Factors Affecting the Wet Rubbing Fastness of Textiles and Improvement Measures
Release Time:
2013-08-20 20:30
Source:
China Textile Economic Information Network
Factors affecting the wet rubbing color fastness of textiles:
1. Dye performance
Some dyes with good water solubility, such as reactive dyes, contain groups with excellent water solubility, which facilitate dye dissolution and uptake during dyeing. However, during wet rubbing tests, the presence of water tends to cause reactive dye molecules to detach from fibers and dissolve in water, reducing the bonding between reactive dyes and fibers. Some dyes with poor water solubility, such as vat dyes, are mechanically applied to fibers in a suspension state during continuous padding processes. After reduction steaming, they become water-soluble dye leuco forms that penetrate fibers, then are oxidized and soaped to fix onto fibers. At this point, vat dye molecules revert to a non-water-soluble state. Therefore, fabrics dyed with vat dyes have better wet rubbing fastness due to the non-water-soluble nature of the dye on the fabric compared to those dyed with reactive dyes.
2. Color depth (dye concentration)
Under the same fabric, pretreatment, and dyeing process conditions, the deeper the color and the higher the dye concentration, the greater the concentration gradient of dye molecules between the tested fabric and the white rubbing cloth. This increases the likelihood of dye transfer to the white cloth during rubbing, resulting in poorer wet rubbing fastness.
3. Effect of loose dye
Loose dye includes hydrolyzed dyes and dyes that have not hydrolyzed but have reacted with fibers. These dyes are attracted to fibers by hydrogen bonds and van der Waals forces, with low affinity to fibers, and can easily detach from the fabric under slight external force. Therefore, loose dye is an important factor affecting the wet rubbing fastness of fabrics.
4. Effect of water quality
Using hard water for dyeing, especially for fixing solutions, introduces anions such as CO32- and OH-, which react with Ca2+ and Mg2+ to form insoluble substances like CaCO3 and MgCO3. These insoluble substances combine with dyes to form color precipitates that deposit on the fabric surface, greatly increasing friction during rubbing and reducing wet rubbing fastness. Additionally, Ca2+ and Mg2+ can react with some anions on dye molecules to form water-insoluble substances, weakening the hydrophilicity of dyes, making them less soluble and diffusible, and making loose dye harder to wash off during rinsing.
5. Fabric structure and surface smoothness
The fabric structure affects the smoothness of the fabric surface, which in turn determines the friction force experienced during rubbing tests, affecting rubbing fastness.
Another important factor affecting the wet rubbing fastness of fabrics is the surface smoothness. Fiber ends exposed on the yarn surface form a layer of fuzz on the fabric surface. During dyeing and finishing, this fuzz is continuously subjected to friction and washing, weakening its adhesion to the fabric. Under external force, some short fuzz detaches from the fabric and stains the white cloth. In actual production, brushed fabrics have rubbing fastness 0.5 to 1 grade lower than mercerized fabrics.
What measures can be taken to improve wet rubbing fastness?
1. Selection of greige fabric
For greige fabrics of the same variety and specification used for dyeing, differences in yarn quality and weaving methods can cause variations in wet rubbing fastness of dyed fabrics processed under the same conditions. Therefore, it is best to select greige fabrics with excellent yarn quality, uniform yarn count, and smooth fabric surface.
2. Pretreatment process
The smoother the fabric surface, the higher the wet rubbing fastness. Therefore, singeing should be clean, and colored fiber particles should be minimized. The pressure and temperature during scouring and bleaching should be uniform to ensure even fuzz effect and whiteness, facilitating dye diffusion and penetration.
3. Dye selection and dyeing process
Choose dyes with higher leveling ability and less loose dye. When blending colors, try to select dyes of the same category and from the same manufacturer, with similar compatibility values. During dye solution preparation, soft water should be used as much as possible, with softening agents added if appropriate, and some penetrants can be added to improve dye penetration. During dyeing, control the fabric surface pH between 4.0 and 7.5 to prevent strong alkalinity from damaging the bond between dye and fiber, which would reduce wet rubbing fastness.
The soaping process should remove loose dye as much as possible by increasing washing times and water flow. Neutral detergents should be used to prevent alkaline detergents from causing dye hydrolysis again.
4. Post-treatment
To improve rubbing fastness after dyeing, a fixing post-treatment should be performed. There are two types of post-treatments: one is cationic fixing agents, which use large molecular weight quaternary ammonium cations to bind with dye anions, blocking their water-soluble groups, thereby reducing dye water solubility and improving wet rubbing fastness, though this often reduces light fastness; the other is wet rubbing fastness enhancers, mostly polyethylene emulsions and special amino-organosilicone softeners, which form crosslinked films on the fabric surface to reduce surface friction and improve wet rubbing fastness.
Improving the wet rubbing color fastness of dyes is a comprehensive issue that must be controlled from all aspects including greige fabric selection, pretreatment, dye selection, and dyeing process.
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