KR20210003821A - Resin composition, inorganic filler, DC power cable, and method for producing DC power cable - Google Patents

Abstract

A resin composition having a base resin containing polyolefin and an inorganic filler, wherein the inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer circumference of the core portion, The content of the inorganic filler is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass, and the volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Description

Resin composition, inorganic filler, DC power cable, and method for producing DC power cable

The present disclosure relates to a resin composition, an inorganic filler, a DC power cable, and a method for producing a DC power cable.

This application claims priority based on the Japanese application ``Japanese Patent Application No. 2018-081547'' filed on April 20, 2018, and the Japanese application ``Japanese Application No. 2018-215560'' filed on November 16, 2018, All the stated contents are used.

In recent years, in DC power transmission applications, solid insulated DC power cables (hereinafter, abbreviated as "DC power cables") have been developed. In a DC power cable, there is a possibility that space charges are generated in the insulating layer when a high voltage is applied, and the direct current characteristics (volume resistivity, DC breakdown electric field strength, space charge characteristics, etc.) of the insulating layer are deteriorated.

Therefore, in order to suppress the accumulation of space charges in the insulating layer of the direct current power cable, the resin composition constituting the insulating layer may be added with a polar inorganic filler such as carbon black or magnesium oxide (MgO). Yes (for example, Patent Document 1).

Japanese Patent Application Laid-Open No. Hei 11-16421

According to an aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

A resin composition is provided.

According to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed by using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to a thickness of 0.15 mm. When the sheet of the insulating layer having a thickness is formed, the volume resistivity of the sheet of the insulating layer measured under the conditions of a temperature of 90° C. and a DC electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.

A resin composition is provided.

According to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to obtain 0.15 mm. When the sheet of the insulating layer having a thickness is formed, the dielectric breakdown electric field strength of the sheet of the insulating layer measured under the condition of a temperature of 90° C. is 250 kV/mm or more.

A resin composition is provided.

According to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to obtain 0.15 mm. When a sheet of the insulating layer having a thickness is formed, and a DC electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions of a temperature of 30° C. and atmospheric pressure, V ₀ is applied to the sheet (kV) When T is the thickness (mm) of the sheet, and E ₁ is the maximum electric field inside the sheet (kV/mm), the electric field enhancement coefficient FEF obtained by the following equation (1) is , Less than 1.15

A resin composition is provided.

FEF=E ₁ /(V ₀ /T) ···(1)

According to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler containing at least MgO

As a resin composition having,

The inorganic filler,

When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

A resin composition is provided.

According to another aspect of the present disclosure,

As an inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed to cover the outer periphery of the core portion

Have,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Inorganic fillers are provided.

According to another aspect of the present disclosure,

As an inorganic filler,

When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Inorganic fillers are provided.

According to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

DC power cables are provided.

According to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

After immersing the DC power cable in a water bath at a temperature of 40° C. for 30 days, when the insulating layer of the DC power cable is cut off to form a sheet of the insulating layer having a thickness of 0.15 mm, the temperature is 90° C. and The volume resistivity of the sheet of the insulating layer measured under the condition of a direct current electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.

DC power cables are provided.

According to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

When the direct current power cable is immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulating layer of the direct current power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, a temperature of 90° C. The dielectric breakdown electric field strength of the sheet of the insulating layer measured under conditions is 250 kV/mm or more.

DC power cables are provided.

According to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

After immersing the DC power cable in a water bath at a temperature of 40° C. for 30 days, the insulating layer of the DC power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, and at a temperature of 30° C. and atmospheric pressure. When a direct current electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions, V ₀ is the voltage applied to the sheet (kV), T is the thickness of the sheet (mm), and E ₁ is The electric field enhancement coefficient FEF calculated by the above equation (1) when the maximum electric field inside the sheet (kV/mm) is less than 1.15

DC power cables are provided.

According to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler containing at least MgO,

The inorganic filler,

When the energy spectrum of the photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

DC power cables are provided.

According to another aspect of the present disclosure,

A step of preparing a resin composition having a base resin containing polyolefin and an inorganic filler,

Process of forming an insulating layer on the outer circumference of a conductor by using the resin composition

And,

The process of preparing the resin composition,

A step of preparing the inorganic filler having a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles installed on the outer periphery of the core portion,

The step of mixing the resin composition so that the content of the inorganic filler is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass.

Have,

In the step of preparing the inorganic filler,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

A method of manufacturing a DC power cable is provided.

1 is a schematic cross-sectional view showing an inorganic filler according to an embodiment of the present disclosure.
2 is a schematic cross-sectional view orthogonal to the axial direction of a DC power cable according to an embodiment of the present disclosure.
Fig. 3 is a schematic diagram of an inorganic filler A on a scanning electron microscope.
Fig. 4A is a diagram showing the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler when the inorganic filler is measured by X-ray photoelectron spectroscopy.
Fig. 4b is a diagram showing the infrared absorption spectrum of an inorganic filler measured by Fourier transform infrared spectroscopy.

[Problems to be solved by this disclosure]

An object of the present disclosure is to provide a technique capable of suppressing a decrease in direct current characteristics of an insulating layer due to long-term immersion.

[Effect of this disclosure]

According to the present disclosure, it is possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[Description of the embodiment of the present disclosure]

<knowledge obtained by the inventors>

First, the knowledge obtained by the inventors will be outlined.

By dispersing the above-described inorganic filler in the insulating layer, the space charge generated in the insulating layer can be trapped by each inorganic filler. Accordingly, it is possible to suppress the accumulation of local space charges in the insulating layer.

As the inorganic filler added to the insulating layer, for example, MgO formed by firing magnesium hydroxide (Mg(OH) ₂ ) may be used.

Here, the trapping ability of space charges by Mg(OH) ₂ is lower than that of MgO. For this reason, conventionally, in order to reduce the Mg (OH) ₂ in the content of the inorganic filler, and was completely burning the Mg (OH) ₂ as a raw material. In the following, the inorganic filler formed by completely firing Mg(OH) ₂ is referred to as "completely fired filler".

However, the inventors have found a novel problem that, as a result of intensive examination, in a DC power cable in which a completely plastic filler is added to an insulating layer, there is a possibility that the direct current characteristics of the insulating layer may decrease when immersed for a long period of time.

In the completely calcined filler, Mg(OH) ₂ is completely calcined during the manufacturing process, so that the entire Mg(OH) ₂ is changed to MgO. At this time, a smooth surface corresponding to the crystal surface of MgO is formed on the surface of the completely plastic filler.

When the DC power cable in which the fully fired filler is added to the insulation layer is submerged for a long period of time, moisture that has penetrated into the insulation layer from the surface side of the DC power cable is adsorbed to the surface of the completely fired filler, thereby damaging the surface of the completely fired filler Constituent MgO is transformed into Mg(OH) ₂ . At this time, since the surface of the completely calcined filler is smoothed as described above, moisture is liable to propagate over the entire surface of the completely calcined filler, and there is a possibility that the entire surface is rapidly deteriorated to Mg(OH) ₂ .

When the entire surface of the fully plastic filler is changed to Mg (OH) _2, due to the trap capacity of the space charge due to the Mg (OH) ₂ low, it can not be sufficiently trapped space charge on the surface of a perfectly plastic filler. For this reason, there is a possibility that local space charge is accumulated in the insulating layer, and the direct current characteristic of the insulating layer is deteriorated.

The present disclosure is based on the novel problem discovered by the inventors.

<Embodiment of the present disclosure>

Next, an embodiment of the present disclosure is opened and described.

[1] The resin composition according to an aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

According to this configuration, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[2] The resin composition according to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to obtain 0.15 mm. When the sheet of the insulating layer having a thickness is formed, the volume resistivity of the sheet of the insulating layer measured under the conditions of a temperature of 90° C. and a DC electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.

With this configuration as well, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[3] The resin composition according to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed by using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to a thickness of 0.15 mm. When the sheet of the insulating layer having a thickness is formed, the dielectric breakdown electric field strength of the sheet of the insulating layer measured under the condition of a temperature of 90°C is 250 kV/mm or more.

