Electrical wire and multicore cable

Abstract

This electrical wire is provided with a conductor and a coating that covers the conductor. The coating includes a first layer and a second layer formed on the first layer. The first layer includes a crosslinked polyolefin resin as a main component and the second layer includes a silsesquioxane as a main component. The silsesquioxane is a polymer having (RSiO3 / 2) as a structural unit, R is a polymerizable group, and the thickness of the second layer is 0.1 μm or more and 100 μm or less.

Description

Wires and multi-core cables

[0001] The present disclosure relates to electrical wires and multi-conductor cables.

[0002] Conventionally, "electric wires having a conductor and a coating covering the conductor" and "multi-core cables having an electric wire" have been used for various purposes such as automobiles, industrial robots, electrical equipment, and thermal equipment (Patent Documents 1 to 5).

[0003] Japanese Patent Application Laid-Open No. 9-288914 Japanese Utility Model Application Laid-Open No. 4-61808 Japanese Patent Application Laid-Open No. 2000-30535 Japanese Patent Application Laid-Open No. 8-255513 International Publication No. 2018 / 074233

[0004] The electric wire of the present disclosure is an electric wire including a conductor and a coating covering the conductor, the coating including a first layer and a second layer formed on the first layer, the first layer including a crosslinked polyolefin resin as a main component, and the second layer including a silsesquioxane as a main component, the silsesquioxane being (RSiO ３／２ ) as a structural unit, R is a polymerizable group, and the thickness of the second layer is 0.1 μm or more and 100 μm or less.

[0005] Fig. 1 is a schematic perspective view of an electric wire according to an embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a schematic view illustrating a part of the evaluation methods of Evaluation Tests 1 to 3.

[0006] [Problem to be Solved by the Present Disclosure] When electric wires are used for various purposes such as automobiles, industrial robots, electrical equipment, thermal equipment, etc., the conditions under which the electric wires are used may be severe. In particular, when the conditions under which the electric wires are used include severe temperature conditions under which deterioration due to oil is likely to occur, it is required to impart excellent heat resistance and excellent oil resistance to the electric wires.

[0007] Therefore, an object of the present disclosure is to provide an electric wire having both excellent heat resistance and excellent oil resistance, and a multi-core cable including such an electric wire.

[0008] Effect of the Present Disclosure According to the present disclosure, it is possible to provide an electric wire having both excellent heat resistance and excellent oil resistance, and a multi-core cable including the electric wire.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) An electric wire according to the present disclosure is an electric wire including a conductor and a coating covering the conductor, wherein the coating includes a first layer and a second layer formed on the first layer, the first layer contains a crosslinked polyolefin resin as a main component, and the second layer contains silsesquioxane as a main component, and the silsesquioxane is (RSiO ３／２ ) as a structural unit, R is a polymerizable group, and the thickness of the second layer is 0.1 μm or more and 100 μm or less.

[0010] According to the present disclosure, it is possible to provide an electric wire having both excellent heat resistance and excellent oil resistance, and a multi-core cable including the electric wire.

[0011] (2) In the above (1), the cross-linked polyolefin resin may be a polyethylene resin, a copolymer of ethylene and a polar comonomer, or both, thereby providing an electric wire and a multi-core cable including the electric wire that have both superior heat resistance and superior oil resistance.

[0012] (3) In the above (2), the copolymer of ethylene and the polar comonomer may be an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, or both, thereby providing an electric wire having both superior heat resistance and superior oil resistance, and a multi-core cable including the electric wire.

[0013] (4) In the above (1), the cross-linked polyolefin resin may be a resin modified with one compound selected from the group consisting of maleic anhydride, carboxylic acid, and compounds having an epoxy group, thereby making it possible to provide an electric wire and a multi-core cable including the electric wire that have both better heat resistance and better oil resistance.

[0014] (5) In the above (1), the cross-linked polyolefin resin of the first layer may be a resin that has been subjected to a hydrophilic surface treatment, thereby making it possible to provide an electric wire and a multi-core cable including the electric wire that have both better heat resistance and better oil resistance.

[0015] (6) In the above (5), the hydrophilic surface treatment may be at least one surface treatment selected from the group consisting of corona treatment, plasma treatment, ozone treatment, and etching treatment with active sodium. This makes it possible to provide an electric wire and a multi-core cable including the electric wire that have both better heat resistance and better oil resistance.

[0016] (7) In any one of the above (1) to (6), the polymerizable group may be a radically polymerizable group or a cationically polymerizable group, thereby making it possible to provide an electric wire having both superior heat resistance and superior oil resistance, and a multi-core cable including the electric wire.

[0017] (8) In any one of the above (1) to (6), the polymerizable group may be one type of polymerizable group selected from the group consisting of an acryloyl group, a methacryloyl group, and an oxetanyl group. This makes it possible to provide an electric wire having both better heat resistance and better oil resistance, and a multi-core cable including the electric wire.

[0018] (9) A multi-core cable of the present disclosure includes the electric wires described in (1) to (8) above.

[0019] According to the present disclosure, it is possible to provide a multi-core cable including electric wires that have both excellent heat resistance and excellent oil resistance.

[0020] [Details of the embodiment of the present disclosure] Specific examples of electric wires and multi-core cables according to one embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference symbols represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0021] In the present disclosure, the notation in the form of "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the units of A and B are the same.

