Using different test methods, the same test method, and different links of the operating methods also have an important impact on the test results of Color Fastness to washing.
- At present, domestic and foreign textiles have endorsed and implemented standards for the Color Fastness to washing. These standards have been revised and improved many times, including the European standard ISO 105 C10:2006, the national standard GB/T 3921-2008, and the American standard AATCC 61:2013. However, the test method is basically the same as in the test principle, but the test conditions are different. The common washing condition parameters are shown in Table 1.
It can be seen from Table 1 that the test conditions of the European standard and the national standard are the same. In contrast, the American standard differs greatly from the European standard and the national standard in whether steel balls are added, the detergent used, and the washing time, all of which ultimately lead to different test results. In the early stage of testing, two sets of knitted fabric samples of dark coffee and dark wine red, as well as two sets of woven fabric samples of blue denim and white and black striped woven fabric were used. Furthermore, the European standard, the national standard and the American standard were used respectively. The same lining conditions were tested, then the Color Fastness to the washing of the test sample was determined. The test results showed that the test results of the national standard and the European standard have a small difference, but there is a big difference between the two and the American standard. In terms of color change, the color change of both the national standard and the European standard is lighter, and both are generally 0.5 grade higher than the American standard. In terms of staining, the national standard and the standard European colors are heavier, and their staining grades are generally 0.5 lower than that of the standard American level.
The Color Fastness test for washing in the laboratory includes multiple procedures: sampling, lining, washing test, drying, grading. Even if it is the same test method and the same test parameters, different inspectors are subject to their habits, subjective judgments and other human factors. The impact of the test results will also lead to certain differences in the test results, so each link must be operated in strict accordance with the standard and unified specifications. Otherwise, it will affect the Color Fastness rating results to a certain extent.
1.The influence of sampling on the test results of Color Fastness to washing: According to GB/T 3921-2008, when the sample is fabric, the sampling size is 40mm×100mm. However, many types of daily test samples in the laboratory are divided into plain, yarn-dyed, printed, and dyed fabrics. The correct extraction of representative samples will have a greater impact on the test results within the specified size. The dark and light gradual dyeing samples have a natural transition from multiple colors and gradually change colors from dark to light or from light to dark. When sampling, avoid the position where the color is gradual and cut two test samples at the evenly dyed light and dark positions. If the color of the sampling location is not uniform, it will easily affect the test results and is not representative.
2.The influence of the selection of multi-fiber standard lining fabrics on the test results of washing fastness: In the GB/T 3921-2008 standard, the choice of lining fabrics can be two single-fiber lining fabrics or more fiber lining fabric, but the last test is more convenient. The multi-fiber interlining fabrics include DW type (multi-fiber interlining fabric containing wool and acetate) and TV type (multi-fiber interlining fabric without wool and acetate). In selecting multi-fiber lining fabrics, the national standard GB/T 7568.7-2008 “Textile Color Fastness test standard for lining fabrics Part 7: Multi-fiber” general requirements stipulate that: some Color Fastness tests cannot use wool and acetate. Also, when using fiber, TV type should be used instead of DW type. However, the expression of “certain Color Fastness tests” is rather vague. The national standard GB/T 3921-2008 does not specify the test conditions, which will lead to the use of different multi-fiber standard lining fabrics, and the results obtained will be different. Randomly select 23 woven fabrics of different colors and various fiber components as samples. According to method C(3) of the national standard GB/T 3921-2008, cut two samples from each of them, and compare them with DW type and TV type multi-fiber. Stitch the standard lining into a combined sample for testing, and the test results show that most samples use DW-type multi-fiber standard lining fabrics more than the TV-type test. The results are lower, while the same fiber strips of acrylic and the staining grade of polyester, nylon and cotton, DW type is 0.5 to 1 grade lower than TV type.
