CARC no worse than automotive polyurethane paint?

[McGuyver]

THe following is an exerpt from TM 43-0139 "PAINTING INSTRUCTIONS FOR ARMY MATERIEL"



2-31. CHEMICAL AGENT RESISTANT COATINGS (CARC)



a. General. Chemical Agents pose a devastating threat to sustained readiness in a combat environment. CARC paints were developed to minimize the impact of this threat. CARC paints are relatively impermeable coatings which do
not absorb/desorb chemical agents, and which do not break down when decontaminated.

(1) A common misconception is that CARC paints present greater health/ safety/ environmental hazards than do other paints. In fact, the health and safety requirements for CARC are the same as those for all paints. And, although CARC paints are currently more expensive and require additional care in application, their durability make overall life cycle costs/efforts less than those of other paint systems.

(2) There are currently three CARC paints:
(a) MIL-C-46168 a two-component aliphatic polyurethane used on exterior surfaces and those interior surfaces frequently exposed (eg, ramps, hatches).
(b) MIL-C-53039 a single component aliphatic polyurethane used wherever MIL-C-46168 may be used.
(c) MIL-C-22750 a two-component epoxy polyamide enamel used only on interior surfaces.



b. Coating, Aliphatic Polyurethane, Chemical Agent Resistant (MIL-C-4616 Two-Component.

(1) Characteristics. This specification covers both camouflage and non-camouflage color chemical agent resistant aliphatic polyurethane coatings (CARC). CARC is designed for easy decontamination after liquid chemical agent exposure. It is available in a standard formula (Type II), and a high-solids VOC compliant formula (TYPE IV). Types II and IV are all lead and chromate free.



It appears to me that CARC paint is nothing more than a high quality automotive polyurethane paint that is no more hazardous than the Alkyd enamel that so many of us on this board are so fond of, or at most no more hazardous than comercially available automotive Polyurethane paint.

Here's another publication that talks about it:
http://www.olive-drab.com/archive/carc_paint.pdf

And another one discussing CARC paint:
http://www.gulflink.osd.mil/carc_paint_ii/carc_paint_ii_s03.htm#iii

Anyone here care to comment on this?

 

[da_sgt]

McGuyver,

First it's all in the wording,

"(1) A common misconception is that CARC paints present greater health/ safety/ environmental hazards than do other paints. In fact, the health and safety requirements for CARC are the same as those for all paints."

Since the introduction of Imron, and the likes, great care needs to be taken when using these products<img src="emoticons/icon_smile_warn.gif" alt="Warning!"> Its the things you don't know that can harm or, yes "Kill" ya <img src="emoticons/icon_smile_warn.gif" alt="Warning!"> You notice it say's "the same as those for other paints" Yes you can go to your local paint supplier and buy some Acrylic Enamel with Gloss/Hardener. But did you know its labled "Industrial Use Only" by professional, trained painters. Not for sale to or use by the general public. The main reason for caution is the isocyanates in one form or another, real killers!!<img src="emoticons/icon_smile_warn.gif" alt="Warning!"> These babys get absorbed right through your exposed skin, eyes, etc. And your Cheap Dust Mask can't filter it out <img src="emoticons/icon_smile_warn.gif" alt="Warning!"> To spray this stuff you need a fresh air mask <img src="emoticons/icon_smile_warn.gif" alt="Warning!"><img src="emoticons/icon_smile_warn.gif" alt="Warning!"> Not trying to scare anyone, cause ya'll will still go buy some paint and do it yourself, but it's the stuff you can't see, or don't know about that will get ya<img src="emoticons/icon_smile_wink.gif" alt="Wink">

 

[MV Trucker]

There was a body shop just down the street from me. John, the owner, painted my fuel delivery trucks. I went down there one day to check progress on one of my trucks that he was shooting Imron on. When I got there, he was spraying inside the hose and meter compartment and was not wearing a filter. I questioned him about that and he said that the fresh air supply hood fogged up, so he doesn't use anything. This was a common practice for him, so a couple of years later he had the shakes so bad due to damage to his nervous system he had to retire.