[0022] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0023] [Embodiment 1: Electric Wire] An electric wire according to an embodiment of the present disclosure will be described with reference to Figs. 1 and 2. Fig. 1 is a schematic perspective view of an electric wire according to an embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view taken along II-II in Fig. 1. One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is an electric wire 1 including a conductor 2 and a coating 5 that coats the conductor 2, wherein the coating 5 includes a first layer 3 and a second layer 4 formed on the first layer 3, the first layer 3 containing a cross-linked polyolefin resin as a main component, and the second layer 4 containing a silsesquioxane as a main component, the silsesquioxane being (RSiO ３／２ ) as a structural unit, R is a polymerizable group, and the thickness of the second layer 4 is 0.1 μm or more and 100 μm or less.

[0024] According to the present disclosure, it is possible to provide an electric wire 1 having both excellent heat resistance and excellent oil resistance, and a multi-core cable including the electric wire 1. The reason for this is presumed to be as follows.

[0025] In the electric wire 1 of this embodiment, the coating 5 includes a first layer 3 and a second layer 4 formed on the first layer 3. The first layer 3 contains a crosslinked polyolefin resin as a main component, and the second layer 4 contains a silsesquioxane as a main component. The silsesquioxane is (RSiO ３／２) as a structural unit, R is a polymerizable group, and the thickness of the second layer 4 is 0.1 μm or more and 100 μm or less. Since the second layer 4 serves as a dense protective film and can prevent oxidative degradation due to oxygen in the air, it is possible to provide an electric wire 1 and a multi-core cable including the electric wire 1 that have both excellent heat resistance and excellent oil resistance.

[0026] Furthermore, in view of restrictions on the use of fluorinated organic compounds (PFAS) in Europe, such an electric wire has the advantage that it can exhibit the effects of the present disclosure without necessarily using PFAS.

[0027] <Electric Wire> The equivalent circle diameter of a cross section perpendicular to the longitudinal direction of the electric wire 1 may be 0.1 mm or more and 50 mm or less, 0.2 mm or more and 20 mm or less, or 0.5 mm or more and 10 mm or less. Note that the longitudinal direction here can be rephrased as the "first direction" described later.

[0028] The circle-equivalent diameter of the cross section perpendicular to the longitudinal direction of the electric wire 1 can be determined by the following method. First, the average cross-sectional area of ​​the electric wire 1 is determined by the same method as the average cross-sectional area of ​​the conductor 2, except that the object of measurement is the electric wire 1. Next, the circle-equivalent diameter is calculated based on the "average cross-sectional area of ​​the electric wire 1," thereby making it possible to determine the circle-equivalent diameter of the cross section perpendicular to the longitudinal direction of the electric wire 1.

[0029] It has been confirmed that, as long as the same electric wire 1 is measured by the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0030] <Conductor> The electric wire 1 includes a conductor 2. The material of the conductor 2 can be a metal material with high electrical conductivity and high mechanical strength. Examples of such metal materials include copper, copper alloys, aluminum, aluminum alloys, nickel, silver, mild steel, steel, and stainless steel. The conductor 2 can be a wire material formed from a single metal material. The conductor 2 can also have a multilayer structure in which the wire material is coated with another metal by a technique such as plating. Examples of the conductor 2 having a multilayer structure include tin-plated copper wire, nickel-plated copper wire, silver-plated copper wire, copper-plated aluminum wire, and copper-plated steel wire.

[0031] The shape of the conductor 2 is not particularly limited, and any conventionally known shape can be used. Examples of the shape of the conductor 2 include a round wire having a circular cross section, a rectangular wire having a square cross section, a rectangular wire having a rectangular cross section, and a twisted wire formed by twisting together multiple wires.

[0032] The equivalent circle diameter of a cross section perpendicular to the longitudinal direction of the conductor 2 may be 0.05 mm to 30 mm, 0.1 mm to 15 mm, or 0.3 mm to 8 mm. Here, the longitudinal direction can be rephrased as the "first direction" described later.

[0033] The equivalent circle diameter of a cross section perpendicular to the longitudinal direction of the conductor 2 can be determined in the same manner as the equivalent circle diameter of a cross section perpendicular to the longitudinal direction of the wire 1, except that the object of measurement is the conductor 2.

[0034] It has been confirmed that, as long as measurements are made on the same conductor 2 using the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0035] The average cross-sectional area of ​​the conductor 2 is not particularly limited and can be appropriately selected depending on the application. ２ Over 550mm ２ It may be 0.006 mm or less, ２ Over 140mm ２ It may be 0.05 mm or less. ２ Over 40mm ２In the present disclosure, the average cross-sectional area of ​​the conductor 2 is measured as follows: One conductor 2 is stretched in a straight line, cut along a plane normal to a first direction connecting one end of the conductor 2 to the other, the cross section is exposed, and the cross-sectional area is measured. For one conductor 2, the conductor 2 is cut along a plane normal to the first direction at any five locations, the cross-sectional areas are measured, and an average value is calculated. The average value corresponds to the average cross-sectional area of ​​the conductor 2.

[0036] <Coating> The electric wire 1 includes a coating 5 that coats the conductor 2. The coating 5 includes a first layer 3 and a second layer 4 formed on the first layer 3. The coating 5 may consist of only the first layer 3 and the second layer 4 formed on the first layer 3, or may further include other layers described below in addition to the first layer 3 and the second layer 4 formed on the first layer 3.

[0037] The thickness of the coating 5 may be 0.025 mm or more and 10 mm or less. If the thickness of the coating 5 is less than 0.025 mm, the coating 5 tends to be easily damaged. If the thickness of the coating 5 exceeds 10 mm, the electric wire 1 tends to be hard and difficult to bend, and the cost tends to be high. The thickness of the coating 5 may be 0.050 mm or more and 2.5 mm or less, or 0.150 mm or more and 1 mm or less.

