CA1229192A - One component, hot melt, thermosettable, epoxy containing composition - Google Patents

Abstract

THERMOSETTING COMPOSITIONS
Abstract of the Disclosure This invention relates to a thermoplastic, epoxy pendant, urethane-containing compound which is the reaction product of an epoxy resin containing more than one, preferably two hydroxyl groups and a diol end-capped, with a diisocyanate. The compound is preferably formed in the presence of a heat reactive epoxy curing agent resulting in a one component material usable as a thermoset adhesive, sealant or coating on heating.

Description

`~L2~29~92 BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to a novel compound which in combination with a heat reactive, epoxy curing agent can be used as an adhesive, sealant or coating composition which, on application of heat, preferably in an accelerated manner, cross links to give a thermoses bond, seal or coating.

2. Description of the Prior Art Conventional hot melt adhesive compositions are thermoplastic bonding materials which are solid at room temperature but become soft and fluid with good nettability of the adherents at elevated temperatures.
These adhesives are readily applied in the molten state between adherents resulting in a strong adhesive thermoplastic bond on cooling and hardening.
-. 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 adherents. 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 adherents 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 not have sufficient cohesive strength at the low molecular weights required for application to a substrate. For ~9~L~g2 example, the low molecular weight polyolefins, especially low molecular weight, low density polyethylene, are widely used in hot melt adhesives for sealing corrugated cartons, multy-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 preexposed to elevated temperatures which will cause the adhesive to sag thereby allowing the bond to break.
The concept of thermosetting or cross linking resin adhesive is also known in the art. Many resin adhesives which undergo an irreversible, chemical and physical change and become substantially insoluble are known Th~rmosetting 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. Cross linking in these patents is achieved by reaction with available sites in the base polymers. U. S. 4,137,364 teaches cross linking of an ethylene/vinyl acetate/vinyl alcohol terpolymer using isophthaloyl, bis-caprolactam or vinyl triethoxy ; Solon whereby cross linking is achieved before heat activation with additional cross linking induced by heat after application of the adhesive. U. S. 4,116,937 teaches a further method of thermal cross linking by the I
use of palomino bis-maleimide class of flexible polyamides, which compounds can be hot melt extruded up to 150C and undergo cross linking at elevated temperatures there above. In these latter two patents, thermal cross linking is also achieved by reactions of the particular cross linking agent with available sites of the base polymers. U. S. 3,934,056 teaches resin compositions of high adhesivity comprising ethylene-vinyl acetate copolymer, chlorinated or chlorosulfonated polyethylene, lo unsaturated carboxylic acids and an organic peroxide.
- Another thermosetting adhesive is known from U. SO 3,945,877 wherein the composition comprises a coal tar pitch, ethylene/vinyl acetate copolymer and ethylene/acrylic acid copolymer plus a cross linking agent such as dicumyl peroxide.
In many of these prior art thermosetting adhesive compositions admixture of 2, 3 or 4 components is necessary in order to get a thermoses bond. Thus, the resultant bond depends on the homogeneity of the admixture. 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 cross linking reaction begins immediately upon admixture and is irreversible.
Additionally, U. S. 3,505,283 teaches the use of simple, organic dip and polyisocyanates as chemical thickness when reacted with hydroxyl-containing epoxy resins at temperatures between 50 and about 200C in the presence of carboxylic acid android as a curing agent.
Material prepared from this process is not suitable as a reactive, hot melted adhesive since the high application temperatures required to afford process ability may trigger - the cross linking reaction of the thermosetting material prematurely. Similarly, U. S. 3,424,719 teaches the use :;

of simple diisocyanates to react with the glycldyl polyether of dihydric phenols in solvents, thereby increasing the cross linking density which results in improved heat distortion temperatures. The solvent is necessary for process ability of the solid forms of glycidyl polyether dihydric phenol and avoid the high temperature conditions required for polymerization which creates not only process problems but also the instability of the reactant mixture after blending with a latent curing agent.
OBJECTS OF THE INVENTION
Structural adhesives and sealants are needed for bonding substrates loaded with significant mechanical stress at the interface. Such adhesive materials must have the following requirements:
High production rates with short, unvarying times for each operation in assembly line use.
Minimal cleaning of surfaces to be bonded which are subject to sudden or gradual contamination.
Low tolerance for health and safety hazards.
Rapid development of handling strength.
Maximum bond strength.
Maximum thermal and environmental resistance.
Adjustable open time based on these requirements, typically thermosetting materials such as epoxy resins, phenolics, polyesters and polyurethane are used as structural adhesives. After the cross linking reaction the adhesive becomes part of the structural component and provides the required bond strength and thermal resistance. Normally, the structural adhesive is composed of liquid resins and curing agents in either two-package or single package form depending on the reactivity between the resin and the curing agent under storage conditions.

