Shoe bonding

Limitations in the VOCs emissions wUl certainly push the shoe industry to use alternative bonding technologies to the current solvent-based surface preparations. Several limitations are found in the removal or substitution of solvents in shoe bonding, such as the use of new equipments and machinery, the modification in the procedure to produce bonding, costs increase, and difficulty in bonding some materials without the use of solvents. 

Abstract This chapter constitutes one of the very few reviews in the existing literature on shoe bonding, and it gives an updated overview of the upper to sole bonding by means of adhesives. The surface preparation of rubber soles and both the formulations of polyurethane and polychloroprene adhesives are described in more detail. The preparation of adhesive joints and adhesion tests are also revised. Finally, the most recent development and technology in shoe bonding is described. 

In this section, a short review of the main materials used in shoe bonding as well as their current surface preparation procedures will be considered. In the last part of this section, the current and alternative surface treatments for upper and sole materials are described. 

Adequate bonding operation. Several cases of poor adhesion in shoe bonding arise from a deficient operation. As a summary, the following aspects must be properly obeyed to assure an adequate upper to sole bonding ... 

In many instances the friction material mix is integrally molded into holes within the backing plate or shoe. Painting of the final assembly, less common in North America, is the rule in Europe and Asia. For controlling brake squeal, noise insulators are widely used. These noise insulating layers are bonded or mechanically attached to the back side of the friction material backing plate. 

Type AD-G is used in an entirely different sort of formulation. The polymer is designed for graft polymerisation with methyl methacrylate. Typically, equal amounts of AD-G and methyl methacrylate are dissolved together in toluene, and the reaction driven to completion with a free-radical catalyst, such as bensoyl peroxide. The graft polymer is usually mixed with an isocyanate just prior to use. It is not normally compounded with resin. The resulting adhesive has very good adhesion to plasticised vinyl, EVA sponge, thermoplastic mbber, and other difficult to bond substrates, and is of particular importance to the shoe industry (42,43). 

Many isocyanates have good adhesive properties and one of them, triphenyl-methane-pp /7"-triyl tri-isocyanate, has been successfully used for bonding of rubber. Isocyanates are, however, rather brittle and somewhat limited in application. Somewhat tougher products are obtained from adhesives involving both polyols and isocyanates, i.e. polyurethane-type materials. The major application of these materials to date is in the boot and shoe industry. 

Another important application of NR is for bonding ceramic tiles, although it needs special compounding with clay filler and cellulose thickener. Water-borne NR adhesives can also be used for bonding canvas and leather shoes and interior trim in some automotive applications. 

Solvent-borne CR adhesives allow almost any two substrates to stick together. The adhesives are extensively used in bonding high-pressure plastic laminates, automotive adhesives, adhesives for construction and shoe adhesives. 

Shoe adhesives. CR adhesives are used for the permanent attachment of shoe soles. For difficult-to-bond sole materials (plasticized PVC, EVA foaming soles, thermoplastic rubber, SBR) graft polymer solutions of Neoprene AD-G combined with a polyisocyanate provide a good adhesion. Another major area for CR contact adhesives is the manufacture of leather goods, particularly leather shoe sole bonding and belt lamination. 

Solvent-home urethanes are still widely used to bond leather and athletic shoes. The OEM automotive market uses some solvent-home urethanes together with chlorosulfonated polyethylene as a primer. Some urethane solvent-home packaging adhesives are used for cap liners and for paper and foil lamination. Some textile laminating applications are still based on solvent-home urethanes. 

Several environment-friendly surface preparation for the treatment of mbber soles with radiations have been recently studied. These treatments are clean (no chemicals or reactions by-products are produced) and fast, and furthermore online bonding at shoe factory can be produced, so the future trend in surface modification of substrates in shoe industry will be likely directed to the industrial application of those treatments. Corona discharge, low-pressure RF gas plasma, and ultraviolet (UV) treatments have been successfully used at laboratory scale to improve the adhesion of several sole materials in shoe industry. Recently, surface modification of SBR and TR by UV radiation has been industrially demonstrated in shoe industry... 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

The monosaccharides have a couple of characteristics that prove to be important in terms of their structure and function. They all have at least one carbon that is bonded to four different groups (a chiral carbon), and most form five-and six-membered rings easily. The presence of chiral carbons allows these compounds to exist as two different optical isomers that are nonsuperimposable mirror images of each other. (Your feet are nonsuperimposable mirror images. Try putting a left shoe on a right foot )... 

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