High-tech and Operational Points in Flexo Printing (2)

High-tech in anilox roller cleaning

The anilox roller is a very precise mechanical part. Many uniformly shaped cells on the surface are evenly distributed. It plays a role of ink storage, ink distribution and quantitative ink transfer in printing. Since the cells on the anilox roller are very fine and delicate, the amount of ink filled in the ink cavity can be transferred to the plate only about 70% to 80%, and the remaining ink remains in the cell site. In the process of ink transfer, due to the dryness of the remaining ink, impurities in the ink, and other reasons, it will block the network and make the ink transfer poor. This not only affects the printing quality, but also increases the number of anilox rollers that are blocked by the mesh for a long time. The loss of large ink shortens the life of the anilox roll. Therefore, the anilox roller should pay great attention to maintenance and cleaning during use. In the anilox roller cleaning, there are currently four commonly used methods: chemical cleaning methods (such as chemical solvent brushing method, chemical solution immersion method); physical cleaning methods (such as medium blowing cleaning method; low pressure spray cleaning method; dry ice cleaning method; Plastic beads spray cleaning method); ultrasonic cleaning method; laser cleaning method. Laser cleaning is a high-tech method introduced in recent years. Laser cleaning technology refers to the use of a special lens to irradiate a high-energy laser beam on the surface of the anilox roller. Without damaging the wall of the anilox roller, the ink, adhesive, wax, silicone, and steel shavings remaining on the surface and the cell site remain. The residue vaporizes or evaporates instantly to form a solid powder to achieve cleansing. The laser cleaning method can clean 1200/inch or more anilox rollers without damaging the cell walls. It can completely remove the dry ink, adhesives, plates and scraper steel shavings. Compared with the traditional cleaning process, laser cleaning technology has the following characteristics:

(1) It is a "dry" cleaning, does not require cleaning fluid or other chemical solutions, so there is no environmental pollution caused by chemical cleaning, and the degree of cleanliness is ideal;

(2) The scope of removal of dirt and the range of applicable substrates are very broad;

(3) Laser cleaning is a kind of non-contact processing, which can easily achieve long-distance operation, such as transmission through optical fiber, cleaning parts that are not easily reached by some methods. In addition, the short-distance operation of the traditional cleaning method can avoid the mechanical force on the surface of the cleaning object and easily damage the surface of the object.

(4) By adjusting the laser process parameters, different types of contaminants on the surface of the material can be effectively removed without damaging the surface of the substrate, so that the surface is clean as new. In addition, laser cleaning can also be easily automated, in line with smart printing;

(5) The laser cleaning equipment can be used for a long period of time. Generally, it only requires electricity and maintenance costs, and the operating cost for long-term use is relatively low;

(6) Laser cleaning technology is a "green" cleaning process that does not substantially pollute the environment. Laser cleaning technology started in the mid-1980s, but it was not until the early 1990s that it actually entered industrial production. In addition to the cleaning of anilox rollers, laser cleaning technology has been used in many fields such as various industries, electronics, and cultural relics. The cleaning technology has been widely used and has gradually replaced the traditional cleaning methods. The laser cleaning technology of anilox roller has been widely used in the United States, and it will promote the development of flexographic printing to high quality and wide range of applications.

Whether it is a ceramic or metal anilox roller, it is a very delicate flexographic press core components. In order to ensure the quality of printing, care must be taken in use to avoid bumping or damage. When installing or removing the anilox roller, be sure to press it evenly and gently, and install the anilox roller securely in the support slot or remove it from the printing press. During the printing process, the pressure between the doctor blade and the anilox roller and the roller and the anilox roller should be as small as possible to reduce the wear on the anilox roller. After shutting down, the anilox roller and the rubber roller must be separated from each other. Otherwise, the anilox roller will be bent and deformed due to the long-term stress in one direction, resulting in uneven ink transfer from the anilox roller. In addition, after the end of each printing, the anilox roller must be cleaned in a timely manner to prevent the pigment particles in the ink from drying in the ink hole, causing blockage of the ink holes and affecting the printing production. In the process of storage, the anilox roller should be protected to prevent the surface from being damaged by foreign matter. In addition, it should be placed in a special storage tank to prevent the surface from being stained with oil, dust or dust.

In addition, the anilox roller should pay attention to some problems during use. Taking laser-engraved ceramic anilox roller as an example, it is made of laser-engraved, high-temperature, abrasion-resistant coating material in aviation and aerospace, and it is formed by laser engraving at a certain density, depth, and a certain angle and shape. This anilox roller is characterized by its high cost and wear resistance. If it is used properly, its life can be as long as several years; if it is used improperly, not only the service life will be shortened, but also the anilox roller will be scrapped. In the process of use, the position of an anilox roll on the printing press depends on the specific print, different prints, and the position of the anilox roll is different. Therefore, the wire roll is often replaced during printing. At present, narrow-width machines use mostly solid steel anilox rollers, which are very heavy. When mounting the anilox roller, care must be taken to avoid touching the surface of the anilox roller against other metal objects. Because the ceramic coating is very thin, permanent damage can be easily caused by a collision. During the printing and cleaning process, the ink should be prevented from drying on the anilox roller. The special detergent recommended by the water-based ink manufacturer should be used. The stainless steel brush should be used for scrubbing. The cleaning must be clean and thorough. And develop a habit of using high-power magnifying glass to observe the anilox roller nets. Once ink is deposited on the bottom of the net and gradually increase, it should be promptly cleaned. If the above method does not work, ultrasonic or sandblasting treatment can be used, but it must be done under the guidance of the anilox roller manufacturer. Under normal use and maintenance conditions, we do not have to worry about the problem of anilox roller wear. The main component of the ink-transfer system which is subject to wear is mainly the squeegee blade. Compared to this, the wear of the anilox roller ceramic coating can be described as negligible. When the anilox roller slightly wears, the ink layer becomes thinner. Anilox roller should pay attention to the following problems in use.

