U.S. patent number RE31,322 [Application Number 06/304,788] was granted by the patent office on 1983-07-26 for process for producing sulfur-curable acrylic rubbers.
This patent grant is currently assigned to Nippon Zeon Co. Ltd.. Invention is credited to Kohichi Handa, Tetsu Ohishi, Haruo Ueno.
United States Patent |
RE31,322 |
Ohishi , et al. |
July 26, 1983 |
Process for producing sulfur-curable acrylic rubbers
Abstract
A process for producing a sulfur-curable acrylic rubber is
provided which comprises radical-copolymerizing (1) an alkyl
acrylate with (2) an alkenyl acrylate or methacrylate, or
radical-copolymerizing (1) an alkyl acrylate, (2) an alkenyl
acrylate or methacrylate, (3) an alkoxyalkyl acrylate and
optionally (4) acrylonitrile. These acrylic rubbers can be cured at
a rate as fast as those for curing diene-type rubbers, and the
cured products exhibit superior properties without long
heat-treatment after curing.
Inventors: |
Ohishi; Tetsu (Tokuyama,
JP), Handa; Kohichi (Miura, JP), Ueno;
Haruo (Tokyo, JP) |
Assignee: |
Nippon Zeon Co. Ltd. (Tokyo,
JP)
|
Family
ID: |
27288633 |
Appl.
No.: |
06/304,788 |
Filed: |
September 23, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
024476 |
Mar 27, 1979 |
04228265 |
Oct 14, 1980 |
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Foreign Application Priority Data
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|
|
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Mar 27, 1978 [JP] |
|
|
53-35050 |
Mar 28, 1978 [JP] |
|
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53-35885 |
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Current U.S.
Class: |
526/230; 525/349;
525/351; 526/320; 526/327 |
Current CPC
Class: |
C08F
220/12 (20130101) |
Current International
Class: |
C08F
220/12 (20060101); C08F 220/00 (20060101); C08F
220/40 () |
Field of
Search: |
;525/327,349,351
;526/230,320,327 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wong, Jr.; Harry
Attorney, Agent or Firm: Sherman & Shalloway
Claims
What we claim is:
1. A process for producing a sulfur-curable acrylic rubber, which
comprises copolymerizing in the presence of a radical initiator
(1) 90 to 99.5% by weight of at least one alkyl acrylate with the
alkyl group containing 1 to 8 carbon atoms, and
(2) 0.5 to 10% by weight of at least one monomer of the general
formula ##STR3## wherein R.sub.1 represents a hydrogen atom or a
methyl group, and R.sub.2 and R.sub.3, independently from each
other, represent an alkyl group containing 1 to 3 carbon atoms.
2. A process for producing a sulfur-curable acrylic rubber, which
comprises copolymerization in the presence of a radical
initiator
(1) 30 to 89.5% by weight of at least one alkyl acrylate with the
alkyl group containing 1 to 8 carbon atoms,
(2) 0.5 to 10% by weight of at least one monomer of the general
formula ##STR4## wherein R.sub.1 represents a hydrogen atom or a
methyl group, and R.sub.2 and R.sub.3, independently from each
other, represent an alkyl group containing 1 to 3 carbon atoms,
(3) 10 to 60% by weight of at least one alkoxyalkyl acrylate with
the alkoxy group containing 1 to 4 carbon atoms and the alkylene
group containing 1 to 4 carbon atoms, and
(4) 0 to 30% by weight of acrylonitrile.
3. The process of claim 1 or 2 wherein the monomer (2) represented
by the general formula is 3-methyl-2-butenyl acrylate.
4. The process of claim 1 or 2 wherein the monomer (2) represented
by the general formula is 3-methyl-2-butenyl methacrylate.
5. The process of claim 1 or 2 wherein the copolymerization is
carried out in emulsion.
6. The process of claim 1 or claim 2 wherein the alkyl group of the
alkyl acrylate contains 2 to 4 carbon atoms.
7. The process of claim 1 or claim 2 wherein the monomer (2) is
present in an amount of from about 2% to about 6% by weight.
8. The process of claim 2 wherein the alkoxyacrylate is present in
an amount of from about 20% to about 50% by weight.
