EP0833874A1 - Adhesive compositions, bonding films made therefrom and processes for making bonding films - Google Patents

Abstract

A photostable adhesive composition comprises: a) an aromatic polyepoxide; b) a heat activated curative for polyepoxide; c) a thermoplastic polymer; d) a polyfunction (meth)acrylate; and e) optionally, a bireactive compound that contains at least one (meth)acrylate group and at least one group that is reactive with aromatic polyepoxide. The adhesive compositions can be used to prepare adhesive bonding films in a process that uses electron beam irradiation.

Description

ADHESIVE COMPOSITIONS, BONDING FILMS MADE THEREFROM AND PROCESSES FOR MAKING BONDING FILMS

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to adhesive compositions, bonding films made therefrom, and processes for making the bonding films. More particularly, this invention relates to adhesive compositions comprising epoxy resin,

(meth)acrylate-containing resin, and thermoplastic polymer, as well as processes for making bonding films therefrom using electron beam irradiation.

Description of the Related Art

Solid, continuous adhesive films are often used to bond two substrates together when manufacturing structural articles and laminates. Such adhesive films are frequently used in the electronics, automotive and aerospace industries. For example, a laminated circuit board can be manufactured by placing an adhesive bonding film between two copper-clad substrates containing etched circuitry and heat curing the adhesive film.

Adhesive bonding films useful in manufacturing structural articles and laminates should, preferably, exhibit several characteristics. For example, they should be easy to handle. That is, they should be capable of being removed from a temporary carrier (e.g., a release liner) and placed on a substrate without wrinkling, tearing or permanently stretching.

The adhesive bonding film should also demonstrate a controlled flow during heat curing (i.e., some, but not extensive, adhesive flow). Some flow of the adhesive is desirable during heat curing to wet the substrate surface and to form an even bondline with uniform bond strength. However, extensive adhesive flow during heat curing may cause the adhesive to bleed out beyond the edges of the substrates, result in an uneven bondline, voids and inconsistent bond strengths. Additionally, after heat curing, the adhesive bonding films should have good adhesion to the substrates. At least for certain applications, the heat cured adhesive bonding films should also have a high glass transition temperature to increase the thermal stability of the laminate and to reduce thermal expansion. This is an especially beneficial property during subsequent high temperature processes, such as the soldering (i.e., wave soldering) of circuit boards.

To promote wide commercial acceptance, the adhesive compositions from which the bonding films are produced should also be easily handled and processed. For example, the adhesive compositions should have a viscosity that permits them to be mixed and then coated at a temperature that is not so high as to risk premature reaction of any heat activated curatives in the adhesive:

Many adhesive compositions include both heat curable materials and materials that polymerize when exposed to actinic radiation (i.e., visible or ultraviolet light). These adhesives require storage under "safe light" conditions. It would be advantageous to have adhesive compositions that did not have to be stored away from visible or ultraviolet light.

Adhesive bonding films comprising both radiation polymerizable resins and heat curable resins have been previously disclosed. For example, U.S. Patent No. 4,552,604 (Green) describes a method of bonding two surfaces together using a liquid composition containing an epoxide resin and a compound that is

photopolymerized to form an essentially solid, continuous film by exposure to actinic radiation (preferably a wavelength of 200-600 nm) but without thermally crosslinking the film. Usually a 10: 1 to 1 : 10 molar ratio of epoxide resin to photopolymerizable compound is employed to provide a satisfactory film and satisfactorily cured bond. Preferably a photopolymerization catalyst is used. The film can bond surfaces together by applying heat and, if desired, pressure.

U.S. Patent No. 4,612,209 (Forgo et al.) discloses the use of actinic radiation (preferably a wavelength of 200-600 nm) to prepare heat curable adhesive bonding films having variable tack. The adhesive is a mixture of a

photopolymerizable compound containing at least one CH₂=C(R)COO- group in which R is hydrogen or methyl, a heat curable epoxide resin containing no photopolymerizable groups, a heat activatable curing agent for epoxide resins, an accelerator, and a photopolymerization catalyst for the photopolymerizable compound.

U.S. Patent No. 5,086,088 (Kitano et al.) discloses an acrylic ester/epoxy resin composition that is exposed to ultraviolet radiation to provide a pressure sensitive thermosetting adhesive. The adhesive comprises about 30 to 80% by weight of a photopolymerizable prepolymeric or monomeric syrup containing an acrylic ester and a copolymerizable moderately polar monomer, about 20 to 60% by weight of an epoxy resin or a mixture of epoxy resins containing no

photopolymerizable groups, about 0.5 to 10% by weight of a heat activatable hardener for the epoxy resin, about 0.01 to 5% of a photoinitiator, and 0 to about 5% of a photocrosslinking agent. The adhesives can be used to structurally bond components to metal surfaces or to seal metal seams.

A resin composition comprising low molecular weight urethane-acrylate, epoxy resin, acrylate or methacrylate monomer, and epoxy curing agent is described in Japanese Patent Kokai No. 61/14274 (Ando et al.). The resin composition forms a thermosetting adhesive through the use of electrolytic radiation (e.g., electron beam, gamma-ray, or X-ray) which reportedly causes the urethane acrylate and acrylate monomer to polymerize and crosslink with each other.

Japanese Patent Kokai No. 1/234417 (Yamamoto et al.) describes an epoxy resin composition that may be crosslinked using electron beam radiation. The composition contains a) an epoxy resin, b) an epoxy resin with at least one epoxy group and at least one unsaturated double bond within one molecule, and c) a heat curing agent for epoxy resin, with a weight ratio for components (a) and (b) of 0.95/0.05 to 0.10/0.90. The composition can first form a surface hardened state by crossiinking through the double bonds using electron beam irradiation. This can then be further heat cured in a second step. Reportedly, if not enough of component (b) is used there is too little crossiinking and the surface is not sufficiently hardened.

A method of producing prepreg is disclosed in Japanese Patent Kokai No. 58/19332 (Takita et al.). A resin solution comprising 100 parts by weight epoxy resin, 2 to 150 parts by weight of a curing agent for the epoxy resin, and 20 to 150 parts by weight acrylate monomer is used to impregnate a reinforcement substrate. This is irradiated with electron beam radiation to cure only the acrylate monomer, giving a prepreg which has no tack and easy handling. Reportedly, when the acrylate-containing component is used in amounts less than suggested, curing via electron beam irradiation is insufficient and tack remains on the surface.

There is still a need for an adhesive composition that can provide a bonding film having some, and preferably all, of the following properties: easy handling, controlled resin flow during heat curing, and a high glass transition temperature after heat curing. The utility of the adhesive composition would be further increased if it could be stored without protection from visible or ultraviolet light, and if it could be processed at temperatures that do not risk premature reaction of a heat activated catalyst.

SUMMARY OF THE INVENTION

In one embodiment, this invention relates to an adhesive composition comprising:

a) an aromatic polyepoxide;

b) a heat activated curative for polyepoxide;

c) a thermoplastic polymer;

d) a polyfunctional (meth)acrylate; and

e) optionally, a bireactive compound that contains at least one (meth)acrylate group and at least one group that is reactive with aromatic polyepoxide (e.g., hydroxyl, carboxyl, amine or 1,2-epoxide).

The adhesive compositions are photostable; they do not rely on actinic radiation to polymerize. Hence they require neither a photocatalyst nor storage under "safe light" conditions (e.g., storage in containers that are not transparent to visible and ultraviolet light). The preferred adhesive compositions of the invention are also easily handled and processed because they can be mixed and then spread (e.g., coated) at a temperature that does not risk premature reaction of the polyepoxide curative (e.g., a temperature that is less than about 120°C, more preferably less than about 90°C, most preferably between about room temperature and 60°C).

Various aromatic polyepoxides may be used but those which are preferred include polyglycidyl ethers of novolacs and the diglycidyl ether of 4,4'- dihydroxydiphenyl dimethyl methane. Similarly, various heat activated curatives may be employed but aromatic polyamines such as fluorene diamines are preferred.

Thermoplastic polymers useful in the invention include polysulfone, poly(methyl methacrylate), phenoxy polymer, polycarbonate and blends of these materials. Preferably, the thermoplastic polymer has a glass transition temperature of about 90 to 200°C and a number average molecular weight of about 10,000 to 100,000. The thermoplastic polymer preferably comprises about 20 to 40 parts by weight per 100 parts by weight aromatic polyepoxide, more preferably about 20 to 30 parts by weight.

The polyfunctional (meth)acrylate is preferably an aromatic di(meth)acrylate and typically comprises about 5 to 20 parts by weight per 100 parts by weight aromatic polyepoxide. The optional though highly desirable bireactive compound usually comprises about 1 to 15 parts by weight per 100 parts by weight aromatic polyepoxide. The combined amount of the polyfunctional (meth)acrylate and the bireactive compound (if the latter is present) is preferably about 10 to 25 parts by weight (more preferably, about 15 to 20 parts by weight) per 100 parts by weight aromatic polyepoxide.

Upon exposure to electron beam irradiation, the polyfunctional

(meth)acrylate and the bireactive compound (if it is present) polymerize and crosslink to form a poly(meth)acrylate network, while the aromatic polyepoxide, the heat activated curative for polyepoxide, and, preferably, the thermoplastic polymer do not polymerize. As a result, the adhesive compositions can provide a heat curable adhesive bonding film that comprises:

a) a heat curable aromatic polyepoxide;

b) a heat activated curative for polyepoxide;

c) a thermoplastic polymer; and d) a (meth)acrylate polymer network that comprises the electron beam irradiation polymerization product of:

1 ) a polyfunctional (meth)acrylate; and

2) optionally, a compound that contains at least one

(meth)acrylate group and at least one group that is reactive with aromatic polyepoxide.

The preferred heat curable adhesive bonding films of the invention are easy to handle and demonstrate controlled flow during heat curing. After heat curing, the preferred adhesive bonding films of the invention have good adhesion to the substrates to which they have been applied and a high glass transition temperature.