3.The influence of different grading methods on the test results of Color Fastness to washing: The Color Fastness can be graded by eye or instrument. A neutral gray background is required for eye grading, the lighting conditions of sunny day and daylight (9:00-15:00), or an equivalent light source with an illuminance of 600lx and above. The incident light should form an angle of about 45˚ with the textile surface. The optimal observation direction is perpendicular to the surface of the textile. Furthermore, the color of the cover plate covering the original sample and the sample after the test should be the same while the size and shape should be similar. The grader must wear neutral gray overalls, and the environmental color influence should be avoided during the grading process. At the same time, the grader must have a clear understanding of the relevant standards, be familiar with the standard requirements and the enterprise’s relevant regulations, and correctly assess the grade of the combined sample. However, due to the differences in gaze between different raters, the rating results will be affected significantly. Therefore, it is necessary to compare the gaze differences within the specified time. This is how some human errors can cause unnecessary losses to enterprises and customers.
Under normal circumstances, for all kinds of fabrics with poor Color Fastness to washing, washing and fixing can effectively prevent the unfixed dyes from fading. Generally, the floating color remaining in the fiber pores and on the surface greatly influences the Color Fastness to wash. A good washing process and corresponding cleaning agents can fully remove the unfixed dyes. For fabrics dyed with direct, reactive, and acid dyes, after the fabric is cleaned, the corresponding reactive fixation and acid fixation processes can effectively improve the fabric’s Color Fastness. NB Fixation can be derived by dividing the mass of dye absorbed in the fabric or yarn by the original mass of dye in the water bath.
5.3.4 Summary of sampling methods for Color Fastness to washing:
Large-scale testing institutions adopt a process-based work method for Color Fastness testing, usually divided into sampling posts, test posts, and rating posts. Therefore, even if it is the same test method, different inspectors are affected by habit and subjective judgment in sampling methods, causing certain differences in test results.
The sampling of Color Fastness to washing must first consider the problem of lining fabric. Taking GB/T 3921-2008 as an example, this standard specifies that the choice of lining fabric can be a multi-fiber lining fabric or two single-fiber lining fabrics.
The multi-fiber lining fabrics include:
(1) Multi-fiber lining fabrics containing wool and cellulose acetate (used for tests at 40°C and 50°C, and in some cases can also be used for tests at 60°C, but needs to be indicated in the test report).
(2) Multi-fiber lining fabrics without wool and acetate (used for some 60°C tests and all 95°C tests). Single-fiber lining fabrics include cotton, wool, viscose, polyamide (nylon), polyester (polyester), polyacrylonitrile (acrylic), ramie, silk, and acetate.
Taking the multi-fiber lining fabric test as an example, the sampling methods of different types of samples in the washing fastness test are analyzed in detail.
The laboratory’s daily test samples are roughly divided into plain samples, yarn-dyed samples, printing samples, dark and light gradient dyeing samples, embroidery and car pattern samples, sequins, hot diamond samples, yarns and loose fibers, hollow fabrics, etc. When GB/T 3921-2008 requires the sample to be fabric, the sample size is 40mm×100mm.
- Plain color samples
According to the requirements of the standard for the size of the sample, the sample is randomly cut along the warp or weft direction of the front of the fabric. But it is required that the sample must be taken from a large sample that is uniformly dyed, wrinkle-free and can represent batch dyeing. The distance from the edge of the cloth should not be less than 10cm so that the entire working surface can produce consistent results during the test.
- Yarn-dyed samples
According to the standard for the size of the sample, it is required that the sample can contain all the colors of the sample. Suppose a sample cannot contain all the colors of the sample. In that case, the sampling amount can be determined according to the proportion of each color of the sample, and the dark part is preferred, or the number of samples taken can be increased, but generally not more than three sets of samples.
Richer colors characterize this type of product. Printed samples include small prints, large prints, inter-color stripes, etc. The basic principle of sampling is to take the excavation method to take all the colors and pay attention to keeping the same color parts around the sample as the original sample for rating comparison when excavating. If a sample cannot contain all the colors, you can increase the number of copies or determine the sampling amount according to each color’s proportion and give priority to the dark color test. The following is a detailed analysis of various samples.
①Single cycle small printing
When sampling a single cycle small print, try to ensure that the sample is sampled on a complete print. Sometimes, due to the influence of the color paste prescription, printing process and fabric structure, the print of the same pattern will also have a certain color difference. Sampling should be taken by digging. When digging, keep the same color around the sample as the original sample for the rating comparison after the test.
