Resin composition and power cable

Abstract

A resin composition comprising: a propylene-based resin; and at least one of a rubber material and an elastomer, the rubber material and the elastomer having at least two types of units selected from ethylene, propylene, butylene, hexene, isoprene, octene, and styrene, and having a viscosity of 200-5000 Pa.s (inclusive) at a temperature of 190 DEG C and a high shear rate of 100 s-1. The viscosity at a low shear rate of 1 s <-1 > at a temperature of 190 DEG C is 7000 Pa * s or more and 50000 Pa * s or less, and the elastic modulus is 150 MPa or more and 700 MPa or less.

Description

Technical Field

[0001] This application claims the priority based on Japanese application "Tokugan 2022-134932" filed on August 26, 2022, and cites all the contents described in the above Japanese application.

[0002] The present invention relates to a resin 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 is a resin composition comprising:

[0008] Acrylic resin; and

[0009] at least one of a rubber material and an elastomer,

[0010] The rubber material and elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene.

[0011] The above resin composition is heated at a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at low shear rate is 7000Pa·s or more and 50000Pa·s or less.

[0012] The elastic modulus of the resin composition is 150 MPa or more and 700 MPa or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic cross-sectional view of an embodiment of the present invention, taken along a direction perpendicular to the axial direction of the DC power cable. DETAILED DESCRIPTION

[0014] (Problems to be solved by the present invention)

[0015] Cross-linked polyethylene deteriorates over time and cannot be reused but must be incinerated, which raises concerns about its impact on the environment.

[0016] Therefore, in recent years, as a resin component constituting the insulating layer, a resin containing propylene (hereinafter also referred to as "propylene resin") has attracted attention. Even if the propylene 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 propylene resin, it is possible to improve operability, processability, and ease of manufacture.

[0017] However, the inventors have conducted research using propylene resin as a resin component constituting the insulating layer, and have confirmed that the outer diameter of the insulating layer is prone to become non-uniform in the cross-section and longitudinal direction of the power cable. This is because the resin component sags due to its own weight during the period from extrusion of the molten resin component as the insulating layer to cooling, and cannot maintain a desired shape.

[0018] 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 resin composition containing a propylene resin is used.

[0019] (Effects of the Invention)

[0020] According to the present invention, when a resin composition containing a propylene-based resin is used, the uniformity of the outer diameter of the power cable can be improved.

[0021] <Description of Embodiments of the Invention>

[0022] (Insights Obtained by the Inventors)

[0023] First, the findings obtained by the inventors will be briefly described.

[0024] In the case of propylene-based resins, the non-uniformity of the outer diameter due to the sagging of the resin component occurs more significantly than in the case of cross-linked polyethylene.

[0025] In the case of forming the insulating layer by cross-linked polyethylene, after a resin component containing polyethylene and a cross-linking agent is extruded as an insulating layer, the cable is introduced into, for example, a cross-linking tube, and the resin component is heated in a high temperature environment to cross-link it. After cross-linking, the cable is introduced into, for example, a cooling tank, and the insulating layer is cooled. In this case, since the viscosity of the resin component increases during the cross-linking process, it is easy to maintain the shape of the insulating layer, and the shape can be fixed by cooling. That is, by cross-linking, the sagging of the resin component and the change in the outer diameter of the power cable accompanying it can be suppressed.

[0026] In contrast, in the case of forming an insulating layer from a propylene resin, since no cross-linking treatment is performed, cooling is performed after the resin component is extruded. At this time, the insulating layer is gradually cooled from the surface side to the inside. Therefore, the shape of the surface side of the insulating layer is fixed by cooling, while the inside may produce a state of being able to melt and flow due to the high temperature. Moreover, since no cross-linking treatment is performed, the viscosity of the resin component cannot be increased. As a result, during the period until the internal cooling shape of the insulating layer is fixed, the resin component constituting the insulating layer sometimes sags due to its own weight. With this sagging, the thickness of the insulating layer sometimes becomes uneven in the outer peripheral direction of the cross section of the power cable, and the thickness also becomes uneven in the longitudinal direction of the power cable. For example, if the power cable is transported in the horizontal direction using a horizontal extruder, the resin component sometimes tends to sag downward in the cross section of the power cable, and if it is transported in the vertical direction using a vertical extruder, it sometimes tends to sag to the lower side in the longitudinal direction of the power cable. When the thickness of the insulating layer becomes non-uniform in the peripheral 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.

[0027] As the thickness of the insulating layer increases and as the ratio of the thickness of the insulating layer to the outer diameter of the conductor increases, the resin component sags more significantly, and thus the uniformity of the outer diameter of the power cable is more likely to decrease.

[0028] In order to solve the above-mentioned problems, the present inventors conducted studies focusing on the viscosity of a resin composition containing a propylene resin when it is melted.

[0029] Usually, the viscosity of the resin component varies greatly according to the shear rate, and has a tendency to become low viscosity at high shear rate and high viscosity at low shear rate. In the production of power cables, there is a tendency that the shear rate is high and the viscosity of the resin composition decreases at the stage of melt mixing and extruding the resin composition. On the other hand, there is a tendency that the shear rate is low and the viscosity of the resin composition increases at the stage until cooling after the extrusion of the resin composition.

[0030] Therefore, the inventors studied the viscosity of the resin composition at high shear rate and low shear rate, and found that by forming the resin composition so that each viscosity is within a predetermined range, it is possible to achieve both extrudability and suppress sagging during cooling until the shape is fixed. It was found that such a resin composition can improve the uniformity of the outer diameter of the power cable.

[0031] Furthermore, power cables are required to have predetermined insulation properties. From the viewpoint of satisfying this requirement, it has been found that it is preferable to adjust both the viscosity and the elastic modulus at each of the above-mentioned shear rates in the resin composition to a predetermined range.

[0032] The present invention has been accomplished based on the above findings.

[0033] (Embodiment of the present invention)

[0034] Next, embodiments of the present invention will be listed and described.

[0035] [1] A resin composition according to one embodiment of the present invention comprises:

[0036] Acrylic resin; and

[0037] at least one of a rubber material and an elastomer,

[0038] The rubber material and elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene.

[0039] The above resin composition is heated at a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at low shear rate is 7000Pa·s or more and 50000Pa·s or less.

[0040] The elastic modulus of the resin composition is 150 MPa or more and 700 MPa or less.

[0041] According to this configuration, the resin composition can be stably extruded with a uniform thickness, and shape deformation in a molten state can be suppressed.

[0042] [2] Another aspect of the present invention provides a power cable having:

[0043] Conductors; and

[0044] an insulating layer formed of a resin composition and covering the outer periphery of the conductor,

[0045] The resin composition comprises:

[0046] Acrylic resin; and

[0047] at least one of a rubber material and an elastomer,

[0048] The rubber material and elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene.

