Corrugated cardboard printing is a common printing process for carton production. This process has the characteristics of simple and fast production process, one machine can realize multi-function, short production cycle and high efficiency. However, since corrugated cardboard is formed by multi-layer papers processed and bonded, quality defects such as warpage and poor flatness are prone to occur, and the accuracy of paper feeding and positioning is relatively poor. The quality is good. Especially for the layout of multi-color interlocking overprinting, if the printing process and technical measures are not appropriate, the phenomenon of overprinting inaccuracy will be more prominent. Therefore, only by scientifically and reasonably arranging the printing color sequence and operating the printing machine correctly can the product overprinting accuracy of the two-color flexo printing machine be improved, and the printing quality of corrugated box products can be improved. Next, the author makes some analysis and discussion on a corrugated box printing quality accident, and talks about my own understanding of the color sequence arrangement of corrugated cardboard direct printing and the correct operation of the printing machine.
Analysis of a quality accident of corrugated box overprinting
The author has seen such a carton printing quality accident: a carton workshop of a factory used a two-color flexographic water-based printing machine that combines printing, indentation and slitting in one machine to print 3-color overprinted 5-layer corrugated cardboard (specification 1150mm) ～ 920mm), there was a printing quality accident that was severely inaccurate, which caused a large number of products to be scrapped because they did not meet the quality requirements, and the economic loss was more than 3000 yuan. After investigation, observation and analysis, the author found that the improper arrangement of printing color sequence was the main reason for this overprint quality accident. In addition, the machine operation technology is not in place, which is another cause of errors in layout overprinting. The design structure of this product is red, blue, and black. The three-color layout is partially overprinted. Among them, the two round logos in the blue layout have both black and red layouts, and only 2mm of margin is left on the edges of the overprinted layout. region. The black version and the red version have no precise overprint relationship. Obviously, if the printing positioning of the product is not 1mm, the overprint deviation of the logo graphic layout will be very obvious.
According to the characteristics of this product overprint, if a multi-color flexo printing machine is used to complete 3 color simultaneous overprinting at a time, the quality effect of the overprint of the layout is the most ideal. But the use of two-color printing machine needs to be divided into two to complete the printing, which must be a good printing process technology, in order to effectively improve the accuracy of product overprinting. Due to the lack of printing process technical knowledge and production process experience, the operator of the machine uses two colors of red and blue plates for printing, and then overprints the black layout. In this way, due to the certain warpage of corrugated cardboard itself, the output is lost. The paper and positioning are not stable and accurate enough. After the red and blue printing, when the black printing is overprinted, it is found that the overprinting phenomenon is obviously inaccurate. The operator also mistakenly believes that the carton product overprinting error is a few millimeters is normal. As a result, after the finished product was rejected by the customer, it caused greater economic losses. The author believes that the occurrence of the above printing quality accidents is mainly due to errors in the printing process. When printing a 3-color corrugated cardboard with a two-color printing machine, the scientific and reasonable arrangement of the printing color sequence is a very important link.
How to arrange the color sequence of 3-color corrugated paperboard with two-color flexo printing machine
Corrugated cardboard products such as the three-color overprinting described above can be registered with the blue layout and the black and red layouts as long as a reasonable arrangement is made in the printing color sequence. The printing layout of the product is divided according to the size of the area: the black version is larger than the red version, the red version is larger than the blue version, that is, the blue version has the smallest area. According to the accuracy of overprinting: the overprinting accuracy of the blue and red editions is higher than that of the black and blue editions; the red and black editions have no accurate overprinting relationship, and the error of 2mm ～ 3mm will not be obvious. The printing color sequence can be arranged as follows: the blue plate is printed first, and the red plate is overprinted on the blue plate, because the blue plate with a small area is arranged in the front color group for printing, and the red plate with a relatively large area is placed on The subsequent color set is used for overprinting, which is helpful to improve the registration and prevent the phenomenon of dirt caused by the friction of the printed products. In the second printing, install the blue version of the black version in the front color group, and install the black version with a larger area in the rear color group for overprinting, which can improve the accuracy of overprinting and prevent the printing from getting dirty. The quality effect, and this overprint color sequence only needs to be changed from the red ink to the black ink during the second printing. It is very easy to change the color or wash the car, which can better avoid the bias that is most likely to occur at the beginning of printing. Color phenomenon. This arrangement of printing color sequence is to use a two-color printing machine to print three-color products. It takes two times to complete, and one of them has an extra printing color group.
