Electric wire

Abstract

The present invention provides an electric wire in which a sheath is provided on the outer circumference of a core wire, and which has high flexibility and heat resistance as well as high abrasion resistance and chemical resistance.　Provided is an electric wire 1 comprising: a core wire 2 including a conductor 3 and an insulating coating 4 that covers the outer circumference of the conductor 3; and a sheath 6 covering the outer circumference of the core wire 2, wherein the insulating coating 4 is constituted by a core coating material containing silicone rubber, the sheath 6 is constituted by a sheath material containing both a cross-linked polyolefin and a flame retardant, and the elastic modulus of the sheath material is no more than 30 times the elastic modulus of the core coating material.

Description

electric wire

[0001] The present disclosure relates to electrical wires.

[0002] For electric wires routed inside automobiles, it is advantageous to have high flexibility and heat resistance due to the need to route them in a limited space and the possibility of them being heated by current flow, etc. High flexibility is particularly important for thick electric wires to which high voltages are applied. Such thick electric wires are becoming increasingly important as electric wires connecting batteries and drivetrain devices in electric vehicles and hybrid vehicles. From the viewpoint of improving the flexibility and heat resistance of electric wires, silicone rubber is preferably used as an insulating coating material. An electric wire using an insulating coating material containing silicone rubber is disclosed, for example, in Patent Document 1.

[0003] In addition to flexibility and heat resistance, important properties of electric wires installed inside automobiles include abrasion resistance and chemical resistance. This is because, inside an automobile, electric wires are likely to come into contact with surrounding objects such as the vehicle body, and also with chemicals such as gasoline and battery fluid. From the viewpoint of improving the abrasion resistance and chemical resistance of electric wires, cross-linked polyolefins are preferably used as insulating coating materials. An electric wire using an insulating coating material containing cross-linked polyolefin is disclosed, for example, in Patent Document 2.

[0004] JP 2015-118835 A JP 2019-163406 A

[0005] Electric wires installed in automobiles, etc., may have a core wire with an insulating coating formed around the conductor and a sheath provided around the core wire. For example, in electric wires for high-voltage applications, such as heavy-gauge electric wires, an outer conductor made of a metal braid or metal foil may be disposed around the core wire, and a sheath may be provided around the outer conductor layer. When a sheath is provided around the core wire in this manner, the same material is typically used for the insulating coating of the core wire and the sheath, from the perspective of simplifying the material configuration. When the insulating coating of the core wire is made of an insulating coating material containing silicone rubber, the sheath is also typically made of the same insulating coating material containing silicone rubber, which provides high flexibility and heat resistance for the entire electric wire. When the insulating coating of the core wire is made of an insulating coating material containing cross-linked polyolefin, the sheath is also typically made of the same insulating coating material containing cross-linked polyolefin, which provides high abrasion resistance and chemical resistance for the entire electric wire.

[0006] Thus, when both the insulating coating and sheath of the core wire are made of a material containing silicone rubber, high flexibility and heat resistance are achieved. However, silicone rubber typically has poor abrasion and chemical resistance, making it difficult for the entire wire to achieve high abrasion and chemical resistance. On the other hand, when crosslinked polyolefin is used in automotive electric wires, a flame retardant such as a metal hydroxide is typically added to impart flame retardancy. However, the addition of the flame retardant reduces the flexibility of the insulating coating material. Therefore, when both the insulating coating and sheath of the core wire are made of a material in which a flame retardant is added to crosslinked polyolefin, high abrasion and chemical resistance are achieved, but the entire wire does not achieve high flexibility. Furthermore, crosslinked polyolefin is not a particularly heat-resistant material. Thus, while it is difficult to obtain an electric wire that combines high flexibility and heat resistance with high abrasion and chemical resistance, a wire that combines these properties is desired for automotive electric wires, especially for heavy-duty electric wires for high voltage applications.

[0007] In view of the above, an object of the present invention is to provide an electric wire in which a sheath is provided around the outer periphery of a core wire, and which has high flexibility and heat resistance as well as high abrasion resistance and chemical resistance.

[0008] The electric wire of the present disclosure comprises a core wire having a conductor and an insulating coating covering the outer periphery of the conductor, and a sheath covering the outer periphery of the core wire, wherein the insulating coating is made of a core coating material containing silicone rubber, and the sheath is made of a sheath material containing a cross-linked polyolefin and a flame retardant, and the modulus of elasticity of the sheath material is 30 times or less than the modulus of elasticity of the core coating material.

[0009] The electric wire of the present disclosure is an electric wire in which a sheath is provided around the outer periphery of a core wire, and has high flexibility and heat resistance as well as high abrasion resistance and chemical resistance.

[0010] 1A and 1B are diagrams illustrating an electric wire according to one embodiment of the present disclosure, in which Fig. 1A is a perspective view showing the end portion from which components are gradually removed, and Fig. 1B is a cross-sectional view.

[0011] [Description of an embodiment of the present disclosure] First, an embodiment of the present disclosure will be described. An electric wire according to an embodiment of the present disclosure has the following configuration.

[0012] [1] An electric wire according to an embodiment of the present disclosure includes a core wire having a conductor and an insulating coating covering the outer periphery of the conductor, and a sheath covering the outer periphery of the core wire, wherein the insulating coating is made of a core coating material containing silicone rubber, and the sheath is made of a sheath material containing a cross-linked polyolefin and a flame retardant, and the elastic modulus of the sheath material is 30 times or less than the elastic modulus of the core coating material.

