Alumina powder, resin composition, and method for producing alumina powder

Abstract

To provide alumina powder capable of realizing a thin film-like thermally conductive member exhibiting high thermal conductivity; a resin composition with high thermal conductivity, containing alumina powder, capable of realizing the thin film-like thermally conductive member; and a method of manufacturing the alumina powder.SOLUTION: According to alumina powder, the alumina powder comprises alumina particles each having a circle-equivalent diameter of less than 0.3 μm. A particle diameter D10 of 10% accumulation from a fine particle side of an accumulation particle size distribution on a number basis is less than 0.15 μm. The particle diameter D10, a particle diameter D100 of 100% accumulation from the fine particle side of the accumulation particle size distribution on the number basis, and a particle diameter D50 of 50% accumulation from the fine particle side of the accumulation particle size distribution on the number basis satisfy formula (1): 4.0≤(D100-D10) / D50≤20. When viewing at least 5 visual fields at a magnification of 10000, a variation coefficient CV (Na / Nb) of a particle ratio (Na / Nb) of the number of alumina particles Na each having a circle-equivalent diameter of less than 0.3 μm to the number of alumina particles Nb each having a circle-equivalent diameter of 0.3 μm or more is 0.3 or less.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to alumina powder, a resin composition, and a method for producing alumina powder.

Background Art

[0002] Heat generated by energizing an electronic component tends to have an adverse effect on the performance of the electronic component, so it is desirable to dissipate the heat promptly. Therefore, the material constituting the heat conductive member for heat dissipation is desired to exhibit high thermal conductivity. As one of the above heat conductive members, there is a heat conductive resin composition containing a resin and inorganic particles, and alumina particles are used as the inorganic particles.

[0003] As the above alumina particles, for example, alumina particles obtained by firing aluminum hydroxide by the Bayer method shown in Patent Document 1, having a BET specific surface area of 5 to 9 m 2 / g, D10 = 0.1 to 0.2 μm, D50 = 0.3 to 0.5 μm, D90 = 0.7 to 2 μm in the particle size distribution, and 80% by mass or more being 1 μm or less, and easily sinterable alumina particles having defined Mg content, Na content, Si content, and Ca content can be mentioned.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, there has been a demand for thin, sheet-like thermal conductive materials for heat dissipation, such as those with a thickness of tens of microns or even just a few microns. Furthermore, these thermal conductive materials are required to exhibit even higher thermal conductivity. To achieve high thermal conductivity, it is necessary to disperse alumina particles in the resin at a high concentration and uniformly.

[0006] However, when a large amount of alumina particles, as shown in Patent Document 1, are incorporated into a resin, the alumina particles tend to aggregate, and coarse particles tend to form in the resin composition. As a result, it is difficult to achieve high thermal conductivity, and it is also difficult to make the thermal conductive material into a thin film.

[0007] This disclosure has been made in view of the above circumstances, and its purpose is to provide an alumina powder that has high thermal conductivity and can realize a thin-film thermal conductive member, a resin composition containing the alumina powder that has high thermal conductivity and can realize a thin-film thermal conductive member, and a method for producing the alumina powder. [Means for solving the problem]

[0008] One aspect of the present invention is: Alumina powder having alumina particles with an equivalent circular diameter of less than 0.3 μm, The particle size D10 of the cumulative particle size distribution based on the number of particles, where the cumulative percentage from the finest particle side is 10%, is less than 0.15 μm. The particle size D10, the particle size D100 representing 100% of the cumulative particle size distribution based on the number of particles from the finest particle side, and the particle size D50 representing 50% of the cumulative particle size distribution based on the number of particles from the finest particle side satisfy the following equation (1): This alumina powder has a coefficient of variation (CV(Na / Nb)) of 0.3 or less when observed at least five fields of view at a magnification of 10,000x, where the number of alumina particles (Na) with an equivalent circle diameter of less than 0.3 μm is equal to the number of alumina particles (Nb) with an equivalent circle diameter of 0.3 μm or more. 4.0≦(D100-D10) / D50≦20 (1)

[0009] Aspect 2 of the present invention is, The alumina particles having an equivalent circular diameter of less than 0.3 μm are the alumina powder described in Embodiment 1, wherein the average circularity is 0.82 or greater.

[0010] A third aspect of the present invention is: The alumina powder according to embodiment 1 or 2, wherein the alumina particles having an equivalent circular diameter of less than 0.3 μm are α-alumina particles.

[0011] Aspect 4 of the present invention is This is a resin composition comprising alumina powder and resin as described in any of embodiments 1 to 3.

