Types and applications of antistatic agents

Currently, the most practical ones are mainly surfactants and hydrophilic polymers.
When surfactants are used as antistatic agents, they must form a layer of antistatic agent molecules on the surface of the material. The lipophilic groups of its molecules are implanted inside the resin, while the hydrophilic groups are oriented on the air side. The former maintains a certain compatibility between antistatic agents and plastics, while the latter absorbs water molecules in the air to form a uniformly distributed conductive solution on the surface of the material, or ionizes itself to conduct surface charges to achieve antistatic effects.

Surfactants used for antistatic plastics mainly include the following varieties:

Cationic type: quaternary ammonium salt, amine salt, etc.;

Anionic type: phosphate, sulfonate, etc.;

Non-ionic: polyols, polyol fatty acid esters, polyoxyethylene additives, etc.;

Amphoteric type: quaternary ammonium salts, alanine salts, etc.

The surfactant can be directly sprayed, impregnated or brushed on the surface of the material in a solution prepared with water, alcohol and other solvents, and the antistatic coating is formed after the solvent is removed. When using this method, cationic surfactants have the best effect. But the most commonly used method at present is to mix surfactants into the resin and distribute them evenly within the polymer. After processing, the antistatic agent molecules will migrate outward and form an antistatic layer. When the surface antistatic layer is missing or damaged, the internal antistatic agent molecules can continue to migrate outward to supplement, so it has a continuous antistatic effect. Nonionic surfactants are most commonly used in this method.

Surfactant-type antistatic agents have many shortcomings during use, such as the lack of permanent antistatic effect, deterioration of the surface due to precipitation, thermal decomposition during processing, and high dependence on temperature and humidity. Using various hydrophilic polymers as antistatic agents can solve the above problems. Adding various hydrophilic polymers such as polyethylene oxide (PEO) as conductive units to the matrix resin to form an alloy can permanently maintain the antistatic effect. These hydrophilic compounds containing conductive units are distinguished from low molecular weight surfactant antistatic agents due to their higher molecular weight, and are called polymer permanent antistatic agents.

The effect of polymer antistatic agents alloyed with plastics depends on the degree and state of dispersion in the resin. The ideal distribution state is that the antistatic agent is finely distributed in the matrix resin, and its shape is rib-like or mesh-like, forming a path for charge leakage. The realization of this distribution state depends on the compatibility and processing conditions of the polymer antistatic agent and the matrix resin. Appropriate compatibilizers can be selected to adjust the particle size of the antistatic agent dispersion, and a suitable viscosity difference between the parent component and the dispersed phase can be achieved by controlling the shear rate and processing temperature. In the microdomain structure controlled in this way, the antistatic agent forms a good 'conductive path'.

In addition to being added to resins and processed into polymer alloys with antistatic effects, polymer antistatic agents are also increasingly used in coatings. For example, when a polymer containing quaternary ammonium ion-conducting units is used as a coating on thin plastic products (sheets, films, etc.), it exhibits good antistatic properties. Commercialized polymer permanent antistatic agents include polyethylene glycol methacrylic acid copolymer, polyether ester amide (PEEA), polyether ester acetamide (PEAI), polyethylene oxide, propylene oxide copolymer (PEO-ECH), PEGMA, etc. Many new products are still emerging.