At present, the effective combination of a variety of materials and a variety of printing processes has become the trend of cigarette pack printing. Gravure printing has many advantages, such as high production efficiency, good hue consistency, good adaptability of printing materials, excellent performance in field, spot color, gold (silver) ink printing, etc., which can meet the stringent requirements of cigarette pack quality. Gravure machines have become a popular choice for cigarette pack printing companies. In addition, the quality inspection of cigarette packets will be further reflected in the printing odor, packaging machine adaptability, color, environmental protection and other aspects, in these aspects, gravure printing is also more advantages than other printing processes. Therefore, the purchase of gravure printing equipment has become a topic of great concern for cigarette pack printing companies. The author will talk about his own opinion about the introduction of web gravure printing machine and hope to help cigarette package printing companies.
Gravure printing machine is mainly divided into three parts: unwinding part, printing part, slitting and die-cutting part. This article first briefly analyzes the printing part. The printing part is the core part of the gravure printing machine, which completes the printing, overprinting and drying of various colors.
1, the number of color groups to choose from.
The number of color groups in the gravure printing machine is very crucial. This is mainly related to the leading products of cigarette pack printing companies and the environment for domestic cigarette decoration. The design and process of domestic cigarette packs are more complex. In the past few years, domestic cigarette pack printing equipment was mainly based on 6 colors and 7 colors. In these two years, there were mainly 8 colors, and the basic configuration mode included a full version of color and four. Universal color, two spot colors and a coating machine. The number of color groups is not as good as possible. The greater the number of color groups is, the more difficult it is to control the deformation of the paper, the overprinting of various colors, etc., and the capital investment will also increase. However, if the number of color groups is selected too small, it is difficult to embody the advantages of fast and efficient gravure printing and one-step molding. Therefore, users must choose according to their needs and in combination with future development plans. Although the group-type gravure printing machine manufacturers have promised to increase the number of units in the future, they will not only increase the investment when the units are added, but will also be affected by factors such as the technical upgrading of the gravure printing machine and the installation position and space of the gravure printing machine. limit.
2, the choice of printing format.
The requirements of various manufacturers on printing format are very different. The wider the format, the higher the requirement for paper and the greater the impact on overprinting. There are two types of 650mm and 820mm webs for cigarette pack printing equipment. In the past, printing companies basically chose the former, and they were more economical in terms of typesetting, plate making, plate installation, die-cutting cylinders, and paper specifications. In the time of typesetting, the soft pack box 6 rows and 4 rows can be arranged, the hard pack box 6 rows and 2 columns, the strip box 1 row and 2 columns, the die cutting cylinder 6 rows and 2 columns or the 8 rows and 2 columns, the paper width can be up to 650mm, due to the format Smaller, less paper distortion during printing, which is very advantageous for overprinting of products. However, there is a key problem, that is, the direction of the paper fiber is perpendicular to the printing direction when printing the barrel products. For the current high-speed cigarette packaging machine, the packaging adaptability is poor, and the appearance molding degree is poor, resulting in a quality problem. many. For this reason, many printing companies have to adopt the practice of printing only one 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 a printing strip box is used, it is better to choose a 820mm format gravure printing machine, so that the typesetting time strip box can be arranged in 1 row and 2 columns, hard package box 6 rows and 3 columns, soft package small Box 6 row 5 columns. For high overlay precision requirements and products that require multiple printing processes. It is advisable to reduce the number of rows. Generally, 12 to 16 pieces are ideal for typesetting, which can reduce waste caused by paper deformation and multi-channel processing. If you use online diecutting, typesetting can be free from this limitation.
3, printing plate installation.
The installation method of the plate cylinder has a great influence on the overlay accuracy, the print flatness, and the runout of the plate cylinder, and plays a key role in whether the printing equipment can operate at a high speed. In the past, it was mostly a mechanical installation method, but there were two problems: the tightness of the installation was inconsistent and loosened easily. In the case of high-speed operation, the accuracy of overprinting was liable to decrease. Now the printing plate installation method is basically changed to pneumatic lock, the same locking force, and not easy to loosen, suitable for high-speed printing.
4, overprint control.
Overprint accuracy is the core index of a gravure printer and plays a key role in product quality and loss control. In the past, the gravure printing machine could only perform longitudinal automatic register control. Overprinting marks were generally 4mm*4mm or 4mm*6mm squares or rectangles. Adjustment of the lateral register was mainly done by hand. At present, both horizontal and vertical registrations use automatic adjustment, which requires the need for horizontal overprinting marks. There are two main types of control. One is to add an overprint mark on the original basis to control horizontal overprinting, so that each color The group must be controlled with two scan positions. Another is to change the overprint mark to a triangle, and use the hypotenuse of the triangle as a control point. The length of the triangle's right-angled edge is 4-8mm, which is currently a relatively large number of control modes. In the adjustment of overprint deviations, the alignment of various overprints was previously mainly achieved by adjusting the position of the plate cylinder with respect to the paper. At present, the position of the paper relative to the plate cylinder is mainly used to adjust. This method does not change the operation of the plate cylinder. The speed is conducive to overprint adjustment under high-speed operation conditions, and the adjustment accuracy is easy to control and the overlay accuracy is high. In order to ensure the high quality requirements of the printed matter, the overlay accuracy of the gravure printing machine should be controlled within ±0.10mm.
