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A Method of Measuring Electrification Of Motion Picture Film Applied to Gleaning Operations
BY H. W. CLEVELAND
EASTMAN KODAK Co., ROCHESTER, N.Y.
SUMMARY: A dielectric, such as photographic film, becomes electrified when rubbed or passed over rollers. The electrostatic charges which are generated attract dust and dirt particles to the film. Since dirt is objectionable to both the manufacturer and the user of film, means are sought to reduce electrification. This paper describes a method that has been devised to evaluate roller-film combinations electrostatically. Film is brought to a given potential, either positive or negative, and the change hi potential measured as it passes over a test roller. Typical data for a variety of rollers are presented. The work was extended to test the effect of rubbing film with cleaning pads of velvet and mouton fur. Measurements were also made with solvents applied to a velvet cleaning pad.
A DIELECTRIC MATERIAL, such as photographic film base, becomes electrified when rubbed against almost any object, or when it passes over a roller, either of dielectric or of metallic composition. One of the effects of this electrification, and one which causes a great deal of trouble, is the electrostatic attraction of dust particles to the film. An attempt to clean the film by brushing or rubbing usually results in higher charges which further increase the difficulty of removing the dust. This problem is serious to the manufacturer of the support who seeks to produce a dust-free film, and to the laboratory technician who handles processed films, particularly when there is dust on negative film in the printing process. If emulsion-coated films become electrified beyond a critical value, discharges occur and fog and other markings are produced.
In the handling of photographic products, one aim is to select materials and to design equipment which will produce a minimum amount of electrification. Naturally, some means of evaluating these materials in contact with different types of photographic films is necessary. This is true also in the selection of the cleaning materials and the methods of their use. The purpose of this paper is to describe a method for determining the electrification properties of roller-film combinations. In addition, it will be shown how the method can be
PRESENTED: April 28, 1950, at the SMPTE Convention in Chicago. Communication No. 1345 from the Kodak Research Laboratories.
JULY 1950 JOURNAL OP THE SMPTE VOLUME 55 37