JPH0244085B2 - - Google Patents

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 bonding and laminating electrically insulating paper made of improved natural or synthetic fibers and biaxially oriented polypropylene film. [Prior Art] The present inventors previously developed a biaxially oriented polypropylene film on both sides as an insulating material for oil-immersed cables.
We have proposed an insulating material that is made by laminating electrical insulating papers made of natural or synthetic fibers, such as cellulose fibers, plastic synthetic paper, and mixed paper of plastic fibers and natural fibers, by laminating them using thermosetting adhesives. . (For example, Japanese Patent Application No. 57-36509, etc.) However, since this insulating material uses a thermosetting adhesive, not only does it increase manufacturing costs, but the polar groups of the adhesive make it difficult to use dielectric materials as an insulating material. This has the disadvantage that the loss and tan δ become 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 corona discharge treatment is applied to the biaxially oriented polypropylene film, which prevents stains caused by ionic components. Perhaps because of this, not only did the tan δ increase, but the withstand voltage also decreased, which was 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, Special Publick No. 54-10712)
number, etc.). 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 insulation oil, Since the insulating paper swells with oil, when used as an oil-immersed cable, the insulating layer becomes tightly wound, which causes insulation defects. Furthermore, since molten propylene homopolymer 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 off when the cable is mechanically bent, resulting in electrical There were some shortcomings that resulted in certain flaws. [Object of the Invention] The present invention was achieved in order to solve the above-mentioned conventional problems such as swelling of insulating materials due to oil immersion, deterioration of tan δ, and decrease in interlayer adhesion, and the accompanying drawbacks. The purpose of this invention is to provide a highly economical insulating material for oil-immersed cables that minimizes the degree of swelling during oil immersion, has excellent electrical properties such as tan δ, and has strong interlayer adhesion. [Structure of the Invention] The insulating material for oil-immersed cables of the present invention 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. It is characterized in that a polyolefin having a melting point of 100 to 150° C. is used for adhesion to the insulating paper, and the thickness of the polyolefin layer is 0.5 to 8 μm. 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 cracks, 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 exceeds 3%. Unfavorable for showing. Further, the ratio Mw/Mn between the weight average molecular weight Mw and the number average molecular weight 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 properties will also decrease, which is not preferable. Moreover, not only the film frequently breaks during film formation, but also the thickness becomes more uneven. In the case of the biaxially oriented polypropylene film of the present invention, the degree of isotacticity is preferably 93% or more, preferably 96% or more, and more preferably 98% or more, since the degree of swelling by oil is small. The polypropylene film also contains antistatic agents, slipping agents, heat stabilizers, antiblocking agents,
It is important not to contain additives such as nucleating agents and viscosity modifiers. The thickness of polypropylene film is 10~1000μ
It is preferably in the range of m. In the present invention, the electrically insulating paper (hereinafter referred to as paper) to be laminated on the biaxially oriented polypropylene film is natural fiber paper mainly composed of cellulose as defined in JIS C2301 to 2308, or natural fiber paper such as cellulose. The paper may be a mixed paper made of fibers and plastic fibrils, or a synthetic paper made only of plastic, but particularly suitable for the present invention is a natural fiber paper containing cellulose as a main component. The maximum surface roughness Rmax of electrical insulating paper is 5~
25μm, apparent density 0.6~1.2g/cm, thickness 15~
Thicknesses in the 150 μm range are often used due to 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 and interlayer adhesive strength. Polyolefin used as an adhesive between layers 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, putene, hexene, etc. is a typical example, but is not necessarily limited to this. As the polyolefin used in the present invention, ethylene/propylene (ethylene content: 1 to 10 mol%) random copolymer and ethylene/propylene (ethylene content: 10 to 50 mol%) block copolymer are particularly preferred. The melting point of the polyolefin should be 100-150°C, preferably 110-145°C. If this melting point is less than 100℃, preferably less than 100℃, the electrical tan δ will be large, and the degree of swelling in oil immersion will be large, resulting in electrical defects, so it is not used as an insulating material for oil-immersed cables. Can not. Further, when the melting point exceeds 150°C, preferably 145°C, the adhesiveness between the electrically insulating paper and the biaxially oriented polypropylene film is poor, the paper 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
