Rubber composition for vehicle coolant transport hose, and vehicle coolant transport hose obtained using same

Abstract

Provided are a rubber composition for a vehicle coolant transport hose and a vehicle coolant transport hose obtained using the same that make it possible to solve various problems associated with increased coolant conductivity and clogging of filters of a vehicle coolant system, these problems having been observed in the past when a sulfur-vulcanized ethylene-propylene copolymer rubber composition was employed as a hose material.　A sulfur-vulcanized rubber composition that contains an ethylene-propylene copolymer rubber (A) as the main component and a vulcanization accelerator (B) and that serves as the material of the innermost layer of a vehicle coolant transport hose, wherein the vulcanization accelerator (B) includes at least one vulcanization accelerator selected from the group consisting of (B-1) to (B-3) below in a specific proportion. (B-1) A dithiocarbamate vulcanization accelerator having a molecular weight of 380 or greater. (B-2) A thiuram vulcanization accelerator having a molecular weight of 380 or greater. (B-3) A sulfenamide vulcanization accelerator.

Description

Rubber composition for vehicle coolant transport hose and vehicle coolant transport hose obtained using the same

[0001] The present invention relates to a rubber composition for a vehicle coolant transport hose and a vehicle coolant transport hose obtained using the same, and more particularly to an improved technology for vehicle coolant transport hoses used in various vehicles such as automobiles for connecting an engine to a radiator, connecting an engine to a heater core, fuel cell systems, etc.

[0002] Ethylene-propylene copolymer rubber, which has excellent water resistance, is generally used as a material for forming vehicle hoses (vehicle coolant transport hoses) that pass coolant mixed with antifreeze liquid coolant (LLC). In addition to the ethylene-propylene copolymer rubber, the forming material typically contains fillers such as carbon black, softeners such as process oil, vulcanizing agents, vulcanization accelerators, etc., and the resulting rubber composition is kneaded to form the desired coolant transport hose. When ethylene-propylene copolymer rubber is used as the main material, there are two types of vulcanization: "sulfur vulcanization" and "peroxide vulcanization" (see, for example, Patent Documents 1 and 2).

[0003] International Publication 2019 / 107415 Publication JP 6-262728 Publication

[0004] As for hose materials, sulfur vulcanization specifications are commonly used, as described in Patent Document 1, for example, due to their cost advantages. However, hoses made with sulfur-vulcanized ethylene-propylene copolymer rubber compositions contain unreacted excess residues of the vulcanization accelerator used in sulfur vulcanization and decomposition products of the vulcanization accelerator. Conventional vehicle coolant transport hoses made with sulfur-vulcanized ethylene-propylene copolymer rubber compositions tend to extract (leach) the above-mentioned components (unreacted excess residues of the vulcanization accelerator and decomposition products of the vulcanization accelerator) into the coolant upon contact with the coolant flowing through the hose. When this occurs, some of the extracted components react with compounds in the coolant to form new compounds, which can have adverse effects such as filter clogging in the vehicle cooling system to which the hose is connected. Furthermore, there is concern that the extractable components may increase the conductivity of the coolant, resulting in various problems (hose deterioration, spark ignition, etc.).

[0005] Furthermore, in recent years, fuel cell systems (particularly polymer electrolyte fuel cells) have been considered a promising next-generation power generation method for automobiles and other vehicles. It is said that the performance of the power generation section of such fuel cell systems is significantly degraded by external contaminants such as sulfur or metal ions. Therefore, hoses and piping components, such as coolant transport hoses, used in such fuel cell systems must be clean and exhibit low extractability (i.e., the property of being less likely to be extracted by the coolant, such as water, flowing through the hose).

[0006] On the other hand, the hose described in Patent Document 2 is a hose that uses a peroxide-vulcanized ethylene-propylene copolymer rubber composition, and does not have the problems caused by the extractable components described above. However, it is disadvantageous in terms of cost and has many issues, such as a tendency for insufficient vulcanization to occur.

[0007] The present invention has been made in view of the above circumstances, and provides a rubber composition for a hose for transporting vehicle coolant, which can solve various problems such as clogging of the filter in the vehicle cooling system and an increase in the conductivity of the coolant, which have conventionally been observed when a sulfur-vulcanized ethylene-propylene copolymer rubber composition is used as a material for a hose for transporting vehicle coolant, and a hose for transporting vehicle coolant obtained using the same.

