The author proves with a typical case that the mesh volume is the best parameter to measure the performance of the anilox roller, and it can ensure that the anilox roller achieves the best ink transfer performance and color reproducibility.
Fifteen years ago, when the author first touched the anilox roller, like many others who are engaged in flexographic printing, the first criterion for judging the anilox roller is the number of screen lines, followed by the mesh volume. For example, an anilox roll has 800 meshes per inch, and each mesh volume is 2BCM (abbreviation of billions of cubic microns, that is, one billion cubic micrometers). . why? Should the screen line number of the anilox roller (that is, the number of mesh holes arranged per inch length) or the mesh volume (that is, the amount of ink transferred to the printing plate and finally to the substrate) be used as the specification parameter in printing?
The purpose of this article is to break past inertial thinking and help printers and suppliers accurately understand which element is more critical in flexo printing: the number of mesh lines or the volume of engraved mesh?
Typical cases in the printing workshop
A frequently printed color job is about to be reprinted, and the printer prepares four anilox rollers for this purpose. Based on the experience of the previous printing, four 800 line / inch anilox rollers are needed to print four colors: yellow, magenta, cyan, and black. There are six 800 line / inch anilox rollers in the workshop, and the printer randomly selected 4 of them for installation and pressure printing. Under the correct printing pressure, the printer used a density meter to measure the solid ink density.
However, the results show that the same substrate, ink, printing plate and plate mounting tape failed to achieve the same color as the previous printing. The anilox roller uses 800 lines / inch as in the last printing, isn't it wrong? The manufacturer clearly marked on the edge of the anilox roller, it is indeed an anilox roller of 800 lines / inch, and the number of lines cannot be changed unless the anilox roller is re-engraved. So why are the colors inconsistent? Why waste paper, ink and time or get different results?
According to the data provided by the anilox roller supplier, select the same volume, the color change of the printed product will be within the allowable range, that is, to achieve consistency. But over time, because of cleaning, damage and wear, etc. will also cause inconsistent color of the printed product. Therefore, selecting 4 of the 6 anilox rollers to print to achieve the same color as the last time, it is not a good method to judge only according to the mesh line number of the anilox roller.
Because these 6 anilox rollers change from half a year to 4 years. The longer the time, the greater the damage caused by the anilox roller due to improper offline cleaning operation. The typical damage of some anilox rollers is caused by the improper use of the doctor blade, and the slight ink clogging of most existing anilox rollers is caused by poor online cleaning and lack of inspection before use. Regular inspection of the anilox roller, effective cleaning, and correct inspection and judgment of the previous work of the anilox roller can minimize waste. By identifying the serial number and mesh volume of the anilox roller, waste can be minimized or even eliminated. Knowing which anilox rolls have a higher volume will help the printer choose the application accordingly. Based on these volume parameters, the printer can choose the best anilox roller to print black ink, and the worst anilox roller to print yellow ink.
Obviously, the key to this problem is the mesh volume of the anilox roller, not the mesh line number, because the mesh line number is the same. In fact, this problem can be avoided through different communication methods, but we spent a lot of time and materials in identifying the cause of this potential problem.
About printing color density
The color density comes from the ink pigment formulated by the ink supplier. Pigments provide color carriers, and additives provide various properties required after printing, such as anti-scratch, anti-wear, anti-fading or anti-moisture properties. The ink system is formulated according to the minimum volume requirement for the anilox roller to achieve solid ink density or form the thinnest ink film. The anilox roll supplier provides the mesh volume parameters necessary for ink production, which can ensure accurate and consistent ink color transfer, and achieve the best performance and color reproducibility.
About mesh line number
The mesh line number refers to the number of mesh holes arranged per inch of length. These mesh holes are engraved along a certain angle with the axis of the anilox roller, generally 30 °, 45 ° or 60 °. Once the engraving is completed, the number of meshes is fixed. The anilox roller with low mesh line number and high mesh volume is suitable for field plate and glazing. The number of meshes engraved by an anilox roll with a mesh volume of 8.0 BCM is 165 to 300 per inch. Anilox rollers with high mesh lines are suitable for smaller mesh volumes. The 2.0 BCM anilox roller used for overprinting and mixed plate printing, the number of engraved mesh ranges from 700 to 1200 per inch. In order to achieve accurate mesh volume and good ink transferability, the mesh wall in the mesh needs to be thin and smooth, and the carving depth should not be too shallow or too deep. According to historical experience, the depth of the cut is mainly used for glazing, so that it is easier to clean it later.
