Plastics are often used as a material of spectacles lenses lately from the aspect of being light and excellent in shock resistance. Antireflection films are coated on both surfaces of the spectacles plastic lens. The antireflection film is provided to prevent surface reflection on the spectacles plastic lens because the surface reflection causes, when it occurs, the drop of light transmittance in the optical system, the increase of light which will not contribute in forming an image and the drop of contrast of the image. The antireflection film of the spectacles plastic lens has been conventionally formed as a single-layer film or a multi-layered film mainly by means of a vacuum evaporation method.
Presently, highly productive methods and systems for forming the antireflection film on an optical lens such as the spectacles plastic lens by the simple arrangement utilizing the sputtering method are being proposed. The sputtering film deposition system is provided with a sputtering film deposition chamber which allows different thin films to be fabricated by exchanging targets in a vacuum container for the chamber. The sputtering system allows a multi-layered antireflection film to be deposited on the surface of the spectacles plastic lens without exposing it to the atmosphere. It also allows the films to be deposited on the both sides of the spectacles plastic lens at the same time. The sputtering film deposition system has a merit that it can form the homogeneous films on the both sides of the lens because it can form the films on the both sides of the lens at the same time and film forming conditions are the same on the both sides of the lens. Further, when a multi-layered film is deposited on the surface of the lens and further the film is formed by laminating two kinds of films having different qualities repeatedly and alternately, for example, high-refractive materials and low-refractive materials the sputtering film deposition system has merits that it can form the multi-layered film readily and can control the thickness of each layer accurately because it just needs to prepare two targets corresponding to the material of each film within the sputtering film deposition chamber and to sputter by exchanging the targets. The antireflection film having highly evaluated film performance may be formed by accurately controlling the thickness of each layer.
Then, as for the antireflection film of the plastic optical devices such as the spectacles plastic lens fabricated by utilizing the aforementioned new film forming method and system utilizing sputtering, it becomes possible to propose the antireflection film having the new multi-layered structure and highly evaluated film performance.
An interference color is an important evaluation item in the evaluation of the film performance of the spectacles lens. The interference color is a color caused by interference of white light, and in case of the spectacles plastic lens on which the multi-layered antireflection film is formed, it is a color of reflected light caused by interference when the transparent thin films having different refractive indices are coated on the surface of the lens. The interference colors of the commercially available lens coated with the antireflection film are divided roughly into three colors of bluish, purplish and greenish colors in general. Although the greenish interference color, among them, excels eye-physiologically and aesthetically and in terms of commercial value in particular, the technology for stably giving this interference color has not been established yet because there have been various technological problems in terms of the selection of raw materials of the film, of setting of the thickness of the film, of the film forming conditions and others. However, the use of the above-mentioned sputtering method may allow this problem to be solved.
There has been another problem that when the high-refractive material is formed as the first layer of the antireflection film on the spectacles plastic base material which is an organic substance, the balance of stress at the interface changes due to water absorption (moisture absorption) and to pressure applied from the outside with an elapse of time and the antireflection film is liable to crack from the interface. For instance, when the spectacles plastic lens on which the multi-layered antireflection film, in which the high-refractive material is formed as the first layer, is fitted into an spectacles frame while it is squeezed by considerably strong force and is further caused to absorb water, there is a case when the spectacles plastic lens cracks from the edge portion thereof. The occurrence of cracks drops its commercial value as an spectacles lens. Accordingly, it has been required to think of measures for preventing the occurrence of cracks.
In depositing the film on the optical lens by the sputtering method presently proposed, normally a plurality of lens base materials (in unit of lot) are set on a circular plate holder (substrate holder or a lens tray) and the film depositing process is carried out per lot while turning the holder. While it is considered that the thickness of the film formed by the sputtering method is well distributed, it is required to have more accurate and uniform distribution of thickness in utilizing the sputtering method for forming a thin film of the optical lens. More strict uniformity is required with regard to the thickness especially when the antireflection film is to be formed on the surface of the optical lens by utilizing the sputtering method as described above. When the thickness of the antireflection film on the surface of the lens is not uniform, its reflection color varies, thus dropping the feeling of wearing and using the optical lens and the commercial value thereof.
Furthers, as for the surfaces of the optical lens, one surface thereof is formed to be a concave surface and the other surface to be a convex surface, having curvatures, respectively. According to the method of forming the antireflection film on the surfaces of the optical lens by utilizing the sputtering method, normally the optical lens is disposed horizontally on the holder and upper and lower targets are disposed so as to face to the both sides of the optical lens, respectively, to carry out the sputtering film deposition on the both sides at the same time. However, it is difficult to deposit the films on the surfaces so as to have uniform thickness because the both sides of the optical lens have the curvatures peculiar to each and therefore distances between the targets facing to the respective surfaces of the optical lens and each part on the surfaces are different.
Accordingly, it is an object of the present invention to provide plastic optical devices having an antireflection film whose film performance is highly evaluated and having a new multi-layered structure by fabricating an antireflection film by utilizing the sputtering method.
Also, when the above-mentioned plastic optical device is to be utilized for a spectacles plastic lens, it is arranged so as to give a greenish interference color stably on the lens to form the antireflection film which excels eye-physiologically and aesthetically and is highly valuable commercially.
Another object of the present invention is to provide a spectacles plastic lens having an antireflection film which is arranged so as to prevent occurrence of cracks by improving the surface of the plastic base material, when forming the multi-layered antireflection film on the spectacles plastic base material which is an organic substance by depositing a high-refractive material as a first layer.
A further object of the present invention is to provide a mechanism which can uniform distribution of thickness of a film on the surface of the optical lens base material in forming the film thereon by the sputtering method.