Note: Descriptions are shown in the official language in which they were submitted.
209~277
Mixture capable of free radical vulcanization on ~he
basis of fluorine-containing rubber and acrvlate rubber
Fluorine-containing rubbers (FKM) based on vinylidene
~ fluoride, hexafluoropropene and optionally tetrafluoro-
ethylene yield vulcanized materials with satisfactory
mechanical properties and high resistance to heat, oil,
ozone and irradiation. Thanks to these characteristics,
fluorine-containing rubbers have opened up areas of
application into which no other type of rubber has been
able to penetrate in the past. However, fluorine-con-
taining rubbers have the considerable disadvantage that
the vulcanized materials possess extremely poor flexi-
bility at low temperatures. In this respect fluorine-
containing rubbers are far inferior to commercial
acrylate and silicone rubbers, which, as regards hea~ageing and ozone resistance! are closest to ~he flu-
orine-containing rubbers. A further disadvantage is the
low degree to which fluorine-containing rubbers can be
filled with reinforcing fillers. Highly ac~ive fillers
give rise to poor processing characteristics, i.e. they
impar~ a high Mooney viscosity ~o the rubber. Hence,
such fillers as are added to fluorine-containing rubbers
are predominantly of inactive type or fillers of low
activity only, said fillers being added in a proportion
of preferably up to 30 parts by weight, and rarely up
to 60 parts by weight, in relation to 100 parts by
weiaht of the fluorine-containing rubber.
~5
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An improvement in ~he low temperature flexibility, the
amount of filler which could be added to, and the pro-
cessability of a fluorine-con~aining rubber composition
should be achievable by blending the said fluorine-con-
taining rubbers with other, cheaper rubbers. In order
~o achieve these enhancements in properties, it is
necessary ~hat the blending partner be finely and evenly
dis~ributed in the fluorinated rubber. Furthermore, a
homogeneous co-vulcanization is necessary in order to
achieve synergy as regards the mechanical properties of
the co-vulcanized composition, i.e. in order that the
profile of characteristics of the vulcanized blend
combines the desirable characteristics of the individual
blend par~ners: such desired blending of the fluorine-
containing rubbers with other blending partners cannot
however normally be achieved.
As regards the potential blending characteristics,
fluorine-containing rubbers and acrylate rubbers appear
to be excellent blending partners.
There have already been proposals to the effect that
both acrylate rubber and fluorine-containing rubbers
should be vulcanized with ~he aid of bisamine. Whereas
this enables an acceptable profile of mechanical
characteristics to be achieved, the ageing character-
~ istics, especially in aggressive oils, of these rubbersvulcanized with the aid of bisamine are inferior (Rubber
Chem. Technol. 63 (1990) 516-522).
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20~0277
Other cross-linking systems common with acrylate rubbers
are not compatible with those of fluorine-containing
rubbers. In the process of co-vulcanization there are
always gradients in cross-linking density resulting in
poor mechanical characteristics (.e.g. low ultimate
~ensile strength values).
Peroxide cross-linking is a vulcanizing system which in
the case of fluorine-containing rubbers resultsin
especially high-grade vulcanization. For a mixture with
a rubber not containing fluorine (e.g. acrylate rubber)
to be sui~able for co-vulcanization, the rubber not
containing fluorine must also be capable of peroxidic
cross-linking, and its reactivity in regard to the
cross-linking system must be similar to that of the
fluorine-containing rubber. Peroxidic vulcanization of
the rubber not containing fluorine by abstraction of
atoms or molecule groups which can be easily split off
(e.g. H-abstraction) generally presupposes more
stringent vulcanization conditions than are necessary
with fluorine-containing rubbers and is frequently
accompanied by chain termination and decay. Special
acrylate-containing rubbers capable of co-vulcanization
with fluorine-containing rubbers are copolymers con-
taining conjugated dienes capable of 1,4-polymeriza-
tion such as butadiene, isopropene, etc., and are
mentioned., e.g., in EP-A 163 971 and US-A 4 251 399.
However, such rubbers are subject to the disadvantage
of low ageing stability owing to the double bonds
remaining in the backbone of the polymer chain, the
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20~77
proportion of such double bonds being reducible only
in par~ by hydrogenation. When mixing soluble rubbers
based on acrylate, i.e. rubbers in which cross-linking
has not taken place, with fluorine-containing rubbers
it is disadvantageous that heterogeneous phases are
formed, the particle size distributions of which are
difficult to reproduce and which may, in addition,
change again in the process of cross-linking.
