Note: Descriptions are shown in the official language in which they were submitted.
-
2186060
Description
The invention relates to a process for the preparation of
vulcanisable rubber mixtures and to the mixtures thus
prepared.
Effecting economies in fuel consumption and lowering the
discharge of pollutants are nowadays receiving a growing
priority as environmental awareness increases. For the tyre
manufacturer, this signifies the development of tyres
distin~l;she~ by a very low rolling resistance combi~ed
with ~cellent wet skid resistance and good abrasion
resistance.
In numerous publications and patents proposals are made for
lowering the rolling resistance of a tyre and consequently
the fuel consumption. In this connection decreasing the
content of carbon black in the mixture and using specific
carbon ~lacks are mentioned (US Patent 4,866,131, US
Patent 4,894,420). None of these proposed solutions has
led, however, to a satisfactory balance between the low
rolling resistance aimed for and the likewise important
tyre properties such as wet skid resistance and abrasion
resistance.
Only the use of highly active silica fillers in combination
with the organosilane bis(triethoxysilylpropyl)-
tetrasulphane (TESPT) largely in exchange for the carbon
black in the rubber mixture appears here to indicate a way
of rendering possible the production of a tyre having
distinctly lowered rolling resistance while simultaneously
maintaining or even improving the two other tyre properties
mentioned above.
- 2 1 ~6060
On the occasion of the ACS Meeting in 1986 in New Yor~, S.
Wolff ~1] showed that in a passenger car the rolling
resistance of a tyre tread based on emulsion styrene-
butadiene rubber (E-SBR) is successfully distinctly lowered
by the use of silica in combination with TESPT as compared
with the standard mixture filled with carbon black, while
wet s~id resistance and abrasion resistance are largely
maintained.
A further optimisation of this system with regard to all
three properties was achieved through the use of particular
styrene-butadiene polymers prepared by the solution-
polymerisation process (EP O 447 066 A1), partly blended
with other polymers, in particular polybutadiene, and the
additional use of novel types of silica (US Patent
5,227,425) as well as polymer blends specially adapted for
this use (EP O 620 250 Al) using proportions of three to
four different starting polymers.
It is characteristic of all these publications and patents
that in order to achieve a low rolling resistance while
maintaining or even improving wet skid resistance and
abrasion resistance, a greater part or the entire content
of the conventionally employed carbon black filler is
replaced by a highly active silica. In all cases the
organosilane bis(triethoxysilylpropyl)tetrasulphane (TESPT)
was used as a coupler between silica and polymer in order
to achieve the tyre properties required nowadays.
The present invention provides rubber mixtures vulcanisable
with sulphur and comprising in addition to the conventional
auxiliary substances
1. S. Wolff, 129'h Meeting of lhe Rubber Division. A nerican Chcmical Socicty, Ncw York, April 8-11, 1986
2. S . Wolff, Third Annual Meeting and C r ~ : of Tirc Science and T. ' . ' g~, The Tire Society, Akron,
OhiolUSA, March 28-~9, 1984
21 86060
a) from 10 to loo parts of a precipitated silica,
b) from O to 100 parts of a rubber carbon black, in each
case referred to 100 parts of the
c) copolymer also comprised,
which consists of a conjugated diene contAining an
aromatic vinyl component, prepared by the solution
polymerisation process, having a styrene content of
between 10 and 40% and a vinyl content of between 20
and 80~, preferably from 40 to 60~, and a glass
transition temperature of from O to -60C, or blends
of these copolymers with other diene rubbers, with the
proportion of these diene rubbers constituting ~p to
60 to 100 parts of the blends,
d) and from 1 to 20 parts, preferably 5 to 10 parts, of
an organosilane compound corresponding to the general
formula (I)
(RO)3Si(CH233SCN (I)
wherein
R signifies alkyl, branched or unbranched having 1
to 8 C atoms, preferably 1 to 4 C atoms, referred
to 100 parts of silica.
Preferably used are precipitated silicas having a BET
surface area (ISO 5794/lD) of between 100 and 250 m2/g, in
particular when they have a C~AB surface area (ASTM D3765-
92) of between 100 and 250 m2/g and a DBP number of ~etween
150 and 300 ml/100 g (ASTM D1208~.
The silicas are added both in powder form and as pellets or
granules. These silicas are the types known for many years
as well as the new developments described, for example, in
DE-OS 44 27 137.
According to the present invention additives such as, for
example, inorganic fillers other than the above-mentioned
21 8606~
.
silica and silicates can be incorporated into the rubber
mixture, provided that the quantities used do not obstruct
the purpose of this invention.
Examples of other inorganic fillers are carbon blacks such
as SRF, GPF, FEF, HAF, ISAF, FT and MT.
If carbon black is employed, a weight ratio of silica to
carbon black of at least 2:1 is used.
The total proportion of fillers is not to exceed 120 parts
per 100 parts of polymer.
The production of vulcanisates from the rubber mixtures
according to the invention requires simply the preparation
of raw rubber mixtures by the method described below,
subsequent shaping of the raw mixtures according to
requirement~, followed by wlcanisation in the same ~nner
as for collve~tional rubber mixtures.
