ACRYLIC COPOLYMER COMPOSITION AND ADHESIVE COATINGS THEREFROM

Abstract: An improved adhesive composition comprising a non-­ acidic aqueous latex copolymer of a lower acrylate, an acrylic nitrile and a glycidyl acrylate having a crosslinking agent dissolved in the aqueous phase.

Description: TITLE ACRYLIC COPOLYMER COMPOSITION AND ADHESIVE COATINGS THEREFROM FIELD OF INVENTION The invention relates to acrylic latex copolymer compositions and to adhesive coatings made therefrom. BACKGROUND OF THE INVENTION The flexible circuit industry requires adhesives for polyimide film and copper which can withstand elevated temperatures and a variety of harsh solvents and chemicals. During the many preparation and processing steps for circuit manufacture, these solvents and chemicals can cause an adhesive to swell. This swelling leads to blister formation and/or delamination, which results in reduced circuit yields. The application of heat. such as in soldering, can similarly cause circuit failures. In preparing multilayer flexible circuits, manufacturers need adhesive-coated polyimide films which can effectively encapsulate patterned metal circuits and also provide a planar surface for subsequent lamination. PRIOR ART Crosslinkable acrylic adhesive compositions which bond to caustic treated polyimide elements are known from U.S. 3,822,175; 3.900.662 and 3,728,150. U.S. 3.336,149 and 3,418,392 disclose acrylic adhesive compositions which can be cured for bonding to textile fibers. Combinations of phenolic resins and acrylic copolymers for adhesive compositions are known from U.S. 4,435.543 and 3,376,279. A curable adhesive composition comprising 25 to 64.8% acrylate, 20 to 40% acrylonitrile and 0.2 to 5% glycidyl methacrylate is described in U.S. 4,404,324, whereas U.S. 4,098,952 describes 3 to 25% glycidyl methacrylate. Adhesive compositions incorporating acrylics and phenolic resins are described with different ranges of glass transition temperature in U.S. 3.758.634; 3,954,898; 4.312,916 and 4,378.450. Other uses of acrylic adhesives are described in U.S. 3,729.338; 3.787,520; 3,959,404; 4,042,645; 4,076,675 and 4,323.659. In spite of the extensive work directed to curable adhesive compositions containing acrylic copolymers and phenolic resins. a need still exists for such adhesives having improved encapsulation and flow properties as well as chemical and thermal stability. BRIEF DESCRIPTION OF THE INVENTION The invention is directed in one aspect to a latex copolymer prepared by free radical-initiated aqueous emulsion polymerization of a mixture of nonacidic monomers comprising 50-60 wt. S lower alkyl acrylate, 30-40 wt. % acrylonitrile, methacrylonitrile or mixtures thereof, and 5-12 wt. S glycidyl acrylate, glycidyl methacrylate or mixtures thereof, having a glass transition temperature (Tg) of 0-550C and a weight average molecular weight (Mw) of 300,0002.000,000. In a second aspect. the invention is directed to an adhesive coating composition comprising (a) 90-99 wt. % of the above-described latex copolymer and (b) 10-1 wt. % of a water-soluble crosslinking agent. In a third aspect. the invention is directed to an adhesive film prepared by (1) applying a layer of the above-described adhesive coating to a substrate, (2) drying the composition at a temperature below the cross linking temperature of the crosslinking agent and (3) heating the dried layer above the crosslinking temperature of the crosslinking agent to effect crosslinking thereof. DETAILED DESCRIPTION OF THE INVENTION A. Latex Copolymer As noted above, the latex copolymer component of the invention is prepared by free radical-initiated aqueous emulsion polymerization of a mixture of nonacidic monomers comprising 50-60 wt. % lower alkyl acrylate, 30-40 wt. % acrylonitrile, methacrylonitrile, or mixtures thereof, and 5-12 wt. % glycidyl acrylate. glycidyl methacrylate or mixtures thereof. The resulting copolymer must have a Tg of O-550C and & M of 300,000-2.000,000. As used herein, the term "lower alkyl" means C14 alkyl groups. When it is desired to have a low flow (high