R&D Perspective: Structural Optimization and Performance Iteration Design of Caviar Tin Boxes with Rubber Band Sealing

　　I. R&D Project Background and Core Product R&D Needs

　　Caviar, as a high-end luxury ingredient, possesses characteristics such as high protein, high activity, easy oxidation, easy moisture absorption, and extreme sensitivity to temperature, humidity, and sealing. Its storage, packaging, and transportation environment directly determines the ingredient's taste, color, nutrient retention, and shelf-life stability. Traditional caviar packaging mostly uses ordinary tin boxes and plastic sealed containers, which suffer from insufficient sealing redundancy, poor ease of opening and closing, weak shock resistance during transportation, and easy oxygen leakage during long-term storage, making it difficult to meet the needs of high-end caviar in refined warehousing, cross-border transportation, terminal retail display, and the consumer's need for immediate consumption.

　　From an R&D perspective, the core R&D logic of high-end food packaging has long since moved beyond the simple function of a container, upgrading to a systematic R&D system integrating five aspects: food preservation, structural protection, human-machine experience, process adaptation, and cost control. Based on market feedback regarding the shortcomings of traditional packaging, we have officially launched a project to develop caviar tin boxes with a rubber band sealing structure. The core R&D objective is to retain the texture, premium feel, and recyclable and environmentally friendly attributes of metal tin boxes, while overcoming the performance limitations of traditional snap-lock seals and embedded sealing rings through an innovative design with an external rubber band-assisted sealing structure. This achieves a balance between high sealing performance, high adaptability, high durability, and aesthetic appeal, while also conforming to industrial mass production standards, ensuring both product quality and production efficiency.

　　This research and development focuses on solving four core industry problems: First, the seal of traditional tin boxes weakens rapidly after opening and closing, and repeated opening and closing widens the gaps, allowing oxygen and moisture to penetrate, causing caviar to spoil, turn black, and deteriorate in taste. Second, purely embedded sealing structures are prone to dust and dirt accumulation, are inconvenient to clean, and breed bacteria with long-term use, failing to meet high-end food hygiene standards. Third, traditional sealing structures rely on precision hardware buckles, resulting in high production costs, low tolerance for errors, and easy loosening of buckles and deformation of the box due to transportation vibrations. Fourth, in high-end packaging scenarios, traditional tin boxes have a simple structure without auxiliary fixing structures, making them unsuitable for display, storage, and secondary storage.

　　II. Overall Structural R&D Design and Innovation Logic The rubber band-sealed caviar tin box developed in this project adopts the basic structure of a classic top-and-bottom tin box. It abandons the traditional single design of all buckles and fully embedded seals, innovatively introducing an external elastic rubber band to assist in locking and sealing, forming a composite structural system of "rigid metal box support + flexible sealing of elastic components," optimizing the sealing performance and deformation resistance of the packaging from a structural principle perspective. The overall structure is divided into three core modules: the lid, the body, and the elastic sealing rubber band. Each module was independently developed, precisely adapted, and works synergistically. This retains the structural strength and premium feel of the metal box while compensating for the inherent limitations of a rigid metal seal through flexible, elastic components.

　　In the development of the basic box structure, we optimized the gap between the lid and the top cover at the micrometer level, based on food packaging safety standards and mechanical load-bearing principles. Traditional caviar tin boxes typically have a lid-to-top gap of 0.3-0.5mm. A gap that is too large can lead to air and water leaks, while a gap that is too small results in jamming during opening and closing and high assembly difficulty in mass production. After hundreds of gap adjustment tests, the optimal gap between the lid and the body was finally controlled within the range of 0.15-0.2mm. This ensures smooth, jam-free opening and closing of the box and reduces the basic gap from a structural perspective, laying the foundation for subsequent rubber band-assisted sealing. Meanwhile, the corners of the box were rounded and blunted, abandoning the right-angle stamping process and adopting a secondary rounding and polishing process. This not only improves the product's appearance but also prevents seal failure caused by corner impacts and deformation during transportation and use, significantly enhancing structural stability.