[0049] The above resin composition is heated at a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1The viscosity at low shear rate is 7000Pa·s or more and 50000Pa·s or less.

[0050] The elastic modulus of the resin composition is 150 MPa or more and 700 MPa or less.

[0051] According to this configuration, it is possible to suppress the outer diameter of the cross section of the power cable from varying in each of the outer peripheral direction and the longitudinal direction.

[0052] [3] In the power cable described in [2] above,

[0053] The resin composition has a heat of fusion of 60 J / g or more and 100 J / g or less.

[0054] According to this configuration, it is possible to more reliably suppress the outer diameter variation.

[0055] [4] In the power cable described in [2] or [3] above,

[0056] The melting point of the resin composition is 140° C. or higher and 150° C. or lower.

[0057] According to this configuration, it is possible to more reliably suppress the outer diameter variation.

[0058] [5] In the power cable described in any one of [2] to [4] above,

[0059] 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.

[0060] According to this configuration, it is possible to more reliably suppress the outer diameter variation.

[0061] [6] In the power cable described in any one of [2] to [5] above,

[0062] The viscosity of the rubber material and the elastic body at the high shear rate is 300 Pa·s or more and 7000 Pa·s or less, and the viscosity at the low shear rate is 4000 Pa·s or more and 80000 Pa·s or less.

[0063] According to this configuration, it is possible to more reliably suppress the outer diameter variation.

[0064] [7] In the power cable described in any one of [2] to [6] above,

[0065] In a cross section perpendicular to the longitudinal direction, the ratio of the major axis to the minor axis is 1.3 or less.

[0066] According to this configuration, it is possible to more reliably suppress the outer diameter variation.

[0067] [8] In the power cable described in any one of [2] to [7] above,

[0068] 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.

[0069] According to this configuration, it is possible to more reliably suppress the outer diameter variation.

[0070] [9] In the power cable described in any one of [2] to [8] above,

[0071] The thickness of the insulating layer is 4 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.

[0072] According to this configuration, even when the insulating layer is formed thickly, it is possible to more reliably suppress the outer diameter variation.

[0073] (Details of Embodiments of the Invention)

[0074] Next, refer to the attached Figure 1 The present invention is not limited to these examples, but is indicated by the patent claims, and is intended to include all modifications within the meaning and scope equivalent to the patent claims.

[0075] (One embodiment of the present invention)

[0076] (1) Resin composition

[0077] The resin composition of this embodiment includes a propylene resin and at least one of a rubber material and an elastomer, and the viscosity and elastic modulus of the resin composition at high shear rate and low shear rate are adjusted to a predetermined range by mixing these components. Specifically, the viscosity of the resin composition is configured as follows: at a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 7000 Pa·s or more and 50000 Pa·s or less. In addition, the elastic modulus of the resin composition is 150 MPa or more and 700 MPa or less.

[0078] Hereinafter, the constituent components of the resin composition, the composition thereof, and physical property values ​​such as viscosity and elastic modulus of the resin composition will be described in detail.

[0079] (1-1) Acrylic resin

[0080] Propylene resin is the base polymer of the resin composition. Examples of propylene resins include propylene homopolymers (hereinafter, also referred to as homo-PP), propylene random polymers (hereinafter, also referred to as random PP), etc. Homo-PP contains propylene units, and random PP has propylene units and ethylene units. From the viewpoint of obtaining higher insulation in the insulating layer, the propylene resin may be random PP. Since random PP contains ethylene units, although the amount of crystallization is lower than that of homo-PP, it is not easy to generate coarse crystals during cooling, and the reduction in insulation caused by the cracking caused by the coarse crystals can be suppressed. That is, compared with homo-PP, random PP can obtain high insulation.

[0081] 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 high insulation can be maintained. On the other hand, by making the content of ethylene units 15% by mass or less, the reduction of the melting point can be suppressed, and the use in the non-crosslinked or slightly crosslinked state can be stably achieved.

[0082] In addition, as the stereoregularity of the propylene resin, isotactic, syndiotactic and atactic can be cited. The stereoregularity is not particularly limited and can be isotactic. When the stereoregularity is isotactic, the reduction of the melting point in the resin composition can be suppressed. As a result, it can be stably used when not cross-linked or slightly cross-linked.

[0083] 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 more than 100 Pa·s and less than 6000 Pa·s. The viscosity at low shear rate can be more than 500 Pa·s and less than 50000 Pa·s. By having such a viscosity, it is easy to adjust to a specified viscosity in the resin composition. By making the viscosity of the propylene resin as the base polymer of the resin composition within the above range, when mixing with an elastomer or the like to prepare a resin composition, each viscosity in the resin composition can be more reliably adjusted to the above range.

[0084] In addition, as the propylene resin, a single propylene resin having a viscosity within a specified 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 of the resin composition to a specified range, two or more propylene resins may be used in combination.

[0085] In addition, from the viewpoint of adjusting the elastic modulus of the resin composition to a specified range, the elastic modulus of the propylene resin can be 600 MPa or more and 1200 MPa or less. Here, the elastic modulus represents the storage modulus at 25°C measured by dynamic viscoelasticity measurement (DMA: Dynamic Mechanical. Analysis). Specifically, the storage modulus of the resin sample is measured while the temperature is raised from -50°C to 100°C while applying a 0.08% stretching (a stretching vibration with an amplitude of 0.08%) to the target resin sample. At this time, the measurement frequency is set to 10 Hz. In addition, the heating rate is set to 10°C / min. Then, the storage modulus at 25°C is calculated.

[0086] In addition, as described later, resin components such as propylene resins have different viscosity curves that can be obtained according to physical property values ​​such as melting point, heat of fusion, molecular weight, etc. In the present embodiment, from the viewpoint of adjusting the viscosity of the resin combination to a specified range, each physical property value of the propylene resin can be set as follows.

[0087] 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 more and 175°C or less. If it is a propylene random polymer (random PP), it can be 140°C or more and 150°C or less. According to such a propylene resin, it is easy to adjust the viscosity of the resin composition to a specified range. In addition, the melting point of the resin composition can be increased, and the heat-resistant temperature of the insulating layer can be increased. Thus, even if the insulating layer is non-crosslinked, high insulation can be stably maintained under high temperature conditions.

[0088] The melting heat of the propylene resin is not particularly limited, but can be 100 J / g or more and 120 J / g or less if it is homopolymer PP, or 90 J / g or more and 105 J / g or less if it is random PP. With such a propylene resin, it is easy to adjust the viscosity of the resin composition to a specified range, and the heat-resistant temperature of the insulating layer can be increased to stably maintain the high insulation of the insulating layer in a high temperature environment.

