JP2022015542A - Resin composition, resin composition molding, power cable, and method for manufacturing power cable - Google Patents

Abstract

To improve water tree resistance in sea water.SOLUTION: A resin composition contains a base resin composed of linear low-density polyethylene, and a silane crosslinking agent, in which a content of the silane crosslinking agent is 0.4 pts.mass or more with respect to 100 pts.mass of the base resin, a DSC curve when a differential scanning calorimetry of a molding obtained by crosslinking the base resin with the silane crosslinking agent is performed has at least one heat history point appearing as a peak or a shoulder at a lower temperature side than a melting point, and a temperature of an intersection between a tangent line of a base line of the DSC curve and a tangent line having the largest inclination in contact with the low temperature side of the heat history point at the lowest temperature side is 79°C or lower.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a resin composition, a resin composition molded body, a power cable, and a method for manufacturing the power cable.

A power cable including an insulating layer obtained by cross-linking a base resin containing an ethylene / α-olefin copolymer with a silane cross-linking agent has been developed (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2001-6448

An object of the present disclosure is to provide a technique capable of improving water tree resistance in seawater.

According to one aspect of the present disclosure
A base resin made of linear low-density polyethylene and
Silane cross-linking agent and
Including
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
The DSC curve when differential scanning calorimetry is performed on a molded body obtained by cross-linking the base resin with the silane cross-linking agent has at least one thermal history point appearing as a peak or shoulder on the lower temperature side than the melting point.
A resin composition is provided in which the temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the tangent line having the largest inclination on the low temperature side of the heat history point on the coldest side is 79 ° C. or lower.

According to another aspect of the present disclosure.
A molded product in which a base resin made of linear low-density polyethylene is crosslinked with a silane cross-linking agent.
The silicon content is 0.07% by mass or more,
The DSC curve when performing differential scanning calorimetry has at least one thermal history point that appears as a peak or shoulder on the cold side of the melting point.
Provided is a resin composition molded body in which the temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the tangent line having the largest inclination on the low temperature side of the heat history point on the coldest side is 79 ° C. or lower.

According to yet another aspect of the present disclosure.
With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor and in which a base resin made of linear low-density polyethylene is crosslinked with a silane crosslinking agent.
Equipped with
The content of silicon in the insulating layer is 0.07% by mass or more, and is
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point.
A power cable is provided in which the temperature of the intersection of the tangent of the baseline of the DSC curve and the tangent of the tangent of the heat history point on the coldest side with the largest slope is 79 ° C. or lower.

According to yet another aspect of the present disclosure.
A step of preparing a resin composition containing a base resin made of linear low-density polyethylene and a silane cross-linking agent, and
A step of forming an insulating layer so as to cover the outer periphery of the conductor using the resin composition, and
A step of cross-linking the base resin in the insulating layer with the silane cross-linking agent,
Equipped with
In the step of preparing the resin composition,
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
In the step of cross-linking the base resin,
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point, and is tangent to the baseline of the DSC curve. Provided is a method for manufacturing a power cable for bridging the base resin so that the temperature of the intersection with the tangent line having the largest inclination tangent on the low temperature side of the heat history point on the lowest temperature side is 79 ° C. or lower.

According to the present disclosure, it is possible to improve the water tree resistance in seawater.

It is a figure which shows an example of the DSC curve when the differential scanning calorimetry is performed in the resin composition molded article which concerns on one Embodiment of this disclosure. It is a schematic cross-sectional view orthogonal to the axial direction of the power cable which concerns on one Embodiment of this disclosure.

[Explanation of Embodiments of the present disclosure]
<Knowledge obtained by the inventor, etc.>
First, the findings obtained by the inventors will be outlined.

Power cables may be laid, for example, in moist or flooded environments. In such an environment, when a predetermined electric field is applied to the insulating layer of the power cable, a water tree may be generated in the insulating layer. If a water tree is generated in the insulating layer, the insulation of the power cable may be deteriorated.

In particular, when the power cable is charged in seawater, water trees can be noticeably generated in the insulating layer.

That is, since seawater contains an electrolyte such as sodium chloride (NaCl), the affinity between seawater and the non-polar base resin is further smaller than the affinity between tap water and the base resin. Therefore, if seawater infiltrates into the insulating layer while the power cable is being charged, the seawater tends to aggregate in foreign substances and voids in the insulating layer. When seawater aggregates, mechanical strain occurs around the water aggregated portion due to the pressure increase of the aggregated water. As a result, tree-like or bow-tie-like water trees can be prominently generated in the insulating layer.

On the other hand, in recent years, the specifications required for power cables laid under the sea or on the seabed have become stricter. Alternatively, there is a need to simplify the configuration of power cables laid underwater or on the seabed and reduce the cost of power cables.

From the above, a power cable with improved water tree resistance in seawater is desired.

The present disclosure is based on the above-mentioned findings found by the inventors.

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

[1] The resin composition according to one aspect of the present disclosure is
A base resin made of linear low-density polyethylene and
Silane cross-linking agent and
Including
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
The DSC curve when differential scanning calorimetry is performed on a molded body obtained by cross-linking the base resin with the silane cross-linking agent has at least one thermal history point appearing as a peak or shoulder on the lower temperature side than the melting point.
The temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the lowest temperature side of the heat history point having the largest slope is 79 ° C. or lower.
According to this configuration, it is possible to improve the water tree resistance in seawater.

[2] The resin composition molded product according to another aspect of the present disclosure is
A molded product in which a base resin made of linear low-density polyethylene is crosslinked with a silane cross-linking agent.
The silicon content is 0.07% by mass or more,
The DSC curve when performing differential scanning calorimetry has at least one thermal history point that appears as a peak or shoulder on the cold side of the melting point.
The temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the lowest temperature side of the heat history point having the largest slope is 79 ° C. or lower.
According to this configuration, it is possible to improve the water tree resistance in seawater.

[3] In the resin composition molded product according to the above [2],
When the molded body was immersed in a NaCl aqueous solution of 2% by mass or more and 8% by mass or less at room temperature, and an AC electric field of 50 Hz or 4.2 kV / mm was applied to the molded body for 120 days.
The maximum length of the water tree generated in the molded body is less than 200 μm.
According to this configuration, it can be suitably applied to an underwater cable or a submarine cable that is constantly exposed to seawater.

[4] In the resin composition molded product according to the above [2] or [3].
The silicon content is 0.30% by mass or less.
According to this configuration, deterioration of tensile properties can be suppressed.

[5] In the resin composition molded product according to the above [4],
The tensile elongation measured according to JIS C3005 is 350% or more.
According to this configuration, the molded product can be suitably applied in an environment where it expands and contracts and bends.

[6] In the resin composition molded product according to any one of the above [2] to [5].
When the molded body is coated on a predetermined object and an inner sample having a position of 1 mm from the object toward the surface of the molded body is collected.
The gel fraction of the inner sample is more than 25%.
According to this configuration, it is possible to suppress thermal deformation of the molded product.

[7] In the resin composition molded product according to any one of the above [2] to [6].
An outer sample in which a predetermined object is coated with the molded body and the position from the surface of the molded body toward the object is 1 mm, and an inner sample in which the position from the object toward the surface is 1 mm. When the sample and the sample are taken,
The difference between the gel fraction in the outer sample minus the gel fraction in the inner sample is less than 35%.
According to this configuration, it is possible to suppress thermal deformation of the molded product.

[8] In the resin composition molded product according to the above [6] or [7].
According to JIS C3005, the heating deformation rate measured by pushing with an iron rod having a diameter of 9.5 mm under the condition that the temperature is 120 ° C. and the load is 23.4 N is 40% or less.
According to this configuration, the shape of the molded product can be stably maintained even when heated.

[6] The power cable according to still another aspect of the present disclosure is
With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor and in which a base resin made of linear low-density polyethylene is crosslinked with a silane crosslinking agent.
Equipped with
The content of silicon in the insulating layer is 0.07% by mass or more, and is
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point.
The temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the lowest temperature side of the heat history point having the largest slope is 79 ° C. or lower.
According to this configuration, it is possible to improve the water tree resistance in seawater.

