JP2005054058A - Rubber composition for radiator hose and radiator hose - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition suitable for automotive radiator hoses continually subjected to high-frequency microvibrations associated with the high-speed revolution of an engine and used in a condition of allowing microelectric current to flow therethrough. <P>SOLUTION: The rubber composition comprises 100 pts.wt. of an ethylene-propylene-nonconjugated diene copolymer rubber and 50-200 pts.wt. of a reinforcing agent. This rubber composition is improved in energization-associated flex resistance and meets the relationship formula (1): R≥3×10<SP>6</SP>×A<SP>-0.5957</SP>( wherein, R is volume resistivity(Ω×cm); and A is flex frequency resulting in crack propagation ). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rubber composition for a radiator hose, and more particularly to a rubber composition for a radiator hose containing an ethylene-α-olefin copolymer rubber.

  Conventionally, it has been known that a deterioration phenomenon called an electrolytic corrosion crack occurs in a radiator hose for an automobile mainly composed of ethylene-propylene copolymer rubber (see Non-Patent Document 1). In addition, it is considered that the cause of such electrolytic corrosion cracks is an electrochemical reaction caused by a minute current flowing inside the vehicle.

  As a method of preventing such electrolytic corrosion cracks generated in a radiator hose for automobiles, for example, a method of using an ethylene-propylene copolymer composition in which a zinc compound is not blended in a rubber layer on a surface in contact with a liquid ( Patent Document 1) has been reported.

R. Keller, “Automotive Polymers and Design”, USA, (Publisher), June 1991, Volume 16 JP-A-10-180941 (paragraph 0016, paragraph 0044, etc.)

  By the way, a radiator hose of an automobile is usually used in a harsh environment that constantly receives high-frequency fine vibrations accompanying high-speed rotation of an engine, and bendability corresponding to such fine vibrations is required. In particular, when high-frequency micro vibrations are applied for a long time with current flowing through the radiator hose, the occurrence and growth of cracks inside the hose are promoted, and it has been confirmed that the cooling water leaks due to bursting in a short time. Yes.

  From this point of view, when examining the method reported in the above-mentioned patent document, the method of Patent Document 1 does not contain a zinc compound that is considered to act as a vulcanization accelerator in the sulfur vulcanization system. The mechanical strength of the rubber vulcanizate decreases. For this reason, when a high frequency micro vibration is received for a long time, the bending resistance of the radiator hose tends to be lowered, and there remains a problem that generation and growth of cracks are not suppressed.

The present invention has been made to solve such problems. That is, an object of the present invention is to provide a rubber composition for a radiator hose in which the occurrence of electrolytic corrosion cracks is suppressed.
Another object of the present invention is to provide a radiator hose.

  For this purpose, a rubber composition for a radiator hose to which the present invention is applied is a rubber composition containing an ethylene-α-olefin copolymer rubber and a reinforcing agent, The relationship between the volume specific resistance value (R) and the number of flexing times (A) leading to crack growth is expressed by the following equation (1).

(In the formula (1), R is a volume specific resistance value (unit: Ω · cm), and A is the number of flexures that lead to crack propagation.)

In the rubber composition for a radiator hose to which the present invention is applied, the volume resistivity value (R) in the formula (1) is less than 10 ⁴ Ω · cm. A radiator hose can be obtained, and the versatility of the quality design becomes possible by increasing the compounding selectivity as a rubber composition.

  In the rubber composition for a radiator hose to which the present invention is applied, the content of the ethylene-α-olefin copolymer rubber is 100 parts by weight, and the reinforcing agent is used for the ethylene-α-olefin copolymer rubber. If the content is 50 to 200 parts by weight, it is possible to improve the balance between the bending resistance (electric current bending property) and the volume specific resistance value in a state where a minute current of the radiator hose is flowing. .

  Further, in the rubber composition for a radiator hose to which the present invention is applied, the reinforcing agent contains (a) 60 to 95% by weight of carbon black and (b) 5 to 40% by weight of silica (provided that (a) + (B) is 100% by weight.), The electrification flexibility is further improved, the generation of cracks in the radiator hose is reduced, and the growth of the generated cracks is further suppressed.

