Spherical alumina particles, method for producing same, and resin composition

Abstract

Provided are spherical alumina particles which, when mixed with a resin, produce a resin composition that exhibits a low dielectric loss tangent. These spherical alumina particles contain at least 90 mass% of an α-alumina crystal phase; have a half-width of the α-alumina (113) peak of 0.124° or less when observed by X-ray diffraction; and have an average particle diameter of 0.5 to 40 μｍ.

Description

[Technical Field]

[0001] The present invention relates to spherical alumina particles, a method for producing the same, and a resin composition. [Background technology]

[0002] In recent years, with the increase in the volume of information communication in the communications field, the use of high frequency bands has expanded in electronic devices and communications equipment, etc., and materials used in high frequency band devices are required to have low dielectric constants and dielectric loss tangents. In addition, the miniaturization and high integration of related electronic materials and components are progressing, and further heat dissipation properties are being required.

[0003] As a high-frequency ceramic material, alumina (Al2O3) has a quality factor index Qf (the product of the inverse of the dielectric tangent and the measurement frequency) of approximately 680,000 and a thermal conductivity of 30 W / m·K, making it a promising filler material with low dielectric tangent and heat dissipation properties. Furthermore, to facilitate blending in resins, the closer the filler shape to a spherical shape, the better. Spherical alumina particles can be easily synthesized (see, for example, Patent Document 1) and are already being used in a variety of applications. Therefore, they are expected to be widely used in high-frequency dielectric devices and other applications.

[0004] However, the crystallinity of spherical alumina particles may decrease during their synthesis, and the amount of moisture and functional groups adsorbed on the surface may increase, resulting in an insufficient dielectric loss tangent of a resin composition filled with spherical alumina particles. For example, Patent Document 2 describes that the dielectric loss tangent can be reduced by surface-treating alumina particles. However, the dielectric loss tangent is still insufficient, and the effect of filling the resin or the effect in the millimeter wave region is not described.

[0005] On the other hand, Patent Document 3 describes a method of improving the gelatinization rate by heat-treating alumina particles, and Patent Document 4 describes a method of reducing the moisture content by drying alumina powder. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4361997 [Patent Document 2] Patent No. 6603777 [Patent Document 3] Patent No. 6755116 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-193704 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide spherical alumina particles that can be mixed with a resin to produce a resin composition that exhibits a low dielectric loss tangent, a method for producing the same, and the resin composition. [Means for solving the problem]

[0008] The present invention includes the following embodiments.

[0009] [1] Spherical alumina particles containing 90% by mass or more of an α-alumina crystalline phase, The half-width of the (113) peak of α-alumina observed by X-ray diffraction is 0.124° or less, Spherical alumina particles having an average particle size of 0.5 to 40 μm.

[0010] [2] The spherical alumina particles according to [1], wherein the spherical alumina particles have an average circularity of 0.90 or more.

[0011] [3] Spherical alumina particles according to [1] or [2], wherein the total content of Li, Na and K in the spherical alumina particles is less than 500 ppm by mass, based on the total mass of the spherical alumina particles.

[0012] [4] The spherical alumina particles according to any one of [1] to [3], which are surface-treated with a surface treatment agent.

[0013] [5] A polyethylene / alumina composite sheet in which 30% by volume of the spherical alumina particles are blended in polyethylene resin has a dielectric loss tangent of 4.0 × 10 measured by a resonator method in the range of 30 to 40 GHz. -4 The spherical alumina particles according to any one of [1] to [4], wherein the spherical alumina particles have a particle diameter of less than 1 / 2 mm.

[0014] [6] A method for producing spherical alumina particles according to any one of [1] to [5], A method for producing spherical alumina particles, comprising the step of heating raw material alumina particles having an average particle diameter of 0.5 to 40 μm and an average circularity of 0.90 or more at 1350 to 1700°C.

[0015] [7] A resin composition comprising the spherical alumina particles according to any one of [1] to [5] and a resin.

[0016] [8] The resin composition according to [7], wherein the content of the spherical alumina particles in the resin composition is 2 to 90 mass %.

[0017] [9] The resin composition according to [7] or [8], wherein the resin is at least one selected from the group consisting of hydrocarbon elastomers, polyphenylene ethers, and aromatic polyene resins.

