What is ground calcined kaolin?
Calcined kaolin is to calcine kaolin at high temperature in a calcining furnace, this process would change the physical and chemical properties of kaolin, to meet certain requirements. Ground calcined kaolin refers to powdered calcined kaolin, it is obtained by grinding calcined kaolin through grinding machine, such as ball mill, for better application.
Ground calcined kaolin is mainly used in coatings industry with two functions. One is for filling, the other one is for covering. So, what are the indicators of ground calcined kaolin for coatings? Let’s discuss below:
Indicators of ground calcined kaolin for coatings:
1. Whiteness
Whiteness is the primary indicator of ground calcined kaolin, the higher the better. Whiteness stability is very important. Different whiteness would cause color differences between different batches of products with the same formula.
2. Particle size
Particle size is actually a superficial indicator, and paint manufacturers rarely test particle size directly. However, due to its relevance with other indicators, if particle size is not fine enough or unqualified, it will be reflected through other indicators. The general requirement is that the proportion of particle size finer than 2μm should be account for 80%.
3. Covering power
Covering power is the most important indicator of calcined kaolin for coatings. It mainly depends on its particle size and dispersibility. The finer the particle size, the better the dispersibility and the stronger the covering power. In addition, the refractive index of calcined kaolin will also affect its covering power. The higher the refractive index, the better the covering power.
4. Dispersibility
The dispersibility of calcined kaolin mainly depends on the particle size and shape. Finer kaolin particles can provide better dispersibility, because they can better fill the gaps between pigment and filler, reducing flocculation and agglomeration.
5. Sieve residue of 325 mesh
The sieve residue of 325 mesh is an important indicator. The coating requirement for this indicator is less than 0.02%, and the smaller the better.
6. Oil absorption value
The oil absorption value of calcined kaolin around 50g/100g~60g/100g is moderate. Oil absorption value of kaolin is closely related to particle size distribution, porosity, specific surface area and crystal form of particles. When particle size is smaller, the specific surface area is larger and the oil absorption value is higher.
7. Sedimentation volume
The sedimentation volume reflects the sedimentation performance of calcined kaolin in the coatings, it directly affects the can opening performance of the coatings. The higher the sedimentation volume, the better. With high sedimentation volume, paint is not easy to settle, and the calcined kaolin would keep good uniformity in coatings.
8. PH value
The PH value reflects the acidity and alkalinity of calcined kaolin. The coating requires that its pH value should be between 6 and 8, which is basically close to neutral. The PH of calcined kaolin is neutral, so there is no need to modify PH value in coatings industry.
9. Weather resistance
The weather resistance of kaolin for coatings mainly include: heat resistance, freeze-thaw resistance, impact resistance, abrasion resistance, yellowing resistance, light aging resistance, acid and alkali resistance etc. These indicators together ensure the stability and durability of kaolin in coatings.
For indicators above, stability is the most important, otherwise it will affect the overall performance of coatings. The application of calcined kaolin improves the performance of coatings, it is an indispensable material in coatings industry. In addition, before applied in coatings, calcined kaolin needs to be ground. The equipment used to grind calcined kaolin is necessary, such as: ball mill. Qingdao Epic Powder Machinery Co., Ltd. is a professional powder equipment manufacturer. The ball mill from Qingdao Epic are very suitable for grinding calcined kaolin. Especially the ball mill, it can be combined with classifier to form a closed-loop circulation system, this is an internationally cutting-edge non-mineral powder processing production line, widely praised by domestic and foreign customers.
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