Plate making process VIII of the most popular PS p

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Plate making process of positive PS plate (VIII)

v. printing plate faults and troubleshooting

due to problems in the process of plate making, the decline of printing plate quality can be found when checking the printing quality, and some can be reflected in printing. Generally, it can be divided into printing plate dirt, poor dot reproducibility, abnormal baking color and poor inking of the plate. All these defects related to plate making quality are collectively referred to as printing plate faults

(I). Printing plate dirt

1. Printing plate dirt caused by improper printing operation. Improper printing operation may cause the printing plate to be dirty. Improper printing operation has the following situations: the printing rack is not clean; There is dust or scratch on the original; The non graphic part of the original has fog; The original has traces of adhesive tape or adhesive paste, as well as insufficient exposure

the way to eliminate this kind of fault is to wipe the glass of the printing frame before printing; Remove the dust on the original and repair the damaged dots on the original; Remove the traces and glue paste left on the original by the adhesive tape, and even return the unqualified original to make it remade. It is difficult to remove the printing plate dirt caused by insufficient exposure. If the dirt is not very serious, the diffuser can be used for supplementary exposure, and the position of the light source should be moved during exposure; You can also increase the concentration of the developer and develop again. However, a thicker alkaline developer will also dissolve the photosensitive layer that has not seen light decomposition, which will reduce the printing resistance of the s version based on P. If the dirt is quite serious, the above remedies can not solve the problem. The fundamental way is to try to avoid underexposure when the printing plate is exposed. For this reason, every time you buy a batch of PS plates, you should conduct exposure tests to accurately find out the exposure amount or exposure time, and make the exposure amount as large as possible without reducing the percentage of the starting point area

2. Printing plate dirt caused by improper development processing. During the development process, the following reasons may cause the printing plate dirty: the temperature of the developer is too low, the development time is too short, the proportion of each component in the developer is inappropriate, and the developer is tired or even invalid; When developing, wipe with inferior sponge or wipe the layout unclearly, and wash it with water incompletely; The automatic developer is out of order, such as poor circulation of developer, unstable temperature, etc

for positive PS plates, the phenomenon of printing plate dirt caused by insufficient exposure and developer failure is the same. In order to distinguish the two causes of printing plate dirt, you can change the developer and develop it. If the development is still insufficient, it means that the cause of printing plate dirt is insufficient exposure; If the development is normal, it means that the cause of printing plate dirt is the failure of the developer

the way to eliminate this kind of fault is to check the temperature and development time of the developer and adjust them to the standard that should be reached; Adjust the developer according to the formula given by the manufacturer and update the developer in time; During development, the layout should be fully cleaned with water, and the layout should be thoroughly wiped with a high-quality sponge; Overhaul the automatic developer, etc. It is preferable to use an enclosed automatic developer with two developing chambers for development. When the exposed PS plate passes through the first developing room, most of the photosensitive layer receiving light and the dye are dissolved. When entering the second developing room, only a small amount of photosensitive layer and pigment are dissolved, which ensures that the color of the developer in the second developing room will not change for a long time, which can not only prolong the service life of the developer, but also facilitate the observation of the developer

3. Printing plate dirt caused by improper dirt removal. In the process of dirt removal, the operation is not careful, and the dirt that should be removed is omitted. The amount of dirt removal liquid is insufficient, the time of using liquid is short, and the dirt removal liquid that has been used for a long time is tired, resulting in incomplete dirt removal; If the dirt removing liquid dries up on the plate after use, it may cause the printing plate to be dirty

the way to eliminate this kind of fault is to remove dirt carefully by dipping a brush into the dirt removal solution; The dirt removal time should be kept at 20 ~ 30s; Cover the dirt remover tightly after use; The layout shall be fully washed with water after dirt removal

4. Dirty layout caused by improper gluing operation. In shangsheng operation, a low concentration of glue is used, oxidation occurs in the non image part, the glue coating is uneven, too thick or striped, and the printing plate is printed with a wet plate, which will cause the printing plate to be dirty

the way to eliminate this kind of fault is to increase the concentration of glue solution, which should not be lower than 5 ° be '; Apply the glue evenly; After the printing plate is glued, the layout is completely dry and then printed on the machine.

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(II). Poor point reproducibility

poor point reproducibility, It is manifested in the phenomenon of "virtual halo" of points (that is, the periphery of points is not smooth, the outline is fuzzy and unclear), points are reduced or lost, and points are expanded. Poor point reproducibility may lead to the decline of image clarity and the change of tone

1. there is virtual halo at the point. The main reason for the virtual halo phenomenon is the failure of the plate printer. For example, the air extraction of the plate printer is insufficient, the vacuum degree is low, or the glass plate and the printing plate cannot be well closed when installing the printing plate. Due to the general trend of paying special attention to the environment and social development in the process of increasing the plate, the scattering effect of air on light will produce the point halo phenomenon

the way to eliminate this kind of fault is to repair the printing machine in time to ensure that the space system is in good working condition, with sufficient air extraction, and the rubber seal of the printing frame is elastic and effectively sealed; When printing, turn on the light source for exposure after confirming that the printing plate is closely attached to the original; When splicing the original, the burr on the edge of the original should be removed, and the adhesive tape should be pasted as far away from the image as possible, or (2) when the cutter cuts, the direction is perpendicular to the fiber axis to form a whole original, so as to ensure that the original fits closely with the printing plate

2. The point is reduced or lost. The main reasons for dot reduction or loss are that the density of the original is too low, the original is thinned too much, the exposure time is too long, the concentration and temperature of the developer are too high, and the development time is too long

the way to eliminate this fault is that the original with image density lower than 1.5 and the original with excessive thinning must be remade; The best exposure time is obtained by trial exposure and used to guide the exposure operation; Adjust the concentration and temperature of the developer, and develop according to the standard development conditions

3. point enlargement. The main reasons for dot expansion are that the concentration and temperature of the developer are too low, the development time is too short, and the developer is aging

the way to eliminate this kind of fault is to adjust the concentration and temperature of the developer, and develop according to the standard development conditions of the specification according to the best exposure time


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