[0018]

[10] The resin composition according to any one of [7] to [9], which is a resin composition for use in a high-frequency substrate. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide spherical alumina particles which, when mixed with a resin, give a resin composition exhibiting a low dielectric loss tangent, a method for producing the same, and the resin composition. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing an X-ray diffraction pattern of the spherical alumina particles of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0022] [Spherical alumina particles] The spherical alumina particles according to this embodiment contain 90% by mass or more of an α-alumina crystalline phase. The spherical alumina particles have a half-width of the α-alumina (113) peak of 0.124° or less as measured by X-ray diffraction. The spherical alumina particles have an average particle size of 0.5 to 40 μm.

[0023] The spherical alumina particles according to this embodiment have a high α-alumina crystalline phase content of 90% by mass or more, and the half-width of the (113) peak of α-alumina observed by X-ray diffraction is 0.124° or less. The large crystallite size of α-alumina is believed to contribute to achieving a low dielectric loss tangent. Furthermore, the average particle diameter of the spherical alumina particles according to this embodiment is 0.5 to 40 μm, which facilitates blending of the spherical alumina particles with resins. It is believed that a sufficiently low dielectric loss tangent can be achieved even when mixed with resins. The term "spherical" in the spherical alumina particles refers to an average circularity of 0.80 or more, as measured by the method described below.

[0024] The spherical alumina particles according to this embodiment contain 90% by mass or more of the α-alumina crystalline phase. If the content of the α-alumina crystalline phase is less than 90% by mass, the dielectric loss tangent becomes high. The content of the α-alumina crystalline phase is preferably 93% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. Alternatively, the content of the α-alumina crystalline phase may be 100% by mass.

[0025] The content of the α-alumina crystalline phase is measured by powder X-ray diffraction. A horizontal sample multipurpose X-ray diffractometer (Rigaku Corporation, product name: RINT-Ultima IV) is used as the measurement device. The measurement is performed under the following conditions: X-ray source: CuKα, tube voltage: 40 kV, tube current: 40 mA, scan rate: 10.0° / min, 2θ scan range: 10° to 80°. The content of the α-alumina crystalline phase is calculated as the ratio (A / B)*100 of the sum of the peak areas (A) of α-alumina (012), (104), and (113) observed when the measurement sample is subjected to X-ray diffraction measurement of a NIST α-alumina standard sample for X-ray diffraction.

[0026] The spherical alumina particles according to this embodiment may contain other crystalline phases besides the α-alumina crystalline phase, so long as they contain 90% by mass or more of the α-alumina crystalline phase. Examples of such other crystalline phases include θ-alumina and γ-alumina. However, from the viewpoint of increasing the content of the α-alumina crystalline phase, the content of such other crystalline phases is preferably low, preferably less than 10% by mass, more preferably less than 5% by mass, and even more preferably less than 2% by mass. Furthermore, it is preferable that the spherical alumina particles according to this embodiment do not contain such other crystalline phases.

[0027] The spherical alumina particles according to this embodiment have a half-width of the (113) peak of α-alumina observed by X-ray diffraction of 0.124° or less. If the half-width exceeds 0.124°, the crystallinity of α-alumina decreases and the dielectric loss tangent increases. The half-width is preferably 0.122° or less, and more preferably 0.120° or less. Furthermore, since the crystallinity of α-alumina improves as the half-width becomes narrower, the narrower the half-width, the more preferable it is. The half-width is a value measured by powder X-ray diffraction of a measurement sample using the same method as used to measure the content of the α-alumina crystalline phase.

[0028] The spherical alumina particles according to this embodiment have an average particle size of 0.5 to 40 μm. If the average particle size is less than 0.5 μm or more than 40 μm, it becomes difficult to blend the spherical alumina particles into the resin. The average particle size is preferably 0.8 to 30 μm, and more preferably 1 to 18 μm. The average particle size is measured using a laser diffraction particle size distribution analyzer. Specifically, it can be measured by the method described below.

[0029] The average circularity of the spherical alumina particles according to this embodiment is preferably 0.90 or more. By having the average circularity of 0.90 or more, it is possible to suppress an increase in viscosity and a decrease in fluidity when mixed with a resin, thereby improving processability and fillability. The average circularity is more preferably 0.93 or more, and even more preferably 0.95 or more. There is no particular upper limit to the range of the average circularity, and a higher average circularity value is preferred, and it may even be 1. Since the shape of the spherical alumina particles reflects the shape of the raw material alumina particles before heating, the average circularity of the spherical alumina particles can be increased by producing spherical alumina particles using raw material alumina particles with a high average circularity. The average circularity can be measured by the method described below.

