A United Nations Environment Program (UNEP) decision to phase out the global use of mercury by 2020 has ignited conversation about the future use of other materials, among them cadmium and lead, which are components of alloy. Within the eye health industry, alloy has long been used as a blocking material in the manufacture of ophthalmic lenses. While some of the world’s larger ophthalmic companies have recently committed to phasing out the use of alloy as a blocking material, Satisloh is well ahead of the game, having introduced the first alloy-free production process for ophthalmic lenses back in 2008.
Satisloh’s first alloy-free process was introduced for On-Block-Manufacturing (OBM), a fully automated lens production line for front-side coated lenses that holds the lenses on the same block during the complete lens production process, including the hard-, sputter- and AR-coating stages (refer to mivision issue 78, April 2013).
Now the company has gone one step further by introducing Alloy-Replacement-Technology (ART), a new alloy-free blocking process that extends beyond the OBM-application.
Satisloh’s Autoblocker-ART is paired with the automated de-blocking system Auto-Deblocker-ART, for fully automated surfacing operations. Additionally, it can be combined with the manual deblocker, known as ART-Deblocker-M for manual based lens production.
the new ART process is environmentally friendly and features an organic ART-block-piece, which fits the existing collet chucks used with most generators and polishers
According to Satisloh, the new ART process is environmentally friendly and features an organic ART-block-piece, which fits the existing collet chucks used with most generators and polishers (see figure 1). The only mandatory requirement is that the mechanical interface is equal to the block-pieces used in the traditional alloy process, as defined in DIN 58766.
Savings to be Had
The ART-block-piece has a diameter of 65mm and is re-usable 100 times or more. With a choice of five different curvatures, the ART process enables the base curvature of the blank and the block-piece to be best matched, from plano to 15dpt.
This ability to find an optimal match between base curvature and block-piece saves on the cost of adhesives and speeds up processing time during dispensing and curing – providing advantages that can be passed on to the customer.
UV-light curable adhesive is used to hold the blank on the block, and there is no need for any extra layers of protection, such as foil, which is used in the alloy process. Additionally, because both the block and the adhesive are fully machineable, optimised lens quality can be achieved by generating the block and the lens to get ‘full support’. This is especially interesting for ‘high +’ lenses, when full support on the lens edge is required. When ‘full support’ is not needed, the amount of adhesive can be reduced and optimised by calculating the final lens diameter instead of the blank diameter.
Unlike Alloy technology, the ART process cures UV glue in the machine within seconds and requires no cooling or waiting time. And, because the process temperature is only about 30° Celsius, there is no stress on the lens material.
The front side of the semi-finished lenses can be uncoated, hard coated (typically for PC) or AR-coated.
The Autoblocker-ART uses ‘spatial blocking’, which does not require block-rings. The machine measures the real base curvature of the blank and offers the option to send this data back to the lab management system (LMS). Depending on the mismatch between the given and the real base curvature, the blank can be rejected by the Autoblocker-ART or the calculation for the back curvature can be optimised by using this measured data to adjust to the correct total optical lens power. Typical applications, such as decentration of up to 5mm and prism of up to 5.5° are possible.
A typical application on PC or Trivex lenses goes like this… once the lens has been surfaced, polished and engraved, it goes to de-blocking or to spin coating. For backside spin coating in the Magna-Spin Auto, the lens stays on the block before de-blocking. The lens is automatically cleaned by warm water, then hard coated on the backside.
The auto-deblocker-ART separates the block-piece, the adhesive and the lens by using the same water-jet-technology used for Satisloh’s OBM applications. The block is sorted into different bins and the adhesive remains in a mash inside the machine. The de-blocked lens is returned to the tray it was in before going into the deblocker.
Once the lens has left the deblocker, it is cleaned, dried and ready to go straight to an automated lens measurement system.
This system does not require any surface saver tape, which significantly reduces waste and lens-cleaning time. Additionally, Satisloh claims it can save up to 40 per cent of the costs of consumables used to produce each lens.
Satisloh’s ‘tray up’ procedure determines the ART-block-pieces in the same way as blanks are determined.
The LMS calculates the data provided by the eye care professional to determine the correct block-curvature and the smallest possible block-diameter. The block is then positioned together with the calculated blank in the job-tray.
During the blocking-process the individual data matrix code is scanned to create a unique serial number. This serial number is then matched in a database with the information for the final lens diameter and the amount of usage. (See figure 1,2)
Once the finished lens is processed and deblocked, the deblocker sends the block back to the correct bin inside the deblocker or, if the maximum number of use-cycles is reached, into a bin for recycling.
A Viable Alternative to Alloy
ART technology provides a viable, more environmentally friendly replacement for Alloy lens production with a working range that covers all common lens materials and dimensions including coated (AR, HC, hydro, super-hydro, polarised, photochromatic, mirrored, tinted). Uncoated versions described as plano, spherical, torical, progressive addition lenses (PAL), Bifocal, Trifocal, Omega including prismatic power and de-centration are also included. The lenses can be made from all existing standard materials, such as CR39, Poly, Trivex, MR7, MR8, MR10, 1.74, Acryl, Mineral. Importantly, the overall lens accuracy (including generating and polishing) meets the standards specified in ISO 8980.