[0038] In the present disclosure, the thickness of the coating 5 can be determined by the following method. The electric wire 1 is stretched in a straight line, and cut along a plane normal to a first direction connecting one end of the electric wire 1 to the other end of the electric wire 1 to expose a cross section. The thickness of the coating 5 is measured at three arbitrary locations on the cross section, and the average value is calculated. The electric wire 1 is cut along a plane normal to the first direction at a total of five arbitrary locations to determine the average values, and the thickness of the coating 5 is determined by calculating the average value.

[0039] It has been confirmed that, as long as the same electric wire 1 is measured by the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0040] <First Layer> The first layer 3 contains a cross-linked polyolefin resin as a main component. Here, "containing a cross-linked polyolefin resin as a main component" means that the first layer 3 contains, for example, 50% by mass or more of the cross-linked polyolefin resin. The first layer 3 may be made of a cross-linked polyolefin resin. The phrase "the first layer 3 may be made of a cross-linked polyolefin resin" means that the first layer 3 may be made of only the cross-linked polyolefin resin, or may contain other components (such as a first inevitable impurity) in addition to the cross-linked polyolefin resin, as long as the effects of the present disclosure are not impaired. Examples of the first unavoidable impurities include crosslinking aids (triallyl isocyanurate, trimethylpentene trimethacrylate, etc.), fillers (silica, talc, calcium carbonate, clay, zinc oxide, etc.), lubricants (oleic acid amide, erucic acid amide, stearic acid, zinc stearate, etc.), coloring pigments (inorganic pigments such as titanium oxide, organic pigments, carbon, etc.), flame retardants (bromine-based flame retardants, antimony trioxide, melamine cyanurate, magnesium hydroxide, aluminum hydroxide, etc.), antioxidants (phenol-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, etc.), and metal deactivators.

[0041] The cross-linked polyolefin resin may be composed of a polyethylene resin, a copolymer of ethylene and a polar comonomer, or both. This makes it possible to provide an electric wire 1 having both superior heat resistance and superior oil resistance, and a multi-core cable including the electric wire 1. Here, "composed of a polyethylene resin, a copolymer of ethylene and a polar comonomer, or both" means that the resin may be composed only of a polyethylene resin, a copolymer of ethylene and a polar comonomer, or both, and may contain other components (such as a third inevitable impurity) other than "a polyethylene resin, a copolymer of ethylene and a polar comonomer, or both" as long as the effects of the present disclosure are not impaired. Examples of the third unavoidable impurities include crosslinking aids (triallyl isocyanurate, trimethylpentene trimethacrylate, etc.), fillers (silica, talc, calcium carbonate, clay, zinc oxide, etc.), lubricants (oleic acid amide, erucic acid amide, stearic acid, zinc stearate, etc.), coloring pigments (inorganic pigments such as titanium oxide, organic pigments, carbon, etc.), flame retardants (bromine-based flame retardants, antimony trioxide, melamine cyanurate, magnesium hydroxide, aluminum hydroxide, etc.), antioxidants (phenol-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, etc.), and metal deactivators.

[0042] The copolymer of ethylene and a polar comonomer may be an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, or both. This makes it possible to provide an electric wire 1 having both superior heat resistance and superior oil resistance, and a multi-core cable including the electric wire 1. Here, "having polarity" refers to a state in which a carbon atom is electrically polarized by bonding to an atom that has a higher electronegativity than the carbon atom (such as an oxygen atom or a nitrogen atom).

[0043] The crosslinked polyolefin resin may be a crosslinked polyolefin resin obtained by crosslinking at least one resin selected from the group consisting of ultra-low density polyethylene, low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, and ethylene-butyl acrylate copolymer by means of electron beam, peroxide, etc. This makes it possible to provide an electric wire 1 and a multicore cable including the electric wire 1 that have both superior heat resistance and superior oil resistance.

[0044] The cross-linked polyolefin resin may be a resin modified with one compound selected from the group consisting of maleic anhydride, carboxylic acid, and compounds having an epoxy group. This makes it possible to provide an electric wire 1 and a multi-core cable including the electric wire 1 with superior heat resistance. Examples of the compound having an epoxy group include epoxy group-containing vinyl monomers. Examples include at least one compound selected from the group consisting of glycidyl methacrylate, glycidyl acrylate, monoglycidyl maleate, diglycidyl maleate, monoglycidyl itaconate, diglycidyl itaconate, monoglycidyl allyl succinate, diglycidyl allyl succinate, glycidyl p-styrenecarboxylate, allyl glycidyl ether, methallyl glycidyl ether, styrene-p-glycidyl ether, p-glycidyl styrene, epoxy olefins such as 3,4-epoxy-1-butene and 3,4-epoxy-3-methyl-1-butene, and vinylcyclohexene monoxide. The state of being "modified with one compound selected from the group consisting of maleic anhydride, carboxylic acid, and compounds having an epoxy group" means a state in which one compound selected from the group consisting of maleic anhydride, carboxylic acid, and compounds having an epoxy group is graft-bonded to a terminal or non-terminal of a polymer molecular chain, or a state in which one compound selected from the group consisting of maleic anhydride, carboxylic acid, and compounds having an epoxy group is copolymerized in a polymer molecular chain.

[0045] The cross-linked polyolefin resin of the first layer 3 may be a resin that has been subjected to a hydrophilic surface treatment, thereby making it possible to provide an electric wire and a multi-core cable including such an electric wire that have both superior heat resistance and superior oil resistance.

