What are the characteristics of various thickeners?
01. cellulose thickener Cellulose thickener has high thickening efficiency, especially for water phase; Less restrictions on coating formula and wide application; The usable pH range is wide. However, there are some shortcomings, such as poor leveling, flying splash during roller coating, poor stability, and susceptibility to microbial degradation. Because it has low viscosity under high shear and high viscosity under static and low shear, the viscosity increases rapidly after coating, which can prevent sagging, but the other side causes poor leveling. Studies have shown that the relative molecular weight of thickener increases, and the splash property of latex paint also increases. Cellulose thickeners are prone to splash because of their large relative molecular weight. And the water resistance of the paint film will be reduced because of the better hydrophilicity of cellulose.
02. acrylic thickener Polyacrylic acid thickeners have strong thickening and leveling properties, and good stability of raw materials, but they are sensitive to pH value and poor in water resistance.
03. associative polyurethane thickener The associative structure of associative polyurethane thickener is destroyed under the action of shear force, and its viscosity decreases. When the shear force disappears, its viscosity can be restored, which can prevent sagging phenomenon during construction. And its viscosity recovery has a certain hysteresis, which is beneficial to the leveling of coating film. The relative molecular mass (several dry to tens of thousands) of the polyhydroxyester thickener is much lower than the relative molecular mass (hundreds of thousands to millions) of the first two types of thickeners, and will not contribute to splashing. Polyurethane thickeners have both hydrophilic and hydrophobic groups on their molecules, and the hydrophobic groups have strong affinity with the substrate of the coating film, which can enhance the water resistance of the coating film. Because latex particles participate in association, they will not produce flocculation, so it can make the coating film smooth and have high glossiness. Many properties of associative polyurethane thickener are superior to other thickeners, but because of its unique micelle thickening mechanism, the components that affect micelles in coating formulation will inevitably have an impact on thickening property. When using this kind of thickener, we should fully consider the influence of various factors on thickening performance, and do not easily change the emulsion, defoamer, dispersant, film-forming assistant, etc.
04. inorganic thickener Inorganic thickeners have many advantages, such as strong thickening, good thixotropy, wide pH range and good stability. However, bentonite is an inorganic powder with good light absorption, which can obviously reduce the surface gloss of the coating film and play a role like a matting agent.
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