The invention also relates to a method of making an adhesive bonding film. The method comprises the steps of:

a) providing an adhesive composition such as those described above;

b) forming a layer of the adhesive composition on a support surface

(for example a permanent backing or temporary carrier such as a release liner); and c) exposing the layer of the adhesive composition to electron beam irradiation to polymerize the polyfunctional (meth)acrylate and the optional bireactive compound (if present) but without causing reaction of the heat activated curative or the aromatic polyepoxide.

A heat curable adhesive bonding film results. A heat cured (i.e., thermoset) adhesive bonding film can be obtained by heating the heat curable adhesive bonding film for a time and at a temperature sufficient to cure the aromatic polyepoxide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one aspect, this invention pertains to adhesive compositions that comprise and, more preferably, consist essentially of:

a) an aromatic polyepoxide;

b) a heat activated curative for polyepoxide (sometimes referred to herein as the "heat activated polyepoxide curative" or the "polyepoxide curative"); c) a thermoplastic polymer;

d) a polyfunctional (meth)acrylate; and

e) optionally, a compound that contains at least one (meth)acrylate group and at least one group that is reactive with aromatic polyepoxide (this compound sometimes being referred to herein as the "bireactive compound").

The invention also relates to heat curable adhesive bonding films made from the adhesive compositions, as well as methods by which the films may be made. Briefly, and by way of example, the heat curable adhesive bonding film may be prepared by forming a layer of the adhesive composition on a support surface such as a permanent backing or a temporary carrier (e.g., a release liner), and then exposing the adhesive layer to electron beam irradiation. (The expressions "bonding film," "adhesive bonding film," and "heat curable adhesive bonding film" are used synonymously herein and refer to the adhesive composition after it has been formed into a film and exposed to electron beam irradiation but before the film has been heat cured.)

The invention further pertains to various articles that may be made with the adhesive compositions and the adhesive bonding films. In the manufacture of laminates, for example, adhesive bonding film is placed between two substrates and heat cured to a thermoset material (i.e., a crosslinked polymer network that does not flow or melt). (The expressions "final adhesive bonding film" and "heat-cured adhesive bonding film" are used synonymously herein and refer to an adhesive bonding film that has been heat cured to a thermoset material.)

Advantageously, the preferred adhesive compositions of the invention may be easily handled and processed. These compositions have a viscosity that permits them to be mixed and then coated at a temperature that does not risk premature reaction of the polyepoxide curative. Because the adhesive compositions of the invention include materials that polymerize when exposed to electron beam irradiation and do not rely on photopolymerization, the adhesive compositions advantageously do not require storage under "safe light" conditions.

The preferred heat curable adhesive bonding films of the invention are also easy to handle. These bonding films may be removed from a temporary carrier and placed on a substrate without wrinkling, tearing or permanently stretching (i.e., without a permanent change in size or thickness). Adhesive bonding films prepared from the preferred adhesive compositions of the invention may also demonstrate controlled adhesive flow during heat curing. In these bonding films, the adhesive flows sufficiently to wet the substrate surface to form an even bondline with uniform bond strength. However, the adhesive flow during heat curing is not excessive. For example, in manufacturing a laminate, the adhesive does not bleed out beyond the edges of the substrates or cause an uneven bondline, voids or inconsistent bond strengths. After heat curing, the adhesive bonding films of the invention have good adhesion to the substrates to which they have been applied. The preferred heat cured adhesive bonding films have a high glass transition temperature (usually, at least 120°C, preferably at least 140°C, more preferably at least 150°C, most preferably at least 160°C), which property can be used to provide thermally stable structural articles and laminates having reduced thermal expansion.

By "polyepoxide" is meant a compound that contains at least two 1,2- epoxide groups; i.e., groups having the structure

Aromatic polyepoxides are desired because they can impart high temperature performance properties (e.g., a high glass transition temperature) to the heat-cured adhesive bonding film and can impart structural properties thereto. Blends of different aromatic polyepoxides may be used.

Aromatic polyepoxides suitable for use in the adhesive compositions and the adhesive bonding films of the invention include polyglycidyl ethers of polyhydric phenols, for example pyrocatechol, resorcinol, hydroquinone, 4,4'- dihydroxydiphenyl methane, 4,4'-dihydroxy-3,3'- dimethyldiphenyl methane, 4,4'- dihydroxydiphenyl methyl methane, 4,4'-dihydroxydiphenyl dimethyl methane, 4,4'- dihydroxydiphenyl cyclohexane, 4,4'-dihydroxy-3,3'-dimethyldiphenyl propane, 4,4'- dihydroxydiphenyl sulfone, tris-(4-hydroxyphenyl)methane, 9,9-bis(4- hydroxyphenyl) fluorene and ortho-substituted analogs thereof, such as disclosed in U.S. Patent No.4,707,534, and the polyglycidyl ethers of the halogenation (e.g., chlorination and bromination) products of the above mentioned polyhydric phenols.

Other suitable aromatic polyepoxides include the polyglycidyl derivatives of aromatic amines (i.e., glycidylamines) obtained from the reaction between the aromatic amines and an epihalohydrin. Examples of such glycidylamines include N,N-diglycidyl aniline, N,N'-dimethyl-N,N'-diglycidyl-4,4'-diaminodiphenyl methane, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl methane,

N,N-diglycidylnapthalenamine (given the name of N-1-napthalenyl-N- (oxiranylmethyl)oxiranemethanamine by Chemical Abstracts 9th Coll. 8505F (1982- 1979)), N,N,N'N'-tetraglycidyl- 1,4-bis[(α-4-aminophenyl)-α-methylethyI]benzene, and N,N,N',N'- tetraglycidyl- 1 ,4-bis[α-(4-amino-3,5-dimethylphenyl)-[α- methylethyl]benzene. The polyglycidyl derivatives of aromatic aminophenols (e.g., glycidylamino-glycidyloxy benzene), as described in U.S. Patent No.2,951,825, are also suitable. An example of these compounds is N,N-diglycidyl- 4-glycidyloxybenzenamine.

Polyglycidyl esters of aromatic polycarboxylic acids, for example the diglycidyl esters of phthalic acid, isophthalic acid, or terephthalic acid, are also useful.

Preferably the aromatic polyepoxide is selected from one of the following : polyglycidyl ethers of novolacs (i .e., reaction products of monohydric or polyhydric phenols with aldehydes, formaldehyde in particular, in the presence of acid catalysts); or the diglycidyl ether of 4,4'-dihydroxydiphenyl dimethyl methane.

Examples of commercially available aromatic polyepoxides which may be used in the adhesive compositions and the adhesive bonding films of the invention include MY™-720 (Ciba-Geigy, Inc , Hawthorne, NY); ERL-0510 (Ciba-Geigy, Inc.), the EPON™ series of materials from Shell Chemical Co., Houston, TX (e.g., EPON HPT- 1071, EPON HPT- 1072, EPON HPT- 1079, and EPON 828); and the D.E.R.™, D.E.N.™ and QUATREX™ families of materials from Dow Chemical Company, Midland, MI (e.g., D.E.R.332, D.E.R.361 , D.E.N.438 and QUATREX 1010). While solid aromatic polyepoxide resins may be used, it is preferred that the polyepoxide or mixture of polyepoxides be essentially liquid at room temperature, by which it is meant that the viscosity of the polyepoxide (or polyepoxide mixture) permits mixing and then spreading (e.g., coating) at room temperature, or upon gentle warming to a temperature that does not risk premature reaction of the polyepoxide curative (e.g., room temperature to about 120°C). Liquid aromatic polyepoxides facilitate mixing and spreading the adhesive composition at low temperatures that do not activate the polyepoxide curative.

Preferably the aromatic polyepoxide (or polyepoxide mixture) has an average epoxide functionality of two to four, and, more preferably, an average epoxide functionality of two to three. This facilitates providing both an adhesive composition that can be mixed and spread without premature reaction of the heat activated curative, and a final adhesive bonding film that is sufficiently crosslinked. It is also preferred that the aromatic polyepoxide (or polyepoxide mixture) have an epoxy equivalent weight of about 80 to 200 grams per equivalent. This promotes the formation of adhesive compositions having a viscosity that permits efficient mixing and coating, and a final adhesive bonding film with an acceptably high glass transition temperature. For electronics applications it is further preferred that the aromatic polyepoxide contain low levels of ionic and hydrolyzable halide since these materials may cause corrosion in printed circuit board laminates made therewith.

The adhesive compositions of the invention also include a heat activated curative for polyepoxide. The heat activated curative may be dissolved or dispersed in the adhesive composition. The term "curative" is used broadly to include not only those materials that are conventionally regarded as curatives but also those materials that catalyze epoxy polymerization as well as those materials that may act as both curative and catalyst. Blends of different heat activated curatives may also be used. Examples of heat activated curatives useful in the adhesive compositions and the adhesive bonding films of the invention include polybasic acids and their anhydrides, for example, di-, tri-, and higher carboxylic acids such as oxalic acid, phthalic acid, terephthalic acid, succinic acid, alkyl substituted succinic acids, tartaric acid, phthalic anhydride, succinic anhydride, malic anhydride, nadic anhydride, pyromellitic anhydride; and polymerized unsaturated acids, for example, those containing at least 10 carbon atoms, such as dodecendioic acid, 10, 12- eicosadiendioic acid, and the like.

Other heat activated curatives which may be used in the invention include nitrogen-containing compounds such as dicyandiamide, melamine, ureas and aliphatic amines (e.g., diethylenetriamine, triethylenetetraamine, cyclohexylamine, triethanolamine, piperidine, tetramethylpiperamine, N,N-dibutyl-1,3-propane diamine, N,N-diethyl-1,3-propane diamine, 1,2-diamino-2-methyl-propane, 2,3- diamino-2-methyl-butane, 2,3-diamino-2-methyl-pentane, 2,4-diamino-2,6- dimethyl-octane, dibutylamine, and dioctylamine).

Also useful as curatives are chloro-, bromo-, and fluoro-containing Lewis acids of aluminum, boron, antimony, and titanium, such as aluminum trichloride, aluminum tribromide, boron trifluoride, antimony pentafluoride, titanium

tetrafluoride, and the like. It is also desirable at times that these Lewis acids be blocked to increase the latency of adhesive compositions containing them.

