Square bottom plastic bags often generate static electricity due to friction during packaging, transportation, or storage, which attracts dust and debris, affecting product cleanliness and even causing damage. To solve this problem, antistatic components need to be added to reduce surface resistance and allow static charge to dissipate promptly. The following systematically describes the methods for adding antistatic components to square bottom plastic bags from seven aspects: material selection, type of antistatic agent, addition process, structural design, environmental control, application scenario adaptation, and performance testing.
Material selection is the foundation of antistatic design. Square bottom plastic bags typically use plastics such as polyethylene (PE) and polypropylene (PP) as the base material, but ordinary plastics have high resistivity and easily accumulate static electricity. To improve antistatic performance, materials with low resistivity or easy modification should be selected. For example, low-density polyethylene (LDPE) is a commonly used base material for antistatic plastic bags due to its flexible molecular chains and ease of adding additives; linear low-density polyethylene (LLDPE), due to its high strength and good toughness, can be blended with LDPE to balance antistatic and mechanical properties. In addition, some high-end products use materials such as copolymer polypropylene (CPP) or polyester (PET) to reduce resistivity through molecular structure optimization.
The addition of antistatic agents is a core method. Antistatic agents reduce the surface resistance of plastics through hygroscopicity or conductivity, and can be divided into internal additives and external coatings. Internally added antistatic agents (such as amine derivatives, quaternary ammonium salts, and phosphate esters) are directly mixed into the raw materials during plastic processing, migrating to the surface to form a conductive layer. The effect is long-lasting, but the addition amount needs to be controlled (usually less than 1%) to avoid affecting transparency or mechanical properties. Externally coated antistatic agents (such as conductive coatings and nano-zinc oxide solutions) are applied to the bag surface through spraying or dipping processes, suitable for applications requiring high transparency, but with poor durability. In actual production, internally added antistatic agents are more widely used due to their ease of operation and stable effect.
The addition process directly affects the antistatic effect. Internally added antistatic agents need to be thoroughly mixed with the plastic raw materials, typically using a high-speed mixer or internal mixer for premixing to ensure uniform dispersion. The mixed raw materials are then formed into bags using blown film or cast film processes. Blown film production is the mainstream method for square-bottom plastic bags due to its simple equipment and low cost. During blown film production, melt temperature and cooling rate must be controlled to prevent the antistatic agent from decomposing at high temperatures or failing to migrate to the surface due to excessively rapid cooling. In addition, some companies use multi-layer co-extrusion technology to combine the antistatic layer with the structural layer, ensuring both antistatic performance and improved bag strength.
Structural design can aid in antistatic function. The edges and bottom of square-bottom plastic bags have a large contact area, making them more prone to static electricity. Optimizing the structural design can reduce friction and static accumulation. For example, adding rounded corners or wavy designs to the bag edges reduces friction during contact; using a thickened or pleated structure at the bottom disperses pressure and reduces static electricity generation. In addition, some products add conductive strips or metallic coatings to the bag opening, utilizing the Faraday cage principle to shield against external electrostatic fields and prevent dust adsorption.
Environmental control is an important supplement to anti-static measures. Static electricity generation is closely related to humidity; dry environments exacerbate static accumulation. Therefore, during the production, storage, and use of plastic bags, the ambient humidity must be controlled between 40% and 60%, regulated using humidifiers or dehumidifiers. Furthermore, avoiding operation in high-temperature, strong-wind, or low-pressure environments can reduce static electricity generation. For scenarios requiring high cleanliness (such as electronic component packaging), production must be carried out in cleanrooms equipped with ion fans and other equipment to eliminate static electricity in real time.
Adapting to the application scenario is key to anti-static design. Different industries have significantly different anti-static requirements for plastic bags. For example, the electronics industry needs to prevent static electricity from damaging sensitive components, requiring the surface resistance of the plastic bag to be below 10⁹ Ω; the food industry, on the other hand, prioritizes safety and requires the selection of non-toxic, odorless anti-static agents (such as polyethylene stearate). Therefore, the antistatic design of square-bottom plastic bags requires adjustments to the formula and process based on specific scenarios. For example, biodegradable antistatic materials are used in medical packaging, while corrosion resistance is enhanced in chemical packaging.
Performance testing is crucial for ensuring antistatic quality. After production, the antistatic performance of the plastic bags must be tested using specialized equipment. Common indicators include surface resistance and static decay time. A surface resistance tester measures the surface resistance of the bag to ensure compliance with industry standards (such as MIL-B-81705B); a static decay tester simulates triboelectric charging to detect the rate of static charge dissipation. Furthermore, practical application tests are necessary, such as placing the plastic bag in a dusty environment to observe adsorption or testing the performance of electronic components after contact to ensure the antistatic effect is truly effective.
