1. Anti Static Fabric Finishing Overview
Static electricity is a ubiquitous electrical phenomenon. Electrostatic technology has been widely used, such as electrostatic dust removal, electrostatic separation, electrostatic spraying, electrostatic flocking, electrostatic copying and so on. At the same time, the harm caused by static electricity is also very huge. There are also many accidents caused by static electricity in industries such as petroleum, chemical, textile rubber, printing, electronics, pharmaceuticals, and powder processing. The static electricity generated in daily life may be harmful to the human body, especially the use of synthetic fibers is quite common, and synthetic fibers are prone to static electricity. How to eliminate the inconvenience caused by static electricity to people’s lives and work has become a new research topic. For the textile industry, it is very necessary to develop fabrics with antistatic properties. Anti static fabric can be used for people’s daily wear, and can also be made into labor protection protective clothing for use in workplaces with stricter requirements. Anti static fabric development is very rapid, and various countries have made different degrees of progress in research in this area.
The so-called static electricity refers to the phenomenon related to the accumulation of electric charge. Generally speaking, the friction between the surfaces of almost any two objects and the subsequent separation will generate static electricity. All matter is composed of atoms, and atoms are composed of a positively charged nucleus and an equal amount of negatively charged electrons orbiting the nucleus. The contact between the surfaces of two objects may cause electrons to flow continuously in two directions across the interface. Even one surface of the same material can get its lost electrons from the other surface. When the two surfaces are separated, due to the change in electron distribution, each material in contact will generate an equal number of charges with opposite signs (materials with excess electrons are generally negatively charged, and materials lacking electrons are generally positively charged).
If it is a conductor, when the object is separated, the electrons flow in the reverse direction at an instant, so that the number of electrons is balanced. If it is an insulator, the charge can continue to exist for a long period of time, resulting in static electricity. The lower the conductivity of the material, the more charge it carries.
“Friction electrification” means that the electrostatic phenomenon of textile materials that generates electric charge through friction on an object may be mainly caused by friction electrification. Various materials can be listed or classified in different tribo-charging sequences. In the arrangement sequence, the two materials that rub against each other are positively charged in the front of the sequence and negatively charged in the back of the sequence. The frictional charging sequence of textile fibers is: wool, nylon, silk, viscose fiber, glass fiber, cotton, ramie, acetate fiber, polyester, acrylic and polyethylene fiber.
2. The influence of Static Electricity
Due to the electrostatic phenomenon of textile fibers, it has brought various problems in textile processing and consumer applications. For example, in the manufacturing and processing of textile fibers, it will bring many difficulties to the opening, squeezing and carding of the fibers, the formation of the yarn package, the anti-pilling and the anti-fouling. Due to the effect of static electricity, the suction of dust and dirt will cause entanglement between clothes, clothes and the human body, and when walking on the carpet or rubbing on the decorative fabric, there will be electric shocks. These are all problems that annoy consumers. . The static electricity of textiles can also interfere with the normal operation of computers and other sensitive electronic instruments, and can also cause parachutes to fail to open, and can cause flammable gas and dust to burn when a large amount of electric charge is released.
Through detailed inspection and research, it is shown that textile materials (and building materials) used in hospital operating rooms have a tendency to generate static electricity. For example, for many years, the National Fire Protection Association has put forward special antistatic requirements for textile materials used in operating rooms where flammable anesthetic gases are present. Obviously, because electric sparks can cause flammable anesthetic gases to burn, of course there are other potential hazards. The discharge phenomenon caused by static electricity entering the conductor may cause current to enter the human body and cause damage to the patient’s heart or main blood vessel; because the discharge can pass through sensitive electronic components and cause the instrument to fail; at the critical moment of surgery, it is caused by electrical shock. The doctor’s unconscious action can lead to major medical accidents; the entanglement of bed sheets or decorative fabrics caused by static electricity reduces the work efficiency of the staff.
3. Fabric Antistatic Method
The fabric antistatic method is carried out from two aspects of controlling the generation of electric charge (electrification) and the leakage of electric charge.
