Insulating resin composition for DC power cables

Abstract

To provide an insulating resin composition which contains modified polyethylene by a less harmful modified monomer, and enables production of a resin crosslinked body that is excellent in insulation property to a DC voltage.SOLUTION: A resin composition has a space charge change rate measured as space charge characteristic evaluation by a pulse electrostatic stress method (PEA method) of less than 10. The resin composition contains modified polyethylene obtained by grafting a modified monomer having a double bond at a terminal to polyethylene, and the modified polyethylene is introduced by the modified monomer, and preferably has a polar group having a bonding energy to positive ions in which hydrogen ions are bonded to acetophenone of 0.44 eV or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulating resin composition for DC power cables, a crosslinked resin product obtained by crosslinking this resin composition, a DC power cable provided with an insulating layer made of this crosslinked resin product, a member for forming a reinforcing insulating layer at a DC power cable joint used when connecting DC power cables, and a DC power cable joint provided with a reinforcing insulating layer made of the crosslinked resin product. [Background technology]

[0002] BACKGROUND ART Conventionally, a DC power cable having an insulating layer formed from an insulating resin composition has been introduced as a DC power cable that is easy to maintain and has no risk of oil leakage (see Patent Document 1 below).

[0003] Furthermore, the insulating resin composition for DC power cables has an appropriate torque during extrusion and excellent extrusion processability, and in the extrusion molded product, sagging that reduces the roundness of the cable insulation is unlikely to occur, has good scorch resistance, generates a small amount of secondary decomposition water upon reheating when connecting cables, and can form an insulating layer that stably exhibits good DC electrical properties, and has stable resin pressure during extrusion, has excellent extrusion stability, and is capable of forming an insulating layer with small thickness variation. (A) Complex viscosity η at 130°C and a frequency of 100 rad / s * 100 is 600 to 1300 Pa·s, and the complex viscosity η at 130°C and a frequency of 0.1 rad / s * 0.1 and the complex viscosity η * 100 The ratio (η * 0.1 / η * 100The present applicant has introduced a resin composition comprising: 100 parts by mass of a low-density polyethylene having a molecular weight (Mw) of 4 or more; (B) 5 to 12 parts by mass of a modified polyethylene in which at least one modifying monomer selected from unsaturated organic acids and derivatives thereof has been grafted onto polyethylene; and (C) 0.01 to 0.8 parts by mass of a stabilizer consisting of a mixture of 40 to 60% by weight of a hindered phenol-based antioxidant and 60 to 40% by weight of a thioether-based antioxidant, wherein the amount of carbonyl groups introduced into the resin composition by component (B) is 7 to 13 μmol / g relative to the total mass of components (A), (B), and (C) (see Patent Document 2 listed below).

[0004] In the resin composition described in Patent Document 2, maleic anhydride (MAH) is described as a suitable modifying monomer for obtaining the component (B). By producing a resin composition containing modified polyethylene modified with maleic anhydride, the crosslinked resin obtained by crosslinking the resin composition is less likely to accumulate space charge under DC voltage and can exhibit excellent insulating properties against DC voltage. As a crosslinking agent for crosslinking the resin composition, an organic peroxide is used. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-7653 [Patent Document 2] Patent No. 6205032 Summary of the Invention [Problem to be solved by the invention]

[0006] However, maleic anhydride is a deleterious substance, and there are concerns that it may be harmful to the human body during the preparation of modified polyethylene. Furthermore, while prior art techniques require measurement of space charge characteristics using a cable, there is a demand for a simple method for evaluating insulating materials that does not require the fabrication of a cable.

[0007] The present invention has been made based on the above circumstances. An object of the present invention is to provide an insulating resin composition for DC power cables, which contains modified polyethylene modified with a less harmful modifying monomer and which can give a crosslinked resin product having excellent insulating properties against DC voltage (having insulating properties equal to or greater than those of a crosslinked resin product containing a modified polyethylene modified with maleic anhydride). Another object of the present invention is to establish a method for simply evaluating whether an insulating material has excellent insulating properties against DC voltage, and to provide an insulating resin composition for DC power cables that has been evaluated by this method as having excellent insulating properties against DC voltage. [Means for solving the problem]

[0008] In order to achieve the above object, the present inventors have conducted extensive research and have found a simple method for evaluating whether a resin composition containing a modified polyethylene modified with maleic anhydride as described in Patent Document 2 has insulating properties equivalent to or greater than those of a crosslinked resin composition. The present inventors have also found that by incorporating modified polyethylene into which a polar group having a high binding energy to a positive ion formed by bonding a hydrogen ion has been introduced (grafted) to acetophenone, which is a decomposition residue of an organic peroxide crosslinking agent, the movement of space charge in the resulting crosslinked resin composition is suppressed, thereby suppressing its accumulation. Based on these findings, the present invention has been completed.

