NZ201278A - Thermosettable compositions comprising a heat reactive epoxy curing agent and a thermoplastic,epoxy pendant,urethane-containing compound,its preparation and uses - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £01 278 201276 Priority Date(s): .1 .U. T. S i Complete Specification Filed: .".7. .fp-Class: I ft if.. C.Q9& .CQCj J|^/.Q £>.v.. (^>3 &&J.I.Q.

Publication Date: ..f;.....P.

P.O. Journal, No: No.. Date: NO DRAWINGS NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION "THERMOSETTING COMPOSITIONS" Jc/We, M. R. GRACE & CO.» a corporation of the State of Connecticut, United States of America, of 1114 Avenue of the America, New York, New York 10036, United States of America, hereby declare the invention for which W/ we pray that a patent may be granted to rxoc/us, and the method by which it is to be performed, to be particularly described in and by the following? stitfeithe'tit: - 4/ 'V - 1 98S3 2 o me 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, crosslinks to give a thermoset 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 wettability of the adherent at elevated temperatures. These adhesives are readily applied in the molten state between adherence 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 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 2012.78 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 not 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.

The concept of thermosetting or crosslinking 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. 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, bis-caprolactam 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 150°C and undergo crosslinking at elevated temperatures thereabove. In these latter two patents, thermal crosslinking is also achieved by reactions of the particular crosslinking 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, unsaturated carboxylic acids and an organic peroxide. Another thermosetting adhesive is known from U. S. 3,945,877 wherein the composition comprises a coal tar pitch, ethylene/vi nyl acetate copolymer and ethylene/acrylic acid copolymer plus a crosslinking 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 ther- moset bond. Thus, the resultant bond depends on the homogeneity of * the admixture. Further, in many cases, e.g. epoxy adhesives, two or 201278 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.

One object of the instant invention is to produce a composition, usable as an adhesive, sealant or coating, which is solventless. Anotehr 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 thermoset coating, adhesive or sealant on heating. Yet another object of the invention is to produce a thermoplastic composition which can be applied as a hot melt and thereafter cured by a thermally triggered initiator to a thermoset adhesive, sealant or coating at a more elevated temperature. Other objects will become apparent from a reading hereinafter.

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 polyisocyanate, preferably a diisocyanate.

OBJECTS OF THE INVENTION DESCRIPTION OF THE INVENTION 201278 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.

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.'s "Epon" resins having the general structure: where n can range from about 1.1 to about 3 to form the novel compound herein. Another epoxy resin usable as a reactant per se is a methy-lolated version of a conventional bis-epi resin sold under the tradename "Apogen-101" by M&T Chemicals having the idealized structure: och2-ch-ch2 0 hoh H2°H ^OCH2CH-CH2 ch2-chch20 ch 3 In may be other instances the hydroxyl-containing, epoxy resin reactant prepared by reacting a bis-epi resin, e.g.,diglycidyl ether or resorcinol with a diol, e.g., bisphenol A, to obtain a hydroxyl containing epoxy resin: 2012ve o / \ 2 ch2~chch20 /°\ och2ch-ch2+ ho 0 oh • ch. oh ^ o CH2-CHCH2O*^noch2CH-CH2-O-<^-C-^_^-O-CH2-CHCH2O^^OCH2CH-CH ch.

Any diol can be used in the reaction with the bis-epi resin with the criteria being the end use of the novel compound. Thus, aliphatic diols 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 a diol end-capped with a polyisocyanate to form a novel thermoplastic, epoxy pendant, urethane-containing compound of the instant invention, to wit: i + r- (nco) 2 2 l2v cc-chch90^ och2ch-ch2 ch, /\ -0-O-C-O'0-CH2-CHCH20>^k0CH2CH-CH2 0 /\ ch. 0 c=0 nh I r nh I *c=0 II wherein R is an organic moiety, , ' "V ^ ' c o 01 20127B The reaction between the hydroxyl-containing epoxy resin reactant and the diol end-capped with a polyisocyanate in the instant invention is preferably carried out in the presence of the latent epoxy curing agent in order to uniformly disperse said agent throughout the solid resulting 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 20-120-C. The reaction is performed in the presence of a catalytic amount, i.e., 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 tin dilaurate, stannous octoate 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 to obtain a uniform admixture thereof.

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 adducts, 4,4'-methylenebis(phenylcyanamide) and the like.

