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ARSCLIST  January 2016

ARSCLIST January 2016

Subject:

Re: One more sticky-shed data point - Richardson treated tape

From:

Tom Fine <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Wed, 20 Jan 2016 13:53:03 -0500

Content-Type:

text/plain

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Parts/Attachments

text/plain (203 lines)

Hi Peter:

Thanks for all that information. Very interesting.

So, why do you think Richardson's treatment has worked so far? Do you predict the tape will 
eventually go back sticky (I think that's what your information indicates)?

Also, what do you make of the sonic degradation I and others have heard and Goran Finberg has 
measured, when tapes are baked and gone back sticky a few times (I don't think we've determined if 
the degradation is audible from the first bake onward, but it definitely has been audible, in my 
experience, after three or four bakes, and probably was to a lesser extent on the second bake)? Do 
you have any theories on what chemical process would cause this? What do you think of my theory that 
the surface gets more and more un-smooth and at least part of the problem is a tape-head contact 
issue?

Again, thank you for your detailed post. Much to absorb!

-- Tom Fine

----- Original Message ----- 
From: "lists" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, January 20, 2016 1:33 PM
Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated tape


> Hello all:
>
> Coming very late to this thread.  I don't intend to talk here about Mr.
> Richardson's process but, in answer to Tom's post, I'll try to address some
> of the issues with "sticky shed".  So, here goes:
>
> First off, the primary cause (not necessarily the only cause) of sticky shed
> has been shown in laboratory testing to be binder hydrolysis.  Each time a
> different observation is made, it seems like someone wants to say "aha"  it
> doesn't fit with the hydrolysis model.  In actuality, most of the
> "exceptions" are well within the hydrolysis model if one looks closely at
> the science.
>
> Hydrolysis of polyester is a well-documented and well known chemical
> reaction in polymer science.  When binder hydrolysis affects magnetic tape,
> water, often absorbed into the binder matrix from humid air, interacts with
> the polyester molecules in the binder and breaks the polymers down into low
> molecular weight oligomers and carbolic acid.  The oligomer residue produced
> has a different frictional coefficient than the original polymers and the
> residue has less internal cohesion than the polymer matrix.  Thus, the
> oligomers create a "sticky" effect and "shed" from the matrix- "sticky
> shed"..
>
> So, why do tapes with backcoating display SS more often than non-backcoated
> tapes?  The answer may be fairly simple if one considers the manufacturing
> of the different parts of the tape from the viewpoint of polymer science.
> The longer the polymer chain, the more stable.  Short or mid-length polymers
> are more subject to hydrolysis than long-chain polymers.  Due to the fairly
> exacting physical requirements of the recording surface on magnetic tape,
> the polymers used in the recording layer are longer, more stable polymers.
> Unfortunately, it takes significant effort, QC and money to create
> relatively long, stable, uniform polymers.  The backcoat of a tape requires
> different (and less exacting)  characteristics so the polymers used in the
> backcoat are shorter and less uniform in length than the polymers in the
> recording surface.  They are much more subject to hydrolysis.
>
> That doesn't mean that the polymers in the recording layer can't hydrolyze;
> the do.  It is just not as likely and, the shorter polymer chains in the
> backcoat will hydrolyze before the long chains (in either the recording
> surface or backcoat) will.  We have tested residue from non-backcaoted tapes
> and detected oligomer residue.  It happens, but there are also many
> circumstances where short-chain molecules will hydrolyze and the
> longer-chain molecules will not.
>
> Another complication is that the oligomer residue from the hydrolysis
> reaction is more hydrophilic then the polymers.  The amount of hydrolysis
> that can occur is dependent on the amount of water available in the tape.
> This is usually a factor of both RH and absolute humidity.  RH determines
> how "willing" the environment is to allow the tape to absorb water for the
> reaction and absolute humidity determines how much water is actually
> available.  If a tape is already partially hydrolyzed, the presence of the
> oligomer residue in the polymer matrix allows the tape to absorb more of the
> available water from the atmosphere than a tape with no oligomer residue and
> will "catalyze" the hydrolysis reaction.  This partially explains why
> treatment for hydrolysis is becoming more intense over time- in some tapes
> the reaction has progressed further and needs more remediation.
>
> This could also partially explain why a small amount of tape known to
> hydrolyze, wrapped in a larger reel of tape that is not greatly subject to
> hydrolysis, might not show the same level of hydrolysis as a full reel of
> the hydrolysis-prone tape;  the lack of oligomer residue in the majority of
> the reel reduces the water available in close proximity to the short section
> of tape.
>
> As for "baking" to temporarily counteract SS, it is not the only procedure
> that works- just the most convenient.  It is possible to get similar (but
> not identical) results using a vacuum chamber or a "desiccating" chamber.
> Both methods have been tested and shown to be effective ( the treated tapes
> play back) but they require significantly more time.  The "not identical"
> results are part of the key to the easy success of baking that is generally
> overlooked.  Baking, vacuum and extreme desiccation can all cause oligomer
