Cardboard Flatness Best Solution--Board Warping Detailed (2)

How to control warpage

We know that the basic causes of warpage in the direction of corrugation and the respective forces of the warpage are still unable to control the warpage of the cardboard, but it is possible to reduce the warpage of the cardboard as much as possible. Rationally control the amount of adhesives and master the rheology of adhesives; can ensure that the quality of the base paper meets the practical requirements at any time; train operators in new operating practices and make full use of newly developed tools such as speed synchronization, single-sided paper Web spray system.

Effect of Water Content on Cardboard Warpage on Paperboard

The uneven moisture content in the tissue paper web has been proven to be the main cause of warpage in corrugated cardboard. If the corrugated board production line and printing equipment can be automated and optimized, the warpage of the board can be controlled. The corrugated board produced under certain production conditions is theoretically considered to be flat, ie the automation equipment of the carton plant minimizes the problems encountered by the carton users during production.

Corrugated board production line can reduce the difference in moisture content between single-sided paper and double-sided bottom paper. Since such a capability is limited, the maximum allowable value of the moisture content difference between the single-sided paper and the double-sided backing paper is first determined, so that the corrugated paperboard production line can control and always produce a straight cardboard.

The difference in moisture content of different base paper rolls is different. If it is within the controllable range of the corrugated cardboard production line, it is harmless; when the moisture content difference exceeds the specified range, it is impossible to continuously produce straight cardboard. In order to make the difference in the moisture content between the paper rolls within the controllable range, the corrugated board production line is required to change the moisture content of the noodles from an uneven state to an equilibrium state so as to produce a straight cardboard. The indicators in the base paper should be consistent in theory. Only the operators of the corrugated board production line can arbitrarily continue the production of the two base paper rolls, and produce straight cardboard by controlling the corrugated cardboard production line. The most pressing task is to Determine the moisture content characteristics of the base paper.

There is experimental data showing that the cardboard is very easy to bend into the more moisture-rich tissue when it passes through the corrugated cardboard production line. When the moisture content of the single-faced paper is more than 3% higher than that of the double-sided bottom liner, or 92% The sample warps towards single-sided paper (ie, positive warpage); when the moisture content of double-sided bottom paper is more than 3% higher than that of single-side paper, 75% of the sample warps towards the double-sided bottom. Paper (ie reverse warpage). For a long time, the moisture content of single-sided paper is much more difficult to overcome than the moisture content of double-sided paper, and the paper with higher moisture content will produce more adhesion at the single-sided machine than at the double-sided machine. problem.

Corrugated paperboard line operators should know their moisture content before using paper rolls. A typical corrugated board production line uses only 3000 meters of length of base paper, or 2/3 of paper rolls. Due to the lack of information on moisture content, corrugated board production lines usually produce only 1,500 meters of base paper. All products are warped before the corrugated cardboard production line is adjusted to produce qualified cardboard. Only after knowing the moisture content of the base paper, the machine can be adjusted from the very beginning. The operator can use this indicator to use the relatively dry one of the two types of tissues as single-sided paper, which helps to avoid the reverse of the cardboard. Warpage, while using a segmented single-sided web spray system, can ultimately avoid the warpage of the board. Tests have shown that the moisture content in the corrugating medium does not correlate with the warpage of the paperboard. It is possible that the warp of the paper is offset by the warpage of the paper on both sides.

The difference in humidity between single-sided paper and double-sided backing paper is a key factor in processing flat paperboard. If the operator of the corrugated board production line wanted to produce consistently straight cardboard, or the corrugated board production line was more fully automated, it was important to first solve the moisture content of all face paper rolls before installing the roll. In most cases, it is better to install a relatively dry base paper roll on a single-sided machine. If you change the use of the base paper at will, warpage cardboard will be produced due to the difference in moisture content between the paper tissues. Understanding the average moisture content of the base paper helps to avoid large-scale imbalances in moisture content between the tissues, and helps the operator to produce straight paperboard within a very short time after the paper roll is changed.

In summary, the main factors influencing the warpage of paperboard are as follows:

â–  The difference in moisture content between single-sided paper and double-sided backing paper exceeds 3%, which will cause the paperboard to warp in the direction of the higher moisture content paperboard, resulting in cardboard warpage produced by the corrugated paperboard production line. Use all existing equipment that controls board warpage. Most corrugated board production lines can overcome the difference of up to three percent moisture content between the paper and the backing paper;
â–  In order to minimize the warpage of cardboard caused by wet lines, the maximum value of the product of the width of the wet lines of the average moisture content and the top height of the wet lines must be less than 40;
â–  The moisture content of the core paper is in the range of 3% to 9%, which has no obvious effect on the warpage of the paperboard.
â–  The shape of the moisture content trace of the tissue paper roll,

The change from the data obtained at the base paper supplier and carton plant is not obvious.

In order to produce straight paperboard all the time, the requirements for the 205 g/m2 specification base paper are as follows:
■ The average moisture content of all base papers of a specific material and basis weight does not vary by more than ±1.5% (total value is 3%);
■ The moisture content should be uniform in the machine direction, and the mean change in scanning should not be greater than ±0.5% of the mean value of the paper roll;
â–  If there are wet lines, its width should be narrow and evenly distributed. The width of the wet lines of the left and right products should be expressed in inches, and the excess moisture content should not exceed 40;
â–  The base paper should be transported to the carton factory in a tight, uniform roll wrap without loose, cracked, split core or core holes. Core paper and lighter basis weight paper should use a high-quality paper roll core of at least 6 mm thickness;
â–  The average moisture content of the roll should be marked for input into the board warpage control system.

(to be continued)