It is an important indicator for measuring the quality of dyes, and the assessment mainly includes color fastness to light, washing, rubbing, sweat, saliva, and ironing.
When conducting color fastness tests, the degree of discoloration of the dyed fabric and the degree of staining on the substrate are usually considered. For color fastness ratings, except for light fastness, which is level eight, all others are level five. The higher the level, the better the color fastness.
Color fastness to light (fastness to sunlight)
Light fastness refers to the ability of printed and dyed fabrics to maintain their original color under light conditions, that is, their ability to resist fading and discoloration under light conditions.
There are eight levels of color fastness to sunlight, with the first level having the highest discoloration and the eighth level having the lowest.
There are three testing methods for color fastness to sunlight: sunlight test, xenon arc lamp tester, and carbon arc lamp tester.
The general testing process for color fastness to sunlight is as follows
The textile sample and the mutually agreed reference standard sample (blue standard wool) are exposed to artificial light source under specified conditions, and the degree of color change between the two is compared. The level of color fastness to light of the sample is determined by the blue wool color fastness standard sample exposed to light simultaneously.
All testing standards for color fastness to sunlight use a relatively comparative method, and the exposure equipment does not directly issue test results. The performance of the equipment mainly depends on the control of parameters that affect the testing environment, including spectrum, light intensity, temperature, relative humidity, etc.
Color fastness to sweat stains
The color fastness to sweat is a reflection of the self discoloration of textiles in different test solutions containing histidine under the combined effects of pressure and temperature, as well as the staining of adjacent fabrics. Evaluate the discoloration of the sample and the staining of the lining fabric using a gray scale, and the results are divided into 5 levels, with 5 levels being the best and 1 level being the worst.
Test method:
Suture the sample with the standard lining fabric, treat it in sweat solution, clip it onto a sweat resistant color fastness tester, place it in an oven at constant temperature, then dry it, and grade it with a gray card to obtain the test results. Different testing methods include different proportions of sweat stains, different sample sizes, and different testing temperatures and times.
Color fastness to rubbing
Rub the textile sample separately with a dry friction cloth and a wet friction cloth to determine the degree of staining of the friction cloth.
Test method:
Place the sample on a friction tester and rub it with a standard friction white cloth under a certain pressure for a certain number of times. Each group of samples needs to be tested for dry and wet friction color fastness. Use a gray card to rate the color on the standard friction white cloth, and the obtained level is the measured friction color fastness. Friction color fastness requires both dry and wet rubbing tests, and all colors on the sample must be rubbed together.
Color fastness to washing
The color fastness test of textiles is a routine inspection item in the internal quality test of textiles. During the test, the fastness level is evaluated based on the discoloration of the sample and the staining of the unstained lining fabric. The color fastness to washing of fabrics is one of the most important properties of textiles. It refers to the degree of color change of colored fabrics in a specific solution at a certain temperature and bath ratio after a certain time of washing process and the degree of staining caused by various fiber fabrics.
Test method:
Water washing color fastness test is the most important and common item in textile inspection. It involves sewing a sample with a white cloth, placing it in a washing solution at a certain temperature, mechanically stirring it, soaking and washing it for a specified time, and then evaluating the color change and staining level with a gray card after drying. Due to the variety of washing methods and solutions, the test results are indicators with strict conditional values.
The specific steps are: suture the sample according to the standard → prepare soap solution according to the standard method → wash according to the standard method → clean thoroughly → dry → grade with a gray sample card or instrument.
The methods to improve the fixation fastness of dyes. Although some dyes can give a relatively bright color, due to the water-soluble groups on the dyes, the wet treatment fastness is poor, leading to severe fading and staining. This not only makes the appearance of the textiles outdated, but also causes the dyes to fall off and stain white or other colored fibers, resulting in staining and color matching.
In addition, although reactive dyes can form covalent bond with cellulose fibers, in dyeing, if there are hydrolytic dyes or insufficient soaping of unbonded dyes, the wet treatment fastness will also be reduced; In addition, reactive dyes that have formed covalent bond with fibers may also break bonds under acidic or alkaline conditions, and have insufficient color fastness to chlorine, perspiration, and sunlight.
In order to improve the color fastness of fabrics, fixation treatment can be carried out, and these additives that can improve various types of dyeing fastness are called fixing agents.
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Fixing agent fixation principle
1. Generate insoluble color lakes on the fabric, block soluble groups, and make the dyes on the fabric difficult to dissolve and fall off when exposed to water, achieving the goal of improving wet treatment fastness. But after these fixing agents fix the color, it is easy to cause changes in the color light of the fabric or cause a decrease in sun fastness.
2. Generate a mesh like film on the fabric to prevent dye detachment.
3. Utilize the reactive groups in the fixing agent molecules to cross-link with the reactive groups on the dye molecules and the hydroxyl groups on the cellulose molecules to improve the fixation effect of the dye on the fiber.
4. Utilize the molecular attraction between the fixing agent and fibers to increase the fixing strength of the fixing agent, thereby improving dyeing fastness