Talking about the technical parameters and selection principle of anilox roller from practical point of view
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The new development of anilox technology has become a decisive factor in the rapid development of the flexographic printing process, especially due to the emergence of laser engraved anilox rolls, making the flexographic printing industry almost in line with the gravure and offset printing industry, with ceramics sprayed. The surface anilox roller improves the transfer performance of the ink layer and improves the quality of the ink layer, which is the result of adopting new technology.
The anilox roller is capable of quantitatively delivering ink to the printing plate according to predetermined criteria, and the ink layer is as thin and uniform as possible. The stability of the ink layer will limit the print quality of the image. In the transfer process, the thinner the ink layer is, the easier it is to adjust the printing, and the smaller the enlargement rate of the dot is; the uniformity of the ink layer helps to increase the consistency of the ink transfer amount.
First, the uniformity of the ink layer
Why use a laser-engraved anilox roll to obtain an excellent uniform ink layer? The main reason is that it can reduce the gap between the cells. In the traditional mechanical engraving method, the metal movement method is used. To form a cell, in laser engraving, the ceramic is vaporized by a laser beam to form a cell. It is this fundamental difference that gives the laser-engraved anilox roll the advantage of tight control. First of all, it can significantly reduce the gap between the holes, that is, the thickness of the mesh wall, and secondly, it can emboss the higher density of the cells in the same true line distance. Based on the above two factors, the ink layer delivered by such a cell has a higher uniformity.
How does the laser-engraved anilox roll make the ink layer thin? The thickness of the ink layer depends on the volume of the cell, such as an anilox roll with a line of 3.50 BCM and a line of 800 lines of 2.00 BCM. Compared with the anilox rolls of volume, it is obvious that the 800-line anilox roll has a thinner ink layer because of its smaller capacity. When laser engraving is used, a cell having a smaller capacity than mechanical engraving can be obtained, thereby forming The advantage of a thinner ink layer. The thinner the ink layer, the more control the printing effect of high-gloss dots.
Second, the specifications of the sculpture
Laser engraving is available in three sizes: 30° hexagon, 45° diamond and 60° hexagon. After polishing the surface of the ceramic anilox roll, a rounded pit with a parabolic crater is etched on the ceramic surface by a laser beam with rounded corners. The diameter of the laser beam can be determined according to the number of lines or the size of the cell. Make adjustments, no matter how you adjust, the beam always stays round.
The geometry of the netting depends on the arrangement between the cells. For example, the diamond-shaped pattern is arranged by four cells surrounding the center, while the hexagonal pattern is composed of six cells. And arranged. The texture of the engraving specification will form a regular diamond shape or a regular hexagon. Once the engraving is wrong, the gap between the cells will increase and the geometry of the mesh will be irregular.
The hexagonal netting is better than the diamond shape for two reasons. First, there is a large wall area around the diamond-shaped cell. Obviously the ink layer it delivers is not uniform. Second, in order to achieve the same capacity, diamond-shaped cells have to be carved deeper. For this, we can learn from nature. The honeycomb of bees is made up of wide holes of hexahedron. The creatures rely on instinct. Know that only this arrangement can store more bee secrets. So hexagons are the most efficient geometry, making the most of space.
According to mathematical calculations, the hexagonal space occupied by the hexagonal area is 15% larger than the diamond shape. Therefore, a hexagonal cell with 15% more space on the anilox roll means that it can reduce the hole depth by 15% without affecting its original capacity. Obviously, the depth of the hexagonal cell can be compared to the diamond shape. Carved more shallowly.
Third, the ink release and cleaning of the cell
If the anilox roller can achieve a thin and uniform ink layer, but the speed of ink release is not fast enough, especially in high-speed printing, or the bottom of the cell can not be cleaned, what should I do? Obviously this is due to The depth of the cell is too large, and the difficulty in ink cleaning causes the problem of insufficient ink transfer in the future.
Of course, the mesh is too shallow and there is no problem. If it is too shallow, it will not be able to print out the desired effect. For example, the depth of the cell is 4 microns and the error is 1 micron, which means that the error in capacity and depth is 25%. For a printer with a quality concept, this deviation is unacceptable. Moreover, when the depth of the cell is too shallow, it will also bring the drawbacks of the ink being easy to dry. Therefore, for laser engraved anilox rolls, the best engraving depth should be chosen, and it must not be extreme.
How is the optimal cell depth determined? The depth of the cell must also consider its relationship to the size of the opening 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, not only because the bowl has a small depth, but also with the bowl. The width of the opening is large. The situation on the anilox roll is also similar.
According to further research, the optimum depth/opening width ratio d/o of the cells should be between 23 and 33%. It means that a cell having an opening width of 100 microns should have a depth of between 23 and 33 microns. The three-dimensional geometry formed in such a proportional relationship enables the cells to have good ink repellency and cleanability. The negative area on the engraving conversion table indicates the relationship between depth and opening degree. For example, when using a 400 line cell with a capacity of 2.6 BCM, the d/o ratio on the conversion table is 18%. If you change the number of mesh lines to 550 lines, then its d/o ratio becomes very pure and gets the best results. Conversely, if a 550-line 4.5 BCM capacity cell with a d/o ratio of 40% is changed to 400 lines, it will maintain the optimal d/o ratio for optimal use.
