Crosslinking resin composition

Abstract

To provide a crosslinkable resin composition capable of forming an insulating layer for power cables that combines good water resistance and good electrical properties (electrical insulation). [Solution] The crosslinkable resin composition of the present invention contains a resin mixture comprising low-density polyethylene (LDPE) and a polar ethylene copolymer (EAA, EEA, EVA, EVOH, etc.), wherein the content of the polar monomer in this resin mixture is 0.05 to 1.9% by mass, particularly 0.1 to 1.8% by mass.

Description

Technical Field

[0001] The present invention relates to a crosslinkable resin composition, and more particularly, to a crosslinkable resin composition containing a resin mixture including low-density polyethylene and a polar ethylene copolymer, which is preferably used for forming an insulating layer of a power cable having both good water tree resistance and good electrical properties.

Background Art

[0002] Crosslinked polyethylene is widely used for the insulating layer (insulating coating layer) of power cables because of its excellent electrical insulation and heat deformation resistance. However, when a power cable is used in a wet environment or a submerged environment, water trees occur and spread in the insulating layer, which is a problem because the insulation of the power cable is significantly reduced.

[0003] Conventionally, in order to form an insulating layer with good water tree resistance, it has been proposed to use a crosslinkable resin composition obtained by adding polyethylene glycol to an ethylene-based polymer (see Patent Document 1 and Patent Document 2 below).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as a result of adding an excessive amount of polyethylene glycol to such a resin composition, the insulating layer formed by the resin composition does not have good electrical properties (electrical insulation). In particular, the dielectric loss tangent (tanδ) under a high electric field becomes extremely high, resulting in adverse effects such as a decrease in power transmission efficiency and a local temperature rise.

[0006] The present invention has been made based on the circumstances described above, and its objective is to provide a crosslinkable resin composition that can form an insulating layer that combines good water resistance and good electrical properties. [Means for solving the problem]

[0007] The crosslinkable resin composition of the present invention contains a resin mixture (resin component) comprising low-density polyethylene and polar ethylene copolymer, characterized in that the content (content rate) of polar monomer in the resin mixture is 0.05 to 1.9% by mass.

[0008] Furthermore, it is preferable that the content of the polar monomer in the resin mixture is 0.1 to 1.8% by mass.

[0009] Furthermore, it is preferable that the polar ethylene copolymer is an ethylene-acrylate derivative copolymer, and that the ethylene-acrylate derivative copolymer is an ethylene-ethyl acrylate copolymer (EEA), an ethylene-butyl acrylate copolymer (EBA), or an ethylene-acrylic acid copolymer (EAA), with EEA or EAA being particularly preferred.

[0010] Furthermore, the polar ethylene copolymer may be an ethylene-vinyl alcohol derivative copolymer, and it is preferable that the ethylene-vinyl alcohol derivative copolymer is ethylene-vinyl acetate copolymer (EVA) or ethylene-vinyl alcohol copolymer (EVOH).

[0011] Furthermore, it is preferable that the crosslinking agent contains an organic peroxide or a silane compound. Furthermore, it is preferable to use it to form an insulating layer for power cables and wires. [Effects of the Invention]

[0012] According to the crosslinkable resin composition of the present invention, by crosslinking it, an insulating material (insulating layer) can be formed that combines good water resistance and good electrical properties. [Modes for carrying out the invention]

[0013] The crosslinkable resin composition of the present invention comprises a resin mixture having low-density polyethylene (LDPE) and a polar ethylene copolymer.

[0014] For low-density polyethylene, any type used to form the insulating layer of power cables and electric wires can be used. The density of low-density polyethylene is typically 0.91-0.94 g / cm³. 3 It is said that the melt flow rate is typically 0.01 to 10 g / 10 min (190°C, 2.16 kg).