In order to achieve the same mesh volume under different mesh lines, the mesh depth with higher mesh lines is required to be deeper. An anilox roller with a high mesh line with the same mesh volume can form a smoother ink film. Add 200 meshes per inch, corresponding to 40,000 meshes per square inch, to provide more support for ink transfer. Although the mesh line number is a traditional specification parameter, the mesh line number corresponds to the mesh volume, and it has little or no effect on the printing quality.
About mesh volume
The mesh volume represents the ink storage capacity per square inch of engraved surface, and its unit is one billion cubic micrometers (BCM). The mesh volume is large, the density of the transferred solid ink is also greater, or the color is denser, and the coating thickness is greater. The mesh volume is small, the ink film thickness is thin, the printing quality is high, and the printing efficiency is high. Due to wear, clogging and cleaning, the mesh volume will change with the passage of time. The mesh is dirty or clogged. This temporary fault can be restored to its original volume and color by correction. However, wear is irreversible and permanent damage, because its smaller volume than the original causes poor color.
According to market experience, according to the different substrates, the mesh volume also has a corresponding recommended range. Field full version / glazing: 5.0 BCM or above; mixed version printing: 2.0 ~ 4.0 BCM; color overprint: 1.3 ~ 3.0 BCM. If the volume of the mesh is used as a reference alone, the effect of judging the printing quality of the anilox roller becomes clear and understandable, and it will not cause trouble because the number of screen lines affects the printing quality. Especially today, anilox roll manufacturers gradually express the engraving effect in combination of mesh volume and mesh line number, which can be changed with the available laser technology.
Assume that the anilox roller is only considered in terms of mesh volume in the following applications-color overprint: 1.5 BCM; mixed printing: 2.2 BCM; line / field version: 3.5 BCM. So, how can it be easier for managers, purchasers, inspectors, and printers to rely only on mesh volume to manage and identify applications?
Today's flexo printing continues to grow, and the existing skilled printing technicians are limited. The printing house relies on the training of internal staff and mechanical assistance from job applicants. Is there a better way to eliminate the variable factors in the printing process and make more experienced operators and printers at the same level?
For example, in the process of color overprinting, there is only an anilox roller of 1.5 BCM. There is no other choice, and there is no opportunity to install the wrong anilox roller, or sacrifice printing quality, choose unqualified materials and repeat the operation to waste time. So what about the performance and types of anilox rolls? Users say their anilox roller is 800s. Do they refer to 800s for the traditional anilox roll with a 2.0 BCM mesh volume, or the improved anilox roll with a 3.5 BCM mesh volume? As an ink supplier, we need to know the mesh volume in order to provide the correct ink volume and ensure accurate color reproduction. The meaning of the mesh line number is too little, it is just a means for the anilox roll manufacturer to achieve its purpose. So, which of 500, 700, 1000 and 1500 lines has better mesh line count? why? Carved in the same volume, the density of the printed solid ink and the dot increase are relatively consistent. According to most of the published chart data, these four kinds of network lines can engrave a 2.5 BCM mesh volume. The mesh of 500 lines is shallow, but this is only the result shown on the chart.
The same mesh volume = the same ink film thickness; the same ink film thickness = the same solid density; the same ink film thickness = the same dot increase value.
What is the line number of the anilox roller supported by the traditional printing plate? In the past, the ratio of the number of anilox rollers to the number of screen plus screen threads used to be 4: 1, but this ratio has now been increased to 6: 1. The ratio of the smallest dot size of the printing plate to the opening size of the mesh carving is exactly a big question.
As flexo has entered the field of traditional high-quality printing, almost all flexo components require higher-quality printing functions, printing efficiency has been improved, and flexo has also entered a market area that was not previously accessible.
Related improvements
Compared with ten years ago, the current printing equipment, materials and post-press processing equipment have little in common in appearance or performance. The printing plate material has changed from rubber plate to resin plate, supporting dot reproduction of less than 1%, resolution of 200 dots per inch or higher, and the production time has also been shortened. The original sensitive PH system has been developed into a water-based ink system with almost no necessary maintenance costs. The UV ink can better maintain the ink color, and the viscosity has dropped to the level of water-based ink. Printing tools, doctor blades, masking tapes, web inspection systems, and every other printing component have been improved, helping to increase the capabilities of the flexo industry and bring about growth.
With the improvement of hardware equipment and the improvement of flexo printing technology, new ideas and views have also been encouraged and supported to make continuous improvement in this dynamic industry. Therefore, after the technological changes over the years, many new concepts and new views have emerged on the relationship between the anilox roller, ink, printing plate and printing quality. We compare the anilox roller to the "heart" of the flexo printing machine, which is related to the volume of the mesh and the thickness of the ink film, not to the number of screen lines.
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