What kind of calcium carbonate is needed in the plastics industry?

• the price is cheap;

• Good color and easy to color;

• Low hardness and a Mohs hardness of 3, so the filled plastic wears less light on the parts and molds that are in contact with the equipment;

• Good thermal stability and chemical stability;

• Easy to dry, no crystal water, and the adsorbed water is easily removed by heating;

• Non-toxic, non-irritating and tasteless.

(1) Influence on density

The difference between true calcium and light calcium is not obvious, and their main difference is apparent density. When the amount of filler added is the same, heavy calcium or light calcium, even heavy calcium with different thickness, will cause the length, area or number of products of the plastic product to be different.

(2) Influence on mechanical properties

The addition of calcium carbonate will reduce the mechanical properties of the plastic material. However, if the surface treatment of calcium carbonate or the interface modification technology is used in advance, the adverse effect of calcium carbonate on the mechanical properties of the filled plastic can be alleviated, and even some performance ratios are pure. The base plastic is even better.

(3) Influence on thermal performance

In the plastic molding process, the heating or cooling rate and the amount of heating heat directly affect the production cost and energy consumption. Since the thermal conductivity of calcium carbonate is ten times larger than that of the base plastic, and the volume of the two is similar to the heat capacity, the thermal conductivity of the filled plastic is improved by the presence of calcium carbonate compared to the pure base plastic, which is advantageous for shortening the molding cycle. Improve work efficiency.

(4) Influence on optical performance

Whether or not the plastic to which the powder filler is added is transparent depends on the difference between the refractive index of the powder filler and the refractive index of the plastic matrix. Unlike titanium dioxide, lead white (lead oxide), and zinc white (zinc oxide) (refractive index of 2.52, 2.01, and 1.79, respectively), the hiding power of calcium carbonate is very weak, so the whiteness is higher. Calcium carbonate cannot be used as a pigment, but it can reduce the reflectance of light on the surface of a filled plastic article and can be used as a matting material.

(5) Effect on combustion performance

Calcium carbonate is generally considered to be a non-combustible non-metallic mineral. When making a flame retardant plastic, the addition of calcium carbonate will be beneficial to flame retardant. In fact, the presence of calcium carbonate does reduce the amount of combustible matrix plastics. Even when the calcium carbonate fill is large, the filled plastic becomes a "low calorific value" material, but the more unfavorable aspect is that the presence of a large amount of calcium carbonate particles is equal to The base plastic such as polyethylene is divided, which is more conducive to the full combustion of the base plastic.

(6) Influence on the dimensional change rate of plastic products

The plastic product will shrink during the cooling process after molding. The addition of calcium carbonate and other non-mineral powder materials will make the dimensional change rate (shrinkage) of the filled plastic much smaller than that of the pure base plastic. For example, by adding 30% to 40% (mass fraction) of calcium carbonate to the polypropylene plastic, the dimensional change rate of injection molding can be reduced from 2.0% of pure PP to 1.0% or less.

(1) The purity of calcium carbonate should be high, and the compounds of elements such as silicon and iron should be as low as possible, and the content of harmful heavy metal elements should be strictly required.

(2) Whiteness should be as high as possible.

(3) The lower the oil absorption value, the better. By surface treatment of calcium carbonate, the surface of the calcium carbonate particles is coated to reduce the oil absorption value.

(4) The fineness should be appropriate, not as fine as possible, and the particle size distribution should be determined according to needs. For filled plastics, the smaller the particle size of the filler used, the better the mechanical properties of the filled plastic material at the same filling ratio, but the premise is that the powder particles are uniformly dispersed in the plastic matrix. The different particle size distributions of the fillers have different effects on the plastic products. For some plastic products, when the basic requirements are met (ie, the maximum particle size does not exceed a certain value), some are finer, and some are coarser.

(5) Whether activation depends on user needs. Plastic processing companies that produce high-volume products with consistent formulation and processing requirements are required to provide activated calcium carbonate products. More plastics processing companies prefer to do their own surface treatments, and the processing equipment and treatments they use tend to have their own characteristics.

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