Tips: What are the anti-ultraviolet finishing of textiles? What are the common UV absorbers?

With the continuous improvement of people's quality of life, research on the effect of ultraviolet radiation on the human body is also deepening. In October 1982, observations of the decrease in stratospheric ozone layer thickness and the existence of ozone holes in the Antarctic, UV radiation problems caused by the destruction of the ozone layer thickness has become one of the focuses of increasing concern.

UV rays

Ultraviolet light is an electromagnetic wave, and the International Commission on Illumination (CIE) divides the ultraviolet light in solar radiation into three wavelength bands.

Long wavelength ultraviolet UV-A (wavelength 3l5nm-400nm). UV-A accounts for 90% of the total amount of ultraviolet rays reaching the ground, causing the skin to become dark and causing serious skin cancer.

Medium wavelength ultraviolet UV-B (wavelength 290nm-3l5nm). This is the root cause of sunburn.

Short wavelength ultraviolet UV-C (wavelength l80nm-290nm). Can be absorbed by the ozone layer, can not reach the ground.

Thus, the most harmful UV rays to the human body are UVA and UVB.

Factors Affecting UV Resistance of Fabrics

The anti-ultraviolet properties of fabrics are as the name implies, the fabric's ability to absorb or reflect ultraviolet light. At present, the UPF (abbreviation of the English Ultraviolet Protection Factor), which is also known as the ultraviolet shielding factor, is mainly used to express the ability of fabrics to protect against UV rays. It is the ratio of the average amount of UV radiation to unprotected skin to the amount of UV radiation that is masked by the fabric being tested. The UPF value and protection class are shown in the table.

Influencing factors

1 yarn raw material

Textile fibers themselves have a certain absorption and shielding effect on ultraviolet rays, and different types of fibers have different absorption and transmission capabilities for ultraviolet rays. The lower the absorption capacity, the higher the transmittance and the worse the UV resistance.

Among all widely used fiber materials, polyester contains benzene rings and has a high UV absorption capacity. Nylon has a poor ability to absorb ultraviolet rays. Protein fiber molecules such as wool and silk contain aromatic amino acids and have a wavelength of less than 300 nm. Strong absorption, its UV resistance properties are between polyester and nylon.

For cellulosic fibers, bleached cotton yarns and viscose fabrics have relatively high UV transmittance, while unbleached cotton yarn fabrics can be used as absorbents due to their natural pigments and lignin. Their UV protection coefficients are slightly higher; The fiber has groove-like voids and more voids in the tube wall, which has better UV resistance; bamboo fiber contains copper chlorophyllin as a safe and excellent UV absorber. Its UV resistance is much better than that of cotton fiber, and it is also obviously superior. In ramie, flax fiber.

In recent years, the use of a method of adding a barrier agent can effectively improve the ultraviolet resistance of the fiber.

2 yarn structure

The twist of the yarn affects the tightness and surface properties of the yarn, which in turn affects the degree of opening of the fabric and affects the transmission properties of the UV rays. Some researchers believe that the main influence parameters of yarns on UV resistance are the thickness (or diameter) of yarns and the crimping rate of yarns. Because these parameters have a direct impact on the structure of the fabric, it is possible to incorporate the effects of the yarn structure. Into the influence of fabric structure parameters.

3 fabric structure parameters

The structural parameters of fabrics that affect the UV protection performance of textiles are mainly organizational structure, tightness, and thickness. The structure of the fabric is related to the tightness, density, thickness, and mass per unit area of ​​the fabric. The tissue structure of the fabric determines the spatial geometry and porosity of the fabric. It is generally believed that its impact on UV resistance is mainly due to the two parameters of tightness and thickness. The more compact and thick the fabric, the better its UV resistance.

4 colors

The color of the fabric is determined by the absorption characteristics of the dye in the visible light region, which is different from the absorption characteristics of the dye in the ultraviolet region. Therefore, the color of the fabric is not the main factor that determines the UV resistance of the fabric.

At present, there is a more consistent conclusion on the effect of color on the UV resistance of textiles: Some dyes have a strong absorption capacity in the visible spectrum, and some absorbance in the UV spectrum. Generally, the protection performance against ultraviolet rays follows the color depth. The increase in the increase, dark blue and black in the best UV resistance in various colors.

5 after finishing

In the finishing process, the UV shielding agent can be fixed on the surface of the fabric to improve the UV resistance of the fabric.

Fabric anti-ultraviolet finishing

According to the anti-ultraviolet mechanism can be divided into: reflective anti-ultraviolet finishing agent, absorbing anti-ultraviolet finishing agent and nano anti-ultraviolet finishing agent.

