GB2109798A - Heat activatable adhesive or sealant compositions - Google Patents

Abstract

A heat activatable adhesive or sealant organic resin composition comprises (1) a member of the group consisting of (a) a liquid, ethylenically unsaturated monomer, oligomer or prepolymer of the formula: <IMAGE> wherein R is H or CH3, R1 is an organic moiety and n is at least 2, (b) an epoxy resin containing at least 2 <IMAGE> groups, and (c) a mixture of (a) and (b); (2) a thermal initiator, and (3) a thermoplastic adhesive material selected from the group consisting of polyesters, polyvinyl acetals, polyamides, butadiene- acrylonitrile copolymers, styrene- butadiene copolymers, styrene- isoprene copolymers, styrene- ethylene-butylene copolymers, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene propylene diene monomer and mixtures thereof. The composition after application to the parts to be bonded or sealed forms a thermoset bond or seal on application of heat thereto, preferably by electromagnetic techniques including dielectric and induction heating.

Description

SPECIFICATION Heat activatable adhesive or sealant compositions This invention relates to thermoplastic adhesive and sealing organic resin compositions which, on application of heat, preferably in an accelerated manner, crosslink to give a thermoset bond or seal.

The invention also relates to a process for forming a crosslinked bond or seal.

The concept of thermosetting or crosslinking resin adhesives is known in the art. Many resin adhesives which undergo an irreversible chemical and physical change and become substantially insoluble are well known. Thermosetting adhesives comprising both condensation polymers and addition polymers are also known and examples include the urea-formaldehyde, phenol-formaldehyde and melamine-formaldehyde adhesives; epoxy, unsaturated polyester and polyurethane adhesives.

More particularly, U.S. 3,723,568 teaches the use of polyepoxides and optional epoxy polymerization catalysts. U.S. 4,122,073 teaches thermosetting resin obtained from polyisocyanates, polyanhydrides and polyepoxides. Crosslinking in these patents is achieved by reaction with available sites in the base polymers. U.S. 4,137,364 teaches crosslinking of an ethylene/vinyl acetate/vinyl alcohol terpolymer using isophthaloyl biscaprolactam or vinyl triethoxy silane whereby crosslinking is achieved before heat activation with additional crosslinking induced by heat after application of the adhesive. U.S.

4,116,937 teaches a further method of thermal crosslinking by the use of polyamino bis-maleimide class of flexible polyimides, which compounds can be hot melt extruded up to 1 500C and undergo crosslinking at elevated temperatures thereabove. In these latter two patents, thermocrosslinking is also achieved by reactions of the particular crosslinking agent with available sites of the base polymers.

In substantially all of these thermosetting adhesives bond formation is dependent on the chemical crosslinking reaction which in most cases is accelerated by means of heat to obtain the bond within a reasonable period of time. Further, in many cases, e.g., epoxy adhesives, two or more components must be admixed just prior to the preparation of the bond. This necessitates a fast application since the crosslinking reaction begins immediately upon admixture and is irreversible. Thus, there has been a desire for a one part thermosetting adhesive which can be applied and thereafter triggered to cure on command.

Methods of achieving delayed tack are known in the art. See U.S. 2,653,880, 2,653,881 and 4,059,71 5 which teach the employment of thermoplastic polymers containing slowly crystallizing segments.

On the other hand, thermoplastic adhesives, which are used in the form of solutions, dispersions or solids, usually bond by purely physical means. Probably the most important means of applying thermoplastic adhesives is the hot melt method wherein bond formation occurs when the polymer melt solidifies in position between adherends. The bonds obtained by this method reach their final strength faster than those obtained from solution type adhesives. Obviously, the thermal stability of the thermoplastic resin determines its potential usefulness as a hot melt adhesive. In order for the thermoplastic to be used as a hot melt, it must also have a low melt viscosity, thus permitting application of the adhesive to the adherends at acceptable rates. Usually this means the polymer must have a low molecular weight.However, many thermoplastic materials cannot be employed as hot melts because they do hot have sufficient cohesive strength at the low molecular weights required for application to a substrate. For example, the low molecular weight polyolefins, especially low molecular weight, low density polyethylene, are widely used in hot melt adhesives for sealing corrugated cartons, multi-wall bag seaming and the like, but they do not have sufficient strength to be used in structural applications such as plywood manufacture. Further, they do not have sufficient heat resistance to be used for bonding components which are intermittently exposed to elevated temperatures such as under the hood automotive applications.That is, thermoplastic adhesives cannot be employed where the adhesive in situ is reexposed to elevated temperatures which will cause the adhesive to sag thereby allowing the bond to break.

In the prior art there are many two-part materials which are cured in situ at elevated temperature, e.g., epoxy and urethane resins. The curing times, however, are relatively long, thereby precluding online production in a continuous operation. The curing time can be substantially reduced by heating, but such methods are rarely used due to the fact that external heating also causes substrate or adherends to be heated. In the case of heat sensitive substrates and adherends, e.g., thermoplastics, it can cause damage or distortion thereof.

The present invention provides a one part adhesive composition which is solventless, and can be applied as a hot melt. The new adhesive composition is rapidly heat curable at a higher temperature than that used during its application as a hot melt using a thermally triggered initiator. The new adhesive compositions can be applied as a free film, tape or as a preformed gasket.

The present invention provides a heat activatable adhesive composition comprising (1) a member of the group consisting of (a) a liquid, ethylenically unsaturated monomer, oligomer or prepolymer of the formula:

wherein R is H or CH, R, is an organic moiety and n is at least 2, (b) an epoxy resin containing at least 2

groups and (c) a mixture of (a) and (b); (2) a thermal initiator, and (3) a thermoplastic adhesive material selected from the group consisting of polyesters, polyvinyl acetals, polyamides, butadiene-acrylonitrile copolymers, styrene-butadiene copolymers, styreneisoprene copolymers, styrene-ethylene-butylene copolymers, ethylene-vinyl acetate copolymers, ethylene-ethyi acrylate copolymers, ethylene propylene diene monomer and mixtures thereof.

The composition after application to the parts to be bonded or sealed forms a thermoset bond or seal on application of heat thereto, preferably by electromagnetic techniques including dielectric and induction heating.

The composition after application to the parts to be bonded or sealed forms a thermoset bond or seal on application of heat thereto, preferably by electromagnetic heating techniques including dielectric and induction heating. Although the composition and process taught herein is operable to .form a thermoset bond or seal, the invention for the most part for reasons of brevity will be explained in terms of adhesive bonding.