9. The process of claim 2 wherein acrylonitrile is present in an
amount of from about 2% to about 20% by weight.
10. The process of claim 1 or claim 2 wherein the radical initiator
is p-menthane hydroperoxide.
Description
This invention relates to a process for producing an acrylic rubber
which can be cured with sulfur.
Acrylic rubber is an elastomeric copolymer composed mainly of an
acrylate unit, and is known to have superior heat resistance and
oil resistance. Since it does not have a double bond at the main
chain of the rubber molecules, a monomeric component having an
active group capable of becoming a crosslinking site is usually
copolymerized with it.
Monomers previously used as the monomeric component for providing
crosslinking sites include, for example, halogen-containing
monomers such as 2-chloroethyl vinyl ether, vinyl benzyl chloride,
vinyl chloroacetate, allyl chloroacetate, and
5-chloroacetoxymethyl-2-norbornene, and epoxy monomers such as
allyl glycidyl ether, glycidyl acrylate and glycidyl
methacrylate.
Because these acrylic rubbers cannot be cured with ordinary sulfur
(or sulfur-containing organic compound), vulcanization accelerator
systems, amines, ammonium salts, metal soap/sulfur, etc. are
generally used as a vulcanizer. Curing with these vulcanizers,
however, has the defect that the rate of cure is slow, and to
obtain vulcanizates of good properties, the cured products must be
heat-treated for a very long period of time after curing.
Furthermore, when the amines or ammonium salts are used as the
vulcanizer, unpleasantly odoriferous gases are generated in places
where rubber products are made, thus causing a sanitary hazard.
This also causes the defect that the cured products cannot be used
in medical and foodstuff applications.
The use of the halogen-containing monomers as the crosslinking
monomeric component may cause the corrosion of the mold at the time
of curing, or the corrosion of metals with which the vulcanized
products will make contact.
In an attempt to remove these defects, a method was suggested which
involves copolymerization of an acrylate ester with such a
crosslinking monomeric component as dicyclopentadiene,
methylcyclopentadiene, ethylidene norbornene, vinylidene
norbornene, butadiene, isoprene, allyl acrylate, 2-butenyl
acrylate, methallyl acrylate, or triallyl isocyanurate to produce
an acrylic rubber. The acrylic rubbers obtained by such a method
are not entirely satisfactory for practical application because of
one or more disadvantages. For example, the rate of cure is
extremely slow, or the properties of the cured product are far from
meeting the requirements of practical application. Or although the
aforesaid problems are solved to some extent, the heat resistance
and compression set of the products are still inferior to acrylic
rubbers obtained by using the halogen-containing monomers or epoxy
monomers as the crosslinking monomeric component.
It is an object of this invention therefore to provide
sulfur-curable acrylic rubbers having superior compression set,
which permit an improved rate of cure as fast as that for curing
natural rubbers and diene-type synthetic rubbers and do not require
long heat-treatment after curing, without sacrificing the superior
heat resistance, oil resistance, weatherability and ozone
resistance of conventional acrylic rubbers.
We have now found that this object can be achieved by using a
certain alkenyl acrylate and/or an alkenyl methacrylate as a
crosslinking component.
Thus, according to this invention, there is provided a process for
producing a sulfur-curable acrylic rubber, which comprises
copolymerizing in the presence of a radical initiator (1) 90 to
99.5% by weight of at least one alkyl acrylate with the alkyl group
containing 1 to 8 carbon atoms and (2) 0.5 to 10% by weight,
preferably 2 to 6% by weight, of at least one monomer of the
general formula ##STR1## wherein R.sub.1 represents a hydrogen atom
or a methyl group, and R.sub.2 and R.sub.3, independently from each
other, represent an alkyl group having 1 to 3 carbon atoms.
We have also found that when a part of the alkyl acrylate (1) is
replaced by another monomer in the aforesaid process for producing
acrylic rubber, there can be obtained an acrylic rubber which has a
well balanced combination of cold resistance and oil resistance in
addition to the aforesaid favorable properties.
