What are the solutions to the warping of paperboard in Automatic High Speed Laminating Machine?
In the carton veneering process, the reasons for the warping defects of the paperboard are mainly caused by the warping of the face paper and the corrugated board itself in a few cases, but most of them are caused by the change of the size of the face paper and the corrugated board after the paperboard absorbs the water in the glue. The inconsistency of the size change leads to the warping defects after mounting.
The more water absorbed, the greater the elongation. If the expansion ratio of the face paper is greater than that of the corrugated board, the mounted board will curl up, otherwise it will bend down. If all the moisture absorbed by the paperboard is separated out and returned to the original moisture content, the face paper will be slightly smaller than the original size, but the corrugated paperboard is slightly larger than the original size, and the shrinkage rate of the face paper is significantly higher than that of the corrugated paperboard, so it is easy to bend up. Through observation, it can be found that the expansion ratio in the transverse direction of paperboard is more than 10 times that in the vertical direction. In other words, if the length of the face paper or corrugated board is in the horizontal grain direction and the width is in the vertical grain direction, the change range of its size will be larger, on the contrary, the change range will be smaller.
If the full-automatic paper mounting machine has serious paperboard warping, it will greatly affect the follow-up die-cutting work, resulting in die-cutting displacement, reducing efficiency, even affecting the squareness after cartons, weakening the compressive strength of the whole carton, etc. Therefore, how to avoid paperboard warping after mounting is an urgent problem to be solved. After the law of warping is obtained through analysis, it can be improved through the following three points:
1. Increase the solid content of glue. Since the facial paper and corrugated board have increased after absorbing too much water, resulting in curling, we can use the mounting glue with high solid content. The higher the solid content of glue, the less water it contains. Moreover, the glue with high solid content can reduce the gluing amount of paperboard per unit area, so it can ensure that the water absorbed by paperboard per unit area can be greatly reduced, so as to achieve the purpose of improving curling.
2. Use the correct grain direction. In order to ensure that the paperboard does not have curling defects in the mounting process, it is necessary to ensure that the length is vertical and the width is horizontal, so that the range of size change will be small. Moreover, because the short side is in the transverse direction and the long side is in the vertical direction, the absolute value of Web shrinkage is much smaller than that of transverse printing, which can reduce the amplitude of curling.
3. Select the correct stacking method. In the process of mounting, the paperboard that has just been mounted is stacked in a positive and negative way, which can also improve the warpage of paperboard to a certain extent. For the paperboard with serious warping after mounting, the more feasible and effective way is to apply a certain amount of heavy pressure on it. After a period of time, the warped paperboard will be significantly improved.
As long as these three aspects are guaranteed, the warping problem of the full-Automatic High Speed Laminating Machine can be solved quickly. At the same time, attention should also be paid to the maintenance of the equipment.
