JP2017066014A - Resin-coated boron nitride powder, and dispersion liquid thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin-coated boron nitride powder capable of stably producing an insulation film having high dielectric strength and heat conductivity and containing a boron nitride particle for a long period of time without damaging heat conductivity of boron nitride, and a dispersion liquid of the resin-coated boron nitride powder, in which the dispersed boron nitride hardly coagulates after preparation of the dispersion liquid.SOLUTION: In the resin-coated boron nitride powder of the present invention, a part or an entire part of the surface of a primary particle of boron nitride, or a part or an entire part of the surface of a coagulated particle of the primary particles is coated with a binder resin. The binder resin is preferably a polyimide resin, a polyamide-imide resin, a polyesterimide resin, a polyester resin, or a polyurethane resin, or a mixed resin thereof. In the dispersion liquid of the present invention, the boron nitride powder is dispersed in a dispersion medium such as NMP.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a resin-coated boron nitride powder that can stably produce an insulating film containing boron nitride particles and having a high withstand voltage and high thermal conductivity for a long period of time without impairing the thermal conductivity of boron nitride. The present invention also relates to a dispersion of a resin-coated boron nitride powder in which the dispersed boron nitride is less likely to aggregate after the dispersion is prepared. More specifically, the present invention relates to a resin-coated boron nitride powder suitable as a heat conductive filler for an insulating electrodeposition coating, and a dispersion suitable as an insulating electrodeposition coating.

  In order to use boron nitride powder as a filler for an insulating electrodeposition coating, it is necessary to use boron nitride in the form of a dispersion. However, boron nitride tends to agglomerate with time, and it has been difficult to prepare a dispersion, ie, a suspension, having long-term stability.

  Until now, in order to improve the dispersibility of boron nitride, the hexagonal boron nitride powder has been modified with a silane coupling agent (see, for example, Patent Document 1), or the boron nitride powder has been polyoxyethylene-based ions. A surfactant is dispersed in water as a dispersant (for example, see Patent Document 2), or is dispersed in water using a nonionic water-soluble cellulose ether and a polycarboxylate-based dispersant. (For example, refer to Patent Document 3).

JP 2012-056818 A (Claim 1) JP-A-6-219714 (Claim 1, paragraph [0001]) JP-A-8-127793 (Claim 1, paragraph [0001])

  However, when the surface of the boron nitride powder is modified with a silane coupling agent, boron nitride has few functional groups on the surface that can react with the silane coupling agent, so that the effect of the surface treatment is limited. When surface oxidation treatment is performed to increase the reactivity, the thermal conductivity of the powder may be lowered. Further, when boron nitride is obtained by dispersing boron nitride using a dispersant, when used as an electrodeposition solution, if diluted with a solvent, the dispersant is removed by a so-called solvent shock, and boron nitride is removed. There was a risk of aggregation. That is, the above-described method has a problem that after the dispersion is prepared by a method that does not impair the thermal conductivity, the dispersed boron nitride tends to aggregate and it is difficult to obtain a stable dispersion and electrodeposition solution over time.

  The first object of the present invention is to solve the above-mentioned problems, and an insulating film containing boron nitride particles and having a high withstand voltage and high thermal conductivity can be stably produced over a long period of time without impairing the thermal conductivity. It is to provide a resin-coated boron nitride powder. The second object of the present invention is to provide a dispersion of resin-coated boron nitride powder in which the dispersed boron nitride powder is less likely to aggregate after the dispersion is prepared.

  A first aspect of the present invention is a resin-coated boron nitride powder in which part or all of the surface of boron nitride primary particles or part or all of the surface of aggregated particles of the boron nitride primary particles is coated with a binder resin. is there.

  The second aspect of the present invention is an invention based on the first aspect, wherein the binder resin is a polyimide resin, a polyamideimide resin, a polyesterimide resin, a polyester resin or a polyurethane resin, or a resin obtained by mixing these resins. Boron nitride powder.

  A third aspect of the present invention is a dispersion obtained by dispersing the resin-coated boron nitride powder of the first or second aspect in a dispersion medium.

  A fourth aspect of the present invention is the invention based on the third aspect, wherein the dispersion medium is N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc ), 1,3 dimethylimidazolidinone, dimethyl sulfoxide (DMSO) or γ-butyrolactone (γBL).

