JPH11339564A - Polyethylene resin composition and self-supporting cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-supporting cable sheathing composition excellent in workability, extraction strength of a supported line, low temperature brittleness, high-temperature characteristics, a constant strain environment stress crack property and abrasion resistance. SOLUTION: This resin composition contains a straight chain ethylene-α-olefin copolymer A having a melt mass flow rate(MFR) of 0.01-5.0 g/10 min, a density of 0.90-0.94 g/ml and a molecular weight distribution of 10-30 and a straight chain ethylene-α-olefin copolymer B having an MFR of 0.5-50 g/10 min, a density of 0.90-0.94 g/ml and a molecular weight distribution of 1.5-6.0 and in this case, the mixing ratio A:B equals (95-30):(5-70) (wt.%). Another example of the resin composition is prepared by mixing 70 pts.wt. of high-pressure method low density polyethylene having an MFR of 0.01-5 g/10 min, a density of 0.90-0.93 g/ml and a molecular weight distribution of 3-15 in 100 pts.wt. of the said composition. This self-supporting type cable is covered with either of the compositions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyethylene resin composition and a self-supporting cable,
More specifically, in a self-supporting cable, a composition for a cable sheath having good adhesion to a support wire, low embrittlement temperature (excellent in low-temperature embrittlement), excellent wear resistance, and good workability. And a self-supporting cable obtained using the composition.

[0002]

2. Description of the Related Art When a cable for electric or optical communication or power supply is installed on a power pole, the cable itself has insufficient tensile strength, causing inconveniences such as disconnection and deterioration of electrical characteristics. For this reason, conventionally, a self-supporting cable in which a reinforcing support wire made of a steel stranded wire or the like is provided in parallel with the cable main body and the both are integrated is used.

The advantage of the self-supporting cable is that, in addition to the reinforcing effect of the cable, the growth of snow accretion is generally less than that of the round cable.
It is mentioned that there is no corrosion or the like, and that an electrostatic induction voltage can be reduced by disposing a support wire. As a sheath material used for such a self-supporting type cable, conventionally, a so-called high-pressure low-density polyethylene produced by a high-pressure radical polymerization method is widely used because it has better workability than polyvinyl chloride and less embrittlement at low temperatures. Has been used. However, when used as a sheath layer, there is a problem that the wear resistance and the constant strain environmental stress cracking resistance (ESCR) are slightly inferior. At present, a sheath material having high low-temperature brittleness is desired. To improve low temperature brittleness,
It is conceivable to blend an ethylene copolymer having a low crystallinity with a polar group such as an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer into a high-pressure low-density polyethylene. Since the hardness of the sheath surface is reduced and the abrasion resistance is also reduced, there is a possibility that a problem may occur in long-term reliability of the cable. Further, since the melting point is usually lowered due to the blending of the ethylene copolymer having a low crystallinity, the reliability at a high temperature is also lowered. As a method of solving these problems, it is conceivable to use a linear ethylene-α-olefin copolymer having a wide molecular weight distribution. In this case, it is possible to maintain workability and improve abrasion resistance, but it has been found that the pull-out strength with respect to the support wire is inferior to that of low-density polyethylene produced by a high-pressure radical polymerization method.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a workability and a pull-out strength of a support wire which are equal to or better than conventionally used high-pressure low-density polyethylene, low-temperature brittleness, high-temperature properties, and durability. An object of the present invention is to provide a sheath resin composition which is excellent in strain environmental stress cracking property, has high surface hardness and excellent wear resistance, and a self-supporting cable manufactured from the composition.

[0005]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by a resin composition comprising a combination of specific polyethylene resins mixed at a specific ratio. And completed the present invention.

