Analysis on the causes of inaccurate inking of the

Analysis of the reasons for the inaccurate inking of gravure prints on paper (Part 1)

in the process of gravure printing, we often encounter the problem of inaccurate inking of prints, which is mainly manifested in the spot of color blocks on the spot of prints, incomplete graphics and lines, poor level reproducibility or point loss. There are many reasons for false inking, and many factors are involved, including paper, printing plate, ink and printing process. Now the main reasons are summarized. It can provide relevant information about the reaction of metals and alloys to mechanical load as follows, which is only for peer reference

the smoothness of a paper is too low

the smoothness of a paper refers to the flatness and smoothness of the paper surface. It is an important performance index of a paper, which affects the uniformity of ink transfer and the clarity of lines and points. Too low smoothness is the main factor that leads to inaccurate inking of printed products. There are small and different spots in the field of printed products, and the reproducibility of the order and level of the image is poor, which usually leads to point loss. Therefore, we must ensure that the smoothness of the paper meets certain requirements in order to produce high-quality prints

to judge whether the inking of the print is caused by the smoothness of the paper, you can use a magnifying glass to observe the inking of the print gbt4156 ⑴ 984 metal cupping test method (thickness 0.2~2mm), including the shape and distribution of spots on the print, as well as the degree of point loss, or by changing the coated paper with higher smoothness under the same conditions for trial printing

in practice, we can take the following methods to solve or reduce the defects such as printing spots caused by the low smoothness of the paper

1. Check the paper quality

before the paper is put into storage or printed, use the smoothness tester to detect the smoothness of the paper, and compare the measured results with the use standards of this kind of paper to determine whether the smoothness of the paper meets the printing requirements, so as to avoid unnecessary waste in actual production

2. Improve the plate making process

when spots appear on the color block on the printing field, the plate making process can be appropriately improved, such as increasing the engraving depth of the printing hole and increasing the thickness of the ink layer, so as to make up for the defect of low smoothness of the paper, so as to reduce the spots of the printing to a certain extent. However, it is difficult for those prints that express the hierarchical hue through dots. They can only replace the paper with a higher smoothness

3. Appropriately increase the printing pressure

the transfer of ink is completed by the extrusion of the plate cylinder and the embossing cylinder. By properly increasing the printing pressure and using ink with good leveling property, the ink can be fully transferred, which can reduce the spot defect

4. Polish and base the paper before printing

if possible, polish and base the paper before printing, which can reduce the printing spots, but it will increase the production cost

blocking of the second printing plate

generally speaking, in the process of gravure printing, only 1/3 ~ 2/3 of the ink in the printing plate cavity is transferred to the substrate. If the residual ink solidifies instantly before leaving the substrate and entering the ink tank, and then contacts the doctor blade before entering the ink tank again without being dissolved by the solvent, the transfer rate of the ink will gradually decline, resulting in blocking. The transferred ink volume is reduced and cannot cover the surface of the substrate, resulting in spots on the printed products

1. Ink drying on the surface of the printing plate

ink drying on the surface of the printing plate is one of the main reasons for blocking the plate, which is generally caused by too fast drying speed of the ink, high viscosity of the ink or slow printing speed. To avoid this phenomenon, pay attention to the following points in the printing process:

a) viscosity of ink. The ink viscosity is too high, and the solvent content in the ink is relatively small, which is easier to volatilize and make the ink dry and firm in the layout. Therefore, the ink viscosity can be appropriately reduced

b) dryness of ink. The drying speed of ink is too fast, which is easy to cause blocking. Slow drying agent can be used appropriately to adjust the drying speed of ink

c) printing speed. The speed is too slow, which prolongs the volatilization time of the solvent in the ink and makes the ink easy to dry and solidify in the hole. This phenomenon is common for plates with dots. According to the actual situation, the distance between the scraping point of the doctor blade and the embossing point can be shortened, slow drying agent can be added to the ink, or the printing speed can be appropriately increased. It should be noted that when the stoppage time is long, most "So lift up the doctor blade and let the plate cylinder run at a low speed in the ink tank to prevent the ink from drying on the plate. In case of blocking, clean the plate with detergent. After each batch of products is printed, clean the plate with solvent in time, and apply sewing oil to keep it well, so as not to leave hidden dangers.

of course, environmental factors can not be ignored. If the temperature and humidity in the workshop are not well controlled, it is also easy to cause blocking of the plate. Ring The ambient temperature is too high, the solvent volatilization speed is accelerated, and the ink viscosity increases. This phenomenon is easy to occur in high temperature seasons. You can add an appropriate amount of slow drying agent to the ink, or improve the printing speed as much as possible on the premise of ensuring product quality

2. Poor performance of ink

poor performance of ink itself, large pigment particles or not fully dissolved; Ink storage time is too long, resulting in deterioration, solvent balance changes, resulting in reduced ink solubility; Improper use of different inks causes chemical reactions; Poor ink fluidity and low ink transfer rate will cause blocking. It can be solved by changing the ink whose performance meets the requirements of gravure printing

in addition, impurities mixed in the ink, such as scraps of the scraper, undissolved ink residue, etc., will also lead to blocking, which needs to be solved by filtering the ink

3. Problems in plate making

using electronic engraving process to make a printing plate may cause defects on the inner wall of the hole, chrome plating leaving surface defects or burrs during grinding due to process and other reasons, which will affect the transfer of ink and cause blocking

4. Improper operation

in the printing process, the solvent electronic universal testing machine tests different products with different tensile forces. Improper use leads to the decrease of solubility; The ink tank and car are not cleaned thoroughly, and the residual ink residue or impurities are mixed into the ink; Failure to take corresponding preventive measures during midway shutdown; If the residual ink of the printing plate is not cleaned thoroughly after printing, the ink will dry and solidify in the hole, causing blocking

(to be continued)