  The fifth aspect of the present invention was prepared by adding the poor solvent of the polymer to the dispersion of the third or fourth aspect and a solution obtained by dissolving the polymer in an organic solvent, and mixing the mixture to precipitate the polymer. This is a method for producing an insulating electrodeposition paint by mixing a polymer dispersion.

  According to a sixth aspect of the present invention, after the insulating layer made of the resin is formed on the surface of the copper wire by the electrodeposition method using the insulating electrodeposition paint manufactured by the method of the fifth aspect, the baking treatment is performed. Thus, the copper wire is coated with an insulating film made of the resin to manufacture an enameled wire.

  A seventh aspect of the present invention is a method of manufacturing a coil by winding an enamel manufactured by the method of the sixth aspect.

  The resin-coated boron nitride powder according to the first aspect of the present invention can be dispersed without impairing the thermal conductivity of boron nitride because boron nitride particles are coated with a binder resin.

  By using a polyimide resin, a polyamideimide resin, a polyesterimide resin, a polyester resin, a polyurethane resin, or a resin obtained by mixing these as a binder resin for forming the resin-coated boron nitride powder according to the second aspect of the present invention, the aggregated particles Has strong adhesive strength and high heat resistance.

  In the dispersion according to the third aspect of the present invention, since the resin-coated boron nitride powder according to the first or second aspect is dispersed in the dispersion medium, the dispersed boron nitride powder is dispersed after the dispersion is prepared. It is difficult to aggregate in the liquid.

  The dispersion medium according to the fourth aspect of the present invention is N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), 1,3 dimethylimidazolidinone, dimethyl sulfoxide. Since it is (DMSO) or γ-butyrolactone (γBL), there is an advantage that the binder resin is well dissolved.

  In the method for producing an insulating electrodeposition paint according to the fifth aspect of the present invention, since the resin-coated boron nitride powder according to the first or second aspect is included as a heat conductive filler, the heat conduction of the insulating film obtained from this paint is achieved. The degree and withstand voltage can be increased stably over the long term. In addition, if the same resin as the binder resin used in the production of the resin-coated boron nitride powder is used as the polymer, this insulating film can be formed without creating an extra interface in the insulating film obtained using this paint. The thermal conductivity can be kept high, and the adhesion of the boron nitride powder to the resin matrix is improved.

  The enameled wire manufacturing method of the sixth aspect of the present invention is an electrodeposition coating method using the paint manufactured by the method of the fifth aspect as an insulating electrodeposition coating for forming an insulating film of copper wire. Therefore, the enamel wire can be uniformly formed on the surface of the copper wire with the insulating film. The insulating film of the enameled wire manufactured from the seventh viewpoint is flexible, and is excellent in that there are no defects such as pinholes after processing. It also has high heat conductivity and high heat resistance.

  The enameled wire manufacturing method according to the seventh aspect of the present invention is formed by winding the enameled wire manufactured according to the sixth aspect, and is excellent in terms of heat dissipation.

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.

[Resin coated boron nitride powder]
The resin-coated boron nitride powder of the present invention is formed by covering a part or all of the surface of primary particles of hexagonal boron nitride with a binder resin, or the surface of aggregated particles of primary particles of hexagonal boron nitride. Part or all is formed by being coated with a binder resin. Examples of the binder resin include a polyimide resin, a polyamideimide resin, a polyesterimide resin, a polyester resin, a polyurethane resin, or a resin obtained by mixing these. The binder resin is characterized by strong adhesion, high flexibility, and high withstand voltage. Of these, polyamide-imide resin is particularly preferable because it has a good balance between solubility and heat resistance. The resin-coated boron nitride powder of the present invention does not need to be coated with the binder resin on the entire surface of the primary particles of the hexagonal boron nitride, or the entire surface of the aggregated particles of the primary particles. It suffices that the coating is performed at a sufficient ratio, for example, a ratio of 50 area% or more of the surface.

  In 100 mass% of the resin-coated boron nitride powder, it is preferable to contain 80 to 99 mass% of primary particles or aggregated particles of hexagonal boron nitride and 1 to 20 mass% of the binder resin. When the content of the binder resin is closer to the lower limit, for example, 1 to 5% by mass, a part of the primary particle surface of the hexagonal boron nitride or a part of the aggregated particle surface is coated with the binder resin, and the upper limit is reached. The closer it is, for example, 15 to 20% by mass, the entire primary particle surface of the hexagonal boron nitride or the entire aggregated particle surface is covered with the binder resin. If the binder resin content is less than the lower limit value, the binding force of the primary particles of boron nitride is poor, and the aggregation tends to break.If the binder resin content exceeds the upper limit value, the portion that precipitates only with the resin increases, and the process Becomes less efficient.

