Urethane coating

[Pat26]

Hi im applying water based urethane coating on a rubber surface at 130 degres celcius. Curing time is 120 sec and surface of the rubber goes up to 250 degres celcius. I got bad result on solvant resistance with Naphta. Result is better when i lower temperature but the rubber is not cure enough.

Q: 250 celcius is it too high for water based uretane coating

Q: Solvant(xylene) base coating support higer temperature than water based?

Thanks

 

[kenvlach]

I don't understand the temperatures you are using. I think water-based coatings of any type have to be dried at max. 90 C before final cure to avoid porosity.
Are you trying to simultaneously cure the rubber?
How does the temperature rise 120 C in 120 sec?

It is dangerous to use high vapor pressure flammable solvents like xylene at high temperatures (way above explosive flashpoint!). Check with the mfr. of the coating for application method; don't kill yourself while experimenting.

 

[Pat26]

Yes i try to cure rubber in same time.
The coating application is in a spary cabin explosion proof. When rubber parts enter hot air ovens all solvant is flash off.

Q) Urethane melt point is above or under 250 degres celcius?

 

[kenvlach]

Re "Q) Urethane melt point is above or under 250 degres celcius?'

There is no definitive answer to this question.
a) Once cured, polyurethane does not have a melting point; it will char and then burn if heated to high temperature. At 250 C in air, I think OK for short term but expect slowly degradation by oxidation over long period.

b) Polyurethane is usually formed by the reaction of 'A' and 'B' components (depends on mfr.), both liquids at room temperature. For some mixtures, you can raise the temperature of the liquid to lower the viscosity (need less solvent) and accelerate the curing rate. I am not familiar with applying heated mixtures at temperature above 52 C, but this is only general knowledge, maybe you have special type. In any case, you must have some concern that when the solvent flashes off it will leave porosity in your coating.

Some polyurethanes form by reaction of one component with moisture in air. I think this kind is unsuitable to apply at high temperature due to insufficient moisture to sustain the reaction rate.

Regardless what type of polyurethane you are producing, follow the manufacturer's instructions. Either you are experimenting or using a polyurethane I am unfamiliar with (some applicators advertise a spray on polyurethane coating with 15 seconds cure time, so maybe there are specialists that can help you).
I wish you good luck & hope you will give your results,
Ken V.