Basic knowledge of glasses matching

A pair of mirror frames usually consists of the main parts such as the mirror ring, nose support, post head, and mirror foot.

Mirror frame: The assembly position of the lens is fixed with metal wire, nylon wire, and screws through grooves or drilled holes, which affects the cutting of the lens and the appearance of the glasses.

Nose bridge: connected to the left and right mirror rings or directly fixed to the lens. The bridge of the nose can be placed directly on the nose or supported on the nose through leaflets.

Nose support: including the peduncle, box, and leaflets, the leaflets are in direct contact with the nose and play a role in supporting and stabilizing the frame. Some cast plastic frames may not have support stems and support boxes, and the support leaves are connected to the mirror ring.

Pile head: The connection between the mirror ring and the mirror angle, usually curved.

Mirror foot: The hook is mounted on the ear, movable, connected to the pile head, and plays a role in fixing the mirror ring.

Hinge: a joint that connects the pile head and the mirror foot.

Locking block: Tighten the screws to fasten the locking blocks on both sides of the lens ring opening, thereby fixing the lens. In addition to the above components, there are also foot covers, bracket screws, hinge screws, eyebrows, etc.

Section 2 Mirror Frame Materials

The materials used to manufacture eyeglass frames can be roughly divided into three categories: metallic materials, non-metallic materials, and natural materials.

1、 Metal materials

There are three main types of metal materials used for eyeglass frames: copper alloys, nickel alloys, and precious metals. It is required to have certain hardness, softness, elasticity, wear resistance, corrosion resistance, light weight, luster, and good color, etc. Therefore, the metal materials used to make eyeglass frames are almost always alloys or used after metal surface processing.

1. Zinc white copper

Also known as foreign white or foreign silver. The main component is copper, which contains 64% copper, 18% nickel, and 18% zinc, with a specific gravity of 8.8. Its characteristics are certain corrosion resistance and good elasticity, as well as low cost and easy processing. Mainly used for making components such as hinges, pile heads, and nose bridge supports, low-end eyeglass frames are mostly made of zinc white copper material. When used, it rusts and turns copper green after being corroded by human sweat.

2. Brass

Also known as copper zinc alloy. Containing 63%~65% copper and 35%~37% zinc, it is yellow in color. Its advantage is that it is easy to cut, but its disadvantage is that it is prone to discoloration. Commonly used for low-end eyeglass frames and nose pads.

3. Copper nickel zinc tin alloy

It is an alloy composed of 62% copper, 23% nickel, 13% zinc, and 2% tin. It has good elasticity and is commonly used for the nose bridge and temple of eyeglass frames after electroplating treatment.

4. Bronze

Generally refers to copper tin alloys, which contain small amounts of zinc and phosphorus. Due to the presence of a certain amount of tin element in bronze, its price is relatively high. Its disadvantages are difficult processing and poor resistance to acid corrosion, but it has good elasticity, diamagnetism, and wear resistance. Its resistance to human corrosion in atmosphere, seawater, and steam is superior to copper and brass, making it suitable as a spring and lens ring material for eyeglass frames.

5. Monel alloy

It belongs to a type of nickel copper alloy. The specific gravity is 8.9, containing 63%~67% nickel, 28%~31% copper, and a small amount of iron and manganese. Its characteristic is that it does not contain chromium. Due to its high nickel content, it has the advantages of good strength, elasticity, corrosion resistance, and strong welding, and is often used to manufacture mid-range eyeglass frames.

6. High nickel alloy

Also known as nickel alloy. The specific gravity is 8.67, containing 84% nickel, 12.5% chromium, 5% silver, 1% copper and other elements. It is a high-grade nickel chromium alloy material, which is more elastic and corrosion-resistant compared to Monel alloy. Some imported eyeglass frames and domestic high-end frames often use this material.

7. Stainless steel

It is a type of nickel chromium alloy. Mainly containing over 70% iron, 18% chromium, 8% nickel, and 0.1% to 0.3% other elements. It has good elasticity and corrosion resistance, and is commonly used as a material for mirror legs. Stainless steel materials containing 1% to 1.5% lead are often used as the base material for making screws or metal frames. Its disadvantages are high strength and difficult welding processing.

8. Titanium

Pure titanium is a silver white metal. The specific gravity is 4.5, with light weight being its biggest feature, and it has high strength, corrosion resistance, and good plasticity. Commonly used in the aerospace industry, it is known as "space metal". At the beginning of the 1980s, it was used to make eyeglass frames and gradually solved processing problems such as cutting, polishing, welding, and electroplating, making titanium eyeglass frames basically popular. The products are mainly sourced from Japan.

Titanium eyeglass frames are generally represented by the symbol Ti-P or TiTAN, which indicates that except for the nose bridge bracket, hinge, and screws, other parts are made of titanium. The Ti-C symbol indicates that a part of the eyeglass frame is made of titanium.

9. Gold and its alloys

Pure gold has a golden yellow color and a specific gravity of 19.3. It is one of the heaviest metals and will not corrode or oxidize in the atmosphere. Gold is softer than silver and has good rolling properties, so pure gold is generally not used as the material for eyeglass frames. Instead, alloys of gold, silver, copper, and other materials are used.

The gold content of its alloy is generally represented by "K". 24K is 100% pure gold, and the eyeglass frame material mostly uses alloys of K18, K14, and K12, with a pure gold content of K18:18/24 × 100=75%; K14：14/24×100=58.3% ； K12:12/24 × 100=50% and so on.

