WO2001040396A2

WO2001040396A2 - Urethane modified epoxy adhesive composition

Info

Publication number: WO2001040396A2
Application number: PCT/US2000/032605
Authority: WO
Inventors: John T. Pacanovsky
Original assignee: Reichhold Inc
Current assignee: Reichhold Inc
Priority date: 1999-12-03
Filing date: 2000-11-30
Publication date: 2001-06-07
Anticipated expiration: 2002-06-03
Also published as: WO2001040396A3; AU2253001A

Abstract

The present invention is comprised of an adhesive composition including an epoxy resin based on a polyglycidyl ether of a polyphenol and an urethane prepolymer having terminal isocyanate groups. The urethane prepolymer is reacted with hydroxyl groups of the epoxy resin so as to provide a multi-functional urethane modified epoxy resin having a functionality of four or more. Optionally, the epoxy resin can be acrylated.

Description

URETHANE MODIFIED EPOXY ADHESIVE COMPOSITION

BACKGROUND AND FIELD OF THE INVENTION

The present invention relates to adhesive compositions and particularly, a urethane modified epoxy adhesive composition. The adhesive compositions of the present invention are particularly adapted for use with fiber reinforced composites, for example, in the form of sheet molding compounds ("SMC").

In various industries, there is a strong desire for a product that will bond various plastics to the same or different plastics, metal to metal, and fiber reinforced plastic (FRP) to metal, or other like or dissimilar substrates. The repair of various metal and plastic body parts in the automotive, truck, recreation vehicle and watercraft industries has become a critical issue. This is particularly an issue in the automotive industry, wherein many metal side and body panels have been replaced with molded plastics such as SMC. SMC has been used to replace such metal parts in an effort to reduce weight and to improve corrosion resistance. SMC is typically a reinforced resin composition comprising unsaturated polyester resin, an ethylenically unsaturated monomer, a low shrink additive, various other additives and glass fiber reinforcement. SMC is molded under heat and pressure to provide a self-supporting thermoset, fiber-reinforced substrate. Such SMC substrates are then bonded to other SMC substrates (parts) or to metal parts or structural parts, preferably without the use of mechanical means such as fasteners. Adhesive compositions utilized with SMC must operate over a wide range of environmental and processing conditions including temperatures of from about -20°C (e.g., cold weather) to 200°C (e.g., paint curing), humidity and exposure to salinity, grease and oil. Such adhesive compositions should be flexible, have high impact strength, tear resistance and high peal strength and be durable. Such adhesive compositions should further be non-staining, particularly when painting, sandable and have an extended shelf life. The cure rate should be fast to improve production rates. Finally, it would be desirable to not to have to treat or prime the surface(s) of the substrate(s) to be bonded together.

Thus, with all of these requirements, there have been various attempts in the art to meet one or more of these requirements. There, however, have been mixed results, e.g., increases in flexibility have typically resulted in nominal impact strength properties resulting in failure at the metal interface. For example, German DE 3,536,246 A1 proposes the use of acrylic and methacrylic acid derivatives of urethane prepolymers as fiexibilization agents for epoxide resin systems. The patentees disclose the reaction of hydroxy alkyl esters of methacrylic acid or acrylic acid and an isocyanate prepolymer e.g., toluenediisocyanate-polyether polyol having a molecular weight of from 400 to 6000 as fiexibilization agents for glycidyl ethers of bisphenol A. The examples show a curable polyepoxide composition comprising modified epoxy resins on the basis of bisphenol A with levels of acrylate terminated polyurethanes cured with a variety of amine curatives, e.g., polyaminoamides, modified cycloaliphatic polyamines and polyamines.

With respect to fast curing, U.S. Patent No. 4,726,868 proposes a fast curing, two-component adhesive composition comprising a mixture of a polyol and a polyepoxide as a first component and a polyisocyanate as a second component. The first component has an equivalent functionality ratio of hydroxyl to epoxy groups of from 98:2 to 50:50. The ratio of the isocyanate to combined hydroxyl: epoxy of the first component is 0.8 to 2.0. U.S. Patent No. 4,383,060 proposes rapidly curing adhesive for SMC comprising an epoxy novolac, an adduct of a diglycidyl either of bisphenol A and a hydrogenated vegetable oil, silica and a liquid imidazole catalyst.

