EP0272497B1 - Pressspan mit niedriger dielektrischer Konstante für ölimpregnierte Isolierung - Google Patents

Pressspan mit niedriger dielektrischer Konstante für ölimpregnierte Isolierung Download PDF

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Publication number
EP0272497B1
EP0272497B1 EP19870117570 EP87117570A EP0272497B1 EP 0272497 B1 EP0272497 B1 EP 0272497B1 EP 19870117570 EP19870117570 EP 19870117570 EP 87117570 A EP87117570 A EP 87117570A EP 0272497 B1 EP0272497 B1 EP 0272497B1
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EP
European Patent Office
Prior art keywords
fiber
press board
poly
kraft pulp
dielectric constant
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP19870117570
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English (en)
French (fr)
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EP0272497A2 (de
EP0272497A3 (en
Inventor
Kenji Hyodo
Masaoki Nozaki
Humihiko Ishizuka
Etsuo Ooe
Hideo Tsukioka
Ichitaro Tani
Yuzuru Kamata
Kaoru Endo
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Hitachi Ltd
Mitsubishi Paper Mills Ltd
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Hitachi Ltd
Mitsubishi Paper Mills Ltd
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Publication date
Priority claimed from JP61283301A external-priority patent/JPH0644411B2/ja
Priority claimed from JP61295790A external-priority patent/JPH0673249B2/ja
Priority claimed from JP61309750A external-priority patent/JP2634589B2/ja
Priority claimed from JP18092687A external-priority patent/JPS6427112A/ja
Application filed by Hitachi Ltd, Mitsubishi Paper Mills Ltd filed Critical Hitachi Ltd
Publication of EP0272497A2 publication Critical patent/EP0272497A2/de
Publication of EP0272497A3 publication Critical patent/EP0272497A3/en
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Publication of EP0272497B1 publication Critical patent/EP0272497B1/de
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/42—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes polyesters; polyethers; polyacetals
    • H01B3/421—Polyesters
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D21H27/30—Multi-ply
    • D21H27/38—Multi-ply at least one of the sheets having a fibrous composition differing from that of other sheets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/008—Other insulating material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/185—Substances or derivates of cellulose
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/48—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials
    • H01B3/52—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances fibrous materials wood; paper; press board
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/02—Chemical or chemomechanical or chemothermomechanical pulp
    • D21H11/04—Kraft or sulfate pulp
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/10—Organic non-cellulose fibres
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/10—Organic non-cellulose fibres
    • D21H13/12—Organic non-cellulose fibres from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H13/14—Polyalkenes, e.g. polystyrene polyethylene
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/10—Organic non-cellulose fibres
    • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H13/24—Polyesters

Definitions

  • the present invention relates to a press board for oil impregnation insulation. More specifically, it relates to a low-dielectric constant press board prepared by mixing a poly(4-methylpentene-1) fiber and/or a poly(3-methyl-butene-1) fiber and a kraft pulp.
  • a conventional press board for oil impregnation insulation comprises 100 wt% of a kraft pulp and has a dielectric constant as high as 4.7.
  • a low-dielectric constant press board for oil impregnation insulation which comprises a laminate of sheets of a kraft pulp alone and mixed sheets composed of the kraft pulp and 30 to 90 wt% of a polymeric fiber (JP-A-156,386/1987).
  • Examples of insulating paper other than the press board include low-dielectric constant insulating paper which can be made by mixing a pulp-like material (a synthetic fibrid) of a synthetic polymer with a polymeric fiber, and then heating/pressing the mixture to melt and shape it (JP-B-13,912/1963); insulating paper made by mixing a pulp with 30 wt% or more of a polymeric fiber having a different molecular structure, and then shaping the mixture (JP-A-124,811/1982); and insulating paper made by laminating the mixed sheets of a polymeric fiber and a pulp, the polymeric fiber being present in the mixed sheets in different proportions, and then shaping the mixture (JP-A-168,418/1982).
  • low-dielectric constant insulating paper which can be made by mixing a pulp-like material (a synthetic fibrid) of a synthetic polymer with a polymeric fiber, and then heating/pressing the mixture to melt and shape it (JP-B-13,912/19
  • the insulating paper described in (JP-B-13,912/1963) mentioned above is made by using, as a pulp, a synthetic fibrid which is a synthetic polymer and heating/pressing the fibrid to melt it. Therefore, its oil impregnation which is necessary as the press board for oil-impregnation insulation is poor and insufficient.
  • the synthetic insulating paper disclosed in (JP-A-124,811/1982) mentioned above has a thickness of 0.2 mm or less and is constituted to be wound around conductors. Therefore, this paper does not have such a compressive strength as to support winding wires and is inconveniently bad in oil impregnation.
