JP7619749B2 - Crosslinkable resin composition and electric wire/cable - Google Patents

Description

The present invention relates to a crosslinkable resin composition containing an ethylene-based resin, and to an electric wire or cable in which a crosslinked product of the resin composition is formed on a conductor as an insulating coating layer.

An insulating coated electric wire/cable for power use is usually produced by coating a conductor with a crosslinkable resin composition by extrusion processing, and then crosslinking the composition to form an insulating coating layer.
Here, the crosslinkable resin composition used in the insulated coated electric wire/cable is required to have scorch resistance, heat deformation resistance of the crosslinked product, and the like.

As a crosslinkable resin composition used for insulating coated electric wires and cables, Patent Document 1 listed below discloses a polymer composition containing an ethylene-based polymer, an organic peroxide, and a polyallyl crosslinking auxiliary.
In Patent Document 1, an attempt is made to improve scorch resistance by using a polyallyl crosslinking auxiliary and reducing the content of the organic peroxide, which is a crosslinking agent, but a sufficient improvement effect is not obtained.

Patent Document 2 listed below discloses a composition containing an ethylene-based polymer, an organic peroxide such as dicumyl peroxide, a dielectric fluid such as alkylated naphthalene, and a crosslinking coagent such as α-methylstyrene dimer.
A crosslinking aid such as α-methylstyrene dimer is said to improve the scorch resistance of the obtained composition and also improve the cured state of the crosslinked product of the composition. However, the crosslinked product of the composition described in Patent Document 2 does not have sufficient heat distortion resistance.

JP 2019-7013 A Special Publication No. 2015-535864

Conventionally known crosslinkable resin compositions, including those disclosed in Patent Document 1 and Patent Document 2, are not satisfactory in both scorch resistance and heat distortion resistance of the crosslinked product. Crosslinked products made from resin compositions with good scorch resistance have poor heat distortion resistance, and resin compositions capable of forming crosslinked products with good heat distortion resistance tend to have poor scorch resistance.

The present invention has been made based on the above circumstances.
An object of the present invention is to provide a crosslinkable resin composition which is capable of giving a crosslinked product having good scorch resistance and excellent resistance to thermal distortion.

The crosslinkable resin composition of the present invention is characterized by comprising 100 parts by mass of an ethylene-based resin (A) made of a high-pressure low-density ethylene homopolymer , 0.85 to 1.25 parts by mass of a crosslinking agent (B) made of an organic peroxide, 0.07 to 0.60 parts by mass of a first crosslinking auxiliary (C1) made of an allyl group-containing compound, and 0.15 to 0.38 parts by mass of a second crosslinking auxiliary (C2) made of an α-methylstyrene dimer.

In the crosslinkable resin composition of the present invention, it is preferable that the crosslinking agent (B) is dicumyl peroxide and the first crosslinking aid (C1) is TAIC or TAC, and particularly TAIC.

In the crosslinkable resin composition of the present invention, it is preferable that the mass ratio of the second crosslinking aid (C2) to the first crosslinking aid (C1) is 0.4 to 2.5.

The crosslinkable resin composition of the present invention preferably contains 0.90 to 1.20 parts by mass of a crosslinking agent (B) made of dicumyl peroxide, 0.10 to 0.55 parts by mass of a first crosslinking assistant (C1) made of TAIC or TAC, and 0.15 to 0.35 parts by mass of a second crosslinking assistant (C2).

The crosslinkable resin composition of the present invention preferably contains 0.91 to 1.16 parts by mass of a crosslinking agent (B) made of dicumyl peroxide, 0.11 to 0.52 parts by mass of a first crosslinking aid (C1) made of TAIC or TAC, and 0.16 to 0.35 parts by mass of a second crosslinking aid (C2).

The electric wire/cable of the present invention is characterized in that the conductor is covered with an insulating covering layer formed by crosslinking the crosslinkable resin composition of the present invention.

The crosslinkable resin composition of the present invention has good scorch resistance, and by crosslinking it, a crosslinked product with excellent thermal deformation resistance can be obtained.

FIG. 2 is a diagram showing the relationship between the content of a first crosslinking aid and the physical properties of the resulting resin composition. FIG. 2 is a diagram showing the relationship between the content of a second crosslinking aid and the physical properties of the resulting resin composition. FIG. 2 is a graph showing the relationship between the content of a crosslinking agent and the physical properties of the resulting resin composition.

The present invention will be described in detail below.
<Crosslinkable resin composition>
The crosslinkable resin composition of the present invention contains an ethylene-based resin (A), a crosslinking agent (B) made of an organic peroxide, a first crosslinking auxiliary (C1) made of an allyl group-containing compound, and a second crosslinking auxiliary (C2) made of an α-methylstyrene dimer.

