Color fastness to rubbing test method


Release time:

2018-12-22

The color fastness to rubbing test refers to the test in which the colored specimen is rubbed against a dry rubbing cloth and a wet rubbing cloth respectively, and then the degree of color staining of the rubbing cloth is evaluated.

The color fastness to rubbing test refers to the test in which the colored specimen is rubbed against a dry rubbing cloth and a wet rubbing cloth respectively, and then the degree of color staining of the rubbing cloth is evaluated. The test results are divided into 5 levels, with level 5 being the best and level 1 the worst. Although the test process is simple, it is the most basic color fastness assessment index for textile products, and it is one of the items that must be assessed by buyers in almost every country when they place orders. The technical conditions of friction fastness test standards in different countries are very similar, but there are some differences.

In the process of friction between textiles and other objects, the degree of color shedding or staining of the object being rubbed is affected by many factors. There are two ways of color shedding staining: one is the textile dye shedding or color loss, staining the surface of the friction object; the other is dyed fiber shedding, adhering to the surface of the friction object. In practice, dye shedding is the main reason for color staining.

Although there are some differences in the covalent bond strength and adhesion between reactive dyes of different chemical structures and cellulose fibers, the effects on the color fastness of wet rubbing of dyed fabrics are basically the same. When the dyed fabric is subjected to wet rubbing, the covalent bond formed between the dye and the fiber does not break and produce floating color. Transfer of dyes usually do not form covalent bonds with the fiber, but only by van der Waals force adsorption, that is, floating color. One of the main causes of color floating is the excessive amount of dye. In wet rubbing, the amount of color transfer is nearly linearly related to the depth of dyeing. When dyeing dark colors, the concentration of dyes used is higher, but should not exceed the saturation value too much. Because excessive dyestuff can't combine with fiber, it can only accumulate on the surface of the fabric and form floating color, which seriously affects the color fastness of the fabric during wet rubbing.

The directness and diffusivity of dyestuff also have close relationship with the rubbing fastness. Although the reactive dyestuff with high directness has high dyeing rate and color fixation rate, it has poor diffusivity, which makes it difficult to diffuse into the interior of fibers, resulting in floating color on the surface, and the hydrolyzed dyestuff is not easy to be washed away, and it is easy to be contaminated to the friction objects. The dyestuffs with good diffusivity are easy to enter into the fiber, which is conducive to the improvement of friction fastness, and at the same time, their washability is also better, and they are easy to diffuse out from the fiber. For some dyes with poor stability, especially those with fast diffusion, even if the unfixed dyes on the surface of the fabric are washed, the hydrolyzed dyes will diffuse out from the inside of the fibers again after placing for a certain period of time, making the soaping and rubbing fastness deteriorate.

The microstructure and morphology of different fibers are different, and the rate of dye diffusion and the degree of dye penetration are also different, so the fixation rate and distribution of dyestuff on different fibers are also different. If the fixation rate is high, the amount of hydrolyzed dyestuff is small, easy to wash away, and the rubbing fastness is better; the surface of the fiber is smooth, the organizational structure is flat and the rubbing factor is low, which can also improve the rubbing fastness. Several common organizational structure of the fabric, the friction factor of the size of the order: plain fabric> twill fabric> satin fabric. Certain thin and lightweight fabrics (synthetic fibers or silk fabrics〉, due to the fabric structure is relatively loose, dry friction, the sample in the pressure and friction under the action of the friction head will be followed by the movement of the friction head and part of the slippage, so that the friction resistance increases, and the friction efficiency is improved. However, when wet friction is performed, the situation is completely different. The hygroscopicity of such fibers is very low, the water expansion effect is not obvious, and the presence of water plays the role of lubricant, resulting in its wet friction fastness is significantly better than dry friction fastness. As for certain surface coarse sugar or abrasive velvet, hairy fabrics, in dry conditions, its surface roughness, hardness, friction resistance, dry friction color fastness decreased.

Fabric pretreatment processing on the impact of friction fastness is also great. Untreated cotton fibers in the wet state conditions will occur swelling, friction increases, fiber strength decreases, these are for the colored fiber breakage, shedding and color transfer to create the conditions. Therefore, appropriate pretreatment of cellulose fibers before dyeing, such as mercerization, burnishing, cellulase finishing treatment, etc., can improve the surface finish of the fabric and gross effect, reduce friction resistance, reduce floating color, thus effectively improving the color fastness to wet friction of the fabric.