10. Platinum

It is a type of gold alloy. The eyeglass frame material mostly uses K14 platinum, which consists of 58.3% pure gold, 17% nickel, 8.5% zinc, and 16% copper.

11. Platinum and Platinum Group

Pure platinum is as soft as gold and silver, and is usually used in alloys with other platinum elements. Platinum elements include platinum, palladium, iridium, osmium, rhodium, and ruthenium, collectively referred to as the platinum group. Glasses frames are often made of platinum iridium alloy, which has a relatively high specific gravity. Rhodium and palladium are commonly used as electroplating materials for metal eyeglass frames.

12. Bao Jin

Also known as grinding gold, adding gold, rolling gold, it is a layer of K gold wrapped around the base metal, with a thickness of about 10-50 μ m. Make it have the properties of gold and be characterized by low cost. Therefore, it is mostly used for high-end mirror frames. The base materials for gold frames are generally white copper, brass, nickel, and gold alloys. Commonly used gold frames include K18, K14, K12, and K10.  

There are two ways to represent the golden eyeglass frame. When the weight ratio of gold content is above 1/20, it is represented by GF, and when it is below 1/20, it is represented by RGP.

For example, 1/10 12K GF: 1/10 represents a gold content of 1/10 × 12/24=1/20; 12K represents an alloy of 12K; GF represents the gold symbol. ② 1/10 10K RGP: 1/10 represents a gold content of 1/10 × 10/24=1/24; 10K represents 10K alloy; RGP represents the gold symbol when it is less than 1/20.

13. Aluminum alloy

Pure aluminum is relatively soft, silver white in color, and is generally made of aluminum alloy. Aluminum alloy is lightweight, has good corrosion resistance, has a certain hardness, and has good cold forming characteristics. The surface can be treated into a thin and hard oxide layer, which can be dyed in various colors. At present, the gasket at the joint of the titanium frame frame and the mirror foot is made of aluminum alloy material, and there are also full set glasses made of aluminum alloy with rich colors.

14. Memory Metal

Also known as memory titanium or NT alloy, it is synthesized by mixing titanium and nickel through high-temperature treatment. It has the advantages of being lighter and more elastic than ordinary titanium alloys.

2、 Non metallic materials

The non-metallic materials commonly used to manufacture eyeglass frames are mainly synthetic resins, which are divided into two categories: thermoplastic and thermosetting resins.

1. Nitrocellulose

Also known as celluloid, it belongs to thermoplastic resin. It is mainly made by blending nitrocellulose with camphor and softeners as raw materials. Due to its flammability and high shrinkage, it is currently rarely used to manufacture eyeglass frames and is considered a low-end product among non-metallic eyeglass frames.

Its characteristics can be summarized as follows:

① Specific gravity ranges from 1.32 to 1.35 Anti infrared, but changes color when exposed to ultraviolet radiation At room temperature, the elasticity is relatively high, with a softening temperature above 60 degrees Celsius, while its elasticity decreases. The processing temperature is between 90 and 100 degrees Celsius When heated to 130 degrees Celsius, bubbles are generated inside Easy to burn when heated above 180 degrees Celsius Long term use is prone to weathering, yellowing, and cracking Good resilience.

2. Acetate fiber

It belongs to thermoplastic resin. It is mainly composed of cellulose acetate, plasticizers, coloring agents, stabilizers, lubricants, etc.

It can be made into two types of frames: sheet metal frames and injection molded frames, and is one of the main raw materials for plastic eyeglass frames. Its characteristics are summarized as follows:

① Specific gravity 1.28-1.32, slightly lighter than celluloid; ② Not easy to burn; ③ Not easily discolored under UV irradiation; ④ Low resilience; ⑤ Has a certain degree of water absorption; ⑥ Strong impact resistance, slightly lower than celluloid.

In summary, celluloid and acetate fiber each have their own similarities and differences. Their common characteristics include good transparency and luster, easy coloring, good dimensional stability, easy processing and shaping, strong impact resistance, and a beautiful appearance when equipped with high myopia lenses.

3. Propionic acid fiber

It belongs to thermoplastic resin, mainly made from cellulose propionate as raw material, and added with a very small amount of plasticizers, colorants, and stabilizers. It has the characteristics of dimensional stability, durability, resistance to discoloration, impact resistance, easy processing and shaping, and good flexibility. Commonly used for injection molded eyeglass frames, imported plastic frames are more commonly used.

4. Epoxy resin

It belongs to thermosetting resin, but has excellent recovery after heating, so it also has thermoplastic properties. Some high-end and branded plastic shelves often use this material.

Its characteristics: ① Light weight, generally 40% lighter than celluloid in competitions, and 20%~30% lighter than acetic acid. ② Good dimensional stability. ③ Easy to color. ④ The shrinkage is extremely poor, and when assembling and processing lenses, the lenses should be slightly larger The minimum heating temperature is 80 degrees Celsius, usually 100-120 degrees Celsius Extremely heat-resistant, can be heated up to 200 degrees Celsius The surface hardness is extremely strong and can maintain its good luster It has excellent strength, so the temple does not require a metal core Easy to break when bent under cooling conditions.

5. Nylon

Also known as polyamide, it is a type of thermoplastic resin. Its characteristics are white opacity, high strength, good heat resistance, impact resistance, wear resistance, and melt resistance, as well as its own lubricity. Its disadvantage is that it has a certain degree of water absorption, so its dimensional stability is slightly poor.