[0013] In the above-described electric wire, the insulating coating that constitutes the core wire is made of a core coating material containing silicone rubber. Therefore, the overall characteristics of the electric wire can utilize the flexibility and heat resistance of the silicone rubber. Meanwhile, the sheath that covers the core wire is made of a sheath material containing a cross-linked polyolefin and a flame retardant. Therefore, the electric wire can utilize the abrasion resistance and chemical resistance of the cross-linked polyolefin to which the flame retardant is added. Abrasion resistance and chemical resistance are problematic properties when the electric wire comes into contact with external substances. Having high abrasion resistance and chemical resistance in the sheath disposed around the outer periphery of the electric wire provides the entire electric wire with high protection against abrasion and chemical contact. Furthermore, the elastic modulus of the sheath material is kept to 30 times or less that of the core coating material, ensuring sufficient flexibility of the entire electric wire. In this way, rather than constructing the insulating coating and sheath of the core wire from the same material, by constructing the insulating coating of the core wire from a material containing silicone rubber and the sheath from a material containing cross-linked polyolefin and a flame retardant, it is possible to manufacture an electric wire that has high flexibility and heat resistance as well as high abrasion resistance and chemical resistance as a whole, and can be used suitably for applications such as wiring inside automobiles.

[0014] [2] In the aspect of [1] above, the electric wire may have a metal braided layer between the core wire and the sheath, in contact with the sheath. The metal braided layer functions as an outer conductor, making the electric wire suitable for applications such as high voltage application. If the sheath were made of a material containing silicone rubber, like the insulating coating of the core wire, the softness of the silicone rubber would allow the sheath material to penetrate into the voids in the mesh of the metal braided layer, making it difficult to peel the sheath. However, in the electric wire according to the embodiment of the present disclosure, the sheath is made of a hard sheath material containing cross-linked polyolefin and a flame retardant, making it difficult for the sheath to penetrate into the voids in the mesh of the metal braided layer, and making it easy to peel and remove the sheath from the metal braided layer at the end of the electric wire, etc.

[0015] [3] In the above aspect [1] or [2], it is preferable that a sheet layer is not provided between the core wire and the sheath. The absence of a sheet such as a metal foil in the electric wire allows the overall flexibility of the electric wire to be maintained high. Conventionally, in an electric wire in which the sheath is made of a material containing silicone rubber, a sheet containing metal foil is often provided around the metal braided layer when the metal braided layer is disposed around the core wire to prevent the sheath material from penetrating into the voids in the mesh of the metal braided layer. However, in the electric wire according to the embodiment of the present disclosure, the sheath material is made of a hard material containing a cross-linked polyolefin and a flame retardant. This prevents excessive adhesion of the sheath to the inner member, such as penetration into the voids in the mesh of the metal braided layer. Therefore, it is not necessary to provide a layer, such as a sheet containing metal foil, inside the sheath to prevent excessive adhesion of the sheath to the inner member.

[0016] [4] In any one of the above aspects [1] to [3], the elastic modulus of the sheath material may be at least five times that of the core coating material, thereby effectively improving the flame retardancy and abrasion resistance of the electric wire due to the contribution of the sheath made of a material containing cross-linked polyolefin and a sufficient amount of flame retardant.

[0017] [5] In any one of the above aspects [1] to [4], the cross-linked polyolefin may be cross-linked polyethylene, which makes it easier to form a sheath with high abrasion resistance and chemical resistance.

[0018] [Details of the embodiment of the present disclosure] Hereinafter, an electric wire according to an embodiment of the present disclosure will be described in detail with reference to the drawings. Hereinafter, various properties are values ​​measured at room temperature in the atmosphere unless otherwise specified.

[0019] 1A and 1B are a perspective view and a cross-sectional view, respectively, showing the structure of an electric wire 1 according to one embodiment of the present disclosure. In Fig. 1A, components are sequentially removed from the end portion.

[0020] The electric wire 1 has a core wire 2 and a sheath 6. The core wire 2 has a conductor 3 and an insulating coating 4 that covers the outer periphery of the conductor 3. The sheath 6 is configured as an insulating layer that covers the outer periphery of the core wire 2. Furthermore, a metal braided layer 5 is disposed between the core wire 2 and the sheath 6, covering the outer periphery of the core wire 2, and the electric wire 1 is configured as a coaxial wire.

[0021] In the core wire 2, various metal materials can be used as the material for the conductor 3, including copper and copper alloys, aluminum and aluminum alloys, etc. Copper or copper alloys are particularly preferred due to their high conductivity and flexibility. The conductor 3 may be configured as a single wire, but is preferably composed of multiple conductor wires 31 to enhance flexibility during bending. The multiple conductor wires 31 may be bundled together to form the conductor 3, or may be twisted together to form a stranded wire. The conductor 3 may be compression-molded. When the conductor 3 includes multiple conductor wires 31, they may all be the same type of conductor wire, or may include two or more types of conductor wires. The insulating coating 4 of the core wire 2 is composed of a core coating material containing silicone rubber. The composition of the core coating material will be described in detail later.

[0022] The metal braided layer 5 is formed by interweaving a plurality of metal wires into a hollow tubular shape, and functions as the outer conductor of the electric wire 1. Examples of the metal wires that make up the metal braided layer 5 include thin wires made of metal materials such as copper, copper alloy, aluminum, aluminum alloy, iron, and iron alloy, as well as plated thin wires whose surfaces are plated with tin or the like. The metal braided layer 5 contacts the insulating coating 4 of the core wire 2 on the inner circumferential side of the tubular body and the sheath 6 on the outer circumferential side.

[0023] The sheath 6 covers the outer periphery of the metal braided layer 5 and serves to protect the inner core wire 2 and metal braided layer 5. The sheath 6 is made of a sheath material containing a cross-linked polyolefin and a flame retardant. The composition of the sheath material will be described in detail later. In many cases, compositions containing a cross-linked polyolefin and a flame retardant have a higher modulus of elasticity than silicone rubber compositions, but in the electric wire 1 according to this embodiment, the modulus of elasticity of the sheath material is kept to 30 times or less the modulus of elasticity of the core coating material that constitutes the insulating coating 4 of the core wire 2. In this specification, the term "modulus of elasticity" primarily refers to the flexural modulus.

