What Is 'KC Grade' Calcium Carbonate? How to Read GCC Grade Codes

In short: "KC grade" calcium carbonate is a supplier's product code, not an industry standard. A "KC-4" from one producer is not the same as another's — the letters usually abbreviate the producer, and the number tracks fineness or sequence. Compare grades by the actual spec — top cut (D97), whiteness with its measurement standard, purity, and coating — not by the code. In the Kantor KC Series, the number tracks the top cut, from KC-4 (≈5.5 µm, finest) to KC-17 (≈17 µm), with the same chemistry across the whole ladder.

Calcium carbonate producers name their grades with short codes: a letter or two that abbreviates the company or the product line, and a number for fineness or sequence. "KC" is one such prefix, and more than one producer uses it. There is no ISO, ASTM, or national standard that defines a "KC grade" of ground calcium carbonate.

That has a practical consequence. Two grades both labelled "KC-4" can differ in particle size, whiteness, purity, and coating, because each producer sets its own numbering. The code is a label, not a promise — so a grade code alone is never enough to compare or qualify a filler.

Four numbers actually decide a GCC grade for plastics. Line these up across suppliers and the code stops mattering:

1. Top cut (D97) — the primary selector. The size below which 97% of the particles fall. Match it to your product's gauge: defects in film and other thin or surface-critical products come from the coarse tail of the distribution, so the D97 predicts performance better than the average size (D50).
2. Whiteness and its measurement standard. A whiteness figure is only comparable if you know how it was measured. ISO brightness (R457 / ISO 2470) is the reference method; a bare "whiteness %" with no stated standard cannot be compared across suppliers. Ask for both the number and the method — see whiteness vs. ISO brightness.
3. Purity and iron. The CaCO₃ content (higher is better) and the Fe₂O₃ level (lower is better — iron dulls whiteness and can drift lot to lot).
4. Coating. Coated (stearic acid) or uncoated — an orthogonal choice driven by loading and your dispersion process, not by the grade number. See coated vs. uncoated.

Some producers code by mesh, others by micron, which is another way the same grade can look like two different products. Mesh counts the openings per inch of a sieve, so a higher mesh number is finer. Micron (D50 / D97) measures the particle size directly by laser diffraction (ISO 13320), so a lower micron number is finer.

Higher mesh and lower micron both mean finer, but the two scales are not exactly interchangeable — mesh describes a sieve, microns describe the particles. As a rough guide, 1250 mesh is around 10 µm. Where a supplier gives only a mesh number, ask for the D97 in microns so you can compare like for like.

In the Kantor KC Series, "KC" is the Kantor product line, and the number tracks the top cut (D97) — the finer the grade, the lower the number:

Every grade shares the same chemistry: CaCO₃ ≥98%, Fe₂O₃ ≤0.05%, whiteness ≥98, ISO brightness (R457 / ISO 2470) ≥95, available coated (stearic acid) or uncoated. Only the fineness changes across the ladder — so choosing a KC grade is a particle-size decision, not a whiteness one. Values are typical; the spec is confirmed per lot on the certificate of analysis. To match a grade to your line, use the grade selector or read which grade for your application.

When you search a grade code, you are often comparing labels that mean different things at different producers. The reliable habit is to put the spec sheets side by side, match the D97 to your gauge, check the whiteness against its stated standard, and then settle it with a free sample on your own line before you commit. Send your application, the gauge or wall thickness, and the spec you run today, and we will recommend a Kantor KC Series grade and dispatch a sample (under a tonne) with a per-lot certificate of analysis.

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.

Is 'KC grade' calcium carbonate an industry standard?

No — "KC" is a supplier's product code, not a standardized designation. No ISO, ASTM, or national standard defines a "KC grade." Different producers use KC-numbered grades to mean different things, so compare by the actual spec (D97, whiteness and its method, purity, coating), not the code.

Does KC-4 mean the same thing from every supplier?

No. Without a common definition, one producer's KC-4 can differ in particle size, whiteness, purity, and coating from another's. Read the technical data sheet: match the D97 to your gauge and check whiteness (with its standard, e.g. R457 / ISO 2470), CaCO₃ content, and Fe₂O₃.

What do the Kantor KC Series numbers mean?

"KC" is the Kantor line and the number tracks the top cut (D97): KC-4 ≈ 5.5 µm (finest) to KC-17 ≈ 17 µm (coarsest). Chemistry and whiteness are the same across the ladder — only fineness changes.

Is calcium carbonate graded by mesh or micron?

Both, depending on the producer. Mesh counts sieve openings per inch; micron (D50 / D97) measures particle size by laser diffraction. Higher mesh and lower micron both mean finer. As a rough guide, 1250 mesh is around 10 µm — but the scales are not exactly convertible, so compare the D97 where you can.

How do I compare two calcium carbonate grades with different codes?

Ignore the codes and line up four numbers: top cut (D97) versus your gauge, whiteness and its measurement standard, CaCO₃ purity and Fe₂O₃, and coated versus uncoated. A code tells you nothing a spec sheet does not.