Note: Descriptions are shown in the official language in which they were submitted.
2~ 2~3
Mixture of fluorocarbon rubber and silicone/acrvlate core/shell rubber
The present invention relates to peroxidically vulcanizable mixtures of fluoro-
carbon rubber and silicone/acrylate core/shell rubbers.
The preferred materials for use in high-temperature applicadons (gaskets, seals,5 linings, etc.), particularly in the presence of aggressive media which may also be
combined with oil or fuel, are fluoroelastomers (FKMs) based on vinylidene
fluoride, hexafluoropropene and optionally tetrafluoroethylene. These yield
vulcanizates having high resistance to heat, chemicals, ozone and weathering, plus
low swelling in oil and fuel.
10 These attributes have opened up to fluorocarbon rubbers fields of applicationhitherto closed to any other type of rubber. However, a substantial disadvantageof FKMs is their extraordinarily poor low temperature flexibility. At temperatures
below the glass transition temperatures, which in the case of vulcanizates of the
conventional commercial VDF/HFPII~E-based fluoroelastomers vary between 0
15 and -15C, FKM finished components are subject to very rapid failure under
mechanical stress, and are extremely brittle.
At the same time, polydimethylsiloxanes provide polymers which have an
extremely low T, of -123C and which excel in terms of low hot air ageing and
high ozone resistance, and which are, moreover, more economical thanlhe FKMs.
20 This class of rubbers in turn has disadvantages in terms of solvent resistance and
mechanical properties. Even the more costly fluorosilicones (trifluoropropyl
substituents) which have a glass transition temperature of -68C do not attain the
resistance values of FKMs in hot, aggressive media.
Much effort has therefore been directed towards combining fluorocarbon rubbers
25 and silicone rubbers. The obvious combination in the form of a simple blend,
however, is destined to fail because the two classes of polymers are incompatible.
Le A 29 562-~oreign Countries
: - ,.: ~, - : . . .
-~ : : .. .
~; - - :: . . i . .~ :
-- 2126~ 43 : ~
A multi-phase blend system might bring synergistic advantages to certain
application-related properties, for example improved low temperature brittle point,
while retaining the advantageous swelling and ageing properties of FKMs, if the
FKM phase and the silicone phase could be successfully prepared in a defined
5 morphology and this could be subsequently fixed by cross-linking. Attempts to
prepare such systems generally fail, either because when the two partners, whichcontain cross-linking groups of similar reactivity, are being mixed it is not
possible to obtain uniform morphology, or because the phases fail to couple,
because of the presence of disparate cross-linking characteristics and cross-linking
10 therefore takes place preferentia11y within the pure phases A and B. Co-
vulcanization then takes place only to a minor degree.
The object of the present invention is to prepare a radically vulcanizable blend of
a fluorocarbon rubber and a si1icone rubber of def~ed morphology. The silicone
rubber should for this be distributed in finely dispersed manner in a matrix of the
15 FKM and be firmly bonded to the 1atter during a subsequent cross-linking
operation.
This object is achieved according to the invention in that an acrylate segment is
grafted on to silicone rubbers in the form of particles having a defined particle
size in an aqueous dispersion, and the resulting silicone/acrylate core/shell rubbers
20 are mixed with fluorocarbon rubbers, which are at least partially compatible and
are (preferably radically) co-cross-linkable with the acrylate graft. Surprisingly,
the original morphology is retained in thecomposition and procedure according tothe invention, and coupling takes place between the silicone phase and
fluorocarbon rubber phase, which manifests itself in good mechanical properties
25 (retention of the high elongation and strength values of the starting components)
above the T8 of FKM and in improved low temperature brittle point below the
glass transition temperature of the FKM component, as compared with pure FKM.
The present invention accordingly provides radically cross-linkable mixtures
containing from 98 to 35 parts by weight of a radically vulcanizable fluorocarbon
Le A 29 562-Foreign Countries 2
! ~
~ ,- ' , ' ., .