[0009] (1) That is, the insulating resin composition for a DC power cable of the present invention has a space charge change rate measured as a space charge characteristic evaluation by a pulse electrostatic discharge (PEA) method. 3% or less It is characterized in that:

[0010] (2) The resin composition of the present invention contains modified polyethylene in which a modifying monomer having a double bond at a terminal is grafted onto polyethylene, The modified polyethylene preferably has a polar group introduced by the modifying monomer, the polar group having a bond energy of 0.44 eV or more with a positive ion formed by bonding a hydrogen ion to acetophenone. Hereinafter, the modified monomer capable of introducing the above polar group will be referred to as a "specific modified monomer."

[0011] According to the investigations of the present inventors, there is a correlation between the binding energy with the positive ions and the charge change rate (described later), which is an index of charge transfer, and the higher the binding energy with the positive ions, the smaller the charge change rate (the more the charge transfer is suppressed). A resin composition is produced containing modified polyethylene having a polar group whose bond energy with the positive ion is 0.44 eV or more, and the resulting crosslinked resin product can capture charge carriers such as acetophenone, which is a decomposition residue of organic peroxide, and suppress the movement of charges. This suppresses the amount of charge accumulation, and ultimately allows the product to exhibit excellent insulation properties against DC voltage.

[0012] (3) In the resin composition of (2) above, the specific modifying monomer is preferably a nitrogen atom-containing (meth)acrylic acid derivative containing two or more nitrogen atoms in the molecule.

[0013] (4) In the resin composition of (3), the nitrogen atom-containing (meth)acrylic acid derivative is represented by the general formula: H2C=C(R 1 )CONR 2 R 3 (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is a hydrogen atom or an alkyl group, R 3 is a monovalent organic group containing at least one nitrogen atom).

[0014] (5) In the resin composition of (2) above, it is particularly preferred that the specific modified monomer is dimethylaminopropylacrylamide (DMAPAA).

[0015] (6) The resin composition of the above (2) to (5) preferably contains (A) polyethylene, (B) the modified polyethylene, and (C) an antioxidant.

[0016] (7) The resin composition of (6) above preferably further contains (D) an organic peroxide.

[0017] (8) In the resin composition of (6) or (7), (B) modified polyethylene is used per 100 parts by mass of (A) polyethylene. 8 parts by mass or more It is preferable that it contains

[0018] (9) In the resin composition of (6) to (8), the concentration of the polar group introduced by the specific modifying monomer is 4μmol / g or more It is preferable that:

[0019] (10) The resin composition of (5) above, comprising: (A) 100 parts by mass of polyethylene; (B) the modified polyethylene 8~ 18 parts by weight, (C) 0.01 to 0.8 parts by mass of an antioxidant; (D) 0.1 to 5 parts by mass of an organic peroxide, The concentration of the polar group introduced by the specific modified monomer is 4~ Preferably, it is 8 μmol / g.

[0020] (11) The crosslinked resin of the present invention is characterized in that it is obtained by crosslinking the resin composition of the present invention.

[0021] (12) The DC power cable of the present invention is characterized in that it comprises an inner semiconductive layer and an insulating layer made of the crosslinked resin of the present invention laminated on the surface of a conductive member.

[0022] (13) The reinforcing insulating layer forming member of the present invention is a repair tape-like member that is wound around a connection portion internal semiconducting layer that covers exposed portions of conductive members, including the connection portions of the conductive members of DC power cables, when connecting DC power cables to each other, and forms a reinforcing insulating layer on the connection portion internal semiconducting layer by crosslinking, and is characterized by being made of the resin composition of the present invention.

[0023] (14) A DC power cable connection of the present invention is formed by connecting two DC power cables together, and is characterized in that a reinforcing insulating layer made of the crosslinked resin product of the present invention is formed on a connection part internal semiconductive layer that covers exposed portions of conductive members of the DC power cables, including the connection parts of the conductive members. [Effects of the Invention]

[0024] According to the resin composition of the present invention, a crosslinked resin product can be obtained that has excellent insulating properties against DC voltage, which are equal to or better than those of a crosslinked resin product made from a resin composition containing modified polyethylene modified with maleic anhydride. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view showing an example of a DC power cable of the present invention. [Figure 2] 1 is a longitudinal cross-sectional view showing an example of a DC power cable connection part of the present invention. [Figure 3] Average value of binding energy <e>10 is a flowchart showing an example of a procedure for calculating DETAILED DESCRIPTION OF THE INVENTION

[0026] The resin composition of the present invention contains component (A) consisting of polyethylene, component (B) consisting of modified polyethylene, component (C) consisting of an antioxidant, and component (D) consisting of an organic peroxide.

[0027] <Component (A)> The polyethylene that is component (A) of the resin composition of the present invention is not particularly limited, and conventionally known high-pressure low-density polyethylenes can be suitably used. Commercially available products of component (A) include "NUC-8160" (manufactured by ENEOS NUC Corporation).

