Shoe upper leather

In terms of area, about 60 % of aU leather produced is further processed as shoe upper leather. Shoe upper leather is the largest sector by far. Finish requirements are dictated not only by the performance characteristics but also greatly by the particular processing methods in the footwear industry. 

In shoe making, the previously moistened leather is wiped (pulled) over the last by heated irons. The folds appearing at the round edges of the shoe are smoothed away by heat treatment with a hot air blower or a smoothing iron (the leather shrinks at these high temperatures). So the finish has to be heat resistant. In addition, the finish must not scratch under the rubbing by the irons. The shoe sole is injection molded on in a further operation. The finish coat therefore has to be solvent-fast and the dyes may not migrate into the shoe sole. 

Shoe upper leather requires good flexing endurance and good adhesion of the finish. Rub-fastness is of minor importance. 

An example of a finish recipe for shoe upper leather is Leather type Cattle leather box-type 

Polyacrylate dispersion (40 %) 200 parts Waxes (40 %) 50 parts Casein binder (20 %) 100 parts Water 350 parts 

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Splitting. In most modem large tanneries that make upholstery leather, and in some that make shoe uppers leather, the hides are spHt in the lime condition. In splitting the hides are cut to the desired thickness with a horizontal belt knife. The hides are fed into the machine grain up. The clearance between the grain and the blade is maintained by a series of narrow rollers supported by a mbber roUer underneath the spacing roUers. The grain layer is then cut to the thickness desired to an accuracy of about 0.1 mm. 

The leather industry is one of the oldest and most complex industries world-wide. It is closely coupled to raw hide production and hence to meat consumption. livestock is bred world-wide. Accordingly, tanneries are located all around the globe. The articles made from leather differ greatly, ranging from shoe upper leather to apparel leather and to automotive leather. 

Apparel leather is the second largest sector after shoe upper leather. It accounts for about 20 % of leather production in terms of area. 

Apparel leathers generally are not provided with a base coat. The pigment content in the pigment coat has been reduced in favor of the spray dyes in order that a more transparent, less coated appearance may be obtained for the finish. This is intensified by means of low concentration of the pigment finish and the large number of spray applications. At present, solvent-containing top coats are still customary for apparel leathers, but, as with shoe upper leather, there is an increasing trend toward the use of aqueous top coats. 

This test is important for finished shoe upper leathers (see above) in particular. 7 iron is moved once back and forth across the leather surface over a shghtly rounded edge as a preliminary test. The damage to the finish and any shift in hue are then evaluated. The test temperatures are increased in intervals of 20 °C. A more sensitive version of this test is carried out on the VESLIC rub-fastness tester using a heatable test punch. Again the temperatures are increased in intervals of 20 °C. The result is assessed in each case after five rubs. 

Sintering has been used to produce a porous polytetrafluoroethylene (16). Cellulose sponges are the most familiar cellular polymers produced by the leaching process (123). Sodium sulfate crystals are dispersed in the viscose symp and subsequently leached out. Polyethylene (124) or poly(vinyl chloride) can also be produced in cellular form by the leaching process. The artificial leather-tike materials used for shoe uppers are rendered porous by extraction of salts (125) or by designing the polymers in such a way that they precipitate as a gel with many holes (126). 

The fiber stmcture is very fine near the surface of the skin and this fine stmcture imparts a silky feel to the leather. The smaller the animal of a given species the finer the surface fibers. The value of the skin or hide is then dependent in part on this smoothness (2). Calfskin leathers are smoother and have a silkier feel than cattle hide leathers. Calfskin leather is used in the shoe uppers of high quahty, expensive men s and women s shoes, and specialty items. 

The chrome tanning is one step in a compHcated series of leather operations leading from the raw hide to the finished products. Chrome tanning is the most important tannage for all hides except heavy catde hides, which are usually vegetable tanned. In heavy shoe uppers and soles, a chrome tanned leather is frequently given a vegetable retan to produce chrome retan leather. 

The injection-compression process is an important variation in which rubber is injected into a partly closed mould under low pressure used for moulding-on of rubber soles to footwear uppers. Rubber is injected into a gap between the shoe upper and the sole plate, which is held 3-4 mm wider than it would be in its final position. After injection at the first mould station of a multistation machine the sole plate is closed in the manner of compression moulding at the second mould station and rubber is pressed along the sole and over the toe cap. The importance of the process is that it becomes possible to mould without using normal high injection pressures which tear and distort canvas, leather or synthetic uppers. 

POROMER1C. A term coined to describe the microporosity, air permeability, and water and abrasion resistance of natural and synthetic leather. The pores decrease in diameter from the inner surface to the outer and thus permit air and water vapor lo leave lire material while excluding water from the outside. Polyester-reinforced urethane resins have been used as leather substitutes with some success, primarily for shoe uppers. 

They are poromeric microporous material that have a urethane impregnation or a silicone coating for shoe uppers and industrial leathers. 

The footwear industry uses polyurethane as microcellular elastomer for shoe soles thermoplastic elastomers for ski boots, coatings for shoe uppers, and adhesives. The microcellular elastomer shoe soles have been used for over 10 years. The polyurethane shoe sole offers lightweight and flexibility in styling. Fine detail simulating wood, cork, leather, and handstitching can be readily reproduced. New style sport shoes have been developed to incorporate multi-colors and multi-density soles. As a result, these shoe soles are used in women s high-fashion shoes, work shoes, and a variety of leisure and sport shoes. The current demand for polyurethane shoe soles is for continued steady growth and demand. There has been a continued shift of the shoe sole market to the Middle East and Eastern European areas. 

Shoe uppers can be made of leather, rubber or polyurethane. Outer and inner soles are made of rubber, polyurethane, polyvinylchloride or Evaflex, a combination of ethyl vinyl acetate and rubber polymers (Podmore 1995). For insoles, fibreboard is also used. Fibreboard is made of wood or leather fibers, suspended in a mixture of rubber resins or acrylic... 

Ex. 4. Royal M6482 and S-5210 adhesives can be applied to adherend surfaces from ketone solution and after drying may be heat or solvent activated. M6482 activates at 180— 240 F and is a good adhesive for vinyl and for wood. S-5210 activates at 135—155°F and was designed for bonding man-made shoe upper stocks, leather, vinyl, etc. ... 

Uses Replacement for sulfated sperni oil emulsifier for raw oil, min. oil, soivs. fatliquor for leathers esp. upholstery leather and pale colored shoe uppers light-fasL heat stable... 

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