  Next, the present invention has an inner layer composed of a rubber material containing an ethylene-α-olefin copolymer rubber and a reinforcing agent, and reaches the volume specific resistance (R) and crack growth of the rubber material. The relationship with the number of bending times (A) is grasped as a radiator hose characterized by the following expression (1).

(In Formula (1), R is a volume specific resistance value (unit: Ω · cm), and A is the number of flexures to reach the crack progress in the flex test.)

  Further, in the radiator hose to which the present invention is applied, if an outer layer and / or an intermediate layer made of weather resistant rubber is further provided, a radiator hose excellent in weather resistance can be obtained by suppressing the occurrence of electrolytic corrosion cracks. be able to.

  The volume specific resistance value (unit: Ω · cm) in the rubber composition for a radiator hose to which the present invention is applied is JIS K 6911 (general test method for thermosetting plastics) and JIS K 7194 (conducting plastics). It is obtained by a measuring method based on a resistivity test method by a four-probe method. In addition, the number of flexures that lead to crack growth in the flexure test is obtained from the result of a dematcher flexure test performed in accordance with JIS K 6260 (demature flex crack test method for vulcanized rubber and thermoplastic rubber).

  ADVANTAGE OF THE INVENTION According to this invention, the radiator hose with which generation | occurrence | production of the electrolytic corrosion crack was suppressed is obtained.

Hereinafter, the best mode for carrying out the present invention will be described in detail (hereinafter referred to as an embodiment of the invention).
In the rubber composition for a radiator hose to which the embodiment of the present invention is applied, the volume specific resistance value (R) of the rubber composition and the number of bending times (A) to reach the crack propagation are expressed by the formula (1). When the above relationship is satisfied, the electric current bending flexibility of the radiator hose in which a minute current flows inside the vehicle is improved in a well-balanced manner, and as a result, the occurrence of electrolytic corrosion cracks inside the hose is suppressed.

  Conventionally, a method of causing an electrochemical reaction by increasing the volume resistivity value of a rubber material is considered to be effective in suppressing the occurrence of electrolytic corrosion cracks inside a radiator hose in a state where a minute current is flowing. . However, in order to suppress the occurrence of electrolytic corrosion cracks inside the hose in a state in which a minute electric current is constantly flowing and a minute current is constantly flowing, like a radiator hose of an automobile, It is not sufficient to increase the volume resistivity of the rubber material. For these reasons, by combining the method of increasing the volume resistivity of the rubber material and the method of improving the flex crack resistance of the rubber material in a balanced manner, the occurrence of electrolytic corrosion cracks inside the radiator hose can be suppressed. I found.

  FIG. 1 is a diagram for explaining the relationship between the volume specific resistance value of a rubber composition for a radiator hose to which the present embodiment is applied and the number of bendings that lead to crack propagation. In FIG. 1, the horizontal axis (A) is the number of flexures that lead to crack growth, and the vertical axis (R) is the volume resistivity (unit: Ω · cm). The straight line graph in FIG. 1 is obtained by the following equation (1a) showing the relationship between the number of flexures (A) to reach the crack propagation and the volume resistivity (R). Note that (actual 1o, actual 2o, actual 3o) and (ratio 1) in FIG. 1 will be described later.

(In the formula (1a), R is a volume specific resistance value (unit: Ω · cm), and A is the number of flexion times to reach the crack propagation in the flex test.)

  As shown in FIG. 1, the rubber composition for a radiator hose to which the present embodiment is applied has a volume specific resistance value of the rubber composition and a bending leading to crack propagation in a region above the straight line graph in FIG. By adjusting the number of times in a well-balanced manner, the occurrence of electrolytic corrosion cracks inside the hose is suppressed.

In the rubber composition for a radiator hose to which the present embodiment is applied, the volume specific resistance value is preferably less than 10 ⁴ Ω · cm. That is, the relationship between the volume specific resistance value (R) of the rubber material and the number of flexing times (A) leading to the crack progress satisfies the relationship represented by the following formula (2), thereby providing excellent flex resistance. A radiator hose can be obtained, and the versatility of the quality design becomes possible by increasing the compounding selectivity as a rubber composition.

(In Formula (2), R is a volume specific resistance value (unit: Ω · cm), and A is the number of flexures that lead to crack propagation in the flexure test.)