[0008] In order to solve the above-mentioned problems, the present inventors have conducted extensive research into rubber compositions for vehicle coolant transport hoses. During the course of their research, the present inventors focused on vulcanization accelerators used in sulfur-vulcanized ethylene-propylene copolymer rubber compositions. Many of the vulcanization accelerators conventionally used in sulfur-vulcanized ethylene-propylene copolymer rubber compositions have low molecular weights, and as mentioned above, their unreacted excess residues and decomposition products tend to be easily extracted (eluted) into the coolant. Therefore, the present inventors have conducted various experiments and have found that by using a specific vulcanization accelerator (at least one vulcanization accelerator selected from the group consisting of dithiocarbamate vulcanization accelerators (B-1) having a molecular weight of 380 or more, thiuram vulcanization accelerators (B-2) having a molecular weight of 380 or more, and sulfenamide vulcanization accelerators (B-3)) in a specific ratio as the vulcanization accelerator, the above-mentioned extraction (elution) into the coolant can be suppressed without impairing the physical properties and functions required for a hose for transporting a coolant for a vehicle, and problems such as clogging of the filter of the cooling system for a vehicle and an increase in the conductivity of the coolant can be solved.

[0009] The gist of the present invention is the following [1] to [5]. [1] A rubber composition for a sulfur-vulcanized vehicle coolant transport hose, comprising an ethylene-propylene copolymer rubber (A) as a main component and a vulcanization accelerator (B), wherein the vulcanization accelerator (B) comprises at least one selected from the group consisting of the following (B-1) to (B-3), the total amount of (B-1) to (B-3) being 3.25 parts by mass or less per 100 parts by mass of the ethylene-propylene copolymer rubber (A), and the total amount of (B-1) to (B-3) being 75% by mass or more of the total amount of the vulcanization accelerator (B): (B-1) a dithiocarbamate-based vulcanization accelerator having a molecular weight of 380 or more; (B-2) a thiuram-based vulcanization accelerator having a molecular weight of 380 or more; and (B-3) a sulfenamide-based vulcanization accelerator. [2] The rubber composition for a vehicle coolant transport hose according to [1], wherein (B-1) is a dithiocarbamate-based vulcanization accelerator having a molecular weight of 400 or more. [3] The rubber composition for a vehicle coolant transport hose according to [1] or [2], wherein (B-2) is a thiuram-based vulcanization accelerator having a molecular weight of 400 or more. [4] The rubber composition for a vehicle coolant transport hose according to [2] or [3], wherein the vulcanization accelerator (B) contains at least a vulcanization accelerator selected from the group consisting of (B-1) and (B-2), and the total amount of (B-1) and (B-2) is 75 mass % or more of the total vulcanization accelerator (B). [5] A vehicle coolant transport hose consisting of at least one layer, the innermost layer of which is made of a vulcanizate of the rubber composition for a vehicle coolant transport hose according to any one of [1] to [4].

[0010] In the present invention, the rubber composition for a vehicle coolant transport hose is a sulfur-vulcanized rubber composition, which is advantageous in terms of cost, etc. Furthermore, the rubber composition contains a specific vulcanization accelerator in a specific ratio, which prevents unreacted excess residues and decomposition products of the vulcanization accelerator from being extracted into the coolant, thereby eliminating various problems caused by these extracts (extracted components), such as clogging of filters in vehicle cooling systems and an increase in the conductivity of the coolant.

[0011] 1 is a structural diagram showing an example of a vehicle coolant transport hose according to the present invention;

[0012] Next, an embodiment of the present invention will be described in detail. However, the present invention is not limited to this embodiment. In this specification, "X and / or Y (X and Y are any configuration)" means at least one of X and Y, and means three cases: X only, Y only, and X and Y.

[0013] A rubber composition for a vehicle coolant transport hose (hereinafter referred to as "the rubber composition"), which is one embodiment of the present invention, is a sulfur-vulcanized rubber composition containing an ethylene-propylene copolymer rubber (A) as a main component and a vulcanization accelerator (B), wherein the vulcanization accelerator (B) comprises at least one selected from the group consisting of (B-1) to (B-3) below, the total amount of (B-1) to (B-3) being 3.25 parts by mass or less per 100 parts by mass of the ethylene-propylene copolymer rubber (A), and the total amount of (B-1) to (B-3) representing 75% by mass or more of the total vulcanization accelerator (B). Here, "main component" refers to a component that has a significant effect on the properties of the rubber composition, and typically refers to a rubber composition in which 50% by mass or more of the entire rubber composition (excluding fillers such as carbon black) is the ethylene-propylene copolymer rubber (A). (B-1) A dithiocarbamate-based vulcanization accelerator having a molecular weight of 380 or more. (B-2) Thiuram vulcanization accelerators having a molecular weight of 380 or more. (B-3) Sulfenamide vulcanization accelerators.

