Ophthalmic lenses

Details Ophthalmic lenses Ophthalmic lenses

1997-09-22

1999-11-30

Sugarman, Scott J.

Optics: eye examining, vision testing and correcting

Spectacles and eyeglasses

Ophthalmic lenses or blanks

351177, G02C 702

Patent

active

059929979

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to ophthalmic lenses, a process for the production of ophthalmic lenses, and the use of diallyl phthalate type oligomers in ophthalmic lenses.
Recently, organic glass has begun to replace inorganic glass in optical elements, such as windows, prisms, cameras, television screens, telescopes, and ophthalmic lenses. The term ophthalmic lenses refers to corrective lenses as well as non-corrective lenses such as sunglasses. Organic glass possesses several favourable characteristics, including a lighter weight and better safety, e.g., better impact resistance, than inorganic glass.
Conventional materials used in organic glass include polystyrene resin, polymethyl methacrylate resin, and polycarbonate resin. However, these polymers have their respective disadvantages. For example, polymethyl methacrylate resin is liable to high moisture absorption which changes its shape and refractive index. Also, polystyrene resin and polycarbonate resin have the disadvantage of giving rise to birefringence, light scattering, and loss of transparency with time. Furthermore, polymethyl methacrylate and polystyrene are neither scratch nor solvent resistant.
Organic glass made up of the products of the radical polymerization of poly(allyl carbonates) of polyhydroxy alcohols is also known, for example from European patent application 0 473 163. These polymers do not have the above-mentioned problems. However, when applying poly(allyl carbonates) of polyhydroxy alcohols in ophthalmic lenses another problem occurs, i.e. mould damage.
Ophthalmic lenses are made by polymerising a monomer between two glass moulds. Glass is the preferred material because the moulds have to be cleaned after casting, and such cleaning is usually carried out with strong lye or strong acid, which glass, unlike metal, is well able to withstand. Also, glass can easily be ground and polished to a very low degree of surface roughness.
The polymerisation process is attended with shrinkage. However, the cast lens has to be a perfect casting of the curve of the glass surface. This requires good adhesion of the monomer Lo the glass mould during polymerisation.
After polymerisation of the monomer the lens has to be released from the glass moulds. In practice, this procedure is as follows: the moulds are prized apart with a wedge. A great deal of energy is released in this process, occasionally even causing a bang.
Such forceful demoulding regularly results in damage to the glass mould. A fragment of glass will be pulled out, rendering the glass mould unfit for use. This is a randomly occurring phenomenon in lens production. Ordinarily speaking, it affects several per cent of the production.
Such damage to the moulds constitutes a major cost item for the manufacturer. While simple moulds (e.g., for single vision lenses) are rather cheap, moulds for semi-finished lenses (e.g., for bifocal lenses or progressive lenses) are very expensive.
In practice, the manufacturer of lenses will optimize the process towards zero mould damage. If there is too much spoilage, one option is to add a little amount of a release agent. However, this may affect other lens properties such, as the adhesion of the anti-scratch coating film subsequently applied. Release agents thus constitute a poor solution to the problem.
Accordingly, it is the object of the present invention to provide an ophthalmic lens which can be produced with a minimum of mould damage. It is also an object of the present invention to minimize the changes in properties as compared with lenses made from poly(allyl carbonate) of a polyhydroxy alcohol, such as barcol hardness and yellowness index. Another object is to provide an ophthalmic lens onto which an anti-scratch coating may be applied without adhesion problems. These and other objects of the present invention will be explained in the description of the invention which follows.
The present invention relates to an ophthalmic lens with a refractive index of between 1.498 and 1.505, comprising the cured product of a composition comprising:

REFERENCES:
patent: 4959451 (1990-09-01), Uchida et al.
patent: 5196492 (1993-03-01), Renzi et al.
patent: 5218067 (1993-06-01), Uchida et al.
patent: 5663279 (1997-09-01), Kuiper et al.
patent: 5694195 (1997-12-01), Engardio et al.
Kirk-Othner Encyclopedia of Chemical Technology, Third Edition, vol. 2, Alkoxides, Metal to Antibiotics (Peptides), A Wiley-Interscience Publication, John Wiley & Sons, p. 111.
Chemical Abstract, JO 3199-218-A.
Chemical Abstract, JO 3054-213-A.
Chemical Abstract, JO 1244-401-A.

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