JPH0471098B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin composition for power cables, and in particular to the electrical resistance, voltage resistance, heat resistance, crosslinkability and The present invention relates to a resin composition for power 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) are being used as high-voltage power cables, and recently, although on a trial basis, CV cables are also beginning to be used under high voltage conditions. It is thought that CV cables will continue to move toward higher voltages in the future due to their various advantages, such as ease of maintenance and inspection and cost reduction. However, low-density polyethylene manufactured by the high-pressure radical polymer method, which is currently used for CV cables, has excellent workability, but its low crystallinity makes it difficult to maintain electrical tree resistance and durability. It has the disadvantage of poor voltage characteristics, particularly inferior to the above characteristics at high temperatures. In addition, high-density polyethylene produced by a medium-low pressure method has high crystallinity and a high melting point, so the above-mentioned properties at high temperatures are excellent. 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. Unfortunately, the load on the extruder becomes abnormally high, and the surface of the extrudate becomes rough, making it impossible to obtain a smooth surface.
There are concerns that the product value will decline and various physical properties will decline.
On the other hand, when the molecular weight distribution is widened in order to improve processability, the degree of crosslinking decreases, resulting in 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 Japanese Patent Publications No. 38-15221, No. 39-17410,
Many proposals have been made in JP-A No. 22904, JP-A No. 51-39744, JP-A No. 52-14647, etc. 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 power cables. That is, the present invention provides a resin composition for insulating crosslinked power cables containing crosslinkable polyethylene and a crosslinking agent as essential components, wherein the polyethylene has (A) a density of
90-30% by weight of linear medium-low density polyethylene of 0.92-0.945 g/cc and (B) branched low-density polyethylene with a density of 0.935 g/cc or less obtained by high-pressure radical polymerization.
The polyethylene of (A) + (B) has a melt index of 0.5 to 5 g/10 minutes and at least 0.13 terminal vinyl groups per 1000 carbon atoms constituting the polyethylene molecule. The present invention relates to a resin composition for insulating a crosslinked power cable, which is characterized by having the following characteristics: Linear medium-low density polyethylene, which is the above component (A) 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. It is 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 0.92 to 0.945 g/cc. The α-olefin to be copolymerized with ethylene is selected from those having 3 to 12 carbon atoms, preferably 4 to 10 carbon atoms, such as propylene, butene-olefin, etc.
1, hexene-1, heptene-1, octene-
Examples include 1,4-methyl-pentene-1. On the other hand, branched low-density polyethylene, which is component (B) of the present invention, is a homopolymer of low-density polyethylene produced by high-pressure radical polymerization using a tubular method or an autoclave method, and is a homopolymer of low-density polyethylene that has ethylene as its main component and a small amount of co-polymerized ethylene. Copolymers with polymerizable monomers, such as ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate, and the like are included. The composition of the present invention contains the above component (A) in an amount of 90 to 30% by weight;
Preferably 50 to 70% by weight, component (B) is mixed in a proportion of 70 to 10% by weight, preferably 50 to 30% by weight,
The melt index of the mixture is 0.5 to 5 g/10
It is essential to have at least 0.13 terminal vinyl groups per 1000 carbon atoms of the polyethylene composition. the above
If component (A) is less than 30% by weight, the electrical properties, especially at high temperatures, will be poor; if it exceeds 90% by weight, the processability will be insufficient, and the melt index of the polyethylene mixture (hereinafter simply referred to as
When the MI is less than 0.5, extrusion processability is poor, heat generation is large in the extruder, and in crosslinking using organic peroxides, not only does gel formation increase, but the surface smoothness is also lost. . If the MI exceeds 5, the melt viscosity is low, causing the copper wire to become eccentric or the resin to sag, resulting in adhesion to the crosslinked pipe. In addition, the present invention focuses on the fact that the terminal vinyl group in the molecule contributes most significantly to crosslinking properties, and this can be greatly improved by having at least 0.13 terminal vinyl groups per 1000 carbon atoms in the polyethylene composition. Even if the crosslinkability is improved and the molecular weight distribution is broadened, processability and crosslinkability are improved by setting the number of terminal vinyl groups to at least 0.13 per 1000 carbon atoms in the composition as described above. This is what we discovered. The density of the polyethylene mixture of the present invention is determined by the branched low-density polyethylene (hereinafter simply B-
Since it is difficult to industrially produce LDPE with a density of 0.935 or higher, it is practically used as component (A) linear medium-low density polyethylene (hereinafter simply L-LDPE).