• The epoxy resin to be used to form the hydroxyl-containing reactants of the invention comprises those materials possessing^ one and preferably more than one epoxy group, i.e., /V .

A „ ^c-cc: V# 201279 9 group. 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. They may be monomeric or polymeric.

For clarity, many of the polyepoxides and particularly those of the polymeric type are described in terms of epoxy equivalent values. The meaning of this expression is described in U. S. 2,633,458. The polyepoxides used in the present composition and process are those having an epoxy equivalency of at least 1.0.

Various examples of polyepoxides that may be used in the composition and process of this invention are given in U.S. 2,633,458 and it is to be understood that so much of the disclosure of that patent relative to examples of polyepoxides is incorporated by reference into this specification.

Other examples include the epoxidized esters of the polyethyleni-cally 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.

Another group of the epoxy-containing materials used in the composition and process of this invention include tl\e epoxidized esters of unsaturated monohydric alcohols and polycarboxylic acids. For 201278 example, di(2,3-epoxybutyl) adipate, di(2,3-epoxybutyl) oxalate, di(2,3-epoxyhexyl) succinate, di(3,4-epoxybutyl) maleate, di(2,3-epoxyoctyl) pimelate, di(2,3-epoxybutyl) phthalate, di(2,3-epoxyoctyl) tetrahydrophthalate, di(4,5-epoxy-dodecyl) maleate, di(2,3-epoxybutyl) tetraphthalate, di(2,3-epoxypentyl) thiodipropionate, di(5,6-epoxy-tetradecyl) diphenyl-dicarboxylate, di(3,4-epoxyheptyl) sulfonyldibutyrate, tri (2,3-epoxypentadecyl) tar-tarate, di(4,5-epoxytetradecyl) maleate, 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 cyclohexane and epoxidized dimer of cyclo-pentadiene.

Another group comprises the epoxidized polymers and copolymers of diolefins, such as butadiene. Examples of this include, among others, butadiene-acrylonitrile copolymers (Hycar rubbers), butadiene-styrene copolymers and the like.

Another group comprises the glycidyl containing nitrogen compounds, such as diglycidyl aniline and di- 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 201178 epichlorohydrin 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 )-ethane (epoxy value of 0.45 eq./lOO g) and melting point 85°C, polyglycidyl ether of l,l,5,5-tretrakis(hydroxy-phenyl )pentane (epoxy value of 0.514 eq./lOO 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 phenyl glycidyl ether, diglycidyl ether of resorcinol, triglycidyl ether of phloroglucinol, triglycidyl ether of methyl phioroglucinol, 2,6-(2,3-epoxypropyl )phenylglycidyl ether, 4-(2,3-epoxy)propoxy-N,N-bi s(2,3-epoxypropyl)ani1ine, 2,2-bis[p-2,3-epoxypropoxy)phenyl]-propane, diglycidyl ether of bisphenol-A, diglycidyl ether of bisphenol-hexaf1uoroacetone, diglycidyl ether of 2,2-bis(4-hydroxyphenylnonadecane, diglycidyl phenyl ether, triglycidyl 4,4-bis(4-hydroxyphenyl)pentanoic acid, diglycidyl ether of tetrachlorobisphenol-A, diglycidyl ether of tetrabromobisphenol-A, triglycidyl ether of trihydroxybiphenyl, tetraglyci doxy bi phenyl, [tetraki s(2,3-epoxypropoxy)diphenyl methane], 3,9-bi s[2,3-epoxy propoxy)-phenyl ethyl]-2,4,8,10-tetraoxaspi ro[5,5] undecane, tri glyci doxy-1,1,3-tri phenyl propane, tetraglycidoxy tetraphenylethane, polyglycidyl ether of phenol formaldehyde novolac, polyglycidyl ether of o-cresol-formaldehyde novolac, diglycidyl ether 201278 of butanediol, di(2-methyl)glycidyl ether of ethylene glycol, polyepichlorohydrin di(2,3-epoxy-propy1)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-epoxy-propoxy)-propyl ]2,4,6,8,10-pentamethyIcyclopentasiloxane, di glycidyl ether of chlorendic diol, diglycidyl ether of dioxanediol, diglycidyl ether of endomethylene cyclohexanediol, diglycidyl ether of hydroge-nated bisphenol-A, vinylcyclohexene dioxide, limonene dioxide, dicyclopentadiene dioxide, p-epoxycyclopentenylphenyl glycidyl ether, epoxydicyclopentenylphenyl glycidyl ether, o-epoxycyclopentenylphenyl glycidyl ether, bis-epoxydicyclopentyl ether of ethylene glycol, [2-3,4-epoxy )-cyclohexyl -5,5-spi ro(3,4-epoxy)-cyclohexane-m-dioxane], 1.3-bis [3-(2,3-epoxy propoxy) propyl ]tetramethyldi si 1 oxane, epoxidized polybutadiene, triglycidyl ester of linoleic trimer acid, epoxidized soybean oil, diglycidyl ester of linoleic dimer acid, 2,2-bis[4-(2,3-epoxypropyl) cyclohexyl)cyclohexyl]propane, 2,2-(4-[3-chloro-2-(2,3-epoxypropoxy)-propoyl]cyclohexyl)propane, 2,2-bi s (3,4-epoxy cycl ohexyl) propane, bi s (2,3-epoxy cycl opentyl )ether (liquid isomer), bis(2,3-epoxycyclopentyl)ether(solid isomer), 1,2-epoxy-6-(2,3-epoxy propoxy )hexahydro-4,7-methanoindane, 3.4-epoxycyclohexymethyl-(3,4-epoxy)cyclohexane carboxylate, 3,4-epoxy-6-methyl cycl ohexyl methyl -4-epoxy-6-methyl cyclohexane carboxylate and bis(3,5-epoxy-6-methylcyclohexylmethyl )adipate. Tri- and tetra- functional epoxides such as triglycidyl is^ocyanurate and tetraphenylolethane epoxy are also operable herein. 201276 The reaction to form hydroxyl grounds on the epoxy resin is carried out in the presence of a catalyst at a temperature ranging from 80-150°C, preferably 90-125°C. Known catalysts include, but are not limited to, triphenyl phosphine, triisopropylamine and 30(p-Chl rophenyl )-l,l-dimethylurea. These catalysts are added to the reaction in amounts ranging from 0.1 - 1.2 parts per 100 parts of the epoxy resin.

