Polychloroprene history

Latex Adhesive Applications. Polychloroprene latex adhesives have a long history of use in foil laminating adhesives, facing adhesives, and constmction mastics. Increasingly stringent restrictions on the emission of photoreactive solvents has heightened interest in latex compounds for broader apphcations, particularly contact bond adhesives. Table 10 makes a general comparison of solvent and latex contact bond adhesives (158). 

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). 

Extrusion. Polychloroprene has been employed in a wide variety of extrusion (qv) processes. Intricate cross-sections such as highway compression seals, bulb weather-stripping, and hose represent a few examples. As with calendering, extrusion is very sensitive to nerve. The DuPont Dow neoprene sol/gel blend types are best suited for extrusion applications. Use of low levels of highly structmed furnace carbon blacks, stearic acid, petroleum, paraffin wax, triethanolamine benzoic acid, and calciiun stearate are particularly effective extrusion aids. The screw of the extruder should have a constant diameter root with increasing pitch. Heat history of the compound should be minimized, with only a brief warm-up before extrusion begins. The barrel and screw should be lun cool, 50°C, and the die hot, 95°C (96,119). 

Crystallization of amorphous polymers is a time-dependent phenomenon. Polychloroprene crystallizes fastest at —12°C (123,124). Below this temperature, thermal stiffening commences and restrains molecular motion and alignment. Crystallization rates and degree of crystallization are heavily impacted by several phenomena, of which polymer pol5unerization temperature and thermal history of the polymer sample before measurements are most important. 

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