Technical indicators of calcium carbonate and its application in plastics
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 in a certain area of the screen. 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.
Application of calcium carbonate in plastics
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:
- Improve the dimensional stability of plastic products
The addition of light calcium carbonate plays a skeletal role in plastic products, and has a great effect on the dimensional stability of plastic products.
- Improve the hardness and rigidity of plastic products
In plastics, especially soft polyvinyl chloride, the hardness gradually increases with the addition of calcium carbonate, and the elongation decreases with the increase in hardness. Light calcium carbonate with fine particles and high oil absorption has a large increase in hardness. Conversely, light calcium carbonate with a small particle coarse oil absorption value has a small increase in the hardness of the plastic. In soft PVC, the hardness growth rate of heavy calcium carbonate is the smallest, followed by light calcium carbonate (light calcium).
The plastic (resin) of light calcium carbonate generally does not have a reinforcing effect, and the particles of light calcium carbonate can often be infiltrated by the resin. Therefore, the normal effect of adding light calcium carbonate is to increase the rigidity of the resin, the elastic modulus and the hardness. Also increase. As the amount of addition increases, both tensile strength and extreme elongation decrease.
Different calcium carbonate, different addition amount, will have different hardness.
- Improve plastic processing performance
The addition of light calcium carbonate can change the rheological properties of plastics. Light calcium carbonate powder is often added in a relatively large amount, which will help it mix with other components and also help the processing and shaping of plastics. The addition of light calcium carbonate, especially after surface treatment of light calcium carbonate, can not only increase the hardness of the product, but also improve the surface gloss and surface smoothness of the product. The addition of light calcium carbonate can reduce the shrinkage, linear expansion coefficient, and creep properties of plastic products, creating conditions for processing and forming.
- Improve the heat resistance of plastic products
Adding light calcium carbonate to general plastic products can improve the heat resistance. For example, adding about 40% light calcium carbonate to polypropylene increases the heat resistance by about 200°C. When the filling ratio is less than or equal to 20%, the heat-resistant temperature increases by 8 to 130°C.
- Improve the astigmatism of plastics
In plastic products, some products require whitening and opacity, and some hope to extinction. The addition of light calcium carbonate can play a certain role in this regard.
Light calcium carbonate with whiteness above 90 has obvious whitening effect in plastic products. When combined with titanium dioxide and lithopone, the matting properties of plastic products have been greatly improved. In calcium plastic paper, low-density polyethylene and high-density polyethylene film, calcium carbonate can be added to achieve the effects of astigmatism and extinction, making it suitable for writing and printing. Calcium carbonate with better whiteness can also replace expensive white pigments.
- It can make the product have some special properties
The addition of light calcium carbonate to the cable material has a certain insulating effect, and the addition of light calcium carbonate can improve the electroplating performance and printing performance of some products. Fine or ultrafine light calcium carbonate is added to polyvinyl chloride (PVC), which has a certain flame retardant effect.
- Reduce the cost of plastic products
The price of ordinary light calcium carbonate and heavy calcium carbonate is far lower than the price of plastics. The addition of light calcium carbonate will reduce the cost of plastic products, so light calcium carbonate is called a filler or extender.
At this stage, adding calcium carbonate to reduce the cost of plastics is the main goal. With the improvement of the surface properties of calcium carbonate and the controllable shape and particle size, calcium carbonate will gradually become a functional filler for the purpose of strengthening or imparting functionality.
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 wear 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.