CA1180491A - Curable epoxy resins - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Curable epoxy resin compositions which exhibit con-trollable cure rates are described which utilize catechol derived accelerators in combination with certain curing agents. These accelerators can be employed in single package curable epoxy resin compositions useful in molding and casting applications.

Description

CUQA~ CYO~Y ~5l~s This invention is concerned with novel, heat-curable, thermosetting e~oxy resin compositions havin~ a cure rate which can be varied over a hroad temperature range utiliæing a cure accelerator derived ~rom the silylation of oatechDl and lts derivatives. More particularly, the invention relates to a composition of matter comprising an epoxy resin, a curing agent, and an accelerator o the general for~tlla I. Anl ~ ~ 5, / ~ ~ m where R is independently selected from the class consisting of hydrogen, monovalent alkyl (including aralkyl) groups of from l to 8 carbon atoms (e.g., methyl, ethyl, benzyl, propyl, iso-propyl, hexyl, 2-ethylhexyl, etc.); aryl (e.~.,phenyl, naphthyl, etc.~; alkaryl (e.g., tolyl, etc.); vinyl, and allyl radicals, and A is independently selected from alkyl radicals the same as R ~bove, alkoxy groups having 1 to 6 carbon atoms; halogen (e.~, chlorine, bromine, etc.) and the nitro radical, where A can be ortho-, meta-, or para- to any of the oxygen atoms attached to silicon, and m is an integer from O to 2 inclusive, with the proviso that at most only one hydrogen can be on any one silicon atom.
The cure accelerators corresponding to formula I, may be prepared by reacting, in the presence of an inert solvent, such as toluene or benzene, a catechol of the general formula:

OH
II. Am ~
OH
with a dîhalogenosilane of the formula III X2 - Si - R2 where X is a halogen radical, e.g., chlorine, bromine, etc., and R, A, and m have the meanings above. More specifically, the compound of formula I, is the reaction product of essentially 1 molar equivalent of the catechol compound of formula II with essentially 1 molar equivalent of a dihalogenosilane of formula III where any hydrohalide formed is removed, An~lysis of the accelerator compositions ~hus formed was accomplished by 29Si NMR and 13C NMR techniques, confirm-in~ the ~redominant ~resence of a com~ound correspondin~ to formula I. F.ield desorption mass spectrometrY further estab lished the presence of small amounts (less. than 10 total Percent) of compounds havin~ the following structural formulas:

