Common faults and troubleshooting methods for flexographic printing
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First, the problem of ink stick
In flexographic printing, the most common failure of a geared (non-shaftless) press is the ink bar, which is the presence of a trail of ink in the axial direction of the print. Most of the ink bars are caused by mechanical reasons. In the flexographic printing, the ink stick can be divided into two types, one is a regular axially distributed comb, and the interval is one pitch (3.175 mm), and the other is axially distributed but irregular. One or several, the interval is not regular, it may be a very thick one or a few thin ones; or one or a half of the body. The first type of ink bar is caused by the transmission gear and can be solved by replacing the gear or replacing the color group (color sequence). The second type of ink bar is mainly caused by the feeler gauge and improper pressure regulation. Everyone knows that the adjustment of the flexographic pressure is the key to ensuring the quality of the printing. It is not sloppy, and the adjustment of the three-roll pressure can not only achieve the parallelism between the three rollers, but also achieve the equal pressure between the three rollers. Especially for the first new product printing, the pressure between the three rolls must be adjusted.
The most important adjustment is two aspects: the pressure adjustment between the ceramic anilox roller and the plate cylinder; the adjustment of the pressure between the plate cylinder and the impression cylinder.
Firstly, the spacing between the three rolls should be adjusted. In the state of pressing, the spacing between the anilox roll and the plate roll, the spacing between the plate roll and the platen roll is the same: 0.38 + 1.70 = 2.08 mm , (0.38 mm is the thickness of the double-sided tape, and 1.70 mm is the thickness of the plate). Two standard feeler gauges with a thickness of 2.08 mm can be used to place the ends (no plates or unprinted) between the two rolls, then manually adjust the anilox roll with the plate roll, plate roll and embossing The distance between the rollers is such that the resistance of the standard feeler pulls at their respective ends is the same. The spacing at this time is the ideal pressure value in the printing, but it is slightly different from the actual printing pressure and requires the operator to adjust it during production.
In the actual production process, a serious three-roller imbalance may also cause the first type of ink stick. Therefore, in order to obtain good printing quality, the first thing is to make a feeler gauge and ensure the balance of the three rollers.
Second, overprint failure
There are many factors affecting the overprinting. At present, the tension control system of the unit type flexo printing machine is an operator setting the appropriate tension value according to the condition of the printing material, and ensuring that the registration line is not elegant when registering. The system uses closed-loop automatic control to keep the tension of the substrate constant from start to finish. The register control is divided into two directions, with the paper feed direction as a reference, and the horizontal registration is to laterally move the plate cylinder, and the handle on the plate roller shaft can be rotated clockwise or counterclockwise. Generally, in the initial stage of trial printing, firstly ensure the lateral registration, and then adjust the vertical registration. First, the first color is pressed until the last unit of printing, and the parking is coarsely adjusted. By rotating the plate cylinder, the registration error is within one tooth, and then the power is turned on, and the fine adjustment is manually performed by using the registration control button. The longitudinal registration system uses a high-speed stepping motor that drives the plate cylinder to rotate through the impression cylinder gear, which actually changes the longitudinal relative position between the plate cylinder and the substrate.
It can also be recorded in the process file after the waste simulation test, and at the same time ensure that the plate is accurate, do not stretch, eliminate the bubbles between the tape, and compact. In order to prevent the printing plate from being deformed, the plate can be peeled off together with the tape. In the overprinting, although our precision can reach 0.05mm, due to the deformation of the paper, the deformation of the printing plate and other factors, we need to further map after the registration of the registration line. The graphics must have a thorough understanding of the graphics. Part and minor parts, the main part is the key to Tudayi, so we can take care of the main part and try to register the main part on the basis of the acceptable part of the secondary part.
Third, the printed parts of the field appear ink, white spots, milky white ribbons, etc.
In flexographic printing, there are often many white spots on the solid parts of printed matter, and white spots still exist after rubbing. When encountering this situation: First, you should immediately check whether the static eliminator and the dust removal part are faulty and need to be treated. Secondly, check whether the ink (UV) viscosity is too high, and then measure the temperature of the ink. If the viscosity is large, the temperature is 30. Below °C, we should add some de-adhesive into it, while stirring more to enhance the fluidity of the ink. The printing suitability of the ink is good at a temperature of 33 ° C in production. In another case, the white points of the solid part are concentrated on the circumference of the fixed part, especially on both sides. At this time, it is necessary to readjust the pressure, and adjusting the balance of the three rolls can solve the problem. Then there is to increase the humidity of the workshop, which can reduce the dust in the air, and also reduce the chance of white spots.
