Abstract: The damage of flexible packaging bags is the main problem affecting the actual packaging quality. How to solve this problem has been plagued by manufacturers. This paper will introduce the reasons for breaking bags and the process improvement methods.
Keywords: heat sealing performance, thermal adhesion, filling, storage, broken bag
The breakage of flexible bags is one of the main problems affecting the quality of product packaging. Usually soft bags are most likely to break in the following two situations: firstly, during the filling process of the product, the contents of the filling will have a strong impact on the bottom of the bag, and if the bottom of the bag cannot withstand the impact force, it will appear. Cracking at the bottom not only affects the cleaning of the production environment, but also affects the filling efficiency. Secondly, when the product is stacked, if the flexible bag can not withstand the increase of internal pressure caused by the pile pressure of the product, etc., the bag may be broken, resulting in the bag rupture. The contents are ineffective and even pollute the surrounding items. How to solve the problem of broken bags has always plagued manufacturers. It is generally believed that the heat-sealing strength of packaging materials is closely related to broken bags, but in fact this view is not completely correct. This article will introduce the reasons for bag breaking and process improvement methods.
1. Broken bag in the filling process
1.1 Reason
With the increasing use of Form-Fill-Seal Machines in food, pharmaceuticals, cosmetics, and other fields, the time interval between packaging manufacturing and content filling has been radically changed. And space distance. In the new filling line, the production of the flexible packaging bag is almost synchronized with the filling of the contents, so that the heat-sealed portion of the bottom of the bag is not completely cooled during the filling of the contents, and the impact force can be greatly reduced. .
The so-called heat seal strength refers to the bond strength of the two films bonded together by heat sealing to complete cooling, but the material does not have sufficient cooling time on the production line, so the heat seal strength of the packaging material is not Appropriate for the evaluation of the heat sealing performance of the material, the hot adhesive force - the peeling force when the heat sealed portion of the material has not been cooled - is selected according to this.
1.2 Detection and application of hot adhesive force
The relationship between the thermal viscosity of the film shown in Figure 1 and the heat sealing temperature and heat sealing time has a certain universality. To achieve the optimum thermal viscosity of the film material, there is a most suitable temperature point, and when the heat sealing temperature exceeds this temperature After the point, the hot tack will show a downward trend. At the same time, from the data analysis, at the same heat-sealing temperature, prolonging the heat-sealing time will increase the heat-adhesive force. For example, the film shown in the figure shows the heat-resistance of the sample at the same heat-sealing temperature when the heat-sealing time is 0.3 s. Significantly lower than when the heat seal time is 0.5 s.
Figure 1. Example of the relationship between film thermal adhesion and heat seal temperature and heat seal time
In actual use, the impact force on the bottom of the flexible packaging bag should be calculated according to the contents of the filling, and then the thermal adhesive force tester can be used to adjust the heat sealing temperature, the heat sealing pressure and the heat sealing time to draw the thermal viscosity curve. And based on the calculation of the data, combined with the actual situation of the production line, select the best combination of heat sealing parameters for the production line.
2, the bag breaking situation in the storage process
2.1 Reason
In addition to vacuum packaging, articles packed in flexible packaging bags may cause an increase in gas pressure in the bag during storage and transportation due to the lifting of the articles, which may cause the flexible packaging bag to rupture. Since the location where the crack occurs is concentrated in the heat sealing position between the materials, that is, the heat seal of the flexible package bag, the broken bag can be avoided by detecting the heat seal strength of the heat seal of the package, replacing the material, or adjusting the heat seal process parameters.
The heat seal strength of the material can be roughly classified into tensile heat seal strength and expansion heat seal strength according to the detection method. Generally, we use the tensile machine to detect the tensile heat seal strength, which is the ability of the packaging material to resist separation when the force direction is uniform and the force value is uniform. It is especially suitable for evaluating the opening of the flexible packaging bag, but it is not applicable. In order to solve the problem of broken bags in soft bags, the direction and size of the pressure inside the bags causing the bags are uncertain, and the materials near the heat seal may be deformed due to partial pressure, but the pressure of the soft bags is damaged. It can be solved by detecting the expansion heat seal strength of the material.
2.2 Detection and application of expansion heat seal strength
The detection of the expansion heat seal strength requires the use of a leak and seal strength tester, which requires pressurization into the flexible package and the detection of the worst strength of the package (not limited to the heat seal). Since the expansion heat seal strength does not represent the average strength of the heat seal, there is no correlation between the expansion heat seal strength and the tensile heat seal strength. The strength of the expansion heat seal is related to the size, geometry, and materials used in the flexible package, but if the material is particularly soft (for example, some flexible packaging materials can be stretched to several times the original length), it will become apparent as the test pressure increases. The deformation also requires the restraining effect of the pressure expansion of the flexible packaging bag and the stretching deformation of the material by means of the restraining plate test device.
The leak and seal strength tester can not only detect the maximum breaking force of the flexible bag, but also test the bursting time of the bag by setting the applied pressure. The operator can design the stacking structure according to the test data, and can further adjust the heat sealing process. The parameters are used to improve the packaging effect, or to analyze the problems in the packaging structure according to the position of the flexible packaging bag.
3 matters needing attention
Adjusting the heat-sealing parameters in the production process by detecting the heat-sealing properties of the material can reduce the probability of breakage of the flexible packaging bag during filling, storage, and transportation, but pay special attention to the following problems.
First of all, special attention should be paid to whether the filler will contaminate the seal during the filling process. The contaminant can cause the thermal adhesive strength or heat seal strength of the material to be significantly reduced, resulting in the soft packaging bag being broken due to the inability to bear the force. Particular attention should be paid to powder-based fillings, which require a corresponding simulation test.
Secondly, the thermal viscosity and expansion heat seal strength of the material obtained through the selected heat sealing parameters of the production line should be left on the basis of the design requirements (should be analyzed according to the equipment and materials), because The heat sealing component or the packaging material (especially the film material for flexible packaging) is not very uniform, and the cumulative error may result in uneven heat sealing effect at the heat seal of the package.
Thirdly, through the detection of the thermal cohesive force of the material and the expansion heat-sealing strength, a set of heat-sealing parameters suitable for a specific product and a specific production line can be obtained separately. At this time, comprehensive consideration should be given to the heat-sealing curve of the material obtained by the test. Choose the best choice.
4 Summary
The optimization of the heat sealing process in the packaging process has been widely recognized as an effective way to shorten the packaging cycle time. However, the selection of the heat sealing parameters directly affects the bag breaking rate of the flexible packaging bag, and the filling production line is Filling efficiency and product loss during storage and transportation. Therefore, the heat sealing parameters can not be set only by experience, and must be carried out in a targeted test, and based on the analysis of the test data, and appropriate adjustments should be made to the specific conditions of the contents and packaging materials to ensure that nothing is lost.