Below, we talk about the control of printing pressure.
The adjustment of flexographic printing pressure is another key factor in ensuring product quality. The pressure between the anilox roll, the plate roll, and the embossing roll must be readjusted before each product print. The adjustment of printing pressure requires the accumulation of normal experience of operators and the standardization and unification of operating practices. The adjustment of the printing pressure mainly includes two aspects: (1) the pressure between the anilox roller and the plate roller; (2) the pressure between the plate roller and the platen roller.
First, we need to adjust the spacing between the three rollers. At the time of printing (machine combined pressure), the interval between the anilox roller and the plate roller and the distance between the plate roller and the platen roller are substantially the same. The 0.38 mm (double-sided tape thickness) + 1.70 mm (print plate thickness) is 2.08 mm. We used two 2.05mm thick kraft paperboards on the old-fashioned crew flexo press. Under the combined pressure of the printing press, the kraft paperboard was placed at both ends between the two rolls, and the anilox roll and the printing plate were manually adjusted. The distance between the roll, the plate roll and the embossing roll is the same as pulling the resistance of the pickup in both ends. The pitch at this time is the ideal pressure value in the printing, but it is slightly different from the printing pressure used in the actual production, requiring the operator to make some fine adjustments in normal production. Now our factory's introduction of the Gallas equipment has changed the series of cumbersome steps in the design, using a special spacing positioning hole, the use of spacing positioning pins to locate the positioning hole, more precisely to ensure the spacing between the three rollers . This positioning distance can also be appropriately fine-tuned in actual production as required. The pressure at the time of printing is adjusted at the combined pressure of each machine.
Before starting production, we first set the spacing for each color group and relax the pressure between the plate roller and the embossing roller (note the synchronization between the operating surface and the drive surface). During the slow running of the flexo printing machine, press the first group of printing units to observe whether the ink transfer roller is evenly distributed to the anilox roller, and then observe whether the ink transfer of the anilox roller to the plate roller is good or not. Gradually increase the pressure between the plate roll and the embossing roll until the text is printed on the composite sheet (be careful to maintain the synchronism between the operating surface and the transmission surface, ensuring that both ends increase the pressure at the same time). Check whether the printed lines and screens on the sheet are clear, whether the pattern letters are complete, whether the field is whitish or hairy. For these problems, adjust the pressure between the plate roller and the embossing roller slightly.
Flexo printing is a light pressure printing process, and its pressure is far less than that of offset printing and gravure printing. We usually require small pressures when printing with flexo printing, but when printing with composite hoses, because printing materials are composite sheets, we intentionally increase printing pressure slightly. Taking the field version as an example, we adjusted the printing pressure to faintly see a pressure frame appearing on the edge of the field, so as to avoid the omission of the printed image due to the uneven thickness in the unit area.
3. Requirements for printing equipment, printing inks and printing materials in the flexible printing process of flexible hoses
Hose Printing Due to the use of higher-cost materials such as composite sheets as substrates, our performance requirements for flexographic printing equipment are higher than those of conventional flexographic printing presses. The printing equipment must be equipped with a corona treatment device. The printing unit must be equipped with a full UV drying curing system. It also requires the equipment to have an accurate tension control system and the overall stability of the machine. According to the author's understanding, although domestic manufacturers such as Ziguang, Black Bull, Beiren Fuji, Sunray Sun, Taihang, etc., manufacture narrow-format flexographic printing presses, the equipment for printing composite hoses relied on imported equipment. . In the printing of composite hoses, we need to ensure the quality of hose products with high overall stability, convenient printing quality control, high printing speed, high product variety flexibility, and superior machine printing efficiency.
Flexographic printing belongs to letterpress printing and has been developed for more than 100 years. However, the popularity of UV inks in domestic flexo printing has only been a few short years. Compared to water-based inks and solvent-based inks, UV inks have a high viscosity. When the hose is printed on the network cable, it is relatively easy to produce poor leveling weaknesses, resulting in poor ink distribution of the anilox roller. During the operation, the pressure between the anilox roller and the plate roller needs to be increased to express the gradation effect of the printed product. However, such operations will often cause problems with stencil printing. The printability of screens will be reduced, and the color saturation of prints will be insufficient. At present, water-based UV inks have been developed in foreign countries, but inks are relatively expensive. When it is used, it often causes waste due to improper operation. From the economical point of view, it must depend on the strong work responsibility of the employees and the accumulation of long-term operating experience, and pay attention to the daily savings.
Printing materials are the largest expense in the cost of hose printing. However, in the printing process, many waste products are caused by unstable sheet quality. The tightness of the composite sheet is uneven at both ends, the surface of the sheet is uneventful, the thickness inside the unit area is uneven, and the internal friction coefficient changes greatly. The problems are the reasons for the decline in the yield. Composite hose printing is very demanding on the printability of composite sheets. We also hope that manufacturers of composite sheets can further improve its overall quality, stabilize its printability, and allow companies to better control the printing quality of hoses. Reduce product costs to achieve a win-win situation for suppliers and users.
4. Advantages of flexographic printing in composite hose printing
The flexographic printing process is not an unfamiliar printing process in China's printing industry. Its overall printing quality, printing cost and production cycle advantages have been fully affirmed in the hose industry. In addition, due to the environmental protection characteristics of flexographic printing, it is more attractive to customers and the production of composite hoses has a relatively abundant source of business. The printing production speed of the flexo printing machine and the production capacity of the equipment connection can ensure that the customer can quickly and timely receive the required composite hose product. The UV ink used in flexo printing in the flexible hose enables the customer's products to be truly green, safe and reliable. The product can be easily opened in foreign markets, creating greater profit margins for customers.
5. Hose in the flexographic printing process problems and solutions
There are still some problems in the flexo printing process of the hose. Since the outer packaging of the hose is lithographically printed, many designers will use the offset proof to print the hose and hope to use different printing methods. The printing process prints exactly the same effect. This practice is never satisfactory. We must tell the designers that when conceiving the artwork, we should try to consider the use of large blocks or lines, and use spot colors to give full play to the bright colors and high saturation of the flexo spot colors. Clearly, it is best to have a gap in the middle. The conventional approach is to prefer more leaks. Do not stack a little more and try to improve the error of overprinting during flexographic printing.
We expect the printing industry to more publicize and introduce the advantages and limitations of the flexographic process features and performance capabilities, and to train more flexographic professionals, hoping that hose designers can design more in line with the flexographic process and products. The manuscript of the promotional effect makes the flexo plate better applied to the printing of the hose.
Author: Bo Li Xiang: Shanghai Chang-hong (Changfu) hose plant
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