Note: Descriptions are shown in the official language in which they were submitted.
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1 BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a multilayer
rubber article, for example, a tubular rubber article,
comprising at least one acrylic rubber layer and an
epichlorohydrin rubber layer, in which the low-temperature
resistance of the acrylic rubber layer is not
substantially reduced after an extended period of time.
BACKGROUND INFORMATION
There has been proposed, for example, in
Japanese Patent Application Kokai (Laid-Open) No.
62-51439, a multiiayer rubber hose comprising (1) an
inner tubular layer 1 formed of an acrylic rubber
composition of a polymer blend of an acrylic rubber and
a vinylidene fluoride resin having resistance to
fractionated gasoline, (2) an outer tubular layer 2 formed
of an epichlorohydrin rubber composition having resistance
to gas permeation and ozone resistance, and (3) an
intermediate layer 5 and a yarn layer 3, placed between
the inner tubular layer 1 and the outer tubular layer 2,
the intermediate layer 5 being formed of a rubber
composition of an acrylic rubber adhering to the inner
tubular layer 1 and the outer tubular layer 2, and
having weather resistance, etc. (see Figure 1).
An ester type plasticizer is included in each
-- 1 --
, .
2 ~ 2.
1 of the above rubber compositions, primarily to enhance the
processability and low-temperature resistance of the
rubber compositions.
Epichlorohydrin rubbers are generally considered
to have excellent low-temperature resistance. Therefore,
there are no particular limitations on the ester type
plasticizers included in the epichlorohydrin rubber
composition. For example, there can be used phthalic acid
ester type plasticizers, such as di-2-ethylhexyl
phthalate, which are general-purpose plasticizers.
Moreover, the amount of the plasticizer blended in the
epichlorohydrin rubber composition may be small.
Acrylic rubbers, on the other hand, generally
do not have satisfactory low-temperature resistance.
Aliphatic dibasic acid ester type plasticizers, such as
dioctyl sebacate (DOS) and dioctyl adipate (DOA), are
usually included in this composition. These plasticizers
are generally considered to have excellent low-temperature
resistance. However, a relatively large amount of these
plasticizers must be included in the acrylic rubber
composition.
OBJECT OF THE INVENTION
It may be seen from the above, that according
to the prior art, a relatively large amount of aliphatic
dibasic acid ester type plasticizer must be added to the
acrylic acid composition. However, it is difficult to
blend large amounts of these plasticizers with an acrylic
rubber; thus, it is difficult to obtain sufficient
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1 low-temperature resistance [generally, a brittleness
temperature (Tb) of -36C or higher, as measured by the
impact brittleness test (JIS K7301)]. Furthermore, it is
known that when an epichlorohydrin rubber layer is
formed in direct contact with an acrylic rubber layer,
as described above, the low-temperature resistance of
the acrylic rubber layer deteriorates over time. Thus,
there is an unmet need for an acrylic rubber layer having
high low-temperature resistance, suitable for inclusion
in a multilayer rubber article, which may be in direct
contact with an epichlorohydrin rubber layer without a
substantial decrease in its low-temperature resistance
over time.
The present invention fills this need, as it
provides a multilayer rubber article, for example a
tubular article, in which the low-temperature resistance
of the acrylic rubber layer substantially does not
deteriorate over an extensive period of time.
SUMMARY OF THE INVENTlON
In order to solve the problems described above,
the present inventors have performed extensive experiments
to improve the low-temperature resistance of the acrylic
rubber layer in a multilayer rubber article by using
plasticizers and have devoted themselves to development
of these plasticizers. As a result of these efforts, it
has been discovered that the initial low-temperature
resistance and the low-temperature resistance of the
-- 3 --
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1 acrylic rubber layer after an extended period of time
improves with the inclusion of one or more specific
plasticizers in the acrylic rubber composition.
Thus, in accordance with the present invention,
there is disclosed:
a multilayer rubber article comprising: (a) at
least one acrylic rubber layer formed of an acrylic
rubber composition, (b) an epichlorohydrin rubber layer
formed of an epichlorohydrin rubber composiiton which
can be in direct contact with the acrylic rubber layer,
wherein each of the two rubber compositions contains at
least one ester type plasticizer, and at least the ester
type plasticizer in the acrylic rubber layer is selected
from the group consisting of ether ester type
plasticizers and plasticizers of esters of aromatic
carboxylic acids having three or more hydroxyl groups.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view showing an example
of a fuel hose (a multilayer rubber hose) to which the
present invention may be applied. In this figure,
1 designates the inner tubular layer,
2 designates an intermediate layer (an acrylic
rubber layer), and
3 designates the outer tubular layer (an epichloro-
hydrin rubber layer).
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1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The multilayer rubber article of the present
invention comprises (a) at least one acrylic rubber layer
formed of an acrylic rubber composition, and (2) an
epichlorohydrin rubber layer formed of an epichlorohydrin
rubber composition which can be in direct contact with
the acrylic rubber layer, wherein each of the two rubber
compositions contains at least one ester type plasticizer.
