JP2023178080A - Semiconductive tape and power cable - Google Patents

Abstract

To achieve a balance between the ease of peeling an outer semiconductive layer and the resistance to water tree formation.SOLUTION: A semiconductive tape constitutes an outer semiconductive layer of a power cable. The power cable includes a conductor, an inner semiconductive layer, an insulating layer, and the outer semiconductive layer in the stated order from the central axis of the conductor to the outer periphery. The semiconductive tape is wound around the outer periphery of the insulating layer, which includes non-crosslinked polyolefin.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD This disclosure relates to semiconducting tapes and power cables.

A power cable has, for example, a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 57-69611

An object of the present disclosure is to provide a technology that can achieve both easy peelability and water tree resistance of an external semiconducting layer.

According to one aspect of the present disclosure,
A semiconductor power cable comprising a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer in this order from the central axis of the conductor toward the outer periphery, which constitutes the outer semiconducting layer. It is a sex tape,
The semiconductive tape is wound around the outer periphery of the insulating layer containing non-crosslinked polyolefin.

According to the present disclosure, it is possible to achieve both easy peelability of the outer semiconducting layer and water tree resistance.

FIG. 1 is a schematic cross-sectional view orthogonal to the axial direction of a power cable according to an embodiment of the present disclosure.

[Description of embodiments of the present disclosure]
<Knowledge obtained by the inventor>
First, the findings obtained by the inventor will be outlined.

Current common power cables, which have undergone equipment improvements, are formed by simultaneously extruding three layers: an inner semiconducting layer, an insulating layer, and an outer semiconducting layer. This can improve adhesion between layers. In addition, compared to extruding the three layers separately using a tandem extruder, by extruding the three layers simultaneously as described above, damage to the inner layer or the incorporation of foreign substances between the layers can be suppressed. Performance deterioration caused by these factors can be suppressed.

While the adhesion between the layers of the power cable has been improved as described above, it is necessary to peel off a portion of the outer semiconducting layer from the insulating layer when connecting a pair of power cables. Therefore, it is required that the external semiconductive layer can be easily peeled off from the insulating layer at the work site.

In order to satisfy the easy peelability of the external semiconductive layer as described above, the inventor studied a power cable in which the external semiconductive layer is made of a semiconductive tape.

However, it has been found that the following problems occur when the insulating layer is formed of crosslinked polyethylene and the outer semiconductive layer is formed of semiconductive tape.

When the polyethylene in the insulating layer is crosslinked, radicals are generated by the reaction during crosslinking. At this time, if the radicals have not completely reacted, the portion where the radicals have not completely reacted becomes the starting point of the water tree as a defective part. Therefore, a large amount of water trees may occur.

In particular, when crosslinking the insulating layer with the insulating layer exposed before wrapping the semiconductive tape of the external semiconductive layer, for example, the surface layer of the insulator becomes high temperature, so some crosslinking may occur. It is possible for the agent to volatilize before being used in the reaction, reducing the concentration of crosslinking agent below that required for crosslinking. Alternatively, for example, even if the crosslinking agent reacts, it may be deactivated by the outside air (oxygen contained as an impurity even in a nitrogen atmosphere). Therefore, in the outermost layer of the insulating layer, crosslinking does not proceed sufficiently, and there are many defective parts where radicals cannot fully react. As a result, a large amount of water trees are likely to occur.

Furthermore, if a semiconductive tape is wrapped around the outer periphery of the insulating layer after extrusion of the insulating layer, the adhesion between the insulating layer and the semiconductive tape will be reduced, regardless of whether the insulating layer is crosslinked or not. Therefore, the situation is such that water trees are likely to occur.

As a result, when the insulating layer is cross-linked, not only does the number of defective parts where radicals cannot fully react increase as described above, but also the adhesion between the insulating layer and the external semiconducting layer decreases. This also makes water trees more likely to occur.

As a result of intensive studies, the inventors have found that the above-mentioned novel problem can be solved by forming the outer semiconductive layer from a semiconductive tape while making the insulating layer non-crosslinked.

The present disclosure is based on the above-mentioned knowledge discovered by the inventors.

<Embodiments of the present disclosure>
Next, embodiments of the present disclosure will be listed and described.

[1] A semiconductive tape according to one aspect of the present disclosure,
A semiconductor power cable comprising a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer in this order from the central axis of the conductor toward the outer periphery, which constitutes the outer semiconducting layer. It is a sex tape,
The semiconductive tape is wrapped around the insulating layer containing non-crosslinked polyolefin.
According to this configuration, it is possible to achieve both easy peelability of the external semiconductive layer and water tree resistance.

[2] The power cable according to one aspect of the present disclosure includes:
a conductor;
an internal semiconducting layer provided to cover the outer periphery of the conductor;
an insulating layer provided to cover the outer periphery of the inner semiconductive layer and containing non-crosslinked polyolefin;
an outer semiconductive layer provided to cover the outer periphery of the insulating layer and made of a semiconductive tape;
has.
According to this configuration, it is possible to achieve both easy peelability of the external semiconductive layer and water tree resistance.

[3] In the power cable described in [2] above,
The height difference of the unevenness on the main surface of the semiconductive tape is 50 μm or less.
According to this configuration, it is possible to suppress the occurrence of water trees at the interface between the insulating layer and the external semiconducting layer during water immersion charging.

[4] In the power cable according to [2] or [3] above,
The sulfur content in the semiconductive tape is 1000 μg/g or less.
According to this configuration, it is possible to suppress the occurrence of water trees in the insulating layer during water immersion charging.

[5] In the power cable according to any one of [2] to [4] above,
The elastic modulus of the insulating layer at 25° C. is 150 MPa or more and 700 MPa or less.
According to this configuration, it is possible to suppress the deformation of the cable core, and also to suppress the generation of water trees at the interface between the insulating layer and the external semiconducting layer during water immersion electrification.

[6] In the power cable according to any one of [2] to [5] above,
The melting point of the insulating layer is 120° C. or higher.
According to this configuration, the shape of the non-crosslinked insulating layer can be stably maintained against a temperature rise during energization of the power cable.

[Details of embodiments of the present disclosure]
Next, one embodiment of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims.

<One embodiment of the present disclosure>

(1) Power Cable Next, with reference to FIG. 1, the power cable of this embodiment will be described.

The power cable 10 of this embodiment is configured as a so-called solid insulated power cable. Moreover, the power cable 10 of this embodiment is configured to be installed, for example, on land (inside a conduit), underwater, or on the bottom of the water. Note that the power cable 10 is used for, for example, alternating current.

Specifically, the power cable 10 includes, for example, a conductor 110, an inner semiconducting layer 120, an insulating layer 130, an outer semiconducting layer 140, a shielding layer 150, and a sheath 160. They are arranged in this order from the top to the outer periphery. Note that the conductor 110, the inner semiconducting layer 120, the insulating layer 130, and the outer semiconducting layer 140 are also referred to as a "cable core."

(Conductor (conductive part))
The conductor 110 is configured by twisting together a plurality of conductor core wires (conductive core wires) containing, for example, pure copper, copper alloy, aluminum, or aluminum alloy.