[Method for producing resin-coated boron nitride powder]
First, primary particles of hexagonal boron nitride having an average particle diameter of more than 1 μm and not more than 10 μm are prepared. Next, the primary particles and the binder resin described above are added and mixed in a first solvent at room temperature to prepare a dispersion in which the binder resin is dissolved and the primary particles are dispersed. At this time, firstly, primary particles of hexagonal boron nitride are added to and mixed with the first solvent, the primary particles are dispersed in the first solvent, then a binder resin is added, and the binder resin is added to the first solvent. Dissolution is preferable because the primary particles can be sufficiently dispersed. As the first solvent, N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), 1,3 dimethylimidazolidinone, dimethyl, in which the binder resin can be dissolved, are used. Examples include sulfoxide (DMSO) or γ-butyrolactone (γBL). In 100% by mass of the solid component in the dispersion, the primary particles and the binder resin are respectively added so that the primary particles of hexagonal boron nitride are 80 to 99% by mass and the binder resin is 1 to 20% by mass. It is preferable to add. If the amount of the primary particles added is less than the lower limit, there is a problem that the portion that precipitates only with the resin increases, and if the upper limit is exceeded, the amount of hexagonal boron nitride powder that is not coated with the resin increases. is there. If the addition amount of the binder resin is less than the lower limit value, the surface of the primary particles of hexagonal boron nitride is not sufficiently covered, and the dispersion effect is limited. When the upper limit is exceeded, the portion that precipitates only with the resin increases, and the process becomes inefficient. Here, the average particle diameter of the primary particles of hexagonal boron nitride is a particle diameter measured using a laser diffraction particle size distribution analyzer (LA960 manufactured by Horiba, Ltd.).

  Next, the dispersion is stirred. In stirring, the dispersion at room temperature is stirred using a stirrer at a rotational speed of 500 to 50000 rpm to uniformly disperse the primary particles of hexagonal boron nitride. Alternatively, dispersion may be performed by applying ultrasonic waves. Subsequently, a second solvent for precipitating the binder resin dissolved in the dispersion is added to the stirring dispersion. Examples of the second solvent include water, methanol, and ethanol, which are poor solvents for the binder resin. The second solvent is preferably added dropwise at a rate of 10 to 100 mL / min for 0.1 to 1 minute in order to uniformly precipitate the binder resin and to uniformly aggregate the primary particles. By adding the poor solvent of the second solvent, the binder resin is precipitated on the surface of the primary particles of boron nitride in which the binder resin is dispersed in the dispersion. As a result, resin-coated boron nitride powder is formed in the dispersion.

  When removing the resin-coated boron nitride powder from the dispersion, the dispersion is solid-liquid separated using a filter, a centrifuge, etc., and the solid content is dried at a temperature of 50 to 120 ° C. Boron powder is obtained. Further, as will be described later, when the dispersion is used as a raw material for the insulating electrodeposition coating, it is not necessary to take out the resin-coated boron nitride powder from the dispersion.

[Method of manufacturing insulating electrodeposition paint]
The insulating electrodeposition coating material of the present invention is prepared by first adding water, which is a poor solvent for the polymer, to a solution in which the polymer is dissolved in an organic solvent to precipitate the polymer to prepare a polymer dispersion. The resin-coated boron nitride powder is prepared by adding and mixing to this polymer dispersion. When the resin-coated boron nitride powder is used in the state of being dispersed in the above-described dispersion, an insulating electrodeposition coating is prepared by adding and mixing the dispersion of the resin-coated boron nitride powder to the polymer dispersion. .

  The polymer is preferably a polyimide resin, a polyamideimide resin, a polyesterimide resin, a polyester resin, a polyurethane resin, an acrylic resin, an epoxy resin, an epoxy-acrylic resin, an acrylic styrene resin, or a resin obtained by mixing these. Among these, by using the same resin as the binder resin used in the production of the resin-coated boron nitride powder as a polymer, the adhesion of the insulating electrodeposition paint is improved, and an extra particle interface is not created. This is particularly preferable in that the thermal conductivity can be kept high and the electrodeposition conditions can be made constant.

