JP7363389B2 - Resin composition molded body and power cable - Google Patents

Description

The present disclosure relates to a resin composition, a resin composition molded article, and a power cable.

Since crosslinked polyethylene has excellent insulation properties, it has been widely used as a resin component constituting an insulating layer in power cables and the like (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 57-69611

However, cross-linked polyethylene that has deteriorated over time cannot be recycled and has no choice but to be incinerated. For this reason, there were concerns about the impact on the environment.

Therefore, in recent years, resins containing propylene (hereinafter also referred to as "propylene-based resins") have attracted attention as resin components constituting the insulating layer. Even if propylene resin is non-crosslinked, it can satisfy the insulation properties required for power cables. That is, it is possible to achieve both insulation properties and recyclability. Furthermore, by using a propylene resin, handling, processability, and ease of manufacture can be improved.

The inventors investigated the use of propylene-based resin as the resin component constituting the insulating layer, and found that it was difficult to ensure various cable characteristics, especially when the thickness of the insulating layer was 3 mm or more. I discovered that.

An object of the present disclosure is to provide a technique that can ensure various cable characteristics in an insulating layer containing propylene and having a thickness of 3 mm or more.

According to one aspect of the present disclosure,
Contains propylene and styrene;
The melting point is 158°C or higher and 168°C or lower,
The heat of fusion is 55 J/g or more and 100 J/g or less,
Resin composition.

According to other aspects of the disclosure:
A molded article formed from a resin composition and coated on an object with a thickness of 3 mm or more,
Contains propylene and styrene;
The melting point of the molded body is 158°C or more and 168°C or less,
The heat of fusion of the molded body is 55 J/g or more and 100 J/g or less,
When collecting an outer sample whose position is 0.5 mm from the surface toward the object, and an inner sample whose position is 0.5 mm from the object toward the surface,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J / g or less,
Resin composition molded body.

According to still other aspects of the present disclosure,
a conductor;
an insulating layer coated on the outer periphery of the conductor with a thickness of 3 mm or more;
Equipped with
The insulating layer contains propylene and styrene,
The melting point of the molded body is 158°C or more and 168°C or less,
The heat of fusion of the molded body is 55 J/g or more and 100 J/g or less,
When an outer sample whose distance from the surface of the insulating layer toward the conductor is 0.5 mm and an inner sample whose distance from the conductor toward the surface is 0.5 mm are taken,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J / g or less,
power cable.

According to the present disclosure, various cable characteristics can be ensured in an insulating layer containing propylene and having a thickness of 3 mm or more.

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

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

Generally, polypropylene alone is harder than polyethylene. Furthermore, polypropylene alone has inferior low-temperature brittleness resistance compared to polyethylene and the like.

When the present inventors formed an insulating layer of a power cable using such polypropylene, it was confirmed that desired cable characteristics could not be obtained. In particular, this tendency became more pronounced as the insulating layer became thicker, such as 3 mm or more. Here, the cable properties are properties required of a power cable, and include, for example, flexibility, low-temperature brittleness resistance, insulation properties, and water tree resistance.

The inventors investigated this point and found that the reason why cable characteristics cannot be obtained is that the crystallinity (crystalline state: size, shape) and amount of crystals (crystallinity) of the resin component are It was found that this is due to variations in the thickness direction. Specifically, the insulating layer of the power cable is formed by melting a resin composition, extrusion coating it around the cable core, and then cooling the melted resin composition. When this molten resin composition is cooled, the surface side is exposed to the outside air and is therefore easily cooled, whereas the inside (conductor side of the insulating layer) is not exposed to the outside air and is thus cooled. Hard to get. In other words, the cooling rate differs in the thickness direction of the insulating layer. On the other hand, crystal growth of polypropylene varies depending on the cooling rate, and the amount of crystals tends to change greatly. Specifically, when the cooling rate is fast, it is difficult for spherulites to grow and the amount of crystals is relatively small, whereas when the cooling rate is slow, spherulites are easy to grow and the amount of crystals is relatively small. It tends to increase. Therefore, when forming a thick insulating layer using only polypropylene, there will be a small amount of crystals (low crystallinity) on the surface side, and a large amount of crystals (high crystallinity) on the inside, and the amount of crystals will increase in the thickness direction. It will change a lot. Such variations in the amount of crystals are less likely to occur when the insulating layer is thin, but become noticeable when the thickness is 3 mm or more, and become a factor that deteriorates various cable properties.

On the other hand, polypropylene is also used in technical fields such as automobile bumpers. Here, ethylene propylene rubber (EPR) or the like is added to polypropylene in order to improve its low temperature brittleness. According to EPR, the resin composition can be made flexible and its low-temperature brittleness can be improved.

Therefore, in the technical field of power cables, in order to improve the flexibility and low-temperature embrittlement resistance of the insulating layer, the inventors used a low-crystalline resin such as EPR in place of propylene-based resin as a resin component constituting the insulating layer. I tried adding .

As a result, it was confirmed that by controlling the crystal growth of propylene-based resin depending on the addition ratio of propylene-based resin and low-crystalline resin, it is possible to suppress variations in the amount of crystals in the film thickness direction and improve various cable properties. It was done. However, there is a limit to the improvement of various cable properties by simply adjusting the addition ratio. For example, adding a low-crystalline resin can control the crystal growth of the propylene-based resin and suppress variations in the amount of crystals, but the amount of propylene-based resin added to the insulating layer as a whole decreases, making it difficult to obtain the desired insulating layer. There were times when it wasn't. In this way, simply adjusting the addition ratio of the low-crystalline resin may not provide a high level of well-balanced cable properties.

Based on this, the present inventors investigated components that could control the crystal growth of polypropylene in the same way as low-crystalline resins such as EPR, and focused on styrene resins.

Styrene-based resins have lower compatibility with propylene-based resins than low-crystalline resins. Therefore, when only the styrene resin is added, the styrene resin does not dissolve into the propylene resin and forms aggregates, which may result in variations in the amount of crystals. However, according to studies by the present inventors, by using a low-crystalline resin and a styrene-based resin together, a unique phase structure can be formed by finely dispersing the styrene-based resin starting from the low-crystalline resin. It has been found that the characteristics originally possessed by propylene resin can be obtained while controlling the crystal growth of propylene resin, and various cable characteristics can be improved.

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

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

[1] The resin composition according to one embodiment of the present disclosure is
Contains propylene and styrene;
The melting point is 158°C or higher and 168°C or lower,
The heat of fusion is 55 J/g or more and 100 J/g or less.
According to this configuration, various cable characteristics can be ensured.

[2] A resin composition molded article according to another aspect of the present disclosure,
A molded article formed from a resin composition and coated on an object with a thickness of 3 mm or more,
Contains propylene and styrene;
The melting point of the molded body is 158°C or more and 168°C or less,
The heat of fusion of the molded body is 55 J/g or more and 100 J/g or less,
When collecting an outer sample whose position is 0.5 mm from the surface toward the object, and an inner sample whose position is 0.5 mm from the object toward the surface,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J/g or less.
According to this configuration, various cable characteristics can be ensured.