(inner semiconducting layer)
Internal semiconducting layer 120 is provided to cover the outer periphery of conductor 110 . The internal semiconductive layer 120 is, for example, extruded. Further, the internal semiconducting layer 120 has semiconductivity and is configured to suppress electric field concentration in a region near the surface of the conductor 110.

The internal semiconductive layer 120 is made of, for example, an ethylene copolymer such as ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-vinyl acetate copolymer, or an olefin. The material contains at least one of a system elastomer, a low-crystalline resin described below, and conductive carbon black.

(insulating layer)
The insulating layer 130 is provided to cover the outer periphery of the internal semiconducting layer 120. In this embodiment, the insulating layer 130 includes, for example, non-crosslinked polyolefin and is extruded as described below.

(External semiconducting layer)
The external semiconducting layer 140 is provided to cover the outer periphery of the insulating layer 130. Further, the external semiconducting layer 140 has semiconductivity and is configured to suppress electric field concentration between the insulating layer 130 and the shielding layer 150.

In this embodiment, the outer semiconductive layer 140 is made of, for example, a semiconductive tape. Moreover, the semiconductive tape as the external semiconductive layer 140 is in direct contact with the outer periphery of the insulating layer 130, for example, without using any other layer. This allows the power cable 10 to be easily manufactured and processed.

Details of the insulating layer 130 and the external semiconducting layer 140 of this embodiment will be described later.

(shielding layer)
The shielding layer 150 is provided to cover the outer periphery of the outer semiconducting layer 140. The shielding layer 150 is configured, for example, by winding a copper tape, or as a wire shield formed by winding a plurality of annealed copper wires or the like. Note that a tape made of rubberized cloth or the like may be wound around the inside or outside of the shielding layer 150.

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

Note that if the power cable 10 of this embodiment is an underwater cable or an underwater cable, it may have a metal water shielding layer such as a so-called aluminum sheathing or a steel wire armoring on the outside of the shielding layer 150. good.

On the other hand, the power cable 10 of this embodiment does not need to have a water shielding layer outside the shielding layer 150, for example. That is, the power cable 10 of this embodiment may be configured with a non-complete water-shielding structure.

(Specific dimensions, etc.)
Although the specific dimensions of the power cable 10 are not particularly limited, for example, the diameter of the conductor 110 is 5 mm or more and 60 mm or less, and the thickness of the internal semiconductive layer 120 is 0.5 mm or more and 3 mm or less. The thickness of the insulating layer 130 is 3 mm or more and 35 mm or less, the thickness of the outer semiconducting layer 140 is 0.5 mm or more and 3 mm or less, and the thickness of the shielding layer 150 is 0.1 mm or more and 5 mm or less. , the thickness of the sheath 160 is 1 mm or more. The AC voltage applied to the power cable 10 of this embodiment is, for example, 20 kV or more.

(2) Insulating layer The resin composition constituting the insulating layer 130 of this embodiment contains, for example, polyolefin as a resin component. Examples of polyolefins include ethylene resins (polyethylene), propylene resins (polypropylene), and ethylene-α-olefin copolymers. Note that two or more of these may be used in combination.

Examples of the ethylene resin include low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE). Moreover, these polyethylenes may be linear or branched, for example.

In addition, the density of LDPE is 0.91 g/cm ³ or more and less than 0.93 g/cm ³ , the density of linear low density polyethylene (LLDPE) is 0.945 g/cm ³ or less, and the density of MDPE is 0. The density of HDPE is .93 g/cm ³ or more and less than 0.942 g/cm ³ , and the density of HDPE is 0.942 g/cm ³ or more.

Examples of propylene-based resins include propylene homopolymers (homopolypropylene) and propylene random polymers (random polypropylene).

The polyolefin constituting the insulating layer 130 of this embodiment is, for example, non-crosslinked. By making the insulating layer 130 non-crosslinked, defects caused by unreacted radicals will not occur in the insulating layer 130. Thereby, water tree resistance of the insulating layer 130 can be ensured.

In this embodiment, the elastic modulus of the insulating layer 130 at 25° C. may be, for example, 150 MPa or more and 700 MPa or less.

Note that the "elastic modulus at 25° C." here is a storage modulus measured by dynamic mechanical analysis (DMA). In dynamic viscoelasticity measurement, for example, the target resin sample is stretched at 0.08% (stretching vibration with an amplitude of 0.08% is applied), and the temperature is adjusted from -50°C to 100°C. The storage modulus of the sample is measured while raising the temperature to ℃. At this time, the measurement frequency is set to 10 Hz. Further, the temperature increase rate is set to 10° C./min.

If the elastic modulus of the insulating layer 130 is less than 150 MPa, the semiconductive tape serving as the outer semiconducting layer 140 may dig into the insulating layer 130. In contrast, in this embodiment, by setting the elastic modulus of the insulating layer 130 to 150 MPa or more, it is possible to suppress the semiconductive tape serving as the external semiconducting layer 140 from digging into the insulating layer 130. On the other hand, if the elastic modulus of the insulating layer 130 exceeds 700 MPa, the semiconductive tape as the outer semiconductive layer 140 will not follow the irregularities on the outer periphery of the insulating layer 130. In contrast, in the present embodiment, by setting the elastic modulus of the insulating layer 130 to 700 MPa or less, the semiconductive tape as the external semiconductive layer 140 can easily follow the unevenness on the outer periphery of the insulating layer 130. be able to.

In this embodiment, the melting point of the insulating layer 130 is, for example, 120° C. or higher.

Note that the "melting point" here is measured by differential scanning calorimetry (DSC). "Differential scanning calorimetry" is performed in accordance with, for example, JIS-K-7121 (1987). Specifically, in the DSC device, the temperature of the measurement sample is raised from room temperature (room temperature, for example 27°C) to 220°C at a rate of 10°C/min. Thereby, a DSC curve can be obtained by plotting the amount of heat absorbed per unit time (heat flow) against the temperature. At this time, the temperature at which the amount of heat absorbed per unit time in the sample becomes maximum (highest peak) is defined as the "melting point (melting peak temperature)".

If the melting point of the insulating layer 130 is less than 120° C., there is a risk that the insulation properties of the non-crosslinked insulating layer 130 may deteriorate with respect to a temperature rise during energization of the power cable 100. In contrast, in the present embodiment, by setting the melting point of the insulating layer 130 to 120° C. or higher, the deterioration of the insulation properties of the non-crosslinked insulating layer 130 is suppressed with respect to the temperature rise during energization of the power cable 100. be able to.

[Resin component 1]
Insulating layer 130 may include, for example, linear low-density polyethylene (LLDPE) as a resin component to meet the above-mentioned elastic modulus and melting point requirements. The elastic modulus of LLDPE at 25° C. is 300 MPa or more and 600 MPa or less. The melting point of LLDPE is 120°C or higher and 135°C or lower. Thus, LLDPE alone can meet the above-mentioned modulus and melting point requirements.