viscosity) composition. it is preferred that Mw of the w copolymer be 1.500,000-2.000,000. On the other hand. when it is desired to have a high flow (low viscosity) composition, it is preferred that Mw of the copolymer be 300.000-900.000. Such latex copolymers can be made by conventional latex polymerization techniques such as those disclosed by Sanderson in U.S. 3.032,521. which is incorporated herein by reference. A preferred low flow copolymer is a latex copolymer of 35/55/10 by weight acrylonitrile/butyl acrylate/glycidyl methacrylate having a Tg of 400C and Mw of 1,600.000. A preferred high flow copolymer is one of the same monomer composition, the Mw of which is only 850.000. B. Crosslinking Agent The above-described latex copolymers are used in conjunction with 1-10% wt. of a water-soluble crosslinking agent such as melamine formaldehyde, phenol formaldehyde, urea formaldehyde and the like. These crosslinkers are present in an amount of about l-lOS by weight of terpolymer. A polyvinyl alcohol thickener can be used to vary viscosity. The composition may contain surface tension and viscosity control agents as well as fillers, colorants and flame retardant additives. In particular, 95S latex copolymer is combined with 5a phenol formaldehyde resin to provide a preferred adhesive composition to which about 0.5% by weight polyvinyl alcohol of molecular weight above 100.000 is added as a thickener. Other compatible thickening agents can be employed to facilitate film formation prior to drying. C. Dispersing Medium In most instances. it will be preferred to use the aqueous phase of the copolymer latex as the dispersing medium for the adhesive composition of the invention. However. if desired, the acrylic adhesive can be contained as a dispersion or dissolved in a suitable organic liquid or mixtures of organic liquids. Examples of these are aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane and octane; esters such as ethyl acetate; ketones such as methyl ethyl ketone and methylisobutyl ketone: and ethers such as monoalkylethers of ethylene glycol. Examples of suitable organic liquids are disclosed in U.S. 3.032.521. D. Formulation and Application The adhesive composition can be prepared in an unsupported form by application to a release substrate such as coated paper or application onto polyimide films and/or metal sheets and the like. Polyimides suitable for use as substrates in this invention are disclosed in Edwards U.S. 3,179,634. the disclosure of which is hereby incorporated by reference. The polyimide or other substrate may contain reinforcing and/or filler material, for example natural or synthetic fibers such as fiberglass, boron. polyester, polyamide, acrylic, Nomexs and Kevlars, aromatic polyamides. nylon. etc. Woven or nonwoven fabrics made from natural or synthetic fibers such as those mentioned above can also be used. Particular filler materials include silica, silicates, carbon black, carbonates, metals and metal oxides, such as magnesium oxide, calcium oxide, aluminum oxides. etc. The composition may also contain flame retardant materials, such as antimony oxides and/or brominated or chlorinated phosphates, for example, tris-(2.3-dibromopropyl) phosphate. The acrylic adhesive composition can be applied to the substrate film by conventional application procedures such as spraying, drying. printing, brushing. extrusion, dip coating, roll coating and the like. If desired the acrylic adhesive can contain reinforcing and/or extender material such as those primarily enumerated as being suitable for the polyimide film. In particular the adhesive composition can be applied to Kaptons polyimide film or used as a bonding medium between Kaptone polyimide film and copper. The adhesive composition can be stored in roll form using coated paper or Molars film. The acrylic adhesive can be applied to the polyimide film or other substrate in varying thickness depending on the desired end use. The acrylic adhesive-coated polyimide films can be adhered to suitable substrates to form laminates. Suitable substrates include metal and especially