighted pendulum. The number of ft-lbs of C
energy absorbed by the sample in producing failure is noted as is the percentage and type of failure, e.g. cohesive or adhesive.
Results of the green strength stress conditioning studies are set forth in Table 3, as follows:
13~)1396 TABLE 3: Environmental Green Strength Properties Example 5 LAP SHEAR Results, psi, % and type of failure CONDITIONING:
1. Initial Green Strength 370 psi 2. Green Strength after 720 p8 i Environmental Exposure 3. Postcured 25 minutes at 171C 1340 psi, 100% Cohesive 4. Postcured 25 minutes at 171C 1310 psi, After Environmental Exposure 100% Cohesive 5. 500 Hours Salt Spray at 35C 1325 psi, After Post cure 25 minutes at 171C 100% Cohesive After Environmental Exposure 6. 10 Thermal Cycles, After Postcure 1260 psi, of 25 minutes at 171C. After 100% Cohesive Environmental Exposure 7. 500 Hours Salt Spray at35-C 9 1300 psi, After Postcure 25 minutes at 100% Cohesive 8. 10 Thermal Cycles, After Postcure 1250 psi, 25 minutes at171C 100% Cohesive 9. 1000 Hours Salt Spray at 35-C, after 1200 psi, post cure 25 minutes at171C 100% Cohesive 10. 1000 Hours Salt Spray at35C, after 1200 psi, post cure 25 minutes at 171C 100~/o Cohesive After Environmental Exposure 139~i , Test coupons prepared with the adhesive compo-sition of Example 5 were also simply oven cured for 30 minutes at 204C and subjected to conditioning to determine full-cure physical and environmental properties the results are reported in Table 4, below:
~3~ 39S~
, .
TABLE 4: OVEN CURED PROPERTIES OF EXAMPLE 5 Test Results - Oven Cured Only Cold Rolled Steel (DQSAK/DQSAK) .03 inch thick, mill oil coated, .5 inch over lap, .005 inch bond line thickness, cured 30 minutes at 204oC
Tensile Lap Shear Pull strength, psi Initial 2080 psi, 100% Cohesive 250 Hours S~lt Spray 2030 psi, 100% Cohesive at 35C
2 Weeks at 38C and 2130 psi, 100% Cohesive 100% RH
4 Weeks Scab Corrosion 1600 psi, 80% Cohesive (Painted Coupons) Torosional Impact 44 in. lb., 100CL Cohesive Galvanizedt G90, .035 inch thick, mill oil coated, .5 inch overlap, .005 inch bond line thickness, cured 30 minutes at 204C
Tensile Lap Shear Pull strength, psi Initial 2900 p5i, 100% Cohesive 2 Weeks 38C and 100% R.H. 2400 psi, 100% Cohesive 100% R.H.
250 Hours Salt Spray 2500 psi, 100% Cohesive at 35C
3 Weeks 38C and 100% R.H. 2450 psi, 90% Cohesive (Cured 20 minutes at 177C
plus 30 minutes at 121C
C
9~;
The data of Tables 3 and ~ indicate that the composition of Example 5 provides an excellent induction curable adhesive for oily galvanized metal parts especially adapted for use ;n modern automobile manufacturing methods.
In the following Examples, a number of different thermoplastic powders were evaluated for suitablility as green strength enhancing agents in the combined induction curing agent of this invention.
The thermoplastic powders were preliminarily evaluated for stability in epoxy resins and for gel behavior in epoxies to pre-screen suitable candidates prior to working up to a complete formulation. The thermoplastic powders were tested by first hand mixing a 70/30 blend of DER
lS 331/thermoplastic powder. Portions of the blendswere placed in sealed containers and stored in a 41C oven for a period of three weeks. The stability samples were regularly checked throughout the period until a marked increase in vi 5COS ity of the blend was noted. In addition, portions of the blend were baked at 149C for 10 minutes and were visually observed to determine whether the thermoplastic showed some gel effect, either by melting or melting and fusing within the epoxy resin. For purposes of this inspection some physical change in the thermoplastic powder was required.
Test samples of the 70/30 blends which exhibited a gel effect ;n epoxy and were stable for a two week period at 41C were considered candidates for further formulation studies.
