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Most sealants and many adhesives include a ground calcium carbonate (GCC) in the formulation as a filler to reduce costs and increase the solids level. They add body or viscosity but their contribution to thixotropy is insufficient for them to be used as the system’s rheological control additive. GCCs also contribute to opacity and whiteness. Ground dolomites (calcium magnesium carbonates) are also used. For products of similar median particle sizes, dolomites have slightly lower oil absorptions so allow higher loadings with lower viscosity build. The GCCs, also called ground limestones, are generally brighter.

Surface-treated ground calcium carbonate products disperse more easily in polymeric systems compared to untreated products. The surface treatment is stearic acid which results in a more hydrophobic GCC, with a lower moisture content. Which is to dry - advantageous in moisture curing systems.

Filler loadings in sealant formulations typically range from 10 to 60 percent. The loading level will be directed by the sealant performance. In products that use a precipitated calcium carbonate (PCC) as the sole or main rheological additive, the amount of PCC is included in the calculation of total filler content. The ratio of PCC to GCC can be adjusted to the rheological profile sought. High shear viscosity and extrusion times can be lowered by reducing the amount of PCC and increasing the amount of GCC. This makes the product easier to spray. Increasing the proportion of PCC and reducing the GCC increases the high shear viscosity and extrusion time, while lowering the spraying rate.


SMI Ground Calcium Carbonates and Dolomites for Adhesives and Sealants
In the U.S., Specialty Minerals Inc. (SMI) manufactures a range of ground calcium carbonates and ground dolomites. These products are used in butene rubber, polysulfide, PVC plastisol, silicone, silyl terminated polyether and urethane high-performance sealants, butyl and water-based acrylic and vinyl acetate caulks, unsaturated polyester auto body filler putties, oil based putties, gypsum wallboard tape joint compounds, and epoxy and other adhesives.

The SMI uncoated GCCs used in adhesives and sealant include families of high-brightness Vicron® fine GCCs, Marblewhite® bright coarser GCCs, and white Rivercal™ GCCs. The coated hydrophobic GCCs include Hi-Pflex® 100, 3.5 microns, and Pfinyl® 402, 5.5 microns. The product chart below shows a representative selection from each of these families. Additional products in the GCC families, large and small, are listed on the data sheets for the various groups of products. Click on the product name to download the data sheet.

 

SMI recommends two ground dolomite grades for sealants, Dolocron® 40-13 and 45-12. They are only available uncoated.

 

Tape joint compounds or cements use even larger particle-sized ground limestones and dolomites than those shown for adhesives and sealants. Click here to read more about tape joint compounds and the SMI calcium carbonates recommended for them.

All SMI GCC and ground dolomite plants are ISO 9001 certified. Processes are carefully controlled with rigorous quality assurance procedures to ensure that customers receive the high-quality, consistent products they require.

 

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