Control ink printing viscosity

First, version fog issues:

In plastic intaglio printing, the non-printing surface of the plate cylinder is often adhered with a layer of ink. Transfer to the printing substrate often presents a splat or line-like smear. This is the dirty version. Also called fog version. The cause of the smudge problem is related to the printing viscosity of the ink in addition to the ink formulation itself, the pressure and contact angle of the doctor blade, and the quality of the plate.

If the ink printing viscosity is too high, the viscosity of the ink becomes larger. Under the high-speed movement of the printing plate, the ink will have a large impact impact on the squeegee. In this way, it is very difficult for the squeegee to scrape off the ink of the non-graphic part smoothly, and the stain is thus generated.

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 re-aggregate. The formation of human pigment groups (both coarse and coarse) causes these large particles to easily form lines or strips of cut lines during printing.

In general, the lower the printing viscosity of the ink, the less likely it is to cause smearing problems. Therefore, in the actual printing process, special attention must be paid to changes in the half-occupancy of the printing ink, and the printing viscosity must be timely adjusted to ensure that the printing quality of the bank is high.

Second, high speed printing ink problem:

When the gravure printing speed exceeds 20m/min or more, if the gravure printing ink uses a chlorinated polyalkylene resin with a wide molecular weight distribution, resulting in a low viscosity of the printing ink, it may bring about a problem of “flying ink”. The reason for this is that the viscosity of the printing ink is too low. The cohesion of the ink is greatly reduced, and when the ink is transferred to the printing brush film, the low-molecular-weight resin can be easily separated, and a small “ink spot” can be seen in the blank portion of the printed matter.

Solving the problem of “flying ink” can be solved in the following two aspects: - Chlorinated polypropylene resin with a narrow molecular weight distribution; Second, according to the printing situation, the printing viscosity of the ink is appropriately increased.

Third, the impact of color, transfer rate and color saturation:

The gravure ink is transferred to the printing substrate by means of the ink of the gravure recessed dot. In contrast, the volume of the printing dot is substantially fixed. With the increase of ink printing viscosity, the viscosity of the ink is also increased, and the more ink is transferred from the dot, the higher the color density and saturation of the printed article, but there is a certain limit.

When the viscosity of the ink is continuously increased to a certain extent, the ink transfer rate is also increased synchronously. If the viscosity of the ink continues to rise, the viscosity of the ink becomes stronger and the ink becomes difficult to enter. In the outlets, the ink in the outlets has become less and less, and the ink transfer rate has gradually declined. The color density of prints also began to decline. Ink manufacturers recommend that gravure ink printing viscosity is generally 13 to 22 seconds (3 # Zahn Cup) This is only an empirical value, in the actual printing process, in order to achieve a good print transfer effect. The printing viscosity should be carefully selected.

Fourth, the impact on the printing speed:

Domestic domestic gravure printing machines (including imported machines and domestic machines) have printing speeds from 30m/min to 300m/min. General printing press speed is 80-200m/min. In actual printing, it is selected according to the printing speed of the printing press. As the printing speed increases, the print viscosity will decrease. Of course the most suitable printing viscosity. It is also affected by other factors:

1, even if the same printing speed, due to ink formulation design differences. The print viscosity will also vary. Therefore, in the actual printing process, it must be adjusted according to the effect of printing.

2. Influenced by seasonal temperature: The viscosity of the same printing ink in the summer and winter is different, and ink manufacturers have also been working hard to reduce the influence of temperature on the viscosity of the ink.

3, but also according to the actual conditions of the printing plate roller to select the most appropriate ink printing viscosity.

Fifth, the impact of the print crystal gloss:

The lower the viscosity of the gravure ink (ie, the addition of more solvent to the original ink), the lower the content of resin and pigment in the printing ink, and the easier the ink to form a smooth ink layer after the ink is transferred to the printing substrate. The phenomenon of white flowers directly leads to lack of glossiness of the printed matter. Therefore, in order to obtain excellent gloss, it is necessary to ensure that the printing ink has a suitable resin and pigment content.

VI. Electrostatic problems:

Under normal circumstances, OPP printing ink itself has limited antistatic ability and is more prone to static electricity than polyamide type surface ink and polyurethane system ink. For OPP printing inks, the higher the viscosity of the printing ink, the easier it is to cause static problems. Under normal temperature conditions, the viscosity of the printing ink is more than 16 seconds (3 # Zahn Cup). If the printing viscosity is lower than 16 seconds/3# cup, defects such as beard-like, zebra-like, edge repulsion and the like easily occur.

If the viscosity of the printing ink is already 15 seconds/3# cups, we recommend not using the method of increasing the viscosity of the printing ink as much as possible, because increasing the printing viscosity of the ink not only increases the printing cost but also brings about difficulty in the transfer of the printing and easily produces stencils, etc. Printing failure. According to the specific situation of static electricity generation, other methods of eliminating static electricity may be adopted, for example, by changing the proportion of diluted solvent. Add 5% isopropanol (which is a polar solvent, good conductivity) or add a small amount of antistatic agent as appropriate to eliminate static.

Reproduced from: Machinery Network