[0030] From the viewpoint of reducing the dielectric loss tangent and the reliability of the electronic material, the total content of Li, Na, and K in the spherical alumina particles according to this embodiment is preferably less than 500 ppm by mass, more preferably less than 250 ppm by mass, and even more preferably less than 150 ppm by mass, based on the mass of the entire spherical alumina particles. It is particularly preferable that the spherical alumina particles do not contain Li, Na, or K. The contents of Li, Na, and K can be measured by the method described below. Furthermore, from the viewpoint of reducing the dielectric loss tangent and the reliability of the electronic material, the spherical alumina particles do not contain impurities of metal elements such as Fe and Cl. - , Br - It is also preferable that the content of anions such as these be as low as possible.

[0031] The spherical alumina particles according to this embodiment are preferably surface-treated with a surface treatment agent. Surface treatment with a surface treatment agent can further increase the compounding amount (loading amount) in the resin and may further reduce the dielectric loss tangent. For example, a coupling agent can be used as the surface treatment agent. Examples of the coupling agent include silane coupling agents, titanate coupling agents, and aluminate coupling agents. Specific examples include hexamethyldisilazane (HMDS), vinyltrimethoxysilane, and 7-octenyltrimethoxysilane. These surface treatment agents may be used alone or in combination. The amount of the surface treatment agent is not particularly limited, but may be, for example, 0.01 to 5 parts by mass per 100 parts by mass of the spherical alumina particles. In addition, when the spherical alumina particles have been surface-treated with a surface treatment agent, the content of the α-alumina crystalline phase, the half-width of the (113) peak of α-alumina, the average particle size, the average circularity, and the contents of Li, Na, and K are measured on the spherical alumina particles after the surface treatment.

[0032] The spherical alumina particles according to this embodiment are a polyethylene / alumina composite sheet in which the spherical alumina particles are blended in a polyethylene resin at 30% by volume, and the dielectric loss tangent measured by a resonator method in the range of 30 to 40 GHz is 4.0 × 10 -4 Preferably, it is less than 3.6 x 10 -4 More preferably, it is less than 3.2 × 10 -4 It is more preferable that the dielectric loss tangent is less than 4.0×10 -4 Since the dielectric loss tangent is less than 1 / 2, a resin composition containing the spherical alumina particles exhibits a low dielectric loss tangent, making it suitable as a filler to be filled into a resin composition for a high-frequency substrate, for example. The dielectric properties in the 30 to 40 GHz range can be measured using, for example, a 36 GHz cavity resonator, a 40 GHz split cylinder resonator, a balanced disk resonator, or the like, and due to their high accuracy, the measurements are preferably performed using a 36 GHz cavity resonator or a 40 GHz split cylinder resonator. The dielectric loss tangent can be measured by the method described below.

[0033] The spherical alumina particles according to this embodiment preferably have a thermal conductivity of 1.1 W / m·K or more, more preferably 1.2 W / m·K or more, and even more preferably 1.3 W / m·K or more, of an epoxy resin / alumina composite sheet in which the spherical alumina particles are blended in an epoxy resin at 40% by volume. A thermal conductivity of 1.1 W / m·K or more ensures that a resin composition containing the spherical alumina particles exhibits high thermal conductivity (heat dissipation), making it suitable for use as a filler in resin compositions for high-frequency substrates, for example. The thermal conductivity can be measured by the method described below.

[0034] The spherical alumina particles according to the present embodiment are useful as a filler to be filled into resin compositions that require a low dielectric loss tangent, for example, resin compositions for high-frequency substrates, because the resin compositions obtained by mixing the spherical alumina particles with resins exhibit a low dielectric loss tangent.

[0035] [Method for producing spherical alumina particles] The method for producing spherical alumina particles according to this embodiment includes a step of heating raw alumina particles having an average particle diameter of 0.5 to 40 μm and an average circularity of 0.90 or more at 1350 to 1700°C (hereinafter also referred to as a heating step). The method according to this embodiment may include other steps in addition to the heating step. According to the method according to this embodiment, the spherical alumina particles according to this embodiment can be produced easily and efficiently.

[0036] (Heating process) In this process, raw alumina particles with an average particle size of 0.5 to 40 μm and an average circularity of 0.90 or more are heated at 1350 to 1700°C. The raw alumina particles may be amorphous, α-phase, δ-phase, γ-phase, or any other crystalline system, and the manufacturing method is also not particularly limited, but it is preferable to use spherical alumina manufactured by a powder fusion method. The powder fusion method is a method in which non-spherical alumina, aluminum hydroxide, boehmite, or the like is introduced into a high-temperature field above its melting point, such as a flame, plasma, electric furnace, or gas furnace, to spheroidize it. Furthermore, since the particle size of the spherical alumina particles obtained by the heating step reflects the particle size of the raw alumina particles, the average particle size of the raw alumina particles is preferably 0.5 to 40 μm, and the average circularity is preferably 0.90 or more, more preferably 0.8 to 30 μm and 0.93 or more, and even more preferably 1 to 18 μm and 0.95 or more. The average particle size and average circularity of the raw alumina particles are measured in the same manner as the average particle size and average circularity of the spherical alumina particles.

