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

the conditions at which it will be used and then rewind at least once on the recorder to insure optimum tension for a particular piece of equipment. Adherence to this practice will greatly improve the performance of any ^-in. magnetic tape product. One complete ^-in. tape from each roll of wide stock is fully tested on a special recorder. The 1000 and 10,000-cycle levels are recorded and an EsterlineAngus curve of the full length is run. Once a week, or whenever required by special conditions, sample distortion, bias, signal-to-noise and full frequencyresponse curves at varying bias conditions, intermodulation, print-through and the like are run. Film Equipment The production of magnetic film called for special coating machines, designed to include the special features which worked so well for ^-in. magnetic tape. Figure 5 is a general view of two of the film coaters. In this operation every effort is made to keep the air supplied to the drying cabinet and coating areas as clean as possible. This equipment is set up in an air-conditioned room, sealed from the rest of the plant. A positive static pressure is created after a triplefilter blower and conditioner device so that any dirt is blown out as the operators enter and leave the room. In addition, the pressure in the drying cabinets themselves is further elevated to insure dust elimination. The relatively highviscosity oxide, binder and solvent mixture is delivered from the constant agitation and filter system seen under the nearest coater and is supplied to the coating hopper under constant head. Base thickness variations are automatically compensated for by special hopper design. Immediately following the coating hopper a bright inspection lamp is placed so that it shines through the film. This permits instantaneous inspection for any physical defect that may arise. From this point on, the coating is dried in a conventional motion picture drying cabinet where nothing con the coated side of the film until finished reels are wound on the tak As will be noted, these are contin coating machines with front and rear vator to permit splicing of new feed and removal of completed ones, the film leaves the drying cabinets, roll is checked for its magnetic chara istics. Complete inspection is delaye for 24 hours to insure that the coating thoroughly set. The equipment use for testing is a capstan-drive type of rru chine to insure that sprocket holes ar not damaged before the film reaches th ! customer. The test procedure is t! check the frequency response of each ro; ' at 1000 and 10,000 cycles. At the begin ning and end of each roll a high-speet ; Brush chart is run to check uniformity, j Following this inspection each roll ij visually checked again on rewind equip I ment under a strong inspection lamp fo 1 evidence of dirt, scratches, etc. Production of striped magnetic filn' (Magna-Stripe) is carried out on th< same equipment as that used for full • width films. The difference is merely i change in the dimension of the hopper, which extrude the oxide mix. From th( technical standpoint, stripes of any dimensions or any position on the base side of the film are feasible. All 35mm and 16mm striped films are supplied with a balancing stripe outside the sprocket holes. This has been found a necessity with all film lengths over a few hundred feet to prevent sloppy winding and consequent film damage. The standard thickness of these coatings, in both the recording stripe and balancing stripe, is approximately 0.0006 in. This added thickness is not so great as to cause any difficulties when the film is wound on standard 16mm reels holding up to 1200 ft in length as long as the balancing stripe is present. Stripes of any dimension from 15 mils and up are feasible. Location of the stripe presents no special problems. 460 AprU1953 Journal of the SMPTE Vol.60