Crosslinked rubber composition, electric wire, cable, and method for manufacturing the crosslinked rubber composition

Abstract

To provide electric wires and cables using a material that combines a high degree of crosslinking and a high crystal content, resulting in excellent abrasion resistance. [Solution] An electric wire comprising a conductor and an insulating layer covering the conductor, wherein the insulating layer is a crosslinked rubber composition comprising a base polymer in which chlorinated polyethylene is mixed with at least an ethylene copolymer resin, the gel fraction of the crosslinked rubber composition is 70% or more, and the residual heat of fusion, expressed as the ratio (percentage) of the heat of fusion obtained by differential scanning calorimetry (DSC) after crosslinking to the heat of fusion obtained by differential scanning calorimetry (DSC) before crosslinking of the crosslinked rubber composition, the crosslinking in the crosslinked rubber composition is performed by electron beam irradiation, and the chlorinated polyethylene is contained in a proportion of at least 50 parts by mass when the base polymer is 100 parts by mass, the electric wire being composed of a crosslinked rubber composition.

Description

Technical Field

[0001] The present invention relates to a crosslinked rubber composition, an electric wire, a cable, and a method for producing the crosslinked rubber composition.

Background Art

[0002] In the coating materials of electric wires and cables, rubber materials are mainly used as coating materials in applications where flexibility or durability is required. General-purpose cables coated with such rubber materials include cab tire cables.

[0003] Cab tire cables are classified into fixed-use and movable-use types depending on their usage. Among these, in movable cab tire cables, since the cable itself moves, resistance to repeated bending and resistance to friction against rubbing in various environments are required.

[0004] On the other hand, there are a wide variety of rubber materials used for the coating materials of electric wires and cables. Among them, chlorinated rubbers are known as high-functional materials excellent in flame retardancy and oil resistance. We have been promoting the development of coating materials using chlorinated polyethylene, which is particularly economical, and have created various inventions so far. In addition, it has been found that alloying an ethylene-based copolymer resin or polyethylene that shows high compatibility with chlorinated polyethylene and has higher heat fluidity than chlorinated polyethylene is effective in improving processability.

[0005] In addition, in the coating materials of electric wires and cables, crosslinking treatment is often performed to chemically bond the intermolecular spaces of the polymer, which is the coating material, in order to improve various properties including heat resistance. Generally, peroxide crosslinking, which is a widely used type of crosslinking treatment, involves blending an organic peroxide as a crosslinking agent in the coating material in advance and heating it after cable coating to decompose the peroxide. The generated active species (radicals) extract hydrogen atoms in the polymer and cause crosslinking (see, for example, Japanese Patent Laid-Open No. 2018-110130).

[0006] To improve the abrasion resistance required for cabtyre cables, measures such as increasing the degree of crosslinking and increasing the molecular weight and crystalline content of the polymer are effective. For example, crystals in a polymer are formed when some molecules adopt a strong crystalline structure at temperatures below the melting point of the crystal. The higher the structural regularity of the polymer molecules, the easier it is to form a crystalline structure. The crystalline content can be indicated by the heat of fusion measured by differential scanning calorimetry (DSC). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2018-110130 [Overview of the project] [Problems that the invention aims to solve]

[0008] While crosslinking using peroxides is desirable due to its high degree of crosslinking, it can reduce the amount of crystals in the polymer, potentially decreasing wear resistance. This is thought to be because crosslinking using peroxides requires heating to high temperatures to decompose the peroxides. As a result, the crystals melt due to the heat, and the crosslinking occurs in this molten state, reducing the structural regularity of the polymer.

[0009] Therefore, the object of the present invention is to provide electric wires and cables using a material that has both a high degree of crosslinking and a high crystal content, and exhibits excellent wear resistance. Other purposes and novel features will become apparent from the description and accompanying drawings herein. [Means for solving the problem]

[0010] An electric wire according to one embodiment of the present invention is an electric wire having a conductor and an insulating layer covering the conductor, wherein the insulating layer is a crosslinked rubber composition containing a base polymer obtained by mixing chlorinated polyethylene with at least an ethylene copolymer resin, wherein the gel fraction of the crosslinked rubber composition is 70% or more, and the residual heat of fusion, expressed as the ratio (percentage) of the heat of fusion obtained by differential scanning calorimetry (DSC) after crosslinking to the heat of fusion obtained by differential scanning calorimetry (DSC) before crosslinking, is 70% or more, the crosslinking in the crosslinked rubber composition is performed by electron beam irradiation, and the chlorinated polyethylene is contained in an amount of at least 50 parts by mass when the base polymer is 100 parts by mass.

