What’s Color Fastness of Dyed Fabrics, How to Test Color Fastness to Washing

Introduction

Today’s consumers are savvier than ever. They not only focus on the ornamental and comfort of textiles, but also on the durability and safety of textiles. They need high-quality products. Market research shows that most of the time consumers buy textiles based on color. Therefore, the ability of the fabric to maintain primary color is one of the most important properties of textiles.

What does Color Fastness Mean?

Colorfastness definition is that the ability to keep original dye color under the influence of other kinds of external factors in the use processes of dyeing textiles. Or we can define color fastness like this: Color fastness refers to the resistance of color to fade or bleed of a dyed or printed textile materials to various types of influences e.g. water, light, rubbing, washing, perspiration etc. It is an important indicator to measure the quality of dyeing products.

Classification of Colour Fastness

Due to the use of chemicals in the late processes of dyeing and finishing, like acid, alkali, oxidants, reductants, etc., and when using in washing, sunlight, rubbing, sweat, high temperature and so on, dyeing textiles may fade or discolor. Therefore, dye color fastness is diverse, including washing fastness, light fastness, rubbing fastness, perspiration fastness, chlorine fastness, ironing fastness, etc.

The color fastness requirement of textiles is different because of their different use and process. For example, the curtain which is less washed requires low colorfastness, but due to exposure to the sun for a long time, it needs high lightfastness. Summer clothing fabrics should have higher light fastness, washing fastness and perspiration fastness for the reason that they always expose to sun and human body always sweats.

Different countries have set different standards for the different colorfastness requirements of different textiles. The main standards for colorfastness are as follows

1. AATCC (American Association of Textile Chemists and Colorists) technical manual:
Describes 66 numbers of different colorfastness tests.
2. SDC (Society of Dyers and Colorists):
In 1927, SDC (Europe) made fastness test committee.
3. ISO(International Organization for Standardization):
In 1947, ISO made color sub committee. ISO also grades the fastness:
For light fastness: 1~8
For other fastness: 1~5

Factors Affecting the Color Fastness Properties

The chemical nature of the fiber. For example, cellulosic fibers dyed with reactive or vat dyes will show good fastness properties. Protein fibers dyed with acid mordant and reactive dyes will achieve good fastness properties and so on. That is to say compatibility of dye with the fiber is very important.

The molecular structure (e.g.) of a dye molecule: If the dye molecule is larger in size, it will be tightly entrapped inside the inter-polymer chain space of a fiber. Thus the fastness will be better. In addition, the actual situation during use and so on will also have varying degrees of impact on the colorfastness of textiles.

Research shows that: As for different types of dyes, we can handle moderately when doing the dyeing process, to improve dye colorfastness. For example, after dyeing textiles, direct dye reacting with a metal salt or cationic fixing agent gives rise to insoluble compounds, so that it can improve direct dye’s wet fastness. After dyeing with disperse dye, polyester fabrics can achieve to remove surface floating color and improve color fastness through a reductive clearing of reductant and an alkaline agent. After dyeing with reactive dye, textiles can improve color fastness to some degree through soap-washing. In addition, different uses and environmental conditions of textiles determine main point and requirement of colorfastness test.

How to Test Color Fastness?

Because the conditions and the requirements of fabric processing and use are very different, most of the current test methods are simulated according to the working environment and conditions, so the testing methods of color fastness are very extensive. But the international standard organization (ISO), American dyestuff and chemist association (AATCC), Japan (JIS), Britain (BS) and so on many standards, most commonly used tests are wash resistance, light resistance, friction resistance and sweat resistance, ironing resistance, weather resistance and so on.

In the actual work, the testing items are mainly determined according to the final use of the product and the product standard. For example, the wool textile product standard stipulates that the light fastness must be tested, and the knitted underwear, of course, has to be tested for perspiration fastness. Outdoor textiles (such as umbrellas, lampbox cloth, canopy materials) are naturally tested for weather fastness. Here is an example of how to test washing colorfastness. If you want to know more about color fastness testing, please contact us.

Definition and Measurement of Washing Color Fastness

1.Washing Color Fastness
It refers to the situation of fade and discoloration of dye textiles when soaping. The main machines used in washing color fastness are Washing Color Fastness Testers. Generally, there are two indicators measured in washing colorfastness test, including testing fade of original sample and staining of white cloth. Fade of original sample is the color change of dyed textiles before and after soaping. Staining of white cloth is the situation of staining of white cloth which it is soaping together with dyed fabrics.