The polyisocynates employed in the instant invention to end-cap the diol and react with the hydroxyl groups in the epoxy resin can be aromatic, aliphatic, cycloaliphatic and combinations thereof. Preferred are the diisocyanates, but tri- and tetraisocynanates are 20127S The diol end-capped with a diisocyanate is preferably a difunctional primary alcohol due to the fast reaction rate of the primary alcohol due to the fast reaction rate of the primary alcohol with the isocyanate group as compared to secondary alcohols present on the epoxy resin. As a first step in the method the diisocynanate is prereacted with a diol, primary, secondary or tertiary alcohols can be employed. The thus formed isocyanate-capped diol is then reacted with the hydroxyl-containing epoxy resin in a second step.

In the above reaction the amount of diisocyanate employed is not more than is suf- 201270 ficient to react with all the hydroxyl groups on the diol. Thus the diol to diisocyanate mole ratio is in the range 1:1.1 to 2. The diols which are isocyanate end-capped herein should have a molecular weight ranging from 400 up to about 3,000. Diols having lower or higher molecular weight (e.g. 200 to 20,000) are operable but they do not afford the processibility. The viscosity of these diols at process temperature should be low to reduce the processing requirements. The hydrozyl -terminated polymers such as polycaprolactone diol, polypropylene glycol, polyethylene glycol and hydrozyl-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 diol 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 diol is used as compared to a diisocyanate per se. 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 isocyanate-capped diols 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 se, results in a brittle product due to the rigidity of the diisocyanate structure as compared with the resultant flexible product obtained from the end-capped diol. Additionally, because of its flexibility, the end*-capped diol herein 201278 results in a cured product having high impact strength which is not afforded by the rigid diisocyanate per se. Further, the flexibility of the end-capped diol 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 diol allows one to improve the adhesion properties, open time and handling strength as compared to a diisocyanate per se. 2012735 In the process the diisocyanate is first reacted with a primary, secondary or tertiary diol at temperatures in the range 20-50°C with or without a urethane-forming catalyst, viz: 20CN-R-NC0 + HO-R'-OH 0 ^ o CCN-R-NHC-O-R '-O-CNH-R-NCO 111 The isocyanate-capped diol in a second step is then reacted through its -NCO groups with the hydrozyl groups on the epoxy resin in the presence of the latent curing agent and curing accelerator to form a solid hot metal adhesive having the following idealized recurring structural formula, to wit: III + HO-R"-OH o 0 ° ? " " , , vtur- n T}n-n-CNH—¥"=*" + Latent Curing ^.r-nbc-o-r'-o-cnh-^-i-r-nhc-o-r ocnh-tj fCHN Agent .01 CH2/y The heating step to cure the epoxy pendant, urethane-containing compound 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 thermoset adhesive, s ZO1210 18 - systems, the 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 effiicent 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) 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 20127| 19 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 magnestizable 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).

