Лако-красочные материалы — производство

The second major classification of common polyurethane adhesives is the two-component system. Two-component polyurethane adhesives are widely used where fast cure speeds are critical, as on OEM (original equipment manufacturers) assembly lines that require quick fixture of parts, especially at ambient or low bake temperatures. Two-component urethanes are required in laminating applications where no substrate moisture is available or where moisture cannot penetrate through to the adhesive bond. Two-component urethanes are also useful where CO2 (generated by a one-component moisture cure) or a volatile blocking agent would interfere with the adhesive properties.

Two-component adhesives typically consist of low-equivalent-weight isocyanate or prepolymer that is cured with a low-equivalent-weight polyol or polyamine. They may be 100% solids or solvent borne. Since the two components will cure rapidly when mixed, they must be kept separate until just before application. Application is followed quickly by mating of the two substrates to be bonded.

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WATER DISPERSED ANIONIC POL YU REA-POLYURETHANE

Figure 26 How functional groups are built into the polymer backbone of urethane.

Efficient mixing of the two components is essential for complete reaction and full development of designed adhesive properties. In-line mixing tubes are adequate for low — volume adhesive systems. For larger-volume demands, sophisticated meter mix machines are required that will mix both components just prior to application. Commercial systems for delivering two-component adhesives are segmented based on the viscosity ranges of the components. The ranges can be broken down into low, middle, and high viscosity, with, for example, Liquid Control Corp., Sealant Equipment and Engineering Inc., and Graco Inc., respectively, supplying equipment for the three ranges [64].

In present-day high-speed assembly line operations, adhesives are applied roboti­cally. The adhesive bead is applied quickly and evenly to parts on a conveyor line just prior to being fitted. These operations, especially the need to handle the adhered substrates soon after assembly, demand fast-curing adhesive systems [65]. Two-component adhesives are used to bond metals to plastics in automobiles, to laminate panels in the construction industry, to laminate foams to textiles, to laminate plastic films together, and to bond poly(vinylidene chloride) films to wood for furniture. A commercial waterborne two — component adhesive is sold by Ashland under the trademark ISOSET. This system is used for exterior sandwich panels by recreational vehicle manufacturers and is composed of a water-emulsifiable isocyanate and a hydroxy-functionalized emulsion latex.