Process of manufacture for high performance epoxy based laminating adhesives

Abstract: A high performance laminating adhesive material is prepared using one or more epoxy components which inter­ react with a high molecular weight polyester component through a two-stage reaction sequence. The first stage of the sequence is the reaction of a isocyanate component with a polyester component. The second stage of the sequence is the reaction of the isocyanate/polyester component with the epoxy component(s). The result of the reaction process is an adhesive material providing a flexible, high temperature resistant, fully crosslinked adhesive with good Z-axis sta­ bility without the evolution of by-products. The adhesive material has application to the bonding of polyimide films, copper or other metal foils and hardboards for use in the manufacture of flexible, hardboard or multilayer substrates as well as surface to surface bonding of other materials.

Description: During the past quarter century, the growth of the electronic circuits industry at an unrivaled pace has resulted in the development of higher performance materials of construction. However, with the development of higher performance materials of construction has not resulted in the development of corresponding high performance adhesive materials and systems to bond the materials of construction together, especially in severe environmental conditions found in under-the-hood automotive and military applications. Adhesive materials and systems that are currently available meet some of the requirements for such properties as peel strength, chemical resistance, moisture resistance, high temperature stability, dimensional stability especially in the Z-axis direction and ease of processing, but typically fail to meet one or more of the requirements for one or more of the properties. A need has therefore been felt for an adhesive material that meets all the requisite property requirements for severe environmental conditions while retaining the ease of application. It is an object of the present invention to provide a process for an improved adhesive material. It is a feature of the present invention to provide an improved material suitable for use with electronic construction materials. It is yet another feature of the present invention to provide an adhesive material that requires a two stage reaction process for bonding. It is yet a further feature of the present invention to combine an isocyanate component, a polyester component and one or more epoxy components using a two stage reaction to provide a high performance adhesive material. The foregoing and other features are accomplished, according to the present invention, by combining at least one epoxy component chosen from the flexible bis-epi and the hard novolac epoxy families and at least one high molecular weight polyester component along with an isocyanate cure mechanism. The isocyanate curing agent and the polyester component interact in a first reaction stage. The isocyanate/polyester compound resulting from the first reaction stage and the epoxy components are combined. The resulting combination can be applied to a surface of a laminate layer or another first surface. A second surface can be placed in contact with the first surface and a second reaction stage permitted to take place, forming the high performance bond. These and other features will be understood by the reading of the following description. According to the process claimed in the present invention at least one and preferably two epoxy components selected from the flexible bis-epi and hard novolac families, such as Celanese Epi-Rez-5132 and Dow D.E.N. 438 respectively; at least one high molecular weight polyester component such as DuPont's 49002 or DeSoto's 301 resin systems; and an isocyanate cure mechanism such as Upjohn's PAPI-135 or Mobay's Mondur MRS are reacted in a specific sequence. The cure sequence of the present invention consists of first reacting the isocyanate component with the hydroxyl groups which terminate the polyester component as shown in the following reaction sequence known in the related art. where (R) x represents a high molecular weight polyester repeating unit with alcohol type hydroxyl end group functionality. This reaction takes place at room temperature slowly and more rapidly with heating of the composition to 250°F. The secondary reaction, involves reaction of the group in the formed urethane linkage with the epoxide groups of the epoxy components as follows: where R x in this formula represents the bis-epi and/or novolac epoxy structures as shown below: " NOVOLAC" EPOXY Example of the Process The components of the adhesive material processed according to the present invention, in one embodiment, are: a polyester resin having a solids content of 17-20% composed of DuPont 49002 base in a solvent mixture of 90% methylene chloride to 10% cyclohexanone by weight; an epoxy novolac at 85% solids composed of Dow DEN 438-EK85 in methylethylketone; and a bis-epi epoxy composed of Celanese Epi-Rez 5132 at 100% solids; and a curative component of a polyfunctional isocyanate sold by Mobay under the trade name Mondur MRS. The components can be combined according to the following two procedures: Procedure 1) The adhesive coating composition is made by adding 80% by solids of the polyester component to 10% by solids of the epoxy novolac to 10% by solids of the bis-epi epoxy to 1.2 parts by weight of the isocyanate in an open container without agitation. The composition is then agitated well for 1-5 minutes. The container is then capped with an air-tight lid for 30 minutes to allow for the onset of isocyanate/polyester reaction; or Procedure 2). The polyester and isocyanate are combined, thoroughly mixed, then allowed to stand at room temperature for a minimum of 30 minutes prior to the epoxy additions to allow onset of the isocyanate/hydroxyl reaction. The adhesive coating composition resulting from either of the foregoing procedures is then applied by means of the reverse roll coating technique to a 0.025mm (1 mil) polyimide film to yield a 0.025mm (1 mil) thick dry coat weight. Drying (i.e., removal of the solvents) is accomplished through a 22.9m (75 foot)-3 zone oven at 100°C (212°F) and 7.6m (25 feet) per minute. The coated substrate is then positioned next to the treated side of 78.3g (1 oz). copper foil, wherein the copper foil surface is treated with Oak CMC-111 compound (to enhance bondability). The polyimide film and copper foil are heated to 148.9°C (300°F) to 162.7°C (325°F) with an applied pressure of 551.6kPa (80psi) (pounds/square inch) to 827.4kPa (120 psi) through a coater/laminator combining station as part of a continuous operation. The resulting composite is rolled onto a 6" core, left at room temperature for one to seven days then post cured as follows: 2 hours @ 65.5°C (150°F) 2 hours @ 135°C (275°F) 2 hours @ 176.7°C (350°F) The resulting composite structure exhibited the properties shown in Table I when tested per ANSI/IPC-FC-232B and 241 B procedures: Initial Peel 357.1Kg/m (20PLI) Peel After Solder 375 Kg/m (21PLI) Chemical Resistance MEK 375 Kg/m (21PLI) TOL 375.1Kg/m (20PLI) IPA 375 Kg/m (21PLI) T111/MC 375 Kg/m (21PLI) Solder Float Pass Aging (96 hrs @ 135°C (275°F) in air circulating oven) No Bond Strength Change where; PLI = Pounds per lineal inch MEK = Methylethyl ketone TOL = Toluene IPA = Isopropylalcohol T111 = Trichloroethylene MC = Methylene Chloride The polyester compound is a high molecular weight hydroxyl terminated polymer, while the curative compound is a polymeric isocyanate. In the preferred embodiment, a combination of a flexible bis-epi epoxy compound and a hard novolac epoxy compound are both included to achieve the properties of both compounds. The second reaction provides a fully cross-linked network between the groups formed in the first reaction and the in the epoxy components without evolution of by-products. The present invention provides what is believed to be the first adhesive system with extremely balanced properties and the added benefit of superior Z-axis stability. More specifically, the present invention provides an epoxy based laminating adhesive which can be continuously processed and cured without the evolution of by-products to provide a flexible bond-ply with the added property of excellent Z-axis stability. The adhesive material is applicable to film substrates (e.g., polyimide), foil substrates (e.g., copper) and hardboard substrates (e.g., FR4 (fiberglass impregnated) hardboard). The foregoing description is included to illustrate the operation of the preferred embodiment.

