Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Rubber comyounds based on aminoisoprene nolymers and the use thereof for
the uroduction of tyre treads which exhibit a low rolling resistance
The present invention relates to rubber compounds based on homo- and
copolymers of
special aminoisoprenes and fillers, and relates to vulcanised products
thereof. The
rubber compounds according to the invention or the vulcanised products thereof
are
suitable for the production of highly reinforced, abrasion-resistant
mouldings,
particularly for the production of tyres which exhibit a low rolling
resistance and a
high abrasion-resistance.
Compared with corresponding emulsion rubbers, anionically polymerised solution
rubbers which contain double bonds, such as solution polybutadiene and
solution
styrene/butadiene rubbers, exhibit advantages for the production of tyre
treads which
exhibit a low rolling resistance. Amongst others, these advantages are the
facility of
controlling the vinyl content and the glass transition temperature which is
associated
therewith, and of controlling the extent of molecular branching. In practical
application, this results in particular advantages in the relationship between
the wet-
slip resistance and the rolling resistance of the tyres. Thus US-PS 5 227 425
describes
the production of tyre treads from a solution SBR rubber and hydrated silica.
In order
to achieve a further improvement in properties, numerous methods have been
developed for modifying the terminal groups, such as that which employs
dimethylaminopropyl-acrylamide and which is described in EP-A 334 042, or such
as
that which employs silyl ethers and which is described EP-A 447 066. However,
due
to the high molecular weight of rubbers, the proportion by weight of terminal
groups
is low, and is therefore only capable of exerting a slight effect on the
interaction
between a filler and a rubber molecule. The object of the present invention
was
therefore to produce solution rubbers having a considerably higher content of
amino
groups.
US-PS 3 544 532 describes cationically unsaturated polymers, for the
production of
which polymers of 2-dialkylaminomethyl-1,3-butadiene are used, amongst other
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substances. These polymers are produced by emulsion polymerisation or by
subsequent reactions analogous to polymerisation, and therefore have a
microstructure
(1,2-vinyl content, long-chain branching, molecular weight distribution,
distribution
of the copolymer in the monomer) which differs from that of the anionically
initiated
solution polymers of the present invention. The aforementioned US Patent does
not
mention of the use of these rubbers for tyres.
Emulsion rubbers which are produced from dimes and vinyl monomers which
contain
amino groups, and the use thereof in tyre treads filled with hydrated silica,
are known
from EP 819 731. However, due to the production of these rubbers under
conditions
of radical-initiated polymerisation, the known advantages of anionically
polymerised
solution rubbers cannot be achieved, as mentioned above. lvloreover, the
monomers
used there are structurally different from the dialkylaminoisoprene monomers
of the
present invention.
The object of the present invention was therefore to provide compounds
comprising
rubbers which contain amino groups, from which tyres can be produced which
exhibit
improved wet slip-resistance as well as high mechanical strength and improved
abrasion behaviour.
The present invention therefore relates to rubber compounds consisting of a
rubber
and 10 to 500 parts by weight, preferably 20 to 200 parts by weight, of a
filler with
respect to 100 parts by weight rubber, wherein the rubber has been produced by
polymerisation in solution and has a content of aminoisoprenes, which are
incorporated by polymerisation, of formula
Rz
R~-N
wherein
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RI and RZ, independently of each other, represent CI-C~8 alkyl- or CS-C12
cycloalkyl
radicals, which can optionally be interrupted by one or more 'nitrogen, oxygen
and/or sulphur atoms or which jointly form a ring, and also represent C6-Cg
aryl- or C~-C24 alkylaryl radicals,
from 0.01 to 100 % by weight, preferably 0.1 to 10 % by weight, a content of
diolefines from 0 to 99.99 % by weight, preferably 55 to 99.9 % by weight, and
a
content of aromatic vinyl monomers, incorporated by polymerisation, from 0 to
50
by weight, preferably 0 to 45 % by weight, with respect to the solution rubber
in each
case, and has a (number average) molecular weight from 10,000 to 2,000,000 and
in
addition has a glass transition temperature from -100°C to
+20°C.
Aminoisoprenes which are suitable for polymerisation and which are
particularly
preferred have the following structures:
~Hs
NCH ~zHs ~~Hs
N a N~..CzHs N,-CHs
a) b) c)
n-C H CaH~ pz~"~zs
N~n~CaH~ ~~j_Ca~r N--CH3
)
~O /--NCH3 ~NCzHs
N~ N~~ N
g) h) i)
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CHs
N N~O~C~
.1) k) 1)
H
3
N
m) n)
Examples of aromatic vinyl monomers which can be used for polymerisation
include
styrene, o-, m- and p-methylstyrene, p-tert.-butylstyrene, a-methylstyrene,
vinylnaphthalene, divinylbenzene, trivinylbenzene and/or divinylnaphthalene.
