How to improve the printing resistance of gravure

How to improve the printing resistance of gravure plates in production

on the premise of ensuring the printing quality, the maximum printing quantity that a printing plate can print is called the printing resistance of a printing plate. The printing resistance of gravure plates is directly related to the economic benefits of gravure production, and it is also the key to reduce costs, improve production and ensure quality

in the gravure printing process, we often encounter that some colors of some layouts are lighter than normal colors, and this phenomenon becomes more serious with the increase of the number of prints, which directly affects the quality of prints. After stopping the machine for observation, it was found that the graphic part of the layout was worn, the opening of the inking hole became smaller, and the depth became shallower. There must be a certificate in the whole box, resulting in the reduction of the area of the hole inking unit, the corresponding reduction of the total inking volume, and the general trend of the change of ink color became lighter, thereby reducing the printing resistance. After analysis, the main factors affecting the plate wear are: surface friction, gravure plate making quality, pressure of doctor blade, printing pressure, linear speed of plate roller and embossing roller, performance of ink and paper, etc. Although the impact of these factors on plate wear is inevitable, how to reduce the impact of these adverse factors on the plate is very necessary to improve the print quality, reduce the printing cost and shorten the printing cycle

I. factors affecting the printing resistance of gravure plates

1 Surface friction is the main reason for reducing the printing resistance of printing plates

printing cannot be separated from pressure. When there is pressure, friction will inevitably occur, resulting in the wear of the printing plate surface. The greater the pressure, the greater the friction, and the more serious the plate wear

there are mainly the following forms of friction on the surface of the plate cylinder:

(1) friction between the doctor blade and the plate cylinder

(2) friction between plate cylinder and impression cylinder

(3) the thickness and particles of pigments and fillers in the ink can cause pollution particles, and the loose structure and texture of the substrate surface and the falling off of dust can produce additional friction

2. The quality of gravure plate making affects the printing resistance of printing plate

(1) the hardness of chromium layer should be high

the quality of chromium layer is the basis of printing plate printing resistance. Chromium layer has low hardness and is easy to be scratched by hard particles, so chrome plating brings confidence to extruder enterprises, and it is better to have higher hardness. In the printing process, the printing plate is constantly worn by various factors, such as low hardness of chromium layer and thin coating, which will reduce the printing resistance of the printing plate

(2) the finish of the chromium layer should be high

the finish of the chromium layer on the surface of the cylinder is high, and the scraper can scrape the ink under light pressure to reduce the occurrence of faults. If the surface is rough, it is difficult for the doctor blade to scrape the ink, which is easy to cause printing failure

(3) the circumferential runout of the printing plate cylinder during printing should be small

if the processing accuracy of the plate cylinder is poor, the dynamic balance is not good, or the cylinder shaft, bearing and transmission gear are worn or deformed, there will be runout during printing, causing the printing knife line. Therefore, the circumferential runout of the printing plate cylinder during printing should be small

(4) the surface of the plate cylinder should be checked and wiped frequently.

the adhesion of hard objects on the surface of the plate cylinder will directly damage the plate cylinder and cause printing failure. Therefore, always check and wipe the drum

in intaglio production, the layout is required to be flat, the chromium layer is smooth, the thickness is uniform, and has good wear resistance. According to the quality requirements and types of prints, the correct choice of laser engraving intaglio or electric engraving intaglio can avoid unnecessary waste and save costs

3. The angle and pressure of the doctor blade have different wear effects on the printing plate. The angle of the doctor blade is small, which has less wear effect on the printing plate, weak scraping effect, thick ink, strong hiding power, good gloss, but it is not easy to scrape clean. 1 until high-strength glass fiber reinforced compulsory products

4 Printing pressure and printing plate resistance

the size of printing pressure has a great impact on the wear of printing plates, as well as on the printing quality and the structure of printing machinery. The printing pressure is too small, and the image and text transfer in printing is incomplete, which reduces the transfer rate of ink and makes the imprint weak; If the printing pressure is too high, there will be excessive ink in some parts, resulting in inaccurate tone of printed products and distortion of graphics and texts. In addition, the gear and drum shaft bear too much pressure and friction, which is bound to aggravate the wear of the printing plate and affect the quality of printing products. Therefore, on the basis of ensuring that the imprinting is strong enough, it will be beneficial to reduce the wear of the printing plate to use as little printing pressure (i.e. ideal printing pressure) as possible

