What effects do the performance parameters of plastic products calcium carbonate have on plastic filled modified masterbatch?

Calcium content

Calcium content is an important quality technical index of calcium carbonate. The modified masterbatch requires higher calcium content of calcium carbonate, generally more 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 impurities such as heavy metals and other non-metals, which will not only affect the use of calcium carbonate, but also affect the processing technology, affecting the quality of products or causing harm to processing equipment.

whiteness

The whiteness of calcium carbonate directly affects the whiteness and coloration of the modified masterbatch. The whiteness of the modified masterbatch is very strict. At present, the whiteness of 400 calcium carbonate 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 the product, some modified masterbatch manufacturers often add fluorescent whitening agents to achieve the effect of increasing whiteness. However, because the chemical components of fluorescent whitening agent are prone to decomposition reaction at high temperature and high shear, if the variety of fluorescent whitening agent is not selected properly or the number of components is excessive, not only will the product decompose yellow, but also will not disperse or agglomerate phenomenon. Fluorescent brightener related to health and safety, contact with the human body of plastic products, will produce a certain irritation, should not be used.

Hue is also a very important technical index of calcium carbonate, and the determining factor of temperature and hue is the structure and source of the ore. These factors will directly affect the coloring of plastic products, affect the color of plastic products, gloss and so on. Therefore, the whiteness and hue of calcium carbonate are important technical indicators that cannot be ignored.

Water and volatile matter content

The raw materials of calcium carbonate - natural marble, calcite, etc., generally do not contain structural water. After processing into ultrafine powder, it is easy to absorb moisture and moisture during processing, storage and transportation. Calcium carbonate sometimes contains trace amounts of volatile substances, if the content of these substances is too high, it will affect the modified masterbatch and plastic products.

Moisture and volatile matter content in calcium carbonate should generally be controlled at about 0.3%, the actual application, when the moisture content of the product is greater than 0.3%, it is easy to affect the quality of the product, the surface of the product is rough, resulting in bubbles, burning, decomposition and other phenomena. Therefore, the control of moisture content is very important for the quality of the modified masterbatch, and the common way is to use high-speed mixer heating and drying treatment to eliminate moisture.

In the production of modified masterbatch filled with high content of calcium carbonate, it is possible to avoid the use of water trough wet strip pelleting and water ring pelleting processes, and the use of track transmission mesh dry pelleting process and grinding surface hot pelleting technology, which can minimize the content of water and volatile substances in the modified masterbatch under the premise of increasing the production yield, and ensure the product quality of the 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 commonly used by a relatively simple screening method, and the commonly used specifications in the screening method are expressed by "mesh". The mesh number is the number of screen holes per inch of screen mesh. However, the more accurate and scientific particle size analysis method is to measure the actual size of the particle size, expressed in microns (μm).

The screening method is the most traditional particle size analysis method, that is, the ultrafine powder with good dispersion is screened with a certain mesh number of screens, and the weight ratio between the sifted powder and the sifted powder is the screening rate. The most commonly used standard screen has 500 mesh (equivalent to about 25μm), and the new electrodeposition screen can screen powders as small as 5μm (2500 mesh), but the screening time is long and it is easy to clog. For ultrafine powders less 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 material performance, and the wider the particle size distribution range, the worse the material performance. For example, 1250 calcium carbonate, the particle size should be about 10μm, if the particle size distribution in 5 ~ 38μm, although the theoretical calculation of the average particle size can be close to 10μm, but because of the small particle size, large specific surface area, easy to condense into clusters; The particle size will cause the product surface roughness and other phenomena, so its processing properties, mechanical properties, etc., will be affected.

Particle shape

According to the different mineral structure, the particle shape of calcium carbonate can be divided into polygonal, flat, polygonal, cuboid, long rod and other irregular 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 polygonal, polygonal and cuboid shapes has good melting fluidity in the processing of modified masterbatch, which is easy to cross-link with coupling agent coating, and the wear of processing equipment is relatively small. The disadvantage is that the modified masterbatch is easy to 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 the flat and long rod calcium carbonate particles is relatively large, so the amount of additives such as coupling agent and plasticizer in the modified masterbatch should be appropriately increased. Otherwise, it is easy to cause uneven coating, poor melting flow, increase the power of the main engine, increase the head resistance, and cause overheating decomposition. However, materials of this shape are beneficial to the physical properties of plastic products, which can improve the tensile strength, bending strength, and reduce the shrinkage rate of plastic products.

Other component content

The content of chemical components, metal impurities and other components in calcium carbonate also has a certain impact on the quality of calcium carbonate, which will have a certain impact on the application of plastic modified masterbatch and plastic products. 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 also 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 properties are similar to calcium carbonate, and generally will not have a greater impact on calcium carbonate.

SiO2 belongs to natural quartzite, which has small specific surface area and good fluidity. However, the hardness of SiO2 is high (Mohs hardness 7), which is serious for equipment wear, especially when the coating is uneven or the amount of plasticizer is small. If the filler modified masterbatch is used in the production and processing of polypropylene flat wire, it is easy to collide with the high-speed slitter and often damage the cutting edge, which affects the production and processing.

Although Fe2O3 content in calcium carbonate is very small, but iron and chemical additives mixed processing is prone to chemical changes, Fe2O3 is easy to decompose and yellow after heating, affecting the whiteness and appearance of the modified masterbatch, so Fe2O3 in the modified masterbatch is a material 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, calcium carbonate can be added into a glass dish with 5% hydrochloric acid dilution solution for chemical analysis, and the amount of precipitate in the solution can be observed to determine the content of SiO2. The color of the solution is slightly yellow, indicating that the Fe2O3 content is higher.