Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-01-11
2004-05-25
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S105000, C523S106000, C524S280000, C524S282000, C524S283000, C524S287000, C524S365000, C524S380000, C524S755000, C524S765000, C524S774000
Reexamination Certificate
active
06740699
ABSTRACT:
BACKGROUND OF THE INVENTION
The present application claims priority to French Application No. 01/00343 filed Jan. 11, 2001, the entire text of which is specifically incorporated by reference herein without disclaimer.
1. Field of the Invention
The invention in general concerns a method for obtaining a photochromic latex whose properties, in particular photochromic, remain stable over time, the thus stabilized photochromic latexes and their use in ophthalmic optics.
2. Description of Related Art
The preparation of photochromic latexes by polymerization of acrylic or methacrylic monomers comprising one or more photochromic compounds in aqueous emulsion is already known.
These photochromic latexes are conventionally obtained by preparing a first solution comprising the monomer(s), the photochromic compound(s) and a second solution comprising the dispersion medium, generally water and a surface-active agent, and mixing the two solutions with vigorous stirring to obtain a pre-emulsion. The pre-emulsion is then transferred in a single step into a reactor and degassed under nitrogen with stirring. After the degassing, a polymerization initiator, generally in solution in a solvent (typically water), is added and the polymerization is performed by heating to give the latex.
The latex obtained is then coarsely filtered through fabric and stored in the absence of light.
Such a method for obtaining a latex with photochromic properties is disclosed in the document FR 2.790.264.
The French patent application N° 00 14903 filed on Nov. 17, 2000 discloses the use of mini-emulsions for preparing photochromic latexes.
More particularly, according to this method, the preparation of a photochromic latex comprises preparing a mixture comprising at least one monomer with a C═C group polymerizable by free-radical mechanism, at least one organic photochromic compound, at least one surface-active agent, water and optionally a polymerization initiator, treating the mixture obtained to form a mini-emulsion comprising an organic phase dispersed in the form of droplets with a diameter of 50 to 500 nm, preferably 50 to 300 nm, in an aqueous phase, adding a polymerization initiator to the mini-emulsion, if this has not already been introduced, or an additional quantity of initiator compared to the quantity initially introduced, polymerizing the reaction mixture obtained and recovering the photochromic latex.
The initial mixture is preferably obtained by separately preparing a first solution comprising the monomer(s), the photochromic compound(s) and optionally the stabilization agent(s) and a second solution comprising water and the surface-active agent(s), then combining the two solutions.
The mini-emulsion is obtained for example by emulsification by means of a micro-fluidizer such as the micro-fluidizer disclosed in the U.S. Pat. No. 4,533,254.
The use of mini-emulsions for emulsion polymerization is also disclosed in the documents FR 2.785.904, EP 852.239, U.S. Pat. No. 5,569,716. U.S. Pat. No. 5,653,965 and WO 98/50436.
The latexes obtained by conventional methods and the method of polymerization in mini-emulsion, although giving satisfactory results when deposited and dried soon after their preparation, nevertheless have the disadvantage of losing a significant amount of their photochromic properties over time.
More exactly, analyses by high-pressure liquid-phase chromatography (HPLC) of photochromic latexes, whatever their method of preparation, conventional or by mini-emulsion, have shown a decrease in concentration of the photochromic compounds within the liquid latex as a function of time. This degradation is generally very rapid and can lead to a 50% decrease in photochromic compounds in the liquid latex in one month.
The problem of stabilizing photochromic compounds present in thin films of resins has already been tackled in the prior art, but mainly as regards stabilization against external degradations such as light, and in particular UV radiation.
Thus, the patent U.S. Pat. No. 5,914,174 discloses photochromic resins containing additives such as antioxidants, radical-trapping agents and UV absorbers. In particular, it is stated in this patent that the use of hindered amines and agents which remove species in the excited state improves performances against bad weather.
In the case of latexes, the technical problem is that of the degradation of photochromic compounds within liquid latexes, in other words before their application as a film, and even in the absence of any external factor likely to modify or degrade the properties of the photochromic compounds.
It is particularly significant to note that the degradation of photochromic latexes occurs even when they are stored in closed containers, in the absence of ambient air or light. This is thus a problem completely specific to latexes.
SUMMARY OF THE INVENTION
The object of the invention is thus a method for obtaining a photochromic latex whose properties, in particular photochromic, remain stable over time, in particular when the latex is stored in the absence of ambient air and of light.
A further object of the invention is a stabilized photochromic latex, whose photochromic properties remain stable over time, in particular when the latex is stored in the absence of ambient air and of light.
An additional object of the invention is substrates, in particular optical articles such as ophthalmic lenses, coated with dried films of the latexes such as those defined above.
The above objectives are achieved according to the invention by a method for obtaining photochromic latexes comprising a polymerization in aqueous emulsion of an initial polymerizable mixture comprising one or more organic monomers containing C═C groups which are polymerizable by free-radical mechanism and one or more photochromic compounds until a final latex is obtained, characterized in that it comprises the addition to the initial polymerizable mixture, during the polymerization of the initial polymerizable mixture or to the final latex of an effective quantity of at least one stabilization agent selected from compounds of cyclopentene, cyclohexene, cycloheptene, cyclooctene and compounds containing an ethylenic unsaturation not forming part of an aromatic ring and which contain, in the &agr; position with respect to the ethylenic unsaturation, a carbon atom bearing a free hydroxy group.
The stabilization agent is preferably introduced into the initial polymerizable mixture.
In the present application, final latex should be understood to mean a latex whose concentration in the dry extract does not change over time. The final latex is generally obtained after about 1 hour of reaction.
The invention also concerns a stabilized photochromic latex comprising a dispersion in an aqueous phase of polymer particles resulting from the polymerization in aqueous phase of a mixture of one or more organic monomers containing C═C groups which are polymerizable by free-radical mechanism and one or more photochromic compounds and an effective quantity of at least one stabilization agent selected from compounds of cyclopentene, cyclohexene, cycloheptene, cyclooctene and compounds containing an ethylenic unsaturation not forming part of an aromatic ring and which contain, in the &agr; position with respect to the ethylenic unsaturation, a carbon atom bearing a free hydroxy group.
The agents for stabilizing the photochromic properties according to the invention are compounds known as anti-yellowing agents in formulations based on bisphenol A dimethacrylates or bisphenol A diallyl carbonate. These agents are disclosed, amongst others, in U.S. Pat. No. 5,702,825 and EP 224.123.
More particularly, these stabilization agents are compounds of cyclopentene, cyclohexene, cycloheptene, cyclooctene and compounds containing an ethylenic unsaturation not forming part of an aromatic ring and which contain, in the &agr; position with respect to the ethylenic unsaturation, a carbon atom bearing a free hydroxy group.
The preferred stabilization agents are the derivatives of cyclohexene.
A wide
Cano Jean-Paul
Maisonnier Sylvette
Robert Anne
Tardieu Pascale
Essilor International (Compagnie Generale d'Optique)
Fulbright & Jaworski L.L.P.
Sanders Kriellion A.
LandOfFree
Method for obtaining a stabilized photochromic latex, latex... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for obtaining a stabilized photochromic latex, latex..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for obtaining a stabilized photochromic latex, latex... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3194267