The liquid ethylenically unsaturated monomer, oligomer or prepolymer, i.e., the acrylate terminated polyene, of the formula:

wherein R is H or CH3, R, is an organic moiety and n is at least 2 of the composition herein, can be made by various reactants and methods. One of these acrylate terminated materials is a polyether polyol urethane polyacrylate formed by reacting a polyether polyol with a polyisocyanate and a hydroxyalkyl acrylate. Another material may be a polyester polyol urethane polyacrylate formed by reacting a polyester polyol with a polyisocyanate and a hydroxyalkyl acrylate. Still another material in this category is an epoxy acrylate formed by reacting a diepoxide with acrylic acid.Yet another acrylate terminated material operable herein is a polyether or a polyester acrylate formed by end-capping a polyether polyol or polyester polyol with acrylic acid or acryoyl chloride. Yet another acrylate terminated material operable herein is a urethane polyacrylate formed by end-capping a diisocyanate with a hydroxyalkyl acrylate. As used herein, the term "acrylate" refers to both acrylates and methacrylates.Examples of the above acrylate terminated materials include, but are not limited to, 1 3- butylene glycol diacrylate, diethylene glycol diacrylate, 1 ,6-hexanediol diacrylate, neopentyl glycol diacrylate, polyethylene glycol 200 diacrylate, tetraethylene glycol diacrylate, triethylene glycol diacrylate, pentaerythritol tetraacrylate, tripropylene glycol diacrylate, ethoxylated bisphenol-A diacrylate, trimethylolpropane triacrylate, di-trimethylol propane tetraacrylate, triacrylate of tris(hydroxyethyl)isocyanate, dipentaerythritol hydroxypenta acrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, triethylene glycol dimethacrylate, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol-200 dimethacrylate, 1,6- hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol-600 dimethyacrylate, 1,3-butylene glycol dimethacrylate, ethoxylated bisphenol-A dimethacrylate, trimethylolpropane trimethacrylate, diethylene glycol dimethacrylate, 1,4-butanediol diacrylate, diethylene glycol dimethacrylate, pentaerythritol tetramethacrylate, glycerin dimethacrylate, trimethylolpropane dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol dimethacrylate and pentaerythritol diacrylate.

The epoxy resin to be used in the composition of the invention comprises those materials possessing at least two epoxy, i.e.,

groups. These compounds may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted with substituents, such as chlorine, hydroxyl groups, ether radicals and the like.

The term "epoxy resin" when used herein and in the appended claims contemplates any of the conventional monomeric, dimeric, oligomeric or polymeric epoxy materials containing a plurality, at least 2, epoxy functional groups. Preferably, they will be members of classes described chemically as (a) an epoxidic ester having two epoxycycloalkyl groups; (b) an epoxy resin prepolymer consisting predominately of the monomeric diglycidyl ether of bisphenol-A; (c) a polyepoxidized phenol novolak or cresol novolak; (d) a polyglycidyl ether of a polyhydric alcohol; (e) diepoxide of a cycloalkyl or alkylcycloalkyl hydrocarbon or ether; or (f) a mixture of any of the foregoing.To save unnecessarily detailed description, reference is made to the Encyclopedia of Polymer Science and Technology, Vol. 6, 1967, Interscience Publishers, New York, pages 209-271, incorporated herein by reference.

Suitable commercially available epoxidic esters are preferably, 3,4-epoxycyclohexylmethyl 3,4epoxycyclohexanecarboxylate (Union Carbide ERL 4221, Ciba Geigy CY-1 79); as well as bis(3,4epoxy-6-methylcyclohexylmethyl)adipate (Union Carbide ERL 4289); and bis(3,4-epoxycyclohexylmethyl)adipate (Union Carbide ERL 4299).

Suitable commercially available diglycidyl ethers of bisphenol-A are Ciba Geigy Araldite 6010, Dow Chemical DER 331, and Shell Chemical Epon 828 and 826.

A polyepoxidized phenol formaldehyde novolak prepolymer is available from Dow Chemical DEN 431 and 438, and a polyepoxidized cresol formaldehyde novolak prepolymer is available from Ciba Geigy Araldite 538.

A polyglycidyl ether of a polyhydric alcohol is available from Ciba Geigy, based on butane-1,4diol, Araldite RD-2; and from Shell Chemical Corp., based on glycerine, Epon 812.

A suitable diepoxide of an alkylcycloalkyl hydrocarbon is vinylcyclohexene dioxide, Union Carbide ERL 4206; and a suitable diepoxide of a cycloalkyl ether is bis(2,3-epoxycyclopentyl)-ether, Union Carbide ERL 0400.

Other examples include the epoxldized esters of the polyethylenically unsaturated monocarboxylic acids, such as epoxidized linseed, soybean, perilla, oiticica, tung, walnut and dehydrated castor oil, methyl linoleate, butyl linoleate, ethyl 9,1 2-octadecadienoate, butyl 9,12,15octadecatrienoate, butyl eleostearate, monoglycerides of tung oil fatty acids, monoglycerides of soybean oil, sunflower, rapeseed, hempseed, sardine, cottonseed oil and the like.

The thermal initiators used herein for curing the ethylenically unsaturated containing group member of the composition are free radical initiators selected from substituted or unsubstituted pinacols, azo compounds, thiurams, organic peroxides and mixtures thereof.

The organic peroxides operable are of the general formula: R-O-O-( R iO0) R wherein n=0 or 1, R is independently selected from hydrogen, aryl, alkyl, aryl carbonyl, alkaryl carbonyl, aralkyl carbonyl and alkyl carbonyl and R, is alkyl or aryl, said alkyl groups containing 1 to 20 carbon atoms.

Examples of operable organic peroxides include, but are not limited to 2,5-dimethyl-2,5-di(t butylperoxy)-hexane, 1 ,3-bis(t-butylperoxyisopropyl)benzene, 1 ,3-bis(cumylperoxyisopropyl)benzene, 2,4-dichlorobenzoyl peroxide, caprylyl peroxide, lauroyl peroxide, t-butyl peroxyisobutyrate, benzoyl peroxide, p-chlorobenzoyl peroxide, hydroxyheptyl peroxide, di-t-butyl diperphthalate, t-butyl peracetate, t-butyl perbenzoate, dicumyl peroxide, 1 , 1 -di(t-butylperoxy)-3 3-5-tri methylcyclohexa ne, di-t-butyl peroxide and t-butyl hydroperoxide.

The organic peroxide is added to the composition in an amount ranging from 0.0110%, preferably 0.15%, by weight based on the weight of the ethylenically unsaturated group members.