[0089] In addition, in this specification, the melting point and the heat of fusion are measured as follows.

[0090] First, for the sample, differential scanning calorimetry (DSC) is performed according to, for example, 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) 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 "melting heat". In addition, based on the theoretical value of the melting heat of the sample and the melting heat of the complete crystal, the crystallinity (%) of the sample can be calculated.

[0091] Propylene resin has a prescribed molecular weight distribution, and the wider the width of the molecular weight distribution is, that is, the larger the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the molecular weight distribution is, the greater the difference between the viscosity at high shear rate and the viscosity at low shear rate is. From the viewpoint of satisfying the viscosity at each shear rate of the propylene resin within the above range, Mw / Mn can be more than 3.0 and less than 8.0, or can be more than 3.5 and less than 7.0. In addition, the number average molecular weight Mn can be, for example, more than 60,000 and less than 150,000. In addition, the weight average molecular weight Mw can be, for example, more than 210,000 and less than 1,000,000.

[0092] (1-2) Rubber materials and elastomers

[0093] The rubber material and the elastomer control the crystal growth of the propylene resin in the resin composition and give flexibility to the insulating layer. The rubber material and the elastomer may change the viscosity of the resin composition at each shear rate due to mixing with the propylene resin, but by mixing in a manner to achieve a predetermined viscosity range, a predetermined flexibility can be given to the insulating layer. The rubber material or the elastomer of this embodiment includes at least two of ethylene, propylene, butene, hexene, isoprene, octene and styrene.

[0094] The viscosity of the rubber material and elastomer at high shear rate and low shear rate is not particularly limited. The viscosity at high shear rate can be 300Pa·s or more and 7000Pa·s or less. In addition, the viscosity at low shear rate can be 4000Pa·s or more and 80000Pa·s or less. Alternatively, for the rubber material, the viscosity at high shear rate can be 500Pa·s or more and 5000Pa·s or less, and the viscosity at low shear rate can be 10000Pa·s or more and 70000Pa·s or less. For the elastomer, the viscosity at high shear rate can be 1000Pa·s or more and 6000Pa·s or less, and the viscosity at low shear rate can be 5000Pa·s or more and 50000Pa·s or less. According to the rubber material or elastomer having such viscosity, each viscosity of the resin composition can be easily adjusted to the desired range when mixed with the propylene resin.

[0095] The melting point of the rubber material and the elastomer is not particularly limited. Generally, no endothermic peak is detected in the DSC measurement of the rubber material, and therefore the rubber material has no melting point. The elastomer may not have a melting point, or even if it has a melting point, the melting point may be 100° C. or less.

[0096] The heat of fusion of rubber materials and elastomers is not particularly limited. The heat of fusion of rubber materials is not available because the melting point cannot be measured. The heat of fusion of elastomers may be 50 J / g or less, and may be 30 J / g or less.

[0097] The elastic modulus (25°C) of the rubber material and the elastomer is not particularly limited, and can be 1 MPa or more and 200 MPa or less from the viewpoint of adjusting the elastic modulus of the resin composition to a specified range. In addition, the elastic modulus of the rubber material and the elastomer sometimes varies greatly depending on the presence or absence of styrene. Specifically, when styrene is not included, there is a tendency that the higher the molecular weight, the higher the elastic modulus, and when styrene is included, there is a tendency that the higher the molecular weight, the lower the elastic modulus.

[0098] The molecular weight distribution of rubber materials and elastomers is the same as that of propylene resins, and sometimes the viscosity at each shear rate varies. In rubber materials and elastomers, from the viewpoint of satisfying the viscosity range at each shear rate, Mw / Mn can be 1.0 or more and 3.0 or less, or 1.0 or more and 2.5 or less. In addition, the number average molecular weight Mn can be, for example, 70,000 or more and 250,000 or less. In addition, the weight average molecular weight Mw can be, for example, 70,000 or more and 600,000 or less.

[0099] Specifically, as the rubber material, a copolymer obtained by copolymerizing at least two of ethylene, propylene, butene, hexene, and octene can be used.

[0100] 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.

[0101] 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, and the insulation is likely to be reduced. 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. As a result, the reduction in insulation can be suppressed. Furthermore, the ethylene content can be 40% by mass or more, or 55% by mass or more. Thus, the crystallization can be controlled more stably, and the reduction in insulation can be stably suppressed.

[0102] On the other hand, the rubber material may be, for example, a copolymer that does not contain propylene. As a copolymer that does not contain propylene, for example, from the viewpoint of easy availability, very low density polyethylene (VLDPE: Very Low Density Polyethylene) can be used. Examples of VLDPE include PE composed of ethylene and 1-butene, PE composed of ethylene and 1-octene, etc. According to the copolymer that does not contain propylene, the crystallization of the propylene-based resin can be stably controlled. In addition, the density of VLDPE is, for example, 0.855 g / cm 3 Above 0.890g / cm 3 the following.

[0103] In addition, as an 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. Like rubber materials, styrene-based thermoplastic elastomers are components dispersed in a resin composition to control the crystal growth of propylene resins, impart flexibility to an insulating layer, or help adjust the viscosity of the resin composition. Furthermore, styrene-based thermoplastic elastomers form stable resonance structures by capturing electrons through aromatic rings, or inhibit the generation of mechanical stress cracking in the insulating layer as an elastomer, thereby also contributing to the improvement of the water-tree resistance of the insulating layer.

[0104] 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-butylene-olefin crystalline block copolymer, etc. Two or more of these may be used in combination.

[0105] In addition, the "hydrogenation" mentioned here refers to the addition of hydrogen at 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, hydrogen is not 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).

[0106] 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 the molding of the resin composition, and the properties of the obtained insulating 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 insulating layer can be maintained at a higher level.

[0107] 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 insulating layer.

[0108] (1-3) Other additives

[0109] The resin composition may contain, in addition to the above-mentioned resin components, for example, an antioxidant, a copper inhibitor, a lubricant, and a colorant.

[0110] However, in the resin composition, the content of the additive that functions as a nucleating agent for generating propylene crystals may be small, or substantially free of such additives. Specifically, 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, when the total of the resin component containing the propylene resin, the rubber material, and the elastomer is taken as 100 parts 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.

[0111] The resin 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.

[0112] (1-4) Viscosity of resin composition

[0113] The resin composition is formed by mixing the above-mentioned propylene resin and at least one of a rubber material and an elastomer. By mixing these components, the resin composition is subjected to a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at a low shear rate is 7000 Pa·s or more and 50000 Pa·s or less.