- 21261~3
rubber (A) and from 2 to 65 parts by weight of a silicone/acrylate core/shell
rubber (B) having a silicone moiety of from 95 to 5 parts by weight and
accordingly an acrylate moiety of from 5 to 95 parts by weight. The
silicone/acrylate core/shell rubber is characterized in that it comprises an at least
5 partially cross-linked core of polyorgano-siloxane and a mantle (shell) grafted
thereto of an at least partially cross-linked acrylate copolymer which is at least
partially compatible with the FKM to be utilized as partner in the blend, and
exhibits a particle diameter of from 60 to 800 nm.
The invention also provides a process for the preparation of the aforementioned
10 mixture, which is characteriæd in that the fluorocarbon rubber (A) and the
silicone/acrylate core/shell rubber (B) are mixed together in the form of aqueous
dispersions thereof and are co-precipitated out of the resulting mixed emulsion or
are utiliæd directly in this form as a coating component and are in each case
cross-linked in subsequent processing steps.
15 Suitable fluoroelastomers (A) which are peroxidically cross-linkable are those such
as contain units of VDF and/or llJIJ. and at least one further fluoro-olefin which is
copolymerizable therewith. The further fluoro-olefin may be CTFE, HFP, PFP,
HFJB, PPAVE, and the like. The fluoroelastomer may additionally contain units
of non-fluorine-containing monomers such as propene, ethylene, vinyl alkyl ether20 and vinyl ester. Monomer combination8 which yield 8uch fluoroela8tomer8 are
fundamentally known and are described, for example, in DE~A 39 25 743 and
D~A 41 14 598. The fluorocarbon rubber must additionally possess reactive sites
for the peroxidic cross-linking. This requirement can be met by both bromine or
iodine, or bromine and iodine, substituents, and also by double bonds in the side
25 position. In the case of the bromine and iodine substituents, such reactive sites
are introduced into the fluoroelastomer in accordance with known processes, either
by copolymerizing bromine and/or iodine-containing vinyl compounds in small
quantities with the fluoromonomers; see, for example, US-A 3,351,619,
US-A 4,035,565, US-A 4,214,060, D~A 3,715,210, or by polymerizing in the
30 presence of saturated iodine or bromine and iodine-containing compounds, for
Le A 29 562-Foreign Countries 3
~, , , . . . . ... . .. . . . . - -
-.. : . ~- . . -
,., .. : . . - ~............. . .
~' . ''~'' ~; - ' ~
~: :- : - - '' '
. ~
,
2~2~
example DE-A 2,815,187, DE-A 3,710,818, or combining the two possibilities, for
example, EP-A 407,937 or US-A 4,948,852. A fluorocarbon rubber having double
bonds in the side position is obtained by copolymerizing fluoromonomers with
small quantities of suitable monomers which have at least two olefinic double
5 bonds, such as alkenyl isocyanurates, alkenyl cyanurates and/or unconjugated
dienes, see DE-A 4,038,588 and DE-A 4,114,598.
'. ,~
Silicone/acrylate core/shell rubbers (B) within the meaning of the invention
contain particulate, highly cross-linked silicone rubber particles of an averagediameter (d50) of from 0.1 to ?~ m, in particular from 0.1 to 1 pm, and gel
10 contents greater than 60 wt-%, in particular greater than 80 wt-%. The acrylate
rubber which is grafted on to the silicone rubber particles is present in the
silicone/acrylate core/shell rubbers preferably in quantities of 50 wt-% or less, in
particular in quantities of from 30 to 5 wt-%. The grafted rubbers (B) preferably
have gel contents > 70 wt-%, in particular > 85 wt-%. The acrylate rubber moiety15 of the silicone/acrylate coretshell rubbers is polymerized on to the silicone rubber
particles; the following can thus form: graft polymers in the sense of covalent
compounds of silicone rubber and acrylate rubber, cross-linked acrylate rubber
moieties which encase the silicone rubber particles in a manner more or less
mechanical, and optiona11y small quantities of soluble acrylate rubbers. Within the
20 meaning of the invention, silicone/acrylate core/shell rubbers designate the reaction
products which are obtained by polymerization of acrylate in the presence of
silicone rubber particles, irrespective of the actual extent of grafting. The silicone
rubber backbone is preferably a cross-linked silicone rubber, and contains units of -
the formulae (I) to (IV) ~ ~;
' '' ':
R2SiO2f2 RSiO3~z R3SiOll2 SiO412
(I) (II) (III) (IV),
in which
R represents a monovalent organic radical.
