1. Introduction Antistatic work clothes are special work clothes with dust-free and antistatic properties suitable for industries such as electronics, optical instruments, pharmaceuticals, microbial engineering, and precision instruments. The fabric is generally a synthetic fiber fabric with woven conductive yarn. Antistatic work clothes (GB12014-1989) are made of antistatic fabric to prevent static electricity accumulation in clothes. They are suitable for wearing in places sensitive to static electricity or places with fire or explosion hazards. The production process of the antistatic fabric used is mainly to mix all or part of the antistatic fibers or antistatic synthetic fibers made of conductive materials made of metal or organic matter at roughly equal intervals or evenly during weaving, or the two are mixed and interwoven. The antistatic work clothes series produced by Dongguan Jiachuang are all made of high-quality fabrics, with good antistatic shielding performance and no dust, suitable for customers with various requirements. The work clothes are available in a variety of styles such as split, one-piece, and pullover styles. Socks, hats, and masks can be freely combined, and can also be processed according to samples and customized according to customer requirements. Antistatic work clothes are suitable for: petroleum industry; mining industry; chemical industry; electronic industry; special industries, such as: atomic energy, aerospace, weapons, etc. Other industries, such as: food, fireworks, medicine, etc. Antistatic work clothes refer to work clothes made of antistatic fabrics to prevent static electricity accumulation on clothing. Antistatic fabrics are fabrics that are roughly evenly or evenly mixed with conductive fibers or antistatic synthetic fibers or a mixture of the two during weaving. Conductive fiber refers to the general term for fibers made of conductive materials or sub-conductive materials made of metal or organic matter in whole or in part, and its volume resistivity ρv~ is between 104 and 109Ω/cm. According to the distribution of conductive components in the fiber, conductive fibers can be divided into three types: uniform conductive component type, conductive component covering type, and conductive component composite type. At present, most antistatic fabrics are made of conductive fibers, especially conductive component composite type, that is, composite fibers are used the most.

Antistatic work clothes made of chemical fiber fabrics with conductive fibers added have two mechanisms of charge leakage and neutralization. When grounded, the static electricity on the fabric is not only neutralized by the corona discharge of the conductive fiber, but also discharged to the ground through the conductive fiber; when not grounded, the static electricity is eliminated by the weak corona discharge of the conductive fiber.

2. Characteristics of anti-static ultra-clean fabrics in anti-static clothing

The anti-static ultra-clean fabrics used in anti-static work clothes are usually called "conductive silk". In fact, this statement is not strict. Conductive silk can be divided into those suitable for anti-static (ESD) and those suitable for clean rooms (Clean Room) according to its own technical characteristics. Only conductive silk suitable for clean rooms can be called anti-static ultra-clean fabrics.

What is anti-static fabric? Fabrics that have been treated with anti-static processing can be called anti-static fabrics. The anti-static processing methods of fabrics are usually:

① The fabric is finished with an anti-static finishing agent;

② Fiber grafting modification, blending and interweaving of hydrophilic fibers for the purpose of improving the hygroscopicity of the fabric;

③ Blending or weaving conductive fibers;

The mechanism of action of the first two methods is to increase the moisture regain of the fabric, reduce the insulation, and accelerate the leakage of static electricity. Therefore, if it is in a dry environment or after multiple washings, the processing effect is either not durable or not significant, and it is usually applied to ordinary clothing fabrics. Only the third method can solve the static electricity problem of textiles in a long-lasting and efficient manner, so it is currently widely used in the production of anti-static work clothes. Fabrics are finished with anti-static finishing agents.

Anti-static fabrics can be woven fabrics, such as conductive silk, anti-static T/C fabrics, or knitted fabrics, such as anti-static knitted gloves, anti-static knitted underwear, etc. In addition to meeting the general technical standards for textiles, anti-static fabrics must also have good anti-static properties to meet the needs of product production and safety. Technical requirements can refer to GB12059-89 "Performance of Synthetic Fiber Antistatic Silk for Electronic Industry"

The difference between super-clean fabrics and ordinary anti-static fabrics in anti-static clothing

The difference between anti-static super-clean fabrics and ordinary anti-static fabrics mainly lies in the concept of "super-clean". Anti-static super-clean fabrics must have the following three characteristics at the same time:

Anti-static function: static electricity will absorb dust and make the absorbed dust difficult to be blown away during wind shower. Therefore, the primary feature of anti-static super-clean fabrics is anti-static performance. At the same time, this anti-static performance must be long-lasting and efficient, and will not be significantly attenuated due to daily washing and friction.

