Note: Descriptions are shown in the official language in which they were submitted.
21~973
RUBBER COMPOSITION HAVING EXCELLENT GRIPPING POWER
AND ROLLING RESISTANCE,AND PRODUCTION THEREOF
This invention relates to a rubber composition suited
for tires, in particular, to a rubber composition
exhibiting excellent wet-gripping property, ice-gripping
property and low rolling resistance. The invention also
relates to a process for producing the same.
In the field of automobiles, such factors as running
stability and braking capability, in particular, braking
capability on a wet road surface and on a road covered with
snow or ice have become increasingly important in recent
years, as well as the lowering of fuel consumpt.ion to save
resources and energy. Because of this, demands for rubber
materials for use in tires have been ever more severe.
Basic properties required for such rubber materials`
to be used for tires.are as follows:
(1) to have a certain level of hardness due to the necessity for
carrying huge static loads, and also to be excellent in
failure characteristics, such as resistance to flexural fatigue,
durability and abrasion resistance, against external
forces repeatedly applied for a prolonged period of
time;
. .
2 ~ 7 ~
(2) to have low rolling resistance required for lowered fuel
consumption, more specifically, to have a small loss
factor (tan ~) determined by a dynamic viscoelasticity
test of vulcanized rubber with a frequency of 10 to 100
Hz at a temperature range of 50 to 80C; and
(3) to be excellent in braking capability on a wet road
surface (wet-gripping property) and in braking capability on a
road surface covered with snow or ice (ice-grippmg property),
more specifically, to have a large loss factor (tan ~)
determined by the dynamic viscoelasticity test ofvulcanized rubber
and measured with a frequency of 10 to 100 Hz at a
temperature range of -20 to +30C.
Of the above properties, the rolling resistance of
item (2~ and the wet- and ice-gripping properties of item (3)
are said to be physical properties caused by the hysteresis
loss of the rubber. That is to say, the rolling resistance of
a tire corresponds to the energy dissipation of the tire
upon driving where the rubber is subjected to a periodic
deformation of relatively low frequency. In order to lower
the rolling resistance, the hysteresis loss of the rubber
composition must be decreased. On the other hand, the wet-gripping
property and ice-gripping property correspond to energy
dissipation upon bra~ing when the rubber is subjected to a
2 ~ 7 .~
periodic high-frequency deformation formed between the tire
tread and the fine irregularities on the road surface.
In order to improve the wet- and ice-gripping properties, the
hysteresis loss of the rubber composition must be increased.
Therefore, it has been thought that the above tw~ physical
properties are contradictory.
However, the frequency of periodic deformation to which
the tire is subjected at the time Of driving is greatly
different from that which it is subjected to at the time of
braking. It is known that, when the deformation frequency is
converted into a temperature in accordance with the
Williams-Landel-Ferry's temperature conversion equation and
the dynamic viscoelasticity test is carried out with a
determination frequency of 10 to 100 Hz, the rolling resistance
has a good correlation with the loss factor ttan ~:an
index for hysteresis loss) in a temperature range of 50
to 80C, the wet-gripping property with tan ~ in the
range of 0 to 30C, and the ice-gripping property with
tan ~ in the range of -20 to 0C, respectively. It would
therefore be understood that low rolling resistance, high wet-
gripping property and high ice-gripping property can be
satisfied simultaneously if the value of tan ~ could be made
larger in the low-temperature range of -20 to +30C and the
value of tan ~ could be made smaller in the high-temerature
range of 50 to 80C.
21Q~7~
The hitherto proposed techniques for satisfying such
requirements for tread rubber materials included, for example, one in
which a polybutadiene rubber or a styrene/butadiene copolymer
rubberhaving a high 1,2-structure content in butadiene units and
obtainable by solution polymerization is used as
a base rubber;one in which a plurality of rubbers having
different glass transition temperatures are blended; one
in which a polybutadiene rubber or a styrene/butadiene
copolymer rubber having a tin-carbon linkage c~n~ained in the
molecular chain, or a polybutadiene rubber or a
styrene/butadiene copolymer rubber having a polymer chain
added with amino group-containing benzophenones, lactams or
ureas is used as a base rubber; and one in which ;
modified carbon black or a modifier is compounded.
It has been practiced to apply such modified rubbers or
modified carbon black to rubbers to be used for tires.
However, such modified rubbers and modified carbon black
have a serious problem concerning the safety of tires in
that, although they reduce to a certain extent the fuel
consumption, their low-temperature properties (such as ice-
gripping property and wet-gripping property) are still not
sufficient, or rather their low-temperature properties are
deteriorated by the lowering of fuel consumption. It has
therefore been desired to improve the two contradicting
properties (fuel consumption and low-temperature property) at
2100~73
the same time, while maintaining the strength of the rubber.
