Four point main experience over TPE overmolding

Elastic part industry usually said TPE is SEBS modified by the composite functional materials. TPE elastomer with excellent overall performance, is the soft material applied mostly during over molding production , two-color injection.

TPE’s main advantages applied to overmolding
1.because TPE material slip-stop is good, and the elastic touch is nice, can enhance the touch of the product feel, good for grip.

2.TPE could adjust to the appropriate hardness (hardness range Shore 25-90A) and the appropriate physical properties (such as wear resistance, adhesion, melt index, etc.). according to product property. To provide a variety of possible materials applications for a variety of products

3.TPE processed by overmolding, commonly used for products such as handle, grip, electronic products. The material gives the product a comfortable touch, enhance grip, enhance product aesthetic and product added value. Most of the products exported to the United States, Japan and the European Union and other developed countries and regions. TPE elastomer soft as green raw materials, materials without phthalates, halogen-free, in line with ROHS environmental testing standards, fully able to meet the United States, Japan, the European Union and other developed countries and regions of environmental protection requirements.

Common TPE molding material
TPE used in overmolding, dual-color injection molding, TPE soft material as a soft coating outside, usually matching with the hard material is mainly plastic, but also metal and fabric. TPE+ fabric cloth is mainly used in luggage products. The process is the same as overmolded with metal, are generally false overmolded. True overmolding is more common in the second injection molding and two-color injection molding. TPE can be used with some commonly used plastic PP, GPPS, HIPS, ABS and engineering plastics PC, PC/ABS, PA and its modified material bonding firm. TPE and POM’s adhesion, in the current elastomer industry, is still a problem. Because the solubility parameter SP (22.6) of POM is very different from SP (7.2-7.6) of TPE, the two materials are not compatible with each other, and no suitable compatibilizer has been found to promote good adhesion.

TPE stick plastic injection sticky molding need to pay attention to the problem
● TPE compatibility with the hard plastic components to match the molecular solubility close to the molecular compatibility is better;
● to avoid sharp corners in the design to ensure that TPE and hard plastic contact together excellent, to enhance the bonding effect;
● to avoid leaving the mold cavity gas through the appropriate venting
● balance the thickness of TPE with the expected touch;
● Keep the temperature of the TPE melt to ensure the bonding effect.
● TPE should be processed after drying material, in order to reduce water mark on surface, access to surface color uniform effect;
● Selective masterbatch The carrier resin is compatible with TPE and structural material;
● To treat specially for the smooth surface, the purpose is to increase adhesive on bonding surface of the soft and hard matrial, to strengthen the bonding effect;
● TPE should have good mobility, TPE molding thickness and size ratio is very small, TPE usually need to flow through the long path and thin wall area to fill the mold;
● TPE flow length/product thickness ratio less than 150:1;
● Use good adhesive.

Common Adhesive Defect Treatment
Lack of plastic-to improve the injection molding temperature; increase the injection pressure; improve material flow.
Split, overflow edge-Lower injection temperature; Increase clamping force; Reduce injection pressure; Reduce liquidity from recipe angle.
Surface matte, not bright - to improve the injection molding processing temperature; drying material, reducing the raw material moisture.
Viscous difference-full baking before injection molding; increase injection temperature; adjust the formula.
Product injection deformation-to strengthen the mold cooling; appropriate to extend the clamping time.
Product stick mold-plus release agent or lubricant (for internal lubricant - release agent should pay attention to the amount added to prevent release agent precipitation and move out.

Experience talk
1. Adequate injection temperatureCovered on nylon, TPE injection temperature above 190 degrees is better, no more than 240 degrees can work. In particular to get the effect of true overmolding, because the softening temperature of nylon in the 250-260 degrees, In condition of TPE does not degrade, TPE and nylon softening temperature the closer, the better of the effect of bonding.

2. Product bonding structure design, as far as possible to achieve the size of sleek, no obvious edges and corners, increased TPE contact with nylon hard plastic tight.

3. To make some holes in some not critical position of the nylon bone pieces, or create some non-smooth surface, increase the contact area of TPE and nylon, so that TPE soft material  through the hole embedded in the nylon material, play hoop Embedded effect.

4. For the newly made mold, pay attention to the mold’s gate and the runner design. TPE coating layer is generally thin, the thickness of 1-2mm is common, and the size of the 1st mold part is generally in the tens or even hundreds of mm, it must ensure that TPE soft plastic can fill the cavity, not lack of plastic, To ensure the adhesion of TPE and nylon.