Next, each component of the rubber composition for radiator hoses to which this embodiment is applied will be described.
(Description of ethylene-α-olefin copolymer rubber)
The ethylene-α-olefin copolymer rubber used in the rubber composition for a radiator hose to which the present embodiment is applied is a copolymer of ethylene and α-olefin or these and a non-conjugated diene. It is a saturated copolymer rubber. Typical examples are ethylene-propylene binary copolymer rubber, ethylene-propylene-butene terpolymer rubber, ethylene-1-butene binary copolymer rubber, or ethylene-propylene-nonconjugated diene terpolymer. An ethylene-propylene-1-butene-nonconjugated diene copolymer rubber, an ethylene-1-butene-nonconjugated diene multipolymer rubber, and the like, and ethylene and an α-olefin having 3 to 14 carbon atoms. A low crystalline or amorphous elastomer or a mixture thereof having a crystallinity of 20% or less, preferably 10% or less as a main component. Among these, ethylene-propylene-nonconjugated diene terpolymer rubber (EPDM) is preferable.

  Here, as the non-conjugated diene, dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylene norbornene, 5-ethylidene-2-norbornene and the like are used, and among these, dicyclopentadiene or 5-ethylidene- A copolymer having 2-norbornene as the third component is preferred. The Mooney viscosity [ML1 + 4 (100 ° C.)] of the ethylene-α-olefin-nonconjugated diene copolymer rubber is usually 10 to 180, preferably 40 to 140, and the iodine value is preferably 20 or less. is there.

  Specific examples of these ethylene-α-olefin-nonconjugated diene copolymer rubbers include ethylene units / α-olefin units of 50/50 to 90/10, preferably 60/40 to 84/16 (molar ratio). The (ethylene + α-olefin) unit / non-conjugated diene unit (in the case of a ternary or multi-component copolymer) is usually 98/2 to 90/10, preferably 97/3 to 94/6 (molar ratio). ).

  The ethylene-propylene copolymer rubber usually includes a copolymer of ethylene and propylene, and a copolymer of ethylene, propylene and non-conjugated dienes. The ethylene unit content in the ethylene-propylene copolymer rubber is 40 to 80% by weight, preferably 60 to 80% by weight.

  Specific examples of non-conjugated dienes copolymerized with ethylene and propylene include linear non-conjugated such as 1,4-hexadiene, 5-methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, etc. Diene: Cyclic non-conjugated diene such as cyclooctadiene, dicyclopentadiene, dicyclooctadiene; complex such as methylene norbornene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, 5-methylene-2-norbornene Examples thereof include cyclic non-conjugated dienes.

  The ethylene-propylene copolymer rubber may be copolymerized with an α-olefin having 3 to 20 carbon atoms, if necessary. Specific examples of such α-olefins include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, Examples include 1-undecene, 1-dodecene, 9-methyl-1-decene, 11-methyl-1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene and the like.

(Description of reinforcing agent)
The rubber composition for a radiator hose to which the present embodiment is applied usually contains a reinforcing agent. The reinforcing agent is not particularly limited as long as it is known as an ordinary rubber reinforcing agent. For example, carbon black such as furnace black, channel black, and thermal black; insulating metal oxides such as tin oxide, zinc oxide, aluminum oxide, molybdenum oxide, magnesium oxide, calcium oxide, silica, zinc oxide, lead oxide; Metal hydroxides such as magnesium, aluminum hydroxide, calcium hydroxide, zinc hydroxide, lead hydroxide; carbonates such as magnesium carbonate, aluminum carbonate, calcium carbonate, barium carbonate; magnesium silicate, calcium silicate, sodium silicate, silicic acid Silicates such as aluminum; sulfates such as aluminum sulfate, calcium sulfate, and barium sulfate; metal powders such as iron powder; conductive fibers such as carbon fiber; and diatomaceous earth, asbestos, lithopone (zinc sulfide / barium sulfate), Graphite, carbon fluoride, fluorine Calcium hydride, wollastonite, glass powder and the like. Among these, carbon black and silica are preferable. These reinforcing agents can be used alone or in combination of two or more.

  In addition, when carbon black and silica are used together as a reinforcing agent, the bending resistance of the rubber material can be improved. When carbon black and silica are used in combination, usually (a) carbon black 60 to 95% by weight, preferably 70 to 90% by weight, and (b) silica 5 to 40% by weight, 10 to 30% by weight (however, (A) + (b) is 100% by weight.).

