Poly cracking... What's up?

[mike.elmes]

How about a test using the same two lenses and a jar of acetone.:p

[DragonLensmanWV]

How about a test using the same two lenses and a jar of acetone.:p

That would be pretty short, huh?:D

[Darryl Meister]

Within the past year or so I have seen repeated pairs of specs with poly lenses cracking. We've dispensed poly for years, however, this past year a crazy amount of lenses have been cracked.

It is usually due either to the release of stress in the polycarbonate material after surfacing/edging/drilling or to chemical attack.

[Matteomix]

I work at a chain of sorts. And we've had the same problem within this past 6 months. We've been very careful to not tighten the screws to tight. As well as cooling the frame immediately after popping a lens into a zyl frame. A lot of mishandling goes on with the retail clerks but that's all that seems to be causing the problems on my end.

[Nikki McGee]

The only time I've had repeated problems with poly cracking it was coming from the lens marking removal pens. I switched brands and had no more trouble.

[Robert Martellaro]

It is usually due either to the release of stress in the polycarbonate material after surfacing/edging/drilling or to chemical attack.

And the chemicals are all around us- acetone in fingernail polish remover, ammonia in glass cleaner, methacrylate-like substances in hair spray, and so on.

Even with the use of first-rate labs, I've seen about 20% of my poly lenses crack over the lifespan of the glasses.

I'll only use poly if I'm reasonably sure they'll be in a non-chemical environment and if there are no other materials available in the lens design that would be best for my client.

[chip anderson]

Any body smart enough to find out and list all the chemicals that can or will attack Poly? Trivex? Various and Sundry Coatings?
This would be a nice thing for us workin stiff opticians to know.

Chip

[Chris Ryser]

Any body smart enough to find out and list all the chemicals that can or will attack Poly?


Chip

I am smart enough, and have posted this same before a few times over the years, but it does not seem to sink in................



The following require caution:
Cyclohexone
Glycerine
Sulphur Dioxide
Diesel Oil
HeatingFuel
Turpentine
Formic Acid
Jet Fuel
Gasoline
Perchloric Acid-Conc.


The following will attack polycarbonate:
Acetone
Caustic Soda
Methyl Ethyl Keytone
Acrylonitrile
Chloroform
Perchloroethylene
AmmoniaDimethyl
Formamide
Styrene
Amyl Acetate
Hydrochloric Acid-Conc.
Toluol
Benzene
Hydroflouric Acid-Conc.
Sulphuric Acid-Conc.
BromineIodine
Xylene
Butyl Acetate
Methanol

Drill Holes.............

Allow for proper expansion in all drill holes. Do not drill within 1 1/2" from the edge of the sheet.

When fastening screws, do not tighten below the surface of the panel.

[chip anderson]

Thanks Chris:

I am a little confused with the drill hole instructions. I would understand this if we were drilling large diameter holes in 4 & 8' sheets, but don't understand not drilling withing 1 1/2" of sheet.

Now how are you on chemicals and other things that Anti Reflective Coatings don't get along with well?

In fact as long as we gittin smarter what are the causes of Scratch Coat failure?


Chip

[DragonLensmanWV]

Just for giggles, when I came back from vacation on Monday, I edged a poly lens and a trivex lens, inscribed a P and a T on them with a diamond scriber and put them in a jar and filled it with the 99% isopropyl I use to clean the lenses before coating.

So far, no damage to either one. Let's see how long it takes.

OK, been a week and a half and I got the lenses out today. The poly lens has it's coating starting to erode around the periphery of the bevel and several spots in the coating elsewhere and the edge has become slightly glazed.
The Trivex lens only has the few spots formed in the lens coating without any other effects.

[Chris Ryser]

The poly lens has it's coating starting to erode around the periphery of the bevel and several spots in the coating elsewhere and the edge has become slightly glazed.
The Trivex lens only has the few spots formed in the lens coating without any other effects.

As you put the lenses into ISP try again into Methanol or Acetone to see a fast response.

[Darryl Meister]

I would understand this if we were drilling large diameter holes in 4 & 8' sheets, but don't understand not drilling withing 1 1/2" of sheet

This really applies mainly to materials with non-negligible coefficients of thermal expansion and contraction, like metals.

[snowmonster]

OK, been a week and a half and I got the lenses out today. The poly lens has it's coating starting to erode around the periphery of the bevel and several spots in the coating elsewhere and the edge has become slightly glazed.
The Trivex lens only has the few spots formed in the lens coating without any other effects.

You need to put those lenses into the frame and the polycarb will likely start cracking within 2-3 days. You're not inducing any stress in the lens by soaking it in IPA, you're just stripping the coatings.

We went through a brief period where we were cleaning edged lenses with 70% IPA and noticed a huge number of cracks in the lenses as described by Jamie Brady. We stopped using the IPA and used regular cleaner (without any IPA content) and everything went back to normal instantly.

[chip anderson]

Please, don't add any new abreviations to the industry, spell out isopropyl alcohol, so us dummies won't have think so hard to know what your are talking about.

Chip

[snowmonster]

I didn't think it was new.

[rinselberg]

You need to put those lenses into the frame and the polycarb will likely start cracking within 2-3 days. You're not inducing any stress in the lens by soaking it in IPA, you're just stripping the coatings.