[0015] The polar ethylene copolymer contained in the resin mixture is a copolymer of ethylene and a polar monomer. Specific examples of polar ethylene copolymers include ethylene-acrylate derivative copolymers such as ethylene-methyl methacrylate (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), and ethylene-acrylic acid copolymer (EAA); and ethylene-vinyl alcohol derivative copolymers such as ethylene-vinyl acetate copolymer (EVA) and ethylene-vinyl alcohol copolymer (EVOH). Of these, EEA, EAA, and EVOH are preferred, and EEA and EAA are particularly preferred.

[0016] The content of polar monomers in the polar ethylene copolymer is preferably 0.1 to 90% by mass, and more preferably 10 to 77% by mass.

[0017] The resin mixture (resin component) may consist of low-density polyethylene and a polar ethylene copolymer, but resins other than low-density polyethylene and polar ethylene copolymer may also be included as long as the object of the present invention is not impaired. Examples of optional resins constituting the resin mixture include ethylene-based (co)polymers and propylene-based (co)polymers other than low-density polyethylene and polar ethylene copolymers. Specifically, high-density polyethylene, medium-density polyethylene, linear low-density polyethylene, ethylene-α-olefin copolymer, ethylene-non-conjugated diene copolymer, polypropylene, etc. can be mentioned.

[0018] The content of the polar monomer in the resin mixture is usually 0.05 to 1.9% by mass, preferably 0.1 to 1.8% by mass.

[0019] When the content of the polar monomer in the resin mixture is less than 0.05% by mass, the resin cross-linked body (insulating layer) formed by the obtained resin composition will not have good water tree resistance (see Comparative Example 3 described later). On the other hand, when the content of the polar monomer in the resin mixture exceeds 1.9% by mass, good electrical properties cannot be exhibited in the resin cross-linked body (insulating layer) formed by the obtained resin composition (see Comparative Example 4 described later).

[0020] Therefore, when producing the crosslinkable resin composition of the present invention, the mixing ratio of low-density polyethylene, polar ethylene copolymer and optional resin is adjusted so that the content of the polar monomer in the resin mixture is 0.05 to 1.9% by mass, and the resin mixture is constituted.

[0021] The crosslinkable resin composition of the present invention can contain, as optional components, components used in ordinary resin compositions as required. Such optional components include crosslinking agents (organic peroxides, silane compounds), antioxidants (hindered phenol stabilizers, sulfur stabilizers, amine stabilizers), inorganic fillers (e.g., calcium carbonate, clay, diatomaceous earth, metal oxides, silica, carbon black, glass fiber, carbon fiber), plasticizers (phthalates, trimellitic acid esters, polyesters), softeners (mineral oil, process oil, fatty acids), UV absorbers (benzophenone-based UVA, benzotriallysol-based UVA, salicylate-based UVA), antistatic agents (glycerin fatty acid esters, alkyl sulfonic acid, tetraalkylammonium salts), flame retardants (metal hydroxides, phosphorus compounds, Examples include halogen compounds, lubricants (fatty acid amides, zinc stearate, silicones), foaming agents (azodicarbonamide (ADCA), sodium bicarbonate, 4,4'-oxybis(benzenesulfonyl hydrazide) (OBSH)), colorants (azo compounds, anthraquinone compounds, phthalocyanine compounds, titanium dioxide, carbon black), crosslinking aids (trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTM), triallyl isocyanurate (TAIC), triallyl cyanurate (TAC)), and light stabilizers (hindered amine type compounds, hindered piperidine type compounds).

[0022] By crosslinking the crosslinkable resin composition of the present invention, a resin crosslinked body constituting an insulating layer can be obtained. The crosslinking method is not particularly limited, and for example, (1) A method of performing chemical crosslinking by heating the resin composition of the present invention containing an organic peroxide at a predetermined temperature, (2) A method of performing silane crosslinking by heating the resin composition of the present invention containing a silane crosslinking agent at a predetermined temperature, (3) A method of performing electron beam crosslinking by irradiating the resin composition of the present invention with an electron beam can be mentioned.

[0023] Various heat treatment methods can be employed, including heating in an atmosphere of nitrogen, steam, silicone oil, or molten salt, and heating during molding using a heating press or injection molding machine. [Examples]

[0024] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. In the following examples and comparative examples, the following compounds were used as low-density polyethylene, polar ethylene copolymer, or water tree inhibitor, antioxidant, and crosslinking agent to constitute the resin composition.

