JP7174973B2 - COMPOSITE INSULATION BOARD AND METHOD OF MANUFACTURING COMPOSITE INSULATION BOARD - Google Patents

Description

The present invention relates to a composite insulating board containing a filler of a thermally conductive material and a resin and a method for manufacturing the same, and more particularly to a composite insulating board having both good thermal conductivity and sufficient insulation and a method for manufacturing the same.

In new powertrains such as hybrid vehicles, electric vehicles, and fuel cell vehicles, an inverter converts direct current into alternating current in order to drive a drive motor with a direct current power supply from a storage battery. In addition, in order to recover regenerative energy, a converter converts alternating current to direct current and stores it. Power modules such as IGBTs are used in such AC/DC converters. A power module generates heat due to the on-resistance of a semiconductor, and cooling by air cooling or water cooling is required to keep the temperature below the junction temperature of the semiconductor element. Although the junction temperature is about 150° C. in the case of silicon semiconductors, the heat dissipation design is carried out so that the temperature of the device during operation is usually suppressed to about 75 to 85° C. in consideration of thermal deterioration of the device. In the case of air-cooling, metal heat-dissipating fins are used and are joined to the power module via an insulating substrate. In the case of water cooling, a water cooling jacket provided with a conduit through which a cooling medium passes through an insulating substrate is joined to the power module in place of heat radiation fins. Therefore, the insulating substrate is required to have good thermal conductivity in the thickness direction and sufficient insulation and thermal conductivity. The higher the dielectric breakdown strength, the thinner the thickness of the insulating substrate with respect to the required withstand voltage, and the better the heat transfer. A commonly used insulating substrate is a rigid substrate that is neither easily bent nor damaged, and has a thickness of, for example, about 100 μm to 1 mm. Ceramic plates such as silicon nitride, which have relatively high thermal conductivity, are currently used as the insulating substrate, but from the viewpoint of cost reduction, it is desired to further reduce the thickness of the substrate.

However, there is a limit to the further thinning of the ceramic plate due to manufacturing difficulties and mechanical strength problems. Therefore, research and development of an insulating substrate (composite insulating plate) using a composite insulating material composed of a polymer insulating material and a filler is being promoted in various places as an alternative to this.

Many of the composite insulating materials that are being developed are produced by mechanically mixing a base material such as epoxy resin, which is a thermosetting resin, and an inorganic filler such as alumina, which has higher thermal conductivity than resin. be done.

As such a filler, the higher the thermal conductivity and the thermal diffusivity, the better, and the higher the volume specific resistivity and dielectric breakdown strength, the better the electrical properties. Alumina is a common choice due to its properties and low cost.

In such a composite insulating plate, the gaps between the particles due to the contact between the alumina filler particles are weak points in terms of electrical insulation, and the uneven distribution of the alumina filler particles causes electric field concentration due to the difference in dielectric constant from the resin, resulting in insulation. There is no substitute for the performance of the ceramic plate as it degrades performance. In order to solve such problems, research to improve the dispersibility of filler particles and research using nanoparticles are also being conducted, and have a thermal conductivity of about 6 to 12 W / m K. A composite insulating board has been developed (Non-Patent Document 1).

In addition to alumina, inorganic fillers such as aluminum nitride (AlN), silicon nitride (SiC), and boron nitride (BN) are known. Its volume resistivity is equivalent to that of alumina, but its thermal conductivity is 2 to 10 times (60 to 200 W/m K) higher than that of alumina, which is 15 to 30 W/m K, although there is anisotropy depending on the crystal direction. showing high values. Aluminum nitride has good thermal conductivity with a thermal conductivity of 150 to 200 W/m·K, but is extremely expensive. For this reason, although it has anisotropic thermal conductivity, studies are being conducted in various places to make full use of BN as a filler for composite insulating plates (Non-Patent Document 2).

For example, the technology disclosed in Patent Document 1 and Non-Patent Document 3 uses a thermosetting resin such as epoxy resin to mix BN in a liquid state before curing, knead, and then cure to form a composite insulation. It shows a method of orienting BN along electric lines of force by an electric field in a liquid state before hardening when fabricating a plate.

Also, in Non-Patent Document 4 cited above, an attempt is made to produce a composite insulating board using a thermoplastic resin as an insulating base material.

Japanese Patent Application Laid-Open No. 2013-159748

Wang, et al.: IEEE Trans. on DEI, 18(6), Development of Epoxy/BN Composites with High Thermal Conductivity and Sufficient Dielectric Breakdown Strength, pp.1963-1972 (2011) X. Huang, et al.: IEEJ Trans on FM, 133(6), "Boron Nitride Based Poly(phenylene sulfide) Composites with Enhanced Thermal Conductivity and Breakdown Strength", IEEJ Transactions on Fundamentals and Materials, Vol.133, No. 3, pp.66-70 (2013) Kosako, et al.: Proceedings of the 44th Electrical and Electronic Insulating Materials System Symposium, "Reduction of Filler Filling Ratio of Filler-Oriented Epoxy Composite by AC Electric Field", pp.47-51 (2011) Imai, et al.: Proceedings of the 44th Electrical and Electronic Insulating Materials System Symposium, "Material Design of Composite Dielectric Materials for High Frequency Applications" pp.37-40 (2011)

However, in the methods of Patent Document 1 and Non-Patent Document 3 cited above, the kinematic viscosity at room temperature of the epoxy resin is at least about 10 centistokes, which is so high that BN can hardly be oriented by an electric field. Furthermore, Non-Patent Document 1 cited above also discloses a method of mixing BN with epoxy resin in a liquid state before curing and orienting the particles by centrifugation, but due to the viscosity of the liquid, it cannot be oriented.

