Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-06-21
2002-11-26
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S113000, C524S267000, C524S068000, C525S479000, C528S015000, C528S032000, C528S034000, C528S031000
Reexamination Certificate
active
06486237
ABSTRACT:
The field of the present invention is that of compositions based on polyorganosiloxanes (POS) which are capable of crosslinking by addition or hydrosilylation reactions involving hydrogen substituents and ethylenically unsaturated radicals, that is to say alkenyls, in particular of the vinyl type. The hydrosilylation is generally catalysed by metal compounds, for example of platinum nature.
The present invention relates more specifically to silicone compositions which can be crosslinked by hydrosilylation at room temperature or at a higher temperature into an adhesive and cushioning gel.
Another subject-matter of the present invention is the gels resulting from the crosslinking of the abovesaid compositions.
Finally, the invention targets the storable precursor systems of such silicone gels.
Within the meaning of the present invention, the term silicone gel denotes a crosslinked silicone product characterized in particular by a degree of penetration of between 50 and 500 tenths of a mm (measurement by ASTM D 217 penetrometry).
The use of silicone gels or elastomers in the fields of hygiene, comfort or cushioning is widespread. Their nontoxic nature, the fact that these products cannot act as substrates for microorganisms, the possibilities of varying their viscoelastic characteristics, their stability with respect to disinfectants, and the like, are the cause of these developments.
These gels have also been used for the protection of electronic equipment sensitive to vibrations, to impacts, to temperature and more generally to physical and chemical attacks from the surrounding atmosphere.
However, silicone elastomers fundamentally exhibited two disadvantages: their price and their relative density. The use of silicone foams was a way of circumventing these limitations and required the development of specific formulations. Another way was to introduce glass microspheres into existing formulations. The introduction of microspheres makes it possible to lower the relative density of the materials. Microspheres of this type have been widespread since the 1970s.
Thus, U.S. Pat. Nos. 4,380,569, 3,986,213 and FR-A-2,487,191 disclose the preparation of prostheses, in particular breast prostheses, from a gel-precursor silicone composition and from rigid hollow microspheres, for example glass microspheres.
However, the use of rigid microspheres very obviously results in the introduction of a rigid phase into an elastomeric phase and in a decline in the cushioning ability.
To overcome these drawbacks, provision has been made for the use of elastomeric microspheres. These more or less elastic microspheres are obtained by expansion of expandable microspheres comprising an organic liquid: see, for example, U.S. Pat. No. 3,615,972 and EP-A-486,080. Their walls are generally based on acrylonitrile polymers or on acrylonitrile/vinylidene chloride copolymers.
The incorporation of expanded or expandable elastomeric microspheres has increased since the 1980s in applications which range from mastics, seals and fittings, and shock, vibration and sound absorbers to prostheses, in particular breast prostheses: DE-A-3,l00,746, DE-A-3,210,094, U.S. Pat. No. 5,202,362, JP-A-58 186677, EP-A-722,989 and EP-A-733,672.
EP-A-186,493 discloses a precursor composition for a silicone elastomer of use as a sound- and vibration-absorbing material which incorporates elastic hollow microspheres. The composition can be of the two-component polyaddition type which can be crosslinked at room temperature, such as the product sold under the name Toray CY52, and can result in an elastomer having a penetration of approximately 50 to 200 according to the standard indicated.
FR-A-2,665,706 provides a compressible material, injectable as a thin layer, for a locking seal composed of a crosslinked polysiloxane elastomer in which are dispersed hollow microspheres formed from copolymer of vinylidene chloride and of acrylonitrile. The composition comprises at least one reactive polysiloxane oil which can be crosslinked under cold conditions and a crosslinking catalyst, for a polycondensation or polyaddition composition of RTV type, to which fillers may also be added.
U.S. Pat. No. 3,865,759, on the other hand, provides a silicone composition which crosslinks into a foam of low relative density but of high compressive strength. It is used in particular in the field of injected linings of ski boots, the processing consisting in injecting the composition into the boot and in then curing the composition in the boot directly around the foot. The use of a very specific catalyst, based on tin carboxylate, makes it possible to achieve a very high degree of crosslinking and, consequently, a high compressive strength. The presence of microspheres makes it possible to confer, on the crosslinked product, its foam aspect and therefore to decrease the relative density thereof. These microspheres can be made of glass, of carbon, of phenolic or epoxy resin, of silica, of vinylidene chloride/acrylonitrile resin or of urea-formaldehyde resin.
EP-A-681,814 relates to the manufacture of breast prostheses from a conventional polyaddition silicone composition to which may be added microspheres as bulking filler.
U.S. Pat. No. 4,451,584 relates to the use of filler-comprising silicone compositions for the moulding of parts of the human body, in particular in the fields of teeth prostheses and orthopaedic prostheses. Conventional inorganic fillers are replaced here by expandable organic microspheres in order to decrease the relative density of the composition and to improve certain characteristics specific to this application.
Finally, U.S. Pat. No. 5,246,973 discloses a precursor composition for a silicone elastomer-foam formed of 100 parts by weight of a precursor formula for a silicone elastomer which can be crosslinked by heating and of 0.1 to 30 parts by weight of hollow microspheres which can be expanded by heating. The precursor formula for a silicone elastomer is exemplified by conventional polyaddition formulae comprising a diorganopolysiloxane having at least 2 alkenyl groups per polymer chain, an organopolysiloxane having, per polymer chain, at least 2 hydrogen atoms bonded to the silicon and a catalyst based on a metal from the platinum group.
Conventionally, the incorporation of microspheres is known, on the one hand, to lighten the final material while retaining the cushioning properties and, on the other hand, to decrease the cost price of these materials.
These improvements are still not sufficient to establish silicone gels in the general field of cushioning where other materials are predominantly used, for example polyurethane gels in the field of cushioning, for example for soles for sports shoes.
The present invention has been given the objective of further improving the mechanical properties of silicone gels/elastomers and very particularly the general cohesion of the final material.
Another objective of the invention is to provide such gels which are capable of competing with polyurethane gels in the field of cushioning, in particular of Coles for sports shoes, and which even exhibit superior mechanical properties, in particular a better crushing fatigue strength.
The Applicant Company has noticed that it is possible to improve the mechanical properties of the gels obtained by synergistically combining elastic hollow microspheres and a promoter which develops the adhesion between the microspheres and the continuous phase in the silicone elastomer. Thus, remarkably, high cohesion between the silicone phase and the dispersed phase is obtained while retaining strong adhesion of the gel to its substrate.
The term “adhesive gel” is understood to mean a gel which develops an internal adhesive nature with respect to microspheres and an external adhesive nature with respect to a possible substrate.
In particular, it has proved to be extremely profitable to use the silicone compositions disclosed in U.S. Pat. No. 5,371,163 and EP-A-0,737,721 comprising an extending polyorganosiloxane as adhesion promoter.
The main subject-matter of the pres
Howe Fabienne
Pusineri Christian
Dawson Robert
Rhodia Chimie
Zimmer Marc S
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