[0011] In one embodiment of the present invention, the electric wire is such that the ethylene-based copolymer resin is an ethylene vinyl acetate copolymer resin or an ethylene ethyl acrylate copolymer resin.

[0012] A cable according to one embodiment of the present invention comprises a conductor, an insulating layer covering the conductor, and a covering layer covering the insulating layer, wherein the covering layer is a crosslinked rubber composition containing a base polymer of chlorinated polyethylene mixed with at least an ethylene copolymer resin, wherein the gel fraction of the crosslinked rubber composition is 70% or more, and the residual heat of fusion, expressed as the ratio (percentage) of the heat of fusion measured by differential scanning calorimetry (DSC) after crosslinking to the heat of fusion measured by differential scanning calorimetry (DSC) before crosslinking, is 70% or more, the crosslinking in the crosslinked rubber composition is performed by electron beam irradiation, and the chlorinated polyethylene is contained in an amount of at least 50 parts by mass when the base polymer is 100 parts by mass.

[0013] A method for producing a crosslinked rubber composition according to one embodiment of the present invention involves preparing a rubber composition containing a base polymer in which chlorinated polyethylene is mixed with at least an ethylene copolymer resin, irradiating the rubber composition with an electron beam to crosslink it, and producing a crosslinked rubber composition, wherein the gel fraction of the crosslinked rubber composition is 70% or more, and the residual heat of fusion, expressed as the ratio (percentage) of the heat of fusion after crosslinking to the heat of fusion obtained by differential scanning calorimetry (DSC) before crosslinking, is 70% or more, and the chlorinated polyethylene is contained in at least 50 parts by mass or more when the base polymer is 100 parts by mass. [Effects of the Invention]

[0014] According to a method for producing a crosslinked rubber composition, which is one embodiment of the present invention, it is possible to provide a material that has both a high degree of crosslinking and a high crystal content, and has excellent wear resistance.

[0015] Furthermore, according to one embodiment of the present invention, the electric wire and cable can have both a high degree of crosslinking and a high crystal content, resulting in excellent abrasion resistance. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic cross-sectional view of a cable, which is one embodiment of the present invention. [Figure 2] This diagram shows the schematic configuration of the extruder used in the example to carry out the cable manufacturing (extrusion) process. [Modes for carrying out the invention]

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all the drawings used to describe the embodiments, the same reference numerals are used for members having the same function, and repeated descriptions of them will be omitted. Furthermore, in the following embodiments, descriptions of the same or similar parts will not be repeated in principle, except when particularly necessary.

[0018] <Embodiment> As described above, in order to obtain a crosslinked rubber composition excellent in wear resistance by making the crosslinking degree high and maintaining a large amount of crystals in the polymer, the inventors considered applying crosslinking by electron beam irradiation that does not require high temperature during crosslinking, and examined a crosslinked rubber composition containing a mixture containing chlorinated polyethylene and at least an ethylene-based copolymer resin as a base polymer.

[0019] Then, the inventors found that a crosslinked rubber composition having predetermined properties in a crosslinked rubber composition having such a composition would result in a crosslinked rubber composition excellent in wear resistance, and completed the present invention. Hereinafter, the crosslinked rubber composition, electric wire, and cable according to the present embodiment will be described in detail.

[0020] [Crosslinked Rubber Composition] The crosslinked rubber composition according to the present embodiment is configured to include a base polymer in which at least an ethylene-based copolymer resin is mixed with chlorinated polyethylene.

[0021] (Base Polymer) The base polymer used in the present embodiment is a base polymer in which at least an ethylene-based copolymer resin is mixed with chlorinated polyethylene. Hereinafter, each component will be described in detail.

[0022] 〈Chlorinated Polyethylene〉 The chlorinated polyethylene used here can be used without particular limitation as long as it is a known chlorinated polyethylene.