With this configuration as well, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[4] The resin composition according to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to obtain 0.15 mm. When a sheet of the insulating layer having a thickness is formed, and a DC electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions of a temperature of 30° C. and atmospheric pressure, V ₀ is applied to the sheet (kV) When T is the thickness (mm) of the sheet, and E ₁ is the maximum electric field inside the sheet (kV/mm), the electric field enhancement coefficient FEF obtained by the following equation (1) is , Less than 1.15

Resin composition.

FEF=E ₁ /(V ₀ /T) ···(1)

With this configuration as well, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[5] In the resin composition according to any one of [1] to [4],

The surface of the covering portion may have irregularities along the outer shape of the plurality of MgO particles.

According to this configuration, when the DC power cable is submerged for a long period of time, it is possible to slow the deterioration from MgO to Mg(OH) ₂ due to moisture penetrating into the insulating layer.

[6] The resin composition according to another aspect of the present disclosure,

A base resin containing polyolefin,

Inorganic filler containing at least MgO

As a resin composition having,

The inorganic filler,

When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Even with this configuration, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[7] In the resin composition according to any one of [1] to [6],

The inorganic filler may be an inorganic powder fired using Mg(OH) ₂ as a raw material.

Thereby, an inorganic filler having a core portion and a covering portion can be easily formed.

[8] In the resin composition according to any one of [1] to [7],

The volume average particle diameter of the inorganic filler may be 5 μm or less.

Thereby, the effect of improving the direct current characteristic by an inorganic filler can be obtained stably.

[9] Inorganic filler according to another aspect of the present disclosure,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

According to this configuration, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[10] The inorganic filler according to another aspect of the present disclosure,

When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Even with this configuration, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[11] A DC power cable according to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

According to this configuration, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[12] A DC power cable according to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

When the direct current power cable is immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulating layer of the direct current power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, the temperature is 90° C. and The volume resistivity of the sheet of the insulating layer measured under the condition of a direct current electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.

Even with this configuration, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[13] A DC power cable according to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

After immersing the DC power cable in a water bath at a temperature of 40° C. for 30 days, the insulation layer of the DC power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm. The dielectric breakdown electric field strength of the sheet of the insulating layer measured under the conditions is 250 kV/mm or more.

With this configuration as well, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[14] A DC power cable according to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

After immersing the DC power cable in a water bath at a temperature of 40° C. for 30 days, the insulation layer of the DC power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, and the temperature is 30° C. and atmospheric pressure. When a DC electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions, V ₀ is the voltage applied to the sheet (kV), T is the thickness of the sheet (mm), and E ₁ is The electric field enhancement coefficient FEF calculated by the above formula (1) when the maximum electric field inside the sheet (kV/mm) is used is less than 1.15.

With this configuration as well, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[15] A DC power cable according to another aspect of the present disclosure,

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler containing at least MgO,

The inorganic filler,

When the energy spectrum of the photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Even with this configuration, it becomes possible to suppress a decrease in the direct current characteristics of the insulating layer due to long-term immersion.

[16] A method of manufacturing a DC power cable according to another aspect of the present disclosure,

A step of preparing a resin composition having a base resin containing polyolefin and an inorganic filler,

Process of forming an insulating layer on the outer circumference of a conductor by using the resin composition

And,

The process of preparing the resin composition,

A step of preparing the inorganic filler having a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles installed on the outer periphery of the core portion,

The step of mixing the resin composition so that the content of the inorganic filler is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass.

Have,

In the step of preparing the inorganic filler,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

According to this configuration, it becomes possible to obtain a DC power cable in which a decrease in the DC characteristics of the insulating layer due to long-term immersion is suppressed.

[Details of the embodiment of the present disclosure]

Next, an embodiment of the present disclosure will be described below with reference to the drawings.

<An embodiment of the present disclosure>

(1) resin composition

The resin composition of this embodiment is a material constituting the insulating layer 130 of the DC power cable 10 to be described later, and, for example, a base resin, an inorganic filler 200, a crosslinking agent, and other additives. Contains.

(Base resin)

The base resin (base polymer) refers to a resin component constituting the main component of the resin composition. The base resin of this embodiment contains polyolefin, for example. Examples of the polyolefin constituting the base resin include polyethylene, polypropylene, an ethylene-α-olefin copolymer, and a thermoplastic elastomer obtained by dispersing or copolymerizing an ethylene-propylene rubber in polypropylene. Among these, polyethylene is preferable. In addition, two or more of these may be used in combination.

Examples of the polyethylene constituting the base resin include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). In addition, these polyethylenes may be linear or branched, for example.

Further, the base resin may contain, for example, a modified polyolefin obtained by grafting a polar group onto a polyolefin, or a copolymer of an olefin and a polar monomer. Thereby, the compatibility (adhesion) of the inorganic filler 200 having polarity and the base resin can be improved, and the dispersibility of the inorganic filler 200 can be improved.

Examples of the modified polyolefin obtained by grafting a polar group onto the polyolefin include maleic anhydride modified polyethylene.

As a copolymer of an olefin and a polar monomer, for example, an ethylene-ethyl acrylate (ethylene-ethyl acrylate) copolymer, an ethylene-methyl acrylate copolymer, an ethylene-butyl acrylate copolymer, an ethylene-methyl methacrylate copolymer Coalescence, ethylene-glycidyl methacrylate copolymer, etc. are mentioned. In addition, you may use combining two or more types of these.

(Inorganic filler)

The inorganic filler 200 acts to trap space charges in the insulating layer 130 and suppress local accumulation of space charges in the insulating layer 130. Thereby, the direct current characteristic of the insulating layer 130 can be improved. On the other hand, "the direct current characteristic of the insulating layer 130" here means the volume resistivity of the insulating layer 130, the direct current breakdown electric field strength, the space charge characteristic, and the like.

Here, the inorganic filler 200 contained in the resin composition of the present embodiment will be described with reference to FIG. 1. 1 is a cross-sectional view showing an inorganic filler according to the present embodiment.

The inorganic filler 200 of the present embodiment is formed by firing, for example, Mg(OH) ₂ as a raw material, and is a particulate material containing at least MgO. Mg(OH) ₂ as a raw material is obtained, for example, from seawater resources (raw materials derived from seawater) or minerals, or produced by an underwater spark discharge method. On the other hand, among these, a method of forming an inorganic filler by firing Mg(OH) ₂ from seawater resources as a raw material is sometimes referred to as a "seawater method". The formation method will be described later.

As shown in FIG. 1, the inorganic filler 200 of the present embodiment includes, for example, a core portion 210 and a covering portion 230.

The core part 210 constitutes, for example, the central part of the inorganic filler 200, and contains Mg(OH) ₂ as a main component. Specifically, the core portion 210 is formed in a particulate form, for example, that is, composed of Mg(OH) ₂ particles 220. The core part 210 may be composed of a single Mg(OH) ₂ particle 220, or may be composed of a plurality of aggregated Mg(OH) ₂ particles 220. On the other hand, if the Mg(OH) ₂ particles 220 contain Mg(OH) ₂ as a main component, for example, MgO or unavoidable impurities may be included.

The covering portion 230 includes, for example, a plurality of MgO particles 240 installed to cover the outer periphery of the core portion 210. Specifically, each of the plurality of MgO particles 240 contains MgO as a main component, for example. Each of the plurality of MgO particles 240 is composed of, for example, fine particles and is smaller than the core portion 210. The covering portion 230 is configured by, for example, a plurality of fine MgO particles 240 agglomerated and in close contact with the outer periphery of the core portion 210. Thereby, on the surface of the covering portion 230, fine irregularities along the external shape of the plurality of MgO particles can be formed. As a result, when the DC power cable 10 is submerged for a long period of time, the deterioration from MgO to Mg(OH) ₂ due to moisture penetrating into the insulating layer 130 can be slowed down. On the other hand, the resistance of the insulating layer 130 when the direct current power cable 10 referred to herein is submerged over a long period of time is sometimes referred to as "long-term water resistance of the insulating layer 130" below.

In this embodiment, the covering portion 230 is provided so as to cover the entire outer periphery of the core portion 210, for example. That is, the core portion 210 containing Mg(OH) ₂ is hidden inside the covering portion 230 and is not exposed to the surface of the inorganic filler 200. Thereby, it is possible to sufficiently secure the ability to trap space charges by the inorganic filler 200.

