CASE STUDY: Sunglasses made of ‘unbreakable’ polyamide

• Sunglasses have to withstand enormous stresses
• Microcrystalline polyamide is flexible, and virtually indestructible
• Dominant colors are the style of the season
• Special: 10 tips for purchasing sunglasses

When people decide to get a new pair of sunglasses, they should be sure not to focus on good looks alone. Sunglasses have to provide protection against harmful UV light and must be highly durable. High-performance polymers play an important role making the plastic lenses literally ‘unbreakable’.

Dominant colors are the style of the season

“Large sunglasses in noticeable, dominant colors are the style of the season. That includes lenses with green, red or orange-yellow mirrored surfaces, even blue. These aren’t pastels, but bold colors that actually make a statement”, says Paul Rottler, an optician who operates some fifty optician’s shops throughout Germany. The summer 2015 trends favor round shapes over angles and delicate features over chunky ones.

Sunglasses have to withstand enormous stresses

Some rules apply regardless of style. Sunglasses have to provide effective protection against UV light and have to withstand enormous stresses. They also have to withstand high temperatures when, for example, left in the car. This presents a special challenge for manufacturers of sunglasses.

Microcrystalline polyamide is flexible, and virtually indestructible

To address these requirements the company Evonik Industries offers its Trogamid CX, a microcrystalline polyamide. With this material sunglasses do not become brittle or hard, and are not affected by sunscreen, hair gel or hairspray. It is flexible, virtually indestructible, and since the substance is also transparent, it can be tinted in different colors.

Tests performed by the TÜV Rheinland testing institute have demonstrated just how sturdy the plastic is. Some test series involved bouncing steel balls off Trogamid lenses–without leaving a trace of damage. Such tests are crucial to determine the breakage safety of lenses, for example during sports, when a ball may hit a pair of glasses. Breaking glass or splintering plastic lenses would be disastrous in that case. And of course breakage safety is particularly important for children.

Protection against facial skin irritation

Although sunglasses primarily protect the eyes, they also have to be gentle on the skin. During the summer heat, our faces tend to sweat more than usual, including in places where glasses touch the skin. That requires additional caution with the metallic temples of sunglasses, especially for those with nickel allergies. Even temples and nose pads that are coated with non-allergenic material may become eroded by sweat and release allergenic material, says Berlin dermatologist Dr. Jeanette Eicholtz. “Glasses made of plastic are relatively unproblematic in that regard,” she advises.

Rodenstock’s Porsche Design is on board

Master optician Paul Rottler is pleased that a growing number of manufacturers use the material for their production of glasses. “We keep a few models such as Porsche Design P‘8592 by Rodenstock in our assortment that have temples made of Trogamid,” he says. Many of Rottler’s customers have their eye on design and are pleased with the combination of high resistance and very low weight, and give preference to stylishly designed sunglasses made of the material.

10 tips for purchasing sunglasses

1. UV filter
   UV light is damaging to the eyes. However, as a word of caution, the best protection does not come from the lenses with the darkest tint (tinting strength), but from sunglass lenses made from high-quality material with an integrated UV filter.
2. Tinting strength 
   Depending on their level of tinting, sunglasses are suitable for different activities, and are organized into so-called lens categories from 0 to 4. While category 2 is a suitable summertime choice for Germany, category 3 is best for Southern Europe and category 4 is recommended for skiing, but not for use in road traffic.
3. Size of lenses 
   Lenses should be large enough to protect the eyes from sunlight coming in from the side or above as well as from below through reflection.
4. Color of lenses
   Brown and gray lenses modify colors the least. For all other lens tints, the eyes require a certain response time to neutralize the color.
5. Quality of protective sunglass lenses
   High-quality lenses do not show any streaks, blisters or inclusions. Inferior lenses can cause headaches and dizziness.
6. CE marking 
   Sunglasses sold in Europe must bear CE marking. While this mark makes reference to quality and UV protection, it is not sufficient to identify high-quality lenses. Professional optician associations also point out that the mark is easy to counterfeit.
7. Sunglasses for driving a car 
   If you drive a lot, select sunglasses with narrow rims and temples to avoid restricting your field of vision. Vision impairments should be corrected by sunglasses as well. The lens category must be below 4.
8. Activity
   Pick sunglasses according to activity You will need different lenses for winter sports than for the beach, sailing or surfing. For example, snow reflects over 90 percent of sunlight.
9. Polarizing effect 
   In simple terms, polarization prevents the visible glare of sunlight on smooth surfaces. As an example, fishermen using highly polarized sunglasses can see fish below the water surface, but not the reflection of the sky and trees.
10. Professional fitting 
    The frame must be individually adjusted to the shape of the head to make sure no damaging UV radiation can reach the eye, for example laterally past the sunglasses. The adjustment needs to keep the width of the temple, eye spacing, and the position of the ears in mind.

Picture: Rodenstock sunglasses in Porsche Design