U.S. Patent No. 5,019,608 proposes an adhesive composition for SMC comprising an epoxy resin and a polyacrylate or polymethacrylate cured with a combination of an amine-functional butadiene-acrylonit le rubber at least one polyamidoamine.

U.S. Patent No. 5,278,257 proposes an adhesive composition having high peel strength and high resistance to crack propagation. The composition comprises a first component being a copolymer based on at least one 1 ,3- diene and a least one polar ethylenically unsaturated comonomer and a second component being a phenol-terminated polyurethane, polyurea or polyurea-urethane.

There, however, remains a need for an epoxy-based adhesive composition having improved adhesive properties, particularly when used with SMC, and more particularly having improved properties with respect to flexibility, durability and cure rate properties.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an adhesive composition which is durable, and has high flexibility, impact strength, tear resistance and high peel strength.

It is another object of the present invention to provide an adhesive composition that has an extended shelf life prior to curing and is fast curing.

It is yet another object of the present invention to provide an adhesive composition that is non-staining and is sandable.

It is still another object of the present invention to provide an adhesive that eliminates or substantially reduces the need for using a pretreatment (priming) of the substrate(s) surface prior to application of the adhesive composition.

These and other objects, features and advantages are achieved by the adhesive composition of the present invention. The adhesive composition of the present invention comprises an adhesive composition including an epoxy resin based on a polyglycidyl ether of a polyphenol having one or more hydroxyl groups and an urethane prepolymer having terminal isocyanate groups. The urethane prepolymer is reacted with hydroxyl groups of the epoxy resin so as to provide a multi-functional urethane modified epoxy resin having a functionality of four or more. Such a multi-functional urethane modified epoxy resin is partially crystalline from the epoxy portion and is partially amorphous from the urethane portion. Optionally, the epoxy resin can be acrylated.

In another embodiment, the present invention provides a method of bonding a substrate to a like or dissimilar substrate. The method comprises applying an adhesive composition which includes an epoxy resin based on a polyglycidyl ether of a polyphenol and a urethane prepolymer having terminal isocyanate groups, to either or both of the substrates and bonding the substrates together.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As summarized above, the present invention provides a multifunctional urethane modified epoxy resin having a functionality of four or more. The composition includes an epoxy resin based on a polyglycidly either of a polyphenol and a urethane prepolymer having terminal isocyanate groups. The epoxy resin preferably has an epoxide equivalent weight of from about 190 to about 4000, and more preferably from about 500 to about 2000. The urethane prepolymer preferably has a molecular weight of from about 500 to about 8000, and more preferably from about 3000 to about 6000.

Preferably, the epoxy resin is in liquid form so as to avoid the need to use volatile organic compounds (solvents), thus reducing environmental concerns related to such compounds. The composition can be in the form of a one- component or a two-component system. Preferably the polyglycidyl ether of a polyphenol is the reaction product of a divalent phenol and an epihalohydrin, methyepihalohydrin, ethylepihalohyd n or dihalohydrins. Suitable divalent polyols include 2,2-bis- (p-hydroxyphenyl)-propane, 2,4'-dihydroxydiphenylmethane, bis-(4- hydroxyphenyl)-methane, bis-(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)- methane 1 ,1-bis-(4-hydroxyphenyl)-ethane 2,2-bis-(3,5-dichloro-4- hydroxyphenyl)-propane, 2,2-bis-(2-isopropyl-4-hydroxyphenyl)-propane, bis- (4-hydroxyphenyl)-sulfone, 2,4'-dihydroxydiphenylsulfone, and 5-chloro-2,4'- dihydroxydiphenylsulfone. Examples of epihalohydrins, methylepihalohydrins, ethylepihalohydrins and dihalohydrins that can be used for the purpose of the present invention include epichlorohydrin, epibromohyd n, methylepichlorohydrin, methylepibromohydrin, ethylepichlorohyd n, ethylepibromohydrin, dichlorohydrin, dibromohydrin and the like, of which epichlorohydrin and methylepichlorohydrin are particularly preferable. The ratio of divalent phenol to the epihalohydrin compound is from about 5 moles to about 10 moles of phenol to from about 0.5 moles to about 1.5 moles of epihalohydrin. The reaction of the phenol and the epohalohydrin is preferably conducted at a temperature of between about 45° and about 175°C, more preferably at a temperature of between about 55° to about 1 15°C. Optionally, catalysts such as tertiary amines (e.g., triethylamine), lead octylate boron trifluoride or dibutyl tinlaurate, etc. may be used.

