In the offset printing process, the backing paper is generally added in the printing plate and the blanket cylinder to increase the thickness of the roller blanket, so as to increase the printing pressure between the rollers. The size, thickness and thickness of the cylinder liner, whether it is flat and correct, and the uniformity and smoothness of the liner are closely linked to the quality of the printed matter. In order to obtain a better printing pressure, it is required that the backing material (such as felt, worsted wool, backing paper, etc.) have certain hardness, smoothness and flatness.
The quality requirements of the cylinder liner
(1) In the offset printing process, the drums are generally in a state of high speed operation, and the drum liner is prone to telescopic deformation after being subjected to a large rolling pressure. Therefore, it is required that the drum liner paper fiber has good silkiness, strong tensile strength, small deformation amount, hard texture, and no decrease in pressure due to looseness.
(2) The cylinder liner is required to be flat, smooth, dense in structure, and uniform in thickness, and will not be thinned or stretched too much after being pressed, and will not cause uneven pressure due to the change in the thickness of the paper. Under the effect of greater pressure, no powder removal, lint-free, the smaller the deformation the better.
(3) Roller liners are required to have good flexibility and no wrinkles. Regardless of the degree of bending or pressure, they must not cause fan-shaped ripples or wrinkles, and they should always be flat and smooth.
(4) Roller liners must be capable of withstanding large pulling forces and will not tear, thin, or wrinkle under the effect of alternating tension.
(5) The cylinder liner must be even and flat. On the same facing liner, the thickness tolerance must not exceed 0.02 mm. If you exceed this range too much, the cumulative error will be relatively large, resulting in uneven pressure between the two rollers and poor print quality.
Clamp roller liner notes
(1) In addition to the excellent texture of the drum liner, it is also necessary for the operator to flatten it in the correct position. At the time of loading, two people should cooperate with each other and carefully lay down the liner underneath the printing plate without skewing or wrinkling. Otherwise, the quality of the printed matter will be seriously affected.
(2) Prevent small pieces of debris and paper scraps from falling into the liner, causing excessive local pressure on the roller, which aggravates the wear of the printing plate and reduces the resistance to printing.
(3) If the offset press is equipped with a paper clip, you can use it to clamp the liner; if not, use a small amount of a dilute adhesive to stick the rinsing and dragging position of the cylinder liner together. Skew.
(4) When the clamped or glued backing paper is wrapped on the surface of the drum body together with cushioning material (such as felt, worsted wool, rubber pad, etc.), the position of the backing material and the backing paper are required to be correct. The side is parallel to the shoulder iron; the backing paper is laid flat to prevent slipping of the backing paper (run paper) due to the tightness of the liner lining, resulting in uneven pressure in the mouthwash.
(5) The plate cylinder liner should be laid flat and must not be skewed. The plate should be clamped. After the plate position is determined, tighten the plate plate screw or hook screw. If the printing plate is not clamped tightly, a slippage or loosening of the platen will occur during printing, which also causes wrinkling of the liner, which not only aggravates the wear of the printing plate, but also reduces the service life of the printing plate and reduces the printing quality.
(6) At the time of loading, the pull plate should be moderate, not tight. Although the PS plate has a certain degree of bending strength and tensile strength, if the plate is too tight and the force is too large, the PS plate will be partially torn due to fatigue.
(7) The backing paper near the metal surface of the blanket cylinder should be thinner. The backing paper near the inner surface of the blanket should be thicker. If the pressure of the printing plate or blanket cylinder is too large or too small, slippage of the liner paper will occur. Therefore, it is preferable to provide a device for fixing the liner and liner in the cylinder to reduce slippage of the liner. The roll mouth is first impacted by rolling, and the backing paper is also most likely to be thinned or wrinkled. Therefore, the machine must be checked for a certain period of time before running. If the liner is wrinkled or deformed, it should be replaced in time.
(8) The specification of the cylinder liner is smaller than that of the blanket. The standard size of the blanket is 835mm x 995mm, and the width of the cylinder liner is 800mm x 980mm. This is conducive to tightness when the rubber cloth is clamped, which helps to improve the transfer quality of printing dots and graphics, and at the same time, it is conducive to the oil stain resistance of the rubber blanket and prolongs its service life.
Source: "Printing Technology"