[3] The resin composition molded article according to [2] above,
The crosslinker residue is less than 300 ppm.
According to this configuration, the recyclability of the resin composition molded article can be improved.

[4] In the resin composition molded article according to [2] or [3] above,
The AC breakdown electric field at room temperature is 60 kV/mm or more.
According to this configuration, the resin composition molded body can be suitably used as an insulating layer of a power cable.

[5] In the resin composition molded article according to any one of [2] to [4] above,
Each of the outer sample and the inner sample has only a single melting peak at 100° C. or higher in the DSC curve in which the differential scanning calorimetry was performed.
According to this configuration, the amount of crystals of the resin component can be easily controlled.

[6] A power cable according to another aspect of the present disclosure,
a conductor;
an insulating layer coated on the outer periphery of the conductor with a thickness of 3 mm or more;
Equipped with
The insulating layer contains propylene and styrene,
The melting point of the insulating layer is 158°C or more and 168°C or less,
The heat of fusion of the insulating layer is 55 J/g or more and 100 J/g or less,
When an outer sample whose distance from the surface of the insulating layer toward the conductor is 0.5 mm and an inner sample whose distance from the conductor toward the surface is 2.5 mm are taken,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J / g or less,
power cable.
According to this configuration, various cable characteristics can be ensured.

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

<One embodiment of the present disclosure>
(1) Resin Composition Molded Article The resin composition molded article (hereinafter also simply referred to as a molded article) of the present embodiment is, for example, a target object coated with a thickness of 3 mm or more. Specifically, the resin composition molded body constitutes, for example, an insulating layer 130 of the power cable 10 described below. The object of the resin composition molded body is, for example, a long linear conductor 110. The resin composition molded body is, for example, extruded so as to cover the outer periphery of the conductor 110. That is, the resin composition molded body has, for example, the same shape in the longitudinal direction of the object. Further, the length of the resin composition molded object in the longitudinal direction of the object is, for example, 30 cm or more, preferably 50 cm or more.

The molded article of this embodiment is formed from a resin composition and contains at least propylene units and styrene units derived from the resin component. The resin component includes a propylene resin, a low crystalline resin, and a styrene resin. Each component will be explained below.

(propylene resin)
The propylene resin constituting the resin component of this embodiment contains only propylene, as described above. That is, the propylene resin is made of, for example, a propylene homopolymer (homopolypropylene).

In this embodiment, the stereoregularity of the propylene homopolymer is, for example, isotactic. Isotactic propylene homopolymer is polymerized using a Ziegler-Natta catalyst and is widely used. By making the stereoregularity of the propylene homopolymer is isotactic, the melting point of the molded article can be kept within the above-mentioned specified range. In addition, by making the stereoregularity of the propylene homopolymer is isotactic, low-temperature brittleness resistance can be improved without adding excessively low crystallinity resin. Thereby, insulation can be easily ensured.

For reference, other stereoregularities include syndiotactic and atactic, but both are not preferred as the stereoregularity of the propylene homopolymer of this embodiment.

Syndiotactic propylene homopolymer is polymerized with a metallocene catalyst and is relatively expensive. If the stereoregularity of the propylene homopolymer is syndiotactic, the melting point of the molded product will be excessively low. Furthermore, if the stereoregularity of the propylene homopolymer is syndiotactic, the low-temperature embrittlement property will be poor. To improve low-temperature embrittlement, it is necessary to add an excessive amount of low-crystalline resin. Therefore, the insulation property deteriorates significantly.

Furthermore, if the stereoregularity is atactic, the resin component will not crystallize, making it impossible to ensure predetermined cable properties.

The melting point of the propylene homopolymer used in this embodiment as a simple substance is, for example, 160°C or more and 175°C or less. Further, the heat of fusion of the propylene homopolymer as a simple substance is, for example, 100 J/g or more and 120 J/g or less. The elastic modulus (25° C.) of a propylene homopolymer as a simple substance is, for example, 1600 MPa.

(Low crystalline resin)
The low crystallinity resin is a component that controls crystal growth (crystal amount) of the propylene resin and imparts flexibility to the molded article of the resin composition. Furthermore, the low crystalline resin acts as a compatibilizer and improves the dispersibility of the styrene resin into the propylene resin. Here, the low-crystalline resin refers to a component that has a low amount of crystals or is amorphous and does not have a melting point, or even if it does have a melting point, the melting point is 100° C. or less. The heat of fusion is, for example, 50 J/g or less, preferably 30 J/g or less.

The low-crystalline resin is preferably a copolymer of at least two of ethylene, propylene, butene, hexene, and octene, from the viewpoint of controlling crystal growth and improving the flexibility of the molded product. preferable. Note that the carbon-carbon double bond in the monomer unit constituting the low-crystalline resin is preferably located, for example, at the α position.

Examples of the low crystalline resin include ethylene propylene rubber (EPR) and very low density polyethylene (VLDPE).

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

The ethylene content of EPR is, for example, preferably 20% by mass or more, preferably 40% by mass or more, and more preferably 55% by mass or more. When the ethylene content is less than 20% by mass, the compatibility of EPR with propylene resin becomes excessively high. Therefore, even if the content of EPR in the molded body is reduced, the molded body can be made flexible. However, the crystallization of the propylene resin cannot be sufficiently controlled, and there is a possibility that the insulation properties will be reduced. On the other hand, by setting the ethylene content to 20% by mass or more, it is possible to prevent the compatibility of EPR with the propylene resin from becoming excessively high. Thereby, crystallization of the propylene resin due to EPR can be sufficiently controlled while obtaining the softening effect due to EPR. As a result, deterioration in insulation properties can be suppressed. Furthermore, by setting the ethylene content to preferably 40% by mass or more, more preferably 55% by mass or more, crystallization can be controlled more stably, and deterioration in insulation properties can be stably suppressed. can.

On the other hand, the low crystalline resin may be, for example, a copolymer that does not contain propylene. As the copolymer not containing propylene, for example, VLDPE is preferable from the viewpoint of easy availability. Examples of VLDPE include PE composed of ethylene and 1-butene, PE composed of ethylene and 1-octene, and the like.

If a copolymer that does not contain propylene is used as the low crystalline resin, complete compatibility can be suppressed while mixing a predetermined amount of the low crystalline resin with the propylene resin. Therefore, by setting the content of such a copolymer to a predetermined amount or more, crystallization of the propylene resin can be stably controlled.

(Styrene resin)
The styrenic resin is a styrenic thermoplastic elastomer containing styrene as a hard segment and at least one of ethylene, propylene, butylene, isoprene, etc. as a soft segment. Like the low-crystalline resin, the styrene resin is a component that is dispersed in the resin composition to control crystal growth of the propylene resin and suppress variations in the amount of crystals in the thickness direction of the insulating layer. In addition, styrene resin traps electrons with its aromatic ring to form a stable resonance structure, and as an elastomer, it suppresses the occurrence of mechanical stress cracks in molded products, allowing them to absorb moisture in molded products. It also contributes to improving resistance.

