The moisture-proof and anti-oxidation functions of OPP self-adhesive bags are the result of the combined effects of the material's own characteristics, structural design, and production process. Its core goal is to prevent moisture and oxygen from contacting the items in the bag through physical barriers and chemical protection, thereby extending the shelf life of the contents.
Polypropylene, the main raw material of OPP self-adhesive bags, has a certain barrier capacity. The molecular structure of polypropylene is stable, and there are no polar groups that easily absorb moisture and oxygen, so it has a natural repulsion to water vapor and oxygen. In addition, during the production process, OPP film will undergo biaxial stretching treatment. This process makes the molecular arrangement of the film more compact and orderly, further reducing the gaps between molecules, making it more difficult for moisture and oxygen to penetrate, laying the foundation for moisture and oxidation prevention from the source.
In addition to the advantages of the material itself, OPP self-adhesive bags also enhance their protective performance through a multi-layer composite structure. The barrier effect of a simple OPP film is limited, and OPP is often compounded with other materials in actual production. For example, a layer of polyethylene (PE) is attached to the outer layer of OPP. PE has good flexibility and heat sealing properties, which can form a tight sealing layer when the bag is sealed; or an aluminum foil layer is added. Aluminum foil is a natural high barrier material that can almost completely isolate oxygen and moisture. These different materials are combined through adhesives or co-extrusion processes, each of which plays its own advantages to form a solid protective barrier.
Process control in the production process is crucial to the moisture and oxidation resistance of OPP self-adhesive bags. The heat sealing process is a key step. By precisely adjusting the temperature, pressure and time, the OPP film and the inner layer material are fully melted and bonded to form a seamless sealing edge. If the heat sealing temperature is not enough or the pressure is uneven, a virtual seal will occur, causing the bag to leak. In addition, the surface of the OPP film needs to be corona treated to increase the surface roughness and activity, so that the printing ink and adhesive can adhere better and prevent the coating from falling off to form a breathable channel.
The adhesive strip of the self-adhesive bag is also an important part of achieving sealing. Commonly used acrylic pressure-sensitive adhesives have good weather resistance, can still maintain stickiness in humid environments, and are highly compatible with OPP films, and are not easily debonded due to temperature changes. During production, the adhesive strips use a high-precision coating process to ensure uniform thickness of the adhesive layer and avoid poor sealing due to insufficient local adhesive. After pasting, the adhesive strips can form a continuous sealing line at the bag opening, and cooperate with heat-sealed edges to further reduce the entry of gas and water vapor.
In order to improve the protection effect, functional additives are also added to the OPP raw materials during the production process. For example, hydrophobic nanofillers are added. The special structure of these fillers can extend the diffusion path of water vapor in the film, greatly improving the moisture-proof ability; adding antioxidants can capture free radicals that may be generated in the bag, delay the oxidative degradation of the OPP material itself, and avoid gaps in the material after aging, which affects the barrier performance.
The actual protection effect of the OPP self-adhesive bag is also related to the use and storage method. Unopened bags should be stored in a dry and ventilated environment, avoiding high temperatures and direct sunlight to prevent film aging and loss of adhesiveness of the adhesive strips. When in use, the filled items must be dry and no liquid can remain, otherwise the internal moisture will evaporate and form condensation water in the bag. And the bag must be used up as soon as possible after opening, and the remaining must be sealed to prevent the adhesive strip from absorbing dust and water vapor and becoming ineffective. Only by strictly controlling every link can the OPP self-adhesive bag fully exert its moisture-proof and anti-oxidation functions and protect the items in the bag.