[Resin component 2]
Alternatively, in order to satisfy the above requirements for elastic modulus and melting point, the insulating layer 130 includes, for example, a propylene resin (a propylene homopolymer or a propylene random polymer) and a low crystalline resin as resin components. You can stay there. In this way, the insulating layer 130 contains propylene resin as a main component, so that the above-mentioned melting point requirement can be satisfied. On the other hand, by mixing the propylene-based resin and the low-crystalline resin in the insulating layer 130, excessive crystal growth of the propylene-based resin can be inhibited, and the elastic modulus of the insulating layer 130 can be reduced. . Hereinafter, details of the propylene resin and the low crystalline resin will be explained.

(propylene resin)
The elastic modulus of the propylene homopolymer at 25° C. is 1400 MPa or more and 2500 MPa or less. The melting point of the propylene homopolymer is 160°C or more and 175°C or less.

On the other hand, the elastic modulus of the propylene random polymer at 25° C. is 500 MPa or more and 1500 MPa or less. The melting point of the propylene random polymer is 140°C or more and 150°C or less.

In this embodiment, the stereoregularity in the propylene resin may be, for example, isotactic. Propylene resin is polymerized using a Ziegler-Natta catalyst and is widely used. Since the stereoregularity is isotactic, it is possible to suppress a decrease in the melting point in a composition in which a propylene-based resin and a low-crystalline resin are mixed. As a result, it is possible to stably realize non-crosslinked use.

For reference, other stereoregularities include syndiotactic and atactic, but both are unfavorable stereoregularities of the propylene resin of this embodiment. Propylene resins having these stereoregularities cannot obtain a predetermined crystal structure and have a low melting point as a single substance. Furthermore, in a composition in which the propylene resin and the low crystallinity resin are mixed, the crystals of the propylene resin are easily eroded by the low crystallinity resin. Therefore, the melting point of the composition is lower than the melting point of the propylene resin alone. As a result, it becomes difficult to use it in a non-crosslinked state. For these reasons, syndiotactic and atactic are not preferred.

When the propylene resin is a propylene random polymer, the propylene resin has propylene units and ethylene units as described above. The content of ethylene units in the propylene random polymer is not particularly limited, but is, for example, 0.5% by mass or more and 15% by mass or less. Spherulite growth can be suppressed by controlling the content of ethylene units in the propylene random polymer to 0.5% by mass or less. On the other hand, by controlling the content of ethylene units in the propylene random polymer to 15% by mass or less, a decrease in the melting point can be suppressed, and use in a non-crosslinked state can be stably realized.

(Low crystalline resin)
The low crystalline resin of this embodiment is configured to control the crystallinity of the propylene resin and impart flexibility to the insulating layer. For example, the low crystallinity resin has no melting point, or the melting point of the low crystallinity resin is less than 100°C.

The elastic modulus of the low crystalline resin is lower than that of the propylene resin. Specifically, the elastic modulus of the low crystalline resin at 25° C. is 1 MPa or more and 200 MPa or less. Note that the low crystallinity resin may be considered as a flexible resin.

The low crystalline resin of this embodiment contains, for example, two or more monomer units. Specifically, the low crystalline resin is, for example, a copolymer obtained by copolymerizing at least two of ethylene units, propylene units, butene units (butylene units), hexene units, octene units, isoprene units, and styrene units. It consists of a combination.

Note that by analyzing the resin composition of this embodiment using a nuclear magnetic resonance (NMR) device, each monomer unit derived from the low crystalline resin is detected.

The carbon-carbon double bond in the olefinic monomer unit may be, for example, at the α position.

Examples of low-crystalline resins that meet the above requirements include ethylene propylene rubber (EPR), very low density polyethylene (VLDPE), and styrene resins (styrene-containing resins). It will be done. Two or more of these may be used in combination.

The low crystalline resin may be, for example, a copolymer containing propylene units from the viewpoint of compatibility with the propylene resin. Among the above-mentioned copolymers containing propylene units, EPR can be mentioned.

The content of ethylene units in EPR is not particularly limited, but may be, for example, 20% by mass or more, preferably 40% by mass or more, or 55% by mass or more. When the content of ethylene units in EPR is less than 20% by mass, the compatibility of EPR with propylene resin becomes excessively high. Therefore, even if the content of EPR in the insulating layer 130 is reduced, the insulating layer 130 can be made flexible. However, the effect of inhibiting crystallization of the propylene resin (also referred to as "crystallization inhibiting effect") is not expressed, and the insulation properties may be reduced due to microcracks in the spherulites. On the other hand, in this embodiment, by setting the content of ethylene units in EPR to 20% by mass or more, it is possible to suppress the compatibility of EPR with propylene resin from becoming excessively high. Thereby, it is possible to obtain the crystallization inhibiting effect due to EPR while obtaining the softening effect due to EPR. As a result, deterioration in insulation properties can be suppressed. Furthermore, by setting the content of ethylene units in EPR to 40% by mass or more, or 55% by mass or more, the crystallization inhibiting effect can be stably expressed, and the decline in insulation properties can be stably suppressed. can do.

On the other hand, the low crystalline resin may be, for example, a copolymer that does not contain propylene units. The copolymer not containing propylene units may be, for example, VLDPE from the viewpoint of easy availability. Note that the density of VLDPE is, for example, 0.855 g/cm ³ or more and 0.890 g/cm ³ or less.

Examples of VLDPE include ethylene/1-butene copolymer and ethylene/1-octene copolymer. By adding a copolymer containing no propylene units as the low crystalline resin in this way, complete compatibility can be suppressed while mixing a predetermined amount of the low crystalline resin with the propylene resin. By setting the content of such a copolymer not containing propylene units to a predetermined amount or more, a crystallization inhibiting effect can be exhibited.

Furthermore, the low crystalline resin may be, for example, a styrene resin as described above. The styrenic resin is a copolymer containing styrene units as hard segments and at least one monomer unit among ethylene units, propylene units, butene units, isoprene units, etc. as soft segments. The styrene resin can also be referred to as a styrene thermoplastic elastomer.

When the styrenic resin contains relatively flexible monomer units and relatively rigid monomer units, moldability can be improved. A fine phase structure can be formed by finely dispersing the low crystalline resin as a starting point in the propylene resin, and the phase structure can suppress excessive crystal growth of the propylene resin. Furthermore, the aromatic ring contained in the styrene resin can trap electrons and form a stable resonance structure. Thereby, the insulation properties of the insulating layer 130 can be further improved.

Further, since the styrene resin contains a monomer unit (for example, a butene unit) that has good compatibility with the propylene resin, the propylene resin and the low crystallinity resin can be uniformly mixed.

Examples of the styrenic resin include styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer, and hydrogenated styrene-butadiene-styrene block copolymer. Examples include styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, and styrene-ethylene-butene-olefin crystalline block copolymers. Two or more of these may be used in combination.

Note that "hydrogenated" here means that hydrogen is added to a double bond. For example, "hydrogenated styrene-butadiene-styrene block copolymer" means a polymer in which hydrogen is added to the double bonds of a styrene-butadiene-styrene block copolymer. Note that no hydrogen is added to the double bond of the aromatic ring of styrene. "Hydrogenated styrene butadiene styrene block copolymer" can be translated into styrene ethylene butene styrene block copolymer (SEBS).

