Note: Descriptions are shown in the official language in which they were submitted.
2010905
SULF'UR-VULCANIZABI.E RUBBER MIXTURES H~VING A REDUCED
BLOOMING EFFECT
This invention relates to vulcanizable rubber mixtures
containing sulfur as a vulcanizing agent; a thiuram c~mpound
as an accelerator and a certain benzenesullanilide as an
additive for reducing blooming, to a process for the pro-
duction of these rubber mixtures by mixing of the compon-
ents and to the use of these rubber mixtures for the pro-
duction of vulcanizates.
It is known that vulcanization accelerators are sub-
stances which shorten the vulcanization time or which
enable vulcanization to be carried out at a relatively low
temperature, cf. Ullmanns Encyclopadie der technischen
Chemie, 3rd Edition, Urban & Schwarzenberg, Munchen-Berlin
1957, pages 383 et seq. Auxiliary accelerators are option-
ally added to develop the full effectiveness of the vulcan-
ization accelerators.
So-called "EV systems" ("EV" = efficient vulcaniza-
tion) are often used for sulfur vulcanization, in which
case thiuram compounds, such as tetraalkyl thiuram mono-
sulfides (for example;tetramethyl thiuram monosulfide),
tetraalkyl thiuram tetrasulfides (for examplejtetramethyl
thiuram tetrasulfide) and, preferably, tetraalkyl thiuram
disulfides (for examplej tetramethyl thiuram disulfide,
hereinafter referred to as TMTD), are generally used as
vulcanization accelerators. By virtue of their excellent
effect, these thiuram compounds are also known as ultra-
accelerators and lead in particular to high hot air resis-
tance of the vulcanizates produced with them.
~hiuram compounds themselves,or the xeaction products
formed therefrom during vulcanization; have a tendency
towards blooming, resulting in an undesirable coating on `~-
the vulcanizate. The tendency towards blooming is influ-
enced inter ~li~ by the type of rubber and by the concen-
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tration of the thiuram compound (cf. W. Hofmann in Gummi-
Asbest-Kunststoffe 9 (1986), pages 422 et ~g~.
Vulcanizates of rubber having a low conten~ of C=C
double bonds, such as EPDM, butyl rubber ana preferably
nitrile rubber, of which the C-C double bonds are selec-
tively hydrogenated either in part or completely, often
have a low degree of crosslinking which is reflected in low
modulus values and in a moderate compression set (CS)
value, as measured after compression under heat, for
example in hot air or in hot oil. There are limits to the
extent to which the CS value can be increased by l~rger
amounts of thiuram compound on account of the blooming
phenomenon mentioned above.
It has now surprisingly been found that a vulcaniza-
tion system containing sulfur in small guantities, thiuram
accelerator and N-trichloromethyl sulfenyl benzenesulf-
anilide
cl3c-S---N---S02 ~
overcomes the disadvantages of the prior art.
: 25 Accordingly, the present invention relates to vulcan-
izable rubber mixtures based on rubber of low c-c double
bona content, cont~ining
0.2 to 1 % by weight sulfur,
1 to 3.5 % by weight thiuram accalerator and
0.1 to 3 ~ by weight and preferably 0.15 to 1% by weight
N-trichloromethyl sulfenyl benzenesulfaniI~
ide,
the percentages being based on the rubber to be vulcanized.
The present invention also relates to a process for
the production of these rubber mixtures by mixing of the
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20109~5
components and to their use for the production of vulcan-
izates.
In the context of the invention, rubbers of low C-C
double bond content are those having iodine values of 2 to
35, preferably from 3 to 30 and more preferably from 5 to
25. The iodine values are generally determined by the Wijs
method, i.e. by addition of iodine chloride in glacial
acetic acid (DIN S3 241, Part 1). The iodine value defines
the quantity of iodine in grams which is chemically bound
by 100 g substance. Examples of preferred rubbers are
EPDM, butyl rubber and, preferably, hydrogenated nitrile
rubber.
The rubbers preferably have glass transition tempera-
tures below 0-C and more especially below -10-C.