That is, the present invention provides a melt mass flow rate of 0.01 to 5.0 g / 10 minutes and a density of 0.90 to 0.1 g.
A substantially linear ethylene-α-olefin copolymer (A) having a molecular weight distribution Mw / Mn of 10 to 30 and a melt mass flow rate of 0.5 to 50 g / 10;
Min, density 0.90 to 0.94 g / ml, molecular weight distribution Mw
/ Mn 1.5 to 6.0, and a substantially linear ethylene-α-olefin copolymer (B), and the mixing ratio (A) :( B) in weight% is 95 to 30. : 5 to 70, which relates to a self-supporting polyethylene resin composition for coating a cable. The present invention also provides a melt mass flow rate of 0.01 to 5.0 g / 10 minutes and a density of 0.90 with respect to 100 parts by weight of the polyethylene resin composition of the present invention comprising the components (A) and (B). ~
The present invention relates to a self-supporting type polyethylene resin composition for cable coating, characterized by mixing up to 70 parts by weight of high-pressure low-density polyethylene (C) having 0.93 g / ml and a molecular weight distribution of Mw / Mn of 3 to 15. Furthermore, the present invention relates to a self-supporting cable characterized by being coated with the polyethylene resin composition of the present invention.

In the present invention, the substantially linear ethylene-α-olefin copolymer is represented by a Ziegler catalyst, a Phillips catalyst and a standard catalyst together with the resin components (A) and (B). It is produced by copolymerizing ethylene and an α-olefin using a single-site catalyst typified by a multi-site catalyst or a metallocene catalyst.

Here, the Ziegler-based catalyst includes a main catalyst composed of a transition metal compound such as a titanium compound or a vanadium compound, a cocatalyst composed of an organic metal compound such as organoaluminum, and an oxide such as silicon, titanium or magnesium. It is a catalyst composed of a catalyst carrier. The Phillips catalyst is a catalyst comprising a main catalyst made of chromium oxide and a catalyst carrier made of an oxide such as aluminum. The standard catalyst is a catalyst composed of a main catalyst made of molybdenum oxide and a catalyst carrier made of an oxide such as aluminum.

The single-site catalyst includes a main catalyst comprising a transition metal compound of Group 3 or 4 of the periodic table containing a ligand having a cyclopentadienyl skeleton, and a co-catalyst such as an organoaluminum compound. The catalyst is composed of The transition metal compound generally has 1 to 3 ligands having a cyclopentadienyl skeleton, and when having 2 or more ligands, the ligands may be mutually bonded by a crosslinking group. Examples of other transition metal compounds include those in which a ligand having a cyclopentadienyl skeleton represented by the following formula (1), another ligand, and a transition metal atom form a ring. : (In the formula, Cp represents the ligand having the cyclopentadienyl skeleton, and X represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, an arylsilyl group, an aryloxy group, an alkoxy group, an amide. Y represents SiR ₂ , CR ₂ , SiR ₂ Si
R ₂ , CR ₂ CR ₂ , CR = CR, SiR ₂ CR ₂ , B
Represents a divalent group selected from the group consisting of R ₂ and BR, and Z is a divalent group represented by —O—, —S—, —NR—, —PR— or OR, SR, NR ₂ And PR ₂ represents a divalent neutral ligand selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group, a silyl group, a halogenated alkyl group, and a halogenated aryl group. Represents, 2 from Y, Z or both Y and Z
More than one R group forms a fused ring system and M represents a transition metal atom of Group 3 or 4 of the Periodic Table). Further, the single-site catalyst may be supported on an inorganic or organic compound carrier, if necessary. The carrier is preferably a porous oxide of an inorganic or organic compound.

Conventional Ziegler catalysts and the like contain active sites having different properties, so that a multi-site catalyst (MS
It is called C), and low molecular weight components other than the target molecular weight are simultaneously polymerized. On the other hand, metallocene catalysts and the like have a uniform active site and are called single-site catalysts (SSCs). A homogeneous polymer having a narrow molecular weight distribution can be obtained, and a molecular weight distribution related to processability and a composition distribution related to product characteristics. Can be arbitrarily controlled.

The α-olefin for producing the ethylene-α-olefin copolymer in the present invention has 3 to 20 carbon atoms, preferably 3 to 12 carbon atoms, specifically, propylene, -Butene, 4-
Methyl-1-pentene, 1-hexene, 1-octene,
Examples thereof include 1-decene and 1-dodecene. These α
-The content of the olefin is desirably selected in the range of usually 30 mol% or less, preferably 20 mol% or less.