Among styrenic resins, hydrogenated materials that do not contain double bonds in their chemical structure except for aromatic rings may be used. When a non-hydrogenated material is used, there is a possibility that the resin component will be thermally degraded during molding of the resin composition, and various properties of the obtained molded article may deteriorate. On the other hand, by using a hydrogenated material, resistance to thermal deterioration can be improved. Thereby, various properties of the molded article can be maintained at higher levels.

The content of styrene units in the styrenic resin is not particularly limited, but may be, for example, 5% by mass or more and 35% by mass or less. By setting the content of styrene units in the styrenic resin within the above range, it is possible to prevent the material from becoming excessively hard. Thereby, separation and cracking of the propylene-based resin and the styrene-containing resin can be suppressed.

(Resin composition)
When the resin composition contains a propylene resin, the contents of the propylene resin and the low crystalline resin may be adjusted so that the insulating layer 130 satisfies the above requirements for elastic modulus and melting point.

Specifically, when the total of the propylene resin and the low crystalline resin is 100 parts by mass, the content of the propylene resin may be, for example, 55 parts by mass or more and 95 parts by mass or less. The content of the low crystalline resin may be, for example, 5 parts by mass or more and 45 parts by mass or less.

Alternatively, the content of the propylene resin may be, for example, 60 parts by mass or more and 95 parts by mass or less. The content of the low crystalline resin may be, for example, 5 parts by mass or more and 40 parts by mass or less.

By adjusting each content as described above, the insulating layer 130 can satisfy the above requirements for elastic modulus and melting point.

[Other additives]
The insulating layer 130 may contain, for example, an antioxidant, a copper inhibitor, a nucleating agent, a lubricant, and a coloring agent in addition to the resin component described above.

(3) External semiconductive layer In this embodiment, the external semiconductive layer 140 that is in direct contact with the outer periphery of the insulating layer 130 is made of a semiconductive tape as described above.

Specifically, the semiconductive tape has, for example, a structure in which a nonwoven fabric holds a semiconductive resin. Examples of the fibers constituting the nonwoven fabric include polyester, polyethylene, and polypropylene. Here, the semiconductive tape may be a film containing only a semiconductive resin, but it is difficult to control the tension of a film containing only a semiconductive resin during use. Furthermore, it becomes difficult to form a semiconductive material containing a large amount of carbon into a film. On the other hand, as mentioned above, semiconductive tape has a structure in which semiconductive resin is held in nonwoven fabric, so when wrapping the semiconductive tape, the necessary tension is applied to the semiconductive tape. can be added. Moreover, since the semiconductive tape has a structure in which a nonwoven fabric holds a semiconductive resin, the semiconductive tape can be easily molded in a state containing the semiconductive resin. Furthermore, the thickness of the semiconductive tape can be reduced while maintaining moldability.

Note that an adhesive layer may be provided on at least one of both main surfaces of the semiconductive tape in order to improve the adhesion between the two main surfaces of the semiconductive tape and the adjacent layer. . However, in this case, the difference in height of the unevenness, which will be described later, may be satisfied with the adhesive layer provided.

In the present embodiment, the difference in height of the unevenness on each of the main surfaces of the semiconductive tape constituting the external semiconductive layer 140 may be, for example, 50 μm or less.

Note that the "principal surface of the semiconductive tape" herein means the surface of the semiconductive tape that is in contact with the insulating layer, or the surface of the semiconductive tape that is in contact with the shielding layer 150. The "height difference between the unevenness on each of the two main surfaces of the semiconductive tape" here means, for example, when observing an arbitrary cross section of the semiconductive tape with a scanning electron microscope (SEM), It means the difference in height in the thickness direction between the convex part (top) and the concave part (bottom) on each of the two main surfaces of.

If the height difference between the unevenness on each of the main surfaces of the semiconductive tape exceeds 50 μm, the adhesion between the insulating layer 130 and the outer semiconductive layer 140 will be reduced. On the other hand, in the present embodiment, the difference in height of the unevenness on each of the main surfaces of the semiconductive tape is set to 50 μm or less, thereby suppressing the decrease in adhesion between the insulating layer 130 and the external semiconductive layer 140. be able to.

Note that the height difference between the unevenness on each of the two main surfaces of the semiconductive tape may be small, for example, there may be no height difference (it may be 0 μm).

In this embodiment, the content of sulfur in the semiconductive tape constituting the outer semiconductive layer 140 is, for example, 1000 μg/g or less. If the sulfur content in the semiconductive tape exceeds 1000 μg/g, the sulfur in the semiconductive tape may be oxidized to produce sulfuric acid. Due to the sulfuric acid generated from the semiconductive tape, the semiconductive tape becomes strongly acidic when immersed in water. Therefore, deterioration near the defective portion of the insulating layer 130 is accelerated, and water trees are more likely to occur. In contrast, in this embodiment, by setting the sulfur content in the semiconductive tape to 1000 μg/g or less, the generation of sulfuric acid from the semiconductive tape can be suppressed, and the semiconductive It is possible to prevent the tape from becoming strongly acidic. Thereby, deterioration in the vicinity of the defective portion of the insulating layer 130 can be suppressed, and the occurrence of water trees can be suppressed.

Note that the sulfur content in the semiconductive tape may be small, for example, the sulfur content may be zero.

Note that the thickness of the semiconductive tape is not particularly limited, but may be, for example, 50 μm or more and 1000 μm or less. By setting the thickness of the semiconductive tape to 50 μm or more, tearing of the semiconductive tape during winding can be suppressed. On the other hand, by setting the thickness of the semiconductive tape to 1000 μm or less, the volume of the semiconductive tape can be reduced and manufacturing costs can be reduced. In addition, the voids in the semiconductive tape during wrap wrapping, which will be described later, can be reduced.

The outer semiconductive layer 140 is formed, for example, by spirally winding a band-shaped semiconductive tape.

As a method of winding the semiconductive tape, so-called butt winding is not preferred. The term "butt winding" used herein means winding the strip in a spiral shape while sequentially butting the ends of the strip in the width direction. In the butt winding, a kink (protrusion) may occur at the portion where the semiconductive tapes are butted. Therefore, due to the kink, moisture may easily penetrate and water trees may easily occur.

On the other hand, the method of winding the semiconductive tape of this embodiment may be, for example, so-called wrap winding. The term "lap winding" as used herein means winding the belt-like body in a spiral shape while sequentially overlapping parts of the belt-like body in the width direction.

The ratio of the overlapping width in wrapping the semiconductive tape may be 1/4 or more and 3/4 or less of the total width of the semiconductive tape. By setting the ratio of the overlapping widths within the above-mentioned range, it is possible to suppress the occurrence of kinks in the semiconductive tape and to reduce the unevenness of the overlapping portion of the semiconductive tape.

(4) Cable Characteristics In this embodiment, the power cable 10 has the above-described configuration, so that the power cable 10 has, for example, water tree resistance and high insulation properties of the insulating layer 130.

(water tree resistance)
In the present embodiment, in the water immersion charging test, the maximum length of water trees generated at the interface between the insulating layer 130 and the external semiconducting layer 140 and within the insulating layer 130 (also referred to as maximum water tree length) is as follows: For example, it may be less than 300 μm or 200 μm or less. Thereby, dielectric breakdown of the insulating layer 130 caused by water trees can be stably suppressed.

