Influence of pigment particle characteristics on coating colour properties

摘要

The purpose of this study was to determine the influence of pigment particle characteristics on coating colour properties and coated surface properties. An initial study was performed on suspensions of two different clays, whose particle size and size distribution were determined. Water transport through a filter cake was studied by determining the dewatering rate and the immobilization solids of the pigment slurries. In this way, an approximate degree of particle packing was obtained. The measurements showed that the dela-minated US clay causes lower particle packing, which results in high dewatering and immobilization solids. Both the pigment slurries and the coating suspensions, to which a thickener was added, showed this behaviour. The shape and content of pigment fines were both found to influence pigment packing and thereby dewatering. Viscosity measurements showed that physical properties such as particle size, shape and size distribution influence the hydrodynamic properties of pigment suspensions, i.e. the ability of the pigment particles to orientate during flow, at high deformation rates. Coating colours containing English clay had higher viscosities than those containing delaminated US clay. Nevertheless, the continuous phase viscosities of the two coating colour systems were roughly the same and were independent of the pigment type. The type of pigment used in the coating colour system also affected the properties of the coated layer, which had a higher light scattering coefficient and gloss for the delaminated US clay coating colours. The larger plate-like particles and wider size distribution of the delaminated US clay means the surface gloss is higher and there are more surfaces to scatter the light. As the concentration and molar mass of the water-soluble thickener were increased, surface gloss diminished.%Tutkimuksen tavoitteena oli selvittää pigmenttipartikkelien ominaisuuksien vaikutukset päällystyspastan ja päällysteen ominai- suuksiin. Alustava tutkimus tehtiin kartoittamalla kaoliiniliettei-den partikkelikoko ja kokojakauma. Vedenkulku muodostetun suodatinkakun läpi tutkittiin määrittämällä pigmenttilietteiden ve-siretentio ja jähmettyminen. Näin saatiin partikkelien pakkautumi-sen suhteellinen arvo. Mittaukset osoittivat, että delaminoitu kaoliini aiheuttaa alhaisemman partikkelien pakkautumisen eli korkeamman vedenpoiston ja alhaisemman jähmettymiskuiva-aineen. Pigmenttilietteet ja pääl-lystyspastat, joihin oli lisätty paksuntaja osoittivat samanlaista käyttäytymistä. On siis todettavissa, että pigmenttihiukkais-ten muodolla ja määrällä on selvä vaikutus pakkautumiseen ja siten vesiretentioon.