Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-02-05
2002-10-29
Edwards, Newton (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S395000
Reexamination Certificate
active
06472066
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to polyester fibers and more particularly, in preferred embodiments, to uncrimped, short-cut polyester fibers suitable for incorporation into wet laid non-woven products.
BACKGROUND
Polyester fibers and fiber products for use in textile applications are well known in the prior art. Typically, such polyester fibers are made from polyethylene terephthalate (‘PET’) polymers by way of multi-step, spin/draw processes. Such processes generally include extruding the PET into a multi-filament tow, drawing the tow of filaments to somewhere between 1.5 and 4 times its original length, and annealing or heat setting the filaments within the tow.
In the production of wet laid non-woven polyester fiber products, the tow is cut into relatively short lengths after being annealed. The short length fibers are dispersed into water and then spread upon a screen. After the water is drained or otherwise removed, the fibers dry to form a wet laid non-woven mat composed of short, intertwined polyester filaments.
The use of polyester fibers for the production of wet laid non-woven products highlights two shortcomings in the traditional production of polyester fiber. First, the individual filaments within the tow tend to adhere to one another and clump together as a result of typical drawing and annealing processes. The clumping is very problematic in the production of wet laid non-woven material since the quality of the non-woven product depends heavily upon the degree of dispersion of filaments within the water.
Second, the individual filaments within the tow tend to deform, or curl, when separated from the other filaments. The deformation occurs due to uneven shrinkage of different filaments within the tow which results from non-uniform annealing of the polyester filaments during the annealing phase of fiber production. Filament deformation adversely affects the production of wet laid non-woven materials because the cut deformed fibers do not intermesh properly when laid upon a screen, resulting in a weakened wet laid non-woven material.
Previous attempts to solve the clumping problems with fiber used in wet laid non-woven. materials have utilized lubricants and other additives to promote the dispersion of the hydrophobic polyester filaments in water. For instance, Shiffler et al., U.S. Pat. No. 5,145,622 discloses a method for improving the dispersibility of polyester fibers by treating them with caustic. In general, the fibers are described as being treated with an appropriate coating as are disclosed, for example, in Hawkins, U.S. Pat. Nos. 4,137,181; 4,179,543; and 4,294,883 and also in U.S. Ser. No. 842,789 filed Mar. 27, 1986 in the names of van Issum and Schluter which discloses the use of a synthetic co-polyester of polyethylene terephthalate units and poly(oxyalkylene) groups derived from a poly(oxyalkylene) glycol having an average molecular weight in the range of 300 to 6,000 as disclosed, e.g. in McIntyre et al., U.S. Pat. Nos. 3,416,952; 3,557,039 and 3,619,269 referred to therein. Other useful segmented co-polyesters are disclosed in Raynolds, U.S. Pat. No. 3,981,807.
Shiffler et al. '622 uses a commercial water dispersible coating (50/50 mixture of potassium salt of mono and diacid phosphate esters of lauryl alcohol/tallow alcohol ethoxylated with 25 moles of ethylene oxide) on fibers having filaments with round and scalloped-oval cross-sections where a higher level of water-dispersible coating was used to offset the scalloped oval's approximately 13% higher surface area. The disclosed coating provided the fibers with favorable dispersion characteristics though the utilization of extended cross-sections and mild crimping taught by Shiffler '622 are not applicable to fibers for use in wet laid non-woven materials.
Similar coatings, which promote dispersion of the short fibers within a water bath, are found in Ring et al., U.S. Pat. No. 4,007,083; Hawkins, U.S. Pat. Nos. 4,137,181; 4,179,543; and 4,294,883; and Viscose Suisse, British Pat. No. 958,350; as well as U.S. Pat. No. 4,713,289 and U.S. Pat. No. 4,707,407. It is noted in the '289 patent that polyester fibers are naturally hydrophobic, so it is necessary to apply a suitable coating to the polyester to overcome the inherent hydrophobic character of the polyester fiber without creating foam or causing the fibers to flocculate.
It is the lubricants and other surface treatments that have distinguished water-dispersible polyester fiber from more conventional polyester fiber, rather than any inherent characteristic of the polyester itself. The prior art has not addressed the effect of actual fiber production on the eventual dispersion of filaments within a water slurry for production of wet laid non-woven materials.
Similarly, traditional methods of annealing polyester fiber do not address the problems of uneven annealing within the tow which causes clumping of chopped filaments. Traditional methods of annealing polyester fibers tend to promote clumping and adhesion between the filaments of the tow. The clumping of the fibers is undesirable because it limits the dispersibility of the fibers within the liquid medium, resulting in the formation of non-uniform wet laid non-woven mats. The precise cause for adhesion is not well understood, but is believed to result, in part, from the sintering of individual filaments to one another during conventional processing, especially during heat-treatment.
The annealing of polyester fiber, and the associated minimization of fiber shrinkage, has conventionally been accomplished by winding the drawn polyester tow around a series of heated rollers. The heated rollers anneal the fibers at a pre-selected temperature. A problem with using heated rollers for annealing polyester fibers is that the rollers only contact a limited number of the polyester filaments within the tow during each pass over a roller, resulting in uneven annealing of the filaments within the tow. Also, the heated roller only contacts one side of the tow during each pass over a roller, with the tow alternately wound through a series of rollers in an attempt to anneal all sides of the tow evenly. The uneven and non-uniform annealing of the fiber results in a fiber which tends to curl. Such unintended deformation of the fibers is detrimental to the production of wet laid non-woven materials.
Many advances having favorable results have been made in the art of heatsetting crimped polyester fiber, but few advances have been made in favorable heatsetting methods for non-crimped fibers used in the production of wet laid non-woven material. At this point, it should be noted that methods of producing uncrimped fibers for use in wet laid non-woven materials are analogous to, but very distinct from methods for producing fibers which will be crimped.
As mentioned above, the production of a high quality wet laid non-woven material depends on the production of polyester fibers having filaments which do not clump together when dispersed in a liquid medium and which do not deform once separated from the tow. Both clumping and deformation depend on the manner in which the fibers are drawn, annealed, and treated after annealing.
The quality of crimped polyester fibers, on the other hand, does not vary depending on clumping or deformation. Crimped fibers are used mostly for production of woven and knit textiles. Crimped fibers are traditionally extruded, drawn, and annealed using the same methods as fibers for use in wet laid non-wovens, but fibers produced for woven and knit materials are subsequently mechanically crimped, cut, carded, and then spun into thread, either alone or in combination with cotton or other fibers. Filament adhesion has little or no effect on a crimped fiber because the step of mechanically crimping the fiberbreaks apart any adhered filaments. The action of carding the crimped fiber further separates any clumped filaments from one another.
Steam treatment has been used in place of heated rollers for the annealing of polyester fibers which are later crimp
Cooper Gary William
Reese Glen Patrick
Arteva North America S.A.R.L.
Clements Gregory N.
Edwards Newton
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