Premium caviar is high-value fresh food material, requiring strict standards in storage tightness, light shielding, preservation stability and surface texture. Custom airtight caviar tin boxes adopt tinplate with excellent barrier performance, combined with precision stamping, airtight structural design and sophisticated surface treatment technology, to produce special packaging containers for caviar applicable to commercial distribution, gift markets and high-end catering scenarios. The whole process covers raw material selection, mold development, forming stamping, airtight structure processing, surface printing, tightness testing and finished goods packaging under standardized full-process control. Every procedure directly affects the storage stability of caviar during cold chain transportation and the visual grade of products.

　　1. Raw Material Selection Process

　　Food-grade electrolytic tinplate is selected as the base material for airtight caviar tins. Material grades are differentiated according to box size and pressure resistance requirements. Tinplate features light-proof property, oxygen isolation, water vapor barrier and mild corrosion resistance, perfectly adapting to low-temperature refrigeration and transportation environment of caviar. Incoming inspection is carried out before raw materials enter production: verify food contact test reports, tin coating thickness, material hardness and surface flatness. Sheets with rust spots, scratches, pinholes and oxidation patches are rejected.

　　Sheet thickness is a core customized parameter. Regular caviar tins adopt 0.20mm–0.28mm food-grade tinplate. Thin sheets suit small-sized separate caviar packaging; thickened sheets are used for large-capacity gift boxes to enhance box rigidity and avoid deformation under stacking pressure in cold chain. CNC shearing equipment cuts tinplate blanks accurately to control cutting burrs. Blanks with excessive burrs will be polished again to prevent scratching the sealing contact surface during subsequent stamping.

　　Food-grade transparent internal lacquer is sprayed on all surfaces contacting food. The internal coating process strictly controls coating uniformity, adhesion and low-temperature resistance. No missing coating, bubbles or shrinkage cavities are allowed. Once coating defects exist on inner walls, metal may slowly react with caviar juice under refrigeration, impairing food flavor and safety. After internal coating, boiling water immersion and low-temperature freezing simulation tests are conducted to verify resistance to water and condensed water erosion.

　　2. Mold Development & Structural Customization Process

　　Custom airtight caviar tins support non-standard size customization. The first stage is mold design and manufacturing. Two mainstream structures are available: screw-top airtight caviar tins and snap-fit airtight caviar tins. The core focus of mold design lies in precision of sealing matching surfaces. Ordinary tinboxes only focus on external dimensions, while tightness-oriented tins require over 3 times stricter tolerance control for box body and lid fitting.

　　Screw-top structure: Thread structure is processed on the box mouth. Thread pitch and tooth depth are precisely calculated to ensure smooth twisting. Tightened threads fit closely. Molds are made of wear-resistant Cr12MoV steel with quenching and tempering treatment to extend service life and prevent enlarged fitting clearance and air leakage caused by long-term production abrasion. Snap-fit sealing structure: A sealing silicone rubber groove is built into the lid, and a pressing rib is formed on the box mouth. The outline of pressing rib is smooth and regular. After snapping, the silicone sealing ring is compressed to form a physically sealed cavity.

　　Trial molding and sampling are carried out after mold completion. First samples are mainly measured for box mouth roundness, fitting clearance and flatness. Eccentricity, uneven joint clearance, uneven pressing rib height will trigger mold modification. Mass production can only start after repeated adjustment to stabilize parameters of continuous samples. All mold parameters are filed to guarantee consistent dimensions for repeated orders.

　　3. Stamping & Forming Process

　　Cut tinplate blanks are sent to multi-station continuous stamping production lines. Forming is completed through multiple progressive procedures to avoid concentrated material stress and micro cracks caused by one-step heavy stamping. Process flow: Pre-stretching → Main body forming → Box mouth curling / thread forming → Pressing rib processing → Edge trimming → Curling polishing.

　　Box mouth curling is critical: Double-layer inward curling is adopted for box edge to remove sharp cutting edges. It prevents operator injury and avoids sharp edges cutting the built-in sealing silicone ring. Curling must be full and smooth without cracking, wrinkling or flattening defects.

　　Thread forming is the core procedure for screw-top tins. Progressive rolling molding slowly extrudes thread patterns to guarantee smooth burr-free thread surface. Burrs or protrusions on threads will wear sealing rings during twisting and damage the sealing system. Sampling inspection on twisting performance is implemented after forming: qualified samples feature smooth screwing without jamming or excessive shaking.

　　Production environment during forming is kept clean. Metal debris on equipment is cleared regularly. Semi-finished tins are separated by plastic sheets during circulation. Direct friction between tins is forbidden to avoid permanent scratches. Semi-products are classified and labeled to distinguish sizes and structures and prevent mixing.

　　4. Sealing Accessory Assembly Process

　　Sealing performance relies on the combination of metal structure and food-grade silicone sealing rings. Sealing rings are made of food-contact silicone, featuring low-temperature resistance, odorless property and anti-aging performance without harmful substance precipitation. Custom rings are molded according to box mouth outline to ensure accurate matching of cross-section size and perimeter with clamping grooves.

