What effect will the properties of calcium carbonate have on the modified masterbatch?
The calcium content
Calcium content is an important quality technical index of calcium carbonate.The content of calcium carbonate in modified masterbatch is higher than 98%.The higher the calcium content, the more stable the processing property of calcium carbonate.When the calcium content is low, it will increase the content of heavy metals and other non-metallic impurities, which will not only affect the use of calcium carbonate, but also affect the processing technology, affect product quality or cause harm to the processing equipment.
The whiteness of calcium carbonate directly affects the whiteness and coloration of the modified masterbatch.The whiteness of the modified masterbatch is very strict to calcium carbonate.At present, the whiteness of calcium carbonate for 400 purposes is required to reach more than 95%, and the whiteness of calcium carbonate processed by some ores can reach about 97%.In order to improve the whiteness of products, some modified masterbatch manufacturers often add fluorescent whitener to achieve the effect of increasing whiteness.However, the chemical components of fluorescent brightener are prone to decomposition reaction under high temperature and high shear. If the variety of fluorescent brightener is improperly selected or the number of added doses is excessive, the product will not only decompose and turn yellow, but also will not disperse or agglomerate.Fluorescent whitening agent for health and safety, contact with human body plastic products, will produce certain irritation, not suitable for use.
Hue is also an important technical index of calcium carbonate. The determining factors of temperature and hue are the structure and source of ore.These factors will directly affect the coloring of plastic products, affect the color of plastic products, glossiness.Therefore, the whiteness and hue of calcium carbonate are important technical indicators that cannot be ignored.
Moisture and volatile content
Calcium carbonate raw materials - natural marble, calcite, generally do not contain structural water.After processing into ultrafine powder, it is easy to be affected by moisture during processing, storage and transportation.Calcium carbonate sometimes contains trace volatile substances, 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 be controlled at about 0.3% in general. In practical application, when the moisture content in the product is ≥0.3%, it is easy to affect the product quality, making the product surface rough, resulting in bubbles, burning, decomposition and other phenomena.Therefore, it is very important to control the moisture content for the quality of the modified masterbatch.
In high content of calcium carbonate filling modified masterbatch production, conditional try to avoid using infiltrating brace sink dicing and water ring granulation process, such as the caterpillar transmission net type dry pelletizing process and mill hot cutting art, but on the premise of improving production, minimize the modified masterbatch moisture and volatile matter content, can ensure the quality of modified masterbatch.
Particle size distribution
The particle size distribution of calcium carbonate is an important quality control index of modified masterbatch.The particle size analysis of inorganic mineral powder is usually a simple screening method, and the commonly used size in the screening method is expressed by "mesh".The number of mesh is the number of mesh holes per inch of screen.However, a more accurate and scientific method of particle size analysis is to measure the actual size of particle size, expressed by micron (particle size m).
Sieving method is one of the most traditional particle size analysis methods, that is, the ultrafine powder with good dispersion is sifted with a certain number of mesh size, the weight ratio of the sieve powder passing under the sieve is the sieving rate.The most commonly used standard sieve is 500 mesh (equivalent to about 25μm), while the new electrodeposition screen can be used to screen powders as small as 5μm (2500 mesh), but the screening time is long and blockage is easy.For ultrafine powder less than 10 micrometers (1250 mesh), the sieving method is difficult to be used for particle size analysis and detection.
In practical application, the particle size distribution range of granular materials such as calcium carbonate fluctuates greatly. The narrower the particle size distribution range is, the more stable the material performance is; the wider the particle size distribution range is, the worse the material performance is.For example, the particle size of calcium carbonate for the purpose of 1250 should be around 10 m. If the particle size distribution is between 5 m and 38 m, the theoretical average particle size can be close to 10 m.However, the surface roughness is caused by the particle size, so the machining properties and mechanical properties are affected.
According to different mineral structures, the particle shapes of calcium carbonate can be divided into polyhedron, flat body, polyhedron, cuboid, long bar body, other irregular bodies and other particle shapes.
The particle shape of calcium carbonate has great influence on the processing technology, product quality, melt fluidity and mechanical properties of the modified masterbatch.Calcium carbonate with polyhedral, polyhedral and cuboid shapes has good melt fluidity in the processing of modified masterbatch and is easy to be cross-linked with coupling agent. The wear of processing equipment is relatively small. The disadvantage is that after the modified masterbatch is applied to plastic products, it is easy to affect the mechanical properties of plastic products (such as tensile strength, bending modulus, etc.).
The specific surface area of flat and long stick calcium carbonate particles is relatively large, so the dosage of coupling agent, plasticizer and other auxiliary agents in modified masterbatch should be increased appropriately.Otherwise, easy to cause uneven cladding, poor melt liquidity, increase in the power of the main engine, increase in the resistance of the head, will also produce overheating decomposition and other phenomena.But this kind of shape material is beneficial to the physical properties of plastic products, which can improve the tensile strength, bending strength and reduce the shrinkage rate of plastic products.
Content of other components
The contents of chemical components, metal impurities and other components in calcium carbonate also have a certain effect on the quality of calcium carbonate.Calcium carbonate generally contains a small amount of magnesium oxide (MgO), silicon dioxide (SiO2), iron trioxide (Fe2O3), alumina and trace heavy metals (aluminum, arsenic, mercury, etc.).The content of other components varies with the origin and ore.
The hardness of MgO in calcium carbonate is small, the whiteness is slightly lower than that of calcium carbonate, the chemical stability and processing performance are similar to that of calcium carbonate, and generally will not bring a big impact on calcium carbonate.
SiO2 is a natural quartzite with small specific surface area and good fluidity.However, the high hardness of SiO2 (mohs hardness 7) causes serious wear on the equipment, especially when the coating is uneven or the dosage of plasticizer is small.If the modified masterbatch is used in the production and processing of polypropylene flat wire, it will easily collide with the high-speed cutting tool and often damage the blade, which will affect the production and processing.
Although the content of Fe2O3 in calcium carbonate is very small, when Fe2O3 is mixed with chemical additives, it is prone to biochemical changes. Fe2O3 is easy to decompose and turn yellow after being heated, which affects the whiteness and appearance of the modified masterbatch. Therefore, Fe2O3 is a material that cannot be ignored in the modified masterbatch.
The lower the content of SiO2 and Fe2O3 in calcium carbonate, the less influence it has 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, and the amount of precipitation in the solution can be observed to determine the content of SiO2.The color of the solution is slightly yellow, indicating that there is more Fe2O3 content.
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