# Optical Forums > Ophthalmic Optics >  Facing problem in hard coating...Need Help

## hardcoat engineer

Hi! Greetings to everyone in this forum. I am a new user of this forum. I am facing a lot of problem in hard coating. We dip coat our lenses. We are getting dots/spots on our lenses. What are the reasons for getting dots? Is it dust or is it the environmental conditions like room temperature, humidity etc. Please help. Thank you in advance

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## Steve Machol

It could be any or all of those. Perhaps if you provide more information then OptiBoard members can help you with this.

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## other_bill_fea

With dip coating, there are quite a number of variables that can cause this. It would be difficult to troubleshoot, even with more information about your system. 

It could range from the lenses not being clean enough, the environment, or any one of the chemicals in the process being contaminated. Your curing oven(s) could also be the source, if they are dirty.

The best recommendation I can make is talking with whoever you got the dip coater from, as they're the best suited to help as they understand the specific process which you are using.

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## hardcoat engineer

I suspect that dust is the main culprit...Can anyone suggest me the daily cleaning procedure of the machine? How often are we supposed to change the filters used for filtering city water and DI  water? We use 1micron filter for city water. Our system is intake fresh city water when lens is there in the basket. When there is no lens the water is circulated through the filter. For etching purpose we use chemical which is diluted by DI water. Here we use a 5 micron filter which is working always. We maintain DI water resistivity greater than 15.please help :Help:

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## hardcoat engineer

" Your curing oven(s) could also be the source, if they are dirty"
Thank you for replying...The dots are visible after pre curing stage...still I will surely take into consideration your suggestion. how do you clean your curing ovens and how often u clean it?

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## other_bill_fea

As I'm not familiar with your equipment or process, I can only offer general ideas. How often you need to clean the machine and ovens can vary, depending on exactly how clean your environment is. I would say at least once a week. The filters can vary as well, as I know some of the coating filters are a 1-2 week change. 

Do you have a machine vendor you can ask about recommended filter life span?

It's also very easy to get coating contaminated, such as if a lens goes through with some kind of coating on it that isn't fully removed by pre-cleaning (like wax from a wax blocking system). This can cause all kinds of 'bad coating' issues.

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## Etienne

Generality, Clean with an alcool all the part inside your machine. 
Have you check your air prefilter for the sur pressure and check you absolut 99% filter?
Use a DI water or city water not strong with your chimical product
Check if the city water flow is correct after your chimical attak 
Check your conductivity for DI Water (maximum 0.3 micro Simens)
Have you a UV lampe on the DI Water pip, maybe make bacterial test
Ckeck the liftout DI water , no drop water
Clean you oven after Di Water
You lens need perfeclty dry after this oven and before the varnish
use a filter 1-5 micro for your varnish
Check the oven after the varnish, maybe so hot

After , you have need your process and you machin type for to have an other solution
Good luck

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## essegn

I think for you is the best to send some defective lenses directly to the dip coating machine manufacturer for an analysis. It will give you another ideas what to check.

All what is written above could be usefull, but if you have the machine for more than 5 years, it would be good to check and clean the varnish pipes - or replace them for a new one. But the basic should be to check the lenses after the first oven.

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## hardcoat engineer

Can anyone suggest me what will happen if I process my lenses at humidity 22%-24%

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## Etienne

I think if you work we humidity 22-24% it's very good but you must know your Air temperature . The problem is if you have a humidy hight , the varnish take the humidy and you have a mist betwenn lens and hardcoated.

You can find on the web , the calcul for know the "point de rosé" in french or dewpoint.
But the best is call your varnish dealer

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## Tito

Check your water filters.How often you change them will depend on how good is your city water.Try changing the filters and make a thorugh clean up ,and change new laquer.Start from the beggining again. 
Where I live I needed to place another pre-filter .

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## hardcoat engineer

can anyone suggest me how to process high curve lens in coating? We are having spots and scratches on them.

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## Trisel24

I've worked in a lab for two years and have had similar problems in the past. Dust and/or debris is the main problem. If you have a nitrogen tank you will want to air spray the lens to get rid of any and all debris. Then spray the lens centrally with isopropyl and use thin lens paper which you can order from most optical tool suppliers. You can also clean the curer with isopropyl.

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## Trisel24

I have a patient specifically requesting a "purple hue" AR. I know that some of the older coatings have had this in the past but I am unable to find one. I've tried three labs and four different coatings. I know provencia has a purple hue but it is not a VSP approved lens and the patient would have to forgo her lens benefit. She ordered her glasses three months ago and though very patient, I would like to resolve this as soon as possible.

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## AngeHamm

Zeiss Purecoat is on the purple side of blue, but of course nowhere near as purple as Prevencia.

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## hardcoat engineer

I am facing problem with transition lenmses.The hard coat is breaking.Inside the machine  we already have 3 etching tanks and the total etching time is 12 mins.Do transition lens require additional etching?Do we have to etch it seperately?Our hard coating thickness is from 2-3.2 micron.need help urgently

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## hardcoat engineer

I am facing problem with transition lenmses.The hard coat is breaking.Inside the machine  we already have 3 etching tanks and the total etching time is 12 mins.Do transition lens require additional etching?Do we have to etch it seperately outside the machine?Our hard coating thickness is from 2-3.2 micron.need help urgently

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## lens_man

Do you have to decoat your transition lenses? Are you sure that when you decoat the lenses all the coating has come off? Usually you have to use a higher concentration of acid while decoating to remove any traces of the old coating. I suggest you take a container and put in your NaOh in Di water and soak the lenses for 10 minutes in this solution and then carry on with your normal process.

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## hardcoat engineer

Hi, I am facing another problem.After coating the power of the hi index lenses  1.67, 1.74 are changing.Is there any particular reason.How do we handle it?Do we have to consider anything in blocking

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## Mauro.Airoldi

> Hi, I am facing another problem.After coating the power of the hi index lenses  1.67, 1.74 are changing.Is there any particular reason.How do we handle it?Do we have to consider anything in blocking


some questions:
1    1.67 is Mr7 or Mr10?
2     what is the polymerization temperature?

remember than the softering temperature for MR7 is 85°c and Mr174 is around 78°C (MR10 is around 100°c)
so if you polymerize at 120°c these two materials you risck surface stress and deformation.

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## dsenk33

Sounds like your problem is heat related, most likely in curing.  Heat is causing stress fractures in transitions and aberrations/waves in hi-index.

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## Tito

After hard coating or after AR coating?

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