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Colour Technology. Colour Technology. Why are we using colours? . Identification Branding Convey a Mood or a Style Choice. Introduction to Colour Technology. Assessment and Measurement of Colour Factors Affecting Colour Matching Methods of Colouring. observer. light source. object.
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Colour Technology • Why are we using • colours? • Identification • Branding • Convey a Mood or a Style Choice
Introduction to Colour Technology • Assessment and Measurement of Colour • Factors Affecting Colour Matching • Methods of Colouring
observer light source object Colour Assessment • 1)Eyesight • 2)Light Source • 3)Size • 4)Background Colour • 5)Surface Finish • 6)Metamerism
The Retina • Retina uses special cells called “rods” and “cones” • 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
The Rods and Cones • Cones Rods • 5 million per eye (more L 100 million per eye • and M cones than S cones) • Responsible for daylight Responsible for low-level • (photopic) vision (scotopic) vision • luminance • ←scotopic→ ←mesopic → ←photopic → → → → → → → Rod function Cone function
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
2)Light source • A red object in red light, appear red - as all the redlight is reflected • A red object in blue light, appear black - as no red light to reflect back • The difference between say daylight and the Tungsten Lights used in homes, could be significant!
3)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.
4)Background colour • Colours viewed against a strong, vivid coloured backgrounds, appears very different against a neutral or pastel coloured background
5)Surface finish • A high gloss finish always appears darker than a matt finish of the same colour 6)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
Colour Measurement • Colour Space • Metamerism 3) Colour Measuring Devices • Colorimeters • Spectrophotometers 4) Light Sources and Illuminates
1) Colour Space • To measure colour objectively, to communicate differences in quantifiable terms • Principle is 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
L* +b* L*=100 +a* +b* -a* -b* -a* +a* L* -b* L*=0 Colour Space + L = Lightness - L* = Darkness + a* = Redness - a* = Greeness + b* = Yellowness - b* = Blueness
Colour Space - Delta E • is the difference between two points in colour space, often use to determine a colour tolerance or specification
Colour Space • A different system (Yxy) is used for transparent colours. • Y = percentage of light transmitted • x = balance between blue and red light • y = balance between blue and green light
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
3)Colour Measuring Devices • 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!
Colour Measuring Devices • Colorimeters • Filters the reflected lights into • Red, Green an blue lights and • measure the relative amounts • of each, then calculates • the numerical lab value
Colour Measuring Devices • Spectrophotometers • 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.
4)Light sources and illuminants • The three most widely used are: • D65 Simulation of Daylight (Artificial Daylight) • A Normal domestic tungsten light • TL84 Standard fluorescent tube used in most shops and showrooms
Colour Matching • 1)Standard Colour Systems • 2)The Material • 3)Colorants • 4)Legal Restrictions
1)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
2)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 accurate match • A painted sheet match to Nylon 6.6, the colourants used in paint will not survive 290oC
3)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
3)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
4)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
Methods of colouring • 1)Dry Colour • 2)Masterbatch • 3)Liquid Colour • 4)Fully Compounded Colour
1)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.
2)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.
3)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.
4)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 • END of presentation