JPS61131309A - 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 relates to an insulating material for oil-immersed cables, which is made by laminating electrical insulating paper made of natural or synthetic fibers and biaxially oriented polypropylene film. .

[Prior art]

The present inventors have previously discovered that natural or synthetic fibers, such as cellulose fibers, plastic synthetic paper, or mixed paper of plastic fibers and natural fibers, are used on both sides of a biaxially oriented polypropylene film as an insulating material for oil-immersed cables. We have proposed an insulating material made by bonding and laminating electrically insulating paper using a thermosetting adhesive. (For example, Japanese Patent Application No. 57-36509, etc.) However, since this insulating material uses a thermosetting adhesive, not only does the manufacturing cost increase, but the polar groups of the adhesive cause dielectric loss as an insulating material. This has the drawback that tan δ becomes large and, for example, ultra-high voltage cables of 500,000 V or more generate too much heat and cannot be used.

Furthermore, in order to improve the adhesion between the thermosetting adhesive and the biaxially oriented polypropylene film, a surface activation treatment such as a corona discharge treatment is applied to the biaxially oriented polypropylene film, so it will not be contaminated by ionic components. Is it because of ta?
Not only does n δ increase, but the withstand voltage also decreases, which is a quality defect.

On the other hand, it is also known that thermoplastic polypropylene is used instead of thermosetting adhesive, that is, insulating paper is made by bonding fiber paper and biaxially oriented polypropylene film with unstretched polypropylene extruded from an extruder as an adhesive. (for example, Japanese Patent Publication No. 54-10712).

However, since this product uses the molten material extruded directly from the extruder as an adhesive, the thickness of this adhesive cannot be made thinner than that of ISμ, so the insulating paper is soaked in electrically insulating oil. When immersed, the insulating paper swells with oil, so if it is used as an oil-immersed cable, the insulating layer will tighten, causing insulation defects.Furthermore, molten propylene is used as an adhesive. Because a homopolymer is used, the crystallization rate during the cooling process is very fast. Therefore, when adhering during the cooling process, crystallization progresses before a sufficient anchoring effect can be expected, resulting in a strong bond. It is not possible to obtain adhesive strength, and as a result, when used in cables, the insulating paper peels off when the cable is mechanically bent, resulting in electrical 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 developed to eliminate the problems associated with deterioration of tan δ, decrease in interlayer adhesion, etc., and its purpose is to minimize the degree of swelling during oil immersion, and to reduce tan δ as much as possible. 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 electric insulating paper made of natural or synthetic fiber paper is laminated on both sides of a biaxially oriented polypropylene film via an adhesive layer. As a layer, the melting point is 10
It is characterized by using a polyolefin having a temperature of 0 to 155[deg.] C. and containing 0.01 to 3 mol% of carbonyl groups in the side chain, and the thickness of the adhesive layer to be 0.5 to 8 [mu]m.

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

When the value of (η) is less than 1.2, preferably less than 1.3, the resulting film is brittle and prone to cracking, and cannot be used as an electrical insulating material.

In addition, when the value of [η] exceeds 2.8, the degree of swelling by oil of the resulting film is hardly improved compared to conventional polypropylene films, and the swelling value is large, that is, the degree of swelling is 3% or more. Not preferred for indicating value.

In addition, the ratio MW/ of the weight average molecular weight axis and the number average molecular weight Mn
Mn is preferably 3 or more.

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

Furthermore, 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 of the present invention, the isotactic degree is preferably 93% or more, preferably 96% or more, and more preferably 98% or more, since the degree of swelling due to oil is small.

In addition, it is important that the polypropylene film does not contain additives such as antistatic agents, slip agents, heat stabilizers, antiblocking agents, nucleating agents, and viscosity modifiers, or that the content thereof is minimized. be.

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 applicable to 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 0.6-1.2 g/cm, and the thickness is 15-1
Thicknesses in the range of 50 μm are often used because of their excellent electrical properties and flowability.

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 and interlayer adhesive strength.

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. Among them, ethylene/propylene (ethylene content 1-10 mol%) random copolymer, ethylene/propylene (ethylene content 10-50 mol%)
% by mole) block copolymers are preferred.

