Definitions

• the present invention
  relates to a prepreg mica tape and a coil using the same.
  
• Prepreg mica tapes
  composed of a resin, mica, and a backing material are often used as the insulation layer of a coil.
  
• a technique of adding an inorganic filler having a higher thermal conductivity than a resin and mica into the tapes
  is employed.
  
• Table 1 and Examples 3 and 4 of Japanese Patent Application Laid-Open (JP-A) No. 2005-199562
  disclose mica tapes each in which, as an inorganic filler, an alumina having a high thermal conductivity is filled in mica, and show that mica tapes having thermal conductivities of from 0.32 W/m ⁇ K to 0.36 W/m ⁇ K can be obtained.
  
• Table 1 and Examples 1 to 7 of JP-A No. 2000-116047
  disclose mica tapes each in which an alumina having a high thermal conductivity as an inorganic filler is filled in a resin, and show that mica tapes having thermal conductivities of from 0.40 W/m ⁇ K to 0.60 W/m ⁇ K can be obtained.
  
• the first problem
  is that, in the case of utilizing a method of papermaking a slurry mixture slurry of mica pieces and alumina particles by using a papermaking machine or the like, the alumina particles tend to easily fall through mesh due to the alumina being included in a mica layer. As a result, it becomes difficult to perform papermaking of alumina-containing mica paper and the production cost increases.
  
• the second problem
  is that while alumina has a higher thermal conductivity than mica and resin, an effect of improving the thermal conductivity of an alumina-filled mica tape is actually not very significant.
  
• the thermal conductivities of the alumina-filled mica tapes
  do not reach 0.4 W/m ⁇ K.
  
• Conventional products containing no highly-thermal conductive inorganic filler
  are known to have a thermal conductivity of about 0.3 W/m ⁇ K. From a practical viewpoint, it is not very meaningful to fill alumina particles into a mica tape unless a thermal conductivity twice or more than that of conventional products is obtained.
  
• the third problem
  is that although addition of alumina slightly increases thermal conductivity of a mica tape, other characteristics required for the mica tape tend to be impaired. For example, since an alumina-filled mica tape is hard, it is difficult to perform coil taping work. In addition, as compared to scale-like mica pieces, addition of spherical alumina particles generally shortens a current path; therefore, the dielectric withstanding voltage of the mica tape may be reduced. Furthermore, alumina has a large dielectric constant and, therefore, is not preferable for use as an electrically insulating material. On the other hand, in a case in which alumina particles are incorporated between mica pieces, the alumina particles cannot suppress tree deterioration and therefore the effect of a mica layer suppressing tree deterioration is reduced. As a result, degradation lifetimes of coils under voltage stress have sometimes become shorter than in conventional coils. Accordingly, it has been difficult to use such coils in actual equipment.
  
• JP-A No. 2000-116047
  also considered a mica tape in which boron nitride (BN) having a higher thermal conductivity was added as an inorganic filler instead of alumina, a thermal conductivity of only 0.40 W/m ⁇ K was obtained.
  
• BN
  boron nitride
  
• a prepreg mica tape
  including:
  
• boron nitride-containing layer
  that is provided on or above one surface of the backing material, and that includes boron nitride and a first resin
  
• a mica-containing layer
  that is provided on or above the one surface of the backing material on which the boron nitride-containing layer is provided, and that includes mica and a second resin.
  
• ⁇ 2>
  The prepreg mica tape according to ⁇ 1>, in which the boron nitride-containing layer and the mica-containing layer are provided in this order on or above the one surface of the backing material.
  
• ⁇ 3>
  The prepreg mica tape according to ⁇ 1> or ⁇ 2>, in which a percentage of mica pieces having a particle size of 2.8 mm or more, obtained by sieving the mica using a JIS standard sieve, is 50% by mass or more.
  
• ⁇ 4>
  The prepreg mica tape according to any one of ⁇ 1> to ⁇ 3>, in which the boron nitride has an average particle size of from 1 to 40 ⁇ m.
  
• a coil
  including an insulation layer that is a layered body of the prepreg mica tape according to any one of ⁇ 1> to ⁇ 4>.
  
• a prepreg mica tape
  that has a high thermal conductivity and exhibits both favorable flexibility and high dielectric withstanding voltage, and a coil using the prepreg mica tape can be provided.
  
