Water-based UV Curing Coatings: Features and Applications

The combination of UV-curing coating technology and water-based coating technology highlights the characteristics of environmental protection and high efficiency. Compared with oil-based UV curing technology, water-based UV-curable coatings have the following characteristics:

1 The viscosity and rheological properties of coatings can be adjusted by adding water or traditional thickeners, rheological additives, and the like.

2 has potential application prospects for harmless spraying.

3 As the amount of acrylate monomer is greatly reduced, the toxicity and irritation of the system are greatly reduced.

4 The equipment is easy to clean with water.

5 Reduces the flammability of the paint.

6 It is possible to reach zero VOC.

7 can get ultra-thin cured film.

8 It can reduce the shrinkage of the cured film and improve the adhesion of the cured film to the substrate.

Of course, the combination of UV curing technology and water-based coating technology, both to get the advantages, but also get the drawbacks of both, such as the need to remove water, so it will consume more energy; water surface tension will bring moisture Sexual problems; water will produce a polymerization inhibitor on free radical polymerization; three-dimensional curing is more difficult.

When a low solid content formulation is used for a non-absorbent substrate, UV curing is generally required after drying and water removal, which weakens the advantages of high UV curing efficiency. However, when a high-solids formula is used for an absorbent substrate, it is not necessary to remove the water and can be directly UV-cured.

Water-based UV-curing coatings can be divided into two major categories: water-soluble and water-dispersible. They can also be classified according to whether they contain MFAs (multi-functional acrylates) and their solid content.

The solid content of the high-solid-content water-soluble UV curing system can reach more than 90%, and a small amount of water is used to reduce the viscosity. After this type of coating is cured, the coating has poor water resistance and is not suitable for the coating of wood products. Water-dispersible UV-curable coatings mainly refer to emulsifying dispersions (including external emulsifying and self-emulsifying). Most of these systems contain acrylate groups. Compared to water-soluble UV-curable coatings, the cured film of UV-curable emulsions has stronger water resistance and a better application prospect.

Water-based UV-curable coatings are generally composed of a base resin containing an unsaturated functional group, a surfactant or other dispersion stabilizer, a photoinitiator, MFAs, and the like.

(1) Base resin

The properties of the cured film are mainly determined by the binder resin. The UV-cured waterborne paint base material is obtained by unsaturated functionalization of common resins. Common functionalized base resins include: acrylated nitrocellulose; urethane acrylate; polyester acrylate; polyether acrylate, epoxy acrylate and acrylated acrylic resin. Among them, the overall performance of polyurethane is better, it can usually be made into a hydrosol dispersion type. Studies have shown that grafting and hybridizing urethane acrylate and acrylic functional acrylic resins can enhance the compatibility of the two resins and increase the cost performance of the coating.

(2) Surfactants

External emulsifying aqueous UV-curable coatings require the use of surfactants, and anionic surfactants, especially ammonium salts of long-chain fatty acids and long-chain hydrocarbon sulfonic acids, are often used as surfactants for aqueous coatings. The use of polymerizable surfactants is the most promising method, and it is fixed in the cured film by UV curing cross-linking process.

(3) Photoinitiator

Photoinitiators are the key to the UV curing of the coating film. For UV-curable waterborne coatings, the photoinitiators should focus on the following points.

1 It is highly compatible with the water-based resin and has good dispersibility. It is not only compatible in the wet system, but more importantly it is uniformly dispersed in the dry film before curing.

2 has a low degree of water vapor volatilization (degree of volatilization with evaporation of water).

3 has a higher reactivity in the aqueous phase.

4 Small yellow degeneration.

At present, there are few kinds of water-soluble photoinitiators widely used in the formulation, and a few water-soluble photoinitiators such as Darocure 2959 with a water solubility of 1.7% are widely accepted. With respect to water-soluble photoinitiators, there are more basic research reports than applications.

UV-curable waterborne coatings can be used as plastic varnishes, overprint varnishes, photopolymer printing plates, screen printing inks, gravure and lithographic printing inks. Many high-quality prints use multi-color overprinting techniques. The dry film weight at the end of the coating is important. Low-solids UV-curable waterborne coatings can meet this requirement. UV-curable water-based coatings also have higher levels in the wood finishing industry. Value.