Flexo printing, gravure printing, offset printing, and screen printing are the four common printing methods for packaging printing. Flexo printing and gravure printing are more distinctive in the printing of printing materials such as flexible packaging materials, folding cartons, paper bags, and gift wrapping paper. From the perspective of the development of modern flexo printing and gravure printing, in addition to the large differences in platemaking, there are many similarities or similarities in the structure and technology of the equipment. In order to compare and understand the similarities and differences between the two printing methods in terms of equipment structure and new technologies, the following will briefly discuss the development and application of flexo and gravure equipment technologies in recent years.
1. Using automatic traction and tension adjusting device to realize roll changing / winding without stopping the machine
The new flexo printing machine and gravure printing machine adopt automatic paper receiving mechanism and pneumatic-electric tension measurement and adjustment device to ensure constant tension and realize roll changing / winding without stopping the machine. In order to ensure that the edge position of the printing material entering the printing part is always correct, for opaque materials such as paper, a correction device composed of a photoelectric scanning head or an ultrasonic sensor must also be used. When printing paper or paper jams, sometimes temperature and humidity adjustments are required. When printing plastic film or aluminum foil, a corona treatment device should also be equipped to improve the inking ability of the film surface.
2. Adopt independent / direct drive technology to realize stepless continuous and selectable printing length.
The independent drive technology has been used in gravure printing machines for many years, but it is only limited to the units of traction, coating, compounding and cross-cutting. Now it has developed into a complete gravure printing machine that does not require mechanical transmission. In each printing unit, a motor is used for driving. The plate cylinder is driven directly by the motor to achieve longitudinal registration during the imprinting process, and is controlled by a stepper motor to control the horizontal registration. The main advantage of the independent drive gravure printing machine is the reduction of mechanical parts (no need of mechanical transmission shaft and registration compensation roller mechanism, etc.), and the shortening of the length of the material belt, which is conducive to improving the printing quality and printing speed.
The plate cylinder of the old-fashioned flexo printing machine drives the gear of the plate cylinder through the gear of the impression cylinder to form a synchronous rotation, and the repeated circumference of the printed product is the same as the pitch of the gear. In each printing unit of the new flexo printing machine, a motor directly drives the plate cylinder, which solves the problem that the repeated length of printed products is limited by the gear pitch. The digital transmission technology is used to directly drive the plate cylinder. When replacing printed products with different circumferences, there is no need to change gears, and stepless continuous selectable printing lengths can be achieved. Due to the use of digital control, there is no need for repeated variable speed adjustment, eliminating the need to change the speed and adjust the gear meshing, thus improving efficiency.
For example, the newly developed ASTRAFLEX CCI satellite-type 8-color packaging flexo printing machine by W & H Company adopts a separate motor drive technology, a main drive device, a drive device for unwinding / rewinding components, and a traction device. . The independent drive flexible packaging gravure press developed by Serrudi has a maximum printing speed of 500 m / min. The Flexline Vario unit-type flexo printing machine developed by BHS uses a gearless plate cylinder, which eliminates the limitation caused by the number of gear teeth and eliminates the limitation caused by the number of gear teeth. Each printing unit has its own Independent servo drive mechanism and fast roll change system, the highest printing speed reaches 500m / min. The POTOPAK 4000-1 shaftless transmission gravure machine developed by Valment Rotomec Company adopts ES (electronic shaft) system and does not use registration compensation rollers. During the acceleration and deceleration stages of the machine, rapid registration settings can be made. Can increase the stability of the machine. The ES concept uses a fully automatic replacement device that does not require any manual intervention by the operator, and the maximum printing speed can reach 650 m / min.
With the combination of direct control technology and CI design, as well as the changeability of printing length and the reduction of machine debugging time, it has changed the situation that flexo used to be difficult to print on a large and variable format.
