Coating Calcium Carbonate with Stearate
Problem: Calcium Carbonate is a commonly used filler in plastics compounding. Typically, a stearate coating is required to improve dispersiblity of this additive into the compounding process. Traditional coating processes can form undesirable agglomerates that increase the amount of additive required. Due to the high costs of stearates, companies looked for an effective, continuous coating process that reduces operational costs. In addition, traditional melted liquid stearate systems present maintenance and operation problems due to re-freezing in the pumping and liquid handling systems.
- Create an industrial process system that increases coating efficiency compared to traditional technologies
- Reduce stearate addition rate below 5% for a melted liquid system.
- If possible, develop a new process that uses solid stearate instead of liquid melt to reduce maintenance costs and increase up-time.
Solution: The Bepex Turbulizer® paddle mixer was used to continuously heat and coat calcium carbonate with solid-phase stearate. This technology incorporates a high-speed horizontal rotor that provides intense and continuous mixing of multiple components, and its compact design can be incorporated into existing processes with limited space.
At Bepex’s Process Development Center, Calcium Carbonate and stearate were fed in as dry powders at ambient temperature. The stearate additive was evaluated both as a small crushed prill or flake. For this trial, an optional heated jacket on the Turbulizer melted with hot oil or steam in attempt to provide melting and coating in a single step (a coating process commonly known as “filming” of a core particle with a frozen liquid). Because of the very short residence time in the Turbulizer, very accurate feed metering equipment was required for both materials. Loss-in-weight feeders with accuracies in the range of 2% were used.
Benefits and Results:
- The heated jacket properly melted both materials, yielding a product discharge temperature of 120°C
- Homogeneous coating was acheived
- Stearate additional levels were reduced to 0.5% – 2%