As an offset printing platemaker, you will encounter various abnormal situations from time to time. Depending on the situation, you need to take different measures.
1. The original density is not enough
It is common for sulfuric acid paper to have insufficient density, especially large prints and solid plots. Generally apply first with a densifier (blackening agent) (note that the amount of the densifier should not be too much), apply it a second time in the same place after drying, and only dry it before printing. But sometimes only the density of the densifier is not enough. At this time, there are two treatment methods.
(1) Apply ink or cover with black paper
Applying ink is suitable for large characters and more complicated patterns, and covering with black paper is suitable for solid strips. You can also combine the two methods, that is, first paint the edges and narrower areas with ink, and then cover the remaining large areas with black paper. Do not use too much ink, otherwise the sulfuric acid paper will wrinkle and affect the quality of printing.
(2) Repeated copy method
The original copy of film with sufficient density can be obtained by repeated copying. First use less exposure time and development time (usually 50% to 70% of normal time) to copy to get a negative picture, scrape the silver particles in the negative part of the negative picture due to insufficient density, and then remove the negative picture The picture takes more time (generally 120% to 150% of normal time) to be copied for the second time. At this time, a film with sufficient density is generally obtained. If it is still not enough, just copy it again.
Second, the film has fog
The fog on the film can be handled by increasing the exposure time or development time, increasing the concentration of the developer, etc., but the quality of the graphics must be guaranteed. If you can not guarantee the quality of the text or the fog is too heavy, you have to remake the film.
3. Uneven thickness of text strokes
This situation is common in sulfuric acid paper, which is caused by the failure of the laser printer or the poor quality of the sulfuric acid paper itself. It is also possible to use the method of applying the densifier to improve the gap between the thickest strokes and the thinnest strokes, but the unevenness of thickness cannot be completely eliminated. At this time, you should repair the printer or replace the sulfuric acid paper and reissue the sulfuric acid paper.
Fourth, the geometric deformation or size of the center of the plate varies
Geometric distortion is often caused by improper adjustment of the printer, but it also happens by accident. The deformation often occurs on sulfuric acid paper, mostly parallelogram deformation, that is, the rows and columns of the plate center are not vertical. When the deformation or size difference is serious, the sulfuric acid paper can only be re-released. If it is not serious, the sulfuric acid paper can not be reissued with the consent of the customer. The top and bottom pages are used as the basis for imposition. Because the center of the plate is on the side of the cut, the inaccuracy of line overprinting is not very serious, but if it is based on the behavior, the phenomenon of inaccuracy of printing is very serious, and when the side of the cut of the plate is the benchmark, the spine Misaligned sides are not easy to spot.
Fifth, the sulfuric acid paper itself is deformed
Sulphuric acid paper deformation is very common. It is shown that unstitched sulfuric acid paper has a lotus leaf edge, which has become longer and affects inhalation. If the length is not serious, you can adjust the vacuum of the plate-making machine appropriately, and it can still suck flat; but if the length is very serious and affects the suction, you can blow it evenly with an electric blower, and the sulfuric acid paper shrinks and you can suck it. If it is flat, it is impossible, so I have to re-export and imposition.
Sixth, the graphic content needs to be changed
Changes to the original version are more common, sometimes because of errors and need to be corrected; sometimes because of customer requirements to change and need to be corrected.
Sulfuric acid paper or film need not be changed to change the original version. You do not need to re-exit in the following situations.
â‘ Change the non-mesh tone graphics;
â‘¡ Manual correction is easier and takes less time;
â‘¢ Hidden dangers left after manual correction, such as film edge marks, transparent plastic edge marks, etc., can be easily eliminated;
â‘£The quality will not be affected after manual correction.
The sulfuric acid paper or film used for correction should be as far away from the existing graphics as possible, otherwise the graphics will shrink or become false.
