Business / Tech | ADVANCES IN PROGRESS

Synthetic fluorite puts lens biz in focus

by Kazuaki Nagata

Staff Writer

Iwatani Corp. brightened the outlook for camera fans in October by announcing it had developed the world’s first viable technology for synthesizing high-purity fluorite — an element critical to making the world’s best lenses.

Lenses in top-flight cameras and telescopes require fluorite to reduce light dispersion, the main cause of the chromatic aberrations and color fringing that plague glass lenses.

The problem is cost: Most of the world’s supply of natural fluorite comes from China, which has a lock on the market.

Iwatani’s goal is to synthesize high-purity fluorite in large volumes so makers of fluorite lenses can procure it more cheaply.

“Fluorite might be treated as a strategic material, and there is a chance that (other countries) may not be able to import it in the future, so lens makers have told us that it would be a huge advantage if we could synthesize it here,” said Kentaro Nakajima of Iwatani’s R&D center in Hyogo Prefecture.

Fluorite with a purity of 99.95 percent — the minimum level for lens making — currently sells for more than ¥1,000 per kilogram. Anything below that only fetches double figures.

“Natural high-purity fluorite used for lenses can only be found at a limited number of mines in China,” Nakajima said.

For Iwatani, the main hurdle to synthesizing the chemical is production costs. The price of synthesized fluorite is double that of natural fluorite, so the company is searching for a way to lower its cost in the future.

According to Nakajima, Iwatani’s fluorite-synthesis technology was originally developed as a recycling technology to benefit a different business: computer chips.

About five years ago, the company developed machinery for recycling perfluorocarbon (PFC) gas, which is used on a large scale in semiconductor factories to clean circuit chips but also poses a risk to the Earth’s ozone layer.

Iwatani’s equipment recovered used PFC gas at factories and decomposed it with heat to collect hydrogen fluoride, which was then made to react with calcium-type chemicals to yield calcium fluoride — the chemical name for naturally occurring fluorite.

Any leftover fluorite was then reused to generate PFC gas again.

But after Japan’s chip makers fell on hard times, they ran out of money to invest in the recycling system. So Iwatani searched for another way to use the technology and stumbled onto the idea of making fluorite for lenses.

Although the fluorite produced by this technology had a purity of more than 90 percent, it was not good enough to make lenses. Fluorite must be at least 99.95 percent pure in order to emerge transparent from the melting and crystallization process used in making lenses.

So Iwatani decided to team up with Uedalime Manufacturing Co., a Gifu-based limestone maker, and Shinji Yasui, an associate professor at Nagoya Institute of Technology, to raise the purity of its synthetic fluorite.

To achieve this, they made use of a highly pure and dense form of calcium carbonate and Iwatani’s chemical expertise, Nakajima said.

A dense form of calcium carbonate was needed for a reaction to increase the density of the sought-after fluorite, but it was only available in powder form. So they decided to pelletize it.

“Lens makers said it is hard to use (calcium carbonate) in powder form, so we decided to produce it in the form of pellets,” said Nakajima. “But turning it into pellets requires a binder, which can become an impure substance.”

To solve that issue, Uedalime came up with a binder that wasn’t an impurity, he said. Impurities can include elements like magnesium, barium and strontium.

The pelletized calcium carbonate was then injected with hydrogen fluoride under optimal conditions set out by Iwatani to produce a highly pure form of fluorite, Nakajima said.

After several years of toiling, the companies developed a way to produce synthetic fluorite with a purity even higher than its naturally occurring counterpart.

This could be a huge breakthrough for Japan and anyone else reliant on Chinese imports, he said, because Japan can stabilize the quality and volume of the synthesized version.

The quality of natural fluorite varies because it is difficult to mine, he said.

While this technology paves the way for the proliferation of affordable, high-quality fluorite lenses in the future, efforts must still be made to reduce production costs, according to Iwatani.

“Raw material costs is the key,” Nakajima said, referring to fluorine and the more difficult to obtain calcium carbonate, which is expensive.

Savings on hydrogen fluoride, Iwatani said, might be achieved by approaching companies that specialize in recycling ozone-damaging fluorocarbons, which are commonly used in home appliances like refrigerators and air conditioners.

Iwatani said it is possible to cheaply extract hydrogen fluoride from fluorocarbons before disposal.

The company said it plans to determine whether this technology can turned into a feasible business next fiscal year.

This section, appearing on the second Monday of each month, features new technologies that are still under research and development but expected to hit the market in coming years.