Лако-красочные материалы — производство

Bituminous binders are a crude type of hydrocarbon resin, gene­rally produced as a by-product during distillation of crude oil or coal. Bituminous resins, based on their chemical composition, are categorized as asphalt-based and coal-tar pitch-based products. We will briefly discuss some important bituminous binders used in coatings and related industries.

Bituminous vehicles are chemically complex mixtures of hydrocarbon resins with varying content of paraffins, cycloparaffins, naphthenes and olefinic materials, depending upon their source. The asphalts are rich in aliphatic components while coal tars are mainly composed of aromatic components. Asphalts are soluble in aliphatic hydrocarbon solvents while coal tars are soluble in aromatic hydrocarbon solvents. They are very black in color due to the presence of colloidal carbon. Important properties for their use in coatings are their chemical inert­ness, excellent water repellency, electrical resistivity, barrier proper­ties and most importantly, lower cost. On the limiting side, they have poor UV resistance and a tendency to bleed in solventbased topcoats, and therefore their usage is restricted to underground structures, coa­tings for immersed conditions and areas not exposed to UV light.

Petroleum asphalts, obtained as a residue in distillation of asphal­tic crude, are used in protective coatings for buried structures and pipelines, coatings for pavements and parking lots, roof coatings and water proofing applications.

Coal tars, obtained from destructive distillation of bituminous coal, are widely used in thick, thermoplastic, hot-applied barrier coatings and linings for the interior as well as exterior of pipelines. Another important use is with other synthetic binders including epoxy-coal tar hybrids and occasionally polyurethane coal-tar hybrids for pro­tecting steel structures in contact with water, soil and back-fills.

Bituminous emulsions are produced by emulsifying an asphalt or coal tar in water using suitable combinations of surfactants along with colloidal clays. After application as coatings, with subsequent evaporation of water, the emulsified bituminous particles coalesce to form a continuous film. Being waterbased, such systems have the potential to comply with VOC regulations.

While bituminous vehicles have been extensively used in barrier coatings over the years, their use is decreasing in recent years due to toxicity issues, especially with coal tars.