Representative of blocked Lewis acids are BF3-monoethylamine, and the adducts of

HSbF₅X, in which X is halogen, -OH, or -OR¹ in which R¹ is the residue of an aliphatic or aromatic alcohol, aniline, or a derivative thereof, as is described in U.S. Patent No. 4,503,21 1. Pyridine, benzyldimethylamine, benzylamine and

diethylaniline are also useful as heat activated curatives. Some of the curatives described herein are more typically used in combination with other curatives rather than being used alone.

Preferably the heat activated curative is an aromatic polyamine such as o-, m-, and p- phenylene diamine, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'- diaminodiphenyl sulfide, 4,4'-diaminodiphenyl ketone, 4,4'- diaminodiphenyl ether, 4,4'- diaminodiphenyl methane, 1,3-propanediol-bis-(4- aminobenzoate), 1,4-bis[α-(4-aminophenyl)-α-methylethyl]benzene, and 1,4-bis[α- (4-amino-3,5-dimethylphenyl)-α-methylethyl]benzene, bis α-(4- amino-3- methylphenyl)sulfone, 1, 1'-biphenyl-3,3'-dimethyl-4,4'-diamine, 1, 1'-biphenyl- 3,3'-dimethoxy-4,4'-diamine, and diaminonapthalenes. Most preferred as the heat activated curative is a fluorene diamine such as 9,9'-bis(4-aminophenyI)fluorene, 9,9'-bis(3-methyl-4-aminophenyl)fluorene, and 9,9'-bis(3-chloro-4-aminophenyl) fluorene.

Examples of commercially available heat activated curatives useful in the invention include EPON™ HPT- 1061 and EPON™ HPT- 1062 ( each from Shell Chemical Co.), HT-9664 (Ciba Geigy, Inc.), and AMICURE™ CG-1400 (Air Products, Pacific Anchor Chemical, Allentown, PA).

The heat activated polyepoxide curatives employed in the adhesive compositions and the adhesive bonding films of the invention do not react with polyepoxide when exposed to electron beam irradiation and, preferably, do not inhibit polymerization by the electron beam irradiation. The preferred heat activated curatives for use in the invention exhibit latent thermal reactivity; that is, they react primarily at higher temperatures (preferably a temperature of at least 120°C, more preferably at least 130°C, most preferably at least 140°C). This allows the adhesive composition to be readily mixed and coated at room temperature

(about 20 to 22°C) or with gentle warming without activating the curative (i.e., at a temperature that is less than the reaction temperature for the polyepoxide curative).

For electronics applications it is further preferred that the polyepoxide curative have little or no ionic or hydrolyzable halide as these may cause corrosion in printed circuit board laminates made therewith.

The adhesive compositions and the adhesive bonding films of the invention also include a thermoplastic polymer. By "thermoplastic" is meant a non- crosslinked polymer that can be repeatedly softened and reshaped upon the application of heat and pressure.

Preferably, the thermoplastic polymer is soluble in the aromatic polyepoxide before exposure to electron beam irradiation. The glass transition temperature of the thermoplastic polymer is preferably between about 90°C and 200°C so as to promote good high temperature performance properties when the adhesive composition is heat cured, such that the adhesive has enhanced utility in, for example, electronics applications. It is also preferred that the number average molecular weight of the thermoplastic polymer be about 10,000 to 100,000. If the number average molecular weight is much below about 10,000, then the adhesive composition is less likely to be able to form an easily handled bonding film. If the number average molecular weight is much above about 100,000, then the viscosity of the adhesive composition increases, making it more difficult to coat the adhesive into a film, and the solubility of the thermoplastic polymer in the aromatic polyepoxide decreases. Preferably the thermoplastic polymer is aromatic to provide more thermally stable adhesive bonding films. It is also preferred that the thermoplastic polymer not react when exposed to electron beam irradiation.

Thermoplastic polymers suitable for use in the adhesive compositions and the adhesive bonding films of the invention include polysulfones, such as those formed by copolymerizing 4,4'-dichlorodiphenyl sulfone and 2,2- bis(4-hydroxyphenyl) propane; poly( methyl methacrylate); phenoxy polymers, such as those formed by copolymerizing 2,2-bis(4-hydroxyphenyl) propane and its diglycidyl ether; polycarbonate; and blends of these materials.

Examples of commercially available thermoplastic polymers which may be used in the invention include PKHP™ 200 (Phenoxy Associates, Rock Hill, SC), PKHJ™ (Phenoxy Associates), UDEL™ 1700 and UDEL™3500 (each from Amoco Performance Products, Inc., Ridgefield, CT), PLEXIGLASS™ (Rohm & Haas, Philadelphia, PA) and LEXAN 141 (General Electric Co.).

The adhesive compositions and the adhesive bonding films of the invention also comprise a polyfunctional (meth)acrylate. By "(meth)acrylate" is meant a compound containing either acrylate or methacrylate moieties; that is, compounds having the group

wherein R is either hydrogen or methyl and R' is an organic radical. By

"polyfunctional" is meant compounds having at least two (meth)acrylate groups.

Polyfunctional (meth)acrylates useful in the invention are preferably difunctional, so as to provide di(meth)acrylates. When mixtures of different polyfunctional (meth)acrylates are employed, it is possible to use minor amounts of monofunctional (meth)acrylates to, for example, adjust the viscosity of the adhesive composition for easier coating. However, too much monofunctional (meth)acrylate may cause excessive adhesive flow during heat curing and/or reduced adhesion.

Both aromatic and aliphatic (meth)acrylates may be used. Preferably the (meth)acrylates are aromatic to improve both solubility in the aromatic polyepoxide before exposure to electron beam irradiation and the thermal stability of the heat cured adhesive bonding film. The preferred polyfunctional (meth)acrylates are soluble in the aromatic polyepoxide prior to electron beam irradiation. It is also preferred that the polyfunctional (meth)acrylate be essentially liquid at room temperature as this facilitates mixing and coating the adhesive composition. Solid polyfunctional (meth)acrylate may be used if the adhesive composition can be mixed and coated at room temperature or with gentle warming.

Examples of suitable polyfunctional (meth)acrylates useful in the invention include bisphenol A epoxy di(meth)acrylate, ethoxylated bisphenol A

di(meth)acrylate, pentaerythritol tetra(meth)acrylate, diethylene glycol

di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, epoxy novolac poly(meth)acrylates, and the like. Preferred polyfunctional (meth)acrylates include the bisphenol A-based di(meth)acrylates such as bisphenol A epoxy di(meth)acrylate and ethoxylated bisphenol A

di(meth)acrylate.

Examples of commercially available polyfunctional (meth)acrylates which are suitable for use in the invention include the SARTOMER™ series of materials from Sartomer Co., Exton, PA, such as SARTOMER 205, SARTOMER 231, SARTOMER 238, SARTOMER 239, SARTOMER 348 and SARTOMER 349, and the EBECRYL™ family of materials from UCB Radcure, Inc., Smyrna, GA, such as EBECRYL 600, EBECRYL 616 and EBECRYL 639.

The adhesive compositions and the adhesive bonding films of the invention optionally, though quite desirably, may include a bireactive compound; i.e., a compound containing at least one (meth)acrylate group and at least one group that is reactive with aromatic polyepoxide. The bireactive compound may improve the adhesion of the final adhesive bonding film. The bireactive compound should be soluble in the aromatic polyepoxide prior to electron beam irradiation. Both aromatic and aliphatic bireactive compounds may be used. Preferably, however, the bireactive compound is aromatic to improve both its solubility in the aromatic polyepoxide prior to electron beam irradiation and the thermal stability of the final adhesive bonding film. It is also preferred that the bireactive compound be essentially liquid at room temperature to facilitate mixing and coating of the adhesive composition. However, solid polyfunctional bireactive compound may be used if the adhesive composition can be mixed and coated at room temperature or with gentle warming.

Examples of groups reactive with polyepoxide for use in the bireactive compound include hydroxyl, carboxyl, amine (preferably aromatic amine), and 1,2- epoxide. Specific examples of bireactive compounds that may be used in the invention include carboxylic acid functional acrylates such as (meth)acrylic acid, and phenyl-containing hydroxy-functional (meth)acrylates such as 2-hydroxy- 3-phenoxypropyl (meth)acrylate and 2-hydroxy-3- phenylphenoxy (meth)acrylate. Also useful are the di(meth)acrylates described previously as suitable polyfunctional (meth)acrylates but in which one of the (meth)acrylate groups has been replaced with a group reactive with polyepoxide, examples of such materials including glycidyl (meth)acrylate, epoxy novolac (meth)acrylate, triethylene glycol

(meth)acrylate, and the like. Especially preferred as the bireactive compound are mono(meth)acrylates of various polyepoxide resins such as bisphenol A epoxy mono(meth)acrylate and the like. Examples of suitable commercially available bireactive compounds that may be used in the invention include EBECRYL™ 3605 (UCB Radcure Inc.) and SARTOMER™ 379 (Sartomer Co.).

The heat activated curative is employed in a curatively effective amount so as to provide the desired high temperature performance properties in the final adhesive bonding film, the desired performance depending on the intended use for the adhesive bonding film. The actual amount of curative employed will also be influenced by the types and amounts of other components in the mixture. Small amounts of curative may result in a heat cured adhesive bonding film that has a low glass transition temperature, a high coefficient of thermal expansion, and reduced solvent resistance. Large amounts of curative, in addition to causing very rapid curing with potentially uncontrolled heat build-up, may result in a final adhesive bonding film that absorbs too much moisture, is brittle, or has a low glass transition temperature.

Within these parameters, the curative is typically used in an amount of about 2 to 1 10 parts by weight, per 100 parts by weight of the aromatic polyepoxide. When the curative is based on a Lewis acid, it is typically used at a level of about 0.1 to 5 parts by weight, per 100 parts by weight of the aromatic polyepoxide. When the curative is a carboxylic acid, an anhydride, or a primary or secondary amine, the curative typically comprises about 0.5 to 1.7 equivalents of acid, anhydride, or amine, per equivalent of epoxy group. With anhydride curatives, an optional accelerator, in the range of about 0.1 to 5 parts by weight, per 100 parts by weight of the aromatic polyepoxide, may be present; e.g., an aromatic tertiary amine such as benzyldimethyl amine, or an imidazole such as 2-ethyl-4- methylimidazole.