For the polymerization of the ethylene-α-olefin copolymer, a method such as a solution polymerization method, a suspension polymerization method, a slurry polymerization method, or a gas phase polymerization method can be preferably used. Generally, the temperature during the polymerization is from 0 to 250C,
Pressure is high (50MPa or more), medium pressure (10-50MPa)
a) or low pressure (normal pressure to 10 MPa).

In the present invention, the substantially linear ethylene-α-olefin copolymer used as the resin component (A) is, as described above, a melt mass flow rate (MF).
R) is 0.01 to 5.0 g / 10 min, and the density is 0.90 to
0.94 g / ml, molecular weight distribution Mw / Mn is 10 to 30
It is. If the MFR is less than 0.01 g / 10 min, the coating speed is reduced, and the polymerization is difficult, which is not practically preferable. If it exceeds 5.0 g / 10 min, the mechanical strength, low-temperature brittleness, and environmental stress are reduced. Cracking properties become insufficient. Density 0.9
If it is less than 0 g / ml, the wear resistance is insufficient,
If it exceeds 0.94 g / ml, the flexibility is insufficient,
In addition, low-temperature brittleness is poor, which is not desirable. Further, when the molecular weight distribution is less than 10, the processability is inferior, and when it exceeds 30, the strength is greatly reduced, which is not desirable. In addition, Mw is a weight average molecular weight and Mn is a number average molecular weight.

The substantially linear ethylene-α-olefin copolymer used as the resin component (B) in the present invention has an MFR of 0.5 to 50 g / 10, as described above.
Min, density 0.90 to 0.94 g / ml, molecular weight distribution M
w / Mn is 1.5 to 6.0. MFR is 0.5g /
If the time is less than 10 minutes, the coating speed is reduced, and the polymerization is difficult, which is not practically preferable. If the time exceeds 50 g / 10 minutes, the mechanical strength, low-temperature brittleness, and environmental stress cracking resistance become insufficient. If the density is less than 0.90 g / ml, the abrasion resistance is insufficient, and if it exceeds 0.94 g / ml, the flexibility is insufficient and the low-temperature brittleness is poor, which is not desirable.
Further, when the molecular weight distribution is less than 1.5, polymerization is practically difficult, and the processability is poor. When it exceeds 6.0, the strength is greatly reduced, which is not desirable. The molecular weight distribution of the component (B) is preferably from 2.5 to 5.0.

The mixing ratio of the above components (A) and (B) is 95 to 30% by weight of component (A) and (B)
Component 5 to 70% by weight. When the amount of the component (A) exceeds 95% by weight (that is, when the amount of the component (B) is less than 5% by weight), the adhesion to the support wire is poor, and when the amount of the component (A) is less than 30% by weight ( That is, when the component (B) is 70
If the amount exceeds 5% by weight), the surface of the sheath tends to have a shark skin shape during processing, and the motor load increases, which is not desirable. For the purpose of obtaining the required MFR for the components (A) and (B), for example, two or more ethylene-α-olefin copolymers are blended so that each resin component can be used as described above in the present invention. It may be a property value range.

