Antistatic Properties and Prevention of Static Electricity in Plastics
**Concept of Static Electricity:** Static electricity refers to relatively stationary electric charges, typically the positive and negative charges generated on the surface of objects due to friction between them.
**Electrostatic Discharge:** Static discharge refers to the transfer of electrostatic charge between objects with different electrostatic potentials due to direct contact or electrostatic induction. It usually refers to the phenomenon where, after the energy of the electrostatic field reaches a certain level, it breaks down the medium between them, resulting in a discharge.
**Causes of Static Electricity:**
1. Microscopic Causes: According to atomic physics theory, matter is in a state of electrical equilibrium when electrically neutral. The gain or loss of electrons due to contact between atoms of different substances causes the matter to lose its electrical equilibrium, resulting in static electricity.
2. Macroscopic Causes: Friction between objects generates heat, stimulating electron transfer; contact and separation between objects generate electron transfer; electromagnetic induction causes an unbalanced distribution of charge on the surface of objects; the combined effect of friction and electromagnetic induction.
Plastics are all polymer materials with surface resistivity and volume resistivity greater than 10^12. Therefore, plastic materials possess excellent insulating properties. Because of this, plastics and their products are highly susceptible to static electricity generation. These situations are extremely likely, if not impossible, to avoid during production, handling, contact, separation, friction, collision, and electromagnetic induction. This creates the factors that generate static electricity. How to effectively prevent and control this has been a topic of concern and expectation for many years.
The concept of antistatic properties in plastics: When the surface resistance of plastics and their products is greater than 10^6, static electricity is easily generated; between 8 and 10^6, they have certain antistatic properties; between 6 and 8^6, they have good antistatic properties; between 4 and 6^6, they have optimal antistatic properties; and below 4^6, they have considerable conductivity, belonging to conductors and semiconductor materials.
Prevention and control of static electricity in plastics:
1. Adding hygroscopic materials that are harmless to plastics (auxiliaries) to reduce their surface resistance. This is the antistatic agent for plastics. The type of antistatic agent used depends on the type of plastic. Whether ionic or non-ionic, they are all hygroscopic antistatic agents. After adding these additives, these materials absorb moisture from the air, reducing surface resistance and achieving antistatic properties. 2. The direct use of conductive plastics to process products is the origin of conductive plastics (resins). Currently, in the domestic market, most conductive plastics are still black, additive-based conductive plastics; light-colored conductive plastics are still under development and research.
Selection of Antistatic Agents and Conductive Plastics:
1. Antistatic Agents: Mainly produced in Zhejiang, Shanghai, Beijing, etc. They are categorized according to plastic type, such as PVC, PP, PE, ABS, HIPS, etc., with prices ranging from tens of yuan/kg. The addition amount is 1-3%. After addition, the surface resistivity is generally 10⁸-10¹⁰, especially in areas with high humidity, where the value is significantly lower. Imported antistatic agents are more effective than domestic ones, achieving 10⁸ even in relatively dry areas. However, the mechanism of action of this type of antistatic agent cannot further improve antistatic performance. Antistatic masterbatch is designed to facilitate manufacturing since most plastic raw materials are granular. Its main components are: carrier + antistatic agent + other additives, with the carrier usually being LLDPE resin or other resins. 2. Conductive Plastics: Currently, most conductive plastics in China are made by adding nano-grade conductive carbon black to resin. Varieties include PC, PET, PP, PE, ABS, HIPS, PVC, and various plastic alloys, but most are black. Light-colored ones are less common. Prices range from 16-30 yuan/kg. Major production areas are Guangdong, Zhejiang, Shandong, and Beijing.
3. Light-colored Antistatic Plastics: These are made by adding nano-zinc oxide whiskers to the plastic, which reduces the surface resistance. Currently, they are expensive and less commonly used, with promotion and testing underway.
The emergence of antistatic plastics has played a crucial role in promoting and developing plastic products and has ensured the supply of antistatic products, especially for packaging electronic products and plastic products used in applications requiring antistatic properties.