6. Carbon fiber

It has certain characteristics such as corrosion resistance, heat resistance, high strength, and good elasticity. After being reinforced and processed into synthetic resin, it is used as a material for eyeglass frames and also belongs to thermoplastic resin.

3、 Natural materials

The natural materials used to make eyeglass frames include tortoiseshell, special wood, and animal horns. Generally, wooden eyeglass frames and horn frames are rare, with tortoiseshell eyeglass frames being the most common.

The hawksbill material is a eyeglass frame made from hawksbill shells produced in tropical oceans, mainly in the West Indies. Its advantages are light weight, beautiful luster, easy processing and polishing, plastic when heated, can be joined when heated and pressurized, non irritating to the skin, and durable with preservation value. Among various types of eyeglass frames, it belongs to high-end products and is very popular among middle-aged and above male wearers. Its disadvantage is that it is more prone to breakage compared to materials such as celluloid, but can be repaired by bonding after breakage. When displaying at the counter, it is necessary to place it in water to prevent drying. Ultrasonic cleaning should not be used during use and maintenance, otherwise it will turn white and lose its luster. Due to the fact that hawksbill turtles are prohibited from being captured in the ocean, their production is limited and their price is high.

Section 3 Types of eyeglass frames

There are usually many classification methods for eyeglass frames, and this chapter mainly analyzes and introduces them from the perspectives of materials, styles, etc.

1、 According to the current available materials, common mirror frames are mainly divided into plastic frames, metal frames, and hybrid frames.

1. Plastic shelves (including natural materials): Plastic shelves are popular among the elderly and children due to their lightweight and non allergenic properties; It has also become a choice for fashionistas as sunglasses or decorations.

Plastic shelves are now mostly made of acetate resin double spliced shelves, which are made of laminated plastic. A thin layer of plastic of one color is pasted on another thicker layer of plastic to make it. The thick material is mostly transparent (or translucent) pigment, and there are also those made of three or more layers of plastic.

2. Metal frame: made of a certain metal material or alloy, often with copper alloy as the substrate, and then subjected to surface treatment processing, often with gold plating, or rhodium or palladium plating white or titanium plating. Due to different electroplating processes, some are prone to fading, while others are not. In addition, there are mirror frames made of pure titanium and memory alloy. The metal frame is sturdy, lightweight, beautiful, with novel styles and a wide variety.

Most metal frames come with nose pads, which are movable to accommodate various nose shapes. The end of the mirror foot is often covered with a plastic sleeve, which not only looks beautiful but also protects the mirror foot and skin.

3. Mixed material frame: Made of a mixture of metal and plastic to create a mirror frame. Some of these frames are made of plastic wrapped in metal, that is, partially or completely wrapped in celluloid; Some use different materials in different parts of the frame, namely the front frame is made of plastic and the mirror legs are made of metal, or the front frame is made of metal and the mirror legs are made of plastic; Some people mix the above two methods, such as using plastic for the eyebrow and nose bridge, stainless steel for the frame, and plastic wrapped metal for the mirror legs.

The hybrid frame has a delicate and beautiful design, giving people an elegant feeling. Due to the close contact between the outer plastic layer and the inner metal material, it is not easy to burn, which increases the strength of the mirror frame.

2、 According to styles, common types of mirror frames include full frame, half frame, frameless, combination frame, and folding frame.

1. Full frame: It is currently the most commonly used type of frame, characterized by firmness, ease of shaping, and the ability to conceal a portion of the lens thickness.

2. Nylon frame: Using a very thin nylon wire as part of the frame edge, the lens is specially ground to flatten its lower edge. There is a narrow groove in the lower edge that allows the nylon wire to be embedded in the groove, forming a bottomless frame style. Therefore, the weight is very light, giving a sense of lightness and uniqueness, and it is also relatively sturdy.

3. No frame: This type of frame does not have a mirror ring, only a metal nose bridge and a metal temple. The lens is directly connected to the nose bridge and temple by screws, and usually requires drilling holes on the lens. Frameless frames are lighter and more unique than regular frames, but their strength is slightly lower.

4. Combination frame: There are two sets of lenses at the front frame, one of which can be flipped up and is usually used for both indoor and outdoor purposes.

5. Folding frame: The mirror frame can be folded into four or six folds, mostly for reading glasses.

Glasses lens material

The materials used to make eyeglass lenses mainly include three categories: optical glass, optical resin, and natural materials.

1、 Optical glass materials

（1） Overview of Optical Glass

The material of eyeglass lenses is mainly composed of oxides such as silicon dioxide, boron trioxide, phosphorus pentoxide, sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesium oxide, zinc oxide, aluminum oxide, etc. These raw materials are melted at high temperatures and then cooled and condensed into a uniform, transparent, brittle, amorphous substance.

Glasses glass mainly uses optical glass materials, which can be divided into two categories: colorless and colored optical glass. There are many types of optical glass, usually divided into crown glass and flint glass based on the refractive index or Abbe number of colorless optical glass.

The most obvious difference between the two is that crown glass has a lower refractive index, generally between 1.49 and 1.53, while flint glass has a higher refractive index, generally around 1.60 to 1.80. Based on an Abbe number of 50, glass with an Abbe number greater than 50 is classified as various types of crown glass, while glass with an Abbe number below 50 is classified as various types of flint glass.

Glasses made of crown glass materials include optical lenses, Krusty lenses, color changing lenses, and various colored glass lenses, while flint glass materials are mostly used for sub lenses of bifocal lenses and various "ultra-thin lenses".

（2） Performance of optical glass

The properties of optical glass materials mainly include optical properties, chemical properties, thermal properties, and mechanical properties.

