Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2047303
FLUORORUBBER COMPOSITIONS ERHIBITING IMPROVED WORKABILITY
AND MECHANICAL PROPERTIES
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The present invention relates to fluororubber
compositions. More particularly, this invention relates
to peroxide-curable fluororubber compositions exhibiting
improved processability during roll milling and
acceptable physical properties at temperatures below 0
degrees centigrade.
Due to their excellent mechanical properties,
heat resistance, oil resistance, and chemical resistance
fluororubbers are used in a wide range of industrial
applications. One shortcoming of this type of rubber is
the poor. workability or processability of curable
compositions on roll-type rubber mills. In addition,
cured fluororubbers typically exhibit relatively poor
mechanical properties at temperatures below zero degrees
Centigrade.
The present inventors have discovered that when
a f.luororubber is combined with an organopolysiloxane gum
and an epoxy-substituted organoalkoxysilane the
shortcomings associated with cured and uncured
fluororubber compositions previously available are
eliminated without adversely affecting other desirable
properties of the unmodified fluororubber. The present
invention is based on this discovery.
An objective of this invention is to provide a
fluororubber composition which prior to curing exhibits
excellent workability on a roll mill and yields a cured
rubber exhibiting acceptable low-temperature mechanical
properties of the cured material.
2 200730 3
The objective of this invention is achieved by
blending the fluororubber with a peroxide-curable
organopolysiloxane gum, an epoxy-substituted
organoalkoxysilane, a reinforcing filler and an amount of
an organic peroxide sufficient to cure both the
fluororubber and the gum.
Figure 1 of the drawing is a plot of retraction
as a function of temperature for a cured fluororubber
sample of this invention and a control sample. The values
were obtained using ASTM test procedure D 1329-79.
The present invention provides a fluororubber
composition comprising
(A) 100 parts by weight of a peroxide-curable organic fluoro-
rubber,
(B) 1 to 60 parts by weight of a peroxide-curable organopoly-
siloxane gum,
(C) 0.1 to 30 parts by weight of an epoxy group-containing
organoalkoxysilane or a partial hydrolysis product thereof,
(D) 1 to 60 parts by weight of a reinforcing filler, and
(E) as the curing agent, an amount of an organoperoxide
sufficient to cure said fluororubber and said gum.
The fluororubber (Component A) portion of the
present compositions includes those fluororubbers having
a fluorine-containing organic polymer as the base
component and which cure in the presence of an
organoperoxide to yield a rubbery elastic material.
Fluororubbers are described, for example, in a Japanese
language publication whose translated title reads
"Compendium of Synthetic Rubber Processing Technology;
Fluororubber/Silicone Rubber" written by Yuzuru Komeya
et al., and published by Kabushiki Kaisha Taisei-sha.
2007303
3
Examples of suitable organic fluororubbers
include but are not limited to copolymers of vinylidene
fluoride with chlorotrifluoroethylene,
pentafluoropropene, or~hexafluoropropene.
The organopolysiloxane gum (Component B) of the
present compositions'can be any of the high-molecular
weight organopolysiloxanes typically used as the base
component of gum-type silicone rubbers. No specific
restrictions apply to these organopolysiloxanes so long
as they exhibit rubbery elasticity upon curing. It is
generally preferred that the gum exhibit a plasticity
number of at least 100. Plasticity can be determined
using ASTM test method D 926.
Examples of suitable organopolysiloxane gums
include but are not limited to .
trimethylsiloxy-terminated dimethylsiloxane-
methylvinylsiloxane copolymers,
dimethylvinylsiloxy-terminated dimethylpolysiloxanes,
dimethylvinylsiloxy-terminated dimethylsiloxane-
methylvinylsiloxane copolymers,
trimethylsiloxy-terminated 3,3,3-trifluoropropylmethyl-
siloxane-methylvinylsiloxane copolymers,
dimethylvinylsiloxy-terminated 3,3,3-trifluoropropyl-
methylsiloxane-dimethylsiloxane copolymers, and
hydroxyl-terminated 3,3,3-trifluoropropylmethylsiloxane-
methylvinylsiloxane copolymers.
x
4 200730 3
Organopolysiloxanes wherein at least a portion of the
silicon atoms are bonded to a 3,3,3-trifluoropropyl
radical are preferred for use in the present
compositions.
Too low a concentration of component B will not
significantly improve the poor low-temperature mechanical
strength exhibited by the fluororubber, while an excess of
component B results in a decrease in some desirable
properties of the unmodified fluororubber. Accordingly,
the concentration of component B should be from 1 to
about 60 parts by weight, preferably from 1 to about 30
parts by weight, per 100 parts by weight of component A.
The presence of an epoxy-containing
organoalkoxysilane (Component C) or a partial hydrolysis
product of such a silane is not only required to achieve
a homogeneous mixture of components A and B, but is also
essential for optimizing the advantages of the present
invention achieved by blending components A and B.
Examples of component C include but are not
limited to gamma-glycidoxypropyltrimethoxysilane,
gamma-glycidoxypropyl-triethoxysilane,
gamma-glycidoxypropylmethyldimethoxysilane, and
beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
The beneficial effects imparted by this
component are not evident when it is present in too low a
concentration, while an excess of this component
adversely affects the workability of the curable
composition during roll milling. Accordingly, the
concentration of component C in the curable composition
should be from 0.1 to 30 parts by weight, preferably from
0.5 to 15 weight, parts per 100 weight parts component A.
In addition, it is also preferred that the concentration
of component C fall within the range of from 0.3 to 10
parts by weight per 100 parts by weight of component B.
