Analysis on the purchase of cigarette label gravur

2022-08-05
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Analysis on the purchase of cigarette label gravure printing machine from the perspective of printing technology in recent two years, great changes have taken place in the domestic tobacco industry. The reorganization and integration of cigarette enterprises, especially the improvement of cigarette brand concentration, means that the production of single brand and single brand cigarettes will be greatly increased, which requires cigarette package printing enterprises to quickly provide large quantities of cigarette packaging. Therefore, cigarette package printing enterprises must have a certain production scale and production capacity

at present, the effective combination of various materials and printing processes has become the development trend of cigarette package printing. Gravure printing has many advantages, such as high production efficiency, good color consistency, good adaptability of printing materials, excellent performance in field, spot color, gold (silver) ink printing, etc., which can meet the strict requirements of cigarette package quality. Gravure printing machine has become a common choice for cigarette package printing enterprises. In addition, the quality inspection of cigarette package printing will be further reflected in printing smell, packaging machine adaptability, color fading, environmental protection, etc. gravure printing also has more advantages than other printing processes in these aspects. Therefore, the purchase of gravure printing equipment has become a topic of great concern to cigarette package printing enterprises. Now the author talks about his own views on the introduction of web gravure printing machine, hoping to help cigarette package printing enterprises

gravure printing machine is mainly divided into three parts: uncoiling part, printing part, slitting and die cutting part. This paper first makes a brief analysis of the printing part

the printing part is the core part of the gravure press, which completes the printing, overprint and drying of various colors

1. Color deck number selection

the selection of color deck number of gravure printing machine is very critical, which is mainly related to the leading products of cigarette package printing enterprises and the general environment of domestic cigarette decoration. The pattern and process of cigarette pack design in China are relatively complex. In previous years, the domestic cigarette pack printing equipment mainly used 6 colors and 7 colors. In the past two years, it mainly used 8 colors. The basic configuration mode includes one full color, four general colors, two spot colors and one polishing unit. The number of color decks is not the more the better. The more the number of color decks, the more difficult it will be to control paper deformation and various color overprint, and the capital investment will also increase. However, if the number of color decks is too small, it is difficult to reflect the advantages of gravure printing machine in fast and efficient and one-time forming. Therefore, users must make choices according to their own needs and in combination with future development plans. Although the manufacturers of the unit gravure printing machine have promised to increase the units in the future, the additional units will not only have a large investment, but also will be subject to many restrictions due to the technical upgrading of the gravure printing machine and the installation location and space of the gravure printing machine

2. Selection of printing format

different manufacturers have different requirements for printing format. The wider the format, the higher the requirements for paper and the greater the impact on overprint. Cigarette package printing equipment is mainly suitable for 650mm and 820mm. In the past, printing plants basically chose the former, which was more economical in typesetting, plate making, plate installation, die-cutting cylinder, paper specifications, etc. During typesetting, you can arrange 6 rows and 4 rows of soft packaging small boxes, 6 rows and 2 rows of hard packaging small boxes, 1 row and 2 rows of strip boxes, 6 rows and 2 rows or 8 rows and 2 rows of die-cutting rollers. The maximum size of the paper is 650mm. Due to the small size, the paper deformation during the printing process is small, which is very beneficial to the overprint of the product. However, there is a key problem, that is, when the printing control software can display the experimental force, the peak value of the experimental force, the time interval, the experimental force time curve and other experimental parameters in real time, the paper fiber direction is perpendicular to the printing direction. For the current high-speed cigarette packaging machine, its packaging adaptability is poor and the appearance formability is poor, resulting in many quality problems. For this reason, many printing houses have to print only one piece at a time, which seriously affects the efficiency of gravure printing machines

in the past two years, the industry has basically reached a consensus that if the strip box is printed, it is best to choose an 820mm format gravure printing machine, so that the strip box can be arranged in one row and two rows, the hard wrapped small box in six rows and three rows, and the soft wrapped small box in six rows and five rows during typesetting. For products with high overprint accuracy requirements and requiring a variety of printing processes, it is recommended to arrange as few as possible. Generally, 12 ~ 16 pieces are the ideal number of typesetting, which can reduce the waste caused by paper deformation and multi-channel processing process. If online die cutting is adopted, typesetting can be exempted from this restriction

3. Installation method of plate cylinder

the installation mode of the printing plate cylinder has a great impact on the overprint accuracy, printing flatness and the runout of the printing plate cylinder, and plays a key role in whether the printing equipment can run at high speed. In the past, it was mostly installed mechanically, but there were two problems: the installation tightness was inconsistent and it was easy to loosen. Under the condition of high-speed operation, it was easy to reduce the overprint accuracy. At present, the installation method of plate cylinder to reduce and eliminate the pollution and impact of plastic packaging materials on the ecological environment is basically changed to pneumatic locking, which has the same locking force and is not easy to loosen, and is suitable for high-speed printing

