Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
  • C08G59/68—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the catalysts used
  • C08G59/70—Chelates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
  • C08F283/10—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polymers containing more than one epoxy radical per molecule
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
  • C08G59/40—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the curing agents used
  • C08G59/50—Amines
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J163/00—Adhesives based on epoxy resins; Adhesives based on derivatives of epoxy resins
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J181/00—Adhesives based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing sulfur, with or without nitrogen, oxygen, or carbon only; Adhesives based on polysulfones; Adhesives based on derivatives of such polymers
  • C09J181/06—Polysulfones; Polyethersulfones
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2666/00—Composition of polymers characterized by a further compound in the blend, being organic macromolecular compounds, natural resins, waxes or and bituminous materials, non-macromolecular organic substances, inorganic substances or characterized by their function in the composition
  • C08L2666/02—Organic macromolecular compounds, natural resins, waxes or and bituminous materials
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/38—Improvement of the adhesion between the insulating substrate and the metal
  • H05K3/386—Improvement of the adhesion between the insulating substrate and the metal by the use of an organic polymeric bonding layer, e.g. adhesive

Definitions

• 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,
• thermoplastic polymer (meth)acrylate-containing resin, and thermoplastic polymer, as well as processes for making bonding films therefrom using electron beam irradiation.
• 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.
• 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.
• a temporary carrier e.g., a release liner
• 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.
• soldering i.e., wave soldering
• the adhesive compositions from which the bonding films are produced should also be easily handled and processed.
• 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:
• 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.
• 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
• actinic radiation preferably a wavelength of 200-600 nm
• 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.
• 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 discloses the use of actinic radiation (preferably a wavelength of 200-600 nm) to prepare heat curable adhesive bonding films having variable tack.
• actinic radiation preferably a wavelength of 200-600 nm
• the adhesive is a mixture of a
• U.S. Patent No. 5,086,088 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.
• electrolytic radiation e.g., electron beam, gamma-ray, or X-ray
• 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.
• the acrylate-containing component is used in amounts less than suggested, curing via electron beam irradiation is insufficient and tack remains on the surface.
• 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.
• this invention relates to an adhesive composition
• an adhesive composition comprising:
• thermoplastic polymer a thermoplastic polymer
• 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).
• 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).
• safe light 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).
• 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.
• 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.
• 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.
• the adhesive compositions can provide a heat curable adhesive bonding film that comprises:
• thermoplastic polymer a thermoplastic polymer
• a (meth)acrylate polymer network that comprises the electron beam irradiation polymerization product of:
• (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:
• 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.
• this invention pertains to adhesive compositions that comprise and, more preferably, consist essentially of:
• thermoplastic polymer a heat activated curative for polyepoxide (sometimes referred to herein as the "heat activated polyepoxide curative” or the “polyepoxide curative”); c) a thermoplastic polymer;
• 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.
• 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.
• a support surface such as a permanent backing or a temporary carrier (e.g., a release liner)
• 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.
• 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).
• a thermoset material i.e., a crosslinked polymer network that does not flow or melt.
• 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.
• the adhesive bonding films of the invention 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.
• 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 polyglycid
• aromatic polyepoxides include the polyglycidyl derivatives of aromatic amines (i.e., glycidylamines) obtained from the reaction between the aromatic amines and an epihalohydrin.
• 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[( ⁇ -4-aminophenyl)- ⁇ -methylethyI]benzene, and N,N,N',N'- tetraglycidyl- 1 ,4-bis[ ⁇ -(4-amino-3,5-dimethylphenyl)-[ ⁇ - methylethyl]benzene.
• polyglycidyl derivatives of aromatic aminophenols e.g., glycidylamino-glycidyloxy benzene
• aromatic aminophenols e.g., glycidylamino-glycidyloxy benzene
• 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.
• 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 MYTM-720 (Ciba-Geigy, Inc , Hawthorne, NY); ERL-0510 (Ciba-Geigy, Inc.), the EPONTM 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.TM, D.E.N.TM and QUATREXTM 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).
• 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.
• 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.
• 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.
• 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.
• 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, p
• 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).
• nitrogen-containing compounds such as dicyandiamide, melamine, ureas and aliphatic amines (e.g., diethylenetriamine, triethylenetetra
• chloro-, bromo-, and fluoro-containing Lewis acids of aluminum, boron, antimony, and titanium such as aluminum trichloride, aluminum tribromide, boron trifluoride, antimony pentafluoride, titanium
• blocked Lewis acids are BF3-monoethylamine, and the adducts of
• HSbF 5 X in which X is halogen, -OH, or -OR 1 in which R 1 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.
• 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[ ⁇ -(4-aminophenyl)- ⁇ -methylethyl]benzene, and 1,4-bis[ ⁇ - (4-amino-3,5-dimethylphenyl)- ⁇ -methylethyl]benzene, bis ⁇ -(4- amino-3- methylphenyl)sulfone, 1, 1'-biphenylene
• 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 EPONTM HPT- 1061 and EPONTM HPT- 1062 ( each from Shell Chemical Co.), HT-9664 (Ciba Geigy, Inc.), and AMICURETM 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
• the polyepoxide curative have little or no ionic or hydrolyzable halide as these may cause corrosion in printed circuit board laminates made therewith.
• thermoplastic is meant a non- crosslinked polymer that can be repeatedly softened and reshaped upon the application of heat and pressure.
• 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.
• 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.
• 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.
• 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.
• thermoplastic polymers examples include PKHPTM 200 (Phenoxy Associates, Rock Hill, SC), PKHJTM (Phenoxy Associates), UDELTM 1700 and UDELTM3500 (each from Amoco Performance Products, Inc., Ridgefield, CT), PLEXIGLASSTM (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.
• (meth)acrylate is meant a compound containing either acrylate or methacrylate moieties; that is, compounds having the group
• R is either hydrogen or methyl and R' is an organic radical.
• 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.
• difunctional (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.