[0023] From the viewpoint of improving wear resistance, it is preferable to use crystalline grade chlorinated polyethylene as this chlorinated polyethylene. Generally, as chlorinated polyethylene having a crystal amount that is regarded as a crystalline grade, specifically, chlorinated polyethylene having a heat of fusion of 2 J / g to 80 J / g by differential scanning calorimetry (DSC) is preferable. The heat of fusion of chlorinated polyethylene is more preferably 5 J / g to 30 J / g, and particularly considering the balance between wear resistance and flexibility, the heat of fusion is even more preferably 10 J / g to 20 J / g.

[0024] In this specification, the heat of fusion is the heat of fusion measured by differential scanning calorimetry (DSC), and it varies depending on the amount of crystals contained in the resin being measured. Melting of chlorinated polyethylene crystals occurs at approximately 100-130°C. The measurement can be performed using an aluminum pan under the conditions of a heating rate of 10°C / min, a cooling rate of 5°C / min, an upper temperature limit of 150°C, and a lower temperature limit of 25°C. To eliminate the influence of thermal history, the heat of fusion value from the second heating was used. The amount of crystals in the resin can be evaluated using this heat of fusion. Therefore, below, this heat of fusion may also be described as the numerical value of the amount of crystals.

[0025] Furthermore, it is preferable that this chlorinated polyethylene has a chlorine content of 20-45% by mass, and a Mooney viscosity of 120 or less after 4 minutes following preheating at 121°C for 1 minute. From the viewpoint of balancing flame retardancy and flexibility, it is more preferable that the chlorine content is 25-40% by mass, and the Mooney viscosity of 90 or less after 4 minutes following preheating at 121°C for 1 minute.

[0026] (Ethylene copolymer resin) The ethylene copolymer resin used here may be any known ethylene copolymer resin and is not particularly limited. Specifically, examples of this ethylene copolymer resin include ethylene vinyl acetate copolymer resin, ethylene methyl acrylate copolymer resin, ethylene ethyl acrylate copolymer resin, ethylene propylene copolymer, ethylene propylene diene copolymer, and modified versions thereof. A mixed resin obtained by mixing multiple types of these ethylene copolymer resins may also be used.

[0027] Among these, it is particularly preferable to use ethylene vinyl acetate copolymer resin, ethylene ethyl acrylate copolymer resin, etc., in order to maintain a balance between abrasion resistance, flexibility, and good moldability when extruding and covering cables.

[0028] Furthermore, as the ethylene copolymer resin, an ethylene copolymer resin with a melting point of 70°C or higher is preferred, and from the viewpoint of the amount of crystals in the resin, an ethylene copolymer resin with a melting point of 80°C or higher is more preferred, and an ethylene copolymer resin with a melting point of 85°C or higher is even more preferred. Multiple types of ethylene copolymer resins with a melting point of 70°C or higher may be used in combination, or an ethylene copolymer resin with a melting point of 70°C or higher may be mixed with an ethylene copolymer resin with a melting point of 70°C or higher in the region in which the properties are expressed. Specifically, examples of this ethylene copolymer resin include ethylene-α-olefin copolymers, and more specifically, ethylene-butene copolymers.

[0029] Furthermore, while the ethylene copolymer resin is not limited to its physical properties, for example, it is sufficient if the melt flow rate (MFR) at 190°C and 2.16 kgf is 6 g / 10 min or less, and from the viewpoint of improving abrasion resistance, it is preferable that the melt flow rate (MFR) at 190°C and 2.16 kgf is 1 g / 10 min or less.

[0030] In the base polymer obtained by mixing the above-mentioned chlorinated polyethylene with at least an ethylene copolymer resin, from the viewpoint of abrasion resistance, processability, and flexibility, it is preferable that the content of chlorinated polyethylene be at least 50 parts by mass when the base polymer is 100 parts by mass.

[0031] The mixing ratio of the resins constituting this base polymer is preferably in the range of 90:10 to 50:50 by mass ratio of chlorinated polyethylene and ethylene copolymer resin, more preferably in the range of 80:20 to 60:40, and a ratio range of around 70:30 is particularly preferred because it allows for excellent properties in all aspects, including abrasion resistance, processability, and flexibility.

[0032] Furthermore, in addition to chlorinated polyethylene and ethylene-based copolymer resins, other rubbers and resins can be mixed into the base polymer. Specifically, examples include polyvinyl chloride, chloroprene rubber, ethylene propylene rubber, polyolefin resins, low-density polyethylene, high-density polyethylene, linear low-density polyethylene, polyurethane, and modified versions thereof, as well as mixtures of multiple types of these.

