During the friction process of substances, charges are continuously generated, and at the same time they are constantly leaking and neutralizing. Charge leakage mainly occurs through three channels: volume conduction of the friction object itself, surface conduction and radiation into the air. Generally, the volume resistance of solids is 2-3 orders of magnitude higher (100-1000 times higher) than the surface resistance. The charge prevention effect is mainly dominated by the surface resistivity of the polymer material, that is, surface conduction is the main factor in charge leakage, so people usually The purpose of preventing static electricity is achieved by reducing its surface resistance and improving surface electrical conduction.
The mechanism of action of external antistatic agents. External antistatic agents generally use water, alcohol or other organic solvents as solvents (or dispersants) to prepare a solution with a concentration of 0.5%-2.0%, and then apply the antistatic agent to the surface of the plastic. , the lipophilic group of the antistatic agent molecule will be adsorbed on the surface of the plastic product. With the presence of the hydrophilic group of the antistatic agent on the plastic surface, it is easy to absorb moisture in the environment, and the moisture will form a single molecule on the plastic surface. conductive layer (for example, the antistatic agent is an ionic compound, which can also play a role in ionic conductivity), thereby reducing the surface resistance and accelerating the leakage of charges; on the other hand, due to the molecular layer of the antistatic agent on the surface of the plastic and adsorbed moisture, so the dielectric constant in the friction gap is significantly higher than the dielectric constant of air during friction, thus weakening the electric field intensity in the gap and reducing the generation of charges.
The mechanism of action of the internal antistatic agent. The internal antistatic agent is a surfactant added to the resin composition during the resin processing. It has moderate compatibility with the resin and good miscibility with the resin. However, it is not completely compatible. During and after the molding process, the antistatic agent will gradually migrate from the inside of the plastic product to its surface. When the amount of antistatic agent added is high enough (the amount is generally 0.1-3 parts of internal antistatic agent per 100 parts of resin), the internal antistatic agent will form a dense arrangement at the resin-air interface. The polar groups (hydrophilic groups) of the antistatic agent are arranged toward the air side to form a single-molecule conductive layer, thus showing antistatic properties. Theoretically speaking, as long as a single molecule conductive layer is formed on the surface of the plastic film, a good antistatic effect can be produced. However, in actual test surfaces, the amount of antistatic agent required for antistatic migration and accumulation on the plastic surface is much higher. Above a single molecular layer, when the average number of antistatic molecules covered on the plastic surface is more than ten layers, a relatively ideal antistatic effect can be achieved. Before the amount of added antistatic agent reaches a critical concentration, as the amount of added antistatic agent increases, the antistatic property of the plastic will be significantly improved. For general polymer compounds, the critical concentration is about 0.5*10 (-2)mg/cm2. Since the distribution of internal antistatic agents in the resin is uneven, with high surface concentration and low internal concentration, the antistatic effect is still the same as that of external antistatic agents, relying on their molecular conductive layer of internal antistatic agents on the resin surface. If If the antistatic agent molecular layer on the surface of the resin is damaged due to stretching, friction, washing, etc., the antistatic property of the film will also be reduced. However, the antistatic agent molecules inside the resin will continue to migrate to the surface, causing the defective antistatic agent molecular layer on the surface. The antistatic properties are gradually restored by being replenished from within. Therefore, generally speaking, internal antistatic agents are much more durable than external antistatic agents.
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