Discussion on the Influence of Shrinkage Rate on TPE Product Molding

When a material is molded, it will shrink due to cooling, resulting in a product size smaller than the mold size. The molding shrinkage rate is expressed as a percentage to indicate the degree of shrinkage. Generally, crystalline resins shrink more than amorphous resins. The molding shrinkage rate can be moderately adjusted by adjusting molding conditions such as injection temperature and pressure.

The shrinkage range of TPE is 1%~2.5%, and that of engineering plastics is 0.2%~1.4%. It is recommended that the thickness of the substrate be twice the thickness of the TPE product. Adding ribs on the substrate's overmolding surface will cause heat shrink marks on the outer surface after TPE molding. When TPE material is fully encapsulated over engineering plastics, attention should be paid to warpage caused by thermal shrinkage.

Causes of shrinkage:

In the molding process, due to changes in pressure and temperature, differences in shrinkage may occur.

In the injection molding process, if TPE only undergoes heating and cooling, the shrinkage rate of the TPE filled into the mold cavity can be considered for refilling. However, in reality, due to simultaneous changes in pressure and temperature, differences in shrinkage still occur.

Process of shrinkage:

During injection molding, TPE expands in volume after being heated and melted.

After the expanded molten TPE is filled into the confined mold cavity, cooling is applied. During this process, the volume of TPE decreases, and the volume reduction rate at this point is the molding shrinkage rate.