~2~2 The liquid structural adhesive has the advantage of easy application to the substrate over the solid adhesive. However, the liquid adhesive, in two-package form after mixing, needs a certain length of pot-life which is the time required to stay as liquid for application purposes. Consequently, the handling strength minimum strength necessary to maintain adhering substrates together) cannot be rapidly developed.
Further, from a safety and health hazard viewpoint, the liquid adhesive usually causes more contamination than the solid Norm. Thus, the two-package structural adhesive requires a very precise measurement and extremely good mixing to obtain any consistency of property control.
The one package liquid adhesive was designed to solve mixing and metering difficulties. To achieve one package reactive adhesive preparation, techniques such as chemical blocking and phase separation are being used in the adhesive industry. The cross linking reaction has to be triggered by heating or other techniques which are difficult to control resulting in long time periods to develop handling strength.
Two forms of solid adhesives, powder and hot melt can be used instead of liquid adhesives. Because of the phase separation between resin powder and curing agent powder, the one package adhesive can be obtained very easily.
However, the application, handling cost and safety considerations make the powder adhesive less attractive to the adhesive industry.
The other solid form of adhesive is hot melt which is a thermoplastic in general. The hot melt adhesive provides a bond between substrates upon cooling the molten adhesive to room temperature. The bonding process is fast and simple. The disadvantage of a thermoplastic hot melt adhesive is the fast decrease in its bonding strength upon reheating because of the nature of thermoplastics. Thus, it cannot be considered as a structural adhesive unless it is further modified.
Conventional solid adhesive such as high molecular weight epoxy resin can be applied as a reactive hot melt adhesive. Without modification, this type of solid adhesive provides poor adhesion properties such as impact resistance and lap shear strength. Modification of this material such as reacting it with a carboxyl-ter~inatPd poly~butadiene-co-acrylonitrile) increases the impact - resistance and the lap shear strength. However, this modification is carried out at elevated temperature, 100 -150C, in the presence of a catalyst, thus making the addition of a latent curing agent such as dicyandiamide I-and curing accelerator difficult since the curing reaction is activated thermally. Hence, due to the combination of a high cost factor and preparation difficulties, this type of adhesive is not attractive commercially.
This invention is concerned with the development of a class of reactive hot melt adhesives which will provide rapid development of handling strength and, also, maximum bond strength and thermal resistance as thermosetting adhesives. Furthermore, this invention relates to process simplification of adhesive preparation, internal property modification through the design of polymer backbone and plasticization of polymers through the addition of a reactive plasticizer to control the application temperature. This invention also relates to a process to utilize the reaction between diisocyanates and hydroxyl groups of the dill and epoxy resin to prepare the reactive hot melt adhesives having latent curability, long storage life, internally modified adhesion properties and well controlled application rheology. The materials for the preparation of this particular reactive hot melt adhesive I
include a polyisocyanate, a hydroxyl-containing epoxy resin for introducing reactive pendant groups and a dill, preferably a difunctional primary alcohol, for improving the physical properties and for reducing the viscosity of the bulk polymerization medium. Optionally, a reactive plasticizer for reducing the viscosity of bulk polymerization and adjusting the application temperature can be added to the system.
One object of the instant invention is to produce a composition, usable as an adhesive, sealant or coating, which is solvent less. Another object of the invention is to produce a composition which can be applied as a hot melt. Still another object of the instant invention is to produce a composition which is heat curable in a minimum time period. A further object of the invention is to produce a novel compound which in combination with a heat reactive epoxy curing agent will result in a thermoses coating, adhesive or sealant on heating.
Yet another object of the invention is to produce a thermos plastic composition which can be applied as a hot melt and thereafter cured by a thermally triggered initiator to a thermoses adhesive, sealant or coating at a more elevated temperature. A further object of the instant invention is to produce one or more methods for making a thermoplastic composition which can be applied as a hot melt. Other objects ; will become apparent from a reading hereinafter.
The invention provides for a one component, hot melt thermosettahle composition comprising (a) dicyandiamide and (b) a thermoplastic, epoxy pendant, urethane-containing compound which is the reaction product of an epoxy resin con-twining more than one hydroxyl group and a dill end-capped with a polyisocyanate.
The invention further provides for a process for adhering two substrates which comprises coating at least one of said substrates with a one component, hot melt composition comprise in (a) dicyandiamide and (b) a thermoplastic, epoxy pendant, urethane-con~aining compound which is the reaction product of an epoxy resin containing more than one hydroxyl group and a $

~L229~9~

dill ena-capped with a polyisocyanate, contacting the thus coated substrates and heating the thus contacted substrates in the range 100 - 300~C to cause adhesion.
DESCRIPTION OF THE INVENTION
This invention relates to a thermoplastic, epoxy pendant, urethane-containing compound which is the reaction product of an epoxy resin containing more than one, preferably two hydroxyl groups, and a dill end-capped with a diisocyanate.
The compound is preferably formed in the presence of a heat reactive, epoxy curing agent resulting in a one : 20 - pa -Z~2 , .
component material usable as a tber~oset adhesive, sealant or coating on heaving.
Some of the epoxy resins used herein as a reactant to form the novel compound are commercially available materials. Such materials include some of Shell Co. I
pun resins having the general structure:

SHEA OH C~2 I C OUCH OH C~2~ 0 OUCH OH C~2 L I Jo C~3 where n can range from about 171 to about 3 to form the novel compound herein. Another epoxy resin usable as a reactant per so is a methylolated version of a conventional bis-epi resin sold under the trademark ~Apogen-101~ by M&T Chemicals having the idealized-structure':

C}12-CHCE120~ ' ~OCH2~-C~12 In other instances the hydroxyl-containing~ epoxy resin reactant may be prepared by reacting a bis-epi resin, e. 9., digly~idyl ether ox resorcinol with a dill, e. 9., bi~phenol A, to obtain a hydroxyl-containing epoxy ennui OOZE I I I , O OH Cal OH O
30 CH2-CHCH20~0CH2fCH-cH;2-04~c~o-cE~2-cHc:~l2o~ocH2cShea c~3 Any dill can be used in the reaction with the bis-epi resin with the criteria being the end use of the novel _ 9 _ I,.

