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3. Mechanical force:
i. Static (the printing plate is installed on the printing press, the machine is stopped, or the printing plate is under the machine, called static). In this stage, due to the man-made bending of the plate; scratches caused by hard objects or sharp objects on the surface of the printing plate; scratches on the surface of the printing plate during the preservation process, etc., all are liable to have a long service life of the printing plate; Force has a great influence.
Ii. Dynamic (called dynamic when the printing plate is printed on the printing press)
In the process of printing, the printing plate continuously contacts the ink roller, the water roller, and the rubber roller. This contact is performed under the pressure. The greater the pressure, the greater the frictional force that can be generated. Besides the ink roller and the water, Rollers, blankets, and the ink, paper, and paper dust that they bring, these materials can also cause wear on the surface of the printing plate due to pressure and speed differences; in addition to rubber rollers, blankets, The speed difference caused by the deformation of the water roller and the printing plate liner can also cause friction on the printing plate surface, thereby abrading the printing plate. Each type of friction begins to damage the surface structure of the printing plate from the beginning of printing.
4. Electrochemical corrosion and photochemical reactions.
i. Static. The printing plate is easy to react with oxygen and other gases in the air during the preservation process, which reduces the hydrophilicity and abrasion resistance of the blank part; the graphic part of the printing plate sees light decomposition and reduces the intensity of the graphic part.
Ii. Dynamic. The acid reaction between the printing plate and the fountain solution during the printing process will cause corrosion of the graphic part and reduce the printing rate.
After discussing the structure of the printing plate and the external factors that affect the printing plate's printing rate, we have further discussed how to protect the printing plate in actual production. Here we introduce some of the protection methods used in print production.
Due to physical and chemical conditions, but also affected by process conditions and process operations, a series of protective measures should be taken to maintain the normal printing of the printing plate and extend its useful life. In daily printing production, printing plate protection can generally be divided into: static protection and dynamic protection.
1. Static protection of printing plates
The general principle of static protection of the plate is: the plate is evenly rubbed with a hydrophilic colloid (eg gum arabic) and the plate is kept dry. However, the following points should be noted in the static protection of printing plates:
A. Prevent oxidation. If the surface of the printing plate is not covered with a protective layer, it is directly covered in the air and can be oxidized. The resulting oxide has a lipophilic and oil-sensitive property that makes the printing plate dirty and destroys the printing plate to reduce the printing resistance.
B. Prevent moisture. The printing plate is placed in moist air, especially when the relative humidity of the air is relatively large, it is the premise of accelerating the oxidation of the plate (the galvanic corrosion occurs). At this time, the oxidation can cause the plate base to be corroded, and the destruction of the blank part changes the hydrophilicity and sparseness. Oily, making the layout dirty.
C. Prevent acid and alkali corrosion. The base plate of the PS plate is aluminum, which is located before the hydrogen in the metal activity sequence. It is a relatively active metal element and can react with acids and alkalis. The products can both damage the plate, and printing must be strictly controlled. Acid and alkali (especially strong acid and strong alkali) contact.
D. Prevent layout rubbing and knocking. When the printing plate is placed on the desktop, the layout should face upwards, and the layout cannot be dragged backwards and backwards to prevent the layout from being scratched. If the printing plate is placed facing downwards, it should be covered with paper. If two plates are stacked, the two plates face each other and are separated by paper. Layouts should strictly prohibit hitting or placing heavy and hard objects (such as wrenches, machine parts, etc.) with hard objects.
E. Prevent horseshoe prints. Take the version of the method to be appropriate, can not be arbitrarily bent, to avoid the local horseshoe India caused by the version, was uneven, resulting in damage to the graphic part.
F. Prevent the layout from gelling. The gum arabic gum that is rubbed on the layout should be of moderate concentration, avoiding over-thickening of the rubber track and corroding the printing plate graphic, not absorbing ink, and not too thin to lose the effect of the glue protection plate. In particular, glue that has deteriorated must not be used.
2. Dynamic protection of printing plates.
When the printing plate is running on the machine, the measure of protecting the plate caused by the interference of external factors or the reduction of external factors is called dynamic protection.
The damage of the printing plate is caused by running imprinting in most cases. There are two factors: First, the printing plate and the blanket cylinder, the ink roller and the water roller are formed in the rolling dynamics. The difference in speed is the friction; the other is in the presence of a variety of friction factors, the water roller containing acid dampening fluid rolling corrosion effect.
In view of the destructive effect of the above two points on the printing plate, how to correctly assemble the machine, adjust the work accuracy of each component, and maintain the accuracy of the machine are very important. In general, the dynamic protection of the plate must do the following:
A. During the contact between the printing plate and blanket cylinder, ink roller and water roller, the printing pressure should be as small as possible to reduce the friction on the printing plate layout.
B. During the adjustment of the machine, try to make the lining of each drum reasonable, and keep the surface speed of each roller and the ink roller and water roller equal to each other and reduce the speed difference.
C. Try to eliminate the axial turbulence of the water roller and ink roller and cause the plate to wear.
D. The correct concentration of the dampening solution in the water fountain is to control the PH value of the solution within a reasonable and appropriate range (this range requires that the dampening solution must first satisfy a certain acid value so that the salt layer on the surface of the printing plate is When the damage can be repaired in time; in addition, the acid value can not be too large, so as not to cause the malignant corrosion of the printing plate).
E. Controlling a smaller amount of water on the layout and maintaining normal water supply.
F. Control the amount of dry oil in the ink, to avoid over-consumption caused by dirty version of the plate and then destroy the plate.
H. Shake off the paper with sand and other debris as much as possible. In case of more sand, and when the powder is severely deposited after removing the powder, always wash the blanket to prevent the deposits from grinding the plate. Always pay attention to observing the buildup on the plate or blanket and clean it up in time, especially when rough paper is printed. Experience has shown that after printing 3-4 thousand sheets of paper, the accumulated thickness caused by paper, ink, and dusting can reach 0.1 mm or more. If it is not cleaned in time, the stacking thickness continues to increase, causing friction to increase and the dots will fall off due to excessive friction.
I. When the rubber blanket is rolled off, it should be thin and thin when it comes to saving the cost.
J. To adjust the accuracy of the machine structure and to try to eliminate the effect of roller bars and ink roller bars on the printing plate's resistance to printing forces.
K. Cleaning during printing Try to avoid using strong plate cleaners or roller cleaners to clean plates and rollers. Rinse with clean water immediately after cleaning.
L. Dispose of or replace aging rubber rollers or blankets in a timely manner to avoid galling of the plates.
Above, we discussed the factors affecting printing plate printing rate from several aspects, and some ways to improve the printing plate printing rate and some protection methods in daily production. I hope to have some help for everyone.
Source: Bison
! Note: During the baking process, baking temperature and baking time must be strictly controlled. Exceeding the specified temperature and time will not only increase the printing rate of the printing plate, but will reduce the service life of the printing plate.