EP-A 424 347 and 424 348 suggest dispersing, in a first
stage, a non-cross-linked copolymer based on ethyl
acrylate in the fluorine-containing rubber and to
effect, in a second stage, dynamic vulcanization by
means of a vulcanization system specific to the acrylate
rubber. The fluorine-containing rubber is subjected to
peroxide vulcanization in a third stage. This gives
rise to a true solid dispersion of vulcanized acrylate
rubber particles by way of dispersed phase within the
vulcanized fluorine-containing rubber by way of con-
tinuous phase. Interpenetration of the blending partners
is not possible. Moreover, owing to the different vul-
canization systems, the matrix is only inadequately
coupled with the dispersed phase. With these mixtures
which have been dynamically vulcanized in two stages the
level of the mechanical characteristics in considerably
poorer than with pure vulcanized fluorine-containing
rubber.
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2090~77
I~ has now been found ~hat considerablv bet~er mu~ual
interpenetration and coupling of fluorine- and acrylate-
containing rubbers can be achieved if use is made, by
way of acrylate rubber. of an acrylate copolymer con-
taining 0.05 to 5 w~.-% of copolymerized units of a
compound con~aining at least 2 but preferably at least
3 double bonds which readily lend themselves to polymer-
ization. The acrylate copolymers are used in the formof partly cross-linked particles with particle diameters
from 60 to 800 nm. According to M. Hoffmann et al.,
Polymeranalytik I and II, Georg-Thieme-Verlag, Stuttgart
1977, the partial cross-linking is characterized by
determining the gel content. The gel contents of the
acrylate copolymer (acrylate rubber) are preferably
within the range between 20 and 99 wt.-%. The swelling
index as measured in dimethyl formamide is prefer-
ably higher than lO.
Accordingly, it is the obJect of the present invention
to provide rubber mixtures capable of vulcanization by
radicals and containing 35 to 98 parts by weight of a
fluorine-containing rubber capable of peroxidic vulcan-
ization and 2 to 65 parts by weight of an acrylate rub-
ber as well as optionally vulcanization aids, processing
aids and fillers. which are characterized in that the
acrylate rubber is a partly cross-linked acrylate rubber
with gel contents between 20 and 99 wt.-% wi~h particle
diameters (d50-values) from 60 to 800 nm.
The mixture should preferably contain 45 to 95 oarts bv
weight of fluorine-containing rubber and 5-55 parts by
weight of acrylate rubber.
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The gel content of the acrylate rubber should preferably
amount to between 40 and 98 wt.-% and in particular
between 50 and 95 wt~-%
The particle diameter of the partly cross-linked
acrylate rubber is preferably between 80 and 600 nm, and
particulary prefered not larger than 350 nm.
Suitable fluoroelastomers capable of psroxidic cross-
linking are such as contain the units of vinylidene
fluoride and at least one further fluoroolefin which can
be copolymerized therewith. The other fluoroolefin may
be tetrafluoroethylene, chlorotrifluoro-ethylene,
hexafluoro-propene, hexafluoro-isobutylene, perfluoro-
alkyl-vinyl ether, etc, The fluorine-containing rubber
may also contain units of monomers not containing
fluorine such as propene, ethylene, vinylalkylether and
vinyl ester. Such fluorine-containing rubbers are in
principle known and disclosed e.g. in US-A 4 981 918 and
DE-A 4 038 588. In addition, fluorine-containing rubber
muxt possess reactive positions for peroxidic cross-
linking. These may be both bromine- or iodine-, bromine-
and iodine substituents, and pendent double bonds. Theintroduction of such reactive positions into the
fluorine-containing rubber is effected, in the case of
bromins and iodine substituents, according to known
processes in which either bromine- and/or iodine-con-
taining vinyl compounds are copolymerized in smallamounts with the fluoromonomer; see e.g. US-A 3,351,619,
US-A 4,035,565, US-A 4,214,060, US-A 4 831 085. More-
over, polymerization may take place in the presence of
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2~9027 7
sa~ura~ed iodine- and/or bromine-containing compounds;
see e.g. US-A 4 243 770, US-A 4 748 22~. Optionally,
both possibilities may be combined; see e.g. EP-A
407 937 or US-A 4,948,852. Copolymerization of
fluoromonomers with small amounts of alkenyl iso-
cyanurates, alkenyl cyanurates andlor non-conjugated
dienes gives rise to a fluorine-containing rubber with
pendent double bonds; see DE-A 4 038 588 and DE-A
4 114 598.
