Offset "Three Levels and Two Little Ones Balance" Mastery

Offset "Three Levels and Two Little Ones Balance" Mastery

The level of mastering of offset printing “three levels and two small ones” directly reflects the level of offset printing technology. The so-called “Sanping” is an offset printing press that requires debugging. It must have a flat cylinder, an ink roller, and a water roller. “Two small” refers to the small concentration of water fountain solution used in the printing process, and the small amount of water in the layout; “a balance”. It means that the ink and moisture of the printing plate should be balanced. When the offset printing machine is running, the axes between the cylinders must be parallel, and the plane of the cylinder must be flat; the axes of the rollers must be parallel, the rollers must be flat, and the pressure between the rollers must be even; the axes of the rollers must be parallel, and the rollers must The body should be flat and the pressure between the water roller and the water roller should be uniform; the axis of the drum body should be kept parallel with the axes of the ink roller and the water roller, and the pressure should be balanced and moderate. According to the machine's technical parameters given to the factory to determine the lining pad, soft lining but also through the use of print plate map process to adjust the rubber roller lining more flat, the error should be below 0.03mm.

1 roller debugging

The roller is the main part of the offset press and its debugging is very important.

First, the center distance of the roller should be determined. Adjusting the center-to-center distance of the rollers to make the axes of the two adjacent rollers parallel is a crucial task. It must be done carefully. It is worth spending more time in this respect. When measuring the gap between the rollers and the rollers, it is necessary to use thin gauges or broken fuses (fuses) to measure the data patiently and carefully. To make it as accurate as possible, measure several times and measure several parts. The gap between the two ends of the measuring roller and the roller must be the same, so that the axis between the rollers is parallel. When measuring, it is generally based on the impression cylinder.

Then according to the data of the technical parameters of the offset press, the reasonable liner is determined. The lining on the blanket cylinder is generally divided into soft, neutral and rigid, and different materials have different soft and hard characteristics. In the 1980s, there had been a fierce discussion on the roller lining theoretically. One said that the respective radii of the roller lining should be equal, that is, the equal diameter theory. On the other hand, the diameter of the rubber roller after the roller lining is considered to be slightly different. Small is not equal diameter theory. Both sides have their own opinions and do not give up each other. The focus of the debate is on the distribution of the compression deformation value (pressure), that is, the value of λ should be placed on that roller. The lambda value is a very small value compared to the drum radius dimension. However, the principle of roller equal diameter and unequal diameter both have the same point of view, that is, when the roller is required to be lining the running process, the three roller line speed is equal to print a good product.

The linear velocity after the cylinder liner is lining can be identified as follows. That is, after printing thousands of sheets of paper (especially domestic offset or book paper), paper hairs and paper powder stick to the blanket cylinder. If the edges of the paper powder and paper are directional (to the direction of the mouth or toward the mouth) The trailing direction) means that the roller line speed is not equal, and only when the roller is lining and printed, the paper dust on the rubber roller is piled without direction, then the lining data is the best. That is, the drum is adjusted to the best state of operation. In the printing process, the transfer of the ink on the printing plate, the blanket, and the paper is the best state.

2 Inking roller

Ink system consists of more than a dozen different diameters of ink roller, uniform ink roller, ink roller, ink roller and ink transfer roller and other components.

First adjust the pressure between the ink roller and the ink roller, and then adjust the pressure between the ink roller and the plate.

Ink roller usually has four, the first two in front of contact with the printing plate is mainly used to supply ink, the pressure is appropriate to provide enough ink for the printing plate; the two ink rollers used to contact the printing plate are mainly used for ink collection. The pressure should be smaller and make it more clean.

Before adjusting the pressure, a flat plate with a thickness error of no more than 0.02 mm should be mounted on the plate cylinder. Because the four rollers have different diameters, the pressure on the ink roller and the plate cannot be represented by data. The important thing is that the pressure at both ends must be the same. When the machine is running, there is no obvious jump between the two ends of the ink roller (by touching the two ends of the plate roller). If the ink roller is inconsistent in pressure on the printing plate, or there is a serious jump in the printing plate, it will cause relative friction of the ink roller on the printing plate, and it is easy to cause ink sticks.