[0028] <(B) component> The component (B) constituting the resin composition of the present invention is a modified polyethylene having a polar group having a bond energy of 0.44 eV or more with a positive ion formed by bonding a hydrogen ion to acetophenone represented by the following formula:

[0029] [ka]

[0030] The "positive ion formed by bonding a hydrogen ion to acetophenone" is a positive ion used to determine the bond energy with the polar group of component (B), and is not an essential component of the resin composition of the present invention. However, this positive ion is inevitably present in the crosslinked product of the resin composition of the present invention as a decomposition residue (charge carrier) of component (D).

[0031] The bond energy between the polar group (polar group derived from the modifying monomer) of the modified polyethylene and the positive ion can be determined by calculation.

[0032] Assuming that the space charge change rate increases due to the diffusion of charge carriers within the modified polyethylene, if the bond strength of the charge carriers to the polar groups of the modified polyethylene is strong, the charge carriers will be less likely to diffuse, and the space charge change rate can be kept low. In the present invention, the strength of the bond between the polar group of the modified polyethylene and the positive ion, which is a charge carrier, is quantified as bond energy, and calculated by molecular simulation.

[0033] To give a specific example, in the case of a modified polyethylene in which maleic anhydride is grafted onto a polyethylene main chain, the bond energy between the polar group derived from maleic anhydride and the positive ion can be obtained by randomly arranging the positive ions around the modified polyethylene molecules and determining the intermolecular force. In this case, a molecular simulation is used to perform a thorough conformational search (100 or more, and if possible, 1000 or more configurations) to calculate the total energy for each structure (configuration), thereby obtaining a distribution of total energies for all structures. The distribution of bond energies is obtained by subtracting the energies of the isolated molecules of the modified polyethylene and the positive ions from the distribution of the total energy obtained. This distribution of binding energy includes states from low energy to high energy. In an actual experimental environment, for example, at room temperature, it is possible to take a high energy state corresponding to that temperature, and that state follows the Boltzmann distribution. Therefore, the average value of the binding energy is <e>is given by the following formula:

[0034]

number

[0035] In the above formula, E(x) is the binding energy in any structure x, k B is the Boltzmann constant, T is the absolute temperature, and N is the normalization constant.

[0036] The "bond energy" defined in the present invention (claim 2) is the "average bond energy" calculated from the distribution of bond energy using the above formula. <e>" This is what I mean.

[0037] Average value of binding energy <e>A flowchart showing an example of a procedure for calculating is shown in Fig. 3. However, the calculation procedure is not limited to this.

[0038] The bond energy between the polar group derived from the compound and the positive ion (average bond energy calculated by the above method) is shown below for each modified polyethylene in which the following compound is grafted onto the polyethylene main chain. <e>) is shown.

[0039] Dimethylaminopropylacrylamide (0.46 eV) N-methyl-N-[3-(dimethylamino)propyl]acrylamide (0.46 eV) Maleic anhydride (0.46 eV) 2-(2-ethoxy)ethoxyethyl acrylate (0.42 eV) 2-(dimethylamino)ethyl acrylate (0.42 eV) 2-allylmalonic acid (0.40 eV) Dimethylaminoethylacrylamide (0.40 eV) Diethylaminoethylacrylamide (0.38 eV) 2-Ethylhexyl acrylate (0.32 eV) Triallyl isocyanurate (0.32 eV) Diallyl adipate (0.30 eV) Aminopropylacrylamide (0.30 eV) N-allyloxyphthalimide (0.30 eV) Hydroxymethylacrylamide (0.28 eV) For reference, the bond energy between ungrafted polyethylene and the positive ions was 0.22 eV.

[0040] The polar group having a bond energy with a positive ion of 0.44 eV or more is introduced by a specific modified monomer (a modified monomer capable of introducing such a polar group and having a double bond at its terminal is the specific modified monomer).

[0041] Component (B), which is a modified polyethylene in which the polar group has been introduced by modifying polyethylene with a specific modifying monomer, is prepared, and by incorporating the resulting component (B) in a specified ratio, charge carriers such as acetophenone, which is a residue of component (D) described below, are captured, thereby making it possible to suppress the migration of charges.

[0042] The specific modified monomer has a double bond at the end of its molecule. This is advantageous in that the reactivity during modification (graft reaction) is higher than that of monomers such as maleic anhydride that do not have double bonds at the molecular terminals. The use of specific highly reactive modified monomers is expected to suppress the formation of high molecular weight gels resulting from the cross-linking reaction of polyethylene as a side reaction. Specific examples of specific modified monomers include nitrogen-containing (meth)acrylic acid derivatives containing two or more nitrogen atoms in the molecule, such as dimethylaminopropyl(meth)acrylamide and N-methyl-N-[3-(dimethylamino)propyl]acrylamide. Of these, dimethylaminopropylacrylamide is particularly preferred.