The thermoplastic polymer is used in an effective amount, by which is meant an amount that is sufficient to provide an adhesive composition that can be mixed and then spread (e.g., by coating), without premature reaction of the polyepoxide curative, into an easily handled bonding film that can be subsequently heat cured with controlled adhesive flow.

Quite advantageously, the adhesive compositions of the invention need only contain small amounts of thermoplastic polymer. The typical amount of thermoplastic polymer is preferably about 20 to 40 parts by weight, more preferably about 20 to 30 parts by weight, per 100 parts by weight of the aromatic

polyepoxide, although the actual amount will vary depending on the type and amount of other constituents of the adhesive composition as well as the ultimate intended use for the adhesive. Above about 40 parts by weight thermoplastic polymer, the mixing and spreading temperatures for the adhesive composition may increase to the point where premature heat curing can occur and an adhesive bonding film formed therefrom may be too brittle for easy handling. Below about 20 parts by weight thermoplastic polymer, an adhesive bonding film may be difficult to handle and there may be too much adhesive flow during heat curing. The polyfunctional (meth)acrylate is used in an effective amount, by which is meant an amount that is sufficient to provide an adhesive composition that can provide an easily handled bonding film that can be subsequently heat cured with controlled adhesive flow. Within these parameters, the polyfunctional

(meth)acrylate is preferably used in amount of about 5 to 20 parts by weight, per 100 parts by weight of the aromatic polyepoxide, more preferably about 12 to 20 parts by weight, although the actual amount will vary depending on the type and amount of other constituents of the adhesive composition as well as the ultimate intended use for the adhesive. When less than about 5 parts by weight are employed, an adhesive bonding film formed therefrom may be difficult to handle, and there may be too much adhesive flow during heat curing. When more than about 20 parts by weight are used, an adhesive bonding film may be difficult to handle, and heat curing may generate a composition having low adhesion and reduced stability under elevated temperatures (such as encountered during soldering of printed circuit boards).

The bireactive compound, when present, is used in an effective amount, by which is meant an amount that is sufficient to provide an adhesive composition that can yield an easily handled bonding film that can be subsequently heat cured with controlled adhesive flow. Within these parameters, the bireactive compound is preferably used in amount of about 1 to 15 parts by weight, more preferably about 4 to 10 parts, although the actual amount will vary depending on the type and amount of other constituents of the adhesive composition as well as the ultimate intended use for the adhesive. At less than about 1 part by weight, a heat cured adhesive bonding film formed therefrom may lose adhesion. At more than about 15 parts by weight, an adhesive bonding film may be difficult to handle and there may be too much adhesive flow during heat curing.

Effective amounts of the polyfunctional (meth)acrylate and bireactive compound (when present) may also be determined by the amounts used in combination, an effective combined amount of these two materials being sufficient to provide an adhesive bonding film that can be easily handled and which heat cures to a thermally stable material having good adhesive strength. Generally, about 10 to 25 parts by weight, per 100 parts by weight of the aromatic polyepoxide, of the polyfunctional (meth)acrylate and bireactive compound are used, more preferably about 15 to 20 parts by weight, although the actual amount will vary depending on the type and amount of other constituents of the adhesive composition as well as the ultimate intended use for the adhesive. When the combined amount of the polyfunctional (meth)acrylate and the bireactive compound is less than about 10 parts by weight, an adhesive bonding film formed therefrom may be difficult to handle. When the combined amount of the polyfunctional (meth)acrylate and bireactive compound exceeds about 25 parts by weight, an adhesive bonding film may be susceptible to tearing and a heat cured adhesive bonding film may have reduced thermal stability and low adhesion.

The weight ratio of polyfunctional (meth)acrylate to bireactive component (when present) can range from about 95:5 to 50:50. More preferably, it is about 80:20 to 50:50, and most preferably it is about 80:20 to 75:25. At a weight ratio above about 95:5, an adhesive bonding film made therewith may be difficult to handle and a heat cured adhesive bonding film may have low adhesion. At a weight ratio below about 50:50, an adhesive bonding film may be difficult to handle and there may be too much adhesive flow during heat curing.

Various additives may be usefully incorporated into the adhesive

compositions and the adhesive bonding films of the invention to impart certain desirable properties thereto. Suitable additives include flame retardants, electrically conductive particles, thermally conductive particles, pigments, hollow or solid microspheres which may be either polymeric or inorganic, inorganic fillers, antioxidants, and woven or nonwoven fibers such as those made from carbon, glass, or polyaramide materials.

The adhesive compositions and the adhesive bonding films of the invention are easily prepared. The various ingredients may be blended by an extruder, a planetary mixer, or a heated mogul to form a mixture having a coatable viscosity. The ingredients should be added sequentially. Preferably the aromatic polyepoxide and the thermoplastic polymer are blended into a solution, followed by the addition of the polyfunctional (meth)acrylate and the bireactive compound (if included), with the curative being added last. No solvents are required. Thus, the adhesive compositions of the invention may be provided as 100% solids mixtures.

Preferably and quite advantageously, the aromatic polyepoxide, the thermoplastic polymer, the polyfunctional (meth)acrylate, and the bireactive compound (if present) are selected so as to be soluble in each other. The heat activated curative may be dissolved or dispersed in these components. By soluble it is meant that to the naked eye there is no visible evidence of phase separation at room temperature after combining the soluble materials (using heat as necessary) and returning the mixture to room temperature. Lack of solubility may be evidenced by inconsistent bond strengths, poor film handling characteristics, low adhesion and poor adhesive flow control. The ingredients comprising the adhesive composition (except for the polyepoxide curative if it is dispersed) remain soluble after mixing and spreading into a film.

Since the adhesive compositions of the invention do not rely upon exposure to actinic radiation to form an adhesive bonding film, the compositions do not require a photocatalyst. Consequently, the adhesive compositions and the adhesive bonding films of the invention are photostable. That is, they are sufficiently unreactive when exposed to visible or ultraviolet light that packaging and storage under "safe light" conditions (e.g., storage in containers that are not transparent to visible and ultraviolet light) would not be considered necessary.

Once the various ingredients have been mixed, a transfer article may be provided by spreading (e.g., by coating) the adhesive composition as a film onto a single removable release liner or between two release liners (which may have the same or different release values). Useful release liners include siliconized paper and plastic films. Alternatively, the adhesive composition may be coated onto a permanent backing, which may be formed of a material such as polyolefin, polyester, polyimide, or paper. Priming of the backing using, for example, chemical primers or corona discharge may be used as needed. The exposed adhesive surface may be protected by a removable release liner such as those mentioned above. In another embodiment, a fiber reinforced composite article may be prepared by applying a layer of the adhesive composition to a woven or nonwoven fibrous support surface (e.g., fibers of carbon, glass, aramide, polyester or polyimide); for example, to impregnate the support with the adhesive composition.

The adhesive compositions of the invention may be spread into a film by various techniques including coating methods such as heated knife-over-bed, roll and die coating. Advantageously, the adhesive compositions can be coated at relatively low temperatures (i.e., about room temperature to about 120°C), preferably about 30 to 120°C, more preferably about 30 to 90°C, most preferably about 30 to 60°C, so as to inhibit premature reaction of the heat activated polyepoxide curative. Coating thicknesses may range from about 10 to 130 μm or thicker.

Once the adhesive composition has been spread into film form, it is subjected to electron beam irradiation for a time and at an exposure level sufficient to cause polymerization and crossiinking of the (meth)acrylate moieties in the polyfunctional (meth)acrylate and in the bireactive compound (when present), but without causing reaction of the heat activated curative, the aromatic polyepoxide, or, preferably, the thermoplastic polymer. Typical irradiation conditions are about 2 to 10 Megarads (Mrads). A 5 Mrad dose is useful. The adhesive bonding films may be tacky to the touch or not, depending on the particular composition.

Exposure to electron beam irradiation forms a (meth)acrylate polymer network in the unreacted aromatic polyepoxide because the (meth)acrylate functional components are soluble in the aromatic polyepoxide prior to irradiation. The (meth)acrylate polymer network and the thermoplastic polymer contribute to the preferred easily handled adhesive bonding films of the invention. These adhesive bonding films can be removed from a temporary carrier (e.g., a release liner) and placed on a substrate without wrinkling, tearing or permanently stretching (i.e., without a permanent change in size or thickness). The adhesive bonding films may be removed from the temporary carrier either manually or by automated machine, although the former method may require films with superior handling properties due to the inconsistency of the stresses applied to the film during removal. An adhesive bonding film with acceptable handling characteristics is facilitated by having a modulus of about 1 to 300 MegaPascals (MPa) after exposure to electron beam irradiation, and a glass transition temperature of about 20°C or less.

The adhesive bonding films of the invention may be used to bond a diverse variety of materials including woven and nonwoven fibers (e.g., glass, carbon and aramide), metals (e.g., aluminum, stainless steel and copper), plastics (e.g., polyimide and polyester), and ceramics. The adhesive compositions and bonding films of the invention are useful for providing composite articles reinforced by fiber webs or tows, and in general industrial bonding applications such as the preparation of structural (i.e., high strength) laminates. The adhesive bonding films are especially useful in the electronics industry. One particularly preferred utility is the construction of laminated printed circuit boards where the adhesive bonding film is used to laminate copper clad polymeric (e.g., polyimide) substrates containing etched circuitry. Other particularly preferred utilities include bonding integrated circuit chips and flexible circuits to rigid printed circuit boards as well as bonding printed circuit boards to each other.

When the adhesive has been prepared between two release liners to give a transferable adhesive bonding film, one release liner is removed, the adhesive bonding film is placed on the substrate to be bonded, the second release liner is removed, and the second substrate is positioned on the adhesive. When the adhesive includes a permanent backing (which provides one substrate) and a protective release liner, the latter is removed and the adhesive layer is positioned against the second substrate.

Once the adhesive bonding film has been properly positioned with respect to the substrates to be bonded, it is heated for a time and at a temperature sufficient to cure the aromatic polyepoxide, the actual time and temperature depending on the specific components in the adhesive composition and the substrates to be bonded. In general, temperatures of about 50 to 250°C, and cure times of about 20 seconds to 5 hours may be used, higher temperatures usually requiring less cure time than lower temperatures. Cure conditions of 180°C for 90 minutes are useful.