The rubber article of the present invention
I0 can be tubular in shape, for example, a hose. In the
case of the multilayer rubber article being used as rubber
hose, for example, a fuel hose or the like, the acrylic
rubber layer is usually formed as the inside layer (see
Figure 1). However, in the case of the multilayer rubber
hose being used in a fuel pump or the like, the
epichlorohydrin rubber layer may be formed as the inside
layer or may be sandwiched between acrylic rubber layers.
The acrylic rubber composition can include, for
example, copolymers of an acrylic acid alkyl ester and
2-chloroethyl vinyl ether (ACM's), and copolymers of an
acrylic acid alkyl ester and acrylonitrile (ANM's).
ACM's are preferred from the viewpoint of low-temperature
resistance.
As a specific example, there can be used the
acrylic rubber exemplified in the above publication
(Japanese Patent Unexamined Publication No. 62-51439),
i.e., an acrylic rubber including (a) an acrylic acid
alkyl ester and/or an acrylic acid alkoxy-substituted
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1 alkyl ester in a proportion of 30 to 99% by weight, (b)
a crosslinkable monomer in a proportion of 1 to 10% by
weight, and (c) another ethylenic compound copolymerizable
with the above monomers (a) and (b), in a proportion
of 0 to 70~ by weight.
The generally used epichlorohydrin rubbers,
for example, epichlorohydrin homopolymers (CO's), and
copolymers of epichlorohydrin and ethylene oxide (ECO's)
can be used as the epichlorohydrin rubber.
To prepare the materials for the rubber
article, the acrylic rubber and the epichlorohydrin rubber
each may be blended with auxiliary materials such as
reinforcing agents (e.g., carbon black), plasticizers,
processing aids, vulcanization accelerators, vulcanizing
agents, antioxidants, etc., then kneaded with a roll mill,
Banbury mixer, intermixer ox the like.
The individual materials used in the rubber
article may then be extruded into a multilayer rubber
hose using a plurality of extruders or a multi-color
extruder.
As noted abGve, at least the ester type
plasticizer in the acrylic rubber composition is selected
from the group consisting of ether ester type plasticizers
and plasticizers of esters of aromatic carboxylic acids
having three or more hydroxyl groups.
The ether ester type plasticizers are
polymerizable plasticizers. A specific example thereof is
a plasticizer commercially available by the name of
-- 6 --
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l ADEKA CIZER RSl07, available from Asahi Denka Co., Ltd.
The esters of aromatic carboxylic acids having
three or more hydroxyl groups are preferably aromatic
carboxylic acids having three or more carboxyl groups
substituted on the aromatic ring (for example, a benzene
ring or a naphthalene ring) in which some, and preferably
all, of the carboxyl groups are esterified with a
long-chain aliphatic alcohol (preferably a straight-chain
aliphatic alcohol).
I0 In general, the larger the number of carbon
atoms of the alcohol, the higher the low-temperature
resistance of the plasticizer, but the lower the
compatibility of the plasticizer with a rubber polymer.
Therefore, the number of carbon atoms of the alcohol is
preferably 4 to 12. The alkyl group is preferably linear
from the viewpoint of low-temperature resistance.
Specific examples of aromatic carboxylic acids
which can be used include trimellitic acid ester type
plasticizers and pyromellitic acid ester type plasticizers.
Specific examples of trimellitic acid ester
type plasticizers include, for example, trioctyl
trimellitate, trinonyl trimellitate, tridecyl trimellitate,
triisodecyl trimellitate, undecyl trimellitate, etc.
Specific examples of pyromellitic acid ester
type plasticizers include, for example, tetraoctyl
pyromellitate, tetranonyl pyromellitate, tetradecyl
pyromellitate, tridecyl pyromellitate, tetraisodecyl
pyromellitate, tetraundecyl pyromellitate, triundecyl
-- 7 --
.
1 pyromellitate, etc.
The proportion of the above plasticizers
incorporated into the acrylic rubber composition to form
the acrylic rubber layer is 25 to 45 parts, preferably
30 to 40 parts, per 100 parts of starting rubber (polymer).
When the proportion of plasticizer is less than 25 parts,
the acrylic rubber layer has insufficient low-temperature
resistance. When the proportion of plasticizer exceeds
45 parts, the vulcanizability of the rubber itself, the
interlaminar bonding, etc., is impaired.
The low-temperature resistant plasticizers
exemplified above may also be included in the rubber
composition forming the epichlorohydrin rubber layer.
Since epichlorohydrin rubbers themselves have high
low-iemperature resistance, there may also be included
other plasticizers such as phthalic acid ester type
plasticizers which have good compatibility with the rubber.
