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
2001-03-05
2003-03-04
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...
C524S858000, C524S261000, C524S492000, C525S474000, C528S034000, C528S012000
Reexamination Certificate
active
06528580
ABSTRACT:
The field of the present invention is that of silicone compositions which can be cured by crosslinking and which can be used in particular either as mastics or other leakproofing and/or water-repelling and/or pointing materials or alternatively to form coatings of any type (for example paints), including in particular flexible coatings of medium thickness. More specifically, the invention relates to an aqueous silicone dispersion capable of forming, by crosslinking (e.g. polycondensation) accompanied by elimination of water (preferably at room temperature), a transparent elastomer which adheres to numerous substrates. Without this being limiting, the crosslinking mechanism more especially envisaged for the conversion of the silicone, as an aqueous dispersion, to a transparent and adhesive elastomer is of the type involving hydrolysis/condensation of ≡SiOR
a
reactive groups with R
a
=H or alkyl. The silicones or polyorganosiloxanes (POS) which come within such a context are in particular &agr;,&ohgr;-dihydroxylated polydiorganosiloxanes, such as, for example, &agr;,&ohgr;-di-OH polydimethylsiloxanes. In addition to this main constituent, which is a POS, aqueous silicone dispersions which are precursors of mastics or other leakproofing/water-repelling coatings optionally comprise adhesion promoters, for example silicon-comprising adhesion promoters (silanes, oligo- or polyorganosiloxanes), and optionally crosslinking agents of the trialkoxysilane type or polyfunctional resins comprising several ≡SiOR
a
functional groups. All these silicon-comprising constituents, when they are not hydrophilic or water-soluble, compose the non-continuous phase (silicone phase &phgr;
s
) of the aqueous silicone dispersion.
Aqueous silicone dispersions which are precursors of mastic, leakproofing/water-repelling or pointing materials, or of coatings form one of the latest generations of silicone compositions employed in this technical field. Their aqueous nature facilitates handling operations, shaping operations and the washing of the tools used for their application. These aqueous silicone dispersions also exhibit the advantage of a lower toxicity with respect to silicone compositions comprising organic solvents or which release volatile organic species.
The hydrophilic phase &phgr;
H
(non-silicone phase) of these aqueous dispersions based on silicone oil which can be crosslinked into an elastomer by (hydrolysis)/condensation with elimination of water and/or alcohol, for example, is continuous and comprises hydrophilic constituents, such as, for example, fillers (e.g. siliceous fillers) and surfactants. This hydrophilic phase &phgr;
H
can additionally comprise an adhesion promoter also capable of acting as crosslinking agent.
These compositions also comprise a condensation catalyst.
These aqueous dispersions of hydroxylated silicone oil can be produced conventionally by mechanical stirring or alternatively by emulsion polymerization.
The conventional method consists in employing devices of colloid mill or homogenizer type (FR-A-2 064 563, FR-A-2 114 130, FR-A-2 094 322 and EP-A-0 169 098). This technique is limited to the emulsification of polymers with a viscosity of less than 5 000 mpa.s. It is possible to mechanically emulsify more viscous oils, for example by using the techniques disclosed in FR-A-2 697 021.
It is also possible to use the technique of emulsion polymerization of cyclic or linear silicone oligomers of low molecular weight which are easy to emulsify according to conventional mechanical techniques. In this alternative, it is preferable for the surfactants also to act as polymerization catalysts (U.S. Pat. Nos. 3,294,725 and 3,360,491).
Although representing a degree of technical progress, these aqueous silicone dispersions which are precursors of mastics and/or of leakproofing/water-repelling coatings have a specification sheet, the specifications of which can be further improved. These improvable specifications are:
the stability on storage,
the excessively long curing time,
the mechanical properties of the elastomer (hardness, elasticity, resistance to abrasion),
the “flowability” of the elastomer,
the possibility of painting the elastomer,
the properties of cohesion and of adhesion of the elastomer to conventional substrates,
the problems of safety and of toxicity due to the solvents or to the alcohols formed by hydrolysis,
and the ease of use.
In the context of the invention, another specification of a more aesthetic nature but which is not without technical repercussions will also be included, namely the translucency or the transparency of the elastomer obtained after at least partial crosslinking of the aqueous silicone dispersion with elimination of water or alcohol. This transparency corresponds to a market requirement which is more particularly felt for silicone mastics.
Some proposals of the prior art have attempted to satisfy, in vain, the specification sheet which is defined above and which relates in particular to transparent aqueous silicone mastics.
European Patent Application EPA-0 542 498 relates to aqueous silicone emulsions which can be converted by crosslinking and drying into a translucent elastomer. These emulsions comprise crosslinked polydimethylsiloxane (PDMS), which is provided in the form of a dispersed phase in which less than 10% of the particles have a size of greater than 1 000 nm. This PDMS is obtained by anionic emulsion polymerization.
This emulsion also comprises a surfactant of formula RSO
4
M of the sodium lauryl sulphate type. The nondisperse aqueous phase of this emulsion comprises a crosslinking agent of the alkoxysilane type (&ggr;-methacryloxypropyl, trimethoxysilane chloropropyltrimethoxysilane, trifluoropropyltrimethoxysilane or vinyltrimethoxysilane) and a filler composed, for example, of precipitated silica with a particle size of the order of 19 nm and of colloidal silica for which the size of the particles is approximately 20 nm. This nondisperse continuous aqueous phase also comprises a condensation catalyst of the tin octoate type.
In Example 5 of EP-A-0 542 498, the translucency obtained for the elastomer resulting from the aqueous silicone emulsions is of the order of 85% of Transmission T for a dry crosslinked elastomer film of 47 mil (1.519 mm).
The transmission T is defined according to the Lambert-Beer law:
log(100/
T
)=&egr;.
e.C
with:
T=transmission varying from 0<T≦100% of a film with a thickness e irradiated with white light with a wavelength &ggr; of between 400 and 700 nm,
&egr;=coefficient of extinction (mm
−1
),
e=thickness of the dry film (mm),
C=total fraction by volume of the non-silicone hydrophilic species in the dry film.
The translucency can be expressed by the transparency index R in %=100-T.
According to the teaching of EP-A-0 542 498, the translucency decreases when the level of silicic filler increases (page 11, line 44). It should be noted that, in accordance with the invention disclosed in EP-A-0 542 498, the achievement of an all things considered improvable translucency is dependent on the presence in the dispersed phase of at least 90% of silicone particles with a size of less than 1 000 nm. The invention disclosed in EP-A-0 542 498 is consequently based on the fineness of the silica particles.
The transparency index R of the crosslinked elastomer films obtained according to EP-A-0 542 498 is greater than 25%. In addition, the coefficient of extinction &egr; of these films is greater than 0.8 mm
−1
.
In addition, the emulsions according to EP-A-0 542 498 are restricted to those comprising a specific surfactant of the sodium lauryl sulphate type.
If the refractive index n
S
of the dispersed silicone phase &phgr;
S
and the refractive index n
H
of the non-silicone continuous hydrophilic phase &phgr;
H
of the aqueous silicone emulsions according to EP-A-0 542 498 are considered, it is apparent that |n
S
−n
H
|>0.05. Such a |n
S
−n
H
| range reflects an unsatisfactory transluce
Feder Michel
Giraud Yves
Guironnet Marcel
Burns Doane Swecker & Mathis L.L.P.
Dawson Robert
Peng Kuo-Liang
Rhodia Chimie
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