[0012] Aspect 5 of the present invention is The resin composition according to embodiment 4, wherein the mass ratio of the alumina powder to the resin is in the range of 85:15 to 95:5.

[0013] Aspect 6 of the present invention is, A raw material preparation step involves preparing alumina raw material particles with an equivalent circle diameter of less than 0.3 μm and a blended raw material containing alumina raw material particles with an equivalent circle diameter of 0.3 μm or more. A method for producing alumina powder, comprising a mixing step of mixing the aforementioned blending materials using a high-speed mixer with a rotation speed of 10,000 rpm or more. [Effects of the Invention]

[0014] According to this disclosure, it is possible to provide an alumina powder that has high thermal conductivity and can realize a thin-film thermal conductive member, a resin composition containing the alumina powder that has high thermal conductivity and can realize a thin-film thermal conductive member, and a method for producing the alumina powder. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is an SEM image of the alumina raw material particles 2 used in the example. [Figure 2] Figure 2 is an SEM image of the alumina raw material particles 5 used in the example. [Figure 3]Figure 3 is a diagram showing the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measuring device for the alumina raw material particles 2 and the alumina raw material particles 5 used in the examples. [Figure 4] Figure 4 is a diagram showing an example of the binarization process performed in the examples. [Figure 5] Figure 5 is a SEM image of the cross-sectional sample of Example 1. [Figure 6] Figure 6 is another SEM image of the cross-sectional sample of Example 1. [Figure 7] Figure 7 is a SEM image of the cross-sectional sample of Comparative Example 1. [Figure 8] Figure 8 is another SEM image of the cross-sectional sample of Comparative Example 1. [Figure 9] Figure 9 is a SEM image of the cross-sectional sample of Comparative Example 3.

Mode for Carrying Out the Invention

[0016] The present inventors have intensively studied to realize alumina powder with high thermal conductivity that can realize a thin film-like thermal conductive member, a resin composition containing the alumina powder and having high thermal conductivity that can realize a thin film-like thermal conductive member, and further a method for producing the above alumina powder. As a result, as the above alumina powder, it has alumina particles with an equivalent circle diameter of less than 0.3 μm. When the particle size at 10% cumulative on the fine particle side of the cumulative particle size distribution based on the number is defined as D10, the particle size at 50% cumulative is defined as D50, and the particle size at 100% cumulative is defined as D100, while defining the range of D10, D10, D50, and D100 satisfy a predetermined formula, and further when observed under a predetermined condition, the coefficient of variation CV(Na / Nb) of the particle ratio (Na / Nb) of the number of alumina particles Na with an equivalent circle diameter of less than 0.3 μm and the number of alumina particles Nb with an equivalent circle diameter of 0.3 μm or more, which is a parameter indicating the dispersion state of the alumina particles, is found to be below a certain value.

[0017] Hereinafter, the alumina powder according to the present embodiment, the resin composition containing the alumina powder, and the method for producing the alumina powder will be described in detail in order.

[0018] [Alumina powder] (Contains alumina particles with an equivalent diameter of less than 0.3 μm) The alumina powder according to this embodiment contains alumina particles with an equivalent circle diameter of less than 0.3 μm (hereinafter sometimes referred to as "small alumina particles"). The alumina powder according to this embodiment may also contain alumina particles with an equivalent circle diameter of 0.3 μm or more (hereinafter sometimes referred to as "large alumina particles"), within the range that includes small alumina particles and satisfies the specified particle size distribution described later. The lower limit of the equivalent circle diameter of small alumina particles may be, for example, 0.01 μm. The upper limit of the equivalent circle diameter of large alumina particles may be 3 μm or less.

[0019] (D10 refers to the particle size that represents the cumulative 10% from the finest particles in the cumulative particle size distribution based on the number of particles.) In this embodiment, the alumina powder has a particle size D10 (hereinafter sometimes simply referred to as "D10") of less than 0.15 μm at the cumulative 10% from the fine side of the cumulative particle size distribution based on the number of particles. By including fine alumina particles with a particle size of less than 0.15 μm in the alumina powder, these alumina particles are present in the gaps formed between the larger alumina particles, making it easy to achieve high packing and improve thermal conductivity. Furthermore, the presence of these alumina particles on the surface of relatively large alumina particles improves the fluidity of the alumina powder in the resin when manufacturing the resin composition. Preferably, D10 is 0.10 μm or less. However, from the viewpoint of fluidity when mixing with the resin composition, the lower limit of D10 may be around 0.01 μm.