Suitable acrylate copolymers are at least partly cross-
linked rubber-type copolymers consisting of one or
several not less than C3-alkyl acrylates, and in
particular C3-C8-alkyl acrylates but preferably not less
than C4-alkyl acrylates and a polyfunctional polyvinyl-
or allyl-compound capable of copolymerization preferably
triallylcyanurate, vinyl ether of polyols, vinyl- or
allyl ether, polyfunctional carboxylic acid, bis-acryl-
amine of diamines such as divinyl benzene, glycol-bis-
acrylate, bis-acrylamide, triallyl phosphate, triallyl
citrate, allyl acrylate or methacrylate or allyl
maleate. Particularly preferred are triallyl cyanurate
and triallyl isocyanurate.
The alkyl acrylate can be substituted up to 40 wt.-% by
acrylonitrile, or in particular C1-C3-alkyl methacrylate
or a mixture thereof. Preferred substances are acrylo-
nitrile and/or alkyl methacrylate.
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2~02~7
The polyfunc~ional polyvinyl- or allyl cGmpounds capable
of copolymerization are used in quantities from 0.05 to
5 wt -% in relation to the acrylate copolymer. The
acrylate cc,polymer can be produced in a known manner by
free radical aqueous emul 5 ion polymerization in the
presence of anionic surfactants at 40 to 95C but
preferably at 50 to 80C.
In order to initiate the free radical copolymerization
use in particular is made in a known manner of water-
soluble inorganic per-compounds such as persulfates,
perborates, percarbonates, e.g., generally in the form
of their sodium-, potassium- or ammonium-salts.
The acrylate copolymer thus produced in the form of at
least partly cross-linked particles in aqueous
dispersion may be used in this form for blending with
fluorine-containing rubbers to create a rubber mixture.
However, it is also possible first to coagulate the
partly cross-linked particles, to separate them from the
aqueous solution, to dry them and to mix the blending
partners in dry compact form, e.g. in a roller device.
Coagulation is effected by acidification with diluted
sulphuric acid to a pH value of about 2, this being
followed by precipitation using a 4% aqueous magnesium
sulfate solution.
The preferred process for producing the rubber mixture
according to the invention consists in mixing the
fluorine-containing rubber and the acrylate copolymer
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2~90277
rubber with one another, whereby each of them is in the
form of an aqueous dispersion, and to coagulate and
precipitate the resulting mixed emulsion before further
processing.
Coagulation is brought about by acidification of the
mixed emulsion with dilute sulphuric acid to a pH-value
of about 2, precipitation with the aid of a 4% aqueous
magneslum sulphate solution applied in a quantity of
about 3,500 ml per S00 g solid rubber, separation from
the emulsion fluid, washing with water and drying.
In order to produce the elastomers, i.e. the vulcanized
rubber, from the rubber mixtures~the latter are mixed
in conventional manner with radical initiators as well
as with other auxiliaries and additives such as co-
cross-linking agents, acid acceptors, fillers,
reinforcing agents, plasticizers, lubricants, processing
aids, pigments, etc., in conventional mixing devices
such as twin-roller rubber mixers and, after shaping,
cross-linked by high-energy irradiation or thermal
meanS-
Preferred radical initiators are peroxides which attemperatures above 100C possess a decay half-life of
not less than 5 minutes as is the case with e.g.
dibenzoylperoxide, t-butylperoxybenzene, bis(t-butyl-
peroxyisopropyl)-benzene, 2,5-bis-(t-butylperoxy~-2,5-
dimethylhexane or 2,5-bis(t-butylperoxy)-2,5-dimethyl-
hexane-(3). The radical initiator is used in quantities
from 0.5 to 10 parts by weight but preferably 1 to 5
parts by weight in relation to 100 parts of polymer
mixture.
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2~277
With a view to achieving better vulcanization character-
istics, in particular with curing in a state of com-
pression so as to improve the mechanical character-
istics, it is possible to incorporate additional co-
cross-linking agents. Suitable by way of co-cross-
linking agents are in particular compounds with several
double bonds such as triallyl cyanurate, triallyl iso-
cyanurate, tri(meth)allyl-lisocyanurate, tetramethyl-or
tetravinyl-cyclotetrasiloxane, triallylphosphite and
N,N -m-phenylene-bis-maleimide, Co-cross-linking agents
may be incorporated in quantities from 0.1 to 15 parts
by weight but preferably 0.5 to 10 parts by weight, in
each case in relation to 100 parts of polymer mixture.
