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CR-39

The abbreviation CR-39 originates from the "Columbia Resin #39" study. It was also the 39th thermoset plastic formula developed by Columbia Resins in 1940.

The first commercial use of CR-39 material was in the creation of glass-reinforced plastic tanks for aircraft, as it reduced weight and increased the range of the aircraft. It is about B-17 bombers in the Second World War. After the war, the Armorlite Lens Company in California was credited with producing the first CR-39 optical lenses in 1947.

To this day, this material is most often used to make organic optical lenses. We cite its lightness and good price-performance ratio as an advantage. The disadvantage is weak UV protection. Therefore, the lens should have additional UV protection. CR-39 is transparent in the visible spectrum and almost completely opaque in the ultraviolet range. It has high wear resistance, i.e. the highest abrasion/scratch resistance of any other uncoated optical plastic.

CR-39 is about half the weight of mineral glass with a slightly lower refractive index, and its high Abe number gives it a low chromatic aberration, making it an overall favorable material for prescription and sunglasses. CR-39 is also resistant to most solvents and other chemicals, gamma radiation, aging, and material fatigue. It can withstand small hot sparks from welding, something glass cannot do. It can be used continuously at temperatures up to 100°C and up to one hour at 130°C. CR-39 is now a trademarked product of PPG Industries.

TRIVEX

Trivex material was originally developed for the military industry. PPG Industries took the technology and adapted it to the optical industry. PPG named the material Trivex because of its three main performance properties:

– top optics,
– ultralight,
– extreme strength.

Trivex has the lowest specific gravity, making it the lightest lens material. Trivex is 16% lighter than CR-39, 25% lighter than 1.67, and 8% lighter than polycarbonate! It can also be machined up to a central thickness of 1 mm. This possibility further reduces weight and thickness. It is stronger and more impact resistant than polycarbonate. Lenses made of Trivex are highly resistant to chemicals. It is even resistant to acetone.

The Trivex lens does not have the internal strain associated with most polycarbonate lenses. The lack of internal strain makes Trivex the perfect choice for drilling and engraving. Trivex does not crack around drilled holes in the lens. Trivex lens provides 100% UV protection.

1.56 MIDDLE INDEX

In 1999, the Korean company KOC (Korean Optical Company) introduced KOC 55 material into commercial use in the production of optical lenses for the first time. With the acquisition made in 2013, the KOC company becomes the Mitsui Chemicals company's property, with a share of 51% of its own capital.

KOC 55 material or 1.56 middle index, with a refractive index of 1.545 offers the possibility of making a lens up to 15% thinner than CR-39 material.

A specific gravity of 1.27 g/cm3 results in a lighter lens compared to a lens made of CR-39 material. Unlike CR-39 material, 1.56 middle index

A lens made of 1.56 material is not recommended for glasses without a frame (so-called rimless frames), as well as for frames without a bottom edge (so-called nylor frames).

1.59 POLY (POLYCARBONATE)

Born in the space race of the 1960s and introduced to the ophthalmic lens market in the late 1970s, polycarbonate enjoys a significant market share, especially in children's and safety glasses due to its superiority-impact resistance.

With a higher refractive index and lower specific gravity, the polycarbonate lens is thinner and lighter. Its popularity is contributed by the complete blocking of UV radiation,as well as wide product availability.

Polycarbonate, however, is not without its drawbacks. One of the main complaints about polycarbonate is its optical quality. With an Abe value of 30, the chromatic aberration of polycarbonate is the highest of any material in use today. With the increasing popularity of rimless frames, some opticians are hesitant to use polycarbonate due to its lack of tensile strength and the likelihood of cracking around drilled holes.

TRIBRID

The revolutionary material technology that combines the best properties of the lens provides customers with improved all-around performance of the lens.

Designed with hybrid technology PPG TRIBRID® material is produced using a unique hybrid technology that is a combination of PPG TRIVEX® material with traditional high-index material technology. As with PPG Trivex materials, PPG TRIBRID material is recommended with confidence, knowing that this newer unique high index material offers similar performance to Trivex with the added thinness of the lens due to the higher refractive index.

Tribrid material was introduced in 2012 as a high-index extension of the Trivex family to meet patients' needs for thinner lenses. The material offers excellent optical quality (Abe 41), is light (specific gravity 1.23 g/cm3), thinner (refractive index of 1.60), and stronger (up to five times more impact resistant than other high index materials). In fact, the lens can withstand more than 160 times higher energy than the drop ball test, making it the perfect lens material.

Tribrid also has superior chemical resistance to cracking or exposure to common laboratory and household chemicals such as isopropyl alcohol, acetone, etc.

HI INDEX 1.60 / 1.67 / 1.74 (MITSUI CHEMICALS)

The first organic eyeglass lens was produced in the 1940s. A material called CR-39 dominated the market for a while as an alternative to mineral glass.

The CR-39 lens had several drawbacks, including a low refractive index, being thick and cosmetically unattractive. This led to a demand for a high refractive index material that would allow for a thinner lens. Later, the organic materials acrylic and polycarbonate came into wide use as medium refractive index materials. However, various problems remained, including solidity and chromatic aberration. Mitsui Chemicals produced MR-6 material in 1987, the first in the MRTM brand product line. This material is based on an innovative molecular structure that has achieved a 1.6 refractive index, high Abe number, and low specific gravity, paving the way for a new age of high refractive index lenses.

Developments in 1991 led to a material with an even higher refractive index of 1.67 (MR-10), followed by 1.60 (MR-8) in 1998. Announced in 2000, MR-174 showed a record high refractive index – 1.74, allowing opticians to provide an unprecedentedly thin lens, even for corrective lenses of larger diopters.

1.5 / 1.6 / 1.7 / 1.8 / 1.9 MINERAL

The first glasses made with mineral lenses date back to the 13th century. This material consists of sand and many organic elements (quartz - about 70%, lime - 20%, oxides - 10%...). Lead and titanium may appear on the component list. Their function is to increase the refractive index.

These different elements are melted at a temperature of 1500° in a special, so-called, glass tank. The mixture is then stirred for many hours to create a paste–liquid glass. Then the material is passed through the press. We call the pressed piece a presling, followed by the processing of the outer side (CX) and then the inner side (CC), depending on the required radius, i.e. diopters. Although the mineral lens can be perfectly adapted to any need, today it is used less and less in practice. The fact remains that it is still desirable in some cases and has many advantages. Therefore, this material has a wide range of refractive index from 1.5 to 1.9 and can be used for all refractive corrections, especially in cases of high corrections.