), generally 0.89~
0.945, preferably in the range of 0.90 to 0.940 g/cc. When the above density exceeds 0.945 g/cc, the melting point becomes high, so using an organic peroxide,
In the case of extrusion molding, gelation may occur in the extruder, making it difficult to perform stable extrusion molding over a long period of time. On the other hand, if it is less than 0.89 g/cc, various physical properties such as heat resistance may deteriorate. In addition, it is preferable that the molecular weight distribution in the polyethylene mixture of the present invention is large, but if it is too large, the elongation will be poor, so the N value should be 1.8 to 2.5.
More preferably, it is in the range of 2.0 to 2.3. The above “N value” (non-Newtonian liquidity value) is
It roughly correlates with the molecular weight distribution of polyethylene and serves as a measure of fluidity.
Using Koka type flow tester (HB-I type), die: 2mmΦ x 40mm, 150Kg and 20Kg at 170℃
The amount of polyethylene flowing out when a load is applied is measured and calculated according to the following formula. N value = log(γ150/γ20)/log(τ150/τ20) where γ: shear rate (Sec ^-1 ) τ: shear stress (dyn/ ^cm2 ) The crosslinking method for the composition of the present invention may be inorganic or organic. There are no limitations as long as the method uses a crosslinking agent, such as a method using a peroxide, a water crosslinking method using an organic silane compound, etc., but a crosslinking method using an organic peroxide is particularly easy and has good extrusion processability and crosslinking properties. This is the most preferable because it exhibits excellent characteristics in all respects, including the electrical characteristics of the cable. The above-mentioned organic peroxides may be those commonly used and are not particularly limited, such as benzoyl peroxide and dicumyl peroxide. 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 with reference to Examples. Examples 1 to 5 and Comparative Examples 1 to 8 Ethylene-butene-1 copolymer was used as L-LDPE resin as component (A). Produced by high-pressure radical polymerization as B-LDPE resin as component (B). 2% by weight of dicumyl peroxide and 0.2% by weight of 4,4thiobis(2-t-butyl-5-methylphenol) were added as crosslinking agents to a composition containing various components (A) and (B). The crosslinked material was then crosslinked at 160° C. for 30 minutes, formed into a sheet or cylindrical shape, and the gel fraction, tree generation voltage, and thermal deformation rate of the crosslinked material were measured. Table 1 shows the evaluation results. Table 1 also shows the results of a parison extrusion test using a small blow molding machine, which correlates with the surface condition of the power cable at the time of 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> Electrical tree...Using a needle with a radius of curvature of 3 μm, inter-electrode distance of 3 m/m, initial applied voltage
The voltage at which trees occurred in 5 out of 10 samples was determined in a single needle test with 5KV applied for 10 minutes and 1KV step-up. Heating deformation rate...Cylinder with diameter 10mmΦ and thickness 6mm is 130
It was pressurized with a load of 2.63 kg in an oil bath at ℃, and the deformation rate was determined after 30 minutes. Gel fraction...Crush the cross-linked product into 20 meshes,
Extraction was performed with xylene at 120°C for 10 hours, and the residual rate was determined. Measurement of vinyl terminals...The wavelength of a 0.6m/m thick sheet is measured using an infrared absorption spectrum.
The absorbance at 11.03μ was determined using the following formula. /1000c=k・logI ₀ /I×1/dl where k: constant (0.116), d: density of polyethylene, l: thickness of sheet, I ₀ , I: characteristic absorption and base absorbance blow parison evaluation method ...Using a blow molding machine, inner diameter 9m/mΦ, outer diameter 10m/mΦ
The surface condition was evaluated when the resin was extruded using a die at a resin temperature of 150°C and at the same shear rate as when covering power cables. 【table】

Claims (1)

[Claims] 1. In a resin composition for insulating crosslinked power cables containing crosslinkable polyethylene and a crosslinking agent as essential components, the polyethylene (A) has a density of 0.92 to 0.945 g/
cc linear medium-low density polyethylene 90-30% by weight
and (B) density 0.935g/ by high-pressure radical polymerization.
It consists of 70 to 10% by weight of branched low-density polyethylene of cc or less, and 0.5 to 5g of (A) + (B) polyethylene/
10 minute melt index and at least 0.13 per 1000 carbon atoms making up the polyethylene molecule
A resin composition for insulating a crosslinked power cable, characterized in that it has terminal vinyl groups.