Textile fabric color fastness testing

The color fastness of fabric (referred to as dyeing fastness) refers to the fading degree of color or printed fabric under the action of external factors (extrusion, friction, washing, rain, exposure, finish, seawater impregnation, saliva impregnation, water stains, sweat stains, etc.) in the process of using or finishing, which is an important index of fabric. Dyeing fastness good, fabric products in the finishing or use process is not simple color loss; dyeing fastness poor, there will be color loss, slightly color, or staining, etc., causing a lot of trouble.

Fabric dyeing fastness usually includes.

Soap wash resistance, friction resistance, finish light resistance, bleach resistance or oxidant resistance (reducer), ironing resistance, sweat resistance and sweat fastness of dyeing. Among them, soap washing resistance, friction resistance, light resistance, water resistance and sweat stain resistance are several dyeing fastness indicators that most buyers pay more attention to in actual production and trade.

1、The common problems of dyeing fastness of fabric products

In the daily sampling and consumer complaints, the common fabric dyeing fastness problems are as follows.

(1) sunlight fastness failed. Jacket workwear in the process of wearing, by the sun shine more parts of the color lightening or discoloration (generally the back and shoulder parts), and shine less or shine less places where the color does not change or change light, resulting in the original color consistency of the product color shades, can no longer continue to use.

(2) fastness to washing dyeing, fastness to soap dyeing and fastness to dry cleaning dyeing is not qualified. Advanced silk workwear, wool workwear, cotton workwear simple problems in this regard.

(3) Fastness to rubbing dyeing is not qualified. Fabric products in the process of use, because different parts of the product by the degree of friction is different, the degree of color loss is different. For example, the elbows of the tops and sleeves, collars and armpits are simple color loss. In addition, the hip and knee parts of the pants are also simple to lose color.

(4) sweat stain dyeing fastness failed. Mainly summer clothing or intimate underwear in the wear, by sweat impregnation and color loss.

2、The factors affecting the fastness of dyeing and improvement methods

Poor dyeing fastness of the product in the wearing process fading, will affect the other work clothes worn on the body, or in and other clothing when cleaning stained other clothing, affecting the beauty and taking performance; on the other hand, dyeing fastness good and bad is also directly related to human health and safety. Dye molecules and heavy metal ions on products with poor dyeing fastness may be absorbed by the human body through the skin and harm the skin, and even damage the health of the body.

The factors that affect the fastness of dyeing of fabrics are internal and external factors. Internal factors refer to the firmness of the bond between the dye and the fiber, while external factors refer to the external forces exerted on the product or the environmental conditions provided by external factors during its use. The external factors cannot be manipulated, so the producer has to make efforts to improve the dyeing fastness of the product itself. The following is a few solutions for your personal practical experience.

2.1 Selection of dyeing material

The choice of dyeing material is especially important for the fastness of dyeing of a product. If the choice of dyeing material is not suitable, then good auxiliaries, then good coloring process, there is no way to dye high quality dyeing fastness. Only after choosing the right dye, we can talk about the next step.

2.1.1 Selecting dyestuffs according to the characteristics of fibers

Different kinds of dyestuffs and fibers have different forms of bonding and different degrees of bonding firmness. After the type of dyestuff is determined, then choose the dyestuff with high coloring performance. For example, when dyeing wool fabric, the same strong acid dyestuff, domestic is not as good as imported strong acid dyestuff coloring performance, not only the color is not good, its bonding firmness is also not as good as the latter; or the same domestic strong acid dyestuff, different dyestuff and wool bonding fastness and color vividness is also different. For example, the fastness of dyeing wool yarn with weak acid dyestuff is higher than strong acid dyestuff; while cotton fabric or regenerated cellulose fiber fabric, both direct and reactive dyestuff can be used; silk fabric can be used in addition to weak acid dyestuff, some reactive dyestuff, but also individual direct dyestuff.

