Color fastness is one of the important quality indexes of textiles. The so-called color fastness refers to the degree to which the color of a dyed textile remains firm under physical and chemical effects, that is, the degree of firmness of the color of a dyed textile under external influence becomes the color fastness. The color change of the sample after the test, and the rating grade of the white cloth dyeing degree indicates the color fastness.

Color fastness Among the various items, the most commonly used color fastness are color fastness to friction, color fastness to sweat, color fastness to washing, color fastness to light, color fastness to water, color fastness to brushing, color fastness to weather, etc.

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Color fastness to friction is one of the inspection items of textile color fastness, and also one of the most common inspection items of textile in the process of trade. It refers to the ability of textile color to resist friction, which can be divided into dry friction and wet friction.

Its principle is to rule the sample size of the textile samples with clamping device on friction tester platform, then respectively with a dry friction cloth and cloth of a wet friction friction, finally with white cloth dipped in color degree evaluation basis, as reference standard of the grey CARDS, is divided into five grades, the rank, the greater the better said rubbing fastness, rubbing fastness of fabric will seriously affect its use.

Dry friction test

Put a piece of (50×50) mm friction cloth (standard white cotton cloth) under the standard atmosphere (temperature 20℃±2℃, humidity 65%±4%), adjust the humidity (more than 4 hours) and then put it flat on the friction head, so that the direction of the friction cloth is consistent with the allowed direction of the friction head. The running speed is a reciprocating friction cycle per second, a total of 10 cycles of friction. The friction motion on the sample was (104±3) mm, and the downward pressure applied was (9±0.2) N. After completing the whole 10 cycles, the friction cloth was removed, humidified (more than 4 hours), and any excess fibers on the friction cloth that might affect the rating were removed. As shown in figure:

Wet friction test

After weighing a piece of friction cloth, completely immersed in distilled water, take out, re-weighing friction cloth, ensure that the moisture content of friction cloth reaches 95%-100%, and then the operation method with dry friction.

A review of the level

Finally, we need to take the moistened friction cloth after friction to the rating room in the standard light source box, and use the gray sample card to evaluate the color staining level of the friction cloth. (Note: Three layers of friction cloth are placed on the back of each evaluated friction cloth.) As shown in the figure below:

Common standard

Common standards for color fastness to friction are GB/T 3920 -- 2008, AATCC 8 -- 2007, AATCC 116 -- 2010 and JIS L 0849 -- 2004. Let's look at the similarities and differences between the four criteria in the table below.

As can be seen from this table, different testing standards have different requirements on the size of sample cloth. When the customer prepares the sample cloth, if the test sample is fabric or carpet, prepare two sets of samples with the size not less than 50 mm× 140mm, two pieces for each group. (For sampling, one fabric is parallel to the warp and the other to the weft.) Another sampling method is to sample the length direction of the sample at a certain Angle with the warp and weft direction of the fabric.

If it is a lint fabric and the lint is easy to identify, the lint direction should be consistent with the length of the fabric when the sample is cut. Under normal circumstances, the national standard and European standard take a piece of longitude and latitude, while the American standard adopts a 45 degree Angle.

If the fabric under test is yarn, it shall be woven into fabric with the sample size not less than 50 mm× 140mm, or the yarn shall be wound parallel to the board with the same sample size along the length direction of the board, and evenly spread in a flat layer.

Influencing factors of color fastness to friction

1 The influence of fabric surface morphology

Because the dye fixation is the main cause of friction fastness difference, under the condition of dry, the 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 form coloured particles, The color fastness to dry rubbing is further decreased. For the wool or wool fabric, the lint on the surface of the fabric and the surface of the friction cloth show a certain Angle, which is not parallel, so that the friction resistance of the friction head in reciprocating movement increases, and the color fastness to dry friction of this kind of fabric decreases.

2 The influence of fabric structure

On the surface of light and thin fabric (usually synthetic fiber or silk fabric), due to the relatively loose fabric structure, the sample will partially slip with the movement of the friction head under the action of pressure and friction force during dry friction, thus increasing the friction resistance and improving the friction efficiency. But when it comes to wet friction, the situation is completely different from that of cellulose fibers.

The COLOR FASTNESS TO WET RUBBING IS BETTER THAN THAT TO DRY RUBBING BECAUSE THE MOISTURE ABSORPTION OF THE FIBER IS very LOW OR THE WATER swelling effect is not obvious, and the presence of water acts as a lubricant.

