Optical lens coating technology

Lens material classification

Glass lenses include optical glass lenses and high-refractive-index lenses (usually called ultra-thin sheets), which have high hardness and good wear resistance. Generally, their quality and various parameters will not change with time, but the resistance of glass lenses Impact and weight are slightly inferior to resin lenses.

Resin lenses are generally much lighter than glass lenses, and their impact resistance is better than that of glass lenses. Due to their soft characteristics, resin lenses and coated lenses should be careful not to let the mirror surface directly touch hard objects. When scrubbing, it is best to wash with water (or mixed with a small amount of detergent), and then use a special test cloth or high-quality cotton paper. Blot the water droplets from the spectacle lenses. In addition, coated lenses should be used with caution in places with poor environmental conditions, so as not to be stained with dirt and difficult to clean.

PC lenses: high refractive index, strong, but easy to wear. Mostly used for children's eyeglasses, frameless assemblies or athletes' goggles.

What are the advantages of lens coating?

Coated lenses can reduce the reflected light on the surface of the lens, see objects clearly, reduce the reflected light on the mirror surface, increase the light transmittance, and also solve the problem of wearing glasses in strong light, and increase the beauty. Coated glasses can prevent ultraviolet, infrared and X-ray damage to vision. Wearing coated glasses is not easy to fatigue. The vision of the staff in front of the screen can be protected.

Coated resin lenses should not only avoid scratching and high temperature, but also avoid corrosion such as acid fumes. For example, it is best not to wear mirrors when cooking in daily life, especially when the ventilation is poor and the fumes are large; at the same time, do not wear (bring) mirrors. When entering (near) a hot shower environment, the lens should be convexly facing upwards when temporarily placed, and the glasses should be put into the box when carrying them with you, and do not put them in a pocket or bag, as it is easy to scratch the film.

How long does the lens last?

If the lens is not scratched, can it be used all the time? The answer is no. Resin lenses are processed by liquefying monomers at high temperature or by curing with ultraviolet light. As the service cycle becomes longer and the environment and temperature change, the film on the surface of the lens and the material of the lens itself will undergo physical changes, and the film will appear under the microscope. If it becomes uneven, the local luminosity of the material itself and the time of fitting have been different, resulting in light scattering and reduced comfort. Long-term use will cause dry and swollen eyes. At this time, it is necessary to replace the lens. The time is about 2 to 3 years.

Spherical and aspherical lenses

The traditional spherical lens, not only the lens is thick, but also the phenomenon of distortion and deformation occurs when looking through the periphery of the lens, which is called aberration. By observing the wearer through the spherical lens, the deformation of the facial contour can also be clearly found. Aspherical lenses not only reduce the thickness of the center and edge of the lens, but also make the lens thinner, eliminate peripheral aberrations, and give the wearer natural vision. For consumers with high visual acuity, it may be more appropriate to choose aspherical lenses.

Compared with the spherical surface of the same material and the same degree, the aspherical lens is flatter, thinner, more realistic, more natural and comfortable. If you look at the shape of the lens coating against the lamp tube, the lamp tube reflected by the aspherical lens is generally straight (except for the high diopter lens); while the spherical lens has a large curvature of the lamp tube shape due to the different curvature of the surface.

Optical lens coating technology and development
Whether spectacle lenses made of inorganic materials or organic materials, in daily use, due to the friction with dust or grit (silicon oxide), the lenses will be worn and scratched on the surface of the lenses. Compared with glass flakes,

Organic materials have lower hardness and are more prone to scratches. Through the microscope, we can observe that the scratches on the surface of the lens are mainly divided into two types, one is the scratches caused by the grit, which are shallow and small, and the wearer is not easy to notice; the other is the scratches caused by the larger grit. , deep and rough around, in the central area will affect vision.

(1) Technical features

The first generation of anti-wear film technology

Anti-abrasion films began in the early 1970s, when it was believed that glass lenses were difficult to grind because they were so hard, while organic lenses were too soft and were prone to wear. Therefore, the quartz material is plated on the surface of the organic lens under vacuum conditions to form a very hard anti-wear film, but due to the mismatch between its thermal expansion coefficient and the film base material, it is easy to peel off and the film is brittle, so it is resistant to wear and tear. The wear effect is not ideal.

The second generation of anti-wear film technology

After the 1980s, researchers have theoretically found that the mechanism of wear is not only related to hardness, but the film material has the dual characteristics of "hardness/deformation", that is, some materials have higher hardness but less deformation, while others have less deformation. The hardness of the material is lower, but the deformation is larger. The second-generation anti-wear film technology is to coat the surface of the organic lens with a material with high hardness and not easy to be brittle by immersion process.

The third generation of 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 an anti-reflection film. Since the hardness of the organic lens base and the hardness of the anti-reflection coating are very different, the new theory believes that a layer of anti-wear coating is needed between the two, so that the lens can act as a buffer when it is rubbed by sand and gravel. Not easy to scratch. The hardness of the third-generation anti-wear coating material is between the hardness of the anti-reflection coating and the lens base, and its friction coefficient is low and it is not easy to be brittle.

Fourth-generation anti-wear film technology

The fourth-generation anti-film technology uses silicon atoms. For example, the TITUS hardening solution of Essilor Company in France contains both organic matrix and inorganic ultra-fine particles including silicon, which makes the anti-wear film. It has toughness and improves hardness at the same time. The most important modern anti-wear coating technology is the immersion method, that is, the lens is immersed in a hardening solution after multiple cleanings, and then lifted at a certain speed after a certain period of time. This speed is related to the viscosity of the hardening fluid and determines the thickness of the anti-wear film. After being lifted, it is polymerized in an oven at about 100°C for 4-5 hours, and the thickness of the coating is about 3-5 microns.

(2) Test method

The most fundamental method for judging and testing the wear resistance of the anti-wear film is clinical use, allowing the wearer to wear it for a period of time, and then observe and compare the wear of the lens with a microscope. Of course, this is usually the method used before the official promotion of this new technology. At present, the more rapid and intuitive testing methods we commonly use are:

Scrub test

The lens is placed in a promotional material containing grit (the particle size and hardness of the grit are specified), and rubbed back and forth under certain control. After the end, use a haze meter to test the diffuse reflection of light before and after the lens is rubbed, and compare it with the standard lens.

Steel wool test

Use a specified steel wool to rub the surface of the lens for a 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 lens is rubbed, and compare it with the standard lens. Of course, we can also do it manually, rub the two lenses with the same pressure for the same number of times, and then observe and compare with the naked eye.

The results of the above two test methods are relatively close to the clinical results of long-term wear of glasses.

The relationship between anti-reflection coating and anti-wear coating

The antireflection coating on the lens surface is a very thin inorganic metal oxide material (less than 1 micron thick), hard and brittle. When coated on glass lenses, the film is relatively difficult to scratch due to the hard base and grit scratches on it; however, when the anti-reflection film is coated on organic lenses, due to the soft base, the grit is on the film. Scratched on the layer, the film layer is prone to scratches.

Therefore, the organic lens must be coated with an anti-wear coating before coating the anti-reflection coating, and the hardness of the two coating layers must be matched.