Rubber composition for extrusion molding, hose, and hose manufacturing method

Abstract

The following is provided as a rubber composition for extrusion molding that has an excellent extruded surface (extrusion processability) during extrusion processing.　This rubber composition for extrusion molding includes a rubber component and recycled carbon black, wherein when the rubber composition for extrusion molding is analyzed using an image analysis condition, the area ratio of recycled carbon black with a particle diameter of 3-12 μm is 5.9-12.1%.

Description

Rubber composition for extrusion molding, hose, and method for manufacturing hose

[0001] The present invention relates to a rubber composition for extrusion molding that is suitable for extrusion molding, a hose made from the rubber composition for extrusion molding, and a method for producing the hose.

[0002] In recent years, as resource conservation and environmental protection have become a focus of attention, the replacement of petroleum-derived carbon black with recycled carbon black obtained by pyrolysis of rubber products containing carbon black, such as waste tires, has been considered with the aim of achieving carbon neutrality (reducing CO2 emissions).

[0003] For example, Patent Document 1 describes a rubber composition for tires containing diene rubber, carbon black, and recycled carbon black.

[0004] Japanese Patent Application Laid-Open No. 2022-146475

[0005] The rubber composition for tires described in Patent Document 1 is suitable for producing tires, but when it is used for extrusion processing, the recycled carbon black has poor interaction (reinforcing properties) with the rubber interface, so cracks form between the recycled carbon black and the rubber during extrusion molding, and these cracks propagate to form larger cracks, resulting in a deterioration of the extrusion surface.

[0006] The present invention has been made in view of the above circumstances, and provides a rubber composition for extrusion molding which has excellent extrusion surface (extrusion processability) during extrusion processing.

[0007] The present inventors have conducted extensive research to solve the above problems and have found that a rubber composition for extrusion that exhibits excellent extrusion surface (extrusion processability) can be obtained by controlling the area ratio of recycled carbon black having a particle size of approximately 10 μm contained in a rubber composition within a specific range.

[0008] That is, in order to achieve the above-mentioned object, the present invention provides the following [1] to [6]: [1] A rubber composition for extrusion molding containing a rubber component and recycled carbon black, wherein when the rubber composition for extrusion molding is analyzed under the following image analysis conditions, the area ratio of recycled carbon black having a particle diameter of 3 to 12 μm is 5.9 to 12.1%. [Image analysis conditions] (CLAHE algorithm) Contrast Limit: 2.0 Grid Size: 8,8 (Non-Local Means Filter) h: 15 Template Window Size: 7 Search Window Size: 21 (Adaptive binarization processing) Black Size: 101 C: -4 [2] The rubber composition for extrusion molding according to [1], further comprising petroleum-derived carbon black. [3] The rubber composition for extrusion molding according to [2], wherein the mass ratio of the recycled carbon black to the petroleum-derived carbon black (recycled carbon black / petroleum-derived carbon black) is 10 / 90 to 90 / 10. [4] The rubber composition for extrusion molding according to any one of [1] to [3], wherein the total amount of carbon black contained in the rubber composition for extrusion molding is 100 parts by mass or more per 100 parts by mass of the rubber component. [5] A hose made of the rubber composition for extrusion molding according to any one of [1] to [4]. [6] The method for producing a hose according to [5], wherein the hose is produced by extrusion molding the rubber composition for extrusion molding using a draw-down extrusion extruder.

[0009] According to the present invention, a rubber composition for extrusion molding having excellent extrusion processability can be provided.

[0010] 1 is a diagram for explaining an example of extrusion molding using an extruder of a drawing-down extrusion type. 2 is a diagram showing the configuration of an example of a hose according to the present invention.

[0011] Next, an embodiment of the present invention will be described in detail, but the present invention is not limited to the embodiment described below.

[0012] In this specification, "X and / or Y (X and Y are any configurations)" means at least one of X and Y, and means three possibilities: X only, Y only, or X and Y.

