Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-10-27
2001-08-28
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S084000, C156S086000, C156S157000, C156S160000, C156S324000, C442S286000, C442S290000
Reexamination Certificate
active
06280546
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cut resistant and abrasion resistant laminates and the process for their production. More particularly, the present invention relates to a method of producing such a laminate by bonding a layer of a thermoplastic film, for example polyethylene or ethylene vinyl acetate (EVA), to a layer of a strong, lightweight fabric constructed of a high performance fiber such as ultra high molecular weight polyethylene fibers.
BACKGROUND OF THE INVENTION
High performance fabrics have been used for a number of applications where tear-resistance, abrasion-resistance, cut- and stab-resistance, and chemical- and cold-resistance are important. As used herein, the term “high performance” refers to fabrics constructed from a group of fibers used to make cut-resistant and abrasion resistant articles such as gloves and aprons. The high strength-to-weight ratios of these fabrics can provide properties having significant improvements in the performance characteristics stated above at a fraction of the weight of other alternatives. It would be desirable to combine the advantages of high performance fabrics with film-laminated fabrics currently used for applications including, but not limited to sail cloth, cargo container covers, side curtains for side-access trucks and bulk mail bags. With the exception of sail cloth, these items typically are constructed from vinyl-coated nylon or similar materials which do not exhibit these high performance characteristics. The vinyl coating is provided for the purpose of creating an impervious barrier to air and fluid penetration. The disadvantages of currently available vinyl-coated nylon or polyester fabric materials is their relative lack of durability and relatively higher weight per unit area. Thus, it would be desirable to take advantage of the high strength and low weight characteristics of high performance fabrics for these applications. A successful lamination process for these fabrics would enhance their abrasion resistance. It is believed that to date no successful process has been developed for the economical lamination of high performance fabrics with a thermoplastic film such as polyethylene or EVA to create a more durable, waterproof, cut and wear resistant flexible laminate.
Numerous attempts have been made to adhere a polyethylene film to a high performance fabric such as a fabric constructed from yarns made up of high strength, ultra high molecular weight polyethylene yarn. A typical example of such a yarn and fabric is Spectra® brand fiber available from Allied Signal. This fiber is also sometimes described as being constructed from an extended chain polyethylene. In the more than ten years since the initial introduction of Spectra fiber, it is believed that no commercially viable process for laminating a polyethylene film to a fabric constructed from Spectra fiber has been developed. There are believed to be several reasons for this result. High molecular polyethylene fibers lose significant strength if exposed to temperatures in the range of about 230-240° F. and higher when the fibers are unconstrained. The loss of fiber properties is a function of both the temperature and the time that the fiber is held at that temperature. Additionally, the temperature range and time required to adhere the polyethylene film to the high performance fiber significantly exceeds the time/temperature exposure required to degrade the unconstrained fiber. Moreover, high strength, high modulus polyethylene fibers shrink significantly with exposure to heat if not tightly constrained. This shrinkage is well in excess of five percent and can result in stretches in the fabric that cause permanent and severe creases to the point that the resulting laminate is not commercially usable.
There is a need then for a process that securely and reliably bonds a thermoplastic film having an ethylene content of at least about 20 percent to a fabric formed of high performance fibers with the application of heat but in a manner that maintains the properties of the high performance fiber.
SUMMARY OF THE INVENTION
The present invention solves the problems previously attendant to the lamination of thermoplastic films to fabrics constructed with a substantial percentage (greater than 25%) of high performance fibers such as high tenacity, high modulus, ultrahigh molecular weight polyethylene fibers.
The solution involves rolling a thermoplastic film having an ethylene content of at least about 20% and the high performance fiber fabric together under tension to form a wound bundle; and heating the wound bundle at a sufficient temperature and for a sufficient length of time so as to soften the thermoplastic film such that shrinkage of the high performance fabric generates the laminating pressure to laminate said thermoplastic film to said high performance fabric.
This technique results in a flexible, cut and abrasion resistant, substantially air and liquid impervious laminate including a woven fabric including warp yams and weft yarns wherein the warp yams are comprised of an ultra high molecular weight polyethylene; and a laminating layer comprised of low density polyethylene film.
In an alternative embodiment, a substantially air and liquid impervious laminate comprised of a first outer layer comprising a laminate of a woven high performance fabric and a thermoplastic film comprised of low density polyethylene is placed on either side of an intermediate layer comprising a scrim fabric. The thermoplastic films of the first and second outer layers face the intermediate layer. Again, the three layers are tightly wound and heated to form a unitary, three-layer laminated film.
Thus one aspect of the present invention is to provide an economical method for laminating a thermoplastic film and a high performance fabric together.
Another aspect of the present invention is to provide a method for making such a laminated lightweight sheet material without losing the strength, or degrading the fiber in the high performance material.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiments when considered in conjunction with the drawings.
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Cunningham David V.
Holland Connie W.
Holland John E.
Ball Michael W.
JHRG LLC
Rhodes & Mason P.L.L.C.
Rossi Jessica
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