A large part of the quality of printed matter lies in the amount of ink: if there is too much ink, there will be stencils, sticky or irrelevant effects; if the amount of ink is too small, problems such as image color cast, whiteness in the field, and text breaks will occur. Therefore, the amount of ink should be moderate, but also quantitatively transfer ink.
There are many factors that affect the ink volume of flexographic prints, such as the anilox roll, the layout of the plate, the type of ink, the temperature, the printing speed, the nature of the substrate, and so on.
One, anilox roller
In the flexographic printing, the amount of ink supply directly determines the anilox roll. The anilox roller is regarded as the heart of the flexographic printing press. It controls the transfer of the ink layer to the printing plate. It not only controls the storage volume of the ink and makes it pass the balance, but ultimately controls the quality and consistency of the printing quality.
The parameters that affect the ink transfer performance of the anilox roller mainly include the following:
1. Anilox roller mesh ink load
The anilox roller's cell angle, network lines, cell shape and cell depth determine the volume of the cell site, ie the amount of ink carried by the cell site. The amount of ink contained in the net points can be accurately detected by advanced computer-based interference detection technology, and the actual number of cell volumes can be obtained, which is represented by BCM/SQIN, abbreviated as BCM (Billion Cubic Micron, 1 billion cubic microns).
BCM has become the standard unit of measure for the volume of the anilox roll. The same BCM has the same ink-carrying capacity, while the same number of net lines and the same depth of the cells do not necessarily have the same ink-carrying capacity, because the ink-carrying capacity is also related to the shape of the cell site.
The choice of the cell volume mainly depends on the printing density, the type of ink scraped, and the type of substrate. Since the actual printing involves the factors such as the quality of the ink, the adhesion viscosity, and the material of the printing material, a wide range of selections are used. The selection can only be made several times. The best method is to use the test. The anilox roller technology quickly and accurately selects the best mesh index to achieve the best printing effect.
The test anilox roller technology is to engrave several sections of screens with different numbers of screen lines and the amount of ink transferred on an anilox roller. Through different substrates, different kinds of inks are tested under different machine operating speeds to obtain the most Good printing effect, to determine the selection of the best screen number and the amount of ink transferred anilox roller.
The test anilox roll must be used in conjunction with the test plate. After being printed on the test roll, the printed matter should be tested with a densitometer. Through the comparative analysis to obtain the index of the best dot and density values, the direct data of the most accurate and best actual printing effect can be obtained to ensure the selection of the most suitable anilox roller parameters.
2. The number of anilox roller
The amount of ink transferred by the anilox roller is generally measured by the number of screen lines (number of inked holes per unit length of the anilox roller surface, in units of lines/inch). When the number of screen lines is low, the amount of ink transferred is large, and when the number of screen lines is high, the ink is transmitted. The amount decreases accordingly. However, it is worth noting that the number of lines of the anilox roller and the number of lines of the printing plate are two different concepts. The line of the printing plate is a halftone layer with a layer, which refers to the high network line of the image fine product, and the size of the dot. There are high light, dark tone, and intermediate tone. The mesh size of the anilox roller is the same. To print high-quality prints, you must select the appropriate anilox roller.
3. The choice of suitable anilox roll
(1) Appropriate anilox roller according to the printing material selection line number
Printing materials include paper, plastic, metal, and film. For non-absorbing substrates, the amount of ink required is less and the number of anilox rollers is higher. Conversely, for printing materials with strong absorption, the amount of ink required is more. The number of anilox roller lines should be lower.
(2) Select the number of anilox roller lines according to the print graphic
As an anilox roller selection for printing plate in the field, lines, text, etc., it is very important to select an anilox roller according to the size of ink supply. For field printing, if the number of lines of the anilox roller is too low, the amount of ink supplied is too large, and the edges of the printing plate will accumulate ink and cause the edge of the printed product to be ghosted; if the number of lines is too high, the amount of ink supplied is insufficient, and the density of the field is insufficient. Flower; If the two on-site overprinting or printing plate surface is small, you can choose a higher number of screen lines; text, line version according to the text size and line thickness, to choose the right anilox roller.
In general, in the case of a sufficient flexo printing machine, the same color cable screen version and field version should be made into two, because the screen printing needs thinner ink layer, and the field, lines need to be thicker Ink layer. However, under certain special circumstances, it is necessary to print the same color network lines and field images on the same plate. In this case, on the one hand, when printing, the selection of anilox rollers has to be taken into account and is usually satisfied. The printing requirements of the cable version are at the expense of the thickness of the ink layer on the ground; on the other hand, different exposure times must be mastered at the time of plate making to ensure the quality of the line and field parts on the same plate.
