JPS61183819A - Insulating material for oil-filled 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] [Technical Field of the Invention] The present invention provides insulation for oil-immersed cables, which is made by laminating and laminating electrical insulating paper made of improved natural or synthetic fibers and biaxially oriented polypropylene film. It is related to the material.

[Prior art]

As an insulating material for oil-immersed cables, electrical insulating paper made of natural or synthetic fibers such as cellulose fibers, plastic synthetic paper, mixed paper of plastic fibers and natural fibers, etc., is heat-cured on both sides of a biaxially oriented polypropylene film. Insulating materials that are bonded and laminated using a mold adhesive are known (for example, JP-A-58-153644).

However, since this insulating material uses a thermosetting adhesive, not only is the manufacturing cost high, but the polar group of the adhesive increases the dielectric loss and tan δ of the insulating material, for example, 500,000 V or more. The disadvantage of this ultra-high voltage cable was that it generated too much heat, making it unusable.

Insulating paper is also known, in which thermoplastic polypropylene is used instead of thermosetting adhesive, in other words, fiber paper and biaxially oriented polypropylene film are bonded together using unoriented polypropylene extruded from an extruder. (For example, Japanese Patent Publication No. 10712/1983).

However, since this adhesive uses a melt extruded directly from an extruder, the thickness of this adhesive cannot be made thinner than 15 μm, and therefore, when the insulating paper is immersed in electrical insulating oil, Since the insulating paper swells with oil, if it is used as an oil-immersed cable, the insulating layer will tighten.
There was a problem that caused insulation defects.

Furthermore, because propylene homopolymer in a molten state is used as an adhesive, the rate of crystallization during the cooling process is very fast. As a result, when used for cables, the insulating paper peels when the cable is mechanically bent, resulting in electrical There were drawbacks that resulted in significant defects.

[Purpose of the invention]

The present invention is directed to the above-mentioned conventional swelling of an insulating material by oil immersion, ta
This was obtained in order to eliminate the deterioration of n δ, decrease in interlayer adhesion, etc., and the accompanying drawbacks, and its purpose is to minimize the degree of swelling during oil immersion, and to reduce jan δ. It is an object of the present invention to provide a highly economical insulating material for oil-immersed cables, which has excellent electrical properties such as, strong interlayer adhesive strength, and the like.

[Structure of the invention]

The insulating material for oil-immersed cables of the present invention which achieves the above object is an insulating material in which electrical insulating paper made of natural or synthetic fibers is laminated on both sides of a biaxially oriented polypropylene film. A polyolefin with a melting point of 100-150°C is used for adhesion to electrically insulating paper, and the polyolefin layer is
It is characterized by having imino-type and/or amino-type nitrogen atoms in the surface layer of up to 00 carbon atoms in an amount of 3 (per 100 carbon atoms) or more.

The intrinsic viscosity [μ] of the biaxially oriented polypropylene film in the present invention is preferably 1.2 to 2.8 d lI /g, preferably 1.3 to 2.2 d J /g.

If the value of [μ] is less than 1.2, preferably less than 1.3, the obtained fillet will be brittle (and prone to cracking).
Cannot be used as an electrical insulating material.

In addition, when the value of [μ] exceeds 268, the degree of swelling by oil of the obtained film is hardly improved compared to the conventional polypropylene film, and the swelling value is large, that is, the degree of swelling is 3% or more. Unfavorable for showing.

Also, the ratio Mw of the weight average molecular weight and the number average molecular weight Mn
/Mn is preferably 3 or more.

If the ratio of MW/Mn is smaller than the above value, the degree of swelling due to oil will increase and the insulation properties will also decrease, which is not preferable.

Moreover, not only does the film frequently break during film formation, but also the thickness becomes more uneven.

In the case of the biaxially oriented polypropylene film in the present invention, the isotactic degree is 93% or more, preferably 96%.
Above, more preferably 98% or more, the degree of swelling due to oil is small.

In addition, it is preferable that the polypropylene film does not contain additives such as antistatic agents, slipping agents, heat stabilizers, antiblocking agents, nucleating agents, and viscosity modifiers, but as long as the additives are not contained in the polypropylene film and do not reduce the electrical properties. You may add a certain amount.

The thickness of polypropylene film is 10 to 1000 μm
It is preferable that it is in the range of .

