Discussion On The Importance Of Studying Antistatic Technology Of Textiles

　　 spin Phenomenon and generation principle of product static electricity

There are many explanations for the mechanism of generating static electricity, Textile materials Static electricity is mainly caused by friction between surfaces. Textile materials are poor conductors of electricity with high specific resistance. In the process of production, processing and use, fibers and their products are prone to generate static electricity due to friction, drafting, compression, peeling, electric field induction, hot air drying and other factors. Especially with the increasing production and application of synthetic fibers in textiles, the inherent high insulation and hydrophobicity of these polymers make them easy to generate and accumulate static electricity.

1. Harm of textile static electricity

In civil use, static electricity will lead to dust absorption and contamination during the use of textiles, clothing Entanglement of human body will cause adhesion discomfort, and some studies have shown that electrostatic stimulation will have adverse effects on human health. In terms of industrial application, static electricity is one of the main inducing factors of fire, explosion and other accidents in industries such as pyrotechnics, chemicals, petroleum and other processing industries, as well as one of the hidden dangers of quality and safety accidents in the processing of textile industries such as chemical fibers. With the development of high-tech, the consequences of electrostatic hazards have broken through the boundaries of safety issues [3]. The spectrum interference hazard caused by electrostatic discharge will lead to equipment operation failure, signal loss and other results in electronics, communications, aviation, aerospace and all applications of modern electronic equipment and instruments. Therefore, the demand for antistatic textiles is increasing.

2. Anti static mechanism of textiles

The static electricity on the insulator surface can disappear in three ways: (1) through air (fog); (2) Disappear along the surface; (3) Disappear through the insulator body.

The elimination of static electricity through air mainly depends on the charged particles with opposite signs flying in the air to neutralize the static electricity on the insulator surface or let the charged particles obtain kinetic energy and fly away. Based on the principle of tip discharge, a high-voltage corona type electrostatic eliminator has been made, which has been applied in chemical fiber production.

The rate at which static electricity disappears along the insulator surface depends on the surface resistivity of the insulator. Increasing the humidity of the air can form a continuous water film on the surface of the hydrophilic insulator. With the dissolution of CO2 and other impurities in the air, the surface conductivity is greatly improved. A further method is to use antistatic agents, mainly ionic or non-ionic surfactants.

The leakage speed of static electricity through the insulator mainly depends on the resistivity of the insulator. Generally speaking, when the polymer resistivity is less than 107 Ω· m, the generated static charge will leak out quickly. In order to improve the volume conductivity of polymer, the most convenient method is to add carbon black, metal powder or conductive fiber.

The fiber polymer material is theoretically higher than the insulator, but the actual conductivity of the fiber is higher than the theoretical estimate because the fiber is not a pure polymer material, which contains water, impurities and other low molecular substances. That is, the conductivity of the fiber mainly depends on the attachments in the fiber, and secondly is related to the conductivity of the fiber molecule itself and the role of external conditions. The conductivity of the fiber will be greatly improved when the conductivity of the surface ionizable material is high and the partial pressure of water vapor is large.

3. Ways of antistatic textiles

Antistatic fabrics can be divided into civil and industrial electrostatic protective clothing. According to the end use, electrostatic protective clothing can be divided into dust-free sterile work clothes, fireproof and explosion-proof work clothes, surgical clothes, safety work clothes (such as electrostatic protective clothing and conductive clothing worn by power workers when working), etc.

Antistatic treatment of fibers

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Hydrophilic treatment of fiber with surfactant

The action principle is that the hydrophobic end of the surfactant molecule is adsorbed on the fiber surface, and the hydrophilic polar group points to space to form a polar surface, which absorbs water molecules in the air, reduces the surface resistivity of the fiber, and accelerates the charge dissipation. The surfactants used include cationic, anionic and non-ionic surfactants, of which the cationic surfactant has the best anti-static effect, and the high molecular weight non-ionic surfactant has the best anti-static effect and durability. The advantage of this method is simple and easy, especially suitable for eliminating electrostatic interference in textile processing; The disadvantages are that the durability of the antistatic effect is poor, the surfactant is easy to volatilize, and is less resistant to washing, and does not show antistatic performance in low humidity environment.

