Type of UV ink
There are mainly three kinds of UV inks for ink jet printing, namely water-based ink, hot-melt ink and low-viscosity ink.
1. Water-based UV jet ink
The water-based UV-jet ink uses water as a solvent to reduce the viscosity of the ink, and its components are mainly UV curable resin emulsions. However, this technique has two disadvantages. First, the ink jet system requires the moisture in the ink to evaporate before the UV light source is irradiated. The moisture in the ink is an annoying problem. Only the rapid removal of moisture can prevent printing defects such as dot gain and moisture penetration into the substrate. If the moisture is not removed in time, the ink cannot adhere well to the substrate. , Which affects the quality of printed matter; Second, there are still some technical difficulties in the dispersion of photoinitiators.
2. Hot melt UV ink
The use of hot-melt UV ink is mainly dependent on the formation of large droplets of viscous ink droplets. Using such ink jets can bring strong rub resistance and burst resistance to flexible substrate prints. The difficulty in production is how to find the balance between the two opposites of ink stability and low viscosity at high temperatures.
3. Low viscosity UV ink jet
How to make traditional UV ink directly applied to inkjet printing technology? The key problem is to try to make UV inks have good printing performance, namely low VOC, excellent curing performance, low viscosity and so on. The biggest difficulty is how to obtain a lower viscosity. For this reason, researchers have developed a UV-curing resin with a lower viscosity, which provides ink manufacturers with new options, but the practical application of this research result is still very good. difficult.
Low viscosity UV jet ink is a type of jet ink modified by conventional UV inks. Low-viscosity UV-jet ink is developed specifically for intermittent inkjet heads, while high-viscosity inks are often printed with industrial-type inkjet heads, such as those produced by Spectra.
The advantage of low-viscosity UV-jet ink is that it introduces UV-jet ink into the wide-format inkjet printing market, which can be matched with the ultra-wide-format inkjet and flat-panel inkjet markets. Ordinary UV inks have higher viscosity. They are only suitable for industrial printing, ultra-wide-format inkjet, and flat-panel inkjet printing markets. The emergence of low-viscosity UV-jet inks has opened up a broad field of development for wide-format inkjet printing. . In addition, there are still some application fields in the printing market that require researchers to further improve the UV ink.
UV inkjet ink challenge
Viscosity
The biggest problem with formulating ink jets is to keep their viscosity low. In general, the viscosity of the ink is usually between 10-20 cps, but this is mainly achieved by raising the operating temperature of the ink-jet device to about 40-45°C. In foreign countries, it is generally required that the thermal foaming ink jet must be maintained at a viscosity of 3 to 5 cps at 25° C., and the piezoelectric ink jet has a viscosity of 3 to 30 cps at 25° C. Only maintaining such a relatively low viscosity can ensure that the ink components can be ejected from the showerhead. Due to the potential volatility and irritation of the cured component, the ink is preferably not above 65[deg.]C, and some are ejected at no more than 50[deg.]C.
2. Pigment wetting
Another factor that affects the performance of UV jet inks is the problem of pigment wetting, which is also a direct factor that affects the durability of the print surface. Therefore, the difficulty in manufacturing UV-jet inks lies in the selection of suitable pigments and their good wetting in low-viscosity solvents.
3. Surface durability
Wide-format and ultra-wide-format inkjet technology is commonly used in the production of advertising banners and slogans. Banners generally do not need to be posted for many years, and usually only need to maintain the printed image for a few months of surface durability. For this reason, manufacturers often introduce fatty chains into the composition of the ink.
4. Surface tension
The formation of ink droplets is mainly affected by surface tension. Too much surface tension causes the ink to be less prone to droplet formation and may exhibit longer break lengths or break off into "tailed" droplets. Too low a surface tension will cause the droplets to become unstable and even form a "satellite" shape, creating a sputtering spot and affecting the pattern. The ink satisfies the following surface tension range: (2.0 to 5.0) 10-2 N/m, more preferably (2.2 to 4.0) 10-2 N/m.
5. Curing speed
The curing speed of the ink is very important for the label industry. Label printers typically operate at speeds of 300-600 ft/min. For such fast printing speeds, UV inks can exhibit excellent printing performance. To achieve this rapid cure rate, high-functionality cured materials are used in the formulation. Wide-format inkjet printers typically print at less than 50 feet per minute, so the cure speed requirements are not very high. However, the need for low viscosity ink jets means that low-viscosity, low-functionality cured materials are used to make the ink, but this will inevitably reduce the curing speed.
6. Toughness
For most wide-format advertisements printed on plastic films, the toughness of the ink is a crucial issue, and the use of mono-functional monomers can increase the elasticity of the UV-jet ink.
7. Adhesion
The adhesion of UV-curable inks to substrates is also a potential influence on wide-format inkjet technology.
UV inkjet printing is still a relatively new concept in China, but it has given people an absolute advantage to see its bright future. However, the above problems have caused some resistance to its development and need to be solved gradually. In addition, raw materials and curing equipment are expensive and irritating. These problems are also the development resistance of UV inks. It is believed that these problems will motivate researchers to develop the progress of UV inks. UV inks will surely benefit its environmental protection and production. Instead of other ink jets. With the ever-increasing demands of the world's environmental protection and the continuous advancement of digital technologies, UV inks will surely gain greater development.