The polyolefin needs to have a melting point of 100 to 155°C, preferably 110 to 145°C. If the melting point is less than the above range, the electrical tan δ will be large and the degree of swelling during oil immersion will be large, resulting in electrical defects and cannot be used as an insulating material for oil immersed cables. In addition, when the melting point exceeds the above range, the adhesion between the electrically insulating paper and the biaxially oriented polypropylene film is poor, and not only is it impossible to laminate at an economical speed, but also thermocompression bonding at high temperatures is required. The thermal shrinkage of the oriented polypropylene film cannot be ignored, and as a result, the adhesive strength cannot be increased.

This polyolefin must further contain 0.01 to 3 mol% of carbonyl groups as side chains, preferably 0.05 to 2.5 mol%. If the carbonyl group content is less than the above range, the adhesive strength during oil immersion will be significantly reduced, and the paper and polypropylene film will easily peel off in oil, which is not preferable. In addition, if the content is higher than the above range, the adhesive 9 strength will increase, but
This is not preferred because the electrical tan δ deteriorates.

Methods for introducing a carbonyl group as a side chain in this manner include, but are not limited to, graft polymerization of an acid having a carbonyl group such as methyl methacrylic acid and maleic anhydride. A particularly preferred method for the insulating material of the present invention is a method in which maleic anhydride is graft-polymerized to a polyolefin so that the carbonyl group content becomes a predetermined amount.

In addition, as polar groups added to the side chains of polyolefins, in addition to carbonyl groups, comonomers having amino groups, hydroxyl groups, carboxyl groups, etc. may be copolymerized, but generally, if they contain carbonyl groups, they will bond. power is good;
Furthermore, other types of polar groups have a lower tan
The increase in δ is significant, and the added effect is small.

The intrinsic viscosity [η] of the polyolefin is 0.4 to 2.5,
Preferably 0.6-1.8, more preferably 0.7-1
．． It has a low viscosity of 4 (di/g), suppresses swelling when immersed in oil, and can improve the adhesive strength between layers.

Furthermore, the thickness of the polyolefin layer should be between 0.5 and 8 μm, preferably between 0.8 and 3.0 μm.

When the thickness of the 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, whereas when the thickness of the layer exceeds 8 μm, it is preferable. When the value exceeds 3 μm, the electrical ta
n δ increases, and the degree of swelling in oil immersion also increases, resulting in electrical defects.

In addition, it is preferable for the polyolefin layer to have 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 refractive index in the longitudinal direction and in the middle direction of the polyolefin layer (Nm
d, denoted by Ntd)) (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.

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

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.

The polypropylene polymer raw material (A>) and polyolefin (B) which is made by graft polymerizing 1% maleic anhydride to an ethylene/propylene block copolymer obtained by copolymerizing propylene with 10 to 40% ethylene as an adhesive polymer.
and (B)/(A) are respectively supplied to the sheet extruder.
/ (B) A three-layer laminated melt is discharged from the nozzle,
Cast onto cooling drum. After preheating this sheet by an external heating method, it is stretched 4 to 8 times in the longitudinal direction at 120 to 150°C, further stretched 6 to 12 times in the width direction at 120 to 170°C, and if necessary 100 to 170 times. C. for 2 to 10 seconds to obtain a three-layer laminated biaxially stretched polypropylene film.

The total thickness of the thus obtained three-layer laminated polypropylene film was 40 to 150 μm, of which ethylene and
The surface of the propylene block copolymer layer is roughened, and its thickness is set to 0.5 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 130 to 220°C for a short time at a linear pressure of 0.01 to it/am. An insulating material consisting of laminated film/insulating paper is obtained.

〔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 with a specific polyolefin at a specific thickness as an adhesive, so that it can exhibit the following effects. can.

+1) Swelling due to oil is 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) The interphase adhesive strength is extremely high when immersed in oil, so there is no risk of peeling.

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

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) Cut the film of the isometric sample into a size of approximately I C11 square,
This is placed in a Soxhlet extractor and extracted with boiling methyl alcohol for 6 hours. The extracted sample is vacuum dried at 60°C for 6 hours. Take a sample of weight W (mg) from this,
This was put into the Soxhlet extractor again and extracted with boiling n-heptane for 6 hours.Then, this sample was taken out and
After thorough washing with acetone and vacuum drying at 60° C. for 6 hours, the weight is measured.

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

Aitsu Takuchi 7 degree (%) -100XW'/(2)1
The refractive index (Ny) in the longitudinal direction and the refractive index (Nx) in the width direction of the film are measured using a refractometer manufactured by Atsube Nagigo, and the absolute value of the difference between Ny and Nx is taken as the birefringence of the film. In addition,
The light source during the measurement is sodium D line, and the mounting liquid is methyl salicylate.

