With the continuous improvement of film final properties and the development of co-extrusion technology, multi-layer structure films have become a common design. The use of different materials in each layer can achieve the integration of various characteristics, thus providing a variety of functions on a thin film at the same time. However, materials with different characteristics often do not have good affinity. As a result, we need a material to combine them. This kind of adhesive material can be resin, which uses multi-layer co-extrusion technology to bond different materials at the same time when the film is produced, or uses the composite process of spraying film to bond two kinds of films. Here we first focus on the extrudable adhesive resin.
Adhesive resin in general sense
Any resin that acts as a bonding agent can be called a bonding resin. When PP and PE are co-extruded, adhesive resin is needed to ensure interlaminar peeling force. When aluminium foil and paper film are combined, they also need to be bonded with adhesive resin. Many adhesive resins are amphiphilic. It has a certain affinity with the materials that need to be bonded, thus realizing the bonding of the two materials. But in many cases, the affinity of the adhesive resin to one material is higher (or lower) than that of the other. Therefore, the resin bonded material suppliers should pay attention to this problem when choosing adhesive resin.
Adhesive resin in narrow sense
In the field of film, the narrow sense of adhesive resin mainly refers to the adhesive resin used in EVOH or PA co-extrusion structure. Generally speaking, the adhesive resin used in EVOH and PA co-extrusion membranes is MAH-g-PE which has the grafting modification of maleic anhydride. Maleic anhydride modified PP is relatively small and expensive. The main reason is that in the process of grafting, polypropylene is prone to chain breakage, resulting in a rapid increase in finger fusion. Therefore, it is difficult to produce maleic anhydride grafted polypropylene.