[0013] A rubber composition for extrusion processing according to one embodiment of the present invention (hereinafter, may be referred to as "the rubber composition") is a rubber composition for extrusion molding containing a rubber component and recycled carbon black, and when the rubber composition for extrusion molding is analyzed under the image analysis conditions described below, the area ratio of recycled carbon black having a particle size of 3 to 12 μm is 5.9 to 12.1%.

[0014] Typically, recycled carbon black is produced by burning carbon black-containing rubber products such as scrap tires, industrial conveyor belts, power transmission belts, and rubber hoses. Therefore, in addition to carbon black, recycled carbon black contains approximately 15 to 20% ash derived from rubber components and other components. This ash forms particles that are composited with the carbon black in the recycled carbon black. The particle sizes vary, but can be broadly divided into three particle sizes: 1 μm or less, approximately 10 μm, and 100 μm or more. Unlike petroleum-derived carbon black, recycled carbon black does not have functional groups on its surface, resulting in poor interaction with the rubber component. When recycled carbon black is blended into a rubber composition for extrusion processing, the recycled carbon black disperses well, but the extrusion surface deteriorates. The inventors have discovered that this deterioration in extrusion surface is due to poor interfacial interaction (reinforcing properties) between recycled carbon black, particularly recycled carbon black with a particle size of approximately 10 μm, and the rubber component, resulting in cracks that form between the recycled carbon black with a particle size of approximately 10 μm and the rubber during extrusion molding, and these cracks then propagate. Therefore, in the present rubber composition, by setting the area ratio of recycled carbon black having a particle size of 3 to 12 μm within a specific range, it is possible to suppress cracks between the recycled carbon black and the rubber, resulting in excellent extrusion processability.

[0015] In the course of their research, the inventors have also found that the use of this rubber composition increases the volume resistivity. That is, when petroleum-derived carbon black is used in a rubber composition for extrusion molding, the volume resistivity decreases because petroleum-derived carbon black is conductive. On the other hand, recycled carbon black contains ash, so the volume resistivity of this rubber composition containing recycled carbon black increases. Therefore, this rubber composition can also suppress electrical degradation. Hereinafter, embodiments of the present invention will be described in more detail.

[0016] [Rubber Component] The rubber component used in the rubber composition is not particularly limited, but examples thereof include diene-based rubbers. Examples of the diene-based rubbers include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), and butyl rubber (IIR). These may be used alone or in combination of two or more. Of these, ethylene-propylene-based rubbers such as EPDM and EPM are preferred, with EPDM being particularly preferred.

[0017] The diene monomer used as the third component constituting the EPDM is not particularly limited, but a diene monomer having 5 to 20 carbon atoms is preferred. Specific examples 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), and 5-butylidene-2-norbornene. These may be used alone or in combination of two or more. Of these, DCP and ENB are preferred.

[0018] The ethylene content of the ethylene-propylene rubber is not particularly limited, but from the viewpoint of significantly exhibiting the effects of the present invention, it is preferably 48 to 70% by mass, more preferably 50 to 60% by mass.

[0019] The propylene content of the EPDM is not particularly limited, but is preferably 22 to 46 mass%, more preferably 30 to 44 mass%, from the viewpoint of significantly achieving the effects of the present invention. The diene monomer content of the EPDM is not particularly limited, but is preferably 3 to 11 mass%, more preferably 3.5 to 6 mass%. The iodine value of the EPDM is not particularly limited, but is preferably 6 to 30, more preferably 10 to 24, from the viewpoint of significantly achieving the effects of the present invention.

[0020] The content of the rubber component is not particularly limited, but is usually 20% by mass or more, preferably 25% by mass or more, and more preferably 28 to 60% by mass, based on the rubber composition (100% by mass).

[0021] [Recycled Carbon Black (Recycled CB)] The recycled carbon black can be obtained by thermally decomposing carbon black-containing rubber products such as waste tires, industrial conveyor belts, power transmission belts, and rubber hoses using known means.

