Typical Structure of a Composite Packaging Bag: How is the "Sandwich" Layered?
A typical composite packaging bag is typically constructed from three or more layers. Let's take the common "potato chip bag" (aluminum-plastic composite bag) as an example:
1.Outer Layer (Printing Layer/Protective Layer)
Material: Typically BOPP (biaxially oriented polypropylene), BOPET (biaxially oriented polyester), or paper.
Function:
Aesthetics: Provides excellent surface printing properties for displaying brand and product information.
Abrasion Resistance: Protects the packaging from scratches.
Moisture-Proof: Serves as the first line of defense, blocking external moisture.
2.Intermediate Layer (Barrier Layer/Functional Layer)
Material: Typically aluminum foil (AL), aluminized film (VMPET/VMCPP), or high-barrier plastics (such as EVOH, PA).
Function:
High Barrier: This is the core of the composite bag. It effectively blocks oxygen, water vapor, light, and odors, preventing food from oxidation, moisture, spoilage, and flavor transfer.
Light-blocking: Aluminum foil completely blocks light, protecting light-sensitive foods (such as oils and milk powder).
3.Inner Layer (Heat Seal/Contact Layer)
Material: Typically made of CPP (cast polypropylene), PE (polyethylene), etc.
Function:
Heat Sealability: Melts when heated, allowing the packaging bag to be tightly sealed, ensuring a tight seal.
Safety: Direct contact with food must comply with food hygiene standards and be non-toxic and odorless.
Corrosion Resistance: Able to withstand corrosion from package contents (such as oil, acid, and salt).