The electrically insulating paper (hereinafter referred to as paper) laminated on the biaxially oriented polypropylene film in the present invention is JIS C2
Natural fiber paper mainly composed of cellulose as defined in 301 to 2308, mixed paper made by mixing natural fibers such as cellulose and plastic fibrils, or synthetic paper made only of plastic may be used. Particularly suitable for the present invention is natural fiber paper whose main component is cellulose.

The maximum surface roughness Rmax of electrical insulating paper is 5 to 25 μm
, the apparent density is 0.6~1.2g/cm, and the thickness is 15~
Thicknesses in the range of 150 μm are often used because of their excellent electrical properties and oil permeability.

In the case of the present invention, the electrically insulating paper is preferably paper whose surface has been smoothed by calendering or the like because it has high voltage resistance, interlayer adhesive strength, etc., but is not necessarily limited to this.

The polyolefin used as the adhesive between the eyebrows is a propylene copolymer containing 50 mol% or more of propylene, such as a binary or ternary copolymer (random, graft, block) consisting of ethylene, propylene, butene, hexene, etc. is a typical example, but is not necessarily limited to this.

In particular, the polyolefin used in the present invention is a random copolymer of ethylene, propylene (ethylene content: 1 to 10 mol%), ethylene/propylene (ethylene content: 10 to 50 mol%),
% by mole) block copolymers are preferred.

The melting point of the polyolefin should be 100-150°C, preferably 110-145°C.

If the melting point is less than 100°C, preferably less than 110°C, the electrical tan δ will be large and the degree of swelling in oil immersion will be large, resulting in electrical defects, making it difficult to use as an insulating material for oil-immersed cables. I can not use it.

Further, when the melting point exceeds 150°C, preferably 145°C, the adhesive strength between the electrically insulating paper and the biaxially oriented polypropylene film is poor, the film peels off during oil immersion, and it is not possible to laminate at an economical speed.

The intrinsic viscosity [η] of the polyolefin is 0.4 to 2.5.
, preferably 0.6 to 1.8, more preferably 0.7 to
If the viscosity is as low as 1.4 (d l /g), swelling during oil immersion can be kept to a small level, and the adhesion between layers can be improved.

Furthermore, in the present invention, at least one side of the polyolefin layer has at least 3, preferably at least 7 imino and/or amino type nitrogen atoms per 100 carbon atoms in the surface layer from the surface to 100. Must do.

When the number of nitrogen atoms is less than 3, preferably less than 7, the temperature at which the bonding starts between the electrically insulating paper and the biaxially oriented polypropylene film is high, and the lamination pressure required for bonding is also high, resulting in poor lamination economy. Not only will the resulting laminate deteriorate, but the resulting laminate will tend to curl or wrinkle due to thermal deformation, resulting in various defects as an electrical insulating laminate. The interlayer adhesion between the insulating paper and the biaxially oriented polypropylene film decreases, leading to the occurrence of freezing and wrinkles, and the electrical properties, especially the withstand voltage, are significantly decreased.

Note that the upper limit of the number of nitrogen atoms is not particularly limited, but from the viewpoint of adhesiveness, it is preferably 30 or less, and more preferably 25 or less.

The surface wetting tension of the polyolefin surface is 45 dyn/
cm or more, preferably 50 dyn/cm or more is preferred for the present invention.

The thickness of the polyolefin layer is preferably 0.5 to 8 μm, preferably 0.8 to 3.0 μm. When the thickness of this layer is less than 0.5 μm, preferably less than 0.8 μm, the adhesion between the electrically insulating paper and the biaxially oriented polypropylene film is poor; on the other hand, when the thickness of this layer exceeds 8 μm When the thickness exceeds 3 μm, the electrical tan δ becomes large, and the degree of swelling during oil immersion becomes large, often resulting in electrical defects.

Further, it is preferable that the polyolefin layer has oriented molecular chains rather than non-oriented from the viewpoint of swelling properties with insulating oil, mechanical properties, and electrical properties. The degree of orientation is determined by the arithmetic average value (Nmd+Nt
It is preferable that the value obtained by subtracting the refractive index Nzd in the thickness direction from d)/2 is 0.01 or more.

〔Production method〕

Next, a method for manufacturing an insulating material according to the present invention will be explained.

[■Law]

The method for producing the raw material for biaxially oriented polypropylene film used in the present invention is not particularly limited, but one preferred example is to use various known titanium tetrachloride catalysts supported on magnesium chloride, organoaluminum compounds, and ester compounds. Propylene is polymerized by a bulk polymerization method using propylene itself as a solvent using a catalyst system consisting of a third component such as Obtained by removing.

