How are leaks in paper-based milk cartons detected?

If carton-packaged milk leaks, it not only causes waste but also potentially means that external bacteria have entered, posing a food safety risk. Currently, leaks are mainly detected using the following principles and methods:

🔍 Common Leak Detection Methods

Currently, the following methods are mainly used to detect leaks in carton-packaged milk, suitable for different scenarios:

• Underwater Vacuum Method (Bubble Method): This is one of the most commonly used and intuitive methods. The sample is immersed in water, and a vacuum is applied to the vacuum chamber using a sealing tester. After a pressure difference is created between the inside and outside of the packaging, if a leak exists, gas will escape from the leak point, producing continuous bubbles in the water, thus determining whether there is a leak and locating the leak point. This method is based on the national standard GB/T 15171 and is a qualitative detection method.

• Dye Penetration Method (Tracer Liquid Method): This method is particularly suitable for detecting very small leaks. The packaging is immersed in a colored liquid (such as red ink), or a dye solution is applied to the outer surface of the packaging, and then a vacuum is applied externally or pressure is applied internally. After the experiment, the packaging is opened to check for penetration of the colored liquid inside, or the outer surface is directly observed for signs of color penetration. This method has high sensitivity and is used in the United States Pharmacopoeia USP1207.2 and the Chinese Pharmacopoeia, and is also found in the internal inspection procedures of some companies.

• Vacuum Decay Method and Pressure Decay Method: Both of these methods are physical detection methods that can quantitatively analyze the degree of leakage. 

Vacuum Decay Method: The packaging is placed in a sealed vacuum chamber, and after vacuuming, the change in pressure inside the chamber is monitored. If the packaging leaks, external gas will enter the chamber through the leak point, causing the pressure to rise. The leakage situation is assessed by measuring the pressure change. Suitable for rigid and semi-rigid packaging. 

Pressure Decay Method: A certain pressure of gas is injected into the packaging, then sealed, and the decrease in internal pressure is monitored. The faster the pressure drops, the greater the potential leak. Suitable for all types of packaging, especially convenient for rapid detection on the production line.

• Near-Infrared Spectroscopy Detection Technology: This is a relatively advanced non-destructive testing method. By collecting the near-infrared spectrum of the heat-sealed area of the packaging box, and using a pre-trained model to analyze the spectral data, it is possible to determine whether the sealing is complete, thus predicting potential leakage risks before filling. This method allows for testing before the liquid is filled into the packaging, helping to avoid resource waste.

📋 Quality Control in Production

In dairy production, the quality of packaging materials is fundamental to preventing leaks. Manufacturers rigorously test several performance indicators of the packaging materials:

• Heat Seal Strength: This tests the strength of the heat seal on the packaging material, which is crucial for ensuring airtightness.

• Peel Strength (Bond Strength): This tests the adhesion strength between the layers of composite packaging, preventing delamination.

• Barrier Properties: This tests the material's ability to block oxygen and water vapor, which is essential for shelf life.

• Seal Performance Test: Using a seal testing instrument, this simulates different negative pressure conditions to test the overall sealing performance of the finished packaging.

🔎 Simple Identification Methods in Daily Life

In daily life, if you are concerned that a carton of milk might be leaking, you can do the following:

• Squeeze and Observe: Squeeze the packaging with your hand to see if it easily leaks air or if any liquid seeps out.

• Check the Appearance: Carefully examine the packaging, especially the edges and corners of the seal, for any obvious wrinkles, damage, or stains.

• Smell the Odor: If the packaging is already bulging, or if you smell a sour or other unusual odor after opening it, it may have spoiled and should not be consumed.

💎 Summary

Leak detection in carton-packaged milk is a multi-faceted system engineering process involving multiple technologies. From material control and online testing in the production process to precise analysis in the laboratory, all aspects work together to ensure the sealing safety of the product.

Hopefully, this information will help you better understand leak detection in carton-packaged milk. If you have more in-depth questions about a specific method or scenario, I would be happy to provide further information.