[7] The method for manufacturing a power cable according to still another aspect of the present disclosure is described.
A step of preparing a resin composition containing a base resin made of linear low-density polyethylene and a silane cross-linking agent, and
A step of forming an insulating layer so as to cover the outer periphery of the conductor using the resin composition, and
A step of cross-linking the base resin in the insulating layer with the silane cross-linking agent,
Equipped with
In the step of preparing the resin composition,
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
In the step of cross-linking the base resin,
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point, and is tangent to the baseline of the DSC curve. The base resin is crosslinked so that the temperature of the intersection with the tangent line having the largest inclination tangent on the low temperature side of the heat history point on the lowest temperature side is 79 ° C. or lower.
According to this configuration, it is possible to improve the water tree resistance in seawater.

[Details of Embodiments of the present disclosure]
Next, an embodiment of the present disclosure will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

<Embodiment of the present disclosure>
(1) Resin Composition The resin composition of the present embodiment is a material constituting the insulating layer 130 of the power cable 10 described later, and is, for example, a base resin, a silane cross-linking agent (silane compound), and a radical generator ( It has a free radical generator) and other additives.

(Base resin)
The base resin (base polymer) is a resin component constituting the main component of the resin composition.

The base resin of the present embodiment is made of, for example, linear low density polyethylene (LLDPE: Linear Low Density Polyethylene). LLDPE is a copolymer of ethylene and α-olefin. LLDPE does not have a long chain branch and has a short chain branch derived from the α-olefin to be copolymerized.

Examples of the α-olefin of the monomer component other than ethylene include propylene, butene-1, pentene-1, octene-1, 4-methylpentene-1, 4-methylhexene-1, 4,4-dimethylpentene-1. , Nonene-1, Desen-1, Undecene-1, Dodecene-1, and the like.

The density of LLDPE is adjusted based on the α-olefin or the like to be copolymerized, and is, for example, 0.910 g / cm ³ or more and 0.945 g / cm ³ or less, preferably 0.919 g / cm ³ or more and 0.925 g / cm. It is ³ or less.

By using LLDPE as a base resin as described above, it is possible to suppress a local decrease in water tree resistance. Here, when seawater invades the base resin, the seawater tends to stay in the amorphous region of the base resin. Therefore, when the base resin is LDPE, when seawater invades the base resin, it may be locally concentrated in a portion where the number of LDPE crystals is small. On the other hand, in LLDPE used as the base resin of the present embodiment, the crystal state is stable because there are few branches as compared with LDPE. As a result, even if seawater invades the LLDPE as the base resin, the seawater can be uniformly dispersed as a whole in the LLDPE whose crystal state is stable. As a result, it becomes possible to suppress a local decrease in water tree resistance.

(Silane cross-linking agent)
The silane cross-linking agent is a material that forms cross-linking points in a resin composition molded product (hereinafter, also simply referred to as “molded product”) by being grafted to a base resin, hydrolyzed, and then dehydrated and condensed with each other. .. By using a silane cross-linking agent, a silyl group (silanol group) having a hydroxyl group as a hydrophilic group can be easily introduced into the molded body and easily dispersed in the molded body. This makes it possible to suppress the aggregation of water in the molded product. As a result, water tree resistance can be improved.

The silane cross-linking agent has a general formula:
RR'SiY ₂
It is represented by.

In the formula, R is an olefinically unsaturated hydrocarbon group or a hydroxycarbon oxy group. Examples of R include a vinyl group, an allyl group, a butenyl group, a cyclohexenyl group, a cyclopentadienyl group and the like. R is preferably a vinyl group.

Y is a hydrolyzable organic group (hereinafter, also referred to as “hydrolyzable group”). Examples of Y include an alkoxy group such as a methoxy group, an ethoxy group and a butoxy group, an acyloxy group such as a formyloxy group, an acetoxy group and a propionoxy group, and other oxime groups, alkylamino groups and arylamino groups. Y is preferably an alkoxy group.

R'is an R group or a Y group.

The most suitable silane cross-linking agent is, for example, vinylalkoxysilane. Examples of the vinylalkoxysilane include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyldimethoxymethylsilane, vinyldiethoxymethylsilane, vinylmethoxydimethylsilane, vinylethoxydimethylsilane and the like. It should be noted that not only one of these may be used alone, but also two or more of these may be used in combination.

The content of the silane cross-linking agent is, for example, 0.4 parts by mass or more, preferably 0.5 parts by mass or more, based on 100 parts by mass of the base resin. By setting the content of the silane cross-linking agent to 0.4 parts by mass or more, a silanol group as a hydrophilic group can be sufficiently introduced into the molded product. For example, the content of silicon (Si) related to the number of silanol groups in the molded product described later can be 0.07% by mass or more. Further, by setting the content of the silane cross-linking agent to 0.5 parts by mass or more, a silanol group as a hydrophilic group can be stably introduced into the molded product. For example, the Si content in the molded product described later can be 0.08% by mass or more.

On the other hand, the content of the silane cross-linking agent is, for example, preferably less than 2.0 parts by mass, more preferably 1.7 parts by mass or less, still more preferably 1. It is 5 parts by mass or less. By setting the content of the silane cross-linking agent within these ranges, it is possible to suppress an excessive increase in the cross-linking points in the molded product described later. For example, the Si content related to the number of cross-linking points in the molded body is preferably less than 0.32% by mass, more preferably 0.30% by mass or less, and further preferably 0.27% by mass or less. be able to.

The details of the Si content in the molded product, which is related to the number of silanol groups or the number of cross-linking points in the molded product, will be described later.

(Radical generator)
The radical generator is a material that generates radicals of the base resin and grafts the silane cross-linking agent to the base resin.

Examples of the radical generator include dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane. ) Hexane-3, α, α'-bis (t-butylperoxy-m-isopropyl) benzene, butylcumyl peroxide, isopropylcumyl-t-butyl peroxide and the like can be mentioned. It should be noted that not only one of these may be used alone, but also two or more of these may be used in combination.

The content of the radical generator is, for example, 0.05 parts by mass or more and 0.15 parts by mass or less with respect to 100 parts by mass of the base resin. By setting the content of the radical generator to 0.05 parts by mass or more, the silane cross-linking agent can be sufficiently grafted on the base resin. This makes it possible to secure a sufficient gel fraction. On the other hand, by setting the content of the radical generator to 0.15 parts by mass or less, it is possible to suppress the generation of voids caused by the decomposition products of the radical generator in the molded body.

(Silanol condensation catalyst)
The silanol condensation catalyst is added to the resin composition or permeated into the molded body from the surface of the molded body. The silanol condensation catalyst is a material that promotes cross-linking with a silane cross-linking agent.

The silanol condensation catalyst is, for example, a carboxylate of a metal such as tin, zinc, iron, lead, or cobalt, an organic base, an inorganic acid, an organic acid, or the like. More specifically, the silanol condensation catalyst includes dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dioctaate, stannous acetate, stannous cabrylate, lead naphthenate, zinc cabrylate, and naphthenic acid. Examples thereof include cobalt, ethylamine, dibutylamine, hexylamine, pyridine, sulfuric acid, hydrochloric acid, toluenesulfonic acid, acetic acid, stearic acid, maleic acid and the like.

The content of the silanol condensation catalyst is not particularly limited, but is, for example, 0.01 part by mass or more and 0.10 part by mass or less with respect to 100 parts by mass of the base resin.

(Other additives)
The resin composition may further contain, for example, an antioxidant, a lubricant, a colorant and the like.

(2) Resin Composition Molded Body The resin composition molded body of the present embodiment is a molded body made of the above-mentioned resin composition and coated with respect to a predetermined object. Specifically, the molded body of the present embodiment constitutes, for example, the insulating layer 130 of the power cable 10 described later. The object of the molded body is, for example, a long linear conductor 110. The resin composition molded body is extruded so as to cover the outer periphery of the conductor 110, for example. That is, the resin composition molded product has, for example, the same shape in the longitudinal direction of the object. The length of the resin composition molded product in the longitudinal direction of the object is, for example, 30 cm or more, preferably 50 cm or more.

