Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
1994-05-02
2002-02-12
Weisberger, Rich (Department: 2164)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S295400, C428S295100
Reexamination Certificate
active
06346319
ABSTRACT:
FIELD OF THE INVENTION
The present invention is concerned with a flexible or resilient composite comprising a polymeric matrix having a fibrous component dispersed therein for reinforcement. The composite is characterized by its high puncture resistance and other useful properties.
BACKGROUND OF THE INVENTION
A great deal of research effort has been, and is currently being, expended towards developing composites of resins and fibrous materials which provide needed properties. Typically such composites may include any one or more conventional resins or other matrix material such as epoxy or polyester resins, reinforced with various types of fibers including, for example, glass or metal fibers or the like.
A useful discussion regarding composites appears in an article by Chou et al entitled “Composites” appearing in
Scientific American
, October, 1986, Volume 255, No. 4, pages 193-203. The article describes a variety of different types of composites comprising fibrous materials dispersed in various matrix materials. The article notes that, in the case of a brittle, ceramic matrix material, a crack in the matrix may cause the reinforcing fiber to fail as well unless the bond between the matrix and fiber is quite weak. Normally, however, steps are taken to provide for maximum bonding between the matrix and fibrous component. This may be accomplished by appropriate selection of the matrix and fibers and/or by pretreatment of the fibers to provide physical or chemical bonding to the matrix.
As noted, a variety of fibrous components in various forms, e.g. metal, glass, polyester, etc. in the form of woven, non-woven or knitted fabrics, or as staple fibers or filament bundles, have been proposed for composite use. More recently such materials as aramid and extended chain polyethylene fibers (e.g. “Spectra” fibers) have been proposed for use in composites. However, as far as can be ascertained, all such previously disclosed uses have required adhesion between the fibrous component and the matrix to provide useful flexible or resilient composites.
SUMMARY OF THE INVENTION
The present invention is based on the finding that a highly useful resilient or flexible composite can be obtained by combining a resilient resin component and a fibrous component such that the resin encases or envelops the fibrous component with essentially no adhesion or bond between the two components. This is substantively different from prior composites where, as noted, bonding between the resin and fibrous components has been considered desirable, if not essential. In the present case, the resin and fibrous components are so chosen that any significant amount of bonding does not occur. As a consequence, the resin, which is itself resilient, can retain its resiliency while performing the matrix function. At the same time, the fibrous component adds strength and other desirable properties, particularly puncture-resistance, to the composite.
Particularly effective results are obtained by forming the resin matrix in situ about the fibrous component which may be in the form of staple fibers, continuous filament, non-woven, woven or knitted fabric.
In a preferred embodiment, the invention contemplates the use of ultra-high molecular weight, high tensile strength, high modulus extended chain polyethylene fibers as the fibrous component and flexible polyurethane formed in situ by positioning the urethane-forming components about the fibers and allowing the desired urethane-forming reaction to occur. Such fibers and resin matrix do not bond together, the non-bonding effect being aided by the highly lubricious nature of the polyethylene fibers. Polyester fibers may also be usefully employed with the flexible polyurethane matrix or the like as long as any significant chemical bonding between the matrix and fibrous component is avoided. According to the invention, the composite is essentially as resilient as the polyurethane itself until the composite is bent to the point where the fibers in the matrix are snubbed, i.e. the matrix contracts around individual fibers to affect a braking action on-the slippage between the matrix and fibers. Up to this point, the composite may be bent without causing tension on the encapsulated fibers which, in a sense, float within the resin matrix. However, when the bending of the composite is such that fiber snubbing or braking occurs, the fibers increase their reinforcing effect by coacting with fibers in proximity thereto so as to spread the load placed on the composite. Then, when the bending force is released, the energy stored up in the snubbed fibers facilitates the return of the composite to its prior dimensions. The composite thus, in essence, retains desired flexibility or resiliency of the resin component while being reinforced by, and otherwise benefiting from, the fibers.
It is to be noted that the manner in which the present composite functions on bending and release would not be possible if the fibers and matrix were physically or chemically bonded together. Thus, significant or intentional adhesion between the fibers and matrix restricts flexibility and the thus encased fibers might well break before sharing the bending load with other adjacent fibers. In the present case, the fibers do not change position before, during or after deformation with respect to the matrix. The fibers instead float unadhered within the matrix until the composite is bent to the point where the fibers are stubbed or squeezed in their position by the bent matrix, the energy stored in the thus stubbed fibers helping to spring the composite back to its original form when the bending force is released.
DETAILED DESCRIPTION OF THE INVENTION
A wide variety of resilient polymeric materials may be used to provide the matrix for the present composite. Preferably, however, as noted above, the matrix comprises a flexible or resilient polyurethane which is formed in situ by application of the polyurethane-forming reactants about the fibrous component followed by reaction and curing. Typically, the polyurethane-forming reactants comprise (A) an aliphatic isocyanate, e.g. an isocyanate prepolymer such as isophrone diisocyanate, or diphenylmethane diisocyanate and (B) an aliphatic hydroxy component such as a polyester polyol or a mixture thereof with polypropylene glycol. Any conventional polyurethane-forming components may be used for this purpose provided the polyurethane reaction occurs at a temperature below the melting point of the fibrous component. Preferably, the polyurethane is formed by separately preheating the reactants (A) and (B) to a temperature of, for example, 30-60° C. and applying these reactants about the fibrous component, the latter being positioned in a mold or otherwise supported at ambient temperature (18-32° C.). The resulting in situ reaction is an exothermic one which should be controlled, if necessary, to keep the temperature well below the melting point of the fibers involved. Usually, for polyethylene fibers, the temperature will be kept below about 70° C. while higher temperatures, e.g. up to about 120° C. may be observed with low shrinkage polyester fibers.
Polyurethane matrix materials, however, are preferred because they tend to have good abrasion resistance and, in the case of aliphate urethanes, good UV resistance; and in the case of polyethers, good hydrolytic stability.
While polyurethane comprises the preferred matrix, it will be recognized that other resins which are resilient may be used. This includes, for example, vinyl resins, ethylene propylene polymers, epoxies and the like. A variety of fibrous components or mixtures thereof may be used for present purposes. However, as noted, it is preferred that this component comprise either polyester fibers or ultra high molecular weight, high tensile strength polyolefin fibers. Of particular preference are extended chain polyethylene fibers, e.g. fibers available as Spectra 900 and Spectra 1000, which have been found to be especially effective. Such polyethylene fibers have exceptionally high tensile strength and, because of thi
RanDemo Inc.
Weisberger Rich
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