Use of Calcite in Elastomers

The number of elastomers is quite large and almost all technical rubber products contain calcium carbonate as filler. The variable is only the ratios according to the application.

For example, fillers with a d50 value between 5 and 15 microns, a ball cut value between 40 and 80 microns, and a specific surface area of up to 1 g/m² are used as expanding and cheapening agents. The most important applications; cable filling mixtures and carpet base production with SBR or NBR latex. Depending on the type of application, the filling rate varies between 20% and 80%.

On the other hand, calcium carbonates with a d50 of 4 to 8 microns, a top cut of 16 to 40 microns, and a specific surface area of 1 to 2 g/m² are the first and foremost reinforcing agents. Their main task is to improve the dimensional stability of mixed non-ebonite items as if they were ebonite. As much filler as possible is added to the extent that the ebonitization process conditions allow. The use of 40% to 60% filler is easily possible, although occasionally higher rates are used.

Natural calcium carbonate, with a d50 of 1-3 microns, a ball cut of 7 to 15 microns, and a surface area of 4 to 10 g/m², act as a dispersant and processing aid. If 15-50% fillers smaller than 1 micron are used, these fillers affect the colloidal proportions of the rubber mixtures. These improve the homogeneous distribution of the agglomerates formed during mixing and help the extrusion and calendering properties of rubber mixtures. They are mainly used in combination with other fillers such as kaolin, silicate and carbon black. Depending on the situation, they are added between 15% and 30%.

Typical fill rates in elastomers

Very fine calcium carbonate types with a d50 value of less than 1 micron, a ball cut of less than 6 microns, and a surface area of 7 to 10 g/m² have properties unique to additives. Their main effect in rubber blends is to improve the colloidal range of sizes. Calcium carbonate, ranging from 1 to 600 nm, is compared with the effects of silica and carbon black. Here, calcium carbonate is added to facilitate the dispersion of active fillers such as silica and carbon black. A 10-15% calcium carbonate additive is sufficient to achieve such effects.

Calcium carbonate particles also have a reinforcing effect on the colloidal knee. It provides a more homogeneous dispersion of other components such as ebonitization accelerator, resins, zinc oxide, peroxide, aging retarding agents, anti-ozonant waxes, pigments or sulfur. This brings other advantages as well.

• Reduction of mixing time
• Drop in mixing temperature
• Constant ebonitization quality and reproducibility of mixer parameters
• Protection of energy costs

In particular, it is recommended to use very fine calcium carbonate in EPDM, NBR, CR, and natural rubber mixtures where silica and carbon black are used in high proportions. Such plastics are used in many areas such as gaskets, shoe soles, V-belts, wheels.

The second importance of the use of calcium carbonate is that it is used as a dust remover and solvent agent. When solvents and talc are expensive to use, calcium carbonate is used to remove the layers of rubber.