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Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������1�

�������������The� complaints�of� poor� colour� fastness�when� sports�dress� loses� color� and� form,� the� seat� fabric�inside�of�a�car�or�the�carpet�fades�too�fast�are�very�common.�All�dyes�will� fade�when�exposed�to�sunlight�and�it�is�possible�for�a�dyed�article�to�fade�noticeably�during�drying�on�a�washing�line�in�bright� sunlight� or,�more� importantly,� under� display� lighting� conditions� in� a� retail� outlet.� Any�reputable� retailer� would,� however,� regard� such� a� level� of� performance� as� quite� unacceptable.�Testing�for�light�fastness�provides�an�objective�framework�for�what�is�acceptable.��Fastness�to�light�is�basically�a�feature�of�the�actual�colourant�molecule�itself;�it�is,�in�fact,�a�measure�of�the�ability�of�the�molecule�to�absorb�radiation�without�being�destroyed,�the�absorbed�radiation�being�dissipated�in�other�ways.�In�a�dye�with�poor�light�fastness�the�molecule�will�be�broken�down�by�the�absorbed�radiation.�No�colourant�is�completely�fast�to� light,�but�it�should�be�emphasized�that� this� is�not�of� real� importance.�All� that�matter� is� the� colourant� should�not� fade� appreciably�during�the�life�of�the�article.��Lightfastness�is�the�degree�to�which�a�colourant�resists�fading�due�to�light�exposure.�Different�dyes�have�different�degrees�of�resistance�to�fading�by�light.�All�colourants�have�some�susceptibility�to�light� damage,� simply� because� their� colors� are� indications� that� they� absorb� the�wavelengths� that�they�do�not�reflect.�Light�is�energy,�and�the�energy�that�is�absorbed�by�the�colourant�compounds�degrade�them�or�nearby�molecules.��The� resistance� to� degradation� (or� fading)� of� fabric� dyes� and� prints� due� to� light� is� therefore� an�important� requirement�of�a� garment�because�without� such� resistance,� the� garment�may� change�colour�and�such�colour�may�not�be�acceptable�to�the�customer.��Retailers� are� also� becoming� more� aware� of� issues� concerning� colour� fastness� to� light.� Higher�colour� fastness� is� now�being�demanded� for� apparel� that�will� be�worn�predominantly� outdoors.�Another�technical�issue�is�the�problem�of�accelerated�colour�fading�on�exposure�to�light�in�alkaline�or�acidic�perspiration�through�the�intense�physical�activity�of�the�wearer.��Nowadays� the�criteria�of� light� fastness� is�hence�becoming�a�major�concern�amongst�buyers�and�consequently�with�dyers.��Standard�Methods�of�light�fastness:Standard�Methods�of�light�fastness:Standard�Methods�of�light�fastness:Standard�Methods�of�light�fastness:�����Generally�two�methods�of�testing�are�widely�accepted�by�most�of�the�customers.�They�are:��

1. American�Test�Method�(AATCC�16,�Option�3)��2. ISO�Test�Method�(ISO�105/BO2)��

�Both�the�methods�recommend�the�use�of�artificial�light�source,�namely�Xenon�Arc�lamp�exposure�as�it�is�representative�of�natural�daylight.��The�graph�below�shows�the�comparison�of�sunlight�with�the�artificial�light�produced�by�the�xenon�arc�lamp.��

COLOUR�FASTNESS�TO�LIGHT�

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������2�

��

���Test�procedure�in�briefTest�procedure�in�briefTest�procedure�in�briefTest�procedure�in�brief��������

Summary� :� �Summary� :� �Summary� :� �Summary� :� � � A� specimen� of� textile� is� exposed� to� artificial� light� source� under� specified�conditions� together� with� dyed� blue� standards� having� known� fading� characteristics.� The�fastness�is�evaluated�by�comparison�of�the�colour�change�of�the�specimen�with�that�of�the�standards�under�standard�viewing�conditions.��

ParameteParameteParameteParametersrsrsrs���� ISO�105�B02ISO�105�B02ISO�105�B02ISO�105�B02���� AATCC�TM�16�(option�3)AATCC�TM�16�(option�3)AATCC�TM�16�(option�3)AATCC�TM�16�(option�3)����Apparatus�and�Materials:Apparatus�and�Materials:Apparatus�and�Materials:Apparatus�and�Materials:����

Apparatus�

Xenon� Arc� lamp� light� fastness� tester� equipped� with� a�xenon� lamp,� suitable� filter� systems� and� various� control�systems� (Water� or�Air� cooled� type);� Specimen� holders;�Masks;� Black� Standard� Temperature� (for� ISO)� Black�Panel� Thermometer� (for� AATCC);� Colour� Matching�Cabinet�

Humidity�Test�Control�fabric�Red�Azoic�dyed�cotton�

cloth�-�

Blue�Wool�Light�fastness��reference�standards�

1�to�8� L�2�to�L�9�

Humidity�Test�Control�fabric�Red�Azoic�dyed�cotton�

cloth�-�

Temperature�Control�fabric� -�Xenon�reference�fabric�

(polyester�dyed)�

Xenon with Window Glass Filters

0.0

0.5

1.0

1.5

2.0

2.5

3.0

250 300 350 400 450 500 550 600 650 700 750 800

Wavelength (nm)

Irra

dia

nce (W

/m²/nm

)

Xenon with Window

Glass Filters

Sunlight Through

Window Glass

Sunlight

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������3�

Exposure�conditions:Exposure�conditions:Exposure�conditions:Exposure�conditions:����Normal�(Moderate�effective�humidity)Normal�(Moderate�effective�humidity)Normal�(Moderate�effective�humidity)Normal�(Moderate�effective�humidity)�L.F.�of�humidity�test�control� 5� -�Max.�Black�standard�temp.� 45º�C� -�Extreme�conditions�(Low�effective�humidExtreme�conditions�(Low�effective�humidExtreme�conditions�(Low�effective�humidExtreme�conditions�(Low�effective�humidity)ity)ity)ity)�L.F.�of�humidity�of�test�control� 6-7� -�Relative�humidity�of�air� -� 30�±�5%�Max.�black�panel�/�standard�temp.�

60º�C� 63�±�1º�C�

Chamber�air�temperature� -� 43�±�2º�C�Irradiance�at�420�nm�or�300-400�nm�

1.1�W/m2/nm�for�water�

cooled�machines�1.10�±�0.03�W/m

2/nm�or�48�

±�1�W/m2�

Extreme�conditions�(High�effective�humidity)Extreme�conditions�(High�effective�humidity)Extreme�conditions�(High�effective�humidity)Extreme�conditions�(High�effective�humidity)����L.F.�of��humidity�test�control� 3� -�Max.�black�panel�temp.� 40º�C� -�

Length�of�exposureLength�of�exposureLength�of�exposureLength�of�exposure�

Expose� until� a� contrast�(change� in� colour)�corresponding� to� grey� scale�grade� 4� and� later� to� grey�scale�3� is�visible�on� the� test�sample,� but� at� most� until�the� blue� wool� reference� 7�shows� a� contrast�corresponding� to� grey� scale�grade�4��Expose�to�a�certain�level�of�irradiance�is�attained;�H�=�E�x�3.6�x�t�where�H�is�the�radiant�exposure�in�kilojoules�per�square�metre;�E�is�the�irradiance�in�watts�per�square�metre�(or�joules�per�square�metre�and�second;�t�is�the�time�in�hours�and�3.6�is�a�conversion�factor�

Expose�until�a�certain�stage�is�reached�and�then�assess�with�the�grey�scale.�This�will�vary�depending�on�the�material;�The�least�durable�exposed�for�least�amount�of�time�(20�accelerated�fading�units�(AFU)�corresponding�to�reference�sample�L4);�40�AFU�of�exposure�for�upholstery�(equivalent�to�L5,�Draperies�60�AFU�and�so�on.��L6�is�equivalent��to�80�hours,�It�is�rare�for�clothing�to�require�a�light�fastness�higher�than�L5����

AssessmentAssessmentAssessmentAssessment���� The� light� fastness� rating�corresponds� to� the�number�of� the� blue� wool� reference�on� the� light� fastness� scale�which� shows� a� similar�contrast.��Rating�between�BWS�1�and�BWS�8�

Using� Colour� Change� Grey�Scale�1-5�

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������4�

��������Comparison�between�commonly�followed�ISO�and�AATCC�testing�methodsComparison�between�commonly�followed�ISO�and�AATCC�testing�methodsComparison�between�commonly�followed�ISO�and�AATCC�testing�methodsComparison�between�commonly�followed�ISO�and�AATCC�testing�methods�����There�is�often�confusion�between�the�two�tests�in�the�minds�of�people�not�familiar�with�the�test�procedures.��The�methods�have�two�distinct�differences�in�terms�of�assessment�and�“duration”�of�testing.��Often,�the�AATCC�method�is�incorrectly�asked�for�a�number�of�hours�whereas�the�correct�measure�is�Accelerated�Fading�Units�or�AFU.����Test�conditions�are�also�different,�as�detailed�in�the�earlier�section.��Typically,�the�most�common�ISO�test�is�conducted�at�low�effective�humidity�(extreme�conditions).��As�a�summary,�the�following�table�shows�the�major�differences.��

