Analysis of the most popular offset printing plate

An analysis of the problem of the dirty tape of the offset printing plate

the dirty tape of the offset printing plate is one of the common printing faults. In the production process, we must make a specific analysis according to the signs and parts of the dirty tape, find out the cause of the fault, and take effective measures to prevent and solve it. Generally speaking, the tape dirt of offset printing plates can be divided into floating dirt. Dirty oil, paste version. Ink bar stripes, etc

floating dirt

floating dirt refers to a phenomenon of dirty non graphic parts with relatively large range and low density. Unlike oil dirt, the dirty parts have no grease base, which is not caused by printing plates, but mainly caused by ink emulsification. There are two types of ink emulsification, water in oil (w/O) and oil in water (O/W). Among them, water in oil ink emulsification is the situation that the ink emulsification is too serious, the viscosity of the ink is reduced, and the ink droplets splash on the plate under the action of centrifugal force to form floating dirt: oil in water ink emulsification is the phenomenon of ink "hydration", which makes the blank part of the printing plate have light ink marks

in the actual operation process, we can judge by the following signs. ① Dirty parts are easy to wipe off; ② Because the hydrophilic salt layer is not damaged, pc/abs alloy plastic is rich in interior materials in the automotive industry, and the dirty parts will often change; ③ The resulting floating dirt or ink residue falls into the fountain solution, resulting in coagulant ink particles (caused by water in oil ink emulsification); ④ There is pigment precipitation or flocculation in the fountain solution, and there is color shadow on the full plate of the print (caused by the emulsification of oil in water ink), that is, the ink "melts water". Causes: ① the pH value of the fountain solution and the paper is not appropriate. When printing, the ink is emulsified due to the large amount of water. At this time, it is mostly the emulsification of water in oil ink; ② The water volume of the layout can even reach 0.2% The volume is too small and the quality of ink binder is poor, resulting in emulsification of oil in water ink and too soft ink; ③ The pigment has poor water and acid resistance and poor affinity with binder; ④ The pigment in the ink is dissolved in the fountain solution, and the ink is dispersed in the fountain solution in flocculent form, causing a large area of floating dirt. It may also be caused by improper printing pressure, improper assembly of water roller and ink application roller, and insufficient hardness of the plate roller

oil dirt

oil dirt is the blank part of the fingerprint plate that should not be greasy, which makes the ink adhere to it, forming a dirty layout. The main reasons for the greasiness of the blank part of the printing plate are: insufficient water in the blank part or weak acidity of the fountain solution; Due to machine operation, paper and other reasons, the hydrophilic salt layer of the blank part of the printing plate is unstable, even worn, resulting in the decline of water retention; The fatty acids in the ink dissolve in the fountain solution, making the blank part of the printing plate greasy

in the actual operation process, we can judge by the following signs. ① Dirty parts are not easy to wipe off; ② The dirty part is relatively fixed; ③ It can be eliminated by adding water, wiping potion and resin, but the oil dirt with serious sand hole wear cannot be eradicated. Causes: ① the pressure of the printing plate and rubber drum is too large or the lining is too thick, resulting in increased friction or sliding friction, accelerating the wear of the printing plate. Through careful observation, we found that the mouth of the printing plate is most likely to lose its water storage capacity and become oily and dirty due to sand holes being ground flat; ② The rubber cloth is aged and hard due to long service time, losing its due elasticity, and the compression deformation is reduced, resulting in insufficient printing pressure. If you do not replace it in time and only add some paper to the liner, although the pressure can be increased, the friction will also increase accordingly. Therefore, during the transfer process, the water storage layer on the surface of the printing plate will be damaged due to long-term use, causing a large area of oil dirt on the printing plate; ③ In view of the aging and hardening phenomenon of rubber blanket, we usually wipe the aging and damaged parts first, and then use polypropylene tape for bonding. Because polypropylene tape is cheap and good, this method is very popular; ④ Plate loading is also crucial. If the plate is not tightened during plate loading, it is easy to cause the printing plate and the drum to be not tight, and the part that is not tight will rub against the rubber drum, and the contact with the water roller is too tight, which will not only generate excessive friction, but also squeeze out the water, so the plate is often oily and dirty due to insufficient water supply. ⑤ Reasons for inking roller: if the inking roller is adjusted too heavy, it will jump when the printing plate cylinder turns to its mouth, and the oil at the mouth of the printing plate will be dirty: when the inking roller rotates, it will also cause the local plate to be too heavy, wear the printing plate and get dirty; ⑥ The grease sensitivity of the ink and the amount of additives are inappropriate, resulting in excessive oiliness; ⑦ When wiping the glue, the moisture content of the wet cloth is too large, resulting in "bottom exposure" after wiping, resulting in oil and dirt; ⑧ The pH value of the paper is too high, which greatly reduces the acidity of the fountain solution. The water roller is too dirty, and the assembly of the water roller is inappropriate, resulting in insufficient water supply and dirty oil

pasted version

pasted version refers to the lines and lines of the printed image and text. There should be no ink between points and highlights, but it sometimes belongs to the category of oil dirt and sometimes belongs to the category of floating dirt

in the actual operation process, 2.4 circuit thousand disturbance control, we can judge by the following signs. ① The imprinting layer is not clear, and more dense (points above 50:6) parts occur; ② If the oil is dirty, the dirty position is fixed and the ink is deep, so it can be found and eliminated as soon as possible; ③ If it is floating dirty, the dirty position will change, and the ink is light, which is easy to eliminate. Causes: ① excessive amount of dry oil will change the suitability of the ink and spread the ink layer of the graphic part during printing; ② The ink layer is too thick. The water content is too small or the ink is too thin and the fluidity is large; ③ Serious emulsification of ink; ④ The pressure is too high, and the ink layer of the graphic part is not spread or lined properly; ⑤ The roller is partially deformed, and the water roller has poor contact with the layout, resulting in insufficient or uneven water supply; ⑥ The surface of the inking roller is aging, especially the adsorption performance of the last two inking rollers is poor, so the floating ink and dirty ink of the layout cannot be taken away; ⑦ When the machine is shut down, the layout dries up, oxidizes and even fuzzes, leaving ink on the ink roller to produce a pile of ink and paste the version

there are various signs and reasons for the dirty fault of offset printing plate. In the actual operation process, it should be carefully distinguished and classified, and the phenomena should be analyzed and solved in time

solve the problem of inaccurate circumferential overprint by using rubber

I have been engaged in four-color offset printing for many years, and I often encounter the problem of inaccurate circumferential overprint of prints. The cross hairs in the middle are very accurate, while the cross hairs at the trailing tip are of different sizes. Generally speaking, it is believed that the peeling tension of the paper after four color group imprinting is large, and the old and new rubber blanket are different. During a patrol inspection of the machine, I heard an abnormal sound from the second color group. According to experience, it was the sound made when the blanket was not tightened, so I stopped the machine immediately, tightened the blanket, and reopened the printing. At this time, the image and text imprinting is more accurate than the original

according to the characteristics of air cushion blanket, the blanket will always deform during the printing process. When the blanket is printed in a loose condition, the imprint obtained by the paper will be longer than the actual imprint. On the contrary, it should be shortened. Changing the tightness of the blanket can change the circumference of the graphic imprint, so as to achieve the purpose of accurate overprint. This method is easy to operate and can achieve satisfactory results, but it needs to be emphasized that this can only be fine tuned when it cannot be solved by the pulling method. In particular, when loosening the blanket, pay attention to safety and prevent the occurrence of ghosting and other faults, which must not be abused