Cardboard Flatness Best Solution--Board Warping Detailed (1)

Now is the era of meager profit for cartons. The cost of controlling cartons has become the key to profitability. Cardboard warpage has been plaguing many carton manufacturers, and the resulting direct or indirect losses are endless. The reason is mainly due to the inconsistency of the paperboard, the surface material and the moisture of the base paper, the temperature, the air pressure, the low vehicle speed, and the frequent stoppage; all of these will cause warp of the board. Next, this publication will give a detailed and comprehensive introduction to the issue of cardboard warping, and it will help you find the best solution for cardboard flatness.

Cardboard Warpage Causes and Solutions

Cardboard warpage has been plaguing many carton manufacturers, and the direct or indirect losses due to warpage in paperboard are endless. Now is the era of meager profit for cartons. The cost of controlling cartons has become the key to profitability. The problem of cardboard warping in production certainly cannot be avoided, but the occurrence of such problems can be minimized.

What kind of cardboard is straight cardboard? Take a piece of 24 inch wide paperboard as an example. The deviation of the inch on this paperboard is called "warping factor". 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–  First, management must resolve to produce straight cardboard;
â–  The moisture content of the base paper is within the specified range;
â–  It is a corrugated board production line in a good mechanical state 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 articles are controlled by the carton manufacturer. As far as the uniformity of the raw paper is controlled by the original paper manufacturer, it is necessary to carefully select the original paper manufacturer.

There are many kinds of cardboard warpage in cardboard, first try the following methods to classify:

basic type

â–  Cardboard warpage parallel to the machine (MD or end-to-end) â–  Board warpage perpendicular to the machine (CD or edge to edge) â–  Warp (composite) (form twisted) Cardboard warp Basic shape â–  Up (normal) Cardboard Warp â–  Down (Reverse) Cardboard Warpage â–  Composite (S) Cardboard Warpage

Observation time

It can be seen directly from the corrugated board production line. â–  It will be seen only after a few hours or more.

The real cause of cardboard warping

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

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 stretch than the lower bottom paper, the cardboard has a greater elasticity at the back, and the tension is released after 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. If there is large-scale fluctuations in the tension on either or both sides of the paperboard, end-to-end S-board warpage occurs.

Corrugated (CD) board warpage is mainly caused by the original unbalanced force in the corrugated parallel (CD) direction and the unevenness of the upper and lower paper in the corrugated direction. The main force here is due to the moisture content, which is the shrinking force and expansion force caused by the so-called "wet-up" characteristic of the base paper. Careful control of the moisture content of the base paper is essential for the production of flat paperboard. 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 are usually accompanied or negotiated and actually cause changes in the moisture content of the base paper. It is credible to explain the warpage of cardboard warpage in the direction of corrugation using the changes and differences in moisture content occurring during the manufacture of 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, single-sided paper (the moisture content of the upper layer is much higher than double-sided tissue (double-sided bottom paper). When the moisture content of the two types of tissues and the surrounding air in the long-term moisture content tends to At that time, the upper layer of paper will release moisture and shrink, while the double-sided bottom paper absorbs moisture and expands, and these two forces eventually cause the cardboard to warp upward (positive).

(to be continued)