Will the drip-free film block ultraviolet rays?

1 Foreword Since the 1920s, due to the extensive use of fluorocarbon solvents and freon, the ozone layer in the earth's atmosphere has been seriously damaged, and the ultraviolet rays reaching the earth's surface have been increasing. Ultraviolet is an electromagnetic wave with a wavelength of 200-40 nm, and the region with a wavelength of 400-32 nm is called UV-A; The region with the wavelength of 320-280nm is called UV-B; The region with the wavelength of 280-200nm is called UV-C. UV-C has a short wavelength and has been absorbed by the air, so it cannot reach the earth's surface. Ultraviolet rays in sunlight account for about 6%, of which the proportion of UV-A is large and that of UV-B is small. UV-A will penetrate the epidermis, make muscles lose elasticity, make the skin rough and form wrinkles. UV-B is related to carcinogens. Therefore, it is necessary to effectively shield the short-wave and long-wave parts of UV-B and UV-A. Generally speaking, moderate ultraviolet irradiation has bactericidal effect, can promote the synthesis of vitamin D, and is beneficial to human health. However, under the continuous exposure of the scorching sun, the human skin will lose its resistance and is prone to burns, erythema or blisters. Excessive ultraviolet radiation can also induce skin diseases (such as dermatitis and xeroderma pigmentosum) and even skin cancer, promote the formation of cataracts and reduce human immune function. According to statistics, every time the ozone layer decreases 1%, the intensity of ultraviolet radiation will increase by 2%, and the possibility of skin cancer will increase by 3%. Therefore, in order to protect human body from excessive ultraviolet radiation, anti-ultraviolet radiation finishing of textiles is imminent. 2 The development trend of anti-ultraviolet textiles at home and abroad The earliest anti-ultraviolet products are anti-ultraviolet cosmetics. After 90' s, UV-resistant fabrics have sprung up everywhere, among which Japanese enterprises are the most prominent. They have successively introduced sportswear, shirts, stockings, hats and umbrellas with anti-ultraviolet radiation function, which are well received by consumers. Take Australia as an example, a country with low latitude and strong sunshine, which took the lead in developing anti-ultraviolet textiles to protect human body, and made anti-ultraviolet textiles enter the commercialization stage. They usually adopt the method of adding anti-ultraviolet finishing agent and ultraviolet shielding agent. In addition, ultraviolet absorber and reflector are applied to fabrics at the same time, which makes the anti-ultraviolet effect more superior. For example, tornado UV of unika Company first made polyester filament containing special ceramic powder into fabric, and then treated with ultraviolet absorbent, and the ultraviolet shielding rate of the obtained fabric was as high as 97%. In addition, nanotechnology is applied to anti-ultraviolet textiles. For example, using the quantum size effect of nano powder, the absorption of a certain wavelength has a "blue shift phenomenon" and the absorption of various wavelengths has a "broadening phenomenon", which leads to a significant increase in the absorption effect of ultraviolet light and ensures the ultraviolet shielding effect of the product. At present, the most commonly used nano-materials for absorbing ultraviolet rays are: 30-4nm TiO2, which has strong absorption ability for ultraviolet rays below 400nm; A 1203 nano-powder has a strong absorption ability for ultraviolet rays with wavelength below 250nm; The reflectivity of silicon dioxide to ultraviolet with wavelength below 400 nm is as high as 95%. At present, the research on anti-ultraviolet textiles in China has just started. The research institute of Tianjin Petrochemical Company has developed anti-ultraviolet polyester staple fiber and network low elastic yarn containing ceramic powder. Shanghai 11th Chemical Fiber Factory has developed UV-resistant polyester staple fiber. Donghua university chemical fiber engineering research center has developed chemical fiber grade ultra-fine anti-ultraviolet powder and masterbatch; Shandong Julong Chemical Company successfully developed the anti-ultraviolet finishing agent for cotton fabric by reasonably matching ultraviolet absorber and shielding agent. Nano-scale ceramic cotton textiles developed by Xiamen Huapu High-tech Industry Co., Ltd. have the functions of anti-ultraviolet, anti-bacterial and far-infrared insulation; Xi Anhuajie Technology Development Co., Ltd. uses superfine powder material mixed fiber to make clothes, which can absorb and isolate more than 95% ultraviolet rays and effectively prevent ultraviolet rays from harming human body. 3 Anti-ultraviolet finishing mechanism of textiles The mechanism of anti-ultraviolet finishing of textiles is to use a substance that can reflect and/or strongly and selectively absorb ultraviolet rays and can convert energy to release or consume energy with heat energy or other harmless low-energy radiation. After the application of these substances, textiles have no adverse effect on the wearability of fabrics, which