[0033] (Additives) The crosslinked rubber composition of this embodiment may contain additives such as plasticizers, lubricants, reinforcing agents, fillers, flame retardants, hydrogen chloride scavengers, antioxidants, and crosslinking aids.

[0034] Examples of plasticizers include mineral oil, phthalates such as bis(2-ethylhexyl) phthalate, diisononyl phthalate, diisodecyl phthalate, and diundecyl phthalate, adipic acids such as bis(2-ethylhexyl) adipate, diisononyl adipate, diisodecyl adipate, and bis(2-butoxyethyl) adipate, polyesters, phosphoric acids, epoxys, and trimellitic acids. These can be used individually or in combination of two or more.

[0035] Examples of lubricants include fatty acid amides, zinc stearate, silicones, hydrocarbons, esters, alcohols, and metal soaps. Examples of reinforcing agents include carbon black and silica.

[0036] Examples of fillers include diatomaceous earth, calcined diatomaceous earth, quartz, cristobalite, kaolinite, kaolin clay, calcined clay, talc, muscovite, wollastonite, serpentine, pyrophyllite, calcium carbonate, barium sulfate, titanium dioxide, magnesium carbonate, dolomite, and aluminum oxide.

[0037] Examples of flame retardants include metal hydroxides, halogen-based, phosphorus-based, and antimony-based flame retardants.

[0038] Examples of hydrogen chloride scavenging agents include epoxy group-containing compounds, hydrotalcites, lead-containing compounds such as tribasic lead sulfate, tin-containing compounds, or metal soaps.

[0039] Examples of antioxidants include phenolic antioxidants, sulfuric antioxidants, phenol / thioester antioxidants, amine antioxidants, and phosphite antioxidants.

[0040] Examples of crosslinking aids include trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate, triallyl isocyanurate, triallyl cyanurate, N,N'-metaphenylene bismaleimide, ethylene glycol dimethacrylate, zinc acrylate, and zinc methacrylate.

[0041] (Regarding the degree of crosslinking and crystalline content) The above-mentioned materials are thoroughly kneaded to prepare a rubber composition before crosslinking, and then subjected to a crosslinking treatment to obtain the crosslinked rubber composition of this embodiment. The kneading of the materials can be done using any known kneading method and is not particularly limited. For example, a kneader is often used, but other than a kneader, any commonly used kneading or reaction equipment such as a roll machine, extruder, mixer, or autoclave is acceptable and is not particularly limited, nor are the kneading conditions limited to those described above.

[0042] Next, the crosslinking treatment can be carried out by irradiation with an electron beam (for example, an accelerating voltage of 2 MV and an electron beam irradiation dose of 100 kGy). The irradiation conditions at this time are not limited in any way, as long as the properties of the resulting crosslinked rubber composition satisfy the following conditions.

[0043] Furthermore, at an acceleration voltage of 2MV, the electron beam irradiation dose is preferably 20 to 100 kGy, and more preferably 30 to 75 kGy, considering the balance between wear resistance and degree of crosslinking.

[0044] The crosslinked rubber composition obtained by this crosslinking treatment preferably has a gel fraction of 70% or more. The gel fraction is an indicator for evaluating the degree of crosslinking of the crosslinked rubber composition, and can be calculated, for example, as follows.

[0045] To measure the gel fraction, the materials to be used should be weighed beforehand. Next, the materials are immersed in xylene heated to 110°C for 24 hours. After immersion, the materials are left at atmospheric pressure at 20°C for 3 hours, and then vacuum-dried at 80°C for 4 hours. The mass of the treated material is then weighed, and the gel fraction can be calculated as the ratio (percentage) of the mass after immersion (after treatment) to the mass before immersion (before treatment).

[0046] Furthermore, this crosslinked rubber composition has a residual heat of fusion ratio of 70% or more, which is expressed as the ratio (percentage) of the heat of fusion B obtained by differential scanning calorimetry (DSC) after crosslinking to the heat of fusion A obtained by differential scanning calorimetry (DSC) before crosslinking. In other words, heat of fusion B is the heat of fusion of the crosslinked rubber composition and the amount of crystals after crosslinking, while heat of fusion A is the heat of fusion of the rubber composition before crosslinking and the amount of crystals before crosslinking can be evaluated. From these heats of fusion, the residual heat of fusion ratio can be calculated using the following formula. Percentage of residual heat of fusion (%) = {(Heat of fusion B) / (Heat of fusion A)} × 100

[0047] By maintaining a residual heat of fusion rate of 70% or more, the reduction in the amount of crystals before and after crosslinking can be suppressed, ensuring a sufficient amount of crystals after crosslinking. As a result, the resulting crosslinked rubber composition can exhibit excellent abrasion resistance.

