Early lenses mostly used natural materials because they were easy to obtain; however, natural materials had obvious defects.

Take natural crystal as an example:

According to the historical records of the Qing palace, Emperor Kangxi felt very good after receiving the crystal glasses presented by the governor of Guangdong and Guangxi. He gave it to his son "Si Ye" Yinzhen, who would later become Emperor Yongzheng.

Emperor Yongzheng became "smart" wearing glasses bestowed by his father, and the efficiency of reviewing memorials was greatly improved. Since then, he has become a complete "glasses control." According to incomplete statistics, there are 35 pairs of spectacles specially made by the manufacturing office for Emperor Yongzheng.

As everyone knows, the dignified emperor of the Qing Dynasty wore "unqualified lenses." Crystal is a natural ore with uneven density, which often causes double refraction to produce double images; and crystal cannot block infrared and ultraviolet rays, so it has no protective effect on the eyes.

However, because of the cold, the temperature around the eyes will be lower when wearing crystal stones. At the same time, some of the crystal lenses are colored, which softens the light entering the eyes, so the theory of "crystal nourishing eyesight" arises.

When the glass lens was born, natural materials withdrew from the stage of history.

Speaking of the birth of glass, there is an interesting story: more than 3000 years ago, a European Phoenician merchant ship, loaded with crystal mineral "natural soda", sailed on the Belus River on the Mediterranean coast. The merchant ship ran aground due to the ebb of the sea, so the crew boarded the beach one after another. Some crew members also brought large pots and firewood, and used a few pieces of "natural soda" as a support for the cauldron to cook on the beach.

The crew finished their meal and the tide started to rise. When they were about to pack up and board the ship to continue sailing, someone suddenly shouted: "Look, everyone, there is something bright and gleaming on the sand under the pot!"

The crew brought these shimmering things to the ship to study them carefully. They found that there was some quartz sand and melted natural soda stuck to these shiny things. It turns out that these shining things are the natural soda that they used to make pot holders when they cook. Under the action of the flame, they chemically react with the quartz sand on the beach. This is the earliest glass.

However, the glass used to make the lens is not the ordinary glass in the story.

Crown glass was first used to make lenses.

Crown glass, the name can easily be misunderstood as a brand, but it is actually just a production process: first blow the glass liquid into a crown or hollow ball shape, and then place it in a rapidly rotating The center of the plate is reheated, and centrifugal force is used to spread it out and flatten it; the relatively flat and thin edges are cut into suitable shapes to make window glass, and the round convex in the middle is the embryonic form of the lens.

This production method was developed and matured by glass craftsmen near Rouen in France around 1320, but it was not disclosed as a trade secret; so the British across the water imported window glass for three hundred years, and it was not until 1628 that London did not disclose it. The same process appears.

The glass material used to make the lens was originally a colorless and transparent glass with a refractive index of 1.523; later, other substances were added to the lens in order to improve its ability to absorb ultraviolet rays: in 1914, William Crox of the United Kingdom made "gram Lenses are light blue in daylight, so they are also called blue lenses. It can absorb ultraviolet light below 340?, part of infrared light and yellow visible light of 580?

Later, someone invented the "Kesai" lens. This kind of lens appears reddish under sunlight and incandescent lamps, so it is also called red film. It can absorb ultraviolet rays below 350°.

In 1978, people invented a glass lens with a refractive index of 1.7, making the appearance of the lens thinner. Today, the highest refractive index of glass lenses is 1.9.

After 300 years of glass material statistics and lens manufacturing, people are finally determined to get rid of this heavy and insecure "thing".

The first pair of resin lenses in the world is made of CR-39 material, which is still the main material of optical lenses in European and American countries.

Why is it CR-39 instead of CR007? The scientific name of CR-39 material is "Allyl Diglycolate". The reason why it is called CR-39 is related to his life experience.

During World War II, the U.S. Air Force commissioned Columbia-Southern Chemical Corporation, a subsidiary of Pittsburgh Plate Glass Company (PPG), to develop a series of materials for military use. In order to keep the formula secret, each material has only one number code, CR-39 is Columbia Resins No. 39 (39th Columbia Resins). The first use of CR-39 is to manufacture fuel tanks for the B17 strategic bomber known as the "flying fortress"! This has nothing to do with the lens.

Why does CR39 become a lens material?

After the end of World War II, people discovered that CR-39 had significant advantages compared with the main lens material glass at that time:

1. High light transmittance

CR-39 ——92%

Glass-91%

2. Light specific gravity (just half of the glass lens)

CR39——1.32g/cm3

Glass-2.54g/cm3

3. Block UV

CR39-absorbs ultraviolet light within 390nm

Glass-can only absorb part of the ultraviolet light of 290-300nm

4. Impact resistance test (use a 16g steel ball to drop freely from a height of 1.27 meters)

CR-39-Not broken

Glass-shattered

In addition, CR-39 also has the advantages of dyeing, not easy to fog, and small dispersion (the Abbe number of CR-39 is 58), and is an ideal optical lens material.

In 1947, Armorlite Lens Company in California, USA, produced the world's first CR-39 resin lens. But it is the French Essilor company that has carried forward the resin lens!

What is a PC?

The chemical name of PC is polycarbonate, also known as "space tablet".

