Although the use of flexible plates in corrugated boxes started late in the country, there are many advantages in flexographic printing, including lower flexo plate prices, faster plate making speed, faster ink drying, better printing performance, and less damage to corrugated cardboard. As well as environmental pollution, etc., the development is very rapid, and the use in carton production is now quite common. At present, corrugated cartons have changed from simple transportation packages to sales packages, and customers' requirements for printing are gradually increasing. Manufacturers in order to increase the amount of customers in order to save costs, the corrugated carton printing of the design of the degree of reduction of the natural requirements of more and more high, which requires the printing of corrugated boxes not only have a simple text printing, but also have a complex network gradient and large format The field printing.
In production, flexo printing does not have much problem in the use of text and color blocks, but it is often plagued by dot expansion in dot printing. The concrete manifestation is that: corrugated printing is obvious. The main reason for this is the limited hardness of the flexo (34?0 degrees), and the expansion of the outlets during compression. This is also determined by the intrinsic properties of the flexographic plate, because the flexographic plate is soft and deformed under certain pressure is its characteristic. In the printing, the printed surface of the corrugated cardboard is uneven, and the deformation of the flexographic plate can make the plate and printing. The surface is fully in contact to achieve ink transfer from the plate to the corrugated board. It is impossible to eliminate the expansion of outlets in actual production, and control network expansion can only be achieved by reducing its deformation.
To control the expansion of outlets will involve the following aspects of corrugated box production.
Paper (Paper)
â– Paper absorbency
The printing of corrugated boxes is basically water-based ink. Ink is combined with paper by penetration and volatilization. If the water absorption of the paper is not good, the ink will be difficult to combine with the paper, resulting in ink particles on the surface of the paper; and the paper's water absorption is too good, it will cause the ink to evaporate insufficiently and the edge of the screen will have the phenomenon of bleeding, which prints in multi-color dots. Especially obvious.
â– Paper moisture
In general, the impact 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 may be prolonged, resulting in the diffusion of the dots causing the visual effect to be unclear. Multi-color dot overprinting can cause large color deviations.
Coated paper
At present, more and more coated papers are used in corrugated boxes. However, the poor water absorption of coated papers will cause difficulties in ink penetration, prolonged drying time, and more ink particles remaining on the surface of the paper. This requires the combination of ink and paper to be increased. Sex, improve the volatility, speed up the drying of the ink by blowing or heating.
â– Weight
The weight of paper has a great influence on the proliferation of outlets. The grammage requirements for different types of paper (A, B, C, E) are different. Generally speaking, the higher the grammage, the less pronounced the spread of the peaks and the valleys are. To achieve a reduction in the proliferation of outlets, it is necessary to increase the weight of the paper.
The difference in shape is different for the spread of outlets, and the higher the level of corrugation, the higher the corrugation. Corrugated board should pay attention to maintain the height of corrugated pipe, glue should be minimized, the temperature of hot plate is high enough, the cardboard is flat and there is no exposed phenomenon.
Ink
The effect of ink quality on printing is crucial. For dot printing, inks with low viscosity and high color density are preferred. At present, alkali-soluble resin system inks are generally used, which have a certain degree of alkalinity, and mainly rely on ammonia-based volatile substances to make the resin soluble in water. In the use of ink must pay attention to the viscosity, PH value, drying speed and other aspects, dot printing requires low ink viscosity, fast drying, re-inking better. It is best to use higher grade inks when printing dots. If necessary, special aqueous dot inks can be used. For printing multi-color overprint outlets, you may encounter such a situation: on the one hand background ink drying is not enough, on the other hand because the tissues have absorbed moisture background ink, water absorption decreased, resulting in ink overprinting Infiltration, proliferation of outlets. Producing this kind of phenomenon needs to adjust ink PH value, drying speed according to printing the color order. The use of ink in actual production is quite complex and can be requested by the ink supplier if necessary.
(to be continued)