Ink with polyurethane as the main resin binder is called polyurethane ink. The molecular structures of different types of polyurethane resins vary, and thus the types of polyurethane inks prepared from them also differ. At present, polyurethane inks can be classified into several types based on their resin structure composition, solvents and curing principles, such as one-component volatile polyurethane inks, two-component reactive polyurethane inks, UV-curable polyurethane inks and water-based polyurethane inks.
1.One-component volatile polyurethane ink
Single-component volatile polyurethane ink works by the evaporation of organic solvents in the ink, causing the resin and other solid components in the ink to form a film and adhere to the surface of the printed film. This type of ink features simple application, stable performance and good reproducibility. It is suitable for various printing requirements and is mainly used in plastic packaging printing and other aspects.
2. Two-component reactive polyurethane ink
Two-component ink is also known as chemically reactive ink. This type of ink is composed of two components: ink (main agent) and curing agent. During printing, they are mixed evenly in a certain proportion. After printing and curing, the
Polyurethane Resin, curing agent and printing substrate undergo chemical cross-linking. This type of polyurethane ink is more complex to operate compared to single-component ink and has a limited usage time. However, it can enhance the adhesion and high-temperature resistance of the ink and is mainly suitable for printing inks in packaging with higher requirements. It is worth mentioning that some one-component polyurethane inks can also be added with curing agents to become two-component polyurethane inks.
3. Uv-curable polyurethane ink
The reaction mechanism of UV-curable ink is that under ultraviolet light radiation, the active oligomers in the ink cure and form a film through free radical polymerization, achieving the purpose of film formation on the printing substrate. This type of ink contains no solvents and features safety and no pollution. It is an environmentally friendly polyurethane ink with great development prospects. At present, photo-curable polyurethane inks have disadvantages such as complex ink formulas and high costs.
4. Water-based polyurethane ink
Water-based polyurethane ink uses water as the dispersion medium. Among them, the polyurethane binder is insoluble in water but uniformly dispersed in water in the form of particles. Due to the fact that water-based polyurethane ink does not contain volatile organic solvents and has the characteristics of being non-flammable, non-toxic, odorless, energy-saving and environmentally friendly, it has attracted increasing attention in recent years and has broad prospects for development. However, water-based polyurethane ink uses water as the solvent, is not volatile, has high requirements for printing equipment and affects production efficiency. Therefore, in order to balance environmental protection and actual production needs, people have developed alcohol-water-based polyurethane ink, which has now been widely applied in printing.
As people pay more and more attention to the safety and environmental friendliness of the packaging field, the research direction of printing inks is gradually expanding towards being green, safe and pollution-free. At present, in China, the printing inks for plastic flexible packaging are mainly ester-soluble and alcohol-soluble inks. Although there has been a significant improvement in safety compared to the previous inks containing benzene and ketone, they are still subject to restrictions on VOCs emissions. Due to the diversity and safety in molecular structure and performance, the application of polyurethane resin in ink has attracted increasing attention. Currently, some related enterprises have launched alcohol-water polyurethane ink and water-based polyurethane ink. With the continuous strengthening of research on polyurethane resin, polyurethane ink will also become increasingly important in the field of packaging printing.
