Low-grade water-soluble coatings are made by dissolving polyvinyl alcohol in water and adding other additives such as pigments. In order to improve its performance and reduce its cost, many methods have been adopted, the most common being 106 and 803 coatings.
This kind of coating has the advantages of low price, non-toxic and tasteless, and convenient construction. Because its film-forming substance is water-soluble, it will always leave some traces after scrubbing with a wet cloth, which is not durable and easy to yellow and change color. But the price is cheap, the construction is convenient, and the consumption is still the largest at present, which is mostly used for interior wall decoration of middle and low-grade rooms or temporary rooms.
Characteristics of film-forming process of water-soluble coatings
The film-forming and curing mechanism of water-soluble coatings is the same as that of general solvent-based coatings, but its film-forming process has other characteristics:
Because water-soluble resin needs to be soluble in water, its molecular weight will not be too large, otherwise it will be difficult to be soluble in water. Therefore, as a polymer material, it is mostly made into thermosetting type.
In the process of heating and curing the coating film, an insoluble network structure is formed through the cross-linking reaction between active groups in the resin system or active groups added with cross-linking agents, thus providing excellent paint film performance. Of course, there are some self-drying water-soluble coatings, but these are cured by oxidative crosslinking in the presence of drier.
In order to increase the water solubility of water-soluble resins, most water-soluble resins exist in the form of carboxylate or amine salts. Therefore, in the process of film forming and curing, ammonia or amine volatilizes first. Of course, amine derivatives may also be formed during heating. Ammonia/zirconium complexes are also used as crosslinking agents for carboxylic acid polymers. When the water and ammonia in the resin volatilize at room temperature, the acidic polymer and zirconium ions can cross-link to form a film through ionic bonds and can be dried at room temperature.
Ionic crosslinking method is simple and easy to operate, and it has also been applied to other water systems at room temperature.
Water-soluble coatings are not only used for general coating such as brush coating, spray coating, roll coating and dip coating, but also for electrodeposition coating. Of course, as electrophoretic coating, there are other requirements in manufacturing. In the process of electrodeposition coating, some molecules with double bonds absorb oxygen produced by water electrolysis, thus speeding up the drying and film formation.
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