Dye fastness has high requirements on the quality of dyed and printed fabrics. The nature or degree of dyeing state variation can be expressed by dye fastness. It is related to yarn structure, fabric organization, printing and dyeing method, dye type and external force. Different dyeing fastness requirements will cause great cost differences and quality differences.
6 main textile fastnesses
1. Sunlight fastness
Sunlight fastness refers to the degree to which colored fabrics change color due to sunlight. The test method can be either sunlight exposure or sunlight machine exposure. The fading degree of the sample after exposure is compared with the standard color sample. It is divided into 8 levels, with 8 being good and 1 being poor. Fabrics with poor sun fastness should not be exposed to the sun for a long time and should be placed in a ventilated place to dry in the shade.
2． Friction fastness
Rubbing fastness refers to the degree of color fading of dyed fabrics after rubbing, and can be divided into dry rubbing and wet rubbing. The rubbing fastness is evaluated based on the staining degree of white cloth, and is divided into 5 levels (1~5). The larger the value, the better the rubbing fastness. Fabrics with poor rubbing fastness have a limited service life.
3． Washing fastness
Washing or soaping fastness refers to the degree of color change of dyed fabrics after being washed with detergent. The gray graded sample card is usually used as the evaluation standard, that is, the color difference between the original sample and the sample after fading is used for evaluation. Washing fastness is divided into 5 levels, level 5 is good and level 1 is poor. Fabrics with poor washing fastness should be dry cleaned. If wet cleaning is performed, extra attention should be paid to the washing conditions, such as the washing temperature should not be too high and the washing time should not be too long.
4． Ironing fastness
Ironing fastness refers to the degree of discoloration or fading of dyed fabrics when ironed. The degree of discoloration and fading is evaluated by the staining of other fabrics by the iron at the same time. Ironing fastness is divided into levels 1 to 5, with level 5 being good and level 1 being poor. When testing the ironing fastness of different fabrics, the test iron temperature should be selected.
5． Perspiration fastness
Perspiration fastness refers to the degree of color fading of dyed fabrics after being immersed in sweat. Since the composition of artificially prepared sweat is different, the perspiration fastness is generally not only measured separately, but also combined with other color fastnesses for assessment. The perspiration fastness is divided into levels from 1 to 5, with the higher the value, the better.
6． Sublimation fastness
Sublimation fastness refers to the degree of sublimation phenomenon that occurs in dyed fabrics during storage. The sublimation fastness uses a gray grading sample card to evaluate the degree of discoloration, fading and white cloth staining of fabrics after dry heat pressing. It is divided into 5 levels, with level 1 being poor and level 5 being good. The dye fastness of normal fabrics generally needs to reach level 3 to 4 to meet the needs of wearing.
How to control various dye fastnesses. After dyeing textiles, the ability of the fabric to maintain its original color can be expressed by testing various dye fastnesses. Commonly used indicators for testing dye fastness include washing fastness, rubbing fastness, sunlight fastness, sublimation fastness, etc. of fabrics. The better the washing fastness, rubbing fastness, sunlight fastness and sublimation fastness of the fabric, the better the dye fastness of the textile.
The main factors that affect the above-mentioned fastness include two aspects: the first is the performance of the dye; the second is the formulation of the dyeing and finishing process. Selecting dyes with excellent performance is the basis for improving various dyeing fastnesses, and formulating a reasonable dyeing and finishing process is the guarantee The key to various dye fastnesses, the two complement each other and cannot be neglected
Washing fastness: The washing fastness of fabrics includes two aspects: fading fastness and staining fastness. Generally, the worse the fade fastness of textiles, the worse the stain fastness. When testing the staining fastness of a certain textile, you can determine the staining of the fiber by testing the staining of the six commonly used textile fibers (these six commonly used textile fibers usually include polyester, nylon, cotton , acetate, wool or silk, acrylic. Tests on the color fastness of the six fibers are generally completed by qualified independent professional inspection companies. Such inspections are relatively objective and fair)
For cellulose fiber products, the washing fastness of reactive dyes is better than that of direct dyes. The dyeing processes of insoluble azo dyes, vat dyes and sulfur dyes are more complicated than those of reactive dyes and direct dyes, so the washing fastness of the latter three dyes is The degree is even better. Therefore, to improve the washing fastness of cellulose fiber products, we must not only choose the correct dye, but also choose the correct dyeing process. Appropriate strengthening of water washing, color fixation and soaping can significantly improve the washing fastness. For polyester fibers with deep colors, the wash fastness of the fabric after dyeing can meet customer requirements as long as it undergoes relatively sufficient reduction and cleaning. However, most polyester fabrics are softened by padding cationic silicone softeners to improve the fabric feel. At the same time, the anionic dispersant in disperse dyes may diffuse on the surface of the fiber due to thermal migration of the dye when the polyester fabric is set at high temperature. Therefore, deep The wash fastness of polyester fabrics with strong colors may not be up to standard after being set. This requires that when selecting disperse dyes, not only the sublimation fastness of the disperse dyes, but also the heat migration resistance of the disperse dyes should be considered.sex. There are many methods for testing the washing fastness. Testing the washing fastness of textiles according to different testing standards will lead to different conclusions. When foreign customers propose specific wash fastness indicators, if specific testing standards can be proposed, it will facilitate smooth communication between the two parties. Although strengthening washing and post-treatment can improve the washing fastness of fabrics, it will also increase the emission reduction of dyeing plants. Finding some efficient detergents, rationally formulating dyeing and finishing processes, and strengthening research on short-process processes can not only improve production efficiency, but also contribute to energy conservation and emission reduction.