(3115 colors according to 2').

Cut out a 100 am square sample, dry it in a constant temperature bath at 120°C for 20 hours, and immediately measure its thickness.
m, ).

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 (%) = 100 X (D' - D) /D
(41~ After immersing the laminated material in dodecylbenzene at 110°C for 3 days, it was taken out and thoroughly washed with acetone, and then left at room temperature at 20°C for 1 day. The peel strength of the adhesive between paper and film is determined by JIS K 68.
The adhesive strength is measured in accordance with the T-peel test method for flexible materials as described in No. 54-1973, and is defined as the adhesive strength.

f5) The method for measuring t-M- and -Mn is as follows.

Equipment Nigel permeation chromatography GPC-150c column: 5hodex A30M Solvent: 0-dichlorobenzene (added with 0.1% ionol) Rate: 1 ml/min Temperature = 135°C Sample concentration = 0.1 (wt/vol)% Filtration: O
, l pm sintered filter injection volume: Q, 4ml Detector; Differential refractive index detector Molecular calibration: Polystyrene standard (6) Measure with. Unit: dt/g.

(71B D V was measured according to ASTM 0149 (20°C).

(8) 1 and 6 were measured using a Nissin electrode at a frequency of 50H2 and a temperature of 100° C. according to ASTM 0150.

(9) The scattering point C is an equilibrium temperature associated with the melting point of the crystal determined by a scanning calorimeter (DSC), and is called an endothermic peak. If the endothermic peak temperature is 2fli or more, the one with the highest endothermic peak height is used, but if they are almost the same, the average temperature of these numbers is used. The OSC measurement conditions are a sample weight of 5 mg, a temperature increase rate of 20° C./min, and a nitrogen flow.

αI Table 11 and 1■■ are JIS BO601-197
Measured according to 6.

[Example 1] As polypropylene, intrinsic viscosity [η) = 2.0 (d
i/g), isotactic index 11=9
Adhesive polyolefin ([η]=1.4, DSC The melting peak temperatures are 130°C and 150°C, but the average melting point is 140°C) and are introduced into separate caps, respectively.
A three-layer laminate sheet consisting of block copolymer layer/polypropylene N/copolymer layer was extruded from the die. This sheet was brought into close contact with a cooling drum maintained at 45°C using air pressure, cooled and solidified, then heated in an open hot air heated to 145°C, stretched 5 times in the longitudinal direction, and immediately cooled to 15°C. It was adhered to a roll and cooled. This sheet is 160
The film was fed into a tenter with a set of stents heated to ℃, stretched 10 times in the width direction, and then heat treated for 2 seconds while allowing 7% lira nox in the width direction to obtain a 3-layer laminated polypropylene film with a thickness of 90 μm. Ta. Here, the thickness of each block copolymer layer was 2 μm, the thickness of the polypropylene layer was 86 μm, and the ratio of weight average molecular weight M− to number average molecular weight Mn was Mw/Mn=4.2. . This 3
Although the laminated polypropylene film did not contain any additives such as slip agents or profkink inhibitors, it exhibited excellent slipperiness with a coefficient of friction of 0.6 due to the use of a specific polymer. Both sides of this three-layer laminated polypropylene film were coated with 25 μm thick electrically insulating kraft paper (specific gravity 0.92 g/ctA).

Surface roughness Rmax = 15 μm) were superimposed and laminated by pressing at 180° C. for 0.1 seconds at a linear pressure of 400 kg/am using the same heated press roll as in Example 1.
An electrical insulating material having a thickness of 140 μm consisting of kraft paper/three-layer laminated polypropylene film/kraft paper was obtained. The thickness fraction of the biaxially oriented polypropylene film was 61%.

The properties of the thus obtained insulating material in dodecyl-Hensen at 20°C are as follows: Dielectric constant: 2.5 tan δ: 0.04 (%) Oil swelling ratio: 4 (%) Breakdown voltage: 66 (KV/5II) Interlayer adhesion crab 140 (g/cm) (before oil immersion) 135
(g/cm) (After oil immersion) Oil flowability: Good Longitudinal breaking strength: 35 (kg/15111)
Breaking elongation in the longitudinal direction: 150 (%) Thus, it can be seen that it has excellent properties and can be used as an oil-immersed ultra-high voltage cable insulation material.