It is also possible to incorporate, by way of acid
acceptors, oxides or hydroxides of metals such as magne-
sium, calcium, lead, zinc, barium, etc., or a basic salt
with an organic acid residue, e.g., stearate, magnesium
oxalate or carbonates, or basic lead phosphate, etc.,into the mixture capable of vulcanization. Different
acid acceptors may be used in combination. The total
proportion of acid acceptors shall not exceed 15 parts
by weight in relation to 100 parts of polymer.
Due to the fact that the rubber mixtures according to
the invention can, by comparison with pure fluorine-
containing rubbers, be filled to a high degree, it is
possible, by the addition of fillers, reinforcing
agents, pigments, plasticizers, lubricants and otherprocessing aids, to achieve vulcanized materials in
which the characteristics cover a wide range.
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2~90277
Thermal vulcaniza~ion is brough~ abou~ in a known manner
at 120 to 180C, initially under pressure and then
without pressure by post-curing in an air-circulation
furnace.
The invention is explained in greater detail with
reference to the following examples:
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2~90277
Example 1
a) Production of the fluorine-containing rubber
110 g vinylidene fluoride, 110 g hexafluoropropene,
230 g of an aqueous solution of 5 9 potassium persulfate
(pH 11), 230 g of an aqueous solution of 2.3 g lithium
perfluoro-octylsulfonate and 3 g triethanol amine (pH
10.5) as well as 8 ml of a solution of 2.5 g triallyl-
isocyanurate in methyl acetate were continuously pumped
every hour into a continuously operated reaction vessel
with stirrer and with a volume of 6 1, the temperature
in the vessel being maintained at 55C and subject to
a pressure of 63 bar. After reaching the state of stable
equilibrium, an emulsion with a proportion of solids
from between 23 and 24 wt.-% is continuously extracted
through a pressure release valve. The emulsion obtained
was used in this form for producing the rubber mixture
(below under c)).
In order to determine the characteristics of the
fluorine-containing rubber thus obtained, a small
quantity of the emulsion extracted was acidified with
dilute sulphuric acid to a pH value of about 2 and
precipitated using a 4% aqueous magnesium sulfate
solution. The solids were separated from the emulsion
fluid, washed with water and then dried. By this means
a rubber-type terpolymer of vinylidene fluoride, hexa-
fluoropropene and triallyl-isocyanurate was obtained. The
molar ratio between vinylidene fluoride and hexafluoro-
propene in the copolymer was determined by 19F-nuclear
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2~9~277
resonance spectroscopy, the proportion of triallyl-
isocyanurate of the polymer being determined by
elemental nitrogen analysis. The molar copolymer
composition proved to be 78.9% vinylidene fluoride,
20.7% hexafluoropropene and 0.4% triallyl-isocyanurate.
The presence of free double linkages can be demonstrated
by addition of iodine bromide. The iodine number
according to HAN~S is 1.5 g iodine/100 g polymer. The
Mooney value ML1o (100C) of the raw polymer is 96, The
glass temperature determined by differential scanning
colorimetry (~.S.C.) is in the region of minus 14C.
b) Production of the acrylate rubber
A solution of 0.7 parts by weight Na-salt of C14-C18-
alkyl sulfonic acids ( ~ ersolat K 30) and 1,545 parts
by weight of water is introduced into a reactor subject
to stirring and in a nitrogen atmosphere. After heating
to 70C one adds 120 parts by weight of a solution of
0,47 wt,-% triallyl cyanurate in butyl acrylate. Then
a solution of 4.5 parts by weight of potassium peroxidi-
sulfate in 100 parts by weight of water is added in
order to initiate polymerization. Once polymerization
has started, further 1,380 parts by weight of a solution
of 4,7 wt.-% triallyl-cyanurate in butyl acrylate and
a solution of 30 parts by weight Na-salt of C14-C18-
alkyl sulfonic acids in 1000 parts by weight of water
are added at a constant rate and over a period of 5
hours at a constant temperature of 70C. Thereafter the
temperature is maintained at 70C for 4 hours. This
results in a latex with a proportion of polymer solids
amounting to 35 wt.-%, which is used in this form for
producing the rubber mixture (see below under c).
