Curable organopolysiloxane compositions

Details Curable organopolysiloxane compositions Curable organopolysiloxane compositions

2001-12-10

2003-05-20

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...

C502S152000, C502S213000, C524S430000, C524S431000, C524S432000, C528S015000, C528S031000, C528S032000, C252S602000

Reexamination Certificate

active

06566430

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to crosslinkable silicone compositions useful for preparing organopolysiloxane elastomers exhibiting low flammability and/or high tracking resistance as well as high arc resistance. The present invention further relates to a method of preparing such preparations, additives employed for this purpose, and to molded articles prepared from crosslinkable preparations containing these compositions.
2. Background Art
Non-tracking, low-flammability, arc-resistant organopolysiloxane elastomers are already known, and are obtained e.g. by the addition of metal oxides, especially metal oxidyhydrates, or by the addition of platinum compounds, optionally in combination with metal oxides and organosilicon compounds. In this context, reference can be made, for example, to EP-B 088624 and DE-A 38 31 478.
It is known to induce crosslinking of crosslinkable silicone composition compounds which form free radicals, for example acyl peroxides, alkyl peroxides and aryl peroxides, by means of condensation, by high-energy radiation, and by the addition of Si-bound hydrogen to aliphatic carbon—carbon multiple bonds (“addition crosslinking”). Addition-crosslinking, curable organopolysiloxane preparations are commercially available as 2-component systems or as 1-component systems. The shelf life of the addition-crosslinking, low-flammability, non-tracking 1-component systems mentioned in DE-A 3831478 is only a few days at room temperature, as the crosslinking reaction proceeds noticeably even at room temperature. While it is possible to extend pot life at will via the type and level of the added inhibitors, a longer pot life inevitably entails impaired crosslinking behavior, characterized, for example, by a low crosslinking rate, by incomplete crosslinking, etc.
SUMMARY OF THE INVENTION
The present invention relates to compositions comprising an admixture of
(A) 50-90 wt % of an organopolysiloxane having a viscosity of from 50 to 100·10
6
mm
2
/s at 25° C.;
(B) 10-50 wt % of one or more of titanium oxide, zirconium dioxide, zinc oxide, cerium(III) and cerium(IV) oxide;
(C) 0.3-5 wt % of an organosilicon compound containing basic nitrogen bound to silicon via carbon;
(D) 0.05-0.5 wt % of platinum, calculated as the element, in the form of a bis(alkynyl)platinum complex which additionally includes donor ligands; and
(E) from 0 to 5 wt %, and preferably 0 wt %, of further components, the sum of the percentages chosen within each of the ranges specified hereinabove under (A) to (E) being 100 wt %, and the wt % in each case being based on the total weight of the component.
The compositions may be used as such, but are preferably used in minor amounts as an additive to produce non-tracking and/or high arc resistance and/or low flammability elastomers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The component (A) of the composition according to the invention can be any organopolysiloxane which is suitable for admixing with components (B) to (D) employed according to the invention. Component (A) is preferably an essentially linear diorganopolysiloxane terminated by triorganylsilyl groups, the organyl groups preferably being alkyl and alkenyl groups, most preferably alkyl groups. Examples of the alkyl groups are those specified below for radical R, the methyl radical being preferred. Examples of alkenyl groups are those specified below for radical R, the vinyl radical being preferred. The component (A) employed according to the invention can optionally, in addition to the diorganylsiloxane units, comprise further siloxane units such as monoorganosiloxy units or SiO
4/2
units.
The organopolysiloxane (A) preferably has a viscosity of from 500 to 20·10
6
mm
2
/s, most preferably from 500 to 100,000 mm
