Almina powder, resin composition, and method of manufacturing almina powder
Patent Information
- Application Number
- JP2022124999
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-08-04
- Publication Date
- 2025-07-17
- Estimated Expiration
- 2042-08-04
AI Technical Summary
Existing thermally conductive members face challenges in achieving high thermal conductivity and thin film thickness due to alumina particle aggregation in resin compositions, making it difficult to dissipate heat effectively.
Development of alumina powder with specific particle size distribution and dispersion characteristics, including particles with an equivalent circle diameter less than 0.3 μm, controlled coefficient of variation, and high circularity, mixed using a high-speed mixer to prevent aggregation, resulting in a resin composition with high thermal conductivity and thin film-like properties.
The alumina powder achieves high thermal conductivity and enables the production of thin film-like thermally conductive members with improved dispersibility and reduced agglomeration, enhancing heat dissipation capabilities.
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Abstract
Description
[Technical field]
[0001] The present disclosure relates to an alumina powder, a resin composition, and a method for producing the alumina powder. [Background technology]
[0002] Heat generated by passing electricity through electronic components is likely to adversely affect the performance of the electronic components, so it is desirable to dissipate the heat quickly. Therefore, it is desirable for the material constituting the thermally conductive member for dissipating heat to exhibit high thermal conductivity. One of the thermally conductive members is a thermally conductive resin composition containing a resin and inorganic particles, and alumina particles are used as the inorganic particles.
[0003] The alumina particles are, for example, alumina particles obtained by calcining aluminum hydroxide by the Bayer method, as shown in Patent Document 1, and have a BET specific surface area of 5 to 9 m. 2 / g, and a particle size distribution in which D10 = 0.1 to 0.2 μm, D50 = 0.3 to 0.5 μm, and D90 = 0.7 to 2 μm, with 80 mass % or more of particles being 1 μm or less, and the Mg content, Na content, Si content, and Ca content are specified. [Prior art documents] [Patent documents]
[0004] [Patent Document 1] JP 2005-206460 A Summary of the Invention [Problem to be solved by the invention]
[0005] In recent years, there has been a demand for thin sheet-shaped thermally conductive members for heat dissipation, for example, thermally conductive members with a thickness of several tens of microns or even several microns. Furthermore, there is a demand for thermally conductive members with higher thermal conductivity. In order to achieve high thermal conductivity, it is necessary to disperse alumina particles uniformly and at a high concentration in the resin.
[0006] However, when a large amount of the alumina particles disclosed in Patent Document 1 is mixed 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 to make the thermal conductive member thin.
[0007] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide an alumina powder that has high thermal conductivity and can realize a thin-film thermally conductive member, a resin composition that contains the alumina powder and can realize a thin-film thermally conductive member that has high thermal conductivity, and a method for producing the alumina powder. [Means for solving the problem]
[0008] Aspect 1 of the present invention is An alumina powder having alumina particles with an equivalent circle diameter of less than 0.3 μm, The particle size D10 of the cumulative 10% from the fine particle side of the cumulative particle size distribution based on the number is less than 0.15 μm, the D10, a particle diameter D100 at 100% cumulative from the fine particle side of the cumulative particle size distribution on a number basis, and a particle diameter D50 at 50% cumulative from the fine particle side of the cumulative particle size distribution on a number basis satisfy the following formula (1), This alumina powder has a CV(Na / Nb) of 0.3 or less, which is the coefficient of variation of the particle ratio (Na / Nb) of the number of alumina particles Na having an equivalent circle diameter of less than 0.3 μm and the number of alumina particles Nb having an equivalent circle diameter of 0.3 μm or more, when observed over at least five visual fields at a magnification of 10,000 times. 4.0≦(D100-D10) / D50≦20 (1)
[0009] Aspect 2 of the present invention is The alumina particles having an equivalent circle diameter of less than 0.3 μm are an alumina powder according to embodiment 1, having an average circularity of 0.82 or more.
[0010] Aspect 3 of the present invention is In the alumina powder according to embodiment 1 or 2, the alumina particles having an equivalent circle diameter of less than 0.3 μm are α-alumina particles.