Thus, according to another aspect, there is provided a process for
producing a sulfur-curable acrylic rubber, which comprises
copolymerizing in the presence of a radical initiator (1) 30 to
89.5% by weight of at least one alkyl acrylate with the alkyl group
containing 1 to 8 carbon atoms, (2) 0.5 to 10% by weight,
preferably 2 to 6% by weight, of at least one monomer of the
general formula ##STR2## wherein R.sub.1 represents a hydrogen atom
or a methyl group, and R.sub.2 and R.sub.3, independently from each
other, represent an alkyl group containing 1 to 3 carbon atoms,
(3) 10 to 60% by weight, preferably 20 to 50% by weight, of at
least one alkoxyalkyl acrylate with the alkoxy group containing 1
to 4 and the alkylene group containing 1 to 4 carbon atoms, and (4)
0 to 30% by weight, preferably 2 to 20% by weight, of
acrylonitrile.
Examples of the alkyl acrylate (1) are methyl acrylate, ethyl
acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl
acrylate, cyclohexyl acrylate, and octyl acrylate. Those in which
the alkyl group contains 2 to 4 carbon atoms are preferred; for
example, they are ethyl acrylate, propyl acrylate and butyl
acrylate.
Examples of the alkenyl acrylate and alkenyl methacrylate (2) of
general formula (I) include 3-methyl-2-butenyl acrylate,
3-methyl-2-pentyl acrylate, and 3-methyl-2-hexenyl acrylate, and
the corresponding methacrylates.
Acrylic rubbers made by the copolymerization of allyl acrylate or
2-butenyl acrylate with alkyl acrylates are known (U.S. Pat. No.
3,476,722). These acrylic rubbers, however, require long
heat-treatment after curing as is the case with the conventional
acrylic rubbers using the halogen-containing monomers or epoxy
monomers as the crosslinking monomeric component, and the
properties of the vulcanizates are not satisfactory for practical
purposes. Moreover, acrylic rubbers obtained by the ternary
copolymerization of allyl methacrylate, an alkyl acrylate and
acrylonitrile are also known (Japanese Patent Publication No.
7893/72). But these acrylic rubbers have poor mechanical strength,
and cannot find practical application.
When in accordance with this invention, at least one monomer of
general formula (I) (i.e., an alkenyl acrylate or alkenyl
methacrylate) is used as the crosslinking monomer, these defects
can be markedly remedied. If the amount of the monomer (2) is less
than 0.5% by weight, the rate of cure is extremely low, and
vulcanizates having satisfactory properties for practical
application cannot be obtained. If the amount of the monomer (2)
exceeds 10% by weight, the cured product has very high hardness,
and a greatly reduced elongation, and therefore, cannot be used
satisfactorily as a rubber product.
Examples of the alkoxyalkyl acrylate (3) include methoxymethyl
acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, and
butoxyethyl acrylate.
The acrylonitrile (4) is used in the aforesaid amounts when it is
necessary to adjust the strength and oil resistance of the acrylic
rubber of this invention.
The process of this invention can be easily performed by
polymerizing a mixture of the monomers (1) and (2) or a mixture of
the monomers (1), (2) and (3) and optionally (4) in the presence of
a radical initiator by a known polymerization method (e.g., in
emulsion, suspension, solution, bulk, etc.). The polymerization is
performed batchwise, or while adding at least one component
continuously and/or intermittently during the reaction. The
polymerization temperature is preferably from -10.degree. C. to
+100.degree. C., more preferably from 2.degree. to 80.degree.
C.
The resulting acrylic rubber can be easily cured with sulfur
vulcanization systems generally used for natural rubbers or
diene-type synthetic rubbers, and this curing treatment does not
require the very long heat-treatment after curing which is
essential in the curing of ordinary acrylic rubbers having a
halogen containing monomer or epoxy monomer as crosslinking sites.
The cured products have superior heat resistance, weatherability
and ozone resistance, and in some cases, a well balanced
combination of cold resistance and oil resistance. Furthermore, the
acrylic rubbers of this invention have markedly improved heat
resistance and compression set over the known sulfur-curable
acrylic rubbers.
In addition to the vulcanization system, various compounding agents
such as reinforcing agents, fillers, plasticizers and antioxidants
may be added to the rubbers of this invention as required.