[0022] As mentioned above, recycled carbon black contains ash derived from rubber components and the like, and the ash content is usually 10 to 30 mass%, preferably 13 to 25 mass%, and more preferably 15 to 20 mass%. When the ash content is within this range, the carbon black tends to have excellent dispersibility with the rubber component. The ash content can be measured by a method in accordance with JIS K 6218-2.

[0023] The amount of recycled carbon black contained may be such that the area ratio of recycled carbon black having a particle size of 3 to 12 μm falls within a specific range when analyzed under the image analysis conditions described below, and is usually 5 to 200 parts by mass, preferably 20 to 180 parts by mass, more preferably 30 to 170 parts by mass, even more preferably 40 to 160 parts by mass, and particularly preferably 50 to 150 parts by mass, per 100 parts by mass of the rubber component. When the amount of recycled carbon black is within the above range, the effects of the present invention tend to be more favorably obtained, and the volume resistivity tends to be high and the carbon neutrality tends to be excellent.

[0024] The rubber composition of the present invention preferably contains, in addition to the rubber component and recycled carbon black, for example, petroleum-derived carbon black.

[0025] [Petroleum-derived carbon black (CB)] The petroleum-derived carbon black is not particularly limited, and examples thereof include furnace blacks (furnace carbon blacks) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF, and ECF; acetylene black (acetylene carbon black); thermal blacks (thermal carbon blacks) such as FT and MT; channel blacks (channel carbon blacks) such as EPC, MPC, and CC; and graphite. These may be used alone or in combination of two or more. Among these, furnace black is preferred, and SRF is particularly preferred.

[0026] The average particle size of the petroleum-derived carbon black is preferably 100 nm or less, more preferably 90 nm or less, and even more preferably 75 nm or less. Although there is no particular lower limit, a value of 15 nm or more is preferred. By setting the average particle size of the petroleum-derived carbon black within the above range, dispersibility with the rubber component tends to be excellent. The average particle size of the petroleum-derived carbon black can be measured using a TEM or the like.

[0027] The dibutyl phthalate (DBP) absorption of the petroleum-derived carbon black is preferably 40 to 250 ml / 100 g, more preferably 50 to 200 ml / 100 g, and particularly preferably 50 to 160 ml / 100 g. When the DBP absorption of the petroleum-derived carbon black is within the above range, it tends to have excellent dispersibility with rubber components. The DPB absorption can be measured on an uncompressed sample in accordance with JIS K 6217-4 (2017).

[0028] When the rubber composition contains petroleum-derived carbon black, the content thereof is preferably 5 to 200 parts by mass, more preferably 20 to 150 parts by mass, still more preferably 30 to 130 parts by mass, and particularly preferably 35 to 110 parts by mass, per 100 parts by mass of the rubber component. When the content of petroleum-derived carbon black is within the above range, the effects of the present invention tend to be more suitably obtained.

[0029] The mass ratio of the recycled carbon black to the petroleum-derived carbon black (recycled CB / CB) is preferably 10 / 90 to 90 / 10, more preferably 20 / 80 to 85 / 15, and even more preferably 40 / 60 to 80 / 20. When the ratio of recycled carbon black to petroleum-derived carbon black is within the above range, the effects of the present invention tend to be more favorably achieved.

[0030] Furthermore, the total amount of carbon black contained in the rubber composition (total amount of recycled carbon black and petroleum-derived carbon black) is preferably 100 parts by mass or more, more preferably 110 parts by mass or more, and particularly preferably 120 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is usually 200 parts by mass or less, preferably 150 parts by mass or less. When the total amount of carbon black is within the above range, the effects of the present invention tend to be more suitably obtained.

[0031] The rubber composition may contain compounding agents that are commonly used in the rubber industry, such as vulcanizing agents, vulcanization accelerators, vulcanization aids, plasticizers, antioxidants, fillers other than recycled carbon black and petroleum-derived carbon black, etc., within the range that does not impair the effects of the present invention. These may be used alone or in combination of two or more.