[0114] 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. The viscosity curve takes a unique shape according to the molecular weight, molecular weight distribution, melting point, heat of fusion, etc. of the resin component. Not only when the types of propylene resins, rubber materials and elastomers are different, but even for the same propylene resin, the viscosity curve is different when the physical properties such as molecular weight distribution and melting point are different. Depending on the difference in the viscosity curve, the slope of the viscosity curve, the viscosity range that can be obtained at high shear rate and low shear rate, etc. are different. In this embodiment, by mixing propylene resins, rubber materials and elastomers with different viscosity curves, the viscosity of the resin composition at each shear rate is adjusted to a specified range.

[0115] In the resin composition, when the viscosity at a high shear rate is less than 200Pa·s, the molten resin composition cannot maintain its shape when it is extruded, and sometimes it cannot be formed into an insulating layer. On the other hand, when the viscosity at a high shear rate is greater than 5000Pa·s, the pressure when the resin composition is extruded becomes high, and the extrusion amount is unstable, so sometimes the resin composition cannot be extruded with a uniform thickness. In this regard, by adjusting the viscosity at a high shear rate to within the range of 200Pa·s to 5000Pa·s, the molten resin composition can be extruded with a uniform thickness while maintaining its shape. The viscosity at a high shear rate can be 800Pa·s to 3000Pa·s.

[0116] When the viscosity at low shear rate is less than 7000Pa·s, the extruded resin composition tends to sag due to its own weight, so the thickness of the insulating layer becomes uneven and the outer diameter of the power cable also becomes uneven. On the other hand, when the viscosity at low shear rate is greater than 50000Pa·s, the viscosity at high shear rate also increases accordingly, so the extrusion amount of the resin composition becomes unstable as described above, and sometimes it is impossible to form an insulating layer with uniform thickness. In this regard, by adjusting the viscosity at low shear rate to within the range of 7000Pa·s to 50000Pa·s, the drooping of the extruded resin composition can be suppressed, and the uniformity of the outer diameter of the power cable can be improved. The viscosity at low shear rate can be 10000Pa·s to 30000Pa·s.

[0117] The ratio of the viscosity at high shear rate to the viscosity at low shear rate is not particularly limited, and when the viscosity at high shear rate is A and the viscosity at low shear rate is B, B / A may be 10 or more and 250 or less. The larger the ratio, the more the molten resin composition can be extruded at a lower pressure, and the more the shape of the resin composition after extrusion can be maintained.

[0118] The viscosities at high shear rates and low shear rates were measured by the procedures described in Examples below.

[0119] (1-5) Elastic modulus of resin composition

[0120] The resin composition is formed by mixing the above-mentioned propylene resin, and at least one of the rubber material and the elastomer. By mixing these components, the elastic modulus of the resin composition is formed in a manner of being more than 150MPa and less than 700MPa. The propylene resin, the rubber material, and the elastomer have different elastic moduli, and the elastic modulus of the resin composition changes according to their mixing amounts. Therefore, the elastic modulus of the resin composition becomes an index of the ratio (composition) of each component. In this regard, in the resin composition, by making the viscosity at each shear speed within the above range and the elastic modulus within the above range, various characteristics required by the cable such as the uniformity of the outer diameter and the insulation can be satisfied in the insulating layer.

[0121] (1-6) Melting Point and Heat of Fusion of Resin Composition

[0122] The melting point and heat of fusion of the resin composition vary depending on the amounts of the propylene resin, the rubber material, and the elastomer, and therefore serve as indices of the ratio (composition) of the components.

[0123] 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, it is low. In addition, the crystallinity of propylene resin is high, and its melting heat is high, while the crystallinity of rubber materials and elastomers is low, or they are amorphous, and their melting heat is low. Therefore, the melting point and melting heat of resin composition have a tendency to be lower than the melting point and melting heat originally possessed by propylene resin, respectively.

[0124] The melting point and heat of fusion of the resin composition are not particularly limited, but may be in the following ranges from the viewpoint of mixing the components at an appropriate ratio and making the viscosities at high and low shear rates fall within predetermined ranges.

[0125] Specifically, the melting point of the resin composition may be 158° C. to 168° C. when containing homo-PP as the propylene resin, and 140° C. to 150° C. when containing random PP as the propylene resin.

[0126] In addition, the heat of fusion of the resin composition may be 75 J / g or more and 110 J / g or less if homopolymer PP is included as the propylene resin, and may be 60 J / g or more and 100 J / g or less if random PP is included as the propylene resin.

[0127] 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 composition is within the above range, the viscosity and elastic modulus at high and low shear rates can be adjusted to the predetermined range.

[0128] (1-7) Resin composition

[0129] The ratio (composition) of each component included in the resin composition can be appropriately adjusted according to the types of propylene resin, rubber material and elastomer, so that the viscosity and elastic modulus at high shear rate and low shear rate in the resin composition are respectively within the specified range. For example, the components can be mixed in a manner that the melting point and heat of fusion of the resin composition are within the above range. Specifically, in the resin composition, the addition ratio of the propylene resin can be more than 50% by mass. In addition, the propylene resin can be used in combination with two or more components having different viscosities, melting points, heats of fusion and molecular weight distributions. For rubber materials and elastomers, two or more components having different physical property values ​​can also be used in combination.

[0130] (2) Power cables

[0131] Next, use Figure 1 The power cable according to this embodiment will be described. Figure 1This is a cross-sectional view perpendicular to the axial direction of the power cable according to the present embodiment.

[0132] 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 alternating current, for example.

[0133] Specifically, the power cable 10 has, 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 jacket 160 .

[0134] (Conductor (conductive part))

[0135] 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.

[0136] (Inner semi-conductive layer)

[0137] The inner semiconductive layer 120 is provided so as to cover the outer periphery of the conductor 110. The inner semiconductive layer 120 has semiconductivity and is configured to suppress electric field concentration on the surface side of the conductor 110. The inner semiconductive layer 120 includes, for example, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, ethylene-vinyl acetate copolymer and other ethylene-based copolymers, olefin-based elastomers, the above-mentioned rubber materials, propylene-based resins, etc., and at least any one of conductive carbon black.

[0138] (Insulation layer)

[0139] Insulating layer 130 is provided so as to cover the outer periphery of inner semiconductive layer 120, and is formed of the above-mentioned resin composition. Insulating layer 130 is molded by extruding the resin composition, for example.

[0140] (Outer semiconductive layer)

[0141] The outer semiconductive layer 140 is provided so as to cover the outer periphery of the insulating layer 130. The outer semiconductive layer 140 has semiconductivity and is configured to suppress electric field concentration between the insulating layer 130 and the shielding layer 150. The outer semiconductive layer 140 is composed of the same material as the inner semiconductive layer 120, for example.

[0142] (Shielding layer)

[0143] 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 is formed as a wire shield wound with a plurality of soft copper wires, etc. Alternatively, a tape made of a rubber-coated cloth or the like may be wound inside or outside the shielding layer 150.

