Corrugated board popping phenomenon and control scheme

We generally refer to the bursting of paper as the crease line of a corrugated carton when it is processed, folded, packaged, and stacked. Bursts seriously affect the appearance of the carton and are one of the major quality defects of the cardboard. Especially during the dry season, the explosion problem has caused many carton companies to suffer. This not only seriously affects the quality of the carton and causes a sharp rise in the rejection rate, but also delays the delivery period, causing the company to suffer economic losses. Through continuous exploration, the author summarized some methods for improving the bursting line and hoped to help the carton industry.

The corrugated box industry refers to two types of cartons, one is corrugated cardboard as the printing substrate, and the other is the flexo-printed cartons that are nailed/glued after ink printing. The flat PS printing, and then through the pit, beer cut and nail / sticky craft cartons, commonly known as box or color box. There is a big difference between the materials used in the two types of carton and the processing technology. Therefore, the influencing factors and control methods of the explosion are also very different.

Cardboard Burst Influencing Factors

There are many reasons for the quality problems of cardboard, and so is the bursting. The root cause involves various factors such as materials, environment, methods, and operators. Mainly in the following areas:

Cardboard moisture content is a key factor affecting carton blowout. Paper is a kind of hydrophilic material, water absorption will become soft and tough, and water loss will become hard and brittle. When the moisture content of the paperboard is low, the impact of moisture on the carton explosion is mainly reflected in two aspects: on the one hand, the folding resistance of the paper decreases, the stiffness of the paperboard increases, and the possibility of carton bursting increases. The paperboard core is increased in flat compressive strength, and the toughness of the paper in the surface is reduced. When the pressure line is pressed, the paper in the surface is easily damaged and the carton bursts. The test data showed that a piece of paper with a surface of 250 g/m2 noodle board paper and a five-ply board with an ECT of 9000 N/m, when the moisture content was less than 8%, the carton began to burst. When the paper is changed from paper to kraft linerboard, which has very good folding-resistance, the carton burst resistance is significantly improved, but if the moisture content is less than 6%, the cartons begin to burst. Therefore, it is very important to keep the cardboard moisture to prevent the carton from bursting.

The folding resistance of the corrugated surface and the paper itself also has an important influence on the bursting of the cardboard. In general, the calf is more durable than the dried noodles, and the softwood is more resistant to folding than the hardwood pulp. The paper made from the raw pulp is more resistant to folding than the recycled pulp. If the carton factory can reasonably select the paper according to the changes in the weather humidity, it can also prevent the carton from bursting to some extent.

The greater the strength of the corrugated paper, the greater the tension that the paper is subjected to during the forming process of the press wire, and the easier it is to cause the cardboard to burst. The more layers of cardboard, the easier it is to burst. For example, three-hole cardboard is more prone to bursting than double-hole cardboard, and double-hole cardboard is easier to produce explosive lines than single-hole cardboard. Paperboards with A crucibles have higher hardness than paperboards without A crucibles and are therefore more prone to bursting.

Improper handling of the printing slot can also cause the carton to burst. For example, if the positions of the up-down concave and convex rollers of the press line device are misaligned, when the pressure is too large, the line burst will occur.

When corrugated cardboard faces a large gap between the weights of the paper and the paper, the cardboard is prone to bursting. The greater the difference in grammage, the more likely the popping occurs. For example, a carton of 140g/lot paper 250g is more susceptible to bursting than a carton of 140g/lot paper. Therefore, attention should be paid to the balance of the paper's grammage when it comes to dispensing paper.

Cardboard detonating cord holding <br> <br> approach control the moisture content of corrugated board, cardboard is the best way to control blasting line. The moisture content of the corrugated board from the tile line is controlled between 12-18%, and the moisture content during the printing should be maintained at 10-13%. Due to some objective conditions, people often think that controlling moisture is not easy. Here, we will introduce some more effective methods:

First of all, the traditional method of adjusting the processing technology of corrugated cardboard has a certain effect. Usually we can use the following methods to control:

During pulping, the formulation of the paste is moderately adjusted to increase the moisture content in the paste.