[0020] (Span value: (D100-D10) / D50) In this embodiment, the alumina powder satisfies the following equation (1) when D10, D100 (the particle size at which 100% of the cumulative particle size distribution from the finest side of the particle count-based cumulative particle size distribution is accumulated) and D50 (the particle size at which 50% of the cumulative particle size distribution from the finest side is accumulated). Hereinafter, (D100-D10) / D50 in equation (1) below may be referred to as the "span value". 4.0≦(D100-D10) / D50≦20 (1)

[0021] The above span value is an indicator of the spread of the particle size distribution. When the above span value falls below 4.0, the difference between the particle size of small alumina particles and the particle size of large alumina particles becomes small. As a result, when the particle size of small alumina particles is close to that of large alumina particles, it becomes difficult to fill the gaps formed between the relatively large alumina particles with fine alumina particles. On the other hand, when the particle size of large alumina particles is close to that of small alumina particles, the majority of the alumina powder consists of relatively small particles, and as a result, it becomes difficult to ensure excellent thermal conductivity and good fluidity. The above span value is preferably 4.1 or higher, more preferably 4.3 or higher, and even more preferably 5.3 or higher.

[0022] On the other hand, if the above span value exceeds 20, it is assumed that the particle size (D50) of relatively large alumina particles will be 5 μm or larger. In this case, considering the particle size distribution of large alumina particles, it becomes difficult to realize a thin-film thermal conductive member, and for example, a thin-film thermal conductive member with a film thickness of 10 μm or less cannot be realized. The above span value is preferably 15 or less, more preferably 12 or less, even more preferably 6.3 or less, and most preferably 6.0 or less.

[0023] (CV(Na / Nb) is the coefficient of variation of the particle ratio (Na / Nb) between the number of alumina particles Na with an equivalent circular diameter of less than 0.3 μm and the number of alumina particles Nb with an equivalent circular diameter of 0.3 μm or more.) The alumina powder according to this embodiment satisfies the condition that when observed at a magnification of 10,000x for at least 5 fields of view, the coefficient of variation of the particle ratio (Na / Nb) between alumina particles with an equivalent circle diameter of less than 0.3 μm (Na) and alumina particles with an equivalent circle diameter of 0.3 μm or more (Nb) is 0.3 or less.

[0024] The alumina powder according to this embodiment yields a resin composition with high dispersibility of the alumina powder and suppressed generation of aggregated particles, even when a large amount of alumina powder is mixed and kneaded with a resin. As a result, thermal conductivity is increased, enabling the realization of a thin-film thermally conductive member. To demonstrate that the alumina powder according to this embodiment disperses well in the resin composition, unlike conventional products, this embodiment uses CV(Na / Nb), which is the coefficient of variation of the particle ratio (Na / Nb) between the number of alumina particles Na with an equivalent circle diameter of less than 0.3 μm and the number of alumina particles Nb with an equivalent circle diameter of 0.3 μm or more, as an evaluation index for the dispersibility of the alumina powder.

[0025] Furthermore, the coefficient of variation CV(Na / Nb) mentioned above can be determined by observing at least 5 fields of view at a magnification of 10,000x. The evaluation of the coefficient of variation CV(Na / Nb) can be performed using a scanning electron microscope.

[0026] To obtain alumina powder that satisfies the above coefficient of variation CV(Na / Nb), it is important to mix the alumina raw material particles using a high-speed mixer with a rotation speed of 10,000 rpm or more, as described in the alumina powder manufacturing method described later, rather than mixing them using conventional methods.

[0027] The coefficient of variation CV(Na / Nb) is preferably 0.25 or less, and more preferably 0.20 or less. The smaller the coefficient of variation CV(Na / Nb), the better.

[0028] (Average circularity of alumina particles with an equivalent circle diameter of less than 0.3 μm) In this embodiment, the alumina powder preferably has an average circularity of 0.82 or higher for alumina particles with an equivalent circle diameter of less than 0.3 μm. Preferably, a higher circularity of the alumina particles allows for greater fluidity during mixing and kneading with the resin. The average circularity of the alumina particles is more preferably 0.85 or higher, and a higher average circularity is preferable, but equivalent fluidity can be ensured if it is 0.95 or lower.

[0029] (Crystal structure of alumina particles with an equivalent circle diameter of less than 0.3 μm) In this embodiment, it is preferable that the alumina powder contains α-alumina particles with an equivalent circle diameter of less than 0.3 μm. The presence of α-alumina particles can be confirmed, for example, by measuring the alumina powder using powder X-ray diffraction and comparing the peak height of the α-phase (012 plane) appearing at 2θ = 25.6° with the peak height of other phases, such as the γ-phase, appearing at 2θ = 46°, from the obtained diffraction spectrum. Alternatively, when evaluating using a resin composition, a thin section of about 0.1 μm in thickness can be prepared using a focused ion beam (FIB), and particles with an equivalent circle diameter of less than 0.3 μm can be confirmed by electron diffraction.

