Sciencemadness Discussion Board

Expensive bottle cap's and their resistant liners

RogueRose - 15-9-2018 at 10:33

I recently got a case of 8oz amber boston rounds for a STEAL (the shipping from some buyers was 2x the price of my case and my shipping was free! - ok enough bragging..)

So the caps are phenolic black with a rubber liner. The liner is .045" thick or 1/21" or ~1.14mm IDK what this is in mils.

I'd like to have PTFE instead of rubber, or some other more resistant liner. I was wondering if some of you could suggest food liner material that I could insert either on top of the rubber lining or replace the rubber liner with. I've pulled the rubber our of one cap and it is easy to replace.

I've found some .04" PTFE sheets and with non-optimal spacing I should be able to get 210-225 caps and with optimal about 300-315 in a 1ft^2 sheet, which is very affordable, I would just need to have a punch made which I already found someone who can do this for a great price - and I figured I might look at different cap sizes that are popular and get some punches made for them.

One of the biggest is the GL45 (also the GL25, Gl35) reagent bottle caps. The PTFE caps can sell for up to $30 a piece on ebay by thieves and like $60-150 for a case of 12 or 20, but I think these are solid PTFE caps, not lined. I'm working with an injection molding company about getting priced for these and they seem very interested and always looking for new products to make in down time, so these may be a possibility!

So I was thinking of making some PTFE liners for these in the meantime, so we can use the normal PP or PE caps and put a PTFE disc on the top of the cap. Can anyone see any issues with this?

I was thinking that maybe using a thin layer of PTFE, like .015 (1/3 what my rubber liner is) and then have a rubber liner behind it at a thickness of .03-.05" (depending on bottle/cap type), so the rubber is attached to the cap, then the PTFE on top of the rubber. This way when it is screwed on the rubber is compressed along with the PTFE seal/chemical resistance. I don't think PTFE compresses much at all so I'm not crazy about using hat alone in replacement of the rubber.

In fact, I may just add a thin PTFE disc on top of my rubber liner already in place (IDK if there is any glue that would bind these two together) again I'm talking thin, like .005-.012" - IDK how thick it has to be to be effective, some testing will be needed.

Does anyone think that once the PTFE liner is pressed to the top of the glass spout and sealed/screwed tightly, that gasses would escape and attack the cap material - thus why some caps are made of all PTFE?

Now I'm not suggesting that his is a replacement for an all PTFE cap, just an alternative for some products that have a crappy liner already.

Can anyone suggest other materials besides PTFE that may be useful with this as well as any other injection molded products which could be useful or popular?



Dr.Bob - 15-9-2018 at 11:05

There are already PTFE cap liners for sale by some company, I have seen bags of them over time. Might be cheaper to buy them than make, but just depends on your costs.

Hot melt glue may work to hold the liner in, but does not always hold. Liners help a lot, but can leak some, it is not a yes or no issue, but what likelihood of leaking you can handle. For most chemicals it is not a major risk, but some like bromine will eventually destroy almost any cap material. Even fluoropolymers can swell or distort (causing leaks) rather than fail or dissolve.

GL45 red caps are not solid Teflon, at least I have never seen them. Solid Teflon is quite weak. Most chemical resistant ones are a hard plastic with a softer PTFE liner. I sell pretty good ones for $2, I don't think you can make them cheaper than that, but good luck.


RogueRose - 15-9-2018 at 12:46

thanks for the info. I'll check out the liners, I do think I saw some being sold in packs of like 100 but the price was way higher than the sheet of PTFE, but they are ready to go, so may def be worth it. $11.33 for a sq ft of .04" PTFE sheet isn't bad, especially if it gets 200-300 liners, that's about 4-6 cents each.

Here is a good page that talks about all the different types of liners. It says that the rubber backed PTFE are just about the best b/c they are autoclaveable. IDK if the PTFE is bonded to the rubber as in molecularly or if it is an adhesive.


https://www.zoro.com/qorpak-disc-38-430mm-ptfe-narrow-white-...

Now this place has the right kind of pricing, well at least better at about $.09 each - in 1,000 packs.
https://www.usplastic.com/catalog/item.aspx?itemid=23488&...

Deathunter88 - 15-9-2018 at 12:50

Quote: Originally posted by Dr.Bob  
There are already PTFE cap liners for sale by some company, I have seen bags of them over time. Might be cheaper to buy them than make, but just depends on your costs.