[Comparative Example 1] [η) = 1.85 dl/g, isotactic index It 99% polypropylene was melted at 250°C, this melt was extruded into a sheet form from a die, and cooled to 50°C by a conventional method. The mixture was cast onto a molded casting drum and allowed to cool and solidify.

After heating this 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 165°
A biaxially oriented polypropylene film with a thickness of 90 μm was produced by heat treatment at C for 4 seconds while allowing 5% relaxation in the width direction.

[η] of the film thus obtained was 1.80 dl/g
, Mw/Ai is 3.9, eye is 99%, birefringence is 0.01
It was 6.

Here, on both sides of the polypropylene film, 3600
After applying a corona discharge treatment in an air atmosphere with a strength of J/rd, the electrical insulating paper used in the example work was attached to both sides of the film using the following solution-type thermosetting adhesive in a conventional manner. Ta. The adhesive thickness was 3 μm each.

[Composition of adhesive solution]

Saturated polyester copolymer*: 15 parts by weight Terylene diisocyanate: 3.5 parts by weight Methyl ethyl ketone:
81.5 parts by weight* Terephthalic acid 72% as acid component
As mol%, sebacic acid 28 mol%, diol component,
A saturated polyester copolymer consisting of 35 mol% of ethylene glycol and 65 mol% of neopentyl glycol, viscosity average molecular weight of about 18,000°, and a 156 μm thick electrically insulating paper/biaxially oriented polypropylene film/electrical insulating paper obtained in this way. Various physical properties of the insulating material were measured in the same manner as in Example 1, and the results are summarized in Table 1.

As is clear from Table 1, it is not used as an insulating material for ultra-high voltage cables.

[Comparative Example 2] The electrically insulating kraft paper used in Example 1 and the biaxially oriented polypropylene film with a thickness of 66 μm produced in the same manner as in Example 2 were mixed with the ethylene/propylene random copolymer used in Example 1. ]i Melt-extrusion lamination of paper and film at 260°C using an adhesive that does not graft-polymerize maleic anhydride in the coalescence process results in paper/random copolymer/film/random copolymer/paper. An insulating material with a thickness of 156 μm was obtained. The thickness of each random copolymer layer was 15 μm, and the thickness fraction of the biaxially oriented polypropylene film was 42%.

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 composition of the insulating material is the same as in Example 1, but the dielectric constant, tan
It can be seen that not only δ is large, but also the degree of swelling is large, and the adhesive strength when immersed in oil is greatly reduced, so that it cannot be used as an oil-immersed cable material.

Table 1 [Example 2 and Comparative Example 3] Example 1 and Comparative Example 2 are used as Example 2 and Comparative Example 3 of the cable structure shown in FIG. 1 with the specifications shown in Table 2 below.
We manufactured an electric cable using this insulating material and investigated its properties.

In FIG. 1, 1 is a six-part conductor made of copper, 2 is an oil passage, 3 is a single layer of conductive binder formed by winding stainless steel tape and carbon paper together, 4 is an oil-immersed insulating layer, 5 is a metal shielding layer made of metallized paper and aluminum tape wound together, 6 is a core binder layer made of woven copper wire cloth tape, etc., 7 is a lead-covered sheath, and 8 is a vinyl chloride-covered sheath. be.

Table 3 shows the characteristics obtained for each cable.

According to the results in Tables 2 and 3, compared to the OF cable using the insulating material of Comparative Example 2, the Kano cable using the insulating material of the present invention has 1. It can be seen that low capacitance and high destructive stress have been achieved. In other words, it can be seen that electrical insulation characteristics better than that of the conventional one can be achieved with an insulating layer that is thinner than that of the conventional one.

Table 2 Table 3

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a cable using the insulating material of the present invention. l...Conductor, 2...Oil passage, 4...Oil-immersed insulation layer,
5... Metal shielding layer, 6... Core binder layer, 7.
...Lead-covered sheath, 8...PVC sheath.

Claims (1)

[Claims] An insulating material in which electric insulating paper made of natural or synthetic fibers is laminated on both sides of a biaxially oriented polypropylene film with an adhesive layer having a melting point of 100 to
An insulating material for oil-immersed cables, characterized in that the temperature is 155°C, the polyolefin contains 0.01 to 3 mol% of carbonyl groups in side chains, and the adhesive layer has a thickness of 0.5 to 8 μm. .