[0046] The hydrophilic surface treatment may be at least one surface treatment selected from the group consisting of corona treatment, plasma treatment, ozone treatment, and etching treatment with active sodium, thereby making it possible to provide an electric wire and a multi-core cable including the electric wire that have both superior heat resistance and superior oil resistance.

[0047] The composition of the first layer 3 can be identified by a combination of an analysis of the chemical bonding state based on measurements of the infrared absorption spectrum by nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FT-IR), and measurements of the crystalline melting temperature and the heat of crystalline melting by a differential scanning calorimeter.

[0048] The weight average molecular weight of the crosslinked polyolefin resin may be 10,000 or more and 5,000,000 or less, 50,000 or more and 2,000,000 or less, or 100,000 or more and 1,000,000 or less. In an electric wire, the weight average molecular weight of the crosslinked polyolefin resin can be determined by measurement using gel permeation chromatography (GPC) in accordance with JIS-K7252-1:2008 "Plastics - Determination of average molecular weight and molecular weight distribution of polymers by size exclusion chromatography - Part 1: General rules."

[0049] The thickness of the first layer 3 may be 0.025 mm or more and 10 mm or less. This can impart better heat resistance to the electric wire 1. Furthermore, the electric wire 1 can be made easier to bend. The lower limit of the thickness of the first layer 3 may be 0.025 mm or more, 0.050 mm or more, 0.100 mm or more, or 0.200 mm or more. The upper limit of the thickness of the first layer 3 may be 10 mm or less, 2.5 mm or less, 1 mm or less, or 0.500 mm or less. The thickness of the first layer 3 may be 0.050 mm or more and 2.5 mm or less, or 0.100 mm or more and 1 mm or less.

[0050] The thickness of the first layer 3 can be determined in the same manner as the thickness of the coating 5, except that the measurement target is the first layer 3.

[0051] It has been confirmed that, as long as the same electric wire 1 is measured by the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0052] <Second Layer> The second layer 4 contains silsesquioxane as a main component. Here, "containing silsesquioxane as a main component" means that the second layer 4 contains silsesquioxane in an amount of, for example, 50 mass % or more. Silsesquioxane is (RSiO ３／２ ) as a structural unit, where R is a polymerizable group. These can impart excellent heat resistance to the electric wire 1. The second layer 4 may be made of silsesquioxane. "The second layer 4 may be made of silsesquioxane" means that the second layer 4 may be made of silsesquioxane alone, or may contain other components (such as second inevitable impurities) in addition to silsesquioxane as long as the effects of the present disclosure are not impaired. Examples of the second inevitable impurities include photoradical polymerization initiators, thermal polymerization initiators, acrylic monomers, organic solvents, lubricants, and pigments.

[0053] Silsesquioxane may contain at least one structure selected from the group consisting of a random structure, a ladder structure, a complete cage structure, and an incomplete cage structure. Here, the "random structure" means a structure represented by formula 1, the "ladder structure" means a structure represented by formula 2, the "complete cage structure" means a structure represented by formula 3 or a structure represented by formula 4, and the "incomplete cage structure" means a structure represented by formula 5 or a structure represented by formula 6. The structure represented by formula 3 is "T ８ ", and the structure represented by formula 4 can be expressed as "T １０ " can be rephrased as "

[0054]

[0055]

[0056]

[0057] The polymerizable group may be a radically polymerizable group or a cationically polymerizable group. These polymerizable groups have excellent polymerization reactivity, particularly photopolymerization reactivity, and therefore can provide an electric wire 1 and a multi-core cable including the electric wire 1 that have both excellent heat resistance and excellent oil resistance.

[0058] The polymerizable group may be one selected from the group consisting of an acryloyl group, a methacryloyl group, and an oxetanyl group. These polymerizable groups have excellent polymerization reactivity, particularly photopolymerization reactivity, and therefore can provide an electric wire 1 and a multi-core cable including the electric wire 1 that have both excellent heat resistance and excellent oil resistance.

[0059] The composition of the second layer 4 can be identified by a combination of an analysis of the chemical bonding state based on measurements of infrared absorption spectra by nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FT-IR) and measurements of the ash content by thermogravimetry (TG).

[0060] The thickness of the second layer 4 is 0.1 μm or more and 100 μm or less. This allows the second layer 4 to fully exhibit its heat resistance effect, making it possible to provide an electric wire 1 having excellent heat resistance and a multi-core cable including the electric wire 1. The lower limit of the thickness of the second layer 4 may be 0.5 μm or more, 1 μm or more, or 2 μm or more. The upper limit of the thickness of the second layer 4 may be 50 μm or less, 20 μm or less, or 10 μm or less. The thickness of the second layer 4 may be 0.5 μm or more and 50 μm or less, or 1 μm or more and 20 μm or less.

[0061] The thickness of the second layer 4 can be determined in the same manner as the thickness of the coating 5, except that the measurement target is the second layer 4.

[0062] It has been confirmed that, as long as the same second layer 4 is measured by the above method, there is no variation in the measurement results even if the measurement location is changed arbitrarily.

[0063] <Other Layers> The coating 5 may further include other layers. Examples of such other layers include a surface layer and an intermediate layer. The surface layer is a layer located on the surface of the coating 5. The intermediate layer is a layer located between the conductor 2 and the first layer 3 or between the first layer 3 and the second layer 4.