In addition, in the "water immersion charging test" herein, the power cable 10 is immersed in a 1N NaCl aqueous solution at room temperature (27°C), and a commercial frequency (for example, 60Hz) of 4kV/mm is applied to the power cable 10. An alternating current electric field is applied for 1000 hours.

(insulation)
In this embodiment, the AC breakdown electric field strength of the insulating layer 130 at room temperature (for example, 27° C.) may be, for example, 45 kV/mm or more, or 50 kV/mm or more.

Note that the "AC breakdown electric field strength" herein is measured, for example, by the following method. At room temperature (27° C.), a high alternating current voltage is applied to the conductor 110 while the external semiconducting layer 140 of the power cable 10 is grounded. At this time, after applying an AC voltage of commercial frequency (for example, 60 Hz) to the insulating layer 130 at 10 kV for 10 minutes, the cycle of increasing the voltage every 1 kV and applying the voltage for 10 minutes is repeated. The breakdown electric field strength when applied under the above conditions is determined as "AC breakdown electric field strength".

(5) Method for manufacturing power cable Next, a method for manufacturing power cable 10 of this embodiment will be described. Hereinafter, step will be abbreviated as "S".

The method for manufacturing the power cable 10 of the present embodiment includes, for example, a preparation step S100, an extrusion step S320, an outer semiconducting layer forming step S340, a shielding layer forming step S400, and a sheath forming step S500. There is.

(S100: Preparation process)
The preparation step S100 includes, for example, a resin composition preparation step S120, a tape preparation step S140, and a conductor preparation step S160.

(S120: Resin composition preparation step)
A resin composition for forming the insulating layer 130 is prepared.

In this embodiment, a resin component containing a polyolefin and other additives (antioxidants, etc.) are mixed (kneaded) using a mixer to form a mixed material. At this time, no crosslinking agent is added to the resin composition. Examples of the mixer include an open roll, a Banbury mixer, a pressure kneader, a single-shaft mixer, and a multi-shaft mixer.

At this time, in this embodiment, for example, LLDPE is prepared alone as the resin component.

Alternatively, at this time, in the present embodiment, for example, a propylene resin and a low crystalline resin are mixed as resin components. In addition, when the total of the propylene resin and the low crystalline resin is 100 parts by mass, the content of the propylene resin is 55 parts by mass or more and 95 parts by mass or less, and the content of the low crystalline resin is 5 parts by mass. It may be more than 45 parts by mass or less.

After forming the mixed material, the mixed material is granulated using an extruder. As a result, a pellet-shaped resin composition that will constitute the insulating layer 130 is formed. Note that the steps from mixing to granulation may be performed all at once using a twin-screw extruder with a high kneading effect.

(S140: Tape preparation step)
A semiconducting tape for forming the outer semiconducting layer 140 is prepared.

At this time, in this embodiment, the difference in height between the unevenness on the main surface of the semiconductive tape may be 50 μm or less. Moreover, at this time, in this embodiment, the content of sulfur in the semiconductive tape may be 1000 μg/g or less.

(S160: Conductor preparation step)
On the other hand, a conductor 110 formed by twisting a plurality of conductor core wires is prepared.

(S320: Extrusion process)
After the preparation step S100 and the conductor preparation step S200 are completed, the internal semiconducting layer 120 and the insulating layer 130 are formed in this order from the central axis of the conductor 110 toward the outer periphery.

Specifically, for example, the internal semiconductive layer 120 is extruded by charging the composition for the internal semiconductive layer into an extruder A for the internal semiconductive layer 120 among the tandem extruders.

The above pelletized resin composition is charged into an extruder B for forming the insulating layer 130. In addition, the set temperature of extruder B is set to a temperature higher than the desired melting point by a temperature of 10° C. or more and 50° C. or less. The set temperature may be adjusted as appropriate based on the linear speed and extrusion pressure. Thereby, the insulating layer 130 is extruded.

At this time, in the present embodiment, the above resin composition may be used in extruding the insulating layer 130 so that the elastic modulus of the insulating layer 130 at 25° C. may be set to 150 MPa or more and 700 MPa or less. Further, at this time, in this embodiment, the melting point of the insulating layer 130 may be set to 120° C. or higher.

Thereafter, in this embodiment, the insulating layer 130 is not crosslinked, and the extruded material is cooled, for example, with water.

(S340: External semiconducting layer forming step)
After forming the inner semiconductive layer 120 and the insulating layer 130, a semiconductive tape is wrapped so as to directly contact the outer periphery of the insulating layer 130 and cover the outer periphery of the insulating layer 130. This forms the outer semiconducting layer 140.

At this time, in this embodiment, a semiconductive tape serving as the external semiconductive layer 140 is wrapped around the outer periphery of the insulating layer 130 while suppressing excessive deformation of the insulating layer 130.

At this time, in this embodiment, the outer semiconductive layer 140 is formed by spirally winding a band-shaped semiconductive tape around the outer periphery of the insulating layer 130. Furthermore, lap winding is performed with the ratio of the overlapping width to the total width of the semiconductive tape being 1/4 or more and 3/4 or less.

Through the above extrusion step S320 and outer semiconducting layer forming step S340, 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 step)
Once the cable core is formed, a shielding layer 150 is formed on the outside of the outer semiconducting layer 140, for example by wrapping copper tape.

(S500: Sheath forming step)
After forming the shielding layer 150, a sheath 160 is formed around the outer periphery of the shielding layer 150 by charging vinyl chloride into an extruder and extruding it.

Through the above steps, the power cable 10 as a solid insulated power cable is manufactured.

(6) Effects of this embodiment According to this embodiment, one or more of the following effects can be achieved.

(a) In this embodiment, the external semiconductive layer 140 provided so as to cover the outer periphery of the insulating layer 130 while being in direct contact with the outer periphery of the insulating layer 130 is constituted by a semiconductive tape. Thereby, a part of the external semiconductive layer 140 can be easily peeled off from the insulating layer 130 at a work site where the pair of power cables 10 are connected.

Further, in this embodiment, the insulating layer 130 includes non-crosslinked polyolefin. By not crosslinking the insulating layer 130 before wrapping the semiconductive tape of the outer semiconductive layer 140 around the outer periphery of the insulating layer 130, defects caused by unreacted radicals will not occur in the insulating layer 130. . As a result, even if the adhesiveness between the insulating layer 130 and the semiconductive tape decreases when the semiconductive tape is wrapped around the outer periphery of the insulating layer 130 after the insulating layer 130 is extruded, the non-crosslinked insulating layer The water tree resistance of 130 itself can be ensured. This makes it possible to suppress the occurrence of water trees at the interface between the insulating layer 130 and the external semiconducting layer 140 or within the insulating layer 130 during water immersion electrification. As a result, dielectric breakdown of the insulating layer 130 caused by water trees can be stably suppressed.

As described above, according to the present embodiment, it is possible to achieve both easy peelability and water tree resistance of the outer semiconductive layer 140.

