Analysis of the problem of inaccurate gravure overprinting of plastic films


Published on:

2009-03-19

Plastic film gravure printing overprint inaccuracy analysis of plastic film gravure printing failure of a variety of types, before and after the graphic overprint inaccuracy is one of the common failures. Due to the inaccurate overprinting will cause material waste. Therefore, it has attracted a lot of attention from the industry. And understanding the causes of inaccurate overprinting and mastering its troubleshooting methods become very necessary. This article relies on the author's experience in gravure printing over the past few years. Overprint inadmissible for the following analysis, for the reference of the industry. Plastic film gravure printing process is; substrate by the discharge device, the conduction roller into the first unit for printing, and then into the drying device, and then driven by the conduction roller into the second unit of printing

Analysis of the problem of inaccurate gravure overprinting of plastic films

Analysis of the problem of inaccurate gravure overprinting of plastic films

 

There are many kinds of faults in gravure printing of plastic films, and inaccurate overprinting before and after the graphics is one of the common faults. Due to the inaccurate overprinting will cause material waste. Therefore, the industry has attracted a lot of attention. And understanding the causes of inaccurate overprinting and mastering its troubleshooting methods become very necessary. This article relies on the author's experience in gravure printing over the past few years. Overprint inadmissible for the following analysis, for the reference of the industry. The process of gravure printing of plastic film is; the substrate is put into the first unit for printing by the discharge device, the conduction roller, and then into the drying device, and then into the second unit of printing driven by the conduction roller, and so on, and finally into 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 substrate's unwinding and winding tensions are consistent, and also pay attention to the direction of inaccurate overprinting, and then take corresponding measures to solve the problem.

There are many reasons for inaccurate overprinting of plastic film gravure, including both the impact of mechanical equipment, ink suitability, environmental temperature and other objective factors, including the impact of subjective factors such as the operator's awareness of quality. The following is a detailed analysis one by one.

Effect of reel diameter

The larger the diameter of the material roll, the easier it is for the plastic to deviate during operation, which brings hidden problems to the overprint. According to experience, the diameter of the material roll is generally 35-40cra more appropriate. When printing, with the gradual reduction of the diameter of the material roll, should be correspondingly reduced release tension, to ensure that the material tension to maintain stable. This is achieved by manual gear or magnetic powder brake. When this operation is carried out, attention should be paid to observe whether the printed color scale is out of shape.

Domestic multi-color gravure printing machine version of the cylinder axis is to rely on the cylinder end of the U-slot and the frame with the bearing to position the bearing thickness is exactly equal to the width of the u-slot, when the U-slot wear caused by an increase in width, the plate shaft driven by the plate cylinder may produce axial movement, causing inaccurate overprinting. When the wear amount exceeds 0.3mm, the overprint is not allowed, the pattern will be very obvious. As an operator, the sliding part of the gravure printing machine, gears and other operating parts of the force mouth injection oil from time to time to ensure the accuracy of overprinting, and to extend the mechanical life, reduce the purpose of wear. When significant wear occurs, the worn parts should be replaced.
When the axial movement of the plate shaft, the color sample on the substrate is not stable, the color scale upward displacement.

Conductive rollers with electricity

Plastic film in the printing process to be traction by the conduction roller into the next unit of printing or into the drying device. However, after the plastic film and the conduction roller friction, the conduction roller will take on static electricity and adsorb the dust in the air, so that the conduction roller local increase, resulting in film axial sliding, causing inaccurate overprinting. For this reason, the conduction roller should be cleaned during the shutdown to lay a good foundation for the next printing.

Incorrectly mounted plates

The register is not allowed to also be related to the mounting plate. The plate should be cleaned before the plate shaft, and then the plate installed in the center of the shaft position. Both ends of the plate plug (also known as "bored") should also be installed flat, and in the lock plate, the force should be uniform, so as to ensure accurate overprinting. Generally speaking, the plate shaft with a clearance of 0.04-0.06mm, when worn to 0.2mm, the color set is very difficult; when worn to 0.4 a 0.6mm, it should be replaced.

Gear wear

After a long period of operation, the gears of each printing unit will also be worn to varying degrees. If the plate cylinder gear and the main drive gear on the drive shaft is not engaged at the index circle, the speed is not stable, resulting in a decline in accuracy, inaccurate overprinting. Performance as the substrate on the color scale appears up and down shift, very unstable.
   Improper selection of rubber rollers

In order to obtain higher accuracy of registration, the choice of rubber rollers should also be very careful. My factory had a register inadmissible failure, by changing the material, re-testing the printing plate. Adjustment of tension, have failed to get good results. Later we found a rubber pressure roller diameter difference of 0.015mm at both ends, replaced on the new rubber pressure roller that troubleshooting.

Generally speaking, when printing a wide film with a thickness of 12μm, the requirements for the rubber
The requirements of the roller are more stringent. At the same time should also ensure that the pressure roller and the pressure of the printing plate is uniform, otherwise it will also cause inaccurate registration and other failures. Unbalanced roller pressure and plastic film thickness deviation will directly lead to inaccurate registration. In the substrate, most of the performance of the image lateral shift.

Influence of ambient temperature and humidity

In the printing process, the last unit compared to the first unit, the film will stretch with the change in temperature, resulting in inaccurate overprinting. Therefore, in the printing process, as long as the solvent can be effectively evaporated, the lower the drying temperature, the better.

At the same time, the temperature of the printing environment should be controlled. Humidity. General temperature control in the workshop at 25 ℃, humidity control at 40% is appropriate, too high, too low will affect the overprinting accuracy.

Ink

Too much viscosity of the ink will also lead to image displacement, so the viscosity value should be adjusted according to the actual situation.

Incremental volume of printing plates

In gravure printing, taking into account the stretching of plastic films, the printing plate has an incremental amount according to the color sequence, which increases gradually. If there is an error in the increment, exceeding the permissible range, the color accuracy will also be reduced. Therefore, before the end of the printing plate cylinder on the machine, it should be carefully checked and recorded, and the printed parts should be carefully compared with the original samples during printing.

Winding tension

During the operation of plastic film, the winding tension is required to be smooth, and with the gradual increase of winding diameter, the winding tension should also increase accordingly. At the same time, we should pay attention to the jittering range of winding, because the winding tension is adjusted by rubbing the friction plate on the rolling bearing at the end of the winding shaft, and if the jittering range is large, the film will shrink and the tension value will increase. General control of the tension value can be achieved through the magnetic powder brake or manual adjustment. We should also note that the longer the material roll, the easier to stretch, the tension value should be changed accordingly, a constant and smooth tension is very important.

In short, in order to get accurate overprinting, printing fine plastic film prints, must deal with each process, but also to make a serious analysis of the problem, summarize the experience for future reference.