First, it is understood that in the elastomer industry is usually referred to as TPE is modified by composite functional materials SEBS. TPE elastomer materials have excellent comprehensive performance, is applied in the molding and two-color injection molding production process of soft materials. What are the advantages of TPE materials for overmolding and the problems to be noted? Next, we will analyze the main advantages of TPE for overmolding.

As TPE material has good anti-slip property and good elasticity, it can enhance the touching feeling of the product, which is favorable to the grip.

TPE can be adjusted to the right hardness (hardness range Shore 25-90A) and appropriate physical properties (e.g. abrasion resistance, adhesion, melt index, etc.). Depending on the product properties, there are various possible material applications for a wide range of products.

TPE is processed by overmolding and is commonly used for handles, grips, electronics and other products. The material gives the product excellent tactility, enhanced grip, enhanced aesthetics and added value. Most of the products are exported to the United States, Japan and the European Union and other developed countries and regions.TPE elastomers are soft, green raw materials, the material does not contain phthalates, halogen-free, in line with the ROHS environmental testing standards, fully able to meet the United States, Japan, the European Union and other developed countries and regions of the environmental requirements.

Second, common TPE molding materials

TPE can be used for overmolding, two-color injection molding, TPE as a soft material, usually matched with hard materials, mainly plastic, metal and fabric. TPE + fabric is mainly used for luggage products. The process is the same as overmolding with metal, usually false overmolding. True overmolding is more common in secondary and two-color injection molding, and TPEs bond strongly to some of the most commonly used plastics such as PP, GPPS, HIPS, ABS, and engineering plastics such as PC, PC/ABS, PA, and their modifiers. In the current elastomer industry, the adhesion of TPEs to POM is still an issue. The two materials are incompatible with each other due to the large difference between the solubility parameter SP of POM (22.6) and that of TPE (7.2-7.6) and no suitable bulking agent has been found to facilitate the bonding of the two materials.

Third, TPE viscose injection molding in the need for attention

TPE compatibility with hard plastic components, solubility close to the molecular compatibility is better;

Avoid sharp corners in the design, to ensure that the TPE and hard plastic contact is good, to enhance the adhesive effect;

Proper setting of mold cavity exhaust port;

Balancing the thickness of the TPE with the desired tactility;

Maintaining TPE melt temperature to ensure bonding effect;

TPE should be dried before processing the material to reduce the surface water stains and obtain the effect of uniform surface color;.

Selection of carrier resin for color masterbatches compatible with TPE and structural materials;

Special treatment of smooth surfaces, the purpose is to increase the adhesion on the bonding surface of soft and hard materials, to enhance the bonding effect;

TPE should have good fluidity, TPE molding thickness and size ratio is very small, TPE usually need to flow through long paths and thin-walled areas to fill the mold;

The TPE flow length/product thickness ratio is less than 150:1;

Use of good adhesives.

Fourth, common adhesive defects to deal with

Missing material: increase the injection temperature; increase injection pressure to improve material flow.

Split, overflow edge: lower injection temperature; increase clamping pressure; reduce injection pressure; reduce flow from the formulation point of view

Lusterless, non-glossy surface: Increase injection molding process temperature; Dry the material, reduce raw material moisture.

Sticky difference: Bake completely before injection; Increase injection temperature; Adjust formulation.

Product injection deformation: strengthen mold cooling; appropriately extend the holding time.

Product sticking to the mold: add mold release agent or lubricant (for internal lubricant - mold release agent should pay attention to the amount added to prevent the mold release agent to precipitate and move out).

Fifth, experience sharing

Injection temperature is suitable, nylon overmolding, TPE injection temperature should be above 190℃, but do not exceed 240℃. Especially when you want to get excellent overmolding effect, because the softening temperature of nylon in 250-260 ℃, in the TPE conditions will not degrade, TPE and nylon softening temperature is closer to the bonding effect is better.

Product bonding structure design, as far as possible to achieve rounded dimensions, no obvious corners, to increase the close contact between TPE and nylon hard plastic.

Make some holes in some non-critical position of nylon, or make some non-smooth surface, increase the contact area of TPE and nylon, so that the TPE soft material through the holes embedded in the nylon material, play the embedding effect.

For newly made molds, pay attention to the gate and runner design of the mold. TPE coating is generally thin, the thickness is generally 1-2mm, the size of the mold part is generally in tens or even hundreds of millimeters, and to ensure that the TPE soft plastic can fill the cavity, not lack of material, to ensure that the bonding of TPE and nylon.

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