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What’s the Associated Phenomena and Key Considerations of ‘Glue Does Not Dry’ After Pouch Making Process

In a considerable number of flexible packaging material processing enterprises, the ‘Glue does not dry’ phenomenon and curing state of the adhesive layer in laminated products is not considered a routine inspection item. In some companies, even the peel strength index of composite materials is not regularly inspected. Therefore, the occurrence of “glue not drying” is often discovered by customers or downstream clients when encountering other defects in composite products. They intentionally inspect the curing state of the adhesive layer and attribute the “glue does not dry” phenomenon they find to be the “culprit” responsible for other defects in the composite products. Consequently, they attribute the cause of “glue does not drying” to the “quality issue” of the adhesive used.

Furthermore, through sample analysis, it has been found that even in the presence of the obvious “glue does not dry” phenomenon in the surface layer of some visually intact PET/VMPET/CPE structure zipper bags, there is a secondary stickiness of hand peel not less than 1N/15mm between PET and VMPET layers. This indicates that for this type of composite film structure, even if there is apparent “glue not drying” between the surface layers, well-appearing zipper bags can still be produced with suitable bag-making process conditions.


Table content:

1. Conclusion

2. Some appearance defects associated with the phenomenon of “glue does not dry”

3. Suggestion


1. Some conclusions:

(1) The phenomenon of “glue does not dry” is a manifestation of the adhesive not reaching complete curing. Therefore, it does not necessarily indicate a “quality issue” with the adhesive used.

(2) In some specific products, such as laminated products containing aluminum-coated film, industry professionals intentionally create a certain degree of “glue does not dry” in the adhesive layer by reducing the -NCO component dosage.

(3) The existence of “glue not drying” does not necessarily mean that the interlayer peel strength value is below the required value. There is no proportional relationship between the “secondary stickiness” value of laminate products with “glue does not dry” and their peel strength value.

 

In a two-layer laminated film, some parts of the adhesive layer may have completely cured, while other parts may exhibit “glue does not dry.” In a multi-layer laminated film, the presence of “glue does not dry” can be even more complex. The reasons for this can be found in the “What is and How to Optimize 'Glue Does Not Dry' in Laminated Flexible Packaging: Key Factors and Comprehensive Solutions.


2. After bag manufacturing/pouch making, other appearance defects associated with the phenomenon of “glue does not dry” include:

(1) Surface wrinkling at the sealing area

(2) Surface wrinkling on the bag body

(3) Surface wrinkling caused by hanging holes or tear openings

(4) Surface wrinkling at the end of zipper bags

(5) Surface wrinkling at the zipper area of zipper bags

(6) Local delamination at the sealing area of heat-sealed products


For the classification and causes of the “glue does not dry” phenomenon, please refer to “What to Do When Facing 'Glue Does Not Dry' in Laminated Products? Step-by-Step Analysis for Adhesive Application


3. Suggestion:

However, it needs to be emphasized that the “glue not drying” phenomenon is not the direct cause of the aforementioned appearance defects. Although some customers may report that they have encountered the mentioned appearance defects during bag manufacturing, but after re-aging the unutilized composite film that has shown these defects, the subsequently processed bag products no longer exhibit the same defects.

In such cases, it is recommended to focus on the changes in the secondary stickiness value after re-aging, the variations in bag-making process conditions, the geometric dimensions of the finished composite film bags, and the relationship between the “exposured aluminum” phenomenon at the edge of the sealing and various appearance defects.

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