The previously polymerized and crosslinked (meth)acrylate polymer network along with the thermoplastic polymer provide the preferred adhesive bonding films of the invention with controlled adhesive flow during heat curing, which results in uniform bond lines and bond strengths. The heat cured adhesive bonding films can possess high temperature performance properties which are not significantly different from those of heat-cured epoxy resins that are free from (meth)acrylate-containing components. Thus, the heat cured adhesive bonding films can tolerate exposure to elevated temperatures such as those encountered during soldering of printed circuit boards.

The invention will be more fully appreciated with reference to the non- limiting examples that follow. The general techniques used to prepare and test the adhesive compositions, the adhesive bonding films and the laminates made therefrom will now be described. Dimensions are nominal and conversion of English units to metric units is approximate.

General Preparation of Adhesive Compositions, Adhesive Bonding Films and

Laminates

General Preparation of Adhesive Compositions

The aromatic polyepoxide was heated for 60 seconds in a 950 Watt microwave oven operating at it highest setting (Model R E53C 002, Hotpoint brand, Hotpoint Company, Louisville, KY) to provide a pourable viscosity for easy weighing and transfer. The resin temperature never exceeded 70°C. The thermoplastic polymer was dissolved in the aromatic polyepoxide at a resin temperature of 120°C using a 0.2 liter metal can, an air stirrer, and a hot plate. The time required for dissolution was typically 20 to 30 minutes. Dissolution was detected by the formation of a clear, homogenous solution.

The polyfunctional (meth)acrylate and bireactive compound (when included) were combined with the aromatic polyepoxide/ thermoplastic polymer blend using either a low speed mixing process or a high speed mixing process.

In the low speed mixing process, the polyfunctional (meth)acrylate and bireactive compound were separately preheated in an air convection oven set at

70°C until they reached a pourable viscosity. These ingredients were then weighed into an 8 ounce glass jar and mixed by hand using a wood tongue depressor. The aromatic polyepoxide/thermoplastic polymer blend was also preheated in an air convection oven set at 70°C until it reached a pourable viscosity, at which time it was added to a 60 gram capacity Plasti-corder PL-2000 mixer (C. W. Brabender Instruments, Inc., Hackensack, NJ) that had been fitted with cam style mixing blades and preheated to 60°C. The mixing speed was 30 revolutions per minute (rpm) during this and all subsequent material additions. After 1 to 2 minutes, the preheated polyfunctional (meth)acrylate/bireactive compound blend was added with further mixing at 60°C for 1 to 2 minutes. Next, the polyepoxide curative was added slowly, in tablespoon portions, with stirring between each addition. Each portion of the curative was thoroughly dispersed to eliminate all visible "clumps" before adding the next portion. After all of the curative had been added, the mixing speed was increased to 100 rpm for 5 minutes.

The high speed mixing process allowed for more rapid sample preparation. More specifically, the polyfunctional (meth)acrylate and bireactive compound were hand blended at room temperature using a wood tongue depressor. The aromatic polyepoxide/thermoplastic polymer blend was heated for 15 seconds in a 720 Watt microwave oven operating at its highest setting (Model ERS-6831B, Toshiba brand, Toshiba America, Wayne, NJ), removed, briefly stirred by hand with a wood tongue depressor, and then heated again for another 15 seconds to provide a pourable viscosity for easy weighing and transfer. The blend temperature never exceeded 70°C. The pourable aromatic polyepoxide/thermoplastic polymer blend was weighed into a 0.05 liter plastic mixing cup, followed by addition of the polyfunctional (meth)acrylate/bireactive compound blend. These ingredients were thoroughly mixed at room temperature for about 30 seconds using a Cordless Driver Drill (Model 621 1DW, Makita Corporation, Japan) fitted with a metal spatula and operating at 1 100 rpm. Next, the complete amount of polyepoxide curative was added to the plastic cup and blended at high speed for no more than about 2 minutes using the cordless drill until there no visible clumps and the curative was thoroughly dispersed. The contents of the mixing cup were occasionally warmed for 5 to 10 second intervals, using the microwave oven as described for the high speed mixing method.

General Preparation of Adhesive Bonding Films

Adhesive bonding films were prepared by coating the adhesive compositions and then exposing the coated adhesives to electron beam irradiation.

More specifically, the adhesive compositions were coated using a knife- over-bed, 6 inch wide, heated coating station. The knife was locked in position to maintain a fixed gap. The bed and knife each contained heating elements, and the area behind the knife, where the adhesive was placed, was fitted with a radiant heater. There were two heating elements (Watlow Firerod cartridge heaters, model G5A1 15, 125 Watt; Watlow, St. Louis, MO) in the bed, and three heating elements (Watlow band heaters, Model STB 1E1E2) wrapped 3/4 around the outside circumference of the knife. One thermocouple was mounted on the side of the bed beneath the knife, and another was in contact with the surface of the radiant heater. The bed and knife heaters were controlled by one Watlow Series 965 temperature controller set at 65°C, and the radiant heater by another set at 140°C. The knife gap was set, using a feeler gauge, at 0.002 in. (50 μm) greater than the combined thickness of the two release liners employed.

The adhesive composition was warmed for 15 seconds in a microwave oven, as described above in the high speed mixing method, to make it pourable. The adhesive composition was then poured between two 0.002 in. (50 μm) thick, silicone coated, polyester release liners. After positioning the radiant heater over this "sandwich" construction, the temperature was allowed to equilibrate for 0.5 to 1.0 minute until the adhesive composition was visually determined to have acquired a coatable viscosity. The release liners with adhesive composition therebetween were then pulled between the knife and bed forcing the adhesive under the knife.

The coated adhesives were exposed to electron beam irradiation, from one side, through the release liner, using an Electro Curtain Model CB300/30/380 (titanium window: 2.5 in. (6.4 cm) long, 14 in. (36 cm) wide. Energy Sciences, Inc., Wilmington, MA) device operating at a speed of 25 feet (7.6 meters)/minute to provide adhesive bonding films according to the invention. The electron beam processing was performed under a nitrogen purge at room temperature using an electron accelerator operating at 250 kiloVolts and 5 milliAmperes (dose = 5 Megarads). The total exposure time was about 0.5 second.

General Preparation of Laminates

The adhesive bonding films were used to make copper clad polyimide film laminates. All copper, polyimide film, release liner, and metal plate surfaces were wiped with a tack cloth or Kimwιpes™-EX-L Delicate Task Wipers (Kimberly- Clark Corporation, Atlanta, GA) to remove dust prior to use.

More specifically, the laminates were prepared by cutting a pair of approximately 0.002 in (50 μm) thick adhesive bonding films to 5 in x 5 in ( 13 cm x 13 cm) and exposing one surface of each bonding film by removing one of the release liners An adhesive bonding film was placed on each side of a 6 in. x 6 in. x 0.001 in. thick ( 15 cm x 15 cm x 25 μm thick) piece of Kapton FPC-ZT polyimide film (E. I . duPont deNemours and Company, Wilmington, DE) The second release liner was removed from each adhesive bonding film and the adhesive-covered polyimide film was then placed between two layers of 1 ounce copper foil measuring 6.5 in x 6.5 in ( 16.5 cm x 16.5 cm) (Class 3 type from Oak-Mitsui, TOB finish) The copper foil layers were oriented such that the grain direction was the same on both sides.

The layup of copper foil/adhesive bonding film/polyimide film/adhesive bonding film/copper foil was positioned between two release liners (Tedlar™MR, from E.I. duPont deNemours and Company) each measuring 7 in. x 7 in. (17 cm x 17 cm). A stack comprising from two to six such layups, a metal separator plate between each layup, a metal base plate, and a metal top plate was assembled. The base plate measured 8 in. x 8 in. (20 cm x 20 cm), the top and separator plates were each 6 in x 6 in ( 15 cm x 15 cm). All plates had a thickness between 0 040 and 0 062 inches ( 1.02 to 1 57 mm). One of two different lamination methods was then employed to heat cure the adhesive bonding film. In both cases an 8 in. x 8 in. (20 cm x 20 cm) single opening lamination press (Pasadena Hydraulics, Inc. (PHI), City of Industry, CA, Model TS-21-H-C-8, with a DT5000 temperature

controller/programmer) was used. After heat curing, the laminates were trimmed to 4.5 in. x 4.5 in. ( 1 1.4 cm x 1 1.4 cm).

In one lamination method (referred to herein as lamination method A), the stack was placed in the press at room temperature. A pressure of 50 pounds/inch^ was applied immediately, and heating to 180°C at 5°C/minute begun. The stack was held at 180°C for 90 minutes, after which the heated platens were internally cooled with tap water back to room temperature over a period of 5 minutes.

The second lamination method (referred to herein as lamination method B) was the same as lamination method A, except that the press was programmed to heat to 190°C and the stack was held at that temperature for 30 minutes. After cooling to room temperature, the laminates were transferred to a preheated air convection oven and post-cured at 180°C for 90 minutes. Test Methods

Glass Transition Temperature (Tg)

A single cell differential scanning calorimeter (DSC) (Model 2920, TA Instruments, New Castle, DE) was used to measure the Tg of the heat-cured adhesive bonding film. About 5 to 15 milligrams of the adhesive bonding film was placed in a DSC sample pan, sealed and heat-cured in a preheated convection air oven at 180°C for 90 minutes. The sample was then scanned under a helium purge from 40 to 250°C at a rate of 20°C/ minute. The Tg was taken as the half-height of the transition on the first scan. Reported values are rounded to the degree. Peel Adhesion Strength

The peel strength of the laminates was measured using The Institute for Interconnecting and Packaging Electronic Circuits (IPC) Test Method-650, Number 2.4.9, Revision D ( 10/88): "Peel Strength, Flexible Printed Wiring Materials, Method A (with Sliding Plate Test Fixture)" except with the following

modifications: the laminate dimensions were 2.25 in. x 2.75 in. (5.72 cm x 6.99 cm); three peel strips were tested; data ( 120 data points) were collected over a 2.0 in. (5.1 cm) distance for each peel strip, and the first and last 0.17 in. (0.43 cm) (20 data points each) for each peel strip were discarded prior to analysis by a Mitutoyo Digimatic Mini-Processor (Model DP-2 DX). The average peel strength of each peel strip was used to calculate an overall average value for the three peel strips, which is reported to the nearest 0.1 pound per inch width (piw).

