Date:         Wed, 29 Oct 2003 09:35:44 -0800
Reply-To:     [log in to unmask]
Sender:       Association for Recorded Sound Discussion List
              <[log in to unmask]>
From:         Jerome Hartke <[log in to unmask]>
Subject:      Re: environment controls
Comments: To: Association for Recorded Sound Discussion List <[log in to unmask]>
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Lubricants, as well as other components, can be proprietary. They can be
either mixed with the magnetic particle-binder slurry (e.g. styrene's or
fatty-acid esters mixed into polyester-polyurethane or epoxy binders),
or topically applied synthetic lubricants such as perfluoropolyethers.
Additional additives are often used to inhibit oxidation and hydrolysis
of the lubricant.

The resulting matrix, and ongoing process modifications to improve
performance or reduce cost, do not facilitate meaningful surveys.
Lubricant evaporation, oxidation, and hydrolysis are the issues, and the
recommended temperature and humidity conditions are designed to minimize
these forms of degradation.

Jerry
Media Sciences, Inc.

Walter Cybulski wrote:
>
> Mr. Brothers:
>
> Is anyone testing to determine what the effects of low RH storage might be on the extended term stability of the lubricants, abrasives, &c.?  Do the manufacturers release information regarding the types and amounts of the ingredients used for their tapes?  Thanks,
>
> Walter Cybulski
> Preservation & Collection Management Section
> National Library of Medicine
>
> >>> [log in to unmask] 10/28/03 12:07PM >>>
> The ISO recommendation not to go below 15% RH is based on contraction of the
> tape thickness that can lead to loose packs and slippage during handling of
> material removed from low-humidity storage.  It is a "shot in the dark" RH
> measurement based on anecdotal evidence and extrapolated tension concerns
> derived from shrinkage formulas from a limited test base.  The low-end RH
> limit has nothing to do with decay vectors in magnetic tape.  There is no
> known component of polyester-base magnetic tape that requires any water
> content in the tape at all.  The ISO technical commission had no
> experimental evidence that storage of polyester-base magnetic tape at 0% RH
> would have any negative effect on the tape other than the above mentioned
> possibility of pack slippage.  Of course, there may be additives such as
> lubricant or abrasives that could be effected but have not been tested for
> low-humidity chemical changes. It should be noted that, from a
> chemistry/decay point of view, no binder hydrolysis at all will occur if
> polyester-base magnetic tapes are stored at 0% RH- an interesting
> consideration for long-term storage.
>
> Recommendations in the ISO document are a combination of "best case" figures
> modified by practical handling concerns.  This means that, within the
> guidelines given, tape should remain in good condition and should be safe to
> handle.  It does not mean that the recommendations given are the absolute
> best for any one specific concern- such as binder hydrolysis decay.
>
> Note: the above mentioned opinions are my own as one of the primary authors
> and editors of the ISO storage document and are not intended as representing
> the commission as a whole.
>
> Peter Brothers
> President
> SPECS BROS., LLC
> (201) 440-6589
> www.specsbros.com
>
> Celebrating 20 Years of Restoration and Disaster Recovery Service
>
> > -----Original Message-----
> > From: Association for Recorded Sound Discussion List
> > [mailto:[log in to unmask]]On Behalf Of Walter Cybulski
> > Sent: Tuesday, October 28, 2003 9:39 AM
> > To: [log in to unmask]
> > Subject: Re: [ARSCLIST] environment controls
> >
> >
> > Thanks for the detailed response, Joe.   Lots of people are
> > looking at that Technical Bulletin.  Walter
> >
> > >>> [log in to unmask] 10/28/03 08:40AM >>>
> > Cooler and drier storage has been cited numerous times for extended term
> > storage conditions of magnetic tapes and other archival materials.  ISO
> > 18923 Polyester-base magnetic tape - Storage Practices is one source.  For
> > a more thorough discussion on the benefits of lower RH and temperature, I
> > would recommend the CCI Technical Bulletin #23 - Guidelines for Humidity
> > and Temperature for Canadian Archives.
> >
> > As for 25% being the "ideal" target, it is not written in stone.  I guess
> > 20-30% RH is the ideal range, but because the ISO standard does not
> > recommend going below 15%, then 25% seems to be the best target
> > (a bit more
> > of a buffer to avoid going below 15% because of fluctuations).
> >
> > Joe Iraci
> > Canadian Conservation Institute