How to Solve the Problem of Electrostatic Adhesion in Plastic Composite Film Bags

Generally, friction causes static electricity to accumulate on the film surface. Once static electricity builds up on the bags, they adhere to each other, making it difficult for workers to align them neatly. During use, this affects the separation of bags, causing two or more bags to stick together, preventing suction cups from opening individual bags and disrupting normal operations. The issue of electrostatic adhesion leads to complaints from workers in packaging factories and customer dissatisfaction, often troubling many packaging plant managers. The root cause is the ineffective elimination of static electricity on the bag surfaces, resulting in adhesion. While customers can employ some temporary measures to mitigate the issue, understanding the causes and solutions is essential for end-users. Below is a brief explanation of the causes and countermeasures for electrostatic adhesion in bags to help industry peers resolve similar problems.

Composite film bags consist of multiple layers of film, and electrostatic adhesion can occur during both the bag-making process and usage. The fundamental reason is the poor conductivity of plastic films. Friction between films or between films and machine rollers causes electron transfer, and the transferred electrons cannot dissipate in time, leading to static buildup. Based on experience, bags made of PET/PE or BOPP/PE structures are most prone to electrostatic adhesion, with thinner products being more susceptible. Bags with PA/PE or PET/VMPET/PE structures also exhibit electrostatic adhesion, though less frequently. Bags with conductive materials, such as those containing aluminum foil, rarely experience this issue. The main causes of electrostatic adhesion in bags are as follows:

High surface resistivity of inner and outer layer materials, poor anti-static performance, or insufficient or low-quality anti-static agents. For example, PET films used for printing and PE films for heat sealing may have inherent formulation flaws in anti-static properties, which is the fundamental cause of electrostatic adhesion.

Inadequate facilities during material processing, such as damaged, insufficient, or missing electrostatic dissipation or elimination devices, preventing effective removal of accumulated static electricity. If the composite film's inner and outer layers lack specialized anti-static formulations, this issue becomes more pronounced, constituting a major cause of electrostatic adhesion.

Environmental factors, such as excessively low humidity and temperature in production workshops, accelerating static buildup and making it harder to eliminate. Combined with ineffective anti-static agents in some materials, these conditions are significant external contributors to electrostatic adhesion.

Induced static electricity from strong electric fields near electrical equipment during bag production or use, or from operators wearing non-anti-static clothing. In such cases, the adhesion strength varies but is usually minor. This type of static may notably affect small or thin-film bags.

The above analysis covers most factors contributing to electrostatic adhesion in bags, and solutions generally address these aspects. Since the principle of static generation involves electron transfer due to film friction or bag movement, with electrons accumulating on the film surface instead of dissipating or neutralizing, all measures aim to reduce static generation and promptly eliminate accumulated charges. Current solutions primarily rely on electrostatic dissipation, neutralization, or shielding. Common targeted measures include:

Using anti-static agents, either incorporated into the film material or applied as a coating to reduce surface resistivity. For example, anti-static agents can be added to PE pellets during processing or coated onto the film surface. Most anti-static agents in the industry work by absorbing environmental moisture through hydrophilic groups, dissipating static electricity.

Controlling environmental humidity by increasing moisture levels to reduce static buildup via water conductivity. However, this method is limited in food packaging facilities where low humidity is required to prevent product moisture absorption.

Installing ionizers or static eliminators, such as near the cutting section of bag-making machines, to neutralize and eliminate static electricity.

Adjusting material structure and formulation to reduce friction coefficient and speed, minimizing static generation.

Using conductive materials in composite bag production, such as metallized films or pure aluminum foil structures.

Grounding static elimination devices, such as static brushes or conductive copper wires, along the film path to discharge accumulated static electricity.

These are general solutions for bag static issues, but practical implementation requires refining measures based on specific production processes. Below are additional detailed methods:

Material Requirements:

Address film static issues by collaborating with suppliers to select suitable anti-static formulations. Adjust anti-static agent ratios seasonally based on humidity changes.

Remove outer packaging (paper or film) from printing materials before sending them to the workshop, and store them vertically on metal pallets for a period before use.

Produce inner PE films with scientifically balanced ratios of anti-blocking, slip, and anti-static agents. Store PE films vertically before use.

Add 10%–15% isopropanol to white ink solvent formulations to reduce static buildup during printing.

Store printed films vertically on metal pallets to dissipate static.

Environmental Requirements:

Maintain humidity above 65% in printing workshops for static-prone products, using humidifiers and sprinkling water near ink stations.

Use humidifiers in solvent-free lamination workshops but exercise caution with solvent-based adhesives to avoid excessive humidity.

Store composite films in a controlled-humidity curing room (40%–50%) if ambient humidity drops below 15%.

Ensure humidity in bag-making workshops stays above 45%, adding humidifiers if necessary.

Store finished products in moderate humidity conditions, avoiding drafty areas.

Equipment Requirements:

Ensure functional static eliminators on printing machines, proper grounding, and operational static elimination at winding stations.

Maintain static elimination devices and grounding on lamination machines.

Install additional static brushes or powder sprayers on bag-making machines (except for special products) to improve slip and static dissipation.

Operational Requirements for Bag Manufacturers:

Follow material, equipment, and environmental guidelines at each production stage.

Place damp cloths on unwinding materials in low-humidity conditions to prevent static buildup.

Line packing boxes with PE film to wrap bags tightly.

Require operators to wear anti-static clothing to minimize induced static.

For non-food bags, consider in-line powder spraying to reduce static (avoid for food bags due to contamination risks).

Use blowers or dampened pallets to separate adhered bags post-production.

Apply anti-static coatings if necessary, testing ratios (typically 0.5%–15%) to avoid quality issues.

User Guidelines for Bag Consumers:

Increase local humidity near packaging machines if product and environment allow.

Handle bags with bare hands, manually separating them to dissipate static.

Use ionizing blowers to separate adhered bags before use.

These measures have been empirically validated with varying effectiveness. Selecting or combining them based on specific production conditions can efficiently resolve electrostatic adhesion issues. Balancing practicality, time, and cost is key to determining the optimal solution.