Application of thin ink flexo printing to improve the quality of prints and reduce material consumption

Flexo printing (hereinafter referred to as flexo printing) has been developed rapidly due to its advantages of low cost, high speed, and high profitability. An important reason for the low cost of flexo printing is that the ink layer is thin. At present, the flexo ink layer is the thinnest in all printing methods. Below, the author analyzes the following aspects: the influence of ink layer thickness on the quality of printed products and the realization of the best ink layer to reduce costs;

First, ink

The ink is composed of three parts: pigment, binder, and auxiliary agent. Since the flexo ink layer is thin, the ink and the offset ink are different. Flexo inks are required to have high concentration, poor flow, high viscosity and other characteristics. Therefore, the ink of the thin ink layer should have a high concentration of pigment and a low concentration of the medium. In the composition of the ink, the pigment is the most expensive, and others such as water, solvents, fillers, and thinners are relatively inexpensive.

The purpose of printing is to obtain the desired color with an ink layer containing a certain amount of pigment. If we use a thin layer of ink in our printing process, we must have the same pigment as the thick layer of ink in order to achieve the same color effect as a thick layer of ink. The profit brought by the thin ink layer is mainly obtained by reducing the ink waste and saving the ink supply. If the ink layer is very thick, the pigment concentration should be diluted, otherwise the color is too dark. If the color of the print is too dark, it means that you have to waste some money, because in the normal color, you need to use more ink to present the desired color.

Second, the shape of the network and the amount of ink

In the flexo printing process, the short ink path is a distinctive feature. The anilox roller is a key component to ensure the short ink path to transmit ink and uniform ink quality. The role of the anilox roller is to quantitatively and evenly transfer the required ink to the graphic part of the printing plate. In the offset printing process, a rubber roller is used to supply ink, and the amount of ink supplied is larger, so that the thickness of the offset ink layer is greater than the thickness of the flexo ink layer. However, if the anilox roller is operating at a high speed, although the ink is scraped with a squeegee, the amount of ink supplied is the same as the use of a blanket cylinder, and the amount of ink supplied is too large. Therefore, we generally use a low-speed anilox roller so that the thin ink layer can have a smooth surface.

However, in the thin ink layer printing process, it is not enough to use only a low-speed anilox roller. At the same time, the smoothness, shape, and structure of the mesh hole are also important. The change in the stretch of the surface of the ceramic anilox roll has no major effect on the adhesion of the ink. On the anilox roll, the ink in the cells can be separated from the cells themselves. Of course, the shape of the cells will affect the separation of the ink. The number of different inks in the shape of the cell is usually different. When hexagonal cells are generally used, the smoothness of the cells is required to be high. At the same time, there are corresponding requirements for the depth of the cyberspace. It is required that the engraving of the cell site should not be too deep. If a cell site is carved too deeply and the surface of the cell site is not smooth enough, the ink will not flow out of the cell site and normal ink separation cannot be performed. So that the quality of the print can not meet the requirements.

Third, overprint and ink layer

The drying system is an indispensable device on the printing press. If the ink layer is thick, the print is not easy to dry. The corresponding printing speed cannot be increased and the printing cost will increase. And in the printing process, the ink is not dry enough to make the ink peel from the substrate, so that the printing plate is dirty. The main reason is that dry and impermeable inks do not print well. Overprinting refers to printing a second color ink on the first color ink to form a third color, for example, magenta ink is printed with yellow ink to form a warm red color or a yellow ink is printed with a yellow ink to form a green color. If the first color ink is not dry, the second color ink tends to form spots on the first color ink during overprinting, and in this case, more yellow ink is required to form red or cyan to achieve a desired color effect. Under normal circumstances, it is impossible to accurately predict the effect of overprinting on the coloration. If the ink layer is thin, the ink is more likely to be dried and the overprinting effect of the printed product is better.

