Example analysis of food packaging bag sealing test
During the storage of food packaging bags, there are many reasons for the contents to rot. among them, * the common reasons are the poor film barrier performance and the poor sealing performance of the packaging bags. For the former, it is necessary to fully consider the performance and thickness of each layer of material when designing the packaging bag to obtain sufficient barrier performance. Here, we focus on the sealing of the packaging bag.
The so-called tightness refers to the characteristics of the package to prevent other substances from entering or escaping from the contents. In the production process of food packaging bags, due to many production links, heat sealing leakage, pressure penetration or cracks and micropores of the material itself may occur, resulting in small holes or weak strength points connected inside and outside. These will have a very adverse impact on food, directly affect the quality of products. In particular, the small holes cause the food part to be exposed to the air directly, thus losing the significance of packaging bag preservation.
For the sealing performance, it is very important to prevent and detect in advance. Among them, strengthening the post inspection and finding the sealing defects in time can undoubtedly be used as a reference for prevention in advance.
Take the milk bag as an example, if it leaks, you can find it by squeezing it by hand. But for instant noodles, biscuits and other solid food, how to find the leakage of food packaging bag?
1、 Decompression in water (vacuum method)
The instant noodles are usually immersed in water and vacuumed. If there is a leak in the bag, there will be bubbles like air leakage in the tire, and the leakage can be clearly found.
It can be known that the commonly used means to determine the sealing performance is the test device with vacuum.
2、 Test device
According to the requirements of GB / t15171-94 test method for sealing performance of flexible packages, the vacuum test device shall include the following parts:
1. Vacuum chamber: it is made of transparent material and can bear the pressure of 100KPA and the sealing cover.
The vacuum container is used to hold the test liquid and test sample; The sealing cover is used to seal the vacuum chamber. When vacuumizing, the sealing cover should be able to ensure the tightness of the vacuum chamber.
2. Sample fixture: it is used to fix the sample in the test liquid in the vacuum chamber, and its material and shape shall not affect the performance of the sample and the test observation, * it is better to select transparent materials.
3. Pipeline: including gas source connecting pipe, vacuum pipe connected with vacuum source and exhaust pipe connected with atmosphere. They shall be equipped with valves to control opening and closing.
4. Vacuum meter: used to measure vacuum degree in vacuum chamber, and its accuracy shall not be lower than 1.5 level;
5. Control device: including vacuum switch, vacuum regulating device, air inlet valve, etc.
3、 Experimental practice of color printing factory
In the application of flexible packaging inspection, the detection device based on the principle of vacuum generator is generally used.
Using vacuum generator and jet principle, the compressed air can be changed from positive pressure to negative pressure to form a stable air source, which can avoid the disadvantages of pressure pulsation and high impurity content caused by vacuum pumping.
Take mfy-01 sealing tester (vacuum generator) of Jinan Chenchi instrument as an example The following steps shall be referred to when using the decompression method in water:
1. Put appropriate amount of tap water in the vacuum chamber, and put the sealed sample bag in the vacuum chamber.
2. Cover the sealed cover of the vacuum chamber, and the fixture will automatically press the sample bag into the water, turn on the power switch and turn the vacuum degree adjustment knob to vacuumize the vacuum chamber. Time and vacuum can be controlled at will.
The vacuum value to be adjusted shall be determined according to the characteristics of the sample (such as the packaging materials used, sealing conditions, etc.) or the relevant product standards. However, the internal and external pressure difference of the sample shall not cause the specimen to crack or the sealing part to crack.
3. Observe the leakage of the sample during vacuum pumping and vacuum holding, and consider that there are five continuous bubbles. A single isolated bubble may be a gas attached to the outside of the packaging bag, which is not considered as leakage of the sample.
4. Close the vacuum knob, open the inlet pipe valve to connect the vacuum chamber with the atmosphere, open the sealing cover and take out the sample bag.
If there are no continuous bubbles during vacuumization and vacuum holding and no water infiltration during unsealing inspection, the sample is qualified, otherwise it is unqualified.
If other methods are used, it is required that under the set test conditions, or when there is no leakage of test liquid, or the pressure in the vacuum chamber is rapidly recovered, if the sample can be restored to the original shape, it will be regarded as qualified; otherwise, it will be judged as unqualified.
Jinan Chenchi instruments professional production and sales of packaging quality testing equipment.