Which Calcium Carbonate Grade for Your Application? A GCC Particle-Size Guide

In short: Choose a GCC grade mainly by top cut (D97) matched to your product's gauge — the thinner and glossier the product, the finer the grade. Whiteness is not the selector between grades (the Kantor KC Series runs ≥98 whiteness across the whole ladder); it is what separates the premium tier from commodity filler. Coating — coated vs. uncoated — is a separate decision. Practical map: KC-4 for BOPP/thin film, KC-6 for breathable film and fine sheet, KC-10 for general masterbatch and injection, KC-17 for PVC pipe, paint, and general filler.

Buyers often ask for "the whitest grade" or "the finest grade," but grade selection is really a match between three things and your specific line:

1. Top cut (D97) / fineness — the primary selector. This is set by your product's gauge and surface demands. Finer grades cost more and are only worth it where the product actually needs them.
2. Whiteness and brightness — the tier, not the grade. Across the KC Series every grade is whiteness ≥98 and ISO brightness (R457/ISO 2470) ≥95, so this does not separate one grade from another. It separates a premium imported grade from an ordinary local filler.
3. Coating (coated or uncoated) — an orthogonal choice. Whether a grade is stearic-acid coated is decided by loading, gauge, and your dispersion process, not by the grade number. See coated vs. uncoated calcium carbonate for that decision.

Every grade shares the same chemistry: CaCO₃ ≥98%, Fe₂O₃ ≤0.05%, whiteness ≥98 / brightness (R457/ISO 2470) ≥95, available coated (stearic acid) or uncoated. Values are typical; the spec is confirmed per lot on the certificate of analysis.

Prefer to answer a few questions instead of reading? The interactive grade selector applies this map to your application and ends with a free qualifying sample. The map itself:

• Thin and high-gloss film (BOPP, high-gloss). Choose the finest — KC-4. A thin gauge cannot hide a coarse particle: one oversize grain becomes a gel, speck, or tear, and gloss depends on a smooth, fine surface.
• Breathable film, fine sheet, tape, thin-wall injection. KC-6 — fine enough for thin gauges and stretched films, without paying for the very finest cut.
• Modified plastics, filler and colour masterbatch, general injection. KC-10 — the general-purpose middle grade; enough fineness for most compounds, economical enough for high loadings.
• PVC pipe and profile, coatings and ink, paper, rubber, general filler. KC-17 — coarser and more economical. Thicker walls tolerate the coarser particle, and here low iron and a consistent top cut matter more than ultrafineness.

The number that predicts defects is not the median (D50) — it is the top cut (D97), the size below which 97% of the particles fall. Problems in film and other thin or surface-critical products come from the coarse tail of the distribution, not the average particle. Two grades can share a similar D50 and behave very differently if one has a longer coarse tail.

That is why you match D97 to gauge: the thinner or more surface-critical the product, the tighter the top cut it needs. It is also why "just use the finest grade everywhere" is a mistake — an ultrafine grade in a thick pipe wall adds cost and can make dispersion harder (finer particles agglomerate more) without improving the part.

Because every KC grade runs ≥98 whiteness and ≥95 ISO brightness, whiteness does not enter the KC-4-vs-KC-17 decision. Where whiteness does matter is one level up: it separates a premium imported grade from a commodity local filler, and on a white product it sets how far you can extend your titanium dioxide before the finished whiteness falls out of spec. If your line is white, run your own numbers on the filler economics calculator — the pigment you displace is usually worth far more than the difference in filler price.

The reliable way to settle a grade is on your own line. Send your application, the gauge or wall thickness, and the spec you run today, and we will recommend a KC grade and send a free sample (under a tonne) with a per-lot certificate of analysis to qualify on your equipment before you commit.

One honesty note: the KC Series figures above are to Kantor's current spec (particle size on a Malvern analyser); a heavy-metals panel at an accredited laboratory is in progress and will be supplied with the COA once complete, which matters if your end-use is food-contact.

Which calcium carbonate grade should I use for BOPP or thin film?

The finest grade with the tightest top cut — KC-4 (D97 about 5.5 µm). Thin film cannot tolerate coarse particles, and high gloss needs a fine, tight distribution.

What calcium carbonate grade for filler masterbatch?

It depends on the thinnest product the masterbatch ends up in. General filler and colour masterbatch → KC-10; masterbatch for fine film or tape → step finer to KC-6.

What grade for PVC pipe and profile?

A coarser, economical grade such as KC-17. Thick walls tolerate the coarser particle; low iron (Fe₂O₃ ≤0.05%) and a consistent top cut matter more than ultrafineness.

How do I choose calcium carbonate particle size?

Match the top cut (D97) to your product's gauge, not the average size — defects come from the coarse tail. Thin/high-gloss → finest; general filler, pipe, thick parts → coarser.

Does the grade determine whiteness?

No — every KC grade runs whiteness ≥98 and ISO brightness ≥95, so grade selection is a particle-size decision. Whiteness separates a premium grade from a commodity filler, but does not vary across the ladder.