Painting Magnets?

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TLD

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#236396 31-May-2018 11:55

We are looking at flyscreens that will fit on the outside of white uPVC windows. The least impact would be flexible screens with a 12mm(ish) wide magnetic strip that is permanently glued to the window frame. The problem is that the magnetic strip is black, and the suppliers don't want to commit to painting it to match the window frames. The screens would probably stay on all year anyway, but it would be nice to have the option to remove them without leaving an ugly black strip.

I can't think of a reason why a thin coat of paint would have a detrimental effect on the magnetic strength of the strip. I'd 'maybe' be reluctant to run wet & dry up the strip (to give the paint a key) with vague thoughts of stroking magnets and hitting them on the end with a hammer, but paint... I can't see it. To be fair, I suppose I would absolutely need to use an etching primer as well, but the total thickness would still be bugger all.

https://www.homeplus.co.nz/products/screens/magnetic-screens/

The suppliers are letting us have a spare length of the magnetic strip to experiment with, but it would be great to hear the thoughts or experiences you guys have (on the subject — the random thoughts of the average Geekzone Netizen are too scary to contemplate).

Trevor Dennis
Rapaura (near Blenheim)

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mdf
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#2026156 31-May-2018 12:13

Strip magnets have multiple poles along their length. You will struggle to demagnetise them hitting them/stroking them. It's most likely iron powder embedded in rubber. No idea how you'd prime that "properly" but I'd probably experiment with a standard acrylic undercoat to start if you were going down that route.

Magnetism falls away sharply with distance (inverse square law, I think). Very different application, but I painted a door with Resene's magnetic paint. It's just paint with iron powder again. It was nice and magnetic bare, but by the time I'd undercoated and two top coats, it was noticeably less magnetic with the same magnets. I guess you're not aiming to actually hold anything heavy up though, just attached.

As a randomish hypothesis though, but I believe at least some uPVC windows have steel reinforcing in the frame. Have you tried holding a magnet to your existing window frames? You might be able to glue the strip to the screen rather than the other way around.

Fred99

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#2026159 31-May-2018 12:19

That strip is usually ferrite powder extruded in plasticised PVC. EPL in Chch used to make it - not sure if they still do. You'd be facing the same problem as painting other flexible plasticised PVC - the paint will flake or peel off either because it's not as flexible as the substrate, or there are co-extrusion waxes and plasticisers in the compound that will interfere with adhesion.

I think this stuff might be your best bet - probably available from supercheap etc:

https://duplicolor.com/product/vinyl-and-fabric-coating

I'm guessing you might also need some strong solvent to clean the surface thoroughly possibly acetone or MEK would do the trick.

White electrical insulation tape might also work - for a while anyway - until the plasticisers probably leach out and start dissolving the glue.

Edit - forget the insulation tape for outdoor use.

That vinyl paint is available from Supercheap at $20/can.

I recommend that you don't expect that as it's got "adhesion promoter" you can avoid having to clean it down with solvent first. That might be okay with aged vinyl, but I'd be surprised if new extruded flexible PVC didn't have quite a waxy surface.

It states for interior use. PVC polymers aren't inherently UV resistant, but it'll probably be okay for quite a while.

TLD

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#2026415 31-May-2018 17:44

I loved the idea of reversing the magnet. That was excellent lateral thinking. Unfortunately, I have tried, and magnets do not stick to the window frame, so any ferrous content is either too little and/or too deep. I'll pick up the length of magnetic strip tomorrow, and try some of the suggested paints.

Trevor Dennis
Rapaura (near Blenheim)

Fred99

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#2026429 31-May-2018 18:19

That actually reminded me - I'd been to a hardware store as I wanted to try some white vinyl paint on the padded vinyl tops of some vintage bar stools we've got, I'd asked about it at a local M10 Mega hardware store - they looked at me blankly and said they'd never heard of it.

So I stopped in at Supercheap Auto this afternoon, picked up a can, painted the vinyl on the bar-stools (they were kind of poo brown). Needed three coats to cover - they're back inside and look great. Dries fast even though it was quite cold today in the garage where I painted them. My wife thought I'd recovered them. It seems to work well - time will tell if it lasts, but it should probably be okay.