In recent years, extremely many kinds of organic photochromic dyes has been developed, and photochromic dyes capable of being obtained as commercially available products have been increasing. The application thereof to a lens for eye glasses also becomes popular along with the trend of plasticization on the marketplace, and a photochromic lens made of plastic, applying an organic photochromic dye comes onto the market for use in eye glasses.
As to methods for manufacturing a photochromic lens, there are disclosed (1) a method of coating a resin liquid containing a photochromic compound on a lens, heating the same to cause the photochromic compound to permeate the lens surface layer, after that, removing the coated resin film, and applying a curable film thereon (for example, see Patent Literature 1), and (2) a method of dissolving a photochromic compound into a lens coating liquid, and coating and curing the same on the lens surface (for example, see Patent Literature 2).
However, in the method of (1), in order to obtain a sufficient photochromic density, it is necessary to cause the photochromic compound with a high concentration to permeate the lens surface and there is a problem in which a lens base material is limited to a material to be highly permeated. Therefore, in terms of heat resistance, mechanical strength and the like, a satisfactory level as a lens for eye glasses is not attained. In addition, in the method of (2), there is a limitation on the solubility of the photochromic compound into the coating liquid and the securement of a sufficient coloration density is difficult.
Furthermore, in these methods, since a film is formed by coating the coating liquid on lens surfaces of variously curved shapes, a high-accuracy technology of homogenizing the film and a high-accuracy technology of controlling a film thickness, which correspond to these methods, are required, and thus the manufacturing cost becomes high.
In contrast, as manufacturing methods other than (1) and (2), (3) a method of dissolving previously a photochromic compound into a monomer mixed liquid for a lens, pouring it into a mold, and after that, polymerizing it to obtain a photochromic lens is disclosed (for example, see Patent Literature 3 and Patent Literature 4).
More particularly, in Patent Literature 3, a photochromic lens is disclosed, the lens having a sufficient light-controlling performance, and excellent surface hardness and abrasion resistance that are important as a lens. In addition, in Patent Literature 4, a photochromic lens is disclosed, the lens having a low yellow level before coloration and having wavelength in coloration made longer, to thereby allow a deep tone to be expressed.
Methods of (1) and (2) require a special process for imparting light controllability such as a coating treatment after lens molding. In contrast to this, the method of (3) is preferable as a manufacturing method because the light-controlling performance is imparted simultaneously at the time of the lens molding and thereby manufacturing number of processes is lowered, and in addition, since the photochromic compound can easily be dispersed homogeneously in a base material, the method of (3) is extremely useful as a method for mass-producing a lens having a certain light-controlling performance irrespective of the lens shape and having a stable quality.
Furthermore, as specific examples of the method of (3), in Patent Literature 5 and Patent Literature 6, it is described that the combination of a specific aromatic (meth)acrylic ester and aromatic vinyl makes it possible to obtain a good light-controlling performance.