Resin composition and power cable

Abstract

A resin composition containing a propylene resin (A) having propylene units and a thermoplastic elastomer (B), the resin composition having a melting point of 110°C or higher, and in measuring the molecular weight distribution of the resin composition, the molecular weight in the resin composition is 1 x 10 4 The proportion of the following component is 3% or less.

Description

Technical Field

[0001] This disclosure relates to resin compositions and power cables. Background Technology

[0002] In recent years, solid-insulated power cables (hereinafter referred to as "power cables") have been developed for DC power transmission applications. In these power cables, cross-linked polyethylene (XLPE) is widely used as a component constituting the insulation layer (e.g., Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 11-086634. Summary of the Invention

[0006] According to one aspect of this disclosure, a resin composition is provided comprising an propylene-based resin (A) having propylene units and a thermoplastic elastomer (B), wherein the melting point of the resin composition is 110°C or higher, and the molecular weight distribution of the resin composition is measured to be 1 × 10⁻⁶. 4 The following ingredients account for less than 3%.

[0007] According to another aspect of this disclosure, a power cable is provided, having a conductor and an insulating layer formed of a resin composition surrounding the conductor. The resin composition contains an propylene resin (A) having propylene units and a thermoplastic elastomer (B). The melting point of the resin composition is 110°C or higher, and the molecular weight of the resin composition is 1 × 10⁻⁶ when the molecular weight distribution of the resin composition is determined. 4 The following ingredients account for less than 3%. Attached Figure Description

[0008] Figure 1 This is a schematic cross-sectional view orthogonal to the axial direction of a power cable according to one embodiment of the present disclosure.

[0009] Figure 2 This is a schematic diagram of the extruder used in a method for manufacturing a power cable according to one embodiment of the present disclosure.

[0010] Figure 3 It is a schematic diagram used to illustrate the shape of the screw thread.

[0011] Figure 4 This is a schematic diagram used to illustrate the retention inhibition component.

[0012] Figure 5 This is a flowchart illustrating a method for manufacturing a power cable according to one embodiment of the present disclosure. Detailed Implementation

[0013] [The problem the invention aims to solve]

[0014] Cross-linked polyethylene that has deteriorated over the years cannot be recycled and can only be incinerated. Therefore, there are concerns about its environmental impact.

[0015] Therefore, in recent years, polymer components containing propylene units, such as polypropylene, have attracted much attention as resin components constituting insulating layers. Polypropylene, even without crosslinking, can achieve high insulation properties. That is, it can balance insulation and recyclability.

[0016] On the other hand, in polymer compositions containing propylene units, insulation is sometimes not stably achieved in the insulating layer.

[0017] The purpose of this disclosure is to provide a technique for consistently achieving insulation in power cables.

[0018] [The effects of the invention]

[0019] According to this disclosure, insulation can be stably obtained in power cables.

[0020] [Description of embodiments of this disclosure]

[0021] <Insights gained by the inventors, etc.>

[0022] First, an overview of the insights gained by the inventors and others is provided.

[0023] In power cables, when the insulation layer is constructed using polymer components containing propylene units, space charge can be generated within the insulation layer, for example, when high voltage is applied, sometimes reducing the insulation's effectiveness. This tendency is more pronounced at high temperatures. Furthermore, the insulation properties referred to here include the volume resistivity, DC breakdown electric field strength, and space charge characteristics of the insulation layer.

[0024] To improve the insulation properties of insulating layers, methods for incorporating modified polymers with polar groups are being investigated. Examples of such modified polymers include modified propylene obtained by modifying propylene with unsaturated carboxylic acids.

[0025] However, it was confirmed that simply adding modified polymers did not result in stable insulation properties in the resin composition and insulating layer. Further investigation revealed that the modified polymers, due to their manufacturing process, generate free radicals or break molecular chains, resulting in low molecular weight components that reduce insulation. These low molecular weight components tend to act as charge carriers, especially at high temperatures. Therefore, it can be assumed that these low molecular weight components locally cause space charge accumulation in the resin composition, particularly migrating within the composition at high temperatures and further contributing to this accumulation. Consequently, even with the addition of modified polymers to acrylic resins, the space charge trapping effect provided by the modified polymers can sometimes be difficult to achieve due to the influence of low molecular weight components. As a result, consistently high insulation properties cannot always be obtained in the insulating layer.

[0026] Therefore, the inventors have researched methods for improving insulation without adding modified polymers, focusing on softening components added to the resin composition forming the insulating layer. Acrylic resins have high crystallinity and are often quite hard when used alone, thus sometimes failing to meet the flexibility required for the insulation layer of power cables. Various elastomers, wax components, etc., can be used as this softening component.

[0027] However, when using softening ingredients, there are concerns about the following aspects.

[0028] Firstly, the melting point of the softening component is lower than that of acrylic resins. The lower the melting point of the softening component, the higher the proportion of amorphous or molten regions in the resin composition may be at high temperatures. Therefore, if a softening component with a low melting point is mixed in, charge movement is more likely to occur at high temperatures, sometimes leading to a decrease in insulation.

[0029] Secondly, the molecular weight of the softening component is lower compared to acrylic resins. Resins and elastomers typically have an inherent molecular weight distribution corresponding to their type. The lower the molecular weight of the softening component, the higher the proportion of low molecular weight components in the molecular weight distribution is likely to be. Low molecular weight components have lower melting points compared to high molecular weight components, and their movement within the resin composition can cause the accumulation of localized space charges, which can sometimes lead to a decrease in insulation properties at high temperatures.

[0030] Therefore, thermoplastic elastomers with high melting points and low molecular weight components are of interest as softening agents added to acrylic resins. Furthermore, it has been found that in resin compositions containing acrylic resins and thermoplastic elastomers, by controlling the melting point to above 110°C and the molecular weight to 1×10⁻⁶, [the following method is suitable]. 4 The proportion of the following low molecular weight components is controlled below 3%, which can suppress the accumulation of space charge under high temperature environment and achieve high insulation.

[0031] This disclosure is based on the above-mentioned insights discovered by the inventors, etc.

[0032] <Implementation Methods of this Disclosure>

[0033] Next, embodiments of this disclosure will be described.

[0034] [1] One aspect of the resin composition disclosed herein contains an propylene resin (A) having propylene units and a thermoplastic elastomer (B), wherein the melting point of the resin composition is 110°C or higher.

[0035] When determining the molecular weight distribution of the above resin composition, the molecular weight of the above resin composition was 1 × 10⁻⁶. 4 The following ingredients account for less than 3%.

[0036] Based on this configuration, high insulation can be stably obtained.

[0037] [2] Another aspect of this disclosure relates to a power cable having a conductor and an insulating layer formed of a resin composition covering the conductor, the resin composition containing an propylene resin (A) having propylene units and a thermoplastic elastomer (B), the resin composition having a melting point of 110°C or higher, and the molecular weight of the resin composition being 1 × 10⁻⁶ when the molecular weight distribution of the resin composition is determined. 4 The following ingredients account for less than 3%.

[0038] Based on this configuration, high voltage resistance can be achieved even in high-temperature environments, enabling stable DC power transmission.

[0039] [3] In the power cable described in [2] above, the thermoplastic elastomer (B) is at least one of an olefin-based thermoplastic elastomer having an olefin unit and a styrene-based thermoplastic elastomer having a styrene unit.

[0040] Based on this structure, it is possible to achieve high insulation performance while improving the flexibility of the insulation layer.

[0041] [4] In the power cable described in [2] or [3] above, the melting point of the thermoplastic elastomer (B) is above 110°C and below 160°C.

[0042] Based on this composition, the melting point of the resin composition can be easily adjusted to above 110°C, and high insulation can be stably obtained.

[0043] [5] In any of the above-mentioned [2] to [4] power cables, the molecular weight of the above-mentioned thermoplastic elastomer (B) is 1×10⁻⁶. 4 The following ingredients account for less than 4.0%.

[0044] Based on this composition, the proportion of low molecular weight components can be adjusted to be low, and high insulation can be stably obtained.

[0045] [6] In any of the above-mentioned power cables [2] to [5], the melting point of the above-mentioned acrylic resin (A) is above 130°C and below 170°C.

[0046] Based on this composition, the melting point of the resin composition can be easily adjusted to above 110°C, and high insulation can be stably obtained.

