In today's market, there are many different lens materials, and the variety of lens materials is growing at an unprecedented rate. As early as the 13th century in Egypt, people were able to produce eye glass lenses with a refractive index of 1.50. The production of crown glass for the eye began in the 18th century, around the time of the Industrial Revolution in Britain and the United States. In the first half of the 20th century, when the White brothers began flying their aircraft, they produced barium glass with a refractive index of 1.70, but the Abbe number was lower. Resin lens CR-39 produced by mass production resin in 1960, with a refractive index of 1.50, has been widely used. In 1982, titanium glass was produced, and the refractive index was still 1.70, and the number of Abbe was greatly improved. As early as 1980, mirror wearers could choose from four materials: ordinary glass, resin, photochromic glass and high refractive index glass.
1. Natural materials:
Mainly refers to crystal lenses, the main component of which is silica. It is divided into two types: colorless and brown. The reason why crystal stone glasses are expensive is not because of the good quality of the lenses, but because of the rarity and habitual impression, and it is more difficult to polish them into lenses.
Advantages: hard, not easy to wear; not easy to wet (fog is not easy to retain on its surface); small coefficient of thermal expansion (poor heat absorption).
Disadvantages: can not absorb ultraviolet and infrared rays, almost no ultraviolet rays, easy to cause visual fatigue; uneven density, easy to contain impurities, birefringence phenomenon (see the object has ghosting); processing difficulties.
There is a folk saying that crystal lenses can nourish the eyes. This is mainly because of the poor heat absorption of crystal, especially in the summer, wearing it has a cool feeling, in fact, this statement is unscientific, crystal lenses (especially dark brown), because there is no ultraviolet protection, the effect is the same as wearing inferior sunglasses, not only does not play a protective role for the eyes, but also has harm. (Examples: summer roads, sunny days after snow, specific concepts of ultraviolet rays)
Attached: Ultraviolet light small common sense
Ultraviolet light is a type of electromagnetic wave with a wavelength ranging from 200 nm to 380 nm, which is called ultraviolet light because it is shorter than the wavelength of the shortest wavelength in visible light.
Ultraviolet rays have a bactericidal effect, but there is harm to the eyes, ultraviolet rays are generally divided into three categories: uvc200-280nm uvb280-315nm uva315-380nm the human eye absorbs more ultraviolet rays, which are easy to cause various eye diseases, such as photokeratitis, cataracts and retinal degeneration.
| ozone layer | cornea | lens | retina | |
| uvc | 99.9% | 0.1% | ---- | ---- |
| uvb | ---- | 70% | 30% | ---- |
| grape | ---- | 35.5% | 63% | 1.5% |
2. Glass material
(1) The development of glass materials
From 1636 to the present, glass has been the main material for the production of lenses and still accounts for the largest sales in the market.
In 1978, glass lenses with a refractive index of 1.70 were produced
In 1983, glass lenses with a refractive index of 1.60 were produced
In 1986, glass lenses with a refractive index of 1.80 were produced
In 1993, glass lenses with a refractive index of 1.90 were produced
The basic ingredient is silica, accounting for 65 to 80%, on this basis plus other common materials. There are two main production processes in its production, namely the traditional circulating process and the flowing process. The produced monolithics (lens blanks) are coarsely ground and polished and then sealed and stored.
(2) Glass material characteristics
1) The refractive index is stable to maintain accurate diopter of the lens.
2) The proportion of raw material formula is reasonable, can absorb the light harmful to the eyes, has good light transmittance, and the general visible light transmittance reaches 80 to 91.6%.
3) Proper hardness, good thermal stability and processability.
4) No impurities, bubbles, streaks. The material quality is uniform and the chemical stability is good.
5． Abbe has a high number, small dispersion, and clear lens imaging.
(3) The type of glass lens
1) Tolik tablets: also known as white sheets, optical white sheets.
The refractive index is 1.523, and the visible light transmittance is 91 to 92%.
Features: colorless transparent, high clarity. Suitable for machining a wide range of diopter lenses. However, ultraviolet light below 340 nanometers cannot be absorbed. Adding cerium dioxide and titanium dioxide in white sheets can block ultraviolet rays below 346 nanometers, so it is called UV white sheets, suitable for indoor work and reading.
1) Crockers tablets: also known as blue films.