In view of the above, the present inventors have
conducted intensive investigations to develop a rubber
composition which has sufficiently high tan ~ at a
temperature range of -20 to +30C to improve the braking
capability of tires on a wet road surface and on a snow-covered or
froze~ road surface (wet-gripping property and ice-gripping
property) and besides has low tan ~ at a temperature
range of 50C to 80C, thereby balancing the low-
temperature property and the rolling resistance. This
invention has been accomplished as a result of the
investigations.
This invention provides a rubber composition which comprises:
(A) 100 parts by weight of a rubber comp~nent comprising at
least 50~ by weight of a styrene/butadiene copolymer
rubber;
(B) 1 to 6 parts by weight of an azodicarboxylic ester
compound represented by the formula (I):
X-OC-N=N-CO-X (I)
O O
2~97~
wherein X is an allcyl of 3 to 8 carbon atoms, an
unsubstituted or substituted phenyl, or an unsubstituted or
substituted benzyl;
(C) 60 to 250 parts by weight of carbon black having a
nitrogen absorption specific surface area of 100 to 250
m~!g and a dibutyl phthalate absorption number of 110
to 170 ml/lO0 g;
(D) 0.5 to 4 parts by weight of sulfur; and
(E) 0.3 to 3 parts by weight of a benzothiazole
vulcanization accelerator;
said components (B) through (E) being incorporated into said
rubber component in a rubber processing machine.
Upon production of the composition, it is preferred to
blend the rubber component (A) at first with the azodicarboxylic
ester compound (8) and carbon black (~) at a high temperature,
followed by the addition of the sulfur (D) and the vulcanization
accelerator (E) at a low temperature. Accordingly, this.
invention also provides a process for producing a rubber compo-
sition which comprises:
blending, by using a rubber processing machine,(A) 100
parts by weight of a rubber component comprising at least 50%
21~7~
by weight of a styrene/butadiene copolymer rubber at a
rubber temperature of 50 to 190C with (B) 1 to 6
parts by weight of the azodicarboxylic ester compound
represented by the above formula (I) and (C) 60 to
250 parts by weight of carbon black having a nitrogen
absorption specific surface area of lO0 to 250 m2/g and a
dibutyl phthalate absorption number of 110 to 170 ml/100 g;
blending the resulting mixture at a rubber
temperature of 10 to 120C with (D) 0.5 to 4 parts by
weight of sulfur, and (E) 0.3 to 3 parts by weight of a
benzothiazole vulcanization accelerator; and
vulcanizing the resulting mixture.
Further, this invention provides a method for increasing
a loss factor of a vulcanized rubber in a low temperature
range of -20 to +30C as well as lowering the loss factor of
the vulcanized rubber at a high temperature range of 50 to
80C, said loss factor being determined by a dynamic
viscoelasticity test with a fre~uency of 10 to 100 Hz, said
method comprising:
blending, in a rubber processing step, (A) 100 parts
by weight of a rubber component comprising at least 50% by
weight of a styrene/butadiene copolymer rubber at a
rubber temperature of 50 to 190C with (B) 1 to 6 parts
by weight of an azodicarboxylic ester compound represented by
the above formula (I) and (C) 60 to 250 parts by
2~00~7~
weight of carbon black having a nitrogen absorption specific
surface area of 100 to 250 mZ/g and a dibutyl phthalate
absorption number of 110 to 170 ml/100 g;
blending the resulting mixture at a rubber temperature
of 10 to 120C with (D) 0.5 to 4 parts by weight of
sulfur, and (E) 0.3 to 3 parts by weight of a benzothiazole
vulcani~ation accelerator; and
vulcanizing the resulting mixture.
A major portion of the rubber component to be used in
the invention is a styrene/butadiene copolymer preFared by copolymerizing
styrene and butadiene. The styrene/butadiene copolymer may
be prepared by either solution polymerization or emulsion
polymerization. It is preferred to use a styrene/butadiene copolymer
rubber containing 10 to 50~ by weight of a styrene
unit and containing 20 to 80% by weight of a 1,2-structure in
a butadiene unit. When butadiene is
(co)polymeri~ed, some part bonds at a
1,2-position,and ano~her part at a 1,4-position. The
term "1,2-structure" herein means a polymerization unit
derived from butadiene and bonded at the
1,2-position. Of the ordinary styrene/butadiene copolymer
rubbers, those having a high styrene unit content, in
particular, those containing 30 to 50% by weight of the styrene
unit are more preferred.
Other examples of preferred styrene/butadiene copolymer
2 ~ a~7 ~
rubbers include those modified by introducing an amino group-
containing benzophenone compound into the terminals of the
copolymer molecules, as well as those coupled with tin or
silicon. The amino group-containing benzophenone compound
which can be introduced into the terminals of the copolymer
molecules is preferably represented by the formula (II):
Q O Q
N _ ~ C ~ ! N (II)
Q Q
wherein Q is methyl or ethyl.
The styrene/butadiene copolymer rubbers modified with the
benzophenone or coupled with tin or silicon, pre~erably have the
following characteristics:
(A1) a styrene unit of 10 to 30% by weight and a butadiene
unit of 90 to 70% by weight;
(A2) a 1,2-structure of 20 to 80% by weight in the butadiene
unit; and
(A3) a Mooney viscosity value of 30 to 80 indicated by
MLl+4 ( 100 C ) .
