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 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 now 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 often related to stain fastness. Good stain fastness will result in better color fastness.
The color fastness of pure cotton fabrics can be improved and strengthened from the following main aspects:
1. Choose the right one Dyes:
Since dyes are often accompanied by a small amount of incompletely reacted dyes during synthesis, the presence of these dyes will not only affect the color fastness but also other color fastnesses. Therefore, 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 The color floats and hinders the diffusion and penetration of the dye, reducing the color fastness and even affecting the color light and brightness. Therefore, soft water or chelating dispersant must be used.
3. Strengthen the washing and soaping process:
Residual alkali salts, hydrolyzed and unbonded dyes on the fiber Floating color is the key to the fastness. A high-efficiency anti-stick soaping agent with excellent performance should be used, and soaping should be carried out under neutral or weak acid as much as possible. At the same time, a higher temperature should be used to wash away the unbound dye inside the fabric. However, it should also be noted that too high a temperature will cause bond breaking of the bound dye to fall off, especially under alkaline conditions.
4. Use fixation treatment:
Use excellent cationic and reactive fixatives to block the dye. The water-soluble group makes the dye become an insoluble lake and deposits 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-fixing cross-linking to further increase the binding force with the fiber, thereby effectively improving the wetness of the dye. processing, color fastness, etc. If necessary, individual special deep and thick colors can also undergo a re-fixation 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 transparent, whether the dyeing process is reasonable, etc. will all affect whether the dye can be fully absorbed, Diffusion and fixation effects, further standardizing the operation and optimizing the process to avoid excessive dye on the fiber surface and the phenomenon of re-dying after dyeing are the basis and guarantee to ensure the color fastness of reactive dyes and to improve the color fastness.
How to test color fastness?
The description of this test can be summarized as: the possibility that the dye in the dyed part of the fabric will dissolve and transfer to a white or light-colored background due to reasons such as washing or being exposed to rain. , among the Japanese testing methods is a testing method called the “Daimaru method”. This method is also called: Daiwan method. Textile color fastness test, textile color fastness test, this method does not have JIS standard number, it is usually called DAIMARUBLEEDINGTEST in Japan.
Testing principle:
One end of the sample is immersed in the water containing the reagent. Due to the The degree of color pollution caused by the rising effect is evaluated with the pollution gray card. Required test materials: balance, beaker, volumetric flask, room temperature dyeing machine
Test method:
1. Cut a 3cmx2.5cm sample. If all the colors of the patterned fabric cannot be cut into one piece, cut the dark color (the most delicious color).
2. Cut the cotton and white cloth into (length) 20~25cm x (width) 2.5cm.
3. Place the test piece under the cotton-added white cloth, and sew a line on both ends where it overlaps 1.5cm.
4. Prepare the nonionic surfactant solution: Dissolve 0.5g of the nonionic surfactant into 1000ml of distilled water.
5. Immerse one end of the test piece in the test solution to a depth of 2cm and leave it at room temperature for 2 hours according to each company’s benchmark method.
6. Remove the solution and let the testThe test piece is left to 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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