In this way, although the blue version is printed in two times, but the number of machine operations has not increased, you can split the blue version that requires both the red version and the black version into two versions separately from the red and black versions. Carry out overprinting, so that the more precise blue and red editions, blue and black editions can be overprinted at the same time, which ensures the accuracy of product overprinting. At present, the 3-color corrugated cardboard printed by the factory's two-color printing machine adopts the printing overprint color sequence arranged by the author. There is no overprint quality problem again, and the customers are also satisfied with the printing quality.
Improper equipment operation is also the cause of inaccurate overprinting of corrugated cardboard
KYO-1600 two-color flexo printing machine is a commonly used equipment for printing corrugated boxes. If the machine is improperly operated, it is easy to produce printing inaccuracy. It should be said that the above-mentioned printing inaccurate quality accidents also have a great relationship with the poor technical quality of operators. The two sets of printing cylinders of this machine are equipped with roller devices before and after. There are 4 sets of roller devices, which can play the role of supporting and friction conveying corrugated cardboard. The lower roller of each set of roller devices can be used to raise and lower the rollers between the upper and lower rollers. The gap is suitable for the friction conveying of corrugated cardboard with different thickness. The upper roller of each group of rollers on the machine is composed of two movable rollers. Each movable roller has a screw that can be tightened or loosened to meet the needs of printing different width cardboard adjustments. During the on-site observation and analysis, the author found that the operator of the machine did not have a good grasp of the use and operation of the equipment, and was very blind to the use of the machine. The 4 sets of rollers on the machine have obvious gaps with some There is poor contact on both sides, which can not play the role of normal friction conveying corrugated cardboard. The screws on some rollers are not tightened at all. When printing, the rollers will have irregular radial or axial slippage on the roller shaft, and some two rollers will cling together in series. The existence of these undesirable conditions makes the cardboard easily produce slippage during each printing and feeding process, which makes the printing of various color plates inaccurate.
When the author asked why the gap of the roller was not adjusted and the screws were tightened, the operator of the machine said that they did not know the role of the roller, thinking that the cardboard conveying was mainly driven by the printing cylinder during pressing, and in the past, the machine was not printed. For two-color products with precise overprinting, the printing cannot be seen within a few millimeters. Therefore, there is no need to adjust the gap and position of the rollers when printing cardboards of different thickness and specifications each time. It can be seen that being unfamiliar with the performance and use requirements of the printing press is another reason that affects the quality of the cardboard printing register. In fact, whether the clearance of the roller is suitable has a great influence on the conveying effect of the cardboard. If the clearance of the roller is too small, it will not only easily leave the trace of the roller on the paper, but also cause the handover and overprinting of the cardboard due to the excessive squeezing quasi. Conversely, if the gap between the rollers is too large, it will affect the speed of friction to drive the normal conveyance of the cardboard, and it is also easy to cause inaccurate registration of the front and rear color groups. Therefore, the gap between the rollers of each group should be compatible with the thickness of the cardboard, and should be kept substantially equal to ensure the normal transportation and delivery speed of the cardboard. To adjust the gap between the rollers of each group, the corrugated cardboard to be printed can be used, which is inserted between the rollers of each group for drawing test and adjustment. When drawing, the cardboard has a slight sense of resistance. Now, when the machine prints corrugated cardboard, it first adjusts the gap and position of the roller, and then there is no similar overprint quality problem when printing.
The occurrence of the above-mentioned printing quality accidents gives the author a great inspiration: Corrugated cardboard printing is the same as other pre-printing processes, only the printing color sequence is arranged scientifically and reasonably, and the layout with high precision of overprinting is arranged as soon as possible to complete printing. Layouts that do not have a precise overprint relationship are arranged in the next printing; try to print the layout with a small area first, and arrange the layout with a large area after printing; use the machine's redundant color group to split a certain color layout into two versions separately and separately Simultaneous overprinting of other color plates; strengthening the technical training of printing operators, using and operating the printing machine correctly, not only can effectively prevent printing quality problems or accidents, but also can improve the printing quality of the product and the carton. Production efficiency and economic benefits of enterprises.
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