GB2108509A - Heat curable epoxy composition - Google Patents

Abstract

The invention provides a heat curable composition comprising (a) an epoxy resin containing at least two <IMAGE> groups, and (b) a thermal initiator comprising in combination (1) a substituted or unsubstituted diaryliodonium salt and (2) a substituted or unsubstituted pinacol. The initiator system is stable at ordinary temperature but on heating is triggered to catalyze the polymerization of the epoxide. The cured composition is useful as a sealant, coating, or adhesive.

Description

SPECIFICATION Heat-curable epoxy composition This invention relates to an epoxy containing heat curable composition. The initiator system for the composition is stable at ordinary temperature but on heating is triggered to catalyze the polymerization of the epoxide.

It is known to polymerize vinyl ethers and cyclic ethers such as tetrahydrofuran at elevated temperatures using an iodonium salt and a pinacol as the initiator. See "Photochemical and Thermal Cationic Polymerizations Promoted by Free Radical Initiators", Firas A. M. Abdul-Rasoul et al, POLYMER, 1978, vol. 19, October, pp. 1219-1222.

The present invention provides an adhesive composition which is solventless and can be used as a sealant or coating. It can also be used as an adhesive which is rapidly heat curable.

This invention relates to a heat curable composition comprising (a) an epoxy resin containing at least two

groups, and (b) a thermal initiator comprising in combination (1 ) a substituted or unsubstituted diaryliodonium salt and (2) a substituted or unsubstituted pinacol.

The initiator system is stable at ordinary temperature but on heating is triggered to catalyze the polymerization ofthe epoxide.

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 momomeric, 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 monomericdiglycidyl ether of bisphenol-A; (c) a polyepoxidized phenol novolakorcresol 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.

Suitable commercially available epoxidic esters are preferably, 3,4-epoxycyclohexylmethyl 3,4epoxycyclohexanecarboxylate (Union Carbide ERL 4221, Ciba Geigy CY-179); as well as bis(3,4-epoxy-6methylcyclohexylmethyl)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-1,4-diol, Araldite RD-2; and from Shell Chemical Corp., based on glycerine, Epon 812.

A suitable diepoxide of an alkylcycloalkyl hydrocarbon is vinyl cyclohexene 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 epoxidized 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, 12-octadecadienoate, butyl 9,12,15-octadecatrienoate, butyl eleostearate, monoglycerides of tung oil fatty acids, monoglycerides of soybean oil, sunflower, rapeseed, hempseed, sardine, cottonseed oil and the like.

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"'- tetrachlorobenzopinacol, 2,4,2',4'4etrachlorobenzopinacol, 4,4'-dimethylbenzopinacol, 3,3'- dimethylbenzopinacol, 2,2'-dimethylbenzopinacol, 3,4,3',4'-tetramethylbenzopinacol, 4,4' dimethoxybenzopinacoI, 4,4', 4",4"'-tetramethoxybenzopinacol, 4,4"-diphenylbenzopinacol, 4,4'-dichloro-4"- 4"'-dimethylbenzopinacol,4,4'-dimethyl-4",4"'-diphenylbenzopinacol, xanthonpinacol, fluorenonepinacol, acetophenonepinacol, 4,4'-dimethylaceto-phenone-pinacol, 4,4'-dichloroacetophenonepinacol, 1,1,2- triphenyl-propane-l,2-diol, 1 ,2,3,4-tetraphenyl-butane-2,3-diol, 1 ,2-diphenylcyclobutane-l ,2-diol, propiophenone-pinacol, 4,4'-dimethylpropiophenone-pinacol, 2,2'-ethyl-3,3'-dimethoxypropionphenone-pinacol, 1,1,1 ,4,4,4-hexafl uoro-2,3-diphenyl-butane-2,3-diol.

As further compounds according to the present invention, there may be mentioned: benzopinacol-mono methylether, 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 0.01 - 10%, preferably 0.1 - 5%, by weight based on the weight of the epoxy resin.

The diaryliodonium salts operable herein as part of the thermal initiator 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 be reference. That is, the diaryliodonium salts which can be utilized in the practice of the invention are shown as follows: [(R)a(Rl)bl] [Y] Z (1) where R is a C(6.13) aromatic hydrocarbon radical, R' is a divalent aromatic organic radical, and Y is an anion, a is equal to 0 or 2, b is equal to 0 or 1 and the sum of a + b is equal to 1 or 2. Preferably, Y is an MOd 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".

alkoxy, Cm 8) alkyl, nitro, chloro, etc. R is more particularly phenyl, chlorophenyl, nitrophenyl, methoxy phenyl, 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(6,3) 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-, AsFe-, SbF6-, FeC14-, SnCI6-, SbCI6-, BiC1S--, etc.

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

The diaryliodonium salt is added to the system in an amount ranging from 1 to 10% by weight of the epoxy resin.