Examples of azo compounds operable herein include, but are not limited to, commercially available compounds such as 2-t-butylazo-2-cyanopropane; 2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile); 2,2'-azobis-(isobutyronitrile); 2,2'-azobis(2,4-dimethylvaleronitrile) and 1 ,1 '-azobis- (cyclohexanecarbonitrile).

The azo compound is added to the composition in an amount ranging from 0.0015%, preferably 0.012% by weight based on the weight of the ethylenically unsaturated group member.

The thiurams operable as thermal initiators herein are of the formula

wherein R1, R2, R3 and R4 taken singly can be hydrogen, linear or branched alkyl having from 1 to about 12 carbon atoms, linear or branched alkenyl having from 2 to about 12 carbon atoms, cycloalkyl having from 3 to about 10 ring carbon atoms, cycloalkenyl having from 3 to about 10 ring carbon atoms, aryl having from 6 to about 12 ring carbon atoms, arkaryl having from 6 to about 12 ring carbon atoms, aralkyl having from 6 to about 12 ring carbon atoms and, when taken together, r1 and r2 and r3 and r4 can each be a divalent alkylene group (-CnH2n-) having from 2 to about 12 carbon atoms, a divalent alkenylene group (-CnH2n-1-) having from 3 to about 10 carbon atoms, a divalent alkadienylene group (-CH2n-) having from 5 to about 10 carbon atoms, a divalent alkatrienylene group (-CnH2n-3-) having from 5 to about 10 carbon atoms, a divalent alkylene-oxyalkylene group (-CxH2xOCxH2x-) having a total of from 4 to about 12 carbon atoms or a divalent alkyleneaminoalkylene group

having a total of from 4 to about 1 2 carbon atoms.

Operable thiurams include, but are not limited to, tetramethylthiuram disulfide, tetraethylthiuram disulfide, di-N-penta methylenethiu ram disulfide, tetrabutylthiuram disulfide, diphenyldimethylthiura m disulfide, diphenyldiethylthiuram disulfide and diethyleneoxythiuram disulfide and the like.

The thiuram is added to the composition in an amount ranging from 0.005-5.0% by weight of the ethylenically unsaturated group member.

The substituted or unsubstituted pinacols operable herein as a thermal initiator have the general formula:

wherein R1 and R3 are the same or different substituted or unsubstituted aromatic radicals, R2 and R4 are substituted or unsubstituted aliphatic or aromatic radicals and X and Y which may be the same or different are hydroxyl, alkoxy or aryloxy.

Preferred pinacols are those wherein R1, R2, R3 and R4 are aromatic radicals, especially phenyl radical and X and Y are hydroxyl.

Examples of this class of compounds include, but are not limited to, benzopinacol, 4,4' dichlorobenzopinacol, 4,4'-dibromobenzopinacol, 4,4'-diiodobenzopinacol, 4,4',4",4"'-tetrachloro- benzopinacol, 2,4-2',4'-tetrachlorobenzopinacol, 4,4'-dimethylbenzopinacol, 3,3'-dimethylbenzo- pinacol, 2,2'-dimethylbenzopinacol, 3,4-3',4'-tetramethylbenzopinacol, 4,4'-dimethoxybenzopinacol, 4,4',4",4"'-tetramethoxybenzopinacol, 4,4'-diphenylbenzopinacol, 4,4'-dichloro-4",4"'- dimethylbenzopinacol, 4,4'-dimethyl-4",4"'-diphenylbenzopinacol, xanthonpinacool, fluorenonepinacol, acetophenonepinacol, 4,4'-dimethylacetophenone-pinacol, 4,4'-dichloroacetophenonepinacol, 1,1,2triphenyl-propane-1,2-diol, 1,2,3,4-tetraphenylbutane-2,3-diol, 1,2-diphenylcyclobutane-1,2-diol, propiophenone-pinacol, 4,4'-dimethylpropiophenonepinacol, 2,2'-ethyl-3,3'-dimethoxy- propiophenone-pinacol, 1 , 1 , 1 ,4,4,4-hexafluoro-2,3-diphenyl-butane-2,3-diol.

As further compounds according to the present invention, there may be mentioned: benzopinacol-mono methyl ether, benzopinacol-mono-phenylether, benzopinacol and monoisopropyl ether, benzopinacol monoisobutyl ether, benzopinacol mono (diethoxy methyl) ether and the like.

The pinacol is added to the composition in amounts ranging from 0.0110%, preferably 0.15%, by weight based on the weight of the ethylenically unsaturated group member.

The thermal initiators employed when the group member is an epoxy containing at least two

groups are thermal initiators selected from dicyandiamide and BF3 adducts and diaryliodonium salts, either per se or combined with a free radical initiator mentioned supra.

The BF3 adducts used herein as thermal initiators include, but are not limited to, C6HsNH2 BF3, 2,6-Et2C6H3NH2. BF3, EtN H2 BF3, sec-Bu2NH BF3, Et2NH BF3, (C6H5)3P BF3, C6HsNMe2 BF3, Pyridine BF3, and Et3N BF3, Et20 BF3, (HOCH2CH2)3N BF3.

The diaryliodonium salts operable herein as thermal initiators in combination with a pinacol are those set out in U.S. 4,238,587, and it is understood that so much of the disclosure therein relative to the diaryliodonium salts is incorporated herein by reference. That is, the diaryliodonium salts which can be utilized in the practice of the invention are shown as follows: [(R)a(R)bI]+[Y]-, (1) where R is a C(6-13) aromatic hydrocarbon radical, R1 is a divalent aromatic organic radical, and Y is an anion, a is equal to 0 or 2, b is equal to O or 1 and the sum of a+b is equal to 1 or 2. Preferably, Y is an MQd anion where M is a metal or metalloid, Q is a halogen radical and d is an integer equal to 4-6.

Radicals included within R of formula (1) can be the same or different aromatic carbocyclic radicals having from 6 to 20 carbon atoms, which can be substituted with from 1 to 4 monovalent radicals selected from C(1-8)alkoxy, C(18 alkyl, nitro, chloro, etc. R is more particularly phenyl, chlorophenyl, nitrophenyl, methoxyphenyl, pyridyl, etc. Radicals included by R1 of formula (1) are divalent radicals such as

where Z is selected from -0-, -S-,

R2 is C(1~8)alkyl or C(8~13)aryl, and n is an integer equal to 1-8 inclusive.