2.1.2 According to the color shade selection dyes

After determining the major categories of dyes, we must further determine which dyes to use according to the color system and depth of the dyed color. If there is deviation, then use other dyes to adjust the color; secondly, look at the dyeing fastness index of the chosen dyestuff itself. Dyestuff itself dyeing fastness is poor, through the process of more than half dyeing fastness can be improved; Third, to see whether the dyeing saturation can reach the depth of the required color. If you choose dyestuff with low dyeing rate, even if you can temporarily achieve the required high depth of color after finishing, the combination of dyestuff will not be strong and will fall off during use or finishing again.

2.1.3 Selecting dyestuff according to its own dyeing fastness grade

In the introduction of each dye, the color fastness grade of that dye is introduced. When selecting dyestuff, it is important to select dyestuff according to the color fastness grade required by the product, and the color fastness of the dyestuff should be similar to each other. For example, if the color fastness of the dyestuff itself is only 2~3, or even 1~2, then the good auxiliaries and coloring process can not dye the products with 4~5 color fastness. Because, the color fastness of dyestuff mainly depends on the bonding force between dyestuff and fiber, if the bond between the two is not strong, how much external force can not make them a strong bond, even if the color fixation has improved, but also can not withstand cleaning, friction and other external factors to destroy.

2.1.4 Dyeing rate of dyestuff on fiber

Different dyes present different dyeing rates, and the dyeing rate of the same dye is different under different coloring conditions. Therefore, the dyeing rate should be considered when choosing dyestuff, otherwise the dye will compete with each other, that is, one of the dyestuffs will occupy the dyeing position of the fiber in advance, so that other dyestuffs can only be dyed on the surface of the fiber and cannot form a solid bond with the fiber evenly, which will be destroyed first in the later process or in daily use. That's why some colors are different from the original color after the color drop. Therefore, when choosing dyestuffs, it is important to use dyestuffs that have similar dyeing rates on the fibers under the same conditions, as this will be particularly beneficial in the next step of the process.

2.1.5 Good compatibility between dyestuffs

Different dyes in the same class of dyes have different compatibility, the greater the compatibility value, the better the ability of dyes to color match each other. The greater the compatibility value, the better the ability of the dyes to match each other. There must be good compatibility between the dyes. It is good to use three primary colors for colors that are not simple to spell. The three primary colors are the three dyes that have good compatibility in each type of dyestuff and are also the three dyestuffs that can spell colors completely and positively. Therefore, it is good to use the three primary colors to match some strange colors that are difficult to dye, and don't use other dyes to spell hard in the finished amount, because it is simple to compete with other dyes, and it is simple to dye flowers.

2.1.6 Reduce the number of dyes needed

Dyestuff selection is, first of all, should choose the dyestuff with similar color to the required color, then use one or two dyestuffs to supplement the missing color of the main dyestuff, and should choose the dyestuff with the same color family, so that the dyed color is pure, complete, bright and full. Don't use four or five dyes to finish the color, that's not good to mix color, and not good to operate a large number of coloring. Moreover, although the color is right, but the dyed color is not bright and full, the dye can not be fully combined with the fiber, resulting in poor fastness of dyeing.

Soap-resistant dyeing fastness

1、Comparison of soap washing fastness to dyeing test methods

Soaping fastness to dyeing is one of the common fastness to dyeing assessment items. Soaping fastness refers to the fading degree of coloring fabric after soaping under the specified conditions, it contains two evaluation contents: fading of the original sample and white cloth staining.

Original fading is the coloring fabric fading before and after soaping; white cloth staining is white cloth and coloring fabric sewn together in a certain way, after soaping, because the coloring fabric fading and the white cloth staining situation. The degree of fading or staining should be tested under the specified finish source, with standard gray card rating, the result is divided into 5 levels, 5 levels for good, 1 level for poor.

