Лако-красочные материалы — производство

Cellulosic thickeners are among the most commonly used thi­ckeners for decorative latex-based paints. They are produced by chemical modifications of cellulose such as carboxymethylation or etherification. The most widely used derivatives are hydroxyethyl cellulose, ethylhydroxyethyl cellulose, methylhydroxyethyl cellulose, methylhydroxypropyl cellulose, and sodium carboxymethyl cellu­lose. The important characteristics that control the properties of dif­ferent grades of individual derivatives are degree of polymerization, degree of substitution and molar substitution.

Though cellulosic thickeners may be added at various stages of paint production, it is more advisable to add them at the premix stage (grin­ding step). Addition of thickeners at the grinding step helps in disper­sion of pigments and extenders by providing high viscosity and hence better de-agglomeration. They are sold in powder form and have a tendency to agglomerate during the solvating process; therefore, it is important that the particles are well dispersed throughout the aque­ous phase before going into solution. Temperature and pH also affect the hydration process.

There is no best cellulosic thickener for all types of waterbased paints; rather, experimental study is needed to select the best suita­ble thickener for a given system because various performance para­

meters of the thickener vary with type of substitution. Cellulosics are the most common thickeners for semi-gloss and flat aqueous paint systems but are quite often unsuitable for glossy aqueous paints.