Structure of a Film Material

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  • Topic: Latent image, Cellulose acetate, Silver halide
  • Pages : 6 (1548 words )
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  • Published : March 9, 2013
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FILM STRUCTURE

FILM STRUCTURE
What is motion picture film? The American National Standards Institute (ANSI) describes it as “a thick flexible strip of plastic, complying with a dimensional standard as defined within, whose use is specific to the process of manufacturing a motion picture.” That definition leads to about a dozen pages of further definitions about various aspects of motion picture film. For our purposes, let’s take a look at how film is made, and how an image is formed on that film.

THE STRUCTURE OF FILM
Film is made up of layers, and it’s the combination of these layers that give each film its character. Motion picture film consists of a transparent support film base, a light-sensitive emulsion, and a number of layers coated on both sides. Some layers are di erent from those coated on still film and are designed to help motion picture film travel smoothly through the camera.

Film Base
The supporting layer in film is called the base. This base has to be transparent (with some optical density), free from imperfections, chemically stable, insensitive photographically, and resistant to moisture and processing chemicals, while remaining mechanically strong, resistant to tearing, flexible, and dimensionally stable. Three plastics have been widely used as a motion picture film base: • Cellulose nitrate was the first material used. Discontinued in the 1950s because it was highly flammable, cellulose nitrate is chemically unstable if stored in conditions that are too damp (it can decompose) or too hot (it can self-ignite). • Cellulose acetates were developed to replace nitrate. Cellulose triacetate, called safety base, is much safer to use and store than nitrate. Most current KODAK and EASTMAN Motion Picture Films are coated on a cellulose triacetate base. • Polyester base is used for all print films, most duplicating films, and some specialty films. Polyester is stronger and wears better than triacetate. Polyester’s storage life is up to ten times that of acetate. ESTAR Base, a polyethylene terephthalate polyester, is used for some KODAK and EASTMAN Motion Picture Films (usually intermediate and print films) because of its high strength, chemical stability, toughness, tear resistance, flexibility, and dimensional stability. The greater strength of ESTAR Base permits the manufacture of thinner films that require less storage room. ESTAR Base films and other polyester base films cannot be successfully spliced with readily available commercial film cements.

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FILM STRUCTURE

These films are spliced with a tape splicer or with a splicer that uses an ultrasonic or an inductive heating current to melt and fuse the film ends.

Emulsion
The most fundamental layer in a film is the emulsion layer(s), adhered to the base by means of a binder. The emulsion is the photographic part of the film, and as noted from ANSI, “consists of dispersions of light-sensitive materials in a colloidal medium, usually gelatin, carried as a thin layer(s) on a film base.” Emulsion is made by dissolving silver bullion in nitric acid to form silver-nitrate crystals. These crystals are dissolved and mixed with other chemicals to form silver-halide grains, and then suspended in the gelatin emulsion coating. The size and degree of light sensitivity of these grains determines the speed or amount of light required to register an image. The faster the film, the greater the apparent “graininess” of the image. In 1991, The Motion Picture and Television Imaging division of Eastman Kodak Company received an OSCAR from the Academy of Motion Picture Arts and Sciences for incorporating KODAK T-GRAIN® Emulsion Technology into motion picture films. This term, now familiar among all types of film, describes flat silver crystals that capture more light without an increase in size. In color films, three dye layers register various parts of the color, one on top of another, for the full color e ect—in cyan, magenta, and yellow dyes. In fact, each color may have up to three layers...
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