[0047] [7] In any of the above-mentioned [2] to [6] power cables, the above-mentioned resin composition contains 50 or more and 90 or less of the above-mentioned acrylic resin (A) and 10 or more and 50 or less of the above-mentioned thermoplastic elastomer (B).

[0048] Based on this composition, the proportion of low molecular weight components can be reduced, and high insulation can be stably obtained.

[0049] [Details of the embodiments disclosed herein]

[0050] Next, one embodiment of the present disclosure will be described with reference to the accompanying drawings. Furthermore, the invention is not limited to these illustrations, as shown in the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0051] <One embodiment of this disclosure>

[0052] (1) Resin composition

[0053] The resin composition of this embodiment can be used, for example, as a material for forming the insulation layer of the power cable described later. The resin composition contains an propylene resin (A) having propylene units, a thermoplastic elastomer (B), and other additives added as needed. Hereinafter, the propylene resin (A) will be referred to as component (A), and the thermoplastic elastomer (B) will be referred to as component (B).

[0054] The resin composition is formed by mixing a propylene resin (A) and a thermoplastic elastomer (B) with different melting points and molecular weight distributions. The resin composition has a melting point above 110°C and a molecular weight of 1 × 10⁻⁶. 4 The proportion of the following components (hereinafter also referred to as low molecular weight components) is 3% or less. The resin composition has a defined phase structure by mixing component (A) and component (B). As a phase structure, for example, it is a structure in which component (B) is finely dispersed in component (A) (so-called island structure), or a structure in which component (A) and component (B) are compatible.

[0055] (Melting point of the resin composition)

[0056] The resin composition contains a thermoplastic elastomer (B) with a lower melting point than the acrylic resin (A), thus resulting in a resin composition with a lower melting point than component (A). The melting point of the resin composition is an indicator of the proportions of components (A) and (B). By setting the melting point of the resin composition to 110°C or higher, the proportion of component (B) with a lower melting point can be controlled within a specified amount. This reduces the impact of amorphization and melting of component (B) at high temperatures. There is no particular upper limit to the melting point of the resin composition; for example, 170°C or lower is preferred. Furthermore, as described later, when using an olefin-based thermoplastic elastomer as component (B), the melting point of the resin composition is preferably, for example, 130°C or higher and 170°C or lower. Additionally, when using a styrene-based thermoplastic elastomer as component (B), the melting point of the resin composition is preferably, for example, 110°C or higher and 170°C or lower.

[0057] In addition, the melting point is determined as follows in this specification.

[0058] First, for the sample, differential scanning calorimetry (DSC) is performed, for example, according to JIS-K-7121 (1987). Specifically, in the DSC apparatus, the temperature is increased from room temperature (room temperature, e.g., 27°C) to 220°C at a rate of 10°C / min. The DSC curve is then obtained by plotting the heat endothermic per unit time relative to the temperature. The temperature at which the heat endothermic per unit time in the sample reaches its maximum value (peak) is then set as the "melting point (melting peak temperature)".

[0059] (Molecular weight distribution of the resin composition)

[0060] When the molecular weight distribution of the resin composition is determined, it has a molecular weight distribution with a specified width derived from the acrylic resin (A) and thermoplastic elastomer (B) contained therein. In this embodiment, the molecular weight distribution of the resin composition is 1 × 10⁻⁶. 4 The following low molecular weight components are present in a concentration of 3% or less. The concentration can also be 2.5% or less, or even 1.5% or less. Furthermore, there is no specific lower limit for the concentration of low molecular weight components; for example, it can be 0.0001%.

[0061] Low molecular weight components refer to components with a molecular weight of 1×10⁻⁶ in the molecular weight distribution of the resin composition. 4 The following components. Low molecular weight components are those derived from thermoplastic elastomers (B) with relatively low molecular weight, or from the thermal decomposition products of component (B) and acrylic resins (A). The proportion of low molecular weight components indicates the percentage of low molecular weight components in the total resin composition, representing the molecular weight distribution with a molecular weight of 1 × 10⁻⁶.4 The area of ​​the following region is the ratio of its area to the total area of ​​the molecular weight distribution. As mentioned above, low molecular weight components have low melting points, which may reduce insulation properties at high temperatures. In this respect, in this embodiment, by keeping the proportion of low molecular weight components in the resin composition to 3% or less, the reduction in insulation properties can be suppressed. Furthermore, the determination of the molecular weight distribution will be described later in the examples.

[0062] The molecular weight distribution of the resin composition is determined by the molecular weight distribution of the acrylic resin (A) and the thermoplastic elastomer (B), and its molecular weight range is not particularly limited, but is preferably 1×10⁻⁶. 3 Above and 1×10 8 The following range. Furthermore, the proportion of low molecular weight components in the resin composition can be adjusted by the content of the low molecular weight thermoplastic elastomer (B) and the molecular weight of the (B) component used.

[0063] (Compositional components)

[0064] Next, the acrylic resin (A), thermoplastic elastomer (B), and other additives constituting the resin composition will be described.

[0065] (Acrylic resin (A))

[0066] Acrylic resin (A) is a resin material that constitutes the main component in a resin composition and is a component containing propylene units. As component (A), at least one of propylene homopolymer (hereinafter also called homopolymer PP) and propylene random polymer (hereinafter also called random PP) can be used. Homopolymer PP contains propylene units, while random PP contains both propylene units and ethylene units. The content of ethylene units in random PP is preferably, for example, 0.5% by mass or more and 15% by mass or less, and may also be 0.5% by mass or more and 10% by mass or less. By making the content of ethylene units 0.5% by mass or more, spherulite growth (the formation of coarse crystals) can be suppressed, and high insulation properties can be maintained. 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 stable use in non-crosslinked or micro-crosslinked states can be achieved.

[0067] From the viewpoint of achieving higher insulation properties in the resin composition, acrylic resin (A) is preferably atactic polypropylene (PP). While homopolymer PP, with its higher crystallinity compared to atactic PP, can achieve high insulation, intracrystalline and intercrystalline cracking can occur within the insulating layer, sometimes preventing the attainment of its intended insulation properties. In contrast, atactic PP, containing ethylene units, has a lower crystallinity, making it less prone to cracking due to coarse crystallization within the insulating layer, thus achieving higher insulation properties compared to homopolymer PP.

[0068] Furthermore, examples of stereoregularity for the acrylic resin (A) include isotactic, syndiotactic, and atactic structures. Stereoregularity is not particularly limited, but isotacticity is preferred. By achieving isotacticity, the decrease in the melting point of the resin composition can be suppressed. As a result, stable use in non-crosslinked or micro-crosslinked states is possible.

[0069] Furthermore, the melting point of the acrylic resin (A) is not particularly limited, but is preferably 130°C or higher and 170°C or lower. When the acrylic resin (A) is homopolymer PP, its melting point is preferably 120°C or higher and 165°C or lower; when the acrylic resin (A) is atactic PP, its melting point is preferably 130°C or higher and 170°C or lower. With an acrylic resin (A) having such a melting point, it is possible to achieve a higher melting point for the resin composition while simultaneously reducing the proportion of low molecular weight components.

[0070] The number average molecular weight of the acrylic resin (A) is not particularly limited, but is preferably 5.0 × 10⁻⁶. 4 The above can also be 8.0×10 4 Above and 5.0×10 5 The following applies. Based on component (A) having such a number average molecular weight, the low molecular weight component is less, and the proportion of low molecular weight component in the resin composition can be adjusted to be even smaller.

[0071] Furthermore, the number-average molecular weight is calculated for acrylic resin (A) by measuring the molecular weight distribution using gel permeation chromatography (GPC) based on a calibration curve prepared with polystyrene (PS) as a standard sample, and then calculating from this molecular weight distribution. The number-average molecular weight of thermoplastic elastomer (B) can also be calculated in the same way. Detailed calculation methods are described later in the examples.

[0072] From the viewpoint of compatibility with the thermoplastic elastomer (B), the melt flow rate (MFR) of the acrylic resin (A) is preferably 0.1 g / 10 min or more and 5.0 g / 10 min or less, and may also be 0.1 g / 10 min or more and 2.0 g / 10 min or less. By employing such an MFR, the phase structure of the resin composition can be formed into a structure in which each component is compatible and finely dispersed. This improves the flexibility and insulation properties of the resin composition. Furthermore, the MFR here refers to the value measured according to JIS K7210 at a temperature of 190°C and a load of 2.16 kg.

