Thermoplastic urethane adhesives

Thermoplastic urethane adhesives may be processed into an adhesive film. I,amination of two substrates can, in theory, be done immediately, but the film is often extruded onto one substrate, covered by a release liner, and allowed to cool. Crystallization follows to create a non-tacky film that may be cut into specific shapes. The release liner is then removed, and the shaped adhesive can be heat-activated on one substrate, using infrared lamps. The second substrate is then nipped under pressure, followed by a cooling press to speed crystallization. Once the backbone has crystallized, the bond should be strong. 

Currently, waterborne adhesives are being introduced into the shoe industry. Their performance is quite similar to that of the solvent-borne adhesives, so it can be estimated that for several years they will be used in shoe industry. However, the future seems to be directed through the use of moisture-curing holt-melt urethane and thermoplastic urethane adhesives as they are 100% solid reactive systems and evaporation of solvents is not necessary. Although hot-melt urethanes could replace solvent-borne adhesives, this could take longer to occur because of the vastly different equipment requirements and the change in bonding concept by the shoe manufacturers. 

Crystalline polyesters are highly important as adhesive raw materials. They are normally crystalline waxes and are highly symmetrical in nature, which can aid the crystallization process [26]. Poly(hexamethylene adipate) and poly(caprolactone), shown in Table 2, are only two of the many crystallizable backbones. Poly(ethylene adipate) and poly(letramethylene adipate) are also commonly used in urethane adhesives. The crystalline polyesters are used in curing hot melts, waterborne polyurethanes, thermoplastic polyurethanes, and solvent-borne urethane adhesives. The adipates are available mostly as diols. The poly(caprolactones) are available as diols and triols. 

The thermoplastic polyurethane (TPU) adhesives must, of necessity, contain low gel content because they must be processable in an extruder. Most adhesives are relatively linear, with a functionality of 2.0, although small amounts of branching may be introduced, usually at the expense of a lower melt flow. Good physical properties of TPU s are obtained when the thermoplastic urethanes have molecular weights of 100,000 or higher (see p. 56 in [63]). Most TPU adhesives are based on symmetrical polyesters with a fast crystallizing backbone or a backbone slightly modified to increase the open time. 

Amoco Resin 18. [Amoco] Poly-a-methylstyrene extrusion and mending process aid in ABS, PVC, CPVC, and semirigid vinyl, thermoplastic urethanes, molded rubbers, and thermoplastic elastomers modifier and rein-forcer in adhesives, thermoplastic powd. coatings, hot-mielt coatings. 

The more viscous, mastic-type cements include some of the epoxies, urethanes and sflicones. Epoxies adhere well to both thermosets and thermoplastics. But epoxies are not recommended for most polyolefin bonding. Urethane adhesives have made inroads into flexible packaging, the shoe industry, and vinyl bonding. Polyester-based polyurethanes are often preferred over polyether systems because of their higher cohesive and adhesive properties. Sflicones are especially recommended where both bonding and sealing are desired. 

Polyester polyols are used widely in urethane adhesives because of their excellent adhesive and cohesive properties. Compared to polyether-based polyols, polyester-based polyol adhesives have higher tensile strengths and improved heat resistance. These benefits come at the sacrifice of hydrolytic resistance, low-temperature performance, and chemical resistance. One of the more important application areas for these products is in the solvent-borne thermoplastic adhesives used in shoe sole binding. These products are typically made from adipic acid and various glycols (see Fig. 15). 

Uses PU intermediate for urethane prepolymers, adhesives, coatings, and thermoplastic urethanes which exhibit outstanding low temp, flexibility, high str., and softness... 

Uses PU intermediate for urethanes for solv.-based coatings and adhesives, and for thermoplastic urethanes Features Sat., aliphatic polyester polyol with primary hydroxyl functionality gives harder coatings with better abrasion resist, and higher gloss Properties Pale, waxy Gardner U solid m.w. 2000 dens. 9.6 Ib/gal vise. 1400 cps (60 C) m.p. 55-65 C acid no. 0.5 hyd. no. 55. Lexorez 1150-110 [Inolex]... 

Uses PU intermediate for thermoplastic urethanes, coatings, and adhesives... 

Chem. Descrip. Linear poly (ethylene glycol 1,4-butanediol adipate) Uses PU intermediate for microcellular cast elastomer applies, such as shoe soles, and for sol n. coalings, adhesives, and thermoplastic urethanes... 

Uses Polyol for adhesives, thermoplastic coatings, thermoplastic urethanes and hot melts, castable and one-shot elastomers, RIM applies. Features Suitable for applies, where reactivity is important Properties APHA 25 color m.w. 2000 sp.gr. 1.058 dens. 8.81 Ib/gal vise. 363 cp acid no. 0.03 hyd. no. 56 pH 6.0. 

Uses Polyol for adhesives, coatings, thermoplastic urethanes and hot melts, castable and one-shot elastomers, potting compds. 

Uses Component of thermoplastic urethane elastomers for inj. molding, extrusion, thermoset PU, castable prepolymers, spandex fibers, metal and textile coatings/linings, adhesives, elastomeric polyesters, as polyester modifiers soft segment in elastomers food pkg. adhesives, poly-... 

Uses Soft segment In formulation of elastomers such as thermoplastic urethanes, coatings, fibers, adhesives and sealants, cast urethanes, and copolymers... 

Uses Soft segment or extender in formation of elastomers such as thermoplastic urethanes, polyether esters, polyether amides, coatings, adhesives and sealants, casting resins, and urethane foams Features Resist, to microbial attack, low temp, flexibility and elasticity Properties APHA 50 max. liq. sol. in most org. solvs. and water m.w. 250 sp.gr. 0.991 (40 C) acid no. 0.05 hyd. no. 408.2-498.4 flash pt. 180C 0.03% water... 

Uses Eunctional polyol for formulation of urethanes for solv.-based coatings and adhesives and for thermoplastic urethane Trade Names Lexorez 1150-55 Lexorez 1150-110... 

Prane (11) reviews the field and concentrates on history citing pivotal patents related to acrylics (or reactive ) adhesives. These patents show that numerous materials have been utilized in toughening acrylic adhesivesr some nonreactive in the systems, others reacting in, while still others using combinations of each general type modifier. Thus, we find examples for polychloroprene, thermoplastic urethanes, urethane adducts, acrylic rubber, chlorosulfonated polyethylene in addition to buta-diene/acrylonitrile rubber (or its carboxylic version). 

Thermoplastic linear polyurethanes which are usually chain-terminated so that no unreacted free NCO groups remain available. Environmental considerations direct growing attention to these newer non-polluting urethane adhesive forms, e.g. powders, films, aqueous dispersions and 100% solids reactive systems. Some systems do possess blocked diisocyanates which are activated on heating to produce chemically reactive solid systems. 

Texin Thermoplastic urethane elastomers, Bayer Thermogrip Hot melt adhesives, Bostik... 

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