Under the premise of ensuring the printing quality, the highest printing quantity that a printing plate can print is called the printing plate's resistance force. The level of gravure resistance 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 gravure printing process, we often encounter some parts of the layout of the color lighter than the normal color, and with the increase in the number of prints, this phenomenon is more serious, a direct impact on the quality of prints. Observed during the shutdown, it was found that part of the layout graphic was worn out, the opening of the ink hole became smaller and the depth became shallower, resulting in a decrease in the area of ​​the ink-passing ink cell and a corresponding decrease in the total ink transfer amount. The overall change in the ink color faded. Reduce the resistance force.
After analysis, the main factors affecting the wear of the printing plate are: surface friction, gravure plate making quality, squeegee pressure, printing pressure, linear speed of printing plate cylinder and embossing roller, performance of ink and paper. Although the influence of these factors on the wear of the printing plate is unavoidable, how to reduce the influence of these undesirable factors on the printing plate is necessary to improve the quality of the printing product, reduce the printing cost, and shorten the printing cycle.
Factors affecting the gravure resistance of gravure printing plates
Surface friction is the main reason for reducing printing plate resistance
Printing can not be separated from the pressure. With pressure, friction is bound to occur, causing the plate surface to wear. The greater the pressure, the greater the friction and the more severe the wear of the printing plate.
There are mainly the following 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.
Ink in the paint, filler thickness and particles, the surface structure of the substrate, the texture of the loose and dust off, etc. can produce additional friction.
Gravure plate quality affects printing plate resistance
Chromium hardness is higher
The quality of the chromium layer is the basis for the printing plate resistance. The chromium layer has a low hardness and is easily scratched by hard particles. Therefore, 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. For example, the hardness of the chromium layer is low, and the thin coating can cause the printing plate to have a reduced printing resistance.
Chrome finish is high
The chromium layer on the surface of the platen roller has a high degree of smoothness, and the blade can scrape the ink under light pressure to reduce the occurrence of failure. If the surface is rough, it is difficult for the squeegee to scrape the ink, which is prone to print failure.
When the printing roller prints, the circumference of the printing roller should be small
For example, the plate cylinder has poor processing accuracy, poor dynamic balance, or wear or deformation of the drum shaft, bearings, and transmission gears, etc., which may cause a runout during printing, resulting in a printed cutter line. Therefore, the printing roller is less likely to beat circumferentially when printing.
The surface of the platen roller should be inspected and wiped hard on the surface of the platen roller to directly damage the plate cylinder and cause printing failure. Always check and wipe the roller.
In gravure production, the layout is required to be smooth, the chromium layer is smooth, uniform in thickness, and has good wear resistance. According to the requirements and types of quality of printed materials, the correct choice of laser engraving gravure or electric engraving gravure, this can avoid unnecessary waste and save costs.
Squeegee and plate printing force
The different angles and pressures of the squeegee have different wear effects on the printing plate. The smaller the angle of the squeegee, the less wear on the printing plate, the weaker squeegee effect, the thicker printing ink, the strong hiding power, the good gloss, but not easy to clean.
Printing pressure and printing plate resistance
The size of the printing pressure has a great influence on the wear of the printing plate, 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 texts in printing is not complete, the ink transfer rate is reduced, and the imprinting is weak; if the printing pressure is too high, the local ink is excessive, so that the prints are inaccurate in color and the graphic and text are distorted. In addition, gears and roller bearings are subjected to excessive pressure and friction, which will inevitably aggravate plate wear and affect the quality of printed products. Therefore, on the basis of ensuring that the imprinting is sufficiently robust, using as little printing pressure as possible (ie, ideal printing pressure) will help reduce the wear of the printing plate.
The linear speed of the plate cylinder and the embossing cylinder should be the same
According to the requirements of the gravure printing process, when the printing plate and the impression cylinder are being rolled, not only the transmission is stable, the instantaneous transmission ratio is constant, and the linear speeds on the surfaces of the two rollers are required to be the same. 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 linear velocity before and after the wear and at the lowest point are not uniform, so that a speed difference occurs and relative slippage occurs. The greater the speed difference of the printing surface, the greater the friction and the increased wear of the printing plate surface. Therefore, the linear velocity of the surface of the printing plate and the impression cylinder in the printing process is as consistent as possible, and the speed difference caused by the wear is reduced, which will help reduce the wear of the plate.
Effect of ink performance on printing plate
For different printing presses, different performance inks should be used. If the pigment of the ink pigment is large, it will act as an abrasive and will aggravate the wear of the printing plate. Although the viscosity of the ink is relatively high, a clear dot can be obtained. However, if the paper strength is not enough, the phenomenon of falling powder and pulling hair easily occurs, which also aggravates the wear of the printing plate. Therefore, choosing a suitable ink is beneficial for reducing the wear of the printing plate and improving the printing quality.
Ways to Improve the Print Resistance of Gravure Printing Plates
A better version of the drum has a higher resistance to printing forces, and the gravure drum has a print resistance of typically more than one million. The surface chrome layer is thinned and can be re-chromed for continued use. High-quality printing plates provide a reliable guarantee for printing. The improvement of the resistance to printing force depends not only on the printed version, but there are many external factors that directly or indirectly affect the printing plate's resistance to printing. Here, the operational aspects of the printing process are summarized as follows:
Under the premise of ensuring the printing quality, use the minimum pressure to reduce the friction between the plate cylinder and the impression cylinder; regularly clean the ink tank and the plate cylinder.
In the premise that the ink on the surface of the printing plate can be scraped off, the smaller the squeegee pressure and the angle of the ink knife are used, the wear of the printing plate by the squeegee is reduced.
Filtration ink, eliminate the static electricity on the surface of the substrate, so as to avoid the coarse particles in the ink or the surface of the substrate to damage the plate due to electrostatic adsorption of hard objects.
The drying of the ink is strictly controlled to prevent the ink from prematurely drying and damaging the plate at the plate surface.
If there is no ink on the surface of the printing plate, the squeegee should not be scraped for a long time. Because the plate surface is not smooth, it is easy to damage the printing plate.
From the process to avoid a variety of abnormal drum damage.
There are many factors that cause plate wear during printing, and these factors also exist objectively. If the printing plate is seriously worn out, it should be diligently handed and grounded to observe and eliminate it one by one. This will reduce the unfavorable factors that will lead to plate wear. This will result in fewer downtimes and fewer plate changes in the printing process, ensuring that production runs smoothly and effectively. Improve productivity.
Reprinted from: "Global Flexible Packaging Industry"