Coating processes – Optical element produced – Transparent base
Reexamination Certificate
2000-01-28
2002-04-02
Barr, Michael (Department: 1762)
Coating processes
Optical element produced
Transparent base
C427S322000, C427S430100, C008S507000
Reexamination Certificate
active
06365223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for tinting a resin for optical materials such as plastic lenses, prisms, optical fibers, information recording substrates and filters, and more particularly to a process for tinting a resin for plastic lenses for glasses.
2. Description of the Prior Art
Plastic materials have widely been used as various optical materials, particularly as lenses of glasses, because of light weight, toughness and easiness of tinting. The properties required for optical materials, particularly for lenses of glasses, are a low specific gravity, optical properties such as a large refractive index and a large Abbe number and physical properties such as high heat resistance and large strength. A large refractive index is important to decrease thickness of a lens. A large Abbe number is important to decrease chromatic aberration of a lens. High heat resistance and large strength are important to facilitate fabrication and also from the standpoint of safety.
However, since plastic materials have smaller refractive indices than those of inorganic lenses, it is necessary that the thickness of plastic lenses be increased. This causes problems in that light weight which is the characteristic property of plastic materials cannot be effectively utilized and that appearance becomes poor. Therefore, development of a resin for optical materials having a larger refractive index has been desired.
As the material having a large refractive index in accordance with conventional technology, resins containing sulfur such as thermosetting optical materials having a thiourethane structure which are obtained by the reaction of polythiol compounds and polyisocyanate compounds (Japanese Patent Application Publication No. Heisei 4(1992)-58489 and Japanese Patent Application Laid-Open No. Heisei 5(1993)-148340) and materials obtained by using 1,4-dithiane-2,5-dimercaptomethyl (Japanese Patent Application Publication Heisei 6(1994)-5323) have been proposed.
A small chromatic aberration is another important property required for an optical material. The larger the Abbe number, the smaller the chromatic aberration. Therefore, a material having a large Abbe number is desirable. Thus, a material having a large refractive index and a large Abbe number is desired. However, the Abbe number tends to decrease with an increase in the refractive index. Plastic materials obtained from conventional compounds have the maximum Abbe number of about 50 to 55 when the refractive index is 1.50 to 1.55, about 40 when the refractive index is 1.60 and about 31 when the refractive index is 1.66. When the refractive index is forced to increase to 1.70, the Abbe number decreases to 30 or less and the obtained material cannot practically be used. To overcome these problems, the present inventors discovered novel sulfur-containing compounds having an episulfide structure from which optical materials having a small thickness and a decreased chromatic aberration, i.e., a refractive index of 1.70 or more and an Abbe number of 35 or more, can be obtained (Japanese Patent Application Laid Open Nos. Heisei 9(1997)-71580, Heisei 9(1997)-110979 and Heisei 9(1997)-255781 and Japanese Patent Application No. Heisei 11(1999)-022199).
As the refractive index is increased, it has become essential that sulfur is incorporated into a resin for optical materials and the sulfur content has been increasing with the increase in the refractive index. Diethyleneglycol bisallyl carbonate (hereinafter, abbreviated as CR-39) is known as a material having the refractive index of 1.50. This material does not contain sulfur. On the other hand, materials having a refractive index of 1.60 or more and an Abbe number of 40 or more contain about 25 to 30% of sulfur. The materials discovered by the present inventors which can achieve both of a large refractive index and a large Abbe number, i.e., a refractive index of 1.70 or more and an Abbe number of 35 or more, contain 50% or more of sulfur.
Due to the increased refractive index described above, the thickness of lenses prepared from the above materials can be made smaller than those of lenses prepared from CR-39 and the thickness of the entire lens can be decreased. Thus, the light weight which is the characteristic property of plastic materials can be advantageously utilized and the appearance can be improved.
Plastic materials have another drawback in that tinting is difficult. CR-30 can be satisfactorily tinted by dipping into an aqueous solution of a disperse dye. On the other hand, the above materials having large refractive indices have a drawback in that these materials have the hydrophobic property (small absorption of water) due to the characteristic structure containing a large amount of sulfur and cannot be tinted satisfactorily in accordance with the conventional method of dipping into an aqueous solution of a disperse dye. Improvement in the conventional method of tinting, for example, by addition of various carriers such as aromatic compounds, phenol compounds, alcohols, carboxylic acids and esters of carboxylic acids or various surfactants to the aqueous solution of a disperse dye has not achieved a sufficient effect. As described above, tinting of resins containing sulfur is difficult and this difficulty is enhanced as the sulfur content increases due to the enhanced hydrophobic property. Therefore, development of a novel process for tinting a resin for optical materials has been desired.
SUMMARY OF THE INVENTION
An object of the present invention is to develop a process for tinting a resin for optical materials, particularly a resin containing sulfur which shows increased difficulty in tinting as the refractive index increases and to obtain a resin for optical materials which has a large refractive index and exhibits excellent tint performance, which heretofore cannot be achieved.
As the result of intensive studies by the present inventors to overcome the above problems, it was found that the problems can be overcome by the process described in the following. The present invention has been completed based on this knowledge.
The present invention provides a process for tinting a resin for optical materials which comprises dipping a resin for optical materials into a liquid comprising an inorganic acid and/or an organic acid and thereafter tinting the resin, wherein the organic acid is a mixture of compound (I) having sulfo group and compound (II) having phenolic hydroxyl group but not having sulfo group and a ratio [(I)/(II)] of an amount by weight of compound (I) to an amount by weight of compound (II) is 0.01 to 2.0.
The present invention also provides a resin for optical materials which is tinted in accordance with the above process.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the process of the present invention, a resin for optical materials, particularly a resin containing sulfur which has a larger refractivity index and shows difficulty in tinting, can be tinted by dipping the resin into an inorganic acid and/or an organic acid and tinting the resin thereafter.
The resin for optical materials used in the present invention is not particularly limited and may be various resins such as (meth)acrylic resins, ester resins, carbonate resins, olefinic resins, epoxy resins, unsaturated polyester resins, urethane resins, thiourethane resins, polystyrene, copolymers of styrene, polyvinyl chloride, polyethylene terephthalate, diethylene glycol bisallylcarbonate polymers and copolymers of tetrabromobisphenol A dimethacrylate and styrene. The process is advantageously applied to resins containing sulfur and more advantageously to resins containing large amounts of sulfur.
Examples of the resin containing sulfur include resins obtained by curing by polymerization of a compound having one or more structures represented by the following formula (1) in one molecule or a composition comprising this compound.
In the above formula, R
1
represents a hydrocarbon group having 1 to 10 carbon atoms, R
2
, R
3
and
Horikoshi Hiroshi
Niimi Atsuki
Takasuka Masaaki
Takeuchi Motoharu
Yoshimura Yuichi
Antonelli Terry Stout & Kraus LLP
Barr Michael
Mitsubishi Gas Chemical Company Inc.
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