Cellulose Acetate Treatment for Textile Insulation — 

 Engineering Development 



By E. B. WOOD and D. R. BROBST 



The development of a cellulose acetate lacquer treatment for textile 

 insulated wire has made available an improved type of wire for telephone 

 central office use. The desired improvement in electrical characteristics is 

 obtained when the textile fibers are laid down and covered by the cellulose 

 acetate film. 



The accompanying graphs show the comparative electrical characteris- 

 tics at various humidities, of wires insulated with commercial and purified 

 cotton and silk servings, before and after treatment with cellulose acetate 

 lacquer. 



Introduction 



THE improved standards of transmission required for present-day 

 telephone communication have greatly increased the importance 

 of improved electrical characteristics for telephone central office wire 

 insulation. At the same time the tremendous growth of telephone 

 systems, together with the increase in complexity of central office 

 equipment due to the introduction of dial switching apparatus, has 

 increased the quantity of insulated wires required to such an extent 

 that the use of comparatively cheap materials is a matter of large 

 economic importance. Silk and cotton yarns applied in the form of 

 wrappings or braidings have been the standard materials for telephone 

 central office wire insulation for many years. These materials in 

 proper combinations and supplemented in certain cases by enamel 

 and impregnating waxes provide sufficient dielectric strength to with- 

 stand the comparatively low voltages employed to operate telephone 

 apparatus. This type of insulation also fulfills certain controlling 

 mechanical requirements, in that it occupies small space, is not easily 

 damaged by normal handling and can be applied in a large number 

 of color combinations. On the other hand, there are disadvantages 

 attendant upon the use of textile insulation, the most serious of which 

 is the wide variation in insulating properties of such materials under 

 different conditions of atmospheric humidity and temperature, caused 

 mainly by changes in the moisture content of the materials. 



The efforts which have been made to improve textile insulation in 

 this respect have had a two-fold objective, namely, to provide at 

 moderate cost a super-quality insulation for use where it is important 

 to have the best electrical characteristics obtainable, and to improve 



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