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

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

The styrenic resin is preferably one that does not contain a double bond in its chemical structure. When a material having a double bond is used, the resin component may be thermally degraded during molding of the resin composition, which may deteriorate the properties of the resulting molded product. In this regard, materials that do not contain double bonds have high resistance to thermal deterioration, so that the properties of the molded product can be maintained at a higher level.

The styrene content of the styrene resin is not particularly limited, but from the viewpoint of controlling crystal growth of the propylene resin and softening the molded product, it is preferably 5% by mass or more and 35% by mass or less.

(Resin composition)
The resin composition constituting the molded article of this embodiment includes the above-mentioned propylene resin, low crystallinity resin, and styrene resin. When analyzed using a nuclear magnetic resonance (NMR) device, this resin composition has at least a propylene unit derived from a propylene resin and a styrene unit derived from a styrene resin in its chemical structure. . If the low crystalline resin is a polymer containing ethylene units, such as EPR, it will further have ethylene units.

Further, from the viewpoint of recycling, the resin composition constituting the molded article is preferably non-crosslinked. Alternatively, even if it is crosslinked, it is preferable to crosslink it so that the gel fraction (degree of crosslinking) is low. Specifically, it is preferable to carry out crosslinking at a degree such that the amount of crosslinking agent residue in the resin composition molded article is less than 300 ppm. Note that when dicumyl peroxide is used as a crosslinking agent, the residue is, for example, cumyl alcohol, α-methylstyrene, or the like.

(Melting point and heat of fusion of molded body)
The molded article of this embodiment can be formed, for example, by extrusion coating a molten resin composition onto an object to a thickness of 3 mm or more and cooling the object. The above-mentioned resin composition is a propylene resin mixed with a low crystalline resin and a styrene resin, so when it is cooled from a molten state and solidified, excessive crystal growth of the propylene resin is suppressed. be able to. Moreover, by adjusting the ratio of the low crystalline resin and the styrene resin, the crystal growth can be appropriately controlled. Therefore, even when producing a molded body with a thickness of 3 mm or more, the difference in crystal growth due to the difference in cooling rate between the surface side and the inside can be suppressed, and the amount of crystals in the thickness direction can be reduced. Variations can be suppressed. Specifically, it is possible to reduce the difference in heat of fusion and melting point of the resin composition, which are indicators of the amount of crystals (crystallinity), between the surface side and the inside of the molded body.

Here, the melting point and heat of fusion of the molded body will be explained.

In the molded article of this embodiment, the resin composition constituting the molded article has a melting point of 158° C. or more and 168° C. or less, and a heat of fusion of 55 J/g or more and 100 J/g or less. Although the amount of crystals varies somewhat in the thickness direction of a molded body, the variation is small, so that the melting point and heat of fusion will be within the above ranges no matter where the sample is taken from the molded body. In other words, the melting point and heat of fusion of the samples collected from the surface side and inside of the molded body are within the above range,

The melting point of the molded body is 158°C or more and 168°C or less. The molded product contains a high melting point propylene resin (propylene homopolymer) as well as a low crystalline resin and a styrene resin that do not have a melting point. It becomes lower than its original melting point (160°C to 175°C). If the melting point of the molded product is less than 158°C, the content of low crystalline resin or styrene resin is high, and if it exceeds 168°C, there is a high content of propylene resin, and the blending balance of each component is poor. Therefore, it becomes impossible to ensure various cable characteristics. By setting the melting point of the molded body to 158° C. to 168° C., it is possible to achieve an appropriate blending balance that ensures various cable properties.

Further, the heat of fusion of the molded body is 55 J/g or more and 100 J/g or less. The molded product contains a crystalline propylene resin (propylene homopolymer) as well as a low crystalline resin with a smaller amount of crystals and a styrene resin, so the heat of fusion of the molded product is higher than that of the propylene homopolymer. It is lower than the heat of fusion (100 J/g to 120 J/g).

The heat of fusion changes depending on the amount of crystals in the resin composition, that is, depending on the amounts of propylene resin, low crystalline resin, and styrene resin, and therefore serves as an index of the ratio of each component.

In a molded product, if the amount of low crystalline resin or styrene resin added increases and the amount of crystalline propylene resin added is excessively low, the degree of crystallinity in the molded product will decrease (the amount of crystals will decrease). ). If the amount of crystals in the molded body is in a range where the heat of fusion is less than 55 J/g, the amount of crystals will be excessively small, making it impossible to ensure the desired insulation properties. On the other hand, by adjusting the ratio of each component and controlling the amount of crystals so that the heat of fusion of the molded product is 55 J/g or more, the insulation properties of the molded product can be improved.

On the other hand, if the amount of crystals in the molded product is in a range where the heat of fusion exceeds 100 J/g, the amount of low-crystalline resin or styrene resin is small and the molded product is similar to a single propylene homopolymer. Equivalent to. In this case, since the amount of crystals is excessively large, the molded product may become hard and have poor low-temperature embrittlement resistance. Furthermore, in the molded article, since the crystal growth of the propylene resin cannot be sufficiently controlled, the spherulites become excessively large, which may result in a decrease in insulation properties due to microcracks in the spherulites. Furthermore, since the amorphous portion decreases due to the growth of coarse spherulites, water tends to concentrate at the spherulite interface, and as a result, water tree resistance may decrease. On the other hand, by adjusting the ratio of each component and controlling the amount of crystals so that the heat of fusion of the molded product is 100 J/g or less, the molded product can be made flexible and its low-temperature brittleness can be improved. Further, it is possible to suppress a decrease in insulation properties caused by microcracks in the spherulites in the molded body. Moreover, since the growth of coarse spherulites can be suppressed and an amorphous portion can be secured, concentration of water at the spherulite interface can be suppressed, and the water tree resistance of the resin composition molded article can be improved.

As described above, the molded article of this embodiment has small variations in the amount of crystals in the thickness direction. Therefore, an outer sample located at a position of 0.5 mm from the surface of the molded object toward the object, and an inner sample located at a position of 0.5 mm from the object toward the surface, were collected. When differential scanning calorimetry (DSC) is performed, the difference in melting point and heat of fusion between the inner sample and the outer sample also becomes smaller. Specifically, the absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample (hereinafter simply referred to as the "difference in melting point") is 8°C or less, and the heat of fusion of the inner sample is equal to the melting point of the outer sample. The absolute value of the difference after subtracting the heat amount (hereinafter also simply referred to as "difference in heat of fusion") is 10 J/g or less.