The diaryliodonium salts are operable per se to initiate the curing reaction. See U.S. 4,225,691. However, in the instant application, these materials are used in combination with a pinacol disciosed herein to obtain a much 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 epoxy resin. Additionally, the thermal initiator can be dissolved or suspended 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 compositions of the present invention may, if desired, include such additives as antioxidants, inhibitors, fillers, antistatic agents, flame-retardant agents, thickeners, thixotropic agents, surface-active agents, viscosity modifiers, plasticizers, tackifiers and the like within the scope of this invention. Such additives are usually preblended with the 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 epoxy resin by weight and preferably about 0.005 to about 300 parts on the same basis.

Additionally, epoxy resin stabilizers such as phosphites, e.g., triphenyl phosphite, diphenyl phosphite and trisnonylphenyl phosphite are added to the system in conventional amounts ranging from 0.001 to 2.0% by weight of the epoxy resin.

The heating step is usually carried out for a period of 10 seconds to 30 minutes at a temperature of 80 300"C, preferably 100 - 200"C which is sufficient to fully cure the composition to a solid adhesive, coating or sealant product.

The heating step is usually carried out for a period of 10 seconds to 30 minutes at a temperature of 100 300"C, preferably 120 - 200"C which is sufficient to fully cure the composition to a solid 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 a forced 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 (b) 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 (10-400 mesh, 2.0 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 (730"-2,040"F; 388" to 1116"C).

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 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 eletromagnetic 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. In liquid form it may be applied by brush to surfaces to be bonded or may be pumped, 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 15 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, all parts and percentages are by weight Strength properties of adhesive in shear by tension loading (metal to metal) were run in accord with ASTMD 1002-64 based on one inch (2.54 cm.) square of lapped area unless otherwise specified.

EXAMPLE 1 Preparation ofiodobenzene diacetate 40.8 g (0.2 mol) of iodobenzene were charged to a 300 ml round bottom flask equipped with thermometer and vented addition funnel. 91.2 g (0.48 mol) of a 40% aqueous solution of peracetic acid was added dropwise to the flask over a 25-minute period while maintaining the flask at 30"C in a water bath. After about 1 hour a yellowish white solid formed. The reaction mixture was cooled in ice and the solid collected, washed with water and vaccuum dried at 40"C. The iodobenzene diacetate product weighed 40.6 g and had a melting point in the range of 157-160"C.

EXAMPLE 2 Preparation of4-methoxydiphenyliodonium tetrafluoroborate 48.6 g iodobenzene diacetate, 16.3 ml anisole, 65 ml acetic anhydride and 725 ml glacial acetic acid were charged to a 2 liter, 3 neck round bottom flask equipped with stirrer, reflux condenser, themometer and addition funnel. 8 ml of concentrated sulfuric acid were added dropwise over a 20 minute period to the flask while maintaining the temperature below 10 C. A viscous brown mixture containing white needles formed.

The mixture was thawed to room temperature over a 1 1/2 hour period at which point it was stirred for a additional 45 minutes at room temperature. 31 g of sodium bromide in 150 cc of water were added to the solution. Tan solid particles formed which were collected, washed with water and dried. The resultant product, i.e., 47 g of 4-methoxydiphenyliodonium bromide, had a melting point of 165-168"C.

39.9 g of the 4-methoxydiphenyliodonium bromide were dissolved in 1,000 cc of water and 500 cc of acetone with heating. To this solution were added 25 g (0.13 moles) of silver tetrafluoroborate in 40 cc of water. The silver bromide formed was removed by filtration and the filtrate was reduced in volume by 2/3 in a Buchi rotovapor resulting in a brown liquid which was then refrigerated. 26.8 g of white and brown damp solids were collected from the refrigerated material and dissolved in 100 cc CH2Cl2 and passed through a 1" by 3" (2.5 by 7.5 cm) long neutral alumina column. 100 cc of pale brown liquid was collected. 150 cc of ether were mixed in with the pale brown liquid resulting in the formation of white solids. The white solids were collected, washed with ether and dried.The resultant white solid product weighed 13.3 g and had a melting point of 1 04-1 05"C. Another 50 cc of the CH2Cl2 from the alumina coiumn were collected, washed with ether and dried. The dried product weighed 2.5 g and had a melting point of 98-99"C. The two resultant products were admixed together. The NMR spectrum of the product was in agreement with the structure for 4-methoxydiphenyliodonium tretrafluoroborate.

Analysis, Calcd. for C13H12BF4 10: C, 39.22; H, 3.02;; B, 2.72; F, 19.11; 1,31.91. Found: C, 39.85; H, 3.02; B, 2.75; F, 17.541,32.78.

EXAMPLE 3 Preparation of diphenyliodonium tetrafluoroborate 20 g of silver tetrafluoroborate were dissolved in 20 g of water in a beaker at 60"C 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 rotovapor 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 132-137"C.

Analysis. Calcd. for C12H10BF41: C, 39.16; H, 2.72; B, 2.94; F, 20.67; 1,34.51. Found: C, 39.15; H, 2.64; B, 3.04; F,20.55;1,34.98.

