PLASTIC MATERIALS IN TELEPHONE USE 497 



A crylate Resins 



The clear water-white plastics derived from the polymerization of 

 the esters of acrylic and methacrylic acid are at present being used 

 only for windows, viewing lenses on designation strips and other optical 

 uses in telephone apparatus. This is a new plastic and applications 

 will no doubt develop in time, taking advantage not only of color but 

 of the mechanical and electrical properties and insensitivity to moisture. 



Vinyl Resins 



Vinyl acetate and vinyl chloride polymers and co-polymer products 

 form interesting thermoplastic resins. Their use in communication 

 work has been limited so far to phonograph records, where the resist- 

 ance of the co-polymer to warping due to humidity and the superior 

 wear resistance of the plastic have been the important factors. The 

 advantage of non-inflammability imparted by chlorine is more than 

 offset by the acidic nature of the fumes given off from vinyl chloride 

 polymers when heated or burned and this has discouraged use of these 

 materials in the telephone plant. 



Polystyrene 



There have been no important commercial applications for poly- 

 styrene as yet in Bell System telephone communication although much 

 experimentation is being carried on with polystyrene plastic. The low 

 electrical losses of this material make it of special interest in high- 

 frequency work but its mechanical properties have not been satis- 

 factory. In Germany and Italy it is reported that polystyrene has 

 been employed as an insulating plastic in various cable structures for 

 experimental and commercial use. However, in this country the 

 spacing insulators for the coaxial cable from New York to Philadelphia 

 have been made of a special grade of hard rubber which has proved to 

 be a tougher material for the purpose.^ 



Synthetic Coatings 



An important application of synthetic organic materials in the tele- 

 phone plant is in the finishes that are put on Bell System apparatus. 

 There are three major reasons why such finishes are needed — (1) for 

 the improvement in appearance of certain fabricated parts, especially 

 the exposed portions of subscriber station apparatus, both in private 

 homes and public places, (2) for the mechanical and chemical protec- 



^ "Systems for Wide-Band Transmission over Coaxial Lines," L. Espenschied and 

 M. E. Strieby, Bell Sys. Tech. Jour., October 1934; and Elec. Engg., Vol. 56, 1937. 