In the composite insulating plates disclosed in Non-Patent Documents 1 and 2, those having dielectric breakdown strength exceeding 100 kV/mm required by the market have thermal conductivity of about 1 W/m·K or less and 10 W/m·K required by the market. It is a very low value compared to K. On the other hand, those with a thermal conductivity exceeding 10 W/m·K have a dielectric breakdown strength of 60 kV/mm, which is lower than the value required by the market, satisfying both thermal conductivity and dielectric breakdown strength. nothing is obtained.

Furthermore, in Non-Patent Document 4 cited above, an attempt is made to produce a composite insulating board using a thermoplastic resin as an insulating base material. A method is shown in which polypropylene is used as a thermoplastic resin, and BN is melted and kneaded after being heated to a temperature above the thermoplastic temperature, and injection molding is performed. The more difficult it is, the more viscous it is, and the more advanced manufacturing technology is required to uniformly disperse BN.

As shown in such prior art documents, a composite insulating board having both good thermal conductivity and sufficient insulating properties has not yet been provided.

The present invention has been made in view of the above problems, and its object is to appropriately control the degree of orientation of the thermally conductive filler in the insulating resin of the base material, and further to increase the packing density. The improvement is to provide a composite insulating board having good thermal conductivity and sufficient dielectric breakdown strength, and a method of manufacturing the same.

In order to achieve this object, a first invention relating to a composite insulating board is a composite insulating board containing a thermoplastic resin and plate-shaped thermally conductive filler particles having a higher thermal conductivity than the thermoplastic resin. a thermally conductive filler so that the density of the composite insulating plate is 1.8 g/cm ³ or more and the thermal conductivity in the thickness direction of the plate is 15 W/m·K or more and 35 W/m·K or less; The particles are oriented and the dielectric breakdown strength in the thickness direction is 95 kV/mm or more.

A second aspect of the invention is the composite insulating plate having the above structure, wherein the thermally conductive filler particles are hexagonal boron nitride particles.

According to a third invention, in the composite insulating board having any one of the above constructions, the thermoplastic resin is a poly(meth)acrylic acid ester polymer compound.

A first invention relating to a method for manufacturing a composite insulating board is a composite insulating plate in which composite particles are contained in a liquid, which are made by using thermally conductive filler particles as main particles and thermoplastic resin particles adsorbed on the surfaces of the main particles. a slurry preparation step of preparing a slurry having a viscosity lower than the melt viscosity of the thermoplastic resin; an introduction step of introducing the slurry prepared by the slurry preparation step into a cavity having a predetermined volume; By applying a centrifugal force to the slurry introduced into the cavity in a predetermined direction, the composite particles are separated from the liquid by solid-liquid separation and deposited on the surface of the cavity intersecting with the direction of action of the centrifugal force. a separation step, a pressing step of pressing the deposit of the composite particles deposited in the cavity by the centrifugal separation step in the same direction as the direction of action of the centrifugal force to form a compact, and a pressing step. and a hot pressing step of taking out the formed article from the cavity and pressing it in a direction intersecting the pressing direction in the pressing step under an environment having a temperature equal to or higher than the melting point temperature of the resin constituting the thermoplastic resin particles. It is a thing.

In a second aspect of the invention, in the method for manufacturing a composite insulator having the above configuration, the composite particles are obtained by adsorbing thermoplastic resin particles to plate-like thermally conductive filler particles, and the thermally conductive The average particle size of the thermoplastic resin particles is 1/9 to 1/15 of the average particle size of the filler particles.

In a third aspect of the invention, in any one of the above methods for manufacturing a composite insulating board, the composite particles include, in a liquid, thermally conductive filler particles whose surfaces are positively or negatively charged, and the thermally conductive filler particles. The material particles are mixed with thermoplastic resin particles having a surface charged with a charge opposite to that of the material particles, and the thermoplastic resin particles are adsorbed to the surfaces of the thermally conductive filler particles.

According to the composite insulating plate of the present invention, since the density is 1.8 g/cm ³ or more, the thermally conductive filler particles densely filled in the substrate form contact points between the thermally conductive filler particles. A large number of layers can be formed, and an improvement in thermal conductivity can be realized. In addition, the thermally conductive filler particles are oriented in the heat transfer direction so that the thermal conductivity in the thickness direction of the composite insulating plate is 15 W/m·K or more to 35 W/m·K or less. Here, the improvement of the degree of orientation can improve the thermal conductivity in the thickness direction. Decrease can be suppressed. Therefore, there is an effect that it is possible to provide a composite insulating board having a dielectric breakdown strength of 95 kV/mm or more while having good thermal conductivity in the thickness direction.

According to the method for producing a composite insulating plate of the present invention, a slurry containing composite particles in a liquid is introduced into a cavity having a predetermined volume, and a centrifugal force is applied in a predetermined direction to separate solid and liquid. By separating the composite particles from the liquid, they are deposited in a state oriented on a plane intersecting the direction of action of the centrifugal force in the cavity, and then pressed in the direction of action of the centrifugal force, so that the composite particles are oriented and dense. It has the effect of making a molded body. Next, under an environmental temperature higher than the melting point temperature of the thermoplastic resin, the compact is pressed in a direction intersecting with the direction of action of the centrifugal force, thereby increasing the distance between the individual thermally conductive filler particles in the thickness direction of the composite insulating board. is shortened, the outer surfaces of the particles are free of voids, and the composite insulating plate is coated with a thermoplastic resin to provide both good thermal conductivity and sufficient dielectric breakdown strength.