[0024] To manufacture the electric wire 1 according to this embodiment, first, an insulating coating 4 is formed on the outer periphery of the conductor 3. To do this, the components constituting the core coating, such as silicone rubber, are kneaded together to prepare a composition, and the composition is then extruded onto the outer periphery of the appropriately preheated conductor 3. Heating is then performed as appropriate to crosslink the silicone rubber. A metal braided layer 5 is formed by braiding a metal element wire into a tubular shape around the outer periphery of the core wire 2 thus obtained. Furthermore, a sheath 6 is formed around the outer periphery of the metal braided layer 5. To do this, the components constituting the sheath material, such as polyolefin and a flame retardant, are kneaded together to prepare a composition, and the composition is then extruded or molded to form a layer around the outer periphery of the metal braided layer 5. Furthermore, a crosslinking operation, such as contact with water vapor, may be performed as appropriate to crosslink the polyolefin.

[0025] As described above, in the electric wire 1 according to this embodiment, the insulating coating 4 constituting the core wire 2 is made of a core coating material containing silicone rubber, and the sheath 6 covering the outer periphery of the core wire 2 is made of a sheath material containing cross-linked polyolefin and a flame retardant. Silicone rubber has high flexibility, and by using this silicone rubber to form the insulating coating 4 of the core wire 2, the core wire 2 and the entire electric wire 1 have high flexibility. In addition, silicone rubber has high heat resistance, and by forming the insulating coating 4, which is disposed immediately outside the conductor 3 and is susceptible to heating when current is passed through the conductor 3, from a material containing silicone rubber, the electric wire 1 has high heat resistance. Meanwhile, by forming the sheath 6 from a material containing cross-linked polyolefin and a flame retardant, the electric wire 1 is imparted with flame retardancy and also achieves high abrasion resistance and chemical resistance. Since abrasion due to contact with other substances and contact with chemicals occurs at the outer periphery of the electric wire, if the sheath 6 constituting the outer periphery of the electric wire 1 has high abrasion resistance and chemical resistance, high abrasion resistance and chemical resistance can be obtained as the overall property of the electric wire 1. Furthermore, by suppressing the modulus of elasticity of the sheath material to 30 times or less than the modulus of elasticity of the core coating material, it is possible to avoid an excessive decrease in the flexibility of the electric wire 1 as a whole due to the contribution of the sheath material, and in combination with the contribution of the core wire 2, it is possible to ensure sufficiently high flexibility of the electric wire 1.

[0026] As described above, the electric wire 1 according to this embodiment has high flexibility and heat resistance as well as high abrasion resistance and chemical resistance because the insulating coating 4 and the sheath 6 of the core wire 2 are made of different materials. If the sheath 6 were made of the same material containing silicone rubber as the insulating coating 4, the electric wire would have excellent flexibility and heat resistance but poor abrasion resistance and chemical resistance because silicone rubber does not exhibit particularly high abrasion resistance and chemical resistance. On the other hand, if the insulating coating 4 were made of the same material containing cross-linked polyolefin and a flame retardant as the sheath 6, the electric wire would have excellent abrasion resistance and chemical resistance but poor flexibility and heat resistance because the cross-linked polyolefin does not have particularly high heat resistance and the addition of the flame retardant reduces the flexibility of the material.

[0027] Furthermore, if the sheath 6 were made of a soft material such as silicone rubber, like the insulating coating 4, the sheath material would easily penetrate into the voids in the mesh of the inner metal braided layer 5 (the space surrounded by the metal wires) during molding of the sheath 6. This would result in excessively strong adhesion of the sheath 6 to the metal braided layer 5, making it difficult to peel and remove the sheath 6 at the end of the wire, etc. However, in the electric wire 1 according to this embodiment, the sheath 6 is made of a hard sheath material containing a cross-linked polyolefin and a flame retardant, so the sheath material is less likely to penetrate into the voids in the mesh of the metal braided layer 5 during molding. Therefore, the adhesion of the sheath 6 to the metal braided layer 5 is maintained at an appropriately low level, and high peelability is maintained when removing the sheath 6 at the end of the electric wire, etc. In addition, silicone rubber often lacks a crystalline melting point, making it difficult to apply molding techniques such as injection molding. Crosslinked polyolefins generally melt with heat and can be firmly bonded to other materials. Therefore, by forming the sheath 6 from a material containing crosslinked polyolefin, the sheath 6 can be formed by molding. Furthermore, while silicone rubber is non-polar because its surface is covered with dimethyl groups, crosslinked polyolefin compositions have polarity due to the contribution of additives such as flame retardants. Because the engineering plastics that make up the molding materials (molds) commonly used in molding are polar, molding using these molding materials can be suitably applied to polar crosslinked polyolefin compositions.

[0028] The specific dimensions of the electric wire 1 are not particularly limited, but from the viewpoint of effectively utilizing the characteristics of the electric wire 1, such as flexibility and heat resistance, which are mainly due to the contribution of the insulating coating 4 of the core wire 2, the conductor cross-sectional area of ​​the core wire 2 is set to be approximately 20 mm ２ The upper limit of the conductor cross-sectional area is not specified, but it is generally 200 mm ２It is preferable that the thickness of the insulating coating 4 be 0.6 mm or more. Although the upper limit of the thickness of the insulating coating 4 is not particularly specified, it is preferable that the thickness be approximately 2.5 mm or less. On the other hand, from the viewpoint of enhancing the properties such as abrasion resistance and chemical resistance imparted to the electric wire 1 by the sheath 6, the thickness of the sheath 6 is preferably 0.8 mm or more. Furthermore, from the viewpoint of ensuring the flexibility of the sheath 6, the thickness of the sheath 6 is preferably 2.0 mm or less. Furthermore, from the viewpoint of utilizing the respective properties of the insulating coating 4 and the sheath 6 in a balanced manner as the overall properties of the electric wire 1, a preferable ratio of the thickness of the insulating coating 4 to the sheath 6 can be, for example, in the range of 1:0.8 or more and 1:2 or less in terms of the insulating coating:sheath thickness ratio. The use of the electric wire 1 is not particularly limited, but since the electric wire 1 has excellent flexibility, heat resistance, abrasion resistance, chemical resistance, and flame retardancy, it can be particularly preferably used as an electric wire for automobiles, where these properties are advantageous.

