Correctly Handling Quality Problems in Carton Preprinting (I)

Generally small and medium-sized packaging, such as beer, beverages, fruit and other food cartons, more and more products using white paper for color printing. The preprinting process of the carton is much better than the quality of printing directly with corrugated cardboard. However, as with other printing processes, it is also not possible to print various cartons or cartons and paper bag products with an offset or letterpress printer. Avoid some quality problems. Therefore, correct understanding and understanding of several fault phenomena in the printing process, and good printing operations and process technology, in order to better improve production efficiency and product quality.

First, the printing pressure is not caused by the problem of ink bars: When the roller bearings are heavily worn, due to excessive roller yield, the roller surface friction caused by the emergence of ink marks, this is a situation; The situation is that due to the use of a hard lining, the ink stick is caused by the sliding phenomenon during the imprinting process. In the third case, the roller gear wears badly, and the center distance of the drum is too large, so that the backlash of the gear is too large, so that the roller After pressing, the gears vibrate and the sliding friction occurs on the surface of the drum to cause ink bars. In the fourth situation, the pressure between the plate cylinder and the blanket cylinder is so great that the blanket is squeezed to form a large frictional slip. Make the layout of the screen vertical distortion and expansion caused by ink bars. The above situation shall be achieved by replacing the roller bearing, adjusting the characteristics of the packing material, and reducing the center distance of the roller, so that the meshing backlash of the gear is less than 0.1mm; according to the specification of the equipment, the thickness of the packing shall be set to avoid the occurrence of excessive pressure. To prevent the phenomenon of ink bars.

II. Inaccurate overprinting problems caused by poor teething of the drum : When the tooth surface of the drum teeth is worn and deformed, the pressure of the teeth is not uniform, and the condition is insufficient. When the printed sheet enters the bite, it is likely to cause slip phenomenon in the printing, resulting in overprinting of the product. Unacceptable, especially in the case of large ink-receiving area of ​​the printing plate and large ink viscosity, overprinting is more likely to occur. In this regard, the solution is: to remove the badly worn teeth and replace the new teeth, will uneven bite paper pressure, insufficient teeth, adjust the correction so that the entire tooth surface bite the edge of the paper; the viscosity of the ink Too large, moderate dilution adjustment with additives to reduce the viscosity of the ink; for printing spot color inks, the ink hue can be appropriately deepened to make the printing ink layer thinner, which can reduce the viscosity of the ink. Can meet the printing hue requirements. In addition, the printing pressure can be appropriately reduced to prevent overprinting of the printed sheet due to slippage during imprinting.

Third, the printing pressure caused by the dirty version and stencil problems : When the offset pressure is too large, the friction surface of the blanket surface will inevitably increase the printing plate, so that the surface of the sand is subject to wear and tear, the hydrophilicity of the blank area Variations occur, and it is easy to attach ink and transfer it to the print. This is a dirty version. In addition, the printing pressure is too large, the expansion and contraction deformation value of the blanket when the pressure is also large, the transfer of the imprint is also easy to produce deformation, especially the printing of dots and small text, there are often paste the ills. If you use the letterpress process to print small, negative, negative, negative layout, the performance of such situations is even more pronounced. Therefore, to prevent the occurrence of dirty and paste, it is necessary to accurately adjust the printing pressure, and to control the thickness of the liner and the center distance of the cylinder according to the specifications of the equipment.

Fourth, the ghost pressure problem caused by the unfavorable printing pressure: When the pressure between the blanket cylinder and the impression cylinder is too large, the displacement of the blanket deformation increases correspondingly. Therefore, the ink layer cannot be transferred immediately after the imprinting process. Recovering the original state in time, so that when receiving the imprint from the plate cylinder, it is easy to generate a slight difference in position, resulting in ghosting. In this regard, it is necessary to reduce the pressure of the roller and reduce the expansion and contraction coefficient of the blanket during imprinting to prevent ghosting failure from occurring. In addition, for the use of aging blankets, should be replaced with a new blanket for printing to eliminate print ghosting failures.

Fifth, the printing ink pressure problems caused by discomfort: When the pad is uneven, uneven pressure or lack of pressure between the printing plate and the rubber, between the blanket cylinder and the impression cylinder or printing plate and lining between the (toppan process ) The phenomenon of bad contact will occur, affecting even and full transfer of the ink layer on the layout, which will easily cause the ink on the layout, which is not under sufficient pressure, to be light and hair to bloom. In order to avoid this bad situation, it is necessary to protect the surface of the impression cylinder to prevent it from being deformed and lose its flatness, and to maintain a uniform and sufficient printing pressure. This is an effective measure to eliminate ink coloring of printed products.