[0030] On the other hand, the crystal structure of alumina particles with an equivalent circle diameter of 0.3 μm or more is not limited. For example, it may be one or more of α-alumina, θ-alumina, γ-alumina, and δ-alumina. From the viewpoint of improving thermal conductivity, it is preferable that the alumina particles with an equivalent circle diameter of 0.3 μm or more are α-alumina particles.

[0031] [Method for producing alumina powder] The method for producing alumina powder according to this embodiment is as follows: A raw material preparation step involves preparing alumina raw material particles with an equivalent circle diameter of less than 0.3 μm and a blended raw material containing alumina raw material particles with an equivalent circle diameter of 0.3 μm or more. The process includes a mixing step of mixing the aforementioned raw materials using a high-speed mixer with a rotational speed of 10,000 rpm or more.

[0032] (Raw material preparation process) A blended raw material containing alumina raw material particles with an equivalent circle diameter of less than 0.3 μm and alumina raw material particles with an equivalent circle diameter of 0.3 μm or more is prepared, but the method for producing these alumina raw material particles is not particularly limited. For example, commercially available products can be used, or they can be produced by conventionally known methods.

[0033] For alumina raw material particles with an equivalent circle diameter of less than 0.3 μm, the average circularity is preferably 0.82 or higher. More preferably, the average circularity of alumina raw material particles with an equivalent circle diameter of less than 0.3 μm is 0.85 or higher, and a higher value is preferable, but it may also be 0.95 or lower. The average circularity of alumina raw material particles with an equivalent circle diameter of 0.3 μm or more is not particularly limited.

[0034] The alumina raw material particles with an equivalent circle diameter of less than 0.3 μm are preferably α-alumina raw material particles. Examples of alumina raw material particles with an equivalent circle diameter of 0.3 μm or more include alumina raw material particles composed of one or more of α-alumina, θ-alumina, γ-alumina, and δ-alumina. From the viewpoint of obtaining alumina powder with high thermal conductivity, it is also preferable that the alumina raw material particles with an equivalent circle diameter of 0.3 μm or more are α-alumina raw material particles.

[0035] To obtain the alumina powder of this embodiment in which D10 and a predetermined span value are within the above-mentioned range, it is preferable to blend alumina raw material particles with an equivalent circle diameter of less than 0.3 μm and alumina raw material particles with an equivalent circle diameter of 0.3 μm or more in a blending ratio (mass ratio) of, for example, 40:60 to 10:90.

[0036] The aforementioned blended raw materials may contain silane coupling agents, dispersants, etc., for the purpose of improving fluidity during mixing.

[0037] (Mixing process) The coefficient of variation CV(Na / Nb) is as described above. is within the above range To obtain alumina powder that satisfies the above requirements, it is important not only to prepare a blended raw material containing alumina raw material particles with an equivalent circle diameter of less than 0.3 μm and alumina raw material particles with an equivalent circle diameter of 0.3 μm or more, but also to use a method for mixing these alumina raw material particles. In the method for producing alumina powder according to this embodiment, a high-speed mixer with a rotation speed of 10,000 rpm or more is used as a means for mixing the particles of different particle sizes, thereby sufficiently suppressing the formation of aggregates and achieving the above coefficient of variation CV(Na / Nb) is within the above rangeAlumina powder that satisfies the requirements can be obtained. As a result, by mixing and kneading the alumina powder with a resin, the aggregation of the alumina powder is sufficiently suppressed, and a resin composition containing alumina powder that is highly packed yet dispersible can be obtained.

[0038] A high-speed mixer with a rotational speed of 10,000 rpm or more is a device that mixes powders at a high rotational speed of 10,000 rpm or more, such as a batch mill or a rotor speed mill. Conventional mixing devices used for mixing powders, such as air blenders, rocking blenders, Henschel mixers (all with rotational speeds of 470-5400 rpm), and planetary stirring mixers (with rotational speeds of 2000 rpm or less), have difficulty breaking down aggregated particles of alumina small particles with an equivalent circle diameter of less than 0.3 μm, and aggregated particles remain when resin compositions are produced. As a result, it is difficult to produce thin-film resin compositions, such as very thin resin compositions with a film thickness of 5 μm or less. Furthermore, by using a high-speed mixer, aggregated particles of alumina small particles with an equivalent circle diameter of less than 0.3 μm can be broken down and dispersed on the primary particle surface of alumina raw material particles with an equivalent circle diameter of 0.3 μm or more. In addition, re-aggregation of alumina raw material particles with an equivalent circle diameter of 0.3 μm or more is prevented, and as a result, the coefficient of variation CV(Na / Nb) is within the above range Alumina powder that satisfies the requirements can be obtained.