• FIG. 1
  is a schematic sectional view showing prepreg mica tapes of Examples 1 to 4.
  
• FIG. 2
  is a schematic sectional view showing a prepreg mica tape of Comparative Example 1.
  
• FIG. 3
  is a schematic sectional view showing prepreg mica tapes of Comparative Examples 2 to 3.
  
• FIG. 4
  is a schematic sectional view showing a prepreg mica tape of Comparative Example 4.
  
• the term “step”
  denotes not only an independent step but also a step that cannot be clearly distinguished from other steps, as long as an intended object of the step is achieved.
  
• a numerical range shown using “to”
  denotes a range including numerical values put before and after “to” as a minimum value and a maximum value, respectively.
  
• the amount of each component included in the composition
  means the total amount of the plurality of substances in the composition unless otherwise noted.
  
• the term “layer”
  encompasses a structure having a shape formed on an entire surface and also a structure having a shape formed on a part of the surface when observed in a plan view.
  
• the prepreg mica tape of the invention
  includes: a backing material; a boron nitride-containing layer that is provided on or above one surface of the backing material, and that includes boron nitride and a first resin; and a mica-containing layer that is provided on or above the one surface of the backing material on which the boron nitride-containing layer is provided, and that includes mica and a second resin.
  
• the prepreg mica tape of the invention
  has a high thermal conductivity and exhibits both favorable flexibility and high dielectric withstanding voltage. It is unclear why the prepreg mica tape of the invention has a high thermal conductivity and exhibits both favorable flexibility and high dielectric withstanding voltage. However, the reason for that is presumed as follows.
  
• the prepreg mica tape of the invention
  includes the boron nitride-containing layer including boron nitride and a first resin, and boron nitride is a highly-thermal conductive filler. Therefore, the prepreg mica tape of the invention including the boron nitride-containing layer including boron nitride is presumed to have a high thermal conductivity.
  
• the prepreg mica tape of the invention
  is presumed to exhibit more favorable flexibility than mica tapes using alumina as a highly-thermal conductive filler.
  
• boron nitride particles
  can be prevented from being incorporated between mica pieces. Incorporation of the boron nitride-containing particles between the mica pieces leads to shortening of a current path, which thereby may cause a decrease in the dielectric withstanding voltage of the mica tape.
  
• incorporation of the boron nitride particles between the mica pieces
  is prevented and, as a result, shortening of the current path hardly occurs. Accordingly, the prepreg mica tape of the invention is presumed to exhibit high dielectric withstanding voltage.
  
• the boron nitride-containing layer and the mica-containing layer
  are both provided on or above the one surface of the backing material, and the backing material is provided on another surface of the prepreg mica tape of the invention, thereby improving workability during wrapping of a coil or the like with the prepreg mica tape of the invention.
  
• the prepreg mica tape of the invention
  is referred to also as “resin rich mica tape”.
  
• a large amount of a resin-containing composition
  is included in advance in the entire prepreg mica tape, making it unnecessary to inject an impregnation varnish.
  
• the content percentage of the resin-containing composition
  is set according to a use purpose in a range of generally about from 15% by mass to 50% by mass with respect to the total mass of the prepreg mica tape, as described in JP-A No. 2010-193673.
  
• the prepreg mica tape
  When wrapping a coil or the like with the prepreg mica tape, since the prepreg mica tape can be wound around the coil or the like with tension, a compression force caused by the tension is applied to the boron nitride-containing layer and the mica-containing layer that are in a prepreg state. Thereby, during heating processing or the like of the coil or the like wound with the prepreg mica tape, movement of a resin component(s) present in the boron nitride-containing layer and the mica-containing layer is more effectively performed, thereby increasing a mica density of the mica-containing layer and a boron nitride density of the boron nitride-containing layer. Accordingly, electrically insulating properties of the prepreg mica tape of the invention as an insulation material and the properties (for example, thermal conductivity) of boron nitride can be more effectively exerted.
  
• the prepreg mica tape of the invention
  has a thickness of preferably from 200 ⁇ m to 400 ⁇ m, and more preferably from 250 ⁇ m to 350 ⁇ m.
  
• the average thickness of the prepreg mica tape
  is obtained as an arithmetic mean value resulting from measurement of thicknesses of 10 points using a micrometer (MDC-SB, available from Mitutoyo Corporation).
  
