Discussion on Factors Affecting Printing Force of Printing Plates and Their Solutions

In the printing process, if the hydrophilic or hydrophilic film of the printing plate is destroyed and the plateau is worn out, the printing plate's resistance to printing will be reduced.

There are two reasons for the wear of the plate grain, one is friction, and the second is the galvanic corrosion and chemical corrosion of the plate. Friction is an important reason for the decrease of printing plate's resistance to printing force. In the printing process, the friction of the printing plate is unavoidable. There are three reasons why friction can cause the printing plate's resistance to drop:

(1) The friction between the water roller, the ink roller, and the blanket cylinder against the printing plate. Improper adjustment of the water roller and its ink pressure will cause the pressure of the water roller to become heavy and accelerate the wear of the printing plate. If the pressure of the ink roller is too light, there will not be enough ink on the printing plate, which will destroy the foundation of the picture and the dot will appear. Some water rollers and ink fountain rollers are used for too long, and some of the inks and papers with poor quality are used for printing, which causes the capillary pores of the plate to be damaged. This also accelerates the frictional damage of the printing plate. In addition, the water used by some companies, as well as the ink roller static balance and dynamic balance are not calibrated, especially if the balance of the dynamic balance is not corrected. The ink roller should make a circular motion along the axis on the printing machine, but because the dynamic balance is not calibrated, it cannot reach the requirement, causing twisting and increasing the friction. In some old machines, water, ink roller support or water locks, and ink roller stops wear out, grooves appear, and water and ink rollers beat at the support, accelerating the wear of the printing plate, usually produced under this condition. Printed products will appear in the mouth of the printing plate ink rod, there dirty version and so on.

(2) Blanket and pad. Bad blanket quality or improper installation will result in reduced surface elasticity of the blanket. In addition, if the liner is used for a long time, it will also cause its convexity, accumulation, wrinkles, and uneven surface.

(3) Plate cylinder pressure. If the printing pressure is too low, the picture and text will not be completely transferred to the paper, and the phenomenon of inaccurate graphics and imprints will appear, and problems such as paper and printing plates will be more easily reflected on the printed products. However, excessive printing pressure increases the friction between the printing plate and the blanket, shortens the service life of the printing plate and the blanket, leads to the expansion and deformation of the dots, ghosting, serious ink sticks, and easy Pull the paper. To reduce friction, it is necessary to emphasize the use of "ideal pressure", and to minimize the printing pressure on the basis of a sufficiently strong print.

The plates of offset printing plates are mainly zinc plates or aluminum plates. When there is an electrolytic solution or a water film on the surface of the plates, they will form primary cells, ie, galvanic corrosion; chemical corrosion will occur when contacted with moist air containing CO2. This will destroy the grain on the surface of the printing plate and make the printing plate less resistant to printing forces. The culprit for galvanic corrosion or chemical corrosion is the fountain solution. The pH of the fountain solution determines the occurrence of various types of corrosion. The acidic or alkaline dampening solution will aggravate the corrosion, and only the neutral dampening solution can reduce the corrosion. The pH of the fountain solution should be exactly what it should be. This does not give a definitive answer. It is generally believed that the pH of the PS plate fountain solution is between 5.0 and 6.0. The key to using fountain solution is to grasp its pH and degree of wetting. At the time of printing, the wetting effect is often improved by adding certain surfactants to control the oil repellency of the fountain solution. Paper has the best pH neutrality and its pH is around 7.0. However, actual production papers are mostly weakly acidic, and some are also slightly alkaline. Only by mastering the acidity and alkalinity of paper and fountain solution, and doing the appropriate processing, can the printing achieve the desired results.

In addition to the above two reasons, the impact of the printing plate's resistance to printing force is related to the following factors: the ink volume on the ink roller due to various causes is too small, and the remaining ink layer is insufficient; the ink flow is not good, the spread is uneven; the ink supply roller Or blanket adhesiveness is too large (especially when the ink layer is thin); ink roller surface adsorption performance is poor; ink viscosity is too large; paper surface sizing quality is poor, the surface is uneven, the pressure is not true, hair removal powder and so on. As long as careful analysis, using scientific and technological means can solve these problems, thereby improving the quality of printing.