How to judge and solve the problem of dirty web offset printing machine?
Web offset presses are favored by many printing companies for their high efficiency, strong adaptability in printing books and newspapers and good economic benefits. However, in printing, the problem of smearing often affects the quality of the product. How can we quickly judge and solve the smearing phenomenon? In the years of machine work, after long-term observation and practice to solve the problem, I now analyze the web The causes of the smearing of offset presses, the solutions, and exchange with your printing colleagues.
Smearing means that the print on the printed matter dries slowly, and part of the ink adheres to the paper guide roller, triangle plate, folding cylinder and conveyor belt passing by the paper belt, and is returned to the paper, causing streaky oil on the printed matter, The ink is dirty. There are many reasons for the smearing phenomenon. It has a lot to do with the paper structure, ink composition, temperature and humidity of the production workshop, and the balance of water and ink during printing. It is an extremely complicated problem.
Common causes of dragging are as follows:
1. The temperature and humidity of the production workshop
Ink is affected by temperature, the higher the temperature, the faster the solidification and drying of the ink; on the contrary, the lower the temperature, the ink has a tendency to harden, which easily causes the paper to fluff and not easy to dry. The humidity of the printing workshop is another important factor affecting the drying of ink. When the temperature is lower than 20 ° C, the higher the humidity, the water content of the printing paper is higher even if it does not affect the ink. The humidity of the paper itself also affects the drying of the ink. The result is poor drying of the ink and smearing.
Solution: Keep the temperature and humidity of the production workshop controlled at a temperature of (23 ± 1) ° C and a humidity of (60 ± 2)%.
Second, the process of transferring paper
After the paper is printed, it passes through paper guide rollers, triangle plates, folding cylinders, conveyor belts and other components. In the process of using ink, the accumulation of ink and the accumulation of dirt will lead to smearing.
Solution: Clean these institutions and keep them clean.
3. Too much auxiliary agent in the ink
When printing, due to the large amount of paper and paper powder, the roughness is more serious, and the ink absorption is also poor. When adding ink adjusting oil and viscosity reducer to the ink, the amount of improper use causes the imprint to dry slowly and become dirty.
Solution: Increase the pad thickness of the printing plate or blanket cylinder properly, and add the auxiliary agent within 5%.
Fourth, blocking ink
A part of the ink in the ink fountain causes the ink to gel and gel due to high temperature, air drying, hardening, skinning, or poor connection, and is accumulated between the ink output adjustment steel sheet and the ink discharge roller. As a result, the amount of ink is poorly adjusted, from large to small. When the amount of ink is suddenly increased, the ink film on the paper is too thick, which is not conducive to penetration and drying, and it will be dirty.
Solution: Clean the ink fountain and ink delivery roller, and add good ink.
5. The water roller is dirty
There are two situations: 1. The water rubber roller is dirty with oil and ink; 2. The pH value of the dampening plate in the water bucket can not meet the printing requirements. They can not keep the blank part of the printing plate clean and form oil stains.
Solution: Clean the water rubber roller; test the pH value of fountain solution to 5-6.
6. Water roller adjustment
Because the pressure of the water rubber roller is not adjusted properly, or the water outlet roller adjustment system is abnormal and the speed is faster, the water content of the paper increases and the ink absorption decreases; the water content of the ink increases and the viscosity decreases, and the adhesion is not very strong Also, the oil film can not be dried quickly, resulting in smearing. Especially in some papers with high whiteness and poor ink absorption, it is very obvious.
Solution: Adjust the pressure of the water rubber roller to about 4 ~ 5mm (fingerprint water mark on the printing plate). Adjust the water roller control system. The key is to master the water content of the printing plate and achieve the balance of water and ink.
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