[0144] (jacket)

[0145] 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.

[0146] In addition, if the power cable 10 of the present embodiment is an underwater cable or an underwater cable, it may also have a metal waterproof layer such as a so-called aluminum coating or a wire armor on the outside of the shielding layer 150. On the other hand, the power cable 10 of the present embodiment may not have a metal waterproof layer such as a so-called aluminum coating on the outside of the shielding layer 150, because it has the above-mentioned water tree suppression effect. That is, the power cable 10 of the present embodiment may also be composed of a non-completely waterproof structure.

[0147] (Specific dimensions, etc.)

[0148] There are no particular limitations on the specific dimensions of the power cable 10. 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. The AC voltage applied to the power cable 10 of the present embodiment is, for example, 20 kV or more.

[0149] 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 be deformed in shape. In this regard, according to the resin composition of the present embodiment, the sagging of the insulating layer 130 is suppressed and its shape is easily maintained. Therefore, even in the case where the insulating layer 130 is formed thicker than the outer diameter of the conductor 110 and the outer diameter of the power cable 10 is increased, the shape deformation and outer diameter variation of the insulating layer 130 can be suppressed. For example, the thickness of the insulating layer 130 may be 4 mm or more, and the ratio of the outer diameter of the power cable 10 to the outer diameter of the conductor 110 may be 4 or less. From the viewpoint of suppressing the variation of the outer diameter, 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 is 8 mm. 2 Above and 900mm 2 The following range.

[0150] (3) Cable characteristics

[0151] In the present embodiment, the insulating layer 130 is formed of a predetermined resin composition, thereby ensuring the following cable characteristics.

[0152] (Uniformity of outer diameter)

[0153] Since the electric power cable 10 of the present embodiment suppresses sagging of the insulating layer 130 , the outer diameters thereof vary little in the cross-sectional and longitudinal directions.

[0154] The small change 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 diameter (maximum value of the outer diameter) in the cross section is set to A1 and the minor diameter (minimum value of the outer diameter) is set to B1, the ratio of the major diameter to the minor diameter (A1 / B1) can be less than 1.3 or less than 1.25. In addition, the lower limit of the ratio is 1.

[0155] Small variation in the outer diameter in the length direction means that in the cross section of two points separated in the length 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 length direction, when the major diameter at one point is set to B2 and the minor diameter at the other point is set to A2 (A2<B2), the ratio (B2 / A2) of the major diameter B2 at one point to the minor diameter A2 at the other point can be 1.3 or less, and can be 1.25 or less. In addition, the lower limit of the ratio is 1.

[0156] (Insulation)

[0157] In the power cable 10, when the insulating layer 130 is formed with a predetermined design thickness, the insulating thickness sometimes becomes thinner locally, and sometimes the insulation (apparent insulation breakdown voltage) is smaller than that at the predetermined thickness. In this regard, in the present embodiment, since the outer diameter of the power cable 10 can be formed uniformly, and in particular, the thickness of the insulating layer 130 can be formed uniformly, the insulation at the designed thickness can be more reliably ensured. Specifically, the AC breakdown electric field strength of the insulating layer 130 at room temperature (e.g., 27° C.) is, for example, 60 kV / mm or more. More specifically, the AC breakdown electric field is 60 kV / mm or more when an AC voltage of a commercial frequency (e.g., 60 Hz) is applied to a 0.2 mm thick sample sample collected from the insulating layer 130 at room temperature under the following conditions: after applying a voltage of 10 kV for 10 minutes, the operation of applying the voltage for 10 minutes with the voltage increased by 1 kV each time is repeated.

[0158] (4) Manufacturing method of power cable

[0159] Next, a method for manufacturing a power cable according to the present embodiment will be described. Hereinafter, the step will be simply referred to as "S".

[0160] (S100: Resin composition preparation step)

[0161] First, a resin composition for forming the insulating layer 130 is prepared.

[0162] In the present embodiment, a mixer is utilized to mix (knead) at least one of the propylene resin, the rubber material and the elastomer, and other additives (antioxidants, etc.) as required to form a mixed material. Examples of the mixer include an open roll mill, a Banbury mixer, a pressure kneader, a single-shaft mixer, a multi-shaft mixer, etc.

[0163] At this time, in the resin combination, the propylene resin, rubber material, and elastomer are mixed at a prescribed ratio in such a manner that the viscosity at high shear rate and low shear rate respectively becomes a prescribed range. For example, each component can be mixed in such a manner that the melting point, heat of fusion, etc. of the resin combination become a prescribed range.

[0164] After the mixed material is formed, the mixed material is granulated by an extruder, thereby forming a granular resin composition for constituting the insulating layer 130. Alternatively, a twin-shaft extruder with a high kneading effect may be used to perform the steps from mixing to granulation at one time.

[0165] (S200: conductor preparation process)

[0166] On the other hand, a conductor 110 formed by twisting a plurality of conductor core wires is prepared.

[0167] (S300: Cable core forming process (extrusion process, insulation layer forming process))

[0168] After the resin composition preparation step S100 and the conductor preparation step S200 are completed, the resin composition is extruded so as to cover the outer periphery of the conductor 110 with a thickness of 3 mm or more. At this time, the resin composition is heated at a temperature of 190° C. and a shear rate of 100 s -1 The viscosity at a high shear rate is 200 Pa·s or more and 5000 Pa·s or less, and therefore the resin composition can be stably extruded at a constant thickness.

[0169] Next, the extruded resin composition is cooled to form the insulating layer 130. During the cooling, the resin composition is heated to 190°C and the shear rate is 1s. -1 The viscosity at a low shear rate is 7000 Pa·s or more and 50000 Pa·s or less, so the resin composition can be prevented from flowing and sagging during the period until the shape of the resin composition is fixed by cooling. That is, the extruded resin composition can be fixed while maintaining its shape. As a result, the insulating layer 130 can be uniformly formed in the peripheral direction of the cross section and in the longitudinal direction of the power cable 10.

[0170] Furthermore, at this time, in the present embodiment, for example, the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140 are simultaneously formed using a three-layer co-extruder.

[0171] Specifically, in a three-layer co-extruder, for example, the composition for the inner semiconductive layer is charged into the extruder A for forming the inner semiconductive layer 120 .

[0172] The pelletized resin composition is introduced 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 be appropriately adjusted based on the line speed and the extrusion pressure.

[0173] The outer semiconductive layer composition containing the same materials as the resin composition for the inner semiconductive layer fed into the extruder A is fed into the extruder C for forming the outer semiconductive layer 140 .

[0174] Next, the extrudates from the extruders A to C are directed to a common head, and the inner semiconductive layer 120, the insulating layer 130 and the outer semiconductive layer 140 are simultaneously extruded from the inside to the outside to the outer periphery of the conductor 110. Thus, an extruded material that becomes a cable core is formed.

