The principle of using UV ink
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UV ink is an environmentally friendly ink that has developed rapidly in recent years. It quickly captures the market with instant curing (drying), free of volatile solvents, and simple and convenient application. UV inks include UV matte, UV ice, UV foam, UV. Special packaging inks such as wrinkles, UV embossing, UV refraction, UV gems, UV-light fixing inks, UV varnishes, etc. On the surface of the substrate with metallic specular gloss, the UV ink is printed on the surface by screen printing process, and after being treated by ultraviolet drying equipment, it produces a unique visual effect, which is elegant, solemn and luxurious. The products are mainly used in high-end, exquisite and unique cigarette, wine, cosmetics, health care products, food, medicine and other packaging and printing.
First, UV ink
1. Composition
The UV ink is an ink that undergoes cross-linking polymerization under the irradiation of UV light and instantly solidifies into a film. It is mainly composed of a photopolymerizable prepolymer, a photosensitive monomer, a photopolymerization initiator, an organic pigment, and an additive. Among them, the photopolymerization initiator is the most important component of the entire UV ink and is the beginning of photopolymerization.
2. Application characteristics of UV ink:
(1) Instant curing, high production efficiency;
(2) It does not contain volatile solvents; it will not cause solvent erosion to damage printed matter; it will not pollute the human body and the environment;
(3) The ink will not be netted, so the best quality lines can be printed with very fine meshes;
(4) The ink concentration is stable, and there is no unevenness due to the difference in concentration;
(5) The ink will not dry out, no smell of solvent;
(6) The speed of light curing is extremely fast, the volume of UV equipment is small, and the space occupied by the factory is small;
(7) The heat emitted by the UV lamp will not cause damage to those printed materials that are afraid of heat;
(8) Transparent or translucent inks with good hardening speed and color effect.
3. Curing mechanism
UV inks are selectively absorbed by UV light, and its drying is affected by the total energy of the UV source and the distribution of light energy at different wavelengths.
Under the irradiation of UV light, the photopolymerization initiator in the UV ink absorbs photons of a certain wavelength and is excited to an excited state to form a radical or an ion. Then, the polymer such as the polymerizable prepolymer and the photosensitive monomer is brought into an excited state by the transfer of the intermolecular energy to generate a charge transfer complex. These complexes are continuously crosslinked and polymerized to form a film.
Second, UV light source
1. Construction
A UV light source is a device that emits UV light in a UV curing system. It usually consists of components such as light boxes, tubes, mirrors, power supplies, controllers, and cooling devices. According to the different substances in the lamp, it can be divided into metal halide lamps, high pressure mercury lamps and odorless lamps. Its performance parameters are: arc length, characteristic spectrum, power, operating voltage, operating current and average life.
2. Spectral characteristics
Although the UV light source emits the main UV light, it is not a single wavelength of light, but a light in a band. Different UV sources have different ranges of emitted light, and the distribution of spectral energy in the band is also different.
The UV source radiates light in one band, and the energy distribution of the light at each wavelength is different. Among them, the energy distribution of light having a wavelength of 300 to 310 nm and 360 to 390 nm is preferable.
Third, the use of UV inks
1, screen selection
The choice of the screen number of the UV ink in the printing should be determined according to the fineness of the printed pattern, the printing effect, and the required printing quality. In general, the number of screens for printing UV light-fixing inks and UV coatings is 350 mesh or more.
2, ink use
The factors such as screen tension, printing pressure, squeegee hardness, and squeegee angle of UV ink will affect the printing quality, and effective technical control will improve the printing effect.
Most of the UV ink thinners are special thinners. When purchasing UV inks, customers should consult the supplier about the use performance and usage methods, reduce the defective rate in use and avoid losses caused by improper use.
3, matters needing attention
(1) High-power ultraviolet rays can cause damage if they are in direct contact with the eyes or skin. Operators must be equipped with glasses or other protective measures.
(2) UV ink storage temperature should be above 5 °C, the ink will be due to light or temperature Change, so avoid direct light.
(3) UV inks do not contain explosive or evaporative solvents. They are caused by ultraviolet light and cause a reaction. Therefore, they cannot be dried in the screen before being exposed to light.
(4) Using a metal halide lamp, the irradiation distance is about 10 cm, and one light passes.
Fourth, the matching of UV ink and UV light source
In summary, the matching of the UV ink with the UV light source is such that the photon selected by the photopolymerization initiator in the UV ink used is the portion of the UV source that has the highest energy distribution. The printing company's technical department should obtain technical information about the spectral characteristics of the UV source from its equipment supplier, and then select the UV ink from the ink supplier's response curve that matches the UV source spectrum, so that it can be better solved. The matching of the two also provides a prerequisite for considering other factors affecting drying.