Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ 6~ ~
This invention is directed to silicone elastomer
~-~ compositions with improved self-extinguishing characteristics.
Although silicone elastomers have various
excellent characteristics, they are flammable. For this
reason, there has been a general demand for silicone
.
elastomers with excellent self-extinguishing characteristics.
This demand has become stronger recently with developments
in the electric and electronic equipment industries, which
are major consumers o~ silicone elastomers.
Various methods for imparting self-extinguishing
properties to silicone elastomers have already been
proposed. In some typical methods, platinum or platinum
compounds are added to the silicone elastomer. However9
because the addition of platinum or platinum compounds
alone is not sufficient to give self-extinguishing
characteristics to silicone elastomers, platinum use in
conjunction with other compounds has been attempted in
many studies. For example, titanium oxide or other metal
oxides, inorganic compounds, carbon black, azo compounds,
etc., are used with platinum or platinum compounds. While
.
these combinations certainly increase the self-extinguishing
properties, the increase is not sufficient, ~nd, at the
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same time, with such additions, the favorable characteristics
of silicone elastomers, such as heat resistance, physical
.;, :,-
properties, and electrical properties are decreased.
. . .
In order to solve these problems, the inventors
discovered a type of silicone composition which shows
improved self-extinguishing properties along with excellent
heat resistance, physical properties, and electrical
properties.
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This invention is related to self-extinguishing
silicone elastomer compositions which consist of: (a) 100
,.~
i parts by weight o~ a curable organopolysiloxane which
:,
contains organic groups directly bonded to silicon atoms,
which organic groups are selected individually from methyl,
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phenyl or vinyl groups such that there are an average of
.:
~ 1.98 to 2.02 such organic groups per silicon atom, the
:,,.
` vinyl groups are present in 0 to 2 percent and the phenyl
groups are present in 0 to 10 percent based on the number
,,
; 10 of organic groups in ~a); (b) 10-100 parts by weight of
" ~,
finely divided silica; (c) 10-100 parts per million of
: .
platinum based on the weight of (a); (d) 0.05-2.0 parts
~ by weight of carbon black; (e) 1-20 parts by weight of
- fumed titanium dioxide, and (f) 0.05-l.0 parts by weight of i~ a triazole compound.
The organopolysiloxanes used as component (a)
of this invention can be homopolymers, copolymers or
`; mixtures of these two, in which the degree of polymerizationof the repeating units such as dimethylsiloxane, methyl-
vinylsiloxane or methylphenylsiloxane is 200-5000 or,
preferably, 2,000-4,000. These organopolysiloxanes
have from 1.98 to 2.02 organic groups per silicon atom,
: `
;~ and the number of vinyl groups and phenyl groups in them
:: `
`~ represent 0-2% and 0-10%, respectively, of the total
:
number of organic groups. The terminating groups on
: `
this type of organopolysiloxane may be triorganosiloxy
`` groups, diorganomonohydroxysiloxy groups and diorgano-
; monoalkoxysiloxy groups. There is no particular restriction
; .~ -
; in this respect. Specific examples of such terminating
groups are: trimethylsiloxy, dimethylvinylsiloxy,
. .
methylvinylphenylsiloxy and dimethylhydroxysiloxy.
.
:
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;- Examples of component (b), the silica fillers
which are used in a finely divided -form, are -fumed silica,
.~ .
precipitated silica, quartz -fines and diatomaceous earth.
What is meant by "finely divided" for purposes of this
, ....
; invention is a particle size of from .001 to 50 microns.
They are the known fillers which are usually combined
with conventional silicone elastomers. Fillers with -
untreated surfaces, fillers whose surfaces have been
previously treated with organosilanes, organosiloxanes,
organosilazanes or other organosilicon compounds, or fillers
~ whose surfaces are treated at the time of the mixing with
i~/ the above-mentioned treating compounds are equally
acceptable.
:'
~he amount of silica filler which should be
added to component (a) should be 10-100 parts by weight
relative to 100 parts by weight of component (a). It
is especially desirable to use a powder whose average
~` particle diameter is .001-.05 micron in combination with
. a powder whose average particle diameter is 0.5-50
micron. When the amount of this type o-f filler is smaller
- than the above given range, the silicone elastomer,
prepared by the addition of organic peroxides followed
by a thermal vulcanization or a radiation vulcanization,
show decreased mechanical properties. On the other hand,
when the above-described levels are exceeded, the mixing
of the components is very difficult, and, the mechanical
properties of the silicone elastomers obtained after
- the vulcanization are decreased.
Component (c), platinum in the amount of 10-100
ppm or, preferably, 20-70 ppm, relative to component (a),
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as well as components (d), (e) and (f), is indispensible
for giving the self-extinguishing characteristics to the
silicone elastomers. Finely powdered platinum, finely
divided platinum supported on carriers such as alumina,
silica gel, asbestos, as well as chloroplatinic acid,
or complexes of chloroplatinic acid with alcohols, ethers,
aldehydes or vinylsiloxanes may be used as component (c).