[0048] As described above, by having a predetermined gel fraction and a predetermined residual heat of fusion, it is possible to achieve both a high degree of crosslinking and a high crystal content, resulting in a crosslinked rubber composition with excellent abrasion resistance.

[0049] [Electric wires, cables] An electric wire or cable in one embodiment of the present invention comprises a conductor and a covering layer that covers and protects the conductor, wherein the covering layer is made of the cross-linked rubber composition of this embodiment described above. The covering layer can be used to directly cover the conductor to form an electric wire, or it can be used to indirectly cover the conductor and an insulating layer that covers the conductor to form a cable.

[0050] A cross-sectional view of the cable according to this embodiment is shown in Figure 1. As shown in Figure 1, the cable 1 is composed of a conductor 2, an insulating layer 3, and a covering layer 4.

[0051] Conductor 2 can be any commonly used metal wire, such as copper wire, copper alloy wire, aluminum wire, gold wire, or silver wire. Alternatively, conductor 2 may be a metal wire plated with tin, nickel, or other metals. Furthermore, a stranded conductor, made by twisting metal wires together, can also be used as conductor 2.

[0052] The insulating layer 3 can be formed from any insulating material commonly used in electric wires, and is not particularly limited. Examples of insulating materials for this insulating layer 3 include ethylene-propylene copolymer, polyvinyl chloride, fluororesin, polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, polyolefin resin, natural rubber, and other synthetic rubbers. These can be used individually or in combination, and the presence or absence of crosslinking treatment is not a requirement.

[0053] The coating layer 4 is composed of the crosslinked rubber composition of this embodiment as described above, and its gel fraction is 70% or more, and its residual heat of fusion is 70% or more.

[0054] As for the manufacturing method of this cable, an extruder is used to coat the outer circumference of the insulating layer 3 formed on the conductor 2 with the rubber composition described above before crosslinking, and then the coating layer is crosslinked by electron beam irradiation, thereby manufacturing the cable 1.

[0055] Figure 2 is a schematic diagram showing an example of an extruder for manufacturing cables in this embodiment. As shown in Figure 2, the extruder 11 comprises a cylinder 20, a screw 13 rotatably mounted within the cylinder 20, a hopper 12 for supplying material into the cylinder 20, and a crosshead 16. The extruder 11 also comprises a neck 15 between the crosshead 16 and the screw 13, and a breaker plate 14 between the neck 15 and the screw 13. The crosshead 16 has a die 17, and a cable core 18, made by twisting together electric wires (conductors covered with an insulator) that pass through the crosshead 16, is covered with a sheath within the crosshead 16, passes through the die 17 and is drawn out from inside the crosshead 16 as an unbridged cable 19.

[0056] The uncrosslinked cable 19 has its outer circumference covered with a rubber composition before crosslinking. This rubber composition is crosslinked by electron beam irradiation to produce a cable 1 covered with a crosslinked rubber composition. The crosslinking treatment can be carried out under the conditions described in the method for manufacturing the crosslinked rubber composition.

[0057] The cable obtained in this way is, for example, a cable with the configuration shown in Figure 1, and is particularly suitable for multi-core cables having wires with a conductor cross-sectional area of ​​38 mm² or less, as specified in the Electrical Appliances and Materials Safety Act (Appendix 1) and JIS C3327.

[0058] Although this has been described in the context of a cable configuration, it is also possible to form the insulator of an insulated wire, which has an insulator covering the conductor 2, using the cross-linked rubber composition of this embodiment. [Examples]

[0059] Next, this embodiment will be described in detail with reference to examples and comparative examples.

[0060] [Examples 1-5, Comparative Examples 1-6] The mixing of various additives into the base polymer, the manufacture of cables using the prepared compounds, and the cross-linking process were carried out as follows. The following conditions are examples only and are not limiting.