metal foils of copper, copper alloys. silver, silver alloys. gold, gold alloys; woven and nonwoven fabrics made from natural or synthetic fibers such as glass, boron, polyester, polyamide, acrylic, etc.; woven and nonwoven fabric impregnated with resin such as polyimide. polyamide, epoxy, acrylic; paper of natural or synthetic fibers such as Nomexs nylon paper. etc.; and film of polymer such as polyimide. polyamide. polyester, acrylic, epoxy, polyurethane, etc. Preferred substrates include metal and especially copper, polyimide film, polyamide paper, woven and nonwoven glass fabric. and polyimide or epoxy impregnated glass fabric. Various techniques can be used to join material surfaces using the adhesive films of the invention. For example when the film has been applied to a release support such as Molar polyester film or polymer coated paper, two materials can be joined by applying the exposed layer of the adhesive film to one of the materials, peeling off the substrate support from the adhesive film, thus exposing a second surface of the adhesive, and then laminating the second layer of material to the exposed surface of the adhesive film under pressure and heat sufficient to effect cross linking of the cross linking agent in the adhesive film. On the other hand when the adhesive film is applied to a nonrelease support, e.g.. a polyimide film the polyimide film can be joined to a second material such as a printed circuit board by laminating the polyimide-coated adhesive film to the second material under heat and pressure sufficient to initiate and effect complete cross linking of the crosslinking agent. Standard lamination procedures can be used to make the laminates such as vacuum bag lamination. press lamination. roll lamination, etc. The laminates are useful as circuit boards. structural members and the like. In the examples, the method used for determining the weight average molecular weight (Mw) is gel permeation chromatography. The analytical procedure consisted of dissolving 0.1-0.3% wt. polymer in tetrahydrofuran (THF) and chromatographing a sample on a micro Styragele column versus a polymethylmethacrylate (PMMA) standard having a Mw of 100.000. ExamPle 1 (Low Flow Terpolymer) In a 2 liter flask equipped with a mechanical stirrer. condenser. two addition funnels, a thermometer and nitrogen inlet were placed 380 g of deionized water, 16.4 g of acrylonitrile, 28.2 g of butyl acrylate, 2.3 g of glycidyl methacrylate and 0.01 g of ferric ammonium sulfate. This mixture was heated with stirring under a nitrogen atmosphere. When the temperature reached 750C an initiator solution of 0.02 g of sodium metabisulfite, and 0.09 g of ammonium persulfate in 14.8 g of deionized water was added to the flask. The reaction mixture turned almost instantly into a blue-white emulsion. Immediately after addition of the initiator solution, two separate feeds were begun simultaneously. The first. a monomer feed consisting of a mixture of 147.9 g of acrylonitrile. 253.5 g of butyl acrylate and 21.1 g of glycidyl methacrylate was added to the reaction mixture over 140 minutes. The second, an initiator and surfactant feed, consisting of 0.1 g of sodium metabisulfite, 0.4 g of ammonium persulfate. 1.17 g of sodium lauryl sulfate and 20.8 g of deionized water. was added over 70 minutes. When the initial initiator and surfactant feed was finished. an identical second feed was added over an additional 70 minutes. The reaction during the feeds was exothermic and the temperature was maintained between 82 and 870C. When the additions were finished, the monomer and initiator feed funnels were rinsed with 22.3 g and 9.4 g of deionized water respectively, and the rinses were added to the reaction mixture which was maintained at 800C for an additional 2-1/2 hours. At the end of that time, the heat was shut off. the flask was cooled with a water bath and the reaction mixture, which was a blue-white emulsion, was filtered through felt to remove traces of coagulum. The emulsion had a viscosity of 40 centipoises and 48.3% solids which corresponds to a 