  • the semisynthetic insulating paper described in (JP-A-168,418/1982 mentioned above is as thin as 0.15 mm or less and therefore is different from the press board having a thickness of 0.5 mm or more.
  • this insulating paper is made by heating and melting the polymeric fiber at a high temperature, and that the content of the polymeric fiber therein is as much as 40 wt% or more. Further, since constituted to be wound around conductors, this paper does not have such a compressive strength as to support winding wires, and its oil impregnation is also inconveniently poor.
  • press boards for oil impregnation insulation have the feature that as the dielectric constant of the press board is decreased, a stress of the electric field which is applied to an oil space between the press board and another insulator is alleviated. From the viewpoint of this effect, it is appreciated that the dielectric constant of the press board is preferably 3.8 or less, more preferably 3.5 or less.
  • the increase in the content of a poly(4-methylpentene-1) fiber or the like in the press board leads to the diminution in the dielectric constant, so that an effect of mitigating the electric field is built up.
  • such a manner causes its compressive strength to decrease disadvantageously.
  • the compressive strength of the press board is required to be 72 N/mm2 (7.3 kg/mm2) (80°C) or more. In this respect, it is necessary that the press board has different properties than the above-mentioned insulating papers.
  • the press board when used in high-voltage oil-impregnated electric machines, the press board is also required to be excellent in insulating properties at a high voltage.
  • an object of the present invention is to provide a low-dielectric constant press board for oil impregnation insulation having a thickness of 0.5 mm or more in which the compressive strength is high, the oil impregnation is good, the dielectric constant is small, insulating properties at a high voltage are excellent, and an electric field which easily concentrates in the oil space between insulators is effectively alleviated.
  • a low dielectric constant press board for oil impregnation insulation which is formed by laminating mixed wet sheets of a poly(4-methylpentene-1) fiber and/or a poly(3-methylbutene-1) fiber and a kraft pulp, the fibers being used in an amount of 5,6 to less than 30 wt-%, based on the press board, and then drying the laminate integrally by heating/pressing at a temperature of 110 to 190 °C under a pressure of 98 to 490 N/cm2 (10 to 50 kgf/cm2).
  • a low-dielectric constant press board for oil impregnation insulation which is formed by mixing a poly(4-methylpentene-1) fiber and/or a poly(3-methylbutene-1) fiber in an amount of 5,6 to less than 30 wt-%, based on the press board, with a kraft pulp to make mixed wet sheets, disposing wet sheets of kraft pulp alone over and under said mixed wet sheets, or over, under and between said mixed wet sheets, and then drying the laminate integrally by heating/pressing at a temperature of 110 to 190 °C under a pressure of 98 to 490 N/cm2 (10 to 50 kgf/cm2).
  • the content of the poly(4-methylpentene-1) fiber and/or the poly(3-methylbutene-1) fiber in the press board is preferably 10 wt% or more and less than 30 wt%. Further, when mixed with the kraft pulp, the amount of the poly(4-methylpentene-1) fiber and/or the poly(3-methylbutene-1) fiber is 5.6 wt% or more and less than 30 wt% based on the press board, and it is preferred that one or more of polyethylene terephthalate fibers and polyphenylene sulfide fibers is mixed therewith in an amount of less than 28 wt% as a third fiber.
  • the dielectric constant of the product is a little worse than in the case of the former fiber alone, but its compressive strength is built up perceptibly. Therefore, the employment of the third fiber can provide the additional advantage that the balance between the dielectric constant and the compressive strength is easily regulated.
  • the above-mentioned two kinds of third fibers have no problems in points of swelling resistance and solubility to an insulating oil.
  • the total amount of the fibers is preferably 30 wt% or less based on the weight of the press board.
  • the dielectric constant of the press board is preferably 3.8 or less, more preferably 3.5 or less (that of a conventional press board is 4.7) from the viewpoint of the effect of mitigating the electric field in the oil space.
  • the content of the poly(4-methylpentene-1) fiber and/or poly(3-methylbutene-1) fiber is preferably 10 wt% or more, more preferably 15 wt% or more, based on the total weight of the press board.
  • the compressive strength of the press board is required to be 72 N/mm2 (7.3 kg/mm2) (80°C) or more, and therefore the content of the poly(4-methylpentene-1) fiber and/or poly(3-methylbutene-1) fiber is preferably less than 30 wt%. Also in the case that the above-mentioned third fiber is mixed, it is preferred that the total amount of the fibers is less than 30 wt%.
  • the mixture of these fibers permits not only decreasing the dielectric constant of the press board effectively but also heightening heat resistance and oil resistance thereof.
  • Thickness and length of these fibers are preferably 6 denier or less and 2 to 10 mm, respectively.
  • At least top and bottom sheets of, or at least top, bottom and intermediate sheets of the laminate comprise sheets of the kraft pulp alone.
