WO2009149143A1

WO2009149143A1 - Adhesion of polyamides to epoxy resins

Info

Publication number: WO2009149143A1
Application number: PCT/US2009/046064
Authority: WO
Inventors: Paul J. Kane
Original assignee: E. I. Du Pont De Nemours And Company
Priority date: 2008-06-03
Filing date: 2009-06-03
Publication date: 2009-12-10

Abstract

The adhesion of polyamide compositions to cured epoxy resins is im-proved when the composition contains relatively small amounts of novolac resins. Preferably the epoxy resin is cured in contact with a preformed poly-amide composition part, or the polyamide composition is molded while the polyamide is in contact with the cured or partially cured epoxy resin. Such assemblies are useful in electrical apparatus.

Description

ADHESION OF POLYAMIDES TO EPOXY RESINS

FIELD OF THE INVENTION

The adhesion of epoxy resins to polyamides is improved by adding a novolac resin to the polyamide.

TECHNICAL BACKGROUND

Oftentimes various assemblies contain polymeric parts which made from different polymers. In some of these assemblies it may be desirable to adhere parts made from two different types of polymers to each other. It is well known in the art that most types (chemical compositions) of polymers are incompatible with other polymers, and so good adhesion between two different polymer types is often difficult to obtain. This is the case with the adhe- sion of epoxy resins to polyamides, particularly when the polyamide part is formed first, for example as by melt forming, and then the epoxy portion is cast onto a surface of the polyamide part. Oftentimes poor or no adhesion between the parts is the result. Thus an improved procedure for adhering such parts is desired. SUMMARY OF THE INVENTION

This invention concerns an apparatus, comprising:

(A) a first part comprising

(i) 80 to 95 weight percent of a polyamide; and (ii) 5 to 20 weight percent of a novolac resin wherein said weight percentages are based on the total weight of said polyamide and said novolac resin; and

(B) a second part comprising a cured epoxy resin; and wherein at least one surface of said first part is adhered to at least one surface of said second part. This invention also concerns a process for adhering a first part comprising a polyamide to a second part comprising a cured epoxy resin, comprising:

(A) contacting said first part, which comprises: (i) 80 to 95 weight percent of a polyamide; and (ii) 5 to 20 weight percent of a novolac resin wherein said weight percentages are based on the total weight of said polyamide and said novolac resin; with an uncured epoxy resin and curing said epoxy resin to form said second part while said epoxy resin is in contact with said first part; or

(B)(1 ) forming said second part so that the epoxy resin is a fully or partially cured epoxy resin; (2) overmolding said fully or partially cured epoxy resin with said polyamide so that said polyamide fully or partially encapsulates said second part wherein said first part comprises:

(3) if said epoxy resin was partially cured, finish curing of said epoxy resin.

DETAILS OF THE INVENTION Herein certain terms are used and some of them are defined below.

By a "polyamide" is meant is polymer in which at least 70 percent of the connecting groups between repeat units are amide groups, preferably at least 80 percent, more preferably at least 90 percent, very preferably at least 95%, and especially preferably essentially all of the connecting groups are amide groups.

By a "partially aromatic polyamide" (PAP) is meant a polyamide or blend of polyamides in which at least 5 mole percent of all repeat units in the polyamide or blend of polyamides have an aromatic ring, which means thermoplastic polyamides having all repeat units containing an aromatic ring may be used. However, no more than 90 mole percent of the repeat units, preferably no than 60 mole percent of the repeat units, have an aromatic ring. By an aromatic ring is meant a group such as phenyl or phenylene, naphthyl or naphthylylene, biphenyl or biphenylene, or pyridyl or pyridylylene. Preferably the aromatic ring is in the main chain of the polymer, i.e., is not a "side group" in the repeat unit. Units in the main chain would include those derived from terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, 1 ,4- diaminobenzene, 1 ,3-diaminobenzene, 1 ,4-bis(aminomethyl)benzene, 1 ,3- bis(aminomethyl)benzene, 4,4'diaminobiphenyl, 4-aminobenzoic acid, and 3- aminobenzoic acid. Repeat units with aromatic side groups include those derived from 3-phenyl-1 ,6-diaminohexane and 2-(4-pyridyl)succinic acid. If more than one polyamide is present (a blend of polyamides) then all repeat units in all polyamides are used in this calculation, whether any particular polyamide has any repeat units containing aromatic groups or not. PAPs are one type of preferred polyamides.