[0073] (Thermoplastic elastomer (B))

[0074] Thermoplastic elastomer (B) has lower crystallinity than propylene resin (A) with propylene units, which can control the crystal growth of component (A) and impart softness to resin compositions and insulation layers.

[0075] Compared to acrylic resins (A), thermoplastic elastomers (B) tend to have a lower melting point and a higher proportion of low molecular weight components, thus tending to lower the melting point of the resin composition and increase the proportion of low molecular weight components in the resin composition. In this respect, in this embodiment, component (B) is preferably selected as a substance with a high melting point and a low proportion of low molecular weight components.

[0076] Specifically, the melting point of the thermoplastic elastomer (B) is preferably 110°C or higher and 160°C or lower. With a component (B) having such a melting point, the melting point of the resin composition is not excessively lowered, and it is easy to adjust the melting point to 110°C or higher.

[0077] Furthermore, the thermoplastic elastomer (B) preferably has a molecular weight of 1×10 when the molecular weight distribution is measured. 4 The proportion of the low molecular weight component is 4.0% or less. Based on component (B) having this molecular weight distribution, the proportion of the low molecular weight component in the resin composition can be stably adjusted to 3% or less. Furthermore, from the viewpoint of reducing its proportion in the resin composition, the lower the proportion of the low molecular weight component contained in component (B), the better. There is no particular limitation on its lower limit, but for example, 0.001% is preferred.

[0078] The number-average molecular weight of the thermoplastic elastomer (B) is not particularly limited, but is preferably 5.0 × 10⁻⁶. 4 The above can also be 8.0×10 4 Above and 7.0×10 5 The following applies. Based on the number-average molecular weight of component (B), the proportion of low molecular weight components is small, which allows the proportion of low molecular weight components contained in the resin composition to be suppressed to a low level.

[0079] As the thermoplastic elastomer (B), any component that can improve the softness of the resin composition can be used, such as known components like amide-based, ester-based, olefin-based, styrene-based, polyurethane-based, polyvinyl chloride-based, and fluorine-based components. From the viewpoint of fine dispersion or compatibility when mixed with the acrylic resin (A), at least one of olefin-based and styrene-based components is preferred. From the viewpoint of further improving insulation, olefin-based components are preferred. Compared to styrene-based components, olefin-based components have higher compatibility with the acrylic resin (A), and it is easier to select substances with high melting points and high molecular weights, thus further improving insulation.

[0080] Olefin-based thermoplastic elastomers (so-called TPOs) are constructed comprising at least one olefin unit selected from polyethylene and polypropylene as a hard segment and ethylene-α-olefin copolymer units as soft segments. The olefin-based thermoplastic elastomer can be a copolymer type of olefin units and ethylene-α-olefin copolymer units, or a mixture type of olefin and ethylene-α-olefin copolymers. Among these, copolymers are preferred from the viewpoint of miscibility with component (A). The α-olefin is a straight-chain or branched α-olefin with 2 to 8 carbon atoms; for example, ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, etc., can be used. Preferably, the TPO has polypropylene as a hard segment and ethylene-propylene rubber as a soft segment. Furthermore, one type of olefin-based thermoplastic elastomer can be used alone, or two or more types can be used in combination.

[0081] Styrene-based thermoplastic elastomers are copolymers containing styrene units as hard segments and at least one monomer unit selected from ethylene, propylene, butene, and isoprene as soft segments.

[0082] Examples of styrene-based thermoplastic elastomers include styrene-butadiene-styrene block copolymers (SBS), hydrogenated styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene copolymers (SIS), hydrogenated styrene-isoprene-styrene copolymers, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, and styrene-ethylene-butene-olefin crystalline block copolymers. Two or more of these can also be used in combination.

[0083] Furthermore, the term "hydrogenation" here refers to the addition of hydrogen to the double bonds. For example, "hydrogenated styrene-butadiene-styrene block copolymer" refers to a polymer in which hydrogen has been added to the double bonds of a styrene-butadiene-styrene block copolymer. Additionally, the double bonds of the aromatic rings in styrene are not hydrogenated. "Hydrogenated styrene-butadiene-styrene block copolymer" can also be interpreted as styrene-ethylene-butene-styrene block copolymer (SEBS).

[0084] As a styrene-based thermoplastic elastomer, a substance whose chemical structure does not contain double bonds except for the benzene ring is preferred. When using a substance containing double bonds, the resin components may sometimes deteriorate due to heat during resin composition molding, which may reduce the properties of the resulting insulating layer. In this regard, substances without double bonds have high resistance to heat deterioration, and therefore the properties of the insulating layer can be maintained better.

[0085] The content of styrene units in styrene-based thermoplastic elastomers is not particularly limited, but from the viewpoint of controlling the crystal growth of propylene-based resin (A) and softening the insulating layer, it is preferably 5% by mass or more and 35% by mass or less. Furthermore, by keeping the content of styrene units within the above range, a specified amount of monomer units, such as ethylene units, can be ensured as soft segments, thus improving the compatibility between the styrene-based thermoplastic elastomer and component (A). This, in turn, allows for a stable improvement in the insulation properties of the insulating layer.

[0086] The melting points of olefin-based thermoplastic elastomers and styrene-based thermoplastic elastomers are not particularly limited. For example, the melting point of olefin-based thermoplastic elastomers is preferably 130°C or higher and 160°C or lower. Furthermore, for example, the melting point of styrene-based thermoplastic elastomers is preferably 110°C or higher and 130°C or lower. Depending on the composition having such melting points, the melting point of the resin composition is not excessively lowered, and the melting point can be easily adjusted to 110°C or higher and 170°C or lower.

[0087] From the viewpoint of compatibility with acrylic resin (A), the molecular weight ratio (MFR) of the thermoplastic elastomer (B) is preferably 0.1 g / 10 min or more and 5.0 g / 10 min or less, or it can be 0.1 g / 10 min or more and 2.0 g / 10 min or less. By employing such an MFR, the aforementioned phase structure can be stably formed in the resin composition.

[0088] From the viewpoint of fine dispersion or compatibility when the thermoplastic elastomer (B) is mixed with the acrylic resin (A), its molecular weight ratio (MFR) preferably deviates little from that of component (A). Specifically, it is preferred that the difference in MFR between component (A) and component (B) in the resin composition is 300 g / 10 min or less.

[0089] (Other additives)

[0090] The resin composition may contain other additives as needed. These other additives may include antioxidants, crosslinking agents, lubricants, and colorants.

[0091] As antioxidants, known antioxidants such as phenolic, sulfur-based, and amine-based antioxidants can be used. The content of the antioxidant is not particularly limited; for example, when the total content of acrylic resin (A) and thermoplastic elastomer (B) is set to 100 parts by weight, it is preferably 0.1 parts by weight or more and 1.0 parts by weight or less.

[0092] Furthermore, from a recycling perspective, it is preferable that the resin composition is not cross-linked, i.e., non-cross-linked, but a cross-linking agent may be included for cross-linking purposes. However, even if cross-linking is performed, it is preferable to cross-link in a manner that reduces the gel fraction (degree of cross-linking). Specifically, it is preferable to cross-link with a degree of cross-linking where the cross-linking agent residue in the resin composition is less than 300 ppm. In addition, when dicumyl peroxide is used as a cross-linking agent, the residue may be, for example, cumyl alcohol, α-methylstyrene, etc.

[0093] Furthermore, to improve the flowability of the resin composition during the extrusion process of the insulating layer, the resin composition may contain a lubricant. As a lubricant, conventionally known components such as fatty acid metal salts or fatty acid amides can be used, for example. These can be used alone or in combination of two or more.

[0094] Furthermore, the resin composition of this embodiment maintains high insulation properties by controlling the melting point and the ratio of low molecular weight components within a specified range, thus eliminating the need for inorganic fillers. As will be described later, inorganic fillers can cause screen clogging during the extrusion process of the resin composition, and the retained resin composition may be overheated, potentially promoting the formation of low molecular weight components. In this regard, by not adding inorganic fillers, the proportion of low molecular weight components can be adjusted to be low.