(1) The circumferential scratches appear on the surface of the anilox roll. The presence of circumferential scratches on the surface of the anilox roller indicates that adhesion of the cell site has occurred and the network wall has been worn or damaged. This is mainly due to the fact that hard particles are caught between the doctor blade and the anilox roller. With the naked eye, it can be seen that the anilox roller has scratches on its circumference, and the typical performance on the printed matter is fine ink lines along the direction of the web. Of course, if you use a microscope, you can surely see the scratches on the anilox roller, but in fact, you can see the scratch with the naked eye even without using a microscope.

(2) The surface of the anilox roll is damaged by embedded metal shavings. Metal scratches generally occur when the anilox roller is loaded and unloaded on a flexo press. The friction between the anilox roller and the ink fountain, squeegee blade holder, or other metal parts may cause metal chips to be embedded in the mesh, which is reflected in the printed matter. Highlights (ie, some areas on the print have not achieved the desired ink density). It may be difficult to see the metal chips embedded in the cells in the naked eye, but it can be clearly seen under a magnifying glass.

(3) Damage to the wall. The effect of excessive mechanical cleaning on the surface of the anilox roll is well known. There are many factors that cause the erosion of the wall. In the ultrasonic cleaning device, the cleaning time is too long or the cleaning frequency is too large may cause the network wall to be destroyed. The old engraving machine may make the carved out of the cells uneven and irregular, resulting in uneven erosion of the network wall. Once the web wall is eroded, the ink of several webs will gather together, and large ink packs will appear on the prints. On the surface of the superabrasive anilox roll, a contrastive local shadow formed between the denuded area and the surrounding polished cell area can be seen. In the media impact cleaning device, excessive or repeated cleaning of the anilox roller will cause cumulative damage on the surface of the roller, and some fine holes on the surface of the roller can be seen, and the image on the printed article will be blurred. Observed under a magnifying glass, it can be seen that the mesh wall has been slightly damaged, and the inks of several network points are lumped together.

(4) Freckle patterns appear on the surface of the anilox roll. Due to the different cleaning strengths of the anilox roller during ultrasonic cleaning, a pattern of spotted spots may appear on the surface of the anilox roller, that is, the hot spots formed by the acoustic waves evoked by the cleaning liquid on the surfaces of the cells. This situation will become more and more serious with increasing wear or gradual saturation of the cleaning fluid, resulting in uneven cleaning of the surface of the anilox roller, resulting in different levels of light reflectance between the residual ink at the dirty spot and the clean spot. Forms a plaque pattern. At this time, the pattern of stenosis presented on the surface of the anilox roller can be seen without high-end detection instruments. Once the naked eye can be seen on the surface of the anilox roller spot, in print will certainly reflect.

(5) Network hole wear. With chrome-plated anilox rollers, wear is a concern. Because the anilox roller base copper is soft, after chrome plating, it is still easy to be worn, and the abrasion is still faster. A chrome plating layer is damaged, which will make the opening of the cell hole smaller, and the network wall will become wider, resulting in the ability to transfer ink to the network Sharply decreased, that is, the volume of the ink roll hole of the anilox roll became smaller. Since the ceramic material is hard, dense and hard material, the hardness rate is second only to diamond, so the service life of the ceramic anilox roller is 2 to 5 times more than the chrome roller (in normal use, and it is carefully protected, stored, cleaned and managed ). In fact, most ceramic anilox rolls that need cleaning have suffered other damage long before the walls have been abraded.

In addition, in flexo printing quality control, many flexo presses now have advanced intelligent management systems. For example, satellite type flexographic printing presses use an advanced modular automatic operating system that can preselect menus to centrally control the operation of each unit to ensure accurate motion and horizontal registration of the printing cylinders and anilox rolls of various color groups. Electronic synchronous adjustment and computer-controlled fast-forward system, through the step motor speed measurement, to ensure a highly precise set of printing pressure, printing length, plate and printing material thickness and other parameters. Ensure that the equipment does not produce waste when the register setting is performed in the stopped state, and the printing unit and the anilox roller are coordinated. In terms of ink supply and cleaning, it is used to quantitatively supply ink to printing components and automatically cleans the anilox roller, cavity type scraping system, ink pump and ink tube. The cleaning sequence is controlled by a computer. Increased efficiency and quality.