[0032] [Vulcanizing Agent] Examples of the vulcanizing agent include sulfur-based vulcanizing agents and peroxide-based vulcanizing agents, which can be used alone or in combination of two or more.

[0033] Examples of the sulfur-based vulcanizing agent include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur.

[0034] Examples of the peroxide vulcanizing agent include 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-dibenzoylperoxyhexane, n-butyl-4,4'-di-t-butylperoxyvalerate, dicumyl peroxide, t-butylperoxybenzoate, di-t-butylperoxy-diisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexyne-3, and 1,3-bis-(t-butylperoxy-isopropyl)benzene.

[0035] When a sulfur-based vulcanizing agent is used as the vulcanizing agent, the content thereof is preferably 0.5 to 15 parts by mass, and particularly preferably 0.6 to 5 parts by mass, per 100 parts by mass of the rubber component, from the viewpoint of significantly exhibiting the effects of the present invention.

[0036] When a peroxide-based vulcanizing agent is used as the vulcanizing agent, the content thereof is preferably 0.5 to 30 parts by mass, more preferably 1 to 20 parts by mass, and even more preferably 1.5 to 10 parts by mass per 100 parts by mass of the rubber component, from the viewpoint of significantly exhibiting the effects of the present invention.

[0037] [Vulcanization Accelerator] The vulcanization accelerator is not particularly limited, but examples thereof include thiuram-based vulcanization accelerators such as dibenzothiazole disulfide, tetramethylthiuram disulfide, dipentamethylenethiuram tetrasulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetrakis(2-ethylhexyl)thiuram disulfide, and tetrabenzylthiuram disulfide; N-oxydiethylene-2-benzothiazolylsulfenamide; N-cyclohexyl-2-benzothiazolylsulfenamide; Examples include sulfenamide-based vulcanization accelerators such as sulfenamide, N-t-butyl-2-benzothiazoylsulfenamide, and N,N'-dicyclohexyl-2-benzothiazoylsulfenamide; thiazole-based vulcanization accelerators such as dibenzothiazyl disulfide, 2-mercaptobenzothiazole, 2-mercaptobenzothiazole sodium salt, and 2-mercaptobenzothiazole zinc salt (ZnMBT); dithioacid salt-based vulcanization accelerators such as zinc dibutyldithiocarbamate; sulfur chloride; and sulfur disulfide. These may be used alone or in combination of two or more.

[0038] When the rubber composition contains a vulcanization accelerator, the content thereof is not particularly limited, but is usually 0.1 to 10 parts by mass, preferably 0.5 to 8 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0039] [Vulcanization Aid] The vulcanization aid is not particularly limited, but examples thereof include zinc oxide, zinc oxide (ZnO), stearic acid, magnesium oxide, etc. These can be used alone or in combination of two or more.

[0040] Examples of the zinc oxide include zinc oxide type 1, zinc oxide type 2, zinc oxide type 3, and fine zinc oxide.

[0041] When the rubber composition contains a vulcanization aid, the content thereof is not particularly limited, but is usually 1 to 25 parts by mass, and preferably 3 to 10 parts by mass, per 100 parts by mass of the rubber component.

[0042] [Plasticizer] The plasticizer is not particularly limited, but examples thereof include aromatic oils, ether ester plasticizers, process oils, etc. These may be used alone or in combination of two or more.

[0043] Examples of the aromatic oils include Diana Process AC-12, Diana Process AC-460, and Diana Process AH-16 (all manufactured by Idemitsu Showa Shell Co., Ltd.), JSO Aroma 790 (manufactured by Japan Sun Oil Co., Ltd.), Aromax 1 and Aromax 3 (both manufactured by Fuji Kosan Co., Ltd.). Examples of the ether ester plasticizers include plasticizers having both an ether bond and an ester bond in one molecule, specifically, adipate ether ester plasticizers such as bis[2-(2-butoxyethoxy)ethyl] adipate. Examples of the process oils include naphthenic oils and paraffinic oils.

