American cinematographer (Jan-Dec 1928)

February, 1928 AMERICAN CINEMATOGRAPHER Nine The Lubrication of Motion Picture Film The above experiments serve to emphasize the importance of apply By J. I. Crabtree and C. E. Ives Projection life tests made with buffed and unbuffed film indicated ins:* the correct quantity of wax to Communication No. 330 from the Eastman that the buffing treatment was of Kodak Research Laboratories. the film and of removing at very frequent intervals any wax which accumulates on the projector gate. Lubrication of the Entire Gelatin Surface of Motion Picture Film At the outset it was considered that by coating the entire gelatin surface of motion picture film with a thin layer of a suitable lubricant, many of the objections to edge lubrication would be overcome. Also, if the coating could be made impermeable to oil, trouble from oil spots would be eliminated likewise. The idea of lubricating the entire gelatin coating of the film is by no means new. A large number of patents have been granted for particular lubricating formulas which include the use of tallow, lard, spermaceti, stearic acid, sodium stearate in methanol, oil of turpentine, olive oil, cotton seed oil, linseed oil, petrolatum, a suspension of gypsum in menthanol, beeswax, and paraffin wax. Before the commencement of the experiments described below, the Dworsky Film Mfg. Co. was supplying a film buffing machine shown in Fig. 9. This consists (Continued from January Cinematographer) Fig. 9 — Film waxing and polishing machine. essentially of a series of four or five cloth buffing wheels similar to those used for polishing electro-plated metals, which buffers rotate at a high speed in contact with the gelatin surface of the film. The film is pulled through the machine by means of two rubber covered rollers of the laundry wringer type, the machine being entirely sprocketless. (The lower application roller attachment was not originally fitted to this machine). Usually a little tripoli (polishing powder) was applied to the buffers to produce more rapid polishing of the film surface. Although it might be expected that this buffing treatment would tend to scratch the gelatin surface, this was not found to be the case. Instead, the treatment produced a noticeable gloss on the gelatin surface (see Fig. 5 as compared with Fig. 4). questionable value. However, the machine appeared to be readily adaptable for the application of lubricants to the entire film surface and the following experiments were therefore made. 1. Machine oil or Russian mineral oil was applied to the entire gelatin surface and then buffed in the above manner. Projection tests indicated that film so treated had a projection life comparable with that of edge waxed film, although after storing in the rolled up condition for two or three days, the film developed oil spots. Attempts were made, therefore, to find a solid lubricant which would be impervious to the effect of oil. 2. Waxes were next applied to the film surface by holding a piece of solid wax against the first buffing wheel, which in turn applied the wax to the film. The remaining buffers then spread out the wax more evenly and imparted a high gloss to the film surface which resembled that of highly polished footwear. Projection tests with film waxed in this manner with various waxes indicated that there is a wide difference in the lubricating quality of different waxes. Data regarding this will be given later. Oil treatment tests after waxing indicated that a surface coating of almost any wax over the gelatin surface of the film will materially reduce the propensity of the film to show oil spots on the screen. Mechanical Methods of Applying Wax to the Film (A) It was soon apparent that the above method of application of the wax was entirely impracticable and that a mechanical method of application was required. The application roller method of applying a solution of various waxes in suitable solvents was tried out and this was ultimately entirely satisfactory. The first arrangements of application rollers is shown in Fog. 10. The wax solution is contained in tank Fig. 10 — Showing method of application of wax solution to film surface. T in which a small flangeless aluminum roller Rl covered with felt rotates. Roller Rl bears against roller R2 which is covered with silk plush. The film runs face downwards against roller R2 and rotates it and in turn this roller rotates the lower roller Rl which is immersed to a depth of about V± inch in the wax solution. By adjusting the distance between the rollers Rl and R2, roller R2 acts as a wringer and squeezes the excess wax solution from roller Rl so that the quantity of liquid applied by the plush coating of roller R2 can be regulated. This method of application had the objection that the plush did not apply the wax solution sufficiently evenly and it was not possible to control the quantity of wax applied with sufficient precision to insure that the wax solution did not pass through the perforations on to the base side of the film.