21~9~
These s~rene~butadiene copolymer rubbers modified with the benzo-
Ehenone compound or coupled with tin or silicon are capable of exhibiting
excellent low rolling resistance and wet- and ice-gripping
properties, in particular, when the azodicarboxylic ester
of the formula(I) is incorporated. In the styrene/butadiene
copolymer rubbers coupled with tin, branched copolymers
having a; tln-butadienyl bond can be contained preferably in an
amount of 30% by weight or more.
The styrene/butadienè copolymer rubbers modified with the
benzophenone ccmpound can be produced by a known method, as described, for
example, in Japanese Patent Kokai (Laid Open) Nos.
197,443/84, 8,341/85 and 8,342/85. More specifically,
styrene may be copolymerized with butadiene by means of
solution polymerization in a hydrocarbon solvent and using an
organic lithium compound as a polymerization initiator (so-
called living polymerization process), and the
resulting copolymer may be reacted with the benzophenone
compound represented by the above formula (II) to produce
the modified styrene/butadiene copolymer rubber.
Considering economic aspects and side reactions,
it is preferred that the copolymerization be carried out at
a temperature of about 0 to about 150C, although the
polymerization temperature may be varied depending on the
21D0~79
desired microstructure. The content of the 1,2-structure in the
butadiene unit can be controlled, for example, by using a
Lewis base such as ethers or tertiary amines and changing the
kind and quantity thereof, or by selecting appropriate poly-
merization conditions including the polymerization temperature.
Specific examples of the benzophenone compound represented
by the formula (II) to be used in the modification include
4,4'-bis(dimethylamino)benzophenone and 4,4~-
bis(diethylamino)benzophenone. The benzophenone compound
is used preferably in an amount of about 0.2 to about 1.5
equivalents, per equivalent weight of the lithium atoms at
the polymerization terminals. It can be effective, with
regard to ~failure characteristics and rolling resistance,to allow
a-part ofthe polymerization terminals to react with a
coupling compoundr such as tin tetrachloride,
before reacting with the benzophenone compound of the
formula (II), so that branched copolymers be contained. In
cases where such a branched copolymer is formed, the coupling
compound, such as tin tetrachloride, must be used in a
quantity not deteriorating the effects of the modification with the
benzophenone compound, and is usually used in an amount of
about 0.01 to about 0.2 equivalent, per equivalent weight
of lithium atoms at the polymerization terminals.
The styrene/butadiene copolymer rubber coupled with tin
210~97~
or silicon can be produced by a known method as described,
for example, in Japanese Patent Kokai (Laid Open) No.
308,011/88. To be more specific, styrene may be
copolymerized with butadiene by means of solution
polymerization in a hydrocarbon solvent and using an
orgapic lithium compound as a polymerization initiator,to give
a copolymer having a butadienyl-lithium bond at a
polymerization terminal, which is then subjected to a
coupling reaction with a halogenated tin compound or a
halogenated silicon compound to produce the desired
copolymer rubber. It can be preferred to add a small
quantity of butadiene at the end of the copolymerization,
so as to form the butadienyl-lithium bond.
Examples of compounds to be used for the coupling
reaction include halogenated tin compounds, such as tin
tetrachloride, phenyltin trichloride and tributyltin
chloride, and halogenated silicon compounds, such as
silicon tetrachloride. The use of silicon tetrachloride is
particularly preferred. The content of the 1,2-structure in
the butadiene unit can be controlled by using a Lewis
base, such as ethers or tertiary amines, and changing the
kind and ~uantity thereof, orlby selecting appropriate poly-
merization conditions including a polymerization tem~erature. -It
is preferred,considering economic aspects and side reactions,
that the copolymerization be carried out at a temperature
12
21~7~
of about 0 to about 150C, although the polymerization
temperature may be varied depending on the desired
microstructure. The halogenated tin compound or
halogenated silicon compound is used for the coupling
reaction preferably in an amount of about 0.08 to about 0.5
equivalent, per equivalent weight of lithium atoms at the
polymerization terminals.
In the case of solution polymer~ed styrene/butadiene copolymer
rubbers, it is also possible to use those whose molecules are modified
with a modifier, including ureas, such as tetramethyl urea
and tetraethylurea, and amino group-containing unsaturated
compounds, such as N-(N',N'~dimethylaminopropyl)acrylamide.
The rubber component according to the invention
mainly comprises the styrene/butadiene copolymer, as has been
e~plained hereinabove. The copolymer can be used either
alone or in the form of a blend containing the copolymer in
an amount of 50% by weight ormore and another rubber in an amount
of up to 50% by weight. Examples of the other rubbers to be blendable
include natural rubber and various kinds of synthetic
rubbers, such as polyisoprene rubber (IR), polybutadiene
rubber (BR), acryloritrile/butadiene copolymer rubber
(NBR), isoprene/isobutylene copolymer rubber (IIR), and
ethylene/propylene/diene copolymer rubber (EPDM). The
use of diene rubbers is preferred, in
13
210~a~
particular, natural rubber, polyisoprene rubber,
polybutadiene rubber, and the like. In the case of
blending another rubber, it is preferred that the other
rubber be blended in an amount of 5% by weight or more,
based on the total weight of the rubber component.