• 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.
• suitable polyfunctional (meth)acrylates include bisphenol A epoxy di(meth)acrylate, ethoxylated bisphenol A
• Preferred polyfunctional (meth)acrylates include the bisphenol A-based di(meth)acrylates such as bisphenol A epoxy di(meth)acrylate and ethoxylated bisphenol A
• Examples of commercially available polyfunctional (meth)acrylates which are suitable for use in the invention include the SARTOMERTM 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 EBECRYLTM 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.
• 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.
• 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
• bireactive compound examples include mono(meth)acrylates of various polyepoxide resins such as bisphenol A epoxy mono(meth)acrylate and the like.
• suitable commercially available bireactive compounds include EBECRYLTM 3605 (UCB Radcure Inc.) and SARTOMERTM 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• an adhesive bonding film formed therefrom may be difficult to handle, and there may be too much adhesive flow during heat curing.
• 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.
• 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.
• a heat cured adhesive bonding film formed therefrom may lose adhesion.
• 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.
• 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.
• an adhesive bonding film formed therefrom may be difficult to handle.
• 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.
• 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.
• 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.
• the adhesive compositions of the invention may be provided as 100% solids mixtures.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• a woven or nonwoven fibrous support surface e.g., fibers of carbon, glass, aramide, polyester or polyimide
• 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.
• 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 ⁇ m or thicker.
• the adhesive composition 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.
• the adhesive 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.
• 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.
• the adhesive bonding film 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 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.
• the polyfunctional (meth)acrylate and bireactive compound were separately preheated in an air convection oven set at
• the preheated polyfunctional (meth)acrylate/bireactive compound blend was added with further mixing at 60°C for 1 to 2 minutes.
• 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.
• Adhesive bonding films were prepared by coating the adhesive compositions and then exposing the coated adhesives to electron beam irradiation.
• 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.
• 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 ⁇ m) 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 ⁇ m) 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 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 Kimw ⁇ pesTM-EX-L Delicate Task Wipers (Kimberly- Clark Corporation, Atlanta, GA) to remove dust prior to use.
• the laminates were prepared by cutting a pair of approximately 0.002 in (50 ⁇ m) 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 ⁇ m thick) piece of Kapton FPC-ZT polyimide film (E. I .
• 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 (TedlarTMMR, 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).
• lamination method A 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.
• lamination method B 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
• a single cell differential scanning calorimeter (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
• 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 ScotchTM 1280 Circuit Plating Tape.
• the other side of the laminate was cleaned and roughened using a wet Heavy Duty 3M Scotch-B riteTM Scour Pad (catalog # 220) and then dried with a paper towel.
• a single additional piece of 3M ScotchTM 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).
• 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.
• 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.
• 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.
• TMA Thermomechanical Analyzer
• Stress applied force
• 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
• the modulus of the adhesive bonding films of the invention is between about 1 and 300 MPa for good film handling characteristics.
• 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.
• 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.
• EPONTM 828 - diglycidyl ether of bisphenol A available from Shell Chemical
• HDDA - 1,6-hexanediol diacrylate available as SARTOMERTM 238 available from
• PEA - 2-phenoxy ethyl acrylate available from CPS Chemical Company, Old Bridge, NJ
• PhEMA - 2-phenoxy ethyl methacrylate (SARTOMERTM 340 available from
• PolyEMA poly(ethyl methacrylate) (available from Aldrich Chemical Company, catalog # 18,208-7)
• TEGDMA - triethylene glycol dimethacrylate available as SARTOMERTM 205 from Sartomer Company
• ULTEMTM 1000 - poly(ether-imide) (available from General Electric Company and subsequently converted to fine particles having a size of about 5 ⁇ m 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 ARACASTTM tradename).
• 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.
• the adhesive bonding films of the invention comprise about 20 to 40 parts thermoplastic polymer, more preferably about 20 to 30 parts.
• 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 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.
• 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.
• thermoplastic polymer comprising a 75 wt.%/25 wt. % blend of EPONTM 828 and P3500, which was prepared by dissolving P3500 into EPONTM 828 at 350°F with vigorous stirring for a minimum of 8 hours in a large batch mixer.
• the thermoplastic polymer was diluted with additional EPONTM 828 to achieve the desired ratio between these two components.
• examples 28 to 30 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.RTM 332 was replaced with QUATREXTM 1010; and (2) the aromatic polyepoxide/thermoplastic polymer blend was made differently.
• 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.
• thermoplastic polymer was UltemTM 1000 and the aromatic polyepoxide/thermoplastic polymer blend was opaque after cooling to room temperature indicating that the UltemTM 1000 had phase separated from the aromatic polyepoxide and thus was not soluble in it at room temperature.
• 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.
• 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 UltemTM 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 UltemTM 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
• 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 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.TM 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.
• 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.
• 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 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, DAROCURTM 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).
• UV ultraviolet
• DAROCURTM 1 173 Ciba- Geigy, Inc., Hawthorne, NY
• the adhesive compositions were coated between the two release liners, they were polymerized with UV irradiation instead of electron beam irradiation.
• 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
• the coated adhesive was exposed to low energy UV radiation under oxygen free conditions using SylvaniaTM 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. cm 2 per side to give a total UV energy exposure of 2451 mJ/cm 2 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).
• 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 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 ARACASTTM 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.
• the aromatic polyepoxide was provided by an equal parts by weight mixture of D.E.R.TM332 and D.E.NTM438.
• the bireactive compound in each example was SARTOMER 379.
• 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-corderTM 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.

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