The cured products of the acrylic rubbers of this invention are
useful in many applications which require heat resistance, oil
resistance, weatherability and ozone resistance. They include, for
example, various rubber products such as gaskets, hoses, conveyor
belts, packings, oil seals and valve seats.
The present invention is more specifically illustrated below with
reference to Examples and the accompanying drawings.
In the drawings,
FIG. 1 shows cure curves of acrylic rubbers obtained in Runs Nos.
3, 9 and 10 in Example 1 which were measured by means of an
oscillating disc rheometer (a product of Toyo Seiki K.K.); and
FIG. 2 show cure curves of acrylic rubbers obtained in Runs Nos. 1,
7 and 8 of Example 2 measured in the same way as described above.
In these graphic representations, the abscissa represents the cure
time (minutes), and the ordinates, the torque (kg.cm). The solid
line refers to the example within the scope of this invention, and
the broken lines, to comparisons.
EXAMPLE 1
A series of copolymers were produced by using the monomeric
mixtures shown in Table 1. The method of polymerization was as
follows:
A 2-liter separable flask equipped with a thermometer, a stirrer, a
nitrogen introducing tube and an evacuation device was charged with
a mixture of the following formulation.
______________________________________ Water 1,000 g Sodium
dodecylbenzenesulfonate 20 g Sodium naphthalenesulfonate 10 g
Sodium sulfate 3 g Tetrasodium ethylenediamine- tetraacetate 0.2 g
Ferrous sulfate 0.005 g Monomeric mixture (Table 1) 1000 g
______________________________________
The pH of the mixture was adjusted to 7, and with stirring, the
temperature of the inside of the flask was maintained at 5.degree.
C. Furthermore, the inside of the flask was deoxygenated fully by
using the nitrogen introducing tube and the evacuation device.
Then, the following compounds were added, and the reaction was
started.
Na.sub.2 S.sub.2 O.sub.4 :0.2 g
Sodium formaldehyde sulfoxylate: 0.2 g
p-Menthane hydroperoxide: 0.1 g
The polymerization was terminated in about 16 hours. The
polymerization conversion was within the range of 95 to 99% in each
run. After the polymerization, the reaction mixture was salted out,
washed with water, and dried under vacuum in a dryer to form the
desired acrylic rubber.
TABLE 1 ______________________________________ Monomers Run No
(parts by Invention Comparison weight) 1 2 3 4 5 6 7 8 9 10
______________________________________ Ethyl acrylate 99 97 95 97
32 97 97 97 98 95 Butyl acrylate -- -- -- -- 65 -- -- -- -- --
3-Methyl-2-butenyl acrylate 1 3 5 -- 3 -- -- -- -- -- Allyl
acrylate -- -- -- -- -- 3 -- -- -- -- 2-Butenyl acrylate -- -- --
-- -- -- 3 -- -- -- Methallyl acrylate -- -- -- -- -- -- -- 3 -- --
Glycidyl methacrylate -- -- -- -- -- -- -- -- 2 --
2-Chloroethylvinyl ether -- -- -- -- -- -- -- -- -- 5
______________________________________
Using the 10 acrylic rubbers obtained, compounds were prepared by
means of an open roll in accordance with the recipes shown in Table
2. The compounds were each press-cured at 160.degree. C. for 20
minutes, and then heat-treated in a Geer oven at 150.degree. C. for
4 hours and 16 hours, respectively.
TABLE 2 ______________________________________ Recipe Run No.
(parts by weight) 1-8 9 10 ______________________________________
Acrylic rubber 100 100 100 Stearic acid 1 1 1 HAF-LS carbon black
60 60 60 Zinc oxide No. 1 3 -- -- Red lead -- -- 5
2-Mercaptobenzimida- zole -- -- 1.5 Ammonium benzoate -- 1 --
Tetramethylthiuram disulfide 2 -- -- 4,4'-Dithiomorpholine 2 -- --
N--cyclohexyl-2-benzo- thiazyl sulfenamide 1 -- --
______________________________________
The properties of the cured products were measured in accordance
with JIS K-6301, and the results are shown in Table 3.
The cure behaviors of a compound containing the acrylic rubber of
this invention (Run No. 3) and compounds containing conventional
acrylic rubbers including an epoxy monomer and a halogen-containing
monomer as the crosslinking monomer (Runs Nos. 9 and 10) were
measured by an oscillating disc rheometer. The relation between the
curing time and the torque were plotted in FIG. 1.