96.6% conversion. The terpolymer had a molecular weight (Mw) of about 1,600,000 and Tg of 400C. In this and the following examples, viscosity was measured using a Brookfield LVF viscometer, No. 1 spindle at 12 rpm at room temperature. A 2 mil (51 gm) Kapton polyimide film was coated on one side with a 45 wt. dispersion in water of an acrylic adhesive composition. The acrylic adhesive is a mixture of a terpolymer and crosslinking resin. The terpolymer is the reaction product of 35 wt. % acrylonitrile, 60 wt. butyl acrylate and 5 wt. % glycidyl methacrylate with a molecular weight of approximately 1.600,000. and a T of 40 C. To 86.2 g of terpolymer dispersion was g added 2.4 g of an aqueous phenol formaldehyde resin solution (66S solids) and 8.2 g of an aqueous polyvinyl alcohol solution (4.2% solids). In this and the following examples the polyvinyl alcohol was Elvanols 85-80. Using a No. 36 wire-wound rod the acrylic composition was coated and dried at 1200C for 5 minutes. After drying, the adhesive coating was 1.0 mil (25.4 wm) thick and tack free. Example 2 (Low Flow TerpolYmer) In a 2 liter flask equipped with a mechanical stirrer, condenser, two addition funnels. a thermometer and nitrogen inlet were placed 380 g of deionized water. 16.4 g of acrylonitrile. 25.8 g of butyl acrylate. 4.7 g of glycidyl methacrylate and 0.01 g of ferric ammonium sulfate. This mixture was heated with stirring under a nitrogen atmosphere. When the temperature reached 730C, an initiator solution of 0.02 g of sodium metabisulfite and 0.09 g of ammonium persulfate in 14.8 g of deionized water was added to the flask. The reaction mixture turned almost instantly into a blue-white emulsion. Right after the addition of the initiator solution, two separate feeds were begun simultaneously. The first, a monomer feed consisting of a mixture of 147.9 g of acrylonitrile. 232.4 g of butyl acrylate and 42.2 g of glycidyl methacrylate was added to the reaction mixture over 140 minutes. The second, an initiator and surfactant feed, consisted of 0.1 g of sodium metabisulfite. 0.4 g of ammonium persulfate, 1.17 g of sodium lauryl sulfate. and 20.8 g of deionized water and was added over 70 minutes. When the first initiator and surfactant feed was finished a second identical feed was added over an additional 70 minutes. The reaction during the feeds was exothermic and the temperature was maintained between 80 and 830C. When the additions were finished, the monomer and initiator feed funnels were rinsed with 22.3 g and 9.4 g of deionized water respectively, and the rinses were added to the reaction mixture which was maintained at 820C for an additional two hours. At the end of that time. the heat was shut off, the flask was cooled with a water bath, and the reaction mixture, which was a blue-white emulsion. was filtered through felt to remove traces of coagulum. The emulsion had a viscosity of 45 cps and 48.5% solids which corresponds to 97X conversion. A 2 mil (51 sm) Kaptons polyimide film was coated on one side with a 45 wt. S dispersion in water of an acrylic adhesive composition. The acrylic adhesive was a mixture of terpolymer and cross linking resin. The terpolymer was the reaction product of 35 wt. % acrylonitrile, 55 wt. % butyl acrylate and 10 wt. t glycidyl methacrylate having a molecular weight of approximately 1,600,000 and a T of 400C. To 90.0 g of the terpolymer dispersion g was added 3.5 g of an aqueous phenol formaldehyde resin solution (66% solids) and 9.0 g of an aqueous polyvinyl alcohol solution (4.2 solids). Using a No. 36 wire-wound rod the acrylic composition was coated and dried at 1200C for 5 minutes. After drying, the adhesive coating was 1.0 mil (25.4 gm) thick and tack free. Example 3 (High Flow Terpolvmer) In a 5 liter flask. equipped with a mechanical stirrer. condenser. two addition funnels. a thermometer and nitrogen inlet were placed 1900 g of deionized water, 62 g of acrylonitrile, 129 g of butyl acrylate. 