(b) In this embodiment, by making the insulating layer 130 non-crosslinked, it is possible to improve the recyclability of the resin composition that constitutes the insulating layer 130. As a result, the impact on the environment can be suppressed.

(c) In this embodiment, the outer semiconductive layer 140 is made of a semiconductive tape, so that the semiconductive tape constituting the outer semiconductive layer 140 is The volume can be reduced. Thereby, the manufacturing cost of the power cable 10 can be reduced.

(d) In the present embodiment, the difference in height of the unevenness on each of both main surfaces of the semiconductive tape constituting the external semiconductive layer 140 may be 50 μm or less. By setting the difference in height of the unevenness on each of the main surfaces of the semiconductive tape to 50 μm or less, it is possible to suppress a decrease in the adhesion between the insulating layer 130 and the external semiconductive layer 140. This makes it possible to suppress the occurrence of water trees at the interface between the insulating layer 130 and the external semiconducting layer 140 during water immersion charging. Further, it is possible to suppress a decrease in the insulation properties of the insulating layer due to a gap between the insulating layer 130 and the external semiconducting layer 140.

(e) In this embodiment, the content of sulfur in the semiconductive tape constituting the outer semiconductive layer 140 is 1000 μg/g or less. By controlling the sulfur content in the semiconductive tape to 1000 μg/g or less, it is possible to suppress the generation of sulfuric acid from the semiconductive tape, and to prevent the semiconductive tape from becoming strongly acidic when immersed in water. can do. Thereby, deterioration in the vicinity of the defective portion of the insulating layer 130 can be suppressed, and the occurrence of water trees can be suppressed.

(f) In this embodiment, the elastic modulus of the insulating layer 130 at 25° C. may be 150 MPa or more and 700 MPa or less. By setting the elastic modulus of the insulating layer 130 to 150 MPa or more, it is possible to suppress the semiconductive tape serving as the external semiconducting layer 140 from digging into the insulating layer 130. As a result, deformation of the cable core can be suppressed. On the other hand, by setting the elastic modulus of the insulating layer 130 to 700 MPa or less, the semiconductive tape as the external semiconductive layer 140 can easily follow the irregularities on the outer periphery of the insulating layer 130. Thereby, the generation of voids at the interface between the insulating layer 130 and the external semiconducting layer 140 can be suppressed. As a result, it is possible to suppress the occurrence of water trees at the interface between the insulating layer 130 and the external semiconducting layer 140 during water immersion charging. Further, it is possible to suppress a decrease in the insulation properties of the insulating layer due to a gap between the insulating layer 130 and the external semiconducting layer 140.

(g) In this embodiment, the melting point of the insulating layer 130 is, for example, 120° C. or higher. Thereby, the shape of the non-crosslinked insulating layer 130 can be stably maintained against a temperature rise during power supply of the power cable 100. As a result, deterioration in the insulation properties of the non-crosslinked insulating layer 130 can be suppressed.

<Other embodiments of the present disclosure>
Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments, and various changes can be made without departing from the gist thereof.

In the above-described embodiment, a case has been described in which the power cable 10 does not need to have a water-blocking layer, but the present disclosure is not limited to this case. The power cable 10 may have a simple water-blocking layer. Specifically, the simple water-blocking layer is made of, for example, a metal laminate tape. A metal laminate tape has a metal layer made of, for example, aluminum or copper, and an adhesive layer provided on one or both sides of the metal layer. The metal laminate tape is, for example, wrapped vertically so as to surround the outer periphery of the cable core (the outer periphery of the outer semiconductive layer). Note that the water-blocking layer may be provided outside the shielding layer, or may also serve as the shielding layer. With such a configuration, the cost of the power cable 10 can be reduced.

Next, examples 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) Production of power cables for samples A1 to A5 Power cables for samples A1 to A5 were produced as follows.

First, as a resin composition for forming an insulating layer, the resin compositions shown in Table 1 below were mixed using a Banbury mixer and granulated into pellets using an extruder. For samples A2 to A4, a propylene resin and a low crystalline resin were mixed so that the insulating layer satisfied the elastic modulus and melting point shown in Table 1.

In addition, tapes 1 to 3 shown below were prepared as semiconductive tapes for forming an external semiconductive layer. In addition, a conductor with a cross-sectional area of 100 mm ² was prepared.

After these were prepared, a resin composition for an internal semiconductive layer containing an ethylene-ethyl acrylate copolymer was charged into an extruder A for internal semiconductivity, and an internal semiconductive layer was extruded. Next, the above-mentioned resin composition was put into an extruder B for an insulating layer, and an insulating layer was extruded at an extrusion temperature of 170°C. As a result, an internal semiconducting layer and an insulating layer were formed on the outer periphery of the conductor from the inside to the outside. At this time, the thicknesses of the internal semiconducting layer and the insulating layer were 0.5 mm and 3.5 mm, respectively. After extrusion, the extruded material was water-cooled without crosslinking.

Next, an outer semiconductive layer was formed by spirally wrapping one of tapes 1 to 3 around the outer periphery of the insulating layer.

As described above, power cables of samples A1 to A5 were manufactured.

In samples A1 to A5, the details of the material used as the resin component of the insulating layer and the semiconductive tape of the outer semiconductive layer are as follows.

[Resin component]
(ethylene resin)
・Linear low density polyethylene (LLDPE)
Melt flow rate: 1.5g/10min,
Density: 0.93g/ml,
Melting point: 125℃,
Heat of fusion: 120J/g
Storage modulus at 25°C: 650MPa

(propylene resin)
・Propylene random polymer (r-PP)
Ethylene unit content: 10% by mass
Stereoregularity: Isotactic Melt flow rate: 1.3g/10min,
Density: 0.9g/ml,
Melting point: 145℃,
Heat of fusion: 100J/g
Storage modulus at 25°C: 900MPa

(Low crystalline resin)
・Ethylene propylene rubber (EPR)
Ethylene content: 52% by mass,
Mooney viscosity ML (1+4) 100℃: 40,
Melting point: None,
Heat of fusion: None,
Storage modulus at 25°C: 180MPa

・Hydrogenated styrene butadiene styrene block copolymer (SEBS)
Styrene content: 12% by mass,
Melt flow rate: 4.5g/10min (230°C, 2.16kg),
Melting point: None,
Heat of fusion: None,
Storage modulus at 25°C: 20MPa

[Semi-conductive tape: Tape 1 to 3]
Material: polyester non-woven fabric,
Tape thickness: 100μm,
Tape width: 35mm,
Difference in height of unevenness: 40 to 70 μm,
Sulfur content: 450-1500μg/g,
Winding method: spiral wrap,
Ratio of overlapping width to full width of semiconductive tape: 1/2

(2) Production of power cables for samples B1 to B3 Power cables for samples B1 to B3 were produced as follows.

