Damage to flexible packaging bags is one of the main problems affecting the quality of packaging products. Usually flexible packaging bags are most likely to break in the following situations.
First of all, in the product filling process, filling the contents of the bag will have a strong impact on the bottom of the bag, if the bottom of the bag can not withstand the impact of the role of the bottom will crack, not only affect the production environment clean, and will affect the filling efficiency; Secondly, in the product stacking, transportation, if the flexible packaging bags can not withstand due to commodity stacking pressure and other reasons caused by the increase in internal pressure, will also cause the bag rupture, high temperature Cooking bag pressure, high temperature, vacuum packaging pressure, flexibility, frozen packaging bag resistance to freezing cracking, puncture resistance and other bad may cause the rupture of the bag.
First, the filling process damage in the new filling production line, the production of flexible packaging bags and the contents of the filling is almost synchronized, so when the contents of the filling at the bottom of the heat sealing part of the bag is not completely cooled, and can withstand the impact will be greatly reduced. Usually said that the heat sealing strength refers to the two films through the heat of bonding together to completely cool the bonding strength, but in the production line of materials did not get enough cooling time, so the heat sealing strength of the packaging material is not suitable for the evaluation of the material heat sealing performance, should be used thermal adhesive force – the peeling force of the material heat sealing part has not yet cooled – based on this material selection. The relationship between the thermal adhesive force and the sealing temperature and sealing time of the film has a certain universality, to achieve the best thermal adhesive force of the film material has a most suitable temperature point, and when the sealing temperature exceeds this temperature point, the thermal adhesive force will show a downward trend. At the same time from the data analysis, at the same sealing temperature, the sealing time will be extended to increase the thermal adhesive force, the film at the same sealing temperature, when the sealing time of 0.3 s of the sample thermal adhesive force is significantly lower than when the sealing time is 0.5 s of the case. In actual use, the impact force on the bottom of flexible packaging bags should be calculated according to the filling contents, and then use the thermal adhesive force tester to draw the thermal adhesive force curve by adjusting the sealing temperature, sealing pressure and sealing time, and choose the best combination of heat sealing parameters for the production line on the basis of reference to the calculated data and the actual situation of the production line.
Second, the storage process of the broken bag case in addition to vacuum packaging, with flexible packaging bags of items in storage and transportation will be due to the stack of items placed in the bag caused by the increase in gas pressure, which can lead to the rupture of flexible packaging bags. As a result of the rupture of the location of more concentrated in the location of the heat between the material, namely, the heat sealing of flexible packaging bags, so broken bags can be detected by testing the heat sealing edge of the packaging materials, heat sealing strength, and then replace the material or adjust the heat sealing process parameters to avoid. The heat seal strength of the material according to the detection method can be broadly divided into tensile heat seal strength and expansion heat seal strength. Usually we use tensile testing tensile heat seal strength, is the packaging material in the same direction of force, force value uniformity of the case of resistance to separation at the heat seal, especially suitable for the evaluation of flexible packaging bag openability, but not for solving the problem of flexible packaging bag breakage, because the direction and size of the bag pressure caused by the breakage of the bag are uncertain, and the heat seal near the material due to bear part of the pressure may be Deformation occurs, but the problem of pressure damage to flexible packaging bags can be solved by testing the material’s expansion seal strength. Expansion seal strength of the detection and application of the expansion seal strength testing needs to use the leak and seal strength tester, the need to pressurize the flexible packaging bags, while detecting the entire package in the worst strength of the location (not limited to the heat seal part). Since the expansion seal strength does not represent the average strength of the heat seal, there is no correlation between the expansion seal strength and the tensile seal strength. However, if the material is extremely flexible (for example, some flexible packaging materials can be stretched to several times the original length), there will be significant deformation with the increase in test pressure, but also with the help of restraint plate test device to restrain the expansion of the flexible packaging bags and the extension of the material deformation. Through the leakage and seal strength tester not only to detect the maximum bursting force of flexible packaging bags, but also through the set of pressure to test the rupture time of the bag, the operator can design stacking structure according to the test data, can further adjust the parameters of the heat sealing process to improve the packaging effect, or according to the location of the rupture of flexible packaging bags on the packaging structure of the problem analysis.
Third, the emergence of vacuum food packaging sealing cracking problem mainly for the food vacuum packaging design and outer vacuum packaging materials two reasons.
1). Food vacuum packaging design, such as the net content or volume of the contents exceeded the scope of the flexible packaging materials used to withstand, in the process of transport or sales circulation, a slight external force, there will be the above broken bags, cracking problems.
(2). Due to the quality of the outer food vacuum packaging materials resulting in the finished packaging sealing and cracking problems are generally concentrated in the following areas.
A ) the physical and mechanical properties of food packaging – such as tensile strength and elongation at break, puncture strength, pendulum impact resistance, peel strength test, can comprehensively judge the toughness of the bag, puncture resistance, impact resistance and other physical and mechanical properties of packaging, storage, stacking and transportation process needs.
(B) the sealing of food packaging – such as bursting pressure test, you can determine the location and mechanical strength of the weak parts of the broken bag. Such as heat sealing strength test can determine whether the strength of the heat seal to meet the requirements of the food content, and to determine the parts of poor heat sealing and heat sealing effect of uniformity. Such as torque force test can determine whether the tightening degree of the cap to meet the requirements of the bottle does not leak. Fourth, high-temperature cooking bag bag breakage problem according to Raoul’s law, the pressure of liquid vaporization in absolute space, determined by the amount of liquefied material substances. At atmospheric pressure, each mole of liquid vaporized completely can give 22.4L space pressure of an atmospheric pressure to GB / T10004-1998 “cooking composite film, bag” as an example, the test requires the bag were loaded 4% HAC, 1% sodium sulfide (Na2S), 5% sodium chloride (NaCI) aqueous solution and refined vegetable oil, and then exhausted and sealed, loaded into the anti-pressure Test in the cooking pot. We tend to think that the temperature has been very precise control, cooling enough to counter pressure, or often found to have burst bag phenomenon, burst bag is certainly because the pressure inside the bag than outside the bag.
(1) first analysis of the boiling bag according to the provisions of the water into the bag, exhaust and seal. Upon closer inspection we found that the air was not exhausted. Its heating process before 100 ℃: time sealed glass ball on behalf of the closed bag, you can see that the expansion of heating water boiling bag is normal. Analysis of the reasons for this: room temperature filled with water seal, when the pressure inside and outside the bag is balanced, in the process of heating to 98 ℃ at room temperature, the liquid water itself to expand, the air in the bag to expand, which produces part of the water vapor also occupies part of the space, resulting in expansion. This is when the pressure inside the bag increases. The burst of the bag is this thermal state of the sealing part of the polymer material to produce creep phenomenon.
(2) boiling bag problem boiling bag in the heating to 100 ℃ before, with the boiling bag changes are the same, in the cooking pot, heating more than 100 ℃, the bag pressure is always higher than the pressure outside the bag.