Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
9~8
N,N'-[(thiocarbonyl)thio]dimorpholine and 2-benzothiazole
sulfenamide are rubber accelerators which are widely used in the rubber
industry. While the compounds are readily prepared according to well-
known procedures in a high state of purity, they deteriorate when exposed
to elevated temperatures and/or humid conditions. The deterioration of the
sulfenamides is manifested by a gradual build-up of mercaptobenzothiazyl
disulfide (MBTS) resulting in an alteration of the cure characteristics
normally exhibited by the accelerator when used in a rubber vulcanizate.
Since elevated temperatures and humid conditions are common in the summer
months and throughout the warmer areas of the world, it is desirable to
find a means for either stopping or retarding this deterioration without
destroying the accelerating activity of the compounds.
It has now been found that the incorporation of a minor amount
of a oxirane (epoxy) compound into the N,N'-[(thiocarbonyl)thio] dimorpholine
and the benzothiazole sulfenamides significantly reduces the deterioration
of the accelerators on exposure to temperature and/or humidity.
Accordingly, the present invention provides a stabilised
accelerator composition for rubber comprising (1) N,N'-[(thiocarbonyl)thio]
dimorpholine or a benzothiazole sulfenamide having the formula:
~ C - S - (S)~ - N \
wherein R and R' are, individually, hydrogen, alkyl i 1 - 8 carbon atoms,
inclusive, cycloaIkyl of 5 - 6 carbon atoms, inclusive or taken with the
nitrogen, combine to form a heterocyclic ring, and n is 0 or 1 and (2)
an effective stabilizing amount of an oxirane compound free of interfering
functional groups and having a molecular weight greater than 60.
2-Benzothiazole sulfenamides may be represented by the general
formula
S - (S)n - N
N R'
- ,~
~s~
wherein R and R' individually represent hydrogen, alkyl of 1 to 8 carbon
atoms, inclusive, cycloaIkyl of 5 to 6 carbon atoms, inclusive, or taken
together with the nitrogen atom, combine to form a heterocyclic ring, and n
is O or 1. They
- la -
_i
1 are readily prepared by well-known procedures, see for ex-
ample, United States Patent Nos. 2,730,526; 2,730,527;
2,758,995; 2,776,297; 2,840,556; 2,981,325; 3,055,909;
3,161,648; and 3,658,808. Some of the more commonly used
accelerators include N-isopropyl-2-benzothiazole sulfenamide;
N,N-diisopropyl-2-benzothiazole sulfenamide; N-t-butyl-2-
-benzothiazole sulfenamide; N-cyclohexyl-2-benzothiazole sul-
fenamide; N,N-dicyclohexyl-2-benzothiazole sulfenamide; N-oxy-
diethylene-2-benzothiazole sulfenamide; 4-morpholinyl-2-benzo-
thiazole disulfide; N-t-octyl-2-benzothiazole sulfenamide;
N,N-dicyclopentyl-2-benzothiazole sulfenamide; N,N-diethyl-2-
-benzothiazole sulfenamide; N-methyl-2-benzothiazole sulfen-
amide and the like.
N,N'-[(thiocarbonyl)thio]dimorpholine is an old
compound. It can be readily made by reacting sodium 4-mor-
pholinocarbodithioate (II) with N-chloromorpholine (III):
. . _ ~ _
~ C S Na ~ Cl N 3 >
20 (II) (III)
~ S
O N C - S ~ ~ NaCl
Another method is described whereby (II) is react-
ed with morpholine and an oxidizing agent such as an aqueous
solution of iodine and potassium iodide or sodium hypochlor-
ite or other oxidizing agent known in the art for the prepara-
tion of thiocarbonylsulfides.
Use of the compound as an accelerator is described
-- 2 --
1 by Taylor, Rubber Chem. ~ Tech. 47 (No. 4), 906-910 (1974).
The oxirane compounds which are useful herein are
those solid or liquid organic oxirane compounds having a
molecular weight of greater than about 60 and have no func-
tional groups reactive with the dimorpholine and sulfenamideother than the oxirane ring. These compounds include, but
are not limited to, alkyl, cycloalkyl and aryl glycidyl ethers;
mono- and diepoxidized alkenes and dienes, including epoxi-
dized diene polymers, such as, for example, 1,2- and 2,3-
-epoxybutane and epoxidized polybutadiene; cycloalkylene ox-
ides such as cyclohexene oxide, vinyl cyclohexene diepoxide,
etc.; diglycidyl ethers of aliphatic diols such as the di-
glycidyl ether of 1,4-butanediol; diglycidyl ethers of bis-
phenols such as the diglycidyl ether of isopropylidene bis-
phenol (Bisphenol A) or diglycidyl ethers of methylene bis-
phenol and oligomers thereof; epoxidized oils such as epoxi-
dized linseed oil, etc.; epoxidized unsaturated diglycidyl
ethers of polymeric diols and polyglycidyl ethers of polyols
and the like.
