Inge,

I have seen many materials that 'string' like crazy when dispensing -
conductives and non-conductives.  I've always used localized ionized blowers
in situations where stringing is observed, in the belief that 'stringing'
was related to charge generation - and for the most part, this has greatly
reduced the stringing.  While not scientific 'proof' of charge generation,
it might support the concept.  

When the dispensed material's tail separates from the dispense needle, it
can take off large distances in any horizontal direction.  Some materials
seem to throw a string equal in length to the dispense height.  

Even the conductive paste materials have a large percentage of
non-conductive resins involved.  Some silicones can be even more messy.

Could charge generation be related to a shearing effect as the material is
extruded through a needle, or past the brush hairs in Doug's case?  Could
the repeated time pressure pulse of a dispenser's compress and release of
the material within the syringe to the extent that charge generation is
taking place within the bulk of the material [on a molecular scale]??? 

And possibly what I call 'stringing' has nothing to do with charge
generation...

Personally, I believe that an antistatic syringe barrel and piston is less
effective than a well controlled workstation.  Even if the barrel and piston
are antistatic, are static dissipative needles available?  What about the
vinyl hose coming from the dispenser to the barrel adapter at the syringe
end of the hose?  Is that antistatic as well?  What about the plastic
fitting on the end of the vinyl hose going into the plastic fitting on the
face of the dispenser unit?

Be interesting to hear comments.

Best regards,

Steve 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Wednesday, September 14, 2011 6:33 AM
To: [log in to unmask]
Subject: Re: [TN] Pneumatic Syringes and ESD

Doug,

Triboelectric means adding or stealing electrons through friction. How can a
uncured glue (liquid with a high viscosity) move electrons from your nozzle?
I've been in the game for decades and not heard about such things. I've
participated in p-p courses, glue courses, read lots of articles etc, but
missed what you insist.

Human and dry hair has a molecular crystal-like surface, and via the Fermi
level you can move electrons from the orbit. However, if your hair is fat,
there will be no charge movements, because the fat has no specific surface
for that purpose. Likewise, I thought uncured glues were no aspirants
either.

Well, never too late to learn something new.

Inge

 Relationship between *triboelectric* charging and surface *...*
<http://search.mywebsearch.com/mywebsearch/redirect.jhtml?qid=62bac059e5f09c
b4c1291b201f0024f4&searchfor=kinetic+explanation+of+triboelectric+charges&ac
tion=pick&pn=1&n=77decd8b&ptb=naCNCR5Azm75RkmBmXss1w&ptnrS=ZRxdm784YYSE&ss=&
st=hp&cb=ZR&pg=GGmain&ord=4&tpr=hpsb&redirect=mPWsrdz9heamc8iHEhldEWVlFOy8LX
VdR6PzojpERxbLlEmRQOowS8Qj5BmJGVqQkswtwN%2FH7EAkxVp0REdxDZ8QU9G9gHdhVQrRQ2vn
%2FnU%3D&ct=AR>
bleaching, and oxidative dyeing has only a small effect on
*triboelectric*charging. Measurements of the
*kinetics* of *charge* decay indicate that none of these *...*
http://journal.scconline.org/pdf/cc1985/cc036n03/p00189-p00212.pdf -
Cached<http://search.mywebsearch.com/mywebsearch/redirect.jhtml?redirect=GGc
ached.jhtml&action=click&searchfor=kinetic%2Bexplanation%2Bof%2Btriboelectri
c%2Bcharges&curl=http%3A%2F%2Fjournal.scconline.org%2Fpdf%2Fcc1985%2Fcc036n0
3%2Fp00189-p00212.pdf&isDirResults=false&tpr=hpsb&cid=KYJrE_TQtsAJ&ptnrS=ZRx
dm784YYSE&st=hp&ptb=naCNCR5Azm75RkmBmXss1w&ct=GC&pg=GGmain&n=77decd8b>




On 13 September 2011 20:06, Douglas Pauls
<[log in to unmask]>wrote:

> The coating is insulative in its liquid state as well.
>
> Doug Pauls
>
>
>
> "Mike Fenner" <[log in to unmask]>
> 09/13/2011 12:48 PM
> Please respond to
> <[log in to unmask]>
>
>
> To
> "'TechNet E-Mail Forum'" <[log in to unmask]>, <[log in to unmask]>
> cc
>
> Subject
> RE: [TN] Pneumatic Syringes and ESD
>
>
>
>
>
>
> You would have to check with supplier, or verify it yourself; but though
> the
> coating is insulating when cured it may well not be uncured in liquid
> form.
>
> Regards
>
> Mike
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
> Sent: Tuesday, September 13, 2011 4:53 PM
> To: [log in to unmask]
> Subject: [TN] Pneumatic Syringes and ESD
>
> Good morning all,
>
> Time for a silly question.  The question has been raised internally as to
> the risk of ESD generation when an acrylic conformal coating (an
> insulative material) is applied using pneumatic syringes (also an
> insulative material), through a nylon brush (a third synthetic material).
>
> 1.  Do you know of any studies done benchmarking static generation levels?
>
>  We have done some here, but want to do a sanity check.
> 2.  If you have such devices in your facilities, what are your mitigation
> efforts?  Air ionizers, grounded tubes?
> 3.  Does anyone use, and can recommend, ESD safe syringe bodies and caps?
>
> Many thanks in advance.
>
> Doug Pauls
> Rockwell Collins
>
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