[0095] (Mix ratio)

[0096] The ratio of acrylic resin (A) to thermoplastic elastomer (B) in the resin composition is not particularly limited as long as it results in a melting point of 110°C or higher for the resin composition. It is preferable to adjust the content of each component according to the components (A) and (B) used. Specifically, when the total content of acrylic resin (A) and thermoplastic elastomer (B) is set to 100 parts by mass, it is preferable that the content of component (A) is 50 parts by mass or more and 90 parts by mass or less, and the content of component (B) is 10 parts by mass or more and 50 parts by mass or less. By using such contents, it is easy to adjust the melting point of the resin composition and the ratio of low molecular weight components to the above-mentioned range.

[0097] (2) Power cables

[0098] Next, use Figure 1 The power cable of this embodiment will be described. Figure 1 This is a cross-sectional view of the power cable involved in this embodiment, orthogonal to the axial direction.

[0099] The power cable 10 in this embodiment is configured as a so-called solid-insulated power cable. Furthermore, the power cable 10 in this embodiment is configured to be laid on land (in a conduit), in water, or underwater. Additionally, the power cable 10 is used for direct current (DC), for example.

[0100] Specifically, the power cable 10 has, for example, a conductor 110, an inner semiconducting layer 120, an insulation layer 130, an outer semiconducting layer 140, a shielding layer 150, and a sheath 160.

[0101] (Conductor (Conductive Part))

[0102] Conductor 110 is formed, for example, by twisting together multiple conductor cores (conductive cores) containing pure copper, copper alloy, aluminum or aluminum alloy.

[0103] (Internal semiconductive layer)

[0104] An internal semiconductive layer 120 is configured to cover the outer periphery of the conductor 110. Furthermore, the internal semiconductive layer 120 is semiconductive, configured to suppress electric field concentration on the surface side of the conductor 110. The internal semiconductive layer 120 may contain at least one of, for example, ethylene-based copolymers such as ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-vinyl acetate copolymer, thermoplastic elastomers, and the aforementioned low-crystallinity resins, and may also contain conductive carbon black.

[0105] (Insulating layer)

[0106] The insulating layer 130 is configured to cover the outer periphery of the inner semiconductive layer 120 and is formed from the aforementioned resin composition. For example, the insulating layer 130 is formed by extruding the resin composition.

[0107] (Outer semiconductive layer)

[0108] The outer semiconductive layer 140 is configured to cover the outer periphery of the insulating layer 130. Furthermore, the outer semiconductive layer 140 is semiconductive and configured to suppress electric field concentration between the insulating layer 130 and the shielding layer 150. The outer semiconductive layer 140 is, for example, made of the same material as the inner semiconductive layer 120.

[0109] (Shielding layer)

[0110] The shielding layer 150 is configured to cover the outer periphery of the outer semiconductive layer 140. The shielding layer 150 is formed, for example, by winding copper tape, or by forming a wire shield with multiple soft copper wires wound around it. Alternatively, a tape made of adhesive tape or the like can be wound around the inner and outer sides of the shielding layer 150.

[0111] (jacket)

[0112] The sheath 160 is configured to cover the outer periphery of the shielding layer 150. The sheath 160 is made of, for example, polyvinyl chloride or polyethylene.

[0113] In addition, if the power cable 10 of this embodiment is an underwater cable or a submarine cable, it may have a metal water-blocking layer such as an aluminum cladding layer or wire armor at a position further outward than the shielding layer 150.

[0114] On the other hand, the power cable 10 of this embodiment may, for example, not have a water-blocking layer at a position further outward than the shielding layer 150. That is, the power cable 10 of this embodiment may also be constructed with a non-completely water-blocking structure.

[0115] (Specific dimensions, etc.)

[0116] 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 insulation 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 DC voltage applied to the power cable 10 of this embodiment is, for example, 20 kV or more.

[0117] (3) Various characteristics of cables

[0118] In this embodiment, as described above, the resin composition contains an acrylic resin (A) and a thermoplastic elastomer (B), and the melting point of the resin composition and the proportion of low molecular weight components in the molecular weight distribution meet the specified requirements, thereby enabling high insulation to be stably obtained in the insulating layer 130.

[0119] Specifically, the insulating layer 130 of this embodiment, for example, meets the following insulation performance requirements measured under high temperature and high electric field conditions. Furthermore, this measurement is performed, for example, using a sheet sampled from the center portion of the insulating layer 130 in the thickness direction. The thickness of the insulating layer 130 sheet at this time is, for example, 0.2 mm.

[0120] Regarding the insulating layer 130, the space charge accumulation measured under conditions of 90°C and a DC electric field of 40 kV / mm is preferably 100% or less, and may also be 25% or less. Furthermore, the space charge accumulation measured under conditions of 90°C and a DC electric field of 80 kV / mm is preferably 100% or less, and may also be 40% or less.

[0121] The amount of space charge accumulated is determined using the current-integrated charge method. In this method, charge is accumulated in a measuring capacitor connected in series with the sheet material serving as the sample, and the amount of charge is evaluated as the integral value of the current. Specifically, a DC electric field of 40 kV / mm or 80 kV / mm is continuously applied to the sample at a temperature of 90°C, and the amount of charge Q after 300 seconds is calculated.300 The amount of space charge accumulated is calculated using the following formula, based on the charge Q0 immediately after application (0 seconds).

[0122]

[0123] Furthermore, the volume resistivity of the insulating layer 130 sheet, measured at a temperature of 90°C and a DC electric field of 40 kV / mm or at a temperature of 90°C and a DC electric field of 80 kV / mm, is preferably, for example, 5.0 × 10⁻⁶. 14 Ω·cm and above, can also be 1.0×10 15 Ω·cm or higher.

[0124] Furthermore, the DC breakdown electric field strength of the insulating layer 130 sheet, measured at a temperature of 90°C, is preferably 160 kV / mm or higher, or may be 200 kV / mm or higher.

[0125] (4) Extruder

[0126] Next, before describing the manufacturing method of the power cable according to this embodiment, using Figure 2 An extruder used for manufacturing power cables is described. Figure 2 This is a schematic diagram of the extruder used in a method for manufacturing a power cable according to one embodiment of the present disclosure.

[0127] The extruder 200 is an apparatus for preparing the above-mentioned resin composition. In the extruder 200, the resin composition is prepared by mixing the components while heating. During this process, the resin components sometimes undergo thermal decomposition and decrease in molecular weight due to heating. For example, when heating and mixing are performed in an oxygen-containing atmosphere, the resin components may sometimes undergo thermal decomposition. Furthermore, for example, if the resin components remain in the extruder 200 and the heating time is prolonged, the resin components may sometimes undergo thermal decomposition. Therefore, in the resin composition, the proportion of low molecular weight components may sometimes be higher than the original value of the contained components.

[0128] In this embodiment, from the viewpoint of adjusting the proportion of low molecular weight components in the resin composition to a predetermined range, it is preferable to configure the extruder 200 such that the resin composition is extruded while the extruder is conditioned to an inactive gas atmosphere, or to configure the screw and outlet of the extruder such that the resin composition is not easily retained. The specific configuration of the extruder 200 will be described below.

[0129] like Figure 2 As shown, the extruder 200 is configured to include: a cylindrical barrel 210 for supplying resin composition material, a hopper 220 for supplying material into the barrel 210, and a first direction from the barrel 210 ( Figure 2A screw 230, which is freely inserted and rotatably configured on the left side of the cylinder 210, a rotary drive mechanism 240 that rotates the screw 230, and a second direction mounted on the cylinder 210 (in the left direction) Figure 2 The barrel 210 (on the right side) is provided with a discharge section 250 for discharging the resin composition through a hole, and an atmosphere conditioning section 260 for adjusting the atmosphere inside the barrel 210 to an inactive gas atmosphere. Furthermore, the first direction will be referred to as the upstream side of the heating and mixing of the resin composition, and the second direction will be referred to as the downstream side of the heating and mixing of the resin composition.