The thermoplastic powders evaluated and the re-sults obtained are set forth in Table 5 as follows:
L3013~6 TABLE 5: 70/30 Blends of DER 331/Thermoplastic Thermoplastic Name Gels in Epoxy Stability Chemical Name Yes/No Polyvinyl Alcohol - DuPont No Yes Acryloid K120N - Rohm & Haas Yes No Acrylic Polymer of Methyl Methacrylate Acryloid A-30 Rohm & HaasYes No Acryloid A-ll Methyl Methacrylate Polymers Yes Yes (Poor) Blendex 311 Borg Warner No Yes Blendex 386 No Yes Blendex 131 Yes No ~lendex 586 Yes Yes (Poor) Hostyren 57 - American Yes Yes Polystyrene Hoecht Phenoxy PKHH - Union Carbide Yes (Excellent) No Polyhydroxyether Polyox WSR-1105 Ethylene Oxide - Union Carbide Yes Yes Effect is too weak Nylon 12 - Huels Polyamide polymer Yes Yes Vestamelt X4053A - Huels Yes Yes Hot Melt Polyester Elvacite - DuPont 2013 Yes No 2021 Yes Yes (Workable Formula) 2045 Yes No FPC-9275 Occidental No Yes polyvinyl chloride polymer FN 510 USI . Yes Yes Polyethylene Powder FE 532 USI Yes Yes Ethylene Vinyl Acetate Formvar 15/95E Monsanto Yes Yes Polyvinyl Formal !.
'' " ~ .
~30:~39~;
- 3~ -TABLE 5 (cont'd.) Thermoplastic NameGels in Epoxy Stability Chemical Name Yes/No .
Butvar - Monsanto Yes Yes Polyvinyl Butyral Chemigum P83 Goodyear Yes No Nitrile Rubber Dylark 232 - ARCO Yes No Styrene/Maleic Anhydride BaylithT Mobay No Yes .
From the foregoing screen testing it was determined that the following thermoplastic powders provided satisfactory properties for induction heat curing:
Formvar 15/95E Polyvinyl Formal FN 510 Low density polyethylene Vestamelt X4053A Polyester Elvacite 2021 Acrylic Resin, Methyl methacrylate Butvar Polyvinyl butyral Hostyren 57 Polystyrene FE 532 Ethylene vinyl acetate Nylon-12 Polyamide Several of the thermoplastic powders evaluated in Example 6, some of which passed the pre-screen testing and some of which did not, were formulated with or without curing agents into adhesive compositions which were tested for stability at 4~C in accordance with the methods of Examples 1-5. Lap shear coupons were prepared, some of them for induction curing on Robotron equipment as in Examples 1-5 above, for other coupons a simulated intermediate cure was achieved by oven heating the lap shear coupons atl35-149C
for 5 to 10 minutes, to provide a green strength value without activating the high temperature cure reaction of the DICY
component. The samples were fully cured by heating lap shear coupons at 191C for 60 minutes.
The compositions prepared and the results obtained are set forth in Table 6 as follows:
3~;
6l109-7529 TABLE 6: Adhesive Compositions COMPOSITIO_ A. EPOXIDES
r:ER 331 32.32 32.32 32.32 32.32 32.32 32.32 WC-68 5.0 5.0 5.0 5.0 5.0 5.0 Z-6040 0.4 0.4 0.4 0.4 0.4 0.4 B. OTHER ADDITIVES
TALC 16.0 16.0 16.0 16.0 16.0 16.0 CAB-O-SIL 2.0 2.0 2.0 2.0 2.0 2.0 DYES 0.08 - 0.08 0.08 0.08 0.08 5 mil. GLASS BEADS
ALUMINUM M0201 6.0 6.0 6.0 6.0 6.0 6.0 C. CURING AGENT
DICY 2.2 2.2 2.2 2.0 2.0 2.0 HY940 25.0 25.0 25.0 25.0 25.0 25.0 FN 510 11.0 - ~ - ~ ~
FN 532 - 11.0 X4053APl - - 11.0 - - -ELVACITE~ 2013 - - - 11.0 ELVACITE~ 2021 - - - - 11.0 ELVACITE~ 2041 - - - - - 11.0 BUTVAR B72 - - - - - ~
PROPERTIES:
Stability at 4lC>3 >2 >2 <1 >2 <1 weeks Green Strength, psi 325 325 325 - 300 (Robotron, cure (1 77C/~s. ) ( 1 77y4s. ) ( 1 ~C/4s. ) ( 1 ~y45- ) conditions) Full cure Pull 2000 1600 1500 2000 1700 1700 Shear Strength, pSi f~
13~)13~j TABLE 6 (cont'd.): Adhesive Compositions EXAMPLE G H I J K
COMPOSITION
A. EPOXIDES
DER 331 45.5 45.5 45.4 52.5 52.5 WC-68 5.; 5.3 5.3 5.3 5.3 Z-6040 0.4 0.4 G.4 0.4 0.4 B. OTHER ADDITIVES
TALC 20.h 20.4 20.4 20.4 20.4 CAB-O-SIL 3.0 3.0 2.0 2.0 2.0 DYES - _ _ _ _ 5 mil. GLASS BEADS 1.0 l.O - - -C. CURING AGENT