[0011] A fourth aspect of the present invention is A resin composition comprising the alumina powder according to any one of aspects 1 to 3 and a resin.
[0012] A fifth aspect of the present invention is Aspect 5. The resin composition according to aspect 4, wherein a mass ratio of the alumina powder to the resin is within a range of 85:15 to 95:5.
[0013] A sixth aspect of the present invention is a raw material preparation step of preparing a blended raw material containing alumina raw material particles having an equivalent circle diameter of less than 0.3 μm and alumina raw material particles having an equivalent circle diameter of 0.3 μm or more; and mixing the raw materials using a high-speed mixer having a rotation speed of 10,000 rpm or more. Effect of the Invention
[0014] According to the present disclosure, it is possible to provide an alumina powder having high thermal conductivity and capable of realizing a thin-film thermally conductive member, a resin composition containing the alumina powder and capable of realizing a thin-film thermally conductive member having high thermal conductivity, and a method for producing the alumina powder. [Brief description of the drawings]
[0015] [Figure 1] FIG. 1 is a SEM photograph of alumina raw material particles 2 used in the examples. [Diagram 2] FIG. 2 is a SEM photograph of the alumina raw material particles 5 used in the examples. [Diagram 3]FIG. 3 is a diagram showing the particle size distribution of the alumina raw material particles 2 and the alumina raw material particles 5 used in the examples. [Figure 4] Fig. 4 shows an example of the binarization process carried out in the embodiment. [Diagram 5] FIG. 5 is an SEM image of a cross-sectional sample of Example 1. [Figure 6] FIG. 6 is another SEM image of the cross-sectional sample of Example 1. [Figure 7] FIG. 7 is an SEM image of a cross-sectional sample of Comparative Example 1. [Figure 8] FIG. 8 is another SEM image of the cross-sectional sample of Comparative Example 1. [Figure 9] FIG. 9 is an SEM image of a cross-sectional sample of Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The present inventors have conducted extensive research to realize an alumina powder capable of realizing a thin-film thermal conductive member having high thermal conductivity, a resin composition containing the alumina powder and capable of realizing a thin-film thermal conductive member having high thermal conductivity, and a method for producing the alumina powder. As a result, the inventors have found that the alumina powder has alumina particles having a circle-equivalent diameter of less than 0.3 μm, and when the particle diameter of 10% of the cumulative particle size distribution on a number basis is defined as D10, the particle diameter of 50% of the cumulative particle size is D50, and the particle diameter of 100% of the cumulative particle size is D100, the range of D10 is specified, and 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 having a circle-equivalent diameter of less than 0.3 μm and the number of alumina particles Nb having a circle-equivalent diameter of 0.3 μm or more, which is a parameter indicating the dispersion state of the alumina particles, is equal to or less than a certain value.
[0017] The alumina powder according to this embodiment, the resin composition containing the alumina powder, and the method for producing the alumina powder will be described in detail below.
[0018] [Alumina powder] (Contains alumina particles with an equivalent circular diameter of less than 0.3 μm) The alumina powder according to this embodiment contains alumina particles having 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 contains small alumina particles, and may also contain alumina particles having an equivalent circle diameter of 0.3 μm or more (hereinafter sometimes referred to as "large alumina particles") within a range that satisfies the specified particle size distribution described below. The small alumina particles may have a lower limit of the equivalent circle diameter of, for example, 0.01 μm. The large alumina particles may have an upper limit of the equivalent circle diameter of 3 μm or less.
[0019] (D10 is the cumulative 10% particle size from the fine side of the cumulative particle size distribution based on number) The alumina powder according to this embodiment has a particle diameter D10 (hereinafter sometimes simply referred to as "D10") of 10% cumulative from the fine particle side of the cumulative particle size distribution based on the number of particles being less than 0.15 μm. By containing alumina fine particles having a particle diameter of less than 0.15 μm as fine alumina small particles in the alumina powder, the alumina fine particles are present in the gaps formed between the alumina large particles, and high filling can be easily achieved, thereby improving the thermal conductivity. In addition, by having the alumina fine particles on the surface of the relatively large alumina particles, the fluidity of the alumina powder in the resin can be improved when producing a resin composition. The above D10 is preferably 0.10 μm or less. In addition, from the viewpoint of fluidity when mixing the resin composition, the lower limit of the above D10 can be about 0.01 μm.