2
/s, in each case measured at 25° C. The organopolysiloxane (A) may be a single organopolysiloxane or a mixture of organopolysiloxanes.
The component (B), employed to achieve tracking resistance and arc resistance, is preferably titanium dioxide or zirconium dioxide only, whereas any of the abovementioned metal oxides can be used to achieve low flammability. Most preferably, the component (B) comprises titanium dioxide and zirconium dioxide, thereby preferentially affording organopolysiloxane elastomers which have both low flammability and high tracking resistance and arc resistance.
The metal oxides (B) preferably have a specific surface area (in accordance with BET), of from 5 to 60 m
2
/g, more preferably from 40 to 60 m
2
/g. Titanium dioxide is, in particular, fumed titanium dioxide prepared in the gas phase.
The organosilicon compounds (C) containing basic nitrogen bound to silicon via carbon are preferably those selected from units of the formula
Y
a
R
b
(OR
1
)
c
SiO
(4−a−b−c)/2
  (I),
where
R are identical or different and represent univalent hydrocarbon radicals having from 1 to 8 carbon atoms per radical,
R
1
are identical or different and represent alkyl groups having from 1 to 4 carbon atoms per radical,
Y are identical or different and represent univalent SiC-bound organic radicals containing basic nitrogen,
a is 0, 1, 2 or 3,
b is 0, 1, 2 or 3,
c is 0, 1, 2 or 3, with the proviso that the sum a+b+c≦4, and that the organosilicon compound comprises at least one unit where a differs from 0 and contains at most 10 silicon atoms.
The organosilicon compounds (C) employed according to the invention can either be silanes, i.e. compounds of formula (I) with a+b+c≦4, or siloxanes, i.e. compounds comprising units of formula (I) with a+b+c≦3. Preferably, the organosilicon compounds employed according to the invention are silanes.
Examples of hydrocarbon radicals R include alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, 2-ethylhexyl radical and butyl radicals; alkenyl radicals such as the vinyl and allyl radicals; cycloaliphatic hydrocarbon radicals such as cyclopentyl, cyclohexyl, and methylcyclohexyl radicals; aromatic hydrocarbon radicals such as the phenyl radical and xylyl radicals; alkaryl radicals such as tolyl radicals; and aralkyl radicals such as the benzyl radical.
Preferably, however, the hydrocarbon radicals R, especially if they are bound to silicon atoms to which basic nitrogen is likewise bound via carbon, are free from aliphatic multiple bonds, the radical R most preferably being the methyl radical.
Examples of radical R
1
are the alkyl radicals specified for radical R, methyl and ethyl radicals being preferred.
The radicals Y are preferably those of the formula
R
10
NHR
11
—  (II),
where
R
10
represents hydrogen, alkyl or cycloalkyl or aminoalkyl radicals having from 1 to 8 carbon atoms per radical, and
R
11
represents divalent hydrocarbon radicals free from an aliphatic multiple bond and having one carbon atom or 3 or 4 carbon atoms per radical.
The radical R
11
in particular is the radical —(CH
2
)
3
—.
Examples of radical R
10
are the cycloalkyl radicals specified for radical R and H
2
N(CH
2
)
3
—, H
2
N(CH
2
)
2
NH(CH
2
)
2
—, H
2
N(CH
2
)
2
—, (H
3
C)
2
NH(CH
2
)
2
—, H
2
N(CH
2
)
4
—, H(NHCH
2
CH
2
)
3
— and C
4
H
9
NH(CH
2
)
2
NH(CH
2
)
2
—.
Preferably employed as organosilicon compounds (C) comprising basic nitrogen bound to silicon via carbon are N-(2-aminoalkyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, N-(cyclohexyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyl-tris(trimethylsiloxy)silane and 1,2-bis[N-(2-aminoethyl)-3-aminopropyl]-1,1,2,2-tetramethyldisiloxane, particular preference being given to the use of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.
Preferably, the component (D) employed according to the invention represents those bis(alkynyl)platinum complexes which include phosphane groups or diene radicals as donor ligands.
Examples of the component (D) employed according to the invention include a) bis(alkynyl)bis(phosphane)platinum compou

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