Electrically conductive materials operable herein when inductive heating is employed include, but are not limited to, the noble metals, copper, aluminium, 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 heat\ng. These polymers may contain a variety of dipoles and ions which orient in an electric 20127$ 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, glossy 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 infraring 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 201270' - 21 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 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, electromagnet!c 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 ?f'6r iome accomplished by proper placement of a conductive coil. When another // s 2O127J0T - 22 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 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 201271 - 23 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 about2 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.

It is critical that the epoxy pendant, urethane-containing compound of the instant 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 polyisicyanate can be any number, preferably 2, depending on the functionality of the polyisocyanate reacted therewith and the equivalent ratio of -OH to -NC0 in the reaction. For example, a monoepoxide containing two hydroxyl groups obtained from bisphenol and glycidaldehyde, i.e. ho-^-CH-Q-OH 0 /\ ch-ch III 201278 can be reacted with a diisocyanate 0CN-R-NC0 to form a polyurethane: iii + ocn-r-nco where n can be any number depending on the mole ratio of III and isocyanate.

The resulting thermoplastic, epoxy pendant, urethane-containlng material can then be admixed with a latent epoxy curing agent, e.g. dicyandiamide and cured through the epoxy groups to a thermoset coating, sealant or adhesive by heating. o o ch-ch2 ~(ctjh-r-nhc-0 -q-ca-q-o^ iv Additionally, a dihydroxyl dlepoxide can be used, e.g. ch2-chch2o ch 3 v Again this is reacted with a diisocynanate to form a polyurethane: v + ocn-r-nco I 0 0 (-cnhrnhc-OHjC 1jc> ch r tD±G -o ch 2 CH3 rw 2 vi wherein n depends on the mole ratio of V and isocyanate.

The resulting thermoplastic material (VI) will form a thermoset 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 Epon resins, commercially available from Shell Chemical Co. i.e., OH CH3 CH^—■>CHCH2--0 I /r-* ° o CH '3 where n is 2.2, can also be used when less than a stoichiometric amount of a diisocyanate is reacted therewith. That is, in systems containing bifunc- 20l27jl 26 tional 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 Carothers equation. A more general functionality factor fav is introduced, defined as the average number of functional groups present per monomer unit. For a system containing N0 molecules initially and equivalent numbers of two function groups A and B, the total number of functional groups is N0fav. The number of groups that have reacted in time to produce N molecules is then 2(N-N) and but this is only valid when equal numbers of both functional groups are present in the system.

For a completely Afunctional system such as an equimolar mixture of an epoxy resin containing two hydrozyl groups and a diisocynanate, fav=2, and xn=20 for p=0.95. If, however, a trifunctional alcohol, is added so that the mixture is composed of 2 mol diisocynanate, 1.4 mol diol, and 0.4 mol of triol, fav increases to fav= (2 x 2 + 1.4 x 2 + 0.4 x 3)/3.8 = 2.1.

The value of xn is now 200 after 95 per cent conversion, but only a small increase to 95.23 per cent is required for xn to approach infi-nity - a most dramatic increase. This is a direct result of incor- p = 2(N0-N)N0fav The expression for xn then becomes xn (2-pfay) > aoia?! 27 porating a trifunctional unit in a linear chain where the unreacted hydroxyl provides an additional site for chain propagation. This leads to the formation of a highly branched structure and the greater the number of multi-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 said to have reached its gel point, i.e., the system is thermoset. 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 to hot metal adhesi ve.

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.