  • the quality of these kraft pulps is comparable to the grade of the press boards in Class 2 (hereinafter referred to as PB-2) which JIS 2311 prescribes.
  • a freeness of the usable kraft pulp is preferably within the range of 200 to 400 ml (Canadian Standard Freeness-CSF).
  • the freeness of the kraft pulp is in excess of 400 ml: (beating and entanglement of the pulp are poor), then the press board manufactured therefrom is insufficient in tensile strength and compressive strength.
  • the press board of the present invention may be manufactured by first making wet sheets in accordance with a wet sheet making process from an aqueous slurry in which the poly(4-methylpentene-1) fiber and/or the poly(3-methylbutene-1) fiber having a thickness of 6 denier or less and a length of 2 to 10 mm are mixed with the kraft pulp, then laminating the thus made wet sheets as many as their optional number, and finally drying the laminate at a temperature of 110 to 190°C under a pressure of 98 to 490 N/cm2 (10 to 50 kgf/cm2).
  • the drying temperature should be less than the melting points of the respective fibers. This point is different from the case of the insulating papers disclosed in the known literature in which a polymeric fiber is molten.
  • the conventional insulating papers made by melting the polymeric fiber do not have such a compressive strength as to support the winding wire and are poor in oil impregnation.
  • the heating process of the present invention does not intend to melt the fiber but to dry it.
  • the formed press board involves serious problems such as linting and dislocation of the mixed fiber.
  • the press board When used in high-voltage oil-impregnated electric machines, the press board must possess excellent insulating properties even at a high voltage. For this purpose, surface properties of the press board are crucial.
  • Forming the top and bottom of the mixed wet sheets with the sheets of the kraft pulp alone is effective to prevent the linting of the synthetic fiber, and interposing the sheets of the kraft pulp alone between the mixed wet sheets builds up the effect of inhibiting the fibers from dislocating.
  • the linting and dislocation of the fiber decrease the lightning impulse breakdown voltage.
  • the thermal treatment For the prevention of the linting on the surface of the press board, for the prevention of the decrease in the lightning impulse breakdown voltage, and for the prevention of the dislocation of the fiber, it is effective to treat thermally both the surfaces of the press board at a temperature of 220°C or more for a short period of time.
  • the range of the suitable temperature is within 230 to 280°C.
  • the thermal treatment may be carried out by the use of one or more hot rolls, a special flatiron suitable for a high temperature, an iron, a hair drier or a hot-air oven. A time period necessary for the thermal treatment depends upon a chosen means for the treatment.
  • the thermal treatment can be achieved instantaneously, but when the hot-air oven is used, a period of 1 minute or more is taken. If the treatment temperature is 250°C, a period of about 5 minutes is necessary.
  • the low-dielectric constant synthetic fiber When, with the intention of lowering the dielectric constant of the press board, the low-dielectric constant synthetic fiber is mixed with the kraft pulp and is then heated and pressed in a usual manner to form the desired press board, a mesh pattern is more liable to appear on the surface of the press board than in the case of a press board only comprising the kraft pulp.
  • the surface roughness; (i.e., a 10 point height,) was measured in accordance with the procedure of JIS B0601, and it was found that the value of the 10 point height was as high as 180 ⁇ m or more.
  • Various press boards having different 10 point heights were formed by the use of nets having different meshes, and for these press boards, the relation between the lightning impulse properties and the 10 point height was inspected. As a result, it was found that both the factors were relative to each other. That is, a relation was appreciated in which the smaller the surface roughness of the press board became, the greater the lightning impulse breakdown voltage became. In particular, when the 10 point height is 100 ⁇ m or less, the lightning impulse breakdown voltage is high, even in the case that the dielectric constant is 3.5.
  • a fine net having e.g., openings of 150 ⁇ m or less (100 meshes or more) may be used in shaping the heated and pressed press board.
  • the surface of the heated and pressed board may be treated with a calender. In this way, the 10 point height can be regulated to a level of 100 ⁇ m or less, and therefore a press board can be obtained having a low dielectric constant and a high lightning impulse breakdown voltage.
  • a specimen (diameter 90 mm) was dried by heating in vacuo and then impregnated with an insulating oil, and the specimen was held between a pair of electrodes manufactured by Nissin Electric Co., Ltd. at a pressure of 2.45 N/cm2 (0.25 kgf/cm2). Afterward, the specimen was impregnated with the insulating oil again, and the dielectric constant was then measured.
  • Specimens (impregnated with oil) having a size of 13 x 13 mm and a thickness of about 1.6 mm were laminated, till their height had reached a level of about 16 to 18 mm.
