Res1cue

After a failed attempt to rebond my new Lens with Nissian Butyl caulking I set out on a quest for more info about our head light/Lens assembly.

The manufacturer of the C6 Headlight assembly was Urgent Plastic Services who is part of 3-Dimensional Services Group.
http://www.3dimensional.com/press/news_2003_09_08.jsp

I spoke with one of the design team and obtained the following info.

The housing is made from polypropylene and the Lens is made from polycarbonate. These two plastics are very difficult to bond together so Urgent Plastic Services purchased a adhesive system to bond the two materials together. The manufacturer of this system was National Starch. The system consisted of plasma surface treatment equipment and a 2 part urethane based adhesive. The Plasma surface treatment was critical to enhance the two plastics ability to grab the adhesive. These plastics have very low surface energy and do not accept adhesives well without help from the plasma treatment process. The equipment to preform the surface treatment is very expensive in the order of multiple 10's of thousands of dollars. National Starch sold out their adhesive division to Henkel who owns loctite and PL adhesives.

So the question remains what is the best option once you have removed your lens and the adhesive out of the housing track?

There seem to be a several options which can be attempted the best of which has yet to be identified. Hopefully the Mods will allow the links below to remain as I don't believe they conflict with corvette vendors.

Butyl rope headlight caulk - $40.00 Nissian http://www.mynismo.com/products/?id=5577&rsku=0

100% silicone - $5.80 Home Depot http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

PL Premium Polyurethane Construction adhesive - $4.58 Home Depot http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

PL Premium Advanced Polyurethane Construction Adhesive - $6.99 Home Depot 4x stronger than Premium and low VOC http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

Pro-Poly 2 part adhesive - $105.96 Fastenal
Applicator - http://www.fastenal.com/web/products...ex?sku=0459733
2 part adhesive - http://www.fastenal.com/web/products...0459732&ucst=t

Pro-Poly which requires surface scuffing with 100grit and cleaning with Isopropyl Alcohol seems from the test data to provide a decent mechanical bond between polypropylene and polycarbonate. Better than the others but no where near as good as the plasma treated and urethane bonded factory seal.

Update:
3M Scotch Weld Structural Plastic Adhesive DP-8005
Similar to pro-poly but a little less expensive
http://www.stealth316.com/misc/dp8005.pdf

mcandrew67

Good investigation
or you could just contact Rl Sebring who has probably done hundreds of these

Justasheet

This should be very helpful. There have been a few vendors and members that do this repair and sell them. I have not heard of any issues. Maybe one of them will join in here and add their expertise.

Jeff

designerRob

Interesting info indeed.

Res1cue

I have trade PM's with RLSebring quite frequently.

Darrelk

Upon advice from RL, I used the PL by Loctite a little over a year ago and just inpected it the other day when doing spring cleaning. Stuff worked great, holding firm.

mcandrew67

Yeah when I crashed I may have been in need of a new headlight so messaged him. But the body guy thinks he can get the scratches off. If not then I will get a new cover from him.

Res1cue

Good to know, I may give the PL Premium Advanced a shot instead since it is an improved version of what you used and is very low on VOC's.

Res1cue

The PL Premium Advanced adhesive does not stick to the housing. I cleaned an area on the housing with a SS brush and acetone. I then applied a small bead to the surface. After 24 hours I was able to grab the edge of the bead with my fingernail and it popped right off. I also placed a bead on a cleaned but not brushed area and same result, it popped right off. Both PL Premium Advanced and PL Premium state that they will not adhere to polypropylene.

I think the folks who have sealed with PL are on borrowed time it is probably only a matter of time before the seal fails.

RLSebring

Even the factory RF adhesive doesn't bond with the housing like you would think.

From the many lights I have taken apart. The factory adhesive does not adhere well to the lens, period. With the right amount of heat and time the lens will slip out of the factory RF adhesive.

The factory adhesive stays in the glue track on the housing. You can peel the adhesive out of the glue track clean with enough time and effort and not leave any trace of the adhesive.

So with the factory adhesive you are not achieving a mechanical bond but rather a somewhat mechanical bond along with a friction bond. If you look at the housing glue channel and the flange of the lens they are compound angles that pretty much hold the lens in place.

I recently received some lights back that were damaged in shipping. They gave me a real opportunity to see what it would take to pull the lens off the housings ( I have tested this in a much lesser degree earlier during initial experimenting with sealants and bonding). You would break something else before the lens came off.

