The sealing design of PE accordion bags is crucial for preventing leakage. It utilizes the synergistic effect of material properties, structural optimization, and process control to create a multi-layered protective system. This design must adapt to the dynamic use scenarios of PE accordion bags being folded and unfolded, while also balancing sealing strength and ease of handling, thus enabling its widespread application in food packaging, industrial parts storage, and other fields.
The inherent flexibility and heat-sealing properties of PE material form the basis of the sealing design. Polyethylene (PE), as a thermoplastic resin, can fuse under pressure to form a uniform sealing layer after being heated to a molten state. The sealing area of PE accordion bags typically employs a double- or multi-layer PE film composite structure, fusing the bag edges together through a hot-pressing process to form a sealing strip up to 1.2 cm wide. This design leverages the low melting point and high fluidity of PE material to ensure a seamless seal, while the multi-layer structure disperses stress, avoiding the risk of leakage due to single-layer breakage. For example, when packaging powdery or granular contents, the thickness and number of sealing layers are increased accordingly to resist friction and puncture of the contents against the bag wall. The folding structure of accordion bags places special demands on the sealing design. The accordion edges, formed by the inward folds on both sides, must remain flat when unfolded to prevent leaks due to fold marks. To address this, a high-frequency hot-pressing device is used during production to create continuous indentations at the folds at a rate of 0.1 times per second. This ensures the bag lays flat along a pre-set trajectory when unfolded, reducing edge warping. Simultaneously, the sealing area avoids the fold lines and is typically located on the straight sections at the top or bottom of the bag. A laser-cutting system ensures a precise tear-off edge with an accuracy of ±0.05 mm, guaranteeing complete detachment of the seal during tearing and preventing residual burrs from scratching the bag.
The notch design on the side sealing edges is a key innovation in preventing leakage. Traditional flat bags have straight sealing edges, which are prone to tearing due to uneven force during tearing. The PE accordion bag features symmetrical notches on the side sealing edges, concentrating the tearing force at the notches for precise lateral opening. The shape and depth of the notches are optimized to ensure a flush opening while preventing excessively large notches from weakening the seal. For example, some designs feature a semi-circular notch whose curvature matches the tearing path of a finger. During operation, a gentle pull at the notch allows for a neat tear along the center of the seal, preventing contents from spilling due to an irregular opening.
Resealable functionality further enhances leak-proof performance. Some high-end PE accordion bags incorporate a flexible metal strip at the opening, achieving a secure seal through two 180-degree folds. The metal strip's material must possess both flexibility and resilience to ensure a tight fit even after multiple folds. This design supports over 50 reseals without allowing air to enter, effectively extending the shelf life of the contents. For instance, in coffee bean packaging, the resealable design prevents aroma evaporation and moisture absorption, while avoiding the wear and tear on the sealing strip caused by repeated opening and closing of traditional zipper bags.
Wideened bottom heat-sealing technology addresses the leak-proof needs of large-capacity packaging. When PE accordion bags are used to hold heavy items such as rice or beans, the bottom must withstand greater pressure. By increasing the width of the bottom sealing edge to 0.6 cm and employing a hot-pressing process with higher pressure (0.8 MPa) and temperature (200°C), the sealing layer becomes denser, resisting bag bottom deformation caused by the weight of the contents. Furthermore, the bottom gusseted edge is widened to form a three-dimensional support structure, distributing pressure and increasing internal space, preventing contents from accumulating and compressing the seal.
Material modification technology offers more possibilities for sealing design. Adding antistatic agents, toughening agents, or nanofillers to PE can improve the puncture resistance and environmental stress cracking resistance of the sealing layer. For example, PE composite films with added nano-silica can increase sealing strength by 30% and maintain flexibility at low temperatures, preventing seal failure due to material brittleness. The application of these modified materials allows PE accordion bags to withstand more demanding storage conditions, such as frozen food packaging or chemical raw material transportation.
The sealing design of PE accordion bags utilizes a comprehensive approach, combining material selection, structural optimization, and technological innovation to create a complete leak-proof system, from sealing layer formation to opening control, resealing, and bottom support. This design not only meets the specific needs of dynamic use of PE accordion bags but also enhances packaging reliability and user experience through refined control, making it a crucial solution in the modern packaging industry.