Le A 29 562-Foreign Countries 4
- 212~1~3
Cl-C40 radicals, for example alkyl groups, preferably Cl-C10-aL~cyl, aryl groups,
preferably C6-C24-aryl, alkylaryl groups, preferably C7-C30-alkylaryl, arylalkylgroups, preferably C7-C30-aralkyl, Cl-C20-aL~oxy, Cl-C20-thioalkyl, unsaturated C2-
C20 radicals, and the like are suitable as monovalent organic radicals.
5 The following might be named particularly preferably: methyl, ethyl, t-butyl,
phenyl, methylphenyl, bisphenyl, phenylmethyl, and the like. The following mightfurthermore be named: Cl-C~0-aLkoxy radicals, radically attacking groups such asvinyl radicals or mercaptopropyl radicals.
At least 80% of all radicals R are preferably methyl; combinations of methyl and10 ethyl are in particular preferred.
Preferably from 0 to 10 mole of RSiO3n units, from 0 to 1.5 mole of R3SiOI/2
units and from 0 to 3 mole of SiO2 units are preferably used per 100 mole of
R2SiO units.
Preferred silicone rubbers contain incorporated units of radically attackable groups.
15 These are rendered capable of radical addition or transfer reaction. Such groups
are preferably vinyl, allyl, chloroalkyl and mercapto groups, preferably in
quantities of from 2 to 10 mole-%, calcu1ated on the radicals R.
,
The rubber polymer b) grafted on to the core a) represents a partially to highlycross-linked acrylate rubber and is a polymer of from 100 to 60 wt-% alkyl
20 acrylate, from 60 to 0 wt-% of other monomers which are copolymerizable with
alkyl acrylate, and, if necessary, from 0.1 to 10 wt-%, calculated on the sum ofalkyl acrylate and other monomers, of a cross-linking monomer having at least
two vinyl and/or allyl groups in the molecule.
AL~cyl acrylates within the meaning of the invention are C4-CI4-alkyl acrylates,25 such as methyl, ethyl, butyl, octyl and 2-ethylhexyl acrylate, chloroethyl acrylate,
benzyl acrylate, phenethyl acrylate, in particular C,-C6-alkyl esters, preferably
Le A 29 562-Forei~n Countries 5
r ' ' ~
212~t~3
butyl acrylate; monomers which are copolymerizable with the alkyl acrylates are
preferably styrene, a-methylstyrene, halostyrene, methoxystyrene, acrylonitrile,methacrylonitnle, Cl-C8-alkyl methac~ylates which may be substituted in the alkyl
radical optionally by functional groups such as hydroxyl, epoxy or amine groups,5 for example metl2yl methacrylate, cyclohexyl methacrylate, glycidyl methacrylate,
hydroxyethyl methacrylate, hydroxypropyl methacrylate, (meth)acrylic acid, maleic
acid (ester), fumaric acid, itaconic acid, (meth)acrylamides, vinyl acetate, vinyl
propionate or N-methylol compounds of (meth)acrylamides.
Cross-linking monomers within the meaning of the invention are esters of
10 unsaturated carboxylic acids having a polyol (preferably from 2 to 20 carbon
atoms in the ester group), such as ethylene glycol dimethacrylate, esters of a
polyfunctional carboxylic acid having an unsaturated alcohol (preferably from 8 to
30 carbon atoms in the ester radical), such as triallyl cyanurate, triallyl
isocyanurate; divinyl compounds such as divinylbenzene; esters of unsaturated
15 carboxylic acids having unsaturated alcohols (preferably from 6 to 12 carbon
atoms in the ester radical) such as allyl methacrylate; phosphoric acid esters, for
example triallyl phosphate and 1,3,5-triacrylolylhexahydro-s-triazine. Particularly
preferred polyfunctional monomers are triallyl cyanurate, triallyl isocyanurate,triallyl phosphate and allyl methacrylate.
