Ground calcium carbonate is among the least expensive mineral fillers on the market, and supply is available from numerous mines located worldwide. Calcium carbonate is available in particle sizes ranging from less than 1.0 micrometer to large white decorative chips.
“Calcium carbonate is a relatively soft, insoluble mineral that is widely used to reduce cost and to control shrinkage in adhesive and sealant formulations,” says Bob Baker, Technical Service director, Huber Engineered Materials’ calcium carbonate and barium sulfate businesses. “It also offers exceptional rheology benefits and is mildly alkaline, making it compatible with most resin systems. Calcium carbonate is blocky in shape, which allows for low surface area and viscosity. Its low surface area allows the formulator to use large amounts in the formulation, compared with most other mineral products.”
However, there can be many differences among calcium carbonate grades, depending upon where they are mined and how they are processed. As a result, brightness, particle-size distribution and surface area can all vary. Calcium carbonate is available in the widest variety of particle-size distributions of any mineral, and an optimum form for an adhesive and sealant application can easily be found.
“In high-end formulations, calcium carbonate helps the product maintain its viscosity, physical strength and properties,” says Baker. “In commodity formulations, it can replace other more-expensive ingredients, improve gap-filling properties and modify viscosity.”
The Hubercarb® lineup of calcium-carbonate products offers a variety of particle-size distributions, resulting in options to meet almost every adhesive and sealant application.
Since calcium carbonate processing involves grinding large rocks into smaller particles - ultimately to sizes useful for formulating - product brightness is heavily dependent on the mine and, thus, the nature of the specific deposit. Some mines yield calcium carbonate with 95 brightness (on a scale of 100), which is ideal for bright-white adhesive applications. Other calcium-carbonate mines may have stone with contaminants that yield lower brightness products. These are used in less-color-critical applications or where the adhesive is not visible. Other deposits have exceptional purity, lower abrasive properties and lower moisture levels than other calcium carbonates.