Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Polymerizing – cross-linking – or curing
Reexamination Certificate
1999-09-29
2001-06-19
Berman, Susan W. (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Polymerizing, cross-linking, or curing
C359S241000, C359S242000, C359S244000, C351S159000, C351S16000R, C351S162000, C522S167000, C522S064000, C522S013000, C522S075000, C522S181000, C523S106000, C523S108000
Reexamination Certificate
active
06248285
ABSTRACT:
The present invention relates to the preparation of organic pieces of optical quality and especially to the preparation of organic lenses. More specifically, the main aim of the present invention is an original method of preparing such photochromic or non-photochromic organic pieces by radical polymerisation of a mixture of radically polymerisable monomers.
The aim of the present invention is also:
novel organic pieces of this type, which are preparable by a variant of said method; this variant makes use of particular monomers;
novel radically polymerisable compositions—mixtures of radically polymerisable monomers—which can be used for preparing organic pieces of this type according to the method of the invention.
The present invention is described below with particular reference to the context of the preparation of organic lenses (sight correction glasses, protective glasses). The present invention is in no way limited to said context and the person skilled in the art will easily understand that the claimed method is suitable for obtaining any type of moulded organic pieces, which is without optical defect, such as, therefore, organic lenses, but also windows, optical pieces . . . .
Purely thermal methods of radical polymerisation of mixtures of monomers (mainly acrylic and/or methacrylic and/or alkenyl monomers, especially vinylic monomers) which contain or do not contain an effective amount of at least one photochromic colorant, have been described and carried out, especially by the Applicant, for preparing photochromic or non-photochromic organic lenses, mainly optical or ophthalmic lenses. Said methods are carried out, in a lens mould, on a mixture containing an effective amount of at least one adequate thermal catalyst or radical polymerisation initiator. Said catalyst, when at least one photochromic colorant intervenes, is generally selected from diazo compounds (catalysts known as “soft” which remain “inert” towards the photochromic colorant(s) present). Such methods do not give entire satisfaction insofar as their implementation is long and insofar as, inescapably, during said implementation, oxygen diffuses into within the mixture undergoing polymerisation, this oxygen coming from the surrounding air and entering into the mould via its leaktight joint. This generates defects in the appearance and constraints (optical defects) in the lenses thus produced.
An alternative process for preparing such organic lenses was described in the U.S. patent U.S. Pat. No. 5,621,017. This alternative method is based on photopolymerisation under ultraviolet irradiation of the mixture of monomers containing an effective amount (0.01 to 1 parts by weight, per 100 parts by weight of monomers) of at least one appropriate photoinitiator. Such a method neither gives entire satisfaction insofar as, especially:
it may reveal to be delicate, even impossible to find satisfactory operating conditions (nature of the photoinitiator/irradiation band) in the light of the nature of the monomers present, in the light of the presence of at least one photochromic colorant (which reveals to be a competitor of absorption for the photoinitiator), and in the light of the specifications established for the final lens . . . .
its field of application is limited. It may in fact be suitable for preparing lenses of relatively low thickness (finished lenses of 2 mm thickness (see the Examples U.S. Pat. No. 5,621,017)) but it is not suitable for preparing thicker lenses (for example, semi-finished lenses of greater than 10 mm thickness). In fact, the problem of penetration of the ultraviolet radiation in the material to be polymerised is then come up against. In order to overcome this difficulty, it has been possible to envisage using a photoinitiator which absorbs in the visible. However, in order to guarantee obtaining a suitable result—a complete polymerisation which is homogeneous throughout the whole thickness—, it remains necessary to use a high concentration of photoinitiator and to use a lot of energy. Under such conditions—severe polymerisation conditions—lenses are generally obtained which possess a high degree of yellowing. In any case, in using a low concentration of photoinitiator (which is not susceptible to generate yellowing), it is very difficult to obtain a complete polymerisation throughout the whole of the mass of the material.
In such a context, the Applicant has developed a novel method of preparing organic pieces which enables obtaining said pieces, which are free from optical defects, up to relatively consequent thicknesses and this from various types of mixtures of monomers (even from mixtures which are known to be relatively difficult to polymerise). Said novel method can be qualified as a mixed method insofar as it includes thermal polymerisation and photochemical polymerisation.
Said original method of preparing organic pieces, and especially organic lenses, is described below. Characteristically, it includes a photogelification and it makes use of a low quantity of photoinitiator(s). Said method of the invention in fact comprises, for preparing photochromic or non-photochromic organic pieces by polymerisation of a mixture of radically polymerisable monomers (said mixture containing, classically in fact, the constituents of the piece or lens under preparation: main and secondary constituents of its matrix, of the monomer type, more generally conventional additives, especially such as the thermal catalyst, the photochromic colorant . . . ), the successive steps below:
a) adjusting, by pre-polymerisation, the viscosity of said mixture, to a value between 0.4 and 2 Pa.s;
b) pouring said pre-polymerised mixture into a mould (especially a lens mould for preparing a lens);
c) photogelifying, in said mould, said pre-polymerised mixture until its gel point;
d) completing the polymerisation of said pre-polymerised and gelified mixture in said mould, by heat treatment;
the steps referred to as pre-polymerisation (a), photogelification (c) and polymerisation (d) being implemented out by the intervention, into said mixture of monomers, of effective amounts of at least one thermal catalyst and of at least one photoinitiator; said photoinitiator(s) intervening in an amount less than or equal to 0.009 parts by weight per 100 parts by weight of said mixture of monomers.
According to the method of the invention, the mixture containing the constituent elements of the piece under preparation is firstly pre-polymerised before it is poured into the mould. The implementation of such a pre-polymerisation out of the mould is very advantageous insofar as:
it enables neutralising the inhibitors present in said mixture (such polymerisation inhibitors are inescapably present in commercial products);
it enables increasing and adjusting the viscosity of the mixture to be poured afterwards in the mould. In said mould, the polymerisation thus implemented on a pre-polymerised and therefore viscous mixture is done so under the best circumstances since, within such a viscous mixture, the oxygen diffuses more slowly, the performances of the intervening photoinitiator are improved, the retraction is reduced, and the gel point is attained faster;
it can be carried out in a perfectly leaktight recipient, i.e. in the absence of oxygen and, therefore, without a constraint as to its duration.
It is highly recommended to implement said pre-polymerisation in order to bring the viscosity of the mixture to a value between 0.4 and 2 Pa.s. Below 0.4, the beneficial effects of said pre-polymerisation hardly manifest themselves (especially in the light of the problem of the diffusion of oxygen); above 2, problems of manipulation of the pre-polymerised mixture are come up against, and the gel point is come too close to.
The pre-polymerisation according to the invention is generally a thermal or photochemical pre-polymerisation which, for its implementation, necessitates the presence, in the mixture to be pre-polymerised, of an effective amount of at least one thermal catalyst and at least one photoinitiator, respectively.
At least one
Henry David
Vachet Andre
Berman Susan W.
Corning S.A.
Nwaneri Angela N.
Rogalskyj Peter
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