IV. Am ~ ~ ~ i ~

and ~ ,~R

V. Am ~ ~ ~m ,~,1 s ~
~>
Am where R, A, and m have ~he meanings above. In addition, vapor phase chromatographv demonstrated the absence o~ cate-chol. Compounds of foxmula I, prepared as described above,demonstrated a tendency ~o rearrange either ~t ambient or elevated temperatures to ~orm ~ompounds of formula V as shown by field desorption mass spectrometry and also dissociates to form compounds o~ formula IV, as disclosed in Chemical Abstracts, Volumn 83 at 205342Y (1975) and more specifically in "Z. Natur-forsch, 3Qb, 488 490 [1975]; Eingegan~en am 24, Marz 197S "
However, as previously stated, the compounds corresponding to formulas IV and V, are generally present in amounts less than 10 percent total and do not ad~ersely affect the acceleration rate for the compound of form~tla I in the cure of the epoxy resins.
Examples of the dihalogenosilanes which may be used in the prepara~ion of the cure accelerators used in the in-stan~ invention include, e.g., allylmethyldichlorosilane, dimethyldibromosilane, n-amylmethyldichlorosilane, t-butyl-phenyldichlorosilane, t-butylmethyldichlorosilane, 2-carbo-methoxyethylmethyldichlorosilane, cyclopentylmethyl-dichlorosilane, diallyldichlorosilane, dimethyldichlorosilane, diphenyldichlorosilane, ethyldichlorosilane, ethylmethyldi.-chlorosilane, phenylallyldichlorosilane, phenyldichlorosilane methyl phenyldichlorosilane, methyldichlorosilane ? etc.
S Epoxy rPsin compositions, heretoore have been u~
lized for example, as electrical insulation for electrical con-ductors. The cure rate of the epoxy resins has previously ~een of prolong~d duratian, e.g., often as long as lC to 15 hours at 160, especially in casting applications, significantly delay-ing u~ilization o~ said epoxy resins in a broad range of appli-cations.
It is an object of the present invention ~o provide a thermosetting epoxy resin composition, the reactivity of which can be controlled over a very wide range having an abili~y to cure rapidly at elevated temperatures, which are often lower than usually required.
It is an additional object of this invention ~o provide epoxy resin compositions containing cure accelerators which impart desirable physical properties, including favorable chemical and electrical properties in the resultant heat-cured epoxy resln.
The term "epoxy resins" is intended to include those selected from both glycidyl and non-glycidyl ether epoxides containing more than one 1,2-epoxy groups per molecule.
Such non-glycidyl ether cycloaliphatic epoxides are charackerized by the absence of the ether oxygen bond, i.e., ~0 , near the epoxide group, and are selected from those which contain a ring structure as well as more than one epoxide group in the molecule. The ep~xide group may be part of the ring structure or may be attached to the rlng structure. These epoxides may also contain ester linkages. These eSter linkages are generally not near the epoxide group and are relatively unreactive, therefore these type ma~erials are properly charaG
terized as ~ycloaliphatic epoxides. These epoxide6 are generally prepared by epoxidizing unsaturated aliphatic hydrocarbon com-pounds, such as cyclic-olefins, using hydrogen peroxide or peracids such as peracet'ic acid and perbenzoic acid.
10Other epoxy resins which may be employed in this invention such as 1,2-epoxy resins having more than one epoxy group per molecule include cycloaliphatic epoxy resins such as 3,4-epoxycyclohexylmethyl- (3,4-epoxy) cyclohexane carboxylate (sold under the trademarks ERL 4221 by Union Carbide Co. or 15~raldi~e CY 179 by Ciba Products Company), bis(3,4-epoxy 6 methyl,cyclohexylmethyl) adipate (sold under the trademarks ERL
~239 by Union Carbide Co. or Araldi~e CY 178 by Ciba Products Company), bis(2,3-epoxycyclopentyl) ether resins (sold under the trademark ERL 4205 by Union Carbide Company), 2-(3,4-epoxy)-cyclohexyl-5, and 5-spiro (3,4-epoxy?-cyclohexane-~-dioxane.
` (sold under the trademark Araldite CY 175 bY Ciba Products CompanY), etc.
Glycidyl ether based ePoxY resins suitable for use accordin~ to the Present invention include ~lYcidYl ethers of phenolic epoxY resins such as liquid or solid bisPhenol-A
di~lYcidYl ether e~oxY resins (such as those sold under trade-marks as Epon 826, EPon 8~8, Epon 830, Epon 1001, Epon 1002, Epon 1004, etc., by Shell Chemical ComPany), phenol-formalde-hyde novolac polyglycidyl ether epoxy resins (such as those ~q~

sold under the trademarks DEN 431, DEN 438, and DEN 439 by Dow Chemical Company), epoxy cresol novolacs ~such as those sold under trademarks ECN 1235, ECN 1273, ECN 1280 and ECN 1299 by Ciba Products Company), resorcinol glycidyl ethers (such as ERE 1359 made by Ciba Products Company~, tetra-glycidyl tetra-phenylethane (Epon 1031, made by Shell Chemical Company);
glycidyl e~her epoxy resins such as diglycidyl ph~halate (ED-5661 by Celanese Resins Company), diglycidyl te~rahydrophthalate (Araldite CY 182 by Ci~a Products Company), and diglycidyl hexahydrophthalate (Araldite CY 183 made by Ciba Products Company); and Elame retardant epoxy resins such as halogen-containing bisphenol-A diglycidyl ether epoxy resins (e.g., DER 542 and DER 511 which have bromine contents o~ 44-48 and 18-20%, respectively, and are made by Dow Chemical Company).
The foregoing epoxy resins are well known in the art and are set forth, for example, in many patents includlng U.S. Patent Nos. 2,324,483, 2,444,333, 2,494,295, 2,500,600, and