Accordingly, in a blending system, the styrene/butadiene
copolymer rubber is preferably blended in an amount of 50
to 95% by weight, and another rubberin an amount of 50 to
5% by weight.
In the invention, it is preferred to use the styrene/
butadiene copolymer alone, or to use a mixture mainly
comprising the styrene/butadiene copolymer and blended
with natural rubber, polyisoprene rubber and/or
polybutadiene rubber.
The azodicarboxylic ester compou~d of the component
(B) represented by the formula (I)can be synthesized, for
example, by reacting hydrazine with a corresponding chloroformic
ester in an aqueous solution and in the presence of a base, such as
sodium carbonate or potassium carbonate, to give a
hydrazodiformate, and then oxidizing the hydrazodiformate
by the use of an oxidant, such as fuming nitric acid,
chlorine or bromine.
In the formula (I), X is an alkyl of 3 to 8
carbon atoms, an unsubstitu~ed or substituted phenyl, or an
unsubstituted or substituted benzyl.
14
21~979
Examples of the alkyl denoted by X include n-propyl,
isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl,
hexyl, octyl, and the like. These alkyls can be, of course,
straight-chained, and besides they can also be branched or
cyclic. Of these groups,acyclic alkyls of 3 to 5 carbon atoms and,
in particular, branched alkyls are preferred.
The phenyl denoted by X can be either unsubstituted or sub-
stituted. In the latter case, it may have such substituent as an alkyl
of 1 to 8 carbon atoms, an alkoxy of 1 to 8 carbon atoms, an
alkanoyl of 2 to 9 total carbon atoms, an N,N-dialkylamino, nitro,
cyano, carboxyl, halogen, or the like. The alkyl contained in the N,N-
dialkylamino may have 1 to 6 carbon atoms. Examples of the
halogen include fluorine, chlorine, bromine and iodine. In
the case where the phenyl has a substituent, the substituent may be
situated at any of the ortho-, meta- and para-positions.
Examples of the preferred phenyl include unsubstituted phenyl, p-nitrophenyl,
p-methylphenyl, and the like.
The benzyl denoted by X can also be either unsubstituted
or substituted. A substituent for the benzyl can be an alkyl
of 1 to 8 carbon atoms, an alkoxy of 1 to 8 carbon atoms, an
alkanoyl of 2 to 9 total carbon atcms, an N,N-dialkylamino, nitro, cyano,
carboxyl, halogen, or the like. The alkyl contained in the N,N-
dialkylamino may have 1 to 6 carbon atomS- Examples of the
halogen include fluorine, chlorine, brcmine and iodine. When the benzyl
has a substituent, the position of the substituent may be any of
ortho-, meta-and para-positions. Examples of the preferred benzyl include
unsubstituted benzyl, p-nitrobenzyl, p-methylbenzyl, and the like.
Representative azodicarboxylic ester ccmpounds of the formula (I)
usable in the i~vention are as follows, but they are given for the purFose
of illustration and not limitation.
2la~79
(1) Di-n-propyl azodicarboxylate
(2) Diisopropyl azodicarboxylate
(3) Di-n-butyl azodicarboxylate
(4) Diisobutyl azodicarboxylate
(5) Di-tert-butyl azodicarboxylate
(6) Dihexyl azodicarboxylate
(7) Dioctyl azodicarboxylate
(8) Diphenyl azodicarboxylate
(9) Bis(p-nitrophenyl) azodicarboxylate
(10) Bis(p-methylphenyl) azodicarboxylate
(11) Bis(p-bromophenyl) azodicarboxylate
(12) Bis(p-chlorophenyl) azodicarboxylate
(13) Bis[p-(N,N-dimethylamino)phenyl] azodicarboxylate
(14) Dibenzyl azodicarboxylate
(15) Bis(p-nitrobenzyl) azodicarboxylate
(16) Bis(p-methylbenzyl) azodicarboxylate
(17) Bis(p-bromobenzyl) azodicarboxylate
(18) Bis(p-chlorobenzyl) azodicarboxylate
(19) Bis[p-(N/N-dimethylamino)benzyl] azodicarboxylate
The azodicarboxylic ester compound of the formula (I)
can be added to rubber either individually or in the form
of a mixture of two or more of the compounds. It is also possible
to add the compound in the form of a mixture with a
carrier such as clay which exerts no adverse
effects on the properties of the rubber. The
16
210~79
azodicarboxylic ester compound can be incorporated in an
amount of from l to 6 parts by weight, per 100 parts by
weight of the rubber. When the amount is less than 1 part
by weight, it will not be possible to attain a sufficiently
improved effect, whereas when it exceeds 6 parts by weight,
the resulting rubber will exhibit a marked decrease in
reinfQrcement, for exam~le, undesirable lowering in
tensile strength, cross-linking density and abrasion
resistance. In addition, the effect on lowering the
rolling resistance tends to be lessened.