[0020] (Span value: (D100-D10) / D50) In the alumina powder according to the present embodiment, the D10, the particle diameter D100 at 100% cumulative from the fine particle side of the cumulative particle size distribution based on the number of particles, and the particle diameter D50 at 50% cumulative from the fine particle side of the cumulative particle size distribution based on the number of particles satisfy the following formula (1). Hereinafter, (D100-D10) / D50 in the following formula (1) may be referred to as the "span value". 4.0≦(D100-D10) / D50≦20 (1)
[0021] The span value is an index showing the spread of the particle size distribution. When the span value is below 4.0, the difference between the particle size of the small alumina particles and the particle size of the large alumina particles becomes small. As a result, when the particle size of the small alumina particles is close to the particle size of the large alumina particles, it becomes difficult to fill the gaps formed between the relatively large alumina particles with the fine alumina particles. On the other hand, when the particle size of the large alumina particles is close to the particle size of the small alumina particles, most of the alumina powder is occupied by particles with a relatively small particle size, and as a result, it becomes difficult to ensure excellent thermal conductivity and good flowability. The span value is preferably 4.1 or more, more preferably 4.3 or more, and even more preferably 5.3 or more.
[0022] On the other hand, if the span value exceeds 20, it is expected that the particle size (D50) of the relatively large alumina particles will be 5 μm or more. In this case, taking into consideration the particle size distribution of the large alumina particles, it becomes difficult to realize a thin-film-like thermal conductive member, for example, a thin-film-like thermal conductive member with a thickness of 10 μm or less cannot be realized. The 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 with a circle equivalent diameter of less than 0.3 μm (Na) and the number of alumina particles with a circle equivalent diameter of 0.3 μm or more (Nb)) The alumina powder according to this embodiment satisfies a CV(Na / Nb) of 0.3 or less, which is a coefficient of variation of the particle ratio (Na / Nb) between the number Na of alumina particles having an equivalent circle diameter of less than 0.3 μm and the number Nb of alumina particles having an equivalent circle diameter of 0.3 μm or more, when observed in at least five visual fields at a magnification of 10,000 times.
[0024] The alumina powder according to the present embodiment can provide a resin composition in which the dispersibility of the alumina powder is high and the generation of aggregated particles is suppressed, even when a large amount of the alumina powder is mixed and kneaded with a resin. As a result, the thermal conductivity is increased, and a thin-film-shaped thermal conductive member can be realized. In order to show that the alumina powder according to the present embodiment disperses well in the resin composition, unlike conventional products, in the present embodiment, CV(Na / Nb), which is the coefficient of variation of the particle ratio (Na / Nb) between the number of alumina particles Na having a circle equivalent diameter of less than 0.3 μm and the number of alumina particles Nb having a circle equivalent diameter of 0.3 μm or more, is used as an evaluation index of the dispersibility of the alumina powder.
[0025] The coefficient of variation CV(Na / Nb) is determined by observing at least five fields of view at a magnification of 10,000. The coefficient of variation CV(Na / Nb) may be evaluated using a scanning electron microscope.
[0026] In order to obtain an alumina powder that satisfies the above-mentioned 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 below, rather than mixing the raw alumina particles 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 more preferable it is.
[0028] (Average circularity of alumina particles with equivalent circle diameter of less than 0.3 μm) In the alumina powder according to the present embodiment, the average circularity of the alumina particles having a circle equivalent diameter of less than 0.3 μm is preferably 0.82 or more. By having the small alumina particles have a high circularity, the flowability can be further increased when mixed and kneaded with the resin. The average circularity of the small alumina particles is more preferably 0.85 or more, and the higher the average circularity of the small alumina particles, the more preferable it is, but if the average circularity is 0.95 or less, the same flowability can be ensured.