[0039] [Resin composition] The resin composition according to this embodiment comprises the alumina powder according to this embodiment and a resin. By using the alumina powder according to this embodiment as, for example, a filler for a thermally conductive resin composition, a resin composition (composite) with high thermal conductivity can be obtained.

[0040] To ensure the thermal conductivity of the resin composition, the proportion (blending ratio) of alumina powder according to this embodiment contained in the resin composition is preferably 40% by volume or more, and more preferably 50% by volume or more. On the other hand, from the viewpoint of ensuring the flexibility characteristic of the resin, the proportion of alumina powder is preferably 90% by volume or less, and more preferably 85% by volume or less. The resin composition according to this embodiment preferably has a high concentration of alumina powder, which can exhibit higher thermal conductivity. A preferred embodiment of the resin composition with a high concentration of alumina powder is one in which the mass ratio of alumina powder to resin is in the range of 85:15 to 95:5.

[0041] The resin used in the resin composition can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. The resin may be used alone or in combination of two or more types.

[0042] Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers; fluorine-based polymers such as polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, polyvinyl acetal, polyvinylidene fluoride, and polytetrafluoroethylene; polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate; polystyrene, polyacrylonitrile, styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene copolymer (ABS) resin; polyphenylene-ether copolymer (PPE) resin; modified PPE resin; aliphatic polyamides; aromatic polyamides; polyimides; polyamide-imides; polymethacrylic acid esters such as polymethacrylic acid and polymethyl methacrylate; polyacrylic acids; polycarbonates; polyphenylene sulfide; polysulfone; polyethersulfone; polyethernitrile; polyetherketone; polyketone; liquid crystal polymers; silicone resins; and ionomers.

[0043] Examples of thermoplastic elastomers include styrene-butadiene block copolymers or their hydrogenated derivatives, styrene-isoprene block copolymers or their hydrogenated derivatives, styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers.

[0044] Examples of thermosetting resins include crosslinked rubber, epoxy resin, phenolic resin, polyimide resin, unsaturated polyester resin, and diallyl phthalate resin. Specific examples of crosslinked rubber include natural rubber, acrylic rubber, butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber, nitrile rubber, hydrogenated nitrile rubber, chloroprene rubber, ethylene-propylene copolymer rubber, chlorinated polyethylene rubber, chlorosulfonated polyethylene rubber, butyl rubber, halogenated butyl rubber, fluororubber, urethane rubber, and silicone rubber.

[0045] From the viewpoint of processability and properties, polyolefin resins, acrylic resins, polyimide resins, polyamide resins, polyamide-imide resins, epoxy resins, phenolic resins, and silicone resins are preferably used.

[0046] Furthermore, these resin compositions may optionally contain, individually or in combination of two or more known additives, such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, antiblocking agents, antistatic agents, leveling agents, and mold release agents, as long as they do not impair the effects of the invention.

[0047] A method for producing a resin composition will now be described. A resin composition can be obtained by mixing the alumina powder and resin according to this embodiment. For example, if the resin is liquid (e.g., liquid epoxy resin), the resin composition can be obtained by mixing the liquid resin, alumina powder, and curing agent, and then curing it with heat or ultraviolet light. Known curing agents, mixing methods, and curing methods can be used. On the other hand, if the resin is solid (e.g., polyolefin resin or acrylic resin), the desired resin composition can be obtained by mixing the alumina powder and resin and then kneading them by a known method such as melt kneading.

[0048] Embodiments of the resin composition according to this embodiment include a compound obtained by blending raw materials containing alumina powder and resin, a mixture obtained by mixing raw materials containing alumina powder and resin, a molded product obtained by molding the mixture, and a molded product (cured product) obtained by, for example, curing the mixture or molded product.

[0049] One embodiment of the resin composition according to this embodiment is a thin film resin composition, and as a further example, a thin film resin composition having a film thickness of, for example, 10 μm or less, and moreover, 5 μm or less. [Examples]

[0050] The present invention will be described in more detail below with reference to examples. The present invention is not limited by the following examples, and can be implemented with appropriate modifications within the scope that is consistent with the spirit described above and below, and all such modifications are included within the technical scope of the present invention.

