Man-made leather

In the second quarter of the twentieth century, with the development of poly(vinyl chloride), nylon, polyurethane, and other polymers, many new and improved leather-like materials, so-called coated fabrics (qv), were placed on the market. Shortages of leather after World War 11 led to the expansion of these leather-like materials ("man-made" leathers) to replace leather in shoes, clothing, bags, upholstery, and other items. DurabiUty and waterproof quahties superior to leather made coated fabrics advantageous, in spite of imperfection in breathabihty and flexibiUty. Demands for shoes, clothing, and other items are stiU increasing due to growing world population and urbanization. 

During the third quarter of the twentieth century, with improved nonwoven fabrics, man-made leathers finally succeeded in simulating leather to such an extent that they are nearly identical in appearance, physical properties, and stmcture. These leathers have enjoyed success in all leather-use areas. With the technology of microfibers, they continue to evolve both in quaUty and quantity. 

Leather-like materials now important in the market are of three main classes (/) vinyl-coated fabrics, (2) urethane-coated (synthetic) fabrics, and (J) man-made leathers. To appreciate their leather-replacement capabiUties it is necessary to know the stmcture of natural leather. 

Significant improvement in the fiber stmctuie of leather is finally achieved by using microfibers as fine as 0.001—0.0001 tex (0.01—0.001 den). With this microfiber, a man-made grain leather Sofrina (Kuraray Co., Ltd.) with a thin surface layer (Fig. 7), and a man-made suede Suedemark (Kuraray Co., Ltd.) with a fine nap (Fig. 8) were first developed for clothing, and have expanded their uses. Ultrasuede (Toray Industries, Inc.) also uses microfibers with a rather thick fineness of 0.01 tex (0.1 den). Contemporary (1995) man-made leathers employ microfibers of not mote than 0.03 tex (0.3 den) to obtain excellent properties and appearance resembling leather. 

Product is nylon in man-made leathers cotton in urethane- and vinyl-coated fabrics. 

Weight, Thickness, and Density. The thickness differs according to appHcation. Vinyl-coated fabrics are very heavy and dense. Urethane-coated fabrics and man-made leather are very light and two-thirds to one-half leather in density. 

Water-Vapor Permeability. Water-vapor permeabiUty depends on the polymer used for the coating layer and its stmcture. Vinyl-coated fabrics have Httie water-vapor permeabiUty due to the coating layer. Although polyurethane polymer is water-vapor permeable, urethane-coated fabrics also have low permeabiUty values due to their soHd layer stmcture. On the other hand, man-made leathers have good permeabiUty values as high as that of leather due to their porous layer stmcture. The permeabiUty of grain-type is lower than that of suede-type, influenced by finishing method. 

Other Properties. With respect to dry-cleanabiUty, vinyl-coated fabrics are worse than the others due to dissolution of plasticizer in the cleaning solvent. Only man-made leathers with poromeric nonwoven can be skived, spHt, and cut in the same manner as leather. 

Man-Made Leathers. These materials contain a nonwoven fabric which is impregnated with a polyurethane to improve fiexibiHty, processibiHty, and conformabiHty (Fig. 9). Advanced man-made leathers contain microfibers as fine as 0.03 tex (0.3 den) or less to imitate coUagen fiber bundles, thereby attaining the soft feel and appearance essential for soft leather use. Polyurethane in the substrate is usually provided with porous stmcture by poromeric technology. The coating layer is also porous in the two-layer type man-made leathers (5—10). 

Fig. 10. Formation of fibers used in Kuraray man-made leather (a) porous fiber, and (b) a bundle of microfibers.

The production of man-made leather has increased rapidly due to its high quaUty (Table 5). Production was first started in Japan, and is expanding to the world. Up to 90% is produced in the Far East, and approximately 50% is exported to the United States and European countries. 

From a view point of imitating a form, a man-made leather, which has ever been drastically dedicated to that purpose, can be identified as one of master pieces in terms of a success in a conscientious reproduction of fluff conditions of micro fibers. 

Modeled after a structure of collagen fiber bundles in a cow leather, a sea -island is made, and its micro fibers are bundled through extracting its sea component, and then they are made into non-woven fabrics, which ultimately turn man-made leathers through following processes. 

Among the technogies of making micro fibers, there has been developed a couple of methods to directly spin through minute spinnerets, or a sea-island fiber and a partition fiber etc.. The technology of spining micro fibers,initiated from the development of man-made leathers,has been applied to that of woven and knitted fabics in general. 

Man-made leathers or poromerics, on the other hand, always consist of several layers—mostly two or three. For example, Corfam the first product of this kind, was made up of an upper moisture permeable polyurethane layer, a central layer consisting of a mixed fabric of 95% poly(ethylene terephthalate) and 5% cotton, and a lower layer of a porous poly(ethylene terephthalate) fleece bound by an elastomeric polyurethane binder. The product produced in... 

Plastics. Journal for the manufacture and application of processed or chemically fabricated materials with special consideration of artificial silk and other man-made fibers, of vulcanized, devulcanized (reclaimed) and synthetic caoutchouc, guttapercha etc. as well as substitute materials, of celluloid and similar cellulose products, of man-made leather and leather fabrics (linoleum), of resins, casein products etc. 

A plasticizer is one of the important additives extensively used for PVC, and its main role is to soften products, improve their resistance to low temperature, and make them easy to process. Plasticizers are generally liquid organics with a high boiling point, and few are solid with a low melting point and rubber-type polymers. The vast majority of plasticizers are phthalate esters others are phosphate esters, dibasic acid esters of fatty acids, and chlorinated hydrocarbons. At present, 80% of plastics enterprises in China commonly use dioctyl-phthalate (DOP), dibutyl phthalate (DBP), and phthalate isono-nylphthalate (DINP), which are still widely used in soft articles such as PVC hose, thin film, man-made leather, and so forth. 

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