Note: Descriptions are shown in the official language in which they were submitted.
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1 This invention relates to a vulcanizable
rubber composition, and more particularly to a rubber
composition excellen-t in oil resistance, heat resistance
and ozone resistance having a small compression set.
Hitherto, acrylic rubber has been used in
packings, O-rings, gaskets and the like which are
required to have oil resistance, heat resistance and
ozone resistance. Although acrylic rubber satisfies the
required performances in respect oE oil resistance, heat
resistance and ozone resistance, it has faults that it
is poor in processability in the steps of blending and
kneading, the vulcanizate obtained by vulcanizing the
composition in a conventional manner has so great a
compression set that a secondary vulcanization is
required, and the composition contaminates the mold in
the step of molding, and is expensive. Therefore, its
improvement is desired.
In order to improve these properties, there
has been proposed the sulfur-vulcanizable acrylic rubber
obtained by copolymerizing an acrylic ester with a
crosslinking component such as cyclopentadiene,
ethylidenenorbornene, vinylidenenorbornene, allyl
acrylate, 2-butenyl acrylate, 3-methyl-2-butenyl acry-
late or the iike. Even in this caser however, a suf-
ficient:Ly small compression set cannot be ob-tained without
seconclary vulcani.zation and the price is high, so that it is
no-t broadly used in prac-tice.
Fur-ther, in order to overcome these disadvantages,
i-t has also been studied to improve -the compression se-t by
blending an acrylic rubber wi-th a butadiene-acrylonitril.e co-
polymer. ~-lowever, a sufficiently satisfac-to:ry produc-t has not
been ob-tained because of rnarked reduction in hea-t resistance
and deterioration in ozone resistance~
The present inven-tors have conducted extensive re~
search Eor the purpose of improviny these properties. As a
result, it has been found -that the purpose can be achieved by
blending a conjugated diolefin-unsatura-ted nitri.le-unsaturated
carboxylic ester terpolymer in-to an acrylic rubber.
According to this inven-tion, there is provided a
rubber composition comprising (A) 10-90% by weight of a ter-
polymer consisting of a conjugated diolefin, an ~,~-unsatur-
ated nitrile and an ~,~-unsaturated carboxylic es-ter, (B)
10-90% by weight of a sulfur--vulcanizable acrylic rubber and
(C) 0-40% by weight of a copolymer consisting of a conjugated
diolefin and an ~ unsaturated nitrile having a combined
~,~-unsa-turated nitrile content of 10-60% by weight.
Another aspect of the inven-tion provides a rubber
vulcanizate based on -the above-mentioned rubber composi-tion.
Still another aspect of the invention provides a
method for produci.ng a rubber vulcanizate, -the method com-
prising vulcanizing the above-men-tioned rubber composition
by heating a-t a -temperature of 100 -to 210C, for abou-t 0.5 to
120 minu-tes.
~ ccording -to this invention, -the disadvan-taye of
the conven-tional acrylic rubber tha-t it has a hiyh
- 2a -
1 compression set can be overcome without impairing the
advan-tages of the conventional acrylic rubber, namely,
the heat resistance, oil resistance and ozone
resistance, and there can be obtained an inexpensive
rubber composition good in processability and small in
mold contamination.
As a result of overcoming the above-mentioned
disadvantages, vulcaniæates of the rubber composition
obtained can be used as extrusion-molded products such
as hose and gasket; composite structures such as fiber
cloth-reinforced hose and belt; and other various molded
products such as O-ring and the like.
Though in this invention the method of pre-
paring the terpolymer (A) is not critical, an emulsion
polymerization is preferable. As the conjugated diole-
fin which is one of the copolymerizing components of the
terpolymer (A), 1,3-butadiene, 1,3-isoprene and the like
may be used. As the ~ unsaturated nitrile which is
another copolymeriæing component, there may be used
acrylonitrile, methacrylonitrile and the like. As the
~,~-unsaturated carboxylic ester which is the other
copolymerizing component, there may be used methyl
esters, ethyl esters, n-butyl esters, 2-ethylhexyl
esters and the like of acrylic acid, methacrylic acid
and the like.
The content of conjugated diolefin in the ter-
polymer (A) is preferably in the range of 20-50% by
1 weight~ more preferably 30 - 45 % by weight. If it
exceeds 50~ by weight, the heat resistance canno-t be
suf~iciently exhibited. On the other hand, from the
viewpoint of obtaining good sulfur-vulcanizability and
good resistance to low temperature, the content is pre-
ferably kept at 20% by weight or more. The content of
,~-unsaturated nitrile in the terpolymer (A) is pre-
ferably in the range of 10-40~ by weight, more preerably
20 - 30% by weight. If it exceeds 40% by weight, the
resistance to low temperature becomes unsatisfactory.