• the prepreg mica tape of the invention
  may be any structure as long as the prepreg mica tape includes: a backing material; a boron nitride-containing layer provided on or above one surface of the backing material; and a mica-containing layer provided on or above the one surface of the backing material on which the boron nitride-containing layer is provided.
  
• the prepreg mica tape of the invention
  may include other layers, if necessary.
  
• the order of the boron nitride-containing layer and the mica-containing layer provided on or above the one surface of the backing material
  is not particularly limited.
  
• the backing material, the boron nitride-containing layer, and the mica-containing layer
  may be provided in this order, or the backing material, the mica-containing layer, and the boron nitride-containing layer may be provided in this order.
  
• the boron nitride-containing layer and the mica-containing layer
  are preferably provided in this order on or above one surface of the backing material in terms of easy manufacturing.
  
• examples of the other layers that are provided if necessary
  include a protection layer (a protection film) that is provided at an outermost surface of the side of the backing material where the boron nitride-containing layer and the like are provided and an adhesion layer.
  
• the boron nitride-containing layer according to the invention
  includes boron nitride and a first resin.
  
• the boron nitride-containing layer according to the invention
  may include other components other than the boron nitride and the first resin, if necessary. Examples of the other components include a curing agent, a curing catalyst, and various kinds of additives.
  
• the thickness of the boron nitride-containing layer
  is not particularly limited, but preferably is in a range of from 80 ⁇ m to 200 ⁇ m.
  
• the thickness of the boron nitride-containing layer
  may be obtained by observing a secondary electron image at an acceleration voltage of 10 kV under high vacuum through a scanning electron microscope (SEM) (XL30, available from Philips Corporation) after platinum deposition on a section of the prepreg mica tape.
  
• SEM
  scanning electron microscope
  
• the boron nitride-containing layer
  may include other inorganic fillers other than boron nitride.
  
• the content percentage of boron nitride with respect to the total amount of inorganic fillers contained in the boron nitride-containing layer
  is preferably from 90 to 100% by mass, more preferably from 95 to 100% by mass, and still more preferably from 98 to 100% by mass.
  
• examples of the other inorganic fillers
  include alumina, magnesium oxide, aluminium nitride, silicon nitride, and silicon oxide.
  
• the mica-containing layer according to the invention
  includes mica and a second resin.
  
• the mica-containing layer according to the invention
  may include other components other than the mica and the second resin, if necessary. Examples of the other components include a curing agent, a curing catalyst, and various kinds of additives.
  
• the thickness of the mica-containing layer
  is not particularly limited, but preferably in a range of from 100 ⁇ m to 250 ⁇ m, and more preferably in a range of from 110 ⁇ m to 230 ⁇ m.
  
• the thickness of the mica-containing layer
  can be obtained by observing a secondary electron image at an acceleration voltage of 10 kV under high vacuum through a scanning electron microscope (SEM) (XL30, available from Philips Corporation) after platinum deposition on a section of the prepreg mica tape.
  
• SEM
  scanning electron microscope
  
• the mica-containing layer
  does not include any other inorganic filler (such as boron nitride) other than the mica.
  
• the content percentage of the inorganic filler other than the mica with respect to the total amount of inorganic fillers contained in the mica-containing layer
  is preferably 3% by mass or less, more preferably 2% by mass or less, still more preferably 1% by mass, and particularly preferably 0% by mass.
  
• the backing material
  the first resin, the second resin, boron nitride, and mica as components of the prepreg mica tape of the invention and other components used if necessary.
  
• the backing material used in the present invention
  may be, for example, a cloth obtained by entirely or partially using a fiber composed of an organic material.
  
• the organic material that is used to obtain the cloth
  include aramid, polyamide, polyimide, and polyester.
  
• the fiber composed of an organic material
  may be used as warp or weft, or as both thereof.
  
• An inorganic fiber such as a glass fiber
  may be used as a fiber other than the fiber composed of an organic material.
  
• a glass cloth using a glass fiber and an organic polymer film
  may be used in combination.
  
• Examples of the boron nitride included in the boron nitride-containing layer according to the invention
  include hexagonal boron nitride (h-BN), cubic boron nitride (c-BN), and Wurtzite boron nitride.
  
• hexagonal boron nitride (h-BN)
  is preferable.
  
