Ophthalmic lenses

Details Ophthalmic lenses Ophthalmic lenses

2001-01-26

2004-01-06

Vargot, Mathieu D. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Optical article shaping or treating

C351S159000

Reexamination Certificate

active

06673276

ABSTRACT:

The present invention relates to a process for providing molded plastic articles, in particular ophthalmic lenses, plastic articles and ophthalmic lenses themselves, and the use of metal organic compounds in such processes.
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 increased mould damage occurs. Understood by mould damage is the damage incurred in a lens or in a mould on opening of the mould wherein the lens is formed.
Another known problem of such lenses is the occurrence of a surface defect of the casted organic glass that is known as “ferns”. The defects are called this way because they always appear in the shape of a fern leaf. The exact nature of these ferns and how they are being formed is unknown, but since the size of such ferns can vary from 0.5 to 30 cm
2
, they pose a real problem. It is possible to remove said ferns from the surface by polishing, however, such a process is undesired.
A further known problem is the uneven tinting of casted lenses with a colouring agent by means of a process of imbibing the lens, such processes being well-known in the art. The fact that the lens is coloured unevenly, may be associated with surface defects as well. A process wherein lenses are coloured more evenly is desired.
The Japanese patents JP 238151 and JP 09241336 teach the use of phosphorous compounds (phosphorous being a group 15 element according to the new IUPAC notation, with an electronegativity of about 2.1) as mould release agents. Common release agent present a number of problems when applied in the manufacturing of optical articles such as ophthalmic lenses. They regularly require high amounts to be effective and thereby negatively effect the mechanical and optical performance of the casted material. Furthermore they negatively affect the surface tension of the polymer, making the application of a coating (anti-scratch or other coating) and evenly tinting very difficult and its performance unreliable.
WO 96/24865 from the applicant teaches the use of diallyl phthalate type oligomers in curing compositions for ophthalmic lenses whereby mould damage in the production of said lenses is reduced.
Moulds used in today's industry to prepare ophthalmic lenses from poly(allyl carbonate) of a polyhydroxy alcohol are only suited for compositions which result in ophthalmic lenses with identical refractive indices. A change in refractive index will result in a change in power of the lens when utilizing these moulds. Compositions resulting in higher refractive index lenses will require different moulds to obtain ophthalmic lenses with the same power. So, improvement of the properties of lenses by introducing certain oligomers and, optionally, comonomers cannot be achieved without limiting the refractive index of the resulting lens so that the moulds do not have to be changed.
An object of the present invention is to provide a process for providing moulded plastic articles whereby the mould damage, the occurring of ferns (ferning) and other tinting failures are being reduced.
The present invention relates to a process for providing a moulded plastic article comprising the step of polymerization casting of a curable composition comprising one or more polymerizable molecules or compounds which are preferably radically polymerizable and are preferably monomers, co-monomers and/or oligomers, for example poly(allyl carbonates) of polyhydroxy alcohols and methacrylic, acrylic, vinylic or allylic comonomers, in the presence of a mould release agent, which in turn comprises a metal organic compound, complexes and/or salts thereof, with the proviso that the metal of the metal organic compound is not Si or P. It is understood that the term metal as used here also includes transition elements. Furthermore it is noted that the term “radical polymerizable monomers” does not comprise conventional monomers that lead to urethane formation. Preferably, the invention relates to the process in which essentially all monomers are radically polymerizable. More preferably, the process involves the polymerization of a composition which consists essentially of radically polymerizable monomer(s), initiator(s), tinting agent(s), and the metal organic compound.
The mould damage, and ferns or other tinting failures in the production of the ophthalmic lens according to the present invention by using the claimed metal organic compounds is reduced without adversely affecting mechanical and/or optical properties of the optical articles, such as hardness and refractive index. Furthermore these metal organic release agents do not substantially negatively effect the surface tension of the polymer and monomer, and hence do not substantially negatively effect the adhesion of (anti-scratch) coatings onto the polymer surface. Preferred metal organic compounds are selected from organometallic compounds, complexes of metals, metal salts, and metal soaps. Most preferred are organometallic compounds wherein the metal is covalently bonded. The valency of the metal will typically vary from 1-6, a valency of 2-6 being preferred. Preferred metal organic compounds are of the formulae 1-111
wherein M is the metal as defined, X=O or S, and R
1
-R
8
are independently selected from the group consisting of hydrogen, halogen, hydrocarbyl, halogen substituted hydrocarbyl, and
wherein R
9
is C
2
-C
22
hydrocarbyl, preferably C
4-12
hydrocarbyl, and X has the meaning as defined above,
whereby R
1
-R
8
are optionally connected to form a ring structure.
Preferred compounds have a structure wherein R
1
-R
8
are independently selected from essentially hydrogen, halogen, octoate, laurate, butyl, hexanoate, and decanoate. More preferred compounds are dibutyl metal dilaurates, dibutyl metal oxides, and metal 2-ethylhexanoates (octoates).
Without wishing to be bound to such theory, it appears that the electronegativity of the metal is an important factor for selecting metal organic compounds that are useful in the process according to the invention. Using the table of electronegativity of elements as calculated according to Allred & Rochow and as published in the textbook by Cotton & Wilkinson in
Basic Inorganic Chemistry
, ISBN# 0471-50532 3, Table 2-3, as a reference, the preferred metal of the metal organic compound has an electronegativy from 1.5 to 1.75. More preferred metals have an electronegativity, as calculated by Allred & Rochow's method, of 1.6 to 1.73. Most preferred metals are Zn, Sn, and Co.
If used to produce ophthalmic lenses, the metal organic release agents must be completely soluble in the monomer to prevent the reduction of transmission of the lens.
The inventors have noted that the claimed metal organic compounds express release agent activity even at very low concentration, and are suitable as both internal, i.e. pr

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