20 The silicone/acrylate core/shell rubbers within the meaning of the invention may
be prepared in aqueous emulsion in the fo11Owing manner: in a first stage, the
silicone rubber, that is to say the core a), is first prepared by emulsion
polymerizing a silicone oligomer.
It is known to prepare an emulsion of a long-chain silicone oil terminating with25 OH groups by emulsion polymerization. For exarnple, reference in this context is
made to US-A 2,891,910 and to GB-A 1,024,024. It is particularly preferable to
emulsion polymerize in the presence of an aL~ylbenzene sulphonic acid, because in
this instance emulsifier and polymerization catalyst are present in one. The acid is
neutralized following polymerization.
Le A 29 562-Foreign Countries 6
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: - . ~ . ~ : . .~ - .
212~43
n-Alkylsulphonic acids may also be utiliæd in place of the alkylbenzene sulphonic
acids. It is possible to utiliæ additionally other emulsifying agents as co-
emulsifiers, in addition to the sulphonic acid which has a catalytic and emulsifying
action.
5 Co-emulsifiers may be nonionic or anionic. Anionic co-emulsifers which are in
particular contemplated are salts of the aforementioned n-aLkyl- or alkylbenzenesulphonic acids. Nonionic co-emulsifers are polyoxyethylene derivatives of fattyalcohols and fatty acids.
.,
Silicone oils obtained by emulsion polymerization in the presence of nonionic co-
10 emulsifiers are generally of lower molecular weight than those prepared withoutco-emulsifier. The molecular weight of the silicone oil terminating with OH
groups which is obtained in the emulsion polymerization can also be influenced by
way of the temperature at which equilibrium is reached between siloxane, water
and the silanol which first forms as a result of opening the siloxane ring.
15 Radically attackable groups may be incorporated in the preferred silicone polymer
by co-use of appropriate siloxane oligomers. Suitable siloxane oligomers here are
for example tetramethyl tetravinyl cyclotetrasiloxane, ~-mercaptopropyl
methyldimethoxysilane and the hydrolysate thereof.
Such "functional" oligomers are added to the basic oligomer, for example
20 octamethylcyclotetrasiloxane, in the requisite quantities.
Longer-chain alkyl radicals R, for example ethyl groups, propyl groups, and
phenyl groups may also be incorporated in an analogous manner. The silicone
rubber must be at least partially cross-linked.
Sufficient cross-linking can already take place when the preferably present vinyl
25 groups and mercaptopropyl groups react together during emulsion polymerization
of the siloxane oligomers. It is not then necessary to add an external cross-linking
Le A 29 562-Foreign Countries 7 ~ ~
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. -:. ., -
~126~ ~3
agent; however, a cross-linking silane may be added in order to increase the
degree of cross-linking of the silicone rubber.
Branching or cross-linking may be built in by addition of, for example,
tetraethoxysilane or of a silane of the general formula RSiX3 or RX4 (wherein X
5 represents a hydrolysable group, in particular the alkoxy radical). R has the
meaning described heretofore. Preferably R = methyl, R = ethyl and R = phenyl.
Methyltrimethoxysilane or phenyltrimethoxysilane are in particular preferred in
addition to tetraethoxysilane.
In a second stage the monomers (alkyl acrylate, optionally cross-linking monomers
10 and optionally further monomers) which form the acrylate rubber b) are then graft
polymerized in the presence of the silicone rubber emulsion of the first stage.
Formation of new particles should be as far as possible suppressed during this
graft polymerization. An emulsion stabilizer must be present in the quantity
necessary for covering the surface of the particles. Graft po1ymerization is
prefcrably accomplished within the temperature range 30 to 90C, in particular 50
to 80C, and is initiated by known radical initiators, for example, azo-initiators,
peroxides, peresters, persulphates, perphosphates or by redox initiator systems.Water-solub1e inorganic peroxydisulphates and peroxydiphosphates are preferred.