It is a schematic diagram of the cross section of a composite insulating board. It is the figure which showed the production process of a composite insulating board. FIG. 5 is a diagram showing the relationship between dielectric breakdown strength and thermal conductivity of composite insulating plates when the particle size of thermoplastic resin particles is changed. FIG. 10 is a schematic diagram of a molded body released from the mold in the release step of S5. FIG. 4 is a diagram showing the relationship between thermal conductivity and dielectric breakdown strength of various composite insulating plates. 1 is an electron micrograph of composite particles. It is a perspective view of a formwork. 1 is an electron micrograph of a cross section of a composite insulating plate. FIG. 4 is a diagram showing the relationship between dielectric breakdown strength and thermal conductivity of composite insulating boards when molding temperature is changed.

Embodiments of the present invention will be described in detail below.

One embodiment of the composite insulating board is a thermoplastic resin matrix with plate-like thermally conductive filler particles dispersed therein.

The thermoplastic resin contained in the composite insulating plate has insulating properties, and its volume resistivity is about 10 ¹⁵ Ωcm. Specifically, such thermoplastic resins include, for example, polyethylene (PE), ethylene vinyl acetate copolymer (EVA), polypropylene (PP), polystyrene (PS), ABS resin, polymethyl methacrylate (PMMA), poly Examples include vinyl chloride (PVC), polyethylene terephthalate, polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), polyamideimide (PAI), polytetrafluoroethylene (PTFE), polyetheretherketone resin (PEEK), and the like. These thermoplastic resins are selected in consideration of the maximum operating temperature, which is a prerequisite for heat dissipation design. As the thermoplastic resin, one type may be used, or a plurality of types may be mixed and used. Furthermore, it may be a homopolymer or a copolymer.

In general, the higher the heating temperature in the molding process during production, the more stress is generated at the interface between the thermoplastic resin and the filler as it cools, which easily induces separation at the interface. On the other hand, the higher the glass transition point, the better the heat resistance, so that it can be suitably used at higher temperatures.

For example, although the maximum operating temperature is close to 100 to 120.degree. C. for Si-based power modules for automobiles, the thermal design temperature for actual modules is 60 to 70.degree. C. in consideration of thermal deterioration. Preferably the thermoplastic resin is a poly(meth)acrylate. Poly(meth)acrylic acid ester is a polymer of acrylic acid ester or methacrylic acid ester, and has a good volume resistivity of 10 ¹⁶ Ωcm as an insulating property.

In SiC power modules, the maximum operating temperature is about 200°C, and the thermal design temperature exceeds 100°C. PTFE and PAI are candidates for this.

The higher the thermal conductivity and thermal diffusivity of the thermally conductive filler particles contained in the composite insulating plate, the better.

Thermally conductive filler particles generally include alumina (Al ₂ O ₃ ), silica (SiO ₂ ) alumina hydrate (Al ₂ O ₃ .H ₂ O), titanium oxide (TiO ₂ ), aluminum nitride (AlN ), boron nitride (BN), and silicon nitride (SiC).

Here, as the thermally conductive filler particles of the present embodiment, those having a plate-like particle shape are used. The term "plate-like" means that the particles have a plate-like shape with a layered hexagonal crystal structure. Also, the thermally conductive filler particles may have an anisotropic thermal conductivity. The term "anisotropic thermal conductivity" means that thermal conductivity differs between the in-plane direction and the thickness direction of plate-like thermally conductive filler particles. As the average particle diameter of the thermally conductive filler particles increases, gaps form between the particles, preventing the density in the insulating plate from increasing, increasing the amount of resin in the base material, and preventing an increase in thermal conductivity. Also, as the average particle diameter becomes smaller, the packing density increases, but the number of interfaces with the base material increases, which causes a decrease in insulation performance. Therefore, thermally conductive filler particles with an average particle size of 0.5 μm to 60 μm are used, and those with an average particle size of 20 μm to 50 μm are more preferably used.

Hexagonal boron nitride (hereinafter BN) is preferably used in the thermally conductive filler particles described above. Since the crystals of BN particles are layered crystals, they break along the crystal plane, so the BN particles are plate-like, and generally have an average particle size of 0.5 to 60 μm and a thickness of about 0.1 to 3 μm. is. The volume resistivity of BN is equivalent to that of commonly used alumina. The thermal conductivity of BN is twice that of alumina in the thickness direction and ten times in the in-plane direction.

In this embodiment, the particle size of the thermally conductive filler particles is measured by a laser diffraction scattering method. For example, the particle size distribution is measured using a laser scattering particle size analyzer (SALD-3100 manufactured by Shimadzu Corporation), and the particle size (D50) at a cumulative distribution rate of 50% by weight is referred to as "average particle size."

Although not particularly limited, a specific example of the BN of the present invention is "PT-110 (trade name)" (manufactured by Momentive Performance Materials Japan LLC, average particle size 45 μm). Not limited to this, the plate-shaped thermally conductive filler particles can be pulverized and crushed to obtain particles having a predetermined average particle size.

The compounding amount of the thermally conductive filler particles in the composite insulating board is in the range of 40 to 80% by volume. If the amount of the thermally conductive filler particles is 40% by volume or less, sufficient thermal conductivity cannot be obtained. is insufficient, resulting in a composite insulating board with insufficient dielectric breakdown strength. Preferably, the blending amount is in the range of 55 to 70% by volume.

FIG. 1 is a schematic cross-sectional view of the composite insulating plate of this embodiment. This composite insulating board is formed in a rectangular shape when viewed from above, and is displayed so that the upper side of the paper surface is the surface of the composite insulating board.