[0044] When the rubber composition contains a plasticizer, the content thereof is not particularly limited, but is usually 5 to 100 parts by mass, and preferably 20 to 80 parts by mass, per 100 parts by mass of the rubber component.

[0045] [Antiaging Agent] Examples of the antiaging agent include carbamate-based antiaging agents, phenylenediamine-based antiaging agents, phenol-based antiaging agents, phenylamine-based antiaging agents, diphenylamine-based antiaging agents, quinoline-based antiaging agents, imidazole-based antiaging agents, waxes, etc. These may be used alone or in combination of two or more.

[0046] When the rubber composition contains an antioxidant, the content thereof is not particularly limited, but is usually 0.5 to 10 parts by mass, preferably 0.7 to 8 parts by mass, and more preferably 1 to 6 parts by mass, per 100 parts by mass of the rubber component.

[0047] [Filler] The filler is not particularly limited, but examples thereof include talc, mica, clay, calcium carbonate, etc. These may be used alone or in combination of two or more.

[0048] When the rubber composition contains a filler, the content thereof is not particularly limited, but is usually 20 to 180 parts by mass, and preferably 50 to 160 parts by mass, per 100 parts by mass of the rubber component.

[0049] [Preparation of the Present Rubber Composition] The present rubber composition can be prepared, for example, by appropriately blending the rubber component, recycled carbon black, and, if necessary, the various optional materials described above, and kneading them using a kneading machine such as a kneader, a roll, or a Banbury mixer.

[0050] The rubber composition thus obtained, when analyzed under the image analysis conditions described below, has an area ratio of recycled carbon black having a particle size of 3 to 12 μm of 5.9 to 12.1%, with a preferred lower limit of 7% or more, more preferably 8% or more, and particularly preferably 9% or more. Because the area ratio of recycled carbon black having a particle size of 3 to 12 μm, which causes cracks during extrusion, is within this range, the rubber composition has excellent extrusion processability. Furthermore, because the area ratio of recycled carbon black having a particle size of 3 to 12 μm is within this range, the rubber composition exhibits high volume resistivity and also has excellent carbon neutrality.

[0051] [Image Analysis Conditions] The rubber composition was molded into a 2 mm thick vulcanized rubber sheet according to standard methods, a smooth surface was prepared using a microtome, and the sheet was photographed using a scanning electron microscope. The photographed image was analyzed using Intel's "OpenCV" under the following image analysis conditions. The photograph was taken at a magnification of 150x. If recycled carbon black with a particle size of 100 μm or more was present at the photographed location, the photographed location was changed and four photographs were taken at locations that did not contain recycled carbon black with a particle size of 100 μm or more. The area proportion of recycled carbon black with a particle size of 3 to 12 μm was the average value of the image analysis results for the four photographed locations. [Image analysis conditions] (CLAHE algorithm) Contrast Limit: 2.0 Grid Size: 8,8 (Non-Local Means Filter) h: 15 Template Window Size: 7 Search Window Size: 21 (Adaptive binarization processing) Black Size: 101 C: -4

[0052] Since the rubber composition contains recycled carbon black, it has a high volume resistivity. The volume resistivity (Ω cm) of the rubber composition at 25°C is usually 10 6 Ω cm or more, preferably 10 8 Ω cm or more, more preferably 10 10 The upper limit is not particularly limited, but is usually 10 12 The volume resistivity is Ω·cm or less. By setting the volume resistivity within this range, electrical deterioration of the rubber composition can be suppressed. The volume resistivity can be determined by measurement in accordance with JIS K 6271-1.

[0053] The rubber composition has excellent extrusion moldability and can therefore be suitably used as a material for hoses obtained by extrusion molding, and in particular, can be suitably used as a material for hoses obtained by extrusion molding using an extruder of a pull-down extrusion type in which the rubber is extruded while being pulled.

