We often add calcium carbonate in order to prepare low prices or improve certain properties.
The calcium carbonate can be applied to the field of plastics are mainly heavy calcium carbonate and light calcium carbonate.
Heavy calcium carbonate and light calcium carbonate have the same chemical formula and similar appearance. In fact, there are great differences in their physical and chemical properties and processing methods.
First of all, the processing methods of the two products are different:
The processing of heavy calcium carbonate is mainly realized by the methods of mechanical crushing and grinding; the production of light calcium carbonate is obtained by chemical reaction precipitation. The latter process is much more complicated than the former, and the requirements are correspondingly stricter.
Secondly, the physical and chemical indicators of the two products are different, the differences are as follows:
(1) The bulk density is different. This is the most obvious difference between the two. The bulk density of heavy calcium carbonate is 0.8~1.3g/cm3, and the bulk density of light calcium is only 0.5~0.7g/cm3. The bulk density can reach below 0.3g/cm3.
(2) Different degrees of whiteness Heavy calcium products have relatively more impurities. The whiteness is generally 89~93%, while the whiteness of light calcium products is generally 92~95%, and some products can reach 96~97%, which is commonly used in light calcium products. The main reason for high-grade or light-colored products.
(3) The moisture content of heavy calcium products is low and stable at the same time, generally 0.2~0.3%, and some high-end heavy calcium products can even reach 0.1%; while light calcium products are generally 0.3~0.8% moisture, and the moisture is stable The performance is poor, and sometimes there are certain fluctuations.
⑷Different particle size Heavy calcium products are currently only micron products, and the particle size is generally 0.5~45μm, which is significantly larger than the particle size of light calcium. ⑸Different crystal forms Heavy calcium products are irregular in shape, also known as amorphous, while light calcium products are generally more regular in crystal form, such as ordinary light calcium is mainly spindle-shaped, while nano-calcium carbonate is mainly cubic crystal form.
The third application process Different heavy calcium products are mainly used in papermaking, rubber, plastics and other industries. They have a large filling amount and are mainly used as volume fillers, while light calcium products have a wider range of applications, mainly volume fillers, and ultrafine ones. (Commonly known as nano-scale) calcium carbonate already has the dual role of functional filler and volume filler, and the filling amount is small.
To sum up, because heavy calcium cannot replace light calcium, the difference in processing cost and application range between the two leads to a large price difference.
As mentioned earlier, because the physical and chemical properties of the two products are quite different, in terms of product fineness, light calcium carbonate is much finer than heavy calcium carbonate. It is better to make the color uniformity of the rubber compound, and the comprehensive mechanical properties such as strength, toughness and fatigue resistance of the rubber compound are improved, and the friction coefficient during the production and granulation process of the rubber compound is also small, so that the plastic has a strong granulation ability. At the same time, the surface of plastic products is smooth, and the molding ability will be enhanced. However, due to the adsorption force between molecules, the high-fineness fillers are prone to agglomeration, and the reverse will reduce the uniformity of the fillers and the comprehensive mechanical energy. And the sedimentation volume of light calcium carbonate is larger than that of heavy calcium carbonate, which can increase the volume and reduce the weight in plastic.
However, the fine oil absorption value of light calcium carbonate is larger than that of heavy calcium carbonate, the light absorption of the rubber compound will increase, and the surface of the product will have a sub-surface or matte effect.
Therefore, the method of mixing light and heavy calcium carbonate is often used in the plastics industry.
For another example, the main purpose of adding heavy calcium carbonate in the rubber industry is to increase the volume and reduce the cost to improve the performance of the rubber itself. There is a certain improvement.
In addition, in terms of production, China is a big country of limestone minerals, but it is by no means inexhaustible and inexhaustible, especially high-purity, high-brightness heavy calcium ore is very rare. Calcium ore will cause several tons of slag, and the damage to the environment is far greater than that of light calcium. For example, calcium carbonate powder in a county in the south is its pillar industry. The situation is not uncommon. However, the production of light calcium carbonate does not have high requirements on ore and causes less damage to the environment, so it will inevitably occupy a larger market.