Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Patent
1997-08-14
1999-05-25
Edwards, Newton
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
428361, 442361, 264181, D02G 300, D01D 514
Patent
active
059068906
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a polypropylene fiber, and more specifically, to a polypropylene fiber which can be processed easily and efficiently by use of heat rollers and is used as a raw material for a heat-bonded non-woven polypropylene fabric, as well as to a method for the manufacture thereof and a non-woven fabric made of such a polypropylene fiber.
2. Background Art
Polypropylene fibers have been used in the production of non-woven fabrics wherein the fibers are thermally bonded to each other by use of heat rollers, and such non-woven fabrics have in turn been used as the surface materials of hygienic products such as disposable diapers or sanitary napkins. Although for years there has been demand for non-woven fabrics having high tenacity and soft feel for use as the surface material of hygienic products, still higher levels of tenacity and softness are demanded in connection with recent decreases in basis weight (weight per unit area). In order for heat rolling to yield a high-tenacity non-woven fabric, there must be complete fusion and bonding between polypropylene fibers. For this reason, the non-woven fabric must be produced under a high-temperature condition so that the fibers are sufficiently softened upon bonding. However, if a non-woven fabric is produced at a high temperature, the polypropylene fibers present in places other than bonding points are affected by heat, thereby resulting in degradation of feel (softness). This phenomenon is more significant for non-woven fabrics of lower basis weight. If a non-woven fabric is produced at a low roller temperature in order to prevent the degradation of feel, the tenacity of the resulting non-woven fabric becomes insufficient due to poor bonding. Therefore, a small difference in processing temperature lowers the tenacity and makes the feel stiffer, thereby reducing the allowable range of heat-processing conditions for producing desired non-woven fabrics having high tenacity and soft feel. Therefore, there has been demand for the development of soft and strong polypropylene fibers having a wide range of allowable processing temperatures suitable for heat rolling.
As a polypropylene fiber suitable for heat rolling, there is proposed in Japanese Patent Application Laid-open No. 62-156310 a polypropylene fiber comprising an ethylene-propylene random copolymer containing a predetermined amount of ethylene and having a softening point of 132.degree. C. or below. However, the non-woven fabric produced from this fiber has a stiff feel, and there is a very narrow range of allowable processing temperature for producing non-woven fabrics having tenacity and feel suited for practical use. A polypropylene fiber containing a specific compound is proposed in Japanese Patent Application Laid-open No. 2-264012, but both feel and tenacity are insufficient. Furthermore, polypropylene fibers whose surfaces have been degraded by oxidation are proposed in Japanese Patent Applications Laid-open Nos. 4-228666 and 7-11508, but the non-woven fabrics produced from these fibers have a stiff feel. Although a number of efforts have been made to provide non-woven polypropylene fabrics having excellent tenacity and feel through the use of heat rolling, none of them have successfully provided both satisfactory properties of non-woven fabrics and a wide range of allowable processing temperatures. Thus, satisfactory polypropylene fibers have not yet been developed.
It is an object of the present invention to provide a polypropylene fiber which is suitable for easily producing non-woven fabrics having high tenacity and good feel, as well as for heat rolling with a wide range of allowable processing temperatures.
DISCLOSURE OF INVENTION
The inventors of the present invention conducted repeated examinations for solving the above problems, and found that the above object was achieved by a polypropylene fiber whose boiling n-heptane extract has a melting point peak of 140.degree. C. or higher and is present in the amount of 1.5 percent by weight
REFERENCES:
patent: 3624194 (1971-11-01), Pirot
patent: 4814032 (1989-03-01), Taniugchi et al.
patent: 5585172 (1996-12-01), Barsotti
patent: 5750256 (1998-05-01), Ito et al.
Ito Hidemi
Taniguchi Masahiko
Tsujiyama Yoshimi
Chisso Corporation
Edwards Newton
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