In such a composite insulating board, the thermally conductive filler particles 1 are dispersed in the thermoplastic resin 2, the thermally conductive filler particles are coated with the thermoplastic resin, adhere to each other, and exist in the thermoplastic resin. . It is set so that both sides thereof are in contact with the semiconductor element and the radiating fins in use. In use, the direction of the arrow in FIG. 1 is the direction of application of the electric field. In this composite insulating plate, the in-plane direction of the thermally conductive filler particles 1 is oriented within a predetermined degree of orientation with respect to the desired direction of heat propagation (thickness direction of the composite insulating plate).

Here, in the present embodiment, the “orientation degree” of the thermally conductive filler particles constituting the composite insulating plate means that the plate-like heat conduction It is an index showing how much the in-plane direction of each of the filler particles 1 is inclined (aligned) with respect to the thickness direction. That is, it is the degree of alignment of the thermally conductive filler particles 1 in the desired direction of heat propagation, and is defined by the thermal conductivity of the composite insulating plate. The angle formed by the in-plane direction of the thermally conductive filler particles with respect to the plane of the composite insulating plate is not constant for each individual thermally conductive filler particle present in the composite insulating plate. The thermal resistance per unit volume in the thickness direction of the composite insulating plate is the thermal resistance of the thermally conductive filler particles present in the unit volume and the thermal resistance of the thermoplastic resin that fills the gaps between the thermally conductive filler particles. It can be calculated by combining series and parallel. Therefore, the thermal conductivity of the composite insulating plate has a certain relationship with the overall orientation of the thermally conductive filler particles in the composite insulating plate. Therefore, the degree of orientation of the thermally conductive filler particles of the composite insulating plate can be represented by the thermal conductivity of the composite insulating plate.

The degree of orientation of the thermally conductive filler particles in the composite insulating plate of this embodiment is such that the thermal conductivity of the composite insulating plate is 15 W/m·K or more to 35 W/m·K or less. If the degree of orientation is such that the thermal conductivity is 15 W/m·K or less, the thermal conductivity of the composite insulating plate is insufficient. In the orientation where the thermal conductivity is 35 W/m·K or more, the dielectric breakdown strength of the composite insulating plate deteriorates rapidly.

The composite insulating plate of this embodiment has a dielectric breakdown strength of 95 kV/mm or more. Preferably, the average dielectric breakdown strength is 110 kV/mm. When the dielectric breakdown strength is 95 kV / mm or less, the thermally conductive filler particles of the composite insulating plate have a high degree of orientation, and the in-plane direction of the thermally conductive filler particles is connected to the thickness direction of the composite insulating plate, which is a weak point in insulation. will increase.

The density of the composite insulating board of this embodiment is 1.8 g/cm ³ or more. If it is 1.8 g/cm ³ or less, the thermal conductivity of the composite insulating board is insufficient.

The thermally conductive filler particles and the thermoplastic resin of the composite insulating plate each have their own dielectric breakdown strength, but due to the difference in dielectric constant between the two, there is deformation of the electric field at the interface, and the electric field is reduced. A high part is created and becomes an insulating weak point. Therefore, as the degree of orientation increases, that is, the in-plane direction of the thermally conductive filler particles is oriented in the direction of the electric field, the interface of the particles becomes continuous in the direction of the electric field, and the insulation performance deteriorates. On the other hand, increasing the degree of orientation improves the thermal conductivity. Thus, since the degree of orientation conflicts with both characteristics, there is an appropriate degree of orientation that has sufficient dielectric breakdown strength and good thermal conductivity, and the conditions of the production method of the present invention are appropriately controlled and used. It is possible to provide a composite insulating board that exhibits the dielectric breakdown strength and thermal conductivity required for the purpose.

The method of manufacturing the composite insulating plate described above is also within the scope of the present invention.

A method of manufacturing a composite insulating board according to one embodiment of the present invention will be described with reference to FIGS. It should be noted that the following embodiment is merely an example of implementing the present invention, and it goes without saying that the embodiment can be changed as appropriate without changing the gist of the present invention.

FIG. 2 is a process drawing showing the method for manufacturing the composite insulating board of the first embodiment.
In this production method, a slurry step (S1) of preparing a slurry containing composite particles in which the thermoplastic resin is adsorbed on the surface of the thermally conductive filler particles to form a composite, and the slurry in which the composite particles are dispersed is introduced into the mold. An introduction step (S2), a centrifugal separation step (S3) in which the composite particles are sedimented by centrifugal force in the mold for solid-liquid separation, a pressing step (S4) in which the sediment is pressurized, and the mold is removed to remove the compact. It is produced through a mold release step (S5) for taking out the molded product, and a hot press step (S6) for pressing while heating the molded product.

Note that the composite particles used in the production method of the present embodiment can also be prefabricated. In addition, in the present embodiment, the method for manufacturing a composite insulating board is constituted by including the manufacturing process (composite particle preparation process (S0)).

Composite particles used in this manufacturing process are composed of main particles (particles with a large particle size), on the surface of which adsorbed particles with a smaller particle size than the main particles are adsorbed, and are integrated as one particle as a whole. The primary particles are thermally conductive filler particles and the adsorbent particles are thermoplastic resin particles.

The primary particles are thermally conductive filler particles with an average particle size of 0.5 μm to 60 μm, and the average particle size of the adsorbent particles is in the range of 1/9 to 1/15 of the average particle size of the primary particles. It is preferably 1/10.

The relationship between the average particle diameters of the thermally conductive filler particles, which are the main particles of the composite particles, and the thermoplastic resin particles, which are the adsorbent particles, greatly affects the dielectric breakdown strength and thermal conductivity of the composite insulating board. Here, with reference to FIG. 3, the effect of the relationship between the average particle size of the main particles and the average particle size of the adsorbent particles on the dielectric breakdown strength and thermal conductivity of the composite insulating board will be described.