Other useful polyamides include nylon-6,6 (sometimes also called polyamide-6,6), nylon-6, nylon 6,12, nylon-12, nylon-10, and nylon-6,10. Nylon-6,6 and nylon-6 are preferred polyamides, and nylon-6,6 is especially preferred. By a novolac resin is typically meant a usually substantially linear polymer produced by the reaction of an aldehyde, particularly formaldehyde, and a phenol, and during the polymer formation the phenol is present in stoichiometric excess. Novolacs may be thought of as polyphenols (that is polymers which have hydroxyl groups attached directly to aromatic ring car- bon atoms) which are not crosslinked, and herein the term novolac shall mean these types of polymers. Typically they have molecular weights of 200-5000, and glass transition temperatures of 45 to 7O⁰C.

An "epoxy resin" is a resinous material which, on average, contains at least two epoxy groups per molecule. Such materials are commercially avail- able and well known in the art, see for instance H. Q. Pham, et al., Encyclopedia of Polymer Science & Technology, 3^rd Ed., Vol. 9, John Wiley & Sons, New York, 2002, p. 678-804. Epoxy resins are cured using compound which have functional groups, such as amino or hydroxyl, which react with epoxy groups. The curing agent has an average of two or more of these functional groups per molecule. Curing conditions for various epoxy resins with any particular curing agent may vary, but typically the (usually liquid) epoxy resin is mixed with the curing agent and then the mixture is usually heated to effect the curing reaction to form the cured epoxy resin. Conditions for any particular epoxy resin/curing agent combination are generally available from their manufacturers. After curing the cured epoxy resin is crosslinked so it usually cannot be reformed, so it is almost always cured in the shape of the desired final part, unless a so-called "stock shape" is being made to be later machined to the final shape. Such curing often takes place in a mold or other similar device, sometimes under superatmospheric pressure.

The polyamide composition used herein comprises a novolac resin. The weight percentage of the novolac resin is about 2 to about 20 weight percent, based on the total weight of the polyamide and novolac resin present, more preferably about 5 to about 15 weight percent, and especially preferably about 8 to about 13 weight percent. It is to be understood that any minimum amount may be combined with any maximum amount mentioned above to form a new concentration range.

Other materials may be present in the polyamide composition such as fillers, reinforcing agent, antioxidants, stabilizers, tougheners (generally rub- bers or rubbery-like polymers), antioxidants, colorants, flame retardants, crystallization accelerators, etc. Preferred additives are fillers and reinforcing agents such as clays, glass fibers, milled glass, carbon fiber, carbon black, aramid fibers, wollastonite, mica, talc, and other minerals. Minerals or other fillers may be present as very small particles, for examples as so-called nano particles, whose average particle size is typically about 1 to about 500 nm. Preferred fillers and reinforcing agents are glass fiber, talc, clays and mica, and glass fiber is especially preferred. It is preferred that the filler(s) and/or reinforcing agent(s) be present as about 10 to about 60 weight percent of the total composition, more preferably about 20 to about 50 weight percent. More than one filler and/or reinforcing agent may be present, and these weight per- cents refer to the total of these materials.

Another preferred material present in the polyamide composition is a toughener, usually a rubber or rubber-like polymer which improves the toughness of the polyamide composition. Useful tougheners for polyamides are well known in the art, see for instance U.S. Patent 4,174,358 and 5,112,908, both of which are hereby included by reference. Preferably the toughener has attached to it functional group which may react with the polyamide end groups, which are typically amino and and/or carboxyl. Such functional groups include epoxy, carboxylic anhydride, and carboxyl. Preferably the toughener is present at a concentration of about 3 weight percent to about 20 weight percent, based on the total composition, more preferably about 6 weight percent to about 15 weight percent.

The polyamide composition may be made by techniques usually used for making similar compositions from thermoplastics, including polyamides. Most commonly the composition may be made by melt mixing the ingredients in an apparatus such as a single or twin screw extruder, or a kneader. The polyamide is heated above its melting point in the apparatus and mixed with the other ingredients. If for instance a twin screw extruder is used all or some of the ingredients may be added at the rear of the extruder, and then ingredients not added at the rear such as reinforcing agent or plasticizers may be "side fed" along the length of the extruder. It is preferred to add the novolac resin at the rear of the extruder.

The polyamide composition may be formed into shaped parts by typical thermoplastic forming techniques, particularly melt forming techniques such as injection molding, extrusion, compression molding, etc. Injection molding is a preferred forming method. These methods are well known in the art.

