Re: A PVA for printing "gum"

From: Katharine Thayer ^lt;kthayer@pacifier.com>
Date: 03/29/06-12:12:52 PM Z
Message-id: <5E7065D3-748F-4ADC-B1B3-0E8169AB2BF6@pacifier.com>

P.S. Then I looked at the research studies I have on dichromated
PVA, and the PVAs specified are all over the map as far as degree of
hydrolysis.. One study specifies PVA of "86.5-89% saponification,
mean degree of polymerization 1400). Another specifies "PVA of
11-31000, 98% hydrolyzed." Another , "PVA, 98% hydrolyzed, Mw
16000". Another says that the PVA used in most of the experiments
described in the paper was Gelvatol 20-30, "which contained 20 mole-%
residual acetate groups" but some of the experiments used Gelvatol
1-90 "containing 1 mole-% residual acetate." FWIW.
kt

On Mar 29, 2006, at 8:53 AM, Katharine Thayer wrote:

>
> On Mar 29, 2006, at 12:08 AM, TERRYAKING@aol.com wrote:
>
>
>>
>>
>> Katherine and Ryuji are off on a side track.
>>
>> .Specific gravity is a guide to whether the material will help us
>> to make gum prints. If it is too light , or thin, highlights are
>> likely to be contaminated. If it is heavy, the mixture will not,
>> among other things, coat properly.
>>
>> The criterion here is whether the material will do the job we
>> demand of it.
>>
>> Simple tests with commonly available PVAs will show us.
>>
>
>
> I don't usually see Terry's posts, but I was looking for something
> from Netflix and wondered if it had got into the junk folder, as
> things from Netflix sometimes do. (Terry's posts go to the junk
> folder, as I've explained before, because my mail program
> automatically puts anything that comes from aol into the junk
> folder, unless I tell it differently, it came that way, and in this
> case for reasons of my own I haven't chosen to override the logic
> of the software).
>
> Having seen this one, I'll say this: You can do "simple tests with
> commonly available PVAs" if you like, but if you don't know where
> the particular PVA you're testing falls on the various parameters
> Ryuji listed, you won't know why that particular PVA works, and why
> someone using a different PVA may get an entirely different result.
> I'm not sure you've grasped that the different PVAs vary not only
> on viscosity but on a number of other variables, as Ryuji spelled out.
>
> Then I remembered that in my correspondence with Mike Ware, I told
> him that I needed to know a good PVA to use for some work a chemist
> was undertaking for me (he got started with that and then got
> diverted to his real work and I haven't heard from him for more
> than a year) Mike told me that a graduate student of his had
> worked out a good PVA for printing. I pulled out the folder and
> found the information, and also found that not only had Dr. Ware
> given me specific permission to share this information, but had
> specified exactly how he wanted it cited. So here it is:
>
> He said that they settled on was a "polyvinyl alcohol-acetate; i.e.
> only partially hydrolysed co-polymer, which is much more easily
> dissolved in water than the pure alcohol. We found an 88%
> hydrolysed PVA, with an RMM around 25 kD in 20% w/v solution, to
> offer the best all-around results-- comparable to a 14 Baume Gum."
>
> "If you make any public use of this information in the future,
> please acknowledge the original experimenter, by citing:
>
> Stephen Beckett, M. Phil. Thesis, University of Derby (UK),
> November 1993. (A private communication from Mike Ware)."
>
> So there it is.
> Katharine
>
>
>
Received on Wed Mar 29 12:13:35 2006

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