Chamber Temperature for Transitions

[Samuel Jong]

What's the chamber temperature to put AR on Transitions?

[Jim Schafer]

Samuel,

We do not know the technical specs of the AR process. We do have temperature and pH guides for cleaning and preparation. The rest of the process is propietary to each AR manufacturers brand. Here are the prepeartion tips.

· The lens surface should be thoroughly cleaned and free from any contamination and detergents prior to AR coating.

· Ultrasonic washing is recommended. The bath temperatures should be around 50°C to 55°C. Check with you equipment suppliers for any further recommendations.

· If a detergent with high pH (>10) is used care should be taken that the hard coat is resistant to the detergent and no damage occurs to the surface*. Any damage to the hard coat will effect the durability of the AR coating. Recommended cleaning conditions: Time in detergent/caustic bath approximately 3 mins; Concentration of caustic wash approximately 3%; Temperature of baths 50°C to 55°C.

· As the caustic solution ages the pH may increase due to contamination.

· The detergent should be thoroughly rinsed from the lens.

· If you must remove factory hardcoat from Transitions: Immersion time in 12% KOH at 60°c is 4 minutes. Rinse thoroughly before next cleaning steps.

· Recommended air drying temperatures for Transitions Lenses is 55°C to 60°C maximum.

· If the lenses are to be degassed or baked it is again recommended to use a maximum temperature of 60°C.Lower temperatures for longer time periods, e.g. 4 hours, will lead to less thermal stress build up in the lens. This will decrease the probability of crazing and cracking development associated with the build up of internal stresses. Degassing over night is not recommended.

· Stresses may build-up while being coated. To reduce the probability of any stress ensure that the clips on the lens are not too tight.

· General checklist: Is the temperature of all baths < 60°C? Is the air drying temperature < 60°C? Is the degassing/baking temperature < 60°C? Is the hard coat etched/eroded by the cleaning process? Does the backside hard coat offer good compatibility with the AR coating – If product was uncoated, does the lab hardcoat offer compatibility.

best regards,
Jim

[Samuel Jong]

Hi Jim, The temperature setting our chamber is around 70°C to 80°C for CR39 lenses, if I put the Transitions in one batch with other lenses, then sometimes cracking of AR coating will be found on Transitions. But if I set the temperature down to 60°C, and it will affect the adhesion of the AR coating.

[Jim Schafer]

Samuel,

Most AR facilities treat all Transitions as if they are high index lenses. Our 1.50 standard index product lens material is based on CR39® but it has been modified enough that the linear thermal expansion rates are almost 50% greater than CR39. This means the expansion and contraction rates of Transitions 1.50 are more sensitive in the same tempertures than CR39. This is not always friendly to rigid thin films. Care must be taken with handling these lenses.

You may want to AR all Transitions with your higher index lenses but first, check your ring holders to see if they are to tight, causing flex enough to crack your AR as the lens heats/cools. You may also want to try a longer ramp on the cool down cycle. You may be thermal shocking the lenses.

Does the manufacturer for your AR equipment have special handling and settings for higher index materials with high linear expansion rates?

regards,
Jim

[Samuel Jong]

You may want to AR all Transitions with your higher index lenses but first, check your ring holders to see if they are to tight, causing flex enough to crack your AR as the lens heats/cools. You may also want to try a longer ramp on the cool down cycle. You may be thermal shocking the lenses.

regards,
Jim

Hi Jim, I will check the ring holder, hope it can solve the AR cracking problem. Thanks for your advise.

Best regards,
Samuel