CA2039292A1

CA2039292A1 - Multilayer rubber article

Info

Publication number: CA2039292A1
Application number: CA002039292A
Authority: CA
Inventors: Masayoshi Ichikawa; Tomoaki Okita
Original assignee: Toyoda Gosei Co Ltd
Current assignee: Toyoda Gosei Co Ltd
Priority date: 1990-04-04
Filing date: 1991-03-28
Publication date: 1991-10-05
Also published as: DE4110746C2; AU625146B1; JPH03288084A; JPH0830544B2; DE4110746A1

Abstract

ABSTRACT OF THE DISCLOSURE

A multilayer rubber article, which can be tubular in shape, comprising at least one acrylic rubber layer formed of an acrylic rubber composition and an epichloro-hydrin 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 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. The acrylic rubber layer has improved low-temperature resistance both in the early stages and after a substantial period of time.

Description

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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 , .

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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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2~3~2~ 2 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 2 ~
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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,, : . ,, ~ , 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 .. . . .- . .

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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 .

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 i~
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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 _ g _ . -' .' ,.: :- . . ' ' ; , ,, ., . . ~. . .

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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 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 , ., - .

Claims

1. A multilayer rubber article comprising:
(a) at least one acrylic rubber layer formed of an acrylic rubber composition, and (b) an epichlorohydrin rubber layer formed of an epichlorohydrin rubber composition in direct contact with the acrylic rubber layer, wherein each of the two rubber compositions contains at least one ester type plasticizer, and 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 acid having three or more hydroxyl groups.

2. The multilayer rubber article of Claim 1, wherein the acrylic rubber composition comprises at least one of a copolymer of an acrylic acid alkyl ester, a copolymer of 2-chloroethyl vinyl ether, a copolymer of an acrylic acid alkyl ester, and a copolymer of acrylonitrile.

3. The multilayer rubber article of Claim 1, wherein the plasticizer of 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.

4. The multilayer rubber article of Claim 3, wherein the ether ester type plasticizer is a polymerizable plasticizer.

5. The multilayer rubber article of Claim 1, wherein the ester of an aromatic carboxylic acid having three or more hydroxyl groups is an aromatic carboxylic acid having three or more carboxyl groups substituted on an aromatic ring.

6. The aromatic carboxylic acid of Claim 5, wherein at least one of the carboxyl groups is esterified with a long-chain aliphatic alcohol.

7. The aromatic carboxylic acid of Claim 6, wherein the number of carbon atoms of the alcohol is 4 to 12.

8. The multilayer rubber article of Claim 5, wherein the aromatic carboxylic acid is a trimellitic acid ester type plasticizer or a pyromellitic acid ester type plasticizer.

9. The multilayer rubber article of Claim 1, wherein the epichlorohydrin rubber composition comprises at least one of a homopolymer of epichlorohydrin, a copolymer of epichlorohydrin or a copolymer of ethylene oxide.

10. The multilayer article of Claim 1, wherein the plasticizer is added to the acrylic rubber composi-tion in a proportion of 25 to 45 parts per 100 parts of starting rubber.

11. The multilayer article of Claim 1, wherein the plasticizer is added to the epichlorohydrin rubber composition in a proportion of 13 to 28 parts per 100 parts of starting rubber.

12. The multilayer article of Claim 1, wherein the thickness ratio of the acrylic rubber layer t1 to the epichlorohydrin rubber layer t0 is t1/t0 = 2/1 to 1/5, wherein t1 is the thickness of the acrylic rubber layer and t0 is the thickness of the epichlorohydrin rubber layer.

13. The multilayer article of Claim 12, wherein the thickness ratio of the acrylic rubber layer t1 to the epichlorohydrin rubber layer to is t1/t0 = 1/2 to 1/3, wherein t1 is the thickness of the acrylic rubber layer and t0 is the thickness of the epichlorohydrin rubber layer.

14. The multilayer article of Claim 1, wherein the article is tubular in form.

15. The multilayer article of Claim 14, wherein the tubular article is a hose.

16. The hose of Claim 15, wherein the acrylic rubber layer is formed as inside layer.

17. The hose of Claim 15, wherein the epichlorohydrin rubber layer is formed as inside layer or is sandwiched between acrylic rubber layers.