The urethane prepolymer having terminal isocyanate groups is typically present in the form of a reaction product of a hydroxy compound and a polyisocyanate. For the purpose of the invention, hydroxy compounds that can be used to produce an isocyanate group-terminated urethane prepolymer include di- or polyvalent polyetherpolyols, polyesterpolyols, caster oil derivatives and tolu oil derivatives. Polyols having a molecular weight between about 500 and about 3,000 may preferably be used.

Examples of polyethyerpolyols that can be used for the purpose of the invention include diols such as polyoxyethylenepolyol, polyoxypropyleneglycol, polyoxybutyleneglycol and polytetramethyleneglycol and trivalent polyetherpolyols obtained by adding one or more than one propyleneglycols to glycerol or trimethylopropane. Examples of polyesterpolyols that can be used for the purpose of the invention may be prepared from polyvalent alcohols such as ethyleneglycol, propyleneglycol, diethyleneglycol, 1 ,4-butanediol, 1 ,6-hexanediol, 2-methyl-1 ,5,pentanediol, 2,2-dimethyl-propanediol, glycerol and trimethylolpropane and polybasic acids such as adipic acid, terephthalic acid, isophthaiic acid, glutaric acid, azelaic acid, dimer acid, and pyromellitic acid. Preferably, polypropylene glycol is used. Additionally, lactone polyols may also be used. Any one of the above- listed hydroxy compounds may be combined for use for any appropriate portion for the purpose of the invention. Suitable isocyanates include thmethylene, tetramethylene, pentamethylene, hexamethylene, 1 ,2-propylene, 1 ,2-butylene, and 1 ,3- butylene diisocyanates, isophorone diisocyanate, 1 ,3-cyclopentane, 1 ,4- cyclohexane and 1 ,2-cyclohexane diisocyanates, m-phenylene, p-phenylene, 4,4'-diphenyl and 1 ,4-naphthalene diisocyanates, diphenylene methane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures of 2,4-tolylene diisocyanate, and 4,4'-toluidine and 1 ,4-xylylene diisocyanates. A preferred isocyanate is 2,4-tolylene diisocyanate.

The reaction of the epoxy and the urethane prepolymer is preferably conducted at a temperature of between about 60° to about 120°C, and more preferably at a temperature of between about 80° to 90°C under conditions known to those skilled in the art to provide the multi-functional urethane modified epoxy resin. The molecular weight of such a hybrid resin is preferably from about 2500 to about 15,000, and more preferably is from about 4000 to about 9000.

Optionally, the reaction can be conducted in the presence of a catalyst such as tertiary amines, lead acrylate or dibutyl tinlaurate or the like.

If desired, the composition can include reactive diluents such as acrylated epoxies, esters of fatty acids, epoxidized polyunsaturated compounds, acrylic acid ester copolymers, hydroxy acrylates and methacrylates, Cι_ to Cι₄ aliphatic glycidyl ethers, trimethylolpropane triacrylates, aromatic glycidyl ethers, functional liquid rubbers and the like. Epoxies can be acrylated in a two step reaction. In the first step, a hydroxy acrylate, a compound having both acrylate groups and a single hydroxyl group, is reacted with an anhydride or a diacid to form an ester having a free carboxylic acid group and a free acrylate group. The reaction occurs between a carboxylic group of the diacid or anhydride, and a hydroxyl group of the hydroxy acrylate. Exemplary hydroxy acrylates include 2- hydroxyethyl acrylate (HEA), 3-hydroxypropyl acrylate, 2-hydroxy methacrylate, hydroxyethyl-betacarboxyethyl acrylate, 3-hydroxypropl methacrylate, hydroxyhexyl acrylate, hydroxyoctyl methacrylate, 2- hydroxypropyl acrylate, and 2-hydroxyethyl methacrylate. Di- and polyacrylates may also be used but they are not preferred as the resulting coatings may be too brittle. The preferred hydroxy acrylate is 2-hydroxyethyl acrylate because it is believed to be very reactive and usually results in a fast curing composition.