compound. Thus, aliphatic dills such as diethylene glycol, polyethylene glycol, polypropylene glycol and the like are operable as well as aromatic polyols.
The hydroxyl-containing epoxy resin I is then reacted through its hydroxyl groups with the remaining isocyanate groups on the end-capped dill to form the novel thermoplastic, epoxy pendant, urethane-containing compound of the instant invention, to wit:

I + R-(NCO)2 I C~2~-C~C~20 ocH~cH-cH2-o c o C~2 , 2 OC~2C~ 2 C~3 o C-O
No .
No II
O

wherein R is the organic moiety remaining after end-capping a dill with a diisocyanate.
The reaction between the hydroxyl-containing epoxy resin reactant and the isocyanate groups remaining on the dill in the instant invention is preferably carried out in the presence o a latent epoxy curing agent and optionally a curing accelerator in order to uniformly disperse said agent throughout the resulting solid reaction product.
Thus the reaction is carried out at a temperature below the decomposition temperature of the latent epoxy curing agent, e. g., at a temperature ranging from 20-120C. The ~2~3~9~
reaction is preferably performed in the presence of a catalytic amount, to eon 0.01-5% by weight of the reactants of well known urethane-forming catalysts. Such catalysts include, but are not limited to, triphenyl phosphine, dibutyl yin dilaurate, stuns octet and the like.
In the instances where the decomposition temperature of the latent epoxy curing agent is below the reaction temperature of the urethane forming reaction, the epoxy curing agent is added to the thermoplastic, epoxy pendant, urethane-containing compound after it has been cooled to room temperature. This can be done by grinding up the compound with the epoxy curing agent Jo obtain a uniform admixture thereof.
The latent epoxy curing agent is any chemical which will cause the cross linking of the adhesive and will not induce the instability of the adhesive below its application temperature. The epoxy curing agent is added to the compound in an amount ranging from 4 to 50 parts per 100 parts of the epoxy resin prior to urethane formation. Well known latent heat activated epoxy curing agents include, but are not limited to, dicyandiamide, BF3 amine adduces, 4,4'-methylenebis(phenylcyanamide) and the like A curing accelerator can also be present in the hot melt adhesive composition to increase the cure speed.
- Such accelerators for epoxy curing are well known and include such materials as phenol urea and the like.
The epoxy resin to be used to form the hydroxyl-containing reactant of the invention comprises those materials possessing at least one and preferably more than one epoxy group, i. e., I
~C-C~

.
.... .

I Z
group. These compounds may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or het~rocyclic and may be substituted with substituent~, such as chlorine hydroxyl groups, ether radicals and the like. They may be monomeric or polymeric.
For clarity, many of the polyepoxide~s and particularly those ox the polymeric type are described in terms of epoxy equivalent value. The polyepoxidle~ used in the present composition and process are those having an epoxy equivalency of at least 1Ø
various examples of polyepoxides that may be used in the composition and process of this invention are given in U. S. 2,~33,458.

Other examples include the epoxidized esters of the polyethylenically unsaturated monocarboxylic acids, finch as epoxidized linseed, soybean, purl, oiticica, lung, walnut and dehydrated castor oil, methyl linoleate, bottle linoleate, ethyl 9,12-octadecadienoate, bottle 9,12,15-octadecatrienoate, bottle eleostearate, monoglyceride~ of lung oil fatty acids, ~onoglycerides of soybean oil, sunflower, rhapsody, hemp seed, sardine, cottonseed oil and the like.
Another group of the epoxy-containing materials used in the composition and process of this invention include the epoxidized esters of unsaturated mandrake alcohols and polycarboxyli~ acids. For example, di(2,3-epoxybutyl) adipate, di(2,3-epoxybutyl) oxalate, di(2,3-epoxyhexyl ~uccinate, di(3,4-epoxybutyl) Malta, di(2,3-epoxyoctyl) pimelate, di(2,3-epoxybutyll phthalate, di(2,3-epoxyoctyl) tetrahydrophthalate, di(4~5-epoxy-dodecyl) Malta, di(2,3-epoxybutyl) tetraphthalate, Dow epoxypentyl) thiodipropionate, di(5~6-epoxy-tetradecyl) diphenyl-dicarboxylate, di(3,4-epoxyheptyl) sulfonyldibutyrate, trit2,3-epoxybutyl) 1,2,4-butane-tricarboxylate, di(5,6-epoxypentadecyl) tartar ate, di(4,5-epoxytetradecyl) Malta, di(2,3-epoxybutyl)-azelate, di(3,4-epoxybutyl) citrate, di(5,6-epoxyoctyl cyclohexane-1,2 dicarboxylate,, di(4,5-epoxyoctadecyl) malonate.
Still another group comprises the epoxidized - polyethylenically unsaturated hydrocarbons, such as epoxidized 2,2-bis(2-cyclohexenyl) propane, epoxidized vinyl cyclohexcene and epoxidized diver of cyclopentadiene.
Another group comprises the epoxidized polymers and copolymers of dolphins such as butadiene. Examples of this include, among others, butadiene-acrylonitrile copolymers Hiker rubbers), butadiene-styrene copolymers and the like.
Another group comprises the glycidyl containing nitrogen compounds, such as diglycidyl aniline and dip and triglycidylamine.
The polyepoxides that are particularly preferred for use in the compositions of the invention are the glycidyl ethers and particularly the glycidyl ethers of polyhydric phenols and polyhydric alcohols. The glycidyl ethers of polyhydric phenols are obtained by reacting epichloro-hydrin with the desired polyhydric phenols in the presence of alkali. Polyether-A and Polyether-B described in the above-noted U. S. 2,633,458 are good examples of polyepoxides of this type. Other examples include the polyglycidyl ether of 1,1,2,2-tetrakis(4-hydroxyphenyl)-ethanes (epoxy value of 0.45 eke g) and melting point 85C, polyglycidyl ether of 1,1,5,5-tretrakis(hydroxy-phenyl)pentane (epoxy value of 0.514 eke g) and the like and mixtures thereof.