<Ethylene-based resin (A)>
The ethylene-based resin (A) constituting the crosslinkable resin composition of the present invention comprises a high-pressure low-density ethylene homopolymer.

The high-pressure low-density ethylene homopolymer can be produced by a conventionally known method.

Examples of the polymerization catalyst used in the production of the ethylene-based resin (A) include radical-generating catalysts such as organic peroxides , azo compounds, and oxygen .

A suitable ethylene-based resin (A) is a high-pressure ^low -density ethylene homopolymer having a density of 0.91 to ^0.94 g/cm, particularly 0.915 to 0.930 g/cm, and a melt mass flow rate of 0.01 to 10 g/10 min, particularly 0.5 to 5 g/10 min .

If an ethylene-based resin with too low a density is used, the abrasion resistance of the insulating coating layer that is finally formed tends to be poor, whereas if an ethylene-based resin with too high a density is used, the flexibility of the insulating coating layer that is finally formed tends to be poor.
Furthermore, an ethylene-based resin with an excessively low melt mass flow rate is poor in processability, while the use of an ethylene-based resin with an excessively high melt mass flow rate tends to reduce the mechanical strength, heat deformation resistance, roundness, etc. of the insulating coating layer that is finally formed.

<Crosslinking Agent (B)>
The crosslinking agent (B) constituting the crosslinkable resin composition of the present invention comprises an organic peroxide.
Specific examples of the crosslinking agent (B) include di-t-butyl peroxide, 1,1-bis-t-butyl peroxybenzoate, 2,2-bis-t-butyl peroxybutane, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butyl peroxyhexane, t-butyl cumyl peroxide, and 2,5-dimethyl-2,5-di-t-butyl peroxyhexyne-3, which may be used alone or in combination of two or more. Of these, dicumyl peroxide is preferred.

In the crosslinkable resin composition of the present invention, the content of the crosslinking agent (B) is usually 0.85 to 1.25 parts by mass, preferably 0.90 to 1.20 parts by mass, and more preferably 0.91 to 1.16 parts by mass, per 100 parts by mass of the ethylene-based resin (A).

If the content of the crosslinking agent (B) is less than 0.85 parts by mass, the crosslinked product of the obtained resin composition will have poor heat distortion resistance (see Comparative Example 5 described later).
On the other hand, if this content exceeds 1.25 parts by mass, the scorch resistance of the resulting crosslinkable resin composition becomes poor (see Comparative Example 6 described later).

<First crosslinking aid (C1)>
The first crosslinking auxiliary (C1) constituting the crosslinkable resin composition of the present invention comprises an allyl group-containing compound.
Specific examples of the first crosslinking aid (C1) include TAIC (triallyl isocyanurate), TAC (triallyl cyanurate), TATM (triallyl trimellitate), etc., which can be used alone or in combination of two or more. Among these, TAIC and TAC are preferred, and TAIC is particularly preferred.

The first crosslinking aid (C1) can be incorporated in a suitable ratio, as described below, to promote the crosslinking reaction caused by the crosslinking agent (B) and improve the thermal deformation resistance of the resulting crosslinked product.

In the crosslinkable resin composition of the present invention, the content of the first crosslinking aid (C1) is usually 0.07 to 0.60 parts by mass, preferably 0.10 to 0.55 parts by mass, and more preferably 0.11 to 0.52 parts by mass, per 100 parts by mass of the ethylene-based resin (A).

When the content of the first crosslinking auxiliary (C1) is less than 0.07 parts by mass, the heat distortion resistance of the crosslinked product of the obtained resin composition is inferior.
On the other hand, if this content exceeds 0.60 parts by mass, the scorch resistance of the resulting crosslinkable resin composition becomes poor (see Comparative Example 2 described later).

<Second crosslinking aid (C2)>
The second crosslinking auxiliary (C2) constituting the crosslinkable resin composition of the present invention comprises α-methylstyrene dimer (AMSD).
The second crosslinking auxiliary (C2) can improve the scorch resistance of the resin composition by being contained in a suitable ratio described later.

In the crosslinkable resin composition of the present invention, the content of the second crosslinking aid (C2) is usually 0.15 to 0.38 parts by mass, preferably 0.15 to 0.35 parts by mass, and more preferably 0.16 to 0.35 parts by mass, per 100 parts by mass of the ethylene-based resin (A).