[0043] The content of the component (B) is usually 5 parts by mass or more, and preferably 5 to 18 parts by mass, per 100 parts by mass of the component (A). If the content of component (B) is less than 5 parts by mass, it becomes difficult to uniformly disperse component (B) in component (A), and as a result, the movement of space charges cannot be sufficiently suppressed in the crosslinked product of the resulting resin composition, and the space charges that accumulate upon application of DC charges prevent the product from exhibiting sufficient performance as an insulating material for DC power cables (see Comparative Example 2 below). On the other hand, even if the content of component (B) exceeds 18 parts by mass, the improvement in effect commensurate with the increase in the amount added is not obtained.

[0044] An example of a method for preparing component (B) is a method in which polyethylene, a specific modified monomer, an antioxidant, and an organic peroxide are mixed in an extruder, heated to react, and then granulated into pellets or granules. The antioxidant used in preparing the component (B) is deactivated during the synthesis of the component (B), and does not become a component of the component (C) in the resin composition.

[0045] <(C) component> The component (C) constituting the resin composition of the present invention is not particularly limited, and examples thereof include conventionally known antioxidants (such as phenol-based antioxidants, amine-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants) that are used in insulating resin compositions for power cables. The content of the component (C) is set to 0.01 to 0.8 parts by mass, and preferably 0.2 to 0.6 parts by mass, per 100 parts by mass of the component (A). If the content of component (C) is less than 0.01 parts by mass, the resulting resin composition will have poor scorch resistance, and the crosslinked resin product obtained by crosslinking the resin composition will have poor heat resistance. On the other hand, if the content of component (C) exceeds 0.8 parts by mass, the resulting resin composition cannot form a crosslinked resin product with a small amount of secondary decomposition water, and bleeding from the resulting crosslinked resin product also increases.

[0046] <Component (D)> The organic peroxide, which is the component (D) constituting the resin composition of the present invention, acts as a crosslinking agent. Specific examples of component (D) include di-t-hexyl peroxide (Perhexyl D, manufactured by NOF Corporation), dicumyl peroxide (Percumyl D, manufactured by NOF Corporation), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Perhexa 25B, manufactured by NOF Corporation), α,α'-di(t-butylperoxy)diisopropylbenzene (Perbutyl P, manufactured by NOF Corporation), t-butylcumyl peroxide (Perbutyl C, manufactured by NOF Corporation), and di-t-butyl peroxide (Perbutyl D, manufactured by NOF Corporation), which can be used alone or in combination of two or more. Of these, dicumyl peroxide is preferred. The content of the component (D) is preferably 0.1 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the component (A). If the blending amount is too small, crosslinking will not be sufficient, resulting in poor mechanical properties and heat resistance of the resulting crosslinked product, whereas if the blending amount is too large, scorching will occur during extrusion molding of the resulting resin composition, resulting in poor electrical properties.

[0047] <Concentration of polar groups introduced by specific modified monomers> In the resin composition of the present invention, the concentration (graft amount) of polar groups introduced by the specific modified monomer is usually 2 μmol / g or more, preferably 2 to 8 μmol / g, and a suitable example is 4 μmol / g. A crosslinked resin obtained from a resin composition having a polar group concentration of less than 2 μmol / g cannot sufficiently suppress the movement of space charges, and therefore cannot exhibit sufficient performance as an insulating material for a DC power cable (see Comparative Example 2 described below).

[0048] Here, the "polar group concentration" refers to the number of moles of polar groups in component (B) introduced by a specific modifying monomer relative to the total mass of components (A), (B), and (C). The concentration (graft amount) of the polar group introduced by the modifying monomer is a measured value as described below.

[0049] <Resin composition> The resin composition of the present invention contains components (A) to (C), and when crosslinking these (to obtain a crosslinked resin product), it contains component (D). Various stabilizers and other additives may also be contained within the range that does not impair the effects of the present invention. Examples of stabilizers include light stabilizers, ultraviolet absorbers, and copper inhibitors. Examples of other additives include inorganic fillers, organic fillers, lubricants, and dispersants.

[0050] <Crosslinked resin> The resin composition of the present invention can be crosslinked with the organic peroxide, which is component (D). The crosslinked resin of the present invention can be obtained by crosslinking the resin composition of the present invention with an organic peroxide, which is component (D).

[0051] The charge change rate of a sheet made of the crosslinked resin of the present invention is preferably 10% or less, and more preferably 3% or less. When space charges accumulate in the cable insulation due to the application of a high DC voltage, the insulation properties deteriorate significantly when an impulse of the opposite polarity is applied or when the polarity is reversed. Therefore, by keeping the charge change rate in the crosslinked resin product at 10% or less, it is possible to obtain a DC power cable that stably exhibits good DC electrical characteristics. By crosslinking the resin composition of the present invention, in which the concentration (graft amount) of the polar group introduced by a specific modified monomer is 2 μmol / g or more, the charge change rate of the resulting crosslinked product can be made 10% or less.

