TREATMENT FOR TEXTILE INSULATION 217 



Treatment of Textile Insulated Wire 

 The cellulose acetate treatment of wire consists essentially in passing 

 the textile insulated conductor through a thin solution of cellulose 

 acetate dissolved in acetone, then through a wiping die to remove the 

 excess lacquer and finally into a heated drying chamber where the 

 solvent is evaporated. This process is repeated several times, usually 

 six, to build up a film of satisfactory thickness and smoothness. The 

 application of heat in the drying process is necessary for two reasons. 

 F"irst, the evaporation of the solvent tends to lower the temperature 

 of the wire considerably and if the temperature falls below the dew 

 point of the surrounding air, moisture will condense on the wet lacquer 

 film, causing it to turn white and opaque. In the second place, the 

 evaporation of the solvent must be rapid in order that the speed of 

 the wire through the lacquering machine may be such as to make 

 application of the treatment to large quantities of wire commercially 

 practicable. 



In the earlier stages of the investigation, the insulated wire was 

 thoroughly dried before being treated to eliminate the moisture in the 

 textile. In addition, the wire was treated under vacuum with the 

 object of thoroughly impregnating the whole textile covering and pre- 

 venting entrance of moisture into the textile after the impregnating 

 process was completed. However, it was found that even with vacuum 

 impregnation, the cellulose acetate did not penetrate the insulation to 

 an appreciable depth, although the solvent appeared to penetrate to 

 the conductor and thoroughly wet the insulating materials. Also, it 

 was found that the coating of cellulose acetate did not prevent the 

 entrance of moisture into the textile to any appreciable extent. 



In consideration of these facts, it was concluded and confirmed by 

 tests that the improvement in electrical characteristics of cellulose 

 acetate treated wire under conditions of high humidity is due mainly 

 to the barrier of high resistance lacquer film interposed in the leakage 

 paths formed by moisture in the textile insulation. It may be seen 

 from Fig. 1 that the fibers of untreated cotton insulation project in 

 all directions, and in a twisted pair, interweave to increase the effec- 

 tive area of contact between the conductors and provide a medium for 

 direct leakage paths when moisture is present. With the fibers 

 smoothed down and covered by the application of several layers of 

 lacquer film, the effective area of contact is decreased and any leakage 

 which takes place must be either through or across this relatively high 

 resistance film. In confirmation of this conclusion, it has been found 

 by repeated tests, that a very reliable indication of the improvement 

 in electrical characteristics which may be expected in a treated wire is 



