Analysis of the Causes of Inaccurate Printing on Intaglio Printing Paper (I)

In the gravure printing process, we often encounter the problem of inaccurate ink printing, which is mainly manifested in spot color patches in printed products, graphic and line defects, poor level reproducibility, or missing dots. There are many reasons for inaccurate ink, and there are many factors involved, including paper, printing plates, inks, and printing processes. The main reasons are summarized below and are for reference only by peers.

A paper smoothness is too low

Paper smoothness refers to the smoothness and smoothness of the paper surface. It is an important performance index of paper, and it affects the uniformity of ink transfer and the clarity of lines and dots. Too low a smoothness is the main factor that causes the printing ink to be inaccurate. The prints on the spot appear a few spots, and the tone and level of the image are poorly reproducible, and dot loss often occurs. Therefore, we must ensure that the smoothness of the paper meets certain requirements in order to produce high-quality prints.

To determine whether the printing ink is not caused by the smoothness of the paper, the magnifier can be used to observe the impression of the ink, including the appearance and distribution of spots on the print, and the degree of loss of the dots, or by changing the smoothness under the same conditions. The coated paper is determined by the method of trial printing.

In actual operation, we can adopt the following methods to solve or reduce defects such as print spots caused by low paper smoothness.

1. Put a good paper quality

Before paper storage or printing, the smoothness of the paper is measured with a smoothness tester, and the measured results are compared with the paper use standards to determine whether the paper smoothness meets the printing requirements, so as to avoid unnecessary production waste.

2. Improve the plate making process

When the spots appear on the printed solid color patches, the plate making process can be appropriately improved, such as increasing the engraving depth of the plate base and increasing the thickness of the ink layer to make up for the defects of low paper smoothness, thereby reducing the spotting of the printed products to some extent. phenomenon. However, for those prints that express hierarchical hue through dots, it is difficult to do so, and only paper with higher smoothness can be replaced.

3. Increase printing pressure appropriately

The transfer of the ink is accomplished by the extrusion of the plate cylinder and the impression cylinder. By appropriately increasing the printing pressure and using the ink with better leveling, the ink can be fully transferred, and spot defects can be reduced.

4 before the printing of the primer

If conditions permit, the paper can be primed before printing, which can reduce the phenomenon of print spots, but this will increase production costs.

Two plates blocked version

Generally speaking, in the gravure printing process, only 1/3 to 2/3 of the ink in the plate cavity is transferred to the printing material. If the remaining ink is solidified immediately before leaving the printing material and entering the ink tank, it will enter again. When the ink tank is exposed to the squeegee before it is dissolved in the solvent, the ink transfer rate will gradually decrease, resulting in blockage. The reduced amount of ink transferred does not cover the surface of the printing material, resulting in spotted prints.

1. The ink is dried on the plate surface

Drying of the ink on the surface of the printing plate is one of the main reasons for blockage, and is generally caused by the reason that the ink is dried rapidly, the ink viscosity is high, or the printing speed is slow. To avoid this phenomenon, pay attention to the following points during the printing process:

a) The viscosity of the ink. The viscosity of the ink is too high, the solvent content in the ink is relatively small, and it is easier to volatilize to make the ink dry on the plate. Therefore, the viscosity of the ink can be appropriately adjusted.

b) Dryness of the ink. The drying speed of the ink is too fast, and it is easy to produce a blockage, and a slow drying agent can be suitably used to adjust the drying speed of the ink.

c) Printing speed. The slow speed prolongs the evaporation time of the solvent in the ink, making it easy to dry the ink in the mesh. For plates with dots, this phenomenon is more common. According to actual conditions, the distance between the squeegee squeegee and the embossing point can be shortened, a slow-drying agent can be added to the ink, or the printing speed can be appropriately increased. It is important to note that when the down time is long, it is best to raise the squeegee to allow the plate cylinder to run at low speed in the ink tank to prevent the ink from drying on the plate. Once the plate is jammed, it is necessary to clean the plate with detergent. After each batch of products is printed, it is necessary to use solvent to clean the plates in a timely manner and coat them with a sewing machine oil to avoid hidden dangers.

Of course, environmental factors cannot be ignored either. The temperature and humidity in the workshop are not well controlled, and it is also easy to cause plate jams. When the ambient temperature is too high, the volatilization rate of the solvent is accelerated and the viscosity of the ink increases. This phenomenon is easy to occur in the hot season, and appropriate amount of slow-drying agent can be added to the ink, or the printing speed can be increased as much as possible under the premise of ensuring product quality.

2. Poor performance of ink

The performance of the ink itself is poor, the pigment particles are large or not fully dissolved; the storage time of the ink is too long to cause deterioration, the solvent balance changes, and the ink solubility is reduced; different inks are used improperly to cause chemical reactions; ink flowability causes ink transfer Lower rates will cause blockages. It can be solved by replacing the ink that meets the requirements of gravure printing.

In addition, the ink mixed with impurities, such as blade scrapings, undissolved ink residue, etc. will also lead to blockage, need to be solved by filtering the ink.

3. Problems with platemaking

The use of electronic engraving process for making printing plates, in the process of printing plate, may cause flaws in the inner wall of the cells due to process and Other reasons, chrome plating to leave surface defects or burrs generated during grinding, which will affect the transfer of ink, resulting in blocking Version.

4. Inappropriate operation

Improper use of solvents in the printing process, resulting in decreased solubility; Ink tanks, ink carts are not clean, residual ink residue or impurities mixed in the ink; no corresponding preventive measures are taken when stopped halfway; residual ink of plates is not printed after printing Thorough cleaning will cause the ink to dry in the mesh and cause blockage.

(to be continued)