The friction 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 between the device and the printing material (film) in the printing process occupies the main factor. It is often both a driving force and a driving force. 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 layer friction coefficient and a suitable outer layer friction coefficient. If the outer layer friction coefficient is too large, it will cause excessive resistance during the printing process, causing the material to deform and affect the printing effect. If it is too small, it may cause the drag mechanism to slip, causing inaccuracy of the correction system, reducing the printing fastness, and 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 conditions on the friction coefficient
When considering the coefficient of friction, special attention should be paid to improve the bonding fastness of the ink and the substrate and increase the printing speed. Generally, the temperature of the printing environment must be increased. Most of the metal parts of the equipment are operated under high temperature conditions above 50 ° C. 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 the waste caused by the friction coefficient of the material in the printing process and improve the production efficiency, the printing manufacturer must choose the appropriate friction coefficient film, which requires the factory environment to prepare Appropriate 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.
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