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An overview of carbon fiber nonwovens; a small but lucrative industry, the Japanese market for carbon fiber nonwoven fabrics is divided into two primary manufacturing methods.

Carbon fibers are manufactured by means of carbonization or graphitization either of PAN (polyacrylonitrile) fibers or of fibers made through the spinning of coal or petroleum pitch. Of the two kinds of carbon fibers, the PAN-based fibers are more widely used, particularly in ACM's (advanced composite materials) in sporting goods and aircraft parts. Japanese major manufacturers of carbon fibers are shown in the accompanying table. There are only four manufacturers of PAN-based carbon fibers, but pitch-based fibers are also manufactured by other companies not listed in the table.

There are two methods for manufacturing carbon fiber nonwovens in Japan. In one method, already carbonized or graphitized carbon fibers are formed into a web by means of carding or papermaking and the web is then fixed by means of a binder or needlepunching. In this method, productivity is low and, in the case of the PAN-based carbon fibers, which are straight rather than curled, the fibers are hard to entangle. Manufacturers can overcome this disadvantage, however, by mixing pulps or PVA (polyvinyl acrylate) fibers into the material.

In the other method, nonwovens are formed at the same time that the coal or petroleum pitch is spun into fibers and the nonwovens are then subjected to carbonization or graphitization. This method is further classified into three methods, grouped according to the process employed by different manufacturers:

1. Centrifugal spinning process--Kureha Chemical

2. Vortes flow spinning process--Osaka Gas

3. Melt blowing spinning process--Ashland, Petoca.

The first process, developed by Kureha Chemical, forms a nonwoven fabric by ejecting the pitch under centrifugal force. In the second process, somewhat similar to the melt blown method and developed by Osaka Gas, pitch fibers ejected from pitch-nozzles are curled by swirling air streams made by several air nozzles positioned around the pitch nozzles. The fibers are thus easily intertwined and provide a bulky nonwoven fabric. The third process, which is essentially the same as the method for making polypropylene or polyester melt blown nonwovens, is employed by Ashland (USA),and Petoca in manufacturing carbon fiber nonwovens. Petoca further varies the process by curling the fibers using different speeds of air streams on the right and left sides.

Carbon fiber nonwovens, formed by randomly entangled short fibers, do not take advantage of the high tenacity and high modulus properties of carbon fibers. Also, the need for those properties is small in applications where heat resistance, thermal insulation, electrical conduction and anti-chemical properties are required. The heat resistant and thermal insulating properties can effectively be used in the insulators and gaskets of high temperature furnaces and the like.

Electronically conducting materials are used in plate-shaped heating materials, battery electrodes, static-electric charge protection materials, electromagnetic wave shielding and satellite broadcasting antennas at home. The anti-chemical and heat resistant properties find effective use of carbon fiber nonwovens in filtering materials. Carbon fiber nonwovens can also be used as base materials of C/C composites.

The carbon fiber nonwovens, which are highly specialized fabrics, are expensive in comparison with traditional synthetic nonwovens, resulting in small demand for them. However, they are widely used in high temperature furnace materials, plate-shaped heaters and the like, taking a firm root in the market in those fields.
 Table 1
JAPANESE MANUFACTURES OF
CARBON FIBER NONWOVENS
 Manufacturer Capacity Brand Name
 (tons/year
Pan-based Toray 2250 Torayca
 Toho Rayon 2050 Besfight
 Mitsubishi Rayon 500 Pyrofil
 Asahi Kasei
 Carbon Fiber 450 Hi-Carbonolon
Pitch-based Kureha Chemical 900 Kureca
 Mitsubishi Chemical 500 Dialead
 Osaka Gas 300 Donacarbo-S
 Nippon Oil 50 Granoc
 Nippon Steel 40 Eskainos
 Tonen 24 Forca
 Petoca 22 Carbonic
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Author:Ohmura, Kin
Publication:Nonwovens Industry
Date:Mar 1, 1993
Words:590
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