The compounding in the composite flexible packaging material is actually the meaning of lamination, which is to bond the films or other flexible materials of different properties together and seal them to carry, protect and decorate the contents. The laminate structure of the flexible package can be classified into many forms according to different combinations. However, conventional structures are usually distinguished by an outer layer, an intermediate layer, an inner layer, an adhesive layer, and the like. (i) Outer material

The outer layer material is usually selected from materials with good mechanical strength, heat resistance, good printing performance and good optical properties. At present, the most commonly used requirements for polyester (PET), nylon (NY), stretched polypropylene (BOPP), paper and other materials are as shown in the table below:

The requirements and functions of the outer layer material

The interlayer material is typically used to reinforce certain characteristics of the composite structure, such as barrier properties, opacity, aroma retention, strength, and the like. Currently most commonly used are aluminum foil (AL), aluminized film (VMCPP, VMPET), polyester (PET), nylon (NY), polyvinylidene chloride coated film (KBOPP, KPET, KONY), EVOH and other materials. The requirements and effects of the intermediate layer materials are shown in the table below.

Requirements and functions of the intermediate layer material (3) Inner layer material

The most critical role of the inner layer material is the sealing property. The inner layer structure is in direct contact with the inner material, so it is required to be non-toxic, tasteless, water resistant and oil resistant. Commonly used materials are cast polypropylene (CPP), ethylene-vinyl acetate copolymer (EVA), polyethylene (PE) and modified materials. The requirements and effects of the inner layer materials are shown in the following table:

Requirements and functions of the inner layer material (4) Adhesive layer

The function of the adhesive layer is to form a composite structure by bonding two adjacent materials together. According to the characteristics of the adjacent materials and the composite process, a binder or a binder resin may be used as the adhesive.

Layered material. The bond strength between the bonded laminates is an important indicator for evaluating the intrinsic properties of the composite packaging materials. Different packaging requirements have different requirements for the indicators.