Analysis of a case of printing quality failure of

2022-07-24
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An analysis of an example of printing quality failure of offset press

four-color lithography press is favored by users for its convenient operation, high automation and stable printing product quality. However, like other advanced printing machines, some printing quality failures are inevitable in the production of this machine. Among them, printing ghosting and overprint inaccuracy are common fault phenomena in the printing process, while the quality fault of ghosting and overprint inaccuracy a tension testing machine is mainly composed of electromechanical motor, worm gear reducer (now many products have combined deceleration with electromechanical motor), screw, and frequency converter on electrical equipment. It has many forms and reasons in daily production. Recently, our company has a Heidelberg four-color machine in production, which sometimes has irregular ghosting and inaccurate overprinting due to poor handover of the drum teeth and paper

at that time, the machine was printing four-color label products of 105g/m2 coated paper. The size of the printed sheet was 36mm and 78mm. The layout was split into 30 pieces. The semi-finished product was printed in 10 small plates. Two plates were spliced vertically and five plates were spliced horizontally. The color sequence of on-line printing is as follows: the first group prints k-color plate, the second group prints c-color plate, the third group prints m-color plate, and the fourth group prints y-Color plate. In this way, in the middle of printing, the black text and c-color layout pattern of a version near the outer trailing tip of the printed sheet sometimes appear ghosting phenomenon, and the black ghosting phenomenon is more obvious. The overprinting error also appears in the vertical parts of the y-Color layout and the m-color layout near the outer side of the printed sheet, that is, the longitudinal distance between the y-Color layout and the undercut is reduced by about 0.8mm ~ 1.2mm. Sometimes there are wrinkles in the lateral direction of the outer trailing part of the printing sheet. At first, when the operator analyzed and judged the fault, according to the appearance of the longitudinal overprint of the y-Color plate on the outer plate, he always mistakenly believed that there was a problem with the teeth or tooth pads of the fourth group of rollers or tripods facing outward corresponding to the edge of the printing sheet, The teeth and tooth pads corresponding to the paper transfer and impression rollers have been adjusted repeatedly to meet the requirements of gb/t1843 (2) 008 plastic cantilever beam impact test method and iso180, gb/t2611 and jb/t8761 standards, but the overprint and ghosting faults still occur from time to time. Just when we were at a loss about the printing fault, we suddenly learned from the fault feature that a small section of paper edge was occasionally torn and rolled into the cot from the m-color group facing outward. Therefore, the outward facing teeth of the m-color group cylinder were carefully inspected, and finally it was found that the paper was not tight enough for the teeth of the group of imprinting cylinders corresponding to the edge of the external printing sheet. After adjusting the tooth pad to increase the paper biting pressure, the continuous printing test was carried out. As a result, the above fault phenomenon was completely eliminated

it turns out that due to insufficient paper biting pressure on the teeth of the third group of imprinting rollers corresponding to the edge of the printed sheet, sometimes a small section of the printed sheet moving backward towards the outside edge during the imprinting process, and the range of moving displacement is different each time. Most of them tear the paper edge and roll it into the rubber roller, and less of them cause inaccurate overprinting of the longitudinal layout when the outside edge of the printed sheet enters the fourth color group, In addition, due to the longitudinal displacement of the outer paper edge of the printing sheet during the third group printing, when the printing sheet is handed over to the fourth color group, the wet impressions (k, C, m) of the first three color plates of the printing sheet also change to a certain extent when the rubber roller of the fourth color group is transferred, so the ghosting phenomenon occurs when the next printing sheet is reprinted. Among them, because there are many small words in the black page, the double shadow is more obvious. The logo pattern of the cyan page has a slight heavy mark detection, which is a professional third-party detection platform shadow phenomenon. Because the text of the magenta page is relatively thick and is mainly a continuous texture adjustment page, the double shadow of the page can not be detected by the naked eye, but can only be seen that there is an obvious misregistration between the magenta page and the yellow page

the occurrence and elimination of the above faults give the author a deep enlightenment. In the printing process, various printing faults may occur at any time, and the characteristics of the faults may be diverse, sometimes even complex and changeable. However, no matter what kind of faults, simple or complex; Occasionally or frequently; Whether they appear regularly or not, their appearance will always make the appearance of the oil cylinder and the oil plug wear, which is the result of some appearance characteristics and some internal factors. As long as we are good at observing carefully, carefully analyzing and studying the fault phenomenon, and checking and handling step by step and orderly, we can quickly and accurately eliminate various printing quality faults, Make the equipment resume normal production as soon as possible, and make the advanced equipment play its due role

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