Examples of the epoxidized polyunsaturated compounds include epoxidized oils such as epoxidized linseed oil, epoxidized soybean oil, epoxidized safflower oil, epoxidized tung oil, epoxidized perilla oil, epoxidized dehydrated castor oil, epoxidized oiticica oil and epoxidized tall oil; epoxidized fatty acids; epoxidized cyclic olefins such as vinylcyclohexene dioxide, 1-(1- methyl-1 ,2-epoxyethyl)-3,4-epoxy-4-methylcyclohexane, 3,4- epoxycyclohexylmethyl, 3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6- methycyclohexanecarboxylate, bis(3,4-epoxy-6methylcyclohexylmethyl) adipate, dicyclopentadiene dioxide, dipentene dioxide, tetrahydroindene dioxide, products of epoxidization of conjugated diene polymers such as epoxidized polybutadiene, epoxidized polypentadiene, epoxidized styrene- butadiene copolymer and epoxidized acrylonitrile-styrene copolymer; products of epoxidization of unsaturated bond containing polymers such as epoxidized polypropylene and epoxidized polyisobutene; polyglycidyl ethers of polysiloxanes; and heterocycle containing epoxy resins such as epoxy resins wherein epoxy groups are bonded to oxazolidinone ring through carbon atoms, diglycidyl ether of furan, diglycidyl ether of dioxane, diglycidyl ether of spirobi(m-dioxane), polyepoxy compounds prepared from imidazolines each having a polyunsaturated alkenyl group at 2-position, and triglycidyl isocyanurate and other epoxy compounds used to improve elongation.

Examples of acrylic acid ester copolymers include monomers of Ci to Ci₈ alkyl acrylates and methacrylates, acrylamide and methacrylamide, Ci to da acrylamides and methacrylamides, polyether esters of acrylic acid and methacrylic acid, hydroxyl and tertiary amine functional esters of acrylic acid and methacrylic acid, and the like. Mixtures of monomers can be used. In such mixtures, any desirable comonomer can be used, such as styrene, alpha-methyl styrene, vinyl esters, dialkyl maleates, and the like. The most preferred comonomers are the alkyl acrylates and more specifically, the C₂ to Cβ alkyl acrylates. The comonomer used in forming the acrylate ester comonomer is an ethylenically unsaturated monomer which has epoxy or amine or alcohol reactive functional groups. Examples of such functional groups include carboxylic acid groups, carboxylic anhydride, isocyanato, hydroxyl, epoxy, aldehyde (e.g., acrolein and methacrolein), siloxyl, halogen and the like. Examples of hydroxyl group containing monomers include hydroxyethyl acrylate and methacrylate and hydroxybutylacrylate. Examples of acid containing functional monomers include acrylic and methacrylic acid, maleic acid, crotonic acid, itaconic acid, and the like. Examples of other possible comonomers include t methoxysilylpropylmethacrylate, chloroethylacrylate, glycidyl acrylate and methacrylate, isocyanatoethylmethacrylate, chioromethylstyrene, and the like. Non-reactive diluents may also be used to adjust viscosity and the like.

Suitable non-reactive diluents include aromatic alcohols (e.g., nonyl phenol, benzyl alcohol), dimethylformamide, ketones (e.g., MEK), esters, ethers, ketoesters, pyrrolidones, hydrogenated furans, and the like.

