For high-speed rotary commercial form printers, the more complete the color numbers and printing cylinders of the printing equipment, the better the quality and quantity can meet the customer's requirements in the shortest time, but under special circumstances, if the customer's product color number exceeds The number of color sets of the equipment, or for computer continuous receipts, when the cylinder is not complete, a situation that requires secondary overprinting, that is, printing part of the color number first, and reprinting after rewinding, to complete the entire Printing process.
The most important problem in the second overprinting is the registration problem in the two printings before and after. In general, the photoelectric detector is used to determine the repeated appearance of the signal block printed on the layout in the first printing. On the second printing Plate , if the position of the signal block deviates from the second printing plate, the device will automatically detect and remind the operator to make timely adjustments, so that the position of the signal block must be as much as possible during the first printing Repeatedly appear continuously, otherwise the regulations will need to be adjusted many times during the second printing, which will bring great waste.
In the first printing, in principle, choose less content, overprinting position requires a more tolerant color, so even if there is a slight misregistration during the second overprinting, it will not affect the quality of the entire product, especially For computer continuous bills.
The following is the problem we should pay attention to in the secondary overprinting of this problem encountered by our factory in production.
This is a triple carbon-free copying computer continuous bill. The second link has three colors, but we only have two sets of rollers. Therefore, we must perform secondary overprinting. Two of the three colors are the main content. Print the seal first, because its printing layout is small and the position requirements are slightly more forgiving than the other two colors. Seals and signal blocks are printed with resin plates for the following reasons:
1. Because the resin version is letterpress printing, the printed seal is clear, realistic, and has a strong three-dimensional sense, which is more beautiful;
2. The water and ink balance requirements for resin printing are not strict and are easier to control;
3. Resin printing ink is not easy to emulsify;
4. In the rotary printing machine, the printing with the resin plate group does not leave the pressure under normal circumstances, and it is generally not necessary to stop for various reasons. In this way, the detection signal strip or block has been in the printed product, that is, it has been repeated at equal distances, as long as the paper strip is clamped at the stop, and this piece of scrap is torn off during the second overprint, there is no need to re-apply the rules Adjustment. If the PS plate is used for printing, the machine will be depressurized after shutdown, and the signal block will not be printed. During the second overprint, the rules need to be readjusted during this period, which increases consumption and causes waste.
After the first printing, due to various reasons, after placing the rewinded printed matter for a period of time, we started overprinting. However, when the second overprinting was found, in addition to the red stamp on the printing, a blue The color stamp and the red stamp alternately appear irregularly. At first, I thought that the blue ink of the previous printing on the resin plate impression cylinder was not wiped clean. After the pressure was applied, it was dirty and produced marks, but after checking the inside of the printing roll, Found that this blue seal continued into the paper roll. This shows that it will not be caused by dirt. After careful inspection, it was found that the blue seal is always located in the same position on the inner paper of the red seal, just like the outer red seal is printed on the inner paper. The original carbonless carbon paper uses microcapsule technology. The paper is coated with microcapsules containing coupler on the back of the base paper, the middle paper is coated with the developer on the front and the microcapsules with coupler on the back, and the bottom paper is coated with the microcapsules of the developer on the front of the base paper. When the pressure or impact force destroys the microcapsules, the colorless coupler flows out, is absorbed by the developer, and at the same time produces a chemical reaction to form a color. For high-speed rotary printing, the roll paper receiving situation will affect the rules. Generally, the paper is collected tightly, so the paper tension is large. Because the resin plate is a relief printing, the pressure during the printing process is too large, which causes the back of the printed product. Due to the slight convexity, the embossing process itself has destroyed some of the color development and coupler capsules. In addition, after the paper is collected, the two layers of paper are actually superimposed together. Under the action of greater paper tension, the outer paper is inward The micro-protrusion will exert pressure on the paper in the introspection, causing the microcapsules to break and develop color. After being placed for a period of time, this pressure will continue to damage the capsules, and the seal will slowly appear clearly. This is the reason for the problem. .
In the secondary overprint of commercial form rotary printing machine, the author believes that the following issues should be noted in the first printing:
1. The signal strips or blocks should be printed with resin plates during the first printing. The reason is that the overprinting rules can be continuous as mentioned above;
2. If the color of the first printing adopts resin printing, the printing pressure should be as low as possible on the premise of ensuring the printing quality;
3. The take-up roll should not be too large. If it is too large, the tension will increase and the pressure between the inner and outer layers of paper will increase;
4. For the first time, the resin plate is used for printing, the rewinding paper roll should not be placed for too long, and the time should not be too long. 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 from happening again.
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