 

[McGuyver]

Hello guys,

thanks for the replies. So what is Imron? I don't recall reading about that here. I think you're right about the "hexamethyl diisocyanates" being the hazardous part of the paint.
So one question I have: do the alkyd enamel paints have this nasty stuff in it, or they safer to use in that respect? I by no means meant to imply that CARC doesn't present a hazard. I just thought it was interesting that for all these years, I've heard people say how dangerous CARC was, that it was especially nasty, and now I find out that there's nothing really all that special about it, that the comercial automotive Polyurethane paint is just as bad. In fact, that's all CARC paint is, an automotive polyurethane paint with a matte finish and controlls on its spectral reflectivity to reduce it's near infrared signature. It kind of took away some of the "voodo and mystery" about CARC for me to learn this. So you mentioned Acrylic Enamel paint also. How hazardous is that stuff? Do you need a fresh air ventilation suit for that too, or will a regular respirator work?

 

[rdixiemiller]

All
This is my first post, so I hope I get it right. I am a paint engineer by trade, been doing that for 20 years. All paints, no matter what type, are hazardous if you inhale enough of them. The alkyd enamels are typically reduced with aliphatic hydrocarbons, which are not great for your lungs. Have we all been exposed to these? Yes. Will we die tomorrow? Probably not. However, it is always better safe than sorry. The catalyzed paints, commonly called 2K in the industry, normally have a DiIsocyanate catalyst, which is really tough on your system. It causes nervous system damage, and causes irritation to the eyes and mucous membranes. The solvents that are normally used to reduce these materials are not great either. Methyl Normal Amyl Ketone, Xylene, Toluene, Isobutyl Acetate, and many others are not good to inhale. They also have an affinity for your liver, and can cause numerous problems down the road. The solids you can breathe in are another problem. You can give yourself a bad case of OD gren lung, or whatever color you are spraying. I like to use an air supplied respirator with any paint, but you can get away with a good, activated carbon, chemical respirator. The only thing to remember is that the cartridge will normally only be good for about 10 days to 2 weeks after you open the bag. After that, it will not remove the chemicals from the air stream.
Many times it will be cheaper to get your vehicle professionally sprayed rather than buy all the equipment yourself. You also need to watch for the local Environmental enforcement people. In quite a few locales, you cannot paint a vehicle unless you meet all kinds of regulations.
CARC is a decent grade of industrial 2K urethane. The resin package is identical to what is used on heavy equipment. If you have experience with that kind of paint, you should have no problems with CARC.
Regards
Robert Miller.
PS, I am looking for a M35A2WOW. I have always wanted to have one to use for a pick up truck.

 

[da_sgt]

rdixiemiller;

First welcome aboard<img src="emoticons/icon_smile_thumzup.gif" alt="Thumb Up"> Glad you said all that! I would have mispelled most of the compounds, and would have gotten finger cramps from all that typing<img src="emoticons/icon_smile_wink.gif" alt="Wink"> I use a "Scott" fresh air pak that I found on ebay. Thats the air pak used by firefighters. I got a great deal ($60.00), and since I have a scuba tank compressor, its pretty handy<img src="emoticons/icon_smile_wink.gif" alt="Wink"> Most times I just use the "shop" air which is a secure fresh air source as my supply line, I also use the same setup for sand blasting<img src="emoticons/icon_smile_thumzup.gif" alt="Thumb Up">

 

[MV Trucker]

As far as I know, Imron is DuPont's trade name for its automotive polyurethane finish and uses a hardner. I've read that it's similar to CARC.
That Scott Air Pak sounds like a good idea. No air line dragging around with you while painting.

 

[MV Trucker]

Oops,
>No air line dragging around with you...
Except for the line to the gun, of course.

 

[McGuyver]

rdixiemiller

Great post!! Glad to have you here, and welcome to the forum. <img src="emoticons/icon_smile_thumzup.gif" alt="Thumb Up"> I guess I know who to come to now when I have questions about paint.

So here's a few: Are the solids the part of the paint that is left over after the volatiles evaporate off? (and of course, after curing.)

