In addition to silica sol, silica sol coatings generally have other film-forming materials added to the base material, mainly of the following types.
1. Mixed type of water-soluble polymer compounds
Water-soluble polymer compounds have good miscibility with silica sol, and no additional surfactant is needed. For example, polyvinyl alcohol (PVA) and silica sol mixed coatings, the ratio of silica sol to PVA can be adjusted arbitrarily within a fairly large range, and can be heated to 95ºC. PVA is dissolved in silica sol to obtain a series of base materials with different properties. As reported in some patents, a mixture of polyvinyl alcohol aqueous solution and silicic acid aqueous solution can form a water-resistant coating film that dries at room temperature and is resistant to hot water.
2. Mixed type of polymer emulsions
Organic polymer emulsions have the advantages of good film-forming properties, good water resistance and alkali resistance of the coating film. Adding them to silica gel can improve the coating performance of the coating, increase the elasticity of the coating film, and effectively prevent the cracking of the silica sol coating film.
Organic polymer emulsions that are well mixed with silica sol include vinyl acetate emulsion, styrene-acrylate copolymer emulsion, vinyl acetate copolymer emulsion, etc. The stability of the mixture varies greatly depending on the amount of the two and the type of emulsion, and it must be explored in experiments. The key to this type of coating is the blending stability of silica sol and polymer emulsion, and special attention must be paid in actual operation.
3. Curing agent type
Silica sol uses certain metal compounds (such as phosphates, etc.) to have a hardening effect. This type of coating has excellent water resistance and aging resistance, especially suitable for high-temperature occasions, which is beyond the reach of general thermoplastic coatings.
4. Single silica sol type
The SIO2 content in silica sol is more than 50%. The silica sol is more active and easy to combine with pigments and fillers and form a film. Drying at 50°C for 1~2 hours can form a weather-resistant, heat-resistant, and impact-resistant coating.
In addition, there are coupling agent-modified silica sol coatings.
In architectural coatings, (1) and (2) are more commonly used. The development trend of silica sol is to directly graft silica sol with organic polymer compounds in polymerization to generate new resins to prepare high-end coatings with excellent aging resistance and durability. Coupling agent silica sol coatings should be further developed.