Moisture causes windshield delamination?

[tomtom72]

Originally Posted by VetteMed

Yep, I'm having that very thing done within the next week or two. My gripe isn't even the delam, it's the pitting and chipping that 21 years and lots of miles brings with it. It's downright dangerous at certain times of day.

Yea the pits, chips and sand blasting makes for some interesting night driving experiences! I just hate to loose our unique apparent tint color. You can pick out the ZR-1 in a line of C4's just by the color of the windshield. I kind of like that. I'll be sad when I decide to give in and replace it with new glass.


Tom

[scottfab]

What is the source of this write-up?

Originally Posted by LGAFF

Laminators are constantly being challenged to reduce or eliminate visual defects in laminated glass structures. Some defects can be directly attributed to glass quality but many are considered to be associated with the laminating process andmore specifically with the commonly used polyvinylbutyral (PVB) interlayer. Defects can look like bubbles or pockets of air with elongated worm-like or dendritic shapes. Elongated worm-like and dendritic defects are often referred to as delamination. Some defects are visible immediately after autoclaving, but others develop hours or days after lamination. Laminators who use vacuum for de-airing tend to experience higher defect rates in warm weather.

Traditionally, delamination is viewed as the result of adhesive bond failure between the glass and the PVB interlayer. That is, the adhesive forces cannot withstand the stresses that are due to mismatches in the glass as well as gaps andpinches. A typical explanation for defects that are near a laminate's edge, is that the PVB absorbs moisture from the environment, which lowers the adhesion level leading to defect formation. Therefore, it is rationalized that during warm and humidseasons, moisture is absorbed at a higher rate, and hence causes more defects.

In the laminating industry there is general agreement that gaps and pinches do lead to defects. In fact gaps of approximately 0.1 mm in height over a distance of 5 cm are suspects for causing defects. The load required to achieve a 0.1 mm gapor pinch can be calculated from mechanical considerations, and it is a surprisingly low, 1.0 N/cm for 2.1-mm thick glass. For this reason, adhesive forces cannot explain the formation of most defects.

If the adhesion level is primarily responsible for defects, then higher adhesion levels should be able to overcome more stress, and hence, would accommodate larger gaps and pinches without causing a defect. However, our findings have shown thisnot to be true.

With respect to moisture absorption, the adhesive interlayer absorbs moisture from the environment until equilibrium is reached. The equilibrium level depends on the relative humidity and may differ for different interlayers. The mechanism formoisture absorption is diffusion, which means that the concentration of the diffusant is highest at the phase boundary (i.e., at the laminate's edge). A typical moisture profile of a PVB laminate exposed to 95% relative humidity at 40.degree. C. forone week shows that only interlayer within 3-4 mm from the edge has moisture higher than 1.5%, and the moisture level hardly changes about 8 mm in from the edge. Most of the observed defects occur about 3-12 mm away from the edge and some extendslightly farther inwards. Very few defects are open to the edge where the moisture level is highest and where one would expect to have the lowest level of adhesion.

It is possible to adjust the adhesivity of the PVB interlayer so that even when laminated at high moisture, the final adhesion is suitable for use in automobile windshields. However, laminates made this way would fail if they are installed intoautomobiles which are driven in or exposed to high ambient temperatures. Bubbles form readily at temperatures less than 100.degree. C. in laminates where the PVB interlayer has been equilibrated prior to lamination to a relative humidity higher than50%. These laminates most likely would not pass the bake test or the boil test required by national and international standards (e.g., ANSI Z26, JIS R-3212, EC R-43, and others).

Another reason moisture intrusion does not explain many of the defects is that even in the absence of high moisture, adhesion at 30.degree. C. is only a fraction of what it is at room temperature. Increasing the adhesion between the glass andthe adhesive interlayer at room temperature, therefore, would not help to eliminate defects which tend to occur at higher temperatures. Further, correlation between data from tests run at temperatures well below room temperature, such as the pummeltest, and delaminations is at least questionable.

We have found that the presence of air plays a most significant role in defect formation in laminated glass. De-airing and edge seal must be as complete as possible in pre-pressed laminates before autoclaving in order to avoid defects. However,optimizing de-airing alone does not appear to solve the delamination problem completely.

The typical approach in attempting to solve delamination problems has been to include various additives in the adhesive sheet to increase the strength of the adhesive bond between the sheet and the glass plate. While such approaches have beensuccessful in changing the adhesive level, and to some extent reducing delaminations, increasing adhesion upsets the delicate balance of properties which make laminated products so desirable in automotive and other fenestration applications. It is wellknown that an adhesion level that is too high can render the laminate monolithic and unable to absorb an impact, or if the adhesion is too low, glass shards fly from the structure on impact. In each instance, changing the adhesion level renders thelaminate unacceptable.

[scottfab]

I've seen a lot of ZR-1s over the years. Given a stock windshield most have some level of delam.
This last weekend I was with a group of ZR-1s. I saw a 91 with 27k mi or so with the worst delam I've ever seen. It was a Texas car so maybe the heat issue is a big factor or maybe that run in 91 was the worst, dunno.
What I did notice was a distinct pattern on both sides.
The patterns were repeated twice on each side.
The patten looked like some sort of handling apparatus marks.
Like a giant two pronged fork extending from the edge in about 100mm toward the middle of the windshield.
Thing was where these marks were had no delam. It was all around the window but not there. Go figure.

