Note: Descriptions are shown in the official language in which they were submitted.
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CURABLE SILOXANE COMPOSITIONS
This invention relates to siloxane compositions which
are curable to elastomers having reduced permeability to
gases, and to the use of such compositions in multiple-pane
insulating glass units.
Curable siloxane compositions have for many years
been employed in a variety of applications. One type of
curable siloxane composition has the ability to cure to an
elastomer at normal ambient or slightly elevated tempe-
ratures, either spontaneously on mixing the components or
as a result of exposure to moisture. Such compositions are
generally termed room temperature vulcanisable (or RTVs)
and they have been formulated into sealant materials having
excellent physical properties, adhesion to sub trates and
weatherability. Such properties, as well as the ability to
cure at normal ambient temperatures, have rendered the
materials particularly suitable for use in the construction
industry, for example in the sealing of glazed units to
masonry structures. Another application of the sealant
materials has involved their use as secondary, edge
sealants in the fabrication of multiple-pane insulating
glass units. According to earlier designs the units
contained dry air in the interior space and were sealed at
the periphery to prevent, as far as possible, the ingress
of atmospheric moisture and the resulting misting of the
glass panes. However, their use in the latter application
has been restricted by the high vapour permeability of the
conventional siloxane sealant materials. It has been
proposed in U.S. Patent 4,131,588 to reduce the rate of
water vapour transmission through certain siloxane sealant
compositions by the incorporation therein of at least 75
parts by weight of mica per 100 parts by weight of siloxane
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base polymer. It has been found that the inclusion of such
largP proportions of mica result in a composition which is
difficult to handle and which when cured has poor physical
properties. In addition more recent developments in the
insulated glazing art have been directed to improving the
thermal and sound insulating properties of the units and
now include filling the interior space with gases such as
argon and sulphur hexa~luoride. As a result of such
innovation the problem of achieving a satisfactory seal
becomes more the prevention of the egress of such gases
rather than the ingress of water vapour.
We have now discovered that a signif icant reduction
in the permeability of curable siloxane compositions to
gases such as argon and sulphur hexafluoride can be
attained by the incorporation of mica at much lower levels
than those proposed in U.S. Patent 4,131,588. The use of
such lower levels of mica represents a significant benefit
inasmuch as it reduces handling diPficulties and results in
a sealant having satisfactory physical properties.
Accordingly, this invention provides a room tempe-
rature vulcanisable composition comprising by weight (A)
100 parts of a curable polydiorganosiloxane having a
viscosity in the range from 150 to 100,000 mPa.s at 25~
and wherein the organic substituents attached to silicon
are selected from alkyl groups having from 1 to 10 carbon
atoms, aryl, alkaryl and aralkyl groups having from 6 to 8
carbon atoms and alkenyl groups having ~rom 2 to 8 carbon
atoms, at least 30% of the said substituents being methyl
groups, (B) a curing agent for polydiorganosiloxane (A) t
(C) from 5 to 45 parts of particulate mica wherein at least
75 percent by weight of the particles have an average
diameter of from 30 to 100 microns and an aspeck ratio in
the range from 25/1 to lOOtl, and ~D) at least 5 parts o~ a
reinforcing or extending filler.
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The invention also includPs a sealed multi-pane
insulating glass unit comprising at least two spaced glass
panes in which at least a part of the sealing means i~ the
product of curing the composition comprising (A) to (D) as
above defined.
The curable polydiorganosiloxanes (~) employed in the
compositions of this invention are those having a visco-
sity in the range from 150 to 100,000 mPa.s at 25C. The
organic substituents attached to the silicon atoms are
selected from alkyl groups having from 1 to 10 carbon
atoms, for example methyl, propyl, hexyl and decyl, alkenyl
groups having from 2 to 8 carbon atoms, for example vinyl,
allyl and hexenyl, and aryl, alkaryl and aralkyl groups
having from 6 to 8 carbon atoms, for example phenyl, tolyl
and phenylethyl. At least 30 percent o~ the total substi~
tuents should be methyl. Preferred from an economic stand
point are polydiorganosiloxanes in which substantially all
of the silicon-bonded substituents are methyl. However, it
has been found that the presence of larger substituents
such as phenyl can contribute to the reduction in gas
permeability. There~ore, where maximum reduction in perme-
ability is required the preferred polydiorganosiloxanes are
those having a proportion, preferably up to 75 percent of
the total, of larger substituents, the most pre~erred being
the polymethylphenylsiloxanes. As hereina~ter described
polydiorganosiloxanes (A) will contain, in addition to the
substituents hereinabove mentioned, silicon-bonded reactive
groups by means o~ which the desired room temperature
curing can be effected. Such groups may be, for example,
hydroxyl, alkoxy/ oximo or acyloxy and are normally
attached to the terminal silicon atoms of the polydiorgano-
siloxane.
