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guidelines for the pressure of printing Guidelines for determining the pressure of off-page printing
- May 16, 2018 -

1. The first principle of printing pressure for color page printing: No relative sliding principle on the roller surface

      In offset printing, because the total amount of deformation of the drum liners can “indirectly indicate the corresponding printing pressure, the plate presses and printing pressures of the lithographic printing presses can be expressed in terms of the amount of compression that is not acceptable for the rubber and the image press. In the roller cylinder and the embossing roller, the plate cylinder and the impression cylinder can be regarded as a rigid cylinder, and the squeegee can be considered as an elastic thick cylinder. The printing process or the imprinting process is the rolling process of the cylinder. The biggest problem that arises in this process is the sliding in the roller rolling.

      Through the rolling process of the elastic roller and the rigid roller, the velocity of each point in the contact width of the roller is analyzed. It is found that within the contact width (except for individual points), the velocity at a point on the elastic cylinder and the velocity at the corresponding point on the rigid roller Not equal, that is, there is relative sliding of the roller surface during rolling. However, the ideal printing process requires a pure rolling without a roller under pressure.

      Through the study of the roller sliding speed, there are two clear points. The first point is that the distribution of the sliding in the embossing area is symmetrical, and when the rotating speed of the roller is fixed, the sliding speed depends on the calculated sliding speed. The position of the corresponding point and the radius of the two moving drums. The second viewpoint is that it is more advantageous to adopt the design principle that the elastic roller is slightly smaller than the diameter of the rigid roller when considering the effect of roller sliding on printing. With this principle, the elastic roller will form a bulge in front of the embossed area during printing. With convex hulls, the absolute speed of the slide is relatively small.

      The inevitable sliding speed and slip in the roller rolling cause friction between the contact surfaces. Sliding and friction may cause the liner and felt to move. Sliding and friction can cause the emergence of convex bulges and convex bulges, which is no different from increasing the radius of the blanket cylinder. Naturally, it may cause the distortion of the graphic and text transfer. When the blanket is subjected to friction acting alternately on both the front and back surfaces, it may produce uneven wear on the printing plate, resulting in wear marks similar to tooth marks.

      Sliding may cause imprinting or dot distortion. The relative displacement of the contact surface during rolling will stretch the imprint and enlarge the dot to an ellipse. Second, due to the wear of the plate due to friction, printing will cause hair prints . In addition, if the backside of the blanket slips too much and cannot be instantly reset, it may cause “reprinting” failures in which the images on the print cannot be accurately reclosed.

      In the actual printing process, considering the influence of various factors, it is often necessary to make appropriate adjustments and compensations for the above-mentioned distributions based on the measurement and experience.

      Therefore, the determination of the offset printing pressure of the color page printing is the determination of the roller printing blanket. The objective of the determination is to make the effective diameters of the plate cylinder and the blanket cylinder equal in the actual printing process. The so-called effective diameter refers to the actual diameter of the two cylinders after the pressure is combined. For the blanket cylinder, it also includes the lining of the surface. The diameter of the part caused by the deformation caused by the material. The effective diameter is equal, which ensures the consistency of the tangential speed of the contact point of the embossing area and the synchronized rolling state of the drum, thereby reducing the slippage and friction of the drum in the rolling process, and improving the quality of the printed product.

      2. The second principle of offset printing pressure determination: Circular tangential cutting principle of rolling gears

  Between the rollers on the offset printing press, gears are used to transmit power. In order to ensure the smoothness of the transmission and reduce gear wear, it is required that the gears mesh in tangential pitch, that is, the center distance of the drum is equal to the index of the two roller gears. The sum of the circle radii. However, in practice, this is not the case. If the rolling center distance is adjusted too large, resulting in a larger gear meshing gap, the transmission stability will be greatly reduced, the gear wear will also be intensified, and the product quality and machine service life will be reduced to varying degrees. .

      3, determine the third principle of offset printing pressure: the principle of appropriate pressure

  The contact pressure between the plate cylinder and the blanket cylinder is called the platen pressure. The contact pressure between the blanket fluid and the impression cylinder is called the printing pressure, ie, the printing pressure. The general printing pressure should be greater than the edition 0.05-0.1mm, the appropriate pressure is the first principle to determine the drum lining. Should pay attention to prevent excessive pressure phenomenon, especially the edition pressure is the most sensitive to the dot expansion, the edition presses the conference to cause the network point to expand seriously, thus affects the printing product color and the level reduction.

      In the practical application of color pages printing, the above principles cannot be met at the same time. Therefore, some technological measures should be taken to satisfy the above principles as much as possible so that the difference is not too great. Can not pay attention to both, it is required to emphasize the principle of simultaneous rolling, give priority to the printing plate, blanket roller pressure principle.

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