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
2001-04-27
2003-02-18
Moore, Margaret G. (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...
C524S837000, C524S838000
Reexamination Certificate
active
06521699
ABSTRACT:
The field of the present invention is that of silicone compositions which are hardenable by cross-linking and which can be used in particular as putty or any other sealing material or to form any type of coating, for example, in paints, are in particular soft Semi-Thick Coatings (STC).
More precisely, the invention relates to an aqueous silicone dispersion which forms an adherent elastomer by elimination of water according to polycondensation mechanisms occurring advantageously at room temperature.
Silicones or polyorganosiloxanes (POS), such as &agr;,&ohgr;-(dihydroxy)polydiorganosiloxane, are known to enter into the composition of standard silicone putties comprising, in addition, cross-linking agents of the alkyltrialkoxysilane type, polycondensation catalysts of the tin salt type and fillers. Such compositions have proved not to be very easy to use to make, for example, leaktight seals, films or coatings because their pasty and viscous states make them difficult to handle and to make into a given form.
Furthermore, these compositions have the disadvantage of not being dispersible or soluble in water, which complicates their use, in particular because the tools used for their application are, as a result, not easy to wash with water.
Moreover, these compositions also have the disadvantage of not being “paintable': paints do not stick over.
As regards STCs some are also known which are prepared from emulsions of organic polymers. These STCs are impermeable to water but have shortcomings as regards permeability to steam.
To overcome these serious deficiencies, systems for forming putty or cross-linkable film (STC) have been developed from an aqueous emulsion based on silicone oil which is cross-linkable to an elastomer by condensation (with elimination of water and alcohol for example).
Although they are easier to apply, these aqueous silicone emulsions have raised a number of technical difficulties:
storage stability of the emulsion,
excessively long hardening time,
poor mechanical properties of the elastomer (hardness, elasticity, abrasion resistance),
defect in thixotropy of the elastomer,
defect in “paintable” character of the elastomer,
weak properties of adherence and cohesion of the elastomer onto the customary supports,
problems of safety and toxicity due to the solvents or to the alcohols formed by hydrolysis,
and ease of use.
As regards the latter two specifications mentioned in the specifications list supra, it should be noted that the question of observing certain standards of safety and of nontoxicity for the aqueous silicone dispersions, as well as for the elastomers cross-linked by condensation which are derived therefrom, is posed with some force, because a good number of commercially available products carry or release during cross-linking or drying volatile organic compounds (VOC) which are toxic or aggressive to a greater or lesser degree, such as for example alcohols (ethanol, ethanol, methoxyethanol), ethers, oximes, acids (acetic acid). It is easy to understand why such compounds are undesirable both from the point of view of storage and of use.
In addition to this toxicity/safety aspect, it would be particularly welcome for the final users to have aqueous silicone dispersions and elastomers which generate only water, so as to be able to be used without any special precaution and so as to be also easy to wash with water while retaining good properties of adherence onto supports such as for example glass, wood, concrete and metals.
Various proposals in the prior art have tried, in vain, to satisfy the specifications defined above.
German Patent Application No. 3,019,655 describes a silicone emulsion which, after elimination of water, may be converted to an elastomer under ambient conditions. This silicone emulsion also comprises amorphous silica introduced in the form of a colloidal dispersion. Such silica dispersions are not particularly stable. The pH of the mixture is a critical parameter as regards stability. It is therefore very delicate to set. Moreover, the incorporation of silica is responsible for a degree of inhomogeneity in the hardness of the cross-linked elastomer which can be obtained. This is due to the fact that silica indeed has the tendency to react spuriously with the reactive OH ends of silicone oil.
In other previous proposals, the siliceous filler is sodium silicate (U.S. Pat. No. 4,244,849) or amorphous silica powder (FR No. 2,463,163).
The latter three patents teach that to obtain a storage-stable monocomponent emulsion, its pH should be set at values greater than or equal to 8.5 or 9, preferably equal to 10. However, the emulsions according to these patents do not meet the expectations of the technical field as regards stability, mechanical properties and adherence. Finally, none of the inventions described in these patents simultaneously solves the problem of the VOCs and the problem of adherence, cohesion and stability.
European Patent Application No. 0,359,676 relates to cross-linkable aqueous dispersions which can be used as patty and which comprise a hydroxylated silicone resin as cross-linking agents for an &agr;,&ohgr;-(dihydroxy)polydiorganosiloxane oil, the said cross-linking being carried out in the presence of a stannous condensation catalyst. It happens that these emulsified compositions are not adherent to any great extent, in particular to glass. At neutral or acidic pH, their adherence is even zero.
American Patent No. 4,554,187 proposes a silicone emulsion which can be converted to an elastomer under ambient conditions, by eliminating water and alcohol, and comprising a polydiorganosiloxane with hydroxyl ends, a reactive functional alkoxy or acyloxy silicone resin useful as cross-linking agent, a catalyst of the organostannous salt type, thixotropic fillers of a siliceous nature or otherwise and nonthixotropic fillers such as Ca(OH)
2
. The dry extract of this emulsion is between 20 and 85%. The acyloxy- or alkoxyfunctional cross-linking silicone resin may be a non-amine-containing methyl or methoxysilicone resin or formula CH
3
Si(O)
1.1
(OCH
3
)
0.8
. This non-water-soluble resin is introduced in the form of an emulsion. The compositions according to this U.S. patent necessarily contain an anionic surfactant, imposed by the method of preparation of the dihydroxylated silicone oil, by polymerization to an emulsion. Such an anionic surfactant interferes with the stability of the emulsion. It should also be noted that the presence of the cross-linking functionalized acyloxy or alkoxy silicone resin is a factor inhibiting the polymerization in emulsion as long as it is added before the polymerization step. Consequently, this technical proposal is not satisfactory and all the more so since the performance in terms of resilience, elasticity and adherence is weak. Finally, the condensation mechanisms which may occur in this emulsion or this elastomer generate undesirable VOCs (alcohols or acids).
European Patent Application No. 0,572,006 discloses aqueous dispersions of ready-for-use, storage-stable aqueous POS dispersions comprising: a POS (A) having condensable groups (OR—OH) such as &agr;,&ohgr;-(diOH-polydimethylsiloxane) (PDMS); a condensation catalyst of the tin salt type; a POS resin (C) containing siloxyl units DT, MT or MQ and having a molecular weight MW≦20,000 (the alkyl substituents of the MDT units being methyls); an adherence promoter (D) containing one or more basic nitrogen-containing residues, and polyvinyl alcohol (E).
The formula for the nitrogen-containing adherence promoter (D) is very general and covers a multitude of compounds. This patent application teaches the use, in a preferential manner, of the promoter (D) of the potassium N-(2-aminoethyl)-3-aminopropylmethylsilanolate type or alternatively of PDMS functionalized with 3-(2-aminoethylamino)propyl units. These recommended adherence promoters (D) are not hydroxylated. Furthermore, the unavoidable presence of polyvinyl alcohol in these aqueous dispersions according to EP-A-0,572,006 is a damaging factor for the coalescence phenomenon w
Duchamp Marie-Cécile
Feder Michel
Jost Philippe
Letoffe Michel
Chimie Rhodia
Moore Margaret G.
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