How to handle peeling and delamination of TPE thermoplastic elastomer during injection molding?
The information comes from:the Internet posted on:2023-09-04
During the injection molding process of TPE, there may be material delamination issues. This layering phenomenon is very common in some cases where the coating thickness is large, such as casting machine coating, handle coating, etc. Sometimes a thin outer layer is torn off, just like a person's hands and feet peeling. However, there is no mention of peeling in this industry abroad, and it is generally believed to be delamination. Therefore, we can consider peeling as a slight delamination and delamination as a serious delamination. So what should we do if this layering phenomenon occurs? Listen to what the manufacturer of Gist TPE materials says
I Material issues
Thermoplastic elastomers, most of which are blends, such as PP/SEBS and PP/EPDM, are often more prone to peeling/delamination when composed of these blends.
Most TPE | TPR materials are composite materials made by blending two or more components. The material contains a variety of ingredients in the formulation, and the compatibility of each component is a crucial consideration in the design of the formula. If the compatibility of the mixing system is not sufficient, peeling and layering phenomena are prone to occur during the molding of TPE | TPR materials, especially at the gate position.
So we should screen out the impurities or replace them with new ones
II Mold aspect
The mold mainly has two parts that affect the material injection molding, a is the gate and b is the cavity. Speaking of this, we first propose two concepts:
① Melt rupture: Polymer materials have a smooth surface and uniform shape when extruded through a die or gate at low fluid shear rates during extrusion and injection molding. When the shear rate or shear stress increases to a certain value, the surface of the extruded material will lose its luster and become rough; When the rate increases again, numerous irregular nodules, twists, or bamboo knots will appear on the surface of the extruded material, and even branch and fracture into fragments or column segments, which is called "melt fracture".
② Uneven flow distribution: Usually, polymer fluids that can flow are wrapped in fillers that are difficult to flow in the gate and cavity; Usually, polymers with good flowability are closer to the surface of the mold than polymers with poor flowability; Usually, the dominant polymer continuous phase carries the non dominant polymer for flow. Usually, polymers that solidify slowly flow further in the mold cavity. These factors result in uneven distribution of material components in the mold cavity.
The peeling phenomenon mentioned above should be relatively mild and not overall in nature; The phenomenon of peeling caused by uneven flow distribution is relatively serious, and sometimes you can even tear a whole piece of skin off the entire product.
For the peeling caused by melt fracture, our solution in the mold aspect is, of course, not to design the gate size too small, and not to have sudden changes in the mold cavity design. The uneven distribution of flow has little to do with mold design, and more importantly, material compatibility needs to be considered.
3、 Process aspect
When injection molding TPE products, the melt of the rubber material changes at the gate position, flow path, and cross-section, leading to changes in the shear rate of high-temperature TPE fluid flow. Some products have smaller gate sizes, and this shear rate change will be more rapid.
As a blended TPE | TPR raw material, it may not cause peeling and delamination problems for most products with size structures. But if the gate of the product is too small and the fluid flow length ratio is large, the shear rate changes quickly at the gate position, and the shear effect on the TPE melt will be intensified. If the compatibility of the TPE blend system is slightly poor, it is easy for peeling and layering to occur at the gate position.
The reason for the peeling of the TPE molding gate is due to fluid shear, which leads to peeling and layering. Improving the compatibility of the mixing system can reduce or eliminate peeling. By appropriately enlarging the gate, it can also be improved.
Dongguan Gist 3D Technology Co., Ltd. is located in Zhongtang Town, Dongguan City, the "World Factory" in Dawan District. The company is mainly engaged in the R&D, production and sales of TPE, TPR, protective materials, luminous masterbatch, non-Newtonian fluid (shear thickener). The founding team of the company has a high level of expertise, with over 60% having a bachelor's degree or above. The company focuses on technological innovation, establishes its own research and development laboratory, improves its quality management system, and scientific process flow, bringing greater value to employees, customers, and shareholders.
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