If the difference in melting point exceeds 8°C or the difference in heat of fusion exceeds 10 J/g, for example, propylene resin spherulites may grow coarsely on the inside of the molded product without sufficient control of crystal growth. It is thought that there is a large difference in the amount of crystals between the surface side and the surface side because the amount of crystals increases due to the progress of crystallization. Therefore, as described above, it becomes difficult to ensure the cable properties such as flexibility, low temperature brittleness resistance, insulation properties, and water tree resistance. In contrast, by controlling the crystal growth so that the difference in melting point and heat of fusion falls within the above range, and by distributing the crystals in a well-balanced manner throughout the molded body, that is, by making the amount of crystals uniform, it is possible to The properties of flexibility, low temperature brittleness, insulation and water tree resistance can be ensured. Note that the above-mentioned "uniform" includes not only a case of being completely uniform but also a case of being uniform with a predetermined error.

Note that since the cooling rate is faster on the surface side of the resin composition molded body, the spherulites of the outer sample rarely grow larger than the spherulites of the inner sample. Therefore, the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is rarely negative. However, even if the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is negative, the difference in melting points is -8°C or more.

Furthermore, in the present embodiment, each of the outer sample and the inner sample has only a single melting peak at 100° C. or higher, for example, in a DSC curve obtained by DSC measurement. That is, the only crystalline resin component having a melting peak is propylene resin. Even if the low-crystalline resin or styrene-based resin added as a resin component has a melting peak, the melting peak of the low-crystalline resin or styrene-based resin is below 100°C, or the low-crystalline resin has a melting peak. The melting peaks of polypropylene resins and styrene resins are negligibly lower than the melting peaks of propylene resins. In other words, the temperature of the highest melting peak is 158°C or more and 168°C or less.

Note that "differential scanning calorimetry" in this specification is performed, for example, in accordance with JIS-K-7121 (1987). Specifically, in the DSC device, the temperature is raised from room temperature (normal temperature, for example 27°C) to 220°C at a rate of 10°C/min. Thereby, a DSC curve can be obtained by plotting the amount of heat absorbed per unit time (heat flow) against the temperature.

At this time, the temperature at which the amount of heat absorbed per unit time in the sample becomes maximum (highest peak) is defined as the "melting point (melting peak temperature)". Also, at this time, assuming that all the heat absorption of the sample is carried out by the resin component, the value (J /g) is the "heat of fusion". Note that the degree of crystallinity (%) of the sample can be determined based on the heat of fusion of the sample and the theoretical value of the heat of fusion of a perfectly crystalline body.

(Resin composition)
The ratio of each component contained in the resin composition constituting the molded article is such that the heat of fusion of the above-mentioned outer sample is 55 J/g or more and 100 J/g or less. It may be adjusted as appropriate depending on the amount of each crystal.

Specifically, the resin composition preferably contains a propylene resin of 55% to 85% by mass, a low crystalline resin of 5% to 15% by mass, and a styrene resin of 5% to 35% by mass. % or less, more preferably 65% to 80% by mass of propylene resin, 5% to 15% by mass of low crystalline resin, and 10% to 30% by mass of styrene resin. By mixing each component in such a ratio, it becomes easy to adjust the heat of fusion and melting point within the above range.

In the resin composition, the total amount of styrene derived from the styrenic resin is preferably 0.5% by mass or more and 8% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. The total amount of styrene refers to the total amount of styrene units in the resin composition. The amount added may be adjusted as appropriate depending on the styrene content of the styrenic resin used so that the total amount of styrene falls within the above range. This makes it possible to obtain a higher level of well-balanced cable characteristics.

Further, from the viewpoint of finely dispersing the styrene resin in the propylene resin, the content of the low crystalline resin is preferably 0.25 times or more and 2.5 times or less relative to the styrene resin. Thereby, the styrene resin can be dispersed more reliably.

(Other additives)
The resin composition constituting the molded article may contain, for example, an antioxidant, a copper damage inhibitor, a lubricant, and a coloring agent in addition to the above-mentioned resin components.

However, it is preferable that the resin composition molded article of this embodiment has a small content of an additive that functions as a nucleating agent for generating crystals of propylene, and it is preferable that the resin composition molded article of the present embodiment contains substantially no such additive. More preferred. Specifically, the content of the additive that functions as a nucleating agent is, for example, less than 1 part by mass when the total content of propylene resin, low crystalline resin, and styrene resin is 100 parts by mass. It is preferably present, and more preferably 0 parts by mass. Thereby, the occurrence of unexpected abnormal crystallization caused by the nucleating agent can be suppressed, and the amount of crystals can be easily controlled.

(2) Power Cable Next, the power cable of this embodiment will be explained using FIG. 1. FIG. 1 is a cross-sectional view orthogonal to the axial direction of the power cable according to the present embodiment.

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

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

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

(inner semiconducting layer)
Internal semiconducting layer 120 is provided to cover the outer periphery of conductor 110 . Further, the internal semiconducting layer 120 has semiconductivity and is configured to suppress electric field concentration on the surface side of the conductor 110. The internal semiconductive layer 120 is made of, for example, an ethylene copolymer such as ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-vinyl acetate copolymer, or an olefin. The material contains at least one of a series elastomer, the above-mentioned low-crystalline resin, etc., and conductive carbon black.

(insulating layer)
The insulating layer 130 is provided so as to cover the outer periphery of the internal semiconductive layer 120, and is configured as the resin composition molded article described above. The insulating layer 130 is, for example, extruded from a resin composition as described above.

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

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

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

Note that if the power cable 10 of this embodiment is an underwater cable or an underwater cable, it may have a metal water shielding layer such as a so-called aluminum sheathing or a steel wire armoring on the outside of the shielding layer 150. good. On the other hand, the power cable 10 of the present embodiment has the above-mentioned water tree suppressing effect, and therefore has a metal water shielding layer such as a so-called aluminum sheathing on the outside of the shielding layer 150. It doesn't have to be. That is, the power cable 10 of this embodiment may be configured with a non-complete water-shielding structure.

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

(3) Cable characteristics In the present embodiment, the melting point and heat of fusion of the insulating layer 130 (resin composition molded body) are each within predetermined ranges, and the melting point and heat of fusion in the thickness direction of the insulating layer 130 are respectively controlled within predetermined ranges. By reducing the variation, the following cable characteristics are ensured.

Note that the "inside sample" hereinafter refers to a sample taken from a location 0.5 mm from the conductor 110 toward the surface of the insulating layer 130 in the insulating layer 130, as described above. Since the amount of crystals tends to be high in the inner sample, if the various cable characteristics are satisfied in the inner sample, it means that the various cable characteristics are satisfied throughout the resin composition molded body.

(insulation)
In this embodiment, the AC breakdown electric field strength of the insulating layer 130 at room temperature (for example, 27° C.) is, for example, 60 kV/mm or more. More specifically, at room temperature, an AC voltage of commercial frequency (for example, 60 Hz) is applied at 10 kV for 10 minutes to an inner sample with a thickness of 0.2 mm, and then the voltage is increased in steps of 1 kV and applied for 10 minutes. The AC breakdown electric field when applied under repeated conditions is 60 kV/mm or more.

(Low temperature resistance)
In this embodiment, for example, in accordance with JIS K7216, no cracks occur when the inner sample is impacted (hit) with an impact tool at -25°C.

