Introduction
Fastness is the most frequently asked question among all dyeing questions. Dye fastness has high requirements on the quality of dyed and printed fabrics. The nature or degree of variation in dyeing state 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 insolation machine exposure. The fading degree of the sample after exposure is compared with the standard color sample. It is divided into 8 levels, with level 8 being the best and level 1 being the worst. 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. Rubbing 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, which 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, with level 5 being the best and level 1 being the worst. 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 from 1 to 5, with level 5 being the best and level 1 being the worst. 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 the worst and level 5 being the best. The dye fastness of normal fabrics generally needs to reach level 3 to 4 to meet the needs of wearing.
How to control various fastnesses
After textiles are dyed, 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 affecting 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 dye fastnesses, and formulating reasonable dyeing and finishing processes is the key to ensuring 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 fiber. 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 the deep color of polyester fiber, the wash fastness of the fabric after dyeing can meet customer requirements as long as it undergoes relatively sufficient reduction and cleaning. However, since most polyester fabrics are softened by padding cationic silicone softeners to improve the fabric feel, and the anionic dispersants in disperse dyes may spread to the fiber surface due to thermal migration of the dye when the polyester fabric is set at high temperatures, so 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 thermal migration resistance of the disperse dyes should be considered.
There are many ways to test the washing fastness.Post-processing and washing to remove more surface floating colors can also significantly improve the sublimation fastness of the fabric. Appropriately lowering the setting temperature during the setting 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 selecting 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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