The surface treatment of tin bags (usually used for food packaging, electronic component protection, laboratory containers, etc.) after completion aims to improve performance (such as corrosion resistance, conductivity), optimize appearance, enhance functionality (such as sealing, adhesion), or meet the requirements of specific application scenarios. The specific treatment method needs to be selected based on the material characteristics (pure tin, tin alloy), application fields, and performance requirements of the tin bag. The following are common surface treatment technology classifications and detailed explanations:
1、 Cleaning and pretreatment: basic premise
Before surface treatment, it is necessary to remove oil stains, oxide layers, and impurities (such as metal shavings from stamping and release agents) on the surface of the tin bag, otherwise it will affect the adhesion and effectiveness of subsequent treatment. This is the 'pre step' for all surface treatments.
treatment methodprincipleApplicable scenariosadvantage
Solvent cleaningUse organic solvents such as alcohol, acetone, trichloroethylene, etc. to remove oil stains and organic impurities through dissolution or emulsificationSmall batch tin bags with light surface oil stainsSimple operation, high efficiency, no residue (volatile solvents need to be selected)
碱性脱脂Use alkaline solutions such as sodium hydroxide and sodium carbonate to decompose oils and fats through saponification reaction, while removing some of the oxide layerIndustrial scenarios with large quantities of tin bags and heavy surface oil stainsLow cost, thorough degreasing, suitable for large-scale processing
pickling and passivationRemove the surface tin oxide layer with acidic solutions such as dilute hydrochloric acid and dilute sulfuric acid, while forming a slight passivation film on the surfaceRemove the oxide layer and improve surface activity (if welding or coating is required later)Combining cleaning and preliminary rust prevention functions
Ultrasonic cleaningUsing the "cavitation effect" generated by ultrasonic vibration, combined with cleaning solution (water-based or solvent based) to remove surface impuritiesComplex shaped tin bags (such as bags with folds and small holes), tin bags for precision electronicsClean without dead corners, does not damage the surface, suitable for precision parts
2、 Anti corrosion and rust treatment: extending service life
Tin itself has a certain degree of corrosion resistance (stable in dry air), but oxidation and rusting may still occur in humid, high-temperature, or corrosive media (such as organic acids in food and salt spray in industrial environments). Surface treatment is required to enhance the anti-corrosion ability.
1. Chemical conversion coating treatment (forming protective oxide film)
Passivation treatment: Immerse the tin capsule in passivation solutions such as chromate, phosphate, molybdate, etc., to form a dense chemical conversion film (such as chromate film, tin phosphate film) on the surface. This film can isolate air, water, and corrosive media, significantly improving corrosion resistance.
Application: Tin bags for food packaging (must meet food grade standards, such as using chromium free passivators), tin containers for outdoor use.
Oxidation treatment: By heating (in air or oxygen) or chemical oxidation (such as using hydrogen peroxide or nitric acid), a uniform layer of tin oxide (SnO ₂) film is formed on the surface of tin. The oxide film is gray or black in color and has both anti-corrosion and decorative functions.
Application: Decorative tin bags, packaging tin bags that require shading.
2. Coating treatment (covering a more corrosion-resistant metal layer)
By electroplating or chemical plating, a layer of more corrosion-resistant metals (such as zinc, nickel, chromium, gold, silver) can be deposited on the surface of the tin bag, while optimizing conductivity and wear resistance.
Electroplating: Using the principle of electrolysis, a tin pouch is used as the cathode, and the metal to be plated is used as the anode to form a uniform coating in the electrolyte (such as nickel plating to improve salt spray resistance, and gold plating to enhance conductivity in the electronic field).
Chemical plating: Without the need for electricity, metal ions are self catalytically deposited on the surface of tin bags through chemical reactions (such as chemical nickel phosphorus alloy plating, which is uniform and suitable for complex shapes).
Application: Tin bags for electronic component packaging (silver/gold), corrosion-resistant tin bags for industrial use (zinc/nickel).
3. Coating treatment (covering organic/inorganic protective film)
Coating a thin film on the surface of the tin bag can physically isolate corrosive media and provide functionality (such as high temperature resistance and anti adhesion).
Organic coating: Apply organic coatings such as epoxy resin, polyurethane, polytetrafluoroethylene (PTFE), etc., and form a protective film through baking or curing.
Example: Food grade tin bags coated with food grade epoxy resin to prevent tin from reacting with acidic substances in food; Industrial tin bag coated with PTFE enhances high temperature resistance and chemical corrosion resistance.
Inorganic coating: Sol gel method, vapor deposition method, etc. are used to coat inorganic films such as silicon dioxide (SiO ₂), aluminum oxide (Al ₂ O ∨), with temperature resistance and hardness superior to organic coating.
Application: Tin bags used in high-temperature environments (such as for heating laboratory samples).