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Colorants for Plastic Industry
Color is an integral part of the plastic material and it should not be
considered as an after thought. The whole system of coloring has to be deal
with using what is called a total systems approach. No doubt the color
enhances the functionality, but it has also the potential to degrade certain
material properties like impact strength, if not applied properly.
The colorants that are used in the Plastic Industries can be both the dyes
and pigments. Both dyes and pigments exhibit color through the process of
visible light absorption and scattering. Typically color formulations
generally have four colorants. Black and white are used basically to control
the value and Chroma, while two colored pigments or dyes are applied to
establish the Hue.
Dyes that are used in the plastics industry must be very strong, show good
heat stability and be transparent. Typically the dyes are used to tint or
shade a resin. In the plastics industry dyes are limited in use, as such
they can be used for only a selected number of resins. Pigments used in this
industry can be organic or inorganic. While pigments offer more choices to
the manufacturers due to its opacifying ability, broader chroma range, and
better heat stability for most of the resins. Pigments are generally
dispersed within a resin matrix, while dyes solubilize in the resin.
Titanium Dioxide is a pigment that has a wide use in Plastics industry. It
is used to make the plastics more whiter, brighter and durable.
Dyes or Pigments?
A base polymer dictates the choice of the colorant
selected. Pigments are typically used in polyolefins as most of dyes show a
tendency to migrate in polyolefins. While Dyes are often successfully used
with polycarbonate, polystyrene, acrylic, and other types polymers because
of their color strength and transparency. The final word is whatever be the
colorant selected it must show compatibility with the base resin. This is in
order to prevent a color shift occurring over time.
Have a look at the properties of few of the colorants that constitutes both
dyes and pigments:
|Type of Effect
||Dyes: PMMS, PET, ABS, Pigments:PE, PP
||PMMS, PE, PS
Factors in selection of right colorant
- End-use application requirements
- Weather fastness
- Colorant loading
- Dispersion method
- Resin type
- Dimensional stability
- Processing Temperature
- Heat stability: A careful choice of inorganic and organic pigments
from the view point of temperature is vital for maximizing color and
- Type of polymer(s) being used
- How is the polymer(s) being processed
- What kinds of functional additives are required like plasticizers,
stabilizers, flame retardants, slip agents, etc.
- The exact application (whether general purpose, food contact item,
toy, package subject to CONEG regulation etc.)