Processing shrinkage 



Films swell during development, and shrink again during drying. 

 Most films undergo a small permanent shrinkage during processing. How- 

 ever, if the film is not brought to equilibrium with air at the same rela- 

 tive humidity after development as it was before, the permanent process- 

 ing may be completely masked by the temporary expansion or contraction 

 due to change in relative humidity. 



Table V shows the effect of processing on several filra bases. Values 

 are given for materials conditioned 4 hours before and after processing 

 at 20 percent relative humidity, 50 percent relative humidity, and 70 per- 

 cent relative humiditv. all at 70°F. 



Elfact of Processing on LItho Film Size 



Representative sensitized films were measured before and after 

 processing to determine processing stability. Values are given 



TABLE V 



for materials conditioned 4 hours before and after processing 

 at 20% RH, 50% RH and 70% RH, all at 70°F. 



AVERAGE SIZE CHANGES IN % 



(All films were developed 2'/2 min. in Du Pont 7-0 Developer, rinsed 20 

 sec. in clear water, fixed 3 min. in Du Pont 20-F Fixer and washed 10 

 min., dried below 1 00°F. and reconditioned at the indicated RH at 70°F.). 



As indicated in Table IV, photographic film shrinks during storage. 

 This shrinkage is accelerated by high tennperatures and by free contact with 

 air. Table VI illustrates shrinkage of EK nitrate MP film (no longer used) 

 in the lengthwise direction for various periods, under three storage con- 

 ditions, all at 70°F and 50-65 percent relative humidity. Fig. 3 shows the 

 shrinkage rate of the newer triacetate base. 



Du Pont literature states that "Cronar" polyester photographic film 

 base is chemically inert, and contains no plasticizer or solvents to be lost 

 gradually as it ages. Normal storage studies, it is added, have given no 

 indication of base change or deterioration, and forty day accelerated stor- 

 age tests at 100°C have caused no significant change in processed film 

 properties. Hence, it is expected that this base will remain substantially 

 unchanged over long periods of time. 



263 



