What kind of heavy calcium carbonate is used in the plastics industry?

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BaiDu

The degree of whiteness mainly affects the color and appearance of the filled plastic products, and does not affect the mechanical properties and processing properties of the materials. The higher the whiteness, the smaller the effect on the coloration of the filled plastic; under the same performance, the whiteness is higher and has a competitive advantage.

In principle, the heavy calcium for plastics requires higher whiteness, such as the whiteness requirement of heavy calcium for ordinary plastics is greater than 92% , and the whiteness requirement for heavy calcium for high-grade plastic filled masterbatch is 95%.

The level of impurities not only affects the color and appearance of the filled plastic products, but also affects the mechanical properties and processing properties of the materials.

In principle, the heavy calcium used in the plastics industry requires that the impurity content be as low as possible. The higher the calcium carbonate content, the better. The main impurity indicators affecting plastics are Fe ₂ O ₃ , MgO , SiO ₂ and the like.

• High Fe ₂ O ₃ content will affect the color of heavy calcium powder, easy to yellow, especially in the surface treatment combined with acidic substances such as stearic acid, it is easy to yellow under high temperature conditions, and iron ions can accelerate plastic aging .

• Heavy calcium powder with high MgO content will be grayed out. If heavy calcium powder containing dolomite is added to polyethylene and polypropylene plastic, the whole filler will be gray, because the main components of dolomite are calcium carbonate and magnesium carbonate.

• The presence of SiO ₂ may cause light cross-linking or thermal degradation of polyvinyl chloride and reduce its thermal stability. Furthermore, high silicon content in heavy calcium powder will lead to an increase in particle hardness, which will affect the wear of plastic processing machinery. Big. For example, when a filler masterbatch made of a silicon-containing heavy calcium powder is used for the production of polypropylene flat yarn, the slitting blade is easily worn.

Particle size and its distribution are an important indicator for measuring the grade of heavy calcium products, mainly affecting the mechanical properties of materials. In theory, the finer the particle size of heavy calcium powder for plastics, the stronger the strength of the product can be filled by filling it into plastic. However, the practical application is not the case. The finer the particle size of heavy calcium, the larger the specific surface area and the larger the surface energy. The particles are easily agglomerated and added to the resin in a multi-aggregate state (aggregate), and the dispersion is uneven, and it is difficult to form a stable interface, which degrades product performance.

Therefore, the heavy calcium for plastics requires appropriate fineness, not the finer the better. Currently, the commonly used heavy calcium powder is generally between 400-1250 mesh, and the 400-800 mesh powder accounts for about 65% of the market share, 800- The 1250 target powder accounts for about 30%, and the 1250 mesh or above accounts for about 5-10%.

For filled plastics, the finer the particle size of the filler used, the better the mechanical properties of the filled plastic under the same filling ratio, but the premise is that the heavy calcium particles need to be uniformly dispersed in the plastic matrix. The particle size distribution of heavy calcium for plastics is different. For example, injection molding products require good fluidity of filler materials, low content of fine powder, and heavy calcium with high coarse powder content, which contributes to the processing fluidity of filler materials, provided that it is guaranteed. Under the conditions of the product D ₁₀₀ index, the average particle size is larger.

The index of particle size and its distribution requires not only the D ₉₇ and D ₁₀₀ indexes, but also the 2 μm content, average particle diameter D ₅₀ and specific surface area of ​​the product, because these indicators indirectly reflect the dispersion of heavy calcium powder and The oil absorption value is high or low.

The particle morphology of heavy calcium has a great influence on the filling and modification of plastics. For example, fibrous and flake-like materials are beneficial to the mechanical strength of polyvinyl chloride composites, but they are not good for molding processability; while spherical fillers can improve the forming of materials. Processing performance, but reduced mechanical strength of the material.

The influence of crystal structure has begun to attract attention in the industry. Generally speaking, the heavy calcium powder produced by natural calcite produced by fine-grained, semi-automorphic crystal, and other granular or massive structures is favored by the plastics industry.

In principle, the heavy calcium for plastics requires that the lower the oil absorption value, the better, because the high oil absorption value will absorb the plasticizer into the filler, so that it loses the role of plasticizing resin. In order to make the material reach a certain degree of flexibility, it must be increased. The amount of plasticizer causes an increase in cost.

                                                      ▼ Domestic enterprises for plastics with heavy calcium oil absorption requirements

Moisture and low molecular substances are a big bogey for any plastic product, because moisture and low molecular substances cause defects and wrinkles on the surface of the product. In severe cases, the product will be honeycombed or material transported to cause bridging and breaking, which not only affects The mechanical properties of the product also affect the appearance of the product.

The whiteness, impurity content and crystal structure of heavy calcium carbonate products are mainly affected by the ore grade. The particle morphology, particle size and distribution are closely related to raw materials, processing equipment, process technology and control level.

Therefore, heavy calcium production enterprises should first select raw ore according to the application requirements of the plastics industry, and then ensure that the processing equipment and processes meet the requirements of refined processing of heavy calcium products, in order to realize the value of heavy calcium products in each adaptive plastics industry. Price advantage, increase product added value.