Ultraviolet light, referred to as UV, has both beneficial and harmful aspects to people. The advantage is that it sterilizes and promotes bone development. However, long-term exposure can cause skin aging, cause spot dermatitis, even skin cancer, and promote cataracts.
When ultraviolet light irradiates the fabric, part of it is absorbed, part of it is reflected, and part of it passes through the fabric. The transmitted ultraviolet rays have an impact on the skin. In order to reduce the damage of ultraviolet rays to the skin, in terms of textiles, it is necessary to reduce the amount of ultraviolet rays transmitted through the fabric; that is to say, the more reflection and absorption of ultraviolet rays irradiated on the fabric, the more UV rays pass through the fabric. The less ultraviolet rays, the better the protection against ultraviolet rays and the less damage to the skin.
1. The principle of ultraviolet protection
The protection principle of existing UV-resistant clothing products on the market is mainly to use UV-shielding agents to treat fibers, yarns or fabrics to achieve the purpose of UV protection. Of course, the fabric itself has a certain ability to protect against ultraviolet rays, and its influencing factors include: fabric structure, fiber raw materials, yarn configuration and fabric color, etc. Generally speaking, the thicker and denser the fabric, the stronger the UV protection ability; from a fiber perspective, the UV protection capabilities from high to low are hemp, polyester, wool, nylon, cotton and viscose; the finer the fiber, the better the protection effect. The protective effect of short fibers is due to filaments. However, some studies believe that the ultraviolet transmittance of human clothing for outdoor activities must be below 10%. The ultraviolet transmittance of clothing for people whose skin is easily reddened by the sun must be below 5%. For those who are allergic to ultraviolet rays, the ultraviolet transmittance of clothing should be below 5%. The ultraviolet transmittance must be below 1%. Therefore, the UV shielding ability of the fabric itself is not enough. UV-resistant fabrics can be obtained through post-finishing.
UV-resistant fabrics can be treated in two ways: post-finishing and UV-blocking fibers. The anti-UV fabric obtained after finishing is generally coated with a layer of anti-UV material on the surface of the fabric. UV-blocking fiber is made by adding ceramic powder that reflects and absorbs UV rays into the fiber-forming polymer.
2. Evaluation of UV protection performance of textiles
According to the new assessment standard “Evaluation of UV Protection Performance of Textiles” implemented on January 1, 2010, UV protection products should be marked with the following three aspects on the label: 1. The number of this standard, that is, GB/T18830; 2 .UPF value: 30+ (UPF measurement is greater than 30, and UVA transmittance is less than 5%) or 50+ (UPF measurement is greater than 50, and UVA transmittance is less than 5%); 3. Long-term use and The protective properties provided by this product may be reduced when stretched or wet.
This national standard is a recommended standard, not a mandatory standard. That is, companies can choose whether to produce anti-UV products according to their own circumstances, but once they want to declare their products as “anti-UV products”, they must follow this standard.
UPF is the abbreviation of English ultraviolet protection factor, that is, ultraviolet protection factor. According to the definition in Chinese national standards, UPF refers to “the ratio of the average effect of ultraviolet radiation calculated when the skin is unprotected to the average effect of ultraviolet radiation calculated when the skin is protected by fabrics.” This definition is relatively abstract. We can understand the physical meaning of UPF in this way. For example, a UPF value of 50 means that 1/50 of the ultraviolet rays can penetrate the fabric. The higher the UPF value, the better the UV protection effect.
Generally, the UV resistance index of men’s shirts is below UPS10, but heavy cotton jeans can easily exceed the high standard of UPS50. Polyester and wool sweatshirts that are too thin and transparent cannot meet the low outdoor standard of UPF15, so they are not recommended. Fabrics that are too UV-resistant must rely on various treatments to increase UPS30 or above to be considered suitable for outdoor use.
3. Testing methods for UV-resistant textile products
There are two main methods for testing UV protection properties of textiles that are widely used at home and abroad: instrumental method (omitted) and direct method. Direct methods include human body irradiation method and discoloration and fading method.
a. Human body irradiation method: Cover the skin with one or more pieces of fabric on similar parts of the same skin, and directly irradiate it with ultraviolet rays. Record and compare the time when erythema appears for evaluation. The longer the time, the better the protective effect.
b. Discoloration and fading method: Cover the sample on the light fastness standard card, 1250px away from the sample, use ultraviolet light to illuminate it, and measure the time it takes for the light fastness standard card to change color at the first level. The longer it takes, the better the masking effect is.
Anti-UV textiles currently have certain limitations, that is, the anti-UV additives are easy to volatilize after being introduced into the fiber, and it is difficult to maintain the sun protection and cooling function for a long time. As modern humans pay more and more attention to the protection of ultraviolet rays and the development of new additives, textiles with this function have very broad prospects.
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