Color Fastness

Also known as color fastness, color fastness. Refers to the resistance of the color of a textile to various effects during processing and use. The fastness grade is assessed according to the discoloration of the sample and the staining of the unstained taped fabric.

Textiles are subjected to various external effects such as illumination, washing, ironing, sweat stains, friction and chemical agents in the process of use. Some printing and dyeing textiles are also subjected to special finishing, such as resin finishing, flame retardant finishing, sanding washing and wool grinding, which requires the color of printing and dyeing textiles to maintain a certain relative fastness.

Factors influencing color fastness:

The so-called color fastness (referred to as color fastness) refers to the fading degree of the dyed fabric under the action of external factors (extrusion, friction, water washing, rain, exposure, light, sea water impregnation, saliva impregnation, water impregnation, sweat impregnation, etc.) during use or processing. It is an important index of the fabric. The most commonly used are washing resistance, light resistance, friction resistance and sweat stain resistance, ironing resistance, weather resistance, etc.

In practice, mainly according to the product and end use of product standards to determine the test items, such as wool textile products specified in the standard must be testing the fastness to sunlight, knitted underwear, of course, the fastness to perspiration, to test and outdoor textiles (such as sunshade, light box cloth, canopy cover material) is to detect the weather fastness, of course.

Including: color fastness to soap washing (sample), color fastness to rubbing, color fastness to chlorine water, color fastness to non-chlorine bleaching, color fastness to dry cleaning, color fastness to actual washing (garments, fabrics), color fastness to sweat, color fastness to water, color fastness to light, color fastness to sea water, color fastness to saliva.

How to test color fastness?

1. Color fastness to washing

The sample is stitched together with the standard lining fabric, washed, washed and dried, and washed under suitable temperature, alkalinity, bleaching and friction conditions to obtain test results in a relatively short time. During the friction is through a small bath ratio and the appropriate number of stainless steel beads roll, impact to complete, with a gray card rating, the test results.

Different test methods have different temperatures, alkalinity, bleaching and friction conditions and sample sizes, which should be selected according to the test standards and customer requirements. Generally, the color fastness of water washing is poor, such as Cuilan, Yan Lan, black bright red, blue, etc.

2, dry cleaning color fastness

Same color fastness as washing, only washing to dry cleaning.

3, color fastness to friction

Put the sample on the friction fastness meter and rub it with a standard friction white cloth at a certain pressure for a certain number of times. Each group of samples shall be tested for dry rubbing color fastness and wet rubbing color fastness. Colour stained on standard friction white cloth is graded by a grey card. The grade obtained is the measured rubbing colour fastness. The color fastness to rubbing requires both dry and wet rubbing tests, and all colors on the sample should be rubbed.

4, color fastness to sunlight

Textiles are usually exposed to light when they are used. Light can destroy the dyes and result in what is known as "fading", which makes the colored textiles become discolored. Generally, they become lighter or darker, and some of them also change their color light. Namely, the sample and blue wool standard cloth with different fastness series are placed together under the specified conditions for sun exposure. The sample and blue wool cloth are compared to evaluate the color fastness to light. The higher the blue wool standard cloth series, the more light resistant it is.

5. Color fastness to sweat stains

The sample is stitched together with the standard pasted fabric, processed in sweat stain solution, clamped on the color fastness tester to sweat stain, put in the oven at a constant temperature, and then dried, and graded with gray card to get the test results. Different test methods have different sweat stain ratio, different sample size, different test temperature and time.

6, water stains color fastness

Treat the sample with water as shown above.

Color fastness to chlorine bleaching: after washing the fabric in chlorine solution under certain conditions, the color change degree is assessed. This is the color fastness to chlorine bleaching.

7, non-chlorine bleaching color fastness

After washing the fabric with non-chlorine bleaching condition, the color change degree is assessed, which is the non-chlorine bleaching color fastness.

8, pressing color fastness

After the dry sample is covered with cotton pasted fabric, it is subjected to pressure 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 pasted fabric are evaluated by the gray sample card. The color fastness of hot pressing is dry pressing, damp pressing and wet pressing. The test method should be selected according to different customer requirements and test standards.、

Types of colour fastness tests and analysis of colour fastness

The nature or degree of variation in dyeing status can be indicated by color fastness.

