EP0263130A1 - Structural film adhesive member curable at ambient temperature and method for its use - Google Patents

Abstract

A composite adhesive film (19) for joining two structures (18) has an adhesive layer (14) welded to each side of a porous carrier layer (12), and can be prefabricated in shape and thickness. desired before being placed between the two structures to be bonded. The adhesive layer (14) is preferably composed of an adhesive mixture of an epoxy resin and a curing agent which undergoes creep and hardens at room temperature, and is coated on the porous carrier layer (12) in desired thicknesses. Detachable non-stick layers (16) of Mylar are placed on each of the exposed surfaces of the adhesive. The coated carrier layer (10) is then refrigerated to a temperature so low that the adhesive mixture can no longer creep or harden, and stored for indefinitely long periods. To glue the structures, the release films (16) are detached, and the cold adhesive film (19) is placed between the two structures (18). The structures are pressed against said film, and the adhesive mixture is allowed to harden, the two structures thus being bonded to each other, while a uniform insulating layer, the porous carrier layer (12), prevents physical contact. between said structures.

Description

STRUCTURAL FILM ADHESIVE M.EMBER CURABLE

_AT AMBIE_NT TEMPERATURE AND METHOD FOR ITS U^SE

BACKGROUND OF THE INVENTION

This Invention relates generally to the joining of two structures, and, more particularly, to a composite film adhesive member for Joining structures.

One of the most important aspects of many manufacturing operations is the Joining of structures that • are separately prepared and then Joined together into larger pieces, which themselves may be Joined to other structures or may be the final assembled parts. Joining of structures is a critical operation, since subsequent failures often occur at the locations where structures are Joined, or because there may be special requirements to be met at the interface between two structures. The surface along which two structures are Joined must therefore be strong, resistant to failure by many different mechanisms such as fatigue and corrosion, and additionally must sometimes meet other requirements such as acting as an electrical insulator.

Structures used in aircraft and space vehicles are often subjected to some of the greatest demands placed upon any structures, since excellent physical properties must be coupled with low weight. Most such structures have, in the past, been Joined using mechanical fasteners such as rivets, bolts or screws, or by metallurgical bonding techniques such as welding, brazing or soldering. More recently, the properties of adhesives have improved so that many aerospace structures can be Joined by adhesives. Adhesively bonded structures have some important structural advantages over structures bonded with fasteners, since the bonded structures may actually be stronger than those using fasteners because the surface loading is distributed over larger areas. Since the loads are distributed, the Incidence of structural failure such as by fatigue cracks initiated at stress concentrations around fasteners is greatly reduced.

In some Joining applications it is necessary that the bondllne provide an electrically insulating barrier, as well as being strong. In one example, the nickel-alloy pressure vessel of a spacecraft electrical storage cell is Joined to aluminum thermal flanges which help to dissipate the heat developed in the cell. It Is Important that the bondline between the cell and the flanges be electrically insulating, so that the charge of the cell cannot be lost to the remainder of the spacecraft, If there is a malfunction which allows the pressure vessel to become charged. Moreover, the adhesive must have very low particle outgassing in a space environment. That is, the presence of the adhesive cannot result in the production of small particles which would enter the atmosphere and possibly adversely affect other spacecraft systems.

Silicone-based adhesives such as RTV 566 adhesive are now used to bond the battery pressure vessels to the thermal flanges. This adhesive cures and hardens at ambient temperature and Is available as a paste that can be applied to each surface to be bonded. The ability to cure at ambient temperature is important In this application, as well as many other applications in the Joining of aircraft and spacecraft structures, since the entire structure to be bonded cannot be heated to elevated temperature to allow the adhesive to cure. Even though the silicone-based adhesive is itself essentially electrically nonconducting, if only the adhesive is placed between the pressure vessel and the flange, it is possible that the two might physically touch at isolated points, so that the resulting bondline would not meet the requirement of electrical Insulation. It is therefore standard practice to place a layer of insulator such as mylar plastic between the pressure vessel and the flange, with the adhesive on either side of the insulator layer. That is, the bonded structure is formed by coating both the pressure vessel and the flange with the silicone adhesive, placing a layer of mylar on top of one of the layers of adhesive, and then pressing the parts together for curing.