3. The sleeve-type plate cylinder structure is used to achieve "fast plate change".
The plate cylinders of old-fashioned flexo printing machines and gravure printing machines basically adopt a monolithic structure, while most of the new flexo printing machines and gravure printing machines adopt a sleeve-type plate cylinder structure. Due to the low cost of the sleeve-type cylinder structure, it is easy to install and remove High flexibility, long service life, convenient storage, high system accuracy, can shorten the preparation time, accelerate the replacement of printed parts, and has a "quick version change" function. It is widely used in flexo and gravure printing, and will gradually replace the traditional cylinder. The biggest advantage of the sleeve-type plate cylinder is that it can be reused. By using sleeves with different wall thicknesses, the printing length of the plate can be changed.
For example, the newly developed sleeve system of W & H Company can be used for plate cylinders of all specifications. After printing a product, all the specification parts that need to be replaced can be quickly replaced in the machine by the operator. The roller mandrel is always left on the machine. Reusing the cylinder not only shortens the preparation time, but also can paste the printing plate on the sleeve at any time, speeding up the replacement of the printing piece and reducing the production cost. Thin-wall sleeve technology, low manufacturing cost, can maintain good radial accuracy when printing. The Heliostar 2000 unit-type gravure printing machine produced by W & H Company adopts the sleeve technology that highlights the gravure cylinder, which provides the printer with greater flexibility and commercial efficiency.
4. The closed doctor blade system is adopted to reduce environmental pollution and facilitate rapid replacement of the doctor blade
The reverse scraper structure is used in the quantitative ink supply system, which is suitable for high-speed operation, reducing the problem of solvent volatilization and environmental pollution in solvent-based inks; solving the foaming problems that occur during the use of water-based inks.
The satellite flexo printing machine adopts a fully enclosed double-squeegee inking system. The ink is sprayed to the surface of the anilox roller through the ink port and stored in the ink chamber. The ink is scraped by the reverse scraper, and the positive scraper acts as a seal. Because of its good sealing, it has great benefits for health and the environment. In a fully enclosed system, the scraper, seal, pad, and pressure plate are all mounted on a cavity type bracket, and they are mechanically (or pneumatically or hydraulically) pushed to the ceramic anilox roller, and a certain pressure is applied, and then Connect the ink delivery tube and the return tube to the ink pump and the ink storage container, respectively. The closed-type doctor blade system ensures that the anilox roller and the printing plate get the best amount of ink. The application of laser engraving of the high-line-count ceramic anilox roller and the closed blade can ensure that the anilox roller and the printing plate get the best amount of ink. The ink transfer performance of the short ink path system is improved, and the stability of the printing quality is improved.
The Heliostar 2000 unit type gravure printing machine produced by W & H Company adopts a newly developed closed-type anti-splash device, which can make the roller inking process completely free of ink splash. The new satellite gravure press also uses a doctor blade rapid pressure and replacement device, significantly reducing the time to replace the doctor blade, and can improve the quality of the doctor blade. Its structural features are: the doctor blade is controlled by a pair of series cylinders. During the production process, the long-stroke cylinder controls the doctor blade to enter the predetermined working position, and the short-stroke cylinder controls the doctor blade to enter the working position and applies pressure; at the same time, the doctor blade The frame is equipped with a turning mechanism (controlled by a tandem cylinder) and an eccentric squeegee clamping mechanism. The former can turn the blade holder to a nearly vertical position, and the latter can simply, accurately, evenly and reliably clamp the doctor blade tight. Therefore, the entire replacement process can be completed on the machine, and the time is greatly shortened. The uniformity of the ink scraping, the life of the ink scraper and the roller can be improved.
5. Automatic cleaning device for printing plate cylinder
At the end of printing, the plate cylinder is automatically cleaned on the machine, which can significantly reduce the manual cleaning workload and improve the operating environment. The quick replacement and cleaning system (Ecoplus) equipped with the Heliostar 2000 unit gravure printing machine produced by W & H Company has obviously reduced the preparation time of the printing machine. The TURBOLEAN ink supply and cleaning system used in the ASTRAFLEX CCI flexo printing machine can automatically supply ink to the printed parts in sequence and clean the anilox roller, cavity scraping system, ink pump and ink tube.