24 g of glycidyl methacrylate and 0.05 g of ferric ammonium sulfate. This mixture was heated with stirring under a nitrogen atmosphere. When the temperature reached 750C. an initiator solution of 0.1 g sodium metabisulfite and 4.5 g of ammonium persulfate in 74 g of deionized water was added to the flask. The reaction mixture turned milky. Right after the addition of the initiator solution, two separate feeds were begun simultaneously. The first. a monomer and chain transfer feed consisting of a mixture of 739 g of acrylonitrile, 1162 g of butyl acrylate. 211 g of glycidyl methacrylate and 20 g of dodecyl mercaptan was added to the reaction mixture over 140 minutes. The second, an initiator and surfactant feed. consisted of 0.5 g of sodium metabisulfite, 2 g of ammonium persulfate, 20 g of sodium lauryl sulfate and 104 g of deionized water. and was added over 70 minutes. When the first initiator and surfactant feed was finished. an identical second feed was added over an additional 70 minutes. The reaction during the feeds was exothermic and maintained itself without external heat between 83 and 910C. When the additions were finished, the monomer and initiator feed funnels were rinsed with 158 g of deionized water. and the rinses were added to the reaction mixture which was heated at 850C for an additional 2 hours. At the end of that time. the heat was shut off, the flask was cooled with a cold water bath, and the reaction mixture, which was a blue-white emulsion. was filtered through felt to remove traces of coagulum. The emulsion had a viscosity of 23 centipoises and 48.2% solids which corresponds to 96.4% conversion. The terpolymer had a molecular weight (Mw) of about 850,000 and a T of 400C. A 2 mil (51 Bm) Kaptone polyimide film was coated on one side with a 45 wt. 8 dispersion in water of acrylic adhesive composition. The acrylic adhesive was a mixture of a terpolymer and crosslinking resin. The terpolymer was the reaction product of 35 wt. % acrylonitrile, 55 wt. % butyl acrylate and 10 wt. % glycidyl methacrylate with a molecular weight of approximately 850.000 and a T g of 400C. To 90.0 g of the terpolymer dispersion was added 3.5 g of an aqueous phenol formaldehyde resin solution (66S solids) and 9.0 g of an aqueous polyvinyl alcohol solution (4.2S solids). Using a No. 36 wire-wound rod the acrylic composition was coated and dried at 1200C for 5 minutes. After drying, the adhesive coating was 1.0 mil (25.4 Bm) thick and tack free. ExamPle 4 (Prior Art Composition BA/AN/MAA 60/35/5) Same as Example 1. except that methacrylic acid was used in place of glycidyl methacrylate. This material did not exhibit the improved chemical and thermal stability of the present invention when used to prepare polyimide laminates. Example S (Prior Art Composition BA/AN/MAA 60/35/5) Same as Example 3. except that 5% methacrylic acid was substituted for 10% glycidyl methacrylate. This material exhibited improved encapsulation and flow. but had significantly reduced chemical and thermal stability. Example 6 A 45S solids by weight acrylic adhesive composition was prepared from the terpolymer dispersion of Example 2. (1) To 86.2 g of dispersion 2 was added with stirring 2.4 g of an aqueous phenol formaldehyde resin solution (66S solids) and 8.2 g of an aqueous polyvinyl alcohol solution (4.2% solids). (2) A portion of the resulting acrylic adhesive mixture from step (1) was coated on a 2.0 mil (51 Bm) thick sheet of Kaptone polyimide film using a No. 36 wire-wound rod and then dried at 1200C for 5 minutes. After drying, the adhesive coating was about 1.0 mil (25.4 Bm) thick and tack free. (3) The adhesive coating of (2) was overlaid with a 36 urn thick sheet of rolled-annealed treated copper and press laminated at 3500F (1770C) and 250 psi (17.6 kg/cm ) for 60 minutes. This produced a copper clad laminate having an adhesive strength of copper to Kaptone film of 12 lbs/in (2.1 kg/cm) and an adhesive flow during lamination of 3 mils (76 urn). This was sufficient to encapsulate etched copper lines but low enough not to flow into pre-drilled holes in the circuit board. This laminate was floated on a solder bath at 6000F (316or) for 5 minutes without blistering. After copper removal by chemical