I tried a number of adhesives and decided on the PL Polyurethane as the normal adhesive to use. I really don't believe the use of PL is on any more borrowed time that any other C6 light out there with the factory adhesive.

Res1cue

I cleaned an area on the underside of the housing with a stainless brush and acetone. I then wiped it clean with alcohol. The surface turned slightly grey due to the abrasion of the brush. I used the process below which gives similar results to Plasma treatment that the manufacturer uses but not as good.

Flame Treatment:
To flame treat a plastic surface, hold a propane torch so the flame just touches the surface and move it across the surface at a rate of 12 or 16 inches per second. Keep the torch moving and overlap the previous pass slightly. When done correctly, the surface will not discolor or burn in any obvious way. This technique oxidizes the surface and improves adhesion. For best adhesion, bond to the surface within 30 minutes of treatment. This is a process that is used in industry to increase bonding to polyolefin plastics.

Example:
http://www.youtube.com/watch?v=Ce3rtPWJuSQ

Once flame treated I applied a small bead of 3M Urethane Windshield Adhesive. Twenty four hours later I tried to remove the urethane and I can attest that it was significantly more difficult to remove the bead than before with out the treatment. I am comfortable stating that the three surface areas inside the track on the housing, once flame treated would be sufficient to hold a good bond between the housing and lens.

I am sure the result would be similar with any urethane based adhesive like the PL products.

Flame treatment plus a product like 3M Scotch Weld Structural Plastic Adhesive DP-8005 would probably give a bond very close to factory.

RLSebring

I have to admit you have put a lot of thought and research in this. I simply found an adhesive that I could not pull apart when cured.

If your baseline is the factory results I wouldn't aim that low. As you can see in the picture that the adhesive pulled right out of the track clean with the exception of the top 8 or 9 inches. The leading edge would be more critical in obtaining a mechanical bond than the top. I think GM's intended results and actual results are some what far apart. If it did indeed bond as intended from the factory you could pretty much forget ever getting these lights apart in one piece. It is a pretty cool method they use.

The rest of the adhesive on this light scraped clean with a sharp screwdriver. As stated before with the compound angles involved with the housing and lens a little glue tightens up the holding power. Hell even simple silicone would hold for quite a while.

I had forgotten and haven't used the blowtorch process on anything in quite some time. I have to use it with the PL and see what it will take to tear the lens off the housing or if the housing will give up first.

Res1cue

I can tell you that when I removed my lens and the factory adhesive my hands hurt for a week. It was a bear pulling that stuff out of the grove, the adhesion was incredible even after heating. The lens did separate from the adhesive a little easier but it was still difficult.

Silverado Desperado

Great info! Thanks for sharing!

keyplyr

Thanks for posting

glenB

What about 3M Window-Weld Super Fast Urethane (Caulking Tube)
Price: $23.85

We used it to reglue windows back into the regulator rail

RLSebring

One thing to watch for is the level of outgassing. It will leave nasty marks on the inside of the new lens.

Knob Jockey

Thanks for sharing your efforts and results. Impressive.

Enough info to convince me to never try a repair/lens replacement myself.

RLSebring

I have did many many lens replacements and not one problem so far over the past 2 years or so. I have sold many many lens to members that did their own replacement with little to no problems reported. There were a few that just could not do it and they sent me the basket case to finish.

Don't let some glue experimentation worry you. PL works just fine with no out gassing and you're not going to pull the lens off bare handed. Is it the best? I don't know. Is there something better? Maybe.

RLSebring

No doubt and I warn about the factory bond being some tough stuff. I have a kung foo grip now after so many lights and have to switch hands often or at least do one light with one hand and the other with the other.

Maybe you had the rare bonded light. If it was indeed bonded it would have left a layer of the adhesive on the housing track. As it is the adhesive usually pulls out of the track like removing a tight piece of rope out of a channel. All the adhesive comes off so it does not have a mechanical bond. I've yet to one that the adhesive didn't come off in just about one piece.

How it strikes me is the adhesive swells/activates when hit with the RF. The housing, adhesive and lens are all together prior to the RF cure. That the only reason the tabs are on the housing and the ears are on the lens. The lens snaps onto the housing to hold it in place while the glue activates and swells up thus sealing and locking the lens in place.

This whole process derived from the lens having to stay on the race cars while going 200+ and was carried over to the production cars. Definitely not needed at the average speed most Vettes are driver overall.