Add 10 to 40% ethylene to the polypropylene polymer raw material (^) and polyolefin as adhesive polymer.
The block copolymerized ethylene/propylene block copolymer (B) is supplied to a sheet extruder, and the BA
A three-phase laminated melt B is discharged from a die and cast onto a cooling drum.

After preheating this sheet using an external heating method,
Stretched 4 to 8 times at 20 to 150°C, and further stretched 120 times in the width direction.
Stretched 6 to 12 times at ~170°C, heat treated at 100 to 170°C for 2 to 10 seconds, and stretched with a mixed gas of carbon dioxide p and nitrogen gas q (with a volume ratio p/q of 1/99 to 10/90). A three-layer laminated biaxially oriented polypropylene film is obtained by corona discharge treatment under the following conditions.

The total thickness of the thus obtained three-layer laminated polypropylene film is 40 to 250 μm, of which the surface of the ethylene-propylene block copolymer layer has nitrogen and oxygen incorporated therein and is roughened. Thickness is 0
．． It is preferable to adjust the thickness to 5 to 8 μm.

The reason for roughening the surface is to improve slipperiness and anti-blocking properties. Electrical insulating paper was superimposed on both surfaces of this three-layer laminated film, and pressed between hot press rolls heated to 100 to 220°C for a short time at a linear pressure of 0.01 to 1 t/cm. An insulating material consisting of a three-layer laminated film/insulating paper is obtained.

[■Law]

Another manufacturing method is to apply a polyolefin as an adhesive, such as an ethylene-propylene random copolymer, onto insulating paper using a hot melt coating method.
It is coated uniformly to a thickness of 5 to 8 μm and subjected to corona discharge treatment under nitrogen gas. A single film of biaxially oriented polypropylene film is wrapped between the two coated insulating papers and pressed between hot press rolls in the same manner as above, and then the insulating paper/biaxially oriented polypropylene film/insulating paper is separated. Obtain an insulating material.

In the case of the insulating material of the present invention, production by [Method I] is particularly preferred in that the polyolefin layer as the adhesive polymer has orientation.

〔Effect of the invention〕

The insulating material of the present invention has a structure in which electrically insulating kraft paper and a biaxially oriented polypropylene film are laminated using a polyolefin having a specific surface structure and melting point as an adhesive, so that it has the following effects. I can do it.

(1) Deterioration in interlayer adhesion and swelling caused by oil are extremely small.

(2) Excellent oil circulation.

(3) Both dielectric constant and dielectric loss tangent are small, and dielectric breakdown voltage is extremely high.

(4) The mechanical properties of the insulating material are excellent.

(5) Since there is little bone dissolved in the oil, the degree of contamination of the oil is extremely small.

(6) The manufacturing cost is low and it is highly economical.

(7) The temperature and pressure during lamination are low,
Highly economical when laminating.

Therefore, the insulating material for oil-immersed cables of the present invention is extremely useful as an insulating layer for oil-immersed cables.

Next, the measurement methods used in the present invention are summarized below.

(1) Isotacticity Cut the sample film into approximately 1 cm square pieces, place them in a Soxhlet extractor, and extract with boiling methyl alcohol for 6 hours. The extracted sample is vacuum dried at 60°C for 6 hours. A sample of weight w (mg) is taken from this and placed again in the Soxhlet extractor and extracted with boiling N-hebutane for 6 hours. Next, this sample is taken out, thoroughly washed with acetone, dried under vacuum at 60° C. for 6 hours, and then weighed.

If the weight is W' (mg), the degree of isotacticity is determined by the following formula.

Isotactic degree (χ) = 100 x W” x W (2)
Using a birefringent Atsube refractometer, measure the refractive index in the longitudinal direction (Ny) and the refractive index in the width direction (Nx) of the film, and
Let the absolute value of the difference between Nx and Nx be the birefringence of the film. Note that sodium D ray is used as the light source during the measurement, and methyl salicylate is used as the mounting liquid.

(3) Swelling degree with electrical insulating oil Cut a 100 mm square sample, dry it in a constant temperature bath at 120°C for 20 hours, and immediately measure its thickness, D (μm
).

This sample was immersed in dodecylbenzene oil at 100℃ for 2 hours.
After leaving it for 4 hours, take it out and immediately measure the thickness of the sample.
Let this be D' (μm).

The degree of swelling is determined by the following formula.

