Expert analysis on the problem of powder loss in t

Expert analysis on the problem of paper printing powder loss

printing powder loss. In printing, due to external force, the coating, fiber or dust on the paper surface is pulled up by the blanket, or the impurities in the ink path are transferred to the blanket, resulting in local graphics and text can not be transferred to the paper normally, which seriously affects the quality of finished products. In offset printing, the loss of printing powder is one of the several quality problems that are easy to appear, which has caused great trouble to the printing and paper mills. Therefore, the printing and paper mills have made a lot of efforts in how to avoid the occurrence of loss of powder, but it cannot be completely eliminated from the aspects of paper and printing

how to deal with powder loss? From the perspective of the paper mill, we have taken many measures in the production process to avoid the occurrence of powder dropping, such as improving the surface strength of the paper and increasing the dust suction device of the rewinder. Improve the frequency of cutter replacement, and achieve better results

from the perspective of printing plants, how to adjust the printing process and conditions to reduce and avoid the occurrence of the problem of falling powder for the paper that has fallen powder? Through our years of experience in dealing with customer complaints and the results of communication with customers, we have summarized the causes of powder loss in different states and how to take remedial measures from the printing process after powder loss, hoping to share with the printing factory. Please correct the mistakes

first define two nouns: original point and transfer point (as shown in Figure 1). The original point is the spot on the first printing sheet with powder falling problem, in which there is no ink; The transfer point is the spot produced on the subsequent printed matter. Its shape is an irregular ring with ink in the middle

Figure 1

1 Conduit joint

conduit joint is a non fibrous material that cannot be completely removed from the pulp. It is relatively brittle and hard, and has relatively small binding force with fibers and coatings. It is relatively easy to be pulled out when subjected to external forces. His appearance is regular, irregular rectangle or square (as shown in Figure 2), and the size is about 1mm

Figure 2

during printing, if it is found that the powder falling on the printed matter belongs to the duct joint, the following methods can be taken, which may be improved:

● reduce the viscosity of the corresponding ink

● reduce the printing speed

● increase the frequency of cleaning blanket

● replace with a new blanket

● reduce the printing pressure of the pink sequence and increase the printing pressure of the front color sequence

● first print the base paper with varnish, stick off the catheter joint, and then print normally

2. Degumming

degumming is due to the coating on the paper surface. The adhesion between the coating and the fiber is insufficient, and the coating is pulled out in printing, which is a kind of powder dropping phenomenon. Its state is irregular (as shown in Figure 3)

Figure 3

the cause of this kind of powder loss may be closely related to the insufficient surface strength from the perspective of paper; From the perspective of printing, it may be related to factors such as excessive ink viscosity, excessive printing pressure, and too fast printing speed

in case of powder falling such as powder falling, the method of handling the powder falling of duct joint type as above can be adopted, which may be improved to a certain extent

3. Paper wool paper powder

if paper wool paper powder is attached to the surface of the paper and adheres to the blanket during printing, it will also cause the graphic part to not be transferred to the surface of the paper normally, forming spots, whose shape is irregular fibrous (as shown in Figure 4)

Figure 4

the main reason for the production of paper wool and paper powder is that the cutting knife is relatively blunt. When cutting, it does not cut the fibers but pull them apart, and at the same time, part of the fibers are pulled out and fall on the paper. In general, this kind of powder dropping mostly occurs on the four sides of the printed matter, and the dragging part is the most serious. To judge whether there is paper wool paper powder on the paper, you can use a dry black rag to wipe it on the surface of the paper, and then see whether there is white powder on it. If there is, it indicates that there is paper wool paper powder on the paper, and vice versa

it is found that there is paper wool bow ring fixed on the lower paper powder of the middle beam. You can print it over the monochrome machine first, stick the paper wool paper powder off, and then print it normally, which will be greatly improved, "Galen said. If the printing factory cuts by itself, we must shorten the sharpening cycle to avoid the production of paper wool and paper powder

4. Ink sheet

if the ink dries and the receiving capacity is redundant, transfer the capacity sheet. There are foreign matters in the ink or the water system is polluted to produce foreign matters, which will adhere to the printing plate or blanket during the printing process, and will also cause spots on the printed matter. On this kind of powdered printed matter, the original point cannot be found, the paper coating has not been damaged, and the spots are in the shape of transfer points. For this kind of powder dropping, the ink path and water path must be thoroughly cleaned first, including the ink tank, ink transfer roller group, and water transfer roller group. Plate and blanket, and then replace with new ink and fountain solution

for the above types of powder falling, if you can't accurately judge which type it belongs to according to the pattern of spots on the print, you can also use transparent tape to stick down the foreign matters on the blanket, observe and analyze their shape and composition under the microscope to confirm the specific causes. For different types, they are divided into soft and rigid PVC types, and take corresponding countermeasures to reduce the occurrence of powder falling and minimize the loss. (author: Jindong paper)