Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1993-01-07
1995-02-14
Cannon, James C.
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
156 624, 264500, 264517, 264518, 264205, D04H 142, D04H 172
Patent
active
053894316
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a nonwoven fabric. More particularly, it pertains to a nonwoven fabric which is excellent in heat resistance, heat resistant dimensional stability and solvent resistance and is suitable for industrial filters, electrical insulating materials, thermal insulating materials and the like; and a process for producing the same.
BACKGROUND ART
In general, a styrenic polymer having syndiotactic configuration (SPS) is known to have high resistance to heat and solvent and there is disclosed a fiber or fabric made of such SPS by melt spinning method or gel orientation method. However, in the case of preparing a nonwoven fabric by melt spinning method, it has been necessary to spin a molten resin extruded from dies at a high speed or to carry out orientation and heat treatment by an appropriate method after spinning the resin for the purpose of enhancing the crystallinity of the SPS, thereby making it difficult to continuously produce a nonwoven fabric. In addition, the gel orientation method has suffered the disadvantage of its low productivity.
There are also publicly known nonwoven fabrics made of polyethylene and polypropylene, respectively by flash spinning method, which however are not sufficient in heat resistance. Under such circumstances, a nonwoven fabric that is further enhanced in heat resistance has been desired.
DISCLOSURE OF THE INVENTION
In order to solve the above-mentioned problems, it has been found by the present inventors that a nonwoven fabric excellent in heat resistance, dimensional stability and solvent resistance is obtained by means of flash spinning of SPS. Specifically, the present invention provide a nonwoven fabric comprising fibrillated there-dimensional network fibers prepared by the use of a high degree SPS as the principal component, and at the same time, a process for producing the aforesaid nonwoven fabric which comprises flash-spinning a homogeneous SPS-containing solution.
THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION
The high degree SPS to be used in the present invention means that its stereochemical structure is of a high degree of syndiotactic configuration, i.e. the stereostructures in which phenyl groups or substituted phenyl groups as side chains are located alternately at opposite directions relative to the main chain consisting of carbon-carbon bonds. Tacticity is quantitatively determined by the nuclear magnetic resonance method (.sup.13 C-NMR method) using carbon isotope. The tacticity as determined by the .sup.13 C-NMR method can be indicated in terms of proportions of a plurality of structural units continuously connected to each other, i.e., a diad in which two structural units are connected to each other, a triad in which three structural units are connected to each other and a pentad in which five structural units are connected to each other. "The high degree SPS as mentioned in the present invention usually means polystyrene, poly(alkylstyrene), poly(halogenated styrene), poly(alkoxystyrene), poly(vinyl benzoate), poly(halogenated alkylstyrene), hydrogenated polymer thereof, the mixture thereof, and copolymers containing the above polymers as main components, having such a syndiotacticity as determined by the above-mentioned method that the proportion of racemic diad is at least 75%, preferably at least 85%, or the proportion of racemic pentad is at least 30%, preferably at least 50%. Examples of the poly(alkylstyrene) include poly(methylstyrene), poly(p-methylstyrene), poly(m-methylstyrene), poly(ethylstyrene), poly(isopropylstyrene), poly(p-tert-butylstyrene) and poly(tert-butylstyrene). Example of the poly(halogenated styrene) include poly(chlorostyrene), poly(p-chlorostyrene), poly(m-chlorostyrene), poly(bromostyrene), poly(fluorostyrene) and poly(p-fluorostyrene). Examples of the poly(alkoxystyrene) include poly(methoxystyrene) and poly(ethoxystyrene). Example of the poly(vinyl benzoate) include poly(vinylnaphthalene) and poly(vinylstyrene). Examples of the poly(halogenated alkylstyrene) i
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patent: 5079075 (1992-01-01), Yamasaki et al.
patent: 5156797 (1992-10-01), Yamasaki et al.
patent: 5166238 (1992-11-01), Nakano et al.
Cannon James C.
Idemitsu Kosan Co. Ltd.
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