[0054] An example of a method for producing a hose made from the present rubber composition using a draw-down extrusion type extruder is described below with reference to Figure 1. First, as described above, the rubber component, recycled carbon black, and, if necessary, the various optional materials are appropriately blended and kneaded using a kneader, roll, Banbury mixer, or other kneading machine to prepare the present rubber composition. The present rubber composition is then fed by extruder 2 into supply line 3 and into crosshead die inlet 5. The present rubber composition is then extruded onto mandrel 4 disposed within crosshead die 1, and is pulled along mandrel 4 by a caterpillar (not shown) disposed outside crosshead die outlet 6, thereby forming an unvulcanized hose around the mandrel 4.

[0055] The ratio a / b (draw-down ratio) of the cross-sectional area a of the space (clearance) surrounded by the inner wall of the crosshead die 1 and the mandrel 4 at the crosshead die entrance 5 to the cross-sectional area b of the inner tube extruded from the crosshead die exit 6 is usually 5 or more, preferably 10 to 100. The above-mentioned draw-down ratio can be achieved by adjusting the cross-sectional area a of the space, the distance between the crosshead die entrance 5 and the crosshead die exit 6, and the pulling speed by a caterpillar or the like. If the inner tube extruded from the crosshead die exit 6 is further pulled by a caterpillar or the like, the wall thickness of the hose inner tube can be further reduced.

[0056] Thereafter, if a single-layer hose is to be produced, the unvulcanized hose is heated and vulcanized under predetermined conditions (for example, at 140 to 160°C for 30 to 60 minutes), and the mandrel 4 is removed, thereby producing a single-layer hose.

[0057] Furthermore, in a layered structure such as the hose shown in Figure 2, in which a reinforcing thread layer 12 is provided between an inner rubber layer 11 and an outer rubber layer 13, an unvulcanized hose is prepared from the rubber composition as described above, and then the reinforcing thread layer 12 is formed on the outer surface of the hose by braiding or the like with a predetermined number of reinforcing threads and a predetermined number of threads. If necessary, an adhesive is then applied to the reinforcing thread layer 12 by dipping, spraying, roll coating, brushing, or other methods. The rubber composition for forming the outer rubber layer 13 is then extruded onto the coated surface (or onto the reinforcing thread layer 12) to produce an unvulcanized laminate (hose structure). The unvulcanized laminate (hose structure) thus obtained is heated and vulcanized under predetermined conditions (e.g., 140 to 160°C for 30 to 60 minutes), and the mandrel 4 is then removed to produce a multilayer hose. The mandrel 4 may have a predetermined curved shape, allowing the hose to be formed into a desired curved shape.

[0058] The above-described method for producing a hose made from the present rubber composition using a drop extrusion type extruder is one example, and the present invention is not limited to this configuration as long as a drop extrusion type extruder is used. For example, in the above configuration, the present rubber composition is pulled by a caterpillar, but the present rubber composition may also be pulled in a die. Furthermore, there is no particular limitation on the presence or absence of a mandrel.

[0059] The hose made from the rubber composition thus obtained is not particularly limited and may have a single layer structure or a multi-layer structure in which two or more layers are laminated, but it is preferable that at least the innermost layer (in the case of a single layer structure, that layer) be made from the rubber composition.

[0060] In a hose made from the present rubber composition 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. When an outer rubber layer 3 is provided as shown in FIG. 2, its thickness is preferably 0.25 to 10 mm, more preferably 0.5 to 5 mm. The inner diameter of the present hose is preferably 5 to 60 mm, more preferably 10 to 40 mm.

[0061] Hoses made from the rubber composition of the present invention can exhibit excellent performance as hoses for transporting coolant for vehicles, such as radiator hoses, heater hoses, hoses for transporting coolant for fuel cell systems, and drain hoses.

[0062] Next, examples will be described together with comparative examples, but the present invention is not limited to these examples.

[0063] First, prior to the Examples and Comparative Examples, the following materials were prepared.

