Plastic lenses for spectacles

Details Plastic lenses for spectacles Plastic lenses for spectacles

2001-03-15

2004-06-01

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C428S425500, C351S159000

Reexamination Certificate

active

06743886

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to plastic lenses for spectacles, in particular to those having a high refractive index and a high Abbe's number and having good transparency, heat resistance, mechanical strength and impact resistance.
Plastics are being much used these days for optical products such as lenses, as being lightweight, hardly broken and easily colored when compared with glass. It is known to use, as the monomer material, an epithio group-having compound in producing plastic lenses. For example, Japanese Patent Laid-Open No. 180977/1999 discloses a plastic lens having optical properties, a refractive index of 1.70 or so and an Abbe's number of from 35 to 37 or so, which, however, still leaves room for improving its heat resistance and mechanical strength.
Japanese. Patent Laid-Open Nos. 292950/1999 and 352302/1999 disclose a resin composition prepared by reacting an epithio group-having compound, an isocyanate group-having compound and a thiol group-having compound in a ratio of thiol group/isocyanate group of at most 1, and its use for plastic lenses. They say that the resin composition has improved heat resistance, mechanical strength and impact resistance. However, the plastic lenses of the resin composition are often cloudy and could not be well cured, and are therefore unsuitable to practical use for spectacles.
The present invention has been made so as to solve the problems as above, and to provide plastic lenses for spectacles having a high refractive index and a high Abbe's number and having good transparency, heat resistance, mechanical strength and impact resistance.
SUMMARY OF THE INVENTION
The present Inventors have found that (1) a plastic lens produced through polymerization of an epithio group-having compound (a), a mercapto (—SH) group-having polythiol compound (b) and an isocyanate (—NCO) group-having, sulfur-free polyisocyanate compound (c
0
) in a ratio (by mol), —SH/—NCO, of at least 2.0; (2) a plastic lens produced through polymerization of an epithio group-having compound (a), a mercapto group-having polythiol compound (b) and an isocyanate group-having, sulfur-containing polyisocyanate compound (c
s
) in a ratio (by mol), —SH/—NCO, of at least 1.2 can attain the desired balance of properties.
DETAILED DESCRIPTION OF THE INVENTION
Specifically, the first aspect of the invention is to provide a plastic lens for spectacles, which is produced through polymerization of an epithio group-having compound, a polythiol compound and a sulfur-free polyisocyanate compound in a ratio (by mol) of the polythiol compound to the sulfur-free polyisocyanate compound, —SH/—NCO, of at least 2.0.
The second aspect of the Invention is to provide a plastic lens for spectacles, which is produced through polymerization of an epithio group-having compound, a polythiol compound and a sulfur-containing polyisocyanate compound in a ratio, (by mol) of the polythiol compound to the sulfur-containing polyisocyanate compound, —SH/—NCO, of at least 1.2.
The polyisocyanate compound (c) may be a mixture of a sulfur-containing polyisocyanate compound (c
s
) and a sulfur-free polyisocyanate compound (c
0
). The plastic lens material may be produced through polymerization of at least one polyisocyanate compound selected from di(isocyanatomethyl)bicycloheptane, bis(isocyanatomethyl)-1,4-dithian and dicyclohexylmethane diisocyanate, and an, epithio group-having compound and a polythiol compound. The plastic lens material may also be produced through polymerization of a polyisocyanate compound prepared by mixing bis(isocyanatomethyl)-1,4-dithian with di(isocyanatomethyl)bicycloheptane and/or dicyclohexylmethane diisocyanate, and an epithio group-having compound and a polythiol compound.
In its first aspect, the plastic lens for spectacles of the invention is produced through polymerization of an epithio group-having compound, a polythiol compound and a sulfur-free polyisocyanate compound in a ratio (by mol) of the polythiol compound to the sulfur-free polyisocyanate compound, —SH/—NCO, of at least 2,0. If the ratio —SH/—NCO is smaller than 2.0, the effect of the first aspect of the invention cannot be obtained.
In its second aspect, the plastic lens for spectacles of the invention is produced through polymerization of an epithio group-having compound, a polythiol compound and a sulfur-containing polyisocyanate compound in a ratio (by mol) of the polythiol compound to the sulfur-containing polyisocyanate compound, —SH/—NCO, of at least 1.2. If the ratio —SH/—NCO is smaller than 1.2, the effect of the invention cannot be obtained. Polyisothiocyanate group-having compounds are outside the scope of the sulfur-containing polyisocyanate compound, as not producing then advantages of the invention.
With the increase in the proportion of thiourethane bonds therein, lenses for spectacles could have an increased tensile strength characteristic of polythiourethanes, but their refractive index could not increase. For further increasing the refractive index of the lenses while producing lenses having an increased tensile strength and an increased Abbe's number, heretofore proposed is adding an epithio group-having compound to the lenses. However, in the system for lenses that comprises an epithio group-having compound, a polythiol compound and a sulfur-free polyisocyanate compound, if the polyisocyanate is excessive over the polythiol, as in the Examples in Japanese Patent Laid-Open Nos. 180977/1999 and 292950/1999, the lenses formed are cloudy.
On the other hand, lenses formed from a sulfur-containing polyisocyanate compound, an epithio group-having compound and a polythiol compounds are not cloudy even when the proportion of the sulfur-containing polyisocyanate compound therein is increased. Since the sulfur content and the thiourethane bond content thereof are high, the lenses have an increased refractive index and their mechanical strength and Abbe's number are not lowered.
Some sulfur-containing polyisocyanate compounds such as bis(isocyanatomethyl)-1,4-dithian are solid at room temperature. Such a solid, sulfur-containing polyisocyanate compound may be dissolved in a sulfur-free polyisocyanate compound that is liquid at room temperature. As being liquid at room temperature, the resulting mixture is easy to handle when it is used in producing lenses. In mixing the two, the ratio of the sulfur-containing polyisocyanate compound to the sulfur-free polyisocyanate compound may be so controlled that the liquid, sulfur-free polyisocyanate compound can dissolve the solid, sulfur-containing polyisocyanate compound to give a mixture that is liquid at room temperature. In practice, the ratio of the sulfur-containing polyisocyanate compound and the sulfur-free polyisocyanate compound may be such that the amount of the sulfur-free polyisocyanate compound is enough for dissolving therein the sulfur-containing polyisocyanate compound which is solid at room temperature. The ratio of the two can be readily determined to produce lenses having the desired balance of properties. For example, from 5 to 30 parts by weight of a sulfur-free polyisocyanate may be added to 10 parts by weight of a sulfur-containing polyisocyanate.
A sulfur-free polyisocyanate compound that can be used in the first and second aspects of the invention is di(isocyanatomethyl)bicycloheptane and/or dicyclohexylmethane diisocyanate. A sulfur-containing polyisocyanate compound that can be used is bis(isocyanatomethyl)-1,4-dithian.
The lens for spectacles may be produced through polymerization of at least one polyisocyanate compound selected from di(isocyanatomethyl)bicycloheptane, bis(isocyanatomethyl)-1,4-dithian and dicyclohexylmethane diisocyanate, and an epithio group-having compound and a polythiol compound. The lens for spectacles may also be produced through polymerization of a polyisocyanate compound prepared by mixing bis(isocyanatomethyl)-1,4-dithian with di(isocyanatomethyl)bicycloheptane and/or dicyclohexylmethane diisocyanate, and an epithio group-having compound and a polythiol

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