In practicing the invention, the N,N'-[(thiocar-
bonyl)thio]dimorpholine or the sulfenamide is blended in any
convenient manner consistent with the invention with the oxi-
rane compound. Since N,N'-[(thiocarbonyl)thio]dimorpholine
is not very stable, the procedure used to blend it with the
oxirane should avoid exposure to elevated temperatures for
too long a period of time. Nevertheless, one method of pro-
ducing the blend is to melt the N,N'-[(thiocarbonyl)thio]-
dimorpholine, blend in the appropriate oxirane compound,
allow the molten blend to cool and either flake or grind the
resultant solid for use. Alternatively, the oxirane and
-- 3 --
P~5~
1 dimorpholine may be dry blended. The blending method is not
critical to the invention; however, it will be understood
that not all stabilizer compounds will melt or dissolve into
the molten accelerator and dispersions may sometimes result,
and that, in some instances, it may be better to dry blend
and vice versa.
The sulfenamides are often prepared by cooling and
flaking the molten compound. In this case, it is possible
to incorporate the oxirane compound into the melt before
cooling and flaking.
The blends may be prepared in any weight ratio
without incident, but the oxirane concentration should range
from about 0.1 percent, by weight, to about 5.0 percent, by
weight, depending on the particular stabilizer, it being
realized that the stabilizers may vary in their effective-
ness in stabilizing the accelerator compound. Preferably,
the dimorpholine or the sulfenamide may be effectively stab-
ilized against deterioration on aging using about 0.5 to 3
percent, by weight, of the oxirane compound, based on the
weight of the dimorpholine or sulfenamide.
Stabilization, as defined for the purposes of this
invention, means any significant improvement in the stability
of the N,N'-[(thiocarbonyl)thio]dimorpholine or the sulfen-
amide after storing for a period of time at normal room temp-
erature or at an elevated temperature. An accelerated agingtest which excemplifies the stabilization of the dimorpholine
is defined hereinbelow. Improvement in stability means any
significant reduction of the loss of cure rate experienced
by use of the unstabilized dimorpholine during a similar per-
iod of storage under the same conditions, and/or any signif-
-- 4 --
~`5~
l icant decrease in the loss of scorch protection (scorchtime) relative to the unstabilized dimorpholine. The un-
stabilized compound ordinarily suffers degradation on stor-
age over a period of time such that its use in a vulcaniza-
tion results in a slower rate of cure and oftentimes a re-
duction in scorch time. This is often manifested in the
vulcanized rubber product by slower development of the
optimum modulus properties and in many cases the extent of
the full cure may be afffcted, i.e., the optimum properties
may not be attained.
Cure rate is determined by use of a Monsanto
Oscillating Disc Rheometer and is reported as the maximum
slope of the cure curve in inch-pounds per 0.5 minute oper-
ating against an oscillating disc embedded in the rubber
stock undergoing vulcanization.
Mooney Scorch Time is the elapsed time from the
onset of the heating cycle to the start of vulcanization
(induction period). With reference to the cure curve traced
by the Mooney Viscometer, scorch is reported as t5, which is
the time, in minutes, from one minute after the start of
heating, for a five point rise in the cure curve above the
minimum in the curve, at the temperature of the test, which
is usually chosen to represent maximum processing temperature
of the unvulcanized rubber composition.
The stabilized N,N-[thiocarbonyl)thio]dimorpholine
is evaluated, as discussed above, in terms of the improvement
over an unstabilized sample thereof after a period of aging.
It is difficult to determine what constitutes normal storage
conditions, in terms of the physical form of storage (drums,
fiber packs, paper bags, etc.), the length of storage in
~5~
1 days, weeks or months, or the temperature of storage (air-
-conditioned warehouses or exposure to ambient temperature
in the warmer climates). In order to evaluate the effect-
iveness of the stabilizers by a reasonable set of conditions,
unless otherwise stated, the stabilized and unstabilized com-
pounds were stored in closed containers for (a) two weeks at
normal room temperature (25 - 30C.), (b) for one month at
45C., and (c) two months at 45C. The compounds were then
evaluated in a standard rubber formulation as described in
the following illustrative examples.
