The problem that should be paid attention to in the second overprinting of commercial form rotary press
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For the high-speed rotary commercial form printing machine, the more complete the number of printing equipment and the printing cylinder, the better the quality and quantity can meet the customer's requirements in the shortest time, but in special cases, if the customer's product color exceeds The number of color groups of the equipment, or for the computer continuous type of ticket, in the case that the drum is not complete, there will be a situation that requires two overprinting, that is, the partial color number is printed first, and the second printing is performed after the rewinding to complete the whole Printing process.
The most important problem in the second overprinting is the registration problem in the two printings before and after. Generally, the photodetector is used to determine the repeated occurrence of the signal blocks preprinted on the printing surface during the first printing. On the second printed layout, if the position of the signal block on the second printing plate is deviated, the device will automatically detect it and remind the operator to make adjustments in time so that the position of the signal block must be as far as possible in the first printing. Repeatedly appearing repeatedly, otherwise it is necessary to adjust the rules multiple times during the second printing, which will bring great waste.
In the first printing, in principle, the selection content is less, and the overprinting position requires a more tolerant color, so that even a slight inaccuracy in the second overprinting does not have a decisive influence on the quality of the entire product, especially For computer continuous tickets.
This is a triple carbonless computer continuous ticket, in which the second has three colors, but we only have two sets of rollers, so we must perform two overprints. Two colors in the three colors are the main content, and finally the first time. The seal is printed first because the print layout is small and the position requirements are slightly more tolerant than the other two colors. Both the stamp and the signal block are printed with a resin plate for the following reasons:
1. Since the resin plate is a letterpress printing, the printed seal is clear, real, and the stereoscopic effect is more beautiful;
2. Resin plate printing ink balance requirements are not strict, easier to control;
3. It is not easy to emulsify with resin plate printing ink;
4. In the rotary printing machine, the printing with the resin plate group does not depressurize under normal conditions, and it is generally not necessary to stop the pressure for various reasons. In this way, the signal strip or block for detection is always in the printed product, that is, it has been repeated at equal distances. As long as the paper strip is placed at the stoppage, the scrap can be torn off during the second overprint, and the rule does not need to be re-executed. Adjustment. If the PS version is used for printing, the machine will be out of pressure after the machine is stopped, and the signal block will not be printed. In the second overprinting, the rules need to be re-adjusted in this section, which will increase the consumption and waste.
After the first printing, for various reasons, after the re-rolling of the printed product was placed for a period of time, we began to overprint, but in the second overprint, it was found that in addition to the red seal on the printed, the printed product also showed a blue The color seal and the red seal position alternately appear irregularly. It is thought that the blue ink on the resin plate impression cylinder has not been wiped clean before being pressed, and the print is dirty after the pressure, but after checking the inside of the print, It was discovered that this blue seal continued into the paper roll. This means that it will not be caused by dirt. After careful inspection, I found that the blue seal is always in the same position as the inner layer of the red seal, just like the outer red stamp is printed on the inner layer of paper. Originally for the carbonless copy paper, the microcapsule technology was used. The paper is coated with a microcapsule containing a coupler on the back side of the base paper. The middle paper is coated with a color developer on the front side and the microcapsule containing the coupler on the back side. The lower paper is coated with a color developer microcapsule on the front side of the base paper, and the paper is used. When the microcapsules are destroyed due to pressure or impact, the colorless coupler flows out, is absorbed by the developer, and simultaneously produces a chemical reaction to form a color. High-speed rotary printing, the paper receiving situation of the paper will have an impact on the rules, generally close, so the tension of the paper is relatively large, due to the use of the resin version of the letterpress printing, the pressure during the printing process is too large, so that the back of the printed product The micro-convex, the embossing process itself has destroyed some of the color developing and color forming agent capsules, and after the delivery, the two layers of paper are actually stacked together, and under the action of a large paper tension, the outer paper is inwardly The micro-convex will exert pressure on the in-flight paper, causing the microcapsules to break down and develop color. After being placed for a period of time, this pressure will continue to damage the capsule and make the seal appear slowly and clearly. This is the cause of the problem. .
In the second overprint of the commercial form rotary press rewinding, the author believes that the following problems should be noted in the first printing:
1. The signal strip or block at the time of the first printing, using resin plate printing, for the reason that the overprinting rule is continuous as described above;
2. If the color of the first printing is printed by resin plate, the printing pressure should be as small as possible under the premise of ensuring the printing quality;
3. The delivery paper should not be too large. If it is too large, the tension will increase and the pressure between the inner and outer papers will increase.
4. For the first time, resin plate printing is adopted. The rewinding paper roll should not be placed for too long, the time should not be too long, and the second overprint should be completed continuously, so that the number of microcapsule damage is small;
5. Use PS plate printing to avoid similar situations happening again.