When the content of the second crosslinking auxiliary (C2) is less than 0.15 parts by mass, the scorch resistance of the obtained crosslinkable resin composition becomes poor.
On the other hand, if this content exceeds 0.38 parts by mass, the heat distortion resistance of the crosslinked product of the obtained resin composition will be poor (see Comparative Example 4 described later).

In the crosslinkable resin composition of the present invention, the mass ratio of the second crosslinking auxiliary (C2) to the first crosslinking auxiliary (C1) is preferably 0.4 to 2.5, and more preferably 0.48 to 2.3.
If this mass proportion is too small, the resulting crosslinkable resin composition may not have sufficient scorch resistance.
On the other hand, if this mass proportion is too large, a crosslinked product having good resistance to thermal distortion may not be obtained from the resulting crosslinkable resin composition.

<Optional ingredients>
In addition to the above-mentioned ethylene-based resin (A), crosslinking agent (B), first crosslinking aid (C1) and second crosslinking aid (C2), the crosslinkable resin composition of the present invention may contain an olefin-based resin other than the ethylene-based resin (A), a stabilizer, various additives and auxiliary materials depending on the purpose of use within a range that does not impair the properties of the resin composition of the present invention.

Examples of the olefin resin, which is an optional component, include ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, ethylene-maleic acid copolymer, ethylene-diene compound copolymer, ethylene-vinyl silane copolymer, maleic anhydride grafted ethylene polymer, acrylic acid grafted ethylene polymer, and silane grafted ethylene polymer.

Specific examples of optional stabilizers (light stabilizers, antioxidants, processing stabilizers) include tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate (LA-52 manufactured by ADEKA), 2,2,6,6-tetramethyl-4-piperidyl methacrylate (LA-87 manufactured by ADEKA), bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (LA-77 manufactured by ADEKA, or TINUVIN manufactured by BASF). hindered amine type light stabilizers such as 4,4'-thiobis-(3-methyl-6-t-butylphenol) (Shipro Chemical Co., Ltd.'s Seenox BCS), 4,4'-thiobis-(6-t-butyl-o-cresol) (Ethanox 736, Ethyl Corporation), tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane (BASF's Irganox 1010), and N,N'-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl] Hydrazine (Irganox 1024 manufactured by BASF), 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanuric acid (Cyanox 1790 manufactured by Cytec), 1,3,5-trimethyl-2,4-6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (Ethanox 330 manufactured by Albert Corporation), triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (Irganox 1024 manufactured by BASF), 245), 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (Irganox 259, manufactured by BASF), octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (Irganox 1076, manufactured by BASF), N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) (Irganox 1098, manufactured by BASF), 1,3,5-trimethyl-2,4,6-tris(3,5-di -t-butyl-4-hydroxybenzyl)benzene (BASF Irganox 1330), tris-(3,5-di-t-butyl-4-hydroxybenzyl)-isocyanurate (BASF Irganox 3114), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (BASF Irganox 1135), 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (Asahi Denka Adeka Stab AO-30), 4,4'-butylidene Examples of such stabilizers include hindered phenol stabilizers such as bis-(3-methyl-6-t-butylphenol (ADEKA STAB AO-40 manufactured by Asahi Denka Co., Ltd.) and 2,2'-thiobis-(4-methyl-6-t-butylphenol); and dialkyl thiodipropionate stabilizers such as dilauryl thiodipropionate (DLTP "Yoshitomi" manufactured by Yoshitomi Pharmaceutical Co., Ltd.), distearyl thiodipropionate (DSTP "Yoshitomi" manufactured by Yoshitomi Pharmaceutical Co., Ltd.), and dimyristyl thiodipropionate (DMTP "Yoshitomi" manufactured by Yoshitomi Pharmaceutical Co., Ltd.).

Optional additives and auxiliary materials include processability improvers, dispersants, copper inhibitors, antistatic agents, lubricants, carbon black, etc.

The crosslinkable resin composition of the present invention can be prepared by blending the essential components [the ethylene-based resin (A), the crosslinking agent (B), the first crosslinking aid (C1) and the second crosslinking aid (C2)] and the optional components in a predetermined ratio, kneading and granulating the mixture.
The crosslinkable resin composition of the present invention is preferably in the form of pellets having an average particle size of about 2 to 7 mm from the viewpoints of ease of feeding into the screw of an extruder, ease of handling, and the like.

<Wires and cables>
The electric wire/cable of the present invention comprises a conductor coated with an insulating coating layer formed by crosslinking the crosslinkable resin composition of the present invention, i.e., an insulating coating layer made of a crosslinked product of the resin composition.
The electric wire/cable of the present invention can be produced by coating a conductor mainly made of copper or aluminum with the crosslinkable resin composition of the present invention by extrusion processing, and then crosslinking the resulting product to form an insulating coating layer.

