JP2017059335A - Insulation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an insulation film excellent in thermal conductivity and also excellent in voltage resistance even if film thickness is low or high without depending on the film thickness.SOLUTION: Provided is an insulation film obtained by dispersing boron nitride particles into a resin for film formation, using boron nitride particles with the average particle diameter in which, provided that the value when film thickness is divided with the average particle diameter of the boron nitride particles is defined as A, the A being 5 to 600, and, provided that the variation coefficient of the concentration of the boron nitride particles in the film face vertical to the film thickness is defined as CV, the CV being 50 to 150%. It is preferable that the average particle diameter of the boron nitride particles is 0.05 μm or higher. Further, it is preferable that the volume concentration of the boron nitride particles in the film being 2 to 30 vol.%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an insulating film in which boron nitride particles are dispersed in a film-forming resin. More specifically, the present invention relates to an insulating film having excellent thermal conductivity and excellent withstand voltage regardless of the film thickness, regardless of whether the film thickness is small or large.

  Conventionally, when a highly heat-conductive filler (filler) such as boron nitride is dispersed and blended in the resin forming the insulating layer, the filling rate of the high heat-conductive filler is increased or the particle size of the filler is increased. In the case of increasing the thickness, it is known that many voids are generated in the insulating layer in the process of forming the insulating layer, and the withstand voltage is lowered (for example, see Patent Document 1).

  A thermally conductive laminate for solving this problem is disclosed (for example, see Patent Document 1). The thermal conductive laminate has a thermal conductive filler content of 35 to 80% by volume in the filler-containing polyimide resin layer containing the thermal conductive filler in the polyimide resin, and the maximum particle size of the thermal conductive filler is Less than 15 μm, the thermally conductive filler contains a plate-like filler and a spherical filler, the average major axis of the plate-like filler such as boron nitride is 0.1 to 2.4 μm, and in the thickness direction of the insulating layer The thermal conductivity is 0.8 W / mK or more. Patent Document 1 describes that this thermally conductive laminate is excellent in heat resistance and voltage resistance.

On the other hand, an insulating heat conductive filler dispersion composition containing a high heat resistant resin, an insulating heat conductive filler and a solvent, and an insulating heat conductive resin composition manufactured by applying and heating this composition are disclosed. (For example, refer to Patent Document 2). The insulating heat conductive filler is made of boron nitride, has a specific surface area of 15 to 25 m ² / g, the content of the insulating heat conductive filler is 35 to 70% by volume, and the insulating heat conductive material. The filler is uniformly dispersed so that the volume average particle diameter is 4.5 to ₁₀ μm, d ₁₀ is 0.3 μm or more, and d ₉₀ is 15 μm or less. Patent Document 2 discloses that an insulating heat conductive filler dispersion composition can achieve both heat conductivity and insulation, and an insulating heat conductive resin composition (insulating) manufactured using this composition. The layer) has a high breakdown voltage.

WO2011-111684A1 (Claim 1, Claim 3, Paragraph [0005]) JP, 2014-156545, A (claim 1, claim 7, claim 9, claim 19, paragraph [0010])

  The heat conductive laminate of Patent Document 1 and the insulating heat conductive filler dispersion composition of Patent Document 2 contain boron nitride particles having an average major axis or an average particle diameter within a predetermined range as the heat conductive filler. If so, regardless of the thickness of the insulating film, the insulating film is said to have both thermal conductivity and insulating properties (voltage resistance), but boron nitride particles having a predetermined average major axis or average particle size are used. In such a case, the withstand voltage may be lowered or the thermal conductivity may not be sufficiently improved when the insulating layer is thin or thick.

  An object of the present invention is to provide an insulating film excellent in thermal conductivity and withstand voltage regardless of the film thickness, regardless of whether the film thickness is small or large.

  The present inventors use boron nitride particles whose average particle diameter is not too small and not too large with respect to the film thickness, and the variation coefficient of the concentration of boron nitride particles on the film surface perpendicular to the film thickness is within a predetermined numerical value. Then, the inventors have found that the object of the present invention can be achieved if the value obtained by dividing the thickness of the insulating film by the average particle diameter of the boron nitride particles is within a predetermined value, and the present invention has been achieved.

