Offset rubber blanket analysis (2)

Since the current version of offset printing is generally a plano-convex PS version, the text portion is slightly higher than the blank portion. When the ink is transferred from the blanket cylinder to the paper surface, the roughness of the surface of the paper is greater than the roughness of the PS plate (of course, different papers are different, and the offset paper has greater roughness than the coated paper), and it is a plane contact, so The ink is less deformed when pressed.

(Figure 2.4)

At the time of printing, L=(Li-Lib)-(Lbp-Lp)=0 is theoretically required. To make this formula necessary to have Li-Lib = Lbp-Lp, the pressure between the plate cylinder and the blanket cylinder must be made smaller than the pressure between the impression cylinder and the blanket cylinder. It is relatively easy to control the deformation of the rough plane ink compared to the smooth plane. In all possible situations, try to increase the roughness of the contact surface. If you change the Plano-Foster to Plano, it may be better from this point of view.

2.3.2 Selection of Lining

The choice of lining should be considered in terms of machine accuracy and print quality. In terms of the precision of the machine, the greater the compressibility of the lining, the better, because the ability to compensate for machining and installation errors will be stronger; from the standpoint of the quality of the printed product, the smaller the amount of compression of the lining, the better. The smaller the contact surface, the closer it is to pure scrolling, ie the smaller the deformation of the print. From the perspective of machine accuracy, under the premise of satisfying the quality of printed products, try to use the largest compression lining; from the perspective of the quality of printed products, under the premise of meeting the accuracy of the machine, try to use the smallest compression lining, but always It should be based on the accuracy of the machine, which must be kept firmly in mind.

The lining is usually composed of two parts: the liner and the blanket. The function of the lining is actually the combined effect of the liner and the blanket.

Liners are generally classified into three categories: soft liners, neutral liners, and rigid liners. The soft liner is mainly made of woolen cloth, which has the strongest ability to make up for the precision error of the machine, but the deformation of the print is the largest. As the precision of random machines continues to increase, such gaskets have become obsolete. The neutral liner is mainly made of tape. The compressibility of the liner is worse than that of the soft liner, but the deformation of the print is small, so the current use is still more. Hard liners are based on special offset paper. This type of pad compensates for the machine's accuracy error, but it has a clear print. Therefore, as the accuracy of the machine is further improved, the amount of hard liners will also increase.

Blanket is generally divided into two categories: elastic blankets and air-cushion blankets. The elastic blanket is easily deformed when it is subjected to force, but it cannot be compressed and it cannot compensate for machine accuracy errors. Air-cushion blankets can be compressed and easily deformed, which can compensate for machine accuracy errors to some extent. When the pressure is increased, the contact area increases less than the elastic blanket, so a larger printing pressure can be used to make the print more clear and strong. The function of the lining is manifested by the deformation of the lining, and there is no deformation, and its function does not exist. Therefore, the key is how to create the conditions for the deformation, and at the same time, it can be used to make up for the machine error and ensure the printing product. The purpose of quality. Thus, the blanket and liner or both have compressible and deformable; either one of them has; or one has a deformation and one has a compressibility. In one word, the two can compensate each other and create the conditions for the existence of deformation and compressibility. From this principle, the matching of blankets and pads can be as follows:

1 elastic blanket + soft pad;
2 elastic blanket + neutral liner;
3 air-cushion blanket + neutral liner;
4 air cushion blanket + hard liner.

The other two are not permitted in use. The reasons are:

1 The lining formed by the elastic blanket + hard liner only has the ability to deform, but does not have compressibility, and can not make up for the accuracy error of the machine.
2 The cushion lining formed by the air-cushion blanket + soft cushion is too large to be deformed and compressible, and does not reflect the complementarity between the two sides. Moreover, the air-cushion blanket is more expensive, so it does not make any sense to do so.