Metals or metalloids included by M of formula (1) are transition metals such as Sb, Fe, Sn, Bi, Al, Ga, In, Ti, Zr, Sc, V, Cr, Mn, Cs, rare earth elements such as the lanthanides, for example, Cd, Pr, Nd, etc., actinides, such as Th, Pa, U, Np, etc., and metalloids such as B, P, As, Sb, etc. Complex anions included by MQd are, for example, BF4, PF6, AsF6, SbF6, FeCl4, SnCl6, SbCl6, BiCl5, etc.

Some of the diaryliodonium salts which can be used in the practice of the invention are as follows:

These thermal initiators are added to the system in an amount ranging from 1 to 10% by weight of the epoxy resin.

Thus, when an ethylenically unsaturated group member and an epoxy resin are added in combination to form a thermoset adhesive, it is necessary to add as a thermal initiator both the aforementioned free radical type and-the type for curing epoxy resins in the amounts specified in order to obtain a cocured adhesive. The diaryliodonium salts and BF3 adducts are operable per se to initiate the crosslinking reaction but preferably are used in combination with a pinacol disclosed herein due to the faster cure rate.

The thermal initiator can be added to the system in various ways. That is, the thermal initiator, per se, can be admixed with the ethylenically unsaturated or epoxy group member. Furthermore, the thermal initiator can be dissolved or suspended in the reactive diluent or in well known commercially available solvents such as dibutyl phthalate; ketones, e.g., acetone and methylethyl ketone or chlorinated hydrocarbons such as methylene chloride, and then added to the system.

The thermoplastic adhesive material component of the heat activatabie adhesive organic resin composition can be made up of various saturated and unsaturated thermoplastic polymers and copolymers, the term "copolymers" including terpolymers, tetrapolymers, etc.' These thermoplastic adhesive materials along with the remainder of the organic resin composition can be applied in hot melt form as a one part adhesive. These thermoplastic adhesive materials are composed of 1 00% non-volatile materials, i.e., containing no water, solvent or other volatile carriers. They are solid or liquid at room temperature but become more fluid at elevated temperatures, thereby allowing for easy application.The thermoplastic adhesive materials operable herein include, but are not limited to, polyamides, polyvinyl acetals and polyester resins, ethylene-vinyi acetate (EVA) copolymers, ethylene-ethyl acrylate (EEA) copolymers, butadiene-acrylonitrile copolymers and styrene-ethylene-butylene copolymers. Some of the newer materials of the more conventional "rubber" variety are the block copolymers, styrene-butadiene or styrene-isoprene sold under the tradename "Kraton". These thermoplastic adhesive materials are sometimes used in conjunction with secondary components including waxes, plasticizers, reactive diluents, fillers and antioxidants. Wax functions as a non-volatile solvent for the thermoplastic adhesive material and reduces melt viscosity.Plasticizers, reactive diluents or liquid modifiers are used to a limited extent to formulate flexibility, specific wetting and viscosity characteristics into hot melt compounds. Fillers are used for cost reduction, color control and to improve cohesive properties. Antioxidants are used to retard oxidation during compounding and application.

One thermoplastic adhesive material useful in the adhesive compositions of the present invention includes those thermoplastic segmented copolyesters disclosed in U.S. Patent No.4,059,715, incorporated herein by reference. These are solid, non-tacky, strongly cohesive, solvent-free thermoplastic polymers which are themselves not subject to cold flow and are non-blocking below their melting temperatures but which become aggressively tacky and bondable upon being melted.

They consist essentially of from about 5 to 75 percent by weight of amorphous ester units and 95 to 25 percent by weight of crystallizable ester units joined through the ester linkages. The term "crystallizable" as used herein includes both crystalline ester units and units which are capable of becoming crystalline.The crystallizable ester units in the copolyesters are of the formula:

and the amorphous ester units are of the formula:

wherein R1 consists of residues (remaining after removal of the carboxyl groups) of one or more diacids selected from saturated aliphatic dicarboxylic acids containing from 4 to 10 carbon atoms (the residues thereof containing from 2 to 8 carbon atoms) and aromatic dicarboxylic acids selected from terephthalic acid, isophthalic acid, phthalic acid, 4,4'-benzophenone dicarboxylic acid, 4,4'diphenylmethanedicarboxylic acid, 4,4'-diphenylether dicarboxylic acid 4,4'-diphenylthioether dicarboxylic acid and 4,4'-diphenylamine dicarboxylic acid, R2 consists of residues (remaining after removal of the hydroxyl groups) of one or more saturated aliphatic diols containing from 2 to 12 carbon atoms, R3 is R1 ore5, R4 is R2 or R6, R5 consists of the divalent radicals containing from 22 to 50 carbon atoms which remain after removal of the carboxyl groups from saturated aliphatic dimer acids (i.e., the polymerized and hydrogenated product of two molecules of an ethylenically unsaturated fatty acid containing from about 1 2 to 26 carbon atoms, the dimer acid thus being saturated and containing from 24 to 52 carbon atoms) and R6 consists of the divalent radicals remaining after removal of the hydroxyl groups from a long chain aliphatic diol having an average molecular weight of 200 to 4,000 (preferably 400 to 2,000), provided that at least one of R3 and R4 in each amorphous ester unit is R5 or R6 and provided that when R1 is aromatic, R2 contains from 6 to 1 2 carbon atoms and the amorphous content is 50-75 percent by weight. The copolyesters have differential thermal analysis melting temperatures of from about 250 to 1 500C, determined as described in U.S. Patent 4,059,715 and inherent viscosities of at least 0.5 dl/g and usually not more than 1.5 dl/g (measured in 0.3 g/dl solutions of polymer in chloroform at 250C). The open times of the copolyesters are at least about 1/4 minute at 200C, and ordinarily they are not more than about 1 hour at 200 C. The copolyesters are also substantially completely soluble in toluene at 250C in the ratio of about 10 percent by weight of copolyester and 90% by weight of solvent.Preferably, the copoiyesters have melting points of at least 400C, i.e., so that they are solids at ordinary temperatures.

Suitable short chain acids, short chain diols and long chain diols useful for preparing the thermoplastic segmented copolyesters include those materials disclosed in U.S. Patent No.4,059,715.

One particularly suitable thermoplastic copolyester comprises radicals of adipic acid, a C36 dimer acid formed from linoleic acid (available under the trade designation "EMPOL 1010" from Emery Industries), 1 ,4-cyclohexane dimethanol and a poly(oxytetramethylene) glycol having a molecular weight of 2,000 and a hydroxyl equivalent of approximately 56 (available under the trade designation "Polymeg 2000" from E. I. DuPont Co.).