Styrene
is most preferably used.
Diolefines which can be used for polymerisation according to the invention
include
1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 1-vinyl-1,3-
butadiene
and/or 1,3 -hexadiene. 1,3-butadiene and isoprene are most preferably used.
The rubbers based on aminoisoprene monomers and optionally other diolefines
and
aromatic vinyl monomers which can be used according to the invention
preferably
have average (number average) molecular weights from 100,000 to 1,000,000,
glass
transition temperatures which preferably range from -40°C to
0°C, and Mooney
viscosities ML 1+4 (100°C) from 10 to 200, preferably from 30 to 150.
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The aminoisoprenes can be produced by methods known in the art: for example
from
2-chloromethyl-1,.3-butadiene and secondary amines as described in US
3,544,532, or
from secondary amines, formaldehyde, allyl alcohol, dimethyl sulphoxide and
potassium-tert.-butylate as described in Angew. Chem. 102 (1990) 929. The
structure
of the secondary amines which can be used can be varied within wide limits.
The aminoisoprene-based rubbers according to the invention are produced by
anionic
solution polymerisation. i.e. by means of a catalyst based on alkali metals,
preferably
in an inert hydrocarbon as a solvent. The known randomising agents and control
agents for the microstructure of the polymer can be used in addition. Anionic
solution
polymerisation methods of this type are known, and are described, for example,
by I.
Franta in Elastomers and Rubber Compounding Materials; Elsevier 1989. pages 73-
74. 92-94 and in Houben-Weyl, Methoden der Organischen Chemie, Thieme Verlag,
Stuttgart, 1987, Volume E 20, pages 114 - 134.
Examples of suitable alkali metal catalysts include lithium, sodium,
potassium,
rubidium, and caesium metals and hydrocarbon compounds thereof, as well as com-
plex compounds thereof with polar organic compounds.
Lithium and sodium hydrocarbon compounds comprising 2 to 20 carbon atoms are
particularly preferred, for example ethyllithium, n-propyllithium, i-
propyllithium, n-
butyllithium, sec-butyllithium, tetr.-octyllithium, n-decyllithium,
phenyllithium, 2-
naphthyllithium, 2-butylphenyllithium, cyclohexyllithium, 4-
cyclopentyllithium, 1,4-
dilithiobutene-2, sodium naphthalene, sodium biphenyl, potassium
tetrahydrofuran
complex, potassium diethoxyethane complex, and sodium tetramethylethylene-
diamine complex. These catalysts can be use on their own or in admixture.
The amounts of catalyst range from 0.1 to 10 mmol /100 g polymer, preferably
from
0.5 to 5 mmol/100 g polymer.
Anionic solution polymerisation is preferably conducted in a hydrocarbon, but
can
also be conducted in another solvent which does not destroy the catalyst, for
example
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in tetrahydrofuran, tetrahydropyran or 1,4-dioxane. Example of hydrocarbons
which
are suitable as solvents include aliphatic, cycloaliphatic or aromatic
hydrocarbons
comprising 2 to 12 carbon atoms. The preferred solvents are propane, butane,
pentane,
hexane, cyclohexane, propene, butene, 1-pentene, 2-pentene, 1-hexene, 2-
hexene,
benzene, toluene and xylene. The solvents can be used on their own or in
admixture.
The appropriate amount of solvent can easily be determined by preliminary
tests.
The polymers, which can be produced by anionic solution polymerisation, can
also be
"coupled" by known methods, for example by means of disulphur dichloride or by
the
reaction of the live polymer anion with silicon tetrachloride.
Suitable fillers for the rubber compounds according to the invention include
all fillers
which are known and used in the rubber industry, comprising both active and
inactive
fillers.
Examples thereof include:
- microdispersed hydrated silicas, for example those produced by precipitation
from solution of silicates or by the flame hydrolysis of silicon halides
having
specific surfaces from 5 - 1000, preferably 20-400 m2/g (BET specific surface)
and having primary particle sizes from 10-400 nm. The hydrated silicas may
optionally also exist as mixed oxides with other metal oxides such as AI, Mg,
Ca, Ba, Zn, Zr or Ti oxides;
- synthetic silicates such as aluminium silicate, or alkaline earth silicates
such as
magnesium silicate or calcium silicate, which have BET specific surfaces from
20-400 m2/g and primary particle diameters from 10-400 nm;
natural silicates such as kaolin, and other naturally occurring hydrated
silicas;
- glass fibres and glass fibre products (mats, strand) or glass microspheres:
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- metal oxides such as zinc oxide, calcium oxide, magnesium oxide, aluminium
oxide;
- metal carbonates such as magnesium carbonate, calcium carbonate, zinc
carbonate;
- metal hydroxides, such as aluminium hydroxide or magnesium hydroxide for
example;
- carbon blacks. The carbon blacks which are used here are produced by the
flame black, furnace black or gas black processes and have BET specific
surfaces from 20-200 m2/g, e.g. SAF, ISAF, HAF, FEF or GPF carbon blacks;
- rubber gels, particularly those based on polybutadiene, butadiene/styrene
copolymers, butadiene/acrylonitrile copolymers and polychloroprene.