In the examples which follow, the compounds were
evaluated for effectiveness of the stabilizer using the
rubber masterbatch shown below (which contains 100 parts by
weight of rubber stock):
Masterbatch
Styrene-butadiene rubber 89.5 ;
(oil-extended)
Cis-4 Polybutadiene 35.0
Aromatic oil 25.5
Carbon black 75.0
Zinc oxide 5.0
Stearic acid 1.5
N-Phenyl-N'-(1,3-dimethylbutyl)- 1.0
p-phenylenediamine
Sulfur 1.8
Example 1
To a sample, comprising 100 parts of N,N-[(thio-
carbonyl)thio]dimorpholine, are added 4.0 parts of 3,4-epoxy-
cyclohexylmethyl-3,4-epoxycyclohexane carboxylate.
The stabilized sample is then added to the above
masterbatch after storage for 6 weeks at 25~ RH and 45C.,
-- 6 --
~ ~5~
1 at a concentration of 0.9 part of stabilized sample to 100
parts of masterbatch, as described above, with compounding.
The sample is then subjected to testing in order
to ascertain the accelerator activity in promoting the vul-
canization reaction as measured by the cure rate and isidentified as Composition A. A sample containing no stabil-
izer is set forth for comparative purposes, in Table I, be-
low.
Table I
None A
Oscillating Disc Rheometer @ 316F.
Maximum Cure Rate
(in.-lbs./0.5 min)
6 Weeks 3.4 3.8
Maximum Torque
15 (inch-pounds)
6 Weeks 44.5 49.5
Scorch Time (t ) Mooney Viscometer @ 270F.
(minutes) 5
6 Weeks 12.8 24.0
The data show that N,N'-t(thiocarbonyl)thio]di-
morpholine is improved (stabilized against degradation) by
the incorporation therein of 4.0 percent, by weight, of the
epoxy compound, as shown by the retention of cure rate after
storage for 6 weeks at 45C. and 25% RH and by the stability
of the Mooney Scorch.
Examples 2 - 5
-
The procedure of Example 1 is again followed ex-
cept that the oxiranes are (B) 2.0% of epoxidized soybean
oil, (C) 1.0~ of vinyl cyclohexene diepoxide, (D) 5.0% of
the diglycidyl ether of 1,4-butanediol, and (E) 0.75% of
a~5~
1 the diglycidyl ether of 4,4'-isopropylidenebisphenol. In
each instance, effective stabilization of the N,N-[(thio-
carbonyl)thio]dimorpholine is accomplished.
Example 6
Again, following the procedure of Example 1, ex-
cept that the oxirane comprises 2.5~ of the diglycidyl ether
of phenol-formaldehyde condensate, satisfactory stabilization
is achieved.
Examples 7 - 10
When the stabilizer of Example 1 is replaced by
(F) 0.5% of 2,3-epoxypropyl-n-hexylether, (G) 1.0~ of epoxi-
dized butyl linseed oil, (H) 3.5% of epoxidized linseed oil,
and (I) 4.0% of 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane;
effective stabilization of the accelerator is achieved.
Example 11
Stabilization of N-Isopropyl-2-Benzothiazole Sulfenamide
Samples of N-isopropyl-2-benzothiazole sulfenamide
are mixed with 2% of (J) 2,3-epoxypropyl-n-hexyl ether and
(K) 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane. The samples
are then exposed for periods of 2 weeks and 4 weeks at nor-
mal room temperature and 75% humidity and then analyzed for
build-up of mercaptobenzothiazyldisulfide (MBTS). The re-
sults are shown below in Table II.
~n d
O In
,~
~1 1 ~D
~n ~
~ a)
dP 3
~r
~ r~
r~
X ~ o o
H
H
R
~ U~
E~ ~ ~
I`
~ U~ o o
.Y o o o
.,1 o o o
~ o o o
H O O O
~1
O 1
~ S~
e ~ ~ ~
X o
1 The data illustrate the effectiveness of the
epoxy compounds in preventing deterioration of the sulfen-
amide on exposure to humidity, as manifested by build-up on
MBTS.
_ample 12
Samples of N-isopropyl-2-benzothiazole sulfenamide
are mixed with 2% of (L) 3,4-epoxycyclohexyl methyl-3,4-
-epoxycyclohexane carboxylate, and (M) epoxidized butyl lin-
seed oil. The samples are then exposed for periods of 2
10 weeks at 75% RH and 2 weeks at 45C./25% RH and then anal-
yzed for build-up of M~TS.
