Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
1998-09-30
2001-03-27
Morris, Terrel (Department: 1771)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S389900, C427S393500, C442S062000, C442S104000, C442S105000, C442S164000
Reexamination Certificate
active
06207237
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to a process for cross-linking thermoplastic polymers used to make fibers and films in order to improve their temperature resistance and to decrease the amount of stress-relaxation that the fibers and films may undergo during use. More particularly, the present invention is directed to cross-linking metallocene-catalyzed elastomeric polymers contained in fibers and films which are used in elastic stretch-bonded and neck-bonded laminates.
BACKGROUND OF THE INVENTION
Webs, films, and laminates made from low density, high comonomer content elastomeric fibers and films are used for a variety of applications where stretchability is required. For instance, waist bands, leg bands, feminine care products, adult care products, and diapers employ elastic components in order to supply such articles with elastic properties and a better fit.
Various methods for producing such elastic products have been previously disclosed in the past. For instance, in U.S. Pat. No. 4,663,220 to Wisneski et al., which is incorporated herein by reference in its entirety, the synthesis of elastomeric products from polyolefin-containing extrudable materials is disclosed. In this reference, extrudable elastomeric compositions are formed by blending an A-B-A′ block copolymer (where “A” and “A′” are each a thermoplastic endblock including styrene and where “B” is an elastomeric midblock) with a polyolefin. The above polymer blend is extrudable when subjected to elevated pressure and temperature conditions. The A-B-A′ block copolymer imparts elastic properties to products formed from the composition.
Such compositions are extruded by being molded at an appropriate combination of elevated pressure and temperature. The pressure and temperature will vary depending on the polyolefin utilized. These extrudable compositions may be formed into a variety of products such as fibrous nonwoven elastomeric webs with varying basis weights. Herein, the terms “elastic” and “elastomeric” are used to refer to materials that, upon application of a force, are stretchable to a stretched length of about 125 percent of their original relaxed length.
However, when such elastomeric materials are released from a stretched position, the fibers typically do not return to their original relaxed length, but exhibit permanent elongation. For example, if an elastic laminate is stretched over a surface and left in this stretched or stressed situation for a period of time, the resistive forces that the elastomeric fibers in the laminate exert on the surface diminish. Thus, when the laminate is removed from the surface and released from its stretched position, the fibers within the laminate will have become permanently elongated when relaxed, reducing the stretch characteristics of the fabric. This elongation process is known as stress relaxation.
When such stress relaxation occurs within elastomeric fibers, the performance of such fibers is negatively affected. Fibers that have undergone significant stress relaxation will not supply laminates with needed fit properties and holding power.
Thus, a need currently exists for a process to improve the performance of elastomeric fibers so that they will undergo significantly less stress relaxation.
SUMMARY OF THE INVENTION
The present invention recognizes and ameliorates the foregoing problems and others experienced in the prior art.
The present invention is generally directed to a process for cross-linking elastomeric polymers, such as metallocene-catalyzed polymers, contained within elastic fibrous webs, laminates, films, foams and the like. For example, metallocene-catalyzed elastic fibers and films can usually contain elastomers which are metallocene-catalyzed from ethylene and a comonomer such as butene, hexene, octene, and the like. The polymers are low-density because of their short chain branching (as opposed to typical high density polymers which do not normally contain a significant amount of chain branching). The polymeric chains contained within the elastomeric polymers are normally not chemically bonded together. A cross-linking process, however, creates bonding between the chains, making fibers and films made from the polymer stronger, more temperature resistant, and less likely to undergo significant stress relaxation.
According to the present invention, there are several methods available in order to cross-link the elastomers contained within the fibers and films. For instance, the elastomers can be cross-linked by exposing the fiber or film to electron beam irradiation.
In an alternative embodiment, a cross-linking agent can be combined with the elastomers which initiates cross-linking after the fibers and films have been formed. For example, in one embodiment, the cross-linking agent can be a peroxide which causes the elastomers to cross-link when exposed to heat.
In another alternative embodiment, a silane can be used as a cross-linking agent. Silane will cause the elastomers to cross-link when exposed to moisture and a catalyst, such as a tin catalyst.
In a further alternative embodiment, the cross-linking agent can be a photoinitiator, which initiates cross-linking of the elastomers when subjected to electromagnetic radiation, such as ultraviolet radiation.
Other objects, features and aspects of the present invention are discussed in greater detail below.
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PCT International Search Report dated Mar. 6, 2000.
Dority & Manning P.A.
Kimberly-Clark Corporation
Morris Terrel
Pratt Christopher C.
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