Title: The Impact of TPE Shrinkage on Product Processing
Time of issue:2025-06-09
When processing products with TPE (Thermoplastic Elastomer) materials, it is crucial not to overlook the shrinkage property, also known as the shrinkage rate, of TPE. What exactly is the impact of the TPE shrinkage rate on product processing?
Shrinkage Property
When TPE cools from its molten state, its molecules align with each other, causing the overall dimensions of the molded part to shrink. Although this shrinkage is typically within a few thousandths of an inch, it can significantly affect the molding and demolding of the part, as well as the appearance of the finished product. If the shrinkage is uneven, a part that should be flat may bend or warp. Additionally, in applications with strict tolerance requirements, unexpected shrinkage can affect the fit of a component with the overall assembly. For these reasons, shrinkage must usually be taken into account during the production process.
Part Demolding
When a part contains cores or hollow sections, as the elastomer shrinks, it can tightly grip these areas of the mold, making demolding difficult. Mold design, mold surface finish, and processing conditions can all help mitigate this effect, even enabling automated demolding.
Molding Conditions
Molding conditions can significantly influence the degree and nature of shrinkage. If the transition from a high-stress to a low-stress state occurs rapidly, the degree of shrinkage will increase. Rapid cooling of the part, as well as high injection speeds or pressures, can also affect shrinkage.
Design Considerations
Taking shrinkage into account, the mold must be machined slightly larger than the required dimensions of the part. Typically, the actual shrinkage value can only be determined once the specific part is molded. Like other properties of elastomers, shrinkage often varies with the direction of polymer flow. The location of the gate will determine the direction in which the melt flows into the mold, and thus also the direction of shrinkage. Furthermore, some TPEs are more anisotropic than others, meaning they may shrink more in one direction than in another. This factor must be taken into account when designing the mold.
The shrinkage rates of TPEs with different base materials vary. For example, TPEs based on SBS (Styrene-Butadiene-Styrene) or SEBS (Styrene-Ethylene-Butylene-Styrene) generally have good water resistance, so the issue of shrinkage is not typically discussed. On the other hand, TPU (Thermoplastic Polyurethane) based on polar materials such as polyester or polyether is not water-resistant, but it generally swells rather than shrinks when exposed to water, and the usage conditions are variable, with a typical shrinkage rate of around 1.5%-3%. In fact, different types and properties of TPE/TPR materials have different shrinkage rates. Feel free to consult us!
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