In the molded product of the present embodiment, the base resin made of LLDPE is crosslinked with a silane cross-linking agent. That is, in the molded product, the silane cross-linking agent is grafted to the base resin. Further, the hydrolyzing group in the silane cross-linking agent is hydrolyzed to form a silanol group. Further, silanol groups are dehydrated and condensed to form cross-linking points.

(Silicon content)
The Si content in the molded body of the present embodiment is related to the number of silanol groups or the number of cross-linking points in the above-mentioned molded body. In other words, by measuring the Si content in the molded body, the number of silanol groups or the number of cross-linking points in the molded body can be indirectly grasped. The Si content in the molded body is measured by elemental analysis such as, for example, inductively coupled plasma (ICP) emission spectroscopy. As the quantification method in the analysis, for example, the calibration curve method is used.

The Si content in the molded product of the present embodiment is, for example, 0.07% by mass or more, preferably 0.08% by mass or more. When the Si content in the molded product is less than 0.07% by mass, the silanol group as a hydrophilic group is not sufficiently introduced into the molded product. Therefore, agglomeration of water may occur in the molded product. As a result, water tree tolerance may decrease. On the other hand, in the present embodiment, by setting the Si content in the molded body to 0.07% by mass or more, the silanol group as a hydrophilic group can be sufficiently introduced into the molded body. This makes it possible to suppress the aggregation of water in the molded product. As a result, water tree resistance can be improved. Further, in the present embodiment, by setting the Si content in the molded body to 0.08% by mass or more, a silanol group as a hydrophilic group can be stably introduced into the molded body. Thereby, the water tree resistance can be stably improved.

On the other hand, the Si content in the molded product of the present embodiment is, for example, preferably less than 0.32% by mass, more preferably 0.30% by mass or less, still more preferably 0.27% by mass or less. Is. When the Si content in the molded product is 0.32% by mass or more, the number of cross-linking points in the molded product is excessively large. Therefore, the flexibility may decrease and the tensile properties may decrease. On the other hand, in the present embodiment, by setting the Si content in the molded product to 0.32% by mass or less, an excessive increase in the cross-linking points in the molded product is suppressed. As a result, it is possible to suppress a decrease in flexibility and a decrease in tensile properties. Further, in the present embodiment, the Si content in the molded product is more preferably 0.30% by mass or less, further preferably 0.27% by mass or less, so that the number of cross-linking points in the molded product is excessively increased. Is stably suppressed. As a result, flexibility can be improved and tensile properties can be improved.

(Gel fraction (crosslinking degree))
The gel fraction (crosslinking degree) of the molded body of the present embodiment depends on, for example, the Si content in the above-mentioned molded body, the cross-linking temperature described later, the cross-linking time, and the position in the thickness direction of the molded body. In the present embodiment, by controlling the Si content, the crosslinking temperature and the crosslinking time, the gel fraction of the molded product is within an appropriate range at each position in the thickness direction of the molded product.

Here, in the following, a sample collected from a portion where the position from the surface of the molded body toward the object is 1 mm is referred to as an "outer sample", and from the portion where the position from the object toward the surface of the molded body is 1 mm. The collected sample is referred to as an "inner sample".

The gel fraction of the inner sample of this embodiment is, for example, more than 25%. When the gel fraction of the inner sample is 25% or less, there are few cross-linking points at the sampling position. Therefore, there is a possibility that the molded product is easily deformed by heating (deformation when heated). On the other hand, by setting the gel fraction of the inner sample to more than 25%, a predetermined amount of cross-linking points can be secured. This makes it possible to suppress thermal deformation of the molded product.

In principle, the gel fraction of the inner sample does not exceed the gel fraction of the outer sample excessively because the cross-linking proceeds from the surface side.

Since the Si content in the molded product of the present embodiment is 0.07% by mass or more, preferably 0.08% by mass or more as described above, the gel fraction of the outer sample is, for example, 35%. It is more than 40%, preferably 40% or more.

On the other hand, the Si content in the molded product of the present embodiment is preferably less than 0.32% by mass, more preferably 0.30% by mass or less, still more preferably 0.27% by mass, as described above. From the following, the gel fraction of the outer sample is, for example, preferably less than 83%, more preferably 79% or less, still more preferably 70% or less.

Further, in the present embodiment, the difference obtained by subtracting the gel fraction of the inner sample from the gel fraction of the outer sample (hereinafter, also referred to as “inner / outer gel fraction difference”) is less than 35%, for example. When the difference between the inner and outer gel fractions is 35% or more, the number of cross-linking points is relatively small at the sampling position of the inner sample. Therefore, as described above, the molded product may be easily deformed by heating. On the other hand, by setting the difference between the inner and outer gel fractions to less than 35%, it is possible to uniformly secure the cross-linking points as a whole in the thickness direction of the molded product. This makes it possible to suppress thermal deformation of the molded product.

The lower limit of the difference between the inner and outer gel fractions is not limited. However, when the difference between the inner and outer gel fractions approaches 0%, that is, when the number of cross-linking points becomes too large over the whole, the water tree resistance tends to be slightly lowered even if it is within the specified range. Therefore, the difference between the inner and outer gel fractions is preferably 5% or more, for example. Here, as the electric field becomes stronger, the water tree tends to be easily generated. In the power cable 10, a water tree is likely to be generated from the inner semi-conductive layer 120 side toward the outer semi-conductive layer 140 side. Therefore, for example, in the power cable 10, the cross-linking points that are local weak points are distributed according to the gradation of the electric field in the thickness direction. That is, the number of cross-linking points is relatively small on the inner semi-conductive layer 120 side (that is, the inner sample side) where the electric field is strong, while the cross-linking points are relative to each other on the outer semi-conductive layer 140 side (that is, the outer sample side) where the electric field is weak. To increase the number. As a result, local weak points can be relatively reduced on the internal semi-conductive layer 120 side where the electric field is strong. As a result, the decrease in water tree resistance can be suppressed. When the difference between the inner and outer gel fractions is 5% or more, the gel fraction gradually increases from the inner semi-conductive layer 120 side to the outer semi-conductive layer 140 side, for example. It is preferable to have.

(Crystal state)
As a result of diligent studies, the present inventors have found that the water tree resistance can be remarkably improved by adjusting the production conditions according to the present embodiment and refining the crystals composed of the base resin in the molded body. I found it.

The crystal state in the molded product can be grasped by, for example, differential scanning calorimetry (DSC).

The "differential scanning calorimetry" is performed, for example, in accordance with JIS-K-7121 (1987). Specifically, in the DSC apparatus, the temperature is raised from room temperature (normal temperature, for example, 27 ° C.) to 220 ° C. at 10 ° C./min. Thereby, the DSC curve can be obtained by plotting the amount of heat absorption (heat flow) per unit time with respect to the temperature. The "DSC curve" referred to below is the DSC curve for the first temperature rise.

Here, with reference to FIG. 1, the characteristics of the DSC curve in the molded product of the present embodiment will be described. FIG. 1 is a diagram showing an example of a DSC curve when differential scanning calorimetry is performed on the resin composition molded product according to the present embodiment.

As shown in FIG. 1, in the DSC curve when DSC is performed in the molded body of the present embodiment, the "melting point (melting peak temperature) MP" has the maximum (maximum) absolute value of the amount of heat absorbed per unit time in the sample. It is calculated as the temperature at which the peak) is reached.

The melting point MP of the molded product of the present embodiment is, for example, 110 ° C. or higher and 135 ° C. or lower. When the melting point MP is within the above range, it means that the molded product contains LLDPE as a crystalline base resin.