For the production of the vulcanisates according to this
invention - in addition to the above-mentioned rubber
components, the organosilane compound and the amorphous
silica and according to the intended application of the
vulcanisates and the requirements placed on them - the
nature and quantity of the plasticisers, the nature and
quantity of the compounds constituting a vulcanisation
system, such as, for example, vulcanising agents,
w lcanisation activators (ZnO, stearic acid), vulcanisation
accelerators and other w lcanisation auxiliaries, as well
as the process for the production of the wlcanisates, are
carefully selected. Petroleum-based plasticisers
conventionally employed in rubber may be used as the above-
mentioned plasticisers.
Sulphur compounds such as those listed below are used as
vulcanising agents for the production of the vulcanisates
according to the invention. These sulphur compounds
include, for example, sulphur, morpholine disulphide,
alkylphenol disulphide, tetramethylthiuram disulphide and
~ 1 8~060
selenium dimethyl dithiocarbamate. Of these, preferably
sulphur is used. The above-mentioned sulphur compounds are
used in quantities of between 0.1 and 4 parts by weight,
preferably between 0.5 and 3 parts by weight, referred to
100 parts by weight of the copolymer or of mixtures thereof
with polymers. If a sulphur compound is used as a
vulcanising agent in the production of vulcanisates
according to this invention, then preferably a
w lcanisation accelerator is used in addition. The
wlcanisation accelerators used include, for example,
thiazole compounds such as N-cyclohexyl-2-benzothiazole
sulphen~ e, N,N-diiso~lo~1-2-benzothiazole sul~hen~m; de,
2-mercapt~h~n~othiazole and dibenzothiazyl disulphide;
guanidine compounds such as, for example,
diphenylguanidine, triphenylguanidine,
diorthotolylguanidine;
imidazoline compounds such as, for example,
2-mercaptoimidazoline;
thiourea compounds such as, for example, diethylthiourea,
dibutylthiourea, trimethylthiourea and
diorthotolylthiourea;
thiuram compounds such as, for example, tetramethylthiuram
monosulphide, tetramethylthiuram disulphide,
tetraethylthiuram disulphide, tetrabutylthiuram disulphide,
pentamethylene thiuram tetrasulphide;
dithioc~rh~m~te compounds such as, for example, zinc
dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc
di-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate,
zinc butylphenyldithiocarbamate, sodium
dimethyldithiocarbamate, selenium dimethyldithiocarbamate
and tellurium dimethyldithiocarbamate;
xanthate compounds such as, for example, zinc
dibutylxanthate.
The said vulcanisation accelerators are used in a quantity
of between 1 and 20 parts by weight, preferably between 0.5
and 10 parts by weight, referred to 100 parts by weight of
6 2186060
the copolymer or of mixtures thereof with the other
polymers.
me organosilane and the æilica are preferably m;~e~ or
even reacted with one another prior to being incorporated
into the rubber mixtures, as is described in US-PS 5,116,886
(EP-B-O 442 143).
It is not absolutely essential to modify in advance the
entire quantity of the silica used by means of the
organosilane correspond;ng to formula (I). It is also
possible to mndify only a portion in advance and to add the
r~m~;nAer without prior modification.
If c~rhon black is provided as additional filler for the
rubber m;Yt~re being prepared, in another variant it is
possible to add the organosilane corresponding to formula
(I) completely or partly as a carbon black/organosilane
mixture. This is used preferably in the fonm of a granular
material cont?;n;ng from 30 to 60 wt.~ of organosilane and
from 70 to 40 wt.~ of cArhon black respectively. The
production of 6;~;l~r granular materials is described in
DE-PS 27 47 277 (US-PS 4,128,438) and can be carried out
here in a corresponding m~nner.
The raw rubber mixture is prepared according to the method
described below. The above-mentioned rubber components, the
organosilane compound, the amorphous silica and the carbon
black optionally present, as well as optionally a
plasticiser, are kne~ for 3 to 10 minutes in a kneader,
for example a Banbury closed mixer, at a temperature of
from about 120 to 200C; a vulcanising agent such as
accelerator and sulphur or another vulcanisation auxiliary
is then added and mixing is continued at suitable
temperatures for a further 5 to 30 minutes, either in a
Banbury closed mixer or on a m; ~i ng roll, and the finished
`- 21 86060
7 ~.
rubber mixture is then drawn out as rubber sheet or in the
form of strips.
StAn~Ard rubber testing carried out on the vulcanisates
produced from the mixtures according to the invention shows
that, through the use of 3-thiocyanatopropyl-
trialkoxysilanes as organosilane in combination with
silicas in styrene-butadiene rubbers produced by the
solution polymerisation process, a distinctly better
abrasion resistance can be obtA; ne~ in cQ~p~rison with the
use of TESPT with an otherwise largely identical set of
values.
These vulcanisates are used for the production of mouldings
and of structural components of tyres.
- 2 1 86060 -
The examples ~elow clearly illustrate the advantages over
the standard silane TESPT of the organosilane corresponding
to formula (I) used in the polymer system according to the
present invention.
