Although the use of flexographic plates in corrugated cardboard boxes started late in China, due to the many advantages of flexographic printing, including the gradual reduction in the price of flexographic plates, fast platemaking speed, fast ink drying, good printing resistance, and little damage to corrugated cardboard And there is no environmental pollution, etc., the development is very rapid, and now the use in carton production is quite common. At present, corrugated boxes have changed from simple shipping packaging to sales packaging, and customers' requirements for printing are gradually increasing. In order to increase the consumption of the manufacturers and the cost savings of the customers, the corrugated box printing has naturally higher and higher requirements on the degree of design reduction. This requires that the corrugated box printing not only have simple text printing, but also have complicated dot gradients and large format. Field printing.
In production, flexographic printing does not have many problems in the use of text and color blocks, but in dot printing, it is often troubled by dot expansion. The specific performance is: corrugated printing is obvious. The main reason for this situation is the limited hardness of the flexographic version (34? 0 degrees), which is caused by the expansion of the dots when pressed. This is also determined by the inherent characteristics of the flexographic plate, because the flexographic plate is soft, deformation is a characteristic under a certain pressure, the printing surface of the corrugated cardboard is uneven during printing, and the deformation of the flexographic plate can make the plate The surface is in full contact to achieve the transfer of ink from the printing plate to the corrugated cardboard. In actual production, if you want to eliminate the expansion of the network, it is impossible to control the expansion of the network by reducing its deformation.
To control the expansion of outlets will involve the following links in the production of corrugated boxes.
Paper (glossy paper)
â– The printing of paper absorbent corrugated boxes is basically water-based ink. Ink is combined with paper through penetration and volatilization. If the water absorption of the paper is not good, the ink will be difficult to combine with the paper.
â– Paper moisture Generally speaking, the effect of paper moisture on printing is not very obvious. However, when the moisture content of the paper is too high, the drying time of the ink will be prolonged, causing the dots to spread and the visual effect to feel unclear. Overprinting of multi-color dots can cause large deviations in color images.
â– Coated paper
At present, coated paper is more and more used in corrugated boxes, and the poor water absorption of coated paper will cause difficulty in ink penetration, longer drying time, and more ink particles left on the surface of the paper, which requires increasing the combination of ink and paper Property, improve volatility, and accelerate the drying of ink by blowing or heating.
â– Gram weight
Paper weight has a great influence on the degree of dot spread. The grammage requirements for tissues used in different corrugated shapes (A, B, C, E) are not the same. Generally speaking, the higher the grammage, the less obvious is the spread of the dots in the corrugated peak and the corrugated valley. To achieve a reduction in dot spread, the tissue weight needs to be higher.
The different corrugated shapes have different influences on the diffusion of the dots. The higher the corrugated shape, the greater the influence of the corrugated shapes. When drawing corrugated paperboard, pay attention to keeping the height of corrugated paper, the glue should be as little as possible, the temperature of the hot plate is high enough, the paperboard is flat, and there is no corrugated phenomenon.
Ink
The effect of ink quality on printing is crucial. For dot printing, it is best to use inks with low viscosity and high color density. At present, generally used is an alkali-soluble resin system ink, which has a certain alkalinity, mainly by ammonia-based volatile substances to make the resin soluble in water. When using it, attention must be paid to the viscosity, PH value, and drying speed of the ink. Dot printing requires low ink viscosity, fast drying, and good ink resolubility. When printing dots, it is best to use higher grade inks, if necessary, you can use special water-based dot inks. When printing multi-color overprinted dots, you may encounter such a situation: on the one hand, the background ink is not dry enough, on the other hand, because the facial paper has absorbed the moisture of the background ink, the water absorption is reduced, resulting in the ink on the overprint Penetration, resulting in network diffusion. In order to produce this phenomenon, it is necessary to adjust the PH value and drying speed of the ink according to the color sequence of printing. In actual production, the use of ink is quite complicated. If necessary, please ask the ink supplier for help.
Printing plate
â– Selection of film
For fine dot printing, films need to use better quality products. For the more demanding dot printing, domestic film is difficult to achieve the expected results, and only foreign films with high price and high quality can be selected.
â– Choice of plate material
Resin plates have different hardness. The dot spread is mainly caused by the expansion of the dots on the printing plate under pressure. In order to reduce the dots, it is a solution to choose a plate with a higher hardness, but in actual use, the phenomenon of the bottom of the corrugated valley will appear due to the small deformation of the plate. In order to eliminate this phenomenon, it is necessary to increase the platen roller Pressure, but at the same time it will increase the deformation of the plate. Therefore, the choice of plate material needs to be carefully considered. At present, there is a liquid version. Its biggest advantage is that it can make the hardness of the top of the printing plate dots higher (the hardness can be selected from 36? 2), and the base part can be selected with a lower hardness. The company where the author has tried it, The effect is more obvious.
â– Choice of outlets
There are many shapes of dots. The dots used on the plate with a hardness of about 36 degrees. According to the author's own experience, the circular effect is better. The square and diamond shapes have obvious deformation of the dots during use, and dots are prone to spread or even stick. The phenomenon. Sometimes, the customer designer does not consider the actual situation of the corrugated box, a series of problems may occur.
â– Carton design
Because there are fewer professionals in carton design, many corrugated carton printing designs are provided by customers, and the customer's design drafts are designed by advertising companies or directly printed by offset printing. Therefore, carton suppliers are required to produce them. This will definitely occur. Less problem. For example, too many colors are required, the number of dots is too high, and the highlights are too high (less than 3% of the dots cannot be guaranteed and may be lost). It is difficult to deal with the relationship between vectors and bitmaps for the production of corrugated boxes. Therefore, carton design requires a carton supplier to have a professional designer or a professional printing plate manufacturer to complete.
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