[0029] As described above, the electric wire 1 may be composed only of the core wire 2, the metal braided layer 5, and the sheath 6, or may include other components. However, it is preferable that the electric wire 1 does not have a sheet body, i.e., a continuous layer of material in a sheet form, between the core wire 2 and the sheath 6. Sheet bodies, such as metal foil, can reduce the flexibility of the entire electric wire. However, the electric wire 1 does not include such a sheet body, thereby ensuring high flexibility. In general coaxial wires, a sheet body such as metal foil may be disposed between the metal braided layer covering the outer periphery of the core wire and the sheath. However, it is preferable that such a sheet body is not disposed in the electric wire 1 according to the present embodiment. In this case, the metal braided layer 5 and the sheath 6 come into direct contact. However, as described above, because the sheath 6 is composed of a sheath material containing a cross-linked polyolefin and a flame retardant, the sheath material is less likely to penetrate into the voids in the mesh of the metal braided layer 5.

[0030] In the above description, the electric wire 1 has a coaxial structure in which a metal braided layer 5 and a sheath 6 are disposed around a single core wire 2. However, the structure of the electric wire 1 is not limited to this coaxial structure, as long as the outer periphery of at least one core wire 2 is covered with a sheath 6, either directly or via another layer such as a metal braided layer 5. For example, a structure in which the sheath 6 is formed by appropriately interposing a layer such as a metal braided layer 5 around the outer periphery of an assembly of bundled or twisted core wires 2 is also conceivable. Furthermore, as in the above-described embodiment, it is preferable that both the insulating coating 4 and the sheath 6 of the core wire 2 are each composed of a single layer having a predetermined composition. However, this does not preclude the insulating coating 4 and / or the sheath 6 from having multiple different layers. In such a case, at least one layer constituting each of the insulating coating 4 and the sheath 6 may be composed of a core coating material and a sheath material having a predetermined composition.

[0031] <Constituent Material of Insulating Coating> Here, the component composition of the core coating material that constitutes the insulating coating 4 of the core wire 2 in the electric wire 1 according to this embodiment will be described in detail.

[0032] As described above, the core coating material constituting the insulating coating 4 is made of a material containing silicone rubber. It is preferable that the silicone rubber be cross-linked. Silicone rubber has an organopolysiloxane main chain and polymer chains to which organic groups such as methyl groups, ethyl groups, vinyl groups, and phenyl groups are bonded, and these polymer chains are cross-linked to each other. It is preferable to use a thermosetting (thermally cross-linked) silicone rubber as the silicone rubber constituting the core coating material. Thermosetting silicone rubbers include millable types that become elastic when kneaded with a cross-linking agent and then heated to cross-link, and liquid rubber types that are liquid before cross-linking. Either type may be used, but millable silicone rubber is particularly preferable.

[0033] The crosslinking of thermosetting silicone rubber can be promoted by heating, but if necessary, crosslinking may be promoted using a crosslinking agent such as an organic peroxide and / or a catalyst such as a platinum catalyst. From the viewpoint of promoting sufficient crosslinking, the content of the crosslinking agent in the silicone rubber composition that becomes the core coating material can be in the range of 0.5 parts by mass or more and 2 parts by mass or less per 100 parts by mass of silicone rubber.

[0034] The core coating material may contain organic polymers other than silicone rubber. However, from the viewpoint of effectively utilizing the properties of crosslinked silicone rubber, such as flexibility and heat resistance, it is preferable that silicone rubber constitutes the main component of the organic polymers constituting the core coating material, and more preferably constitutes the entire amount. It is also preferable that the core coating material does not contain crosslinked polyolefin as an organic polymer. In addition to the above-mentioned crosslinking agent and catalyst, the core coating material may also contain additives as appropriate. These additives include crosslinking inhibitors, heat stabilizers, reinforcing fillers, extending fillers, dispersion promoters, lubricants, colorants, and acid acceptors (Ca(OH) ２ , Mg(OH) ２ etc.)

[0035] The physical properties that the core coating material should have are not particularly specified. However, from the viewpoint of improving flexibility, it is preferable that the core coating material have an elastic modulus of 5 MPa or less. The lower limit of the elastic modulus is not particularly specified, but is generally 0.5 MPa or more.

[0036] <Constituent Material of Sheath> Next, the component composition of the sheath material that constitutes the sheath 6 in the electric wire 1 according to this embodiment will be described in detail.

[0037] As described above, the sheath material constituting the sheath 6 is composed of a material containing a cross-linked polyolefin and a flame retardant. Cross-linked polyolefins have a structure in which the polyolefin main chain is cross-linked. The type of polyolefin constituting the cross-linked polyolefin is not particularly limited, and examples include homopolymers of olefins such as ethylene and propylene, and copolymers of ethylene or propylene with α-olefins such as butene and octene. Alternatively, olefin-based polyolefin elastomers may be used. In particular, cross-linked polyethylene (PE), i.e., a cross-linked product obtained from a homopolymer of ethylene or a copolymer of ethylene and an α-olefin, such as an ethylene-butene copolymer or an ethylene-octene copolymer, is preferably used as the cross-linked polyolefin. Cross-linked polyethylene has particularly excellent abrasion resistance and chemical resistance.

