Nov. 15, 2002
Acrylic-styrene-acrylonitrile (ASA) polymers are amorphous plastics which have mechanical properties similar to those of ABS resins.

Acrylic-styrene-acrylonitrile (ASA) polymers are amorphous plastics which have mechanical properties similar to those of ABS resins. However, the ASA properties are far less affected by outdoor weathering.

ASA is a terpolymer that can be produced by either a patented, proprietary reaction process or by a graft process. In the reaction method, ASA is made by introducing a grafted acrylic ester elastomer during a copolymerization of styrene and acrylonitrile (SAN). The finely divided powder is uniformly distributed in and grafted to the SAN molecular chains. The outstanding weatherability of ASA is due to the acrylic ester elastomer.

ASA resins are available in natural, off white, and a broad range of standard and custom-matched colors. Base ASA resins are sold under the trade names Luran S (BASF Plastic Materials), Geloy (General Electric Plastics) and Centrex (Monsanto Chemical Co.). ASA resins can be compounded with other polymers to make alloys and compounds that benefit from ASA's weather resistance. Also, ASA sheet is used as a capstock over other plastics.

Properties: ASA parts have high gloss, good chemical and heat resistance, and high impact strength, even at low temperatures. Typical heat-deflection temperatures for ASA are 180 to 220 °F (82 to 104 °C) at 264 psi. Tensile strengths are 4,000 to 7,000 psi; elongation at break, 25 to 40%, flexural modulus, 220,000 to 250,000 psi; and notched Izod impact strengths are 9.0 to 11.0 ft-lb/in. (at 73 °F) and 4.0 to 6.0 ft-lb/in. (at -40 °F).

ASA is resistant to saturated hydrocarbons, low-aromatic gasoline and lubricating oil, vegetable and animal oils, water, aqueous solutions of salts, and dilute acids and alkalis. However, it is attacked by concentrated inorganic acids, aromatic and chlorinated hydrocarbons, esters, ethers, ketones, and some alcohols. ASA offers better resistance to environmental stress cracking than ABS. With respect to flame resistance, ASA is available with UL 94-HB classification.

Processing: ASA resins can be processed by most conventional methods. These include profile and sheet extrusion and coextrusion, injection molding, structural foam molding, and extrusion-blow molding. Extruded sheet can be thermoformed. ASA should be blow molded using extruders with grooved, cooled, and thermally insulated feed sections. Screws should have somewhat deeper flights in order to reduce frictional heat. Optimum results are obtained with machines having accumulators.

ASA parts can be welded using thermal and spin techniques. In some cases, ultrasonic welding is possible. ASA parts also can be solvent welded using 2-butanone, dichloroethylene, or cyclohexane. ASA parts readily accept and retain print and coatings without prior surface treatment. Vacuum metallizing by conventional methods is also possible.

Applications:Building/construction -- Gutters and fittings, drain pipe and fittings, signs, mail boxes, mobile home skirting, flower boxes, and shutters. Recreation/leisure -- Outdoor furniture, windsurfer boards, swimming pool pumps, boat hulls, pickup truck caps, and filter housings and spas. Automotive/transportation -- Exterior sideview mirror housings, grilles, drip rails, and bumper covers. Miscellaneous -- Lawn-mower components, garden-hose reels, snowmobile housings, machinery covers, and covers for outdoor lighting.

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