Resin composition, direct-current insulated electrical wire, and direct-current cable

Abstract

The purpose of the present invention is to provide: a resin composition that has excellent insulation properties with respect to direct-current voltage; and to provide a direct-current insulated electrical wire that does not readily experience electrical breakdown, even when direct-current voltage is continuously applied. This resin composition is for forming an insulation layer for a direct-current insulated electrical wire and contains a polyethylene resin and a metal chelating agent. The metal chelating agent is preferably 1,2-bis[3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyl]-hydrazine. This direct-current insulated electrical wire comprises a conductor 10 and an insulating layer 30 that coats the outer circumference of the conductor 10 with an adhesive layer 20 therebetween.

Description

Resin composition, DC insulated wire and DC cable

[0001] The present invention relates to a resin composition, a DC insulated wire, and a DC cable, and more specifically to a resin composition that has excellent insulating properties when a DC voltage is applied, a DC insulated wire having an insulating layer made of the resin composition, and a DC cable including the DC insulated wire.

[0002] 2. Description of the Related Art As an insulated wire, a single-layer insulated wire is known, which is made up of a conductor and an insulating layer covering the outer periphery of the conductor (see Patent Document 1).

[0003] JP 2016-17108 A

[0004] However, conventionally known insulated wires, including the one described in Patent Document 1, have a problem in that the insulating layer constituting the wire has poor insulating properties against DC voltage, and when a DC voltage above a certain level is continuously applied to the insulated wire, dielectric breakdown occurs in a short period of time.

[0005] The present invention has been made in light of the above circumstances. An object of the present invention is to provide a resin composition having excellent insulating properties against DC voltage, which can be used as a material for forming the insulating layer of a DC insulated wire. Another object of the present invention is to provide a DC insulated wire and a DC cable that are less likely to suffer from dielectric breakdown even when a DC voltage is continuously applied.

[0006] In order to achieve the above object, the inventors of the present invention have conducted extensive research and have found that dielectric breakdown (short circuit) due to the application of a DC voltage is induced when ions of the metal (copper, aluminum, etc.) that constitutes the conductor diffuse into the insulating layer and migrate within the insulating layer, and that dielectric breakdown can be prevented by capturing these metal ions and preventing their migration. Based on this finding, the present invention has been completed.

[0007] The resin composition of the present invention is a resin composition for forming an insulating layer of a DC insulated wire, and is characterized by containing a polyethylene resin and a metal chelating agent.

[0008] In the resin composition of the present invention, it is preferable that the metal chelating agent comprises a hydrazine derivative, and particularly 1,2-bis[3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyl]-hydrazine.

[0009] It is also preferable that the polyethylene resin contains 0.01 to 0.5 parts by mass of the metal chelating agent per 100 parts by mass of the polyethylene resin.

[0010] It is also preferable that the composition contains 100 parts by mass of the polyethylene resin, 0.01 to 0.5 parts by mass of the metal chelating agent, and 0.01 to 0.5 parts by mass of an antioxidant.

[0011] The resin composition of the present invention is suitable as a resin composition for forming an insulating layer of a DC insulated electric wire to which a DC voltage exceeding 750 V is applied.

[0012] The DC insulated wire of the present invention is characterized by having an insulating layer made of the resin composition of the present invention.

[0013] The DC insulated wire of the present invention preferably includes a conductor or a waveguide, and the insulating layer that covers the outer periphery of the conductor or the waveguide directly or via a thin layer, wherein the thin layer is preferably an adhesive layer having a thickness of 500 μm or less.

[0014] The DC insulated wire of the present invention preferably does not undergo dielectric breakdown even when a DC voltage is applied for 80 minutes under an applied electric field condition of 250 kV / mm.

[0015] The DC cable of the present invention is characterized in that at least one DC insulated wire of the present invention is housed within an outer sheath.

[0016] The resin composition of the present invention has excellent insulating properties against DC voltage and can be suitably used as a material for forming an insulating layer of a DC insulated wire. The DC insulated wire / cable of the present invention is less likely to suffer from dielectric breakdown even when a relatively high DC voltage (for example, an applied electric field of 250 kV / mm) is continuously applied thereto.

[0017] The present invention relates to an insulated wire for DC use, and to an insulated wire for DC use according to the present invention.