[0064] <<Method for Manufacturing Electric Wire>> The method for manufacturing the electric wire 1 of this embodiment includes, for example, a first step of preparing the conductor 2, a compound for forming the first layer 3, and a varnish for forming the second layer 4, a second step of forming the first layer 3 on the outer peripheral surface of the conductor 2, and a third step of forming the second layer 4 on the surface of the first layer 3, in this order. The first step includes a 1A step of preparing the conductor 2, a 1B step of preparing the compound for forming the first layer 3, and a 1C step of preparing the varnish for forming the second layer 4. The method for manufacturing the electric wire 1 of this embodiment can further include a "step of forming other layers." Note that the "step of forming other layers" can be performed by a conventionally known method.

[0065] <Step 1> <Step 1A: Step of Preparing a Conductor> In Step 1A, a conductor 2 is prepared. The conductor 2 may be prepared by manufacturing using a conventionally known method, or may be prepared by purchasing a commercially available product.

[0066] <Step 1B: Step of Preparing Compound for Forming First Layer> In step 1B, a compound for forming the first layer 3 is prepared. For example, the compound for forming the first layer 3 can be prepared by the following method. First, a cross-linked polyolefin resin is prepared as a raw material. In addition to the cross-linked polyolefin resin, for example, a cross-linking aid, a lubricant, a filler, etc. may also be prepared as raw materials. Next, the raw materials are kneaded to prepare the compound for forming the first layer 3.

[0067] Examples of crosslinked polyolefin resins include those obtained by crosslinking at least one resin selected from the group consisting of ultra-low density polyethylene, low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, and ethylene-butyl acrylate copolymer by means of electron beam, peroxide, or the like.

[0068] The weight average molecular weight of the crosslinked polyolefin resin may be 10,000 or more and 5,000,000 or less, 50,000 or more and 2,000,000 or less, or 100,000 or more and 1,000,000 or less.

[0069] The kneading can be carried out using rolls heated to, for example, 160° C. or more and 200° C. or less. The kneading time can be 5 minutes or more and 30 minutes or less.

[0070] <Step 1C: Step of Preparing Varnish for Forming Second Layer> In step 1C, a varnish for forming the second layer 4 is prepared. For example, the varnish for forming the second layer 4 can be prepared by the following method. First, a silsesquioxane derivative is prepared as a raw material. The silsesquioxane derivative may be prepared by manufacturing it using a conventionally known method, or may be prepared by purchasing a commercially available product. In addition to the silsesquioxane derivative, for example, a photoradical polymerization initiator, an acrylic monomer, a solvent, etc. may also be prepared as raw materials. Next, the photoradical polymerization initiator, etc., can be added to the silsesquioxane derivative and stirred to prepare the varnish for forming the second layer 4.

[0071] The stirring speed may be, for example, 10 rpm or more and 1000 rpm or less. The temperature during stirring may be 10° C. or more and 40° C. or less. The temperature during stirring may be room temperature. The stirring time may be 5 minutes or more and 30 minutes or less.

[0072] <Second Step> In the second step, the first layer 3 is formed on the outer peripheral surface of the conductor 2. For example, the first layer 3 can be formed by the following method. First, a compound for forming the first layer 3 is pressure-loaded into an extruder whose head is set to 175°C or higher and 225°C or lower and whose cylinder is set to 170°C or higher and 210°C or lower. Next, the compound for forming the first layer 3 is extrusion-coated onto the outer peripheral surface of the conductor 2. Next, the extrusion-coated compound for forming the first layer 3 is irradiated with an electron beam of 0.1 kGy or higher and 500 kGy or lower, thereby forming the first layer 3 on the outer peripheral surface of the conductor 2.

[0073] <Third Step> In the third step, the second layer 4 is formed on the surface of the first layer 3. For example, the second layer 4 can be formed by the following method. First, a varnish for forming the second layer 4 is applied to the surface of the first layer 3. Next, the varnish for forming the second layer 4 applied to the surface of the first layer 3 is subjected to a photo-curing treatment under the following conditions, thereby forming the second layer 4 on the surface of the first layer 3. Note that the third step may be repeated until the second layer 4 reaches a predetermined thickness. (Photo-curing treatment conditions) Light source: high-pressure mercury lamp (input power: 10 W / cm to 300 W / cm) Lamp height: 1 cm to 50 cm Conveyor speed: 1 m / min to 10 m / min Integrated light intensity per pass: 1,000 mJ / cm ２ 30,000mJ / cm or more ２ Number of passes: 1 to 10 Atmosphere: Air

[0074] [Embodiment 2: Multi-core cable] A multi-core cable of this embodiment includes the electric wire according to embodiment 1.

[0075] According to the present disclosure, it is possible to provide a multi-core cable including electric wires that have both excellent heat resistance and excellent oil resistance.

[0076] The multi-core cable according to the present embodiment is not particularly limited as long as it includes the electric wires described in embodiment 1. In the present disclosure, a multi-core cable refers to a cable including a plurality of electric wires. "The multi-core cable according to the present embodiment includes the electric wires described in embodiment 1" means that at least one of the plurality of electric wires included in the multi-core cable according to the present embodiment is the electric wire described in embodiment 1.

[0077] <<Method for Manufacturing Multi-Core Cable>> The method for manufacturing the multi-core cable according to this embodiment can be carried out in the same manner as a conventionally known method, except that the electric wire according to the first embodiment is used.

[0078] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0079] <<Preparation of Electric Wires>> Electric wires according to Samples 1 to 11 and 101 to 108 were prepared as follows.

