Storage-stable organopolysiloxane compositions which can be...

Details Storage-stable organopolysiloxane compositions which can be... Storage-stable organopolysiloxane compositions which can be...

2000-03-14

2001-10-16

Dawson, Robert (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...

C524S366000, C524S391000, C524S588000, C524S863000, C528S018000, C528S034000

Reexamination Certificate

active

06303678

ABSTRACT:

TECHNICAL FIELD
The subject invention pertains to storage stable RTV-1-alkoxy compositions comprising a tin catalyst and an effective amount of one or more storage-stabilizing surfactants.
BACKGROUND ART
In the context of the present invention, the term organopolysiloxanes is intended to include dimeric, oligomeric and polymeric siloxanes.
The use of dialkyltin(IV) compounds as condensation catalysts in RTV-1- and RTV-2-silicone rubbers is generally known. However, in RTV-1-alkoxy compositions these tin compounds have the disadvantage that they also catalyze the unwanted cleavage of the siloxane chains by alcohol radicals, i.e. “equilibration”, whereupon alkoxy end groups on the polysiloxane chain which are no longer capable of crosslinking are formed, and adequate crosslinking of the composition is therefore no longer possible: i.e. no adequately stable vulcanization product is obtained when the composition is used for the intended purpose. The storage stability, stated as the period of time which the RTV-1-alkoxy composition can be stored without noticeably losing its commercially acceptable properties, is drastically reduced by equilibration.
Known methods for prolonging the storage stability include:
The replacement of the tin catalyst by a titanium or aluminum chelated catalyst, for example as disclosed in U.S. Pat. No. 3,334,067. The disadvantage here is the yellow coloration of the compositions, as a result of which only opaque but no transluscent compositions are possible.
The replacement of the tin catalyst by a titanium catalyst of the general formula Ti(OR)
4
, for example, as disclosed in EP-A-747 443, with the disadvantage that only siloxanes which contain no silanol groups can be processed. The use of adhesion promoters with such catalysts is limited because of adverse effects on t he activity of the catalyst.
Reduction in the amount of the tin catalyst, with the disadvantage of a very slow vulcanization.
The use of less aggressive tin catalysts, for example tin chelated catalysts, for example as disclosed in U.S. Pat. No. 4,517,337. An excess of chelating compound such as acetylacetonate, is necessary. However, this chelating agent is volatile, toxicologically unacceptable, a health hazard, and can also lead to yellowing of the vulcanization product.
The addition of alcohol-trapping agents, scavengers which react with alcohols on the basis of their high reactivity, for example as disclosed in U.S. No. 4,417,042. However, the addition of such scavengers is not only expensive, but also impairs adhesion properties.
DISCLOSURE OF INVENTION
An object of the present invention is to provide RTV-1-alkoxy compositions which comprise a tin catalyst, have an increased storage stability and do not have the disadvantages of the known methods. The inventive to RTV-1-alkoxy compositions comprise a tin catalyst and surfactants (S) which contain divalent polyether un its of the general formula (I)
—O—[(CR
&agr;
R
&bgr;
)
u
—O]
v
—  (I)
in which
R
&agr;
and R
&bgr;
are hydrogen or a monovalent C
1
-C
10
-hydrocarbon radical optionally substituted by hydroxyl, fluorine, chlorine, bromine, C
1
-C
10
-alkoxyalkyl or cyano groups,
u is from 1 to 6 and
v is from 3 to 100,
the RTV-1-alkoxy compositions being free of acid phosphoric acid esters of the general formula (II)
(HO)
a
OP(—O—[(CR
1
2
)
b
—O]
c
[(CR
2
2
)
d
]
e
—L—M)
(3−a)
  (II)
in which
a is 1 or 2,
R
1
and R
2
are independently hydrogen, methyl, or hydroxyl radicals, b and d are 2or 3,
c is from 2 to 15,
e is 0 or 1,
L is a radical from the group consisting of —O—, —COO—, —OOC—, —CONR
3
—, —NR
4
CO—and —CO—,
R
3
and R
4
independently are hydrogen or, C
1
-C
10
-alkyl radical(s), and
M is a monovalent C
1
- to C
20
-hydrocarbon radical which is optionally substituted by hydroxyl, fluorine, chlorine, bromine, C