On the other hand, each MgO particle 240 may contain, for example, Mg(OH) ₂ or inevitable impurities as long as it contains MgO as a main component.

Here, it can be confirmed by the following measurement that the inorganic filler 200 of this embodiment has the core part 210 and the covering part 230 as mentioned above.

3 is a schematic diagram of a scanning electron microscope image (SEM: Scanning Electron Microscope) showing the inorganic filler A in Examples described later. As shown in FIG. 3, when the SEM image of the inorganic filler 200 is observed, the particle shape and the surface state of the inorganic filler 200 can be confirmed. Specifically, a state in which a plurality of fine particles are agglomerated and adhered to the surface side per particle of the inorganic filler 200 can be confirmed. It can be confirmed that the microparticles correspond to the MgO particles 240, for example, by the following measurement.

The composition analysis on the surface side of the inorganic filler 200 can be performed by X-ray photoelectron spectroscopy (XPS). Specifically, in the XPS method, the inorganic filler 200 is irradiated with X-rays, and the energy spectrum of photoelectrons generated thereby is measured.

4A is a diagram showing the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler when the inorganic filler is measured by X-ray photoelectron spectroscopy. As shown in FIG. 4A, when a narrow scan spectrum related to the 2p orbit of Mg is measured near 50 eV, a peak derived from MgO (near 49 eV) appears, whereas in Mg(OH) ₂ The derived peak (near 47 eV) does not appear. From this, it was confirmed that only MgO was present and Mg(OH) ₂ was not present in the region where photoelectrons were emitted to the outside at a position in the surface layer of the inorganic filler 200 with a depth of 0 nm or more and 3 nm or less from the surface. I can. On the other hand, the inventors, has been confirmed that the surface forced into Mg (OH) was subjected to XPS measurement of the MgO powders was changed to _2, the peak derived from Mg (OH) ₂ at 47eV.

Further, information on functional groups in the inorganic filler 200 can be obtained by Fourier Transform Infrared Spectroscopy (FTIR) method. Specifically, infrared light is irradiated to the inorganic filler 200 by the transmission method in the FTIR method, and the infrared absorption spectrum of the inorganic filler 200 is measured based on the infrared light transmitted through the inorganic filler 200 do.

4B is a diagram showing an infrared absorption spectrum of an inorganic filler measured by Fourier transform infrared spectroscopy. As shown in Fig. 4B, a peak derived from Mg(OH) ₂ (peak derived from an OH group) appears near 3700 cm ^-1 . From this, it can be confirmed that Mg(OH) ₂ is present in at least a part of the inner side of the inorganic filler 200.

From the above, the inorganic filler 200 includes, as described above, a core portion 210 containing Mg(OH) ₂ and a plurality of MgO particles 240 installed to cover the outer circumference of the core portion 210 It can be seen that it has the covering part 230.

In this embodiment, the volume fraction of Mg(OH) ₂ in one particle of the inorganic filler 200 (hereinafter, sometimes abbreviated as ``the volume fraction of Mg(OH) ₂ '') is, for example, 10% It is less than 50%. On the other hand, the "volume fraction of Mg(OH) ₂ in 1 particle of the inorganic filler 200" as referred to herein refers to the volume of 1 particle of the inorganic filler 200 with respect to the volume of Mg in 1 particle of the inorganic filler 200. It means the ratio of the volume occupied by (OH) ₂ .

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler 200 can be obtained, for example, based on the loss on ignition of the inorganic filler 200. The term ``loss on ignition of the inorganic filler 200'' as used herein refers to the inorganic filler 200 when Mg(OH) ₂ contained in the inorganic filler 200 is transformed into MgO by the following reaction equation. It is the reduction rate of the mass of the filler 200.

Mg(OH) ₂ →MgO+H ₂ O

On the other hand, when the volume fraction of Mg(OH) ₂ in one particle of the inorganic filler 200 is obtained based on the loss on ignition of the inorganic filler 200 described above, the particles of the plurality of inorganic fillers 200 A value obtained by averaging the volume fraction of Mg(OH) ₂ is obtained. That is, the art the volume fraction of the Mg (OH) ₂ are obtained, equivalent to Mg (OH) ratio of the average value of the volume of the _second to the average value of the volume of one particle of an inorganic filler (200).

When the volume fraction of Mg(OH) ₂ is less than 10%, sufficient unevenness cannot be formed on the surface of the inorganic filler 200, and the surface of the inorganic filler 200 approaches smoothness. For this reason, there is a possibility that the capacity of trapping space charges by the inorganic filler 200 may not be sufficiently obtained. In addition, there is a possibility that long-term water resistance of the insulating layer 130 cannot be exhibited. On the other hand, when the volume fraction of Mg(OH) ₂ is 10% or more, fine irregularities can be formed on the surface of the inorganic filler 200. Thereby, the ability to trap space charges by the inorganic filler 200 can be sufficiently obtained. In addition, long-term water resistance of the insulating layer 130 may be improved.

On the other hand, when the volume fraction of Mg(OH) ₂ is 50% or more, the proportion of MgO in the surface layer side of the inorganic filler 200 decreases. For this reason, there is a possibility that the direct current breakdown electric field strength of the insulating layer 130 decreases from the initial stage (the time point at which it is not submerged). Although details are unknown about this causal relationship, the following mechanism is assumed. When the volume fraction of Mg(OH) ₂ is 50% or more, the portion of Mg(OH) _{2 in} the core portion 210 is liable to collapse, and thus the particles of the inorganic filler 200 are liable to collapse. When the particles of the inorganic filler 200 disintegrate, the disintegrating particles cause dispersion defects, and a spot where the disintegrating particles locally gather is formed in the insulating layer 130. When the collapsed particles are locally collected, the localized collection spots of the collapsed particles act as an outlier (foreign substance) when the entire insulating layer 130 is viewed. As a result, there is a possibility that the DC breakdown electric field strength of the insulating layer 130 decreases from the beginning. On the other hand, by making the volume fraction of Mg(OH) ₂ less than 50%, the ratio of MgO on the surface layer side of the inorganic filler 200 can be made more than a predetermined value. Thereby, the collapse of the inorganic filler 200 can be suppressed, and local aggregation of the collapsed particles can be suppressed. As a result, it is possible to suppress a decrease in the DC breakdown electric field strength of the insulating layer 130 from the initial stage.

In this embodiment, the content of the inorganic filler 200 in the resin composition is, for example, 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass.

When the content of the inorganic filler 200 is less than 0.1 parts by mass, the space charge not trapped by the inorganic filler 200 increases. For this reason, there is a possibility that the volume resistivity of the insulating layer 130 is lowered. In addition, when the DC power cable 10 is submerged for a long period of time, the amount of moisture that affects per particle of the inorganic filler 200 becomes excessively large. For this reason, there is a possibility that the long-term water resistance of the insulating layer 130 is deteriorated. On the other hand, when the content of the inorganic filler 200 is 0.1 parts by mass or more, an increase in the space charge not trapped by the inorganic filler 200 can be suppressed. Thereby, a decrease in the volume resistivity of the insulating layer 130 can be suppressed. Further, when the DC power cable 10 is submerged for a long period of time, it is possible to suppress an excessive increase in the amount of water that affects per particle of the inorganic filler 200. Thereby, the long-term water resistance of the insulating layer 130 can be improved.

On the other hand, when the content of the inorganic filler 200 is more than 5 parts by mass, the moldability by the resin composition decreases, and the dispersibility of the inorganic filler 200 in the insulating layer 130 decreases. For this reason, there is a possibility that a region in which the inorganic filler 200 is relatively small is generated in the insulating layer 130. As a result, there is a possibility that the DC breakdown electric field strength of the insulating layer 130 decreases, or the long-term water resistance of the insulating layer 130 decreases. On the other hand, when the content of the inorganic filler 200 is 5 parts by mass or less, the moldability of the resin composition can be improved, and the dispersibility of the inorganic filler 200 in the insulating layer 130 can be improved. Thereby, it can suppress that the region in which the inorganic filler 200 is relatively small is generated in the insulating layer 130. As a result, a decrease in the DC breakdown electric field strength of the insulating layer 130 can be suppressed, and a decrease in long-term water resistance of the insulating layer 130 can be suppressed.