It has a low viscosity of 1.4 (dl/g), suppressing swelling during oil immersion and improving interlayer adhesion. Furthermore, the thickness of the polyolefin layer is 0.5 to 8 μm,
Preferably it should be 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;
When it exceeds m, preferably exceeds 3 μm, the electrical tan δ becomes large and the degree of swelling in oil immersion becomes large, 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 subtracting the refractive index Nzd in the thickness direction from the arithmetic mean value (Nmd+Ntd)/2 of the refractive index in the longitudinal direction and width direction (indicated by Nmd and Ntd, respectively) of the polyolefin layer, which is 0.01. It is preferable that there be more than one. [Manufacturing Method] Next, a method for manufacturing an insulating material according to the present invention will be described. [Method] The method for producing the raw material for biaxially oriented polypropylene film used in the present invention is not particularly limited, but
A preferred example is a bulk polymerization method using propylene itself as a solvent using a catalyst system consisting of a titanium tetrachloride catalyst supported on various known magnesium chlorides, an organoaluminum compound, and a third component such as an ester compound. Polymerize propylene with
It is then obtained by removing the polypropylene, which is soluble in propylene and has low stereoregularity, with a low boiling point hydrocarbon such as propylene. 10% of ethylene is added to the polypropylene polymer raw material (A) and polyolefin as an adhesive polymer.
~40% block copolymerized ethylene/propylene block copolymer (B) is supplied to a sheet extruder, and a three-layer molten material called BAB is discharged from a die and cast onto a cooling drum. After preheating this sheet by external heating method,
Stretched 4 to 8 times at 120 to 150℃, and further stretched to 120 degrees in the width direction.
Stretch 6 to 12 times at ~170℃, and stretch to 100~100% as necessary.
Heat treatment is performed at 170° C. for 2 to 10 seconds to obtain a biaxially stretched polypropylene film having three layers. The total thickness of the three-layer laminated polypropylene film thus obtained was 40 to 250 μm, of which the surface of the ethylene-propylene block copolymer layer was roughened, and the thickness was adjusted to 0.5 to 8 μm. do. The reason for roughening the surface is to improve slipperiness and anti-blocking properties. Electrical insulating paper is superimposed on both surfaces of this three-layer laminated film, and
It is pressed for a short time between hot press rolls heated to 220°C at a linear pressure of 0.1 to 1 t/cm to obtain an insulating material consisting of insulating paper/three-layer laminated film/insulating paper. [Method] Another manufacturing method is to apply polyolefin as an adhesive, such as ethylene, on top of insulating paper.
A propylene random copolymer is uniformly coated to a thickness of 0.5 to 8 μm using a hot melt coating method. 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. Obtain an insulating material. In the case of the insulating material of the invention, the production method is particularly preferred in that the polyolefin layer as adhesive polymer has an orientation. [Effects of the Invention] The insulating material of the present invention comprises electrically insulating kraft paper,
Since it has a structure in which a biaxially oriented polypropylene film is laminated with a specific polyolefin at a specific thickness as an adhesive, the following effects can be achieved. (1) Swelling due to oil is extremely small. (2) Excellent oil distribution. (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 the amount dissolved in oil is small, the degree of contamination of oil is extremely small. (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) 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 weighing W (mg) is taken from this, placed again in the Soxhlet extractor, and extracted with boiling N-heptane 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 its weight is W' (mg), the degree of isotacticity is calculated by the following formula. Isotacticity (%) = 100 x W'/W (2) Birefringence Using Atsube's refractometer, calculate the refractive index in the longitudinal direction (Ny) and the refractive index in the width direction (Nx) of the film.
is measured, and the absolute value of the difference between Ny and Nx is taken as 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 due to electrical insulating oil Cut a 100mm square sample, dry it in a constant temperature bath at 120℃ for 20 hours, and immediately measure its thickness.
Let it be D (μm). This sample is immersed in dodecylbenzene oil at 100°C and left for 24 hours, then taken out and the thickness of the sample is immediately measured, and this is defined as D' (μm). The degree of swelling is determined by the following formula. Swelling degree (%) = 100 x (D'-D)/D (4) Adhesive strength between paper and film after oil immersion The laminated material was immersed in dodecylbenzene at 110°C for 30 minutes.