Blending, copolymerization or graft modification of fiber forming polymers

The same as the previous method is that hydrophilic monomer or polymer is added to the fiber forming polymer to improve the moisture absorption, so as to obtain anti-static performance. In addition to the typical blend spinning mode of ordinary fiber forming polymer and hydrophilic polymer, there is also the blending mode of adding hydrophilic polymer in the polymerization process to form micro multiphase dispersion system. For example, when polyethylene glycol is added to caprolactam reaction mixture, polyethylene glycol is dispersed in PA6 as fibril. At the same time, polyethylene glycol also has a small amount of hydroxyl end reacting with the hydroxyl in the amino caproic acid generated after the ring opening of caprolactam, which improves the durability of the antistatic property.

In addition, copolymerization of hydrophilic polar monomers onto the main chain of hydrophobic synthetic fibers, such as embedding polyethylene glycol into PET macromolecules, can also improve the hygroscopicity and antistatic properties of the fibers.

The grafting on the fiber surface initiated by chemical initiation, thermal initiation, high-energy radiation and ultraviolet radiation can effectively improve the hygroscopicity of synthetic fibers, and the amount of hydrophilic monomer is far less than other methods, with good durability. This kind of antistatic fiber still accelerates the leakage of charge by improving the hydrophilicity of the fiber, so the antistatic performance of the fiber will be lost in a dry environment with relative humidity less than 40%.

Production anti-static yarn

The antistatic yarn can be produced by mixing a small amount of conductive staple fibers into the spinning process, and at the same time, the electrostatic problems existing in the spinning process can be reduced or even eliminated. When spinning, ordinary textile fiber is used as the main fiber, in which a small amount of conductive fiber is mixed. The amount of conductive fiber mixed depends on the end use and cost of the product. A large number of experiments show that the resistivity of the yarn will be significantly reduced (the conductivity will be greatly improved) when a small amount (several percent) of organic conductive fibers are mixed into the yarn.

Conductive fibre

The conductive fibers include metal fibers, metal plated fibers and organic conductive fibers. The widely used metal fiber is mainly stainless steel fiber, and its manufacturing methods are mainly wire drawing method, melt spinning method, cutting method, etc. Stainless steel fiber has better electrical conductivity and mechanical properties, but for textile processing, metal fiber has small cohesion, poor spinning performance, and the price for high fineness is expensive. Therefore, except for some occasions with special requirements, metal fiber is not widely used in the development of anti-static products. Metal plated fiber is to coat metal layer on the surface of ordinary fiber to improve the anti-static effect. Its cost is significantly lower than that of metal fiber, but it is not resistant to washing and has poor hand feel. At present, organic conductive fibers are mostly used to develop antistatic blended yarns.

Organic conductive fiber is a kind of conductive fiber which is based on ordinary fiber forming polymer and added with conductive materials by coating or composite method. The organic conductive fibers currently used are mainly nylon based, polyester based and acrylic based, and the conductive materials include carbon and metal compounds. The fiber made of carbon conductive material is dark (black, gray), and the fiber made of metal compound conductive material is white. The latter has a slightly poor conductivity, but is conducive to the processing of the subsequent finishing process (dyeing, etc.).

Spinning process

Due to the high cost of conductive fiber and small mixing proportion, it is generally opened manually. In order to make the mixing even, the conductive fiber and the main fiber are fed into the carding machine at the same time according to the pre calculated and weighed weight, and go through multiple carding processes. In addition, the selected conductive fiber should be as consistent as possible with the material of the main fiber. The blending process is as follows: carding (one pass) → carding (two pass) → head doubling → second doubling → third doubling → roving → spinning → winding.