  Examples of the organic solvent include N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (γBL), anisole. 1 type (s) or 2 or more types chosen from tetramethylurea and sulfolane.

  In this embodiment, a polyimide dispersion is prepared using a solvent-soluble polyimide resin as a polymer and NMP as an organic solvent. Specifically, first, a polyimide solution in which a polyimide resin is dissolved in NMP is prepared. Next, a neutralizing agent is added to the polyimide solution and stirred to neutralize the polyimide, and then water which is a poor solvent for the polyimide is added and mixed and stirred to precipitate the polyimide. Here, basic compounds such as aminoethanol, triethylamine, triethanolamine, and pyridine can be used as the neutralizing agent. The polyimide dispersion thus prepared is a suspension in which polymer particles made of polyimide resin are dispersed. It is preferable that 1 to 15% by mass of polymer particles made of polyimide resin is dispersed in 100% by mass of the polyimide dispersion.

  The average particle size of the polymer particles of this embodiment is preferably 0.01 to 10 μm, more preferably 0.05 to 1 μm. Here, the average particle diameter of the polymer particles is a particle diameter measured using a particle size distribution measuring apparatus (LA-950 manufactured by Horiba, Ltd.), and is a volume-based average particle diameter.

  The insulating electrodeposition paint of the present invention is prepared by adding and mixing the above-mentioned resin-coated boron nitride powder in a polyimide dispersion and uniformly dispersing it. It is preferable to add 5 to 50% by mass of the resin-coated boron nitride powder in 100% by mass of the solid content in the insulating electrodeposition coating. If the addition amount of the resin-coated boron nitride powder is less than the lower limit, the thermal conductivity of the insulating film made from this insulating electrodeposition coating is difficult to improve. On the other hand, if the amount added exceeds the upper limit, the concentration of the resin-coated boron nitride powder 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 above-mentioned insulating electrodeposition paint will be described with reference to the drawings. As shown in FIG. 1, an insulating layer (not shown) is formed by electrodepositing the insulating electrodeposition coating 11 on the surface of a copper wire 12 by an electrodeposition coating method using an electrodeposition coating apparatus 10. 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 insulating electrodeposition paint 11 is stored in the electrodeposition tank 18 and maintained at 5 to 60 ° C., and the rectangular electrodeposited paint wire 11 in the electrodeposition tank 18 is filled with a rectangular copper wire 12. Let it pass. Here, a cathode 19 electrically connected to the negative electrode of the DC power source 14 is inserted into the insulating electrodeposition coating 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 insulating electrodeposition coating 11 in the electrodeposition tank 18, a DC voltage in the range of 1 to 300 V is applied by the DC power source 14 to the rectangular copper wire 12 and the insulating electrodeposition coating 11. Is applied for 0.01 to 30 seconds. As a result, the water-dispersed polymer particles (not shown) as the insulating electrodeposition coating material 11 and the resin-coated boron nitride powder are electrodeposited on the surface of the flat 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 baking the rectangular copper wire 12 having an insulating layer electrodeposited on the surface. In this embodiment, the copper wire 12 having the insulating layer formed on the surface is passed through the baking furnace 22. The baking treatment is preferably performed in a hot air heating furnace. Moreover, it is preferable that the temperature of a baking process exists in the range of 100-500 degreeC, and it is preferable that the time of a baking process exists in the range of 1-10 minutes. Here, the reason why the temperature of the baking treatment is limited to the range of 100 to 500 ° C. is that when the temperature is less than 100 ° C., the insulating layer cannot be sufficiently dried and cured, and when the temperature exceeds 500 ° C., the polymer is thermally decomposed. . The reason for limiting the baking time to 1 to 10 minutes is that the insulating layer cannot be sufficiently dried and cured if it is less than 1 minute, and if it exceeds 10 minutes, the resin is thermally decomposed. Note that the temperature of the baking treatment is the temperature of the central portion in the 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 a resin-coated boron nitride powder is manufactured. By winding this enamel wire 23 around a winding frame such as a plastic bobbin using an automatic winding machine (for example, a flat wire edgewise coil winding machine HIT-01, manufactured by Nittoku Engineering Co., Ltd.), a coil ( (Not shown) is formed. Although not shown, the insulating layer may be dried and baked at a temperature of 200 to 250 ° C. in the same furnace.

