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Sticking problems in thermoplastic elastomer TPE TPR TPU TPV materials injection molding
August 20 , 2021

Sticking is a common problem in the injection molding process of thermoplastic elastomer TPE/TPR/TPU/TPV. Sticking problem is quite common when the hardness is relatively low, such as TPE/TPR/TPU is lower than 60A and TPV is lower than 40A. There are two main parts that occur mold sticking problem.

1. Thermoplastic elastomer TPE/TPR/TPU/TPV sticking in the main runner

Because the pressure in the main runner which is the closest position to the injection nozzle is he largest, it leads to the smallest material shrinkage in this area and make greater friction between the material and the inner wall of the sprue

Solutions are as follows:

1.1. As the particularity of the thermoplastic elastomer material the smoother the surface of the mold, the greater the adsorption force, so add electrical discharge lines in the Sprue bushing can reduce adsorption force of the runner. electrical discharge lines can add by electrical discharge process.

1.2. The runner pin adopts the undercut shape of the runner pin to increase the force of pulling the runner. Don’t worry about the runner will not be taken out, because it is soft rubber. Of course, the angle of the undercut can be changed from small. The pulling force may be insufficient if the runner pins is Z-shaped which cause the runner to stick to the master mold.

2. Thermoplastic elastomer TPE/TPR/TPU/TPV injection products sticky to the mold
Injection products sticking happened probability is relatively lower than runner sticking. Injection products sticking usually happened when the draft angle of the male mold is too large. In such situation it can add lines in the male mold to prevent injection products sticking.

Solutions are as follows:
2.1. The male mold is polished to a mirror surface as much as possible to increase the adsorption force.

2.2. The draft angle of the male mold can be made small appropriately.
2.3. Cross ribs can be added to the head of the thimble;
2.4. Considering the molding process, the female mold can be set as high mold temperature, and the male mold can be set as low mold temperature;
2.5. Adjust the formula of the thermoplastic elastomer material and lower the injection processing temperature;
2.6. Reduce the holding pressure;
2.7. Inject a release agent in the mold cavity before molding.
Usually products sticking is stick to the female mold. But sometimes due to material, process parameter setting or mold design reasons, the product will stick to the male mold (for example, the male mold has a large adsorption force), it is difficult to demold and the product may even be deformed or damaged. In addition, it may be due to high holding pressure. For thermoplastic elastomers with medium hardness and above, the depth of the lines increases will be easy to sticking mold.

3. Adjust the formula of thermoplastic elastomer to solve the sticking problem

3.1. Increase the external lubricant such as silicone, oleic acid amide, erucamide, EBS, etc.o in the thermoplastic elastomer elastomer materials,;

3.2. Reduce the addition of softening oil;

3.3. Increase the crystallization temperature and crystallization rate of continuous phase materials;

3.4. Add fillers if feasible.


Treatment method

Injection pressure or melt barrel temperature is too high

Reduce injection pressure or melt barrel temperature

Holding pressure time is too long

Reduce pressure holding time

Insufficient cooling

Increase cooling cycle time

Mold temperature is too high or too low

Adjust mold temperature and relative temperature on both sides

There are demoulding chamfers in the mold

Repair the mold to remove the chamfer

Unbalanced mold inlet

Restrict the flow of raw materials, as close to the main channel as possible

Poor mold exhaust design

Set up reasonable vents

Dislocation of mold core

Adjust the mold core

The mold surface is too smooth

Improve mold surface

Lack of release agent

When it does not affect the secondary processing, use a release agent


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