4. Overprint control

overprint accuracy is the core index of gravure printing machine and plays a key role in product quality and loss control. In the past, gravure printing machines were only able to carry out longitudinal automatic registration control. The overprint marks were generally 4mm * 4mm or 4mm * 6mm Square or rectangular. The adjustment of horizontal registration was mainly completed manually. At present, both horizontal and vertical registration are automatically adjusted, which requires that there must be horizontal overprint marks. There are two main types of control. One is to add an overprint mark on the original basis to control horizontal overprint, so that each color deck can be controlled only with two scanning positions. The other is to change the overprint mark to triangle, using the hypotenuse of the triangle as the control point, and the length of the right angle of the triangle is 4 ~ 8mm, which is a more commonly used control mode at present. As for the adjustment of overprint deviation, previously, the alignment of various colors was mainly realized by adjusting the position of the printing plate cylinder relative to the paper. At present, the position of the paper relative to the printing plate cylinder is mainly adjusted. This method does not need to change the running speed of the printing plate cylinder, which is conducive to the overprint adjustment in the case of high-speed operation. The adjustment accuracy is easy to control and the overprint accuracy is high. In order to ensure the high quality of the printed matter, the overprint accuracy of the gravure press should be controlled within ± 0.10mm

5. Drying method

in the past, gravure printing machines mainly used hot air drying, mainly for solvent based inks, but now gravure printing machines use many types of inks and varnishes, such as alcohol soluble inks, water-based inks and varnishes, UV inks and varnishes, and the problem can not be solved only by hot air drying. At present, the drying method of infrared heating air is mainly adopted, especially after a large number of water-based inks are used, the hot air drying device with large air volume becomes the basic configuration. Some hot air drying devices use electric heating or steam heating. The electric heating method has a great demand on the electric capacity, about 150KVA. If the electric capacity needs to be increased and there are ready-made steam pipes, the steam heating method can be directly adopted. At the same time, the number of equipment adopting UV curing method is also increasing, but there are still some problems in ink and process. It is believed that UV curing method will also become the standard configuration in the near future

6. Ink circulation system

gravure printing inks, especially spot color inks, are prone to precipitation if two or more binder resins have poor compatibility. In addition, gold and silver inks with large particles are also prone to precipitation. Therefore, the circulation of ink is very important. The ink circulation system must have the following functions: mixing ink to avoid sedimentation or ratio change; It is not easy to produce bubbles, precipitation and splash during the normal transmission of ink; Filter the ink, and the filter mesh should be about 120; It has solvent replenishment function to ensure proper ink viscosity

7. Electrostatic ink transfer device

the disadvantage of gravure printing process is that the eye tone printing is greatly limited, especially when printing full plate transition or local layer effect, it is very difficult to achieve the accuracy of 175 lines/inch, and small dots are easy to be lost, and the printing effect is very rough. The electrostatic ink transfer device can significantly improve this situation. It forms a high-voltage electrostatic area between the conductive surface between the electrostatic pressure roller and the paper, and between the paper and the plate cylinder. Under the action of static electricity, the ink is sucked out of the hole of the plate cylinder and transferred evenly to the paper surface. The oil ink transfer rate reaches or approaches 100%. It is not necessary to configure each color deck with an electrostatic ink transfer device. Generally, it is sufficient for a production line to have four color decks. An installation position shall be reserved on each color deck. When the printing color deck position changes, the electrostatic ink transfer device can convert between color decks. At present, the function of domestic electrostatic ink transfer device has been very ideal, and it can also be exchanged with foreign devices. The price is only about 1/5 of that of imported devices

8. Shaftless transmission mode

gravure printing machines generally adopt cardan shaft transmission, but the linear speed of the printing cylinder changes greatly during the transmission, even affecting the overprint accuracy. In recent two years, shaftless transmission technology has developed rapidly. Shaftless transmission is basically adopted for high-grade gravure printing machines, which greatly improves the transmission and overprint accuracy of multi-color gravure printing machines, and can fundamentally realize the transmission control of single unit, which will be the main transmission method of multi-color units in the future. Nowadays, shaftless transmission mode is widely used, that is, each unit is directly driven by a DC motor, and then centralized control is realized on the basis of unit control. For example, the speed change of a single unit can be realized, and the unused monochrome unit can be controlled to stop running, so as to reduce wear and energy consumption, and it is also very important to improve the overprint accuracy under high-speed operation

9. Tension control mode

in the past, the whole gravure press production line only used a set of tension control system, which was placed behind the last printing unit to adjust the tension of the whole production line by controlling the relative speed difference between the paper feed speed and the paper output speed. The tension variation range is large, generally more than 50 Newtons. In addition, the overprint is realized by adjusting the position of the printing plate cylinder, and the tension variation between color groups is greater, so the stability of overprint between colors is also very poor. Now it is basically changed to the tension control of the color separation group, which disperses the tension control of the whole production line to each color group, greatly reducing the variation range of tension. Generally, the tension change of each color group is about 5 newtons, which lays a good foundation for accurate overprint. In the process of use, how to eliminate faults and ensure the good luck of the machine. In the whole production line, the tension value of each color group should be as consistent as possible. Generally, a fixed value between 200 ~ 300 Newtons should be selected according to the difference of the paper to make the tension of the paper uniform during the printing process and reduce the deformation of the paper to a certain extent

10. Quality monitoring

quality monitoring can be divided into three levels: local overprint monitoring, product pattern monitoring and alarm, product pattern and ink monitoring. Local overprinting monitoring refers to the process of magnifying the overprinted cross hairs or key fine patterns on the printed format through the digital camera, which is generally enlarged by 15 ~ 20 times and tracked synchronously. The operator can monitor the overprint effect of the whole printing format and make timely adjustment in case of any problem. Local overprint monitoring is the most basic and necessary quality monitoring mode. Generally, one or

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