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Coating Calcium Carbonate with Stearate

THE PROBLEM

Calcium Carbonate is a commonly used filler in plastics compounding. Typically, a stearate coating is required to improve dispersibility 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.

Process Requirements

  • 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 uptime

Operational Considerations

  • Footprint requirements limited available floorspace for a suitable technology
  • Design needed to be robust enough to withstand inconsistent loading from upstream processes

THE 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.

In our 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 and flake. For this trial, an optional jacket on the Turbulizer, heated with steam or hot oil, was utilized to provide melting and coating in a single step. This coating process is 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 solids. Loss-in-weight feeders with accuracies in the range of 2% were used.

BENEFITS & RESULTS

  • Homogeneous coating of the calcium carbonate was achieved
  • Stearate addition levels were reduced to 0.5-2%
  • The heated jacket on the Turbulizer melted both forms of stearate which efficiently coated the calcium carbonate, and yielded a product discharge temperature of 120°C

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