On the other hand, from the viewpoint of maintaining the
oil resistance satisfactory, the content is preferably
kept at 10~ by weight or more. The content of ~
unsaturated carboxylic ester in the terpolymer (A) is
preferably 10 - 70% by weight, more preferably 25 - 50
by weight.
The sulur-vulcanizable acrylic rubber (B)
used in this invention is a sulfur-vulcanizable acrylic
copolymer comprising as its main component, at least one
member selected from an alkyl acrylate such as ethyl
acrylate, butyl acrylate or the like; an alkoxy alkyl
acryla-te such as ethoxyethyl acrylate, methoxyethyl
acrylate or the like; an alkylthioalkyl acry]ate such as
methylthioethyl acrylate, ethylthioethyl acrylate or the
like; and a cyanoalkyl acrylate, and also comprising a
small amount of cyclopentadiene, ethylidenenorbornene,
vinylidenenorbornene, 2-butenyl acrylate, 3-methyl-2-
-- 4
1 butenyl acrylate or the li]ce as a crosslinking component, and optionally a small amount of a vinyl compound
such as acrylonitrile, acrylamide or the like. The
sulfur-vulcanizable acrylic rubber (B) is preferably a
copolymer consisting of 90-95% by weight of ethyl acry-
late, butyl acrylate, methoxyethyl acrylate, or a mix-
ture thereof and 5~10% by weight of ethylidenenorbornene.
The copolymer (C) used in this invention is
produced according to the recipe of emulsion polymeriza-
tion. Among the copolymerizing components of the copo-
lymer (C), the conjugated diolefin includes, for
exampler 1,3-butadiene, 1,3 isoprene and the like, and
the ~ unsatura-ted nitrile includes, for example, acry
lonitrile, methacrylonitrile and the like. The content
of a, 3-unsaturated nitrile in the copolymer (~) is pre-
ferably 10-60% by weight, more preferably 20 - 40% by
weight, from the viewpoint of oil resistance and physical
properties of rubber. If it is less than 10~ by weight,
the composition is inferior in oil resistance. If it is
more than 60% by weight, the composition is inferior in
resistance to low temperature.
In this invention, the proportion of the ter-
polymer (A) in the rubber composition is 10-90~ by
weight, preferably 20-80% by weight, and more preferably
30-60% by weight. If the proportion of the terpolymer
(A) is less than 10% by weight, the compression set,
processability and mold-contamination are not improved.
If it exceeds 90~ by weight, the ozone resistance beco-
-- 5
1 mes unsatisfactory. In this invention, the proportion
of the acrylic rubber (B) is 10-90~ by weight, pre~
ferably 20 ~0% by weight. If it i5 less than 10~ by
weight, the ozone resistance becomes unsatisfactory. If
it exceeds 90% by weight, the compression set is not
improved.
In the rubber composition of this invention,
the proportion of the copolymer (C) is 0~40% by weight.
Although a higher proportion oE the copolymer ~C) gives
a less expensive composition having better oil
resistance, the ozone resistance becomes unsatisfactory
if its proportion exceeds 40% by weight. From these
viewpoints, it is more preferable that the proportion of
the copolymer (C) in the composition is ~-35~ by weight.
In this invention, as the means or kneading
polymers and the like, there can be used conventional
mixing means such as roll mill, Banbury mixer and
ex~ruder, as well as other internal mixers capable of
mixing the components without unduly heating them.
Into the rubber composition of this invention
may be incorporated compounding agents which are conven-
tionally used such as filler (carbon black, calcium car--
bonate, hydrocarbon resin, phenolic resin and the like),
vulcanizing agent, vulcanizing assistantr antioxidant,
softening agent and the like.
In general, the vulcanization is effected by
heating the composition at a temperature of 100-210C for
about 0.5-120 minutes by means of steam, a high tem-
-- 6 --
perature fluld or micro-wa~7e.
This invention will be explained below more spe-
cifically referring to Examples. This invention is not
limited to these Examples.
In the Examples, the measurements of physical
properties were conducted in ~he following manner:
I) Physical properties of vulcanizate (tensile
strength, elongation and hardness): They were measured
according to the tensile test and hardness test defined
10 in JIS K 630L.
II) Heat resistance: It was measured according to the
aging test defined in JIS K 6301. It was the Geer oven
heat aging test and the conditions were as follows:
temperature, 130C; time, 120 hours.
15 III) Ozone resistance: It was measured according to
the ozone deterioration test defined in JIS K 6301.
