Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1997-07-08
2000-06-06
Manuel, George
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
G02C 702
Patent
active
060709790
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to plastic lenses for spectacles with high refractive indices, which have excellent impact resistance.
BACKGROUND ART
Plastic lenses for spectacles have various characteristics, which glass lenses do not have, in that they are lightweight, they are hardly broken and they are easily dyeable. Heretofore, acrylic resins, polycarbonate resins and ADC resins have been used to produce such plastic lenses. At present, urethane resins with high refractive indices are used to produce them, and plastic lenses with refractive indices of higher than 1.60 are sold in the market. Minus lenses with refractive indices of 1.60 or higher may be thinned even at their peripheries, and such thin lenses look nice. However, in order to reduce the weight of plastic lenses, it is still desired to further thin their center parts as much as possible, while removing the aberration to occur on their aspherical areas, thereby to further thin their peripheries.
As having good optical characteristics and other various excellent characteristics, plastic lenses are superior to glass lenses but the scratch resistance of the former is much lower than that of the latter. Therefore, for plastic lenses for use in spectacles, it is indispensable to coat their surfaces with a hard coat layer.
In order to improve their scratch resistance, plastic lenses may be coated with a hard coat layer comprising any of organic silicon compounds and epoxy resins. The hard coat layer of that type is very advantageous, when it is further coated with a thin metal film to form a non-glare layer thereon. However, the lens with the constitution of that type is seriously defective in that, if the hard coat layer and the non-glare layer are cracked on impact, the base lens will also be cracked often resulting in complete breakage of the lens. In general, if a plastic lens is directly coated with a hard coat layer and if the hard coat layer is over-coated with an inorganic layer of, for example, TiO.sub.2, ZrO.sub.2 or SiO.sub.2, through vacuum vapor deposition, the thus-coated lens shall have poor impact resistance and is easily cracked since the layers are very brittle though being hard. Therefore, it is said that, if such layers are simply formed on a plastic lens, the impact resistance of the coated lens will be lowered to 1/20 or less of the original impact resistance of the non-coated lens.
In order to ensure the reliable safety of spectacles for users, we, the present inventors have assiduously studied to develop plastic lenses for spectacles which have high impact resistance satisfying the requirements for commercial use and which are as safe as possible, and, as a result, have found that a plastic lens having a primer layer with a predetermined thickness or larger as formed between the base lens and the hard coat layer may have improved impact resistance.
In Japanese Kokai Patent Publication Nos. 63-87223 and 63-141001, disclosed are polyurethane primers to be obtained from a particular polyol or active hydrogen-having compound and a diisocyanate or polyisocyanate. These primers are applied to lenses of diethylene glycol bisallyl carbonate or its copolymer for the purpose of improving the adhesiveness between the lenses and the hard coat layers to be formed on the lenses. In the present invention, preferably used are primers of that type.
The thickness of the center parts of the lenses used in the above-mentioned prior art techniques is 1.6 mm or 1.2 mm. At present, however, recent lenses with high refractive indices may be further thinned with the increase in their refractive indices. For example, the thickness of the center parts of such lenses with high refractive indices may be from 0.7 mm to less than 1.2 mm. Accordingly, it has become possible to provide minus lenses having thin peripheries and plus lenses having thin center parts, which are fashionable. However, the reduction in the thickness of lenses inevitably results in significant reduction in the impact resistance thereof. Therefore, we, the presen
REFERENCES:
patent: 5059673 (1991-10-01), Kanemura et al.
patent: 5736609 (1998-04-01), Irizato et al.
Kagei Kazunori
Kobayashi Tadashi
Asahi Lite Optical Co., Ltd.
Manuel George
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