Swelling degree (χ) = 100 X (D' - D) /D(
4) Adhesive strength between paper and film after oil immersion The laminated material is 11
After being immersed in dodecylbenzene at 0°C for 3 days, it is taken out, thoroughly washed with acetone, and then left at room temperature at 20°C for 1 day. Using this as a sample, the peel strength of the adhesive between paper and film was determined according to JIS K 6854-1973.
The adhesive strength is determined by measuring according to the method of the T-peel test between flexible materials described above.

(5) The methods for measuring weight average molecular weight and number average molecular weight Mn are as follows.

Equipment Nigel permeation chromatography GPC-150C column: 5hodex A30M Solvent: 0-dichlorobenzene (0,1χ ionol added) Rate: 1 ml/min Temperature: 135°C Sample concentration: 0.1 (wt/vol)% Filtration = 0 .1 μl sintered filter injection volume: 0.4 ml Detector: Differential refractive index detector Molecular calibration: Polystyrene standard (6) Intrinsic viscosity [η] Measured in tetralin at 135° C. according to ASTM 01601. Unit d: 17g.

(7) Dielectric breakdown voltage (BDV) Measured according to ASTM 0149. (Atmosphere: 20
℃) (8) Dielectric loss (tan δ) ASTM D150 Accordingly, frequency 50H2, temperature 1
Measurement is performed at 00°C using an insulated paper measurement electrode MED-C type (manufactured by Nissin Electric Co., Ltd.).

(9) Melting point (Tm) The melting point is the equilibrium temperature associated with the melting point of the crystal determined by a scanning calorimeter (DSC), and if there are two or more endothermic peak temperatures, the one with the highest endothermic peak height. However, if they are almost the same, the average temperature of these numbers is used.

DSC measurement conditions were: sample weight: 5 mg; heating rate: 20°C.
/min under nitrogen flow.

(10) Surface roughness Rmax) Measured according to JIS B 0601-1976.

(11) The imino type and/or amino type nitrogen atom is directly bonded to the carbon of the polypropylene polymer chain, and the amount thereof is measured using the ESCA method.

The ESCA method referred to in the present invention is an abbreviation for soft X-ray excitation photoelectron spectroscopy, which detects elements near the surface of a sample from the spectrum of photoelectrons ejected from atoms in the sample compound by soft X irradiation. This is a method to analyze the type and chemical bond state. In the ESCA method, the ability of photoelectrons to pass through hydrocarbon-based polymer materials is small;
Measurement by this method has the characteristic that relatively strong information can be obtained from within 100 people from the surface, especially the extremely superficial layer.

The amino-type and/or imino-type nitrogen referred to in the present invention is F, a bonded nitrogen identified by the SCA method, and the Is orbital (N) of the bonded nitrogen measured by ESCA, which is typified by amine groups and imino groups. It has a peak in the spectrum binding energy range of 397.0 to 402.5 eV (however, the main peak of C in polypropylene is 285.OeV) (hereinafter simply referred to as amino type and/or imino type nitrogen). ).

Specifically, an ESCA spectrometer ES-200 manufactured by Kokusai Denki Co., Ltd. was used to measure the N spectrum and C spectrum of the treated surface of the treated film, and in the N spectrum, amino-type and/or imino-type nitrogen was detected. The ratio of the integrated intensity of the peak corresponding to the binding energy of and the integrated intensity of the C spectrum was calculated.

The number ratio N/C of amino type and/or imino type nitrogen and carbon atoms in the present invention is calculated based on the above-mentioned integrated intensity ratio.

Examples of the present invention will be described below.

〔Example〕

Example 1 Ethylene/propylene copolymer (intrinsic viscosity [η] 0.8 di/g, melting point 129°C) obtained by randomly copolymerizing 6 mol% ethylene was supplied to a hot melt coater and heated to 260°C under a nitrogen blanket. After that, pressurize and reduce the slit gap to 0.4.
30 μm thick electrical insulating kraft paper (specific gravity 0.90 g/d, surface roughness Rmax = 18 μm)
A hot-melt coat was applied onto one side of the sample (m) to a thickness of 3 μm, and the sample was subjected to a corona discharge treatment under a nitrogen stream, and then wound up.

The polyolefin film contained 4 amino and imino nitrogen atoms per 100 carbon atoms from the surface.

