Need help on hardcoating

[brandon76]

Hi All,

I am new to this forum and I'd like to say that I'm very glad to discover this great avenue for sharing information about our industry. For the last three years I have been working in a lab owned by uncle. I have been assigned to work in the surfacing department until recently when the operator for our cleaning and dip-hardcoating machine left without notice to work overseas. I am now forced to learn this process almost from scratch. I hope you could help me be enlightened with some maybe very basic questions that I have that I have listed below. Thanks in advance for your help.

1) What is a primer?
2) Is a primer meant only as a pre-coat for polycarbonate lenses? Why can't we dip polycarbonate lenses straight into our varnish tank without coating them with a primer?
3) Can we use our primer to improve adhesion for other indices like 1.6 and 1.67 lenses.
4) IS it advisable to just keep on refilling our varnish tanks without having to completely change its content with fresh varnish. Or how would you know when your varnish has reached it's usable life?
5) What is the ideal varnish thickness in microns?
6) What could happen if have coated too much or too little varnish?
7) Is there any cheap/easy way to test scratch resistance of a hard-coated lens?

Best regards,
Brandon

[Chris Ryser]

All your above questions can vary depending the coating material and if it is thermal or UV curing. You better get back to the supplier of the machinery or/and the coating material.

[brandon76]

Hi Chris,

Thanks for your response. We do thermal curing. I have already written to our varnish and primer supplier, although all I have been given at the moment is a technical data sheet that don't have enough information. Anyhow, I just thought soliciting some information from members in this forum who have lab experience would certainly help:)

BR,
Brandon

[Chris Ryser]

4) IS it advisable to just keep on refilling our varnish tanks without having to completely change its content with fresh varnish. Or how would you know when your varnish has reached it's usable life?

As you are only pulling material out of the tank there should be no problem of contamination.

5) What is the ideal varnish thickness in microns?

Usually 2 microns is a good layer.

6) What could happen if have coated too much or too little varnish?

Too thick a layer might not flex with the lens and you coul;d get crazing.


7) Is there any cheap/easy way to test scratch resistance of a hard-coated lens?

Cut at least 10 parallel lines into the layer and then 10 more at 90 dgrees to make 1mm squares of the coating.
The take a good packing tape and press it on the area. Then rip it off. If all the squares are still holding to the surface, your adhesion is good.

[brandon76]

Thanks again Chris, greatly appreciate your reply. I hope it's alright to have some follow-up questions based on your response. On Q#4- based on our records the last time we changed our varnish was 6 months ago. What comes out of the machine seems to still look good cosmetically. Moreover, adhesion test results are still good. Are we just lucky or is this normal? What I don't see normal though is the color of the varnish is yellowish. On Q#5- are there cheap yet reliable devices that check the layer thickness? We don't have a spectrophotometer for my uncle doesn't want to invest in this equipment at the moment. On Q#7- we are already doing this test which as you say would tell if adhesion is good. How about scratch resistance? What tests could we do?

Brandon