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Component (B) of the compositions of this invention
is a curing agent which is effective in converting polydi-
organosiloxane (A) to the solid elastic state at normal
ambient or slightly elevated temperatures, usually about 15
to 30OC. Polydiorganosiloxane (A) and curing agent (B)
thus comprise a room temperature vulcanising system. A
variety of compositions based on such systems are well-
known in the art and any of these can be employed as the
basis of the compositions of the present invention.
Examples of such compositions are:
~i) vulcanisable organosiloxane compositions based
on an organosiloxane polymer having in the
molecule silicon-bonded oxime radicals, and/or
a mixture of an organosiloxane polymer having
silanol groups and a silane having at least 3
silicon-bonded oxime groups. Such compo-
sitions are described for example in U.K.
Patents 975 603 and 990 107;
(ii) vulcanisable organosiloxane compositions based
on an organosiloxane polymer having terminal
silicon-bonded acyloxy groups, and/or a
mixture of a silanol terminated organosiloxane
polymer and a silane having at least 3
silicon-bonded acyloxy groups per molecule.
Such compositions are described for example in
U.K. Patents 862 576, 894 758 and 920 036;
(iii) vulcanisable compositions based on an organo-
siloxane polymer having terminal silicon-
bonded amide or amino groups, and/or a mixture
of silanol-terminated organosiloxane polymer
and a silylamine or silylamide. Such
vulcanisable compositions are described for
example in U.K. Patents 1 078 214 and
1 175 794, and
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(iv) vulcanisable organosiloxane compositions based
on an organosiloxane polymer having in the
molecule silicon-bond2d alkoxy groups, and/or
a mixture of an organosiloxane polymer having
silanol groups with a silane having alkoxy
groups or a partial hydrolysis product of 6aid
silane, for example ethyl polysilicate.
Compositions of this type are described in
U.K. Patents 957 255r 962 061 and 841 825.
It will thus be understood by those skilled in the
art that the curing agent (B) may be a silane or siloxane
crosslinking agent, a catalyst such as an organo metal
compound, for example stannous octoate, dibutyltin
dilaurate or a titanium chelate, or the curing agent may
comprise both of these. The proportion of curing agent (B)
employed in the compositions will depend on the type of
curing reaction desired. For example when the curing agent
is a metal compound catalyst it will generally be employed
in catalytic quantities, that is from about 0.05 to 5 parts
by weight based on 100 parts of (A). When a silane or
siloxane crosslinking agent is employed it is normally
incorporated into the composition in an amount of from
about 0.2 to about 20 parts per 100 parts of ~A).
Although the compositions o~ this invention may
utilise any room temperature curing reaction the preferred
compositions are those o~ the so-called 2 part type, for
example those described under (iv) above which comprise a
mixture of a polydiorganosiloxane having terminal silanol
~-SioH) groups, an alkoxy silane or siloxane, for example
methyltrimethoxysilane, ethylpolysilicate or n-propylpoly~
silicate and a metal salt of a carboxylic acid, *or example
stannous octoate, dibutyltin dilauxate or dioctyltin
dilaurate. As is well known such compositions are normally
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prepared and stored as two packages, the packages being
mixed at the point of useO
Component (C) is a particulate mica wherein at least
75 perc~nt by weight of the particles have an average
diameter of from 30 to 100 microns and an aspect ratio in
the range from 25/1 to loO/1. For the purpose of this
invention the aspect ratio of the particles is defined as
the ratio of the average diameter to the average thickness
of the particles. Mica of the ~ype required for use
according to this invention may be obtained by wet or dry
processes. Not more than 45 parts of mica should be
present. It has been found that increasing the amount of
mica above this level provides no further advantage and can
result in a loss of the benefits obtained at lower
loadings.
The compositions of this invention contain at least 5
parts of a reinforcing and/or an extending filler in
addition to (C). Examples of such fillers include fume
silica, precipitated silica, crushed quartz/ aluminium
oxide, calcium carbonates, which may be of the ground or
precipitated types, microballoons and clays. The fillers,
particularly those such as the reinforcing silicas and
calcium carbonate may be treated, for example by coating
with organosilicon compounds or calcium stearate. It is
preferred that at least a part of the filler ~D) is calcium
carbonate. At least 5 parts and up to about 100 parts of
filler ~D) may be present depending on the physical or
other properties desired in the cured elastomer.