[0038] The crosslinked polyolefin may be crosslinked by any method, such as silane crosslinking or radical crosslinking, but silane crosslinking is preferred from the viewpoint of ease of crosslinking. In this case, the crosslinked polyolefin may be formed by subjecting a silane-grafted polyolefin, in which a silane coupling agent is graft-polymerized onto the polyolefin main chain, to crosslinking using a catalyst. As the crosslinking catalyst, a known silanol condensation catalyst such as a tin compound may be used. The silane-grafted polyolefin can be crosslinked by contact with water vapor using a crosslinking catalyst. Below, a preferred composition of the sheath material will be described, mainly assuming the use of silane crosslinking.

[0039] The silane-grafted polyolefin preferably has the following physical properties: Density: 0.86 to 0.89 g / cm ３ (Especially 0.88 g / cm ３ or less) Melting point: 70 to 135°C (especially 80°C or higher) Melt flow rate (MFR): 0.5 to 5.0 g / 10 min (especially 1.0 to 3.0 g / 10 min) Flexural modulus: 3 to 50 MPa (especially 25 MPa or less) Gel fraction: 80% or more (especially 85% or more)

[0040] The sheath material may contain only crosslinked polyolefin as a polymer component, or may contain polymer components other than crosslinked polyolefin. In addition to crosslinked polyolefin, preferred polymer components include unmodified polyolefin and modified polyolefin.

[0041] Unmodified polyolefins are polyolefins composed of hydrocarbons to which no modifying groups have been introduced by graft polymerization, copolymerization, or the like, and do not form crosslinked bodies. Specifically, homopolymers of olefins such as ethylene and propylene, or copolymers of ethylene or propylene with α-olefins such as butene and octene, can be used. Alternatively, olefin-based polyolefin elastomers can be used. In particular, unmodified polyethylene, i.e., unmodified ethylene homopolymers or copolymers of ethylene and α-olefins such as ethylene-butene copolymers and ethylene-octene copolymers, are preferred. The unmodified polyolefin may be the same as or different from the polyolefin constituting the main chain of the crosslinked polyolefin, but using the same type of polyolefin provides excellent compatibility. Unmodified polyolefins play a role in the sheath material, such as improving flexibility.

[0042] The modified polyolefin is a modified polyolefin having one or more functional groups selected from a carboxy group, an ester group, an acid anhydride group, an amino group, and an epoxy group. The modified polyolefin may be one in which a functional group has been introduced by graft polymerization of a polymerizable compound having the functional group onto an unmodified base polyolefin, or one in which a functional group has been introduced by copolymerizing a polymerizable compound having the functional group with an olefin polymerizable with the polymerizable compound (excluding those in which a silanol derivative has been introduced). Because of the functional group, the modified polyolefin exhibits high interaction with inorganic components such as flame retardants, and acts as a compatibilizer between the polymer component and the inorganic component, improving the dispersibility and adhesion of the inorganic component. Furthermore, the polarity of the modified polyolefin makes it easier to inkjet print letters, symbols, etc. on the surface of the sheath 6 containing the modified polyolefin.

[0043] As the unmodified polyolefin and the modified polyolefin, those having the following physical properties can be suitably used: Density: 0.86 to 0.95 g / cm ３ (Especially 0.88 to 0.90 g / cm ３ ) Melting point: 65 to 150°C (especially 100°C or higher) MFR: 0.5 to 5.0 g / 10 min (especially 1.0 to 3.0 g / 10 min) Flexural modulus: 3 to 900 MPa (especially 10 to 200 MPa)

[0044] In the composition that becomes the sheath material, the total amount of the unmodified polyolefin and the modified polyolefin is preferably 10 parts by mass or more and 70 parts by mass or less, where the total amount of the silane-grafted polyolefin, the unmodified polyolefin, and the modified polyolefin is 100 parts by mass. This allows the sheath material to have excellent flexibility and a sufficient crosslinking density, resulting in excellent heat resistance and abrasion resistance. Furthermore, the content of the modified polyolefin is preferably 3 parts by mass or more and 15 parts by mass or less, relative to the 100 parts by mass. More preferably, it is 4 parts by mass or more and 10 parts by mass or less. This allows the effect of the modified polyolefin as a compatibilizer to be sufficiently obtained. Note that the sheath material preferably does not contain silicone rubber. Preferably, the silane-grafted polyolefin, the modified polyolefin, and the unmodified polyolefin account for the entire amount of the polymer components that make up the composition that becomes the sheath material.

[0045] The sheath material contains a flame retardant in addition to a polymer component such as cross-linked polyolefin. The inclusion of the flame retardant in the sheath material imparts flame retardancy to the sheath 6 and the entire electric wire 1. The type of flame retardant contained in the sheath material is not particularly limited, and examples include metal hydroxides and bromine-based flame retardants. It is particularly preferable to use a metal hydroxide as the flame retardant. Metal hydroxides alone can impart high flame retardancy to the sheath material. Furthermore, a relatively large amount of a flame retardant made of a metal hydroxide must be added to achieve sufficient flame retardancy, and adding a large amount of flame retardant reduces the flexibility of the sheath material. However, in the electric wire 1 according to this embodiment, a core coating material containing highly flexible silicone rubber is used as the insulating coating 4 of the core wire 2, thereby compensating for the low flexibility of the sheath 6 and achieving sufficiently high flexibility for the electric wire 1 as a whole.

[0046] In addition to or instead of metal hydroxides, bromine-based flame retardants can be used as flame retardants. In this case, by using them in combination with antimony trioxide as a flame retardant aid, the flame retardancy of the sheath material can be effectively improved.

