How to determine the amount of powder in flexographic printing press?

How to determine the amount of powder in flexographic printing press? How to determine the dosage of powder spraying is a difficult problem to solve. So far, no one can and cannot give a specific data. The amount of powder spraying can not be too little or too much, which can only be determined by the continuous exploration and experience accumulation of the operator. According to many years of practical experience, we must comprehensively consider the following factors.

Thickness of product ink layer

The thicker the ink layer, the more likely the product is to be sticky and dirty, and the greater the amount of powder spraying, and vice versa.

Height of stack

The higher the height of the paper stack, the smaller the gap between the papers, and the greater the molecular binding force between the surface of the ink film on the printing sheet and the next printing sheet, the more likely it is to cause the back of the print to rub dirty, so the amount of powder spraying should be increased.

In practical work, we often find that the upper part of the printed matter is not rubbed and dirty, while the lower part is rubbed and dirty, and the more it goes down, the more serious it is.

Therefore, qualified printing plants can also use special drying racks to separate the products layer by layer, so as to reduce the height of the paper stack and prevent the back from rubbing dirty.

Properties of paper

Generally speaking, the greater the roughness of the paper surface, the more conducive to the penetration of ink and the drying of oxidized conjunctiva. The amount of powder spraying can be reduced or even not used. On the contrary, the amount of powder spraying should be increased.

However, art paper with rough surface, sub powder coated paper, acid paper, paper with opposite polarity static electricity, paper with larger water content and paper with uneven surface are not conducive to the drying of ink. The amount of powder spraying should be appropriately increased.

In this regard, we must be diligent in inspection in the production process to prevent the product from sticking and dirty.

Properties of ink

For different types of inks, the composition and proportion of binder and pigment are different, the drying speed is different, and the powder spraying amount is also different.

Especially in the printing process, the printability of the ink is often adjusted according to the needs of the product. Some ink blending oil or debonding agent is added to the ink to reduce the viscosity and viscosity of the ink, which will reduce the cohesion of the ink itself, prolong the drying time of the ink and increase the risk of rubbing on the back of the product. Therefore, the amount of powder spraying should be increased as appropriate.

PH value of fountain solution

The smaller the pH value of the fountain solution, the more serious the emulsification of the ink, the easier it is to prevent the ink from drying in time, and the amount of powder spraying should be increased as appropriate.

Printing speed

The faster the speed of the printing press, the shorter the embossing time, the shorter the penetration time of the ink into the paper, and the less powder is sprayed on the paper. In this case, the dosage of powder spraying should be increased as appropriate; On the contrary, it can be reduced.

Therefore, if we are printing some high-grade picture albums, samples and covers with a small number of prints, because the paper and ink performance of these products are very good, as long as the printing speed is properly reduced, we can reduce the amount of powder spraying, or there is no problem without powder spraying at all.

In addition to the above considerations, Xiaobian also provides two kinds of experience:

Look: the printing sheet is placed flat on the sample table. If you can see a layer of powder spraying casually, you should be careful. The powder spraying may be too large, which may affect the surface treatment of the subsequent process;

Pick up the printing sheet and aim at the light reflection direction with your eyes to check whether it is uniform. Don’t rely too much on the data displayed by the computer and the scale of the instrument on the machine. It’s common to bet on the plug of the powder tube!

Touch: sweep the blank space or the edge of the paper with clean fingers. If the fingers are white and thick, the powder is too large. Be careful if you can’t see a thin layer! To be on the safe side, first print 300-500 sheets, and then gently move them away for inspection in 30 minutes. After confirming that there is no problem, drive all the way again, which is much safer!

In order to minimize the pollution of powder spraying on product quality, equipment operation and production environment and reduce the impact on human health, it is recommended that each printing manufacturer purchase a powder spraying recovery device and install it above the cover plate of the paper receiving chain.