Semiconductive composition and power cable

Abstract

The present invention provides a semiconductive composition for forming a semiconductive layer in a power cable, the semiconductive composition comprising: a resin component comprising a propylene-based resin and at least one of a rubber material and an elastomer; the rubber material and the elastomer have at least two units selected from ethylene, propylene, butylene, hexene, isoprene, octene, and styrene, and have a viscosity of 1000-5000 Pa.s inclusive at a temperature of 190 DEG C and a high shear rate of 100 s-1, and a viscosity of 100000-1000000 Pa.s inclusive at a temperature of 190 DEG C and a low shear rate of 1 s-1.

Description

Technical Field

[0001] This application claims the priority based on Japanese application "Tokugan 2022-134933" filed on August 26, 2022, and cites all the contents described in the above Japanese application.

[0002] The present invention relates to a semiconductive composition and a power cable. Background Art

[0003] Since cross-linked polyethylene has excellent insulating properties, it is widely used as a resin component constituting an insulating layer in power cables and the like (for example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent document 1: Japanese Patent Application Laid-Open No. 57-69611. Summary of the invention

[0007] According to one embodiment of the present invention, the present invention provides a semiconductive composition for forming a semiconductive layer in a power cable, wherein the semiconductive composition comprises a resin component and carbon black, wherein the resin component comprises at least one of a rubber material and an elastomer and a propylene resin, wherein the rubber material and the elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, and the semiconductive composition is subjected to a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic cross-sectional view perpendicular to the axial direction of a DC power cable according to an embodiment of the present invention. DETAILED DESCRIPTION

[0009] (Problem to be solved by the invention)

[0010] However, cross-linked polyethylene, which deteriorates over time, cannot be reused and must be incinerated, which raises concerns about its impact on the environment.

[0011] Therefore, in recent years, as a resin component for forming an insulating layer in a power cable, a resin containing propylene (hereinafter also referred to as a "propylene-based resin") has attracted attention. Even if the propylene-based resin is non-crosslinked, it can satisfy the insulation required for a power cable. In other words, it can take both insulation and recyclability into account. Furthermore, by using a propylene-based resin, it is possible to improve operability, processability, and ease of manufacture.

[0012] However, according to the research of the present inventors, it has been confirmed that when propylene resin is used, the outer diameter of the power cable is more likely to become uneven in the cross section and length direction of the power cable than when polyethylene is used for crosslinking. In particular, it has been confirmed that when a relatively thick insulating layer is formed on the conductor to increase the outer diameter of the power cable, the outer diameter is more likely to become uneven.

[0013] An object of the present invention is to provide a technique for improving the uniformity of the outer diameter of a power cable when a propylene-based resin is used as a resin component.

[0014] (Effects of the Invention)

[0015] According to the present invention, when a propylene-based resin is used as a resin component, the uniformity of the outer diameter of the power cable can be improved.

[0016] <Description of Embodiments of the Invention>

[0017] (Insights Obtained by the Present Invention)

[0018] First, the findings obtained by the inventors will be briefly described.

[0019] As described above, when a propylene-based resin is used as a covering material of a power cable, since cross-linking is not performed, the outer diameter is more likely to vary compared to cross-linked polyethylene.

[0020] Generally, in the production of power cables, first, a coating material for forming an inner semiconductive layer, a coating material for forming an insulating layer, and a coating material for forming an outer semiconductive layer are extruded simultaneously in a stacked manner on the outer periphery of the conductor. When these coating materials are cross-linked, for example, the cable is introduced into a cross-linking tube and heated in a high temperature environment. After cross-linking, the cable is introduced into, for example, a cooling tank, and the coating materials such as the inner semiconductive layer, the insulating layer, and the outer semiconductive layer are cooled. In this case, since the viscosity of the coating material increases during the cross-linking process, it is easy to maintain the coating material in the extruded shape, and its shape can be fixed as it is by cooling. That is, by cross-linking, it is possible to suppress the sagging caused by the flow of the coating material and the accompanying change in the outer diameter of the power cable.

[0021] In contrast, when propylene resin is used in the coating material, since no cross-linking treatment is performed, the coating material is cooled after extrusion. At this time, the coating material is gradually cooled from the surface side to the inside of the stacked coating material. Therefore, the surface side of the stacked coating material is fixed in shape by cooling, but the inside can produce a state of melt flow due to high temperature. Moreover, since no cross-linking treatment is performed, the viscosity of the coating material cannot be increased. As a result, during the period from the inside of the coating material cooling to the fixed shape, the coating material sometimes sags due to its own weight. With this drooping, the thickness of the coating layer in the cross section of the power cable in its peripheral direction sometimes becomes uneven, and the thickness in the length direction of the power cable sometimes also becomes uneven. For example, when a horizontal extruder is used to transport the power cable in a horizontal direction, the coating material sometimes sags in the lower side of the cross section of the power cable, and when a vertical extruder is used to transport it in a vertical direction, it sometimes sags to the lower side in the length direction of the power cable. When the thickness of the insulating coating becomes non-uniform in the circumferential direction or the longitudinal direction of the cross section, there may be a portion where the insulation is locally reduced, and the desired insulation may not be achieved.

[0022] The thicker the extrusion, the more likely the coating material will sag. The thicker the insulating layer is and the greater the ratio of the thickness of the insulating layer to the outer diameter of the conductor is, the more significant the sag will be.

[0023] Therefore, the present inventors have studied a method for suppressing the sagging of the coating layer including the inner semiconductive layer, the insulating layer and the outer semiconductive layer, especially the insulating layer which has a large influence on the outer diameter variation. Then, the present inventors focused on the viscosity of the semiconductive composition forming the outer semiconductive layer. This is because by setting the viscosity of the semiconductive composition high, the sagging caused by the flow of the resin composition forming the insulating layer arranged inside the semiconductive composition can be suppressed and the shape can be maintained. On the other hand, the semiconductive composition is also required to have extrusion moldability, and a viscosity that can be stably extruded with a fixed thickness is required.

[0024] In general, the viscosity of a resin varies greatly with shear rate, and there is a tendency for the viscosity to be low at high shear rates and high at low shear rates. In the production of power cables, the semiconductive composition has a tendency to have a high shear rate and a low viscosity during the melt-mixing and extrusion stage. On the other hand, there is a tendency for the viscosity to be high at a low shear rate during the cooling stage after extrusion. In addition, in the semiconductive composition, by further adding carbon black, there is a tendency for the viscosity to be higher at high and low shear rates as a whole.

[0025] Therefore, the inventors studied the viscosity of the semiconductive composition at high shear rate and low shear rate, and found that by adjusting each viscosity within a predetermined range, it is possible to achieve both extrusion moldability and suppress sagging during cooling and fixing the shape. The inventors found that such a semiconductive composition can improve the uniformity of the outer diameter of the power cable.

[0026] The present invention has been accomplished based on the above findings.

[0027] (Embodiment of the present invention)

[0028] Next, embodiments of the present invention will be described by way of examples.

[0029] [1] A semiconductive composition according to one embodiment of the present invention is used to form a semiconductive layer in a power cable, the semiconductive composition comprising a resin component and carbon black, the resin component comprising at least one of a rubber material and an elastomer and a propylene resin, the rubber material and the elastomer having at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, the semiconductive composition being resistant to sintering at a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

[0030] According to this configuration, the uniformity of the outer diameter of the power cable can be improved.

