Control the printing viscosity of inks to improve the quality of gravure printing

First, the version of the fog problem:

In plastic gravure printing, the non-printed side of the plate cylinder is often adhered with a layer of ink. Transfer to the printed substrate often results in a sheet or line-like stain. This is the dirty version. Also called the fog version. The cause of the stain 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 printing plate.

If the ink printing viscosity is too high, the viscosity of the ink becomes large, and under the high-speed movement of the printing plate, the ink will have a large impact force against the doctor blade. In this way, it is difficult for the squeegee to smoothly scrape off the ink of the non-image portion, and the smudge is 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 re-aggregate between them. The large pigment particles that form the human pigment group (both coarse) are easily formed into linear or strip-shaped cut lines during printing.

In general, the lower the printing viscosity of the ink, the less likely it is to cause the problem of the stain. Therefore, in the actual printing process, special attention should be paid to the change of the halfness of the printing ink, and the printing viscosity and the quality of the printed product should be adjusted in time.

Second, the problem of flying ink at high speed printing:

When the gravure printing speed exceeds 20 m/min or more, if the gravure ink adopts a domestically produced chlorinated polyene resin having a wide molecular weight distribution, resulting in a viscosity of the printing ink being too low, the problem of "flying ink" may be caused. The reason for this is that the viscosity of the printing ink is too low. The cohesive force of the ink is greatly reduced. When the ink is transferred to the printing brush film, the low molecular weight resin is easily separated, and a small "ink dot" can be seen in the blank portion of the printed matter.

Solving the problem of "flying ink" can be solved from the following two aspects: - using a chlorinated polypropylene resin with a narrow molecular weight distribution; and secondly, appropriately increasing the printing viscosity of the ink according to the printing condition.

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

The gravure ink is transferred to the printing substrate by means of ink which is recessed by the intaglio plate. In contrast, the volume of the printing dot is substantially fixed. As the ink printing viscosity increases, the viscosity of the ink also increases, and the more ink is transferred from the dot, so the color density and saturation of the printed product are higher, but there is a limit.

When the viscosity of the ink is continuously increased to a certain extent, the transfer rate of the ink is also increased synchronously. If the viscosity of the ink continues to rise, the viscosity of the ink becomes stronger and stronger, and the ink becomes difficult to enter. At the outlets, there are fewer and fewer inks in the outlets, and the ink transfer rate begins to decline. The color density of the prints also began to decline. The ink manufacturer recommends that the printing viscosity of the gravure ink is generally 13 to 22 seconds (3#Zahn Cup). This is only an empirical value, in order to achieve a good printing transfer effect in the actual printing process. The printing viscosity should be carefully selected.

Fourth, the impact on printing speed:

The printing speed of existing gravure printing machines (including imported machines and domestic machines) in China is from 30m/min to 300m/min. Generally, the printing speed of the printing machine is 80-200m/min. In actual printing, it is necessary to select according to the printing speed of the printing press. As the printing speed increases, the printing viscosity value will decrease. Of course the most suitable printing viscosity. Also affected by other factors:

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

2, affected by seasonal temperature: the same printing inks have different viscosities in summer and winter, and ink manufacturers have been working hard to reduce the effect of temperature on ink viscosity.

3. The most suitable ink printing viscosity should be selected according to the actual conditions of the printing plate cylinder.

Fifth, the impact on the printing crystal gloss:

The lower the viscosity of the gravure ink (i.e., the more solvent is added to the original ink), the lower the resin and pigment content of the printing ink, and the ink is not easily formed into a smooth ink layer after being transferred to the printing substrate. The appearance of white flowers directly leads to the lack of gloss in the prints. Therefore, in order to obtain excellent gloss, it is necessary to ensure that the printing ink has a suitable resin and pigment content.

Sixth, static problem:

Under normal circumstances, the printing ink itself in OPP has limited antistatic ability, and it is more likely to generate static electricity than polyamide type surface printing ink and polyurethane system ink. For the printing ink of OPP, the higher the viscosity of the printing ink, the more likely the problem is to generate static electricity. 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, whiskers, streaks, edge repulsion and the like are prone to occur.

If the printing ink viscosity is already at 15 sec / 3 # cup, we recommend that you try not to increase the viscosity of the printing ink, because increasing the printing viscosity will not only increase the printing cost, but also cause printing transfer difficulties, easy to produce stains, etc. Printing failure. Other methods of removing static electricity may be employed depending on the specific conditions in which static electricity is generated, for example, by changing the proportion of the diluted solvent. Add 5% isopropanol (a polar solvent, good conductivity) or add a small amount of antistatic agent as appropriate to eliminate static.