The color fastness of textiles usually includes resistance to soaping, rubbing, light, bleaching or oxidants (reducing agents), ironing resistance, perspiration resistance and perspiration color fastness. Among them, soaping resistance, friction resistance, light resistance, water resistance and perspiration resistance are several color fastness indicators that most buyers pay high attention to in actual production and trade.
Color fastness ratings are: Level 1, Level 1-2, Level 2, Level 2-3, Level 3, Level 3-4, Level 4, Level 4-5, Level 5. Level 5 and level 9. Level 1 is the worst, level 3 is basic, and level 5 is the highest, but it’s almost impossible. Level 3 can only be a basic level, an intermediate level.
01 Color fastness to soaping
1. Test method for color fastness to soaping
Color fastness to soaping is one of the most common color fastness assessment items. Color fastness to soaping refers to the degree of fading of colored fabrics after soaping under specified conditions. It includes two evaluation contents: original fading and white cloth staining. Original fading refers to the fading of colored fabrics before and after soaping; white cloth staining refers to the situation where white cloth and colored fabrics are sewn together in a certain way, and after soaping, the white cloth is stained due to the fading of the colored fabrics. The degree of fading or staining should be tested under the specified light source and rated on a standard gray card. The results are divided into 5 levels, with level 5 being the best and level 1 being the worst.
2. The relationship between dye structure, dyeing and post-treatment technology and soaping color fastness
In daily tests, a considerable number of textiles, including cotton, wool, polyester, nylon and their blended fabrics, as well as elastic fabrics containing spandex, stained nylon and acetate fiber linings at level 3 or below. Although the dyes and printing and dyeing processes used in different fiber materials are different, the problems that arise are quite similar. This is mainly related to the floating color on the cloth surface and the transfer of some colored fiber particles, and is therefore related to the type of dye used, the dyeing process and the post-processing process.
3. The color fastness of reactive dye dyeing products to soaping depends on the unfixed dye.
Taking reactive dyes as an example, theoretically speaking, due to the covalent bonding between dyes and fibers, washing with water cannot easily cause dye desorption, fading and bleeding. Therefore, the color fastness of reactive dye dyeing products to soaping depends on Amount of unfixed dye (hydrolyzed dye and a small amount of unreacted dye). If the hydrolyzed dye cannot be completely removed by soaping, the color will continue to fade after subsequent washing. Soaping fastness is also related to the bonding stability of bonded dyes, and bond-broken dyes will also fade when washed.
Therefore, the most important factors that affect the color fastness to soaping are the dye structure and properties, followed by dyeing and post-dye treatment processes. Reactive dyes have a high fixation rate or a slow hydrolysis rate, resulting in a small amount of hydrolyzed dye and a small amount of dye that needs to be removed by washing. Unfixed dyes and hydrolyzed dyes have low directness, good water solubility, are not easy to stain, and are easy to wash off. However, if the dye concentration is high and the amount of residual dye is large, it is difficult to wash off.
4. Soaping fastness is also closely related to the dyeing process
In addition, soaping fastness is also closely related to the dyeing process. The dye adsorption and diffusion are sufficient, the color fixation rate is high, the residual dye and hydrolyzed dye are less, and it is easy to wash off. The dyeing process is reasonable, the covalent bond between the dye and the fiber is not easy to break during dyeing and post-processing, and the color fastness to soaping is good.
02 Color fastness to rubbing
1. Comparison of test methods for color fastness to rubbing
The rubbing color fastness test refers to a test in which a colored sample is rubbed with a dry rubbing cloth and a wet rubbing cloth respectively, and then the staining degree of the rubbing cloth is evaluated. The test results are divided into 5 levels, with level 5 being the best and level 1 being the worst. Although the testing process is simple, it is the most basic color fastness assessment indicator for textile products. It is almost one of the items that buyers from all over the world must assess when placing orders. The technical conditions of rubbing fastness testing standards in various countries are very similar, but there are also some differences.
2. Main factors affecting color fastness to rubbing and their control measures
During the friction process between textiles and other objects, the color of the textiles falls off or the degree of staining of the rubbed objects is affected by many factors. There are two ways of color shedding and staining: one is that the dye on the textile falls off or fades and is stained on the surface of the friction object; the other is that the dyed fibers fall off and adhere to the surface of the friction object.
3. Main reasons for staining
Although there are certain differences in the covalent bond strength and adhesion between reactive dyes with different chemical structures and cellulose fibers, their effects on the wet rubbing fastness of dyed fabrics are basically the same. When dyed fabrics are wet rubbed, the covalent bonds formed between the dye and the fiber will not break and cause floating color. The transferred dye usually does not form a covalent bond with the fiber, but only relies on van der Waals forces to produce adsorption, that is, floating color.
03 Color fastness to light
1. Light fastness test method
The light fastness test refers to placing a textile sample and a set of blue wool standard samples under artificial light sources and exposing them under specified conditions, and then comparing the discoloration of the two to evaluate the color fastness.
2. Ways to improve light fastness
The photofading mechanism of dyes is very complex, but the main reason is that the dye is excited after absorbing photons, and a series of photochemical reactions occur to destroy the structure, resulting in discoloration and fading. The light fastness of textiles mainly depends on the chemical structure of the dye, as well as its aggregation and binding state.�� test, sun color fastness test, is to put the sample together with blue wool standard cloth of different fastness levels under specified conditions for sunlight exposure, compare the sample with the blue wool cloth, and evaluate the light fastness Color fastness, the higher the grade of blue wool standard cloth, the more lightfast it is.
5. Color fastness to perspiration
The sample is sewn together with the standard lining fabric, treated in perspiration solution, clamped on the perspiration color fastness tester, placed in an oven at constant temperature, and then dried, and rated with a gray card to obtain the test results. Different testing methods have different sweat liquid ratios, different sample sizes, and different testing temperatures and times.
6. Color fastness to water stains
Treat the sample with water and test as above.
7.Chlorine bleaching color fastness:
After the fabric is washed in chlorine bleach under certain conditions, the degree of color change is evaluated. This is the color fastness to chlorine bleaching.
8. Non-chlorine bleaching fastness
After the fabric is washed under washing conditions with non-chlorine bleaching, the degree of color change is evaluated. This is the non-chlorine bleaching color fastness.
9. Press color fastness
After the dry sample is covered with cotton lining fabric, it is pressed for a certain period of time in a heating device with specified temperature and pressure, and then the gray sample card is used to evaluate the discoloration of the sample and the staining of the lining fabric. The color fastness of hot pressing includes dry pressing, tidal pressing and wet pressing. The specific test method should be selected according to different customer requirements and testing standards.
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