Causes and solutions of yellowing of the hottest f

Reasons and solutions for film yellowing

in the process of plate making, the film copied, photographed and output by the computer turns yellow or turns brown. The main reason is that there is a kind of sulfide sulfur insoluble in water in the photosensitive emulsion film. The reasons for the yellowing of photosensitive film in actual work are as follows

1. The developer was not prepared strictly according to the proportion of the formula. The alkaline of the developer is too strong, and the developer is very easy to oxidize and change color. If the developer is used for too long, the development effect will be significantly reduced. Because the value of the lower yield point of the developer is relatively stable, the developer will oxidize to reddish brown, and the development efficiency is also very easy to weaken or even disappear. Therefore, the film developed by these developers will be dyed yellow or brown due to the color change of the surface film

generally, hard line films are used in photography, copying and electronic separation. High contrast and high stability developer can realize automatic folding and printable expanded polymer materials. All of them use a bag of medicine, which can continuously develop 8m2 film. If the developer is used for a long time, it should be replaced with a new drug in time

2. The fixing solution adopts sodium thiosulfate + water + sodium sulfite. The formula of fixing solution: sodium thiosulfate: 350g, sodium sulfite: 8g, water: 1000ml

the purpose of fixing is to permanently fix the image with appropriate density and contrast after development. The function of the fixing solution is to neutralize the alkaline substance of the developing solution with its acidic substance, so as to stop the development, fix the image and dissolve the non photosensitive silver halide. The sodium thiosulfate in the fixing solution will precipitate free sulfur under the influence of too strong acidic substances or too high temperature from the selection of materials. These free sulfur can react with the silver particles on the negative to produce silver sulfide. The color of silver sulfide is brown, so the color of the film will be dyed brown. Therefore, the acidity should not be too strong when preparing the fixing solution, and the temperature of the fixing solution should not be too high

3. Improper concentration of the fixing solution can also cause the film to turn yellow. Because the speed of film fixing is related to the amount of sodium thiosulfate added in the fixing solution. If the concentration of the fixing solution is higher than 45%, the fixing speed will be faster. If the concentration of the fixing solution is more than 45%, and the fixing solution is too thick, the solubility of silver halide that is not photosensitive in the film will be the smallest, but the solubility will be reduced, making it counterproductive. Therefore, if the fixing concentration is not properly controlled, the effectiveness of the fixing solution can be weakened, At the same time, the fixing is not deep and yellowing occurs

4. The film can turn yellow if the fixing solution is old and insufficient. After using the fixing solution for a long time, the performance of fixing decreases and lacks the effect of fixing, so that the non photosensitive silver halide is completely dissolved. These undissolved silver salts, remaining in the emulsion film, will cause the film to appear yellow after development

5. When fixing, after the photographic film is put into the fixing basin, be sure to pay attention to the shaking operation method. It is required to shake the developing basin to shake the fixing solution, or turn the film up and down, in order to fully fix the photosensitive film and completely dissolve the non photosensitive silver halide in the fixing solution. If the photosensitive film is placed in the fixing basin without turning and shaking, and is fixed in a static state, insufficient fixing will occur, and the residual sulfide will adhere to the film, yellowing and brown

6. Yellowing caused by insufficient water washing after fusing is the system part that controls the operation of the experimental machine. After the film is completely fixed, it should be put into the developing tank