Reasons for yellow spots in color box printing

When the color box printing on the presentation of non-graphic planning mottling, usually the first judgment is the color group ink roller “flying ink”, splash in the color box on the occurrence of mottling. However, this judgment does not apply to all cases.

Fault phenomenon

In the packaging box of an electronic product, there are different sizes of yellow mottling, from the size and orientation of the mottling, it is unlikely to be caused by the ink roller flying ink.

Cause analysis and test verification

The yellow mottled electronic product box production process for: white cardboard by printing and line varnishing, and then laminated in micro-corrugated paper, and finally by die-cutting, box gluing and other post-processing molding. From the raw materials used in the processing process, the cause of the yellow mottling may be out of the white cardboard, water-based varnish, corrugated paper and adhesives used in laminating.

I began to suspect that the yellow mottling is caused by some kind of substance in the water-based varnish, but by carefully examining the performance of the yellow mottling, it sweeps away this element. The reason is to open the yellow mottled white cardboard, found that its corresponding parts of the corrugated cardboard on the presence of the same color material, and is clearly dispersed from the inside to the outside; and varnish is attached to the white cardboard exterior, if the yellow mottling is occurring on the white cardboard, then the form of its performance should be dispersed from the outside to the inside. Along this line of thought, further consideration, the most likely cause of yellow mottled material is adhesive and corrugated paper. The author thought that the adhesive is the most likely, and therefore the first for the adhesive test.

Test planning as shown in Figure 1. Because the primary components of the adhesive for alkali, borax and starch, etc., the author in the two white cardboard were coated between the borax solution, caustic soda solution, borax and caustic soda mixed solution, starch solution, starch glue, but in addition to containing caustic soda solution specimen appearance of light red phenomenon, the other are no discoloration reaction, and thus can be swept away adhesive reasons, the author turned to consider the possibility of corrugated paper.

The author has visited the production workshop of corrugated paper, and has some understanding of its processing: corrugated paper is reconstructed from recovered materials, and the composition of recovered materials is relatively messy, with many impurities that may be intermingled, so its papermaking process is more complicated than that of ordinary paper, which requires the addition of more chemical auxiliaries, and at the same time, because the papermaking process involves rinsing, pulping, coloring and other procedures, there are many fine particles in the corrugated paper that have not been completely dissolved. particles. In order to verify this speculation, the author uncovered the white cardboard at the site of the yellow mottling, and then mounted a new white cardboard from the beginning, placing it in a constant temperature and humidity environment, which soon showed yellow mottling again, a process shown in Figure 2.

I also cut down the corrugated paper on the yellow mottled part of the wash and then sandwiched between two pieces of white cardboard from the beginning of the laminating, a period of time after the yellow mottled and presented, the process shown in Figure 3. However, if it is placed in the air for a period of time or heated in the oven and then laminated from scratch, the yellow mottling will completely disappear.

Test conclusion

Through the above tests, the author now has a good grasp of the presentation of yellow mottling and corrugated paper has a direct link, the composition of yellow mottling is the pulp and paper production process to join the failure to completely dissolve the sulfide particles or retrieve the guessing entrained in the insoluble chemical raw materials. Later, I came to the supplier to discuss together, and ultimately they also thought that this is related to corrugated paper. I speculate that some whiteboard products present yellow mottled problem is also attributable to this nature, because the domestic manufacturing process of whiteboard paper is relatively crude, with the manufacturing process of corrugated paper is very close, slightly different is the former used to recover the material will be better, and more than one coating process.

Response

(1) Notify the supplier of the return and exchange of the same batch of corrugated paper in the supplier’s inventory, and inform the supplier that the product cannot be supplied again. The presentation of yellow mottling is usually a concentrated outbreak, which is mainly related to the corrugated paper production process, because a paper machine can produce 80-100 tons of corrugated paper a day. If yellow mottling is present, it means that there may be a problem with the same batch of corrugated paper, and that the corrugated paper should not be used to make color boxes again.

(2) With regard to the batch that shows yellow mottling, more quality inspectors should be put in to check it out. Because the yellow mottling will only show up after a period of time, when the relevant personnel find out that there may now be a batch of products with this risk, it is necessary to carry out a full inspection of the same batch of products with yellow mottling, and comprehensively check the batch of corrugated paper used, the date of receipt of the material, and check whether there are any other products that have used this batch of corrugated paper.