` In order to produce silicone elastomers with
,.......
; self-extinguishing properties, the platinum or platinum
compounds as described above should be homogeneously
dispersed in the compositions of silicone elastomers
` before the compositions are vulcanized. In order to
. 1
achieve the homogeneous dispersion, they may be dissolved
or dispersed in organic solvents such as isopropyl alcohol,
ethanol, benzene, toluene, xylene, or in an organopolysiloxane
oil.
:....
~ Bxamples of carbon blacks that can be used as
;i~ component ~d) are acetylene black and furnace black. It
;': ;
is also desirable that these carbon blacks do not contain
sulfur. The proper amount to be added is 0.05-2.0
parts by weight to 100 parts by weight of component (a).
When the amount of the addition is below the
.::
` above-mentioned range, the desired improvement in the
self-extinguishing character of the vulcanized silicone
~ elastomers is not achieved~ If the amount of the addition
`` is above the range, the electrical properties of the product; are unfavorably affected.
~umed titanium dioxide whose average particle size
is smaller than 0.1 micron can be used as component (e).
It is added at a rate of 1-20, or, preferably, 3-10 parts
by weight per 100 parts by weight of component (a).
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Triazole compounds used as component (f) are
an especially important component in this invention.
Typical examples oE such compounds are 1,2,3-triazoles,
1,2,4-triazoles, and benzotriazoles.
Speci-fic examples of 1,2,3-triazoles and their
,''
derivatives are: l-methyl-1,2,3-triazole, 1-phenyl-1,2,3-
triazole, 4-methyl-2-phenyl-1,2,3-triazole, 1-benzyl-1,2,3-
triazole, 4-hydroxy-1,2,3-triazole, l-amino-1,2,3-triazole9
l-benzamide-4-methyl-1,2,3-triazole, 1-amino-4,5-diphenyl-
1,2,3-tr azole, 1,2,3-triazole-4-aldehyde, 2-methyl-1,2,3-
..
triazole-4-carboxylic acid, 4-cyano-1,2,3-triazole and
5-hydroxy-1,2,3-triazole-l-yl acetic acid.
i Specific examples of benzotriazoles and their
derivatives are: l-methylbenzotriazole, 5,6-dimethyl-
benzotriazole, 2-phenylbenzotriazole) l-hydroxybenzo
..,
triazole and methylbenzotriazole-l-carboxylate.
Specific examples of 1,2,4-triazoles and their
~ derivatives are: l-methyl-1,2,~-triazole, 1,3-diphenyl-
: 1,2,4-triazole, 5-amino-3-methy1-1,2,4-triazole, 3-mercapto-
.,
1~2,4-triazole, 1,2,4-triazole-3-carboxylic acid, l-phenyl-
1,2,4-triazole-5-one and l-phenyl-urazole. -
Of all the compounds mentioned above, the
benzotriazoles are the most desirable as component (f).
Component ~f), like component (c), should be homogeneously
....
dispersed in the silicone elastomers in order to produce
a product with self-extinguishing properties. For -
,: . . ~ .
achieving this objective, ~) may be used as a solution
` in an organic solvent such as isopropyl alcohol, ethanol,
benzene, toluene or xylene. When component (f) is present
. .
~:~ 30 with the above-mentioned components (c), ~d) and (e)
..
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:
during the vulcanization o-f the compositions, the cured
silicone elastomers show strikingly improved self-
extinguishing characteristics without deterioration of
.
the good heat resistance, physical properties and
electrical properties of the ordinary thermosetting type
silicone elastomers. The amount of the addition of
component (f) should not be above or below the range
; of 0.05-1.0 parts by weight per 100 parts by weight
of component (a). Although this component itself can
not act to significantly irnprove the self-extinguishing
properties of the silicone elastomers, it synergistically
, ;,
` ~ improves the self-extinguishing character of the product
.; .,
~ when it is used with components (c) 9 (d) and (e) in the
.:. . ..
`` above-mentioned ratios.
,.,
:`~ The self-extinguishing silicone elastomer
; ~ compositions o~ this invention can be produced by a
~,~..,;
homogeneous mixing of the above-described components
(a)-(f) with, two-roll mills, kneader mixers or any
other suitable means which gives a homogeneous mixture.
In order to obtain the improved self-extinguishing silicone
elastomer without sacrificing the good heat resistance,
physical properties and electrical properties of ordinary
thermosetting silicone elastomers, the above-mentioned
compositions are cured by exposure to radiation with a G
value of ~.5-3.0, or mixed with some suitable known
organic peroxide selected from benzoyl peroxide,
2,4-dichlorobenzoylperoxide, 2,5-bis(t-butylperoxy)-2~5-
dimethylhexane, dicumyl peroxide, p-dichlorobenzoyl
.1.,:,
~ peroxide, di-t-butylperoxide or t-butylperben~oate,
,~
~ 30 depending on the uses of the products. The peroxides
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.. ..
