JPS59215342A - Resin composition for power cable - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin composition for electric cables, and in particular to the electric tree resistance, withstand voltage characteristics, heat resistance, crosslinking properties, and The present invention relates to a resin composition for electric cables that can improve processability.

Conventionally, OF cables have been mainly used as high voltage power cables. However, due to improvements in the quality of polyethylene, which is an insulating material, and improvements in cable manufacturing methods, cross-linked polyethylene cables (hereinafter simply referred to as CV cables) have been used as high-voltage power cables, and recently, although on a trial basis, 254 KV CV cables are beginning to be used even under such high voltage conditions. It is thought that CV cables will continue to move in the direction of higher voltages due to their various advantages such as ease of maintenance and inspection and cost reduction.

However, low-density polyethylene manufactured by high-pressure radical polymerization, which is currently used for CV cables, has excellent workability, but its low crystallinity makes it difficult to withstand electricity and withstand voltage. It has the disadvantage of poor properties, especially inferior to the above properties at high temperatures.

In addition, high-density polyethylene produced by a medium-low pressure method has high crystallinity and a high melting point, so it has excellent properties at high temperatures. However, on the other hand, high-density polyethylene manufactured using a medium-low pressure method has a high melting point, so high temperatures are required during crosslinking with organic peroxides, so organic peroxides are mixed uniformly in an extruder, etc. Problems such as decomposition and gelation are likely to occur. In addition, in high-density polyethylene, in order to improve the degree of crosslinking and improve the above-mentioned physical properties, it is preferable to narrow the molecular weight distribution of the resin, that is, to reduce the low molecular weight components, but narrowing the molecular weight distribution impairs extrusion processability. It is extremely bad, and the load on the extruder becomes abnormally high, and the surface of the extrudate becomes rough, making it impossible to obtain a smooth surface, reducing the product value, and causing concerns about deterioration of various physical properties. On the other hand, when the molecular weight distribution is widened in order to improve processability, the degree of crosslinking decreases, leading to a decrease in the above-mentioned physical properties, resulting in the problem that it cannot be used as a high voltage CV cable.

In addition, methods for improving the surface roughness of the above products include Tokuko Showa No. 15221, No. 39-17410, No. 44-2.
No. 2904, JP-A-51-39744, JP-A No. 52-14
Publication No. 647 has made many proposals for equal pressure. However, in either case, the crosslinkability is insufficient and the above-mentioned physical properties cannot be improved.

The present invention was made as a result of intensive studies in view of the above problems, and has achieved both processability and crosslinking properties, improved voltage resistance and electrical resistance, and has excellent electrical properties, especially at high temperatures. The present invention provides a resin composition for an electric cable.

That is, the present invention provides a crosslinked polyethylene for power cables containing a crosslinkable polyethylene composition as an essential component, in which the polyethylene composition comprises: and ■ 70-10% by weight of branched low-density polyethylene with a density of 0.935 or less obtained by high-pressure radical polymerization, with a melt index of 0.5-5 f/l 0 minutes and at least 0 terminal vinyl groups in the molecule. The present invention relates to a resin composition for an electric cable, characterized in that the number of carbon atoms is 13/1000.

Linear medium-low density polyethylene, which is the above component (4) of the present invention, is produced using various catalysts such as Ziegler catalysts and chromium catalysts, under medium-low pressure or high pressure, by gas phase method, solution method, suspension method, etc. A copolymer with α-olefin containing ethylene as a main component produced by various polymerization methods such as turbidity polymerization, and has a density of 0.9.
45 t/CL or less.

The α-olefin to be copolymerized with ethylene is selected from those having 3 to 12 carbon atoms, preferably 4 to 1 o carbon atoms, such as H, t haf'lobylene, butene-1, hexene-
1, heptene-1, octene-1'S4-methyl-pentene-1, and the like.

On the other hand, branched low-density polyethylene, which is the component Copolymers with possible monomers are included, such as ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate, and the like.

The composition of the present invention contains the above component (4) in an amount of 90 to 30% by weight,
Preferably 50 to 70% by weight, component (g) 70 to 10%
Mixed preferably in a proportion of 50 to 30% by weight,
The melt index of the mixture is 0.5 to 5 r/10
It is important that the number of terminal vinyl groups in the molecule is at least 0.13/1000 carbons. The above (if the four components are less than 30w/w, the electrical properties, especially at high temperatures, will be poor; if they exceed 90w/w, the processability will be insufficient.) (hereinafter simply referred to as MI), when it is less than 0.5, extrusion processability is poor, heat generation in the extruder is large, and when crosslinking using an organic peroxide, gel formation increases. If the MI exceeds 5, the melt viscosity will be low, causing the copper wire to become eccentric, the resin to sag, and the present invention to prevent adhesion to crosslinked pipes. Focusing on the fact that carbon contributes the most to crosslinkability, by setting this to at least 0.13 carbons/1000 carbons, the crosslinkability is greatly improved, and even if the molecular weight distribution is widened, the above-mentioned It has been discovered that processability and crosslinkability can be improved by adjusting the number of terminal vinyl groups to at least 0.13/1000 carbons.

