In the formula design of filling master material, the quality of other additives is relatively stable, but the largest amount of calcium carbonate becomes the key factor affecting the quality of master material. Calcium carbonate filled masterbatch is made by mixing calcium carbonate with carrier resin, mixing and granulating particles with similar volume to the base resin of plastic products, which has a wide application value in the plastic industry.
Calcium carbonate affects the quality of filling masterbatch by the following factors:
1. Calcium content
For the filling masterbatch, the calcium content is better than 97%, with good lubrication, high whiteness, low oil absorption value and better dispersion. The impurities in calcium powder mostly exist in the form of oxides such as silicon, magnesium, iron and aluminum. These impurities determine the base color, hardness and dispersion of calcium powder.
The higher the calcium content, the more stable the processability of calcium carbonate. When the calcium content is low, it will increase the content of heavy metals and other non-metallic impurities, which will not only affect the use of calcium carbonate, but also affect the processing technology, affect the product quality or cause harm to the processing equipment.
2. Particle size distribution of calcium carbonate
The particle size distribution of calcium carbonate is an important control index to determine the quality of calcium powder. Its particle size distribution is determined by calcium powder equipment, calcium powder production technology, experience and equipment debugging level.
We mainly consider three indicators, the first is D50, the second is D97, and the third is D100.
D50 index shows fine powder content, which determines oil absorption value, dispersion and mechanical properties of filling.
D97 index determines the total size level of calcium powder.
D100 index determines the maximum particle size of calcium powder, which affects the fineness of the master material. Excessive D100 will affect the mechanical properties of the master material, such as tensile properties, strength, etc. In practical application, the particle size distribution range of calcium carbonate and other granular materials fluctuates greatly. The narrower the particle size distribution range is, the more stable the material performance is, while the wider the particle size distribution range is, the worse the material performance is.
3. Water content of calcium carbonate
The ore needs to be cleaned before entering the grinder. When grinding, it also needs to add water or additives. The unmodified calcium powder itself is easy to absorb moisture in the air and get damp. Calcium carbonate sometimes contains trace volatile substances. If the content of these substances is too high, it will affect the modified masterbatch and plastic products. After the moisture content of calcium powder exceeds the standard, if the downstream masterbatch manufacturing enterprises operate improperly, the screen changer will often be blocked, the masterbatch particles will not melt, and the masterbatch quality will be unstable.
The content of moisture and volatile matter in calcium carbonate should generally be controlled at about 0.3%. In practical application, when the moisture content in the product is≥0.3%, it is easy to affect the product quality, make the product surface rough, and produce bubbles, charring, decomposition and other phenomena.
Therefore, controlling the moisture content is very important for the quality of modified masterbatch. The common method is to use high-speed mixer for heating and drying to eliminate moisture.
4. Pollutants in calcium carbonate
In the process of masterbatch manufacturing, many black and reddish brown impurities often appear on the filter screen of the screw, resulting in frequent screen change and failure of normal production. Most of these things are foreign matters brought into the production site during the production process, such as forklift tire debris, conveyor belt debris, wood debris, calcium powder storage bin and pipeline rust.
Filling masterbatch manufacturing is a systematic consideration of the project, from powder to equipment to raw material and then consider the manufacturing and use process of downstream customers, must be considered in order to make qualified filling masterbatch, calcium powder as one of the most important raw materials, it is worth our time to study.
