About Precipitated Calcium Carbonate (PCC)
Precipitated calcium carbonate, or PCC, is made chemically rather than by grinding. Quicklime is slaked with water to form milk of lime, and carbon dioxide is then passed through it under controlled temperature and concentration, so that calcium carbonate crystallises as fine, uniform particles. Process conditions set crystal shape and size, which is why PCC can be tailored in ways ground calcite cannot.
The result is a grade with consistently higher purity and brightness than most GCC, a narrow size distribution with a median typically of 1–3 µm, and a lower bulk density. In paper, PCC is used as a filler that raises the brightness, opacity and bulk of the sheet. In premium emulsion paints it acts as a high-brightness extender and spacer for titanium dioxide, and contributes to dry hide in matt finishes. Sealants, adhesives and PVC compounds use PCC to build controlled thixotropy, slump resistance and a smooth surface.
Obsidian Minerals supplies PCC with brightness, particle size, oil absorption and pH reported on each batch Certificate of Analysis. PCC has a higher surface area than ground grades and absorbs more binder, so formulators moving from GCC should adjust binder and dispersant levels and run trials before full-scale use.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| CaCO₃ | ≥ 98.5 % | Internal method (titration) |
| Brightness (GE) | ≥ 96 | Internal method |
| Median particle size (D50) | 1–3 µm | Laser diffraction (ISO 13320) |
| Specific surface area (BET) | 5–12 m²/g | ISO 9277 |
| Oil absorption | 30–50 g/100 g | ASTM D281 |
| Loose bulk density | 0.3–0.6 g/cm³ | Internal method |
| pH (10 % slurry) | 9.0–10.5 | ISO 787-9 |
| Moisture | ≤ 0.5 % | Internal method (105 °C) |
Typical values for guidance. Guaranteed limits and crystal form are stated on the Technical Data Sheet and batch CoA.
Key features & benefits
High brightness
Typical GE brightness of 96 or higher makes PCC one of the brightest calcium carbonate fillers, useful for high-white papers, premium interior paints and light-coloured sealants.
Fine, uniform crystals
Controlled precipitation produces a narrow particle size distribution with a median of about 1–3 µm and very few coarse particles, giving smooth surfaces and consistent rheology.
Low impurity level
Precipitated from lime, PCC carries less iron, silica and acid-insoluble matter than most ground grades, which helps in clean shades and in formulations sensitive to trace impurities.
Light and bulky
Low bulk density and high void volume increase sheet bulk in paper and contribute to dry hide in matt paints formulated above the critical pigment volume concentration.
Tailored morphology
Crystal shape and size are set by process conditions, so PCC with different morphologies and surface areas can be developed on request for specific paper, coating or sealant needs.
Applications
Paper filler
Added at the wet end of uncoated and coated paper grades to raise brightness, opacity and bulk, and to allow higher filler levels in the sheet subject to strength requirements.
Premium matt and interior paints
A high-brightness extender and TiO₂ spacer in premium interior emulsions, where its oil absorption and particle packing help dry hide and a clean, flat matt finish.
Sealants and adhesives
Provides controlled thixotropy, slump resistance and a smooth surface in sealant and adhesive formulations; surface-treated PCC types can be discussed on request for moisture-sensitive systems.
PVC and rubber compounds
Used in PVC plastisols, flexible compounds and light-coloured rubber goods where fine, uniform particles help surface finish, colour and gloss while extending the compound cost-effectively.
Usage & handling
- Paint formulations commonly use PCC at about 5–20 % by weight as a partial replacement for other extenders, with the level set by trials.
- Raise dispersant and binder levels gradually when converting from GCC, because PCC's higher surface area increases demand.
- Add slowly to the mill base under high-speed dispersion to avoid lumps forming from the light, bulky powder.
- Keep bags sealed and dry, as fine PCC picks up moisture and can cake in humid storage.
Packaging & supply
- 25 kg multi-wall paper or HDPE bags with inner liner
- 1 MT or 1.2 MT jumbo bags for bulk users; actual fill weight depends on the grade's bulk density
- Custom bag weights and private labelling on request
Frequently asked questions
How is PCC different from GCC?
PCC is made by precipitating calcium carbonate from milk of lime with carbon dioxide, while GCC is natural calcite that has been ground. PCC has higher purity and brightness, a finer and narrower size distribution, higher surface area and lower bulk density. Those differences make it better suited to paper and premium coatings, while GCC remains more economical for volume filling.
What is PCC used for in paper?
In papermaking, PCC is added as a filler at the wet end of the paper machine. It increases brightness and opacity, adds bulk so the sheet feels thicker for its weight, and allows part of the more expensive fibre to be replaced. The achievable filler level depends on the paper grade and its strength requirements.
Why does PCC have higher oil absorption than GCC?
PCC particles are finer and have a higher specific surface area, typically 5–12 m²/g, and many crystal forms pack loosely with more internal voids. Both factors mean more binder or oil is needed to wet the powder. In matt paints this can be used to advantage for dry hide, but formulations should be rebalanced when switching from GCC.
Can PCC be used in PVC?
Yes. PCC is used in PVC plastisols, flexible compounds and some rigid applications where fine particle size and high brightness help surface finish and colour. For rigid pipe and profile extrusion, the stearic-coated GCC grade is often more economical. The right choice depends on the compound and should be confirmed with processing trials.
What particle size and crystal form is your PCC?
The standard PCC grade has a typical median particle size of 1–3 µm and a BET surface area of 5–12 m²/g. Crystal form and size can vary with production conditions and can be discussed for specific requirements. The applicable values are confirmed on the Technical Data Sheet, and each batch CoA reports the measured results.