Negative Pressure Method Sealing Tester for Detecting Leakage in Food Packaging

Principle

The core principle of the negative pressure seal tester, as a widely used equipment for seal integrity testing of food packaging, is based on the pressure difference theory in physics. The instrument pumps the air inside the sealed test chamber through a vacuum pump, causing its internal pressure to be lower than atmospheric pressure, creating a stable negative pressure difference inside and outside the package. If there is a leakage defect in the package, the liquid (usually water) in the chamber will enter the package through the leakage point under the pressure difference, or the gas/liquid inside the package will overflow outward, creating continuous bubbles, so as to intuitively judge the sealing performance of the package. The process can be briefly described as observing whether the medium migration of the tested packaging due to the pressure difference between the inside and outside is caused by the controlled negative pressure condition.

Standard basis

During the testing process, a number of parameters need to be strictly controlled to ensure the accuracy and repeatability of the results. The main parameters include test vacuum, vacuum holding time and leak observation time. These parameters are set according to the material, structure and expected conditions of the packaging being tested, and refer to relevant national or international standards. Common standards at home and abroad clearly stipulate the tightness test of food packaging, which provides a reliable basis for testing.

The common reference standards are listed below:

The choice of vacuum level is key to ensure that it is sufficient to stimulate leaks without damaging the conforming packaging. The theoretical relationship can be approximated as the correlation between detection sensitivity and applied pressure difference ΔP.

Operational points

A standardized inspection process is the basis for reliable data. The operation typically begins with sample preparation, where the packaged sample is submerged in liquid in the test chamber. The device is then started, vacuumed according to the set parameters and maintained. The operator should closely observe the surface of the sample for continuous bubbles during the holding period. After the process, slowly release the vacuum, remove and evaluate the sample.

There are several key points to pay special attention to throughout the operation: First, the sample should be sufficiently submerged to ensure that potential leakage points are below the liquid level; Secondly, it is crucial to distinguish between "continuous bubbles" and "isolated bubbles" caused by air release on the packaging surface, the former is a sign of leakage; Finally, for some packages containing contents, it is necessary to evaluate whether the contents will vaporize or seep under negative pressure before testing to avoid interfering with the judgment.

Analysis of results

Through the negative pressure test, multiple leakage patterns of packaging can be effectively identified. Based on the rate, location, and persistence of bubble generation, a preliminary analysis of the severity and possible causes of the leak can be performed. Common types of leaks include continuous linear leakage at the closure, pinhole leakage on the packaging body, and penetrating leakage in the material itself. For rigid or semi-rigid packaging, it is also necessary to pay attention to the sealing effect of the cover fit.

The results should be documented in detail, including sample identification, test parameters, observed phenomena (e.g., bubble generation location, rate), and final qualification determination. A complete test report provides direct feedback on packaging process improvements.

Scope of application

Negative pressure sealing test plays an important role in online quality control and laboratory testing in the food industry due to its easy operation, intuitive results, relatively low cost and non-destructive packaging (for qualified products). It is suitable for testing the sealing integrity of various types of flexible plastic packaging, hard plastic containers, glass bottles and jars, metal can lids, etc. Especially for food packaging containing liquid contents or requiring freshness and moisture-proofing, tightness testing is a key link to ensure shelf life and food safety.

It is important to note that this method mainly detects leaks of macro or larger size. For very small leaks or "seepages", supplemental testing with more sensitive techniques such as tracer gas detection may be required. In practical applications, appropriate testing methods and judgment standards should be selected according to product risk levels and packaging requirements.