How to improve the shrinkage of high permeability and ultra-soft TPE materials in injection molding

Time：2021-02-26Hits：2315

In the injection molding process of TPE/TPR adult products, due to insufficient pressure in some parts of the mold cavity, when the melt begins to cool, the volume shrinkage of the plastic parts with larger wall thickness is slow and tensile stress is formed. If the surface hardness of TPE/TPR plastic products is not enough and there is no melt supplement, the surface of TPE/TPR product oil will be pulled down by stress, that is, shrinkage phenomenon. So, how to solve the shrinkage problem of TPE/TPR materials for adult products? The following summarizes the reasons for the shrinkage of TPE/TPR injection molding for adult products and the improvement methods for your reference! The shrinkage phenomenon of TPE adult products mainly occurs in the melt aggregation part of mold cavity and the thick wall area of products. For example, the shrinkage phenomenon appears on the surface of injection-molded parts at the interface between reinforcing ribs and support columns, which not only affects the appearance of plastic parts, but also reduces the strength of plastic parts. Shrinkage is closely related to the types of plastics used, injection molding process, plastic parts and mold structure. 1. TPE plastic raw materials Different plastic materials have different shrinkage rates, and the raw materials that are easy to shrink usually belong to crystalline plastics (such as nylon and polypropylene). In the process of injection molding, when the crystalline plastic is heated to become a flowing state, the molecules are arranged irregularly; When injected into the cold mold cavity, the plastic molecules will gradually arrange orderly to form crystals, which will lead to large volume shrinkage, and its size is smaller than the specified range, that is, the so-called "shrinkage" appears. 2. TPE injection molding process In the process of injection molding, shrinkage is caused by insufficient holding pressure, too slow injection speed, too low mold temperature or material temperature, and insufficient holding time. Therefore, when determining the injection molding process parameters, it is necessary to check whether the molding conditions are correct and whether the holding pressure is sufficient to prevent shrinkage. Generally speaking, extending the holding time can ensure that the product has enough time to cool and replenish the melt. 3. TPE plastic parts and die structure The root cause of shrinkage is the uneven wall thickness of plastic products. A typical example is that plastic parts are easy to shrink on the surface of reinforcing ribs and supporting columns. In addition, the runner design, gate size and cooling of the mold have a great influence on the product. Because the heat transfer capacity of plastic is low, the farther away from the cavity wall, the slower its condensation and cooling will be. Therefore, there should be enough melt to fill the cavity, which requires that the melt will not reduce the pressure due to backflow when the screw of the injection molding machine is injected or pressure maintained; On the other hand, if the runner of the mold is too thin or too long or the gate is too small to cool down too quickly, the semi-solidified melt will block the runner or gate, resulting in a decrease in the cavity pressure and a shrinkage of the product.

德创化工 (edit：dechuang)