In the manufacturing process of bubble bags, the control of bubble forming pressure is the core element determining the balance between bubble size uniformity and cushioning. This requires optimization through mold design, pressure gradient control, matching of material rheological properties, and coordinated optimization of process parameters. This process must consider both the stability of physical foaming and the mechanical properties of the material, ensuring that the bubbles maintain dimensional consistency while forming an effective cushioning structure during the forming process.
Mold design is the foundation for controlling bubble forming pressure. Bubble bag molds typically employ a porous honeycomb structure, where the pore size, distribution density, and arrangement directly affect the initial morphology of the bubbles. For example, excessively large pore sizes can lead to over-expansion of bubbles, resulting in significant differences in bubble size; while excessively small pore sizes may cause incomplete filling of localized bubbles due to excessive material flow resistance. Therefore, mold design needs to incorporate material properties (such as melt viscosity and elastic modulus) through simulation to optimize the pore size gradient distribution, ensuring uniform pressure distribution across all areas of the mold and providing a stable foundation for subsequent pressure control.
Dynamic control of the pressure gradient is crucial for achieving bubble size uniformity. During bubble forming, pressure undergoes three stages: "pressurization-holding-depressurization." The pressurization stage rapidly establishes initial pressure (usually through high-pressure gas or hydraulic systems) to quickly fill the mold pores with molten material. The holding stage precisely controls the pressure decay rate to prevent bubble shrinkage or merging due to sudden pressure drops. The depressurization stage slowly releases pressure to ensure the bubble is fully formed before solidification. Real-time feedback from pressure sensors and the linkage with a PID control system are crucial in this process. Dynamic adjustments to valve opening or pump speed can maintain pressure fluctuations within a target range (typically ≤±5%), ensuring consistent bubble size.
The matching of material rheological properties with pressure directly affects cushioning performance. Commonly used materials for bubble bags are low-density polyethylene (LDPE) or copolymers. The viscoelastic behavior of their melt under high pressure determines the bubble's expansion capacity and resilience. For example, high-viscosity materials require higher forming pressure to overcome flow resistance, but excessive pressure may lead to excessively thin bubble walls, reducing puncture resistance; while low-viscosity materials are easy to form, excessive bubble expansion may result in uneven bubble size. Therefore, it is necessary to adjust the melt rheological parameters through material modification (such as adding nanofillers or plasticizers) to achieve an optimal match with the molding pressure, ensuring both bubble size uniformity and enhancing the energy absorption capacity of the buffer structure.
Coordinated temperature field control is a supplementary method to pressure control. During bubble formation, material temperature directly affects its melt strength and gas solubility: excessively high temperatures lead to rapid gas escape, resulting in bubble coalescence or rupture; excessively low temperatures may cause incomplete mold filling due to insufficient material fluidity. Therefore, it is necessary to establish a temperature gradient from the die head to the mold (usually die head temperature > mold temperature) through zoned control of heating coils and cooling channels. This ensures high material fluidity during the mold filling stage, while cooling enhances melt strength during the holding pressure stage, thereby forming a stable bubble structure under pressure.
The introduction of multi-layer co-extrusion technology can further optimize buffer performance. By bonding materials of different hardnesses on both sides of the bubble layer (such as an outer layer of rigid PE and an inner layer of soft EVA), a "hard-soft-hard" sandwich structure can be formed under pressure: the outer rigid material provides puncture resistance, the inner soft material absorbs impact energy through deformation, and the middle bubble layer disperses stress through compression and rebound. This structure requires a co-extrusion die head flow channel design (such as a spiral distributor) to ensure uniform distribution of materials in each layer under pressure, avoiding a decrease in cushioning performance due to interlayer slippage.
Closed-loop pressure control in automated production lines is crucial for ensuring batch consistency. Modern bubble bag production lines typically integrate pressure sensors, vision inspection systems, and PLC controllers to monitor bubble diameter, wall thickness, and distribution density in real time, and predict pressure adjustments using algorithmic models (such as neural networks). For example, when a localized bubble diameter is detected to be too large, the system can automatically increase the pressure in that area or decrease the pressure in adjacent areas, forming a dynamic compensation mechanism to ensure the uniformity of cushioning performance throughout the entire roll of bubble bag.
In bubble bag manufacturing, controlling the bubble forming pressure requires multi-dimensional coordination, including mold design, pressure gradient control, material rheological matching, temperature field coordination, multi-layer co-extrusion structure, and automated closed-loop control, to achieve a balance between bubble size uniformity and cushioning performance. This process not only requires high-precision hardware support but also relies on a deep understanding of materials science, fluid mechanics, and control theory, ultimately providing users with a stable, efficient, and reliable cushioning packaging solution.