2, dye structure, coloring and post-treatment process and soaping dyeing firmness relationship

Daily test, there is a considerable part of fabric products, including cotton, wool, polyester, nylon and its blended chemical fiber fabric fabric, as well as spandex-containing elastic fabric, to nylon and vinyl acetate fiber lining staining are in the 3 grade or below 3 grade.

Although the dyestuffs and printing and finishing processes used for different fiber materials vary, the problems that arise are quite similar. This is mainly related to the fabric surface floating color and the transfer of some colored fiber particles, so that is also associated with the variety of dyes used, the coloring process and the post-treatment process.

3, reactive dyestuff products soap dyeing fastness of good or bad decision on the unconsolidated dyestuff

Take reactive dyestuff as an example, theoretically speaking, because the dyestuff and fiber form a covalent bond, washing can not easily cause dye desorption, fading and bleeding, therefore, reactive dyestuff coloring products soap dyeing fastness decision on the number of unconsolidated dyestuff (hydrolyzed dyestuff and a small amount of unreacted dyestuff). If the hydrolyzed dyestuff is not removed by soaping, subsequent washing will result in constant color loss. Soap fastness is also related to the bonding stability of bonded dyes, and broken bond dyes will also occur in the wash.

Therefore, the factors affecting the soap dyeing fastness, the important is the dye structure and performance, followed by the coloring and post-dyeing treatment process. Reactive dyes have high fixation rate, or slow hydrolysis rate, and the amount of hydrolyzed dyes is less, and the amount of dyes to be removed by washing is also less. The unconsolidated dyestuff and hydrolyzed dyestuff have low directness, good water solubility, not easy to stain, and easy to wash out. While the dye concentration is high, the amount of residual dye, it is not easy to wash clean.

4、Soap fastness is also closely related to the coloring process

In addition, soap fastness is also closely related to the coloring process. Dye adsorption and diffusion is sufficient, the solid color rate is high, residual dyes and hydrolyzed dyes are less, easy to wash out. If the coloring process is reasonable, the covalent bond between dye and fiber is not easy to break during coloring and post-treatment, and the soaping fastness is better.

Fastness to friction dyeing

1、Comparison of fastness to rubbing dyeing test methods

Fastness to rubbing dyeing test refers to the test that the coloring specimen rubs with dry rubbing cloth and wet rubbing cloth respectively, and then evaluates the degree of rubbing cloth staining. The test result is divided into 5 levels, 5 good and 1 poor. Although the test process is simple, it is the basic fastness to dyeing assessment index of fabric products, and is one of the items that buyers from almost all countries must assess when placing orders. The technical conditions of the friction fastness test standards are particularly similar, but there are some differences.

2, the main factors affecting the friction fastness of dyeing and its manipulation measures

Fabric products and other objects in the process of friction, its color shedding or the degree of staining of the object being rubbed by many factors.

There are two ways of color shedding staining:

First, the fabric products on the dye off or color, staining the surface of the friction object;

Second, the color fiber off, adhering to the surface of the friction object.

3、In practice, dye shedding is the main reason for staining

Although different chemical structure of the reactive dyes and cellulose fibers form covalent bond strength and adhesion there is a definite difference, but the impact on the color fabric wet friction dyeing fastness is basically the same.

The covalent bonds formed between dyestuff and fiber do not break and produce floating colors when wet rubbing of colored fabrics is carried out. The transferred dye does not usually form a covalent bond with the fiber, but is only adsorbed by van der Waals forces, i.e. floating color.

Fastness to dyeing

1、Comparison of fastness to dyeing test methods

Finishing fastness test means that the fabric specimen and a group of blue wool specimens are exposed to the sun under the artificial finishing source according to the specified conditions, and then the two are compared for color change to evaluate the fastness of dyeing.

2、Ways to improve the fastness of dyeing

The mechanism of finish fading of dyestuff is particularly complicated, but it is mainly because the dyestuff is excited after drawing the finish, and a series of finish chemical reactions occur to destroy the structure, resulting in discoloration and fading. The fastness of the fabric to complete dyeing depends mainly on the chemical structure of the dye, as well as its aggregation state, bonding state and mixed color combination. Therefore, it is especially important to choose dyestuff reasonably.

