Talking about technical parameters and selection principle of anilox roller from practical point of view

Today's flexographic printing is taking the lead in the development of the printing industry in today's world.

The new progress of the anilox roll technology has become a decisive factor in promoting the rapid development of the flexo printing process, especially due to the emergence of laser-engraved anilox rolls, which enables the flexographic printing industry to produce almost the same position as the gravure and offset printing industry and spray ceramics. The surface anilox roller improves the transferability of the ink layer and improves the quality of the ink layer, which is the result of adopting new technologies.

The anilox roller can quantitatively deliver ink to the printing plate according to a predetermined standard, and the ink layer should be as thin and uniform as possible. The stability of the ink layer will restrict the print quality of the image. During the transfer process, the thinner the ink layer, the easier the printing adjustment and the smaller the dot expansion rate; the evenness of the ink layer helps to increase the consistency of the ink transfer amount.

First, the uniformity of the ink layer

Why the use of laser-engraved anilox roller can obtain excellent uniform ink layer? The main reason is that it can reduce the gap between each cell gap, in the traditional mechanical engraving method, the use of metal movement method To form a network of holes, and in laser engraving, the ceramic gasification is formed by a laser beam to form a network of holes. It is precisely because of this fundamental difference that the laser-engraved anilox roll brings the advantages of strict control. First of all, it can significantly reduce the gap between the holes, that is, the thickness of the wall, and secondly it can create a denser hole in the same distance of the true line. Based on the above two factors, the ink layer delivered by this cell has higher uniformity.

How does the laser-engraved anilox roller make the ink layer thin? The thickness of the ink layer depends on the volume of the cell, such as an anilox roller with a 300-line 5.50 BCM volume and an 800-line 2.00 BCM Compared with the volumetric anilox roller, it is obvious that the 800 lined anilox roller has a smaller ink volume because of its small capacity, and when laser engraving is used, a mesh hole with a smaller capacity than the mechanical engraving can be obtained, thereby forming a The thinner layer of ink. The thinner the ink layer, the better it is to control the printing effect of the high light dot.

Second, the specifications of engraving

Laser engraving has three sizes: 30° hexagon, 45° diamond, and 60° hexagon. After the surface of the ceramic anilox roller is polished, round pits with parabolic bottom pits are etched on the ceramic surface by a radiused laser beam. The diameter of the laser beam can be based on the number of lines or the size of the cells. To make adjustments, the beam always remains circular regardless of adjustment.

The geometry of the reticulation depends on the arrangement of the cells. For example, a diamond-shaped pattern is arranged by four cells surrounding a central hole, while a hexagonal pattern is surrounded by six network cells. And arranged. Wherever the sculpted mesh is formed, it will form a regular diamond or regular hexagon. Once the sculpting error occurs, the gap between the cells will increase, and the geometry of the screen will not be standardized.

Hexagonal reticulates are superior to diamonds for two reasons. First, there are larger wall areas around diamond-shaped cells. Obviously the ink layer it conveys is not quite uniform. Second, in order to achieve the same capacity, diamond-shaped cells have to be carved deeper. We can learn from the natural world. Bees' honeycombs are made up of wide holes of hexahedrons. Creatures rely on instincts. Knowing that only this arrangement can store more bee secrets. So the hexagon is the most efficient geometry and it maximizes space.

According to mathematical calculations, the area occupied by hexagons in the same area is 15% more than diamonds. So a hexagonal net with 15% more space on the anilox roller means that it can reduce the depth of the hole by 15% without affecting its original capacity. Obviously, when using a hexagonal cell, the depth is comparable to the diamond shape. Carved more shallowly.

Third, the ink release and cleanliness

If the anilox roller can deliver a thin and uniform layer of ink, but the ink release speed is not fast enough, especially in high-speed printing, or the bottom of the cell can not be cleaned, what to do? Obviously this is due to Due to the large depth of the cell, the problem of insufficient ink transfer is caused by the difficulty in cleaning the ink.

Of course, the shallowness of the cyberspace is not without its problems. If it is too shallow, it will not be able to print the results it deserves. 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 reaches 25%. For a quality-conscious printer, this deviation is unacceptable. And when the depth of the cell is too shallow, it will bring the disadvantage of ink drying. Therefore, for the laser engraving anilox roller should choose the best engraving depth, must not be extreme.

How is the best depth of the net hole determined? The depth of the net hole must consider the relationship between the depth of the net hole and its size. If we compare soup and test tubes, 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 of the small depth of the bowl, but also with the bowl. The width of the opening is large. The situation on the anilox roller is also similar.

According to further studies, the optimum depth/opening ratio d/o of the cell site should be between 23% and 33%. It means that the depth of the cell with an opening width of 100 μm should be between 23 and 33 μm. The three-dimensional geometric shape formed by this proportional relationship can make the cell site have good ink release and cleaning properties. The female area on the engraving conversion table shows 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 the number of mesh lines is changed to 550 lines, then its d/o ratio becomes very pure and optimal. On the contrary, if the 550-line 4.5 BCM capacity cell with a d/o ratio of 40% in the table is changed to a 400-line cell, it will maintain the optimal d/o ratio at this time, so as to obtain the best use effect.

