In general, the structure of a multilayer coextruded film depends on the functional requirements of the film. Under the premise of meeting the process requirements, through the combination of different polymers, to meet the packaging material barrier, heat sealing, body strength, hot puncture, environmental resistance, secondary processing characteristics, extended storage and shelf life and other functional requirements. From the functional requirements analysis, the combination formed by the five polymers is sufficient. However, in the market has begun to apply seven, nine, eleven or more layers of co-extruded composite film, making it a trend, and rapid development. The structural design of co-extruded film is gradually required to systematically achieve the ideal state of integrating function, technology, cost, environmental protection, safety and secondary processing.
Barrier
(1) In the barrier layer, the stability of the barrier layer can be improved by using multiple layers of the same polymer instead of a single layer of polymer. For example, if the PA material is a barrier layer, the oxygen barrier rate is 40 units. In order to ensure the stability of its oxygen barrier performance, the setting value of its thickness is usually the theoretical calculation value of the material + the negative error value of the equipment + the safety factor. When we use the same multi-layer polymer instead, the negative error value of the thickness of the device is significantly reduced, and the safety factor is significantly improved.
(2) When we confirm that the set thickness of the barrier layer is sufficient to meet the barrier requirements, we inject multiple layers of the same polymer into the barrier layer instead of a single layer of polymer, which can reduce the cost of high value-added raw materials for the barrier film.
(3) In the barrier layer, the use of two different polymers instead of a single variety of polymers can significantly improve the barrier properties of the film. For example, combining the EVOH layer with a typical PA layer can not only protect the puncture resistance of the PA, but also increase the strength of the EVOH and improve the crack resistance of the EVOH. For a five-layer structure, two different barrier layers are used at the same time, and one of them can only be in the outermost layer. In order to prevent the outer barrier film from being easily damaged by external force and causing the barrier effect to decrease, the method of increasing the thickness of PA is usually used to make up for it, resulting in an increase in cost.
Other
(1) The heat seal layer and the composite layer are divided into two groups, one of which uses cheaper polymers to replace higher-priced polymers to reduce the cost of the film while maintaining the strength of the film. The other group uses functional polymers that meet their functional requirements. More economical composite films are made with the multilayer concept. For example, comparing two 1KB heavy films, the material cost required for a five-layer structure film is about 19% higher than the material cost required for a seven-layer structure film.
(2) the use of more layers of co-extruded film can improve the performance of five layers of PA co-extruded film. For example, the barrier properties of the film can be improved by increasing the water vapor barrier effect of the film by using an additional adhesive layer. At the same time, another advantage is obtained that the film can be made softer, feel good and has good crack resistance.
(3) the use of more layers of co-extruded film can improve the stress warpage resistance of five layers of PA co-extruded film. At the same time, it meets the needs of secondary processing such as bag making.
(4) set dry composite film in addition to printing other functions in one, so that the composite process is simple, the composite structure tends to be flexible, the function tends to be diverse, the cost is significantly reduced, more safe, more in line with health and environmental protection requirements, social and economic benefits are more significant.
With the continuous progress of polymer synthesis technology, new polymers with unique physical and mechanical properties can be widely used to meet the needs of packaging. The function and structure of multi-layer co-extruded composite substrate film will have greater flexibility and economy. Through the application and improvement of molding equipment and technology, and the unique and effective design of composite structure, the film manufacturer will have a revolutionary effect on the pursuit and thinking mode of the concept of diversification of packaging function, rationalization of packaging structure and maximization of packaging efficiency. However, the scientific use of raw materials, the design of reasonable product structure and the close cooperation with the processing technology are the endless challenges in front of each of our composite film manufacturers. Because only when the processing equipment, processing raw materials, structural design (plus process) of the three technical resources are fully utilized, and to achieve the best state, in order to make the packaging substrate in its final product in the most economical, most reasonable, the most adequate, The cheapest form appears and meets the needs of the market.
