1. Printing wrinkles, inaccurate overprinting and ghosting caused by uneven paper surface
The fibrous structure of the paper has strong hygroscopicity, and it is easy to change its water content with the change of environmental humidity and humidity. Then, once the moisture content of the paper increases, the fibrous structure will be elongated; on the contrary, when the moisture 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 uneven paper. These deformations of the paper are the main reasons for printing wrinkles, inaccurate overprinting and ghosting failures. The daily production practice shows that if the moisture on the four sides of the paper is too dispersed and the middle part is larger than the moisture on the sides, a tight edge situation will be formed. Wrinkles are likely to occur in the middle of the paper when printing on tight edges. The solution to this is to splash water on the ground around the stack of paper and increase the environmental humidity to allow the paper edge to wet to restore the flatness. If conditions permit, you can use a paper dryer to hang the paper and pour water on the ground, which works better. The curl of the paper edge is due to the difference in the water content of the front and back sides of the paper, which causes the difference in the water content of the paper surface, so that the side with the low water content of the paper surface curls due to shrinkage. When the edge of the paper is curled, it is easy to cause wrinkling of the printing, inaccurate overprinting or ghosting problems due to the inadequate paper feeding and the corners of the paper edge when biting the paper. Printing wrinkles caused by curling of the paper edge generally have a large irregular shape, and the position of the wrinkles is not fixed. The method to eliminate is to adjust the curled edge of the paper to make it straight and firm. Ruffles are also susceptible to printing wrinkles, inaccurate overprinting, or ghosting failures. The most common problem is printing wrinkling failures. The generation of ruffles is a manifestation of the hygroscopic elongation of the paper edge, making the linear size of the paper edge longer than the middle part, so that the national paper is slack and the middle is smoother. During printing, the wavy paper edge is squeezed during the imprinting process Wrinkle phenomenon occurs when pressed, and this kind of wrinkle generally appears on the side of the paper, especially the trailing part of the printed product is most prone to wrinkle phenomenon. For paper with ruffled edges, the processing method is: hang and dry the paper to make the moisture content of the paper surface uniform and uniform, and maintain relative balance with the humidity and humidity of the printing workshop, so that the paper edge restores its proper levelness degree. To maintain the good flatness of the paper, we should pay attention to the control from the quality source: first, to maintain the stability of the paper performance, the paper that has just been fed should not be used immediately, it is best to rotate it for a period of time, and the effect is better; The temperature and humidity of the paper warehouse, paper cutting workshop and printing workshop must be kept in a correspondingly balanced condition and cannot be stored in a large disparity to prevent deformation. This is also an effective measure to reduce or avoid the occurrence of printing wrinkles, overprinting inaccuracy and ghosting failures.
2. Phenomenon of dusting, fluffing and peeling (delamination) printing caused by poor plane strength of paper
The surface strength of the paper refers to the degree of bonding between the fiber structure of the paper, filler and rubber. If the papermaking process is not properly controlled, the surface strength of the paper is poor, and it is prone to dusting, pulling and peeling during the printing process. It may even cause chain quality failures such as stacking, rubber stacking, paste, pattern, and reducing the printing resistance of the printing plate. The main reasons for the paper printing powder, brushing and peeling are: the ink on the blanket is in contact with the paper surface during the imprinting process, which causes sticking and pulling force and peeling force on the surface of the paper, and this force increases as the printing speed increases . Therefore, when the surface strength of the paper is not good, the faster the printing speed, the worse the paper surface will fall off. After the poor surface strength of the paper becomes a fact, the emergency remedy method at the production site can only reduce or eliminate the phenomenon of powder, brushing and peeling printing through technical adjustment and control of the printing operation process. The main technical measures are as follows: one is to appropriately reduce the printing speed and reduce the sticking force and peeling force during imprinting; the other is to appropriately reduce the printing pressure and reduce the impact and peeling force on the paper surface; the third is to properly adjust the viscosity of the ink Adjustment, add some debonding agent or ink to the ink to reduce the viscosity of the ink; the fourth is to use the smallest amount of fountain solution to print, to avoid the disadvantages of "big ink and big viscosity" Effect; Fifth, check if there is aging and sticky phenomenon on the rubber cloth. If there are some shapes, a layer of sulfur powder should be coated on the surface of the rubber cloth. If this method is invalid, a new rubber cloth should be replaced; To dry the paper, some paper scraps can be scattered through the rotation of the machine and the effect of air blowing; Seventh, the paper is embossed once to make the paper flour fall off; Eighth, the paper with poor surface strength is used for adjustment It is used to print the layout with less ink absorption to ensure the printing quality of the product.
3. The printing quality failure phenomenon caused by the acidity of the paper surface
Paper for printing generally requires neutrality, but due to poor control of the papermaking process, such as the presence of acidic substances in the slurry during sizing, the paper becomes acidic. The acidic paper will play a role of conjunct with the oxygen layer of the ink layer, causing the adverse reaction of the ink layer of the printed product drying slowly. If the printing ink layer dries slowly, on the one hand, it is easy to print over the bottom phenomenon, on the other hand, it is difficult to achieve normal overprinting and overprinting, and the printed board surface is also easy to be dirty, affecting product quality and reducing production efficiency. The properties of acid paper are constant and cannot be corrected for a while. Only by adjusting the printing process technical measures can we better avoid the occurrence of printing quality failures. The main process measures are: First, adjust the drying performance of the ink, add some desiccant in the ink or use quick-drying ink for printing; Second, use the "deep ink thin printing" process for printing, that is, adjust the hue of the ink appropriately Deeper, make the printing ink layer correspondingly thinner, which is not only conducive to the rapid drying of the printing ink layer, reducing the chance of printing stickiness, but also making the hue of the printed product meet the quality requirements. This is a technical measure commonly adopted in the printing industry. , You can get better results.
Fourth, poor paper smoothness caused by printing quality failure phenomenon
Smoothness refers to the degree of smoothness of the paper surface, it is also an indicator to measure the degree of unevenness of the paper surface. The smoothness of the paper depends on the density of fine fibers, fillers, rubber compounds and the quality of the surface sizing. When paper with poor smoothness is printed, it is easy to cause unfavorable phenomena such as ink color blooming, poor gradation of the layout pattern, large ink absorption, slow imprint drying speed, and fast plate wear. Paper smoothness is also a constant property, and the printing operator cannot change its inherent properties. Therefore, for the paper with poor smoothness, only through the control of the operation process measures during printing, to improve the printing quality of the product. One is to appropriately increase the printing pressure to make up for the ink color blooming caused by poor contact during rough paper imprinting; 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, it is easy The ink color is darker. In this case, the ink hue can be adjusted appropriately. In this way, after the printing ink is increased, it can not only meet the printing hue requirements, but also saturate the ink color of the printing plate, and the printing quality is good.
In summary, as the basic condition of printing, paper has a decisive influence on product printing. Therefore, to correctly understand the nature of paper and its relationship with the printing process, control and adjust through the control of printing process technology Not only can better prevent and avoid the occurrence of printing quality failures of one kind or another, but also can effectively improve product efficiency.
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