UV curing (photocuring) refers to the use of UV light to excite monomers in the ink to polymerize into a polymer. It is a technique for curing ink droplets. In recent years, with the continuous improvement of digital imaging technology and the rapid promotion of the application range, it has promoted the application of UV curing technology in the field of printing, and has achieved good results. Because UV curing materials have fast curing, high efficiency, and low pollution , Energy saving and other characteristics, so that it has rapidly developed into a new type of digital imaging materials.
In order to meet the needs of the modern printing industry, manufacturers use the advantages of inkjet technology and UV curing technology to combine inkjet printheads, printing devices, UV light curing systems and UV light curing inks to form UV light curing inkjets Printing Technology. The emergence of UV curing technology has greatly improved the printing speed of UV inkjet printing. UV inkjet printing is being adopted by more and more printers. It can be said that UV curing technology has saved inkjet printing and made it It can be applied to wider and newer markets and fields.
UV curing device
1.UV lamp device
The important part of the UV curing device is the UV lamp device. The lamp device must meet the ideal design requirements. The specific requirements are as follows.
1) Miniaturized design and compact equipment design. The UV lamp installed on the small inkjet printer must be of a structure that does not occupy volume and is easy to install and remove. The auxiliary equipment such as the cooling and blowing equipment for the lamp should also be small, the air volume is small, and the ink is not caused when ejected from the print head influences.
2) It can be installed in the office and used as a copier.
3) Refrigerated air. In order to keep the surface temperature of the light-emitting lamp valve constant, the surface of the UV system lamp valve must be cooled, and air cooling is often used.
4) Images can be formed on any substrate: for substrates that have no heat resistance, or substrates that wrinkle due to the rapid evaporation of moisture in the substrate due to heat, a low-heat UV lamp device should be used.
5) Stable images can be obtained without skilled skills.
6) Luminous output stability and long life. The UV curing reaction is affected by the irradiance, luminescence spectrum, and temperature during the curing reaction. Irradiation using strong light and ensuring the stability of the luminescence spectrum during use time are very important factors. The key factors to ensure the illuminance of illumination and the stability of the luminous spectrum are the luminous light valve itself, the optical system, and the stability of the power supply that provides energy to the luminous light valve.
7) High illuminance output and spectrum matching. In order to obtain a high-quality output image, the high-illuminance output from the UV lamp is required to match the spectral band required for curing. This is because the irradiation of high-illumination UV lamps has advantages. According to most studies in Europe and the United States, high-illumination UV lamps have a certain effect on the prevention of oxygen obstruction and are beneficial to increasing the curing speed.
2. UV curing process
The process of UV curing is as follows: 1) First, the UV ink is sprayed onto the surface of the substrate: pigment particles, photoinitiator, monomer and prepolymer; 2) Then, the UV light stimulates the photoinitiator to become free radicals, and the single The chemical reaction between the polymer and the prepolymer; 3) The monomer and the prepolymer continue to react to form a photosensitive polymer; 4) Finally, the UV ink is dry and the pigment particles are attached to the surface of the substrate.
UV inkjet ink
Although UV-curable inks have been used in the screen printing industry since the 1980s, they are now commonly used in digital printing, especially in inkjet printing. Due to the advancement of inkjet technology and the improvement of printing accuracy, the UV inkjet printer is designed and manufactured with an appropriate UV light source on the inkjet printer, and the continuous development of new raw materials for the preparation of UV ink finally makes UV ink enter Inkjet printing field.
UV inkjet ink is composed of photoactive monomer, photoactive prepolymer, photoinitiator, colorant and other auxiliary agents. It has three major characteristics, that is, energy-saving drying, wide printing suitability for the substrate, and high-speed curing can shorten the time passed to the post-process. UV inkjet ink must have strict performance requirements before it can be ejected from the nozzle. Among all the properties, viscosity and surface tension are the two most important aspects.
1. Viscosity. The biggest formulation problem of UV inkjet ink is to maintain a low viscosity, usually the viscosity is between 10-20mPa · s, which mainly depends on raising the operating temperature of the inkjet equipment to about 40 ~ 45 ℃.
2. Surface tension. The quality of UV inkjet ink droplets is mainly affected by surface tension. If the surface tension is too high, the ink is not easy to form droplets and may have a long break; the surface tension is too low will cause the droplets to become unstable, generate spattering points, and affect the final pattern. The surface tension of the ink should meet 0.2 × 10-3 ～ 0.5 × 10-3N / cm, the more ideal range is between 0.22 × 10-3 ～ 0.4 × 10-3N / cm.
3. Wettability of pigments. The wettability of the pigment to the substrate is the main factor that affects the durability of outdoor applications. Therefore, the difficulty of manufacturing UV jet inks is to select a suitable pigment and make it wet well in a low viscosity solvent.
4. Durability. Wide-format inkjet technology is mainly used for outdoor advertising banners and slogans, so the durability is better. Usually, fat chains are introduced into the ink composition to meet the requirements.
In addition, UV-curable inkjet inks must have a certain curing speed, flexibility, and good adhesion to inkjet substrates and film materials used for wide-format printing. Its most important instant curing property makes no components of the UV inkjet ink penetrate the surface of the substrate after being ejected from the nozzle, so it will not affect the surface performance of the substrate.
The biggest advantage that UV curable ink brings to inkjet equipment is that it will not be cured in the nozzle, so it reduces the trouble of cleaning the nozzle to remove insoluble components. Due to the shortened maintenance time of inkjet equipment, the use of UV inkjet printing can achieve greater production efficiency.
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