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The particle diameter (d50) of the acrylate copolymer
is found to be 170 nm, The gel content (with dimethyl-
formamide by way of solvent) at 23C of the acrylate
copolymer is found to be 97 wt.-%.
c) Production of the rubber mixture
The fluorine-containing rubber emulsion produced ac-
cording to a) and the acrylate copolymer emulsion
produced according to b) are mixed at a ratio of 80
parts by weight of fluorine-containing rubber: 20 parts
by weight of acrylate copolymer (each in relation to the
polymer solids concentration), This is followed by
acidification with dilute sulphuric acid to a pH value
of about 2 and precipitation using a 4% aqueous magne-
sium sulfate solution ~3,500 ml~per 500 g solid rubber).
The solids are separated from the emulsion fluid, washed
with water and dried.
d) Production of the vulcanization mixture and
vulcanized material
Using a twin-roller rubber mixer, 100 parts by weight
of the rubber mixture produced according to c), 3 parts
by weight calcium hydroxide, 30 parts by weight carbon
black MT N 990, 2 parts by weight of 50% triallyliso-
30 cyanurate in inactive fillers t~Percalink 301-50) and
3 parts by weight 2,5-dimethyl-2,5-bis(tert,-butyl)-
hexane, 45% in inactive fillers (~Luperco 101 XL) were
mixed ln.
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2090,~77
The mixture was then subjected to vulcanization for 10
minutes at 170C and at a pressure of 200 bar and
postcuring over a period of 24 hours at 180C in the
air-circulation furnace.
It was found thet the tensile strength of the vulcanized
material was 12.5 I~Pa. The tensile elongation was 340%.
The glass transition determined by temperature-dependent
shear-module measurements ("Brabender" automatic torsion
measuring apparatus) was found to be at minus 20C.
Example 2
The procedure was as in Example 1 with the difference
that the rubber mixture was produced from 60 parts by
weight fluorine-containing rubber and 40 parts by weight
acrylate copolymer (determined in each case as polymer
solids concentration).
The vulcanized material produced has a tensile strength
of 11.5 ~Pa and a tensile elongation of 190%. The glass
transition was found to be at minus 25C.
Example 3
The procedure was as in Example i with the difference
that 70 parts by weight of fluorine-containing rubber
and 30 parts by weight of acrylate copolymer (consisting
of 10% by weight of 2-ethylhexylacrylate, 89,5% by
weight of butylacrylate and 0,5% by weight of triallyl-
cyanurate) were u~ed, the acrylate copolymer having a
gel content of 97% by weight and a particle diameter of
185 nm.
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The vulcanized material produced therefrom had a tensile
strength of lOMPa, a tensile elongation of 200~/.. The
glass transition was found to be at minus 21C.
Example 4
Example 3 was repeated with the difference that the
acrylate copolymer consisted of 20% by weight of 2-
ethylhexylacrylate, 79,5% by weight of butylacrylate and
0,5/. by weight of triallylcyanurate, having a gel
content of 98% by weight and a particle diameter of
180 nm.
The vulcanized material produced therefrom had a tensile
strength of 9,7 MPa, a tensile elongation of 190%. A
slightly broadened glass transition was found to be at
minus 26C.
Example 5
The procedure was as in Example 1 with the difference
that for the production of the acrylate copolymer a
mixture of 50% butyl acrylate and 50% 2-ethylhexyl
acrylate was used instead of butyl acrylate.
The acrylate copolymer had a gel content of 98 wt.-% and
a particle diameter of 180 nm.
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2090~7
The vulcanized material produced from the mixture had
a tensile strength of 10 MPa and a tensile elongation
of 280/.. Two broadened overlapping glass transition
effects were found at minus 38C and minus 13C. This
led to the conclusion that this was a multiphase
vulcanized material.
Example 6
The procedure was as in Example 1 with the difference
that use was made of an acrylate polymer according to
Example 5 and that the quantitative ratio between the
fluorine-containing rubber and the acrylate copolymer
was as in Example 2.
The tensile strength of the vulcanized material was
found to be MPa and the tensile elongation 160%. Two
broadened and overlapping glass transition effects were
found at minus 38 and minus 14C.
Example 7
The procedure was as in Example 1 with the difference
that instead of butyl acrylate a mixture consisting of
78 wt.-% ethylhexyl acrylate and 22 wt.-% acrylonitrile
was used in order to produce the acrylate copolymer.
Fluorine-containing rubber and acrylate copolymer were
used at a quantitative ratio of 60 parts by weight
fluorine-containing rubber to 40 parts by weight
acrylate copolymer (in each case in relation to the
proportion of polymer solids).
