The relationship between gravure printing plate and printing durability
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Under the premise of ensuring the printing quality, the highest printing quantity that a printing plate can print is called the printing durability of the printing plate. The high printing and lowing of gravure printing plates is directly related to the economic benefits of gravure printing, and is also the key to reducing costs, increasing production and ensuring quality.
In the process of gravure printing, we often encounter some parts of the color of the layout is lighter than the normal color, and as the number of prints increases, this phenomenon becomes more serious, directly affecting the quality of the print. When the machine was stopped, it was found that the part of the layout was worn out, the opening of the ink hole became smaller, the depth became shallower, the area of the ink transfer unit of the cell was reduced, the total ink transfer amount was also reduced, and the total trend of the change of the ink color became lighter. Reduce the printing durability.
After analysis, the main factors affecting the wear of the printing plate are: surface friction, plate making quality of the gravure, pressure of the squeegee, printing pressure, line speed of the plate cylinder and the embossing roller, and performance of the ink and paper. Although the influence of these factors on plate wear is inevitable, how to reduce the impact of these undesirable factors on the printing plate is necessary to improve the quality of printed products, reduce printing costs and shorten the printing cycle.
Factors affecting the printing durability of gravure plates
Surface friction is the main reason for reducing the printing durability of printing plates
Printing is inseparable from stress. If there is pressure, it will inevitably cause friction and cause wear on the surface of the printing plate. The greater the pressure, the greater the friction and the more severe the plate wear.
There are mainly several forms of friction on the surface of the plate cylinder:
The friction between the squeegee and the plate cylinder.
The friction between the plate cylinder and the impression cylinder.
The thickness of the pigment in the ink, the thickness and particles of the filler, the structure of the surface of the substrate, the looseness of the texture, and the shedding of the dust can generate additional friction.
The quality of the gravure plate affects the printing durability of the plate
Chromium layer hardness is high
The quality of the chrome layer is the basis for the printing durability of the printing plate. The chrome layer has a low hardness and is easily scratched by hard particles, so it is better to have a higher hardness when chrome plating. In the printing process, the printing plate is affected by various factors and is constantly subject to wear and tear. For example, the hardness of the chrome layer is low and the plating layer is thin, which may cause the printing durability of the printing plate to decrease.
Chrome finish is high
The chrome layer on the surface of the plate has a high surface finish, and the blade can scrape the ink under lighter pressure to reduce the occurrence of malfunction. If the surface is rough, the doctor blade is difficult to scrape the ink, which is prone to printing failure.
When the plate cylinder is printed, the circumferential beating is small.
Such as the plate drum processing accuracy is poor, the dynamic balance is not good, or the drum shaft, bearings and transmission gears are worn or deformed, which will cause jumping when printing, causing the printing knife line. Therefore, the circumferential slip of the plate cylinder is small when printing.
The surface of the plate cylinder should be inspected frequently, and adhering hard objects on the surface of the wiper cylinder will directly damage the plate cylinder, causing printing failure. Always check and wipe the rollers.
In the gravure production, the layout is required to be flat, the chrome layer is smooth, the thickness is uniform, and the wear resistance is good. According to the requirements and types of printed products, the laser engraving gravure or electro-engraving gravure is correctly selected, which avoids unnecessary waste and saves costs.
Squeegee and printing plate
The angle and pressure of the doctor blade have different wear effects on the printing plate. The angle of the squeegee is small, the wear effect on the printing plate is less, the squeegee effect is weak, the ink of the printed product is thick, the hiding power is strong, the gloss is good, but it is not easy to scrape clean.
Printing pressure and printing durability
The printing pressure has a great influence on the printing plate wear, and also has a great influence on the printing quality and the structure of the printing machine. The printing pressure is too small, the transfer of graphics and text in printing is not complete, the transfer rate of the ink is reduced, and the print is faint; if the printing pressure is too large, the local ink is excessive, so that the color tone of the print is not accurate, and the graphic is distorted. In addition, the gear and roller bearings are subject to excessive pressure and friction, which will inevitably increase the wear of the printing plate and affect the quality of the printed product. Therefore, on the basis of ensuring that the print is sufficiently strong, it is advantageous to reduce the wear of the printing plate by using a small printing pressure (i.e., ideal printing pressure) as much as possible.
The plate roller and the impression roller have the same line speed
According to the requirements of the gravure printing process, when the printing plate and the impression cylinder are rolled, not only the transmission is stable, the instantaneous transmission ratio is constant, and the line speeds of the surfaces of the two rollers are required to be uniform. However, due to the wear of the surface of the impression cylinder, the radius of the impression cylinder changes during printing. It can be seen from V=W×R that the line speeds before and after the wear are inconsistent, which causes a speed difference and causes relative slip. The greater the speed difference of the printed surface, the greater the friction and the increased wear of the printing surface. Therefore, it is beneficial to reduce the wear of the printing plate by making the speed of the surface of the printing plate and the impression cylinder as uniform as possible during the printing process and reducing the speed difference caused by the abrasion.
The effect of ink performance on the plate
For different presses, different performance inks should be used. If the particles of the ink pigment are large, it will act as an abrasive, which will aggravate the wear of the printing plate. The viscosity of the ink is high, although a clear dot can be obtained, but if the strength of the paper is not enough, it is easy to produce powder and pull, which will also aggravate the wear of the printing plate. Therefore, selecting a suitable ink is beneficial for reducing plate wear and improving print quality.
Ways to improve the printing durability of gravure printing plates
A better quality plate cylinder has a higher printing durability, and the gravure resistance of the gravure cylinder can generally reach more than one million. The surface chrome layer is thinned and can be re-plated for continued use. High-quality printing plates provide a reliable guarantee for printing. The improvement of printing durability depends not only on the printed version, but also on many external factors that directly or indirectly affect the printing durability of the printing plate. Here, the operation aspects of the printing process are summarized as follows:
Under the premise of ensuring the printing quality, the minimum pressure is used to reduce the friction between the plate cylinder and the impression cylinder; the ink tank and the plate cylinder are regularly cleaned.
Under the premise of being able to scrape off the ink on the surface of the printing plate, try to use a smaller squeegee pressure and ink blade angle to reduce the wear of the squeegee on the printing plate.
Filter the ink to eliminate static electricity on the surface of the substrate to prevent the coarse particles in the ink or the surface of the substrate from damaging the plate due to hard objects adsorbed by static electricity.
Strictly control the drying of the ink to avoid premature drying of the ink on the surface of the printing plate to damage the printing plate.
When there is no ink on the surface of the printing plate, the squeegee should not be scratched for a long time. Because the layout is not smooth, it is easy to damage the printing plate.
Various abnormal damages of the plate cylinder are avoided from the process.
There are many factors that cause plate wear in printing, and these factors are also objective. If the printing plate wear phenomenon is serious, it should be diligently and diligently observed, and analyze and eliminate one by one to reduce the unfavorable factors that easily lead to plate wear, so that less stoppage and less plate change in the printing process, ensuring smooth production and effective Improve productivity.