6. Quick replacement and positioning system
On the transmission side of the gravure printing machine or flexo printing machine, there is a small cart guide rod. The guide rod is raised and lowered by a cylinder, which can accurately control the movement of the small cart and speed up the installation and disassembly of the small cart. The PORTACIFT manipulator roll change system developed and produced by W & H is used to automatically change the plate cylinder and anilox roll; it takes only 1 minute to change one roll. Through the intelligent transmission system and positioning system, the accurate movement and horizontal registration of the plate cylinder and anilox roller of each color group are guaranteed.
7. Combined unit structure and diverse post-press connection processing forms.
The RCS330 narrow width flexo printing machine developed by Heidelberg's partner gallus adopts all digital drive technology, full computer control, and different printing interchange units such as flexo / silk screen / offset / embossed printing. Arsoma EM series unit-type flexo printing machine adopts optional modular unit and open interface structure. According to needs, it can flexibly choose die cutting, hot stamping, marking, glazing, laminating, embossing, printing control, etc. A post-press processing unit.
The FG500 series of flexo presses produced by Comprint can be configured as combined gravure and flexo printing presses according to user needs.
According to the processing needs of users, the B250 unit type 6-color narrow-width flexo printing machine developed by Edale Company can choose the corresponding configuration to complete holographic anti-counterfeiting, UV glazing, hot stamping, molded patterns, magnetic stripe, die knife, paper tape Online post-sequence processing functions such as punching, slitting and stacking.
The new paper gravure printing, in-line compounding, and die-cutting production line developed by Rudi is dedicated to the printing of cigarette packs and other thick papers. Tachys (fast) satellite flexo printing machine series has a variety of configuration methods, you can use the line once stacked flexo printing unit for glazing, cold / hot coating, compounding and other processes.
It can be seen that one-stop production is becoming more and more important, and a single production unit is developing towards the integration of a complete production line.
8. Apply computer control technology to carry out intelligent operation management.
Adopting advanced computer technology and management system, not only can realize the monitoring system from single control to centralized control, from single machine control to the entire production line, but also ensure that the equipment will not generate waste when registering the equipment in the shutdown state.
Using the modular automatic operating system, you can pre-select the menu, centrally operate the unwinding / rewinding unit, printing unit, and drying unit, and you can also use the camera "printing" observation module to view the entire printing process on the display screen. Using CAN communication technology, the functional modules are connected into a network to exchange information. Use a modem to select a remote fault diagnosis device to help customers.
The newly developed ASTRAFLEX CCI satellite type 8-color packaging flexo printing machine by W & H Company realizes the coordination between the printing station and the anilox roller through the electronic synchronous adjustment system. The traction device can be set in proportion and can work according to the actual tension.
Edale's B250 unit type 6-color narrow-width flexo printing machine is equipped with a simultaneous printing quality inspection device and a computer-controlled automatic registration system. With various functions such as parameter storage, sampling content setting, pattern blocking and focusing. The registration system is connected with the main control cabinet computer to form a network, which performs system control on the operation of the entire production.
With the establishment of the digital era, the high-speed satellite-type flexo printing machine of Serudi Flexo Technology's Tachys series of electronically driven printing units and variable printing lengths has been introduced.
Nine, the application of related advanced technology to improve the quality of printing
The new flexo printing machine and gravure printing machine adopt high-efficiency servo stepping motor, which can automatically monitor the rotation speed to ensure that the parameters such as printing pressure, printing length, printing plate and printing material thickness are set with high precision. The unwinding / winding unit can be accurately controlled by the DC motor.
The use of thin-plate technology, computer-to-plate technology, UV ink and high-net line ceramic anilox roller can greatly improve the quality and level of flexographic printing.
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