[0014] A vehicle coolant transport hose (hereinafter referred to as "the present hose") according to one embodiment of the present invention is a vehicle coolant transport hose comprising at least one constituent layer, the innermost layer of which is made of a vulcanized product of the present rubber composition. Examples of the present hose include a three-layer hose having an inner rubber layer 1, a reinforcing fiber layer 2, and an outer rubber layer 3 laminated in this order, each of which is made of a vulcanized product of the present rubber composition, as shown in FIG. 1 , and a single-layer hose having only a rubber layer made of a vulcanized product of the present rubber composition. The outer rubber layer 3 may be a rubber layer made of a vulcanized product of the present rubber composition or a rubber layer made of a vulcanized product of another rubber composition. However, if adhesive-free interlayer bonding is achieved between the inner rubber layer 1 and the outer rubber layer 3 via the mesh of the reinforcing fiber layer 2, the outer rubber layer 3 is preferably also a rubber layer made of a vulcanized product of the present rubber composition.

[0015] Next, each component constituting the present rubber composition will be described.

[0016] Ethylene-Propylene Copolymer Rubber (A) Examples of the ethylene-propylene copolymer rubber (A) used in the rubber composition include ethylene-propylene-diene terpolymer rubber (EPDM) and ethylene-propylene copolymer rubber (EPM), which may be used alone or in combination of two or more. The ethylene-propylene copolymer rubber (A) preferably has an ethylene content of 50 to 70% by mass, more preferably 52 to 58% by mass. The diene content of the EPDM is preferably 3% by mass or more, more preferably 4 to 5.5% by mass.

[0017] The diene component of the EPDM is preferably, for example, a diene monomer having 5 to 20 carbon atoms, and specific examples thereof include 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene, 1,4-octadiene, 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene (DCP), 5-ethylidene-2-norbornene (ENB), 5-vinyl-2-norbornene (VNB), 5-butylidene-2-norbornene, 2-methallyl-5-norbornene, 2-isopropenyl-5-norbornene, etc. These may be used alone or in combination of two or more.

[0018] <<Sulfur-Based Vulcanizing Agent>> Because the rubber composition is sulfur-vulcanized, a sulfur-based vulcanizing agent is used as the vulcanizing agent. Examples of the sulfur-based vulcanizing agent include sulfur such as powdered sulfur, surface-treated sulfur, precipitated sulfur, colloidal sulfur, and insoluble sulfur, as well as sulfur compounds that can serve as sulfur donors (excluding those that fall under the category of vulcanization accelerators), such as sulfur chloride, 2-mercaptoimidazoline, and dipentamethylenethiuram pentasulfide. These may be used alone or in combination of two or more types.

[0019] The content of the sulfur-based vulcanizing agent is preferably in the range of 0.1 to 3.0 parts by mass, more preferably in the range of 0.3 to 1.2 parts by mass, relative to 100 parts by mass of the ethylene-propylene copolymer rubber (A) from the viewpoint of vulcanizability, etc. That is, if the amount of the sulfur-based vulcanizing agent is too small, vulcanization will be insufficient and the hose strength will be poor, while if the amount of the sulfur-based vulcanizing agent is too large, the hose will tend to be too hard and have poor flexibility, as well as a shortened scorch time and poor processability.

[0020] <<Vulcanization Accelerator (B)>> The vulcanization accelerator (B) refers to all vulcanization accelerators used in the present rubber composition. As described above, the vulcanization accelerator (B) includes at least one selected from the group consisting of the following (B-1) to (B-3). The vulcanization accelerators (B) are added in such a manner that the total amount of (B-1) to (B-3) is 3.25 parts by mass or less per 100 parts by mass of the ethylene-propylene copolymer rubber (A) and the total amount of (B-1) to (B-3) accounts for 75% by mass or more of the total amount of the vulcanization accelerator (B). (B-1) A dithiocarbamate vulcanization accelerator having a molecular weight of 380 or more. (B-2) A thiuram vulcanization accelerator having a molecular weight of 380 or more. (B-3) A sulfenamide vulcanization accelerator.

