Calcium carbonate has been used as an inorganic filler in plastic filling for many years. In the past, calcium carbonate was generally used as a filler to reduce costs and received better results. In recent years, with the extensive use in production and a large number of studies, it has been found that filling a large amount of calcium carbonate can not significantly reduce the performance of the product, and even some aspects will be greatly improved, such as mechanical properties, thermal properties, etc.
There are two main types of calcium carbonate: heavy calcium carbonate (commonly known as heavy calcium) and light calcium carbonate (commonly known as light calcium).
Heavy calcium is made by mechanical methods (using Raymond mill or other high-pressure mills) to directly crush natural calcite, limestone, chalk, shells, etc.
Light calcium, also known as precipitated calcium carbonate, is made by calcining raw materials such as limestone to produce lime, then adding water to digest the lime to produce milk of lime, then passing carbon dioxide into carbonization precipitation, and finally dehydrating, drying and crushing. Or firstly use sodium carbonate and calcium chloride to carry out the metathesis reaction to generate calcium carbonate precipitation, and then it is prepared by dehydration, drying and pulverization.
Due to different preparation methods, light calcium has a large accumulation volume and appears light. In fact, the density difference between the two is very small. The density of light calcium is 2.4 to 2.7 g/cm3, and the density of heavy calcium is 2.7 to 2.9 g/cm3.
The particle size of heavy calcium is generally larger, the distribution is wider, and the particle shape is irregular; while the light calcium has a crystal shape and the particle size is smaller.
Some of the main technical indicators of calcium carbonate are: mesh number, whiteness, calcium carbonate content.
Mesh number: Mesh number refers to the number of holes on a screen in a certain area. The larger the mesh number, the smaller the particle size, and the required production process will be more complicated. The larger the mesh, the stronger the activity of the filler particles, the easier it is to bond with the plastic matrix, the better the compatibility, but the worse the dispersibility. Common meshes are 400, 600, 800, 1000, 1200, 2000. Generally, fillers with large meshes need to be surface treated to improve their dispersibility.
Whiteness: Since pure calcium carbonate is white, the higher the purity of the calcium carbonate product, the whiter the product and the less variegated color. Ferrite, silicon, etc. will make the product appear yellow, dark and other variegated colors. Generally speaking, when the whiteness is higher than 90%, calcium carbonate can be used as a white dye for plastics, but many manufacturers are not satisfied with the 90% standard, and even launched products with a whiteness as high as 97%. Products with higher whiteness have higher grades, less impurities, and are not easy to damage processing equipment. When the plastic is colored, the color is purer and more stable.
Calcium carbonate content: refers to the calcium carbonate content of limestone raw materials, which can also be said to be purity.
Calcium carbonate has a wide range of applications, and most plastics can be used. Adding calcium carbonate has a certain effect on improving certain properties of plastic products and expanding their application range. They can reduce resin shrinkage, improve rheological behavior, and control viscosity in plastic processing. It can also play the following roles:
Filling the plastic with calcium carbonate is like adding a skeleton to the plastic, which improves the dimensional stability and hardness of the plastic, and can also improve the abrasion resistance and gloss of the plastic to a certain extent. As usual, it is used for PP, PE, PVC sheets and pipes.
Calcium carbonate is non-toxic, tasteless, and environmentally free. It is a common mineral in the natural environment. It is suitable to be added to biodegradable plastics and food packaging plastics without adversely affecting people and the environment. Studies have also shown that biodegradable plastics added with calcium carbonate degrade faster in the soil.
Light calcium carbonate has a characteristic. It is relatively oil-absorbing and easy to absorb plasticizers in plastics, resulting in poor plasticizing effect. To improve this situation, calcium carbonate can be modified.