Some printing defects caused by bad paper

First, printing wrinkles, overprinting and ghosting failures caused by uneven paper

The fibrous tissue of paper has a strong hygroscopicity and it is easy to change its moisture content with the change of the environment humidity and humidity. Then, once the moisture content of the paper increases, the fibrous tissue will exhibit elongation. Conversely, if the moisture content of the paper decreases, the fibrous tissue will shrink. Therefore, this is also the reason why paper has tight edges, curls, ruffles, and uneven paper. These paper deformations are the main cause of printing wrinkles, misprints, and ghosting failures. The daily production practice shows that if the moisture on the four sides of the paper is excessively dispersed and the middle part is larger than the water on the side, a tight edge will be formed. In the case of tight-edge printing, wrinkling is likely to occur in the middle of the printing area. The solution to this problem is to splash water around the stack of paper, increase the humidity of the environment, and allow the edges of the paper to dampen to restore flatness. If there are conditions, you can use hanging paper machine to hang paper, and splash water on the ground, so that better. Curl curling is due to the difference in water content between the front and back of the paper, which causes differences in the amount of water on the paper surface, causing curling on the side of the paper with low moisture content due to shrinkage. When the edge of the paper is curled, during the printing process, it is easy to cause wrinkling, misregistration, or ghosting failure because the paper is not fed or the paper edge is bent when the paper is bitten. Printing wrinkles and creases caused by curling of the paper edge generally have a large non-positive oblique shape, and the position of the wrinkle is not fixed. The way to eliminate it is to adjust the curled edge of the paper to make the edge of the paper straight and strong. Ruffles also tend to cause wrinkling, misprints, or ghosting problems. The most common problem is printing wrinkle failure. The appearance of the lotus leaf is the performance of the moisture absorption and elongation of the paper edge, making the straight edge of the paper edge longer than the middle part, so that the paper edge is loose and the middle is relatively flat. During printing, the wavy paper edge is impressed during the imprinting process. The phenomenon of wrinkling occurs due to pressing. Such wrinkles generally appear on the side of the paper, and the wrinkle is most likely to occur in the trailing parts of printed products. For the paper with flounced edges, the treatment method is: Hanging the paper on the paper to make the water content of the paper surface uniform and consistent with the wetness and humidity of the printing shop, so that the edge of the paper can be restored. degree. To maintain good flatness of the paper, attention should be paid to the control of the quality from the source of the check: First, to maintain the stability of the paper performance, the newly entered paper should not be put into use immediately, it is better to use after a period of time is better; second is to store The temperature and humidity of paper warehouses, paper cutting workshops and printing workshops must maintain corresponding balance conditions and cannot be stored in large disparities to prevent deformation. This is also an effective measure to reduce or avoid printing wrinkles, misprints, and ghosting failures.

Second, the paper plane caused by poor strength of the powder off, pulling and peeling (delamination) printing failure phenomenon

The surface strength of paper refers to the degree of bonding between the paper fiber structure, filler and rubber compound. If the papermaking process is not properly controlled, the surface strength of the paper is poor, and the phenomenon of powder dropping, pulling and peeling is likely to occur during the printing process. It even caused chain faults such as stacking, stacking, erasing, stencil printing, and reducing printing rate of printing plates. The main reasons for the generation of printed powder, napped and peeled paper are as follows: Ink on the blanket touches the surface of the paper. During the imprinting process, the paper surface has a sticky force and a peeling force, and this force increases with the printing speed. . Therefore, when the surface strength of the paper is not good, the faster the printing speed is, the more the paper is powdered off. After the fact that the surface strength of the paper is not sufficient, the emergency remedial measures at the production site can only be achieved through the adjustment and control of the printing operation technology, so as to reduce or eliminate the phenomenon of powder failure, dusting, and peeling. The main process measures are: First, reduce the printing speed, reduce the sticking force and peeling force when printing; Second, reduce the printing pressure, reduce the impact force and peeling force on the paper surface; The third is the appropriateness of the ink viscosity. Adjustment, to add some ink remover or transfer ink to the ink to reduce the viscosity of the ink; Fourth, to minimize the amount of fountain solution on behalf of the printing, to avoid the "water and large ink viscosity is also large," the bad Effect; Fifth, check whether there is aging sticky phenomenon on the rubber cloth, if there is some shape, it should be coated with a layer of sulfur powder on the surface of the blanket; if this method is invalid, it should be replaced with a new blanket; six is ​​through the use of paper machine hanging Dry paper, through the machine rotation and the role of blowing, some paper pieces of paper can be scattered down; seven is the air imprinting once, so that the paper flour flakes off; eight is the paper surface strength of the paper, adjust the paper For printing less ink absorption layout, to ensure product printing quality.

Third, the paper surface caused by the acidic quality of the printing quality failure phenomenon

The paper used for printing generally requires neutrality, but due to the discomfort of the papermaking process, such as the presence of acidic substances in the slurry during sizing, the paper is somewhat acidic. The acidic paper will act as an oxygen conjunctiva with the ink layer, causing the slow-drying reaction of the ink layer. If the printing ink layer is slow-drying, on the one hand, it is easy to print on the bottom, and on the other hand, it is difficult to realize normal overprinting and overprinting. The printing layout is also likely to be dirty, affecting product quality and reducing production efficiency. Acidic papers, whose properties are constant, cannot be corrected at one time. Only through the adjustment of printing technology measures can better avoid the occurrence of printing quality problems. The main process measures are: First, adjust the drying performance of the ink, add some desiccant to the ink or use the fast-drying ink for printing; second, use the “deep ink thin printing” process to print, that is, the hue of the ink is properly adjusted. Deeper, making the printing ink layer thinner, which is not only conducive to the rapid drying of the printing ink layer, reducing the chances of the occurrence of printing dirty, but also to meet the quality requirements of the print hue, which is the printing industry more commonly used technology and technical measures , can receive better results.

Fourth, poor paper smoothness caused by the phenomenon of printing quality failure

Smoothness refers to the degree of smoothness of the surface of the paper. It is also an indicator of the degree of unevenness on the surface of the paper. The smoothness of the paper depends on the density of the fine fibers, the filler, the size, and the quality of the surface sizing. When paper with poor smoothness is printed, it can easily cause problems such as ink coloring, poor gradation of the layout pattern, large amount of ink sucked, slow drying of the print, and rapid wear of the printing plate. Paper smoothness is also a constant property and print operators cannot change their inherent properties. Therefore, for the paper with poor smoothness, the quality of the product can be improved only by controlling the technical measures during printing. The first is to increase the printing pressure appropriately to make up for the ink coloration caused by bad contact when the rough surface of the paper is imprinted; the second is to use the “light ink thick printing” process for printing, such as printing plate products due to the large amount of ink absorption, easy Ink darker conditions, which can be appropriate to deepen the hue of the ink, so that increased printing ink, can meet the printing hue requirements, but also make the printing layout saturated ink, printing quality and good results.



Source: Life Forum