Compared to sheet-fed printing, rotary printing is more suitable for large-volume, high-quality cigarette packs. As a flexible printing machine manufacturer with more than 40 years of history, OMET Limited (0MET) in Italy entered into the Chinese market, and based on its experience in cooperation with cigarette printing companies, it has developed some technologies for medium and narrow web transfer printing. Valuable new technologies are shared here with colleagues dedicated to cigarette pack printing. The following is mainly about the model of shaftless gearless transmission.
1. Link compound. After the composite laser film and paper are combined, they can be peeled off or not peeled off after compound drying. This will not only help reduce the cost of printing materials, but also make them more environmentally friendly. If the positioning printing is performed on the basis of local transfer of the laser layer, the bronzing technology can be partially replaced, and the overlay/transfer and printing overlay accuracy is the same, and a new idea can be explored in anti-counterfeiting.
2. Based on radiant film fixed-length stretching version of the seam avoidance technology. In the laser film production process, the fluctuation of tension and mold temperature caused by the drift caused the laser film distance is not constant. The error in the accumulation of the plate distances causes some printing patterns to be printed on the plate seams during the rotary printing process. The resulting bad film is usually not less than 20% of the material, which brings a huge material waste to the cigarette pack printing company. Omet's seam avoidance technology provides a solution for this. The specific method is to install a plate distance detecting device in the unwinding part of the laser film, and the error of the laser film plate distance is controlled within a certain range through the fixed-length stretching. The printing unit adjusts the phase of the cylinder in real time to avoid the accumulation of plate distance errors. The plate seam on the printing plate and the printing film on the laser film are always overlapped together so that the laser paper can be printed and processed on the rotary machine.
3. Shaftless gearless transmission. The mechanical long axis of the traditional rotary printing press was cancelled. The plate cylinder and the impression cylinder of the printing unit were driven by independent servo motors, and each printing and processing unit was relatively independent. Tobacco packaging companies can flexibly configure their machines according to their product requirements. This simplifies the printing press transmission and eliminates the limitation of the roller gear transmission. The thickness of the printing material is in the range of 0.0l to 0.60mm. Replacement of the film material and cardboard material does not require replacement of any spare parts on the machine. The tension control system also uses non-shaft technology. Each plate cylinder uses an electronic virtual axis, the electronic gear is accurately adjusted to 32 bits, and the registration accuracy is up to 4 millionth, which is much better than the traditional mechanical register method. Because the mechanical structure of the machine is simplified, the operation of the machine is also easy and the daily maintenance work of the machine is also simplified.
4. Sleeve technology. Omet's machines use air-cushioned plate sleeves, eliminating the need for heavy plate cylinders, reducing the labor intensity of the operator's print job changes, and replacing a six-color print within ten minutes. The sleeve is driven by an independent motor, without the limitation of the gear pitch, and the imposition size can be changed steplessly, which is advantageous for saving paper. For special prints, seamless sleeve plates can be used.
5. Multi-process combination printing. Flexible printing, gravure printing, and screen printing have different printing application ranges, and each has its own merits in terms of level performance, on-site printing, and the use of ink for special effects. Omet can insert gravure and screen printing units at different positions of the flexo line. The drive and tension of each process unit are independently controlled and do not interfere with each Other, ensuring high-precision overprinting. Cigarette printing companies can flexibly combine various printing processes, flexibly match the features of different products, combine equipment combinations, and avoid weaknesses to develop technological routes that have their own characteristics.
6. Positioning printing. Some laser films have been imprinted on the film during the manufacturing process, requiring printing and pattern overprint on the laser film, which puts special requirements on the overprinting system of the rotary printing press. OMIT's presses use shaftless transmission. The roller motor of each unit can position the pattern on the laser film in both vertical and horizontal directions. Therefore, this type of laser paper also has good adaptability.
7. screen printing. Rotary screen mesh drum plate-making materials are divided into two kinds: woven mesh and electroplated metal mesh. The weaving nets have low plate-making materials cost and flexible platemaking methods, but their ink transfer performance and their own strength are relatively poor, and the printing speed is limited. This type of roller is suitable for products with low quality requirements, and the production volume is not particularly large. It can also be used for white-on-white processes. The metal mesh is welded with a monolithic electroplated nickel mesh, and the ink transfer performance is relatively good. The printing speed is about 50% faster than the braided mesh, but the cost of plate making is relatively high. This method is suitable for products with high quality requirements and large production volumes. In general rotary printing presses, only one kind of material can be used as a screen. Omit's newly-produced screen printing unit can use the mesh drums of the above two materials. Companies can weigh the quality and cost when designing processes, and can use flexible screens. Plate making method.