After being immersed for one day, it was taken out, thoroughly washed with acetone, and then left at room temperature of 20°C for one day. Using this sample as a sample, the peel strength of the bond between the paper and the film was measured according to the T-peel test method for flexible materials with each other as described in JIS K 6854-1973, and this was taken as the adhesive strength. (5) The method for measuring weight average molecular weight Mw and number average molecular weight Mn is as follows. Equipment: Gel permeation chromatograph GPC-150C Column: Shodex A80M Solvent: o-dichlorobenzene (0.1% ionol added) Rate: 1 ml/min Temperature: 135°C Sample concentration: 0.1 (wt/vol)% Filtration: 0.1 μm calcination Injection amount of filter: 0.4ml Detector: Differential refractive index detector Molecular calibration: Polystyrene standard (6) Intrinsic viscosity [η] is measured according to ASTM D1601 and is measured in tetralin at 135°C. Unit: dl/g. (7) Breakdown voltage (BDV) was measured according to ASTM D149 (20°C). (8) Electrical tanδ is the frequency according to ASTM D150.
50Hz, temperature 100℃, insulated paper measurement electrode MEP-C
The measurement was performed using a mold (manufactured by Nissin Electric Co., Ltd.). (9) The melting point Tm is the equilibrium temperature associated with the melting point of the crystal determined by a scanning calorimeter (DSC), and is called the endothermic peak. If there are two or more endothermic peak temperatures, 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 DSC measurement conditions are a sample weight of 5 mg, a heating rate of 20°C/min, and a nitrogen flow. (10) Surface roughness Rmax was measured according to JIS B0 601-1976. Example 1 Ethylene/propylene copolymer obtained by randomly copolymerizing 6 mol% ethylene (intrinsic viscosity [η] 0.8
dl/g, melting point 129°C) was supplied to a hot melt coater, heated to 260°C under a nitrogen seal, pressurized, extruded through a die with a slit gap of 0.4 mm, and the thickness was
30μm electrically insulating kraft paper (specific gravity 0.90g/ ^cm3 ,
A hot-melt coating was applied to one side (surface roughness Rmax=18 μm) to a thickness of 3 μm, and the film was wound up. On the other hand, the intrinsic viscosity is 1.85 dl/g, the weight average molecular weight
Ratio of Mw to number average molecular weight Mn Mw/Mn = 4.0,
Isotactic Index II 99% polypropylene was melted at 250°C, this melt was extruded into a sheet from a die, 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, and stretched 10 times in the width direction,
Further, the film was heat treated at 165° C. for 4 seconds while allowing 5% relaxation in the width direction to produce a biaxially oriented polypropylene film with a thickness of 90 μm. [η] of the film thus obtained was 1.80 dl/
g, Mw/Mn were 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 biaxially oriented polypropylene film, and then
Insulating paper/biaxially oriented polypropylene film/
A three-layer insulating material made of insulating paper and having a thickness of 156 μm was obtained. The thickness fraction of the biaxially oriented polypropylene film of the insulating material thus obtained was 57%. Subsequently, the insulating material was immersed in dodecylbenzene oil and its physical properties were measured. Swelling rate: 3% Dielectric constant: 2.5 (20℃), 2.5 (100℃) Tanδ: 0.04% (20℃), 0.05% (100℃) Adhesive strength: 120g/cm As described above, the insulating material of the present invention It can be seen that it exhibits excellent properties as an insulating material for oil-immersed cables, as it has not only excellent electrical properties but also excellent adhesive strength and swelling resistance. Comparative Example 1 Instead of applying the ethylene-propylene copolymer to the electrically insulating kraft paper using a hot melt coater in Example 1, the following solution-type thermosetting adhesive was used to coat the electrically insulating paper with a biaxially oriented polypropylene film. Both sides were pasted together using a conventional method. In this case, both surfaces of the biaxially oriented polypropylene film were subjected to corona discharge treatment with an electrical energy of 3600 J/m ² in order to improve adhesion. The adhesive thickness is
Each was 3 μm. [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 *As acid components, 72 mol% of terephthalic acid, 28 mol% of sebacic acid, as diol components, Saturated polyester copolymer consisting of 35 mol% ethylene glycol and 65 mol% neobentyl glycol, viscosity average molecular weight approximately 18,000 Thickness of electrically insulating paper/biaxially oriented polypropylene film/electrically insulating paper thus obtained
Various physical properties of the 156 μm insulating material were measured in the same manner as in Example 1, and the results are summarized in Table 1. Table 1
As is clear from the above, when a compound having a polar group is used as an adhesive, the electrical 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 are melt-extruded and laminated at 260°C to create a thickness of paper/random copolymer/film/random copolymer/paper.
A 156 μm insulating material was obtained. Here, 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 because the composition thickness is different, not only the dielectric constant and tan δ are large, but also the degree of swelling is large, making it suitable as an oil-immersed cable material. It turns out that it is not used.

