Heavy calcium carbonate powder is widely used in modified PFA particles, and its performance index has great influence on modified PFA particles. We analyze the influence of calcium carbonate performance index on modified PFA particles in detail from the following six aspects.

(1) Effect of calcium content of calcium carbonate on modified PFA particles

Calcium content is an important quality technical index of calcium carbonate. The calcium content of modified PFA particles is higher, generally more than 98%. The higher the calcium content, the more stable the powder processability 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, affect product quality or cause harm to processing equipment.

(2) Effect of whiteness of calcium carbonate on modified PFA particles

The whiteness of calcium carbonate directly affects the whiteness and colorability of modified PFA particles. Modified PFA particles have very strict requirements on the whiteness of calcium carbonate. More than ten years ago, manufacturers generally required the whiteness of calcium carbonate for 400 purposes to be 92% ~ 93%. As the use of modified PFA particles becomes more and more extensive, the whiteness of calcium carbonate is required to be higher and higher. 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%. Some modified PFA particle manufacturers in order to improve the whiteness of the product, often add fluorescent whitening agent, to increase the whiteness of the effect. However, due to the chemical components of fluorescent whitening agent in high temperature, high shear decomposition reaction, if the type of fluorescent whitening agent is not properly selected or add excessive parts, not only the product decomposition yellow, but also there will be no dispersion or agglomeration agglomeration phenomenon. Fluorescent whitening agent for health and safety, contact with the human body PFA products, will produce a certain degree of irritation, should not be used.

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

(3) The moisture content of calcium carbonate is modified.PFA GranulesThe impact

The raw materials of calcium carbonate-natural marble, calcite, etc., generally do not contain structural water. After being processed into ultrafine powder, it is easy to be affected with moisture and 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 PFA particles and PFA products.

Moisture and volatile matter content in calcium carbonate should generally be controlled at about 0.3 percent, polyolefin filled PFA particles QB1126-1991 to the national industry standards for water content of less than 0.5 percent. However, in practical application, when the moisture content in the product is more than or equal to 0.3%, it is easy to affect the quality of the product, make the surface of the product rough, produce bubbles, scorch, decomposition and other phenomena. Therefore, controlling the moisture content is very important to the quality of modified PFA particles. The commonly used method is to use high-speed mixer to heat and dry to eliminate moisture. In the production of modified PFA granules filled with high content of calcium carbonate, it is necessary to avoid the use of water tank infiltration, strip cutting and water ring granulation processes, and the use of crawler drive net dry cutting process and grinding surface hot cutting granulation process, which can minimize the moisture and volatile content of modified PFA granules and ensure the product quality of modified PFA granules on the premise of increasing production output.

(4) Effect of particle size distribution of calcium carbonate on modified PFA particles

The particle size distribution of calcium carbonate is an important quality control index of modified PFA particles. The particle size analysis of inorganic mineral powder is commonly used in simple screening methods, and the specifications commonly used in screening methods are expressed as "mesh. The so-called mesh is the number of holes on each inch of the screen. However, the more accurate and scientific particle size analysis method is to measure the actual size of the particle size, which is expressed in microns (μm).

Sieving method is one of the most traditional particle size analysis method, that is, the fine powder with good dispersion is sieved with a certain number of sieve, and the weight ratio of the powder under the sieve is the sieving rate. The most commonly used standard sieve is 500 mesh (equivalent to about 25μm), and the new electrodeposition screen can screen powder as small as 5μm(2500 mesh), but the screening time is long and it is easy to block. For the ultrafine powder less than 10 μm(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 for 1250 purposes should have a particle size of about 10μm. If the particle size is distributed between 5μm and 38μm, although the theoretically calculated average particle size can be close to 10μm, it is easy to agglomerate due to its small particle size and large specific surface area. However, the particle size assembly will cause the surface roughness of the product, so its processing performance and mechanical properties will be affected.

(5) Effect of particle shape of calcium carbonate on modified PFA particles

According to the different mineral structure, the particle shape of calcium carbonate is divided into multi-body, flat body, multi-prism body, cuboid, long rod body, other irregular body and other particle shapes.

The shape of calcium carbonate particles has a great influence on the processing technology, product quality, melt fluidity and mechanical properties of modified PFA particles. The calcium carbonate in the shape of multi-body, multi-prism and cuboid has good melt fluidity in the processing of modified PFA particles, is easy to be coated and crosslinked with coupling agent, and the wear of processing equipment is relatively small. The disadvantage is that after the modified PFA particles are applied to PFA products, it is easy to affect the mechanical properties of PFA products (such as tensile strength, bending modulus, etc.).

The specific surface area of the flat and long rod-shaped calcium carbonate particles is relatively large, and the amount of additives such as coupling agent and plasticizer in the modified PFA particles 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. However, this type of material is beneficial to the physical properties of PFA products, which can improve the tensile strength, bending strength, and reduce the shrinkage of PFA products.

(6) Effect of other components of calcium carbonate on modified PFA particles

The content of chemical components, metal impurities and other components in calcium carbonate also has a certain influence on the quality of calcium carbonate, and the application of modified PFA particles and PFA products will have a certain impact.

The composition of each substance of calcium carbonate varies with the origin and the ore, which is easy to produce differences. 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 do not have a great impact on calcium carbonate.

Silica (SiO2) belongs to natural quartzite, which has a small specific surface area and good fluidity. However, the hardness of SiO2 is high (Mohs hardness 7), which is particularly prominent for equipment wear, especially when the coating is uneven or the amount of plasticizer is small. If the filled modified PFA particles are used in the production and processing of polypropylene flat wire, it is easy to collide with the high-speed slitting tool and often damage the blade, affecting the production and processing.

Although the content of ferric oxide (Fe2O3) in calcium carbonate is very small, chemical changes are easy to occur when iron is mixed with chemical additives. Fe2O3 is easy to decompose and turn yellow after heating, which affects the whiteness and appearance of modified PFA particles, so Fe2O3 is a material that can not be ignored in modified PFA particles.

The lower the content of SiO2 and Fe2O3 in calcium carbonate, the smaller the influence on the quality of modified PFA particles. Generally, 5% hydrochloric acid diluted solution can be used to add calcium carbonate to glass dish 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 content of Fe2O3 is more.

This article comes from:www.tflpfa.com

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