Apr.2024 17
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Problem Set of Using Uv Curing Ink (1)

1. When the uv ink is cured and transformed

There is a that when the ink surface is exposed to too much ultraviolet radiation, it will become harder and harder. When people print another ink on this hardened ink film and dry it again, the adhesion between the inking and inking will become very poor.
Another holds that curing transformation will cause photo-oxidation of ink surface. The occurrence of light oxidation will destroy the chemical bonds on the surface of the ink film. If the molecular bonds on the surface of the ink film are degraded or damaged, the adhesion between the ink film and another ink layer will be reduced. The ink film during curing is not only inflexible, but also prone to surface oxidation.

2. Why does the polycarbonate (pc) film turn yellow when I use uv ink?

Polycarbonate is sensitive to ultraviolet light with wavelength less than 320 nm. The yellowing of the film surface is caused by molecular chain breakage caused by photooxidation. The molecular bonds of plastics absorb ultraviolet energy and generate free radicals. These free radicals react with oxygen in the air, which will change the appearance and physical properties of plastics.

3. How to avoid or eliminate yellowing of polycarbonate surface?

If uv ink is used to print on polycarbonate film, the yellowing of its surface can be reduced, but it cannot be completely eliminated. Curing the bulb with iron or gallium can effectively reduce this yellowing. These bulbs can reduce the emission of short-wavelength ultraviolet rays to avoid damaging polycarbonate. In addition, proper curing of each ink color is also helpful to reduce the exposure time of the substrate under ultraviolet light and the possibility of discoloration of polycarbonate film.

4. What is the difference between millijoule and milliwatt?

The total energy irradiated to a specific surface in a certain period of time is usually expressed in joules/cm2 or millijoules/cm2. It is mainly related to the speed of conveyor belt, the power, quantity, service life and state of curing lamps, and the shape and state of reflector in curing system.
However, the power of ultraviolet energy radiated to a specific surface is mainly expressed in watts/cm2 or millijoules/cm2. The higher the ultraviolet energy radiated to the substrate surface, the more energy it penetrates into the ink film. Whether it is milliwatt or millifocal, it is necessary to measure the wavelength sensitivity of radiometer to meet certain requirements.

5. If the colors don't overlap, should I worry about over curing?

When the ink film surface absorbs too much ultraviolet light, the problem of excessive curing will occur. If we can't find a solution to this problem in time, the surface of the ink film will become harder and harder. Of course, as long as we don't overprint in color, we don't have to pay too much attention to this problem. However, we need to consider another important factor, that is, printing film or substrate. Ultraviolet rays can affect the surface of most substrates and some plastics sensitive to ultraviolet rays with specific wavelengths. This sensitivity to specific wavelengths, coupled with oxygen in the air, may lead to the degradation of the plastic surface. The molecular bonds on the surface of the substrate may be destroyed, and the adhesion between UV ink and the substrate will fail. The degradation of the surface function of the substrate is a gradual process, which is directly related to the received ultraviolet energy.

6. Is 6.UV ink green ink? Why?

Compared with solvent-based inks, UV inks are indeed more environmentally friendly. UV curing ink can be 100% solid, which means that all components in the ink will become the final ink film. As the ink film dries, solvent-based ink will discharge the solvent into the atmosphere. Because solvents are volatile organic compounds, they will do harm to the environment.

7. What is the measurement unit of density data displayed on the densitometer?

Optical density is unitless. The densitometer measures the amount of light reflected or transmitted from the printing surface. The photoelectric eye connected to the densitometer can convert the percentage of reflected or transmitted light into a density value.

8. What factors will affect the density?

In screen printing, the variables that affect the density mainly include the thickness, color, size and quantity of pigment particles and the color of the substrate. The optical density is mainly determined by the opacity and thickness of the ink film, and the opacity is influenced by the size and quantity of pigment particles and their light absorption and scattering characteristics.

9. How does flame treatment work?

Essentially, plastics are non-porous and have an inert surface (low surface energy). Flame treatment is a method to pretreat plastics, which can improve the dyne level of substrate surface. Besides the field of plastic bottle printing, this method is also widely used in automobile and film processing industries. Flame treatment can not only improve surface energy, but also eliminate surface pollution. Flame treatment involves a series of complex physical and chemical reactions. The physical mechanism of flame treatment is as follows: high-temperature flame transfers energy to oil stains and impurities on the surface of substrate, which are heated and evaporated to play a cleaning role; The chemical mechanism is that the flame contains a large number of ions, which are highly oxidizing and react 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, and its surface energy is improved, thereby improving its ability to absorb liquid.

10. What is corona treatment?

Corona discharge is another method to improve dyne level. By applying high pressure to the media roller, the surrounding air can be ionized, and when the substrate passes through the ionization region, the molecular bonds on the surface of the material will be broken. This method is usually used for rotary printing of film materials.

11. How many lamps do I need to solidify?

Although the types of ink systems and substrates are different, generally speaking, one lamp curing system is enough. Of course, if you have enough budget, you can also choose a double-lamp curing unit to increase the curing speed. The reason why two curing lamps are better than one is that the dual lamp system can provide more energy for the substrate at the same transmission speed and parameter setting. A key problem that we need to consider is whether the curing unit is enough to dry the ink printed at normal speed.

12. How does the viscosity of ink affect printability?

Most inks are thixotropic, which means that their viscosity will change with the change of shear force, time and temperature. In addition, the higher the shear rate, the lower the viscosity of the ink; The higher the temperature, the lower the age of the ink. Generally speaking, the screen printing ink can achieve good results on the printing press, but according to the setting of the printing press and prepress adjustment, occasionally there will be problems of printability. In addition, the viscosity of the ink on the printer is different from that 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 viscous, users can also add diluents. In addition, you can contact the ink supplier for product information.

13. 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 or not) is put into the mold, and the molten plastic supports the part when it is molded. The labels used in the former are produced by different printing technologies, such as gravure printing, offset printing, flexo printing or screen printing. These labels are usually printed only on the upper surface of the material, while the unprinted side is connected to the injection mold. Interior decoration is mostly used to produce durable parts, usually printed on the second side of transparent film. Interior decoration is usually printed by screen printer, and the film and UV ink used must be compatible with the injection mold.