On the other hand, polypropylene having an intrinsic viscosity of 1.85 d lag, a ratio of weight average molecular weight and number average molecular weight Mn = 4.0, and an isotactic index II = 99χ was melted at 250°C, and this melt was placed in a mouthpiece. It was extruded into a sheet shape, cast on a casting drum cooled to 50° C. by a conventional method, and solidified by cooling.

After heating the cooled and solidified sheet to 146°C, it was stretched 6 times in the longitudinal direction, then fed into a stenter heated to 160°C, stretched 10 times in the width direction, and further stretched at 165°C for 4 seconds in the width direction. A biaxially oriented polypropylene film with a thickness of 90 μm was produced by heat treatment while allowing 5% glue lax.

[η] of the film thus obtained was 1.80 dl/g
, Mw/Mn was 3.9, II was 99%, and birefringence was 0.016.

Next, the ethylene-propylene copolymer surface coated on the insulating paper was made to overlap both sides of the above-mentioned biaxially oriented polypropylene film, and then fed between chrome-plated rolls with an outer diameter of 250 mmφ heated to 190°C, and a linear pressure of 300 kg/ cm for 0.1 seconds to obtain a thickness of 156 cm made of insulating paper/biaxially oriented polypropylene film/insulating paper.
A three-layer insulating material of μm was obtained. The thickness fraction of the biaxially oriented polypropylene film of the insulating material thus obtained was 57.
%Met.

Subsequently, the insulating material was immersed in dodecylbenzene oil and its physical properties were measured.

Swelling degree: 3% Dielectric constant: 2.5 (20℃), 2.5 (100℃) t
an δ: 0.04χ (20°C), 0.05χ (10
0°C) adhesive crab 380 g/cm As described above, the insulating material of the present invention not only has excellent electrical properties but also has excellent adhesive strength and swelling resistance, so it is excellent as an insulating material for oil-immersed cables. It can be seen that this shows the characteristics.

Comparative Example 1 Instead of applying ethylene-propylene copolymer to electrically insulating kraft paper using a hot melt coater in Example 1, the following solution type thermosetting adhesive was used to coat electrically insulating paper with biaxially oriented polypropylene film. It was attached to both sides by a conventional method. In this case, both surfaces of the biaxially oriented polypropylene film were heated at 3600 J/n? to improve adhesion.
(7) Corona discharge treatment was performed using electrical energy.

The adhesive thickness was 3 μm in each case.

The composition of the adhesive solution is as follows.

Saturated polyester copolymer*: 15 parts by weight Terylene diisocyanate: 3.5 parts by weight Methyl ethyl ketone: 81
．． 5 parts by weight* Acid component: 72 mol% terephthalic acid, 28 mol% sebacic acid; Diol component: saturated polyester copolymer consisting of 35 mol% ethylene glycol, 65 mol% neopentyl glycol, viscosity average molecular weight: approximately 18
Various physical properties of the thus obtained insulating material consisting of electrically insulating paper/biaxially oriented polypropylene film/electrically insulating paper with a thickness of 156 μm were measured in the same manner as in Example 1. Table 1
The results are summarized in .

As is clear from Table 1, when a compound having a polar group is used as an adhesive, the electric tan δ becomes large, and it can be seen that it cannot be used as an insulating material for ultra-high voltage cables.

Comparative Example 2 The electrically insulating kraft paper used in Example 1 and the 66 μm thick biaxially oriented polypropylene film produced in the same manner as in Example 1 were combined with the ethylene-propylene random copolymer used in Example 1. Using as an adhesive, paper and film were melt-extruded and laminated at 260° C. to obtain an insulating material consisting of paper/random copolymer/film/random copolymer/paper with a thickness of 156 μm.

Here, the thickness of each random copolymer layer is 15 μm, and the thickness fraction of the biaxially oriented polypropylene film is 4
It was 2%.

Comparative Example 3 A similar insulating material was obtained by processing in exactly the same manner as in Example 1, except that the polyolefin layer in Example 1 was not subjected to the corona discharge treatment under nitrogen gas.

Various physical properties of the thus obtained insulating material were measured in the same manner as in the examples, and the results are summarized in Table 1.

As is clear from Table 1, the compositions of the insulating materials obtained in Comparative Examples 1 to 3 are the same as those of Example 1, but because the composition thickness is different, not only the dielectric constant and tan δ are large, but also the swelling It also has a large degree of resistance, making it unsuitable as an oil-immersed cable material. It can also be seen that without certain surface treatments, this too cannot be used as an oil-immersed cable material.

