Calcium carbonate (CaCO₃) is widely used in the paper industry as a filler and coating pigment to improve brightness, opacity, smoothness, and printability. Grinding CaCO₃ to the right particle size and distribution is crucial for optimal performance in papermaking. Here’s an overview of the process:
1. Types of Calcium Carbonate Used in Paper Industry
– Ground Calcium Carbonate (GCC): Produced by mechanical grinding of limestone or marble.
– Precipitated Calcium Carbonate (PCC): Chemically synthesized for finer particles and controlled morphology.
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2. Grinding Process for GCC
– Crushing & Pre-Grinding:
– Large limestone/marble rocks are crushed into smaller pieces (~5–20 mm).
– Jaw crushers, hammer mills, or impact crushers are used.
– Fine Grinding:
– Ball mills, vertical roller mills (VRM), or stirred media mills refine particles to the desired size (typically 0.5–10 µm).
– Wet grinding is often preferred for ultra-fine GCC (98% CaCO₃) ensures minimal impurities.
– Rheology Control: For coating slurries, viscosity must be optimized to avoid issues in paper machines.
– Energy Efficiency: Wet grinding consumes less energy for ultrafine particles but requires drying.
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4. Advantages of GCC in Paper Manufacturing
– Cost-effective compared to PCC.
– Improves paper bulk and reduces fiber usage.
– Enhances optical properties (brightness, opacity).
– Compatible with alkaline papermaking processes.
5. Comparison with PCC
| Feature | GCC (Ground CaCO₃) | PCC (Precipitated