[Table] Example 2 As polypropylene, [η] = 2.0, isotactic index II = 98% chips and ethylene were copolymerized to form a 20 mol% block of ethylene/propylene block copolymer ([η] =1.4,
Melting peak temperature by DSC is 118℃, 147℃, 160℃
℃, but the melting point is 133 as the average of the first two.
C) were introduced into separate nozzles, and a three-layer laminate sheet consisting of block copolymer layer/polypropylene layer/copolymer layer was extruded from the nozzles. This sheet was brought into close contact with a cooling drum maintained at 45°C using air pressure, cooled and solidified, then heated in a hot air oven 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 fed into a stenter type tenter heated to 160℃, stretched 10 times in the width direction, and then heat treated for 2 seconds while allowing 7% relaxation in the width direction, resulting in a 3-layer laminated polypropylene film with a thickness of 90μm. I got it. Here, the thickness of each block copolymer layer was 2 μm, and the thickness of the polypropylene layer was 86 μm, Mw/Mn=4.2.
Although this three-layer laminated polypropylene film did not contain any additives such as slip agents or anti-blocking agents, it exhibited excellent slipperiness with a coefficient of friction of 0.6 due to the use of a specific polymer. On both sides of this three-layer laminated polypropylene film, electrically insulating kraft paper (specific gravity
0.92 g/cm ³ , surface roughness Rmax = 15 μm), and using the same hot press roll as in Example 1, press at 200°C and a linear pressure of 400 Kg/cm for 0.1 seconds to laminate. An electrically insulating material with a thickness of 140 μm consisting of 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 dodecylbenzene at 20℃ are as follows: Dielectric constant: 2.5 tanδ: 0.04 (%) Oil swelling ratio: 4 (%) Breakdown voltage: 66 (KV/mm) Layer Adhesive strength: 140 (g/cm) Oil flowability: Good Longitudinal breaking strength: 35 (Kg/15mm width) Longitudinal breaking elongation: 150 (%) In this way, as an oil-immersed ultra-high voltage cable insulation material, , it can be seen that it is used as an excellent property. Example 3 and Comparative Example 3 As Example 3 and Comparative Example 3 of the cable structure shown in the figure with the specifications shown in Table 2 below, power cables using the insulating materials of Example 2 and Comparative Example 2 were manufactured, and various We investigated the characteristics. In the figure, 1 is a six-part conductor made of copper, 2 is an oil passage, 3 is a conductor binder layer formed by winding together, for example, stainless steel tape and carbon paper, 4 is an oil-immersed insulating layer, and 5 is an oil-immersed insulating layer. A metal shielding layer made by wrapping metallized paper and aluminum tape together,
6 is a core binder layer formed by winding, for example, a copper wire woven cloth tape, 7 is a lead-covered sheath, and 8 is a vinyl chloride-covered sheath. Table 3 shows the characteristics obtained for each cable.
Shown below.

【table】

【table】

[Table] According to the results in Tables 2 and 3, compared to the OF cable using the insulating material of Comparative Example 2, the OF cable using the insulating material of the present invention has lower capacitance and higher breakdown stress. It is clear that this has 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.

[Brief explanation of drawings]

The figure is a sectional view showing an example of a cable using the insulating material of the present invention. DESCRIPTION OF SYMBOLS 1... Conductor, 2... Oil passage, 4... Oil-immersed insulating layer, 5... Metal shielding layer, 6... Core binder layer, 7... Lead sheath, 8... PVC sheath.

Claims (1)

[Claims] 1. On both sides of the biaxially oriented polypropylene film,
In an insulating material made by bonding and laminating electrically insulating papers made of natural or synthetic fibers, the adhesion between the polypropylene film and the electrically insulating paper depends on the melting point.
An insulating material for oil-immersed cables, characterized in that polyolefin having a temperature of 100 to 150°C is used, and the thickness of the polyolefin layer is 0.5 to 8 μm.