Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-11-16
2001-06-26
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S209000, C523S211000, C502S158000, C502S339000
Reexamination Certificate
active
06251969
ABSTRACT:
TECHNICAL FIELD
The invention relates to organopolysiloxane particles containing hydrosilylation catalysts, and to storage-stable, one-component, addition-crosslinking, thermocurable silicone compositions.
BACKGROUND ART
U.S. Pat. No. 4,481,341, EP-A-661349 and U.S. Pat. No. 5,525,425 describe silicone resins which display a glass transition temperature, softening point, or melting point. These silicone resins can be used as encapsulation materials for hydrosilylation catalysts. To prepare such encapsulated catalysts, the silicone resins are dissolved in an organic solvent, and a hydrosilylation catalyst is added. The encapsulated hydrosilylation catalysts are obtained, for example, by removing the solvent and subsequently powdering the product, or by spray-drying the catalyst-containing silicone resin solution. With the aid of these encapsulated catalysts, one-component addition-crosslinking silicone compositions can be prepared.
The disadvantage of these encapsulated catalysts is that siloxane particles with different morphological structures cannot be synthesized using different siloxane units. It is therefore not possible to produce core/shell structures or to adjust the surface composition in a specific manner, and thus it is not possible to modify the compatibility or dispersibility of the encapsulated catalyst particles in the silicone composition by varying the particle surface composition. There is likewise a risk that the encapsulated catalyst, owing to the temperature increase during compounding, is liberated very quickly after the softening point or glass-transition temperature of the encapsulant has been reached, causing the silicone composition to crosslink prematurely during compounding.
DISCLOSURE OF INVENTION
An object of the present invention was to provide organopolysiloxane particles containing hydrosilylation catalysts suitable for producing storage-stable, one-component silicone compositions, without the disadvantages of prior art encapsulated catalysts.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention relates to organopolysiloxane particles containing hydrosilylation catalysts (H) and organopolysiloxanes (O) which have a particle size of 0.01-10 &mgr;m and which, at least in the outermost shell, do not have a glass-transition temperature softening point or melting point in the range of 20° to 250° C.
The organopolysiloxane particles of the present invention are readily dispersible in addition-crosslinkable silicone compositions. It has been found that organopolysiloxane particles of this type containing hydrosilylation catalysts (H) are capable of liberating the catalyst (H) at temperatures below 250° C., although they do not exhibit, at least in the outermost shell, a glass- transition temperature, melting point or softening point in the range 20-250° C. as measured by DSC. Consequently these encapsulated hydrosilylation catalysts (H) enable the preparation of storage-stable, one-component, addition-crosslinking, thermocurable silicone compositions. Owing to the morphological variety and variation of the siloxane units in such organopolysiloxane particles, the liberation of the catalysts, i.e. the crosslinking characteristics, and the pot life of addition-crosslinking silicone compositions, as well as the dispersibility of the siloxane particles in the silicone composition can be adjusted in a targeted manner.
The organopolysiloxane particles can be homogeneous throughout and consist only of a core or can be built up from core and shell(s), similarly to an onion. If the organopolysiloxane particles are built up from a core and shell(s), the outermost shell constitutes at least 0.1% by weight, in particular at least 0.5% by weight, of the total organopolysiloxane particle. The compositions of core and shell(s) can differ, for example, through their content of hydrosilylation catalysts (H) and/or the type of their organopolysiloxane constituent (O).
The organopolysiloxane (O) of the organopolysiloxane particles is preferably built up from
from 0 to 40.0% by weight of units of the general formula
[R
3
SiO
1/2
] (1),
from 0 to 95.0% by weight of units of the general formula
[R
2
SiO
2/2
] (2),
from 0 to 100% by weight of units of the general formula
[RSiO
3/2
] (3),
and
from 0 to 60.0% by weight of units of the general formula
[SiO
4/2
] (b
4
),
where
R are identical or different monovalent, SiC-bonded, optionally substituted C
1
- to C
18
-hydrocarbon radicals, with the proviso that the units of the general formulae (1) to (4) together contain at most 10% by weight, in particular at most 5% by weight, of uncondensed radicals ≡Si—OH and unhydrolyzed radicals ≡Si—OR
1
, where
R
1
are identical or different monovalent, SiOC-bonded, optionally substituted C
1
- to C
8
-hydrocarbonoxy radicals.
The total amount of the units of the general formulae (3) and (4) is preferably at least 5.0% by weight, in particular at least 10.0% by weight. This total number of units is based on the overall composition of the organopolysiloxane constituent (O), which can, if desired, consist of core and shell(s) of different composition. The particles can also have, for example, individual shells containing less than 5.0% by weight of units of the general formulae (3) and (4).
The organopolysiloxane in the organopolysiloxane particles preferably comprises
from 0.5 to 20% by weight of units of the general formula (1),
from 0 to 75% by weight of units of the general formula (2),
from 5 to 99% by weight of units of the general formula (3), and
from 0 to 40% by weight of units of the general formula (4).
Examples of unsubstituted hydrocarbon radicals R are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl and tert-pentyl radicals, hexyl radicals such as the n-hexyl radical, heptyl radicals such as the n-heptyl radical, octyl radicals such as the n-octyl radical and isooctyl radicals such as the 2,2,4-trimethylpentyl radical, nonyl radicals such as the n-nonyl radical, decyl radicals such as the n-decyl radical, dodecyl radicals such as the n-dodecyl radical, and octadecyl radicals such as the n-octadecyl radical; alkenyl radicals such as the vinyl, allyl, n-5-hexenyl, 4-vinylcyclohexyl and 3-norbornenyl radicals; cycloalkyl radicals such as cyclopentyl, cyclohexyl, 4-ethylcyclohexyl, cycloheptyl, norbornyl and methylcyclohexyl radicals; aryl radicals such as the phenyl, biphenylyl, naphthyl, anthryl and phenanthryl radicals; alkaryl radicals, such as o-, m-, and p-tolyl radicals, xylyl radicals and ethylphenyl radicals; aralkyl radicals such as the benzyl radical and the &agr;- and &bgr;-phenylethyl radicals, and the fluorenyl radical.
Examples of substituted hydrocarbon radicals as radicals R are halogenated hydrocarbons, such as the chloromethyl, 3-chloropropyl, 3-bromopropyl, 3,3,3-trifluoropropyl and 5,5,5,4,4,3,3-hexafluoropentyl radicals and the chlorophenyl, dichlorophenyl and trifluorotolyl radicals.
The hydrocarbon radical R is preferably an unsubstituted or substituted C
1
- to C
6
-alkyl radical or a phenyl radical, in particular a methyl, phenyl or vinyl radical. It is preferred for 10-98 mol % of the hydrocarbon radicals R to comprise phenyl groups and 2-25 mol % of the hydrocarbon radicals R to comprise vinyl groups.
The hydrocarbonoxy radical R
1
is preferably an unsubstituted or substituted C
1
- to C
6
-alkoxy radical or a phenoxy radical, in particular a methoxy or ethoxy radical.
The hydrosilylation catalyst (H) used can be any known catalyst which catalyzes the hydrosilylation reactions occurring during crosslinking of addition-crosslinking silicone compositions. The hydrosilylation catalysts (H) employed can be, in particular, metals and their compounds, such as platinum, rhodium, palladium, ruthenium and iridium, preferably platinum and platinum compounds. Particular preference is given to platinum compounds which are soluble in polyorganosiloxanes. Examples of soluble platinu
Achenbach Frank
Ebenhoch Jochen
Worner Christof
Brooks & Kushman P.C.
Moore Margaret G.
Wacker-Chemie GmbH
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