As an example, Fig. 3 shows the relationship between dielectric breakdown strength and thermal conductivity when BN particles with an average particle size of 45 µm are used as the main particles and PMMA particles are used as the adsorbent particles, and the average particle size of the PMMA particles is varied from 1 to 12 µm. It is a figure showing.

In FIG. 3, the horizontal axis represents the average particle size of PMMA particles, the left vertical axis represents dielectric breakdown strength (kV/mm), and the right vertical axis represents thermal conductivity (W/m·K). In FIG. 3, the dashed line indicates changes in dielectric breakdown strength, and the solid line indicates changes in thermal conductivity. As can be seen from FIG. 3, the dielectric breakdown strength increases as the particle size of PMMA particles increases, and the dielectric breakdown strength in the case of an average particle size of 4 μm reaches about twice that of the average particle size of 1 μm. However, even if the average particle size of the PMMA particles is further increased to 8 μm and 12 μm, the dielectric breakdown strength does not increase proportionally, and the variation also increases. On the other hand, the thermal conductivity does not change until the PMMA particle size reaches about 4 μm, but it tends to decrease as the particle size increases. The thermal conductivity in the case of 8 μm is about half that of 1 μm. From this, when the average particle size of the BN particles is 45 μm, the optimum PMMA particle size is between 4 μm and 6 μm. This is an example in which the main particles are 45 μm, but even if the average particle size of the main particles is changed, the particle size of the adsorbed particles is in the range of 1/9 to 1/15 as in FIG.

Returning to FIG. 2, description will be made.

In the composite particle preparation step (S0), particles with a smaller particle size (thermoplastic resin particles) are adsorbed as adsorption particles onto the surfaces of main particles with a larger particle size (thermally conductive filler particles) to form composites. In this embodiment, the surface charge of the adsorbing particles and the surface charge of the thermally conductive filler particles are adjusted so that they are opposite to each other. By mixing, the thermoplastic resin particles (adsorption particles) are adsorbed to the thermally conductive filler particles (main particles) by electrostatic attraction.

Here, the case of adjusting the surface charge of the adsorbed particles to be negative and the surface charge of the main particles to be positive will be described. You can

Specifically, the adsorption particles were immersed in a surfactant in order to increase the hydrophilicity and the negative surface potential. Next, the adsorbent particles were immersed in two types of polymer electrolyte solutions in order. These concentrations are sufficient for each solution to adsorb to the entire adsorbent particle surface. The adsorbent particles were washed in ion-exchanged water before being immersed in each solution. Finally, the surface potential of the adsorbed particles was adjusted to be negative. On the other hand, the surface potential of the thermally conductive filler particles was finally adjusted to be positive by the same method, and the main particles were obtained. Adsorbed particles with a negative surface potential and main particles with a positive surface potential were mixed in ion-exchanged water to prepare composite particles in which the adsorbed particles were adsorbed on the surfaces of the main particles by electrostatic interaction.

The slurry step (S1) is a step of mixing the composite particles with a low-viscosity liquid to form a slurry. In this step, by making a slurry using a low-viscosity liquid that does not dissolve the composite particles, the composite particles can be easily densified with a low centrifugal force. The solvent at this time is desirably a low-viscosity liquid containing as few ionic substances as possible. Low viscosity means that the kinematic viscosity at room temperature is about 1 centistoke or less. Ion-exchanged water is preferred.

The introduction step (S2) is a step of putting the slurry prepared in the step of S1 into a mold. In the present embodiment, the formwork is a bottomed container with an open top, preferably with a flat bottom.

The centrifugal separation step (S3) is a step of applying centrifugal force for orienting the composite particles and performing solid-liquid separation. The centrifugal force is calculated by centrifugal force = (number of rotations) x (distance from center of rotation to composite particles) x (weight of composite particles). By applying a centrifugal force to the slurry introduced into the cavity, the composite particles of the slurry are separated from the liquid and deposited on the surface intersecting the direction of action of the centrifugal force. By dispersing the composite particles in a low-viscosity liquid such as water to form a slurry, the composite particles can be easily sedimented by centrifugal force, and the orientation of the composite particles can be improved in the obtained composite particle deposits. can.

There is also a method of increasing the density of composite particles by simply putting them in a mold in a dry powder state without dispersing them in a low-viscosity liquid and applying only mechanical pressure. In addition, gaps are likely to form between particles, preventing a dense structure.

On the other hand, according to the present production method, in the centrifugal separation step (S3), by applying centrifugal force to the mold, the plate surface of the composite particles settles so as to intersect the direction of action of the centrifugal force, and the composite particles are Sediments are formed by sedimentation while being oriented.

The pressing step (S4) is a step of mechanically applying surface pressure to the sediment produced in the centrifugal separation step (S3) in the same direction as the centrifugal force acting direction. In the preceding centrifugal separation step (S3), only the centrifugal force determined by the weight of the composite particles can be applied to the composite particles. Therefore, in order to further increase the density of the deposit, this step of mechanically applying surface pressure in the same direction as the centrifugal force is provided.

The mold release step (S5) is a step of removing the molded body produced in the pressing step (S4) from the mold. FIG. 4 is a schematic diagram of the molded body taken out. The molded article is in a state in which the composite particles are aggregated, and the plate surfaces of the thermally conductive filler particles constituting the composite particles are oriented so as to align with the bottom surface of the molded article.