Fourth, the number of traditional mesh lines

In the previous introduction, we emphasized the capacity of the cells on the anilox roller, the optimal ink layer quality, and the best cell geometry. In the past, only the line number of the mesh was emphasized. In Fig. 4, three types of laser engraved anilox roller cells are shown. They all have the same number of mesh lines, capacity and configuration, but their characteristics are different. The depth of the topmost cell is shallow and the wall is thin, so its ink release performance is good, easy to clean, and the formed ink layer is also very uniform; the bottom one is the deepest of the cell points, and the net wall is thicker. Therefore, the cleaning performance is poor and the formed ink layer is not uniform. These differences have led to differences in their print quality.

In 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, and the porosity should be as small as possible. The hardness of the ceramic will affect the resistance force. The flatness of the surface, whether before or after engraving, has important significance. Before engraving it will affect the consistency of the cell surface sculptured on the roller surface, which will in turn affect the consistency of the ink layer thickness; the less the porosity of the ceramic surface, the more it can reduce the erosion of the solvent on the roller body. effect.

V. Moire

Another important aspect to be considered in the laser-engraving anilox roller is the relationship between the angle of the reticulate pattern and the angle of the printing plate, and it will be related to the formation of the moiré on the printed matter. There are three angles available for laser engraving on the anilox roller: 30°, 45°, 60°. The advantage of hexagonal screens at 30° and 60° is that the danger of moiré can be avoided regardless of the angle of the printing plate. The reason is that the arrangement of the hexagonal texture corresponds to the arrangement of the two axes on the printing plate in the arrangement of the three axes, while on the anilox roller of 45° it corresponds to the printing plate with two axes.

The number of reticule lines depends on the printing method and the quality of the ink, because it determines the capacity of the cells and the corresponding mesh lines. For example, for the printed version of the cable screen, in order to facilitate the control of the highlights, the ink layer needs to be thinner, which means that the capacity of the cells must be reduced. Therefore, a finer mesh line number must be used. For solid prints, a coarser mesh should be used to obtain more ink content, thus forming a thick ink layer. In some specific prints, the effect of high-quality ink is better than the effect of ink volume. At the same time, it also affects the selection of the number of mesh lines.
In the U.S., when the screen is printed on a film, the capacity of the cell is generally controlled in the range of 1.0 to 3.3 BCM/VPSI, and then converted to the optimum engraving parameters. If the aforementioned d/o ratio is used, the number of mesh lines should be chosen between 1200 and 400 LPI.

In color mesh printing, the optimum number of anilox roller lines should be selected based on the strength of the ink, the thickness of the printing plate, and the percentage (size) of the dots to be copied. For example, an 800LIP anilox roller can adapt to the copy requirements of high-light dots on plates of 85 to 150 LPI, while the traditional 4x roller/plate mesh line ratio is only suitable for medium-tone prints. For copying high light small outlets.

Six, cleaning and maintenance

When it comes to anilox rollers, it involves all the difficulties in cleaning and maintenance. Whether the laser anilox roller can always maintain a constant ink release rate is related to the reproduction effect of a fine image. The laser-engraved anilox roller itself is a very expensive investment. Once the moire is damaged or the cells are plugged, it is not possible to print good prints. To be updated is a big loss.

What is commonly concerned with cleaning is the effective means of cleaning the anilox roller, and preventing the ink from drying on the textured surface is the best way to maintain the anilox roller. The key to cleaning is that the pigment particles and the resin are completely removed from the cells in time before the ink is dried. Once the ink is dried in the cells, the capacity of the cells will be reduced. The ink of the dry knot is removed. There are two methods commonly used, the solvent combustion method and the ultrasonic method. The former is the most commonly used traditional method. This method is effective but inconvenient. The anilox roller must be removed from the machine and burned immediately or when the ink no longer flows. In many packaging and printing plants, it is customary to clean it with a cloth or other wiping material. This will only clean the surface of the net wall and the craters will still not be accessible. When the combustion method is cleaning, the anilox roller should be continuously rotated to facilitate the complete burning of the ink particles. Stainless steel brushes are used to clean ceramic surfaces, and copper brushes are used to brush the surfaces of chrome-plated anilox rollers. The two can not be mixed, otherwise, the stainless steel brush will brush the chromium layer, and the copper brush will sink the copper particles on the ceramic surface, even mixed into the ink. Some factories use lye to wash the dried ink in the pits. Although this non-standard method is easy to popularize, it is not recommended due to the susceptibility of the lye to erode the roller body or further damage the surface.

Ultrasonic cleaning of the roller is very effective, but it must 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 mesh anilox roller should be between 2 and 5 minutes. The cleaning time of the coarse mesh anilox roller can be slightly extended. The other thing to note is that the operation must follow the ultrasound. Equipment manufacturers operating procedures and establish regular monitoring measures.

Anilox roll maintenance also includes storage, use, and periodic identification.

The use of factories should establish the corresponding rules for cleaning and maintenance in accordance with the following guidelines:

1. Use a suitable brush to remove wet ink in time.

2. Use a rotating brush when brushing.

3. There must be someone responsible for cleaning and operation.

4. Should be stored