3 water roller debugging

There are two kinds of water rollers. One type of water roller uses a colloid roller to transfer water, and the other kind of roller is coated with a water roller cover to transfer water. The biggest weakness of the water roller velvet sleeve is that fluff is dropped during the printing process. If it is transferred to the printing plate and the printed product, it will have an impact on the quality of the printed product, especially the full-print version of the field or hollow word. The water transfer system is generally composed of two water rollers, a water roller, a water transfer roller, and a water roller. The general focus of debugging is on two water rollers. When the machine is in operation, the water roller that touches the printing plate first is called the upper water roller, and it plays the role of the water needed for the printing plate; the water roller that touches the printing plate is called the water receiving roller, mainly used to print the water. The effect of excess water on the plate. Because of the difference in the role of the two plate water rollers, the commissioning pressure requirements are different: the pressure of the upper water roller is greater than the pressure of the water receiving roller, and the width of the water roller is generally about 5mm. Water roller width is 4mm.

4 Water fountain

The general hopper solution is weakly acidic and its pH should be controlled between 4.5 and 5.5. When the pH is less than 4.5, the pattern of the printing plate will be seriously eroded, resulting in a "flower" version and a bad version; when the pH is higher than 5.5, the inorganic salt layer in the blank part of the printing plate is not supplemented and the hydrophilic colloid layer is damaged. Make the blank part of the pattern part subject to "invasion" causing the hairs of the mesh to become dirty and even dirty. The minimum amount of water should be used on the premise that the text is not dirty. Visually observe the plate in the printing process, the amount of light reflected from the plate can not be too large, and the amount of reflected light on the plate is viewed at a viewing angle of 30° to 45° to the plate: too bright like a mirror to explain the amount of water is too large; only light gray matt The layout is the most suitable plate water.

When there are greasy dots and pastes in the layout, avoid using the method of increasing the amount of water, and increase the concentration of the fountain solution. Once there is a water stain on the graphics, increase the amount of ink, it will cause ink water. Large, severe emulsification and a vicious circle. It is very important to master the size of the ink. A conditional factory can buy a color density meter to measure the density of the ink layer. Generally, the density of the yellow plate is 1.1 to 1.2, the density of the magenta plate is 1.3 to 1.4, and the density of the cyan plate. The value is 1.4 to 1.5, and the density of the black plate is 1.8 to 2.0.
The control of printing plate surface moisture should be strict. Generally speaking, the ink and water mix together to become emulsified state. The maximum water content in the ink cannot exceed 30% of the emulsification value. When the maximum emulsification value is exceeded, the hue of the ink will become lighter, and the printed image will not be easily dried. The back of the paper will be dirty, causing the printed paper to stretch and causing overprinting. Therefore, the personnel on a machine platform must have a good grasp of the amount of water fountain solution used on the layout when printing, neither too small nor too large.

5 Mastering ink and water balance is a basic skill

Offset printing is inseparable from water, and the entire process of printing cannot be used with too much water consumption. To master the balance between ink and water is not an easy task. This is a skill that depends on the accumulated experience of our staff. In general, without a densitometer, a printed product is placed on the stage to see its ink print. If the dots are printed full, take the clothes on the ground, and then take them up to face the prints. Look at the prints with the naked eye on the back of the prints. The prints are slightly translucent under the transmitted light. Explain that the ink layer is too thick, the amount of ink is too much, the printed matter is printed out, and then whether the ink of the original or the proofing is consistent is better than that of the dried proofs, which is slightly better than the proofs.) Opened. The determination and balance of the amount of ink and water in the layout must be applied throughout the printing process. For the operator is a basic skill that must be well mastered.

Source: "Printing World" Author: Kim Yu Hua

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