Analysis of Causes of Deformation of Printing Iron Dots

The so-called dot distortion refers to the increase or decrease of dots, and when the dots are serious, they become square dots or shaped dots. Distortion of light dots at the outlets will distort the images and images, and cause images to be distorted, resulting in product obsolescence. There are several reasons for the deformation of the Yintie outlet.

1. Sliding friction causes dot distortion
The compressive deformation of the elastomer and the resultant sliding friction, as reflected in the printed iron products, will cause the dot distortion. When the pressure is proper, the friction is small, and the quality of dot copying is high: When the relative sliding friction is too large, the dots will have a directional increase or decrease. The malady occurs mainly on iron printing equipment with poor parts precision. When using such equipment, soft cushion materials can be properly selected to compensate for the lack of equipment accuracy. At the same time, it causes the compression and deformation of the elastomer of the plate cylinder and the blanket and the corresponding sliding friction phenomenon. Solution: Improve the accuracy of the equipment.

2. Inflection of dots caused by changes in ink volume

The amount of ink transferred by the inking system is too high, so that the printing surface of the printing plate may be excessively dispersed in the ink layer due to ink diffusion during the rolling. Solution: First of all, it is necessary to understand the distribution of graphic materials in the printed sheets in detail, and to know how much ink is in each part. During operation, the amount of ink is appropriately enlarged for a large area of ​​the solid or halftone area, and a minimum amount of ink or no ink is given to an area where the halftone dot area is small or not. The work must be controlled from the ink supply section, ie, the gap between the ink fountain roller and the ink knife is adjusted. The area with a large amount of ink is properly enlarged. The area with a small amount of ink is properly narrowed to avoid ink in the ink transfer system. .

3. Deformation caused by improper pressure
Imprinting iron is the same as other lithographic offset printing, under proper pressure conditions, that is, the use of the minimum pressure, so that the print imprint is neither "empty" nor "spread." Adjust the size of the printing iron pressure must be based on the characteristics of different products. The magnitude of the adjustment is determined by various objective factors such as quality conditions, etc. The iron pressure is usually controlled within the range of 0.10 to 0.15mm, and the following factors must be taken into account in the pressure adjustment.
(1) Contact pressure of water roller, ink roller and printing plate (2) Friction of printing plate (3) Density value of picture and text, deformation degree of dot (4) Engagement and operation of roller gear (5) Imprinting Transfer of ink (6) Life of the blanket (?) Friction between the tinplate and the drum (8) Displacement of the cushion To adjust the pressure, a key condition is that the three-roller line speed is uniform. General knowledge assumes that the same three-roller radius can achieve the same linear velocity, but the problem is that the quality of the three-roller is inconsistent, and the compression deformation causes the blanket and the underlay to have a certain extension. The printing plate and the underlay also have some extension, and the imprinting Roller does not extend. In order to avoid the emergence of rubber roller line speed> printing plate line speed> impression roller line speed nano phenomenon, after careful calculation, design the impression roller radius> plate cylinder radius> rubber roller radius ideal value to guide the printing equipment Manufacturing. The compression amplitude between the printing drums is large and the contact area has a large speed difference. Excessive sliding friction will cause the outlets to be elongated and deformed. Therefore, the pressure adjustment of the three rollers is the key to print quality.

In the pressure debugging, pay attention to the pressure between the ink roller and the plate cylinder. Ink roller and plate cylinder pressure is too large, the elastic roller will increase the amount of compression deformation, sliding friction in the contact arc is larger, resulting in the network point is not clear, hair or increase. Under normal circumstances, with a 0.2mm feeler gauge, the pressure between the ink roller and the plate cylinder is measured to make it easier to insert and feel. If the pressure is too high, the amount of compression of the ink roller itself will inevitably increase, and the friction in the contact arc between the two will be large. The hardness of the ink roller is preferably HS30~HS40. The lower the hardness is, the more the elastic deformation is. Therefore, it is very important to maintain the proper hardness of the roller.

4. Blanket problems cause dot distortion
The blanket used for printing iron must be flexible and have a strong resistance to strain. Smaller elongation and proper hardness, good flatness, lipophilicity, abrasion resistance, acid and solvent resistance. The blanket is generally composed of a surface oil-resistant adhesive layer, a cotton cloth skeleton layer and an elastic adhesive layer, so as to ensure that the blanket has sufficient radial tension resistance and minimum elongation. If the radial tension is insufficient, the blanket is tightened and rolled. When it is pressed, it is easy to tear or cause a large amount of deformation and cannot be reset at the moment of rolling.

The maintenance of the blanket is very important. When scrubbing a new blanket, first use kerosene, sprinkle some talcum powder, and wipe it repeatedly with a soft, clean rag. The average length and length is used to show the rubber's natural color and the inherent micropores. It is better to thoroughly clean the talcum powder with gasoline. Only put into use. After printing, clean it with gasoline. After removing and disassembling the blanket, it usually takes two times of tensioning: the first time is the tension of the blanket; after tightening the boot, it runs for 10 minutes at a uniform speed, and then the second tightening is performed to prevent the rubber from being printed during the printing process. The cloth slackened due to lack of tension. However, the degree of tightness of the blanket varies depending on the strength of each person, and there are also tightness differences. The blanket is too loose, of course, too tight, it will also bring printing defects, resulting in the surface of the blanket due to tension, friction concentrated on the surface, the elasticity should be reduced, even if the pressure of the printing iron is normal, there will be surface speed difference, the cabinet should Occurrence of network distortion.

Source: Printing Technology