The average primary particle size of superfine calcium carbonate should be 0.02–0.1 μm. This is a basic requirement. Otherwise, it cannot be called “ultrafine.” However, this is only half the task. If surface treatment and dispersion technology are insufficient, the primary particles will agglomerate into secondary particles hundreds of nanometers in diameter. Transmission electron microscopy (TEM) shows the size of primary particles. BET testing reflects the specific surface area. Only by combining TEM and BET results can we make a scientific judgment on fineness, crystal form, and dispersion.
Particle size and specific surface area are closely related. Some researchers use sedimentation volume to determine particle size. However, this method is affected by raw limestone quality, calcination conditions, carbonation process, and crystal morphology. The error is significant. Therefore, surface modification is necessary to prevent agglomeration. For special-purpose grades, product design must combine crystal form, particle size, surface modifiers, and process know-how.
Calcium Carbonate Grinding Mahcine
The grinding of superfine calcium carbonate relies on advanced powder processing equipment. Common systems include ball mill with classifier, vertical roller mill, stirred mill, and jet mill. Ball mill production lines are suitable for large-scale operations. Jet mills deliver contamination-free ultrafine grinding, especially for products above 2000 mesh. Vertical roller mills and stirred mills balance energy efficiency with performance. Modern grinding equipment ensures stable particle size control and ideal specific surface area.
Crystal Form
Crystal form is another key parameter. Ordinary light calcium carbonate often has a spindle shape. In PVC, it causes internal stress and whitening in plastic films. Ultrafine calcium carbonate should be produced with different crystal forms based on application.
Plastics
For plastics, cubic or spherical crystals are ideal. They have simple structures, lower oil absorption, and smaller packing volume. Superfine calcium carbonate with a particle size of 0.072 μm improves PVC properties. It enhances surface smoothness, gloss, and electrical insulation. In soft cable compounds, even when the filling level is doubled, performance remains within national standards. In plastic films, whitening is reduced and low-temperature elongation improves. In rigid plastics like windows and profiles, impact resistance is enhanced. Notched impact strength can reach 49.1 kJ/m².
Rubber
For rubber, chain-like ultrafine calcium carbonate shows the best reinforcement. Chain structures consist of many particles bonded along one direction. They have a spatial 3D network and excellent dispersion. During mixing, the chains break to form active surfaces. These bond strongly with rubber chains, greatly enhancing reinforcement. The order of reinforcement strength is: chain-shaped > needle-shaped > spherical > cubic.
Inks
For inks, cubic crystals are preferred. They provide gloss, transparency, and fluidity in resin-based inks. In paper coating, precipitated calcium carbonate is often used. Its particle size is 0.1–1 μm, not in the ultrafine range. However, crystal form is still important. Plate-like and cubic shapes are ideal for opacity, whiteness, and ink absorption.
Oil Absorption Value
Oil absorption is crucial for plastics, coatings, and inks. High oil absorption increases plasticizer consumption in plastics. It also raises viscosity in inks and coatings. Therefore, a lower oil absorption value is preferred.
Particle size and dispersion strongly influence oil absorption. Poor dispersion leads to secondary agglomeration and small specific surface area. In this case, even with low oil absorption, the product is not effective. Thus, ultrafine calcium carbonate must first ensure fine particle size, high dispersion, and large specific surface area. On this basis, reducing oil absorption has real value.
Main Content
The main content of ultrafine calcium carbonate is CaO. Within a reasonable range, strict limits are unnecessary. As a functional filler, physical properties matter more than chemical composition. During processing, dispersants, control agents, and surface modifiers are often added. These additives improve dispersion and activation, and they do not harm product performance. However, harmful impurities such as iron and manganese must be strictly controlled. They affect color, accelerate resin degradation, and shorten service life. Other impurities such as silicon, aluminum, and magnesium can reduce whiteness and complicate production. Raw material selection must therefore be carefully controlled.
Conclusion
The development of superfine calcium carbonate should focus on specialization, diversification, and functionalization. Simply achieving a particle size of 0.02–0.1 μm is not enough. Morphology, dispersion, and surface modification are equally critical. Each industry, from plastics and rubber to inks, coatings, and paper, requires tailored performance.
Epic Powder has more than 20 years of expertise in ultrafine grinding and classification. We provide advanced milling and classification systems, including ball mills, jet mills, and classifiers. These solutions ensure precise control of particle size, morphology, and surface properties. By combining efficient grinding with customized modification technology, Epic Powder helps customers produce high-performance ultrafine calcium carbonate tailored to the needs of different industries.