The test conditions were as follows: ozone
concentration, 50 pphm; temperature, 40C; elongation
2096.
IV) Compression set: It was measured according to the
compression set test defined in JIS K 6301.
The test conditions were as follows: tem-
perature, 120C; compression, 25%; time, 70 hours.
V) Oil resistance: It was measured according to the
25 immersion test defined in JIS K 6301.
The test conditions were as follows: oil,
testing oil Wo. 3; temperature, 120C; time, 70 hours.
VI) Processability: A mixturé according to the com-
-- 7 --
l pounding recipe me~tioned in Table l was kneaded with a
Banbury mixer and rolls. If a composition showed a
great winding tendency to the Banbury rotor and a great
stickiness to roll, and accordingly the composition was
inferior in processability, its processability was
expressed "bad". If a composition showed a small ten-
dency of winding and stickiness, its processability was
expressed "good".
VII) Mold-contamination property: A kneaded mixture
with the compounding recipe mentioned in Table l was
press-vulcanized 50 times on one metallic plate and the
state of contamination was observed. When contamination
was found, it was expressed '~contaminated"~
Examples 1-5
Mixtures with the compounding recipes (parts
by weight) mentioned in Table l were kneaded with a
Banbury mixer and open rolls and thereafter press-
vulcanized at 150C for 30 minutes. The results
obtained are shown in Table 2.
Compara-tive Examples 1-5
Mixtures with the compounding recipes shown in
Table 1 were kneaded with a Banbury mixer and open
rolls, and thereafter press-vulcanized at 150C for 30
minutes. The results obtained are shown in Table 2.
-- 8
ar ~
Table 1
\ No. Example _
Compound ~ 1 2 3 4 5 _
ingredients
~ __ _ _ ~ _
Terpolymer (A) (1) 25 50 75 30 20
Acrylic rubber (8) (~)75 50 25 50 50
Copolymer (C) (3) _ _ _ ~ 20 30 _
Zinc o~ide 3 3 3 3 3
Stearic acid 1 1 1 1
MAF Carbon 45 45 45 45 45
Vulcanization
accelerator TT (4) 2 2 2 2 2
Vulcanization
accelerator CBS (5) 2 2 2 2 2
Sulfur 0.5 0 5 0.5 0.50.5 _
(continued)
aS~
Table 1 (Cont'd)
_
Comparative Example
_
_ ._ _ _ 100
725 50 25100
_ 3 3 3 3 3
45 45 45
2 2 2 2 2
_ 0.5 0.5 0.5 0.5 l
Note:
(1) Butadiene-acrylonitrile-butyl acrylate terpolymer
obtained by emulsion polymerization process
(acrylonitrile content 25% by weight, butadiene
content 40~ by weight).
(2) Sulfur-vulcanizable acrylic rubber (butyl acrylate/
ethylidenenorbornene (90/10) copolymer).
(3) JSR N230S manufactured by Japan Synthetic Rubber
Co., Ltd. (butadiene-acrylonitrile copolymer having
a combined acrylonitrile content of 35~ by weight)
(4) Tetramethylthiuram disulEide.
(5) N-cyclohexyl-2~benzothiazolyl sulfenamide.
-- 10 --
Table 2
~ _ _
No.
~~
Item of test ~---_
_ . ~
Physical properties of vulcanizate
Tensile strength (kgf/cm2)
Elongation (~)
Hardness (JIS A)
_' _ _ _ _ _
Heat resistance (130C x 120 hrs)
Percentage of change in tensile s-trength (%)
Percentage o change in elongation (%)
_ _ _ _
Ozone resistance (40C x 50 pphm x 20% elongation)
Crack initiation time (hr)
_ __ _
Compression set (120C x 70 hrs x 25% compression) (%)
~ _
Oil resistance (120 C x 70 hrs, No. 3 oil)
Percentage o change in volume (%)
_ _
Processability
_ _
Mold-con-tamination _
Table 2 (Cont'd)
_ _ __ _
Example
_ _ _ _ . _
l 2 3 4 5
_
llO 136 18~ 152 130
350 320 320 3~0 400
74 74 74 73 72
_ . ____ _ _
+30 +13 -13 ~10 ~3
-35 -46 -50 -56 -57
_ _ _ . . _ _ _
200 200 200 200
100
or more or more or more or more
_ _ _ _ _ _
39 29 39 39
_ __ __
14 16 16 17 18
~_ _ _ _ _
Good Good GoodGood Good
_ _ _ _
None None NoneNone None
_
Table 2 (Cont'd)
Comparative Example
_
1 2 3 4 5
~ _ _ _ - ~ 1
71 97 117 111 102
300 370 490 ~20 390
68 67 66 70
_ _ _ _
+69 +80 +38 +~0 +25
-82 -80 -80 -14 -Sl
_ _ _. _
Breakdown 5 1 200
at chuck or more
_ _ _ __
43 32 86 25
_ _
14 15 17 13 17
_ _ _ .