While this approach is operable, It is slow, since the silicone adhesive requires about fourteen days to cure to a strength sufficiently high that the assembled part can be moved. This approach is also not efficient from a weight standpoint, since the adhesive is heavy and the thickness cannot be controlled accurately when the adhesive is applied as a paste. The total thickness of the interlayer between the bonded structures is typically about .030 inches, but depends upon the skill of the workman who applies the adhesive. This excessive thickness adds significantly to the weight of the spacecraft. This adhesive bonding technique is also slow and costly, since the workman must carefully apply the adhesive to each area, being careful to coat all areas with as uniform a layer as he can. Finally, and most significantly, the resulting bonded structure is weak, not because the adhesive itself is weak, but because of the mylar film that is interposed between the adhesive layers. The structures are bonded together through the mylar film, not directly to each other.

There has therefore existed a need for an improved adhesive bonding technique for Joining structures at ambient temperatures. This technique should produce a strong bond, and also be economical both as to total use of adhesive and to the labor required, and as to the amount of time required to accomplish the bonding operation before the bonded structure can be moved. The bonding approach should produce an acceptably low level of particle outgassing. The technique should provide an electrically insulating bondline when used in applications such as the bonding of battery pressure vessels and thermal flanges. However, the technique would have much broader applicability to the bonding of other structures. The present invention fulfills this need, and further provides related advantages.

SUMMARY OF THE INVENTION

The present Invention resides In a structural film adhesive member that can be prefabricated prior to use, to the correct size corresponding to the size of the surfaces to be bonded, and a method for its use. The film adhesive member can be precisely prepared to the desired adhesive thickness with provision for ensuring electrical separation and insulation of the structures being bonded. The bond formed is of uniform and controllable thickness and is stronger than the bond obtainable with prior approaches. The film adhesive member can be prepared well before its use is required, in large lots to allow economical fabrication of the member itself, and then stored for later use with no loss of effectiveness. In accordance with the invention, a method for bonding two structures together comprises preparing a film adhesive member, the film adhesive member comprising a porous carrier layer and two unhardened adhesive layers, one on either side of the porous carrier layer, and Joined thereto to form an adhesive structure, with sufficient strength that the adhesive structure can be handled without separating, the adhesive layers being formed of an ambient-temperature curing adhesive material; cooling the adhesive member to a temperature sufficiently low such that the adhesive layers cannot cure; storing the adhesive member at the low temperature; and placing the adhesive member between the structures to be bonded under pressure at a temperature at which the adhesive material can cure, and allowing the adhesive to cure. A release film layer of a material such as mylar plastic, Joined to each of the layers of unhardened adhesive, on the side not in contact with the porous carrier material, is preferably provided so that the film adhesive member can be readily handled during storage and application. The porous carrier layer is preferably a mat of glass fibers, most preferably about .004 inches thick. The adhesive material preferably Includes an epoxy resin, most preferably with a polyamide curing agent. The thickness of each adhesive layer is preferably about .003 inches.

More specifically, a method for bonding two structures together comprises preparing a film adhesive member, the film adhesive member comprising a porous mat of glass fibers and two unhardened adhesive layers, one on either side of the mat of glass fibers, wherein the adhesive material of the adhesive layers has flowed into the mat of glass fibers, thereby Joining the adhesive layers to the mat of glass fibers with sufficient strength that the film adhesive member can be handled without separating, the adhesive layers being formed of an adhesive mixture of an epoxy resin that cures at ambient temperatures and a polyamide curing agent, the adhesive mixture being fluid at ambient temperature so that the adhesive mixture would flow away from the mat of glass fibers if handled at ambient temperature, the film adhesive member further comprising a pair of strippable release film layers on the free surfaces of the adhesive layers not in contact with the mat of glass fibers; immediately cooling the film adhesive member to a temperature sufficiently low that the adhesive mixture is not fluid and cannot cure, so that the adhesive mixture is in a substantially solid, uncured state; storing the film adhesive member at the temperature whereat the adhesive mixture Is solid and cannot cure; removing the strippable release film layers in an order compatible with the assembly of the two structures; and placing the film adhesive member between the two structures to be bonded under pressure, and allowing the temperature of the film adhesive member to rise to a temperature at which the adhesive mixture can cure. Again, the thickness of the mat of glass fibers is preferably .004 inches, and the thickness of each of the adhesive layers .003 inches.