[0080] <Step 1> The conductors listed in Table 4 were prepared by purchasing commercially available products (Step 1A). Furthermore, the raw materials listed in Table 1 were kneaded in the compositions listed in Table 1 using rolls heated to the temperatures listed in Table 1 for the times listed in Table 1 to prepare compounds for forming the first layer (Step 1B). The resins listed in Table 4 were used as the cross-linked polyolefin resins. Specifically, "Sumikathene C215" (trademark) manufactured by Sumitomo Chemical Co., Ltd. was used as the low-density polyethylene. Furthermore, "Rexpearl A3100" (trademark) manufactured by Japan Polyethylene Corporation was used as the ethylene-ethyl acrylate copolymer. Furthermore, "Suntech EVA EF1510" (trademark) manufactured by Asahi Kasei Corporation was used as the ethylene-vinyl acetate copolymer. Furthermore, "Admer LB540" (trademark) manufactured by Mitsui Chemicals, Inc. was used as the maleic anhydride-modified resin. Furthermore, "FUSABOND E100" (trademark) manufactured by Dow Chemical Co., Ltd. was used as the carboxylic acid-modified resin. Furthermore, the resin modified with a compound having an epoxy group was "Bondfast E" (trademark), a polyethylene manufactured by Sumitomo Chemical Co., Ltd. The cross-linking aid was "TAIC" (trademark) manufactured by Nippon Kasei Kasei Co., Ltd. The flame retardants were "Cytex BT93" (trademark) manufactured by Albemarle Japan Co., Ltd. and antimony trioxide in a 2:1 ratio by mass. The values ​​listed in the "Flame Retardant [Parts by Mass]" column in Table 1 refer to the total parts by mass of "Cytex BT93" (trademark) and antimony trioxide. The antioxidant was "Irganox 1076" manufactured by BASF Japan Co., Ltd. The lubricant was "Powdered Stearic Acid Sakura" manufactured by NOF Corporation. In Table 4, "PO" stands for "polyolefin" and "PE" stands for polyethylene.

[0081] Furthermore, the raw materials listed in Table 2 (in other words, raw materials other than the silsesquioxane derivative) were added to the silsesquioxane derivative so as to obtain the composition listed in Table 2, and the mixture was stirred under the conditions listed in Table 2 to prepare a varnish for forming a second layer (Step 1C). Note that if "-" is entered in all columns in the "Step 1C" column, this means that "Step 1C" was not performed. Note that the silsesquioxane derivatives listed in Table 5 were used as the "silsesquioxane derivatives." As the silsesquioxane derivative in which R (polymerizable group) is an acryloyl group (radical polymerizable group), "AC-SQ TA-100" (trademark) manufactured by Toagosei Co., Ltd. was used; as the silsesquioxane derivative in which R (polymerizable group) is a methacryloyl group (radical polymerizable group), "MAC-SQ TM-100" (trademark) manufactured by Toagosei Co., Ltd. was used; and as the silsesquioxane derivative in which R (polymerizable group) is an oxetanyl group (cationically polymerizable group), "QX-SQ SI-20" (trademark) manufactured by Toagosei Co., Ltd. was used. As the photoradical polymerization initiator, "BLUESIL PI 2074" (trademark) manufactured by ELKEM was used.

[0082] <Second Step> First, the compound for forming the first layer was pressed into an extruder whose head and cylinder were set to the temperatures shown in Table 3. Next, the compound for forming the first layer was extrusion coated onto the outer periphery of the conductor so that the thickness of the first layer was as shown in Table 4. Next, the extrusion-coated compound for forming the first layer was irradiated with an electron beam at a dose shown in Table 3, thereby forming a first layer on the outer periphery of the conductor.

[0083] <Third Step> First, a varnish for forming a second layer was applied to the surface of the first layer. Next, a photo-curing treatment was carried out on the varnish for forming a second layer that had been applied to the surface of the first layer under the following conditions, thereby forming a second layer on the surface of the first layer. The application of the varnish for forming a second layer and the photo-curing treatment were repeated until the thickness of the second layer reached the value shown in Table 5. Note that if "-" is written in all of the fields in the "Third Step" column, this means that the "Third Step" was not carried out. (Photo-curing Treatment Conditions) Light source: high-pressure mercury lamp (input power [W / cm] as shown in Table 3) Lamp height: as shown in Table 3 Conveyor speed: as shown in Table 3 Integrated light intensity per pass: as shown in Table 3 Number of passes: as shown in Table 3 Atmosphere: air

[0084] In this manner, electric wires according to Samples 1 to 11 and 101 to 108 were produced.

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091] <Evaluation of Electric Wire Properties> <Composition of First Layer> For each electric wire sample, the composition of the first layer was determined by the method described in Embodiment 1. The results obtained are shown in the "Composition" column of the "First Layer" column in Table 4. Note that when a resin is listed in the "Composition" column of the "First Layer" column in Table 4, this means that the first layer contains that resin as a main component. For example, when "Crosslinked PO resin (low-density PE)" is listed in the "Composition" column of the "First Layer" column in Table 4, this means that the first layer contains a crosslinked polyolefin resin as a main component, and the crosslinked polyolefin resin is low-density polyethylene.

[0092] <Composition of Second Layer> For each sample electric wire, the composition of the second layer was determined by the method described in Embodiment 1. The obtained results are shown in the "Composition" column of the "Second Layer" column in Table 5. When a component name is listed in the "Composition" column of the "Second Layer" column in Table 5, it means that the second layer contains the component listed in the "Composition" column of the "Second Layer" column in Table 5 as a main component. For example, when "Silsesquioxane" is listed in the "Composition" column of the "Second Layer" column in Table 5 and "Acryloyl group (radical polymerizable group)" is listed in the "R" column of the "Second Layer" column in Table 5, it means that the second layer contains silsesquioxane as a main component, and the silsesquioxane is (RSiO ３／２ ) as a constituent unit, and R is a polymerizable group, which is a radical polymerizable group and an acryloyl group.