  • the breaking load was then measured at a compressive velocity of 0.5 mm/minute at a temperature of 80°C by the use of an autographic recording device, and the aimed compressive strength was calculated from the breaking load and a sectional area of the laminate.
  • Linting was evaluated by visually observing the surface of the press board.
  • a press board 7 for which lightning impulse breakdown voltage would be measured was put between two coils where a conductor 3 was coated with oil-impregnated paper 4 and another coil where another conductor 5 was coated with oil-impregnated paper 6, in order to construct a model for the measurement of the lightning impulse breakdown voltage.
  • the thus constructed model was then immersed into an oil, and after the conductors 3 and 5 had been connected respectively to an application side and a ground side, the lightning impulse breakdown voltage was applied to the model, increasing the voltage one shot by one shot from a low voltage level.
  • a lightning impulse streamer was delivered from a wedge-like oil space 8 defined between the oil-impregnated paper 4 and the press board 7 to the surface of the oil-impregnated paper 6 of the coil on the ground side, and the streamer was finally passed through the oil-impregnated paper 6, so that an insulation breakdown occurred between the coils.
  • the applied lightning impulse breakdown voltage was measured.
  • a ratio of the lightning impulse breakdown voltage was sought relatively by regarding, as 100%, a lightning impulse breakdown voltage of the conventional press board PB-2 comprising a kraft pulp alone.
  • a poly(4-methylpentene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm was mixed with a kraft pulp having a freeness of 365 ml (CSF) in a proportion shown in Table 1 given below, in order to prepare an aqueous slurry, and wet sheets were made from this slurry in accordance with a wet paper making process.
  • the 19 wet sheets were laminated and then heated/pressed at a temperature of 140°C at a pressure of 392 N/cm2 (40 kgf/cm2) in order to dry them and to thereby obtain a press board having a thickness of 1.6 to 1.7 mm integrally.
  • dielectric constant, compressive strength and oil impregnation distance were measured, and the results are set forth in Table 1.
  • the press board can be obtained in which the dielectric constant is 3.8 or less and the compressive strength is 72 N/mm2 (7.3 kg/mm2) or more.
  • the drying treatment under the heating/pressing operation is carried out at a temperature within the range of 110 to 190°C, so that the impregnation of the insulating oil in every example is better than Comparative Example 3 regarding a conventional press board (PB-2) and Comparative Example 1 in which the content of the poly(4-methylpentene-1) fiber is in excess of the upper limit of the present invention.
  • a poly(4-methylpentene-1) fiber having a thickness of 3 denier and a length of 5 mm was mixed with a kraft pulp having a freeness of 365 ml (CSF) in a proportion shown in Table 2 given below in order to prepare an aqueous slurry, and wet sheets were then made from this slurry in accordance with a wet paper making process. Then, the 19 wet sheets were laminated and treated in the same manner as in Examples 1 to 5 in order to form press boards having a thickness of 1.6 to 1.7 mm.
  • the press board formed in each example was passed through hot rolls at a temperature shown in Table 2 so as to perform a surface treatment.
  • a poly(3-methylbutene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm was mixed with a kraft pulp having a freeness of 365 ml (CSF) in a proportion shown in Table 3 given below in order to prepare an aqueous slurry, and wet sheets were made from this slurry in accordance with a wet paper making process. Then, the 19 wet sheets were laminated and dried by heating/pressing for 45 minutes at a temperature of 140°C at a pressure of 392 N/cm2 (40 kgf/cm2) in order to integrally form a press board having a thickness of 1.6 to 1.7 mm.
  • CSF freeness of 365 ml
  • the content of the poly(3-methylbutene-1 fiber is preferably less than 30 wt%.
  • the dielectric constant of 3.8 or less when the dielectric constant of 3.8 or less is desired, the content of the poly(3-methylbutene-1) fiber is required to be 10 wt% or more.
  • the results in Table 3 indicate that when the content of the poly(3-methylbutene-1) fiber is more than 15 wt% or more and is less than 30 wt%, the formed press board has a dielectric constant of 3.8 or less and a compressive strength of 72 N/mm2 (7.3 kg/mm2) or more.
  • the press boards regarding the present invention are dried at 110 to 190°C in the heating/pressing process, the poly(3-methybutene-1) fiber does not fuse thermally, and therefore all of them are more excellent in insulating oil impregnation than the conventional press board (PB-2).
  • a poly(3-methylbutene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm was mixed with a kraft pulp having a freeness of 365 ml (CSF) in a proportion shown in Table 4 given below in order to prepare an aqueous slurry, and wet sheets were made from this slurry in accordance with a wet paper making process. Then, the 19 wet sheets were laminated and treated in the same manner as in Examples 12 to 15 in order to form press boards having a thickness of 1.6 to 1.7 mm.
