NEWS
Colour fastness of textiles
  • 2022-01-19 11:05:59

1.Color fastness to soap washing

1. Test method for colour fastness to soap washing

Soaping colour fastness is one of the most common assessment items.  Soaping color fastness refers to the degree of fading of colored fabric after soaping under specified conditions, which includes two evaluation contents: fading of original sample and staining of white cloth.  Original color fading refers to the fading of colored fabric before and after soaping;  White cloth stained with color is the white cloth and colored fabric in a certain way stitched together, after the soap, because of colored fabric faded white cloth stained with color.  The degree of discoloration or staining shall be tested under a specified light source using a standard gray card rating of 5, with 5 being the best and 1 being the worst.

2. Relationship between dye structure, dyeing and post-treatment process and color fastness to soaping

In daily tests, a considerable number of textiles, including cotton, wool, polyester, nylon and its blends, as well as elastic fabrics containing spandex, are stained at grade 3 or below for nylon and acetate fiber lining.  Although the dyes and printing and dyeing processes used for different fiber materials are different, the problems are quite similar.  This is mainly related to the transfer of cloth surface floating color and some colored fiber particles, so it is also related to the variety of dyes used, dyeing process and post-treatment process.

3. The soaps fastness of reactive dyes depends on unfixed dyes

Taking reactive dyes as an example, theoretically speaking, due to the covalent bond between dyes and fibers, washing cannot easily cause dye desorption, fading and coloration. Therefore, the color fastness of reactive dyes depends on the quantity of unfixed dyes (hydrolyzed dyes and a small amount of unreacted dyes).  If the hydrolytic dye soaping can not be removed, the subsequent washing will appear continuous fading.  The soaping fastness is also related to the bonding stability of bonded dyes.

Therefore, the most important factors affecting the color fastness of soaps are the structure and properties of dyes, by dyeing and post-dyeing processing.  Reactive dyes have high fixation rate, or the hydrolysis rate is slow, the amount of hydrolyzed dyes is less, and the amount of dyes to be washed away is also less.  Unfixed dyes and hydrolyzed dyes have low directness, good water solubility, not easy to stain and easy to remove.  And the dye concentration is high, the amount of residual dye, it is not easy to wash clean.

4. Soaping fastness is also closely related to dyeing process

In addition, soaping fastness is also closely related to dyeing process.  Sufficient adsorption and diffusion of dyes, high fixation rate, less residual dyes and hydrolyzed dyes, easy to wash.  The dyeing process is reasonable, the covalent bond between dye and fiber is not easy to break during dyeing and post-treatment, and the color fastness of soaping is good.


2.Color fastness to rubbing

1. Comparison of testing methods for color fastness to friction

The rubbing color fastness test refers to the test that the colored sample is rubbed with dry and wet rubbing cloth respectively, and then evaluates the rubbing cloth stain degree.  The test results are divided into 5 levels, with 5 being the best and 1 the worst.  Although the testing process is simple, it is the most basic index of color fastness assessment of textile products, and is almost one of the items that must be assessed when buyers place orders.  The technical conditions of testing standards of rubbing fastness in different countries are very similar, but there are some differences.

2. Main factors affecting rubbing colour fastness and their control measures

In the process of friction between textiles and other objects, the color shedding or the degree of staining to the object being rubbed is affected by many factors.  There are two ways to fall off the color stained with color: one is that the dye on the textile falls off or fades and is contaminated with the surface of the friction object;  Second, the dyed fibers fall off and adhere to the surface of the friction object.

3. The main reason for staining

Although the covalent bond strength and adhesion between reactive dyes with different chemical structures and cellulose fibers are different, their influence on the color fastness to wet rubbing is basically the same.  When dyeing fabric is wet rubbed, the covalent bond formed between dye and fiber will not break and produce floating color.  The transferred dyes usually do not form covalent bonds with the fibers, but rely only on van der Waals forces to produce adsorption, i.e., floating colors.

3.Color fastness to light

1. Test method for colour fastness to light

Light fastness test refers to the textile sample and a group of blue wool standard samples are exposed under artificial light source in accordance with the specified conditions, and then the two color contrast to evaluate the color fastness.

2. Ways to improve color fastness to light

The photofading mechanism of dyes is very complex, but the main reason is that dyes are activated after absorbing photons, and a series of photochemical reactions occur to destroy the structure, resulting in discoloration and fading.  The color fastness to light of textile mainly depends on the chemical structure of dye, its aggregation state, combination state and mixed color.

3. Dyes are selected according to fiber properties and textile uses

For cellulose fiber textiles, dyes with better oxidation resistance should be selected.  For protein fiber, should choose good reducibility or containing weak oxidation additives dyes;  Other fibers should be selected according to the effect of fading.  In order to enhance the photooxidation resistance of azo groups in the molecular structure of dyes, some strong electron-absorbing groups are usually introduced into the adjacent positions of azo groups during the synthesis of dyes, so as to reduce the electron cloud density of azo group gas atoms.

In addition, hydroxyl groups can also be induced in the two ortho positions of the azo group, and their coordination ability can be used to complex with heavy metals, so as to reduce the electron cloud density of the azo hydrogen atom, and the azo group plays a shielding role, and ultimately improve the light fastness of the dye.