2,511,913. The curing agents used in the practice of this in-vention are no~ only effective wi~h various epoxy resins and mixtures oS epoxy resins, but they are also effective in mix-tures containing reactive and nonreactive epoxy diluents (or ex~enders), epoxy ~lexibilizers and fillers.
There are many epoxy resin curing agents in use.
Among the most common are the arom~tic polyamines, aliphatic polyamines and their adducts, carboxylic acid anhydrides~ poly-amines and catalytic curing agents, as, for example, tertiary amines, imidazoles, BF3 monoethylamine, and dicyanodiamide.
In addition, there are metal acetylacetonates in which the metal is aluminum, barium, beryllium, cadmium, calcium, cerous, chromic, cobaltic, cobaltous, cupric, ferric, ferrous, lead lithium, magnesium, manganic, molybdenum,nickel, po-tassium, titanium, zinc, zirconium, etc.
Phenolic cure accelerators are frequently used in conjunction with an initiator in the curing of epoxy resins.
Among the more common accelerators are bisphenol-A (i.e, 2,2-bis(~-hydroxyphenyl) propane, catechol, resorcinol, and hydroquinone. Other phenolic accelerators include halogenated phenols such as ortho , meta-, and parachlorophenols or bromophenols.
The curing rate of epoxy resin compositlons of the present invention can be tailored to cure over a time span of Erom about one minute to several hours based on the resinsor resin mixture selected, and the type of curing agent, the amount and -type of accelerator utilized in relation to the cure temperature chosen, etc. Further, blends of epoxy resins such as ERL 4221 epoxy resin/ECN 1235 epoxy cresol novolac resin, or glycidyl ether and glycidyl ester pepoxy resins may be cured using the accelerators of general formula I.
The curable epoxy resin compositions comprising a suitable epoxy resin or epoxy resin mixture, a titanate or zirconate curing agent and an accelerator corresponding to formula I can be heat cured at a temperature of from 75C
to 200C, and advantageously cured a-t a temperature of from 25 100C to 175C, to obtain the heat cured product.
The composite heat curable epoxy resins of the present invention are available as a one-component, ready to use package not requiring the blending of ingredients immediately prior to utilization. The epoxy resin compositions generally consist of a mixture of a resin, an organic titanate or zirconate cure initiator or curing agent and an accelerator of formula lo Some of the applications in which the curable com-positions o the present i~lvention can be used, are, for eæample, protective coatings, liquid injection molding compounds, wire insulation, encapsulation o Plectronic components, laminates, bulk molding compounds (BMC), e.gO, as housin~s for motors, grills for automobiles, ~c.
The organic titanate initiators which are added to the epoxy resin composition to initiate the cure of the epoxy resins include chelated titanates such as acetylacetonate titanate, lactate ti~anate, triethanolamine titanate, polyhydroxystearate titanat~e, a glycol~te titanate (e.g., tetraoctylene glycol ti~anate containing approximately 7.8% Ti and sold under the trademark Tyzor OG by E.I. du Pont de Nemours and Company or di-n-butyl hexylene glycol titanate), and nonchelated ti~anates such as tetraisopropyl titanate (TPT), tetrabutyl titarate, polymerized ~etrabutyl titanate, and tetralcis (2-ethylhexyl) t.itanate (TOT). In general, the chosen titanate should be present in the mixture in a concentration ~etween 0.03 and 15~/o by weigh~, based on the weight of the epoxy resin, with optimum cure rates generally being obtained utilizing titanate concen-trations between 1 to 10%, by weight, of the epoxy resin. The amount of curing agent used will depend on such factors as type of epoxy resin used, temperature at which cure is to take place, type of accelerator used, etc.
In place of organic titanates, organic zirconate cur-ing agents can be used for the curing of the epoxy resins, and these include, for example, zirconium acetylacetonate, zirconium-tert-butoxider zirconium hexafluoroacetylacetonate, zirconium naphthena~e (sold by Witco Chemical Company, Incorporated), zirconium propoxide and zlrconium isopropoxide (sold by Ventron Corporation), etc.
Such æirconate curing agents can be used in amounts similar to those for the titanate curing agents, that is, t~e chosen zirconate should be present in a concentration between 1.0 and 15% by weight, based on the weîght of the epoxy resln, with a preferred concentration between 1.0 to lOV/o by weight, o~ the epoxy resin.
In order tha~ those skilled in the art may better under-stand how the present invention may be practiced, the follow-ing examples are given by way of illustration ~nd not by way of -limitation. All ~arts are by weigh~ unless otherwise indica~ed.

An accelerator having the formula \ /5 VI. ~ 5 was prepared following substantially the procedure disclosed in Chemical Abstracts, ~olumn 35 at 8677d (1957). In a reac-tion vessel fitted with a refLux condenser were introduced 132 parts benzene and 0.5 par~ activated charcoal. Thereafter, a mixture of 11 parts catechol and 19.4 parts dimethyldichloro-silane was added to the flask with stirring. The mixture was heated to reflux for 15 hours at 80C under an atmosphere of nitrogen. When the reaction was completed, the mix~ure was cooled and the charcoal removed by filtration. The liquid phase was con-densed by rotovap and the residue distilled to yield 15.1 ,a4~1 parts of the accelera~or described abov~ in ~ormula VI.

A mixture of 100 parts Epon 828, 1.53 parts Tyzor TPT and 4.89 parts of theaccelerator of Example 1 was prepared. The gela~ion time of this thermo-setting epoxy resin composition measured with a Sunshine Ge~
Meter (Sunshine Scientific Instruments Co., Philadelphia, PA.) at 150C was 1.3 minutes.

