Calcium Carbonate
GEOLOGIC CONTEXT
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The calcium carbonates used as filler are generally obtained by grinding of natural rocks in order of increasing whiteness chalks, limestones and marbles.
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whiteness chalks
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limestones
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marbles
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Carbonates used as filler contain mostly more than 95 % of CaCO3. The most wide-spread mineral is:
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The calcite
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The aragonite
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The dolomite
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Certain number of impurities can affect the physical or chemical characteristics of these limestones:
Limestones and chalks are sedimentary rocks deposited essentially in marine or lakeside environment. Among rocks containing more than 50 % of CaCO3 we distinguish, according to their origin:
A very pure calcium carbonate maybe also obtained by synthetic processes. It is known under the name of Precipitated Calcium Carbonate (PCC).
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PROPERTIES
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The hardness of the calcite is 3 in the scale of Mohs, against 3.5 for aragonite and from 3.5 to 4 for the dolomite (this last one is thus too abrasive for certain uses as the manufacture of paper).
The characteristics of the calcium carbonates used as mineral fillers depend essentially on the aimed use:
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Uses
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Carbonate fillers have very numerous industrial applications. They bring certain properties to the finished product (whiteness for example) and often allow reducing the cost.
In France, the uses of white limestones for fillers divide up, in volume, in the following way:
In the USA, we can consider that the market of these products divides up, in values, in the following way:
Manufacture of paper
Mineral fillers allow to improve printability of paper and to reduce its manufacturing cost. The pulverized calcium carbonate is used, in the mass of paper, to fill chinks between cellulose fibres.
It is also used for paper coating what corresponds to the deposit on the surface of the paper of a mixture of mineral fillers, latex and water. Globally, the proportion of minerals in the paper varies from 15 to 30 % and can reach 40 % in luxury papers.
Sought specifications are:
Use in plastics and rubbers
Most of the resins which enter in the manufacture of these products are not used pure, but mixed with other materials to make "compounds".
We use fillers in more than 20 types of resins although only four of them (polypropylene, polyamides, thermoplastics polyesters and polyvinyl chloride) represent 90 % of the market of mineral fillers in plastics. The PVC and the rubber constitute the main markets for the calcium carbonate. The PVC contains it frequently from 17 to 40 % and until 40 - 80 in the ground paving stones in PVC. Thermo polyesters contain from 60 to 70 %.
The calcium carbonate allows improving the finish of surface, to control well the manufacture of the product and to increase its electric resistance. To improve the link between the plastic and its filler, we use mostly treated carbonates stearic.
Sought specifications are
Use in the paints
The calcium carbonate allows reducing the proportion of necessary oxide of titanium.
It enters, on average for 10 to 35 % (exceptionally 50 %) in the composition of the paints with solvent and especially the paints with aqueous dispersal.
The specific qualities of carbonates for the paints are
On the other hand, they present the inconvenience to be sensitive to chemical attacks.
Sought specifications are:
For the top of the range paints, the used carbonates of calcium undergo a surface treatment of stearic acid, which confers them the following qualities:
Use in putties, coatings and adhesives
Putties consist of 85 % of carbonates and 15 % of linseed oil. The used carbonates are generally neither very white (crushed chalk), nor very fine (15 - 20 µm).
Waterproofness coatings concerned by these uses are soft enough organic substances to be applied in liquid or viscous state, and hardening afterward to stick in a permanent way to the support. An adhesive can be defined as an organic substance or not, natural or synthetic, which allows to stick two other substances by a link of surface.
The calcium carbonate is the filler the most used because of its whiteness, costs and performances (absorption of oil, particle size analysis).
Use in pharmacy and cosmetics
In pharmacy, the calcium carbonate, essentially the CCP, is used as excipient in the manufacture of pills and tablets and as active agent for the manufacture of tablets facilitating the digestion. In cosmetics, the crushed calcium carbonate and especially the CCP are essentially used for the manufacture of toothpastes. The specifications are very strict, specific treatments are operated and of numerous controls made. The controls appearing in the monograph " Calcium carbonate " of the French pharmacopoeia 10th edition (in January, 1989) are the following ones:
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