Huida PS plate

How to determine the exposure time of the PS Plate?

The exposure time of the PS version mainly depends on the photosensitive range of the PS version. Sensitivity and spectral characteristics of the light source, the strength of the light source and other factors. Therefore, every time you change the PS version of a different brand or change the light source, you need to use the measurement and control strip to conduct a series of tests on the PS version to determine the correct exposure time.

How to adjust the exposure time of PS version according to specific conditions?

1、There are no dots, only thicker text. The original version of lines and solids can increase the exposure time, remove the small dirty spots and stains, and reduce the time for cleaning.

2、The negative is stored for a long time, the blank part turns yellow, or after manual imposition, there are two or three layers of blank film bases superimposed together, which can slightly increase the exposure time; the original plate with low density in the solid part can reduce the exposure time.

3、The pressure of the proofing machine is lower than that of the printing machine, so the increase of the proofing dots is smaller than the increase of the printing dots, so the exposure time of the proofing plate should be less than the exposure time of the printing plate. For the proofing version, 0.5% of the outlets are generally removed, and 1% of the outlets are retained.

Strictly speaking, for the color separation plate making of layered drafts, when determining the tone reproduction curve, the difference in dot gain under various circumstances should be considered and compensated. In fact, the standardization of this process in China is not very good, so it is necessary to adjust the exposure time according to the production conditions of the respective printing plants. If the dot increase rate is large during the printing process of our factory, the exposure time can be increased. Depending on the substrate to be printed, when printing the printing plate of offset paper, the exposure time should be longer than that of printing the printing plate of coated paper.

Why do you need to pump air when printing and exposing?

Taking the production of the positive pattern PS plate as an example, when printing the plate, if the film surface of the negative film is not in close contact with the photosensitive coating of the PS plate. If there is a gap in the middle, there will be light from the edge of the blank part of the negative film obliquely to the picture and text. Part of the photosensitive coating directly below causes the edge of the graphic part to be decomposed by light, making the image blurred. The dots become smaller, and the small dots and thin lines are lost.

Because one side of the printing frame is transparent glass, and the other side is a rubber pad. When the vacuum pump draws out the air in the printing frame, the air pressure inside is low, and the rubber pad will release the PS plate under the action of the external atmospheric pressure. The original negatives face the glass and are tightly bonded together.