Following the graft polymerization of b) on to the silicone rubber particles a),20 stable aqueous emulsions of the silicone rubber/acrylate rubber particles arise,
normally with polymer solids contents within the range 20 to 50 wt-%.
The graft polymers thus prepared may be worked up by known processes, for
example by coagulating the latices with electrolytes (salts, acids or mixtures
thereof). They may then be purified and dried.
25 The mixture is formed according to the invention preferably by mixing the
aqueous dispersion of the fluorocarbon rubber (A) with the aqueous dispersion ofthe silicone/acrylate coreishell rubber (B), optionally with addition of furtherprocessing agents, additives, etc. This mixture of the aqueous dispersions is either
Le A 29 562-Foreign Countries 8
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2;` : '~ - - .
2126~3
utilized directly in this form, for example as a coating component or as an additive
for coating components, or is precipitated. Other procedures are possible, such as
mixing the individual coagulated, dry solid rubbers in a roll mill or in internal
mixers, by extrusion, etc.
5 The rubber mixtures according to the invention may be cross-linked radically
using conventional methods. Radical initiation may be by high-energy radiation or
thermally in the presence of radical initiators. Peroxides which exhibit
decomposition half-lives of at least S minutes at temperatures above 100C, suchas for example dibenzoyl peroxide, t-butylperoxybenzene, bis-(t-butylperoxy-
isopropyl)-benzene, 2,5-bis-(t-butylperoxy)-2,5-dimethylhexane or 2,5-bis-(t-
butylperoxy)-2,5-dimethylhexine-(3), preferably serve as radical initiators. Theperoxides are preferably utilized in quandties of from 0.5 to 10 parts by weight,
preferably from 1 to 5 parts by weight, in each case calculated on 100 parts by
weight of the polymer mixture.
15 The cross-linkable mixture may furthermore contain, serving as acid acceptor,oxides or hydroxides of metals such as magnesium, calcium, lead, zinc, barium
and the like or of a basic salt having an organic acid radical, such as sodium
stearate, magnesium oxalate or carbonates or basic lead phosphate and the like, or
combinations of a plurality thereof in proportions not exceeding 15 parts by
20 weight, calculated on 100 parts by weight of polymer.
It is possible to add further known fillas, reinforcing agents, piasticizers,
1ubricants, processing agents, pigments, and the like, the fillability of the rubber
mixture according to the invention being as a matter of principle greater than that
of the pure fluorocarbon rubber.
25 The aforementioned mixture constituents are also incorporated into the rubbermixture according to the invention using conventional methods of forming a
rnixture. Thus, for example, the mixtures according to the invention, which are to
afford high-elasticity molded bodies, may be processed on a roll mill or in a mixer
Le A 29 562~oreign Countries g
21261~3
into vulcanizing mixtures which are then vulcanized in known manner at elevated
temperatures and under pressure in forming devices, and are then post-cured
without pressure in forced air ovens in order to adjust the f~al properties.
It is equally possible to process in solution or in the melt, wherein after forming at
5 elevated temperatures, drying and cross-linking may be accomplished in a single
step, if for example molded bodies in the form of sheets, films, fibers or compact
molded bodies are prepared. A liquid composition optionally prepared with
solvent is eminently suitable for use in coatings or sealing masses.
The aqueous mixed emulsions already mentioned above are also, with the
10 appropriate additives, uti1izable directly for casting, after which they may be dried
and cured.
Curing may optionally also be effected by UV or high-energy radiation, without
the need for heat treatment.