  The compounding amount of the reinforcing agent in the rubber composition for a radiator hose to which the present embodiment is applied is 50 to 200 parts by weight, preferably 80 to 100 parts by weight with respect to 100 parts by weight of the ethylene-α-olefin copolymer rubber. 150 parts by weight. If the compounding amount of the reinforcing agent is excessively large, processability may be reduced. Moreover, when there are too few compounding quantities of a reinforcing agent, there exists a possibility that mechanical strength may fall.

(Description of silane coupling agent)
In addition, when silica is used as a reinforcing article, the compression set resistance as a rubber material for hoses can be improved by blending a silane coupling agent. Examples of the silane coupling agent include halogen-based silane coupling agents such as vinyltrichlorosilane and γ-chloropropyltrimethoxysilane; vinyltris (β-methoxyethoxy) silane, vinyltrimethoxysilane, vinyltriethoxysilane, γ- Alkoxy silane coupling agents such as (methacryloyloxypropyl) trimethoxysilane; β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidyloxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxy Epoxy silane coupling agents such as silane; N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysila And amino-based silane coupling agents such as N-phenyl-γ-aminopropyltrimethoxysilane; and mercapto-based silane coupling agents such as γ-mercaptopropyltrimethoxysilane. The compounding quantity of a silane coupling agent is 0.1-10 weight part with respect to 100 weight part of ethylene-alpha-olefin type copolymer rubber, Preferably it is 0.5-5 weight part. If the amount of the silane coupling agent is excessively large, scorch may occur. Moreover, when there are too few compounding quantities of a silane coupling agent, there exists a possibility that mechanical strength may fall.

(Description of vulcanizing agent)
A rubber composition for a vulcanizable hose is prepared by blending a vulcanizing agent with a rubber composition for a radiator hose to which the present embodiment is applied. The vulcanizing agent is not particularly limited, and a vulcanizing agent that is frequently used in rubber applications can be used. Examples of such a vulcanizing agent include a peroxide vulcanizing agent and a sulfur vulcanizing agent. Among these, a peroxide vulcanizing agent is preferable. Examples of the peroxide vulcanizing agent include 1,1-bis (t-butylperoxy) -3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5 dihydroxyperoxide, and di-t. -Butyl peroxide, t-butyl cumyl peroxide, dicumyl peroxide, α, α-bis (t-butylperoxy) -p-diisopropylbenzene, 2,5-dimethyl-2,5-di (t-butyl) Peroxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane-3, benzoyl peroxide, t-butylperoxybenzene, 2,5-dimethyl-2,5-di ( And organic peroxide compounds such as benzoylperoxy) hexane, t-butylperoxymaleic acid, and t-butylperoxyisopropylcarbonate.

  When these peroxide vulcanizing agents are used, as vulcanization aids or co-curing agents, triallyl cyanurate, triallyl isocyanurate, triacryl formal, triallyl trimellitate, N, N ′ A remarkable effect is observed by using a compound such as -m-phenylenebismaleimide, diprovalgyl terephthalate, diallyl phthalate, tetraallyl terephthalamide, polydimethylvinylsiloxane, polymethylphenylvinylsiloxane and the like.

  Examples of the sulfur vulcanizing agent include sulfur donating compounds such as sulfur or thiuram compounds and morpholine compounds. Sulfur vulcanizing agents are used together with known vulcanization aids such as zinc white and stearic acid, and various known vulcanization accelerators such as thiuram, guanidine, sulfenamide, thiazole, and dithiocarbamic acid. used.

  The amounts of these vulcanizing agents and vulcanizing aids are not particularly limited, and are 0.1 to 10 parts by weight and 0.5 to 0.5 parts by weight, respectively, with respect to 100 parts by weight of the ethylene-α-olefin copolymer rubber. 20 parts by weight, preferably 0.2 to 8 parts by weight and 0.7 to 10 parts by weight, respectively. The rubber composition for the radiator hose to which the present embodiment is applied includes a filler, a softening agent, an anti-aging agent, an antioxidant, a light stabilizer, a scorch inhibitor, and a vulcanization retarder as necessary. Various additives such as processing aids, activators, pressure-sensitive adhesives, flame retardants, and colorants may be blended.