200730 3
Partial hydrolysis products of alkoxysilanes,
including those suitable for use as component C are well
known to those skilled in the chemistry of organosilicon
compounds. A portion ox all of component C in the
present compositions can be replaced by its partial
hydrolysis product.
The presence of a reinforcing filler (Component
D) is responsible for the excellent mechanical properties
of the present compositions following curing. The
reinforcing filler can be any of those typically used in
fluororubber and/or silicone rubber compositions, and no
specific restriction apply to this material. Useful
reinforcing fillers include but are not limited to
dry-method silica, also referred to as fume silica,
wet-method silica, also referred to as precipitated
silica, and carbon black. The concentration of
reinforcing filler is typically from 1 to 60 parts by
weight per 100 parts of fluororubber (component A).
The present compositions are cured using an
organoperoxide (Component E) as the curing agent or
catalyst. No specific limitations apply to the
organoperoxide as long as it is capable of bringing
about the curing of both the fluororubber and the
organopolysiloxane gum. Useful peroxides include but are
not limited to benzoyl peroxide, 2,4-dichlorobenzoyl
peroxide, dicumyl peroxide, and 2,5-dimethyl-2,5-di(t-
butylperoxy)hexane. The concentration of peroxide is
typically from 0.1 to 10 percent by weight based on the
weight of component A.
20030 3
6
The fluororubber compositions of the this
invention can be easily prepared by simply mixing the
aforementioned components A, B, C, D, and E to
homogeneity using any Rf the known techniques, which
include but are not limited to blending using a two- or
three-roll rubber mill or dough-type mixer.
Examples
The present invention will be explained in
greater detail through the following illustrative
examples. Unless otherwise specified all parts and
percentages are by weight and viscosity values are
determined at 25 degrees Centigrade.
Example 1
70 Parts of a vinylidene fluoride-based
fluororubber available as "Dai-el G901"' from Daikin Kogyo
Company, Limited, 20 parts of a wet-method (precipitated)
silica with a specific surface area of 200 m2/g, 30 parts
of a hydroxyl-terminated 3,3,3-trifluoropropyl-
methylsiloxane-methylvinylsiloxane copolymer gum, and 2
parts of gamma-glycidoxypropylmethyldimethoxysilane were
blended to homogeneity in a kneader-type mixer. 0.75
Parts 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 1.25
parts triallyl isocyanurate were added to the resulting
mixture followed by blending of the ingredients on a
two-roll mill to yield a curable fluororubber composition
of this invention.
The fluororubber composition did not stick to
the surface of the two-roll mill during blending, and
the workability of the composition on the roll was
excellent, as evidenced by the fact that a homogeneous
composition was prepared in 12 minutes of milling time.
* Trademark
7 X00730 3
The fluororubber was aired by heating at 170
degrees Centigrade. The hardness, tensile strength,
elongation, modulus and tear strength of the fluororubber
following curing were measured in accordance with the
procedures described in Japan Industrial Standards (JIS)
K 6301, which is available in an English translation. The
results of these measurements are reported in Table 1.
The low-temperature retraction of an elongated
sample was measured according to the method (TR test)
described in ASTM test procedure D-1329, and these
results are plotted on the graph represented in the
accompanying drawing identified as Figure 1.
For comparison, a fluororubber composition
(Comparison Example 1) was prepared as described in the
first part of this example, but omitting the
3,3,3-trifluoropropylmethylsiloxane- methylvinylsiloxane
copolymer gum. A fluororubber composition (Comparison
Example 2) was also prepared as described in the
preceding section of this example above, but omitting the
gamma-glycidoxypropylmethyldimethoxysilane. Finally, a
fluororubber composition (Comparison Example 3) was
prepared as described in this example, but omitting both
the 3,3,3-trifluoropropylmethyl-
siloxane-methylvinylsiloxane copolymer and the
gamma-glycidoxypropylmethyldimethoxysilane. The
mechanical properties of these compositions were measured
as described in the preceding section of this example,
and these results are also reported in Table 1 as
Comparison Examples 1, 2, and 3.
The accompanying drawing identified as Figure 1
plots the results of the low temperature retraction (TR)
test conducted on 1) the fluororubber composition of the
present invention and 2) the composition identified as
Comparison Example 3.
200730 3
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2007303
Example 2
The following ingredients were introduced into
a kneader extruder and mixed to homogeneity: 70 parts
vinylidene fluoride-based fluororubber ("Dai-el G901"'~ from
Daikin Kogyo Company, Limited), 30 parts
dimethylvinylsiloxy=terminated
3,3,3-trifluoropropylmethylsiloxane-dimethylsiloxane
copolymer gum (plasticity no. - 300), 20 parts
wet-method silica with a specific surface area of 200
m2/g, and 2 parts gamma-glycidoxypropyltrimethoxysilane.
The operating conditions of the
kneader/extruder were as follows:
kneading temperature (temperature at the center of the
kneader/ extruder) - 100 degrees Centigrade,
temperature at extrusion discharge = 180 degrees
Centigrade,
extrusion rate = 1 kg/hour.
0.75 Parts
2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 1.25 parts
triallyl isocyanurate were subsequently added to the
mixture obtained from the kneader/extruder, and this
mixture was blended on a two-roll mill to yield a
curable fluororubber composition. The composition was
then cured and the mechanical properties of the
fluororubber measured using the procedures described in
Example 1. The results are reported in Table 2.
* Trademark
.:
l0 200730 3
TABLE 2
Specific gravity 1.689
Hardness 78
Tensile strength, kg/cmz 147
Elongation, % 264
100 modulus, kg/cmz 57
Tear strength, kg/cm 36
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