TITA

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Colour Technology

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Why use Colours?

IdentificationIdentificationBrandingBranding

Convey a Mood or a Style Convey a Mood or a Style ChoiceChoice

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Introduction

• Assessment and Measurement of Colour.

• Factors Affecting Colour Matching.

• Methods of Colouring.

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Colour Assessment

• Eyesight

• Light Source

• Size

• Background Colour

• Surface Finish

• Metamerism

observer

object

light source

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Human Visual System

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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.

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The Rods and Cones

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The Rods and Cones

5 million per eye (more L and M cones than S cones)

100 million per eye

Responsible for daylight (photopic) vision

Responsible for low-level (scotopic) vision

Cone function

Rod function

scotopic mesopic photopic

luminance

Cones Rods

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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.

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Light source• A red object in red light, appear red - as all

the red light 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!!


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 Hence, it is important when decorating to paint a sufficiently large area.paint a sufficiently large area.


Background colour

• Colours viewed against a strong, vivid coloured backgrounds, appears very different against a neutral or pastel coloured background.

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Surface finish

• A high gloss finish always appears darker than a matt finish of the same colour.


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• Colour Measuring Devices

Colorimeters Spectrophotometers

• Metamerism• Light Sources and Illuminates


Colour


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.


Colour Space

+a*

+b*

-a*

-b*

L*=100

L*=0

L*

L*

-a*

+a*

-b*

+b*

+ L = Lightness + L = Lightness - L* = Darkness- L* = Darkness+ a* = + a* = RednessRedness - a* = - a* = GreenessGreeness+ b* = + b* = Yellowness Yellowness - b* = - b* = BluenessBlueness


Colour Space - Delta E

a*

b* C*H*

SC

SH

222***

H

ab

C

ab

L S

H

cS

C

lS

LE

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.


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

• SpectrophotometersMeasure 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.


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!!!!


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

• Standard Colour Systems

• The Material

• Colorants

• Legal Restrictions


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.


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.


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.


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.


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

• Dry Colour

• Masterbatch

• Liquid Colour

• Fully Compounded Colour


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.


MasterbatchCompounds 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.


Liquid colourSimilar 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.


Fully compounded colourThe 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.

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A Polymer for Every Application

TITA

Documents

measurement of colour

weaker colour

colour tolerance

colour technology

background colour colours

cones senses colour

small area of colour

colour space delta e