Help with AR coatings

[EdSheridan]

Can anyone recommend a good AR coating lab. We've been having some failure recently with our current lab & haven't been able to figure out what's happening. Kodak progressives have been a particular challenge and I've been told that's not unusual. I've also been told that wax blocking can cause problem (but I'm not sure why it doesn't get cleaned off in their ultrasonic processes).

Thanks in advance,
Ed

[Steve Machol]

Ed,

In the interest on fairness, I'm going to refrain form recommending any particular AR Coating lab. (I helped developed a major manufacturer's coating and lab network. I also do some work for the AR Council.)

However, I encourage to heed to recommendation about the wax blocking since not all ultrasonic cleaning processes will adequately remove the wax. I recommend you use surface-saver tape on any lens that is going to be AR coated.

Also be sure to ask any AR lab you are considering what experiences they have coating the lenses you use. They may or may not have similar issues as your current lab. Some processes work better with particular types of coatings. The more the lab knows about the lenses you use, the better they'll be able to do.

[Peter Z]

Dear Ed,

Steve is correct. Wax from the blocking operation can cause many problems. Most ultrasonic systems will not remove all the wax or worse will contaminate the ultrasonic baths so that the wax moves to other lenses. The best way to avoid this problem is to use surface saver tape.

As for A/R coating adhesion on kodak progressive's, the coating lab has to etch the surface to promote better adhesion. The hardcoating used on the Kodak product requires additional lens preparation which most ultrasonic systems will not do.

[Jim G]

I can't reinforce enuf Pete and Steve's point about wax blocking. It's also a bear on getting hard coats to stick. We've found it in polishing slurry as well, being ground into the lens while polishing.

An untrasonic cleaner will generally remove the wax...which then floats to the surface of the solution...thru which the lens is withdrawn when removing from the unit. Gotta figure out a way to get the lenses out of the bottom....

[RT]

Ouch. As one of the designers of the "wax" blocking system, I feel compelled to defend the concept. And I thought of you guys as my friends...<g>

a) Our lab uses wax blocking, doesn't tape, and has an extremely low incidence of AR coating failures using our in-house system. Conclusion: it can be done. This simple observation that lenses can be blocked on wax and still AR coated may drastically change your approach to the situation.

b) Stealth Ultrasonics manufactures an ultrasonic cleaner that includes a feature called a "sparger". This simple device blows bubbles across the surface of the wash tank, pushing any floating wax over the edge of the tank into a collection chamber. This prevents the problem of drawing the clean lens up through floating wax. I highly recommend this machine. Call Ed at Stealth. Tell him I sent you. I might get a free beer!

c) Bad hygiene in the surface room is problem on a variety of levels (doesn't matter if you're talking about lenses or people!), whether or not the lens is to be AR coated. Allowing polish to dry on the lens is a FAR more frequent problem than the wax--it's just a hygiene issue. The price you pay for bad hygiene on the front of the lens is to have to tape lenses, which can lead to a variety of other potential problems: added cost, aberrations due to wrinkles or bubbles, unintended alignment errors (prism) due to decreased visibility, and thickness variations if you don't tape all lenses. Pay attention to cleaning. If you can't clean it, then you need to follow my esteemed colleagues' recommendation and tape it. Or you may make the decision to tape if you determine that's cheaper than good hygiene. Just be sure to understand what's really going on.

d) If you spread wax across the face of the lens during polishing, you have unobservant people who allow an obviously bad situation to occur. The problem could be prevented inside the generator, or manually by your personnel. The software in the Gerber generators anticipates this problem, and bevels away the wax if it is in danger of contacting the lap during fining. Unfortunately, other more popular computerized generators do not have such intelligence.

e) Our lab uses a Satis MC 260 coater. Perhaps there is some magic in the ultrasonic cleaning system for Satis coaters that removes the villainous wax. Ed--perhaps you might quiz potential AR labs as to what equipment they use. At the very least, you should understand their position on wax blocking. If they can't handle it...well, then they can't handle it.

f) DAC makes a wax (available in either Red or Blue) that deblocks much cleaner than the original Gerber FreeBond. Some labs have reported difficulty using this wax with Loh generators, but I haven't heard of any difficulty when using a Gerber generator. You might look into this product.

Now: what's the nature of your failure, Ed? All materials, only certain materials, crazing, peeling, all of the above?

Regards,
RT

[John R]

Originally posted by RT
Ouch. As one of the designers of the "wax" blocking system, I feel compelled to defend the concept. And I thought of you guys as my friends...<g>

c) The price you pay for bad hygiene on the front of the lens is to have to tape lenses, which can lead to a variety of other potential problems: added cost, aberrations due to wrinkles or bubbles, unintended alignment errors (prism) due to decreased visibility, and thickness variations if you don't tape all lenses

Regards,
RT

Cant see how tape causes aberrations in a lens? or how it decreases visibility either as you look through the lens at the marks under the tape, or we do anyway.

[RT]

JohnR: Tape can cause aberrations if not firmly pressed down, particularly on the ledge on a bifocal. The air bubble represents an area of weak support for the lens, and particularly with a single point cutter, it will turn into an aberration, particularly on thin lenses. Also, a wrinkle in the tape can lead to polish wicking between the tape and the lens, which also can lead to front side cosmetic problems.

Some tapes make it harder to see the features of the lens when aligning it in the Gerber Step One.

The point is, taping lenses is not totally benign.