Curing agents can be used. Preferably, the curing agent contains at least one nucleophilic or electrophilic group which reacts with the epoxy ring to cross-link the adhesive composition. Suitable base curing agents include polyamide resins, aliphatic amines, polyether diamines, aromatic amines, polyamines, polyamidoamines, polyetherdiamines, phenol compounds, and mercaptan resins. Examples of primary amines include di-(4- aminophenyl)sulfone, di-(4-aminophenyl)-ethers, and 2,2-bis(4- aminophenyl)propane, ethylene diamine, hexamethylene diamine, isomers of hexamethylene diamine, diethylene triamine, triethylene tetmmine, tetraethylene pentamine, bishexamethylene triamine, N,N'-bis(3-aminopropyl)- 1 ,2-ethane diamine, N-(3-aminopropyl)-1 ,3-propane diamine N-(2- aminoethyl)-1 ,3 propane diamine, isomers of cyclohexane diamine, 4,4'- methylene biscyclohexanamine, 4'4-methylene bis[2- methylcyclohexanamine], isophorone diamine, and phenalkylene polyamines. Examples of useful tertiary amines are dimethylaminopropylamine and pyridine. Examples of useful aromatic amines include di-(4- aminophenyl)sulfone, di(4-aminophenyl) ether, 2,2-bis(4-aminophenyl propane, 4,4'-diamino diphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenyl methane, m-phenylene diamine, p-phenylene diamine, m-xylyiene diamine, toluene diamine, 4,4'-methylene dianiline, benzidine, 4,4'-thiodianiline, 4- methoxy-1 ,3-phenyldiamine, 2,6-diaminopyhdine, and dianisidine.

Examples of polyether diamines include 4,9-dioxadodecane-1 ,12- diamine, 4,7,10-trioxatridecane-1 ,12 diamine, bis(3-amino propyl)polytetrahydrofurans of varying molecular weights.

Examples of phenol compounds include phenol, substituted alkyl phenols (nonyl phenol), diphenols such as catechol, and alkyl substituted catechol, resorcinol, and hydroquinone.

Examples of mercaptan resins include alkyl dimercaptans such as ethane dithiol, nonane dithiol, pentaerythritol tetra (3-mercapto propionate), trimethylol propane th(3-mercaptopropionate), glycol dimercapto acetate, thiol terminated polyethers and thiol terminated polysulphides.

Also useful are boron complexes, and in particular, boron complexes with monoethanolamine; imidazoles such as 2-ethyl-4-methyl imidazole; guanidines such as tetmmethyl guanidine; substituted ureas such as toluene diisocyanate urea; dicyandiamide; and acid anhydrides such as 4- methyltetrahydroxyphthalic acid anhydride, and methylnorbornenephthalic acid anhydride. Mixtures of more than one curing agent may be used. Preferred curing agents for one-part adhesive compositions are amines, acid anhydrides, guanidines, dicyandiamide, and mixtures thereof.

Accelerators known in the art can also be added to increase the cure rate of the epoxy adhesive. Such accelerators include compounds that can act as a curative when used alone, but when combined with a different class of curatives, will accelerate the curing of the epoxy adhesive composition. Examples of useful accelerators include phenolic compounds (e.g., tris, dimethylamino (methyl phenol) tertiary amines, dicyandiamides, imidazole, substituted imidazole hexabis imidazole nickel phthalate complex, substituted ureas, and calcium trifluoromethylsulfonate.

These accelerators may be used alone or in combination together to accelerate the cure of an epoxy adhesive combination. Some examples of useful combinations include phenolic compounds with tertiary amines, dicyandiamides with imidazole and/or substituted imidazoles, dicyandiamides with substituted ureas, dicyandiamides with hexakis imidazole nickel phthalate complex, and calcium t fluoromethyl sulphonate with imidazoles. Various additives may be included. Suitable additives include plasticizers such as phosphates and phthalates; flame retardants such as borates, metaborates, aluminum hydroxide, magnesium hydroxide, and bromine compounds, thixotropic agents such as fumed silica to provide flow control; pigments to enhance color tones such as ferric oxide, brick dust, carbon black, and titanium dioxide; fillers such as talc, silica, magnesium, calcium carbonate, calcium sulfate, beryllium aluminum silicate; clays such as bentonite; glass and ceramic beads and bubbles; compounds imparting X-ray opacity, such as barium metaborate; and reinforcing materials, such as woven and nonwoven webs of organic and inorganic fibers such as polyester, polyimide, glass fibers, and cemmic fibers. Dispersing agents and wetting agents, such as silanes, can also be added so long as they do not interfere with the curing reaction of the epoxy adhesive composition. The additives can be added in an amount effective for the intended purpose; typically, amounts up to about 50 parts of additive per total weight of formulation can be used. In operation, the adhesive composition is used by applying it to one or more surfaces of like or dissimilar substrates to be bonded. Exemplary substrates include metals (e.g., iron, copper, nickel, aluminum, brass, steel), plastics (e.g., polyvinyl chloride resin, nylon, polyacrylic resin, various SMC, polycarbonate/polybutylene terephthalate, thermoplastic polyolefins), ceramic, wood, glass and the like. Advantageously no primer or other surface treatment is required for most substrates. In some circumstances, such as when polyolefins are used as the substrate, a primer (e.g., an acrylic latex can be used.) The bonding surfaces are then contacted together under conditions sufficient to cure the adhesive composition. Suitable conditions can include pressure and temperature.