In 1914, by the Englishman William. Crocus invented it, hence its name. It has the advantages of white flakes.
In its basic composition, rare earth oxides are incorporated to form a light blue, which is light blue in daylight, so it is called blue flakes. However, it is reddish in incandescent light, and has strong absorption performance for ultraviolet light below 340 nanometers, and can also absorb some infrared and 580 nanometers of yellow visible light. The refractive index is 1.523. The visible light transmittance is about 87%. Blue flakes are suitable for outdoor operators, highland snow workers, welders and those with crystalless eyes. It is currently less used.
2) Croceto tablets: also known as red films.
Add cerium dioxide and manganese dioxide to the white flakes to create a beautiful light pink appearance. It is reddish in sunlight and incandescent lamps, so it is called red flakes.
It has an absorption effect on ultraviolet light below 350 nanometers. The refractive index is 1.523, and the visible light transmittance is about 88%. Optical red sheets can be processed into glasses of various diopters, especially suitable for women.
3) High refractive index lenses and ultra-thin lenses.
Add titanium dioxide and lead oxide to the raw material to increase the refractive index.
It is characterized by the fact that it can be made into a thinner lens with the same diopter, and the light transmission area is increased, the field of view is enlarged and the beauty is generous. Generally about 1/3 thinner than ordinary lenses. However, the proportion of high refractive index lenses is higher. Much higher than ordinary optical glass sheets. Therefore, the weight reduction of the lens is limited.
At present, ultra-thin lenses are available on the market for dispensers with refractive errors of more than 3.00D, but some customers with higher heights can choose ultra-thin lenses with refractive indexes of 1.8 or 1.9 and very thin lenses.
5) 1.60 glass lenses are also known as ultra-light ultra-thin lenses.
The refractive index is 1.60. Thinner than ordinary white films, and ultra-thin lenses have a smaller proportion, so they are lighter, which is very suitable for those with moderate refractive errors.
3. Resin material
1) Development of resin materials
At present, the global sales of plastic lenses reach 1/3 of the total number of lenses, and it can be expected that in the near future, plastic lenses will replace glass lenses as the mainstream of the market.
Synthetic synthetic synthetic plastic lenses include: thermoplastic resin, which is plastic between 50 and 120 degrees. Below this temperature is the solid; thermoset resin, which is formed by heating.
In 1940, the first thermoplastic lenses (acrylic lenses) were made]
In 1942, the Pittsburgh Flat Glass Company invented the CR-39 material (C for Columbia Space Agency and R for Fossil Resin) when making materials for the U.S. Space Shuttle.
In 1954, the French company Essilor made sunglass lenses from CR-39 material.
In 1956, the French company Essilor successfully tried to produce eye glasses with CR-39 material. Since then, plastic lenses have been widely used all over the world.
2) Characteristics of resin materials (compared with glass materials)
merit:
A. Light, small specific gravity, the weight is only 30 to 50% of the glass.
b. Safety, impact resistance is better than glass, even more than some specially hardened glass, and when broken, a relatively large fragment is produced, the spike is also less, and its danger is less than that of glass.
c. Lenses are easily stained.
d. The atomization trend is 60 to 75% lower than that of glass.
e. UV-resistant materials can be added at the time of production, so that the resin lenses have strong UV resistance.
f. Simplified process and can be used for the processing of aspherical mirrors.
shortcoming:
a. Easier to wear.
b. The shape of the lens can be deformed due to unexpected close to the high temperature, but the body temperature and daily life of the general human body will not deform it.
c. The refractive index of ordinary resin lenses is lower than that of glass lenses.
In general, the properties of plastic lenses, in addition to wear resistance, are at least equal to glass lenses.
3) Types of plastic lenses
A. Acrylic tablets
Chemical full name: polymethyl methacrylate
Advantages: Lighter than glass lenses, density of 1.19 at 20 degrees, refractive index of 1.499.
Disadvantages: The surface hardness is not as good as glass lenses, and it is easy to wear. The optical performance is not as good as glass lenses.
Acrylic lenses were initially used in lensless spectacle lenses, deep myopia lenses and hardness contact lenses, but quickly developed into all corrective lenses and are now used for presbyopia lenses.
CR-39: The most popular basic material today.