DICY - 2.4 2.4 2.4 2.4 HY940 - - 6.1 X4053APl ELVACITE~ 2013 ELVACITE~ 2021 ELVACITE~ 2041 NYLON-12 22.0 22.0 FORMVAR 15/95E - - 10.0 10.0 10.0 HQSTYREN 57 - - 6.0 BUTVAR B72 - - - 6.0 ACRYLOID A-30 - - - - 6.0 PROPERTIES:
Stability at 41C,~3 ~3 >3 ~3 <1 weeks Green Strength, psi 66 - 5Q 65 36 (Robotron, cure conditions) Full cure Pull - 1800 2100 2000 2000 Shear Strength, psi 13~1396 . ~
The results of Table 6 verify the accuracy of the pre-screening methods employed in Example 6. The compo-sitions of Examples 6-8 all subtantially met the stability green strength and final cure criteria. The compositions of Examples E, 9, and F show that of the polyacrylic resins tested only the Elvacite 2021 provided acceptable results.
Examples G and H were formulated without HY940. Example G
demonstrates that the NYLON 12 does contribute to green strength and does not adversely effect final cure properties, as shown in the DICY containing formulation of Example H.
Similarly, the compositions of Examples I and J show that a combination of FORMVAR~ and HOSTYREN~ and FORMVAR~ and BUTVAR~ resins contributed to green strength enhancement, respectively, even though the compositions did not contain a sufficient amount of HY940. In contrast, the composition of Example K, containing AC~YLOID A-30~ resin did not enhance green strength and had poor stability.
In the following Examples, test panels were pre-pared and tested in accordance with E~amples 1-4, with the exception that, instead oE employing HY940 as the inter-mediate temperat~lre curing agent, a modified polyamine, ANCAMINE 2014A~ ~rom Anchor Chemical Corporation was used.
The compositions prepared and the results obtained are set Eorth in Table 7 as follows:
TABI.E 7: Induction Curable Adhesives Comprising ANCAMINE 2014A~
Composition, pbw A. Epoxides:
DER 331 47.5 47.5 WC-68 8.0 8.0 B. Curing Agent:
DICY 2.0 2.0 FORMVAR 15/95E 4.0 4.0 FN 510 3.4 3.4 CIBA HT939 12.7 ANCAMINE 2041 - 12.8 C. Other Additives:
Talc 19.~ 19.9 Cab-o-sil N70TSD 3.0 3.0 Dyes 0.08 0.08 PROPEP~TIES
Stability at 41C, weeks >2 >2 Green Strength, lbs. 350 450 Final Cure strength, psi 2200 2100 C
3~i As shown by the data of Table 7, the composition of Example 11 containing ANCAMINE 2041A~ provided a satis-factory induction curable adhesive for bonding oily gal-vanized metallic parts having properties as good as the same formulation prepared with HY939, the active ingredient in HY9~0.
Although the present invention has been described with reference to certain preferred embodiments, modifi-cation or changes may be made therein by those skilled in this art. For example, a different mixture of polyepoxides may be used as the epoxy component. For end use applications where the adhesive is used to bond non-oily metals, some or all of the mineral filler adhesion promoters may be omitted. All such obvious modifications may be made without departing from the scope and spirit of the present invention as defined by the appended Claims.
Claims (13)
1. A curing agent additive for induction curing of epoxy-based adhesive compositions said curing agent comprising:
(i) a latent high temperature curing agent;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene ethylene vinyl acetate polystyrene polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate) NYLON 12 and hot melt polyester resins and mixtures of any of the foregoing resins wherein component (i) comprises from about 7 to about 12% by weight component (ii) comprises from about 35 to about 65% by weight and component (ii) comprises about 26 to about 53% by weight, based upon the total weight of said curing agent additive.