5, drying method.
In the past, gravure printing machines mainly used hot air drying methods, mainly for solvent-based inks, but gravure inks and gloss oils are now used in many types, such as alcohol-soluble inks, water-based inks and varnish, UV inks, and varnish, which rely solely on hot air drying. Can't solve the problem. At present, the infrared heating air drying method is mainly adopted. Especially after a large number of water-based inks are used, a large amount of hot air drying apparatus becomes a basic configuration. The hot air drying device uses electric heating, but also uses steam heating. The electric heating method has a large capacity requirement for electricity, about 150kVA or so, if the power needs to increase capacity, there are ready-made steam pipes, you can directly use steam heating the way. At the same time, the number of devices using UV curing is also increasing, but there are still some problems in the ink and process, I believe in the near future, UV curing will also become the standard configuration.
6, ink circulation system.
Gravure inks, especially formulated spot inks, tend to precipitate if they have poor compatibility with two or more binder resins. In addition, the larger particles of gold and silver ink are also prone to precipitation. Therefore, the circulation of the ink is crucial. The ink circulation system must have the following functions: Mixing ink to avoid sedimentation or change in proportion; Normally transporting ink, it is not easy to produce air bubbles, sedimentation and splash during the conveying process; Filter ink, the mesh number of the filter mesh should be around 120 mesh; Solvent supplementation function ensures proper ink viscosity.
7, electrostatic ink transfer device.
The disadvantage of the gravure printing process is that the halftone printing is greatly limited, especially when printing full screen transitional mesh or local level effects. It is difficult to achieve an accuracy of 175 lines/inch, and the small dots are easily lost and the printing effect is very rough. The electrostatic transfer device can significantly improve the situation. It forms a high voltage electrostatic region between the electrostatic pressure roller and the conductive surface that the paper is in contact with, the paper and the plate cylinder. Under the effect of static electricity, the ink is taken from the plate cylinder It is sucked out and evenly transferred to the surface of the paper. The ink transfer rate reaches or close to 100%. It is not necessary to configure an electrostatic transfer device for each color group, and it is usually sufficient to have 4 color group configurations for a production line. The installation position should be reserved on each color group. When the position of the printing color group is changed, the electrostatic ink transfer device can switch between the color groups. Now, the function of the domestic electrostatic transfer ink device has been very satisfactory, and it can also be exchanged with foreign devices, the price is only about 1/5 of imported devices.
8, no shaft drive mode.
The gravure printing machine generally adopts the universal shaft drive, but the linear speed of the printing plate cylinder in the drive changes greatly, and even affects the overprint accuracy. In the past two years, the non-shaft drive technology has developed rapidly. The high-end gravure printing press basically adopts the non-shaft drive, which greatly improves the accuracy of multi-color gravure printing machine transmission and overprinting, and can fundamentally realize the transmission control of single units. , is the main method of multi-color unit transmission in the future. Now more non-shaft transmission mode is used. Each unit is directly driven by a DC motor, and then centralized control is implemented on the basis of the control of the subunits. For example, the speed change of a single unit can be achieved, and the unused monochrome can be controlled. The unit is shut down to reduce wear and energy consumption, and it is also critical to improve the accuracy of overprinting at high speeds.
9, tension control mode.
Previously the whole gravure press production line used only one tension control system, placed behind the last printing unit, and adjusted the tension of the entire production line by controlling the relative speed difference between the feed speed and the paper exit speed. The range of tension changes is relatively large, generally more than 50 Newtons, plus the adjustment of the position of the plate cylinder to achieve overprinting, the tension change between the color groups is greater, so the stability of overprint between the colors is also very poor. Now basically changed to the tension control of the color separation group, and the tension control of the entire production line is distributed to various color groups. The tension variation range is greatly reduced. In general, the tension change of each color group is about 5 Newtons. Accurate overprinting laid a good foundation. In the entire production line, the tension value of each color group should be consistent as much as possible. Generally, according to the difference of the paper, a fixed value between 200 and 300 newtons should be selected, so that the tension of the paper during the printing process is even and to a certain extent Deformed paper.
10, online quality monitoring.
On-line quality monitoring can be divided into three levels: on-line partial overprint monitoring, on-line product pattern monitoring and alerting, on-line product patterning and ink color monitoring. On-line local overprint monitoring is to partially overprint a crosshair or a key fine pattern on a printing surface, pass a digital camera, and then perform an enlargement process, which is generally enlarged by 15 to 20 times and synchronously tracked. The operator can monitor the overprint effect of the entire printing format and find problems in a timely manner. On-line local overprint monitoring is the most basic and necessary on-line quality monitoring mode. Generally, one or two parts are installed. The price of a system is about 50,000 to 80,000 yuan. On-line product pattern monitoring and alarm is to enter the sample pattern into the computer, the online print is also scanned, and compare the print pattern position and sample pattern position changes, if there is a change, the alarm, remind the operator to adjust and online The product is marked or rejected. This method is now used more often. The price of a system is about 800,000 yuan. On-line product pattern and ink monitoring is based on the second online quality monitoring method. It adds automatic adjustment of equipment and control of ink color. This method is used very rarely, mainly in the banknote printing industry, because monitoring The cost of equipment is relatively high.