The outdoor durability of textiles is directly related to the color fastness to light. In international trade, many products are returned due to their light fastness rating can not meet the contract requirements, which has caused great losses to enterprises. The main reason is that in the use of textile inspection standards of the exporter or inspection organization is different, so it is more and more important to fully understand the light fastness test method, which directly affects the consistency of the test results.
1 Standard and method for light fastness test
In international trade, the most common standards for light fastness test are AATCC 16, ISO 105 B02, ISO 105 B04, ISO 105 B06. The ISO 105 B02 has five test methods, AATCC 16 has six test options, in which the option 6 in AATCC 16 is equivalent to ISO 105 B01 and option 3 is equivalent to ISO 105 B02.
Five test methods for ISO 105 B02
Six test options for AATCC 16
2 Common questions in the test process of color fastness to light
Color fastness to light is one of the most controversial and problematic tests in textile and garment testing. In practice, a variety of problems have often occurred. Below, we analyze the problems in the test process and the common questions in ISO and AATCC standards, which can be used as a reference for your.
2.1 Among the standards of some products, some of them choose method 3 to test the color fastness to light, and the quality requirement is intermediate level (for example, 3 – 4). How to test?
This is true in some product standards, and some experts think that the formulation is entirely wrong because the experimenter cannot choose the blue wool reference. However, because some product standards are stipulated in this way at present, it is suggested that operators should use method 3 to carry out experiments, and then evaluate according to method 1. For example, the standard requirement is 3 – 4, so we chose the blue wool reference of level 4 and level 3 to test with method 3, and then rate the sample according to method 1. Because there are grade 4 and grade 3 blue wool reference, in theory, we can evaluate whether the test results of the sample have reached level 3 – 4.
2.2 What is the difference between 1 – 8 and L2 – L9 of blue wool reference? Can they replace each other?
In ISO 105 B02, there have detail describe for blue wool reference of 1 – 8 & L2 – L9, all of which are wool and all have eight grades of blue wool standard, and the light fastness of each higher-numbered blue wool reference is approximately one time higher than the previous one. They use different dyes and processes. The 1 – 8 grade blue wool references are dyed with eight different fastness dyes, which is suitable for the European exposure conditions in ISO 105 B02. The blue wool reference L2 – L9 is dyed with two kinds of dyes, and then make the dyed fibers into blue wool sample L2 – L9 in different proportion. It is suitable for the US exposure conditions specified in AATCC TM 16 and ISO 105 B02 – 1994. The blue wool references 1 – 8 & L2 – L9 can’t be mixed with each other, and the test results cannot be interchanged.
2.3 The relative humidity in the box is shown on the surface of the light fastness tester, but why we need to calibrate with humidity-test control fabric? How to calibrate?
At present, most of the light fastness tester (weatherometer) can show the relative humidity in the box, but in ISO 105 B02, it is required to calibrate the humidity in the box every day by humidity-test control fabric. The reason is that the humidity control standard calibration is not the “relative humidity”, but the “effective humidity” in the box. Effective humidity, which is defined by air temperature, sample surface temperature and air relative humidity during exposure. “Effective humidity” directly affects the light fastness test results of humidity sensitive samples. Therefore, ISO 105 standards require that the humidity in the box should be checked every day.
The humidity control standard sample is a cotton fabric dyed with red azo dyes. It is used as follows:
2.3.1 Place a humidity control standard sample (not less than 45mm*10mm) on the hard card with the blue wool reference, place them in the middle of the sample clip as much as possible.
2.3.2 Expose the partially covered humidity control standard sample and blue wool reference at the same time until the color difference between the exposed and unexposed part of the humidity control standard sample reached level 4.
2.3.3 At this time, use the blue wool reference to assess the color change grade of the humidity control standard sample. For example, under the general European exposure conditions, the color difference between the exposed and unexposed part of the humidity control standard sample shall be the same as the grade 5 blue wool reference. In case of inconsistency, re-adjust the controller to maintain the specified black-panel temperature and humidity.
2.4 What is the unit of AFU in the AATCC standard? What is the relationship with the number of hours?
AFU is an energy unit, an acronym for AATCC FADING UNIT, which is defined as 1/20 of the required exposure energy to make the L4 blue wool reference fade up to grade 4 of the discoloration gray card. Or, there need 20 AFU energy to make the L4 blue wool reference fade to the grade 4 color change.
The relationship between AFU and the number of hours can be calculated by a formula, assuming that when the xenon arc lamp is operated under 1.10W/(m2·nm), the energy to make L4 up to grade 4 color change is 85 kJ/m².
85 kJ/m²=1.10 W/m²* Time
Time= (85 kJ/m²) / (1.10W/m²)=21.5H
It can be seen that when the radiation energy of xenon arc lamp changes, the time of exposure to the prescribed AFU will also change. When the lamp is only operated at 1.10 W/(m2·nm), the energy can achieve 20 AFU in 21.5 hours.
2.5 Why is it wrong to say that “The xenon arc lamp used in the light fastness tester can continue to be used as long as it glows normally”?
With the prolongation of the use time of xenon arc lamp, the luminescence intensity and the wavelength range of the spectrum have changed. Over a certain period of time, although xenon arc lamp is still “normal” light, in fact, the performance index of the xenon arc lamp is no longer in line with the test requirements, the test result is not reliable. According to the test result of manufacturer, the xenon arc lamps need to be replaced after using 1500H.
With regard to the problems that may arise during the test of color fastness to light, you should have a certain understanding through this article. Of course, the light fastness test has been developing all the time, there may be mistakes and omissions in the article, welcome to your message correction. As a professional supplier of textile testing equipment, we are committed to helping our users improve textile quality in the right way. TESTEX textile testing instrument is your reliable choice.