Analysis of the most popular plastic film gravure

2022-08-23
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Plastic film gravure overprint inaccurate problem analysis

plastic film gravure printing has a wide range of faults, and inaccurate overprint before and after pictures and texts is one of the common faults when the atmosphere is dry. Incorrect overprint will cause material waste. Therefore, people in the industry attach great importance to it. It is very necessary to understand the causes of inaccurate overprint and master its elimination methods. This paper relies on the author's experience in gravure printing for several years. The following analysis is made on the overprint inaccuracy for the reference of insiders. The process of gravure printing of plastic film is; The substrate passes through the feeding device, the conduction roller enters the first unit for printing, then enters the drying device, and then enters the second unit for printing driven by the conduction roller, and so on, and finally enters the winding device. In this process, in order to avoid or reduce the loss caused by inaccurate overprinting, it is necessary to ensure that the unwinding and rewinding tension of the substrate are consistent, and pay attention to the direction of inaccurate overprinting, and then take corresponding solutions

there are many reasons for inaccurate gravure overprint of plastic film, including the influence of objective factors such as mechanical equipment, ink suitability, environmental temperature, and subjective factors such as the quality awareness of operators. Here is a detailed analysis one by one

influence of reel diameter

the larger the reel diameter, the easier it is for the plastic to deviate during operation, which brings hidden dangers to overprint. According to experience, the diameter of coil is generally CRA. During printing, with the gradual reduction of the coil diameter, the unwinding tension should be reduced accordingly to ensure that the feeding tension remains stable. This is achieved by manual gear or magnetic particle brake. During this operation, pay attention to observe whether the printed color code is out of shape

the axial direction of the plate cylinder of the domestic multicolor gravure press is positioned by the matching of the U-shaped groove at the cylinder end and the bearing on the frame. The thickness of the bearing is exactly equal to the width of the U-shaped groove. When the width increases due to the wear of the U-shaped groove, the plate shaft may drive the plate cylinder to produce axial movement, causing inaccurate overprint. When the wear is more than 0.3mm, the inaccurate overprint and pattern aliasing will be very obvious. As an operator, oil should always be injected into the sliding part, gear and other operating parts of the gravure press to ensure the accuracy of overprint, and achieve the purpose of prolonging the mechanical life and reducing wear. When significant wear occurs, the worn parts should be replaced

when the plate axis moves axially, the color sample on the substrate is unstable and the color code moves upward

the guide roller is charged

during the printing process, the plastic film will be pulled by the guide roller into the next unit for printing or into the drying device. However, after the plastic film rubs with the conduction roller, the conduction roller will carry static electricity, absorb the dust in the air, and make the conduction roller locally increase, resulting in axial sliding of the film and inaccurate overprint. Therefore, when the machine is stopped, the conduction roller should be cleaned to lay a good foundation for the next printing

incorrect edition

inaccurate overprint is also related to edition. Wash the plate shaft before installing the plate, and then install the printing plate in the center of the shaft. The plugs (also known as "bulkhead") at both ends of the printing plate should also be installed smoothly, and the force should be even when locking the plate, so as to ensure the accuracy of overprint. Generally speaking, the fitting clearance of the plate shaft is 0..06mm. When it is worn to 0.2mm, it is very difficult to register; When it is worn to 0.4-0.6mm, it should be replaced

gear wear

after long-term operation, the gears of each printing unit will also be worn to varying degrees. If the plate cylinder gear and the main transmission gear on the transmission shaft are not meshed at the graduation circle, the speed will be unstable, resulting in a decline in accuracy and inaccurate overprinting. It is shown that the color code on the substrate is offset up and down, which is very unstable

improper selection of rubber rollers

in order to obtain higher precision registration, the selection of rubber rollers should also be very careful. There was an inaccurate overprint fault in our factory, which failed to achieve good results through changing materials, re testing printing plates and adjusting tension. Later, we found that the diameter difference between the two ends of a rubber pressure roller was 0.015mm, and the fault was eliminated by replacing a new rubber pressure roller

generally speaking, the printing thickness is 12 μ M wide film, the requirements for glue

rollers are more stringent. At the same time, it should also ensure that the pressure between the pressure roller and the printing plate is uniform, otherwise it will also cause problems such as inaccurate overprint. Uneven cot pressure and plastic film thickness deviation will directly lead to inaccurate overprinting. On the substrate, it is mostly shown as horizontal image offset

influence of ambient temperature and humidity

in the printing process, compared with the first unit, the film will stretch with the change of temperature, resulting in inaccurate overprint. Therefore, in the printing process, as long as the solvent can be effectively volatilized, the lower the drying temperature is, the better

at the same time, it is also necessary to control the temperature of the printing environment. Humidity. Generally, the temperature and humidity in the workshop should be controlled at 25 ℃ and 40%. Too high or too low will affect the overprint accuracy

ink

excessive viscosity of ink will also cause image displacement, so the viscosity value should be adjusted according to the actual situation

printing plate increment

in gravure printing, considering the stretching of plastic film, according to the color sequence, the printing plate has a increment, which increases gradually. If the incremental error exceeds the allowable range, the chromatic accuracy will also decline. Therefore, before the plate cylinder is put on the machine, it is necessary to carefully check and make records, and carefully compare the printed piece with the original during printing

winding tension

the proportion of plastic film exports to emerging countries will also be greatly increased during operation. It is required that the winding tension be stable. With the gradual increase of winding diameter, the winding tension should also be increased accordingly. At the same time, pay attention to the jitter range of the winding, because the winding tension is adjusted by the friction plate on the rolling bearing at the end of the winding shaft. If the jitter range is large, the film shrinks, and the tension value increases. Generally, the tension value can be controlled by magnetic particle brake or manual adjustment. We should also note that the longer the coil is, the easier it is to stretch, and the tension value should change accordingly. Constant and stable tension is very important

in a word, in order to obtain accurate overprint and exquisite plastic film prints, we must deal with each process well, and carefully analyze the problems and summarize the experience for future reference

(author/chenjindong)

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