10 Evaluation of Colour fastness
V. RameshBabu
INTRODUCTION
Colour fastness is the property of a dye that enables it to retain its colour in its original depth and tone throughout the wear life of the product to which it has been applied.
Property of a pigment or dye to retain its original hue, especially without fading, running, or changing when wetted, washed, cleaned; or stored under normal conditions when exposed to light, heat, or other influences.
Factors Affecting Colourfastness
The textile color fastness is the capacity of a dyed textile to keep its original aspect without loosingcolor when being wet, washed or exposed to the light. It is one of the main issue of the textile industry.
In the article « Textile color fastness tests: ISO 105 » we learned how to test the textile color fastness. Today we will see which are the factors affecting the color fastness.
- Fiber Type
- Class of Dye Used
- Dyeing or Printing Process used
- Types of Finishing Treatments Used Action Of Laundering Detergents
The fiber type used
The dye and the fiber used have to be compatible. A cellulosic fiber and a vat dye will have a good resistance. And the polyesters provide a very good result with substantive dyes.
The dye type
The way the dye is fixed on the fiber is a factor affecting the textile color fastness: the bigger is the dye molecule the easier it will fix on the fiber. There are also insoluble dyes in water so that the textile color fastness is improved when washing.
The tone
The color fastness depends on the dye quantity present on the fiber. A neutral or pastel color is more resistant than a dark color.
Other chemical elements: the fiber finishing
The textile color fastness can be altered by different finishing used to improve the user comfort.
Colour Fastness of Dyed Textiles
This is probably the most important property of coloured textile material, since any shortcoming in this property may adversely affect the useability of the end products.
Colour fastness is the property of a dye that enables it to retain its colour in its original depth and tone throughout the wear life of the product to which it has been applied.
There are several agencies or factors to which colour fastness testing is prescribed. An agency or factor in this context is a deteriorating influence. Some agencies are of consumer significance, i.e. of importance to the end user of textile products; others are producer significant, i.e. those related to the manufacturer of textile products. Some agencies are listed below:
A number of tests may therefore have to be done to determine the resistance of a given dye to all of the above agencies.
Colour fastness of textile materials to washing
1) Principle of the test A specimen of textile in the form of fibre yarn or fabric, in contact with pieces of specified adjacent fabrics in mechanically agitated in a soap or soap- soda solution, rinsed and dried.
The change in colour of the specimen and the staining of the adjacent fabrics are assessed with the grey scale.
2) Sampling: the sample should be a representative sample or one agreed to between the buyer and the seller
3) Apparatus: A suitable mechanical washing device conforming to the following requirements to be used.
a) A water bath containing a roller by means of which containers usually stainless steel, sometimes glass) of 500ml capacity are rotated at a speed of 40+2 rev/min
b)Means of thermostatically controlling the temperature of the water bath so as to maintain the temperature in the containers at that specified for the washing test performed, to an accuracy of 40+2ºC.
A schematic figure of a typical mechanical washing device, sometimes called a `Launder-o-meter’ is shown here.
Essentially the device consists of an outer vessel in which water or other heating medium can be filled up to the desired level. A rotating arrangement is fitted in the vessel, as shown in the figure. The test specimens and the soap or soap-soda solution, as the test demands, can be placed in a set of four, six or eight stainless steel containers, depending upon the size of the launder-o-meter.
The containers are closed with lids such that they fit tightly to the containers. The containers are mounted on to the rotating device, the outer vessel is covered and the device is switched on.
4) The five washing tests: The washing fastness of dyed textiles may be performed under five different standard test conditions as shown in the table below. It can be easily seen that the severity of the test increases as we go from Test 1 to Test 5.
(Test specimen = 10 x 4 cm, made of 100% cotton; first adjacent fabric = cotton) Washing Fastness Test No. Second Adjacent Fabric
5) General Test Procedure
a) Place one composite specimen, with or without steel balls as specified, in the container. Add the necessary amount of soap or soap-soda solution previously heated to the temperature specified in the test to give the liquor ratio of 1:50 Treat specimen for the specified time at the specified temperature.
b) Remove the composite specimen; rinse it twice in cold water and then in cold running tap water for 10 minutes. Squeeze it.
c)Remove the stitches along the two long sides and one short side. Open out the composite specimen and dry in air at 60°C at room temperature.
d) Evaluate the change of the treated test specimen and the degree of staining of the pieces of adjacent fabric with the help of grey scales and assign the ratings, bearing in mind the conditions stated earlier.
Determination of colour fastness to Rubbing (Crocking) (IS766L1988)
This test is designed to determine the degree of colour that may transfer from the surface of coloured textiles to other surfaces by rubbing. It is applicable to textiles made from all fibres in the form of yarn or fabric whether dyed, printed or otherwise coloured.
1.Principle of the test
Specimens of the textile are rubbed with dry rubbing cloth and with wet rubbing cloth, by means of a rubbing finger of specified dimensions. The staining of rubbing cloth is assesses with the grey scale for staining and ratings are assigned for dry-rubbing fastness and wet-rubbing fastness of the specimen.
2.Sampling
The sample shall be representative of the original lot of fabric to be tested or as agreed to between the buyer and the seller.
