Offset printing plate abnormal phenomenon and treatment (2)

Abnormal film

Abnormal situation of photosensitive film is more common in regenerated PS plate, if there are scratches, uneven thickness, foreign matter, stripping (white spots), etc., the treatment of this situation is generally handled by evasive method, that is, a small amount of deviation from top to bottom , For the other side to do mouthwash, for another PS version of re-lighting and so on.

Edition base exception

The situation of abnormalities in plate base is also more common in regenerated PS plates, such as creases and pits. If the situation is not serious, you can roll the PS plate a little to the convex side. Use hand-drawn, finger or other round and soft objects, and press the convex side to the concave side until it is relatively flat. If the situation is more serious, it can be dealt with by the avoidance method, and it cannot be exchanged. The presence of holes or cracks on the edge of the plate is also an indication of an abnormality in the plate base.

Hole-printed plates must not be used because the fountain solution will enter the lining and cause corrosion of the plate cylinder. When the edge of the plate is broken, the cracked area should be cut off. It is better to cut off the edge of the rear plate to show the arc or obtuse angle.

Abnormal after printing

Plate making is a job that requires patience and carefulness. Even if it is already very careful, there is still the possibility that abnormalities will be discovered after the printing.

1. After the development there is a residual film on the blank

Most of the residual film is caused by insufficient exposure or insufficient development, which can cause viscera and severely affect the quality of printed products. If the quality requirements are not high and the residual film is thin, the residual film can be removed by forced development. However, if the quality requirements are high, you can only re-smoke after finding out the cause of the abnormality and adjusting it properly. If the quality requirements are not high and residual film is present at non-web sites, re-exposure can be used. The specific methods are described below.

2. Graphic loss

It is unavoidable that the picture and text in the print copy will be lost. However, if the loss exceeds the allowable range, the consent of the relevant person must be obtained.

Can not re-sun, or only re-sun.

3. There are dirty marks on the picture

Debris marks are caused by foreign objects, such as opaque objects (confetti, black film, etc.) or transparent colloids. The former cause un-exposed and dirty marks due to light blocking. The latter exposes but the colloids block the developer. Causes no development and marks. If the quality requirements are high, only re-lighting can be performed; if the quality requirements are not high, some treatments can be performed to avoid wastage.

For the former, the methods for dealing with several situations are as follows:

1 When the dirty marks are large and appear on the dots, they can only be re-lighted.

2 If the dirty marks are large and appear on non-mesh lines, text, or bar, you can perform another exposure to remove the dirty marks.

Specific methods: the PS version of the development, drying with a hair dryer, under the magnifying glass will be the original near the dirty marks on the PS text on the same graphics, the original version of the tape firmly stuck to the PS plate, the inspection does After the registration has been made, black and white paper is used to mask the images other than the dirty marks for double exposure. After the exposure is completed, a small amount of developer is picked up with cotton, and the dirty mark is repeatedly applied until the dirty mark is removed. Note that after the second exposure, the full-size development cannot be performed so as to avoid affecting the quality due to excessive development.

3 If the dirty mark is small, use a pointed tip, a sharpened wooden stick, a writing brush, etc. to pick up a few correction pastes, accurately located on the dirty marks, and rinse immediately with water. Once incomplete, repair it a second time.

For the latter, after drying the plate with cotton and rubbing a little petrol, the viscose can be completely wiped off. After the gasoline is volatilized clean, apply another piece of cotton to a small amount of developer to scratch the mark until it becomes dirty. Shown until clean.

Graphically inappropriate position on the PS version

Graphic and text on the PS version of the improper position is mostly due to the operation is not carefully caused by the performance of the mouth is too long or too short, the side gauge is too long or too short, the mouth is not uniform at both ends. If the improper position is not serious, the machine can adapt, and can not do the processing; if the gargle is too long, the ends of the gargle are inconsistent, or the side gauge is too long, the PS version can be cut without affecting the use of the upper computer. Methods to deal with; If the side gauge is too short and hit a positioning hole, should be re-positioning holes, once the impact on the use of the machine should be re-sun; if the fistula is too short, can only re-sun.

Source: Printing Technology