Several Factors Affecting Printing Force of Printing Plates

The original PS version used in the factory is the reproduction PS version of “Huaguang” brand PS, “Vida” brand and “Starlight” brand produced by the second film factory of China Lucky Film Group. Nowadays, it is produced by Linyi Xinhua Factory. "Huarui" brand PS version and reproduction version. At the beginning of this edition, apart from the shorter exposure time of the “Huaguang” PS plate, no other special features were found, including the printing plate's resistance to printing. However, in the printing of student books (long-run business), especially in the printing of books in the Chinese-language book and the Tian-word book, the printing plate has particularly low resistance to printing, especially when printing with the JS2102 double-sided offset printing machine. The resistance of the upper and lower printing plates is very low, which is nearly 3 times that before the plate change. In order to respond to emergencies, we temporarily adopted the method of shortening the exposure time. Because the student book is not high in print quality, the writing paper used in this core is a yellow anti-myopic paper, so it is not easy to show a certain degree of bottom left by the printing plate. dirty. Using this method can also relatively improve the printing plate's resistance to printing force, so that the printing resistance of the upper printing plate can reach 50,000 to 60,000 printing, and the printing resistance of the next printing plate can reach more than 20,000 printing. However, for the sun staff, I believe that this method is not desirable, this is not a long-term strategy, can only be used for emergency purposes.

After investigating and analyzing this fault, the author found that the following factors can cause the printing plate's resistance to printing force to decrease.

Factor 1: The quality of the paper used for printing is poor and contains many impurities. The bookbook used by students advocates the use of anti-myopic paper. Most of them are red and yellow. In general, compared to other printed matters, the quality requirements for the printed book paper are not too high. With burrs can be. The paper used by the factory this time is rough, loose, sandy, and has many additives. During the printing process, if there are too many additives and sand grains in the paper, the damage to the surface of the printing plate will be great. For example, the graphic part of the printing plate is subject to wear under the effect of surface friction, which changes the hydrophilicity and hydrophobicity of the graphic part; the blank part of the printing plate, under the action of the surface friction, is originally stable. Hydrophilic oleophobic damage, damage the hydrophilic layer of the printing plate, so that the fountain solution can not act directly on the oxidation plate of the plate, causing the blank part of the dirt. Especially those faster offset presses, such as the factory's JS2102 double-sided offset press and J2205 offset press. The faster the speed, the more paper is input, and the more sand and other particles are mixed in the paper, the greater the damage to the surface of the printing plate. The oxide film on the surface of the light plate is traced by grains of sand. For the long version of the business, the scratched area of ​​the plate is oxidized and a pattern appears. Severe persons directly injure the graphic part of the printing plate, causing the printing plate to be scrapped. If this happens, the processing methods are mostly: (1) replace high-quality, low-grain paper; (2) paper should be aired before starting, so that you can remove the impurities; (3) Wipe the blanket. These processing methods can extend the printing plate's resistance to printing.

Factor 2: The PS version used has quality problems. In this failure, the PS version of the change is clearer, and the graphic parts are covered with glue, but only hydrophilic is not ink. When the “Huaguang” brand PS plate used in the past has reached the limit of the printing force resistance, the adhesive layer in the graphic part is different from that in the past. This point can be explained that there is a problem with the glue layer of the “Huarui” brand PS plate, that is, there is a problem with the quality of the PS plates produced by the manufacturers. The exposure time of the “Huarui” brand PS version is shorter than the exposure time of other branded PS versions and does not match the exposure time provided by the factory. Although the actual exposure of the PS version (affected by the degree of use of the machine and lamp tube and the printing plate material used) is different from the time provided by the manufacturer of the PS plate (based on scientific determination), according to the information I checked, it shows that: In China, the difference between the exposure time provided by the manufacturer of the current PS version and the actual exposure time is not too great. Under the same conditions as the printing film, exposure time, developing time, and operating personnel, the difference in printing plate resistance should not be too large, and the application of shortening the exposure time can be used to improve the printing resistance. From the process of plate making, I found that, under normal circumstances, the exposure and development latitude of the “Huarui” brand PS plate is smaller than that of the “Huaguang” brand PS plate. For example, when the “Huaguang” brand PS version is used for non-mesh printing, the exposure latitude is less than 20 seconds, and the “Warray” brand PS version has an exposure latitude less than 10 seconds; “Huaguang” brand PS version. In the drying non-mesh version, the development latitude is 15 seconds, that is, artificial development in the developer tank back and forth evenly shaking the developer 4 times, and "Huarui" brand PS version of the development latitude less than 5 seconds, namely Artificial development shakes the developer evenly back and forth twice in the developer tank. From this point of view, the PS version of the exposure, development latitude directly affects the quality of each version, especially those who are not skilled in the plate-making technology, but also should use the quality of the PS version.

Factor 3: Problems with the offset press itself. In this observation, we found several offset presses of the factory, such as the JS2102 double-sided offset press, J2205 offset press, and J2108B offset press. The used plates were worn out in a certain position. In particular, the JS2102 double-sided offset printing press is not only the same as the damage of the printing plate, but also the gap between the upper and lower printing plates and the printing force, and the maximum printing resistance of the upper printing plate can reach 60,000 impressions. The next version of India's resistance force is only a maximum of 20,000 prints. With such a gap, it is not difficult for everyone to see that there are problems with the machine itself, and it is not possible to criticize the quality of the plate. The problems with the press are nothing more than the following:

(1) The actual contact distance between the blanket cylinder and the impression cylinder is uneven, so that the actual contact line between the two is not evenly subjected to force. Excessive force of the contact site will inevitably damage the printing plate; or Because the pressure between the blanket cylinder and the impression cylinder is too large, the grain of the plate surface is compressed and deformed, and the dot foundation is worn out, thereby making the printing plate and the like. If the pressure between the two is too great or uneven, the pressure between the two should be adjusted; if the blanket is unevenly laid, it should be re-laid.

(2) The distance between the transfer roller, the water roller and the actual contact line of the printing plate surface is unbalanced, so that the contact lines between the first two and the latter are not uniformly stressed, and the parts with the large force will damage the printing plate. If one of the three surfaces is attached to a hard object, the attachment should be removed immediately; if one of the three axes deviates, it should be immediately adjusted.

(3) Each new machine has a running-in process before normal use. If it is speeding during the running-in period, so that a part or a part is damaged, or the normal running-in effect is not achieved, then this Parts or components will not work properly unless new parts are replaced, so the offset press must not run faster during the run-in period.

(4) The machine itself has an aging process, which is often referred to as the normal wear process. If a part of the machine ages, it should be replaced, otherwise it will affect the printing plate's resistance to printing forces.

Reprinted from: Ke Yin Network