[0037] The heating device for heating the raw alumina particles is not particularly limited as long as it is capable of high-temperature heating, and examples include an electric furnace, rotary kiln, and pusher furnace. The heating atmosphere is not particularly limited, and examples include air, N2, Ar, and vacuum. The heating temperature is preferably 1350 to 1700°C, more preferably 1400 to 1600°C, and even more preferably 1400 to 1550°C. A heating temperature of 1350°C or higher increases the content of α-alumina crystalline phase and enhances the crystallinity of α-alumina, thereby achieving a lower dielectric loss tangent. Furthermore, a heating temperature of 1700°C or lower suppresses the formation of aggregates due to particle fusion, making the raw alumina suitable for use as a filler to be mixed with resin. The heating time, although depending on the heating temperature, is preferably 1 to 24 hours, more preferably 2 to 20 hours, and even more preferably 2 to 12 hours. By setting the heating time to 1 hour or more, the content of the α-alumina crystalline phase increases and the crystallinity of the α-alumina can be improved, resulting in a lower dielectric tangent. Furthermore, by setting the heating time to 24 hours or less, productivity can be improved.

[0038] The spherical alumina particles obtained after heating may be in the form of agglomerates in which multiple particles are aggregated. The agglomerates themselves may be used as spherical alumina particles, or, if necessary, the agglomerates may be crushed and then used as spherical alumina particles. The method for crushing the agglomerates is not particularly limited, and examples thereof include crushing methods using an agate mortar, ball mill, vibration mill, jet mill, wet jet mill, etc. Crushing may be performed in a dry manner, or in a wet manner by mixing with a liquid such as water or alcohol. In wet crushing, spherical alumina particles are obtained by drying after crushing. The drying method is not particularly limited, and examples thereof include heat drying, vacuum drying, freeze drying, supercritical carbon dioxide drying, etc.

[0039] (Other processes) In addition to the heating step, the method for producing spherical alumina particles according to this embodiment may further include other steps such as a classification step for classifying the spherical alumina particles to obtain a desired average particle size, a surface treatment step for performing surface treatment using a surface treatment agent such as a coupling agent, a washing step for reducing impurities, etc. The type and amount of the surface treatment agent used in the surface treatment step may be the same as those described above.

[0040] [Resin composition] The resin composition according to this embodiment includes the spherical alumina particles according to this embodiment and a resin. Because the resin composition according to this embodiment includes the spherical alumina particles according to this embodiment, it can exhibit a low dielectric loss tangent. Furthermore, the resin composition including the spherical alumina particles according to this embodiment has a low viscosity, so it has good flowability and excellent moldability.

[0041] The resin is not particularly limited, but examples thereof include polyethylene, polypropylene, epoxy resin, silicone resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyamide such as polyimide, polyamideimide, polyetherimide, polyester such as polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, etc. These resins may be used alone or in combination of two or more.

[0042] The content of the spherical alumina particles in the resin composition is appropriately selected depending on the desired physical properties such as the dielectric loss tangent, but is preferably 2 to 90 mass%, more preferably 10 to 80 mass%, and even more preferably 10 to 70 mass%. The content of the resin in the resin composition is preferably 10 to 98 mass%, more preferably 30 to 90 mass%, and even more preferably 30 to 70 mass%.

[0043] A resin composition may be prepared by mixing a powder obtained by mixing another powder having a different specific surface area, average particle size, or composition from the spherical alumina particles according to the present embodiment with the spherical alumina particles according to the present embodiment, and then mixing the resulting powder with a resin. By mixing the powder with a resin, the dielectric constant, dielectric loss tangent, thermal expansion coefficient, thermal conductivity, packing ratio, and the like of the resin composition can be more easily adjusted.