[0031] [2] An electric power cable according to one embodiment of the present invention comprises: a conductor; an insulating layer, which is coated on the outer periphery of the conductor and is formed of a resin composition; and an outer semiconductive layer, which is coated on the outer periphery of the insulating layer and is formed of a semiconductive composition, wherein the semiconductive composition comprises a resin component and carbon black, wherein the resin component comprises at least one of a rubber material and an elastomer and a propylene resin, wherein the rubber material and the elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, and the semiconductive composition is resistant to sintering at a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

[0032] According to this structure, the uniformity of the outer diameter can be improved.

[0033] [3] In the electric power cable described in [2] above, the content of the carbon black is 10 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the resin component.

[0034] According to this configuration, the uniformity of the outer diameter of the power cable can be further improved, and the electric field can be made more uniform.

[0035] [4] In the power cable described in [2] or [3] above, the heat of fusion of the resin component is 55 J / g or more and 90 J / g or less.

[0036] According to this structure, the uniformity of the outer diameter can be improved more reliably.

[0037] [5] In the power cable described in [2] or [3] above, the melting point of the resin component is 140° C. or higher and 170° C. or lower.

[0038] According to this structure, the uniformity of the outer diameter can be improved more reliably.

[0039] [6] In the power cable described in [2] or [3] above, in a cross section perpendicular to the longitudinal direction, the ratio of the major diameter to the minor diameter is 1.3 or less.

[0040] According to this configuration, the uniformity of the outer diameter in the outer peripheral direction of the cross section of the power cable can be improved.

[0041] [7] In the power cable described in [2] or [3] above, in a cross section at two points separated in the longitudinal direction, a ratio of a major axis at one point to a minor axis at another point is 1.3 or less.

[0042] According to this configuration, the uniformity of the outer diameter of the power cable in the longitudinal direction can be improved.

[0043] [8] In the power cable described in [2] or [3] above, the thickness of the outer semiconductive layer is 0.5 mm or more, and the ratio of the outer diameter of the power cable to the outer diameter of the conductor is 4 or less.

[0044] According to this configuration, even when the outer diameter of the power cable is increased by forming an insulating layer relatively thick with respect to the outer diameter of the conductor, the uniformity of the outer diameter can be maintained.

[0045] (Details of Embodiments of the Invention)

[0046] Next, one embodiment of the present invention will be described below with reference to the drawings. The present invention is not limited to these examples, but is represented by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0047] (One embodiment of the present invention)

[0048] (1) Semiconductive composition

[0049] The semiconductive composition of this embodiment can be used as a material for forming a semiconductive layer of a power cable. In the semiconductive layer, it can be used for an outer semiconductive layer or an inner semiconductive layer. The semiconductive composition includes a resin component and carbon black, wherein the resin component includes at least one of a rubber material and an elastomer and a propylene resin, and by mixing these components, the viscosity at high shear rate and low shear rate is adjusted to a specified range. Specifically, as the viscosity of the semiconductive composition, at a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

[0050] Hereinafter, the constituent components of the semiconductive composition, the composition thereof, and physical properties such as the viscosity of the resin composition will be described in detail.

[0051] (1-1) Acrylic resin

[0052] The propylene resin is the base polymer of the semiconductive composition. Examples of the propylene resin include propylene homopolymers (hereinafter also referred to as homo-PP), propylene random polymers (hereinafter also referred to as random PP), and the like. Homo-PP contains propylene units, while random PP has propylene units and ethylene units. From the viewpoint of obtaining higher flexibility in the semiconductive layer, the propylene resin may be random PP. Random PP contains ethylene units and has a lower crystallinity than homo-PP, so it is difficult to generate coarse crystals during cooling, which can further improve the flexibility of the semiconductive layer.

[0053] The content of ethylene units in random PP can be, for example, 0.5% by mass or more and 15% by mass or less. By making the content of ethylene units 0.5% by mass or more, the formation of coarse crystals can be easily suppressed, and the flexibility of the semiconductive layer can be maintained high. On the other hand, by making the content of ethylene units 15% by mass or less, the decrease in melting point can be suppressed, and the use in non-crosslinking or slightly crosslinking can be stably achieved.

[0054] In addition, examples of the stereoregularity of the propylene resin include isotactic, syndiotactic and atactic. The stereoregularity is not particularly limited and may be isotactic. When the stereoregularity is isotactic, the melting point of the semiconductive composition can be suppressed from decreasing. As a result, the use in non-crosslinking or slightly crosslinking can be stably achieved.

[0055] The viscosity of the propylene resin at high shear rate and low shear rate is not particularly limited. The viscosity at high shear rate can be greater than 100 Pa·s and less than 6000 Pa·s. The viscosity at low shear rate can be 500 Pa·s to less than 50000 Pa·s. By having such a viscosity, it is easy to adjust to a specified viscosity in the semiconductive composition. By making the viscosity of the propylene resin as the base polymer within the above range, when mixed with an elastomer, etc., the viscosity of the semiconductive composition at each shear rate can be more reliably adjusted to the above range.

[0056] In addition, as the propylene resin, a single propylene resin having a viscosity in a predetermined range at high shear rate and low shear rate may be used alone, or two or more propylene resins having different viscosities may be used in combination. From the viewpoint of adjusting the viscosity in the resin composition to a predetermined range, two or more propylene resins may be used in combination.

[0057] In addition, as described later, resin components such as propylene resins can obtain different viscosity curves according to physical properties such as melting point, heat of fusion, molecular weight distribution, etc. In this embodiment, from the perspective of adjusting the viscosity of the semiconductive composition to a predetermined range, the physical properties of the propylene resin can be set as follows.

[0058] The melting point of the propylene resin is not particularly limited. If it is a propylene homopolymer (homopolymer PP), it can be 160°C or higher and 175°C or lower. If it is a propylene random polymer (random PP), it can be 140°C or higher and 150°C or lower. With such a propylene resin, it is easy to adjust the viscosity of the semiconductive composition to a specified range. In addition, the melting point of the semiconductive composition can be increased, and the heat resistance temperature of the semiconductive layer can be increased. As a result, even if the semiconductive layer is non-crosslinked, high performance can be stably maintained in a high temperature environment.

[0059] The heat of fusion of the propylene resin is not particularly limited, but can be 100 J / g to 120 J / g in the case of homopolymer PP, or 90 J / g to 105 J / g in the case of random PP. Such a propylene resin can easily adjust the viscosity of the semiconductive composition to a predetermined range, and can also increase the heat resistance temperature of the semiconductive layer, thereby stably maintaining various properties even in a high temperature environment.

[0060] In addition, in this specification, the melting point and the heat of fusion are measured as follows.

[0061] First, for the sample, differential scanning calorimetry (DSC) is performed, for example, according to JIS-K-7121 (1987). Specifically, in the DSC device, the temperature is raised from room temperature (normal temperature, such as 27°C) to 220°C at a rate of 10°C / min. Thus, by plotting the amount of heat absorbed per unit time (heat flow) against the temperature, a DSC curve is obtained. At this time, the temperature at which the amount of heat absorbed per unit time of the sample reaches a maximum value (peak value) is taken as the "melting point (melting peak temperature)". In addition, at this time, it is assumed that the heat absorption of the sample is entirely performed by the resin component, and the value (J / g) obtained by dividing the amount of heat absorbed by the sample from room temperature to 220°C (J) by the total mass (g) of the resin component in the sample is taken as the "heat of fusion". In addition, based on the theoretical value of the heat of fusion of the sample and the heat of fusion of the complete crystal, the crystallinity (%) of the sample can be calculated.

