Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-12-16
2003-04-22
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C264S172170, C264S176100, C264S185000, C264S211000, C264S211220, C264S331160, C264S331150, C264S210800, C428S374000, C428S394000, C428S364000, C428S369000, C428S373000, C428S401000, C428S457000, C428S500000, C524S377000, C524S503000, C525S056000, C525S058000, C525S060000, C525S061000, C525S062000
Reexamination Certificate
active
06552123
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fibers comprising, as at least one component, a thermoplastic polyvinyl alcohol with good solubility in water, and to a melt-spinning method for them. The invention also relates to fibrous structures such as yarns, woven fabrics, knitted fabrics and others comprising the fibers, and to fibrous products as obtained by processing the fibrous structures with water. The invention further relates to non-woven fabrics comprising a thermoplastic polyvinyl alcohol with good solubility or good flushability (disintegratability into fibers) in water.
2. Description of the Related Art
Water-soluble fibers comprising polyvinyl alcohol (PVA) are known, which are produced, for example, 1) in a wet-spinning or dry-jet-wet-spinning method in which both the dope solvent and the solidifying medium are of aqueous systems; 2) a dry-spinning method in which the dope solvent is of an aqueous system; and 3) a wet-spinning or dry-jet-wet-spinning (that is, gel-spinning) method in which both the dope solvent and the solidifying medium are of non-aqueous solvent systems.
These water-soluble PVA fibers are used as staple or short-cut fibers for dry non-woven and spun yarns and also in the field of papermaking, etc., or are used as multi-filaments for woven fabrics and knitted fabrics. Of those, in particular, short-cut fibers soluble in hot water at 80 to 90° C. hold an important place in the papermaking industry, serving as a fibrous binder therein; and multi-filaments are much used as the base fabric for chemical lace. To solve the recent problems with the environment, they are specifically noticed as biodegradable fibers favorable to the ecology.
However, in the conventional spinning methods mentioned above, high-speed spinning, for example, at a rate over 500 m/min is difficult, complicatedly modified cross-section fibers having a high degree of cross-section modification are difficult to produce, and specific equipment for recovering various solvents used in the spinning step is needed. Therefore, as compared with a melt-spinning method, the conventional spinning methods are much restrained in various aspects and therefore inevitably require specific care.
In ordinary spinning technology of removing the solvent from the substance having been spun out through a spinning nozzle to give fibers, the surface of each fiber obtained is seen to have fine hillocks and recesses such as longitudinal streaks or the like running thereon in the direction of the fiber axis, when magnified to the size of 2000 times or more. Such fine hillocks and recesses formed on the fiber surface will induce fibrillation, when rubbed against the guide and others in the subsequent steps after the spinning step, thereby causing one reason for failed appearance and even end breakage of spun fibers.
Some examples of producing PVA fibers through melt-spinning are known. For example, in Japanese Patent Laid-Open No. 152062/1975, proposed is a technique of producing crapy woven fabrics, which comprises melt-spinning PVA copolymerized with a minor olefin to be a sheath component and a hydrophobic polymer substance to be a core component in a bi-component fiber spinning manner to give core/sheath bi-component fibers, weaving the resulting fibers into a fabric, and processing the fabric in an aqueous solution to dissolve and remove the PVA copolymer component of the bi-component fibers constituting the fabric. In Japanese Patent Laid-Open No. 152063/1975, another technique of producing crapy woven fabric is proposed. In this, core/sheath bi-component fibers composed of a mixture of PVA and a plasticizer serving as the sheath component and a hydrophobic polymer substance serving as the core component are woven into a fabric, and the fabric is processed in an aqueous solution to dissolve and remove the sheath component of the fibers constituting the fabric. In Japanese Patent Laid-Open No. 105122/1988, proposed are bi-component fibers comprising a modified PVA as one component. In this, the modified PVA is dissolved and removed in the step of post-processing the fibers.
However, the prior art techniques noted above are still problematic in that the solubility of PVA in water is poor and the fibers being spun are often broken. It has heretofore been impossible to produce PVA fibers satisfying both the requirements of good solubility in water and good spinning process stability. On the other hand, in the technique of completely removing water-soluble fibers, for example, for producing chemical lace or spun yarn with hollow structure, single-component fibers of PVA alone but not bi-component fibers are used. For bi-component fibers comprising PVA, even when the fiber-forming capability of the water-soluble PVA used as one component is not good, spinning them is possible so far as the other polymer to be combined with PVA has the capability of forming fibers. However, for single-component fibers of PVA alone, PVA must have good capability of forming fibers by itself. Therefore, the problem in fiber spinning is that planning polymer constitution and settling spinning conditions are more difficult in single-component fiber spinning than in bi-component fiber spinning.
Non-woven fabric structures are often used for disposable fiber products, and non-woven fabrics comprising PVA fibers have been proposed for them. In some applications, those not completely soluble in water but capable of losing their non-woven texture to be disposable are used. However, for most non-woven fabrics of water-soluble PVA that have heretofore been proposed, PVA fibers are produced in a wet or dry-jet-wet spinning method. In Japanese Patent Laid-Open No. 345013/1993, partially proposed is a melt-spinning method for non-woven PVA fabrics. However, this has no concrete description of the method, and, needless-to-say, does neither disclose nor suggest what type of PVA shall be used for satisfying all the requirements of spinning process stability and solubility or flushability in water.
SUMMARY OF THE INVENTION
The present invention is to solve the problems with the conventional water-soluble PVA fibers noted above for their process stability and solubility in water, and its one object is to provide a stable melt-spinning method for fibers comprising a water-soluble polyvinyl alcohol as at least one component. Being different from the conventional wet-spinning, dry-jet-wet-spinning, dry-spinning and solvent-spinning methods noted above, the method provided herein is free from productivity limitation and cross-section profile limitation of the fibers produced, and does not require any specific equipment for product recovery.
Another object of the invention is to provide non-woven PVA fabrics with good solubility or good flushability (disintegratability into fibers) in water for which the PVA fibers are produced in a stable melt-spinning method but not in the conventional wet-spinning, dry-jet-wet-spinning, dry-spinning or solvent-spinning method.
Specifically, the invention provides thermoplastic polyvinyl alcohol fibers which comprise, as at least one component, a water-soluble polyvinyl alcohol containing from 0.1 to 25 mol % of C1-4 &agr;-olefin units and/or vinyl ether units, having a molar fraction, based on vinyl alcohol units, of a hydroxyl group of vinyl alcohol unit located at the center of 3 successive vinyl alcohol unit chain in terms of triad expression of being from 70 to 99.9 mol %, having a carboxylic acid and lactone ring content of from 0.02 to 0.15 mol %, and having a melting point(Tm) falling between 160° C. and 230° C., and which contain an alkali metal ion in an amount in terms of sodium ion of 0.0003 to 1 part by weight based on 100 parts by weight of the polyvinyl alcohol.
The invention also provides a method for producing thermoplastic polyvinyl alcohol fibers, which comprises melt-spinning the polyvinyl alcohol noted above at a spinneret temperature falling between melting point(Tm) and Tm+80° C., at a shear rate (&ggr;) of from 1,000 to 25,000 sec
−1
,
Fujiwara Naoki
Hokimoto Akihiro
Kanehira Hiroshi
Katayama Takashi
Kawamoto Masao
Kuraray Co. Ltd.
Reddick Judy M.
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