Other thermoplastic adhesive materials which are useful in the adhesive compositions of the present invention include other thermoplastic polyesters (e.g., that available under the trade designation "5096" from Cooper Polymers, Inc.), thermoplastic polyurethanes (e.g., that available under the trade designation "Q"-thane PH 56" from K. J. Quinn Co., Inc.), thermoplastic polyamides (e.g., that available under the trade designation "Coramid 2430" from Cooper Polymers, Inc.), "Elvamides" available frsm DuPont and "Macromelt" available from Henkel; thermoplastic rubbers (e.g. those available under the trade designation "Kraton 1101" and "Kraton 1107" from Shell Chemical Co.) and ethylene vinylacetate (e.g., that available under the trade designation "Elvax 40" from E. I.DuPont de Nemours Co., Inc. and "Ultrathene" available from USI). Still other thermoplastic adhesive materials operable as a component in the adhesive organic resin composition include, but are not limited to, butyldieneacrylonitrile copolymers available under the trade designation "Hycar" from B. F. Goodrich, urethaneacrylates, urethane-epoxides and urethane-polyenes. In addition, other thermoplastic materials are polyvinyl acetals such as polyvinyl formal and polyvinyl butyrals. The thermoplastic adhesive material is present in the composition in amounts ranging from 195% by weight of the composition with the balance being the ethylenically unsaturated and/or epoxy resin.

In the instances where the thermoplastic adhesive material contains ethylenic unsaturation, e.g., styrene-butadiene copolymers and ethylene propylene diene monomer, it is possible for cocuring with the ethylenically unsaturated group member to occur on heating. When the thermoplastic adhesive material is void of such groups, it merely acts as a matrix for the crosslinkable ethylenically unsaturated or epoxy group member thereby providing additional adhesive properties.

The compositions of the present invention may, if desired, include such additives as antioxidants, inhibitors, fillers, antistatic agents, flame-retardant agents, thickeners, thixotropic agents, surfaceactive agents, viscosity modifiers, plasticizers, tackifiers and the like within the scope of this invention.

Such additives are usually preblended with the ethylenically unsaturated or epoxy compound prior to or during the compounding step Operable fillers which can be added to the system to reduce cost include natural and synthetic resins, glass fibers, wood flour, clay, silica, alumina, carbonates, oxides, hydroxides, silicates, glass flakes, borates, phosphates, diatomaceous earth, talc, kaolin, barium sulfate, calcium sulfate, calcium carbonate, wollastonite, carbon fibers and the like. The aforesaid additives may be present in quantities up to 500 parts or more per 100 parts of the organic resin composition by weight and preferably about 0.005 to about 300 parts on the same basis.

Additionally, scavengers and antioxidants such as hydroquinone, pyragallol, phosphorous acid, triphenyl phosphine, tert-butyl hydroquinone, tert-butyl catechol, p-benzoquinone, 2,5-diphenylbenzo- quinone, 2,6-di-tert-butyl-p-cresol, etc., are added to the system in conventional amounts ranging from 0.001 to 2.0% by weight of the ethylenically unsaturated or epoxy group member.

The heating step is usually carried out for a period of 1 second to 30 minutes at a temperature of 70200C C, preferably 90-1 7O0C which is sufficient to fully cure the composition to a solid thermoset adhesive or sealant product.

The heating step using a thermal initiator to cure the adhesive organic resin composition can be accomplished in several ways. In simple systems, the adhesive composition can be applied by manual means to an adherend, contacted with another adherend and the assembled system heated in an air oven until a thermoset bond results.

Additionally and preferably, electromagnetic heating can be utilized as a faster and more efficient means of curing, especially where the substrates to be bonded are plastic materials. In addition to the formation of high strength bonds, electromagnetic bonding techniques aid in (a) fast bond setting times, and tb) automated part handling and assembly.

In practicing the instant invention, electromagnetic heating can be employed with the adhesive composition herein to adhere (1) plastic to plastic, (2) plastic to metal and (3) metal to metal. For example, dielectric heating can be used to bond (1) and (2) supra if the adhesive composition contains sufficient polar groups to heat the composition rapidly and allow it to bond the adherends. Inductive heating can also be used to bond (1), (2) and (3). That is, when at least one of the adherends is an electrically conductive or ferromagnetic metal, the heat generated therein is conveyed by conductance to the adhesive composition thereby initiating the cure to form a thermoset adhesive. In the instance where both adherends are plastic, it is necessary to add an energy absorbing material, i.e., an electrically conductive or ferromagnetic material, preferably in fiber or particle form (1 400 mesh, 2 to 0.037 mm) to the adhesive composition. The energy absorbing material is usually added in amounts ranging from 0.1 to 2 parts by weight, per 1 part by weight of the adhesive organic resin composition.

It is also possible to impregnate the plastic adherend at the bonding joint with particles of the energy absorbing material in order to use inductive heating, but care must be exercised that the plastic is not distorted.

The particulate electromagnetic energy absorbing material used in the adhesive composition when induction heating is employed can be one of the magnetizable metals including iron, cobalt and nickel or magnetizable alloys or oxides of nickel and iron and nickel and chromium and iron oxide.

These metals and alloys have high Curie points (7300--2,0400F or 388 to 111 60C).

Electrically conductive materials operable herein when inductive heating' is employed include, but are not limited to, the noble metals, copper, aluminum, nickel, zinc as well as carbon black, graphite and inorganic oxides.

There are two forms of high frequency heating operable herein, the choice of which is determined by the material to be adhered. The major distinction is whether or not the material is a conductor or non-conductor of electrical current. If the material is a conductor, such as iron or steel, then the inductive method is used. If the material is an insulator, such as wood, paper, textiles, synthetic resins, rubber, etc., then dielectric heating can also be employed.

Most naturally occurring and synthetic polymers are non-conductors and, therefore, are suitable for dielectric heating. These polymers may contain a variety of dipoles and ions which orient in an electric field and rotate to maintain their alignment with the field when the field oscillates. The polar groups may be incorporated into the polymer backbone or can be pendant side groups, additives, extenders, pigments, etc. For example, as additives, lossy fillers such as carbon black at a one percent level can be used to increase the dielectric response of the adhesive. When the polarity of the electric field is reversed millions of times per second, the resulting high frequency of the polar units generates heat within the material.

