Paste and reason in printing
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In the printing process, we often encounter the phenomenon of paste, the paste is the darkening of the layout of the screen to expand the deformation, merge with each other, so that the level of the dark tone is gone, forming a blurred imprint on the printed product, a serious formation The main reasons for the dirty spots and the resulting paste are the following.
First, the amount of ink supply is too large and the printing adaptability of the ink is not strong
1 The amount of ink supply is too large, causing the ink layer accumulated on the layout to be too thick. Under the action of printing pressure, the image and dot dots are spread, and the lines are thick and without corners, thereby causing paste.
2 The ink is too thin and has a large fluidity, causing the dot spread to cause a paste.
3 Excessive dry oil in the ink will make the ink emulsification worse, so that the ink layer on the printing plate can not be broken from the middle, and most of the ink remains on the printing plate, causing the ink to be piled up. Under the action of the pressing force of the roller, the dot is gradually enlarged. The paste is caused by an excessive amount of desiccant to enhance the viscosity of the ink, and the adhesion to the blank portion is enhanced, so that the dark portion of the printed matter is easily caused to cause a paste.
4 In daily work, we use varnish or excessive de-adhesive agent, which will increase the oiliness of the ink. During the printing process, the boundary between the screen dots will be blurred and cause a paste.
Solution:
According to the graphic elements of the printed product, properly control the amount of ink supply, control the amount of dry oil, varnish and de-adhesive. When using oil with strong oil, increase the acidity of the dampening solution.
Second, the paste caused by insufficient water supply
Because the pressure between the water roller and the plate cylinder is too small; the surface of the water roller is dirty; the water roller is used for a long time and the fluff loses its elasticity; when printing, the corresponding water roller sleeve wears on the printing plate. Relatively serious, the water absorption is also relatively poor, and the water supply is insufficient due to some reasons. The loss of ink and water balance during the printing process leads to the paste.
Solution:
1 According to the workload and the degree of use of the water roller, replace the water roller cover in a timely manner.
2 Put the dampening liquid on the bottle filled with the bottle cap, and spray the water properly in the place where the water roller is worn seriously. This can reduce the number of times of replacing the water roll cover and reduce the paste. This method is soiled. Point, but very practical.
Third, the blanket is too loose or the printing pressure is too large
The blanket is too loose, resulting in a large pile deformation during the printing process, which easily causes a paste. Excessive printing pressure not only aggravated the wear of the printing plate, but also directly increased the spread of the graphic ink layer, resulting in paste.
Solution:
When changing the blanket, it should be tight and the pressure of the cylinder should be adjusted before printing, so that the paste can be reduced.
Fourth, the printing plate is seriously caused by the paste
The area of the graphic part of the dark oil on the printing plate is much larger than the area of the hydrophilic blank part. Once the blank part of the blank is worn, the hydrophilicity is weakened, and it is easy to be spread by the surrounding ink, resulting in a paste. phenomenon.
Solution:
1 Adjust the pressure between the rollers to avoid excessive pressure and cause the printing plate to wear.
2 Do not collide and rub the plates during shipping and plating.
Fifth. The paste caused by the weakening of the wetting fluid
Alkaline paper and paper powder falling off during the printing process will be transferred to the water bucket, neutralizing the acidic dampening solution, so that the acidity of the dampening solution is weakened, and the phosphoric acid or citric acid in the dampening solution is on the oil surface. It has a cleaning effect, the acidity of the dampening solution is too weak, and the cleaning ability for the oil on the plate is insufficient, and it is easy to paste when printing the oil with a heavy oiliness.
Solution:
1 Periodically change the water in the bucket.
2 If the paper for printing is conditional, it is best to blow it with a paper machine. This can blow off the impurities, paper, and paper powder in the paper, and make the water content of the paper uniform and uniform. The water content of the paper is balanced with the temperature and humidity of the printing workshop, so that the hysteresis of the paper occurs before printing, that is, the sensitivity of the paper to water is reduced, so that the paper adapts to the temperature and humidity of the printing workshop before printing, so that the entire printing process can be Done successfully.