Most of the current color fastness test methods are based on simulation tests or comprehensive tests based on the environment and conditions of action, and the fastness grade is evaluated based on the discoloration of the sample after the test and the staining of the lining fabric. What is special is that the color fastness to light is rated by the blue label, while the color fastness to dry cleaning will evaluate the staining of solvents.
When rating color fastness
It is necessary to comprehensively assess changes in the three attributes of color
That is, changes in hue, brightness and purity
1. Hue: 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 is called hue.
2. Brightness: Depending on the degree of light reflection on the surface of the object, the brightness of the color will be different. The brightness of this color is called brightness.
3. Purity: Purity refers to the degree of saturation of color. The simpler the wavelength of light, the higher the purity of the hue, and vice versa.
Color fastness rating can be divided into visual rating and instrument rating
Gaze Rating
It requires that the background should be neutral gray, approximately between level 1 and level 2 of this gray sample card (approximately Munsell color card N5). The lighting conditions should be northern daylight (9:00-15:00) on a sunny day, or an equivalent light source with an illumination of 600lx and above. The incident light is at an angle of approximately 45º to the textile surface, and the observation direction is roughly perpendicular to the textile surface. Cover the original and The color of the plate of the sample after the test should be consistent, preferably neutral color or gray or black, and the size and shape should be roughly the same. Rating personnel should wear neutral gray work clothes, and the rating process should avoid the influence of environmental colors.
▼Color fastness rating: Compare the sample after testing with the original sample to see that the degree of discoloration is closest to the level of the gray card.
Stain fastness rating: Ratio of tested lining to untested lining Yes, get the closest staining series.
Instrument Rating:
Instrument Rating The principle is to use the absolute reflectance of a known standard white plate for calibration, measure the spectral power distribution of the sample reflection or its own reflection photometric characteristics, and then calculate the tristimulus value and color of the object under the standard illumination based on the spectral measurement data. degree coordinates, CIELAB uniform color space, etc., and converted into gray card series of discoloration and stain fastness through a series of formulas.
Sometimes when reading the report, you will have questions as to why the test report shows soaping resistance. The color fastness and discoloration test result is level 3. Is the standard requirement ≥3-4, or is it judged to be unqualified? Was the report judged wrong?
In fact, the result is correct. The color fastness assessment grade 3-4 is not an interval in the general mathematical concept. It is a grade, which means that the test result is between grade 3 and grade 4.
Attachment: Problems and solutions for unqualified color fastness
1. Color fastness to water, washing and perspiration
1) Frequently Asked Questions
Staining is not up to standard
2) Cause analysis
On the cloth The floating color is related to the transfer of some colored fiber particles;
It is related to the selected dye species, dyeing process and post-treatment process;
acetate and nylon at lower temperatures It has a good coloring rate for a variety of dyes;
Thermal migration phenomenon when dyeing with disperse dyes;
Water has a plasticizing effect on spandex, and under wet conditions, it enters the amorphous zone of spandex The dye is easy to migrate to the fiber surface. Under the action of external force, the dye transfer is easy to occur, causing the lining cloth to be stained;
In fact, in elastic fabrics containing spandex, the proportion of spandex yarn is quite low, and usually not Without being exposed on the surface of the fabric, the color fastness problem of spandex will not seriously affect the color fastness of the entire fabric. The color fastness problem of spandex-containing elastic fabrics is mainly due to the color fastness problems of cotton, polyester, nylon and other fibers on the surface of the fabric itself;’
3) How to improve
improve the dyeing properties of fabrics, such as dye penetration, sufficient color fixation, and strengthen soaping, washing, and reduction Clean and fully remove floating color;
Use color-fixing agents to improve the water and washing color fastness of the fabric;
Use corresponding additives to prevent sweat from destroying the dye carrier Structure
