Study On TPU Fly-knit Upper Based On Heat Pressing Process

Knitted shoe uppers produced on computerized flat knitting machines can be called Flyknit uppers.They are lightweight,breathable,low production cost and can be seamlessly knitted.High elastic polyester multifilaments are the most used materials for Flyknit uppers to achieve better elasticity,but permanent deformation can occur after long term uses.Normally,polyester or nylon heat melting multifilaments are added into the knitted uppers to improve the stiffness and dimensional stability.However,the rigid fused yarns are brittle and can be fractured subject to external forces,which cannot completely preserve the original dimension of the knitted uppers.In addition,although the loop structure of the knitted uppers results in good softness and air permeability,raindrops can also be easier to penetrate the fabrics,thereby not suitable for wearing in rainy days.The use of waterproof coating or waterproof yarns in knitted upper can improve the waterproofness but cannot completely solve the problem to meet the requirement for wearing in rainy days.Hence,it is necessary to explore new yarn materials to improve the dimensional stability and waterproofness for broadening the application of Flyknit uppers and to increase added value.Thermoplastic polyurethane elastomer(TPU)has good elasticity and extraordinary ability to remodel,which is a good candidate to be used in shoe uppers to enhance the dimensional stability.The knitted fabrics made with hydrophobic TPU monofilament can be heat pressed to flatten the monofilament and reduce the mesh size,thereby increasing the waterproofness.The introduction of TPU monofilament in knitted uppers can diversify the yarn materials.The TPU fabrics are transformable from fabric to film by controlling the heat pressing process to produce the transparent effect and 3D texture for knitted shoe uppers.In this thesis,a TPU knitted fabric was knitted on a computerized flat knitting machine and treated by different heat pressing processes.The structural changes of the treated fabrics and the effects of heat pressing temperature,duration and pressure on the permeable and mechanicalproperties were studied.It was found that the fabric knitted with the transparent TPU monofilament had better transparency.The light transmittance and mechanical properties of the fabrics were significantly enhanced after heat pressing,but the air and moisture permeability was decreased.The changes in permeability of the fabrics after heat pressing were interpreted in terms of fabric thickness,loop change and porosity based on image processing.It is considered that the optimal heat pressing parameters for TPU upper are 165?,6.7 MPa and 2 min.TPU monofilament and colored polyester multifilaments were knitted and heat pressed together to form knitted shoe upper fabrics.The effect of TPU/polyester ratios on the hydrophobicity,comfort,color and mechanical properties of the fabrics were investigated.The results showed that the hydrophobicity of the resultant fabrics was improved,the binding among the loops in the fabric was enhanced,but the breathability and moisture permeability of the fabric were decreased.The addition of transparent TPU monofilament into colored knitted shoe uppers increases the diversity of shoe upper design.Based on the experimental results,a series of TPU knitted shoe uppers were designed and knitted.The advantages of TPU monofilament were fully imparted to knitted shoe uppers to improve the waterproofness,unravelling of loops,visional designability.