1. What adverse effects will the separation of different pigments in the paint have on the entire system?
In the paint industry, it is very common for pigments to separate from each other in powder coatings, especially if there are two or more pigments in the formulation. Pigment separation can result in uneven distribution of pigment across the surface of the coating once it dries.
If it is due to the difference in the concentration of the pigment on the surface of the coating film, the phenomenon of excessive pigment in the local area is called blooming. Flooding is actually a vertical dispersion of the pigment mixture that separates the components of the pigment mixture from each other.
In the vertical direction of the paint film, the pigment concentration is the same, the color is the same, and the concentration in the horizontal direction is different, the color is different, and the appearance of the paint film is uneven in color and stripes.
If the pigments have the same concentration on the surface of the coating film and different concentrations inside the coating film, we call it floating color. Floating is a horizontal dispersion of a pigment mixture.
In the horizontal direction, the pigment concentration is the same, and the color is consistent, but the color of the lower layer is not consistent, and the pigment concentration is different. When the paint is applied to the glass, we can observe the floating phenomenon.
Pigment segregation is largely related to the different mobility of the different pigments in the formulation. Dispersants can improve this kind of paint disease.
2. How to avoid the use of toxic lead chromate and lead molybdate without affecting the color of the paint?
Due to the toxicity of lead-containing pigments, countries are increasingly restricting the use of lead-containing pigments in paints. Formulators usually replace lead-containing pigments with organic pigments and titanium dioxide.
However, in some applications, organic pigments combined with metal oxide mixed pigments (inorganic composite coloring pigments) show better performance than titanium dioxide.
The inherent vivid hue, saturation and high hiding power of metal oxide hybrid pigments give formulators more possibilities to reduce expensive organic pigments in the formulation, reduce or even eliminate titanium dioxide.
For organic pigments, there are also many pigments that show very good hiding power and weather resistance and can be used to replace lead pigments. Red pigments include Pigment Red 48:4, Red 112, Red 170, Red 254, Red 255, Purple 19, etc.
Orange pigments include Pigment Orange 36, Orange 73 and the like. Yellow pigments include pigment yellow 74, yellow 109, yellow 110, yellow 139, yellow 151, yellow 154, etc.
Especially in yellow pigments, we recommend using bismuth vanadium molybdenum yellow (pigment yellow 184), bismuth vanadium molybdenum yellow is much brighter than metal oxide mixed pigment titanium nickel (pigment yellow 53), and has stronger tinting power, more Good hiding power (even without adding titanium dioxide), outstanding heat and weather resistance.
3. What types of phthalocyanine blue can be used in the coating industry?
Phthalocyanine blue is mainly composed of copper phthalocyanine, with complex chemical structure, and the appearance is dark blue powder. Phthalocyanine blue has many crystal states.
There are three kinds of products, namely, α-type phthalocyanine blue (pigment blue 15) with red light and relatively the highest tinting strength; β-type phthalocyanine blue (pigment blue 15) with green light and relatively the best thermodynamic stability 15:3).
Compared with the ε-type phthalocyanine blue (pigment blue 15:6) with the most vivid red light. In aromatic solvents (such as xylene), α-phthalocyanine blue will be converted to more stable β-phthalocyanine blue.
In order to prevent this transformation, usually during the pigmentation process of crude phthalocyanine blue, a part of monochlorinated copper phthalocyanine is added to form solvent-stabilized α-type phthalocyanine blue or pigment blue 15:1.
Since the surface of the phthalocyanine blue pigment is non-polar, the interaction with the binder in many coating systems is weak, resulting in poor stability of the pigment dispersion system.
4. What method can be used to quickly judge the dispersion performance of a pigment?
We have many direct and indirect methods to evaluate the dispersion effect of pigments. Examples of direct methods are the fineness plate method, optical and electron microscopy.
Fineness plate method:
The Hegman test method for fineness of grind is a simple and quick test method for fineness of grind in liquid systems.
Haishi fineness plate is a rectangular stainless steel material with two shallow grooves processed on the surface. The shallow groove gradually becomes shallower from 100 microns deep to 0 microns after precision machining. A small amount of abrasive material is added to the deepest part of the groove. The edge scraper scrapes at a uniform speed across the entire surface to the end where the groove depth is zero.
The scale is equidistantly marked beside the groove, from the scale zero in the deepest groove to the scale 8 or 10 on the horizontal surface of the fineness plate.
Observe the point where the dense particle point first appears in the sample, that is, the scale of the pigment particles that can clearly be observed protruding from the surface of the grinding material is considered to be an indicator for judging the degree of dispersion. Usually at least a scale of 7 is considered valid for dispersion.
Fineness test method:
The use of light microscopy provides a rapid, size-intuitive method of fineness detection of pigments. And the tinting strength of the pigment can also be observed.
In addition, the shape, size and distribution of pigment particles, as well as the flocculation of pigments can be observed. The specific experimental method is to drop a small drop of grinding material on a glass slide, and then cover it with a cover glass.
Be careful not to use excessive force when covering the cover glass to prevent excessive separation of the materials to be observed and affect the inspection. The main disadvantage of optical microscopy is that the resolution is too low, and the minimum resolution is only about 2 microns.
Electron microscope fineness test method:
The high resolution of the electron microscope is a highlight. It can directly observe the particle size of the pigment, and it is the particle size of the pigment that has a decisive impact on the transparency, fluidity and color of the coating.
The disadvantages of the electron microscope fineness test method are mainly that the equipment is expensive, the test time is long, and experienced technicians are required to analyze and interpret the test data. In addition, the sample must be dried before measurement.