Views: 11 Author: Site Editor Publish Time: 2023-12-28 Origin: Site
Calcium content
Calcium content is an important quality and technical indicator of calcium carbonate. The modified masterbatch requires a high calcium content of calcium carbonate, generally above 98%. The higher the calcium content, the more stable the processing performance of calcium carbonate. When the calcium content is low, it will increase the content of heavy metals and other non-metallic impurities, which not only affects the use of calcium carbonate, but also affects the processing technology, affects product quality, or causes harm to processing equipment.
whiteness
The whiteness of calcium carbonate directly affects the whiteness and coloring of modified masterbatch. The modified masterbatch has very strict requirements for the whiteness of calcium carbonate. At present, the whiteness requirement for 400 mesh calcium carbonate is to reach over 95%, and some ore processed calcium carbonate can reach a whiteness of about 97%. Some modified masterbatch manufacturers often add fluorescent whitening agents to increase the whiteness of their products. However, due to the tendency of the chemical components of fluorescent whitening agents to undergo decomposition reactions at high temperatures and high shear rates, improper selection or excessive addition of fluorescent whitening agents can not only cause the product to decompose and turn yellow, but also result in non dispersion or agglomeration. Fluorescent whitening agents can cause certain irritation to plastic products that involve hygiene and safety and come into contact with the human body, and are not suitable for use.
Color is also a very important technical indicator of calcium carbonate, and the determining factors of temperature and color are the structure and source of the ore. These factors will directly affect the coloring properties of plastic products, affecting their color, glossiness, and so on. So, the whiteness and hue of calcium carbonate are important technical indicators that cannot be ignored.
Moisture and volatile matter content
The raw materials of calcium carbonate, such as natural marble and calcite, generally do not contain structural water. After being processed into ultrafine powder, it is prone to moisture absorption during processing and storage. Calcium carbonate sometimes contains trace amounts of volatile substances, and if the content is too high, it can have an impact on modified masterbatch and plastic products.
The moisture and volatile matter content in calcium carbonate should generally be controlled at around 0.3%. In practical applications, when the moisture content in the product is ≥ 0.3%, it is easy to affect the product quality, make the product surface rough, produce bubbles, burning, decomposition and other phenomena. So controlling the moisture content is very important for the quality of modified masterbatch, and the commonly used method is to use a high-speed mixer for heating and drying to eliminate moisture.
In the production of modified masterbatch with high content of calcium carbonate filling, it is advisable to avoid using processes such as soaking in water tanks, pulling and granulating, and water ring granulation as much as possible. Instead, the use of track transmission network dry granulation process and grinding surface hot cutting granulation process can reduce the moisture and volatile matter content of the modified masterbatch to the maximum extent while increasing production output, ensuring the product quality of the modified masterbatch.
Particle size distribution
The particle size distribution of calcium carbonate is an important quality control index for modified masterbatch. The particle size analysis of inorganic mineral powders often uses a relatively simple screening method, and the commonly used specifications in the screening method are represented by "mesh". The so-called mesh size refers to the number of sieve holes per inch of mesh. But a more accurate and scientific particle size analysis method is to use the actual size of the measured particle size, measured in micrometers（ μ m) Represent.
The sieving method is the most traditional particle size analysis method, which involves sieving ultrafine powders with good dispersibility through a certain number of sieves. The weight ratio of the sieved powder passing through the sieve is the sieving rate. The thinnest standard sieve commonly used is 500 mesh (equivalent to 25) μ About m), the new electrodeposition screen can screen up to 5 particles μ M (2500 mesh) powder, but with a long screening time, it is prone to clogging. For less than 10 μ The ultra-fine powder of m (1250 mesh) is difficult to use for particle size analysis and detection by sieving method.
In practical applications, the particle size distribution range of granular materials such as calcium carbonate fluctuates greatly. The narrower the particle size distribution range, the more stable the material's performance is. The wider the particle size distribution range, the worse the material's performance is. For example, 1250 mesh calcium carbonate should have a particle size of 10 μ About m, if the particle size distribution is between 5-38 μ m. Although the theoretical calculation of the average particle size can approach 10 μ m. But due to its small particle size and large specific surface area, it is easy to agglomerate into clusters; The large particle size can cause surface roughness and other phenomena of the product, so its processing performance, mechanical properties, etc. will be affected.
Particle shape
The particle shape of calcium carbonate can be divided into polyhedra, flattened bodies, polyhedra, rectangular bodies, elongated bodies, and other irregular bodies according to the different mineral structures.
The particle shape of calcium carbonate has a significant impact on the processing technology, product quality, melt flowability, and mechanical properties of modified masterbatch. Calcium carbonate with the shapes of polyhedra, prisms, and rectangles has good melting and flowability in the processing of modified masterbatch, and is easy to be coated and crosslinked with coupling agents. The wear of processing equipment is relatively small. The disadvantage is that the modified masterbatch can easily affect the mechanical properties of plastic products (such as tensile strength, bending modulus, etc.) after being applied to plastic products.
The specific surface area of flat and long rod shaped calcium carbonate particles is relatively large, and the amount of coupling agents, plasticizers, and other additives in the modified masterbatch needs to be appropriately increased. Otherwise, it is easy to cause uneven coating, poor melt fluidity, increased host power, increased head resistance, and overheating decomposition. But materials of this shape are beneficial to the physical properties of plastic products, such as improving tensile strength, bending strength, and reducing the shrinkage rate of plastic products.
Content of other components
The content of chemical components, metal impurities, and other components in calcium carbonate also has a certain impact on the quality of calcium carbonate, and its application in plastic modification masterbatch and plastic products will have a certain impact. Calcium carbonate generally contains small amounts of magnesium oxide (MgO), silicon dioxide (SiO2), iron trioxide (Fe2O3), aluminum oxide, and trace heavy metals (aluminum, arsenic, mercury, etc.). The content of other components varies depending on the origin and ore.
The MgO in calcium carbonate has a low hardness, slightly lower whiteness, and similar chemical stability and processing performance to calcium carbonate. It generally does not have a significant impact on calcium carbonate.
SiO2 belongs to natural quartzite, with a small specific surface area and good fluidity. However, SiO2 has a high hardness (Mohs hardness of 7), which causes severe equipment wear, especially when the coating is uneven or the amount of plasticizer is small, making it particularly prominent. If filled modified masterbatch is used in the production and processing of polypropylene flat wire, it is prone to collision with high-speed cutting tools and often damages the cutting edge, affecting production and processing.
Although Fe2O3 has a low content in calcium carbonate, it is prone to chemical changes when iron is mixed with chemical additives for processing. Fe2O3 is prone to decomposition and yellowing when heated, which affects the whiteness and appearance of modified masterbatch. Therefore, Fe2O3 is an essential substance in modified masterbatch.
The lower the content of SiO2 and Fe2O3 in calcium carbonate, the less impact it has on the quality of modified masterbatch. Generally, a 5% hydrochloric acid dilution solution can be used to add calcium carbonate to a glass dish for chemical analysis, and the amount of precipitate in the solution can be observed to determine the SiO2 content; The solution has a slightly yellow color, indicating a higher content of Fe2O3.
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