Motion Picture News (Sep-Oct 1922)

1792 Motion Picture News Difference Between Inflammable and Non-Inflammable Film Essential Characteristics and Materials Used in Manufacture of Two T y pcs THE Department of Commerce, Bureau of Standards. Washington, D. C., has made an investigation with reference to the safety and recommendable practices for motion picture projection. One division of the report takes up the subject of film, both the inflammable and non-inflammable stock as follows : “ As it developed from these examinations that the principal hazard is inherent in the film itself, a brief statement of the characteristics of motion picture film will be given. Preparation of Raw Film “ In the manufacture of motion picture films, it is customary to distinguish between the raw film, and the same film after it has been coated with a photographic emulsion. For present purposes we shall consider briefly the preparation of the raw film. It is a flexible, waterresistant transparent material prepared from cellulose nitrate, commonly called nitrocellulose, or from cellulose acetate. Films are prepared by pouring a solution of the film material upon a moving belt or revolving drum, and allowing the solvents to evaporate. It is customary to recover the solvents used. The steps involved consist of the preparation of a suitable solution, filtering and removing air bubbles from the solution, formation of the film, removal from the belt, and the drying of the film. The common type of motion picture film is made from cellulose nitrate, an inflammable material prepared by treating cotton or cellulose with a mixture of concentrated nitric and sulphuric acids. The product must be thoroughly washed and stabilized, and is subsequently dissolved with the addition of camphor in suitable solvents and diluents. The solvents commonly used are amyl acetate or “ banana oil,” ethyl acetate, and acetone ; the diluents are generally benzene (benzol), and denatured alcohol. The film obtained consists of an intimate mixture of cellulose nitrate and camphor, and is essentially celluloid. Substitutes for camphor have been proposed from time to time, and a few of these are occasionally used. Camphor however, appears to produce maximum strength, transparency, and elasticity. The prepared film must be carefully dried and seasoned, before it is ready to be coated with a photographic emulsion. The second type of motion picture film is the so-called non-inflammable film. It is prepared by treating cotton with acetic anhydride in the presence of a catalyst such as sulphuric acid, zinc chloride, or sulphuryl chloride, and the product is Prediction for Future ''p' HIS rticle on inflammable and non1 inflammable motion picture film is presented as it brings forth the various materials used in the manufacture of these two types of film and also the variations in their essential characteristics. As there is caused a great amount of discussion concerning the advantages and disadvantagse of these two general types of film, there should be an interest in their qualifications. It may be predicted with a fair degree of certainty that in the relatively near future a much larger percentage of non-inflammable film will come into use. In case the cost of the manufacture of non-inflammable film is reduced to that of the inflammable stock and its few other limitations are overcome, then in all probability a general adoption of noninflammable film will be made throughout the motion picture industry. Such a course would be exceedingly welcome. known as cellulose acetate. The temperature must be carefully controlled, as slight variations in temperature during acetylation give rise to brittle films and products of low viscosity, particularly when sulphuric acid is used to catalyze the reaction. The product of acetylation is soluble in chloroform and as a rule insoluble in acetone. It must be carefully hydrolyzed to a hydroacetate which is insoluble in chloroform, but soluble in acetone. Brittleness of Non-Inflamable “ Cellulose acetate (non-inflammable) is inherently more brittle than cellulose nitrate (inflammable film), and the brittleness is overcome by incorporating in the film so-called plastics. These have a function analogous to that of camphot in the inflammable films. Cellulose acetate may be combined with a great number of plastics, with the production of varying degrees of hardness and elasticity. Camphor is not suitable for the purpose. Triphenyl phosphate is commonly used. It possesses Exterior view of Sweden’s most beautiful theatre, the Palladium the advantage of reducing the combustibility of the acetate film. Other useful plastics are calol, benzyl benzoate, benzyl acetate, diethyl phthalate, and triacetin. These are but a few among many which have been proposed. The most important solvents of cellulose acetate consist of tetrachlorethane, generally used in combination with alcohol, ethyl lactate, di-acetone alcohol, methyl ethyl keytone, acetone, methyl acetate and ethyl acetate. The ordinary (inflammable) type of film is that prepared from cellulose nitrate. It contains oxygen, the element of its potential destruction, in a highly available form. The readiness with which it burns is too well known to require comment. The gases resulting from combustion of celluloid consist chiefly of oxides of carbon and nitrogen, methane, hydrogen and nitrogen, together with volatilized camphor, which under certain conditions may form an explosive mixture with air. Films prepared from cellulose acetate (non-inflammable) do not contain available oxygen. They are combustible but not inflammable. When subjected to temperatures higher than 150° C., (302 F.) cellulose acetate melts and is decomposed. The gelatin emulsion used on all films has some fire-proofing action. However, the amount of this used is insufficient to produce any marked effect. For all practical purposes, films of cellulose acetate containing triphenyl phosphate may be considered safe as used in motion picture projectors. A film of such material (noninflammable), if ignited while being used, will cease to burn as soon as the source of heat is removed. It is claimed that such films become brittle more readily and have proven less durable than films of cellulose nitrate. Acetate films are said to possess or develop a “ grained ” surface. These defects may have been caused by faulty methods of manufacture. Advancement Expected The manufacture of cellulose acetate plastics is a more recent development than the manufacture of cellulose nitrate or pyroxylin plastics. Cellulose acetate admits of a variety of combinations with other compounds. As new combinations become known, it may be expected that films will be developed which present none of the disadvantages of present-day acetate films, assuming that such disadvantages exist. Future developments should make possible a non-inflammable film with qualities equal to those of the nitrate film, and the product should practicallv compete with the nitrate film in price.