Further, as shown in FIG. 1, the DSC curve when DSC is performed in the molded product of the present embodiment has, for example, at least one thermal history point TP. The "heat history point TP" referred to here is, for example, more than the melting point MP due to the heat history received until the molded product is molded (that is, until the power cable 10 is manufactured). It is a characteristic point that appears as a peak (sub-peak) or shoulder on the low temperature side. The "peak (sub-peak)" here means a point where the slope of the heat flow with respect to temperature is inverted up and down, and the "shoulder" means that the slope of the heat flow with respect to temperature is not inverted up and down but changes in a stepped manner. It means the point to do. In the DSC, when the molded product is heated to a temperature equal to or higher than the melting point MP (for example, 200 ° C.), cooled, and then heated again, the above-mentioned heat history point TP disappears. That is, the heat history in the molded product can be grasped by the heat history point TP.

The absolute value of the heat flow at the heat history point is smaller than the absolute value of the heat flow at the melting point. Further, not only one heat history point TP but also a plurality of heat history points TP may appear.

In the present embodiment, the temperature of the intersection CP between the tangent line of the baseline BL of the DSC curve and the tangent line tangent to the lowest temperature side of the heat history point TP1 having the largest slope is, for example, 55 ° C. or higher and 79 ° C. or lower. It is preferably 65 ° C. or higher and 75 ° C. or lower. The term "tangent to the baseline BL" as used herein means, for example, a tangent to the baseline BL within the range of 40 ° C. or higher and lower than 55 ° C. Further, the "tangent line having the largest inclination in contact with the heat history point TP1 on the coldest side" can be rephrased as, for example, a tangent line at the inflection point between the heat history point TP1 and the baseline BL. ..

The temperature of the intersection CP being less than 55 ° C. corresponds to the water cross-linking temperature of the molded product as a thermal history being less than about 55 ° C. In this case, at least one of the hydrolysis and dehydration condensation of the silane cross-linking agent does not occur, and the molded product is hardly cross-linked. On the other hand, in the present embodiment, the temperature of the intersection CP is set to 55 ° C. or higher. This corresponds to the water cross-linking temperature of the molded product as a thermal history of about 55 ° C. or higher. This can cause hydrolysis and dehydration condensation of the silane cross-linking agent. As a result, the molded product of the present embodiment is crosslinked.

The temperature of the intersection CP of less than 65 ° C. corresponds to the water cross-linking temperature of the molded product as a thermal history being less than about 65 ° C. In this case, the molded product is not sufficiently crosslinked. As a result, at least one of a decrease in tensile strength and a decrease in tensile elongation may occur. On the other hand, in the present embodiment, the temperature of the intersection CP is 65 ° C. or higher. This corresponds to the water cross-linking temperature of the molded product as a thermal history of about 65 ° C. or higher. As a result, the molded product is sufficiently crosslinked. As a result, it is possible to suppress a decrease in tensile strength and a reduction in tensile elongation.

On the other hand, the temperature of the intersection CP exceeding 79 ° C. corresponds to the water cross-linking temperature of the molded product as a thermal history being approximately 79 ° C. or higher. Since the water cross-linking temperature was high, the crystals in the molded product were coarse. When the crystal is coarse, the strain tends to be large at the portion where water is aggregated at the crystal interface. As a result, water tree tolerance may decrease. On the other hand, in the present embodiment, the temperature of the intersection CP is 79 ° C. or lower. This corresponds to the water cross-linking temperature of the molded product as a thermal history of about 79 ° C. or lower. By setting the water crosslinking temperature to a predetermined temperature or lower, the crystals in the molded product can be made finer. By refining the crystal, it is possible to suppress an increase in strain at a portion where water is aggregated at the crystal interface. As a result, water tree resistance can be improved. In particular, it is possible to improve the water tree resistance in seawater. Further, in the present embodiment, by setting the temperature of the intersection CP to 75 ° C. or lower, the crystals in the molded product can be stably refined. Thereby, the water tree resistance can be stably improved.

(Water tree resistance)
In the present embodiment, as described above, the silanol groups are sufficiently introduced into the molded body and the crystals in the molded body are made finer, so that the water tree resistance of the molded body is remarkably improved. There is.

Specifically, in the present embodiment, when the molded body is immersed in tap water at room temperature (27 ° C.) and an AC electric field of 50 Hz 4.2 kV / mm is applied to the molded body for 120 days, the molded body The maximum length of the water tree generated therein is, for example, less than 200 μm, preferably 185 μm or less.

Further, in the present embodiment, in a state where the molded body is immersed in a NaCl aqueous solution of 2% by mass or more and 8% by mass or less at room temperature (27 ° C.), an AC electric field of 50 Hz 4.2 kV / mm is applied to the molded body for 120 days. The maximum length of the water tree generated in the molded body when applied is, for example, less than 200 μm, preferably 196 μm or less.

(Tensile characteristics)
In the present embodiment, as described above, the tensile properties of the molded product can be improved by appropriately adjusting the cross-linking points in the molded product.

Specifically, in the present embodiment, the tensile elongation of the molded product measured according to JIS C3005 is, for example, 350% or more, preferably more than 380%, and more preferably 420% or more.

The tensile elongation of the molded product is not limited as it is larger. However, in the molded product of the present embodiment, the tensile elongation is, for example, 1000% or less.

(Heating deformation rate)
In the present embodiment, as described above, by appropriately adjusting the gel fraction in the molded product, that is, the cross-linking point, the thermal deformation of the molded product can be suppressed.

Specifically, in accordance with JIS C3005, the heating deformation rate measured by pushing with an iron rod having a diameter of 9.5 mm under the condition that the temperature is 120 ° C. and the load is 23.4 N is, for example, 40%. It is as follows.

The thermal deformation rate of the molded product is not limited as it is smaller.

(3) Power cable Next, the power cable of the present embodiment will be described with reference to FIG. FIG. 2 is a cross-sectional view orthogonal to the axial direction of the power cable according to the present embodiment.

The power cable 10 of the present embodiment is configured as a so-called solid-state insulated power cable. Further, the power cable 10 of the present embodiment is configured to be laid underwater or underwater, for example. The power cable 10 is used for alternating current, for example.

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

The power cable 10 of the present embodiment has the above-mentioned remarkable water tree suppressing effect, and thus has, for example, a metal impermeable layer such as a so-called aluminum cover outside the shielding layer 150. do not have. That is, the power cable 10 of the present embodiment is configured by a non-complete impermeable structure.

(Conductor (conductor))
The conductor 110 is configured by twisting a plurality of conductor core wires (conductive core wires) including, for example, pure copper, a copper alloy, aluminum, an aluminum alloy, or the like.

(Internal semi-conductive layer)
The internal semi-conductive layer 120 is provided so as to cover the outer periphery of the conductor 110. Further, the internal semi-conductive layer 120 has semi-conductivity and is configured to suppress electric field concentration on the surface side of the conductor 110. The internal semi-conductive layer 120 is conductive with at least one of, for example, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, an ethylene-butyl acrylate copolymer, and an ethylene-vinyl acetate copolymer. Contains carbon black and.

(Insulation layer)
The insulating layer 130 is provided so as to cover the outer periphery of the inner semi-conductive layer 120, and is configured as a molded body formed from the above-mentioned resin composition.

The insulating layer 130 has excellent water tree resistance and good tensile properties as the characteristics of the above-mentioned molded product.

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

(Shielding layer)
The shielding layer 150 is provided so as to cover the outer periphery of the outer semi-conductive layer 140. The shielding layer 150 is configured by, for example, winding a copper tape, or is configured as a wire shield in which a plurality of annealed copper wires or the like are wound. A tape made of a rubberized cloth or the like may be wound around the inside or the outside of the shielding layer 150.

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

(Specific dimensions, etc.)
The specific dimensions of the power cable 10 are not particularly limited, but for example, the diameter of the conductor 110 is 5 mm or more and 65 mm or less, and the thickness of the internal semi-conductive layer 120 is 0.1 mm or more and 3 mm or less. The thickness of the insulating layer 130 is 1 mm or more and 35 mm or less, the thickness of the external semi-conductive layer 140 is 0.5 mm or more and 3 mm or less, and the thickness of the shielding layer 150 is 0.05 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 the present embodiment is, for example, 6.6 kV 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, the step is abbreviated as "S".