[0047] When a metal hydroxide is used alone as the flame retardant, it is preferable to add the metal hydroxide in an amount of 10 parts by mass or more and 100 parts by mass or less relative to a total of 100 parts by mass of the polymer components constituting the sheath material. This provides high flame retardancy in the sheath 6 and prevents a decrease in the flexibility of the sheath 6. Preferably, the amount added is 50 parts by mass or more. When a brominated flame retardant is used, from the same viewpoint, it is preferable to blend the brominated flame retardant in an amount of 10 parts by mass or more and 40 parts by mass or less and antimony trioxide in an amount of 5 parts by mass or more and 20 parts by mass or less relative to a total of 100 parts by mass of the polymer components.

[0048] The sheath material may contain additives other than the crosslinking catalyst and flame retardant, such as antioxidants, metal deactivators, lubricants, zinc oxide, zinc sulfide, imidazole compounds, colorants, and silicone oils.

[0049] As described above, the elastic modulus of the sheath material is kept to 30 times or less that of the core coating material. This ensures sufficiently high flexibility for the entire electric wire 1. Preferably, the elastic modulus of the sheath material is kept to 25 times or less, further 20 times or less, or 15 times or less that of the core coating material. The elastic modulus of the sheath material can be adjusted by the type of polymer component used, such as silane-grafted polyolefin, unmodified polyolefin, or modified polyolefin, and the type and amount of flame retardant and other additives. A low elastic modulus of the sheath material can be achieved, for example, by using a polymer component with a low elastic modulus. Alternatively, the amount of flame retardant and other additives can be reduced. For example, the amount of flame retardant added can be limited to 100 parts by mass or less relative to the total amount of polymer components. Alternatively, a brominated flame retardant can be used in place of part or all of the metal hydroxide flame retardant, and the amount of the brominated flame retardant added can be limited to 40 parts by mass or less relative to the total amount of polymer components. In addition, it is advisable to limit the total amount of solid additives (excluding crosslinking catalysts) other than flame retardants, such as antioxidants, metal deactivators, lubricants, zinc oxide, zinc sulfide, and imidazole-based compounds, to 20 parts by mass or less, and further to 10 parts by mass or less.

[0050] The elastic modulus of the sheath material is not particularly specified as long as it is kept to 30 times or less that of the core coating material. However, from the viewpoint of ensuring sufficiently high flexibility of the electric wire 1 as a whole, it is preferably 90 MPa or less, further 75 MPa or less, or 50 MPa or less. The lower limit of the elastic modulus of the sheath material is not particularly specified, but it is preferably 5 times or more, further 8 times or more that of the core coating material. Furthermore, it is preferably 15 MPa or more, further 25 MPa or more. This is because a high elastic modulus of the sheath material achieves high abrasion resistance. Furthermore, since the elastic modulus of the sheath material increases with the content of flame retardant, a high elastic modulus of the sheath material is an indicator of high flame retardancy of the electric wire 1.

[0051] Examples are shown below. Here, the relationship between the core coating material and sheath material and the characteristics of a coaxial electric wire was evaluated. In these examples, the characteristics were evaluated at room temperature in the atmosphere unless otherwise specified.

[0052] [Sample Preparation] A conductor (conductor cross-sectional area: 51.95 mm) made of a twisted copper alloy wire was used. ２ A core wire was obtained by extruding a core coating material to a thickness of 0.71 mm around the outer periphery of the core wire to form an insulating coating. A metal braided layer was formed around the outer periphery of the core wire by braiding copper alloy wires into a cylindrical shape. Further, a sheath material was extruded to a thickness of 0.88 mm around the outer periphery of the metal braided layer to form a sheath, and the electric wire was obtained as a sample. However, for sample B4 only, a metal foil (a PET sheet having a 25 μm thick Cu layer) was wrapped around the outer periphery of the core wire, and then a metal braided layer was formed around the outer periphery of the metal foil.

[0053] The core coating material constituting the insulating coating of the core wire of each sample and the sheath material constituting the sheath were silicone materials 1 and 2 (materials mainly composed of silicone rubber), whose component compositions are shown in Table 3 below, and olefin-based materials 1 to 6 (materials mainly composed of uncrosslinked or crosslinked polyolefin), whose component compositions are shown in Table 4, in the combinations shown in Table 5 for each sample. For silicone materials 1 and 2, the molded body was heated after extrusion molding to crosslink the silicone rubber. For olefin-based materials 2 to 6, the molded body was exposed to water vapor to crosslink the silane-grafted polyolefin.

[0054] The materials used in preparing the silicone material are as follows: Silicone rubber: "ELASTOSIL R401-60" manufactured by Wacker Asahi Kasei Silicone Co., Ltd. Cross-linking agent: "DS-13" manufactured by Wacker Asahi Kasei Silicone Co., Ltd. Reinforcing filler: calcium carbonate "Softon 15000" manufactured by Shiraishi Calcium Co., Ltd.

[0055] The materials used in preparing the olefin-based materials are as follows. (Polymer Materials) (1) Silane-grafted Polyolefins Silane-grafted PE1 and silane-grafted PE2 were prepared as follows. The physical properties of the resulting silane-grafted polyolefins are shown in Table 1 below. Silane-grafted PE1: 100 parts by mass of base polyolefin (a mixture of 50% by mass of "Engage 7256" manufactured by Dow Elastomers and 50% by mass of "INFUSE 9107" manufactured by Dow Elastomers) were dry-blended with 2.0 parts by mass of vinyltrimethoxysilane ("KBM1003" manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.1 parts by mass of dicumyl peroxide ("Percumyl D" manufactured by NOF Corporation). This material was kneaded at 200°C in a single-screw extruder kneader with an inner diameter of 25 mm until the density reached 0.87 g / cm. ３Silane-grafted PE2: 100 parts by mass of base polyolefin ("Engage 7256" manufactured by Dow Elastomers) was dry-blended with 1.5 parts by mass of vinyltrimethoxysilane ("KBM1003" manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.1 parts by mass of dicumyl peroxide ("Percumyl D" manufactured by NOF Corporation). This material was kneaded at 200°C in a single-screw extruder kneader with an inner diameter of 25 mm to obtain a mixture having a density of 0.89 g / cm. ３ It was adjusted so that

