How to master the "three flat two small one balance" of offset printing
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The level of mastery of offset printing "three flats, two small ones and one balance" directly reflects the level of technical skills of offset printing. The so-called "three flats" is the offset printing machine that requires debugging. The roller body should be flat, the inking roller is flat, and the water conveying roller is flat. "Two small" means that the concentration of the water bucket solution used in the printing process is small, and the water content of the plate is small; "one balance" It means that the ink and moisture of the printing layout should be balanced.
When the offset printing machine is running, the axis between the roller bodies must be parallel, and the plane of the roller body should be flat; the axis of the ink roller should be parallel, the roller body should be flat, the pressure between the roller and the roller should be uniform; the axis of the water roller should be parallel, the roller The body should be flat, the pressure between the water roller and the water roller should be uniform; the axis of the roller body should be parallel with the axis of the ink roller and the water roller, and the pressure balance should be moderate. According to the technical parameters given by the machine at the factory to determine the liner, the soft lining should also be adjusted to make the rubber roller lining more flat by the full-stamp map process, the error should be below 0.03mm.
1. Commissioning of the drum
The drum is the main part of the offset press and its commissioning is very important.
First determine the center distance of the drum. Adjusting the center distance of the rollers makes the axes of the two rollers parallel to each other. This is a crucial task. It must be done carefully. It is worthwhile to spend more time in this area. When detecting the gap between the roller and the roller, it is necessary to use a thick gauge or a broken wire (fuse) to measure the data with patience and meticulousness. In order to be as accurate as possible, it is possible to measure several times and measure several parts. The gap between the measuring rollers and the rollers must be the same, so that the axes between the rollers are parallel. The measurement is generally based on an impression cylinder.
Then determine the reasonable lining according to the technical parameter data of the offset printing machine. The lining on the blanket cylinder is generally soft, neutral and rigid, and different materials have different soft and hard properties. In the 1980s, there was a heated discussion on the theory of roller lining. One party said that the radius of the roller lining should be equal, that is, the equal diameter theory. The other side thinks that the diameter of the blanket cylinder after the roller lining is slightly Small is the theory of unequal diameter. The two sides hold their own opinions and do not give each other. The focus of the debate is on the printing compression deformation value (pressure) distribution problem, that is, the λ value should be placed on the roller. The value of λ is a negligible value compared to the size of the drum radius. However, the equal diameter of the drum has the same viewpoint as the theory of unequal diameter, that is, the operation of the drum after the lining is required, the speed of the three rollers is equal to print a good product.
Whether the linear velocities after the lining of the drum are equal can be identified as follows. That is, after printing thousands of sheets of paper (especially domestic offset paper or book paper), paper wool and paper powder will stick to the blanket cylinder. If the paper powder and paper wool on the edge of the print are directional (to the direction of the bite or toward If the direction of the tip is not the same, it means that the line speed of the roller is not equal. Only when the roller is lining and printing, the paper powder on the blanket cylinder has no directionality, so the lining data is the best. That is, the drum is adjusted to the optimum state of operation, and the transfer of ink on the printing plate, blanket and paper is the best state during the printing process.
2. Debugging of the ink roller
The inking system consists of more than ten different diameters of the ink roller, the ink roller, the ink roller, the ink roller and the ink roller.
First adjust the pressure between the ink roller and the ink roller, and then adjust the pressure between the ink roller and the plate.
The inking roller usually has four branches, and the two first contacts of the printing plate are mainly for supplying ink, and the pressure is appropriately larger to supply the ink to the printing plate; the two inking rollers contacting the printing plate mainly serve as the ink collecting function. The pressure should be appropriately small to make the ink clean.
Before commissioning the pressure, a plate with a flatness and a thickness error of not more than 0.02 mm should be selected on the plate cylinder. Due to the different diameters of the four inking rollers, the pressure on the inking roller and the printing plate cannot be expressed by data. It is important that the pressure at both ends be the same. When the machine is running, there is no obvious jump at both ends of the ink roller (contact the two ends of the plate ink roller with the hand). If the pressure of the inking roller on the printing plate is inconsistent at both ends, or there is a serious beating on the printing plate, it will cause relative friction of the ink roller on the printing plate, which easily causes the ink bar.
3. Debugging of the water roller
There are two types of water rollers. One type of water roller uses a gel roller to transfer water, and the other is a rubber roller that is covered with a water roller to transfer water.
The biggest weakness of the water roller velvet cover 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 printed version of the solid or hollow word. The water delivery system generally consists of two water rollers, one water roller, one water roller and one water roller. The general debugging focus is two water rollers. The water roller that touches the printing plate when the machine is running is called the water-feeding roller, which functions as the water required for the foot printing plate; the water roller that touches the printing plate is called the water-receiving roller, and mainly plays the printing plate. The effect of excess water on the plate. Due to the difference in the function of the two plate water rollers, the commissioning pressure requirements are different: the pressure of the water roller is relatively larger than the pressure of the water collecting roller. Generally, the water roller width of the water roller is about 5 mm. The water roller has a water mark width of 4 mm.
4. Water bucket
Generally, the water bucket solution is weakly acidic, and its pH should be controlled at 4.5 to 5.5. When the pH is <4.5, the pattern pattern will be severely eroded, resulting in a "flower" version and a bad version; when the pH is >5.5, the inorganic salt layer in the blank portion of the printing plate is not replenished, and the hydrophilic colloid layer is damaged. The blank portion of the pattern portion is "invaded" to cause the dots to become hairy or even dirty. The minimum amount of water should be used if the graphics are not dirty. Observing the printing plate in the printing process with the naked eye, the amount of reflected light on the printing plate should not be too large, and the amount of reflected light on the printing plate at a viewing angle of 30° to 45° with the layout: too bright like a mirror, indicating that the amount of water is too large; only light gray and dull The layout is the most suitable amount of water on the plate.
When there is a greasy mesh point and paste in the blank of the layout, it is forbidden to increase the water volume. The concentration of the water bucket solution should be increased. Once the water and water stains appear in the image, the ink volume will increase. Large and severe emulsification and cause a vicious circle. The amount of ink is mastered. It is also very important. If you have a conditional factory, you 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, and the density of the magenta plate is 1.3 to 1.4. The value is 1.4 to 1.5, and the black plate density is 1.8 to 2.0.
The control of the water content of the plate should be strict. In general, the ink and the water will become emulsified, and the water content in the ink should not exceed 30% of the emulsification value. When the maximum emulsification value is exceeded, the ink color 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 elongate and causing inaccuracies in the overprint. Therefore, the personnel on a machine must master the amount of water solution on the plate when printing. It should not be too small or too large.
5. Mastering ink and water balance is a basic skill
Offset printing is inseparable from water, and too much water is used in the whole process of printing. It is not an easy task to master the relationship between ink and water balance. This is a skill that relies on the accumulated experience of our machine personnel. In general, in the absence of a densitometer, a printed product is placed on a sample stand to view its ink footprint. If the dot is printed more plump, the ground is flat, then pick it up, face the printed product, and look at the printed product with the naked eye on the back of the printed product. The printed product is slightly translucent under the transmitted light, completely opaque. It means that the ink layer is too thick and the amount of ink is too much. After the printed matter is printed, it is better to compare the original or the proofed ink color, which is slightly deeper than the dried proofing sample. Finally, it is signed with the appropriate amount of ink. Printed. The determination and balance of the amount of ink and water in the layout must be throughout the printing process. For the operator, it is a basic skill that must be well mastered.