[0051] [Preparation of alumina raw material particles] As alumina raw material particles, alumina raw material particles 1 to 5, as described below, were prepared. The crystalline phase of each raw material particle was determined by analyzing its crystal structure using X-ray diffraction. In this specification, "particle size" refers to the volume-based median diameter measured with a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Microtrac Bell), and is distinct from the aforementioned D50. (Alumina raw material particles 1) Product name: AA-07 (manufactured by Sumitomo Chemical Co., Ltd.), granules Diameter: 0.9 μm, crystalline phase: α-alumina (Alumina raw material particles 2) Development product 1 (manufactured by Sumitomo Chemical Co., Ltd.), granules Diameter: 0.15 μm, Crystalline phase: α-alumina (Alumina raw material particles 3) Development product 2 (manufactured by Sumitomo Chemical Co., Ltd.), granules Diameter: 0.10 μm, Crystalline phase: α-alumina (Alumina raw material particles 4) Product name: ASFP-20 (manufactured by Denka Co., Ltd.), granules Diameter: 0.3 μm, crystalline phase: θ-alumina and δ-alumina (Alumina raw material particles 5) Product name: AKP-53 (manufactured by Sumitomo Chemical Co., Ltd.), granules Diameter: 0.17 μm, Crystalline phase: α-alumina

[0052] The alumina raw material particles 2 (development product 1) were manufactured as follows. First, a seed crystal (α-alumina) slurry was prepared. Specifically, alumina particles (raw material for seed crystals) were dispersed in water, and then wet-milled in a ball mill to obtain a wet-milled product. The wet-milled product was then centrifuged at a rotation speed of 4000 rpm for 30 minutes to remove the precipitate and obtain a seed crystal slurry in which seed crystals were dispersed. Next, the seed crystal slurry and aluminum isopropoxide were mixed at high speed and hydrolyzed to obtain an aluminum hydroxide slurry. The obtained aluminum hydroxide slurry was dried at 150°C to obtain aluminum hydroxide particles. Next, the aluminum hydroxide particles were calcined in a gas furnace at 965°C to obtain alumina raw material particles 2. Furthermore, the alumina raw material particles 3 (development product 2) were obtained by changing the mixing ratio of aluminum isopropoxide and seed crystal slurry in the manufacturing method of alumina raw material particles 2 (development product 1).

[0053] SEM images of alumina raw material particles 2 and alumina raw material particles 5 used in this example are shown in Figures 1 and 2, respectively. Furthermore, the volume basis of these raw material particles was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Microtrac Bell). The particle size distribution is shown in Figure 3.

[0054] [Preparation of alumina powder] Using alumina raw material particles 1-5 and a silane coupling agent (product name: OFS-6040), the raw materials were prepared by blending them in the proportions specified in Examples 1-3 and Comparative Examples 1-3, as shown in Table 1. Then, as shown in Table 1, the raw materials were mixed using either a high-speed mixer or planetary stirring to obtain alumina powder. In the high-speed mixer method, a batch mill (IKA A10, rotation speed 20,000 rpm) was used to mix for 30 seconds to obtain the mixed alumina powder. In the planetary stirring method, a rotating / revolving mixer (ARV-310, rotation speed 2,000 rpm) was used to mix for 30 seconds to obtain the mixed alumina powder.

[0055] Using the obtained alumina powder, the particle size distribution of the alumina powder was measured as described below.

[0056] [Measurement of particle size distribution of alumina powder] (Preparation of resin compositions for particle size distribution measurement) First, as a resin composition for particle size distribution measurement, a molded body was obtained by mixing and kneading the alumina powder shown in Table 1 with epoxy resin. The epoxy resin used was a mixture of resin 1 (Type 53 epoxy main agent (manufactured by Sankei Co., Ltd.)) and resin 2 (Type 53 epoxy curing agent (manufactured by Sankei Co., Ltd.)) in a ratio of 2:1 (mass ratio). Each alumina powder and epoxy resin was weighed so that the powder filling rate was 85% by mass, and the mixture was kneaded using a rotation / revolution mixer (ARV-310) manufactured by Thinky Co., Ltd., and cured at room temperature for 24 hours to obtain a molded body (cured product).

[0057] (Particle size distribution measurement) The resulting molded body was subjected to cross-sectional polishing using a cross-section polisher (registered trademark, SM-09010 manufactured by JEOL Ltd.) at an accelerating voltage of 6.0 kV for 12 hours to obtain a cross-sectional sample.

