Discussion on antistatic technology of textiles

1.1 Textile static electricity phenomenon and its generation principle

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

1.2 Hazards of static electricity on textiles

In terms of civilian use, static electricity can cause dust contamination during the use of textiles, and clothing can become entangled in the human body, causing adhesion and discomfort. Studies have shown that static electricity stimulation can have adverse effects on human health. In terms of industrial applications, static electricity is one of the main causes of fires, explosions and other accidents in the pyrotechnics, chemical, petroleum and other processing industries. It is also one of the hidden dangers of quality and safety accidents in the processing of chemical fiber and other textile industries. With the development of high technology, the consequences of electrostatic hazards have exceeded the boundaries of safety issues [3]. Spectrum interference hazards caused by electrostatic discharge can cause equipment malfunctions, signal loss and other consequences in electronics, communications, aviation, aerospace and all situations where modern electronic equipment and instruments are used. Therefore, the demand for antistatic textiles is currently increasing.

2. Antistatic mechanism of textiles

Static electricity on the surface of an insulator can disappear in three ways: (1) disappear through the air (mist); (2) disappear along the surface; (3) disappear through the body of the insulator.

Eliminating static electricity through the air mainly relies on charged particles of opposite signs in the air to fly to neutralize the static electricity on the surface of the insulator or allow the charged particles to gain kinetic energy and fly away. Using the principle of tip discharge, a high-voltage corona-type static eliminator is made, which has been applied in chemical fiber production.

The speed at which static electricity dissipates along the surface of an insulator 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, coupled with the dissolution of CO2 and other impurities in the air, greatly improving the surface conductivity. A further method is to use antistatic agents, mainly ionic or nonionic surfactants.

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

Fiber polymer materials are theoretically better than insulators, but the actual conductivity of fibers is higher than the theoretical estimate. The reason is that fibers are not pure polymer materials and contain low-molecular substances such as moisture and impurities. That is, fiber conductivity mainly depends on the fiber content. The appendages are secondly related to the conductivity of the fiber molecules themselves and the effects of external conditions. When the conductivity of easily ionizable substances on the surface is high and the partial pressure of water vapor is large, the conductivity of the fiber will be greatly improved.

3 Ways to Antistatic Textiles

Antistatic fabrics can be divided into two categories: civilian and industrial antistatic protective clothing. According to the end use, electrostatic protective clothing can be divided into dust-free sterile work clothes, fire-proof and explosion-proof work clothes, surgical clothes, safety work clothes (such as electrostatic protective clothing and conductive clothing worn by electric workers when working), etc.

3.1 Antistatic treatment of fibers

3.1.1 Use surfactant to hydrophilize the fiber

The principle of action is that the hydrophobic end of the surfactant molecule is adsorbed on the surface of the fiber, and the hydrophilic polar group points to the space to form a polar surface, which absorbs water molecules in the air, reduces the surface resistivity of the fiber, and accelerates the escape of charges. The surfactants used include cationic, anionic and nonionic surfactants. Among them, cationic surfactants have good antistatic effects, and high molecular weight nonionic surfactants have good antistatic effects and durability. The advantage of this method is that it is simple and easy to implement, and is especially suitable for eliminating electrostatic interference during textile processing; the disadvantage is that the durability of the antistatic effect is poor, the surfactant is easy to volatilize, and it is not resistant to washing, and it does not show resistance in a low-humidity environment. Electrostatic properties.

3.1.2 Blending, copolymerizing or grafting modification of fiber-forming polymers

The same as the previous method is to add hydrophilic monomers or polymers to fiber-forming polymers to improve hygroscopicity and thereby obtain antistatic properties. In addition to the typical blending spinning method of blending ordinary fiber-forming polymers and hydrophilic polymers, there are also blending methods in which hydrophilic polymers are added during the polymerization process to form a micro-multiphase dispersion system. For example, polyethylene glycol is added to the caprolactam reaction mixture, and polyethylene glycol is dispersed in PA6 in the form of fibrils. At the same time, polyethylene glycol also has a small amount of terminal hydroxyl groups that react with the hydroxyl groups in aminocaproic acid generated after caprolactam ring-opening, improving the durability of antistatic properties.

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

Using chemical initiation, thermal initiation, high energyGrafting on the fiber surface triggered by rays and ultraviolet irradiation can effectively improve the hygroscopicity of synthetic fibers, and the amount of hydrophilic monomer used is much less than other methods, and the durability is good. This type of antistatic fiber still accelerates the leakage of charges by increasing the hydrophilicity of the fiber. Therefore, in a dry environment with a relative humidity of less than 40%, the antistatic performance of the fiber will be lost.

3.2 Production of antistatic yarn

Mixing a small amount of conductive short fibers into spinning yarn can produce antistatic yarn, while reducing or even eliminating static electricity problems in the spinning process. When spinning, ordinary textile fibers are used as the main fibers, with a small amount of conductive fibers mixed in. The amount of conductive fiber mixed in is determined by the end use and cost of the product. A large number of experiments have shown that after a small amount (a few percent) of organic conductive fibers are mixed into the yarn, the resistivity of the yarn will be significantly reduced (the conductivity will be greatly improved).