(Flexibility)
In this embodiment, the tensile modulus of the inner sample is, for example, 1200 MPa or less. In addition, "tensile modulus" is measured using DVA-200 manufactured by IT Instrument Control Co., Ltd. in tensile mode at a heating rate of 10 °C/min from -50 °C to 200 °C. , storage modulus recorded at 30°C.

Further, in this embodiment, for example, when the inner sample is bent to a diameter of 500 mm, the inner sample does not whiten. Note that "whitening" as used herein refers to a state in which a difference in color occurs between the folded portion and the non-folded portion before and after bending, resulting in haze.

(water tree resistance)
In this embodiment, the resin composition molded body serving as the insulating layer 130 is immersed in a 1N NaCl aqueous solution at room temperature (27° C.), and a commercial frequency (for example, 60 Hz) of 4 kV/4 kV is applied to the resin composition molded body. When an alternating current electric field of mm is applied for 1000 hours, the maximum length of water trees generated in the molded resin composition is, for example, less than 150 μm. Thereby, dielectric breakdown of the insulating layer 130 caused by water trees can be stably suppressed.

Note that the maximum length of water trees generated in the resin composition molded product is not limited, since the shorter the better. However, in this embodiment, since a predetermined amount of water trees may be generated in the above-mentioned test, the maximum length of water trees generated in the resin composition is, for example, 30 μm or more.

Further, in this embodiment, the resin composition molded body as the insulating layer 130 is immersed in a 1N NaCl aqueous solution at room temperature (27° C.), and the resin composition molded body is exposed to a commercial frequency (for example, 60 Hz). When an alternating current electric field of 4 kV/mm is applied for 1000 hours, the number concentration of water trees generated in the resin composition molded body and having a length of 30 μm or more is, for example, less than 150 pieces/cm ³ . Thereby, dielectric breakdown of the insulating layer 130 caused by water trees can be stably suppressed.

Note that the concentration of the number of water trees generated is not limited, since the lower the concentration, the better. However, in this embodiment, since a predetermined amount of water trees can be generated by the above-mentioned test, the number concentration of water trees generated is, for example, 10 pieces/cm ³ or more.

(4) Method for manufacturing a power cable Next, a method for manufacturing a power cable according to the present embodiment will be described. Hereinafter, step will be abbreviated as "S".

(S100: Resin composition preparation step)
First, a resin composition for forming a molded body is prepared.

In this embodiment, a resin component including a propylene resin, a low crystalline resin, and a styrene resin, and other additives (antioxidants, etc.) as necessary are mixed (kneaded) using a mixer, Form a mixture. Examples of the mixer include an open roll, a Banbury mixer, a pressure kneader, a single-shaft mixer, and a multi-shaft mixer.

At this time, in the resin composition, the content of propylene resin is 55% by mass or more and 85% by mass or less, the content of low crystalline resin is 5% by mass or more and 15% by mass or less, and the content of styrene resin is 5% by mass. % or more and 35% by mass or less.

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

(S200: Conductor preparation step)
On the other hand, a conductor 110 formed by twisting a plurality of conductor core wires is prepared.

(S300: Cable core forming process (extrusion process, insulation layer forming process))
When the resin composition preparation step S100 and the conductor preparation step S200 are completed, the above-described resin composition is extruded so as to cover the outer periphery of the conductor 110 to a thickness of 3 mm or more, and is cooled to form the insulating layer 130. .

When cooling the extruded resin composition, excessive crystal growth of the propylene resin can be suppressed by the low crystallinity resin or styrene resin, so variations in crystal growth in the thickness direction can be reduced. Thereby, in the obtained insulating layer, variations in the amount of crystals between the front side and the inside can be reduced. Specifically, the melting point of the outer sample is 158°C or more and 168°C or less, the heat of fusion of the outer sample is 55J/g or more and 100J/g or less, the difference in melting point is 8°C or less, and the difference in heat of fusion is 8°C or less. The insulating layer 130 can be formed to have a power of 10 J/g or less.

Further, at this time, in this embodiment, the inner semiconducting layer 120, the insulating layer 130, and the outer semiconducting layer 140 are simultaneously formed using, for example, a three-layer coextruder.

Specifically, of the three-layer coextruder, for example, the composition for an internal semiconductive layer is charged into extruder A that forms the internal semiconductive layer 120.

The above pelletized resin composition is charged into extruder B for forming the insulating layer 130. In addition, the set temperature of extruder B is set to a temperature higher than the desired melting point by a temperature of 10° C. or more and 50° C. or less. It is preferable to adjust the set temperature appropriately based on the linear speed and extrusion pressure.

A composition for an outer semiconducting layer containing the same material as the resin composition for an inner semiconducting layer charged into the extruder A is charged into an extruder C for forming the outer semiconducting layer 140.

Next, the respective extrudates from extruders A to C are led to a common head, and the inner semiconducting layer 120, the insulating layer 130, and the outer semiconducting layer 140 are simultaneously applied to the outer periphery of the conductor 110 from the inside to the outside. extrude This forms an extruded material that will become the cable core.

The extrudate is then cooled, for example with water.

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

(S400: Shielding layer forming step)
Once the cable core is formed, a shielding layer 150 is formed on the outside of the outer semiconducting layer 140, for example by wrapping copper tape.

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

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

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

(a) The molded article of this embodiment contains propylene (units) and styrene (units) when measured by NMR, has a melting point of 158°C or more and 168°C or less when subjected to DSC, and has a heat of fusion of 55J. /g or more and 100J/g or less. This resin composition contains a propylene homopolymer, a low crystalline resin, and a styrene resin as crystalline resin components in a ratio such that the heat of fusion is 55 to 100 J/g. According to this resin composition, when the resin composition is cooled from a molten state, excessive crystal growth of the propylene resin can be suppressed and controlled by the low crystallinity resin and the styrene resin. Therefore, when forming a molded object by coating the object with a resin composition to a thickness of 3 mm or more, for example, when forming an insulating layer of a power cable as a molded object, the amount of crystals in the thickness direction is variation can be reduced. In other words, the crystals can be distributed in a well-balanced manner throughout the molded body, and the amount of crystals can be made uniform. Specifically, the difference in melting point between the outer sample on the surface side of the molded body and the inner sample on the conductor side can be set to 8° C. or less, and the absolute value of the difference in heat of fusion can be set to 10 J/g or less. In this way, by reducing the variation in the amount of crystals in the thickness direction of the molded body (insulating layer), we can make the insulating layer flexible and improve its low-temperature embrittlement resistance even though polypropylene resin is used. be able to. Further, it is possible to suppress a decrease in insulation properties due to an insufficient amount of crystals, and also to suppress a decrease in insulation properties due to microcracks in coarse spherulites. In addition, since the growth of coarse spherulites can be suppressed and an amorphous portion can be secured, the concentration of water at the spherulite interface can be suppressed, and as a result, the water tree resistance of the resin composition molded product is improved. can be done. In this way, in this embodiment, it is possible to ensure various cable characteristics.