Microdispersed hydrated silicas and/or carbon blacks are preferably used as
fillers.
The aforementioned fillers can be used on their own or in admixture. In one
particular
preferred embodiment, the rubber compounds contain, as fillers, a mixture of
light
fillers such as microdispersed hydrated silicas, and carbon blacks, wherein
the mixture
ratio of light fillers to carbon blacks ranges from 1:0.05 to 1:20, preferably
from 1:0.1
to 1:10.
In addition to the aforementioned solution rubbers which contain
aminoisoprenes, the
rubber compounds according to the invention may also other rubbers, such as
natural
rubber and other synthetic rubbers also.
The preferred rubbers used for synthesis are described by W. Hofmann,
Kautschuk-
technologie, Gentner Verlag, Stuttgart 1980, and by I. Franta, Elastomers and
Rubber
Compounding Materials, Elsevier, Amsterdam 1989, for example. Amongst other
substances, they comprise
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BR - polybutadiene
ABRs - butadiene/acrylic acid C,~ alkyl ester copolymers
CR polychloroprene
IR - polyisoprene
SBRs - styrene/butadiene copolymers with styrene contents from 1 to 60,
preferably from 20 to 50 % by weight
IIRs - isobutylene/isoprene copolymers
NBRs - butadiene/acrylonitrile copolymers with acrylonitrile contents from 5
to
l0 60, preferably from 10 to 40 % by weight
HNBR - partially hydrogenated or completely hydrogenated NBR rubber
EPDM - ethylene/propylene/diene copolymers
as well as mixtures of these rubbers. Rubbers which are particularly suitable
for the
production of motor vehicle tyres, and which contain surface-modified fillers,
include
natural rubber, emulsion SBR rubbers and solution SBR rubbers with a glass
transition temperature above -50°C, which may optionally be modified
with silyl
ethers or other functional groups according to EP-A 447 066, polybutadiene
rubber
with a high 1,4-cis content (>90 %) which has been produced using catalysts
based on
Ni, Co, Ti or Nd, and polybutadiene rubber with a vinyl content of up to 75 %,
as well
as mixtures thereof which are of interest.
As mentioned above, additional rubbers can also be admixed with the rubber
compounds according to the invention, in addition to the solution rubber which
contains aminoisoprene. The amount of these additional rubbers usually falls
within
the range from 0.5 to 70, preferably from 10 to 50 % by weight with respect to
the
total amount of rubber in the rubber compound. The amount of rubbers which are
additionally added again depends on the respective purpose of use of the
rubber
compounds according to the invention.
The rubber compounds according to the invention may also of course contain
other
rubber adjuvant substances, which may be employed for crosslinking vulcanised
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products which are produced from the rubber compounds, for example, or which
improve the physical properties of vulcanised products produced from the
rubber
compounds according to the invention for the specific purpose of use thereof.
Examples of crosslinking agents which can be used include sulphur or compounds
which provide sulphur, or crosslinking agents which supply radicals, such as
organic
peroxides for example. Sulphur is preferably used as a crosslinking agent. In
addition,
and as mentioned above, the rubber compounds according to the invention may
contain other adjuvant substances such as known reaction accelerators, anti-
ageing
IO agents, thermal stabilisers, light stabilisers, ozone stabilisers,
processing aids,
plasticisers, tackifiers, foaming agents, colorants, pigments, waxes,
extenders, organic
acids, retardants and metal oxides, as well as activators.
The rubber adjuvant substances according to the invention are used in the
known
customary amounts, the amount used depending on the subsequent purpose of use
of
the rubber compounds. The customary amounts of rubber adjuvant substances fall
within the range from 2 to 70 parts by weight with respect to 100 parts by
weight of
the total amount of rubber which is present, for example.
The use of additional filler activators is particularly advantageous for the
rubber
compounds according to the invention, which are filled with highly active
hydrated
silicas. The preferred filler activators are silyl ethers which contain
sulphur,
particularly bis-(trialkoxisilylalkyl) polysulphides such as those described
in DE 2 141
159 and DE 2 255 577. Other suitable filler activators which can be used
include
mercapatoalkyltrialkoxysilanes, particularly mercaptopropyltriethoxysilane and
thiocyanatoalkylsilyl ethers (see DE 19 544 469). The filler activators are
used in the
customary amounts, i.e. in amounts from 0.1 to 15 parts by weight with respect
to 100
parts by weight of the total amount of rubber.
