The advantages of flexographic printing
The flexographic printing process has become familiar to the printing industry in China. Its advantages in printing quality, printing cost, and production cycle have been fully recognized in the hose printing industry. For example, the production of composite hoses has a relatively abundant source of business. The printing speed and line processing capability of the flexographic printing presses ensure that users receive the required hose products in a timely manner.
In addition, flexographic printing is environmentally friendly, making it popular with users. For example, the flexographic printing plate adopts UV inks in the printing of hoses, so that the user's products are completely green, safe and reliable. The product can be easily opened in foreign markets to create greater profit margins for customers.
Flexible hose printing process
Before printing, we must first make a feasibility analysis of the prepress process. When receiving the sample of the toothpaste tube provided by the customer, carefully analyze the designer's design focus, determine the main screen (such as the product's brand identity, product background level, etc.) and the auxiliary screen (such as the product's text description, product composition, Weight marking, etc.) Determine the color number and color sequence of the product colors, perform appropriate scaling on the color of two or more fasteners, and add the tube cursor and filling to the sample draft according to the customer's requirements. cursor. After completing the above preparatory work, the revised sample will be submitted to the plate making company.
Then, the anilox roller of each color unit is configured with reference to the pattern of each color of the printing plate (such as solid, line, halftone, gradient, etc.) and the color concentration of each color, and it is made when proofing. Final adjustments to restore the color to its best condition. Our factory has deployed dozens of anilox rollers for hose printing. The number of network lines is 250 to 800 lines/inch, and the BCM value is in the range of 3.0 to 12.0. When printing the field version, use an anilox roller of 250-400 lines/inch, an anilox roller of 400-600 lines/inch for printing text and line printing, and 550-800 lines for printing halftone and gradient printing. Inches of anilox roller. After selecting the number of lines of the anilox roller, the BCM values â€‹â€‹of the same line number of anilox rollers are also compared, so that the final selected anilox roller configuration is more reasonable and the color reproduction is closer to the original color.
Then you can do the printing operation.
Our factory introduced the Jarus EM410 flexo printing machine, equipped with 8 color group full UV printing units and 2 sets of die cutting and slitting units. The main program for printing production is: on the upper composite sheet roll material â†’ go material â†’ adjust the corrective device â†’ install each color group anilox roll â†’ install the plate roll â†’ adjust the anilox roll, plate roll, between the impression roll Pressure â†’ Embossing â†’ Adjusting tension â†’ Register printing â†’ UV ink curing â†’ Cutting composite sheet â†’ Winding.
Control of printing parameters
The process of printing hoses and printing coated paper, offset paper, and self-adhesive paper with a unit type flexographic printing press is basically the same, but due to the thicker composite sheet, the total thickness is about 300 Î¼m, and the basis weight is large, and the internal and external surfaces are PE film, so compared with the general paper or stickers, cardboard, etc., the control of printing tension and printing pressure is particularly critical.
1. Control of printing tension
The tension system of the unit type flexographic printing press is divided into three parts: the unwinding part, the printing part and the winding part. Our factory's Juras EM410 flexo printing machine is equipped with a set of roll roll tension control system, two sets of printing tension control system and a set of winding tension control system to ensure the stability of the tension.
The function of the unwinding part tension control system (also called the pre-leveling tension system) is mainly to straighten and tighten the composite sheet in advance, so as to improve the elasticity and surface tension of the sheet produced on the composite sheet during the manufacturing process. Wrinkles, unevenness, and "foliage" and other phenomena.
The printing part tension control system refers to a rubber roller that passes through the second leveling tension system until the tension value after a constant printing process after printing. These two sets of tension control devices are collectively referred to as the printing tension control system. Their role is to balance the printing pressure of the composite sheet subjected to each plate roller during the printing process and the pressure generated between the composite sheet and the feed roller and the UV cooling roller. Tension and resistance, and keep the tension in the printing process constant. The size of the printing tension should be based on the degree of buckling of the composite sheet. The higher the degree of buckling of the composite sheet, the greater the tension value; otherwise, the tension of the composite sheet should be smaller. In actual production, since the friction coefficient of the surface of the composite sheet is relatively small, and the middle has â€œaluminum foilâ€ as the skeleton, we must set the tension as large as possible, but we must also ensure that the composite sheet is not stretched after printing. . Taking a composite sheet with a width of 400 mm and a total thickness of 275 Î¼m as an example, the printing tension is usually set to be about 320 N at the front end and about 360 N at the rear end, and the appropriate point for the printing tension control is to use various â€œcolor registration pointsâ€ in multi-color printing. Registration, no before and after "move" as a standard. In addition, it should be noted that the speed of printing can also affect the stability of printing. Our approach is to first set the printing tension in the common range of the used sheet size, and then basically register the printing plates of each color group to gradually increase the speed to the normal production speed, and then according to the â€œmovingâ€ trend of the â€œcolor registration pointâ€ for printing. Tension is properly fine-tuned.
The winding section tension system refers to the constant winding force and torque force of the rear end winding when the flexographic printing machine performs roll-to-roll production. Its role is to neatly roll up the printed material, and keep the rolling force of the entire roll from the inside of the core to the outside of the core. When printing composite sheets, in order to make the two sides of the toothpaste sheet that has been cut into smaller rolls flatter, the roll force and the torsional force of each roll are more stable. We have set a relatively fixed roll force value based on the data obtained during the actual operation. And torque value. The set values â€‹â€‹are: roll force 60% and torque 50%, which guarantees the stability of the quality of each roll of sheet during tube manufacturing.