[0052] <DC power cable> The DC power cable of the present invention comprises an inner semiconductive layer and an insulating layer made of the crosslinked resin of the present invention laminated on the surface of a conductive member. FIG. 1 is a cross-sectional view showing an example of a DC power cable according to the present invention. In a DC power cable 10 shown in FIG. 1, an inner semiconductive layer 12, an insulating layer 13 made of the crosslinked resin of the present invention, and an outer semiconductive layer 14 are laminated on the outer peripheral surface of a conductor 11, and further, a metal shielding layer 15 and a sheath 16 are laminated on the outer peripheral surface of the outer semiconductive layer 14.

[0053] The DC power cable 10 of the present invention shown in FIG. 1 can be produced by extrusion molding the resin composition of the present invention together with an inner semiconductive layer 12 that covers a conductor 11 (in this case, an outer semiconductive layer 14 may be extruded simultaneously), crosslinking the resin composition to form an insulating layer 13 made of a crosslinked resin, and then providing a metal shielding layer 15 and a sheath 16 according to a conventional method.

[0054] The cross-linking method for forming the insulating layer 13 (cross-linked resin body) is not particularly limited, but typically, a pressurized heat treatment or the like is used. For example, the resin composition is heated and pressurized in a nitrogen atmosphere at a pressure of 10 kg / cm 2 and a temperature of 280° C. to promote crosslinking of the resin composition through a radical reaction using component (D) as an initiator.

[0055] The DC power cable 10 of the present invention exhibits good DC electrical characteristics, and the insulating layer 13 is less likely to break down.

[0056] <DC power cable connection> The DC power cable joint of the present invention comprises a reinforcing insulating layer made of the crosslinked resin product of the present invention formed on a joint internal semiconductive layer that covers exposed portions of conductive members of a DC power cable, including the joint portion of the conductive members.

[0057] FIG. 2 is a vertical cross-sectional view showing an example of a DC power cable joint according to the present invention. The DC power cable connection 20 shown in FIG. 2 is formed by connecting two DC power cables 10A, 10B, and is formed by laminating a reinforcing insulating layer 23 made of the crosslinked resin of the present invention and a connection part external semiconductive layer 24 on a connection part internal semiconductive layer 22 that covers exposed portions of the conductors including a connection part 17 between the conductor 11A of the DC power cable 10A and the conductor 11B of the DC power cable 10B.

[0058] In the figure, 13A is an insulating layer of a DC power cable 10A, 13B is an insulating layer of a DC power cable 10B, and the insulating layers 13A and 13B are made of the crosslinked resin of the present invention. Furthermore, 12A, 14A, 15A and 16A respectively denote the inner semiconductive layer, the outer semiconductive layer, the metallic shielding layer and the sheath of the DC power cable 10A. Furthermore, 12B, 14B, 15B and 16B respectively denote the inner semiconductive layer, the outer semiconductive layer, the metal shielding layer and the sheath of the DC power cable 10B.

[0059] When connecting DC power cables 10A and 10B to form DC power cable connection 20 as shown in FIG. 2, a tape-shaped member (reinforcing insulating layer-forming member of the present invention) made from the resin composition of the present invention is wound around connection internal semiconducting layer 22 covering the exposed portions of the conductors, including connection portion 17 between conductors 11A and 11B, and crosslinked by heat treatment to form reinforcing insulating layer 23 made of the crosslinked resin body of the present invention.

[0060] When the reinforcing insulating layer-forming member of the present invention is heat-treated to form the reinforcing insulating layer 23, the insulating layer 13A of the DC power cable 10A and the insulating layer 13B of the DC power cable 10B are also heated. However, since the insulating layers 13A, 13B are made of the crosslinked resin of the present invention, the amount of secondary decomposition water generated from the insulating layers 13A, 13B can be reduced. Furthermore, the accumulation of space charges in the formed reinforcing insulating layer 23 can also be suppressed.

[0061] Various methods can be used to manufacture cable connections depending on the voltage class, application, installation environment, etc., such as tape mold joints (TMJ), extrusion mold joints (EMJ), and block mold joints (BMJ). [Example]

[0062] The present invention will be described below with reference to examples.

[0063] <Analysis method> (1) MFR: Measured in accordance with JIS K 7210 at a measurement temperature of 190°C and a load of 21.18N.

[0064] (2) Density: Measured in accordance with JIS K 7112.

[0065] (3) Measurement of the concentration of polar groups introduced by modified monomers: (3-1) Sample preparation The resin composition was preheated at 120°C and 1 MPa for 5 minutes, and then heated in a press at 180°C and 15 MPa for 15 minutes to produce a crosslinked sheet (sheet-shaped crosslinked resin) with a thickness of approximately 0.2 mm. The crosslinked sheet was immersed in chloroform to remove unreacted modified monomer.