[0018] <Resin Composition> The resin composition of the present invention is a resin composition for forming an insulating layer of a DC insulated wire, and contains a polyethylene resin and a metal chelating agent as essential components.

[0019] As the polyethylene-based resin constituting the resin composition of the present invention, any of the known materials used as insulating materials for electric wires and cables (high-density polyethylene, medium-density polyethylene, low-density polyethylene, modified polyethylene, ethylene-diene copolymer) can be used.

[0020] As the polyethylene-based resin constituting the resin composition of the present invention, it is preferable to use a mixture of a high-density polyethylene-based resin and a low-density polyethylene-based resin, or to use a medium-density polyethylene, as this improves the processing stability of the resin composition and the electrical properties and abrasion resistance of the insulating layer formed.

[0021] The metal chelating agent included in the resin composition of the present invention is a compound that can capture (inactivate) metal ions (such as copper ions and aluminum ions) diffused in an insulating layer made of the resin composition by forming a chelate. By capturing the metal ions with the metal chelating agent, migration of the metal ions within the insulating layer when a DC voltage is applied to the insulated wire is suppressed, thereby preventing dielectric breakdown caused by this migration.

[0022] Examples of metal chelating agents include hydrazine derivatives, salicylic acid derivatives, triazole compounds, etc. Among these, hydrazine derivatives are preferred, and 1,2-bis[3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyl]-hydrazine (trade name: Irganox MD1024, manufactured by BASF Japan) is particularly preferred.

[0023] The content of the metal chelating agent in the resin composition of the present invention is preferably 0.01 to 0.5 parts by mass, more preferably 0.075 to 0.3 parts by mass, and particularly preferably 0.15 to 0.3 parts by mass per 100 parts by mass of the polyethylene-based resin. If this content is less than 0.01 part by mass, the insulating properties of the resin composition against DC voltage cannot be sufficiently improved. On the other hand, even if this content exceeds 0.5 parts by mass, not only will the insulating properties be insufficient to be improved commensurate with the amount added, but an excessive content may also result in a decrease in the dispersibility of the metal chelating agent, resulting in a decrease in mechanical strength, or the metal chelating agent may bloom on the surface of the insulating layer, impairing surface smoothness.

[0024] The resin composition of the present invention may contain other additives. Examples of optional additives include antioxidants, light stabilizers, crosslinking agents, crosslinking aids, colorants, UV absorbers, softeners, lubricants, plasticizers, and inorganic fillers. In particular, when an antioxidant is used in combination, the synergistic effect with the metal chelating agent can sufficiently suppress oxidative degradation.

[0025] Preferred examples of the antioxidant added to the resin composition of the present invention include hindered phenol-based antioxidants such as pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: "Irganox 1010FF" (manufactured by BASF Japan)), and thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (trade name: "Irganox 1035FF" (manufactured by BASF Japan)).

[0026] The method for producing the resin composition of the present invention is not particularly limited, and the resin composition can be produced by melt-kneading a polyethylene resin, a metal chelating agent, and optional components such as additives.

[0027] The resin composition of the present invention is suitably used for forming an insulating layer of a DC insulated wire to which a DC voltage exceeding 750 V is applied. Insulated wires to which a high DC voltage exceeding 750 V is applied are prone to problems of dielectric breakdown, and therefore, from the viewpoint of preventing dielectric breakdown, it is particularly effective to include a metal chelating agent in the resin composition.

[0028] <DC insulated wire> The DC insulated wire of the present invention includes an insulating layer made of the resin composition of the present invention. The DC insulated wire of the present invention is an insulated wire to which a DC voltage is applied, and the concept of "wire" includes electric power transmission wires and communication wires. Furthermore, the material coated with the insulating layer may be a conductor (conductive material) or a waveguide (optical fiber).

[0029] The structure of the insulated wire is not particularly limited and includes all of the conventionally known structures of insulated wires and cables. Preferred DC insulated wires include those comprising a conductor and an insulating layer that covers the conductor directly or via a thin layer, and those comprising a waveguide and an insulating layer that covers the waveguide directly or via a thin layer. In DC insulated wires having such a structure that does not include an intermediate layer such as a semiconductor layer, it is particularly effective from the viewpoint of preventing dielectric breakdown to include a metal chelating agent in the insulating layer.