8. Gravure printing. The gravure has a large amount of ink, and the effect is very good when the printing requires a thick print such as a solid ground ink. In the case of a metal ink printed with particles, it is also stronger than the flexo and offset printing. Omet's installation of a gravure printing machine on the machine can effectively solve the problem of the customer's picking on the hue when the cigarette packet turns from the traditional gravure printing process to the flexo printing process. Gravure printing pressure is much greater than flexo and screen printing. The effect of gravure printing on roll paper force is different from flexo printing and screen printing. In multi-process assembly printing lines, overprinting problems often occur. Omet's method is gravure and flexo printing, and the tension control between screen printing units is controlled. The tension between the units is relatively independent and does not interfere with each other, ensuring accurate printing registration.
9. Compound drying. For water-based inks and UV inks, hot-air, infrared, and UV drying methods are common for flexo printing. In the actual production process, common ink drying is not thorough, and part of the drying system design originated from the equipment is unreasonable. OMIT's printing machine drying system can use three kinds of drying devices to improve the drying efficiency by configuring high-efficiency high-power UV lamps. For the characteristics of water-based inks, the combination of infrared dryers and hot air devices is used to solve high-speed printing. When the ink is not easy to dry the problem.
10. temperature control. Different substrates have different temperature sensitivity, and increasing the drying power in actual production can cause deformation of the material and affect the print registration. Omet is equipped with a large-diameter cooling drum in each printing unit, and the cooling water temperature in the cooling roller is adjustable. The printing material is wrapped on the cooling drum with a wrap angle of nearly 320 degrees. The hot air oven is designed to be mounted on the cooling roller in an arc shape. The UV drying lamp shade can also be placed on the cooling roller. This drying/cooling method allows the most effective control of the temperature of the material, preventing web deformation and ensuring accurate overprinting. There is no difficulty in printing heat-shrinkable film materials that are sensitive to temperature.
11. Automatic pre-register. When a rotary press is changed from a stop to a change or when a roll is changed, it will inevitably be wasted due to misalignment. OMIT's printing plate cylinder is independently driven by the motor. Before the paper is not fed, the printing roller of each color group will automatically go to the reference position, and each color has been basically registered. In actual operation, as long as the length of a paper path, each color group can be accurately registered. The automatic pre-registration function not only saves printing time, but also saves printing materials, greatly improving the yield.
12. Secondary overprint. Since the printing material has undergone a change in the properties of the printing material after the first printing has been dried, even if the same tension is applied during the second printing, it is difficult to ensure that the amount of deformation of the web is the same as in the first printing. Using a conventional rotary press for secondary printing, it becomes difficult to obtain accurate overprints. Only one set of markings is used on OMIT shaftless printing presses, which is overprinted with a roller chase cursor. The second printing and the first time use the same overprint mark. The registration no longer depends on the amount of deformation of the material and the accuracy of the secondary overprint. It is basically the same as the first printing. If the printing machine color group is not enough, this function can be solved temporarily.
13. Cold stamping gold. At present, some cigarette factories on the market have eliminated the paper packaging for cigarette packs and replaced them with color films to reduce packaging costs. Using cold gilding technology, similar hot stamping effects can be made on paper and film to increase the attractiveness of cigarette packs. Omet's cold stamping units are modular in design and can be repositioned anywhere between printing units.
14. Holographic positioning stamping. After extracting the ink supply system of a printing unit, Oemite's newly developed circular press circle holographic positioning hot stamping unit can be installed in an empty position. This kind of design can make the hot stamping unit and the printing color group interchangeable position, and it is easy to deal with such as hot stamping and printing. On models with a width of 520mm, the gilding unit can install up to five gilding film tapes. Each film tape roll is driven by an independent servo motor. Each film tape can be individually programmed. General bronzing design speed 130m/min, holographic positioning bronzing speed up to 80 ~ 90m/min. The post-processing value-added services of the cigarette pack printing factory will be considerably extended.
15. Cold pressed holographic simulation. With the use of a cold foil stamping unit on the Omidity press, special varnish can be used to achieve similar holographic imprint on paper and film. The holographic gloss embossed in this way varies depending on the color of the underlying ink. The use of cold-pressed holograms can partially replace laser paper, which has positive significance both in terms of environmental protection and the saving of paper materials.
16. Twin-cut die cutting technology. Traditional round bale round die-cutting uses a one-piece die cutter. When the die cut size or pattern of the job is changed, the printer needs to re-customize the entire die drum. The factory not only has to invest a lot of money to buy all kinds of knife rollers, but also has a lot of space and manpower resources for knife roll storage. In recent years, the introduction of magnetic die-cutting drum technology, the bottom roller is a magnetic steel roller, can be used repeatedly, die-cutting steel knife skin installation is very convenient, like the tape can be adsorbed on the magnetic bottom roller. If the die-cut repeat lengths of the two batches of jobs are the same, only the die-cutting blade can be replaced when the job is changed. Instead of replacing the die-cutting roller, the die-cutting blade is much cheaper than the die-cutting drum. Technology, companies can save considerable costs. If the die-cut repetition circumferences of the two batches of jobs are different, companies will not only have to replace the die-cutting blade but also need to purchase expensive magnetic bottom rollers, which still has many limitations.
Source: Print Magazine, Issue 6, 2005