Summary:Calcium content is an important quality and technical index of calcium carbonate. Modified masterbatch requires a higher calcium content of calci
Calcium content is an important quality and technical index of calcium carbonate. Modified masterbatch requires a higher calcium content of calcium carbonate, generally above 98%. The higher the calcium content, the more stable the processing properties of calcium carbonate. When the calcium content is low, it will increase the content of impurities such as heavy metals and other non-metals, which not only affects the use of calcium carbonate, but also affects the processing technology, affects product quality or harms processing equipment.
The whiteness of calcium carbonate directly affects the whiteness and coloring of the modified masterbatch, and the modified masterbatch has very strict requirements on the whiteness of calcium carbonate. At present, the whiteness of 400 mesh calcium carbonate is required to reach more than 95%, and the whiteness of calcium carbonate processed by some ore can reach about 97%. In order to improve the whiteness of products, some modified masterbatch manufacturers often add fluorescent whitening agents to achieve the effect of increasing whiteness. However, because the chemical components of the fluorescent whitening agent are prone to decomposition reactions under high temperature and high shear, if the type of the fluorescent whitening agent is not properly selected or the amount of addition is excessive, not only will the product be decomposed and yellow, it will also appear non-dispersed or Agglomeration phenomenon. Fluorescent brighteners will cause some irritation to plastic products that are involved in hygiene and safety and contact the human body, and should not be used.
Hue is also a very important technical indicator of calcium carbonate. The determinants of temperature and hue are the structure and source of the ore. These factors will directly affect the colorability of plastic products, and affect the color and gloss of plastic products. Therefore, the whiteness and hue of calcium carbonate are important technical indicators that cannot be ignored.
Moisture And Volatile Content
The raw materials of calcium carbonate-natural marble, calcite, etc., generally do not contain structural water. After being processed into superfine powder, it is easy to absorb moisture during processing, storage and transportation. Calcium carbonate sometimes contains a small amount of volatile matter. If the content of these substances is too high, it will affect the modified masterbatch and plastic products.
The content of moisture and volatile matter in calcium carbonate should generally be controlled at about 0.3%. In actual application, when the moisture content in the product is ≥0.3%, it will easily affect the product quality, make the product surface rough, generate bubbles, burn, decompose, etc. phenomenon. Therefore, controlling the moisture content is very important to the quality of the modified masterbatch. The common method is to use a high-speed mixer to heat and dry to eliminate the moisture.
In the production of modified masterbatch with high content of calcium carbonate, it is possible to avoid the use of sink infiltration strand cutting and water ring granulation as much as possible, and the crawler drive net type dry granulation process and grinding surface hot cutting granulation process , Under the premise of increasing production output, the moisture and volatile content of the modified masterbatch can be minimized, and the product quality of the modified masterbatch can be guaranteed.
Particle Size Distribution
The particle size distribution of calcium carbonate is an important quality control index for the modified masterbatch. In the particle size analysis of inorganic mineral powders, simpler sieving methods are commonly used, and the commonly used specifications in sieving methods are represented by "mesh". The so-called mesh is the number of sieve holes per inch of screen. However, a more accurate and scientific particle size analysis method is to measure the actual size of the particle size, expressed in micrometers (μm).
The sieving method is one of the most traditional particle size analysis methods. The ultrafine powder with good dispersibility is sieved with a certain mesh sieve. The weight ratio of the powder passing under the sieve to the sieve is the sieving rate. The commonly used standard sieve has the finest 500 mesh (equivalent to about 25μm). The new electrodeposition screen can screen powder as small as 5μm (2500 mesh), but it takes a long time to screen and is prone to blockage. For ultrafine powders smaller than 10μm (1250 mesh), it is difficult to use the sieving method for particle size analysis and detection.
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 performance of the material, and the wider the particle size distribution range, the worse the performance of the material. For example, calcium carbonate of 1250 mesh should have a particle size of about 10μm. If the particle size is distributed between 5 and 38μm, although the theoretically calculated average particle size can be close to 10μm, due to the small particle size and large specific surface area, it is easy to aggregate into agglomerates; The assembly causes the surface roughness of the product, so its processing performance and mechanical properties will be affected.
According to the different mineral structure, the particle shape of calcium carbonate can be divided into multi-cube, flat, poly-prism, cuboid, long rod, and other irregular shapes.
The particle shape of calcium carbonate has a great influence on the processing technology, product quality, melt fluidity and mechanical properties of the modified masterbatch. Multi-cube, multi-prismatic, and cuboid-shaped calcium carbonate has good melt fluidity in the processing of modified masterbatch, and is easy to be coated and cross-linked with coupling agent. The processing equipment is relatively small. After the product is finished, it is easy to affect the mechanical properties of the plastic product (such as tensile strength, flexural modulus, etc.).
The flat and long rod-shaped calcium carbonate particles have a relatively large specific surface area, and the amount of auxiliary agents such as coupling agents and plasticizers in the modified master batch should be appropriately increased. Otherwise, it is easy to cause uneven coating, poor melt fluidity, increase in main engine power, increase in head resistance, and overheating and decomposition. However, materials of this type are beneficial to the physical properties of plastic products, and can increase tensile strength, bending strength, and reduce shrinkage of plastic products.
Other Component Content
The content of chemical components, metal impurities and other components in calcium carbonate also have a certain impact on the quality of calcium carbonate, and will have a certain impact on the application of plastic modified master batches and plastic products. Calcium carbonate generally contains a small amount of magnesium oxide (MgO), silicon dioxide (SiO₂), iron trioxide (Fe2O3), aluminum oxide and trace heavy metals (aluminum, arsenic, mercury, etc.). The content of each other component varies depending on the place of origin and the ore.
The MgO in calcium carbonate has low hardness and slightly lower whiteness than calcium carbonate. Its chemical stability and processing properties are similar to calcium carbonate, and generally will not have a major impact on calcium carbonate.
SiO₂ belongs to natural quartzite, which has a small specific surface area and good fluidity. However, SiO2 has high hardness (Mohs hardness 7), which is serious for equipment wear, especially when the coating is uneven or the amount of plasticizer is small. If the filled modified masterbatch is used in the production and processing of polypropylene flat yarn, it is easy to collide with the high-speed slitting tool and often damage the blade, which affects the production and processing.
Although the content of Fe2O3 in calcium carbonate is very small, it is prone to chemical changes when iron is mixed with chemical additives. Fe2O3 is easy to decompose and turn yellow after heating, which affects the whiteness and appearance of the modified masterbatch. Therefore, Fe2O3 is used in the modified masterbatch. China is a substance that cannot be ignored.
The lower the content of SiO₂ and Fe2O3 in calcium carbonate, the smaller the impact on the quality of the modified masterbatch. Generally, 5% hydrochloric acid diluted solution can be used to add calcium carbonate to the glass for chemical analysis to observe the amount of precipitate in the solution To determine the content of SiO₂; the color of the solution is slightly yellow, indicating that the Fe2O3 content is higher.
Read More About