On the whole, cardboard distortion is not a single issue. Preventing this from happening can be accomplished by simultaneously removing the warpage (imbalance of moisture content and web tension) of the cardboard in the direction of the corrugations and parallel to the machine. Cardboard warping is usually caused by uneven web tension in the direction of the corrugations, usually occurring at the bond of the double-sided backing paper. This uneven web tension may be caused by the condition of the roll (damaged and inconsistent in shape), unregistered webs of the original paper rack and downstream equipment, or different degrees of rubbing in the direction of the corrugations above the hot plate. In addition, faults on the belts of corrugated board production lines, especially on split belts, may also be the cause of cardboard distortion.

The real cause of cardboard warping

In a broad sense, cardboard warping is caused by non-uniform variations in the size of the components on the corrugated board, especially core paper, which usually occurs when the corrugated tip and the bottom paper are firmly adherent and no relative movement between the two occurs. (Sliding) after. Machine-direction (MD) board warpage is caused by the unbalanced change of the upper and lower paper in the rolling direction of the machine due to the various forces of the machine's rolling direction that were originally unbalanced and the unbalanced cyclic changes. End S-board warpage). The main force here is the web tension.

If the tension of the upper sheet is higher than the tension of the lower sheet, the warping of the end-to-end upturned cardboard is caused. This kind of warpage occurs because the upper sheet has a higher degree of stretch than the lower sheet after the sheet is bonded. Therefore, the elasticity of the cardboard back is greater and the tension is released when the cardboard is cut. Conversely, if the tension of the underlying paper is higher than the tension of the paper on the upper sheet, the end-to-end undercut cardboard warps. As a result, end-to-end warpage of the S-board can occur if large amounts of tension occur on the paper or both sides of the paperboard on either side. Cardboard warpage in corrugated direction (CD) is mainly caused by non-uniform variations in the corrugation direction of the upper and lower sheets caused by the original unbalanced force in the corrugated parallel direction (CD). The main force here is due to the change in moisture content, the shrinking force and expansion force caused by the so-called "wet-up" characteristics of the base paper. This wet-up behavior is much larger in the corrugation direction than in the machine direction. This shows that the most serious problem we encountered was the warpage of the cardboard in the direction of the corrugations, and also how inconvenient the wet and mottled lines were in the base paper. Therefore, most carton companies do most of their work on cardboard warpage in the direction of corrugation, that is, the research and control of corrugated cardboard warpage.

Roughly speaking, a 1% change in the moisture content of the base paper will change the size of the corrugated cardboard by 0.6% to 0.10%. Because during the board through the corrugated cardboard production line, the water content can be changed by 15% to 20%, which may cause the relative change in the size of the board from 09% to 2.0%. On an 80-inch (2.03m) wide cardboard, this value is O.72-inch to 1.6-inch (18-41mm). This large size change has a great effect on the warpage of the cardboard. Therefore, careful control of the moisture content of the base paper is crucial for the production of flat cardboard.

The change in temperature also causes a change in the size of the board. However, its effect is relatively minimal for cardboard warpage. It is difficult to treat the temperature factor in isolation because changes in temperature are usually accompanied by, or actually cause, changes in the moisture content of the base paper. It is credible to explain the cause of cardboard warpage in the direction of the corrugations by the changes and differences in water content occurring during the manufacture of cardboard.

Cardboard Warpage Problem Solution

It is well-known that carton bending is the most important obstacle for all carton manufacturers. It will bring about various production problems, such as lower vehicle speeds and increased adhesive and energy costs. And it will affect the operation of the box department, such as die cutting difficulties, poor printing and so on. Waste paper also increased, making work more annoying and less smooth.

The main cause of warpage in corrugated board is the uneven water content of the upper and lower paper. There is too much water in the single-sided paper to bend upwards, and too much water in the double-sided paper to bend downwards. To produce flat, strong cardboard, it is important to control the moisture content and sizing method of the two papers.

INTERFlC's pressure bar and hot bar help control these two important factors. To produce straight and strong cardboard, the speed of single-sided and double-sided machines must be kept in sync. Some studies have found that low speed does not cause warp in the board. As long as the single-sided machine and the double-sided machine are kept in sync, there will be no problem.

So how do you produce straight corrugated cardboard? The answer is that there must be a third opposing force that counteracts the two face forces. This counter force arises from the fact that the top and roots of the corrugations at the double-sided bond are very moist, and the water content of the double-sided backing paper and the adhesive itself is due to the adhesiveness of the double-sided tissue on the top and roots of the corrugations. When the top and root of the corrugated fiber shrink to lose moisture in order to conform to the surrounding air, the force generated will try to warp the formed cardboard backsheet. Therefore, in order to produce a straight corrugated cardboard, this counter force must be able to accurately balance out the force generated by the aforementioned two facing papers in the paperboard forming process. The shrinkage of the corrugated tip not only affects the loss of the size of the cardboard caused by the loss of moisture content, but also reflects the fact that the paper is wetted and then dried and shrunk, ultimately resulting in the size of the cardboard being smaller than the original size.

Coated with the following conditions, can be made of flat corrugated board (ie 24 inches wide cardboard, deviation of 0.25 inches or 600mm wide cardboard, deviation 6mm)

â– Management promises to process straight cardboard:

â–  The uniformity of moisture content of the base paper is within the specified range:

â–  The corrugated cardboard production line is in good mechanical condition, with some kind of cardboard warpage control tool:

â–  The operating procedures of the corrugated board production line have been improved and the staff has been fully trained in the board warpage control method: In order to produce straight paper boards at all times, the above four conditions must be met.

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