[0175] The extruded material is then cooled, for example using water.

[0176] 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 semiconductive layer 140 is formed.

[0177] (S400: Shielding Layer Forming Step)

[0178] After the cable core is formed, the shielding layer 150 is formed by winding, for example, a copper tape around the outside of the outer semiconductive layer 140 .

[0179] (S500: Sheath Forming Step)

[0180] 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 .

[0181] In the above manner, the power cable 10 as a solid insulated power cable can be manufactured.

[0182] (5) Summary of this embodiment

[0183] According to the present embodiment, one or more of the following effects are achieved.

[0184] (a) The viscosity of the resin composition of the present embodiment at a high shear rate is 200Pa·s to 5000Pa·s. Thus, when the resin composition is melted and extruded, it can be stably extruded with a uniform thickness while maintaining the extruded shape. In addition, the viscosity at a low shear rate is 7000Pa·s to 50000Pa·s. Thus, during the period when the extruded resin composition is cooled until its shape is fixed, the sagging caused by the dead weight of the resin composition is suppressed, and the extruded shape is easily maintained. In this way, the resin composition of the present embodiment is excellent in extrusion moldability, and is not easy to flow or deform in shape in a molten state.

[0185] (b) According to the resin composition of the present embodiment, when forming the insulating layer 130 of the power cable 10, the insulating layer 130 can be formed to a uniform thickness in the peripheral direction of the cross section and the longitudinal direction of the power cable 10. As a result, in the power cable 10, the variation of the outer diameter can be reduced in the cross section and the longitudinal direction. 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 can be made less than 1.3 in the peripheral direction. In addition, in the cross section of two points separated in the longitudinal direction of the power cable 10, the ratio of the long diameter at one point to the short diameter at another point can be made less than 1.3.

[0186] (c) In addition, according to the resin composition of the present embodiment, the elastic modulus is 150 MPa or more and 700 MPa or less. Therefore, in the insulating layer 130, a high AC breakdown electric field strength can be maintained, and the prescribed insulation can be ensured. Specifically, the AC breakdown electric field strength can be 60 kV / mm or more.

[0187] (d) The resin composition contains at least one of a rubber material and an elastomer together with the propylene resin, so that excessive crystal growth of the propylene resin can be suppressed during cooling from a molten state. Thus, insulation and flexibility can be well-balanced in the insulating layer 130 at a high level.

[0188] (e) In addition, the melting point in the resin composition can be 140°C to 150°C if it contains random PP, and can be 158°C to 168°C if it contains homopolymer PP. In addition, its heat of fusion can be 60J / g to 100J / g if it contains random PP, and can be 75J / g to 110J / g if it contains homopolymer PP. In the resin composition, by making at least one of the melting point and the heat of fusion satisfy the specified range, the addition ratio of the propylene resin, the rubber material and the elastomer can be set to 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 insulating layer 130, insulation and flexibility can be obtained at a high level and in a balanced manner.

[0189] (f) In addition, according to the resin composition, even when the thickness of the insulating layer 130 is greater than 4 mm and the ratio of the outer diameter of the power cable 10 to the outer diameter of the conductor 110 is less than 4, that is, when the insulating layer 130 is formed in a manner that is thicker than the outer diameter of the conductor 110, the outer diameter variation can be suppressed to a small level.

[0190] (g) In addition, according to the resin composition, when the power cable 10 is produced, the outer diameter variation in the longitudinal direction, which is particularly likely to occur when a vertical extruder is used, and the outer diameter variation in the outer peripheral direction of the cross section, which is particularly likely to occur when a horizontal extruder is used, can be suppressed.

[0191] (h) In addition, according to the resin composition, in the cross section of the power cable 10, by reducing the ratio of the major diameter to the minor diameter, for example, to 1.3 or less, the uniformity of the outer diameter can be improved, thereby shortening the processing time when the power cable 10 is connected. In addition, when the power cable 10 is connected to the connecting member, the gap at the connection can be suppressed, and the connection can be made more reliably.

[0192] <Other embodiments of the present invention>

[0193] 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.

[0194] In the above-mentioned embodiment, the case where the resin composition molded body as the insulating layer is mechanically mixed and extruded is described, but the resin composition molded body may be polymerized and extruded.

[0195] 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 also 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 provided on one side or both sides of the metal layer. The metal laminate tape is, for example, wound by longitudinal attachment in a manner of surrounding the outer periphery of the cable core (closer to the outer periphery than the outer semiconductive layer). In addition, the waterproof layer can be provided on the outside than the shielding layer, and can also serve as a shielding layer. With such a structure, the cost of the power cable 10 can be reduced.

[0196] 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 to this case. For example, the power cable 10 may be configured as a so-called overhead wire (overhead insulated wire).

[0197] In the above-mentioned embodiment, three-layer co-extrusion is performed in the cable core forming step S300 , but it may also be extruded layer by layer.

[0198] Example

[0199] Next, examples of the present invention will be described. These examples are examples of the present invention, and the present invention is not limited to these examples.

[0200] (1) Materials

[0201] As the resin composition for forming the insulating layer, materials A to E shown in the following Table 1 were prepared. In the preparation of materials A to E, the following substances were used as the respective components.

[0202] As the propylene resin, 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, an elastic modulus of 600 MPa to 1200 MPa, a ratio of a weight average molecular weight (Mw) to a number average molecular weight (Mn) (Mw / 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.

[0203] As the rubber material, a plurality of different EPR and VLDPE having a viscosity of 500 Pa·s to 5000 Pa·s at a high shear rate, a viscosity of 10000 Pa·s to 70000 Pa·s at a low shear rate, no melting point and heat of fusion, an elastic modulus of 1 MPa to 200 MPa, an Mw / Mn of 1.0 to 3.0, an Mn of 70000 to 250000, and an Mw of 70000 to 600000 are prepared.

[0204] As elastomers, a plurality of styrene resins 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, a heat of fusion of 5 J / g to 50 J / g, an elastic modulus of 1 MPa to 200 MPa, an Mw / Mn of 1.0 to 3.0, an Mn of 70000 to 250000, and an Mw of 70000 to 600000 and being different from each other are prepared.

[0205] 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 so that each viscosity of the obtained resin composition becomes a specified value, and the materials A to E shown in Table 1 are prepared. Here, the addition ratio of the propylene resin is adjusted to 50% by mass or more of the resin composition. In addition, with respect to the material E, 5 parts by mass of an inorganic filler are further added to 100 parts by mass of the resin component to prepare it.

[0206] [Table 1]

[0207]

[0208] In Table 1, the melting point, heat of fusion, viscosity at a high shear rate, viscosity at a low shear rate, and elastic modulus of Materials A to E were measured as follows.