  A first aspect of the present invention is that boron nitride particles are dispersed in a film-forming resin, and when A is a value obtained by dividing the film thickness by the average particle diameter of the boron nitride particles, A is 5 Boron nitride particles having an average particle diameter of ˜600 are used, and when the coefficient of variation of the concentration of boron nitride particles on the film surface perpendicular to the film thickness is CV, the insulating film has a CV of 50 to 150%. .

  A second aspect of the present invention is an insulating film according to the first aspect, wherein the boron nitride particles have an average particle size of 0.05 μm or more.

  A third aspect of the present invention is an insulating film according to the first or second aspect, wherein the volume concentration of boron nitride particles in the film is 2 to 30% by volume.

  A fourth aspect of the present invention is an enameled wire having the insulating film according to any one of the first to third aspects.

  Since the insulating film according to the first aspect of the present invention has a value A related to the local concentration of boron nitride particles of 5 to 600, the boron nitride particles are distributed in the film reasonably and uniformly. The thermal conductivity is excellent. Further, since the coefficient of variation CV of the concentration of boron nitride particles on the coating surface perpendicular to the film thickness is 150% or less, the concentration of boron nitride particles does not become too high locally, so it does not depend on the film thickness. Excellent withstand voltage. Further, since the coefficient of variation CV of the concentration of boron nitride particles on the coating surface perpendicular to the film thickness is 50% or more, the concentration of boron nitride particles does not become too uniform, so that the thermal conductivity is not dependent on the film thickness. Excellent. As a result, even if the film thickness changes, the thermal conductivity can be improved while minimizing the decrease in withstand voltage.

  In the insulating film according to the second aspect of the present invention, the average particle diameter of the boron nitride particles dispersed in the film-forming resin is 0.05 μm or more. Therefore, the contribution of the interfacial thermal resistance between the boron nitride particles and the resin The heat transfer resistance as a whole is small and the thermal conductivity is excellent.

  Since the volume concentration of the boron nitride particles in the coating is 2% by volume or more, the insulating coating according to the third aspect of the present invention has a larger occupation volume of the boron nitride particles in the coating and has a higher thermal conductivity. Moreover, since the said volume concentration is 36 volume% or less, a membrane | film | coat is flexible and it is excellent in flexibility.

  The enamel film according to the third aspect of the present invention has an insulating film with excellent thermal conductivity and withstand voltage, and therefore has excellent heat dissipation and long life.

It is the figure which represented typically the electrodeposition coating apparatus of embodiment of this invention.

  Next, the form for implementing this invention is demonstrated.

[Insulating film]
The insulating film of the present invention is constituted by dispersing boron nitride particles in a film forming resin. The insulating film of the present embodiment has a thickness of 5 to 60 μm. The boron nitride particles in the film have an average particle size of 0.05 μm or more, preferably 0.1 to 5 μm. When the thickness is less than 0.05 μm, the contribution of the interfacial thermal resistance between the film-forming resin and boron nitride is large, the heat transfer resistance is large, and the thermal conductivity is poor. If the average particle diameter of the boron nitride particles is too large, the unevenness on the free surface of the coating is large, which increases the contact resistance with the heat radiating partner member, resulting in poor thermal conductivity and reduced withstand voltage. The average particle diameter of the boron nitride particles is a median diameter D ₅₀ measured using a laser diffraction particle size distribution analyzer (manufactured by Horiba, Ltd. LA960).

  In the insulating film of the present invention, when A is a value obtained by dividing the film thickness by the average particle diameter of boron nitride particles, A is 5 to 600, and the concentration of boron nitride particles on the film surface perpendicular to the film thickness When the coefficient of variation is CV, the CV is 50 to 150%. Here, A is preferably 10 to 300, and the coefficient of variation CV is preferably 60 to 110%. When A is in the above range, the concentration of boron nitride particles is reasonably uniform, so that the balance between thermal conductivity and withstand voltage is good. The coefficient of variation (CV value, unit:%) is calculated from the concentration distribution of boron nitride particles in the film measured by an X-ray fluorescence analysis (EDX) apparatus or the like: [(standard deviation / average particle size) × 100] Ask for. When the CV exceeds 150%, the portion where the concentration of the boron nitride particles becomes too high locally increases, and the dielectric breakdown tends to occur at that portion, so that the withstand voltage decreases. On the other hand, if the CV is less than 50%, the concentration of boron nitride particles becomes too uniform, resulting in a decrease in thermal conductivity.