[0066] (3-2) Infrared absorption spectrum measurement: An infrared spectrophotometer "FT / IR-4200" (JASCO Corporation) was used, with 16 accumulations and a resolution of 4 cm. -1 Under the condition of 500cm -1 ~4000cm -1 Measured in the wavenumber range from 1650 to 1750 cm -1 Absorbance of the absorption peak characteristic of the modified monomer (baseline 1600-1840 cm -1 ) and 2020cm -1 The absorbance of the absorption peak characteristic of polyethylene in the vicinity (baseline 1980-2110 cm -1 ) ratio was recorded.

[0067] (3-3) Calculation of polar group concentration: Using a calibration curve prepared from samples of known concentrations, the concentration of the polar group introduced by the modified monomer was calculated from the modified monomer / polyethylene ratio.

[0068] <Calculation conditions for the bond energy between polar groups and positive ions> (1) Software used: Matlantis cloud service (PFP ​​version 1.1.0, Grimme D3 dispersion force correction)

[0069] (2) References: So Takamoto, Chikashi Shinagawa, Daisuke Motoki, Kosuke Nakago, Wenwen Li, Iori Kurata, Taku Watanabe, Yoshihiro Yayama, Hiroki Iriguchi, Yusuke Asano, Tasuku Onodera, Takafumi Ishii, Takao Kudo, Hideki Ono, Ryohto Sawada, Ryuichiro Ishitani, Marc Ong, Taiki Yamaguchi, Toshiki Kataoka, Akihide Hayashi, and Takeshi Ibuka, PFP: Universal Neural Network Potential for Material Discovery. arXiv:2106.14583v1 Condensed Matter

[0070] (3) Structural optimization calculation: Optimization algorithm: FIRE (atomic coordinates), Exp Cell Filter (periodic structure) Calculation convergence condition: 0.05 eV / Å or less ·PE periodic structure: C 12 H 24 , a=15.2533Å, b=20.0Å, c=20.0Å, cuboid

[0071] (4) Binding energy sampling: Number of states: 2000 Boltzmann distribution: 300Kelvin

[0072] <Preparing polyethylene> Obtained by high-pressure tubular method, MFR = 2.0-3.0 g / 10 min, density = 0.92 g / cm 3 A low-density polyethylene (A1) was prepared.

[0073] <Preparation of modified polyethylene> (1) Preparation Example B1 (for the present invention): To 100 parts by mass of low-density polyethylene (A1), 1.1 parts by mass of dimethylaminopropylacrylamide and 0.05 parts by mass of the hindered phenol-based antioxidant "Irganox 1010" (manufactured by BASF) were added, and the mixture was reacted by mixing and heating in an extruder using 0.05 parts by mass of the organic peroxide 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexyne-3 "Perhexyne 25B" (manufactured by NOF Corporation), to obtain a modified polyethylene (B1) consisting of a graft copolymer. Here, the bond energy between the polar group of the modified polyethylene (B1) introduced by dimethylaminopropylacrylamide and the positive ion formed by bonding a hydrogen ion to acetophenone (the average value of the calculated bond energy) is <e>) is 0.46 eV.

[0074] (2) Preparation example B2 (for comparison): A modified polyethylene (B2) consisting of a graft copolymer was obtained in the same manner as in Preparation Example B1, except that 0.7 parts by mass of hydroxymethylacrylamide was used instead of dimethylaminopropylacrylamide. Here, the bond energy between the polar group of the modified polyethylene (B2) introduced by hydroxymethylacrylamide and the positive ion formed by bonding a hydrogen ion to acetophenone (the average value of the calculated bond energy) is <e>) is 0.28 eV.

[0075] (3) Preparation example B3 (for comparison): A modified polyethylene (B3) consisting of a graft copolymer was obtained in the same manner as in Preparation Example B1, except that 1.2 parts by mass of 2-ethylhexyl acrylate was used instead of dimethylaminopropylacrylamide. Here, the bond energy between the polar group of the modified polyethylene (B3) introduced by 2-ethylhexyl acrylate and the positive ion formed by bonding a hydrogen ion to acetophenone (the average value of the calculated bond energy) <e>) is 0.32 eV.

[0076] (4) Preparation example B4 (for comparison): A modified polyethylene (B4) consisting of a graft copolymer was obtained in the same manner as in Preparation Example B1, except that 1.1 parts by mass of 2-(2-ethoxy)ethoxyethyl acrylate was used instead of dimethylaminopropylacrylamide. Here, the bond energy between the polar group of the modified polyethylene (B4) introduced by 2-(2-ethoxy)ethoxyethyl acrylate and the positive ion in which a hydrogen ion is bonded to acetophenone (the average value of the calculated bond energy) <e>) is 0.42 eV.

