High composite packaging bag breakage rate: 7 major reasons finally found!

Composite packaging bags break, it turns out that it is caused by these 7 major sources. Shunxingyuan Packaging, a professional flexible packaging manufacturer, summarizes 7 reasons to help enterprises that use composite packaging bags in clothing, apparel, cosmetics, hardware electronics, food, etc., better choose packaging products.

Hardware composite packaging bag

Cosmetic composite packaging bag

Clothing composite packaging bag

Food composite packaging bag

1. Heat sealing temperature has the most direct impact on heat sealing strength

The melting temperature of various materials directly determines the minimum heat sealing temperature of the composite bag. In the production process, due to the heat sealing pressure, bag making speed, and the thickness of the composite substrate, the actual heat sealing temperature used is often higher than the melting temperature of the heat sealing material. The smaller the heat sealing pressure, the higher the required heat sealing temperature; the faster the machine speed, and the thicker the surface material of the composite film, the higher the required heat sealing temperature. If the heat sealing temperature is lower than the softening point of the heat sealing material, it is impossible to make the heat sealing layer truly sealed no matter how much pressure is increased or the heat sealing time is prolonged. However, if the heat sealing temperature is too high, it is easy to damage the heat sealing material at the weld, causing extrusion and "root cutting", which greatly reduces the heat sealing strength and impact resistance of the bag.

2. The type, thickness, and quality of the heat sealing layer material have a decisive impact on the heat sealing strength

Commonly used heat sealing materials for composite packaging include CPE, CPP, EVA, hot melt adhesive, and other ion-type resin co-extruded or co-blended modified films. The thickness of the heat sealing layer material is generally between 20 and 80 μm, and in special cases, it can also reach 100 to 200 μm. For the same heat sealing material, its heat sealing strength increases with the increase of the heat sealing thickness. The heat sealing strength of retort pouches generally requires 40 to 50 Newtons, so the thickness of its heat sealing material should be above 60 to 80 μm.

3. A certain amount of pressure is essential to achieve ideal heat sealing strength

For thin packaging bags, the heat sealing pressure must reach at least 2 kg/cm2, and it increases accordingly with the increase of the total thickness of the composite film. If the heat sealing pressure is insufficient, it is difficult for the two layers of film to achieve true fusion, resulting in poor local heat sealing, or it is difficult to remove the air bubbles trapped in the weld, resulting in false welding; of course, the heat sealing pressure is not the greater the better, it should not damage the weld, because at a higher heat sealing temperature, the heat sealing material at the weld is in a semi-molten state, and too much pressure will easily squeeze away part of the heat sealing material, causing the weld edge to form a semi-cut-off state, the weld becomes brittle, and the heat sealing strength is reduced.

4. If the weld after heat sealing is not cooled well, it will not only affect the appearance flatness of the weld, but also affect the heat sealing strength to a certain extent

The cooling process is to shape the weld that has just been melted and heat-sealed under a certain pressure and at a lower temperature to eliminate stress concentration. Therefore, insufficient pressure, poor cooling water circulation, insufficient circulation volume, too high water temperature, or untimely cooling will all cause poor cooling, heat sealing edge warping, and reduced heat sealing strength.

5. Heat sealing time is mainly determined by the speed of the bag making machine

Heat sealing time is also a key factor affecting the sealing strength and appearance of the weld. With the same heat sealing temperature and pressure, the longer the heat sealing time, the more fully the heat sealing layer is fused, and the more firmly it is bonded, but if the heat sealing time is too long, it is easy to cause wrinkles in the weld, affecting the appearance.

6. The more heat sealing times, the higher the heat sealing strength

The number of longitudinal heat sealing times depends on the ratio of the effective length of the longitudinal welding rod to the bag length; the number of transverse heat sealing times is determined by the number of sets of the transverse heat sealing device of the machine. Good heat sealing requires at least two heat sealing times. General bag making machines have 2 sets of hot knives, and the higher the degree of overlap of the hot knife positions, the better the heat sealing effect.

7. For composite films with the same structure and thickness, the higher the interlayer peel strength of the composite layer, the greater the heat sealing strength

For products with low composite peel strength, the weld failure is often caused by the interlayer peeling of the composite film at the weld, causing the inner heat sealing layer to independently bear the destructive tensile force, and the surface material loses its reinforcing effect, thus greatly reducing the heat sealing strength of the weld. If the composite peel strength is large, interlayer peeling will not occur at the weld, and the actual heat sealing strength measured will be much greater.

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