The letters "EPDM" stand for ethylene/propylene/diene
terpolymers. EPDMs comprise rubbers in which the ratio by
weight of ethylene to propylene residues is from 40:60 to
65:35 and which may contain from 1 to 20 C-C double bonds/
1,000 C atoms. Suitable diene monomers in the EPDM are,
for example, conjugated dienes, for example isoprene and
1,3-butadiene, and unconjugated dienes containing from 5 to
25 C atoms, for example 1,4-pentadiene, 1,4-hexadiene, 1,5-
hPxadiene, 2,5-dimethyl-1,5-hexadiene nd 1,4-octadiene;
cyclic dienes, for example cyclopentadiene, cyclohexadiene,
cyclooctadiene and dicyclopentadiene; alkylidene and
alkenyl norbornenes, for example 5-ethylidene-2-norbornene,
5-butylidene-2-norbornene, 2-methylallyl-5-norbornene, 2-
isopro~enyl-5-norbornene and tricyclodienes.
The uncon~ugated dienes; 1,5-hexadiene, ethylidene
norbornene and dicyclopentadiene;are preferred. The diene
content of the EP~M i8 preferably from 0.5 to 10% by
weight, based on EPDM.
EPDM rubbers of the type in questlon are described,
for examFle, in DE-OS 2 808 709.
In the context of the invention, the term "butyl
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rubber" encompasses isobutene copolymers of 95 to 99.5% by
weight and preferably 97.5 to 99.5% by weight isobutene and
0.5 to 5% by weight and preferably 0.5 to 2.5% by weight
copolymerizable diene, such as,for examplejbutadiene, di-
methyl butadiene, 1,3-pentadiene, more especially isoprene.
On an industrial scale, butyl rubber is produced almost
exclusively as an isobutene/isoprene copolymer by cationic
solution polymerization at low temperatures; cf. for
example Kirk-Othmer, Encyclopedia of Chemical Technology,
2nd Ed., Vol. 7, page 688, Intersciene Publ., New York/Lon-
don/Sydney, 1965 and Winnacker-Xuchler, Chemische Technolo-
gie, 4th Edition, Vol. 6, pages 550-555, Carl Hanser
Verlag, Munchen-Wien 1962.
The preferred hydrogenated nitrile rubbers are based
on butadiene/acrylonitrile copolymers containing from 5 to
60% by weight and preferably from 10 to 50% by weight
copolymerized acrylonitrile. "Hydrogenated" in this
context means that 90 to 98.5% and preferably 95 to 98% of
the hydrogenatable C-C double bonds are hydrogenated. The
degree of hydrogenation can be determined by IR-spectros- -copy. ' -
The hydrogenation of nitrile rubber is known: US-PS
3,700,637, DE-OS 25 39 132, 30 46 008, 30 46 251, 32 27
650, 33 29 974, EP-A 111 412, FR-PS 2 540 503. Hydrogenat-
ed nitrile rubber is distinguished above all by compara-
tively high stability to oxidation.
The rubbers suitable for the process according to the
invention generally have Mooney viscosities (DIN 53 523) of
from 10 to 150 and preferably from 25 to 80 (ML 1+4)/100-C.
Preferred thiuram accelerators include the above-
mentioned tetraalkyl thiuram mono- and polysulfides, the
alkyl groups generally containing 1 to 4 and preferably 1 -
or 2 C atoms.
- The N-trichloromethyl sulfenyl benzenesulfanilide to
be used ln accordance with the invention i8 known and is ;
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commercially available, for example, as ~ ulkalent E (a
product of Bayer AG, Leverkusen).
Vulcanization auxiliaries and, as required, scti-
vators, filler6, such as for example carbon blac~,
pIasticizer~, antiagers andtor processing aids, may be
added in the uCual quantities before vulcanization.
Preferred vulcanization auxiliaries, which are
generally used in quantities of from 0.1 to 2, prefer-
ably from 0.2 to 1, X by weight (based on rubber),
include thiazole accelerators, such as 2-mercapto-
benzothiazole, dibenzothiazyl disulfide, benzothiazyl-
2-cyclohexyl sulfenamide (CBS), benzothiazyl-2-tert.-
butyl sulfenamide (TBBS), N-morpholinothio-2-benzothia-
zol (MBS), benzothiazyl-2-diisopropyl sulfenamide
(DIBS), benzothiazyl-2-tert.-amyl sulfenamide (AMZ),
benzothiazyl dicyclohexyl ~ulfenamide (DCBS) and
morpholinothioearbonyl sulfene morpholide (OTOS).