Optical properties, including refractive index, transmittance, and dispersion coefficient, are the most important optical constants of optical glass. The refractive index is measured based on yellow light with a wavelength of 587.6nm and is one of the constants that determine the refractive power of a lens. The dispersion coefficient is an important indicator for measuring the imaging clarity of a lens, usually expressed as the reciprocal of the dispersion coefficient, also known as the Abbe number. The larger the Abbe number, the smaller the dispersion; conversely, the smaller the Abbe number, the greater the dispersion and the poorer the imaging clarity. Transmittance is an important indicator of visual clarity, and the transmittance of colorless optical glass to visible light should be above 92%. The higher the transmittance, the clearer the view.

Chemical performance, also known as chemical stability, generally refers to the corrosion resistance of lenses to chemicals such as water, acid, alkali solutions, and polishing agents during processing or use. Because these chemicals can interact with glass, causing changes in the surface smoothness of the lens and affecting its service life.

Thermal performance mainly includes thermal expansion coefficient, thermal conductivity, and thermal stability. The thermal expansion coefficient of optical glass is very low compared to metal materials, so optical glass is not easily deformed. When wearing glasses indoors in winter, a layer of water vapor often condenses on the surface of the lenses due to the very low thermal conductivity of optical glass. Thermal stability refers to the property of glass that does not rupture under severe temperature changes. It is related to the coefficient of thermal expansion and thermal conductivity. Generally, when the thermal conductivity is high or low, the thermal stability is good.

Mechanical properties mainly include specific gravity (density), hardness, surface tension, and elasticity coefficient. Specific gravity and hardness are extremely important parameters in eyeglass glass. The specific gravity of general optical glass is relatively high, and there is a certain relationship between specific gravity and refractive index. The higher the refractive index, the greater the weight of the lens. The surface of optical eyeglass lenses requires a certain degree of hardness, which not only affects the service life, but also directly affects the quality and speed of lens grinding and processing.

（3） Characteristics of optical glass lenses

1. Colorless optical glass lens

Colorless glass lenses are commonly known as white lenses, also known as white lenses. It can be divided into two types: ordinary and optical white film.

The main component of ordinary white film is the sodium calcium silicate system, with a refractive index of 1.51 and a visible light transmittance of over 89%. It can absorb ultraviolet light below 280nm.

The main component of optical white film is the sodium calcium silicate system, with a refractive index of 1.531, an Abbe number of 60.5, a transmittance of over 91%, and the worst UV protection performance.

UV optical white film is made by adding a small amount of titanium oxide and cerium oxide to the composition of optical white film, making it have the ability to absorb ultraviolet light. Its refractive index is 1.523, Abbe number is 58.7, transmittance is over 91%, and it can absorb ultraviolet light below 330nm. And with good mechanical properties and chemical stability, it is a commonly used white high-quality lens that absorbs ultraviolet rays both domestically and internationally.

2. Crookes lenses

By the Englishman William; Crookes invented it in 1914 and named it Crookes lens, abbreviated as Crookes lens. X-ray films are divided into two types: ordinary and optical X-ray films.

Ordinary Kesi film, abbreviated as Guangke film, is a type of barium crown glass that contains trace amounts of cerium oxide, neodymium oxide, praseodymium oxide, and other substances to create a clear two-color effect on the lens. It appears light purple red under incandescent light and light cyan blue under fluorescent light, and can absorb ultraviolet light below 340nm. Its refractive index is 1.523 and its transmittance is over 87%.

3. Cruxite lenses

Krusty lenses are also divided into two types: regular and optical Krusty lenses. The former is abbreviated as Kesai Film, while the latter is abbreviated as Guangsai Film.  

Kesai tablets are made by adding a certain amount of selenium oxide to ordinary white tablets, resulting in a light pink color. They can absorb ultraviolet light below 300nm, have a refractive index of 1.510, and a transmittance of over 85%.

Guangsai lenses are made by adding substances such as manganese oxide and cerium oxide to the composition of barium crown glass, resulting in a light pink color, a refractive index of 1.523, a transmittance of over 87%, and the ability to absorb ultraviolet light below 350nm.

4. Photochromic lens

Abbreviated as color changing film. It is to add compounds such as silver halide to colorless or colored optical glass components, so that the lens can decompose into silver and halogen atoms when exposed to ultraviolet radiation, and the color of the lens changes from light to dark. On the contrary, when the light becomes dim, silver and halogens recombine to form colorless silver halide, causing the lens to return to its original colorless or colored state. There are two types of color changing lenses: tea changing and gray changing. They are characterized by their ability to correct vision and can also be used as sunglasses, making them suitable for outdoor wear. Photochromic resin materials appeared around 1986, which used a permeation method to penetrate a layer of photochromic photosensitive material on the convex surface of the resin material. This type of lens changes color quickly, is not completely controlled by temperature, and is not affected by the degree of refractive power, resulting in different shades of color in the central and peripheral areas.

5. Colored glass lenses

Colored glass lenses are made by adding various coloring agents to colorless optical glass to present different colors and selectively absorb or filter various monochromatic light. Its main purpose is to serve as a light blocking and various protective goggles, protecting the eyes from harmful rays, as well as wind, sand, chemicals, toxic gases, etc., playing a role in protecting the eyes. Common colored glass lenses include gray, brown, green, blue, red, and yellow.

(1) Grey glass lens

Add coloring agents such as cobalt oxide, copper oxide, iron oxide, and nickel oxide. It can absorb light evenly and has the ability to absorb ultraviolet and infrared rays. It can be used as sunglasses and is suitable for drivers to wear.

