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Silicone Sacs: Are They Really Silicone?


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46 replies to this topic

#1 Vintagepens

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Posted 02 May 2012 - 15:49

A friend has been testing various pen materials, and to my surprise reported that the sacs commonly sold as silicone aren't -- that they are instead some sort of plastic. I did a flame test myself, and sure enough, the sample melted and burned. If there was any silicone in it, there wasn't much.

My stock of silicone sacs was purchased some time ago, so I'd very much like to hear what the results are for more recent production. But the sac I tested was definitely sold as silicone, not as a silicone-containing plastic, which is what it actually appears to have been.

This was a real shock, and opens up the question whether these "silicone" sacs are indeed any better than conventional latex sacs in preventing discoloration of vintage celluloid pens. Silicone is known to be highly nonreactive, but if 90% of these sacs consists of some other plastics, who knows how they will behave as they age?

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#2 777

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Posted 02 May 2012 - 16:43

A very good point David.

I always guessed they weren't fully silicone. They just don't feel or look like it to me. I have some more recent ones, purchased just a month or so ago. Would you like me to send you one for testing? I'm very curious to know about the chemical composition of these, if it's possible to find out.

It definitely gets me thinking - how much better are these plastic/silicone sacs. has anyone actually seen a pen prone to discoloration, that's had one in it for 50 years?

Interesting stuff. Thanks for sharing with us.

Need a pen repaired or a nib re-ground? I'd love to help you out.


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#3 algabatz

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Posted 02 May 2012 - 17:15

Very interesting indeed. Do you know how many manufacturers there are of pen sacs? I thought everything came from the pen sac company and was only re-sold?/Tony

#4 hari317

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Posted 02 May 2012 - 18:12

I am curious, have you determined what the rest of the 90% is made of? PVC?
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#5 eckiethump

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Posted 02 May 2012 - 18:41

Very interesting indeed. Do you know how many manufacturers there are of pen sacs? I thought everything came from the pen sac company and was only re-sold?/Tony


As far as I am aware Martin at Woodbin makes his own latex sacs and silicon ones, Pen Sac Co. don't advertise for sale any silicon sacs. There is a bit of difference in the two companies latex sacs, particularly the vacumatic diaphragms.

On topic, IIRC it is thought to be the out gassing of the sulphur content in latex sacs that causes the discolouration problem in celluloid, possibly the sacs referred to as silicon do not use sulphur in their formulation, so considered safe ?

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#6 Ron Z

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Posted 02 May 2012 - 21:33

Interesting information. Some have expressed concern over the acids that are released as silicone cures, and that are released for some time, so the fact that they may not be silicone may actually be a plus.

There are some applications though where I do and will use these sacs whether silicone or some other material. They do stand up to ink and last longer than latex sacs. I use them where red ink is the owners favorite color, in 51 and VP fillers, and in other areas where clear sacs or ink resistant qualities are desired.

Given the testing, why not contact Martin and ask?

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#7 Vintagepens

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Posted 03 May 2012 - 13:02

I certainly will, Ron, but am scrambling at the moment to get ready for the Chicago show.

The acid bloom that can form on the surface of peroxide-cured silicones can be removed by baking the items after curing. Though I think there may be some confusion here between silicone rubber and silicone sealants, the latter being the ones that really put out loads of acid, and which do have an extended curing period.

The problem with the sacs not being 100% silicone is that whatever plastic(s) make up the bulk of the mix, they are almost surely going to be far more problematical than either silicone or conventional latex rubber. That would be very much the case if there is any PVC incorporated. While PVC holds up very well as a sac material, it leaches plasticizer at a tremendous rate, and is well-known to react badly with celluloid if allowed in direct contact. It also dumps hydrochloric acid as it ages.

#8 Buzz J

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Posted 03 May 2012 - 21:58

I sent a link to this thread to Martin.
John
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#9 Ron Z

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Posted 03 May 2012 - 22:52

Interesting. I have a number of my own pens in which I've installed the "silicone" sacs, some in use for about 10 years now. No sign of them causing damage to the celluloid. I will be checking.

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#10 gweddig

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Posted 04 May 2012 - 01:50

I have a load of them coming in a week if anyone needs sample material. I hope Martin will chime in.

