Reasonable control of corrugated flexographic printing pressure (on)

Flexo printing has made great progress in recent years, especially in packaging and printing, showing its unique advantages. In corrugated board printing, although there are offset printing, screen printing, etc., but due to flexographic printing plate is a flexible plastic material, it has the advantage of other printing methods can not be compared, according to statistics, foreign in corrugated cardboard In printing, flexo printing accounted for more than 95% of the market share. In China, more than 70% of corrugated board use flexographic printing.

However, it is also due to the flexibility of the flexographic printing plate material is a flexible plastic material, making it a very difficult to avoid the defects, which is easy to print the dots and expansion of text paste, etc., causing the main failure One of the factors is improper control of printing pressure. In printing, if the pressure is too heavy, it will cause network expansion and text expansion and paste, 30% to 40% outlets have hollow spots, and there will be serious hard-mouth phenomenon when printing; The pressure of the printing plate and the anilox roller is too large, the paper surface (especially the fine text) is blurred, the edge of the printed image is not clear, in addition, in the multi-color printing, if the former color printing pressure is too large and the color ink If the viscosity is too high and the drying is too slow, the overprinting effect is not good. However, if the printing pressure is insufficient, since the surface of the corrugated cardboard is not as smooth and flat as other papers, and has unevenness, the ink will have a bad transfer effect. . Therefore, in the corrugated flexo printing, the reasonable control of the pressure is an important aspect affecting the printing quality.

We know that in the flexo printing process, there are mainly three pressure points (actually three embossing belts, namely the ink fountain roller and anilox roller, anilox roller and plate cylinder, plate cylinder and impression cylinder), These three pressure points are all very important in terms of operation technology. In the printing process, great care must be taken. It is not possible to rely solely on experience, but should be controlled under controlled conditions. It is impossible to make the three pressure points out of control, even under the wrong operating conditions. If so, the quality of the printed matter will not be discussed.

So, how to correctly control the printing status of these three pressure points? Generally speaking, the following three aspects can be considered.

Contact pressure between ink fountain roller and anilox roller

Relative to the pressure of the anilox roller and the plate cylinder, the plate cylinder and the impression cylinder, since the role of the ink fountain roller is to squeeze out the ink on the surface of the anilox roller, the pressure may be slightly larger, and the control method is: With a 0.10mm thick gauge, stuff it in at the point of contact. Need to plug in a few more points, and it should be stuffed in tight conditions. Kraft paper can also be cut into 60 ~ 80mm strips, placed on the contact point, according to the length of the anilox roll, long and evenly put 4 to 6, short put 3. Adjusting the ink fountain roller to the kraft paper can be pulled under relatively tight conditions. If it is easy to pull it up or it is easy to insert the thick gauge into it, there is a gap between the two, which is abnormal. The ink fountain roller and the anilox roller must work under contact. In some companies, the number of anilox rollers used in printing is high, and the amount of ink is insufficient when printing color blocks and large letters. Therefore, the operator often increases the ink supply by increasing the gap between the ink fountain roller and the anilox roller. . However, if there is a gap between the two, the effect of quantitative ink supply by the anilox roller is lost. Therefore, the use of anilox roller must have a "quantitative" concept of ink supply, can not use the gap to adjust the amount of ink, there is a gap in the control of the ink is not good, the actual print incontestably, there will be corduroy-like streak; cable version will produce Chromatic aberration. If the ink fountain roller and the anilox roller are under normal contact, the ink on the roller wall of the anilox roller still cannot be squeezed out, which means the viscosity of the ink is too high. The viscosity of the ink should be adjusted. Between the ink roller and the anilox roller, The pressure is ineffective.

Contact pressure between anilox roller and plate cylinder

In general, the contact pressure is light, that is, the anilox roller is in contact with the plate, and the plate is deformed to meet the light pressure requirement. Excessive pressure not only affects the service life of the printing plate, but also it is very unfavorable for improving the printing quality. Due to the excessive pressure, the anilox roller touches the side of the printing plate at the time of printing, and the printing plate is compressed after the printing plate is deformed. As a result, the front end of the printing pattern and the text appears hard and the burrs are serious. At present, quality issues in this area can be observed on many prints. When printing the cable version, the pressure is too large to produce a paste, so the contact pressure must be light. Users in the actual operation but also depending on the actual situation and flexible control, if the machine is poor accuracy, can increase the pressure; the other hand, can reduce the pressure. For example, the plate thickness is 3.94mm, the lining thickness is 3.05mm, the double-sided adhesive is 0.11mm, the hanging polyester is 0.10mm, and the total thickness is 7.20mm. According to the requirement of lighter pressure, it is better that the two rollers are in tangential contact, that is, the distance between the anilox roller and the plate cylinder is kept at 7.20mm. However, due to the fact that the anilox roller, the plate, and the roller both have positional errors, the phase It is impossible to cut the state. After testing the anilox roll misalignment and jump force 0.02 ~ 0.04mm, plate cylinder jump force 0.01 ~ 0.02mm, plate thickness error is ± 0.02mm, the maximum error is 0,08mm, plus 0.02mm Printing pressure, the total is 0.1mm. As long as the anilox roller is fully accessible to the printing plate, the ink in the anilox roller can be transferred to the printing plate, and the requirements for ink transfer are achieved. Therefore, with a feeler gauge and thickness gauge of 6 mm, the distance between the anilox roller and the plate cylinder is controlled to be 7.10 mm, which can meet the requirement of light pressure. In the normal printing process, the linear velocity of the surface of the printing plate cylinder should be less than the linear velocity of the anilox roller surface, and the ink transfer effect is good. As the pressure between the two increases, the amount of ink transfer is small.

(to be continued)