Tips to store paint once it is opened!

[var10]

Hi Everyone,

We use aerospace grade paint(2 part) and primer (2 part). Some times the batch sizes are really small that the paint and primer is not completely utilised. According to the supplier we cannot use the cans after 8-10 hours of opening. Fair enough because you have oxygen entering the can. I was thinking of filling the can with nitrogen and close it (hopefully the can is not damaged) and store it at recommended temperature. Does any one have any better suggestions to preserve and reuse the paint.

Thanks for any help, its much appreciated.

V.

 

[Compositepro]

It really helps to know the basic chemistry of the paint to answer your question. 2-part epoxy should not be so sensitive. I guess that you have a urethane paint. The components of urethane paints react with moisture and will go bad. One part urethanes are moisture curing. I use these, in small quantity as well, and buy pint cans to minimize the amount of times they are opened before they are consumed. The 8-10 hours after opening must be based on the assumption that the can remains open during this time.
I suggest that you open the can only long enough to transfer out what you need. There are cans of nitrogen or argon that a sold specifically for purging air out of cans to preserve the contents. I've considered using readily available freeze spray which is R-134 but I not sure how nonreactive that is. I store cans in a freezer, opened or not, as cold will slow down all reactions. Some paints may not tolerate freezing.
Alkyd paints cure by reacting with oxygen in the air. There are anti-skinning agents that are ingredients of these paints, which are also available as preservatives, where you add a drop or two to the can before resealing it. This prevents the paint from forming a cured skin on the surface of the paint remaining in the can.

 

[moltenmetal]

Don't know what your paint system is so can't comment, other than to say that most paint system people don't recommend partial use of their 2 part kits either- as if you always need a gallon or 2 gallons of paint at a go. We ignore those instructions frequently for 2 part epoxy and 2 part polysiloxane systems, and as long as you do the measurement of the partial quantities accurately there are no problems.

Oxygen-cured systems such as alkyds (drying oils) are frequently stored under N2 or argon- argon being more effective because it's denser than air.

 

[var10]

The smallest they come is in 4 litre cans. Paint PPG - CA - 8200 Urethane Top coat and Primer PPG - CA - 7233. Compositepro can you please give more information on nitrogen cans for purging. Did a search but it returns with nitrogen cylinders. How do you suck the oxygen out of the container even if I was to use nitrogen or argon?

 

[Compositepro]

http://www.innate.com/Supplies/Bloxygen.htm.

 

[var10]

Thank you Compositepro. Have you used this before? I have a nitrogen cylinder here, wondering because they don't tell you what gas the paint saver can has got (obviously!). If it was just any inert gas I could use nitrogen I have.

 

[IRstuff]

"How do you suck the oxygen out of the container even if I was to use nitrogen or argon?"

You don't; you displace the gas in the paint can with the gas you dispense from the dispenser. Assuming that their sales pitch isn't totally bogus, a heavy, inert gas would tend to settle into the paint can and push out other, lighter, gases.

This comment:

http://homefixated.com/keep-paint-and-stains-fresh/#comment-13978

might also be feasible.

TTFN
faq731-376

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[Compositepro]

Nitrogen would work best if you already have it. Argon has the advantage of higher density so it will displace air more efficiently. Conduct the purge process in a plastic bag to keep air from getting back into the can before you can seal it. I've not yet found it necessary to do a purge for my applications. Freezer storage has worked great for items I work with. It is more important to purge when you have sensitive materials in large containers with a large head space. It is not very difficult to make an inflatable "glove box" for a clear plastic bag.

http://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Aldrich/Bulletin/al_techbull_al211.pdf

If you must buy in gallon cans and cannot find another supplier for smaller cans then repackage the paint yourself into smaller cans the first time you open the gallon can. But, repackaging is troublesome. That's why many companies have a business model based on buying drums and selling small cans at a huge mark-up.

 

[var10]

Thanks heaps guys. I will experiment it and will let you know of the result.

 

[moltenmetal]

Do be careful- some polyurethanes contain free isocyanates which are sensitizers (causing what amounts to a potentially lethal allergic reaction in certain people). They require very special handling (supplied air rather than merely respirators etc.) Most of those materials have gone by the wayside in favour of the prereacted isocyanate forumulations which are much safer.

Note also that the isocyanates are moisture rather than oxygen-sensitive. What you don't want to do is to entrain a bunch of moist air in with your dry nitrogen or argon or you'll be doing more harm than good. You need to introduce it slowly and flow just enough to displace the air completely before replacing the lid, assuming that these materials are stored in metal cans with press-fit lids. Transferring the contents to other containers for storage is likely to do more harm than good.

 

[Compositepro]

The other containers should be new paint cans not empty mayonnaise jars.

 

[var10]

Molten metal - I had a look at the msds for my 2 part ppg 8200 series paint and 7233 primer. The chemical composition of the urethane components do not contain any form of cyanate and the other ingredients are not mentioned because they are not dangerous according to the local authority. I also did find that urethane paint contains isocyanate and could be very toxic. My question for you is - can there be urethane paint made without cyanate ? the paint is also never handled in moist environment and yet they form a layer of skin, so I think they are also oxygen sensitive.

Paint msds:

https://buyat.ppg.com/ehsdocumentma...D9=0&FolderID10=0&SearchAllPublicFolders=True

Primer msds:

https://buyat.ppg.com/ehsdocumentma...D9=0&FolderID10=0&SearchAllPublicFolders=True

 

[moltenmetal]

There are polyurethane resins dissolved in solvent or emulsified with water, with a curing mechanism other than isocyanate-alcohol or isocyanate-amine crosslinking. An example is the polyurethane varnishes popular with woodworkers as more durable alternatives to the old alkyds (drying oils). These materials are low in toxicity and also low in physical durability and chemical resistance relative to industrial coatings.

There are polyurethane formulations which involve pre-reacted isocyanates, i.e. short polymers of isocyanate and polyol with live isocyanate functionality available to form crosslinks. These materials are very durable and hazardous than the old formulations which had free isocyanates like TDI or HMDI etc., but they do still contain reactive isocyanate functionality.

There are likely many others.

You'll notice that your MSDS does contain the language related to respiratory distress, sensitization etc. even for the base material which should contain no isocyanate. I suggest you speak with PPG's applications staff and find out what you're really working with.

 

[var10]

Do be careful- some polyurethanes contain free isocyanates which are sensitizers (causing what amounts to a potentially lethal allergic reaction in certain people). They require very special handling (supplied air rather than merely respirators etc.) Most of those materials have gone by the wayside in favour of the prereacted isocyanate forumulations which are much safer.

.

Argon and nitrogen are inert gasses, so how and why do you think they may react? I noticed that you didn't use the word react, so may be previous question is irrelevant? But how will they be harmful if there was no reaction?