Both of our product series start from exactly the same place: ground Egyptian limestone at 99.9% CaCO₃ purity and 97% brightness. The difference is a fraction of one percent of stearic acid on the particle surface — and in the right application, that fraction changes everything.
What the coating actually does
Calcium carbonate is naturally hydrophilic — it prefers water to polymer. Drop an untreated particle into molten polyethylene and it would rather cling to its neighbors than wet into the melt. The result at high loadings: agglomerates, weak points and rough surfaces.
Stearic acid treatment reverses the particle's preference. The fatty acid anchors to the mineral surface and presents a hydrocarbon tail to the outside world — the same chemistry as the polymer around it. The treated particle disperses instead of clumping, which is why coated grades improve processing behavior and surface finish in PVC, PE and PP systems.
Why finer grades carry more coating
Coating requirement follows surface area, and surface area explodes as particles get finer. Our measured values show the relationship directly:
| Grade | D50 (µm) | Measured stearic coating |
|---|---|---|
| 5 µm | 1.52 | 1.47% |
| 8 µm | 2.10 | 1.36% |
| 10 µm | 2.56 | 1.14% |
| 12 µm | 2.78 | 1.06% |
| 15 µm | 3.05 | 0.88% |
| 20 µm | 3.38 | 0.75% |
A supplier quoting one flat coating percentage for every fineness is telling you something about how carefully they measure.
When to specify coated
- PVC pipes and profiles — improved fusion, processing and surface finish
- PE/PP masterbatch, film and injection molding — dispersion at high loadings
- Rubber and cable compounds — uniform distribution through the elastomer
- Moisture-sensitive systems — the hydrophobic surface resists water pickup
When uncoated is the right answer
- Water-based paints and coatings — you want the mineral to wet into water, not repel it
- Paper filling and coating — brightness and printability, no polymer matrix involved
- Construction compounds, adhesives and sealants built on aqueous or mineral binders
- Any application where the treatment adds cost without adding function
The practical rule
If your matrix is a molten polymer or an elastomer, start with coated. If your system is water-based or mineral-based, start with uncoated. If you're between the two — plastisols, hybrid sealants, specialty systems — send us the formulation and we'll recommend from measured data rather than a guess.