etching (aqueous ammonium persulfate/sulfuric acid). the exposed adhesive was resistant to alkaline semi-aqueous stripper (1 part J & 732 to 3 parts water) for over 10 minutes at 1500F (680C) without blistering or delamination. ExamPle 7 A 45b solids by weight acrylic adhesive composition was prepared from the terpolymer dispersion of Example 3. (1) To 90.0 g of dispersion 3 was added with stirring 3.5 g of an aqueous phenol formaldehyde resin solution (66S solids) and 9.0 g of an aqueous polyvinyl alcohol solution (4.2t solids). (2) A portion of the resulting acrylic adhesive mixture from step (1) was coated on a 2.0 mil (51 Bm) thick sheet of Kaptone polyimide film using a No. 36 wire-wound rod and then dried at 1200C for 5 minutes. After drying. the adhesive coating was about 1.0 mil (25.4 Bm) thick and tack free. (3) The adhesive coating of (2) was overlaid with a 36 urn thick sheet of rolled-annealed treated copper and press laminated at 2 350 F (177 C), 250 psi (17.6 kg/cm ) for 60 minutes. This produced a copper clad laminate having an adhesive strength of copper to Kaptone film of 11.5 lbs/in (2.1 kg/cm) and an adhesive flow during lamination of 18 mil (457 Bum), which is sufficient to completely encapsulate the inner layers of a printed circuit without excessive resin overflow. This laminate was floated on a solder bath at 6000F (3160C) for 5 minutes without blistering or delamination. After copper removal by chemical etching (aqueous ammonium persulfate/sulfuric acid), the exposed adhesive was resistant to alkaline semi-aqueous resist stripper (1 part J & 732 to 3 parts water) for 10 minutes at 1500F (680C) without blistering or delamination. ExamPle 8 A 45% solids by weight acrylic adhesive composition was prepared from the terpolymer dispersion of Example 3. (1) To 90.0 g of dispersion 3 was added with stirring 3.5 g of an aqueous phenol formaldehyde resin solution (66% solids). (2) A portion of the resulting acrylic adhesive mixture from step (1) was used to impregnate by dip coating a 2.3 mil (58.4 Bm) thick sheet of Nomex aramid fabric and then dried at 1200C for 5 minutes After drying, the Nomexe reinforced adhesive composition was about 3.7 mil (94 from) thick and tack free. (3) The Nomexs reinforced adhesive composite of (2) was overlaid with a 36 Wm sheet of rolled-annealed treated copper and press laminated at 3500F (1770C). 250 (17.6 kg/cm) psi for 60 minutes. This produced a copper clad laminate having an adhesive strength of copper to Nomexs of 10.5 lbs/in (1.9 kg/cm). This laminate was floated on a solder bath at 6000F (3160C) for 30 sec without blistering or delamination. After copper removal by chemical etching (aqueous ammonium persulfate/sulfuric acid). the exposed adhesive was resistant to alkaline semi-aqueous resist stripper (1 part RistoneS1100 X to 3 parts water) for 5 minutes at 130OF (540C) without blistering or delamination. Example 9 A 45% solids by weight acrylic adhesive composition was prepared from the terpolymer dispersion of Example 3. (1) To 90.0 g of dispersion 3 was added with stirring 3.5 g of an aqueous phenol formaldehyde resin solution (66% solids). (2) A portion of the resulting acrylic adhesive mixture from step (1) was used to impregnate by dip coating a 2.8 mil (71 Bm) thick sheet of Kevlar aramid fabric and then dried at 1200C for 5 minutes. After drying, the Kevlare fiber-reinforced adhesive composition was about 4.2 mils (107 Bm) thick and tack free. (3) The Kevlar fiber-reinforced adhesive composite of (2) was overlaid with a 36 urn sheet of rolled-annealed treated copper and press laminated at 3600F (1820C). 