[0029] (Crystal structure of alumina particles with an equivalent circle diameter of less than 0.3 μm) In the alumina powder according to the present embodiment, it is preferable that the alumina particles having a circle equivalent diameter of less than 0.3 μm are α-alumina particles. The alumina powder is, for example, measured by powder X-ray diffraction, and the peak height of the α-phase (012 plane) appearing at 2θ=25.6° from the obtained diffraction spectrum is compared with the peak height of other phases such as the γ-phase appearing at 2θ=46°, or when evaluating using a resin composition, a thin piece having a thickness of about 0.1 μm is prepared using a focused ion beam (FIB), and the particles having a circle equivalent diameter of less than 0.3 μm are confirmed by electron beam diffraction.
[0030] On the other hand, the crystal structure of the alumina particles having a circle equivalent 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 having a circle equivalent diameter of 0.3 μm or more are also α-alumina particles.
[0031] [Method of producing alumina powder] The method for producing the alumina powder according to this embodiment is as follows: a raw material preparation step of preparing a blended raw material containing alumina raw material particles having an equivalent circle diameter of less than 0.3 μm and alumina raw material particles having an equivalent circle diameter of 0.3 μm or more; The method also includes a mixing step of mixing the blended raw materials using a high-speed mixer having a rotation speed of 10,000 rpm or more.
[0032] (Raw material preparation process) A blended raw material containing alumina raw material particles having a circle equivalent diameter of less than 0.3 μm and alumina raw material particles having a circle equivalent diameter of 0.3 μm or more is prepared, but the manufacturing method of these alumina raw material particles is not particularly limited. For example, a commercially available product can be used. Or, the alumina raw material particles can be manufactured by a conventionally known method.
[0033] The average circularity of the alumina raw material particles having an equivalent circle diameter of less than 0.3 μm is preferably 0.82 or more. The average circularity of the alumina raw material particles having an equivalent circle diameter of less than 0.3 μm is more preferably 0.85 or more, and the higher the better, but it may be 0.95 or less. The average circularity of the alumina raw material particles having an equivalent circle diameter of 0.3 μm or more is not particularly limited.
[0034] The alumina raw material particles having an equivalent circle diameter of less than 0.3 μm are preferably α-alumina raw material particles. Examples of the alumina raw material particles having 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 an alumina powder with high thermal conductivity, it is preferable that the alumina raw material particles having an equivalent circle diameter of 0.3 μm or more are also α-alumina raw material particles.
[0035] To obtain the alumina powder of this embodiment in which the D10 and the span value of the specified range are within the above-mentioned ranges, it is preferable to mix the alumina raw material particles having an equivalent circle diameter of less than 0.3 μm and the alumina raw material particles having an equivalent circle diameter of 0.3 μm or more in a mixing ratio (mass ratio) of, for example, 40:60 to 10:90.
[0036] The raw materials may contain a silane coupling agent, a dispersant, etc., for the purpose of improving the flowability during mixing.
[0037] (Mixing process) In order to obtain an alumina powder that satisfies the above coefficient of variation CV (Na / Nb), it is important not only to prepare a blended raw material containing alumina raw particles having a circle equivalent diameter of less than 0.3 μm and alumina raw particles having a circle equivalent diameter of 0.3 μm or more, but also to use a method for mixing these alumina raw particles. In the method for producing an alumina powder according to the present embodiment, a high-speed mixer having a rotation speed of 10,000 rpm or more is used as a means for mixing the particles of different particle sizes, so that the formation of aggregates is sufficiently suppressed and an alumina powder that satisfies the above coefficient of variation CV (Na / Nb) can be obtained. As a result, by mixing and kneading the alumina powder with a resin, the aggregated portion of the alumina powder is sufficiently suppressed, and a resin composition containing alumina powder that is highly filled but well dispersed can be obtained.
