"Spots" appear on the color box is not "flying ink"

February 10, 2023

Fault phenomenon

In the box of an electronic product, yellow spots of different sizes appear. From the size and position of the spots, it is unlikely that the ink is flying by the ink roller.

Cause analysis and experimental verification

The production process of this yellow-spotted electronic product packaging box is as follows: after the white cardboard is printed and wired, it is pasted on the micro corrugated paper, and finally processed by die cutting, paste box and other subsequent processes. From the raw materials used in the processing, the cause of yellow spots may be caused by the adhesive used for white cardboard, water-based varnish, corrugated paper and paste .

The author initially suspected that the yellow spots were caused by a substance in the aqueous varnish, but after carefully studying the performance of the yellow spots, this factor was ruled out. The reason is to uncover the white cardboard at the yellow spot and find that the same color material exists on the corrugated paper of the corresponding part, and it is apparently diverged from the inside to the outside; and the varnish is attached to the surface of the white cardboard, if the yellow spot is white The paper is produced on the paper, then its form should be diverged from the outside to the inside. Further thinking along this line of thought, the material most likely to cause yellow spots is the adhesive and corrugated paper. The author believes that the adhesive is the most likely, so the experiment was first carried out on the adhesive.

The experimental design is shown in Figure 1. Since the main components of the adhesive are alkali, borax and starch, the author applied borax solution, caustic soda solution, borax and caustic soda mixed solution, starch solution and starch glue between two white cardboards, except The surface of the sample containing the caustic soda solution showed a reddish color, and the others did not change color. Therefore, the reason for the adhesive can be eliminated, and the author turned to the possibility of corrugated paper.

I have visited the production workshop of corrugated paper and have some understanding of the processing process: corrugated paper is rebuilt from recycled materials. The composition of the recycled materials is rather messy, and many impurities may be mixed with it. Therefore, the papermaking process is more than ordinary paper. Chemical additives, and because the papermaking process has to go through many processes such as rinsing, beating, coloring, etc., there will be more incompletely dissolved fine particles in the corrugated paper. In order to verify this conjecture, the author uncovered the white cardboard in the area where the yellow spots appeared, and then re-applied a new white cardboard, placed it in a constant temperature and humidity environment, and soon appeared yellow spots again . as shown in picture 2.