  • CSF freeness of 365 ml
  • Each press board was passed through hot rolls at 270°C and 300°C so as to fuse or remove fibrous fluffs from its surface.
  • dielectric constant, surface linting and oil impregnation distance were measured, and the results are set forth in Table 4.
  • a poly(3-methylbutene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm was mixed with a kraft pulp having a freeness of 365 ml (CSF) in a weight ratio of the fiber : the kraft being 11.2 : 88.8 in order to prepare a 1% aqueous slurry.
  • CSF 365 ml
  • a 1% aqueous slurry comprising the kraft pulp alone having a freeness of 365 ml (CSF) was utilized to make 17 wet sheets in which an absolute dry weight would be 9 g/m2.
  • FIG. 1 is a mixed layer and numeral 2 is a pulp single layer.
  • the top and bottom sheets of the laminate were constituted by the wet sheets of the kraft pulp alone.
  • the composite wet sheets were heated and pressed at 140°C at 392 N/cm2 (40 kgf/cm2) for 45 minutes by the use of a hot press in order to form a press board integrally.
  • combination type press boards were formed which were each composed of the mixed wet sheets of the poly(3-methylbutene-1) fiber and the kraft pulp and the wet sheets of the kraft pulp alone.
  • the mixing ratios of the poly(3-methylbutene-1) fiber : the kraft pulp were 16.8 : 83.2, 22.4 : 77.6 and 28.0 : 72.0
  • the top, bottom and intermediate sheets of each combination type press board were constituted by the sheets of the kraft pulp alone.
  • the contents of the poly(3-methylbutene-1) fiber were 10, 15, 20 and 25 wt% in the respective examples.
  • combination type press boards were likewise formed which were each composed of the mixed wet sheets of the poly(3-methylbutene-1) fiber and the kraft pulp and the wet sheets of the kraft pulp alone.
  • the mixing ratios of the poly(3-methylbutene-1) fiber : the kraft pulp were 5.6 : 94.4 and 39.2 : 60.8
  • the top, bottom and intermediate sheets of each combination type press board were constituted by the sheets of the kraft pulp alone.
  • the content of the poly(3-methylbutene-1) fiber in these press boards is 10 wt% or more and less than 35 wt%.
  • dielectric constant is 3.8 or less
  • compressive strength is 72 N/mm2 (7.3 kg/mm2) (80°C) or more
  • any linting is not present on the surfaces, and oil impregnation distance is also good.
  • the dielectric constant is high, and also in the case that the content of the fiber is as small as about 5 wt%, the value of the dielectric constant is at a similar level.
  • the content of the fiber is inversely as great as about 40 wt%, the compressive strength deteriorates remarkably.
  • the content of the fiber is 10 wt% or more and less than 30 wt%, the linting is present on the surfaces of the press boards, unless the kraft pulp layers are used for the top and bottom sheets. This fact leads to the degradation in the lightning impulse breakdown voltage.
  • a poly(4-methylpentene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm was mixed with a kraft pulp having a freeness of 365 ml (CSF) in a weight ratio shown in Table 6 in order to prepare a 1 wt% aqueous slurry.
  • CSF 365 ml
  • a 1 wt% aqueous slurry comprising the kraft pulp alone having a freeness of 365 ml (CSF) was utilized to make 17 wet sheets in which an absolute dry weight would be 9 g/m2.
  • top and bottom sheets of the laminate were made up of the wet sheets of comprising the kraft pulp alone.
  • the composite wet sheets were heated and pressed at 140°C at 392 N/cm2 (40 kgf/cm2) for 45 minutes by the use of a hot press in order to form a combination type press board integrally in which the top, bottom and intermediate sheets were composed of the layers of the kraft pulp alone.
  • Comparative Example 20 no poly(4-methylpentene-1) fiber was used, and in Comparative Examples 21 and 22, combination type press boards were prepared from the mixed wet sheets of the poly(4-methylpentene-1) fiber and the kraft pulp and the sheets of the kraft pulp alone.
  • the mixing ratios of the kraft pulp : the poly(4-methylpentene-1) fiber were 95 : 5 and 65 : 35, and the top, bottom and intermediate sheets of the press board were made up of by the sheets of the kraft pulp alone.
  • wet sheets in which an absolute dry weight would be 80 g/m2 were made in the mixing ratios of a kraft pulp : poly(4-methylpentene-1) fiber were 85 : 15 and 75 : 25.
  • the suitable number of the wet sheets was laminated and then heated and pressed at 140°C at 392 N/cm2 (40 kgf/cm2) for 45 minutes by the use of a hot press in order to form combination type press boards integrally.
  • the press boards can be obtained having the aimed properties in points of the dielectric constant and compressive strength.
  • the thus obtained press boards have no problems of the linting and dislocation in contrast to such press boards as in Comparative Examples 23 and 24 in which the poly(4-methylpentene-1) fiber and the kraft pulp are merely mixed.
