Color paste, as the main auxiliary agent used in polyurethane foaming, is widely used in various polyurethane materials. Our factory, as a professional polyurethane color paste manufacturer in East China, produces color pastes with high color density, good fluidity, large additions without affecting foaming, bright colors, and strong weather resistance.......
In other thermoplastic materials, when the processing temperature is greater than the melting temperature of the raw material, the melt is mainly viscous. The higher the processing temperature, the better the fluidity of the melt; when the processing temperature is low: the fluidity of the melt is poor, Even if it does not flow, the melt exhibits less elasticity. For elastomers such as TPU, when the processing temperature is higher than a certain temperature, the virtual crosslinks between the molecules are completely released, the melt fluidity is better, and the melt shows more viscous flow. When the processing temperature is lower than a certain temperature, the virtual cross-linking between the molecules is partially released, and the melt exhibits both fluidity and elasticity. It is a viscoelastic body. When the temperature of the melt is high during injection molding, TPU, like other thermoplastic materials, mainly exhibits viscous flow, and the product can obtain a better shape, dimensional stability, and small deformation. When the temperature of the melt is low, the TPU exhibits viscoelasticity. Due to the poor fluidity, the product does not naturally fill the mold cavity, but has a certain elastic expansion to fill the mold cavity. When the injection pressure is removed, the external force that causes elastic expansion When it disappears, the swollen part returns to deformation, so the shrinkage rate is large and the size is small, and the deformation is large. Therefore, TPU injection processing molding process adjustment needs attention: 1. The control of processing temperature has a crucial influence on the final size, shape and deformation of the product. The processing temperature depends on the TPU brand and the specific conditions of the mold design. The general trend is that in order to obtain a small shrinkage rate, the processing temperature needs to be increased. 2. Slow speed and long time holding pressure will lead to molecular orientation. Although it may be possible to obtain a smaller product size, the product deformation is larger and the difference between lateral and longitudinal shrinkage is large. Large holding pressure will also cause the gel to over-compress in the mold, when the product is demolded, the size is larger than the size of the cavity. 3. The position of the injection speed and pressure conversion should be set accurately. Inaccurate position setting will increase the difficulty of cause analysis and is not conducive to rapid and accurate process adjustment. 4. The choice of injection molding machine model should be appropriate. For small-sized injection products, it is necessary to select injection machines with small models as much as possible in order to increase the injection stroke and facilitate the position control to reasonably convert the injection speed and pressure. If the size of the mobile phone accessories is relatively small, if the injection molding machine is relatively large, sometimes the screw is only 1mm forward and the product is full of glue, and the position control cannot be performed at all. 5. When the moisture content of the TPU exceeds 0.2%, not only the appearance of the product is affected but the mechanical properties are obviously deteriorated, and the injected product has poor elasticity and low strength. Therefore, it should be dried at 80℃/110℃ for 2/3 hours before injection molding. 6. The barrel of the injection molding machine should be cleaned, and the mixing of very few other materials will reduce the mechanical strength of the product. The cylinder cleaned with ABS, PMMA, PE is best to be cleaned again with TPU nozzle before injection, and the residual material in the cylinder is removed with TPU nozzle. When cleaning the hopper, pay special attention to the cleaning of a small amount of raw materials with other properties remaining in the connection between the hopper and the base of the injection molding machine. This part is the place that most technical workers easily overlook.
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