The high-pressure low-density polyethylene optionally used as the resin component (C) in the present invention is, for example, a reaction temperature of 150 to 350 ° C. and a reaction pressure of 100 to 300 M.
It can be produced by polymerizing ethylene using a radical polymerization catalyst such as an organic peroxide under the condition of Pa, and has an MFR of 0.01 to 5.0 g / 10
And a molecular weight distribution of Mw / Mn of 3 to 15. MFR is 0.
When it is less than 01 g / 10 minutes, the coating speed is reduced, and the polymerization is difficult, which is not practically preferable.
If the amount exceeds the above range, the mechanical strength, low-temperature brittleness resistance and environmental stress cracking resistance become insufficient, which is not desirable. 0.90g density
/ Ml, the abrasion resistance is insufficient, and 0.9
If it exceeds 3 g / ml, the flexibility is insufficient and the low-temperature brittleness resistance is poor, which is not desirable. If the molecular weight distribution Mw / Mn is less than 3, the processability is poor, and if it exceeds 15, the mechanical strength is greatly reduced, which is not desirable. When the high-pressure low-density polyethylene is used as the component (C), the component (C) is a composition 10 composed of the components (A) and (B).
It is blended up to 70 parts by weight with respect to 0 parts by weight. This is because if the amount of the component (C) exceeds 70 parts by weight, the abrasion resistance and low-temperature brittleness resistance become insufficient, which is undesirable.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In order to obtain the polyethylene resin composition of the present invention, the above components (A) and (B) and, optionally, component (C) are melt-kneaded in advance, and are mixed in a solid state. For example, various methods can be adopted, such as feeding the extruder directly to an extruder at a predetermined ratio by an automatic feeding device or the like. In the present invention, the component (A) and the component (B)
The shape of each of the component and the component (C) is not particularly limited. However, when a method other than melt-kneading is adopted in advance in the operation of forming the above composition, each component is easily dispersed uniformly, Then, in order to prevent separation during the feeding of the extruder and uneven melting in the extruder to obtain a uniform extruded coating, it is preferable that each component has a similar particle size and shape. Antioxidants, ultraviolet absorbers, light stabilizers, carbon black, etc. are usually added to each of the above components to provide the heat resistance, weather resistance, etc. required as a sheath material. Agents, lubricants, inorganic fillers and the like can be added. These additives may be added to each of the components (A), (B) and (C),
May be added to only the components (A) and (B).
It may be added to two or more kinds of compositions selected from the group consisting of the component and the component (C).

The polyethylene resin composition of the present invention is included in the present invention as long as it does not impair wear resistance, low-temperature brittleness and resistance to constant-strain environmental stress cracking. Other than a linear ethylene-α-olefin copolymer or a high-pressure low-density polyethylene other than those described above, an ethylene copolymer having a polar group or a synthetic rubber such as ethylene propylene rubber may be added.

As described above, the self-supporting cable manufactured by coating the cable body and the supporting wire thereof with the above-mentioned polyethylene resin composition of the present invention also constitutes the present invention. It can be manufactured by a known method. Although the self-supporting cable of the present invention uses the polyethylene resin composition of the present invention as a material of the sheath layer, it may have a cross-linked structure to enhance abrasion resistance and the like in the sheath layer. It is. As a crosslinking method, a known technique such as chemical crosslinking, irradiation crosslinking, or water crosslinking can be used. In addition, for the purpose of further improving the adhesion strength to a reinforcing support wire made of a steel stranded wire or the like disposed substantially parallel to the cable body,
Prior to extrusion of the resin composition, the support wire may be washed with an organic solvent such as methanol or acetone to remove oil and the like on the support wire, or the support wire may be preheated. The self-supporting cable of the present invention can be used as a cable for electric or optical communication or power supply.

[0020]

Next, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. First, the method and conditions for measuring the physical properties of the resin and the self-supporting cable used in the present example and the processing conditions for the cable will be described, and then the actual examples of the present invention and comparison for comparison will be described. Here is an example.

Measurement method, measurement conditions and processing conditions (1) Melt mass flow rate (MFR): JIS K
7210. The unit is g / 10 minutes. (2) Density: Based on JIS K7112. The unit is g
/ Ml. (3) Molecular weight, molecular weight distribution: Measured by size exclusion chromatography (SEC). (4) Discharge pressure: Measured at the extruder neck using a pressure sensor. The unit is kg / cm ² . (5) Pulling force: 7 × 1.8 mm at a die extrusion temperature of 230 ° C.
A (18 sq) high corrosion-resistant steel stranded wire was coated so as to have a cable outer diameter of 7.4 mm (sheath thickness 1.0 mm) without washing or preheating. The test was performed at a die diameter of 7.5 mm, a nipple diameter of 5.5 mm, and a linear velocity of 10 m / min. The coated cable was cut to a length of 20 cm, and the upper and lower ends of the cut cable were peeled off by 5 cm each so that the sheath layer remained only at the center at 10 cm. A support wire pull-out test of this sample was performed using a tensile tester. Perform (unit is kgf). If this value is 30 kgf or more, it is determined that there is no practical problem. (6) Abrasion resistance index: measured according to ASTM D630. (7) brittle temperature: conforms to the JIS K7216, was measured by the F ₀ notched. The unit is ° C. (8) Heat deformation: 100 in accordance with JIS C3005
° C and a load of 3 kg. Units%. (9) Constant strain environmental stress crack resistance (ESCR): JIS
It was measured at F ₀ according to K6760. (10) Processing conditions: The following conditions were employed. Extruder diameter (50 mm), die diameter (7.5 mm), cable outer diameter (7.4 mm), support wire [7 × 1.8 mm (1
8sq) High corrosion-resistant steel twisted wire], L / D (24/1), nipple diameter (5.5 mm), sheath thickness (1.0 mm) Note that high pressure was used in all Examples and Comparative Examples except Comparative Example 2. A carbon black masterbatch based on a process polyethylene is used in an amount of 1 part by weight per 100 parts by weight of the polyethylene resin composition comprising the components (A) and (B).
0 parts by weight were added to obtain a sheath material.

