Summary of factors affecting the color fastness to rubbing of textiles

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Textile dyeing is a necessary production item in the textile industry. The colorful clothes worn by consumers can only be displayed after dyeing. When textiles are dyed, fading and fading will inevitably occur, and the dyeing of textiles and fading are more affected by external conditions.

Causes that affect the rubbing fastness of dyed fabrics
The color fastness to rubbing is one of the color fastness tests of textiles and one of the common inspection items in the trade process of textiles. It refers to the friction of dyed fabrics. The final degree of discoloration is an assessment of the dye’s resistance to mechanical friction, which is divided into dry friction and wet friction. The principle is to fix the textile sample of the specified size on the friction tester platform with a clamping device. Then rub it with a dry rubbing cloth and a wet rubbing cloth respectively, and then use the staining degree of the white cloth as the basis for evaluation. Compared with the standard gray sample card, it is divided into 5 levels. The higher the level, the better the rubbing fastness. The rubbing fastness Poor fabric can seriously affect its use. There are many factors that affect the color fastness of fabrics to rubbing. Several of them are analyzed below.

1. Influence of fabric surface morphology
Since unfixed dyes are the main reason for poor color fastness to rubbing, under dry conditions, for fabrics with rough or brushed or raised surfaces, and hard fabrics such as linen, For denim fabrics and pigment-printed fabrics, dry rubbing can easily remove dyes, paints or other colored substances accumulated on the surface of the fabric, and even cause some colored fibers to break and form colored particles, further reducing the color fastness to dry rubbing. For brushed or raised fabrics, the fluff on the surface of the fabric is at a certain angle with the surface of the friction cloth and is not parallel, which increases the friction resistance of the friction head during reciprocating motion, making this type of fabric more resistant to drying. Color fastness to rubbing is reduced.

2. Influence of the chemical structure of reactive dyes
When the cellulose fiber fabrics dyed with reactive dyes are tested for color fastness to wet rubbing, there are two main factors that cause color transfer:
First, water solubility The dye is transferred to the friction fabric during friction, causing it to fade as it is and stain the friction cloth;
The second is that the partially dyed fibers break during friction, forming tiny colored fiber particles and being transferred to the friction fabric , causing staining.

Therefore, the factors that may affect the color fastness of reactive dyes to wet rubbing include:
The structure and characteristics of the reactive dye itself;
The properties of the fabric;
The effect of pre-treatment, damage to the cloth and surface finish, etc. ;
Dyeing process and the effect of soaping after dyeing;
The effect of color fixation treatment after dyeing fabrics;
The influence of finishing of dyed fabrics, etc.

Research shows that although there are certain differences in the covalent bond strength, bond stability and adhesion between reactive dyes with different chemical structures and cellulose fibers, they have no impact on the color fastness to wet rubbing of dyed fabrics. Significant differences.
When dyed fabrics are wet rubbed, the covalent bonds formed between the dye and the fiber will not break and cause floating color. The transferred dyes are usually supersaturated dyes that do not form covalent bonds with the fiber and only rely on van der Waals forces to produce adsorption, which is the so-called floating color.

3. Influence of the degree of dyeing
Research has also proven that the color fastness to wet rubbing of reactive dye dyed fabrics is closely related to the depth of dyeing, that is, when wet rubbing is performed, the amount of color transfer is almost proportional to the dyeing depth. Among them, the supersaturation of the dye during dyeing is an important factor. When dyeing dark colors, the dye concentration used is higher, but it cannot greatly exceed the saturation value, because the excess dye cannot be combined with the fiber, but can only It accumulates on the surface of the fabric to form floating colors, which seriously affects the color fastness of the fabric to wet rubbing.

In addition, cotton fibers without special treatment will swell under wet conditions, increase friction, and decrease fiber strength. These create good conditions for the breakage, shedding and color transfer of colored fibers. Therefore, proper pre-treatment of cellulose fibers before dyeing, such as mercerization, singeing, cellulase polishing treatment, scouring, bleaching, washing, and drying, can improve the surface finish and wool effect of the fabric and reduce friction resistance. , Reduce floating color, thereby effectively improving the fabric’s color fastness to wet rubbing.

4. The influence of fabric structure
People have not paid too much attention to the influence of fabric structure and surface morphology of fabric on color fastness to rubbing. On the sample surface of light and thin fabrics (usually synthetic fiber or silk fabrics), due to the relatively loose structure of the fabric, when dry rubbing is performed, the sample will undergo friction with the movement of the friction head under the action of pressure and friction. Partial slippage increases friction resistance and improves friction efficiency.

But when wet rubbing is performed, the situation is completely different from that of cellulose fibers. Since the hygroscopicity of the fiber is extremely low or the water swelling effect is not obvious, and the presence of water acts as a lubricant, the color fastness to wet rubbing of this type of fabric is significantly better than the color fastness to dry rubbing, which is consistent with people �It is commonly believed that the color fastness to dry rubbing of textile products should be better than the color fastness to wet rubbing, which creates an obvious contrast and often causes people’s doubts. Therefore, it is not uncommon for certain fabrics to have better color fastness to wet rubbing than to dry rubbing. At this time, although the type of dye selected, the performance of the dye, the process conditions of dyeing and finishing, etc. will also have an impact on the color fastness to rubbing, compared with the physical factors such as the tissue structure and surface morphology of the fabric, it is It doesn’t seem very important anymore. Dyers Without Borders often discusses various fastness treatments.

Statistics show that most of these situations occur with dark-colored products, such as black, red, and navy blue. Of course, for fabrics such as corduroy, twill and pigment printing, under wet conditions, due to the dyes and printing and dyeing processes used, the color fastness to wet rubbing is usually level 2, or even lower, and No better than its color fastness to dry rubbing.

5. The influence of softeners
Improving the color fastness of reactive dye printing through soft finishing. Softeners have a lubricating effect and reduce the coefficient of friction, thus preventing the dye from coming off. Cationic softeners can also form lakes with anionic dyes, making the dyes less likely to fall off. At the same time, the lake reduces the solubility of the dye and improves the wet rubbing fastness.

But softeners with hydrophilic groups are not conducive to the improvement of wet rubbing fastness. In the production practice, fixatives can be used to block the water-soluble groups of dyes, control the pH value of the finished cloth, remove floating colors, improve the smoothness of the fabric, and thereby improve the wet rubbing fastness of the fabric. Proper pre-baking can avoid dye “migration”. Factors that need attention include the amount of alkali agent, steaming time, washing method, sufficient soaping, etc. The first two are closely related to the degree of hydrolysis of the dye, and the latter two are directly related to the floating color of the dye.

Dyeed fabrics, especially long-car pad dyeing, must undergo sufficient water washing, soaping and other processes to remove floating colors and unreacted and hydrolyzed dyes on the fiber surface, so as not to affect the color fastness. If you do not pay attention to the final dyeing process, Processing will result in poor color fastness and the color will become dull.

Summary
Among the above-mentioned factors that affect the color fastness to rubbing of fabrics, the working principles of each factor are very different, and the degree of influence is also different. The color fastness issue seems simple, but the factors involved are quite complex. Over the years, whether in the field of dye research and production or in the field of textile dyeing and finishing, people have invested a lot of manpower and material resources in efforts to solve the color fastness problem of textile products, and have made great progress. Various new Dyes, new processes and new additives are constantly emerging, but there are still many problems that need to be solved.

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