Leak testing for packaging might seem straightforward but is, in fact, one of the most complex challenges in leak testing. In other fields, the products we test are pretty uniform in volume and shape. That is to say, part handling is relatively simple, we have a multitude of test to choose from and the results are quantitative – sccm/min or delta P, and very repeatable.
Packaging is a different matter. The parts volumes vary amongst the sample selection, the shape can vary, and frequently the package is flexible. And, it is the latter that presents the most challenges.
The industry standard tests for flexible packaging are ASTM D3078, ASTM F1140, ASTM F2096, ASTM F2054, and ASTM F2095. There are variations for packages which incorporate porous barrier material, and trays with flexible lid-stock. The most common method encountered is ASTM D3078, often referred to as the vacuum bubble test. Simply, it involves placing the pack underwater in a vacuum chamber and evacuating the chamber. The differential pressure in the pack causes it to expand and if there is a leak the operator may be able to see bubbles of gas escaping.
Leak testing following ASTM D3078 is a very subjective test, it’s not really feasible to set reject levels, it’s a destructive test –it’s not advisable to return the samples to the production lot because they may have been contaminated by unobserved water ingress, and it can be messy. Depending on the size of the package the detection limit is around 150 microns or more. For years Uson has marketed a very suitable alternative to this method which we refer to as vacuum force decay.
Vacuum force decay leak testing utilizes the principle of the vacuum bubble test but without the water and introduces reliable reject levels that can be challenged with known hole sizes and specially made challenge units. We named the instruments Qualipak and they have been the method of choice for many pharmaceutical, medical device, and food packaging companies in the form of models Q710 and Q720. But time marches on.
Now we have the Qualipak 770, a stand-alone chamber which communicates, and is controlled by, Qualitek mR or Optima vT. Qualipak 770 can be configured using the existing infills of older Qualipak Q710 and Q720 leak testing instruments. This makes it an easy upgrade for users wanting better graphics and shorter test times. More on that later, but first let’s look at how it works and the output.
The model 770 consists of a vacuum chamber, load cell (1 or 2), nylon infills and a communications interface. The infills are designed to accommodate with a close fit and reduce the empty volume in the chamber. This speeds up the test cycle and increase sensitivity. Different sized packs can be addressed with their own infills or by using packing pieces.
When the package is loaded into the machine, the lid is closed and an internal restraining plate is brought lightly to bear on the upper surface of the infill. When it is correctly positioned the operator starts the test and the machine monitors the force measured by the load cell as the pack expands and presses down on the test plate to which the load cell is attached. When the target vacuum level is reach the vacuum source is switched of and the load cell will remain under pressure if the pack does not leak. Leaks are quantified by the rate of force decay over time and reject levels can be set by the use of know and calibrated orifices.
Leaks are characterized accordingly:
The ability to distinguish a change in force is referred to as the sensitivity. The sensitivity is the minimum suggested value to base a pass/fail decision. Force Decay Measurement sensitivity is approximately 10 micron although a hole as small as 5 micron can be detected. Sensitivity is highly influenced by test time and package size. In specific applications, a simple pass/fail decision may be made with smaller decay values.
With advances in data processing Qualipak 770 is capable of faster testing than its predecessors, one user has reported cycle time reduction of 20%.
Major Benefits :
Summary
Testing flexible packaging can be complicated, time consuming and mostly a subjective measurement.
Most methods are outdated, destructive and inaccurate.
Uson has a professional, objective, method of measuring approximate leak size in flexible packages and lidded tray.
For more information:
To learn more and find out if Qualipak 770 can assist with your flexible package testing needs please contact me at joe.pustka@uson.com or call 281-671-2000.