Лако-красочные материалы — производство

Extender pigments, also referred to as fillers, supplemental pig­ments or functional filler, are fine white powders of low refractive index (<1.7), which are substantially insoluble in the vehicle, reaso­nably chemically inert, and commonly but not always inexpensive. In addition to their traditional use for reducing cost (and thus why they are also called fillers, though this terminology is not appropriate with modern extenders), modern-day extenders are also used to modify and/ or improve certain characteristics and the performance of coatings.

While the principal function of most extenders is to occupy volume in the coating film at lower cost, careful selection of type and quan­tity of fillers also modifies some of the key properties of coatings such as rheology (flow properties), antisettling properties, gloss control (sheen or matte finish) and mechanical strength of the coa­ting (reinforcement) at relatively low cost. Due to their low refractive indices, closer to those of binders, they themselves do not contribute much to opacity of coatings, but they tend to enhance opacity by

providing spacing between true pigments (which increases light scattering). In coating formulations, they are frequently used to control PVC, which in turn controls many paint properties such as opacity, gloss, porosity and permeability. They are extensively used in high-PVC formulations such as putties, filling compounds, primers, primer surfacers and undercoats.

Extenders are generally produced by grinding natural minerals, and in some cases, are synthetically produced by a precipitation pro­cess. In general, fillers are coarser than white pigments and availa­ble in grades varying from coarse (up to 250 pm) through fine (10 to 50 pm) to ultrafine (<5 pm). They also vary in their particle shapes and hence modify various properties of coatings that are influenced by shape of the dispersed particles, as discussed in Section 3.2.2.4. Fillers commonly used in the coating industry may be classified into the following groups: carbonates, silica, sulfates, and silicates.