3.2.1 Conductive fiber

Conductive fibers include metal fibers, metal-plated fibers and organic conductive fibers. The most 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, the metal fiber cohesion is small, the spinning performance is poor, and it is expensive when made into high fineness, so except for some special requirements, The use of metal fibers in the development of antistatic products is not yet widespread enough. Metal-plated fiber coats a metal layer on the surface of ordinary fiber to improve the antistatic effect. Its cost is significantly lower than that of metal fiber, but it is not resistant to washing and has a poor feel. At present, organic conductive fibers are mostly used to develop antistatic blended yarns.

Organic conductive fibers are conductive fibers that use ordinary fiber-forming polymers as the matrix and add conductive substances in a coating or composite manner. The organic conductive fibers currently used are mainly nylon-based, polyester-based and acrylic-based, and the conductive substances include carbon and metal compounds. Among them, the fibers made of carbon conductive materials are dark (black, gray), and the fibers made of metal compounds are white. The latter has slightly poor conductivity, but it is convenient for subsequent finishing processes (dying, etc.).

3.2.2 Spinning process

Due to the high cost of conductive fibers and the small mixing ratio, manual opening is generally used. In order to make the mixture 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: carding (one pass) → carding (two passes) → first and second combinations → third and second combinations → roving → spun yarn → winding.

3.3 Embed conductive filaments or antistatic yarns during weaving

In addition to improving raw materials, the development of antistatic textiles can also embed conductive filaments (or conductive fiber composite yarns) into the fabric at certain intervals when weaving the fabric. It can be embedded along the warp or weft direction, or it can be embedded along the warp and weft directions at the same time to form a grid. A large number of experiments have proven that no matter which way the conductive yarn is embedded, the antistatic effect of the fabric is significantly improved, but the effect is better when the conductive yarn or antistatic yarn is embedded in the form of a grid. Moreover, the antistatic properties of the fabric weaken as the spacing between embedded conductive filaments increases. The embedding spacing of conductive threads (or the content of conductive fibers in the fabric) should be determined based on the end use of the antistatic product and the conductive performance requirements. Please refer to the following table for details:

Since the price of conductive fibers is high and the fabric cost is high, the use of less conductive fibers should be considered in the design to obtain the best antistatic properties. By optimizing and analyzing various influencing factors (conductive filament spacing, fabric density, etc.), the optimal embedding spacing (conductive fiber content) that meets the product usage requirements can be obtained. In addition, since most of the conductive filaments used are black, when designing the fabric weave, we should try our best to hide the warp weave points of the conductive filaments under the warp weave points of the base tissue to ensure that the front fabric structure is not destroyed. On the reverse side of the fabric, the conductive threads should be exposed on the surface of the fabric as much as possible to facilitate discharge.

3.4 Use antistatic agent to finish the fabric

The method of directly antistatic treatment of fabric surfaces with surfactants began in the 1950s. This method is suitable for various fiber materials. Most of the antistatic agents used are polymers with structures similar to those of the fibers to be treated. They adhere to synthetic fibers or fabrics after dipping, rolling, and baking. These polymers are hydrophilic, so coating them on the surface can increase the conductivity of the fiber by absorbing moisture, preventing the fiber from accumulating more static charges and causing harm. In addition to making the fabric antistatic, this method also has the functions of moisture absorption, antifouling, and non-dust absorption. Since the antistatic method is relatively simple, the price of the finished product is also relatively cheap.

The process flow is: gray cloth → padding with antistatic resin (two dips and two rollings) → drying (100~110℃) → baking (150~160℃, 2min) → tentering → there are many methods for antistatic finishing of the finished product. There are currently three main types.

(1)Auxiliary adsorption and fixation method

(2) Surface graft polymerization method

(3) Low-temperature plasma surface treatment method

Since the latter two methods require more specialUsing hair spray or high-energy rays or plasma treatment, etc., the process is complex and the operation is complex, so the first method is generally used. It can be used for antistatic processing in the post-finishing process or in the same bath during the dyeing process, both of which can achieve ideal results.

4 Development status and prospects of textile antistatic technology

4.1 The current status and existing problems of antistatic technology at home and abroad

At present, the antistatic method of civil textiles mainly uses post-finishing. In electrostatic protection fabrics, conductive fibers are distributed in the fabric at certain intervals along the longitudinal or transverse direction or simultaneously to form vertical strips, horizontal strips or grids. According to the requirements of antistatic performance, the spacing range is often selected from 3mm to 15mm. It has good wash resistance, friction resistance, heat resistance, light resistance and permanent antistatic properties, and is not affected by changes in ambient temperature and humidity. It is being increasingly widely developed and used. From the perspective of textile development, it is advisable to use conductive fibers and then undergo antistatic post-treatment to achieve excellent antistatic properties.

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

4.2 Prospects

With the improvement of people’s requirements for clothing performance and the consideration of production precision and safety, the requirements for anti-static textiles are getting higher and higher. The current anti-static technology needs to be continuously improved and improved. Judging from the current situation, it will The mixed use of the above-mentioned antistatic methods can achieve excellent antistatic effects.