What is color fastness?
Color fastness is a type of color fastness, also called color migration fastness or bleeding resistance. Color fastness refers to the migration and staining of dyes or residual floating colors on fabrics. Color mainly reflects the degree of contamination caused by the dye dissolving out of the dyeing area and transferring color to the white or light-colored base fabric after the fabric is washed or exposed to rain. It comes from Japan and is also called the “Daimaru method” in the Japanese test method. .
Color fastness has become one of the common testing items in Japan. It is generally required to reach level 4 or above level 4-5, mainly in medium and dark colors. It is closely related to stain fastness. They are often related. If the stain fastness is good, the color fastness will also be good.
The improvement of color fastness of pure cotton fabrics can be improved and strengthened from the following main aspects:
1. Choose appropriate dyes
Because dyes are Synthesis is often accompanied by a small amount of incompletely reacted dyes. The presence of these dyes will not only affect the color fastness but also other color fastnesses, so color fastness testing should be done before use. At the same time, attention should be paid to the selection of reactive dyes whose water-soluble groups in the dye structure should not be too high and whose directness is medium.
2. Pay attention to the influence of water quality
Calcium and magnesium ions in the water will form insoluble substances with dyes and adsorb on the surface of the fiber, becoming floating colors and hindering the absorption of dyes. Diffusion and penetration will reduce the color fastness and even affect the color light and brightness, so soft water must be used or chelating dispersants must be added.
3. Strengthen the washing and soaping process
The residual alkali salts, hydrolyzed and unbonded dye floating colors on the fiber are factors that affect the fastness. The key is to use a high-efficiency anti-stick soaping agent with excellent performance, and try to soap under neutral or weak acid. At the same time, use a higher temperature to wash away the unbound dye inside the fabric, but you must also pay attention to excessive temperature. High will cause bond breaking of the bound dye to fall off, especially under alkaline conditions.
4. Use color-fixing treatment
Use excellent cationic and reactive color-fixing agents to block the water-soluble groups of the dye. It becomes an insoluble lake and is deposited in the fiber, reducing the water solubility of the dye. At the same time, a small amount of hydrolyzed dye can also participate in color fixation and cross-linking to further increase the binding force with the fiber, thereby effectively improving the wet treatment and color fastness of the dye. etc. If necessary, some particularly deep and thick colors can also undergo a re-fixing process.
Of course, in addition to paying attention to the above points, the quality of the gray fabric itself, whether the pre-treatment, boiling, bleaching and impurity removal are even and thorough, and whether the dyeing process is reasonable will all affect the dye. Whether the adsorption, diffusion and fixation effects can be fully achieved, further standardizing the operation and optimizing the process to avoid excessive dye and re-dying on the fiber surface after dyeing are the basis and guarantee for ensuring the color fastness of reactive dyes and improving the color fastness.
How to test color fastness?
The description of this test can be summarized as: the possibility of the dye in the dyed part of the fabric dissolving and moving to a white or light-colored background due to reasons such as washing or being exposed to rain. The test method in Japan Among them is a testing method called the “big pill method”. This method is also called: Daiwan method. Textile color fastness test, textile color fastness test, this method does not have a JIS standard number, and is usually called the DAIMARUBLEEDINGTEST in Japan.
Testing principle:
One end of the sample is immersed in the water containing the reagent, and the color produced due to the rising effect of the water The degree of pollution is assessed using the pollution gray card. Required test materials: balance, beaker, volumetric flask, room temperature dyeing machine
Test method:
1. Cut a 3cmx2.5cm sample. The patterned fabric cannot be all When cutting into a piece of sample, cut the dark color (the most delicious color).
2. Cut the cotton and white cloth into a size of (length) 20~25cm x (width) 2.5cm.
3. Place the test piece under the cotton-padded white cloth, and sew one strip at each end where it overlaps by 1.5cm. Wire.
4. Prepare the nonionic surfactant solution: Dissolve 0.5g of the nonionic surfactant into 1000ml of distilled water middle.
5. Immerse one end of the test piece in the test solution to a depth of 2cm, and test it at room temperature according to the standards of each company. Method is left for 2 hours.
6. Remove the solution and let the test piece dry naturally in its original state.
7. Judgment: Use the JIS staining gray card to rate the sample (staining of the white or light-colored parts of the sample).
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