TABLE 3-1
__________________________________________________________________________
Run No. Invention Comparison Test items 1 2 3 4 5 6 7 8 9 10
__________________________________________________________________________
Properties after curing at 160.degree. C. for 20 minutes Tensile
strength (kg/cm.sup.2) 121 153 152 111 140 64 73 70 106 98 100%
Tensile stress (kg/cm.sup.2) 11 36 49 18 31 11 15 13 40 19
Elongation (%) 710 330 190 510 340 320 300 300 340 490 Hardness
(Shore A) 50 67 69 54 65 48 52 50 63 58 Compression set (%)(*) 69
54 55 76 68 84 80 83 80 89
__________________________________________________________________________
(*): Compression ratio 25%, 150.degree. C. .times. 70 hours
TABLE 3-2
__________________________________________________________________________
Run No. Invention Comparison Test items 1 2 3 4 5 6 7 8 9 10
__________________________________________________________________________
Properties after curing at 160.degree. C. for 20 minutes and then
heat-treatment at 150.degree. C. for 4 hours
__________________________________________________________________________
Tensile strength (kg/cm.sup.2) 134 149 149 120 139 67 81 73 113 119
100% Tensile stress (kg/cm.sup.2) 14 36 49 19 36 15 23 20 53 31
Elongation (%) 600 320 190 470 310 270 280 270 290 350 Hardness
(Shore A) 54 67 69 57 67 54 58 55 66 62 Compression set (%)(*) 30
27 22 38 34 63 56 61 56 77
__________________________________________________________________________
Properties after curing at 160.degree. C. for 20 minutes and then
heat-treatment at 150.degree. C. for 16 hours
__________________________________________________________________________
Tensile strength (kg/cm.sup.2) Since the properties reached 69 70
68 134 137 100% Tensile stress (kg/cm.sup.2) an equilibrium as a
result of 21 29 25 69 62 Elongation (%) the curing at 160.degree.
C. for 20 230 220 220 210 220 Hardness (Shore A) minutes and heat
treatment at 59 61 60 69 69 Compression set (%)(*) 150.degree. C.
for 4 hours, the 51 44 45 29 59 testing of the properties after the
16-hours heat- treatment was omitted
__________________________________________________________________________
TABLE 3-3
__________________________________________________________________________
Run No. Invention Comparison Test items 1 2 3 4 5 6 7 8 9 10
__________________________________________________________________________
Heat aging test (in Geer oven at 175.degree. C. for 170 hours) (**)
Percent change in tensile strength (%) -47 -28 -4 -32 -27 -48 -26
-41 +15 -37 Percent change in elonga- tion (%) +8 .+-.0 -8 -15 -7
-48 -32 -50 -20 -43 Change in hardness (point) +12 +11 +12 +15 +13
+20 +18 +20 +9 +8 Heat aging test in oil (150.degree. C. for 70
hours in ASTM No. 3 oil) (**) Percent change in volume (%) +17.0
+15.1 + 13.6 +16.2 +26.3 +16.5 +16.0 +16.5 +16.7 +17.8 Cold
resistance test (low-temperature torsion test in JIS K-6301 (**)
T-10 (.degree.C.) -12.0 -10.0 -9.5 -10.0 -21.0 -10.0 -10.0 -10.0
-10.0 -10.0
__________________________________________________________________________
(**): In Runs Nos. 1 to 8 samples cured at 160.degree. C. for 20
minutes (not heattreated subsequently) were used, and in Runs Nos.
9 and 10, samples cured at 160.degree. C. for 20 minutes and then
heattreated at 150.degree. C. for 16 hours were used.
It is seen from FIG. 1 that while the conventional acrylic rubbers
(Runs Nos. 9 and 10) cure very slowly, the acrylic rubber of this
invention (Run No. 3) cures very rapidly after starting of
vulcanization and then reaches an equilibrium, thus exhibiting the
same vulcanization behavior as a diene-type rubber. Hence, the
acrylic rubber of the invention shows satisfactory properties for
practical application when cured at 160.degree. C. for 20 minutes,
and its compression set is improved by heat-treatment at
150.degree. C. for as short as 4 hours. To obtain vulcanizates
having properties equivalent to the acrylic rubber of this
invention, the conventional acrylic rubbers must be heat-treated at
150.degree. C. for as long as 16 hours.