The component (C)!used in the invention is carbon black
having a nitrogen absorption specific surface area
(hereinafter referred to as "N2SA") of from 100 to 250 m2/g
and a dibutyl phthalate absorption number ~hereinafter
referred to "DBP absorption number") of 110 to 170
ml/100 g. An N2SA of less than 100 m2/g will result in a
deterioration of the wet-gripping property and the ice-
gripping property, whereas an N2SA of greater than 250 m2/g
will result in an inferior heat build-up resistance, and in no
improvement of rolling resistance. ~ When the
DBP absorption number is less than 110 ml/100 g, inferior
wet- and ice-gripping properties will be attained, w~ereas when it
exceeds 170 ml/100 g, deteriorations in abrasion resistance
and rolling resistance will be observed.
The carbon black is incorporated in an amount of 60 to
17
7 J
250 parts by weight, or preferably from about 60 to about
150 parts by weight. When the amount of the carbon black
incorporated is less than 60 parts by weight, an inferior
reinforcement of the rubber will be attained and wet- and
ice-gripping properties will not be sufficiently improved,
whereas when it is greater than 250 parts by weight,
results in undesirable lowering of the heat
build-up resistance and blow out resistance will be observed.
In the invention, any sulfur generally employed in
the rubber industry can be used as the component (D)- From
the viewpoints of the heat resistance, tensile strength and
abrasion resistance of the rubber, the
sulfur is incorporated in an amount o* 0.5 to 4
parts by weight, per 100 parts by weight of the rubber.
As thebenzothiazole vulcanization accelerator f the
component (E), various compounds having a benzothiazole
nucleus can be used. Specific examples of usable
benzothiazole vulcanization accelerators include
2-mercaptobenzothiazole, dibenzothiazyl disulfide,
N-cyclohexyl-2-benzothiazylsulfenamide,
N-tert-butyl-2-benzothiazylsulfenamide, N,N-dicyclohexyl-2-
benzothiazylsulfenamide, N-oxydiethylene-2-
benzothiazylsulfenamide, and the like. From the viewpoints
of heat resistance, abrasion resistance,tensile strength and
flex cracking resistance, the benzothiazole vulcanization
18
210~'7~
accelerator is used in an amount of 0.3 to 3 parts by weight,
per 100 parts by weight of the rubber.
Upon compounding rubber materials for tire treads,
process oils have often been used to improve the gripping
performance of tires. In this invention, too, the use of a
process oil is admissible and advantageous. Though there is
no particular restriction on the amount of the process oil
to be blended, it is, in general, used in an amount not
greater than 100 parts by weight, and preferably in an amount
of 5 to 100 parts by weight, per 100 parts by weight of the
rubber. There is also no particular restriction on the kind
of the process oil to be used, and any process oils which
have hitherto been employed in the rubber industry can also
be used in the invention.
It is a matter of course that various other chemicals
which have hitherto been employed in the rubber industry can
also be used in the invention, as occasion demands, and such
chemicals include, for example, antioxidants, retarders,
peptizers, softeners, petroleum resins, and the like.
There is no particular restriction on the method used
to produce the rubber composition of the invention, but each
of the components is blended by using a rubber processing
machine. The rubber processing machine herein means a roll-
type or closed-type kneading machine which is conventionally
used in rubber compounding. Examples of usable closed-type
kneading machines include Bambury mixers, kneaders, intermixes,
and the like. The rubber component and other ingredients are
directly kneaded in such a rubber processing machine.
19
2 1 ~
Upon compounding the components, it is possible to
adopt a method in which the rubber component (A) is at first
blended and kneaded with the azodicarboxylic ester compound
of the component (B), and thereafter the carbon black of
the component (C) is added to the resulting mixture, followed
by the compounding of the sulfur of the component (D) and
the vulcanization accelerator of the component tE). In this
case, the azodicarboxylic ester is added to the rubber
component at a relatively low temperature, for example, at
a rubber temperature of around 4~ to 100C, and after
kneading, the carbon black is added at a temperature higher
than the above temperature, for example, at a rubber tem-
perature of around 100 to 180C. After kneading, the
resulting mixture is then cooled to a rubber temperature of
around 40 to 100C, followed by adding the sulfur and the ~-
vulcanization accelerator.
However, in order to achieve the effects of the invention
more advantageously, it is preferred to adopt a method in
which the azodicarboxylic ester compound and the carbon black
are added at first to the rubber component, and after kneading
the resulting mixture for about 0.5 to 30 minutes, the
sulfur and the vulcanization accelerator are added thereto,
followed by vulcanization.
