Note: Descriptions are shown in the official language in which they were submitted.
1 33~387
The present invention relates to a vulcanization activator and a
process for its pl~par~lion. More particularly, the present invention relates
to a vu'c. ~ Lion activator based on zinc salts of organic carboxylic acids
for a rubber mixture to be vulcanized with sulfur.
It is known from Ullmanns Encyklopadie der technischen
Chemie, vol. 9, 1957, p. 387, that the system rubber-sulfur-accelerator zinc
oxide can be additionally activated by adding fatty acids, such as stearic acid
or zinc salts of fatty acids, such as zinc stearate or zinc laurate. These
activators lead to an additional improvement in the mechanical characteris-
tics of the vulcanizers and, in part, to a shortening of the vulcanization time.In addition, fatty acids and fatty acid salts lead to an improvement in the
processibility and, often, to a delayed start to vl~'c-ni~lion, as well.
It is further known from R.F. Grossman et al Rubber and Plastic
News, 1987, how to use zinc salts of an aromatic carboxylic acid, such as,
e.g., terephathalic acid. However, due to the high melting point thereof, it is
only generally possible to prepare the same by precipitation. Moreover, zinc
salts of such aromatic carboxylic acid are often difficult to homogeneously .
disperse in the rubber compound.
It is, Ihere~ore, an object of the present invention to provide an
improved vulcanization activator, which can be homogeneously dispersed in
rubber and which provides a longer reversion time and a higher elastic
modulus during vulc~ni~alion.
It is a further object of the present invention to provide a
process for the expeditious preparation of a vulcanization activator which
can be easily pelletized.
It has surprisingly been discovered that the foregoing and
related objects are accomplished by a vulcanization activator of mixed zinc
C salts of a carboxylic acid, or a carboxylic acid mixture, of the general formula
R-COOH, in which R stands for an alkyl, cycloalkyl or arylalkyl radical with 5 ~7)
to 17 and, prefe
rably, 7 to 11 carbon atoms, and further of an aromatic
~ ~ f.
: :~'''""' ,'
1 3353~7
carboxylic acid. The vl ~' ankdlion activator can be prepared as a homo-
genous material and can be dispersed in a homogeneous manner in the
rubber. Compared with the activators known to the prior art, such as stearic
acid, zinc stearate and zinc-2-ethyl capronate, the activator of the present
invention gives longer reversion times during vulcanization and supplies
vulc-ni~ales with a higher elasticity modulus. In addition, the vu'csnkdles
have a reduced compression set, a higher thermal stability, and a beKer
dynamic loadability.
The process, according to the invention, involves reacting 1 to
1.5 moles of zinc oxide, zinc hydroxide or zinc carbonate with 2 moles of a
carboxylic acid mixture comprising 0.1 to 1.9 mole of carboxylic acid or a
carboxylic acid mixture of the aforementioned formula and 0.1 to 1.9 mole of
an aromatic carboxylic acid; particular preference being given to benzoic
acid or substit~ ~ted benzoic acids, such as, e.g., chlorobenzoic acid or
methylbe" ~ c acid. Other suitable aromatic carboxylic acids are of a
polycyclic nature, such as, e.g., naphthoic acid and the substitution products
thereof, as well as carboxylic acids of heterocyclic aromatics.
Generally, the carboxylic acid mixture is heated to a tempera-
ture of 100 to 200OC and is reacted with the zinc compound while mixing
under stirring. The volatile reaction products or by-products, such as water
and/or carbon dioxide, are thereby removed. Following the cooling of the
melt, hard wax-like products are obtained, which can be pelletized or filled
from the melt in conventional i"~lc'l~liQns.
The present invention will now be described in greater detail,
with reference being made to the following examples, which further include
re~rence to the accompanying drawing figure and tables, which illustrate the
results of comparison testing procedures.
It should be understood, however, that the accompanying
e~d",~'~s and test results are intended as being merely illustrative of the
present invention and are not intended as defining the scope thereof.
- 2 -
~ ........................................... ..
1 3353~7
Example 1
1.0 mole of zinc oxide was introduced, accompanied by
stirring, into a mixture of 1.4 moles of C" to C,O-coconut fatty acid and 0.6
mole of benzoic acid heated to 150 o C. The resulting mixture was then
maintained at this temperature until no further water vapor emerged. The
clear melt obtained, following cooling, gave a colorless, brittle material with a
drop point of 100C.
Example 2
The procedures described in Example 1 were followed except,
in this case, use was made of a mixture of 1.4 mole of a C8 to C,O- coconut
fatty acid and 0.6 mole of 2-methylbenzoic acid. A colorless material with a
drop point of 99 o C was obtained.