..
,, .

Additional examples of epoxy resins operable herein include, but are not limited to, diglycidyl isophthalate, diglycidyl phthalate, o-glycidyl phenol glycidyl ether, diglycidyl ether of resorcinol, triglycidyl ether of phloroglucinol, triglycidyl ether of methyl phloroglucinol, 2,6-(2,3-epoxypropyl)phenylglycidyl ether, [4(2,3-epoxy)propoxy-~,N-bis(2,3-epoxypropyl)anilinee, 2,2-bis[p-2,3-epoxypropoxy)phenyl]-propane, diglycidyl ether of bisphenol-A, diglycidyl ether of bisphenol-hexafluoroacetone, diglycidyl ether of 2,2-bis(4-hydroxyphenyl)nonadecane, diglycidyl phenol ether, triglycidyl 4,4-bis(4-hydroxyphenyl)pentanoic acid, diglycidyl ether of tetrachlorobisphenol-A, diglycidyl ether of tetrabromobisphenol-A, triglycidyl ether of trihydroxybiphenyl, tetraglycidoxy biphenyl, [tetrakis~2,3-epoxypropoxy)diphenylmethane], 12,2',4,4'-tetrakis(2,3-epoxypropoxy)benzophenone, 3,9-bis[2-~2,3-epoxypropoxy)-phenylethyl]-2,4,8,10-tetraoxaspiro15,5]undecane, triglycidoxy-1,1,3-triphenylpropane, tetraglycidoxy tetraphenylethane, polyglycidyl ether of phenol-formaldehyde novolac, polyglycidyl ether of o-cresol-formaldehyde novolac, diglycidyl ether of butanediol, di(2-methyl)glycidyl ether of ethylene glycol, polyepichlorohydrin dit2,3-epoxy-propyl)ether, diglycidyl ether of polypropylene glycol, epoxidized polybuadiene, epoxidized soybean oil, triglycidyl ether of glycerol, triglycidyl ether of trimethylol-propane, polyallyl glycidyl ether, 2~4,6,8,10-pentakis-[3-(2,3-epoxypropoxy)-propyl~2,4,6,8,10-pentamethylcyclopentasiloxane, diglycidyl ether of chlorendic dill, diglycidyl ether of dioxanediol, diglycidyl ether of endomethylene cyclohexanediol, diglycidyl ether of hydrogenated bisphenol-A, vinylcyclohexene dioxide, limonene dioxide, dicyclopentadiene dioxide, p-epoxycyclopentenylphenyl 22~

glycidyl ether, epoxydicyclopentenylphenyl glycidyl ether, o-epoxycyclopentenylphenylglycidyl ether, bespeaks-dicyclopentyl ether of ethylene glycol, epoxy)-cyclohexyl-5,5-spiro(3,4-epoxy)-cyclohexane-m-dioxZion, 1,3-bis[3-(2,3-epoxypropoxy)propyl~tetramethyldisiiloxane/
epoxidized polybutadiene, triglycidyl ester of linoleic trirner acid, epoxidized soybean oil, diglycidyl ester of linoleic diver acid, 2,2-bis[4-(2,3-epoxypropyl)cyclo-hexyl]propane, 2,2-(4-[3-chloro-2~(2,3-epoxypropoxy)-propolyl~cyclohexyl)propane, 2,2-bis(3,4-epoxycyclo-hexyl~propane/ bis(2,3-epoxycyclopentyl)ether(liquid isomer), bis(2,3-epoxycyclopentyl)ether(solid isomer), 1,2-epoxy-6-(2,3-epoxypropoxy)hexahydro-4,7-methannoindane,

