UV curing water-based wood coatings use water as solvent, which reduces the cost of coatings and can reduce VOC content. It has the advantages of fast curing speed, low energy consumption, low pollution, green environmental protection and energy saving, and high production efficiency. It is suitable for assembly line production and is widely used in various industries such as electronic components, printing, glass, wood coatings, construction, and wood.
However, since the raw materials of UV-curable waterborne wood coatings are mostly toluene diisocyanate, which has a low double bond content and relative molecular weight, the mechanical properties are poor. By improving its performance through certain means, the quality and application range of UV-curable waterborne wood coatings can be improved.
The silica particles in silica sol are widely used in papermaking, architectural coatings, and the electronics industry due to their excellent properties such as high rigidity, high strength, ultraviolet absorption, high adsorption, high dispersion, and green and non-toxic.
During the use of UV-curing water-based wood coatings, the mechanical properties, solid content, anti-ultraviolet aging and thermal insulation properties cannot meet the use requirements, but silica sol can modify them. Silica sol colloidal particles have a large specific surface area, and the particles themselves are colorless and transparent, and will not affect the original color of the covered object.
The introduction of silica sol can affect the wear resistance, hardness, adhesion, impact strength, glossiness, etc. of the coating. The appropriate amount of silica sol added can obtain UV-curable water-based wood coatings with better overall performance.
When the proportion of silica sol in the coating is 1% to 3%, the wear resistance of the coating is significantly improved, but when the proportion of silica sol is higher than 3%, the wear resistance of the composite coating decreases.
The main component of silica sol is silica particles. A small amount of silica can significantly improve the wear resistance of the coating without affecting the transparency of the coating. However, as the amount of silica added increases, due to its large specific surface area, it is unevenly distributed in the coating solution and self-agglomerates, which increases the wear value of the coating, that is, the wear resistance of the coating decreases.
When the silica sol content is ~1%, the hardness of the composite coating reaches H level, and the hardness is significantly improved. Although the amount of silica sol added is small, it can fully react with water-based UV wood coatings to generate chemical bonds, which significantly improves the hardness of the paint film;
However, too high a silica sol content will lead to a decrease in the hardness of the paint film. This may be due to the uneven dispersion of silicon dioxide in the silica sol, which causes the coating to be unable to form a continuous network structure.
The amount of silica sol added has a significant change in the adhesion of the composite coating. When the silica sol is less, it can fully react with the water-based UV wood coating, so that the internal and external stresses of the coating are balanced and the adhesion of the coating is enhanced;
When the silica sol is too much, the reaction is not complete and a stable structure cannot be formed, which reduces the firmness of the coating and the substrate, thereby reducing the adhesion of the coating.
When the content of silica sol is low, it can fully react with the UV-curing water-based paint matrix to form chemical bonds, which significantly improves the impact strength of the paint film. When the content of silica sol is too high, the impact strength of the coating decreases due to the agglomeration and self-crosslinking reaction of silica particles in the silica sol.
Silica sol has a great influence on the gloss of the coating. With the increase of silica sol, the gloss of the coating shows a downward trend.
This is because silica sol is a colloidal solution. Because the particles are fine (close to the molecular state), the silica during the gelation has a high activity, which binds and wraps the powder particles in the coating, and forms new silicate inorganic polymer compounds with certain inorganic salts and metal oxides, and hardens into a film.
The fine particles have strong penetration into the base layer and can penetrate into the interior of the substrate through capillary action. Therefore, it reacts chemically with UV-curing water-based wood coatings to form inorganic opaque substances, which greatly reduces the gloss and transparency of the coating.