Corrugated board printing process (on)

Color corrugated cartons (boxes) occupy an important position in product packaging. Due to the non-pollution of paper packaging, environmental protection requirements, and low cost, they are increasingly favored by businesses.
The prosperity of commodity economy and fierce competition in the market have promoted the improvement of the quality of product packaging. Landscaping has become an important means of marketing and propaganda. The printing quality of corrugated boxes has been increasingly valued by commodity producers and consumers.
With the advancement of carton processing and packaging machinery, the scope of corrugated carton packaging is getting bigger and bigger. It can not only pack mechanical parts and electrical components, but also package motorcycles, washing machines, refrigerators, and pianos. As the demand for packaging of goods above 50KG will increase substantially, the demand for heavy corrugated packaging boxes such as five-story, seven-story and nine-storey will increase significantly.
First, the printing method of corrugated board (1) Post-printing process, that is, the use of light pressure flexographic printing in the forming corrugated board.
(2) Face-to-face processing: Fine color screen printing is performed on the surface of 150 g/m2 coated paper or offset paper, and the printed matter and corrugated paperboard are then bonded with an adhesive.
(3) Pre-printing process: A web-type web flexographic printing is performed on the cardboard material of corrugated cardboard, and then the web printing surface paper is placed on a production corrugated cardboard production line to produce corrugated cardboard.
The above-mentioned first process is currently used in China, accounting for about 70%, this process is in line with the principle of rapid, convenient, environmentally friendly, economical, but it is difficult to avoid the emergence of product "washboard" stripes. Since the second and third processes are not directly printed on the corrugated board, there is no possibility of reducing the strength of the corrugated board. The effect of printing area on the compressive strength of the carton is shown in Figure 1.
The second pairing process, high production costs, suitable for a small number of high-definition requirements, special-shaped corrugated boxes, fine corrugated box production.
The third pre-printing method is suitable for the production of large-volume products and is rarely used in China.

Fig.1 Effect of printing area on the post-carton pressure strength

Second, corrugated board flexo process points 1. Corrugated board printing plate corrugated box printing plate thickness of 3 to 7mm, the hardness of Shore hardness (HS) 25 ~ 50. When the quality of corrugated paper is poor, a thicker plate with a lower hardness should be used. When the corrugated paper is of good quality and needs to be printed in small prints or screens, thin plates with high hardness should be selected.
2. As shown in Fig. 2, when thick printing is used and the printing pressure is too low, the printing substrate is likely to produce corrugated and “sawboard”-like patterns, as well as affecting the field and fine lines; when the printing pressure is too high, the printing substrate is easily deformed. Even if it is damaged, the resin plate is deformed and the printing dots are enlarged.

a Damaged cardboard b Dots enlarged Figure 2 Comparison of thick and thin processes

When the printing pressure is too low, the printed substrate is susceptible to corrugated and washboard-like patterns, as well as affecting field and fine line printing.
When the printing pressure is too high, the printed substrate is easily deformed or even damaged, and at the same time, the resin plate is deformed and the printing dots are enlarged.
At the same printing plate thickness and the same printing speed, the flexographic printing pressure distribution with different hardness is different from the imprinting condition. The plate with higher hardness has no obvious expansion of the imprint, but the imprint of the edge parallel to the edge parallel to the corrugated sheet is less realistic. On the contrary, the soft imprint is imprinted with strong imprinting, but the edge is expanded. The reason is that the flexibility of the flexographic plate is different, resulting in a difference in elasticity, high hardness, and low elasticity, that is, the deformation of the surface layer of the printing plate is small, whereas the deformation of the printing plate surface layer is large, and the fidelity of the imprinting is poor. In order to make two kinds of plates with different hardness, the two-layer flexible plate appeared, including two types:
1 overall structure. That is divided into two layers, the surface layer after the hardness in the Shore hardness of about 55, the middle and lower plate hardness in the Shore hardness of 35 to 45 or so. In the market, there is a "GS flexo" carton B version.
2 bond type. That is to take a thick 2.5 ~ 3mm thin carton flexo (such as listed in Table 1), in the back of a layer thickness of 3 ~ 4mm foam rubber plate.

Table 1 Thin TDR Series for Dupont Carpet Printing