Sixth, the white paper surface strength caused by poor powder off, hair loss, blistering and peeling failure problems: In the case of poor white paper surface strength, when printing is prone to falling powder, hair loss, blistering and peeling failure phenomenon. Falling powder refers to the fact that the paper surface falls off the powdery material, such as paint, fillers, pigments, etc., from the paper surface. Lint off means that the fibers on the paper are peeled off from the surface of the paper during the printing process. Paper blistering and peeling refer to the fact that under the action of external forces such as peeling force and ink sticking force, the surface layer of the paper is detached and the battering or peeling occurs due to the splitting of the paper coating, the surface layer and the underlying fibrous structure during the printing process. . From a print quality point of view, the use of paper with high surface strength and good quality is the best choice for avoiding the problems of powder falling, pulling, blistering and peeling on the paper surface and improving the printing quality of the product. However, what kind of paper is used for printing is often not unilaterally determined by a printing factory. Some common products, customers only require the use of low-end white paper to print. This requires that some necessary measures be taken from the printing process in order to prevent the occurrence of printing quality failures. According to the experience of the printing production process, the following measures can be taken for the paper with poor paper surface strength to reduce or avoid the occurrence of powder failure, nap, blistering, and peeling quality failures.

1, adjust the viscosity of the ink. Papers with poor surface strength on paper, if printed with high-viscosity inks, are most prone to powder failures, naps, blisters, and peeling quality problems. In this regard, additives suitable for the printing process conditions may be selected to adjust the flowability and viscosity of the ink in order to reduce the adhesion and stripping tension of the ink layer to the paper surface during the printing process.

2, adjust the printing pressure. If the printing pressure is too light or uneven, the ink layer on the plate cannot be completely and evenly transferred to the surface of the paper, and the printing defects of the printing are likely to occur. However, if the printing pressure is too high, the coating layer and the fiber structure on the paper surface are easily destroyed, and powder falling, linting, blistering, and peeling quality defects are likely to occur. Therefore, the use of uniform and appropriate printing pressure is an important condition for good ink transfer, and it is also one of the technical measures to prevent the occurrence of undesirable problems.

3, adjust the printing speed. In the daily production, if the cardboard with poor surface strength is printed at a higher speed, the phenomena of falling powder, pulling hair, blistering and peeling quality will be obviously exacerbated. On the contrary, if the speed of the machine is lowered for printing, this failure phenomenon will be significantly reduced. This is because the printing speed is high, and the peeling tension during the printing process is also large. In this way, the adhesive ink layer on the printing surface is not quickly, evenly and completely absorbed by the paper surface during printing and separation, but it is easy to put on the paper surface. The partial coating or fiber pulls off. Therefore, paper with poor printing surface strength should be printed at a lower speed, which is beneficial to reduce or avoid the occurrence of powder failure, nap, blistering, and peeling quality failures.

4, choose the right machine for printing. For a paper with poor surface strength, what structure of the printer is used for printing has a great influence on the printing quality. For example, the letterpress process is used as an example. If a flat and flattened machine is used to print, the ink layer on the print sheet and the plate surface are in contact with and separated from each other at the same time. Thus, the greater the separation area, the greater the tension when peeling. The coated layer or fiber on the surface is easily pulled off. In a circular press or circular press structure, the contact between the printed sheet and the ink layer on the plate is linear, and the tension when the printed sheet is peeled off after absorbing the ink is also small, and it is not easy to destroy the paper surface. Therefore, for the paper with poor surface strength, printing with a circular press structure will help improve the printing quality of the product.

5, a reasonable arrangement of printing color sequence. The reasonable arrangement of the printing color sequence is an important part of preventing the paper from falling off or fluffing. Therefore, for the paper with poor surface strength, a small layout should be printed first and a large layout should be printed first; first, the low viscosity printing ink should be printed. Large ink (non-color overlay printing plate products). If multi-color printing is used, if there are extra color groups, the front color group may not be used, so that the printed sheets can be left empty past the previous color group, or the blank sheet can be imprinted or "overwatered" by the preceding color group. This can greatly reduce the print off or pull the hair phenomenon.

6, the paper with poor surface strength, adjust for printing small products. For some paperboards with poor surface strength, despite various methods, they still cannot solve the problems of powder and paper blistering. This is because the adjustment of the ink viscosity and the peeling tension is, after all, limited, and there is no certain sticky ink, and it is difficult to achieve normal printing. Therefore, according to the characteristics of printing products, choosing the right cardboard for printing is also one of the important measures to prevent quality problems.