Colouring of Polymers and Composites - Introduction to Polymeric Composites with Rice Hulls - page 108

8.6 Custom Colours for Polymers
If processing straight polymer resins, whether it is a single or multiple blend mix,
one may say that it is easy to colour and process. However, processing of polymer
composites, especially with wood flour or rice hull flour, is more complicated, especially
in terms of colouring and obtaining a uniformity and stability of colour. Many factors
can affect colour, including: resins, additives, texture shapes, lighting conditions,
usage environment, processing conditions/ methods and, most importantly, human
perception of what is required.
In addition, colour fastness, regulatory compliance and industry guidelines can
impact the selection of pigments and dyes used to achieve an accurate colour
match. Addressing of all these issues is not easy, and processors probably find it
cost-effective to work with colour experts or be satisfied with what is on offer. If
a custom colour is requested from a supplier, some of the information that may be
requested includes:
• Type of application the colour is intended for and how it is used will help determine
which pigments are best for matching and whether they remain consistent during
environmental exposure.
• Base polymer resin system and speciic grades : Some pigments are not compatible
with all polymers and certain grades need processing parameters, especially
temperature ranges, which can degrade many pigments.
• Processing method : For example, are the polymer composites to be extruded,
injection moulded or compression moulded? This knowledge helps to determine
if appropriate dispersion will occur.
• Levelofcolourtarget : An indication will help the suppler to achieve the best
colour and quality match possible.
• Match type : Whether an exact match or a several trials are expected can impact
on which pigments or dyes are used to control colouring costs.
• Opacity : If the composite material needs to maintain transparency, translucency
or become opaque is an important factor in meeting match criteria with many
polymer resin systems.
• Final product parameters (e.g., thickness, width and length weight) will help in
recommendations for the use of sufficient concentrations of colour to achieve
uniform colour throughout.