[0209] (Melting point and heat of fusion)

[0210] The melting point and heat of fusion of materials A to E 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 is 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, the DSC curve is obtained by plotting the amount of heat absorbed (heat flow) per unit time against the temperature.

[0211] At this time, the temperature at which the heat absorption per unit time in each measured sample reaches a maximum value (highest peak) is taken as the “melting point.” In addition, at this time, the area of ​​the region surrounded by the melting peak and the baseline in the DSC curve is obtained to obtain the “heat of fusion”.

[0212] (Viscosity)

[0213] The viscosity of materials A to E at different shear rates was measured using a rotational rheometer ("MCR302" manufactured by Anton Paar) with a PP-12 fixture at 190°C from a shear rate of 0.001 s -1 Up to 1000s -1 The shear rate was varied and measured.

[0214] (Elastic modulus)

[0215] The elastic modulus of materials A to E was measured by dynamic viscoelasticity measurement (DMA). Specifically, first, a compressed sheet for evaluation was made from each material. While applying 0.08% expansion and contraction to the compressed sheet, the storage modulus of the compressed sheet was measured while the temperature was raised from -50°C to 100°C. In addition, the measurement frequency was set to 10 Hz. In addition, the heating rate was set to 10°C / min. As a result of the measurement, the storage modulus at 25°C was obtained.

[0216] (2) Production of power cable samples

[0217] In this example, materials A to E were used as resin compositions for forming an insulating layer, and samples simulating power cables were prepared.

[0218] (Sample 1)

[0219] Specifically, as shown in Table 2 below, first, a 2500 mm 2(conductor diameter is about 56.4mm). After preparing the conductor, the resin composition for the inner semiconductive layer containing ethylene-ethyl acrylate copolymer, the above-mentioned material A as the resin composition for forming the insulating layer, and the outer semiconductive layer resin composition composed of the same material as the resin composition for the inner semiconductive layer are respectively put into extruders A to C. The extrudates from extruders A to C are guided to a common head, and the inner semiconductive layer, the insulating layer and the outer semiconductive layer are extruded from the inside to the outside to the outer periphery of the conductor at the same time. At this time, the thickness of the inner semiconductive layer, the insulating layer and the outer semiconductive layer are set to 1.0mm, 24mm, and 1.0mm, respectively, and the thickness of the insulating coating is set to 26mm. As a result, a sample 1 of a power cable having a conductor, an inner semiconductive layer, an insulating layer and an outer semiconductive layer from the center to the periphery is manufactured (the cable outer diameter is 108.4mm). 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.

[0220] Furthermore, a power cable was produced with the same cable configuration except that the resin composition for forming the insulating layer was changed from material A to material B.

[0221] (Samples 2 to 11)

[0222] In samples 2 to 11, as shown in Table 2 below, power cables were produced in the same manner as in sample 1, except that material A or material B was used as the resin composition for forming the insulating layer, and the conductor diameter and the insulating coating thickness were changed, thereby obtaining samples 2 to 11. In each sample, the thickness of the inner semiconductive layer and the outer semiconductive layer was the same, and the insulating coating thickness was appropriately changed by adjusting the thickness of the insulating layer.

[0223] [Table 2]

[0224]

[0225] (Samples 12-14)

[0226] In Samples 12 to 14, power cables were produced in the same manner as Sample 1 except that Materials C to E were used as the resin compositions for forming the insulating layer and the conductor diameter and the insulating coating thickness were appropriately changed as shown in Table 3 below.

[0227] [Table 3]

[0228]

[0229] (3) Evaluation

[0230] For Samples 1 to 14 produced as power cables, the uniformity of the outer diameter in the cross section of the power cables, the uniformity of the outer diameter in the longitudinal direction, and the insulation properties were evaluated.

[0231] The uniformity of the outer diameter in the cross section is evaluated as follows. Specifically, select any point in the length direction of the power cable, measure the outer diameter in the circumferential direction in the cross section, 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 in the cross section.

[0232] 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 at each point are measured, and the ratio of the major diameter at one point to the minor diameter at another point is calculated. The smaller the ratio, the less the variation of the outer diameter in the length direction.

[0233] The insulation is evaluated by an AC breakdown test. Specifically, a test sample is cut out of the insulating layer of the manufactured sample with a thickness of 0.2 mm. Then, at room temperature (27°C), an AC voltage of a commercial frequency (e.g., 60 Hz) is applied to the 0.2 mm thick test sample under the condition of applying a voltage of 10 kV for 10 minutes and then repeatedly applying a voltage of 1 kV for 10 minutes each time. The electric field strength when the insulation of the inner sample is broken down is measured. As a result, the case where the AC breakdown strength is 60 kV / mm or more is evaluated as good.

[0234] (4) Evaluation results

[0235] The evaluation results are summarized in Tables 2 and 3.

[0236] As shown in Table 2, it was confirmed that in samples 1 to 11, when material A was used as the resin composition for forming the insulating layer, the variation of the outer diameter in each of the cross-sectional and longitudinal directions tended to be smaller than when material B was used. This is because material B tends to sag more easily than material A and cannot maintain its shape.

[0237] Specifically, as shown in Table 1, it is confirmed that the viscosity of material B at high shear rate is 1000Pa·s, within the range of 200Pa·s to 5000Pa·s, so the resin composition is stably extruded with a certain thickness. On the other hand, the viscosity at low shear rate is 5000Pa·s and less than 7000Pa·s, so material B is easy to flow and sag during the period from cooling to fixing the shape after extrusion. Therefore, it can be inferred that when material B is used, the insulating layer is deformed until the shape is fixed, and the outer diameter of the power cable changes accordingly. In material B, as shown in samples 2 and 8, it is confirmed that if the thickness of the insulating coating is small or the ratio (Y / X) of the cable shape Y to the conductor diameter X is small, the outer diameter change can be suppressed, but as shown in samples 1, 3 to 7, 9 to 11, if the thickness of the insulating coating is 4 mm or more or Y / X becomes larger, the outer diameter change becomes larger.

[0238] In contrast, material A has a low viscosity at high shear rates and excellent extrusion moldability, but also has a higher viscosity at low shear rates than material B and is less likely to flow in a molten state. Therefore, material A can suppress outer diameter fluctuations compared to material B.

[0239] In addition, as shown in samples 2, 8, and 9, it was confirmed that the outer diameter variation is not easy to occur when the thickness of the insulating coating is reduced. As shown in samples 7, 10, and 11, it was confirmed that the outer diameter variation is easy to occur when the power cable is manufactured in a manner in which the ratio of the cable outer diameter to the conductor diameter is too high. Furthermore, as shown in samples 1, 3 to 6, it was confirmed that according to material A, if the thickness of the insulating layer is 4 mm or more and the ratio of the cable outer diameter to the conductor diameter is 4 or less, the outer diameter variation can be suppressed to a ratio of 1.3 or less.