In the case of low-voltage cables, typically only one layer is coated using a single-layer extruder, while in the case of high-voltage cables, a laminate consisting of a first layer made of the internal semiconductive layer resin composition, a second layer made of the crosslinkable resin composition of the present invention, and a third layer made of the external semiconductive layer resin composition is coated on the conductor using a three-layer extruder at a temperature equal to or higher than the melting temperature of each resin and lower than the decomposition temperature of the crosslinking agent (B), and then the resin composition is crosslinked by heating to a temperature equal to or higher than the decomposition temperature of the crosslinking agent (B) in an atmosphere of nitrogen, water vapor, silicone oil, molten salt, etc.

The electric wire/cable of the present invention has excellent electrical properties (insulating properties of the coating layer) and mechanical properties, and can be extruded stably for a long period of time during its manufacture (extrusion molding process).

The following describes examples of the present invention, but the present invention is not limited to these examples. The ethylene-based resins, crosslinking agents, and crosslinking aids used to produce the resin compositions of the examples and comparative examples are as follows.

Resin (A-1):
High pressure low density ethylene homopolymer, melt mass flow rate (MFR) = 2.2 g/10 min, density 0.922 g/cm ³ (ENEOS NUC Corporation)

Cross-linking agent (B-1): Dicumyl peroxide

First crosslinking assistant (C1-1): TAIC
First crosslinking assistant (C1-2): TAC
Second crosslinking assistant (C2): AMSD
Crosslinking aid (C3): TMPTA (trimethylpropane triacrylate)

Example 1
According to the formulation shown in Table 1 below, 100 parts by mass of resin (A-1), 1.02 parts by mass of crosslinking agent (B-1), 0.29 parts by mass of first crosslinking aid (C1-1), and 0.25 parts by mass of second crosslinking aid (C2) were mixed for 16 hours in a state heated to 60° C., and then cooled to room temperature, thereby obtaining a crosslinkable resin composition of the present invention.

<Examples 1 to 7>
According to the recipe shown in Table 1 below, the crosslinkable resin composition of the present invention was obtained in the same manner as in Example 1, except that the amount of at least one of the crosslinking agent (B-1), the first crosslinking assistant agent (C1-1), and the second crosslinking assistant agent (C2) was changed.

Example 8
A crosslinkable resin composition of the present invention was obtained in the same manner as in Example 2, except that 0.15 parts by mass of the first crosslinking auxiliary (C1-2) was used instead of the first crosslinking auxiliary (C1-1).

<Comparative Example 1>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 2, except that the first crosslinking auxiliary (C1-1) was not used.

<Comparative Example 2>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 1, except that the amount of the first crosslinking auxiliary (C1-1) used was changed to 0.72 parts by mass.

<Comparative Example 3>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 4, except that the second crosslinking auxiliary (C2) was not used.

<Comparative Example 4>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 5, except that the amount of the first crosslinking auxiliary (C2) used was changed to 0.47 parts by mass.

<Comparative Example 5>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 6, except that the amount of the crosslinking agent (B-1) used was changed to 0.76 parts by mass.

<Comparative Example 6>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 7, except that the amount of the crosslinking agent (B-1) used was changed to 1.38 parts by mass.

<Comparative Example 7>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 2, except that 0.15 parts by mass of the crosslinking auxiliary (C3) was used in place of the first crosslinking auxiliary (C1-1).

<Comparative Example 8>
A comparative crosslinkable resin composition was obtained in the same manner as in Example 2, except that 0.20 parts by mass of the crosslinking auxiliary (C3) was used in place of the first crosslinking auxiliary (C1-1).

The scorch resistance and heat deformation property were evaluated for each of the crosslinkable resin compositions obtained in Examples 1 to 8 and Comparative Examples 1 to 8. The evaluation method is as follows. The results are shown in Table 1 and Figures 1 to 3.

FIG. 1 shows the relationship between the content of the first crosslinking aid (C1-1) and the physical properties (scorch resistance and heat distortion resistance of the crosslinked product) of the resulting resin composition when the contents of the crosslinking agent (B-1) and the second crosslinking aid (C2) are substantially constant.
FIG. 2 shows the relationship between the content of the second crosslinking aid (C2) and the physical properties (scorch resistance and heat distortion resistance of the crosslinked product) of the resulting resin composition when the contents of the crosslinking agent (B-1) and the first crosslinking aid (C1-1) are substantially constant.
FIG. 3 shows the relationship between the amount of the crosslinking agent (B-1) added and the physical properties (scorch resistance and heat distortion resistance of the crosslinked product) of the resulting resin composition when the contents of the first crosslinking aid (C1-1) and the second crosslinking aid (C2) are substantially constant.

