Thermoplastic powder coatings are made up of thermoplastic resins, pigments, fillers, plasticizers and stabilizers, and other components. Thermoplastic powder coatings include: polyethylene, polypropylene, polyester, polyvinyl chloride, chlorinated polyether, polyamide system, cellulose system, and polyester system.
Water-based paints use water as the dispersion medium or water as the solvent. For example, latex paints use water as the dispersion medium and water-soluble paints use water as the solvent. The viscosity of water is very low and cannot meet the requirements of coatings. Therefore, the rheology is generally adjusted by adding a thickener during production to meet various requirements. Latex paint is the most widely used water-based paint. The thickener [1.21] is mainly introduced below with latex paint, and other water-based paints wax can be used as reference.
The first section latex paint on the rheological requirements
In the process of production, storage, construction and film formation, latex paint requires a corresponding rheology.
Viscosity and viscosity test
The resistance of fluid to flow is called viscosity, expressed as x, defined as the ratio of shear stress to shear rate, in Pa·s (Pa·s). In the past, the units were poise (P) and centipoise (cP). , 1Pa·s=10P, 1mPa·s=1cP.
The test ranges of several commonly used viscometers in the latex paint industry are roughly as follows:
Brookfield viscometer generally tests the viscosity at low shear rates of about 10-2~10s-1, which reflects the viscosity of storage, stratification, leveling and sagging. Stormer viscometer generally tests the viscosity at about 10~10²s-shear rate, which is related to coating treatment and dipping. The ICI viscometer generally tests the viscosity at a high shear rate of about 10*s, which represents the situation in applications such as roller coating and spraying.
Latex paint is a non-Newtonian fluid, and its viscosity changes with shear stress. It is of little significance to only measure the viscosity at a certain shear rate. Usually the viscosity at least two shear rates is measured, and sometimes the entire curve is even measured.
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