[0061] (Preparation of rubber composition before crosslinking) In a 25L pressurized kneader (kneader tank temperature controlled to 100°C), chlorinated polyethylene, ethylene copolymer resin, hydrogen chloride scavenger, plasticizer, lubricant, reinforcing agent, filler, flame retardant, crosslinking aid, etc., were added according to the formulations shown in Tables 3-4, and the mixture was pressurized and kneaded for 10 minutes at a rotor speed of 10 rpm.

[0062] By adding the ethylene copolymer resin at the end of the mixing process, it is possible to increase the material viscosity during additive mixing and improve the dispersibility of the additive. Note that these conditions are examples only and are not limiting.

[0063] After the mixing process is complete, the material is promptly discharged into a single-screw extruder hopper, extruded into strands, water-cooled, and then pelletized to produce pellets of the rubber composition. The granulation method is not limited to the above; for example, pellets may be produced using a hot-cutting device without water cooling. A release agent can also be used to prevent the pellets from sticking together. The release agent can be of any form, such as powder, liquid, or mist, but using talc, for example, is effective for economic reasons.

[0064] (Cable manufacturing and cross-linking process) In this embodiment and comparative example, the extruder 11 shown in Figure 2 was used to produce uncrosslinked cables as follows.

[0065] First, a wire core was obtained by twisting together multiple strands of tin-plated soft copper wire to form a conductor with a cross-sectional area of ​​38 mm² (outer diameter 9.1 mm), onto which an ethylene-propylene rubber copolymer mixture was extruded to a thickness of 1.2 mm as an insulator and then crosslinked. Three of these wire cores were twisted together to form a cable core, and then pellets of the rubber compositions described in each example above were extruded to a thickness of 3.0 mm using a single-screw extruder with a screw diameter of 90 mm under the conditions described in Table 1 or Table 2 to produce an uncrosslinked cable (finished outer diameter approximately 31 mm). The produced uncrosslinked cable was then wound onto a drum.

[0066] Tables 1 and 2 show the extrusion conditions in the cable extrusion process. In this case, cylinders 1 to 5 are connected from the hopper side to the head side in order from top to bottom, forming cylinder 20. Also, the flanges in Tables 1 and 2 are the ends of cylinder 20, specifically the ends on the neck 15 side.

[0067] Table 1 shows the extrusion conditions for uncrosslinked cables (Examples 1-5, Comparative Examples 1-3) for electron beam irradiation crosslinking, and Table 2 shows the extrusion conditions for uncrosslinked cables (Comparative Examples 4-6) for peroxide crosslinking.

[0068] In peroxide crosslinking, extrusion must be performed at a temperature above the melting point of the crystal and below the decomposition temperature of the peroxide, thus limiting the extrusion temperature and reducing manufacturing flexibility. However, electron beam irradiation crosslinking has the advantage of offering greater manufacturing flexibility, as there are no restrictions on the extrusion temperature as long as it is above the melting point of the crystal.

[0069] Next, in Examples 1-5 and Comparative Examples 1-3, uncrosslinked cables were pulled from drums and irradiated with an electron beam (acceleration voltage 2 MV, electron beam irradiation dose 100 kGy) using an electron beam irradiation device to produce cables coated with a crosslinked rubber composition. The electron beam irradiation conditions at this time are not limited to those specified.

[0070] The crosslinking treatment conditions are not limited to those described above.

[0071] In Comparative Examples 4-6, the uncrosslinked cables were pulled out of the drum and heated to a temperature above the decomposition temperature of the peroxides to perform the crosslinking treatment.

[0072] [Table 1]

[0073] [Table 2]

[0074] [Evaluation of characteristics] The compound after mixing and the cable after cross-linking were evaluated as follows. The evaluation results, along with the composition, are shown in Tables 3 and 4.

[0075] (1) Crystallized amount (heat of fusion) Differential scanning calorimetry (DSC) was performed to measure the heat of fusion of the crosslinked rubber composition before and after crosslinking. Peaks around 100-130°C were attributed to chlorinated polyethylene, and peaks around 60-100°C were attributed to ethylene copolymer resin. The heat of fusion values ​​at each peak were summed and evaluated as the amount of crystals. Measurements were performed using an aluminum pan under the conditions of a heating rate of 10°C / min, a cooling rate of 5°C / min, an upper temperature limit of 150°C, and a lower temperature limit of 25°C. To eliminate the influence of thermal history, the heat of fusion value from the second heating cycle was used.