meets the use requirements. Therefore, the anti-ultraviolet radiation finishing of textiles is similar to the photostability of polymers. But the light resistance is to protect polymer compounds from automatic oxidation caused by ultraviolet radiation, which leads to polymer degradation and changes in appearance and structural properties. Anti-ultraviolet finishing is to protect human body from excessive ultraviolet rays. From the optical principle, when light shines on an object, part of it is reflected on the surface, part of it is absorbed by the object, and the rest is transmitted through the object. For the fabric treated with ultraviolet protection, the light hits the fabric, and part of it passes through the fabric through the gap. The ultraviolet shielding agent on the fabric either reflects ultraviolet rays or selectively absorbs and releases its energy into low energy, thus shielding ultraviolet rays. Factors affecting the anti-ultraviolet radiation function of textiles The anti-ultraviolet ability of fabrics mainly depends on the anti-ultraviolet ability of fabrics themselves. Fabric usually has a complex surface, which can not only absorb light, but also scatter and reflect light. However, due to the different surface morphology, fabric weave specifications, color depth and finishing methods of single fiber after printing and dyeing, the scattering and reflection have changed significantly. Therefore, various factors should be considered comprehensively when studying the anti-ultraviolet radiation performance of textiles. 4. 1 Different fiber types have different ultraviolet transmittance and ultraviolet protection coefficient (UPF). The ultraviolet transmittance and ultraviolet protection coefficient of polyester and wool fibers are lower than those of cotton and viscose fibers. Because of benzene ring in polyester structure and aromatic amino acids in wool protein molecules, it has great absorption of light below 300nm. Therefore, wool, hemp, silk, polyester and anti-ultraviolet chemical fiber with anti-ultraviolet function are the first choice raw materials. However, cotton fabric has relatively poor anti-ultraviolet ability and is the most easily penetrated fabric. Therefore, anti-ultraviolet finishing of cotton fabric is a top priority. Table 1 UPF value of undyed fabrics with different fibers; fiber type; fabric thickness (mm) g/m2; UPF value of cotton poplin (unbleached) 0. 18 107 6 cotton grade (bleached) 0.221kloc-0. Fabric structure includes thickness, compactness (coverage coefficient or porosity) and so on. Compact structure requires a large number of warp and weft yarns, with large coverage coefficient, low ultraviolet transmittance and great protection. The coverage coefficient of the scrim is low, and the light is not easy to block, so its protective effect is small. Ultraviolet protection coefficient (UPF) increases with the increase of fabric density. A similar situation exists for heavy fabrics with heavy fabric weight. Table 2 Fabric parameters and ultraviolet transmittance Fiber type warp and weft density (root/inch) thickness (inch) compactness (%) coverage (%) transmittance (%) cotton1/20.7 88.8 25.1viscose1550.0/. 9.4 86.0 27.3 nylon163 0.000+001.022 20.693.1.8.6 silk179 0.018.690.0/kloc-0. This is because in order to obtain a certain color, dyes must selectively absorb visible radiation, and some dyes have absorption bands extending to the ultraviolet spectrum, so they play the role of ultraviolet absorbers. Generally speaking, with the deepening of textile color, the ultraviolet transmittance of fabric decreases and the ultraviolet resistance improves. In addition, the extinction treatment of chemical fiber also affects its ultraviolet transmittance. See Table 3 for the relationship between different dyes and ultraviolet transmittance. Table 3 the relationship between different dyes and ultraviolet transmittance dyes 0.5%owf bath 1.0%owf bath exhaustion rate (%) transmittance (%) exhaustion rate (%) transmittance (%). Direct Yellow126013.18.6 Direct Yellow 28 80 19.9 86 29.3 Direct Yellow 44 58 18.4 6 1 28.6 Direct Yellow L06 68/Kloc-. 74 37. 1 direct red 28 88 38.7 89 50.7 direct red 80 74 17.3 73 24.7 direct violet 9 80 20.9 75 28.8 direct blue176 210.5 70 30.2 direct blue 86 36/kloc. 6 Direct Blue 218 6813.1.6719.0 Direct Green 26 72 22.3 65 29.2 Direct Brown 154 82 22.8 80 30.6 Direct Black 38 76 29.8 77 40.3 4 As a clothing fabric, considering the requirements of softness and comfort when wearing in summer, for synthetic fiber fabrics such as polyester and spandex, suitable ultraviolet absorbers can be selected and dyed with disperse dyes at high temperature and high pressure, so that ultraviolet absorber molecules can be integrated into the fibers; For cotton and linen fabrics, padding method can be used, and after drying and heat treatment, the ultraviolet absorber can be fixed on the surface of the fabric. For decorative and industrial textiles, the reflective ceramic glue with anti-ultraviolet effect can be coated on the surface of the fabric by pigment printing or coating to form a protective film; It is also possible to accurately coat ultraviolet shielding agent or ultraviolet absorbent on the fabric surface, and then form a film on the fabric surface after drying and heat treatment. The coating agent can be PVC, PA, PU, etc. It can also be mixed with ceramic micropowder for coating. In addition, the application of nanotechnology and microcapsule technology can also enhance the anti-ultraviolet function of fabrics. See Table 4 for the ultraviolet transmittance of different fabrics before and after anti-ultraviolet finishing. Table 4 Ultraviolet transmittance of different fabrics before and after finishing Ultraviolet transmittance of plain fabric and satin fabric before and after finishing (%)18.641.4318.650.041. 