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The vulcanization material had a tensile strength of 10
MPa and a tensile elongation of 200%. The glass
transition was found to be at minus 9C.
Example 8
a) Fluorine-containing rubber
Use was made of a commercially available rubber (~Viton
GF). This is a copolymer consisting of 69 mol-% vinyl- :
idene fluoride, about 14 mol-% hexafluoropropene, about
17 mol-% tetrafluoroethylene and a bromine cure-site
(about 0.6 wt.--/. bromine in the polymer). The raw poly-
mer has, in its non-cross-linked state, a glass
transition (measured by D.S.C,, temperature at half unit
function response) of minus 4C and a Mooney value MLlo
20 (100C) of 103.
b) Acrylate copolymer
An acrylate copolymer is produced according to Example
16, coagulated, precipitated and separated from an
emulsion according to Example lb), washed and dryed.
c) Production of the mixture
~ To begin with, 90 parts by weight fluorine-containing
rubber is applied to the roller of a twin-roller rubber
mixer, and then 10 parts by weigh'. acrylate copolymer
are incorporated.
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2030277
d) Produc~ion of vulcanization mixture and
vulcanization material
The Drocedure is as in Examole 1.
The vulcanization material has a tensile strength of 15
MPa and a tensile elongation of 300%. Two broadened
overlapping glass transition effects were found at minus
20C and minus 1C.
Examole 9
The procedure was as in Example 8 with the difference
that the mixture was produced from 60 parts by weight
fluorine-containing rubber and 40 parts by weight
acrylate copolymer.
The tensile strength of the vulcanized material was
found to be 8 MPa and the tensile elongation 110%. Two
broadened overlapping glass transition effects were
found at minus 20C and minus 2C.
Examole 10 (comparative example)
The procedure was as in Example 8 with the difference
that only butyl acrvlate was used for oroducing ~he
acrylate copolymer instead of a mixture of butyl
acrylate with 0.47 wt.-% triallvl-isocyanura~e. The
precipita~ed acrylate polymer was entirelv soluble in
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20~277
dime~hyl formamide. The gel content was accordingly O
S wt.-% Owing to the extrPme tackiness of the non-cross-
linked butyl acrylate rubber used in this case, a rolled
sheet could not be formed while it was being mixed with
the fluorine-containing rubber on the roller. For this
reason the rubber mixture and the vulcanization mixture
were produced in an internal kneader.
The vulcanized material had a tensile strength of 8 MPa
and a tensile elongation of 170%.
Example 11 (comparative example)
The procedure was as in Example 10 with the difference
that use was made of 80 parts by weight fluorine-
containing rubber and 20 parts by weight butyl acrylate
rubber. Also in this case processing on the twin-roller
rubber mixer was not possible.
The tensile strength of the vulcanization material
amounted to 6 MPa, and the tensile elongation to 110%.
Example 12 (comparative example)
The procedure was as in Example 11 with the difference
that use was made of a fluorine-containing rubber sold
~ commercially under the tradename ~Viton A, this being
a copolymer consisting of about 78 mol-% vinylidene
fluoride and 22 mol-% hexafluoropropene. The glass
temperature in the non-cross-linked state is minus 16C,
and the M~oney value ML1o (100C) to 72. The fluorine-
~5 containing rubber is not capable of peroxidic cross-
linking.
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209~277
Devia~ing further from Example 9. ~he vulcanization
S mix~ure was accordingly structured as follows: 6 parts
by weight calcium hydroxide~ 3 parts bv weight magnesium
oxide. 30 parts by weight carbon black MT Black N 990,
2 parts by weight bisphenol AF 2,2-bis-t4-hydroxyphenyl~
hexafluoropropane) and 0.66 parts by weight benzyl-
triphenyl phosphonium chloride were added to the rubbermixture consisting of 80 parts by weight fluorine-
containing rubber and 20 parts by weight butyl acrylate
rubber and mixed in an internal kneader.
The vulcanized material oroduced has a tensile strength
of Z.5 MPa and an ultimate tensile elongation of 225%.
The specimens produced according to Example 10~ ll and
12 shrank in the course of oost-curing and lost their
original shape (lOOxlOOxl mm 3 plates~ when molded by
vulcanization in the compressed state.
It will be apprecia~ed that the instant soecification
and c-laims are set forth by way of illustration and not
limitation. and that various modifications and changes
may be made without departina from the spirit and scooe
of the present invention.
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