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006-Measurement of Pigments With Dry Jet Dispersion Technology
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Measurement of Pigmentswith 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
Standard Operation Procedure Dry Mode
Figure 2 : Reproducibility of 3 measurements of blue toner
Vibratory Feeder
Level of vibration 2 on 9
Aquisition Time 10s
Pressure 500 mbars
The results are very reproducible, less than 1% for this blue toner (figure 2).
With DJD technology, this type of powder can be easily dispersed and measured with a reproducibility
better than 1%.
Results
Table 1 : Experimental conditions
The pressure needed to disperse powders is low
(less than 1 bar) and prevents the possible
erosion of particles (table 1).
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
important for the measurement.
Measurement Parameters
