2. Why use Colours? Identification Branding Convey a Mood or a
Style Choice 3. Introduction
- Assessment and Measurement of Colour.
- Factors Affecting Colour Matching.
4. Colour Assessment
observer object light source 5. Human Visual System 6. The
Retina
- Retina uses special cells calledrodsandcones .
- Rods sees in black, white & shades of grey and tell us the
form or shape. (Super-sensitive allowing us to see when it's very
dark.)
- Cones senses colour but need more light. Three types and each
is sensitive to one of three different colours - red, green, or
blue. Together these can sense combinations of light waves. (To see
millions of colours.)
- Rods and cones together process the light to give you the total
picture.
7. The Rods and Cones 8. The Rods and Cones 5 million per eye
(more Land M cones than S cones) 100 million per eyeResponsible for
daylight(photopic) vision Responsible for low- level (scotopic)
vision Cone function Rod function scotopic mesopic photopic
luminance Cones Rods 9. Eyesight
- Individuals perceive colour differently. Is Sky Blue the same
as Pale Blue ?
- How many People are Colour-Blind?
- Experts are turned in to Colours.
10. Light source
- Aredobject inredlight, appearred- as all thered light is
reflected.
- Aredobject inbluelight, appearblack- as noredlight to reflect
back.
- The difference between say daylight and the Tungsten Lights
used in homes, could be significant!!
11. Size
- A small area of colour may look very different to a large area
of the SAME colour.
Hence, it is important when decorating to paint a sufficiently
large area. 12. Background colour
- Colours viewed against a strong, vivid coloured backgrounds,
appears very different against a neutral or pastel coloured
background.
13. 14. Surface finish
- A high gloss finish always appears darker than a matt finish of
the same colour.
15. Metamerism
- Change in appearance of a colour under different light
source.
- Describe the relative changes in colour between two samples,
i.e. Good match in day light, different in fluorescent shop
lighting.
- Occurs when different colourants are used in each sample.
16. Colour Measurement
- Light Sources and Illuminates
17. Colour 18. Colour Space
- To measure colour objectively, to communicate differences in
quantifiable terms.
- Principleis that all colours can be inside a Colour Space i.e.
this space being a sphere.
- Each colour can then be give a position in the colour
space.
- Differences between colours can be quantified by comparing the
values of the co-ordinates.
19. Colour Space + L= Lightness- L* = Darkness + a* =Redness -
a* =Greeness + b* =Yellowness- b* =Blueness +a* +b* -a* -b* L*=100
L*=0 L* L* -a* +a* -b* +b* 20. Colour Space - Delta E a* b* C* H*
is the difference between two points in colour space, often use to
determine a colour tolerance or specification. S C S H 21. Colour
Space
- A different system (Yxy) is used for transparent colours.
- Y = percentage of light transmitted
- x = balance betweenblueandredlight
- y = balance betweenblueandgreenlight
22. More on Metamerism
- Two colours with the same L*,a*,b* values which are arrived at
by a different route will show metamerism.
- Their colour will be different if the light source is
changed.
23. Colour Measuring Devices
- Filters the reflected lights into Red, Green an blue lights and
measure the relative amounts of each, then calculates the numerical
lab value.
24. Colour Measuring Devices
- Measure the reflected lights at regular intervals across the
visible spectrum, then produces a graph of the spectrum of light
reflected by the colour called the Spectral Curve.
25. Colour MeasuringDevices
- Spectrophotometers more accurate than colorimeters.
- Spectrophotometers better at identifying metamerism than
colorimeters.
- Differences between the human eye and colour measuring devices
> Possible to have an accurate reading but does not visually
look right!!!!
26. Light sources and illuminants
- The three most widely used are;
- D65 Simulation of Daylight (ArtificialDaylight).
- A Normal domestic tungsten light.
- TL84Standard fluorescent tube used inmost shops and
showrooms.
27. Colour Matching
28. Standard Colour Systems
- Colours presented as printed paper patterns books. (RAL and
PANTONE system.)
- Building industry has its own set of BS colours.
- NCS (Scandinavian) a measuring system rather than a fixed set
of colours.
29. The Material
- Processing temperatures and chemical characteristics, means a
colourant can work in one polymer, but degrade or discolour in
another.
- The more different the standard material is to the match
material, the less likely an accuratematch.
- A painted sheet match to Nylon 6.6, the colourants used in
paint will not survive 290 o C.
30. The colourants-Pigments
- Very fine powdered chemicals dispersed in the polymers.
- Poor dispersion results in a weaker colour and often a grainy
surface.
- Inorganic pigments are mineral based, i.e. Metal Oxides &
Sulphides.
- Organic pigments are chemical compounds, less heat stable and
more difficult to disperse. Usually give richer and more vivid
colours. Less pigment is required.
31. The colourants-Dyes
- Chemical substances that dissolves in the polymer.
- Chemically interact, as such allows light to pass through. When
use in transparent materials remain transparent.
- A limit how much dye can be added to a polymer,the dye can
bleed out!
- Insoluble in Polyolefins.
32. Legal Restrictions
- Food, Medical and Toy - mainly base on purity and inability to
extract the colourant from the finish item.
- Cadmium pigments - base on the premise when the Plastic part is
incinerated, they can release Cadmium metals. Applies mainly in the
packaging industry.
- If a colour is required for safety purposes, then Cadmium
pigments can be use regardless of the Cadmium legislation.
- Many companies have a Cadmium Free policy regardless of the
details of the legislation.
33. Methods of colouring
34. Dry Colour or Dry Blend
- The colourants are mixed with the polymer. Some dispersion aids
may be added and often a wetting agent to help bind the powder onto
the surface.
- Advantages :Cheap because the conversion cost is low. Quick to
prepare. Very small lot.
- Disadvantages :Can be very Messy, can affect drying, colour can
vary with different machine due to dispersion.
35. Masterbatch
- Compounds contains very high levels of colourants (up to 80%),
then mixed at a fixed ratio to give a specific colour.
- Polymer Specific - Carrier is the same material as the base
material.
- Universal - Carrier will readily mix with a wide variety of
polymers.
- Advantages :Better colour control, cleaner and less drying
problems than Dry-colour. A stock range of colours and specific
colours can be develop.
- Disadvantages :May not always be compatible with the base
polymer. Accuracy depends on the Moulder with mixing.
36. Liquid colour
- Similar to masterbatches, contains a high level of colourants,
but the carrier is a liquid.
- Advantages :Better colour control than Dry blend. More even
distribution than masterbatch. Stock range of colours.
- Disadvantages :Special dosing equipment is required. Spillage
is messy. Colour can depends on processing. Properties can be
affected by the liquid carrier.
37. Fully compounded colour
- The colourants are added to the base Polymers, then extruded to
encapsulate the colour into the polymer and is fully
dispersed.
- Advantages :Specific, accurate and controlled colours. The
performance of the compounds is more predictable. Ease of
handling.
- Disadvantages :Less flexible than the other methods.
38. A Polymer for Every Application