[0062] The propylene resin has a prescribed molecular weight distribution, and the wider the width of the molecular weight distribution, that is, the greater the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the molecular weight distribution, the greater the difference between the viscosity at a high shear rate and the viscosity at a low shear rate tends to be. From the viewpoint of adjusting the viscosity at each shear rate in the semiconductive composition to the above range, Mw / Mn can be 3.0 or more and 8.0 or less, or 3.5 or more and 7.0 or less. In addition, the number average molecular weight Mn can be, for example, 60,000 or more and 150,000 or less. In addition, the weight average molecular weight Mw can be, for example, 210,000 or more and 1,000,000 or less.

[0063] (1-2) Rubber materials and elastomers

[0064] The rubber material and the elastomer control the crystal growth of the propylene resin in the semiconductive composition and give the semiconductive layer flexibility. In addition, the rubber material and the elastomer may change the viscosity of the semiconductive composition at each shear rate by mixing with the propylene resin, but by mixing in a predetermined viscosity range, the semiconductive layer can be given a predetermined flexibility. The rubber material or the elastomer of this embodiment contains at least two of ethylene, propylene, butene, hexene, isoprene, octene and styrene.

[0065] The viscosity of the rubber material and the elastomer at high shear speed and low shear speed is not particularly limited. The viscosity at high shear speed can be 300Pa·s or more and 7000Pa·s or less. In addition, the viscosity at low shear speed can be 4000Pa·s or more and 80000Pa·s or less. Alternatively, for the rubber material, the viscosity at high shear speed can be 500Pa·s or more and 5000Pa·s or less, and the viscosity at low shear speed can be 10000Pa·s or more and 70000Pa·s or less. For the elastomer, the viscosity at high shear speed can be 1000Pa·s or more and 6000Pa·s or less, and the viscosity at low shear speed can be 5000Pa·s or more and 50000Pa·s or less. According to the rubber material or elastomer having such viscosity, when mixed with the propylene resin, the viscosity of each semiconductive composition can be easily adjusted to the desired range.

[0066] The melting points of rubber materials and elastomers are not particularly limited. Rubber materials generally do not have a melting point because no peak of endothermic heat is detected in DSC measurement. Elastomers may not have a melting point, or even if they have a melting point, the melting point may be 100° C. or less.

[0067] The heat of fusion of the rubber material and the elastomer is not particularly limited. Since the melting point cannot be measured, the heat of fusion of the rubber material is zero. The heat of fusion of the elastomer may be 50 J / g or less, or 30 J / g or less.

[0068] Specifically, as the rubber material, a copolymer obtained by copolymerizing at least two of ethylene, propylene, butene, hexene, and octene can be used.

[0069] From the viewpoint of compatibility with the propylene resin, the rubber material may be a copolymer containing propylene. As the copolymer containing propylene, for example, ethylene propylene rubber (EPR: Ethylene Propylene Rubber) can be used.

[0070] The ethylene content of EPR can be, for example, 20% by mass or more, 40% by mass or more, or 55% by mass or more. When the ethylene content is less than 20% by mass, the crystallization of the propylene resin cannot be fully controlled. In contrast, by making the ethylene content 20% by mass or more, the softening effect brought about by EPR can be obtained, and the crystallization of the propylene resin brought about by EPR can be fully controlled. Furthermore, by making the ethylene content 40% by mass or more or 55% by mass or more, the crystallization can be controlled more stably. In addition, the density of VLDPE is, for example, 0.855 g / cm 3 Above 0.890g / cm 3 the following.

[0071] On the other hand, the rubber material may be, for example, a copolymer not containing propylene. As a copolymer not containing propylene, for example, from the viewpoint of easy availability, very low density polyethylene (VLDPE: Very Low Density Polyethylene) etc. can be used. As VLDPE, for example, PE composed of ethylene and 1-butene, PE composed of ethylene and 1-octene etc. can be cited. According to the copolymer not containing propylene, the crystallization of the propylene-based resin can be stably controlled.

[0072] In addition, as the elastomer, for example, a styrene-based thermoplastic elastomer containing styrene as a hard segment and at least one of ethylene, propylene, butylene, and isoprene as a soft segment can be used. The styrene-based thermoplastic elastomer is a component that is dispersed in the semiconductive composition, controls the crystal growth of the propylene resin, imparts flexibility to the semiconductive layer, and helps adjust the viscosity of the semiconductive composition, just like the rubber material. Furthermore, the styrene-based thermoplastic elastomer also helps improve the water tree resistance of the semiconductive layer by suppressing the generation of mechanical stress cracks in the semiconductive layer.

[0073] Examples of the styrene-based thermoplastic elastomer include styrene butadiene styrene block copolymer (SBS), hydrogenated styrene butadiene styrene block copolymer, styrene isoprene styrene copolymer (SIS), hydrogenated styrene isoprene styrene copolymer, hydrogenated styrene butadiene rubber, hydrogenated styrene isoprene rubber, styrene ethylene butene olefin crystalline block copolymer, etc. Two or more of these may be used in combination.

[0074] In addition, the "hydrogenation" mentioned here means that hydrogen is added to the double bonds. For example, "hydrogenated styrene butadiene styrene block copolymer" refers to a polymer in which hydrogen is added to the double bonds of styrene butadiene styrene block copolymer. In addition, no hydrogen is added to the double bonds of the aromatic rings possessed by styrene. "Hydrogenated styrene butadiene styrene block copolymer" can also be called styrene ethylene butylene styrene block copolymer (SEBS).

[0075] The styrene-based thermoplastic elastomer may be a substance that does not contain a double bond in its chemical structure. When a substance having a double bond is used, the resin component may be thermally degraded during molding of the semiconductive composition, and the properties of the obtained semiconductive layer may be reduced. In this regard, since a substance that does not contain a double bond has high resistance to thermal degradation, the properties of the semiconductive layer can be maintained at a higher level.

[0076] The styrene content in the styrene-based thermoplastic elastomer is not particularly limited, but may be 5% by mass or more and 35% by mass or less from the viewpoint of controlling the crystal growth of the propylene-based resin and softening the semiconductive layer.

[0077] (1-3) Carbon black

[0078] Carbon black is added and mixed into the resin component to impart conductivity to the resin component. As carbon black, furnace black and acetylene black can be used, for example. Here, furnace black refers to carbon black generated by burning oil or the like. Acetylene black refers to carbon black generated by thermally decomposing acetylene as a raw material.

[0079] The average particle size of carbon black is not particularly limited and can be appropriately dispersed in the semiconductive layer and appropriately set within a range that can obtain a predetermined conductivity. For example, the average particle size can be greater than 35 nm and less than 100 nm. In addition, the average particle size here refers to the particle size at which the cumulative value of the particle size distribution obtained by particle size measurement using a laser diffraction scattering method is 50%.

[0080] (1-4) Other additives

[0081] The semiconductive composition may contain, in addition to the above-mentioned resin component and carbon black, for example, an antioxidant, a copper inhibitor, a lubricant, and a colorant.

[0082] However, in the semiconductive composition, for example, the content of the additive that functions as a nucleating agent for generating propylene crystals may be reduced, or such an additive may be substantially absent. Specifically, for example, when the total amount of the resin component including at least one of the rubber material and the elastomer and the propylene resin is 100 parts by mass, the content of the additive that functions as a nucleating agent may be less than 1 part by mass, or may be 0 part by mass. Thus, the occurrence of unexpected abnormal crystallization caused by the nucleating agent can be suppressed, and the amount of crystallization can be easily controlled.

