The Physical Properties and Dimensional Behavior of Motion Picture Film

A general discussion is given of the physical properties of both nitrate and safety motion picture film and how these properties are influenced by heat, moisture and other factors. Some of the improvements made in safety base in recent years are described together with some of its present weaknesses. — The manufacture of film base is mentioned briefly and the influence of structure on physical properties is pointed out. The effects of moisture on film are discussed including the relation between equilibrium moisture content and relative humidity, the rate of swell in water, the rate of drying, and the rate of conditioning. The physical changes which occur in the processing and drying of film by continuous machine are described. — The mechanical properties of film, such as tensile strength, elongation, modulus of elasticity, cold flow, folding endurance, and tearing resistance, are discussed and comparisons made between various films. The effect of relative humidity and temperature on the brittleness of film is described, with particular reference to low relative humidities and subzero temperatures. Tackiness is mentioned briefly. — Temporary and permanent film shrinkage of various types is explained, and the factors which affect shrinkage throughout the life of the film are discussed. The shrinkage characteristics of a number of Eastman motion picture films are tabulated. The cause of curl is explained, as well as the changes in curl, which occur during processing and storage. Recommendations are made throughout on the handling and storage of film to obtain the best performance.