In the process of plate-making, copying, photographing, and computer output of the yellowing of the film, or browning, are mainly caused by a sulfur insoluble in the emulsion film--sulfur, in practical work. There are several factors that cause the yellowing of the photo film.
1, the preparation of the developer is not strictly formulated according to the proportion of formula. The alkalinity of the developer is too strong, the developer is easily oxidized and discolored, the developer is used for too long, the effect of the development is significantly reduced, the developer is oxidized to reddish brown, and the performance of the development is also easily weakened or even disappeared. The above films developed by these developing solutions will be colored yellow or brown due to the discoloration of the surface film.
Under normal circumstances, hard lines are used for photocopying, copying, and electrical separation. High-contrast, high-stability developing solutions are all used as a kit, which can continuously wash 8m2 of film. The developer must be used for a long time. Replace new medicine.
2. The fixing solution uses sodium thiosulfate + water + sodium sulfite. The formulation of the fixing solution: sodium thiosulfate: 350 g, sodium sulfite: 8 g, water: 1000 mL.
The purpose of the fixing is to permanently fix the image of the proper density and contrast after development. The function of the fixing solution is to neutralize the alkaline substance of the developer with its acidic substance to stop the development, fix the image and dissolve the non-photosensitive silver halide. Sodium thiosulfate in the fixer is exposed to excessively strong acidic substances, or the temperature is too high, free sulfur will precipitate, and these free sulfurs can react with the silver particles on the film to produce silver sulfide. The color of silver sulfide is brown, so the color of the film is also dyed brown. Therefore, the acidity during the preparation of the fixing solution should not be too strong, and the temperature of the fixing solution should not be too high.
3, inappropriate fixing agent concentration can also cause the film to yellow. Since the fixing speed of the film is fast, it depends on the amount of sodium thiosulfate in the fixing solution, the fixing solution concentration is high, and the fixing speed is fast. If the fixing solution concentration exceeds 45%, the fixing solution is too thick, the film is The unsensitized silver halide has the smallest solubility, but it lowers the solubility, making it counterproductive. Therefore, when the fixing density is not properly grasped, the effectiveness of the fixing solution can be weakened, and the fixing is not deeply penetrated and yellowing occurs.
4, the fixing solution is old and lack of fixing, not completely can make the film yellow. The use of the fixer for a long period of time degrades the performance of the fixer and lacks the effect of fixing, so that the unsensitized silver halide is completely dissolved. These undissolved silver salts, which remain in the emulsion film, can cause the film to appear yellow after washing.
5. After fixing the photosensitive film into the fixing basin, it is necessary to pay attention to the shaking operation method. It is required to shake the developer basin to shake the fixer, or to turn the film upside down, in order to fully dissolve the photosensitivity film completely through the fixing solution. If the sensitive film is not put into the fixing basin, it will not roll or shake. Fixing in a standing state will result in insufficient fixing, and residual sulfides will adhere to the film, yellowing and appearing brown.
6. Yellowing due to insufficient washing after fixing. After the film is fully and thoroughly fixed, it should be put in the flushing tank.