In the printing process, we often encounter the phenomenon of stencil. The stencil refers to the darkening of the layout of the dark spots, and they merge with each other, so that the level of dark tone disappears, and a fuzzy mark is formed on the printed matter. Severe formation occurs. Dirty spots, resulting paste version of the main reasons are the following aspects.
First, the ink supply is too large and the ink's printing adaptability is not strong.
1 The ink supply is too large, causing the ink layer on the layout to be too thick. Under the effect of the printing pressure, a graphic network spreads out, and the lines are bold and free from angularity, thus causing a paste.
2 The ink is too thin and the liquidity is large, causing the paste of the outlets to spread.
3Excessive dry oil in the ink will make the ink emulsification worse, so that the ink layer on the plate can not be broken from the middle, most stay on the plate, causing heaping ink, under the role of roller squeeze force, so that the network gradually expanded , Caused by paste version, excessive desiccant makes the viscosity of the ink increased, the adhesion to the blank part is enhanced, and it is easy to cause the paste adjustment on the dark part of the printed product.
4 In daily work, we use excessive varnish or detackifiers to increase the oiliness of the ink. During the printing process, the borderline between the dots of the graphic and text will be blurred and the paste will be caused.
Solution:
According to the graphic elements of printed products, the amount of ink supply should be properly controlled to control the amount of dry oil, varnish and detackifier used, and when the ink with strong oiliness is used, the acidity of the dampening solution should be appropriately increased.
Second, the water supply caused by the lack of paste
Because the pressure between the water roller and the plate cylinder is too small; the water roller surface is dirty; the water roller is used for too long; the fluff loses its elasticity; when printing, the corresponding water roller sleeve wears at places where there are many elements on the plate. Relatively serious, where the water absorption is also relatively poor and some other reasons caused by the lack of water supply, the printing process lost the balance of ink resulting in paste version.
Solution:
1 According to the workload and the degree of use of the water roller, timely replacement of the water roller sleeve.
2 Use a bottle of the perforated bottle in the bottle and apply the wetting fluid to the water roller. This will not only reduce the number of water roller sleeves but also reduce the number of paste plates. Point, but it is practical.
Third, the blanket stretch too loose or print pressure caused by the paste version
The rubber blanket is too loose, causing a large deformation during the printing process, which can easily cause a paste plate. Excessive printing pressure not only aggravates the wear of the printing plate, but also directly aggravates the spreading of the graphic ink layer, leading to paste printing.
Solution:
When changing the blanket, it should be tight and proper. Before printing, adjust the pressure of the printing cylinder. This can reduce the stencil.
Fourth, the version of the plate caused by wear and tear
The area of ​​graphic and oleophilic graphics on the plate is much larger than that of the hydrophilic blank area. Once the blank part of the blank is worn, it will cause the hydrophilicity to weaken, and it will be easily invaded and spread by the surrounding ink to produce a paste plate. phenomenon.
Solution:
1 Adjust the pressure between the rollers to avoid excessive pressure and cause plate wear.
2 Do not bump and rub the plate during transport of plates and plates.
V. Paste caused by the weakening of wetting fluid acidity
Alkaline paper fluff and paper powder that fall off during the printing process will be transferred to the water bucket to neutralize acidic wetting fluid, weakening the wetting fluid, and phosphoric acid or citric acid in the dampening solution will affect the plate surface. With the cleaning effect, the wetting liquid is too weak in acidity, and the cleaning ability of the oil on the plate surface is insufficient. When the ink with heavy oiliness is printed, it is easy to paste the plate.
Solution:
1 Change the water in the bucket regularly.
2 If the paper used for printing is conditional, it is best to use a paper machine for blowing air. This can not only blow off impurities, paper dust, and paper powder contained in the paper, but also make the water content of the paper even and consistent. The moisture content of the paper is balanced with the temperature and humidity of the printing shop, which causes the hysteresis of the paper to occur before printing, ie, reducing the sensitivity of the paper to water, so that the paper can be adapted to the temperature and humidity of the printing shop before printing, enabling the entire printing process. Done successfully.