Hello All,
Is it just me or has anyone else noticed that since Ansi has changed the recommendations for a safety bevel being placed on the front surface of a finished edged lens that the number of spontaneous fissure cracking of polycarb lenses has increased dramatically??
It has been an ongoing issue!
I despise poly and have cut my usage dramatically over the last few years.
Plenty of threads on this same issue.
http://www.optiboard.com/forums/show...-Poly-Cracking
http://www.optiboard.com/forums/show...king-What-s-up
http://www.optiboard.com/forums/show...-Cracking-poly
Is your lab edge treating your lenses after edging?
Eyes wide open
I'm not sure what ANSI has to do with this. ANSI Z80.1 does not mention safety bevels in either 2005 or 2010 revisions. To which ANSI standard and section are you referring?
RT
Same question here...
Originally Posted by RT
Nothing new to add, but...
14 years ago, poly never had an issue.
Mysteriously, about 6 years ago, poly became 'unstable'.
"Starring" started to appear on drill mounts, and edge cracks on rimless lenses began to show...
4 years ago, we started seeing 'splitting' down the middle of poly lenses edged in full frame mounts, as well as in groove mounts.
We questioned solvents, and cleaning chemicals. We questioned the manufacturers about manufacturing changes.
We were told nothing had changed.
Most of us kept with the old ANSI Z80.1 standards (as they were more strict (and ethically sound))
As of late, the manufacturers claim no changes have been made. And, dozens of us have carried out tests on different cleaners and solvents.
No conclusive results have been found...
Yet...
:/
The name Polycarbonate is linked to specific chemical formulas that have notchanged over the years. It is delivered in pellets to an injection company who heat's it up and injects it into certain molds to form a product.
In the matter of optical lenses the product has to be protected as it is extremely soft on the surface, and is sensitive to a series of solvents and, or their aircarried fumes ------- Chemical Resistance :
Chemical Resistance Acids – concentrated Poor Acids – dilute Good Alcohols Good Alkalis Good-Poor Aromatic hydrocarbons Poor Greases & Oils Good-fair Halogenated Hydrocarbons Good-poor Halogens Poor Ketones Poor
Therefore the applied hard coat protects the lens materialfrom scratching and chemical attacks.
Two parts of the lens remain unprotected after edging and mounting into the eyeglass frame and that are the edges as well as the drill holes. Specially the edges are prone to all sorts of chemical attacks from cheap lens cleaners to invisible fumes in certain environments. The drill holes these days are drilled automatically by the automated lens edger's that do not have the feel for different materials and use often dull drill bits that rip or melt the inside of the hole, and should be changed more often.
Check at --------------> http://www.vision-ease.com/Portals/VisionEase/Specifications/LensDrillRimlessMounts.pdf
If the optician or lab technicians would follow the instructions of polycarbonate lens manufacturers as "Vision Ease" the OB main sponsor, these complaints would not have to happen.
I have tested poly edges after applying a silicon polymer tothe edges of poly lenses and found them to become resistant to chemical attacks by the way of the edges. So there are solutions and cures for many complaints on a material, if you do a little research.
Polycarbonate has not changed, but the way of treating the lenses has.
Last edited by Chris Ryser; 12-03-2012 at 03:50 AM.
It is my opinion that most poly cracking is caused by dull wheels, blades and drills. A dull tool will "rip" the material away instead of "slicing" it...on a microscopic level. Other materials like CR-39 and mid index do not seem to be susceptible to this. High index will either crack or slip in the chuck if your tool is dull.
That's why I favor dry edging poly. The cutting blades are cheap and easy to change regularly.
How are you edging?
+1. Chris's exhaustive information aside, I have noticed a huge increase in poly cracking in the past three years, and I'm not doing anything differently than I was. Except now I'm ordering more CR39, Trivex, and 1.60.
Considering my last work environment where I did 1200 RX jobs a month which were all Poly and Z87 stamped. I haven't had a single complain about the lens cracking so I have no idea what you guys are doing to achieve this. I should mention all of my edging was done on MEI system and lens edges where threaded with chemicals (might be silicon polymer).
i have the same experience... about 6 years ago Hard Coats began improving dramatically, so maybe the issues are tied?
Although the chemicals used in Poly have not changed, the way its manufactured has. Early Polys were very yellowish, then Sola released their great "Water White" poly in the 1990's, or maybe it was Tegra? Technlogy barrowed from the CD industry.
As well, some guy in Connecticut patented a way to vacuum extrude poly into a hot mold, instead of cold pressing. The result is a cleaner less stressed poly structure. He has licensed the tech to Shamir and Zeiss, as well as making SV under the brand Resolutions.
a few manufactures us a perfectly ABBE matched hard coat as well now, but its still fairly rare.
...
Last edited by MEB; 12-05-2012 at 08:13 AM.
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