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Thread: Spider web crack on AR coating.

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    Spider web crack on AR coating.

    I am a newbie in this field. I was bother by a problem which is quite important related to AR quality. I was coating the CR39 with thermal cured tintable hardcoat applied on it with SiO2 and ZrO2. the quality of the lenses are not consistent and i found some of the lens have spider web cracks. Can anyone give me any opinion or advices on this problem.

    AR process is done with ion-assisted vacuum coater, however, i just apply the ion source for pre-cleaning purpose and it doesn't really involve in the coating process.
    I was told by some other people that used to work in this field and they told me it might be the problem of the moisture that trapped on the surface of the hardcoated lens. Is it really the source of the problem? or any others?
    Please advice!
    Last edited by hean; 11-04-2007 at 10:48 AM.

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    Blue Jumper humidity

    Quote Originally Posted by hean View Post
    ...............it might be the problem of the moisture that trapped on the surface of the hardcoated lens. Is it really the source of the problem? or any others?
    You are in a very humid climate.

    CR29 is a very porous material and there is a possibility of trapped moisture. The cure for this is very simple place the lenses in an oven for 30-60 minutes at 110C before hard coating. That should evaporate all humidity from the lens pores.If that dont help look for further causes.

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    Rising Star mauroventura's Avatar
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    kind of defect

    Hello Hean,
    I'm very curious, can you explain me what is the really shape of defect?
    This defect is the same on positive and negative lenses ? In the same position ?
    AR questions:
    .) which kinds of materials are involved in AR process ??
    .) The Ion source use Argon or O2 for pre etching phase ??
    .) The temperature in High Vacuum chamber is correctly Handled??
    .) Did you have a cool trap installed in your machine ??

    hardcoat questions:

    .) did you check the thickness of your hardcoat film ??:idea:
    .) did you check the RH% on your hardcoat room ??


    It would be very interesting for me to know this details in order to give you my impressions.

    HI:)

    Mauro Ventura

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    I suggest checking temperature of the vacuum process, maybe it's to high for this lenses.
    Also, it is very important what is a temperature of an oven, what is a time for it.

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    Reply to mauroventura

    The shape of defects is whole surface with the spider web shape cracks. it happens to positive and negative lens.

    AR question.
    1. The AR material involved in the process is SiO2, ZrO2, ITO and hydrophobic.

    2. Ion source use argon for precleaning, after that during the coating of the ITO layer, it is coat along with argon, oxygen and ion source.

    3. I have monitored the temperature of the vacuum chamber, it stay around 70 celcius during the process. during the coating process, the peak temperature climbs to 74 celcius.

    4. Yes, the vacuum coater are using cyropump as well.

    Hardcoat question.
    1. The hardcoat thickness is about 3.3um

    2. the RH% in the hard coat room is around 40% humid.

    Besides, I found that the concave surface tends to be smoother than the convex though i am using the same hydrophobic material and thickness for both side.

    The curing time for the hardcoat is 3 hours 85 celcius. But during the curing time, the ovens is open frequently for putting lens inside. this is what i am worried about, will be this the cause of the crack?

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    Quote Originally Posted by Chris Ryser View Post
    You are in a very humid climate.

    CR29 is a very porous material and there is a possibility of trapped moisture. The cure for this is very simple place the lenses in an oven for 30-60 minutes at 110C before hard coating. That should evaporate all humidity from the lens pores.If that dont help look for further causes.
    110C of curing temperature? will the lens overcured? it seems kind of too hot for CR39 rite?

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    Quote Originally Posted by hean View Post
    110C of curing temperature? will the lens overcured? it seems kind of too hot for CR39 rite?
    I do 80C for pre-curing and 110C for full-curing.

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    May i know how long is your pre-curing time and full-curing time.

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    Thanks to everybody who give me some opinion and advice. The problem was solved.

    I had tried with the solution provided by Chris Ryser. This resulting the same problems with spider web shape cracking on the lens.
    However, i noticed a very special thing, the cracks only happened on the convex site which i coated firstly. And the convex surface is not as smooth as the concave surface of the lens though i used the same hydrophobic material and same thickness for both surfaces.

    After that i tried to reduced the chamber temperature as from 70C to 65C and the problem was solved.

    Besides, i notice that the 1.5 and 1.56 material tends to crack more often during my previous test before i reduced the chamber temperature.

    This is my conclusion, lens material for 1.5 and 1.56 are more softer and having much more thermal expansion under high temperature than 1.6 and 1.67 lens.

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    my opinion on Hean's problem

    Quote Originally Posted by hean View Post
    Reply to mauroventura

    The shape of defects is whole surface with the spider web shape cracks. it happens to positive and negative lens.

    AR question.
    1. The AR material involved in the process is SiO2, ZrO2, ITO and hydrophobic.

    2. Ion source use argon for precleaning, after that during the coating of the ITO layer, it is coat along with argon, oxygen and ion source.