(Description of manufacturing method of rubber composition for hose)
The method for producing a rubber composition for a radiator hose to which the present embodiment is applied is not particularly limited, and usually an ethylene-α-olefin copolymer rubber, a reinforcing agent, and other blends added as necessary. A method of mixing and kneading the product with a kneading machine such as a roll, a banbury, a kneader, an internal mixer or the like. The rubber vulcanized molded article obtained by vulcanizing and molding the rubber composition for a vulcanizable hose thus produced can be used as an inner layer material for a radiator hose. The conditions for vulcanization molding are not particularly limited. For example, in the case of using a vulcanization can, pressure vulcanization is usually performed at a temperature of 120 to 180 ° C. and a pressure of 0.1 to 1 MPa for 5 to 120 minutes. .

(Description of radiator hose)
In the radiator hose, an outer layer and / or an intermediate layer formed from the weather resistant rubber composition can be further provided outside the inner layer formed from the ethylene-α-olefin copolymer rubber composition. Examples of the weather resistant rubber include ethylene-propylene copolymer rubber, chloroprene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, silicone rubber, butyl rubber, and ethylene-vinyl acetate copolymer. Among these, ethylene-propylene copolymer rubber is preferable. An intermediate layer made of another rubber composition may be provided between the first layer and the second layer. Moreover, you may provide the 3rd layer which consists of another rubber composition on a 2nd layer further. In addition to the inner layer, the outer layer, and / or the intermediate layer, a reinforcing yarn layer may be configured.

  Although the manufacturing method of a radiator hose is not specifically limited, For example, it is based on the following method. That is, after forming an ethylene-α-olefin copolymer rubber composition layer forming an inner layer and a weather resistant rubber layer forming an intermediate layer or an outer layer into a laminated tube by a two-layer extrusion method, polyester fiber, etc. The reinforcing yarn layer is knitted by blade knitting at an appropriate knitting angle, and a weather resistant rubber layer is extruded and coated as an outer layer on the outer side to obtain an unvulcanized rubber hose. A metal mandrel is inserted into the unvulcanized rubber hose using compressed air, and then this is vulcanized directly by steam vulcanization, and then the metal mandrel is pulled out, washed and heated to produce a hose. The thickness of the ethylene-α-olefin copolymer rubber composition layer forming the inner layer of the radiator hose is, for example, usually 0.3 to 2 mm, and the thickness of the weather resistant rubber layer forming the intermediate layer and / or the outer layer. The thickness is usually 0.5 to 5 mm.

Below, based on an Example, this invention is demonstrated further in detail. In addition, this invention is not limited to an Example. In the examples and comparative examples, all parts and% are based on weight.
(1) Measurement of Volume Specific Resistivity A sheet of 150 mm × 50 mm × 2 mm was prepared using an ethylene-α-olefin copolymer rubber composition, and JIS K 6911 (general test method for thermosetting plastic) and JIS K 7194. The volume resistivity was measured (unit: Ω · cm) in accordance with (Resistivity Test Method by Conductive Plastic 4-Probe Method).

(2) Bending test Using an ethylene-α-olefin copolymer rubber composition, a test piece of 25 mm × 150 mm × 6 mm having a 2 mm crack at the center was prepared, and JIS K 6260 (vulcanized rubber and thermoplastic was used. The dematcher bending test was conducted in accordance with the rubber dematcher bending crack test method), and the number of bendings until the crack progressed was determined. The larger the value, the better the bending resistance (unit: number of times).

(3) Electric current bending test Using an ethylene-α-olefin copolymer rubber composition, a hose test piece having an inner diameter of 7 mm, an outer diameter of 13 mm, and a length of 50 mm was prepared. The current bending test was conducted. FIG. 2 is a view for explaining a current bending test apparatus for a hose test piece. The electric bending test apparatus 100 shown in FIG. 2 connects two hose test pieces 11 and 12, fixed pipes 21 and 22 for fixing these hose test pieces 11 and 12, and the hose test pieces 11 and 12, respectively. Connecting pipe 23, clamps 31 and 32, clamps 41 and 42, electrodes 51 and 52 attached to the hose test pieces 11 and 12, respectively, a vibration part 61, and a fixing part 62.

