Tabic I. Average Processing Shrinkage, Humidity Expansion and Thermal Expansion 

 of Current Eastman Motion Picture Films. 



Cronar 



A new polyester film support, "Cronar", is now being produced by the 

 Photo Products Division of E. I. Du Pont de Nemours and Company. At pre- 

 sent, it is being coated only with the slow, high contrast "photolith" emulsion. 

 Reference to Tables II and III, and Figures 1 and 2, will indicate that 

 "Cronar" shows considerable improvement in dimensional stability over 

 other flexible film supports, in regard to temperature, relative humidity, 

 and processing. There is reason to hope that when "Cronar" is available 

 in larger quantities, it will be coated with an aerial emulsion, in addition 

 to the litho emulsion now available. 



Permanent changes 



There are three principal causes of permanent dimensional changes 

 in film supports. The first, and most important, is the gradual loss of 

 volatile chemicals (plasticizer and solvents). Film base is cured for about 

 five hours, which eliminates about 96 percent of the volatile chemicals. 

 The subsequent loss of the remaining 4 percent causes shrinkage and re- 

 lated troubles. Shririkage from this cause is accelerated by heat and 

 moisture, and reduced by preventing free access to air. As with tempor- 

 ary changes in dimension, shrinkage is greater in the widthwise direction. 



The compressive force of the emulsion upon the base results in a 

 certain amount of plastic flow or permanent shrinkage. Dimensional 

 changes from this cause are increased by heat, because of increased film 



plasticity at high temperatures. Moisture also increases base plasticity 

 but inhibits the contraction of the base, and the latter has the greater 

 effect. Thus, an increase in relative humidity, at constant temperature 

 greatly decreases this type of shrinkage. Plastic flow of the base may also 



be the result of stretching in hetndling and processing ~ resulting in extension 



lengthwise. Such changes are increased by heat, moisture, amount of 



tension applied, and the duration of the tension. 



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