Results are shown below in Table III.
-- 10 --
i5~
N
o O O ~r
U~
JJ ~ O o
,Y ,'
N
A~ æl
E~ ~
U~ 0~
~D O O~
~ N O
~ O O O
N
~1 N N
.,1 O O O
~ O O O
H O O O
X O N N
~1t ) ~1 ~1
-- 11 --
~5~
1 Example 13
A sample of N-isopropyl-2-benzothiazole sulfen-
amide is mixed with 2% of (N) epoxidized linseed oil and
the sample is exposed for periods of 2 weeks at 45C. and 4
weeks at 75% RH. The sample is then analyzed for build-up
of MBTS.
The results are set forth in Table IV, below.
- 12 -
~5~
tn ~
tn In
~r
~o~ ~
Il) U~N--1
U1 .Y
u~ a
U~
o~o
N
U~~10
.~C ;,
-''~
.
~ .
'.
,,~
H
. C~
~' ~ :: ~_I O
~: ~1 0
cn .~. -:
~ O O
; : N . ~ .
~ ~ ~ .
.,1 O O
~ O O
,1
~ O O
a~
~1O
~ ~ :
Z
X O
1~1
.
-- 13 --
; : ,.` ,. ; !
~!5~
1 Example 14
Stabilizaton of N,N-Diisopropyl-2-Benzothiazole Sulfenamide
A sample of N,N-diisopropyl-2-benzothiazole sul-
fenamide is mixed with 2% of (P) epoxidized linseed oil and
then exposed for lO weeks at 45C./25% RH. The sample is
then analyzed for MBTS build-up.
The results are set forth in Table V, below.
- 14 -
`s`~
u~
0o
~ ~a~ ..
. :
~ ~ o
u~
~R
op
.
u~
~ ~ o
~ o ~ o
a) ~ o o
R 0
E~ ~ .
E~ ,1
d~
.~dl o o
~ o o
~1
~ o o
H
a~ ~
O
S~
e
X
-- 15 --
1 Example 15
The following sulfenamides are mixed with epoxide
(L), as shown in Table VI, and then exposed for periods of
one week and 2 weeks at 45C./25% RH. The samples are then
analyzed for MBTS build-up.
I. N-tert.butyl-2-benzothiazole sulfenamide
.
~ /C -S -NH - C - C~3
II. N-oxydiethylene-w-benzothiazole sulfenamide
15 ~ ~ -S - ~
III. N-cyclohexyl-2-benzothiazole sulfenamide
~ ~ - S - N~ -
Table VI
% MBTS
-
ExampleInitial 1 Week 2 Weeks 5 Weeks
25 15-I 0.003 1.02 --- ---
15-I+1% L0.004 0.18 --- ---
15-II 0.002 0.008 0.12 3.94
15-II+3% L0.002 0.004 0.02 0.02
15-III 0.004 0.56 1.62 ---
30 15-III+1% L 0.01 0.06 0.06 ---
- 16 -
~5~
1 Examples 16-21
The procedure of Example 14P is again followed ex-
cept that the epoxy compound, in each instance, is replaced
by:
16. 3% of vinylcyclohexene diepoxide
17. 1.5% of styrene oxide
18. 2.0% of the diglycidyl ether of 1,4-butanediol
19. 1.0% of the diglycidyl ether of 4,4'-iso-
propylidenebisphenol
20. 2.0% of the glycidyl ether of phenol-formal-
dehyde condensate
21. 3.0% of epoxidized soybean oil
In each instance, a substantially equivalent reduction in
MBTS build-up is observed.
Examples-22-29
The procedure of Example llK is again followed
except that the N-isopropyl-2-benzothiazole sulfenamide is
replaced by:
22. 4-morpholinyl-2-benzothiazole disulfide
23. N,N-dicyclohexyl-2-benzothiazole sulfenamide
24. N-t-octyl-2-benzothiazole sulfenamide
25. N,N-dicyclopentyl-2-benzothiazole sulfenamide
26. N-methyl-2-benzothiazole sulfenamide
27. N-isopropyl-2-benzothiazole disulfide
28. N,N-diisopropyl-2-benzothiazole disulfide
29. N,N-diethyl-2-benzothiazole sulfenamide.
In each instance, the 2,2-bis[4-(2,3-epoxypropoxy)phenyl]-
propane effectively prevented deterioration of the compounds.
- 17 -