[0064] [Rubber component] Rubber component (EPDM, manufactured by Sumitomo Chemical Co., Ltd., product name: Esprene 532, ethylene content: 51% by mass, diene content: 3.5% by mass)

[0065] [Recycled carbon black (recycled CB)] Recycled CB (ash content 17% by mass, "P365" manufactured by Taiwan Environmental Technology Co., Ltd.) [Petroleum-derived carbon black (CB)] CB (DBP absorption capacity: 125 ml / 100 g, average particle size: 62 nm, "SPHERON 5200" manufactured by Cabot Japan Co., Ltd.)

[0066] [Vulcanizing agent] Vulcanizing agent (sulfur-based vulcanizing agent, "SULFAX T-10" manufactured by Tsurumi Chemical Industry Co., Ltd.)

[0067] [Vulcanization accelerators] Vulcanization accelerator 1 (Sansera TET-G manufactured by Sanshin Chemical Industry Co., Ltd.) Vulcanization accelerator 2 (Noccela DM-P manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Vulcanization accelerator 3 (Noccela TRA manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Vulcanization accelerator 4 (Suncerer CZ-G manufactured by Sanshin Chemical Industry Co., Ltd.)

[0068] [Vulcanization aids] Vulcanization aid 1 ("Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd.) Vulcanization aid 2 (powdered stearic acid manufactured by Kao Corporation)

[0069] [Plasticizer] Plasticizer (paraffin-based process oil, Idemitsu Kosan Co., Ltd. "Diana Process PW-380")

[0070] Examples 1 and 2, Comparative Examples 1 and 2, Reference Example 1 The various materials described above were blended in the proportions shown in Table 1 below, and kneaded using a Banbury mixer and an open roll to prepare rubber compositions for extrusion molding.

[0071] The rubber compositions for extrusion molding of the Examples, Comparative Examples, and Reference Examples thus obtained were subjected to the following evaluations, the results of which are shown in Table 1 below.

[0072] [Area proportion of recycled carbon with particle diameter of 3 to 12 μm] The rubber compositions for extrusion molding of the Examples and Comparative Examples were each press-molded using a press vulcanizer to produce a vulcanized rubber sheet with a thickness of 2 mm. A smooth surface was prepared on this vulcanized rubber sheet using a microtome, and photographs were taken with a scanning electron microscope (magnification 150x) at four positions where recycled carbon black with particle diameters of 100 μm or more was not contained. The photographed images were analyzed using Intel's "OpenCV" under the following conditions, and the average value of the four positions analyzed was calculated. [Image analysis conditions] (CLAHE algorithm) Contrast Limit: 2.0 Grid Size: 8,8 (Non-Local Means Filter) h: 15 Template Window Size: 7 Search Window Size: 21 (Adaptive binarization processing) Black Size: 101 C: -4

[0073] [Extrusion Processability] The rubber compositions for extrusion molding of the Examples, Comparative Examples, and Reference Examples were extruded using a φ50 extruder (manufactured by Mitsuba Manufacturing Co., Ltd.) under the following extrusion conditions, and drawn down at a discharge speed 1.5 to 2.0 times faster than the extrusion speed to produce unvulcanized tubes. [Extrusion Conditions] Jig settings: Die 14φ, Spindle 10φ Temperature settings: Head 130°C, Cylinder head 120°C, Cylinder 110°C, Screw 90°C Rotation speed: 20 rpm The unvulcanized tubes obtained above were visually observed and evaluated according to the following evaluation criteria. [Evaluation Criteria] ◯ (Very good): No roughness on the tube surface × (Poor): Roughness on the tube surface (shark skin appearance)