[0240] In addition, as shown in Sample 12, it was confirmed that the viscosity of Material C at a high shear rate was too high, so the extrusion moldability was poor and it could not be molded into an insulating layer. On the other hand, as shown in Sample 13, it was confirmed that the viscosity of Material D at both a high shear rate and a low shear rate was too low, so it could not be extruded in a stable state, and the extruded shape could not be maintained, so it could not be molded into an insulating layer.

[0241] Furthermore, as shown in Sample 14, it was confirmed that the material E contained an inorganic filler and had a high viscosity at both high and low shear rates, so the extrudability of the resin composition was unstable, and the outer diameter fluctuation in the longitudinal direction was particularly large.

[0242] Furthermore, it was confirmed that in Samples 1 to 14, when the uniformity of the outer diameter in the cross-sectional and longitudinal directions was high and the outer diameter variation ratio was 1.3 or less, the AC breakdown strength was 60 kV / mm or more, and high insulation properties could be obtained more reliably.

[0243] <Note>

[0244] Hereinafter, embodiments of the present invention will be described in detail.

[0245] (Note 1)

[0246] A resin composition comprising:

[0247] Acrylic resin; and

[0248] at least one of a rubber material and an elastomer,

[0249] The rubber material and elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene.

[0250] The above resin composition is heated at a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at low shear rate is 7000Pa·s or more and 50000Pa·s or less.

[0251] The elastic modulus of the resin composition is 150 MPa or more and 700 MPa or less.

[0252] (Note 2)

[0253] A power cable, comprising:

[0254] Conductors; and

[0255] an insulating layer formed of a resin composition and covering the outer periphery of the conductor,

[0256] The resin composition comprises:

[0257] Acrylic resin; and

[0258] at least one of a rubber material and an elastomer,

[0259] The rubber material and elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene.

[0260] The above resin composition is heated at a temperature of 190°C and a shear rate of 100s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at low shear rate is 7000Pa·s or more and 50000Pa·s or less.

[0261] The elastic modulus of the resin composition is 150 MPa or more and 700 MPa or less.

[0262] (Note 3)

[0263] The power cable according to Supplementary Note 2, wherein the resin composition has a heat of fusion of 60 J / g or more and 100 J / g or less.

[0264] (Note 4)

[0265] The power cable according to Appendix 2 or 3, wherein the resin composition has a melting point of 140° C. or higher and 150° C. or lower.

[0266] (Note 5)

[0267] The power cable according to any one of Supplementary Notes 2 to 4, 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.

[0268] (Note 6)

[0269] The power cable according to any one of Supplementary Notes 2 to 5, wherein, in cross sections at two points separated in the longitudinal direction, a ratio of a major diameter at one point to a minor diameter at another point is 1.3 or less.

[0270] (Note 7)

[0271] The power cable according to any one of Supplementary Notes 2 to 6, wherein the thickness of the insulating layer is 4 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.

[0272] (Note 8)

[0273] The power cable according to any one of Appendixes 2 to 7, wherein the elastic modulus of the propylene resin is 600 MPa or more and 1200 MPa or less.

[0274] (Note 9)

[0275] 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 to 6000 Pa·s, and the viscosity at the low shear rate is 500 Pa·s to 50000 Pa·s.

[0276] (Note 10)

[0277] The 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.

[0278] (Note 11)

[0279] The power cable according to any one of Appendixes 2 to 10, wherein the propylene-based resin has a ratio Mw / Mn of 3.0 or more and 8.0 or less, when the weight average molecular weight in molecular weight distribution is Mw and the number average molecular weight is Mn.

[0280] (Note 12)

[0281] The power cable according to any one of Appendixes 2 to 11, 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.

[0282] (Note 13)

[0283] The power cable according to any one of Supplementary Notes 2 to 12, wherein the elastic modulus of the rubber material and the elastomer is 1 MPa or more and 200 MPa or less.

[0284] (Note 14)

[0285] The electric power cable according to any one of Supplementary Notes 2 to 13, wherein the rubber material has no melting point or has a melting point of 100° C. or less.

[0286] (Note 15)

[0287] The power cable according to any one of Supplementary Notes 2 to 14, wherein the heat of fusion of the rubber material is 50 J / g or less.

[0288] (Note 16)

[0289] The power cable according to any one of Appendixes 2 to 15, wherein the rubber material and the elastomer have a ratio Mw / Mn of 1.0 to 3.0, when the weight average molecular weight in molecular weight distribution is Mw and the number average molecular weight is Mn.

[0290] Description of Reference Numerals

[0291] 10: Power cable;

[0292] 110: Conductor;

[0293] 120: inner semiconductive layer;

[0294] 130: insulation layer;

[0295] 140: outer semiconductive layer;

[0296] 150: shielding layer;

[0297] 160: Sheath.

Claims

1. A resin composition comprising: Acrylic resin; and at least one of a rubber material and an elastomer, The rubber material and the elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, The resin composition is heated to 190°C and sheared at 100 s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at low shear rate is 7000Pa·s or more and 50000Pa·s or less. The resin composition has an elastic modulus of 150 MPa or more and 700 MPa or less.

2. A power cable, comprising: Conductors; and an insulating layer formed of a resin composition and covering the outer periphery of the conductor, The resin composition comprises: Acrylic resin; and at least one of a rubber material and an elastomer, The rubber material and the elastomer have at least two units of ethylene, propylene, butene, hexene, isoprene, octene and styrene, The resin composition is heated to 190°C and sheared at 100 s -1 The viscosity at high shear rate is 200Pa·s or more and 5000Pa·s or less. -1 The viscosity at low shear rate is 7000 Pa·s or more and 50000 Pa·s or less. The resin composition has an elastic modulus of 150 MPa or more and 700 MPa or less.

3. The power cable according to claim 2, wherein: The resin composition has a heat of fusion of 60 J / g or more and 100 J / g or less.

4. The power cable according to claim 2 or 3, wherein: The resin composition has a melting point of 140° C. or higher and 150° C. or lower.

5. The power cable according to any one of claims 2 to 4, 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.

6. The power cable according to any one of claims 2 to 5, wherein: The viscosity of the rubber material and the elastic body at the high shear rate is 300 Pa·s or more and 7000 Pa·s or less, and the viscosity at the low shear rate is 4000 Pa·s or more and 80000 Pa·s or less.

7. The power cable according to any one of claims 2 to 6, 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.

8. The power cable according to any one of claims 2 to 7, wherein: 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.

9. The power cable according to any one of claims 2 to 8, wherein: The thickness of the insulating layer is 4 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.

Images