EXAMPLE 4 1 ,4-butanediol diglycidyl ether was stirred on a hot plate at 1 OO"C for 25 minutes and then placed in a forced air oven maintained at 1600C for 3 3/4 hours. On removal from the oven the sample was still a liquid with no apparent change in viscosity.

EXAMPLE 5 The following mixtures were made up by weighing the components into 4 dram (14.8 ml.) vials each of which was then stirred on a hot plate at 60"C for 20 minutes: (a) 1,4-butanediol diglycidyi ether 10 g 4-methoxydiphenyliodonium tetrafluoroborate 0.3 g (b) 1,4-butanediol diglycidyl ether 10 g diphenyliodonium tretrafluoroborate 0.3 g (c) 1,4-butanediol diglycidyl ether 10 g 4-methoxydiphenyliodonium tetrafluoroborate 0.3 g benzopinacol 0.3g (d) 1,4-butanediol diglycidyl ether 10 g diphenyliodonium tretrafluoroborate 0.3 g benzopinacol 0.39 (e) 1,4-butanediol diglycidyl ether 10 g benzopinacol 0.39 (f) 1,4-butanediol diglycidyl ether 10 g Each mixture was placed in a 1600C oven until it became solid and the time required to solidify was recorded for each mixture as shown in Table I: TABLE I Mixture Time to Solidify fin.) (a) 16.4 (b) 10.2 (c) 4.6 (d) 4.6 (e) unchanged after 20 minutes (f) unchanged after 20 minutes EXAMPLE 6 10 g of a diglycidyl ether of bisphenol A, commercially available from Dow under the tradename DER-331, 3.3 g diphenyliodonium tetrafluoroborate and 0.3 g benzopinacol were dissolved in 20 cc of CH2C12. After dissolution the solvent was removed under vacuum at 40"C. The remaining admixture was drawn down on cold-rolled steel to form a 7 mil (0.18 mm.) thick coating. The thus coated steel was placed in a forced air oven at 160"C for 20 minutes. A cured tack-free hard coating on the steel resulted.

EXAMPLE 7 50 g of a diglycidyl ether of bisphenol A commercially available from Dow under the trade name DER-331, 1.5 g of diphenyliodonium tetrafluoroborate and 1.5 g benzopinacol were mixed at 100 C on a hot plate with stirring for 30 min. A portion of the admixture was spread between as received cold-rolled steel adherends.

Five samples were made up. The adherends were clamped together and placed in a forced air oven at 150"C for 20 minutes. The average lap shear of the adherends was 2580+690 psi (17800+4800 kPa).

EXAMPLE 8 15 g of 1,4-butanediol diglycidyl ether, 0.45 g diphenyliodonium tetrafluoroborate and 0.45 g benzopinacol were dissolved together at room temperature. 4 g of the above admixture were charged to a 4 dram (14.8 ml.) vial along with 0.04 g of Ketjenblack. The vial was placed in a J.Trembley Co. radio frequency heater, Model EO*1 A, and exposed to approximately 100 milliamps of radio frequency energy for about 30 seconds.

A cured rubbery solid product resulted.

EXAMPLE 9 10 g of an epoxidized polybutadiene having a number average molecular weight of 1,100 and containing 8 weight percent epoxy sold under the tradename BF-1 ,000 by Nippon Soda Co. Ltd., 0.3 g of diphenyliodonium tetrafluoroborate and 0.3 g of benzopinacol were dissolved in 10 cc of methylene chloride. 3.38 g of Standard-03 iron powder, commercially available from EMABond, was mixed into the solution. After dissolution the solvent was removed under vacuum at 40"C and 1" x 11/2" x 20 mils (25 x 38 x 0.5 mm.) bond joint of the thus formed composition was applied between 2 glass fiber reinforced polyester adherends and cured by a 2 kw EMABond generator, Model EA-20, at 95-100% load for 60 seconds. A solid bond resulted.

The adherends could not be pulled apart by hand.

Claims (9)

1. A heat curable composition comprising (a) an epoxy resin containing at least two

groups, and (b) a thermal initiator comprising in combination (1) a substituted or unsubstituted diaryliodonium salt and (2) a substituted or unsubstituted pinacol.

2. A composition according to Claim 1 wherein the thermal initiator is diphenyliodonium tetrafluoroborate and benzopinacol.

3. A composition according to claim 1 substantially as hereinbefore described.

4. A process for forming a coating on a substrate which comprises coating a heat curable composition as claimed in claim 1,2 or 3 on a substrate and heating said coating in the range 80-300"C to effect curing.

5. A process for adhering two substrates which comprises coating at least one of said substrates with a heat curable composition as claimed in claim 1,2 or 3, contacting the thus coated substrates and heating the thus contacted substrates in the range 100-200 C to cause adhesion.

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

7. The process according to Claim 6 wherein the electromagnetic heating is by dielectric heating.

8. The process according to Claim 6 wherein the electromagnetic heating is by induction heating.

9. A composition according to Claim 1,2 or 3 which has been cured and in the form of a sealant, coating, or adhesive.