Method of making washable, dryable elastic articles

Details Method of making washable, dryable elastic articles Method of making washable, dryable elastic articles

1999-05-27

2003-05-06

Mulcahy, Peter D. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S236000, C524S251000, C428S500000, C428S515000

Reexamination Certificate

active

06559208

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of making improved polyolefinic elastic articles from cured, irradiated or crosslinked amorphous ethylene interpolymers. In particular, the invention relates to a method of making a shaped article (e.g. film or fiber) characterized by improved elevated temperature elasticity as well as washability and dry ability. The inventive elastic article comprises a substantially cured, irradiated, or crosslinked (or curable, irradiated or crosslinkable) homogeneously branched ethylene interpolymer characterized as having a density less than 0.90 g/cm
3
and containing at least one nitrogen-containing stabilizer. The improved elastic article of the present invention is particularly suitable for use in applications where good elasticity must be maintained at elevated temperatures and after laundering such as, for example, elastic waist bands of undergarments and other clothing.
BACKGROUND OF THE INVENTION
Materials with excellent stretchability and elasticity are needed to manufacture a variety of disposal and durable articles such as, for example, incontinence pads, disposable diapers, training pants, clothing, undergarments, sports apparel, automotive trim, weather-stripping, gaskets, and furniture upholstery. Stretchability and elasticity are performance attributes which can, for example, function to effectuate a closely conforming fit to the body of the wearer or to the frame of the item. While numerous materials are known to exhibit excellent stress-strain properties and elasticity at room temperatures, it is often desirable for elastic materials to provide a conforming or secure fit during repeated use, extensions and retractions at elevated temperatures such as at body temperatures or in automobile interiors during summer months. Maintaining tight tolerances throughout temperature cycles are also instances where elevated temperature elasticity is important. Further, where an elastics material is employed in clothing or garment items, the material must maintain its integrity and elastic performance after laundering.
Disposable elastic articles are typically elastic composite materials prepared from a combination of polymer film, fibers, sheets and/or absorbent materials as well as a combination of fabrication technologies. Whereas elastic fibers can be prepared by well known processes such as spun bonding, melt blowing, melt spinning and continuous filament wounding techniques, the film and sheet forming processes typically involve known extrusion and coextrusion techniques, e.g., blown film, cast film, profile extrusion, injection molding, extrusion coating, and extrusion sheeting.
Conversely, durable elastic articles are often molded or profile items such as, for example, automotive door and window trim, clothing waist band threads or strips, and building weather-stripping. Such durable articles can be made by well known molding, thermoforming and profile technologies.
A material is typically characterized as elastic when it is characterized as having a high percent elastic recovery (i.e., a low percent permanent set) after application of a biasing force. Ideally, elastic materials are characterized by a combination of three, temperature independent properties, i.e., a low percent permanent set, a low stress or load at strain, and a low percent stress or load relaxation. That is, there should be at low to elevated service temperatures (1) a low stress or load requirement to stretch the material, (2) no or low relaxing of the stress or unloading once the material is stretched, and (3) complete or high recovery to original dimensions after the stretching, biasing or straining is discontinued.
Lycra® is the trademark of Dupont Fibers for its elastic spandex fibers. The U.S. International Trade Commission defines spandex fiber as a manufactured fiber in which the fiber-forming substance is a long-chain synthetic polymer comprised of at least 85 percent segmented polyurethane. Lycra is known to exhibit nearly ideal, temperature independent elastic properties rendering it very suitable for use in garments, sports apparel and swimsuits. However, one significant shortcoming of Lycra is it typically exhibits fair to poor elevated temperature serviceability and washability. Similar to ordinary uncrosslinked polyolefin-based elastic materials, Lycra articles tend to lose their integrity and shape and elastic properties when subjected to elevated service temperatures such as during laundering and drying. Another major shortcoming of Lycra is its cost. That is, Lycra tends to be extremely cost prohibitive for a many of applications.
Elastic materials such as films, strips, coating, ribbons and sheet comprising at least one substantially linear ethylene polymer are disclosed in U.S. Pat. No. 5,472,775 to Obijeski et al., the disclosure of which is incorporated herein by reference. However, U.S. Pat. No. 5,472,775 does not disclose the performance of these materials at elevated temperatures (i.e., at temperatures above room temperature), nor their performance after laundering.
WO 94/25647, the disclosure of which is incorporated herein by reference, discloses elastic fibers and fabrics made from homogeneously branched substantially linear ethylene polymers. The fibers are said to posses at least 50 percent recovery (i.e., less than or equal 50 percent permanent set) at 100 percent strain. However, there is no disclosure in WO 94/25647 regarding the elasticity of these fibers at elevated temperatures or the effects of laundering on these fibers.
WO 95/29197, the disclosure of which is incorporated herein by reference, discloses curable, silane-grafted substantially ethylene polymers which are useful in wire and cable coatings, weather-stripping, and fibers. In the Examples, inventive samples include fibers comprising silane-grafted substantially ethylene polymers having densities of 0.868 g/cm
3
and 0.870 g/cm
3
. The inventive examples are shown to exhibit improved elastic recovery at elevated temperatures. However, there is no disclosure in WO 95/29197 regarding the percent stress or load relaxation performance at elevated temperatures for these silane-crosslinked fibers, nor is there any disclosure as to washability.
U.S. Pat. No. 5,324,576, the disclosure of which is incorporated herein by reference, discloses an elastic nonwoven web of microfibers of radiation crosslinked ethylene/alpha olefin copolymers, preferably having a density less than 0.9 g/cm
3
. In the examples set forth in U.S. Pat. No. 5,324,576, ethylene polymers having polymer densities greater than or equal to 0.871 g/cm
3
are subjected to electron beam radiation. However, there is no disclosure regarding the elastic performance of these radiated polymers at elevated temperatures, nor is there any disclosure regarding their resistance to washing and drying.
U.S. Pat. No. 5,525,257 to Kurtz et al., the disclosure of which is incorporated herein by reference, discloses that low levels of irradiation of less than 2 megarads of Ziegler catalyzed linear low density ethylene polymer results in improved stretchability and bubble stability without measurable gelation. However, '257 provides no disclosure respecting the elasticity and/or washability at elevated temperatures.
U.S. Pat. No. 4,957,790 to Warren, the disclosure of which is incorporated herein by reference, discloses the use of pro-rad compounds and irradiation to prepare heat-shrinkable linear low density polyethylene films having an increased orientation rate during fabrication. In the examples provided therein, Warren employs Ziegler catalyzed ethylene polymers having densities greater than or equal to 0.905 g/cm
3
.
Various compounds are disclosed in the art and/or sold commercially as high temperature stabilizers and antioxidants. However, the criteria employed to distinguish these compounds as stabilizers and antioxidants typically relates to their ability to resistance yellowing, crosslinking and/or the ill-effects of irradiation (e.g., gamma irradiation for purposes of sterilization).
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