Structure of a Film Material
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.
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.