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

<Example 1>
First, primary particles of hexagonal boron nitride having an average particle diameter of 4 μm (SP3: manufactured by Denki Kagaku Kogyo Co., Ltd.) are prepared. After adding the primary particles to N-methylpyrrolidone (NMP), water was added. 20% by mass of the primary particles and 10% by mass of water were added to and mixed with 100% by mass of NMP. The mixed solution was ultrasonically applied to uniformly disperse the primary particles. Next, a polyamideimide resin was added to the dispersion at a ratio of 10% by mass with respect to 100% by mass of NMP, and the mixture was stirred at a rotational speed of 10,000 rpm to dissolve the polyamideimide resin in NMP. While stirring the solution in which the polyamideimide resin was dissolved, 2.5 g of water, which is a poor solvent for the polyamideimide resin, was added dropwise to this solution. As a result, the polyamideimide resin was precipitated, the polymer particles adhered to the surface of the primary particles of hexagonal boron nitride, and the resin-coated boron nitride powder was formed by stirring. The liquid was filtered, and the solid content was dried to obtain a resin-coated boron nitride powder. Subsequently, this resin-coated boron nitride powder was added to an NMP solution in a ratio of 30% by mass of pure water and 70% by mass of NMP so as to have a concentration of 5% by mass, and an ultrasonic wave was applied to prepare a dispersion. In this dispersion, another dispersion in which 7% by mass of polymer particles made of a polyamideimide resin as a base resin is dispersed is adjusted so that the ratio of the polyamideimide resin is 80% by mass in the solid content of the dispersion. An insulating electrodeposition paint was prepared by addition.

  Here, the polyimide dispersion is composed of 66% by mass of NMP, 7% by mass of water, 20% by mass of 1-methoxy-2-propanol, and 0.1% by mass of 100% by mass of the polyimide dispersion. What dispersed the polymer particle which consists of aminoethanol and a polyimide resin 7 mass% was used. After producing the insulating electrodeposition paint, it is electrodeposited on the surface of a copper plate having a thickness of 0.3 mm by an electrodeposition coating method to form an insulating layer having a thickness of 40 μm, which is dried at 250 ° C. for 3 minutes in an air atmosphere. An insulating film was produced by baking treatment.

<Example 2>
Resin-coated boron nitride powder was obtained in the same manner as in Example 1, except that a polyimide resin was used instead of the polyamide-imide resin for forming the resin-coated boron nitride powder of Example 1.

<Example 3>
Resin-coated boron nitride powder was obtained in the same manner as in Example 1, except that a polyesterimide resin was used instead of the polyamide-imide resin for forming the resin-coated boron nitride powder of Example 1.

<Example 4>
Resin-coated boron nitride powder was obtained in the same manner as in Example 1, except that a polyester resin was used instead of the polyamide-imide resin for forming the resin-coated boron nitride powder of Example 1.

<Example 5>
Resin-coated boron nitride powder was obtained in the same manner as in Example 1, except that a polyurethane resin was used instead of the polyamide-imide resin for forming the resin-coated boron nitride powder of Example 1.

<Example 6>
Instead of the primary particles of hexagonal boron nitride in Example 1, primary particles of hexagonal boron nitride having an average particle diameter of 8 μm (GP: manufactured by Denki Kagaku Kogyo Co., Ltd.) were used. A resin-coated boron nitride powder was obtained. Further, an insulating film was produced in the same manner as in Example 1.

<Example 7>
Resin in the same manner as in Example 1 except that primary particles of hexagonal boron nitride having an average particle diameter of 16 μm (PCTP16: manufactured by Saint Gobain) were used instead of the primary particles of hexagonal boron nitride in Example 1. Coated boron nitride powder was obtained. Further, an insulating film was produced in the same manner as in Example 1.

<Comparative Example 1>
The primary particles of hexagonal boron nitride (SP3: manufactured by Denki Kagaku Kogyo Co., Ltd.), which is the starting material of Example 1, was used as Comparative Example 1. That is, an insulating film was produced from the primary particles in the same manner as in Example 1 without using the primary particles as resin-coated boron nitride powder.

<Comparative example 2>
The primary particles of hexagonal boron nitride (GP: manufactured by Denki Kagaku Kogyo Co., Ltd.), which is the starting material of Example 6, was used as Comparative Example 2. That is, an insulating film was produced from the primary particles in the same manner as in Example 1 without using the primary particles as resin-coated boron nitride powder.