Appropriately increase the amount of paste. It has been proved by practice that increasing the amount of paste can effectively increase the moisture content of the paperboard, and increasing the amount of paste can also improve the adhesion effect to some extent.

Appropriately reduce the contact area between the base paper and the preheating wheel to avoid excessive evaporation of water on the preheating cylinder.
Reduce the residence time of the cardboard on the hot plate. By maintaining a higher speed, reducing the length of the hot plate, and reducing the hot plate vapor pressure, etc., the excessive moisture evaporation of the cardboard when passing the hot plate is avoided. When using this method, care must be taken to ensure that the cardboard does not come off.

Secondly, the lack of understanding of the law of moisture change from the time the tile is out of the tile to the printing on the machine is an important reason for the explosion. When the cardboard comes out of the tile line, although its overall moisture content is relatively high, the moisture content of each layer of paper is extremely unbalanced. Tests showed that during the dry season, when the cardboard was just produced from the cardboard line, the moisture content of the facial tissue was about 8%, and some were even lower than 6%. After the cardboard was stacked for 4 hours, the moisture of the layers of paper tended to be balanced. Water increased to more than 9%. Therefore, if the paperboard is printed on the machine just after it comes out of the tile line, since the water content of the paper is very low at this time, the pressure line position may easily burst. Therefore, after the cardboard is produced, it should be piled up for enough time until the moisture of the layers of paper reaches equilibrium and then printed on the machine. Paper board surface, the paper inside the water is printed on the pressure line is low, the pressure line will produce micro-cracking, and even if the surface, the paper increased moisture, popping problems can not be avoided.

If the customer's delivery time is too short to allow sufficient time for water balance on the board, warm water on the board surface is the most direct and effective way. When wet, it is best to avoid spilling over the printed area, otherwise it will have an adverse effect on printing. If the conditions permit, we can use the waste field version to make a wet version. We first use a printing station to wet the press lines and then print. In this way, fast wet water can be applied to the press line without affecting the print quality.

When it is impossible to improve the board burst by controlling the moisture content, the use of better kraft liner board with better folding resistance can also effectively reduce the bursting degree of the carton. At present, there is no reliable test to completely avoid the problem of bursting. Paperboard with test data indicating that both the surface paper and the liner paper are 100% raw wood pulp, and the moisture content of which is as low as 6%, will also exhibit popping. In general, the bending resistance of the base paper can be reflected from the two physical properties of the longitudinal tearing degree and the bursting resistance of the paper to a certain degree. The original paper with a high longitudinal tearing degree and a high bursting resistance has a corresponding folding resistance. The higher ones.

In the allocation of paper, unless there are special requirements, we should try to reduce the difference in surface weight. For example, we should try to avoid the production of K=B, K=C cardboard, because it will easily lead to B or C paper burst. In fact, most corrugated board manufacturers do not produce corrugated cardboard with K=B and K=C. This shows that this principle has long been recognized and followed by counterparts. If this configuration has to be used for objective reasons, then the best way is to use a long fiber kraft linerboard for the lower grammage.

For the different strengths of corrugated paperboard, we should treat the matching of paper and paper in the opposite. The higher the cardboard side pressure strength or the whole box compressive strength requirements of the carton, surface, the paper should also use a higher degree of folding paper matching.

For A, BA, BCA and other corrugated boards with A-shaped combination, selective use of base paper with good folding endurance and A corrugated sheets can also effectively prevent cardboard popping.

When the paperboard is slotted and pressed, attention should be paid to adjusting the position of the concave and convex roller on the pressure line, and the slight deviations in the process of the slotted pressure line must be adjusted in time. Moderate pressure reduction can also improve the burst, but this approach may cause poor carton formation.

If the conditions permit, the printing pressure can be increased, and the dry cardboard can be appropriately softened, which can also reduce the burst. However, this method will greatly reduce the compressive strength of the carton, so it should not be abused.


(Guang Guoping)
Source: China Packaging 2005/3

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