    3. I have monitored the temperature of the vacuum chamber, it stay around 70 celcius during the process. during the coating process, the peak temperature climbs to 74 celcius.

    4. Yes, the vacuum coater are using cyropump as well.

    Hardcoat question.
    1. The hardcoat thickness is about 3.3um

    2. the RH% in the hard coat room is around 40% humid.

    Besides, I found that the concave surface tends to be smoother than the convex though i am using the same hydrophobic material and thickness for both side.

    The curing time for the hardcoat is 3 hours 85 celcius. But during the curing time, the ovens is open frequently for putting lens inside. this is what i am worried about, will be this the cause of the crack?

    Hello Hean,
    thank U , for your reply.
    looking your info ,it is difficult to find the correct solution ...:idea: ,anyway
    I would prefer to follow this path:


    1) check problems on hardcoat film: do a dummy hardcoat coating reducing the tickness from 3.3 to about 2.5 microns and look the result after AR coating( even if depends on tech. sheet of your resin, 3.3 microns seems to much and 85 deg. cels for curing seems low).

    2) check problems on AR film : check exactly the substrate temperature with a PTC thermometer fixed on the calotte

    3) check problems on AR film : Do a dummy AR process without the ITO layer and look if the cracks are still on.


    Finally you must consider 2 questions:

    when did you start to have this problem ?

    What has changed from before?

    hi
    Mauro Ventura:cheers:

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    Quote Originally Posted by hean View Post
    May i know how long is your pre-curing time and full-curing time.
    Pre-curing 15 minutes and full-curing 3 hours.

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    Quote Originally Posted by hean View Post
    Thanks to everybody who give me some opinion and advice. The problem was solved.

    After that i tried to reduced the chamber temperature as from 70C to 65C and the problem was solved.
    Usually don't reduce the chamber temperature below 70C.

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    i have tried the same process as well as ITO layer with uncoat lens and they appeared to be no problem at all. By the way, may i know what is the effect of the overcured lens? for example, curing time is too long or temperature is too high. These should show different effects rite?

    I suspect the temperature sensor inside the vacuum chamber is not accurate since i solved the problem after reduced chamber temperature from 70C to 65C.

    Quote Originally Posted by mauroventura View Post
    Hello Hean,
    thank U , for your reply.
    looking your info ,it is difficult to find the correct solution ...:idea: ,anyway
    I would prefer to follow this path:


    1) check problems on hardcoat film: do a dummy hardcoat coating reducing the tickness from 3.3 to about 2.5 microns and look the result after AR coating( even if depends on tech. sheet of your resin, 3.3 microns seems to much and 85 deg. cels for curing seems low).

    2) check problems on AR film : check exactly the substrate temperature with a PTC thermometer fixed on the calotte

    3) check problems on AR film : Do a dummy AR process without the ITO layer and look if the cracks are still on.


    Finally you must consider 2 questions:

    when did you start to have this problem ?

    What has changed from before?

    hi
    Mauro Ventura:cheers:

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    By the way, answer to your question.

    1.This problem started since i having my uncoat lens coated with hardcoat.

    2.I have tested so many test, and even try to improved the cleaning method, curing time and hardcoat thickness. and finally i come to the chamber temperature.

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    May I know what is the effect if the chamber temperature is too low?


    Quote Originally Posted by Samuel Jong View Post
    Usually don't reduce the chamber temperature below 70C.

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    Quote Originally Posted by hean View Post
    May I know what is the effect if the chamber temperature is too low?

    In my opinion you shouldn't have any problem with temperature 65 for organic lenses. Of course it depends what kind of machine do you use, because of kind of heaters and where they are in the chamber. However, if the temperature is not good during the deposition, I suppose you will have a problem with repeatability of a residual color.

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    Quote Originally Posted by hean View Post
    May I know what is the effect if the chamber temperature is too low?
    If the chamber temperature is below 70C, then it will effect the adhesion of the ARC. Sorry, if my statement is wrong.

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    May i know what is the meaning of repeatability of residual colour?

    I face another problem again, The AR coating i am getting is not uniform and the color is slightly difference from the previous process, is it cause by the decent of the temperature inside vacuum chamber?

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    I have already solved the stated problem and just found out it was the Hydrophobic top coat that cause the color shifting. It seems that when i was trying to increase the top coat thickness to get enough hydrophobic effects, it will affect the outcomes of the AR color.

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    My lab is doing the hardcoat as well. but some minor problem arised after the lens was cleaned by ultrasonic cleaning, they tends to stick on with some dust and form a small dot after the hardcoat layer was applied. By the way, my lab is a class 10K cleanroom. Is it anyway i can improved my process?

    Below is my process flow.

    Preclean -----> ultrasonic clean ------> Curing (30 minutes 85C) -------> hardcoat --------> curing (3 hours 85C)-------> Multicoat.

    I found that most of the dust is hard to removed by the deionzed air gun. they seems to stick on the lens itself.

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