AR Lens Success Begins with the Hardcoat

By John Quinn
Hardcoating, the first and one of the most important layers of a successful AR lens, must be comprised of superior materials applied according to the exacting standards of the manufacturer. When priority is given to both materials and application, the hardcoat can ensure your success in producing a premium AR lens. One key variable in backside UV hardcoating is the energy output of the UV bulb. All UV bulbs degrade over time, resulting in decreased energy and, therefore, decreased polymerization of the coating.

Eventually, the energy level will reach a point where it will not cure the coating so that the coating is still wet to the touch. Long before this obvious sign, the energy level can be below an acceptable level required to produce a quality product. While it may not be immediately obvious, this can result in a range of defects including: adhesion failure, tinting problems, scratches and AR coating failure.

If you’re lucky, these problems will show up as breakage in the lab. Otherwise, they will come back in the form of customer returns and/or lost customers.

So how does one know when the UV energy falls below acceptable standards? There are a few tools that can help. Wireless radiometers are available that can measure the intensity of the UV lamp. Several manufacturers offer products, including International Light, EIT, and UV Process Supply. Quantum Technologies (www.uvsensor.com) have developed one specifically for the ophthalmic market. They offer two models measuring different spectral ranges, the Quant-300 from 185-320nm and the Quant-400 from 320-390nm. Both units are roughly the size of a semi-finished lens and can be placed directly on the suction cup.

This puts the sensor in the same position as the lens rather than some other position, an important factor in obtaining accurate information.

Some basic tests should be incorporated into the daily startup procedure for the coating machine, whether or not you have a radiometer. Before beginning production, coat one pair of poly, plastic and high index. After coating, tint the lenses for 15 minutes and measure the tint density (light transmission). By charting the tint density over time, you may notice that the coating is absorbing more dye or the tint is blotchy and uneven, a sign that the coating is not fully cured. After tinting, let the lens cool for 15 minutes and then perform a cross hatch adhesion test. Adhesion failure is a sure sign that something is wrong with the process.

The AR Council offers a crosshatch adhesion test kit to its members which includes a special tool for performing the crosshatch, specified tape used to test adhesion, and the full procedure for conducting the test. The crosshatch adhesion test is a critical quality control test and should be performed daily. The test is applicable to both hardcoats and AR coatings, and can be performed quickly and easily. By incorporating this simple test into your daily procedure, you can help ensure the quality of your product.

Success in building your AR lens business is dependent upon close attention to all facets of producing a quality product. Special attention to applying a premium hardcoat, whether it is UV cured or thermal cured, is a critical factor of your future in developing a successful delivery system, which your customers can consistently depend upon. Combined with premier customer service, they’re certain to remain committed to both your company and your product. John Quinn is the president of Lens Technology International.

CURRENT ISSUE


May/June LabTalk 2017