01

Reflective anti-ultraviolet finishing agent

Reflective anti-ultraviolet finishing agents have no absorption effect on ultraviolet rays, but rely on the reflection of light to reduce the transmittance of ultraviolet rays. Also known as ultraviolet shielding agent. This type of shielding agent is non-toxic, odorless, non-irritating, good thermal stability, non-decomposition and non-volatile properties, mostly metals, metal oxides and salts, typically Ti02, Zn0, Al02, kaolin, talc Powder, carbon black, iron oxide, lead oxide, and CaC03, etc., can reflect up to 95% of ultraviolet rays with a wavelength of 310-400 nm.

Although the UV shielding agent has unique advantages, the air permeability, feel and washability of the fabric after finishing are poor, and the color, fastness, and whiteness of the fabric are reduced, and some of them even cause allergic reactions in the human body. Therefore, such finishing agents are mostly used for parasols, tents, etc., and are rarely used for apparel fabrics.

02

Absorption type UV curing agent

Absorptive anti-ultraviolet finishing agents, also known as ultraviolet absorbers, strongly and selectively absorb high-energy ultraviolet light and release it in other, lower-energy forms (eg, longer wavelength light or heat) to avoid ultraviolet light. Human skin damage, and the absorbent itself is not damaged by ultraviolet light. The principle of the absorbent is generally considered to be the transfer of intramolecular protons: the hydroxyl group in the structure forms an intramolecular six-membered ring containing hydrogen bonds with the N or O atoms in the nearby structure, and the six-membered ring is opened after being absorbed by ultraviolet irradiation, with accompanying The conversion of enol- and keto-type structures converts harmful energy into harmless light waves or thermal energy release, and the six-membered ring recloses and recovers.

As a fabric UV absorber should have the following conditions:

(1) It is safe and non-toxic, has no allergic reaction to human body, and cannot pose a threat to human health;

(2) comply with environmental protection requirements;

(3) Good resistance to common solvents and washability;

(4) No coloring after UV absorption;

(5) Does not affect or lessen the physical properties and fabric styles such as whiteness, fastness, strength and handfeel of fabrics;

(6) Has a certain degree of stability.

Different kinds of UV absorbers

03

Nano-type anti-ultraviolet finishing agent

The development of nanomaterials provides a new approach for UV screening agents. Compared with general ultraviolet shielding agents, the nano-ultraviolet shielding agent has a large specific surface area, high surface energy, easy combination with materials, small particle size, low diffuse reflectance to visible light, high transparency, and a style of the finished fabrics. Less affected.

The absorption mechanism of ultraviolet light by nanomaterials is different from the above-mentioned various types of organic absorbents. Take nano-Ti02 as an example: The electronic structure of Ti02 is a full valence band and an empty conduction band, with a band gap energy of 3.OeV to 3.2 eV, and a band gap of 3.02 eV or less. After Ti02 absorbs UV photons whose energy is greater than or equal to its band gap, electrons in the valence band are excited to the conduction band, resulting in highly active free-moving photoelectrons (e-) on the valence and conduction bands, respectively. And holes (h+)

The electron-hole pairs generated when the nano-TiO 2 absorbs ultraviolet light recombine on the one hand upon occurrence of various redox reactions, releasing energy in the form of heat or fluorescence, and on the other hand can dissociate into free migration to the lattice surface in the crystal lattice. Or other reaction sites have free holes and free electrons and are immediately captured by surface groups. Under normal circumstances, titanium dioxide will surface water activation to produce surface hydroxyls to trap free holes and form hydroxyl radicals, while free radicals will absorb oxygen to produce superoxide radicals, killing the surrounding bacteria and viruses. Therefore, fabrics finished with nanomaterials not only have the ability to resist UV, but also have the effect of sterilization.

Deng Hao and other self-made nano-titanium dioxide finishing agent on the cotton fabric finishing, after finishing the fabric not only has excellent anti-ultraviolet properties, but also good washability, does not affect the fabric's breathability, feel and other properties. Li Hong and others used nano-Zn0 to study the anti-ultraviolet finishing of linen fabrics, and also achieved good results.

Source: China Textile Quanzhou, "Anti-UV Finishing of Textiles"

※ The hot and dry weather in summer and strong ultraviolet radiation have become an important issue faced by field workers in the oil industry in the field. Related industries have incorporated moisture absorption and quick dryness as a basic assessment index for summer wear protection. However, the strong ultraviolet radiation environment in the summer may cause potential health hazards to the frontline workers.

After repeated research by technical experts of the special fabrics R&D center of the Jiangnan branch of the China Textile Science Research Institute, the 6F30D polyester-based high-performance conductive material and fine denier UV-protective fiber were used, and through special production processes, the “Blue Xiang” UV-resistant coating was successfully developed. & Anti-static security protection tooling fabric , the fabric set anti-static protection, anti-ultraviolet function, high ventilation function as a whole, both soft and feel.