The invention is explained in greater detail in the examples which follow~
15 Example la
eparation of a fluorocarbon Nbber emulsion
15,000 ml deionized water was placed in a 40 liter autoclave. 54 g lithium
perfluorooctyl sulphonate and 90 g potassium peroxydisulphate were dissolved in
the water. This solution has a pH of 11. The closed autoclave was then raised
20 three times to a nitrogen pressure of in each case 10 bar, the pressure then being
reduced to no~mal. 4230 g hexafluoropropene and 2938 g vinylidene fluoride, and
3 g perfluorobutyl iodide and 24 ml of a solution (= solution 1) of 13 g triallyl
isocyanurate in acetic acid methyl ester were added to the autoclave and the
reaction mixture was heated to 50C with stirring. The pressure within the
Le A 29 562-~Oreign Countries 10 ~ ~
~":'- '' ' ' ':'- -.; . . - . :.
21261~3
autoclave was 35 bar after reaching this temperature. Polymerization was initiated
by continuous addition of 120 ml per hour of an aqueous solution ~= solution 2)
containing triethanolamine in a concentration of 75 g/l. Parallel to this,
continuous addition of 30 ml/h of solution 1 commenced. After 90 minutes,
5 dispensing of solution 2 was reduced to 90 ml/h. During polymerization, which
manifested itself after 20 minutes by an incipient fall in pressure, the initialpressure was maintained by pressure from continuous introduction over a period of
80 minutes of a monomer mixture of 1430 g vinylidene fluoride and 970 g
hexafluoropropene. The contents of the autoclave were cooled to terminate
10 polymerization, and the unreacted gas mixture was condensed and recovered. A
coagulate-free aqueous emulsion exhibiting a pH of 4.9 at a solids content of 19%,
was obtained. The emulsion was utilized in this form directly for the preparation
of the mixtures in accordance with Examples ld to 9.
Comparative Example
15 The emulsion in accordance with Example la was acidulated to pH approximately2 with dilute sulphuric acid, and was precipitated with a 4% aqueous magnesium
sulphate so1ution (3500 ml to 500 g solid rubber). The product was washed with
water and then dried, to give a rubber-like copolymer containing vinylidene
fluoride, hexafluoropropene and triallyl isocyanurate, incorporating iodine as end
2 0 groups.
The copolymer is soluble in solvents such as dimethylformamide,
dimethylacetamide, acetone, metnyl ethyl ketone and tetrahydrofuran. The molar
ratio of vinylidene fluoride to hexafluoropropene in the copolymer, determined by
~'F nuclear resonance spectroscopy, was 81: 19. T'ne TAiC combined in tne
25 polymer, determined by elemental ana1ysis for nitrogen, was 0.6 wt-% . An iodine
content of <100 ppm was determined by elemental analysis for iodine. The
Mooney ML~ (100C) of the raw polymer is lS0.
Le A 29 562-Foreign Countries 11
212~3
Example lb
Preparation of the silicone rubber backbone
38.4 parts by weight octamethylcyclotetrasiloxane, 1.2 parts by weight
tetramethyltetravinylcyclotetrasiloxane and 1 part by weight ~-mercaptopropyl-
5 methyldimethoxysilane are stirred together. 0.5 parts by weight dodecyl-
benzenesulphonic acid are added, and 58.a parts by weight water are then
dispensed over a period of 1 h. Intensive stirring follows. The preliminary
emulsion is homogenized twice at 200 bar with the aid of a high pressure
emulsifying machine. A further 0.5 part by weight dodecylbenzenesulphonic acid
10 is added.
The emulsion is stirred at 85C for 2 hours and then at room temperature for 36
hours Neutralization is with lN-NaOH. 100 parts by weight of a stable emulsion
having a solids content of approximately 37% (determined per DIN 53 182) are
obtained. Particle size is 285 nm (average value d50). The gel content of the
15 polymer is 83 wt-% (measured in toluene).
Le A 29 562-Foreign Countries 12
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-: . ., . ~
, . ... . . ,~ . . .... - ., .. . , . - ... . ~
21261~3
Example lc
,:" '
: -
Preparation of the silicone/acrvlate core/shell rubber dispersion
1960 wt-% of the silicone emulsion from Example lb and 115 parts by weight
water are placed in a reactor under a slow nitrogen strearn, and are heated to 70C.