A composite film adhesive member comprises a porous mat of glass fibers; a pair of adhesive layers contacting the mat of glass fibers, one on each side thereof, each of the adhesive layers comprising an adhesive mixture that cures at ambient temperature and is sufficiently fluid at ambient temperature that the adhesive mixture flows away from the mat of glass fibers; and a pair of mylar release layers, each of said release layers contacting one of the adhesive layers on the side of the adhesive layer remote from the mat of glass fibers. The adhesive mixture Is preferably a mixture of an epoxy resin and a polyamide curing agent.

The composite film adhesive member of the Invention can be conveniently prepared in large lots, frozen, cut to size, and stored in packages until needed. When the structures are to be bonded, one of the release films is stripped away, the film adhesive member Is pressed against one of the surfaces to be bonded, the other release film is stripped away, and the other surface is pressed into place. This operation Is precise, readily repeatable, and uses far less adhesive than prior approaches while achieving a stronger bond. It is also accomplished in less than two minutes, as compared with far greater times in the prior approach. With the preferred epoxy resin and curing agent, sufficient strength is developed after about 16 hours that the bonded structure can be moved about without parting of the bond line, but full curing occurs after about seven days. The strength developed after seven days is significantly in excess of that developed with conventional silicone adhesives.

It will now be appreciated that the adhesive member and method of the present Invention provide a significant Improvement in_. the art of adhesively Joining structures, particularly where the structures must be electrically insulated from each other. The adhesive member can be readily and economically fabricated in a highly controllable and reproducible manner, and then stored indefinitely until use without loss of effectiveness when used. A workman can bond two structures together in minutes instead of hours, and the curing operation proceeds rapidly so that the bonded structure can be handled in less than a day. The bonded structure is stronger than those obtained with prior bonding techniques and weighs less. Other features and advantages of the invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side sectional view of a film adhesive member in accordance with the invention;

Figure 2 is a side sectional view of two structures bonded together using the film adhesive member of Figure 1; and Figure 3 is an enlarged detail of Figure 2, illustrating the porous carrier layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is embodied in a film adhesive member, indicated in Figure 1 by the numeral 10, that is used to bond two structures together. The film adhesive member 10 is an article that may be prepared, stored and handled prior to its use to bond the structures together. The film adhesive member 10 includes a porous carrier layer 12. On each side of the carrier layer 12 is an unhardened adhesive layer 14, each adhesive layer 14 being Joined to the carrier layer 12 with sufficient strength that the entire film adhesive member 10 can be handled without causing the adhesive layers 14 to separate from the carrier layer 12. Because the carrier layer 12 is porous, a small amount of the material of the adhesive layer 14 can penetrate into the carrier layer 12 during fabrication of the film adhesive member 10, thereby creating the necessary Joining between the adhesive layers 14 and the carrier layer 12 to provide sufficient strength to hold the film adhesive member 10 together even before curing. Preferably, on each face of the adhesive layer 14 not in contact with the carrier layer 12 there is provided a strippable release film layer 16. The film adhesive member 10 is manufactured with this release film layer 16 in place, and then the release film layer 16 is removed Just prior to use of the film adhesive member 10 in a bonding operation.

The use of the film adhesive member 10 to bond two structures 18 together is depicted in Figure 2, which illustrates the bondline 19 between the structures 18. The release film layers 16 have been removed, and the remainder of the film adhesive member 10 is In place between the two structures 18. Each structure 18 is bonded to the other at the bondline 19 through two layers of adhesive 14 and the porous carrier layer 12. The preferred material of the carrier layer

12 is a mat of glass fibers such as a woven fiberglass cloth. Fine glass fibers 20 may be woven, pressed, or extruded together to form a mat that is commercially available in a variety of thicknesses, as needed. A thickness of the mat of glass fibers of about .004 inches has been found satisfactory. The layer 12 is porous in the sense that, like all mat or cloth materials, there is some degree of spacing between the fibers, allowing the penetration of other materials into the porosity. This porosity is important for the operability of the invention, for the reason illustrated in Figure 3. After fabrication of the film adhesive member 10, the material of the adhesive layer penetrates between the fibers 20 as inter-fiber adhesive material 22. A continuous path of inter-fiber adhesive .material 22 remains through the thickness of the carrier layer 12, so that the carrier layer 12 becomes a fiber composite material. The fibers 20 cooperate with the inter-fiber adhesive material 22 to carry shear loadings, while the inter-fiber adhesive material 22 bears tensile loadings perpendicular to the fibers 20. By contrast, a non-porous layer would not allow penetration of the adhesive material in this way, so that the tensile and shear loadings being carried through the bondline would necessarily be borne fully at the relatively weak interface between the non-porous layer and the adhesive layer.