1
-C
10
-alkoxyalkyl or cyano groups,
with the proviso that not more than one of the radicals R
1
and R
2
on a given carbon atom can simultaneously be a hydroxyl radical.
The invention also relates to a process for stabilizing RTV-1-alkoxy compositions comprising a tin catalyst, in which surfactants (S) which contain divalent polyether units of the above general formula (I) are added to the compositions.
BEST MODE FOR CARRYING OUT THE INVENTION
The addition of surfactants (S) to RTV-1-alkoxy compositions comprising a tin catalyst has the effect of retarding or suppressing the equilibrating action of the tin catalysts, as a result of which the storage stability is increased drastically. At the same time, the desired condensation catalysis of the tin compounds used is activated. Polysiloxanes blocked on the ends in situ by phosphoric acid esters also remain processable.
Preferably, the surfactants (S) contain at least 20% by weight, in particular at least 50% by weight, of divalent polyether units of the general formula (I).
Preferably, in the general formula (I), independently of one another,
R
&agr;
and R
&bgr;
are a hydrogen radical or a monovalent unsubstituted hydrocarbon radical, in particular hydrogen or C
1
-C
3
-alkyl radicals, such as the methyl or ethyl radical;
u is an integer from 1 to 4, in particular 2 or 3; and
v is an integer from 3 to 25, in particular from 5 to 10.
The surfactants (S) can be nonionic, anionic or cationic surfactants, in particular, emulsifiers. Examples of surfactants (S) are: fatty acid esters, for example of the formula R′—C(=O)—Y—R″; fatty alkyl ether carboxylates, for example of the formula R′—Y—CH
2
COOX; fatty alcohol polyglycol ethers, for example of the formula R′—Y—R″; phenol polyglycol ethers, for example of the formula Ar—Y—R′; fatty alkyl ether sulfates, for example of the formula R′—Y—SO
3
X; alkyl ether phosphates, polydimethylsiloxanes having polyether groups, oxyethylates and ethers thereof, such as, for example, polyethylene glycol, polypropylene glycol, polyethylene glycol diethers, polypropylene glycol diether and copolymers thereof, fatty amine oxyethylates, and polyglycol sulfonates.
In the above surfactants (S)
R′ and R″ are C
6
-C
30
-alkyl radicals,
Y is a divalent polyether unit of the general formula (I),
X is Na or K and
Ar are C
6
-C
30
-aryl radicals or C
7
-C
30
-aralkyl radicals.
Preferably, the RTV-1-alkoxy compositions comprising a tin catalyst comprise at least 0.01%, in particular at least 0.1%, by weight, and preferably not ore than 10%, in particular not more than 5%, by weight of surfactants (S).
The RTV-1-alkoxy compositions comprising a tin catalyst comprise
(A) organopolysiloxane(s) with terminal alkoxy groups and
(B) alkoxysilane(s) which contain at least three alkoxy groups, and/or partial hydrolysis products thereof.
The organopolysiloxanes (A) with terminal alkoxy groups are preferably linear diorganosiloxanes of the general formula (III)
R
5
f
(R
6
O)
3−f
Si—(O—SiR
2
)
g
—O—SiR
5
f
(R
6
O)
3−f
  (III)
in which
R, R
5
and R
6
are each independently monovalent C
1
-C
8
-hydrocarbon radicals, optionally substituted by fluorine, chlorine, bromine, C
1
-C
4
-alkoxyalkyl or cyano groups,
f is 0 or 1 and
g is a value which corresponds to a viscosity of the organopolysiloxane (A) of from 0.05 to 1000 Pa·s.
Preferred radicals R, R
5
and R
6
are unsubstituted C
1
-C
4
-alkyl radicals, the methyl radical being particularly preferred. The organopolysiloxanes (A) preferably have a viscosity of from 100 to 700,000 mPa·s, in particular from 20,000 to 350,000 mPa·s, in each case measured at 23° C. Preferably, the RTV-1-alkoxy compositions comprising a tin catalyst comprise at least 35%, more preferably at least 45%, by weight, preferably not more than 80%, and more preferably not more than 70% by weight of organopolysiloxanes (A).
The alkoxysilanes (B) preferably have the general formula (IV)
 R
7
&mgr;
Si (OR
8
)
4−&mgr;
  (IV)
in which R
7
and R
8
are monovalent C
1
-C
13
-hydrocarbon radicals which are optionally substituted by fluorine, chlorine, bromine, C
1
-C
4
-alkoxyalkyl or

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