In this embodiment, the volume average particle diameter (MV: Mean Volume Diameter) of the inorganic filler 200 is not particularly limited, but is, for example, 5 μm or less, preferably 1 μm or less.

On the other hand, the "volume average particle diameter (MV)" referred to herein is obtained by the following equation when the particle diameter of the particle is d _i and the volume V _i of the particle.

MV=Σ(V _i d _i )/ΣV _i

On the other hand, for the measurement of the volume average particle diameter, a dynamic light scattering particle diameter/particle size distribution measuring device is used.

If the volume average particle diameter of the inorganic filler 200 is more than 5 μm, it may become difficult to uniformly disperse the inorganic filler 200 in the insulating layer 130. For this reason, there is a possibility that it becomes difficult to obtain the effect of improving the direct current characteristics by the inorganic filler 200. On the other hand, when the volume average particle diameter of the inorganic filler 200 is 5 μm or less, the inorganic filler 200 can be uniformly dispersed in the insulating layer 130. Thereby, the effect of improving the direct current characteristic by the inorganic filler 200 can be obtained stably. Moreover, by making the volume average particle diameter of the inorganic filler 200 1 μm or less, it becomes easy to uniformly disperse the inorganic filler 200 in the insulating layer 130. Thereby, the effect of improving the direct current characteristic by the inorganic filler 200 can be obtained more stably.

On the other hand, the lower limit of the volume average particle diameter of the inorganic filler 200 is not particularly limited. However, from the viewpoint of stably forming the inorganic filler 200 by firing Mg(OH) ₂ as a raw material, the volume average particle diameter of the inorganic filler 200 is, for example, 0.1 μm or more, preferably It is 0.5 μm or more.

On the other hand, in the present embodiment, the particle diameter of the MgO particles 240 included in the covering portion 230 is dependent on, for example, the volume fraction of Mg(OH) ₂ described above. When the fired state of the inorganic filler 200 is close to the fully fired state and the volume fraction of Mg(OH) ₂ decreases, the particle diameter of the MgO particles 240 increases. On the other hand, when the calcination state of the inorganic filler 200 is incomplete and the volume fraction of Mg(OH) ₂ increases, the particle diameter of the MgO particles 240 decreases. Specifically, when the volume fraction of Mg(OH) ₂ is 29.2%, the particle diameter of the MgO particles 240 is, for example, about 0.01 μm. Incidentally, the particle diameter of the MgO particles 240 referred to herein is an average value of the particle diameters of the MgO particles 240 measured in the SEM image.

In addition, at least a part of the inorganic filler 200 may be surface-treated with a silane coupling agent. Thereby, the adhesiveness of the interface between the inorganic filler 200 and the base resin can be improved, and the mechanical properties and low-temperature properties of the insulating layer 130 can be improved.

As a silane coupling agent, for example, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldi Methoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropylmethyldi Methoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxy Silane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl) -3-Aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene ) Propylamine, etc. are mentioned. In addition, you may use combining two or more types of these.

(Crosslinking agent)

The crosslinking agent is, for example, an organic peroxide. As the organic peroxide, for example, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,3-bis(t-butylperoxyisopropyl)benzene And the like. In addition, you may use combining two or more types of these.

(Other additives)

The resin composition may further contain an antioxidant and a lubricant, for example.

As an antioxidant, for example, 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], pentaerythrityl-tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,4-bis-[(octylthio)methyl]-o-cresol, 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butyl Anilino)-1,3,5-triazine, bis[2-methyl-4-{3-n-alkyl (C12 or C14)thiopropionyloxy}-5-t-butylphenyl]sulfide, and 4 , 4'-thiobis(3-methyl-6-t-butylphenol), etc. are mentioned. In addition, you may use combining two or more types of these.

The lubricant works to improve the fluidity of the resin composition during extrusion molding of the insulating layer 130 while suppressing aggregation of the inorganic filler. The lubricant of this embodiment is, for example, a fatty acid metal salt or a fatty acid amide. As a fatty acid metal salt, magnesium stearate, zinc stearate, aluminum stearate, magnesium montanate, etc. are mentioned, for example. Moreover, as a fatty acid amide, an oleic acid amide, stearic acid amide, etc. are mentioned, for example. In addition, you may use combining two or more types of these.

On the other hand, the resin composition may further contain, for example, a colorant.

(2) DC power cable

Next, a DC power cable of this embodiment will be described with reference to FIG. 2. 2 is a cross-sectional view orthogonal to the axial direction of the DC power cable according to the present embodiment.

The DC power cable 10 of the present embodiment is configured as a so-called solid insulated DC power cable, and, for example, the conductor 110, the inner semiconducting layer 120, the insulating layer 130, and the outer semiconducting layer It has 140, a shielding layer 150, and a sheath 160.

(Conductor (conductive part))

The conductor 110 is constituted by joining a plurality of conductor core wires (conductive core wires) made of pure copper, copper alloy, aluminum, or aluminum alloy, for example.

(Internal semiconducting layer)

The inner semiconducting layer 120 is provided so as to cover the outer periphery of the conductor 110. In addition, the inner semiconducting layer 120 has semiconducting properties and is configured to suppress concentration of an electric field on the surface side of the conductor 110. The inner semiconducting layer 120 is, for example, at least any one of an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, an ethylene-butyl acrylate copolymer, and an ethylene-vinyl acetate copolymer, Contains conductive carbon black.

(Insulation layer)

The insulating layer 130 is provided so as to cover the outer periphery of the inner semiconducting layer 120. The insulating layer 130 is crosslinked by extrusion molding the resin composition of the present embodiment described above and heating. That is, polyethylene as the base resin in the resin composition constituting the insulating layer is a crosslinked polyethylene. In addition, uncrosslinked polyethylene may be contained in the resin composition.

(External semiconducting layer)

The outer semiconducting layer 140 is provided so as to cover the outer periphery of the insulating layer 130. Further, the outer semiconducting layer 140 has semiconducting properties and is configured to suppress concentration of an electric field between the insulating layer 130 and the shielding layer 150. The outer semiconducting layer 140 is made of the same material as the inner semiconducting layer 120, for example.

(Shielding layer)

The shielding layer 150 is provided so as to cover the outer periphery of the outer semiconducting layer 140. The shielding layer 150 is constituted by winding a copper tape, for example, or is constituted as a wire shield in which a plurality of interlocking wires and the like are wound. On the other hand, on the inside or outside of the shielding layer 150, a tape made of rubber information or the like may be wound.

(Cis)

The sheath 160 is provided so as to cover the outer periphery of the shielding layer 150. The sheath 160 is made of polyvinyl chloride or polyethylene, for example.

(Long-term water resistance)

In the DC power cable 10 configured as described above, the inorganic filler 200 added in the insulating layer 130 covers the core portion 210 including Mg(OH) ₂ and the outer periphery of the core portion 210. By having the covering portion 230 including a plurality of MgO particles 240 arranged so as to be arranged, for example, long-term water resistance of the insulating layer 130 as follows is obtained.

After immersing the DC power cable 10 in a water bath at a temperature of 40° C. for 30 days, the insulation layer 130 of the DC power cable 10 is cut off, thereby forming a sheet of the insulating layer 130 having a thickness of 0.15 mm. When is formed, the volume resistivity of the sheet of the insulating layer 130 measured under the conditions of a temperature of 90° C. and a DC electric field of 80 kV/mm is, for example, 1×10 ¹⁵ Ω·cm or more.

In addition, when the sheet of the insulating layer 130 is formed after the aforementioned immersion, the dielectric breakdown electric field strength of the sheet of the insulating layer 130 measured under the condition of a temperature of 90° C. is, for example, 250 kV/mm or more. to be.

In addition, when the sheet of the insulating layer 130 is formed after the aforementioned immersion, when a direct current electric field of 50 kV/mm is applied to the sheet of the insulating layer 130 under conditions of a temperature of 30° C. and atmospheric pressure, the following The electric field enhancement coefficient FEF obtained by equation (1) is less than 1.15.

FEF=E ₁ /(V ₀ /T) ···(1)

(However, V ₀ is the voltage applied to the sheet of the insulating layer 130 (kV), T is the thickness of the sheet of the insulating layer 130 (mm), E ₁ is the inside of the sheet of the insulating layer 130 Is the maximum electric field of (kV/mm).)