Acrylic rubbers including allyl acrylate, 2-butenyl acrylate, and
methallyl acrylate (Runs Nos. 6, 7 and 8, respectively) have very
poor roll processability, and even when heat-treated in the same
way as in the case of the conventional acrylic rubbers, cannot have
satisfactory vulcanization properties for practical
application.
It is appreciated from the experimental results given above that
the acrylic rubber of this invention is an acrylic rubber of very
good quality which shows equivalent or better vulcanization
properties to or than the conventional acrylic rubbers without
performing the long heat-treatment which is essential to the
vulcanization of the conventional acrylic rubbers.
EXAMPLE 2
A 2-liter separable flask equipped with a thermometer, a stirrer, a
nitrogen introducing tube and an evacuation device was charged with
a mixture of recipe (I) below. The pH of the mixture in the flask
was adjusted to 7, and with stirring, the temperature of the inside
of the flask was maintained at 5.degree. C. The oxygen in the flask
was sufficiently removed by repeated deaeration and nitrogen
introduction. Then, a mixture of recipe (II) below was added, and
the polymerization was started. The polymerization was terminated
in about 16 hours. The polymerization conversion was within the
range of 95 to 99% in each run. After the polymerization, the
product was salted out, washed thoroughly with water, and dried
under reduced pressure in a dryer to obtain the desired acrylic
rubber.
Polymerization Recipe
Recipe (I)
______________________________________ Water 1000 g Sodium
dodecylbenzenesulfonate 20 g Sodium naphthalenesulfonate 10 g
Sodium sulfate 3 g Tetrasodium ethylenediamine- tetraacetate 0.2 g
FeSO.sub.4 0.005 g Monomeric mixture (Table 4) 1000 g
______________________________________
Recipe (II)
______________________________________ Na.sub.2 S.sub.2 O.sub.4 0.2
g Sodium formaldehyde sulfoxylate 0.2 g p-Menthane hydroperoxide
0.1 g ______________________________________
TABLE 4 ______________________________________ Run No. Monomers
Invention Comparison (parts by weight) 1 2 3 4 5 6 7 8
______________________________________ Ethyl acrylate 53 47 37 --
52 52 98 95 Butyl acrylate 25 15 -- 47 20 25 -- -- Methoxyethyl
acrylate 20 35 60 50 20 20 -- -- Acrylonitrile -- -- -- -- 5 -- --
-- 3-Methyl-2-butenyl acrylate 3 3 3 3 3 -- -- --
3-Methyl-2-hexenyl acrylate -- -- -- -- -- 3 -- -- Glycidyl
methacrylate -- -- -- -- -- -- 2 -- 2-Chloroethylvinyl ether -- --
-- -- -- -- -- 5 ______________________________________
Using the 8 acrylic rubbers so obtained, compounds were prepared by
means of an open roll under cooling in accordance with the recipes
shown in Table 5, and then each press-cured at 160.degree. C. for
20 minutes. Then, the cured products were each heat-treated in a
Geer oven at 150.degree. C. for 4 hours, and 16 hours,
respectively.
TABLE 5 ______________________________________ Run No. Invention
Comparison Recipe (parts by weight) 1-6 7 8
______________________________________ Acrylic rubber 100 100 100
Stearic acid 1 1 1 HAF-LS carbon black 60 60 60 Zinc oxide No. 1 3
-- -- Red lead -- -- 5 2-Mercapto benzimidazole -- -- 1.5 Ammonium
benzoate -- 1 -- Tetramethyl thiuram disulfide 2 -- --
4,4'-Dithiomorpholine 2 -- -- N--Cyclohexyl-2-benzothiazyl
sulfenamide 1 -- -- ______________________________________
The properties of the cured products were measured in accordance
with JIS K-6301, and the results are shown in Table 6.
The vulcanization behaviors of a compound containing the acrylic
rubber of this invention (Run No. 1) and compounds containing the
comparative acrylic rubbers (Runs Nos. 7 and 8) were measured in
the same way as in Example 1, and the results were plotted in FIG.