• the boron nitride
  may be a primary particle of boron nitride formed into a scale-like shape, or a secondary particle formed from aggregates of such primary particles.
  
• the boron nitride
  has an average particle size of preferably from 1 ⁇ m to 40 ⁇ m, more preferably from 5 ⁇ m to 20 ⁇ m, and still more preferably from 5 ⁇ m to 10 ⁇ m.
  
• the boron nitride
  has an average particle size of 1 ⁇ m or more, thermal conductivity and dielectric withstanding voltage tend to be further improved.
  
• the boron nitride
  has an average particle size of 40 ⁇ m or less, an excessive increase in anisotropy of the thermal conductivity due to anisotropy of the particle shape may be prevented.
  
• the average particle size of the boron nitride
  can be measured using a laser diffraction scattering type particle size distribution analyzer (MICROTRAC MT3000II, available from Nikkiso Co., Ltd).
  
• a boron nitride powder
  is put into pure water and then dispersed using an ultrasonic disperser.
  
• the particle size distribution of the boron nitride
  is measured by measuring the particle size distribution of the dispersion. Based on the particle size distribution, the average particle size is obtained as a particle size corresponding to a cumulative volume of 50% from a small size side.
  
• the boron nitride
  may be used singly or in combination of two or more kinds thereof.
  
• Examples of combination of two or more kinds of boron nitrides
  include use of two or more kinds of boron nitrides that are the same in component and different in average particle size, use of two or more kinds of boron nitrides that are the same in average particle size and different in component, and use of two or more kinds of boron nitrides that are different in average particle size and kind.
  
• the content percentage of the boron nitride with respect to the total amount of all solid contents except the backing material and the mica included in the prepreg mica tape of the invention
  is preferably from 10 to 50% by volume, and more preferably from 15 to 35% by volume.
  
• the content percentage of the boron nitride
  is 10% by volume or more, the thermal conductivity of the prepreg mica tape of the invention tends to be further improved.
  
• the content percentage of the boron nitride
  is 50% by volume or less, it is not likely that filling of the boron nitride into the resin is difficult.
  
• the first resin included in the boron nitride-containing layer according to the invention
  is not particularly limited.
  
• a curable resin
  is desirably used as the first resin, and examples thereof include epoxy resins, phenolic resins, unsaturated polyester resins, and silicone resins. Epoxy resins are preferable in terms of adhesion and electrical insulation properties.
  
• the second resin included in the mica-containing layer according to the invention
  is not particularly limited.
  
• a curable resin
  is desirably used as the second resin, and examples thereof include epoxy resins, phenolic resins, unsaturated polyester resins, and silicone resins. Epoxy resins are preferable in terms of adhesion and electrical insulation properties.
  
• the first resin and the second resin
  may be of the same kind or of different kinds from each other.
  
• the first resin and the second resin
  are preferably of the same kind.
  
• examples of the epoxy resin
  include bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolak type epoxy resins, cresol novolak type epoxy resins, naphthalene type epoxy resins, biphenyl type epoxy resins, and cyclic aliphatic epoxy resins.
  
• the epoxy resins
  it is preferable to use biphenyl type epoxy resins that contain a mesogen group having an easily self-aligned structure, such as a biphenyl group, in the molecule thereof, in terms of obtaining high thermal conductivity.
  
• the mesogen group referred to in the invention
  means a group that, in a case in which an epoxy resin is cured to form a resin cured product, is capable of forming a high-order structure in the resin cured product.
  
• the high-order structure referred to in the invention
  means a state in which molecules are oriented and aligned after curing of the epoxy resin, and for example, means that a crystal structure body is present in the resin cured product.
  
• the presence of such a crystal structure body
  may be confirmed by observation through a polarizing microscope under crossed nicols or by X-ray scattering spectra.
  
• the epoxy resins
  may be used singly or in combination of two or more kinds thereof.
  
• mica included in the mica-containing layer according to the invention
  examples include uncalcined hard mica paper, calcined hard mica paper, uncalcined soft mica paper, calcined soft mica paper, synthetic mica, and flake mica. Among these, it is preferable to use uncalcined hard mica paper as the mica in terms of price and availability.
  
• the percentage of mica pieces having a particle size of 2.8 mm or more, obtained by sieving the mica using a JIS standard sieve
  is preferably 50% by mass or more, more preferably 55% by mass or more, and still more preferably 60% by mass or more.
  