3,4-epoxycyclohexylmethyl-(3,4-epoxy)cyclohexane carboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-4-epoxy-6-methylcyclohexane carboxylate and bespeaks-6-methylcyclohexylmethyl)adipate. Trip and twitter-functional epoxies such as triglycidyl isocyanurate and tetraphenylolethane epoxy are also operable herein.
The reaction to form hydroxyl groups on the epoxy resin is carried out in the presence of a catalyst at a temperature ranging from 80-150C, preferably 90-125C.
Known catalysts include, but are not limited to, triphenyl phosphine, triisopropylamine and 3-~p-chlorophenyl)-l,l dimethylurea. These catalysts are added to the reaction in amounts ranging from 0.1 - 1.2 parts per lo parts of the epoxy resin.
In forming the solid hot melt adhesive from the liquid reaction mixture, it is possible and sometimes preferable to have a liquid reactive plasticizer present in the mixture. The function of the reactive plasticizer is twofold. First it lowers the viscosity of the reaction mixture thereby improving process ability. Secondly it improves the physical properties such as lap shear Jo strength of the cured product. The liquid reactive plasticizer is selected on the basis that it be non-reactive with either the NO or OH groups during the polymerization reaction to form the hot melt adhesive but will participate in the cross linking reaction when the adhesive is utilized and cured. Any of the aforementioned liquid epoxies used to form the hydroxyl-containing epoxy resin can be used as a reactive plasticizer in the instant invention. The reactive plasticizer when used is added in amounts up to 40% by weight of the final polymerized adhesive.
The polyisocyanates employed in the instant invention to end-cap the dill and react with the hydroxyl groups in the epoxy resin can be aromatic, aliphatic, cycloaliphatic and combinations thereof. Preferred are the - diisocyanates, but in- and tetraisocyanates are also operable. More specifically, illustrative of the diisocyanates are Tulane diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, 4-chloryl-1,3-phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 1,4-tetramethylene and 1,6-hexamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate and ethylene dicyclohexylene diisocyanate.
Diisocyanates in which each of the diisocyanate groups is ; 25 directly attached to a ring are preferred since usually they react more rapidly.
The dill end-capped with a diisocyanate is preferably a difunctional primary alcohol due to the fast reaction rote of the primary alcohol with the isocyanate group as compared to secondary alcohols present on the epoxy resin. Thus, in the one step method where all the reactants, i. e., diisocyanate, difunctional primary alcohol and hydroxy-containing epoxy resin are admixed simultaneously, the diisocyanate will preferentially end-cap the difunctional primary alcohol and then the remaining isocyanate groups on the end-capped dill will react with the secondary hydroxyl groups on the epoxy resin. In the two-step method where in the first step the diisocyanate is prereacted with a dill, then primary/
secondary or tertiary alcohols can be employed. The thus formed isocyanate-capped dill is then reacted with the hydroxyl-containing epoxy resin in a second step.
In the above reactions, whether it be a one step or two-step reaction, tune amount of diisocyanate employed is not more than is sufficient to react with all the hydroxyl groups on the dill. Thus the dill to diisocyanate mole ratio is in the range 1:1.1 to 2. The dills which are isocyanate end-capped herein should have a molecular weight ranging from 400 up to about 3,000. Dills having lower or higher molecular weight are operable but they do not afford the processibility. The viscosity of these dills at process temperature should be low to reduce the processing requirement. The hydroxyl-terminated polymers such as polycaprolactone dill, polypropylene glycol, polyethylene glycol and hydroxyl-terminated polybutadiene have low viscosities at process temperature. Any material having the aforesaid physical properties and can be end-capped with hydroxyl groups can be used as a dill ; 25 herein.
As will be shown in examples hereinafter, it is critical in order to obtain processibility during preparation and flexibility and high impact resistance of ; the cured product that an isocyanate-capped dill is used as compared to a diisocyanate per so. For example, since some of the diisocyanates and epoxy resins are solids at room temperature, the mixing and processibility require use of a solvent or heating to high temperatures for uniform admixture. This is avoided by the use of the Jo go isocyanate-capped dills which are liquids and allow for homogeneous mixing with the epoxy resin even when the resin is a solid. Further, the use of diisocyanates, per sex results in a brittle product due to tune rigidity of the diisocyanate structure as compared with the resultant flexible product obtained from the end-capped dill.
Additionally, because of its flexibility, the end-capped dill herein results in a cured product having high impact strength which is not afforded by the rigid diisocyanate lo per so. Further, the flexibility of the end-capped dill also allows one to reduce the application temperature of the hot melt adhesive thereby allowing a wider range of application temperatures to be used. In addition, the proper choice of dill allows one to improve the adhesion properties, open time and handling strength as compared to a diisocyanate per so.
As aforementioned, the reactive hot melt adhesive can be made in a one step process or a two-step process. In the one step process all the reactants, i e., diisocyanate, difunctional primary alcohol, hydroxyl-containing epoxy resin, latent curing agent and optionally a reactive plasticizer and a curing accelerator, are admixed together to form a liquid reaction mixture. The polymerization reaction is carried out at a temperature in the range ~0-60C for periods ranging from l hour to 2 days depending on temperature with high speed stirring during the initial 10-15 min. period. Optionally, a urethane-forming catalyst such as dibutyl tin dilaurate in amounts in the range 0.1 to 5% by weight of the reactants can be added to the system. A solid hot melt adhesive `".;

product results, viz.:
OCN-R-NCO HERR HERR + Latent Curing Agent (, O) 2/y Liquid Reaction Mixture O O O O
n Al I n Jo R-NHC-O-R'-O-CNH R-NHC-O-R"-O-CNH + Latent Curing (OH I
a solid idealized recurring structural polymer to be used as hot melt adhesive.
In the two-step process the diisocyanate is first reacted with a primary secondary or tertiary dill at temperatures in the range 20-50C with or without a urethane-forming catalyst, viz.:
20CN-R-NCO t HO-RI-OH
O O
OCN-R-NHC-O-R'-O-CNH-R-NCO III
The isocyanate-capped dill in a second step is then reacted through its -NO groups with the hydroxyl groups on the epoxy resin in the presence of the latent curing agent and optionally a reactive plasticizer and curing -accelerator to form a solid hot melt adhesive-having the following idealized recurring structural formula, to wit:
III + HERR
oh ' O O O O
,. .. .. ..
_~_R-NHC-O-R'-O-CNH R-NHC-O-R"-O-CNH + Latent Curing (OH yo-yo ' Jo .

Jo .

.