  • a poly(4-methylpentene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm and a polyethylene terephthalate fiber having a thickness of 1.5 denier and a length of 5 mm were mixed with a kraft pulp having a freeness of 365 ml (CSF) in a proportion shown in Table 7 given below in order to prepare a 1 wt% aqueous slurry. From this slurry, 16 wet sheets were made in which an absolute dry weight would be 80 g/m2. Further, a 1 wt% aqueous slurry comprising the kraft pulp alone having a freeness of 365 ml (CSF) was used to make 17 wet sheets in which an absolute dry weight would be 9 g/m2.
  • Fig. 1 These two kinds of wet sheets were laminated alternately, as shown in Fig. 1.
  • the top and bottom sheets of the laminate were made up of the wet sheets comprising the kraft pulp alone.
  • This composite wet sheets were heated and pressed at 140°C at 392 N/cm2 (40 kgf/cm2) for 45 minutes to form a press board integrally.
  • the content of the polyethylene terephthalate fiber is preferably less than 25 wt% based on the total weight of the press board (in terms of a fraction in the mixed wet sheets, the content of the terephthalate fiber is preferably less than 28 wt%). If the content of the polyethylene terephthalate fiber is in excess of this level, the content of the poly(4-methylpentene-1) fiber is restricted, so that the feature of the poly(4-methylpentene-1) fiber will be lost. Further, since the kraft pulp sheets are used for the top and bottom sheets of the press board, the linting and dislocation on the surface thereof can be prevented.
  • a poly(4-methylpentene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm and a polyphenylene sulfide fiber having a thickness of 4.2 denier and a length of 5 mm were mixed with a kraft pulp having a freeness of 365 ml (CSF) in a proportion in Table 8 given below in order to prepare a 1 wt% aqueous slurry. From this slurry, 16 wet sheets were made in which an absolute dry weight would be 80 g/m2. Further, a 1 wt% aqueous slurry comprising the kraft pulp alone having a freeness of 365 ml was used to make 17 wet sheets in which an absolute dry weight would be 9 g/m2.
  • Fig. 1 These two kinds of wet sheets were laminated alternately, as shown in Fig. 1.
  • the top and bottom sheets of the laminate were constituted by the wet sheets comprising the kraft pulp alone.
  • the composite wet sheets were heated and pressed at 140°C at 392 N/cm2 (40 kgf/cm2) for 45 minutes to form a press board integrally.
  • the content of the polyphenylene sulfide fiber is preferably less than 25 wt% based on the total weight of the press board, as in Examples 31 to 33. Further, since the kraft pulp sheets are used for the top and bottom sheets of the press board, the linting and dislocation on the surface can be prevented.
  • Fig. 2 shows a relation between a ratio of a lightning impulse breakdown voltage and the dielectric constant of the press board. This ratio of the lightning impulse breakdown voltage is a value measured by the use of the model for a lightning impulse breakdown test and is a relative proportion in the case that the lightning impulse breakdown voltage of the conventional press board PB-2 is regarded as 100%. The result of Fig.
  • the dielectric constant of the formed press board can be reduced to 3.8 or less and simultaneously the comressive strength can be maintained at a level of 72 N/mm2 (7.3 kg/mm2) or more.
  • Example 25 The laminate was then heated and pressed at a temperature of 140°C under a pressure of 392 N/cm2 (40 kgf/cm2) for 45 minutes to integrally form a low-dielectric constant press board of 1.6 mm in thickness.
  • Comparative Example 25 the same procedure as in Example 37 was repeated with the exception that nets of 270 ⁇ m (55 mesh) were used.
  • Table 9 sets forth the opening in ⁇ m (mesh numbers) of the used nets, dielectric constants and values (Rz) of a 10-point height of the formed press boards.
  • Table 9 Kind of Net Dielectric Constant at 20°C Surface Roughness* ( ⁇ m)
  • Example 37 150 ⁇ m (100 mesh) 2.90 95 Comp. Ex. 25 270 ⁇ m (55 mesh) 2.90 210 * A value (Rz) of the 10-point height which was measured in accordance with JIS B0601.
  • a poly(4-methylpentene-1) fiber having a thickness of 0.33 tex (3 denier) and a length of 5 mm was mixed with a kraft pulp having a freeness of 365 ml (CSF) in a proportion of the fiber : the pulp being 11.2 : 88.8 in order to prepare a 1 wt.% slurry. From this slurry, 16 mixed wet sheets (the content of water was about 80%) were made in which an absolute dry weight would be 80 g/m2.
  • aqueous slurry comprising the kraft pulp alone the freeness of which was 365 ml (CSF), and from this slurry, 17 wet sheets were made in which an absolute dry weight would be 9 g/m2.