Table 1 Example 2 As polypropylene, chips with [η) = 2.0 and isotactic index II = 98χ and an ethylene-propylene block copolymer ((η) = 1.4, melting peak temperature by DSC is 118℃, 147℃1160℃
However, the average melting point of the first two is 133°C)
were introduced into separate nozzles, and a three-layer laminate sheet consisting of block copolymer layer/polypropylene W/copolymer layer was extruded from the nozzles. This sheet was brought into close contact with a cooling drum kept at 45°C using air pressure to cool and solidify, then heated in a hot air oven heated to 145°C, stretched 5 times in the longitudinal direction, and immediately 15°C It was cooled by adhering it to a cooling roll. This sheet was put into a tenter set of stenters heated to 160°C, stretched 10 times in the width direction,
Next, it was heat treated for 2 seconds while allowing 7% relaxation in the width direction, and subjected to corona discharge treatment under a mixed gas with a volume ratio of carbon dioxide/nitrogen = 2/9B to obtain a three-layer laminated polypropylene film with a thickness of 90 μm.

Here, the thickness of each block copolymer layer was 2 μm, and the thickness of the polypropylene layer was 86 μm. Further, the block copolymer contained 8 nitrogen atoms per 100 carbon atoms from the surface layer to 100 carbon atoms.

This three-layer laminated polypropylene film contains a slip agent,
Although it does not contain additives such as anti-blocking agents, it uses a specific polymer and has a specific surface treatment, so it has excellent slipperiness with a coefficient of friction of 0.6.
It exhibited high adhesiveness with a surface wetting tension of 65 dyn/cm.

On both sides of this three-layer laminated polypropylene film, a thickness of 2
5μm electrically insulating kraft paper (specific gravity 0.92g/crA
, surface roughness Rmax = 15 p m), and laminated by pressing at 200°C for 0.1 seconds at a linear pressure of 400 kg/cm using the same heated press roll as in Example 1, and then laminated with Kraft IIE/3. Laminated polypropylene film/
An electrically insulating material made of kraft paper and having a thickness of 140 μm was obtained. The thickness fraction of biaxially oriented polypropylene film is 6
It was 1%.

Table 2 shows the properties of the insulating material thus obtained in dodecylbenzene at 20°C.

From the same table, it can be seen that the characteristics are excellent.

Comparative Example 4 An insulating material was obtained in the same manner as in Example 2 except that the corona discharge treatment performed in Example 2 was not performed, and the properties were measured and shown in Table 2.

Table 2 Example 3 and Comparative Example 5 As Example 3 and Comparative Example 5 of the cable structure shown in the figure with the specifications shown in Table 3 below, power cables using the insulating materials of Example 2 and Comparative Example 4 were manufactured. , the characteristics of the cord were investigated.

In addition, in the figure, 1 is a 6-segment conductor made of copper, 2
3 is an oil passage, 3 is a conductive sheet formed by winding together, for example, stainless steel tape and carbon paper. 4 is a single layer of body binder, 4 is an oil-immersed insulating layer, and 5 is formed by winding metallized paper and aluminum tape together. The metal shielding layer 6 is a core binder layer formed by winding, for example, copper fiber-filled cloth tape, 7 is a lead-coated sheath, and 8 is a vinyl chloride-coated sheath.

Table 4 shows the characteristics obtained for each cable.

According to the results in Tables 3 and 4, compared to the OF cable using the insulating material of Comparative Example 4, the OF cable using the insulating material of the present invention can achieve lower capacitance and higher breakdown stress. I know that there is. That is, it can be seen that it is possible to achieve better electrical insulation characteristics than before with a thinner insulating layer than before.

[Brief explanation of drawings]

The figure is a sectional view showing an example of a cable using the insulating material of the present invention. 1--conductor, 2--oil passage, 3--one layer of conductor binder, 5--metal shielding layer, 6--one layer of core binder, 7--lead sheath, 8--PVC sheath. Procedural Amendment '20 February 1986

Claims (1)

[Claims] In an insulating material in which electrically insulating paper made of natural or synthetic fibers is laminated on both sides of a biaxially oriented polypropylene film, a polyolefin with a melting point of 100 to 150°C is used to bond the polypropylene film and the electrically insulating paper. 100% from the surface of the polyolefin layer.
An insulating material for an oil-immersed cable, characterized in that the surface layer has three or more imino-type and/or amino-type nitrogen atoms per 100 carbon atoms.