Antistatic Material

in modern industrial production and daily life, the accumulation of static charge often causes significant losses and disasters. For example, in the textile industry, the suction, repulsion, electric shock and discharge caused by static electricity bring great harm to the production and processing of fibers; in the chemical, oil refining, mining and military industries, due to the application of various non-metallic materials, The hazards caused by electrostatic accumulation have been reported many times; in plastic processing, photosensitive materials, printing, etc., electrostatic interference is also often encountered; in daily life, because of the clothes with static electricity, often make people have trouble electric shock, discharge phenomenon is common. Therefore, elimination of static charge and prevention of static electricity accumulation have attracted increasing attention. However, if we make reasonable use of these electrostatic mechanical effects and physical phenomena, we can make a variety of products according to the principle of static electricity, and use static electricity to benefit mankind.
Because the volume resistivity of the polymer is generally as high as 1010 to 1020 Ω. cm, it is easy to accumulate static electricity and cause danger. In some special occasions, antistatic polymers need to be used. A polymer containing an antistatic agent and having a volume resistivity of less than 1010 Ω · cm as measured according to the IEC60093 (Test Methods for Volume Resistivity and Surface Resistivity of Solid Insulating Materials) is referred to as an antistatic polymer. In order to make the polymer have antistatic properties, antistatic agents are often added to the polymer, or conductive fillers are introduced into the polymer, so that static electricity can be leaked in time. There are two methods for the preparation of antistatic polymers, one is to introduce antistatic agents, and the other is to introduce conductive fillers.
1. Classification of antistatic agents
At present, the antistatic agent for polymer is multi-series surfactant, which can make the polymer surface affinity to moisture and antistatic, and the ionic surfactant also has a conductive effect. They can be divided into different types according to their usage and chemical structure. According to the different ways of using antistatic agents, they can be generally divided into two types: external coating type and internal mixing type.

2. According to the chemical composition
(1) Surface active type antistatic agent
The molecular structure of the surfactant type antistatic agent is O-R-W. wherein O is a lipophilic group, W is a hydrophilic group, and R is a linking moiety between the lipophilic group and the hydrophilic group.
Ionic hydrophilic groups have ionization characteristics, according to the charged nature of hydrophilic group ions, ionic antistatic agents are generally divided into cationic, anionic and amphoteric antistatic agents. Cationic surfactants (the hydrophilic head is cation) mainly include various alkyl amine salts, quaternary ammonium salts and alkyl amino acid salts, among which the quaternary ammonium salt directly connected to the hydrophobic group on the N atom is the most typical. The cationic antistatic agent is excellent in antistatic property and has performances such as bactericidal property, flexibility and emulsifiability, but is poor in heat resistance.
Anionic surfactants (hydrophilic head is anionic), according to the different structure of its hydrophilic base, can be divided into organic carboxylate, sulfonate, sulfate ester salt, phosphate ester salt. Anionic antistatic agent has good heat resistance and antistatic effect, but its compatibility with resin is poor, which affects its transparency.
Zwitterionic surfactants (hydrophilic heads contain both anions and cations). Hydrophilic groups are dissociated in aqueous solution, which is characteristic of cationic surfactants in some media and anionic surfactants in some media. According to the structure of the hydrophilic group, it can be divided into imidazole type, betaine type, amino acid type and lecithin type. Amphoteric antistatic agent and cationic, anionic, non-ionic antistatic agent has good compatibility, it has strong adhesion to resin, antistatic effect is remarkable. The antistatic effect is similar to the cationic type, but the heat resistance is not as good as the anionic type.
② non-ionic non-ionic surfactants (hydrophilic head for some polar groups, such as in water can not be dissociated from the hydroxyl or polyoxyethylene ether, that is, dissolved in water is not charged), mainly hydroxyethyl alkyl amine, fatty amides, polyoxyethylene, polyol esters, etc. Good compatibility and heat resistance, non-toxic or low toxicity, can be used for food packaging materials, but there is a problem of large addition amount. It can be used in conjunction with cationic or anionic antistatic agents, and the antistatic effect is better.
(2) Polymer permanent antistatic agent
Polymeric antistatic agents have permanent antistatic properties and have become a hot topic in the study of antistatic agents in recent years. Generally can be divided into hydrophilic polymer type and composite type antistatic agent.
① Hydrophilic polymer antistatic agent Many hydrophilic polymers have relatively good antistatic performance and are stable and lasting. In the presence of a special compatibilizer, the hydrophilic polymer is stretched under a lower shear force, and the surface of the matrix polymer is a fine rib-like, that is, a layered dispersion structure, while the central part is close to the spherical distribution. The lamellar dispersion state of the hydrophilic polymer in this "core shell" structure can effectively reduce the surface resistance of the blend and has permanent antistatic properties. However, when the atmospheric humidity is less than 20%, the antistatic effect is no longer exhibited.
Polymer permanent type antistatic agent antistatic effect lasting, no induction period, not easily affected by wiping, washing and other conditions, but the addition amount is larger, the price is higher, and can only be added to the resin by mixing method.
Composite antistatic agent usually refers to two or more organic low molecular weight antistatic agent used in a certain proportion of products. Composite antistatic agent is an important way to improve the antistatic property and balance other properties. At present, the composite antistatic agents generally used in industry mainly include anion-non-ionic compound system, cation-non-ionic compound system, and non-ionic-non-ionic compound system.
3. Filling antistatic composite material
Another way to prepare antistatic polymers is to add inorganic conductive fillers or other conductive polymers into the matrix polymer, and to obtain composite materials with certain antistatic functions and good mechanical properties by physical or chemical methods. There are many kinds of inorganic filling antistatic materials, mainly carbon-based antistatic materials, metal-based antistatic materials and metal oxide-based antistatic materials.
Carbon-based conductive fillers mainly include carbon black, carbon fiber, graphite, and carbon nanotubes. The shape, size and distribution of carbon-based fillers in the polymer matrix are the main factors that control the performance of polymer-based antistatic composites. Table 2.4 shows the main performance characteristics of carbon-based conductive fillers.