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
2001-06-15
2003-09-23
Dawson, Robert (Department: 1712)
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...
C528S012000, C528S491000, C528S494000, C528S501000, C549S215000
Reexamination Certificate
active
06624237
ABSTRACT:
This invention relates generally to a method for preparing a hydrolysate of organoalkoxysilanes, in particular a hydrolysate in which the hydrophobic organic and low polar molecules exhibit excellent solubility, as well as the use of this organoalkoxysilane hydrolysate for obtaining transparent films or substrates, including or not organic molecules and/or inorganic particles, and the applications of these substrates and films in the field of optics, in particular ophthalmic optics.
Below in this request, the organoalkoxysilane hydrolysate will be called organo-silicon sol.
Generally, preparing organo-silicon sols is difficult.
The final properties of the sol and consequently of the derived substrates and/or transparent films depend to a large extent on the sol preparation method, even if the final sol drying/condensation step for obtaining the substrate and/or the film also plays a significant role.
Such sols should exhibit stability properties, i.e. after its preparation, the essential characteristics of the sol (condensation rate, proportion of the various hydrolysed and/or precondensed species, viscosity) do not change or very little with time.
Besides, in the optical field, it has also be sought to obtain organo-silicon sols capable of solubilising low polar, hydrophobic organic additives, in particular for obtaining films of a few microns in thickness.
This latter property of the sol must be preserved during the drying step, i.e. when eliminating solubilisation solvents and during final condensation of the species derived from hydrolysis, so that the additive does not precipitate during this step.
Among organic additives that are particularly interesting in the optical field, photochromic compounds can be mentioned.
The document FR-A-2 704 851 describes a method for preparing an organo-silicon sol in which the following operations are conducted: complete hydrolysis of a solution containing one or several organo-alkoxysilanes in an organic solvent or mixtures of organic solvents using an acid aqueous solution with a pH equal to or smaller than 3, elimination of the organic solvent(s) and of the residual alcohols and concentration of the solution by distillation for obtaining a sol.
However, the method of the patent FR-A-2 704 851 leads to sols certain properties of which strongly vary with time, in particular the condensation rate and the composition of the species present in the sol.
Moreover, it is difficult to solubilise in the sols of patent FR-A-2 704 851 low polar, hydrophobic organic additives and in particular photochromic compounds.
The article entitled “Organosiloxane Resin with High Silanol Content” Furuya et al.—Silicones in Coatings II—A Technology Forum Exploring the Versatility of Silicone—Mar. 24-26, 1998—Florida—USA—Conference Papers”, describes the synthesis of an organosiloxane resin by hydrolysing trialkoxysilanes with acidified water in the absence of an organic solvent. The alcohol produced during hydrolysis is eliminated by heating or under reduced pressure in order to precipitate a viscous product that is a siloxane resin with high silanol content.
Although the method of the article leads to more stable sols, it would be nevertheless desirable to obtain sols with increased stability as well as better solubility of additives such as photochromic compounds.
It has been found according to the invention that by hydrolysing an organo-silicon precursor with large water excess, then by concentrating the hydrolysate and by leaving it until segregation into an aqueous phase and an organo-silicon phase, and by dispersing again the collected organo-silicon phase having a very low water content, and possibly dried, in a hydrophobic solvent, a very stable sol could be obtained, in which it was possible to solubilise additives such as photochromic compounds.
According to the invention, the method for preparing an organo-silicon sol comprises
a) hydrolysis of an initial volume V
si
of a precursor material containing at least an organo-silicon monomer precursor with formula:
R
1
n
Si (OR
2
)
4-n
(I)
in which
the radicals R
1
, identical or different, represent an alkyl group, an aryl group, a vinyl group or H,
the radicals R
2
, identical or different, represent H or an alkyl group, and
n is an integer varying from 1 to 2,
n=2 if R
1
represents H, with a water quantity such as
x
H
2
O
x
Si
≥
10
and, with a possible quantity of an organic solvent such that
0
≤
x
Solvent
x
Si
≤
8
where x H
2
O, x Si and x Solvent represent, respectively, the number of moles of H
2
O, Si and Solvent present. and under the condition that when
x
H
2
O
x
Si
=
10
,
x
Solvent
=
0
,
to obtain a hydrolysate of the precursor material;
b) concentration of the hydrolysate down to a volume substantially equal to the initial volume V
si
;
c) leaving the concentrated hydrolysate until a distinct aqueous phase and a distinct organo-silicon phase are obtained, and
d) separation and collection of the organo-silicon phase.
The recovered organo-silicon phase is preferably subjected to a drying step (e), either (1) by addition of a solvent with a boiling point above 100° C. at atmospheric pressure or a solvent forming an azeotrope element with water (for example 2-butanone Teb≈79.6° C.) and evaporation of the solvent, or (2) by extraction with a hydrophobic solvent.
Using a solvent with a boiling point greater than 100° C. calling for heating at relatively high temperature in order to eliminate the solvent, has the shortcoming of causing the soil (condensation rate) to evolve.
Azeotropic distillation, although resorting to lower temperatures, calls for repeated distillations and the quantity of water remaining in the sol remains relatively important.
It is therefore preferable to dry by extraction with a hydrophobic solvent exhibiting a boiling point equal to or smaller than 80° C. Preferably, ethyl acetate or diethyl ether is used.
The recommended drying method is diethyl ether extraction that, however, implies replacing ether with another solvent.
Indeed, diethyl ether is not a solvent appropriate for usage of the sol. The sol is polar and its solubility in diethyl ether does not enable to achieve the volume V
si
by evaporation. Moreover, this volatile solvent does not enable the shaping of materials.
Diethyl ether can be replaced easily with any solvent with higher boiling point and in which organo-silicon species are soluble.
Diethyl ether is therefore evaporated partially under reduced pressure (down to the solubility limit of the sol), the replacement solvent is added in excess (for example 2 V
si
), then the evaporation is carried on until the volume V
si
is obtained.
This latter operation is conducted twice in order to evaporate all the diethyl ether present in the sol.
The solvents used are, for instance, acetone, 2-butanone, tetrahydrofuran.
When the diethyl ether extraction step is used both the obtained silicon organic phase and aqueous phase can be extracted with ether and both ethereal phases are gathered before replacing ether with another solvent.
Hydrolysis water is an aqueous solution with a pH ranging generally between 3 and 10, and preferably acid. The hydrolysis solution can be acidified by an inorganic acid such as HCl, HNO
3
or H
2
SO
4
or an organic acid such as acetic acid.
As stated above, the quantity of aqueous solution used for hydrolysis is such that the following ratio
x
H
2
O
x
Si
≥
10
preferably
10
≤
x
H
2
O
x
Si
≤
20
The hydrolysis medium may comprise an organic solvent selected preferably among THF (tetrahydrofuran), inferior alcohols such as ethanol or inferior ketones such as acetone.
The hydrolysable precursor material comprises at least one organo-silicon monomer precursor with the following formula:
R
1
n
Si (OR
2
)
4-n
(I)
where R
1
, R
2
and n are such as defined previously.
R
1
represents preferably a methyl, ethyl, phenyl radical or
Biteau John
Boilot Jean-Pierre
Chaput Frederic
Dawson Robert
Essilor International (Compagnie Generale d'Optique)
Fulbright & Jaworski L.L.P.
Peng Kuo-Liang
LandOfFree
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