Properties and uses.
Polystyrene resin is a clear, colorless, highly thermoplastic molding material with high insulating property, moisture resistance, inertness, dimensional stability, and impact strength. It can be molded directly by heat and pressure, and the molded articles are remarkably resistant to discoloration by light. Polystyrene has a dielectric constant of 2.6, a power factor of 0.02 percent, and is equivalent to fused quartz as an electrical insulator of low dielectric loss. Films of 0.002 inch thickness have a dielectric strength of more than 2,000 volts per mil thickness, which is better than that of any other available synthetic resin and even better than that of shellac. The tensile strength of the resin is 5,500 to 7,000 pounds per square inch, and its impact resistance remains unchanged at temperatures as low as minus 70° C. It transmits all wave lengths of light down to 3,000 Angstrom units.
Polystyrene is adapted to large scale production of transparent, translucent, and opaque moldings in a wide variety of colors. It is easily molded by injection processes, softening at about 150° F. and is molded at 300° to 375° F., under 3,000 to 30,000 pounds pressure per square inch. As much as 40 percent filler may be used without seriously affecting the tensile strength, although the filler does affect the dielectric properties. Since the resin is thermoplastic there is no waste in the molding operation; scrap material may be reground and used again.
The unusual properties of these polystyrene resins should give them widespread applications when the cost is low enough to make them competitive with other materials. Potentially large volume outlets are in radio frequency insulation; in dentures because of the strength, low specific gravity, ease of coloring, and absence of odor and taste of the material; in electrical parts for submarine and aircraft storage battery cases and separators; and for the manufacture of glass eyes.
Other possible applications of polystyrene resins are in metal lacquers and in light colored enamels. Their toughness and light color, together with their solubility in cheap solvents, suggest their use for these purposes. Such lacquers are said to be quick-drying, resistant to water, and moderately so to acids and alkalies.
Production in the United States.
For a number of years, the Naugatuck Chemical Division of the United States Rubber Co. produced small quantities of polystyrene resins, which were marketed under the trade name Victron when for general purposes and under the trade name Marvelyn when for use in dentures. Little progress was made because of high costs and failure to produce a water-white product. The sales price was between $1.50 and $2 per pound. Early in 1937 the Naugatuck Chemical Division transferred its patents on polystyrene resins to the Carbide and Carbon Chemicals Corporation.
The Dow Chemical Co., Midland, Mich., late in 1937 announced commercial production of clear, colorless polystyrene in several forms. Styron is the trade name for the resin from this source. In January 1938, the Bakelite Corporation announced Bakelite Polystyrene. The plants manufacturing polystyrene have a capacity in excess of 2,000,000 pounds a year, and the resin is currently offered at 72 cents per pound.
At least one other domestic firm is doing research on the polystyrenes and expects to produce commercially in the near future.