[0083] The semiconductive composition may contain an inorganic filler. From the viewpoint of adjusting the viscosity at high shear rate and low shear rate to a predetermined range, the amount of the inorganic filler added may be small or no inorganic filler may be added.

[0084] (1-5) Viscosity of the Semiconductive Composition

[0085] The semiconductive composition is formed by mixing at least one of a rubber material and an elastomer, an propylene resin, and carbon black. By mixing these components, the semiconductive composition is subjected to a temperature of 190° C. and a shear rate of 100 s. -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

[0086] Propylene resins, rubber materials and elastomers each have a unique viscosity curve. The viscosity curve refers to a curve in which the horizontal axis represents the shear rate and the vertical axis represents the viscosity, and the viscosity decreases as the shear rate increases, showing a downward trend. The viscosity curve takes a unique shape according to the molecular weight, molecular weight distribution, melting point, heat of fusion, etc. of the resin. Not only when the types of propylene resins, rubber materials and elastomers are different, but even if they are the same propylene resins, the viscosity curves are different when the physical properties such as molecular weight distribution and melting point are different. Due to the difference in viscosity curves, the slope of the viscosity curve, the viscosity range that can be obtained at high shear speed and low shear speed, etc. are different. In this embodiment, the viscosity at each shear speed is adjusted by mixing propylene resins, rubber materials and elastomers with different viscosity curves. In addition, the viscosity curve of the semi-conductive composition is controlled by adding carbon black to the resin component to adjust the viscosity at each shear speed.

[0087] In the semiconductive composition, when the viscosity at a high shear rate is less than 1000Pa·s, it is sometimes impossible to maintain the shape of the molten semiconductive composition and stably extrude it with a uniform thickness. On the other hand, when the viscosity at a high shear rate is greater than 5000Pa·s, the pressure when the semiconductive composition is extruded becomes high, and the extrusion amount is unstable, so that the semiconductive composition cannot be extruded with a uniform thickness. In this regard, by adjusting the viscosity at a high shear rate within the range of 1000Pa·s to 5000Pa·s, the semiconductive composition can be extruded with a uniform thickness, and the flow of the coating material for forming the insulating layer can be suppressed to maintain its shape. The viscosity at a high shear rate can be 1000Pa·s to 3000Pa·s.

[0088] When the viscosity at a low shear rate is less than 100,000 Pa·s, the flow (droop) of the coating material used to form the insulating layer cannot be suppressed when manufacturing the power cable, and the outer diameter is easily changed. On the other hand, when the viscosity at a low shear rate is greater than 1,000,000 Pa·s, the viscosity at a high shear rate also increases accordingly, so as mentioned above, the extrusion amount of the semiconductive composition becomes unstable, and sometimes the semiconductive layer cannot be formed with a uniform thickness. In this regard, by adjusting the viscosity at a low shear rate within the range of 100,000 Pa·s to 1,000,000 Pa·s, the droop of the extruded semiconductive composition can be suppressed, and the uniformity of the outer diameter of the power cable can be improved. The viscosity at a low shear rate can be 100,000 Pa·s to 300,000 Pa·s.

[0089] The ratio of the viscosity at a high shear rate to the viscosity at a low shear rate is not particularly limited, and when the viscosity at a high shear rate is defined as A and the viscosity at a low shear rate is defined as B, B / A may be 30 or more and 1000 or less. The larger the ratio, the lower the pressure at which the molten semiconductive composition can be extruded, and in the production of a power cable, the droop of the material forming the insulating layer can be suppressed.

[0090] The viscosity at high shear rate and low shear rate is measured by the procedure shown in the Examples described later.

[0091] (1-6) Melting Point and Heat of Fusion of Semiconductive Composition

[0092] The melting point and heat of fusion of the semiconductive composition vary depending on the amount of each of the acrylic resin, rubber material, and elastomer mixed as the resin component. That is, the melting point and the like are indicators of the ratio (composition) of each component. In addition, the melting point and heat of fusion of the semiconductive composition are substantially the same as those of the resin component other than carbon black.

[0093] The melting point of propylene resin is relatively high, while rubber materials and elastomers do not have a melting point, or even if they have a melting point, the melting point is low. In addition, propylene resin has high crystallinity and high heat of fusion, while rubber materials and elastomers have low crystallinity or are amorphous and low heat of fusion. Therefore, there is a tendency that the melting point and heat of fusion of the resin component in the semiconductive composition are respectively lower than the melting point and heat of fusion originally possessed by the propylene resin.

[0094] The melting point and heat of fusion of the resin component are not particularly limited, but may be in the following ranges from the viewpoint of mixing the components at an appropriate ratio so that the viscosities at high and low shear rates are within the prescribed ranges.

[0095] Specifically, when homo-PP is included as the propylene resin, the melting point of the resin component may be 158° C. to 168° C. Furthermore, when random PP is included as the propylene resin, the melting point of the resin component may be 140° C. to 150° C.

[0096] In addition, when homopolymer PP is included as the propylene resin, the heat of fusion of the resin component may be 75 J / g or more and 110 J / g or less. In addition, when random PP is included as the propylene resin, the heat of fusion of the resin component may be 60 J / g or more and 100 J / g or less.

[0097] By mixing the propylene resin, rubber material and elastomer at a predetermined ratio so that at least one of the melting point and heat of fusion of the resin component is within the above range, the viscosity at high shear rate and low shear rate can be easily adjusted to the predetermined range.

[0098] (1-7) Resin composition

[0099] The ratio (composition) of each component in the semiconductive composition can be appropriately adjusted according to the types of propylene resin, rubber material, and elastomer so that the viscosity at high shear rate and low shear rate is respectively within the specified range. From the viewpoint of more reliably adjusting the viscosity to the specified range, the components can be mixed in a manner such that the melting point and heat of fusion of the resin component are within the above range. Specifically, in the resin composition, the addition ratio of the propylene resin can be 50% by mass or more. In addition, the propylene resin can use two or more components with different viscosities, melting points, and heats of fusion. For rubber materials and elastomers, two or more components with different physical property values ​​can be used.

[0100] In addition, the content of carbon black in the semiconductive composition is not particularly limited. Carbon black is the main reason for increasing the viscosity at each shear rate by mixing with the resin component. Therefore, the content of carbon black can be appropriately changed in a manner that satisfies the conductivity required by the semiconductive layer and the viscosity at each shear rate is within a specified range. For example, the content of carbon black can be more than 10 parts by mass and less than 100 parts by mass, or more than 10 parts by mass and less than 80 parts by mass relative to 100 parts by mass of the resin component.

[0101] (2) Power cables

[0102] Next, use Figure 1 The power cable according to this embodiment will be described. Figure 1 This is a cross-sectional view perpendicular to the axial direction of the power cable according to the present embodiment.

[0103] The power cable 10 of this embodiment is configured as a so-called solid insulation power cable. The power cable 10 of this embodiment is configured to be laid on land (in a pipeline), in water, or on the bottom of the water. The power cable 10 is used for AC power, for example.

[0104] Specifically, the power cable 10 includes, for example, a conductor 110 , an inner semiconductive layer 120 , an insulating layer 130 , an outer semiconductive layer 140 , a shielding layer 150 , and a sheath 160 .

