Corrosion of the closure

A failure that is usually blamed on the bottle and is almost always the closure.

The bottle is fine and the cap is not

A plastic bottle is chemically simple. A trigger sprayer is a dozen components including a metal spring, several elastomer seals, a dip tube and sometimes a metal ball.

Every one of them is in contact with the formula continuously, and the metal parts are the vulnerable ones.

Where the metal is

The spring inside a trigger, which is the usual failure.

A ball in a pump valve.

A metal cap or an induction seal liner.

And any metal in your filling equipment, which is a manufacturing problem rather than a product one and shows up the same way.

What it looks like

Rust particles in the liquid, which is the most visible and the most alarming to a customer.

Discoloration of the product, often brown or yellow.

A trigger that stops working, stiffens or fails to prime.

A seal swelling, shrinking or hardening, which produces leaks and loss of prime.

And a metal cap corroding at the seal line, which stains the shoulder of the bottle.

Fixing it

Specify a closure rated for your chemistry. Suppliers offer triggers with stainless or plastic-coated springs, and entirely metal-free versions, for exactly this reason.

Check the liner material against the formula, because it is a component with its own compatibility and it is the one nobody asks about.

Avoid metal caps on acidic and strongly alkaline products.

And test the closure, not just the bottle, for months. A compatibility program that fills bottles and caps them loosely has not tested the thing most likely to fail.

References