Лако-красочные материалы — производство

Both natural and synthetic silica are used as extenders in the coa­ting industry. Naturally occurring silica exists as three types:

• Crystalline silica (the mineral quartz)

• Amorphous silica (cryptocrystalline; the mineral tripoli)

• Diatomaceous silica, also known as diatomaceous earth (kieselgur)

Most of the natural silica used in coating industry has a SiO2 con­tent higher than 95 %, and up to 99 % in some cases. Some of the important features of these relatively cheap extenders include high hardness, chemical inertness, durability and a low oil absorption value (the exception is diatomaceous silica). Crystalline and amor­phous silica are used in compositions such as wood fillers for their abrasiveness; in road marking paints and floor coatings to improve abrasion resistance; in exterior flat house paints for sheen unifor­mity, burnishing resistance and durability; and in primers and undercoats to improve intercoat adhesion.

Diatomaceous silica is a very lightweight, fluffy hydrous silica. Diato­maceous silica, found in natural deposits, consists of the skeletons of various species of diatoms, which are minute marine plants that died millions of years ago. Their structure is very open and they present a large ratio of surface area to weight (and thus have a high oil absorp­tion value). They are used to increase the consistency of coatings and as low-cost flatting agents.

Synthetic silica types are used in coatings less as filler than as thixo­tropic, antisettling and matting additives. The different types include pyrogenic silica, precipitated silica and silica aerogels and hydrogels. They consist of coagulated amorphous spherical particles of very fine particle size (5 to 50 nm). Precipitated synthetic silica is coarser than most other grades and is predominantly used as a flatting agent.