Study on Technology and Printing Suitability of Coated Whiteboard III

From the above analysis, we know that the stripping, decontamination, and lint removal during printing are basically determined by the surface strength of the coated white paperboard, but the T value for a particular coated white paperboard is hard to increase in the printing plant. Therefore, only the right side of the above relation is used to adapt the T value on the left side of the relation. Below we discuss some of the items on the right side of the relationship.

The change of W value can be started from two aspects:

Reduce the viscosity of the ink or reduce the thickness of the ink film under possible conditions;

The change of Q value depends on the speed of the printing press and the radius of the impression cylinder. The faster the speed of the printing press, the greater the peeling tension. If the speed is the same, the smaller the radius of the impression cylinder, the smaller the peeling tension. The bigger, of course, the larger the radius, the smaller the peel tension.

The change of N value is mainly for lithography. It refers to whether the blanket has excessive viscosity, such as sulfur loss and stickiness. At this time, the value of N must be large. Therefore, certain measures must be taken to reduce the value of N.

We mentioned earlier that it is difficult to increase the T value when printing, but because we do not properly handle it will cause the T value to decrease. This requires our printers to maintain the original T value of the paper as far as possible in the actual work, while also trying to reduce the influence of external factors on the paper surface, ensure that the paper reaches the balance of force in the printing process, and make the printing work smoothly. get on.

The surface strength of coated white paperboard is mainly determined by the raw materials and processes of papermaking. For example, the surface strength of coated white paperboard made from straw fibers such as wheat straw pulp and eucalyptus pulp is generally low, and it is made from wood pulp and cotton pulp. The coated white paperboard has a higher surface strength. Paper surface strength is also related to the selection of fillers and compounds, the degree of calendering and other factors.
4.5 Smoothness Smoothness indicates the smoothness and smoothness of the coated surface. The application of the white paperboard coating layer is to improve the smoothness of the paperboard surface, and the smoothness that cannot be obtained by the application of the calender can be obtained by the coating. The printing effect depends to a large extent on the smoothness of the paperboard surface. The clarity of the text printed on the uneven paperboard surface is affected because the smoothness is related to the ink transfer and the smoothness is determined. The tightness of the board in contact with the printing plate. The thickness of the ink film on the printing plate is generally 3 to 10 μm. About half of the ink is transferred to the cardboard when it is imprinted with the cardboard. If the depth of the pit on the cardboard exceeds the thickness of the ink film, the plate is imprinted during printing. Corresponding to this pit can not be in contact with the paper. If the site is a field, a white point will be produced; if it is a text, it will result in the phenomenon of a broken pen and less painting.
4.6 Absorption performance The absorption properties of coated white paperboard include oil absorption and water absorption. Oil absorption and water absorption are two completely different properties of paper. Of these two properties, we are more concerned with oil absorption because the vast majority of printing inks are oil-based materials. The printing process requires that the paperboard has a considerable absorption capacity, so that the paperboard can absorb the ink as soon as possible, the paperboard absorbs the link material in the ink during printing, and the pigment particles are left on the paperboard surface to quickly dry. In general, the pores between cardboard fibers are larger than the diameter of the pigment particles. During printing, the ink is pressed into the pores of the paperboard. Under the effect of the fiber capillary, the binder is absorbed into the small fiber gaps smaller than the diameter of the pigment particles. Paper fibers are interwoven into an infinite number of capillaries. The amount of ink sucked can be discussed by the size of the gap. After the ink fills the gap, the capillary in the cardboard absorbs the binder in the ink. If the gap between the fibers is small, the capillary action of the fibers is damaged and the ink absorption performance is poor. If the pores are too large, the capillary not only absorbs the binder but also absorbs the pigment, resulting in the phenomenon of print-through.

The oil-absorbing property of the coated white paperboard is closely related to the printability. Low oil absorption, the ink will not be quickly absorbed by the paper after it is transferred to the paper, so that the ink that has not dried will be transferred to the back of the other paper covered above, causing it to become dirty. If the oil absorption is too high, it will infiltrate excessively, and the cardboard surface will lose its luster. The linking material will penetrate into the paper fibers. The rapid penetration may cause the powder to become powdery, so that the paint remaining on the surface will not be protected.

After the ink film layer printed on the surface of the paper is dried, the phenomenon that the pigment encounters a slight friction and becomes powdery and falls off occurs. After printing, the pigment on the surface of the paper is separated from a white line by the fingernail. When the carton is in transit, its printed surface may be scratched sometimes. The main reason is that the carton of the ink is excessively absorbed by the carton, so there is no film with enough fixed pigment left. The root cause of this effect lies in both paper and ink: In terms of ink, because the viscosity of the vehicle is too low, the ink dries too slowly; in paper, due to too low water, the ink in the coating layer absorbs too quickly; The reasons for both paper and ink are that the ink vehicle penetrates too much into the paper. The measures taken in printing are to add a varnish capable of forming a hard dry film in the ink, and it is also possible to consider adding more desiccants for accelerating the drying of the ink. On the paperboard, the composition of some coating layers can be changed slightly to slow the absorption of the ink.

In summary, the printability of paperboard has a great influence on the quality of packaging products. We can improve the print quality of paperboard by improving the printability of paperboard. In the actual printing, the overall appraisal of the printability of the paperboard, but also through the actual printing or analog printing methods, the paperboard glossiness, the quality of the ink transfer, the phenomenon of lint removal, etc. to evaluate the cardboard Printing performance. (Author: Chen Chang)