(S100: Resin composition preparation step)
First, a resin composition is prepared.

In the present embodiment, a base resin made of LLDPE, a silane cross-linking agent, a radical generator, and other additives are mixed (kneaded) with a mixer such as a Banvarimixer or a kneader to form a mixed material.

At this time, the content of the silane cross-linking agent is, for example, 0.4 parts by mass or more with respect to 100 parts by mass of the base resin. The content of the radical generator is, for example, 0.05 parts by mass or more and 0.15 parts by mass or less with respect to 100 parts by mass of the base resin.

At this time, for example, a predetermined amount of silanol condensation catalyst is added to the resin composition.

After forming the mixed material, the mixed material is granulated by an extruder. As a result, a pellet-shaped resin composition that constitutes the insulating layer 130 is formed. A twin-screw extruder having a high kneading action may be used to collectively perform the steps from mixing to granulation.

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

(S300: Cable core forming step (insulating layer forming step, extrusion step))
After the resin composition preparation step S100 and the conductor preparation step S200 are completed, the extruder A for forming the internal semi-conductive layer 120 among the three-layer simultaneous extruders is, for example, an ethylene-ethyl acrylate copolymer and a conductive material. The composition for the internal semi-conductive layer mixed with carbon black in advance is charged.

The pellet-shaped resin composition described above is charged into the extruder B that forms the insulating layer 130.

The composition for the external semi-conductive layer containing the same material as the resin composition for the internal semi-conductive layer charged into the extruder A is charged into the extruder C for forming the external semi-conductive layer 140.

Next, each extruded product from the extruders A to C is guided to the common head, and the inner semi-conductive layer 120, the insulating layer 130, and the outer semi-conductive layer 140 are simultaneously formed on the outer periphery of the conductor 110 from the inside to the outside. Extrude.

At this time, in the extruder B forming the insulating layer 130, for example, the silane cross-linking agent is grafted to the base resin in the extruder B by the so-called "one-shot method", and the insulating layer 130 is extruded. do.

That is, first, an oxyradic is generated by thermally decomposing peroxide as a radical generator. After the oxy radicals are generated, the radicals of the base resin are generated by the oxy radicals. Once the polyethylene radicals are generated, the polyethylene radicals react with the unsaturated bonds of the silane cross-linking agent to bond them together. This makes it possible to graft the silane cross-linking agent to the base resin.

By the above cable core forming step S300, a cable core composed of a conductor 110, an internal semiconductive layer 120, an insulating layer 130, and an external semiconductive layer 140 is formed.

(S400: Cross-linking step)
After forming the cable core, the base resin in the insulating layer 130 is crosslinked with a silane crosslinking agent.

Specifically, the cable core extruded from the extruder is put into a constant temperature and humidity chamber kept at a predetermined temperature and a predetermined humidity, or a hot water tank kept at a predetermined temperature. At this time, the hydrolyzing group of the silane cross-linking agent grafted to the base resin is hydrolyzed by the water permeating into the insulating layer 130 and the silanol condensation catalyst to generate silanol groups, and the silanol groups are generated from each other. Is dehydrated and condensed. In this way, the base resin of the insulating layer 130 can be crosslinked in the presence of moisture.

At this time, in the present embodiment, the DSC curve has at least one heat history point TP on the lower temperature side than the melting point MP, and the tangent to the baseline BL of the DSC curve and the heat history point TP1 on the lowest temperature side. The base resin is crosslinked so that the temperature of the intersection CP with the tangent line having the largest tangent on the low temperature side is 79 ° C. or lower.

Specifically, at this time, the cross-linking temperature in the constant temperature and humidity chamber or the hot water tank is set to, for example, a temperature corresponding to (equal to) the temperature of the intersection CP. Specifically, the cross-linking temperature is set to, for example, 79 ° C. or lower. As a result, at least one thermal history point TP can be formed on the DSC curve of the molded product, and the temperature of the intersection CP on the DSC curve can be set to 79 ° C. or lower.

The cross-linking temperature is preferably 65 ° C. or higher, for example. Thereby, the temperature of the intersection CP in the DSC curve can be set to 65 ° C. or higher.

At this time, the cross-linking time is, for example, 12 hours or more and 168 hours or less, preferably 24 hours or more and 72 hours or less. By setting the cross-linking time to 12 hours or more, even if the cross-linking temperature is 79 ° C. or lower as described above, the gel fraction at least on the outside of the insulating layer 130 can be secured to a predetermined value or more. Further, by setting the crosslinking time to 24 hours or more, even if the crosslinking temperature is 79 ° C. or lower as described above, the difference in gel fraction between the inside and outside of the insulating layer 130 can be reduced. On the other hand, by setting the crosslinking time to 168 hours or less, productivity can be maintained. Further, by setting the crosslinking time to 72 hours or less, it is possible to prevent the difference in gel fraction between the inside and outside of the insulating layer 130 from excessively approaching 0%.

(S500: Shielding layer forming step)
After forming the cable core, the shielding layer 150 is formed on the outside of the outer semi-conductive layer 140, for example, by winding a copper tape.

(S600: Sheath forming step)
After the shielding layer 150 is formed, vinyl chloride is put into an extruder and extruded to form a sheath 160 on the outer periphery of the shielding layer 150. In the sheath forming step S600, the sheath 160 is extruded from the outside of the external semi-conductive layer 140, and the sheath 160 and the like are immediately cooled. Therefore, the temperature application time to the insulating layer 130 is short. As a result, it is considered that the thermal history of the insulating layer 130 caused by the sheath forming step S600 hardly occurs.

As described above, the power cable 10 as a solid-state insulated power cable is manufactured.

(5) Effects of the present embodiment According to the present embodiment, one or more of the following effects are exhibited.

(A) In the present embodiment, the base resin in the molded product is crosslinked with a silane cross-linking agent, and the silicon content in the molded product is 0.07% by mass or more, so that a silanol group as a hydrophilic group can be obtained. It can be sufficiently introduced into the molded body. This makes it possible to suppress the aggregation of water in the molded product. As a result, water tree resistance can be improved.

(B) The DSC curve of the molded product of the present embodiment has at least one thermal history point TP that appears as a peak or shoulder on the lower temperature side than the melting point MP. Further, the temperature of the intersection of the tangent line of the baseline BL of the DSC curve and the tangent line tangent to the lowest temperature side of the heat history point TP1 having the largest slope is 79 ° C. or lower. This corresponds to the water cross-linking temperature of the molded product as a thermal history of about 79 ° C. or lower. This makes it possible to miniaturize the crystals in the molded product. By refining the crystal, it is possible to suppress an increase in strain at a portion where water is aggregated at the crystal interface. As a result, water tree resistance can be improved.

Due to the synergistic effect of (a) and (b), in the present embodiment, the water tree resistance can be remarkably improved as compared with the conventional case. In particular, it is possible to improve the water tree resistance in seawater.

(C) In the present embodiment, when the molded body is immersed in seawater at room temperature and an AC electric field of 50 Hz, 4.2 kV / mm is applied to the molded body for 120 days, it is generated in the molded body. The maximum length of the water tree is less than 200 μm. By significantly improving the water tree resistance in this way, it can be suitably applied to an underwater cable or a submarine cable that is constantly exposed to seawater. Further, by significantly improving the water tree resistance, the configuration of the impermeable layer of the power cable 10 can be simplified. For example, the impermeable layer can be eliminated or the shielding layer can be simply configured. As a result, the cost of the power cable 10 can be reduced.

(D) In the present embodiment, the silicon content in the molded product is less than 0.32% by mass, so that an excessive increase in the cross-linking points in the molded product is suppressed. As a result, it is possible to suppress a decrease in flexibility and a decrease in tensile properties. Further, by setting the Si content in the molded product to 0.30% by mass or less, the flexibility can be improved and the tensile properties can be improved.