6.84 0.010.4.5 other factors The general rule of ultraviolet radiation resistance of textiles: staple fiber fabrics are better than filament fabrics; Processed silk products are better than chemical fiber precursor products, and fine fiber fabrics are better than coarse fiber fabrics. Flat special-shaped chemical fiber fabric is better than circular cross-section chemical fiber fabric; Woven fabrics are superior to knitted fabrics. 5 ultraviolet shielding agent the so-called ultraviolet shielding agent is a substance that can absorb or reflect ultraviolet rays. Ultraviolet screening agents can be divided into inorganic and organic compounds. 5. 1 inorganic ultraviolet shielding agent Inorganic ultraviolet shielding agent, also known as ultraviolet reflector, mainly reflects or refracts incident ultraviolet rays to achieve the purpose of preventing ultraviolet radiation. They have no conversion of light energy, but only use fine powders such as ceramics or metal oxides to combine with fibers or fabrics to increase the reflection and scattering of ultraviolet rays on the fabric surface, thus preventing ultraviolet rays from penetrating the fabric and hurting human skin. These powders include kaolin, calcium carbonate, talcum powder, iron oxide, zinc oxide, lead oxide and so on. Experiments show that in the wavelength range of 3 10-370nm, zinc oxide and lead oxide have the best reflection or protection effects on ultraviolet rays, and iron oxide and kaolin also have certain effects. Compared with organic ultraviolet shielding agents, these inorganic components have some advantages besides excellent light resistance and ultraviolet protection, and their heat resistance is also outstanding. In particular, zinc oxide has antibacterial and deodorizing functions. 5.2 Organic UV Shielding Agent Organic UV Shielding Agent, also known as UV absorber, mainly absorbs ultraviolet rays and converts them into heat energy with lower energy or electromagnetic waves with shorter wavelength, thus achieving the purpose of preventing ultraviolet radiation. As an ultraviolet absorber for textiles, it should have the following characteristics: (1) It is safe and non-toxic, especially it has no irritation and allergic reaction to skin; (2) Wide ultraviolet absorption range and good effect; (3) It is stable to heat, light and chemicals and has no photocatalytic effect; (4) does not change color after absorbing ultraviolet rays; (5) It does not affect the color fastness, whiteness, strength and hand feel of textiles; (6) Good solvent resistance and washing resistance. There are many kinds of ultraviolet absorbers at home and abroad. The first generation products commonly used are salicylate, metal ion integrator, menthyl ester, benzotriazole and benzophenone. These ultraviolet absorbers have no reactive functional groups, and are not easy to fix and diffuse. The second generation absorbent, including o-hydroxybenzene-dibenzotriazole derivatives developed by Ciba Jiaji Company in Switzerland, is a cationic self-dispersion formula, which can be used for high-temperature dyeing, pad dyeing, printing and so on. And has excellent sublimation fastness and heat fixation properties. Rayosan series developed by Colijn Company in Switzerland can react with hydroxyl groups on cellulose fibers and amino groups on polyamide, without changing the appearance, feel and air permeability of fabrics, and also has light fastness and washing fastness. Ultraviolet absorber can convert ultraviolet energy into light, heat and other forms of release, which has certain stability, but long-term and large-dose ultraviolet irradiation will cause molecular decomposition of absorber. Therefore, in order to improve the durability of finishing effect, we can usually use microcapsule technology to put absorbent into microcapsules to finish fabrics. In a word, the research on ultraviolet shielding agent should focus on improving the ultraviolet radiation resistance and durability of fabrics, which is suitable for fabrics with different fiber materials, without affecting the softness, color fastness and strength of fabrics, and trying to ensure that the finishing agent itself, human body, fabrics and environment will not be harmed and polluted. It is also necessary to study the general law between the concentration of finishing agent and different fabric varieties, strengthen the research on processing technology, and reduce the production cost as much as possible on the basis of meeting the requirements of textile anti-ultraviolet performance indicators. Ways to improve the anti-ultraviolet radiation function of textiles In order to reduce the damage of ultraviolet rays to the skin, it is necessary to reduce the amount of ultraviolet rays penetrating through the fabric. There are three main ways to reduce the transmission of ultraviolet rays. 6. 