You must know these about antistatic agents!

Plastics have electrical extinction (except for conductive polymers), which can accumulate static electricity when they come into contact with or rub against other materials. If the accumulated static electricity is not eliminated in time, it may cause electrostatic adsorption, vacuuming, cremation and discharge, etc., causing combustion and explosion.

The method for eliminating static electricity includes a conductive material (conductive carbon black, metal powder, etc.) filling method, a conductive device method, and an antistatic agent.

The antistatic agent (surfactant) is used to eliminate the static electricity of the plastic product, and there are an external coating method and an internal addition method. The former is poor in durability, and is mostly used for temporary or short-term electrostatic treatment, and has a narrow application range; the ionic and nonionic surface activities used in the internal addition method are selected depending on the structural characteristics of the substrate resin.

Antistatic principle

The friction coefficient is lowered to make the glass fiber difficult to generate static electricity, and the cationic quaternary ammonium lubricant and the imidazoline lubricant have antistatic effects.

A conductive path is formed to allow charge to be quickly removed from the surface of the fiber. For organic antistatic agents, such as polyoxyethylene castor oil, polyoxyethylene laurate, polyethylene glycol and the like. They all contain ether segments, which are easily combined with moisture in the air by hydrogen bonds to form conductive channels. These hygroscopic organic compounds are used together with ionic quaternary ammonium salts, tertiary amine salts or carboxylate organic compounds. Get better antistatic effects.

Another type of antistatic agent most commonly used is inorganic salts, which have a tendency to form hydrates strongly and become salts with crystal water. That is to say, it has a strong moisture absorption property, and it absorbs water on the smear film while dissociating into ions, so the conductive effect is very good.

Antistatic agent

Depending on the chemical composition. Antistatic agents can be classified into sulfuric acid derivatives, phosphoric acid derivatives, amines, quaternary ammonium salts, imidazoles, and ethylene oxide derivatives.

According to whether the hydrophilic group in the antistatic agent molecule can be ionized, it is divided into two types: ionic type and non-ionic type. The ionic antistatic agent is further classified into three types: cationic type, anionic type and zwitterionic type according to the positive and negative charges of the ionization.

â–¶ 1, cationic antistatic agent:

(1) monofunctional group: stearyl trimethyl quaternary ammonium hydrochloride, mainly used for polyolefin, ABS, polycarbonate, etc.;

(2) Bifunctional group: antistatic agent stearamidopropyl hydroxyethyl quaternary ammonium nitrate, mainly used as antistatic agent for polyester, polyvinyl chloride, polyethylene thin and products.

â–¶2, anionic antistatic agent:

(1) a monofunctional antistatic agent sodium p-nonylphenoxypropyl sulfonate (NP), mainly used for chloroacetic resin, ABS, polyolefin, etc.;

(2) a multifunctional antistatic agent alkyl bis(α-hydroxyethylamine phosphate), mainly used for synthetic fibers;

(3) The polymer type antistatic agent is a salt of a polyacrylate, a copolymer of maleic anhydride and another unsaturated monomer, polystyrene benzenesulfonic acid, or the like. Mainly used for fiber.

â–¶3, non-ionic antistatic agent:

(1) Tetrabromobisphenol A is mainly used for ABS, epoxy resin, and polyurethane. Also a flame retardant;

(2) Stearic acid monoglycerides, such as ADA-10M and ASA-10, are mainly used for polyolefins.

â–¶4, amphoteric antistatic agent:

(1) alkyl dicarboxymethyl ammonium lactone, mainly used for polyester, nylon, etc.;

(2) Dodecyl dimethyl quaternary ethylene salt, mainly used for polyester, polypropylene, nylon, and the like.

Various antistatic agents have different chemical properties and different properties, and the effects are different.

Cationic quaternary ammonium salts have strong adhesion to polymer materials and good antistatic properties. They are a kind of antistatic agent used in plastics, but they are irritating to the skin and toxic. Food packaging film.

Anionic antistatic agents, usually have no effect on the skin, and do not affect the coloration of plastics, but are rarely used in plastics except for acid alkyl phosphates or salts and alkyl sulphates.

Generally, the anti-static property of the non-ionic type is inferior to that of the ionic type, but the thermal stability is good, and it is not easy to cause aging of the plastic, and is particularly suitable for use under low temperature conditions; and it can also be used together with an anionic or cationic antistatic agent.

The most important feature of the amphoteric antistatic agent is its ability to be used with an anionic or cationic type. They all have strong adhesion to the polymer and thus exhibit excellent antistatic properties.

How to use antistatic agent

Depending on the mode of use, antistatic agents can be classified into two types: external coating type and internal mixing type.