(3) Select the number of anilox roller lines according to the number of screen lines of the printing plate
In order to accurately reproduce the dots of each hue level of the printing plate, it is necessary to ensure that each dot on the printing plate is accurately inked. For this reason, the area of â€‹â€‹the opening portion of the anilox roller should be smaller than the dot area, so that one or a few ink holes can be used for ink, so that the dot network will not sink into the mesh hole, and the printing product dot network will expand.
The number of anilox roller lines generally has a certain ratio relationship with the number of lines of the printing plate. If the ratio of the number of printing plate lines to the number of anilox roller lines is improper, moirÃ© will be generated. In addition, the improper relationship between the plate and the anilox roller can cause moirÃ©.
4. Anilox roll mesh angle, mesh shape and cell depth
Several common network cell shapes for the anilox roller are triangular, quadrangular, quadrangular, hexagonal, hexagonal, dot-shaped, trapezoidal, and additional channels. The opening degree and depth of the cell site have a considerable influence on the ink transfer performance of the cell site. The greater the opening degree and the shallower the depth, the better the ink-transporting property; otherwise, the ink-transmitting property is relatively poor.
The angle of the screen of the anilox roller refers to the angle formed by the continuous arrangement direction of the cells and the axial direction of the anilox roller. Anilox roll cable angles are 30Â°, 45Â°, and 60Â°. The actual metal anilox roller mesh used in the current shape is a quadrangular pyramid with a mesh line angle of 45Â°; while the ceramic anilox roller mesh has a hexagonal shape with a mesh line angle of 60Â°. Because the hexagon is the most effective geometric shape, the area utilization is highest in unit area. Between the meshes, there is the narrowest wall and the smallest remaining area, the large amount of ink is transmitted, can produce the most uniform ink film, has a shallower depth and a wider opening, most conducive to ink transfer, and easy to clean . It is worth noting that the cells on the anilox roller are generally engraved in the direction of 45Â° on the same axis, such as the above-mentioned metal anilox roller, which is the same angle as the black version of the network cable in general color printing. In the case of ordinary anilox printing, mesh lines connected to the anilox roller mesh easily interfere with the black mesh lines to form a moirÃ© pattern. Therefore, for flexo color printing, the plate should avoid the use of a 45Â° screen angle.
In short, in order to obtain better flexo products and obtain the best ink, it is necessary to make new progress in the anilox roll technology, which will promote the rapid development of the flexographic printing process. At present, due to the appearance of laser-engraved anilox rollers, the flexo printing industry can be produced in almost the same manner as the gravure and offset printing industry. The anilox roller with a ceramic surface layer improves the transferability of the ink layer and improves the quality of the ink layer. This is the result of adopting new technologies.
Second, other factors
In the actual production process, there are many factors that affect the amount of flexo ink, such as the type of ink, the layout of the layout, temperature, printing speed, the nature of the substrate, and so on.
Frequently used in flexo printing are water-based inks, solvent-based inks, UV inks, and varnishes. These different inks may differ in their transmission, resulting in flexographic products with different ink volumes. Therefore, in the actual production process, different types of inks should be used as needed. From the layout of the layout of the layout, when printing a large area on the ground, the ink should be thickened, the field version was only printed in plain clothes, not easy to pull the hair; but when printing the cable version, the ink is required to be thin to prevent the dot deformation from expanding. Hair paste. In general, under the conditions of low ambient temperature and relatively dry climatic conditions, the layout ink layer can be appropriately thinned; conversely, when the temperature is high, the printing ink layer should be thicker. From the operation of the machine, the machine speed, the ink roller in the rapid operation, will generate heat, ink flow will increase, so the ink should be thicker; the other hand, the machine speed is slow, the relative heat generated by the ink roller operation To be lower, so the ink should be thinner. From the surface smoothness of the paper, the surface of the paper is rough, and the texture is soft. When the absorption is large, the ink should be thinned. On the contrary, the surface of the paper is smooth, the texture is tight, and the absorption is small. The ink should be thickened because the ink is too thin. Can easily cause dereliction and other ills.
There are many factors that affect the flexographic ink volume. As long as we grasp the standards in the actual production process, we can print higher quality flexographic products. â€»
Author: School of Press and Publication, Hangzhou Dianzi University
Author: Tang Yixiang
Reprinted from: Chinese Flexo
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