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Comparison of lenses with different materials
23-02-27 13:16:22 By Bestsea eyewear
Whether sunglasses, optical glasses or presbyopia glasses are inseparable from lenses, and the quality of lenses also directly determines the quality of an eyewear. Especially for high-end glasses, lenses are more important. Just think, if a pair of exquisite plate glasses, metal glasses or titanium eyewear, coupled with a pair of inferior sunglasses, can it still be regarded as high-end glasses?
What are the materials and requirements of lenses? The lens must be made of transparent material, with safety, comfort, beauty and good optical performance. The lens can be roughly divided into natural materials, glass materials and resin materials.
1.Natural materials. The most commonly used natural material is crystal lens, which is grinded from quartz ore. The main ingredients are silica, pure crystal, etc. There are two main categories: one is colorless lens, with high purity of silica; The other is the brown lens (commonly known as the brown crystal lens), which shows different colors due to its containing other elements, which greatly reduces the transmittance of visible light and makes the people who are afraid of light comfortable to wear, so there is a saying of "eye care".The advantage of crystal lens is that the material is hard and not easy to wear; The disadvantage is that it can't completely absorb short-wave ultraviolet rays;can't reduce the infrared transmittance; The density of the material is uneven. If it contains impurities, stripes and bubbles will appear, causing birefringence, which will affect the vision; Moreover, this kind of material is scarce and difficult to obtain, and the price is relatively expensive.
2.Glass material. The glass suitable for making lenses belongs to optical glass, with strict quality requirements. Such as refractive index, dispersion, transmissivity, etc. The main component is silicon dioxide, followed by boron trioxide and phosphorus pentoxide. The advantage is good hardness, not worse than crystal; It can be colored after mixed with various oxides, which can not only reduce strong light stimulation but also absorb harmful rays such as ultraviolet ray and infrared ray. The disadvantage is that the weight is heavy, and the specific gravity is twice that of the resin material. With the increase of refractive index, the specific gravity increases obviously, which makes wearing uncomfortable; Poor impact resistance, mechanical damage is easy to cause eye injury, so the safety is poor.
3.Resin material. The main components are organic substances, mainly carbon, hydrogen, nitrogen and oxygen. The resin material used to make lenses must be uniform, transparent and not easily deformed. At present, the commonly used resin materials are as follows:
①.Poly methy1 meth acrylate, also known as acrylic. Refractive index 1.49, dispersion 58, specific gravity 1.19. The advantages are light weight, 1/2 of glass; Good impact resistance, relatively safe. The disadvantage is that it is a thermoplastic material, its solubility is 75 ℃, it is heated and easy to deform, resulting in changes in diopter, insufficient surface hardness and poor wear resistance.
②.Allyl diglycidy celcat bonate (also known as allyl glycol ester), also known as Columbia resin, also known as CR-39. The refractive index is 1.4985, the color scattered is 57.8, and the specific gravity is 1.32. The advantage is light weight; Good impact resistance, relatively safe; Anti-ultraviolet, which can completely prevent ultraviolet rays below 350nm; Easy to dye, modern casting technology, can be produced in large quantities. CR39 is one of the most used lenses at present. It is widely used in acetate eyewear, metal glasses and horn glasses.
③.PC (Polycarbonate). It is polymerized by a flexible carbonic acid ring and an immovable bisphenol A. The molecular weight is between 20000 and 38000, and the refractive index is 1.586 at 25 ℃. The lens made of this material is called "space lens". The advantages are light weight, 57% lighter than traditional glass sheet; Its impact resistance is 60 times that of glass lens, which is relatively safe; When the thickness is 2.5 cm, it can be made bulletproof; The thickness is thin, equal to the thickness of CR-39 lens with refractive index of 1.6. The disadvantage is poor wear resistance. PC is generally used for plastic glasses, TR90 glasses and some sports glasses such as ski glasses.
4.Nylon lens. The material of the nylon lens:transparent polyamide is a new variety of polyamide.Because it destroys the regularity of molecules and inhibits the formation of crystals by introducing side groups into the molecular chain, transparent polyamides can be obtained. Many sports brand sunglasses and luxury brand sunglasses are made of nylon. Nylon lens has very good toughness and good transmittance, but it is a little worse than CR39. It is especially suitable for some half-frame and frameless. It is suitable for glasses of various material types, such as acetate glasses, metal eyewear and titanium frames.
The development trend of lens is ultra-thin, ultra-light, ultra-wear-resistant, ultra-flat, ultra-transparent, ultra-solid, ultra-ultraviolet and electromagnetic wave protection. At present, the lenses on the market have gradually transitioned from glass to resin, and from uncoated to coated. Different types of glasses, or different customer needs, have different requirements for lenses. For example, some fashionable high-end sunglasses may use CR39 lenses or CR39 coated lenses; The most common optical glasses in our daily life are now mostly resin lenses, such as CR39 or PC lenses
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