. Good Good Good Bad Good
_ _ _
None None None Comtami- None
_ nated
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1 It is apparent from the results in Table 2
that when Examples 1-3 are compared with Comparative
Examples 1-4, the heat resistance and ozone resistance
are markedly lower in Comparative Examples 1-3 in which
a mixed system of the acrylic rubber (B) and the copo-
lymer (C) is used, while the heat resistance is not
impaired and the ozone resistance is good in ~xamp]es
1-3 in which the mixed system of this invention con-
sisting of the terpolymer (A) and the acrylic rubber (~)
is used. Further, the compression set is also
remarkably improved as compared with Comparative Example
4 in which a single system of the acrylic rubber (B) is
used. Thus, it i5 understandable that a practically
useful and less expensive rubber composition can be
obtained according to this invention without secondary
vulcanization.
When Examples 4 and 5 are compared with
Comparative Example 2, Examples 4 and 5, in which a ter-
nary mixture system of the terpolymer (A), the acrylic
rubber (B) and the copolymer (C) is used, are good in
ozone resistance withou-t great deterioration of heat
resistance as compared with Comparative Example 2 in
which a system free from the terpolymer (A) is used.
Further, they are remarkably improved in compression set
as compared with Comparative Example 4 in which a single
system of the acrylic rubber (B) is used. Thus, it is
understandabLe that a practically useful and less expen-
-- 14 -
l sive rubber composition can be obtained according to
this invention wil:hout secondary vulcanization.
Example 6
The same procedure as in Example 2 was
repeated, except that the terpolymer (A) was replaced by
a butadiene-acrylonitrile~butyl acrylate terpolymer
having a butadiene content of 30% by weiyht and an acry-
lonitrile content of 20% by weight obtained by emulsion
polymerization process, to obtain the results shown in
Table 3.
Example 7
The same procedure as in Example 4 was
repeated, except that the copolymer (C) was replaced by
JSR N241H manufactured by Japan Synthetic Rubber Co.,
Ltd. (butadiene-acrylonitrile copolymer having a com-
bined acryloni-trile content of 29% by weight), to obtain
the results shown in Table 3.
Example 8
The same procedure as in Example 2 was
repeated, except that the terpolymer (A) was replaced by
a butadiene-acrylonitrile-ethyl acrylate terpolymer
having an acrylonitrile content of 25% by weight and a
butadiene content of 40% by weight obtained by emulsion
polymerization process, to obtain the results shown in
Table 3.
- 15 -
1 Example 9
The same procedure as in Exarnple 2 was
repeated~ except that the terpolymer (A) was replaced by
a butadiene-acrylonitrile-methoxyethyl acrylate ter-
polymer having an acrylonitrile content of 25% by weightand a butadiene content of 40% by weight obtained by
emulsion polymerization process, to obtain the results
shown in Table 3.
Example lO
The same procedure as in Example 2 was
repeated, except that the acrylic rubber (B) was
replaced by a butyl acrylate/methoxyethyl acrylate/ethyl
acrylate/ethylidenenorbornene (40/25/25/lO by weight)
rubber, to obtain the results shown in Table 3.
- 16 -
Table 3
_
~--______ Example No.
Item of test ~ _
_
Physical properties of vulcanizate
Tensile strength (kgf/cm2)
Elongation (%)
Hardness (JIS A)
__ _
Heat resistance (130 C x 120 hrs)
Percentage oE change in tensile strength (%)
Percentage of change in elongation (%)
_
Ozone resistance (40C x 50 pphm x 20% elongation)
Crack initiation time (hr)
_ _
Compression set (120C x 70 hrs x 25% compression) (%)
. . . _
Oil resistance (120 C x 70 hrs, No. 3 oil)
Percentage of change in volume (%)
_ __ _ _ _
Processability _
Mold-contamination
- 17 -
Table 3 (Cont'd)
____ .___
__ ___
122 155 138 13S 140
340 370 310 310 320
74 73 7~ 74 7
_
+19 +11 +12 +18 +15
-40 -57 -45 -50 48
_ _
200 200 ~00 200 200
or more or more or more or more or more
_ _ _ ~ _ _ ,
42 39 ~0 40 40
_
17 13 14 14
_ . i
Good Good Good Good Good
_ _ _._____ ;
None NoD~ None None None
-
- 18 -