The peel adhesion test samples were prepared by etching peel strips on one side of the laminate. One side of the laminate was completely covered with 3 in. (7.6 cm) wide 3M Scotch™ 1280 Circuit Plating Tape. The other side of the laminate was cleaned and roughened using a wet Heavy Duty 3M Scotch-B rite™ Scour Pad (catalog # 220) and then dried with a paper towel. A single additional piece of 3M Scotch™ 1280 Circuit Plating Tape was used to seal the edge of the longer side of the laminate and to form a border along the length of the roughened surface of the laminate (a separate piece of tape being used for each of the two sides). Next, 0.125 in (0 318 cm) wide strips of 3M Scotch™ 218 Fine Line Tape were used to mask off 8 parallel test strips, spaced 0.125 in. (0.318 cm) apart, down the length of the roughened surface of the sample. A tongue depressor was used to gently rub the Fine Line Tape so as to remove all voids and completely wet the copper surface with the tape adhesive. This was visible as a darkening of the surface under the tape.

The taped laminates were etched for 3 minutes using a KEPRO Bench-Top

Etcher (Model BTE-202, KEPRO Circuit Systems, Inc., Fenton, MO) containing ferric chloride etchant (catalog # E- 4G, KEPRO Circuit Systems, Inc.) at 43°C and a pH of 1 to remove unmasked copper. If copper still remained on the unmasked areas of the laminate, the laminate was rotated 180° in the sample holder and etched for an additional 1 minute to completely remove the remaining unmasked copper. The etched sample was then removed, rinsed first in a bath of tap water for 1 minute, then rinsed again under running tap water for 1 minute, and then air dried. All tape was removed from the sample without bending or damaging the sample.

The etched laminates were tested using a Copper Clad Peel Tester (Model TA- 630; CECO Industries, Anaheim, CA) fitted with a 2 pound force gauge.

Samples were mounted onto the sliding holding stage with the copper test strips facing up. The laminate was aligned and held in place by a slotted cover plate that was securely fastened to the holding stage. The copper test strip on the laminate was positioned directly under the 0.188 in. (0.476 cm) wide slot and attached through the slot to the force gauge. The sliding holder and force gauge were at an angle of 90° to each other. The sample was peeled at a rate of 2 in. (5 cm)/minute. For electronic applications it is preferred that the peel adhesion be at least 6.0 piw, more preferably at least 8.0 piw. For other applications, less peel adhesion may be acceptable. Film Handling

The adhesive bonding films were evaluated for their film handling characteristics by removing a 0.5 in. x 5.0 in. ( 1.3 cm x 12.7 cm) sample from the release liners, taking it between the thumb and forefinger of both hands with a 1 in. (2.5 cm) gap, and stretching until it broke. The resistance to stretching and tearing were qualitatively determined and given a relative grading.

Adhesive bonding films graded triple plus (+++) exhibited moderate resistance to stretching and tearing. Removal of, or from, the release liner was readily accomplished without wrinkling, tearing or permanent stretching (i.e., without a permanent change in size or thickness) of the film. The adhesive bonding films could be easily handled by either automated machine or manual methods.

Adhesive bonding films graded double plus (++) had either less resistance to stretching or less resistance to tearing as compared to the (+++) samples. Removal of, or from, a release liner without wrinkling, tearing or permanent stretching of the adhesive bonding film would be best accomplished by either automated machine methods or careful manual handling.

Adhesive bonding films graded single plus (+) were deemed suitable for use only by automated machine handling methods to ensure removal from the release liner without wrinkling, tearing or permanent stretching of the adhesive bonding film because of the lower resistance to stretching as compared to the triple plus and double plus rated films.

Adhesive bonding films rated single, double or triple plus were useful as transfer films (i.e., adhesive bonding films carried between a pair of release liners or other temporary carriers) or for use in conjunction with a permanent backing Adhesive bonding films graded double or triple plus were also useful as freestanding films, i.e., an adhesive bonding film that can be physically removed from and handled free of a support (e.g., a release liner or other temporary carrier) Adhesive bonding films that wrinkled, tore, crumbled or permanently stretched upon removal of, or from, the release liners were graded minus (-) and were considered difficult to remove by either automated machine or manual methods but could be useful for direct lamination to a permanent backing (especially those which are porous) without first removing the film from the release liner.

The handling characteristics for some of the adhesive bonding films were also evaluated by measuring their modulus. More specifically, a Thermomechanical Analyzer (TMA), Model 2940 (TA Instruments, Inc.) was used to obtain Young's modulus at room temperature Sample dimensions were length = 0.16 to 0.50 in. (4.0 to 12.7 mm), and thickness = approximately 0.002 in (50 μm). The width:length ratio was maintained at 1 :6, or greater (e.g., 1 :8), in order to meet test requirements. The sample was put under an applied force (stress) of 0.001 Newton and the initial length was measured. The force was then increased to 1.0 Newton at a rate of 1.0 Newton/minute and the change in length (strain) was recorded. The length of the sample was selected such that the sample broke at 1 Newton or less of applied force. The modulus was calculated from the initial slope of the stress vs strain curve and is reported to the nearest 0.1 MPa Preferably, the modulus of the adhesive bonding films of the invention is between about 1 and 300 MPa for good film handling characteristics.

Adhesive Flow

During heat curing the adhesive composition flows. Some adhesive flow is desirable to wet the substrate surface and to form an even bondline with uniform bond strength. However, extensive adhesive flow during heat curing such that the adhesive bleeds out beyond the edges of the substrates or may cause an uneven bondline, voids or inconsistent bond strengths should be avoided in the manufacture of laminates. However, the amount of adhesive flow which can be tolerated depends on the ultimate use for the adhesive composition. For example, if the adhesive composition or adhesive bonding film is used to impregnate a fibrous reinforcing web or tow, a larger amount of adhesive flow may be permissible.

The degree of adhesive flow was determined by visual examination of the laminate after removal from the press and before trimming for the peel adhesion test. The grading described below is relative.

More specifically, the distance between the initially centered adhesive bonding film (before heat curing) and the outer edge of the copper foil was 0.75 in. ( 1.91 cm). If the adhesive flow, after heat curing, was 0.50 in. ( 1.27 cm) or more from the outer edge of the copper foil, a double plus (++) rating was assigned, indicating a low degree of adhesive flow. If the adhesive was between 0.50 in. ( 1.27 cm) and 0.125 in. (0.32 cm) from the outer edge of the copper foil, a single plus (+) rating was given, indicating a moderate degree of adhesive flow. Both single plus and double plus ratings represent the best adhesive flow control properties for use in bonding applications where this property is important. A minus (-) rating, indicating increased adhesive flow, was given when the adhesive was closer than 0.125 in. (0.32 cm) to the outer edge of the copper foil, or had advanced beyond the foil edge.

Glossary

Various abbreviations are used in the following examples. The

abbreviations are defined according to the following schedule: CAF - 9,9'-bis(3-chloro-4-aminophenyl)fluorene

CG- 1400 - dicyandiamide (available from Air Products)

D.E.H.™ 85 - phenol curing agent (available from Dow Chemical Company.)

D.E.N.™ 438 (available from Dow Chemical Company)

D.E.R.™ 332 - diglycidyl ether of bisphenol A (available from Dow Chemical Company) EBECRYL™ 3605 - mono-acrylate of diglycidyl ether of bisphenol A (available from UCB Radcure, Inc.)

EPON™ 828 - diglycidyl ether of bisphenol A (available from Shell Chemical

Company)

GMA - glycidyl methacrylate (available as SARTOMER™ 379 from Sartomer

Company)

HDDA - 1,6-hexanediol diacrylate (available as SARTOMER™ 238 available from

Sartomer Company)

IBA - isobornyl acrylate (available from San Esters Corporation, New York, NY) IBMA - isobornyl methacrylate (available as SARTOMER™ 423 A from Sartomer

Company)

P3500 - Udel™ P3500 poly(ether-sulfone) (available from Amoco Performance

Products, Inc.)

PEA - 2-phenoxy ethyl acrylate (available from CPS Chemical Company, Old Bridge, NJ)

PhEMA - 2-phenoxy ethyl methacrylate (SARTOMER™ 340 available from

Sartomer Company)

PKHJ™ - phenoxy resin (available from Phenoxy Associates)

PMMA - poly(methyl methacrylate) (molecular weight = 33,000; available from Scientific Polymer Products, Inc., Ontario, NY)

PolyEMA - poly(ethyl methacrylate) (available from Aldrich Chemical Company, catalog # 18,208-7)

QUATREX™ 1010 - diglycidyl ether of bisphenol A (available from Dow Chemical

Company)

TEGDMA - triethylene glycol dimethacrylate (available as SARTOMER™ 205 from Sartomer Company)

THFA - tetrahydrofuran acrylate (available from San Esters Corporation)

ULTEM™ 1000 - poly(ether-imide) (available from General Electric Company and subsequently converted to fine particles having a size of about 5μm or less by an emulsion precipitation process such as described in U.S. Patent No. 5,276, 106.) XU AY 238 - a hydantoin epoxy (available from Ciba Geigy, Inc. under the ARACAST™ tradename).

Unless noted otherwise, in the following examples all amounts are given in parts; i.e., parts by weight per 100 parts by weight aromatic polyepoxide rounded to the nearest whole number.

Examples 1 to 17

A series of laminates was prepared as described above in the "General Preparation of Adhesive Compositions, Adhesive Bonding Films and Laminates" and as shown below in Table 1 Based on the descriptions given above, Table 1 indicates the lamination method and the mixing method, the latter being identified as either "HS" (high speed) or "LS" (low speed) In each example, the adhesive composition comprised D E R™ 332 aromatic polyepoxide, CAF heat activated aromatic polyepoxide curative, PKHJ™ thermoplastic polymer, a polyfunctional (meth)acrylate provided by a 90:10 (wt. /wt.) blend of the dimethacrylate of diglycidyl ether of bisphenol A and TEGDMA, and EBECRYL 3605 bireactive compound. The relative amount of each component is shown below in Table 1. The combined amount of the polyfunctional (meth)acrylate and the bireactive compound was varied although the weight ratio of these two components was kept constant at 80 :20. Examples 1 to 8 contain 30 parts by weight thermoplastic polymer, examples 9 to 12 contain 25 parts by weight, and examples 13 to 17 contain 20 parts by weight.