  • the mixed wet sheets and the kraft pulp sheets were alternately laminated as many as required so that the kraft pulp sheets might be used over and under the mixed wet sheets so as to sandwich them.
  • the thus made composite wet sheets were heated and pressed at 140°C under 392 N/cm2 (40 kgf/cm2) for 45 minutes by the use of a net of 150 ⁇ m (100 mesh) and a hot press in order to form a press board integrally.
  • the poly(4-methylpentene-1) fiber and/or the poly(3-methylbutene-1) fiber is selected as the fiber which is mixed with the kraft pulp, in order to form the press board having a thickness of 0.5 mm or more. Therefore, the content of the fibers can be reduced to a low level of 10 wt% or more and less than 30 wt% based on the total weight of the press board, and the compressive strength of the press board, which is the essential requirement thereof, can be maintained at 72 N/mm2 (7.3 kg/mm2) (80°C) or more, with the dielectric constant thereof kept at 3.8 or less.
  • the compressive strength of the press board can be built up, without sacrificing the dielectric constant, by mixing at least one selected from polyethylene terephthalate fibers and polyphenylene sulfide fibers with the above-mentioned fiber.
  • the wet sheets made from the kraft pulp alone are used for the top, bottom and intermediate sheets of the mixed wet sheet laminate which is composed of the fiber and the kraft pulp, the linting and dislocation of the fiber can be prevented, whereby the lightning impulse breakdown voltage can be inhibited from deteriorating.
  • the heating/pressing process for drying the mixed wet sheets is carried out at a temperature below a melting point of the fiber, the impregnation of the oil into the press board remains good.
  • the linting on the surface of the press board can be eliminated by thermally treating this surface alone at a temperature of 220°C or more, and the lightning impulse breakdown voltage can be maintained at a high level by reducing a value of the 10 point height to 100 ⁇ m or less.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Organic Insulating Materials (AREA)
  • Paper (AREA)

Claims (11)

  1. Preßspan mit niedriger Dielektrizitätskonstante zur Ölimprägnierungsisolation, der hergestellt wird durch Laminieren gemischter, feuchter Bögen aus einer Poly(4-methylpenten-1)faser und/oder einer Poly(3-methylbuten-1)faser und einem Kraftzellstoff, wobei die Fasern in einer Menge von 5,6 bis weniger als 30 Gew.-%, bezogen auf den Preßspan, verwendet werden, und anschließend durch vollständiges Trocknen des Laminats durch Erhitzen/Pressen bei einer Temperatur von 110 bis 190°C unter einem Druck von 98 bis 490 N/cm² (10 bis 50 kgf/cm²).
  2. Preßspan mit niedriger Dielektrizitätskonstante zur Ölimprägnierungsisolation, der hergestellt wird durch Mischen einer Poly(4-methylpenten-1)faser und/oder einer Poly(3-methylbuten-1)faser in einer Menge von 5,6 bis weniger als 30 Gew.-%, bezogen auf den Preßspan, mit einem Kraftzellstoff, wobei gemischte, feuchte Bögen hergestellt werden, Auslegen feuchter Bögen aus Kraftzellstoff alleine über und unter vorstehenden gemischten, feuchten Bögen oder über, unter und zwischen diesen gemischten, feuchten Bögen und nachfolgend vollständiges Trocknen des Laminats durch Erhitzen/Pressen bei einer Temperatur von 110 bis 190°C unter einem Druck von 98 bis 490 N/cm² (10 bis 50 kgf/cm²).
  3. Preßspan mit niedriger Dielektrizitätskonstante zur Ölimprägnierungsisolation gemäß einem der Ansprüche 1 oder 2, wobei die Menge der Poly(4-methylpenten-1)faser und/oder der Poly(3-methylbuten-1)faser, bezogen auf den Preßspan, 10 Gew.-% oder mehr und weniger als 30 Gew.-% beträgt.
  4. Preßspan mit niedriger Dielektrizitätskonstante zur Ölimprägnierungsisolation gemäß einem der Ansprüche 1 bis 3, wobei der Kraftzellstoff einen Mahlgrad von 200 bis 400 ml (CSF) besitzt.
  5. Preßspan mit niedriger Dielektrizitätskonstante zur Ölimprägnierungsisolation gemäß einem der Ansprüche 1 bis 3, wobei der Preßspan Zusätzlich Polyethylenterephthalatfasern und/oder Polyphenylensulfidfasern in einer Menge von weniger als 28 Gew.-% enthält.
  6. Preßspan mit niedriger Dielektrizitätskonstante zur Ölimprägnierungsisolation gemäß Anspruch 1, wobei die Oberfläche des getrockneten Laminats einer thermischen Behandlung bei einer Temperatur von 220°C oder mehr unterzogen wurde.
