Offset pad knowledge

Jinjia boasts of the Heidelberg CD-102 fleet. The advanced machines and superb personal technology make Jinjia Offset one of the leaders in offset printing in the domestic cigarette industry for a long time. In the recently produced Jin Mingpin "Tian Xia Xiu" hard pack box, my offset printing machine No. 2 was adjusted to meet the requirements of the new process, and the parameters of the machine's liner and blanket lining were adjusted to meet the requirements of the new process. Through the study of the theoretical knowledge of the school and the operating time of the machine, we have gradually found out that the selection of offset pad has deep knowledge. Here we only briefly introduce some relevant knowledge and hope to get more guidance and correction.

Packing lining

Offset printing plate cylinder and blanket cylinder (rubber roller) surface lining, blanket cylinder roller lining generally can be divided into the following three categories:

1. Hard liner

Generally, a few sheets of paper under the blanket constitute a hard lining. This kind of lining is relatively hard, the elastic modulus of the lining is large, and a small amount of deformation can produce a great printing pressure. Therefore, the use of this type of lining reduces the amount of compression of the lining, that is, the deformation of the lining is small, and the dot enlargement and deformation are also small. Therefore, the hard lining is better for the transmission of the dots, thereby facilitating the reproduction of the color and the gradation. Printed textured prints. However, special attention should be paid when using such a lining. The lining compression should be controlled within 0.2mm, preferably around 0.1mm. If the compression of the lining is too large, it will not only be detrimental to the machine, but will also cause other failures, and it will also be bad for the transmission of the dots, losing the advantage of using a hard lining. Therefore, the use of rigid lining requires high precision of the machine and accurate printing pressure adjustment. Otherwise, it will not only reflect the advantages of rigid lining, but will also bring about new shortcomings. In other words, the rigid bag is lined with its unique conditions of use and applications and cannot be used anywhere.

2. Soft liner

The soft lining is generally under the blanket and it is added with several thin papers. The software lining is just opposite to the hardware lining. Its elastic modulus is small, and the lining compression required to produce the same printing pressure is relatively large. Generally, the compression amount is controlled between 0.2mm and 0.3mm. The soft lining has less transmission to the dots, but the contact area is wider when the soft lining is imprinted, and the contact is relatively good. The ink is relatively full and full, especially when it is printed in real products. It is suitable for printing text, color blocks, field prints. In addition, the soft lining cushioning ability, the blanket is not easy to crush, and the machine accuracy and printing pressure adjustment accuracy requirements are relatively low, so the soft lining is suitable for use on the old machine or the new machine with low precision .

3. Neutral liner

Neutral lining is generally composed of rubber blanket under the blanket, its elastic modulus is centered, so its performance is also in the middle, and its use occasion is also in the machine between the new and old machines alternately stage, can also be used on new and old machines, This kind of lining is more general, and the performance is also OK. At present, the company's offset pad has been in such standards according to the requirements of products and raw materials: the substrate is usually 0.36mm ~ 0.45mm (according to the characteristics of the process and the blanket: red UV blanket and black air cushion UV blanket performance and requirements are different ), According to different product processes to make adjustments to meet the requirements.

At present, Jinjia's CD-102 cluster in Heidelberg is generally around three liners. This not only satisfies the shrinkage and deformation of the liner, but also ensures that the three liners guarantee the various points of the blanket. The same thickness, but also play a role in shock absorption and pressure buffer.

Lining and overprinting relationship

Roller lining has a significant impact on product overprinting, mainly in the following aspects

1. Roller lining and the relationship between print length

The three rollers per color group of the offset press are equal angular speed rotations. Under the same rotation angle, the arc length crossed by each roller surface is proportional to its free radius. The free radius of the blanket cylinder is independent of the length of the print graphic, that is, the change of the blanket cylinder package. The lining has no effect on the print length of the printed sheet (but in the recent production, the golden text changed in the liner box lining during the change of the liner box. The reason was that the liner speed was added after the plate was changed and the angular velocity was changed. As a result of the invariability), the print length of the printed matter is only related to the free radii of the plate cylinder and the impression cylinder.

The amount of change in the circumferential length of the printing product graphic is increased or decreased by the increase or decrease of the radius of the plate cylinder liner or the impression cylinder:
ΔL/ΔR=Lp/Rp
ΔL The length of print image length change, ΔR is the drum radius change, ie ΔR = R before -R, Lp is the length of the graphic on the plate (the normal size of the film on the film), Rp is the printing plate Roller free radius. When the ΔL is negative, the length of the picture decreases, and when the ΔL is positive, the length of the picture increases. That is to say, when the lining of the printing plate is increased or the radius of the printing roller is reduced, the length of the printed picture will be reduced, otherwise it is the opposite.

2. The relationship between multicolor printing and pressure

The rolling radius of the rubber roller is changed. When the platen pressure and pressure are increased or decreased at the same time, the rubber liner lining is increased or decreased, and the length of the printed image will not be changed. If only the platen pressure is increased without changing the printing pressure, this is equivalent to increasing the printing pressure. The lining of the printing plate will shorten the graphic of the printing product; if only the imprinting is increased without changing the printing plate pressure, this is equivalent to increasing the radius of the printing roller, and the printing product graphic will grow, otherwise the contrary. The amount of change can also be obtained from the previous formula, where ΔR is calculated by replacing Δλ.

3. The relationship between lining and overprinting in monochrome machine printing

Assume in advance that there is no change in the size of the paper, the offset press bite the paper correctly, and the paper is positioned accurately. According to the above discussion, as long as the monochrome machine does not change the drum parameters (mainly refers to the printing plate lining), the length of the text after printing is always the same, so the overprinting will completely overlap. From this perspective, the monochrome machine is more than the multi-color machine cover. Qualification is better.

4. The relationship between lining and overprinting in multicolor printing

In the same way, it is assumed in advance that the paper is not dimensionally deformed, and the offset press bite the paper accurately. According to the analysis of the length of the lining and the text, it can be seen that the latter color must be completely coincided with the previous color, which inevitably requires that the latter color of the impression cylinder, plate cylinder, and its lining should be exactly the same as the previous color. For the pre-color group replica, but in fact the machine can not be completely consistent in the color group, there will always be a little error, so multi-color machine registration is not as good as a monochrome machine, but as long as the manufacturing accuracy of the given requirements Registering is not a problem. If the cylinder is corroded, worn, crushed, or the processing accuracy of the roller itself is low, the difference between the rollers is large, and it is no longer possible to register the various colors. Therefore, the plate cylinders, the impression cylinders and the linings of the multicolor machines are consistent. Sex is particularly important, and special attention should be paid to the protection and maintenance of the impression cylinder.

Author/Wu Wei