2 1 ~ 7 ~
Such a two-step blending process is a simple and
convenient manner and exhibits an improvement in the
ice-gripping and wet-gripping properties, as well as
lowering in the rolling resistance. In the case where such
a two-step compounding is employed, the addition of the
azodicarboxylic ester compound and carbon black is carried
out usually at a rubber temperature in the range of
50 to 190C, preferably 50 to 120C. On the other hand,
the addition of the sulfur and vulcanization accelerator is
carried out usually at a rubber temperature in the
range of 10 to 120C, preferably 10 to 70C. It is
preferred that the sulfur and the vulcanization
accelerator are added to the rubber at a temperature not higher
than that at which the preceding addition of the
azodicarboxylic ester compound and the carbon black is
carried out.
The thus compounded rubber composition according to
the invention can be advantageously used, e.g., in
various parts of tires, in particular, in a tread. For
example, the rubber composition can be applied to the
tread or other parts of tires, shaped according to a
method conventionally employed in the tire industry and
then subjected to vulcanization, to produce the tires. The
vulcanization is preferably carried out at a temperature
range of approximately 80 to 180C.
21
210Q97~
This invention will further be explained in detail by
way of examples. It should, however, be understood that
the invention is by no means limited by the examples. In
the following examples, percentages and parts denoting
amounts or contents are based on weight unless otherwise
specifically noted. The following is a list of
azodicarboxylic ester compounds used in the examples and
their symbols.
A: Diisopropyl azodicarboxylate
B: Di-tert-butyl azodicarboxylate
C: Diisobutyl azodicarboxylate
D: Diphenyl azodicarboxylate
E: Bis(p-nitrophenyl) azodicarboxylate
F: Dibenzyl azodicarboxylate
21~7~
Example 1
[Compounding Formulation]
Parts
Styrene/butadiene copolymer rubber prepared by 137.5
emulsion polymerization (having a styrene unit
content of 35% and a 1,2-structure content
of 25% in a butadiene unit and containing
37.5 parts of aromatic oil per 100 parts of
the rubber) -
ISAF carbon black (N220) (having an N2SA of 80
125 m2/g and a DBP absorption number of
130 ml/100 g~
Stearic acid 3
Zinc oxide 5
Aromatic process oil 12.5
Antioxidant (N-phenyl-N'-1,3-dimethylbutyl-p- 2
phenylenediamine)
V~lcanization accelerator (N-cyclohexyl-2-
benzothiazylsulfenamide)
Sulfur 2
Azodicarboxylic ester Shown in Table 1
The rubber component shown in the above formulation
was charged into an open mill. While maintaining its
temperature at 40 to 50C, the azodicarboxylic ester shown
in Table 1 was added thereto, and the mixture was kneaded
for 5 minutes. The resulting rubber blend was transferred
into a 250 ml Laboplastomill (a type of Bambury mixer)
23
2~Q0~7~
manufactured by Toyo Seiki Co. At an oil bath temperature
of 170C, the carbon black, stearic acid, process oil,
antioxidant and zinc oxide shown in the formulation were
charged into the mill, and the mixture was kneaded for 5
minutes at a mixer revolution of 50 rpm, during
which the rubber temperature was 160 to 170C. The
rubber blend was then transferred into the open mill, and
the vulcanization accelerator and the sulfur were added at
a temperature of 40 to 50C. After kneading, the
resulting rubber composition was vulcanized at 170C by use
of a vulcanization press, formed into a predetermined shape
and then subjected to the following tests. A control
sample, in which the azodicarboxylic acid was not used, was
also prepared, starting from the kneading in the Bambury
mixer.
Determination of tan ~
Tan ~ was determined at temperatures in the range of
from -50C to +100C under conditions of an initial static
strain of 10%~ a dynamic strain amplitude of 0.25% and a
frequency of lO Hz, using a viscoelasticity spectrometer
manufactured by Iwamoto Seisakusho Co.
Tensile Test_ accordinq to JIS K 6301
Test pieces (dumbbell No. 3)
24
210~97~
of vulcanized rubbers were prepared from the above rubber
compositions. The test pieces were subjected to a tensile
testat a room temperature to determine tensile stress (Mloo,
M300 and Msoo)-
Of the test results obtained, tan ~ at 0C, 20C, 40Cand 60C and Mlcol M300 and M500 are shown in Table 1,
together with the kinds and quantity of the azodicarboxylic
ester used.
210G97~
_ ~
~ , , , ~ ~ ~ , I
1~ 1~1 ~o i-- O N N ~JI tl~ ~ ¦ ~P
0 O ~1 1_ 1_ ~ ~ ~n ~ ~n ~
~ o o~ I_ ~ ~ ~n _~ ~1
,_ ~, ,_ O O o o l l co n ,~
__= _ _ _ _ = ~ ~o
2 1 ~ 3
Example 2
[Compounding Formulation]
Parts
Styrene/butadiene copolymer rubber prepared by
solution polymerization (having a styrene unit 144content of 40% and a 1,2-structure content
of 49% in a butadiene unit, and containing
44 parts of aromatic oil per 100 parts of
the rubber~
SAF c~rbon black (NllO) (having an N2SA of 100140 m /g and a DBP absorption number of
132 ml/100 g)
Stearic acid 3
Zinc oxide 5
Aromatic process oil 50
Vulcanization accelerator (N-cyclohexyl-2-
benzothiazylsulfenamide)
Sulfur 2
Azodicarboxylic ester Shown in Table 2
The procedure of Example 1 was repeated, except that
the f ormulation was changed to the above. The results are
shown in Table 2. In this case, however, it was not
possible to determine M500 since the test pieces were broken
before reaching an elongation rate of 500% in the tensile
test.
