Quality issues:
After a period of storage, the air-packed milk powder collapsed, but no leakage was seen with the naked eye.
Cause Analysis:
(1) Packaging materials
• Poor barrier property - the gas inside the package has a high amount of gas permeated through the packaging material, that is, the gas permeation rate is large and the barrier property is poor, such as carbon dioxide and nitrogen inside.
• Poor kneading resistance - after being kneaded by external forces, the packaging bag will have defects such as creases and pinholes, resulting in poor barrier properties.
(2) Finished product packaging process
• Poor airtightness - the bag body or heat-sealed part of soft plastic packaging is prone to air leakage under certain pressure or long-term storage, especially the sealing quality of the heat-sealed part is poor, such as the heat-seal strength is too low or too high 1. If the heat sealing strength is not uniform, air leakage is more likely to occur.
Expert advice:
——Pay attention to the daily monitoring of barrier properties such as nitrogen permeation, carbon dioxide permeation, nitrogen permeation after rubbing, carbon dioxide permeation after rubbing, etc., barrier performance after rubbing, sealing performance (negative pressure method), heat seal strength, etc. .
——Adjust the parameters of the heat-sealing machine to improve the quality of the heat-sealed parts; choose packaging materials with high barrier properties and good rubbing resistance or improve the quality of existing packaging materials.
Typical quality cases:
——Test sample: aluminum-plastic composite film for milk powder packaging (the customer reported that the milk powder was packed with nitrogen, and as the storage time increases, the shrinkage of the packaging bag becomes more and more obvious).
——Targeted testing items: nitrogen gas permeation, nitrogen gas permeation after kneading, sealing performance (negative pressure method), heat sealing strength.
——Test results: The nitrogen permeation rate of the aluminum-plastic composite film package before and after rubbing is not much different, and the test values are all low (that is, the barrier property to nitrogen is better), which shows the barrier property and rubbing resistance of the composite film Good performance; the uniformity of the heat-sealing strength value is poor, the heat-sealing strength is only 18N/15mm in the poor heat-sealing place, and the heat-sealing strength can reach 45N/15mm in the good heat-sealing place; at the same time, in the sealing performance (negative pressure In the test, when the milk powder finished product was packaged at -65KPa, the heat seal leaked, which was lower than the average pressure -90KPa of similar high-quality products, which further proved that the heat seal effect of the heat seal was poor. Therefore, the occurrence of the deflated bag problem is mainly related to the heat sealing quality of the heat seal.
2. What should we do if the liquid milk packaging leaks or breaks?
Quality issues:
During the production, transportation and sales of bagged liquid milk, there are problems such as liquid leakage and bag breakage.
Cause Analysis:
(1) Packaging materials
• Poor toughness—the packaging material is brittle and has poor toughness. When the finished package falls or is impacted by external forces, it is easy to break the bag at the bag body.
• Poor thermal viscosity - when the heat seal is just heat-sealed and has not cooled down, the impact force generated by the liquid milk being filled is likely to cause the heat-sealed part to rupture immediately, that is, the thermal bonding strength of the packaging material is poor.
(2) Finished product packaging process
• Poor heat-sealing strength—the sealing quality of the heat-sealing port is poor, and it is easy to leak liquid and break the bag when it is impacted by liquid milk or squeezed by external force.
Expert advice:
——Pay attention to the monitoring of various performance indicators such as burst pressure, drop resistance, pressure resistance, heat seal strength, hot bond strength, tensile strength and elongation at break, pendulum impact resistance, etc. of the packaging.
——Improve the parameters of the heat-sealing machine, and choose packaging materials with good flexibility and heat-sealing performance.
Typical quality cases:
——Test sample: liquid milk milky white film packaging bag (the customer reported that the liquid milk packaged in milky white film has a high proportion of broken bags and liquid leakage during the shelf life).
——Targeted testing items: burst pressure, drop resistance, pressure resistance, heat seal strength, tensile strength and elongation at break, pendulum impact resistance.
——Test results: the tensile strength, elongation at break and pendulum impact energy of the milky white film of the problematic sample can meet the quality requirements of the product, that is, the flexibility of the milky white film is better; in the burst pressure test, at 30KPa, the liquid state The milk package was broken at the heat seal. In the drop resistance test and pressure test, the finished package was broken at the heat seal, and the heat seal strength of the package was low, only reaching about 14N/15mm, far lower than The market average for similar quality product packaging. The above test phenomenon shows that the broken bag and liquid leakage of the problem sample are mainly caused by the poor heat seal strength of the heat seal.
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