Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – High energy or particulate radiation
Reexamination Certificate
2002-07-10
2004-10-12
Berman, Susan (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
High energy or particulate radiation
C522S075000, C522S076000, C522S078000, C522S079000, C522S082000, C522S112000, C522S157000, C522S158000, C522S159000, C522S160000, C522S161000
Reexamination Certificate
active
06803014
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for making a heat-resistant elastic article and a heat-resistant elastic article. The invention especially relates to a method of making elastic fibers and polymeric elastic fibers wherein the elastic fibers are capable of withstanding dyeing and heat-setting processes that typically are conducted at elevated temperatures (such as 110-230° C. and especially at greater than or equal to 130° C. for minutes). The inventive method comprises radiation crosslinking an article (or plurality of articles) under an inert or oxygen limited atmosphere (for example, in N
2
, argon, helium, carbon dioxide, xenon and/or a vacuum) wherein the article (or articles) comprises at least one amine stabilizer and preferably another optional stabilizer additive. More preferably, the radiation crosslinking is performed at a low temperature (−50 to 40° C.). The elastic article (or articles) comprises a homogeneously branched ethylene interpolymer (preferably a substantially linear ethylene interpolymer), a substantially hydrogenated block polymer, or a combination of the two. The heat-resistant elastic articles (especially fibers) are useful in various durable or repeated-use fabric applications such as, but not limited to, clothing, under-garments, and sports apparel. The heat-resistant elastic fibers can be conveniently formed into fabrics using well-known techniques such as, for example, by using co-knitting techniques with cotton, nylon, and/or polyester fibers.
BACKGROUND OF THE INVENTION
Disposable articles are typically elastic composite materials prepared from a combination of polymer film, fibers, sheets and absorbent materials as well as a combination of fabrication technologies. Whereas the fibers are 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, for example, blown film, cast film, profile extrusion, injection molding, extrusion coating, and extrusion sheeting.
A material is typically characterized as elastic where it has a high percent elastic recovery (that is, a low percent permanent set) after application of a biasing force. Ideally, elastic materials are characterized by a combination of three important properties, that is, 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 (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.
To be used in the durable fabrics, the fibers making up the fabric have to be, inter alia, stable during dyeing and heat setting processes. We found that the polyolefinic fibers that were irradiated in air tended to fuse together when subjected to the high temperatures typical of dyeing processes (about 120° C. for 30 min). Conversely, we surprisingly and unexpectedly found that when irradiated under an inert atmosphere, resultant crosslinked fibers were highly stable during the dyeing process (that is, the fibers did not melt or fuse together). The addition of a mixture of hindered phenol and hindered amine stabilizers further stabilized the fibers at heat setting condition (200-210° C.).
Block polymers generally are elastomeric materials that exhibit excellent solid-state elastic performance attributes. But unsaturated block polymers such as, for example, styrene-butadiene-styrene triblock polymers, tend to exhibit mediocre thermal stability, especially in the molten state and poor UV stability.
Conversely, known partially hydrogenated (or partially saturated) styrene block copolymers (for example, KRATON G block copolymers supplied by Shell Chemical Company) are difficult to melt process and draw into fibers or films. In fact, preparation of fine denier fiber (that is, less than or equal to 40 denier) or thin film (that is, less than or equal to 2 mils) from partially hydrogenated or partially saturated block polymers is generally not possible at commercial fabrication rates. To overcome characteristic melt processing and drawing difficulties, partially hydrogenated block copolymers are commonly formulated with various additives such as oils, waxes and tackifiers. But in order to achieve good melt processability and drawability, very high levels of low molecular weight additives are typically required which tend to compromise strength and elastic properties.
Lycra™ (trademark of Dupont Chemical Company), a segmented polyurethane elastic material, is currently used in various durable fabrics. But a shortcoming of Lycra is that it is not stable at typical high heat setting temperatures for PET fiber (200-210° C.). 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. As such, Lycra can not be successful used in co-knitting applications with high temperature fibers such as polyester fibers. Another major shortcoming of Lycra is its cost. That is, Lycra tends to be extremely cost prohibitive for many of applications.
WO 99/63021, the disclosure of which is incorporated herein by reference, describes elastic articles comprised of 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 described elastic articles are disclosed as 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. WO 99/63021 also generally teaches that the nitrogen-containing stabilizer can be used in combination with phenolic and phosphite stabilizers and reported examples therein are known to include a combination of amine, phenol and phosphorus-containing stabilizers. But there is no description of crosslinking or irradiation under an inert or reduced oxygen atmosphere and there is no specific teaching of improved heat-setting and high temperature dyeing performance.
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, wherein a substantially linear ethylene polymer (that is, INSITE technology polymer XUR-1567-48562-9D from The Dow Chemical Company) is set forth in the reported inventive example. The substantially linear ethylene polymer is subjected to electron beam radiation in a nitrogen inerted chamber at an oxygen level of approximately 5 ppm. While the substantially linear ethylene polymer is known to contain 500 ppm of a phenolic antioxidant, there is no teaching to add a nitrogen-containing stabilizer to the polymer. Moreover, there is no disclosure regarding the elastic performance of the radiated substantially linear ethylene polymer at elevated temperatures.
Chemical abstract N1993:235832 (D. W. Woods and I. M. Ward,
Plast., Rubber Comps. Process. Appl.
(1992), 18(4), 255-61), the disclosure of which is incorporated herein by reference, describes the use of radiation under nitrogen to crosslink HDPE fiber to improve creep resistance.
WO 99/60060, the disclosure of which is incorporated herein by reference, discloses heat resistant elastic fiber comprised of polyolefinic elastomers made using single site catalyst.
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. But Obijeski et al. do not disclose the performance of their elastic materi
Bensason Selim
Chum Pak-Wing S.
Ho Thoi H.
Houchens Kimberly S.
Patel Rajen M.
Berman Susan
Dow Global Technologies Inc.
Whyte Hirschboeck Dudek SC
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