Claims: A two-stage process for providing an adhesive material which comprises: a) reacting an isocyanate component at a temperature of from room temperature up to 121.1°C (250°F) with at least one hydroxy terminated polyester compound of high molecular weight; and b) reacting the -NH- groups in the isocyanate/polyester component resulting from said isocyanate/polyester reacting step at a temperature of from 121.1°C (250°F) to 204.4°C (400°F) with at least one epoxy component from the groups of bis epi and novolac epoxy components to form a cross-linked product. The process for providing an adhesive material of claim 1 further comprising: mixing said isocyanate/polyester component with said epoxy compound and applying a resulting mixture to a location requiring said adhesive material prior to reaction between said isocyanate/polyester component and said at least one epoxy component. The process for providing an adhesive material of claim 1 or 2, further comprising: using 50% - 90% by weight of the said polyester compound and 10 - 50% by weight of said at least one epoxy compound. The process for providing an adhesive material of any of claims 1 to 3 wherein said isocyanate component, said polyester component and said epoxy component are mixed together prior to reacting the components. The process for providing an adhesive material of any of claim 1 to 4 wherein reacting said isocyanate/polyester component with said at least one epoxy component includes reacting group in the formed urethane linkage with the expoxide groups of the epoxy components. The use of an adhesive prepared by the process for providing an adhesive material of any of claims 1 to 5 to bond substrates selected from film substrates, foil substrates and hardboard substrates.

Inventors: GARDESKI THOMAS F, GARDESKI, THOMAS F.
Applicants: COURTAULDS PERFORMANCE FILMS
Application year: 1989
Main classification: C08G18
IPC codes: C08G18, C09J175, H05K3