<Comparative Example 3>
The primary particles of hexagonal boron nitride (PCTP16: manufactured by Saint Gobain), which is the starting material of Example 7, was used as Comparative Example 3. That is, an insulating film was produced from the primary particles in the same manner as in Example 1 without using the primary particles as resin-coated boron nitride powder.

<Comparative example 4>
Primary particles of hexagonal boron nitride (SP3: manufactured by Denki Kagaku Kogyo Co., Ltd.), which is the starting material of Example 1, are prepared. The primary particles were dispersed in ethanol at a ratio of 5% by mass, and a silane coupling agent (KBM-603: manufactured by Shin-Etsu Chemical Co., Ltd.) was added to the dispersion to 2% by mass with respect to the boron nitride powder. . This solution was stirred at room temperature for 24 hours, and then the reaction solution was filtered. Further, the solid content was dried at 120 ° C. for 12 hours to obtain a boron nitride powder modified with amino groups. An insulating film was produced from this boron nitride powder in the same manner as in Example 1 without using this boron nitride powder as a resin-coated boron nitride powder.

<Comparative Example 5>
Primary particles of hexagonal boron nitride (SP3: manufactured by Denki Kagaku Kogyo Co., Ltd.), which is the starting material of Example 1, are prepared. The primary particles were dispersed in water to a concentration of 5% by mass with a sodium cholate dispersant (2% by mass added to boron nitride), and ultrasonic waves were applied to obtain a boron nitride powder dispersion. This dispersion was used as it was to obtain boron nitride powder treated with a dispersant. An insulating film was produced from this boron nitride powder in the same manner as in Example 1 without using this boron nitride powder as a resin-coated boron nitride powder.

<Comparative test and evaluation 1>
NMP solution of 30% by mass of pure water and 70% by mass of NMP so that the boron nitride powder or the hexagonal boron nitride primary particles obtained in Examples 1 to 7 and Comparative Examples 1 to 4 have a concentration of 1% by mass. And a dispersion was prepared by applying ultrasonic waves. These dispersions were (1) immediately after preparation, (2) 5 hours after preparation, and (3) 24 hours after preparation, and the particle size distribution measuring device (LA-960, manufactured by Horiba, Ltd.) as a solution. It was determined median diameter D ₅₀ by measuring the particle size distribution using. As for Comparative Example 5, the dispersion prepared in Comparative Example 5 was added to an NMP solution having a ratio of 30% by mass of pure water and 70% by mass of NMP so that the boron nitride concentration was 1% by mass, and ultrasonic waves were applied. A dispersion was prepared. Thereafter, (1) immediately after preparation, (2) 5 hours after preparation, and (3) 24 hours after preparation, measurement was performed using a particle size distribution analyzer (Horiba, LA-960), and the median It was determined diameter _{D 50.} The dispersion was stirred at a rotational speed of about 50 rpm until 5 hours passed and 24 hours passed. The results are shown in Table 1.

As apparent from Table 1, when examining the particle size distribution of the boron nitride powder of the dispersion of Comparative Examples 1 to 3 and Comparative Examples 4 and 5, the average particle diameter D ₅₀ in accordance with the lapse of time from the preparation of the dispersion increases did. In contrast, examining the particle size distribution of the boron nitride powder of a dispersion of Examples 1-7, the dispersion average particle diameter D ₅₀ over time from the preparation of hardly changed.

<Comparative test and evaluation 2>
Insulating films were prepared every time elapsed after the dispersions of the boron nitride powders or the hexagonal boron nitride primary particles obtained in Examples 1 to 7 and Comparative Examples 1 to 5 were prepared. Specifically, an insulating film was prepared from (1) the dispersion immediately after preparation, (2) the dispersion after 5 hours from the preparation, and (3) the dispersion after 24 hours from the preparation. The thermal conductivity and withstand voltage of these insulating films were measured by the following methods, respectively. These results are shown in Table 2.

(1) Thermal conductivity of insulating film The thermal conductivity in the vertical direction 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.

(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. .