• the percentage of the mica pieces having a particle size of 2.8 mm or more
  is 50% by mass or more, mica paper is capable of supporting by itself even without any fibrit. No use of fibrit is more advantageous for thermal conductivity.
  
• the particle size of mica pieces
  are measured according to the following method.
  
• One percent by mass of a mica as a measurement object
  is added into 20 g of pure water and dispersed using an ultrasonic disperser to prepare a dispersion.
  
• the dispersion
  is applied onto a film, and then the film is placed on a hot plate to dry at 110° C. for 30 minutes. After drying, the sizes of mica pieces on the film are visually observed to measure the particle size of the mica.
  
• the percentage (by mass) of mica pieces having a particle size of 2.8 mm or more
  is measured by the following method.
  
• the micas
  may be used singly or in combination of two or more kinds thereof.
  
• Examples of combination of two or more kinds of micas
  include use of two or more kinds of micas that are the same in component and different in average particle size, use of two or more kinds of micas that are the same in average particle size and different in component, and use of two or more kinds of micas that are different in average particle size and kind.
  
• Examples of other components that may be included in the boron nitride-containing layer and the mica-containing layer according to the invention
  include a curing agent, a curing catalyst, and various kinds of additives.
  
• the boron nitride-containing layer and the mica-containing layer according to the invention
  preferably further include at least one curing agent as a curable component in addition to the curable resin.
  
• the curing agent
  is not particularly limited and may be selected, as appropriate, according to the kind of the curable resin.
  
• the curing agent
  can be used by selecting, as appropriate, from curing agents commonly used as epoxy resin curing agents.
  
• curing agents
  commonly used as epoxy resin curing agents.
  
• the curing agent
  include amine curing agents such as dicyandiamide or an aromatic diamine, and phenolic resin curing agents such as phenol novolak or cresol novolak.
  
• the ratio of the curing agent to the epoxy resin
  is preferably set to an equivalent ratio (curing agent/epoxy resin) ranging from 0.8 to 1.2 in terms of curing property and electrical characteristics of a cured product.
  
• a curing catalyst
  may be added to the boron nitride-containing layer and the mica-containing layer according to the invention in order to accelerate a curing reaction of the curable resin or a curing reaction between the curable resin and a curing agent.
  
• the curing catalyst
  is not particularly limited and may be used by selecting, as appropriate, according to the kinds of the curable resin and a curing agent used if necessary. Examples of the curing catalyst include triphenylphosphine, trimethylamine, 2-methyl-4-ethyl imidazole, and BF 3 monoethylamine.
  
• the percentage of a curing catalyst to be added in the case in which the curable resin is an epoxy resin
  is typically from 0.01 to 5% by mass with respect to the total amount of the epoxy resin and a curing agent used if necessary.
  
• the boron nitride-containing layer and the mica-containing layer according to the invention
  may further include various kinds of additives, if necessary.
  
• the other additives
  include various kinds of additives commonly used in resin compositions, such as coupling agents, elastomers, antioxidants, anti-aging agents, stabilizers, flame retardants, and thickeners.
  
• the amounts of the additives contained
  are not particularly limited as long as the effects of the invention are not impaired.
  
• the prepreg mica tape of the invention
  may be manufactured through any steps, and a conventionally known manufacturing method may be applied.
  
• One example of the method of manufacturing the prepreg mica tape of the invention
  is a method including: a boron nitride mixed solution preparation step of preparing a boron nitride mixed solution (BN-containing resin varnish) obtained by mixing a resin, boron nitride, and other materials to be used if necessary in a solvent; a coating step of coating one surface of the backing material with the boron nitride mixed solution; and a bonding step of bonding mica paper to the surface of the backing material coated with the boron nitride mixed solution.
  
• a boron nitride mixed solution preparation step
  of preparing a boron nitride mixed solution (BN-containing resin varnish) obtained by mixing a resin, boron nitride, and other materials to be used if necessary in a solvent
  
• a coating step
  of coating one surface of the backing material with the boron nitride mixed solution
  
• the resin
  may be diluted with a solvent.
  
• the solvent to be used
  is selected, as appropriate, from commonly used organic solvents. Specific examples of the solvent include solvents such as methyl ethyl ketone, methanol, or cyclohexane.
  