A mixture of 100 parts Epon 828, 3.37 parts Tyzor OG
and 4.89 parts of theaccelerator of Example 1 was prepared. The gelation time of this composition measured as above, at 150C was 1.2 minute~.

A thermosetting epoxy resin composition was prepared by mixing 100 parts Epon 828 with 2.63 parts zirconium ~,4-pen~anedionate and 4.89 parts of theaccelerator of Example l.
The gelation time of this composition, measured as above, at 150C was 36.2 minutes.

A~thermosetting epoxy resin composition was prepared by mixing 100 parts Epon 828 with 1.5 parts Tyzor TPT and 4.9 parts of theaccelerator of Example 1. The gelation ti~e o~
this composition, ~easured as above, at 50C was 74.5 minutes.

A thermosetting epoxy resin composition was prepared by mixing 100 parts Epon 828 with 2.6 parts zirconium 2,4-pentanedionate and 4.9 parts of the accelerator of Ex~mple 1.

The gelation time of this compositlon measured as above, at 50C was 8529.5 minutes (~6 days.,~

A thermosetting epoxy resin composition was prepared by mixing 100 parts Epon 828 with 2.6 parts zirconium 2,4~
pentanedionate and 3 parts catechol. The gelation time of this composition, measured as above, at 50C was 2880 minutes (2 days).

A thermosetting epoxy resin composition was prepared by mixing 100 parts Epon 828, with 1.5 parts Tyzor TPT and 5.2 parts `~atechol. The gelation time of this composition, measured as above, was 1.9 minutes at 50C.

A t~er~osettîng epoxy resin composition was prepared by mixing 100 parts Epon 828, with 1.5 parts Tyzor TPT and 6.2 parts ~f an accelerator o~ the formula Ph ~3 VII.

H3 h (prepared similarly ae: the accelerator of Example 1~ by reacting methylRhenyldichlorosilane and catechol). The gelation time of this composition, measured as above, at 50C was 64 minutes.

A thermosetting epoxy rPsin composition was prepared by mixing 100 parts Epon 828, with 3.4 parts Tyzor OG and 6.2 parts of the accelerator of Example 9. The gelation ~ime of this composition, measured as above, at 50C was 88 minutes.

1 ~3 ~a~l A ~hermosetting epoxy resin composition was prepared by mixing 100 par~s Epon 828, with 3.4 parts Tyzor OG and 6.2 parts catechol. The gelation time of this composition, measured as above, at 50C was 9.3 minutes . Comparison of the results of this example with the resul~s in Example 10 shows the ability of our accelerators to stabilize epoxy resins for storage purposes at temperatures as low as 50C.

A thermosetting epoxy resin composition was prepared by mixing 100 parts Epon 828 with 3.3 parts Tyzor OG and 8.6 parts o an accelerator having the formula Ph ~h 0~ ,//

P~ P~
(prepared similarly as the accelerator of Example 1, by reactin~
diphenyldichlorosilane and catechol). The gelation time of thls composition measured as above, at 150C was 1.8 minutes.

A thermosetting epoxy resin composition is prepared by mixing 100 parts Epon ~28 with 2.63 parts zirconium acetyl acetonate and 4.5 par~s of an accelerator of the formula

3~ ~ 3 IX.

v~

(prepared similarly as the accelerator of Example 1, by reactin~
dimethyldichlorosilane and 4-methoxycatechol). ~en this mix-ture of lngredien~s using the accelerator of formula IX is tested as in the precedin~ exampJes, it will be found that the storage .stability of the uncured material is enhanced and the rate of cure at elevated ~emperatures is accelerated.

A the~mosetting epoxy resin composition is prepared by mixing 100 parts Epon 828, with 2.6 parts zirconium octyl-aeetonate and 5 parts o~ an accelerator of the formula H3~ CH3 X. H3C ~ 5 ~ H

(prepared siMilarly as the accelerator of Example 1, by react-i.ng dimethyldichlorosilane and 4-isopropylcatechol). ~en this mixture of ingredients using the accelera~or of formula X
is tested a5 in the prece~in~ examples, it wi.ll be found that the storage stability of the incurred material is enhanced and the rate of cure-at elevated temperatures is a!ccelerated.