[0021] By containing a specific vulcanization accelerator in a specific ratio as described above, the rubber composition can suppress the extraction of unreacted excess residues and decomposition products of the vulcanization accelerator into the coolant, and can solve various problems caused by these extracts (extracted components), such as clogging of filters in vehicle cooling systems and an increase in the conductivity of the coolant.

[0022] From the viewpoint of obtaining the above-mentioned advantageous effects of the present invention satisfactorily, the total amount of (B-1) to (B-3) in the present rubber composition is preferably in the range of 2.0 to 3.25 parts by mass relative to 100 parts by mass of the ethylene-propylene copolymer rubber (A). Also, from the viewpoint of obtaining the above-mentioned advantageous effects of the present invention satisfactorily, the total amount of (B-1) to (B-3) in the present rubber composition is preferably 80% by mass or more, particularly preferably 100% by mass (wherein the vulcanization accelerator (B) consists solely of (B-1), (B-2), and / or (B-3)).

[0023] Here, from the viewpoint of obtaining the effects of the present invention as described above, the molecular weight of (B-1) is preferably 400 or more. The molecular weight of (B-1) is usually 1,000 or less, and preferably 670 or less. Examples of the dithiocarbamate vulcanization accelerator of (B-1) include zinc dibutyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc dibenzyldithiocarbamate, and zinc N-ethyl-N-phenyldithiocarbamate. These may be used alone or in combination of two or more.

[0024] Furthermore, from the viewpoint of obtaining the effects of the present invention as described above, the molecular weight of (B-2) is preferably 400 or more. The molecular weight of (B-2) is usually 1,000 or less, and preferably 700 or less. Examples of the thiuram vulcanization accelerator (B-2) include tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, dipentamethylenethiuram tetrasulfide, and N,N,N',N'-tetrabenzylthiuram disulfide. These may be used alone or in combination of two or more. Of these, tetrakis(2-ethylhexyl)thiuram disulfide and dipentamethylenethiuram tetrasulfide are preferred.

[0025] Furthermore, from the viewpoint of obtaining the above-mentioned advantageous effects of the present invention well, it is preferable that the vulcanization accelerator (B) contains at least a vulcanization accelerator selected from the group consisting of (B-1) and (B-2), the molecular weight of (B-1) and / or (B-2) is 400 or more, and the total amount of (B-1) and (B-2) is 75% by mass or more of the entire vulcanization accelerator (B). From the above-mentioned viewpoint, the total amount of (B-1) and (B-2) in the rubber composition is preferably 80% by mass or more, particularly preferably 100% by mass (the vulcanization accelerator (B) consists only of (B-1) and / or (B-2)).

[0026] Examples of the sulfenamide vulcanization accelerator (B-3) include N-cyclohexyl-2-benzothiazolylsulfenamide, N-oxydiethylene-2-benzothiazolylsulfenamide, N-t-butyl-2-benzothiazoylsulfenamide, and N,N'-dicyclohexyl-2-benzothiazoylsulfenamide. These may be used alone or in combination of two or more. Of these, N-cyclohexyl-2-benzothiazolylsulfenamide is preferred.

[0027] It is also possible to use a small amount of a vulcanization accelerator that does not fall under any of the above (B-1) to (B-3) as the vulcanization accelerator (B). Examples of such vulcanization accelerators include dithiocarbamate-based vulcanization accelerators having a molecular weight of less than 380 (e.g., zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate), thiuram-based vulcanization accelerators having a molecular weight of less than 380 (e.g., tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide), thiazole-based vulcanization accelerators (e.g., di-2-benzothiazolyl disulfide, dibenzothiazyl disulfide, 2-mercaptobenzothiazole, 2-mercaptobenzothiazole sodium salt, 2-mercaptobenzothiazole zinc salt), aldehyde ammonia-based vulcanization accelerators, aldehyde amine-based vulcanization accelerators, guanidine-based vulcanization accelerators, and thiourea-based vulcanization accelerators. However, since there is a high possibility that it will hinder the resolution of the problems of the present invention, it is desirable in the present invention not to use (not to contain) thiuram vulcanization accelerators (tetramethylthiuram disulfide, tetraethylthiuram disulfide, etc.) having a molecular weight of less than 380. For the same reason, it is desirable in the present invention not to use (not to contain) thiazole vulcanization accelerators, or to reduce the content to less than 20 mass% of the total vulcanization accelerator (B).