The proportion of the plasticizers included in
the rubber composition of the epichlorohydrin rubber layer
is 13 to 28 parts, preferably 15 to 25 parts, per 100
parts of starting rubber (polymer). When the proportion
of plasticizer is less than 13 parts, the transfer of
the plasticizers from the acrylic rubber layer may
accelerate, resulting in deterioration of the low-
temperature resistance of the acrylic rubber layer with thelapse of time. When the proportion of plasticizer exceeds
28 parts, the plasticizer bleeds, thereby exerting an
undesirable influence on the vulcanizability of the
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1 rubber itself, the interlaminar bonding, etc.
With regard to the transfer of the plasticizers
from the acrylic rubber layer to the epichlorohydrin
rubber layer, the thickness ratio of the acrylic rubber
layer to the epichlorohydrin rubber layer to is preferably
as follows: tl/to = 2/1 to 1/5 (more preferably 1/2 to
1/3) wherein tl is the thickness of the acrylic rubber
layer and to is the thickness of the epichlorohydrin
rubber layer. When the thickness of the acrylic rubber
layer is higher than the above range, the thickness of
the epichlorohydrin rubber layer decreases to such an
extent that the effect of the epichlorohydrin rubber
layer is difficult to obtain. When the acrylic rubber
layer is too thin, the transfer of the plasticizers to the
epichlorohydrin rubber layer is disadvantageously
accelerated.
As described above, the multilayer rubber
article of the present invention comprises (a) at least
one acrylic rubber layer formed of an acrylic rubber
composition, and (2) an epichlorohydrin rubber layer formed
of an epichlorohydrin rubber composition which can be in
direct contact with the acrylic rubber layer, wherein ^
each of the two rubber compositions contains at least
one ester type plasticizer, and at least the ester type
plasticizer in the ac.rylic rubber layer includes one or
more members selected from the group consisting of
ether ester type plasticizers and plasticizers of esters
of aromatic carboxylic acids having three or more
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1 hydroxyl groups. As described in the examples provided
below, by virtue of such a constitution, the acrylic
rubber layer formed of the acrylic rubber composition
has an improved low-temperature resistance both in the
early stages and after an extended period of time.
EXAMPLES
Tests were carried out to confirm the improved
properties of the present invention.
For each of the acrylic rubber compositions
and epichlorohydrin rubber compositions listed in Tables
1 and 2 below, dry physical property tests (Hs, Tb, EB),
a compression set test (Cs) and a low-temperature impact
brittleness test (Tb) were carried out in accordance with
the procedure of JIS-K-6301. The physical properties
identified by the above abbreviations are listed below:
Hs (A) : Hardness [measured by a spring type
hardness tester (JIS A)],
TB : tensile strength (kgf/cm ~,
EB : elongation at break (~),
CS : compression set (%), and
Tb : brittleness temperature (C).
` The test pieces were vulcanized at a temperature
of 150C for 60 minutes.
The results of the physical property tests are
~` 25 shown in Tables 1 and 2 below.
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Table 2
.
Epichlorohydrin rubber A B C
compositlon
ECO 100 100 100
MAF .
Carbon black 55 55 55
Ether ester type
Recipe plasticizer 15 20 25
Processing aid 2 2
Antioxidant 1 1
MgO 3 3 3
CaCO3 5 5 5
Vulcanizing agent 1.8 1.8 ~ 1.8
Dry physical
properties
HS(JIS-A) 63 63 60
TB(kgf/cm2) 108 106 98
TRe.-t (MPa) (10.5)(10.4) (g.6)
sults EB(%) 400 430 450
Compression set CS
120C x 22 ~r 25 28 36
low-temperatuxe
no-failure
temperature -38 -44 -46
~,
1 A laminate of ECO layer/ACM layer/ECO layer
~thickness of each layer: 2mm) was formed using each
combination of the compounded rubbers listed in Table 3
: below. The compounded rubbers were vulcanized and molded
(conditions : 150C x 60 minutes) to form test pieces.
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1 The test pieces were allowed to stand in a 40C
atmosphere for 5 days, following which the acrylic rubber
layer of each test piece was sliced. These slices were
then subjected to the above described low-temperature
impact brittleness test.
The test results are shown in Table 3, where
it may be seen that the examples of the present invention
generally have excellent low-temperature .resistance.
Table 3
ECO layer Low-
Test ACM layer (Tb) ~the amount temperature-
No. of resistance of
plasticizer ACM layer
blended) Tb (C)
1 Example 1 (-38C) A (15 parts) -36
2 Example 1 (-38C) B (20 parts) -38 .
3 Example 1 (-38C) C (25 parts) -38
4 Example 2 (-44C) A (15 parts) -38
Example 2 (-44C) B (20 parts) -42
fi Example 2 (-44C) C (25 parts) -42
7 Example 3 (-46C) A (15 parts) -40
8 Example 3 (-46C) B (20 parts) -44
__ __ Example 3 (-46C) C (25 parts) -44
Example 4 (-42C) B (20 parts) -40
11 Example 5 (-38C) B (20 parts) -36
12 Comparative
Example 4 (-33C) B (20 parts) -30
~` 13 Comparative
Example ~ (-33C) B (20 parts) -30
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