[0093] <Coating Thickness> The coating thickness of each sample electric wire was determined by the method described in embodiment 1. The obtained results are shown in the "Thickness [mm]" column of the "Coating" column in Table 5.

[0094] <Circle-equivalent diameter of cross section perpendicular to the longitudinal direction of electric wire> For each sample electric wire, the circle-equivalent diameter of the cross section perpendicular to the longitudinal direction of the electric wire was determined by the method described in embodiment 1. The obtained results are shown in the "Circle-equivalent diameter [mm]" column of the "Electric wire" column in Table 5.

[0095] <Evaluation Test 1 (Heat Resistance Evaluation Test)> First, eight electric wires (length: 350 mm) for each sample were prepared. Next, the coating was stripped from both ends of the electric wires in the region between the end and a position 25 mm away from the end in the longitudinal direction of the electric wire. Next, each of the eight electric wires (length: 350 mm) for each sample was left in a thermostatic oven at temperatures of 85±2°C, 100±2°C, 125±3°C, 150±3°C, 175±3°C, 200±3°C, 225±4°C, and 250±4°C for 3,000 hours. Next, the electric wires were removed from the thermostatic oven and left at room temperature for 16 hours. Next, a weight 13 having a mass of 5 kg was placed on a mandrel 11 having a diameter 1.5 times the equivalent circle diameter of a cross section perpendicular to the longitudinal direction of the electric wire 12, and the weight 13 was wound at a winding speed of 1 s. －１The wire was wound twice at two locations at room temperature (Figure 3). Next, after visually confirming that the conductor of each sample wire was not exposed, the wire was immersed in salt water (3 mass%) for 10 minutes. Next, a voltage of 1 kV was applied to the wire for 1 minute. Next, the wire was visually observed to determine whether or not the coating had been damaged. Next, the heat resistance of the wire was evaluated based on the following evaluation criteria. The obtained results are shown in the "Evaluation Test 1" column of Table 6. An evaluation result of D, E, F, G, or H means that the wire has excellent heat resistance. (Evaluation criteria) A: No breakdown of the coating when the temperature of the thermostatic bath is 85±2°C or less B: No breakdown of the coating when the temperature of the thermostatic bath is 100±2°C or less C: No breakdown of the coating when the temperature of the thermostatic bath is 125±3°C or less D: No breakdown of the coating when the temperature of the thermostatic bath is 150±3°C or less E: No breakdown of the coating when the temperature of the thermostatic bath is 175±3°C or less F: No breakdown of the coating when the temperature of the thermostatic bath is 200±3°C or less G: No breakdown of the coating when the temperature of the thermostatic bath is 225±4°C or less H: No breakdown of the coating when the temperature of the thermostatic bath is 250±4°C or less

[0096] Evaluation Test 2 (Heat Resistance Evaluation Test) First, eight electric wires (length: 350 mm) for each sample were prepared. Next, the coating was stripped from both ends of the electric wires in the region between the end and a position 25 mm away from the end in the longitudinal direction of the electric wire. Next, each of the eight electric wires (length: 350 mm) for each sample was left in a thermostatic chamber at temperatures of 110±2°C, 125±3°C, 150±3°C, 175±3°C, 200±3°C, 225±4°C, 250±4°C, and 275±4°C for 240 hours. Next, the electric wires were removed from the thermostatic chamber and left at room temperature for 16 hours. Next, a weight 13 having a mass of 5 kg was placed on a mandrel 11 having a diameter five times the equivalent circle diameter of a cross section perpendicular to the longitudinal direction of the electric wire 12, and the wire was wound at a winding speed of 1 s. －１The wire was wound twice at two locations at room temperature (Figure 3). Next, after visually confirming that the conductor of each sample wire was not exposed, the wire was immersed in salt water (3% by mass) for 10 minutes. Next, a voltage of 1 kV was applied to the wire for 1 minute. Next, the wire was visually observed to determine whether or not the coating had been damaged. Next, the heat resistance of the wire was evaluated based on the following evaluation criteria. The obtained results are shown in the "Evaluation Test 2" column of Table 6. An evaluation result of D', E', F', G', or H' means that the wire has excellent heat resistance. (Evaluation criteria) A': No breakdown of the coating when the temperature of the thermostatic bath is 110±2°C or lower B': No breakdown of the coating when the temperature of the thermostatic bath is 125±3°C or lower C': No breakdown of the coating when the temperature of the thermostatic bath is 150±3°C or lower D': No breakdown of the coating when the temperature of the thermostatic bath is 175±3°C or lower E': No breakdown of the coating when the temperature of the thermostatic bath is 200±3°C or lower F': No breakdown of the coating when the temperature of the thermostatic bath is 225±4°C or lower G': No breakdown of the coating when the temperature of the thermostatic bath is 250±4°C or lower H': No breakdown of the coating when the temperature of the thermostatic bath is 275±4°C or lower