[0028] In addition to the ethylene-propylene copolymer rubber (A), the sulfur-based vulcanizing agent, and the specific vulcanization accelerator (B), the rubber composition may contain an acid acceptor, an adsorbent, a pH adjuster, a filler, a vulcanization aid, a process oil, an antioxidant, and the like, as needed.

[0029] <<Acid Acceptor>> Examples of the acid acceptor include magnesium oxide, calcium hydroxide, hydrotalcite, etc. These may be used alone or in combination of two or more.

[0030] <<Adsorbent>> Examples of the adsorbent include Lionite SF manufactured by Lion Corporation.

[0031] <pH Adjusting Agent> Examples of the pH adjusting agent include diethylene glycol, polyethylene glycol, alum, etc. These may be used alone or in combination of two or more.

[0032] <<Filler>> Examples of the filler include carbon black, calcium carbonate, talc, etc. These may be used alone or in combination of two or more. Among these, carbon black is preferred because it can effectively increase mechanical strength such as tensile strength.

[0033] The content of the filler is preferably in the range of 5 to 350 parts by mass, more preferably in the range of 80 to 250 parts by mass, per 100 parts by mass of the ethylene-propylene copolymer rubber (A).

[0034] <<Vulcanization Aid>> Examples of the vulcanization aid include zinc oxide, stearic acid, etc. These may be used alone or in combination of two or more.

[0035] The content of the vulcanization aid is preferably in the range of 1 to 25 parts by mass, more preferably in the range of 3 to 8 parts by mass, per 100 parts by mass of the ethylene-propylene copolymer rubber (A).

[0036] <<Process Oil>> Examples of the process oil include naphthenic oil, paraffinic oil, and aromatic oil. These may be used alone or in combination. Among these, naphthenic oil and paraffinic oil are preferred because of their excellent tensile strength and processability.

[0037] The content of the process oil is preferably in the range of 5 to 140 parts by mass, more preferably in the range of 30 to 90 parts by mass, per 100 parts by mass of the ethylene-propylene copolymer rubber (A).

[0038] <<Antiaging Agent>> Examples of the antiaging agent include carbamate-based, phenylenediamine-based, phenol-based, diphenylamine-based, and quinoline-based antiaging agents, waxes, etc. These may be used alone or in combination of two or more.

[0039] The rubber composition can be prepared, for example, by blending the ethylene-propylene copolymer rubber (A) with an acid acceptor, an adsorbent, a pH adjuster, a filler, a vulcanization aid, a process oil, an antioxidant, etc., as necessary, kneading the mixture using a kneader, a Banbury mixer, a roll mill, or other kneading machine, and further adding a sulfur-based vulcanizing agent and the specific vulcanization accelerator (B) and kneading the mixture.

[0040] The present hose can be produced, for example, as follows using the present rubber composition prepared as described above. That is, first, the present rubber composition prepared as described above is extruded into a hose to produce an unvulcanized hose. It is also possible to produce an unvulcanized hose by inserting a mandrel into the unvulcanized hose or by extruding the present rubber composition onto a straight mandrel. To produce a single-layer hose, the unvulcanized hose is heated and vulcanized under specified conditions (140 to 160°C for 30 to 60 minutes), and if a mandrel is used, the desired present hose can be produced by removing the mandrel. Furthermore, in a layer structure such as the hose shown in Figure 1, in which a reinforcing thread layer 2 is provided between an inner rubber layer 1 and an outer rubber layer 3, an unvulcanized hose is prepared from the present rubber composition as described above. Then, the reinforcing thread layer 2 is formed on the outer surface of the hose by braiding or the like using a predetermined number of reinforcing threads and a predetermined number of threads. If necessary, an adhesive is then applied to the reinforcing thread layer 2 by dipping, spraying, roll coating, brushing, or other methods. The rubber composition for forming the outer rubber layer 3 is then extruded onto the coated surface (or onto the reinforcing thread layer 2) to produce an unvulcanized laminate (hose structure). The unvulcanized laminate (hose structure) thus obtained is then heated and vulcanized under predetermined conditions (140-160°C for 30-60 minutes). If a mandrel is used, the mandrel is removed to produce the desired hose. The present hose can also be formed into a desired curved shape by using a mandrel with a predetermined curved shape.

