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Medical Forum / General / Vision / September 2005Stripped plastic lenses
About 18 months ago, I got plastic bifocals. Recently, I got new GLASS glasses because the AR coating on the old glasses was deteriorating. Apparently, the base material was not really damaged. I just got them back after having the coating stripped off. They seem be nice and clear now. I will keep them as backup glasses. The consequence of this is that I will not get plastic glasses again. Moreover, until I can get hard AR coatings on the glass, I will do without them. By the way, unless new techniques have been developed, hard coatings cannot be stripped off of glass. Using any acid to remove magnesium fluoride commonly used for such coatings will generate enough hydrofluoric acid to etch the glass substrate. Bill >About 18 months ago, I got plastic bifocals. Recently, I got new GLASS >glasses because the AR coating on the old glasses was deteriorating. >The consequence of this is that I will not get plastic glasses again. >Moreover, until I can get hard AR coatings on the glass, I will do without >them. I've been wearing plastic lenses with AR for more than 10 years and I've never had the problem you describe. How would one "strip" surface coatings from plastic lenses without etching the plastic? +++++++++++++ Reply to the list as I do not publish an email address to USENET. This practice has cut my spam by more than 95%. Of course, I did have to abandon a perfectly good email account... On 9/11/05 7:05 AM, in article 0be8i19vf84hacgk3pnc2qeobq64tnri06@4ax.com, > I've been wearing plastic lenses with AR for more than 10 years and > I've never had the problem you describe. > > How would one "strip" surface coatings from plastic lenses without > etching the plastic? It would depend on the coating and substrate materials. As far as I am concerned, if the coatings are strippable, then they are not worth having. That is why I am sticking to glass without AR. If I could get hard AR for glass, I would get them. Bill > On 9/11/05 7:05 AM, in article 0be8i19vf84hacgk3pnc2qeobq64tnri06@4ax.com, > [quoted text clipped - 8 lines] > That is why I am sticking to glass without AR. If I could get hard AR for > glass, I would get them. It's a tradeoff. With my prescription, I would never consider getting glass lenses. I have a difficult enough time with the weight of my non-corrective glass-lens sunglasses. The AR coating on my 3 year old high-index lenses is more or less damaged. There's a tradeoff to having plastic lenses that are more impact and lighter than glass. >On 9/11/05 7:05 AM, in article 0be8i19vf84hacgk3pnc2qeobq64tnri06@4ax.com, > [quoted text clipped - 5 lines] > >It would depend on the coating and substrate materials. But the question remains, and both the coating and substrate in this case were at least broadly defined: plastic lenses, AR coating. How on EARTH would one strip any sort of coating from a plastic lens without damaging hte lens or at the very least altering its optics? Wooly Who averages four years on a pair of high-index AR-coated plastic lenses. +++++++++++++ Reply to the list as I do not publish an email address to USENET. This practice has cut my spam by more than 95%. Of course, I did have to abandon a perfectly good email account... > But the question remains, and both the coating and substrate in this > case were at least broadly defined: plastic lenses, AR coating. How > on EARTH would one strip any sort of coating from a plastic lens > without damaging hte lens or at the very least altering its optics? I asked a lab guy who does it. He says he uses acid etching cream from a craft store. Evidently CR39 resists hydrofluoric acid well enough. Mylar is similar to CR39, and in decorative etching, Mylar is recommended for masking off patterns, and for dropcloths. Acid-etch is sold in polyethylene containers because it corrodes metals and anything containing silicon. AR coatings are silicates. Silicon and carbon form similar compounds, but carbon-based polymers are more resistant to HFl. -MT On 9/13/05 8:08 AM, in article UXBVe.11225$_84.4605@newsread1.news.atl.earthlink.net, "Mike Tyner" <mtyner@mindspring.com> wrote: >> But the question remains, and both the coating and substrate in this >> case were at least broadly defined: plastic lenses, AR coating. How [quoted text clipped - 14 lines] > > -MT Most of the polymers used for lenses will resist hydrofluoric acid (HF). Before suitable polymers were available, HF was shipped in wax containers. HF is not a particularly strong acid in a pH way, but it does react with silicates; glass that is. It is also not good for people. It is the fluoride in the solution that gets into you and does the terrible things. Fluorine is an example of an element vital to life but not good for you in larger quantity. Simple magnesium fluoride (MgF2) AR coatings will be readily removed by many mineral acids such as nitric acid. The trouble is that the fluorine in the coating material forms HF which can then attack glass. There is very little material in a coating, but often it is enough to end up with a degraded glass surface. Silicates are not often used for optical coatings, at least not for high quality optics. The main exception is that silica (SiO2 quartz) is often used for such coating. It would be highly susceptible to HF. In thin-film design, silica acts as a high index material with low index fluorides and a low index for high index materials such as titanium dioxide. That is probably more than anyone on this newsgroup wants to know. Bill > On 9/13/05 8:08 AM, in article > UXBVe.11225$_84.4605@newsread1.news.atl.earthlink.net, [quoted text clipped - 50 lines] > That is probably more than anyone on this newsgroup wants > to know. You would be surprised. Most excellent technical explanation in layman's terms. Thanks. -Quick > About 18 months ago, I got plastic bifocals. Recently, I got new GLASS > glasses because the AR coating on the old glasses was deteriorating. [quoted text clipped - 5 lines] > Moreover, until I can get hard AR coatings on the glass, I will do without > them. Now this seems to be a contradiction. Your plastic lenses came through the stripping process just fine, and you "will not get (them) again"! And then you say you will do without the (glass) lenses???? > By the way, unless new techniques have been developed, hard coatings cannot > be stripped off of glass. Using any acid to remove magnesium fluoride > commonly used for such coatings will generate enough hydrofluoric acid to > etch the glass substrate. It's been ages since I ordered AR coated glass lenses, but I do recall them being strippable. I have no idea what chemical or other process they used, but the same lab that coated 'em could strip 'em... w.stacy, o.d. On 9/11/05 8:41 PM, in article CN6Ve.177$7x4.91@newssvr13.news.prodigy.com, >> The consequence of this is that I will not get plastic glasses again. >> Moreover, until I can get hard AR coatings on the glass, I will do without >> them. Sorry about the ambiguity. I meant doing without the coatings. > Now this seems to be a contradiction. Your plastic lenses came through > the stripping process just fine, and you "will not get (them) again"! [quoted text clipped - 8 lines] > them being strippable. I have no idea what chemical or other process > they used, but the same lab that coated 'em could strip 'em... One could always try stripping MgF2 coatings. Usually, for high quality optics such as in high intensity laser equipment, not ophthalmologic optics, there would be etching of the glass if acid were used. The coatings are so tenacious that mechanical removal is impossible short of repolishing. Softer coatings using cryolite or chiolite were once used because they were easier to deposit. They also had lower index and would give slightly better AR performance. Bill there is a commercial chemical solution available that can strip AR coatings. I wish I new what the active ingredient is. http://www.storminnormans.com/opticalshop.htm |
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