Therefore, it is not uncommon for certain fabrics to have better colour fastness to wet rubbing than to dry rubbing. At this time, the selected dye varieties, dye properties, dyeing and finishing process conditions, although 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 darker products, such as black, red and navy blue. Of course, for corduroy, twill and paint printing fabrics, the color fastness to wet rubbing is usually 2 or even lower, not better than the color fastness to dry rubbing, because of the dye and printing process used in the wet condition.

3 The influence of chemical structure of reactive dyes

In the experiment of color fastness to wet rubbing of cellulose fiber fabric dyed with reactive dyes, there are two main factors that cause color transfer. One is that the water-soluble dyes are transferred to the rubbing fabric during friction, so that the original samples fade and the rubbing cloth is stained with color. Second, part of the dyed fiber breaks during friction, forming tiny colored fiber particles and are transferred to the friction fabric, resulting in stained.

The following factors may affect the color fastness of reactive dyes to wet rubbing: the structure and characteristics of reactive dyes themselves; The nature of the fabric; Pretreatment effect, cloth damage and surface finish, etc.; Dyeing process and the effect of washing after dyeing; Color fixing effect after fabric dyeing; The influence of finishing after dyeing fabric.

The RESULTS SHOW THAT ALTHOUGH THERE ARE SOME DIFFERENCES IN THE STRENGTH, STABILITY AND ADHESION OF coVALENT BONDS FORMED BETWEEN REACTIVE DYES AND CELLULOSE FIBERS WITH DIFFERENT chemical STRUCTURES, there IS no significant difference IN THE influence on the color FASTness to wet friction of dyed fabrics. When the dyed fabric is rubbed wet, the covalent bond formed between the dye and the fiber will not break to produce floating color. The dye transferred is usually supersaturated, does not form a covalent bond with the fiber, only by van der Waals force and produce adsorption of dye, that is, the so-called floating color.

4 Influence of dyeing degree of reactive dyes

The color fastness to wet rubbing of fabrics dyed with reactive dyes is closely related to the depth of dyeing, that is, the amount of color transfer has a good linear relationship with the depth of dyeing during wet rubbing. Excessive dye can not be combined with the fiber, but can only accumulate on the surface of the fabric and form floating color, which seriously affects the color fastness of the fabric to wet friction.

Cotton fibers without special treatment will swell, increase friction and decrease fiber strength under wet conditions, which create good conditions for the breakage, shedding and color transfer of colored fibers. Therefore, appropriate pretreatment of cellulose fiber before dyeing, such as mercerizing, burring, cellulase polishing treatment, scouring, bleaching, washing, drying, can improve the surface finish and wool effect of fabric, reduce friction resistance, reduce floating color, so as to effectively improve the color fastness of fabric to wet friction.

5 The effect of softener

Improve color fastness of reactive dyes printing by soft finishing. The softener lubricates and reduces the coefficient of friction, thus preventing the dye from falling off. Cationic softener and anionic dyes can also form lake, dye is not easy to fall off. At the same time, the lake makes the dye solubility decrease, can improve the wet rubbing fastness. But the softener with hydrophilic group is not conducive to the improvement of wet rubbing fastness. In the process of production practice, we can use color fixing agent to block the water-soluble group of the dye, control the pH value of the finished color cloth, remove floating color, improve the smoothness of the fabric, so as to improve the fastness of the fabric to wet friction. Proper pre-drying prevents the dye from "swimming". The factors that need to be paid attention to are the dosage of alkali agent, steaming time, washing method, sufficient soap, etc. The former two are closely related to the degree of dye hydrolysis, and the latter two are directly related to the floating color of the dye.

The dyed fabric, especially the long car pad dyeing, should undergo sufficient washing, soap washing and other processes to remove the floating color and unreacted and hydrolyzed dyes on the fiber surface, 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.

Among the above factors affecting the color fastness of fabric to friction, the principle of action of each factor is very different, and the degree of influence is also different. The color fastness problem may seem simple, but the factors involved are quite complex. Over the years, both in the field of dye research and production, or in the field of textile dyeing and finishing, people spend a lot of manpower and material resources, efforts to solve the problem of the color fastness of textile products, and made great progress, all kinds of new dyes, new technology and new additives, but still a lot of problems, needs to be solved.