4. Dyes should be selected according to the color depth

A large number of experiments have shown that the color fastness to light of reactive dyes on cellulose fibers is proportional to the depth of color, that is, the darker the color, the better the color fastness to light.  This is because the higher the concentration of dye on the fiber, the greater the concentration of dye molecules, the smaller the surface area exposed to air, water and light for the same amount of dye, and the lower the chance that the dye will be photooxidized.

On the contrary, the lighter the color, the dye on the fiber is mostly highly dispersed, the probability of exposure to light is higher, and finally the color fastness to light decreased significantly.  Therefore, dyed light varieties, should be selected to light fastness higher dye.  In addition, the addition of many finishing agents, such as softeners and anti-wrinkle finishing agents, can also reduce the light fastness of the product.  Therefore, dyes that are not sensitive to these finishing agents should be selected.

5. Dyes with good light stability and compatibility should be selected

Different dyes have different fading properties and even different photofading mechanisms.  Sometimes the presence of one dye sensitizes the fading of another.  Color, should choose mutual sensitization, and can even improve the light stability of the dye, which is particularly important in the dark variety such as black.

Fast fading of one dye in the three primary colors will soon lead to discoloration of dyed fibers or fabrics, and the fading residue will affect the photostability of the other two dyes that are not fading.  Reasonable control of dyeing process to fully combine dye with fiber and to avoid residue of hydrolyzed dye and unfixed dye on fiber is an important way to obtain high light fastness.

4.Color fastness to water/sweat

1. Test method for colour fastness to water and perspiration

The color fastness to water reflects the discoloration of textile and its adherence to the lining fabric under the combined action of certain moisture, pressure and temperature.  During the test, after the sample and the lining fabric are fully soaked, they are placed in the oven at a certain temperature for a certain time under a certain pressure. Then they are taken out and dried to evaluate the discoloration and staining series.  There are 5 grades of discoloration and staining, with 5 being the best and 1 the worst.

Color fastness to perspiration reflects the discoloration of textiles and their adherence to the lining fabric under the combined action of pressure and temperature in different test solutions containing histidine.  Gray card was used to evaluate the discoloration of the sample and the adhesion of the lining fabric. The results were divided into 5 grades, 5 is the best and 1 is the worst.

2. Ways to improve color fastness to water and sweat stains

The most important way to improve the color fastness of fabric to water and sweat is to choose dyes reasonably, especially dyes with high fixation rate and good stability.  Reasonable formulation and control of dyeing process, strengthening of fixation conditions, formation of covalent bonds with high stability, can make the dye fully fixed.  For example, when dyeing dyes with poor reactivity, catalyst can be selected, or appropriate fixing agent can be selected, or fixed color at a higher temperature.

5.How to test color fastness?

1. Color fastness to washing

The sample is sewn together with the standard stick lining fabric, washed, cleaned and dried, and washed under suitable temperature, alkalinity, bleaching and friction conditions, so that the test results can be obtained in a short time.  The friction is accomplished by rolling and impingement of a small bath ratio and an appropriate number of stainless steel beads, which are rated by gray cards and obtained by test results.

Different test methods have different temperature, alkalinity, bleaching and friction conditions and sample sizes, depending on test standards and customer requirements.  General washing color fastness is poor blue, blue, black red, navy blue and so on.

2. Dry cleaning color fastness

The color fastness is the same as washing, but washing is changed to dry cleaning.

3. Rubbing color fastness

The sample is placed on the rubbing fastness tester and rubbed with a standard rubbing white cloth at a certain pressure for a certain number of times. The dry rubbing colour fastness and wet rubbing colour fastness are required for each group of samples.  Color stains on standard friction white cloth are graded by gray card, resulting in a series of measured friction color fastness.  Both dry and wet rubbing tests are required for color fastness to friction. All colors on the sample should be rubbed.

4. Light fastness

When textiles are used, they are usually exposed to light, which can destroy the dyes and cause what is known as "fading", causing colored textiles to become discolored, generally light and dark, and some of them to change color. Therefore, it is necessary to test for color fastness.  The blue wool standard cloth with different fastness grades was exposed to sunlight under specified conditions. The blue wool standard cloth with different fastness grades was compared with the blue wool standard cloth to evaluate the light fastness. The higher the blue wool standard cloth with different fastness grades, the more light fastness the blue wool standard cloth was.

5. Color fastness to sweat stains

The samples were sewn together with standard pasted lining fabric and treated in perspiration solution, then clipped on the color fastness to perspiration tester, placed in oven at constant temperature, then dried, and rated with gray card to obtain test results.  Different test methods have different perspiration ratio, different sample size, different test temperature and time.

6. Color fastness to water stains

The sample treated with water was tested as above.

7. Chlorine bleaching fastness:

After washing the fabric in chlorine bleaching solution under certain conditions, the color change degree is assessed, which is the chlorine bleaching fastness.

8. Non-chlorine bleaching fastness

The colour fastness to non-chlorine bleaching is assessed after washing the fabric in a washing condition with non-chlorine bleaching.

9. Color fastness to pressing

The dry sample was covered with cotton lining fabric and pressed for a certain time in a heating device with specified temperature and pressure, and then the color change of the sample and the color staining of the lining fabric were evaluated with gray sample card.  Hot pressing color fastness to dry pressing, wet pressing, wet pressing, specific according to different customer requirements and test standards to select test methods.

Colour fastness test for textile clothing



Email: hello@utstesters.com

Direct: + 86 152 6060 5085

Tel: +86-596-7686689

Web: www.utstesters.com


Previous Next

Copyright © UTS International Co., Ltd

Contact Us