The common types of original paper used for corrugated box surface paper include: box board paper, hanging surface paper, kraft cardboard, tea board paper, white board paper, and single-sided coated white board paper.
Due to differences in the manufacturing materials and papermaking processes of each type of original paper, there are significant differences in the physical and chemical indicators, surface properties, and printing suitability of the above-mentioned types of original paper.
Below, we will discuss the problems caused by the above-mentioned paper products in the starting process of corrugated cardboard ink printing.
01 Problems caused by low density original paper
When using low density original paper to make corrugated cardboard surface paper, there may be a problem of exposed corrugated marks on the surface of the corrugated cardboard. It is easy to cause corrugation and the inability to print the required graphic content in the low recesses of the corrugations. In response to the uneven surface of the corrugated cardboard caused by exposed corrugations, a flexible resin plate with good resilience should be selected as the printing plate to overcome the defects of unclear printing and exposed bottom.
The images, especially the A-type corrugated cardboard produced from low-grade paper, will suffer significant damage to the flat compressive strength of the corrugated cardboard after being printed by a printing machine. In addition, the edge compressive strength of the corrugated cardboard will also be greatly damaged after passing through the printing and embossing rollers.
If the difference in surface roughness of corrugated cardboard is too large, it is also easy to cause the corrugated cardboard produced by the corrugated cardboard line to warp. Warped cardboard can cause inaccurate overprinting and irregular printing grooves, so warped cardboard should be flattened before printing. If uneven corrugated cardboard is forcibly printed, it can easily cause deviation from the specifications. It can also cause a decrease in the thickness of corrugated cardboard.
02 Problems caused by different surface roughness of original paper
Printing on rough and loosely structured original paper results in high ink permeability and fast ink drying, while printing on paper with high surface smoothness and dense and tough fibers results in slow ink drying.
Therefore, on rougher paper, the amount of ink applied should be increased, and on paper with a smooth surface, the amount of ink applied should be reduced. Printing ink on unglued paper dries quickly, while printing ink on unglued paper dries slowly, but the reproducibility of the printed pattern is good.
For example, coated whiteboard paper has lower ink absorption compared to box board paper and tea board paper, slower ink drying, and higher smoothness than box board paper, hanging face paper, and tea board paper. Therefore, the resolution of printing small dots on it is also high, and the reproducibility of its patterns is also better than hanging face paper, box board paper, and tea board paper.
03 Problems caused by differences in absorption of original paper
Due to the differences in papermaking raw materials and the differences in sizing, calendering, and coating of the original paper, there are differences in absorption energy. For example, when overprinting on single-sided coated white board paper and kraft card, the drying speed of the ink is slower due to the low absorption performance. Therefore, it is necessary to reduce the concentration of the previous layer of ink and increase the viscosity of the subsequent overprinting ink. And print the lines, text, and small patterns in the first color, and print the full plate in the last color, which can improve the overprint effect.
In addition, placing dark colors in the front for printing and placing light colors in the back for printing can cover the overprinting error, as the strong coverage of dark colors is conducive to overprinting standards, while the weak coverage of light colors makes it difficult to observe any deviation even when placed in the back for printing.
The different gluing conditions on the surface of the image original paper can also affect the absorption of ink stains. Paper with a small amount of glue absorbs more ink, while paper with a large amount of glue absorbs less ink. Therefore, the gap between each ink roller should be adjusted according to the glue state of the paper, that is, the gap between each ink roller should be reduced to control the inking amount of the printing plate.
From this, it can be seen that the absorption performance of the original paper should be tested when it enters the factory, and the printing slotting machine and ink mixing personnel should be given an absorption performance parameter of the original paper to facilitate their ink mixing and equipment adjustment. And adjust the viscosity and pH value of the ink based on the absorption status of different original papers.
