Paint Indentions

[wlfpck]

I noticed something weird about the factory paint. The bumper paints seem to be really soft.

If you take your fingernail and push on the paint on the rear bumper, you can leave a small indention. Not really noticeable.

However, if you do this on painted metal, there is no indention.

My GTI is white and a friend did the same on his Tiguan (also white) and the same thing happened.

Is this due to the plasticizer that they put in the paint for the bumpers? Do they even put plasticizer in the paint for the bumpers at the factory?

 

[russiankid]

Bumper paint is flexible because it is on a plastic surface that can bend, pretty normal IMO.

 

[wlfpck]

Well it's not like the bumper itself got dented. It's a small mark that is in the clear coat itself.

Kind of like when you push on pine wood, you can dent it. Same thing here. There's a small indention in the clear coat.

You think it's due to the bumper being flexible? That would cause the clear to get dented?

 

[sprinks]

Polyurethane clear coat is pretty soft material typically. It got dented because that's what it's meant to do. It's meant to have give and flex and allow for impacts without flaking and leaving pits. Basically your material properties go hard and brittle on one extreme and soft and flexible/tough on the other. Typically paint engineers like to formulate to the demands of the system, and tough clear coat polyurethanes have to be on the tougher end of the scale. This improves resistance to rain/wind erosion, abrasion from the elements and debris, and minimizes delamination should a critical impact occur.
-coatings enginerd.

 

[wlfpck]

Polyurethane clear coat is pretty soft material typically. It got dented because that's what it's meant to do. It's meant to have give and flex and allow for impacts without flaking and leaving pits. Basically your material properties go hard and brittle on one extreme and soft and flexible/tough on the other. Typically paint engineers like to formulate to the demands of the system, and tough clear coat polyurethanes have to be on the tougher end of the scale. This improves resistance to rain/wind erosion, abrasion from the elements and debris, and minimizes delamination should a critical impact occur.
-coatings enginerd.

I get that part. The concern I have is why doesn't this happen on the painted metal parts? Doors, Roof, etc.

Do they use a different clear for the plastic bits?

 

[sprinks]

What you're likely seeing is the effect of the base material beneath the clears, color, and primer layers. When working with thin layers like paint, macro hardness (what you've roughly tested) is not necessarily indicative of coating performance. What you've done is essentially tested adhesion in a high flex situation. The metal doesn't have the opportunity to flex like that because the local hardness/stiffness of the metal prevents it. Most coatings people would likely use a pencil hardness test or a microhardness test if they were looking to know the hardness of the coatings. I imagine for cost of coating a vehicle that the clears are in fact identical polyurethanes.

 

[The Fed]

Where's the facepalm when you need it.

 

[martin.bainbridge.98]

Paint is water based these days so more prone to indentation, paint on VW cars isn't that bad, I moved from Seat Leon where paint was even more brittle and chipped very easily


Sent from my iPhone using Tapatalk

 

[wlfpck]

Where's the facepalm when you need it.

Relax. Not your car.

And, not really noticeable at all unless you bust out the expensive detailing lights. Not like there was any paint chipping off or flaking off. There's no break in the clear coat. Just a small indention you can't see unless you get the detailing lights out.

And... doubt anyone is looking in the wheel arch of my car.

additional note... if you bust out the detailing lights and look at your front bumper, you'll see the same indentions that are caused by rocks and debris as you're driving along. Unless you have something like Xpel or whatever.

What you're likely seeing is the effect of the base material beneath the clears, color, and primer layers. When working with thin layers like paint, macro hardness (what you've roughly tested) is not necessarily indicative of coating performance. What you've done is essentially tested adhesion in a high flex situation. The metal doesn't have the opportunity to flex like that because the local hardness/stiffness of the metal prevents it. Most coatings people would likely use a pencil hardness test or a microhardness test if they were looking to know the hardness of the coatings. I imagine for cost of coating a vehicle that the clears are in fact identical polyurethanes.

That makes sense. In that aspect, color of the paint wold not affect the what was observed. Didn't think about the material beneath the coating at all. That would make sense. Given the flexible nature of the polyurethane bumper, it allowed for indentions to form versus the extremely rigid metal.

So in a way, the coating is the same... but due to being on softer material, intentions form.

Thanks for the explanation! Appreciate it.

 

[sprinks]

Water based (reducible) has nothing to do with it.
I agree with you that VW paint isn't bad. Orange-peely, sure, but that's more to do with the low-VOC coatings than anything. It's present on the 6 figure cars too.
Unfortunately modern paints are designed to a dollar sign, VOC-limit, and expected lifespan. And again, it's about compromise. Do you want hard paint that chips and delaminates or do you want tougher albeit soft-ish paint. Compound that with exposure to outdoors (Y'all... UV damage is insane) wherein UV reacts with the polymer and embrittles it there it makes for a real challenge to have good paint forever.

Also, no problem for the explanation. It's how we learn. As for that dent, it's likely small enough that with a little time and temperature (say a warm sunny day) that it'll just relax and flex back to a close to original finish. If it doesn't and it bothers you, a little buff will like go a long way.

 

[wlfpck]

Water based (reducible) has nothing to do with it.
I agree with you that VW paint isn't bad. Orange-peely, sure, but that's more to do with the low-VOC coatings than anything. It's present on the 6 figure cars too.
Unfortunately modern paints are designed to a dollar sign, VOC-limit, and expected lifespan. And again, it's about compromise. Do you want hard paint that chips and delaminates or do you want tougher albeit soft-ish paint. Compound that with exposure to outdoors (Y'all... UV damage is insane) wherein UV reacts with the polymer and embrittles it there it makes for a real challenge to have good paint forever.

That's actually what we're going though now. A client is looking for paint in the plant that will resist UV damage and be extremely tough in the petrochem industry.

 

[wlfpck]

What you're likely seeing is the effect of the base material beneath the clears, color, and primer layers. When working with thin layers like paint, macro hardness (what you've roughly tested) is not necessarily indicative of coating performance. What you've done is essentially tested adhesion in a high flex situation. The metal doesn't have the opportunity to flex like that because the local hardness/stiffness of the metal prevents it. Most coatings people would likely use a pencil hardness test or a microhardness test if they were looking to know the hardness of the coatings. I imagine for cost of coating a vehicle that the clears are in fact identical polyurethanes.

Also... didn't think the polyurethane bumper was that soft. Starting to think maybe an unpainted polyurethane bumper could be dented as well.

 

[Gawernator]

Bumper paint has flexible additives added to it

 

[sprinks]

This is true. The basecoat may have flexiblilizers added, but the clear won't as it's a poly and already very flexible.

 

[wlfpck]

Car guy at work told me that on some cars, the bumpers actually have less clear which could be a contributor/part of the reason that happens. He said that when the cars are sprayed at the factory, the bumpers get less paint than the metal parts of the car.

He said the Focus ST was an example as such. And on some STs, if you get a very bright light just right, you can see the black polyurethane through the paint.

Think this is true on the VWs? Where the bumpers get less paint/clear than the metal bits?