Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2000-09-12
2003-04-22
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S500000, C428S522000, C428S523000, C522S049000, C522S051000
Reexamination Certificate
active
06551710
ABSTRACT:
The present invention relates to the manufacture of plastic optical articles such as video discs and ophthalmic lenses, and in particular coatings for such lenses.
The most widely used plastic ophthalmic lens material is polymerised diethylene glycol bis (allyl carbonate) (e.g. CR-39). This polymer has proved a satisfactory material for the manufacture of ophthalmic tenses because of a combination of features, including excellent transmission, resistance to discolouration, high strength and high impact resistance. The material has only a reasonable abrasion resistance.
Such lenses can be made to be hard and abrasion resistant by the use of abrasion resistant coatings; however, their impact resistance can be greatly reduced by these hard, abrasion resistant coatings, especially in combination with a brittle vacuum deposited anti-reflection coating. Thin lenses, with a center thickness of about 1.0 mm, are highly desired for cosmetic and weight considerations. However, the thickness of a lens is related to the impact properties of the lens. Specifically, thinner lenses have a lower impact resistance.
Coatings have been used in the prior art mainly to promote adhesion or provide a physical barrier as protection against chemicals, dirt, oxidation, etc. It is known in the prior art, in ophthalmic applications, to utilise coats (via back-surface coating) to enhance the fracture resistance of lenses which are coated with thin layers of glasslike anti-reflection (AR) coatings. However, the coatings commercially available in the prior art are based on (blocked) polyurethane chemistry, and the curing involves a lengthy period where the material is tacky, leading to contamination by airborne particles and yield loss.
Further whilst it is known in the prior art that dyes, including photochromic dyes, may be directly introduced into low index refractive lens materials and certain medium to high refractive index material directly by way of imbibition, this is not possible with polycarbonates such as CR-39 and other high index materials.
Accordingly, for such materials it is necessary to apply a coating material to a surface of the lens which material is capable of receiving a dye material. However, such a technique presents optical problems, e.g. in matching refractive indices and physical problems in that the coating, when applied, is in a tacky, gel-like state and may take 1 hour or more to cure to a dry state.
During this tacky step, the coating is susceptible to dust, other airborne contaminants and yield loss.
Lenses formed from polymers including divinyl benzene and discussed in the prior art are generally brittle and have a high yellowness index.
Japanese Patent Application 63-309509 to Showa Denko KK discloses the formation of a prepolymer of divinyl benzene and a polythiol compound which may be used in the formation of optical materials with high refractive indexes.
Japanese Patent Application 63-19498 to Mitsubishi Gas discloses a high refractive index composition of divinyl benzene and a thiol compound. However optical lenses produced thereby exhibit unacceptable strain characteristics and cure times.
However, there remains a need in the prior art for optical articles having high refractive indexes, having improved impact resistance, and preferably improved abrasion resistance. There further remains a need for optical articles of medium to high refractive index which permit introduction of dyes.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties related to the prior art.
Accordingly, in a first aspect the present invention provides a cross-linkable primer coating composition which is UV curable, exhibits a very short cure time, and includes an effective amount of
a di-or polythiol compound.
Preferably, the cross-linkable primer coating composition further includes an effective amount of
an allyl or vinyl monomer; and optionally
a polymerisable comonomer.
The primer coating composition may be UV-curable. The primer coating composition may be UV-curable in air. This provides a highly pure product, substantially free of by-products, and improved process control. Further, the primer coating composition is receptive to the inclusion of dyes, including photochromic dyes. The dyes may be included directly in the composition or may be introduced into a coating formed from the composition, e.g. by imbibition.
It will be understood that this is a significant improvement over the prior art. With acrylic resins, the inclusion of a photochromic material would render a UV cure extremely difficult, if not impossible, as the dye is competing with the monomer acrylate. This is particularly so in an air environment where the air would normally further exhibit UV cure.
Whilst we do not wish to be restricted by theory, it is postulated that the high purity relates to the fact that there is no or substantially no homopolymerisation of the allylic or vinyl monomer under UV reaction conditions. This may be contrasted with prior art coatings in which acrylic monomers are a major component.
It will be further understood that as the coating composition according to the present invention may be subjected to a UV cure having a very short cure time, a hard, non-tacky coat is formed virtually immediately, so the possibility of contamination or yield loss may be substantially reduced or eliminated.
In a preferred aspect of the present invention there is provided a coated optical article including
an optical article; and
a primer coating on at least a surface of the optical article, the primer coating being formed from a primer coating composition which is
UV curable,
exhibits a very short cure time; and
includes an effective amount of a di- or polythio compound.
Preferably, the primer coating composition further includes an effective amount of
an allyl or vinyl monomer; and optionally
a polymerisable comonomer.
An optical article coated with the primer coating composition of the present invention may be optically clear and substantially aberration free. The primer coating may provide improved impact resistance to the optical article and may provide improved adhesion for other coatings including abrasion resistant coatings.
The thickness of the primer coating may be varied to adjust adhesion and/or impact strength of the final product. Thickness may vary from approximately 0.01 &mgr;m to 100 &mgr;m, preferably approximately 0.1 &mgr;m to 50 &mgr;m.
As discussed below, the primer coating may, in one preferred embodiment, incorporate a dye material, e.g. a photochromic material. Where the primer coating includes a photochromic material, the thickness of the primer coating is preferably at the upper end of the above ranges. For medium to high refractive index optical articles such as CR39 lens, the primer coating thus functions to permit introduction of a dye either directly in the primer coating composition or indirectly, e.g. by imbibition into the primer coating so formed.
For example, preferably when the primer coating includes a dye component the coating has a thickness of approximately 10 to 75 micron
In contrast, preferably when the primer coating does not include a dye component, the primer coating has a thickness of approximately 0.1 to 5 micron. In this form, the primer coating functions principally to provide an improvement in impact resistance and optionally improved adhesion.
The coating formed from the primer coating composition may exhibit a high refractive index and a low glass transition temperature (Tg), preferably below approximately 60° C. The refractive index may be tailored to that of the optical substrate. The refractive index may be varied for example between approximately 1.50 to approximately 1.65.
By the term “high refractive index”, as used herein, we mean a polymer having a refractive index of at least approximately 1.55, preferably 1.57. By the term “very high refractive index” as used herein, we mean a polymer having a refractive index of approximately 1.59 or above, preferably 1.60 or above.
As stated above, the
Chen Fang
Cuthbertson Matthew John
Fisher Mark Christopher
Toh Huan Kiak
Burns Doane , Swecker, Mathis LLP
Sola International Holdings Ltd.
Tarazano D. Lawrence
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