(2) Tea colored glass lens

Add coloring agents such as manganese oxide, iron oxide, or nickel oxide. It has the functions of absorbing ultraviolet rays and anti glare, with clear and distinct visual layers, and can be used as sunglasses.

(3) Green glass lens

Add coloring agents such as cobalt oxide, copper oxide, chromium oxide, iron oxide, and cerium oxide. It has the function of absorbing ultraviolet and infrared rays, and can be used as goggles for personnel such as gas welding, electric welding, and argon arc welding.

(4) Blue glass lens

Add coloring agents such as cobalt oxide, iron oxide, copper oxide, and manganese oxide. Protective goggles with anti glare function, suitable for personnel in front of high-temperature furnaces.

(5) Red glass lens

Add coloring agents such as cadmium selenide and cadmium sulfide. It has the function of preventing fluorescent glare and is suitable as goggles for X-ray medical personnel.

(6) Yellow glass lens

Add cadmium sulfide, cerium oxide, and titanium oxide for coloring. It has the ability to absorb ultraviolet rays and has clear and bright vision, making it suitable for drivers to wear on rainy, foggy days.

6. High refractive index lens

Also known as "ultra-thin lenses". Most domestically produced ultra-thin lenses use barium flint optical glass materials with a refractive index of 1.7035, a specific gravity of 3.028, and an Abbe number of 41.6. Compared with crown glass lenses, the thickness of the lens is about one-fifth thinner at the same refractive power, making it particularly suitable for people with high refractive errors to wear. However, due to the high content of lead oxide, the specific gravity is relatively high, and the Abbe number is also small, which can easily cause dispersion phenomena at the edge of the lens. At present, titanium oxide has been added to replace lead oxide in high refractive index glass, which has improved its specific gravity and optical coefficients such as Abbe number, making up for the above shortcomings.

2、 Optical resin materials

（1） Overview of Optical Resin

The resin material used for manufacturing eyeglass lenses is an optical resin made of high molecular weight organic compounds, which are molded or injection molded. It can also be divided into two types: thermosetting and thermoplastic resins. The commonly used optical resin materials include propylene glycol carbonate (CR-39), polymethyl methacrylate (PMMA), and polycarbonate (PC).

（2） CR-39 resin lens:

CR-39 material belongs to thermosetting resin and is manufactured by compression molding. Currently, most resin lenses for correcting vision use CR-39 resin material, which was developed by PPG Columbia Research Institute in 1942, is called "Columbia resin". The refractive index of a regular CR-39 lens is 1.5. Today, most of the materials with medium refractive index (n=1.56) and high refractive index (n>1.56) are thermosetting resins, which have developed rapidly. Their refractive index can be increased using any of the following techniques:

Changing the structure of electrons in atomic molecules, such as introducing a benzene ring structure;

Add heavy atoms such as halogens (chlorine, bromine, etc.) or sulfur to the original molecule.

Compared to traditional CR-39, using medium to high refractive index resin materials to manufacture sheets is lighter and thinner. Their specific gravity is roughly the same as CR-39 (between 1.20 and 1.40), but they have a large dispersion (Abbe number 45), poor heat resistance, but good UV resistance. They can also be dyed and subjected to various surface coating treatments. The manufacturing process of lenses using these materials is generally consistent with the manufacturing principle of CR-39. Nowadays, 1.67 resin materials have become widely popular, and resin materials like 1.7 have also been sold in the market. Professional personnel in the field of optometry are constantly researching and developing new materials, improving existing materials, in order to achieve better performance of resin materials in the future.

（3） Thermoplastic material (polycarbonate, abbreviated as PC)

Thermoplastic materials such as PMMA were first used to manufacture lenses as early as the 1950s, but due to their susceptibility to deformation under heat and poor wear resistance, they were quickly replaced by CR-39. However, today, the development of polycarbonate has brought thermoplastic materials back to the field of lenses and has been recognized by optometry professionals as the dominant lens material of the 21st century. In fact, polycarbonate is not a new material. It was discovered around 1995, but its actual use in the field of optometry is only in recent years. After years of development and multiple improvements, especially in the CD industry, its optical quality has become comparable to other mirror materials.

Polycarbonate is a thermoplastic polymer with a linear amorphous structure, which has many optical advantages: excellent impact resistance (more than 10 times that of CR39), high refractive index (ne=1.591, nd=1.586), very light (specific gravity=1.20g/cm3), 100% UV resistance (385nm), and high temperature resistance (softening point of 140 ℃/280 ° F). Polycarbonate materials can also undergo systematic coating treatment. Its Abbe number is relatively low (Ve=31, Vd=30), but it does not have a significant impact on the wearer in practice. In terms of dyeing, due to the inherent difficulty of polycarbonate materials in coloring, most colors are absorbed through dyeable wear-resistant films.

（4） Performance of optical resin

The properties of optical resin materials mainly include optical properties and physical and mechanical properties.

（5） Characteristics of Optical Resin

Optical resin materials are widely used in the manufacture of lenses for correcting vision, contact lenses, magnifying glasses, and sunglasses. Generally, CR-39 resin lenses (mainly including various corrective vision lenses, sunglasses lenses, and lenses for cataract surgery), PMMA lenses (mainly including sunglasses lenses, corneal contact lenses), and PC space lenses (mainly including industrial eye protection lenses, polarizing lenses, sports lenses, etc.) can be classified according to materials

The biggest feature of optical resin materials used to manufacture eyeglass lenses is their light weight, which is about half that of glass lenses. Secondly, they have strong impact resistance, which is 10 times higher than glass, good safety, good chemical stability, good transparency, excellent coloring properties, can be dyed into various colors, and have good UV absorption and forming processing properties. Its biggest disadvantages are low hardness, easy scratching, poor heat resistance, easy deformation, and thicker lenses compared to glass lenses.