Chemical full name: propyldiethylene glycol carbonate. is a hard and transparent substance;
Refractive index: 1.499; transmittance: 92%; Abbe number about 58.
Thermal stability: no deformation below 150 degrees Celsius;
Water resistance, corrosion resistance (except strong acids) is better, insoluble in general organic solvents, can add anti-ultraviolet materials to the material, absorb 350nm or less ultraviolet rays.
Because of the material, CR-39 is generally not coated, otherwise it is very easy to fall off.
With a light transmittance of 90% for 1.56 lenses and 88% for 1.60 lenses, lenses with high refraction need to be coated.
Advantages: the specific gravity is 1.32, one-half of the glass, light weight;
Impact resistant, not fragile, strong sense of security; (Complies with U.S. FDA standards)
Comfortable to wear;
Convenient processing and wide range of uses(including half-frame and rimless frames)
Rich product range;(single light, dual light, multifocal, cataract, discoloration, etc.)
Its absorption capacity of ultraviolet rays is easily higher than that of glass lenses;
Can be dyed in various colors;
The thermal conductivity is low, and the situation of "water mist" caused by water vapor is better than that of glass lenses;
Disadvantages: the lens wear resistance is poor, easy to abrasion, low refractive index, the lens is relatively thicker than the glass lens 1.2-1.3 times;
develop:
(1) To overcome the wear resistance of the material:
In the mid-1980s, the lens surface hardening technology was successful; ordinary resin lenses, the surface hardness surface hardness was 2-3H, and after hardening, the hardness reached 4-5H.
At present, many companies have introduced ultra-hard resin lenses with a hardness of 6-7H.
(2) In order to reduce the thickness of the lens, resin sheets with different refractive indexes were successfully developed
1985 1.56 mid-fold resin sheet
1988 1.60 Ultra-thin resin sheet
1988 1.61
1992 1.67 Ultra-thin resin sheet
1998 1.71
(3) Waterproof fog treatment:
Coated with a layer of dura film: molecules responsible for viscous wetness, molecules responsible for moisture absorption, and surface hardness molecules.
When the ambient humidity is lower than the lens humidity, the film layer emits moisture outward;
When the ambient humidity is higher than the lens humidity, the film layer absorbs moisture;
When the ambient humidity is much higher than the lens humidity, the viscous wet molecules turn a large amount of water into a film of water.
C. PC tablets
Chemical full name: polycarbonate, also known as space lenses, cosmic lenses on the market.
Features: Refractive index 1.586; specific gravity 1.19, so another method is called ultra-light resin lens, Abbe number 31 light weight; especially suitable for rimless frames.
Advantages: Extremely impact resistant, more impact resistant than resin lenses, and can even be used as bulletproof glass, especially suitable for teenagers and sports adults; in the case of no coating, almost 100% UV protection.
Disadvantages: the processing is more difficult; the surface is very easy to scratch, the thermal stability is not good, and the 100 degrees Celsius becomes soft.
D、 Free monomer resin sheet (OMB-91)
Commonly known as the United States fast lens, the refractive index is about 1.51, the proportion is 1.19, the number of Abbe is about 59, the lens does not need to be stocked, it can be processed on the spot through special equipment, so the operation mode of the former store and back shop is more.
E. Comparison of resin lenses and glass lenses
refractive index
| Plastic lenses | Glass mirror | ||
| 1.499 | Ordinary plastic lenses | 1.523 | Ordinary glass lenses |
| 1.56 | Mid-fold resin lenses | 1.60 | Ultra-light and ultra-thin glass sheets |
| 1.60 | Ultra-thin plastic lenses | 1.70 | Ultra-thin glass lenses |
| 1.67 | Ultra-thin resin lenses | 1.80 | Ultra-thin glass lenses |
| 1.90 | Extra-ultra-ultra glass lenses |
Comprehensive comparison
| Glass slides | Resin flakes | |
| Impact resistance | difference | Good |
| specific gravity | 2.49-3.99 | 1.16-1.32 |
| Scratch resistance | Good | difference |
| thickness | thin | thick |
| security | difference | Good |
| color | monotony | Stainable |
| processing | difficult | easy |
| Radiation resistant | strong | weak |
| UV resistant | Better | Good |
| Optical properties | Good | Better |
| Atomization trend | big | small |