Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2003-01-08
2004-05-18
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...
C524S451000, C524S493000, C524S496000, C524S588000, C524S790000, C524S789000, C524S730000, C524S731000, C524S714000, C524S791000, C524S862000, C528S015000, C528S031000, C528S032000
Reexamination Certificate
active
06737458
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to silicone compositions which comprise inactive fillers and nitrogen compounds which can be crosslinked to provide elastomers, and to the silicone elastomers obtainable therefrom.
2. Background Art
As is known, the oil resistance of silicone elastomers can be improved by addition of, for example, quartz or talc. U.S. Pat. No. 4,131,588 describes mica- and optionally talc-containing addition- and condensation-crosslinking silicone compositions having reduced gas permeability. European published application EP-A-953675 describes the use of talc as filler in textile coating compositions. The condensation- or addition-crosslinking silicone elastomers have reduced friction owing to the talc. These compositions are principally employed in airbag coating.
However, talc and other non-reinforcing fillers cause a considerable weight loss in silicone compositions or silicone elastomers at temperatures above 100° C. It has been found, for example, that talc and quartz cleave the siloxane chain at elevated temperatures and thus catalyze the formation of cyclic, volatile siloxane compounds. This results in the heat stability of the silicone compositions and silicone elastomers being unsatisfactory at temperatures above 100° C.
SUMMARY OF THE INVENTION
An object of the present invention was to provide silicone compositions and silicone elastomers which, despite being filled with non-reinforcing fillers, have improved heat stability. This and other objects are met by peroxidically crosslinkable or addition crosslinkable silicone compositions which can be crosslinked to form elastomers, these crosslinkable compositions containing both a non-reinforcing filler and a nitrogen-containing compound.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The invention thus relates more particularly to silicone compositions which can be crosslinked to give elastomers and which comprise the constituents
(A) from 20 to 99% by weight of a polyorganosiloxane containing at least two alkenyl groups per molecule and having a viscosity at 25° C. of from 0.1 to 500,000 Pa.s,
(B) from 1 to 80% by weight of a non-reinforcing filler having a mean particle size of from 0.1 to 200 &mgr;m and a specific surface area of <100 m
2
/g,
(C) a crosslinking component selected from
(C1) an organic peroxide and
(C2) an organosilicon compound containing at least two SiH functions per molecule in combination with a hydrosilylation catalyst, and
(D) a nitrogen compound which is selected from amino, ammonium and amido compounds and nitrogen-containing organosilicon compounds.
The inventors have surprisingly discovered that the addition of amino or ammonium compounds to silicone compositions which can be crosslinked to give elastomers drastically reduces cyclization and thus weight loss at elevated temperatures and therefore enables more stable mechanical properties to be achieved on exposure to heat.
The composition of the polyorganosiloxane (A) containing alkenyl groups preferably conforms to the average general formula (1)
R
1
x
R
2
y
SiO
(4-x-y)/2
(1),
in which
R
1
is a monovalent, optionally halogen- or cyano-substituted C
1
-C
10
-hydrocarbon radical containing aliphatic carbon—carbon multiple bonds which is optionally bonded to silicon via a divalent organic group,
R
2
is a monovalent, optionally halogen- or cyano-substituted C
1
-C
10
-hydrocarbon radical containing no aliphatic carbon—carbon multiple bonds which is bonded via SiC,
x is a non-negative number such that at least two radicals R
1
are present in each molecule, and
y is a non-negative number such that (x+y) is in the range from 1.8 to 2.5.
The alkenyl groups R
1
are able to undergo an addition reaction with an SiH-functional crosslinking agent. Use is usually made of alkenyl groups having from 2 to 6 carbon atoms, such as vinyl, allyl, methallyl, 1-propenyl, 5-hexenyl, ethynyl, butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl or cyclohexenyl groups, preferably vinyl or allyl groups. The radicals R
1
can be bonded in any position of the polymer chain, in particular to the terminal silicon atoms.
Divalent organic groups via which the alkenyl groups R
1
can be bonded to silicon in the polymer chain consist, for example, of oxyalkylene units, such as, but not limited to, those of the general formula (2)
—(O)
m
[(CH
2
)
n
O]
o
— (2),
in which
m has a value of 0 or 1, in particular 0,
n has a value of 1 to 4 in particular 1 or 2, and
o has a value of from 1 to 20, in particular from 1 to 5, including oxyalkylene moieties where the repeating methylene groups bear lower alkyl substituents. The oxyalkylene units of the general formula (2) are bonded on the left to a silicon atom.
Examples of unsubstituted radicals R
2
are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl or 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, or decyl radicals such as the n-decyl 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 and cycloheptyl radicals, norbornyl radicals and methylcyclohexyl radicals; aryl radicals such as the phenyl, biphenylyl and naphthyl radicals; alkaryl radicals such as o-, m- and p-tolyl radicals and ethylphenyl radicals; and aralkyl radicals such as the benzyl radical, and the alpha- and &bgr;-phenylethyl radicals.
Examples of substituted hydrocarbon radicals R
2
are halogenated hydrocarbons, such as the chloromethyl, 3-chloropropyl, 3-bromopropyl, 3,3,3-tri-fluoropropyl and 5,5,5,4,4,3,3-hexafluoropentyl radicals and the chlorophenyl, dichlorophenyl and trifluorotolyl radicals.
R
2
preferably has from 1 to 6 carbon atoms. Particular preference, is given to methyl and phenyl.
Constituent (A) may also be a mixture of polyorganosiloxanes which contain various alkenyl groups and which differ, for example, in the alkenyl group content, the nature of the alkenyl group or structurally. While it is possible for some of the molecules of constituent (A) to contain less than 2 unsaturated groups, on average, at least two of such groups should be present per molecule.
The structure of the polyorganosiloxanes (A) containing alkenyl groups can be linear, cyclic, or branched. The content of tri- and/or tetrafunctional units resulting in branched polyorganosiloxanes is typically very low, preferably at most 20 mol %, and in particular at most 0.1 mol %.
Particular preference is given to the use of polydimethylsiloxanes containing vinyl groups whose molecules conform to the general formula (3)
(ViMe
2
SiO
1/2
)
2
(ViMeSiO)
p
(Me
2
SiO)
q
(3),
where the non-negative integers p and q satisfy the following relations: p≧0, 50<(p+q)<20,000, preferably 200<(p+q)<1000, and 0<(p+1)/(p+q)<0.2.
The viscosity of the polyorganosiloxane (A) at 25° C. is preferably from 0.5 to 100,000 Pa.s, in particular from 1 to 2000 Pa.s. The silicone compositions preferably comprise from 30 to 80% by weight, more preferably from 35 to 75% by weight, of polyorganosiloxane (A), and preferably constitute neat compositions optionally containing organic solvents, but are preferably not in the form of aqueous dispersions.
Examples of the non-reinforcing filler (B) are mineral and/or organic fillers. Examples of non-reinforcing fillers (B) are quartz, for example as quartz flour, talc, diatomaceous earth, clays, chalk, lithopones, carbon blacks, graphite, metal oxides, metal carbonates, metal sulfates, metal salts of carboxylic acids, metal dusts, fibers, such as glass fibers and plastic fibers, and plastic powders. Preference is given to talc and quartz. The fillers (B) may also have been surface-modified, for e
Birneder Richard
Woerner Christof
Brooks & Kushman P.C.
Moore Margaret G.
Wacker-Chemie GmbH
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