The effect of friction coefficient during printing

The friction in the gravure printing process mainly includes the friction of the equipment itself and the friction between the equipment and the printing material. The friction between the equipment and the printing material (film) is the main factor in the printing process, and it is often both the driving force and the resistance. Therefore, the control of its size plays a very important role in the print quality and printing speed in a proper range.

1. Selection of friction coefficient in printing

Film rolls for automatic printing generally require a smaller inner layer friction coefficient and a suitable outer layer coefficient of friction, and the outer layer has a large coefficient of friction, which may cause excessive resistance in the printing process and cause the material to be stretched and deformed to affect the printing effect. If it is too small, it may cause slippage of the drag mechanism, resulting in inaccurate correction systems, reduced print fastness, and speed of packaging. Therefore, the film surface should have suitable smoothness to ensure that it can perform high-speed printing smoothly. At room temperature, the dynamic friction coefficient of the film surface is generally required to be between 0.2-0.4.

2. Effect of high temperature service conditions on friction coefficient

When considering the friction coefficient, special attention should be paid to improving the bonding environment of the ink and the substrate and increasing the printing speed. Generally, the temperature of the printing environment must be increased. The metal parts of the equipment are mostly operated at a high temperature of 50° C. or more. However, the increase of temperature has a great influence on the friction coefficient, because the heat transfer ability of the polymer macromolecules under high temperature conditions is strengthened, the activity speed is increased, the molecular gap becomes larger, and the change of the surface performance changes the friction coefficient of the film. In addition, the smoothness of the film is mainly achieved by adding a slip agent. After the film is formed, the slip agent migrates from the film to the surface and accumulates into a uniform thin layer, which can significantly reduce the coefficient of friction of the film. The film has a good smoothness effect. Most of these auxiliaries are inorganic polymer materials (such as amines or waxes), and have poor compatibility with the resin, usually starting from 30°C. Commonly used lubricants have become close to their melting point and become bonded. The friction of the film The coefficient rises sharply and the force exerted during the test fluctuates greatly, presenting an intermittent sliding or bonding effect. If the content of the slip agent is too high, it also affects the printability of the film, which is extremely unfavorable for printing.

In general, with the increase of the ambient temperature, the friction coefficient of the material surface will have a certain change, but the size of the change will vary greatly depending on the sensitivity of the material to the temperature and the types and amounts of the additives added.

3. Determination of coefficient of friction

With the rapid development of gravure printing technology, the printing speed is getting higher and higher. In order to avoid the waste caused by the friction coefficient of the material in the printing process and increase the production efficiency, the printing manufacturer must select the appropriate coefficient of friction film, which requires the manufacturer to have suitable Thin film testing equipment. Before printing, it is not only necessary to measure the coefficient of friction of the film material at room temperature, but also the friction coefficient at the actual use environment temperature. Generally according to GB 10006 (plastic film and sheet friction coefficient measurement method) and ASTM D1894 to determine the positive and negative film surface dynamic and static friction coefficient. Labthink's FPT-F1 Friction Coefficient/Peel Tester is a special device for measuring the dynamic and static friction coefficient of materials at very low temperatures. It simulates a test environment at room temperature -99.9°C and is closer to the friction coefficient in the actual printing process. Moreover, the accuracy of the test can reach 0.5-level accuracy, which can take into account both domestic and foreign standards. It is very suitable for printing companies to choose suitable printing materials.

Source: Shanghai Packaging