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MOISTURE IN MOTION PICTURE FILM
V. B. Sease*
MOISTURE plays an important part in determining many of the properties of motion picture film. The amount of moisture to be found in film is approximately a linear function of the relative humidity of the atmosphere with which the film is in equilibrium. The moisture content of a number of uncoated samples of film base which had been stored at room temperature (70° F.) at different humidities varied from 1.2% at a relative humidity of 20% to 4.1% at a relative humidity of 95%.
The length and width pitches of film perforated under given humidity conditions become larger upon further humidification and smaller upon desiccation. Two samples of film, one in equilibrium with an atmosphere at 0% and the other with an atmosphere at 95% relative humidity were perforated on the same machine immediately after removal from their respective humidors. They were then brought to equilibrium with an atmosphere at 70% relative humidity and measured. The dimensions were found to differ by 0.75%. This difference is quite significant in view of the fact that the Engineering Standards Committee has set a tolerance figure of 1.5% for the shrinkage of raw stock. On account of the fact that film dimensions change with variation in moisture, the manufacturer has found it necessary to condition thoroughly the stock before slitting and perforating, and to maintain rigid humidity conditions during these operations.
The foregoing observations indicated that a change of 30% in relative humidity would produce about 0.25% change in dimensions. This figure was checked by a series of experiments and found to hold very closely for both positive and negative film of two manufacturers. The details of one of the experiments are shown in Fig. 1. Graph A represents the changes in a sample of film perforated under 70% humidity conditions to standard length pitch and conditioned alternately for periods of 24 hours in humidors at 70% and 40% relative humidities. The transfer of the sample from 70% to 40% to 70% humidity constituted the cycle referred to on the graph. The average temporary change due to lowering the humidity in one half of the cycle was 0.3%; to increasing the
Director Research Laboratory, DuPorit-Pathe* Film Mfg. Co., Par
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