[0041] The present hose obtained in this manner may have a single-layer structure or a multi-layer structure in which two or more layers are laminated, but it is preferred from the viewpoint of obtaining the advantageous effects of the present invention that at least the innermost layer (in the case of a single-layer structure, that layer) be made of the present rubber composition.

[0042] In the present hose obtained as described above, the thickness of its innermost layer (or that layer in the case of a single-layer structure) is preferably 0.25 to 10 mm, more preferably 0.5 to 5 mm. Furthermore, when an outer rubber layer 3 is provided as shown in Figure 1, its thickness is preferably 0.25 to 10 mm, more preferably 0.5 to 5 mm. Furthermore, the inner diameter of the present hose is preferably 5 to 60 mm, more preferably 10 to 40 mm.

[0043] Because the present hose exhibits the above-described effects, it can exhibit excellent performance as a hose for transporting coolant in vehicles, such as a radiator hose, a heater hose, a hose for transporting coolant in a fuel cell system, or a drain hose.

[0044] Next, examples will be described together with comparative examples, but the present invention is not limited to these examples.

[0045] First, prior to the Examples and Comparative Examples, a vulcanization accelerator corresponding to any one of the following (i) to (iv) was prepared.

[0046] [(i) Dithiocarbamate-based vulcanization accelerators (B-1) having a molecular weight of 380 or more] Sancerer BZ (zinc dibutyldithiocarbamate, manufactured by Sanshin Chemical Industry Co., Ltd., molecular weight: 474) Noccelaer ZP (zinc N-pentamethylenedithiocarbamate, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., molecular weight: 386)

[0047] [(ii) Thiuram-based vulcanization accelerators (B-2) having a molecular weight of 380 or more] Noccela TOT-N (tetrakis(2-ethylhexyl)thiuram disulfide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., molecular weight: 633) Noccela TRA (dipentamethylene thiuram tetrasulfide, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., molecular weight: 385)

[0048] [(iii) Sulfenamide-based vulcanization accelerator (B-3)] Sancerer CM-G (N-cyclohexyl-2-benzothiazolyl sulfenamide, manufactured by Sanshin Chemical Industry Co., Ltd., molecular weight: 264)

[0049] [(iv) Vulcanization accelerators other than (B-1) to (B-3)] Noccela PZ (zinc dimethyldithiocarbamate, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., molecular weight: 306) Sancerela TT (tetramethylthiuram disulfide, manufactured by Sanshin Chemical Industry Co., Ltd., molecular weight: 240)

[0050] Examples 1 to 11, Comparative Examples 1 to 4 100 parts by mass of EPDM (manufactured by Sumitomo Chemical Co., Ltd., product name: Esprene 532, ethylene content: 51% by mass, diene content: 3.5% by mass) were blended with 120 parts by mass of SRF grade carbon black (manufactured by Cabot Japan, product name: SPHERON 5200), 68 parts by mass of process oil (manufactured by Idemitsu Kosan Co., Ltd., product name: Diana Process PW-380), 1 part by mass of stearic acid (manufactured by Kao Corporation), and 5 parts by mass of zinc oxide (manufactured by Mitsui Mining and Smelting Co., Ltd.), and 1.2 parts by mass of sulfur (manufactured by Tsurumi Chemical Co., Ltd., product name: Sulfax T-10) and each of the vulcanization accelerators were blended in the proportions shown in Tables 1 and 2 below, and the blend was kneaded using a Banbury mixer and an open roll to prepare a rubber composition (rubber composition for a hose for transporting a coolant for a vehicle).

[0051] The rubber compositions of the Examples and Comparative Examples thus obtained were evaluated for the amount of extractables according to the following criteria, and the results are shown in Tables 1 and 2 below.

