Influence of printing viscosity of the hottest ink

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The influence of ink printing viscosity on gravure printing quality release date: Source: China paper

in the production process of packaging and printing, the causes of dirty plate problems are not only related to the ink formula itself, the pressure and contact angle of the doctor blade and the quality of the printing plate, but also related to the printing viscosity of the ink. Today, China's paper industry starts with ink printing. Let's introduce the relevant influencing factors

I. version fog problem:

in plastic gravure printing, the non printing surface of the printing plate roller is often stuck with a layer of hazy ink. Transfer to the printing substrate often presents a sheet or line like dirty plate. This is the dirty version. Also called fog version. The cause of the dirty plate problem is not only related to the ink formula itself, the pressure and contact angle of the doctor blade and the quality of the printing plate, but also related to the printing viscosity of the ink

if the printing viscosity of the ink is too high, the viscosity of the ink becomes larger. Under the high-speed movement of the printing plate, the ink will have a great impact on the doctor blade. In this way, it is difficult for the doctor blade to smoothly scrape off the ink of the non graphic part, resulting in version pollution

if the pigment in the ink is unevenly distributed in the ink system, or the resin in the ink fails to wrap the pigment particles well, the pigment particles will regroup. The formation of human pigment groups (i.e. coarsening phenomenon) these larger particles are easy to form linear or strip knife lines in printing

generally speaking, the lower the printing viscosity of the ink, the less likely it is to cause the problem of dirty plate. Therefore, during the actual printing process, special attention should be paid to the change of the half occupancy of the printing ink, and the printing viscosity should be adjusted in time to improve the printing quality

II. Flying ink problem in high-speed printing:

when the gravure printing speed exceeds 20m/min, if the domestic chlorinated polyene resin with wide molecular weight distribution is used as the gravure printing ink, resulting in the low viscosity of the printing ink, it may cause the problem of "flying ink". The reason is that the viscosity of printing ink is too low. The cohesion of the ink is greatly reduced. When the ink is transferred to the printing brush film, the low molecular weight resin is easy to be separated, and a small "ink dot" can be seen in the blank part of the print

the problem of "flying ink" can be solved from the following two aspects: - chlorinated polypropylene resin with narrow molecular weight distribution; Second, according to the printing situation, appropriately improve the printing viscosity of the ink

III. Influence on color, transfer rate and color saturation:

gravure ink relies on the ink of the concave point of gravure to transfer to the substrate when selecting the supplier for printing. Relatively speaking, the volume of the printing point is basically fixed. With the increase of the printing viscosity of the ink, the viscosity of the ink also increases. The more ink is transferred from the point, the higher the color concentration and saturation of the print, but there is a certain limit

when the viscosity of the ink continues to rise to a certain degree, the transfer rate of the ink also increases synchronously. If the viscosity of the ink continues to rise, the viscosity of the ink becomes stronger and stronger, and it becomes difficult for the ink to enter a small point. The ink in the point becomes less and less, and the transfer rate of the ink begins to decline gradually. The color density of printed matter also began to decline. The ink manufacturer suggests that the printing viscosity of gravure ink is generally 13-22 seconds (3chaen cup), which is only an empirical value. In the actual printing process, in order to achieve a good printing transfer effect. Choose printing viscosity carefully

IV. impact on printing speed:

the printing speed of the existing gravure printing machines in China (including imported and domestic machines) ranges from 30m/min to 300m/min. Generally, the printing speed of the printing machine is m/min. In actual printing, it is necessary to select according to the printing speed of the printing machine. When the printing speed increases, the printing viscosity value will decrease. Of course, the most appropriate printing viscosity. It is also affected by other factors:

1. Even at the same printing speed, due to the difference of ink formula design. The printing viscosity will also be different. Therefore, in the actual printing process, it must be adjusted according to the printing effect

2. Affected by seasonal temperature: the viscosity of the same printing ink is different in summer and winter. Ink manufacturers have been working hard to reduce the impact of temperature on ink viscosity

3. Select the most appropriate ink printing viscosity according to the actual conditions of the printing plate roller

v. influence on Printing Crystal Gloss:

the lower the viscosity of gravure ink (i.e. adding more solvents to the original ink), the lower the content of resin and pigment in the printing ink, and the ink is not easy to form a smooth ink layer after being transferred to the printing substrate for drying. The appearance of white flowers directly leads to the lack of glossiness of printed matter. Therefore, in order to obtain excellent gloss, we must ensure that the printing ink has the appropriate resin and pigment content

VI. electrostatic problem:

generally, OPP internal printing ink has limited anti-static ability, which is easier to generate static electricity than polyamide surface printing ink and polyurethane system ink. For OPP internal printing ink, the higher the viscosity of printing ink, the more likely it is to generate static electricity. Under normal temperature conditions, static electricity generally does not occur when the viscosity of printing ink is more than 16 seconds (3chaen cup); If the printing viscosity is lower than 16 seconds/33cup, beard, stripe, edge rejection and other faults are easy to occur

if the viscosity of the printing ink has been within 15 seconds/3cup, we suggest not to use the method of increasing the viscosity of the printing alignment marking brush ink as far as possible, because increasing the printing viscosity of the ink will not only increase the printing cost, but also bring difficulties in printing transfer, which is prone to printing failures such as dirty plates. Other methods of eliminating static electricity can be adopted according to the specific situation of generating static electricity, for example, by changing the proportion of diluted solvent. Adding 5% isopropanol (a polar solvent with good conductivity) or adding a small amount of antistatic agent as appropriate can achieve the purpose of eliminating static.

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