Control difficulties in mask bag sealing

The vast majority of face mask bags are packaging bags containing aluminum foil or aluminum-plated materials. The basic physical characteristics and inherent needs of face mask bags are:

Beyond excellent performance, the most intuitive aspect of aluminum foil packaging bags is the reflection of quality and the guarantee of the mask's shelf life. Most face masks have a shelf life exceeding 12 months, some even 36 months. For such a long shelf life, the most basic requirements for packaging are sealing and high barrier properties. Given the consumption characteristics of face masks and their shelf-life requirements, the material structure and requirements of the face mask packaging bag are essentially determined. Currently, most face masks use structures such as PET/AL/PE, PET/AL/PET/PE, PET/VMPET/PE, BOPP/VMPET/PE, BOPP/AL/PE, MAT-OPP/VMPET/PE, MAT-OPP/AL/PE, etc.

So what are the common problems encountered when sealing face mask bags? Let's have a brief discussion by Shunxingyuan Packaging, a professional flexible packaging manufacturer.

1. Wrinkles on the Seal

Taking PET/AL/PE as an example, the PE in general face mask bags is usually made of face mask-specific PE material, and its general characteristic is low-temperature heat sealing performance. During operation, high-temperature wrinkles often occur at high temperatures, and false sealing is prone to occur at low temperatures. Therefore, our production management personnel and machine operators must clearly understand that the temperature of each heat sealing knife is different at a certain speed point in production, and clear data records are needed. Of course, some processing can also be done on the face mask PE raw materials, which is to mark a suitable temperature control range for the PE film to better control the temperature range of the seal (Note: The thickness uniformity of PE is higher than the general structural requirements, that is, there cannot be too large a deviation in thickness). In terms of mechanical equipment, if the cooling temperature of the cooling knife is insufficient, wrinkles on the seal will also occur, which means that the cooling temperature of the aluminum foil structure has not been adjusted in the cooling knife section. In the heat sealing knife section, if the pressure adjustment is unbalanced, wrinkles will also appear on the seal. Compared with MAT-OPP as the fabric structure, the wrinkling phenomenon on the seal with PET as the fabric structure is relatively less.

2. False Sealing

Again, taking PET/AL/PE as an example, we all know that for aluminum foil structured materials, whether it is ester-soluble dry lamination or solvent-free lamination, there will always be a width of about 5mm that is not completely laminated at both ends of the semi-finished product. When there is this unlaminated edge, problems are easily generated. Because the laminating machine cannot achieve an absolutely parallel and flat surface when laminating multiple layers of materials, during the bag-making process, when passing through various guide rollers, there is a possibility of the aluminum foil being scratched or scraped off. The scratched aluminum foil debris is easily rolled into the space between the PE and PE layers (i.e., the inside of the bag), so it is rolled in with the material and forms a false seal in the seal. In addition, in double-web bagging or single-web bagging, on the transverse seal, sometimes the temperature on one side is too high and the temperature on the other side is insufficient. In this case, it is mostly due to the unbalanced pressure of the heat sealing knife or the heat sealing knife screws not being tightened. Of course, it may also be due to the uneven thickness of the raw material PE, which will also cause false sealing on the heat seal. Therefore, for face mask-specific PE, the uniformity of thickness requirements is higher than that of ordinary PE.

3. Bubbles on the Seal

Generally speaking, bubbles on the seal of aluminum foil bags are caused by the temperature of the heat sealing knife being too high. However, on the other hand, it may also be caused by the unbalanced or excessive pressure of the heat sealing knife.

4. Uneven Seal

Taking PET/AL/PE as an example, the first reason is the same as the first aspect of point (2), the aluminum foil may be scratched, and then it moves along with the laminated film, easily staying on the edge of the sealing knife, forming a hard object, causing pits and indentations; the second aspect is that PE particles adhere to the cooling knife, causing pits on the seal.

Therefore, when officially starting the machine, the sealing knife, guide rollers, and other positions need to be cleaned to avoid the formation of the above-mentioned defects. Another reason is defects in the sealing knife, which easily lead to this phenomenon. On the other hand, if the silicone rubber on the auxiliary plate is pressed for too long, when a certain production capacity is reached, softening or grooves appear, this defect is easily produced; at the same time, this reason will also lead to bubbles or false sealing on the seal, so after reaching a certain amount of production capacity, the silicone rubber must be replaced.