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Insert conductive filament or antistatic yarn during weaving

In addition to improving the raw materials, the development of antistatic textiles can also embed conductive filaments (or conductive fiber composite yarns) into the fabric at a certain distance when weaving on the fabric. It can be embedded along longitude or latitude, or it can be embedded along both longitude and latitude to form a grid. A large number of experiments have proved that the antistatic effect of the fabric is significantly improved no matter which way the conductive wire is embedded, but the best effect is when the conductive wire or antistatic yarn is embedded in the grid form. Moreover, the antistatic properties of the fabrics decrease with the increase of the distance between the embedded conductive wires. The embedding distance of conductive wire (or the content of conductive fiber in the fabric) shall be determined according to the end use of anti-static products and the requirements for conductive performance. Refer to the following table for details:

Due to the high price of conductive fibers and the high cost of making fabrics, the least conductive fibers should be considered in the design to obtain the best anti-static performance. The optimal embedding spacing (conductive fiber content) that meets the product use requirements can be obtained through the optimization analysis of various influencing factors (conductive fiber spacing, fabric density, etc.). In addition, since most of the conductive filaments used are black, the warp weave point of the conductive filament should be hidden below the warp weave point of the basic weave as far as possible when designing the fabric fabric, so as to ensure that the fabric fabric structure on the front side is not damaged. On the reverse side of the fabric, the conductive wire is exposed on the surface of the fabric as far as possible to facilitate the discharge.

Fabric finishing with antistatic agent

The method of anti-static treatment of fabric surface directly with surfactant began in the 1950s, which is suitable for various fiber materials. Most of the antistatic agents used are polymer fabrics with similar structure to the finished fibers, which are adhered to synthetic fibers or their fabrics after immersion, rolling and baking. These polymers are hydrophilic, so coating on the surface can increase the conductivity of the fiber through moisture absorption, so that the fiber will not accumulate more static charges and cause harm. In addition to making the fabric antistatic, the treated fabric also has the functions of moisture absorption, antifouling, and no dust absorption. Because the antistatic method is relatively simple, the price of finished products is also relatively cheap.

The process flow is: grey cloth → dip rolling of anti-static resin (second dip and second rolling) → drying (100~110 ℃) → baking (150~160 ℃, 2min) → stretching → anti-static finishing of finished products. There are three main methods at present.

(1) Auxiliary absorption fixation

(2) Surface grafting polymerization

(3) Low temperature plasma surface treatment

Since the latter two methods require more special initiators or high-energy rays or plasma treatment, the process is complex and the operation is complex, so the first method is generally used. It can be used for anti-static processing in the finishing process, and can also be used for the same bath treatment in the dyeing process, which can achieve ideal results.

4 Development status and prospect of textile antistatic technology

Current situation and existing problems of antistatic technology at home and abroad

At present, the antistatic of civil textiles mainly uses the post finishing method. In the electrostatic protection fabric, conductive fibers are distributed in the fabric at certain intervals along the longitudinal or transverse direction or in both directions to form longitudinal strips, transverse strips or grids. According to the requirements of anti-static performance, the spacing range is usually 3mm~15mm, because it has good washing resistance, friction resistance, heat resistance, light resistance and permanent anti-static property, and is not affected by changes in ambient temperature and humidity, It is being developed and applied more and more widely. From the point of view of textile development, conductive fibers should be used after anti-static treatment to achieve excellent anti-static performance.

The problem of antistatic fabrics developed with conductive fibers is the finishing (dyeing, etc.) of fabrics. Since most conductive fibers are dark, their dyeing performance becomes a problem.

Outlook

With the improvement of people's requirements for clothing performance and the consideration of precision and safety in production, the requirements for antistatic textiles are becoming higher and higher. The current antistatic technology needs to be constantly improved. From the current situation, the combination of the above antistatic ways can achieve excellent Antistatic effect.