What Is a Photoreceptor?

The phenomenon that a substance undergoes a chemical change by the action of light. Often refers to photographic film and other changes caused by light.

The process by which photographic materials are illuminated by light. The photosensitivity process of ordinary silver halide emulsions is basically: upon exposure, the silver halide particles absorb photons, generate photoelectrons, and the photoelectrons are trapped by the photonucleus to form a negatively charged core; the positively charged free silver ions are attracted to the photonuclei by negative electricity And is neutralized by electrons, thereby reducing to silver atoms. The accumulation of silver atoms (usually tens or hundreds) constitutes a latent image nucleus. The photosensitivity of silver-free photosensitive materials and electrophotography and thermography are different, and basically, they can develop latent images with the aid of the photochemical or photoelectric effects of photosensitive materials. ^[1]

The photosensitive element is equivalent to the film of a film camera and is used to receive the light signal from the lens and convert it into an electrical signal j. Therefore, the photosensitive element determines the final imaging quality of the photograph after shooting. The size of a photosensitive element, the number of pixels in a unit area, and its sensitivity to light are the three major indicators for judging the performance of a photosensitive element. CMOS is a widely used photosensitive element material. ^[3]

Photographic imaging uses the sensitivity of silver halide to light. The silver halide is prepared by mixing a soluble silver salt such as a nitrate with an alkali metal halide such as sodium halide or potassium bromide. ^[4]

At present, plate making of photosensitive emulsion is still the main method of plate making. Photosensitive adhesive is an important consumable material in the plate-making process. The selection of the photosensitive adhesive has an important influence on the quality of the plate making, printing effect and printing products. The photoresist used as a flat screen and a round screen should have the following requirements: good water dispersibility, easy development, and economical safety; the film-forming film layer should have high adhesion to the mesh and netting, and have Certain mechanical strength so as not to be separated from the mesh blank; the photosensitive adhesive should be resistant to acid, alkali and chemicals. With the advent of inkjet and wax spray platemaking technology, it is also required that the photoresist has good compatibility and washability with inkjet and wax spray materials; the photoresist requires a higher resolution, so that the printing effect is fine, Clearly, the main composition of the photosensitive adhesive is a film-forming agent, a photosensitizer (photosensitizer) and an auxiliary agent. The photosensitizer initiates and participates in the cross-linking reaction of film-forming macromolecules under the illumination of a specific light source, causing the film-forming agent to form a network structure and lose its solubility, and is firmly combined with the mesh and the mesh blank.

The film-forming agents of the early photosensitive resin for flat screens were mainly water-soluble natural polymer materials such as gelatin and polyvinyl alcohol. Although some improvements have been made to this type of material, and the print resistance has been improved to some extent, in general, the resistance of this type of material is poor. In the printing production process, the flower film of the photosensitive rubber layer cannot bear the erosion of acid, alkali and chemical agents in the printing paste and the scraping of the printing scraper by the printing blade 10 million times. Therefore, reinforcement treatment is generally required. That is, after the photosensitive development is dried, it is reinforced by the method of post-coating, or the screen is pre-washed and coated with vinyl chloride before the photosensitivity. The standby pre-painting method is used for reinforcement. After development and drying, the paint is no longer applied, but butyl acetate should be used to make clear patterned meshes. The photosensitizer used in the above-mentioned film-forming agent is dichromate. Reinforcing agents are raw lacquer and perchloroethylene. ^[5]