The following examples illustrate specific embodiments of the present invention. In the examples and throughout the specification, all parts and percentages are by weight, unless otherwise indicated. EXAMPLES

Example 1

(Two-Component System)

A structural adhesive comprising the following is prepared:

Component A

Lbs. Component Source

619.26 EpotufAD 1047 Reichhold (a multi-functional urethane modified epoxy resin)

234.7 Microwhite No. 25 E.C.C. Chemicals

235.7 Bentone 34 Rheox

290.8 TiPure R-960 DuPont

114.0 Cab-o-Sil M-5 Cabot Corp.

Component B

Lbs. Component Source

183.87 Epotuf 37-640 Reichhold (polyamide)

12.15 Tris, dimethy amino Air Products (methyl phenol)

504.0 Microwhite No. 25 E.C.C. Chemicals

61.7 Lampblack 10 Degussa

48.3 Byk 410 Byk

The compounds are in paste from and are mixed together Component

A/Component B in a 2 to 1 ratio by volume until a smooth gray color is achieved. The mix viscosity was 900,000 cps.

Performance data was done as lap shear using ASTM D 1002-94 metal-to-metal and ASTM D 5868-95 for plastic-to-plastic on samples cured one day at 25°C, then one hour past cure at 100°C. The samples had a 1x1 inch overlap, with a 0.050 inch bond line with no primer and the failure was measured. A liquid epoxy resin control, Reichhold 37-140 was also tested. The results are as follows:

Invention (psi) Control (psi)

Substrate Lap Shear Lap Shear

SMC 1490 520

FRP 800 800

Invention (psi) Control (psi)

Substrate Lap Shear Lap Shear

Xenoy® polycarbonate/ Polybutylene terephthalate 750 260

Lexan® Em-1 (GE Products) 770 450

Lexan® 1210 (GE Products) 1310 565

Bayblend® ABS/Polycarbonate 490 210

Cold Rolled Steel 1950 1430

Galvanized Steel 2120 1360

Aluminum 2010 860

FRP Wetlay Up 420 150

T-peel resistance was measured using Test No. ASTM D-1876 on a sample having 3x1 inch bond overlap with a 0.050 inch bondline with no primer. The results are as follows on a cold rolled steel sample.

Cure Conditions T-peel Resistance (PLI)

1 day cure at 25°C, then 1 hour post cure at 100°C 27 30 minute cure at 120°C 33

Example 2 An adhesive composition comprising the following is prepared: Lbs. Component

100.0 Epotuf AD 1047

7.0 Amicure CG-1200 dicyanamide

4.0 Imidazole accelerator

40.0 Aluminum

42.0 Cab-O-Sil TS 720 The composition was applied to a pair of cold rolled steel substrates along a 0.050 inch bondline and cured at 150°C for 20 minutes. The peel strength was 28 pli and the lap shear strength was 600 psi.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

THAT WHICH IS CLAIMED IS:

1 . An adhesive composition comprising an epoxy resin based on a polyglycidyl ether of a polyphenol and a urethane prepolymer having terminal isocyanate groups wherein the urethane prepolymer is reacted with hydroxyl groups of the epoxy resin to provide a multi-functional urethane modified epoxy resin having a functionality of four or more.

2. The adhesive composition according to Claim 1 , wherein the polyglycidyl ether of a polyphenol is a reaction product of a divalent phenol and a compound selected from the group consisting of epihalohydrins, methylepihalohydrins, ethylepihalohydrins and dihalohydrins.