[0038] The high-speed mixer having a rotation speed of 10,000 rpm or more is a device that mixes powder at a high rotation speed of 10,000 rpm or more, and examples thereof include a batch mill and a rotor speed mill. Conventionally, with general mixing devices that have been used for mixing powder, such as an air blender, a rocking blender, a Henschel mixer (all with a rotation speed of 470 to 5,400 rpm), and a planetary stirring mixer (with a rotation speed of 2,000 rpm or less), it is difficult to disintegrate agglomerates of small alumina particles having a circle equivalent diameter of less than 0.3 μm, and agglomerates are present when a resin composition is produced. As a result, it is difficult to produce a thin-film resin composition, for example, a very thin resin composition with a film thickness of 5 μm or less. In addition, by using a high-speed mixer, agglomerates of small alumina particles having a circle equivalent diameter of less than 0.3 μm can be disintegrated and dispersed on the surface of primary particles of alumina raw material particles having a circle equivalent diameter of 0.3 μm or more. In addition, re-aggregation of alumina raw material particles having an equivalent circle diameter of 0.3 μm or more is prevented, and as a result, an alumina powder satisfying the coefficient of variation CV(Na / Nb) is obtained.
[0039] [Resin composition] The resin composition according to the present embodiment includes the alumina powder according to the present embodiment and a resin. By using the alumina powder according to the present embodiment as, for example, a filler for a thermally conductive resin composition, a resin composition (composite) having high thermal conductivity can be obtained.
[0040] In order to ensure the thermal conductivity of the resin composition, the ratio (mixing ratio) of the alumina powder according to this embodiment contained in the resin composition is preferably 40% by volume or more, more preferably 50% by volume or more. On the other hand, from the viewpoint of ensuring the flexibility specific to resin, the ratio of the alumina powder is preferably 90% by volume or less, more preferably 85% by volume or less. The resin composition according to this embodiment is preferably highly filled with alumina powder and can exhibit higher thermal conductivity. As a preferred embodiment of the resin composition highly filled with alumina powder, the mass ratio of the alumina powder to the 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 resins may be used alone or in combination of two or more.
[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 copolymers, acrylonitrile-butadiene-styrene copolymer (ABS) resins, polyphenylene-ether copolymers (PPE) resins, modified PPE resins, aliphatic polyamides, aromatic polyamides, polyimides, polyamideimides, polymethacrylic acid, polymethacrylic acid esters such as polymethacrylic acid methyl ester, polyacrylic acids, polycarbonates, polyphenylene sulfide, polysulfones, polyether sulfones, polyether nitriles, polyether ketones, polyketones, liquid crystal polymers, silicone resins, and ionomers.
[0043] Examples of the thermoplastic elastomer include a styrene-butadiene block copolymer or a hydrogenated product thereof, a styrene-isoprene block copolymer or a hydrogenated product thereof, a styrene-based thermoplastic elastomer, an olefin-based thermoplastic elastomer, a vinyl chloride-based thermoplastic elastomer, a polyester-based thermoplastic elastomer, a polyurethane-based thermoplastic elastomer, and a polyamide-based thermoplastic elastomer.
[0044] Examples of the thermosetting resin include crosslinked rubber, epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin, diallyl phthalate resin, etc. Specific examples of the 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, polyamideimide resins, epoxy resins, phenol resins, and silicone resins are preferably used.
[0046] Furthermore, these resin compositions may contain, as necessary, any of known additives, such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weather resistance agents, anti-blocking agents, antistatic agents, leveling agents, and release agents, either alone or in combination, within the scope of the invention.
[0047] A method for producing a resin composition will be described. A resin composition can be obtained by mixing the alumina powder according to this embodiment with a resin. For example, when the resin is liquid (such as liquid epoxy resin), the liquid resin, alumina powder, and a curing agent are mixed, and then cured with heat or ultraviolet light to obtain a resin composition. Known curing agents, mixing methods, and curing methods can be used. On the other hand, when the resin is solid (such as polyolefin resin or acrylic resin), the alumina powder and the resin are mixed, and then kneaded by a known method such as melt kneading to obtain the desired resin composition.
[0048] The resin composition according to the present embodiment may be a compound obtained by compounding a raw material containing alumina powder and a resin, a mixture obtained by mixing a raw material containing alumina powder and a resin, a molded product obtained by molding the mixture, and a molded product (cured product) obtained by, for example, curing the mixture or the molded product.