[0030] Fig. 1 is a cross-sectional view showing a DC insulated wire according to one embodiment of the present invention. The DC insulated wire shown in Fig. 1 is a single-layer insulated wire including a conductor 10, an adhesive layer 20, and an insulating layer 30.

[0031] The conductor 10 is formed from a known metal material used as a conductor for insulated wires, such as copper wire, aluminum wire, copper alloy wire, copper pipe, etc. The outer diameter of the conductor 10 is, for example, 6 to 60 mm.

[0032] The insulating layer 30 is formed from the resin composition of the present invention. The thickness of the insulating layer 30 varies depending on the outer diameter of the conductor 10, but is usually 2 to 40 mm, and preferably 4 to 30 mm.

[0033] The adhesive layer 20 is a resin layer for adhering the insulating layer 30 to the conductor 10. The resin constituting the adhesive layer 20 is formed from an adhesive resin that can suitably adhere the conductor 10 and the insulating layer 30. Examples of such adhesive resins include ethylene acrylic acid resin (EAA), ethylene ethyl acrylate resin (EEA), ethylene vinyl acetate resin (EVA), ethylene glycidyl methacrylic resin (E-GMA), and maleic anhydride-modified polyethylene.

[0034] The thickness of the adhesive layer 20 is preferably 500 μm or less, and more preferably 50 to 200 μm. If the adhesive layer 20 is too thick, it may be impossible to ensure a sufficient thickness for the insulating layer 30, and the performance of the insulated wire may not be fully exhibited. Furthermore, when the conductor 10 is coated with the insulating layer 30 via such a thin adhesive layer 20, it is significant that the insulating layer 30 is formed from the resin composition of the present invention.

[0035] The DC insulated wire of the present invention can be produced by extruding the materials for forming the adhesive layer 20 and the insulating layer 30 so as to cover the outer periphery of the conductor 10 .

[0036] The DC insulated wire of the present invention preferably does not undergo dielectric breakdown even when a DC voltage is applied for 80 minutes under the condition of an applied electric field (applied voltage per 1 mm of insulating layer thickness) of 250 kV / mm. According to findings obtained through separate studies by the present inventors, an insulated wire having a dielectric breakdown time of 80 minutes or more under the condition of an applied electric field of 250 kV / mm has particularly excellent insulating properties in practical use.

[0037] <DC Cable> The DC cable of the present invention comprises at least one DC insulated electric wire of the present invention housed in an outer sheath. The insulated electric wire housed in the outer sheath may be a single wire or a plurality of wires. The cable structure is not particularly limited, and includes all conventionally known insulated wire / cable structures.

[0038] <Example 1> According to the formulation shown in Table 1 below, a density of 0.945 g / cm3 60 parts by mass of ethylene-hexene-1 copolymer (hereinafter referred to as HDPE) having an MFR of 0.80 g / 10 min and a density of 0.923 g / cm 3 The resin composition of the present invention was produced by kneading 40 parts by mass of an ethylene-hexene-1 copolymer (hereinafter, L LDPE) having an MFR of 0.80 g / 10 min, 0.20 parts by mass of a hindered amine light stabilizer "Chimassorb 2020FDL" (manufactured by BASF Japan), 0.15 parts by mass of a metal chelating agent "Irganox MD1024" (manufactured by BASF Japan), and 0.15 parts by mass of a hindered phenol antioxidant "Irganox 1010FF" (manufactured by BASF Japan).

[0039] Examples 2 to 5 Resin compositions of the present invention were produced in the same manner as in Example 1, except that the amounts of the metal chelating agent and / or hindered phenol-based antioxidant were changed according to the formulations shown in Table 1 below.

[0040] Example 6 A resin composition of the present invention was produced in the same manner as in Example 1, except that no hindered phenol-based antioxidant was used, according to the formulation shown in Table 1 below.

[0041] Comparative Example 1 According to the formulation shown in Table 1 below, a comparative resin composition was obtained in the same manner as in Example 1, except that no metal chelating agent was added.

[0042] Comparative Example 2 A comparative resin composition was obtained in the same manner as in Comparative Example 1, except that 0.15 parts by mass of a hindered phenol-based antioxidant “Irganox 1035FF” (manufactured by BASF Japan) was used in place of the hindered phenol-based antioxidant “Irganox 1010FF” according to the formulation shown in Table 1 below.

