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ARSCLIST  May 2018

ARSCLIST May 2018

Subject:

Re: Issues Baking a Reel-to-Reel Audiotape

From:

lists <[log in to unmask]>

Reply-To:

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

Date:

Thu, 31 May 2018 17:20:18 -0400

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (86 lines)

Christopher:

Here is some background information and some additional information on your specific problem.

To excerpt from a post back in September (background info):

" Sticky shed is caused by binder hydrolysis.  This is ... a function of ....the interaction of water (often absorbed from humid air) with the long-chain polymers in the tape resulting in the polymers breaking down into short-chain, low-molecular-weight oligomers.
.... Many people perform short-term baking.  The issue with this is how hydrolysis affects the tape.  When hydrolysis occurs, polymers in the tape matrix as well as polymers on the tape surface are effected.  The oligomer residue created inside the tape matrix may partially migrate to the tape surface.  Heating the tape during short-term baking primarily causes some of the oligomer residue to be re-absorbed into the tape matrix leaving less on the surface and making the tape, temporarily, playable.  It has little effect on the oligomers other than their absorption into the tape and away from the surface.  As soon as the tape begins to cool, these oligomers (slowly) start to migrate back to the surface again.  This is one of the reasons that individuals who do short-term baking state that you must play back the tape as soon after baking as possible.  More sustained treatment (whether by "baking" or exposure to very low RH environments or a vacuum) actually forces cross-linking of the oligomer residue back into polymers.  As such, there is no great abundance of oligomer residue to migrate back to the surface and the tapes (so long as they are not exposed to elevated humidity) remain playable for an extended time."

Binder-base adhesion failure:

Now, the problem you seem to be having is binder-base adhesion failure.  This issue is definitely not addressed by short-term baking.  The integrity of the binder matrixes (both recording layer and backcoat layers) is dependent on chemical bonds between the polymers.  In addition, however, the bond between both the recording matrix and the backcoat matrix to the base layer is also a function of bonds between the polymers.  When hydrolysis occurs, it can not only produce "sticky" oligomers in/on the recording and backcoat layers, it can weaken the bonds between the recording and backcoat layers and the base layer.  If a hydrolyzed tape is also subjected to repeated dimensional changes due to alterations in moisture content or temperature, the weakened bonds between the layers can shear: binder-base adhesion failure.  

Short-term baking is just as likely to make this condition worse as it is to help it as it drives the sticky oligomers into the binder matrix away from both the outer surface and the binder-base interface.  Long-term baking that forces cross-linking of some oligomers back into polymers may help reform some binder-base adhesions but is not optimal as it lessens the amount of oligomer residue at the interface.  A better solution to binder-base adhesion failure is cold desiccation where the oligomers remain on the surface/interface while the forced cross-linking is occurring.  This procedure might raise the concern that oligomers on the recording surface of one tape wrap might bond with oligomers on the backcoat of the adjacent wrap.  This, however,  generally does not occur when using cold desiccation (rather than simply a vacuum) as the cold causes a dimensional contraction of the tape width resulting in a loosened tape pack.  As such, the binder-base interface is in much more intimate contact than are adjacent tape wraps and forced cross-linking will occur at the interface rather than between adjacent tape layers.

Hope this helps.


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 Banuelos, Christopher A
Sent: Friday, May 25, 2018 5:32 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] Issues Baking a Reel-to-Reel Audiotape

Hi Richard,

It's more like the back coat pulled off.

I will definitely bake at a lower temp next time and for much longer.

Thanks!

-----Original Message-----
From: Association for Recorded Sound Discussion List <[log in to unmask]> On Behalf Of Richard L. Hess
Sent: Friday, May 25, 2018 3:31 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] Issues Baking a Reel-to-Reel Audiotape

John has provided good advice. 133 °F is a wee bit high. The Ampex patent states 50 or 54 °C which is 122 or 129 °F.

I routinely bake at about 50 °C for a minimum of 24 hours for 1/4-inch tape in lots of one or two.

I baked over 100 1/2-inch Ampex 406 tapes about a decade ago and putting eight in the food dehydrator at once, I had to bake the lot for 48 hours to have them playable.

How is the shedding happening? Is it falling off, or did the back coat pull off the mag coat?

Cheers,

Richard




On 2018-05-25 3:05 PM, John Chester wrote:
> On 5/25/18 2:54 PM, Banuelos, Christopher A wrote:
> 
>> Thanks for your reply. I have a probe thermometer, but I have it just 
>> kind of sitting in there through the gap in the front door/plate 
>> thing. I have been able to maintain a temp of 133. I will adjust this 
>> down. But overnight, you say? I didn't think I was supposed to bake 
>> it that long. I will give that a shot for sure.
> 
> As tapes continue to age, the required baking time seems to be 
> increasing.  Once upon a time 12 hours was OK.  I've done a lot of 
> Ampex tape from the 1970's, and my minimum baking time is now 24 
> hours.  Reels which are in bad shape may require 48 hours.  12 hour 
> cooldown is OK, but 24 is better.
> 
> -- John Chester
> 
-- 
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.

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