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——Introduce the technical parameters and selection principles of anilox from a practical perspective
Today's flexographic printing is in a leading position in the development of the printing industry in the world today.
The new progress of the anilox roller technology has become a decisive factor to promote the rapid development of the flexographic process, especially because of the emergence of laser engraved anilox rollers, making the flexographic industrial production almost the same as the gravure and offset printing industrial production The anilox roller on the surface layer improves the transfer performance of the ink layer and improves the quality of the ink layer, which is the result of adopting new technologies.
The anilox roller must be able to deliver ink to the printing plate quantitatively according to predetermined standards, and the ink layer should be as thin and uniform as possible. The stability of the ink layer will restrict the printing quality of the image. In the transfer process, the thinner the ink layer, the easier it is to adjust the printing, and the smaller the dot expansion rate; the uniformity of the ink layer helps to improve the stability of the ink transfer amount.
1. Uniformity of the ink layer
Why can the laser engraved anilox roll be used to obtain an excellent uniform ink layer? The main reason is that it can reduce the gap between the mesh holes. In the traditional mechanical engraving method, the metal movement method is used. In order to form a net hole, in laser engraving, the ceramic beam is vaporized by a laser beam to form a net hole. It is precisely because of this fundamental difference that the laser engraved anilox roller brings the advantage of strict control. First, it can significantly reduce the gap between the holes, that is, the thickness of the mesh wall, and secondly, it can carve a higher density of mesh holes at the same true line distance. Based on the above two factors, the ink layer transferred by such a net hole has higher uniformity.
How does the laser engraved anilox roller make the transferred ink layer slim? The thickness of the ink layer depends on the volume of the mesh, such as a 300 line 5.50BCM volume anilox roller and an 800 line 2.00BCM Compared with the volume of the anilox roller, it is obvious that the 800-line anilox roller has a smaller capacity, so the ink layer it transmits is thinner. When using laser engraving, it can obtain a mesh with a smaller capacity than mechanical engraving, thereby forming The advantage of thinner ink layer. The thinner the ink layer, the better it can control the printing effect of high-gloss dots.
Second, the carving specifications
There are three specifications for laser engraving: 30 ° hexagon, 45 ° diamond and 60 ° hexagon. After polishing the surface of the ceramic anilox roller, a round pit with a parabolic pit is etched on the ceramic surface by a laser beam with rounded corners. The diameter of the laser beam can be based on the number of lines of the mesh or the size of the hole No matter how it is adjusted, the beam will always remain round.
The geometric shape of the net pattern depends on the arrangement position of each net hole, for example, the diamond-shaped pattern is arranged by four net holes surrounding a center hole, and the hexagonal pattern is surrounded by six net holes And arranged. Where the standard engraving pattern will form a regular diamond or regular hexagon. Once the engraving mistakes, the gap between the net holes will increase, and the geometry of the net pattern will be irregular.
The hexagonal mesh is better than the diamond shape for two reasons. First, there is a large mesh wall area around the diamond-shaped mesh hole. Obviously the ink layer it transmits is not even. Secondly, in order to achieve the same capacity, the diamond-shaped net hole has to be carved deeper. For this, we can also learn from the nature. The honeycomb of a bee is composed of a wide hole of a hexahedron. Know that only this arrangement can store more bees. Therefore, the hexagon is the most efficient geometric shape, which maximizes the use of space.
According to mathematical calculations, within the same area, the hexagonal area occupies 15% more space than the diamond shape. Therefore, a hexagonal mesh cell with 15% more space on the anilox roller means that it can reduce the depth of the cavity by 15% without affecting its original capacity. Obviously, the depth of the hexagonal mesh cell is comparable to the diamond shape Carved lighter.
3. The ink release and cleaning properties of the net hole
What if the anilox roller has been able to transfer the ink layer to be thin and even, but the ink release speed is not fast enough, especially in high-speed printing, or the bottom of the mesh can not be cleaned? Obviously this is due to The depth of the mesh cavity is too large, and the problem of insufficient ink transfer in the future is caused by the difficulty of ink cleaning. Of course, it is not without problems if the net hole is too shallow, and if it is too shallow, the desired effect cannot be printed. For example, the depth of the cell is 4 micrometers, and the error is 1 micrometer, which means that the error of capacity and depth reaches 25%. For a printer with a quality concept, this deviation is unacceptable. And when the depth of the cell is too shallow, it will also bring the disadvantage that the ink is easy to dry up. Therefore, the optimal engraving depth should be selected for the laser engraved anilox roller, and it should never be extreme.
How to determine the optimal cell depth? The depth of the cell must also consider its relationship with the opening size of the cell. If we compare the soup bowl and the test tube, although they have the same capacity, when the liquid in the container is poured out, the bowl is faster than the test tube. This is not only because the depth of the bowl is smaller, it is also The width of the opening is large. The situation on the anilox roll is similar.
According to further research, the optimal depth / opening width ratio d / o of the cell should be between 23 and 33%. It means that a cell with an opening width of 100 microns should have a depth between 23 and 33 microns. The three-dimensional geometric shape formed according to this proportional relationship can make the net cavity have good ink release and cleaning properties. The negative area on the engraving conversion table shows the relationship between depth and opening. For example: when using 400 lines and a capacity of 2.6BCM, the d / o ratio on the conversion table is 18%. If the number of mesh lines is changed to 550 lines, then its d / o ratio becomes very pure and the best results are obtained. On the contrary, if the cell with a 4.5BCM capacity of 550 lines and a d / o ratio of 40% in the table is changed to 400 lines, then it will maintain the optimal d / o ratio and obtain the most ideal use effect.