(E) In the present embodiment, the tensile elongation of the molded product measured according to JIS C3005 is 350% or more. As described above, in the present embodiment, a predetermined tensile property can be ensured. As a result, the power cable 10 can be suitably laid even in an environment where the power cable 10 expands and contracts or bends. Specifically, the power cable 10 of the present embodiment can be applied to, for example, an array cable (dynamic cable, riser cable) that is flexibly connected to a floating floating device in water. ..

(F) In the present embodiment, the gel fraction of the inner sample is more than 25%. This makes it possible to secure a predetermined amount of cross-linking points. As a result, it is possible to suppress thermal deformation of the molded product.

(G) In the present embodiment, the difference obtained by subtracting the gel fraction of the inner sample from the gel fraction of the outer sample is less than 35%. As a result, the cross-linking points can be uniformly secured as a whole in the thickness direction of the molded product. As a result, it is possible to suppress thermal deformation of the molded product.

(H) In the present embodiment, the heating deformation rate measured by pushing with an iron rod having a diameter of 9.5 mm under the condition that the temperature is 120 ° C. and the load is 23.4 N in accordance with JIS C3005 is 40. % Or less. As described above, in the present embodiment, it is possible to suppress the thermal deformation of the molded product. As a result, the shape of the insulating layer 130 can be stably maintained even under the condition that the insulating layer 130 as the molded body of the present embodiment is heated by the energization of the power cable 10.

<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 case where the power cable 10 does not have the impermeable layer has been described, but the present disclosure is not limited to this case. The power cable 10 may have a simple impermeable layer because it has the above-mentioned remarkable water tree suppressing effect. Specifically, the simple impermeable layer is made of, for example, a metal laminated tape. The metal laminated tape has, for example, a metal layer made of aluminum, copper, or the like, and an adhesive layer provided on one side or both sides of the metal layer. The metal laminated tape is, for example, wound by vertical attachment so as to surround the outer circumference of the cable core (outer circumference than the outer semi-conductive layer). The water-impervious layer may be provided outside the shielding layer, or may also serve as a shielding layer. With such a configuration, the cost of the power cable 10 can be reduced.

In the above-described embodiment, the case where the power cable 10 is configured to be laid underwater or underwater has been described, but the present disclosure is not limited to this case. For example, the power cable 10 may be laid underground or above ground.

In the above-described embodiment, the case where the silane cross-linking agent is grafted to the insulating layer base resin and the insulating layer 130 is extruded in the extruder B by the so-called "one-shot method" has been described. Is not limited to this case. The so-called "two-shot method" may be used. In the two-shot method, first, a silane cross-linking agent is pre-grafted to the base resin. Next, the grafted base resin and the silanol condensation catalyst are put into an extruder to extrude the insulating layer. The graft copolymerization of the silane cross-linking agent may be carried out by such a method.

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

(1) Preparation of power cable First, the resin composition described below was mixed with a Bambali mixer and granulated into pellets by an extruder. Next, a conductor having a cross-sectional area of 60 mm ² was prepared. After preparing the conductor, the outer semi-conductive layer resin is composed of the resin composition for the inner semi-conductive layer containing the ethylene-ethyl acrylate copolymer, the following resin composition, and the same material as the resin composition for the inner semi-conductive layer. The composition and the composition were charged into the extruders A to C, respectively. Each extrusion from the extruders A to C was guided to a common head, and the internal semi-conductive layer, the insulating layer and the outer semi-conductive layer were simultaneously extruded from the inside to the outside on the outer periphery of the conductor. At this time, the thicknesses of the inner semi-conductive layer, the insulating layer, and the outer semi-conductive layer were set to 0.5 mm, 3.1 mm, and 0.5 mm, respectively. The cable core thus obtained was put into a hot water tank kept at a predetermined cross-linking temperature, and the base resin in the insulating layer was cross-linked with a silane cross-linking agent. Next, a shielding layer was formed by winding a copper tape on the outside of the outer semi-conductive layer 140. Then, a sheath made of vinyl chloride was formed on the outer periphery of the shielding layer. From the above, the respective power cables of Samples 1-1 to 4-3 were manufactured.

[Samples 1-1 to 1-5]
<Each component of the resin composition>
(Base resin)
Linear low density polyethylene (LLDPE):
(Density d = 0.923 g / cm ³ , MFR = 0.7 g / 10 min) 100 parts by mass (silane cross-linking agent)
Vinyltrimethoxysilane: 0.3 to 1.8 parts by mass (radical generator)
Dicumyl peroxide: 0.1 part by mass (silanol condensation catalyst)
Dibutyl tin dilaurate: 0.03 parts by mass <Manufacturing conditions>
Crosslink temperature (hot water tank temperature): 70 ° C
Crosslink time: 48 hours

[Sample 2-1]
It was prepared in the same manner as Sample 1-3 except that the content of the silane cross-linking agent was 2 parts by mass and the cross-linking temperature was 80 ° C.
[Sample 2-2]
It was prepared in the same manner as Sample 2-1 except that LLDPE and high-density polyethylene (HDPE) were mixed as a base resin.
High Density Polyethylene (HDPE):
(Density d = 0.940 g / cm ³ , MFR = 1.0 g / 10 min) 15 parts by mass [Sample 2-3]
It was prepared in the same manner as Sample 1-3 except that the cross-linking temperature was set to 80 ° C.

[Samples 3-1 to 3-3]
It was prepared in the same manner as Sample 1-3 except that the cross-linking time was 12 hours, 24 hours, and 72 hours, respectively.

[Sample 4-1]
It was prepared in the same manner as Sample 2-3 except that the crosslinking temperature was 80 ° C. and the crosslinking temperature was 6 hours.
[Samples 4-2 and 4-3]
It was prepared in the same manner as Sample 1-3 except that the cross-linking temperature was 50 ° C. and 55 ° C., respectively, and the cross-linking time was 96 hours.

(2) Evaluation (collection of evaluation sheet)
The insulating layer of each power cable of Samples 1-1 to 4-3 is stripped off, and the outer sheet where the position from the surface of the insulating layer toward the conductor is 1 mm and the position from the conductor toward the surface of the insulating layer are. An inner sheet having a size of 1 mm was collected. In each of the following evaluations of "Si content", "DSC tangential intersection temperature", and "tensile elongation", the average value between the measured value of the outer sheet and the measured value of the inner sheet was obtained. The tests of "water tree resistance" and "heat deformation rate", which will be described later, were performed in the state of a power cable before collecting the sheet.

(Si content)
Elemental analysis of the evaluation sheet obtained from the insulating layer was performed by ICP emission spectroscopy. The Si content (mass%) in the evaluation sheet was determined by elemental analysis. The calibration curve method was used as the quantification method.

(Gel fraction (crosslinking degree))
The gel fractions of the outer sheet and the inner sheet were measured according to JIS C3005. Specifically, first, the mass of the evaluation sheet was measured. Next, the sheet was immersed in a predetermined solvent (for example, hot xylene) to dissolve the sheet. At this time, the portion of the sheet on which the base resin was crosslinked remained without being dissolved as a gel. After the sheet was dissolved, the mass of the gel remaining without dissolution was measured. As a result, the "gel fraction" was obtained by calculating the ratio (%) of the mass of the remaining gel to the mass of the sheet before dissolution.

In addition, the difference obtained by subtracting the gel fraction of the inner sheet from the gel fraction of the outer sheet was calculated, and the "inner-outer gel fraction difference" was obtained.

(DSC tangent intersection temperature)
DSC measurement of the evaluation sheet was performed. DSC measurements were performed in accordance with JIS-K-7121 (1987). Specifically, as the DSC device, a DSC8500 (input compensation type) manufactured by PerkinElmer Co., Ltd. was used. The reference sample was, for example, α-alumina. The mass of the sample was 8 to 10 mg. In the DSC apparatus, the temperature was raised from room temperature (27 ° C.) to 220 ° C. at 10 ° C./min. As a result, a DSC curve was obtained by plotting the amount of heat absorption (heat flow) per unit time with respect to temperature.