(b) In this embodiment, the amount of crosslinking agent residue in the resin composition molded article is less than 300 ppm. Thereby, the recyclability of the molded body can be improved. As a result, the impact on the environment can be suppressed.

(c) According to the present embodiment, the size of the crystals in the molded body as a whole is suppressed from becoming too small or too large. Moreover, not only the amount of crystals is uniform throughout the molded body, but also the size of the crystals is uniform. Thereby, the insulation properties of the molded body can be improved. Specifically, the AC breakdown electric field of the molded body at room temperature can be 60 kV/mm or more. As a result, the molded article of this embodiment can be suitably used as an insulating layer of a power cable.

(d) In this embodiment, each of the outer sample and the inner sample has only a single melting peak at 100° C. or higher, for example, in a DSC curve obtained by DSC measurement. That is, the only crystalline resin component having a melting peak is propylene resin. Thereby, the amount of crystals in the resin component can be easily controlled.

(e) In the molded article of this embodiment, the content of the additive that functions as a nucleating agent to generate crystals of propylene is, for example, 100% of the total content of propylene resin, low crystallinity resin, and styrene resin. When expressed as parts by mass, it is preferably less than 1 part by mass.

Here, if the molded body contains an additive that functions as a nucleating agent, the amount of crystals of the resin component can be made uniform in the molded body due to the nucleating agent. However, since the resin composition contains the above-mentioned additives, there is a possibility that the insulation properties of the molded article decrease due to the additives. In this case, microcracks may occur in the abnormal crystal growth portion, and the insulation may deteriorate.

In contrast, in the present embodiment, even if there is a small amount of the additive that functions as a nucleating agent in the resin composition molded article, the amount of crystals in the resin component may become excessive due to the addition of the low crystallinity resin or styrene resin. The variation in the amount of crystals of the resin component in the thickness direction of the resin composition molded article is suppressed. Furthermore, by reducing the amount of the additive that functions as a nucleating agent in the resin composition molded article, it is possible to suppress a decrease in the insulation properties of the resin composition molded article caused by the additive. Additionally, by reducing the amount of the additive that functions as a nucleating agent in the resin composition molded article, it is possible to suppress the occurrence of unexpected abnormal crystallization caused by the nucleating agent and easily control the amount of crystals. . Thereby, deterioration in the insulation properties of the resin composition molded article can be suppressed.

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

In the above-described embodiment, the resin composition molded body serving as the insulating layer is mechanically mixed and extruded. However, the resin composition molded body is not polymerized and extruded. There may be.

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

In the embodiments described above, a case has been described in which the power cable 10 is configured to be installed on land, underwater, or on the bottom of the water, but the present disclosure is not limited to this case. For example, the power cable 10 may be configured as a so-called overhead wire (overhead insulated wire).

In the above-mentioned embodiment, three layers were simultaneously extruded in the cable core forming step S300, but it is also possible to extrude one layer at a time.

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

(1) Production of power cable In this example, a power cable was produced by the following procedure.

(1-1) Materials The following components were prepared as materials for a resin composition for forming an insulating layer.

The following was used as the propylene resin (A).
Homopolypropylene (isotactic): Melt flow rate: 0.5g/10min, density: 0.9g/ml

The following (b1) to (b3) were used as the low crystalline resin (B).
(b1) Ethylene propylene rubber (EPR): Ethylene content: 52% by mass, Mooney viscosity ML (1+4) 100°C: 40
(b2) Very low density polyethylene (copolymer of ethylene and 1-butene, VLDPE1): 1-butene content: 40% by mass, melting point: 95°C, density: 0.88 g/ml, Shore A hardness: 66
(b3) Very low density polyethylene (copolymer of ethylene and 1-octene, VLDPE2): 1-octene content: 10% by mass, melting point: 55°C, density: 0.87 g/ml, Shore A hardness: 70

As the styrene resin (C), the following (c1) to (c6) having different styrene contents were used.
(c1) Hydrogenated styrene thermoplastic elastomer (SEBS1): Styrene content: 35% by mass, hardness: A35, melt flow rate: 0g/10min (230°C, 2.16kg)
(c2) Hydrogenated styrene thermoplastic elastomer (SEBS2): Styrene content: 30% by mass, hardness: A84, melt flow rate: 5g/10min (230°C, 2.16kg)
(c3) Hydrogenated styrene thermoplastic elastomer (SEBS3): Styrene content: 20% by mass, hardness: A67, melt flow rate: 13g/10min (230°C, 2.16kg)
(c4) Hydrogenated styrene thermoplastic elastomer (SEBS4): Styrene content: 12% by mass, hardness: A42, melt flow rate: 4.5g/10min (230°C, 2.16kg)
(c5) Hydrogenated styrene thermoplastic elastomer (SEBS5): Styrene content: 42% by mass, hardness: A96, melt flow rate: 0.8g/10min (190°C, 2.16kg)
(c6) Hydrogenated styrene thermoplastic elastomer (SEBS6): Styrene content: 47% by mass, hardness: A93, melt flow rate: 3g/10min (190°C, 2.16kg)

(1-2) Preparation of resin composition The above-mentioned materials were mixed using a Banbury mixer in the formulation shown in Table 1 below, and granulated into pellets using an extruder.

(Samples 1-3)
In sample 1, 70 parts by mass of propylene resin (A) which is a homopolymer, 10 parts by mass of (b1) EPR as low crystalline resin (B), and styrene content of 20 mass% as styrene resin (C). A resin composition was prepared by mixing 20 parts by mass of certain (c3) SEBS3 so that the total amount of styrene was 4.0% by mass. Further, in Samples 2 and 3, resin compositions were prepared in the same manner as Sample 1 except that the type of low crystalline resin (B) was changed from (b1) to (b2) and (b3).

(Samples 4-6)
In Samples 4 to 6, resin compositions were prepared in the same manner as Sample 2, except that the type of styrene resin (C) was changed from (c3) to one of (c1), (c2), or (c4). .

(Samples 7 and 8)
In Samples 7 and 8, resin compositions were prepared in the same manner as Sample 1 except that the ratios of propylene resin (A), low crystalline resin (B), and styrene resin (C) were changed.

(Sample 9)
In sample 9, the resin composition was prepared in the same manner as sample 1 except that the styrene resin (C) was not added, the propylene resin (A) was 75 parts by mass, and the low crystalline resin (B) was 25 parts by mass. was prepared.

(Samples 10 and 11)
In Samples 10 and 11, resin compositions were prepared in the same manner as Sample 1 except that the type of styrene resin (C) was changed from (c3) to (c5) or (c6).

(Samples 12, 13)
In Samples 12 and 13, the ratios of propylene resin (A), low crystalline resin (B), and styrene resin (C) were set so that the melting point and heat of fusion of the molded product were outside the above range. A resin composition was prepared in the same manner as Sample 1.