Example 1 The component (A) had an MFR of 0.7 g / 10 min and a density of 0.9.
70 g by weight of a linear ethylene-α-olefin copolymer having a molecular weight distribution (Mw / Mn) of 15.4 (manufactured by Nippon Unicar, trade name: GS-650) having a molecular weight distribution (Mw / Mn) of 15.4;
The component (B) has an MFR of 2.0 g / 10 min and a density of 0.9.
A pellet is blended with 30 parts by weight of a linear ethylene-α-olefin copolymer having a molecular weight distribution (Mw / Mn) of 4.6 (manufactured by Nippon Unicar, trade name: NUCG-5220) having a molecular weight distribution of 4.6 (Mw / Mn). 7 × with a die extrusion temperature of 230 ° C. and no cleaning, preheating, etc.
A 1.8 mm (18 sq) high corrosion resistant steel stranded wire was coated so that the cable outer diameter was 7.4 mm (sheath thickness 1.0 mm). The test was performed at a die diameter of 7.5 mm, a nipple diameter of 5.5 mm, and a linear velocity of 10 m / min. The coated cable was subjected to a support wire pull-out test. In the following Examples and Comparative Examples, the support wire coating was performed in the same manner as described above. Table 1 shows the physical property values and compounding amounts (blend ratios) of the resin components in each Example and Comparative Example, and Table 2 shows the evaluation results of the cables. Comprehensive evaluation comprehensively judges pullout strength, low temperature characteristics, high temperature characteristics, abrasion resistance and appearance,
Indicated by 〇, △ and ×. 〇 means that it can be used without any problem as a sheath material, △ means that it is somewhat difficult to use, and × means that it cannot be used. From the results shown in Table 2, the cable obtained in Example 1 had the following characteristics: pull-out strength, low-temperature characteristics, abrasion resistance,
Both the high-temperature characteristics and the appearance are good, and it is clear that the composite can be used without any problem in the comprehensive evaluation.

Example 2 The component (A) had an MFR of 0.7 g / 10 min and a density of 0.9.
70 g by weight of a linear ethylene-α-olefin copolymer having a molecular weight distribution (Mw / Mn) of 15.4 (manufactured by Nippon Unicar, trade name: GS-650) having a molecular weight distribution (Mw / Mn) of 15.4;
The component (B) has an MFR of 2.0 g / 10 min and a density of 0.9.
18 g / ml, 30 parts by weight of a linear ethylene-α-olefin copolymer having a molecular weight distribution (Mw / Mn) of 4.6 (manufactured by Nippon Unicar, trade name: NUCG-5220),
MFR 0.24 g / 10 min, density 0.919 g / ml,
High-pressure low-density polyethylene having a molecular weight distribution (Mw / Mn) of 5.1 (manufactured by Nippon Unicar, trade name: DFDJ-67)
75) was blended with 30 parts by weight of pellets, and the same operation as in Example 1 was performed. From the results shown in Table 2, the cable obtained in Example 2 was
Although low-temperature characteristics, abrasion resistance, and high-temperature characteristics are slightly inferior to those of Example 1, it is not so much as to cause any problems in practical use, and the pull-out strength and appearance are good, and the motor load during cable processing can be reduced. It can be seen that the workability was further improved.

