Finishes to Improve Colour Fastness
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Transcript of Finishes to Improve Colour Fastness
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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.
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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
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Techniques for better wet Fastness
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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Techniques for better wet Fastness
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
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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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Chemistry of techniques for better wetFastness
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
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Chemistry of techniques for better wetFastness
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
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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
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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
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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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Chemistry of LF improving finishes
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
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Chemistry of LF improving finishes
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.
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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)
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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
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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.
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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
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