1 UV-proof fiber mainly refers to the mixed spinning of UV shielding agent and * * * mixed core skin in the production process of synthetic fiber, so that the fiber has the function of shielding ultraviolet rays. The fabric obtained by this method has long-lasting effect and good hand feeling, but it has high processing requirements and high cost, is not easy to be used in natural fibers, and the effect is difficult to control when blending. In the early 1990s, Japan Cola Company took the lead in introducing "Esmo" fiber with anti-ultraviolet function, that is, fine ceramic powder was evenly mixed in PET polymer melt to spin polyester fiber. In recent years, it has been found that the fiber made of ceramic ultrafine particles with special structure can not only shield ultraviolet rays, but also have heat insulation (that is, reflect visible light and infrared rays). 6.2 Anti-ultraviolet finishing technology of textiles is related to its final use. There are four finishing processes: 6.2. 1 exhaustion at high temperature and high pressure for ultraviolet shielding finishing of synthetic fiber fabrics such as polyester and nylon, which can be carried out in the same bath with disperse dyes at high temperature and high pressure. At this time, the ultraviolet absorber molecules dissolve into the fiber, as long as the appropriate ultraviolet absorber (including low skin toxicity) is selected. 6.2.2 Atmospheric Exhaustion Method For wool, silk, cotton and nylon textiles treated with some water-soluble absorbents, they only need to be treated in their aqueous solution at atmospheric pressure, which is similar to water-soluble dye dyeing. Some absorbents can also be dyed and finished in one bath with dyes. 6.2.3 Pad dyeing method Because most UV shielding agents are insoluble in water and lack affinity for natural fibers such as cotton and hemp, the exhaustion method cannot be adopted, and the shielding agent should be fixed on the surface of the fabric (fiber) in the same bath with resin (or adhesive). The padding liquid consists of ultraviolet shielding agent, resin, softener, etc. However, after dry heat treatment, the holes in the fabric are easily covered by resin (adhesive), which will affect the style, water absorption and air permeability of the finished fabric. 6.2.4 Coating method Generally, a proper amount of ultraviolet shielding agent is added to the coating agent, and the surface of the fabric is coated with a coating machine (such as hanging scraper, rotary screen, etc.). ), and then drying and necessary heat treatment to form a film on the surface of the fabric. Although this method affects the washing fastness and hand feeling, it has wide applicability to fiber types, low treatment cost and low requirements for application technology and equipment. The ultraviolet shielding agent used in coating method is mostly inorganic compound with high refraction, and its ultraviolet absorption effect is related to its particle size. As the UV shielding agent is almost insoluble in water, if it is dissolved in non-aqueous solvent for finishing, it will not only be inconvenient to operate, but also pollute the environment. Generally, the ultraviolet shielding agent is emulsified, so that the shielding agent is evenly dispersed in the water phase, and the ultraviolet shielding effect can be stably maintained to finish the fabric. Or by changing the molecular structure of the ultraviolet shielding agent, the shielding agent is given water solubility, but the structure of the finishing agent is affected and the cost is increased because of the small molecular structure of the parent material. 6.3 Combination of ultraviolet resistant fiber and fabric finishing: When ultraviolet absorber and ultraviolet reflector are applied to fiber or fabric at the same time, the efficiency can be increased and the protective effect is superior. For example, tornado UV of unika Company uses polyester filament containing special ceramic powder as fabric first, and then finishes it with ultraviolet absorbent, and the ultraviolet shielding rate of the fabric obtained is above 90%. At present, there is no uniform test method and standard for anti-ultraviolet fabrics in the world. There are four commonly used testing methods: 7. 