Latex paint is a mixture of pigments, filler dispersions and polymer dispersions, and additives must be used to adjust its viscosity so that it has the rheological properties required for each stage of production, storage and construction. Such additives are generally called thickeners, which can increase the viscosity of coatings and improve the rheological properties of coatings, so they are also called rheological thickeners.

The following only introduces the main characteristics of commonly used cellulose thickeners and their application in latex paints.
Cellulosic materials that can be applied to coatings include methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. The biggest feature of cellulose thickener is that the thickening effect is remarkable, and it can give the paint a certain water retention effect, which can delay the drying time of the paint to a certain extent, and also make the paint have a certain thixotropy, preventing the paint from drying out. Precipitation and stratification during storage, however, such thickeners also have the disadvantage of poor leveling of the paint, especially when using high-viscosity grades.

Cellulose is a nutrient substance for microorganisms, so anti-mildew measures should be strengthened when using it. Cellulosic thickeners can only thicken the water phase, but have no thickening effect on other components in the water-based paint, nor can they cause significant interaction between the pigment and the emulsion particles in the paint, so they cannot adjust the rheology of the paint , Generally, it can only increase the viscosity of the coating at low and medium shear rates (commonly referred to as KU viscosity).

1. Hydroxyethyl cellulose

The specifications and models of hydroxyethyl cellulose products are mainly distinguished according to the degree of substitution and viscosity. In addition to the difference in viscosity, the varieties of hydroxyethyl cellulose can be divided into normal solubility type, rapid dispersion type and biological stability type through modification in the production process. As far as the method of use is concerned, hydroxyethyl cellulose can be added at different stages in the coating production process. The fast-dispersing type can be added directly in the form of dry powder, but the pH value of the system before adding it should be less than 7, mainly because hydroxyethyl cellulose dissolves slowly at a low pH value, and there is sufficient time for water to infiltrate into the inside of the particle , and then increase the pH value to make it dissolve quickly. Corresponding steps can also be used to prepare a certain concentration of glue and add it to the paint system.

2. Hydroxypropyl Methyl Cellulose

The thickening effect of hydroxypropyl methylcellulose is basically the same as that of hydroxyethylcellulose, that is, to increase the viscosity of the coating at low and medium shear rates. Hydroxypropyl methylcellulose is resistant to enzymatic degradation, but its water solubility is not as good as that of hydroxyethyl cellulose, and it has the disadvantage of gelling when heated. For surface-treated hydroxypropyl methylcellulose, it can be directly added to water when used, after stirring and dispersing, add alkaline substances such as ammonia water, adjust the pH value to 8-9, and stir until fully dissolved. For hydroxypropyl methylcellulose without surface treatment, it can be soaked and swelled with hot water above 85°C before use, and then cooled to room temperature, then stirred with cold water or ice water to fully dissolve it.

3. Methyl cellulose

Methylcellulose has similar properties to hydroxypropylmethylcellulose, but is less stable in viscosity with temperature.

Hydroxyethyl cellulose is the most widely used thickener in latex paint, and it is used in high, medium and low grade latex paints and thick build latex paints. Widely used in the thickening of ordinary latex paint, gray calcium powder latex paint, etc. The second is hydroxypropyl methylcellulose, which is also used in a certain amount due to the promotion of manufacturers. Methyl cellulose is hardly used in latex paints, but it is widely used in powdery interior and exterior wall putty because of its instant dissolution and good water retention. High-viscosity methyl cellulose can endow the putty with outstanding thixotropy and water retention, making it have good scraping properties.