[0105] (Conductor (conductive part))

[0106] The conductor 110 is formed by twisting a plurality of conductor core wires (conductive core wires) made of, for example, pure copper, copper alloy, aluminum, or aluminum alloy.

[0107] (Inner semi-conductive layer)

[0108] The inner semiconductive layer 120 is provided in a manner covering the outer periphery of the conductor 110. In addition, the inner semiconductive layer 120 has semiconductivity and is configured in a manner to suppress electric field concentration on the surface side of the conductor 110. The inner semiconductive layer 120 is formed of a semiconductive composition containing a resin component and carbon black. As the resin component, at least any one of ethylene-based copolymers such as ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-vinyl acetate copolymer, olefin-based elastomer, propylene-based resin, etc. can be used. In addition, a semiconductive composition whose viscosity at each of the above shear rates is adjusted to a specified range can also be used.

[0109] (Insulation layer)

[0110] The insulating layer 130 is provided so as to cover the outer periphery of the inner semiconductive layer 120. As a material for forming the insulating layer 130, a propylene resin can be used from the viewpoint of non-crosslinking. In addition, from the viewpoint of improving the flexibility of the insulating layer 130, a resin component containing at least one of the above-mentioned rubber material and elastomer and a propylene resin can also be used. The insulating layer 130 is molded by, for example, extruding a resin composition containing the resin component.

[0111] (Outer semiconductive layer)

[0112] The outer semiconductive layer 140 is provided so as to cover the outer periphery of the insulating layer 130. In addition, the outer semiconductive layer 140 has semiconductivity and is configured so as to suppress electric field concentration between the insulating layer 130 and the shielding layer 150. The outer semiconductive layer 140 is formed of a semiconductive composition whose viscosity at each of the above-mentioned shear rates is adjusted to a predetermined range.

[0113] (Shielding layer)

[0114] The shielding layer 150 is provided so as to cover the outer periphery of the outer semiconductive layer 140. The shielding layer 150 is formed, for example, by winding a copper tape or by winding a plurality of soft copper wires or the like as a wire shield. In addition, a tape made of a rubber-coated cloth or the like may be wound inside or outside the shielding layer 150.

[0115] (jacket)

[0116] The sheath 160 is provided so as to cover the outer periphery of the shield layer 150. The sheath 160 is made of, for example, polyvinyl chloride or polyethylene.

[0117] In addition, if the power cable 10 of the present embodiment is an underwater cable or an underwater cable, it may have a metal waterproof layer such as a so-called aluminum clad layer or a wire armor on the outside of the shielding layer 150. On the other hand, since the power cable 10 of the present embodiment has the above-mentioned water tree suppression effect, it may not have a metal waterproof layer such as a so-called aluminum clad layer on the outside of the shielding layer 150. That is, the power cable 10 of the present embodiment may also be composed of a non-completely waterproof structure.

[0118] (Specific dimensions, etc.)

[0119] 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, the thickness of the inner 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 semiconductive layer 140 is 0.5 mm or more and 3 mm or less, the thickness of the shielding layer 150 is 0.1 mm or more and 5 mm or less, and the thickness of the sheath 160 is 1 mm or more. The outer diameter of the power cable 10 is, for example, 15 mm or more and 170 mm or less. In particular, from the viewpoint of further suppressing the change in the outer diameter, the thickness of the outer semiconductive layer 140 may be 0.5 mm or more, or may be 1 mm or more. The AC voltage applicable to the power cable 10 of the present embodiment is, for example, 20 kV or more.

[0120] As described above, the greater the thickness of the insulating layer 130, especially the higher the ratio of the thickness of the insulating layer 130 to the outer diameter of the conductor 110, the easier it is for the insulating layer 130 to deform in shape. In this regard, in the present embodiment, since the outer semiconductive layer 140 is formed using a semiconductive composition whose viscosity at each shear rate is adjusted to a predetermined range, it is easy to suppress the sagging caused by the flow of the insulating layer 130 and to maintain its shape. Therefore, even in the case where the outer diameter of the power cable 10 is increased by forming the insulating layer 130 thicker than the outer diameter of the conductor 110, the outer diameter variation can be suppressed. For example, even if the thickness of the insulating layer 130 is 4 mm or more and the ratio of the outer diameter of the power cable 10 to the outer diameter of the conductor 110 is 4 or less, the outer diameter variation can be suppressed. From the viewpoint of more reliably suppressing the outer diameter variation, the thickness of the insulating layer 130 may be 13 mm or less. In addition, the ratio of the outer diameter of the power cable 10 to the outer diameter of the conductor 110 may be 4 or less. In addition, the outer diameter of the conductor 110 may be such that the cross-sectional area of ​​the conductor 110 becomes 8 mm. 2 Above and 900mm 2 The following range.

[0121] (3) Cable characteristics

[0122] In this embodiment, by forming the outer semiconductive layer 140 with the above-described semiconductive composition, the following cable characteristics can be ensured.

[0123] (Uniformity of outer diameter)

[0124] Since the drooping of the insulating layer 130 is suppressed in the power cable 10 of this embodiment, the variations in the outer diameter in the cross-sectional and longitudinal directions are small.

[0125] Less variation in the outer diameter in the cross-section means that in the cross-section perpendicular to the longitudinal direction of the power cable 10, the difference between the maximum value and the minimum value of the outer diameter in the outer circumferential direction is small. Specifically, when the major axis (the maximum value of the outer diameter) of the cross-section is set as A1 and the minor axis (the minimum value of the outer diameter) is set as B1, the ratio of the major axis to the minor axis (A1 / B1) can be 1.3 or less, or can be 1.25 or less. In addition, the lower limit value of the ratio is 1.

[0126] Less variation in the outer diameter in the longitudinal direction means that in the cross-sections of two points separated in the longitudinal direction of the power cable 10, the difference in the outer diameter between the two points is small. Specifically, when comparing the outer diameters of two points separated by 5 m in the longitudinal direction, when the major axis of one point is set as B2 and the minor axis of the other point is set as A2 (A2 < B2), the ratio of the major axis B2 of one point to the minor axis A2 of the other point (B2 / A2) can be 1.3 or less, or can be 1.25 or less. In addition, the lower limit value of the ratio is 1.

[0127] (4) Manufacturing method of power cable

[0128] Next, the manufacturing method of the power cable of this embodiment will be described. Hereinafter, the steps will be abbreviated as "S".

[0129] (S100: Coating material preparation process)

[0130] First, prepare the coating materials for forming the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140.

[0131] The semiconductive composition for forming the outer semiconductive layer 140 can be prepared as follows.

[0132] First, at least one of the rubber material and the elastomer, the propylene resin, the carbon black, and other additives (antioxidants, etc.) as needed are mixed (kneaded) by a mixer to form a mixed material. At this time, in the semi-conductive composition, the propylene resin, the rubber material, the elastomer, and the carbon black are mixed in a prescribed ratio in such a way that the viscosity at high shear speed and low shear speed is respectively within a prescribed range. Alternatively, the propylene resin, the rubber material, and the elastomer can be mixed in such a way that the melting point and the heat of fusion of the resin components are within a prescribed range, and the content of the carbon black can be appropriately adjusted within the range in which the desired semi-conductivity can be obtained. In addition, as a mixer, for example, an open roll, a Banbury mixer, a pressure kneading machine, a single-shaft mixer, a multi-shaft mixer, etc. can be cited.

