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.
So, my question is: Is anyone else seeing this issue surface?
I have to believe that it is a substrate issue. Has something changed in the raw material of poly?
Collective wisdom please.
Jamie
This was discussed recently!
http://www.optiboard.com/forums/showthread.php?t=33901
I've read the posts on the link you provided, however, I can't believe that all the sudden my in house lab and all of the wholesale labs we use have dull cutting surfaces on the equipment nor can I believe that it is an alcohol issue.
I agree that these (dull cutting surfaces or alcohol) can cause these problems, but has all of our industry's labs' edgers blades become dull this past year or perhaps they have all of the sudden began using alcohol to clean lenses. I can't buy that premise.
The cracks are occuring not just in the cold weather but summer also. It's happening on SV, D-segs, PAL's, all designs. The cracks are starting just about anywhere on the lens edge not just at the barrels.
Something is up with the substrate. Hmmm?
Still looking for answers.
Jamie
Chi-Com Plastic.
We also have seen an unidentifiable increase in cracked poly, and we have been near 90% poly fitting for 5 years. As well as I know poly from manufacturing through dispensing, I also am surprised. New Poly materila supplier, manufacturing coating process?
denny
Chip,
Are you suggesting that the raw poly material that lens casters are using is of low quality and that is the problem?
Couldn't quite understand your post.
Read up on Chi-Com sheet rock. Don't expect thier plastics are of any higher quality. Their vaccines aren't either.
Chip
Are there any other reasons not to ue poly. Guaranteed solution to your problem: quit using poly.
I recently tried to show a new kid in our industry how poly was bulletproof. I took a brand name poly stock lens out of the package, put it on the bench and slammed it with a hammer.
The lens shattered all over the tech bay!!!
It seems some companies are using some kind of poly blends. I would assume its for better optics, but they sure are not bulletproof anymore.
I did however find some other poly lenses and they took a .45 caliber hit with only a big dent.
I've only had problems with surfaced poly lately. Haven't had much problem with stock poly. I mostly use Polycore for my stock poly lens.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
What has come out of this ?
Has it calmed down i.e. were really all drill bits in the US dull at the same time, suggest you go after them..... ;-)
However if OpticLabRat's hammer test is typical, in the US there is a potential problem. Anybody submitted a Poly to a FDA test recently ?
More facts would be helpful.
In Europe we do find during edging differences in PC material coming from different sources, but we don't need to pass an FDA.
I have come across bargain CR39 lenses without UV absorbers added, they transmitted UV down to about 310nm and will go yellow and brittle when exposed to sunlight over time. Similar thing could be happening here.
Georg Mayer
Rodenstock-Munich
Vision Ease has recommended.................
Vision Ease has recommended the use of "DRILLSEAL" in the drill holes to seal off rips and cracks on Poly lenses which will prevent cracking from the holes out with great success.
Vision-Ease Lens, Inc.
TECHNICAL SERVICES DEPARTMENT
TECHNICAL TIP
EDGING:
Edge lens to desired shape and size.
Safety bevel both sides of lens after rimless edging procedures.•
Edge polishing and tinting should be done prior to drilling.•
Drill lenses prior to anti-reflection coating.
MANUAL LAYOUT:
Mark horizontal axis/ 180-degree line on each lens with a water-soluble pen; duplicate pattern axis line if no
prescription axis is applicable.
•
With a felt-tip pen, carefully place a dot at each drilling location on the lens front and verify correct positioning.
•
Location should be double- checked for accuracy to +/-0.5mm.
DRILLING:
Polycarbonate cuts best with a sharp burr operated at low speed and minimal to moderate pressure. Twist
style drills, cutting less aggressively, often leave subsurface damage.•
Place lens with front towards drill bit and slowly operate drill through lens; back drill bit out of hole often to
remove cutting debris that will increase heat damage.•
Be sure to chamfer around the hole when finished drilling. (Much like safety beveling after edging)•
Note that excessive pressures and speed create damaging heat, which may create eventual fractures.•
An extra precautionary step to avoid fractures would be to place a drop of OMS Drillseal into the hole.
Distribute the Drillseal evenly with a toothpick. This will seal the hole and it dries instantly.
Please note the
dropper may gel if left in the bottle.
CLEAN-UP:
Cleaning should be done prior to mounting with warm soapy water with a clean water rinse.•
Wiping should be minimized to avoid abrasion from cutting debris.
MOUNTING:
Assemble lenses with appropriate hardware, minimizing excess tension.•
Frames should be fully aligned and formed to lens prior to final assembly.•
Excess stress on assembled eyewear may eventually create fractures. Use of plastic bushings is
recommended.
INSPECTION:
• Mounted lenses should be inspected for excess stress, correct positioning, and alignment.
My company pulled all of our spray cleaner, we think that is what is causing it. We have tried switch poly brands but that didn't work. We should start noticing a difference in the the coming months.......hopefully.
Enough of it touching the bevel periodically will do the trick ......
Polycarbonate is what it says. Changing brands will not help as the chemical formula is the same for everybody.Originally Posted by regional_manager
The edges are not protected by the hard coat, and most lens cleaners contain between 20 + 30% ISP (Isopropyl Alcohol). Enough of it touching the bevel periodically will do the trick to start a destructive action.
You can always put a sealer coat on the edges.
Two things cause cracks on poly on a regular basis in our shop....1. Locktite on screw/nuts
2. screws and nuts....nut tightened too tight.
I refuse to sell poly in rimless unless its a plug mount, and I can't get Trivex. PERIOD.
I do however see many chains and or discounters using poly as its cheap...
Many similar problems with scracks around drill holes where nuts are overtightened, or some unknowing Optician/ lab tech administers Locktite.
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.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
Dragon:
At last grass roots real world research!
Bravo!
Chip
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.
DragonlensmanWV N.A.O.L.
"There is nothing patriotic about hating your government or pretending you can hate your government but love your country."
You will.
It is usually due either to the release of stress in the polycarbonate material after surfacing/edging/drilling or to chemical attack.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.
Darryl J. Meister, ABOM
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.
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.
ABOC
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.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
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
I am smart enough, and have posted
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.
Last edited by Chris Ryser; 08-12-2009 at 02:43 AM.
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