200 psi (14 kg/cm ) for 60 minutes. This produced a copper clad laminate having an adhesive strength of copper to Kevlar of 9.5 lbs/in (1.7 kg/cm). This laminate was floated on a solder bath at 5500F (2870C) for 5 min. without blistering or delamination. After copper removal by chemical etching (aqueous ammonium persulfate/sulfuric acid), the exposed adhesive was resistant to alkaline semi-aqueous resist stripper (1 part RistonOSllOO X to 3 parts water) for 5 minutes at 1300F (540C) without blistering or delamination. Glossary of Tradenames The following are tradenames of E. I. du Pont de Nemours and Company, Inc.. Wilmington. Delaware for the indicated materials. Elvanole Polyvinyl alcohol Kaptone Polyimide film Kevlar Aramid fiber Mylar Polyester film Nomexe Aramid fiber and sheet material Pistons Photopolymer resist equipment and stripping agents Styragele is a tradename of Water's Associates. Milford, MA for polystyrene-based chromatographic separation materials. J & 732 is a tradename of J & Laboratories, Los Angeles. CA for alkaline aqueous glycol ether/alkanolamine mixtures

Claims: CLAIMS 1. A latex copolymer prepared by free radical initiated aqueous emulsion polymerization of a mixture of nonacidic monomers comprising 50-60 wt. % lower alkyl acrylate, 30-40 wt. % acrylonitrile, methacrylonitrile or mixtures thereof. and 5-12 wt. % glycidyl acrylate, glycidyl methacrylate or mixtures thereof, having a T of 0-55 C and a weight average g molecular weight of 300.000-2,000,000. 2. An adhesive coating composition comprising (a) 90-998 wt. of the latex copolymer of claim 1 having dissolved in the aqueous phase; (b) 10-1% wt. of a crosslinking agent. 3. The coating composition of claim 2 in which the copolymer M is 1.500,000-2,000,000. 4. The coating composition of claim 2 in which the copolymer Mw is 300,000-900,000. 5. The coating composition of claim 2 in which the crosslinking agent is a phenol formaldehyde resin. 6. A method for forming a supported adhesive film comprising a. applying to a surface of a substrate a continuous thin layer of the adhesive coating composition of claim 2; and b. drying the layer by heating and maintaining it at a temperature and for a time sufficient to effect substantially complete removal of water and residual monomer by vaporization from the layer without incurring crosslinking of the crosslinking agent. 7. The method of claim 6 in which the substrate is a release substrate. 8. The method of claim 6 in which the substrate is a nonrelease substrate. 9. The method of claim 8 in which the substrate is a polyimide film. 10. The method of claim 8 in which the nonrelease substrate is a fabric of aramid fiber. 11. A method for joining two material layers comprising the steps of (a) applying to the first of the two material layers an adhesive film made by the method of claim 7; (b) separating the substrate from the applied adhesive film: (c) applying to the exposed surface of the adhesive film the second material layer and (d) subjecting the assemblage of steps (a) through (c) to pressure and heat sufficient to effect cross linking of the cross linking agent. 12. The method of claim 11 in which the second material layer is a fabric of aramid fiber. 13. A method for joining two material layers comprising the steps of (a) applying to the first of the two material layers an adhesive film made by the method of claim 8; (b) applying to the exposed surface of the adhesive film the second material layer and (c) subjecting the assemblage of steps (a) and (b) to pressure and heat sufficient to effect crosslinking of the crosslinking agent. 14. The method of claim 13 in which the first layer is a polyimide film and the second layer is a flexible metal foil. 15. The method of claim 14 in which the foil metal is copper. 16. A method for joining two material layers comprising the steps of (a) applying to the first of the two material layers an adhesive film made by the method of claim 7; (b) separating the substrate from the applied adhesive film; (c) applying to the exposed surface of the adhesive film the second material layer and (d) subjecting the assemblage of steps (a) through (c) to pressure and heat sufficient to effect crosslinking of the cross linking agent. 17. The method of claim 16 in which both material layers are metal foils.

Inventors: FRYD, MICHAEL, PYE, WALTER E., REDFEARN, RICHARD DANIEL
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1986
Main classification: C08F220
IPC codes: C09J5, H05K3, C08J5, C09J7, C09J133, B32B15, C08F220, C08L33, C08F20, C09D133