3、 Natural materials

Mainly crystal stone, it is a natural transparent quartz crystal, mainly composed of silicon dioxide, with a refractive index and specific gravity slightly higher than optical glass. The characteristics of crystals are high hardness, high temperature resistance, abrasion resistance, resistance to moisture, heavy weight, and difficulty in grinding and processing.

The eyeglass lenses made of crystal materials are called "crystal lenses", and there are two commonly used types: natural crystal stones and artificial crystal stones. Each color can be divided into two types: white crystal and tea crystal. Due to the presence of various impurities such as cotton or frozen patterns in crystal stones, their optical properties are far inferior to those of optical glass. At present, it has gradually been replaced by optical glass or optical resin materials.

1、 Wear resistant film (dura mater)

Whether made of inorganic or organic materials, eyeglass lenses can cause wear and scratches on the surface of the lens due to friction with dust or gravel (silicon oxide) in daily use. We can observe that scratches on the surface of the lens are mainly divided into two types. The first is scratches caused by small gravel, which are deep and rough around the edges. If they are located in the central area, they will affect vision.

(1) Technical features

1) The first generation anti-wear film technology

Anti wear film began in the early 1970s, when it was believed that glass lenses were less prone to wear due to their high hardness, while organic lenses were too soft to wear easily. Therefore, quartz material is deposited on the surface of organic lenses under vacuum conditions to form a very hard anti-wear film. However, due to the mismatch between its thermal expansion coefficient and the substrate material, it is easy to peel off and the film layer is brittle, resulting in unsatisfactory anti-wear effect.

2) Second generation anti-wear film technology

After the 1980s, researchers theoretically discovered that the mechanism of wear is not only related to hardness, but also to the dual characteristics of "hardness/deformation" in membrane materials. Some materials have higher hardness but smaller deformation, while others have lower hardness but larger deformation. The second generation of wear-resistant film technology is to coat the surface of organic lenses with a high hardness and non brittle material through immersion process.

3) Third generation anti-wear film technology

The third-generation anti-wear film technology was developed after the 1990s, mainly to solve the wear resistance problem of organic lenses coated with anti reflective film layers. Due to the significant difference in hardness between the organic lens substrate and the anti reflective film layer, a new theory suggests the need for an anti-wear film layer between the two to provide cushioning for the lens when subjected to abrasive wear and reduce the risk of scratches. The hardness of the third-generation wear-resistant film layer material is between that of the anti reflective film and the lens substrate, and its friction coefficient is not easily brittle.

4) The fourth generation anti-wear film technology

The fourth generation of anti-wear film technology uses silicon atoms, which contain both organic matrix and inorganic ultrafine particles including silicon elements in the hardening solution, making the anti-wear film tough and increasing its hardness. The most important modern wear-resistant coating technology is the immersion method, which involves immersing the lens in a hardening solution after multiple cleaning steps, and then lifting it up at a certain speed after a certain period of time. This speed is related to the viscosity of the hard liquid and plays a decisive role in the thickness of the anti-wear film layer. After lifting, polymerize in an oven at around 100 ℃ for 4-5 hours, with a coating thickness of about 3-5 microns.

(2) Testing method

The most fundamental method for assessing and testing the wear resistance of wear-resistant films is clinical use, where the wearer wears the lenses for a period of time and then observes and compares the wear of the lenses under a microscope. Of course, this is usually the method adopted before the official promotion of this new technology. Currently, the faster and more intuitive testing methods we commonly use are:

1) Matte test

Place the lens in a container filled with gravel (the particle size and hardness of the gravel are specified) and rub back and forth under certain control. After completion, use a haze meter to test the diffuse reflection of light before and after friction of the lens, and compare it with a standard lens.

2) Steel Velvet Test

Using a prescribed velvet, rub the surface of the lens a certain number of times under a certain pressure and speed, and then use a haze meter to test the diffuse reflection of light before and after the friction of the lens, and compare it with a standard lens. Of course, we can also manually apply the same pressure to rub the two lenses the same number of times, and then observe and compare them with the naked eye.  

The above two testing methods and results are relatively close to the clinical results of long-term wearing of glasses by wearers.

3) The relationship between anti reflection film and anti-wear film

The anti reflective film layer on the surface of the lens is a very thin inorganic metal oxide material (thickness less than 1 micron), hard and brittle. When plated on glass lenses, due to the relatively hard substrate, gravel runs over it, making the film layer relatively less prone to scratches; However, when the anti reflection film is coated on a lens, due to the soft substrate, the sand and gravel can easily scratch the film layer (Figure 12).

Therefore, organic lenses must be coated with an anti-wear film before being coated with an anti reflection film, and the hardness of the two film layers must match.

2、 Anti reflective film

(1) Why is it necessary to coat with anti reflective film?

1) Specular reflection

When light passes through the front and rear surfaces of a lens, it not only refracts but also reflects. The reflected light generated on the front surface of the lens will make others see a white light on the surface of the lens when they look at the wearer's eyes. When taking photos, this kind of reflection can seriously affect the beauty of the wearer.

