In the process of offset printing, sometimes the same ink on the same sheet will produce inconsistencies in the depth of the ink before and after, that is to say, the ink sheet is deep in front of the blotting ink at the two positions of the mouthpiece and the tip, and the back is shallow, most of which is dark before the ink. After dark, very few cases are dark and dark, especially when printing full-size products on the ground. Inconsistent ink colors on the same sheet before and after printing will affect the quality of the printed products. Reasons for this failure and the methods for handling the problems are as follows. Analysis is as follows:
1. The surface of the ink roller is smooth and aging causes the print to fade in
The ink roller of the offset printing press generally has four sticks. After the ink roller surface is smooth and aged, it will affect the ink adsorption performance and transmission ability. The surface of the ink roller cannot absorb enough ink. When it transfers the ink on the printing plate for the first time, due to the small amount of ink stored, the dark portion of the image or the ground has sucked the transfer ink on its surface. Most of the time, but also on the ink roller, it is impossible to immediately obtain enough ink to replenish it. Therefore, in the second transfer of ink, the dark tone of the image or the ink obtained in the field is better than the first one. When the ink is much less, although there are four ink rollers to convey the ink, there will still be a phenomenon of dark ink.
Solution: The offset roller of the offset printing press is removed. Under the premise that the ink roller diameter is allowed, it can be ground to make its surface rough to increase the ink adsorption and transfer performance. Too small diameter ink roller, only the replacement of the new ink roller, at the end of the usual work, the four inking roller scrub clean to prevent the ink roller smooth and aging.
2. The diameter of the ink roller is too small
The diameter of the offset roller is too small. Some of them are design issues. This type of printing machine is prone to the phenomenon of deep front and back when printing full-scale printing. This is a defect in the design of the offset printing press. The offset printing operator It cannot be changed. Some ink roller diameters are small. The ink roller grinds too small during the grinding process. It can barely be used. Therefore, the pressure between the ink roller and the ink roller is too small, which affects the ink transfer. There is no problem in printing products with less ink. However, in the case of printing products with large amounts of ink, the disadvantages of inconsistent ink color will be revealed.
Solution: Replace the ink roller with a suitable diameter.
3. Ink roller aging affects the effect of ink transfer
The surface of the offset ink roller is composed of nitrile rubber. There are two forms of rubber aging: First, the aging of the rubber will affect the ink roller transfer performance; Second, the thermal aging of rubber, affect the rubber The surface becomes soft, sticky, and even cracked. The printing ink roller is required to be able to absorb and transfer ink to the maximum while minimizing the adsorption of moisture, as well as having good oil resistance and a certain acid resistance, since the printing process is often in constant contact with moisture, ink, paper, etc. Adsorption with the surface of the rubber ink roller to form a film layer, so that its lipophilic weakened, hydrophilicity increased.
Solution: The aging of the ink roller is always a phenomenon. The ink roller should be stored in a dry and clean place without direct sunlight. To avoid excessive humidity or overheated environment, the roller should be flat at the journal end, and The surface between the ink roller and the ink roller should not be in contact with each other or contact with other surfaces to deform and adhere.
4. Too few ink rollers
In offset printing, sometimes the operator manually removes some ink rollers for convenience. For example, removing the first ink roller and the upper ink roller will cause the ink roller to have insufficient ink storage, resulting in an ink transfer cycle that is shorter and faster.
Solution: The ink roller on the offset printing machine is required to be fully placed to ensure the ink storage capacity of the ink transfer system. Doing so will have a certain effect on solving the problem of ink darkness and darkness.
5. The pressure between the rubber ink roller and the ink roller is too light
The rubber ink roller plays a role in transferring ink. The pressure between the rubber ink roller and the ink roller is too light to affect the normal transmission of the ink. Sometimes, the upper part of the ink roller sets, the ink roller piles up the ink volume, and The amount of ink on the half of the ink roller is still too low, which is due to the light pressure of the uniform ink roller and the ink roller.