At this time, the temperature of the intersection of the tangent of the baseline of the DSC curve and the tangent with the largest slope tangent on the low temperature side of the heat history point on the coldest side (also referred to as "DSC tangent intersection temperature") was obtained.

(Water tree resistance)
In the power cable, tap water or an aqueous NaCl solution of 2% by mass or more and 8% by mass or less was injected between the surface of the conductor and the inner surface of the sheath. As a result, the insulating layer was immersed in a predetermined aqueous solution. The water temperature was set to room temperature (27 ° C.).

Next, with the insulating layer immersed in a predetermined aqueous solution at room temperature, an AC voltage of 50 Hz and 13 kV was applied between the conductor and the shielding layer. As a result, an AC electric field of 50 Hz and approximately 4.2 kV / mm was applied to the insulating layer. The state in which the AC electric field was applied to the insulating layer was maintained, and the charging period was set to 120 days.

After applying a predetermined AC electric field, the cross section of the insulating layer of the power cable was sliced to prepare a sheet for evaluating a water tree. Once the sheet was obtained, the sheet was dried and the sheet was boiled and stained with an aqueous methylene blue solution. After dyeing the sheet, the water tree generated in the sheet was observed by observing the sheet with an optical microscope. At this time, the maximum length of the water tree generated in the sheet was measured.

In Table 1 below, the "maximum length of the water tree" is the length of the water tree that was the longest by observing the water tree evaluation sheet as slice pieces for 5 cc of the insulating layer randomly sampled. Rounded to the nearest.

(Tensile characteristics)
The tensile elongation of the evaluation sheet was measured according to JIS C3005. Specifically, the tensile elongation of the sheet was measured by pulling the evaluation sheet at a tensile speed of 200 mm / min using a JIS-3 dumbbell.

(Heating deformation rate)
According to JIS C3005, under the condition that the temperature is 120 ° C and the load is 23.4N, the heating deformation rate is increased by pushing into the power cable of each sample using an iron rod with a diameter of 9.5 mm. Was measured.

The applied load was set from the following equation (2).

（ただし、Ｗは荷重（Ｎ）であり、ρは内部半導電層および絶縁層を含む厚さ（ｍｍ）であり（外部半導電層は含まれない）、Ｒは絶縁層の外径、およそ電力ケーブルの外径（ｍｍ）である。）

(However, W is the load (N), ρ is the thickness (mm) including the inner semi-conductive layer and the insulating layer (excluding the outer semi-conductive layer), and R is the outer diameter of the insulating layer, approximately. The outer diameter (mm) of the power cable.)

(3) Results The results of evaluation of each sample will be described using Table 1 below. In Table 1 below, the unit of the content of the compounding agent is "part by mass".

(Water tree resistance)
In Sample 1-1 having a Si content of less than 0.07% by mass, the maximum length of the water tree was 200 μm or more regardless of the type of the immersed aqueous solution. In Sample 1-1, the Si content was less than 0.07% by mass, and the silanol group as a hydrophilic group was not sufficiently introduced. Therefore, it is considered that the water tree resistance has decreased.

In the samples 2-1 to 2-3, 4-1 whose DSC tangential intersection temperature was more than 79 ° C., the maximum length of the water tree, especially in seawater, was 200 μm or more. In Samples 2-1 to 2-3, 4-1 the Si content was 0.07% by mass or more, and it is considered that a sufficient silanol group was introduced. However, since the water crosslinking temperature was high, the crystals in the molded product were coarse. Therefore, it is considered that the water tree resistance in seawater decreased.

On the other hand, the samples 1-2 to 1-5, 3-1 to 3-3, 4-2 having a Si content of 0.07% by mass or more and a DSC tangential intersection temperature of 79 ° C. or less. In ~ 4-3, the maximum length of the water tree could be less than 200 μm regardless of the type of the immersed aqueous solution. In the samples 1-2 to 1-5, 3-1 to 3-3, and 4-2 to 4-3, the Si content was 0.07% by mass or more, so that the silanol group as a hydrophilic group was contained. It was well introduced. Further, in the samples 1-2 to 1-5, 3-1 to 3-3, and 4-2 to 4-3, the DSC tangential intersection temperature was 79 ° C. or lower, so that the crystals in the molded product were made finer. We were able to. As a result, in Samples 1-2 to 1-5, 3-1 to 3-3, and 4-2 to 4-3, it was possible to improve the water tree resistance in seawater where water trees are likely to occur. It was confirmed.

(Tensile elongation)
In the samples 1-5, 2-1 and 2-2 having a Si content of more than 0.30% by mass, the tensile elongation was less than 350%. In Samples 1-5, 2-1 and 2-2, the Si content was more than 0.30% by mass, and the number of cross-linking points in the insulating layer was excessively large. Therefore, it is considered that the flexibility is lowered and the tensile properties are lowered.

On the other hand, among the samples having a Si content of 0.30% by mass or less, the above-mentioned samples with good water tree resistance 1-2 to 1-4, 3-1 to 3-3, 4- In 2 to 4-3, the Si content was 0.30% by mass or less, and the excessive increase in the cross-linking points in the molded product was stably suppressed. As a result, it was confirmed that in the samples 1-2 to 1-4, 3-1 to 3-3, and 4-2 to 4-3, the flexibility was improved and the tensile properties could be improved. That is, it was confirmed that these samples were able to achieve both improvement in water tree resistance and improvement in tensile properties.

(Heating deformation rate)
Samples 1-1, 3-1, 4-1 and 4-2 in which the gel fraction on the inner sheet was 25% or less, or the difference between the inner and outer gel fractions was 35% or more, had a heat deformation rate. It was over 40%. Samples 1-1, 3-1, 4-1 and 4-2 had fewer cross-linking points. Therefore, it is considered that the molded product was easily deformed by heating.

On the other hand, among the samples in which the gel fraction on the inner sheet was more than 25% and the difference between the inner and outer gel fractions was less than 35%, the above-mentioned sample 1-2 having good water tree resistance. In 1-5, 3-1 to 3-3, and 4-3, the heating deformation rate was 40% or less. In the samples 1-2 to 1-5, 3-1 to 3-3, and 4-3, it was possible to secure a predetermined amount of cross-linking points and evenly secure the cross-linking points as a whole in the thickness direction. As a result, it was confirmed that the heating deformation could be suppressed in the samples 1-2 to 1-5, 3-1 to 3-3, and 4-3.

<Preferable aspect of the present disclosure>
Hereinafter, preferred embodiments of the present disclosure will be added.

(Appendix 1)
A base resin made of linear low-density polyethylene and
Silane cross-linking agent and
Including
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
The DSC curve when differential scanning calorimetry is performed on a molded body obtained by cross-linking the base resin with the silane cross-linking agent has at least one thermal history point appearing as a peak or shoulder on the lower temperature side than the melting point.
A resin composition in which the temperature of the intersection of the tangent of the baseline of the DSC curve and the tangent of the thermal history point on the lowest temperature side and the tangent line having the largest inclination on the low temperature side is 79 ° C. or lower.

(Appendix 2)
A molded product in which a base resin made of linear low-density polyethylene is crosslinked with a silane cross-linking agent.
The silicon content is 0.07% by mass or more,
The DSC curve when performing differential scanning calorimetry has at least one thermal history point that appears as a peak or shoulder on the cold side of the melting point.
The temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the tangent line having the largest inclination on the low temperature side of the heat history point on the lowest temperature side is 79 ° C. or lower.

(Appendix 3)
When the molded body was immersed in a NaCl aqueous solution of 2% by mass or more and 8% by mass or less at room temperature, and an AC electric field of 50 Hz or 4.2 kV / mm was applied to the molded body for 120 days.
The resin composition molded product according to Appendix 2, wherein the maximum length of the water tree generated in the molded product is less than 200 μm.

(Appendix 4)
The resin composition molded product according to Appendix 2 or Appendix 3, wherein the content of silicon is 0.30% by mass or less.

(Appendix 5)
The resin composition molded product according to Appendix 4, wherein the tensile elongation measured in accordance with JIS C3005 is 350% or more.

