GCC is the backbone of most coating colours. This article explains how particle size, brightness and particle shape affect opacity, gloss, printability and coating runnability — and how to specify the right GCC grade for your coater.
Ground calcium carbonate is the most widely used pigment in paper and board coating. It is cheaper than clay, brighter, and easier to run at high solids — which is why a typical coating colour contains more GCC than any other pigment, often blended with fine clay to balance opacity against gloss.
What GCC contributes to a coating colour
- Brightness. Our GCC grades run 75–97 whiteness. High brightness at the coating surface is what makes a sheet look white rather than grey, and it lets you reduce optical brightener dosage.
- Opacity. Calcium carbonate has a higher refractive index than the binder system, so it scatters light at the coating surface. Lower brightness grades with a broader distribution are often used deliberately in pre-coats to cut cost while building opacity.
- Smoothness and gloss. After calendering, fine and narrowly distributed GCC produces a smoother surface and higher gloss. Coarse particles protruding through the film are a direct cause of poor gloss and of print mottling.
- Printability. A uniform surface accepts ink evenly. Coarse tail particles cause missing dots in rotogravure and uneven ink lay in offset.
- Runnability. GCC has a lower water demand than clay at the same solids, so coating colours can be run at higher solids and lower viscosity — less drying energy, fewer coating defects.
Selecting the grade
| Coating layer | Typical GCC fineness | Why |
|---|---|---|
| Pre-coat | 600–1000 mesh (D50 3–8 µm) | Cost-effective opacity, high solids, good coverage of base sheet |
| Top coat | 1500–2500 mesh (D50 1.5–3 µm) | Gloss, smoothness and print resolution |
| Board / packaging | 600–1250 mesh | Balance of coverage and print quality |
Specifications that matter at the coater
Ask for D50 and D97 (not just mesh), top-cut control, brightness (R457), moisture below 0.3%, and a consistent particle size distribution batch to batch. Abrasion is another consideration on high-speed machines: quartz contamination raises blade wear, so specify a controlled SiO₂ content and ask for the acid-insoluble residue figure.
Every batch we ship is tested in-house and can be issued with a batch certificate. Samples and TDS are available for bench trials.
Written by the technical team at TDHX Minerals, Haicheng, Liaoning, China.