(1-3) Preparation of power cable sample Next, a conductor with a cross-sectional area of 100 mm ² was prepared. After preparing the conductor, add the resin composition for the internal semiconductive layer containing the ethylene-ethyl acrylate copolymer, the resin composition for the insulating layer prepared in (1-2) above, and the resin composition for the internal semiconductive layer. and an outer semiconducting layer resin composition made of the same material as the sample were respectively put into extruders A to C. The respective extrudates from extruders A to C were led to a common head, and an inner semiconducting layer, an insulating layer and an outer semiconducting layer were simultaneously extruded from the inside to the outside around the outer periphery of the conductor. At this time, the thicknesses of the inner semiconducting layer, the insulating layer, and the outer semiconducting layer were set to 0.5 mm, 3.5 mm, and 0.5 mm, respectively. As a result, a power cable was manufactured that had a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer from the center to the outer periphery.

(2) Evaluation In this example, the following items were evaluated for the insulating layer of the produced power cable.

(2-1) Melting point and heat of fusion First, the insulation layer of the power cables of Samples 1 to 13 is peeled off, and a sample piece at a depth of 0.5 mm from the surface of the insulation layer toward the conductor is used as the outer sample. Collected. In addition, a sample piece was taken as an inner sample at a location 0.5 mm from the conductor toward the surface, that is, at a depth of 2.5 mm from the surface toward the conductor. The thickness of each of the outer sample and the inner sample was 0.5 mm.

The melting point of each sample was determined by DSC measurement. DSC measurements were performed in accordance with JIS-K-7121 (1987). Specifically, a PerkinElmer DSC8500 (input compensation type) was used as the DSC device. The reference sample was, for example, α-alumina. The mass of the sample was 8 to 10 g. In the DSC device, the temperature was raised from room temperature (27°C) to 220°C at a rate of 10°C/min. Thereby, a DSC curve was obtained by plotting the amount of endotherm (heat flow) per unit time versus temperature.

At this time, the temperature at which the amount of heat absorbed per unit time in each sample becomes maximum (highest peak) was defined as the "melting point." At this time, the "heat of fusion" was determined by determining the area of the region surrounded by the melting peak and the baseline in the DSC curve.

(2-2) Low-temperature embrittlement In accordance with JIS K7216, the inner sample was subjected to impact (beaten) at -25°C with an impact tool. At this time, the presence or absence of cracks was visually confirmed. As a result, the case where there was no cracking was rated as "A (good)", and the case where there was cracking was rated as "B (poor)".

(2-3) Tensile modulus Using DVA-200 manufactured by IT Instrument Control Co., Ltd., measurements were carried out in tensile mode at a heating rate of 10°C/min from -50°C to 200°C. Storage modulus was recorded at °C. As a result, cases where the tensile modulus was 1000 MPa or less were evaluated as good.

(2-4) AC breaking strength AC breaking strength was determined by an alternating current breaking test. Specifically, first, a 0.5 mm thick inner sample was cut into a 0.2 mm thick piece. After that, at room temperature (27°C), apply an AC voltage of commercial frequency (for example, 60 Hz) at 10 kV for 10 minutes to the inner sample with a thickness of 0.2 mm, and then increase the voltage in steps of 1 kV and apply the voltage for 10 minutes. It was applied under repeated conditions. The electric field strength was measured when the inner sample suffered dielectric breakdown. As a result, cases where the AC breaking strength was 60 kV/mm or more were evaluated as good.

(2-5) Bending test The inner sample was bent to a diameter of 500 mm, and whitening of the inner sample was visually confirmed. As a result, a case where there was no whitening was rated as "A (good)", and a case where there was whitening was rated as "B (poor)".

(2-6) Water tree resistance Water tree resistance was evaluated by the following test.

Specifically, first, the insulating layer was peeled off to produce two sheets each having a thickness of 1 mm. After producing the sheet, a predetermined semiconductive sheet was sandwiched between two sheets to form a laminated sheet. After forming the laminated sheet, wiring was formed on the semiconductive sheet. Next, with the laminated sheet immersed in a 1N NaCl aqueous solution at room temperature (27° C.), an alternating current electric field of 60 Hz and 4 kV/mm was applied to the sheet between the semiconductive sheet and the aqueous solution for 1000 hours. After applying a predetermined alternating current electric field, the laminated sheet was dried, and the laminated sheet was boiled and dyed with a methylene blue aqueous solution. After dyeing the laminated sheet, the laminated sheet was sliced to a thickness of 30 μm along the lamination direction (that is, the direction perpendicular to the main surface of the laminated sheet) to form slice pieces for observation. Thereafter, water trees generated in the creeping direction of the semiconductive sheet or in the direction orthogonal to the main surface of the semiconductive sheet were observed in the sheet of the observation slice by observing the observation slice using an optical microscope.

At this time, the maximum length of water trees generated in the sheet was measured. In addition, the number concentration of water trees generated in the sheet and having a length of 30 μm or more was measured. The "maximum length of water trees" is determined by rounding off the length of the longest water tree among 10 randomly selected observation slices, and the "number concentration of water trees" is The average value of the number concentration of water trees in 10 randomly selected slices for observation was rounded off.

In this example, the case where the maximum length of the water tree was less than 150 μm was evaluated as good. In addition, a case where the number concentration of water trees having a length of 30 μm or more was less than 150 pieces/cm ³ was evaluated as good.

For reference, in conventional water tree resistance evaluation, a power cable having an insulating layer made of a predetermined resin composition was prepared, the power cable was immersed in water, and water tree resistance was evaluated. At this time, a shielding layer and a sheath were provided outside the insulating layer of the power cable. Therefore, the insulating layer never came into direct contact with water. In contrast, in this example, as described above, the laminated sheet was directly immersed in a predetermined aqueous solution to evaluate the water tree. For this purpose, the sheet was brought into direct contact with the aqueous solution. Therefore, the evaluation of water tree resistance in this example was conducted under stricter conditions than evaluations using conventional power cables.

(3) Evaluation results The evaluation results are summarized in Table 1.

As shown in Table 1, in Samples 1 to 3, by mixing propylene resin (A), low crystalline resin (B), and styrene resin (C) in a predetermined composition, It was confirmed that by reducing the difference in heat of fusion and melting point, it was possible to obtain a high level of well-balanced cable properties. That is, it was confirmed that desired cable characteristics could be obtained as the low crystalline resin (B) regardless of the type of EPR or VLDPE.

According to Samples 4 to 6, by using a styrene resin (C) with a styrene content of 5% to 35% by mass, the styrene content in the molded product can be reduced even though each component is mixed at a predetermined ratio. It was confirmed that the total amount could be adjusted to 0.5% by mass to 8% by mass, and that a high level of well-balanced cable properties could be obtained.

According to Samples 7 and 8, the propylene resin (A) and the low crystalline resin (B) were mixed so that the melting point in the molded product was 158°C or more and 168°C or less, and the heat of fusion was 55J/g or more and 100J/g or less. It was confirmed that a high level of well-balanced cable properties could be obtained by mixing styrene resin (C) and styrene resin (C) in a predetermined ratio.

