The outdoor durability of textiles is directly related to the colorfastness to light. In international trade, many products are returned because their light fastness grades cannot meet the contract requirements, causing great losses to the enterprise. The main reason is that exporters or inspection agencies use different textile inspection standards, so it is more and more important to fully understand the lightfastness test method, which directly affects the consistency of test results.
Light fastness test standards and methods
In international trade, the common standards for light fastness testing are AATCC 16, ISO 105 B02, ISO 105 B04, ISO 105 B06. ISO 105 B02 has five test methods, and AATCC 16 has six test options, where option 6 in AATCC 16 is equivalent to ISO 105 B01, and option 3 is equivalent to ISO 105 B02.
Common problems in the process of light fastness test
Colorfastness to light is one of the most controversial and problematic tests in textile and clothing testing. In practice, various problems often occur. Below, we analyze the problems in the testing process and common problems in ISO and AATCC standards, which can be used as your reference.
1. In the standards of some products, some choose method 3 to test the color fastness to light, and the quality requirements are at a medium level (such as 3-4). How to test?
In some product standards, this is true, and according to some professionals, the formulation is simply wrong, as the blue wool reference is not an option for the experimenter. However, since some product standards are currently specified in this way, it is recommended that operators use Method 3 to conduct experiments and then evaluate according to Method 1. For example, the standard calls for a 3-4, so we chose to test using method 3 on blue wool references grades 4 and 3 and then evaluate the samples according to method 1. Since there are blue wool references for classes 4 and 3, theoretically, we can assess whether the test results have achieved class 3 – 4 for a sample.
2. What is the difference between 1 – 8 and L2 – L9 of Blue Wool Benchmark? Can they replace each other?
In ISO 105 B02, blue wool reference standards for 1 – 8 and L2 – L9 are detailed, all of which are wool and all have eight grades of blue wool standards, each of the higher numbered blue wool reference standards The light resistance is about twice as high as the previous one. They use different dyes and processes. Class 1 – 8 blue wool reference dyed with 8 different fastness dyes for European exposure conditions in ISO 105 B02. The blue wool standard L2-L9 was dyed with two dyes, and then the dyed fibers were made into blue wool samples L2-L9 in different proportions. It is suitable for US exposure conditions specified in AATCC TM 16 and ISO 105 B02 – 1994. Blue wool references 1 – 8 and L2 – L9 cannot be mixed with each other and test results are not interchangeable.
3. The relative humidity in the box is shown on the surface of the lightfastness Tester, but why do we need to use the humidity test control fabric for calibration? How to calibrate?
Currently, most lightfastness Testers (anemometers) can show the relative humidity in the box, but in ISO 105 B02 the humidity in the box needs to be calibrated daily using a humidity test control fabric. The reason is that the humidity control standard calibration is not "relative humidity" in the box, but "effective humidity". Effective humidity, defined by air temperature, sample surface temperature, and air relative humidity during exposure. "Effective humidity" directly affects the lightfastness test results of humidity-sensitive samples. Therefore, the ISO 105 standard requires a daily check of the humidity in the box.
The moisture control standard sample is a cotton fabric dyed with a red azo dye. It is used as follows:
1. Place the humidity control standard sample (not less than 45mm*10mm) on the hard card with blue wool reference, and place it in the middle of the sample holder as much as possible.
2. Simultaneously expose the covered humidity control standard sample and the blue wool reference until the color difference between the exposed part and the unexposed part of the humidity control standard sample reaches level 4.
3. At this point, evaluate the color change grade of the humidity control standard sample using the blue wool reference material. For example, under general European exposure conditions, the color difference between the exposed part and the unexposed part of the humidity control standard sample should be the same as the reference value of grade 5 blue wool. If not, readjust the controller to maintain the specified black panel temperature and humidity.
4. What is the unit of AFU in the AATCC standard? What does that have to do with the number of hours?
AFU is an energy unit, which is the abbreviation of AATCC Fading Unit, which is defined as 1/20 of the exposure energy required to fade the L4 blue wool reference to level 4 of the discoloration gray card. Alternatively, 20 AFU of energy is required to fade an L4 blue wool reference to level 4 color change.
Assuming that when the xenon arc lamp is working at 1.10W/(m 2 ·nm), the energy for L4 to achieve level 4 discoloration is 85 kJ, then the relationship between AFU and hours can be calculated by the formula. / square meter.
85 kJ/m²= 1.10 W/m²*time
Time = (85 kJ/m²)/(1.10W/m²) = 21.5H
It can be seen that when the radiant energy of the xenon arc lamp is changed, so is the time of exposure to the specified AFU. The energy can reach 21.5 AFU in 21.5 hours when the bulb is running at only 1.10 W/(m 2 ·nm).
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 can emit light normally"?
As the xenon arc lamp is used for a longer period of time, the luminous intensity and the wavelength range of the spectrum have changed. For a period of time, although xenon arc lamps were still "normal" lamps, in fact, the performance indicators of xenon arc lamps no longer met the test requirements, and the test results were not reliable. According to the manufacturer's test results, the xenon arc lamp needs to be replaced after using 1500H.