[0074] [Volume Resistivity] The rubber compositions for extrusion molding of the Examples, Comparative Examples, and Reference Examples were each press-molded using a press vulcanizer to produce vulcanized rubber sheets with a thickness of 2 mm, a length of 100 mm, and a width of 100 mm. The volume resistivity VR (Ω·cm) of the resulting vulcanized rubber sheets was measured in accordance with JIS K 6271-1:2015 (Vulcanized rubber and thermoplastic rubber - Determination of electrical resistivity). Specifically, the volume resistivity VR was determined under the following measurement conditions. [Measurement Conditions] Measurement method: Double ring electrode method Guard electrode: Outer diameter 80 mm, inner diameter 70 mm Main electrode: 50 mm Sample outer dimensions: 100 mm x 100 mm Sample thickness: 2 mm Applied voltage: 1 V Detection current range: 200 pA to 20 mA The volume resistivity VR was evaluated according to the following criteria. [Evaluation Criteria] ◯ (very good): Volume resistivity is 10 6 Ω cm or more × (poor): Volume resistivity is 10 6 Less than Ω cm

[0075]

[0076] The results in Table 1 above show that the rubber compositions for extrusion molding in Examples 1 and 2, which contained recycled carbon black with particle sizes of 3 to 12 μm at a specific area ratio as determined by image analysis, exhibited excellent extrusion processability. On the other hand, the rubber compositions for extrusion molding in Comparative Examples 1 and 2, which contained recycled carbon black with particle sizes of 3 to 12 μm at a ratio greater than a specific area ratio as determined by image analysis, exhibited cracks during extrusion molding and exhibited poor extrusion processability. Furthermore, the rubber compositions for extrusion molding in Examples 1 and 2, which contained recycled carbon black, exhibited excellent carbon neutrality due to the presence of recycled carbon black. Furthermore, the rubber compositions for extrusion molding in Examples 1 and 2, which contained recycled carbon black, had higher volume resistivities than the rubber composition for extrusion molding in Reference Example 1, which did not contain recycled carbon black. Such volume resistivities allow them to be used as earths.

[0077] 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.

[0078] The rubber composition for extrusion molding of the present invention can be suitably used for extrusion molding, particularly extrusion molding using an extruder of the die-drawing type. The rubber composition for extrusion molding of the present invention is also suitable as a rubber layer for a hose, and can be suitably used as an automobile hose, for example, an engine cooling system hose such as a radiator hose used to connect the engine and radiator in a vehicle such as an automobile, a heater hose used to connect the engine and heater core, a refrigerant transport hose for an air conditioner, a hose for fuel cell vehicles such as a methanol fuel hose or a hydrogen fuel hose, or a gasoline fuel hose. The hose can also be used in other transportation machinery (airplanes, industrial transportation vehicles such as forklifts, excavators, and cranes, railway vehicles, etc.).

[0079] REFERENCE SIGNS LIST 1 Crosshead die 2 Extruder 3 Supply line 4 Mandrel 5 Inlet of crosshead die 6 Outlet of crosshead die 11 Inner rubber layer 12 Reinforcing thread layer 13 Outer rubber layer

Claims

1. A rubber composition for extrusion molding containing a rubber component and recycled carbon black, wherein when the rubber composition for extrusion molding is analyzed under the following image analysis conditions, the area ratio of recycled carbon black having a particle size of 3 to 12 μm is 5.9 to 12.1%. [Image analysis conditions] (CLAHE algorithm) Contrast Limit: 2.0 Grid Size: 8,8 (Non-Local Means Filter) h: 15 Template Window Size: 7 Search Window Size: 21 (Adaptive binarization processing) Black Size: 101 C: -4 2. The rubber composition for extrusion molding according to claim 1, further comprising petroleum-derived carbon black.

3. The rubber composition for extrusion molding according to claim 2, wherein the mass ratio of the recycled carbon black to the petroleum-derived carbon black (recycled carbon black / petroleum-derived carbon black) is 10 / 90 to 90 / 10.

4. A rubber composition for extrusion molding according to any one of claims 1 to 3, wherein the total amount of carbon black contained in the rubber composition for extrusion molding is 100 parts by mass or more per 100 parts by mass of the rubber component.

5. A hose made from the rubber composition for extrusion molding according to any one of claims 1 to 4.

6. A method for producing a hose according to claim 5, wherein the hose is produced by extrusion molding the rubber composition for extrusion molding using a draw-down extruder.

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