PLASTICS — KLLNE 227 



ous materials having the hardness of stone, the transparency of 

 glass, the elasticity' of rubber, or the insulating ability of mica. These 

 synthetic resins, in combination with suitable fillers, are readily 

 molded into products characterized by excellent strength, light 

 weight, dimensional stability, and resistance to moisture, moderate 

 heat, sunlight, and other deteriorating factors. They lend them- 

 selves especially to the rapid manufacture of large quantities of 

 accurately sized parts by the application of heat and pressure to 

 the material placed in suitable molds and to the use of original or 

 imitative effects in a variety of colors. Some of the cheap raw 

 materials used in their production include phenol, urea, formalde- 

 hyde, glycerol, phthalic anhydride, acetylene, and petroleum. Syn- 

 thetic resin plastics are known commercially under such trade 

 names as Bakelite, Catalin, Beetle, Glyptal, and Vinylite. They 

 are used in an ever-growing variety of applications, such as electrical 

 parts, automotive parts, closures, containers; costume accessories in- 

 cluding buttons, buckles, and jewelry; hardware, tableware, and 

 kitchenware, and miscellaneous novelties. 



The powdered molding compositions are generally sold to custom 

 molders who produce the finished parts. Casting resins and lam- 

 inated resinous products, described in more detail later, are, how- 

 ever, usually made into sheets, rods, or tubes by the manufacturer of 

 the resin. Blanks are cut from these for the preparation of the 

 finished product by machining operations. 



Natural resins. — These are more familiarly known to the public 

 by their common names, such as shellac, rosin, asphalt, and pitch, 

 than by the proprietary names attached by manufacturers to mold- 

 ing compositions prepared from them. They are used in industry 

 for the production of the fusible type of molded product as dis- 

 tinguished from the infusible articles formed by some of the syn- 

 thetic resins. Hot-molding compositions are prepared by mixing 

 shellac, rosin, and asphalts with suitable fillers. Compositions con- 

 taining chiefly shellac as the binder are used in electrical insulators 

 for high-voltage equipment, in telephone parts, and in phonograph 

 records. The terms rosin and resin are often confused. Eosin is a 

 natural resin recovered as a solid residue after distillation of turpen- 

 tine from pine tree extracts. 



Cellulose derivatives. — The third type of organic plastics, the cellu- 

 lose derivatives, is probably the most widely used and best known 

 of any of these materials. To this group belong celluloid plastics 

 used for making toys, toiletware, pen and pencil barrels, and the 

 like; cellulose acetate commonly used in the Celanese type of rayon, 

 safety film, and in place of the slightly less expensive nitrated cellu- 

 lose when noninflammability is desired; and regenerated cellulose, 



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