(Specific dimensions, etc.)

Specific dimensions of the DC power cable 10 are not particularly limited, but for example, the diameter of the conductor 110 is 5 mm or more and 60 mm or less, and the thickness of the inner semiconducting layer 120 is 1 mm or more and 3 mm or less. And, the thickness of the insulating layer 130 is 1mm or more and 35mm or less, the thickness of the outer semiconducting layer 140 is 1mm or more and 3mm or less, and the thickness of the shielding layer 150 is 1mm or more and 5mm or less, and the sheath 160 The thickness is more than 1mm. The DC voltage applied to the DC power cable 10 of the present embodiment is, for example, 80 kV or more and 600 kV or less.

(3) Method of manufacturing DC power cable

Next, a method of manufacturing the DC power cable of the present embodiment will be described. Hereinafter, the step is abbreviated as "S".

(S100: resin composition preparation step)

First, a resin composition having a base resin containing polyolefin and an inorganic filler is prepared. The said resin composition preparation process S100 has an inorganic filler preparation process S120 and a mixing process S140, for example.

(S120: inorganic filler preparation process)

For example, the inorganic filler 200 is formed by seawater method.

Specifically, for example, a magnesium raw material such as an aqueous magnesium salt solution extracted from seawater is reacted with an alkali such as calcium hydroxide to produce a slurry of Mg(OH) ₂ as a precursor. When a slurry of Mg(OH) ₂ is produced, the Mg(OH) ₂ slurry is filtered and washed with water to produce a wet cake of Mg(OH) ₂ . When a wet cake of Mg(OH) ₂ is formed, the wet cake of Mg(OH) ₂ is dried and fired at a predetermined temperature. Thereby, fine powder of the inorganic filler 200 is produced.

Here, when firing a wet cake of the _two above-mentioned Mg (OH) at a predetermined temperature, Mg (OH) Mg (OH) constituting the wet cake of ₂₂ particles, gradually dehydration from the outer circumferential side of the particle This advances and changes to MgO. At this time, the entire Mg(OH) ₂ particle is not completely transformed into MgO, and firing is stopped in the middle of the alteration. As a result, by varying the outer peripheral side only of Mg (OH) ₂ particles of MgO, it may be the remaining Mg (OH) Mg (OH) ₂ on at least a portion of the center of the _second particles. As a result, the inorganic filler 200 having a core portion 210 containing Mg(OH) ₂ and a covering portion 230 containing a plurality of MgO particles 240 installed to cover the outer circumference of the core portion 210 Can be formed.

In addition, at this time, by adjusting the firing conditions (firing temperature, firing time, etc.), the volume fraction of Mg(OH) ₂ in one particle of the inorganic filler 200 is, for example, 10% or more and less than 50%. .

When the inorganic filler 200 is produced, at least a part of the inorganic filler 200 may be surface-treated with a silane coupling agent.

Further, by performing a predetermined pulverization treatment, the volume average particle diameter of the inorganic filler 200 may be adjusted. At this time, the volume average particle diameter of the inorganic filler 200 is, for example, 5 μm or less, and preferably 1 μm or less.

(S140: mixing process)

A base resin containing polyethylene, an inorganic filler 200, a crosslinking agent made of an organic peroxide, and other additives (antioxidants, lubricants, etc.) are mixed (kneaded) with a mixer such as a Banbury mixer or a kneader to form a mixed material. do. When the mixed material is formed, the mixed material is granulated with an extruder. As a result, a pellet-shaped resin composition constituting the insulating layer 130 is formed. On the other hand, the process from mixing to granulation may be performed collectively by using a twin-screw extruder having a high kneading action.

(S200: conductor preparation process)

On the one hand, a conductor 110 formed by joining a plurality of conductor core wires is prepared.

(S300: cable core forming process (extrusion process))

Next, among the three-layer co-extruders, in extruder A forming the inner semiconducting layer 120, for example, an ethylene-ethyl acrylate copolymer and a resin composition for an inner semiconducting layer in which conductive carbon black are premixed. Put it in.

In the extruder B forming the insulating layer 130, the above-described pellet-shaped resin composition is introduced.

In the extruder C that forms the outer semiconducting layer 140, the resin composition for an outer semiconducting layer made of the same material as the resin composition for an inner semiconducting layer put into the extruder A is put.

Next, each extrudate from extruders A to C is guided to a common head, and on the outer periphery of the conductor 110, from the inside to the outside, the inner semiconducting layer 120, the insulating layer 130 and the outer semiconducting layer (140) is extruded simultaneously. Thereafter, in the crosslinked tube pressurized with nitrogen gas or the like, the insulating layer 130 is formed by heating by radiation by an infrared heater or by transferring heat through a heat medium such as high temperature nitrogen gas or silicon oil. Crosslinked. Thereby, a cable core composed of the conductor 110, the inner semiconducting layer 120, the insulating layer 130, and the outer semiconducting layer 140 is formed.

(S400: shielding layer forming process)

Next, the shielding layer 150 is formed outside the outer semiconducting layer 140 by winding a copper tape, for example.

(S500: sheath formation process)

Next, vinyl chloride is put into the extruder and extruded to form a sheath 160 on the outer periphery of the shielding layer 150.

As described above, the DC power cable 10 as a solid insulated DC power cable is manufactured.

(4) Effects according to this embodiment

According to this embodiment, one or more effects shown below are exhibited.

(a) The inorganic filler 200 added in the insulating layer 130 is a core portion 210 containing Mg(OH) ₂ and a plurality of MgO particles 240 installed to cover the outer circumference of the core portion 210 It has a covering portion 230 including. Thereby, on the surface of the covering part 230, minute irregularities along the external shape of the plurality of MgO particles 240 can be formed. By forming fine irregularities on the surface of the covering part 230, when the DC power cable 10 is submerged for a long period of time, the change from MgO to Mg(OH) ₂ due to moisture penetrating into the insulating layer 130 By generating only a small portion of the surface of the inorganic filler 200, the period until the entire surface of the inorganic filler 200 is changed to Mg(OH) ₂ can be lengthened. That is, on the surface of the inorganic filler 200, a portion made of MgO can remain for a long period of time.

Even when the DC power cable 10 is submerged for a long period of time, the ability of the inorganic filler 200 to trap space charges can be maintained by remaining a portion made of MgO on the surface of the inorganic filler 200. Accordingly, it is possible to suppress the occurrence of local space charge accumulation in the insulating layer 130. As a result, it becomes possible to suppress the deterioration of the direct current characteristic of the insulating layer 130 due to long-term immersion.

(b) The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler 200 is 10% or more and less than 50%. When the volume fraction of Mg(OH) ₂ is 10% or more, fine irregularities can be formed on the surface of the inorganic filler 200. Thereby, the ability to trap space charges by the inorganic filler 200 can be sufficiently obtained. In addition, long-term water resistance of the insulating layer 130 may be improved. In addition, by making the volume fraction of Mg(OH) ₂ less than 50%, the ratio of MgO on the surface layer side of the inorganic filler 200 can be made more than a predetermined value. Thereby, it is possible to suppress a decrease in the DC breakdown electric field strength of the insulating layer 130 from the initial stage.

(c) The content of the inorganic filler 200 in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass. By setting the content of the inorganic filler 200 to 0.1 parts by mass or more, an increase in space charge not trapped by the inorganic filler 200 can be suppressed. Thereby, a decrease in the volume resistivity of the insulating layer 130 can be suppressed. Further, when the DC power cable 10 is submerged for a long period of time, it is possible to suppress an excessive increase in the amount of water that affects per particle of the inorganic filler 200. Thereby, the long-term water resistance of the insulating layer 130 can be improved. In addition, when the content of the inorganic filler 200 is 5 parts by mass or less, the moldability by the resin composition can be improved, and the dispersibility of the inorganic filler 200 in the insulating layer 130 can be improved. Thereby, it can suppress that a region in which the inorganic filler 200 is relatively small is generated in the insulating layer 130. As a result, a decrease in the DC breakdown electric field strength of the insulating layer 130 can be suppressed, and a decrease in long-term water resistance of the insulating layer 130 can be suppressed.