3.1 Control of electrification
(1) Reduce the chance of contact friction, such as adding wool oil on wool, adding lubricating agent during spinning, to increase the lubricity of the fiber, or to improve the smoothness of processing equipment, such as chrome plating, to reduce the friction coefficient, and at the same time to reduce friction Pressure and friction speed to reduce electrification.
(2) Use materials that are close to the triboelectric sequence as much as possible. The closer the material, the less the amount of charge generated.
(3) Increase the relative humidity of the environment, such as the dampness in the weaving workshop, to reduce the electrification.
(4) Use materials that can generate opposite charges, so that the generated charges cancel each other out. For example, when polyester is blended with cotton, the friction between polyester and steel wire is negatively charged, and the friction between cotton and steel wire is positively charged. When polyester-cotton blends, the positive and negative charges can be neutralized.
3.2 Elimination of Static Electricity
Elimination of static electricity is an effective way to prevent static electricity from quickly leaking out the generated charges. Elimination of static electricity can be used with a dissipator, and it can quickly leak to the ground. There are roughly three antistatic methods.
(1) Grounding. Connect live objects to the ground.
(2) Increase the humidity of the surrounding environment. The surface resistance of polymer materials decreases with the increase of relative humidity. When the relative humidity reaches a certain value, the decrease will be rapid. Generally, the effect of eliminating static electricity can be achieved when the relative humidity is greater than 70%.
(3) Increasing the conductivity of materials is the most basic and important method of antistatic.
① Internal antistatic agent method: Incorporating antistatic finishing agents into high polymers such as rubber, paper, plastics, and fibers can achieve a long-lasting antistatic effect, but the antistatic agent must be compatible with it, and It has molding stability, processability, and has no adverse effects on metals. Pay more attention to its toxicity.
② External antistatic agent method: spraying, dipping or coating antistatic agent on the outside of the material is generally temporary and not durable. The lubricating agent during spinning and the antistatic finishing of textiles belong to this method.
③ External permanent antistatic agent method: add antistatic agent during post-processing of high polymer to make the material and antistatic agent become anion and cation adsorption, or crosslink by heat treatment, or fix it on the fiber with an adhesive. It has washable and antistatic properties.
④ The material surface modification method forms a hydrophilic polymer skin layer with antistatic effect on the surface of the material. For example, the copolymer of polyethylene glycol and PET is used as the skin layer on the polyester fiber, and the grafting method can also be used to increase the moisture absorption rate.
⑤ Mixing with conductive materials: Mixing high polymers with conductive materials such as metals, graphite, etc., usually mixed with 0.05% to 2% of conductive materials, can obtain a durable antistatic effect.
4. The Anti Static Fabric
The anti static fabric properties are usually obtained by the following ways: the anti static fabric contains antistatic fibers; the conductive fibers are blended or interwoven with other fibers; the antistatic agent finishes of ordinary fabrics.
4.1 Anti Static Fabrics Containing anti static Fibers
The key to anti static fabric properties containing anti static fibers is antistatic fibers. There are two sources of anti static fibers: the use of external anti static agents and the use of internal anti static agents for processing. become. Therefore, the use of external anti static agents is to use physical or chemical methods to process the fiber surface, such as using ionic or non-ionic external anti static agents to coat the surface of the fiber to absorb moisture in the air and reduce the resistance value of the fiber. Or the hydrophilic anti static resin is adhered to the surface of the fiber through a series of processing to form an extremely thin continuous film, which uses the hygroscopicity of the film to increase the conductivity of the fiber. There are many ways to use internal anti static agents to make anti static fibers:
(1) In the polymerization stage, the antistatic monomer is added through the copolymerization method.
(2) Introduction of hygroscopic antistatic groups by graft copolymerization.
(3) The composite spinning method is used to form a continuous structure containing an antistatic agent inside the fiber.
(4) The blending spinning method is used to make the antistatic agent exist in the inside of the fiber in a microfiber state, and so on.
Since the anti static agent exists inside the fiber instead of the fiber surface, it is not easy to wear and lose due to washing, so the fiber anti static property is durable and the anti static effect is significant. Among these methods, the blending spinning method is the most widely used. .
Anti static fiber is a kind of differentiated fiber. In addition to having anti static properties, it also maintains the characteristics of the original fiber. It can be spun purely or blended or interwoven with other ordinary fibers, so that the fabric can be antistatic. At the same time, it has the style and performance of other fibers.