[0049] One embodiment of the resin composition according to the present embodiment is a thin-film resin composition, and a further example of such a thin-film resin composition has a thickness of, for example, 10 μm or less, and further 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 to the following examples, and can be practiced with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.
[0051] [Preparation of Alumina Raw Material Particles] The following alumina raw material particles 1 to 5 were prepared as the alumina raw material particles. The crystal phase of each raw material particle was determined by analyzing the crystal structure by X-ray diffraction. (Alumina raw material particles 1) Product name: AA-07 (manufactured by Sumitomo Chemical Co., Ltd.), particle size (D50): 0.9 μm, crystal phase: α-alumina (Alumina raw material particles 2) Developed product 1 (manufactured by Sumitomo Chemical Co., Ltd.), particle size (D50): 0.15 μm, crystal phase: α alumina (Alumina raw material particles 3) Developed product 2 (manufactured by Sumitomo Chemical Co., Ltd.), particle size (D50): 0.10 μm, crystal phase: α-alumina (Alumina raw material particles 4) Product name: ASFP-20 (manufactured by Denka Co., Ltd.), particle size (D50): 0.3 μm, crystal phase: θ alumina and δ alumina (Alumina raw material particles 5) Product name: AKP-53 (manufactured by Sumitomo Chemical Co., Ltd.), particle size (D50): 0.17 μm, crystal phase: α-alumina
[0052] The alumina raw material particles 2 (developed product 1) were produced as follows. First, a seed crystal (α-alumina) slurry was prepared. Specifically, alumina particles (raw material of seed crystals) were dispersed in water, and then wet-ground in a ball mill to obtain a wet-ground product. The wet-ground 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 the 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 fired in a gas furnace at 965°C to obtain alumina raw material particles 2. The alumina raw material particles 3 (developed product 2) were obtained by changing the compounding ratio of the aluminum isopropoxide and the seed crystal slurry in the manufacturing method of the alumina raw material particles 2 (developed product 1).
[0053] SEM photographs of the alumina raw material particles 2 and the alumina raw material particles 5 used in this example are shown in Figures 1 and 2, respectively. Also, the particle size distributions thereof are shown in Figure 3.
[0054] [Preparation of alumina powder] Alumina raw material particles 1 to 5 and a silane coupling agent (product name: OFS-6040) were used and blended in the amounts shown in Table 1 for Examples 1 to 3 and Comparative Examples 1 to 3 to obtain blended raw materials. Then, as shown in Table 1, the blended raw materials were mixed with a high-speed mixer or planetary stirring and mixing to obtain alumina powder. In the high-speed mixer mixing, the materials were mixed for 30 seconds using a batch mill (IKA A10, rotation speed 20,000 rpm) to obtain a mixed powder as alumina powder. In the planetary stirring and mixing, the materials were mixed for 30 seconds using a rotation-revolution mixer (ARV-310, rotation speed 2,000 rpm) to obtain a mixed powder as alumina powder.
[0055] The obtained alumina powder was used to measure the particle size distribution of the alumina powder as described below.
[0056] [Measurement of particle size distribution of alumina powder] (Preparation of resin composition for particle size distribution measurement) First, a molded body was obtained by mixing and kneading the alumina powder and epoxy resin shown in Table 1 as a resin composition for particle size distribution measurement. The epoxy resin used was a mixture of resin 1 (53 type epoxy base agent (manufactured by Sankei Co., Ltd.)) and resin 2 (53 type epoxy hardener (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 mass%, mixed and kneaded using a planetary centrifugal mixer (ARV-310) manufactured by Thinky Corporation, and cured at room temperature for 24 hours to obtain a molded body (cured product).
[0057] (Particle size distribution measurement) The obtained molded body was subjected to ion beam cross-section polishing at an acceleration voltage of 6.0 kV for 12 hours using a cross-section polisher (registered trademark, SM-09010 manufactured by JEOL Ltd.), to obtain a cross-section sample.
