A solar (eclipse) powered boom for specialty film business

Millions of people aiming to take in the Aug. 21 total eclipse of the sun can thank plastics for making the experience affordable and safe.

Thin polymer sheets are the key ingredient in paper- and plastic-framed eyeglasses being bought by the truckload to view the eclipse. The polymer film lens of the glasses cuts down the solar intensity by a factor of 250,000, allowing viewers to look directly at the sun as it transits behind the moon.

Compared to regular dark sunglasses, which reduce the solar intensity by 15 to 40 percent, eclipse glasses transmit only 0.004 percent of sunlight to the viewer's eyes, estimated Ralph Chou, an expert in eye protection and solar viewing, in an Aug. 6 interview.

"Special plastic lenses allow people to look at the eclipse in perfect safety," Chou said. "They will allow ordinary people to do real science."

The Aug. 21 event will be the first total eclipse in the United States since 1979. Chou said an estimated two-thirds of the U.S. population — more than 200 million people — will be in the eclipse's path or within a day's drive to prime viewing locations. In addition to local viewers, tourists from around the world will make the trek, filling up hotels along the path.

The combination of inexpensive viewing glasses and the solar transit across the United States during midday promises to make this the most popular eclipse in the nation's history. Manufacturers of the eclipse glasses are being run off their feet trying to keep up with orders.

"We're seeing 2,500 to 3,000 orders per day," said John Jerit, president and CEO of American Paper Optics, one of the biggest U.S. suppliers of eclipse glasses that are recommended by the American Astronomical Society.

"We're limiting orders to 50 glasses per order," Jerit told Plastics News in a telephone interview on Aug. 3 while he was rushing to fulfill the crush of purchasing requests. The rush is overwhelming despite American Paper Optic's ability to produce 50,000 glasses per hour at its Bartlett, Tenn., factory.

Chou said the polymer composition in the affordable glasses is a closely guarded secret, but he does know that carbon black is finely dispersed in the polymer and the polymer film is metalized with a thin aluminum layer. The combination of black film with a metallic layer cuts solar intensity to a level that is safe for the human eye. The film typically is about 2 mils thick.

Plain versions of eclipse glasses with cardboard frames or plastic frames are the main items sold by retailers, but the eclipse glasses makers are also doing brisk business for customized glasses used to promote a business or to raise money for charity. Cheap glasses run about $2 a pair, with plastic-framed ones starting at about $15.

The modern eclipse glasses had their origins in the 1970s, when amateur astronomers began experimenting with metalized Mylar, a biaxially oriented polyester film developed by DuPont Co. At that time, a big use of the metalized film was to protect seedlings as ground cover in agriculture, Chou recalled. Viewers were preparing for the 1979 U.S. total eclipse.

Chou has seen the evolution of plastic eclipse glasses from these early days. For 30 years he was an astronomy professor at Canada's University of Waterloo until he retired in 2012. Since then he has been a consultant to most major U.S. eclipse glasses producers. He was in a group that devised an international safety standard for eclipse glasses, the ISO-12312-2 standard adopted by the major solar glasses manufacturers. As president of the Toronto branch of the Royal Astronomical Society of Canada, he won't miss the event.

During the 1980s, black-loaded polymer films cropped up as competitors to metalized BOPET film. A disadvantage of the metalized film was it presented solar rays in bluish-white shades. The black films, however, cast the light in orange and yellow shades, which "are a lot more pleasing to the eye," Chou explained.

For years, controversy swirled around the plastic lens choices, with proponents claiming the rival material was subject to pinholes or other defects. Today, the common affordable glasses combine metalization and carbon loading in the polymer film. The composition of the polymer also evolved to overcome manufacturing drawbacks of conventional, thin BOPET film. The early thin films were difficult to mount into the glasses' frames. The search for alternatives faced stringent requirements. The treated polymer film must be dimensionally stable and scratch-resistant. The polymer must disperse the carbon black particles well.

Professional astronomers, not surprisingly, opt for higher tech eclipse viewing options. One standard filter type has a mixed-metal film deposited under vacuum on glass. These filters are far more expensive than the mass-market polymer film types.

Electric arc welding glasses have also been used to view solar eclipses. The glasses can be a thick polycarbonate film with proprietary dyes that block out harmful UV, infrared and visible rays. These filters are expensive and difficult for an amateur to buy. A "shade 14" welding filter is often recommended.

Chou said he's amazed at how important plastics have become in the whole range of optical applications.

"In the past few years, the plastics industry has been very creative in coming up with new materials," Chou said. Plastics are choice materials for prescription lenses, eyeglass frames and protective eyewear.

"There is a huge range of plastics for spectacles now," he said.

On Aug. 21, the eclipse shadow is due to hit landfall at 12:16 p.m. Eastern Time at Depoe Bay, Ore., and exit the country at 2:47 p.m. ET at Awendaw, S.C. Along the total eclipse's 70-mile wide path each viewpoint will experience about 2½ minutes total solar darkness.