There are many types of anti static fiber blending or interweaving. In order to obtain the best blending and interweaving effect, so that the fabric has good anti static properties, the anti static fiber should be dispersed as evenly as possible in the fiber or fabric when blending or interweaving. At the same time, pay attention to the mutual matching with other fibers, learn from each other’s strengths, and improve the composite effect.
4.2 Use of conductive fiber
4.2.1 Types and Manufacture of Conductive Fiber
Like anti static fiber, conductive fiber is also a differentiated fiber. Conductive fibers are divided into three categories:
(1) Metal fibers: such as stainless steel, copper, nickel, aluminum and other fibers. The manufacturing methods include stretch die method, glass fiber coating method, molten metal centrifugal spinning method, molten metal jet spinning method, suspension spinning method of metal powder in polymer solution, etc. The fiber diameter is usually 4~16μm.
(2) Carbon fiber: sintered with acrylic fiber, viscose or pitch fiber as raw materials.
(3) Conductive fibers made by coating the surface of chemical fibers or adding conductive substances inside them: such as plating the surface of the fiber with metals such as aluminum and nickel; metal vapor adheres to the surface of the fiber in a vacuum; conductive resin coating On the surface of the fiber; add conductive particles such as metal or carbon fiber to the polymer before spinning; use composite spinning technology to coat the surface of the fiber with conductive materials and so on.
The conductive components of conductive fibers include metals, metal compounds, carbon black and so on. Conductive fibers have good electrical conductivity, and the generated static electricity can be dispersed and leaked faster, which can effectively prevent the local accumulation of static electricity; at the same time, conductive fibers also have corona discharge capability, which can discharge static electricity into the atmosphere. Compared with antistatic fibers, the conductivity of conductive fibers is mainly based on the movement of free electrons, rather than relying on moisture absorption to increase conductivity, so it is less affected by environmental humidity, and it can still perform well under extremely low environmental humidity. Antistatic performance.
4.2.2 Weaving of Conductive Fiber
Conductive fibers can be interwoven or blended with other fibers in the form of filaments or staple fibers. Conductive fibers should be evenly mixed with other fibers as much as possible, evenly mixed weave, so that the spacing of conductive fibers is shortened, conductive fibers are carefully organized into various networks in the fabric, so that the uniform distribution of the fabric’s antistatic properties can be achieved. Practice has proved that for fabrics mixed with conductive fibers, the smaller the spacing of the conductive fibers, the more uniform the addition of conductive fibers, and the stronger the antistatic effect.
For metal fibers, due to the difficulty of textile processing, when blending or interweaving with other fibers, the maximum amount does not exceed 2% to 3%. For other composite conductive fibers, the amount depends on the requirements, usually not more than 10%.
Because the conductive fiber has corona discharge characteristics, the sharper its shape, the larger the specific surface, the stronger the electric field, and the easier the corona discharge. Therefore, the ultra-fine, profiled, and porous conductive fibers are beneficial to enhance the corona discharge effect of the conductive fibers.
4.3 The Antistatic Agent Finishing of Ordinary Fabrics
Comparing with the method of adding antistatic agents to the chemical modification and blending spinning from the polymerization stage. The antistatic agent finishing method of the fabric is simple, quick to take effect, and less investment. It is suitable for In order to meet the changing requirements of the current textile market, its antistatic mechanism has the following points:
(1) Inhibit the amount of static electricity, that is, give the fiber a certain hygroscopicity and increase the leakage amount of the fiber.
(2) Increase the amount of static electricity dissipation, that is, increase the fiber conductivity by neutralizing the surface charge of the fiber and relying on ionization.
(3) Reduce the friction coefficient of the fiber surface to inhibit the occurrence of friction static electricity.
The fabrics finished with antistatic agents can be widely used for various purposes, such as underwear and outerwear. However, due to the different properties of underwear, the finishing of the fabrics should be based on the requirements of its use. Through practice, there are the following requirements for antistatic agents used in fabric finishing:
(1) The antistatic effect is good, the dosage is small, and it is not affected by other additives, and it can also have a good antistatic effect under low humidity environmental conditions.
