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Extender pigments in paint - Section 1: Calcium carbonate, Talc


1. Calcium carbonate

1.1. Calcium carbonate (natural)

Proportion: 2.7; refractive index: 1.5-1.7, oil permeability: 6-24 mL/100g; Particle size: 1-50 μm.

Calcium carbonate is the most widely used of the fillers and is available in various grades in terms of average particle size and particle size distribution. It is used in water- and solvent-based paints for interior and exterior applications. In exterior applications, calcium carbonate has good weather resistance except in highly acidic environments.

Calcium carbonate's low oil permeability is an advantage as it requires less resin to bond to it, thus leaving more resin to bond to the substrate. High pigment content within the CPVC range is suitable for a wide range of products with good drying time and fallibility for putty, undercoating, and matt coatings.

1.2. Calcium carbonate (synthetic)

Precipitated or synthetic calcium carbonate is also used as a filler. It is much finer with particle size ranges below micro size. Oil permeability of these finer grades can be up to 80 mL/100g. They are used as opacifiers, sagging control agents, and anti-settling agents. They are also available in a surface-treated form for easier dispersion.

2. Talc

Proportion: 2.7; refractive index: 1.55, oil permeability: 30-50 mL/100g; Particle size: 5-50 μm.

Talc is very soft and is characterized by a slippery feel. It is produced from various minerals (soapstone, steatite, asbestine), of varying purity, and in sheet and fiber form. Therefore, the properties can be highly dependent on the mineral source.

In paint production, talcum powder is used to increase the dispersion efficiency of titanium dioxide pigments and improve the construction properties of the paint film. Talc has good dispersing properties in both water-based paints and solvents. The softness of talcum powder causes less wear on construction and production equipment.

Due to its grain shape, talc offers resistance to cracking, making it suitable for exterior applications.

3. Barite (barium sulfate).

Density: 4.5; refractive index: 1.64, oil permeability: 8-15 mL/100g; Particle size: 1-40 μm.

In mineral deposits, barite is the most abundant and has the highest refractive index among fillers. The small nodule shape results in a low oil permeability requirement, allowing tightly arranged paint films to be obtained to achieve low hygroscopicity, good corrosion, and chemical resistance. It provides good undercoat and primer retention and shows good wear resistance in traffic paints.

Precipitated barium sulfate, also used as a filler, has now been replaced mainly by improved natural barites.

4. Mica

Proportion: 2.82; refractive index: 1.58; Oil permeability: 50-80 mL/100g.

The mineral muscovite is the main source of commercial mica powder, which has extremely thin sheet grains with a diameter-to-thickness ratio of 25:1. In paint, the finely ground mica sheets tend to be oriented parallel to the surface of the paint film, providing an inert and flexible shield against chemical attack and solar radiation. Mica flakes provide and enhance properties such as washability, adhesion, film life, moisture resistance, corrosion resistance, and retardation of pigments.

Mica is widely used in exterior decorative paints and in wood primers. In addition, mica is used as a filler in aluminum emulsion finishes and has been used to create pearl-effect pigments when coated with metal oxides or carbon.

For more information, please contact Mega Vietnam New Materials Research and Development Center for advice and answers to your questions.

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