(i) a latent high temperature curing agent;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene ethylene vinyl acetate polystyrene polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate) NYLON 12 and hot melt polyester resins and mixtures of any of the foregoing resins wherein component (i) comprises from about 7 to about 12% by weight component (ii) comprises from about 35 to about 65% by weight and component (ii) comprises about 26 to about 53% by weight, based upon the total weight of said curing agent additive.
2. A curing agent additive as recited in Claim 1 wherein said high temperature curing agent remains relatively inert up to about 149°C, but above 149°C is capable of rapidly catalyzing the crosslinking of an epoxy resin.
3. A curing agent additive as recited in Claim 1 wherein component (ii) is present in an amount effective to partially cure an adhesive composition in conjunction with component (iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive to temperatures of about 185°C or less.
4. A curing agent additive as recited in Claim 1 wherein said intermediate temperature curing agent is unreactive up to temperatures of between about 100° and 150°C.
5. A curing agent additive as recited in Claim 1 wherein said green strength enhancing agent has a particle size of between about 5 to about 500 microns and a glass transition temperature or a crystalline melt temperature of between about 50°C to about 160°C
6. A curing agent additive as recited in Claim 1 wherein said high temperature curing agent comprises dicyandiamide.
7. A curing agent additive as recited in Claim 1 wherein said intermediate temperature curing agent is selected from the group consisting of Dibenzo (i,t)(1,4,7,12,15,18)hexa-azacyclodocosine-5,13,18,26(6H,19H)tetrone(9CI), SB-7,8,9,10,11,12,20,21,22,23,24,25-decahydro and ANCAMINE? 2041A.
8. An induction curable adhesive composition comprising:
(a) an epoxy resin comprising a polyepoxide or mixture of polyepoxides; and (b) an effective amount of a combination curing agent therefor comprising:
(i) a latent high temperature curing agent, which remains relatively inert up to about 149°C, but above 149°C is capable of rapidly catalyzing the crosslinking of the epoxy resin;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures thereof, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185°C or less.
(a) an epoxy resin comprising a polyepoxide or mixture of polyepoxides; and (b) an effective amount of a combination curing agent therefor comprising:
(i) a latent high temperature curing agent, which remains relatively inert up to about 149°C, but above 149°C is capable of rapidly catalyzing the crosslinking of the epoxy resin;
(ii) a latent intermediate temperature curing agent; and (iii) a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures thereof, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185°C or less.
9. An induction curable adhesive composition comprising:
(a) 100 parts by weight of an epoxy resin comprising a polyepoxide or a mixture of epoxides having an epoxy equivalent weight of at least about 150; and (b) from about 30 to about 50 parts by weight of a combination curing agent comprising:
(1) from about 2 to about 8 phr of a latent high temperature curing agent, which remains relatively inert up to about 149 C, but above 149°C is capable of rapidly catalyzing the epoxy resin; and (ii) from about 12 to about 30 phr of a latent intermediate temperature curing agent; and (ill) from about 12 to about 28 phr of a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly (methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures thereof, based upon the total weight of said adhesive composition, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185°C or less.
(a) 100 parts by weight of an epoxy resin comprising a polyepoxide or a mixture of epoxides having an epoxy equivalent weight of at least about 150; and (b) from about 30 to about 50 parts by weight of a combination curing agent comprising:
(1) from about 2 to about 8 phr of a latent high temperature curing agent, which remains relatively inert up to about 149 C, but above 149°C is capable of rapidly catalyzing the epoxy resin; and (ii) from about 12 to about 30 phr of a latent intermediate temperature curing agent; and (ill) from about 12 to about 28 phr of a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly (methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures thereof, based upon the total weight of said adhesive composition, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185°C or less.
10. An induction curable adhesive composition as recited in Claim 9, wherein component (a) comprises a diglycidyl ether of bisphenol -A and wherein component (b)(i) comprises dicyandiamide.
11. An induction curable adhesive composition as recited in Claim 9, wherein component (b)(ii) is selected from the group consisting of Dibenzo(i,t)(1,4,7,12,15,18)hexaazacyolodocosine-5,13,18,26,(6H,19H)tetrone (9CI), SB-7,8,9,10,11,12,20,21,22,23, 24,25-decahydro and ANCAMINE ? 2041A.