The material of the adhesive layer 14 is an adhesive mixture, preferably a mixture of an epoxy resin and its curing agent that cures at ambient temperature. A satisfactory epoxy resin is 828 Epon epoxy of the bisphenol-A type. Such an epoxy resin is available from 3M Corporation as type EC 2216 epoxy resin. A preferred curing agent is a polyamide curing agent derived from the nylon structure. The preferred epoxy resin and curing agent are present in a ratio of 7 parts by weight epoxy and 5 parts by weight of curing agent, although this ratio will vary depending upon the exact epoxy and curing agent chosen. The use of the polyamide curing agent is important, since it imparts a glass transition temperature of about 125 degrees Fahrenheit to the mixture of epoxy resin and curing agent. The mixture is flexible in the range of 125 degrees Fahrenheit down to at least -50 degrees Fahrenheit, so that flexibility is retained during preparation and storage of the film adhesive member 10. When this mixture cures in the adhesive layer, there is no production of undesirable particles, termed particle outgassing. The resulting film adhesive layer after curing is strong and adheres well to metallic surfaces such as those typically present in the structures 18. No particular preparation of the surfaces of the structures 18 is necessary beyond usual cleaning procedures. Wire brushing has been found effective to promote the bonding. The thickness of the adhesive layer may be varied arbitrarily by the manufacturing method to be described, but a thickness of each adhesive layer 14 of about .003 inches has been found satisfactory.

The material of the release film layer 16 is preferably a plastic such as mylar plastic film. This film is readily available in a range of thicknesses, and a thickness of about .0008 inches has been found satisfactory.

The film adhesive member 10 may be conveniently manufactured in large quantities by placing a sheet of the release film layer 16 onto a smooth surface. A mixture of the material of the adhesive layer 14 is prepared by mixing the epoxy resin and the curing agent in the proper ratio. This mixture cures at ambient temperature, but initially the curing is sufficiently slow ^"that the there Is time to prepare the adhesive member 10. The mixture has a consistency like that of cold sugar syrup, so that it may be spread into a layer that flows slowly. A layer of the adhesive material having the desired thickness is placed onto the release film layer. The thickness of the layer may be made extremely uniform by smoothing the top surface of the layer with a roller or smoothing bar spaced up from the underlying surface.