In 1978, the American Gentex Company took advantage of the military aerospace project and first used PC to manufacture safety lenses.

Essilor acquired Gentex in 1996

Essilor universe film was born in 1997

PC lenses accounted for 35% of the U.S. market in 2002

PC lens has extremely strong toughness and does not break (2cm can be used for bulletproof glass), so it is also called safety lens. With a specific gravity of 2g/cm3, it is currently the lightest material used for lenses.

The safety performance of PC lenses makes them the preferred material for making rimless frames. At the same time, in some countries and regions, it is also used as the designated material for teenagers' glasses.

▼A few tips

1. What kind of people are suitable for PC lenses?

PC lenses are suitable for all ages, but because of their excellent eye protection (impact resistance and UV protection), they are more suitable for children and teenagers.

2. Is the PC material bulletproof glass?

One of the materials in bulletproof glass is PC, and the bulletproof effect is directly related to the thickness of the PC board.

3. Why do some people feel dizzy after wearing a PC tablet?

Because the PC material is softer and not as hard as the CR39 resin lens, if it is not processed as required during processing, the lens will be affected by external forces and produce stress, which will change the original refractive power. This phenomenon is more common in full-frame glasses. . When making glasses, check whether there is any stress on the lenses.

▼MR is the brand name of optical lens raw materials produced by Mitsui Chemicals, Japan, and MR is the abbreviation of Mitsui Resin.

The raw material is a high molecular polymer monomer. It is the first high refractive index lens material produced by polyurethane technology in the world. It has the characteristics of high refractive index, high Abbe number, low specific gravity and high impact resistance. It is an excellent serialization. Optical materials.

Characteristics and series of MR materials

MR series materials have excellent mechanical strength, high impact resistance, good tensile strength and minimal internal stress. They are very suitable for all kinds of uniquely designed lens products, such as rimless glasses and high-bend lenses; at the same time, it is also With good processability, dyeability and weather resistance, it is suitable for progressive multifocal lenses and fashionable sunglasses with special requirements for color. The color of the lens changes little after many years of use.

The MR series has three different refractive index (1.60, 1.67, 1.74) products, specifically: MR-7, MR-8, MR-10, MR-174.

MR-7 and MR-10 have higher heat distortion temperature and excellent dyeability, and are widely used in the field of sunglasses;

MR-8 has the most balanced performance indicators, suitable for the production of spectacle lenses of any degree, and has the highest market share in the lens material market with a refractive index of 1.60;

MR-174 is a high refractive index lens material, which is mostly used in the production of ultra-thin lenses.

▼Trivex is a special material of PPG company in the United States.

Compared with PC lenses, although the refractive index is lower (only 1.53) but the Abbe number is higher (up to 45), this will make the lens dispersion smaller and higher image quality. At the same time, the impact resistance of Trivex lenses is 10 times higher than that of PCs. Under normal use, the lenses will not be broken for life. It is currently the only explosion-proof safety lens on the market that can withstand the twists and turns of external forces.

However, Trivex is more difficult to process, which is why the product has not been popularized.

▼For spectacle lenses, an indispensable element is the refractive index of the lens. The higher the refractive index, the thinner and lighter the lens can be achieved. In the past many years, the refractive index has developed from 1.5 to 1.6, 1.7... In order to meet consumers' demands for lighter and thinner lenses, lens manufacturers have been struggling to develop high-refractive-index products.

In April 2006, TOKAI (Tokai Optical) launched a lens with a refractive index of 1.76.

The 1.76 double aspheric lens can be about 50% thinner than the general single vision lens, and the 1.76 single aspheric lens can also be about 47% thinner than the general single vision lens.

▼Looking at the "evolutionary history" of lens materials, the development has always been in the direction of "lighter, thinner and safer"; however, different regions have different development priorities due to different consumer demands.

In Europe, CR-39 material still dominates the market so far. On the one hand, the short-sighted population in Europe is relatively low, but farsightedness is more; on the other hand, small circle frames and no frames are popular in Europe, which makes CR- The impact resistance of the 39 material has room for display.

In the United States, PC and CR-39 have the highest market share, which is related to the US FDA's regulations on safety lenses (drop ball test). Some of the materials introduced in this article are not sold in the United States because they failed to pass the FDA safety test.

In Asia, due to the high incidence of myopia and the high proportion of high myopia, the focus of users is on the thinner appearance of the lenses. Therefore, the research and development of high refractive materials is concentrated in Japan.

▼There are two immature tips to share with you:

First, when choosing lens materials, don't just limit the appearance of the thickness, but also take into account other indicators. Such as anti-ultraviolet performance, Abbe number (dispersion coefficient), yellow index and impact resistance. For patients with high myopia, it is of course necessary to choose high-refractive lenses, but the frame shape and safety should also be considered.

Second, even the same ingredients will become completely different dishes in the hands of different chefs; the materials of many lenses are the same, but due to factors such as the production process, hard coating technology, surface bending design, etc., the final The quality of lenses can be very different. For example, some consumers asked about the yellowing of the lens after use, which is related to the aging of the lens material; some brands use additives in the lens to delay the aging of the lens, and it is not so easy to turn yellow.

When choosing lenses, consumers should listen to the advice of professional opticians and combine their needs to make the most suitable choice.