7. Abnormal photosensitive film
The abnormality of the photosensitive film is more common in the regenerated PS version, such as scratches, uneven thickness, foreign matter, and peeling (with white spots). , Change the other side to do the mouth, change another PS version to re-burn and so on.
8. Abnormal Edition
The abnormality of the plate base is also more common in the regenerated PS version, such as creases, bumps, etc. If the situation is not serious, you can roll the PS version a little toward the convex side, use your hands, fingers or other round and soft objects to press the convex side to the concave side properly until it is relatively flat. If the situation is more serious, you can also use the avoidance method to deal with it. Holes or cracks in the edge of the plate are also anomalies of the plate base.
The plate with holes must not be used, because the fountain solution will enter the liner and cause corrosion to the plate cylinder. When the edge of the plate is broken, the cracked area should be cut off. It is better to cut the edge of the plate to show an arc or obtuse angle.
9. Abnormality after printing
Plate making is a job that requires patience and care. Even if you have been very careful, there is still the possibility that you will find anomalies after printing.
1. There is residual drug film in the blank space after development
Most of the residual drug film is caused by insufficient exposure or insufficient development, which can cause staining and seriously affect the quality of the print. If the quality requirements are not high and the residual drug film is very thin, the residual drug film can be removed by forced development. But if the quality requirements are very high, you can only reprint after finding the cause of the abnormality and adjusting it properly. If the quality requirements are not high and the residual drug film appears at the non-dots, it can be treated by the re-exposure method. The specific method is described below.
2. Graphic loss
The loss of the pictures and texts in the printing version is inevitable, but when the loss exceeds the allowable range, the relevant personnel must obtain the consent of the relevant personnel before they can not be re-exposed, otherwise they can only be re-exposed.
3. Dirty marks on the text
Dirty marks on the picture and text are caused by foreign objects, such as opaque objects (paper scraps, black film, etc.) or transparent colloids. The former is dirty due to blocking light and is not exposed to light. The latter is exposed but the colloid blocks the developer. Dirty marks caused by undeveloped. If the quality requirements are high, they can only be re-dried; if the quality requirements are not high, some treatments can be performed to avoid waste.
For the former, the treatment methods for several situations are as follows:
â‘ When the dirt is large and appears on the outlet, it can only be re-dried.
â‘¡ Dirty marks are large, and appear on non-mesh-tone lines, text, and bars, and can be exposed again to remove the dirty marks.
Specific method: develop the PS version, dry it with a hair dryer, align the graphics near the original dirty marks under the magnifying glass with the same graphics on the PS version, and use the tape to firmly adhere the original version to the PS version. After registration, use black paper to cover up the images other than the dirty marks, and then perform double exposure.
After the exposure is completed, dip a small amount of developer with cotton, and wipe the stains repeatedly until the stains are removed. Note that the full version cannot be developed after the second exposure, so as not to affect the quality due to excessive development.
â‘¢If the stain is small, use a needle tip, sharpened wooden stick and brush to dip a little revision paste, place it on the stain accurately, and immediately rinse with water. Once is not thorough, then repair the second time.
For the latter, blow the plate dry and wipe it with cotton dipped in a little gasoline. The adhesive can be completely wiped off. After the gasoline has evaporated, use another group of cotton dipped in a little developer to wipe the stains until the stains are removed. Except clean.
Ten, the position of the picture and text on the PS version is improper
The improper position of the picture and text on the PS version is mainly caused by inadequate operation, which is manifested as the mouth is too long or too short, the side rule is too long or too short, and the ends of the mouth are inconsistent. If the improper position is not serious and the machine can adapt, no treatment is required; if the mouth is too long, the ends of the mouth are inconsistent or the side rules are too long, the PS version can be cut without affecting the use of the machine Method treatment; if the side gauge is too short and the positioning hole is punched, the positioning hole should be re-punched. Once it affects the use of the machine, it should be re-dried; if the mouth is too short, it can only be re-dried.
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