PROCESS FOR THE PRODUCTION OF A CROSS-LINKED NITRILE RUBBER

PROCEDE DE FABRICATION DE CAOUTCHOUC NITRILE RETICULE

English Abstract

ABSTRACT

Process for the production of a cross-linked nitrile
rubber"


Nitrile rubbers, from 85 to 96% of the double bonds
of which are hydrogenated, may be cross-linked with
peroxides to produce products which have outstanding
ozone-resistance, if peroxides are used, the half-life
of which is longer than 2 minutes in benzene at 170°C.

Claims

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THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of a cross-linked nitrile
rubber, from 85 to 96% of the double bonds of which are hydrogenated,
which comprises using as the cross-linking agent from 1 to 10%, by
weight, based on the rubber, of a peroxide having a half-life at
170°C of more than 2 minutes in benzene and more than 8 minutes in
low density polyethylene at the same temperature.

2. A process as claimed in claim 1 wherein the nitrile rub-
ber is from 90 to 95% hydrogenated.

3. A process as claimed in claim 1 wherein from 4 to 7%, by
weight, of peroxide is used.

4. A process as claimed in claim 1, 2 or 3 wherein the rubber
comprises from 10 to 50%, by weight, of acrylonitrile units and
from 90% to 50%, by weight, of conjugated diene units.

5. A process as claimed in claim 1, 2 or 3 wherein the pe-
roxide is selected from the following: bis-t-butylperoxiisopropyl)-
benzene; 2,5-dimethyl-2,5-di(t-butylperoxi)-hexane and 2,5-dimethyl-
2,5-di(t-butylperoxi)-hexene-(3).

6. A process as claimed in claim 1, 2 or 3 wherein the rubber
comprises from 10 to 50%, by weight, of acrylonitrile units and from
90% to 50%, by weight, of conjugated diene units and the peroxide is
selected from the following: bis-t-butylperoxiisopropyl)-benzene;
2,5-dimethyl-2,5-di(t-butylperoxi)-hexane and 2,5-dimethyl-2,5-di
(t-butylperoxi)-hexene-(3).

Description

846
,
"Process for the production of a cross-linked nifrile
rubber"
This invention relates to a process for the
production of a cross-linked nitrile rubber, from 85 to
S 96% of the double bonds of which are hydrogenated.
It is known from DE-OS 29 13 992 to vulcanise
part;ally hydrogenated nitrile rubbers using a sulphur
vulcanising system. Cross-linking with certain peroxides
(Exarnple 4, No. 16) produces only unsatisfactory results.
Appropriate choice of peroxide has been found not
only to avoid these poor results, but even to produce
better results, partlcularly with regard to ozone-
resistance, than when sulphur vulcanisation is used.
Thus, an object of the present invention is to
provide a process for the production of cross-linked
nitrile rubbers, from 85 to 98%, preferably from 90 to
95%, of the double bonds of which are hydrogenated, using
from I to 10%, by weight, preferably from 4 to 7%, by
weight, of peroxides, based on the quantity of polymer
in the mixture, characterised in that peroxides are
used, the half-life of which is longer thun 2 minutes
in benzene at 170C and is longer than 8 mintues in
LDPE (low-density polyethylene)at the same temperature.
Suitable nitrile rubbers consist of from 10 to
50%, by weight, of acrylonitrile units and from 90 to
50%, by weight, of conjugated diene units, such as
butadiene, isoprene or l,3-pentadiene. The partial
hydrogenation of nitrile rubbers is known.
The following are examples of suitable peroxides:
bis-t_butylperoxiisopropyl)-benzene; 2,5-dim~thyl-2,5-
di (t-butylperoxi)-hexane-a~d ~,~-dîmelhyl-2,5-di(t-
butylperoxi)-hexene-(3).
The term "half-life" means that, at a given temper-
ature and after one half-life 50% of the quantity of
peroxide which was present at the beginning of the half-


8~
life has decomposed.
The rubber mixture nay contain other constituentswhich are conventionally used in the peroxlde cross-
linking of polymers, such as fillers, plasticisers, anti-
agents, processing auxiliaries, pigments, co-activators,
such as triallyl isocyanurate, and acid acceptors.
The products which may be obtained according to the
present invention have rnany uses: they may be used, for
example, for sealings of all types, tubes, in particular
hydraulic pipes, toothed belts, cable coverings, profiles,
linings, rollers, membranes and rubber/metal parts.
Example
Rubber compositions having the compositions given
in the following Table are vulcanised at 1~C for 18
minutes.
A nitrile rubber consisting of 39%, by weight, of
acrylonitrile and 61%, by weight, of butadiene and having
a degree of hydrogenation of 90% is used.
The ozone-resistance of the vulcanisates is
determined at various elongations according to DIN 53
509 (23C, 60% rel. air humidity, 250 pphm of ozone
in air.)
Peroxide cross-linking is found to result in better
products with regard to the ozone-resistance thereof,
than sulphur cross-linking.

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Table
Parts, by weight

Rubber 100 100
5tea~ic acid
Wax (Lunacera C44) 2
ZnO active 3 5
MgO 7 7
Styrenised diphenylamine 1,1 2
Zinc salt of 2-nercaptobenzimidazole 0,4 3
Carbon black (Corax N 550) 50 50
Processing auxiliary - 2
Sulphur -0,125
Tetramethyl thiuram disulphide - 2
Sulphur donors
TrialIylisocyanurate 1,75
Bis-(t-butylperoxiisopropyl-benzene) 7,5


Results (in hours) of 020ne ageing until the first
sign of a crack

Elongation
10% ~168 168
20% ~168 6
30% ~168 4
60% 24 4