What is the chemical composition of the film?

1。 Cinematographic film: A general term for photosensitive materials used for making films. 2。 The general term for movies is synonymous with "movies" and "cinemas".

Cinematographic film is a photosensitive material coated with emulsion on a transparent flexible film base, including negative film for cinematography, positive film for printing and reproduction, intermediate film for reproduction and vocal cords for recording. These films are basically the same in structure, and they are composed of two parts: photosensitive silver halide gelatin emulsion layer and supporting film base layer.

At the beginning of the film, the film base is nitrocellulose ester, which is similar to gunpowder cotton and easy to burn. 1923 acetic acid safety tablet base was successfully studied, and then gradually replaced nitric acid tablet base. Acetic acid tablet base has been improved many times in composition, among which triacetic acid tablet base has better performance. After 1950s, the production of nitric acid tablet base stopped completely.

The main component of emulsion is silver halide suspended in gelatin. Because gelatin can not only suspend silver halide without precipitation, but also contain sensitizing substances, it can increase the sensitivity of emulsion to light and make the film have higher sensitivity to meet the requirements of film formation. Silver halide itself is only sensitive to blue-violet light with a wavelength of 400~500 nm, and the brightness of the photographed image is different from that of various colors seen by human eyes, so it is called color-blind film. 1873, German H.W. vogel discovered that dyes can expand the photosensitive range of silver halide, so he made a positive film that can perceive both blue-violet light and green light. After 1906, various cyanine dyes appeared one after another, which made the photosensitive range of film develop to a long wavelength and developed a full-color film sensitive to visible light. In addition, with the development of photosensitive range to infrared region, infrared film was born. Infrared film is mainly used for aerial photography, special effects and special photography. Black-and-white films used for shooting are generally full color, while those used for printing black-and-white film copies are generally color blind.

Although full-color photography can make the layering of various colors clear and bring a lot of convenience to artistic creation, the tone of black-and-white movies can only be gray with different shades, which is far from meeting people's requirements of expressing colorful nature. Therefore, many physicists, chemists and photographers have studied color photography methods.

There are hundreds of color photography methods in the history of photography, but they can be divided into the following two categories in principle: one is to add the three primary colors of red, green and blue in different proportions to obtain various colors or even white, so it is called additive method. The other is to subtract different proportions of red, green and blue from white light to get different shades of color, even black, so it is called subtractive method. They are all based on the visual trichromatic theory put forward by J.C. Maxwell in 186 1. According to this theory, human visual organs are only sensitive to three primary colors: red, green and blue. When the red and green sensitive units are stimulated at the same time, the yellow feeling is produced; When blue and green are stimulated at the same time, it will produce the feeling of cyan; When red and blue are stimulated at the same time, it will produce a magenta feeling. Therefore, red, green and blue are called three primary colors, while yellow, magenta and cyan are complementary colors of blue, green and red, which are called three primary colors, also known as subtractive three primary colors.

Color film is made of subtractive color film. The earliest successful subtractive film is the spot color from 1927. Because the replica is made of dye transfer printing, it is also called dye printing. The inventor is Dr. H.T. Calmus. According to this method, three negatives are shot with a complicated beam-splitting camera, and exposed with red, green and blue light at the same time, and then three relief modules are printed from these negatives, dyed with cyan, magenta and Huang San complementary dyes respectively, and then superimposed on a blank, which becomes a color copy for projection (see dyeing printing method).

In 1980s, the color film widely used in the world was reduced to multilayer film. This kind of film will be coated with three layers of emulsion that can sense the three primary colors of red, green and blue respectively on the same film base, and then a color image can be obtained after photographic exposure and development (see coaxial multi-layer color film).

The structure of film consists of two main parts: film base and emulsion. In addition, a protective layer is coated on the surface of the emulsion layer to prevent damage caused by external force, a bottom layer is coated between the emulsion and the substrate to promote adhesion between them, and a back layer is coated on the back to prevent halo, static electricity and curl.

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