[0058] The obtained cross-sectional sample was fixed on carbon tape, and a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, product number: S-4800) was used to obtain an SEM image at a magnification of 20,000 times at a specified acceleration voltage. The obtained SEM image was then automatically binarized using image analysis software (ImageJ) to obtain an image in which particles were extracted. An example of binarization is shown in FIG. 4. FIG. 4 shows that the binarized image shown in FIG. 4B can be obtained by binarizing the SEM image in FIG. 4A. Note that particles that protrude from the analysis range were excluded from the analysis. The extracted particles were subjected to particle separation processing ("Watershed processing" in the case of the above-mentioned image analysis software "ImageJ"), and the circle equivalent diameter was calculated from the area of each particle. Then, the particle diameter D10 of the cumulative 10% from the fine particle side of the cumulative particle size distribution based on the number of particles, the particle diameter D100 of the cumulative 100% from the fine particle side of the cumulative particle size distribution based on the number of particles, and the particle diameter D50 of the cumulative 50% from the fine particle side of the cumulative particle size distribution based on the number of particles were calculated. Furthermore, using these calculated values, the span value of 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 above particle size distribution measurement, the area and perimeter of particles with a circle-equivalent diameter of less than 0.3 μm were calculated. Then, the circularity of each particle with a circle-equivalent diameter of less than 0.3 μm was calculated using the following formula (2). From the calculation results, the average circularity of particles with a circle-equivalent diameter of less than 0.3 μm was calculated. The results are shown in Table 2. Circularity of one 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 a circle-equivalent diameter of less than 0.3 μm and the number of particles with a circle-equivalent diameter of 0.3 μm or more] The coefficient of variation CV(Na / Nb) of the particle ratio (Na / Nb) of the number of particles Na having an equivalent circle diameter of less than 0.3 μm and the number of particles Nb having an equivalent circle diameter of 0.3 μm or more was determined by the following method.
[0061] Using the above cross-sectional sample, 10,000x images were obtained in 5 visual fields with SEM (magnification 10,000x), and similarly to the case of the particle size distribution measurement, images were obtained in which particles were extracted by automatic binarization processing using image analysis software (ImageJ). Note that particles that protrude from the analysis range were excluded. Particle separation processing ("Watershed processing" in the case of the above image analysis software "ImageJ") was performed on the extracted particles, the circle equivalent diameter was calculated from the area of each particle, and the number of particles Na less than 0.3 μm and the number of particles Nb of 0.3 μm or more were measured. Na / Nb was measured in 5 visual fields, and the average value, standard deviation, and coefficient of variation CV of Na / Nb were obtained. Na / Nb in each visual field was obtained, and the average value and standard deviation of Na / Nb in multiple visual fields were obtained. The standard deviation of the particle ratio (Na / Nb) was then divided by the average value 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) is evaluated in a state where the obtained alumina powder is mixed with a small amount of resin, but the evaluation result is considered to show the same dispersion state as in a state where the resin is not present. In other words, the measurement result shows the dispersion state of the alumina powder.
[0063] [Presence or absence of coarse particles of 10 μm or more] For the cross-sectional sample, 1,000x images were taken in five fields of view using an SEM, and the presence or absence of coarse particles with a minor axis of 10 μm or more was confirmed in the images. The results are shown in Table 2.
[0064] As an example of the SEM image of the cross-sectional sample, the SEM images of the cross-sectional sample of Example 1 are shown in Figs. 5 and 6. In addition, the SEM images of the cross-sectional sample of Comparative Example 1, in which the alumina raw material particles are the same as those of Example 1 but the mixing method is different, are shown in Figs. 7 and 8. Furthermore, the SEM image of the cross-sectional sample of Comparative Example 3 is shown in Fig. 9. In these photographs, the black parts indicate resin. The parts surrounded by white dashed lines in Figs. 7 and 8 indicate the areas where aggregated particles are generated. In addition, in Fig. 9, only the alumina raw material particles 1 are used as the alumina powder, and the gaps between the large alumina particles are not filled. In contrast, in the SEM photographs (Figs. 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 the alumina raw material particles 1 are filled with the small alumina particles derived from the alumina raw material particles 2. By realizing such a form, the number of heat conduction paths is increased, the thermal conductivity is improved, and it can be used as a filler with excellent heat dissipation properties.