• the one surface of the backing material
  is coated with the boron nitride-containing solution and dried, whereby the boron nitride-containing layer according to the invention is formed.
  
• the mica paper bonded to the surface of the backing material coated with the boron nitride mixed solution
  is impregnated with the resin included in the boron nitride mixed solution and other materials to be used if necessary, whereby the region of the mica paper is formed as the mica-containing layer according to the invention.
  
• the first resin and the second resin according to the prepreg mica tape of the invention manufactured through the above-described steps
  are both the same kind of resin originating from the resin included in the boron nitride mixed solution.
  
• the prepreg mica tape of the invention
  encompasses a prepreg mica tape including the boron nitride-containing layer also formed on the other surface of the backing material.
  
• the prepreg mica tape of the invention
  may be used to form an insulation layer of a coil.
  
• the prepreg mica tape of the invention
  can also be used as a heat-resistant electrically insulating heat-dissipating spacer, for example, as a material that exhibits improved heat dissipation performance in a power transistor heat dissipating insulation plate.
  
• the coil of the invention
  includes an insulation layer that is a layered body formed by layering the prepreg mica tape of the invention.
  
• An example of a method of forming an insulation layer using the prepreg mica tape of the invention
  is a method in which the prepreg mica tape of the invention is wound around a region of a coil on which an insulation layer is to be formed, and the first resin and the second resin included in the boron nitride-containing layer and the mica-containing layer are cured or fused by heating and pressurizing or by heating and pressurizing after a vacuum treatment to integrate the prepreg mica tape, thereby forming an insulation layer.
  
• the prepreg mica tape of the invention
  exhibits favorable flexibility and thus is excellent in workability when winding the tape.
  
• the coil of the invention
  is excellent in insulation reliability.
  
• the prepreg mica tape of the invention
  has a high thermal conductivity. Accordingly, in cooling the coil of the invention, a hydrogen cooling system or an air cooling system may be employed even for a coil having a size for which a water direct cooling system has conventionally been employed, allowing simplification of a coil structure.
  
• a mica
  (the content percentage of mica pieces having a particle size of 2.8 mm or more was 63% by mass) was dispersed in water to prepare mica particles, and papermaking was performed using a papermaking machine to produce a sheet of mica paper having an average thickness of 0.13 mm.
  
• the average thickness of the mica paper
  was obtained as an arithmetic mean value resulting from measurement of thicknesses of 10 points using a micrometer (MDC-SB, available from Mitutoyo Corporation).
  
• MDC-SB
  micrometer
  
• the content percentage of the boron nitride in the total solid content volume of the BN-containing resin varnish
  was 35% by volume.
  
• the obtained BN-containing resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the mica paper. After drying, the resulting product was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the average thickness of the prepreg mica tape
  was obtained as an arithmetic mean value resulting from measurement of thicknesses of 10 points using a micrometer (MDC-SB, available from Mitutoyo Corporation).
  
• MDC-SB
  micrometer
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the average thickness of the mica tape cured product
  was obtained as an arithmetic mean value resulting from measurement of thicknesses of 10 points using a micrometer (MDC-SB, available from Mitutoyo Corporation).
  
• MDC-SB
  micrometer
  
• the prepreg mica tape or the mica tape cured product obtained above
  was evaluated as follows. Table 1 shows the results.
  
• Flexibility of the obtained prepreg mica tape
  was measured in accordance with JIS C2116: 2011. The temperature of the measurement was 23 ⁇ 2° C., and the speed of pressing in was 10 mm/min.
  
• the flexibility of the prepreg mica tape obtained as above
  was 66 N/m. Handling thereof was favorable, and no problem occurred during taping work thereof.
  
• the thermal resistance value of the obtained mica tape cured product
  was measured using a thermal resistance apparatus (YST-901S, available from Yamayo Tester Co., Ltd).
  
• the thermal conductivity (W/m ⁇ K) thereof
  was obtained by inverse calculation of the obtained thermal resistance value.
  
• the mica tape cured product
  had a thermal conductivity of 0.75 W/m ⁇ K.
  
• the dielectric breakdown electric field of the obtained mica tape cured product
  was measured using a dielectric breakdown tester (SOKEN insulating material test system, DAC-6032C). The measurement was performed by locating the product between cylindrical electrodes having a dimeter of 10 mm, at a voltage increase rate of 500 V/s, an AC frequency of 50 Hz, a cut-off current of 10 mA, and room temperature (25 ⁇ 1° C.) in oil.
  