[0076] The amount of crystals in the rubber composition before crosslinking is shown as "Amount of crystals (before crosslinking)," and the amount of crystals in the crosslinked rubber composition after crosslinking is shown as "Amount of crystals (after crosslinking)."

[0077] (2) Crystal ratio after crosslinking In (1) above, the heat of fusion of the rubber composition before crosslinking was denoted as heat of fusion A, and the heat of fusion of the crosslinked rubber composition after crosslinking was denoted as heat of fusion B. The residual heat of fusion rate obtained by the following formula was evaluated as the amount of crystals remaining after the crosslinking treatment. A residual heat of fusion rate of 70% or more was considered good (symbol ○) as having a sufficient amount of crystals to contribute to wear resistance, a rate of 77% or more was considered excellent (symbol ◎) as having a particularly sufficient amount of crystals, and a rate of less than 70% was considered poor (symbol ×). • Percentage of remaining heat of fusion (%) = (Heat of fusion B / Heat of fusion A) × 100

[0078] (3) Degree of crosslinking (gel fraction) A 0.5 g sample taken from the crosslinked rubber composition was placed in a 40-mesh brass wire mesh and extracted with xylene in a 110°C oil bath for 24 hours. After air drying overnight and vacuum drying at 80°C for 4 hours, the mass was weighed. From the obtained value, the gel fraction, an index indicating the degree of crosslinking of the material, was calculated using the following formula. A gel fraction of 70% by mass or more was classified as good (symbol ○), indicating sufficient heat resistance for practical use and also contributing sufficiently to abrasion resistance; 80% by mass or more was classified as excellent (symbol ◎), indicating a particularly sufficient degree of crosslinking; and less than 70% by mass was classified as poor (symbol ×). Gel fraction = (b / a) × 100 a: Mass of ingredients (g) b: Mass (g) after extraction and drying

[0079] (4) Abrasion resistance (abrasion characteristics) The pellets of the above rubber composition were formed into 2 mm thick sheet pieces using a hot press at 180°C. In Comparative Examples 4 to 6, crosslinking was performed simultaneously with this forming. In Examples 1 to 5 and Comparative Examples 1 to 3, the sheet pieces were irradiated with an electron beam (acceleration voltage: 2 MV, electron beam irradiation dose: as shown in Tables 3 to 4) using an electron beam irradiation device to produce crosslinked sheet pieces.

[0080] Cross-linked sheet pieces were mounted on a jig simulating a cable shape, and abrasion tests were conducted in accordance with JIS C3005. The mass of the weight was 5 kg, and the rotation speed of the grinding wheel disc was set to 75 rpm. The abrasion volume was calculated from the mass loss before and after the test and the specific gravity of each sample. Samples with an abrasion volume of 0.6 mL or less were classified as good (symbol ○), those with an abrasion volume of 0.5 mL or less were classified as excellent (symbol ◎) indicating particularly superior abrasion resistance, and those exceeding 0.6 mL were classified as poor (symbol ×). • Wear volume = (Sheet mass before test - Sheet mass after test) / Specific gravity

[0081] (5) Overall Judgment In the characteristics shown in (2) to (4) above, those that were good or excellent in all characteristics were marked as passing (indicated by ○ or ◎, where ◎ indicates that all characteristics were excellent), and those that were poor in even one characteristic were marked as failing (indicated by ×).

[0082] [Table 3]

[0083] [Table 4]

[0084] Of the products shown in Tables 3 and 4, *1: "Elastrene 252B" (crystal weight 20 J / g) is manufactured by Showa Denko Corporation, *2: "VF-120T" (melting point: 85°C, MFR: 1 g / 10 min, crystal weight 11 J / g) is manufactured by Ube Maruzen Polyethylene Co., Ltd., *3: "Carbon Black" (arithmetic mean particle size: 68 nm) is HTC#S manufactured by Nippon Steel Carbon Co., Ltd., and *4: "DCP" is dicumyl peroxide manufactured by NOF Corporation.