A piece of the porous carrier layer material is gently placed onto the top surface of the adhesive layer. Then another layer of the adhesive material is spread onto the top of the porous carrier layer material. Finally, another sheet of the release film material is placed over the top layer of adhesive, thereby completing the stack of porous glass mat, two adhesive layers, and two release film layers. During this operation, some of the adhesive mixture flows Into the porous spaces between the fibers of the mat of glass fibers. The stack may then be vertically pressed to force more of the adhesive material between the fibers 20 to form the inter-fiber adhesive material 22. The vertical pressing may be conveniently accomplished by passing the stack between a pair of rollers set with a gap between the rollers of the desired thickness of the film adhesive member 10. The pressing adjusts the thickness of the member 10 uniformly to the desired standard value, and also forces adhesive between the fibers of the mat. Because some of the adhesive is thereby Impregnated into the porous carrier layer 12, the thickness of the adhesive layers that are initially spread must be somewhat greater than the desired final thickness of the adhesive layer 14. It has been found that, using a .004 inch thick fiberglass carrier layer 12, about .004 inches of the adhesive material must be spread initially to obtain a final thickness of each of the adhesive layers 14 of about .003 Inches. The film adhesive member 10 is then immediately cooled to a temperature below which the adhesive mixture cures, and below which the adhesive mixture solidifies. At ambient temperatures, the freshly spread, uncured adhesive mixture Is sufficiently fluid that it would flow away from the porous carrier layer if allowed to sit, and the film adhesive member would disintegrate. Only by cooling to such a low temperature can the structure of the film adhesive member 10 be preserved, and additionally the cooling halts the curing process so that the uncured film adhesive member can be stored indefinitely. The temperature to which the film adhesive member is cooled varies with the nature of the adhesive mixture, but temperatures of about -40 degrees Fahrenheit to about 0 degrees Fahrenheit are preferred because they achieve the necessary suspension of curing and solidification of the adhesive mixture, and are also readily available In commercial freezers. After the film adhesive member is cooled so that the adhesive mixture is solid, the film adhesive member may be cut by scissors or die to the desired final shape of the surfaces to be bonded, if that is known, to form precut pieces. The precut pieces or the larger sheets are then stored at a reduced temperature for later use. It is often desirable to prefabricate larger quantities of the film adhesive member 10 than will be immediately used, to take advantage of economies of scale in manufacturing. The prefabricated film adhesive member may be stored by sealing it within an airtight container such as an aluminum pouch and storing it at a temperature at which the curing process is arrested. A storage temperature of -40 degrees Fahrenheit has been found to allow storage of the film adhesive member for up to one year without loss of effectiveness when used subsequently. When a frozen piece of the film adhesive member 10 is to be used in a bonding operation, it is removed from cold storage and one of the release film layers immediately stripped off, leaving an exposed adhesive face. The exposed adhesive face is placed against the surface of one of the structures to be bonded, and pressed tightly to conform the shape of the adhesive member 18 to that of the surface before the cold film adhesive member heats up to ambient temperature. The use of an adhesive mixture of an epoxy resin and polyamide curing agent having some flexibility at the cold storage temperature aids at this stage of the bonding operation, since the adhesive member can be bent without cracking. It is found that the pressing of the film adhesive member 10 to the surface usually results in sufficient adhesion so that the film adhesive member 10 sticks to the surface. The second release film layer is then stripped away, leaving a second exposed adhesive face. The surface of the other structure to be bonded is then pressed into place, moved slightly as necessary to a conforming fit, and then clamped tightly. This part of the bonding process is accomplished quickly, preferably before the film adhesive member heats up to ambient temperature. At ambient temperature the adhesive mixture would flow slowly out of the member, disintegrating the film adhesive member. A short period of time at ambient temperature before completing the bond is acceptable, since the viscosity of the adhesive mixture is typically sufficiently high that it will not flow rapidly.

The resulting bonded structure, as illustrated in Figure 2, is strong in the bondline and also permits electrical isolation of the two bonded structures from each other. If the porous carrier layer and the adhesive layers are both nonconductors, then the two structures 18 cannot come into physical contact to allow a charge to pass. If the carrier layer were not present, then it would be possible for the two structures to contact at points where the adhesive was thin.

The approach of the present invention is particularly useful in bonding nickel-alloy electrical storage cells to aluminum-alloy thermal flanges, forming structures to be used in satellites or other types of spacecraft. Such bonding was previously done using sil cone adhesive of the RTV 566 type, which has low particle outgassing and is rubbery, but is also relatively weak. This material is rather difficult to obtain in the small quantities desired, with lead times between the placing of an order and delivery typically about 4 months. A mylar plastic layer was used between the layers of the silicone adhesive that were placed between the pieces to be bonded. The silicone adhesive was applied to the surface in as uniform a layer as possible, the mylar film was laid in place, and then another layer of the adhesive was applied. The technique is messy and slow, often requiring over one hour of labor by a skilled technician to obtain a satisfactory bondllne. Slight disturbances during preparation can disrupt the preparation of the bondline and greatly lengthen the time required. When successful, the process results in bondline thicknesses of about .030 inches, over three times the thickness of the bondline using the present approach. Even skilled workmen cannot obtain consistently good bonds of smaller thicknesses.

By contrast, using the present approach the bond can be formed consistently and repeatably in about two minutes by a semi-skilled workman. The bondline is thin, on the order of .008-.010 in thickness, saving about .020 thickness. Through this saving in thickness of bondline material, and because the mixture of epoxy resin and curing agent has a slightly lower density than the silicone adhesive, a total of about forty-one pounds weight can be saved on each spacecraft when using the film adhesive member in this one application. The value of saving one pound in orbit is currently $12.000-S20,000, so that the commercial value of the invention is immediately apparent.

