How to optimize the rim roll and bottom seal structure design of paper cups to ensure sealing and pressure resistance

The sealability and pressure resistance of disposable paper cups are key quality indicators. In professional manufacturing, optimizing the design of the rim and bottom seal structures is crucial. This not only impacts the user experience but also serves as the cornerstone for ensuring product functional safety.

Rim Roll Structural Design Optimization

The rim is the top structure of a paper cup. Its primary function is to enhance the rigidity of the rim, prevent liquid splashing, and ensure a tight fit with the lid.

1. Precise Control of Rigidity and Roundness

Professional Optimization Point: The rim's roundness and geometric dimensions must be maintained to extremely high tolerances.

Implementation Method: A multi-stage progressive crimping process is employed, rather than a single-step process. On the crimping machine, precise control of heating temperature and roller pressure ensures that the PE or other coating material softens appropriately without disrupting the paper fiber structure.

Result: A rim roll with high density and uniform thickness is achieved. This highly rigid rim effectively resists radial deformation when held or holding hot beverages, maintaining a tight seal and preventing burns.

2. Compatible Design with the Lid

Professional Optimization Point: Designing the optimal ratio of the inner and outer rolls optimizes the lid's retention and separation forces.

Implementation: The inner roll diameter should be slightly smaller than the lid's inner gasket diameter. The end of the rim should be designed with a slight chamfer to guide the lid for smooth installation.

Effect: When the lid is pressed in, a double locking mechanism is created: first, a friction fit, then a mechanical lock between the lid's rim and the bottom of the rim. This design prevents the lid from falling out if the paper cup is accidentally tipped or subjected to lateral pressure.

3. Edge Thickness and Material Selection

Professional Optimization Point: For double-wall paper cups, the simultaneous forming of the outer and inner edges must ensure balanced tension.
Implementation Method: Use high-grammage, food-grade paperboard to ensure the structural strength of the edge itself. For compostable PLA-coated paper cups, the edge forming temperature must be strictly below the glass transition temperature (Tg) of the PLA to prevent embrittlement.
Effect: Significantly improves the paper cup's ability to withstand vertical gravity and stacking strength, reducing damage during storage and transportation.

Bottom Seal Structural Design Optimization

The bottom seal is the area of ​​the paper cup most prone to leakage, and the quality of its seal directly determines the cup's pressure resistance and impermeability.

1. Die-cutting Precision and Bottom Diameter Matching

Professional Optimization Point: The die-cutting diameter of the cup bottom disc must be precisely matched to the shrinkage diameter of the cup tube bottom, down to the micron level.
Implementation Method: Use high-precision CNC die-cutting tools and monitor the impact of ambient humidity on cardboard dimensions in real time. Preheat the bottom of the cup tube before heat sealing to ensure the cardboard fibers are in their optimal thermoplastic state.
Effect: Ensures a maximized and uniform overlap area between the bottom cardboard and the cup wall during subsequent hot pressing.

2. Heat Sealing Pressure and Temperature Profile Control

Professional Optimization Point: The three elements of temperature, pressure, and time (T-P-T) during the heat sealing process must form an optimized heat sealing profile.
Implementation Method: Use high-frequency induction heating or ultrasonic welding technology instead of traditional resistance wire heating. Heat sealing pressure must be dynamically adjusted based on the cardboard basis weight and coating thickness. Effect: A molecular-level fusion seal is formed, particularly at the interface with the PE coating, ensuring full penetration and adhesion of the coating material. This seal can withstand higher hydrostatic pressures without leaking.

3. Bottom Roll Structure and Leakage-Proof Groove Design

Professional Optimization Point: The bottom structure should be designed as a mechanical-heat-seal composite structure that combines multiple layers of folding and locking.
Implementation Method: After the bottom heat seal is completed, a secondary bottom curling is performed on the bottom edge to enclose the cut edge. Some high-end designs incorporate a leakage-proof groove as a first line of defense.
Effect: Even if the coating in the heat-sealed area is slightly damaged by long-term immersion or external forces, the secondary bottom curling and mechanical locking provide an additional physical barrier, significantly improving the long-term leakage resistance and structural stability of the paper cup.