After the polyamide part is formed it is brought into contact with the un- cured or partially cured epoxy resin and the curing of the epoxy resin is com- pleted, usually by heating. Since it will usually be desired to form the epoxy resin into a particular shape it will usually be placed in a mold or similar device. The PAP part may form part of that mold (surface) so that part of the interior surface of that mold is the PAP part, and the epoxy resin contacts that surface while curing. The PAP part may be completely or partially over- molded by the epoxy rein. If the PAP part is completely overmolded, it becomes encapsulated inside the epoxy resin. Thus the epoxy resin is cured while in contact with the PAP part and an assembly is formed containing both the PAP part and the epoxy part. These two parts are held together by adhesion, although the adhesion may supplemented by mechanical fasteners, in- terlocking of the parts, or other devices to hold the parts together in the desired configuration. Indeed the adhesion may be used to temporarily hold the parts together until stronger means of attachment, such as mechanical means, can be applied. Other factors may affect the adhesion level. For example the PAP part surface finish, for example matte or glossy, may affect the adhesion. Sometimes the surface morphology may be affected by molding conditions, for example higher mold temperatures often give smoother (glossier) surfaces. An- other factor is the cleanliness of the PAP composition surface when brought into contact with the epoxy resin. It is well known that dirty surfaces often don't adhere as well as clean surfaces. Therefore cleaning of the PAP composition surface, either mechanically, as by wiping, or using a surfactant solution or a solvent to clean the surface may improve adhesion. For example the surface may be wiped with an isopropanol containing cloth or wipe, or dipped in isopropanol, and then dried.

In another method to make the apparatus, a cured or partially cured (cured enough so the part retains its shape) epoxy part is first made by standard epoxy resin molding methods. This epoxy part is then overmolded or partially overmolded with a PAP composition, for example by injection molding. The epoxy part may be cleaned or not as described above for the PAP part. The epoxy part may be completely overmolded so it is encapsulated in the PAP composition, or only part of the surface of the epoxy part is contacted with the PAP composition during the molding process. Again, these two parts are held together by adhesion, although the adhesion may supplemented by mechanical fasteners, interlocking of the parts, or other devices to hold the parts together in the desired configuration. Indeed the adhesion may be used to temporarily hold the parts together until stronger means of attachment, such as mechanical means, can be applied. Preferably there is no additional adhesive used to bond the PAP composition and cured epoxy resin together. That is in the region of the "bond" between the PAP composition and epoxy resin they contact each other directly and are held together without any additional adhesive.

Typical uses for such an apparatus include automotive parts such as ignition components, and other electrical and electronic parts for automotive and nonautomotive uses.

Adhesion Procedure A Tensile bars prepared according ASTM Method D638, Type 1 bars, 0.16 cm (1/16") thick are made. These bars are cut in half perpendicular to their long axis, and the two halves form a set which will be tested together.

A silicone rubber "frame" is made by cutting out a piece 19.05 mm square from a sheet 1.8 mm thick. A 6.2x10 mm section (6.2 mm dimension is parallel to the edge from which it is cut) is cut from this piece along one of the edges so that one has a piece resembling the letter "u" when the cutout is on the top portion of the piece. The frame is then positioned at the narrower ends of a set of test pieces (see above) between the two pieces, so that the open part of the "u" is along an edge of and parallel to the long axis of both bars. In other words, the open center part of the frame forms and the surfaces of the two bars form a containers into which the epoxy resin will be poured.

Two pieces of silicone, each 1.27 mm wide by 5.08 cm long by 1.8 mm thick are then placed on the two outside surfaces of the assembly (the outer surfaces of the bars) and then 1.27 mm wide by 5.08 cm long mending plates are placed on the outer surfaces of these silicone strips. The whole assembly is then clamped with binder clips so that the bars and the silicone frame are held securely with respect to one another and a liquid tight (to epoxy resin) cavity is formed by the silicone rubber frame, to form a testing array.

In preparing the set bars, if degreasing of the surfaces (as by alcohol) of the bars is carried out, the assembly of the testing array shall be done using cotton gloves to protect the cleaned surfaces.

The testing array is preheated in aluminum pans (as secondary catch basins) to 12O⁰C for 2 hours. The assembly should be supported so that the epoxy resin may be easily poured into cavity formed by the silicone frame.

While preheating the testing array the epoxy resin is heated for 1 hour in a convection oven, then subjected to a vacuum at room temperature to remove gases. The hardener (curing agent) is also be subjected separately to vacuum at the same time. The epoxy resin and hardener are then mixed in the proper proportions. Remove gases under vacuum and place in a convection oven at 6O⁰C for 30 min. The epoxy resin/hardener mixture and the testing arrays are then removed from their respective ovens and the epoxy mixture is then placed into each of the cavities formed by the silicone rubber frames by injecting the epoxy mixture into the cavities using a 10 ml syringe with a 16 gauge needle. Fill to the top of the cavities. Inject up to 5 assemblies at a time. Record the times these are done.

Each set of 5 (or less) is then cured in a convection oven at 9O⁰C for 150 minutes and then at 13O⁰C (second oven) for 150 minutes (these curing times and temperatures may be varied according to the epoxy resin and hardener used). The arrays are allowed to cool to ambient temperature.

