UV ink printing into two stages
Abstract: The film-forming mechanism of UV-curable water-based inks is very important for the preparation of water-based UV inks. Only by understanding the entire curing film-forming process can we find a theoretical basis in the choice of resin, initiator, and water.
The drying mechanism of water-based UV light curing systems is still controversial. It is generally believed that the drying mechanism of water-based UV inks is: after removing water through a drying device, under the irradiation of ultraviolet rays, the photoinitiator absorbs radiation energy and decomposes into free radicals or cations. Causes the polymer to polymerize and crosslink, and solidifies into a three-dimensional network polymer in a short time. Radiation curing systems can be divided into free radical systems and cationic systems according to the type of photoinitiator. Since free radical systems are widely used in radiation curing inks, it is recommended to use free radical systems in the development of water-based UV inks.
Water-based UV ink film formation process is roughly divided into two stages:
1, Pre-evaporation drying mechanism
Pre-drying is a necessary process before photo-curing. Without pre-drying, the final result of photo-curing is not ideal. UV-curable water-based inks generally use appropriate heating methods, such as infrared baking or hot air drying, to shorten the initial evaporation process. As the water gradually evaporates, the dispersed polymer particles gradually come closer, but still move freely. Then, as the water further volatilizes, the polymer particles reach a tight packing and become irreversible contact with each other. It is generally believed that the theoretical volume solid content at this time is 74%.
2, UV curing film formation mechanism
In the later stage, the dispersed phase particles started to coagulate, and about 3% of water remained at this time. At the same time, the curing group molecules containing functional groups undergo a curing reaction at the interface and inside of the dispersed phase particles under the initiation of a photoinitiator.
Its curing process can generally be divided into four stages:
① the interaction between light and photoinitiator, which may include the absorption of light and the interaction between photoinitiator;
② the rearrangement of photoinitiator molecules to form free radicals Intermediates;
③ Free radicals interact with unsaturated groups in the oligomer to initiate a chain or polymerization reaction;
④The polymerization reaction continues, and the liquid components are transformed into solid polymers.