My 90 with 92k mi has a relatively low delam issue. Only the upper corners. And since i have very little pitting I plan to keep it for the time being. I agree too. It's easy to spot the micro screen tint on a ZR-1 and I too like it.

[Bob Eyres]

I've had my 91',#1236, since nearly new. It now has 66K mi.

It has slight windshield delamination. Approx. 1" on the top, and 1 1/2" on the sides, none on the bottom. Aesthetically, not too bad.

For eighteen years it has been garaged inside, in a non-air conditioned garage here in tropical South Florida. Definitely a high heat, 90+f. much of the time, and high humidity, 85-95%, environment. It is only subjected to water when it's washed.

I have no technical expertise, but I suspect the problem is caused by inadequate edge sealing at the time of manufacture.

BTW, this might be a subject for an interesting poll of owners. Ask all the environmental questions of guys who actually know what conditions the car has been subjected to over it's lifetime. You might be able to draw some conclusions from the aggregate of answers.

[scottfab]

There is a tremendous amount of archived email on delamination. I know somewhere in there a definitive explanation was given for the pathology of the failure on our particular windshield.

When searching I get 201 hits on "delamination".
Thing is, what is in the ZR-1 Net Registry as "Archives" is incomplete.
It only goes back to 2001 or so. I have personal copies of all email on the ZR-1 email list going back to 1995. This traces back to before the current ZR-1 NET Registry was created out of dissolving the then ZR-1 NET in order to liquidate the "Lifetime membership" idea.
Even before the ZR-1 NET there was a ZR-1 Registry which was discontinued before the ZR-1 NET was created.
The point is, the older emails (1995-2000) may also have to be searched to find important work done on finding the root cause for GMs foobar windshields.
I may do that later this week.

[rhipsher]

Originally Posted by scottfab

I've seen a lot of ZR-1s over the years. Given a stock windshield most have some level of delam.
This last weekend I was with a group of ZR-1s. I saw a 91 with 27k mi or so with the worst delam I've ever seen. It was a Texas car so maybe the heat issue is a big factor or maybe that run in 91 was the worst, dunno.

I think it depends on the individual windshield itself. Mines a Texas car and in my opinion has minimal delam. 98 degrees with 56% humidity is typical here in Houston.

And all of the Z guys I know in Houston don't have what I would consider severe delamination. I do think its subject to each individual windshield. Of course im no expert. I just know what Ive seen with my own eyes.

[scottfab]

Here is a reprint of an opinion by Dave Bright (mom) some 10yrs ago after taking a poll of the delam issue:
************************
From: ZR-1 Corvette enthusiast list. [mailto:[log in to unmask]]On Behalf Of Dave Bright Sent: Wednesday, August 07, 2002 10:27 AM To: [log in to unmask] Subject: [ZR1] TECH: Re: [ZR1] Possible causes of Delamination Well I'll give you my theory or $.02 (50 years worth. :-) ) If I understand that our windshields are the process of the "gluing" of two pieces of glass together then one issue could be what if the two pieces are not shaped exactly the same. If not then you would have the stress of the two pieces trying to pull apart and maybe why in many cases the problem starts in the corners. Or maybe the glue is too thin at the corners... My other thought is the "glue" process itself which sometimes was successful and sometimes it wasn't and why for example a whole windshield (last ZR-1 at the NCM) suddenly delaminates. Over the years I'm seen many windshields, some brand new, some old, some daily drivers and some waxers. I just don't see any relationship to the climate or care of these cars, garage queens or stored outside. My opinion is it all boils down to the process used when they were made. A process that was new and not perfected. Based on my survey I would guess 70% or more of the ZR-1's out there have this problem to some degree. Finally my last $.02 on this. Will GM fix this issue? - NO Will GM offer to build more ZR-1 windshields? - NO If GM were to issue a Service Bulletin it would say to replace the ZR-1 windshield with the stock C4 windshield. It's maybe possible, but there is now a question on where the tooling is, for the glass manufacturer to make additional runs "if" they is enough justification to do so. Mom********************************************

[scottfab]

Originally Posted by rhipsher

I think it depends on the individual windshield itself. Mines a Texas car and in my opinion has minimal delam. 98 degrees with 56% humidity is typical here in Houston.

And all of the Z guys I know in Houston don't have what I would consider severe delamination. I do think its subject to each individual windshield. Of course im no expert. I just know what Ive seen with my own eyes.

wow, I guess all this time I have been seeing cars with delam similar to mine. Now I have seen for the first time some with more. In all 5 trips to BG I have not see many that were very bad.

[LGAFF]

It sounds like there may be sealing processes out there that stop this..

[ghlkal]

Originally Posted by scottfab

wow, I guess all this time I have been seeing cars with delam similar to mine. Now I have seen for the first time some with more. In all 5 trips to BG I have not see many that were very bad.

I wish I could provide some information that would help, but I have no records or knowledge of the POs. If you want to see bad delamination, here's mine


The pictures make it look better than it is

This car was in Texas for some of its life and it's obvious that it spent some time outside too.