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aboard_epsilon
08-19-2009, 12:15 PM
2k polyurethane

and 2k acrylic ..

are they one and the same ..

i cant seem to find out on the net ..as some sites people say acrylic-polyurethane :confused:

if they are not the same ..which is Superior .

and all the car paint shops around here seam to be selling low VOC stuff ..is this stuff not as good ?


and all 2k paints sold by them are called acrylic ..not poly anymore
all the best.markj

motomoron
08-19-2009, 12:53 PM
2K acrylics (like PPG Omni AE and the old and I believe no-longer made PPG Delstar) are a 3 component system consisting of an acrylic enamel, a temperature-specific reducer, and a urethane hardener. It's not mother's milk by any stretch but an organic vapor respirator is considered adequate protection.

2K urethanes generally consist of a basecoat and clearcoat. The base is a single component air-curing material while the clear is a urethane based material with a urethane catalyst/hardener.

Urethanes are a source of isocyanates which are a particularly nasty neurotoxin, and supplied air is the only accepted method for working around these.

I've done it outdoors a couple times w/ a respirator, but felt "funny" afterwards. Never again.

aboard_epsilon
08-19-2009, 01:21 PM
2K urethanes generally consist of a basecoat and clearcoat. The base is a single component air-curing material while the clear is a urethane based material with a urethane catalyst/hardener.

yes that i can understand ..as regards metallic paints.

but I'm sure i was supplied in the past with 2k non metallic paint that required no clear coat.

another question ..
if a car was painted with in the past the above 2k non metallic, can it be overcoated after keying, with acrylic ..

cause Ive just been doing this and the adhesion of acrylic to the brand new old style poly stuff is not good...this is garage door hinges ..
first sprayed with 1k etch (all i can get )......then 2k poly..non metallic finish ...then two days later sprayed with 2k acrylic.

i need to paint my car and I'm now worried that the crappy acrylic stuff will peal off in a couple of years time

all the best.markj

lazlo
08-19-2009, 01:45 PM
Urethanes are a source of isocyanates which are a particularly nasty neurotoxin, and supplied air is the only accepted method for working around these.

The 3M organic vapor filters are specifically rated for Isocyanates. The reason the manufacturers tend to recommend fresh-air systems is because Isocyanates are odorless, so there's no straight-forward way to determine if the vapor filter is still good.

But the Isocyanate urethanes have some of the nastiest smelling reducers known to man (like MEK), so I just use a fresh filter, and make sure I can't smell the MEK.

This is from an old post of mine. I'm still as "normal" as I ever was ;)

http://bbs.homeshopmachinist.net/showpost.php?p=236113&postcount=12


I paint my machine tools with Sherwin-Williams Polane, a urethane enamel. This is a 2-part isocyanate catalzed enamel. I use the 3M 7192 Organic Vapor Half Facepiece Respirator, which is specifically rated for 30 hours of exposure to Isocyanates:

http://www.autobodydepot.net/images/MMM7192.JPG

3M 7192 Organic Vapor Respirator (http://www.sjdiscounttools.com/3m7192.html)

You might recognize that this is the respirator that all the painters use on the Biker Build-off Shows.

Isocyanates have no smell, so you don't have a direct warning that the charcol in the filter has expired, but if you can smell anything, especially the solvent, you're past due. The masks are really cheap -- around $17 on-line, so I use the mask for around 10 hours (1/3 of it's isocyanate rating) and throw it away.

If you search on the 3M web page, they have several scientific white papers describing the isocyanate exposure ratings on the 7192 face mask.

This article from Steve Wieczorek, the Senior Engineer for Finishes, Materials and Processes at Sikorsky Aircraft, recommends an earlier model of the same mask for isocyanate-based finishes:

http://www.seqair.com/skunkworks/Tools/Respirators/Respirators.html

...and here is an OSHA-sponsored paper by Dow Chemical. "MDI" is diphenyl methane-4,4'-diisocyanate -- the isocyanate used in polyurethane catalyzers:

Evaluation of the Effectiveness of Air-Purifying Respirator Cartridges in Removing MDI Aerosols from Air (http://www.osha.gov/SLTC/isocyanates/mdi/mdi.html)

lazlo
08-19-2009, 01:49 PM
if a car was painted with in the past the above 2k non metallic, can it be overcoated after keying, with acrylic...

Yes, but the urethane is hard as glass after it's fully cured (48 hours). If you're going to overcoat, you need ~ 400 grit scratches for a sound mechanical bond. I just go over it lightly with some 400 grit on a soft backing pad -- enough to knock-off the gloss.

That's described in the Polane application notes, by the way...

John Stevenson
08-19-2009, 01:52 PM
i need to paint my car and I'm now worried that the crappy acrylic stuff will peal off in a couple of years time

all the best.markj

Don't worry the car will rust away in 23 months.

.

aboard_epsilon
08-19-2009, 01:54 PM
yes im using the 3m mask 4000 series one

they aint cheap here... at 20

all the best.markj