Hot melt glue may work to hold the liner in, but does not always hold. Liners help a lot, but can leak some, it is not a yes or no issue, but what likelihood of leaking you can handle. For most chemicals it is not a major risk, but some like bromine will eventually destroy almost any cap material. Even fluoropolymers can swell or distort (causing leaks) rather than fail or dissolve.

GL45 red caps are not solid Teflon, at least I have never seen them. Solid Teflon is quite weak. Most chemical resistant ones are a hard plastic with a softer PTFE liner. I sell pretty good ones for $2, I don't think you can make them cheaper than that, but good luck.




You're right, solid PTFE caps are white, not red. An example:
https://item.taobao.com/item.htm?spm=a230r.1.14.145.2c6e6399...

monolithic - 15-9-2018 at 12:59

Great find. Saved for later.

RogueRose - 15-9-2018 at 14:41

Quote: Originally posted by Deathunter88  
Quote: Originally posted by Dr.Bob  
There are already PTFE cap liners for sale by some company, I have seen bags of them over time. Might be cheaper to buy them than make, but just depends on your costs.

Hot melt glue may work to hold the liner in, but does not always hold. Liners help a lot, but can leak some, it is not a yes or no issue, but what likelihood of leaking you can handle. For most chemicals it is not a major risk, but some like bromine will eventually destroy almost any cap material. Even fluoropolymers can swell or distort (causing leaks) rather than fail or dissolve.

GL45 red caps are not solid Teflon, at least I have never seen them. Solid Teflon is quite weak. Most chemical resistant ones are a hard plastic with a softer PTFE liner. I sell pretty good ones for $2, I don't think you can make them cheaper than that, but good luck.




You're right, solid PTFE caps are white, not red. An example:
https://item.taobao.com/item.htm?spm=a230r.1.14.145.2c6e6399...


Any suggestions on how to use the site? The translate option leaves a lot to be desired. I tried signing up for an account but it was impossible as only some was translated and some I think was mistranslated..

Herr Haber - 17-9-2018 at 03:46

Duran Blue caps: PP & conical seal --> You cant put a liner
Duran Red caps: Dunno what they are made off but come with a thick PTFE liner
Duran Premier: fluoropolymer + conical seal. My choice for everything really corrosive and that builds up pressure. Expensive as hell (12-15 Eur if memory serves).

There's no reason why your idea wouldnt work.
If your seal leaks you may end up with a destroyed cap and the seal intact. I'd listen to Dr Bob if I was on a budget though, perfectly cutting your liner is going to be a pain.

greenlight - 17-9-2018 at 08:30

@Herr haber,
Where do you get these Duran premier caps? Is there an online source?

My 70% nitric whiten's the blue GL45 caps on my reagent bottles over time and is obviously not doing them any good. They show no other signs of deteriation though.

Herr Haber - 18-9-2018 at 02:54

@Greenlight:

Yeah, I believe you. Those blue caps are not good for much. Or not for long !
I used the red ones for HNO3. As long as you remove the pouring ring there should be no problem. I once placed a pouring ring that had a small barb facing the liner. That allowed enough vapors to attack the cap and discolour it. The liner was intact though...

I got my Duran Premier caps from a supplier that had a large enough catalogue of Duran items. I just had to make a few calls to find one willing to order some but that was a long time ago when those caps were novelty. Cant remember which supplier it was but being close to Germany definitely helps find Schott Duran stuff.

I vent some bottles every now and then so I can replace a cap if needed but those Premier caps have not changed for over a year now.

greenlight - 18-9-2018 at 07:50

Thanks herr haber, I might remove those pouring rings.

I can't find the premier caps anywhere online but I did find replacement blue ones so maybe will have to just replace them when they get really deteriorated.

Those premier caps you have sound like they are worth holding onto if you find them:)

Dr.Bob - 19-9-2018 at 17:06

If anyone is looking for smaller bottles, I found two more cases of 60 ml Boston rounds from Qorpak, one in each amber and clear, which have the really good green PTFE lined caps. They are only $2 each or 3 for $5, even less in bulk. I also still have some 120 ml amber and clear bottles (even some plastic coated ones), also with the really good green PTFE lined caps, they are from $2-3 each, less in bulk.

I don't have much in larger bottles but have been looking out for any good deals for group purchases. I got some of the above bottles for a few people who wanted some, and bought about half of them. I even did a couple of deals where I gave people an entire medium flat rate Priority Mail box of various bottles for $50 total, which can be customized.