Colour Matching explained

1. Colour matching
and
colour theory
An introduction to Computer
Aided Colour Management
For the Injection Moulder
Siddhartha Roy
1

2. •Special thanks to Mr. V. C. Gupte for
p
p
elaborating and educating us on ‘Colour
g
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
contribution.

3. Importance of Colours in
Mouldings
• Aesthetics are as important as Physical properties in
mouldings.
• Th ability to integrally colour Plastic Moulded
The bilit t i t
ll
l
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.
3

4. Trends in Colouring
• More and more Auto Interiors, Appliances
and other Plastic assemblies will be
requiring exact colour matched components
4

5. Components must have the same colour even
when
•
•
•
•
Moulded at different Vendors/ Locations
Moulded from different Plastics
Moulded with addition of regrind.
Moulded from different lots of Resin/ Masterbatch
5

6. Perception of colour
• The Light source
•The object
j
•The human eye
Th h
6

7. The Human Eye and Brain
• Light receptors
– Rods - Perceives light and darkness
– Cones-Perceive Colours
• Rods
– The black & white world. (Night vision)
• C
Cones
– Red, Green & Blue sensitive receptors
• The optic nerves transmits stimuli to the
brain which interprets colour.
7

8. Optical Overload
• There is a mismatch between the large number of
rods and cones in the retina and the transmitters to
the brain.
• This results in false perception of colour
especially when the eye is exposed to bright
i ll h h
i
d bi h
images for a length of time.
• I the next slide concentrate on the central white
In th
t lid
t t
th
t l hit
dot for 30 seconds.
• Ob
Observe what happens when the screen turns
h th
h th
t
white.

9. 9

11. Even Black and white images can
give strange results

12. Optical Illusions

14. • The optical illusions can be resolved by
actual measurements by simple instruments
like a measuring scale, Compass etc.

15. Need for Quantifying Colours
• Like in the previous examples we need a
system for measuring and quantifying
colours..
colours
• Subjectivity in Colour perceptions is
common
– All brains do not process Colour information
identically.
identically
– Prime example is Colour blindness- Inability to
distinguish between Red and Green.
Green
15

16. Colour Theory
• A Standardised scientific method is required
to record Colour Information.
• Two of the major Colour quantification
systems are
–Munsell Colour Theory
–The CIE Theory

17. The Munsell Colour Theory
17

18. Definitions
• 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
illuminance level.
• Value- The lightness or darkness, i.e. the
attribute by which a sample appears to
reflect a greater or smaller fraction of the
fl t
t
ll f ti
f th
incident light.

19. The CIE Theory
Standard Illuminants
Red
Standard Observer
Magenta
Yellow
Y ll
Green
White
Cyan
Blue
19

20. CIE Colour Specifications:
• XYZ Tristimulus Values
• LabCh
20

21. Computerised Colour
Measurement
• Spectrophotometers are very effective in
measuring and recording Colours
• The CIE System is commonly used
• Software is crucial in recording, analysing,
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
h
l for
comparison and the Software takes over. 21

22. Colour Difference
• dE = (LabCh of sample)-(LabCh of Standard)
(L bCh f
l ) (L bCh f St d d)
– dL- When positive -- lighter negative-- darker
lighter,
darker.
– da- When positive-- redder, negative-- greener
– db- When positive-- yellower, negative-- bluer
– dC-When positive-- brighter, negative-- duller
– dh Indicated hue address
dh- di
dh
dd
22

23. Colour differenceColour on Screen
Batch 1
Standard
Batch 2
23

24. Colour DifferenceL a b Plot
24

25. Colour Strength
25

26. Pass - Fail
26

27. Formulation
27

28. Batch Correction
28

29. Recap
29

30. Pigment Database
• The effectiveness of the Spectrophotometer
– Colour Matching software is very
dependant on the Pigment Database loaded.
loaded
• The LabCh values for each pigment being
used h to b painstakingly generated
d has be i
ki l
d
– In full strength and white and black reduction.
– On the different Polymer bases (PO, Styrenic,
PVC etc.)
– Some Pigment manufacturers provide such
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data.

31. Important Aspects for Colouring
of Plastics
• 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
plastic
•
•
•
•
Polyolefin base
Styrenic base
PVC base
Universal base
31

32. Major Causes of Colour
Variation
• 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
32
discolour if Tin Stabilisers are present.

33. 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)
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
ti
t f ibl
• Making use of Colour matching facilities.
33

34. For more Info on Colour Theory:
• http://www.premiercolorscan.com/color_theory/colo
r_theory.htm
y
• http://www hunterlab com/ColorEducation/ColorTh
http://www.hunterlab.com/ColorEducation/ColorTh
eory
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35. Email: royplastech@rediffmail.com
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Mobile: 9890366632