The mast significant inorganic activators are the
metal oxides, particularly zinc oxide. In some cases,
magnesium oxide or calcium hydroxide may also be used. -~
Suitable processing aids are, for example, fatty
acids, such as stearic acid, for example, and their zinc
~alts which may cause an advantageous effect on the
properties of the resulting vulcanizates.
The components may be m;xed in standard mixing
units.
Preferred mixing units are the kneaders, rolls,
internal mixers,and mixing extruders typically used in
the rubber industry which generally oparste at shear
rates of 1 to 1~000 sec~1 and preferably 1 to 20 sec~l.
Vulcanization may be carried out at temperatures
in the range from 100 to 200C and preferably at
temperatures in the range from 130 to 180C, opt;onally
under a pres~ure of 10 to 200 bar.
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The oustanding v~l~niza~e pr~per~ies arQ generally
achieved withou~ post-curing, bu~ can often be improv~d
by pos~-curing.
The vulsaniza~es ob~ainable in acccrdance with ~he
invention are excellent material~ for drive belts and
gear belts by virtue of their high resilience. In
addi~ion, they show excellen~ properti0s as sealing
materials of all kinds and may be used in~er alia a3
hose cores or shea~hs.
EXAMPLES
A hydrogenated acrylonitrile/butadiene copolymer
having an acrylonitrile content of 33.7% by weight, a
degree of hydrogenation of 96.4~, based on the C-C double
bonds originally present, and a Mooney viscosity of 67 (ML
114)/l00-C was used as rubber for the following Examples.
In a laboratory kneader, l00 parts rubber were masti-
cated for 0.5 minute at 50 C, after which 0.5l part sulfur,
l part stearic acid, 2 parts zinc oxide, l part octylated
diphenylamine (~a~Vulkanox OCD, a product of Bayer AGj, 0.4
part methyl mercaptobenzimidazole (~R~Vulkanox ZMB2, a
product of Bayer AG) and 45 parts carbon black (Corax N550,
a product of Degussa~Wesseling) were added and the mixture
8~æd wa8 by kneading (4.5 minutes).
After cooling of the rubber mixture to approximately
l00-C on rolls, an accelerator system consisting of 2 parts
tetramethyl thiuram disulfide (~R~ Vulkacit Thiuram, a
product of Bayer AG), 0.5 part benzothiazyl-2-cyclohexyl
sulfenamide (~R~Vulkacit CZ, a product of Bayer AG) and
varying amounts (see Table l) of N-trichloromethyl 6ulfenyl
benzene~ulfanilide (~Vulkalent E, a product of Bayer AG)
were added.
The properties of the ~ixtures obtained are listed in
the following:
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Table 1 Mixture properties
5 Examples 1 ~ 2 3 4 5
. . _ _ . . _ _ _ . .
N-trichlorome~hyl sulfenyl - 0.5 1 1.5 0.4
benzenesulfanilide (parts)
zincstearate - - - - 2
10 Scorch time
Mooney scorch MS-t5/130C 18.5 20.9 17.9 16.2 21~9
(min.)
Vulcameter 160C t1o (min.) 4.5 5.0 4.7 4.6 4.9
t90 (min.)12.6 12.7 11.7 12.4 12.5
FmaX (cN) 43.8 57 60 61 59
The mixtures obtained were vulcanized for 30
minutes at 160C. The vulcanizate properties were de-
termined on S2 test specimens (2 mm thick) in accordance
2~ with IS0 standard 37-1977; for results, see Tsble 2.
Table 2 Vulcanizate properties
Example 1 2 3 4 5 ~ ;
Tensile strength (MPa) 29 28 28 28 29 ~ -~
~ Elon~ation at break (%)5Z0500 490 470 500
; ~odulus S10O (MPa)3.43.83.94.03.6
Shore A hardneas 72 73 73 73 72
30 Compression set according7053 55 57 54
to DIN 53 517, te~t speci-
men 2, 70 h/100C (X)
Ditto after post-curing for 54 35 ~8 42 33
6 hours at 140C (%)
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