[0130] A cylindrical barrel 210 has an internal space for containing and mixing materials. Within the cylindrical barrel 210, materials supplied to its internal space are mixed by a screw 230. The screw 230 is inserted from one end of the barrel 210 in a first direction and is positioned at the axial center of the barrel 210. The screw 230 is connected to a rotary drive mechanism 240 and is rotatably supported. The screw 230 rotates via the rotary drive mechanism 240, configured to extrude materials towards a discharge section 250 while mixing them. The screw 230 can be single-shaft or dual-shaft. Figure 2 In the diagram, two screws 230 are arranged parallel to each other in the longitudinal direction of the paper, with one screw 230 shown. Furthermore, the rotary drive mechanism 240 can be, for example, a known rotary motor.

[0131] In the screw 230, the screw thread 232 is spirally arranged on the surface of the screw body 231. The cross-sectional shape of the screw thread 232 is not particularly limited, such as... Figure 3 As shown, it is preferably conical in shape. Figure 3 It is a schematic diagram used to illustrate the shape of the screw thread, and is a cross-sectional view along the axial direction of the screw 230. Figure 3 In the diagram, the right side represents the front end direction of the screw 230 (the second direction of the barrel 210), and the left side represents the rear end direction of the screw 230 (the first direction of the barrel 210). When the screw thread 232 has the following characteristics... Figure 3 When the shape is rectangular as shown by the dashed line, the resin composition tends to remain on the end side of the screw thread 232, and the retained resin composition may sometimes undergo thermal decomposition. Therefore, from the viewpoint of suppressing the retention of resin composition on the surface of the screw 230, the cross-sectional shape of the screw thread 232 is preferably as shown in the figure. Figure 3 As shown, the end side has a tapered shape. In other words, it is preferable that the angle between the side of the screw thread 232 in the first direction and the surface of the screw body 231 is an obtuse angle. For example, the angle is preferably 120° to 145°.

[0132] The discharge section 250 is disposed at the end of the barrel 210 in a second direction. The discharge section 250, for example, has a plurality of holes extending through in the thickness direction, configured to extrude the resin composition prepared by mixing inside the barrel 210 to the outside. A perforated plate can be used as the discharge section 250, for example. Additionally, a screen or the like can be disposed between the barrel 210 and the discharge section 250 to remove foreign matter contained in the resin composition.

[0133] In addition, such as Figure 4 As shown, a retention suppression member 270 can be disposed at the end of the material cylinder 210 in the second direction, at the position where it connects with the discharge part 250. Figure 4 This is a schematic diagram illustrating the retention suppression component, and is a cross-sectional view of the end of the barrel 210 in the second direction. (Example) Figure 4 As shown, the retention suppression member 270 is used to suppress the retention of the resin composition within the barrel 210, facilitating its extrusion from the discharge section 250. The retention suppression member 270 has a plurality of tapered orifices 271 extending through the thickness direction and decreasing in diameter towards the thickness direction. The retention suppression member 270 is configured such that the smaller diameter side of the tapered orifices 271 communicates with the orifices 251 of the discharge section 250. According to the retention suppression member 270, the retention of the resin composition at the edges of the orifices 251 of the discharge section 250, the inner wall of the barrel 210, and the corners of the discharge section 250 can be suppressed. The retention suppression member 270 is preferably made of the same material as the perforated plate, for example.

[0134] An atmosphere regulating unit 260 is connected to the barrel 210 to regulate its interior to an inert gas atmosphere. The atmosphere regulating unit 260 is configured to supply an inert gas into the interior of the barrel 210. During the supply of material from the hopper 220, air may sometimes mix into the interior of the barrel 210, but the atmosphere regulating unit 260 can regulate the interior of the barrel 210 to an inert gas atmosphere. This prevents the mixed material and the resulting resin composition from oxidizing and thermally decomposing due to air. In other words, in the resin composition, it is possible to maintain a high proportion of high molecular weight components while suppressing an increase in the proportion of low molecular weight components.

[0135] As an inactive gas, there are no particular limitations; for example, nitrogen or argon are preferred.

[0136] Alternatively, the extruder 200 may also have a heating element (not shown) for heating the interior of the barrel 210. Conventionally known heating elements can be used as the heating element.

[0137] (5) Manufacturing method of power cables

[0138] Next, use Figure 5 The manufacturing method of the power cable according to this embodiment will be described. Figure 5This is a flowchart illustrating a method for manufacturing a power cable according to one embodiment of the present disclosure. Hereinafter, the steps will be abbreviated as "S".

[0139] (S100: Resin composition preparation process)

[0140] First, a resin composition for forming the insulating layer 130 is prepared.

[0141] In this embodiment, for example, an propylene resin (A), a thermoplastic elastomer (B), and other additives (antioxidants, etc.) added as needed are supplied to... Figure 2 The extruder 200 is shown. Then, the materials supplied from the hopper 220 are mixed while being heated inside the barrel 210. At this time, the interior of the barrel 210 is conditioned to a non-reactive gas atmosphere via the atmosphere conditioning unit 260. Then, the resin composition obtained by heating and mixing is extruded from the discharge unit 250 and granulated. Thus, a granular resin composition constituting the insulating layer 130 is obtained.

[0142] The content of each component is preferably adjusted appropriately so that the melting point of the resin composition is 110°C or higher and the proportion of low molecular weight components is 3% or less. For example, it is preferred that the acrylic resin (A) is 50 parts by mass or more and 90 parts by mass or less, and the thermoplastic elastomer (B) is 10 parts by mass or more and 50 parts by mass or less.

[0143] In the resin composition preparation step S100, by heating and mixing the components under an inactive gas atmosphere and then extruding, the low molecular weight reduction that accompanies the heating of the resin composition can be suppressed, and its proportion can be reduced.

[0144] (S200: Conductor preparation process)

[0145] On the other hand, a conductor 110 is prepared to be formed by twisting together multiple conductor cores.

[0146] (S300: Cable core forming process (extrusion process, insulation layer forming process))

[0147] Once the resin composition preparation step S100 and the conductor preparation step S200 are completed, the above-mentioned resin composition is used to form an insulating layer 130 by covering the outer periphery of the conductor 110 with a thickness of, for example, 3 mm or more.

[0148] In this embodiment, for example, a three-layer co-extruder is used to simultaneously form an inner semiconductive layer 120, an insulating layer 130, and an outer semiconductive layer 140.

[0149] Specifically, a composition for forming the internal semi-conductive layer, for example, is fed into extruder A, which forms the internal semi-conductive layer 120, in a three-layer co-extruder. The aforementioned particulate resin composition is fed into extruder B, which forms the insulating layer 130. Figure 2 The extruder 200 is shown. At this time, the interior of the barrel 210 of the extruder 200 is adjusted to a non-reactive gas atmosphere. Furthermore, the set temperature of the extruder B is set, for example, to a temperature 10°C or higher than the desired melting point and 80°C or lower. It is preferable to appropriately adjust the set temperature based on the linear speed and extrusion pressure. An external semi-conductive layer composition containing the same material as the resin composition for the internal semi-conductive layer fed into the extruder C that forms the external semi-conductive layer 140 is fed into the extruder C.

[0150] Next, the extrudates from extruders A through C are guided to a common die head, where an inner semiconductive layer 120, an insulating layer 130, and an outer semiconductive layer 140 are simultaneously extruded from the inside to the outside around the conductor 110. This forms the extruded material that becomes the cable core.

[0151] Then, for example, the material is extruded by cooling with water.

[0152] In the cable core forming process S300, by heating the particulate resin composition while mixing and extruding it under an inactive gas atmosphere, the increase in the proportion of low molecular weight components due to heating can be suppressed. As a result, the proportion of low molecular weight components in the insulation layer 130 can be kept low.

[0153] Through the above cable core forming process S300, a cable core consisting of conductor 110, inner semiconductive layer 120, insulation layer 130 and outer semiconductive layer 140 is formed.

[0154] (S400: Shielding layer formation process)

[0155] Once the cable core is formed, a shielding layer 150 is formed outside the outer semiconductive layer 140, for example, by winding copper tape.

[0156] (S500: Sheath Forming Process)

[0157] Once the shielding layer 150 is formed, a sheath 160 is formed on the outer periphery of the shielding layer 150 by feeding polyvinyl chloride into an extruder and extruding it.

[0158] Through the above processes, a power cable 10, which is a solid insulated power cable, is manufactured.

[0159] (6) Effects of this implementation method

[0160] According to this embodiment, one or more of the effects shown below are achieved.

