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

plied into recessed grooves of a coating wheel and subsequently transferred to the film. Experiments with this method have shown that satisfactory transfer of the dispersion from the intaglio grooves to the film is difficult to obtain. A more successful process has proved to be a bead coating method. In this case, an applicator wheel rotates in a tray of dispersion and transfers the magnetic composition by means of a liquid bead to the film, which passes above the applicator wheel. This is a well-established coating method and is used for film lacquering.2 Consequently, most mechanical problems connected with obtaining satisfactory coating uniformity have already been solved. One disadvantage is that surface tension causes the dry surface to be slightly convex. Flatter surfaces can be obtained by pressing the coatings. Also, this method is limited to coatings under 0.20 in. in width. Wider magnetic tracks cannot be made sufficiently uniform in thickness when coated by the bead method. The cause for this is the high viscosity needed to obtain proper oxide concentration in the track. Lowviscosity bead applications can be very uniform. The bead method, to be successful, requires rigid control of the viscosity of the dispersion, the rotation speed of the applicator wheel, the speed of the film, and the separation between the applicator wheel and the film. Bead Coating Method Referring to Fig. 1, the coating machine consists of a supply reel (A), a bead coating mechanism (B), a drying cabinet (C), a pressing device (D), and a take-up reel (E). The film is transported and kept at proper tensions by three friction-driven rolls. A rubbercovered drive roll (F) is located before the coating is applied. Another drive roll is in the drying cabinet. A third drive roll (H) is after the pressing device. The motor beneath the table is connected by silent chains to the drive rolls. At present, the coatings are made at 20 fpm. At this speed, the curing time has been 2.8 min. The air temperature in the curing cabinet should not exceed 110 F, otherwise film brittleness problems may result. Higher coating speeds are undoubtedly possible. The maximum practical speed has not yet been determined. Figure 2 is a close-up of the coating mechanism. Referring to this picture, the entering film first contacts a positioning roll (A), which, by means of an outside flange, forces the film toward an inner flange on a positioning roll (B). In this manner, film is made to leave roll B always from the same position. As a result, the film is fed to idler (C) so that the inner edge which is to be coated is in a constant position. Below the idler is an applicator wheel (D) which dips into tray (E) and brings up liquid dispersion. The film on the idler can be raised or lowered by the adjusting knob (L). A dial gauge records the positioning of the film. In raising or lowering the film, the plate (K) on which the idler and positioning rolls are attached pivots about point (F). The applicator roll rotates so that the top of the roll moves in the same direction as the film. A setscrew (H) prevents the idler roll from contacting the applicator roll. A spring (J) balances the mounting plate (K) so that if an excessively thick splice should pass between the applicator roll and the idler roll, no large forces would be acting on the bearings. The coating formulas are adjusted so that a normal splice can pass through without having the applicator roll touch the film. Figure 3 shows the pressing device. This device is used because it produces flatter surfaces on the coatings, providing better contact with pickup heads and less wear of pickup heads. Referring to Fig. 3, the film leaving the drying cabinet passes under idler (A) which is on a pivot. The film passes between two rollers (E) (neither is Thomas R. Dedell: Magnetic Tracks for Processed 16mm Film 495