ABS resins, available from Allplastics , are terpolymers of acrylonitrile, butadiene and styrene. These medium-priced amorphous thermoplastics are hard, rigid and tough, even at low temperatures. Various grades offer different levels of impact strength - a function of butadiene content. Heat resistant, flame-retardant and platable grades are also available. Most natural ABS resins are translucent to opaque, but they are also produced in transparent grades, and they can be pigmented to almost any colour. Grades are available for injection molding, extrusion, blow molding, foam molding and thermoforming.
Some grades of ABS are compounded with other resins to achieve special properties. For example, ABS is alloyed with polycarbonate to achieve a better balance of heat and impact properties at an intermediate cost. Deflection temperature is improved by the polycarbonate; molding ease, by the ABS. Other ABS resins are used to modify rigid PVC for use in pipe, sheeting and molded parts.
Related to ABS is SAN, a copolymer of styrene and acrylonitrile (no butadiene) that is hard, rigid, transparent and characterized by excellent chemical resistance, dimensional stability and ease of processing.
SAN resins are usually processed by injection molding but extrusion, injection blow molding and compression molding are also used. They can also be thermoformed provided that no postmold trimming is necessary.
ABS plastics offer a good balance of tensile strength, impact and abrasion resistance, dimensional stability, surface hardness, rigidity, heat resistance, low temperature properties, chemical resistance and electrical characteristics. ABS parts have enough spring to accommodate shallow, snap-fit assembly requirements.
Impact properties of ABS are exceptionally good at room temperature and with special resin grades at temperatures as low as -40 degrees F. General purpose ABS grades may be adequate for some outdoor applications (depending on design and performance requirements) but prolonged exposure to sunlight causes a colour change and reduces surface gloss, impact strength, hardness and elastic modulus. Pigmenting the resins black, laminating with opaque acrylic sheet and applying certain coating systems provide optimum resistance to weathering.
Molded ABS parts are almost completely unaffected by water, salts, most inorganic acids, food acids and alkalines, but much depends on time, temperature and stress levels. Molded ABS products are used in both protective and decorative applications in many industrial and consumer products. Examples include football helmets, camper tops, housing for small appliances, communications equipment, business machines, automotive instrument panels, pipe and fittings and home security devices. Chrome-plated ABS has replaced die cast metals in plumbing hardware and automobile grills, wheel covers and mirror housings. Typical products vacuum-formed from extruded ABS sheet are refrigerator lines, luggage shells, tote trays, mower shrouds, boat hulls and large components for recreational vehicles.
Properties of SAN resins are controlled primarily through acrylonitrile content and by adjusting the molecular weight of the copolymer. Increasing both improves physical properties at a slight penalty in processing ease. Properties of resins can also be enhanced by controlling orientation during molding. Tensile and impact strength, barrier properties, and solvent resistance are improved by this control.
Special grades of SAN are available with improved UV stability, vapour-barrier characteristics and weatherability. Their barrier resins - designed for the blown bottle market - are also tougher and have greater solvent resistance than the standard grades.