20 classical problem of UV ink - Part 3

Previous: 20 classical problem of UV ink - Part 2

12. What is the dyne level?

    Dyne/cm is a unit used to measure surface tension. This tension is caused by the intermolecular attraction of a particular liquid (surface tension) or solid (surface energy). In order to facilitate practical use, we usually call this parameter the dyne level.

    The dyne level or surface energy of a particular substrate represents its wettability and ink adhesion. Surface energy is a physical property of a substance. Many films and substrates used in printing have low printing levels, such as 31 dyne/cm polyethylene and 29 dyne/cm polypropylene, etc., so they need special treatment.

    Proper treatment can increase the dyne level of certain substrates, but this is only temporary. When you are ready to print, there are other factors that will affect the dyne level of the substrate, such as: processing time and number of times, storage conditions, environmental humidity and dust. Since the dyne level will change over time, most printing houses believe that it is necessary to process or reprocess these films before printing.

13. How is the flame treatment performed?

    In essence, plastics are non-porous and have an inert surface (low surface energy). Flame treatment is a method of pretreatment of plastics, which can improve the dyne level of the substrate surface. In addition to the field of plastic bottle printing, this method is also widely used in the automotive and film processing industries. Flame treatment can not only increase surface energy, but also eliminate surface contamination.

    Flame treatment involves a series of complex physical and chemical reactions. The physical mechanism of flame treatment lies in the fact that the high-temperature flame transfers energy to the oil and impurities on the surface of the substrate, causing it to evaporate when heated, and play a cleaning effect; and its chemical mechanism lies in: the flame contains a large number of ions, which has a strong Oxidation: It will oxidize with the surface of the object to be treated at high temperature, so that a layer of charged polar functional groups is formed on the surface of the object to be treated, which increases its surface energy and improves its ability to absorb liquids.

14. What is corona treatment?

    Corona discharge is another way to increase dyne levels. By applying high voltage to the media roller, the surrounding air can be ionized. When the substrate passes through this ionization area, the molecular bonds on the surface of the material will be broken. This method is usually used in the web printing of film materials.

15. How does plasticizer affect the adhesion of ink on PVC?

    Plasticizer is a chemical that can make printed materials softer and more flexible, and its use in PVC (polyvinyl chloride) is very common. The type and amount of plasticizer added to flexible PVC or other plastics mainly depends on people's requirements for the mechanical, heat dissipation and electrical properties of the printed material.

    The plasticizer may migrate to the surface of the substrate and affect the adhesion of the ink. The plasticizer remaining on the surface of the substrate is a kind of pollution, which will reduce the surface energy of the substrate. The more pollution on the surface, the lower the surface energy, and the lower its adhesion to the ink. To avoid this, people can clean the substrate with a mild cleaning solvent before printing to improve their printability.

16. How many lamps do I need for curing?

    Although the types of ink systems and substrates are different, in general, a light curing system is sufficient. Of course, if you have enough budget, you can also choose a dual-lamp curing unit to increase the curing speed. The reason why two curing lamps are better than one is because the dual lamp system can provide more energy for the substrate under the same transmission speed and parameter settings. One issue we need to consider is whether the curing unit is sufficient to dry the ink printed at normal speed.

17. How does the viscosity of the ink affect the printability?

    Most inks are thixotropic, which means that their viscosity changes with changes in shear, time, and temperature. In addition, the higher the shear rate, the lower the viscosity of the ink; the higher the ambient temperature, the lower the annual ink. Screen printing inks can generally achieve good results on the printing press, but depending on the settings of the printing press and pre-press adjustments, printing suitability problems may occasionally occur. And the viscosity of the ink on the printing press is different from the viscosity of the ink in the ink cartridge.

    Ink manufacturers will set a specific viscosity range for their products. For inks that are too thin or too low in viscosity, users can also add thickeners appropriately; for inks that are too thick or too high in viscosity, users can also add diluents. In addition, you can also contact the ink supplier and ask for product information.

18. What are the factors that affect the stability or shelf life of UV inks?

    An important factor affecting the stability of ink is the storage of ink. UV inks are usually stored in plastic ink cartridges instead of metal ink cartridges, because plastic containers have a certain degree of oxygen permeability, which can ensure that there is a certain air gap between the ink surface and the container lid. This air gap—especially the oxygen in the air—helps minimize the premature crosslinking of the ink. In addition to packaging, the temperature of ink containers also plays a vital role in maintaining their stability. High temperature will cause premature reaction and cross-linking of the ink.

    The adjustment of the original ink formula may also affect the stability of the ink on the shelf. Additives, especially catalysts and photoinitiators, may shorten the shelf life of inks.

19. What is the difference between in-mold labeling (IML) and in-mold decoration (IMD)?

    The basic meaning of in-mold labeling and in-mold decoration is the same, that is, the label or decorative film (prefabricated, not prefabricated) is placed in the mold, and the molten plastic supports it when the part is formed. The labels used in the former are produced using different printing techniques, such as gravure, offset, flexo or screen printing. These labels are usually only printed on the top surface of the material, and the unprinted side is connected to the injection mold.

    In-mold decoration is mostly used to produce durable parts, and it is usually printed on the second surface of the transparent film. In-mold decoration is generally printed by a screen printer, and the film and UV ink used in it must be compatible with the injection mold.

20. If a nitrogen curing unit is used to cure color UV inks, what will happen?

    The curing system that uses nitrogen to cure printed matter has appeared as early as ten years ago. These systems are mainly used in the curing process of textiles and membrane switches. The reason why people use nitrogen to replace oxygen is mainly because oxygen inhibits the curing of ink. However, since the light from the bulb in this type of system is very limited, the curing effect on pigments or colored inks is not very good.