[0161] (a) The resin composition of this embodiment contains an propylene-based resin (A) having propylene units and a thermoplastic elastomer (B). The melting point of the resin composition is 110°C or higher, and the molecular weight of the resin composition is 1 × 10⁻⁶ when the molecular weight distribution of the resin composition is measured. 4 The proportion of the following low molecular weight components is 3% or less. The resin composition sometimes contains low molecular weight components derived from component (B), which may become amorphous or melt at high temperatures. The molten low molecular weight components move within the resin composition, causing the accumulation of space charge, which acts as charge carriers and may reduce insulation. In this regard, by raising the melting point of the resin composition to 110°C or higher, the melting of the resin components and the resulting flow can be suppressed, allowing them to be immobilized within the resin composition. That is, the low molecular weight components can be maintained in a finely dispersed or compatible state within the resin composition. Furthermore, by reducing the proportion of low molecular weight components in the resin composition, the resulting reduction in insulation can be further suppressed. As a result, the resin composition can maintain high insulation even at high temperatures. Therefore, by forming the insulation layer 130 with the above-described resin composition, the insulation layer 130 can withstand high voltage even at high temperatures. As a result, the power cable 10 of this embodiment can perform stable DC power transmission.

[0162] (b) In the resin composition, the thermoplastic elastomer (B) can be finely dispersed in the acrylic resin (A), or they can be made compatible. That is, component (B) can be uniformly distributed in the resin composition. As a result, the excessive crystallization growth of component (A) can be suppressed by component (B), and the resin composition can be endowed with softness. That is, the resin composition can exhibit softness to a higher degree and with greater stability.

[0163] (c) The thermoplastic elastomer (B) is preferably at least one of an olefin-based thermoplastic elastomer and a styrene-based thermoplastic elastomer. According to the olefin-based thermoplastic elastomer, it can be finely dispersed in or compatible with the propylene-based resin (A), and since it has a higher melting point than the styrene-based thermoplastic elastomer, the aforementioned effects (a) can be obtained more reliably. On the other hand, according to the styrene-based thermoplastic elastomer, since it can trap electrons through the aromatic ring to form a stable resonant structure, the insulation properties of the resin composition can be further improved.

[0164] (d) The melting point of the thermoplastic elastomer (B) is preferably 110°C or higher and 160°C or lower. Based on this (B) component, when preparing a resin composition by mixing it with an acrylic resin (A), the melting point of the resin composition can be adjusted to 110°C or higher without excessively lowering it. Therefore, the aforementioned effect (a) can be obtained more reliably.

[0165] (e) The thermoplastic elastomer (B) preferably has a molecular weight of 1×10⁻⁶. 4 The proportion of the following components is 4.0% or less. Based on this component (B), when preparing the resin composition, the proportion of low molecular weight components can be more reliably adjusted to 3% or less. As a result, the aforementioned effect (a) can be obtained more reliably.

[0166] (f) The melting point of the acrylic resin is preferably 130°C or higher and 170°C or lower. According to this (A) composition, when mixed with the thermoplastic elastomer (B), the flexibility required for power cables can be achieved while maintaining the melting point of the resin composition above 110°C.

[0167] (g) For the resin composition, when the total content of acrylic resin (A) and thermoplastic elastomer (B) is set to 100 parts by mass, it is preferable to contain 50 parts by mass and 90 parts by mass of component (A) and 10 parts by mass and 50 parts by mass of component (B). By using such proportions, the melting point of the resin composition can be more reliably adjusted to 110°C or higher, and the proportion of low molecular weight components in the resin composition can be adjusted to 3% or lower, thus more reliably obtaining the aforementioned effect (a).

[0168] (h) The number average molecular weight of the thermoplastic elastomer (B) is preferably 8.0 × 10⁻⁶. 4 The above. Based on this component (B), since the proportion of low molecular weight components is low, the proportion of low molecular weight components in the resin composition can be reduced when it is mixed with acrylic resin (A) to prepare the resin composition. As a result, the above-mentioned effect (a) can be obtained more reliably.

[0169] (i) The resin composition may substantially be free of modified polymers and inorganic fillers used to improve insulation. Since the resin composition is formed with a melting point and low molecular weight components within a specified range, high insulation can be achieved even without modified polymers and inorganic fillers. Furthermore, when the resin composition contains inorganic fillers, it is prone to clogging the screen during extrusion from the extruder 200, and the resin composition tends to remain within the extruder 200. In this regard, by being free of inorganic fillers, the retention of the resin composition and the accompanying decrease in molecular weight can be more reliably suppressed. In addition, modified polymers tend to deteriorate easily due to heat, but by being free of modified polymers, the deterioration of the resin composition during the manufacture of power cables can be suppressed for extended periods. Thus, for example, when manufacturing long-length power cables, the heat deterioration of the resin composition can be suppressed, the characteristic deviation in the length direction of the insulation layer can be reduced, and the characteristics can be maintained at a high level.

[0170] (j) In preparing the resin composition, it is preferable to supply the acrylic resin (A), the thermoplastic elastomer (B), and other additives as needed to the barrel 210 of the extruder 200 and heat-mix them under an inert gas atmosphere. Alternatively, it is preferable to configure the screw ribs 232 of the screw 230 in the extruder 200 to be tapered in the first direction. Alternatively, it is preferable to provide a retention-inhibiting member 270 having a plurality of tapered holes 271 extending in the thickness direction and decreasing in diameter from the first direction to the second direction between the barrel 210 and the discharge section 250 of the extruder 200. According to at least one of these configurations, it is possible to suppress the thermal decomposition of the resin components and reduce their molecular weight during the preparation of the resin composition. As a result, it is possible to more reliably adjust the proportion of low molecular weight components in the resin composition to 3% or less, and the above-mentioned effect (a) can be obtained.

[0171] <Other embodiments of this disclosure>

[0172] The embodiments of this disclosure have been described in detail above, but this disclosure is not limited to the above embodiments and various changes can be made without departing from its spirit.

[0173] In the above embodiments, the case where the power cable 10 may not have a water-blocking layer has been described, but this disclosure is not limited to this case. The power cable 10 may also have a simple water-blocking layer. Specifically, the simple water-blocking layer is, for example, made of a metal laminate. The metal laminate has, for example, a metal layer made of aluminum or copper and an adhesive layer disposed on one or both sides of the metal layer. The metal laminate is, for example, wound longitudinally around the outer periphery of the cable core (outer periphery than the outer semiconductive layer). In addition, this water-blocking layer may be disposed at a position further outward than the shielding layer, or it may also serve as a shielding layer. With this configuration, the cost of the power cable 10 can be reduced.

[0174] In the above embodiments, the power cable 10 has been described as being laid on land, in water, or underwater, but this disclosure is not limited to this. For example, the power cable 10 may also be configured as a so-called overhead wire (overhead insulated wire).

[0175] In the above embodiment, three-layer co-extrusion is performed in the cable core forming process S300, but it can also be extruded layer by layer.

[0176] Example

[0177] Next, embodiments related to this disclosure will be described. These embodiments are examples of this disclosure, and this disclosure is not limited to these embodiments.

[0178] (1) Regarding materials

[0179] The materials used to prepare the resin composition are listed below.

[0180] As the propylene-based resin (A), a propylene random polymer (PP1) was prepared; and as the thermoplastic elastomer (B), olefin-based elastomers (TPO1) to (TPO2) and styrene-based thermoplastic elastomers (SEBS1) to (SEBS2) were prepared. The physical properties of each component are described below. Furthermore, the melting point, number-average molecular weight, MFR, and the proportion of low molecular weight components were determined beforehand using methods described later.

[0181] PP1: Melting point 160℃, number average molecular weight 1.5×10⁻⁶ 5 MFR 0.6g / 10min

[0182] • TPO1: An olefin-based thermoplastic elastomer with polypropylene as the hard segment and ethylene-propylene rubber as the soft segment, melting point 135℃, low molecular weight component proportion 5.1%, number average molecular weight 9.0×10⁻⁶ 4 MFR 4.7g / 10min

[0183] • TPO2: An olefin-based thermoplastic elastomer with polypropylene as the hard segment and ethylene-propylene rubber as the soft segment; melting point 140℃; low molecular weight component proportion 1.5%; number average molecular weight 1.6 × 10⁻⁶. 5 MFR 3.2g / 10min

[0184] SEBS1: Melting point 115℃, low molecular weight component ratio 5.4%, number average molecular weight 1.2×10⁻⁶ 5 MFR 4.5g / 10min, styrene content 10% by mass

[0185] SEBS2: Melting point 120℃, low molecular weight component ratio 2.0%, number average molecular weight 1.5×10 5 MFR 3.7g / 10min, styrene content 12% by mass

[0186] In addition, hindered phenolic pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] was prepared as an antioxidant as another additive.