[0052] <Extraction Amount> Each rubber composition obtained was press-vulcanized at 160°C for 60 minutes to produce a 2 mm thick vulcanized rubber sheet (sample). Four 2.8 cm square rubber pieces were then punched out from this rubber sheet. These four rubber pieces were placed in a 100 ml polypropylene container with a lid along with 100 ml of pure water (conductivity 1.0 μS / cm) and heat-treated at 90°C for 336 hours to extract the components in the rubber pieces. The conductivity of the extracted solution in the container at 25°C was then measured using a conductivity meter (D-210PC-S, manufactured by Horiba Advanced Techno Co., Ltd.) to determine the change in conductivity due to the components extracted into the pure water. The higher the conductivity, the greater the amount of unreacted excess residue and decomposition products of the vulcanization accelerator extracted from the sample. Therefore, the extraction amount (evaluation of low extractability) was evaluated according to the following criteria. <Criteria> ◯ (very good): The measured value of the conductivity is less than 230 μS / cm × (poor): The measured value of the conductivity is 230 μS / cm or more

[0053]

[0054]

[0055] From the results in Tables 1 and 2, it can be seen that the type and ratio of the vulcanization accelerator in the rubber compositions of the Examples satisfied the requirements of the present invention, and as a result, the amount of unreacted excess residue and decomposition products of the vulcanization accelerator extracted was reduced. Therefore, the hose for transporting a vehicle coolant having an innermost layer made of a vulcanizate of the rubber composition of the Examples is judged to have excellent low extractability, and can solve various problems (such as hose deterioration and spark ignition) associated with an increase in the conductivity of the extracted solution.

[0056] In contrast, the rubber composition of Comparative Example 1 had an excessively large total amount of the vulcanization accelerators corresponding to (B-1) to (B-3) (the amount of "i + ii + iii" was 3.5 parts by mass relative to 100 parts by mass of EPDM, exceeding the 3.25 parts by mass specified in the present invention), and therefore did not have excellent low extractability. The rubber compositions of Comparative Examples 2 to 4 had a reduced total amount of the vulcanization accelerators corresponding to (B-1) to (B-3), but the ratio of the vulcanization accelerators corresponding to (B-1) to (B-3) to the total vulcanization accelerators was low (the value of "{(i + ii + iii) / (i + ii + iii + iv)} x 100" was less than 75% by mass), and therefore did not have excellent low extractability.

[0057] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0058] The rubber composition for a hose for transporting a coolant for a vehicle of the present invention can be used as a rubber composition for a hose for transporting a coolant for a vehicle, such as a radiator hose, a heater hose, a hose for transporting a coolant for a fuel cell system, a drain hose, etc. The hose for transporting a coolant for a vehicle is preferably used not only for automobiles but also for other transport machines (industrial transport vehicles such as airplanes, forklifts, excavators and cranes, railway vehicles, etc.), vending machines, etc.

[0059] 1 inner rubber layer 2 reinforcing thread layer 3 outer rubber layer

Claims

1. A hose for transporting coolant for vehicles, comprising at least one constituent layer, the innermost layer of which is a sulfur-vulcanized rubber composition for a hose for transporting coolant for vehicles, the rubber composition comprising an ethylene-propylene copolymer rubber (A) as a main component and a vulcanization accelerator (B), The vulcanization accelerator (B) contains at least one selected from the group consisting of the following (B-1) to (B-3): the total amount of (B-1) to (B-3) is 3.25 parts by mass or less per 100 parts by mass of the ethylene-propylene copolymer rubber (A), and a hose for transporting a coolant for a vehicle, comprising a vulcanizate of a rubber composition for a hose for transporting a coolant for a vehicle, wherein the total amount of (B-1) to (B-3) is 75 mass % or more of the total amount of the vulcanization accelerator (B), the vulcanization accelerator (B) contains at least a vulcanization accelerator selected from the group consisting of the following (B-1) and (B-2), and does not contain a thiuram vulcanization accelerator having a molecular weight of less than 380: (B-1) A dithiocarbamate vulcanization accelerator having a molecular weight of 380 or more. (B-2) Thiuram vulcanization accelerators with a molecular weight of 380 or more. (B-3) Sulfenamide vulcanization accelerator.

2. 2. The hose for transporting a coolant for a vehicle according to claim 1, wherein the (B-1) is a dithiocarbamate-based vulcanization accelerator having a molecular weight of 400 or more.

3. 3. The hose for transporting a coolant for a vehicle according to claim 1, wherein said (B-2) is a thiuram vulcanization accelerator having a molecular weight of 400 or more.

4. 3. The hose for transporting a coolant for a vehicle according to claim 2, wherein the total amount of (B-1) and (B-2) is 75% by mass or more of the total amount of the vulcanization accelerator (B).