The clamps, mending plates and outer silicone pieces are removed, and the silicone rubber frame is removed by gently pulling it from between the two bars. An array is then placed in a tensile testing machine and then tab ends of the array are clamped to the draw bars of the machines and the tabs are pulled apart at a rate of 0.51 cm/min (0.027min). The maximum amount of force before breaking apart of the array, and the elongation at break, are recorded. All testing is done a standard laboratory atmosphere (ASTM D618) unless otherwise noted.

This adhesion test, which is basically a so-called lap-shear adhesion test, may or may not simulate actual use conditions, but is particularly useful for comparing the adhesion of various polymer compositions to epoxy resins.

In the Examples, the following materials were used:

Color Concentrate - A carbon black containing color concentrate in a polymer binder.

Fiberglass A - Grade FT756X from Asahi Fiberglass Co., Tokyo 101-0045, Japan Irganox® 1010 - antioxidant available from Ciba Specialty Chemicals, Tarrytown, NY 10591 , USA.

Lubricant A - Licomont® CaV102 lubricant, available from Clariant Intl., Ltd., 4132 Muttenz, Switzerland.

Novolac A - A novolac resin with a number average molecular weight of about 1000 and a glass transition temperature of about 8O⁰C.

Polymer A - A PAP copolymer made from terephthalic acid, 1 ,6- hexandiamine, and 2-methyl-1 ,5-pentanediamine, in which the molar ration of 1 ,6-hexanediamine to 2-methyl-1 ,5-pentaediamine was 1 :1. The PAP had a melting point of 300⁰C. Polymer B - An ethylene/1 -octene copolymer grafted with 1.8 weight percent maleic anhydride.

Polymer C - A PAP copolymer made from terephthalic acid, adipic acid, and 1 ,6-hexanediamine wherein the molar ratio of terephthalic acid to adipic acid is 55:45. The PAP had a melting point of 31O⁰C.

Stabilizer A - A stabilizer containing 1 part of CuI and 4 part of Kl. In the Examples unless otherwise noted all parts shown are parts by weight.

Examples 1-3 and Comparative Example A

The ingredients for each composition were fed to a 30 mm Werner & Pfleiderer twin screw extruder having 9 sections, running at 300 rpm with a throughput of 15 kg/h. All of the ingredeients were fed to the rear of the extruder except for the fiberglass which was side fed. The temperatures were (zone 2 and above) set at 300⁰C. The compositions were cut into pellets upon exiting the extruder. Compositions are shown in Table 1.

Table 1

The compositions were injection molded on a 6-oz. barrel capacity machine. Melt temperatures were 325⁰C, and the mold temperature was 16O⁰C. The compositions were then tested per Adhesion Testing Procedure A. The results are shown in Table 3.

Examples 4-5

The PAP compositions were prepared in the same manner as in Examples 1-3 except. Compositions are shown in Table 2. Melt and mold temperatures are shown in Table 3. Table 2

The compositions were injection molded on a Nissei FN4000 molding machine. Polymer melt and mold surface temperatures are given in Table 3. The compositions were then tested for adhesion per Adhesion Testing Procedure A. The results are shown in Table 3.

Table 3^a

a Epoxy resin was TCG2129A from Kyocera Chemical Corp. (Kawaguchi-city, 332-853 Japan) and the hardener (curing agent) was TCG2129B from Kyo- cera used in 100 parts epoxy resin to 28 parts hardener. The resin is reported to be 90% diglycidyl ether of bisphenol-A, and that hardener is described as 99% methyltetrahydrophthalic acid anhydride and <1 % 2-ethyl-4- methylimidazole.

Claims

CLAIMS What is claimed is:

1. An apparatus, comprising:

(A) a first part comprising (i) 80 to 95 weight percent of a polyamide; and

(ii) 5 to 20 weight percent of a novolac resin wherein said weight percentages are based on the total weight of said polyamide and said novolac resin; and

(B) a second part comprising a cured epoxy resin; and wherein at least one surface of said first part is adhered to at least one surface of said second part.

2. A process for adhering a first part comprising a polyamide to a second part comprising a cured epoxy resin, comprising:

(A) contacting said first part, which comprises: (i) 80 to 95 weight percent of a polyamide; and

(ii) 5 to 20 weight percent of a novolac resin wherein said weight percentages are based on the total weight of said polyamide and said novolac resin; with an uncured epoxy resin and curing said epoxy resin to form said second part while said epoxy resin is in contact with said first part; or

(B)(1 ) forming said second part so that the epoxy resin is a fully or partially cured epoxy resin;

(2) overmolding said fully or partially cured epoxy resin with said polyamide so that said polyamide fully or partially encapsulates said second part wherein said first part comprises:

(i) 80 to 95 weight percent of a polyamide; and

(3) if said epoxy resin was partially cured, finish curing of said epoxy resin.