2.
TABLE 6-1
__________________________________________________________________________
Run No. Invention Test items 1 2 3 4 5 6 7 8
__________________________________________________________________________
Properties after curing at 160.degree. C. for 20 minutes Tensile
strength (kg/cm.sup.2) 122 126 134 98 148 103 106 98 100% Tensile
stress (kg/cm.sup.2) 35 34 35 38 37 36 40 19 Elongation (%) 290 300
310 240 320 240 340 490 Hardness (Shore A) 66 66 66 67 67 67 63 58
Compression set (%) (*) 63 68 67 62 59 73 80 89
__________________________________________________________________________
(*):Compression ratio 25%, 150.degree. C. .times. 70 hours
TABLE 6-2
__________________________________________________________________________
Run No. Invention Comparison Test items 1 2 3 4 5 6 7 8
__________________________________________________________________________
Properties after curing at 160.degree. C. for 20 minutes and then
heat-treatment at 150.degree. C. for 4 hours
__________________________________________________________________________
Tensile strength (kg/cm.sup.2) 119 124 131 103 141 107 113 119 100%
Tensile stress (kg/cm.sup.2) 35 34 34 39 38 39 53 31 Elongation (%)
290 300 310 240 310 220 290 350 Hardness (Shore A) 66 66 66 67 67
67 66 62 Compression set (%) (*) 30 33 31 37 32 39 56 77
__________________________________________________________________________
Properties after curing at 160.degree. C. for 20 minutes and then
heat-treatment at 150.degree. C. for 16 hours
__________________________________________________________________________
Tensile strength (kg/cm.sup.2) Since the properties reached an 134
137 100% Tensile stress (kg/cm.sup.2) equilibrium as a result of
the 69 62 Elongation (%) curing at 160.degree. C. for 20 minutes
210 220 Hardness (Shore A) and heat treatment at 150.degree. C. for
69 69 Compression set (%) (*) 4 hours, the testing of the pro- 29
59 perties after the 16-hour heat- treatment was omitted
__________________________________________________________________________
TABLE 6-3
__________________________________________________________________________
Run No. Invention Comparison Test items 1 2 3 4 5 6 7 8
__________________________________________________________________________
Heat aging test in oil (150.degree. C. for 70 hours in ASTM No. 3
oil) (**)
__________________________________________________________________________
Percent change in volume (%) +18.9 +13.8 +8.5 +22.4 +14.2 +19.7
+16.7 +17.8
__________________________________________________________________________
Cold resistance test (low-temperature torsion test in JIS 6301)
__________________________________________________________________________
(**) T-10 (.degree.C.) -21 -21.5 -23.5 -34.5 -16 -21.5 -10 -10
__________________________________________________________________________
(**): In Runs Nos. 1 to 8, samples cured at 160.degree. C. for 20
minutes (not heattreated subsequently) were used, and in Runs Nos.
9 and 10, samples cured at 160.degree. C. for 20 minutes and then
heattreated at 150.degree. C. for 16 hours were used.
It is seen from FIG. 2 that while the conventional acrylic rubbers
cure slowly, the acrylic rubber of this invention exhibits a
vulcanization behavior equivalent to a diene-type rubber.
Accordingly, as shown in Table 6, while the conventional acrylic
rubbers require heat-treatment at 150.degree. C. for as long as 16
hours after the curing, the acrylic rubber of this invention
affords cured products having equivalent characteristics to the
conventional acrylic rubbers by heat-treatment at 150.degree. C.
for as short as 4 hours. Moreover, the acrylic rubbers of this
invention have markedly improved heat resistance and compression
set over the conventional sulfur-curable acrylic rubbers, and
exhibit a well balanced combination of cold resistance and oil
resistance.
According to this invention, therefore, the slow cure rate of the
conventional acrylic rubbers can be increased to a level equivalent
to that of diene-type rubbers without impairing the good heat
resistance, oil resistance, weatherability, ozone resistance and
cold resistance of the conventional acrylic rubbers, and acrylic
rubbers having a low compression set and a well balanced
combination of cold resistance and oil resistance can be
obtained.
* * * * *