Today, the importance of high-quality, high-tech lens materials is paramount—and essential to ensure patient comfort and visual performance. Mitsui Chemicals has a history of excellence in the high-index lens category and with its world-class MR™ portfolio: MR-8™ (1.60), MR-7™ and MR-10™ (1.67), and MR-174™ (1.74).
WHO IS MITSUI CHEMICALS?
With roots dating back to 1912, Mitsui Chemicals, Inc., is a major global producer and supplier of specialty chemicals. Headquartered in Tokyo, Mitsui Chemicals Group has nearly 17,000 employees and satellite headquarters in Germany, Singapore, and the United States.
The company’s divisions include Life & Healthcare Solutions, Mobility Solutions, ICT Solutions, and Basic & Green Materials.
The Vision Care Division of Mitsui Chemicals has a legacy of developing and manufacturing high-tech optical lens materials for global markets. The company’s Quality of View (QoV) commitment seeks to provide optimal QoV for anyone who wears glasses. Also, its DoGreen™ initiative is a focus on making sustainable eyeglass lenses a reality.
MEET THE MR HIGH-INDEX LENS MATERIAL PORTFOLIO
Mitsui Chemicals introduced the world’s first thiourethane 1.60-index lens material in 1987, which subsequently evolved into MR-8. Since then, the company has continued to expand its MR portfolio and advance its offerings of premium high-index lens materials.
Here, we explore how the characteristics of MR high-index lens materials help to differentiate this portfolio from other high-index lens materials.
THE IMPORTANCE OF REFRACTIVE INDEX
When it comes to high-index lenses, refractive index is only part of the story, as demonstrated by the characteristics and performance of the MR portfolio.
A lens material’s refractive index describes its ability to bend or refract light—and an increase in refractive index facilitates a thinner lens. The Mitsui Chemicals MR portfolio offers a broad range of premium thiourethane high-index materials, including MR-8 (1.60 refractive index), MR-7 (1.67 refractive index), MR-10 (1.67 refractive index), and MR-174 (1.74 refractive index).
The recently released MR-8plus, another version of MR-8, has higher impact resistance and a 1.60 refractive index. MR-8 provides a thinner lens than a low-index alternative, both MR-7 and MR-10 are even thinner, and MR-174 is the thinnest.
However, refractive index is not the only characteristic to keep in mind for high-index lenses.
UNDERSTANDING OPTICAL CLARITY AND ABBE VALUE
In simple terms, a lens material’s Abbe value loosely describes its clarity—the degree to which it disperses or spreads white light into its individual spectral components. Materials with low Abbe values, such as polycarbonate, have high dispersive properties, which can present as color fringes around words or objects in the wearer’s periphery and compromise their visual experience.
MR-8, with its Abbe value of 41, is much less prone to dispersive effects than polycarbonate with its lower Abbe value. The recently released MR-8plus offers similar characteristics to MR-8, with a 1.60 refractive index and Abbe value of 39.
The ultimate visual performance goal is to balance clarity with thinness. By and large, only going as thin as the situation calls for ensures the best overall results: uncompromised quality of vision, aesthetically pleasing lens cosmetics, and excellent wearer comfort.
A BIT ABOUT WEIGHT AND COMFORT
A lens material’s specific gravity loosely reflects its weight. MR-8 and MR-8plus have a specific gravity of 1.30, compared with 1.38 for an acrylic 1.60. In fact, the specific gravity of an acrylic 1.60 is even higher than MR-7 and MR-10, despite their higher refractive indices (1.67). This lower specific gravity equates to a lighter-weight lens, which enhances wearer comfort.
WHAT IS HEAT DISTORTION INDEX?
A lens material’s heat distortion index is an often-overlooked characteristic, but it plays a major role when it comes to coating compatibility. The enhanced heat distortion index of MR-8 compared to an acrylic alternative, for example, serves to prevent surface cracks under severe conditions such as tinting.
While both MR-7 and MR-10 have a refractive index of 1.67, MR-10 offers a higher heat distortion index (100 vs. 85). This difference illustrates how materials with the same refractive index can still offer different lens performance, including compatibility.
HIGHLIGHTING STRENGTH AND DURABILITY
A lens material’s ability to withstand impact and stress is referred to as its mechanical strength. Premium thiourethane MR lens materials offer high toughness. Accordingly, they are more likely to bend under stress rather than cracking or chipping.
Due to its tensile strength proper-ties, MR-8 is more resistant than polycarbonate to the stress fractures and deformation that can occur at the drill holes of three-piece mounts. MR-10 has also been shown to perform well under similar conditions. With a refractive index of 1.67, it delivers an even thinner option for high-powered prescriptions. These properties also make MR materials well suited for applications including grooved or rimless frames and steep-curve designs.
The recently introduced MR-8plus provides a stronger, more durable lens to the wearer. MR-8 and MR-8plus both pass the basic drop ball test for impact resistance, while additional testing demonstrated that MR-8plus lenses are capable of passing both the safety drop ball and high-velocity impact tests. The testing results would allow lenses of this material to be properly prescribed as safety lenses for certain applications.
MORE THAN A NUMBER
Refractive index is only one characteristic that differentiates a premium high-index lens material. The MR portfolio combines varying levels of thinness with characteristics such as optical clarity, light weight, optimal comfort, heat performance, plus outstanding strength and durability.
Partner content supported by Mitsui Chemicals.
Learn More About Mitsui Chemicals High-Tech Optical Lens Materials Here: https://jp.mitsuichemicals.com/en/special/mr/