The density of the composition of the present invention is determined by the fact that it is difficult to industrially produce a branched low-density polyethylene (hereinafter simply referred to as B-LDPE) having a density of 0.935 or more.
Substantially (to) linear medium-low density polyethylene (
(hereinafter simply referred to as L-LDPE), generally 0.89 to 0.945, preferably 0.90 to 0.
．． Selected in the range of 940 f /CC.

When the above density exceeds 0.9451, the melting point becomes high, and when extrusion molding is performed using an organic peroxide, gelation occurs in the extruder, making stable extrusion molding for a long time difficult. cause fear. On the other hand, 0
．． If it is less than 89f/CC, various physical properties such as heat resistance may deteriorate.

Further, it is preferable that the molecular weight distribution in the composition of the present invention is large, but if the thickness is too thick, the elongation will be poor, so the N value should be 1.8 to 2.5, more preferably 2.0 to 2.
A range of 3 is good.

The rJV value (non-Newtonian fluidity value) is correlated with the molecular weight distribution of polyethylene and serves as a measure of fluidity. ), die: 2-tone ΦX4 (hs, 1
The outflow amount of polyethylene was measured when a load of 150 Kr and 20 Kg was applied to an IC test at 70°C, and was calculated according to the following formula.

where -γ: shear rate C3eC"1) τ: shear core force (dttn/d) The crosslinking method for the composition of the present invention is a method using an inorganic or organic peroxide, an electron beam crosslinking method, or an organic 7 run compound. Although there are no particular limitations on the water crosslinking method used, a crosslinking method using an organic peracid is the most preferred because it is simple and exhibits excellent characteristics in all respects such as extrusion processability, crosslinkability, and electrical properties of the cable. The above-mentioned organic peroxides may be those commonly used, such as benzoyl peroxide and dicumyl peroxide, but are not particularly limited.

Further, in the present invention, customary additives such as antioxidants, ultraviolet inhibitors, pigments, voltage stabilizers, carbon black, and inorganic fillers may be added at any stage.

As mentioned above, the composition of the present invention has good processability and crosslinkability, and also has excellent electrical properties such as electric tree resistance, voltage resistance, and heat resistance.

The present invention will be explained in more detail below using examples.

Examples 1 to 5 and Comparative Examples 1 to 8 (A) As the component L-LDPE4tA fat, ethylene-
Butene-1 copolymer (1) As the component B-LDPE resin, 2% by weight of dicumyl peroxide as a crosslinking agent was added to a composition prepared by high-pressure radical polymerization and formulated with various components (2) and [3] respectively. ,
4. Add 0.2% by weight of 4thiobis(2-t-butyl-5-methylphenol), crosslink at 160'CX for 30 minutes, form into a sheet or cylinder, and evaluate the gel fraction, tree generation voltage and The thermal deformation rate was measured and the evaluation results are shown in Table 1.

Table 1 also shows the results of a parin extrusion test using a small blow molding machine, which correlates with the surface condition of the electric cable during manufacture, to observe and evaluate the surface condition.

As a result, the composition of the present invention has excellent gel fraction, tree generation voltage, thermal deformation rate, and surface condition.

The test method is as follows.

Test method〉 Electric tree ・・・・・・ 1 in a single needle test using a needle with a radius of curvature of 3 μm, a distance between electrodes of 3%, an initial applied voltage of 5 KV, energization for 10 minutes, and an IKV step-up.
The voltage at which trees occurred in 5 out of 0 samples was determined.

Heating deformation rate --- A cylinder with a diameter of 10 mm and a thickness of 6 m was pressurized in a 130 C oil bath under a load of 2.63 Kp, and the deformation rate after 30 minutes was determined.

Gel fraction: The crosslinked product was ground into a '520 mesh, extracted with xylene at 120°C for 10 hours, and the residual ratio was determined.

Terminal vinyl #Jlll determination... The absorbance at a wavelength of 11.03μ was determined using an infrared absorption spectrum of a 0.6% thick sheet, and was calculated using the following formula.

Where: Constant (0,116), d Nipolyethylene density l: Sheet thickness, Io, I: Characteristic absorption and base absorbance Blow parison evaluation method... Using a blow molding machine, Using a die with an inner diameter of 9% Φ and an outer diameter of 1 (lΦ), the surface condition was evaluated when extruded at a resin temperature of 150° C. and at the same shear rate as when covering the electrical cable.

Claims (3)

[Claims] (1) In a resin composition for an electric cable having a crosslinkable polyethylene composition as an essential component, the polyethylene composition is a linear medium-low density polyethylene having a density of 0.945 f/CC or less (90 to 30% by weight) % and ■ Branched low-density polyethylene 70-10% by weight or less with a density of 0.9352A or less obtained by high-pressure radical polymerization, with a melt index of 0.5 to 5t/1o, and a terminal vinyl group in the molecule of at least 0.13 1. A resin composition for an electric cable, characterized in that the carbon content is carbon/1000. (2) The resin composition for an electric cable according to claim 1, wherein the linear medium-low density polyethylene is an ethylene-butene-1 copolymer. (3) The resin composition for an electric cable according to claim 1 or 2, characterized in that an organic peroxide is used as a crosslinking agent.