  The concentration of boron nitride particles in the insulating film is calculated by measuring thermogravimetry (TG) after peeling the film from the substrate and setting the weight loss up to 700 ° C. as the resin component. Further, the coefficient of variation CV of the concentration of boron nitride particles on the film surface perpendicular to the film thickness is determined by first using a fluorescent X-ray analysis (EDX) apparatus on the scale (Y-axis direction) at which the film thickness is at the limit. Or, the boron concentration is measured at 50 points. The measurement result image is converted to Biary (binarization conversion) using image analysis software (ImageJ). After the conversion, the area concentration of the boron nitride portion is calculated along the X axis of the image, and this value is used as the coefficient of variation CV. Instead of measuring the concentration of boron nitride particles or the boron concentration, the area of the resin may be calculated based on the components contained only in the resin and subtracted from the entire area.

  As a resin used for forming an insulating film by binding boron nitride particles, a resin having strong adhesive force, high heat resistance, high flexibility, and high withstand voltage is preferable. Examples of this resin (polymer particles) include polyimide resin, polyamideimide resin, polyesterimide resin, polyester resin, polyurethane resin, acrylic resin, epoxy resin, epoxy-acrylic resin, acrylic styrene resin, or a mixture of these. Can be mentioned. In 100% by mass of the insulating film, boron nitride particles are preferably contained in an amount of 2 to 30% by volume, and the film-forming resin is preferably contained in an amount of 70 to 98% by volume. When the content of the film-forming resin is less than the lower limit, the binding force of the boron nitride particles becomes poor, and when the content of the film-forming resin exceeds the upper limit, the thermal conductivity of the insulating film decreases.

[Insulating film manufacturing method]
A method for manufacturing the insulating film of the present embodiment will be described. In this method, boron nitride particles are added to and dispersed in the electrodeposition paint, and an insulating film is produced on the conductor surface by the electrodeposition coating method, as well as a film forming resin using a ball mill, jet mill, bead mill, etc. A liquid composition for forming an insulating film is prepared by uniformly dispersing particles, boron nitride particles, and an organic solvent. The liquid composition is applied to the surface of a metal plate, glass plate, metal foil, resin film, or the like on a knife coater or roll coater. And a method of producing an insulating film by coating with a coating apparatus such as a reverse coater, a die coater, or a gravure coater, and heat-treating the coating film.

  In order to produce an insulating film on the conductor surface by the electrodeposition coating method, first, this film is formed by adding water, which is a poor solvent for the film-forming resin, to a solution obtained by dissolving the film-forming resin in an organic solvent. A resin dispersion is prepared by precipitating a resin for coating, and then boron nitride particles are added to and mixed with the resin dispersion to prepare an electrodeposition paint. Examples of the organic solvent include N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (γBL), anisole, tetra 1 type, or 2 or more types chosen from methylurea and sulfolane are mentioned. It is preferable to add 2 to 30% by volume of boron nitride particles in 100% by volume of the solid content in the electrodeposition paint. When the amount of boron nitride particles added is less than the lower limit, the thermal conductivity of the insulating film made from this electrodeposition paint is difficult to improve. On the other hand, if the amount added exceeds the upper limit, the concentration of boron nitride particles in the film becomes too high, and the withstand voltage and flexibility are significantly reduced.

[Method of manufacturing enameled wire with insulation film]
Next, a method for producing an enameled wire with an insulating film using the electrodeposition paint will be described. As shown in FIG. 1, an electrodeposition coating apparatus 10 is used to electrodeposit the electrodeposition paint 11 on the surface of a copper wire 12 by an electrodeposition coating method to form an insulating layer (not shown). Specifically, a cylindrical copper wire 13 having a circular cross section that is wound in a cylindrical shape is electrically connected to a positive electrode of a DC power source 14 via an anode 16 in advance. Then, the cylindrical copper wire 13 is pulled up in the direction of the solid line arrow in FIG.

  First, as a first step, a cylindrical copper wire 13 is rolled flat by a pair of rolling rollers 17 and 17 to form a rectangular copper wire 12 having a rectangular cross section. Next, as a second step, the electrodeposition paint 11 is stored in the electrodeposition tank 18 and maintained at 5 to 60 ° C., and the rectangular copper wire 12 is passed through the electrodeposition paint 11 in the electrodeposition tank 18. . Here, a cathode 19 electrically connected to the negative electrode of the DC power supply 14 is inserted into the electrodeposition paint 11 in the electrodeposition tank 18 with a space from the flat rectangular copper wire 12 passing therethrough. When the rectangular copper wire 12 passes through the electrodeposition coating 11 in the electrodeposition tank 18, a DC voltage in the range of 1 to 300 V is applied between the rectangular copper wire 12 and the electrodeposition coating 11 by the DC power source 14. In between, it is applied for 0.01 to 30 seconds. As a result, the water-dispersed polymer particles (not shown) and the boron nitride particles that are the electrodeposition coating material 11 are electrodeposited on the surface of the flat rectangular copper wire 12 to form an insulating layer.

