Analysis of Corrugated Cardboard Offset Preprinting Technology (Part 2)

Third, issues related to surface finishing

1. Polishing

Shining is a commonly used surface finishing method for the printing of corrugated cardboard paper. The four companies that were interviewed used the glazing process. For corrugated boxes, UV glazing is an ideal choice because UV-cured prints have better water resistance, moisture resistance, and abrasion resistance. Only UV coating oil has poor adhesion to paper and ink, poor post-processing adaptability, and it is not easy to paste the cartridge; if UV glazing is not properly handled, the product is poor in folding resistance when die-cutting and is prone to burst. However, better glazing equipment can be used to overcome the glazing process. The use of different printing equipment by different manufacturing companies can cause problems with this or that. According to people's reports, after finishing the printing of the glossy paper, the drying speed of the ink is too slow. After the glossy paper is printed, it usually takes more than ten hours before it can be polished, which seriously affects the production efficiency.

Laminated film

Lamination is also a post-press processing method that is used more often. Most of the companies interviewed used the lamination process. The function of the film is generally to improve the waterproof, folding and abrasion resistance of the printed product. However, for corrugated cartons, coated film is not the best choice, because the corrugated cartons after the film are poor in moisture resistance, and once dehydrated, they are likely to debond, resulting in separation of the film from the tissue. According to everyone's opinions, air bubbles, wrinkles, peeling, poor adhesion of the film, etc. may easily occur in the film.

The causes and solutions are:

(1) The paper is uneven and the ink layer is too thick and sticky. The appropriate paper and ink should be selected according to actual conditions to increase the amount of adhesive coating and increase the printing pressure.

(2) In order to prevent the paste from adding dry oil, the surface of the ink layer is crystallized, the surface of the tissue is smooth and tough, the adhesiveness is lost, and the adhesive fastness is reduced. The dry oil should be added in an appropriate amount.

(3) There is dust on the surface of the tissue, which can be wiped off with a dry cloth; debris on the film should be removed as soon as possible.

(4) The correct adhesive was not selected and the amount of glue was not properly set. It was necessary to reselect other types of adhesive.

(5) After printing, the ink layer is not dry, and the tissue should be allowed to dry for a sufficient period of time.

(6) The film itself has wrinkle relaxation phenomenon, and the film can be changed.

(7) The white ink is used as a diluting agent in the ink, because the white ink has relatively large silt particles, which are not tightly combined with the linking material, and a bright light paste or a light diffusing agent can be used instead of the white ink.

In addition, it is easy to cause scratches and stains on the face paper when performing various types of post-press processing on the facing paper. Therefore, it should be left for a while after printing, and use fast-drying ink.

Taking into consideration the need for surface finishing, the teacher Wang Dongjing of Baoding Xingliang Printing Factory specially emphasized that in the printing operation, attention should be paid to not spraying too much, otherwise bubbles would appear when laminating or stamping.

Fourth, related issues with the cover

After printing the glossy paper, the paper needs to be twisted onto a single-faced corrugated cardboard. Everyone has reflected that the following two types of failures are more likely to occur during the coupling process.

1. "seesaw" failure

There is sometimes a groove in the form of a groove, such as a seesaw, which is recessed on the corrugated cardboard. This kind of failure will not only affect the appearance of corrugated boxes, but also affect the strength and thickness of the carton. What's more, the manufacturers of corrugated cartons will be dissatisfied and even return them, affecting the reputation and benefits of corrugated cartons manufacturers.

Reasons for formation: In the process of facing paper and corrugated paperboard, the adhesive agent is not well coated, and the excess amount of adhesive agent that accumulates on the two sides of the peak is excessive. When dry, it will cause the tissue to shrink on both sides of the peak to form a "seesaw." Before starting the sticker, check the coating amount of the adhesive. If there is a very thin line on the surface paper, it indicates that the adhesive is normal and there will be no “sawboard” phenomenon; if a heavy double line appears, it indicates that the adhesive has been applied. Too much, there will be "seesaw" phenomenon, especially the low-quantity pasta paper is more serious.

Solution:

(1) Replace the face paper. Replacing low-precision tissue papers with high-precision tissue papers is the easiest method and can significantly eliminate “seesaw” phenomenon. However, this will increase production costs and significantly increase the price of corrugated cartons.

(2) Make full use of the texture characteristics of the paper. The longitudinal filaments of the tissue should be blended perpendicular to the direction of the corrugated cardboard. This is the most basic and most effective method. However, sometimes the web width is not the same as the size of the cardboard box, thus wasting paper and increasing the cost.

(3) Increasing the viscosity of adhesives can reduce the amount of glue applied on the peaks, significantly reduce the phenomenon of “seesaw board”, and the cost does not increase too much.

(4) The paper is wetted (hanging, humidifying, etc.) to absorb a certain amount of moisture before use, to avoid too dry paper and excessive absorption of the adhesive, causing "seesaw" phenomenon.

Collapse failure

Collapse refers to the two sides of the corrugated board that are flattened and stretched after two minutes. If the adhesive is of good quality, it can also be bonded; if the quality is not good, it will cause serious open glue.

Reasons for formation: The corrugated base paper has insufficient sizing, and the elongation rate is large. As a result, the glue has not penetrated into the surface paper fibers yet formed a film on the corrugated core paper, and the fibers are elongated, resulting in collapse and a large area of ​​open glue.

Solution: Use qualified corrugated paper. Corrugated paper quality inspection before use, the method is: use your fingers and dipped in a little water on the corrugated paper, observe its penetration rate, repeated several times. It has been proved that the corrugated base paper that has penetrated after 6 seconds is qualified.

V. Problems related to molding processing

Forming and processing is the last step in the production of corrugated cartons. Currently, there are mainly two methods of die cutting and grooving in China. Here, we mainly talk about the easier problems in the die-cutting process.

(1) The position of the paper is not accurate. The position of the paper-feeding positioning of the die-cutting machine can be adjusted so that the paper-feeding position is consistent.

(2) Deformation of cardboard affects the precision of die-cutting. The cause of the deformation of the cardboard should be found and improved.

(3) Die cutting edge not only. According to the different properties of corrugated board, die cutters with different qualities and characteristics should be selected, or new die cutters should be replaced in time.

(4) uneven pressure die-cutting. The die press pressure should be properly adjusted.

(5) Indentation is not clear, there are dark lines, fried lines. The dark line refers to the indentation that should not be present, and the fry line refers to the breakage of the cardboard due to excessive indentation pressure. The indentation process should be adjusted according to the nature of the paperboard, so that the two are adapted as much as possible, or the pressure of the die-cutting machine can be adjusted to achieve the best value.

(6) When folded, the cardboard cracks at the crease. The height of the indentation can be appropriately reduced, or the indentation line can be widened according to the thickness of the cardboard, and the pressure of the die cutting machine can be appropriately reduced.

Source "Printing Technology"