Most scaring reports about silicon 'oil'smear (spreading, migration ..)
are from the 60's when silicon was found to contaminate relay contacts
and connectors in general. Few incidents were found, but they were
enough to start hysteria. So, silicon was banned and forbidden for (too)
many applications. Still, many are deadly afraid of 'silicon'. People
with a more balanced insight know that there is a variety of silicon
products, most of which can be used without fear. In fact, we use a lot
of silicon glues, silicon O-rings, silicon insulators etc. Then what was
so catastrophic about silicon? I'm not like Brian, a chemistry
specialist, so I may need some correction. I found that:
1. Silicon 'oil' use to be an oil with a very small additive of a
silicon compound.
2. The oil is often a mineral oil, and there are many...
3. The additive is often a polymerized siloxane like dimethylsiloxane or
diphenylsiloxane.
4. It's the surface energy and the viscosity of the mineral oil, that
decides if the 'silicon oil' will spread or not. If the mineral oil is
'slow', there is little risk of spreading, while a 'rapid' oil may cause
wetting and spreading (or 'migration', if you prefer to use that word).
There are oils with viscosity 200,000 mPa.s and those with viscosity as
low as 40 mPa.s. The time to equilibrium of wetting can vary from days
to seconds.
5. The micro-geometry or topography/porosity of the surface is also an
important factor. If the surface is microscopically very porous, it will
take longer time for the 'silicon oil' to creep into all voids an
supersede air with oil. If the proportion between the viscosity and the
topo/porosity is adverse for the oil, any wetting may be stopped, and
the oil can't creep.
6. So, as so oftenly else, ID(tm)(it depends). You can't ban all silicon
products based on the fear of silicon migration.
Right?
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg
Sent: den 12 november 2007 17:14
To: [log in to unmask]
Subject: [TN] Silicone Lens Cleaner Problem
I'm hoping that somenone on TechNet this morning can help my understand
a little more about this. I received a letter from a customer stating
that silicone can introduce contaminants which are detrimental to the
manufacturing process. The notice specifically mentioned lens cleaner.
Can someone enlighten me as to what problems silicone can cause?
Thanks,
Blair
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