[0065] [Measurement of Viscosity of Resin Composition] (Preparation of resin composition for viscosity measurement) Alumina powder of each example and resin 1 (53 type epoxy base, manufactured by Sankei Co., Ltd.) were prepared. Then, 10 g of alumina powder of each example and 2.5 g of resin 1 were weighed out, and mixed and kneaded using a planetary centrifugal mixer (ARV-310) manufactured by Thinky Corporation 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 measuring device ("Rheosol-G3000" manufactured by UBM). Parallel plates with a diameter of 40 mm were used, with a gap of 1 mm and a shear rate of 5 s -1 The measurements were performed under conditions of 25°C.
[0067] [Measurement of thermal conductivity of resin composition] (Preparation of resin composition for thermal conductivity measurement) Alumina powder for each example was prepared, along with resins Resin 1 (53-type epoxy base, manufactured by Sankei Co., Ltd.) and Resin 2 (53-type epoxy hardener, manufactured by Sankei Co., Ltd.). Resin 1 and resin 2 were mixed in a ratio (mass ratio) of 2:1 to obtain an 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 Corporation to obtain a resin composition for measuring thermal conductivity.
[0068] (Measurement of thermal conductivity of resin composition for thermal conductivity measurement) The obtained resin composition for thermal conductivity measurement was placed in a mold with a diameter of 20 mm in 2 g, molded under a pressure of 30 MPa, and left at room temperature for 24 hours to harden the resin. The hardened molded body was then processed to a size of 10 mm square x 2 mm thick, and the surface was polished to obtain a test piece. The thermal conductivity of this test piece in the thickness direction was measured by the laser flash method using a xenon flash analyzer (NETZSCH, LFA467). The measurement was performed under the condition of 25°C in an air atmosphere. Then, a test piece with a thermal conductivity of 2.0 or more was evaluated as having high thermal conductivity, and a test piece with a thermal conductivity of less than 2.0 was evaluated as having 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 to 3 reveal the following. In Examples 1 to 3, the shape of the alumina powder is within the range specified in this embodiment, so that the thermal conductivity is high, there are no coarse particles of 10 μm or more, and a thin-film thermal conductive member can be realized. In contrast, in Comparative Example 1, the coefficient of variation CV is high, coarse particles of 10 μm or more are present, the viscosity is so high that it cannot be measured, and the thermal conductivity is low. Furthermore, since coarse particles of 10 μm or more are present, a thin-film thermal conductive member cannot be realized. In Comparative Example 2, the coefficient of variation CV is high, coarse particles of 10 μm or more are present, and a thin-film thermal conductive member cannot be realized. In Comparative Example 3, the D10 and span value are outside the specified range, the viscosity is so high that it cannot be measured, and the thermal conductivity is low.
Claims
1. An alumina powder having alumina particles with an equivalent circle diameter of less than 0.3 μm, The particle size D10 of the cumulative 10% from the fine particle side of the cumulative particle size distribution based on the number is less than 0.15 μm, the D10, a particle diameter D100 at 100% cumulative from the fine particle side of the cumulative particle size distribution on a number basis, and a particle diameter D50 at 50% cumulative from the fine particle side of the cumulative particle size distribution on a number basis satisfy the following formula (1), The alumina powder has a coefficient of variation (CV(Na / Nb)) of a particle ratio (Na / Nb) of the number of alumina particles Na having an equivalent circle diameter of less than 0.3 μm to the number of alumina particles Nb having an equivalent circle diameter of 0.3 μm or more, of 0.3 or less, when observed in at least five visual fields at a magnification of 10,000 times. 4.0≦(D100-D10) / D50≦20...(1)
2. 2. The alumina powder according to claim 1, wherein the alumina particles having an equivalent circle 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 circle diameter of less than 0.3 μm are α-alumina particles.
4. A resin composition comprising the alumina powder according to any one of claims 1 to 3 and a resin.
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 of preparing a blended raw material containing alumina raw material particles having an equivalent circle diameter of less than 0.3 μm and alumina raw material particles having an equivalent circle diameter of 0.3 μm or more; and mixing the raw materials using a high-speed mixer having a rotation speed of 10,000 rpm or more.