  Next, an insulating film (not shown) is formed on the surface of the copper wire 12 by subjecting the flat rectangular copper wire 12 having an insulating layer electrodeposited thereon to dry baking. In this embodiment, the copper wire 12 having the insulating layer formed on the surface is passed through the baking furnace 22. The dry baking process is preferably performed in a hot air heating furnace. Moreover, it is preferable that the temperature of a drying baking process exists in the range of 100-500 degreeC, and it is preferable that the time of a drying baking process exists in the range of 1-10 minutes. Here, the reason why the temperature of the drying baking process is limited to the range of 100 to 500 ° C. is that the insulating layer cannot be sufficiently dried and cured at a temperature lower than 100 ° C., and the polymer is thermally decomposed when the temperature exceeds 500 ° C. is there. Moreover, the reason why the time for the drying and baking treatment is limited to the range of 1 to 10 minutes is that the insulating layer cannot be sufficiently dried and cured in less than 1 minute, and if it exceeds 10 minutes, the resin is thermally decomposed. . In addition, the temperature of a drying baking process is the temperature of the center part in a baking furnace. By passing through the baking furnace 22, an enameled wire 23 in which the surface of the copper wire 12 is coated with an insulating film containing boron nitride aggregated particles is manufactured. A coil (not shown) is formed by winding the enameled wire 23.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, boron nitride particles having an average particle diameter of 0.05 μm are prepared. The boron nitride particles are added to an aqueous dispersion of polyimide so that the volume concentration of boron nitride in the insulating film is 10% by volume, and ultrasonic waves are applied to uniformly disperse the boron nitride particles. A paint was prepared. Here, as the polyimide aqueous dispersion, 7% by mass of polymer particles made of polyimide resin were used in 100% by mass of the polyimide aqueous dispersion. The aqueous dispersion of polyimide contained 50% by mass of N-methylpyrrolidone (NMP), 15% by mass of 1 methoxy-2-propanol (1M2P), and 25% by mass of water in 100% by mass of the aqueous dispersion. The electrodeposition paint thus prepared was electrodeposited on the surface of a copper plate having a thickness of 0.3 mm and a thickness of 30 mm × 20 mm by applying a DC voltage of 100 V by an electrodeposition coating method, and an insulating layer was formed. An insulating film was prepared by baking at 250 ° C. for 3 minutes.

  Table 1 shows the average particle diameter of boron nitride particles, the film thickness of the insulating film, the coefficient of variation (CV) of the concentration of boron nitride particles in the film surface perpendicular to the film thickness, and the film thickness divided by the average particle diameter of the boron nitride particles. The value (A) and the volume concentration of boron nitride particles are shown. In Table 1, “BN” means boron nitride particles.

<Examples 2-28 and Comparative Examples 1-8>
As shown in Table 1, boron nitride particles having an average particle size different from that of the boron nitride particles described in Example 1 were used, and as shown in Table 1, the amount of electric charge flowing during the electrodeposition of the insulating film was also changed. The film thickness of the film and the volume concentration of the boron nitride particles were changed to be Examples 2 to 28 and Comparative Examples 1 to 8.

<Comparative Example 9>
An electrodeposition paint was prepared without adding boron nitride particles to the aqueous polyimide dispersion of Example 1. An insulating film was produced in the same manner as in Example 1 using this electrodeposition paint.

<Comparison test and evaluation>
About the insulation film produced in Examples 1-28 and Comparative Examples 1-9, the film thickness, the withstand voltage and the thermal conductivity in the direction perpendicular to the film surface, and the flexibility of the insulation film are respectively determined by the following methods. It was measured. These measurement results of Examples 1 to 28 and Comparative Examples 1 to 9 are shown in Tables 1 and 2.

(1) Film thickness of the insulation film The film thickness of the insulation film is obtained by embedding a copper plate with a film in an epoxy resin, and then polishing this to cause a cross section of the film to appear. Was measured.

