Thickener is a special kind of rheological additive, its main function is to increase the viscosity of paint liquid, improve the storage performance, construction performance and paint film effect of paint.
The role of thickeners in coatings
thicken
Anti-settling
Waterproof
Anti-sagging
Anti shrinkage
Improve dispersion efficiency
Improve construction performance
Increase paint film thickness
Improve the surface effect
Characteristics of various thickeners
1. Inorganic thickener
The most commonly used is organic bentonite, whose main component is montmorillonite. Its lamellar special structure can endow the coating with strong pseudoplasticity, thixotropy, suspension stability and lubricity. The principle of thickening is that the powder absorbs water and swells to thicken the water phase, so it has a certain water retention.
The disadvantages are: poor flow and leveling performance, not easy to disperse and add.
2. Cellulose ether
The most commonly used is hydroxyethyl cellulose (HEC), which has high thickening efficiency, good suspension, dispersion and water retention properties, mainly for thickening the water phase.
The disadvantages are: affecting the water resistance of the coating, insufficient anti-mold performance, and poor leveling performance.
3. Acrylic
Acrylic thickeners are generally divided into two types: acrylic alkali-swellable thickeners (ASE) and associative alkali-swellable thickeners (HASE).
The thickening principle of the acrylic acid alkali-swellable thickener (ASE) is to dissociate the carboxylate when the pH is adjusted to alkaline, so that the molecular chain is stretched from a helical to a rod through the same-sex electrostatic repulsion between carboxylate ions, improving the The viscosity of the aqueous phase. This type of thickener also has high thickening efficiency, strong pseudoplasticity and good suspension.
The associative alkali-swellable thickener (HASE) introduces hydrophobic groups on the basis of ordinary alkali-swellable thickeners (ASE). Similarly, when the pH is adjusted to alkaline, the same-sex electrostatic repulsion between carboxylate ions makes The molecular chain extends from a helical shape to a rod shape, which increases the viscosity of the water phase; and the hydrophobic groups introduced on the main chain can associate with the latex particles to increase the viscosity of the emulsion phase.
Disadvantages are: sensitive to pH, insufficient flow and leveling of paint film, easy to thicken after.
4. Polyurethane
Polyurethane associative thickener (HEUR) is a hydrophobically modified ethoxylated polyurethane water-soluble polymer, which belongs to non-ionic associative thickener. It consists of three parts: hydrophobic base, hydrophilic chain and polyurethane base. The polyurethane base expands in the paint solution, and the hydrophilic chain is stable in the water phase. The hydrophobic base associates with hydrophobic structures such as latex particles, surfactants, and pigments. , forming a three-dimensional network structure, so as to achieve the purpose of thickening.
It is characterized by the thickening of the emulsion phase, excellent flow and leveling performance, good thickening efficiency and more stable viscosity storage, and no pH limit; and it has obvious advantages in water resistance, gloss, transparency, etc. .
The disadvantages are: in the medium and low viscosity system, the anti-settling effect on powder is not good, and the thickening effect is easily affected by dispersants and solvents.