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How to control various fastness?

Views: 6     Author: Site Editor     Publish Time: 2022-02-11      Origin: Site Inquire

After dyeing of textiles, the ability of fabrics to retain their original color can be expressed by testing various dye fastnesses. Commonly used indicators for detecting dyeing fastness include washing fastness, rubbing fastness, light fastness, sublimation fastness and so on.

The better the washing fastness, rubbing fastness, light fastness and sublimation fastness of the fabric, the better the dyeing fastness of the textile.

The main factors affecting the above fastness include two aspects: the first is the performance of the dye; the second is the formulation of the dyeing and finishing process. The selection of dyes with excellent performance is the basis for improving the dyeing fastness, and formulating a reasonable dyeing and finishing process is the key to ensuring the dyeing fastness. The two complement each other and cannot be neglected.

 

1. Washing fastness

The washing fastness of fabrics includes two aspects: fading fastness and staining fastness. Generally, the worse the color fastness of textiles, the worse the color fastness.

When testing the staining fastness of a certain textile, the staining of the fiber can be judged by examining the staining of the fiber to the six commonly used textile fibers (the six commonly used textile fibers usually include polyester, nylon, cotton, etc.). , acetate, wool or silk, acrylic fiber. The color fastness test of the six fibers is generally completed by a qualified independent professional inspection company, and this test is relatively objective and fair)

For cellulose fiber products, the washing fastness of reactive dyes is better than that of direct dyes. The dyeing process of insoluble azo dyes, vat dyes and sulfur dyes is more complicated than that of reactive dyes and direct dyes. Therefore, the washing fastness of the latter three dyes is more complicated. degree is more excellent.

Therefore, to improve the washing fastness of cellulose fiber products, it is necessary not only to choose the correct dye, but also to choose the correct dyeing process. Appropriate strengthening of washing, strengthening of color fixing and soaping can significantly improve the washing fastness. For polyester fiber with deep color and luster, as long as it is fully restored and cleaned, the washing fastness of the fabric after dyeing can meet customer requirements. However, since polyester fabrics are mostly softened by padding cationic silicone softeners to improve the fabric feel, and at the same time, anionic dispersants in disperse dyes may diffuse to the fiber surface due to thermal migration of dyes during high temperature setting of polyester fabrics. The washing fastness of polyester fabrics with strong colors may be unqualified after setting. This requires that not only the sublimation fastness of disperse dyes, but also the thermal migration resistance of disperse dyes should be considered when selecting disperse dyes.

There are many ways to test the washing fastness. According to different testing standards, the washing fastness of textiles will be tested, and the conclusion will be drawn. When foreign customers put forward specific washing fastness indicators, if they can put forward specific testing standards, it will be conducive to smooth communication between the two parties. Although the strengthening of washing and post-treatment can improve the washing fastness of the fabric, it will also increase the emission reduction of the dyeing factory.

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.

 

2. Rub fastness

The rubbing fastness of the fabric is the same as the washing fastness, and it also includes two aspects: one is the dry rubbing fastness, and the other is the wet rubbing fastness. The dry rubbing fastness and wet rubbing fastness of the fabric are obtained through the testing of the fabric rubbing fastness testing instrument. Very convenient.

Usually, when testing the rubbing fastness of dark-colored textiles, the grade of dry rubbing fastness is generally about 1 level higher than that of wet rubbing fastness. Taking direct dyeing of cotton fabric black as an example, although it has been effectively fixed, the level of dry rubbing fastness and wet rubbing fastness will not be 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 fixing treatment and soaping are effective measures to improve the rubbing fastness of textiles.

In order to improve the wet rubbing fastness of dark-colored cellulose fiber products, special additives that can improve the wet rubbing fastness of textiles can be selected. Spend. For chemical fiber filament dark-colored products, the wet rubbing fastness of the product can also be improved by adding a small amount of fluorine-containing water repellent when the final product is finalized.

When acid dyes are used to dye polyamide fibers with a deep color, the use of a special nylon fixing agent can significantly improve the wet rubbing fastness of the nylon fabric with a deep color. For sanded dark-colored products, when testing their wet rubbing fastness, the shedding of short fibers on the fabric surface of sanded products will be more obvious than other products, so the wet rubbing fastness grade may be lowered.

 

3. Light fastness

Sunlight has wave-particle duality, and sunlight that transmits energy in the form of photons has a strong impact on the molecular structure of dyes. When the basic structure of the chromophore in the dye structure is destroyed by photons, the color of the light emitted by the dye chromophore will change, usually the color becomes lighter until it is colorless. The more obvious the color change of the dye under sunlight, the worse the light fastness of the dye.

In order to improve the light fastness of dyestuffs, dyestuff manufacturers have taken many measures. Increasing the relative molecular weight of the dye, increasing the chance of internal complexation of the dye, increasing the coplanarity of the dye and the length of the conjugated system can relatively improve the light fastness of the dye.

For phthalocyanine dyes that can reach grade 8 light fastness, adding appropriate metal ions during the dyeing and finishing process to form complexes inside the dye molecules can significantly improve the brightness and light fastness of the dyes. Spend. For textiles, choosing a dye with better light fastness is the key to improving the light fastness grade of the product. The effect of improving the light fastness of textiles by changing the dyeing and finishing process is not obvious.

 

4. Sublimation fastness

As far as disperse dyes are concerned, since the dyeing principle of polyester fibers is different from 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. In the dry heat state, the dyes in the solid state are easily detached from the inside of the fiber in the gas state. So in this sense, the sublimation fastness of dyes can also indirectly express the ironing fastness of the fabric.

In order to improve the sublimation fastness of dyes, we must start from the following aspects:

The first is the selection of dyes. The relative molecular weight is relatively large, and the basic structure of the dye is similar to or similar to the fiber structure, which can improve the sublimation fastness of textiles.

The second is to improve the dyeing and finishing process, fully reduce the crystallinity of the crystalline part of the macromolecular structure of the fiber, and increase the crystallinity of the non-crystalline region, so that the crystallinity between the regions inside the fiber tends to be consistent. The bonding with the fibers is more uniform.

This can not only improve the level of dyeing, but also improve the sublimation fastness of dyeing. If the crystallinity of each part of the fiber is not balanced enough, and most of the dyes stay in the amorphous area with relatively loose structure, then after the extreme state of the external conditions, the dye will be more easily detached from the amorphous area inside the fiber and sublimated to the surface of the fabric , thereby reducing the sublimation fastness of textiles.

Scouring and mercerizing of cotton fabrics, and pre-shrinking and pre-sizing of polyester fabrics are all processing steps to balance the internal crystallinity of fibers. After scouring and mercerizing processing cotton fabrics, after pre-shrinking and pre-shaped polyester fabrics, its dyeing depth and dyeing fastness can be significantly improved.

Strengthening post-treatment and washing, and removing more surface floating color can also significantly improve the sublimation fastness of the fabric. Appropriately reducing the setting temperature during the setting process can significantly improve the sublimation fastness of the fabric. The reduced dimensional stability of the fabric due to cooling can be compensated by appropriately reducing the setting speed. In the selection of finishing agents, attention should also be paid to the influence of auxiliaries on color fastness. For example, after the use of cationic softener in the softening of polyester fabrics, it is possible that the disperse dyes may fail to pass the sublimation fastness test due to the thermal migration of disperse dyes. From the temperature type of the disperse dye itself, the sublimation fastness of the high temperature type disperse dye is better.


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