Colour Technology (1)

7/27/2019 Colour Technology (1)

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Colour Technology


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Why use Colours?

IdentificationBranding

Convey a Mood or a Style

Choice


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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 andcones.

Rods sees in black, white & shades of grey andtell 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 differentcolours - red, green, or blue. Together these can

sense combinations of light waves. (To see millionsof colours.)

Rods and cones together process the light to giveyou 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 redobject in redlight, appearred- as allthe redlight is reflected.

A redobject in blue light, appear black - as

no redlight to reflect back.

The difference between say daylight and the

Tungsten Lights used in homes, could besignificant!!


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Size

A small area of colour may look very

different to a large area of the SAME

colour.

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


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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.


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Metamerism

Change in appearance of a colour underdifferent 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.


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Colour Measurement

Colour Space

Colour Measuring Devices

Colorimeters

Spectrophotometers

Metamerism

Light Sources and Illuminates


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Colour


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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.


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Colour Space

+a*

+b*

-a*

-b*

L*=100

L*=0

L*

L*

-a*

+a*

-b*

+b*

+ L = Lightness - L* = Darkness

+ a* = Redness - a* = Greeness

+ b* =Yellowness - b* = Blueness


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Colour Space - Delta E

a*

b* D C*DH*

SC

SH

222

***

D

D

DD

H

ab

C

ab

LS

H

cS

C

lS

LE

is the difference between two points in colour

space, often use to determine a colour

tolerance or specification.


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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


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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 ischanged.


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Colorimeters

Filters the reflected

lights into Red, Green

an blue lights and

measure the relative

amounts of each, then

calculates thenumerical lab value.


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Spectrophotometers

Measure the reflectedlights at regular intervals

across the visiblespectrum, then producesa graph of the spectrumof light reflected by thecolour called the SpectralCurve.


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Spectrophotometers more accuratethan colorimeters.

Spectrophotometers better at

identifying metamerism thancolorimeters.

Differences between the human eye and

colour measuring devices > Possible tohave an accurate reading but does not

visually look right!!!!


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Light sources and illuminants

The three most widely used are;

D65 Simulation of Daylight (ArtificialDaylight).

A Normal domestic tungsten light.

TL84 Standard fluorescent tube used inmost shops and showrooms.


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Colour Matching

Standard Colour Systems

The Material

Colorants

Legal Restrictions


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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.


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The Material

Processing temperatures and chemicalcharacteristics, means a colourant can workin one polymer, but degrade or discolour inanother.

The more different the standard material isto the match material, the less likely anaccurate match.

A painted sheet match to Nylon 6.6, thecolourants used in paint will not survive290oC.


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The colourants-Pigments

Very fine powdered chemicals dispersed inthe polymers.

Poor dispersion results in a weaker colour andoften 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.


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The colourants-Dyes

Chemical substances that dissolves in thepolymer.

Chemically interact, as such allows light topass through. When use in transparentmaterials remain transparent.

A limit how much dye can be added to a

polymer, the dye can bleed out! Insoluble in Polyolefins.


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Legal Restrictions

Food, Medical and Toy - mainly base on purity andinability to extract the colourant from the finishitem.

Cadmium pigments - base on the premise when

the Plastic part is incinerated, they can releaseCadmium metals. Applies mainly in the packagingindustry.

If a colour is required for safety purposes, thenCadmium pigments can be use regardless of the

Cadmium legislation. Many companies have a Cadmium Free policy

regardless of the details of the legislation.


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Methods of colouring

Dry Colour

Masterbatch

Liquid Colour

Fully Compounded Colour


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Dry Colour or Dry Blend

The colourants are mixed with the polymer. Somedispersion aids may be added and often awetting agent to help bind the powder onto the

surface.

Advantages : Cheap because the conversioncost is low. Quick to prepare. Very small lot.

Disadvantages : Can be very Messy, can affectdrying, colour can vary with different machinedue to dispersion.


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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


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Liquid colour

Similar to masterbatches, contains a high level ofcolourants, but the carrier is a liquid.

Advantages : Better colour control than Dryblend. More even distribution than masterbatch.

Stock range of colours.

Disadvantages : Special dosing equipment isrequired. Spillage is messy. Colour can

depends on processing. Properties can be

affected by the liquid carrier.


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Fully compounded colour

The colourants are added to the basePolymers, 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

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Colour Technology (1)

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