[0133] After the mixed material is formed, the mixed material is granulated by an extruder, thereby forming a granular semiconductive composition for forming the outer semiconductive layer 140. Alternatively, a twin-screw extruder with a high kneading action may be used to perform the steps from mixing to granulation at one time.

[0134] The semiconductive composition used to form the inner semiconductive layer 120 can be a conventionally known composition. For example, a composition containing an propylene resin and carbon black that can be used without crosslinking can be used. In addition, for example, the semiconductive composition used to form the outer semiconductive layer 140 can also be used.

[0135] The resin composition used to form the insulating layer 130 is not particularly limited, and a conventionally known resin composition can be used. For example, a composition containing a propylene resin can be used. In addition, a composition containing at least one of the above-mentioned rubber material and elastomer and a propylene resin can be used.

[0136] (S200: conductor preparation process)

[0137] On the other hand, a conductor 110 formed by twisting a plurality of conductor core wires is prepared.

[0138] (S300: Cable core forming process)

[0139] After the coating material preparation step S100 and the conductor preparation step S200 are completed, each coating material is extruded using, for example, a three-layer co-extruder so as to coat the outer circumference of the conductor 110 with a predetermined thickness.

[0140] Specifically, in the three-layer co-extruder, for example, a semiconductive composition for forming the inner semiconductive layer is introduced into the extruder A for forming the inner semiconductive layer 120 .

[0141] A pelletized resin composition is fed as a coating material for forming the insulating layer into the extruder B for forming the insulating layer 130. The set temperature of the extruder B is set to a temperature that is 10° C. or higher and 50° C. or lower than the desired melting point. The set temperature can also be appropriately adjusted according to the line speed and the extrusion pressure.

[0142] The above-mentioned semiconductive composition is introduced into the extruder C for forming the outer semiconductive layer 140 .

[0143] Next, the extrudates from the extruders A to C are guided to a common head, and the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140 are extruded simultaneously from the inside to the outside to the outer periphery of the conductor 110. At this time, the viscosity of the semiconductive composition used to form the outer semiconductive layer 140 is adjusted to be 1000 Pa·s or more and 5000 Pa·s or less at a high shear rate, so that it can be stably extruded with a uniform thickness. Thus, an extruded material that becomes a cable core is formed.

[0144] Thereafter, the extruded material is cooled, for example, using water, thereby solidifying each coating material and fixing its shape.

[0145] In this embodiment, since the viscosity of the semiconductive composition for forming the outer semiconductive layer at a low shear rate is adjusted to be 100000 Pa·s or more and 1000000 Pa·s or less, the flow (droop) of the coating material forming the insulating layer 130 located inside the outer semiconductive layer can be suppressed. Therefore, each coating material can be fixed in the extruded shape. As a result, the thickness of the insulating coating formed by the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140 can be formed uniformly in the outer and longitudinal directions of the cross-section of the extruded material.

[0146] Through the above cable core forming step S300 , a cable core composed of the conductor 110 , the inner semiconductive layer 120 , the insulating layer 130 and the outer semiconductor layer 140 is formed.

[0147] (S400: Shielding Layer Forming Step)

[0148] After the cable core is formed, the shielding layer 150 is formed by winding, for example, a copper tape on the outside of the outer semiconductive layer 140 .

[0149] (S500: Sheath Forming Step)

[0150] After the shield layer 150 is formed, vinyl chloride is put into an extruder and extruded to form the sheath 160 on the outer periphery of the shield layer 150 .

[0151] Thus, the power cable 10 as a solid insulated power cable is manufactured.

[0152] (5) Summary of this embodiment

[0153] According to the present embodiment, one or more of the following effects are achieved.

[0154] (a) The viscosity of the semiconductive composition of the present embodiment at a high shear rate is 1000 Pa·s to 5000 Pa·s. Thus, when the semiconductive composition is melted and extruded, the extruded shape can be maintained and the material can be stably extruded with a uniform thickness. In addition, the viscosity at a low shear rate is 100000 Pa·s to 1000000 Pa·s. Thus, when the semiconductive composition is extruded on the periphery of the coating material forming the insulating layer 130, the coating material of the insulating layer 130 can be pressed by the semiconductive composition. As a result, the sagging caused by the dead weight of the coating material can be suppressed, and the insulating layer 130 can be kept in the extruded shape. That is, it is easy to fix the insulating layer 130 in the extruded shape. As such, the semiconductive composition of the present embodiment has a moderate viscosity during melt extrusion, thereby obtaining the desired extrusion moldability, and on the other hand, has a high viscosity after extrusion, thereby being difficult to flow and being able to maintain the extruded shape.

[0155] (b) In the power cable 10 of the present embodiment, by forming the outer semiconductive layer 140 using the above-mentioned semiconductive composition, a uniform outer diameter can be formed in the outer peripheral direction and the longitudinal direction of the cross section of the power cable 10. That is, in the power cable 10, the variation of the outer diameter in the cross section and the longitudinal direction can be reduced. Specifically, in the cross section of the power cable 10, the ratio of the maximum value (long diameter) of the outer diameter to the minimum value (short diameter) of the outer diameter in the outer peripheral direction can be made 1.3 or less. In addition, in the cross section of two points separated along the longitudinal direction of the power cable 10, the ratio of the long diameter of one point to the short diameter of the other point can be 1.3 or less.

[0156] (c) The semiconductive composition contains a propylene resin and at least one of a rubber material and an elastomer, so that excessive crystal growth of the propylene resin can be suppressed during the cooling process from a molten state. As a result, the desired conductivity and flexibility can be obtained in a high-level and balanced manner in the outer semiconductive layer 140.

[0157] (d) In the semiconductive composition, the content of carbon black may be 10 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the resin component. By setting such a content, the viscosity of the semiconductive composition at each shear rate can be more reliably adjusted to a predetermined range, and a predetermined semiconductivity can be obtained. As a result, the outer diameter variation of the power cable 10 can be more reliably suppressed, and the electric field in the power cable 10 can be made more uniform to suppress partial discharge.

[0158] (e) In addition, in the semiconductive composition, when random PP is included, the melting point of the resin component can be 140°C to 150°C, and when homo-PP is included, the melting point of the resin component can be 158°C to 168°C. In addition, when random PP is included, the melting heat of the resin component can be 60J / g to 100J / g, and when homo-PP is included, the melting heat of the resin component can be 75J / g to 110J / g. In the semiconductive composition, by making at least one of the melting point and the melting heat of the resin component meet the specified range, the addition ratio of the propylene resin, the rubber material and the elastomer can be set within an appropriate range, and the viscosity at high shear speed and low shear speed can be more reliably adjusted to the above range. Moreover, in the outer semiconductive layer 140, higher flexibility can be obtained.

[0159] (f) In addition, since the viscosity of the semiconductive composition at a low shear rate is relatively large, that is, 100,000 Pa·s or more, deformation of the insulating layer 130 can be suppressed even when the insulating layer 130 is formed thicker than the outer diameter of the conductor 110. Specifically, by forming the outer semiconductive layer 140 to have a thickness of 0.5 mm or more, even when the insulating layer 130 is formed thicker than the outer diameter of the conductor 110 so that the ratio of the outer diameter of the power cable 10 to the outer diameter of the conductor 110 is 4 or less, the outer diameter variation can be suppressed to be small.