The strength of the bond developed by the silicone adhesive used with a mylar interlayer is measured at about 10 pounds per square inch (psi). The present approach of an epoxy film adhesive mixture with a porous interlayer has been measured by lap shear tests to have a bond strength of about 1700-2100 psi.

As is now apparent, the present invention represents an important advance in the art of adhesively bonding structures. A prefabricated adhesive member can be prepared in bulk and then stored until needed. The adhesive member can be quickly installed between structures to be bonded, and cures to a bond that is much stronger than prior bonds, and also exhibits low particle outgassing and quick setting. Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method for bonding two structures together, comprising: preparing a film adhesive member, the film adhesive member comprising a porous carrier layer and two unhardened adhesive layers, one on either side of the porous carrier layer, and Joined thereto to form an adhesive structure, with sufficient strength that the adhesive structure can be handled without separating, the adhesive layers being formed of an ambient-temperature curing adhesive material; cooling the adhesive member to a temperature sufficiently low such that the adhesive layers cannot cure; storing the adhesive member at the low te - perature; and placing the adhesive member between the structures to be bonded under pressure at a temperature at which the adhesive material can cure, and allowing the adhesive to cure.

2. The method of claim 1, wherein the film adhesive member further includes a release film layer Joined to one of the layers of unhardened adhesive, on the side not in contact with the porous carrier material.

3. The method of claim 1, wherein the carrier layer of the film adhesive member is formed of a mat of glass fibers.

4. The method of claim 1, wherein the carrier layer of the film adhesive member is about .004 inches thick.

5. The method of claim 1, wherein at least one of the adhesive layers of the adhesive member includes an epoxy resin.

6. The method of claim 5, wherein the epoxy resin is capable of curing fully at ambient temperature.

7. The method of claim 5, wherein the adhesive layer further includes a polyamide curing agent.

8. The method of claim 1, wherein at least one of the adhesive layers of the adhesive member is about .003 inches thick.

9. The method of claim 2, wherein the release film layer is mylar film.

10. A method for bonding two structures together, comprising: preparing a film adhesive member, the film adhesive member comprising a porous mat of glass fibers and two unhardened adhesive layers, one on either side of the mat of glass fibers, wherein the adhesive material of the adhesive layers has flowed into the mat of glass fibers, thereby Joining the adhesive layers to the mat of glass fibers with sufficient strength that the adhesive film member can be handled without separating, the adhesive layers being formed of an adhesive mixture of an epoxy resin that cures at ambient temperatures and a polyamide curing agent, the adhesive mixture being fluid at ambient temperature so that the adhesive mixture would flow away from the mat of glass fibers if handled at ambient temperature, the adhesive film member further comprising a pair of strippable release film layers on the free surfaces of the adhesive layers not in contact with the mat of glass fibers; immediately cooling the film adhesive member to a temperature sufficiently low that the adhesive mixture is not fluid and cannot cure, so that the adhesive mixture is in a substantially solid, uncured state; storing the film adhesive member at the temperature whereat the adhesive mixture is solid and cannot cure; removing the strippable release film layers in an order compatible with the assembly of the two structures; and placing the film adhesive member between the two structures to be bonded under pressure, and allowing the temperature of the adhesive film member to rise to a temperature at which the adhesive mixture can cure.

11. The method of claim 10, wherein the mat of glass fibers is about .004 inches thick.

12. The method of claim 10, wherein each of the adhesive layers is about .003 inches thick.

13. A composite film adhesive member, comprising: a porous mat of glass fibers; a pair of adhesive layers contacting the mat of glass fibers, one on each side thereof, each of said adhesive layers comprising an adhesive mixture that cures at ambient temperature and is sufficiently fluid at ambient temperature that the adhesive mixture flows away from said mat of glass fibers; and a pair of mylar release layers, each of said release layers contacting one of said adhesive layers on the side of said adhesive layer remote from said mat of glass fibers.

14. The film adhesive member of claim 13, wherein the mat of glass fibers is about .004 inches thick.

15. The film adhesive member of claim 13, wherein each of said adhesive layers is about .003 inches thick.

16. The film adhesive member of claim 13, wherein the adhesive mixture comprises a mixture of an epoxy resin and a polyamide curing agent.