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YuanLei little knowledge | Application and index requirement of nano calcium carbonate in plastics
Nano calcium carbonate refers to the particle size of 1-100nm functional inorganic filler, widely used in rubber, plastics, paper, ink, paint, sealant and adhesives, medicine, toothpaste, food and other fields. However, different applications have different requirements on particle size, crystal shape, oil absorption value and dispersion of nano-calcium carbonate.
The plastic industry is currently the world's largest use of nano calcium carbonate industry, it can act as plastic regulator and reinforcement agent, the demand is very large. Because nano calcium carbonate has good dispersion, it can remove the voids and bubbles in plastics well, so that plastics can shrink more evenly, and improve the mechanical properties and thermal stability of plastics.
The technical requirements of the plastic industry for nano calcium carbonate are as follows:
Oil absorption value: plastic industry on nano calcium carbonate oil absorption value requirements are generally very low, because nano calcium carbonate particle size is small, specific surface area is large, if the oil absorption value is large, mixing consumption of plasticizer is more, so that the system viscosity increases, not only affects the processing performance, but also increases the production cost.
Crystal shape: The morphology of nano calcium carbonate can be divided into: cube, nearly spherical, spindle shape, rod shape, chain shape, needle shape, etc. The cube with low oil absorption value, or the cube part of the chain shape and spherical is appropriate.
Particle size: The particle size of nano-calcium carbonate used in plastics is generally controlled at about 80-120nm. Too large particle size can not reflect the effect of nano-calcium carbonate and affect the smooth surface of products. Particle size is too small will lead to the increase of surface energy, serious particle agglomeration, processing is not easy to completely disperse, resulting in the surface of the product particles.
Dispersion: should choose the high dispersion of nano calcium carbonate, if the nano calcium carbonate agglomeration is serious, the secondary particle size will be much larger than the primary particle size, and plastic processing mixing shear force is not too strong, some serious agglomeration of nano calcium carbonate is not easy to break up, in application will cause local defects, resulting in product quality problems.
Moisture: Moisture control should not be higher than 0.5%, if the moisture is too high, the plastic surface will produce bubbles or empty drum phenomenon.
pH value: The pH value of nano calcium carbonate should be controlled below 10. If the PH value is high, it will affect the whiteness and surface glossiness of the products and make the appearance deteriorate. At the same time, high pH will also increase the viscosity of the system, affecting the processing process.
Hydrochloric acid insoluble matter: mainly refers to the product in the black spots, yellow spots and other impurities particles, need strict control, otherwise more particles, easy to cause in the process of processing extruder filter frequent blockage, affect the production efficiency, sometimes in the surface of the product formed obvious black spots, affect the appearance of the product quality; Fine particles containing iron may increase the yellowness and decrease the whiteness of products. Special attention should be paid to nano-sized calcium carbonate used in light-colored products.
Among all kinds of non-metallic mineral powder materials applied in the plastic industry, calcium carbonate is the largest, accounting for about 60 ~ 70% of the total amount of plastic additives, but there are still many problems in the high performance application research, especially how to solve the agglomeration of nano-calcium carbonate, how to improve the dispersion effect of nano-calcium carbonate, how to improve the bonding strength of composite materials and other aspects have not been effectively solved.