Hard Coat Crazing?

[Oscar]

Anyone with a coating background have some insight on this? I thought "crazing" mainly happens to AR since the layer is so thin. What woud cause a hardcoat to break down like this? Patients are adamant they aren't doing anything harmful to the lenses

[Kwill212]

That looks like it was cleaned with harsh chemicals rather than crazing, or the coating was bad to start with.

[Lensman11]

This looks like an insufficient curing of the hard coat. This is most likely a uv cure coating which are prone to this problem. The uv source degrades over time and user neglects to replace it. The assumption is at the time of curing if the coating is dry it is cured that absolutely not the case.

[Oscar]

That looks like it was cleaned with harsh chemicals rather than crazing, or the coating was bad to start with.

I get both patients who are obviously lying and those that I genuinely believe or not mistreating the lenes with this same issue.

[Oscar]

This looks like an insufficient curing of the hard coat. This is most likely a uv cure coating which are prone to this problem. The uv source degrades over time and user neglects to replace it. The assumption is at the time of curing if the coating is dry it is cured that absolutely not the case.

Interesting. I will have to poke the lab about this further. thank you.

[Lensman11]

Who ever does the hard coating must do a cross hatch test every day. This involves cutting lines in the coating in a cross hatch similar to a tic tac toe pattern with the lines 2mm apart. A tool is available with blades already separated by the correct distance so you just pass once horizontally and once vertically, then you apply a special tape let stay on the lens for 2 minutes and pull it off rapidly. If the coating is not cured correctly some of the little squares you created with the tool will release the coating on to the tape. Time to change uv source.

[Oscar]

Who ever does the hard coating must do a cross hatch test every day. This involves cutting lines in the coating in a cross hatch similar to a tic tac toe pattern with the lines 2mm apart. A tool is available with blades already separated by the correct distance so you just pass once horizontally and once vertically, then you apply a special tape let stay on the lens for 2 minutes and pull it off rapidly. If the coating is not cured correctly some of the little squares you created with the tool will release the coating on to the tape. Time to change uv source.

Is UV cure used for dip coatings? I thought it was only spincoat?

[Lensman11]

Uv is for spin coat only the cross hatch test is universal as well as a haze test to check the hardness of the coating. Check if your lab has the capacity to do both. If you apply AR coating these tests along with several others are critical to maintain consistency and integrity of your coatings.

[Quince]

Who ever does the hard coating must do a cross hatch test every day. This involves cutting lines in the coating in a cross hatch similar to a tic tac toe pattern with the lines 2mm apart. A tool is available with blades already separated by the correct distance so you just pass once horizontally and once vertically, then you apply a special tape let stay on the lens for 2 minutes and pull it off rapidly. If the coating is not cured correctly some of the little squares you created with the tool will release the coating on to the tape. Time to change uv source.

...Oh the things that I was never taught...

[Uncle Fester]

Always learning.

I've added this to the Hall of Fame Forum dealing with AR; #30.

[jefe]

Poly lens?

[lensmanmd]

Poly lens?

Probably, but what lensman11 was discussing has to do with backside spin coating, and will affect any substrate that would require a backside hard coat.

In this case, by reviewing the picture posted, this is a backside issue, as the front is not affected.

Adding to lensman11's post, humidity/moisture is also a factor that can affect the proper cure of the coating. Again, an adhesion test will assist in verifying that the cure is satisfactory.

[lensmanmd]

Some light reading

https://www.2020mag.com/article/testing-scratch-resistant-and-ar-lenses

https://qtmi.net/courses/salt-water-boil-test/

https://kta.com/kta-university/coating-adhesion-testing-knife-tape/

https://www.ascottshop.com/acatalog/cross-hatch-cutter.html

[PRECISIONLAB]

First question is material? Next question type of coater? Last question have lenses been exposed to extreme heat?

As far as cure time and coating thickness, Ultra Optics coaters use a timed system for best results. With respect to coating thickness, two actions control this. The amount of time coating is dispensed / applied to backside then spin rpm and duration. UV lamp is also set based on time yielding a cured lens.

With some 1.67 backside crazing can be an issue especially if left in extreme heat. I never backside 1.70 and above as dip coat is the preferred method.

[jefe]

Poly is the problem. I've never seen such problems on any other material.