Injection molding is a manufacturing process that produces parts from thermoplastic and thermoset polymers.

Injection molding project is used to make a wide variety of parts, from small individual parts to large complex assemblies.

TPE injection molding is a type of injection molding that uses thermoplastic elastomers (TPE) as the molding material.

In general, TPE material molding needs to go through the plastic molding process, and injection molding is a very important method in the plastic molding process, which applies to almost all TPE materials except for a few.

However, in the process of molten polymer into liquid resin under high temperature and filling the mold cavity of TPE products, if the filling performance of the products is not good, it will happen that the pressure decreases too much, the filling time is too long, the filling is not enough, and so on so that the products have quality problems, which shows the importance of the injection molding process of TPE materials.

So do you know what is the TPE material injection molding process?

What is thermoplastic elastomers TPE material?

Thermoplastic elastomer TPE/TPR is also known as synthetic rubber or synthetic rubber. It is a physical mixture of copolymers or polymers, consisting of materials with both thermoplasticity and elasticity.

Its products have the excellent properties of traditional cross-linked vulcanized rubber in terms of the high elasticity, aging resistance, and oil resistance, but also have the characteristics of easy processing of ordinary plastics and wide processing methods.

It can be produced by injection molding, extrusion, blow molding, and other processing methods, and 100% of the edges of the water outlet are crushed for direct secondary use.

Both simplify the processing process and reduce processing costs, so thermoplastic elastomer TPE / TPR material has become the latest material to replace traditional rubber, its environmental protection, non-toxic, comfortable to the touch, exquisite appearance, making the product more creative.

Therefore, it is also a more humane, high-grade new synthetic material, but also the world’s standard environmental protection raw material.

Characteristics of thermoplastic elastomer TPE materials

TPEs are typically elastic products with a low modulus of elasticity that can be repeatedly stretched to more than twice their original length at room temperature and have the ability to recover almost completely to their original length after stress relief.

An early material with this property was thermoset rubber, but much injection-moldable thermoplastic elastomer (TPE) families are replacing traditional rubber.

In addition to their use in their basic form, TPEs are widely used in the modification of rigid thermoplastics, often for improved impact strength. For sheet and general molding grade composites, this is quite common.

Types of thermoplastic elastomer TPE

They can be divided into two categories, block copolymers (styrene resins, copolyesters, thermoplastic polyurethane, and polyamides), and thermoplastic elastomer blends and elastomeric alloys (thermoplastic olefins and thermoplastic vulcanized rubber).

TPE is a kind of rubber with high elasticity, high strength, high resilience, but also has the characteristics of injection molding processing, environmental protection, non-toxic safety, a wide range of hardness, excellent colorability, soft-touch, weather resistance, fatigue resistance, and temperature resistance, superior processing performance, no vulcanization, can be recycled to reduce costs, both secondary injection molding, and PP, PE, PC, PS, ABS, and other substrates It can also be injection molded separately.

Injection molding is a fast process and the properties of TPE make it a desired material for the injection molding. The products in which TPE is used are Thermoplastic polyurethanes (TPU), Thermoplastic olefins (TPE-o), Styrenic block copolymers (TPE-s), Thermoplastic copolyester, Elastomeric alloys (TPE-v or TPV), Thermoplastic polyamides.

TPE material injection molding process

Drying before injection molding

The injection molding process of TPE materials, according to the characteristics of the material and the supply of material, should generally be tested before molding the appearance and process performance of the material.

The supplied granules often contain different degrees of moisture, melt, and other volatile low molecular substances, especially TPE with a moisture-absorbing tendency always containing more water than the limit allowed for processing. Therefore, it must be dried and the moisture content measured before processing.

Use low-temperature injection whenever possible

Under the premise of ensuring plasticization quality, extrusion temperature should be lowered as much as possible, injection pressure and screw speed should be increased, melt viscosity should be lowered, and flowability should be improved.

When the surface of the strip injected from the nozzle is smooth and shiny, it can be determined that the plasticization quality is good. If the strip injected from the nozzle is very bright, it can be determined that the cylinder temperature can also be reduced. Using low-temperature injection as much as possible will shorten the cooling time and increase the productivity of the customer.

Upper parabolic temperature setting

The temperature is highest in the middle of the screw, slightly lower in the feed section, and slightly lower in the nozzle. Typical temperatures are 150°C 170°C (feed), 170°C 180°C (middle), 190°C 200°C (front), 180°C (nozzle). This temperature setting is for reference data only.

The specific temperature can be adjusted according to the specific physical properties of different TPE and TPR materials. If the content of the product is found to be convex (gas wrapped around it), the gate is prone to breakage during molding and can be adjusted concerning the known 2.

The holding pressure should be as low as possible

Generally, the holding pressure is less than the injection high pressure. The pressure holding time can be determined by weighing the product, depending on the weight of the product no longer increasing, or by the shrinkage mark accepted by the customer. If it is found that the gate is fragile during demolding and the second process does not work, the holding pressure can be reduced.

The injection speed should be from slow to fast

In the case of several stage injections, the speed goes from slow to fast. Therefore, the gas in the mold can be easily discharged. If the interior of the product is wrapped in gas (swelling inside), or if there are dents, the trick is ineffective and this method can be adjusted.