The dyeing fastness of fabric is related to the type of fiber, yarn structure, fabric structure, printing and dyeing method, dye type and external force.

The test of color fastness generally includes color fastness to light, weather, washing, rubbing and perspiration, etc. Sometimes there are some special requirements for color fastness according to different textiles or different use environments.

Usually, the color fastness test is the degree of color change of the dye and the degree of sticking to the lining. The color fastness rating is Grade 5 except Grade 8 for the color fastness to light. The higher the series, the better the color fastness.

1, sun fastness

Sunfastness is the degree to which colored fabrics change color when exposed to sunlight. The test method is to compare the fading degree of the sample after simulated sun exposure with the standard color sample. It is divided into 8 grades, 8 grades are good grades, and 1 grades are the worst. The fabric with poor insolation fastness must not be insolated for a long time below sunshine, it is appropriate to dry in ventilated place.

2, washing fastness

Washing or soap-washing fastness refers to the degree of color change of dyed fabric after washing with detergent. Gray grading sample card is usually used as the assessment standard, which depends on the color difference of the original sample and the sample after fading. There are five grades of washing fastness, with 5 being the best and 1 the worst. Fabrics with poor washing fastness should be dry cleaned. If wet washed, double attention should be paid to washing conditions, such as washing temperature should not be too high or time should not be too long.

3, friction fastness

Friction fastness refers to the color loss of dyed fabric after friction, which can be dry friction and wet friction. The friction fastness is evaluated by the color staining degree of white cloth, which is divided into 5 grades. The greater the value, the better the friction fastness.

4. Perspiration fastness

Perspiration fastness refers to the discoloration of dyed fabric after a small immersion in sweat.

5. Ironing fastness

The degree of discoloration or discoloration of a dyed fabric during ironing.

6, sublimation fastness

Refers to the degree of sublimation of the dyed fabric during storage. The color fastness of normal fabric is generally required to reach 3-4 grade in order to meet the needs of wearing.

Methods to improve color fastness

The factors affecting the color fastness of textiles are mainly divided into internal factors and external factors. Internal factor refers to the firmness of the combination of dye and fiber, and external factor refers to the external force or environmental conditions provided by external factors during the use of the product. External factors cannot be controlled, so manufacturers must strive to improve the color fastness of the product itself.

Dyeing material selection: the color fastness of a product, the choice of dyes is very important. If the selection of dyes is not appropriate, no matter how good the additives, no matter how good the dyeing process, there is no way to dye high quality color fastness. Only when the right dye has been chosen can we talk about the next step.

(1) choose the dye according to the characteristics of the fiber

Different types of dyes and fibers have different binding forms, and the firmness of the bond is also different. After the dyestuff type is determined, the dyestuff with high dyeing performance is selected again. For instance, when dyeing wool fabric, it is strong acid dyestuff likewise, home-made dyestuff dyeing performance is good as the strong acid dyestuff of import, not only colour and lustre is bad, the firm degree of its union is not as good as the latter also; Or the same domestic strong acid dyes, different dyes and wool binding fastness and dyeing brightness are also different. For example, the color fastness of wool yarn dyed with weak acid dyes is higher than that of strong acid dyes. For cotton fabrics or regenerated cellulose fibers, either direct dyes or reactive dyes can be used. Silk fabrics can be used in addition to weak acid dyes, some reactive dyes, but also some direct dyes.

(2) choose the dye according to the color

After determining the major types of dyes, it is necessary to further determine the specific use of which dyes according to the color and depth of the dyed color. *, try to choose the color light and the desired color close to the dye, if there is a deviation, then use other dyes color. Second, look at the color fastness index of the dye itself. The dye itself color fastness is poor, through the process can improve the color fastness of half stage. Third, see if the dye saturation can reach the desired depth of color. If a dye with a very low dyeing rate is selected, even if the dye can be temporarily processed to achieve the desired high depth of color, the combination of the dye will not be strong and will fall off during use or reprocessing.