The fabric itself does not generate dust: Since it is worn in a clean room, the fabric is required not to become a dust source in the clean room, which determines that super-clean fabrics can only be produced with chemically synthesized long fibers. Natural short fibers such as cotton, linen, and silk cannot be used in super-clean fabrics, although these raw materials can make the fabrics more wearable. At the same time, the amount of dust generated by the selected chemical fiber filaments must also be strictly controlled. Generally speaking, full matte polyester filament is not suitable for weaving anti-static ultra-clean fabrics. Because the matting agent added in polyester production - titanium dioxide will become a source of pollution.

Fabrics must have good dust filtration: dust in clean rooms mainly comes from indoor air flow and human activities. When the equipment conditions are determined, improving cleanliness means that the tiny dust generated by the human body is controlled in the clothes to the maximum extent, allowing it to pass through the fabric into the air. This is what is called a high dust filtration rate of the fabric. Improving the dust filtration rate is at the expense of the breathability of the fabric, so knitted fabrics and loosely woven fabrics are not suitable for clean rooms.

How to choose anti-static clothing ultra-clean fabrics

Since our country has not yet formulated corresponding ultra-clean fabrics or clean clothing testing standards, the selection of anti-static ultra-clean fabrics can only be selected by each application unit according to the requirements of the working environment or after testing or experience. Powerful users can spend hundreds of thousands to purchase a complete set of equipment, and test each batch of clean clothing according to ISO standards in an environment with the same cleanliness as the actual application environment. Most users can only make choices based on experience (including other people's experience). To learn how to choose ultra-clean fabrics correctly, you must first understand some basic knowledge about fabrics.

Woven fabrics are made of yarns in the warp and weft directions interwoven with a specific arrangement density and a specific organizational structure. In general, it is about what raw materials are used, how much elasticity is arranged, and what pattern is woven. To weave anti-static ultra-clean fabrics, conductive fibers must also be added. Here, yarn, (warp and weft) arrangement density, fabric organization and conductive fibers are the four elements of anti-static ultra-clean fabrics. Selecting anti-static ultra-clean fabrics is to compare the four elements of fabrics according to the cleanliness requirements of the working environment.

Identification of ultra-clean fabrics for anti-static clothing

Measure warp and weft density: Use a warp and weft density mirror to measure the warp and weft density of the fabric respectively, and compare them.

Measure resistance: Use a surface resistance tester to measure the warp and weft resistance of the fabric respectively, and compare them.

The principle of comparison is:

Choose the one with smaller resistance;

If the resistance is the same, choose the one with stable resistance value;

Pay attention to distinguish whether antistatic agent is added to the fabric during finishing (applicable to conductive silk with conductive fiber added only in the warp direction, commonly known as striped cloth). The method is to use a surface resistance tester to measure the resistance in the warp and weft directions respectively. If they are the same, it means that antistatic agent is added. Then the measured resistance does not represent the real level.

Look at the microstructure: use a high-power magnifying glass to look at the quality of the cloth surface, compare the size of the gap between the fibers (related to the dust filtration rate), see if there are attachments on the fiber surface (related to the amount of dust), see if the fiber arrangement is neat and the tightness is consistent (if the tightness is inconsistent, the loose part of the fiber is easy to be abraded when wearing and washing, and dust will be generated when wearing later).

Check the conductive fiber: conductive fiber is the key raw material in anti-static ultra-clean fabrics. Checking the conductive fiber is to see whether the conductive fiber is added according to the specifications and what kind of conductive fiber is added.

The inspection method is: carefully cut the fabric along the edge of the black conductive fiber with scissors, separate the black conductive fiber, use a magnifying glass to observe whether there are one or several relatively thick fibers, and use a surface resistance tester to measure the resistance of the separated conductive fiber. After removing several strands in a row, it can be basically determined whether each black silk in the fabric contains conductive fiber. (Conductive silk uses carbon organic conductive fiber, which is black or gray, generally around 20D, between 1F and 6F. In order to meet the strength requirements when weaving, an ordinary black or white polyester fiber is required).

Compare fabric process parameters: require suppliers to provide basic fabric parameters, such as yarn fineness (how many D, how many F), warp and weft density, fabric organization, finished width, dyeing shrinkage, and what kind of conductive fiber is used.