  7. Preßspan mit einer niedrigen Dielektrizitätskonstante zur Ölimprägnierungsisolation gemäß einem der Ansprüche 1 bis 6, wobei die Oberfläche des Preßspans eine 10-Punkt-Höhe von 100 µm oder weniger besitzt.
  8. Verfahren zur Herstellung eines Preßspans mit einer niedrigen Dielektrizitätskonstante zur Ölimprägnierungsisolation gemäß Anspruch 1, das das Laminieren gemischter, feuchter Bögen aus einer Poly(4-methylpenten-1)faser und/oder einer Poly(3-methylbuten-1)faser und einem Kraftzellstoff umfaßt, wobei die Fasern in einer Menge von 5,6 bis weniger als 30 Gew.-%, bezogen auf den Preßspan, verwendet werden, und nachfolgend vollständiges Trocknen des Laminats durch Erhitzen/Pressen bei einer Temperatur von 110 bis 190°C unter einem Druck von 98 bis 490 N/cm² (10 bis 50 kgf/cm²).
  9. Verfahren zur Herstellung eines Preßspans mit niedriger Dielektrizitätskonstante zur Ölimprägnierungsisolation gemäß Anspruch 2, das das Mischen einer Poly(4-methylpenten-1)faser und/oder einer Poly(3-methylbuten-1)faser in einer Menge von 5,6 bis weniger als 30 Gew.-%, bezogen auf den Preßspan, mit einem Kraftzellstoff umfaßt, wobei gemischte, feuchte Bögen hergestellt werden, Auslegen feuchter Bögen aus Kraftzellstoff alleine über und unter vorstehenden gemischten, feuchten Bögen oder über, unter und zwischen diesen gemischten, feuchten Bögen und dann vollständiges Trocknen des Laminats durch Erhitzen/Pressen bei einer Temperatur von 110 bis 190°C unter einem Druck von 98 bis 490 N/cm² (10 bis 50 kgf/cm²).
  10. Verfahren gemäß Anspruch 8 oder 9, das die Verwendung eines Netzes mit Öffnungen von 150 µm oder weniger (100 Maschen oder mehr) beim Schritt des Erhitzen/Pressen umfaßt.
  11. Verfahren gemäß Anspruch 8, das die thermische Behandlung des getrockneten Laminats bei einer Temperatur von 220°C oder mehr umfaßt.
EP19870117570 1986-11-28 1987-11-27 Pressspan mit niedriger dielektrischer Konstante für ölimpregnierte Isolierung Expired - Lifetime EP0272497B1 (de)

Applications Claiming Priority (8)

Application Number Priority Date Filing Date Title
JP61283301A JPH0644411B2 (ja) 1986-11-28 1986-11-28 低誘電率油浸絶縁用プレスボ−ド
JP283301/86 1986-11-28
JP61295790A JPH0673249B2 (ja) 1986-12-12 1986-12-12 低誘電率油浸絶縁用プレスボ−ド
JP295790/86 1986-12-12
JP309750/86 1986-12-24
JP61309750A JP2634589B2 (ja) 1986-12-24 1986-12-24 低誘電率油浸絶縁用プレスボード
JP18092687A JPS6427112A (en) 1987-07-22 1987-07-22 Low permittivity oil immersed insulating press board
JP180926/87 1987-07-22

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Publication Number Publication Date
EP0272497A2 EP0272497A2 (de) 1988-06-29
EP0272497A3 EP0272497A3 (en) 1990-01-31
EP0272497B1 true EP0272497B1 (de) 1993-06-23

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Publication number Priority date Publication date Assignee Title
DE4314620A1 (de) * 1993-05-04 1994-11-10 Basf Ag Elektroisolationspapier
ATE478425T1 (de) 2007-12-27 2010-09-15 Abb Research Ltd Elektrisches isoliermaterial, elektrische vorrichtung mit dem isoliermaterial und wandler
US8085120B2 (en) * 2009-08-13 2011-12-27 Waukesha Electric Systems, Incorporated Solid insulation for fluid-filled transformer and method of fabrication thereof

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS54137082A (en) * 1978-04-18 1979-10-24 Mitsui Petrochem Ind Ltd Laminate and its manufacturing method
GB2021037B (en) * 1978-05-08 1982-06-03 Solvay Laminated structure for furnishing comprising at least onedecorative layer combined with a support
JPS57168418A (en) * 1981-04-07 1982-10-16 Tomoegawa Paper Co Ltd Method of producing electrically insulating sheet
JPH0718116B2 (ja) * 1985-12-27 1995-03-01 三菱製紙株式会社 低誘電率油浸絶縁用プレスボ−ド

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EP0272497A3 (en) 1990-01-31
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