The heating step to cure the epoxy pendant, urethane-containing, hot melt adhesive compound to a thermoses material is usually carried out for a period of 10 seconds to 30 minutes at a temperature of 100 - 300C, preferably 120 - 200C, which is sufficient to fully cure the composition to a solid thermoses adhesive, coating or sealant.
The heating step using a latent epoxy curing agent to cure the compound can be accomplished in several ways. In simple adhesive systems, the composition can be applied by manual means to an adherent, contacted with another adherent and the assembled system heated in a forced air oven until a thermoses 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 ox 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) swooper if the adhesive composition contains sufficient polar groups to heat the composition rapidly and allow it to bond the adherents. Inductive heating can also be used to bond (1), (2) and (3). That is, when at least one of the adherents 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 therlnoset adhesive. In the instance where both adherents are plastic, it is necessary to add I

an energy absorbing material, i. e., an electrically conductive or ferromagnetic material, preferably in fiber or particle form (10-400 mesh 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 composition. It is also possible to impregnate the plastic adherent 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 (730-2,040F).
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 I

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, lousy 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 Jo the bulk of the plastic by conduction. pence, heating of plastics by these methods is a relatively slow process with a nonuniform 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 tune 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 veneration 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 ox 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 the hot melt adhesive composition herein. These electromagnetic energy absorbing materials can be added to the liquid hot melt reaction mixture prior to solidification or ground up with the hot melt adhesive after solidification. 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 thermoses 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 I I
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 frown 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 Jo 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 S 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 thermoses material, including fiber reinforced thermoses material.
It is critical that the epoxy pendant, urethane-containing hot melt adhesive compound of the instant - 10 invention be linear or cyclic, i. e., a thermoplastic, prior to its use with a latent epoxy curing agent. Thus, the number of OH groups present in the epoxy resin prior to reaction with the isocyanate-cappèd dill can be any number, preferably 2, depending on the functionality of I-the polyisocyanate employed for end-capping the dill and the equivalent ratio of -OH to -NO in the reaction. For example, a monoepoxide containing two hydroxyl groups obtained from bisphenol and glycidaldehyde, i. e., I
CH-CH
HO OH OH IV
can be reacted with an isocyanate-capped dill to form a polyurethane: - -O O
IV OCN-R-NH-C-O-R'-O-C-NH-R-NCO
I
O O O O CHCH
" " ,. .............. .
~CNH-R-NHC-O-R'-O-CNH-R-NHC-O OH o V
where n can be any number depending on the mole ratio of IV and isocyanate.
The resulting thermoplastic, epoxy pendant, urethane-:

, .

I

containing material can then be admixed with a latent epoxy curing agent, e. 9., dicyandiamide and cured through the epoxy groups to a thermoses coating, sealant or adhesive by heating.
Additionally, a dihydroxyl diepoxide can be used, e. 9., C~2~ Ooze 2 YIP
Again this is reacted with a dill, end-capped with a diisocyanate to form a polyurethane:
O O
VI + OCN-R-NH-C-O-R'-O-C NH-R-NCO
o O O O
-I OUCH I CH2O-CNH-R-NH-C-O-R'-O-CNH-R-NHC-~-n SHEA SHEA SHEA

SHEA okay VII

wherein n depends on the mole ratio of VI and isocyanate.
The resulting thermoplastic material (VII) will form a thermoses material useful as an adhesive, sealant or coating on heating with a latent epoxy curing agent An epoxide terminated polymeric material containing more than 2 OH groups formed by the reaction of bisphenol A and epichlorohydrin such as the Eon resins, commercially available from Shell Chemical Co., i.e., Cliche O _ l _ OUCH, CACHE o @3--C I oCH,Ci~--CH~

where n is 2.2, - I -can also be used when less than a stoichiometric amount of a diisocyanate is reacted therewith That is, in systems containing bifunctional monomers a high degree of polymerization is attained only when the reaction is forced almost to completion The introduction of a trifunctional monomer into the reaction produces a rather startling change which is best illustrated using a modified form of the Car others equation. A more general functionality factor fax is introduced, defined as the average number of functional groups present per monomer unit. For a system containing No molecules initially and equivalent numbers of two function groups A and B, the total number of functional groups is NofaV. The number of groups that have reacted in time to produce N
molecules is then Nina) and p = 2(NO-N)/Nofav The expression for on then becomes xn=2/(2~Pfav) but this is only valid when equal numbers of both functional groups are present in the system.
For a completely bifunctional system such as an equimolar mixture of an epoxy resin containing two hydroxyl groups and a diisocyanate, fovea, and xn=20 for p=0.95. If, however, a trifunctional alcohol, is added so that the mixture is composed of 2 mow diisocyanate, 1.4 mow dill, and 0.4 mow of trio, fax increases to avow= (2 x 2 + 1.4 x 2 + 0.4 x 3)/3.8 = 2.1.
The value of on is now 200 after 95 per cent conversion, but only a small increase to 95.23 per cent is required for on to approach infinity - a most dramatic increase.
This is a direct result of incorporating a trifunctional unit in a linear chain where the unrequited hydroxyl provides an additional site for chain propagation. This 33L9~