(3) select dyes according to their own color fastness series

In the introduction of each dye, there is a description of the dye fastness series. When selecting dyes, dyes must be selected according to the color fastness series required by the product, and the color fastness of the matching dyes should be similar. For example, the dye itself can only reach 2~3 levels of dye fastness, or even 1~2 levels, no matter how good the additives and dyeing process can dye 4~5 levels of dye fastness products. Because the dye fastness mainly depends on the binding force between the dye and the fiber, if the bond between the two is not strong, how much external force can not make them firmly combined, even if the solid color after some improvement, also can not withstand washing, friction and other external factors.

(4) Dyeing rate of dye on fiber

Different dyes show different dyeing rates, and under different dyeing conditions, the same dye dyeing rate is also different. So to consider when choosing the dye uptake rate, otherwise there will be a race between dye dyeing phenomenon, that is one of the dye fiber dyeing position ahead of the other dye dyeing only on the surface of fiber, not evenly with the combination of fiber form strong bond, thus in the process or daily use is first destroy. This is why some colors fade and appear to be completely different from the original color. Therefore, the dyes must be selected under the same conditions, and the dye rate of the fiber is similar, which is also very beneficial to the formulation of the next process.

(5) there should be good compatibility between dyes

Different dyes in the same kind of dye, its compatibility is different, the greater the compatibility value, the better the ability of the dye to match each other. There must be good compatibility between the matching dyes. Not easy to spell the color is best to use three primary colors. Trichromatic is the best compatibility of each type of dye, but also can spell the color light of the most complete, the most positive three dyes. Therefore, some of the more difficult to dye strange colors to use the three primary colors to match color, try not to use other dyes hard work, easy to appear race dyeing phenomenon, and dye flowers. 2.1.6 Minimize the number of dyes needed When selecting dyes, first of all, dyes with similar color light should be selected, and then one or two dyes should be used to supplement the lack of color light of the main dyes, and the dyes should be selected to belong to the same color system, so that the color dyed is pure, bright, gorgeous and full. Try not to use four or five kinds of dyes to color, it is not good to color, and not good to operate a large number of dyeing. And, although the color is on, but the dyed color light is not bright, not full, the dye can not be fully combined with the fiber, resulting in poor color fastness.

Selection and use of auxiliaries

(1) choose the appropriate auxiliary agent

After determining the variety of dyes, the choice of auxiliaries is also very important. Generally, as far as possible to choose auxiliaries with dyes, if the conventional use of common dyes, we should focus on the determination of the amount of auxiliaries and the use of methods. For deep colors, dyes are not easy to absorb, can be added in batches of additives, can improve the absorption rate, can also improve the fastness of dye adsorption, play a role in fixing the color.

(2) minimize the amount of retarding agent

The retarder of dyeing effect should be reduced as far as possible, otherwise it will have the effect of stripping. On the one hand, it will reduce the dyeing rate, on the other hand, it will weaken the binding force of dye and fiber, so that the color fastness is poor. For the color which is easy to dye the flower, the levelling effect can be achieved by adjusting the dye and heating rate.

(3) the selection of fixing agent

The use of fixing agent will greatly improve the dyeing fastness of dyes, generally at least 0.5~1 level can be improved, but the choice of fixing agent should consider the fastness of dyes at the same time, rather than just look at individual projects. For example, when reactive dyes are treated with cationic low molecular or polyamine fixers, the fabric's wash fastness is at grade 4~5, but its sun fastness will be reduced. Fixation must strictly control the amount of fixing agent, fixing temperature and fixing time.

(4) Soaping and washing

When soaping and washing, it is necessary to wash thoroughly and ensure the temperature and time of washing, otherwise, the floating color on the surface of the fabric will fade in use.

(5) the use of softeners

In order to make the product get plump soft feel, to add softener treatment. Softeners are cationic, anionic, non-ionic and silicone. Softener is a process after the end of the dyeing process, the dye and softener further reaction, it is possible to reduce the color fastness, especially the use of silicone softener after acid dye dyeing, in the soft treatment will even return part of the dye, so that the color slightly lighter. Therefore, the amount of softener should be just right when soft processing, otherwise, it will not only feel sticky, but also affect dyeing.

Conclusion:

There are many factors that affect the dyeing fastness of textiles. For the internal factors, the production process should be in place to ensure that the products can have excellent color fastness index and meet the requirements of daily use and reprocessing. For external factors, we must pay attention to washing temperature, detergent and washing method, friction strength, exposure time and other factors that can reduce color fastness, so that the product can be better used.