5 A solution of 2 parts by weight potassium peroxydisulphate and 80 parts by
weight water is added. At 70C the following flows are then added in
concurrently over a period of 5 hours:
Flow 1: 310 parts by weight n-butyl acrylate
0.9 parts by weight triallyl cyanurate
Flow 2: 6.5 parts by weight sodium salt of Cl4-C,8-aL~cylsulphonic acids
400 parts by weight water.
After dispensing is complete, stirring continues at 70C for 4 hours. A latex ~ -
having a 36% solids content is obtained.
~amyle Id
Preparation of the rubber mixture
The coagulate-free fluorocarbon rubber emulsion obtained in Example la and the
silicone/acrylate core/shell rubber emulsion obtained in Example lc are mixed inthe ratio 90 parts by weight fluorocarbon rubber : 10 parts by weight
silicone/acrylate core/shell rubber (in each case calculated on polymer solids
20 content). The silicone/acrylate core/shell rubber comprises 70 parts by weight
silicone rubber in accordance with Exarnple lb and 30 parts by weight
silicone/acrylate rubber in accordance with Example lc.
615.31 g fluorocarbon rubber emulsion (solids content: 21.94%) are stirred
thoroughly with 49.31 g silicone/acrylate core/she11 rubber emulsion (solids
content: 35.45%). -
Le A 29 562-Foreign Countries 13 ~ ;
2126143
The emulsion is then acidulated with dilute sulphuric acid to pH approximately 2,
and precipitated with a 4% aqueous magnesium sulphate solution (0.2 g MgSO4 in
5 g H2O per g solid rubber). The solid is separated, washed with water and dried.
Example 2 - ~ -
The procedure is as for Example ld, but with the fluorocarbon rubber and the ~-
silicone/acrylate core/shell rubber being mixed in the ratio 60 parts by weight: 40
parts by weight (calculated on polymer solids content). For this purpose 410 g ~-
fluorocarbon rubber emulsion (solids content 21.94%) and 169.25 g
silicone/acrylate core/shell rubber emulsion (solids content: 35.45%) are stirred
1 0 thoroughly.
Example 3
The procedure is as for Example ld, but with the fluorocarbon rubber and the
silicone/acrylate core/shell rubber being mixed in the ratio 40 parts by weight:60 parts by weight (calcu1ated on polymer solids content). For this purpose 273 g
silicone/acrylate core/shell rubber emulsion (solids content 35A5%) are stirred ~ -
thoroughly.
Examples 4 to 9
Examples 4 to 6 and 7 to 9 are effected in a manner analogous to that of
Examples ld to 3. Table 1 gives detailed information.
e A 29 562-Poreip,n Countries 14
212~43 - ~
- Table I
Exaimple No. FKM emulsion S/A-K/M Si moiety in FKM/S/A-K/M
from Example emulsion S/A-K/M ratio in
la [g] from Example rubber mixture
lc)[g3 [wt.-%) mixture
(% solids)
Id 615.31 49.31(35.45) 70 90:10
2 410 169.25(35.45) 70 60:40
3 273 253.87(35.35) 70 40:60
4 615.31 48(36.5) 50 90:10
410 164(35.5) 50 60:40
6 273 246(36.5) 50 40:60
7 615.31 48.2(36.4) 30 90:10
8 410 165(36.4) 30 60:40
lS 9 273 247(36.4) 30 40:60
Abbreviations:
FKM = fluorocarbon rubber; S/A-K/M = silicone/acrylate core/shell rubber
Le A 29 562-Foreign Countries 15
" ::
2 1 2 6 ~
Vulcanization
A mixture of 100 parts by weight rubber mixture (from Examples ld and 4 to 9,
the products from Examples 2 and 3 were no longer workable) with 3 parts by
weight of calcium hydroxide, 30 parts by weight carbon black, MT black N 990,
4 parts by weight Percalink 301-50 (triallyl isocyanurate, 50% concentration in
inert fillers) and 3 parts by weight Luperco 101 XL (2,5-dimethyl-2,5-bis(t-
butyl)hexane, 45% concentration in inert fillers) is prepared on a two-roll mill for
rubber mixing. This mixture was pressure-vulcanized at 200 bar for 15 minutes ata temperature of 175C. Post-curing then fo11Owed by heating the molded bodies
(100 x 100 x 1 mm pressed plates) stepwise in a forced air oven over a period of4 hours at the said temperature. The results of mechanical examination of these
vulcanizates are shown in Table 2 (the vulcanizate using the product from
Example 9 gives a brittle plate).