[0058] The obtained cross-sectional samples were fixed onto carbon tape, and SEM images were acquired at 20,000x magnification using a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, model number: S-4800) at a predetermined acceleration voltage. The acquired SEM images were then automatically binarized using image analysis software (ImageJ) to obtain images with extracted particles. An example of the binarization process is shown in Figure 4. Figure 4 shows that by binarizing the SEM image in Figure 4A, the binarized image shown in Figure 4B is obtained. Particles that extended beyond the analysis range were excluded from the analysis. Particle separation processing (Watershed processing in the case of the image analysis software "ImageJ") was performed on the extracted particles, and the equivalent diameter of a circle was calculated from the area of ​​each particle. Then, the particle size D10 representing 10% of the cumulative particle size distribution based on particle count, the particle size D100 representing 100% of the cumulative particle size distribution based on particle count, and the particle size D50 representing 50% of the cumulative particle size distribution based on particle count were calculated from the finer end of the distribution. Furthermore, using these calculated values, the span value for each example was calculated from the following formula (1a). The results are shown in Table 2. Span value = (D100 - D10) / D50 ... (1a)

[0059] [Measurement of the average circularity of particles with an equivalent circle diameter of less than 0.3 μm] In the particle size distribution measurement described above, the area and perimeter of particles with an equivalent circle diameter of less than 0.3 μm were calculated. Then, the circularity of each particle with an equivalent circle diameter of less than 0.3 μm was calculated using the following formula (2). From these calculation results, the average circularity of particles with an equivalent circle diameter of less than 0.3 μm was determined. The results are shown in Table 2. The circularity of a single particle = 4 × π × area / (perimeter) 2 )···(2)

[0060] [Measurement of the coefficient of variation CV(Na / Nb) of the particle ratio (Na / Nb) between the number of particles with an equivalent circular diameter of less than 0.3 μm and the number of particles with an equivalent circular diameter of 0.3 μm or more] The coefficient of variation CV(Na / Nb) of the particle ratio (Na / Nb) of particles with an equivalent circle diameter of less than 0.3 μm (Na) and particles with an equivalent circle diameter of 0.3 μm or more (Nb) was determined by the following method.

[0061] Using the above cross-sectional sample, images at 10,000x magnification were acquired in five fields of view using SEM (magnification 10,000x). Similar to the particle size distribution measurement, images were obtained by automatically binarizing the particles using image analysis software (ImageJ). Particles that extended beyond the analysis range were excluded. For the extracted particles, particle separation processing (Watershed processing in the case of the image analysis software "ImageJ") was performed, the equivalent diameter of a circle was calculated from the area of ​​each particle, and the number of particles smaller than 0.3 μm (Na) and the number of particles larger than 0.3 μm (Nb) were measured. The Na / Nb ratio was measured for the five fields of view, and the mean, standard deviation, and coefficient of variation (CV) of Na / Nb were calculated. The Na / Nb ratio for each field of view was calculated, and the mean and standard deviation of the Na / Nb ratio across multiple fields of view were determined. The standard deviation of the particle ratio (Na / Nb) was then divided by the mean of the particle ratio (Na / Nb) to obtain the coefficient of variation (CV(Na / Nb)) of the particle ratio (Na / Nb). The results are shown in Table 2.

[0062] In this embodiment, for convenience, the coefficient of variation CV(Na / Nb) was evaluated when the obtained alumina powder was mixed with a small amount of resin. However, the evaluation results are considered to indicate a dispersion state similar to that of the state without the resin. In other words, the above measurement results can be said to indicate the dispersion state of the alumina powder.

[0063] [Presence or absence of coarse particles larger than 10 μm] Images were acquired at 1,000x magnification in five fields of view of the above cross-sectional sample using SEM, and the presence or absence of coarse grains with a short diameter of 10 μm or more was checked in these images. The results are shown in Table 2.

[0064] As an example of SEM images of cross-sectional samples, Figures 5 and 6 show SEM images of the cross-sectional sample of Example 1. Figures 7 and 8 show SEM images of the cross-sectional sample of Comparative Example 1, which uses the same alumina raw material particles as Example 1 but with a different mixing method. Furthermore, Figure 9 shows an SEM image of the cross-sectional sample of Comparative Example 3. In these images, the black areas represent resin. The areas enclosed by the white dashed lines in Figures 7 and 8 indicate regions where aggregated particles have formed. In Figure 9, only alumina raw material particle 1 is used as the alumina powder, and the gaps between the large alumina particles are not filled. In contrast, in the SEM images (Figures 5 and 6) of the alumina powder of Example 1, which corresponds to the alumina powder of this embodiment, the gaps between the large alumina particles derived from alumina raw material particle 1 are filled with small alumina particles derived from alumina raw material particle 2. This configuration increases the number of heat conduction paths, improving thermal conductivity and allowing it to be used as a filler with excellent heat dissipation properties.

[0065] [Measurement of viscosity in resin compositions] (Preparation of resin compositions for viscosity measurement) Alumina powder and resin 1 (Type 53 epoxy main component, manufactured by Sankei Co., Ltd.) were prepared for each example. Then, 10 g of alumina powder and 2.5 g of resin 1 were weighed out and mixed and kneaded using a rotation / revolution mixer (ARV-310) manufactured by Thinky Co., Ltd. to prepare a resin composition for viscosity measurement.

