Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Staple length fiber
Reexamination Certificate
2000-09-26
2003-01-28
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Staple length fiber
C428S393000
Reexamination Certificate
active
06511746
ABSTRACT:
This invention pertains to cellulosic microfibers useful in making threads, yams, and fabrics; and to methods for manufacturing cellulosic microfibers useful in making threads, yarns, and fabrics.
Microfibers are fibers that are suitable for use in textiles, and that have a very small diameter. The only microfibers currently available commercially are certain polyester microfibers. Nylon microfibers have also been reported, but are not commercially available. Microfibers have a much softer hand (or feel) than ordinary fibers of identical composition, because the diameter of microfibers is an order of magnitude smaller. Fabrics made from polyester microfibers feel like a soft brushed cotton fabric to the hand, and have the flexibility of fine silk. However, neither polyester nor nylon microfibers have the water absorbency of virgin or regenerated cellulosic fibers, and they therefore lack the comfort of fabrics made from cellulose. Fabric made of cellulosic microfibers, if available, would have the very soft feel of polyester microfiber fabric, together with the water absorbency and comfort of other cellulosic fabrics. However, no one has previously reported cellulosic microfibers suitable for use in textiles, either natural or artificial.
(The size of fibers is defined in terms of linear density. Although there is no precise cut-off as to what constitutes a “microfiber,” the term “microfiber” may be considered to refer to a fiber about 1 decitex (1 decitex=1 g/ 10,000 m) or less. A microfiber of cellulose would thus be about 9 &mgr;m in diameter or less, while the diameter of a microfiber of less-dense polyester is about 10 &mgr;m; in round numbers, a microfiber may thus be considered as a fiber having a diameter about 10 &mgr;m or less.)
Prior methods for making polyester or nylon microfibers are based on spinning “sea and island” type composite fibers. The “islands” are the microfibers embedded in a “sea” of the second component, generally another polymer that is incompatible (immiscible) with the first under the spinning conditions. This second component is removable by a combination of mechanical action and solvation. This second component is generally not removed until the microfibers have been converted to yarns or fabrics in order to protect the microfibers. Direct production of microfibers, with subsequent drawing of multiple individual microfibers external to the channel, would cause an unacceptable level of line breaks. See generally S. Warner, “Fiber Cross-Section and Linear Density,” Chapter 5 (pp. 80-98)
Fiber Science
(1995)
P. Kerr, “Lyocell fibre: Reversing the Decline of Cellulosics,”
Technical Textiles
, vol. 3, pp. 18-23 (1994) discloses the use of N-methyl morpholine-N oxide (NMMO.H
2
O) as a solvent for cellulose, and the use of the resulting solutions to spin cellulosic “lyocell” fibers as small as 1.1 decitex. It was reported that the lyocell fibers tended to fibrillate (i.e. break under stress into smaller pieces on the surface). These fragments, even if detached, would not be useful in textiles because they are too short and tangled.
S. Mortimer et al., “Methods for Reducing the Tendency of Lyocell Fibers to Fibrillate,”
J. Appl. Polym. Sci
., vol. 60, pp. 305-316 (1996) discloses methods for modifying process conditions to increase or decrease fibrillation in lyocell fibers. See also M. Nicolai et al., “Textile Crosslinking Reactions to Reduce the Fibrillation Tendency of Lyocell Fibers,”
Textile Res. J
., vol. 66, pp. 575-580 (1996), which discloses the use of certain crosslinking agents with lyocell fibers for the same purpose.
A. Dufresne et al., “Mechanical Behavior of Sheets Prepared from Sugar Beet Cellulose Microfibrils,”
J. Appl. Polym. Sci
., vol. 61, pp. 1185-1193 (1997) discloses the preparation of and properties of certain films prepared from sugar beet fiber by-product.
L. Robeson et al., “Microfiber Formation: Immiscible Polymer Blends Involving Thermoplastic Poly(vinyl alcohol) as an Extractable Matrix,”
J. Appl. Polymer Sci
., vol. 52, pp. 1837-1846 (1994) discloses a “sea and island” method for producing microfibers from polypropylene, polystyrene, polyester, and other synthetic polymers by melt extrusion with poly(vinyl alcohol).