[0077] (5) Preparation example B5 (for reference): A modified polyethylene (B5) consisting of a graft copolymer was obtained in the same manner as in Preparation Example B1, except that 0.7 parts by mass of maleic anhydride, a modified monomer that does not have a double bond at the end, was used instead of dimethylaminopropylacrylamide. Here, the bond energy between the polar group of the modified polyethylene (B5) introduced by maleic anhydride and the positive ion of the hydrogen ion bonded to acetophenone (the average value of the calculated bond energy) is <e>) is 0.46 eV.

[0078] <Preparation of antioxidants> As component (C), a thioether-based antioxidant "Seenox BCS" (manufactured by Shipro Chemical Co., Ltd.) was prepared.

[0079] <Preparation of organic peroxide> As component (D), a crosslinking agent made of dicumyl peroxide was prepared.

[0080] < Comparative Example 6, Examples 2 to 3 > By mixing 100 parts by mass of low-density polyethylene (A1), modified polyethylene (B1) in the amounts shown in Table 1 below, 0.2 parts by mass of component (C), and 1.5 parts by mass of component (D), More resin composition The concentrations of polar groups introduced by the modified monomers measured for each of the obtained resin compositions are also shown in Table 1.

[0081] <Comparative Example 1> According to the recipe shown in Table 1 below, except that component (B) was not used. Comparative Example 6 A comparative resin composition was obtained in the same manner as above.

[0082] <Comparative Example 2> According to the recipe shown in Table 1 below, the amount of modified polyethylene (B1) used was changed to 3 parts by mass. Comparative Example 6 A comparative resin composition was obtained in the same manner as in Example 1. The concentration of polar groups introduced by the modified monomer in this resin composition was 1 μmol / g.

[0083] <Comparative Example 3> According to the formulation shown in Table 1 below, except that 18 parts by mass of modified polyethylene (B2) was used instead of modified polyethylene (B1), Comparative Example 6 A comparative resin composition was obtained in the same manner as in Example 1. The concentration of polar groups introduced by the modified monomer in this resin composition was 8 μmol / g.

[0084] <Comparative Example 4> According to the formulation shown in Table 1 below, the modified polyethylene (B1) was replaced with 18 parts by mass of modified polyethylene (B3). Comparative Example 6 A comparative resin composition was obtained in the same manner as in Example 1. The concentration of polar groups introduced by the modified monomer in this resin composition was 8 μmol / g.

[0085] <Comparative Example 5> According to the recipe shown in Table 1 below, except that 18 parts by mass of modified polyethylene (B4) was used instead of modified polyethylene (B1), Comparative Example 6 A comparative resin composition was obtained in the same manner as in Example 1. The concentration of polar groups introduced by the modified monomer in this resin composition was 8 μmol / g.

[0086] <Reference example 1> According to the formulation shown in Table 1 below, except that 15 parts by mass of modified polyethylene (B5) was used instead of modified polyethylene (B1), Comparative Example 6 A reference resin composition was obtained in the same manner as in Example 1. The concentration of polar groups introduced by the modified monomer in this resin composition was 7 μmol / g.

[0087] <Evaluation> For each of the resin compositions obtained in the above Examples, Comparative Examples, and Reference Examples, the space charge characteristics of the crosslinked resin products obtained from the resin compositions were evaluated (measurement of the charge change rate). The measurement methods, evaluation methods, and evaluation criteria are as follows. The results are also shown in Table 1 below.

[0088] (1) Measurement of space charge change rate (evaluation of space charge characteristics): Examples 2 and 3 , Comparative Examples 1 to 6 Each of the resin compositions obtained in Example 1 and Example 2 was pressed at a temperature of 120°C and a pressure of 1 MPa for 5 minutes to form a sheet, and then pressed at a temperature of 180°C and a pressure of 15 MPa for 15 minutes to obtain a crosslinked sheet (crosslinked resin) having a thickness of 0.2 mm. For each of the obtained crosslinked sheets, the space charge change rate was measured as an evaluation of the space charge characteristics by the pulse electrostatic discharge (PEA) method. Specifically, a negative DC electric field of 40 kV / mm was applied to the crosslinked sheet continuously for 30 minutes under a temperature condition of 23°C, and the maximum charge density (unit: C / m) at the start of application was measured. 3 ) value (C0) and the maximum charge density value at the end of application (C 30 ) from the formula [(C0-C 30 The space charge change rate calculated by [ ] / C0 × 100 was measured. The smaller this space charge change rate, the less space charge migration and accumulation occurs when a high DC voltage is applied, and the better the space charge characteristics. The evaluation criteria are the charge change rate 3% or less If it is, it is considered a "pass" 3% If it exceeds this, it is considered a "fail."