Preparation of Diisocyanate Adduct 127.8 g of polypropylene glycol (MW = 725 g/mole) were added drop-wise over a 6-hour period to a flask containing 61.4 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 1 20127j! Example 2 g of bi sphenol A and 0.12 g of triphenyl phosphine were added in 4 equal portions over a 30-minute period at a reaction temperature of 120°C for 21/2 hours. The modified reaction product had an epoxide equivalent weight of 292 g/eq based on titration. 100 g of the modified epoxy reaction product was mixed with 61 g of diisocyanate adduct A from Example 1 and 6 g f dicyandiamide at room temperature resulting in tacky hot melt adhesive containing reactive epoxide groups. The hot melt adhesive was applied between cold roll steel adherends at 100°C pressed together and placed in an air oven at 180°C 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 adherends. The adherends 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 g/eq of OH, commercially available from Shell Chemical Co. under the tradename "Epon-IOOIF", 6 g of dicyandiamide and 1 g of triphenyl phosphine was added 71.6 g of di isocynanate adduct A from Example 1. After heating at 80°C for 1 hour, the adhesive was cooled to room temperature and solidified as a reactive hot melt adhesive. After being applied to substrates at 125°C and cured at 160°C for 30 minutes, the adhesive showed a lap shear strength of 3,200 psi to steel and substrate rupture to glass fiber reinforced polyester. oft 201270 29 Example 4- To a mixture containing 100 g of Epon-IOOIF, 25 g of an epoxy resin containing 0.2 OH groups/mole and commercially available from Shell Chemical Co. under the tradename "Epon-828", 7.5 g of dicyandiamide was added 71.6 g of diisocyanate adduct A from Example 1. After heating at 80°C overnight, the adhesive was applied to substrates at 125°C and cured at 160°C for 30 minutes. The adhesive had a lap shear strength of 4,400 psi to steel and 460 psi to glass fiber reinforced polyester.

To 100 g of Epon-828 was added a mixture containing 21 g of bisphenol A and 0.14 g of triphenyl phosphine at 120°C. After reaction at 120°C for 3 hours, 100 g of this epoxy terminated, hydroxyl containing product was dissolved in 100 g of methylene chloride and then, reacted with 61 g of diisocyanate adduct A, from Example 1, in the presence of 0.5 g of dibutyl tine dilaurate. The reaction was monitored by IR until no isocyanate could be detected. To the reaction mixture was added 6 g of dicyanidiamide and 2 g of triphenyl phosphine. The solvent methylene chloride was removed under vacuum. The final hot melt adhesive was applied to substrates at 125°C and cured at 160°C for 30 minutes. This adhesive had a lap shear strength of 1,500 psi to steel and 900 psi to glass fiber reinforced polyester.

Example 5 2OU70 Example 6 To 100 g of "Epon-IOOIF" dissolved in 100 g of methylene chloride was added 48.9 g diisocyanate adduct A from Example 1 and 0.75 g of dibutyl tin dilaurate as catalyst. The reaction was continued until no trace of isocyanate could be detacted from the IR spectrum.

Example 7 To 100 g of the product solution from Example 6 was added 40 g of an amine adduct, commercially available under the tradename "Ancamine-870" from Pacific Anchor. After drying under vacuum, the material was cured to a thermoset solid in a radio frequency (RF) oven at 100 amperes in 290 seconds.

To 100 g of the product solution from Example 6 was added 50 g of Standard-03 iron powder (supplied by EMABond) and 40 g of "Ancamine-870". After drying under vacuum, the final adhesive was cured to a thermoset solid by induction heating in an electromagnetic field in 75 seconds.

Example 8 Example 9 Solid Epoxy Resin without any Modification g of Epon-IOOIF, a solid epoxy resin containing hydroxyl groups, commercially available from Shell Chemical, were melted at 80OC and then mixed with 0.6 g of dicyandiamide and 0.4 g of triphe-nylphosphine. After applying to 2 pieces of steel substrates having a 1/2 in.^ overlapping area, the adhesive was cured at 160°C for 30 minutes.

Example 10 Solid Adhesive Prepared Simply from Hydroxyl-Containing Epoxy Resin and diphenylmethane-p,p'-diisocyanate MDI) 50.4 g of Epon-IOOIF were melted at 80°C, uniformly mixed with 3.6 g of dicyandiamide and 2.4 g of tri phenyl phosphine and then reacted with 4.1 g of MDI. 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 100°C. After applying the adhesive to two pieces of steel having 1/2 in.2 overlapping area, the adhesive was cured at 160°C for 30 minutes.