1 ultraviolet spectrophotometer method. By measuring the spectral transmittance curves of various anti-ultraviolet samples with ultraviolet spectrophotometer or ultraviolet intensity meter, the transmittance of each wavelength can be judged, and the average transmittance of a certain ultraviolet region can be calculated by area ratio to evaluate the protection effect. But this method has its imperfections. Therefore, most fiber fabrics are translucent and the surface is uneven, so the transmission of light in fabrics is more complicated. In addition to some light being absorbed by the material, there is also refraction and reflection of light. The amount of refraction and reflection is closely related to the surface morphology, fabric structure and thickness of single fiber, so the measured transmittance is low. Only by adopting perfect detection means, such as integrating sphere capture device or opalescent glass diffusion elimination method, and using spectrophotometer with photomultiplier tube to capture light in all directions, can accurate values be obtained. The anti-ultraviolet radiation effect of the finished fabric is better than that of the original fabric. Therefore, in addition to measuring the absolute value, it can also be used as a blank test to compare the percentage reduction of ultraviolet transmittance and show the anti-ultraviolet effect of the finished fabric. 7.2 Direct skin irradiation method In the same skin, cover the skin with one or several pieces of fabric, and directly irradiate with ultraviolet rays, and record and compare the time of appearance for evaluation. Measure the sun protection coefficient. In order to adapt to the strict scientific significance of protecting against ultraviolet radiation, UPF (ultraviolet protection factor) has been gradually changed, which refers to the ratio of the time required for ultraviolet radiation to reach the critical dose of skin erythema after using protective equipment to the time value of reaching the same degree of injury without using protective equipment. According to the test results of UPF, the ultraviolet protection effect of fabric was evaluated. The greater the UPF value, the better the protection effect. (See Table 5) Table 5 UPF Protection Category 15-24 Good Protection) 25-39 Very Good Protection) 40-50,50+Excellent Protection) 7 3 Discoloration and Fading Method) Place the substrate dyed with photosensitive dyes under a standard ultraviolet light source, cover the fabric to be tested, turn on the light source, and observe the color change of the substrate dyed with photosensitive dyes under the cover after a certain period of illumination. The smaller the color change, the better the anti-ultraviolet effect of the fabric to be tested. 7.4 Ultraviolet Intensity Accumulation Method The fabric placed on the ultraviolet intensity accumulator is irradiated with ultraviolet rays for a certain period of time, and the accumulated amount of ultraviolet rays passing through the fabric is measured and then calculated. At present, the evaluation index of anti-ultraviolet fabric quality is mostly ultraviolet shielding rate. At present, the ultraviolet shielding rate is the standard to distinguish the ultraviolet protection effect of domestic products. Grade A: UV shielding rate is greater than 90%; Grade B: UV shielding rate is 80%-90%; Class C: UV shielding rate is 50%-80%. Generally, grade A is appropriate. Shielding ratio is obtained by the integral value of transmittance in the wavelength range of 280-400nm. In addition, since the anti-ultraviolet finishing fabric is mainly used for making summer clothes and is in direct contact with human skin, it is necessary to strengthen a series of safety tests such as skin allergy test, acute toxicity test and teratogenic test of anti-ultraviolet finishing agent to ensure that the product is safe to human body and harmless to the environment. Looking forward to joining WTO, China textile enterprises will inevitably participate in international competition. In order to win in the fierce market competition, we must study the product quality, grade, functionality, health care, environmental protection and other aspects to comprehensively improve the level of China's textiles and increase the added value of products. The anti-ultraviolet finishing of textiles should make full use of the advantages of various resources in China, adopt high-tech to study raw materials and spinning, and comprehensively consider the selection of raw materials, fabric structure, fabric color and finishing technology to improve the anti-ultraviolet performance of fabrics. A new type of environment-friendly reactive finishing agent was developed to improve the durability of the protective performance of the finished fabric without causing harm to human body and environment. In the development and application, based on the anti-ultraviolet function of fabric, it can be combined with antibacterial and far-infrared warmth to carry out multifunctional composite finishing to improve the added value of products. Vigorously develop anti-ultraviolet products for clothing, decoration and industry. In summer, we should vigorously develop knitting, woven inner and outer coats, swimsuits, socks, sun hats, umbrellas and sportswear. We should also explore the industrial textile market, such as outdoor buildings in agriculture and construction, workers' work clothes and hats, uniforms for traffic police, military protective equipment, industrial, agricultural and commercial awnings, etc. If this kind of textile can form its own characteristics, it has a wide range of applications, large quantities and good benefits. The market potential of anti-ultraviolet textiles at home and abroad is huge. Tracking the research of advanced technology at home and abroad and insisting on developing new products will surely form new economic growth points.