Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Woven fabric – Woven fabric including an additional woven fabric layer
Reexamination Certificate
1999-01-12
2002-04-09
Morris, Terrel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Woven fabric
Woven fabric including an additional woven fabric layer
C442S013000, C442S134000, C442S135000, C442S246000, C428S911000, C036S044000, C036S03000A
Reexamination Certificate
active
06368989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to puncture resistant structures and includes woven layers of high performance yarns combined with a nonsaturating level of flexible polymeric matrix resins.
2. Discussion of the Prior Art
French Certificate of Utility No. 2,572,260, published Jul. 24, 1987 teaches, very generally, that layers of aramid fabric can be placed in the sole of footwear to protect against injury which might result from stepping on sharp objects.
International Publication WO 97/04675, published Feb. 13, 1997 teaches a boot sole with at least 10 layers of aramid fabric having an areal density of less than 4 ounces/square yard (136 g/m
2
) for protection from explosive blasts.
International Publication WO 96/26655, published Sep. 6, 1996 teaches a boot sole with at least one layer of aramid fabric having an areal density of more than 15 ounces/square yard (509 g/m
2
) for protection from explosive blasts.
U.S. Pat. No. 5,185,195, issued Feb. 9, 1993 on the application of G. A. Harpell et al, teaches a puncture resistant construction using at least two layers of fabric made from a variety of high performance fibers.
U.S. Pat. No. 5,578,358, issued Nov. 26, 1996 on the application of B. E. Foy et al, teaches a fabric-only, penetration resistant, article of apparel.
SUMMARY OF THE INVENTION
This invention relates to a puncture resistant composite and especially a puncture resistant footwear sole component comprising a plurality of layers of woven aramid yarn and a matrix resin combined with the layers of woven yarn to hold adjacent layers together and to limit relative movement of individual yarns in each layer, wherein the layers of aramid yarn are woven to a tightness factor of 0.9 to 1.0 and the matrix resin is present in an amount of from 4 to 30 weight percent of the total weight of the layers and the matrix resin.
The matrix resin is present in an amount which holds the yarns in place but does not completely fill voids among the yarns or voids among fibers in the yarns.
DETAILED DESCRIPTION
Footwear which is impervious to puncture from beneath by nails and thorns and the like, is very important in varied fields such as construction and forestry. This invention relates to a puncture resistant composite for use as a footwear sole component and includes a plurality of specified layers of woven aramid yarn in a particular combination with a matrix resin.
By “aramid” is meant a polyamide wherein at least 85% of the amide (—CO—NH—) linkages are attached directly to two aromatic rings. Suitable aramid fibers are described in Man-Made Fibers—Science and Technology, Volume 2, Section titled Fiber-Forming Aromatic Polyamides, page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibers are, also, disclosed in U.S. Pat. Nos. 4,172,938; 3,869,429; 3,819,587; 3,673,143; 3,354,127; and 3,094,511.
Additives can be used with the aramid and it has been found that up to as much as 10 percent, by weight, of other polymeric material can be blended with the aramid or that copolymers can be used having as much as 10 percent of other diamine substituted for the diamine of the aramid or as much as 10 percent of other diacid chloride substituted for the diacid chloride or the aramid.
Para-aramids are the primary polymers in fibers of this invention and poly (p-phenylene terephthalamide)(PPD-T) is the preferred para-aramid. By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts up to as much as about mole percent of the p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups which interfere with the polymerization reaction. PPD-T, also, means copolymers resulting from incorporation of other aromatic diamines and other aromatic diacid chlorides such as, for example, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride; provided, only that the other aromatic diamines and aromatic diacid chlorides be present in amounts which permit preparation of anisotropic spin dopes. Preparation of PPD-T is described in U.S. Pat. Nos. 3,869,429; 4,308,374; and 4,698,414.
The yarns used in this invention must have a high tenacity combined with a high elongation to break to yield a high toughness. The tenacity should be at least 19 grams per dtex (21.1 grams per denier) and there is no known upper limit for tenacity. Below about 11.1 grams per dtex, the yarn doesn't exhibit adequate strength for meaningful protection. The elongation to break should be at least 3.0 percent and there is no known upper limits for elongation. Elongation to break which is less than 3.0 percent results in a yarn which is brittle and yields a toughness which is less than necessary for the protection sought herein. “Toughness” is a measure of the energy absorbing capability of a yarn up to its point of failure in tensile stress/strain testing. Toughness is sometimes, also, known as “Energy to Break”. Toughness or Energy to Break is a combination of tenacity and elongation to break and is represented by the area under the stress/strain curve from zero strain to break. A yarn toughness of at least 35 Joules/gram is believed to be necessary for adequate penetration resistance in practice of this invention; and a toughness of at least 38 Joules/gram is preferred.
High performance yarns are available in a wide variety of linear densities and it has been determined by the inventors herein that acceptable penetration resistance, for purposes of this invention, can be obtained over a wide range of linear densities. Aramid yarns of greater than about 1000 dtex, even when woven to a fabric tightness factor of nearly 1.0, are believed to yield between the adjacent yarns and permit easier penetration of a sharp instrument. The improvement in penetration resistance of this invention can be expected to continue to very low linear densities; but, at about 100 dtex, the yarns begin to become very difficult to weave without damage. With that in mind, the aramid yarns of this invention have a linear density of from 100 to 1000 dtex.
While some protection is provided by a single layer of the woven aramid yarn and matrix resin of this invention, it has been determined that a single layer does not provide protection which is adequate for most needs or which will pass the usually-used penetration tests for footwear. It has been found that adequate protection is obtained using at least two layers of the material; and that more than about fourteen layers are unnecessary. When more than about fourteen layers are used, the composite becomes too thick and stiff for comfortable use as well as difficult to use in footwear manufacture.
The fabric layers are woven using para-aramid yarns with a linear density of 100 to 1000 dtex. Plain weave is preferred at a fabric tightness factor of greater than about 0.90, although other weave types, such as basket weave, satin weave, or twill weave, can be used.
In the event that fabrics are used having weaves which are more open than a plain weave, there is a need for more matrix resin to hold the yarns in place. For that reason, plain weave fabrics and fabrics with close weaves are preferred.
A wide variety of polymers can be used as the matrix resin of this invention. The matrix resin is preferably a thermoplastic polymer with melt properties which limit penetration of the resin into the fabric layers during processing under heat and pressure.
The matrix resin should adhere to the fabric layers and prevent lateral movement of the yarns, while still permitting flex in the composite after molding. Eligible matrix resins include polyethylene, ethylene copolymers, polyesters, polyurethane, thermoplastic
Pascual Xuaco
Schaffer Marvin Frank
Tsimpris Constantine William
E. I. du Pont de Nemours and Company
Guarriello John J.
Morris Terrel
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