Note: Descriptions are shown in the official language in which they were submitted.
z!~naPf~
A PR~Ci~ L~HE PRODUCTION OF RUBBER W LCANIZATES
HAVING REDyCED HYSTERESIS LOSSES AND MOLDINGS OF HESE
W LCANIZATES
m is invention relates to a process for the production
of carbon-black-filled rubber vulcanizates having reduced
hysteresis losses by shearing of carbon-black-filled rubber
in the presence of certain disulfides. The invention also
relates to moldings of vulcanizates produced by this pro-
cess, including for example vehicle tires, conveyor belts,
drive belts and compressed-air bellows.
In rubber technology, a hysteresis loss is understood
to be the energy loss which is irreversibly converted into
heat in the event of dynamic stressing of the elastomer.
The measured quantity for hysteresis losses is the tan ~
which is defined as the ratio of loss modulus to storage
modulus, cf. for example DIN 53 513 and DIN 53 535. Any
reduction in the tan ~ in the applicationally important
temperature/frequency or amplitude range leads, for ex-
ample, to reduced heat buildup in elastomers. Tires of
rubber having a reduced hysteresis 108s are distinguished
by reduced rolling resistance and, hence, by lower fuel
consumptlon of the vehicles fitted with them.
US-PS 4,690,965 describes, for example, carbon-black-
filled rubber vulcanizates which show reduced heat buildup
and, hence, a reduced hysteresis loss by virtuç of their
content of nitrosoanilines. However, on account of the
danger of carcinogenic nitrosamines being formed trans-
nitrosation, there i8 a need for rubber auxiliaries which
are ~ree ~rom nitro~o groups.
It has now surprisingly been found that carbon-black-
filled rubber vulcanizates having reduced hysteresis losses
can be obtained by mixing unvulcanized rubber with carbon
black in the presence of di(acylaminoaryl) disulfide free
~rom nitroso groups at elevated temperature and vulcanizing
Le A 26 398
the resulting mixture in known manner. The principal
advantage of the process according to the invention is that
the disulfides used to improve hysteresis do not affect the
mechanical properties of the vulcanizates, such as for
example their strength, elongation and modulus, to the
extent where the vulcanizates no longer satisfy the demands
made of the end products (for example tires or drive
belts).
The use of di(o-acylaminoaryl) disulfides as masti-
cating agents for natural and synthetic rubber is known
(US-PS 2,470,948). It is known that rubbers are masticated
to reduce viscosity. Accordingly, the auxiliaries accord-
ing to US-PS 2,470,948, as normal for masticating agents,
are mixed with the rubber before addition of the usual
fillers and auxiliaries, particularly before the addition
of carbon black (for example on mixing rolls or in an in-
ternal mixer at 120C), and the resulting mixture is then
sheared until the desired viscosity is reached. The re-
duced viscosity established in this way enables fillers and
auxiliaries to be incorporated without difficulty; a homo-
geneous mixture could otherwise only be obtained with dif-
ficulty. The shearing of carbon black/rubber mixtures in
the presence of di(o-acylaminoaryl) disulfides is neither
disclosed nor suggested in US-PS 2,470,948.
The present invention relates to a process for the
production of carbon-black-filled rubber vulcanizates by
mixing of unvulcanized rubber, carbon black and, option-
ally, other auxiliaries and subsequent vulcanization, com-
prising adding
(i) to the unvulcanized rubber,
(ii~ 10 to 120~ by weight and preferably 30 to 80% by
weight, based on rubber (i), carbon black and
(iii) 0.1 to 10% by weight and preferably 0 1 to 3~ by
weight, based on rubber (i), diphenyl sulfide
corresponding to the following formula
Le A 26 398 2
z~ p~
R3 R6
1 ~ s ~ R7 (I)
5 R~-CO-NH NH-co-Rlo
in which
Rl to R8 independently of one another represent
hydrogen, fluorine, chlorine, bromine, C~-8 and
preferably C~ alkyl, more especially methyl, C~
~ and preferably C~ alkoxy, more especially
methoxy, nitro and
R~ and Rl independently of one another represent
hydrogen, C~, preferably C~2and more preferably
Cl_3 alkyl, C2~8, preferably Cz-~2 and more
preferably C2~ alkenyl, C5-~2 cycloalkyl and
alkenyl, C~-~2 aryl,
the above-hydrocarbon radicals for R9 and Rl
optionally being ~ubstituted by halogen
(~luorine, chlorlne), carboxyl, hydroxy, nltro,
amino, di-C~a-alkylamino, mercapto, C~aalkoxy and
nltro,
at melt temperatures o~ at least 140-C and preferably of at
lea~t 150-C and at ~hear rates of 1 to 1000 sec~~ in such
a way that at least 10% by weight carbon black ~ , based
on rubber (i), are added be~ore there ls any ~ignificant
reduction in the molecular weight o~ the rubber.