[Method of evaluating scorch resistance]
In accordance with JIS K 6300-2, measurements were performed using a Moving Die Rheometer (MDR) at a test temperature of 140° C. for 8 hours. The time ts1 required for the torque to increase by 1.0 dNm from the minimum value was measured.
As the evaluation criteria, a ts1 of 45 minutes or more was rated as "pass", and a ts1 of 45 minutes or less was rated as "fail".

[Method for evaluating heat deformation (hot set)]
The resin composition was press molded (temperature 120°C, preheating pressure 0.5 MPa x 5 minutes, pressing pressure 15 MPa x 15 minutes) to obtain a crosslinked sheet having a thickness of 1 mm. A dumbbell No. 6 test piece was prepared from the crosslinked sheet obtained, and two benchmark lines were drawn in the center of this test piece (marker distance (L ₀ ) = 20 mm).
A tensile load of 20 N/cm ² was applied to the test piece in a high-temperature atmosphere of 200° C., the gauge length (L ₁ ) was measured after 15 minutes, and the hot set (%) was calculated according to the following formula.
The evaluation criteria were as follows: a hot set of 80% or less was rated as "pass", and a hot set of more than 80% was rated as "fail".

Formula: Hot set (%) = [(L ₁ - L ₀ )/L ₀ ] x 100

As shown in Table 1 above, all of the crosslinkable resin compositions obtained in Examples 1 to 8 have good scorch resistance, and all of the crosslinked products thereof have excellent heat distortion resistance.
In contrast, the composition according to Comparative Example 2 in which the content of the first crosslinking aid exceeded 0.60 parts by mass, the composition according to Comparative Example 3 in which the second crosslinking aid was not used, and the composition according to Comparative Example 6 in which the content of the crosslinking agent exceeded 1.25 parts by mass all had poor scorch resistance.
In addition, the composition according to Comparative Example 1 in which the first crosslinking aid was not used, the composition according to Comparative Example 4 in which the content of the second crosslinking aid exceeded 0.38 parts by mass, the composition according to Comparative Example 5 in which the content of the crosslinking agent was less than 0.85 parts by mass, and the compositions according to Comparative Examples 7 and 8 in which a crosslinking aid consisting of an acryloyl group-containing compound was contained instead of the first crosslinking aid all had poor heat distortion resistance of the crosslinked product.

It can also be seen from Figures 1 to 3 that only by incorporating the first cross-linking aid (TAIC), the second cross-linking aid (AMSD), and the cross-linking agent (dicumyl peroxide) in specific ranges can a resin composition be obtained that has good scorch resistance and excellent thermal deformation resistance of the cross-linked product.

Claims (7)

100 parts by mass of an ethylene-based resin (A) consisting of a high-pressure low-density ethylene homopolymer ,
0.85 to 1.25 parts by mass of a crosslinking agent (B) consisting of an organic peroxide;
A crosslinkable resin composition comprising: 0.07 to 0.60 parts by mass of a first crosslinking auxiliary (C1) made of an allyl group-containing compound; and 0.15 to 0.38 parts by mass of a second crosslinking auxiliary (C2) made of an α-methylstyrene dimer. the crosslinking agent (B) is dicumyl peroxide,
The crosslinkable resin composition according to claim 1, wherein the first crosslinking auxiliary (C1) is TAIC or TAC. The crosslinkable resin composition according to claim 2, characterized in that the first crosslinking aid (C1) is TAIC. The crosslinkable resin composition according to any one of claims 1 to 3, characterized in that the mass ratio of the second crosslinking aid (C2) to the first crosslinking aid (C1) is 0.4 to 2.5. 0.90 to 1.20 parts by mass of a crosslinking agent (B) consisting of dicumyl peroxide,
The crosslinkable resin composition according to claim 1, comprising: 0.10 to 0.55 parts by mass of a first crosslinking auxiliary (C1) consisting of TAIC or TAC; and 0.15 to 0.35 parts by mass of a second crosslinking auxiliary (C2). 0.91 to 1.16 parts by mass of a crosslinking agent (B) consisting of dicumyl peroxide,
The crosslinkable resin composition according to claim 1, comprising: 0.11 to 0.52 parts by mass of a first crosslinking auxiliary (C1) consisting of TAIC or TAC; and 0.16 to 0.35 parts by mass of a second crosslinking auxiliary (C2). An electric wire or cable in which a conductor is coated with an insulating coating layer formed by crosslinking the crosslinkable resin composition according to any one of claims 1 to 6.

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