3.Apparatus
A suitable testing device called crockmeter should be used. It consists of the following features, as shown in the figure below.
a) A flat base to which the test specimen is fixed so as to be free from slack, that may cause folds and wrinkles during rubbing.
b) A rubbing finger comprising a cylinder of 1.6 cm track on the specimen with a downwards force of 9 newtons.
c)Rubbing cotton cloth – this should be desized, bleached and without finish and cut into a 5 cm x 5 cm square.
4. Test Specimen
This should not be less than 14 cm x 5 cm. Two pieces are to be used for dry rubbing, one warp-way and the other weft-way. Similarly two pieces are required for wet rubbing.
5. Test procedure
Fix the test specimen to the rubbing device by means of clamps such that the long direction of the specimen follows the track of the device.
When testing multi-coloured textile, care should be taken to position the specimen in such a way that all coloured of the design are rubbed in the test. If the areas of colour are sufficiently large, more test specimens may be taken and individual colours assessed separately.
a) Dry Rubbing: The dry rubbing cloth is fixed flat in place over the end of the finger of the testing device. Operate the apparatus and rub the test specimen to and fro in a straight line along a track 10 cm long, 10 times to and fro in 10 seconds, ensuring that there is a downward force of 9 N on the rubbing finger.
b) Repeat the test described above with a fresh dry test specimen and with a wet rubbing cloth that has been wetted to ensure a take up about 100 percent of its mass of water. Dry the rubbing cloth at room temperature.
c) Assign ratings for the staining of the cotton cloths with the grey scale for staining. Assign one rating each in the warp-way and weft-way directions of the fabric for the dry rubbing fastness and similarly one in each of these directions for the wet rubbing fastness of the test fabric.
Color Fastness to Perspiration
The color fastness to perspiration (acid and alkaline) shall be at least level 3-4 (color change and staining). This criterion does not apply to white products, to products that are neither dyed nor printed, to furniture fabrics, curtains or similar textiles intended for interior decoration. A level of 3 is nevertheless allowed when fabrics are both light colored (standard depth < 1/12) and made of silk or of blends with more than 20% silk. This kind of test is specially applied for the sports wear and heavy dresses which is used specially. Normal cloths is also tested by perspiration test.
The garments a\which come into contact with the body where perspiration is heavy may suffer serious local discoloration. This test is intended to determine the resistance of color of dyed textile to the action of acidic and alkaline perspiration. Before knowing about the Color Fastness to perspiration you must have to know about Color Fastness to Wash and Color Fastness to Rubbing.
Purpose and Scope
This method is used to determine the resistance of the colour of textile of all kinds and in all forms to perspiration.
- Equipment For Fastness Measurement
- Perspiration tester
- Oven, Maintained at 37+-2 Degree centigrade
- Multifiber test fabric
- Grey scale
- Color matching chamber
- Acidic and Alkaline solution
- Glass or Acrylic plat
- Weight.
Reagent for Perspiration Test
Solution freshly prepared, containing 0.5g 1-histidine mono-hydrochloride mono-hydrate, 5g sodium chloride, and 2.5g disodium hydrogen ortho phosphate per litre brought to PH 8.0 with 0.1N sodium hydroxide.
Solution freshly prepared, containing 0.5g 1-histidine mono-hydrochloride mono-hydrate, 5g sodium chloride, and 2.2g sodium dihydrogen ortho phosphate per litre brought to PH 5.5 with 0.1N sodium hydroxide.
Two undyed cloths for each specimen each 6×6cm of the same kind of fibre as the sample. Place the specimen between the two pieces of white cloth and sew along one side to form a composite sample.
Working Procedure :
Thoroughly wet one composite sample in a solution of PH8.0 at the liquor ratio of 20:1 and allow it to remain in this solution at room temperature for 30min. pour off the solution and place the composite sample between two glasses plates measuring about 7.5×6.5cm under a force of about 4.5kg.
- Treat the other sample in the same way but with the solution at PH 5.5.
- Place the apparatus containing the samples in the oven for 4 hour at 37±2C˚
- Separate the sample from the white cloth and dry them apart in air at the temperature not exceeding 60C˚
- Assess the change in colour of the specimen and the staining of the white cloth with the greigh scale.
Color Fastness to Light
The purpose of Color fastness to light test is to determine how much the color will fade when exposed to a known light source. It is an off line quality assurance system. Generally man wears the fabric and goes outside of the home for doing their job. In day; sun light fall on the fabric surface. So it needs to know how much protection ability have a fabric to sun light. It is determined by an experiment called color fastness to light. To measure the color fastness a blue scale is used. After completing the test, sample is compared with the blue scale.
Principle of Color Fastness to Light:
This test measures the resistance to fading of dyed textile when exposed to day light. The test sample is exposed to light for a certain time which is about 24 hours to 72 hours or by customer/buyer demand and compare the change with original unexposed sample the changes are assessed by Blue Scales.
Color Fastness to Light with the Microsol light Fastness Tester:
- The testing is done step by step. Following step is maintained during measure the color fatness to light.
- Cut the four pieces of test specimens according to the length & width wise and attached with the specimen holder.
- Then the holder set in to the Microsol light fastness tester.
- Then the experiment continued at 72 hours according to the buyer’s requirement. After 72 hours later the specimen taken from the light fastness tester
- Then the test specimen compare with the Blue scale or computer color matching system (CCMS).
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REFERENCES and URLs
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