Colour matching and colour theory


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Colour Matching explained

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Colour matching and colour theory

  1. 1. Colour matching and colour theory An introduction to Computer Aided Colour Management For the Injection Moulder Siddhartha Roy 1
  2. 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. 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. 4. Trends in Colouring • More and more Auto Interiors, Appliances and other Plastic assemblies will be requiring exact colour matched components 4
  5. 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. 6. Perception of colour • The Light source •The object j •The human eye Th h 6
  7. 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. 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. 9
  10. 10. Even Black and white images can give strange results
  11. 11. Optical Illusions
  12. 12. • The optical illusions can be resolved by actual measurements by simple instruments like a measuring scale, Compass etc.
  13. 13. 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
  14. 14. 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
  15. 15. The Munsell Colour Theory 17
  16. 16. 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.
  17. 17. The CIE Theory Standard Illuminants Red Standard Observer Magenta Yellow Y ll Green White Cyan Blue 19
  18. 18. CIE Colour Specifications: • XYZ Tristimulus Values • LabCh 20
  19. 19. 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
  20. 20. 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
  21. 21. Colour differenceColour on Screen Batch 1 Standard Batch 2 23
  22. 22. Colour DifferenceL a b Plot 24
  23. 23. Colour Strength 25
  24. 24. Pass - Fail 26
  25. 25. Formulation 27
  26. 26. Batch Correction 28
  27. 27. Recap 29
  28. 28. 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 30 data.
  29. 29. 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
  30. 30. 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.
  31. 31. 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
  32. 32. For more Info on Colour Theory: • r_theory.htm y • http://www hunterlab com/ColorEducation/ColorTh eory 34
  33. 33. Email: 35 Mobile: 9890366632