Hard dip coatings are usually produced with polysiloxane lacquers. With their elastic properties, these lacquers form an almost ideal buffer between the lens surface and the more brittle AR coating. At ZEISS the dipping technique is used to apply all hard coatings to plastic lenses. After a cleaning and pre-treatment process, several lenses are placed in special racks and immersed in the polysiloxane lacquer.
The thickness of the hard coating is regulated both by the speed at which the lenses are immersed and removed, and by the viscosity of the lacquer. To guarantee that the required viscosity is always obtained, the ambient temperature must remain constant at 18 °C.
Since the introduction of the first hard dip coating at ZEISS in 1986, the quality of the coatings has been constantly improved. The result: all hard-coated lenses from ZEISS now display a high quality standard.
The use of newly developed plastics for spectacle lenses means that new, high-performance lacquer systems are also required.
The development of lens materials is centred on increasing the refractive index. To achieve the same quality standard for hard coatings on every material, ZEISS uses hard lacquers which have been precisely matched to the material’s properties. The higher the refractive index of the material, the higher the index of the lacquer.
To guarantee the high quality standard of the hard coatings, cleanroom conditions are used at ZEISS.