Structural Design of Multilayer Co extruded Films

The structures of multi-layer co extruded films can be divided into two categories, namely symmetric structures (A/B/A) and asymmetric structures (A/B/C). At present, the barrier film in China is mainly composed of 5, 7, 8, and 9 layers (some foreign companies achieve 10 and 11 layers). Taking a 5-layer co extruded film as an example, introduce the relevant structures.

The symmetrical structural layer of a multi-layer co extruded barrier membrane consists of three types of functional layers: barrier layer, adhesive layer, and support layer.

Barrier layer: The barrier layer has functions such as oxygen resistance, moisture resistance, and oil leakage prevention. By controlling the material and thickness of the barrier layer, the barrier performance of the film material is adjusted to meet different packaging needs (commonly used barrier materials in the market include PA, EVOH, PVDC, etc.). Various barrier materials can be applied separately to form high and medium barrier series packaging films, while the sandwich structure formed by the combination of PA and EVOH has high barrier performance.

Support layer: Generally, symmetrical structural materials have two support layers, the inner layer is used for heat sealing, called heat sealing layer, and the outer layer is directly used as the outer layer of packaging film or for printing as a printing layer. The support layer requires good mechanical strength, heat sealing performance, water vapor resistance, transparency, and printability. The commonly used materials for this layer are LDPE or LDPE/LLDPE blend materials.

Adhesive layer: The function of the adhesive layer is to bond the barrier layer and the support layer to ensure interlayer peeling force. The selection of adhesive layer material and thickness is generally determined based on the material of the support layer and barrier layer, as well as the required adhesive strength to be achieved.

At present, there are 7, 8, and 9 layers of barrier films commonly used in China. PE/PP represents the support layer material and PA represents the barrier layer material, and a multi-layer co extruded film structure is explained.

Symmetrical structure barrier film

PE/Tie/PA/Tie/PE multilayer co extruded film equipment with five or more layers

PE/Tie/EVOH/Tie/PE multilayer co extruded film equipment with five or more layers

PE/Tie/PA/EVOH/PA/Tie/PE seven layer and above multi-layer co extruded film equipment

Asymmetric structural barrier film

PA/Tie/PE/Tie/PA/Tie/PE multi-layer co extruded film equipment with seven or more layers

PA/Tie/PP/Tie/PA/Tie/PP multi-layer co extruded film equipment with seven or more layers

PA/Tie/PE/Tie/PA/EVOH/PA/Tie/PE Nine layer and above multi-layer co extruded film equipment

PA/Tie/PP/Tie/PA/EVOH/PA/Tie/PP nine-layer and above multi-layer co extruded film equipment

From the above structure, it can be seen that co extruded film structures with nine or more layers have great flexibility. However, as the number of layers increases, the difficulty of processing increases. Therefore, in China, multi layered co extruded films are generally controlled at 5-9 layers.