Various examples were evaluated for one or more of the following properties using the test methods described above and with the results shown below in Table 1 : film handling, modulus (in MegaPascals or MPa), adhesive flow control, glass transition temperature (Tg, in °C), and peel adhesion (in pounds per inch width or piw). Example 1 was not coated into film form and was not exposed to electron beam irradiation so as to provide an adhesive bonding film.

The data of Table 1 illustrates the advantages in using about 5 to 20 parts polyfunctional (meth)acrylate, 1 to 15 parts bireactive compound, and a combined amount of these materials that is in the range of about 10 to 25 parts, more preferably, about 15 to 20 parts. Especially good results were obtained when the combined amount of the polyfunctional (meth)acrylate and the bireactive compound was about 10 to 20 parts by weight. Outside these ranges, the peel adhesion and/or glass transition temperature were reduced. The Tg of examples 2 to 17 compared favorably with the Tg of example 1 which did not include (meth)acrylate-containing components showing that the adhesive compositions of the invention can cure to a material having a Tg similar to adhesives based largely on aromatic polyepoxide.

Examples 18 to 20

In examples 18 to 20 laminates were prepared and tested as described above in conjunction with examples 1 to 17 and as shown below in Table 2. The amount of thermoplastic polymer was varied while the amounts of all other reactants were kept constant. Examples 4, 1 1 and 14 are repeated in Table 2.

Table 2 shows the benefit of increasing amounts of thermoplastic polymer on the film handling and adhesive flow control properties of the adhesive bonding films. Preferably, the adhesive bonding films of the invention comprise about 20 to 40 parts thermoplastic polymer, more preferably about 20 to 30 parts.

Examples 21 and 22

In examples 21 and 22 laminates were prepared and tested as described above in conjunction with examples 1 to 17 and as shown below in Table 3. The individual and combined amounts of the polyfunctional (meth)acrylate and the bireactive compound were varied. The amounts of the aromatic polyepoxide and the curative were kept constant. The amount of thermoplastic polymer was either 0 or 30 parts. Examples 4, 7 and 8 are repeated in Table 3.

Table 3 shows that when the amount of polyfunctional (meth)acryiate is outside the preferred range of 5 to 20 parts, the amount of optional bireactive compound is outside the preferred range of 1 to 15 parts, and the combined amount of these two materials is outside the preferred range of 10 to 25 parts, the peel adhesion decreases and/or there is increased adhesive flow during heat curing.

Examples 23 to 25

Examples 23 to 25 were prepared and tested as described above in conjunction with examples 1 to 17 and as shown below in Table 4 but with the following exceptions: ( 1 ) the polyfunctional (meth)acryiate was replaced as follows: example 23 (TEGDMA), example 24 (HDDA), and example 25 (PhEMA); and (2) these materials were not preblended with the bireactive compound but were weighed separately, at room temperature, into the plastic cup described in the high speed mixing method which already contained the aromatic

polyepoxide/thermoplastic polymer blend before beginning the high speed mixing.

Table 4 shows that different polyfunctional (meth)acrylates may be used in the adhesive compositions and the adhesive bonding films of the invention, although some polyfunctional (meth)acrylates may provide less peel adhesion. In example 25, the polyfunctional (meth)acrylate was replaced by a monofunctional acrylate which resulted in a less adhesive flow control and reduced film handling properties. The Tg was also substantially reduced. Peel adhesion in example 25 was not evaluated because an effective laminate test sample could not be produced.

Examples 26 and 27

In examples 26 and 27 laminates were prepared and tested as described in conjunction with examples 1 to 17 and as shown below in Table 5 except that: (1) the D.E.R.™ 332 was replaced with EPON™ 828; and (2) the PKHJ™ was replaced by a thermoplastic polymer comprising a 75 wt.%/25 wt. % blend of EPON™ 828 and P3500, which was prepared by dissolving P3500 into EPON™ 828 at 350°F with vigorous stirring for a minimum of 8 hours in a large batch mixer. In example 27 the thermoplastic polymer was diluted with additional EPON™ 828 to achieve the desired ratio between these two components.

Examples 28 to 30

In examples 28 to 30 laminates were prepared and tested as described in conjunction with examples 1 to 17 and as shown below in Table 5 except that: (1) the D.E.R™ 332 was replaced with QUATREX™ 1010; and (2) the aromatic polyepoxide/thermoplastic polymer blend was made differently. In example 28 PMMA thermoplastic polymer and aromatic polyepoxide were weighed into an 8 ounce glass jar and placed into a preheated air convection oven set at 130°C. The blend was stirred occasionally by hand with a wood tongue depressor until fully dissolved as evidenced by a clear homogeneous mixture. The blend was allowed to cool to room temperature. The blend was not turbid after cooling, indicating that the PMMA remained soluble in the aromatic polyepoxide at room temperature.

In example 29 the thermoplastic polymer was Ultem™ 1000 and the aromatic polyepoxide/thermoplastic polymer blend was opaque after cooling to room temperature indicating that the Ultem™ 1000 had phase separated from the aromatic polyepoxide and thus was not soluble in it at room temperature.

In example 30 (made like example 28) the thermoplastic polymer was PolyEMA and the aromatic polyepoxide/thermoplastic polymer blend was not turbid after cooling, indicating that the PolyEMA was soluble in the aromatic polyepoxide at room temperature.

Example 31

The laminate of example 31 was prepared and tested as described in conjunction with examples 1 to 17 and as shown below in Table 5 except that the aromatic polyepoxide/thermoplastic polymer blend was made differently. The thermoplastic polymer was Ultem™ 1000, and it was not dissolved in the aromatic polyepoxide. The polyfunctional (meth)acrylate bireactive compound blend was mixed with the aromatic polyepoxide using the high speed mixing method. The Ultem™ 1000 was added to this blend in one portion and mixed using the high speed method until completely dispersed as evidenced by the absence of clumped or non-wetted particles. The curative was added according to the high speed mixing method.

Examples 26 and 27 show that when the thermoplastic polymer is polysulfone, a larger amount is required for enhanced performance. Examples 4 and 28 demonstrate the utility of soluble, high Tg (between about 90 and 200°C) thermoplastics polymers in providing good performance while the lower Tg (less than about 90°C) thermoplastic polymer of example 30 yielded a laminate having less peel adhesion.

Example 29 shows that a thermoplastic polymer which dissolved but then phase separated upon cooling to room temperature can have low peel adhesion, and poor film handling characteristics, and reduced adhesive flow control. It is preferred that the thermoplastic polymer remain soluble in the adhesive

composition.

Example 3 1 shows that having the thermoplastic polymer present in a dispersed, undissolved form can reduce the handling characteristics of the adhesive bonding film but still has good peel adhesion and a high Tg.

Examples 32 and 33

In examples 32 and 33 laminates were prepared and tested as described above in conjunction with examples 1 to 17 and as shown below in Table 6 except that the CAF curative was replaced by CG-1400 in example 32 and D.E.H.™ 85 in example 33.

Example 32 shows that curing agents other than aromatic amines can be employed in the adhesive compositions and the adhesive bonding films of the invention. However, the use of a phenolic curative in example 33 gave an adhesive composition in which the polyfunctional (meth)acrylate and the bireactive compound did not polymerize when exposed to electron beam irradiation. Peel adhesion was not evaluated in example 33 because an effective laminate test sample could not be prepared.

Examples 34 to 38

In examples 34 to 38 laminates were prepared and tested as described above in conjunction with examples 1 to 17 and as shown below in Table 8 except that the EBECRYL 3605 bireactive compound was replaced by various monofunctional (meth)acrylates as shown in Table 7.

Table 8 shows that the bireactive compound need not be included in the adhesive compositions of the invention. Though an optional component, the presence of the bireactive compound is highly desirable as it beneficially affects the adhesive flow control and/or the peel adhesion of an adhesive bonding film.

Examples 39 and 40

The adhesive compositions for examples 39 and 40 were prepared as described above in the "General Preparation of Adhesive Compositions" using the formulations shown below in Table 9. Examples 39 and 40 also included an ultraviolet (UV) radiation polymerization initiator, DAROCUR™ 1 173 (Ciba- Geigy, Inc., Hawthorne, NY), in an amount of 2% wt./ wt. (based on the combined amount of the polyfunctional (meth)acrylate and the bireactive compound). In addition, once the adhesive compositions were coated between the two release liners, they were polymerized with UV irradiation instead of electron beam irradiation.

More specifically, in example 39 the coated adhesive was exposed to high energy UV radiation under oxygen free conditions with an RPG UV Processor (Model QC 1202AN3IR from PPG Industries, Inc., Plainfield, IL) equipped with two high intensity mercury lamps whose maximum emission was at 365 nm. One side was exposed nine times for 4.6 seconds each time at an average intensity of

57.83 mW/cm² for a total UV energy exposure of 2394mJ/ cm². The intensity was measured using a UVIRAD UV Integrating Radiometer (Model UR365CH3 from Electronic Instrumentation & Technology, Sterling, Virginia) and converted to National Institute of Standards and Technology (NIST) units (which are reported here).

In example 40 the coated adhesive was exposed to low energy UV radiation under oxygen free conditions using Sylvania™ fluorescent lamps, which had 90% of their emission between 300 and 400 nm with a maximum at 351 nm. Each side was exposed for 20 minutes to an average intensity of 2.045 mW. cm² per side to give a total UV energy exposure of 2451 mJ/cm² per side. The intensity was measured as described above.

Table 9 shows that even though useful adhesives and adhesive bonding films can be produced using UV irradiation, the use of electron beam irradiation according to the invention is more efficient. The total radiation exposure time was 41 seconds for example 39 and 40 minutes for example 40. However, only 0.5 second of electron beam irradiation exposure was used to make the other examples.

