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
2002-11-27
2004-08-03
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...
C524S588000, C524S847000
Reexamination Certificate
active
06770700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to crosslinkable compositions comprising organosilicon compounds and glass flakes, and to moldings produced therefrom.
2. Background Art
A large number of crosslinkable compositions based on organosilicon compounds with various types of fillers and additives are known. In this respect, reference may be made, for example, to EP-B-841 377, which describes, in particular, organopolysiloxane compositions which, after crosslinking, provide vulcanizates having a touch-dry surface. Furthermore, U.S. Pat. No. 5,767,185 discloses moldable silicone rubber compositions which comprise glass particles as fillers.
SUMMARY OF THE INVENTION
The present invention pertains to crosslinkable silicone compositions which include glass flakes. It has been surprisingly discovered that use of glass flakes in lieu of or in addition to conventional fillers improves physical properties of the cured compositions, particularly tear strength. The products may have a dry-touch surface and may also exhibit a low coefficient of friction.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention thus relates to crosslinkable compositions based on organosilicon compounds which contain glass flakes having a thickness of from 0.1 to 20 &mgr;m, a length of from 1 to 5000 &mgr;m and a width of from 1 to 5000 &mgr;m.
The glass flakes present in the compositions can consist of any desired types of glass, preferably inorganic glass. Examples of types of glass of which the glass flakes are composed include industrial glass, quartz glass, borosilicate glass, flat glass, pressed glass, bottle glass, table glass, mirror glass and ceramic glasses, particular preference being given to industrial glass, flat glass, borosilicate glass and ceramic glasses, especially flat glass, industrial glass and borosilicate glass.
The glass flakes employed in the invention may be untreated or may be surface-treated with functional silanes. Examples of functional silanes with which the glass flakes may have been surface-treated include aminopropyltrialkoxysilanes, aminoethylaminopropyltrialkoxysilanes, vinyltrialkoxysilanes, vinyltriacetoxysilanes, glycidoxypropyltrialkoxysilanes and methacryloxypropyltrialkoxysilanes.
Furthermore, the glass flakes employed in the invention may have been metal vapor-coated or provided with a surface coating of a purely organic or purely inorganic nature.
The glass flakes preferably have a thickness of from 0.1 to 10 &mgr;m, more preferably from 0.5 to 10 &mgr;m, and most preferably from 1 to 7 &mgr;m; preferably have a length of from 1 to 3000 &mgr;m, more preferably from 1 to 1500 &mgr;m, and most preferably from 1 to 500 &mgr;m; and preferably have a width of from 1 to 3000 &mgr;m, more preferably from 1 to 1500 &mgr;m, and most preferably from 1 to 500 &mgr;m. The width or length to thickness ratio is preferably in the range from 10:1 to 2000:1, more preferably from 20:1 to 1500:1, and most preferably from 30:1 to 1000:1. It is preferable that both the width and length are numerically greater than the thickness. Preferably, the width to length or length to width ratio is less than 100.
The glass flakes can have very different geometries, such as, for example, planar platelet-shaped, wavy, rolled or twisted, but are preferably planar. Such glass flakes are commercially available, and can be purchased, for example, from Glass Flake Ltd., Leeds, GB. As a consequence of production, the glass flakes may be in the form of a mixture with other glass particles, such as powders or fibers. However, at least 80% by weight of all particles are preferably in flake form and not in powder or fiber form.
The compositions according to the invention preferably comprise glass flakes in amounts of from 1 to 80 parts by weight, more preferably from 1 to 70 parts by weight, and most preferably from 2 to 60 parts by weight, in each case based on 100 parts by weight of crosslinkable composition. Compositions having glass flake contents of 2 to about 20 parts by weight may be advantageous for numerous applications.
The curable compositions can be any desired type of organosilicon compound-based composition which can be crosslinked to give elastomers, for example, one-component or two-component organopolysiloxane compositions which can be vulcanized at room temperature (so-called RTV compositions) or elevated temperature (so-called HTV compositions), it being possible for the crosslinking to be carried out by condensation, addition of Si-bound hydrogen onto aliphatic multiple bonds, or peroxidically through the formation of free radicals. The crosslinkable compositions can be free from fillers, but may also contain active or inactive fillers.
The type and amount of the components usually used in compositions of this type, other than glass flakes, are already known. In this respect, reference may be made, for example, to U.S. Pat. No. 5,268,441, DE-A 44 01 606, DE-A 44 05 245 and DE-A 43 36 345.
The glass flakes employed in accordance with the invention can be mixed as desired with the other components of the crosslinkable compositions. They can be incorporated as a final step into the otherwise finished silicone rubber formulation or incorporated during preparation of the silicone rubber mixture. However, the glass flakes can also be pre-mixed into one or more of the components employed.
The mixing process for the preparation of the compositions is preferably simple mechanical combination. Depending on the consistency and viscosity of the base medium, the mixing process can be carried out in roll mills, compounders, dissolvers, Z mixers, ball mills or simple stirrers. Merely for the sake of simplicity, the mixing process is preferably carried out at ambient pressure. However, mixing under reduced or elevated pressure is also possible. Likewise for the sake of simplicity, the mixing process is preferably carried out at ambient temperature, although it is also possible to carry out the mixing at elevated temperature or with cooling.
The inventive compositions have the advantage of being simple to prepare and having good processing properties. Furthermore, the compositions have the advantage that vulcanizates which have a touch-dry surface with a low coefficient of friction can be prepared therefrom.
The compositions can be crosslinked under the same conditions as previously known crosslinkable compositions based on organosilicon compounds. Preparation processes which can be used include all common processes for the processing of silicone rubbers. Non-limiting examples thereof are calendering, compression molding, injection molding, extrusion, and casting.
The present invention furthermore relates to moldings produced by crosslinking the inventive compositions.
The compositions can also be used for coating textile sheet-like structures such as woven fabrics, knitted fabrics, laid fabrics, nonwoven fabrics, felts, etc. The coating can be applied by the knife-coating method, dipping method, extrusion method or spraying method. In addition, all types of roll coatings, such as engraved rolls, slop padding or application via multiroll systems, as well as screen printing are possible.
The coated woven fabrics can be employed in all cases where reduced surface friction, high transparency, reduced thermal value and high tear propagation strength and tear strength are advantageous. Examples are hang gliders, parachutes, hot-air balloons, leisure clothing, and leisure articles such as tents or rucksacks, sails or airbags. In the industrial sector, the coated woven fabrics are advantageously employed for conveyor belts, compensators, awnings, textile structures or in insulation applications. Thus, the present invention furthermore relates to textile or non-textile sheet-like structures which have been coated with the compositions of the invention.
Crosslinking of the inventive compositions provides vulcanizates which advantageously have a surface with a reduced coefficient of friction without after-treatment. The vulcanizates have the further advantage of exhibiting impr
Madl Gerhard
Mueller Johann
Brooks & Kushman P.C.
Moore Margaret G.
Wacker-Chemie GmbH
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