Example 11 Reactive Hot Melt Adhesive Prepared for this Invention 59.4 g of Epon-IOOIF, 12.4 of PCP-240 (a poly.caprolactone diol having a molecular weight of 2,000g/mole, commercially available from 201270 20127$ Union Carbide, and 23.8 g of WCC-8006 (a liquid epoxy resin modified by carboxyl-terminated poly(butadiene-co-acrylonitri1e from Wilmington Chemical) as reactive plasticizer were uniformly mixed at 80°C. After obtaining a homogeneous mixture 3.6 g of dicyandiamide and 2.4 g of triphenyl phosphine were added. The mixture was stirred for 2 hours, cooled to 60°C and blended with 4.5 of MDI 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 9, 10 and 11 Example 9 Example 10 Example 11 Adhesive Adhesive Adhesive 100 Composition Epon-IOOIF (phr) PCP-240 WCC-8006 MDI Dicyandiamide Triphenyl-phosphine Processing Condition at the Beginning 70°C -h x 10-4 (cps) 80oC 1 90°C Application Condition <h x 10"4 (cps) 80°C ' 90°C 100°C Lap Shear Strength to Steel at Room Temperature (psi) Impact Resistance at Room Temperature (in-lb) 100 - 6.9 6 6 4 4 57.9 57.9 12.5 12.5 4.0 4.0 12.5 Solid 4.0 Solid - Solid 3110 2530 46 21 100 20.9 40.1 7.6 6 4 2.8 0.8 0.3 326 36.2 12.8 4250 >60 Another important property afforded by the u^e of isocyanate-capped diols in the instant invention is the ability to extend open 20127$ 33 time by proper selection of the diol. That is, 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 diol. In practice, before crystallization, the adhesive melt is deformable and provides a certain handling strength at room temperature. After recrystal1ization 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 diol, polycaprolactone diol was used to illustrate this concept.

To a mixture containing 100 g of Epon-IOOIF and 70 g of PCP-230 (a polycaprolactone diol having an average molecular weight of 1,250 and commercially available from Union Carbide) were added 14.8 g of diphenylmethane-p,p'-diisocyanate (MDI) after the mixture had been warmed to 80°C and blended with 6 g of dicyandiamide and 4 g of triphenylphosphine. After agitating to a homogenous solution, the reaction mixture was cooled and stood at room temperature until the disappearance of isocyanate in the IR spectrum. A white tough solid Example 13 having a melting temperature at 80°C was obtained. 2012^1 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 adherends after being cured at 170°C for 20 minutes.

Example 14 Using the same procedures as described in Example 13, the adhesive prepared from 100 g of Epon-IOOIF, 100 g of PCP-230, 6 g of dicyandiamide, 4 g of triphenyl phosphine and 15.3 g of MDI 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 adherends. 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-IOOIF, 70 g of PCP-240, a polycaprolactone diol 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 MDI had a 3,300 psi of lap shear strength and 35 in-lb of side impact resistance on a 1/2" overlap of steel adherends. The open time was longer than 25 minutes. This adhesive also had 6,740 psi of tensile modulus and 97% of elongation. jF: 20J27S

Claims (15)

WHAT WE CLAIM IS:

1. 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. A thermosettable composition comprising (a) a heat reactive epoxy curing agent 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.

3. A process for adhering two substrates which comprises coating at least one of said substrates with a composition comprising (a) a heat reactive epoxy curing agent 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.

4. The composition according to claimy^wherein the diol has a mole- cular weight in the range 200 to 20,000 prior to end-capping.

. . 5. The composition according to claim^'wherein the diol has a mole- Pi I rifV* w, cular weight in the range 400 to 3000 prior to end-capping. l *

6. The process according to claim 3 wherein the heating step is carried out by electromagnetic heating. < I v >. . on - J- (af W * i4>. 201278:

7. The process according to claim 6 wherein the electromagnetic heating is by induction heating.

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

9. The curable composition of claim 2 suitable for use as a sealant or when used as a sealant.

10. The curable composition of claim 2 suitable for use as a coating or when used as a coating.

11. The curable composition of claim 2 suitable for use as an adhesive or when used as an adhesive.

12. A compound as claimed in claim 1 substantially as hereinbefore described j^ith reference to any examples thereof.

13. A composition as claimed in any one of claims 2, 9, 10 and 11 substantially as hereinbefore described with reference to any examples thereof.

14. A process as claimed in any one of claims 3 to 8 when performed as hereinbefore described.

15. The product of a process as claimed in any one of claims 3 to 8 when performed substantially as hereinbefore described. By J-trS"/Thcir authorised Agent A. J. PA.iK. & SON Per;