The production process of photosensitive emulsion directly affects its sensitivity

The production process of photosensitive emulsion directly affects its properties such as sensitivity, contrast and resolution. Its raw material specifications and reaction conditions (temperature and time, etc.) must be strictly controlled, and any slight changes will lead to changes in the performance of the photosensitive emulsion. In the production process of photosensitive emulsion, in addition to dosing, from the beginning of emulsification to the end of preparation, it must be carried out under a safe light in a dark room. The brightness of security lights (usually red) must also be tightly controlled. The robot operation is realized, and the whole process can be carried out in complete darkness.

The production of photosensitive emulsion is divided into four stages:

① Compounding The various raw materials used in the preparation of photosensitive emulsions need to be prepared into solutions of a certain concentration first.

② Emulsification and physical maturity Add gelatin solution to the emulsification reactor first, then add silver nitrate solution and alkali metal halide solution at a specified speed, taking silver bromide emulsion as an example, the following reaction occurs:

The silver bromide produced by the reaction of AgNO3+KBr─→AgBr+KNO3 is uniformly dispersed in the gelatin solution with tiny crystals. This process is called the emulsification process. The potassium bromide solution is first added into the kettle, and then the silver nitrate solution is injected, which is called the single-injection emulsification process; the process of injecting the silver nitrate solution and the potassium bromide solution into the reaction kettle at the same time is called the double-injection emulsification process. The silver halide crystallites generated in the emulsification process of the photosensitive emulsion are too small, and it is necessary to continue stirring at a certain temperature to dissolve part of the crystallites. The supersaturated state of silver halide in the medium is used to make the crystallites continue to grow and reach a certain level. size. This process is known as the physical maturation process.

③ Sedimentation and water washing The photosensitive emulsion is coagulated and sedimented by a macromolecule precipitation agent, and then washed with water to remove water-soluble salts. Washed with frozen cut strips.

④ After the chemically mature photosensitive emulsion is washed with water, it needs to react with a small amount of chemical sensitizer at a certain temperature for a certain period of time, so that a very small photosensitive center is generated on the surface of the silver halide crystallite, so that the sensitivity can be greatly improved. improve. This process is called chemical maturation. Commonly used chemical sensitizers include sulfur-containing compounds and precious metal salts. The chemically matured photosensitive emulsion is condensed and stored in a cold storage, heated and melted when necessary, and some photosensitive emulsion additives are added, and then the photosensitive material can be obtained by coating.