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Yuan Lei's Little Knowledge | Refractive Index of Powder

Release time:

2024-01-29 09:34

refractive index

(1) Absolute refractive index

Refers to the refraction of light from the vacuum into the medium, the ratio of the sine of the incident angle I to the refraction angle R is called the "absolute refractive index" of the medium, referred to as "refractive index". That is, the refraction of light when light enters from one angle and comes out from another angle. Because light has this kind of refraction, it will produce a kind of refraction in any medium, and the medium is different, the angle of refraction is different, that is, the refractive index is different, we also refer to the refraction principle of light to make various coatings with different hiding power.

(2) the refractive index of the powder in the coating

In the production of coatings, the use of different powders will produce different hiding power, and the hiding power of the coating is a combination of the refractive index of various powders and media (I. e. water and resin). When the difference in refractive index between the powder and the medium becomes larger, the hiding power of the coating is strong, otherwise the covering is poor. When the refractive index of the two is the same, the coating film is transparent.

The hiding power of powder is mainly determined by its refractive index. Generally, the refractive index of film-forming material is about 1.5. The higher the refractive index of powder, the better the hiding power. We usually call fillers (or physical fillers) when the refractive index is 1.7. It is conducive to the improvement of hiding power, when the amount of more, the coating inside the filler particles around the formation of small air voids, thereby improving the hiding power.

For example, the wet hiding power of light calcium carbonate slurry is very poor (because the refractive index of calcium carbonate is 1.58 and that of water is 1.33, which is not much different). However, after drying, water around light calcium carbonate becomes air, and the difference in refractive index becomes larger (the refractive index of calcium carbonate is 1.58 and that of water is 1.0), so the hiding power is improved.

Another example: when the film-forming material content is high, the wet hiding power is better than the dry hiding power. The reason for this phenomenon is that water is around the powder when it is wet, and when it is dry, water becomes resin around the powder, the refractive index changes from 1.33 to 1.5, and the difference between the refractive index of powder and resin becomes smaller, so the hiding power becomes worse. This is the use of light calcium after the coating dry cover becomes better.

Therefore, in the paint at the same time, we must know some of the basic properties of the powder.

 

Refractive index, hiding power, refraction, medium, produce, paint, that is, around, calcium carbonate

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