Example 3 In place of the component (B) in Example 1, 1.0 g of MFR was used.
/ 10 min, density 0.921 g / ml, molecular weight distribution (Mw
/ Mn) 4.2 linear ethylene-α-olefin copolymer (manufactured by Nippon Unicar, trade name: NUCG-521)
The same operation as in Example 1 was performed except that 0) was used. From the results shown in Table 2, it can be seen that the cable obtained in Example 3 has good pull-out strength, wear resistance, low-temperature characteristics, high-temperature characteristics, and the like.

Example 4 The same operation as in Example 1 was performed except that the blend ratio of the component (A) and the component (B) in Example 1 was changed to 95% by weight: 5% by weight. From the results shown in Table 2, it can be seen that the cable obtained in Example 4 had good pull-out strength, abrasion resistance, low-temperature characteristics, high-temperature characteristics, and good appearance.

Example 5 The same operation as in Example 1 was performed except that the blend ratio of the component (A) and the component (B) in Example 1 was changed to 30% by weight: 70% by weight. From the results shown in Table 2, it can be seen that the cable obtained in Example 5 had good pull-out strength, wear resistance, low-temperature characteristics, high-temperature characteristics, and appearance.

Example 6 MFR 0.23 was used in place of the component (C) in Example 2.
g / 10 min, density 0.920 g / ml, molecular weight distribution (M
The same operation as in Example 2 was performed except that 60 parts by weight of a high-pressure method low-density polyethylene (w / Mn) 7.5 (manufactured by Nippon Unicar, trade name: DFD-6005) was used. From the results shown in Table 2, the cable obtained in Example 6 was
Although low-temperature characteristics, abrasion resistance, and high-temperature characteristics are slightly inferior to those of Example 1, it is not so much as to cause any practical problems, the pull-out strength and appearance are good, and the motor load during cable processing can be reduced. It can be seen that the workability was further improved.

Comparative Example 1 Coating was performed using only the component (A) in Example 1 as a sheath material. The results are shown in Table 2. As shown in Table 2, the cable obtained in Comparative Example 1 had good low-temperature characteristics, abrasion resistance, high-temperature characteristics and appearance, but had poor pull-out strength.

Comparative Example 2 The sheath material was a high-pressure method low-density polyethylene (manufactured by Nippon Unicar, trade name: DFDJ-0588, MFR 0.16 g /
The same operation as in Example 1 was performed except that only the density was changed to 0.924 g / ml for 10 minutes. Since carbon black was already added to this resin, no carbon black masterbatch was added. The results are shown in Table 2. The cable obtained in Comparative Example 2 had good pull-out strength, but was inferior in wear resistance, low-temperature characteristics and ESCR.

Comparative Example 3 Coating was performed using only the component (B) in Example 1 as a sheath material. The results are shown in Table 2. The cable obtained in Comparative Example 3 had good pull-out strength, low-temperature characteristics, abrasion resistance, and high-temperature characteristics, but had melt fracture and had an extremely poor appearance.

Comparative Example 4 In place of the component (A) in Example 1, 0.9 g of MFR was used.
/ 10 min, density 0.945 g / ml, molecular weight distribution (Mw
/ Mn) 18.4 linear ethylene-α-olefin copolymer (manufactured by Nippon Unicar, trade name: DGDN-33)
64) The same operation as in Example 1 was performed except that (64) was used.
The results are shown in Table 2, and the cable obtained in Comparative Example 4 was:
Although the pull-out strength, abrasion resistance and high-temperature properties were good, the low-temperature properties were inferior and the ESCR was slightly inferior. In particular, this cable was inferior in flexibility and unsuitable for practical use.

Comparative Example 5 The same operation as in Example 1 was carried out except that the blend ratio of the components (A) and (B) in Example 1 was changed to 20% by weight: 80% by weight. The results are shown in Table 2. As shown in Table 2, the cable obtained in Comparative Example 5 had good pull-out strength, low-temperature properties, abrasion resistance, and high-temperature properties, but had melt fracture and had an extremely poor appearance.