(d) The covering portion 230 is provided so as to cover the entire outer periphery of the core portion 210. That is, the core portion 210 containing Mg(OH) ₂ is hidden inside the covering portion 230 and is not exposed to the surface of the inorganic filler 200. Here, as described above, the trapping ability of space charges by Mg(OH) ₂ is lower than that of MgO. For this reason, by not exposing the core portion 210 containing Mg(OH) ₂ on the surface of the inorganic filler 200 as in the present embodiment, the ability to trap space charges by the inorganic filler 200 can be sufficiently secured. I can.

(e) Since the adhesion of MgO to Mg(OH) ₂ is high, the plurality of MgO particles 240 constituting the covering portion 230 can be firmly adhered to the core portion 210. Thus, even if the resin composition containing the inorganic filler 200 is mixed or the insulating layer 130 is extruded with the resin composition, the separation of the MgO particles 240 from the core part 210 is reduced. Can be suppressed. By suppressing the dispersion of the MgO particles 240 from the core part 210, the surface of the covering part 230 maintains fine irregularities formed to follow the external shape of the plurality of MgO particles 240, and Mg(OH) ₂ It is possible to suppress the exposure of the core portion 210 is included. As a result, even if various processes have been passed, the ability to trap space charges by the inorganic filler 200 can be sufficiently secured.

(f) The inorganic filler 200 is formed by firing Mg(OH) ₂ as a raw material. Thereby, the inorganic filler 200 having the core portion 210 and the covering portion 230 can be easily formed. Moreover, compared with the "gas phase method", the inorganic filler 200 can be formed at low cost.

On the other hand, as a method for forming an inorganic filler by the "gas phase method", first, metal Mg is heated to generate Mg vapor. When the vapor of Mg is generated, the vapor of Mg is oxidized by bringing the vapor of Mg into contact with the oxygen-containing gas. Thereby, fine powder of the inorganic filler made of MgO is produced. In the gas phase method, MgO of high purity is obtained, but the cost is high. On the other hand, Mg(OH) ₂ is not contained in the inorganic filler formed by the gas phase method.

<Another embodiment of the present disclosure>

As mentioned above, although the embodiment of this disclosure was demonstrated concretely, this disclosure is not limited to the above-described embodiment, and various changes are possible within the range not deviating from the gist.

In the above-described embodiment, the case where the resin composition has the inorganic filler 200 formed by firing using Mg(OH) ₂ as a raw material has been described, but the resin composition is an inorganic material comprising MgO formed by a gas phase method. You may further have a filler.

In the above-described embodiment, the case where the resin composition has the inorganic filler 200 containing MgO has been described, but the resin composition may further have an inorganic filler made of carbon black.

In the above-described embodiment, it was said that the inorganic filler 200 is surface-treated with a silane coupling agent, but the inorganic filler 200 does not need to be surface-treated with a silane coupling agent. Alternatively, the inorganic filler 200 may be a mixture of a powder subjected to a surface treatment with a silane coupling agent and a powder not subjected to a surface treatment.

Example

Next, an embodiment according to the present disclosure will be described. These examples are examples of the present disclosure, and the present disclosure is not limited by these examples.

(1) Samples of DC power cables

(1-1) Preparation of resin composition (production)

The following compounding agents were mixed with a Banbury mixer and granulated with an extruder to prepare a pellet-shaped resin composition. Here, nine resin compositions having different inorganic fillers were produced.

(Base resin)

100 parts by mass of low-density polyethylene (LDPE) (density d=0.920, MFR=1g/10min)

(Inorganic filler)

Any one of the following inorganic fillers A to F was used.

Inorganic filler A: volume average particle diameter 0.5 μm, Mg(OH) ₂ volume fraction 29.2%

Inorganic filler B: volume average particle diameter 3.5 μm, Mg(OH) ₂ volume fraction 29.2%

Inorganic filler C: volume average particle diameter 3.5 μm, Mg(OH) ₂ volume fraction 12.0%

Inorganic filler D: volume average particle diameter 3.5 μm, Mg(OH) ₂ volume fraction 52.9%

Inorganic filler E: volume average particle diameter 3.5 μm, Mg(OH) ₂ volume fraction 7.3%

(Crosslinking agent)

1.3 parts by mass of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane

(Other additives)

Lubricant: Oleic acid amide prescribed amount

Antioxidant: 4,4'-thiobis (3-methyl-6-t-butylphenol) predetermined amount

(1-2) Preparation of samples of DC power cables

Next, a conductor formed by joining a conductor core wire made of a lean copper alloy having a diameter of 14 mm was prepared. When the conductor is prepared, the resin composition for the inner semiconducting layer containing an ethylene-ethyl acrylate copolymer, the resin composition for the insulating layer prepared in (1-1) above, and the same material as the resin composition for the inner semiconducting layer. The external semiconducting layer resin composition was put into extruders A to C, respectively. Each extruded product from extruders A to C was guided to a common head, and an inner semiconducting layer, an insulating layer, and an outer semiconducting layer were simultaneously extruded on the outer periphery of the conductor, from the inside to the outside. At this time, the thicknesses of the inner semiconducting layer, the insulating layer, and the outer semiconducting layer were set to 1 mm, 14 mm, and 1 mm, respectively. Thereafter, the above-described extruded product was heated at about 250° C. to crosslink the resin composition for an insulating layer. As a result, a sample of a DC power cable having a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer was prepared from the center toward the outer periphery.

By the above process, samples 1 to 9 of DC power cables were produced using each of nine resin compositions with different inorganic fillers.

(2) Evaluation of samples of DC power cables

In each of samples 1 to 9 of the DC power cable, the following initial evaluation and long-term immersion evaluation were performed.

(2-1) Initial evaluation

(Sample processing)

Each of the samples 1 to 9 of the DC power cable was cut from the outer peripheral surface to form a sheet of an insulating layer having a thickness of 0.15 mm.

(Volume resistivity)

The volume resistivity was measured by immersing the sheet of the insulating layer described above in silicone oil at a temperature of 90°C, and applying a direct current electric field of 80 kV/mm to the sheet of the insulating layer using a flat electrode having a diameter of 25 mm. The case where the volume resistivity was 1×10 ¹⁵ Ω·cm or more was evaluated as good.

(DC breakdown electric field strength)

The above-described sheet of the insulating layer was immersed in silicone oil at a temperature of 90°C, and a flat electrode having a diameter of 25 mm was used to increase the applied voltage at a rate of 4 kV/min. When the sheet of the insulating layer reached dielectric breakdown, the voltage applied at this time was divided by the sheet thickness to calculate the DC breakdown electric field strength of the sheet of the insulating layer. The case where the DC breakdown electric field strength was 250 kV/mm or more was evaluated as good.

(Space charge characteristics)

The space charge characteristics of the sheet of the insulating layer were evaluated using a space charge measuring device (manufactured by Fibrabo) by the pulsed electrostatic stress method (PEA method: Pulsed Electro-Acoustic Method). Specifically, a direct current electric field of 50 kV/mm was continuously applied over 1 hour to the sheet of the insulating layer under conditions of a temperature of 30° C. and atmospheric pressure, and the maximum electric field inside the sheet was measured. At this time, the electric field enhancement coefficient FEF was determined by the above-described equation (1). The case where the electric field enhancement coefficient FEF was less than 1.15 was evaluated as A (good), and the case where the FEF was 1.15 or more was evaluated as B (defective).

(2-2) Long-term immersion evaluation

(Immersion test and sample processing)

Each of the samples 1 to 9 of the DC power cable was cut into 500 mm in length, and the end portion was sealed (sealed) with silicone rubber so that water did not penetrate from the end portion of the cut cable. Thereafter, the cut cable was immersed in a water bath at a temperature of 40° C. for 30 days. On the other hand, the end of the cut cable was not immersed. After immersion, a sheet of an insulating layer having a thickness of 0.15 mm was formed by cutting off the central portion of the cut cable from the outer peripheral surface.

(Volume resistivity, DC breakdown electric field strength, space charge characteristics)

The volume resistivity, direct current breakdown electric field strength, and space charge characteristics were evaluated in the same manner as the initial evaluation for the sheet of the insulating layer after immersion described above.