27
21~979
~=~ r~
.~ o~
_ O ~ A --~ ~ n q
I ~ ~ ~ ~n ~n ~ 1-
o= _ o o __ _
~ N N OO O _ ~ N H
1~ ~' u~ ~ (~ ~, ~ ~3
O~) ¦_ O O O O _ N
1'~ ~ ~ ~Jl ~i ~
~ ~ r ~ ~ ~
21~G97!~
ExamPle 3
(1) Synthesis of Benzophenone-modified Styrene/Butadiene
Copolymer Rubber (SBR-1)
Under a nitrogen atmosphere, cyclohexane, 1,3-butadiene,
tetrahydrofuran and styrene are charged into a reactor
equipped witha stirrer and a jacket. After a temperature
is ~ adjusted to 30C, n-butyl lithium is added to
start polymerization. After the temperature is raised
to 70C, polymerization is carried out for 2 hours, so as
to allow the polymerization conversion rate to reach 100%.
A small quantity of tin tetrachloride is then added, and
a coupling reaction is allowed to proceed at 70C for 15
minutes. Thereafter, 4,4'-bis(diethylamino)benzophenone is
added, and a modification reaction is allowed to proceed at 60~C for
30 minutes. To a copolymer solution obtained in such a way
2,6-di-tert-butyl-p-cresol is added~ and then the solvent
is removed by means of steam stripping. The resulting
product is then dried on a heat roll of 110C to obtain a
modified copolymer. The content of a styrene unit in the
thus obtained copolymer and the content of a 1,2-structure in
a butadiene unit are determined by using an infrared
spectrophotometer.
A modified styrene/butadiene copolymer rubber (SBR-1)
29
210~7~
having a styrene unit content of 24%, a 1,2-structure
content of 34% in a butadiene unit and a Mooney
viscosity of 45 MLl~4(loooc) was prepared in accordance
with the above procedure.
(2) Production and Tests of Rubber Composition
[Compounding Formulation]
Parts
Styrene/butadiene copolymer rubber (SBR-1) 100
HAF-HS carbon black (having an N2NA of 60
104 m2/g and a DBP absorption number of
124 ml/100 g)
Stearic acid 3
Zinc oxide 2
Antioxidant (N-phenyl-N'-1,3-dimethylbutyl-p-2
phenylenediamine)
Vulcanization accelerator (N-cyclohexyl-2-
benzothiazylsulfenamide)
Sulfur 2
Azodicarboxylic ester Shown in Table 3
According to the above formulation, the
2~00979
styrene/butadiene copolymer rubber, azodicarboxylic
ester, carbon black, stearic acid, zinc oxide and
antioxidant were charged into a 250 ml Laboplastomill (a
Bambury mixer manufactured by Toyo Seiki Co.), and the
contents were kneaded for5 minutes at an oil bath temperature
of 120C, with a mixer revolution of 50 rpm.
During.the kneading, the temperature of the contents was
105 to 117C. The resulting rubber blend was transferred
into an open mill, and it was mixed and kneaded with the vulcanization
accelerator and the sulfur shown in the above formulation
a~ a temperature of 60 to 70C. After kneading,
the resulting rubber composition was vulcanized at 160C
for 40 minutes by use of a vulcanization press and then
subjected to the following tests.
Determination of tan ~
Tan ~ was determined at 60C, 20C and -20C under
conditions of an initial static strain of 10%, a dynamic
strain amplitude of 0.5% and a frequency of 10 Hz, using a
viscoelasticity spectrometer manufactured by Iwamoto
Seisakusho Co. The value of tan ~ at 60C corresponds to
the rolling resistance; a smaller tan ~ value means a larger
improvement in lowering the rolling resistance. On the other
hand, the value of tan ~ at 20C corresponds to the wet-
gripping property, and the value of tan ~ at -20C
31
21~0979
corresponds to the ice-gripping property. A greater value
of tan ~ at 20C and -20C means a greater effect of
improving the wet- and ice-gripping properties.
Tensile Test according to JIS K 6301
Test pieces (dumbbell No. 3)
of vu~canized rubbers were prepared from the above rubber
compositions. The test pieces were subjected to a tensile
test at a room temperature to determine their tensile
strength and tensile stress (M300).
Test results obtained are shown in Table 3, together
with the kinds and quantity of the azodicarboxylic ester used.