② No circulation and irregular small prints all over the floor
This type of sample has rich colors. Before sampling, you must first observe the sample and select a representative place with uniform dyeing to pick the sample. Often, one sample cannot contain all colors, then the number of samples should be increased.
③Large printing without circulation
Among the samples submitted by customers for inspection, such as some bedsheets, quilts, etc., these samples are characterized by relatively large margins and relatively large prints. The color of each flower type of this kind of sample is different. Usually, a sample can not cover all colors. In this case, it is necessary to pick the sample in a relatively dark position. Moreover, it is necessary to consider the ratio of each color to a certain ratio of dark and light to sample. It is impossible to pick up only the dark position because there may be dark and light color migration during the test. So, not only must the staining of the sample be considered when sampling, but also consider the discoloration of the sample.
④A large circular printing
This type of sample is usually rich in color, but it is cyclic. Just pick a sample from one of the looped patterns. Also, if other colors are not available, consider increasing the number of samples.
⑤ Inter-color stripe printing sample
The color of all strips should be included in the sampling within the specified sample size. Since the Color Fastness to soaping is a rolling test, which is different from the static test of the Color Fastness to sweat, there is no specified pressure requirement. When sampling, it is unnecessary to take samples in the direction of the strip as long as all colors are collected. Suppose a sample cannot contain all colors. In that case, you can increase the number of copies or determine the sampling amount according to the proportion of each color, and take priority to take the relatively dark part for testing.
5.4 Testing for thermal sublimation (dry heat) of textiles
5.4.1 Comparison of the main test methods for the Color Fastness to heat pressure and ironing of textiles:
The operation process of the standard three test methods is roughly the same. The preparation tools are as follows:
5.4.2 Take the AATCC Color Fastness test method as an example:
This test method is a test method to determine the color resistance of various textile materials and textiles and the ability of heat-resistant roller processing.
Textiles can be subjected to hot press tests in dry, wet, and wet states, usually determined by the textile’s final use.
- Sample size:
AATCC 133-2009: 40*120mm (sample size for other test methods: 40*100mm)
- Heating device:
It is composed of a pair of smooth parallel plates equipped with a precise control electric heating system. The pressure of the sample is 4±1kpa. The heat should only be transferred from the upper parallel plate to the sample. Regardless of if the lower parallel plate is heated or not, the asbestos plate should always be covered. The m2 two-layer synthesis contains about 3mm thick wool flannel, undyed and bleached cotton fabric without mercerizing treatment.
- Test procedure
Dry pressing: The dry sample is pressed for a certain period of 15 seconds in a heating device at a specified temperature and pressure.
Tidal pressure: After the dry sample is covered with a wet cotton lining fabric, it is pressed for a certain period of 15 seconds in a heating device at a specified temperature and pressure.
Wet pressing: After the wet sample is covered with a piece of wet cotton lining fabric, it is pressed for a certain period of 15 seconds in a heating device at a specified temperature and pressure.
- Hot pressing temperature
110 ± 2℃
150 ± 2℃
200 ± 2℃
If necessary, different test temperatures can be used, but they must be noted in the report. The critical temperature is determined according to the type of fiber and the structure of the fabric. If it is a blended product, it is recommended to adapt it to the most heat-resistant fiber.
Immediately after the test, use the grayscale to evaluate the sample’s color change and the staining of the lining fabric. Make another assessment after 4 hours of humidity control in a standard atmosphere.
5.4.3 Regarding ironing Color Fastness, ironing tips in daily life:
- Before ironing clothes, be aware of the fabric characteristics of the clothes, because some fabrics are not resistant to high temperatures, while others are. For instance, natural fibers like silk and wool are not suitable for high-temperature ironing, while textiles such as cotton and linen are.
- For some special fabrics, it’s advisable to iron directly on the fabric’s surface, and the fabric will be shiny and white. At this time, you only need to cover the surface of the fabric with a piece of lining cloth or cloth of the same texture and then iron; it will not appear in this case.
- Before ironing, it is best to spray the clothes evenly with water mist with a sprayer and put the clothes in a plastic bag so that the moisture can be spread evenly, and the clothes will be ironed better.
- Hang the ironed clothes in a ventilated place to dry for a while to evaporate the water vapor, so that the clothes can be kept flat and mildewed.