Whether it is made of inorganic or organic materials, in daily use, friction with dust or grit (silicon oxide) will cause the lens to wear and scratches on the surface of the lens. Compared with a glass sheet,
the hardness of organic materials is relatively low, and scratches are more likely to occur. Through the microscope, we can observe that the scratches on the lens surface are mainly divided into two types. One is the scratches caused by grit, which is shallow and small, and it is not easy for the wearer to detect; the other is the scratches caused by larger grit, Deep and rough periphery, in the center area will affect vision.
Technical characteristics
- 1) The first generation of anti-wear film technology
The anti-wear film began in the early 1970s. At that time, it was believed that glass lenses were not easy to grind because of their high hardness, while organic lenses were too soft and were easy to wear. Therefore, the quartz material is plated on the surface of the organic lens under vacuum conditions to form a very hard wear-resistant film. However, due to the mismatch between its thermal expansion coefficient and the base material, it is easy to peel off and the film is brittle, so it is resistant The wear effect is not ideal.
- 2) 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. The film material has the dual characteristics of “hardness/deformation”, that is, some materials have higher hardness but less deformation, and some The hardness of the material is low, but the deformation is large. The second generation of anti-wear film technology is to plate material with high hardness and not brittle cracking on the surface of the organic lens through the immersion process.
- 3) The third generation of anti-wear film technology
The third generation of anti-wear film technology was developed after the 1990s, mainly to solve the problem of wear resistance after the organic lens is coated with an anti-reflection film. Since the hardness of the organic lens base and the hardness of the anti-reflective coating are quite different, the new theory believes that there needs to be an anti-wear coating between the two, so that the lens can act as a buffer when it is rubbed by grit. Not easy to produce scratches. The hardness of the third-generation anti-wear film material is between the hardness of the anti-reflection film and the lens base, and its friction coefficient is low and it is not easy to be brittle.
- 4) The fourth generation of anti-wear film technology
The fourth-generation anti-film technology uses silicon atoms. For example, French Essilor’s TITUS hardening fluid contains both organic matrix and inorganic ultrafine particles including silicon to make the anti-wear film It has the toughness and at the same time increases the hardness. The most important modern anti-wear coating technology is to use the immersion method, that is, the lens is immersed in a hardening liquid 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 plays a decisive role in the thickness of the anti-war film. After lifting, polymerize in an oven at about 100°C for 4-5 hours, and the coating thickness is about 3-5 microns.
Test method
The most fundamental way to judge and test the abrasion resistance of the anti-wear film is to use it clinically, let the wearer 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 formal promotion of this new technology. At present, the quicker and more intuitive test methods we commonly use are:
- 1) Frosting test
Put the lens in a promotional material containing gravel (the grain size and hardness of the gravel are specified), and rub back and forth under certain control. After the end, use a haze meter to test the amount of diffuse reflection of light before and after the lens is rubbed, and compare it with the standard lens.
- 2) Steel wool test
Use prescribed steel wool to rub the surface of the lens a number of times under certain pressure and speed, and then use a haze meter to test the amount of 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 the same number of times with the same pressure, and then observe and compare them with the naked eye.
The results of the above two test methods are relatively close to the clinical results of long-term wear by the wearer.
- 3) The relationship between anti-reflection coating and anti-wear coating
The anti-reflection coating on the surface of the lens is a very thin inorganic metal oxide material (thickness less than 1 micron), hard and brittle. When it is plated on a glass lens since the base is relatively hard and the grit is scratched on it, the film layer is relatively difficult to scratch; but when the anti-reflection film is plated on the organic lens because the base is soft, the grit is on the film. Scratched on the layer, the film is easily scratched.
Therefore, the organic lens must be coated with an anti-wear coating before an anti-reflection coating, and the hardness of the two coatings must match.