3、According to the nature of the fiber and the use of fabric products to choose dyestuff

For cellulose fiber fabric products, we should use dyestuff with good antioxidant property; for protein fiber, we should use dyestuff with good anti-reduction property or containing weak oxidizing additives; for other fibers, we should choose dyestuff according to the effect on fading. In order to enhance the oxidation resistance of the azo group in the molecular structure of dyestuff, some strong electron-absorbing groups are usually introduced in the neighboring positions of the azo group during the synthesis of dyestuff, thus reducing the electron cloud density of the azo gas atoms.

Other, can also be in the azo group of the two neighboring positions to attract hydroxyl, the use of its coordination ability and heavy metal complex, thus reducing the azo group of hydrogen atom electron cloud density, and azo group to play a shielding role, and finally improve the dyes of the end of dyeing fastness.

4、Dye should be selected according to the color depth

A large number of tests have proved that the fastness of reactive dyes on cellulose fiber and the depth of the color are proportional to each other, that is, the deeper the color, the better the fastness of the dye. This is because the higher the concentration of the dye on the fiber, the greater the aggregation of the dye molecules, and the smaller the surface area of the same amount of dye in contact with air, moisture and finish, the lower the chance of the dye being finished oxidation.

Conversely, the lighter the color, most of the dyestuff in the fiber is highly dispersed state, the higher the chance of completion of the light, and finally make the fastness of the finished dyeing decreased significantly. Therefore, dyeing light-colored varieties, should use the dyestuff with high fastness. In addition, many finishing agents such as softener and anti-wrinkle finishing agent are added to the fabric, which will also reduce the fastness of the product. Therefore, we should choose dyestuffs that are not sensitive to these finishing agents.

5, should choose to use the dyestuff with good stability and compatibility color matching

Different dyes have different fading performance and even different fading mechanism. Sometimes, the presence of a dye will sensitize the fading of another dye. When color matching, should choose each other will not be sensitized, and can even improve the stability of the dyes, which is particularly important when dyeing dark varieties such as black.

One of the three primary colors fade too quickly, will soon lead to discoloration of the colored fiber or fabric, and the faded dye residue will also affect the stability of the other two dyes that have not faded. Reasonable manipulation of the coloring process, so that the dyestuff and fiber fully combined, complete amount to avoid hydrolysis dyestuff and unconsolidated dyestuff residue on the fiber, is an important way to obtain a higher fastness to dyeing.

Water/sweat fastness to dyeing

1、Comparison of water and sweat fastness dyeing test methods

Water resistance dyeing fastness reflects the fabric products in a certain water, pressure and temperature under the joint action, their own discoloration and staining of the lining fabric. When testing, the specimen and the lining fabric are fully wetted, placed in an oven at a certain temperature for a certain time under a certain pressure, taken out and dried, and evaluated for color change and staining grades. Discoloration and staining grade is divided into 5 levels, 5 good and 1 poor.


The fastness to perspiration dyeing is to reflect the color change of the fabric and the staining of the lining fabric under the joint action of pressure and temperature in different test solutions containing histidine. Using gray card to assess the color change of the specimen and the staining of the lining fabric, the results are divided into 5 levels, 5 levels of good, 1 level of poor.

2、Way to improve the fastness of water and sweat resistance dyeing

Improve the water resistance of the fabric, sweat resistance dyeing fastness, the main way is the reasonable choice of dyes, very should choose the high rate of solid color and good stability of dyes. Reasonable formulation and manipulation of the coloring process to strengthen the color fixation conditions, the formation of covalent bonds with high stability, can make the dye fully fixed. For example, in the less reactive dyestuff coloring can be used catalyst, or the use of appropriate color fixing agent, or the adoption of high temperature color fixation.



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