leads to the formation of a highly branched structure and the greater the number of rnulti-functional units the faster the growth into an insoluble three-dimensional network. When this happens, the system is said to have reached its gel point, i.e., the system is thermoses. In the instant invention it is critical that the composition remain thermoplastic and not reach its gel point prior to use as a coating, sealant or hot melt adhesive.
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 1" square of lapped area.
Example 1 Preparation of Isocyanate-Capped Dill 127.8 g of polypropylene glycol (MY = 725 g/mole) were added drops over a 6 hour period to a flask containing 61.4 g of Tulane 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 isocyanate-capped dill A.
Example 2 15 g of bisphenol A and 0.12 g of triphenyl phosphine were added in 4 equal portions over a 30-minute period at a reaction temperature of 120C to a flask containing 100 g of diglycidyl ether of bisphenol A. The reaction was continued at 120C for 2 1/2 hours. The modified reaction product had an epoxide equivalent weight of 292 gawk. based on titration.
100 g of the modified epoxy reaction product was mixed with 61 g of isocyanate-capped dill A from Example 1 and 6 g of dicyandiamide at room temperature resulting in a tacky hot melt adhesive containing reactive epoxide groups. The hot melt adhesive was applied between cold roll steel adherents at 100C pressed together and placed in an air oven at 180C for 30 minutes. The resulting lap shear was 3,500 psi.
The adhesive was employed in the same manner between fiber glass and polyester composite adherents. The adherents failed prior to the adhesive bond in the lap shear test.
Example 3 - To a mixture containing 100 g of an epoxy resin containing 357 gawk of OH, commercially available from Shell Chemical Co. under the trade name "Epon-1001~", 6 g of dicyandiamide and 1 g of triphenyl phosphine were added 71.6 g of isocyanate-capped dill A from Example 1. After heating at 80C for 1 hour, the adhesive was cooled to room temperature and solidified as a reactive hot melt adhesive. After being applied to substrates at 125C and cured at 160C for 30 minutes, the adhesive showed a lap shear strength of 3,200 psi to steel and substrate rupture to glass fiber reinforced polyester.
Example 4 To a mixture containing 100 9 of Epon-lOOlF~ 25 g of an epoxy resin containing 0.2 OH groups/mole and commercially available from Shell Chemical Co. under the trade name "Epon-828" and 7.5 g of dicyandiamide were added 71.6 g of isocyanate-capped dill A from Example 1. After heating at 80C overnight, the adhesive was applied to substrates at 125C and cured at 160C for 30 minutes.
The adhesive had a lap shear strength of 4,400 psi to steel and 460 pi to glass fiber reinforced polyester.
Example 5 To 100 9 of Epon-828 was added a mixture containing 21 g of bisphenol A and 0.14 g of triphenyl phosphine at I
11. or 120C. After reaction at 120C for 3 hours, 100 g of this epoxy terminated, hydroxyl containing product was do solved in 100 g of ethylene chloride and then, reacted with 61 9 of isocyana~e capped dill A, prom Example 1, in the presence of 0.5 9 of dibutyl tin dilaur~te. The reaction was monitored by IT us o isocyanate could be detected. To the reaction mixture were added 6 g of dicyandiamide and 2 9 of triphenyl phospkline. The solvent ethylene chloride was remove under vacuum. The final hot melt adhesive was applied to substrates at 125C and cured at 160C for 30 minutes. This adhesive had a lap shear strength of 1,50Q psi to steel and 900 psi to glass -fiber reinforced polyester.
example 6 To 100 9 of ~Epon-lQOlF~ dissolved in 100 9 of ethylene chloride was added 48.9 9 isocyanate-capped dill A from Example 1 and 0.75 9 of dibutyl tin dilaurate a catalyst. The reaction was continued until no trace of isocyanate could be detected from the IT spectrum.
Example 7 To 100 9 of the product solution from Example 6 were added 40 g ox an amine adduce, commercially available under the trademark ~Ancamine-870~ from Pacific Anchor.
After drying under Vacuum the material was cured to a thermoses solid in a radio frequency OF oven at 100 amperes in 290 seconds.
Example 8 To 100 g of the product solution from Example 6 were added 50 9 of Standard-03 iron powder (supplied by EMABond) and 40 9 of "Ancamine-870~. After drying under vacuum, the final adhesive was cured to a thermoses solid by induction heating in an electromagnetic field in 75 seconds.

I. YO-YO

I
The following 4 examples show comparative results between the adhesive of the instant invention and the prior art.
Exam Solid Epoxy Resin without any Modification 10 g of Epon-lOOlF, a solid epoxy resin containing hydroxyl groups, commercially available from Shell Chemical, were melted at 80C and then mixed with 0.6 g of - dicyandiamide and 0.4 9 of triphenylphosphine. After applying to 2 pieces of steel substrates hazing a 1/2 inn overlapping area, the adhesive was cured at 160~C fur 30 minutes.
Example 10 Solid Adhesive Prepared Simply from Hydroxyl-Containin~
Epoxy Resin and diphenylmethane-p,p'-diisocyanate (MID) 59.4 9 of Epon-lOOlF were melted at 80C, uniformly mixed with 3.6 g of dicyandiamide and 2.4 g of triphenyl-phosphine and then reacted with 4.1 9 of MID. Due to the high processing temperature the mixture quickly became thick and the uniformity of mixing was poor. The solid adhesive had an application temperature higher than 100C. After applying the adhesive to two pieces of steel having 1j2 inn overlapping area, the adhesive was cured at 163C for 30 minutes.
Example 11 Reactive Hot Melt adhesive Prepared for this Invention 59.4 g of Epon-lOOlF, 12.4 9 of PCP-240 (a polyp caprolactone dill having a molecular weight of 2,000 g/mole, commercially available from Union Carbide, and 23.8 9 of ~CC-8006 (a liquid epoxy resin modified by carboxyl-terminated poly(butadiene-co-acrylonitrile prom Wilmington Chemical) as reactive plasticizer were . uniformly mixed at 80C~ After obtaining a homogeneous mixture 3.6 g of dicyandiamide and 2.4 9 of triphenyl * Trademark I

. . .

