Color fastness to water is an important test item for textiles and one of the assessment indicators stipulated in the mandatory national standard GB18401 "National Basic Safety Technical Specifications for Textile Products". Currently, the water fastness standard for textiles used in my country is GB/T57131997. The color fastness test of this standard is equivalent to the international standard ISO105-E01: 1994. The level of water fastness is directly related to the performance of textiles. However, there is a special situation in actual testing, that is, some printed fabrics will produce obvious visible marks after being soaked in water and dried. However, according to the current standards, the water fastness is The fastness was tested, but it was found that the tested fastness level was very high, so the test results did not reflect the actual performance.

Test principle

The test principle of color fastness to water in standard GB/T57131997 is to sew the textile and the backing fabric together, soak it in test water, squeeze out the water, and place it in a perspiration fastness tester for pressure treatment; then put it into 37 Take it out from the oven at ℃ for 4 hours, and then hang it in the air to dry at a temperature not exceeding 60 ℃; after drying, use the discoloration and staining gray card to evaluate the fabric discoloration and lining staining levels.

Problems in applying standards

1. Standard test results

The problem sample tested in this experiment is a reactive dye printed fabric, with white ground and dark blue color. Tested according to GB/T57131997, its discoloration level and staining level are both level 4~5, which has reached the most stringent requirements of Class A level 3~4 of GB18401, and the detection level is very high.

2. Actual usage

According to the standard test results, a qualified report on water resistance and color fastness can be issued, but clothing made of this fabric has obvious problems in actual use, and marks appear after soaking and drying. As shown in Figure 1.

3. Analysis of standard issues

①. The generation of imprints

The printed fabric may still have unfixed dyes or hydrolyzed dyes remaining. Reactive dyes are water-based. They will migrate with the movement of water during drying after washing, forming dye accumulation on the surface of the fabric, and marks will be produced where the dye accumulation occurs. .

② Reasons why marks appear but pass the test

1) In the test of standard GB/T5713, it has been processed in an oven at 37°C for 4 hours before drying. There is very little moisture before drying; but during self-washing and drying, there is relatively more moisture, and the migration rate is 1. prone to happen.

2) GB/T5713 stipulates that when the sample is dried in the air, once an air-dried sample is found, it must be discarded and redone. This requirement is due to the fact that when the air-dried sample is drying, the water is dispersed too quickly, and the dye on it will be unevenly distributed due to migration, making the final result unable to be accurately judged. And when washing and drying by yourself, do not avoid air drying.

3) There are marks on this sample after washing and drying. The main reason is that the print is printed on a white ground, and a little stain will be very obvious. However, no staining was found on the lining cotton fabric during the test. This is because the standard GB/T5713 test fabric used is small, with a size of only 4cm10cm, and the concentration of migrating and accumulated dye is not enough to produce obvious marks. In fact, as can be seen from Figure 1, only one mark can be found on a larger area.

suggestion

1. Standard aspects

Similar confusion may occur with printed or white ground printed fabrics with a light background color, or even light-colored dyed fabrics. That is, the color fastness to water is fully qualified after standard testing, but larger samples may be immersed in water and dried due to dye. Imprints appear due to migration and accumulation. In addition to GB/T5713 and the equivalent ISO105-E01: 1994, the current water color fastness standards for textiles mainly include the American Association of Dyers and Chemists standard AATCC107 and the Japanese Industrial Standard JISL0846. These standards are based on constant temperature time, affixing There are certain differences in the selection of lining fabrics and oven temperatures. Through a large number of sample tests and comparisons, some researchers have found that the test results of different water fastness standards for the same fabric have small differences in discoloration and large differences in staining [1], but These standard testing principles and processes are basically the same, and cannot reflect the actual performance in such special circumstances.

This kind of situation is caused by the dark part contaminating the light part. It can be self-stained, but its color fastness is not bad enough to contaminate the lining. Therefore, it is necessary to establish an independent detection method for this type of product. There are two aspects that need to be studied in the detection method. One is the selection of sample size, because the effect of dye accumulation in this case requires a sufficient area for the sample to appear; the other is the establishment of the rating method, because the discoloration is uneven. It is its characteristic that it requires an overall evaluation of a larger area, which requires the development of corresponding sample cards or descriptive regulations.

2. Production

After this sample was washed, obvious marks were found, which undoubtedly indicates a problem with the fastness, but it passed the test according to current standards. For this type of fabric, special attention needs to be paid to this possible phenomenon in clothing production. If the clothing is put into production based on a qualified test report, only to find out after washing that marks appear after the finished product is made, it will cause huge irreparable losses.Because this fabric is printed on a white ground, and the color is dark, the difference is obvious, which requires its color fastness to be processed much more strictly than ordinary printing. If the pattern and color of the printed fabric are similar to the ground color, using the same process, even if there are prints, they may not be visible due to the cover up of the ground color. Therefore, in printing and dyeing production, strict requirements are required for such samples in the printing, color fixing and washing processes. Omissions in any process may cause problems. In fact, the sample with the problem this time was later re-fixed, soaped and rinsed by the printing and dyeing company, and no traces appeared again.

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