PLASTIC MATERIALS IN TELEPHONE USE 485 



plant. Phenol plastics have been employed in the molding of the 

 regular telephone hand set, recent production being in excess of 

 1,000,000 units per year. Cellulose acetate is widely used in foil form. 

 Plastics in the form of synthetic organic finishes are used for protection, 

 decoration and insulating purposes on apparatus and equipment. 

 For the purpose of discussion, plastics in the telephone plant may be 

 grouped as follows: 



1. Molding plastics. 



2. Sheet materials (phenol fiber, acetate foil, etc.). 



3. Synthetic organic finishes, adhesives and miscellaneous special items. 



Objectives of Ideal Telephone Plastics 



Telephone apparatus and equipment are not sold as consumption 

 goods but the service rendered by it is sold to the subscriber. Good 

 service means a minimum of breakdown due to replacement of mal- 

 functioning parts, repairs and maintenance. High maintenance costs 

 are inconsistent with the best service at the lowest cost. Uniformly 

 high quality of materials throughout the economic life of the telephone 

 plant is therefore essential. 



The molding plastics and sheet materials account for the bulk of the 

 plastics used in the telephone plant and the objectives of these materials 

 are similar enough to permit them to be listed together. There are 

 given below the general and specific properties that must be considered 

 in such materials when they are to be used in the telephone industry. 

 The level of quality demanded in specific properties will obviously 

 depend on the application. 



1. General requirements. 



a. Strength, hardness, toughness. 



b. Low density (to decrease mechanical inertia, aid manual use). 



c. Chemical inertness in air, or in contact with other materials. 



d. Resistance to humidity (minimum of swelling and shrinkage 



with variations of moisture content of the air). 



e. Ability to withstand temperature, heat and cold without too 



great impairment of strength and shape. 



/. Ability to reproduce die surface accurately and give good ap- 

 pearance to finished part. 



g. Light stability. 



h. Relative non-inflammability. 



i. No odor, no harm to the skin. 



j. Resistance to insect attack. 