I

phosphine were added. The mixture was stirred for 2 hours, cooled to 60C and blended with 4.5 g of MID
until a homogeneous solution was obtained. The reaction mixture was allowed to stand overnight at room temperature to complete the reaction.
Example 12 The Comparison of the Processing Conditions, Application Conditions and Adhesive Properties of Three Adhesives Prepared from Examples I 10 and_ll Example 3 Example 10 Example 11 Adhesive Adhesive Adhesive Composition Epon-lOOlF 100 100 100 (phi) PCP-240 - - 20.9 ~CC-8006 - - 40.1 MID - 6.9 7.6 Dicyandiamide 6 6 6 Triphenyl-phosphine 4 4 4 Processing Condition at Thea Beginning 70C 57.9 57.9 2.8 ox 10 4 (cups) ~0C 12.5 12.5 0.8 90C 4.0 4.0 0.3 Application Condition x 10 4 (cups) 80C 12~5 Solid 326 2590C 4.0 Solid 36.2 100C - Solid 12.8 Lap Shear Strength to Steel at Room Temperature (psi) 3110 2530 4250 Impact Resistance at Room Temperature (in-lb) 46 21 >60 Another important property afforded by the use of isocyanate-capped dills in the instant invention is the ability to extend open time by proper selection of the dill. That it, by incorporating a crystalline backbone into the polymer it is possible to increase the operation time after the application of the reactive hot melt adhesive composition. Such crystallization is supplied by the dill. In practice, before crystallization, the adhesive melt is deformable and provides a certain handling strength at room temperature. After recrystallization the adhesive recovers its mechanical strength and turns to a tough, rigid, solid with an increased handling strength The time interval between the application of the adhesive melt and the recrystallization is called open time. The open time depends on the rate of crystallization of the adhesive. In essence, the open time is controlled by polymer structure, molecular weight, crystalline segment content and amount of crystalline nucleus. In the following examples a crystalline dill, polycaprolactone dill was used to illustrate this concept.
Example 13 To a mixture containing 100 g of Epon-lOOlF and 70 g of PCP-230 (a polycaprolactone dill having an average molecular weight of 1,250 and commercially available from Union Carbide) were added 14.8 g of diphenylmethane-p,p'-diisocyanate (MID) after the mixture had been warmed to 80C and blended with 6 g of dicyandiamide and 4 g of triphenylphosphine. After agitating to a homogeneous solution, the reaction mixture was cooled and stood at room temperature until the disappearance of isocyanate in the IT spectrum. A white tough solid having a melting temperature at 80C was obtained.

--, ...... .

~Z;;~9~
After applying to an oily steel surface, the adhesive remained in a sticky, transparent form for 2 1/2 minutes.
The adhesive provided 2,400 psi of lap shear strength and 24 in-lb of side impact resistance in a 1/2" overlap of steel adherents after being cured at 170C for 20 minutes.
Example 14 Using the same procedure as described in Example 13, the adhesive prepared from 100 g of Epon--lOOlF, 100 g of PCP-230, 6 g of dicyandiamide, 4 g of triphenyl phosphine and 15.3 g of MID had a 1,700 psi of lap shear strength - and a 24 in-lb of side impact resistance on a 1~2" overlap of steel adherents. The open time of this adhesive was longer than 25 minutes.
Example 15 Using the same procedure as example 13, the adhesive synthesized from 100 g of Epon-lOOlF, 70 g of PCP-240, a polycaprolactone dill having a molecular weight of 2,000 and commercially available from Union Carbide, 6 g of dicyandiamide, 4 g of triphenyl phosphine and 12.2 g of MID had a 3,300 psi of lap shear strength and 35 in-lb of side impact resistance on a 1/2" overlap of steel adherents. The open time was longer than 25 minutes.
This adhesive also had 6,740 psi of tensile modulus and 97% of elongation.

Claims (14)

WHAT IS CLAIMED IS:

1. A one component, hot melt thermosettable composition comprising (a) dicyandiamide and (b) a thermoplastic, epoxy pendant, urethane-containing compound which is the reaction product of an epoxy resin containing more than one hydroxyl group and a diol end-capped with a polyisocyanate.

2. The composition according to claim 1 wherein the diol has a molecular weight in the range 400 to about 3,000 prior to end-capping.

3. The composition according to claim 1 containing in addition up to 40% by weight of a liquid reactive plasticizer.

4. The composition of claim 3 wherein the liquid reactive plasticizer is an epoxy resin.

5. A process for adhering two substrates which com-prises coating at least one of said substrates with a one component, hot melt composition comprising (a) dicyandiamide and (b) a thermoplastic, epoxy pendant, urethane-containing compound which is the reaction product of an epoxy resin containing more than one hydroxyl group and a diol end-capped with a polyisocyanate, contacting the thus coated substrates and heating the thus contacted substrates in the range 100 - 300°C to cause adhesion.

6. The process according to Claim 5 wherein the composition contains in addition up to 40% by weight of a liquid reactive plasticizer.

7. The process according to Claim 6 wherein the liquid reactive plasticizer is an epoxy resin.

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

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

10. The process according to Claim 8 wherein the electromagnetic heating is by dielectric heating.

11. The cured composition of Claim 1 as a sealant.

12. The cured composition of Claim 1 as a coating.

13. The cured composition of Claim 1 as an adhesive.

14. The thermosettable composition according to claim 1 containing in addition triphenyl phosphine as a curing accelerator.