[0089] Table 1 Examples 2 and 3 and Comparative Example 2 、6 These results show that the space charge change rate of the crosslinked sheet depends on the concentration of polar groups introduced by the dimethylaminopropylacrylamide used, and that the space charge change rate is less than 10% at concentrations of 2 μmol / g or higher. Furthermore, when the monomer concentration is 4 μmol / g or higher, there is almost no change in the space charge change rate of the crosslinked sheet, and the effect of improving space charge characteristics is saturated. In contrast, Comparative Example 3 ~5 From the results, it can be seen that even if the concentration of polar groups introduced by the modified monomer used was 8 μmol / g, the effect of improving the space charge characteristics was insufficient.

[0090] [Table 1] [Explanation of symbols]

[0091] 10, 10A, 10B DC power cable 11, 11A, 11B conductor 12,12A,12B Internal semiconducting layer 13, 13A, 13B insulating layer 14,14A,14B External semiconducting layer 15,15A,15B Metal shielding layer 16, 16A, 16B sheath 17 Conductor Connections 20 DC power cable connection 22 Semiconductive layer inside the connection 23 Reinforced insulation layer 24. Outer semiconductive layer of connection< / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e>

Claims

1. An insulating resin composition for DC power cables, having a space charge change rate of 3% or less when measured and calculated by the pulse electrostatic discharge (PEA) method using the following method. [Method for measuring and calculating space charge change rate] The resin composition is pressed at 120°C and 1 MPa for 5 minutes to form a sheet, and then pressed at 180°C and 15 MPa for 15 minutes to produce a crosslinked sheet with a thickness of 0.2 mm. A negative 40 kV / mm DC electric field is applied to the resulting crosslinked sheet continuously for 30 minutes at 23°C, and the maximum charge density value (C0) at the start of application and the maximum charge density value (C30) at the end of application are measured, and the space charge change rate is calculated using the formula [(C0 - C30) / C0] x 100.

2. The resin composition contains a modified polyethylene in which a modifying monomer having a double bond at a terminal is grafted onto polyethylene, 2. The insulating resin composition for a DC power cable according to claim 1, wherein the modified polyethylene has a polar group introduced by the modifying monomer, the polar group having a bond energy of 0.44 eV or more with a positive ion formed by bonding a hydrogen ion to acetophenone.

3. 3. The insulating resin composition for a DC power cable according to claim 2, wherein the modified monomer is a nitrogen atom-containing (meth)acrylic acid derivative containing two or more nitrogen atoms in the molecule.

4. The nitrogen atom-containing (meth)acrylic acid derivative is represented by the general formula: 2 C=C(R 1 ) CONR 2 R 3 (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is a hydrogen atom or an alkyl group, R 3 4. The insulating resin composition for a DC power cable according to claim 3, wherein the (meth)acrylamide is represented by the formula:

5. 3. The insulating resin composition for a DC power cable according to claim 2, wherein the modified monomer is dimethylaminopropylacrylamide (DMAPAA).

6. (A) polyethylene; (B) the modified polyethylene; The insulating resin composition for a DC power cable according to any one of claims 2 to 5, further comprising (C) an antioxidant.

7. 7. The insulating resin composition for a DC power cable according to claim 6, further comprising (D) an organic peroxide.

8. 8. The insulating resin composition for a DC power cable according to claim 6, comprising 8 parts by mass or more of the modified polyethylene (B) per 100 parts by mass of the polyethylene (A).

9. 9. The insulating resin composition for a DC power cable according to claim 6, wherein the concentration of the polar group introduced by the modified monomer is 4 μmol / g or more.

10. (A) 100 parts by mass of polyethylene; (B) 8 to 18 parts by mass of the modified polyethylene; (C) 0.01 to 0.8 parts by mass of an antioxidant; (D) 0.1 to 5 parts by mass of an organic peroxide, 6. The insulating resin composition for a DC power cable according to claim 5, wherein the concentration of the polar groups introduced by the modified monomer is 4 to 8 μmol / g.

11. A crosslinked resin obtained by crosslinking the resin composition according to any one of claims 1 to 10.

12. 12. A DC power cable comprising an electrically conductive member having an inner semiconductive layer and an insulating layer comprising the crosslinked resin product according to claim 11 laminated on the surface of the electrically conductive member.

13. 11. A repair tape-shaped member for forming a reinforcing insulating layer on a connection portion of a DC power cable, the repair tape-shaped member being wound around a connection portion internal semiconducting layer that covers exposed portions of conductive members of the DC power cables, including the connection portions of the conductive members, and forming a reinforcing insulating layer on the connection portion internal semiconducting layer by crosslinking, when connecting DC power cables together, the repair tape-shaped member being made of the resin composition according to any one of claims 1 to 10.

14. 12. A DC power cable joint formed by connecting two DC power cables together, wherein a reinforcing insulating layer made of the crosslinked resin product according to claim 11 is formed on a joint internal semiconductive layer that covers exposed portions of conductive members of the DC power cables, including the joints of the conductive members.

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