Parameter control of printing hose for flexographi

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Parameter control on the printing hose of flexographic printing machine

the process of printing hose of unit type flexographic printing machine is basically the same as that of printing coated paper, offset paper and self-adhesive paper, but the total thickness is 300 due to the thick composite sheet μ M, the quantity is large, and the inner and outer surfaces are PE films, so the control of printing tension and printing pressure is particularly critical compared with general paper, self-adhesive, cardboard, etc

1. Control of printing tension

the tension system of the unit flexographic press is divided into three parts: unwinding part, printing part and winding part. For example, the gelas em410 unit flexographic printing machine is equipped with a set of swing roll unwinding tension control system, two sets of printing tension control systems and one set of winding tension control system to ensure the stability of tension. The function of the tension control system of the unwinding part (also known as the pre leveling tension system) is mainly to pre straighten and tighten the composite sheet, so as to improve the phenomenon of uneven tightness, surface wrinkling, unevenness and "Lotus edge" on both sides of the composite sheet in the manufacturing process

the tension control system of the printing part refers to the rubber pressure roller that passes through the constant tension value during the printing process from the second leveling tension system to the completion of printing. These two groups of tension control devices are collectively referred to as the printing tension control system. Their function is to balance the printing pressure of each plate roller on the composite sheet during the printing process and the tension and resistance between the composite sheet and the paper feeding roller, UV cooling roller and other rollers, and to keep the tension constant during the printing process. The printing tension shall depend on the bending stiffness of the composite sheet. The higher the bending stiffness of the composite sheet, the greater the tension value; On the contrary, the tension of the composite sheet should be smaller

in actual production, since the surface friction coefficient of the composite sheet is relatively small and there is "aluminum foil" as the skeleton in the middle, we should set the tension as large as possible, but also ensure that the composite sheet will not be stretched and deformed after printing. The width is 400mm and the total thickness is 275 μ Taking the composite sheet of m as an example, the printing tension is usually set to about 320n at the front end and 360n at the rear end to ensure accurate lofting. The suitable point for printing tension control is that all "chromatic points" in multi-color printing are accurate and there is no "movement" before and after. In addition, it should be noted that the printing speed will also affect the stability of printing. Our approach is to first set the printing tension within the common range of the sheet specification used, then basically register the printing plates of various color groups, gradually increase the speed to the normal production speed, and then make appropriate fine adjustments to the printing tension according to the "moving" trend of "color registration point"

the tension system of the winding part refers to the constant winding force and torque of the rear winding during the roll to roll production of the flexographic press. Its function is to roll the printed materials neatly and keep the rolling force of the whole roll of sheet from the inside of the roll core to the outside of the roll core consistent. When printing composite sheets, in order to make both sides of the toothpaste sheets that have been cut into small rolls smoother and the roll force and torque of each roll more stable, we set relatively fixed roll force and torque values according to the data obtained in the actual operation. The set value is: coil force 60%, torque 50%, which ensures the stability of the quality of each coil of sheet during pipe manufacturing

the accuracy of tension control determines the overprint quality of printing and the overall quality of finished products when printing tube sheets with the characteristics of simple soft operation by the unit type flexographic printing machine. There are many factors that determine the tension value, including the change of the production environment of each batch of composite sheets, different sheet manufacturers, different equipment for manufacturing sheets, and different composite sheet widths and printing equipment during printing

2. Control of printing pressure

the adjustment of printing pressure is another key factor to ensure product quality. Before each printing, the pressure between the embossing roller, plate roller and embossing roller must be readjusted. The adjustment of printing pressure mainly includes two aspects: one is the pressure between the wrinkle roller and the plate roller; The second is the pressure between the plate roller and the impression roller

first, adjust the spacing between the 3 rollers. During printing (when the unit is pressed), the spacing between the wrinkle roller and the plate roller is basically the same as that between the plate roller and the impression roller. Namely: 0.38mm (thickness of double-sided adhesive tape) +1.70mm (thickness of printing plate) =2.08mm. When the old unit is pressed together, place the kraft paperboard at both ends of the roll gap, and manually adjust the spacing between the embossing roll and the printing plate roll, the printing screw plate roll and the embossing roll, taking the same resistance of pulling the kraft paperboard at both ends as the standard. At this time, the spacing is the ideal pressure value in printing, but it is slightly different from the printing pressure used in actual production, so the operator needs to make fine adjustment in normal production

before production, pressure positioning shall be carried out for each color deck, and the pressure between the plate roller and the impression roller shall be relaxed (pay attention to the synchronization of the operating surface and the driving surface). When the flexographic printer is running at a slow speed, start pressing from the first color group printing unit, first observe whether the ink transfer between the inking roller and the embossing roller is uniform, and then observe whether the ink transfer between the embossing roller and the printing plate roller is good, and then gradually increase the pressure between the printing plate roller and the embossing roller until pictures and texts are printed on the composite sheet (pay attention to keep the synchronization between the operating surface and the driving surface, and ensure that the pressure is increased at both ends at the same time and uniformly). Check whether the printed points on the sheet are clear, whether the patterns and words are complete, and whether there are problems such as whiteness and emptiness in the field. In view of these problems, slightly adjust the pressure between the plate roller and the embossing roller

flexographic printing is a light pressure printing process, and its printing pressure is far less than that of offset printing and gravure printing. When setting the flexographic printing pressure, it is mainly required to be small. However, during hose printing, the printing pressure should be increased slightly because the substrate is a composite sheet. Taking the field version as an example, adjust the printing pressure so that a pressure frame appears at the edge of the field, so as to avoid the leakage of printed pictures and texts caused by the uneven thickness of the composite sheet per unit area

source: HC printing industry channel

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