(Appendix 6)
The temperature of the intersection of the tangent of the baseline of the DSC curve and the tangent of the thermal history point on the coldest side and the tangent with the largest slope on the cold side is 55 ° C. or higher, whichever is one of Supplements 2 to 5. The resin composition molded body according to.

(Appendix 7)
When the molded body is coated on a predetermined object and an inner sample having a position of 1 mm from the object toward the surface of the molded body is collected.
The resin composition molded product according to any one of Supplementary note 2 to Supplementary note 6, wherein the gel fraction of the inner sample is more than 25%.

(Appendix 8)
An outer sample in which a predetermined object is coated with the molded body and the position from the surface of the molded body toward the object is 1 mm, and an inner sample in which the position from the object toward the surface is 1 mm. When the sample and the sample are taken,
The resin composition molded product according to any one of Supplementary note 2 to Supplementary note 7, wherein the difference obtained by subtracting the gel fraction of the inner sample from the gel fraction of the outer sample is less than 35%.

(Appendix 9)
According to JIS C3005, the heating deformation rate measured by pushing with an iron rod having a diameter of 9.5 mm under the condition that the temperature is 120 ° C. and the load is 23.4 N is 40% or less. 8. The resin composition molded product according to 8.

(Appendix 10)
An outer sample in which a predetermined object is coated with the molded body and the position from the surface of the molded body toward the object is 1 mm, and an inner sample in which the position from the object toward the surface is 1 mm. When the sample and the sample are taken,
The resin composition molded product according to any one of Supplementary note 2 to Supplementary note 9, wherein the difference obtained by subtracting the gel fraction of the inner sample from the gel fraction of the outer sample is 5% or more.

(Appendix 11)
When the molded body is coated on a predetermined object and an outer sample having a position of 1 mm from the surface of the molded body toward the target object is collected.
The resin composition molded product according to any one of Supplementary note 1 to Supplementary note 10, wherein the gel fraction of the outer sample is 35% or more.

(Appendix 12)
A molded product in which a base resin made of linear low-density polyethylene is crosslinked with a silane cross-linking agent and coated on a predetermined object.
The gel fraction of the outer sample whose position from the surface of the molded body toward the object is 1 mm is 35% or more.
The DSC curve when performing differential scanning calorimetry has at least one thermal history point that appears as a peak or shoulder on the cold side of the melting point.
The temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the tangent line having the largest inclination on the low temperature side of the heat history point on the lowest temperature side is 79 ° C. or lower.

(Appendix 13)
A molded product in which a base resin made of linear low-density polyethylene is crosslinked with a silane cross-linking agent.
When the molded body was immersed in a NaCl aqueous solution of 2% by mass or more and 8% by mass or less at room temperature, and an AC electric field of 50 Hz or 4.2 kV / mm was applied to the molded body for 120 days.
A resin composition molded product having a maximum length of water tree generated in the molded product is less than 200 μm.

(Appendix 14)
With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor and in which a base resin made of linear low-density polyethylene is crosslinked with a silane crosslinking agent.
Equipped with
The content of silicon in the insulating layer is 0.07% by mass or more, and is
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point.
A power cable having a temperature of 79 ° C. or lower at the intersection of the tangent of the baseline of the DSC curve and the tangent of the thermal history point on the coldest side and having the largest slope.

(Appendix 15)
A step of preparing a resin composition containing a base resin made of linear low-density polyethylene and a silane cross-linking agent, and
A step of forming an insulating layer so as to cover the outer periphery of the conductor using the resin composition, and
A step of cross-linking the base resin in the insulating layer with the silane cross-linking agent,
Equipped with
In the step of preparing the resin composition,
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
In the step of cross-linking the base resin,
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point, and is tangent to the baseline of the DSC curve. A method for manufacturing a power cable for bridging the base resin so that the temperature of the intersection with the tangent line having the largest inclination tangent on the low temperature side of the heat history point on the lowest temperature side is 79 ° C. or lower.

(Appendix 16)
In the step of cross-linking the base resin,
The method for manufacturing a power cable according to Appendix 15, wherein the cross-linking temperature is set to a temperature corresponding to the temperature at the intersection of the DSC curves.

10 Power cable 110 Conductor 120 Internal semi-conductive layer 130 Insulation layer 140 External semi-conductive layer 150 Shielding layer 160 Sheath

Claims (10)

A base resin made of linear low-density polyethylene and
Silane cross-linking agent and
Including
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
The DSC curve when differential scanning calorimetry is performed on a molded body obtained by cross-linking the base resin with the silane cross-linking agent has at least one thermal history point appearing as a peak or shoulder on the lower temperature side than the melting point.
A resin composition in which the temperature of the intersection of the tangent of the baseline of the DSC curve and the tangent of the thermal history point on the lowest temperature side and the tangent line having the largest inclination on the low temperature side is 79 ° C. or lower. A molded product in which a base resin made of linear low-density polyethylene is crosslinked with a silane cross-linking agent.
The silicon content is 0.07% by mass or more,
The DSC curve when performing differential scanning calorimetry has at least one thermal history point that appears as a peak or shoulder on the cold side of the melting point.
The temperature of the intersection of the tangent line of the baseline of the DSC curve and the tangent line tangent to the tangent line having the largest inclination on the low temperature side of the heat history point on the lowest temperature side is 79 ° C. or lower. When the molded body was immersed in a NaCl aqueous solution of 2% by mass or more and 8% by mass or less at room temperature, and an AC electric field of 50 Hz or 4.2 kV / mm was applied to the molded body for 120 days.
The resin composition molded product according to claim 2, wherein the maximum length of the water tree generated in the molded product is less than 200 μm. The resin composition molded product according to claim 2 or 3, wherein the content of silicon is 0.30% by mass or less. The resin composition molded product according to claim 4, wherein the tensile elongation measured according to JIS C3005 is 350% or more. When the molded body is coated on a predetermined object and an inner sample having a position of 1 mm from the object toward the surface of the molded body is collected.
The resin composition molded product according to any one of claims 2 to 5, wherein the gel fraction of the inner sample is more than 25%. An outer sample in which a predetermined object is coated with the molded body and the position from the surface of the molded body toward the object is 1 mm, and an inner sample in which the position from the object toward the surface is 1 mm. When the sample and the sample are taken,
The resin composition molded product according to any one of claims 2 to 6, wherein the difference obtained by subtracting the gel fraction of the inner sample from the gel fraction of the outer sample is less than 35%. According to claim 6 or claim 6, the heating deformation rate measured by pushing with an iron rod having a diameter of 9.5 mm under the condition that the temperature is 120 ° C. and the load is 23.4 N in accordance with JIS C3005 is 40% or less. The resin composition molded body according to claim 7. With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor and in which a base resin made of linear low-density polyethylene is crosslinked with a silane cross-linking agent.
Equipped with
The content of silicon in the insulating layer is 0.07% by mass or more, and is
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point.
A power cable having a temperature of 79 ° C. or lower at the intersection of the tangent of the baseline of the DSC curve and the tangent of the thermal history point on the coldest side and having the largest slope. A step of preparing a resin composition containing a base resin made of linear low-density polyethylene and a silane cross-linking agent, and
A step of forming an insulating layer so as to cover the outer periphery of the conductor using the resin composition, and
A step of cross-linking the base resin in the insulating layer with the silane cross-linking agent,
Equipped with
In the step of preparing the resin composition,
The content of the silane cross-linking agent is 0.4 parts by mass or more with respect to 100 parts by mass of the base resin.
In the step of cross-linking the base resin,
The DSC curve when differential scanning calorimetry is performed on the insulating layer has at least one thermal history point that appears as a peak or shoulder on the lower temperature side than the melting point, and is tangent to the baseline of the DSC curve. A method for manufacturing a power cable for bridging the base resin so that the temperature of the intersection with the tangent line having the largest inclination tangent on the low temperature side of the heat history point on the lowest temperature side is 79 ° C. or lower.

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