2) Ghost Shadow

The theory of eyeglass optics holds that the refractive power of eyeglass lenses causes the object being viewed to form a clear image at the wearer's far point, which can also be explained as the light of the object being viewed being refracted through the lens and focused onto the retina, forming an image point. However, due to the different curvatures of the front and rear surfaces of refractive lenses and the presence of a certain amount of reflected light, internal reflection light will be generated between them. Internal reflection light will generate virtual images near the far spherical surface, which means virtual image points will be generated near the image points of the retina. These virtual image points can affect the clarity and comfort of the visual object.

3) Glare

Like all optical systems, the eye is not perfect, and the image formed on the retina is not a point, but a blurry circle (Figure 14-1). Therefore, the feeling of two adjacent points is generated by the more or less overlapping fuzzy circles of two parallel examples. As long as the distance between two points is large enough, the imaging on the retina will produce a feeling of two points (Figure 14-2). However, if the two points are too close, the two blurred circles will tend to overlap and be mistaken for one point (Figure 14-3).

Contrast can be used to reflect this phenomenon and express the clarity of vision. The contrast value must be greater than a certain threshold (perception threshold, equivalent to 1-2) to ensure that the eyes can distinguish between two adjacent points.

The formula for calculating contrast is: C=(a-b)/(a+b)

Among them, C is the contrast, the highest perceived value of two adjacent object points on the retina is a, and the lowest value of adjacent parts is b. If the contrast C value is higher, it indicates that the visual system has a higher resolution for the two points and feels clearer; If two object points are very close, and the lowest value of their adjacent parts is closer to the highest value, then the C value is low, indicating that the visual system feels unclear about the two points or cannot distinguish them clearly.

Let's simulate a scene like this: at night, a driver wearing glasses can clearly see two bicycles riding towards him in the distance opposite. At this point, the headlights of the car following behind generate reflections on the surface behind the driver's lens: the image formed by the reflected light on the retina increases the intensity of two observed points (bicycle headlights). So, as the lengths of "a" and "b" increase, since the denominator (a+b) increases while the numerator (a-b) remains unchanged, it causes a decrease in the value of C. The result of reduced comparison will cause the initial feeling of two cyclists to overlap and become a single image for the driver, just like the angle that distinguishes them being suddenly reduced!

4) Transmitting quantity

The percentage of reflected light to incident light depends on the refractive index of the lens material and can be calculated using the formula for reflection.  

Reflection formula: R=(n-1) 2/(n+1) 2

R: The single-sided reflection of the lens n: the refractive index of the lens material

For example, the refractive index of ordinary resin material is 1.50, and the reflected light R=(1.50-1) 2/(1.50+1) 2=0.04=4%. A lens has two surfaces. If R1 is the reflection amount on the front surface of the lens and R2 is the reflection amount on the back surface of the lens, then the total reflection amount of the lens R=R1+R2 (when calculating the reflection amount of R2, the incident light is 100% - R1). The transmittance T of the lens is: T=100% - R1-R2.

The refractive index n has a single-sided reflection rate of R1% and a transmittance rate of T%. Therefore, it can be seen that high refractive index lenses without anti reflection films will cause strong discomfort to the wearer when reflecting light.

(2) Principle

The anti reflection film is based on the fluctuation and interference phenomena of light. As shown in Figure 15, when two light waves with the same amplitude and wavelength are superimposed, the amplitude of the light waves is enhanced; If two light waves have the same amplitude but different paths, and these two light waves are superimposed, they cancel each other out. The anti reflection film utilizes this principle by coating the surface of the lens with an anti reflection film, so that the reflected light generated on the front and rear surfaces of the film interferes with each other, thereby canceling out the reflected light and achieving the effect of anti reflection.

1) Amplitude condition

The refractive index of the film layer material must be equal to the square root of the refractive index of the lens substrate material.

When N=√ n1 n1=1.50, n=√ 1.50=1.225

2) Phase condition

The thickness of the film layer should be 1/4 wavelength of the reference light.

When d=λ/4 λ=555nm, d=555/4=139nm

For anti reflective film layers, many eyeglass lens manufacturers use light waves with high human eye sensitivity (wavelength of 555nm).

When the thickness of the coating is too thin, the reflected light will appear light brownish yellow. If it appears blue, it indicates that the thickness of the coating is too thick.

The purpose of coating with anti reflective film is to reduce the reflection of light, but it is impossible to achieve no reflection of light. There will always be residual colors on the surface of the lens, but there is no standard for which residual color is the best. Currently, it is mainly based on personal color preferences, with more green color options available.

We will also find some differences in the color of residual colors in the central and edge parts of the convex and concave surfaces of the lens, and there will also be differences in the reflected light of the convex and concave surfaces. This is mainly because the anti reflection film adopts the vacuum coating method. After one surface of the lens is coated, flip it over to coat the other surface; Moreover, during coating, the areas with small curvature changes are prone to coating, so even when the required film thickness is reached in the central part of the lens, the edges of the lens still have not reached the required thickness; At the same time, the different curvatures of the convex and concave surfaces also result in different coating speeds, so the central part of the lens appears green, while the edge part appears light purple red or other colors.

(3) Coating anti reflection film technology

The difficulty of organic lens coating technology is higher than that of glass lenses. Glass materials can withstand high temperatures above 300 ℃, while organic lenses will turn yellow and quickly decompose when they exceed 100 ℃.

The anti reflective film material that can be used for glass lenses usually uses magnesium fluoride (MgF2), but because the coating process of magnesium fluoride must be carried out in an environment above 200 ℃, it cannot adhere to the surface of the lens, so organic lenses do not use it.