5. the linear speed of the printing plate roller and the embossing roller should be the same

according to the requirements of the gravure printing process, when the printing plate and the embossing roller are rolled, not only the transmission should be stable, the instantaneous transmission ratio should be constant, but also the linear speed of the two roller surfaces should be consistent. However, due to the wear of the surface of the imprint cylinder, the radius of the imprint cylinder will change during printing. By v=w × R shows that the linear velocity before and after wear and at the lowest point is inconsistent, which will produce a speed difference and cause relative slip. The greater the speed difference of the printing surface, the greater the friction, and the wear of the printing plate also intensifies. Therefore, making the linear speed of the surface of the printing plate and the embossing cylinder as consistent as possible during the printing process and reducing the speed difference caused by wear will help to reduce the wear of the plate

6. The influence of paper performance on the printing plate

the printing performance of paper determines whether the printing process can be carried out smoothly and whether high-quality prints can be obtained

smoothness, ink absorption and surface strength of paper are important printing properties of paper. Under normal pressure, when printing on paper with low smoothness, due to the uneven surface, the imprint of printed products will be false. In order to get clear graphic information and increase the printing pressure, although it makes up for the false impression, it intensifies the wear of the layout. The surface strength of the paper is not high enough, and the viscosity of the ink is high. It is easy to produce powder dropping and galling in printing, and adhere to the embossing cylinder and the printing plate, which not only affects the transfer rate of the ink, but also intensifies the roughness of the printing plate surface, and also intensifies the wear of the printing plate. Therefore, selecting paper with smooth and flat surface, high strength and less paper powder, or cleaning the printing plate cylinder frequently, will help to reduce the printing plate wear phenomenon in printing

7. influence of ink performance on printing plate

for different printing machines, ink with different performance should be selected. If the particles of ink and pigment are large, they will play the role of abrasive and aggravate the wear of printing plates. The viscosity of the ink is high, although clear points can be obtained, but if the paper strength is not enough, it is easy to produce powder dropping and galling, which will also aggravate the wear of the printing plate. Therefore, choosing the appropriate ink is beneficial to reduce the wear of the printing plate and improve the printing quality

Second, the way to improve the printing plate printing resistance

a good quality version cylinder has relatively high printing resistance, and the printing resistance of gravure cylinder can generally reach more than onemillion. The chromium layer on the surface has been ground thin, and can be re chrome plated for further use. High quality printing plates provide a reliable guarantee for printing. The improvement of printing resistance not only depends on the printing plate itself, but also many external factors directly or indirectly affect the printing resistance of printing plates. Here, the operation of the printing process is summarized as follows:

(1) on the premise of ensuring the printing quality, use the minimum pressure to reduce the friction between the plate cylinder and the embossing cylinder; Clean the ink tank and cylinder regularly

(2) on the premise of scraping the ink on the surface of the printing plate, try to use a small scraping pressure and blade angle to reduce the wear of the blade on the printing plate

(3) filter the ink and eliminate the static electricity on the surface of the substrate, so as to avoid the coarse particles in the ink or the hard objects adsorbed by static electricity on the surface of the substrate damaging the printing plate

(4) strictly control the drying of the ink to avoid premature drying of the ink on the surface of the printing plate and damaging the printing plate

(5) when there is no ink on the surface of the printing plate, the doctor blade should not scrape for a long time, because the plate is not smooth, it is easy to damage the printing plate

(6) avoid all kinds of abnormal damage to the plate cylinder from the process

in a word, there are many factors causing plate wear in printing, and these factors also exist objectively. In case of serious plate wear, you should work hard and observe frequently, analyze and eliminate one by one, and reduce the adverse factors that are easy to cause plate wear, so as to reduce downtime and plate replacement in the printing process, ensure the smooth progress of production and effectively improve productivity

reprinted from: printer