(2) Dielectric withstand voltage of the insulating film The withstand voltage of the insulating film was measured using a multifunctional safety tester 7440 of Keiki Giken Co., Ltd. The electrodes were connected to the copper plate and the insulating film, respectively, boosted to 6000 V in 30 seconds, the voltage when the current flowing between both electrodes reached 5000 μA was divided by the thickness of the insulating film, and this value was taken as the withstand voltage. .

(3) Thermal conductivity in the vertical direction of the insulating film The vertical thermal conductivity of the insulating film was measured by a laser flash method using an LFA477 Nanoflash manufactured by NETZSCH-Geratebau GmbH. A two-layer model that does not consider the interfacial thermal resistance was used for the measurement. As described above, the thickness of the copper plate was 0.3 mm, and the thermal diffusivity of the copper plate was 117.2 mm ² / sec. For calculating the thermal conductivity of the insulating film, the density of boron nitride was 2.1 g / cm ³ , the specific heat of boron nitride was 0.8 J / gK, the density of polyimide resin was 1.4 g / cm ³ , and the specific heat of polyimide resin was 1.13 J / GK was used.

(4) Flexibility of insulating coating Two copper plates having a thickness of 0.3 mm are stacked, and the coatings of Examples 1 to 28 and Comparative Examples 1 to 8 having a length of 30 cm are placed thereon, along the two copper plates. And bent the insulation film. The bent 30 cm long film was immersed in a phenolphthalein solution, and these films were applied as negative electrodes for 1 minute at 12 V to confirm whether purple reaction products or bubbles were generated (JIS C3216-5). . When no purple reaction product or bubbles appeared, it was determined as “good”, and when one or two purple reaction products or bubbles were observed, it was determined as “good”.

  As is clear from Table 1 and Table 2, when Examples 1-28 and Comparative Examples 1-7 are compared, the value of CV is 150% or less and the value of A is 5 or more. It was found that an insulating film having a good balance between withstand voltage and thermal conductivity can be produced. In addition, when Examples 1 to 28 are compared with Comparative Example 8, when the CV value is 50 or more and the A value is 600 or less, insulation with a balanced withstand voltage and thermal conductivity is achieved. It was found that a film could be produced.

  In addition, when Examples 1 and 5 are compared with Examples 2 to 4 and 6 to 9, when the average particle size of the boron nitride particles is 0.1 μm or more, the balance between withstand voltage and thermal conductivity is further improved. It was found that a detached insulating film could be produced. Further, as apparent from Table 1, when Examples 2, 3, 6-8, 11-13, 15-22 and Examples 4, 5, 9, 10, 14, 23-26 are compared, CV It was found that when the value of 60 to 110% and the value of A was 10 to 300, an insulating film with a better balance between withstand voltage and thermal conductivity could be produced.

  Further, comparing Examples 1 to 26 and Example 27, it was found that when the concentration of the boron nitride particles was 2% by volume or more, an insulating film with a better balance between withstand voltage and thermal conductivity could be produced. It was. Moreover, when Examples 1-26 and Example 28 were compared, when the density | concentration of the boron nitride particle was 45 volume% or less, it turned out that an insulating film with more flexibility can be produced.

  Further, comparing Example 7 and Example 27, it was found that the volume concentration of boron nitride particles is preferably 1% or more. Further, comparing Example 7 and Example 28, it was found that the volume concentration of the boron nitride particles is preferably 40% or less in order to keep the flexibility good. Furthermore, in Comparative Example 9, since the boron nitride particles did not contain the insulating film, the thermal conductivity was 0.21 W / mK, which was low in Examples 1 to 28.

  The insulating film of the present invention is used for an enameled wire covered with the insulating film and a coil wound with the enameled wire.

Claims (4)

  Boron nitride particles are dispersed in the film-forming resin, and when the film thickness is divided by the average particle diameter of the boron nitride particles, A is nitriding with an average particle diameter of A from 5 to 600. An insulating film that uses boron particles and has a CV of 50 to 150% when the coefficient of variation of the concentration of boron nitride particles on the film surface perpendicular to the film thickness is CV.   The insulating film according to claim 1, wherein an average particle diameter of the boron nitride particles is 0.05 μm or more.   The insulating film according to claim 1 or 2, wherein the volume concentration of boron nitride particles in the film is 2 to 30% by volume. An enameled wire having the insulating film according to any one of claims 1 to 3.

Images