Most of the color fastness test methods are simulated tests or comprehensive tests according to the environment and conditions of the action, and the fastness grade is evaluated according to the discoloration of the sample after the test and the staining of the lining fabric. What is more special is that the color fastness to light is rated by the blue label, while the color fastness to dry cleaning is rated for solvent staining.
In the rating of color fastness, it is necessary to comprehensively evaluate the changes of the three attributes of color, that is, the changes of hue, lightness and purity. Hue refers to the appearance of color. Among the three attributes, hue can be used to distinguish colors. According to different wavelengths of light, colors have properties such as red, yellow or green, which are called hues. Depending on the degree of reflection of light on the surface of the object, the degree of light and shade of the color will be different, and the degree of light and shade of this color is called lightness. Purity refers to the degree of saturation of the color. The simpler the wavelength of the light wave, the higher the hue purity, and vice versa.
Color fastness rating can be divided into eye rating and instrument rating. When rating eyes, it requires the background to be neutral gray, approximately between the 1st and 2nd level of the gray sample card (approximately Munsell color card N5). The lighting conditions should be sunny northern daylight (9:00-15:00), or an equivalent light source with an illuminance of 600lx and above, the incident light and the textile surface should be at an angle of about 45º, the viewing direction should be roughly perpendicular to the textile surface, cover the original and The color of the panels of the samples after the test should be the same, neutral color or gray or black should be used, and the size and shape are roughly the same. The graders should wear neutral gray overalls, and the grading process should avoid the influence of environmental colors.
Color fastness rating: compare the test sample with the original one, and see that the degree of discoloration is the closest to that of the gray card.
Staining Fastness Rating: The tested lining is compared with the untested lining to obtain the closest staining grade.
The principle of instrument rating is to use the absolute reflectivity of the known standard whiteboard to calibrate, measure the spectral power distribution reflected by the sample or its own reflected photometric characteristics, and then calculate the tristimulus value of the object under the standard illuminator according to the spectral measurement data. , chromaticity coordinates, CIELAB uniform color space, etc., and are converted into gray card series of discoloration and color fastness through a series of formulas.
Sometimes when I look at the report, I will have questions. Why is the test result of the color fastness to soaping and discoloration displayed on the test report grade 3, and the standard requirement is ≥3-4, or is it judged to be unqualified? Is the report judged wrong?
In fact, the result is correct. The grade 3-4 of the color fastness evaluation is not an interval in general mathematical concepts, it is a series, which means that the test result is between grades 3 and 4.
How to judge the level of fastness:
Standard 1. Light fastness
Airing in daily life is the most common method to test color fastness, because under the irradiation of sunlight, photosynthesis can excite the molecules in the dye, causing it to fade. Although this fading is common, the reaction process is more complicated. . At the same time, the fastness of different fibers is different, and the light fastness of the low concentration is worse than that of the high concentration. In the judgment standard, there are also corresponding grades, which are divided into eight grades, with grade 1 being the worst and grade 8 being the best.
Standard 2. Soaping fastness
The so-called soaping is to wash the dyed textiles together after the fusion of water and soap powder or other laundry detergents. The fading produced in this process is the standard for judging the fastness. For example: in our lives For common jeans, many jeans bought in the market will fade during the cleaning process. After a long time, you will find that the color of the jeans will become lighter and lighter, so that they will be eliminated. According to the test, the reason why the color fades quickly after cleaning is because in addition to chemical reactions, there are also reasons for photosynthesis. This makes the evaluation criteria of soaping fastness the fastest way to test. In the judgment, it is divided into five grades and nine grades. The first grade fades the most, and the fifth grade does not fade.
Standard three, rubbing fastness
This method of evaluation is simpler than the evaluation of soaping fastness, mainly through friction between objects. And this method is also divided into two kinds in the experiment, one is dry friction (direct object-object friction), and the other is wet friction (mainly through the change of reaction with water). The so-called dry rubbing refers to taking a piece of white unprinted and dyed fabric and rubbing it with a dyed textile. If there is color on the white fabric, it means that the dyed textile has low color fastness. The darker the color, the lower the fastness. Therefore, if the general public is buying textiles, they can make judgments by dry friction. In the judgment, it is divided into five levels, the first level fades the worst, and the fifth level does not fade the best.
The above methods are easy to distinguish color fastness in daily life. If conditions permit, it can also be tested by the "gray faded sample card" rated by the national standard.