[0187] (2) Preparation of resin composition

[0188] The materials described above were fed into an extruder in the amounts shown in Table 1 below, and were heated, mixed, and granulated in the extruder to produce Samples 1 to 5. The extrusion conditions were modified as follows when preparing the resin compositions. In Samples 1 to 4, the extruder described above was used, the barrel was purged with nitrogen, and a screw with a tapered shape on the first direction side of the screw thread was used for extrusion. In Sample 5, the barrel was not purged with nitrogen, and a rectangular screw was used for extrusion. Furthermore, the amount of antioxidant in each sample was set to 0.1 parts by weight.

[0189] Table 1

[0190]

[0191] (3) Fabrication of power cables

[0192] Next, a conductor was prepared by twisting together conductor cores made of a thin copper alloy with a diameter of 14 mm. Once the conductor was prepared, an inner semiconductive layer resin composition containing an ethylene-ethyl acrylate copolymer, an insulation layer resin composition prepared in Table 1, and an outer semiconductive layer resin composition made of the same material as the inner semiconductive layer resin composition were fed into extruders A to C, respectively. The extrudates from extruders A to C were guided to a common die head, and the inner semiconductive layer, insulation layer, and outer semiconductive layer were simultaneously extruded from the inside to the outside of the conductor. Thus, a sample of a power cable having a conductor, an inner semiconductive layer, an insulation layer, and an outer semiconductive layer from the center outwards was produced.

[0193] (4) Evaluation

[0194] The melting point, proportion of low molecular weight components, space charge properties, volume resistivity, and DC breakdown strength of the prepared resin compositions and samples cut from the insulation layer of the manufactured power cables were evaluated. The evaluation methods are described below.

[0195] (Melting point)

[0196] The melting point of the resin compositions prepared for each sample was determined by DSC. The DSC determination was performed according to JIS-K-7121 (1987). Specifically, a PerkinElmer DSC8500 (power-compensated type) was used as the DSC apparatus. The reference sample was, for example, α-alumina. The mass of the test sample was 8–10 g. In the DSC apparatus, the temperature was increased from room temperature (27°C) to 220°C at a rate of 10°C / min. The DSC curve was obtained by plotting the heat endothermic per unit time relative to the temperature (heat flux). The temperature at which the heat endothermic per unit time of each test sample reached its maximum value (peak) was then defined as the "melting point".

[0197] (Molecular weight distribution)

[0198] The molecular weight distribution of the resin composition forming the insulating layer was determined by GPC under the following conditions, based on a calibration curve prepared using PS as a standard sample, to determine the number-average molecular weight of the base resin. In this embodiment, based on the obtained molecular weight distribution, a molecular weight of 1 × 10⁻⁶ was calculated. 4 The following region's area is used as a ratio to the total area of ​​the entire molecular weight distribution to calculate the molecular weight of 1×10. 4 The following are the proportions of low molecular weight components.

[0199] Device: Tosoh HLC-8321GPC / HT

[0200] Eluent: 1,2,4-trichlorobenzene

[0201] Temperature: 140℃

[0202] Concentration: 1.0 mg / mL

[0203] Flow rate: 1.0 mL / min

[0204] In addition, the PS calibration curve is based on results for molecular weights above 1000 and below 5.5 million.

[0205] (Space charge properties)

[0206] The space charge characteristics of the insulation layer were evaluated by the amount of space charge accumulated in the insulation layer. The amount of space charge accumulated was determined by the current-integrated charge method. Specifically, firstly, a sheet-like sample was collected from the insulation layer of a power cable. Then, the sample was connected in series with a measuring capacitor, and the charge was accumulated in the measuring capacitor. The amount of charge was measured as the integral value of the current. In this embodiment, a DC electric field of 40 kV / mm or 80 kV / mm was continuously applied to the sample at a temperature of 90°C, and the amount of charge Q after 300 seconds was measured. 300The space charge accumulation at 90°C and 40 kV / mm DC electric field, and the space charge accumulation at 90°C and 80 kV / mm DC electric field, were calculated using the following formula, based on the initial charge Q0 immediately after application (0 seconds). In this embodiment, the case where the space charge accumulation at 90°C and 40 kV / mm DC electric field is less than 25% was designated as A (best), the case where the space charge accumulation exceeds 25% but is less than 100% was designated as B (good), and the case where the space charge accumulation exceeds 100% was designated as C (poor). Furthermore, the case where the space charge accumulation at 90°C and 80 kV / mm DC electric field is less than 40% was designated as A (best), the case where the space charge accumulation exceeds 40% but is less than 100% was designated as B (good), and the case where the space charge accumulation exceeds 100% was designated as C (poor).

[0207]

[0208] (Volume resistivity)

[0209] The volume resistivity of the insulation layer was measured using sheet-like samples taken from the insulation layer of power cables, similar to the space charge characteristics. Specifically, the sample was immersed in silicone oil at 90°C, and a DC electric field of 40 kV / mm or 80 kV / mm was applied to the sample using a 25 mm diameter flat electrode. The volume resistivity was then measured. This volume resistivity was set at 1 × 10⁻⁶. 15 For values ​​above Ω·cm, let's define A (optimal), with a volume resistivity of 5 × 10⁻⁶. 14 Ω·cm or higher and less than 1×10 15 The case with Ω·cm is designated as B (good), and the volume resistivity is less than 5×10. 14 The Ω·cm value was set as C (poor) and evaluated.

[0210] (DC breakdown strength)

[0211] The DC breakdown strength of the insulation layer was measured using sheet-like specimens collected from the insulation layer of power cables, similar to the space charge characteristics. Specifically, the specimen was first immersed in silicone oil at 90°C, and a 25mm diameter flat electrode was used to increase the applied voltage at a rate of 4 kV / min. Then, when the specimen reached insulation breakdown, the DC breakdown strength was determined by dividing the applied voltage by the thickness of the specimen. Cases with a DC breakdown strength of 200 kV / mm or higher were designated A (best), those with a DC breakdown strength of 160 kV / mm or higher but less than 200 kV / mm were designated B (good), and those with a DC breakdown strength less than 160 kV / mm were designated C (poor).

[0212] (5) Evaluation Results

[0213] The above evaluation was performed on each sample, and the evaluation results are summarized in Table 1.

[0214] As shown in Table 1, although samples 1 and 2 have high melting points, the use of TPO1 and SEBS1, which have a high proportion of low molecular weight components, resulted in a failure to maintain the proportion of low molecular weight components below 3%, despite achieving a melting point above 110°C. Consequently, insulation performance decreased at high temperatures. It is presumed that the high proportion of low molecular weight components in these samples causes them to melt and flow within the resin composition at high temperatures, leading to localized charge accumulation. Furthermore, in particular, sample 2, compared to sample 1, is presumably due to the lower melting point of the resin composition, making it easier for the low molecular weight components to melt, further reducing insulation performance.

[0215] On the other hand, in Samples 3 and 4, due to the use of TPO2 and SEBS2, which have high melting points and low proportions of low molecular weight components, it was confirmed that the resin composition could achieve a melting point of 110°C or higher and a low molecular weight component proportion of 3% or less. In particular, in Sample 3, by using TPO2, which has a higher melting point than SEBS2, the melting point of the resin composition was increased, resulting in further improvement in insulation performance at high temperatures. This is presumably because it further suppresses the melting of the resin components in the resin composition at high temperatures, maintaining the dispersion and compatibility of the low molecular weight components.