In addition to ingredients (A) to (D) the cura~le
compositions may optionally contain additives for modifying
the elastomer properties. For example there may be incor-
porated into the compositions plasticisers such as trior-
ganosilyl endstopped polydimethylsiloxanes, pigments such
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as titanium dioxide, carbon black and iron oxide,
additives, for example aminoalkyl- and epoxyalkyl- silanes
for improving the adhesion of the cured elastomer to glass~
metal or other substrates and low molecular weight polydi-
organosiloxanes as in situ filler treatments or for modi-
fying the Plastomeric modulus~ Preparation of the compo-
sitions can be effected by known mixing techniques. As
hereinbefore stated they may be formulated into the single
lo package or multiple package configurations depending on
type.
The compositions of this invention cure at ambient,
or slightly elevatedr temperatures to elastomers having
permeability to argon and other gases which is signifi-
cantly reduced in comparison with elastomers not containingthe specific mica filler (D). In addition, the ability to
achieve such a reduction at low loadings of mica enables
the retention of acceptable physical properties in the
elastomer. Such benefits render the compositions parti-
cularly adapted for use as primary or secondary sealants in
multi-pane insulating glass units.
The following Examples, in which the parts and
percentages are expressed by weight, illustrate the
invention. In the Examples the membrane permeability is
expressed in cm3 cm cm 2 sec. ~cm Hg) 1 x 10 10 units
Exam~le 1
Four base compositions were prepared by mixing
together
* Polydimethylsiloxane having a viscosity
of 12,000 mPa.s at 25C 100 parts
Treated CaC03 filler x
** Mica y
Hydroxyl-terminated polydimethylsiloxane
having a M.Wt of approximately 900 3 parts
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* A mixture of polydimethylsiloxanes having on
average more than one but less than two terminal
silicon-~ond~d hydroxyl groups per moleculer
** Wet ground, 32 micron particle size, 30/1 aspect
ratio.
The ~iller contents x and y were varied as follows:
x (Parks~ y (parts~
Base 1 80 20
Base 2 70 30
Base 3 55 45
Control100 0
Each of the bases (100 parts) was mixed with a
catalyst composition (6.5 parts) consisting o~ n-propyl-
orthosilicate (2.4 parts) and dibutyltin dilaurate (0.12
part) dispersed in a li~uid polydimethylsiloxane (4.0
parts). The catalysed compositions were poured into a
mould formed by two polyethylene sheets separated by a
spacer having a thickness of 0.5mm. The compositions were
allowed to cure for 7 days at laboratory ambient tempe-
rature (about 20C) and th~ resulting siloxane elastomer
memhranes removed -Erom the moulds.
The permeabilities of the membranes to argon were
measured employing a Brugger GDP permeability tester. The
physical properties of the cured catalysed bases were
measured on samples separately prepared ~or that purpose.
The results obtained were as follows:
Tensile Elongation
Permeability stren~th(MPa! at break(~L
Base 1 99 1.4 75
Base 2 75 1.5 67
Base 3 60 1.3 57
Control 320 1.8 170
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Example 2
The procedure of Example 1 was repeated except that
the mica component was replaced with the same quanti~ies of
a wet ground mica having a particle size of 100 micron and
an aspect ratio of 55/l. The bases were designated Bases
4, 5 and 6 respectively with increasing mica content, and
the results obtained were as follows:
Tensile Elongation
lo Permeability Strength(MPa) at break(%)
Base 4 108 1.5 95
Base 5 79 1.3 70
Base 6 64 1.5 75
ExamPle 3
When the procedure of Example 1 was repeated
employing a wet ground mica having a particle size of 70
micron and an aspect ratio of 100/1 the bases were desig-
nated respectively Bases 7, 8 and 9 and the following test
results were obtained:
Tensile Elongation
Permeability Strenqth(MPaL at break(%~
Base 7 90 1.3 64
Base 8 72 1.9 . 77
Base 9 59 2.1 66
Exam~le 4
The procedure of Example 3 was twice repeated except
that the polydimethylsiloxane component of the base was
replaced by a polyphenylmethylsiloxane having terminal
silanol groups and a viscosity of 12,000 mPa.s at 25C. In
one experiment the polyphenylmethylsiloxane was prepared ~y
the copolymerisation of low molecular weight polydimsthyl-
siloxanes and polyphenylmethylsiloxanes in a ratio such
that the ratio of total methyl groups to phenyl groups was
3/1. In the second experiment the polyphenylmethylsiloxane
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had a ratio of methyl groups to phenyl groups of 3/7.
Values ~or x and y were 34.5 and 14.75 respectively.
The cured membranes were tested for permeability to
argon. A value of 23 was obtained in the case o~ the 3/1
copolymer and 12 for the 3/7 copolymer.
ExamPle 5
Compositions according to the invention prepared as
described in Examples 1 to 4 herein were employed to manu-
facture multi-pane insulating glass units. When tested,
each of the units was found to comply with DIN 1286, part
2, which sets a maximum of 1% gas leakage rate per annum.
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