　　The core innovation lies in the development and design of an external rubber band sealing structure. Unlike the traditional fixed sealing mode with an embedded silicone sealing ring, this development uses a detachable, high-elasticity, food-grade rubber band locking structure. The R&D team determined the core parameters of the rubber band—diameter, elongation ratio, and locking force—through extensive material elasticity tensile testing, fatigue testing, and temperature change testing. The rubber band adopts a ring-shaped, fully enclosed design, which can tightly fit the outer edge of the seam between the lid and the box body. Through elastic recoil force, it continuously applies uniform locking pressure to the box body, offsetting gaps caused by slight deformation of the metal box body, achieving a secondary reinforced seal. Compared to traditional embedded sealing structures, the external rubber band structure boasts three major R&D advantages: First, it provides a seamless seal, with full-coverage locking to prevent oxygen leakage through gaps; second, it is removable and replaceable, allowing individual replacement of aged or worn rubber bands without replacing the entire metal box, increasing product reusability; and third, the external structure eliminates hygiene blind spots, with a smooth, easy-to-clean surface that fully meets food-grade hygiene requirements.

　　Furthermore, to address the issues of rubber band slippage and inaccurate positioning, the R&D team designed concealed limiting grooves on the top and bottom edges of the box. The depth and width of these grooves, precisely calculated mechanically, perfectly fit the rubber band dimensions, ensuring that the rubber band does not shift or slip after locking, resulting in even and stable force distribution. This prevents box deformation caused by excessive localized pressure and eliminates seal failure due to loosening or shifting, ensuring the stability of the flexible sealing structure meets mass production standards.

　　III. Core Material Selection, Development, and Performance Testing

　　The material is the core foundation determining the preservation, safety, and durability of the caviar tin box. This development focused on two core raw materials: the metal body and the elastic material for the rubber bands. Specialized selection testing and performance iterations were conducted to strictly adhere to national food contact material safety standards while also adapting to the specific needs of high-end caviar storage.

　　The box body is made of thickened food-grade tinplate. Unlike the thin sheet metal used in ordinary packaging, this development uses 0.23mm thickened tin-plated tinplate, which possesses high strength, compression resistance, oxidation resistance, and corrosion resistance. Given the high salt and high activity of caviar, ordinary tinplate is prone to oxidation, plating peeling, and metal precipitation. Therefore, we optimized the tin plating and passivation processes, employing a double-layer tin plating + food-grade passivation film composite treatment technology. This significantly improves the corrosion resistance and oxidation resistance of the inner wall of the box, preventing direct contact between metal and caviar, avoiding cross-contamination and flavor transfer, while effectively isolating external air, moisture, and dust. Its basic preservation performance far exceeds that of ordinary tin boxes. Furthermore, the thickened tinplate's rigid structure effectively resists squeezing, collisions, and vibrations during transportation, protecting the caviar particles inside the box and preventing damage that could affect its appearance and taste.

　　The selection of the rubber band material was a core key to this research and development, directly determining the lifespan of the auxiliary sealing structure and food safety. The R&D team compared more than ten materials, including natural rubber, ordinary silicone, food-grade silicone, and TPU elastic material, and selected the optimal solution through rigorous multi-dimensional testing. The tests included food safety testing, high and low temperature weathering resistance testing, elastic fatigue testing, aging resistance testing, and waterproof and oil-proof testing. Natural rubber is prone to aging, yellowing, and rapid elasticity loss, and it easily retains odors, failing to meet the requirements of high-end food packaging; ordinary silicone has insufficient elongation and easily hardens and fails at low temperatures; TPU material is too rigid, resulting in uneven locking pressure and easily causing deformation of small tin boxes.

　　After multiple rounds of testing and iteration, highly elastic food-grade fumed silica was ultimately selected as the core raw material for the rubber band. This material has passed food contact safety certification, is odorless, releases no harmful substances, and is safe and non-toxic, allowing direct application to food packaging containers. Its elastic elongation ratio exceeds 300%, exhibiting excellent resilience and resisting deformation and loosening even after repeated stretching and tightening. It possesses exceptional weather resistance, adapting to a wide temperature range from -20℃ to 60℃, maintaining stable elasticity under cold chain storage, ambient temperature transportation, and high-temperature storage conditions without hardening, softening, or breakage. Furthermore, it boasts excellent waterproof, oil-proof, and anti-aging properties, making it suitable for the high-oil, high-salt storage environment of caviar, with a service life more than three times that of ordinary rubber rings.