Comparative Example 6 The MFR of the component (B) in Comparative Example 5 was changed until the appearance was improved, that is, MFR52 was used as the component (B).
g / 10 min, density 0.926 g / ml, molecular weight distribution (M
w / Mn) 3.8 linear ethylene-α-olefin copolymer (manufactured by Nippon Unicar, trade name: NUCG-53)
The same operation as in Comparative Example 5 was performed, except that 91) was used.
The results are shown in Table 2. The cable obtained in Comparative Example 6 was:
Not only the appearance but also the low-temperature characteristics and the high-temperature characteristics were good, but the pull-out strength was poor. This is probably because the MFR of the component (B) was too high, and the strength of the sheath itself was insufficient. Further, since the strength of the sheath itself is insufficient, the self-supporting type cable sheath is inferior in its original purpose of reinforcing the cable.

Comparative Example 7 The same operation as in Example 2 was carried out except that the blending amount of the component (C) in Example 2 was changed to 80 parts by weight. From the results shown in Table 2, the cable obtained in Comparative Example 7 had good pull-out strength, but had abrasion resistance, low-temperature characteristics, high-temperature characteristics,
Environmental stress cracking resistance was poor.

[0035]

[Table 1] (Footnotes to Table 1) ^{1) The} amounts of each component are shown in parts by weight in the order of component (A) / component (B) / component (C).

[0036]

[Table 2] (Footnotes in Table 2) ¹⁾ Melt fracture. ²⁾ Poor flexibility was observed.

[0037]

As described above in detail, the polyethylene resin composition of the present invention has, as one component, a linear ethylene-α-olefin copolymer having a wide molecular weight distribution and a specific MFR and density. And a linear ethylene-α-olefin copolymer having a narrow molecular weight distribution and a specific MFR and density as the other component at a specific compounding ratio. Has a pull-out strength equal to or better than that of high-pressure low-density polyethylene (HP-LDPE) which has been conventionally used for cable sheaths, and has sufficient adhesion to support wires and low-temperature brittleness. Copolymer (E
Since it is not necessary to use a copolymer having a polar group such as VA), the surface hardness is high and the abrasion resistance is greatly improved. Furthermore, when compared with EVA or HP-LDPE, the melting point is high, and Excellent properties, and also excellent resistance to constant strain environmental stress cracking. Further, by mixing the polyethylene resin composition of the present invention with a specific amount of a high-pressure low-density polyethylene having a specific molecular weight distribution, MFR and density, the processability is further improved while maintaining the above-mentioned excellent properties. improves. For this reason, by using the polyethylene resin composition of the present invention as a sheath material, the cable reinforcing effect by the support wire of the self-supporting cable can be further enhanced, and various physical properties have been conventionally used in HP- L
Since it is superior to materials such as DPE, it is possible to maintain the reliability of the cable for a long period of time. By using a composition containing a high-pressure low-density polyethylene, it is possible to coat a self-supporting cable having excellent characteristics as described above with higher moldability.
In addition, the self-supporting cable obtained by coating with the polyethylene resin composition of the present invention further enhances the cable reinforcing effect, and is excellent in low-temperature brittleness, high-temperature properties, constant strain environmental stress cracking resistance, and wear resistance. It can be used with high reliability for a long period of time even under severe conditions such as cold regions.

Claims (3)

[Claims] 1. A melt mass flow rate of 0.01 to 5.
A substantially linear ethylene-α-olefin copolymer (A) having 0 g / 10 min, a density of 0.90 to 0.94 g / ml, and a molecular weight distribution Mw / Mn of 10 to 30 and a melt mass flow rate of 0.5 ~ 50g / 10min, density 0.90 ~
0.94 g / ml, molecular weight distribution Mw / Mn 1.5-6.
And a substantially linear ethylene-α-olefin copolymer (B) having a mixing ratio of (A) :( B) of 95 to 30: 5 to 70 in weight%. A polyethylene resin composition for coating a self-supporting cable, comprising: 2. A melt mass flow rate of 0.0 with respect to 100 parts by weight of the polyethylene resin composition according to claim 1.
1 to 5.0 g / 10 min, density 0.90 to 0.93 g / m
1. A self-supporting type polyethylene resin composition for coating a cable, wherein up to 70 parts by weight of a high pressure method low density polyethylene (C) having a molecular weight distribution Mw / Mn of 3 to 15 is mixed. 3. A self-supporting cable coated with the polyethylene resin composition according to claim 1.