3. The adhesive composition according to Claim 2, wherein the divalent polyol is selected from the group consisting of 2,2-bis-(p- hydroxyphenyl)-propane, 2,4'-dihydroxydiphenylmethane, bis-(4- hydroxyphenyl)-methane, bis-(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)- methane 1 ,1 -bis-(4-hydroxyphenyl)-ethane 2,2-bis-(3,5-dichloro-4- hydroxyphenyl)-propane, 2,2-bis-(2-isopropyl-4-hydroxyphenyl)-propane, bis- (4-hydroxyphenyl)-sulfone, 2,4'-dihydroxydiphenylsulfone, and 5-chloro-2,4'- dihydroxydiphenylsulfone.

4. The adhesive composition according to Claim 1 , wherein the epoxy resin is acrylated.

5. The adhesive composition according to Claim 1 , wherein the urethane prepolymer having terminal isocyanate groups is a reaction product of a hydroxy compound and an isocyanate selected from the group consisting of t methylene, tetramethylene, pentamethylene, hexamethylene, 1 ,2- propylene, 1 ,2-butylene, and 1 ,3-butylene diisocyanates, isophorone diisocyanate, 1 ,3-cyclopentane, 1 ,4-cyclohexane and 1 ,2-cyclohexane diisocyanates, m-phenylene, p-phenylene, 4,4'-diphenyl and 1 ,4-naphthalene diisocyanates, diphenylene methane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures of 2,4-tolylene diisocyanate, and 4,4'- toluidine and 1 ,4-xylylene diisocyanates.

6. The adhesive composition according to Claim 5, wherein the hydroxy compound is selected from the group consisting of di and polyvalent polyetherpolyols, castor oils, polyesterpolyols, and tall oil derivatives.

7. The adhesive composition according to Claim 1 , wherein the epoxy resin has an epoxide equivalent weight of from about 190 to about 4000.

8. The adhesive composition according to Claim 5, wherein urethane prepolymer has a molecular weight of from about 500 to about 8000.

9. The adhesive composition according to Claim 1 , wherein the composition includes a reactive diluent selected from the group consisting of epoxy resins, acrylated epoxy resins, esters of fatty acids, epoxidized aliphatic polyols, hydroxy acrylates and methacrylates, do to Cι₄ aliphatic glycidyl ethers, trimethylolpropane triacrylates, aromatic glycidyl ethers, and functional liquid rubbers.

10. A method of preparing an adhesive composition comprising reacting at least one hydroxyl group of a epoxy resin based on a polyglycidyl ether of a polyphenol with a urethane prepolymer having terminal isocyanate groups to provide a multi-functional urethane modified epoxy resin adhesive composition having a functionality of four or more.

11. The method according to Claim 1 wherein the reacting of hydroxyl groups of the epoxy resin with the urethane prepolymer is conducted at a temperature of from about 60°C to 120°C.

12. The method according to Claim 10, wherein the polyglycidyl ether of a polyphenol is a reaction product of a divalent phenol and a compound selected from the group consisting of epihalohydrins, methylepihalohydrins, ethyiepihalohyd ns and dihalohydrins.

13. The method according to Claim 12, wherein the divalent polyol is selected from the group consisting of 2,2-bis-(p-hydroxyphenyl)-propane, 2,4'-dihydroxydiphenylmethane, bis-(4-hydroxyphenyl)-methane, bis-(4- hydroxy-2,6-dimethyl-3-methoxyphenyl)-methane 1 ,1-bis-(4-hydroxyphenyl)- ethane 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, 2,2-bis-(2-isopropyl-4- hydroxyphenyl)-propane, bis-(4-hydroxyphenyl)-sulfone, 2,4'- dihydroxydiphenylsulfone, and 5-chloro-2,4'-dihydroxydiphenylsulfone.

14. The method according to Claim 10, wherein the epoxy resin is acrylated.

15. The method according to Claim 10, wherein the urethane prepolymer having terminal isocyanate groups is a reaction product of a hydroxy compound and an isocyanate selected from the group consisting of thmethylene, tetramethylene, pentamethylene, hexamethylene, 1 ,2-propylene, 1 ,2-butylene, and 1 ,3-butylene diisocyanates, isophorone diisocyanate, 1 ,3- cyclopentane, 1 ,4-cyclohexane and 1 ,2-cyclohexane diisocyanates, m- phenylene, p-phenylene, 4,4'-diphenyl and 1 ,4-naphthalene diisocyanates, diphenylene methane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures of 2,4-tolylene diisocyanate, and 4,4'- toluidine and 1 ,4-xylylene diisocyanates.

