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Buyer's Guide to Pigments
Pigments find enormous types of application in
broad range of industries and encompasses a huge variety of Colorants.
High performance inorganic pigments offer comparatively weak color
strength, but can give excellent opacity and durability. To give another
example, high cost organic pigments though offer excellent color strength
but comes with the limitation of poor opacity. Thus Formulators are left
with very difficult choices to make.
One thing to remember is that, pigment selection in most cases is
application-specific. Some of the important factors that plays a vital role
can be of choices like:
- Color and Tinctorial strength.
- Long-term performance vis-a-vis coloring cost.
- High melt temperature of polymers: For example take the case of
fluoropolymers. Typical melt temperatures are high and can vary from 165°C-
370°C. Here the pigment selection is restricted and the majority of
pigments applied are inorganic in nature.
Here are few tips that are valuable in pigment
- Selection of Pigment generally is balancing of many types of
variables, therefore changes made in the existing commercial
formulations should be done judiciously considered and only after color
rematching. For example a manufacturer who randomly switches colorant
suppliers or reduces expenditure by adopting less costly colorants is
under the risk of problems during processing and end-use.
- Consideration should be given towards particle size of the Pigment as
it affects light scattering, which in turn can affect shading. To cite
an example, finer particles has a tendency to shift a red pigment's
shade towards blue, while coarser particles tends to move it towards
- In the case of application in plastics, adding pigments and dyes asks
for matching the right mix of colorants to the shade and intensity of
the required colors.
- Organic pigments generally can withstand temperatures 400°F and
475°F, while inorganic pigments has been seen to withstand 550°F
or even more. In case of some complex inorganic pigments, there is a
greater heat stability than some polymers. In case of inorganic pigments
like yellow iron oxide, a surface treatment is required to increase
their heat stability above 400°F. So, it is imperative that a
careful selection of inorganic and organic pigments must be done from
the standpoint of temperature so as to maximize color and performance.
- It has been seen that in some cases, organic pigments has a tendency
to cause part warpage. This generally occurs when pigments interfere
with the polymer crystallization. Now the point here is that warpage
issues arises more with some kind of pigments than with others. Examples
are that of green or blue phthalocyanine pigments. Resins like
high-density polyethylene, are more prone to warpage due to their rapid
- The pigment that is chosen must show compatibility with the base
resin so as to prevent a color shift over time.
Important Selection criteria in Pigment applications
Different applications require different sets of
properties. The table given below follows some popular applications along
with selection criteria for pigments:
||Transparency- The most significant criteria for the colored pigment
in the case of a metallic/effect shade.
||Important criteria for selection are:-
- Complete hiding
- Heat resistance
- Good durability
- Chemical resistance
||Powder coating can involve complex procedures. Pigment selection
among others include:
- Heat stability
- Resistance to wear and tear
- Stability of the dispersions
- Ability for blending
- Heat Stability
- Compatibility with the base resin
- Proper dispersion