1 ~ 2 0 09 7~
3 n n n o ~ c
~- O O O _, _. _
I .P Ul ~_ I_ ~D ~n ~ ~ I
~ ~I o o o ~n ~ ~ 1 1~3
~ ~P ~ ~ _ _ _~ jC ,
w 1,- ,_ o o o o I
I ~ ~ ~ ~ ~ ~n ~ ~ ~ i
~ o o o 1
I ~ c~ ~ I_ ~o ~n ~ ~ I ~
~ 1- o __ _ ~n ~ (D
~ ~ o o ~ _ _ n I
~ -o o- ~n ~ cn 0~
~1 ~ ~
O _ O o ~n ~ c
L~ a~ ~ ~= ~n _ _
21~979
Example 4
(1) Synthesis of Tin-coupled Styrene/Butadiene Copolymer
~ubber (SBR-2)
Under a nitrogen atmosphere, cyclohexane, 1,3-butadiene,
tetrahydrofuran and styrene are charged into a reactor
equipped with a stirrer and a jacket. After a temperature
is adjusted to 30C, n-butyl lithium is added to
start polymerization. After the temperature is
raised to 70C, polymerization is carried out for 2 hours,
so as to allow the polymerization conversion rate to reach
100~. A small quantity of 1,3-butadiene is added to render
the polymerization terminals to butadienyl anions, and a
coupling reaction is allowed to proceed at 70C for 30
minutes with the addition of tin tetrachloride. To the
copolymer solution obtained 2,6-di-tert-butyl-p-cresol is
added, and then the solvent is removed by means of steam
stripping. The resulting product is then dried on a heat
roll of 110C to obtain a copolymer. The content of a styrene
unit in the thus obtained copolymer and the content of a
1,2-structure in a butadiene unit are determined by
using an infrared spectrophotometer. The ratio of a
branched copolymer is determined by means of gel permeation
chromatography ~GPC), based on the relative height of peaks
of molecular weight distribution.
34
21~979
A styrene/butadiene copolymer rubber (SBR-2) having a
styrene unit content of 24~, a 1,2-structure content
of 35% in a butadiene,unit and a Mooney viscosity of 55
ML1~4 ( lO C ) and containing 38% of a branched copolymer
was prepared in accordance with the above procedure.
(2) Pr,oduction and Tests of Rubber Composition
The procedure described in paragraph (2) of Example 3
was repeated, except that SBR-2 obtained above was used as
a styrene/butadiene copolymer rubber. Results of the tests
are shown in Table 4, together with the kinds and amount of
the azodicarboxylic esters used.
210~9~3
1~
~ I =~ ~ o ~n ~ I I
~ ~1
l ~t~
21~B`97~
Example 5
[Compounding Formulation]
Parts
Styrene/butadiene copolymer rubber prepared by
emulsion polymerization (having a styrene unit 137.5
content of 35% and a 1,2-structure content
of 25% in a butadiene unit and containing
37.5 parts of aromatic oil per 100 parts of
the rubber)
ISAF carbon black (having an N2SA of 90
126 m2/g and a DBP absorption number of
114 ml/100 g)
Stearic acid 3
Zinc oxide 2
Aromatic process oil 12.5
Antioxidant (N-phenyl-N'-1,3-dimethylbutyl-p-
phenylenediamine)
Vulcanization accelerator (N-tert-butyl-2- 1
benzothiazylsulfenamide)
Sulfur 2
Azodicarboxylic ester Shown in Table 5
The procedure described in paragraph (2) of Example 3
was repeated, except that the formulation was changed as
above. Results of the tests are shown Table 5, together
with the kinds and amount of the azodicarboxylic esters used.
21 ~G979
=~
~ ~ n n ~ ~ ~ ~ ¦
O O ~ ~ _~ ~
~, Lll o o o
o o o ~n W ~ r~l
~ o~ o o o I n ~ 1~ r ~
~ o o o o (n ~ P -I
I ~1 o~ ~ ~ ~ l l ~n I
_ O O ~ _ __ rO~ I ~n
~: ~
I O ~ ~ CO ~_~ CO ~ I
_ o o o _ f~,
~n ~P ~> 1.~ ~ (D __ ~
210~979
When a particular azodicarboxylic ester, a particular
carbon black, sulfur and a benzothiazole vulcanization
accelerator are compounded with a styrene/butadiene
copolymer rubber at a rubber processing step in accordance
with the invention, the braking performance of a tire
driving on a wet road surface or on a snow-covered or
frozen road surface twet-gripping property and ice-
gripping property) can be improved and, at the same time,
the rolling resistance can be lowered. Further the compounded
composition is not deteriorated in mechanical properties of
vulcanized rubber. Therefore, the rubber composition according
to the invention, when applied to an automobile tire, in
particular to the tread thereof, enables the production of
a tire which is excellent not only in its gripping properties,
which are closely related to the acceleration and braking
performance of autcmobiles on the wet road surfaces and on
the snow-covered or frozen surfaces, but also in fuel
consumption.
39
