| Résumé : |
The rheologic of coatings determines important performance properties such as roller and spray application, brush marks and dry film texture and appearance. To control these properties, coatings are formulated with a variety of rheology modifiers, sometimes also referred to as thickeners.
Two major types of rheology modifiers for aqueous coatings are those based on cellulose ethers and those based on acrylic polymers. Both types are high molecular weight, water-soluble polymers. The cellulose ethers are polysaccharides that are ethoxylated to make them water soluble whereby the most commonly used type is hydroxyethyl cellulose, or HEC. The acrylic polymers are copolymers of an acrylic acid and an acrylic ester monomer.
The radio of the two monomers is carefully chosen so that the polymer is insoluble in water at acidic pH but becomes soluble at the basic pH of aqueous coatings. Because of this property, these products are often called alkali soluble emulsion, or ASE. Unlike cellulosic ethers, which are offered as powders and must be dissolved, the acrylic polymers are offered as low viscosity, ready-to-use aqueous emulsions. It is also possible to further modify the structure of each of these types by the addition of hydrophobic groups, resulting in hydrophobically modified HEC (HMHEC) and hydrophobically modified ASE (HASE) materials. A third type of thickener, hydrophobically modified ethylene oxide-based urethane (HEUR), is also commonly used but offers rheologyquite different from that of cellulosics and so will not be included in this discussion. |
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Hydrophobically modified acrylic technology to create cellulosics coatings in POLYMERS PAINT COLOUR JOURNAL - PPCJ, Vol. 202, N° 4570 (03/2012)
