Principle and film-forming process of dryer for water based UV ink

The film-forming mechanism of UV-curable Water Based Ink is very important for the preparation of water based UV Ink. Only by understanding the whole curing film-forming process can we find a theoretical basis in the selection of resin, initiator and water.

The drying mechanism of water based UV curing system is still controversial at present. It is generally believed that the drying mechanism of water based UV ink is:
After the water is removed by the drying device, under the irradiation of ultraviolet rays, the photoinitiator absorbs the radiation energy and decomposes into free radicals or cations, which causes the polymer to undergo polymerization, cross-linking and grafting reactions and solidify into a three-dimensional reticular polymer in a short time. Radiation curing system can be divided into free radical system and cationic system according to different types of photoinitiators. Since free radical system is often used in radiation curing ink, it is recommended to use free radical system in the development of water based UV ink.

The film-forming process of waterborne UV ink is roughly divided into two stages:
1. Pre-volatilization drying mechanism
Pre-drying is a necessary process before photocuring. Without pre-drying, the final result of photocuring will be unsatisfactory. Generally, proper heating methods, such as infrared baking or hot air drying, are used to shorten the initial water evaporation process. With the gradual evaporation of water, the dispersed polymer particles gradually get closer, but they can still move freely. Then, with the further evaporation of water, the polymer particles reach close packing and become irreversible contact with each other. It is generally considered that the theoretical volume solid content at this time is 74%.
2. Mechanism of UV curing film formation
In the later stage, the dispersed phase particles began to coagulate, and about 3% water remained at this time. At the same time, the curing group molecules containing functional groups undergo curing reaction at the interface and inside of dispersed phase particles under the initiation of photoinitiator.
The curing process can be generally divided into four stages:

(1) the interaction between light and photoinitiator, which may include the absorption of light and the interaction between photoinitiators;

(2) The photoinitiator molecules are rearranged to form free radical intermediates;

(3) The free radical reacts with unsaturated group in oligomer to initiate chain or polymerization reaction;

(4) Polymerization continues, and liquid components are transformed into solid polymers.

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