3. Things to note when managing anti-static work clothes are as follows

1. All clothing should be made of anti-static fabrics, and lining is generally not used. When lining must be used, the exposed area of the lining should not exceed 20% of the total inner surface area of the clothing.

2. Different levels of anti-static fabrics and anti-static work clothes should be selected according to the electrostatic sensitivity of different processing objects in different places.

3. Washing of work clothes should be carried out in a simple way as much as possible, and strong mechanical and chemical operations should be avoided.

4. It is forbidden to attach or wear any metal objects on anti-static work clothes.

5. It is not allowed to put on or take off work clothes at the site of operating electrostatic sensitive products (changing clothes should be done in the designated dressing room). All buttons of work clothes should be buttoned, and try not to put them in a state close to taking off clothes.

6. Several pieces of anti-static work clothes purchased in bulk should be randomly selected for testing of charge before wearing. After wearing for a certain period of time, especially when the wearer feels an electric shock when taking off the clothes, retesting is required.

IV. Performance testing of anti-static work clothes

1. Purification performance testing The polluted particles attached to the inside and outside of the anti-static work clothes used in clean rooms are measured by the following four methods: ASTM F-51 method (microscope method), F-51 revision method (counting method), HELMKE drum method (drum method, equivalent to ASTM test method) and vibration test method (vibration method).

(1) ASTM-F-51 method (microscope method) The test probe is equipped with a filter membrane and is directly connected to the suction metering pump. The air volume passing through is 28L/min. During the test, air is passed through the test clothes, and the dust particles contained in the air are captured on the test filter membrane. The number of dust particles is observed and counted with a 400x microscope. The number of particles of 0.5-5 and above 5 on the filter membrane is read. There are 3.08mm grids printed on the filter membrane, and the number of particles in one grid can be read.

(2) ASTM-F-51 revised method (counting method) Air is passed through the test clothing, and the size and number of dust particles are measured with a particle counter. The sample is placed on a stand with a metal mesh, and a sampler (replaced with a 47mm filter holder) is used for contact attraction. The amount of air passing through is 28L/min.

(3) Helmke Drum Test The sample is placed in a rotating drum with a side opening and rotated. The dust particles are sampled from the drum. The number of particles is measured with a particle counter to determine the cleanliness level. The size of the rotating drum is 43cm×33cm, and there are 4 blades on the inside of the drum. The drum rotates at 10 rpm.

(4) Vibration method The sample is placed in a small chamber, and particles are generated by vibration and torsion, and measured with a particle counter. At the same time, particles with large particle sizes (above 25) are captured on the filter membrane and the number of particles is read. The air volume is 3.5 feet/minute (0.099m/mim) and the vibration frequency is 150 times/minute. At present, there is no national standard in my country for the dust-free performance test of clean work clothes. You can refer to the Japanese Industrial Standard JIS-B-9923 studied by the Special Committee of the Japan Air Cleanliness Association and the American IES Standard RP-CC-003-87-T. For the evaluation of dust-free performance, each industry can use the clean room standards specified by the international standard ISO/TC209 in combination with their own cleanliness levels.

2.2 Antistatic Performance Test Antistatic property is an important characteristic of antistatic work clothes, especially in industries such as microelectronics, where the antistatic performance requirements of clothing are more stringent. The test method can be based on the National Standard of the People's Republic of China GB/T12703-91 "Test Methods for Electrostatics of Textiles". Since the fabric used for clean work clothes is polyester filament fabric with woven conductive threads, only the friction charging voltage (B method), charge surface density (C method) and friction charging of work clothes (E method) in this standard are suitable for the anti-static performance test of clean work clothes. In addition, you can also refer to the National Standard of the People's Republic of China GB/T12059-89 "Performance and Test Methods of Synthetic Fiber Antistatic Silk for Electronic Industry".

(1) Friction charging voltage method The test principle of this method is to make the sample and the standard cloth rub against each other under certain tension conditions, and evaluate the friction charging relationship between the wearer and the outerwear based on the highest voltage and average voltage generated at this time. The method is to clamp the sample (4 pieces, 2 warps and 2 wefts, size 4cm×8cm) on a sample clamp on a rotating drum (outer diameter 150±1mm, width 60±1mm). The drum is rubbed with a standard cloth (nylon or polypropylene) at a speed of 400rpm, and the maximum value (V) of the sample's charged voltage within 1min is tested.

