Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1999-08-13
2001-02-13
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S023000, C502S152000, C502S155000, C502S213000, C525S478000, C525S479000, C987S010000
Reexamination Certificate
active
06187890
ABSTRACT:
TECHNICAL FIELD
The present invention relates to silicone compositions which crosslink thermally by hydrosilylation, their preparation and their use.
BACKGROUND ART
Addition-crosslinking silicone compositions crosslink by reaction of aliphatically unsaturated groups with Si-bonded hydrogen (hydrosilylation) in the presence of a catalyst, typically a platinum compound. Owing to the fact that the crosslinking reaction commences when the essential constituents are simultaneously present, addition-crosslinking silicone compositions have hitherto been prepared virtually exclusively as two-component formulations, with the composition of the individual components being such that all three essential constituents are present together only after the components are mixed. Customarily, one of the components comprises the alkenyl-functional polyorganosiloxane and the platinum catalyst while the other component comprises the SiH-functional crosslinker, if desired in combination with the alkenyl-functional polyorganosiloxane. After mixing the individual components, complete curing to form the silicone elastomer can be carried out at room temperature, but it is customarily carried out at elevated temperature.
The two-component system for addition-crosslinking silicone compositions is associated with numerous disadvantages, for instance logistics, the high risk of contamination by traces of platinum and the presence of an additional mixing step. Although mixing of the components does give a ready-to-use composition, this composition has only a very limited pot life at room temperature. This not only makes immediate processing necessary but also requires frequent cleaning of the stock vessels, metering units, processing machines, etc., since any material remaining, for example as a result of backmixing or sticking to the walls, ultimately gels.
Owing to the disadvantages of such two-component compositions, there has been no lack of attempts to make addition-crosslinking silicone compositions available as one-component formulations. Since in the case of a one-component system all constituents necessary for crosslinking are present simultaneously, the problem is essentially to suppress premature commencement of the crosslinking reaction which normally proceeds even at room temperature. Possible ways of setting (increasing) the pot life of an addition-crosslinking composition in a targeted way have been known for some time, e.g. by the use of inhibitors which are capable of considerably reducing the activity of the platinum catalyst at room temperature, for example phosphorus compounds in combination with peroxides as described in U.S. Pat. No. 4,329,275 or azodicarbonyl compounds as described in EP-A-490 523. Although choice of type and amount of such inhibitors makes it possible to increase the pot life to any desired extent, an adverse effect on the crosslinking behavior is unavoidably associated with this increasing pot life. This is particularly true when the pot life is extended to a number of months by means of high inhibitor contents. In such cases, increased start temperature and undesirable crosslinking behavior ranging from a low crosslinking rate to insufficient crosslinking, are the result.
A further, fundamentally different technique is encapsulation of the platinum catalyst in a finely divided material which releases the platinum only at elevated temperature. This can be achieved, for example, by microencapsulation of the platinum catalyst in a thermoplastic silicone resin or an organic thermoplastic as described, for example, in EP-A-363 006. However, such techniques are relatively complicated.
A third possibility is to select, as catalyst, specific platinum complexes whose activity is such that the hydrosilylation reaction proceeds sufficiently rapidly at elevated temperature but at room temperature proceeds only to such a small degree that pot lives of a number of months are achieved. Addition-crosslinking compositions comprising such platinum complexes have been described, for example, in EP-A-583 159 and DE-A-36 35 236. Although the compositions described have significantly improved pot lives at sometimes sufficiently high crosslinking rates, there continues to be a need to improve the pot life and crosslinking rate of one-component, addition-crosslinking compositions by means of better platinum catalysts without having to accept the abovementioned disadvantages. This object is achieved by the present invention.
SUMMARY OF THE INVENTION
The present invention provides curable organopolysiloxane compositions comprising
(A) compounds having radicals containing aliphatic carbon—carbon multiple bonds,
(B) organopolysiloxanes containing Si-bonded hydrogen atoms, or, in place of (A) and (B),
(C) organopolysiloxanes having SiC-bonded radicals containing aliphatic carbon—carbon multiple bonds and Si-bonded hydrogen atoms, and
(D) a platinum catalyst exhibiting little or no activity at low temperatures, and excellent crosslinking behavior at elevated temperatures as hereinafter described.
For the purposes of the present invention, the term organopolysiloxanes includes polymeric, oligomeric and dimeric siloxanes.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides curable organopolysiloxane compositions comprising
(A) compounds having radicals containing aliphatic carbon—carbon multiple bonds,
(B) organopolysiloxanes containing Si-bonded hydrogen atoms, or, in place of (A) and (B),
(C) organopolysiloxanes having SiC-bonded radicals containing aliphatic carbon—carbon multiple bonds and Si-bonded hydrogen atoms, and
(D) a platinum catalyst selected from the group consisting of
(PR
2
3
)
2
Pt(—C≡C—R
3
)
2
(III),
(R
2
2
P—R
4
—PR
2
2
)Pt(—C≡C—R
3
)
2
(IV)
and
H—C≡C—R
5
—C≡C—[—Pt(PR
2
3
)
2
—C≡C—R
5
—C≡C—]
e
—H (V)
where
R
2
may be identical or different and are monovalent, substituted or unsubstituted hydrocarbon radicals having from 1 to 24 carbon atoms, halogen atoms, hydrogen atoms, hydroxy radicals, —CN or —SCN, which are bound to phosphorus either directly or via oxygen, nitrogen or sulfur,
R
3
are identical or different monovalent, substituted or unsubstituted hydrocarbon radicals having from 1 to 24 carbon atoms,
R
4
are identical or different divalent, substituted or unsubstituted hydrocarbon radicals having from 1 to 14 carbon atoms,
R
5
are identical or different divalent, substituted or unsubstituted hydrocarbon radicals having from 1 to 24 carbon atoms, and
e is an integer greater than or equal to 1.
If the radicals R
2
, R
3
, R
4
and R
5
are substituted hydrocarbon radicals, preferred substituents are halogen atoms such as F, Cl, Br and I, cyano radicals and —OR
6
groups, where R
6
may be identical or different and are each a hydrogen atom or a monovalent hydrocarbon radical having from 1 to 20 carbon atoms.
The compositions of the invention can be one-component organopolysiloxane compositions or else two-component organopolysiloxane compositions. In the latter case, the two components of the composition of the invention can contain all constituents in any combination, generally with the proviso that one component does not simultaneously contain siloxanes having an aliphatic multiple bond, siloxanes containing Si-bonded hydrogen and catalyst, i.e. the constituents (A), (B) and (D) or (C) and (D) are essentially not present together. The compositions of the invention are preferably one-component compositions.
The compounds (A) and (B) or (C) used in the compositions of the invention are, as is known, selected so that crosslinking is possible. Thus, for example, but not by limitation, compound (A) may have at least two aliphatically unsaturated radicals and siloxane (B) may have at least three Si-bonded hydrogen atoms, or compound (A) may have at least three aliphatically unsaturated radicals and siloxane (B) may have at least two Si-bonded hydrogen atoms. Alternatively, in place of compound (A) and (B), use may be made of siloxane (C) which has aliphatically unsatur
Achenbach Frank
Dietl Stefan
Fehn Armin
Brooks & Kushman P.C.
Dawson Robert
Wacker-Chemie GmbH
Zimmer Marc S.
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