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

no attempt has been made to show the equipment in detail and necessary items such as film drive, take-up mechanism, fan and controls have been omitted. There are many ways in which this length of thread-up and air system could be arranged and this is not presented as the best. It does serve to point out graphically how compact the equipment can be. The cost of the equipment would probably be less than for conventional driers of similar capacity. The power requirements are actually less than for many conventional driers of less capacity. Remarks In contemplating the installation of impingement driers for commercial work there are several factors which should be considered. The first of these is the problem of squeegeeing. In rapid drying the removal of all surface water is essential if water spots are to be avoided. It should also be noted that once the drier is built experiments will have to be made with each film which it is intended to dry, in order to determine the operating conditions which will satisfactorily dry the film at the design film speed. The operator's judgment will not be adequate in this case. The curl level of rapidly dried film, as it emerges from the cabinet, is not the same as it will be after the support and the emulsion have equilibrated. Furthermore, the film may feel dry and warm as it emerges even though insufficiently dry. This film may become tacky after it is rolled up and the base and emulsion have equilibrated. The proper conditions can be found by trial and error or by making moisture analyses of the film dried under different air conditions. Once these conditions are established the acceptable moisture range provides liberal margins of safety with respect to either air temperature or velocity. It is also possible that one such set of conditions will be satisfactory for drying a variety of films. For example, it was found that with a drying time of 12 sec and air at 200 F and 4,000-fpm velocity, Fine Grain Release Positive, as well as both types of Sound Recording film would be dried properly. However, this could not be determined by observation of the film. It is believed that this is the principal disadvantage of this type of drying. The purpose in presenting these data has not been to encourage the use of this type of drying for any and all applications. The experiments do indicate that the method is applicable to a variety of films. It is known, however, that 16mm Kodachrome will become extremely brittle if impingement dried at temperatures higher than 125 F. It is possible that other films will have similar limitations. It is therefore urgently suggested that before designing or installing this type of equipment, the manufacturers of the various types of films which are to be processed in the machine be consulted. Conclusions This survey has shown that many motion picture films can be safely dried with hot impinged air. Drying times ranging from 10 to 30 sec with air temperatures as high as 200 F did not have undesirable effects on the physical properties of the films tested. There is an indication that the film density is affected by the treatment but the amount of change is small. Consideration of several methods which might be used for rapidly drying motion picture film seem to indicate that the most suitable method for commercial application is by means of highvelocity hot air. While the method has been used successfully in experimental tests on a wide variety of films, it would be wise for anyone contemplating the installation of such equipment to determine first its effects on each of the types of film which he intends to use in it. F. Dana Miller: Rapid Film Drying 103