Keywords: composite film; formulation; SEBS; POE SEBS/POE composite films are mainly produced by co-extrusion technology. With excellent weather resistance, high resilience, outstanding low-temperature toughness, and good compatibility with polyolefin substrates, they are widely used as a bonding layer for multi material composites, including plastics, metals, leather and textiles. They are suitable for key applications such as packaging sealing, construction waterproofing and automotive interiors. To meet the core requirements of high adhesion and high rigidity in these applications, the formulation needs to be optimized from two aspects. I. Precise Selection of Base Materials 1.SEBS Selection Criteria: General-purpose POE typically features high melt flow rate and low viscosity. It must be blended with low-MFI, high-viscosity, star-branched SEBS. Star-branched SEBS has high molecular chain entanglement density and excellent melt strength. It balances processing fluidity and bubble stability during co-extrusion, preventing bubble rupture or melt delamination. Meanwhile, it enhances interfacial molecular entanglement with POE to meet high bonding requirements. Its high-viscosity nature improves film rigidity, satisfying structural stability demands in applications such as automotive interiors and building waterproofing. 2.POE Compatibility Principles: Prioritize medium to high MFI POE. When paired with low MFI SEBS, the MFI difference should be controlled within 5 g/10min (test condition: 200℃/5kg) to avoid uneven co extrusion caused by excessive flow variation. The POE content should be controlled at 50%–70%. An excessively high ratio will reduce the adhesive film’s bonding strength and rigidity, while an excessively low ratio will compromise low temperature toughness and processability. The recommended blending ratio of SEBS to POE is 3:7 to 5:5. II. Formula Optimization Tips 1.Bonding Enhancement for Polar Substrates When bonding polar substrates such as ABS, PVC, and metals, add 1%–2% high-grafting-ratio MAH-g-SEBS to the formulation. The main molecular chain of MAH-g-SEBS is compatible with the SEBS/POE system due to the same polymeric structure.Its maleic anhydride groups can react with functional groups on the surface of polar substrates — such as nitrile groups in ABS and hydroxyl groups on metal surfaces — to form stable chemical bonds. This can improve adhesion strength by 30%–50% and prevent delamination after lamination with polar substrates. 2.Precise Addition of Additives: Add 0.2%–0.3% antioxidant (blend of 1010 and 168 at a ratio of 1:1) to prevent thermal-oxidative aging during processing and ensure long-term weather resistance of the adhesive film. For packaging and sealing applications, add 0.1%–0.2% slip agent (e.g., oleamide) to improve surface smoothness for easier subsequent processing and usage. If higher rigidity is required, a small amount of 3%–5% C5 petroleum resin can be added to increase stiffness without compromising adhesion performance. 3.Oil Extension Ratio Control The oil addition amount for SEBS shall be ≤ 150 phr.Excessive oil will cause white oil precipitation, leading to film surface blocking, reduced heat-sealability, and poor slitting and application performance. Before oil extension, SEBS and white oil must be blended at high speed to ensure uniform dispersion of the oil phase.