The uniqueness of dielectric heating is in its uniformity, rapidity, specificity and efficiency. Most plastic heating processes such as conductive, convective or infrared heating are surface-heating processes which need to establish a temperature within the plastic and subsequently transfer the heat to the bulk of the plastic by conduction. Hence, heating of plastics by these methods is a relatively slow process with a non-uniform temperature resulting in overheating of the surfaces. By contrast, dielectric heating generates the heat within the material and is therefore uniform and rapid, eliminating the need for conductive heat transfer.In the dielectric heating system herein the electrical frequency of the electromagnetic field is in the range 1-3,000 megahertz, said field being generated from a power source of 0.5-1 ,000 kilowatts.

induction heating is similar, but not identical, to dielectric heating. The following differences exist: (a) magnetic properties are substituted for dielectric properties; (b) a coil is employed to couple the load rather than electrodes or plates; and (c) induction heaters couple maximum current to the load.

The generation of heat by induction operates through the rising and falling of a magnetic field around a conductor with each reversal of an alternating current source. The practical deployment of such field is generally accomplished by proper placement of a conductive coil. When another electrically conductive material is exposed to the field, induced current can be created. These induced currents can be in the form of random or "eddy" currents which result in the generation of heat. Materials which are both magnetizable and conductive generate heat more readily than materials which are only conductive. The heat generated as a result of the magnetic component is the result of hysteresis or work done in rotating magnetizable molecules and as a result of eddy current flow. Polyolefins and other plastics are neither magnetic nor conductive in their natural states.Therefore, they do not, in themselves, create heat as a result of induction.

The use of the electromagnetic induction heating method for adhesive bonding of plastic structures has proved feasible by interposing selected electromagnetic energy absorbing materials in an independent adhesive composition layer or gasket conforming to the surfaces to be bonded, electromagnetic energy passing through the adjacent plastic structures (free of such energy absorbing materials) is readily concentrated and absorbed in the adhesive composition by such energy absorbing materials thereby rapidly initiating cure of the adhesive composition to a thermoset adhesive.

Electromagnetic energy absorbing materials of various types have been used in-the electromagnetic induction heating technique for some time. For instance, inorganic oxides and powdered metals have been incorporated in bond layers and subjected to electromagnetic radiation. In each instance, the type of energy source influences the selection of energy absorbing material. Where the energy absorbing material is comprised of finely divided particles having ferromagnetic properties and such particles are effectively insulated from each other by particle containing nonconducting matrix material, the heating effect is substantially confined to that resulting from the effects of hysteresis. Consequently, heating is limited to the "Curie" temperature of the ferromagnetic material or the temperature at which the magnetic properties of such material cease to exist.

The electromagnetic adhesive composition of this invention may take the form of an extruded ribbon or tape, a molded gasket or cast sheet or film. In liquid form it may be applied by brush to surfaces to be bonded or may be sprayed on or used as a dip coating for such surfaces.

The foregoing adhesive composition, when properly utilized as described hereinafter, results in a solvent free bonding system which permits the joining of metal or plastic items without costly surface pretreatment. The electromagnetically induced bonding reaction occurs rapidly and is adaptable to automated fabrication techniques and equipment.

To accomplish the establishment of a concentrated and specifically located heat zone by induction heating in the context of bonding in accordance with the invention, it has been found that the electromagnetic adhesive compositions described above can be activated and a bond created by an induction heating system operating with an electrical frequency of the electromagnetic field of from about 5 to about 30 megacycles and preferably from about 1 5 to 30 megacycles, said field being generated from a power source of from about 1 to about 30 kilowatts, and preferably from about 2 to about 5 kilowatts. The electromagnetic field is applied to the articles to be bonded for a period of time of less than about 2 minutes.

As heretofore mentioned, the electromagnetic induction bonding system and improved electromagnetic adhesive compositions of the present invention are applicable to the bonding of metals, thermoplastic and thermoset material, including fiber reinforced thermoset material.

The following examples are set out to explain, but expressly not limit, the instant invention.

Unless otherwise noted, al parts and percentages are by weight.

Strength properties of adhesive in shear by tension loading were run in accord with ASTMD 1002-64 based on one inch square (2.54x2.54 cm) of lapped area.

Example 1 Preparation of diphenyliodonium tetrafluoroborate 20 g of silver tetrafluoroborate were dissolved in 20 g of water in a beaker at 600C with stirring.

33.52 g of 97% diphenyliodonium chloride were dissolved in 720 g of water in another beaker at 600C with stirring. The silver tetrafluoroborate solution was slowly poured into the diphenyliodonium chloride solution and the AgCI precipitate was removed by filtration. The filtrate was refrigerated for 2 days resulting in the formation of white crystals. The filtrate was thawed and refiltered. The resulting white crystal solids from this filtration were washed with water, air dried and then vacuum dried over night to obtain 11.1 g of white crystals. The filtrate was reduced to 2/3 its volume in a Bucchi rotorvapor and then refrigerated. After thawing at room temperature the filtrate was refiltered and the white crystals were collected as set out above. The two resultant long white needle products weighed 28.6 g and had a melting point in the range 132-1 370C.

Analysis. Calcd. for C2H10BF41: C, 39.16; H, 2.72; B, 2.94; F, 20.671,34.51. Found: C, 39.15; H, 2.64; B, 3.04; F, 20.551, 34.98.

Curing of heat activatable adhesive composition Example 2 8 g of a polyamide having a softening point in the range 87-1 000C sold under the tradename "Macromelt-6071" by Henkel Adhesives Co. were dissolved in a 50/50 methyl alcohol-methylene dichloride solvent at 400C. 2 g of a bisphenol-A diepoxide sold under the tradename "DER-331" by Dow Chemical Co. was added to the solvent along with 0.06 g benzopinacol and 0.06 g of diphenyliodonium tetrafluoroborate.After all the adhesive composition materials were dissolved in the solvent, the solvent was removed by vacuum at 300C. 5 samples were prepared for lap shear test by applying the thus formed adhesive composition to an as received cold rolled steel adherend which was clamped to a similar adherend to form a i" (1.27 cm) lap. The clamped adherends were placed in a forced air oven maintained at 1 6O0C for 20 minutes. After removal from the oven and cooling to room temperature, the lap shear was 2410+370 psi (16616+2551 kPa).

A control run without any bisphenol-A diepoxide resulted in a lap shear of 420+70 psi (2896+483 kPa).

The following examples in Table I show the strength properties of various heat activatable adhesive compositions in shear. In all the examples, the thermoplastic adhesive material was dissolved in a solvent, i.e., 50/50 MeOH/CH2Cl2, or CH2CI2 at 400 C, followed by the dissolution of the ethylenically unsaturated and/or epoxy group member. Next, the thermal initiator is dissolved in the solvent. The solvent was removed by vacuum and the remaining solid heat-activatable adhesive composition was applied between two adherends in a 1/2" (1.27 cm) lap. 5 sets of test samples were made up for each adhesive composition. The adherends were clamped together by binder clamps and placed in a forced air oven maintained at 1 600C for 20 minutes. The test samples were removed from the oven, unclamped and allowed to cool to room temperature before lap shear measurements (psi or kPa) were taken. The average of the five test values is shown in Table I.

