Web offset presses are highly favored by many printing companies for their high efficiency, strong professional adaptability and good economic benefits for printed books and newspapers. However, in the printing, the problem of dragging the dirty product often affects the quality of the product. How to judge and solve the phenomenon of dragging dirty quickly? In many years of machine work, after a long period of observation and practice to solve the problem, I am now analyzing the web. The cause of offset printing on the offset printing press and the countermeasures are communicated to each other.
Dragging dirt refers to the fact that the print on the printed matter is drying slowly. Some ink adheres to the paper guide roller, triangle plate, folding roller, and belt conveyed by the paper, and is transmitted back to the paper, causing smeared oil on the print. Dirty ink. There are many reasons for the phenomenon of smearing, which is related to the paper structure, ink composition, temperature and humidity in the production workshop, the ink balance during printing, and so on. It is an extremely complicated issue.
The common causes of dragging dirty phenomenon mainly include the following situations and solutions:
First, the temperature and humidity of the production workshop
The ink is affected by the temperature, the higher the temperature, the faster the ink will solidify and dry. On the contrary, the temperature will decrease and the ink will tend to harden. It is easy to cause the paper to fluff and difficult to dry. The humidity in the printing room is another important factor that affects the ink drying. When the temperature is lower than 20°C, the higher the humidity, the water content of the printing paper is high even if it does not affect the ink. The humidity of the paper itself also affects the drying of the ink. As a result, the ink is dried poorly and dragging is caused.
Solution: Keep the temperature and humidity of the production workshop within the temperature (23±1)°C and humidity (60±2)%.
Second, the process of transmitting paper
After the paper is printed, it passes through the guide roller, triangle plate, folding roller, conveyor belt and other components. During use, the ink is accumulated and the pile is dirty.
Solution: Cleanse these institutions and keep them clean.
Third, the ink added too much adjuvant
Due to the large amount of paper powder in the printing, the pulling of the paper is severe, and the ink absorption is also poor. When ink is added to the ink and the viscosity-reducing agent is used, the amount is improper, causing the print to dry slowly and drag the dirty.
Solution: Appropriately increase the pad thickness of the plate or blanket cylinder, and add the amount of adjuvant within 5%.
Fourth, blocking ink
Part of the ink in the ink fountain is caused by high temperature, air-drying hardened crust, or poor adhesion, resulting in ink coagulation, and accumulates between the ink output adjustment steel sheet and the ink delivery roller. As a result, the amount of ink is poorly adjusted. When the time is large or small, when the amount of ink is suddenly increased, the ink film on the paper is too thick to permeate and dry.
Solution: Clean ink fountain and ink roller, add good ink.
Fifth, the dirty water roller
There are two situations: 1. Water roller oil is dirty, dirty ink; 2. The pH values ​​in the fountains do not meet the printing requirements. They do not keep the blanks of the plates clean and dirty.
Solution: Clean the water roller; test the pH of the dampening solution to reach 5-6.
Six, water roller adjustment
Because the pressure adjustment of the water roller is not in place, or the adjustment system of the water roller is not normal, the rotation speed is faster, the water content of the formed paper increases, and the ink absorption decreases; the ink moisture content increases, the viscosity decreases, and the adhesion is not strong. Oil film can not be quickly dried, resulting in dirty. Especially in the case of some papers with high whiteness and poor ink absorption, it is very obvious.
Solution: Adjust the pressure of the water roller to about 4 to 5mm (mark of imprinted water on the printing plate). Adjust the outlet roller control system. The key lies in grasping the size of the printing plate's moisture, so that the ink and water balance.