www.cilas.com [email protected]Measurement of Pigments with Dry Jet Dispersion Technology Pigments are chemical compounds which reflect only certain wavelengths of visible light (figure 1). This makes them appear colorful. Pigments generally are dry, fine powders that are practically soluble in many usual solvents. Pigments are used because of their color power. The first using of these compounds was about 30,000 years ago in prehistoric caves. Artists used organic pigments such as ochre earth, yellow and red clay, and iron oxide. Figure 1 : Pigments Introduction The ability of a pigment to absorb light increases with decreasing size until a size in which the particles become translucent. Over the years, the size of pigments has decreased because of different problems (such as heterogeneity) which influence the final characteristics of the product. It is very important to control size to guaranty production quality. For these reasons, particle size analysis is very important for pigment applications. - Viscosity, - Gloss, - Sedimentation, - Durability. - Optical properties, - Color, - Hue, - Opacity, Today, there are many different types of pigments: - Natural Vegetables, earth, animals, flowers, plants, trees - Chemical Obtained by amalgam or fusion of different materials The use of pigments has increased and they are found in the following applications: toner, paint, coatings, ink, plastics, rubber, textiles, cosmetics, food, pharmaceuticals... Particle size analysis of the pigments can influence some primary properties in the final product, such as : 006
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006-Measurement of Pigments With Dry Jet Dispersion Technology
006-Measurement of Pigments With Dry Jet Dispersion Technology
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When measuring pigments, you need to use a small quantity of the sample in order
to improve measurement accuracy (an obscuration around 15%).
This is because of the great light absorption of the pigment samples in wet mode. The small quantity of sample can introduce measurement errors since the result
may not be reproducible or representative of all the particles in the batch.
In Dry mode with DJD Technology, this problem is solved because the user can
use 5 times more powder with a reduced acquisition time (around 10s instead of
30s in liquid mode). The larger quantity of pigment sample is more representative
of the mother batch. This allows a better accuracy.
Our experience has shown that pigments must be carefully analyzed because the optical properties of
pigments can affect the results of laser diffraction analysis.
Conclusion
Pigments are small size particles (around 50µm for toner and less than 10µm for
others).
Correct analysis depends on the control of several important parameters.
Their properties of light reflection and/or absorption during a measurement require
pigments to be measured using the Mie theory. This means that you need to know
the refractive index (both real and imaginary parts).
The imaginary part represents the degree of absorbance of a sample at a certain
wavelength. The imaginary part is different for each color pigment and is very