Tech Talk: The Advantages of On-The-Block Spin Coating


The optical industry is going through an enormous amount of change. There are acquisitions taking place at all levels including some of the industry’s largest players. Our products are being called upon to answer new challenges such as blue light protection, faster photochromic reactions, high-index materials and anti-fog applications. Automation is expanding at every phase of our process from lens picking to final inspection and this redundancy in equipment is proving added value and reduced costs to your bottom line.

One of these production processes, backside hard coating, is evolving and improving as well. For many years, the standard process was to surface the backside of a lens, then prior to spin coating an employee would de-block and remove surface-saver tape by hand. After these steps were complete, the lenses were washed by hand, stacked into groups of 10+ trays and brought to the coating machine for spin application. However, in an effort to reduce breakage approximately six years ago the concept of applying the backside hard coat while the lenses are still on-the-block was introduced. Since then, this concept is rapidly catching on as many customers are realizing the benefits of coating on-the-block, including an immediate reduction in spoilage.

When one employee manually de-blocks, de-tapes and washes an uncoated/unprotected lens it increases chances of damaging the lens surface prior to protecting it with scratch resistant coating. Fully automated lines help reduce this handling risk, but it is still there. There is considerable risk of transferring tape adhesive from the front to the backside of the lens surface from an employee’s gloved hand resulting in defects during backside coating. This risk is amplified by new hires and floating employees who are often placed into these roles while training. It’s generally a great place to start while they grasp what’s involved in producing optical work but it’s also the unknown gentle giant for producing defects and tray mix-ups during production. When de-blocking, de-taping and wash-up is moved after coating, the lens is much less likely to get damaged.

As lens manufacturers develop improved materials, today’s mass marketing touchpoints pass along their advantages to doctors and patients at a rapid speed. This means we must adapt to processing them faster and embrace changes to lab procedures while mitigating risk. In many instances, these new materials result in thinner and lighter lenses for the patient. While it’s great for the person wearing them, these thinner high-index lenses can be challenging for labs to process due to heat generated during surfacing and curing. However, if that lens remains mounted to the surfacing block throughout the entire process, you’ll eliminate the risk of warping. The block not only provides physical support, but also serves as a heat sink to reduce the heat absorbed by the lens.

If your lab isn’t prepared for automation today, you can still experience the advantages of coating while on-the-block using manual loading/unloading coating equipment. There are many different machine types developed specifically with you in mind. We’re all vested in your success through this partnership; together we can learn how to adapt change and support customers by offering more than one solution.

There are some common misconceptions about on-the-block coating. The first is that heat generated during the coating process will melt alloy and cause lenses to fall off. However this is not the case for alloy, wax or Satisloh ART processes. The short time duration a block is exposed in the process simply cannot generate enough heat to cause these materials to melt.

A second misconception is that the alloy and surface-saver tape could come off during production and that will change the liquid coating chemistry in the reservoir. This is also not true. The coatings used in backside spin coating machines today are almost always solvent-free. Tests have been done over time to ensure that the chemistry of the coating does not change due to alloy or tape being introduced into the liquid. It does not affect adhesion or scratch-resistance properties. In addition, the coating machine utilizes a filter so that foreign materials cannot get pushed through the coating pump and onto lenses during production.

There are many advantages and benefits from utilizing an on-the-block backside hard coating process in your lab. Reduced operator handling which increases yields, eliminates warping on high-index and other thin lens materials, surface-saver tape remains on the front-side which protects against overspray and more consistent loading/unloading of odd shaped lenses because the block centers the lens during production. Our businesses and processes are changing, don’t over-look the many benefits spin coating on-the-block can bring to your lab.

For more information on backside scratch resistant coatings, new machinery and SOP suggestions from Ultra Optics, contact them at (800) 365-9993, or visit

Matt Ramlet is regional account manager at Ultra Optics, Brooklyn Park, Minn.