Example 3
The procedures described in Examples 1 and 2 were again
followed, however, the carboxylic acid mixture was constituted by a mixture
of 1.4 mole of a C~ to C~O-coconut fatty acid and 0.6 mole of 2-chlorobenzoic
acid. A colorless material with a drop point of 1030C was obtained.
Example 4
A natural rubber compound with the following formulation was
prepared:
Constituents Parts by Weight
Natural rubber (RSS 1) 100
Carbon black N-330 40
ZnO 5
Antioxidant (TMQ)
Acceler~lor
Sulfur 2.5
For (a) comparative activator comprised evaluation, the accele-
rator consisled of N-morpholinyl benzothiacyl sulfenamide and the accele-
rator activator was comprised, on the one hand, by 1 or 3 or 5 parts by
- 3 -
., ~ .,
- 1 335387
- weight of stearic acid (tests 1 to 3) and, on the other hand, 1 or 3 or 5 parts
by weight of the activator prepared according to Example 1 (tests 4 to 6), as
well as 5 parts by weight of an activator according to Example 2 (test 7) and
5 parts by weight of an activator according to Example 3 (test 8).
The physical data are given in the following Table 1, namely:
(a) The vu'c-ni~Lion time at 1600C;
(b) The 300% modulus, measured according to DIN 53 504
in MPa;
(c) The tensile strength according to DIN 53504;
(d) The elongation in percent according to DIN 53504;
(e) The vu'cani~lion data determined at 160C with a
Monsanto rheometer, namely:
t2 The scorch time in minutes; the time after which
the rotor torque had risen by 2 units was measur-
ed;
t~o The time after which 90% of the maximum rotor
torque was reached;
t~R The time required by the torque acting on the
rotor to drop from the vulcanization optimum
(100%) to 95% and corresponding to the rever-
sion time.
(f) The reversion stability, measured as the quotient of
t65R t~o;
(g) The compression set of the vulcanizate, measured in
percent according to DIN 53517;
(h) The dynamic loadability of the vulcanizate determined
with a cor"pression flexometer (according to Goodrich);
through the temperature rise of the testpiece following a
clearly defined number of deformation cycles at the
.. . .
-t
~ 1 33~3~7
given frequency and by the permanent set of the test
pieces following the measurement.
It is possible, on the basis of the reversion times measured, to
draw conclusions regarding the thermal stability because the overvulcaniza-
tion, in principle, represents an anaerobic thermal aging.
Table I clearly shows a consider~ble improvement to the
reversion times and the conlpression, set as well as deformation residue, as
well as a rise in the moduli. FIG. 1 is a graph of the reversion times of the
individual tests 1 to 8.
Table ll shows the improvement of the dynamic loadability,
apparent from the lower temperature rise of the test pieces or the longer life
of the latter. Conventional activators, such as stearic acid, zinc stearate and
zinc-2-ethyl capronate were used for comparison purposes.
The reduced permanent set following the test also reveals the
improved dynamic loadability of the vu'c ~ni~les.
While only several embodiments of the present invention have
been shown and described, it will be obvious to those of ordinary skill in the
art that many modifications may be made to the present invention, without
departing from the spirit and scope thereof.
- 5 -
1 335387
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TABLE I
(continued)
Test 1 2 3 _ 5 _ 7
V~ lion data- Monsanto
rheometer, 160C
t2 [min] 2.8 2.8 2.5 2.5 2.3 2.6 2.5 2.3
t90 [min] 8.2 9.0 9.6 8.0 8.9 10.2 10.6 10.2
t95R [min] 28 32 35 28 45 75 85 70
t95R:t90 3.4 3.6 3.6 3.5 5.1 7.4 8.0 6.9
Col l lpression set [%]
at 24 h, 70 O C 38 26
at 24 h, 50OC 23 14
TABLE ll
Dynamic Loadability, Measured on the Goodrich Flexometer
Chambertemperature [~C] 100
Stroke [in cm x 2.4] 0.175
Static load [in kg x 0.45] 30
Frequency [in s~~] 30
Activator Used (per 5 parts)
0~ Stearic
Acid Zn-Stearate Zn-2-ethyl capronate Activator in Ex. 1
Testpiece temperature rise [ o C] w
after 2000 seconds 21 23 34 22
~n
after 3000 seconds 25 27(testpiece destroyed) 25
after 6000 seconds 39 41(testpiece destroyed) 30
Testpiece permanent set [%]
after 7200 seconds 33 34(testpiece destroyed) 23
. . .
