Internal coating of aerosol cans
Internal coating of aerosol cans
The internal coating of aerosol cans is a key process to ensure its safety and functionality. It is mainly used to prevent chemical reactions, corrosion or contamination between the contents and the tinplate can body. The following is a detailed description of the internal coating of aerosol cans:
1. Main Function
1.1 Anti-corrosion protection: prevent the contents (especially corrosive components such as alcohol, organic solvents, acidic/alkaline substances) from reacting with the metal can body (usually tinplate or aluminum).
1.2 Content stability: prevent metal ion migration from affecting product quality (such as medicines, cosmetics, food-grade aerosols).
1.3 Lubricity: Some coatings can reduce friction in the valve system to ensure smooth spraying.
1.4 Sealing: assists in the sealing of the can body to prevent leakage.
2. Common internal coating materials
Depending on the contents differences, the coating material needs to be selected specifically:
2.1 Epoxy resin (Epoxy):
The most commonly used, with excellent chemical resistance, suitable for most chemicals, cosmetics (such as hair spray, perfume), household cleaners, etc.
2.2 Polyester:
High temperature and corrosion resistance, used in some industrial aerosol cans.
2.3 Phenolic:
High corrosion resistance, suitable for strong solvents (such as paints, pesticides).
2.4 Polyethylene (PE) or Polypropylene (PP):
Used in food, medicine and other fields with high safety requirements (such as cream spray cans, medical sprays).
2.5 Special coatings:
Fluorine-containing coatings (such as PTFE): Extreme chemical resistance, used for highly corrosive industrial products.
3. Key points of internal coating process
3.1 Pretreatment: The can body needs to be thoroughly cleaned and degreased to ensure coating adhesion.
3.2 Spraying/electrostatic spraying: Evenly cover the inner wall, usually with a thickness of 5-20 microns.
3.3 High temperature curing: The coating is cured in a baking oven to form a dense protective layer.
3.4 Quality inspection:
3.4.1 Conductivity test: Detect coating integrity (no pinholes).
3.4.2 Corrosion resistance test: Simulate long-term contact with the contents (such as salt spray test).
1. High risk of can corrosion
Direct contact between metal and contents:
Acidic, alkaline or salt-containing ingredients (such as detergents, pesticides) will corrode aluminum or tinplate cans, causing can wall thinning, perforation or leakage.
Propellants (such as propane, dimethyl ether) may accelerate metal oxidation.
Consequence: The strength of the can decreases, which may cause explosion or contamination of the contents.
Metal ion migration:
Uncoated cans may release metal ions such as aluminum and iron, affecting the safety of drugs, cosmetics or foods (such as discoloration, odor, degradation of active ingredients).
For example: Perfumes or spray drugs may undergo chemical reactions due to metal catalysis.
Case: Acidic products in iron cans may produce hydrogen, causing the can to swell ("bulging can").
Micropore leakage: There are microscopic pores in the metal tank body. When there is no internal coating:
Propellant (such as LPG) or volatile components are prone to slowly leak through the pores, resulting in insufficient pressure and spray failure.
Oxygen or moisture penetration may oxidize the contents (such as paint, grease).
Rust or discoloration:
Rust on the inner wall of the tank may contaminate the contents (such as brown particles sprayed out of white spray).
The outer wall is uneven and the paint surface falls off due to internal corrosion.
Nozzle blockage: Particles produced by corrosion may block the valve and affect the uniformity of spraying.
Inconsistency with industry standards:
Food and medical grade aerosols (such as asthma sprays, edible oil sprays) must be certified by FDA, EP, etc., and migration limits cannot be met without internal coating.
Industrial products (such as paints and chemicals) may cause transportation or storage accidents due to corrosion.
Short-term savings, long-term losses:
Although eliminating the internal coating process reduces initial costs, it may cost more due to returns, claims or damaged brand reputation.
For example: corrosion and leakage of the can body will contaminate other packaging or storage environment.
In rare cases, simple neutral contents may not require internal coating (such as pure water spray, some inert gas packaging), but compatibility must be strictly tested.
Internal coating is the key guarantee for the reliability of aerosol cans. Unless the contents are absolutely compatible with the can body and there is no risk of corrosion, internal coating must be carried out. When selecting the coating, the material (such as epoxy resin, polyester, etc.) must be matched according to the chemical properties of the contents (pH, solvent type, etc.).
According to customer needs, GUANGDONG HONGYUAN METAL PACKAGING CO., LTD basically adopts epoxy inner coating process to ensure the provision of high-quality products and avoid quality problems such as missing coating during filling and consumer use.
During the coating and printing process, GUANGDONG HONGYUAN METAL PACKAGING CO., LTD will not only meet the brand appearance requirements, but also ensure the adhesion, corrosion resistance and stability of the ink under high pressure environment. We use high-quality inks that meet current environmental protection standards and use Japanese Fuji coating and printing equipment. We have a variety of printing technologies and experienced workers to meet the various printing needs of customers and provide printed tinplate sheets with good printing effects. Our quality inspection department will carry out quality control and inspection during the coating and printing process, including color proofing test, defect detection test and wear resistance test to ensure the provision of high-quality aerosol can printing effects.
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