Rubber~ (i) suitable for the process according to the
lnvention include not only natural rubber, but al~o ~yn-
theti¢ rubber~ cont~lnlng at lea~t 5~ by weight copoly-
merized unit~ emanating ~rom a C~2 dlene. Pre~erred syn-
thetic rubbers are de~cribed, ~or example, in W. Ho~fmann,
Kaut whuk-Technologie, Genter Verlag, Stuttgart 1980. They
include i~çr ~
e A ~6 398 3
Z!~ Pfi:~1
BR - polybutadiene
ABR - butadiene/Cl4 alkylacrylate copolymers with
acrylate contents of 5 to 60% by weight and pref-
erably 15 to 50% by weight,
CR - polychloroprene
IR - polyisoprene
SBR - styrene/butadiene copolymers with stirene con-
tents of 1 to 60% by weight and preferably 20 to
50% by weight,
NBR - butadiene/acrylonitrile copolymers with acrylo-
nitrile contents of 5 to 60% by weight and pref-
erably 10 to 50% by weight
and mixtures of these rubbers. The rubbers to be used for
the process according to the invention have glass tran-
sition temperatures below 20C and preferably below OoC, as
determined in the torsion pendulum test according to DIN 53
445.
Particularly preferred rubbers (i) are polybutadiene
and styrene/butadiene copolymers. SBR solution and emul-
sion polymers are preferred for vehicle tires, particularly
for treads. SBR solution polymers are particularly prefer-
red. The content of 1,2-bonds may vary within wide limits
and is generally between 5 and 80%, based on the number of
copolymerized butadiene groups.
If desired, other rubbers (i) may be added to and
mixed with individual rubbers (i) before vulcanization and
before or after the addition of carbon black (ii) and di-
sulfide (iii).
Any reinforcing carbon blacks may be used for the
process according to the invention. Preferred surfaces are
in the range from 35 to 200 m2/g ~CTAB determination). SAF,
HAF, FEF, ISAF and SRF carbon blacks are mentioned in par-
ticular. Mixtures of two or more different carbon blacks
or mixtures of carbon blacks with silicas (with and without
filler activators) may readily be used. The degree of
Le A 26 398 4
- Zf~ fi:~1
filling may be varied within wide limits, 30 to 80 parts by
weight carbon black (ii), including silica if any, to 100
parts rubber (i) being preferred.
Preferred disulfides (iii) include, for example, those
in which all the substituents Rl to R~ are hydrogen and in
which the acylamino qroups are in the 2,2', 3,3' or 4,4'-
position, the substituents R~ and R10 independently of one
another, but preferably together, assuming the following
meanings:
-H
-CH
-CH2CH3 `13
~ Cl
-CH2CH2CH3
C17H35
~,N02
CH2C 1 ~
-CHC12 ~ H
-CC
Le A 26 398 5
?~
-CF3 -CH=CH ~
c~3
-CH2CH2C1 ~
~0
-CH2COOH ~ ~OH
- CH2CH2CH ~N~CH3
CH3
-(CH2)3-COOH ~ NH2
-(CH2)4-~
-CH~CH2
-C~ CH2
CH3
C17H33
~0
-CH-CH-C
~OH
Le A 26 398 6
2S~
Preferred sulfides (iii) also include, for example,
compounds in which the substituents R~ and Rl are hydrogen
and in which the phenylene radicals each bear a chlorine,
nitro, methyl, butyl or ethoxy group.
The following are preferred examples of such
compounds:
Cl Cl
OHC-HN ~ S-S ~ NH-CHO
N2 02N
OHC-HN ~ S -S ~ NH-CHO
OHC-HN NH-CHO
H3C ~ S-S ~ H3
C4H9 H9C4
OHC-H ~ 8~ 8 ~ NH-CHO
OC2H5 ~5Cæ
OHC-H ~ 8------6 ~ ~H-CHO
The disulfidss (iii) are known from the literature or
may be produced by methods known ~er ~e, cf. for example
US-PS 2,470,948; Farm., Ed. Sci. 29 ~1974) 2, 120-128.
