Soft rubber compound for yoga mat

[jeewan karu]

Hi friends,
I just developed a compound for low hardnes(38-45 shore A) product(yoga mat) and moulded using a compression moulding but one side appears to be defective(flow marks or short mould) still could not find the root cause of problem
whether arising from mold or compound?

If you can give any advice/suggestion highly appreciated..thanks

 

[Compositepro]

It looks like air entrapment against your mold surface. A major factor in this would be how your rubber is placed in the mold The rubber should be mounded in the center so that it can roll the air out as it flows out to the edges where the part line can vent the air. Random placement of rubber will cause random areas of air entrapment, which then gets compressed into a small volume at the mold surface. This can also result in scorching of the rubber due to the heat of compression.

 

[tom1953]

Besides molding technique, the formulation and compound properties will also play a part in molding success, especiallyy for soft compounds. The compound should have as high viscosity as possible; low viscosity compounds will tend to trap air more than high viscosity compounds. Using a higher viscosity polymer may be one way to increase viscosity without changing cured properties.
Also, any low molecular weight materials (e.g., plasticizers) may tend to volatilize at curing temperatures. Plasticizers with lower volatility and/or curing at lower temperatures may minimize air entrapment.

Good luck!

 

[GrahamBennett]

Definitely trapped air in the mould. One other thing you can try, if your are compression moulding, is to "bump" the mould 3 or 4 times at the beginning of the cure cycle. If all else fails, then you will have to scratch vents in the top mould to allow air to escape to the outside of the mould.

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