plastic injection for Pet product
In the process of filling the mold cavity of TPE products, if the filling performance of the product is not good, the pressure drop will be too large, the filling time will be long, and the filling will be unsatisfactory, which will cause the product to have quality problems. Let me share with you some things that need to be paid attention to in the TPE molding process.
TPE injection molding
The matters needing attention in the TPE molding process are as follows:
Coloring: The color masterbatch carrier should be compatible with the selected TPE material. For SBS-based TPE, PS or EVA-based colors are more appropriate, while SEBS-based TPEs use PE or PP-based colors. The color is more suitable, the color with EVA as the base has poor thermal stability, and the color with PVC as the base cannot be used for TPE. In order to make the dispersion process easier, the color masterbatch should have a lower viscosity than the basic TPE composite material ( higher melt flow index). For many overmolding materials, the use of a polyethylene (PE) carrier may adversely affect adhesion, and if the wax content in the color masterbatch is high, adhesion may also be reduced.
Shrinkage rate: The shrinkage rate of TPE material depends on the formula. In the range of 0.5-2%, the shrinkage rate of the melt flowing into the mold in the reverse direction will be higher. Generally speaking, the shrinkage rate of SBS is smaller, while that of SEBS is smaller. The shrinkage rate of materials with higher density will be slightly larger than that of materials with lower density. In addition, processing conditions such as mold temperature, melt temperature, injection speed and product thickness will affect the product shrinkage rate.
Drying: TPE generally does not have hygroscopicity and does not need to be dried. However, excessive moisture in the secondary injection molding material or matrix will have an adverse effect on the adhesion. For varieties that need to be dried, the moisture content is required to be 0.1. %the following.
Cooling time: The required cooling time depends on the melt temperature, the wall thickness of the workpiece and the melt index of the material. Harder varieties set faster than softer varieties and are easier to demould. Due to the poor thermal conductivity of the plastic matrix, the TPE can only be cooled from one side, so the overmolded workpiece needs a longer time to cool. The cooling time required for an overmolded workpiece is typically 20-40 seconds per 0.100" of overmolded layer thickness.
