What is color fastness
Color fastness (Color fastness) is also called dye fastness and dye fastness. During the use of dyed fabrics or post-dyeing and finishing processing, the dyes are affected by various external factors and whether they can maintain their original color. The fastness grade is evaluated based on the discoloration of the sample and the staining of the undyed backing fabric.
It is an important indicator to measure the quality of dyes. The assessment content mainly includes color fastness to light, color fastness to washing, color fastness to rubbing, color fastness to perspiration, color fastness to saliva, and color fastness to saliva. Ironing color fastness, etc.
When color fastness is usually tested, the degree of discoloration of the dyed material and the degree of staining of the backing material are used to rate the color fastness. Except for the light fastness level eight, the rest are Level five.
The higher the grade, the better the color fastness.
Light fastness (sunlight fastness)
Sunlight fastness refers to the ability of printed and dyed fabrics to maintain their original color under light conditions, that is, light fastness Excellent colorfastness and non-fading ability. There are eight levels of color fastness to sunlight, with Level 1 being the largest discoloration and Level 8 being the smallest.
There are three methods for testing color fastness to sunlight: sunlight test method, xenon arc lamp tester and carbon arc lamp tester.
The general test process for color fastness to sunlight is:
Put the textile sample and the mutually agreed reference standard sample (blue standard wool) under artificial light at the same time according to the Expose under specified conditions, then compare the degree of discoloration of the two, and determine the light fastness level of the sample through the blue wool light fastness standard sample exposed at the same time.
All test standards for color fastness to sunlight adopt a relative comparison method, and exposure equipment does not directly issue test results. The performance of the equipment mainly depends on the control of parameters that affect the test environment, including spectrum, light intensity, temperature, relative humidity, etc.
Color fastness to perspiration
The color fastness to perspiration reflects the effect of textiles in different test solutions containing histidine under the combined action of pressure and temperature. Self-discoloration and staining of the backing fabric. Use a gray card to evaluate the discoloration of the sample and the staining of the backing fabric. The results are divided into 5 levels, with level 5 being the best and level 1 being the worst.
Test method:
Sew the sample and the standard lining fabric together, and then treat them in sweat liquid. Clamp it on the perspiration color fastness meter, place it in an oven at a constant temperature, and then dry it. Use a gray card to rate it and get the test results. Different testing methods have different sweat liquid ratios, different sample sizes, and different testing temperatures and times.
Color fastness to rubbing
Rub the textile sample with a dry rubbing cloth and a wet rubbing cloth respectively to determine the staining degree of the rubbing cloth.
Test method:
Put the sample on the friction fastness tester, 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 Color fastness to dry rubbing and color fastness to wet rubbing. Use a gray card to rate the color stained on a standard rubbing white cloth, and the resulting grade is the measured color fastness to rubbing. Rubbing color fastness requires two tests, dry rubbing and wet rubbing, and all colors on the sample must be rubbed.
Color fastness to washing
Textile color fastness test is a routine test item in the intrinsic quality test of textiles. During the test , the fastness grade is evaluated based on the discoloration of the sample and the staining of the undyed backing fabric. The color fastness to washing of fabrics is one of the most important properties of textiles. It refers to the degree and cause of color change of colored fabrics after a certain period of washing in a specific solution with a certain temperature and a certain liquor ratio. The degree of staining of various fiber cloths.
Test method:
Washing color fastness test is the most important and common item in textile inspection. Sew the sample with white cloth, put it into a washing liquid of a certain temperature, immerse and wash it for a specified time under mechanical stirring, and use a gray card to evaluate the discoloration and staining levels after drying.
Due to the variety of washing methods and washing liquids, the test result is an indicator with strict condition value meaning.
The specific steps are: sew the sample according to the standard → prepare the soap solution according to the standard method → wash according to the standard method → clean → dry → grade with a gray sample card or instrument.
Methods to improve the color fastness of dyes
Although some dyes can produce brighter colors, due to the water-soluble groups on the dyes, wet processing Poor fastness, serious fading and staining will not only make the textile itself look old, but also the dye will fall off and stain white or other colored fibers, resulting in staining and color matching.
In addition, although reactive dyes can form covalent bonds with cellulose fibers, the presence of hydrolyzed dyes or insufficient soaping of unbonded dyes during dyeing will also make the wet treatment fast. In addition, the reactive dyes that have formed covalent bonds with the fiber may also decompose and break the bonds under acidic or alkaline conditions, and the color fastness to chlorine and theProblems such as insufficient stain fastness and sun fastness.
In order to improve the color fastness of fabrics, color fixing treatment can be performed. These additives that can improve the color fastness of various types of dyes are called color fixing agents.
Principle of color fixing agent
1. Generate insoluble lake on the fabric, block the soluble groups, and make the fabric The dye on it is not easy to dissolve and fall off when exposed to water, thereby achieving the purpose of improving the wet processing fastness. However, after these color-fixing agents are fixed, the color of the fabric may change or the light fastness may decrease.
2. Create a mesh film on the fabric to prevent the dye from falling off.
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. Use the molecular attraction between the fixing agent and the fiber to increase the fixing strength of the fixing agent, thereby improving the dye fastness. </p