(3) result

The results of evaluating samples of the DC power cable are shown in Table 1 below. In addition, in Table 1, the unit of content of a compounding agent is "mass part." In addition, the volume average particle diameter of the inorganic filler is described as "MV", and the volume fraction of Mg(OH) _{2 in} the inorganic filler is described as "Mg(OH) ₂ VF". In addition, the result of the initial evaluation is described as "initial", and the result of the immersion evaluation is described as "after immersion".

(Sample 6)

In Sample 6 using the inorganic filler D having a volume fraction of Mg(OH) ₂ of 50% or more, the DC breakdown electric field strength was less than 250 kV/mm from the beginning. In the sample 6, since the particles of the inorganic filler were disintegrating, it is considered that local gathering spots of the disintegrating particles were formed.

(Sample 7)

In Sample 7 using the inorganic filler E in which the volume fraction of Mg(OH) ₂ was less than 10%, the space charge characteristic was B from the beginning. In the sample 7, since sufficient irregularities were not formed on the surface of the inorganic filler, it is considered that the ability to trap space charges by the inorganic filler could not be sufficiently obtained.

In addition, in Sample 7, the DC breakdown electric field strength after immersion was less than 250 kV/mm, and the space charge characteristic after immersion was B. In this sample 7, since sufficient unevenness was not formed on the surface of the inorganic filler as described above, it is considered that the entire surface of the inorganic filler was quickly deteriorated to Mg(OH) ₂ . For this reason, it is thought that long-term water resistance of an insulating layer was not obtained.

(Sample 8)

In Sample 8 in which the content of the inorganic filler A was less than 0.1 parts by mass, the volume resistivity was less than 1×10 ¹⁵ Ω·cm from the beginning. In the sample 8, since the content of the inorganic filler was small, it is considered that the space charge not trapped by the inorganic filler was increasing. For this reason, it is considered that the volume resistivity of the insulating layer has decreased.

In addition, in Sample 8, the volume resistivity after immersion, the DC breakdown electric field strength, and the space charge characteristics were all poor. In the sample 8, when the DC power cable was submerged for a long period of time, it is considered that the amount of moisture that affects per particle of the inorganic filler increased excessively. For this reason, it is considered that the long-term water resistance of the insulating layer has decreased.

(Sample 9)

In Sample 9 in which the content of the inorganic filler A was more than 5 parts by mass, the DC breaking electric field strength was less than 250 kV/mm from the beginning. In addition, in Sample 9, the volume resistivity and DC breakdown electric field strength after immersion were poor.

In the sample 9, since the content of the inorganic filler A was large, the moldability of the resin composition was lowered, and it is considered that the dispersibility of the inorganic filler in the insulating layer was lowered. For this reason, it is thought that the area|region with relatively few inorganic fillers was generated in the insulating layer. As a result, it is thought that the DC breakdown electric field strength of the insulating layer is lowered from the beginning, or the long-term water resistance of the insulating layer is lowered.

(Samples 1-5)

In samples 1 to 5 in which any one of inorganic fillers A to C having a volume fraction of Mg(OH) ₂ of 10% or more and less than 50% was used and the content of the inorganic filler was 0.1 parts by mass or more and 5 parts by mass or less, the initial The volume resistivity, DC breakdown electric field strength, and space charge characteristics were all good, and the volume resistivity after immersion, DC breakdown electric field strength, and space charge characteristics were all good.

In the samples 1 to 5, by making the volume fraction of Mg(OH) ₂ less than 50%, the ratio of MgO on the surface layer side of the inorganic filler could be set to a predetermined value or more. Thereby, the collapse of the inorganic filler could be suppressed, and local aggregation of the collapsed particles could be suppressed. As a result, in Samples 1 to 5, it was confirmed that the DC breakdown electric field strength of the insulating layer could be suppressed from decreasing from the initial stage.

In addition, in the samples 1 to 5, when the volume fraction of Mg(OH) ₂ was 10% or more, fine irregularities were formed on the surface of the inorganic filler (see Fig. 3). As a result, in Samples 1 to 5, it was confirmed that the space charge trapping ability by the inorganic filler could be sufficiently obtained, and the space charge characteristics could be improved from the beginning.

In addition, in the samples 1 to 5, since fine irregularities were formed on the surface of the inorganic filler, it was possible to delay the deterioration of the entire surface of the inorganic filler to Mg(OH) ₂ during prolonged immersion, and thus The portion made of MgO could remain in the. Thereby, in Samples 1 to 5, it was confirmed that the deterioration of the direct current characteristics of the insulating layer caused by long-term immersion could be suppressed.

In addition, in the samples 1 to 5, when the content of the inorganic filler is 0.1 parts by mass or more, an increase in space charge that is not trapped by the inorganic filler 200 can be suppressed. Thereby, in Samples 1 to 5, it was confirmed that the decrease in the volume resistivity of the insulating layer could be suppressed from the beginning.

In addition, in the samples 1 to 5, when the content of the inorganic filler is 0.1 parts by mass or more, when the DC power cable is submerged for a long period of time, an excessive increase in the amount of moisture that affects per particle of the inorganic filler can be suppressed. there was. Thereby, in Samples 1 to 5, it was confirmed that the long-term water resistance of the insulating layer could be improved.

In addition, in the samples 1 to 5, when the content of the inorganic filler is 5 parts by mass or less, the moldability by the resin composition can be improved, and the dispersibility of the inorganic filler in the insulating layer can be improved. Thereby, it was able to suppress that a region with a relatively small amount of inorganic filler was generated in the insulating layer. As a result, in Samples 1 to 5, it was confirmed that the decrease in the DC breakdown electric field strength of the insulating layer could be suppressed, and the decrease in the long-term water resistance of the insulating layer could be suppressed.

<Preferred aspect of the present disclosure>

Hereinafter, a preferred aspect of the present disclosure is added.

(Annex 1)

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Resin composition.

(Annex 2)

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to obtain 0.15 mm. When the sheet of the insulating layer having a thickness is formed, the volume resistivity of the sheet of the insulating layer measured under the conditions of a temperature of 90° C. and a DC electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.

Resin composition.

(Annex 3)

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed by using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to a thickness of 0.15 mm. In the case of forming a sheet of the insulating layer having a thickness, the dielectric breakdown electric field strength of the sheet of the insulating layer measured under the condition of a temperature of 90°C is 250 kV/mm or more.

Resin composition.

(Annex 4)

A base resin containing polyolefin,

Inorganic filler

As a resin composition having,

The inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

A DC power cable having an insulating layer formed using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to obtain 0.15 mm. When a sheet of the insulating layer having a thickness is formed, and a DC electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions of a temperature of 30° C. and atmospheric pressure, V ₀ is applied to the sheet (kV) When T is the thickness (mm) of the sheet, and E ₁ is the maximum electric field inside the sheet (kV/mm), the electric field enhancement coefficient FEF obtained by the following equation (1) is , Less than 1.15

Resin composition.

FEF=E ₁ /(V ₀ /T) ···(1)

(Annex 5)

The surface of the covering portion has irregularities along the outer shape of the plurality of MgO particles.

The resin composition according to any one of Appendix 1 to Appendix 4.

(Annex 6)

The plurality of MgO particles in the covering portion are aggregated and adhered to the outer periphery of the core portion.

The resin composition according to any one of Appendix 1 to Appendix 5.

(Annex 7)

The covering portion is installed on the entire outer periphery of the

The resin composition according to any one of Appendix 1 to Appendix 6.

(Annex 8)

A base resin containing polyolefin,

Inorganic filler containing at least MgO

As a resin composition having,

The inorganic filler,

When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Resin composition.

(Annex 9)

The inorganic filler is an inorganic powder calcined using Mg(OH) ₂ as a raw material.

The resin composition according to any one of Appendix 1 to Appendix 8.

(Annex 10)

The volume average particle diameter of the inorganic filler is 5 μm or less.

The resin composition according to any one of Appendix 1 to Appendix 9.

(Annex 11)

As an inorganic filler,

A core portion containing Mg(OH) ₂ ,

A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion

Have,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Inorganic filler.

(Annex 12)

As an inorganic filler,

When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Inorganic filler.

(Annex 13)

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

DC power cable.

