Types of paint thickeners
There are many varieties of thickeners available on the market, mainly inorganic thickeners, cellulose, polyacrylates and polyurethane thickeners of four types of bonding.
Inorganic thickener is a class of water-absorbing expansion and the formation of thixotropic gel minerals. Mainly bentonite, bumpy clay, aluminum silicate, etc., of which bentonite is more commonly used.
Cellulose thickener has a long history of use, many varieties, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, etc., was the mainstream of the thickening agent, which is more commonly used is hydroxyethyl cellulose.
Polyacrylate thickeners can be basically divided into two kinds: one is a water-soluble polyacrylate; the other is acrylic acid, methacrylic acid homopolymer or **** polymer emulsion thickener, this thickener itself is acidic, must be neutralized with alkali or ammonia to pH8 - 9 to achieve the thickening effect, also known as the Acrylic alkali swelling thickener.
Polyurethane thickeners are newly developed in recent years.
Characteristics of paint thickeners:
Cellulose thickeners
Cellulose thickeners have a high thickening efficiency, especially for the thickening of the aqueous phase; less restriction on the coating formula, widely used; can be used in a wide range of pH. However, there are disadvantages such as poor leveling, more splashing phenomenon when roller coating, bad stability and susceptibility to microbial degradation. Because of its low viscosity in high shear, in static and low shear have high viscosity, so the viscosity increases rapidly after the coating is completed, which can prevent hanging, but on the other hand cause poor leveling. Some studies have shown that the relative molecular mass of the thickener increases, and the splashability of the latex coating also increases. Cellulose-based thickeners are prone to splashing because of their large relative molecular mass. And because cellulose hydrophilicity is good, will reduce the water resistance of the paint film.
Polyacrylic acid thickeners
Polyacrylic acid thickeners have strong thickening and good leveling, good biostability, but sensitive to pH and poor water resistance.
Conjugated polyurethane thickeners
Conjugated polyurethane thickeners, the structure of this conjugation in the action of the shear force is damaged, viscosity is reduced, when the shear force disappears viscosity can be restored, to prevent the construction process of hanging phenomenon. And its viscosity recovery has a certain lag, which is conducive to coating film leveling. The relative molecular mass of polyurethane thickeners (thousands to tens of thousands) is much lower than that of the first two types of thickeners (hundreds of thousands to millions), and will not contribute to splashing. Polyurethane thickener molecules have both hydrophilic and hydrophobic groups, hydrophobic groups and the matrix of the coating film has a strong affinity, can enhance the water resistance of the coating film.
Since the latex particles are involved in the conjugation, no flocculation will occur, thus making the coating film smooth with high gloss. Conjugated polyurethane thickener has many properties better than other thickeners, but because of its unique micelle thickening mechanism, and therefore those components in the coating formula that affect the micelles will inevitably have an impact on the thickening. When using this kind of thickener, should fully consider the impact of various factors on the thickening performance, do not easily replace the coating emulsion, defoamer, dispersant, film-forming additives and so on.
Inorganic thickeners
Inorganic thickeners have the advantages of strong thickening, good thixotropy, pH value to adapt to a wide range of good stability. But because bentonite is an inorganic powder, light absorption, can significantly reduce the surface gloss of the coating film, play a similar role as a matting agent.
The above is some of my introduction to the types of paint thickeners and the characteristics of paint thickeners, I hope it can help you.