A particularly ~uitable method is the acylation of
diamlnodiphenyl disul~ides which in turn may largely be
produced by three different methods, namely:
a) by hydrolysis of benzthiazoles and oxidation to the
disulfide, ç~. Beil~tein, Vol. 13 E III, 907;
b) by nucleophilic substitution of aromatic nitro com-
Le A 26 398 7
pounds by sodium hydrogen sulfide with simultaneous
reduction of the nitro group to the amino group,
followed by oxidation of the mercaptan to the disul-
fide; cf. Methoden der Organischen Chemie (Houben-
Weyl), Vol. 11/1, Georg-Thieme-Verlag, Stuttgart 1957,
page 416 and
c) by reduction of nitroaryl sulfochlorides to amino-
thiophenols, followed by oxidation to the disulfide,
cf. Methoden der Organischen Chemie (Houben-Weyl),
Vol. 11/1, Georq-Thieme-Verlag, Stuttgart 1957, page
431.
The disulfides (iii) used will generally be those of
which the half life period in the rubber mixture used at
the processing temperature (melt temperature) is less than
half the processing time, i.e. disulfides (iii) which have
a half life period of less than 3 minutes. Particularly
preferred disulfides (iii) are those of which the half life
period is between one tenth and one third of the processing
time.
For the process according to the invention, standard
fillers and auxiliaries such as, for example, plasticizers,
resin~, factlces and stabilizers may be added to the rubber
mixtures to obtain certain crude mixture or vulaanization
properties.
The melt temperature of the mixture required for the
process according to the invention of preferably 140 to
250C and more preferably 150 to 200C may be obtained by
external application of heat or by corresponding friction
during the mixing process. The desired melt temperature is
generally below the decomposition temperature of the rubber
(i) used. In special cases, i.e. where the mixture has an
extremely short residence time in the high temperature
zone, the decomposition temperature of the rubher (i) may
even be exceeded providing no significant decomposition
occurs (on account of the short residence time). In most
Le A 26 398 8
fi;~
cases, it may be advisable to base the choice of the melt
temperature on the half life period of the disulfide (iii)
used at that temperature.
Preferred mixing units are the mixing rolls, internal
mixers and mixing extruders typically used in the rubber
industry which generally operate with shear rates of 1 to
1000 sec.~l and preferably 1 to 200 sec.~1.
The mixing times are governed by the desired degree of
dispersion of the carbon black (ii) and the remaining mix-
ture constituents in the mixture. They are often between
30 and 1000 seconds and are preferably between 30 and 360
seconds. Where internal mixers are used, excellent results
are obtained with mixing times of this order.
In the context of the invention, a "significant reduc-
tion" in the molecular weight of the rubber would be a re-
duction of more than 10% and preferably more than 5~ in the
weight average molecular weight Mw.
The carbon black (ii) is preferably added before a
melt temperature of 140C and preferably 150~C is reached.
The disul~ides (iii) may be added to the rubber (i) to-
gether with the total quantity of carbon black (ii) or with
parts thereof, in which case the remaining quantity of car-
bon black is sub~equently added in accordance with the
~ormulation.
The crosslinklng systems known from rubber technology,
~uch ~s sulfur, peroxides, polyisocyanates, metal oxides,
phenolic resins and combinations thereof, may be used for
vulcanization. The crosslinking system used for vulcaniz-
ation will preferably be adapted to the type of rubbers (i)
used. Sulfur crosslinking systems are particularly prefer-
red.
The crosslinking systems are pre~erably added at
temperatures below 130C and preferably at temperatures
below lOO'C. Vulcanization may take place at temperatures
in the range from 100 to 200~C and preferably at temper-
Le A 26 398 9
2n(~fi~1
atures in the range from 130 to 180C, optionally under a
pressure of lO to 200 bar.
Articles subjected to severe dynamic stressing, such
as vehicle tires, conveyor belts, drive belts, such as V
belts and gear belts, compressed-air bellows, etc., may be
produced by the process according to the invention.
Accordingly, the present invention relates to moldings of
vulcanizates obtainable by the process according to the
invention.
In the following Examples, parts are parts by weight.
EXAMPLES
The following compositions were prepared in accordance
with the following mixing sequence in a laboratory com-
pounder (of the type manufactured by Haake Mess-Technik
GmbH ~ Co., Karlsruhe 41) at various shell temperatures of
the mixing compartment and at rotational speeds of the CAM
blades of 30 to 100 r.p.m.:
A~ter
[mins.]
I addition of rubber
0.5 addition of half the carbon black to-
gether with the disulfide
1.5 addition of the other half of the car-
bon black and the remaining aomponents
4-6 ejection
The final batch temperature is shown in the Tables.
The vulcanization system was subsequently incorporated in
the mixture on laboratory mixing rolls at 40 to 60C.
