Liquid curing for rubber hose extrusion 2

[Julia Mahir]

We have one product that currently being produced using extrusion with liquid curing (hot oil).

The end products tend to be sticky. Even with silicon bath to prevent sticky during handling & packaging, eventually the products will still end up stick to one another while in packaging.

We thought it's caused by the products overcured or undercured. We tried adjust the temperature but still sticky.

1) How to determined if one compound is undercured or overcured (reversion)? Any testing?
2) If we were to get rid of the silicon, how to make it non-sticky?
3) any other reason of product being sticky other than it's undercured/overcured?

 

[GrahamBennett]

What polymer/s is/are being used in the rubber?

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[btrueblood]

Sounds like your polymer is absorbing excess oil that acts as a tackifier. Try post curing at a temperature hot enough to oxidize the residual oil. Or try a dry heat curing system (microwaves? steam autoclave?).

 

[Julia Mahir]

@GrahamBennet

we're using natural rubber.


@btrueblood

thanks for the great ideas! thing is, we hope there wouldnt be additional process. lol.
but yes will give it a try and see if that really helps. if it is, meaning by hook or by crook it need to be done. thanks!

 

[GrahamBennett]

As you are using natural rubber then you should not use oil (especially mineral oil) baths. Hot air tunnels combined with ballotini would be better.

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[Julia Mahir]

@GrahamBennett Why is the NR and hot oil curing not a suitable option? Thanks for the great idea, but thing is we would really like to continue using liquid curing. Sigh.

 

[GrahamBennett]

Because NR has no mineral oil resistance especially when the oil is hot. Hot silicone oil will do the job but the stickiness you find is the result of the rubber reverting because either a) the temperature is far too high or, b) the time spent in the tunnel is too long or a combination of both of these.

One point I ought to add about using oil baths is the fact that your product will probably float on the surface of the oil unless either its SG is higher than that of the oil or, you prevent the tube/hose from floating by using rods to hold it under the surface of the oil so the whole of the tube's/hose's surface will be cured.

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[stancom]

I agree with Mr Bennett but don't forget LCM curing as an alternative to a fluidised bed. The Liquid Curing Medium usually consists of a molten entectic mixture of sodium and potassium salts and could have the advantages over a ballotini bed of excluding air and sometimes avoiding need for a desiccant. Ensure the compound is submerged because the salts are heavier the rubber. As with all continuous curing methods health and safety consideration are paramount

 

[Julia Mahir]

Thank you everyone for the replies. We've been experimenting with temperature and time in the hot oil to see f we can get optimum cure. It appears that we cannot rely on rheometer graph all the way.

Another issue that we face with another compound though the same process is blister. We've tried 2, 3 and 4 minutes residence time - all turned out with blisters. Let alone to check if it's under/over cured. Could there be possibility the problem is with the compound?

 

[GrahamBennett]

Julia - For the compound that is blistering, the first question is, "Does the compound contain any desiccant?" If not, you should add at least 5phr of calcium oxide to it.

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