An introduction to Computer
Aided Colour Management
For the Injection Moulder
•Special thanks to Mr. V. C. Gupte for
elaborating and educating us on ‘Colour
Measurement’ and ‘Colour Management’.
• A major part of this presentation covers the
concepts and theories taught by him to our
team at V.I.P. Industries.
• I would like to record my appreciation to his
Importance of Colours in
• Aesthetics are as important as Physical properties in
• Th ability to integrally colour Plastic Moulded
The bilit t i t
Pl ti M ld d
articles is an important edge over other materials
like metals and even Rubber.
• Matching of colours, especially across assembled
mouldings is crucial in many applications.
• The task becomes more difficult when colours need
to be exactly matched with different Polymers.
• Understanding Colour theory and its applications
has become a must for the Injection Moulder.
Trends in Colouring
• More and more Auto Interiors, Appliances
and other Plastic assemblies will be
requiring exact colour matched components
Components must have the same colour even
Moulded at different Vendors/ Locations
Moulded from different Plastics
Moulded with addition of regrind.
Moulded from different lots of Resin/ Masterbatch
Perception of colour
• The Light source
•The human eye
The Human Eye and Brain
• Light receptors
– Rods - Perceives light and darkness
– Cones-Perceive Colours
– The black & white world. (Night vision)
– Red, Green & Blue sensitive receptors
• The optic nerves transmits stimuli to the
brain which interprets colour.
• There is a mismatch between the large number of
rods and cones in the retina and the transmitters to
• This results in false perception of colour
especially when the eye is exposed to bright
i ll h h
d bi h
images for a length of time.
• I the next slide concentrate on the central white
t l hit
dot for 30 seconds.
Observe what happens when the screen turns
• The optical illusions can be resolved by
actual measurements by simple instruments
like a measuring scale, Compass etc.
Need for Quantifying Colours
• Like in the previous examples we need a
system for measuring and quantifying
• Subjectivity in Colour perceptions is
– All brains do not process Colour information
– Prime example is Colour blindness- Inability to
distinguish between Red and Green.
• A Standardised scientific method is required
to record Colour Information.
• Two of the major Colour quantification
–Munsell Colour Theory
–The CIE Theory
• Hue- An attribute by which a sample
appears to be similar to one or a mixture of
two of the perceived colours –red, yellow,
green and blue.
• Chroma- Is the colourfulness of a given
• Value- The lightness or darkness, i.e. the
attribute by which a sample appears to
reflect a greater or smaller fraction of the
ll f ti
The CIE Theory
• Spectrophotometers are very effective in
measuring and recording Colours
• The CIE System is commonly used
• Software is crucial in recording, analysing,
comparing and matching colour samples.
• Samples should have the same surface finish
and shape as far as possible.
• The S
h Spectrophotometer scans samples f
comparison and the Software takes over. 21
• dE = (LabCh of sample)-(LabCh of Standard)
(L bCh f
l ) (L bCh f St d d)
– dL- When positive -- lighter negative-- darker
– da- When positive-- redder, negative-- greener
– db- When positive-- yellower, negative-- bluer
– dC-When positive-- brighter, negative-- duller
– dh Indicated hue address
Colour differenceColour on Screen
• The effectiveness of the Spectrophotometer
– Colour Matching software is very
dependant on the Pigment Database loaded.
• The LabCh values for each pigment being
used h to b painstakingly generated
d has be i
– In full strength and white and black reduction.
– On the different Polymer bases (PO, Styrenic,
– Some Pigment manufacturers provide such
Important Aspects for Colouring
• Pigments should be thoroughly dispersed
– Very difficult with powder pigments
– Much easier with Masterbatches
• Colour of base plastic
– Colourability of different plastics vary widely
– Masterbatch selection should be appropriate to base
Major Causes of Colour
• Weighing and mixing of colourants.
– Cleanliness of Blending Equipment
– Adequate mixing time
• Interference from regrind. Contamination.
• Degradation during processing.
– Machine stoppages and inadequate purging.
• Improper selection of Colourant/ Masterbatch.
• Interference with processing additives
– E.G. With PVC chrome pigments containing lead will
discolour if Tin Stabilisers are present.
How to Face the Challenge?
• Accent on cleanliness
– Poor housekeeping = colour contamination
• Selecting correct Colourant
– Clear understanding of colour behaviour in Polymer
involved. Masterbatch supplier plays crucial role.
• Use of Precoloured Materials (esp ABS PC/ABS)
– Best for replicating same colours at different locations
– Cost is more
– Inventory and logistics issues
• Use of Pigment colouring for small quantities
where M t b t h development is not feasible
h Masterbatch d l
t f ibl
• Making use of Colour matching facilities.
For more Info on Colour Theory:
• http://www hunterlab com/ColorEducation/ColorTh