Terpolymer With a High Refractive Index

1. Field of the Invention

This invention relates to a terpolymer with a high refractive index and the plastic lenses made of the terpolymer.

2. Description of the Prior Art

Recently lenses of organic glass have been widely used instead of lenses of inorganic glass, because organic glass is superior to inorganic glass in its lightness, safety due to its high impact resistance, workability, dyeability, etc. For example, lenses made of diethylene glycol bisallyl carbonate (hereinafter referred to CR39) have already been used widely. But, lenses of CR39 have such a disadvantage that the lenses must be thicker than those of inorganic glass, because of their relatively low refractive index such as 1.499. There is known a method for overcoming the disadvantage comprising copolymerizing CR39 with benzyl methacrylate so as to increase the refractive index. However, lenses obtained by the copolymerization are inferior to lenses of CR39 in their superficial hardness, so that the lenses must be more carefully handled.

We have now found that copolymerization of ternary monomers consisting of CR39, benzyl methacrylate, and triallylisocyanurate enables to produce lens with a high refractive index and a high superficial hardness.

An object of this invention is to provide a plastic lens with a high refractive index and a high superficial hardness.

This invention relates to a terpolymer produced by the polymerization of ternary monomers comprising diethylene glycol bisallyl carbonate, triallylisocyanurate and benzyl methacrylate.

In this invention, CR39 is preferably used in the range of 40 wt.% to 80 wt.%. Benzyl methacrylate is preferably used in the range of 10 wt.% to 30 wt.%. Triallylisocyanurate is preferably used in the range of 10 wt.% to 30 wt.%. And, it is preferable that the amount of benzylmethacrylate is not larger than that of triallylisocyanurate. The more the amount of benzylmethacrylate than that of triallylisocyanurate, the lower the transparency of the lens produced therefrom. On the contrary, when the amount of triallylisocyanurate is extremely larger than that of benzyl methacrylate, the lens thereof is liable to be easily cracked.

The lens of this invention can be prepared by pouring the mixed solution consisting of CR39, benzyl methacrylate, triallylisocyanurate, and initiator into a mold made of two plates of glass mold and a plastic gasket, and then curing the resulting one by means of heating it or irradiating it with ultraviolet ray.

The high refractive lens of this invention is more improved than the lens obtained by copolymerizing CR39 with a methacrylate such as benzyl methacrylate in its superficial hardness, transmittance, and adhesion of coating material. Namely, the lens of this invention is the one whose refractive index and superficial hardness are increased with keeping the same excellent physical properties as are inherent in the lens of CR39. Such remarkable effect seems to have never been performed in the copolymer of binary monomers.

This invention will be more clearly understood with reference to the following Examples.

A mixed solution consisting of 60 wt. parts of CR39, 20 wt. parts of benzylmethacrylate, 20 wt. parts of triallylisocyanurate, and 5 wt. parts of diisopropylperoxydicarbonate was poured into a mold made of two plates of glass mold and a plastic gasket. The one was heated to elevate the temperature from 40.degree. C. to 90.degree. C. in 24 hours. After curing, the lens was taken out of the mold, and heat-treated at 120.degree. C. for one hour. The lens obtained possessed 1.523 of refractive index, 92% of transmittance (550 nm), 3H of pencil hardness, and an impact resistance which passed inspection of FDA Standard. Adhesion of a glass film coated on the lens surface by vacuum evaporation method stood the cross cut test and alkali-resisting test.

In example 2 and 3, and comparative example 1-5, lenses were prepared in the same manner as in Example 1, except that the monomer composition in Table 1 were used. Table 1 shows the result.