The bottom structure design of a paper cup is a key factor affecting its resistance to deformation and leakage when filled with liquid. Traditional paper cups often use a single-layer flat bottom structure. While this design is simple to manufacture, it is prone to indentation or leakage under liquid pressure due to insufficient paper strength or stress concentration. Optimizing the bottom structure requires a mechanical approach, improving overall stability by increasing support points, distributing pressure, and enhancing sealing. For example, a raised bottom design, with a circular or conical protrusion at the center of the bottom, distributes liquid pressure evenly across the cup wall, reducing localized stress concentration and thus lowering the risk of deformation. Simultaneously, the connection between the protrusion and the cup wall should be rounded to avoid stress concentration caused by right angles, further improving impact resistance.
Reinforced bottom edge design is crucial for improving leakage prevention. Traditional paper cups often have a right-angle fold where the bottom edge meets the cup wall. This structure is prone to gaps when liquid sloshes or is subjected to external pressure, leading to leakage. Optimization solutions can employ a double-layer crimping process, folding the bottom edge inward twice to form a sealing layer, and applying food-grade waterproof adhesive to the folds to enhance the seal and structural strength of the joint. Additionally, some high-end paper cups add ring-shaped reinforcing ribs to the bottom edge, creating a textured surface through molding. This increases friction to prevent slippage and disperses liquid pressure, reducing the risk of side leakage.
The synergistic optimization of material selection and bottom structure is equally important. The bottom of the paper cup must withstand both hydrostatic pressure and dynamic impact, therefore, high-basis-weight, high-stiffness paper is necessary as the base material. For example, using double-layer composite paper or paper with an added polyethylene (PE) coating can significantly improve the bottom's water resistance and deformation resistance. In structural design, high-strength materials can be concentrated in the central area of the bottom, while flexible materials are used in the edge areas, balancing impact resistance and sealing through a combination of rigidity and flexibility. Furthermore, some biodegradable paper cups embed bio-based plastic sheets in the bottom, maintaining environmental friendliness while enhancing structural stability.
Geometric optimization of the bottom shape is an effective means of improving deformation resistance. A round bottom is the mainstream design due to its even stress distribution and simple manufacturing process. However, it is prone to bulging due to thermal expansion when filled with hot liquids. To address this issue, a polygonal bottom structure, such as a hexagon or octagon, can be used. This increases the number of support surfaces at the bottom, distributing pressure, while the stability of the polygon reduces thermal deformation. Furthermore, a wavy design at the bottom edge can increase the contact area, reducing localized stress and further improving impact resistance. It is important to note that geometric optimization must be balanced with manufacturing complexity to avoid increased costs due to overly complex structures.
The connection between the bottom and the body directly affects the overall seal. Traditional paper cups often use hot melt adhesive, but high-temperature liquids can soften the adhesive layer, causing leakage. An optimized solution is to use ultrasonic welding technology, which uses high-frequency vibration to fuse the paper fibers, forming a sealable structure without an adhesive layer. This improves heat resistance and avoids the risk of chemical migration. Additionally, some paper cups add a ring-shaped indentation at the connection between the bottom and the body, enhancing structural stability through physical reinforcement and preventing liquid penetration.
The design of the bottom ventilation holes must balance breathability and leak-proofness. Some paper cups have tiny ventilation holes at the bottom to balance internal and external air pressure and prevent deformation due to negative pressure. However, the presence of these ventilation holes may increase the risk of leakage. An optimized solution involves using laser perforation technology to control the hole diameter between 0.1-0.3 mm, ensuring breathability while utilizing liquid surface tension to prevent leakage. Simultaneously, raised structures can be added around the ventilation holes to prevent liquid from directly contacting the holes during sloshing, further improving leak-proof performance.
Optimizing the bottom structure of paper cups requires comprehensive consideration of mechanical properties, material characteristics, and manufacturing processes. By using a raised bottom design to distribute pressure, a double-layer rolled edge process to strengthen the seal, high-strength materials and geometric optimization in synergy, ultrasonic welding to improve connection stability, and laser perforation to balance breathability and leak prevention, the paper cup's resistance to deformation and side leakage when filled with liquids can be significantly improved. In the future, with advancements in materials science and molding technology, the bottom structure of paper cups will develop towards lighter weight, higher strength, and more environmentally friendly designs to meet market demand for high-quality paper products.