[0097] Evaluation Test 3 (Heat Resistance Evaluation Test) First, eight electric wires (length: 350 mm) for each sample were prepared. Next, the coating was stripped from both ends of the electric wires in the area between the end and a position 25 mm away from the end in the longitudinal direction of the electric wire. Next, each of the eight electric wires (length: 350 mm) for each sample was left in a thermostatic oven at temperatures of 135±3°C, 150±3°C, 175±3°C, 200±3°C, 225±4°C, 250±4°C, 275±4°C, and 300±4°C for six hours. Next, the electric wires were removed from the thermostatic ovens and left at room temperature for 16 hours. Next, a weight 13 having a mass of 5 kg was placed on a mandrel 11 having a diameter 1.5 times the equivalent circle diameter of a cross section perpendicular to the longitudinal direction of the electric wire 12, and the weight 13 was wound at a winding speed of 1 s. －１The wire was wound twice at two locations at room temperature (FIG. 3). Next, after visually confirming that the conductor of each sample wire was not exposed, the wire was immersed in salt water (3% by mass) for 10 minutes. Next, a voltage of 1 kV was applied to the wire for 1 minute. Next, the wire was visually observed to determine whether or not the coating had been broken. Next, the heat resistance of the wire was evaluated based on the following evaluation criteria. The obtained results are shown in the "Evaluation Test 3" column in Table 6. An evaluation result of D", E", F", G", or H" means that the wire has excellent heat resistance. (Evaluation criteria) A": No breakdown of the coating when the temperature of the thermostatic bath is 135±3°C or less B": No breakdown of the coating when the temperature of the thermostatic bath is 150±3°C or less C": No breakdown of the coating when the temperature of the thermostatic bath is 175±3°C or less D": No breakdown of the coating when the temperature of the thermostatic bath is 200±3°C or less E": No breakdown of the coating when the temperature of the thermostatic bath is 225±4°C or less F": No breakdown of the coating when the temperature of the thermostatic bath is 250±4°C or less G": No breakdown of the coating when the temperature of the thermostatic bath is 275±4°C or less H": No breakdown of the coating when the temperature of the thermostatic bath is 300±4°C or less

[0098] Evaluation Test 4 (Evaluation of Oil Resistance) was performed in accordance with ISO 6722 Method 2. Specifically, a 600 mm test sample was prepared from each electric wire. The test sample was then immersed in gasoline as specified in ISO 1817 at 23±5°C for 20 hours. The test sample was then removed, the surface was wiped, and the test sample was dried at room temperature for 30 minutes. The outer diameter of the test sample was measured within 5 minutes. The outer diameter change rate was calculated using the following formula 7. The results are shown in the "Outer diameter change rate [%]" column in the "Evaluation Test 4" section of Table 6. The "outer diameter" was determined using the same method as in the measurement method for the "equivalent circle diameter of a cross section perpendicular to the longitudinal direction of an electric wire" described in Embodiment 1. An outer diameter change rate of 20% or less indicates excellent oil resistance. (Outer diameter change rate [%]) = {(outer diameter after immersion [mm] - outer diameter before immersion [mm]) / (outer diameter before immersion [mm])} × 100 [%] Formula 7

[0099] Evaluation Test 5 (Evaluation of Oil Resistance) The outer diameter change rate was determined in the same manner as in Evaluation Test 4, except that "diesel fuel as specified in ISO 1817" was used instead of "gasoline as specified in ISO 1817." The results obtained are shown in the "Outer diameter change rate [%]" column in the "Evaluation Test 5" column of Table 6. An outer diameter change rate of 20% or less indicates excellent oil resistance.

[0100] The electric wires according to Samples 1 to 11 correspond to Examples. The electric wires according to Samples 101 to 108 correspond to Comparative Examples. The results in Table 6 show that the electric wires according to Samples 1 to 11 have both excellent heat resistance and excellent oil resistance compared to the electric wires according to Samples 101 to 108.

[0101] From the above, it was found that the electric wires according to Samples 1 to 11 had both excellent heat resistance and excellent oil resistance.

[0102] Although the embodiments and examples of the present disclosure have been described above, it is originally intended that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways.

[0103] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0104] 1 Electric wire, 2 Conductor, 3 First layer, 4 Second layer, 5 Coating, 11 Mandrel, 12 Electric wire, 13 Weight

Claims

1. An electric wire comprising a conductor and a coating that coats the conductor, wherein the coating includes a first layer and a second layer formed on the first layer, the first layer contains a crosslinked polyolefin resin as a main component, the second layer contains silsesquioxane as a main component, and the silsesquioxane is a polymer having (RSiO ３／２ ) as a structural unit, R is a polymerizable group, and the thickness of the second layer is 0.1 μm or more and 100 μm or less.

2. The crosslinked polyolefin resin of claim 1 is composed of a polyethylene resin, a copolymer of ethylene and a polar comonomer, or both. The wire according to claim 1.

3. The copolymer of ethylene and the polar comonomer of claim 2 is an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, or both. The wire according to claim 2.

4. The crosslinked polyolefin resin of claim 1 is a resin modified with one compound selected from the group consisting of maleic anhydride, carboxylic acid, and a compound having an epoxy group. The wire according to claim 1.

5. The crosslinked polyolefin resin of the first layer is a resin in a state where a hydrophilic surface treatment has been performed. The wire according to claim 1.

6. The hydrophilic surface treatment of claim 5 is at least one surface treatment selected from the group consisting of corona treatment, plasma treatment, ozone treatment, and etching treatment with active sodium. The wire according to claim 5.

7. The polymerizable group is a radical polymerizable group or a cationic polymerizable group. The wire according to any one of claims 1 to 6.

8. The polymerizable group is one polymerizable group selected from the group consisting of acryloyl group, methacryloyl group, and oxetanyl group. The wire according to any one of claims 1 to 6.

9. A multi-core cable comprising the wire according to any one of claims 1 to 8.

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