Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

1. Selection of friction coefficient in printing

       The film coil for automatic printing generally requires a small inner friction coefficient and an appropriate outer friction coefficient. If the outer friction coefficient is too large, it will cause excessive resistance in the printing process, cause material tensile deformation and affect the printing effect. Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

       If it is too small, it may cause the drag mechanism to slip, cause inaccurate deviation correction system, reduce printing fastness and affect the packaging speed. Therefore, the film surface should have appropriate smoothness to ensure its smooth high-speed printing. The dynamic friction coefficient of the film surface is generally required to be between 0.2-0.4 at room temperature.Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

2. Effect of high temperature service conditions on friction coefficient

       When considering the friction coefficient, special attention should be paid to the fact that in order to improve the combination fastness of ink and substrate and improve the printing speed, the printing ambient temperature should generally be increased. Most of the metal parts of the equipment operate at a high temperature above 50 ℃.Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

       However, the increase of temperature has a great impact on the friction coefficient, because under the condition of high temperature, the thermal movement ability of macromolecules of polymer materials is strengthened, the activity speed is accelerated, the molecular gap becomes larger, and the change of surface properties will change the friction coefficient of the film. In addition, the smoothness of the film is mainly realized by adding a smoothing agent. Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

         After the film is formed, the smoothing 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 have a good smoothing effect. Most of these additives are inorganic polymer materials (such as amines or waxes) have poor compatibility with resin. Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

         Generally, starting from 30 ℃, the commonly used lubricants have approached their melting point and become bonded, and the friction coefficient of the film will rise sharply. The force applied during the test will fluctuate greatly, showing an intermittent sliding or bonding effect.Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

         If the content of lubricant is too high, it will also affect the printability of the film, which is very important for printing Is unfavorable.Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

         Generally speaking, with the increase of ambient temperature, the friction coefficient of the material surface will change to a certain extent, but the magnitude of the change varies greatly due to the sensitivity of the material to temperature and the type and amount of additives added.V

3. Measurement of friction coefficient

         With the rapid development of gravure printing technology, the printing speed is higher and higher. In order to avoid waste caused by material friction coefficient in the printing process and improve production efficiency, printing manufacturers must choose appropriate friction coefficient film, which requires manufacturers to have appropriate film testing instruments. Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

        Before printing, we should not only measure the friction coefficient of the film material at room temperature, but also study the friction coefficient at the actual ambient temperature. Generally according to GB 10006 (measurement method of friction coefficient of plastic film and sheet) and ASTM d1894 to determine the dynamic and static friction coefficient of the positive and negative surfaces of the film.  Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

       Labthink’s fpt-f1 friction coefficient / peel tester is a special equipment for measuring the dynamic and static friction coefficient of materials at extraordinary temperature. It can simulate the test environment at room temperature – 99.9 ℃, which is closer to the friction coefficient in the actual printing process. Moreover, the test is accurate .Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing

          The accuracy can reach grade 0.5, and can take into account domestic and foreign standards. It is very suitable for printing manufacturers to select appropriate printing materials.Influence of Water Absorption and Expansion of Paper in Color Newspaper Printing