Pigments encompasses a huge variety of Colorants as
well an enormous types of applicaion in broad range of industries.
Sometimes what happens is that all of the properties expected do not
come together to give an illustration, 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:
- Colour and Tinctorial strength.
- Long-term performance vis-a-vis colouring 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 a few of such tips have been outlined which
would prove valuable in pigment selection.
- 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.
- 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
colourant suppliers or reduces expenditure by adopting less costly
colorants is under the risk of problems during processing and
- 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 yellower shades.
- 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 crystallization.
- 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.
- The pigment that is chosen must show compatibility with the base
resin so as to prevent a colour shift over time.
Different applications require different sets of
properties. As an informed buyer absolute knowledge of various
applications along with their respective requirements from pigments are
a must for success of the products. In this table that follows some
popular applications along with selection criteria for pigments are
- Transparency- The most significant criteria for the colored
pigment in the case of a metallic/effect shade.
||Important criterias 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
- Stabilty of the dispersions
- Ability for blending
- Heat Stablity
- Compatability with the base resin
- Proper dispersion