[0025] • Low-density polyethylene (LDPE): Density=0.92g / cm 3 Low-density polyethylene with MFR (190℃, 2.16kg) = 2.0g / 10min.

[0026] • Polar ethylene copolymer (EAA): Density=0.93g / cm 3 Ethylene-acrylic acid copolymer with MFR (190℃, 2.16kg) = 1.0g / 10min and AA content of 10% by mass (4.1 mol%).

[0027] • Polar ethylene copolymer (EEA-1): Density=0.94g / cm 3 Ethylene-ethyl acrylate copolymer with MFR (190℃, 2.16kg) = 6.0g / 10min and EA content of 18% by mass (5.8 mol%).

[0028] • Polar ethylene copolymer (EEA-2): Density=0.93g / cm 3 Ethylene-ethyl acrylate copolymer with MFR (190℃, 2.16kg) = 250g / 10min and EA content of 25% by mass (8.5 mol%).

[0029] • Polar ethylene copolymer (EVOH): Density=1.19g / cm 3 Ethylene-vinyl alcohol copolymer with MFR (190℃, 2.16kg) = 3.8g / 10min and VOH content of 77% by mass (68 mol%).

[0030] • Water tree inhibitor (PEG): Polyethylene glycol with a number-average molecular weight of 20,000.

[0031] • Antioxidants: Hindered phenol type stabilizer, 4,4'-thiobis-(3-methyl-6-t-butylphenol)

[0032] • Crosslinking agent: Dicumyl peroxide

[0033] <Manufacturing of crosslinked resin compositions> [Example 1] According to the formulation shown in Table 1 below, 99 parts by mass of low-density polyethylene (LDPE), 1 part by mass of polar ethylene copolymer (EAA), and 0.15 parts by mass of antioxidant were melt-kneaded together, 1.5 parts by mass of crosslinking agent were added to the resulting composition, and the mixture was heated to 60°C for 12 hours. After cooling to room temperature, a resin composition (the crosslinkable resin composition of the present invention) was prepared.

[0034] [Example 2] The crosslinkable resin composition of the present invention was prepared in the same manner as in Example 1, except that 90 parts by mass of low-density polyethylene (LDPE), 10 parts by mass of polar ethylene copolymer (EAA), and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0035] [Example 3] The crosslinkable resin composition of the present invention was prepared in the same manner as in Example 1, except that 95 parts by mass of low-density polyethylene (LDPE), 5 parts by mass of polar ethylene copolymer (EEA-1), and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0036] [Example 4] The crosslinkable resin composition of the present invention was prepared in the same manner as in Example 1, except that 90 parts by mass of low-density polyethylene (LDPE), 10 parts by mass of polar ethylene copolymer (EEA-1), and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0037] [Example 5] The crosslinkable resin composition of the present invention was prepared in the same manner as in Example 1, except that 99.5 parts by mass of low-density polyethylene (LDPE), 0.5 parts by mass of polar ethylene copolymer (EVOH), and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0038] [Comparative Example 1] A comparative crosslinkable resin composition was prepared in the same manner as in Example 1, except that 100 parts by mass of low-density polyethylene (LDPE) and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0039] [Comparative Example 2] A comparative crosslinkable resin composition was prepared in the same manner as in Example 1, except that 100 parts by mass of low-density polyethylene (LDPE), 0.6 parts by mass of a water tree inhibitor (PEG), and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0040] [Comparative Example 3] A comparative crosslinkable resin composition was prepared in the same manner as in Example 1, except that 99.8 parts by mass of low-density polyethylene (LDPE), 0.2 parts by mass of polar ethylene copolymer (EAA), and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0041] [Comparative Example 4] A comparative resin composition was prepared in the same manner as in Example 1, except that 91.5 parts by mass of low-density polyethylene (LDPE), 8.5 parts by mass of polar ethylene copolymer (EEA-2), and 0.15 parts by mass of an antioxidant were melt-kneaded according to the formulation shown in Table 1 below.