The hot pressing step (S6) is a step of pressing while heating in the direction intersecting with the centrifugal force (shown in FIG. 4), that is, in the in-plane direction of the composite particles, at a temperature higher than the melting point temperature of the thermoplastic resin and lower than the heat resistance temperature. The duration of hot pressing is a time appropriately determined according to the melting temperature of the thermoplastic resin. Through this process, the thermoplastic resin reaches a melting point temperature or higher, melts, and flows to the interfaces of the thermally conductive filler particles to form a resin layer so as to eliminate gaps. The temperature at the time of hot pressing is set above the melting point determined by the composition of the thermoplastic resin. The higher the heating temperature of the hot press, the higher the fluidity of the resin, and the easier it is to flow between the filler particles. Therefore, even if the packing density of the filler particles is increased in order to increase the thermal conductivity and the gaps between the filler particles are reduced, the resin flows more easily, so that the dielectric breakdown strength can be prevented from lowering. The upper limit of the heating temperature is a temperature lower than the temperature at which the polymer constituting the resin begins to deteriorate. By increasing the hot press pressure, the distance between the thermally conductive filler particles can be shortened, voids in the thermoplastic resin can be expelled, and the density of the composite insulating board can be increased. A force is applied to bring the oriented thermally conductive filler particles closer to each other in the in-plane direction, and the gaps existing between the thermally conductive filler particles are eliminated or the distance is shortened, resulting in a decrease in thermal resistance. . Furthermore, the ends (side surfaces) of some of the thermally conductive filler particles are in direct contact with each other. This is because in the composite particles, the thermoplastic resin particles are adsorbed on the plate surface of the thermally conductive filler particles, and the particle size of the thermoplastic resin particles is sufficiently large compared to the thickness of the thermally conductive filler particles on the plate. Since it is difficult to adsorb to the side surfaces of the thermally conductive filler particles, the thermally conductive filler particles come into direct contact with each other under the pressure during hot pressing. If this step is carried out in a vacuum, voids in the resin can be further eliminated and the dielectric breakdown strength can be improved.

For the insulating property and thermal conductivity of the composite insulating plate produced by the manufacturing method of the present invention, values measured by the following evaluation methods are used. In addition, since the characteristics of the composite insulating plate differ greatly depending on the direction, the measured value in the direction of actual use, that is, the thickness direction is used.

The insulation evaluation method will be explained. A composite insulating plate of the present invention is polished with abrasive paper to a thickness of about 1 mm as a sample, which is sandwiched between a pair of McKeon type electrodes to prevent dielectric breakdown in the air on the surface of the sample. , the sample and electrodes were molded with epoxy resin. A DC lamp voltage was applied at room temperature with a rate of increase of 1 kV/sec, and the dielectric breakdown voltage was measured. The dielectric breakdown strength (kV/mm) was calculated by dividing the dielectric breakdown voltage by the actual sample thickness after the McKeon electrode system was produced. The test is performed several times, preferably 10 times or more, with different samples, and the average value is taken as the "dielectric breakdown strength".

A method for evaluating thermal conductivity will be described. A disc having a diameter of 10 mm and a thickness of 1 mm was cut out from the composite insulating plate of the present invention as a sample, and thermal diffusivity (m ² /sec) and specific heat capacity (J/g·K ) and As for the thermal conductivity (W/m·K), the value calculated from this measured value and the density measured at room temperature by the Archimedes method is defined as “thermal conductivity”.

Experimental examples for verifying the effects of the manufacturing method of the present invention will be described below. FIG. 5 is a diagram showing the relationship between dielectric breakdown strength and thermal conductivity when manufacturing conditions are changed using the manufacturing method of the present invention. In the figure, the vertical axis is dielectric breakdown strength (kV/mm), and the horizontal axis is thermal conductivity (W/m·K). Plots marked with x and + in the figure are the results disclosed in Non-Patent Documents 1 and 2 cited above.

In Non-Patent Document 1, composite insulating boards are manufactured using BN as thermally conductive filler particles and an epoxy resin under different manufacturing conditions, and dielectric breakdown strength and thermal conductivity are measured. According to the results, the dielectric breakdown strength of the composite insulating plate manufactured here exceeds the 100 kV/mm required by the market, but the thermal conductivity is about 1 W/m·K or less, which is the 10 W/m required by the market.・It is a very low value compared to K. On the other hand, those with a thermal conductivity exceeding 10 W/m·K have a dielectric breakdown strength of 60 kV/mm, which is lower than the value required by the market, satisfying both thermal conductivity and dielectric breakdown strength. nothing is obtained.

Similarly, in Non-Patent Document 2, the dielectric breakdown strength of the composite insulating plate having the same configuration is 60 kV/mm or less and the thermal conductivity is 1 W/m·K or less, which are extremely low values.

(Experimental example 1)
Plot A in FIG. 5 shows the thermal conductivity and dielectric breakdown strength of sample A produced under the following conditions. The thermal conductivity was 19±2 W/m·K, and the average dielectric breakdown strength (X) was 110 kV/mm. The standard deviation (σ) of the dispersion of dielectric breakdown voltage at this time was 5%. The lower limit of the dielectric breakdown strength considering variations is X(1-2σ), that is, 99 kV/mm when calculated with a probability of occurrence of 95%.

As the thermoplastic resin for sample A, polymethyl methacrylate (PMMA) was used. Since the maximum operating temperature of Si-based power modules for automobiles is 100 to 120°C and the thermal design temperature of actual modules is 60 to 70°C, PMMA with good formability was selected. As the thermally conductive filler particles, the hexagonal BN "PT-110 (trade name)" (manufactured by Momentive Performance Materials Japan LLC) was used. BN has a plate-like crystal particle shape similar to graphite, and has a thermal conductivity of 200 W/m·K in the in-plane direction, which is more than three times the thermal conductivity of 60 W/m·K in the thickness direction.