30Formulation:
137.5 parts Buna SL 750 (a product of Bunawerke Huls
GmbH, Marl) containing 100 parts solution
SBR and 37.5 parts oil
70 part~ carbon black N 220 (a product of Degussa,
Wesseling)
Le A 26 398 10
2n~p~
l part stearic acid
3 parts zinc oxide
1 part Vulkanox 4010 NA (a product of
BAYER AG, Leverkusen = IPPD = N-isopropyl-N'-phenyl-p-
phenylenediamine
1 part disulfide of formula I
1.8 parts sulfur
1.2 parts Vulkacit NZ (a product of BAYER AG,
Leverkusen) = TBBS = benzthiazyl-2-tert -
butyl sulfenamide
Vulcanization took place for 20 minutes at 150~C
EXAMPLES 1-3 and COMPARISON EXAMPLE 1
These Examples demonstrate the effect of the final
batch temperature with reference by way of example to 2,2'-
diformamidodiphenyl disulfide (Rl-R10 = H). Comparison
Example C-l contains no hysteresis promoter ~ tan ~
represents the percentage change in the tan ~ in relation
to the di~ulflde-~ree standard.
Le A 26 398 ll
2(~
o
c~ v
o o OD ~ ~ ~ ~
o ~ ~ o
7 ~ o o o
a.
o o ~ u~
o ~ ~ ~ .q
` o o o o
~ ~ ~ u~
o o o ~ ~ ~ ~
/ ~ O O O
:~
u o 0
o o ~ u~ ~ l` ~ `
O 1~ ~D ~` ~ ~ -
o ~ ~ . ~ o
--~ ~1 ~ ~ N ~1 O O I O I
C~ C.) oD
O O m u7 ~ ~
O 0 ~ O ~1 ~ ~ ~ ~ O
1~ ) O ~ o\
~1 ~1 ~ U~ O O I O I o
O
C) U
o U~ O ~ O ~1` ~ 0 0
O N ~ 1 0 r/
~ ~ O
~1 ~1~1~JIr1 N ~1 OO I O 1 ~1
0 0
~ _l
~ a)
~l~
~ - ~ 0
C ~ ~ O L
~ o o C) ~,) o ~ ~
Q~~ ~ O Ot~ C.) o O ~ 0
~ O O ~
_1 ~ ~ ~ ~ ~ 0 u~ a~ ~ -I ' ~
X ~ ~ ~
~ ~ ~ U~ ~ ~ X ~ ~ ~ ~ C
Le A 26 398
- 12 -
2~ r~l'fi~31
COMPARISON EXAMPLES 2-4
In these Comparison Examples, the effect of the mixing
sequence is demonstrated by comparison with Example 3.
Once again, the addition was 2,2'-diformamidodiphenyl di-
sulfide.
In Comparison C-2, the disulfide was subsequently
added to the mixture together with the vulcanization
system. Tensile strength deteriorated considerably as a
result.
Buna SL 750 was first mixed with the disulfide to be
used in accordance with the invention (as in conventional
mastication) for 5 minutes at a shell temperature of 120C
(melt temperature 150C) in comparison C-3 and for 5
minutes at a shell temperature of 170~C (final melt temper-
ature 190C) in comparison C-4, the basic mixture was pre-
pared in a second mixing step and the vulcanization system
subsequently added on mixing rolls. There was no clear
reduction in the hysteresis losses.
Le A 26 398 13
~!~ f ~
C~O
o o oo o
~r oo o
NU') 1~11~ O t~
OC~
O O
O ~ OD_I -
~U~ O ~ O ~1
C~ ~ I +
~) V
o o
U~
U V
o oD ~
O 00 ~ ~D~ ~1 CO
t~O~ O
Ul
U _-
O
~ ~p, ~ o~ ~ o~
~ OOOOO
Il) ~ O R ~ ~ 0oo ~
~ ~ X ~ ~ o ~ ~ ~ ~ ~ ~O
X ,q-r~ O O
1~ U7 ~ X <I G <I
Le A 26 398
- 14 -
2(~
EXA~E~ =9
These Examples demonstrate the influence of the
position of the acylamino group and of the substituents R~
and R10 on the effect of the process according to the inven-
tion.
R9-oC-NN:~S S~NH-CO-R10
Le A 26 398 15
Pfi;~
~ C~
,a o
o ~ ~ ~ _,
o ,, ,, ,i ,1 CO ,
l l l l l l
o
o
_,
~ ~ a~ ~ o~ ~ I` I~
o X ,~ o ,,_, o ,
X--~
,a o ~ 1 0
P~
X o ,1 o,~,
U~
o
O ~ ~ N N NNd' d'
~ ~ t~ ~ ~ d'
~ O=t~
O
Le A 26 398
-- 16 --