[Sample B1]
First, as a resin composition for forming an insulating layer, resin compositions containing LDPE shown in Table 1 below were mixed using a Banbury mixer and granulated into pellets using an extruder. Next, the same conductor as sample A1 was prepared. After preparing the conductor, a resin composition for the inner semiconducting layer containing an ethylene-ethyl acrylate copolymer, the above-mentioned resin composition, and an outer semiconducting layer resin made of the same material as the resin composition for the inner semiconducting layer are prepared. and the composition were respectively charged into extruders A to C. The respective extrudates from extruders A to C were led to a common head, and an inner semiconducting layer, an insulating layer and an outer semiconducting layer were simultaneously extruded from the inside to the outside around the outer periphery of the conductor. At this time, the thicknesses of the inner semiconducting layer, the insulating layer, and the outer semiconducting layer were set to 0.5 mm, 3.5 mm, and 0.5 mm, respectively. After extrusion, the above extruded product was heated at about 250° C. to crosslink the insulating layer. As described above, a power cable of sample B1 was produced.

The details of the material used as the resin component of the insulating layer of sample B1 are as follows.

(ethylene resin)
・Low density polyethylene (LDPE)
Melt flow rate: 2g/10min,
Density: 0.91g/ml,
Melting point: 105℃,
Heat of fusion: 100J/g,
Storage modulus at 25°C: 400MPa

[Sample B2]
In sample B2, a power cable was produced in the same manner as sample B1, except that after crosslinking the insulating layer, an outer semiconductive layer was formed using the same semiconductive tape as in sample A1.

[Sample B3]
In sample B3, the power cable was made in the same way as sample B1, except that the insulating layer was extruded using the same resin composition as sample A2, and the insulating layer was water-cooled without crosslinking. Created.

(3) Evaluation (melt flow rate (MFR))
The melt flow rate of the resin composition constituting the insulating layer of each sample was measured. At this time, measurement was performed in accordance with the test method of JIS-K7210 (2014), the measurement temperature was 190° C., and the load was 2.16 kgf.

(melting point)
DSC measurement of the resin composition constituting the insulating layer of each sample was performed. DSC measurements were performed in accordance with JIS-K-7121 (1987). Specifically, a PerkinElmer DSC8500 (input compensation type) was used as the DSC device. The reference sample was, for example, α-alumina. The mass of the sample was 8 to 10 mg. In the DSC device, the temperature was raised from room temperature (27°C) to 220°C at a rate of 10°C/min. Thereby, a DSC curve was obtained by plotting the amount of endotherm (heat flow) per unit time versus temperature. At this time, the temperature at which the amount of heat absorbed per unit time in each sample becomes maximum (highest peak) was defined as the "melting point."

(Modulus of elasticity)
A press sheet for evaluation was produced using the resin composition constituting the insulating layer of each sample. Dynamic mechanical analysis (DMA) was performed on a press sheet of the target resin. Specifically, the storage modulus of the press sheet was measured while increasing the temperature from -50° C. to 100° C. with 0.08% expansion and contraction applied to the press sheet. At this time, the measurement frequency was set to 10 Hz. Further, the temperature increase rate was set to 10° C./min. As a result of the measurement, the storage modulus at 25°C was evaluated.

(Height difference in unevenness of semiconductive tape)
An arbitrary cross section of the semiconductive tape of each sample was observed by SEM. As a result, the height difference in the thickness direction between the convex portion and the concave portion on each of both principal surfaces of the semiconductive tape was measured.

(Sulfur content in semiconductive tape)
The content of sulfur in the semiconducting tape was determined by combustion-ion chromatography method. Specifically, first, a semiconductive tape was burned in a flask containing oxygen, and the generated combustion gas was absorbed into an absorption liquid (for example, a potassium hydroxide solution). Next, the amount of sulfate ions (SO ₄ ^2- ) in the absorption liquid was measured by ion chromatography. Thereafter, the measured amount of sulfate ions was converted into the content of sulfur in the semiconductive tape.

(Water tree resistance test and interface observation)
An alternating current electric field of 60 Hz and 4 kV/mm was applied to the power cable for 1000 hours while the power cable was immersed in a 1N NaCl aqueous solution at room temperature (27° C.).

After applying a predetermined alternating current electric field, a sheet 1 having a thickness of 0.5 mm was sampled from the center in the thickness direction of the insulating layer of the power cable. Also, a sheet 2 having a thickness of 0.5 mm was taken from the area containing the interface between the insulating layer and the external semiconducting layer of the power cable.

After collecting the sheet 2, the presence or absence of voids at the interface between the insulating layer and the external semiconducting layer was confirmed using an optical microscope.

Sheet 1 and Sheet 2 described above were dried, and each sheet was boiled and dyed with a methylene blue aqueous solution. After dyeing each sheet, each sheet was sliced along the main surface to a thickness of 30 μm to form slice pieces for observation. Thereafter, water trees were observed in the observation slice by observing the observation slice using an optical microscope.

At this time, the maximum length of water trees generated in each sheet was measured. The "maximum water tree length" in Table 1 was determined by rounding off the length of the longest water tree in 10 randomly selected observation slices.

(AC destructive test)
At room temperature (27° C.), an alternating current high voltage was applied to the conductor 110 while the external semiconducting layer 140 of the power cable 10 was grounded. At this time, an AC voltage of a commercial frequency (for example, 60 Hz) was applied to the insulating layer at 10 kV for 10 minutes, and then the voltage was increased in steps of 1 kV and applied for 10 minutes, repeating the cycle. The electric field strength when the sheet of the insulating layer suffered dielectric breakdown was measured as "AC breakdown electric field strength."

(4) Results The results of evaluating each sample will be explained with reference to Table 1 below.

[Samples B1 and B3]
For samples B1 and B3, the insulating layer and outer semiconducting layer were extruded and the insulating layer was crosslinked as described above.

In samples B1 and B3, there were no voids at the interface between the insulating layer and the external semiconducting layer, and no water trees were generated at the interface. In sample B3, water trees did not occur within the insulating layer. Further, in samples B1 and B3, the AC breakdown electric field strength of the insulating layer was 50 kV/mm or more.

However, in sample B1, water trees were generated within the insulating layer, and the maximum water tree length was 300 μm or more.

[Sample B2]
In sample B2, as described above, after crosslinking the insulating layer containing LDPE, the outer semiconducting layer was formed from semiconducting tape.

In sample B2, the AC breakdown electric field strength of the insulating layer was 45 kV/mm or more as an initial performance.

However, in sample B2, water trees occurred at the interface between the insulating layer and the external semiconducting layer and within the insulating layer, and the maximum water tree length was 300 μm or more.

In sample B2, there were many defective parts where radicals could not fully react in the crosslinked insulating layer. Furthermore, the adhesion between the insulating layer and the external semiconducting layer was reduced. As a result, in sample B2, the interface between the insulating layer and the outer semiconducting layer and the inside of the insulating layer gradually deteriorated over a long period of time, and the interface between the insulating layer and the outer semiconducting layer and the inside of the insulating layer gradually deteriorated. It is thought that water trees were more likely to occur.

[Samples A1 to A5]
In samples A1 to A5, the insulating layer was non-crosslinked, and the outer semiconductive layer was composed of semiconductive tape.

In samples A1 to A5, the maximum water tree length at the interface between the insulating layer and the outer semiconducting layer and within the insulating layer was less than 300 μm. Further, in samples A1 to A5, the AC breakdown electric field strength of the insulating layer was 45 kV/mm or more.

