Why is the can part of the formulation rather than just packaging?
An aerosol can is a pressure vessel with a protective internal coating, and that coating is in continuous contact with solvent, propellant, water, and active ingredients.
The two body types behave differently:
- Tinplate (three-piece, welded side seam): steel with a thin tin layer plus an organic lining. Widely used, economical, and dependent on the lining for chemical resistance. - Aluminium (monobloc, seamless): no side seam to corrode and better suited to higher pressures and smaller diameters.
Inside a tinplate can, the lining - typically epoxy-phenolic, organosol, or polypropylene-based - is the only barrier between the formula and steel. If the formula attacks it, corrosion starts from the inside out, where no incoming inspection will catch it. That is why the lining grade belongs in the specification, not the can supplier's discretion.
How does the formula type dictate lining selection?
Four formula families pull the specification in different directions:
- Solvent-based (alkyd, acrylic, nitrocellulose): most tolerate a standard epoxy-phenolic lining. Solvent power is the variable - aggressive aromatic or ketone-rich blends demand a higher-grade lining. - Water-based: the hardest case. Water plus oxygen accelerates steel corrosion, and the product needs a premium lining, often double-coated or polypropylene-based. - Two-component and moisture-sensitive systems: require can and valve components that do not introduce or absorb moisture, plus tighter sealing. - Acidic, alkaline, or stripper-type formulas: need a lining selected against the specific pH and active chemistry, not a default grade.
Ask three questions in order: pH and solvent system, water content, and required shelf life. Those answers set the lining grade.
What happens when the lining and the formula are incompatible?
Failure usually appears on a timeline that embarrasses the brand rather than the factory:
- Pitting or perforation at the side seam and bottom dome, leading to slow leaks in storage or transit - a dangerous goods incident. - Lining blistering and delamination, which releases flakes into the product and blocks the valve. - Product discolouration and metallic contamination from dissolved iron or tin. - Pressure loss and poor spray performance, often blamed on the valve when the can is the cause.
Most appear between six and twenty-four months after filling - usually after the containers have shipped. That is why compatibility is proven by accelerated testing before a bulk order rather than by a customer complaint.
How do you match can pressure rating to the propellant?
Every can carries a maximum allowable pressure, normally specified at 55 degrees Celsius (130 degrees Fahrenheit), because that is a realistic worst case for a can stored in a warehouse or a vehicle in summer.
The matching logic:
1. Establish the vapour pressure of the chosen propellant blend at 55 degrees Celsius. 2. Compare it against the can's maximum allowable pressure, and confirm the safety margins the can supplier publishes - deformation pressure and burst pressure above that allowable figure. 3. Check the same for the valve, which has its own pressure and temperature limits. 4. If the propellant runs close to the limit, move to a stronger can body or adjust the blend rather than accepting a thin margin.
For LPG and DME systems this decides can selection before any artwork discussion; for compressed-gas and low-pressure formats the constraint moves to the valve.
What testing and documentation should precede a bulk order?
A defensible compatibility package contains four things:
- Accelerated storage testing: cans filled with the production formula, held at 40 to 55 degrees Celsius for 4, 8, and 12 weeks against a room-temperature control, then opened and inspected for lining blistering, corrosion at the seam and dome, product discolouration, valve function, and spray pattern. - Weight-loss data to catch slow leaks that visual inspection misses. - Material certificates: lining type and grade, tin coating weight, can dimensions, valve and actuator specification, and the pressure rating figures. - Batch records and a retained sample set, so a future complaint can be traced against the approved standard.
Buyers often test the formula and skip the packaging, which inverts the risk: a formulation failure is caught in your own plant, a packaging failure by your customer.
What does this mean commercially for the buyer?
The can is a small share of unit cost and an outsized share of the risk, which drives three practical rules:
1. Specify the lining grade and tin coating weight in the purchase order, not just can size and diameter. "Aerosol can, 65 mm" is not a specification. 2. Retest after any change of can supplier, lining grade, or formula - even when nothing else moves. Compatibility is a property of the pair, not of either part alone. 3. Align the shelf-life claim with test data. A two-year claim needs accelerated evidence behind it, and markets that require it will ask for the file.
For private-label buyers the cleanest arrangement is one supplier accountable for both fill and can, with compatibility testing in the sampling stage - removing the gap where the filler blames the can supplier and the can supplier blames the formula.