[0043] <Evaluation of DC insulation properties> Test specimens simulating the laminated structure of a DC insulated wire were prepared using each of the resin compositions obtained in Examples 1 to 6 and Comparative Examples 1 and 2, and a DC insulation property evaluation test was conducted in which a DC voltage was applied to the obtained test specimens to measure the time to dielectric breakdown. The test specimen preparation method and evaluation test method were as follows.

[0044] (1) Test Piece Preparation Method: The resin composition was loaded into a heat press, preheated at 160°C for 5 minutes at 0.5 MPa, then heated and pressed at 15 MPa for 3 minutes, and then cooled in a water-cooled press for 3 minutes to prepare a press sheet simulating an insulating layer. A press sheet simulating an adhesive layer (hereinafter referred to as the "adhesive layer sheet") made of EAA resin and copper foil simulating a conductor, which were separately prepared by the same method, were laminated onto the obtained press sheet (hereinafter referred to as the "insulating layer sheet"). This was loaded into a heat press, preheated at 105-110°C for 5 minutes at 0.5 MPa, then heated and pressed at 15 MPa for 3 minutes, and then cooled in a water-cooled press for 3 minutes to prepare a test piece consisting of a laminate of insulating layer 35, adhesive layer 25, and copper foil 15 as shown in FIG. 2. By using an appropriate spacer, laminate test pieces were prepared without affecting the thickness of the insulating layer sheet. Three test pieces were prepared for each type of resin composition.

[0045] (2) Evaluation Test Method: Each test piece obtained in (1) above was placed between spherical electrodes 50 as shown in Figure 3, and a DC voltage was continuously applied to measure the time to breakdown. The applied electric field (voltage per mm of insulating layer thickness) was 250 kV / mm. The evaluation criteria were as follows: a test piece whose average time to breakdown was 80 minutes or more and which did not experience breakdown within 80 minutes was rated as "pass," and a test piece whose average time to breakdown was less than 80 minutes was rated as "fail." The evaluation results are also shown in Table 1 below.

[0046]

[0047] As is clear from the results shown in Table 1, the resin compositions of Examples 1 to 6, which contained a metal chelating agent, all had excellent insulating properties against DC voltage. Although not shown in Table 1, a tendency for the time to breakdown to increase with an increase in the amount of metal chelating agent was observed. In contrast, the resin compositions of Comparative Examples 1 and 2, which contained an antioxidant but no metal chelating agent, both had poor insulating properties against DC voltage.

[0048] 10 Conductor 20 Adhesive layer 30 Insulating layer 15 Copper foil forming test piece 25 Adhesive layer of test piece 35 Insulating layer of test piece 50 Spherical electrode

Claims

1. A resin composition for forming an insulating layer of a DC insulated wire, the resin composition comprising a polyethylene resin and a metal chelating agent.

2. The resin composition according to claim 1, wherein said metal chelating agent comprises a hydrazine derivative.

3. The resin composition according to claim 2, wherein said metal chelating agent comprises 1,2-bis[3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyl]-hydrazine.

4. The resin composition according to claim 1, which contains 0.01 to 0.5 parts by mass of said metal chelating agent per 100 parts by mass of said polyethylene resin.

5. The resin composition according to claim 1, comprising: 100 parts by mass of said polyethylene resin; 0.01 to 0.5 parts by mass of said metal chelating agent; and 0.01 to 0.5 parts by mass of an antioxidant.

6. The resin composition according to claim 1 for forming an insulating layer of a DC insulated electric wire to which a DC voltage exceeding 750 V is applied.

7. A direct current insulated wire having an insulating layer made of the resin composition according to any one of claims 1 to 6.

8. A DC insulated wire as claimed in claim 7, comprising a conductor or a wave conductor, and the insulating layer covering the outer periphery of the conductor or the wave conductor directly or via a thin layer.

9. The DC insulated wire according to claim 8, wherein the thin layer is an adhesive layer having a thickness of 500 μm or less.

10. A DC insulated electric wire as claimed in claim 9, which does not suffer from dielectric breakdown even when a DC voltage is applied for 80 minutes under an applied electric field condition of 250 kV / mm.

11. A DC cable comprising at least one DC insulated electric wire according to claim 7 housed within an outer sheath.

Images