When printing flexible tube sheets with a flexographic printing press, the accuracy of the tension control determines the print quality and the overall quality of the finished product. There are many factors that determine the magnitude of the tension value, including changes in the production environment of each batch of composite sheet, differences in sheet manufacturers, different equipment for sheet production, width of composite sheet during printing, different printing equipment, etc. . We need to grasp the properties and construction of various sheets and various equipment, find out the range of tension values, and then adjust the optimal tension value during normal production.
2. Control of printing pressure
The adjustment of printing pressure is another key factor in ensuring product quality. Before each printing, the pressure between the anilox roll, the plate roll and the embossing roll must be readjusted. The adjustment of the printing pressure mainly includes two aspects: one is the pressure between the anilox roller and the printing plate roller; the other is the pressure between the printing plate roller and the embossing roller.
First, the distance between the three rollers is adjusted. At the time of printing (combined pressure state), the interval between the anilox roller and the plate roller and the distance between the plate roller and the platen roller are basically the same. That is: 0.38mm (double-sided tape thickness) + 1.70mm (print plate thickness) = 2.08mm. In the case of the combined pressure of the old machine, the kraft cardboard is placed at both ends of the nip, and the distance between the anilox roller and the plate roller and the plate roller and the embossing roller is manually adjusted to pull the kraft cardboard at both ends. The same resistance as the standard. The pitch at this time is the ideal pressure value in the printing, but there is a slight difference with the printing pressure used in the actual production, requiring the operator to fine-tune in normal production. The introduction of the company's Gallas flexo press has changed the design of this series of cumbersome steps, which uses a dedicated pressure positioning hole, the use of pressure positioning positioning positioning holes, more precisely to ensure that between the 3 rollers Printing pressure, but this positioning pressure also needs to be fine-tuned in actual production.
Before we start production, we first perform pressure positioning 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 transmission surface). When the flexographic printing press is running at a slow speed, starting from the printing unit of the first color group to start pressuring, firstly observe whether the ink transfer roller has uniform ink transfer to the anilox roller, and then observe whether the ink transfer by the anilox roller to the plate roll printing plane is Good, and then gradually increase the pressure between the plate roller and the embossing roller until the graphics are printed on the composite sheet (pay attention to maintain the synchronization of the operation surface and the transmission surface, ensure that the two ends simultaneously and evenly increase the pressure) . Check whether the dots printed on the sheet are clear, whether the pattern letters are complete, whether there are problems such as whitening and hair dripping in the field, and for these problems, the pressure between the plate roller and the embossing roller is finely adjusted.
Flexo printing is a light pressure printing process, and its printing pressure is far less than offset and gravure printing pressure. Usually, the flexographic printing pressure is set to be small, but when the hose is printed, the printing pressure is slightly increased because the printing material is a composite sheet. Taking the field version as an example, we adjusted the printing pressure to a vaguely visible pressure frame at the edge of the field. This can prevent the printed sheet from leaking due to the uneven thickness in the unit area.Requirements for printing equipment and consumables
1. Requirements for flexo printing machine
Due to the use of high-cost materials such as composite sheets as substrates, the performance of flexible printing equipment is higher than that of ordinary flexographic printing. The printing equipment must be equipped with a corona treatment device and the printing unit must be installed. Full UV curing system requires equipment with precise tension control system and overall stability of the whole machine. The printing quality is controlled easily, the printing speed is fast, and the product variety has high flexibility in replacement. According to the author's understanding, although domestic manufacturers such as Ziguang, Heiniu, Beiren Fuji, Sunray Sun, Taihang, etc., manufacture narrow-format flexographic printing presses, they still rely mainly on imported equipment.
2. The requirements of the ink
Flexographic printing is a type of letterpress printing. Although it has a history of nearly one hundred years, the popularity of UV inks in domestic flexographic printing is only a few short years. Compared with water-based inks and solvent-based inks, UV inks have a high viscosity and poor leveling in the screen printing hoses, resulting in poor ink distribution on the anilox roll. The anilox roll and the printing plate roll need to be enlarged during operation. Between the pressure to express the level effect of the print. However, such operations will often cause problems with paste plate, printing plate resistance to printing force, and insufficient print color saturation. At present, foreign countries have developed water-based UV inks, which greatly improved the above situation, but the price is relatively expensive. When used, it often causes waste due to improper operation. From the perspective of economic efficiency, employees are required to have a strong sense of responsibility and pay attention to daily savings.
3. Requirements for printing materials
Printing materials accounted for the largest proportion of hose printing costs. However, in the printing process, many waste products are often caused by instability of the quality of the sheet, such as uneven tension at both ends of the composite sheet, crumpling on the surface, non-uniform thickness per unit area, and internal friction coefficient. Problems such as large changes are all factors that cause the decline in the yield. Hose printing has very high requirements on the printability of composite sheets. We hope that domestic manufacturers of composite sheets can further improve their overall quality, stabilize their printability, allow printing companies to better control the printing quality of hoses, and save products. Cost to achieve a win-win situation for suppliers and users.
Existing problems and solutions
Since the outer packaging of the hose is offset, many designers will copy the offset proof to the printing of the hose. It is hoped that different printing methods can achieve the same effect. This will never achieve satisfactory results. When designing artwork, designers should consider using large blocks or lines as much as possible, and use spot colors to give full play to the characteristics of the bright, bold, and highly saturated colors of the flexo printing. The color and color are preferred to be more white and missing. Set to minimize overprinting errors in flexographic printing.
We look forward to the printing industry developing more flexible printing professionals
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