Table I Concentional curing of adhesive compositions Acrylate or epoxide group member (wt. %) Lap shear, psia (kPa) Adhesive thermoplastic material 1,4-Butane- Fiberglass Example DER diol Digly- TMOP- SR- Initiator reinforced No. Type Wt. % 331b cidyl ether TAc 209d (wt. %) Steele polyester 3 Butadiene- 100 - - - - - 65g (448) 14% Acrylonitrile copolymerf 4 Butadiene- 79.84 - - 19.96 - Benzopinacol, 0.2 113g (779) 14% Acrylonitrile copolymerf 5 Styrene- 100 - - - - - 100g (689) isoprene copolymerh 6 Styrene- 79.84 - - 19.96 - Benzopinacol, 0.2 185g (1276) isoprene copolymerh 7 Polyvinyl 100 - - - - - 200 (1379) formall 8 Polyvinyl 73.89 24.63 - - - Amine BF3 2700 (18600) formall Adductj 1.48 9 Polyvinyl 89.11 - 9.90 - Benzopinacol 0.99 450 (3100) formall 10 Polyvinyl 73.89 24.63 - - - Dicyanodiamide, 1.48 1740 (12000) formall 11 Polyvinyl 100 - - - - - 720 (4960) 600 butyralk 12 Polyvinyl 89.11 - - 9.90 - Benzopinacol, 0.99 2100 (14500) butyralk Table I (cont).

Concentional curing of adhesive compositions Acrylate or epoxide group member (wt.%) Lap shear, psia (kPa) Adhesive thermoplastic material 1,4-Butane- Fiberglass Example DER diol Digly- TMOP- SR- Initiator reinforced No. Type Wt.% 331b cidyl ether TAc 209d (wt.%) Steele polyester 13 Polyvinyl 73.89 24.63 - - - Amine, BF3, 2600 (17900) butyralk Adductj, 1.48 14 Polyvinyl 74.40 24.80 - - - Onium salti, 0.79 1700 (11700) butyralk 15 Polyvinyl 73.89 24.63 - - - Onium salti, 2380 (16408) butyralk 0.74+ Benzopinacol 0.74 16 Polyvinyl 89.82 - - 9.98 - Azobisiso- - 700 (4800) butyralk butyronitrile, 0.2 17 Polyvinyl 89.91 - - 9.99 - Tetramethylthiuram 1080 (7450) 800 (5500) butyralk disulfide, 0.1 18 Polyvinyl 47.16 23.58 - 23.58 - Onium salt - 576 (3970) butyralk 2.8+ Benzopinacol 2.8 19 Ethylene- 100 - - - - - 200 (1520) 570 (3930) 28% vinyl acetate copolymerm 20 Ethylene- 74.81 - - 24.94 - Benzopinacol 0.25 1000 (6890) 1120 (7720) 28% vinyl acetate copolymerm 21 Ethylene- 49.75 - - - 49.75 Benzopinacol 0.50 - 1200 (8270) 28% vinyl acetate copolymerm Table I (cont).

Concentional curing of adhesive compositions Acrylate or epoxide group member (wt.%) Lap shear, psia (kPa) Adhesive thermoplastic material 1,4-Butane- Fiberglass Example DER diol Digly- TMOP- SR- Initiator reinforced No. Type Wt.% 331b cidyl ether TAc 209d (wt.%) Steele polyester 22 Ethylene- 79.05 19.76 - - - Onium saltl 1120 (7720) 28% vinyl 0.59 + acetate Benzopinacol copolymerm 0.59 23 Polyamiden 100 - - - - - 1200 (8270) 24 Polyamiden 89.91 - - - 9.99 Benzopinacol 0.1 1700 (11700) 25 Polyamiden 100 - - - - - 710 (4900) 26 Polyamiden 79.05 - 19.76 - - Onium saltl 1540 (10600) 0.59+ Benzopinacol 0.59 27 Polyesterp 100 - - - - - 230 (1600) 28 Polyesterp 89.82 - - 9.98 - Peroxideq 0.20 1060 (7310) Footnotes:: (a) Cured at 160 C for 20 min., then lap shear measured at R.T., all laps inch except where noted; (b) DER 331=Bisphenol-A diepoxide, commercially available from Dow Chemical; (c) TMOP-TA=Trimethylolpropane triacrylate; (d) SR 209=Sartomer tetraethylene glycol dimethacrylate, commercially available from Sartomer; (e) All on as received steel, except where noted; (f) Hycar 1041, commercially available from B.F.Goodrich; (g) 1 inch lap on degreased steel; (h) Kraton 1107, commercially available from Shell Chemical; (i) Formvar 5195E, average molecular weight 10,000 to 15,000, Monsanto; (j) Leepoxy B-550, commercially available from Leepoxy Plastics; (k) Butvar B-76, average molecular weight 45,000 to 55,000 Monsanto; (l) Diphenyliodonium tetrafluoroborate; (m) Ultrathene 636-04, softening point 106 C, commercially available from USI Chemicals;; (n) Macromelt 6900, softening point 130 to 150 C, Henkel Adhesives Co,; (o) Elvamide, melting point 145 to 160 C, DuPont; (p) Dynapol S-142, softening point 99 C, Dynamit Nobel; (q) 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, commercially available from Pennwalt.

The examples in Table II show the strength properties of various heat activatable adhesive compositions in shear when the heat cure is carried out using dielectric heating. The adhesive compositions were made up as in the examples in Table I, placed between adherends in a " (1.27 cm) lap and cured by radio frequency radiation at 200 volts and 0.8 ampere of direct current for 2 minutes.