When you speak of a catalysed paint, are you refering to an epoxy and resin paint that starts out as a bunch of unlinked monomers and once it cures creates cross linked polymer chains similar to a thermoset plastic? THis is my understanding of what a urethane paint is (please correct me if I'm wrong.) Could you talk about what ever differences there are between Urethanes and acrylic and alkyd enamels? Why are urethanes more durable (is is because of that cross linking of the polymer chains?) Thanks a lot for your input. <img src="emoticons/icon_smile_thumzup.gif" alt="Thumb Up">

 

[da_sgt]

OK lets keep it simple, catalysed simply means adding a catalyst. Its a two part system, paint and catalyst. Catalyst simply means adding a substance that initiates a chemical reaction which will enable the paint to proceed at lower temperatures than normal. In other words "cure", and the faster the cure, you get a harder/glossier finish. The hardner (or activator) or "catalyst" is where most of the evils are. Thats where you find the isocyanates<img src="emoticons/icon_smile_warn.gif" alt="Warning!"> You don't have to use the two part system to get good results, but I prefer to<img src="emoticons/icon_smile_wink.gif" alt="Wink">
Just a last thought...Always use some protection...Even the "Rattle Can" has enough crap to make ya ill<img src="emoticons/icon_smile_warn.gif" alt="Warning!">

 

[rdixiemiller]

OK, I will see how I do with the answers.
1) Be careful using shop air for an air supply! I have to use oil free compressors with some serious filtration and a CO monitor to supply my painters. If your compressor is passing a little oil, you can get deathly ill by getting a lung full. I would definately use air from your SCUBA compressor, it should be properly filtered. Air supplied hoods are normally $75 to $125, but if you paint a lot they are worth it. I am used to the type that has a replaceable cover.

2) You are correct about the solids. High solids paint is generally 50%+ solids weight after curing. You evaporate out the solvents and carriers and are left with the resins and pigments.
Epoxies, urethanes, and some more exotic materials are catalyzed 2 component paints. The resin will never really cure without the catalyst. The catalysts, however, will glue just about anything to anything. they are closely related to super glue. We spilled a pint of catalyst on a SS floor, it glued a 60 gallon pressure pot to the floor! It took 3 of us and a forklift to finally break everything loose! Ruined the pressure pot and buckled the floor in the process.
3) Your understanding of the chemistry is just about right, except that a thermoset material can be remelted once the temperature exceeds a certain point. An catalyzed paint would be more like a thermocure material. Once a thermocure has been at cure temp. for the required time, it is permanently set. You can heat it up way past cure temp and it remains solid. Eventually it will break down at high enough heat, but it will not re-melt.
4) The differences between urethanes and alkyd enamels/acrylics is the resin base. Most alkyds and acrylics will start cross linking when the chains get close enough together, in the presence of oxygen. The solvent keeps everything far enough apart to apply, then evaporates off. As the chains get close together, they cross link. The bonds are not as strong as a urethane. Most alkyds and acrylics can be re-dissolved in an agressive solvent, most urethanes will not.
5)The main difference between an epoxy and a urethane is UV resistance. Epoxies have phenomenal corrosion resistance, but break down under UV (sunlight) and get chalky. Urethanes are not as corrosion resistant, but have very good UV resistance.
Regards
Robert
All of you remember the blue and silver cars and trucks of the late '80's that peeled all the way to the metal when they were only a couple of years old? That was what happens when the topcoat (the blue base/clear paint) does not have enough UV inhibitors to protect the epoxy electrocoat primer. The primer broke down and the topcoat came off in sheets and strips. The vehicle then immediately started rusting. The big three learned an extremely expensive lesson about paint properties at that time.

 

[da_sgt]

rdixiemiller;

Your right about the "shop" air, if you notice I said "secure" but others might have thought they could just plug-in and be good to go. Always know what you are doing! Just wondering why do you need a CO monitor? I guess I must be out of the loop on the new regs? As a side note I was certified MSHA/OSHA respirator instructor<img src="emoticons/icon_smile_wink.gif" alt="Wink">

 

[da_sgt]

About the paint peeling and fading on the Eighty's cars.... That was a major rush job to comply with a new Federal Standard...Yes it resulted in bad paint. But not the fault of the "Big Three" which is now the big"TWO" I happen to own more than one of those poor souls. Total rush job pushed by the environmental groups that think they have a better plan <img src="emoticons/icon_smile_.gif" alt="My 2 Cents">

 

[McGuyver]

Originally posted by rdixiemiller


3) Your understanding of the chemistry is just about right, except that a thermoset material can be remelted once the temperature exceeds a certain point. An catalyzed paint would be more like a thermocure material. Once a thermocure has been at cure temp. for the required time, it is permanently set. You can heat it up way past cure temp and it remains solid. Eventually it will break down at high enough heat, but it will not re-melt.

