Cardboard warp issue Raiders

The problem of cardboard warping has been plaguing many carton manufacturers, and the direct or indirect losses caused by cardboard warping are endless. Now is the era of meager profit of cartons. The cost of controlling cartons has become the key to profitability. The issue of cardboard in production is certainly inevitable. However, the occurrence of such problems can be minimized. Controlling the quality of cardboard is the key to improving the profitability of cartons. The following is a detailed and comprehensive introduction to the problem of cardboard warping.

What kind of paperboard is straight paperboard? Take a 24 inch wide paperboard as an example. The deviation of the inch on this paperboard is called "warping factor". If the warpage factor of the paperboard is 0.25N (6 Millimeters of N, positive warpage, and 0.25R (6 mm R, reverse warpage), the cardboard is flat. After study, in the following cases, a straight corrugated paperboard (ie 24 inches wide paperboard with deviation of 0.25 inch or 600 mm wide paperboard with a deviation of 6 mm) can be made:

â–  The management attaches great importance to the flatness of the board;

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

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

â–  Improve the corrugated board production line operation procedures and train the relevant staff on the board warpage control method.

The first three are controlled by the carton manufacturers themselves. As the paper's moisture uniformity is controlled by the base paper manufacturers, it is necessary to carefully select the base paper manufacturers.

Cardboard has many types of cardboard warpage that can be classified as follows:

basic type

â–  Cardboard warpage parallel to the machine (MD or end-to-end)
â–  Cardboard warpage in the direction perpendicular to the machine (CD or edge to edge) â–  Warp in the composite (somewhat twisted) cardboard warp

Basic shape

â–  Up (Normal) Cardboard Warpage Down (Reverse) Cardboard Warpage
â–  Composite (S-shaped) cardboard warping

Observation time

â–  Can be seen directly from the corrugated cardboard production line
â–  Seen after hours or days

The real cause of paperboard curls

Cardboard warping is caused by non-uniform variations in the size of the corrugated board assembly components, especially the core paper, and usually occurs after the corrugated tip and the bottom paper are firmly bonded until no relative movement (sliding) between them occurs. .

Machine direction (MD) board warping is due to the fact that the forces in the direction of movement of the machine are originally unbalanced. This unbalanced cyclic change causes uneven changes in the roll direction of the upper and lower papers, resulting in warpage of the paperboard. The main force is the web tension. If the tension of the upper sheet is higher than the tension of the lower sheet, the end-to-end upturned cardboard warps. This kind of warpage occurs because after the paperboard is glued, the upper layer paper has a higher degree of stretching than the lower bottom paper, and the cardboard has a greater elasticity at the back, which is produced when the cardboard is released through the cutting tension. 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. If there is large-scale fluctuations in the tension on either or both sides of the paperboard, end-to-end S-board warpage occurs.

Cardboard warpage in the corrugation direction (CD) is mainly caused by the original unbalanced force in the corrugated parallel direction (CD) and uneven variations in the corrugation direction of the upper and lower paper. The main force here is the shrinkage force and expansion force caused by the “wet-up” characteristic of the so-called base paper, which is caused by the change in the moisture content. Careful control of the moisture content in the base paper is essential for the production of flat cardboard. The change in temperature also causes a change in the size of the cardboard, but its impact is relatively minimal for cardboard warpage. It is difficult to treat the temperature factor in isolation because changes in temperature often accompany or actually cause changes in the moisture content of the base paper. It is credible to explain the cause of warpage in the direction of the corrugations by the changes and differences in moisture content that occur during the manufacture of the cardboard.

The condition of the moisture content of the bond between the base paper and the corrugated tip, which occurs on the hot plate, is of particular importance. This state usually occurs when the glue is glued. The force that causes a change in the state of moisture content refers to the various forces that are mechanically confined between the upper belt and the hot plate and the formed cardboard remains in a straight state. In the bonding of the base paper and the corrugated tip, it can be expected that the moisture content of the single-sided paper is much higher than that of the double-sided bottom paper. Not only is the additional moisture content of the single-sided paper bonded, it cannot pass through the single-sided machine and When the bridge is completely removed, the water content produced when the double-sided backing paper is bonded is transferred to the single-sided paper when it is pasted. The double-sided backing paper can only be firmly bonded after most of the moisture content is removed when the paste is glued. Detailed temperature measurement shows that the surface of the facial paper located between the corrugated tips will be dry and sticky. From these two factors, it is generally expected that the bond of the double-sided backing paper will be very dry.

When the cardboard leaves the machine, the moisture content of single-sided paper (upper-layer paper) is much higher than double-sided paper (double-sided liner). When the moisture content of the two kinds of tissues and the moisture content of the surrounding air tend to be the same, the upper layer of paper will release moisture and shrink, double-sided bottom paper absorbs moisture and expands, these two forces eventually cause the cardboard upward (positive ) Warping.

(to be continued)