Breakdown voltages for carton tape, teflon-containing paints('silky' paint)?

Hi chaps ,
I'm in need of help. I am working on a capacitor (home brewed for some old project). It has two metal sheets roughly 50mm by 80mm. I have a NMOS driving a flyback transformer whose output is directed to the plates. Following some calculator on the net, I have an arc of 3-4cm which gives me some 3000 volts(minimum) .
To prevent arcing, I have sealed the positive sheet with carton-sealing tape. It's not even, but with some observation, I was able to seal all sections that are archy/leaky parts.
What I'ld like to know is: at what voltage does this tape breakdown? Based on this knowledge, what is the true breakdown of the teflon-containing paint (I know it's 1000-2000 but a bit sceptical based on the fact that tape isn't as thick as 2 layers of this paint )?

Can't answer the break down question, but in the older days these caps were made using glass plates as the dielectric. With a 1" (25mm) margin around the edge of the metal plate. By that I mean if you had a 6"square metal plate, the glass would be 8" square.

Now days you could use one of these methods - http://www.kronjaeger.com/hv/hv/comp/cap/caps.html

Thanks a lot man.
That gives me an idea of how much to expect. However, just to be clear, if that plastic yoghurt can can withstand 20-30kV, does it contain the said component...teflon?
If so, I am confident(ish) in doing this thing...

All depends on the material/thickness,etc.. used to make this "carton tape"
Packing tape is not intended for electrical insulating and as such is probably not rated for dielectric strength.

use a tape with a specified "dielectric strength" value.
1000V to 3000V/mil is not out of the ordinary

Ok. I'm using normal brown tape (less than 1mm thick per layer).
I'm working with this tape out of necessity and scarcity of what is recommended for such voltages. So far, it has held to that punishing voltage. Most likely, my suspision that these teflon-based paints can withstand much more punishment might be valid...
Thanks all for your contrib.

well you are working with that tape because you are either cheap or live in a country that can't get the proper materials to do a job correctly.

Not sure what this "teflon-based" paint is but I suspect its used for its lubricity not its dielectric properties.

You are completely right; for the first observation.
Anyway teflon-based paint (my perception) is that water-based paint that on painting and drying leaves a smooth shiny surface; kind of what people call silk paints...

I've used some floor polish that contained Teflon,definitely left a layer of something that was a massive pain to strip back off..

My question now as it was then,Teflon being Teflon won't adhere to anything but..Teflon.
So there is no way you can get a "solid" coat of Teflon w/o the priming process used in cookware and others.
There has to be a suspension of binders which is going to have different electrical properties then Teflon itself.
You may find some place on your conductor sheet where the Teflon has settled un evenly causing a fault point.
At least w/ a products like glass and kapton you have even coverage and known properties.

You got the idea right. Once painted, I wish that it sticks forever. I have no intention of removing it no matter what. I am aiming at this type of paint for water wear resistance and dirt reasons. I need the cap in question to function in a damp/almost soaking wet environment all its useful life.
As regards sticking, I am thinking of automotive paint that contains this material.
Finally, are car paints electrostatic by nature (here meaning naturally occurring or engineered by man)? I mean because when such paints are applied using a electrostatic spray gun, it holds up and no arcing occurs while spraying.

Google " Corona Dope " it has the dielectric strength you are looking for, can -- or used to be - be had in an aerosol. I have used the stuff successfully in repairing minor arc and scuff damage in electric motor coils, armatures and commutators -- and it has bailed me out of untold [ I ain't talkin' ] amounts of trouble.