[0216] Furthermore, although the same materials as Sample 3 were used in Sample 5, the proportion of low molecular weight components was found to be higher than in Sample 3. As a result, the insulation performance at high temperatures was found to be lower than that of Sample 3. The reason for the higher proportion of low molecular weight components in Sample 5 is presumably because, in Sample 5, nitrogen purging and a conical screw were not used in the extruder used for heating and mixing the materials. Therefore, the resin composition was more likely to remain inside the extruder, and the resin composition decreased in molecular weight due to thermal decomposition. It is also presumed that the low molecular weight components melt and flow at high temperatures, causing localized charge accumulation and reducing insulation performance.

[0217] As described above, it has been confirmed that by using an propylene-based resin (A) having propylene units and a thermoplastic elastomer (B) in the resin composition, and by ensuring that the melting point and the proportion of low molecular weight components in the resin composition meet the specified requirements, it is possible to suppress the accumulation of space charge and improve volume resistivity and DC breakdown electric field strength even under high-temperature environments. In other words, it has been confirmed that high insulation can be stably obtained in the resin composition. Therefore, even under high-temperature environments, the insulation layer can withstand high voltage, enabling stable DC power transmission through power cables.

[0218] <Preferred methods of this disclosure>

[0219] The following are preferred embodiments disclosed in this appendix.

[0220] (Postscript 1)

[0221] A resin composition comprising an propylene-based resin (A) having propylene units and a thermoplastic elastomer (B),

[0222] The melting point of the above resin composition is above 110°C.

[0223] When determining the molecular weight distribution of the above resin composition, the molecular weight of the above resin composition was 1 × 10⁻⁶. 4 The following ingredients account for less than 3%.

[0224] (Postscript 2)

[0225] A power cable having:

[0226] conductors, and

[0227] An insulating layer formed of a resin composition is wrapped around the aforementioned conductor.

[0228] The above resin composition contains an propylene resin (A) having propylene units and a thermoplastic elastomer (B).

[0229] The melting point of the above resin composition is above 110°C.

[0230] When determining the molecular weight distribution of the above resin composition, the molecular weight of the above resin composition was 1 × 10⁻⁶. 4 The following ingredients account for less than 3%.

[0231] (Note 3)

[0232] According to Appendix 2, the power cable, wherein, preferably,

[0233] The above-mentioned thermoplastic elastomer (B) is at least one of an olefin-based thermoplastic elastomer having an olefin unit and a styrene-based thermoplastic elastomer having a styrene unit.

[0234] (Note 4)

[0235] According to the power cable described in Appendix 3, wherein, preferably,

[0236] The above-mentioned thermoplastic elastomer (B) is an olefin-based thermoplastic elastomer having olefin units.

[0237] (Note 5)

[0238] The power cable according to any one of Appendices 2 to 4, wherein, preferably,

[0239] The above-mentioned thermoplastic elastomer (B) has a melting point of 110°C or higher and 160°C or lower.

[0240] (Note 6)

[0241] The power cable according to any one of Appendices 2 to 5, wherein, preferably,

[0242] The molecular weight of the thermoplastic elastomer (B) mentioned above is 1×10⁻⁶. 4 The following ingredients account for less than 4.0%.

[0243] (Note 7)

[0244] The power cable according to any one of Appendices 2 to 6, wherein, preferably,

[0245] The aforementioned propylene resin (A) is a random polymer of propylene.

[0246] (Postscript 8)

[0247] The power cable according to any one of Appendices 2 to 7, wherein, preferably,

[0248] The melting point of the aforementioned acrylic resin (A) is above 130°C and below 170°C.

[0249] (Note 9)

[0250] The power cable according to any one of Annexes 2 to 8, wherein, preferably,

[0251] The resin composition described above contains 50 parts by weight and 90 parts by weight of the aforementioned acrylic resin (A) and 10 parts by weight and 50 parts by weight of the aforementioned thermoplastic elastomer (B).

[0252] (Postscript 10)

[0253] The power cable according to any one of Appendices 2 to 9, wherein, preferably,

[0254] The number-average molecular weight of the above-mentioned thermoplastic elastomer (B) is 5.0 × 10⁻⁶.4 above.

[0255] (Postscript 11)

[0256] The power cable according to any one of Appendices 2 to 10, wherein, preferably,

[0257] The number-average molecular weight of the aforementioned acrylic resin (A) is 5.0 × 10⁻⁶. 4 above.

[0258] (Postscript 12)

[0259] A method for manufacturing a power cable, the power cable having a conductor and an insulation layer formed of a resin composition covering the conductor, the method comprising:

[0260] The preparation steps for the above resin composition, and

[0261] An insulation layer forming process involves extruding the above-mentioned resin composition to cover the periphery of the above-mentioned conductor, thereby forming the above-mentioned insulating layer.

[0262] In the above preparation process, an propylene-based resin (A) having propylene units and a thermoplastic elastomer (B) are added, such that the melting point of the resin composition is 110°C or higher, and the mixture is heated and mixed so that when the molecular weight distribution of the resin composition is measured, the molecular weight is 1×10⁻⁶. 4 The following ingredients account for less than 3%.

[0263] (Postscript 13)

[0264] According to the method for manufacturing power cables described in Appendix 12, wherein, preferably,

[0265] In the above preparation process, heating and mixing are carried out under an inactive gas atmosphere.

[0266] (Postscript 14)

[0267] According to the method for manufacturing power cables described in Appendix 12 or 13, wherein, preferably,

[0268] In the above preparation process, an extruder is used to prepare the above resin composition. The extruder has a cylindrical barrel, a screw that is inserted into and rotatably disposed from a first direction of the barrel, a discharge section that is installed in a second direction of the barrel and has a discharge port for discharging the above resin composition, and an atmosphere conditioning section for adjusting the atmosphere inside the barrel to an inactive gas atmosphere.

[0269] (Postscript 15)

[0270] According to the method for manufacturing power cables described in Appendix 14, wherein, preferably,

[0271] The aforementioned screw has a screw body portion and screw threads arranged in a helical shape on the surface of the screw body portion.

[0272] The aforementioned screw thread is configured such that the side surface of the first direction side is tapered.

[0273] Explanation of reference numerals in the attached figures

[0274] 10: Power cables;

[0275] 110: Conductor;

[0276] 120: Internal semiconductive layer;

[0277] 130: Insulation layer;

[0278] 140: External semiconductive layer;

[0279] 150: Shielding layer;

[0280] 160: Sheath;

[0281] 200: Extruder;

[0282] 210: Material cylinder;

[0283] 220: Hopper;

[0284] 230: Screw;

[0285] 231: Screw body section;

[0286] 232: Screw thread;

[0287] 240: Rotary drive mechanism;

[0288] 250: Discharge section;

[0289] 251: Hole section;

[0290] 260: Atmosphere Control Department;

[0291] 270: Retention and suppression component;

[0292] 271: Tapered hole.

Claims

1. A resin composition comprising an propylene-based resin (A) having propylene units and a thermoplastic elastomer (B), The resin composition has a melting point of 110°C or higher. When determining the molecular weight distribution of the resin composition, the molecular weight of the resin composition was 1 × 10⁻⁶. 4 The following ingredients account for less than 3%.

2. A power cable, comprising: conductors, and An insulating layer formed of a resin composition is wrapped around the conductor. The resin composition contains an propylene resin (A) having propylene units and a thermoplastic elastomer (B). The resin composition has a melting point of 110°C or higher. When determining the molecular weight distribution of the resin composition, the molecular weight of the resin composition was 1 × 10⁻⁶. 4 The following ingredients account for less than 3%.

3. The power cable according to claim 2, wherein, The thermoplastic elastomer (B) is at least one of an olefin-based thermoplastic elastomer having an olefin unit and a styrene-based thermoplastic elastomer having a styrene unit.

4. The power cable according to claim 2 or 3, wherein, The thermoplastic elastomer (B) has a melting point above 110°C and below 160°C.

5. The power cable according to any one of claims 2 to 4, wherein, The thermoplastic elastomer (B) has a molecular weight of 1×10⁻⁶. 4 The following ingredients account for less than 4.0%.

6. The power cable according to any one of claims 2 to 5, wherein, The propylene resin (A) has a melting point above 130°C and below 170°C.

7. The power cable according to any one of claims 2 to 6, wherein, The resin composition contains 50 parts by weight and 90 parts by weight of the acrylic resin (A) and 10 parts by weight and 50 parts by weight of the thermoplastic elastomer (B).

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