[0160] (g) Furthermore, according to the semiconductive composition, when producing the power cable 10, it is possible to suppress the outer diameter variation in the longitudinal direction which is particularly likely to occur when using a vertical extruder and the outer diameter variation in the outer peripheral direction of the cross section which is particularly likely to occur when using a horizontal extruder.

[0161] (h) In addition, in the power cable 10, since the viscosity of the semiconductive composition at a low shear rate is low, the shape of the insulating layer 130 can be maintained even if the viscosity of the coating material forming the insulating layer 130 is low. Specifically, even if the viscosity of the coating material forming the insulating layer 130 at a low shear rate is in the range of 3000 Pa·s or more, the shape of the insulating layer 130 can be maintained.

[0162] <Other embodiments of the present invention>

[0163] As mentioned above, although embodiment of this invention is specifically described, this invention is not limited to the said embodiment, Various changes are possible within the range which does not deviate from the summary.

[0164] In the above embodiment, the case where the resin composition molded product as the insulating layer is mechanically mixed and extruded is described, but the resin composition molded product may be extruded after polymerization.

[0165] In the above-mentioned embodiment, the case where the power cable 10 may not have a waterproof layer is described, but the present invention is not limited to this case. The power cable 10 may have a simple waterproof layer by having the above-mentioned significant water tree suppression effect. Specifically, the simple waterproof layer is composed of, for example, a metal laminate tape. The metal laminate tape, for example, has a metal layer composed of aluminum or copper and an adhesive layer arranged on one side or both sides of the metal layer. The metal laminate tape is, for example, longitudinally wound to surround the outer periphery of the cable core (closer to the outer periphery than the outer semiconductive layer). In addition, the waterproof layer can be arranged to be closer to the outside than the shielding layer, and can also serve as a shielding layer. Through such a structure, the cost of the power cable 10 can be reduced.

[0166] In the above embodiment, the power cable 10 is configured to be laid on land, in water, or on the bottom of the water, but the present invention is not limited thereto. For example, the power cable 10 may be configured as a so-called overhead wire (overhead insulated wire).

[0167] Example

[0168] Next, embodiments of the present invention will be described. These embodiments are examples of the present invention, and the present invention is not limited to these embodiments.

[0169] (1) Materials

[0170] First, as a semiconductive composition, materials A to D shown in the following Table 1 were prepared. In the preparation of materials A to D, the following components were used.

[0171] As propylene resins, a plurality of propylene random polymers having a viscosity of 100 Pa·s to 6000 Pa·s at a high shear rate, a viscosity of 500 Pa·s to 50000 Pa·s at a low shear rate, a melting point of 140° C. to 145° C., a heat of fusion of 90 J / g to 105 J / g, a ratio of a weight average molecular weight (Mw) to a number average molecular weight (Mn) of 3.0 to 8.0, Mn of 60,000 to 150,000, and Mw of 210,000 to 1,000,000 and different from each other are prepared.

[0172] As rubber materials, a plurality of EPR and VLDPE having a viscosity of 500 Pa·s to 5000 Pa·s at a high shear rate and a viscosity of 10000 Pa·s to 70000 Pa·s at a low shear rate and having no melting point and heat of fusion and being different from each other are prepared.

[0173] As elastomers, a plurality of styrene resins different from each other are prepared, having a viscosity of 1000 Pa·s to 6000 Pa·s at a high shear rate, a viscosity of 5000 Pa·s to 50000 Pa·s at a low shear rate, a melting point of 30°C to 80°C, and a heat of fusion of 5 J / g to 50 J / g.

[0174] As carbon black, carbon black having an average particle size of 10 nm was used.

[0175] In this embodiment, as the propylene resin, one or more propylene resins having physical property values ​​within the above ranges are used alone or in combination, and as the rubber material and the elastomer, one or more rubber materials and elastomers having physical property values ​​within the above ranges are used. Then, the ratio of each component is appropriately changed, and a predetermined amount of carbon black is added to 100 parts by mass of these resin components, so that the viscosity of the obtained semiconductive composition at each shear rate becomes a predetermined value to prepare materials A to D. Here, the addition ratio of the propylene resin is adjusted to 50% by mass or more of the resin component.

[0176] [Table 1]

[0177]

[0178] In Table 1, the melting points and heats of fusion of the resin components contained in Materials A to D, the viscosities of Materials A to D at high shear rates, and the viscosities at low shear rates were measured as follows.

[0179] (Melting point and heat of fusion)

[0180] The melting point and heat of fusion of the resin components contained in materials A to D are determined by DSC measurement. The DSC measurement is carried out in accordance with JIS-K-7121 (1987). Specifically, as a DSC device, DSC8500 (power compensation type) manufactured by PerkinElmer was used. The reference sample is, for example, α-alumina. The mass of the measured sample is 8 to 10 g. In the DSC device, the temperature is raised from room temperature (27°C) to 220°C at 10°C / min. Thus, by plotting the amount of heat absorbed (heat flow) per unit time against the temperature, a DSC curve is obtained.

[0181] At this time, the temperature at which the heat absorption per unit time of each measured sample reaches a maximum value (highest peak) is taken as the “melting point.” In addition, at this time, the “heat of fusion” is obtained by obtaining the area of ​​the region surrounded by the melting peak and the baseline in the DSC curve.

[0182] (Viscosity)

[0183] The viscosity of materials A to D at various shear rates was measured using a rotational rheometer ("MCR302" manufactured by Anton Paar) using a PP-12 fixture at 190°C from a shear rate of 0.001 s -1 To 1000s -1 The measurement was performed by changing the shear rate.

[0184] (2) Production of power cable samples

[0185] In this embodiment, a resin composition for forming an insulating layer is prepared separately from the materials A to D as the semiconductive compositions. Specifically, the propylene resin, rubber material and elastomer used in the preparation of the semiconductive composition are appropriately mixed to adjust the viscosity of the insulating layer forming composition A to 1000 Pa·s at a high shear rate and 5000 Pa·s at a low shear rate. In addition, the mixing ratio of each component is appropriately changed to adjust the viscosity of the insulating layer forming composition B to 100 Pa·s at a high shear rate and 800 Pa·s at a low shear rate.

[0186] Next, a sample simulating a power cable was prepared using the compositions A and B for forming an insulating layer and the materials A to D as semiconductive compositions.

[0187] (Sample 1)

[0188] Specifically, as shown in Table 2 below, first, a 200 mm 2 (conductor diameter is about 16.0mm). After preparing the conductor, the above-prepared material A as a coating material for forming an internal semiconductive layer, the composition A for forming an insulating layer, and the above-prepared material A as a coating material for forming an external semiconductor layer are respectively put into extruders A to C. The extrudates from the extruders A to C are guided to a common head, and the internal semiconductive layer, the insulating layer, and the external semiconductive layer are extruded simultaneously to the outer periphery of the conductor from the inside to the outside. At this time, the thickness of the internal semiconductive layer, the insulating layer, and the external semiconductive layer are 0.5mm, 9.0mm, and 0.5mm, respectively, and the insulating coating thickness is 10mm. As a result, a sample 1 of a power cable having a conductor, an internal semiconductive layer, an insulating layer, and an external semiconductive layer from the center to the periphery was manufactured (the cable outer diameter is 36mm). In addition, when the conductor diameter is set to X and the outer diameter of the power cable (cable outer diameter) is set to Y, the ratio of the cable outer diameter to the conductor diameter (Y / X) is 1.9.