Fourth, the traditional mesh line number
In the previous introduction, we emphasized the cell volume, the best ink layer quality and the best cell geometry on the anilox roller, while in the past, we only emphasized the number of screen lines. Figure 4 shows a schematic diagram of three laser-engraved anilox roll cells. They all have the same mesh line number, capacity and configuration, but their characteristics are different. The top one is shallower in depth and the wall is thinner, so its ink release performance is good, easy to clean, and the ink layer formed is also very uniform; the bottom one is the deepest, and the wall is thick, Therefore, the cleaning performance is poor, and the ink layer formed is not uniform. These differences result in differences in print quality.
On the laser engraved anilox roller, the quality of the ceramic itself is one of the key factors affecting the quality of the anilox roller. The ceramic surface should be hard and smooth, the porosity should be as small as possible, the hardness of the ceramic will affect the printing resistance, and the flatness of the surface has important significance before or after engraving. Before engraving, it will affect the consistency of the engraving of the mesh on the surface of the roller, and after engraving, it will affect the consistency of the thickness of the ink layer. effect.
Five, turtle pattern
On the laser engraved anilox roller, another important aspect to be considered is the relationship between the angle of the anilox and the screen angle of the printing plate, which will be related to the formation of moire on the printed matter. There are three kinds of angles available for laser engraving on the anilox roller: 30 °, 45 °, and 60 °. The advantage of the 30 ° and 60 ° hexagonal mesh pattern is that no matter what angle the printing plate adopts, the risk of moire can be avoided. The reason for this is that the arrangement of the hexagonal anilox with three axes corresponds to the arrangement of the two axes on the printing plate, while on the anilox roller of 45 °, the two axes correspond to the printing plate.
The selection of the number of anilox lines depends on the printing method and the quality of the ink, because they determine the capacity of the mesh holes and the corresponding number of mesh lines. For example, in order to facilitate the control of highlight dots on the screen printing, the ink layer needs to be thinner, which means that the capacity of the mesh hole should be reduced. For this reason, a thinner number of mesh lines must be selected. For solid printing, a thicker mesh should be used to obtain more ink capacity, thereby forming a thick ink layer. On some specific prints, the effect of high-quality ink is better than the effect of ink volume, and it also affects the selection of mesh lines.
In the United States, when printing a screen version on a film, the capacity of the mesh hole is generally controlled in the range of 1.0 to 3.3 BCM / VPSI, and then converted into the best engraving parameters based on this. If the aforementioned d / o ratio is used, the number of mesh lines should be selected between 1200 and 400LPI.
In color screen printing, the optimal number of anilox rollers should be selected according to factors such as the strength of the ink, the thickness of the screen line of the printing plate, and the percentage (size) of the dots to be copied. For example, an 800LIP anilox roller, which can adapt to the reproduction requirements of high-gloss dots on the printing plate of 85 ~ 150LPI, while the traditional 4 times roller / plate mesh ratio is only suitable for medium-adjusted prints and not For copying highlights and small outlets.
Six, cleaning and maintenance
When it comes to the anilox roller, it is all related to the difficulty of cleaning and maintenance. Whether the laser anilox roller can always maintain a constant ink release amount is related to the reproduction effect of fine images. The laser engraved anilox roller itself is a fairly expensive investment. Once the anilox is damaged or the mesh hole is blocked, it is impossible to print good prints, and it is not a small loss to update.
Cleaning is generally concerned with what means to effectively clean the anilox roller, and preventing the ink from drying on the anilox surface is the best way to maintain the anilox roller. The key to cleaning is to thoroughly remove the pigment particles and resin from the mesh in time before the ink dries. Once the ink dries in the mesh, the net capacity of the mesh will be reduced. There are two methods commonly used to clean dry ink, solvent burning method and ultrasonic method. The former is the most commonly used traditional method. This method works well, but it is troublesome. You must first remove the anilox roller from the machine and burn it immediately or burn it immediately when the ink no longer flows. In many packaging and printing factories, it is customary to use wipes or other wiping materials to clean. In this way, only the surface of the mesh wall can be cleaned, but the pits are still not in contact. When cleaning by combustion method, the anilox roller should be continuously rotated to facilitate the complete burning of ink particles. Stainless steel brushes are used to clean the ceramic surface, and copper brushes are used to clean the surface of the chrome anilox roller. The two cannot be mixed, otherwise, the stainless steel brush will damage the chromium layer, and the copper brush will sink the copper scraps on the ceramic surface, or even mixed into the ink. Some factories use lye to clean the dried ink in the pits. Although this non-standard method is easy to popularize, it is not recommended because it erodes the roller body or further damages the surface.
Ultrasonic cleaning of the mesh roller is very effective, but it should be checked frequently during cleaning to avoid excessive impact and damage to the ceramic surface. The ultrasonic cleaning time must be strictly controlled. The ultrasonic cleaning time of the fine anilox roller should be between 2 and 5 minutes. The cleaning time of the coarse anilox roller can be slightly extended. Another thing to note is that the operation must follow the ultrasonic The operation rules of the equipment manufacturer, and establish regular monitoring measures.
The maintenance work of the anilox roll also includes storage, use and periodic identification.
The using factory should establish the corresponding cleaning and maintenance rules and regulations according to the following guidelines:
1. Use a suitable brush to remove the wet ink in time.
2. Swipe to swipe when brushing.
3. The cleaning and operation shall be carried out by a special person.
4. Use a protective cover when storing.
5. The storage location of the anilox roller should be selected carefully.
6. Regular self-assessment and inventory statistics of the anilox roll.
7. Regularly educate and train operators.
With the continuous promotion of the flexo process, if you want to compete with the gravure and offset printing processes, you must work closely with ink factories, plate manufacturers and pre-press system suppliers to meet the needs of printing factories. Only in this way can you obtain your own Greater development.
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