A thermosetting epoxy resin composilion is prepared by mixing 100 parts Epon 828 with 3.3 parts Tyzor OG, and 4 parts of an accelerator of the formula ~ D~

CH3 ~ ,D ~ i~ ~ CH3 XI. H3C-C ~ ~ 0~/ i~ ~ C'H~H3 ~prepared simllarly as the accelerator of Example 1, by react-ing dimethyldichlorosilane with 4-t-butylcatechol). ~en this mixture of ingredients using the accelerator of formula XI is tested as in the preceding examples, it will be Iound that the storage stability of the uncured material is enhanced and the rate of cure at elevated temperatures is accelerated.
Although the above examples are directed to only 2 few of the very many variables included by the curable comPo-sitions of the present invention, it should be understood that the curable compositions can comprise a much broader va-Liety of accelerators, initiators, and resins as 5hown in the description precedin~ these ex~mples.

Claims (29)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A composition of matter comprising an epoxy resin, a cure initiator, and an accelerator of the general formula I. where R is independently selected from the class consisting of hydrogen, monovalent alkyl groups of from 1 to 8 carbon atoms, aryl, alkaryl, vinyl, and allyl radicals; A is independently selected from alkyl radicals the same as R above; alkoxy groups having 1 to 6 carbon atoms; halogen and the nitro radical, where A can be ortho-, meta or para- to any of the oxygen atoms, attached to silicon and m is an integer from 0 to 2, inclusive, with the proviso, that at most only one hydrogen can be on any one silicon atom.

2. A composition of matter as in claim 1, wherein the cure initiator is a titanium or zirconium ester.

3. A composition of matter as in claim 1 wherein the accelerator has the formula

4. A composition of matter as in claim 1 wherein the accelerator has the formula

5. A composition of matter as in claim 1 wherein the accelerator has the formula

6. A composition of matter as in claim 1 wherein the accelerator has the formula

7. A composition of matter as in claim 1 wherein the accelerator has the formula

8. A composition of matter as in claim 1 wherein the cure initiator is a zirconium ester and the accelerator has the general formula I. where R is independently selected from the class consisting of from 1 to 8 carbon atoms, aryl, alkaryl, vinyl, and allyl radicals; A is independently selected from alkyl radicals the same as R above; alkoxy groups having 1 to 6 carbon atoms;
halogen and the nitro radical, where A can be ortho-, meta-, or para- any of the oxygen atoms attached to silicon, and m is an integer from 0 to 2 inclusive, with the proviso that at most only one hydrogen can be on any one silicon atom.

9. A composition of matter as in claim 1, wherein the cure initiator is a titanium ester and the accelerator has the general formula I. where R is independently selected from the class consisting of hydrogen, monovalent alkyl groups of from 1 to 8 carbon atoms, aryl, alkaryl, vinyl, and allyl radicals; A is independently selected from alkyl radicals the same as R above; alkoxy groups of from 1 to 6 carbon atoms; halogen and the nitro radical, where A can be ortho-, meta- or para- to any of the oxygen atoms attached to silicon, and m is an integer from 0 to 2 inclusive, with the proviso that at most only one hydrogen can be on any one silicon atom.

10. A composition of matter as in claim 9, wherein the accelerator has the formula

11. A composition of matter as in claim 9, wherein the cure accelerator has the formula

12. A composition of matter as in claim 9, wherein the cure accelerator has the formula

13. A composition of matter as in claim 9, wherein the cure accelerator has the formula

14. A composition of matter as in claim 9, wherein the cure accelerator has the formula

15. A method for curing an epoxy resin which comprises (1) forming a mixture of ingredients comprising an epoxy resin, a cure initiator, and an accelerator of the general formula R is independently selected from the class consisting of hydrogen, monovalent alkyl groups of from 1 to 8 carbon atoms;
aryl, alkaryl, vinyl, and allyl radicals, A is independently selected from alkyl radicals the same as R above, alkoxy groups of from 1 to 6 carbon atoms; halogen and the nitro radical, where A can be ortho-, meta-, or para to any of the oxygen atoms attached to silicon, and m is an integer from 0 to 2, inclusive, with the proviso, that at most only one hydrogen can be on any one silicon atom.
(2) heating the aforesaid mixture of ingredients at a temperature and for a time sufficient to effect curing of said epoxy resin.

16. The heat cured composition of claim 1.

17. The heat cured composition of claim 2.

18. The heat cured composition of claim 3.

19. The heat cured composition of claim 4.

20. The heat cured composition of claim 5.

21. The heat cured composition of claim 6.

22. The heat cured composition of claim 7.

23. The heat cured composition of claim 8.

24. The heat cured composition of claim 9.

25. The heat cured composition of claim 10.

26. The heat cured composition of claim 11.

27. The heat cured composition of claim 12.

28. The heat cured composition of claim 13.

29. The heat cured composition of claim 14.