We went through a brief period where we were cleaning edged lenses with 70% IPA and noticed a huge number of cracks in the lenses as described by Jamie Brady. We stopped using the IPA and used regular cleaner (without any IPA content) and everything went back to normal instantly.

Don't use "IPA" to abbreviate isopropyl alcohol. Fezz will think you are talking about India Pale Ale.

[Fezz]

Fezz will think you are talking about India Pale Ale.

:cheers::cheers::cheers::cheers::cheers::cheers:

[RJMurfster]

I've been complaining about poly cracking for years. Some cracks show up in the outer edge but occasionally I have seen them in the dead center. I believe eccessive heat during edging might be the problem. I did have the oppurtunity to ask a poly manufacturer's rep about the problem and the answer was awesome. he asked back "What cracks?"
That answer made my poly usage drop to 4%. I prefer most any other material.

[Wes]

Don't use "IPA" to abbreviate isopropyl alcohol. Fezz will think you are talking about India Pale Ale.

:cheers:Made me want to take a trip to the Flying Saucer.:cheers:

[carnzo]

He is a simple fix for your problem with Polycarbonate cracking, Don't use it. Polycarbonate is a terrible material. Use plastic, trivex or index materials and let your patients finally see. Leave Polycarbonate to the box stores.

[jrh291]

at least to my satisfaction, and that of my officemates, that the problem is solvent related.
I've seen the cracking lens problem before this, but never in these numbers. 20+ years ago I was a dispenser in a busy superstore and got sick to death of the "They can send a man to the moon, but they can't keep the screws in my glasses...." One day I happened on Loktite and passed a bottle on to a couple of my fellow dispensers, and the problem went from 60 to almost zero inside a couple months.
Some years later, after seeing cracks appearing on lenses at the screw barrels, one of the bright guys I shared the bottles with contacted the Loktite company and they said that there was an ingredient that may react with polycarbonate. I changed to a poly safe threadlock from Vigor-now labeled not safe for poly, and the problem all but went away. When I'd see it happen in later years occuring away from the screw barrels, I always suspected a cleaning solvent, probably something that accelerated evaporation, or perhaps a caustic work environment for the individual presenting his cracked lenses to me. The problem was rare, but seemed to happen to the same few people in an office, time after time.
Last fall, we got a good deal on some lens cleaner in printed bottles we give to our customers at dispense. It took a month or two, but these cracking lens returns became a daily occurence. It only happened on polycarbonate lenses. I let the staff know my strong hunch. They all had had the experience of wiping the progressive marks off a poly lens and had it split under no other stress, so it seemed plausible enough for one of them to say "let's test it!" To the man (person, every patient returning these lenses was asked "how are you cleaning them?" and responded "with that lens cleaner you gave me." I grabbed a frame off the board, cut some lenses and left them at the front desk to be cleaned twice a day. It only took a day for one lens to fail. Another test, another failure. Late March we pulled the cleaner off the shelves and told patients to just use soap and water. The cleaner was manufactured in China. The company has it made in a couple other countries also, but ours was from China. Another theory of mine was Chinese metallurgy or paint additives, but I've seen enough occurences in plastic frames to make me doubt that.
Anyway, it's late August and cracked lenses are just about a thing of the past. Furthermore, if we do see one come in from our office, the date of the original eyeglass sale ALWAYS falls between the time we took delivery and suspended our delivery to patients. I have no choice but to believe.

[chip anderson]

How come we can mention Loctite by name in causing Poly cracking but won't name the brand on lens cleaners known to cause problems?

Chip

[eyemanflying]

He is a simple fix for your problem with Polycarbonate cracking, Don't use it. Polycarbonate is a terrible material. Use plastic, trivex or index materials and let your patients finally see. Leave Polycarbonate to the box stores.

Poly is cheap and crap period. I agree that Trivex is an excellent alternative to provide and your patients/customers will love you for it!

Let's put ourselves in the customer's shoes...it's a huge inconvenience!

[jrh291]

Duplicate post deleted.

[Chris Ryser]

How come we can mention Loctite by name in causing Poly cracking but won't name the brand on lens cleaners known to cause problems?
Chip

When somebody wants to sell lens cleaners to optical retailers is not a matter what it contains, it has to clean and it has to be cheap.

It actually is a fight for prices, who is 1/2 cent cheaper than the competition, and it has been like that forever. Chains or independent Opticians are all the same when it comes to lens cleaners. It should cost just about near to nothing and nobody cares what is in the formula. The most common formula is 20% ISP and 80% water. That is cheap to make for anybody and can be sold at any price you can get away with and that was what happened in above post.

Last fall, we got a good deal on some lens cleaner in printed bottles we give to our customers at dispense.

Nobody cares what such lens cleaners can do as long as it cost's barely nothing so that we can give them to customers as advertising, instead of selling a good product that will clean and protect.

The same goes also for eyeglass cases they have to be the absolute cheapest because they have to given away. I feel sorry for sales reps that sell those two items as they are under pressure to nearly give these items away for nearly nothing. So don't wonder why when greedy you get what you pay for.

..........................:finger:.........................