Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-05-24
2002-04-23
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S517000, C428S521000, C525S240000, C525S241000, C526S347000, C526S348000, C526S943000
Reexamination Certificate
active
06376095
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
FIELD OF THE INVENTION
This invention pertains to elastic films prepared from polymers which comprise at least one substantially random interpolymer comprising polymer units derived from one or more &agr;-olefin monomers with specific amounts of one or more vinyl aromatic monomers and/or aliphatic or cycloaliphatic vinyl or vinylidene monomers, or blend compositions therefrom with other polymers. Films prepared from such interpolymers exhibit a unique balance of properties including, good elasticity as measured by high strain recovery (≧80% Recovery in CD and ≧60% Recovery in MD).
The invention covers films, sheets, and multi-layer laminates. The films according to the invention may be obtained also as co-extruded and multi-layer films, such as one side sealable films, two sides sealable films, coated films, tinted films, cavitated films, untreated films, one side treated films, two sides treated films, and metallized plastic films. The inventive films can also be laminated to polyester films, styrenic polymer films, polyethylene films, non-woven fabrics, fibers, foams, and conventional oriented polypropylene films, and others to impart elastic properties to such multilayer composite structures.
BACKGROUND OF THE INVENTION
Materials with excellent stretchability and elasticity are needed to manufacture a variety of disposable and durable articles, such as tapes, bandages, incontinence garments, disposable diapers, disposable and protective clothing and fabrics. Stretchability and elasticity are desirable characteristics to effectuate a closely conforming fit to the body of the wearer or to the frame of the item. It is also desirable to maintain the conforming fit during repeated use, extensions and retractions. For incontinence articles, stretchability and elasticity are particularly desirable to insure comfort and provide security against unwanted leaks. Elastic films may also be of value for food wraps, meat wraps and household wraps where recovery is of value.
Disposable articles are typically prepared by the combination of polymer fibers, films, sheets and absorbent materials. Whereas the fibers are prepared by well known processes such as spunbonding, melt blown and continuous filament wounding, the film and sheet forming processes typically involve known extrusion and coextrusion processes, e.g., blown bubble extrusion, extrusion casting, profile extrusion, injection molding, extrusion coating and extrusion sheet. The resultant elastic film, coating or sheet may be subsequently cut or slit to short lengths and/or narrow widths to prepare strips, tapes, bands, ribbons or the like.
There are at least two ways elastic films are employed to manufacture disposable and durable articles. Elastic films, strips and sheets are used as uncombined elastic components (panels or portions), or they are constructed as or into multilayer structures to provide elastic composite materials with enhanced elasticity and stretchability. In a diaper, for example, experimental and commercial uses include in or as side panels, waist bands, backsheets, leg bands, and even topsheets where the elastic material is rendered pervious or “breathable” by such methods as apperturing, slitting, or microperforating as suggested by Lippert et al. in U.S. Pat. No. 4,861,652 (the disclosure of which is incorporated herein by reference).
An example of the use of elastic films to construct elastic composite materials is provided by Van Gompel et al. in U.S. Pat. No. 4,940,464, U.S. Pat. No. 4,938,757 and U.S. Pat. No. 4,938,753 (the disclosures of all of which are incorporated herein by reference). Van Gompel et at. disclose disposable incontinence garments containing elastic gathering means and stretchable side panels. The gathering means and stretchable side panels are made from film of block or graft copolymers such as butadiene, isoprene, styrene, ethylene-methyl acrylate, ethylene-vinyl acetate, ethylene-ethyl acrylate or blends thereof.
An example of use of elastic films to construct composites with the particular benefit of enhanced stretchability is a stretchable fastening tape for a disposable diaper disclosed by Gesp in U.S. Pat. No. 5,057,097, the disclosure of which is incorporated herein by reference.
There has been a persistent need for extrudable materials suitable for producing films, strips, sheets and composites with excellent stretchability and elasticity. Although there are a variety of elastic films currently available, these known solutions require blending or additive incorporation to meet desire levels of extrusion processability, stretchability or elasticity. Still other proposed solutions such as the method disclosed by Butin in U.S. Pat. No. 3,849,241, the disclosure of which is incorporated herein by reference, require “controlled thermal and oxidative degradation” of the elastic material to affect viscosity adjustments prior to extrusion. Moreover, prior art elastic films can involve elastomers such as styrene butadiene copolymers, polyether block amides, polyether esters and polyurethanes which typically necessitate blending with polyolefins for adequate extrusion processability.
Where polyolefins themselves have been previously employed as elastic films, other problems have arisen. For example, ethylene/&agr;,&bgr;-unsaturated copolymers are known to possess improved elasticity as a function of increased comonomer levels. Daponte in U.S. Pat. No. 4,803,117, the disclosure of which is incorporated herein by reference, discloses ethylene vinyl ester copolymers where high vinyl ester levels are requisite to effectuate adequate elasticity for disposable articles. However, these high vinyl ester levels invariably render the polymer susceptible to undue thermal degradation.
In the modern distribution and marketing of food products, a multitude of different packaging materials are used. One principal category of food packaging materials is plastic film. Many different kinds of plastic film exist, both in composition and structure, and some are tailored to specific applications while others are more generic in nature.
Currently, polyvinyl chloride (PVC) film is the predominate plastic film used to wrap retail-cut red meat and similar products, e.g. fresh fish, poultry, vegetables, fruits, etc., due to its many desirable properties and its low cost relative to other plastic films. Representative of these desirable properties are clarity, oxygen transmission, flexibility, toughness, heat sealability, elastic recovery, and processability. However, most PVC films include a plasticizer to obtain the desired flexibility, and a growing concern exists as to the carcinogenic properties of the most commonly used PVC film plasticizer and the tendency of this plasticizer to migrate from the film to the food product. A growing concern also exists regarding the use in food wrapping applications of any plastic film comprising one or more chlorinated polymers. The concern includes the tendency for chlorinated polymers to yield corrosive acid when thermally degraded or incinerated, as well as concern regarding the general difficulty involved in recycling chlorinated polymers.
In the search for alternatives to PVC film, various monolayer olefin films, particularly polyethylene films, have been considered but none have been found to be without at least one major flaw that has blocked its utility. High density polyethylene (HDPE) is much too inelastic to be useful as a commercial wrap, while the various low density polyethylenes, e.g. low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra low density polyethylene (ULDPE), etc., do not possess sufficient elastic recovery, and the film retains impressions or dents caused by handling of the packaged goods by potential purchasers while inspecting its contents.
Various multilayer films have also been considered (e.g. those taught in U.S. Pat. No. 5,112,674 and in EPO 0 243 965, EPO 0 333 508, and EPO 0 404 969), and significant among these are films made
Cheung Yunwa W.
Guest Martin J.
Van Volkenburgh William R.
Tarazano D. Lawrence
The Dow Chemical Company
Thibodeau Paul
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