The composite 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 then seal, 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.
(1) Outer materials
The outer layer material usually uses 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 following table:
The requirements and functions of the outer layer material
The interlayer material is generally used to enhance certain characteristics of the composite structure, such as barrier properties, light blocking properties, aroma retention, strength, and the like. At present, the most commonly used materials are aluminum foil (AL), aluminized film (VMCPP, VMPET), polyester (PET), nylon (NY), polyvinylidene chloride coated film (KBOPP, KPET, KONY), EVOH and the like. The requirements and effects of the intermediate layer materials are shown in the table below.
The requirements and functions of the intermediate layer materials
(3) Inner layer materials
The most critical role of the inner layer material is the sealing property. The inner layer structure directly contacts 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 thereof. The requirements and effects of the inner layer materials are shown in the following table:
Requirements and effects of inner materials
(4) Adhesive layer
The function of the adhesive layer is to form a composite structure by bonding two adjacent layers of materials together. According to the characteristics of the adjacent materials and the composite process, an adhesive or a binder resin may be used as the adhesive layer 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.