16. The method according to Claim 15, wherein the hydroxy compound is selected from the group consisting of di and polyvalent polyetherpolyols, castor oils, polyesterpolyols, and tall oil derivatives.

17. The method composition according to Claim 10, wherein the epoxy resin has an epoxide equivalent weight of from about 190 to about 4000.

18. The method according to Claim 15, wherein urethane prepolymer has a molecular weight of from about 500 to about 8000.

19. The method according to Claim 10, wherein the composition includes a reactive diluent selected from the group consisting of epoxy resins, acrylated epoxy resins, esters of fatty acids, epoxidized aliphatic polyols, hydroxy acrylates and methacrylates, do to C₁ aliphatic glycidyl ethers, trimethylolpropane triacrylates, aromatic glycidyl ethers, and functional liquid rubbers.

20. A method of bonding one or more substrates together, the method comprising applying an adhesive to at least one surface of at least one of the substrates, the adhesive composition comprising an epoxy resin based on a polyglycidyl ether of a polyphenol and a urethane prepolymer having terminal isocyanate groups wherein the urethane prepolymer is reacted with hydroxyl groups of the epoxy resin to provide a multi-functional urethane modified epoxy resin having a functionality of four or more, and subjecting the one or more substrates to conditions sufficient to cure the adhesive composition and to bond the substrates together.

21. The method according to Claim 20, wherein one or more substrates are selected from the group consisting of metals, plastics, ceramic, wood and glass.

22. The method according to Claim 20, wherein the polyglycidyl ether of a polyphenol is a reaction product of a divalent phenol and a compound selected from the group consisting of epihalohydrins, methylepihalohydrins, ethylepihalohydrins and dihalohydrins.

23. The method according to Claim 22, wherein the divalent polyol is selected from the group consisting of 2,2-bis-(p-hydroxyphenyl)-propane, 2,4'-dihydroxydiphenylmethane, bis-(4-hydroxyphenyl)-methane, bis-(4- hydroxy-2,6-dimethyl-3-methoxyphenyl)-methane 1 ,1-bis-(4-hydroxyphenyl)- ethane 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane, 2,2-bis-(2-isopropyl-4- hydroxyphenyl)-propane, bis-(4-hydroxyphenyl)-sulfone, 2,4'- dihydroxydiphenylsulfone, and 5-chloro-2,4'-dihydroxydiphenylsulfone.

24. The method according to Claim 20, wherein the epoxy resin is acrylated.

25. The method according to Claim 20, wherein the urethane prepolymer having terminal isocyanate groups is a reaction product of a hydroxy compound and an isocyanate selected from the group consisting of thmethylene, tetramethylene, pentamethylene, hexamethylene, 1 ,2-propylene, 1 ,2-butylene, and 1 ,3-butylene diisocyanates, isophorone diisocyanate, 1 ,3- cyclopentane, 1 ,4-cyclohexane and 1 ,2-cyclohexane diisocyanates, m- phenylene, p-phenylene, 4,4'-diphenyl and 1 ,4-naphthalene diisocyanates, diphenylene methane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and mixtures of 2,4-tolylene diisocyanate, and 4,4'- toluidine and 1 ,4-xylylene diisocyanates.

26. The method according to Claim 25, wherein the hydroxy compound is selected from the group consisting of di and polyvalent polyetherpolyols, castor oils, polyesterpolyols, and tall oil derivatives.

27. The method composition according to Claim 20, wherein the epoxy resin has an epoxide equivalent weight of from about 190 to about 4000.

28. The method according to Claim 25, wherein urethane prepolymer has a molecular weight of from about 500 to about 8000.

29. The method according to Claim 20, wherein the composition includes a reactive diluent selected from the group consisting of epoxy resins, acrylated epoxy resins, esters of fatty acids, epoxidized aliphatic polyols, hydroxy acrylates and methacrylates, do to C-ι aliphatic glycidyl ethers, trimethylolpropane triacrylates, aromatic glycidyl ethers, and functional liquid rubbers.