Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Patent
1996-04-11
1997-09-02
Mosley, Terressa
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
528198, C08G 6400
Patent
active
056632797
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. By ophthalmic lenses is meant corrective lenses as well as non-corrective lenses such as sunglasses. Organic glass possesses several favourable characteristics, including a lighter weight and better safety 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 two other problems often occur, i.e. tinting failure and prerelease in the mould.
Tinted ophthalmic lenses, including both corrective and non-corrective lenses (e.g. for sunglasses), are prepared almost exclusively by means of surface impregnation, immersing the ophthalmic lenses in aqueous dispersions of dyes. However, ophthalmic lenses made from poly(allyl carbonates) of polyhydroxy alcohols often show inhomogeneous tinting of the surface in the form of arches. This tinting failure in tinted ophthalmic lenses results in the rejection of a large percentage of the lenses produced because they are not suitable commercial products.
Prerelease or premature release in the mould is a phenomenon whereby the casted ophthalmic lens tends to come loose from the mould's surface during polymerization. Accordingly, failures occur on the surface of the lens and without correction by grinding and/or polishing, the lens cannot be used. In finished lenses made from poly(allyl carbonates) of polyhydroxy alcohols this prerelease is an especially significant problem.
A finished lens is a type of corrective lens for which the final shape is determined by the dimensions of the mould. Accordingly, after removing the lens from the mould it should have the right curvature and power without needing to be processed further. This requires that the product of the polymerization casting of the finished lens meet the end-product specifications since there are no further processing steps to correct defects in the lens. The use of poly(allyl carbonates) of polyhydroxy alcohols to make finished lenses results in the rejection of up to 70% of the finished lenses produced because of the occurrence of prerelease during polymerization casting.
Although we do not wish to be bound by any theory it is thought that prerelease occurs because of the shrinkage common to poly(allyl carbonates) of polyhydroxy alcohols. For example, diethylene glycol diallyl carbonate shrinks 14% during polymerization, Kirk Othmer, Encyclopedia of Chemical Technology, 3rd ed., John Wiley & Sons, 1978, Vol. 2, p. 112. In addition, the shrinkage does not occur uniformly. Accordingly, the prerelease in finished lenses could be the result of shrinkage during polymerization casting. More particularly, because the thickness of the finished lens differs widely from the edge to the centre of the lens, the amount of shrinkage also differs widely and thus prerelease of the finished lens occurs quite frequently. Therefore, the problem of prerelease must be solved.
One method of preventing premature release is by the use of adhesion
REFERENCES:
patent: 4959451 (1990-09-01), Uchida et al.
Abstract Derwent, 1995, J03054213.
Abstract No. 91-299693/41 for, JO 3199-218-A, Dec. 27, 1989.
Encyclopedia of Chemical Technology, Kirk Othmer, Third Edition, vol. 2, John Wiley & Sons, pp. 111-112. No Date.
Kuiper Hans Leonard
Ruisch-Mocking Mieke
van de Graaf Robert Winston
Akzo Nobel nv
Mancini Ralph J.
Morris Louis A.
Mosley Terressa
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