Le A 29 562-Forei~n Countries 16
$ ........ . ~ . . i: . -
2126143
Table 2
¦ E~amples No- Commr, Id ~ 5 6 7 8 9
N/hlm2 a~ 100% 4.24 4.975.15 7.52 5.12 7.52 l
elongalion _ ¦
bElonga[ti%]n at 4302 366 ` ~,192 132.1 93 2 466.8 Iff.6
5m s ~re~ 2L9 13.5 13 9 2A ld l 9 2
T~(l) rCl -17.9 -17.8 -16.7-18.1 -16.4 -16.1 -17.4
10 ¦ T~(2) r~ - 131.1 130.8 -125.7 -122,9 131 125.6 _
The glass transition temperatures (T6(1) and T6(2) indicated in Table 2 were deter-
rnined by plotting module curves on a Brabender torsional oscillation measuring
apparatus.
The invention wi11 be further described with reference to the accompanying
15 drawings wherein:
Figs. 1 and 2 are comparadve module-in-torsion curves, as a function of
temperature;
Figs. 3 and 4 are comparative energy absorption curves;
: ~ :
Figs. 5 and 6 are comparative Tg curves.
20 Referring now more particularly to the drawings, Figs. 1 and 2 show by way ofexample module-in-torsion curves G and G", as a function of temperature, in
respect of a sample in accordance with the Comparative Example (Fig. 1) and
Example ld (Fig. 2).
Le A 29 562-Foreign Countries 17
:" . , . .. , ~ .. :,~, . ,
21 2S~43
The curves were plotted at a heating-up time of 1C/min. The second moment of
area was 102.47 kg mm2. The thickness of the sample of the Comparative
Example was 1.12 mm, and that of Example ld 1.23 mm.
Fig. 1 shows the glass transition of the fluoropolymer as a peak on the G" curve at
5 approximately -18C.
Fig. 2 additionally shows the glass transition of the silicone plate at -131C. The
glass transition of the pure silicone phase is normally approximately -120C. The
shift to lower temperatures is indicative of marked coupling effects between theacrylate mantle and the fluoropolymer matrix.
10 The glass transition of the fluoropolymer matrix is substantially unchanged at
approximately -18C, although it does exhibit slight asymmetrical broadening.
The glass transition of the acrylate mantle is concealed in the G" background inthe region between -35 and -45C.
The improved low temperature brittle point of the fluorocarbon rubbers modified
15 according to the invention is confirmed by plate indentation tests performed using
a recording dropping apparatus.
The energy absorption under multiaxial impact stressing over a wide temperature
range, based on DIN 53 443, was a1so examined. Figs. 3 and 4 show the pure
fluorocarbon rubbers (Fig. 3) determined at 25C, [Tg(1)]C, [Tg(1)-25]C and
20 [Tg(1~40]C as expected a high deformability with high energy absorption. Themodified system (Fig. 4), on the other hand, is markedly less deformable. As canbe read directly from Figs. 3 and 4, at [Tg(1)-25]C and [Tg(1)-40]C, energy
absorption in the case of the system modified according to the invendon is
appreciably greater than in the case of the pure fluorocarbon rubber. The fracture
25 behavior can therefore also be designated markedly less brittle.
Le A 29 562-Forei~n Countries 18
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It will be understood that the specification and examples are illustrative but not
limitative of the present invention and that other embodiments within the spiritand scope of the invention will suggest themselves to those skilled in the art.
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