After the 1990s, with the development of vacuum coating technology, the use of ion beam bombardment technology improved the bonding between film layers and lenses. And the extracted high-purity metal oxide materials such as titanium oxide and zirconium oxide can be deposited on the surface of resin lenses through evaporation process, achieving good anti reflection effect.

The following is an introduction to the anti reflective coating technology for organic lenses.

1) Preparation before coating

Before receiving coating, the lens must be pre cleaned, which requires a high level of cleaning at the molecular level. Place various cleaning solutions in the cleaning tank and use ultrasonic waves to enhance the cleaning effect. After the lens is cleaned, it should be placed in a vacuum chamber. During this process, special attention should be paid to avoiding dust and garbage in the air from adhering to the surface of the lens. The final cleaning is carried out before coating in the vacuum chamber. The ion gun placed in the vacuum chamber will bombard the surface of the lens (such as using argon ions), and after completing this cleaning process, the anti reflection film coating is carried out.

2) Vacuum coating

The vacuum evaporation process can ensure the pure coating material is applied to the surface of the lens, and at the same time, the chemical composition of the coating material can be tightly controlled during the evaporation process. The vacuum evaporation process can accurately control the thickness of the film layer, achieving precision.

3) Membrane firmness

For eyeglass lenses, the firmness of the film layer is crucial and an important quality indicator of the lens. The quality indicators of lenses include wear resistance, corrosion resistance, temperature difference resistance, etc. Therefore, there are now many targeted physical and chemical testing methods to test the fastness quality of coating layers under simulated conditions of wearing glasses. These testing methods include: saltwater test, evaporation test, deionized water test, steel wool friction test, dissolution test, adhesion test, temperature difference test, and humidity test, etc.

3、 Anti fouling film (top film)

(1) Principle

After the surface of the lens is coated with multiple layers of anti reflection film, the lens is particularly prone to stains, which can damage the anti reflection effect of the anti reflection film. Under the microscope, we can observe that the anti reflection film layer has a porous structure, so oil stains are particularly infiltrated into the anti reflection film layer. The solution is to coat a top film with anti oil and anti water properties on top of the anti reflection film layer, and this top film must be very thin so as not to change the optical properties of the anti reflection film.

(2) Craftsmanship

The material of the anti fouling film is mainly fluoride, and there are two processing methods: soaking method and vacuum coating, with the most commonly used method being vacuum coating. After the anti reflection film layer is completed, fluoride can be deposited onto the anti reflection film using evaporation technology. Anti fouling film can cover the porous anti reflective film layer and reduce the contact area between water and oil and the lens, making it difficult for oil and water droplets to adhere to the surface of the lens. Therefore, it is also known as waterproof film.

For organic lenses, the ideal surface system treatment should be a composite film consisting of anti-wear film, multi-layer anti reflection film, and top film fouling film. Usually, the anti-wear film coating is the thickest, about 3-5um, the thickness of the multi-layer anti reflection film is about 0.3um, and the top anti fouling film coating is the thinnest, about 0.005-0.01um.

The usual composite film process is as follows: first, a wear-resistant film with organic silicon is coated on the substrate of the lens; Then, using IPC technology, ion bombardment is used for pre cleaning before plating the anti reflection film; After cleaning, use high hardness materials such as zirconia (ZrO2) for vacuum plating of multi-layer anti reflection film layers; Finally, a top film with a contact angle of 110 is coated. The successful development of drilling crystal composite film technology indicates that the surface treatment technology of organic lenses has reached a new height.

Common knowledge of eyeglass lens coating:

Do stained and discolored lenses need to be coated with anti reflective film?

The light transmission of colored or discolored lenses will decrease, but the reflected light on the surface of the lens still exists. Therefore, the ghosting and glare generated by the reflected light on the concave surface of the lens and the internal reflection on the front and rear surfaces of the lens will still interfere with vision, affecting the clarity and comfort of the wearer's vision.

For example, a person wearing unpainted anti reflective film color changing lenses is drinking coffee and reading newspapers by the swimming pool, with the sun right behind them. Assuming the height of the tea cup seen by the wearer is 100Lx and the brightness of the sun is 500Lx.

At this point, the color changing lens of the wearer darkens due to sunlight, and the transmittance of the lens decreases. Assuming only 33% of the light can pass through, combined with the reflected light from the front and rear surfaces of the lens, the amount of light from the teacup that the wearer is looking at entering the eyeball is about 30Lx, which is 100%; 96%× 33%× 96%=30Lx.

The sunlight of 500Lx behind the wearer will be reflected on the surface of the lens, and 4% of the light will enter the eyeball. 500Z4%=20Lx. These lights will interfere with the clarity of the tea cup that the wearer wants to see, with an interference amount of 20/30=67%.

What would happen if the wearer's color changing lenses were coated with anti reflective film? At this point, the amount of light from the teacup that the wearer is looking at entering the eyeball will slightly increase. Assuming the reflection on the surface of the lens is 0.6%, the amount of light from the teacup entering the eyeball is approximately 33Lx, which is 100%; 99.4%× 33%× 99.4%=3Lx, but the reflected light on the back surface of the coated lens is greatly reduced, and the amount of sunlight entering the eyeball through the surface of the lens is 500; 0.6%=3Lx, at which point the interference level is 3&# 247; 33=9%.

From this, it can be seen that the interference level after coating has decreased from 67% to 9%, greatly improving the clarity and comfort of the wearer.