[0085] From the above results, it was found that by applying electron beam crosslinking to a rubber composition mixed with chlorinated polyethylene and ethylene copolymer resin, it is possible to maintain high levels of both crystal content and degree of crosslinking even after crosslinking treatment, thereby obtaining excellent abrasion resistance. Furthermore, from Comparative Examples 4 to 6, it became clear that in peroxide crosslinking, while the degree of crosslinking increased with increasing peroxide content, the crystal content decreased significantly. Therefore, by performing electron beam crosslinking on this rubber composition, it is possible to obtain excellent abrasion resistance in a well-balanced manner by achieving both high crystal content and degree of crosslinking, in addition to oil resistance and good processability when extruding and coating cables, and the appearance is also good. Furthermore, it was found that by setting the electron beam irradiation amount to 30 to 100 kGy at an acceleration voltage of 2 MV, excellent abrasion resistance can be obtained.

[0086] Although the present inventors have described the invention in detail based on embodiments above, it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from its essence. [Explanation of symbols]

[0087] 1 Cable 2 conductors 3. Insulating layer 4 Covering layer 11 Extruder 12 Hoppers 13 Screw 14 Breaker Plate 15 neck 16 Crosshead 17 dice 18 Cable Cores 19 Unbridged Cables 20 cylinders

Claims

1. A wire having a conductor and an insulating layer covering the conductor, The insulating layer is a crosslinked rubber composition comprising a base polymer in which chlorinated polyethylene is mixed with at least an ethylene copolymer resin, wherein the gel fraction of the crosslinked rubber composition is 70% or more, and the residual heat of fusion, expressed as the ratio (percentage) of the heat of fusion measured by differential scanning calorimetry (DSC) after crosslinking to the heat of fusion measured by differential scanning calorimetry (DSC) before crosslinking, is 70% or more. The crosslinking in the aforementioned crosslinked rubber composition was performed by electron beam irradiation. The electric wire is made of a cross-linked rubber composition, in which the chlorinated polyethylene is present in an amount of at least 50 parts by mass when the base polymer is 100 parts by mass.

2. In the electric wire described in claim 1, An electric wire wherein the ethylene-based copolymer resin is an ethylene vinyl acetate copolymer resin or an ethylene ethyl acrylate copolymer resin.

3. In the electric wire described in claim 1, An electric wire in which the ethylene copolymer resin has a melting point of 80°C or higher.

4. A cable having a conductor, an insulating layer covering the conductor, and a covering layer covering the insulating layer, The coating layer is a crosslinked rubber composition comprising a base polymer in which chlorinated polyethylene is mixed with at least an ethylene copolymer resin, wherein the gel fraction of the crosslinked rubber composition is 70% or more, and the residual heat of fusion, expressed as the ratio (percentage) of the heat of fusion measured by differential scanning calorimetry (DSC) after crosslinking to the heat of fusion measured by differential scanning calorimetry (DSC) before crosslinking, is 70% or more. The crosslinking in the aforementioned crosslinked rubber composition was performed by electron beam irradiation. The cable is made of a cross-linked rubber composition, in which the chlorinated polyethylene is present in an amount of at least 50 parts by mass when the base polymer is 100 parts by mass.

5. In the cable according to claim 4, A cable in which the ethylene-based copolymer resin is an ethylene vinyl acetate copolymer resin or an ethylene ethyl acrylate copolymer resin.

6. In the cable according to claim 4, A cable in which the ethylene copolymer resin has a melting point of 80°C or higher.

7. A rubber composition is prepared that includes a base polymer in which chlorinated polyethylene is mixed with at least an ethylene copolymer resin. A method for producing a crosslinked rubber composition by irradiating the aforementioned rubber composition with an electron beam to cause crosslinking, The gel fraction of the crosslinked rubber composition is 70% or more, and the residual heat of fusion, expressed as the ratio (percentage) of the heat of fusion measured by differential scanning calorimetry (DSC) after crosslinking to the heat of fusion measured by differential scanning calorimetry (DSC) before crosslinking, is 70% or more. A method for producing a crosslinked rubber composition, wherein the chlorinated polyethylene is contained in an amount of at least 50 parts by mass when the base polymer is 100 parts by mass.

8. In the method for producing the crosslinked rubber composition described in claim 7, A method for producing a crosslinked rubber composition, wherein the ethylene-based copolymer resin is an ethylene vinyl acetate copolymer resin or an ethylene ethyl acrylate copolymer resin.

9. In the method for producing the crosslinked rubber composition described in claim 7, A method for producing a crosslinked rubber composition, wherein the melting point of the ethylene copolymer resin is 80°C or higher.

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