• SOKEN insulating material test system
  DAC-6032C
  
• the dielectric breakdown electric field of the mica tape cured product
  was 39 kV/mm.
  
• the content percentage of the boron nitride in the total solid content volume of the BN-containing resin varnish
  was 25% by volume.
  
• the obtained BN-containing resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the mica paper. After drying, the resulting product was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the obtained prepreg mica tape and mica tape cured product
  were evaluated in the same manner as in Example 1.
  
• the flexibility of the prepreg mica tape obtained as above
  was 76 N/m. Handling thereof was favorable, and no problem occurred during taping work thereof.
  
• the obtained mica tape cured product
  had a thermal conductivity of 0.63 W/m ⁇ K.
  
• the obtained mica tape cured product
  had a dielectric breakdown electric field of 38 kV/mm.
  
• the content percentage of the boron nitride in the total solid content volume of the BN-containing resin varnish
  was 35% by volume.
  
• the obtained BN-containing resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the mica paper. After drying, the resulting product was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the obtained mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the obtained prepreg mica tape and mica tape cured product
  were evaluated in the same manner as in Example 1.
  
• the flexibility of the prepreg mica tape obtained as above
  was 59 N/m. Handling thereof was favorable, and no problem occurred during taping work thereof.
  
• the obtained mica tape cured product
  had a thermal conductivity of 0.67 W/m ⁇ K.
  
• the obtained mica tape cured product
  had a dielectric breakdown electric field of 37 kV/mm.
  
• the content percentage of the boron nitride in the total solid content volume of the BN-containing resin varnish
  was 25% by volume.
  
• the obtained BN-containing resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the mica paper. After drying, the resulting product was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the obtained prepreg mica tape and mica tape cured product
  were evaluated in the same manner as in Example 1.
  
• the flexibility of the prepreg mica tape obtained as above
  was 62 N/m. Handling thereof was favorable, and no problem occurred during taping work thereof.
  
• the obtained mica tape cured product
  had a thermal conductivity of 0.61 W/m ⁇ K.
  
• the obtained mica tape cured product
  had a dielectric breakdown electric field of 36 kV/mm.
  
• the obtained filler-non-containing resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the mica paper. After that, the resulting product was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the obtained prepreg mica tape and mica tape cured product
  were evaluated in the same manner as in Example 1.
  
• the flexibility of the prepreg mica tape obtained as above
  was 95 N/m. Handling thereof was favorable, and no problem occurred during taping work thereof.
  
• the obtained mica tape cured product
  had a thermal conductivity of 0.30 W/m ⁇ K.
  
• the obtained mica tape cured product
  had a dielectric breakdown electric field of 35 kV/mm.
  
• the content percentage of the alumina in the total solid content volume of the alumina-containing resin varnish
  was 35% by volume.
  
• the obtained alumina-containing resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the mica paper. After drying, the resulting product was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the obtained mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the obtained prepreg mica tape and mica tape cured product
  were evaluated in the same manner as in Example 1.
  
• the flexibility of the prepreg mica tape obtained as above
  was 300 N/m. Since the tape was hard, it was impossible to perform coil taping.
  
• the obtained mica tape cured product
  had a thermal conductivity of 0.41 W/m ⁇ K.
  
• the obtained mica tape cured product
  had a dielectric breakdown electric field of 30 kV/mm.
  
• the content percentage of the alumina in the total solid content volume of the alumina-containing resin varnish
  was 25% by volume.
  
• the obtained alumina-containing resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the mica paper. After drying, the resulting product was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the obtained mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the obtained prepreg mica tape and mica tape cured product
  were evaluated in the same manner as in Example 1.
  
• the flexibility of the prepreg mica tape obtained as above
  was 250 N/m. Since the tape was hard, it was impossible to perform coil taping.
  
• the obtained mica tape cured product
  had a thermal conductivity of 0.35 W/m ⁇ K.
  
• the obtained mica tape cured product
  had a dielectric breakdown electric field of 31 kV/mm.
  
• a mica
  (the content percentage of mica pieces having a particle size of 2.8 mm or more was 63% by mass) and a boron nitride (trade name “SP-3”, average particle size 5 ⁇ m, available from Denka Company Ltd.) were dispersed in water, and papermaking was performed using a papermaking machine to produce BN-containing mica paper having a thickness of 0.13 mm.
  