When the ink filament in the circumferential direction appears on the printed product, it is first necessary to see if there is ink on the surface of the anilox roller after the ink is applied. If there is ink on the surface of the anilox roller, there may be a problem with the doctor blade (such as a gap). If there is any scraper, check the scraper. If the scraper is intact, check the viscosity of the ink. If the viscosity is high, add the adhesive.
A milky white ribbon appears on the field of the print. We use domestic UV inks and imported UV inks in our production. When using domestic inks, add some kinds of inks such as transparent white or cover white in ordinary four-color inks to form spot color inks, which will be printed on the products. The appearance of milky white ribbons is presumed to be caused by poor compatibility of various binders and solvents and free bodies. The best method is to let the manufacturers directly supply the matched spot color inks with good results. Or, after mixing at the time of production, add more stirring, or drive at high speed, or you can mix the ink two or three days in advance, which can effectively alleviate. When the ink is dispensed, it is not the same manufacturer's ink that can't be matched with the spot color without the experiment. Especially the domestic ink and the imported ink are used for blending. It is also a taboo in printing, and this will cause different depths and the like. And the ink will soon deteriorate.
Fourth, the failure of the die cutter
The die cutters in production mainly have two types of cut and full cut.
In semi-cutting die-cutting, if placed within the printing tension range, it will affect the registration of the nearest printing color set, so it should be placed outside the printing tension range. The adjustment of the pressure during the die-cutting process is very important, especially for the knife that is approaching the life of the tool. When increasing the speed, the pressure should be appropriately increased. When the paper is registered, the pressure should be slightly reduced to prevent the paper from breaking or being broken. paper. After the machine is shut down, do not hit or touch hard objects, and pay attention to cleaning gears, shoulder irons and bottom rollers.
In the full cutting, the knife is outside the printing tension range, so pay attention to sticking the elastic sponge to the knife. According to different workpieces, different types of medium and hard sponges can be selected, which can ensure the die cutting precision and normality of the finished product. Output. If the area of the die-cut finished product is large, attaching the entire sponge to the stencil will cause the die-cut product to be stuck with the rotation of the knife roll, so the sponge can be cut into strips and attached in the circumferential direction, but at the same time Also increase the number of static eliminator sets, especially near the knife roll.
V. Failure in blowing waste and collecting waste
In the production of self-adhesive glue, the use of wire die cutting, slitting, blowing waste, waste collection, rewinding is completed. The common fault in blowing waste is that there is a bad edge on the paper side, which makes it difficult to collect waste and blow waste. Therefore, when the paper is on the machine, carefully check whether there is a bad edge on the paper edge. If there is a bad edge, the paper should be removed. Also, when printing the full width, when you just take the paper or adjust the edge, pay special attention to the paper edge will hit the gear and smash slightly, or check the edge of each paper guide roller, mesh roller, rubber roller, whether there is a large rubber block, It will also cause damage to the edge of the paper. When blowing waste, it is preferable that the paper pull-down direction is perpendicular to the paper feed direction. The collection of waste, especially the non-adhesive type of waste, is thinner because of the thinner paper, and it is more difficult to collect waste. The most important thing to collect waste is typesetting. When formatting according to the direction of paper feeding, pay special attention to avoid sharp edge effect. If there is an acute angle on the printed product, the concave part can be placed on the front side and the convex part on the back side. Note that the spacing between the labels is related to the material and the speed of the production. The spacing between the two ends can be less than 3 to 4 mm. If the arrangement is most prone to breakpoints, that is, due to the arrangement of irregular labels, the sharp edge effect and the pulling force in the middle interval are increased sharply, and should be considered before typesetting. When the waste is collected, the waste roller and the platen roller sometimes make the waste roll into an elliptical shape, so that the speed of the waste at the high speed is unstable, which is easy to cause the waste to be broken, so the waste can be used in the low recess. The method of padding is used to correct.
The above five points are common faults in the production process, welcome to peer correction.