(2) Charge surface density method The sample is rubbed with a nylon standard cloth in a specific way under specified conditions and then

V. Technical requirements for the production of anti-static work clothes

Anti-static work clothes must be equipped; anti-static work clothes can be used for work in A02 combustible dust places. "Labor Protection Equipment Standard (Trial)" (National Economic and Trade Commission Safety [2000] No. 189) also requires that gas station operators, liquefied petroleum gas tankers and similar types of workers must be equipped with anti-static work clothes.

Selection

The anti-static performance of anti-static work clothes has a certain durability. Therefore, when choosing anti-static work clothes, it is also necessary to choose work clothes with corresponding anti-static levels according to the washing requirements determined by the pollution situation in the workplace.

Anti-static work clothes are used in fire and explosion places, so anti-static work clothes with flame retardant properties should usually be selected to provide more reliable protection for workers. Anti-static work clothes used by gas station operators and similar types of work should also have oil-proof effects.

All-cotton work clothes have the effect of preventing static electricity, but they may not meet the requirement of anti-static work clothes that the charge of a single piece of clothing is less than 0.6μC, especially after washing, due to the selection of detergents and other reasons, the effect of preventing static electricity will be reduced. Therefore, when choosing anti-static work clothes made of cotton fabrics, especially in the dry northern regions, you must be cautious.

Quality Verification

When choosing anti-static work clothes, you should ask the supplier for a test report to check the product characteristics, production batch, production date, and whether the fabric samples provided in the test report are consistent with the products supplied. Since the structure of anti-static work clothes has a great relationship with their anti-static effect, you should pay attention to the following when checking the ordered anti-static work clothes:

1. The buttons, zippers, hooks, trips and other accessories of the work clothes should preferably be made of non-metallic materials such as plastic and nylon. If metal accessories are selected when making the work clothes, you should try them on to ensure that the metal accessories are not exposed when wearing and engaging in various activities.

2. Look at the back of the work clothes. It is best to use anti-static fabrics for pockets, edges, reinforcements, etc.; if made of other materials, the exposed area should be less than 20% of the exposed area of the entire anti-static clothing.

3. For cotton clothes and fully lined work clothes made for cold protection or other special requirements, the cotton inner cover and full lining should be detachable.

4. Check the anti-static fabric. For the same type of conductive fiber, the higher the density added, the better the anti-static performance.

VI. Maintenance

Packaging and storage

During transportation, it should be noted that the anti-static work clothes must be covered, the packaging must not be damaged, and the sun and high temperature must not be exposed. It is strictly forbidden to use hand hooks to drag during transportation.

Anti-static work clothes should be stored in a dry and ventilated warehouse to prevent mildew and deterioration. When storing, keep them more than 200mm away from the ground and walls, and more than 1m away from all heating elements. Avoid direct sunlight and do not place them in the open air.

Anti-static wool knitted fabrics must be packed and stored with an appropriate amount of mothproofing agent.

Maintenance and maintenance

It is best to use neutral detergent to wash anti-static work clothes. Do not mix with other clothes when washing. Use hand washing or washing machine soft washing program to avoid breaking the conductive fibers. The washing water temperature should be below 40℃, and rinse with normal temperature water. The washing time should be as short as possible, but it must be fully rinsed to remove residual detergent. Anti-static work clothes with flame retardant and oil-proof properties should not be decontaminated with bleaching powder or organic solvents.

VII. Wearing precautions

1. Anti-static work clothes must be worn with anti-static shoes specified in GB4385.

2. It is forbidden to attach or wear any metal objects on anti-static clothes. Tools that need to be carried with you should have anti-static and anti-spark functions; metal tools should be placed in the belt of anti-static work clothes, and metal parts should not be exposed.

3. It is forbidden to wear and take off anti-static work clothes in flammable and explosive places.

4. Anti-static work clothes cannot be worn in strong electromagnetic environments or areas with high-voltage bare wires nearby

VIII. Service life Anti-static work clothes should be scrapped in time if they are damaged, the seams are broken, moldy, the conductive fibers are broken, or the washing resistance time specified by the anti-static level has been reached. The user unit should sample and inspect the anti-static work clothes that have reached half of the service life or have been stored for 1 year. Products that have lost their anti-static properties after testing should be scrapped in batches in time to ensure qualified use of the products.