Fourth, print tone, details and ink layer

Flexocopy uses many dots of different sizes to copy originals. The high-light and high-light areas are reproduced with a small percentage of small dots. Dark areas are printed with a high percentage of dots.

A wide tone has a finer level. Because the thick ink layer makes the dot enlargement more serious, thus compressing the tone, there is not enough hierarchy when copying a good image, and the printed product is flat and dull. The thin ink layer, the small dot expansion, has a wide range of gradation, so it can well copy the original.

We know that when we want to get a thin layer of ink, we must first determine the best value, and then we can determine the best ink layer.

1 The best ink layer selection, how to choose the best ink layer thickness? First, consider the ink properties and the amount of ink supplied by the anilox roller, as well as the empirical value of the ink layer on the substrate. The test of the number of screen lines of the anilox roller should be performed with a high concentration, poor flowability, and high viscosity ink. Under a given standard low-speed anilox roller, a series of tests were performed on the surface of the anilox roller with different numbers of engraving screen lines, and finally, the optimum number of screen lines of the anilox roller was obtained. The anilox selected by this test method is more scientific. Different engraving bands show different effects on the surface of the anilox roll. This anilox roller is often referred to as a band anilox roller. The anilox roller is generally selected by the number of screen lines. Since the role of the anilox roller is to quantitatively and evenly transfer the required amount of ink to the graphic portion of the printing plate, the optimum ink layer is determined after the optimum anilox roller is selected.

However, we should also consider the saturation of the thin ink layer. In addition, there are also print quality issues that should also be considered. For example: the fluff of the paper, the field printing has the paper hair, the white dot and the line are too hard. Thick ink layers can mask these problems and endanger the following processes. The thin layer of ink can immediately find these problems, and then can be resolved in time. Therefore, while choosing the best ink layer, we should consider the quality of the printed product, especially the saturation of the printed product.

2 Reduce print failures. The thin ink layer is very advantageous in reducing print failures. The problem of dirty spots in many screen prints comes from excessive ink. The thick ink layer and the large amount of ink on the dots make the ink flow and the dots to be connected. In this case, the image in the intermediate tone part is most obvious, and the phenomenon of vignetting will be formed. The reason for this phenomenon is that due to the enlargement of the intermediate tone points. If the ink layer is thin, the ink on the dots is small, and there is not enough ink to spread around the dots. Therefore, the dots are enlarged little, so when the printing plate and the printing material are separated, it is not easy to get dirty, and it is not easy to form dirty spots.

Although midtones are more difficult to control, high light should also be cleared at low speeds. The number of high screen lines, the anilox roller running at a low speed, the ink hole on the anilox roller is small and shallow, and the shallow network hole has less gambling ink, thus forming a thin ink layer. Small cells, high-line number of anilox rollers have a thin network wall, so that the ink layer is smooth while the ink transfer is convenient, so that the problem of small white spots on the print product can be solved.

3 Reduce production costs. The thin ink layer makes the printing operation easier. In the flexo printing process, a low-speed anilox roller is used to print the thin ink layer, so that the ink supply amount is controlled better, so the probability of ghosting and ink deposition is small, and the dot expansion is not significant. At the same time, in the flexo printing process, the thin ink layer is not easy to saturate the printing plate, which can reduce the number of times of cleaning the printing plate, thereby saving a lot of time for cleaning the printing plate, thereby improving the production efficiency and reducing the production cost.

4 Little pollution to the environment. In today's world, atmospheric pollution has a greater impact on people's physical and mental health. We cannot ignore the effects of ink evaporation on the environment. Under normal circumstances, we think that the thin ink layer, the solvent in the ink less volatile, as well as the printing plate, substrate and anilox roller on the amount of ink is very small. Therefore, the thin ink layer has little environmental pollution. In summary, the use of thin layers of ink in flexo printing is a general trend, and we should actively promote it. Not only is it contributing to the protection of the environment, but it can also bring huge profits to printing companies.

Source: Art Union