Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-06-11
2004-08-03
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S242000, C523S106000
Reexamination Certificate
active
06770692
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a plastic base material that cuts off ultraviolet and short wavelength optical radiations harmful to eyes.
BACKGROUND ART
As compared with glass, transparent plastic base materials are characterized in that they are lightweight, unbreakable, and in that they are easily dyed or colored. As such transparent plastic base materials, styrene resins, acrylic resins, polycarbonate resins, and ADC resins are commercially available; further nowadays, sulfur-containing urethane resins, sulfur-containing episulfide resins and the like are also utilized, and those having refractive indices exceeding 1.60 are put into market to be used in eyeglasses, optical articles, light-intake windows, and the like.
On the other hand, sunlight contains, in addition to visible radiation, ultraviolet radiation harmful to cornea, crystal lens, retina, etc., of the eyeballs. Ultraviolet radiation is classified into UV-C, UV-B, and UV-A (near ultraviolet radiation), and each has unfavorable influences on the eyeballs.
In case of eyeglasses, for instance, there have been proposed, or put into market, optical lenses that not only correct the abnormal refraction of the wearer, but also are imparted with a function of absorbing ultraviolet radiation to some extent, such that they may protect the eyeballs of the wearer from such harmful ultraviolet radiation.
However, conventionally used in practice were optical lenses designed so as to cut off ultraviolet radiation of 380 nm or shorter in wavelength, because ultraviolet radiation of 380 nm or shorter in wavelength were believed harmful. With progress in the research on the damage of eyeballs, however, it is demanded to cut off ultraviolet radiation of 400 nm or shorter in wavelength. Further recently, not only the ultraviolet radiation of 400 nm or shorter in wavelength, but also blue color radiation of 400 nm or longer in wavelength are being considered problematic, because it has the possibility of causing damages such as macular degeneration with aging. Moreover, glaring can be suppressed by controlling blue color radiation 400 nm or longer in wavelength.
Conventionally, special lenses generally denoted as “UV400 processed”, which cuts off ultraviolet radiation, have been supplied in the eyeglass optical lens industry. This type of lens is imparted with an ultraviolet absorbing function, and it utilizes a lens base material colored with an ultraviolet-absorbing compound available as a ultraviolet absorbent by means of immersion coloring or the like. However, the lens produced by the method above has disadvantages, such that the lens undergo extreme yellow coloring with passage of time; in extreme cases, it was found that the feeling on wearing becomes extremely impaired due to yellow coloring of the lens which occurs in about a month after starting wearing.
In the light of the aforementioned circumstances, there are proposed lenses which effectively suppress the transmission of ultraviolet radiation of 400 nm or shorter in wavelength, and which are also free from yellow coloring with passage of time. There are proposed, for instance, a lens such as that comprising a base material and/or a hard coating layer containing mixed therein an ultraviolet absorbent or that using titanium dioxide having a ultraviolet absorbing function, and comprising an antireflection layer having, as the constituent layer thereof, a titanium dioxide layer having a thickness capable of efficiently suppressing the transmission of ultraviolet radiation.
For instance, the lens proposed in Japanese Patent Laid-Open No. 51706/1985 effectively suppresses the transmission of ultraviolet radiation of 380 nm or shorter in wavelength, however, suppressing ultraviolet radiation of 380 to 400 nm in wavelength is still insufficient.
In Japanese Patent Laid-Open No. 265059/1997 is proposed an optical lens for eyeglasses capable of cutting off ultraviolet radiation up to 400 nm in wavelength, having a base material and/or a hard coating layer containing an ultraviolet absorbent, with a multi-layered antireflection film containing a titanium dioxide layer provided thereon at a predetermined thickness or thicker. Further, in Japanese Patent Laid-Open No. 186291/1998 is disclosed a plastic lens containing an ultraviolet absorbent having an average light transmittance of 0.5% or lower for radiation in the wavelength region of 300 nm or longer but not longer than 400 nm. Furthermore, in Japanese Patent Laid-Open No. 218602/1999 is disclosed a plastic lens containing at least two types of ultraviolet absorbents differing in maximum absorption wavelength.
The lenses proposed above are effective for controlling the ultraviolet radiation of 400 nm or shorter in wavelength since the development was done mainly on the control of the radiation of the wavelength; however, the control of blue color radiation in the visible region remains still insufficient.
Further, if ultraviolet absorbents should be added in large quantities, it is certainly possible to suppress the transmission of radiation in the blue color region; however, the resulting lens becomes yellow-colored to impair the product value. Moreover, the addition of the agents in large quantities may cause unfavorable results, such as fogging of the plastic base lens material, inferior heat-resistance due to the drop in softening point of the resin, etc.
On the other hand, in Japanese Patent Laid-Open No. 133801/1997 is described a method comprising mixing a trace amount of blue-colored colorant with an aim to obtain a colorless and transparent lens by suppressing the yellow coloring which occurs with heat treatment and the like of lens base material such as a urethane resin lens. However, in case blue-color colorant is applied to a lens base material containing an ultraviolet absorbent in large quantities, the lens results in a green colored material to make it difficult to obtain the transparent appearance. Furthermore, although lenses colored to blue to an excessive extent to stress transparency are partly put into market, there is another disadvantage that, in colored lenses which are the characteristic products for plastic lenses, the desired color cannot be obtained and result in an unclear color hue.
An object of the present invention is to provide a plastic base material, which suppresses the transmission of not only the ultraviolet radiation of 400 nm or shorter in wavelength, but also the blue color radiation of 400 to 420 nm in wavelength, harmful to eyeballs, while preventing glaring and yet providing a transparent appearance. In further detail, the object is to provide a plastic base material having a transmittance of 10% or lower for radiation of 400 nm in wavelength and a transmittance in a range of from 40 to 60% for radiation of 410 nm in wavelength, i.e., an average transmittance of about 50% in a wavelength range of from 400 to 420 nm, and yet having a transparent appearance. The plastic base material according to the present invention can be applied not only to eyeglasses, but also to construction materials such as light-intake windows and the like, which will protect the inhabitants living indoors from harmful rays.
DISCLOSURE OF THE INVENTION
The inventors have conducted extensive studies on the control of visible radiation of 420 nm or shorter in wavelength and ultraviolet radiation, as well as on the prevention of glaring. As a result, it has been found that a base material in compliance with the object above can be obtained by mixing an ultraviolet absorbent and a colorant each having a specific chemical structure into the plastic base material. The present invention has been accomplished based on those findings.
The present invention provides a plastic base material characterized by that it contains a benzotriazole based ultraviolet absorbent expressed by the general formula (1) and an anthraquinone based violet colorant expressed by the general formula (2), and that it yields a transmittance of 1% or lower for a radiation of 390 nm in wavelength and a transmittance of 10% or lowe
Kobayashi Tadashi
Tsujibata Kazuhiko
Asahi Lite Optical Co., Ltd.
Jordan and Hamburg LLP
Sanders Kriellion A.
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