In the testing, dyed sample is stitched together with one or two specified woven fabrics, placed in a soap solution, mechanically stirred at a specified time and temperature, then rinsed and dried. At this moment, dyed sample fades and contaminates the white adjacent fabric. Discoloration of dyed sample and staining of adjacent fabric are measured by gray cards. Water color fastness is divided into 5 grade and 9 files, among which the best is grade 5 while the worst is grade 1.

2. Washing Color Fastness Test
(1) Laboratory equipment and materials
Washing Color Fastness Tester (Figure 1), Gray Cards of Evaluating Discoloration, Gray Cards of Evaluating Staining, Beaker, Anhydrous Sodium Carbonate (C.P.), Standard Soap Sheet, Standard Multi-Fiber Patch Cloth (consist of wool, polyacrylonitrile fiber, polyester, polyamide fiber, cotton, vinegar fiber) or Single Fiber Patch Cloth, Sample to be tested.

Figure 1 Washing Color Fastness Tester

Figure 1 Washing Color Fastness Tester

1-Drain Pump  2-Heating Protector  3-Passive Gear  4-Motor  5-Reducer  6-Motor Vice Gear  7-Drainage Interface 

8-Active Gear  9-Rotating Frame  10-Test Cup  11-Studio Temperature Controller  12-Time Relay  13-Buzzer 

14-Preheating Room Temperature Controller  15-Drainage Switch  16-Door Cover  17-Power Switch 18-Insulation

19-Temperature Sensor  20-Tubular Heater  21-Drainage Pipe  22-Drain Pipe Interface  23-Water Pipe  24-Wheel

 

(2) Testing Methods
a) Preparation of Sample
① Fabric sample. Taking a 40mm*100mm sample, then its positive is stitched together with a 40mm*100mm multi-fiber patch cloth, along a short edge, to form a combined sample; or placing the sample into two 40mm*100mm single fiber patch cloth, and the first single fiber patch cloth is made from same fiber as the sample, the second is made from corresponding fiber of the first piece woven fabric in Table 1. If the sample is mixed textile or intertwined fabric, the first piece is made from fiber of main content and the second piece is made from fiber of secondary content.

② Yarn or scattered fiber sample. Taking yarn or scattered fiber approximately equal to half the total quality of adjacent fabric is embedded between a 40mm*100mm multi-fiber adjacent fabric
and a 40mm*100mm fabric that is unable to dye (such as polypropylene fiber ), sewing them along four edges to form a combined sample. Or Taking yarn or scattered fiber approximately equal to half the total quality of adjacent fabric is embedded between two 40mm*100mm single fiber adjacent fabrics, sewing them along four edges to form a combined sample. If the sample is yarn, you can weave it as a woven fabric and test it according to textiles testing method.

Table 1 Choices of Adjacent Fabric When Testing Washing Color Fastness

First PieceSecond PieceFirst PieceSecond Piece
40℃/50℃60℃/95℃40℃/50℃60℃/95℃
CottonWoolSticky FiberVinegar FiberSticky FiberSticky Fiber
WoolCotton---Polyamide FiberWool/CottonCotton
SilkCotton---PolyesterWool/CottonCotton
LinenWoolSticky FiberPolyacrylonitrile FiberWool/CottonCotton
Sticky FiberWoolCotton---------

b) Operating Procedure
① According to types of product and requirements, the parameters of washing color fastness should be set as Table 2. If fabric raw material is silk, viscose fiber, wool, nylon, you can adopt method 1; if raw material is cotton, polyester, nitrile, you can adopt method 3.

Table 2 Color Fastness to Washing Test Parameters

ConditionsTemperature (℃)Time (min)Soap Composition (bath ratio)Steel Ball
Standard Soap Sheet (g/L)Anhydrous Sodium Carbonate (g/L)
Method 140±2305------
Method 250±2455------
Method 360±23052
Method 495±2305210
Method 595±22405210
② Combined sample prepared in advance is placed in container, pouring soap liquid having been pre-heated to specific temperature in it.
③ Switch on Washing Color Fastness Tester.
④ Combined sample is taken out in a certain time and washed by grade 3 water for twice. Then it is rinsed cleanly in flowing cool water, squeezed excess water. Finally separated, the sample is linked with adjacent fabric in a short side stitching, hung and dried in air of no more than 60℃.
⑤ Discoloration of original sample and staining of adjacent fabric is evaluated by gray cards.

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