> residue to cross-link  back into polymers.  Yes, binder hydrolysis is a
> bi-directional chemical reaction.  Please let us avoid the argument about
> hydrolysis not being reversible.  The reaction is not reversible; it is
> bi-directional.  The two are not the same but do have the same practical
> result so far as returning a tape to potentially playable condition.  If you
> remove sufficient water/moisture from a hydrolyzed tape, the oligomers will
> cross-link "back" into polymers but not the same polymers as were there
> originally and the new polymers will tend to be shorter than the originals.
> We have removed oligomer residue from a tape, treated it and shown through
> chemical extraction in a laboratory that the treated material had
> significantly more polymer content than the material had before treatment.
>
> The effect that is frequently overlooked during the baking process is the
> re-absorption of residue into the binder matrix due to the elevated
> temperature.  When tape hydrolyzes, the polymers don't just break down on
> the tape surface.  They also break down inside the depth of the matrix.
> When the polymers interact with water, and oligomer residue is produced, the
> volume of the residue produced for any given volume of polymer is somewhat
> greater than the volume of the original polymers.  Thus, not only does the
> tape surface become sticky due to surface breakdown, this is aggravated by
> migration of additional oligomer residue from inside the binder matrix to
> the tape surface.  Initial, short-term baking does not cause sufficient
> cross-linking of oligomers into polymers to make a tape playable.  What it
> does, initially, is raise the absorption capacity of the binder matrix and
> some of the oligomer residue on the tape surface is re-absorbed back into
> the binder matrix.  Depending on the condition of the tape, it is possible
> for sufficient oligomer residue to be absorbed into the tape ( and off of
> the surface) to make the tape playable without significant cross-linking to
> occur at all.  If the tape is badly enough hydrolyzed, however, the matrix
> cannot absorb the volume of oligomer necessary to make the surface usable
> and significantly longer treatment is required to actually cause
> cross-linking.
>
> As for whether cold/dry storage has any effect on sticky-shed, we have taken
> tapes with sticky-shed that would not play, placed them in cool/dry storage
> for extended times and were later able to play the tapes without any other
> treatment.  We have done this numerous time so the test is repeatable.  The
> key is more the issue of dry than of cool.  Once again, following the
> chemistry of hydrolysis, water is removed from the tapes due to the long
> exposure to dry conditions and the volume of free oligomers is reduced.
> That said, the environment we put the tapes in was very dry (20% RH and 60
> degrees Fahrenheit).
>
> All that said, hydrolysis of the polyester binder is not the only decay
> vector identified in/on magnetic tape.  Laboratory testing has identified a
> number of other decay residues.  Among these are cyclic tri-mers from the
> polyester base, sodium or calcium impurities from the magnetic powder,
> various fatty acids or stearates from the lubricant and surfactants left
> over from the manufacturing process. Further testing has shown that "baking"
> does not seem to have a positive or "corrective" effect on these other
> residues.  In some testing, "baking" has made the surface effects of a few
> of these other residues worse.
>
> As for Tom indicating that getting the "recipes" for the different tape
> binders likely being a "dead end", I would have to agree.  I had a somewhat
> unique relationship with some manufacturers' R&D departments- we shared data
> that was not, otherwise, available.  From correspondence and personal
> contact, I know that, in at least some instances, the information on the
> "recipes" no longer exist.
>
>
> Peter Brothers
> SPECS BROS., LLC
> 973-777-5055
> [log in to unmask]
> Audio and video restoration and re-mastering since 1983
>
>
>
>
>
> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of Tom Fine
> Sent: Tuesday, December 22, 2015 7:12 PM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated
> tape
>
> I was hoping for more input from the tape-degradation experts on the list. I
> know Richardson's treatment is very controversial with some people. I was
> _very_ skeptical, which is why I asked him to treat that test tape for me.
> To be honest, I'm pleasantly surprised that it's still not sticky.
> I'm not ready to say, I believe all his claims, but I am ready to say that
> more independent scientific testing should be done, especially given that
> it's been tested and shown (by Goran
> Finberg) and heard (by me and others) that baking, at some point, causes
> audio degradation. That, too, should be tested in a more scientific manner.
> I'd like to know WHY the AM distortion increases, heard by me and others as
> a "fuzzing out" of the sound quality. My theory -- totally a theory since I
> don't have a powerful microscope or other tools to study it -- is the
> surface of the tape gets less smooth from baking, and there's a tape-to-head
> contact issue or a sort of scrape-flutter is being caused by less-smooth
> tape rubbing against the face of a stationary head. We also need more
> scientific testing on whether cold/dry storage has any preventative effect
> on sticky-shed. Perhaps the ARSC board could consider research grants, maybe
> working with AES and NARAS and perhaps the government? One avenue I think is
> a dead end, which has had plenty of talk and speculation over the years, is
> ever getting any reliable documentation on "the recipes" used to make the
> sticky-shed tapes -- or even knowing for sure if "the recipes" varied over
> time during the sticky-shed era.
>
> -- Tom Fine
>
> 

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