In this example, composite particles were produced in step S0 using a thermoplastic resin and thermally conductive filler particles. For the composite particles, BN having an average particle size of 45 μm in the in-plane direction was used as main particles (particles having a large particle size). A thermoplastic resin, PMMA, was used as the adsorbent particles around the large main particles. Since the average particle diameter of the adsorbent particles is preferably 1/10 of the average particle diameter of the main particles, it is set to 4 μm.

Next, the PMMA particles were immersed in sodium deoxycholate (SDC), a surfactant, at a concentration of 5 g/l in order to increase the hydrophilicity of the PMMA particle surface and at the same time increase the negative surface potential. Next, the PMMA particles were immersed in polyelectrolyte polydiallyldimethylammonium chloride (PDDA) with a concentration of 50 g/l and polystyrene sodium sulfonate (PSS) with a concentration of 10 g/l in this order. The concentrations of SDC, PDDA and PSS were sufficient for their adsorption over the entire PMMA surface. The PMMA particles were washed in deionized water before being immersed in each solution. Finally, the surface potential of PMMA particles was adjusted negatively. On the other hand, the BN particles were finally adjusted to have a positive surface potential in the same manner as the main particles. PMMA-adsorbed particles with a negative surface potential and BN main particles with a positive surface potential were mixed in ion-exchanged water to fabricate composite particles in which the PMMA-adsorbed particles were adsorbed on the surface of the BN main particles by electrostatic interactions. FIG. 6 is an electron micrograph showing that PMMA particles with an average diameter of about 4 μm are uniformly adsorbed on the outer surface of BN single particles. The plate surface of the BN single particle is covered with spherical PMMA particles, and no PMMA particles are adsorbed on the edges in the thickness direction of the plate.

The composite particles produced in step S0 were dissolved in deionized water having a conductivity of 1 to 10 μS/cm in step S1 to form a slurry.

In step S2, the slurry prepared in step S1 was introduced into a mold (FIG. 7) having a plate-like cavity measuring 12 mm×40 mm and 3 mm thick.

In step S3, centrifugal force was applied to the formwork containing the slurry in step S2 in the direction of the arrow in the figure using a centrifuge. A centrifugal force of about 5 μN per composite particle was applied for 10 minutes to effect solid-liquid separation and sedimentation of the composite particles. The centrifugal force per particle was calculated by centrifugal force = (number of rotations) x (distance from center of rotation) x (weight of composite particles). Here, the number of revolutions: 3000 rpm, the average distance from the center of rotation to the composite particles: 1700 mm, the weight of the composite particles: 2.87 × 10 ^-9 g [= (PMMA density: 1.2 g/cm ³ ) × (PMMA particles Volume: 3.35×10 ⁻¹¹ cm ³ )+(BN density: 2.1 g/cm ³ )×(BN volume: 1.35×10 ⁻⁹ cm ³ )]. By applying centrifugal force in a direction that intersects the lower surface (A surface) of the formwork, the plate-like surface of the composite particles settles toward the bottom surface of the formwork, and the slurry liquid escapes through the gaps in the formwork. yielded a deposit of composite particles 12 mm x 13 mm and 3 mm thick.

In step S4, mechanical pressure is applied in the same direction as the centrifugal force acting direction with a plate having the same shape as the opening 3 of the formwork, and the deposit of 12 mm × 13 mm and 3 mm thick is compressed to 12 mm × 10 mm and 3 mm thick. A molded body was obtained.

In step S5, the compact produced in step S4 was removed from the mold.

In the step of S6, hot pressing was performed for 1 hour at a temperature of 160° C., which is higher than the melting point of PMMA, in the thickness direction of 3 mm of the compact produced in the step of S5. PMMA softens at 80 to 100°C and melts and thermoforms at 160 to 260°C, so hot pressing was performed at 160°C here. The hot press pressure is 50 MPa on the surface of φ10 mm.

FIG. 8 is an electron micrograph of a cross section of a composite insulating plate produced by such a process. The plate-shaped BN particles are oriented in the direction of the thickness of the composite insulating plate (vertical direction in the photo) where the electric field is applied, and the outer surface of the BN particles is coated with PMMA. Some of the BN particles are in contact with each other in the thickness direction. This is because the composite particles, in which PMMA particles of an appropriate particle size are uniformly attached to the surface of the BN particles, are melted by heating and the PMMA particles cover the surface of the BN particles. This is because the end surfaces of the BN particles are in contact with each other.

The composite insulating plate of this example had a density of 1.84 g/cm ³ and a blending amount of BN particles of 59% by volume. The BN particles used here had a density of 2.1 g/cm ³ and the PMMA particles had a density of 1.2 g/cm ³ .

(Experimental example 2)
Sample B plotted at B in FIG. 5 is a sample for which the effect of the pressing step of S4 was verified by omitting the step of S4 in the manufacturing method and conditions of sample A. That is, in step S3, the composite particles are oriented by a centrifuge, liquid is removed by solid-liquid separation, and a sediment is produced. It is a sample that was removed from the formwork in the step of , and hot-pressed in the step of S6. B had a dielectric breakdown strength about 20% higher than that of A, but its thermal conductivity was about half. The composite insulating plate of Sample B had a density of 1.82 g/cm ³ and a blending amount of BN particles of 57% by volume. The density of sample A increased by 0.02 g/ ^cm3 compared to sample B, and the omitted step S4 increased the density of the composite insulating plate by applying a force in the same direction as the sedimentation of the composite particles. It has a boosting effect. Furthermore, the degree of orientation of BN in sample A is increased by the step of S4. As a result, the through-thickness heat flow resistance of Sample A was lower than that of Sample B over the entire surface, and the thermal conductivity was greatly reduced. In addition, the degree of orientation of BN in sample A is higher than in sample B, and the number of interfaces in the in-plane direction of the BN particles in the direction of the electric field increases, so the discharge easily progresses in the in-plane direction of the BN interface, and the dielectric breakdown strength decreases. did. That is, by controlling the degree of orientation and density by centrifugal force and mechanical force, it is possible to manufacture a composite insulating plate having required dielectric breakdown strength and thermal conductivity. Although not described here, since the degree of orientation and mechanical strength are closely related, the process conditions of the present invention are combined to have mechanical strength according to the application, good thermal conductivity and sufficient dielectric breakdown. A strong composite insulating board can be fabricated.

