Expert analysis of paper printing problem

Print off the powder. In printing, due to the external force, the paper surface coating, fibers or dust are pulled up by the blanket, or the impurities in the ink path are transferred to the blanket, resulting in that the local graphics and text cannot be properly transferred to the paper, which seriously affects the quality of the finished product. A printing phenomenon.

In offset printing, printing out of powder is one of several quality issues that can easily occur. It has caused major problems for printing plants and paper mills. For this reason, printing plants and paper mills have to avoid falling powder. A lot of work, but it can not be completely eliminated from the paper and printing.

How to deal with if powder falls? From the point of view of the paper mill, we have taken many measures in the production process to avoid the occurrence of powder falling, such as improving the surface strength of the paper and increasing the rewinder dust collection device. Improve the frequency of cutter replacement, and achieved better results.

In terms of printing plants, for paper that has fallen out of powder, how do we adjust the printing process and conditions to reduce and avoid the problem of powder dropping? Through our experience in dealing with guest complaints for many years and the results of communicating with customers, Aiming at the problem of powder falling in different states, we made a summary of how to take remedial measures from the printing process after the cause and the occurrence of powder failure. We hope that we can share it with the printing factory. Please correct me.

First define two nouns: the original point and the transfer point (as shown in Figure 1). The original point is the first spot on the printed sheet where the powder falling problem occurred, and there is no ink in the middle. The transfer point, which is the spot generated on the subsequent print, has an irregular ring shape with ink in the middle.

Figure 1

Catheter section

The catheter section is a non-fibrous material that cannot be completely removed from the pulp. It is relatively brittle, hard, and has a relatively small binding force with the fibers and the paint. When exposed to external forces, it is relatively easy to be pulled up. His appearance is more regular, irregular rectangular or square (as shown in Figure 2), about 1mm in size.

Figure II

In the printing, if you find that the printout is in the form of a catheter section, the following methods may be taken and may be improved:

● reduce the corresponding ink viscosity;
● Reduce the printing speed;
● increase the cleaning blanket frequency;
● Replace the new blanket;
● Reduce the printing pressure of the pink sequence, increase the printing pressure of the previous color sequence;
● First print the base paper with varnish, stick the catheter section, and then print normally.

2. Powder removal

Destaining is due to the coating between the surface of the paper. The binding force between the coating and the fiber is insufficient, and a powder off phenomenon occurs when the coating is pulled up during printing. Its state is irregular (as shown in Figure 3).

Figure 3

The reasons for this type of powder dropping may be related to the lack of surface strength in terms of paper; from the printing point of view, it may be related to factors such as excessive ink viscosity, excessive printing pressure, and excessive printing speed.

The phenomenon of powder falling, such as de-dusting, can be taken as the above-mentioned method of handling off-powder of the catheter section type, and may be improved to some extent.

3. Paper powder

If paper paper powder adheres to the surface of the paper, it adheres to the blanket when printed, which may cause the graphic part to not be properly transferred to the surface of the paper and form spots. The shape of the paper is irregular fibrous (Figure 4).

Figure 4

The reason for the generation of paper powder is mainly due to the fact that the cutting knife is relatively blunt. When cutting, it is not the fact that the fiber is cut but it is pulled off. At the same time, part of the fiber is pulled out onto the paper. Under normal circumstances, this type of powder drop appears on the four sides of the printed matter, and the dragging part is the most serious. To determine if there is any paper powder on the paper, use a dry black cloth to wipe the surface of the paper and see if there is a white powder on it. If yes, it means that there is paper powder on the paper, and vice versa.

It was found that there was paper paper powder on the paper, which could be printed on the monochrome machine first, sticking the paper paper powder off, and then printing normally, which would greatly improve. If the printing company cuts itself, it is necessary to shorten the grinding cycle and avoid the generation of paper powder.

4. Mexican skin

If the ink dries the skin. Foreign matter in the ink or the water system is contaminated to produce foreign matter. Adhesion to the printing plate or blanket during the printing process can also cause spots on the print. On this type of powdered print, no original point was found, and the paper coating was not damaged. The spots were all transfer point shapes. For this type of powder dropping, the ink path and water path must be thoroughly cleaned, including the ink tank sink and the transfer roller group of the transfer roller group. Plates and blankets, then replace the new ink and fountain solution.

For the above types of powder, if you can not accurately determine which type belongs to the spot pattern on the print, you can also use the transparent tape to stick the foreign material on the blanket and observe the shape and composition under the microscope. Confirm the specific reasons, and take corresponding countermeasures to reduce the occurrence of powder falling problems and minimize the loss for different types. (Author: Gold East Paper)