ParameterParameterParameterParameter���� ISO�105�B02ISO�105�B02ISO�105�B02ISO�105�B02���� AATCC�16AATCC�16AATCC�16AATCC�16����Assessment� Blue�Wool�Scale�1�to�8� Standard�Grey�Scale�1�to�5�Duration�of�test� Not�relevant.��Test�completed�

when�sample�shows�specific�fading.�

Defined�by�Buyers,�typically�20�AFU�for�apparel,�higher�for�home�textiles��

Temperature� Black�Standard�Thermometer� Black�Panel�Thermometer���Factors�affecting�Light�FastneFactors�affecting�Light�FastneFactors�affecting�Light�FastneFactors�affecting�Light�Fastness�Ratingsss�Ratingsss�Ratingsss�Ratings�����There�are�quite�a�few�issues�that�affect�colourfastness�to�light.��Some�of�these�are�discussed�below�–��

1.1.1.1. Dyestuff�usedDyestuff�usedDyestuff�usedDyestuff�used�����

The� colourfastness� to� light� is� a�property�of� the� colourant�molecules� themselves.� �Therefore,�selection�of�colourants�clearly�influences�the�light�fastness�property.��Combination�shades�also�are�affected�by�the�light�fastness�of�individual�dyes.�

�2.2.2.2. Dye�shade�/�depthDye�shade�/�depthDye�shade�/�depthDye�shade�/�depth����

�Unlike�other�colourfastness�tests,�a�higher�shade�depth�gives�much�better�light�fastness�ratings�than�a�pale�shade�of�the�same�combination.�

�3.3.3.3. Fabric�surfaceFabric�surfaceFabric�surfaceFabric�surface����

�It�has�been� found� that� the� surface� area�of� the� fabric� can�greatly� affect� the� colourfastness� to�light.� �As� an� example,� see� the� example�below.� �One� is� a� single� jersey� fabric� and� the�other�a�pique.��Both�were�dyed�in�the�same�bath�for�the�purposes�of�testing�and�a�marked�difference�was� seen� in� the� light� fastness.� �The�pique� construction� showed�a�much�worse� light� fastness�than�the�single�jersey.�

�4.4.4.4. Finishing�chemicalsFinishing�chemicalsFinishing�chemicalsFinishing�chemicals����

�Some� finishing� chemicals� can� also� affect� the� light� fastness� ratings.� �While� there� is� not� too�much�information�on�which�chemicals�do,�it�is�a�point�to�be�kept�in�mind�by�processors.�

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������5�

�Summary�of�Important�Issues�for�ProcessorsSummary�of�Important�Issues�for�ProcessorsSummary�of�Important�Issues�for�ProcessorsSummary�of�Important�Issues�for�Processors�����

• Selection�of�Dyestuff�must�be�made�based�on�requirements�and�end�use�

• Remember�lighter�shades�give�poorer�light�fastness�properties�

• Finishing�chemicals�can�affect�lightfastness..��

Example�of�fabric�with�poor�Example�of�fabric�with�poor�Example�of�fabric�with�poor�Example�of�fabric�with�poor�colourfastness�to�light.colourfastness�to�light.colourfastness�to�light.colourfastness�to�light.����

� ����� ����

Water�cooled�light�fastness�Water�cooled�light�fastness�Water�cooled�light�fastness�Water�cooled�light�fastness�machinemachinemachinemachine����

� ����

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������6�

Arrangement�of�water�cooled�Arrangement�of�water�cooled�Arrangement�of�water�cooled�Arrangement�of�water�cooled�xenon�arc�lampxenon�arc�lampxenon�arc�lampxenon�arc�lamp����

� ����

Variation�in�light�fastness�due�to�Variation�in�light�fastness�due�to�Variation�in�light�fastness�due�to�Variation�in�light�fastness�due�to�differences�in�knit�structuredifferences�in�knit�structuredifferences�in�knit�structuredifferences�in�knit�structure����

� ����

Texanlab Laboratories Pvt. Ltd. Colourfastness Testing Series

����������������������������������������������Colour�fastness�to�Light� ������������������������������������7�

Blue�wool�standards�Blue�wool�standards�Blue�wool�standards�Blue�wool�standards�––––�ISO�105�B02��ISO�105�B02��ISO�105�B02��ISO�105�B02�test.test.test.test.����BWS�1�to�BWS�5,�showing�BWS�1�to�BWS�5,�showing�BWS�1�to�BWS�5,�showing�BWS�1�to�BWS�5,�showing�geometric�progression�of�fadinggeometric�progression�of�fadinggeometric�progression�of�fadinggeometric�progression�of�fading����

����

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