Fibers and fibrous moldings made by using the same

Details Fibers and fibrous moldings made by using the same Fibers and fibrous moldings made by using the same

1998-07-24

2001-03-27

Morris, Terrel (Department: 1771)

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Knit fabric

Strand is a monofilament composed of two or more polymeric...

C442S199000, C442S361000, C442S400000, C442S401000, C428S373000, C526S089000, C526S090000

Reexamination Certificate

active

06207600

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to fiber formed of specific polypropylene and to fiber-processed products using the same. More particularly, the present invention relates to fiber widely applicable to hygienic materials such as sanitary napkins and disposable diapers, filter materials such as those for air and liquid, agricultural materials such as insect netting, or reinforcing materials for concrete; and to fiber-processed products using the same.
BACKGROUND
Conventionally, polypropylene fiber has widely been used in the field of hygienic materials such as surface materials of disposable diapers, since it is lightweight, has excellent heat-retaining properties and softness, and is significantly advantageous in balance between performance and economy. In recent years, non-woven fabrics having physical properties of even higher toughness and softness are demanded for hygienic materials.
In order to obtain non-woven fabrics having higher toughness, melt-adhesion of polypropylene fibers must be improved. To this end, non-woven fabrics must be processed under conditions of high temperature so as to satisfactorily soften polypropylene fibers upon melt-adhesion of the non-woven fabrics by way of heat-rolling. However, high-temperature processing of non-woven fabrics thermally affects part of polypropylene fibers other than melt-adhesion sites to produce non-woven fabrics having sufficient tenacity but decreased softness. In contrast, low-temperature processing of non-woven fabrics results in poor melt-adhesion, and tenacity of the obtained non-woven fabric becomes low. There is also a problem that, when used under high-temperature conditions, non-woven fabrics or processed products thereof such as cylindrical filters have poor durability, decreased shape-retention, and decreased rigidity.
As described above, processing and use of conventional polypropylene fiber at high temperature are restricted due to the disadvantage of low heat resistance, and therefore improvement of performance of polypropylene fiber is strongly desired for development of further uses.
Moreover, conventional polypropylene fiber is difficult to be made micro-fine on account of the occurrence of fuming or thread breakage during spinning due to low-molecular-weight components contained in the polymer, and the level of ultra-fining is therefore limited.
Japanese Patent Application Laid-Open (kokai) No. 62-156310 discloses a polypropylene fiber endowed with excellent properties for heat-roll processing and formed of an ethylene-propylene random copolymer containing ethylene in a specific amount and having a softening point of 132° C. or less. However, non-woven fabric made of this fiber has disadvantages of poor softness and a narrow temperature range that enables processing into non-woven fabrics having tenacity and softness suited for actual use.
Meanwhile, in recent years, J. A. Ewen et al. have found that syndiotactic polypropylene having a narrow molecular weight distribution and a high syndiotactic pentad fraction is obtained through polymerization of propylene by combined use of an asymmetric transition metal catalyst which differs from a conventional Ziegler catalyst and a metallocene catalyst comprising aluminoxane (J. Am. Chem. Soc., 110, 6255 (1989)). In connection with the metallocene catalyst, Japanese Patent Application Laid-Open (kokai) No. 3-82814 discloses a fiber formed of syndiotactic polypropylene having a syndiotactic pentad fraction of 0.7 or more. The polypropylene fiber disclosed therein is endowed with excellent softness, but heat resistance during melt-adhesion of fiber-bonding sites is particularly inferior to that of conventional polypropylene fibers.
Accordingly, no polypropylene fiber having satisfactory tenacity and softness has yet to be developed.
DISCLOSURE OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a fiber and fiber-processed products exhibiting lightweight and soft qualities possessed by polypropylene fiber per se and having improved heat-resisting properties.
The present inventors have conducted earnest studies to overcome the aforementioned drawbacks, and have found that fiber manufactured from polypropylene which has no double bond, has substantially no singular bond, has a narrow molecular weight distribution, and has remarkably high stereoregularity has remarkably high heat resistance, satisfactory tenacity and softness, and good spinning stability, to thereby attain the object of the invention while solving the above-mentioned problems.
The present invention is directed to the following aspects.
(1) A fiber formed from a polypropylene serving as at least one raw material, wherein the polypropylene is confirmed with NMR spectrometry that (a) an isotactic pentad fraction (mmmm) of 0.950-0.995, (b) a syndiotactic pentad fraction (rrrr) of 0-0.004, (c) different bonds due to 2,1-insertion reaction and 1,3-insertion reaction in an amount of 0-0.3 mol %, and (d) absence of terminal double bonds, and has (e) a weight average molecular weight (Mw) of 50,000-1,000,000, and has (f) a ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 1.5-3.8.
(2) A fiber according to (1), wherein the polypropylene has (a) an isotactic pentad fraction (mmmm) of 0.960-0.995, (b) a syndiotactic pentad fraction (rrrr) of 0-0.004, and (c) different bonds due to 2,1-insertion reaction and 1,3-insertion reaction in an amount of 0-0.2 mol %.
(3) A fiber according to (1), wherein the polypropylene is manufactured through use of at least one catalyst selected from among dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2′, 4′,5′-trimethylcyclo-pentadienyl)hafnium dichloride and dimethylsilylene(2,3,5-trimethylcyclopentadienyl)(2′, 4′,5′-trimethylcyclo-pentadienyl)zirconium dichloride.
(4) A fiber according to (1), wherein the polypropylene has a melting point of 160-168° C.
(5) A fiber according to any of (1) to (4), wherein the fiber is a composite fiber containing polypropylene as one component.
(6) A non-woven fabric in which the fiber according to any of (1) to (5) is employed.
(7) A non-woven fabric according to (6), wherein the non-woven fabric is long-fiber non-woven fabric obtained through a spun bond method.
(8) A non-woven fabric according to (6), wherein the non-woven fabric is long-fiber non-woven fabric obtained through a melt blow method.
(9) A knit fabric in which the fiber according to any of (1) to (5) is employed.
(10) A filter in which the fiber according to any of (1) to (5) is employed.
(11) A filter in which the non-woven fabric according to any of (6) to (8) is employed.
(12) An absorptive article partially using the non-woven fabric according to any of (6) to (8).
Best Modes for Carrying Out the Invention
The present invention will next be described in detail.
Among the characterization conditions of polypropylene as a raw material of the fiber of the present invention, the above-described (a), (b), (c), and (d) are determined based on the results of
13
C nuclear magnetic resonance spectrometry performed in accordance with the following method; i.e., measurement by use of a solution containing the polymer in a concentration of 20 wt. % dissolved in a mixture of o-dichlorobe nzene/bromobenzene (8/2, weight ratio) at 67.20 MHz and 130° C. As the measuring apparatus, a JEOL-GX270 NMR measuring apparatus (JEOL, Ltd.) may be used.
In the present invention, the words “isotactic pentad fraction (mmmm)” and “syndiotactic pentad fraction (rrrr)” respectively refer to isotactic fraction and syndiotactic fraction in a pentad unit of polypropylene molecular chains as determined through 13C nuclear magnetic resonance spectrometry, wherein the isotactic and syndiotactic fractions are proposed by A. Zambelli, et al. in “Macromolecules 6, 925 (1973).” Assignment of peaks in the
13
C nuclear magnetic resonance spectrometry was determined through a method proposed by A. Zambelli, et al. in “Macromolecules 8, 687 (1975).”
The isotactic pentad fraction

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