The outer coating type antistatic agent refers to a type of antistatic agent used for coating on the surface of a polymer material. Generally, it is formulated into a solution having a mass fraction of 0.5% to 2.0% by water or ethanol, and then adhered to the surface of the polymer material by coating, spraying or dipping, and then dried at room temperature or hot air. An antistatic coating is formed. These are mostly cationic antistatic agents, and some are amphoteric and anionic antistatic agents.

The internal mixed type antistatic agent refers to a type of antistatic agent added to the resin during the processing of the product. The resin and the antistatic agent added with 0.3% to 3.0% of its mass are usually mechanically mixed and then processed. Such non-ionic and polymeric permanent antistatic agents are mainly used, and anionic and cationic types can also be added in some varieties.

In addition to imparting certain lubricity to the surface of the polymer material, reducing the friction coefficient, suppressing and reducing the generation of static charge, various antistatic agents have different chemical compositions and different ways of use, and the mechanism of action is also different.

Factors affecting antistatic effect

1. Molecular structure and characteristic group properties and addition amount

The effect of an antistatic agent depends first on its basic properties as a surfactant - surface activity.

The surface activity is related to the type of hydrophilic group, the type of hydrophobic group, the shape of the molecule, and the molecular weight.

When the antistatic agent molecules are oriented and adsorbed at the phase interface, the free energy of the phase interface and the critical contact angle between water and plastic are reduced. According to the polarity similarity rule, the hydrocarbon chain portion of the surfactant molecule tends to contact the polymer segment, and the polar group portion tends to contact with water in the air. As a hydrophobic material, the main role of the antistatic agent on its surface is to form a regular hydrophilic adsorption layer facing the water in the air. In the case of the same air humidity, the hydrophilic antistatic agent will combine more water, so that the surface of the polymer adsorbs more water, and the conditions of ion ionization are more sufficient, thereby improving the antistatic effect.

The molecular weight of the antistatic agent is too high, which is unfavorable for its migration to the surface of the polymer; the molecular weight is too low, and the washing resistance and surface abrasion resistance are not good. Generally, the molecular weight of the antistatic agent is much smaller than the molecular weight of the polymer. The addition of low molecular weight materials may deteriorate the physical and mechanical properties of the polymer material. In order to reduce such adverse effects, the antistatic agent is generally added in an amount of 0.3% to 2.0%. The amount of the antistatic agent to be added also varies depending on the use of the product.

The CMC (Critical Micelle Concentration) value is a measure of the surfactant surface activity. The smaller the CMC value, the lower the concentration at which the surfactant reaches the surface (interface) adsorption, or the lower the concentration required to form the micelle, and thus the lower the effective concentration of the antistatic property. Different amounts of antistatic agents are added in different amounts and vary with the form of the article. There is a range for the amount added. Too low, the antistatic effect is not obvious, too high, will affect the physical and mechanical properties of the material. The amount of thin products such as films and sheets is small, and the amount of thick products added is relatively large.

Second, the impact of other additives

When processing high polymer materials, it is often necessary to add additives such as stabilizers, pigments, plasticizers, lubricants, dispersants or flame retardants. The interaction of these additives with antistatic agents also has a large impact on the electrostatic effect.

The anionic stabilizer forms a complex with the cationic antistatic agent, thereby reducing the respective effects. Lubricants usually migrate quickly to the surface of the polymer, inhibiting the transfer of the antistatic agent.

If the molecular layer of the lubricant is coated on the molecular layer of the antistatic agent, the surface concentration of the antistatic agent is lowered, which significantly affects the antistatic effect; sometimes, due to the influence of the lubricant, the transfer of the antistatic agent to the surface is also promoted.

The plasticizer increases the distance between the macromolecular chains, makes the molecular movement easier, increases the porosity of the high polymer, and facilitates the antistatic effect of the antistatic agent on the surface of the product. Some plasticizers lower the glass transition temperature of the polymer and also increase the effectiveness of the antistatic agent.

Inorganic additives such as dispersants, stabilizers and pigments generally have strong adsorption capacity, making it difficult for the antistatic agent to migrate to the surface, counteracting the diffusion and migration of the antistatic agent, and the antistatic effect will be deteriorated.

Most inorganic additives are fine particles with a large surface area and are easy to adsorb antistatic agents, making them unable to effectively exert antistatic effects. Pigment particles are easily enriched around the antistatic agent, affecting its outward diffusion. For example, when titanium dioxide is added to ABS of the same antistatic agent concentration, the antistatic effect is lowered. The adsorption of different inorganic fillers is different, and the effect of antistatic effect is also different.

In addition, the elastomer in the high polymer component also degrades the effectiveness of the antistatic agent. For example, in a composite of polypropylene and rubber, it has been found that an antistatic agent is enriched around the rubber component, making it difficult to migrate to the surface.