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Color fastness of textiles to sunlight



The color fastness of textiles to sunlight has attracted more and more attention at home and abroad. At present, my country’s textile industry product standards, especially t…

The color fastness of textiles to sunlight has attracted more and more attention at home and abroad. At present, my country’s textile industry product standards, especially the new standards promulgated in recent years (except underwear standards), all use light and color fastness as one of the assessment standards. For example, the silk product standards previously promulgated by our country did not stipulate the assessment of light fastness, but the promulgated standards have used the light fastness of elastic silk as an assessment indicator. In the product standards of chemical fiber fabrics and cotton fabrics, color fastness to light is also used as an important assessment indicator. Some product standards even use color fastness to light as an assessment indicator.

Note

In the context of new requirements and standards for color fastness to sunlight at home and abroad, Chinese textile companies must understand and master the testing standards and technical requirements for color fastness to sunlight to ensure product quality. This article discusses the color fastness to sunlight from various aspects such as testing standards and technical parameters.

Sunlight color fastness tester Related Standards

1. my country’s current effective test method standards for sunlight color fastness testers

Light fastness: Sunlight refers to sunlight exposure under specified conditions without being exposed to rain, and then the light fastness is evaluated with reference to the blue wool standard.

Color fastness to artificial light: Xenon arc refers to exposure under specified conditions under an artificial light source equivalent to sunlight, and then evaluating the color fastness to light with reference to the blue wool standard.

Weather color fastness: Outdoor exposure refers to exposure in the open air under specified conditions without any protection, and then comparing it with the blue wool standard to evaluate its color fastness.

Color fastness to artificial weathering strong>: Xenon arc refers to spraying and exposing in a xenon lamp tester under specified conditions, and then comparing it with the blue wool standard to evaluate the color fastness.

For composite color fastness to light and perspiration, the sample treated with sweat is exposed to the sun in the instrument, and then its light fastness and composite color fastness to light and perspiration are evaluated, and its sensitivity to light is determined. Among them, xenon arc is a commonly used standard for color fastness to artificial light. Most textiles in my country are tested according to the method in this standard when assessing the color fastness to light.

2. American sun color fastness Tester related standards
Light fastness , suitable for interior textiles. Weather resistance of fabrics: Xenon arc, suitable for outdoor textiles. Weather resistance: Solar carbon arc. Among them, light color fastness is a widely used standard for light stability of textiles.

Its main measurement range:

1. Sunlight fastness of dye Test: Conduct a dye fastness test under light (wavelength 380nm ~ 750nm) and certain temperature and humidity conditions

2. Dye climate fastness test : Determine the climate fastness of dyes under the combined influence of light (wavelength 380nm ~ 750nm) and a certain temperature, humidity and rain

3. Weather fastness of textiles, etc. Test: Under the combined action of light (wavelength: visible light 380nm ~ 750nm; ultraviolet light 300nm ~ 380nm) and climate conditions, the weather fastness of textiles, etc. is measured.

The best way to test light fastness

In all color fastness tests, testing the reaction of fabrics to light may be one of the important test items. Of course, how fabrics perform in laundering, dry cleaning, rubbing, sweat absorption, and subsequent exposure to different types of solutions is crucial information for manufacturers. However, because fabrics are sensitive to light and difficult to predict, accurate and reliable testing is critical.

For many manufacturers, light fastness testing is an important part of R&D and quality control. However, it is also one of the more difficult tests to master. Because most materials take months or even years to respond to sunlight, it is not feasible to test fabrics under natural light in real-world applications. What’s more, how many R&D departments are willing to wait patiently?

Many manufacturers choose laboratories for testing. They simulate natural light to speed up the testing process. The technology used successfully is the xenon long arc radiation method. This only reliable method of simulating and recreating the natural light spectrum uses a variety of filters to reproduce specific optical conditions.

Light fastness testing is not as simple as just placing the fabric under a specific light source to observe its performance. Temperature and humidity must also be taken into account, as they have a greater impact on how fabrics react to light. Therefore, the light fastness tester must be able to control these environmental factors, that is, create corresponding environmental conditions for each test and maintain them constant during the entire process.

In addition, if a certain fabric is used outdoors, weather factors, especially rainy days, are another issue that must be considered. Therefore, the equipment must include a water sprinkler system that simulates rainy weather, as well as simulating climatic conditions in different parts of the world.

How to improve light fastness

The photofading mechanism of dyes is very complex, but the main reason is that the dye is excited after absorbing photons, and a series of photochemical reactions occur to destroy the structure, resulting in discoloration and fading. The light fastness of textiles mainly depends on the chemical structure of the dye, as well as its aggregation state, combination state and mixed color matching. Therefore, the rational selection of dyes is very important.

First,Select dyesaccording to fiber properties and textile uses. For cellulose fiber textiles, dyes with better oxidation resistance should be selected; for protein fibers, dyes with better resistance to reduction or containing weak oxidizing additives should be used; for other fibers, dyes should be selected based on their impact on fading. In order to enhance the photooxidation stability of the azo group in the dye molecular structure, during the dye synthesis process, some strong electron-withdrawing groups are usually introduced at the ortho-position of the azo group, thereby reducing the electron cloud density of the nitrogen atom of the azo group. In addition, hydroxyl groups can also be introduced into the two ortho-positions of the azo group, and their coordination ability can be used to complex with heavy metals, thereby reducing the electron cloud density of the hydrogen atoms of the azo group and shielding the azo group, ultimately improving the dye quality light fastness.

The second should be selected according to the color depth Dyes. A large number of tests have proven that the light fastness of reactive dyes on cellulose fibers is directly proportional to the depth of the dye, that is, the darker the color, the better the light fastness. This is because the higher the concentration of the dye on the fiber, the greater the aggregation of the dye molecules, the smaller the surface area of ​​the same amount of dye exposed to air, moisture and light, and the lower the chance of the dye being photo-oxidized. On the contrary, the lighter the color, the dye is mostly highly dispersed on the fiber, and the probability of being exposed to light is higher, resulting in a significant decrease in light fastness. Therefore, when dyeing light-colored varieties, dyes with higher light fastness should be used. In addition, many finishing agents such as softeners and anti-wrinkle finishing agents are added to the fabric, which will also reduce the light fastness of the product. Therefore, dyes that are not sensitive to these finishing agents should be used.

Third,Dye color matching 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 can sensitize the fading of another dye. When color matching, you should choose dyes that will not sensitize each other and can even improve light resistance. This is especially important when dyeing dark colors such as black. If one of the three primary colors of dye fades too quickly, it will quickly cause the dyed fiber or fabric to discolor, and the faded dye residue will also affect the light stability of the other two dyes that have not faded. Reasonable control of the dyeing process to fully combine the dye with the fiber and try to avoid hydrolyzed dyes and unfixed dyes remaining on the fiber is an important way to obtain higher light fastness.

Source: Standard Group (Hong Kong)

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