12. An induction curable adhesive composition for bonding oily metallic substrates, said composition comprising:
(a) 100 parts by weight of an epoxy resin comprising a polyepoxide or a mixture of epoxides having an epoxy equivalent weight of at least about 150;
(b) from about 30 to about 50 parts by weight of a combination curing agent comprising:
(i) from about 2 to about 8 phr of a latent high temperature curing agent, which remains relatively inert up to about 149 C, but above 149°C is capable of rapidly catalyzing the epoxy resin component; and (ii) from about 12 to about 30 phr of a latent intermidiate temperature curing agent; and (iii) from about 12 to about 28 phr of a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures of any of the foregoing resins, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185°C or less; and (c) from about 27 to about 100 parts by weight of a metal adhesion promoter comprising a finely-divided mineral filler selected from the group consisting of talc, calcium carbonate, fumed silica and mixtures of any of the foregoing mineral fillers.
(a) 100 parts by weight of an epoxy resin comprising a polyepoxide or a mixture of epoxides having an epoxy equivalent weight of at least about 150;
(b) from about 30 to about 50 parts by weight of a combination curing agent comprising:
(i) from about 2 to about 8 phr of a latent high temperature curing agent, which remains relatively inert up to about 149 C, but above 149°C is capable of rapidly catalyzing the epoxy resin component; and (ii) from about 12 to about 30 phr of a latent intermidiate temperature curing agent; and (iii) from about 12 to about 28 phr of a green strength enhancing agent comprising a finely-divided thermoplastic resin powder selected from the group consisting of low density polyethylene, ethylene vinyl acetate, polystyrene, polyvinyl formal, polyvinyl butyral, poly(methyl methacrylate), NYLON-12 and hot melt polyester resins and mixtures of any of the foregoing resins, wherein component (b)(ii) is present in an amount effective to partially cure the adhesive composition in conjunction with component (b)(iii) to provide a green strength of at least about 200 psi in 6 seconds or less upon induction heating of the adhesive composition to temperatures of about 185°C or less; and (c) from about 27 to about 100 parts by weight of a metal adhesion promoter comprising a finely-divided mineral filler selected from the group consisting of talc, calcium carbonate, fumed silica and mixtures of any of the foregoing mineral fillers.
13. A method for fixturing oily metallic parts to provide handling strength for storage and shipment, said method comprising:
(a) providing a plurality of oily metallic parts;
(b) disposing intermediate at least two adjacent surfaces of said parts an effective amount of an adhesive composition as recited in Claim 12 to form an adhesive joint therebetween; and (c) thereafter, inductively heating said adhesive joint for a time sufficient to provide a metal temperature of between about 150° and 185°C to provide a green strength in said adhesive joint of at least about 200 psi.
(a) providing a plurality of oily metallic parts;
(b) disposing intermediate at least two adjacent surfaces of said parts an effective amount of an adhesive composition as recited in Claim 12 to form an adhesive joint therebetween; and (c) thereafter, inductively heating said adhesive joint for a time sufficient to provide a metal temperature of between about 150° and 185°C to provide a green strength in said adhesive joint of at least about 200 psi.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000536251A CA1301396C (en) | 1987-05-04 | 1987-05-04 | High green strength induction curable adhesives |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000536251A CA1301396C (en) | 1987-05-04 | 1987-05-04 | High green strength induction curable adhesives |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1301396C true CA1301396C (en) | 1992-05-19 |
Family
ID=4135572
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000536251A Expired - Lifetime CA1301396C (en) | 1987-05-04 | 1987-05-04 | High green strength induction curable adhesives |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1301396C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6509555B1 (en) | 1999-11-03 | 2003-01-21 | Nexicor Llc | Hand held induction tool |
-
1987
- 1987-05-04 CA CA000536251A patent/CA1301396C/en not_active Expired - Lifetime
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6509555B1 (en) | 1999-11-03 | 2003-01-21 | Nexicor Llc | Hand held induction tool |
| US6639197B2 (en) | 1999-11-03 | 2003-10-28 | Nexicor Llc | Method of adhesive bonding by induction heating |
| US6639198B2 (en) | 1999-11-03 | 2003-10-28 | Nexicor Llc | Hand held induction tool with energy delivery scheme |
| US6710314B2 (en) | 1999-11-03 | 2004-03-23 | Nexicor Llc | Integral hand-held induction heating tool |
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