The friction force in the gravure printing process mainly includes the friction of the device itself and the friction between the device and the printing material and ink. Among them, the friction force between the device and the printing material (film) in the printing process accounts for the main factor. It is often both a driving force and a It is resistance, so whether its size control is within an appropriate range plays a very important role in printing quality and printing speed.
1. Selection of friction coefficient in printing Film rolls for automatic printing generally require a smaller inner friction coefficient and a suitable outer friction coefficient. If the outer friction coefficient is too large, it will cause excessive resistance during the printing process, causing The tensile deformation of the material affects the printing effect. If it is too small, it may cause the drag mechanism to slip, causing the correction system to be inaccurate, reducing the printing fastness, and also affecting the packaging speed. In addition, the fineness of the ink is low, the particles of the pigment are coarse, the coefficient of friction during printing is large, and the printing durability of the printing plate is low. It is also easy to produce scumming, ink accumulation, and uneven ink transfer and ink distribution during printing. Therefore, the film surface should have appropriate smoothness to ensure its high-speed printing, and the dynamic friction coefficient of the film surface is generally required to be between 0.2-0.4 at room temperature.
2. The effect of high-temperature use conditions on the friction coefficient When considering the friction coefficient, special attention should be paid to improve the bonding fastness of the ink and the substrate and increase the printing speed. Generally, the printing environment temperature must be increased. The metal parts of the equipment are mostly in Operate under high temperature conditions above 50 ℃. However, the increase of temperature has a great influence on the friction coefficient, because under high temperature conditions, the macromolecular material macromolecules have enhanced thermal movement ability, faster movement speed, larger molecular gaps, and changes in surface properties will change the film friction coefficient. In addition, the slip 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 friction coefficient of the film and make The film has a good slip effect. Most of these additives are inorganic high-molecular materials (such as amines or waxes), which are not compatible with resins. Generally, starting from 30 ℃, the commonly used lubricants have become close to their melting points and become cohesive, and the friction of the film The coefficient rises sharply, and the force applied during the test fluctuates greatly, showing an intermittent sliding or sticking effect. If the content of slip agent is too high, it will also affect the printability of the film, which is extremely unfavorable for printing. Generally speaking, as the ambient temperature increases, the friction coefficient of the surface of the material will change to a certain extent, but the size of the change will vary greatly depending on the temperature sensitivity of the material and the type and amount of additives added.
3. Determination of friction coefficient With the rapid development of gravure printing technology, the printing speed is getting higher and higher. In order to avoid waste caused by the friction coefficient of materials in the printing process and improve production efficiency, printing manufacturers must choose a suitable friction coefficient film. This requires manufacturers to have suitable thin film testing equipment. Before printing, it is necessary to not only measure the friction coefficient of the film material at room temperature, but also study the friction coefficient at the actual use environment temperature. Generally, the dynamic and static friction coefficients of the front and back surfaces of the film should be determined according to GB 10006 (Method for Measuring the Friction Coefficient of Plastic Films and Sheets) and ASTM D1894. At present, Jinan Languang Electromechanical Technology Co., Ltd., a professional manufacturer of packaging testing instruments in China, has launched a FPT-F1 type friction coefficient / peeling test machine specifically for measuring the dynamic and static friction coefficients of materials at very high temperatures, which can simulate room temperature-99.9 The test environment at ℃ is closer to the friction coefficient in the actual printing process. And the test accuracy can reach 0.5 grade accuracy, which can take into account domestic and foreign standards, which is very suitable for printing manufacturers to choose the appropriate printing materials.
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