(2) Does not reduce the color fastness of the fabric and does not change its hue.
(3) Basically does not reduce the physical properties of the fabric and the fabric feel style.
(4) No adverse effects on processing equipment, such as rust, etc.
(5) No peculiar smell and no skin irritation.
(6) It has the durability to adapt to the use of fabrics and has good heat resistance.
There are usually three methods for antistatic finishing of ordinary fabrics:
4.3.1 Padding Method
After the fabric is immersed in the antistatic dipping liquid, it is squeezed and rolled by rollers to control the amount of liquid. The number of rollers is different, and various forms of padding can be performed on the fabric. The processing technology usually includes: padding→drying→baking, padding→drying→steaming, padding→steaming, etc.
4.3.2 Coating Method
Use a coating scraper to scrape the coating containing the antistatic agent on the cloth surface. There are various shapes of squeegee. By choosing different squeegees, coating films of different thicknesses can be obtained.
4.3.3 Resin Method
For indirect hot-melt resin antistatic agents, the above-mentioned padding and coating methods can be used to cure on the surface of the fabric. Direct hot-melt resin antistatic agents should be directly melted by special equipment and then fixed on the surface of the fabric or laminated Way to form a continuous antistatic film.
Choose a suitable fabric finishing method and an antistatic agent with good effect to form a uniform antistatic film on the surface of the fiber or improve the adhesion between the antistatic agent and the surface of the fiber, and promote the penetration of the finishing agent into the fiber to obtain durability. Good antistatic effect.
At present, the development and research of anti static fabrics in European and American countries and Japan are progressing rapidly, especially in the area of differentiated fibers. Some have begun industrial production, such as the nylon BCF fiber Antron III of DuPont in the United States, and the conductivity of Toray in Japan. Acrylic SA-7, Ultron, a polyamide fiber from Monsanto in the United States, and Epitropic, a polyester fiber from ICI in the United Kingdom, etc. The application of these fibers can make the fabric have excellent antistatic effects. Adapting to market needs and accelerating the pace of research in this field is an arduous task for my country’s textile industry.
5. Types and Characteristics of Antistatic Agents
Among them, the cationic antistatic agent has excellent antistatic properties, but the heat resistance is relatively poor, and it is harmful to the skin, so it is generally used as an external coating type. Anionic antistatic agents have better heat resistance and antistatic effects, but they have poor compatibility with resins and have an impact on the transparency of the product. The non-ionic antistatic agent has good compatibility and heat resistance, and has no adverse effect on the physical properties of the product, but the dosage is relatively large. The biggest feature of amphoteric antistatic agent is that it can be used in combination with cationic antistatic agent and anionic antistatic agent. The antistatic effect is similar to cationic, but the heat resistance is not as good as nonionic.
6. Antistatic Performance Test
6.1 Surface Specific Resistance
The non-conductive ability of a material is called resistance R, which is usually expressed by Ohm’s law. Resistance is the current produced by the voltage V (volt) of the material against the current IV (ampere). Ratio. The surface specific resistance represents the size of the static attenuation speed of the fiber material, which is equal to the resistance when the width and length of the surface of the material are both equal to 1 cm, and the unit is Ω. The surface specific resistance Rs of general fibers is less than 109Ω, and the antistatic effect is good, and its half-life t1/2=0.01s; R3 is less than 1010Ω, the antistatic effect is general, the half-life t1/2=0.1s; Rs is between 1011~1012Ω, then the effect of static electricity is poor, and more than 1013Ω is a substance prone to static electricity.
6.2 Half-life t1/2
Half-life is also a physical quantity that measures the electrostatic decay rate on the fabric. It represents the time required for the electrostatic charge on the fabric to decay to half of the original value, and the unit is s.
6.3 Mass Specific Resistance
Mass specific resistance is the resistance value expressed in Ω when a uniform sample is 1cm long and weighs 1g, and the unit is Ω•g/cm2.
6.4 Static voltage
After the textile rubs against each other or with other articles, the voltage value when the frictional electrification or leakage reaches the equilibrium. It is generally believed that when the static voltage is below 500V, the fabric has antistatic properties.