Antistatic agents refer to the chemical reagents capable of increasing the dielectric surface conductivity and volume conductivity to prevent static electricity. Electrostatic hazard has widely spread throughout various industrial and mining enterprises. It not only affects the quality of products, but also may cause serious burning and explosive accidents due to that the intensity of the electric field of the electrostatic is too large which generated sparks and further igniting flammable vapors, gases or dust mixture with air. When the dielectric caused static electricity reach certain charge density, there appears interaction between different parts of the processed dielectric material, affecting the normal production process, which is the technical interference caused by static electricity. Weak current caused by static electricity, either flows through the human body in long-term or transiently sparks in the human body, will do harm to the human health.
Kind of antistatic agent
Based on the exact property, antistatic agents can be divided into absorbent type and surfactant-type two categories.
Hygroscopic antistatic agent has moisture or moisturizing properties, is capable of forming a water film on the surface of the dielectric; antistatic agents belonging to this kind include polysiloxane, polyol amine, ethylene glycol, glycerol, sorbitol and inorganic salts (calcium chloride, lithium chloride, magnesium chloride).
Surfactant type antistatic agent; the lipophilic moiety in the molecule can firmly adhered to the dielectric surface with the hydrophilic portion absorbing water from the air, thus forming a thin conductive layer on the resin surface, being able to eliminate the static.
Based on the usage method, antistatic agents can be divided into external and internal antistatic agent.
In the field of mining, mineral processing and metallurgical industries, to prevent electrostatic effects produced during the process of mineral powder and metal powder, people generally apply topical antistatic agents; the surface coating antistatic agents used in the production process of synthetic fiber also belongs to external use. The added antistatic agent during the manufacturing process of synthetic resin film and moldings belong to internal applied antistatic agent. In circumstances of spraying the antistatic agent on the surface of the material (external), the conductive layer formed on the surface can have its antistatic effect be significantly reduced after being removed with rubbing or washing; while the surface conductive layer formed through the inner used antistatic agent, although may lose, but can still produce antistatic effect later due to that shortly after that new antistatic agent molecule move from internal to the surface, thus being able to maintain long-term antistatic effect. Topical antistatic agent includes surfactant and silicon compound while internal antistatic agent, in addition to the surfactants also include other inorganics such as filling metal powder and carbon black in the solid dielectric material, being able to achieve antistatic effect through improved volume conductivity.
Antistatic agents having surface activity can be divided according to their ionic form into three categories including cationic, anionic, and nonionic.
The representative products of anionic antistatic agent include high-grade alcohol sulfate ester salts, aliphatic sulfonate, and high-grade alcohol phosphate ester salt. The cationic part of such kind antistatic agent, in addition to use sodium, potassium and other metal ions, you can also choose alkanolamine such as triethanolamine. The feature of the anionic antistatic agent is the excellent thermal stability.
Cationic antistatic agents have alkyl quaternary ammonium salts and alkyl amine salts having 8 to 22 carbon atoms as the representatives. The balance ion of its anion part, in addition of using a halogen ion, we may also choose nitric acid, sulfuric acid, perchloric acid and so on. This kind of surfactant is of the strongest capability in antistatic agents but has its thermal stability be slightly inferior to other types.
Nonionic antistatic agent includes the polyvinyl chloride derivatives and some esterified product of polyols with excellent thermal stability and can be used as the internal-used antistatic agent of food packaging films.
In addition, there is also high-molecular antistatic agent used for spraying with the advantage being durable and washable.
Mechanism of action of the antistatic agent
There are major four ways in which antistatic agents can eliminate the static electricity as follow:
(1) The hydrophilic group of the antistatic agent can increase the hygroscopicity of the surface of the product, forming a single-molecule conductive film.
(2) Ionic antistatic agent can increase the ion concentration of the surface of the product, thereby increasing the conductivity.
(3) Antistatic agent of large dielectric constant can increase the di-electricity in the gap between different friction bodies.
(4) Increase the surface smoothness of the product to reduce the friction coefficient.
In the above four kinds of action modes, (1) and (2) to reduce the resistance of the product, increase the conductivity and accelerate the charge leakage. (3) and (4) can reduce the generated electric charge during the friction. It is generally believed that effects of the (1) and (2) are the main function of the antistatic agent. Of course, an antistatic agent is not necessarily to have all the above functions.
The performance requirement of the antistatic agent
Ideal antistatic agent should have the following conditions:
(1) Large and long-lasting anti-static performance.
(2) Excellent thermal resistance; it should not decompose in the high temperature of molding process (120 ~ 300 ℃) or under repeated thermal processing.
(3) Moderate compatibility with the plastics with both certain compatibility and a certain degree of incompatibility; during the process of mixing and melt processing, it can be well compatible with the resin and will not significantly be subject to blooming precipitation after the modeling. However, there should also be a certain degree of incompatibility between antistatic agent and the resin in order to ensure that when an antistatic agent molecular layer on the surface get destroyed, internal antistatic agent can timely come out, leading to the formation of new molecular layer and the recovery of the anti-electrical performance.
(4) It does not affect the plastic processing properties (such as melting point, viscosity, solubility, etc.) and product performance (such as transparency, color, printability, heat resistance and mechanical properties, etc.).
(5) Excellent compatibility with other additives, and has no confrontation effect.
(6) It is non-toxic, odorless and non-irritating to the skin.
(7) Low price.