The influence of the hottest static electricity on

2022-08-13
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Effects of static electricity on plastic products and solutions (Part I)

when two solids with different physical states are in contact and friction, charge redistribution will occur on their respective surfaces. After re separation, each solid surface will have excessive positive (or negative) charges than before contact. This phenomenon is called static electricity. In order to characterize the conductivity of materials, the concept of resistivity is introduced. The volume resistivity is the ratio of the potential gradient parallel to the current direction on the material surface to the current on the unit width of the surface. Generally, polymers are high insulating materials with high resistivity, so once charged, it is difficult to eliminate. In daily life, when people walk on the plastic floor, the friction between the sole of shoes and the floor will make the human body electrified. In serious cases, if the hand contacts the door handle or object, it may also produce discharge phenomenon, making people feel electric numbness; Electric fibrillation accident caused by medical operation. In the electronic industry, when the human body is charged, it is easy to puncture the circuit, causing the damage of the integrated circuit; Textile industry causes fiber aggregation and so on

there are two ways to eliminate the static electricity of polymers

(I) add conductive fillers: for example, metal, carbon fiber, carbon. This method requires a large amount of filler. Only when the filler reaches a certain percentage can the conductivity suddenly decrease, so as to achieve the antistatic effect. However, the color and quality of the products will be greatly limited by the amount of carbon black added. For example, when the conductivity of Carbon Black Filled PP reaches 15%, the conductivity is 4.1, and the shape and size of the sample will change significantly. At this time, the color of the material can no longer meet the requirements of various and beautiful. Metal fillers make materials of high quality. Metal fiber filler is of low quality, but it is easy to be broken and oxidized during processing, and the price is relatively expensive

(II) add antistatic agent to activate its surface and improve its surface conductivity: 1. Surface coated antistatic agent has low durability, is easy to be lost due to friction and washing, and can only provide temporary or short-term antistatic effect. 2. Mixed antistatic agent has high durability, but it has high requirements for antistatic agent

antistatic agent

static electricity generated on the plastic surface may cause various problems, such as hindering production, sparks, explosion and damage to the integrated circuit of electronic equipment. The way to remove static electricity is generally to use surfactants, such as antistatic agents, to reduce the surface resistance of polymers. Because such additives are hygroscopic, they absorb moisture from the atmosphere on the surface of the polymer to form a thin conductive film, so that static electricity can be quickly eliminated. In this process, water plays an important role. With the increase of atmospheric humidity, the surface conductivity of polymers also improves, causing the rapid loss of electrostatic charges, resulting in better antistatic properties

according to the usage, there are two kinds of surface active antistatic agents, namely external and internal, external, or local antistatic agents, which are applied to the surface of polymers by spraying, rubbing or dipping. Although this kind of external antistatic agent is applicable to a variety of polymers, their effectiveness is only temporary, and it is easy to lose it after contacting with solvents or rubbing with others. The internal antistatic agent is mixed in the polymer processing process. Such a surface active antistatic agent can supplement the antistatic function abraded due to handling. The effect of this internal antistatic agent depends on spraying cream. The meaning of frost spraying here refers to the process that the internal antistatic agent added to the resin partially migrates to the surface of the polymer. Therefore, the internal antistatic agent has long-term antistatic protection

surface active antistatic agents can be divided into cationic, anionic and non-ionic

cationic antistatic agents are usually long-chain alkyl quaternary, phosphorus second or collar salts, with chloride as the equilibrium ion. They are effective in polar matrices, such as rigid polyvinyl chloride and styrene polymers, but have adverse effects on their thermal stability. Such antistatic agents should not be used in articles in contact with food; And the antistatic effect is only 1/5 to 1/10 of that of internal antistatic agents such as ethoxylated amines

anionic antistatic agents are usually alkali metal salts of alkyl sulfonic acid, phosphoric acid or dithiocarbamate, which are also mainly used in PVC and styrene resins; Their application effect in polyolefin resins is similar to that of cationic antistatic agents. Among anionic antistatic agents, sodium alkyl sulfonate has been widely used in styrene resin, polyvinyl chloride, polyethylene terephthalate and polycarbonate

non ionic antistatic agents such as ethoxylated aliphatic alkyl amines represent the largest class of antistatic agents. They are widely used in polyethylene, polypropylene, ABS and other styrene based polymers. There are several ethoxylated alkyl amines produced and sold now. The difference lies in the length of alkyl chain and the size of unsaturation. Ethoxylated alkyl amine is a very effective antistatic agent, even in the case of low relative humidity, and it is effective for a long time. Such antistatic agents have been approved by the Federal Food and Drug Administration and are used in articles in indirect contact with food. Other commercially valuable non-ionic antistatic agents include ethoxylated alkyl amine, such as ethoxylated lauryl amine, and glycerol monostearate (GMS). Ethoxy laurylamine is suitable for polyethylene and polypropylene used in low humidity environment, and requires quick and long-term antistatic function. GMS antistatic agents are only considered for electrostatic protection during processing. Although GMS migrates rapidly to the polymer surface, it cannot play a lasting antistatic effect like ethoxylated alkyl amines or ethoxylated alkyl amines

up to 75% of liquid or ethoxylated alkylation with low melting point can be mixed with polymers to make concentrated masterbatches. These masterbatches are free flowing small spherical products, which are easy to ship, and they are easy to disperse when mixing. The advantages of ethoxylated alkyl amine masterbatch can be summarized as follows:

(1) good dispersibility, adding pre greatly reduces the loss of dispersing active materials

(2) small spherical products with good shipping performance and free flow, easy to measure and mix

(3) good processing performance, few screws slip in the extruder

the best selection and addition amount of antistatic agent depends on the nature of polymer, processing method, processing conditions, the type and amount of other additives, relative humidity and the end use of polymer. The time required to obtain sufficient antistatic effect is different. The generation speed and duration of antistatic protection can be increased by increasing the concentration of antistatic agent. However, excessive use of antistatic agents may cause the surface of the final product to be oily, which is detrimental to the printing performance or adhesion performance. Untreated inorganic fillers and pigments can adsorb antistatic agent molecules onto their surfaces, thereby reducing the effect of antistatic agents. This phenomenon can be compensated by increasing the amount of antistatic agent. However, for those products that come into contact with food, the amount of antistatic agent added must comply with the regulations of the Federal Food and Drug Administration (see "code of federal regulations, 21 (21cfr)"). (Code of Federal Regulations,Title 21(21CFR))。

when used in polyethylene, the physical form of ethoxylated alkyl amine antistatic agent, i.e. paste, liquid, small particles or solid, should be considered. If ethoxylated tallow amine cannot be treated because of its paste shape, the service life of the available liquid can reach several 10 years. Under the condition of high temperature processing (above 180 ℃), ethoxylated stearphthalein amine can be selected. If you need quick antistatic effect, you can choose ethoxylated laurylamine. When used in polypropylene, the problems to be considered are similar to those when used in polyethylene. No matter what kind of resin is used, the limits specified by the Federal Food and Drug Administration for various uses must be considered. For styrene based polymers, it is recommended to choose ethoxylated coconut amine or one of its appropriate masterbatches

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