Standard test methods for the assessment
Test method Unit
Tensile strength DIN 53 504 MPa
Modulus 300~ DIN 53 504 MPa
Stretch at break DIN 53 504
Shore hardness DIN 53 505
Impact resilience DIN 53 512
DIN abrasion DIN 53 516 mm3
MTS test DIN 53 515
The following names and abbreviations are used in the
Examples of application:
Buna VSL 1950 S 25 Oil-filled L-SBR from the firm Bayer AG
having a vinyl content of 50~ and a
styrene cont~nt of 25~; the glass
transition temperature is -25C.
*
Buna VSL 1955 S 25 Oil-filled L-SBR from the firm Bayer AG
having a vinyl content of 55~ and a
styrene content of 25~; the glass
transition temperature is -20C.
*
Buna CB 24 Butadiene rubber having a proportion of
1,4 cis of at least 96~.
Naftolen ZD AFomatic oil from the firm Chemetal.
Protector G 35 Antiozonant wax from the firm Fuller.
* t rad ema rk
- 21 86060
* g
Vulkanox 4020 Antioxidant from BAYER AG.
*
Vulkacit D Diphenyl~l~n;~;ne, acce~erator from
BAYER AG.
*
Vul~acit CZ Benzothiazyl-2-cyclohexyl sulph~n~;de,
accelerator from BAYER AG.
Ultrasil VN 3 GR Precipitated silica having an N2 surface
area of 175 m2/g, a CTAB surface area of
about 170 m2/g and a DBP number of
220 ml/100 g (Degussa AG).
*
Ultrasil 3370 GR Precipitated æilica according to the
Patent DE P 44 27 137.9, ha~ing an N2
surface area of 170 m2/g, a CTAB surface
area of 165 m2/g and a DBP number of
250 ml/100 g (Degussa AG).
20 Si 69 Bis~triethoxysilylpropyl)tetrasulphane,
organosilane from Degussa AG.
Si 264 3-thiocyanat~ o~yltriethoxysilane,
organosilane from Degussa AG.
* t rad emark
- lO 2186060
Example 1: Comparison of Si 264 against Si 69 in the tyre
tread of a passen,ger car, with ~ltrasi~*-vN 3
GR as filler
Fol lAtion
BUI~VSL 1950 S 25 96 96
Buna CB 24 30 30
Vltrasil*VN 3 GR 80 80
Si 69 6.4
Si 264 - 6.4
ZnO RS
Stearic ~cid 2 '2
NaftoleD~ZD 10 10
Pr~tectQ~*G 35
~1 k~ng~ 4020 - 1.5 1.5
~1 k~; t~D 2 2
Vulkacit~ CZ 1.7 2
~"rh"~ 1.4 1.7
~heometer: 165C
t~ min: S.9 3 9
t,o~ ,min: 30.0 16.8
t,~ in' 57.8 47.5
t,~- t~o~ :min: 24.2 12.9
Data on ~ulc~ni~Ate:
165 C/t9b~
T~nsile sL~uy~h tMpa~ 14.1 13.7
Mo~ c 300~ tMPa3 10.0 9.3
Shore A hardness 74 75
DIN abrasion rmm3] 97 69
Viscoelasticity data
according to DIN 53 513
tan h 0C 0.437 0.424
tan ~ 60C 0.164 0.172
Si 264 in combination with ~ltrasi~ VN 3 GR shows in comparison with
Si 69 distinct im~o~ - 's in abrasion where vulcAnisate properties
are otherwise largely identical. In the rheometer test the advantage
of Si 264 lies in the more rapid complete w lcanisation.
* trademark
21 86060
11
Example 2: Comparison of Si 264 against Si 69 in t*~e tyre
tread of a passenger car, with Ultrasil 3370
GR as filler
Formulation
Buna*VSL 1955 S 25 96 96
Buna CB 24 30 30
Ultrasil*3370 GR 80 80
Si 69 6.4
Si 264 - 6.4
ZnO RS 3 3
Stearic acid 2 2 .
Naftolen*ZD 14 14
Protector*G 35
~llkAnn~4020 1.5 1.5
Vulkaci~*D 2 2
VlllkAc;t CZ 1.7 2
Snlrhllr 1.4 1.7
Data on vulcAniæAte:
165C/tg5~
T~n~ile ~ ~yLh tMPa] 14.6 14.1
Modulu~ 300~ tMPa] 7.7 7.4
Stretch at break t~] 470 460
Impact resilience t%] 33 34
Shore A hardness 66 67
DIN abrasion tmm3] 111 75
ViscoelAsticity data
according to DIN 53 513
E' 0C tMPa] 26.6 31.2
E" 0C lMPa] 12.2 13.3
tan ~0C 0.437 0.427
E~ 60C [MPa] 9 7 10.3
E" 60C [MPa] 1.1 1.3 -
tan ~ 60C 0.116 0.123
The combination Ultrasil 3370 GR/ Si 264 e~h;b;ts distinct
advantages in abrasion in comparison with Ultrasil 3370 GR/ Si 69.
* trademark
