Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1998-06-30
2004-09-28
Pratt, Christopher C (Department: 1771)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C264S218000, C428S373000, C428S375000, C442S327000, C442S365000, C442S400000, C442S401000, C523S200000, C524S431000, C524S447000
Reexamination Certificate
active
06797377
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally directed to cloth-like nonwoven webs. More particularly, the present invention is directed to a process for increasing the softness and decreasing the stiffness of nonwoven webs made from thermoplastic polymers and to a composition which produces softer webs with low luster.
BACKGROUND OF THE INVENTION
Many woven and nonwoven webs and fabrics are formed from thermoplastic polymers, such as polypropylene and polyethylene. For instance, spunbond webs, which are used to make diapers, disposable garments, personal care articles, and the like, are made by spinning a polymeric resin into fibers, such as filaments, and then thermally bonding the fibers together. More particularly, the polymeric resin is typically first heated to at least its softening temperature and then extruded through a spinnerette to form fibers, which can then be subsequently fed through a fiber draw unit. From the fiber draw unit, the fibers are spread onto a foraminous surface where they are formed into a web of material.
Besides spunbond webs, other fabrics made from polymers include meltblown fabrics. Meltblown fabrics are made by extruding a molten polymeric material through a die to form fibers. As the fibers exit the die, a high pressure fluid, such as heated air or steam, attenuates and breaks the fibers into discontinuous fibers of small diameter. The fibers are randomly deposited onto a foraminous surface to form a web.
Spunbond and meltblown fabrics have proven to be very useful for many diverse applications. In particular, the webs are often used to construct liquid absorbent products, such as diapers, feminine hygiene products, and wiper products. The nonwoven webs are also useful in producing disposable garments, various hospital products, such as pads, curtains, and shoe covers and recreational fabrics, such as tent covers. Although well suited for these applications, recently, attention has focused on making the nonwoven webs more cloth-like in order to avoid the plastic-like feel and look of such fabrics. Cloth, as opposed to plastic fabrics, has a more pleasing appearance and feel.
In the past, various attempts have been made to produce more cloth-like fibers from plastic materials in order to produce fibrous webs. For instance, in U.S. Pat. No. 4,254,182 to Yamaguchi, et al., polyester synthetic fibers are disclosed having an irregular uneven random surface formed by microfine recesses and projections to provide more natural feeling fibers. The microfine recesses and projections are produced by incorporating into the fibers silica in a size ranging from 10 to 150 microns and in an amount so as to produce surface projections. It is taught that the surface projections effectively increase the surface area of the fibers and contribute to greater frictional forces, which reduce the slick, waxy feel that is typically associated with plastic resins.
The prior art, however, merely teaches increasing the frictional characteristics of the polymeric fibers in order to remove the wax-like feel of plastics. A need remains for a method that will alter the physical properties of the fibers so that webs made from the fibers will feel more cloth-like and have other cloth-like characteristics. In particular, a need exists for more cloth-like fibrous webs and laminates thereof made from thermoplastic fibers that are less stiff and softer than conventionally made webs.
DEFINITIONS
As used herein the term “nonwoven fabric or web” means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes, such as for example, melblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in micros. (Note that to convert from osy to gsm, multiply osy by 33.91).
As used herein the term “spunbond fibers” refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinnerette with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel, et al., and U.S. Pat. No. 3,692,618 to Dorschner, et al., U.S. Pat. No. 3,802,817 to Matsuki, et al. U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinnery, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Levy, and U.S. Pat. No. 3,542,615 to Dobo, et al. Spunbond fibers are generally not tacky when they are deposited onto a collecting surface. Spunbond fibers are generally continuous and have diameters larger than 7 microns, more particularly, between about 10 and 20 microns.
As used herein the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in diameter, and are generally tacky and self adherent when deposited onto a collecting surface.
As used herein the term “polymer” generally includes but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof.
As used herein, the term “machine direction” or MD means the length of a fabric in the direction in which it is produced. The term “cross machine direction” or CD means the width of fabric, i.e. a direction generally perpendicular to the MD.
As used herein the term “homopolymer” fiber refers to the fiber or part of a fiber formed from one extruder using only one polymer. This is not meant to exclude fibers formed from one polymer to which small amounts of additives have been added for coloration, anti-static properties, lubrication, hydrophilicity, etc. These additives, e.g. titanium dioxide for coloration, are generally present in an amount less than 5 weight percent and more typically about 2 weight percent. The term “homopolymer” is also not meant to exclude a fiber formed from two or more extruders wherein both of the extruders contain the same polymer.
As used herein the term “bicomponent fibers” refers to fibers which have been formed from at least two polymers extruded from separate extruders but spun together to form one fiber. Bicomponent fibers are also sometimes referred to as multicomponent fibers. The polymers are usually different from each other though bicomponent fibers may be homopolymer fibers. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the bicomponent fibers and extended along the length of the bicomponent fibers. The configuration of such a bicomponent fiber may be, for example, a sheath/core arrangement wherein one polymer is surrounded by another or may be a side by side arrangement or an “islands-in-the-sea” arrangement. Bicomponent fibers are taught in U.S. Pat. No. 5,108,820 to Kaneko, et al., U.S. Pat. No. 5,336,552 to Strack, et al., and European Patent No. 0586924. For two component fibers, the polymers may be present in ratios of 75/25, 50/50, 25/75 or any other desired ratios.
As used herein the term “biconstituent fibers” refers to fibers which have been formed from at least two polymers extruded from the same extruder as a blend. The term “blend” is defined below. Biconstituent fibers do not have the various
DeLucia Mary Lucille
Hudson Robert L.
Dority & Manning P.A.
Kimberly--Clark Worldwide, Inc.
Pratt Christopher C
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