Several printing failures caused by poor paper quality and their elimination methods
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Paper is the main printing material for printing, and its characteristics have a great influence on printing. The experience of production junior high school shows that the probability of paper failure is high, and the production efficiency and product quality must also have a bad influence. Therefore, it is of great significance to correctly understand and understand the printing failure caused by poor paper quality.
First, Printing wrinkles, overprinting defects and ghosting failure caused by uneven paper surface
The fibrous structure of the paper has strong hygroscopicity, and it is easy to change the water content as the environment wet and humidity changes. Then, once the water content of the paper increases, the fiber structure will appear to be elongated; on the contrary, if the water content of the paper decreases, the fibrous structure will shrink. Therefore, this is also the reason why the paper has tight edges, curls, ruffles, and unevenness of the paper. These deformations of the paper are the main cause of print wrinkles, misregistration, and ghosting failures. The daily production practice shows that if the water on the four sides of the paper is too scattered and the middle part is larger than the side water, a tight edge will be formed. When the paper is printed on the tight side, the middle part is prone to wrinkle. The solution is to splash water on the ground around the stacking paper to increase the humidity of the paper to make the paper edge wet to restore the flatness. If you have the conditions, you can use the paper machine to hang the paper and pour water on the ground, which is better. The curling of the paper edge is caused by the difference in water content between the front and back sides of the paper, so that the water content of the paper surface is different, and the side with a low water content on the paper surface is curled due to shrinkage. When the paper edge is curled, during the printing process, it is easy to cause the printing wrinkles, overprinting, or ghosting problems due to the paper feeding being out of position and the paper edge being folded when the paper is bitten. Printing wrinkles caused by curling of the paper generally have a large irregular shape, and the position of the wrinkles is not fixed. The way to eliminate it is to tune the curled paper edge to make the paper edge straight and firm. The ruffles are also prone to print wrinkles, overprinting, or ghosting failures, most commonly printing wrinkles. The generation of the ruffled edge is the expression of the moisture absorption elongation of the paper edge, so that the linear dimension of the paper edge is longer than that of the middle portion, so that the paper edge is relaxed and the middle is relatively flat, and the embossed paper edge is pressed during printing. Wrinkles appear when pressed, and such wrinkles generally appear on the side of the paper, especially the tip of the printed product is most likely to wrinkle. For the paper with the ruffled edge, the treatment method is: hang the paper to make the water content of the paper surface uniform, and maintain the balance with the wetness and humidity of the printing workshop, so that the paper edge can be restored to the leveling degree. To maintain a good flatness of the paper, attention should be paid to the control of the quality from the source: First, to maintain the stability of the paper performance, the paper that has just entered should not be put into use immediately. It is better to use it after a period of rotation. The second is to store The temperature and humidity of the paper warehouse and paper-cutting workshop and the printing workshop should be balanced and should not be stored in a large disparity to prevent deformation. This is also an effective measure to reduce or avoid the possibility of printing wrinkles, misregistration and ghosting failures.
Second, the paper's plane strength difference caused by the phenomenon of powder drop, napping and peeling (delamination) printing failure
The surface strength of paper refers to the degree of bonding between the fibrous structure of the paper, the filler and the rubber. If the papermaking process is improperly controlled, the surface strength of the paper is poor, and the phenomenon of powder falling, pulling and peeling is likely to occur during the printing process. It even caused chain quality failures such as stacking, stacking, paste, and plate printing, as well as reducing the printing durability of the printing plate. The main reason for the paper to produce powder, lint and peeling is as follows: the ink on the blanket is in contact with the paper surface, and the adhesive force and peeling force are generated on the surface of the paper, and the force increases with the printing speed. . Therefore, when the surface strength of the paper is not good, the faster the printing speed, the more the paper is dropped, and the like. After the surface strength of the paper is different, the emergency remedy at the production site can only reduce or eliminate the phenomenon of powder, napping and peeling printing by adjusting and controlling the printing process technology. The main technical measures are as follows: First, the printing speed is appropriately reduced, and the adhesive force and peeling force at the time of imprinting are reduced; secondly, the printing pressure is appropriately reduced, the impact force and the peeling force on the paper surface are reduced; and the third is appropriate for the viscosity of the ink. Adjustment, add some debonding agent or varnish to the ink to reduce the viscosity of the ink; Fourth, print with the smallest amount of dampening solution, avoiding the "great large ink and large viscosity" The fifth is to check whether there is aging and sticky phenomenon on the rubber cloth. If there is some shape, a layer of sulfur powder should be applied on the surface of the blanket. If the method is invalid, the new blanket should be replaced. The sixth is to use a paper machine to hang. Drying the paper, through the machine rotation and blowing, can make some paper scraps on the paper surface; seventh, the paper is embossed once, so that the paper flour is off; eight is the paper with poor surface strength, adjustment In the printing of a small amount of ink, the quality of the product is guaranteed.
Third, the paper quality is caused by the acidity of the paper surface
Paper 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 acidic. The acidic paper will act as the oxygen conjunctiva of the ink layer, causing the ink layer to dry slowly. If the printing ink layer is slow to dry, on the one hand, it is easy to imprint the bottom phenomenon, on the other hand, it is difficult to achieve normal overprinting and overprinting, and the printed product layout is also easily stained, affecting product quality and reducing production efficiency. Paper that is acidic, its properties are constant and cannot be corrected at one time. Only through the adjustment of the printing process technology measures can the printing quality failure be better avoided. The main technical measures are as follows: First, adjust the drying performance of the ink, add some desiccant in the ink or use fast-drying ink for printing; second, use the "deep ink thin printing" process for printing, that is, the ink hue is properly adjusted. Deeper, the printing ink layer is correspondingly thinner, which is beneficial to the rapid drying of the printing ink layer, reducing the chance of printing and viscous, and making the color of the printing product meet the quality requirements. This is a common technical measure adopted by the printing industry. , can receive better results.
Fourth, poor paper smoothness caused by printing quality failure phenomenon
Smoothness is the degree to which the surface of the paper is smooth. It is also an indicator of the degree of unevenness on the surface of the paper. The smoothness of the paper depends on the fine fiber, the filler, the density of the compound and the quality of the surface sizing. When the paper with poor smoothness is printed, it is easy to cause ink color, poor texture of the layout, large amount of ink absorption, slow drying speed of the print, and fast wear of the printing plate. Paper smoothness is also a constant property that print operators cannot change their inherent properties. Therefore, for papers with poor smoothness, the printing quality can be improved only by controlling the process measures during printing. First, the printing pressure is appropriately increased to compensate for the ink coloration caused by poor contact when the paper is rough embossed; the second is to use the "light ink thick printing" process for printing, such as printing plate products, because of the large amount of ink absorption, easy The ink color is deeper, and the hue of the ink can be appropriately adjusted to a certain degree, so that the amount of printing ink is increased, which can meet the requirements of the printing hue, and the ink color of the printing plate is saturated, and the printing quality is good.
In summary, as the basic condition of printing, paper plays an important role in the printing of the product. Therefore, the correct understanding of the nature of the paper and its relationship with the printing process, through the control and adjustment of the printing process technology Not only can the prevention and avoidance of printing quality failures be prevented and avoided, but also the product efficiency can be effectively improved.