Thermoplastic Polyurethane (TPU) integrates the high elasticity of rubber and the processability of plastic, and is widely applied in shoe materials, automotive shock absorbers, electronic protective covers and other fields. The molding quality of TPU elastic products directly determines their mechanical properties and service life, with the core lying in achieving a balance between material melting plasticization and molding setting through precise control of process parameters to avoid hydrolysis, degradation and other issues. Currently, the industry is moving towards green environmental protection, automated control and lightweight molding, and new technologies such as supercritical foaming and 3D printing are gradually expanding application scenarios, injecting new vitality into the production of TPU elastic products.
Suitable for complex-structured elastic products such as sports shoe midsoles and automotive shock absorbers. The core of the process is to achieve uniform filling and precise setting of the melt, with key steps including raw material pretreatment, temperature control, pressure regulation and post-treatment.Raw materials need drying: polyether-type TPU is dried at 80-100℃, polyester-type TPU at 100-120℃ due to easy hydrolysis, with moisture content below 0.05% to avoid bubbles in finished products.The barrel adopts gradient heating: feeding section 140-170℃, compression section 170-190℃, homogenization section 180-200℃, and head temperature 190-210℃; injection pressure is 80-120MPa, holding pressure 50-80MPa to prevent material shortage and shrinkage.After molding, annealing at 60-80℃ for 2-4 hours to eliminate internal stress and stabilize elastic performance.
Used for the production of continuous elastic products such as pipes, films and conveyor belts. Single-screw extruders with a length-diameter ratio of 20-30:1 and compression ratio of 1.5-3:1 are selected, equipped with barrier-type screw ribs to enhance plasticization effect.The focus of the process is to control the stability of melt flow, with temperature settings similar to injection molding. The traction speed must be accurately matched with the extrusion speed, with an error of no more than 5% to avoid reduced elasticity caused by excessive stretching of products.Cooling systems are adjusted according to product types: pipes use vacuum sizing sleeves plus spray cooling with water temperature 20-40℃; films use cooling rolls plus air cooling with cooling roll temperature 50-80℃ to reduce internal stress.Screws and molds should be cleaned regularly during production to avoid product quality issues caused by material accumulation and degradation.
Mainly adopting supercritical fluid foaming technology, it is suitable for lightweight and high-resilience products such as shoe midsoles and buffer protectors. The process is divided into two steps: bead preparation and compression molding.Supercritical CO₂ or N₂ is injected into the TPU melt to form uniform microbubbles with a size of 50-100μm and expansion ratio of 5-10 times; then steam compression molding is carried out to control molding temperature and pressure for complete fusion of beads.The finished products have a density of 0.18-0.30g/cm³, rebound rate of 50-60%, and compression set of less than 30%, meeting high elasticity requirements. This process does not require chemical foaming agents, conforms to the trend of green production, and has become the mainstream molding method for high-end elastic shoe materials.
1 Raw Material Control: Ensure the purity of TPU raw materials, avoid impurities, install magnetic separation devices and 80-120 mesh filters at the hopper to prevent mold orifice blockage and product scratches.
2 Process Monitoring: Real-time monitoring of melt pressure and temperature, with pressure fluctuation controlled within 5-15MPa and temperature fluctuation within ±2℃ to ensure molding stability.
3 Defect Handling: For surface bubble defects, strengthen raw material drying or reduce head temperature; for cracking problems, reduce cooling speed or extend annealing time; for dimensional instability, adjust rotation speed and traction speed synchronously.
1 Green Process Upgrading: Promote low-carbon raw material synthesis routes such as maleic anhydride method and PBTL method to replace traditional high-emission processes and reduce the environmental impact of production processes.
2 Intelligent Production: Introduce automated control systems and digital twin technology to realize real-time optimization of process parameters and visualization of production processes, improving product batch stability.
3 Application of Emerging Technologies: 3D printing technology is used for customized production of personalized elastic products, with special TPU wires developed to regulate rebound direction and strength through path design; composite molding technology realizes the combination of TPU with PC, ABS and other materials to expand the functional boundaries of products.