#11 Vintagepens

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Posted 09 May 2012 - 23:18

I've been testing some thin-wall silicone tubing for comparison purposes. When heated, the results are dramatically different from what I get with the "silicone" sac samples. Might post some videos to illustrate.

#12 algabatz

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Posted 10 May 2012 - 07:36

I got an email from Martin. He says that the sacs are made for him specifically and that they are ordered as injection molded industrial silicone, but that he doesn't have the specific formula for the silicone.
He tells me that silicone injection machines uses two liquids mixed at the point of injection and that plastic molding machines use plastic granules and hence the two are not the same. He has never had any complaints about the sacs.


/T

#13 Garageboy

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Posted 14 May 2012 - 18:36

I'm real curious if the material used in Parker 51 fillers is PVC or not. If yes, should I keep my un sacced pristine green Sheaffer Jade in the same box as one.

#14 Ron Z

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Posted 14 May 2012 - 20:47

Plyglass sacs in the 51 are not PVC.

Just a comment. I've been routinely using Martin's silicone sacs in celluloid pens, including many of my own, for many years without any hint of reaction to the sac material.

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#15 Vintagepens

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Posted 15 May 2012 - 01:26

Sorry, Ron, but Parker's "Pliglass" 51 sacs most certainly are PVC -- it is clearly specified in Parker documents, including patent applications.

As PVC ages, it does outgas plasticizer -- but if it's an old sac, I'd think the amount being outgassed would not be large enough for concern. And as far as I can tell, the real danger with PVC sacs is leaving them in direct contact with plastic pen parts.

#16 Garageboy

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Posted 15 May 2012 - 16:31

Cool, I assumed it was a PVC variant from the smell
Now I wish there was a way to get new PVC sacs to replace the dark/punctured sacs

#17 Vintagepens

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Posted 15 May 2012 - 17:13

We (American Art Plastics) will have newly-made repro 51 sacs available in about a week's time.

#18 Vintagepens

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Posted 11 January 2013 - 18:10

Fast forward update:

The reproduction Parker 51 sacs came in on schedule and turned out great.

After finding out that the sacs we thought were silicone really weren't, and after looking unsuccessfully for anyone selling sacs that really were silicone, Mark and I decided to start manufacture of genuine 100% silicone sacs. The first size is #18, and the sacs are everything we'd hoped for. We will be having more sizes coming in within the next couple of months.

It took a while, but I also finally put together that video of the test results (the "silicone" sacs that everyone's been using for the past several years are definitely PVC instead): Silicone pen sacs: identification and testing

If anyone wants to carry out tests of their own, I still have a lot of silicone tubing and would happily send along snippets to anyone who wants one -- just send me a self-address stamped envelope and it's yours. Conversely, if you have a sac that you are convinced is silicone and want it tested, feel free to send it to me and I'll report the results.

best

David

#19 Seville

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Posted 12 January 2013 - 23:47

I am a bit confused. Are you saying that the silicone sacs from Woodbin are actually PVC or not really silicone?

Philip




Fast forward update:

The reproduction Parker 51 sacs came in on schedule and turned out great.

After finding out that the sacs we thought were silicone really weren't, and after looking unsuccessfully for anyone selling sacs that really were silicone, Mark and I decided to start manufacture of genuine 100% silicone sacs. The first size is #18, and the sacs are everything we'd hoped for. We will be having more sizes coming in within the next couple of months.

It took a while, but I also finally put together that video of the test results (the "silicone" sacs that everyone's been using for the past several years are definitely PVC instead): Silicone pen sacs: identification and testing

If anyone wants to carry out tests of their own, I still have a lot of silicone tubing and would happily send along snippets to anyone who wants one -- just send me a self-address stamped envelope and it's yours. Conversely, if you have a sac that you are convinced is silicone and want it tested, feel free to send it to me and I'll report the results.

best

David


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#20 raging.dragon

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Posted 13 January 2013 - 07:47

Is there any evidence that the non-silicone sacs are made from heavily plasticized PVC and not one of the many other elastomers (synthetic rubbers) on the market?

I am a bit confused. Are you saying that the silicone sacs from Woodbin are actually PVC or not really silicone?

Philip


Do you have any Woodbin sacs, or better yet scraps from trimmed sacs, on hand to test?






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