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THE SURFACE TREATMENT OF SOUND FILM* J. I. CRABTREE, OTTO SANDVIK, AND C. E. IVES
Practical experience has shown that with newly processed motion picture positive prints it is necessary to apply some form of lubricant to the film surface in order to facilitate the passage of the film through the projector. Sound record prints require similar lubrication in which case it is very necessary that the applied lubricant should not be the cause of extraneous noise in the projector-reproducer mechanism.
In an earlier communication1 it has been shown that the so-called ground noise is due to scratches, dirt, dust, and finger marks on the film. It is therefore desirable to protect the sound record in such a manner that it is not damaged by the accumulation of those factors which are responsible for excessive ground noise. The problem of a suitable surface treatment therefore resolved itself into the devising of:
1. A suitable method of lubricating sound film which would not increase ground noise.
2. A method of treating either the entire film surface or the surface of the sound record area so as to reduce to a minimum its tendency to become scratched and accumulate dirt during projection and thereby retard the accumulation of ground noise on repeated projection.
3. If possible, a method of treatment combining methods 1 and 2.
I. THE LUBRICATION OF SOUND FILMS
Effects of Lack of Lubrication. — As stated in a previous communication2 the gelatin emulsion of a newly developed positive print is very adherent to hot metal surfaces, and the adhesion of the film to the hot gate or pressure shoes in the projector causes small particles of gelatin to be rubbed off the film. Some of these particles become pressed together to form a crust which increases greatly the resistance to travel of the film through the gate. After these crusts form, the
* Communication No. 413 from the Kodak Research Laboratories.
1 SANDVIK, OTTO: "A Study of Ground Noise," Trans. Soc. Mot. Pict. Eng.t 12, No. 35 (1928), p. 790.
2 CRABTREE, J. I., AND IVES, C. E.: "The Lubrication of Motion Picture Film,"
ians. Soc. Mot. Pict. Eng., 11, No. 31 (1927), p. 522. 275