[0066] (Measurement of viscosity of resin composition for viscosity measurement) The viscosity of the obtained resin composition for viscosity measurement was measured using a dynamic viscoelasticity analyzer (UBM "Rheosol-G3000"). A 40 mm diameter parallel plate was used, with a gap of 1 mm and a shear rate of 5 s. -1 The measurements were taken at 25°C.

[0067] [Measurement of thermal conductivity of resin composition] (Preparation of resin compositions for thermal conductivity measurement) For each example, alumina powder and two resins were prepared: Resin 1 (Type 53 epoxy main component, manufactured by Sankei Co., Ltd.) and Resin 2 (Type 53 epoxy curing agent, manufactured by Sankei Co., Ltd.). Resin 1 and Resin 2 were mixed in a ratio of 2:1 (mass ratio) to obtain epoxy resin. 9 g of each alumina powder and 1 g of epoxy resin were weighed into a cup and mixed and kneaded using a rotation / revolution mixer (ARV-310) manufactured by Thinky Co., Ltd. to obtain a resin composition for thermal conductivity measurement.

[0068] (Measurement of thermal conductivity of resin composition for thermal conductivity measurement) The obtained resin composition for thermal conductivity measurement was placed in a 20 mm diameter mold at a rate of 2 g, molded under a pressure of 30 MPa, and allowed to cure at room temperature for 24 hours. The cured molded body was then processed to a size of 10 mm square × 2 mm thick, and the surface was polished to obtain a test specimen. The thermal conductivity in the thickness direction of this test specimen was measured using a xenon flash analyzer (NETZSCH, LFA467) with a laser flash method. The measurement was performed under atmospheric conditions at 25°C. A thermal conductivity of 2.0 or higher was evaluated as high thermal conductivity, and a thermal conductivity of less than 2.0 was evaluated as low thermal conductivity. The results are shown in Table 3.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] The results in Tables 1-3 show the following: Examples 1-3 have alumina powder shapes within the range specified in this embodiment, resulting in high thermal conductivity and the absence of coarse particles larger than 10 μm, thus enabling the realization of a thin-film thermal conductive member. In contrast, Comparative Example 1 had a high coefficient of variation CV, contained coarse particles larger than 10 μm, had a viscosity too high to measure, and low thermal conductivity. Furthermore, the presence of coarse particles larger than 10 μm prevented the realization of a thin-film thermal conductive member. Comparative Example 2 also had a high coefficient of variation CV and contained coarse particles larger than 10 μm, preventing the realization of a thin-film thermal conductive member. Comparative Example 3 had D10 and span values ​​outside the specified range, had a viscosity too high to measure, and low thermal conductivity.

Claims

1. Alumina powder having alumina particles with an equivalent circular diameter of less than 0.3 μm, The particle size D10 of the cumulative particle size distribution based on the number of particles, where the cumulative percentage from the finest particle side is 10%, is less than 0.15 μm. The particle size D10, the particle size D100 representing 100% of the cumulative particle size distribution based on the number of particles from the finest particle side, and the particle size D50 representing 50% of the cumulative particle size distribution based on the number of particles from the finest particle side satisfy the following formula (1): Alumina powder in which, when observed at least five fields of view at a magnification of 10,000x, the coefficient of variation of the particle ratio (Na / Nb) of alumina particles with an equivalent circle diameter of less than 0.3 μm (Na) to alumina particles with an equivalent circle diameter of 0.3 μm or more (Nb), CV (Na / Nb), is 0.3 or less. 4.0≦(D100-D10) / D50≦20...(1)

2. The alumina powder according to claim 1, wherein the alumina particles having an equivalent circular diameter of less than 0.3 μm have an average circularity of 0.82 or more.

3. The alumina powder according to claim 2, wherein the alumina particles having an equivalent circular diameter of less than 0.3 μm are α-alumina particles.

4. A resin composition comprising the alumina powder and resin according to any one of claims 1 to 3.

5. The resin composition according to claim 4, wherein the mass ratio of the alumina powder to the resin is in the range of 85:15 to 95:

5.

6. A raw material preparation step involves preparing alumina raw material particles with an equivalent circular diameter of less than 0.3 μm and a blended raw material containing alumina raw material particles with an equivalent circular diameter of 0.3 μm or more. A method for producing alumina powder according to claim 1, comprising a mixing step of mixing the aforementioned blending materials using a high-speed mixer with a rotational speed of 10,000 rpm or more.

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