  As is clear from Table 2, the withstand voltage and thermal conductivity of the insulating films of Examples 1 to 7 are the withstand voltages of the insulating films made immediately after the preparation, even after 5 hours and 24 hours from immediately after the preparation. And almost no change compared to thermal conductivity. On the other hand, the withstand voltage and heat conduction of the insulating coatings made after 5 hours and after 24 hours from the preparation of the insulating electrodeposition coating containing the boron nitride powder not coated with the resin of Comparative Examples 1 to 3 A rate falls compared with the withstand voltage and heat conductivity of Comparative Examples 1-3 immediately after preparation. That is, the insulating electrodeposition coating material of boron nitride powder not coated with resin lacks storage stability, whereas the insulating electrodeposition coating materials of Examples 1 to 7 coated with resin have good storage stability and are stable over a long period of time. In particular, it was found that an insulating film excellent in withstand voltage and thermal conductivity was produced.

  Further, the withstand voltage and heat of an insulating film produced after 5 hours and 24 hours from the preparation of an insulating electrodeposition coating containing boron nitride powder obtained by treating hexagonal boron nitride with the silane coupling agent of Comparative Example 4 The conductivity is lower than the withstand voltage and thermal conductivity immediately after preparation of Comparative Example 4. That is, the insulating electrodeposition paint of Comparative Example 4 is also not sufficiently stable in storage. Further, the withstand voltage and thermal conductivity of an insulating film formed after 5 hours and 24 hours from the preparation of an insulating electrodeposition coating containing boron nitride powder obtained by treating hexagonal boron nitride with the dispersant of Comparative Example 5 Decreases compared to the withstand voltage and thermal conductivity immediately after preparation of Comparative Example 5. That is, the insulating electrodeposition paint of Comparative Example 5 is also not sufficiently stable in storage.

  In addition, when using the insulating electrodeposition paints of Comparative Examples 1 to 5, considering the result that the film characteristics deteriorate with time, this result shows that the decrease in withstand voltage is caused by the aggregation of the boron nitride powder. This is thought to be due to the formation of internal vacancies and the unevenness of boron nitride concentration due to the increase in particle size, resulting in the formation of a locally high portion of boron nitride concentration, which tends to cause dielectric breakdown. . The reason why the thermal conductivity slightly decreases is considered to be that voids are generated inside the aggregated particles. On the other hand, the withstand voltage and the thermal conductivity of the insulating film made after 5 hours and 24 hours from the preparation of the insulating electrodeposition paint containing the resin-coated boron nitride powder of Examples 1 to 7 are As compared with the respective withstand voltages and thermal conductivities immediately after preparing the insulating electrodeposition paints containing the resin-coated boron nitride powders of Examples 1 to 7, there is almost no decrease. This is because the resin-coated boron nitride powder is less likely to agglomerate, so there are no vacancies derived from the agglomerated particles, and the boron nitride concentration in the film is more uniform, so local dielectric breakdown is less likely to occur. Conceivable.

  The resin-coated boron nitride powder of the present invention is used as a filler for an insulating electrodeposition coating, and is used for an insulating film made from this insulating electrodeposition coating. Further, the resin-coated boron nitride powder is used for an enameled wire coated with this insulating film and a coil wound with the enameled wire. A dispersion of resin-coated boron nitride powder is used as an insulating electrodeposition coating.

Claims (7)

  A resin-coated boron nitride powder in which a part or all of the surface of the boron nitride primary particles or a part or all of the surface of the aggregated particles of the boron nitride primary particles is coated with a binder resin.   The resin-coated boron nitride powder according to claim 1, wherein the binder resin is a polyimide resin, a polyamideimide resin, a polyesterimide resin, a polyester resin, a polyurethane resin, or a resin obtained by mixing these.   A dispersion obtained by dispersing the resin-coated boron nitride powder according to claim 1 or 2 in a dispersion medium.   The dispersion medium is N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), 1,3 dimethylimidazolidinone, dimethyl sulfoxide (DMSO) or γ-butyrolactone ( The dispersion according to claim 3, which is γBL).   The dispersion according to claim 3 is mixed with a polymer dispersion prepared by adding a poor solvent of the polymer to a solution in which the polymer is dissolved in an organic solvent, and precipitating the polymer, thereby insulating the dielectric. A method of manufacturing a paint.   The insulating layer made of the resin is formed on the surface of the copper wire by the electrodeposition method using the insulating electrodeposition coating produced by the method according to claim 5, and then the baking process is performed to remove the copper wire from the resin. A method for producing an enameled wire by coating with an insulating film.   A method of manufacturing a coil by winding an enameled wire manufactured by the method according to claim 6.

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