Paint and Clear Coat

[DetailDan14]

I have some questions I would like someone to clear up with actual FACTS.

1. Does/ can clear coat oxidize? I have read that it cannot and or that it does not like single stage does. If clear coat cannot oxidize, or does not oxidize like single stage then is there a more proper term for the hazy/ cloudiness we see? And can anyone explain in detail what is physically happening to the paint?

2. Clear coat is the same as base coat minus color pigment? If this were true, then wouldn't clear coat be susceptible to the same oxidation as single stage?

3. Paint is porous. I've read yes, no, becomes more porous with age, water based is more porous than solvent based, etc. Anyone have any facts?

4. Modern paint has oils and can dry out. I have spoke with a few people about this and don't believe it is true at all.

5. UV protection is located near the top of the clear coat, hence the maximum recommended removal rates from Ford, GM, etc.

Thank you

[the other pc]

Re: Paint and Clear Coat

"1. Does/ can clear coat oxidize? I have read that it cannot and or that it does not like single stage does. If clear coat cannot oxidize, or does not oxidize like single stage then is there a more proper term for the hazy/ cloudiness we see? And can anyone explain in detail what is physically happening to the paint?"
Clear coat absolutely, positively does oxidize.

They can't fade like a single stage because they don't have (visible) pigments to fade. But oxidation is a much more complex chemical process than simple fading.

You'd need to ask a polymer chemist for a detailed description of photodegradation in coatings. And you'd likely get answers that sound something like this.


"2. Clear coat is the same as base coat minus color pigment?"
No. Factory clear/base coatings are designed as systems. Each has unique and complimentary characteristics. They work together and wouldn't work independently.


"If this were true, then wouldn't clear coat be susceptible to the same oxidation as single stage?"
Clear is susceptible to many of the same oxidation effects. Just not pigment photodecomposition, since there isn't any pigment. (Well, there are some tinted clears....)


"3. Paint is porous. I've read yes, no, becomes more porous with age, water based is more porous than solvent based, etc. Anyone have any facts?"
Everything is porous at a molecular level. It's not as simple as sponges with big holes vs sponges with small holes.


"4. Modern paint has oils and can dry out. I have spoke with a few people about this and don't believe it is true at all."
I don't believe it either.


"5. UV protection is located near the top of the clear coat, hence the maximum recommended removal rates from Ford, GM, etc."
I've heard that from a number of reliable sources. But I'd still like to hear the technical reasons for it. (But there's never a polymer chemist around when you need one. )



pc.

[Marc08EX]

Re: Paint and Clear Coat

For item #5, the CC is providing the UV protection so it's not just near the top of the CC but the whole CC layer itself isn't it?

[the other pc]

Re: Paint and Clear Coat

That would be the case if the UV protection came from the molecules of the clear resin itself.

But from what I've read (admittedly, not all that much) the clear resins provide relatively little UV protection by themselves and the UV protection comes mostly from a collection of additives.

If those additives tend to migrate or otherwise integrate differently toward the surface during curing they would be concentrated in the outermost region of the film.

Again, I haven't heard what the actual mechanism is.



pc

[Michael Stoops]

Re: Paint and Clear Coat

I have some questions I would like someone to clear up with actual FACTS.

1. Does/ can clear coat oxidize? I have read that it cannot and or that it does not like single stage does. If clear coat cannot oxidize, or does not oxidize like single stage then is there a more proper term for the hazy/ cloudiness we see? And can anyone explain in detail what is physically happening to the paint?

While it can, it's not as common an occurrence as you used to see with single stage lacquer paints, and it manifests itself a bit differently as well. SS lacquer has pigments in the paint that are subject to fading when exposed to UV light. There is nothing on top of it to protect from UV like a clear coat does with the color coat beneath it. So a SS paint is subject to color fade while a clear coat is not. But there's a whole lot more to it than just the fading of pigment. The chemistry of an old SS lacquer and a modern, catalysed clear coat are vastly different, so they respond very differently to almost everything; from scratching to polishing, UV resistance, chemical resistance, etc. A lot of times the hazy or cloudy appearance in a clear coat is the beginning of actual clear coat failure. Again, due to the chemical differences a clear coat can start to literally break apart or even delaminate from the color coat beneath it. You don't see that type of reaction with an old SS paint simply because the chemistry is different. And a bit part of that is the level of UV protection built into the clear coat.

2. Clear coat is the same as base coat minus color pigment? If this were true, then wouldn't clear coat be susceptible to the same oxidation as single stage?

To the first question here: Not necessarily. Yes, clear coat is indeed paint minus the pigment, but in many cases the color coats used today are water based while the clears are still solvent based. To the second question: as noted above, the chemistry of today's paint is vastly different from old SS paints. The color coat in a modern base/clear system is not at all the same as a SS paint from years ago - they didn't just start shooting clear over existing paint technology. In fact, if you were to paint a car with a current technology color coat but skipped the clear, it would never shine like a properly clear coated finish does. The gloss of a single stage paint is in the paint, essentially, and brought out through proper finish buffing of the paint. In a modern base/clear system all of the gloss and UV protection is found in the clear coat.

3. Paint is porous. I've read yes, no, becomes more porous with age, water based is more porous than solvent based, etc. Anyone have any facts?