Rubbing fastness The rubbing fastness of fabrics is the same as the washing fastness, and also includes two aspects: one is dry rubbing fastness, and the other is wet rubbing fastness. Obtain the physical sample cards of the dry rubbing fastness and wet rubbing fastness of the fabric through the detection of the fabric rubbing fastness testing instrument, and compare the fabric discoloration sample card and staining sample card to test the dry rubbing fastness and wet rubbing fastness of the textile. Very convenient. Usually when testing the rubbing fastness of deep-colored textiles, the dry rubbing fastness grade is generally about 1 level higher than the wet rubbing fastness grade. Take the black cotton fabric dyed with direct dyes as an example. Although it has undergone effective color fixation treatment, the dry rubbing fastness and wet rubbing fastness levels are not very high, and sometimes it cannot meet customer requirements. In order to improve the rubbing fastness, reactive dyes, vat dyes and insoluble azo dyes are mostly used for dyeing. Strengthening dye screening, strengthening color fixation treatment and soaping are effective measures to improve the rubbing fastness of textiles. In order to improve the wet rubbing fastness of deep-colored cellulose fiber products, you can choose additives that can specifically improve the wet rubbing fastness of textiles. By padding special additives when finalizing the finished product, you can significantly improve the wet rubbing fastness of the product. Spend. For dark-colored chemical fiber filament products, the wet rubbing fastness of the product can also be improved by adding a small amount of fluorine when setting the finished product. When using acid dyes to dye polyamide fibers with deep colors, the use of nylon-specific color fixing agents can significantly improve the wet rubbing fastness of nylon fabrics with deep colors. For sanded dark-colored products, when testing their wet rubbing fastness, since the shedding of short fibers on the surface of the fabric of sanded products will be more obvious than other products, the wet rubbing fastness grade may be reduced.
Sunlight fastness Sunlight has wave-particle duality. Sunlight that transfers energy in the form of photons has a strong impact on the molecular structure of dyes. When the basic structure of the color-producing part of the dye structure is destroyed by photons, the color of the light emitted by the dye color body will change, usually becoming lighter in color until it is colorless. The more obvious the color change of the dye is under sunlight conditions, the worse the light fastness of the dye is. In order to improve the light fastness of the dye, dye manufacturers have adopted many methods. Increasing the relative molecular weight of the dye, increasing the opportunity for internal complexation of the dye, and increasing the coplanarity and length of the conjugated system of the dye can relatively improve the light fastness of the dye. For phthalocyanine dyes that can reach level 8 light fastness, adding appropriate metal ions during the dyeing and finishing process to form complexes within the dye molecules can significantly improve the dye’s brightness and light fastness. Spend. For textiles, choosing dyes with better sun fastness is the key to improving the sun fastness grade of the product. The effect of improving the light fastness of textiles by changing the dyeing and finishing process is not obvious.
Sublimation fastness As far as disperse dyes are concerned, since the dyeing principle of polyester fiber is different from that of other dyes, sublimation fastness can directly express the heat resistance of disperse dyes. For other dyes, testing the ironing fastness of the dye has the same meaning as testing the sublimation fastness of the dye. The sublimation fastness of dyes is not good. Under dry heat, the solid dyes can easily detach directly from the inside of the fiber in a gaseous state. So in this sense, the sublimation fastness of dyes can also indirectly express the ironing fastness of fabrics.
In order to improve the sublimation fastness of dyes, we must start from the following aspects:
The first is to choose a dye with a larger relative molecular mass, and the basic structure of the dye is similar or similar to the fiber structure, which can improve the sublimation fastness of the textile. The second step is to improve the dyeing and finishing process to fully reduce the crystallinity of the crystalline part of the fiber macromolecular structure and increase the crystallinity of the non-crystalline area, so that the crystallinity of each area inside the fiber becomes consistent, so that after the dye enters the inside of the fiber, it will The bond between fibers is more even. This can not only improve the leveling degree, but also improve the sublimation fastness of dyeing. If the crystallinity of each part inside the fiber is not balanced enough and most of the dye stays in the amorphous area with a relatively loose structure, then after extreme external conditions occur, the dye will be more likely to break away from the amorphous area inside the fiber and sublime to the surface of the fabric. , thereby reducing the sublimation fastness of textiles. The scouring and mercerization of cotton fabrics, and the pre-shrinking and pre-shaping of polyester fabrics are all processing steps that balance the crystallinity inside the fiber. The dyeing depth and color fastness of cotton fabrics that have been scoured and mercerized, and polyester fabrics that have been preshrunk and pre-shaped can be significantly improved.
Strengthening post-processing and washing to remove more floating colors on the surface can also significantly improve the sublimation fastness of the fabric. In shapingAppropriately lowering the setting temperature during the process can significantly improve the sublimation fastness of the fabric. The problem of reduced fabric dimensional stability due to cooling can be compensated by appropriately reducing the setting speed. When choosing finishing agents, you should also pay attention to the impact of auxiliaries on dye fastness. For example, after using cationic softeners for soft finishing of polyester fabrics, the thermal migration of disperse dyes may cause the disperse dyes to fail the sublimation fastness test. Judging from the temperature type of disperse dyes themselves, high-temperature disperse dyes have better sublimation fastness.
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