Finishes to Improve Colour Fastness

8/11/2019 Finishes to Improve Colour Fastness

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09/07/201

Finishes to Improve Colour Fastness

By

Dr. Tanveer Hussain

Definitions

Colour Fastness The resistance of a material:

to change in any of its colour characteristics,

to the transfer of its colourants to adjacent materials or both

Fading Means that the colour changes and lightens

Bleeding The transfer of colour to a secondary, accompanying

fibre material

Soiling or Staining Coming of a colour on to accompanying material

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Types of Fastness

Washing

Water

Light

Rubbing

Perspiration

Ironing

Chlorine Peroxide, etc.


Fastness Rating

Washing

1-5 Grey scale

Light

1-8 Blue scale



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Techniques for better wet Fastness

Intensive Washing-off For cellulosics dyed with reactive dyes

Washing at high temperature often with special auxiliariesthat have dispersing, sequestering and dissolving (hydration,increased solubility) properties

Using compounds with high affinity for hydrolysed dye, theso-called colour transfer inhibitors e.g. polyacrylic acidderivatives

Using peroxidases (oxidative active enzymes such asbaylase RP).

Low energy, water and time

Restricted only to jet applications

Potential toxicity



Intensive Washing-off

For wool dyeings:

Washing under mild alkaline conditions withammonia, soda or sodium hydrogen carbonate

For polyester dyeings:

Reduction clearing for unfixed or loosely fixed dye

Colour fastness elevated up one rating



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Molecule enlargement

For anionic dyes (such as reactive, direct and aciddyes)

Results in reduced water solubility, generated by dye-salt

formation with anionic dyestuff in the fibre

Enclosure of the dyestuffs in cellulosic fibres withformaldehyde condensation products


Chemistry of techniques for better wetFastness

Cationic Products e.g. polyammonium compounds (polyquats); quaternary

polyhetrocycles such as polydiallyldimethyl ammonium chloride(DADMAC)

Mostlly used for direct and reactive dyes Improvements up to 1-2 rating

Washing fastness more improved than water or perspirationfastness



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Formaldehyde condensation products

Comparable to the corresponding products forpermanent press and easy care finishes

Often improve perspiration more than washingfastness

Mostly used for lining fabrics

Disadvantages:

Harsh handle (requiring use of softeners)

Decreased light fastness up to 2 ratings Shade change

Formaldehyde release



Condensation products of aromaticsulphonic acids Common name is syntan, derived form

synthetic tannin

Used for dyeing and printing on nylon fibres

Improvement in wet fastness up to 2 ratings



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Washing fastness evaluation methods

ISO

AATCC

ASTM

BS

DIN

FTMS

Marks& Spencer


Light fastness: Definitions

Light fastness

The resistance of dyestuffs to the influence oflight energy, especially the UV part of theelectromagnetic spectrum.

UVA (320-400 nm)

UVB (280-320 nm)

UVC (100-280 nm)

The shorter the wavelength, the higher the energyand the dyestuff damage.



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Light fading: Mechanism

Light protection of dye is related to lightprotection of fibre

Fibre damage also accelerate dyedecomposition

Fading is promoted by:

Moisture

Heat Oxygen in air


Factors influencing light fastness [LF]

Type of light (energy content, exposure time, rhythm of change fromlight to dark)

Dyestuff or pigment Type (better LF for lower specific surface) Concentration (better LF for dark shades) Distribution (better LF for even distribution than for ring dyeing)

Dyestuff combination (catalytic fading or protection)

Fibre type: PES > PA ; PAN > meta-aramid (nomex)

Moisture: less LF with high moisture Heat: less LF with high temperature

Accompanying substances Titanium dioxide; residual size; thickners; cationic fixers; formaldehyde

condensation products; oxidising & reducing agents (except LFimprovers)



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Basis of the effect

Interaction with the light UV-absorber or UVscreener, which have light filter

(UV-cutting) effects

Interaction with the dyestuff After-treatment with copper salts (formation of copper

complexes with high light fastness)

Application of radical traps, so-called anti-oxidants,which are mostly sterically hindered phenols andamines

Decomposition of intermediate peroxides andsinglet-oxygen quenching


Chemistry of LF improving finishes

UV light absorbers Colourless organic compounds, mostly with aromatic

structures Benzophenone, benzotriazol, phenyl triazine &

cynoacrylic acid derivatives; Titanium dioxide

Mechanism

Absorb high UV energy and transform it to vibration energy(and then into heat energy) without photodegradation;

Disadvantages High price

High concentration required



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Copper complexes Requires special structure to be present in the

dyestuff

Work only for selected dyes

A content of 40-60 ppm copper in the finished productis sufficient for good light protection

Disadvantages: High residual copper in waste water



Anti-oxidants

Hindered phenol light stabilisers (HPLS)

Hindered amine light stabilisers (HALS)



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Application of LF improvement finishes

UV absorbers can be combined withdyeing or after treatment with exhaustionor pad-dry techniques.


Evaluation of LF

ISO 105 B01-B06

AATCC test methods

FAKRA tests

SAE J1885 for automotive textiles



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Rubbing & Crocking Fastness: Definitions

Rubbing fastness

A change in colour of the rubbed textile (bybleeding and fading)

Crocking fastness

The migration of colour from the dyed surfaceto another surface by intense contact, e.g. byrubbing (soiling/staining)


Rubbing & Crocking Fastness

Factors Type of fibre (tensile strength, wet abrasion)

Kind and concentration of dye

Dyeing or printing procedure

Degree of fixation

Ring dyeing

Wet fastness

After-treatment with softeners, silicones, crosslinking agents

Type of textile in contact: shade, surface, kind of fibre and fabric

Intensity of the contact:: pressure, time, moisture andtemperature



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Rubbing & Crocking Fastness

Rating

1(poor) to 5 (best)

Wet rubbing may be less than dry up to 2ratings


Basis for improvement in rubbing fastness

Formation of films coating the fibres

Reduced rubbing of the smoothed surface

The finish products can behave similarly to lubricantsin reducing the rubbing forces.

Hydrophobation

Finishes that reduce the swelling of hydrophilicfibres cause an effect (durable press and easy-care finishes with crosslinking agents forcellulose fibres)



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Applied chemistries for improving rubbingfastness

Partially hydrolysed polyvinylacetate(PVAc/PVA) or polyvinylether

Application of pigment binders, mostlybased on acrylic copolymers similar tothose used as hand builders.

Application methods mostly used pad-dry

techniques.


Methods for evaluating rubbing fastness

ISO 105-X12

AATCC Crockmeter Method 8: Colourfastness to crocking

AATCC Test Method 116: for small fabric

samples and printed samples


Finishes to Improve Colour Fastness

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