Coatings are primarily composed of four components: resins, pigments and fillers, solvents, and additives. They serve decorative and protective purposes, and sometimes offer specialized functionalities. Among these, fillers are crucial as they significantly influence the performance of coatings. Common fillers include calcium carbonate, talc, mica, silica powder, barium sulfate, kaolin, and wollastonite.
Functions of Fillers in Coatings
- Cost Reduction: Fillers are often used to lower the overall cost of coatings without compromising basic performance.
- Performance Enhancement: Fillers can improve specific properties of the coating film, including:
- Weather resistance, acid/alkali resistance, salt spray resistance, water resistance, and temperature resistance
- Mechanical strength, hardness, scratch resistance, and anti-cracking properties
- Application performance, such as flow, leveling, and anti-sagging
- Storage stability
- Overall physical and chemical performance, enhancing both decorative and protective functions
Common Fillers and Their Properties
1. Mica
Mica is a layered silicate with a flaky structure, high aspect ratio, and excellent chemical stability. It is resistant to acids, alkalis, and high temperatures (over 600°C), has good electrical insulation, and offers excellent abrasion resistance. In coatings, mica particles align in parallel layers, creating a barrier that blocks corrosive substances, improving water and salt spray resistance, and enhancing anti-corrosion performance. Mica also provides UV shielding, which increases weather resistance and prevents cracking, discoloration, and chalking.
Applications: Architectural coatings, anti-corrosion paints, waterborne industrial coatings, powder coatings, high-temperature coatings, insulating coatings, damping coatings, waterproof coatings, fire-retardant coatings, and other functional coatings.
Production Note: Mica produced via the wet process has higher purity, fewer impurities, and more complete flakes than dry-processed mica. Wet-process mica more effectively improves weather resistance, water resistance, and anti-corrosion performance in coatings.
2. Silica Powder (Quartz Powder)
Silica powder, such as Gery Quartz Powder from Chuzhou, is refined through multiple processes. It has low oil absorption, chemical stability, easy dispersibility, and anti-settling characteristics. It enhances abrasion resistance, corrosion resistance, and coating hardness.
Applications: Anti-corrosion coatings, floor coatings, powder coatings, waterborne industrial coatings, waterproof materials, fire-retardant coatings, etc.
3. Calcium Carbonate
Calcium carbonate is classified into heavy calcium (ground from natural calcite) and light calcium (synthetic).
- Heavy Calcium Carbonate: Stable, low-cost, mainly used as a filler. Its poor acid resistance limits its use in outdoor or acidic environments.
- Light Calcium Carbonate: Fine particle size and low density, but less stable.
4. Talc
Talc is widely used in industrial coatings, especially primers. It has good adhesion, easy sanding, and anti-sag properties, improving application performance. However, talc has high oil absorption, a matting effect, and poor weather resistance, making it unsuitable for high-gloss or outdoor coatings.
5. Barium Sulfate
Barium sulfate includes natural barite and precipitated barium sulfate.
- Barite: Common in primers, improves film strength, has low oil absorption but tends to settle.
- Precipitated Barium Sulfate: Higher whiteness and finer texture, but heavier and more expensive than natural barite.
6. Kaolin
Kaolin improves anti-settling performance, dispersion, and suspension in coatings. It enhances leveling, scrub resistance, anti-sagging, storage stability, and opacity, and is widely used in architectural coatings.
7. Wollastonite
Wollastonite (CaSiO₃) has needle-like or fibrous particles, improving coating strength and scrub resistance. However, it tends to settle, and high-quality resources are limited.
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