How to determine the amount of powder spraying in a flexographic printing machine? How to determine the amount 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 neither be too small nor too much, and can only be determined by the operator's continuous exploration and experience accumulation. According to years of practical experience, the following factors must be comprehensively considered.
The thickness of the product ink layer
The thicker the ink layer, the more likely the product will be dirty, and the amount of powder spraying will be larger, and vice versa.
the height of the stack
The higher the height of the paper stack, the smaller the gap between the papers, the greater the molecular binding force between the ink film surface on the printed sheet and the next printed sheet, the easier it is to cause the back of the printed product to be dirty, so the amount of powder spraying should be increased. big.
In actual work, we often find that the upper part of the printed product is not smudged, but the lower part has smudges, and the reason why it gets worse as it goes down is this.
Therefore, qualified printing factories can also use special drying racks to separate the products layer by layer to reduce the height of the paper pile and prevent the backside from being dirty.
The nature of paper
Generally speaking, the rougher the paper surface is, the better it is for the penetration of the ink and the drying of the oxidized conjunctiva, and the amount of powder spraying can be reduced or even not used. Otherwise, increase the amount of powder spraying.
However, art paper with rough surface, sub-powder coated paper, slightly acidic paper, paper with opposite polarity static electricity, paper with more water content, paper with not smooth surface, etc. are not conducive to the drying of ink, and powder spraying The dosage should be appropriately increased.
In this regard, we must be diligent in inspection during the production process to prevent the product from being sticky and dirty.
Properties of Ink
Different types of inks have different compositions and proportions of binders and pigments, different drying speeds, and different amounts of powder spraying.
Especially in the printing process, the printing suitability of the ink is often adjusted according to the needs of the product, and some varnishes or detackifiers are added to the ink to reduce the viscosity and viscosity of the ink, which will lead to the ink itself. The cohesion of the product is reduced, the drying time of the ink is prolonged, and the risk of smearing on the back of the product is increased. 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 printing press, the shorter the embossing time, the shorter the penetration time of the ink to the paper, and the less the powder falling on the paper. In this case, the amount of powder spraying should be increased as appropriate; otherwise, it can be reduced.
Therefore, if we are printing some high-end picture albums, samples, and covers with a small number of prints, because the paper and ink used in these products have good performance, as long as the printing speed is appropriately reduced, the amount of powder spraying can be reduced, or simply not used. Dusting is also no problem.
In addition to the above considerations, the editor also provides two other experiences:
Look: The printed sheet is placed flat on the viewing table. If you can see a layer of powder spray, you must be careful. The powder spray may be too large, which may affect the surface treatment of the subsequent process;
Pick up the printed sheet and aim at the direction of the light reflection with your eyes to check whether it is even. (Don't rely too much on the computer display data and the meter scale on the machine, the powder tube gambling plug is a common thing!)
Touch: Use a clean finger to sweep the blank space or the edge of the paper, such as a thick white layer of the finger, the powder is too large. If there is a thin layer or you can't see it, be careful! Print 300-500 sheets to be on the safe side, and then gently remove it after 30 minutes to check, confirm that there is no problem, and then open it all the way, so that it is more insurance!
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, which is installed above the cover plate of the delivery chain.
