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

l|)ricant where it belongs, on the surface, her than diluting the critical loading the pigment mix and encouraging cier problems of blush, etc., as hudity changes occur. Surface polishit improves the high-frequency response c unused tape and therefore decreases t : frequently noted changes with actual lining. At the time of polishing, the t)e is given a rigorous visual inspection f coating defects. Jtting and Testing All slitting and testing equipment has ten especially designed for the manufacit*e of recording tape. Weave and tckle in slitting have been minimized I ;atly. The slitter take-ups are equipped vth constant-tension drives. The tension i adjusted to minimize the effect of sisonal weather conditions after the s:ting process has been completed. The test procedure and apparatus are c signed so that the entire length of all t3e produced is tested completely for liformity, frequency response, etc. Im Operations Logically the application of magnetic citings to motion picture film followed tt use of such coatings on tape. The line red oxide pigment is used and I the same magnetic characteristics list on ^-in. tape and all film products. Knee, bias and erase conditions are s ndardized regardless of the end use of ti product, whether the product be 2mm Magna-Stripe for professional use c 8mm amateur film. In the case of fn, attention was paid to the physical ipperties of the coating to insure freecm from curl in all use conditions. A Ipi and well-anchored coating miniBzes handling problems and surface Ipion. These are important factors •cause of the naturally high head presIjres required in motion picture applicjtions. •jln the manufacture of magnetic film Ipducts, it was our conclusion that a Itter product would be achieved by us ing already slit and perforated film base, rather than coating in wide widths and slitting and perforating after coating. We believed it would be to our advantage to profit from the experience accumulated in this field by the film companies, who for over 30 years have been constantly striving to improve their slitting and perforating techniques. It was also our belief that the wear on punches and dies would be excessive due to the abrasive action of the oxides if we attempted to perforate after coating. Wear on film sprockets is avoided by not coating over the perforations. In addition, we concluded that the control of coating uniformity over a 1 in. wide strip was immeasurably simpler than on 30 or 40-in. sheet. We also planned and have realized yields of approximately 100% as a result of using film already slit and perforated. Our process is fundamentally an extrusion process rather than the dip-coating method employed by motion picture film manufacturers. It was found early that the dip-coating or roller-coating methods which worked on gelatinous photosensitive materials were not applicable to noncohesive mud-like magnetic coating mixtures. Film Striping Magna-Stripe was a logical step after the full-width film items, although historically striped-film development work started first. Striping presents some special and unique problems. Some of these are: 1. Very close dimensional tolerances; 2. Smooth, straight edges, so that an overlapping head will ride smoothly without amplitude modulation; 3. Flat and uniform top contour, to provide uniformity of output; 4. A balancing stripe — absolutely essential when handling any roll over 400 ft in length, or whenever any photosensitive product is coated ; 5. High electrical output to produce a Schmidt and Franck: Magnetic Recording Materials 455