　　Assembly is completed in a clean area. Metal dust and oil stains inside lid grooves are cleaned before assembly. Sealing rings are fully embedded into grooves without distortion, overturning or partial disengagement. Manual pressing and rotating inspection is conducted after assembly to confirm full positioning of rings. Glue adhesion for sealing rings is prohibited to avoid food contact risks; physical clamping fixation is adopted.

　　Opening & closing cycle tests are carried out after assembly: 50 times of repeated opening/closing or twisting to check ring displacement and deformation. Structures passing the test can proceed to subsequent surface processing. Large-capacity caviar tins additionally undergo pressure resistance tests to simulate stacking pressure in cold chain transport and verify long-term sealing reliability under compression.

　　5. Surface Printing & Appearance Treatment Process

　　As premium food packaging, printing technology directly determines product added value. Multiple customized surface options are supported: CMYK four-color offset printing, spot color printing, hot stamping, embossing, debossing, partial UV coating, matte varnish, glossy varnish and frosted varnish.

　　Printing workflow: Plate making → Design verification → Trial printing sample confirmation → Mass printing → Top varnish coating. Customer artwork is strictly verified before printing, including LOGO, text, origin information, specification, barcode position and color values. The confirmed color sample is filed as standard for mass production to control color difference. Specially formulated metal-compatible food-grade ink is applied for tinplate printing with strong adhesion and resistance to ink cracking under low temperature.

　　Protective outer varnish is sprayed uniformly after printing. Matte varnish delivers premium light-luxury texture, the mainstream choice for caviar packaging; glossy varnish offers higher color saturation; frosted varnish brings delicate tactile feeling. Varnish improves visual effect, isolates air to prevent external oxidation and fingerprint marks, and allows easy surface wiping.

　　Special process control: Hot stamping and embossing cannot be excessively raised, otherwise flat lid closure will be affected and sealing effect disrupted. All surface treatments are avoided on box mouth sealing contact areas. Printing and hot stamping are forbidden on sealing surfaces to ensure tight fitting between metal and silicone rings.

　　6. Cleaning, Drying & Food-Grade Purification Process

　　Deep internal purification is required for printed and formed tins. Combined ultrasonic cleaning and hot air drying process removes fine metal dust and residual processing oil inside containers. Deionized water is used for cleaning to avoid mineral spots left on inner walls.

　　Stable and controllable drying temperature prevents damage to internal food coating under high heat. Tins are transferred to dust-free temporary storage area for natural cooling after drying. Special staff conduct full visual inspection on inner walls after cooling: no stains, dust, water marks or coating peeling are allowed. Strict cleanliness standards are enforced for food-grade packaging to prevent debris contaminating caviar. Purified products are covered for dust prevention before tightness testing.

　　7. Tightness Testing Process (Core Quality Control)

　　Sealing performance is the most critical indicator for caviar tins. Sampling air tightness test is implemented for each batch. Main testing method: Negative pressure immersion air tightness test. Sealed tins are vacuumed and immersed in clean water. Continuous air bubbles indicate leakage. Samples without persistent bubbles are qualified. Leakage products will be traced for problems in structure, silicone ring or box mouth fitting.

　　For high-end export orders, high-low temperature cycle simulation tests are added: alternate environment simulating refrigeration and normal transportation temperature. Tightness is re-tested after temperature variation cycles to check leakage risks caused by minor material deformation under temperature difference.

　　Sampling ratio is adjusted according to order grade. Higher sampling proportion is applied for premium caviar gift sets. Once unqualified samples appear in batches, sampling scope will be expanded and full inspection arranged if necessary to identify abnormalities in molds and assembly procedures.

　　Along with air tightness test, drop simulation test is carried out to simulate slight falling during logistics loading and unloading, verifying sealing integrity after impact to meet long-distance cross-border transportation requirements.

　　8. Final Inspection, Anti-Rust Treatment & Finished Goods Packaging Process

　　All finished products go through comprehensive final inspection after all procedures. Inspection items include surface scratches, color difference, blurred printing, peeling hot stamping, box deformation, curling cracking, thread matching, sealing ring assembly status, opening smoothness and inner wall cleanliness. Defective products are stored separately for rework or scrapping.

　　Qualified finished products receive short-term anti-rust protection. Each tin is independently packed with PE dust-proof bag to isolate moisture. High-strength corrugated cartons are used for outer packaging with separators inside to avoid scratch during transit. Outer cartons are marked with model, quantity and production batch for traceability.

　　9. Optional Custom Supporting Processes

　　Expandable processes can be selected as required by clients: Custom EVA flocked inner tray for precise positioning of caviar cans for gift sets; laser engraved LOGO on tin body; customized anti-counterfeit labels; optional handle structures; multi-grid combined gift tins. All newly added supporting structures will be evaluated in advance in design phase to guarantee no damage to original sealing system.

　　10. Process Quality Control System

　　Full-process batch traceability system is established. Raw material batch, mold number, production team and test records are all archived. Production complies with relevant specifications for food contact packaging; material test reports can be provided upon request. Tolerance standards are strictly maintained: sealing matching tolerance is controlled within ±0.03mm, far stricter than ordinary gift tin standards, ensuring stable sealing performance for mass production. The whole set of processes is developed targeting low-temperature preservation, long-distance transportation and high-end gift positioning of caviar, balancing practicality, safety and commercial aesthetics.