Fourth, the number of traditional mesh lines
In the previous introduction, we emphasized the cell capacity on the anilox roll, the best ink layer quality, and the best cell geometry. In the past, only the number of mesh lines was emphasized. A schematic representation of three laser-engraved anilox roll cells is shown in Figure 4, all of which have the same mesh number, capacity, and configuration, however, their characteristics vary. The uppermost one of the cells has a shallow depth and a thin mesh wall, so the ink discharge performance is good, easy to clean, and the formed ink layer is also very uniform; the bottom one is the deepest, the mesh wall is thick, Therefore, the cleaning property is poor, and the formed ink layer is not uniform. These differences have caused them to differ in print quality.
On laser engraved anilox rolls, the quality of the ceramic itself is one of the key factors affecting the quality of the anilox roll. The ceramic surface should be hard and smooth, and the porosity should be as small as possible. The hardness of the ceramic will affect the printing durability, and the flatness of the surface has important significance both before and after engraving. Before engraving, it will affect the consistency of the engraving of the surface of the roller. After engraving, it will affect the consistency of the thickness of the ink layer. The less the porosity of the ceramic surface, the more the solvent can reduce the corrosion of the roller body. effect.
Five, moiré
Another important aspect to consider on laser engraved anilox rolls is the relationship between the angle of the web and the angle of the screen web, which will be related to the formation of moiré on the print. The mesh on the laser engraved anilox roll is available in three angles: 30°, 45°, 60°. The advantage of the 30° and 60° hexagonal textures is that the risk of moiré can be avoided regardless of the angle of the plate. The reason for this is that the hexagonal mesh has an arrangement of three axes corresponding to the arrangement of the two axes on the printing plate, while the 45° anilox roller has two axes corresponding to the printing plate.
The choice of the number of netting lines depends on the way of printing and the quality of the ink, because they determine the capacity of the cells and the corresponding number of mesh lines. For example, in order to facilitate the control of high-gloss dots, the screen printing requires a thinner ink layer, which means lowering the capacity of the cells, so that a finer mesh line number is required for this purpose. For solid printing, a thicker mesh should be used to obtain more ink capacity to form a thick ink layer. On some specific prints, the quality of the ink is better than the ink, and it also affects the selection of the number of mesh lines.
In the United States, when a screen is printed on a film, the capacity of the cells is generally controlled in the range of 1.0 to 3.3 BCM/VPSI, and then converted into optimal engraving parameters. If the aforementioned d/o ratio is used, the number of mesh lines should be selected between 1200 and 400 LPI.
In color mesh printing, the number of mesh lines of the best anilox roller should be selected according to the strength of the ink, the thickness of the screen and the percentage (size) of the dots to be copied. For example, an 800LIP anilox roller can adapt to the copying requirements of high-light dots on the printing plate of 85-150LPI, while the traditional four-fold roll/version mesh line ratio is only suitable for medium-printing printing. Copy the high-gloss small dots.
Six, cleaning and maintenance
When it comes to anilox rolls, it is difficult to deal with the difficulty of cleaning and expansion. Whether the laser anilox roller can always maintain a constant amount of ink release is related to the reproduction of fine images. The laser engraved anilox roller itself is a very expensive investment. Once the netting is damaged or the cell is blocked, it is impossible to print a good printed product. To be updated is a big loss.
Cleaning is generally concerned with the means to effectively clean the anilox roll, and preventing the ink from drying out on the textured surface is the best way to maintain the anilox roll. The key to cleaning is to thoroughly remove the pigment particles and resin from the cells before the ink is dried. Once the ink is dry in the cells, the proper capacity of the cells will be reduced. To remove the dry ink, there are two methods, solvent combustion and ultrasonic. The former is the most commonly used traditional method. This method works well, but it is troublesome. The anilox roller must be removed from the machine and burned immediately or immediately when the ink no longer flows. In many packaging and printing factories, it is customary to use a crepe or other wiping material to clean the surface of the wall and the hole remains untouchable. When the combustion method is cleaned, the anilox roller should be continuously rotated to facilitate the complete burning of the ink particles. Stainless steel brushes are used for the cleaning of ceramic surfaces, while copper brushes are used for brushing the surface of chrome-plated anilox rolls. The two can't be mixed. Otherwise, the stainless steel brush will hurt the chrome layer, while the copper brush will sink the copper chips on the ceramic surface and even mix into the ink. Some factories use lye to clean the dry ink in the pits. This non-standard method is easy to popularize. However, it is not recommended because the lye easily erodes the roller or worsens the surface damage.
Ultrasonic cleaning of the web roller is very effective, but it should be checked frequently during cleaning to avoid excessive damage and damage to the ceramic surface. The ultrasonic cleaning time must be strictly controlled. The ultrasonic cleaning time of the fine mesh anilox roller should be between 2 and 5 minutes. The cleaning time of the coarse mesh anilox roller can be slightly extended. Another thing to note is that the operation must follow the ultrasound. Equipment manufacturing plant operating procedures and establish regular monitoring measures.
The maintenance work of the anilox roll also includes storage, use and periodic identification.
The use of the plant should establish appropriate cleaning and maintenance regulations in accordance with the following guidelines:
1. Use a suitable brush to remove wet ink in time.
2. Brush by brushing when brushing.
3. Cleaning and operation should be carried out by someone.
4. Use a protective cover when storing.
5. The storage area of the anilox roller should be carefully selected.
6. Regularly perform in-plant self-assessment and inventory statistics on the anilox roller.
7. Regularly educate and train operators.
With the continuous promotion of the flexo printing process, in order to compete with the gravure and offset printing process, it is necessary to closely cooperate with the ink factory, the printing plate manufacturer and the prepress system supplier to meet the needs of the printing factory. Only in this way can we obtain itself. Greater development