A vial closure is a system of three parts: the rubber stopper that plugs the neck, the aluminum seal crimped over it, and the plastic button on top. Each has one job. Understanding them explains what a receiving inspection is looking for and why a loose cap is a reject rather than a cosmetic flaw.
The crimp seal
The aluminum seal is a cup with a skirt that is rolled under the flange of the vial neck by a crimping tool. Crimping compresses the stopper between the seal and the glass, and it is that compression, maintained for the life of the vial, that keeps the closure tight against leakage and microbial ingress. The quality of a crimp is measured as residual seal force, the compressive load the seal continues to exert on the stopper; too little gives a leak path, too much can deform the stopper or crack the glass. Manufacturers control crimping force and verify it on samples. See container closure integrity.
The flip-off button
The plastic button, usually polypropylene, snaps into the center of the aluminum seal and covers the stopper’s target area. Its purposes are to keep the stopper face clean until first use and to provide tamper evidence: removing it breaks the tabs that held it, and it cannot be put back. A vial that arrives with the button missing or loose is rejected because the stopper face has been exposed and the vial may have been entered. The button is removed at first opening and discarded. See how to open a vial.
Finishes: 13 mm and 20 mm
Vial necks come in standard finishes, and the stopper and seal must match. Small vials such as 3 mL commonly use a 13 mm finish; 10 mL and 30 mL vials commonly use 20 mm. The number is the diameter of the neck opening the stopper fits, and it is why a 20 mm stopper has a larger target area than a 13 mm one. See vial sizes compared.
What to inspect
| Check | Acceptable | Reject |
|---|---|---|
| Seal skirt | Smoothly rolled under the flange all the way round | Gaps, wrinkles, a lifted edge, or a seal that rotates when turned |
| Seal cap | Flat, tight against the stopper | Domed or dented, suggesting internal pressure or impact |
| Button | Present, seated, tabs intact | Missing, loose, or reattached |
| Stopper (visible after opening) | Flush, undamaged target | Torn, cored, or displaced |
| Glass at the neck | No cracks or chips | Any crack, especially under the seal |
The printable receiving checklist covers these items in order. See also how to inspect a vial before use.
Removing the seal at disposal
The crimp seal is removed with a decapper only when an empty vial is being separated for recycling; it is never removed from a vial that is still in use, because the compression that keeps the closure sterile is lost. See recycling the packaging.
Related
Vial stoppers explained · Type I borosilicate glass · Vials: glass vs. plastic
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