The "Intaglio-to-Flexographic" Printing Technique of Thin-film Printing
Soft packaging printing usually adopts two methods: intaglio printing and flexographic printing. With the increasing popularity of flexographic printing, a number of soft packaging factories will undoubtedly want to switch from intaglio printing to flexographic printing. According to the experience of an industry expert, in this process, flexographic printing needs to undergo some special treatments to achieve a similar effect as intaglio printing, in order to meet the requirements of customers.
Choosing the right mesh roller is very important.
In flexographic printing production, the matching between the screen roller and the printing plate is of great significance. It is essential to ensure that the diameter of the smallest dot (circular dot) on the printing plate is larger than the opening diameter of the screen holes on the screen roller. This is the most fundamental requirement.
In actual production, the theoretical calculation method can be adopted. By using the known screen mesh count and the minimum dot percentage, the minimum dot area can be calculated. Then, the dot diameter can be obtained using the area formula of a circle, and it can be compared with the opening diameter of the mesh holes on the screen roller to determine if they match. For example, if the screen mesh count on the printing plate is 150 lines per inch and the minimum dot percentage is 1%, through calculation, the minimum dot diameter can be determined to be 19.1 μm. This method is applicable to circular dots. For chain-shaped dots and square dots, there are also their own theoretical calculation methods. The empirical method is to summarize experience through mass production and thereby determine the appropriate screen roller parameters. For flexible printing and soft packaging enterprises, the high-line-count screen rollers usually only have a fixed number of settings. After some time of exploration by the operators, they can summarize some experience, which is also helpful for the correct selection of screen rollers.
Select adhesive tape of the appropriate hardness
The hardness of the die-cutting tape can be classified into three types: hard, medium, and soft. In actual production, the appropriate hardness of the die-cutting tape should be selected based on the graphic content of the plate surface. Generally, neutral die-cutting tape is sufficient for printed products; when printing fine halftone images with high screen line numbers, soft die-cutting tape should be used; when printing solid areas and lines, hard die-cutting tape should be used; when halftone images, solid areas, and lines are on the same printing plate, to balance the printing effects of both, neutral or slightly harder die-cutting tape should be used as much as possible.
Adjustment and control of printing pressure is crucial.
The printing pressure mainly consists of two aspects: the pressure between the screen roller and the plate cylinder, and the pressure between the plate cylinder and the center impression cylinder. Both of these printing pressures are extremely important. Excessive pressure between the plate cylinder and the center impression cylinder is the main cause of the enlargement of flexographic printing dots; excessive pressure between the screen roller and the plate cylinder, with excessive ink supply, can easily cause ink to adhere to the edge of the dots, resulting in dirty plates. Only by maintaining a light printing pressure can the desired printing effect be stably achieved.
Each group of pressure adjustment requires at least "two increases and one decrease" to accurately determine the pressure. During the low-speed operation and combined pressing state of the flexographic printing machine, first manually adjust the pressure between the mesh roller and the plate cylinder. After the mesh roller is pressurized, observe whether the ink is evenly and fully applied on the plate surface; then adjust the pressure between the plate cylinder and the center impression cylinder. After the plate cylinder is pressurized, observe the substrate until a complete graphic impression is formed on it; next, reduce the pressure on the mesh roller. When the graphic impression on the substrate disappears, slowly pressurize the mesh roller again until a complete and uniform graphic impression appears on the substrate and stop the pressure application; then slowly reduce the pressure on the plate cylinder and pressurize it again. If the graphic impression appears almost simultaneously along the axial direction on the substrate and the plate surface has a complete graphic, immediately stop the pressure application. Thus, the pressure adjustment is completed. By following this method, the light pressure printing state can be ensured.