Discuss again how to master the "three levels, two smalls and one balance" of offset printing

The level of mastering "three levels, two smalls and one balance" in offset printing directly reflects the level of offset printing technicians. The so-called "three levels" means that the offset printing machine that needs to be debugged must have a flat cylinder body, an inking roller level, and a water conveying roller level; It means that the ink and moisture on the printing plate should be balanced. When the offset press is running, the axis between the cylinder bodies must be parallel and the plane of the cylinder body should be flat; the axis of the ink roller should be parallel, the roller body should be flat, and the pressure between the rollers should be uniform; the axis of the water roller should be parallel, the roller The body should be flat, and the pressure between the water roller and the water roller should be uniform; the axis of the cylinder body should be parallel to the axis of the ink roller and the water roller, and the pressure should be balanced and moderate. Determine the liner liner according to the technical parameters given when the machine leaves the factory. The soft liner should also be adjusted to be smoother by using the full print map process, and the error should be less than 0.03mm.

1. Commissioning of the roller

The cylinder is the main component of the offset press, and its debugging is very important.

First, determine the center distance of the drum. Adjusting the center distance of the rollers so that the axes of the two adjacent rollers are parallel is a vital task and must be done carefully. It is worthwhile to spend a little more time on this. When testing the gap between the roller and the pillow, a thick gauge or a broken wire (fuse) must be used to measure the data patiently and meticulously. In order to be as accurate as possible, it can be measured several times and several parts. The gap between the measuring roller and the roller pillow must be the same, so that the axis between the rollers is parallel. The measurement is generally based on the impression cylinder.

Then according to the technical parameter data of this offset printing machine leaving the factory to determine a reasonable liner. The covering on the rubber roller is generally divided into soft, neutral and hard, and different materials have different soft and hard characteristics. In the 1980s, there was an intense theoretical discussion on the drum liner. One side said that the radius after the drum liner should be equal, that is, the same diameter theory, and the other side thought that the diameter of the rubber drum after the drum liner was slightly Small is not equal diameter theory. The two sides hold their own opinions and do not compromise with each other. The focus of the debate is the distribution of printing compression deformation value (pressure), that is, the lambda value should be placed on that cylinder. The value of λ is very small compared to the radius of the drum. However, the theory of equal diameter and unequal diameter of the drum has the same view, which requires that the linear speed of the three drums is equal during the operation after the drum is lined to print a good product.

Whether the linear speed after drum lining is equal can be identified as follows. That is, after printing thousands of sheets (especially domestic offset paper or book paper), paper wool and paper powder will stick to the rubber cylinder. If the paper powder and paper wool at the edge of the imprint have directionality (toward the bite or direction) Trailing direction), it means that the linear speed of the cylinder is not reached. Only when printing after the roller is lined, the paper and paper piles on the rubber cylinder are not directional, then this liner data is the best, and That is, the cylinder is adjusted to the best state of operation, and the transmission of ink on the printing plate, blanket, and paper is the best state during the printing process.

2. Commissioning of the ink roller

The inking system is composed of dozens of ink-blowing rollers, ink-uniform rollers, ink-filling rollers, ink fountain rollers and ink-transfer rollers of various diameters.

First adjust the pressure between the inking roller and the inking roller, then adjust the pressure between the inking roller and the printing plate.

There are usually four inking rollers. The first two are in contact with the printing plate. The main function is to supply ink. The pressure is appropriately large to provide sufficient ink for the printing plate. The two inking rollers that contact the printing plate after the main function , The pressure should be appropriately lower to make it clean.

Before commissioning the pressure, a flat plate with a thickness error not exceeding 0.02mm should be selected and installed on the plate cylinder. Due to the different diameters of the four inking rollers, the pressure on the ink-blowing roller and the printing plate cannot be represented by data. The important thing is that the pressure on both ends must be the same. When the machine is running, there is no obvious jump on both ends of the ink roller (touch the two ends of the printing ink roller by hand).