[0042] <Evaluation of Crosslinked Resin Compositions> (1) Water tree acceleration test (water tree resistance): Each of the crosslinkable resin compositions obtained in the examples and comparative examples was supplied to a mold, and a disc-shaped test piece having notch-like defects made of a crosslinked resin was produced by press molding (crosslinking treatment) at 180°C for 15 minutes using a heated press machine (Toho Machinery, TBD-50 type). According to ASTM D6097, prepared disc-shaped test specimens were immersed in a 1.0N sodium chloride aqueous solution, and a water tree acceleration test was performed under the conditions of applied voltage of 5kV, frequency of 1,000Hz, temperature of 30°C, and energization time of 500 hours. After energization, the test specimens were stained, sliced, and observed under a microscope. The probability of water tree formation and the maximum water tree length per test specimen were determined. The evaluation criteria were as follows: a water tree occurrence probability of 50% or less and a maximum water tree length of 600 μm or less was considered a "pass (○)", while failure to meet either of these conditions was considered a "fail (×)". The results are shown in Table 1 below.

[0043] (2) Measurement of dielectric loss tangent (electrical properties): Each of the crosslinkable resin compositions obtained in the examples and comparative examples was crosslinked by pressing them at 180°C for 15 minutes using a heated press (Toho Machinery, TBD-50 model) to produce sheet-like crosslinked resin bodies, and test specimens were prepared from each of the resulting crosslinked bodies. The dielectric loss tangent was measured in accordance with JIS C 2138 under conditions of a temperature of 90°C and an electric field of 10kV / mm.

[0044] (3) Measurement of volume resistivity (electrical properties): Each of the crosslinkable resin compositions obtained in the examples and comparative examples was crosslinked by pressing them at 180°C for 15 minutes using a heated press (Toho Machinery, TBD-50 model) to produce sheet-like crosslinked resin bodies, and test specimens were prepared from each of the resulting crosslinked bodies. The volume resistivity was measured in accordance with JIS C 2139-3-1 under conditions of a temperature of 90°C and an electric field of 10kV / mm.

[0045] The evaluation criteria for electrical properties are that the dielectric loss tangent is 0.1% or less, and the volume resistivity is 1015 A value of Ω·cm or greater was marked as "Pass (○)," and any failure to meet either of these criteria was marked as "Fail (×)." The results are shown in Table 1 below.

[0046] [Table 1]

Claims

1. It contains a resin mixture comprising low-density polyethylene and polar ethylene copolymer. A crosslinkable resin composition having a polar monomer content of 0.05 to 1.9% by mass in the resin mixture.

2. The crosslinkable resin composition according to claim 1, wherein the content of the polar monomer in the resin mixture is 0.1 to 1.8% by mass.

3. The crosslinkable resin composition according to claim 2, wherein the polar ethylene copolymer is an ethylene-acrylate derivative copolymer.

4. The crosslinkable resin composition according to claim 3, wherein the ethylene-acrylate derivative copolymer is ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), or ethylene-acrylic acid copolymer (EAA).

5. The crosslinkable resin composition according to claim 3, wherein the ethylene-acrylate derivative copolymer is ethylene-ethyl acrylate copolymer (EEA) or ethylene-acrylic acid copolymer (EAA).

6. The crosslinkable resin composition according to claim 2, wherein the polar ethylene copolymer is an ethylene-vinyl alcohol derivative copolymer.

7. The crosslinkable resin composition according to claim 6, wherein the ethylene-vinyl alcohol derivative copolymer is ethylene-vinyl acetate copolymer (EVA) or ethylene-vinyl alcohol copolymer (EVOH).

8. A crosslinkable resin composition according to any one of claims 1 to 7, comprising an organic peroxide or a silane compound as a crosslinking agent.

9. A crosslinkable resin composition according to any one of claims 1 to 7, used for forming an insulating layer for power cables and electric wires.

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