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Do You Know What Is Rubbing Color Fastness?

Aug. 17, 2020
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Color fastness is one of the important quality indexes of textiles, and is also one of the most common inspection items of textiles in the trade process. The so-called color fastness refers to the degree of color fastness under the physical and chemical action of dyed textiles, namely the ability of color resistance to friction of textiles, which can be divided into dry friction and wet friction.

1. The effect of fabric surface morphology - because the dye fixation is the main cause of friction fastness difference, under the condition of dry, for rough surface or sanded, pile fabric, as hard as hemp fabrics, denim fabrics and pigment printing fabric, if dry friction will easily fabric surface accumulation of dye, coating, or other non-ferrous material grinding down, and even cause some colored fiber fracture and forming non-ferrous particles, the fastness to dry friction decline further.

For the fabric, the pile on the fabric surface and the friction cloth surface show a certain Angle, is not parallel, so that the friction head in the reciprocating movement of the increase of friction resistance, so that the color fastness to dry friction of this kind of fabric decreases.

2. The influence of fabric structure - lightweight fabric (usually synthetic fiber or silk fabric) of the surface of the specimen, due to the fabric structure is relatively loose, in the dry friction, the sample under the action of pressure and friction occur along with the movement of the friction head part of the slip, so that the friction resistance increases, and the friction efficiency.But when it comes to wet friction, the situation is completely different from that of cellulose fibers.Due to the extremely low hygroscopicity of the fiber or the non-obvious water-swelling effect, and the presence of water ACTS as a lubricant, the color fastness to wet friction of this kind of fabric is obviously better than that to dry friction.Therefore, it is not uncommon for certain fabrics to have better color fastness to wet friction than to dry friction.At this point, the selection of dye varieties, dye performance, dyeing and finishing process conditions, although will also have an impact on the color fastness to friction, but compared with the fabric structure and surface morphology and other physical factors, it is not very important.This happens mostly with dark products, such as black, red and navy blue.Of course, for fabrics such as corduroy, twill and paint prints, their color fastness to wet friction is usually level 2 or even lower under wet condition due to the dyestuffs and printing and dyeing process used by them, which is not better than their color fastness to dry friction.

3. Influence of reactive dye-chemical structure-during the experiment of color fastness to wet friction of cellulose fiber fabric dyed with reactive dye-there are mainly two factors that cause color transfer: (1) water-soluble dyes are transferred to the friction fabric during friction to make the original dye fade and stain the friction cloth; (2) The second is that some dyed fibers break during friction, forming tiny colored fiber particles and are transferred to the friction fabric, resulting in staining.The factors that may affect the color fastness to wet friction of reactive dyes are as follows: (1) the structure and characteristics of reactive dyes themselves; (2) The nature of the fabric; (3) Pre-treatment effect, fabric damage and surface finish, etc.; (4) Dyeing process and soaping effect after dyeing; (5) The solid color treatment effect after fabric dyeing; (6) Influence of finishing on dyed fabrics, etc.The results show that although there are some differences in the strength, stability and adhesion of the covalent bond between the reactive dyes and cellulose fibers with different chemical structures, there is no obvious difference in the effect on the color fastness to wet friction of dyed fabrics. When a dyed fabric is rubbed wet, the covalent bond formed between the dye and the fiber does not break and produce a floating color. And the dye that happens transfer is supersaturated normally, did not form covalent bond with fiber, the dye that relies on van der Waals force to produce adsorptive action only, namely so-called float color.

4. Influence of dyeing degree of reactive dyes -- The color fastness to wet friction of fabrics dyed with reactive dyes is closely related to the dyeing depth, that is, in the case of wet friction, the amount of color transfer has a close linear relationship with the dyeing depth.Excessive dyes can not be combined with fibers, but can only accumulate on the fabric surface to form floating color, which seriously affects the fabric's color fastness to wet friction.Under the wet condition, cotton fiber without special treatment will be swollen, friction force will increase, fiber strength will decrease, all of which create good conditions for the fracture, shedding and color transfer of colored fiber.

Therefore, proper pretreatment of cellulose fiber before dyeing, such as mercerization, singeing, cellulase polishing treatment, scouring, bleaching, washing and drying, can improve the surface finish and wool effect of fabric, reduce friction resistance, reduce floating color, and thus effectively improve the color fastness to wet friction.

5. Influence of softeners -- Improving the color fastness of reactive dyes by soft finishing.The softener has a lubricating effect and can reduce the friction coefficient, thus preventing the dye from falling off. Cationic softener can also form a anionic dye lake, dye is not easy to fall off.At the same time, the dye solubility decreases and the wet rubbing fastness can be improved.However, the softener with hydrophilic groups is not conducive to the improvement of wet rubbing fastness. In the process of production practice, the water-soluble groups of dyes can be closed by using color fixing agent to control the pH value of the finished color cloth, remove the floating color, improve the smoothness of the fabric, and thus improve the fabric's fastness to wet rubbing.Proper front drying can prevent the dye from "swimming". The factors to be paid attention to include the amount of alkali, steaming time, way of washing, adequate soaping, etc. The first two are closely related to the degree of hydrolysis of the dye, while the second two are directly related to the color of the dye.The dyed fabric, especially the long rolling dyeing, should go through sufficient washing, soaping and other processes to remove the floating color on the fiber surface and the unreacted and hydrolyzed dyes, so as not to affect the color fastness.

If we do not pay attention to the post-treatment of dyeing, it will cause very poor color fastness, and the color light will become dark. In the above factors affecting the color fastness to friction, the principles of action of each factor vary greatly and the degree of influence is also different. The problem of colour fastness may seem simple, but the factors involved are quite complex.

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