I think you've got a thermoset polymer confused with a thermoplast polymer.
Thermoplasts have only very weak crosslinking, and therefore can be reflowed by reheating without burning the material.
A thermoset polymer is like what you called a "thermocure." Once cross linking occurs between the polymer chains, the material can not be reflowed by applying heat, this will only serve to "burn" the material by breaking down not only the crosslinking, but the polymer chains as well.
Vulcanized rubber is an example of a thermoset viscoelastic material. Phenolic is another thermoset material (although its not a viscoelastic, just a very tough "plastic")

As an aside, RTV silicone is also a viscoelastic thermoset material (Room Temperature Vulcanizing) It merely uses water vapor from the atmosphere as part of a catalyst(?) for curing at room temerature (instead of at a raised temperature like other elastomers.)
I believe cyanoacrylate (super glue) works the same way (very reactive stuff.)

As a little aside, I went to the store one day to buy some of this stuff, and I was puzzled to learn that as a matter of routine, the cashier was required to ask for picture I.D. to prove that I was over 18 yrs. old before purchasing this. I mulled this over for a while and came to the conclusion that the answer was in the name -- cyano acrylate. Rememmber the nasty stuff from the paint? isocyanate? my guess is these are probably some compounds of cyanide, which obviously is poisonous. I guess they don't want little kids buying super glue and ingesting it. <img src="emoticons/icon_smile_warn.gif" alt="Warning!">


P.S. If my memory serves me correctly, the higher the carbon loading in the material the better the U.V. resistance. I recall something about titanium dioxide giving UV resistance to some plastics as well. Does this sound right?

 

[rdixiemiller]

Although we are probably a little off topic with this...
Please forgive me if this is considered improper on this forum.
My experience with thermosets vs thermocures is only with powder coating materials. The thermosets are able to be re-flowed with heat, the thermocures are not. The military really pushed for powder coating on equipment a few years ago, trying to meet EPA mandates. They were concerned about products that could not be repaired by touching up. Thermosets can be touched up with a small powder gun, then the area can be re-flowed with a heat lamp. Obviously, this was quite attractive from a maintenance standpoint. However, the types of coatings the military needs to meet their requirements generally do not allow the use of these materials.
I used to buy military surplus camo paint at the Mountain Top flea market in Gadsden Alabama. I think I paid $3 a gallon for the stuff. I helped a friend re-paint a M-38, and we painted a few pick-ups in the process. It was an alkyd enamel, made in the late eighties by Red Spot, I believe. OD green, desert sand, brown, black, field drab (kind of a blue-green.
When did CARC become the standard coating on military vehicles?
Regards to All
Robert Miller

 

[hot rod deuce]

hey uhh how bout the torch? what happens when i hack a chunk of my truck off or weld on somthing. whats that smoke goona do to me? is that as bad as the wet paint? most of the time i set up a fan to blow it out the door or to the central suction system in the roof but you can only do so much without a hood and who wants to put that on each time you cut or even risk burning a spendy set up....just a thought and thanks for you time and all the info.

maybe i should skip the welder and use that catalyst stuff to GLUE my truck together...

 

[McGuyver]

Hello rdixiemiller,

thanks for your post, in regards to the whole thermoplast/thermoset/thermocure question, perhaps your terminology is more correct when speaking about paint. My terminology is coming from my understanding of plastics, although apparently paint and plastics share a good deal of common territory.

 

[rdixiemiller]

I hadn't considered that! Urethanes are really nasty when they burn. If you can use a sanding disk to remove the paint from the area you are going to weld you will be better off. If you are using a MIG gun, the urethane smoke will make it hard to get a good weld.
Regards
Robert