If the pressure of the inking roller on the printing plate is inconsistent at the two ends, or there is a serious jump on the printing plate, it will cause the relative friction of the ink roller on the printing plate, and it is easy to cause ink sticks.

3. Commissioning of water roller

There are two types of water rollers. One type of water roller uses a gel roller to transfer water, and the other type is a rubber roller covered with a water roller fleece sleeve to transfer water. The biggest weakness of the water roller covered velvet sleeve is that the fluff falls during the printing process. If it is transferred to the printing plate and the printed product, it will affect the quality of the printed product, especially the solid or hollow characters of the full version. The water delivery system is generally composed of two water rollers, a water channeling roller, a water transfer roller and a water bucket roller. The focus of general debugging is two water rollers. When the machine is running, the water roller that first touches the printing plate is called the upper water roller, which plays the role of supplying the water required for the full printing plate; the water roller that touches the printing plate afterwards is called the water collecting roller, which mainly serves to control the printing The effect of collecting excess water on the plate. Because the functions of the two printing plate water rollers are different, the commissioning pressure requirements are different: the pressure of the water supply roller is relatively larger than the pressure of the water collection roller. Generally, the water mark width of the water supply roller is about 5mm. The water trace width of the water roller is 4mm.

Four, water bucket liquid

Generally, the water bucket solution is weakly acidic, and its pH value should be controlled at 4.5 to 5.5. When the pH is less than 4.5, the printing plate pattern will be severely eroded, resulting in "flower" plates and bad plates; when the pH is greater than 5.5, the inorganic salt layer in the blank part of the printing plate cannot be replenished, and the hydrophilic colloid layer is destroyed. The blank part of the pattern part is "invaded", causing the dots to fluff or even hang dirty. Under the premise that the text is not dirty, the minimum amount of water should be used. Observe the printing plate in the printing process with the naked eye. The amount of reflected light on the plate should not be too large. View the reflected light on the plate at a viewing angle of 30 ° to 45 ° with the plate: too bright like a mirror, indicating that the amount of water is too large; only light gray and dull The most suitable layout is the amount of water on the printing plate.

When there are greasy dots and paste on the blank page of the layout, avoid increasing the amount of water. The concentration of the water solution should be increased. Once there are water stains on the graphic, increase the amount of ink, which will cause heavy ink. Severe emulsification and cause a vicious circle. It is also very important to master the size of the ink volume. Conditional factories can buy a color density meter to determine the density of the ink layer. The general yellow plate density value is 1.1 to 1.2, the magenta plate density value is 1.3 to 1.4, and the blue plate density The value is 1.4 to 1.5, and the black plate density value is 1.8 to 2.0.

The control of the water content of the printing plate should be strict. Generally speaking, the ink and water become emulsified when mixed together. The maximum moisture content of the ink cannot exceed 30%. If the maximum emulsification value is exceeded, the ink hue will become lighter and the printed text will not dry easily. The back of the paper will be dirty, causing the post-printed paper to elongate and cause inaccurate overprinting. Therefore, a person on a machine must grasp the amount of the water bucket solution on the layout when printing is started, which should be neither too small nor too large.

5. Mastering ink and wash balance is a basic skill

Offset printing is inseparable from water, and too much water is used in the entire printing process. It is not a simple and easy task to master the relationship between ink and water. This is a skill that our machine staff have accumulated over time. Generally speaking, in the absence of a density meter, a printed product is placed on the sample stand to check its ink layer imprint. If the dots are full, print them on the ground, then pick them up, face them, face the printed matter, and see the printed matter with naked eyes under the condition of light on the back of the printed matter. Explain that the ink layer is too thick and the amount of ink is too much. After the printed matter is printed, check whether the ink color of the original or the proof is consistent, which is slightly darker than the dried proof.) Finally, sign the sample with the appropriate amount of ink Print. The determination and balance of the ink volume and water volume of the layout should be carried out throughout the printing process. For the operator is a basic skill that must be well mastered.

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