Table II RF Dielectric curing of adhesive compositions Lap shear psi (kPa) Adhesive Acrylate or epoxide thermoplastic material member (wt. /0) Fiberglass Example reinforced No. Type Wt. % DER 331 b TMOP-TAC InitiatorRvat. %J polyester 29 Polyamided 89.91 - 9.99 Benzopinacol, 0.1 860 (5930) 30 Polyvinyl 89.91 - 9.99 Benzopinacol, 0.1 430 (2960) butyra le 31 Polyvinyl 73.89 24.63 - Amine BF3 490 (3380) butyrale Adductf, 1.5 32 Polyvinyl 47.16 23.58 23.58 Onium salth 2.8+ 575 (3960) butyrale Benzopinacol 2.8 33 Ethylene-vinyl 89.91 - 9.99 Benzopinacol, 0.1 600 (4140) acetate copolymer Footnotes:: (a) Cured 2 min., + inch (1.27 cm) laps; (b) DER-331=Dow bisphenol-A dlepoxide; (c) TMOP-TA=Trimethylolpropane triacrylate; (d) Macromelt 6900, Henkel Adhesive Co.; (e) Butvar B-76, Monsanto; (f) Leepoxy B-550, Leepoxy Plastics; (g) Ultrathene 636-04, USI Chemicals Co.; (h) Diphenyliodonium tetrafluoroborate.

The examples in Table Ill show strength properties of various compositions in shear when the curing step is performed using inductive heating. The adhesive compositions were made up as in the examples in Table I with the iron filler used herein being added at the end with stirring. After placing the adhesive between adherends in a 1 '2" (36 cm) lap, curing was carried out on a 2 kw EMABond generator Model EA-20 at 95-100% load for 2 minutes.

Table Ill RF inductive curing of adhesive compositions Lap shear, psia (kPa) Acrylate or epoxide Adhesive thermoplastic material Wt. % member (wt. /OJ Fiberglass Example from reinforced No. Type wt. % filler DER 331 b TMOP-TAC Initiator ("vt. %) polyester 34 Polyamided 58.37 35.02 - 6.49 Benzopinacol, .13 870 (6000) 35 Ethylene-vinyi 58.37 -35.02 - 6.49 Benzopinacol, .13 625 (4310) acetate copolymera 36 Polyvinyl butyralf 55.35 25.09 18.45 - Amine BF3 Adductg, 370 (2550) 1.11 37 Polyvinyl butyralf 35.88 23.92 17.94 17.94 Onium salth 2.15+ 408 (2810) Benzopinacol 2.15 38 Polyvinyl butyralf 58.37 35.02 - 6.49 Benzopinacol, .13 790 (5450) Footnotes: : (a) Cured 2 min., inch (1.27 cm) lap (b) DER-331=Dow bisphenol-A diepoxide; (c) TMOP-TA=Trimethylolpropane triacrylate; (d) Macromelt 6900, Henkel Adhesives Co.; (e) Ultrathene 636-04, USI Chemicals; (f) Butvar B-76, Monsanto; (g) Anchor 1222, Anchor Chem.

(h) Diphenyliodonium tetrafluoroborate.

The compositions herein for the most part are solids at room temperature which can be used as reactive hot melt adhesives. That is, the solid composition can be heated to a molten or plastic mass at a temperature below the decomposition temperature of the thermal initiator and be placed between 2 substrates to be adhered. Upon cooling to a lower temperature the adhesive solidifies to a thermoplastic adhesive with properties sufficient to adhere the substrates. Thereafter, the assembled works can be heated to a higher temperature to trigger the thermal initiator and form a thermoset adhesive between the substrates. A further refinement can be the use of the solid composition in the form of film, tape or gasket to be placed between adherends. This is shown in the following examples.

Example 39 100 g of polypropylene glycol (MW=1025 g/mole) were added dropwise over a 6-hour period to a flask containing 34 g of toluene diisocyanate in a nitrogen atmosphere. The reaction was continued with stirring for 4 days at room temperature. The resultant chain-extended isocyanate terminated product will hereinafter be referred to as diisocyanate adduct A.

Example 40 Into 100 g of methylene chloride solvent was charged 100 g of an epoxy resin containing 357 g/eq of OH, commercially available from Shell Chemical Co. under the tradename "Epon-1 001 F", 0.1 g of dibutyl tin dilaurate and 40.89 g of diisocyanate adduct A from Example 39. The reaction was stirred at room temperature for 24 hours and monitored by IR until no isocyanate could be detected resulting in a thermoplastic, epoxy pendant, urethane containing compound. To 7.5 g of said compound in methylene chloride was added 2.5 g of a liquid bisphenol A epoxy acrylate, commercially available from Shell Chemical Co. under the tradename "Epocryl Resin-i 2", 0.3 g of diphenyiiodonium tetrafluoroborate and 0.3 g of benzopinacol. After stirring until a homogeneous mixture was obtained, the methylene chloride solvent was removed under vacuum leaving a heat activatable, solid, hot melt adhesive composition. The composition was applied in a 2 4 mil (0.05 to 0.1 mm) thickness between 2 cold roll steel adherends. The adherends were clamped together and heated at 700C for 5 minutes and then cooled to room temperature. On removal of the clamps the thermoplastic composition maintained adherence between the assembled work. The assembled work was reheated to 1 600C for 20 minutes resulting in a thermoset adhesive between the adherends.

Claims (9)

Claims

1. A heat activatable adhesive or sealant organic resin composition comprising (1) a member of the group consisting of (a) a liquid, ethylenically unsaturated monomer, oligomer or prepolymer of the formula:

wherein R is H or CH3, R, is an organic moiety and n is at least 2, (b) an epoxy resin containing at least 2

groups and (c) a mixture of (a) and (b); (2) a thermal initiator, and (3) a thermoplastic adhesive material selected from the group consisting of polyesters, polyvinyl acetals, polyamides, butadiene-acrylonitrile copolymers, styrene-butadiene copolymers, styreneisoprene copolymers, styrene-ethylene-butylene copolymers, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene propylene diene monomer and mixtures thereof.

2. A resin composition according to claim 1 substantially as hereinbefore described.

3. A process for forming a coating on a substrate which comprises coating a heat curable composition as claimed in claim 1 or 2, on a substrate and heating said coating in the range 70-2000C to effect curing.

4. A process for adhering two substrates which comprises contacting said substrates with a solid, heat curable composition as claimed in claim 1 or 2, heating said composition to a temperature whereat said composition becomes sufficiently plastic to act as a thermoplastic adhesive between said substrates, said temperature being below the decomposition temperature of the thermal initiator and thereafter heating to a higher temperature, sufficient to decompose the thermal initiator and form a thermoset adhesive between the substrates.

5. The process according to claim 3 or 4 wherein the heating step is carried out by electromagnetic heating.

6. The process according to claim 5 wherein the electromagnetic heating is by dielectric heating.

7. The process according to claim 5 wherein the electromagnetic heating is by induction heating.

8. A sealant or adhesive in the form of a composition as claimed in claim 1 or 2 which has been cured.

9. The composition according to claim 1 or 2 which is solid and in the form of a film, tape or gasket.