6 important indicators of Ground Calcium Carbonate products for plastics
Ground calcium carbonate is the preferred filler in the plastic industry, widely used in plastic film, profiles, pipes, plastic knitting wire drawing and artificial leather and other plastic industrial production, and can replace expensive white pigments play a certain role in whitening, improve the surface luster and surface flatness of products.
So, what are the indicators required for Ground calcium carbonate in the plastics industry? Why are these metrics required?
1. Whiteness
The whiteness mainly affects the color and appearance of the filled plastic products, and does not affect the mechanical properties and processing properties of the material. The higher the whiteness, the less the influence on the coloring of the filling plastic; Under the same performance conditions, high whiteness has a competitive advantage.
In principle, the whiteness of plastic Ground calcium is required as high as possible, such as the whiteness of ordinary plastic heavy calcium is required to be greater than 92%, and the whiteness of high-grade plastic filled masterbatch with Ground calcium is required to reach 95%.
2. Impurity content
The impurity content 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, Ground calcium in the plastic industry requires the lower the impurity content, the better, the higher the calcium carbonate content, the better, the main impurity indicators affecting plastics are Fe2O3, MgO, SiO2 and so on.
High Fe2O3 content will affect the color of Ground calcium powder, easy to yellow, especially in the surface treatment with stearic acid and other acidic substances, easy to yellow under high temperature conditions, while iron ions can accelerate the aging of plastics.
Ground calcium powder with high MgO content will be gray, such as Ground calcium powder containing dolomite added to polyethylene and polypropylene plastics will make the entire filling gray, because the main components of dolomite are calcium carbonate and magnesium carbonate.
The presence of SiO2 may cause mild cross-linking or thermal degradation of PVC, and reduce its thermal stability. In addition, the high silicon content of Ground calcium powder will lead to the increase of particle hardness, which has a greater impact on the wear of plastic processing machinery. For example, when the filler masterbatch made of Ground calcium powder with high silicon content is used in the production of polypropylene flat wire, the slitting blade is easy to wear.
3. Particle size and distribution
Particle size and its distribution is an important index to measure the grade of Ground calcium products, which mainly affects the mechanical properties of materials. In theory, the smaller the particle size of Ground calcium powder used in plastics, the strength of the product can be greatly improved when filled into the plastic, but the actual application is not the case, the smaller the particle size of Ground calcium, the larger the specific surface area, the greater the surface energy, the primary particles are easy to aggregate in the form of polyaggregation (condensate) to join the resin, the dispersion is not uniform, it is difficult to form a stable interface, so that the product performance is reduced.
Therefore, plastic Ground calcium requirements for fineness is appropriate, not the finer the better, the current commonly used Ground calcium powder particle size is generally between 400-1250 mesh, 400-800 mesh of powder about 65% of the market share, 800-1250 purpose powder accounted for about 30%, 1250 mesh or more about 5-10%.
For the filled plastic, under the same filling ratio, the finer the particle size of the filler used, the better the mechanical properties of the filled plastic, but the premise is that the Ground calcium particles need to be evenly dispersed in the plastic matrix. Plastic Ground calcium particle size distribution requirements are different, such as injection molding products require the filling material to have good fluidity, fine powder content is small, coarse powder content is high heavy calcium, it is helpful to the processing fluidity of the filling material, the premise is to ensure that the product D100 index conditions, the average particle size is better.
The index of particle size and its distribution not only requires its D97, D100 index, but also requires its product's 2μm content, average particle size D50 and specific surface area, because these indicators indirectly reflect the dispersion of Ground calcium powder and the oil absorption value.
4. Particle morphology and crystal type
The particle shape of Ground calcium has a great influence on the filling and modification of plastics, such as fiber and sheet are good for the mechanical strength of PVC composite, but bad for the processing performance. The spherical packing, on the contrary, can improve the processing performance of the material, but reduce the mechanical strength of the material.
The influence of crystalline structure has begun to receive attention in the industry, in general, fine granular allomorphic, semi-idiopathic crystal, equal granular or massive structure of natural calcite production of Ground calcium powder is more favored by the plastic industry.
5. Oil absorption value
Plastic with Ground calcium in principle requires its oil absorption value as low as possible, because the high oil absorption value will absorb the plasticizer into the filler, so that it loses the role of plasticizer, in order to make the material to achieve a certain degree of flexibility and must increase the amount of plasticizer, resulting in increased costs.
6, water and low molecular matter
Water and low molecular matter for any plastic products are a big no-no, because water and low molecular matter to produce defects and wrinkles on the surface of the product, serious will make the product is honeycomb or material conveying bridge broken material, it not only affects the mechanical properties of the product, but also affects the appearance of the product.
The whiteness, impurity content and crystal structure of Ground calcium carbonate products are mainly affected by raw ore grade, and the particle shape, particle size and distribution are closely related to raw materials, processing equipment, technology and control level.
Therefore, Ground calcium production enterprises should first select raw ore according to the application requirements of the plastic industry, and then ensure that the processing equipment and process meet the requirements of the fine processing of heavy calcium products, in order to achieve the value and price advantages of heavy calcium products in their respective plastic industry, and improve the added value of products.