(Annex 14)

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

After immersing the DC power cable in a water bath at a temperature of 40° C. for 30 days, when the insulating layer of the DC power cable is cut off to form a sheet of the insulating layer having a thickness of 0.15 mm, the temperature is 90° C. and The volume resistivity of the sheet of the insulating layer measured under the condition of a direct current electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.

DC power cable.

(Annex 15)

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

When the direct current power cable is immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulating layer of the direct current power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, a temperature of 90° C. The dielectric breakdown electric field strength of the sheet of the insulating layer measured under conditions is 250 kV/mm or more.

DC power cable.

(Annex 16)

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,

The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,

After immersing the DC power cable in a water bath at a temperature of 40° C. for 30 days, the insulating layer of the DC power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, and at a temperature of 30° C. and atmospheric pressure. When a direct current electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions, V ₀ is the voltage applied to the sheet (kV), T is the thickness of the sheet (mm), and E ₁ is The electric field enhancement factor FEF obtained by the following equation (1) when the maximum electric field inside the sheet (kV/mm) is less than 1.15

DC power cable.

FEF=E ₁ /(V ₀ /T) ···(1)

(Annex 17)

Conductor,

Insulation layer installed on the outer periphery of the conductor

As a DC power cable having a,

The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler containing at least MgO,

The inorganic filler,

When the energy spectrum of the photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,

When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

DC power cable.

(Annex 18)

A step of preparing a resin composition having a base resin containing polyolefin and an inorganic filler,

Process of forming an insulating layer on the outer circumference of a conductor by using the resin composition

And,

The process of preparing the resin composition,

A step of preparing the inorganic filler having a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles installed on the outer periphery of the core portion,

The step of mixing the resin composition so that the content of the inorganic filler is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass.

Have,

In the step of preparing the inorganic filler,

The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.

Method of manufacturing a DC power cable.

(Annex 19)

In the step of preparing the inorganic filler,

Mg(OH) ₂ to form the inorganic filler by firing as a raw material

A method of manufacturing a DC power cable as described in Appendix 18.

10 DC power cable
110 conductor
120 inner semiconducting layer
130 insulation layer
140 outer semiconducting layer
150 shielding layer
160 sheath
200 inorganic filler
210 Nuclear Department
220 Mg(OH) ₂ particles
230 sheath
240 MgO particles

Claims (16)

A base resin containing polyolefin,
Inorganic filler
As a resin composition having,
The inorganic filler,
A core portion containing Mg(OH) ₂ ,
A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion
Have,
The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,
The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.
Resin composition. A base resin containing polyolefin,
Inorganic filler
As a resin composition having,
The inorganic filler,
A core portion containing Mg(OH) ₂ ,
A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion
Have,
A DC power cable having an insulating layer formed using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to obtain 0.15 mm. When the sheet of the insulating layer having a thickness is formed, the volume resistivity of the sheet of the insulating layer measured under the conditions of a temperature of 90° C. and a DC electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.
Resin composition. A base resin containing polyolefin,
Inorganic filler
As a resin composition having,
The inorganic filler,
A core portion containing Mg(OH) ₂ ,
A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion
Have,
A DC power cable having an insulating layer formed by using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to a thickness of 0.15 mm. When the sheet of the insulating layer having a thickness is formed, the dielectric breakdown electric field strength of the sheet of the insulating layer measured under the condition of a temperature of 90° C. is 250 kV/mm or more.
Resin composition. A base resin containing polyolefin,
Inorganic filler
As a resin composition having,
The inorganic filler,
A core portion containing Mg(OH) ₂ ,
A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion
Have,
A DC power cable having an insulating layer formed by using the resin composition was prepared, and the DC power cable was immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulation layer of the DC power cable was cut to a thickness of 0.15 mm. When a sheet of the insulating layer having a thickness is formed, and a DC electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions of a temperature of 30° C. and atmospheric pressure, the voltage (kV) applied to the sheet is V ₀ When T is the thickness (mm) of the sheet, and E ₁ is the maximum electric field inside the sheet (kV/mm), the electric field enhancement coefficient FEF calculated by the following equation (1) is , Less than 1.15
Resin composition.
FEF=E ₁ /(V ₀ /T) ···(1) The method according to any one of claims 1 to 4,
The surface of the covering portion has irregularities along the outer shape of the plurality of MgO particles.
Resin composition. A base resin containing polyolefin,
Inorganic filler containing at least MgO
As a resin composition having,
The inorganic filler,
When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,
When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,
The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,
The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.
Resin composition. The method according to any one of claims 1 to 6,
The inorganic filler is an inorganic powder calcined using Mg(OH) ₂ as a raw material.
Resin composition. The method according to any one of claims 1 to 7,
The volume average particle diameter of the inorganic filler is 5 μm or less.
Resin composition. As an inorganic filler,
A core portion containing Mg(OH) ₂ ,
A covering portion including a plurality of MgO particles installed on the outer periphery of the core portion
Have,
The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.
Inorganic filler. As an inorganic filler,
When the energy spectrum of photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,
When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,
The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.
Inorganic filler. Conductor,
Insulation layer installed on the outer periphery of the conductor
As a DC power cable having a,
The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,
The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,
The content of the inorganic filler in the resin composition is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass,
The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.
DC power cable. Conductor,
Insulation layer installed on the outer periphery of the conductor
As a DC power cable having a,
The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,
The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,
When the direct current power cable is immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulating layer of the direct current power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, the temperature is 90° C. and The volume resistivity of the sheet of the insulating layer measured under the condition of a direct current electric field of 80 kV/mm is 1×10 ¹⁵ Ω·cm or more.
DC power cable. Conductor,
Insulation layer installed on the outer periphery of the conductor
As a DC power cable having a,
The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,
The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,
When the direct current power cable is immersed in a water bath at a temperature of 40° C. for 30 days, and then the insulating layer of the direct current power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, a temperature of 90° C. The dielectric breakdown electric field strength of the sheet of the insulating layer measured under conditions is 250 kV/mm or more.
DC power cable. Conductor,
Insulation layer installed on the outer periphery of the conductor
As a DC power cable having,
The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler,
The inorganic filler has a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles disposed on the outer periphery of the core portion,
After immersing the DC power cable in a water bath at a temperature of 40° C. for 30 days, the insulation layer of the DC power cable is cut to form a sheet of the insulating layer having a thickness of 0.15 mm, and the temperature is 30° C. and atmospheric pressure. When a DC electric field of 50 kV/mm is applied to the sheet of the insulating layer under conditions, V ₀ is the voltage applied to the sheet (kV), T is the thickness of the sheet (mm), and E ₁ is The electric field enhancement factor FEF obtained by the following equation (1) when the maximum electric field inside the sheet (kV/mm) is less than 1.15
DC power cable.
FEF=E ₁ /(V ₀ /T) ···(1) Conductor,
Insulation layer installed on the outer periphery of the conductor
As a DC power cable having,
The insulating layer is composed of a resin composition having a base resin containing polyolefin and an inorganic filler containing at least MgO,
The inorganic filler,
When the energy spectrum of the photoelectrons emitted from the surface side of the inorganic filler was measured by X-ray photoelectron spectroscopy, a peak derived from MgO was shown, whereas a peak derived from Mg(OH) ₂ was not shown,
When the infrared absorption spectrum of the inorganic filler was measured based on the infrared light transmitted through the inorganic filler by Fourier transform infrared spectroscopy, a peak derived from Mg(OH) ₂ was shown,
The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.
DC power cable. A step of preparing a resin composition having a base resin containing polyolefin and an inorganic filler,
Process of forming an insulating layer on the outer circumference of a conductor by using the resin composition
And,
The process of preparing the resin composition,
A step of preparing the inorganic filler having a core portion containing Mg(OH) ₂ and a covering portion containing a plurality of MgO particles installed on the outer periphery of the core portion,
The step of mixing the resin composition so that the content of the inorganic filler is 0.1 parts by mass or more and 5 parts by mass or less when the base resin is 100 parts by mass.
Have,
In the step of preparing the inorganic filler,
The volume fraction of Mg(OH) ₂ in one particle of the inorganic filler is 10% or more and less than 50%.
Method of manufacturing a DC power cable.

Images