Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coating or impregnation is anti-slip or friction-increasing...
Reexamination Certificate
1995-12-18
2001-06-19
Copenheaver, Blaine (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coating or impregnation is anti-slip or friction-increasing...
C428S378000, C428S902000, C428S911000, C442S135000, C442S394000
Reexamination Certificate
active
06248676
ABSTRACT:
The present invention relates to combinations of polymeric fibers having low coefficients of friction with polymeric coatings having high coefficients of friction to provide a fabric which is more resistant to penetration by metallic or other objects such as bullets, flechettes, shrapnel, etc.
Polymer fibers having high tensile strength and high modulus typically are highly oriented, resulting in very smooth fiber surfaces and a low coefficient of friction. Such fibers, when used in the construction of ballistic fabrics, exhibit poor energy transfer to neighboring fibers during ballistic impact, resulting in loss of stopping efficiency. Because of this loss of efficiency, more fabric layers are required to stop a projectile of a given velocity. Known methods of increasing the coefficient by roughing such as sanding or corona treatment have limited utility due to the degradation in tensile strength of the fiber.
Another method of increasing energy transfer between adjacent fibers or yarns in ballistic fabric is to coat the fabric with a polymer having a high coefficient of friction. One deficiency in this approach is fiber to fiber bonds that may form, resulting in stress reflections at yarn crossovers during ballistic impact and premature fiber breakage. Another deficiency is the large weight gain typical of coatings, which may be several percent. This added weight degrades the ballistic efficiency, which is taken as the energy adsorbed per unit areal density. Since the coating itself has negligible tensile strength when compared to the fiber, it reduces the average tensile strength of the fabric. Yet another deficiency of some coatings is a lack of adequate adherence of the coating to the smooth fiber surface. Material that is stripped off during a ballistic impact can serve to reduce the effective coefficient of friction by acting as a dry lubricant between fibers.
Hogenboom, et al., U.S. Pat. No.5,035,111, disclose a method for improving the ballistic performance of fabric by core spinning high strength fibers in combination with weaker fibers having a higher coefficient of friction. These relatively high friction fibers, present at a 5 to 25% level by weight, degrade the ballistic efficiency in the same manner as high add-on coating. Although gains in ballistic performance may be made by increasing the energy transfer yarn to yarn, concomitant reductions in performance must necessarily result from the presence of large amounts of ballistically inferior fiber.
Kevlar® is the preferred fiber used in the fabrics but other fibers which could conventionally be used includes other high tenacity fibers such as aramid fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers and the like so long as the tensile strength is equal to 10 grams/denier or above to qualify as high tenacity fibers.
It is an object of the present invention to supply a ballistic fabric composed of high strength, high modulus polymeric fibers, coated with a thin, high friction polymeric material.
It is a further object of this invention to supply said fabric with a coating tenaciously adhering to the fibers of the substrate with few or substantially no fiber to fiber bonds.
Other objects and advantages of the invention will become readily apparent as the specification proceeds to describe the invention with resect to accompanying drawings, in which: a flexible impact resistant article of clothing is shown with a portion thereof in cross-section to show the construction thereof.
Looking now to the drawing, the fabric
10
is shown made into a bullet resistant vest
12
and basically comprises a multiplicity of Kevlar® fabrics
14
treated as herein-described and connected together by stitching or other means to form the vest
12
. The outer face of the vest
12
can be treated with a water repellant finish, if desired.
According to the invention, it has been found that a polymer film deposited on the fiber by the method described in Kuhn, et al., U.S. Pat. Nos. 4,803,096; 4,877,646; 4,981,718; 4,975,317; and 5,030,508 improves the ballistic performance of fabrics measurably. A polypyrrole film, when deposited onto the fiber composing a Kevlar® fabric at a film thickness of less than about 2 microns and preferably about 0.15microns, was found to increase the flechette resistance by about 19%. A flechette is a military weapon that resembles a nail with small fins which when launched at ballistic velocities is unusually penetrating. When tested against a 0.22 caliber bullet fired from a rifle, an 18 layer stack of coated Kevlar® fabric was penetrated to a depth of only 3 or 4 layers, as compared to a depth of 6 or 7 layers for an 18 layer stack of uncoated fabric. Furthermore, the coating remained completely adhered to the fiber even in the area of direct impact. Other films, such as polyaniline can be formed so long as the coating has a coefficient of friction higher than the high tenacity fiber of the basic fabric.
In the case of ballistic fabric of exceptionally tight weave, it is found that some debris and crossover bonds do form during the coating, due to a certain amount of dendritic growth. In this case, it is necessary to remove the debris and break apart the bonding which can be accomplished most efficiently by vibrating the fabric by means of air stream directed between the fabric and a rigid plate by one or more air jets as described in U.S. Pat. No. 4,837,902.
REFERENCES:
patent: 4623574 (1986-11-01), Harpell et al.
patent: 4650710 (1987-03-01), Harpell et al.
patent: 4688604 (1987-08-01), Griffiths
patent: 4816336 (1989-03-01), Allou, Jr. et al.
patent: 4847115 (1989-07-01), Warren et al.
patent: 4878920 (1989-11-01), Russell et al.
patent: 5035111 (1991-07-01), Hogenboom et al.
patent: 5316830 (1994-05-01), Adams, Jr. et al.
Encyclopedia of Textiles, Fibers, and Nonwoven Fabrics; Editor—Martin Grayson; Publisher John Wiley & Sons; 1984; pp. 32-34, 42-43, 348-349.
Copenheaver Blaine
Milliken & Company
Moyer Terry T.
Parks William S.
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