We often add calcium carbonate to prepare low-cost products or to enhance certain properties. The main types of calcium carbonate used in the plastics industry are heavy calcium carbonate and light calcium carbonate. Although heavy calcium carbonate and light calcium carbonate have the same chemical formula and similar appearance, there are significant differences in their physical and chemical properties as well as processing methods.

Different processing methods

The processing of heavy calcium carbonate is mainly achieved through mechanical crushing and grinding.

The production of light calcium carbonate is obtained through chemical reaction and precipitation.

The latter has a much more complex process and stricter requirements.

Different physical and chemical indicators

(1) Different bulk densities. This is the most obvious difference between the two; the bulk density of heavy calcium carbonate is 0.8~1.3g/cm3, while the bulk density of light calcium carbonate is only 0.5~0.7g/cm3, and the bulk density of nano calcium carbonate products can reach below 0.3g/cm3.

(2) Different whiteness. Heavy calcium products generally contain more impurities, with whiteness typically ranging from 89% to 93%, while light calcium products have a whiteness of 92% to 95%, with some products reaching 96% to 97%. This is the main reason why light calcium products are commonly used in high-end or light-colored products.

(3) Different moisture content. Heavy calcium products have lower moisture content and are more stable, generally around 0.2% to 0.3%, with some high-end heavy calcium products even reaching 0.1%; while light calcium products generally have moisture content ranging from 0.3% to 0.8%, and their moisture stability is poorer, sometimes showing certain fluctuations.

(4) Different particle sizes. Currently, heavy calcium products are only available in micron-sized products, with particle sizes generally ranging from 0.5 to 45μm, which are significantly larger than those of light calcium.

(5) Different crystal forms. Heavy calcium products are all irregular in shape, also known as amorphous, while light calcium products generally have more regular crystal forms, such as ordinary light calcium being mainly spindle-shaped, and nano calcium carbonate being mainly cubic.

Different application processes

Heavy calcium products are mainly used in industries such as papermaking, rubber, and plastics, with a large filling amount, primarily serving as volume fillers, while light calcium has a wider range of applications, mainly as volume fillers. Among them, ultra-fine (commonly known as nano-level) calcium carbonate has already taken on the dual role of functional filler and volume filler, with a smaller filling amount.

Differences in the application of heavy and light calcium in plastics

As mentioned earlier, due to the significant differences in the physical and chemical properties of the two products, in terms of product fineness, light calcium carbonate is much finer than heavy calcium carbonate. Light calcium carbonate can be evenly distributed in plastic materials, has better dispersibility, which improves the uniformity of color, strength, toughness, fatigue resistance, and other comprehensive mechanical properties of the rubber material. The friction coefficient during the granulation process of rubber material is also smaller, enhancing the granulation ability of plastics, while the surface of plastic products is smooth, and the molding ability is also strengthened. However, due to the adsorption force between molecules, high-fineness fillers are prone to agglomeration, which can reduce the uniformity of fillers and overall mechanical properties. Additionally, light calcium carbonate has a larger sedimentation volume than heavy calcium carbonate, which can increase volume and reduce weight in plastics. However, light calcium carbonate has a higher oil absorption value than heavy calcium carbonate, which increases the light absorption of the rubber material, resulting in a satin or matte effect on the product surface.

Therefore, in the plastics industry, a mixed addition of light and heavy calcium carbonate is often used. For example, in the rubber industry, the main purpose of adding heavy calcium carbonate is to increase volume and reduce costs, which does not significantly improve the performance of the rubber itself, while light calcium carbonate, in addition to having the same effect as heavy calcium carbonate, can also improve the performance of rubber to a certain extent.

Additionally, from a production perspective, China is a major country for limestone minerals, but it is by no means inexhaustible. High-purity and high-whiteness heavy calcium ore is very rare. For every ton of heavy calcium ore mined, several tons of slag are produced, causing far greater environmental damage than light calcium. For example, in a certain county in the south, calcium carbonate powder is a pillar industry, and after several years of intensive mining, heavy calcium resources are also beginning to approach depletion, which is no longer uncommon. In contrast, the production of light calcium carbonate has lower requirements for ore and causes less environmental damage, which will inevitably occupy a larger market.