(Experimental example 3)
In order to see the effect of the density of the composite insulating plate, sample C plotted in FIG. This is the prepared sample. The dielectric breakdown strength of this sample was lowered by about 10% in average value compared to sample A, but the thermal conductivity was increased by about 10% in average value. The composite insulating plate of this example had a density of 1.94 g/cm ³ and a blending amount of BN particles of 68% by volume. The density of the composite insulating board increased by 0.1 g/ ^cm3 . This is because the amount of BN particles increased from 59% by volume of sample A to 68% by volume due to the decrease in the number of PMMA particles in the composite insulating plate, which increased the heat flow path and thermal conductivity. It is considered that the increase in BN particles increased the number of electrical weak points, and the dielectric breakdown strength of sample C was lower than that of sample A.

(Experimental example 4)
The compact produced in the steps S1 to S5 described in Experimental Example 1 was hot-pressed in the thickness direction of 3 mm in the step S6 at a temperature of 120° C. and 200° C. for 1 hour. The hot press pressure is 50 MPa on the surface of φ10 mm. In FIG. 9, with respect to the hot pressing temperature on the horizontal axis, the left vertical axis is the dielectric breakdown strength, and the right vertical axis is the thermal conductivity. Although it was about 10% lower than the one, the thermal conductivity was 33.4 w/m·K, which is 1.7 times.

As described above, a composite insulating board can be manufactured according to the embodiment of the manufacturing method. The present invention includes a composite insulating board manufactured by such a manufacturing method.

1 Thermally conductive filler particles 2 Thermoplastic resin 3 Mold opening (cavity opening)

Claims (7)

by polymethyl methacrylate (PMMA) Thermoplastics and their higher thermal conductivity than thermoplasticsby boron nitride (BN)A composite comprising plate-shaped thermally conductive filler particles, a thermal conductivity in the thickness direction of 15 W/m·K or more and 35 W/m·K or less, and a dielectric breakdown strength in the thickness direction of 95 kV/mm or more An insulating plate,
with an average particle size of 4 μm The thermoplastic resinaccording toThe average grain size in the base material45The thermally conductive filler particles of μm are dispersed, and the in-plane direction of the thermally conductive filler particles is oriented in a predetermined direction,
The density of the composite insulating plate is set to 1.8.2 to 1.94g/cm ³ Whenis to
A composite insulating board characterized by: 2. The composite insulating board according to claim 1, wherein said thermally conductive filler particles are adhered to each other while being coated with said thermoplastic resin. 3. The in-plane direction of the thermally conductive filler particles is oriented according to a desired degree of orientation based on the degree of orientation represented by the thermal conductivity when oriented in the direction in which heat is to be propagated. The composite insulating plate according to . It contains a thermoplastic resin and plate-shaped thermally conductive filler particles having higher thermal conductivity than the thermoplastic resin, and has a thermal conductivity in the thickness direction of 15 W/m·K or more and 35 W/m·K or less. Yes, and the dielectric breakdown strength in the thickness direction is 95 kV/mm or more A method for manufacturing a composite insulating board, comprising:
Composite particles comprising thermally conductive filler particles as main particles and thermoplastic resin particles adsorbed on the surfaces of the main particles are contained in a liquid, and the viscosity is lower than the melt viscosity of the thermoplastic resin. A slurry preparation step of preparing a slurry of
an introduction step of introducing the slurry prepared in the slurry preparation step into a cavity having a predetermined volume;
By applying a centrifugal force in a predetermined direction to the slurry introduced into the cavity in the introduction step, the composite particles are separated from the liquid by solid-liquid separation, and the composite particles are separated from the liquid on a plane intersecting the direction of action of the centrifugal force of the cavity. a sedimentary centrifugation step;
A pressing step of pressing the deposit of the composite particles deposited in the cavity by the centrifugal separation step in the same direction as the direction of action of the centrifugal force to form a compact;
The molded body produced by the pressing step is taken out from the cavity, and the resin constituting the thermoplastic resin particles is removed.Melting temperature or higher, heat resistant temperature or lowerA hot pressing step of pressing in a direction intersecting the pressing direction in the pressing step under the environment of
A method of manufacturing a composite insulating board, comprising: The composite particles are obtained by adsorbing thermoplastic resin particles to plate-like thermally conductive filler particles, and the average particle size of the thermoplastic resin particles is greater than the average particle size of the thermally conductive filler particles. 5. The method of manufacturing a composite insulating board according to claim 4 , wherein the ratio is 1/9 to 1/15. The composite particles are composed of thermally conductive filler particles whose surfaces are positively or negatively charged and thermoplastic resin particles whose surfaces are charged oppositely to the thermally conductive filler particles in a liquid. 6. The method for producing a composite insulating board according to claim 4 , wherein the thermoplastic resin particles are adsorbed on the surfaces of the thermally conductive filler particles. 7. The method for producing a composite insulating board according to claim 4 , wherein the liquid kinematic clay constituting said slurry has a viscosity of 1 centistoke or less at room temperature.

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