What Are The Printing Characteristics And Process Difficulties Of Film Self-adhesive Materials? One Article To Figure It Out!

Film self-adhesive material is a kind of polymer, its surface has no absorption to the printing ink, printing ink on the surface of the film self-adhesive material drying methods include: volatilization, conjunctiva, cross-linking, curing, basically no penetration mode, compared with paper self-adhesive materials are very different. The surface energy of the film self-adhesive material is low, and it must be pretreated before printing to meet the wetting and leveling requirements of the printing ink, otherwise there will be problems such as poor adhesion fastness of the ink.In addition to the drying problem, because the film self-adhesive material is a polymer, the free electrons on the surface are very unstable, and in a dry environment, friction will generate a lot of static electricity. Static electricity will affect the printing and processing of materials, so controlling static electricity, improving the environment, and increasing the corresponding configuration of equipment are the printing film self-adhesive materials must be paid attention to, otherwise the quality of the printed matter cannot be guaranteed. In addition, the film self-adhesive material is sensitive to temperature changes and has large heat deformation, so the drying (curing) temperature, printing speed, film thickness, tension setting, etc. in the printing process must pay attention to matching, otherwise it is very easy to have problems.

Types and characteristics of commonly used film materials

The physical characteristics of commonly used film materials are detailed in Table 1, where the surface tension is the surface tension value before material treatment, it can be seen that the surface tension of the material after leaving the factory is basically lower than 38mN/m, and 38mN/m is the lower limit to ensure the normal printing of ink, so these film materials must be treated accordingly before they can be printed normally.

In order to ensure that the ink is well fixed on the surface of the film material, we need to understand the surface tension requirements of the ink on the substrate material, especially the film material, and pay special attention. Table 2 lists the requirements of different types of flexographic printing inks for different types of film materials before printing. Comparing Table 1 and Table 2, we find that untreated film materials basically do not meet the requirements, so the surface treatment of film materials is very important for printing.

Surface treatment of thin film materials
The surface treatment of film materials is divided into two methods: corona treatment and surface coating, the purpose is to increase the energy of the surface of the material or change the surface characteristics of the material, so that the ink can be normally wetted, leveled, dry, and has a certain firmness.

Corona treatment TECHNOLOGICAL
Through high-voltage discharge, the surface energy of the film is increased, the surface tension of the material is improved, and the surface of the material is coarsed appropriately (the comparison chart before and after treatment is shown in Figure 1) to achieve the purpose of suitable printing. Figure 2 shows a schematic diagram of a common corona treatment device.

Corona processing is divided into two types: the first is online processing, which is carried out on the printing press; The second is done by the supplier and supplied to the printing company.Usually corona treatment is applied to soft material surfaces, such as PE, PVC; For materials with a hard surface, such as PET and BOPP, the corona effect is not good.

Surface coating TECHNOLOGICAL
Before making self-adhesive materials, the film material is evenly coated with a special coating on its surface to improve the surface wetting ability, so that the ink and the coating can be firmly combined during printing, so as to achieve the purpose of the ink not falling off after printing on its surface. The treatment method of surface coating is mainly applied to the surface of hard materials, such as PET, BOPP, etc. The schematic diagram of the structure of the film material after surface coating is shown in Figure3.

The surface coated material generally has the following characteristics. Can be printed directly, no corona is required; Can be online corona, does not affect the printing effect, and sometimes improves the printing quality; Surface tension measurement is meaningless and subject to on-site verification.