Advice needed about choice of adhesive

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Advice needed about choice of adhesive gautham.vanya 05-13-2008
Posted by James Waldby on May 15, 2008, 11:49 am
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 On Thu, 15 May 2008 02:55:23 -0700, gautham.vanya wrote:
> Will try those hotmelt varieties.
>
> The bond seems to give up on the plastic side i.e. there is adhesive on
> the magnet which seems difficult to get off but the plastic surface is
> clean.
>
> Wondering if roughing up the plastic film with a bit of sandpaper will
> make any difference.

While it makes a difference, other methods are more effective. From page
355 at the end of section D, "Surface Grafting" of "Adhesives in Joining
Plastics", a chapter in Patrick and Minford's "Treatise on adhesion and
adhesives": "increases in adhesion were seen" (by abrading under epoxy
vs abrading in air) but "failure surfaces of the adhesive bonds were
apparently adhesion failure" vs. "Yamakawa's work in which grafted
surfaces exhibited primarily substrate failure in practical adhesion
testing." Yamakawa grafted saponified methyl acrylate on PE, PTFE,
and PCTFE surfaces, via Co60 radiation -- impractical to try unless
you work in a hospital with a radiation-therapy department.

http://www.corotec.com/techinfo/papers2.html?id=997131402 describes
high voltage RF plasma techniques that are commonly used to prepare
PE surfaces for printing and gluing. Also see the chemical surface
preps (for metals but maybe relevant to some plastics) described in
http://www.wmrc.uiuc.edu/info/library_docs/manuals/coatings/surface.htm
many of which are practical at home.

-jiw

Posted by Doug White on May 16, 2008, 6:06 pm
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gautham.vanya@gmail.com wrote:
>Will try those hotmelt varieties.
>
>The bond seems to give up on the plastic side i.e. there is adhesive
>on the magnet which seems difficult to get off but the plastic surface
>is clean.
>
>Wondering if roughing up the plastic film with a bit of sandpaper will
>make any difference.

I came in on the middle of this thread, so I'm not sure what sort of
plastic you are working with. There areseveral possible contributing
reasons why adhesives don't stick to plastic:

1) Residual monomers. These can be oily, and prevent the adhesive from
attaching to anything structural. The right solvent can clean off a lot
of this.

2) Too smooth a surface. The adhesive just can't hang on to anything.
Thsi is where roughing it up will help.

3) No molecules on the surface that want to hook up with the glue. If
all of the ploymers in the plastic are long chains happily hooked
together, the adhesive can't find anything to chemically bond with. This
is sort of like 2, only at the molecular level. Chewing it up with
abrasive may help, but chemically etching the surface to break up the
long polymer chains is best. Sometimes you can achieve soemthtign
similar by lightly scorching the surface. The chemicals required to etch
some plastics are pretty nasty.

For most things, I use some sandpaper & then give it a good cleaning with
a solvent.

I haven't used it myself, but I've heard good things about the Cyanopoxy
system:

http://www.coolchem.com/index.cfm?fuseaction=cyanopoxy

Doug White

Posted by on May 14, 2008, 6:09 pm
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Where's the bond part, from the magnet or the plastic? Divide &
conquer, so to speak.

Hul

gautham.vanya@gmail.com wrote:
> While this is not strictly metal related, I'm sure I will get some
> good advice here.

> I need to stick tiny (about 1/8th inch dia) rare earth magnets to
> plastic film (think laminated paper) and I am looking for a glue to do
> the job. The result needs to be fairly difficult to break.Tried CA,
> but I can break the bond with some effort. Same with Araldite
> (epoxy).

> Any suggestions? Any tips to get it to work better?

> TIA - I'm back to lurking now
> Gautham

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