2. Color fastness to sunlight
1) Unqualified factors
The organizational structure of the fabric;
The molecular structure of the dye²;
Fiber The bonding state of the dye�� changes with dye concentration;
Use dyes with different light fastnesses to match colors;
Dye with good diffusion performance and uniform penetration in the fiber will have higher light fastness;
Some additives applied to fabrics will affect the color fastness to sunlight;
2) How to improve
Choose the correct dye
Develop and implement a reasonable dyeing process Conditions allow the fabric to be dyed evenly and thoroughly and fully fixed; it is also strengthened to avoid the adverse effects of post-finishing. After dyeing, soap and wash to fully remove floating color
Use sun fastness enhancer
Use anti-UV finishing agent as appropriate
3. Chlorine bleaching and non-chlorine bleaching color fastness
1) Unqualified factors
Active chlorine reacts with dyes, causing oxidative decomposition of dyes;
Peroxide reacts with the dye matrix, causing the dye to change color or fade, or destroy the combination of the dye and the fiber;
The color fastness of the dye to chlorine bleaching and non-chlorine bleaching is related to the dye structure;
2) How to improve
reasonably screen dyes and select Dyes with chlorine bleaching resistance and non-chlorine bleaching structure;
Full scouring before dyeing and washing after dyeing, striving to remove impurities and keep the fabric neutral, because the presence of impurities and acid , alkaline will accelerate the decomposition of dyes under chlorine bleaching and non-chlorine bleaching conditions;
Use chlorine-resistant color fixing agents to improve the chlorine resistance of dyes and strengthen the combination of dyes and fibers;
Use active chlorine capture agents to prevent dyes from being affected by active chlorine. The disadvantage is that most of these additives are not durable and are rarely used;
4. Ozone color fastness of denim fabric
1) Unqualified factors
Indigo will decompose into indigo under the action of strong oxidants, and ozone has a strong oxidizing effect;
Indigo should be red, but the actual test result The phenomenon seen is more yellowing, which is related to the purity of the dye used, other chemicals added in the dyeing process, the fabric and the finishing process;
2) How to improve
choose dyes whose structure is resistant to ozone oxidation
Antioxidant and anti-yellowing additives
5. Phenol yellowing
White fabrics sometimes turn yellow during storage. The yellowed parts will disappear and return to their original white color after acid treatment. If alkali solution is added again, the yellow color will return. The main reason is phenol yellowing.
1) Reasons
Antioxidants commonly used in packaging materials BHT (2,6-di-tert-butyl-p-cresol) chemically reacts with nitrogen oxides (NOx) in the air to form DTNP (2,6-di-tert-butyl-p-nitrophenol). DTNP in an acidic state It is colorless and easily sublimates and transfers at room temperature. When encountering alkaline substances, it immediately turns yellow.
2) How to improve
Use BHT-free packaging materials, such as PE film, packaging paper and cartons
Add low-volatile acids such as citric acid, oxalic acid or tartaric acid to maintain the acidic pH of the processed cloth Around 4.5~6.0
Choose additives that do not contain BHT and are not easily absorbed, such as weak cationic softeners²
Cloth processing Avoid air pollution in the storage place and reduce the concentration of NOx
Fluorescent whitening agent treatment (the acid and alkali resistance of the fluorescent whitening agent must be considered)
6. Color fastness of pigment printed fabric
Dig printing: Yes A printing method in which insoluble pigments are mechanically fixed on the fabric with the help of an adhesive.
1) Frequently Asked Questions
The color fastness to dry and wet rubbing is poor
The printed surface turns white
After the washing resistance test, it was found that the printed parts were cracked or even peeled off. Breakage
2) Analysis of causes of failure
Printing adhesives are divided into three categories: hard monomers, soft monomers and functional monomers. Adding too much hard monomer will help improve the color fastness to rubbing of printing, but will make the printed parts feel hard and prone to cracking, light resistance will steadily decrease, and it will easily turn yellow.
Adding too much soft monomer can improve the feel and light resistance, but the film strength is too low, which reduces the color fastness to rubbing.
Polyacrylic acid swells easily under wet conditions, which reduces the strength of the film and the color fastness to wet rubbing.
3) How to improve the selection of appropriate adhesives
Use appropriate softener
Pay attention to the baking and color-fixing process</p
