In the inkjet printing process, the ink on the inkjet head needs to be kept in a certain state, and it can be quickly solidified to form ink dots after being attached to the substrate. Compared with other printing methods that use toner or high-viscosity ink, the ink used is greatly restricted. Inkjet printing belongs to non-contact pressureless printing. Although it can print on any substrate, in order to allow UV ink to be ejected from the nozzle smoothly and achieve the printing effect, the ink must be mechanically, chemically, and mechanically Visibility and persistence meet certain requirements, which are specifically manifested in the following aspects.
(1) Viscosity
Inkjet inks maintain their low viscosity. Generally speaking, the appropriate viscosity is usually 10-20mPa·s, but this can only be achieved by raising the operating temperature of the inkjet equipment to 40-45°C. Since the curing components of UV inks are potentially volatile and irritating, the temperature is better controlled below 65°C, and some of them cannot be sprayed at a temperature higher than 50°C.
(2) Surface tension
The quality of ink drop formation is affected by surface tension. If the surface tension is too large, the ink is not easy to form small droplets, and may have a longer break length, or break into "tail-like" droplets. If the surface tension is too small, the droplet will be unstable, and even form a "satellite" shape, resulting in sputtering spots, which will affect the graphic effect.
(3) Curing speed
Cure speed is an important factor to consider in industrial inkjet applications. When the speed of the inkjet system reaches 300-600 inches per minute, UV curing can show strong competitiveness. In order to cure quickly, UV inks need to use high-functionality curing materials, but due to low viscosity requirements, a large amount of low-functionality monomers are used, which affects the curing speed to a certain extent.
The above three points influence each other and restrict each other. Inks that can achieve low viscosity without the use of diluting solvents are better, but to obtain high-quality images, photopolymerization needs to be completed immediately after the ink falls on the substrate, otherwise the quality will be affected by the deformation of the ink dots. The surface tension of UV ink can keep the shape of the attached ink drop for a long time, but it is difficult to maintain a certain surface tension between various substrates and ink, but the curing speed of the ink can be improved by using UV lamp irradiation.
