Journal of the Society of Motion Picture and Television Engineers (1950-1954)

Table III. Relation of Track Width to Viscosity of Coating Composition Width of Track width Amyl acetate Brookfield viscosity applicator wheel Film speed 0.100 in. 0.050 in. 0.032 in. 906 906 515 11 11 76 0.061 in. 0.032 in. 0.020 in. 20 fpm 20 fpm 20 fpm driven) which are under tension by means of spring (B). Splices will not pass through these rolls except by using prohibitive tensions from the drive roll (C). When a splice hits the pressing rolls, the film momentarily stops allowing idler (A) to drop, thereby actuating a micro switch which energizes a solenoid (D) which opens the pressing rolls and allows the splice to pass. The film tension then returns to normal and pressing continues. The rolls are 2 in. in diameter. The spring tension is adjusted so that an unpressed coating 0.55mil thick is pressed to a 0.40 to 0.45mil thickness. In applying coatings by use of this equipment, it is necessary to adjust the viscosity of the coating composition to the width of track to be applied. The formula, as given in Table I, is for tracks having a width of 0.100 in. For narrower tracks, it is necessary to use a higher viscosity coating composition. Viscosity adjustments are made by varying the amyl acetate content. The formula, with appropriate viscosity adjustments, can give acceptable sound tracks for 16mm film perforated along one edge, using either 0.100-in. or 0.050-in. tracks, and film perforated along both edges on which a 0.032-in. track is coated outside the perforations. Specific data are listed in Table III for making tracks 0.100, 0.050 or 0.032 in. wide. In each case, the applicator wheel was 2 in. in diameter and was rotated at 28 rpm. The formulas used for different width tracks vary only in amyl acetate content. Viscosity readings are on a Brookfield viscometer using a #2 spindle at 6 rpm at 80 F. The Brookfield viscometer has been used because of the ease of measuring viscosity. For experimental work, it is very helpful to know the viscosity of all dispersions. For production work, it has been found that a given formula can be reproduced so well that viscosity measurements are unnecessary. Before using a dispersion, check coatings are made to insure proper width and thickness of the coating. Coating Problems It is necessary that the coating solution lend itself to application to either the base side or the emulsion side of the film. In the case of Eastman films, two types of base are in current use.3-4 At the present time, Cine Kodak 16mm and 8mm Kodachrome films and Cine Kodak black-and-white films for reversal processing are on a cellulose acetatepropionate base. Kodak Blue Base Reversal film and positive print films are on tri-acetyl cellulose acetate base. Adhesion to the emulsion is primarily determined by the type of binder used. Small amounts of water in the formula tend to increase adhesion to the emulsion but reduce adhesion to the film base. Most binding agents give poor adhesion to emulsion regardless of the solvents used. Magnetic sound tracks coated from the proposed coating composition have satisfactory adhesion to the emulsion. On the base side of film, much of the adhesion results from solvent attack. For a given magnetic oxide formula, the high-acetyl acetate base will be attacked less than the cellulose acetate-propionate 496 April 1953 Journal of the SMPTE Vol.60