• the filling percentage of the boron nitride
  was 35% by volume with respect to the volume sum of the boron nitride and the mica.
  
• the obtained filler-noncontaining resin varnish
  was applied onto a glass cloth (WEA 03G 103, available from SOYO Co., Ltd.) using a roll coater and then bonded with the BN-containing mica paper.
  
• the content percentage of the boron nitride with respect to the sum of the total solid content except for the backing material and the mica included in the prepreg mica tape
  was 35% by volume.
  
• the resulting product
  was cut to a width of 30 mm to form a prepreg mica tape.
  
• the obtained prepreg mica tape
  had an average thickness of 280 ⁇ m.
  
• the prepreg mica tape obtained by the above-described method
  was heated under a pressure of 10 MPa at 110° C. for 10 minutes. After that, the prepreg mica tape was heated under a pressure of 10 MPa at 170° C. for 60 minutes to obtain a cured product of the mica tape.
  
• the mica tape cured product
  had an average thickness of 180 ⁇ m.
  
• the obtained prepreg mica tape and mica tape cured product
  were evaluated in the same manner as in Example 1.
  
• the flexibility of the prepreg mica tape obtained as above
  was 80 N/m. Handling thereof was favorable, and no problem occurred during taping work thereof.
  
• the obtained mica tape cured product
  had a thermal conductivity of 0.40 W/m ⁇ K.
  
• the obtained mica tape cured product
  had a dielectric breakdown electric field of 34 kV/mm.
  
• FIG. 1
  is a schematic sectional view showing the prepreg mica tapes of Examples 1 to 4.
  
• FIG. 2
  is a schematic sectional view showing the prepreg mica tape of Comparative Example 1.
  
• FIG. 3
  is a schematic sectional view showing the prepreg mica tapes of Comparative Examples 2 to 3.
  
• FIG. 4
  is a schematic sectional view showing the prepreg mica tape of Comparative Example 4.
  
• reference sign 1
  denotes a boron nitride-containing layer
  
• reference sign 2
  denotes a mica-containing layer
  
• reference sign 3
  denotes a backing material
  
• reference sign 4
  denotes a resin (first resin and second resin)
  
• reference sign 5
  denotes a boron nitride particle
  
• reference sign 6
  denotes mica
  
• reference sign 7
  denotes an alumina-containing layer
  
• reference sign 8
  denotes an alumina particle
  
• reference sign 9
  denotes a boron nitride-containing mica-containing layer, respectively.
  
• the inorganic filler
  refers to BN or alumina, and not mica.
  
• a highly-thermal conductive prepreg mica tape
  can be obtained which, while having a high thermal conductivity of 0.6 W/m ⁇ K or more, is also capable of achieving favorable coil taping work and high dielectric breakdown voltage, by filling boron nitride as the inorganic filler into the inorganic filler-containing layer of the prepreg mica tape and independently providing the inorganic filler-containing layer and the mica-containing layer.
  

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Classifications

• • C—CHEMISTRY; METALLURGY
    
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    
  • C09J7/00—Adhesives in the form of films or foils
    
  • C09J7/20—Adhesives in the form of films or foils characterised by their carriers
    
    
• • 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
    
  • H01B3/02—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances
    
  • H01B3/04—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of inorganic substances mica
    
    
• • H—ELECTRICITY
    
  • H01—ELECTRIC ELEMENTS
    
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    
  • H01F5/00—Coils
    
  • H01F5/06—Insulation of windings
    
    

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• Chemical & Material Sciences
  (AREA)
• Inorganic Chemistry
  (AREA)
• Engineering & Computer Science
  (AREA)
• Power Engineering
  (AREA)
• Organic Chemistry
  (AREA)
• Insulating Bodies
  (AREA)
• Laminated Bodies
  (AREA)
• Insulated Conductors
  (AREA)
• Reinforced Plastic Materials
  (AREA)
• Insulating Of Coils
  (AREA)
• Insulation, Fastening Of Motor, Generator Windings
  (AREA)
• Inorganic Insulating Materials
  (AREA)
• Compositions Of Macromolecular Compounds
  (AREA)

Abstract

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US10373727B2

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• 2014
  • 2014-10-09
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    PCT/JP2014/077108
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• 2017
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