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:`:
; are combined with the above composition on a two-roll
mill and the mixture is thermally cured at 100-450C.
: for about 20 seconds to an hour. If necessary, a post-curing
can be carried out. The G value is a measure of efficiency
of the radicals in a radiation treatment. G-value is
.
the number of cross-links per 100 electron-volts of
absorbed energy. A typical value for a dimethylsiloxane
polymer having a viscosity of 10,000 cs. at 25aC., is 1.47.
.. ~ ...................................................................... .
The self-extinguishing silicone elastomer
composition of this invention may contain organopolysiloxanes
- other than those defined as component ~a) of this invention,
`~` or may contain organosilanes if desired, as long as the
;; organopolysiloxane contains essentially no hydrogen bonded
to silicon atoms. When hydrogen atoms bonded to silicon
., .
` atoms are present in the composition, the self-extinguishing
character decreases, inerior electrical properties and
;~` workability result due to foaming, and other decreases in
'!'~'' quality result. The composition of this invention may
-i.
, contain the usual nonsiliceous fillers, heat resistance -
..~.
agents, pigments and other additives. -
, The self-extinguishing silicone elastomers of
this invention are quite useful as self-extinguishing
; elastomer materials for the electric, electronic and
i machine industries.
This invention will be shown in greater detail
with the experimental examples below. In the examples,
; "part" and "%" are expressed on the basis of weight. In
` the examples, the testing of the self-extinguishing
character was conducted according to the fire retardancy
test specified in the Underwriters Laboratory test 94
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_7
. .
., .
..
: -
:`~
~;~ (UL-94) ~vertical). In this kest, the silicone elastomer
; obtained by the curing of the composition with radiation
or heating and peroxide is cut to a sample size o-f
12.7 x 1.27 x 0.2 cm to use as a test specimen. The
specimens were hung vertically in a place where there
were no air drafts, and was twice exposed to a 1000 BTU/ft3
~.,
gas burner flame, ten seconds each time. In each case
the time (seconds) required for the flame to be self-
:
extinguished was measured. 5 specimens were
- 10 prepared for each sample, and each specimen was exposed
" twice to the flame. The mean value of the total 10
: .
exposures was considered to be the self-extinguishing
character ~in units of seconds)
. . .
Example l
100 parts of organopolysiloxane uncured rubber
(degree of polymerization = 3,000), consisting of 99.8
......
mol% dimethylsiloxane units and 0.2 mol% methylvinylsiloxane
units, 5 parts of dimethylpolysiloxane ~degree of
polymerization = 10) having hydroxyl groups at both ends,
,; ~
20 parts of fumed silica with a specific surface area o~
200 m2/g were mixed homogeneously in a mill. This mixture
then was heat treated at 150C. for 2 hours and was used
!
as the base compound. To this base compound, 50 parts of
quartz powder, 5 parts of fumed titanium dioxide, 0.2
part of a 3% isopropyl alcohol solution of chloroplatinic
acid and 0.1 part of carbon black were added. To this
mixture, a 30% solution of benzotriazole in isopropyl
alcohol was added in various volumes so that the amount
of triazole addition could be varied. Thereafter, each
mixture was homogeneously blended with a two-roll mill.
'.,',~
; -8-
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.. . .
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; Af~er a further addition of 0.5 parts of 2,5-bis(t-butyl-
peroxy)-2,5-dimethylhexane paste (purity = 50%), the
composi-tion was mixed again with a two-roll mill to
: .
prepare a composition for curing.
This composition was pressed into a sheet at
; 160C. under 15 kg/cm2 pressure for 10 minutes. The
` sheet was then thermally cured in a hot-air circulating
oven at 200C. ~or 4 hours to produce a silicone elastomer.
,. . .
The results of the measurement of the self-extinguishing
charac~er of the elastomer product are shown in Table I.
Example 2
. ,
; .. ,:i
To 100 parts of the base compound used in ~ -
` Example 1, quartz powder, fumed titanium dioxide, a 3%
~ isopropyl alcohol solution of chloroplatinic acid,
;: carbon black, a 30% isopropyl alcohol solution of
,.. .
benzotriazole and 2,5-bis(t-butylperoxy)-2,5-dimethyl-
....
hexane, were added in various ratios as shown in Iable II,
and mixed with a two-roll mill. The sel-f-extinguishing
i`, ;
character o the products was tested as described in
Example 1.
In addition, silicone elastomers as controls
; were prepared with chloroplatinic acid as the indispensable
component and, in addition, fumed titanium dioxide, carbon
black and benzotriazole. The thus prepared control products
were also subjected to the self-extinguishing test.
The results for both experimental and comparison
samples are shown in Table II. -
... .
The sample of Experiment No. 3 proved to be
i s~rikingly eficient.
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