[0056]

[0057] (2) Other polymer materials The following were prepared as other polymer materials. The physical properties of each are summarized in Table 2 below. Unmodified PE1: "Engage 7256" manufactured by Dow Elastomers Unmodified PE2: "Engage 7457" manufactured by Dow Elastomers Unmodified PP: "Novatec EG7F" manufactured by Japan Polypropylene Modified PE1: "Modic AP M512" manufactured by Mitsubishi Chemical Modified PE2: "Newcon NAR6" manufactured by Japan Polypropylene

[0058]

[0059] (Flame retardants) ・Metal hydroxide flame retardant: Magnesium hydroxide "Kisuma 5C" manufactured by Kyowa Chemical Industry Co., Ltd. ・Brominated flame retardant: "SAYTEX 8010" manufactured by Albemarle Corporation ・Flame retardant assistant: Antimony trioxide "MSW" manufactured by Yamanaka Sangyo Co., Ltd. (Other additives) ・Antioxidant: "Irganox 1010FF" manufactured by BASF Japan Ltd. ・Metal deactivator: "CDA-1" manufactured by ADEKA Corporation ・Lubricant: "Alflo P10" manufactured by NOF Corporation ・Zinc oxide: "Zinc oxide type 1" manufactured by Hakusui Tech Co., Ltd. ・Imidazole compound: 2-mercaptobenzimidazole "Antage MB" manufactured by Kawaguchi Chemical Industry Co., Ltd. (Crosslinking catalyst) ・Crosslinking catalyst 1: "Linkron LZ015" manufactured by Mitsubishi Chemical Corporation ・Crosslinking catalyst 2: "Linkron LZ082Z" manufactured by Mitsubishi Chemical Corporation

[0060] The component compositions of silicone materials 1 and 2 and olefinic materials 1 to 6 used as the core coating material and sheath material are shown in Tables 3 and 4 below, respectively.

[0061]

[0062] [Evaluation Method] (1) Elastic Modulus The elastic modulus of each silicone material and olefin-based material was measured by a bending test in accordance with ASTM D790 using a sheet-shaped sample of each material.

[0063] (2) Flexibility The flexibility of each sample electric wire was evaluated by a U-shape flexibility test. Specifically, each electric wire was cut into a length of 400 mm and bent into a U-shape, and the maximum bending stress was measured. If the measured value was 55 N or less, the flexibility was evaluated as "A", indicating high flexibility. Furthermore, if the measured value was 35 N or less, the flexibility was evaluated as "A+", indicating very high flexibility. On the other hand, if the measured value was greater than 55 N, the flexibility was evaluated as "B", indicating low flexibility.

[0064] (3) Abrasion Resistance The abrasion resistance of each sample electric wire was evaluated by a tape abrasion test in accordance with ISO 6722. That is, a tape-shaped sandpaper was pressed against the outer periphery of each electric wire with an added mass of 1.9 kg, and the sandpaper was moved at a speed of 1500±75 mm / min. Then, the distance the tape moved until the metal braid layer was exposed was measured. The longer the movement distance, the better the abrasion resistance was judged to be. If the movement distance was 3000 mm or more, the abrasion resistance was judged to be high "A". On the other hand, if the movement distance was less than 3000 mm, the abrasion resistance was judged to be low "B".

[0065] (4) Chemical Resistance The resistance of the wires to sulfuric acid was evaluated using a chemical resistance test in accordance with ISO 6722. Sulfuric acid is a chemical that simulates battery fluid. Specifically, the wires were immersed in 25% by mass dilute sulfuric acid for 10 seconds, then removed from the liquid and left for 3 minutes to remove excess liquid. The wires were then left at 150°C for 240 hours. After high-temperature storage, the wires were left at room temperature for 30 minutes. After storage, a winding test was performed at a diameter of 5 times the original diameter, and the insulation was visually inspected for cracks. For samples without cracks, a voltage test after environmental testing in accordance with ISO 6722 was performed. That is, a voltage of 3 kV was applied for 1 minute, and samples that did not exhibit problems such as dielectric breakdown were deemed to have passed. The samples that passed the test were further subjected to a chemical resistance test in accordance with JASO D625, as described below.

[0066] In a chemical resistance test conforming to JASO D625, the resistance of the electric wire to sulfuric acid was further evaluated. Again, dilute sulfuric acid with a concentration of 25% by mass was used. Specifically, dilute sulfuric acid was dripped onto the electric wire, and the electric wire was left in an aging tank at 150°C for 8 hours. The electric wire was then removed from the aging tank, and dilute sulfuric acid was dripped onto the same spot again. The electric wire was then left in the aging tank for 16 hours (24 hours in total), and then removed from the aging tank. This cycle was repeated for a total of two times. The electric wire was then removed from the aging tank and left at room temperature for 30 minutes. Then, a winding test was performed at a diameter of 1.5 times the normal diameter, and the insulation was visually inspected for cracks. Samples without cracks were deemed to have passed the test.

[0067] Samples that passed both the ISO 6722 test and the JASO D625 test were rated "A" for high chemical resistance, while samples that did not pass the ISO 6722 test or passed only the ISO 6722 test were rated "B" for low chemical resistance.

