1. Inorganic thickener
Inorganic thickeners are a kind of gel minerals that can absorb water and swell and have thixotropy, mainly including organic bentonite, water-based bentonite, organically modified hectorite, etc. Water-based bentonite not only acts as a thickener in water-based paints, but also prevents sinking, sagging, and floating color, but has poor water retention and leveling properties. It is often used in conjunction with cellulose ether or for primers and paints. High build paint.
2. Cellulose thickener
Cellulosic thickeners are an important thickener with a long history of application and a wide range of applications, mainly including hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, of which hydroxyethyl cellulose It is the most widely used and was once the mainstream of thickeners.
Compared with other thickeners, cellulose thickeners have the advantages of high thickening efficiency, good compatibility with coating systems, excellent storage stability, high anti-sag performance, little influence of pH on viscosity, and no influence on adhesion. Advantages, but the use of cellulose thickeners also has major defects, mainly in the following aspects.
A. The anti-mold performance is poor. The cellulose thickener is a natural polymer compound, which is vulnerable to mold attack, resulting in a decrease in viscosity. It has strict requirements on the production and storage environment.
B. Leveling, under the action of shear stress, the hydration layer between the thickener and water is destroyed by the latex paint thickened with cellulose, which is easy to construct. After the coating is completed, the destruction of the hydration layer stops immediately, and the viscosity Recovers quickly and the paint does not level off adequately, causing brush marks or stick marks.
C. Splashing. During high-speed warm coating construction, small paint particles are often produced at the exit gap between the roller and the substrate, which is called atomization; during manual low-speed roller coating, it is called splashing.
D. Cellulose thickeners are likely to cause flocculation and phase separation of latex particles, affect the stability of the coating, and cause glue shrinkage.
3. Polyacrylate thickener
Polyacrylate thickeners can basically be divided into two types: one is water-soluble polyacrylate; the other is homopolymer or copolymer emulsion thickener of acrylic acid and methacrylic acid.
This thickener itself is acidic and needs to be neutralized with alkali or ammonia water to a pH value of 8-9 to produce a thickening effect. It is also called an acrylic acid alkali swelling thickener.
They mainly rely on the electrostatic repulsion of carboxylate ions dissociated under alkaline conditions to make the molecular chains stretch into rods and thicken, and the pH needs to be kept higher than 7.5.
Acrylic thickener is anionic, and its water resistance and alkali resistance are poor. Compared with cellulosic thickeners, it has good leveling property and anti-splash, and has little effect on gloss, so it can be used in glossy coatings.
4. Polyurethane thickener
Compared with the aforementioned cellulose thickeners and acrylic thickeners, polyurethane thickeners have the following advantages:
A. Both good hiding power and good leveling.
B. Low molecular weight, not easy to produce splash when roller coating.
C. It can associate with latex particles without volume-limited flocculation, so it can make the coating film have a higher gloss;
D. Good hydrophobicity, scrub resistance, scratch resistance and biological stability.
Polyurethane thickeners are more sensitive to formula composition, and their adaptability is not as good as that of cellulose thickeners. The influence of various factors should be fully considered when using them.
There are many kinds of thickeners. When choosing to use them, the thickening efficiency and the influence on the rheology should be considered first, and the influence on the construction performance, the appearance of the coating film and the stability should be considered secondly.
Post time: Feb-14-2025