In samples A1 to A5, the insulating layer was non-crosslinked and the outer semiconducting layer was made of semiconductive tape, so that defects caused by unreacted radicals were not generated in the insulating layer. This made it possible to ensure the water tree resistance of the non-crosslinked insulating layer itself. As a result, it was confirmed that in samples A1 to A5, the occurrence of water trees could be suppressed at the interface between the insulating layer and the outer semiconducting layer or within the insulating layer.

[Dependence on elastic modulus of insulating layer]
In sample A5, since r-PP was used alone, the elastic modulus of the insulating layer at 25° C. was over 700 MPa. Therefore, in sample A5, voids were generated at the interface between the insulating layer and the external semiconducting layer, and water trees were slightly generated.

Further, the AC breakdown electric field strength of the insulating layer of sample A5 was lower than the AC breakdown electric field strength of the insulating layers of samples A1 and A2.

In sample A5, the semiconductive tape as the outer semiconductive layer did not follow the irregularities on the outer periphery of the insulating layer, and voids were generated at the interface between the insulating layer and the outer semiconductive layer. Conceivable.

On the other hand, in samples A1 and A2, the elastic modulus of the insulating layer at 25° C. was 700 MPa or less. As a result, in samples A1 and A2, no voids were generated at the interface between the insulating layer and the outer semiconducting layer, and no water trees were generated.

In samples A1 and A2, the AC breakdown electric field strength of the insulating layer was 50 kV/mm or more.

In samples A1 and A2, the semiconductive tape as the external semiconductive layer was able to easily follow the irregularities on the outer periphery of the insulating layer. As a result, it was confirmed that in samples A1 and A2, the generation of water trees at the interface between the insulating layer and the outer semiconducting layer could be suppressed. In samples A1 and A2, it was confirmed that the AC breakdown electric field strength of the insulating layer could be increased.

[Irregularity dependence of semiconductive tape]
In samples A3 and A4, the difference in height of the unevenness on both main surfaces of the semiconductive tape was more than 50 μm. For this reason, some water treeing occurred at the interface between the insulating layer and the outer semiconducting layer.

Further, the AC breakdown electric field strength of the insulating layer in samples A3 and A4 was lower than the AC breakdown electric field strength of the insulating layer in samples A1 and A2.

In samples A3 and A4, it is considered that the adhesion between the insulating layer and the external semiconductive layer was reduced due to the unevenness of the semiconductive tape.

On the other hand, in samples A1 and A2, the difference in height of the unevenness on each of the two main surfaces of the semiconductive tape was 50 μm or less. As a result, in samples A1 and A2, no water tree occurred at the interface between the insulating layer and the outer semiconducting layer.

In samples A1 and A2, as described above, the AC breakdown electric field strength of the insulating layer was 50 kV/mm or more.

In samples A1 and A2, it was possible to suppress the decrease in adhesion between the insulating layer and the external semiconductive layer due to the unevenness of the semiconductive tape. As a result, as described above, it was confirmed that in samples A1 and A2, the generation of water trees at the interface between the insulating layer and the outer semiconducting layer could be suppressed. In samples A1 and A2, it was confirmed that the AC breakdown electric field strength of the insulating layer could be increased.

[Sulfur content dependence of semiconductive tape]
In sample A4, the sulfur content in the semiconductive tape was more than 1000 μg/g. For this reason, some water treeing occurred within the insulating layer.

In sample A4, sulfur in the semiconductive tape was oxidized to produce sulfuric acid, and it is thought that defects such as voids were generated in the insulating layer.

On the other hand, in samples A1 and A2, the sulfur content in the semiconductive tape was 1000 μg/g or less. As a result, in samples A1 and A2, no water trees were generated within the insulating layer.

In samples A1 and A2, generation of sulfuric acid from the semiconductive tape could be suppressed, and deterioration near the defective portion of the insulating layer could be suppressed. As a result, it was confirmed that in samples A1 and A2, the generation of water trees within the insulating layer could be suppressed.

<Additional notes>
Aspects of the present disclosure will be additionally described below.

(Additional note 1)
A semiconductor power cable comprising a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer in this order from the central axis of the conductor toward the outer periphery, which constitutes the outer semiconducting layer. It is a sex tape,
The semiconductive tape is wound around the outer periphery of the insulating layer containing non-crosslinked polyolefin.

(Additional note 2)
a conductor;
an internal semiconducting layer provided to cover the outer periphery of the conductor;
an insulating layer provided to cover the outer periphery of the inner semiconductive layer and containing non-crosslinked polyolefin;
an outer semiconductive layer provided to cover the outer periphery of the insulating layer and made of a semiconductive tape;
with power cable.

(Additional note 3)
The power cable according to Supplementary Note 2, wherein the height difference between the unevenness on each of the two main surfaces of the semiconductive tape is 50 μm or less.

(Additional note 4)
The power cable according to appendix 2 or 3, wherein the sulfur content in the semiconductive tape is 1000 μg/g or less.

(Appendix 5)
The power cable according to any one of Supplementary notes 2 to 4, wherein the insulating layer has an elastic modulus of 150 MPa or more and 700 MPa or less at 25°C.

(Appendix 6)
The power cable according to any one of appendices 2 to 5, wherein the insulating layer has a melting point of 120° C. or higher.

(Appendix 7)
In the water immersion charging test, the maximum length of water trees occurring at the interface between the insulating layer and the external semiconducting layer and within the insulating layer is less than 300 μm;
However, in the water immersion charging test, an AC electric field with a commercial frequency of 4 kV/mm is applied to the power cable 10 for 1000 hours while the power cable is immersed in a 1N NaCl aqueous solution at room temperature. A power cable according to any one of the following.

(Appendix 8)
a step of preparing a conductor;
forming an internal semiconducting layer to cover the outer periphery of the conductor;
forming an insulating layer containing non-crosslinked polyolefin so as to cover the outer periphery of the internal semiconductive layer;
forming an external semiconductive layer by wrapping a semiconductive tape so as to cover the outer periphery of the insulating layer;
A method for manufacturing a power cable.

10 Power cable 110 Conductor 120 Inner semiconducting layer 130 Insulating layer 140 Outer semiconducting layer 150 Shielding layer 160 Sheath

Claims (6)

A semiconducting power cable comprising a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer in this order from the central axis of the conductor toward the outer periphery. It is a sex tape,
The semiconductive tape is wound around the outer periphery of the insulating layer containing non-crosslinked polyolefin. a conductor;
an internal semiconducting layer provided to cover the outer periphery of the conductor;
an insulating layer provided to cover the outer periphery of the inner semiconductive layer and containing non-crosslinked polyolefin;
an outer semiconductive layer provided to cover the outer periphery of the insulating layer and made of a semiconductive tape;
with power cable. The power cable according to claim 2, wherein the height difference between the unevenness on each of both main surfaces of the semiconductive tape is 50 μm or less. The power cable according to claim 2 or 3, wherein the sulfur content in the semiconductive tape is 1000 μg/g or less. The power cable according to claim 2 or 3, wherein the insulating layer has an elastic modulus of 150 MPa or more and 700 MPa or less at 25°C. The power cable according to claim 2 or 3, wherein the insulating layer has a melting point of 120° C. or higher.