Sure it is. But it seems people often over think this. Your skin is porous, and so is a sponge, but the level of porosity is vastly different between the two. If you put a sponge into a bucket of water and pull it out, it carries a lot of water out with it. Dunk your hand in the same bucket and you just don't get the same result. But sit in a bathtub long enough and your fingertips start looking like prunes because of the water absorbed into the pores. It's not much, but it doesn't take much to do this. Paint is a whole lot more like your skin than a sponge. As far as becoming more porous with age, it can happen if the paint suffers UV damage, dries out and becomes almost brittle. But "more porous" may not be the best way to describe it, technically, since people can't seem to get that sponge analogy out of their heads. It's not like a sponge becomes "more porous" over time - that could potentially mean that a sponge gets better at picking up water over time, and that's not really the case. But as paint ages and dries out or becomes damaged, the microscopic surface fissures can become larger and more open. To what degree, and how that impacts the appearance (if at all), will vary dramatically.

4. Modern paint has oils and can dry out. I have spoke with a few people about this and don't believe it is true at all.

Modern paint does not have oils, but it can dry out. Again though, people tend to take terms like "dry out" too literally. They think of spraying paint, which is wet when it comes out of the can, and then it dries or cures after a period of time, so it's dry. How does it get any drier than that? Try working on a neglected finish with something like M105, a compound that does not have a huge amount of lubricant in it (it was designed for use on fresh paint). That paint is described as "dry" and that dried paint will pull any moisture out of M105 very quickly and cause it to gum up on the surface. You can go over that same paint with something like M80 Speed Glaze, which is a high oil paint cleaner, and those oils will get down into the pores of the finish (more like a skin lotion gets into your skin and not at all like water gets into a sponge), making it easier to work on while increasing the gloss and color depth. By getting into the pores, admittedly to a very small degree, these oils can mask some of the damage done through exposure over time, and/or just help lubricate a product like M105 so that it can do it's job of removing surface defects more effectively and efficiently. This isn't super common - I've only experienced it first hand on two cars - but it can happen.

5. UV protection is located near the top of the clear coat, hence the maximum recommended removal rates from Ford, GM, etc.

Apparently there is some migration of the UV screeners toward the upper reaches of the clear coat. How much will vary with the formulation of the paint, how it's applied, cured, etc. And one can only assume that the amount of UV screeners present to start with will vary from one paint supplier to another. But even if the UV protection was uniform throughout the clear coat, if you were to remove half of the clear you'd remove half of the UV protection. If there is any migration of UV screeners toward the top of the clear and you remove half the clear, you've removed more than half the UV protection. Obviously there's a bit of wiggle room here as the paint isn't formulated to have just enough UV protection and no more, otherwise you'd never be able to fix anything without compromising the health of the paint. That wiggle room is the amount of repair than can be safely accomplished before you do compromise the paint. And going on the very popular assumption that clear coat is, on average, 2 mils thick and the max recommended removal is 0.5 mils, it would seem that most paint suppliers feel that 25% removal is the limit of their wiggle room.

Another thing that hasn't been brought up here is the differences between factory paint and aftermarket paint. While a good body shop can fix collision damage and paint a replaced panel so that it matches the factory finish in gloss, color and even texture of the orange peel, the paint the body uses is vastly different from the paint used in the factory. Starting with the primer, which these days in most factories involves an electrostatic full submersion bath for the body, continuing with the color coat which is also often an electrostatic deposition (though sprayed instead of dipped like the primer) and finishing with the clear coat which is then baked on at high heat for 30 to 60 minutes, the differences in chemistry between factory and aftermarket paints are huge. No body shop could afford the ovens that an OEM factory uses. Even if they could, the vinyl, rubber, plastic and leather of a fully assembled car would have a hard time surviving that curing oven. And if a body shop were to use the exact same paint that the OEM uses, it would never fully cure since they couldn't bake it long enough or hot enough. So not only is the chemistry very different between those old single stage paints, but between modern OEM and aftermarket paints as well.

[davey g-force]

Re: Paint and Clear Coat

Awesome answer Mike

Thanks!

[TOGWT]

Re: Paint and Clear Coat

[Modern paint has oils and can dry out. I have spoke with a few people about this and don't believe it is true at all.]

Modern auto paints do not contain oils, its the resin binder system that dries out, leading to structural instability.

Photo-oxidation of polymers, sometimes incorrectly described as photo degeneration, is the degradation of a polymer surface in the presence of ozone. Oxidation is the way a polymer protects the under laying paint by acting as a sacrificial layer.

This is a consequence of ultra violet (UV) radiation, which instigates a chemical change that reduces the polymer's molecular weight. As a consequence of this change the material becomes brittle, with a reduction in its tensile, impact and elongation strength. Discoloration, a chalky appearance and loss of surface smoothness accompany photo-oxidation. Infra red (IR) radiation or high surface temperature significantly increases the effect of photo-oxidation.

[UV protection is located near the top of the clear coat; hence the maximum recommended removal rates from Ford, GM, etc.]

There is ultra violet (UV) protection all the way through the paint, but the majority of it migrates to the top as the paint of cross-links along with the thinner solvents and particulates, the paint is also less dense (softer) below this level. Therefore removing clear coat ultra violet protection is not a linear process; by removing a small percentage of the clear coat paint tends to remove a larger percentage of the ultra violet (UV) inhibitors.

Density (or specific weight); different materials usually have different densities, so density is an important concept as less dense fluids float on more dense fluids if they do not mix (we have Archimedes to thank for this discovery) If the average density of an object is less than that of water, which is 1.0 g/ml, it will float in and if it’s density is higher than water's it will sink. Most organic solvents have a lower density ~0. 8 g/ml than water, which means they are lighter and will form a separate layer on top of water.

[RaskyR1]

Re: Paint and Clear Coat

I have some questions I would like someone to clear up with actual FACTS.


5. UV protection is located near the top of the clear coat, hence the maximum recommended removal rates from Ford, GM, etc.

Thank you

Please see post #3 and #37 in the thread below....the whole thread is a good read though.

http://www.autopia.org/forum/epic-threads/136546-clear-coat-thickness-paint-removal-polishing.html