U.S. Pat. No. 3,097,991 discloses feltable paper forming fibers, prepared by the melt extrusion of mutually incompatible thermoplastic materials, such as polyamides, polyesters, polyurethanes, and vinyl and acrylic polymers. The resulting monofilaments were reported to have diameters in a range 0.2 to 100 microns and lengths between {fraction (1/32)} and ½ inch. See also U.S. Pat. No. 3,099,067, disclosing the formation by similar means of various synthetic fibers (but specifically excluding regenerated cellulosic fibers), having a small cross section (0.1 to 5.0 micron diameter).
M. Tsebrenko et al., “Mechanism of Fibrillation in the Flow of Molten Polymer Mixtures,”
Polymer
, vol. 17, pp. 831-834 (1976) discloses experiments supporting the conclusion that ultra-fine fibrils of one of two incompatible polymers formed in flow of melts of the two polymers through an extrusion orifice occur in the entrance to the orifice, rather than in the extrusion duct or in the exit.
“Murata: Spinning Microfiber Yams on the MJS System,”
Textile World
, vol. 144, pp. 42-48 (January-June 1996) discloses the use of a commercial spinning machine to form yam from microfibers of polyester.
M. Isaacs et al., “Race Is on to Find New Uses for Microfibers,”
Textile World
, vol. 144, pp. 45-48 and 73-74 (August 1994) discusses practical uses for various currently commercially available microfibers, none of which are cellulosic.
T. Hongu et al.,
New Fibers
, pp. 30-34, Ellis Horwood Series in Polymer Science and Technology (1990) disclose the fine structure of certain polyester fibers.
T. Hongu et al.,
New Fibers
, pp. 55-66, Ellis Horwood Series in Polymer Science and Technology (1990) disclose that microfibers can be produced by “sea and island” bicomponent extrusion and fiber spinning of nylon (polyamide) and polyester, polyester and polystyrene, or nylon and polystyrene, as each pair of components is immiscible at spinning conditions. After spinning, the two phases are separated from one another, and one may be removed in a solvent. Polyester microfibers partially separated from one another in a fabric may be used in cloths for cleaning automobiles or microchips. See also U.S. Pat. Nos. 3,382,305, 4,350,006, and 4,784,474.
The “sea and island” approach has not been used to produce cellulose microfibers, presumably because that approach either forms a single phase of the two polymers in the melt state prior to extrusion, or mechanically combines two melt streams. Such techniques may not be used with cellulose, because cellulose degrades on heating before reaching the pertinent melting points.
U.S. Pat. No. 5,357,784 discloses a method and apparatus for measuring elongational viscosity in a hyperbolic or semi-hyperbolic die geometry with lubricated flow, by measurements of pressure drop and flow rate data.
U.S. Pat. No. 4,680,156 discloses a composite extrusion, such as a fiber, film or ribbon, having an inner core and an outer sheath, formed by melt transformation coextrusion. The inner core was transformed to a molecularly oriented polymer capable of being rigidified by imposition of a temperature gradient. The sheath was made of a polymer whose molecules were generally not oriented. See also U.S. Pat. No. 4,053,270.
U.S. Pat. No. 4,350,006 discloses sea-and-island type polymer filaments, formed from the continuous discharge of fluids of two different polymers through a single orifice, preferably by melt spinning. Examples of the two-polymer combinations included polyethylene terephthalate with nylon 6, and polyacrylonitrile with cellulose acetate. Unlike cellulose, cellulose acetate may be melted without decomposing.
Certain East European poplar trees produce fine cellulosic fibers, but these fibers are not suitable for use in textiles, because the fibers form individual filaments as opposed to packets o
Collier Billie J.
Collier John R.
Negulescu Ioan I.
Board of Supervisors of Louisiana State University and Agricultu
Edwards N.
Runnels John H.
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