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Japanese microfiber nonwovens.

Microfiber nonwovens are now attracting attention in Japan. Not a new technology, microfiber nonwovens were begun by Toray (Escaine) in 1970. During the 1970s, Kuraray, Asahi Chemical and Mitsubishi Rayon also started production.

However, the microfiber nonwovens now attracting attention are not for manmade leather, but rather are for wipes. The production technology of microfibers and microfiber nonwovens for wipes is different from that used in producing manmade leather. Table 1 shows Japanese manufacturers of microfiber nonwovens (excluding melt blown and flash spun nonwovens).

Microfiber Nonwoven Technology

A high technology level is required for the production of microfibers finer than 0.3 denier. Such thin microfibers are now made either from bicomponent fibers or by means of direct spinning from a nozzle. Since directly spun microfibers cannot be subjected to carding, they are formed into a web first by a paper making technique, then subjected to water jets to be turned into a microfiber nonwoven fabric.

On the other hand, bicomponent fibers are made to form a web through carding and then the web forming fibers are made thin to form a microfiber nonwoven fabric. The bicomponent fiber, which consists of two kinds of polymers, has its one constituent polymer dissolved (dissolution type) or exfoliated (exfoliation type) from the other constituent polymer to form microfibers. Figure 1 shows Toray's bicomponent fiber (dissolution type) and Kanebo's (exfoliation type).

The nonwovens currently attracting attention are of the exfoliation type microfibers. This type was first developed by Mitsubishi Rayon for apparel insulation in 1983. The nonwovens are formed by applying water jets to fibers obtained by being exfoliated from the parent bicomponent during the carding process. However, these fibers, whose size was not less than 0.4 denier, could not be in the same class with microfibers. The company has since developed a new bicomponent fiber and started production of nonwovens with much finer fibers.

Kanebo and Daiwabo have also started production of microfiber nonwovens with similar technology. In the process of manufacturing such new microfiber nonwovens, the exfoliation of microfibers from the parent bicomponent fiber is tobe achieved not at the stage of carding, but at the later stage of water jet application. Therefore, the adhesive strength between two polymers constituting the parent bicomponent fibers is the most important technological point. An adhesiveness that is too weak causes a web formed by carding to be lacking in uniformity because of undesirable exfoliation of fibers, while an adhesiveness that is too strong prevents microfibers from being easily exfoliated by the water jets.

A High Value Added Market

Microfiber nonwovens are primarily used in man-made leather, apparel insulation and wipes applications in Japan. The production scale, which now remains at a low level, is about 13 million sq. meters for manmade leather, not more than one million sq. meters for apparel insulation and not more than five million sq. meters for wipes.

However, roll goods for microfiber nonwovens are priced very high and the nonwovens themselves are very high value added. Demand for microfiber nonwovens, though not expected to increase signficantly for manmade leather and apparel insulation applications, will grow in wipes, probably with a stronger preference shown particularly for those made of exfoliation type microfibers. This is because these type microfibers, whose cross-sectional patterns are polygonal, have larger specific surface areas (surface areas per unit weight of fibers) than dissolution type microfibers, whose cross-sections are circular. Larger specific surface areas of microfibers used in wipes provide more excellent wiping functions.
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Title Annotation:technological developments
Author:Ohmura, Kin
Publication:Nonwovens Industry
Date:May 1, 1991
Words:577
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