[0068] (5) Flame Retardance The flame retardance of each electric wire was evaluated by a combustion test in accordance with ISO 6722. That is, the communication electric wire for each sample was cut to a length of 600 mm and held in a 45° inclined position. A gas burner was then set 100 mm below the sample, and a flame was applied to the sample for 15 seconds. After the flame was removed, the time until the fire was extinguished was measured. If the time until the fire was extinguished was within 70 seconds, the flame retardance was evaluated as "A", indicating high flame retardance. On the other hand, if the time until the fire was extinguished was longer than 70 seconds, the flame retardance was evaluated as "B", indicating low flame retardance.

[0069] (6) Core Heat Resistance The heat resistance of the insulating coating of the core wire was evaluated by a heat life test in accordance with ISO 6722. Specifically, the core wire constituting each sample electric wire was held at 175°C for 3000 hours. After that, a winding test was performed at 1.5 times the diameter, and the insulation was visually inspected for cracks. Samples without cracks were rated "A" for high core heat resistance. On the other hand, samples with cracks were rated "B" for low core heat resistance.

[0070] (7) Sheath Peelability The sheath peelability of each sample electric wire was evaluated. A cut was made in the sheath in a region 50 mm from the end of the electric wire using a Schleuniger automatic cut and strip machine "MegaStrip 9680" to a depth that did not touch the metal braided layer, and the sheath was peeled off. The electric wire after peeling was visually observed, and samples in which the metal braided layer was free of scratches and no sheath pieces were attached to the metal braided layer were evaluated as having high sheath peelability, or "A." On the other hand, samples in which at least one of scratches on the metal braided layer and adhesion of sheath pieces had occurred were evaluated as having low sheath peelability, or "B."

[0071] [Evaluation Results] Table 5 shows the results of each evaluation for samples A1 to A3 and B1 to B6, along with the material type and elastic modulus of the core coating material constituting the insulating coating and the sheath material constituting the sheath, and the presence or absence of metal foil.

[0072]

[0073] In Table 5, samples A1 to A3 all have core coating materials made of a silicone material containing silicone rubber, and sheath materials made of an olefin-based material containing cross-linked polyolefin and a flame retardant. The sheath material has a modulus of elasticity that is 30 times or less that of the core coating material. All of the electric wires of samples A1 to A3 have high flexibility, abrasion resistance, chemical resistance, flame retardancy, core heat resistance, and sheath strippability. Of these properties, flexibility and core heat resistance are primarily attributed to the insulating coating properties, while abrasion resistance, chemical resistance, flame retardancy, and sheath strippability are primarily attributed to the sheath properties. The sheath materials of samples A1 to A3 have different moduli of elasticity. Among them, samples A1 and A2, which have a low sheath material modulus of elasticity, exhibit particularly high flexibility.

[0074] In sample B1, a polyolefin resin is used as the sheath material, but the polyolefin resin is not crosslinked and no flame retardant is added. In sample B2, a crosslinking catalyst is added to the silane-grafted polyolefin in the sheath material, crosslinking the polyolefin resin, but no flame retardant is added. In accordance with the sheath material composition, the elastic modulus of the sheath material in both samples B1 and B2 is significantly lower than that of samples A1 to A3. Corresponding to the low elastic modulus of the sheath material, the abrasion resistance of both samples B1 and B2 is low. The absence of a flame retardant in the sheath material also results in low flame retardancy. On the other hand, in sample B3, the sheath material contains crosslinked polyolefin and a flame retardant, but the elastic modulus of the sheath material is more than 30 times higher than that of the core coating material. Correspondingly, the flexibility of the wire is low.

[0075] In samples B4 and B5, both the sheath material and the core coating material are made of silicone material. The low-elasticity silicone material occupies the outer periphery of the wire, resulting in poor abrasion resistance. Sample B4, which uses a low-elasticity silicone material for the sheath material, also has poor chemical resistance. In sample B4, metal foil is placed between the core wire and the metal braid layer, resulting in high sheath peelability. In contrast, sample B5 does not have metal foil, and the sheath is in direct contact with the metal braid layer, resulting in poor sheath peelability. The poor sheath peelability is thought to be due to the sheath material penetrating into the voids in the mesh of the metal braid layer. In sample B6, both the sheath material and the core coating material are made of a material containing cross-linked polyolefin and a flame retardant. Correspondingly, the wire has poor flexibility. The core's heat resistance is also poor.

[0076] The above test results show that in an electric wire having a sheath around the outer periphery of a core wire, if the insulating coating of the core wire is made of a core coating material containing silicone rubber, while the sheath is made of a sheath material containing cross-linked polyolefin and a flame retardant, and the elastic modulus of the sheath material is kept to 30 times or less that of the core coating material, an electric wire can be obtained that combines high flexibility and heat resistance with high abrasion resistance and chemical resistance. Furthermore, even if a metal braided layer is provided between the core wire and the sheath in contact with the sheath, the peelability of the core coating material can be maintained at a high level.

[0077] Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0078] REFERENCE SIGNS LIST 1 Electric wire 2 Core wire 3 Conductor 31 Conductor wire 4 Insulating coating 5 Metal braided layer 6 Sheath

Claims

1. An electric wire comprising: a core wire having a conductor and an insulating coating covering the outer periphery of the conductor; and a sheath covering the outer periphery of the core wire, wherein the insulating coating is made of a core coating material containing silicone rubber, and the sheath is made of a sheath material containing a cross-linked polyolefin and a flame retardant, and the modulus of elasticity of the sheath material is 30 times or less than the modulus of elasticity of the core coating material.

2. The electric wire according to claim 1, further comprising a metallic braided layer between said core wire and said sheath and in contact with said sheath.

3. The electric wire according to claim 1 or 2, wherein no sheet layer is provided between the core wire and the sheath.

4. The electric wire according to claim 1 or 2, wherein the modulus of elasticity of the sheath material is at least five times the modulus of elasticity of the core coating material.

5. The electric wire according to claim 1 or 2, wherein the cross-linked polyolefin is cross-linked polyethylene.

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