　　IV. Process Optimization and Mass Production Adaptability Development A high-quality packaging product requires not only excellent structural design and material performance but also mature and stable production processes to achieve a balance between design performance and mass production quality. This R&D effort involved simultaneous mass production optimization, iterating and upgrading the entire process from stamping, polishing, lamination, printing, and groove processing of the tin boxes to rubber band forming and assembly. This addressed industry challenges such as difficulty in mass-producing new structures, low yield rates, and poor consistency.

　　In the tin box processing technology development, to address the processing difficulties of the concealed limiting grooves, the traditional one-time stamping process was abandoned in favor of a precision CNC micro-adjustment stamping process. CNC equipment precisely controls the groove depth, curvature, and flatness, ensuring uniform dimensional control of the limiting grooves in each box, with an error within ±0.02mm, guaranteeing the universality and stability of the rubber band fitment. Simultaneously, the box sealing and folding process was optimized, employing a double-layer folding and compaction technology to eliminate burrs and sharp edges, improving product feel and safety, while further strengthening the box structure to prevent deformation over long-term use.

　　In terms of surface treatment, aligning with the product positioning of high-end caviar, a composite process of matte coating and partial glossy hot stamping was developed. This retains the premium feel of the metal tin box while adding a scratch-resistant, fingerprint-resistant, and oxidation-resistant protective layer, enhancing the product's appearance and durability, making it suitable for high-end retail and gift packaging scenarios. The inner wall uses a food-grade, odorless, and environmentally friendly coating, cured at high temperatures, resulting in no odor, no peeling, and no leaching, fully complying with import and export food packaging safety standards, and meeting the needs of cross-border sales.

　　Regarding assembly process development, a modular assembly mode is adopted. After the main body of the tin box is mass-produced, standardized equipment is used for precise assembly of the elastic bands. Space is also provided for manual replacement, allowing consumers to disassemble and replace the elastic bands themselves, balancing mass production efficiency with user convenience. After process optimization, the product's mass production yield rate increased to 99.2%, production efficiency increased by 15%, production costs were effectively controlled, and a balance between high-end quality and large-scale mass production was achieved.

　　V. Performance Testing and the Value of R&D Results To verify the product's performance, we conducted specialized tests on the finished product across five dimensions: sealing, weather resistance, deformation resistance, service life, and food safety. These tests simulated various scenarios including warehousing, transportation, cold chain logistics, and daily use, comprehensively verifying the product's overall performance. Sealing test results showed that under three extreme environments—normal temperature and pressure, low temperature in a cold chain, and high temperature and humidity—the iron box with rubber band-assisted sealing exhibited oxygen and water vapor permeability far below industry standards. It remained leak-free, moisture-proof, and deteriorated for 90 days without any issues, demonstrating sealing stability far exceeding that of traditional ordinary iron boxes.

　　In the deformation resistance test, after 500 opening and closing cycles and 100 simulated transportation vibration tests, the box showed no deformation, no widening of gaps, and no significant decrease in the elasticity of the rubber band, maintaining consistently stable sealing performance. Third-party food safety testing results showed that all materials, coatings, and elastic components of the product met national and EU food contact standards, with no heavy metal leaching or harmful residues, making its safety level suitable for high-end imported and exported caviar packaging requirements.

　　From a research and development perspective, this caviar tin with a rubber band seal completely solves the core pain points of traditional caviar packaging. Through structural innovation, it achieves a product upgrade that is low-cost, highly preservative, durable, and easy to maintain. Compared to high-end sealed tins with complex and precise buckles, this product has a simpler structure, more mature technology, and lower repair and replacement costs. Compared to ordinary sealed tins, it offers a significant leap forward in preservation performance, protection, and user experience. Furthermore, the detachable and flexible structure design is more environmentally friendly and energy-efficient, greatly increasing the packaging's reusability and aligning with the current trend of green and environmentally friendly food packaging.

　　In terms of market adaptability, this product is perfectly suited for the storage, packaging, gift storage, and cross-border transportation of caviar of various sizes. It meets both the industrial-scale mass packaging needs of enterprises and the personalized needs of end consumers for refined storage and repeated use. It provides a new structural research and development approach and implementation solution for high-end, light luxury food packaging, possessing extremely high market promotion value and industry reference value.