Comprehensive analysis of UV printing
UV ink is an environmentally friendly ink that has developed rapidly in recent years. It has quickly occupied the market with its instant curing (drying), no volatile solvents, and simple and convenient application. UV ink includes UV frosting, UV ice flowers, UV foaming, UV wrinkles, UV embossing, UV refraction, UV gems, UV light-fixing inks, UV varnishes, and other special packaging inks.
One. UV ink
1. Composition
UV ink is an ink that undergoes cross-linking polymerization reaction under UV light and instantly cures into a film. It is mainly composed of photopolymer prepolymers, photosensitive monomers, photopolymerization initiators, organic pigments and additives. Among them, the photopolymerization initiator is the most important component of the entire UV ink and is the beginning of the photopolymerization reaction.
2. Application characteristics of UV ink
(1) Instant curing, high production efficiency;
(2) Contains no volatile solvents; no solvent erosion and damage to printed materials; no pollution to the human body and the environment;
(3) The ink will not clog the screen, so the best quality lines can be printed with a very fine mesh;
(4) The ink concentration is stable, and there will be no unevenness due to different concentrations, such as too thick or too thin;
(5) The ink will not dry out, and there is no foul smell of solvent;
(6) The light curing speed is extremely fast, the UV equipment is small in size, and occupies less factory space;
(7) The heat emitted by the UV lamp will not damage those printed materials that are afraid of heat;
3. Curing principle
UV ink selectively absorbs UV light, and its drying is affected by the total energy of the UV light source and the energy distribution of light of different wavelengths. Under the irradiation of UV light, the photopolymerization initiator in the UV ink absorbs photons of a certain wavelength, excites to an excited state, and forms free radicals or ions. Then, through the transfer of intermolecular energy, polymerizable prepolymers and photosensitive monomers are turned into excited states, generating charge transfer complexes. These complexes are continuously cross-linked and polymerized to form films.
Two. UV light source
1. Structure
The UV light source is a device that emits UV light in the UV curing system. It is usually composed of components such as a light box, a lamp tube, a reflector, a power supply, a controller, and a cooling device. According to the different materials filled in the lamp tube, it can be divided into metal halide lamps, high-pressure mercury lamps, and odorless lamps. Its performance parameters mainly include: arc length, characteristic spectrum, power, working voltage, working 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 light within a band. Different UV light sources have different wavelength ranges of emitted light, and the distribution of spectral energy within the band is also different. The UV light source radiates light within a band, and the energy distribution of each wavelength of light is different. Among them, the energy distribution of light with a wavelength of 300-310nm and 360-390nm is better.
Three. Use of UV ink
1. Screen selection
The selection of screen mesh for UV ink printing should be based on the fineness of the printed pattern, printing effect, and required printing quality. Generally speaking, the screen mesh for printing UV light-fixing ink and UV varnish is above 350 mesh.
2. Use of ink
The screen tension, printing pressure, scraper hardness, scraper angle and other factors of UV ink in use will affect the printing quality. Effective technical control will improve the printing effect. Most of the diluents for UV ink are special diluents. When purchasing UV ink, users should consult the supplier about the performance and usage methods to reduce the defective rate during use and avoid losses caused by improper use.
3. Precautions
(1) If high-power ultraviolet rays come into direct contact with the eyes or skin, they will cause damage to them. Operators must wear glasses or take other protective measures.
(2) The storage temperature of UV ink should be above 5°C. The ink will change due to light or temperature, so avoid direct light.
(3) UV ink does not contain explosive or evaporative solvents. Since it will react when exposed to ultraviolet light, it cannot be dried in the screen before being exposed to light.
(4) Use a metal halide lamp with an irradiation distance of about 10 cm and one light pass.
Four. Matching of UV ink and UV light source
In summary, the matching of UV ink and UV light source is to make the photopolymerization initiator in the UV ink selectively absorb the light quantum with the highest energy distribution in the UV light source spectrum. Solving the matching of UV ink and UV light source is conducive to accelerating the drying speed of ink, improving energy utilization, and reducing the production cost of enterprises.