[0189] [Table 2]

[0190]

[0191] (Samples 2 to 5)

[0192] In Samples 2 to 5, power cables were prepared in the same manner as Sample 1 except that the type of the semiconductive composition was appropriately changed to Material B to Material D or the type of the composition for forming the insulating layer was appropriately changed to Composition B as shown in Table 2, thereby obtaining Samples 2 to 5.

[0193] (3) Evaluation

[0194] For samples 1 to 5 produced as power cables, uniformity of the outer diameter in the cross section of the power cables and uniformity of the outer diameter in the longitudinal direction were evaluated.

[0195] The uniformity of the outer diameter of the cross section is evaluated as follows. Specifically, select any point in the length direction of the power cable, measure the outer diameter of the cross section in the outer circumferential direction, find the major diameter (maximum value) and the minor diameter (minimum value), and calculate the ratio of the major diameter to the minor diameter. The smaller the ratio, the less the variation of the outer diameter of the cross section.

[0196] The uniformity of the outer diameter in the length direction is evaluated as follows. Specifically, two points 5 m apart in the length direction of the power cable are selected, the major diameter and minor diameter of each point are measured, and the ratio of the major diameter of one point to the minor diameter of the other point is calculated. The smaller the ratio, the less the variation of the outer diameter in the length direction.

[0197] (4) Evaluation results

[0198] As shown in Table 2, in Samples 1 and 2, it was confirmed that the variation of the outer diameter in the cross-sectional and longitudinal directions can be reduced by using Material A or Material B as the semiconductive composition. This is considered to be because Material A and Material B can suppress the sagging of the composition A for forming the insulating layer and maintain its shape.

[0199] In Sample 3, it was confirmed that since Material C having too low a viscosity at a low shear rate was used, the sagging of the insulating layer forming composition A could not be suppressed, and the change in the outer diameter of the power cable could not be sufficiently suppressed.

[0200] In addition, in Sample 4, since Material D having an excessively high viscosity at a high shear rate was used as the semiconductive composition, it was confirmed that the extrusion moldability was poor and the semiconductive layer could not be molded.

[0201] In addition, in Sample 5, it was confirmed that the outer diameter of the power cable varied greatly compared with Sample 1 because the composition B having a lower viscosity at a low shear rate than the composition A for forming the insulating layer was used.

[0202] <Modes of the Invention>

[0203] Hereinafter, embodiments of the present invention will be described in detail.

[0204] (Note 1)

[0205] A semiconductive composition for forming a semiconductive layer in a power cable, the semiconductive composition comprising a resin component and carbon black, the resin component comprising at least one of a rubber material and an elastomer and a propylene resin, the rubber material and the elastomer having at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, the semiconductive composition having a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

[0206] (Note 2)

[0207] A power cable, comprising: a conductor; an insulating layer, which is coated on the outer periphery of the conductor and is formed of a resin composition; and an outer semiconductive layer, which is coated on the outer periphery of the insulating layer and is formed of a semiconductive composition, wherein the semiconductive composition comprises a resin component and carbon black, wherein the resin component comprises at least one of a rubber material and an elastomer and a propylene resin, wherein the rubber material and the elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, and the semiconductive composition is resistant to sintering at a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

[0208] (Note 3)

[0209] The electric power cable according to Supplementary Note 2, wherein the content of the carbon black is 10 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the resin component.

[0210] (Note 4)

[0211] The electric power cable according to Supplementary Note 2 or Supplementary Note 3, wherein the resin component has a heat of fusion of 55 J / g or more and 90 J / g or less.

[0212] (Note 5)

[0213] The electric power cable according to any one of appendixes 2 to 4, wherein the melting point of the resin component is 140° C. or higher and 170° C. or lower.

[0214] (Note 6)

[0215] The electric power cable according to any one of Supplementary Notes 2 to 5, wherein a ratio of a major diameter to a minor diameter in a cross section perpendicular to the longitudinal direction is 1.3 or less.

[0216] (Note 7)

[0217] The electric power cable according to any one of Supplementary Notes 2 to 6, wherein in cross sections at two points separated in the longitudinal direction, a ratio of a major axis at one point to a minor axis at another point is 1.3 or less.

[0218] (Note 8)

[0219] The power cable according to any one of Supplementary Notes 2 to 7, wherein the thickness of the outer semiconductive layer is 0.5 mm or more, and the ratio of the outer diameter of the power cable to the outer diameter of the conductor is 4 or less.

[0220] (Note 9)

[0221] The power cable according to any one of Appendixes 2 to 8, wherein the viscosity of the propylene resin at the high shear rate is 100 Pa·s or more and 6000 Pa·s or less, and the viscosity at the low shear rate is 500 Pa·s or less and 50000 Pa·s or less.

[0222] (Note 10)

[0223] The electric power cable according to any one of Appendixes 2 to 9, wherein the propylene resin has a melting point of 140° C. to 150° C. and a heat of fusion of 90 J / g to 105 J / g.

[0224] (Note 11)

[0225] The power cable according to any one of Appendixes 2 to 10, wherein the viscosity of the rubber material and the elastomer at the high shear rate is 300 Pa·s to 7000 Pa·s, and the viscosity at the low shear rate is 4000 Pa·s to 80000 Pa·s.

[0226] (Note 12)

[0227] The electric power cable according to any one of Supplementary Notes 2 to 11, wherein the rubber material has no melting point or has a melting point of 100° C. or less.

[0228] (Note 13)

[0229] The electric power cable according to any one of Supplementary Notes 2 to 12, wherein the heat of fusion of the rubber material is 50 J / g or less.

[0230] Description of Reference Numerals

[0231] 10: Power cable

[0232] 110: Conductor

[0233] 120: Inner semi-conductive layer

[0234] 130: Insulation layer

[0235] 140: Outer semi-conductive layer

[0236] 150: Shielding layer

[0237] 160: Sheath

Claims

1. A semiconductive composition for forming a semiconductive layer in a power cable, The semiconductive composition comprises a resin component and carbon black, The resin component comprises at least one of a rubber material and an elastomer and a propylene resin, The rubber material and the elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, The semiconductive composition is subjected to a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

2. A power cable, comprising: conductor; an insulating layer covering the outer periphery of the conductor and formed of a resin composition; and an outer semiconductive layer, which covers the outer periphery of the insulating layer and is formed of a semiconductive composition, The semiconductive composition comprises a resin component and carbon black, The resin component comprises at least one of a rubber material and an elastomer and a propylene resin, The rubber material and the elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, The semiconductive composition is subjected to a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at high shear rate is 1000Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 100,000 Pa·s or more and 1,000,000 Pa·s or less.

3. The power cable according to claim 2, wherein: The content of the carbon black is 10 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the resin component.

4. The power cable according to claim 2 or claim 3, wherein: The resin component has a heat of fusion of 55 J / g or more and 90 J / g or less.

5. The power cable according to any one of claims 2 to 4, wherein: The melting point of the resin component is 140° C. or higher and 170° C. or lower.

6. The power cable according to any one of claims 2 to 5, wherein: In a cross section perpendicular to the longitudinal direction, the ratio of the major axis to the minor axis is 1.3 or less.

7. The power cable according to any one of claims 2 to 6, wherein: In a cross section of two points separated in the longitudinal direction, a ratio of a major axis at one point to a minor axis at another point is 1.3 or less.

8. The power cable according to any one of claims 2 to 7, wherein: The thickness of the outer semiconductive layer is 0.5 mm or more, and the ratio of the outer diameter of the power cable to the outer diameter of the conductor is 4 or less.

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