As shown in FIG. 2, two hose test pieces 11, 12 are fixed by clamps 41, 42 with fixed tubes 21, 22 inserted from each one side. The connecting tube 23 is inserted on the opposite side of the two hose test pieces 11 and 12 from the side where the fixed tubes 21 and 22 are inserted, and is fixed by clamps 31 and 32. A voltage of 12 V is applied between the attached hose test pieces 11 and 12 by the battery 70 and energized. Further, cooling water (LLC solution) is sealed in the hose test pieces 11 and 12. When the vibration part 61 vibrates in a direction perpendicular to the longitudinal direction of the hose test pieces 11 and 12, the hose test pieces 11 and 12 are repeatedly deformed through the fixed pipes 21 and 22 on the basis of the high-frequency slight vibration. The The vibration condition was a deformation with an amplitude of 1.4 mm over 5 hours at 12 V and 100 Hz. Moreover, the quality of current-carrying flexibility was determined according to the following criteria.
A crack with a length of 0.5 mm occurred.
No crack with a length of 0.5 mm ... ○ (Good current flexibility)

(Examples 1-3, Comparative Example 1)
A rubber vulcanized molded product obtained by vulcanizing the rubber composition having the composition shown in Table 1 under conditions of 160 ° C. × 15 minutes was subjected to measurement of volume resistivity, dematcher bending test, and current bending test. It was. The results are shown in Table 1. Further, the volume resistivity value and the result of the dematcher bending test are plotted on FIG. The results (Examples 1 to 3) of Examples 1 to 3 are the above-mentioned formulas (1) showing the relationship between the number of flexures (A) and the volume resistivity (R) leading to the crack growth in FIG. The results of Comparative Example 1 (ratio 1) are plotted in the lower region of the straight line graph.

  From the results shown in Table 1, when the volume specific resistance value (R) of the rubber material and the number of bends (A) leading to crack growth satisfy the relationship represented by the above formula (1) (Examples 1 to In 3), the current bending flexibility of the rubber hose is improved in a balanced manner, and as a result, the occurrence of electrolytic corrosion cracks inside the hose is suppressed. On the other hand, when the volume specific resistance value (R) and the number of bends (A) leading to crack propagation do not satisfy the relationship represented by the above formula (1) (Comparative Example 1), the rubber hose is energized. It can be seen that the flexibility is not improved.

It is a figure for demonstrating the relationship between the volume specific resistance value of the rubber composition for radiator hoses to which this Embodiment is applied, and the frequency | count of bending which reaches a crack progress. It is a figure for demonstrating the electricity bending test apparatus of a hose test piece.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11,12 ... Hose test piece, 21,22 ... Fixed tube, 31, 32, 41, 42 ... Clamp, 51, 52 ... Electrode, 61 ... Vibrating part, 62 ... Fixed part, 70 ... Battery

Claims (6)

A rubber composition containing an ethylene-α-olefin copolymer rubber,
A rubber composition for a radiator hose, characterized in that a relationship between a volume resistivity value (R) of the rubber composition and the number of flexing times (A) leading to crack propagation is represented by the following formula (1).

(In the formula (1), R is a volume specific resistance value (unit: Ωcm), and A is the number of times of bending leading to crack propagation.) The rubber composition for a radiator hose according to claim 1, wherein the volume resistivity (R) in the formula (1) is less than 10 ⁴ Ωcm. The rubber composition contains 100 parts by weight of the ethylene-α-olefin copolymer rubber and 50 to 200 parts by weight of a reinforcing agent with respect to the ethylene-α-olefin copolymer rubber. The rubber composition for a radiator hose according to claim 1. The reinforcing agent contains (a) 60 to 95% by weight of carbon black and (b) 5 to 40% by weight of silica (provided that (a) + (b) is 100% by weight). The rubber composition for a radiator hose according to claim 3. An inner layer composed of a rubber material containing an ethylene-α-olefin copolymer rubber and a reinforcing agent;
A radiator hose characterized in that the relationship between the volume specific resistance value (R) of the rubber material and the number of flexing times (A) leading to crack propagation is expressed by the following equation (1).

(In the formula (1), R is a volume specific resistance value (unit: Ωcm), and A is the number of flexures to reach the crack progress in the flex test.) 6. The radiator hose according to claim 5, further comprising an outer layer and / or an intermediate layer made of weather resistant rubber.

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