Understanding Button Closures and Vacuum Sealing in Packaging

Vacuum Requirements and the Capper

The most critical factor in the successful application of a button closure is the vacuum level. For a button to "go down"—meaning to seat itself firmly and create an airtight seal—the capper must deliver a sufficient amount of vacuum into the package.

In industrial settings, vacuum is measured in inches of mercury (inHg) or pounds per square inch (psi). For button closures, the standard requirement typically ranges from 18 to 20 inches of mercury. To put this into a more common engineering perspective, this vacuum level is approximately equivalent to 9 to 10 psi.

The capper is the piece of machinery responsible for this task. It must manage the transition of the product into the container and ensure that the headspace (the empty space between the liquid product and the top of the container) is prepared to receive the vacuum.

Exam Tip: If you are asked to convert vacuum requirements for button closures, remember that 18–20 inches of mercury translates to approximately 9–10 psi.

Troubleshooting: "Up Buttons" and Loss of Seal

In a production environment, a common quality control issue is the occurrence of "up buttons." An "up button" refers to a closure that has failed to seat properly and remains partially or fully raised above the rim of the container. This is a clear indicator of a failure in the sealing process.

When troubleshooting up buttons, technicians generally look at two primary culprits:

1. Loss of Seal During Processing: The button may have been seated correctly initially, but a failure occurred during subsequent processing steps, leading to a loss of the vacuum or a breach in the seal.
2. Insufficient Initial Vacuum: The capper may simply be failing to deliver enough vacuum into the headspace. If the vacuum is below the required 18–20 inches of mercury, there is not enough atmospheric pressure pushing the button down to create a permanent seal.

Summary Table of Button Specifications

By understanding the relationship between the capper's performance, the vacuum levels in the headspace, and the physical dimensions of the GPI finishes, operators can effectively minimize seal failures and ensure product integrity.