The rubber compounds according to the invention can be produced, for example,
by
mixing the aminoisoprene-containing solution rubbers, and optionally other
rubbers,
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with the corresponding fillers and rubber adjuvant substances in suitable
mixing
apparatuses such as kneaders, rolls, or extruders.
The present invention further relates to the use of the rubber compounds
according to
the invention for the production of vulcanised products, which in turn are
employed
for the production of highly reinforced rubber mouldings, particularly for the
production of tyres.
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Examines
Example 1:
S A solution of 120.1 g ( 1.15 mol) styrene, 175.0 g (3.24 mol) butadiene and
4.93 g
(0.044 mot) 5-(N;N-dimethylamino)-isoprene in 2300 ml of dry hexane were
placed in
a stirred autoclave. 1.54 ml of a 1.3 molar solution of sec-butyllithium in
cyclohexane/hexane were added thereto at 35°C. The reaction was
exothermic and
was restricted by cooling the batch to 60°C. After 1.5 hours,
polymerisation was
stopped by adding 0.1 ml methanol. The polymer was subsequently precipitated
in 14
litres of methanol and dried.
The dimethylaminoisoprene SBR rubber which was thus obtained had an average
(number average) molecular weight of 120,000 and a styrene content of 36 % by
weight. The butadiene content was 62.4 % by weight, with a 1,2-vinyl content
of 16
(with respect to the total polymer). The content of diaminoisoprene
incorporated by
polymerisation was 1.6 % by weight. The glass transition temperature was -
33°C, and
the viscosity ML 1+4 (100°C) was 20.
Examule 2:
A solution of 116.1 g ( 1.12 mol) styrene, 160.0 g (2.96 mol) butadiene and
23.8 g
(0.215 mol) 5-(N,N-dimethylamino)-isoprene in 2300 ml of dry hexane were
placed in
a stirred autoclave. 1.54 ml of a 1.3 molar solution of sec-butyllithium in
cyclohexane/hexane were added thereto at 35°C. The reaction was
exothermic and
was restricted by cooling the batch to 60°C. After 1.5 hours,
polymerisation was
stopped by adding 0.1 ml methanol. The polymer was subsequently precipitated
in 14
litres of methanol and dried.
The dimethylaminoisoprene SBR rubber which was thus obtained had an average
(number average) molecular weight of 120,000 and a styrene content of 36 % by
weight. The butadiene content was 56 % by weight, with a 1,2-vinyl content of
17
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* (with respect to the total polymer). The content of diaminoisoprene
incorporated by
polymerisation was 8 % by weight. The glass transition temperature was -
48°C.
Egamule 3:
'The following rubber compounds were produced at 130°C in a 1.5 litre
kneader.
Finally, were sulphur and an accelerator were admixed on a roll at
50°C.
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Comparative example Example according to
the invention
Mixed in the kneader:
$ Buna VSL 2035-0 solution SBR (Bayer75 0
AG)
rubber according to Example 1 0 75
Buna CB 11 polybutadiene rubber 25 25
(Bayer AG)
Vulkasil S precipitated hydrated 80 80
silica(Bayer AG)
Corax N 339 carbon black (Degussa) 6.5 6.5
Renopal 450 aromatic plasticiser 32.5 32.5
zinc oxide 2.5 2.5
stearic acid 1 1
Vulkanox 4020 antioxidant (Bayer 1 1
AG)
1654 ozone-protective wax (Rheinchemie)1.5 1.5
1$ Si 69 silane (Degussa) 3.5 3.5
admixed on the roll (50C):
sulphur 1.5 1.5
Vulkacit CZ N-cyclohexyl-mercaptobenzthiazole1.5 1.5
sulphenamide
Vulkacit D diphenylguanidine (Bayer2 2
AG)
Mooney viscosity ML I+4 (100°C) 106 106
vulcanisation kinetics at 160°C:
time to reach 6 % of the final torque value (minutes) 2.3 2.1
2$ time to reach 90 % of the final torque value (minutes) I 5.2 14.2
The rubber compounds were subsequently vulcanised at 160°C. The
vulcanised
products had the following properties:
3~ stress value at 300 % elongation8.8 12.9
(MPa)
tensile strength (MPa) 17.4 19.9
elongation at break (%) 520 459
hardness at 23C (Shore A) 75 79
rebound resilience at 30C (%) 39 45
3$ abrasion according to DIN 101 85
53 516 (ccm)