Examples 39 and 40 were repeated but without including the photoinitiator. Film handling properties and adhesive flow control were graded (-); other properties were not measured. After exposure to UV radiation, the repeated examples dissolved immediately in methyl ethyl ketone indicating that the adhesive compositions of the invention do not sufficiently polymerize and crosslink when exposed to UV radiation to require special storage and packaging (e.g., in containers that are not transparent to actinic radiation).

Examples 41 to 46

In examples 41 to 46 laminates were prepared and tested as described above in conjunction with examples 1 to 17 and as shown below in Table 10 with the exception of example 46 in which there was no premixing of the polyfunctional (meth)acrylate and bireactive compound because this example did not contain bireactive compound.

Table 10 shows the effect of varying the ratio of polyfunctional

(meth)acrylate to bireactive compound. Examples in the ratio range of 80:20 to 50:50 showed superior performance. At ratios outside this range, peel adhesion is reduced. The ratio of polyfunctional (meth)acrylate to bireactive compound may broadly vary from 95:5 to 50:50. Example 45, having a combined amount of 25 parts by weight polyfunctional (meth)acrylate and bireactive compound exhibited good performance.

Examples 47 to 49

In examples 47 to 49 laminates were prepared and tested as described above in conjunction with examples 1 to 17 and as shown below in Table 1 1 with several exceptions. Each of examples 47 to 49 included 9 parts hexa-(4-methoxy- phenoxy)cyclotriphosphazene flame retardant and 6 parts of ARACAST™ XU AY 238 hydantoin epoxy. The flame retardant was dissolved in the aromatic polyepoxide/thermoplastic polymer blend and then the hydantoin epoxy was dissolved into this blend. In each of these examples, the aromatic polyepoxide was provided by an equal parts by weight mixture of D.E.R.™332 and D.E.N™438. The bireactive compound in each example was SARTOMER 379.

In examples 48 and 49, the aromatic polyepoxide/thermoplastic polymer blend was preheated in an air convection oven set at 100°C until it reached a pourable viscosity before being added to the Plastic-corder™ PL-2000 mixer which was set to 65°C for example 48 and 70°C for example 49.

Table 1 1 shows that blends of different aromatic polyepoxides may be used in the adhesive compositions and the adhesive bonding films of the invention, as can glycidyl methacrylate bireactive compound and various flame retardants.

Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of the invention. It should be understood that this invention is not limited to the illustrative embodiments set forth herein.

Claims

CLAIMS The embodiments for which an exclusive property or privilege is claimed are defined as follows:

1. A solvent-free photostable adhesive composition comprising:

a) an aromatic polyepoxide;

b) a heat activated curative for polyepoxide;

c) a thermoplastic polymer;

d) a polyfunctional (meth)acrylate; and

e) optionally, a bireactive compound that contains at least one (meth)acrylate group and at least one group that is reactive with aromatic polyepoxide.

2. A solvent-free photostable adhesive composition according to claim 1 wherein the thermoplastic polymer has a glass transition temperature of about 90 to

200°C.

3. A solvent-free photostable adhesive composition according to claim 1 wherein the thermoplastic polymer has a number average molecular weight of about 10,000 to 100,000.

4. A solvent-free photostable adhesive composition according to claim 1 wherein the thermoplastic polymer is selected from the group consisting of polysulfone, poly(methyl methacrylate), phenoxy polymer, polycarbonate, and blends of these materials.

5. A solvent-free photostable adhesive composition according to claim 1 wherein the thermoplastic polymer comprises about 20 to 40 parts by weight per 100 parts by weight aromatic polyepoxide.

6. A solvent-free photostable adhesive composition according to claim 1 wherein the polyfunctional (meth)acrylate is di(meth)acryiate.

7. A solvent-free photostable adhesive composition according to claim 1 wherein the polyfunctional (meth)acrylate comprises about 5 to 20 parts by weight per 100 parts by weight aromatic polyepoxide.

8. A solvent-free photostable adhesive composition according to claim 1 wherein the bireactive compound is present and comprises about 1 to 15 parts by weight per 100 parts by weight aromatic polyepoxide.

9. A solvent-free photostable adhesive composition according to claim 1 wherein the bireactive compound is present and the combined amount of the polyfunctional (meth)acrylate and the bireactive compound is about 10 to 25 parts by weight per 100 parts by weight aromatic polyepoxide.

10. A solvent-free photostable adhesive composition according to claim 1 wherein the polyfunctional (meth)acrylate and the optional bireactive compound polymerize when exposed to electron beam irradiation, and further wherein the aromatic polyepoxide and the heat activated curative for polyepoxide do not react when exposed to electron beam irradiation.

1 1. A solvent-free photostable adhesive composition according to claim 1 that has a viscosity that permits the adhesive composition to be coated at a temperature less than the reaction temperature for the heat activated curative for polyepoxide.

12. A solvent-free photostable adhesive composition according to claim 1 1 wherein the adhesive composition can be coated at a temperature that is less than about 90°C.

13. A solvent-free photostable adhesive composition according to claim 1 wherein the aromatic polyepoxide, the thermoplastic polymer, the polyfunctional (meth)acrylate, and the optional bireactive compound can be provided in the form of a solution at room temperature.

14. A solvent-free adhesive composition that is essentially free of photoreactive materials, the adhesive composition comprising:

a) 100 parts by weight aromatic polyepoxide;

b) a curatively effective amount of heat activated curative for polyepoxide;

c) about 20 to 40 parts by weight thermoplastic polymer selected from the group consisting of polysulfone, poly(methyl methacrylate), phenoxy polymer, polycarbonate, and blends of these materials;

d) about 5 to 20 parts by weight di(meth)acrylate; and e) about 1 to 15 parts by weight of a compound that contains at least one (meth)acrylate group and at least one group that is selected from the group consisting of hydroxyl, carboxyl, amine and 1,2-epoxide.

15. A solvent-free adhesive composition according to claim 14 that is a solution having a coatable viscosity at a temperature of less than or equal to about

90°C.

16. A solvent-free adhesive composition according to claim 14 comprising about 20 to 30 parts by weight thermoplastic polymer.

17. A solvent-free adhesive composition according to claim 14 wherein the combined amount of component (d) and component (e) is about 15 to 20 parts by weight.

18. A heat curable adhesive bonding film comprising:

a) a heat curable aromatic polyepoxide; b) a heat activated curative for polyepoxide;

c) a thermoplastic polymer; and

d) a (meth)acrylate polymer network that comprises the electron beam irradiation polymerization product of:

1) a polyfunctional (meth)acrylate; and

2) optionally, a compound that contains at least one (meth)acrylate group and at least one group that is reactive with aromatic polyepoxide.

19. A heat curable adhesive bonding film according to claim 18 that is disposed on a support surface.

20. A heat curable adhesive bonding film according to claim 19 wherein the support surface is a temporary carrier.

21. A heat curable adhesive bonding film according to claim 19 wherein the support surface is a permanent backing.

22. A heat curable adhesive bonding film according to claim 18 than can be removed from a temporary carrier without wrinkling, tearing or permanently stretching.

23. A heat curable adhesive bonding film according to claim 18 that has a modulus of about 1 to 300 MPa.

24. A heat curable adhesive bonding film according to claim 18 that demonstrates controlled adhesive flow upon heat curing.

25. A heat curable adhesive bonding film according to claim 18 that has been heat cured.

26. A heat cured adhesive film according to claim 25 that has a glass transition temperature of at least about 150°C.

27. A fiber-reinforced heat curable adhesive bonding film according to claim 18.

28. A heat curable adhesive bonding film comprising:

a) 100 parts by weight heat curable aromatic polyepoxide;

b) a curatively effective amount of heat activated curative for polyepoxide;

c) about 20 to 40 parts by weight thermoplastic polymer selected from the group consisting of polysulfone, poly(methyl methacrylate), phenoxy polymer, polycarbonate, and blends of these materials;

d) a (meth)acrylate polymer network that comprises the electron beam irradiation polymerization product of:

1) about 5 to 20 parts by weight di(meth)acrylate; and

2) about 1 to 15 parts by weight of a compound that contains at least one (meth)acrylate group and at least one group that is selected from the group consisting of hydroxyl, carboxyl, amine and 1,2-epoxide.

29. A heat curable adhesive bonding film according to claim 28 than can be removed from a temporary carrier without wrinkling, tearing or permanently stretching.

30. A heat curable adhesive bonding film according to claim 29 that has a modulus of about 1 to 300 MPa.

3 1. A printed circuit board that includes a heat curable adhesive bonding film according to claim 28 that has been heat cured.

32. A method of making an adhesive bonding film, the method comprising the steps of:

a) providing an adhesive composition comprising:

1 ) a heat curable aromatic polyepoxide;

2) a heat activated curative for polyepoxide;

3) a thermoplastic polymer;

4) a polyfunctional (meth)acrylate; and

5) an optional, a bireactive compound that contains at least one (meth)acrylate group and at least one group that is reactive with aromatic polyepoxide;

b) forming a layer of the adhesive composition on a support surface; c) exposing the layer of the adhesive composition to electron beam irradiation to polymerize the polyfunctional (meth)acrylate and the optional bireactive compound but without causing reaction of the heat activated curative or the aromatic polyepoxide, whereby an adhesive bonding film that is heat curable is formed.

33. A method according to claim 31 wherein the heat curable aromatic polyepoxide, the thermoplastic polymer, the polyfunctional (meth)acrylate, and the optional bireactive compound form a solution in step (a).

34. A method according to claim 32 wherein the layer of the adhesive composition is formed by coating the adhesive composition on the support surface at a temperature that is between about room temperature and 120°C.

35. A method according to claim 33 wherein the adhesive composition is coated at a temperature that is between about room temperature and 60°C.

36. A method according to claim 32 further comprising the step of removing the heat curable adhesive bonding film from the support surface without wrinkling, tearing or permanently stretching the heat curable adhesive bonding film.

37. A method according to claim 32 further comprising the step of heating the heat curable adhesive bonding film for a time and at a temperature sufficient to cure the aromatic polyepoxide to provide a heat cured adhesive bonding film.