On the other hand, in sample 9, it was confirmed that the AC breakdown strength of the insulating layer was low by adding only the low crystalline resin (B) without adding the styrene resin (C). This is presumed to be because the amount of crystals in the insulating layer was excessively reduced by adding the low crystalline resin (B).

In addition, in Samples 10 and 11, it was not possible to control the amount of crystals in the thickness direction of the insulating layer, and the variation in the amount of crystals became large. was confirmed to be lower. This is presumed to be because the total amount of styrene in the resin composition is excessively large at 9.4% by mass or 8.4% by mass.

In sample 12, propylene resin (A), low crystalline resin (B), and styrene resin (C) were mixed, but since the content of propylene resin (A) was relatively high, Although it was possible to obtain insulation properties, it was confirmed that the insulation layer had low-temperature embrittlement and poor flexibility. On the other hand, in sample 13, the content of styrene resin (C) was increased and the content of propylene resin (A) was relatively reduced, so the amount of crystals in the insulating layer as a whole was small and the desired It was confirmed that it was not possible to obtain the insulation properties of

<Preferred embodiments of the present disclosure>
Preferred embodiments of the present disclosure will be described below.

(Additional note 1)
Contains propylene and styrene;
The melting point is 158°C or higher and 168°C or lower,
The heat of fusion is 55 J/g or more and 100 J/g or less,
Resin composition.

(Additional note 2)
A molded article formed from a resin composition and coated on an object with a thickness of 3 mm or more,
Contains propylene and styrene;
The melting point of the molded body is 158°C or more and 168°C or less,
The heat of fusion of the molded body is 55 J/g or more and 100 J/g or less,
When an outer sample whose distance from the surface toward the object is 0.5 mm and an inner sample whose distance from the object toward the surface is 2.5 mm are taken,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J / g or less,
Resin composition molded body.

(Additional note 3)
In Appendix 2,
The crosslinker residue is less than 300 ppm.

(Additional note 4)
In supplementary note 2 or 3,
The AC breakdown electric field at room temperature is 60 kV/mm or more.

(Appendix 5)
In any of appendices 2 to 4,
Each of the outer sample and the inner sample has only a single melting peak at 100° C. or higher in the DSC curve in which the differential scanning calorimetry was performed.

(Appendix 6)
In any of appendices 2 to 5,
The resin composition includes a propylene resin, a low crystalline resin, and a styrene resin,
The propylene resin has a heat of fusion of 100 J/g or more and 120 J/g or less, and a melting point of 160° C. or more and 175° C. or less,
The low crystalline resin is a copolymer containing at least two of ethylene, propylene, butene, hexene, and octene.

(Appendix 7)
In Appendix 6,
The resin composition contains the propylene resin in an amount of 55% by mass or more and 85% by mass or less, the low crystalline resin in an amount of 5% by mass or more and 15% by mass or less, and the styrene resin in an amount of 5% by mass or more and 35% by mass or less. .

(Appendix 8)
In appendix 6 or 7,
The styrene resin has a styrene content of 5% by mass or more and 35% by mass or less.

(Appendix 9)
In any of appendices 6 to 8,
The total amount of styrene in the resin composition is 0.5% by mass or more and 8% by mass or less.

(Appendix 10)
In any of appendices 6 to 9,
The propylene resin is a propylene homopolymer.

(Appendix 11)
a conductor;
an insulating layer coated on the outer periphery of the conductor with a thickness of 3 mm or more;
Equipped with
The insulating layer contains propylene and styrene,
The melting point of the insulating layer is 158°C or more and 168°C or less,
The heat of fusion of the insulating layer is 55 J/g or more and 100 J/g or less,
When an outer sample whose distance from the surface of the insulating layer toward the conductor is 0.5 mm and an inner sample whose distance from the conductor toward the surface is 0.5 mm are taken,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J / g or less,
power cable.

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

Claims (7)

A molded article formed from a resin composition and coated on an object with a thickness of 3 mm or more,
The resin composition includes a propylene resin, a low crystalline resin, and a styrene resin,
The propylene resin has a melting point of 160° C. or more and 175° C. or less, and a heat of fusion of 100 J/g or more and 120 J/g or less,
The low crystalline resin is ethylene propylene rubber or ultra-low density polyethylene that does not have a melting point or has a melting point of 100 ° C. or less and a heat of fusion of 50 J / g or less,
Contains the propylene resin in an amount of 55% by mass or more and 85% by mass or less, the low crystalline resin in an amount of 5% by mass or more and 15% by mass or less, and the styrene resin in an amount of 5% by mass or more and 35% by mass or less,
The melting point of the molded body is 158°C or more and 168°C or less,
The heat of fusion of the molded body is 55 J/g or more and 100 J/g or less,
an outer sample whose position from the surface of the molded body opposite to the target object is 0.5 mm; and a position from the target object toward the surface of the molded body opposite to the target object. When taking an inner sample with a diameter of 0.5 mm,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J / g or less,
Resin composition molded body. The AC breakdown electric field at room temperature is 60 kV/mm or more,
The resin composition molded article according to claim 1. Each of the outer sample and the inner sample has only a single melting peak at 100° C. or higher in a DSC curve obtained by performing differential scanning calorimetry .
The resin composition molded article according to claim 1 or 2. The styrene resin has a styrene content of 5% by mass or more and 35% by mass or less,
The resin composition molded article according to any one of claims 1 to 3. The total amount of styrene in the resin composition is 0.5% by mass or more and 8% by mass or less,
The resin composition molded article according to any one of claims 1 to 4. The propylene resin is a propylene homopolymer,
The resin composition molded article according to any one of claims 1 to 5. a conductor;
an insulating layer formed from a resin composition and coated on the outer periphery of the conductor with a thickness of 3 mm or more;
Equipped with
The resin composition is
Contains propylene resin, low crystalline resin and styrene resin,
The propylene resin has a melting point of 160° C. or more and 175° C. or less, and a heat of fusion of 100 J/g or more and 120 J/g or less,
The low crystalline resin is ethylene propylene rubber or ultra-low density polyethylene that does not have a melting point or has a melting point of 100 ° C. or less and a heat of fusion of 50 J / g or less,
Contains the propylene resin in an amount of 55% by mass or more and 85% by mass or less, the low crystalline resin in an amount of 5% by mass or more and 15% by mass or less, and the styrene resin in an amount of 5% by mass or more and 35% by mass or less,
The melting point of the insulating layer is 158°C or more and 168°C or less,
The heat of fusion of the insulating layer is 55 J/g or more and 100 J/g or less,
When an outer sample whose distance from the surface of the insulating layer toward the conductor is 0.5 mm and an inner sample whose distance from the conductor toward the surface is 0.5 mm are taken,
The absolute value of the difference obtained by subtracting the melting point of the outer sample from the melting point of the inner sample is 8 ° C. or less,
The absolute value of the difference obtained by subtracting the heat of fusion of the outer sample from the heat of fusion of the inner sample is 10 J / g or less,
power cable.

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