[0044] The optimum value of the dielectric loss tangent of the resin composition according to this embodiment varies depending on the type of resin, the blending amount, the presence or absence of additives, etc. However, when blended at 30% by volume with a low dielectric loss tangent resin, such as polytetrafluoroethylene, polyethylene, or polypropylene, the dielectric loss tangent measured by the resonator method at 30 to 40 GHz is 4.0 × 10 -4 Preferably, it is less than 3.6 x 10 -4More preferably, it is less than 3.2 × 10 -4 The optimal thermal conductivity of the resin composition according to this embodiment varies depending on the type and amount of resin, the presence or absence of additives, and other factors. For example, when blended with an epoxy resin at 40% by volume, the thermal conductivity is preferably 1.1 W / m K or more, more preferably 1.2 W / m K or more, and even more preferably 1.3 W / m K or more. The dielectric loss tangent and thermal conductivity of the resin composition are values ​​measured by the methods described below.

[0045] The resin composition according to this embodiment exhibits a low dielectric loss tangent and is therefore particularly useful as a resin composition for high-frequency substrates. Specific examples of high-frequency substrates include fluorine substrates, PPE substrates, and ceramic substrates. When the resin composition according to this embodiment is used as a material for such high-frequency substrates or as an insulating material, a low-dielectric resin can be used as the resin constituting the resin composition. Examples of low-dielectric resins include hydrocarbon-based elastomers, polyphenylene ethers, and aromatic polyene-based resins, with hydrocarbon-based elastomers and polyphenylene ethers being preferred. These resins may be used alone or in combination. After blending the spherical alumina particles according to this embodiment into these resins, the resin may be crosslinked or cured as necessary. The mass ratio of the spherical alumina particles or the mixed powder to the resin (spherical alumina particles or the mixed powder:resin) is optional and can be, for example, 5:95 to 80:20 or 5:95 to 70:30.

[0046] Examples of hydrocarbon-based elastomers include ethylene-based elastomers, propylene-based elastomers, conjugated diene polymers, block or random copolymers of aromatic vinyl compounds and conjugated dienes, and hydrogenated products thereof. Examples of ethylene-based elastomers include ethylene-α-olefin copolymers such as ethylene-octene copolymer and ethylene-1-hexene copolymer, EPR, EPDM, etc. Examples of propylene-based elastomers include atactic polypropylene, low stereoregular polypropylene, and propylene-α-olefin copolymers such as propylene-1-butene copolymer. Examples of conjugated diene polymers include polybutadiene and 1,2-polybutadiene. Examples of aromatic vinyl compound-conjugated diene block or random copolymers and hydrogenated products thereof include SBS, SIS, SEBS, SEPS, SEEPS, SEEBS, etc.

[0047] These hydrocarbon-based elastomers may be used alone or in combination of two or more. Among these, conjugated diene polymers are preferred as hydrocarbon-based elastomers, with 1,2-polybutadiene being more preferred. Commercially available 1,2-polybutadiene is available, for example, as a product from JSR Corporation, and also as liquid polybutadiene (product names B-1000, 2000, and 3000) from Nippon Soda Co., Ltd. Furthermore, commercially available copolymers containing a 1,2-polybutadiene structure that can be suitably used include, for example, "Ricon 100" from Total Cray Valley. The number-average molecular weight of the hydrocarbon-based elastomer is preferably 1,000 or more, more preferably 10,000 or more.

[0048] As the polyphenylene ether, commercially available known polyphenylene ethers can be used. The number-average molecular weight of the polyphenylene ether is optional. Considering the moldability of the compound, the number-average molecular weight is preferably 10,000 or less, more preferably 5,000 or less. Furthermore, the number-average molecular weight is preferably 500 or more. Furthermore, when the polyphenylene ether is added for the purpose of curing the compound, it is preferable that the molecular end is modified and / or that one molecule contains multiple functional groups. Examples of functional groups include allyl groups, vinyl groups, and epoxy groups. Furthermore, the functional group is preferably a radically polymerizable functional group, more preferably a vinyl group. Examples of vinyl groups include (meth)acrylic groups and aromatic vinyl groups. Furthermore, bifunctional polyphenylene ethers in which both molecular chain ends are modified with radically polymerizable functional groups are more preferred. Commercially available examples of such polyphenylene ethers include Noryl™ SA9000 from SABIC and bifunctional polyphenylene ether oligomer (OPE-2St) from Mitsubishi Gas Chemical Company, Inc.

[0049] Aromatic polyene resins include divinylbenzene-based reactive hyperbranched copolymers (PDV). Such PDVs are described, for example, in the literature "Synthesis of Polyfunctional Aromatic Vinyl Copolymers and Development of New IPN-Type Low Dielectric Loss Materials Using Them" (Kawabe Masanao et al., Journal of the Japan Institute of Electronics Packaging, p. 125, Vol. 12 No. 2 (2009)). Commercially available products include PDVs manufactured by Nippon Steel Chemical & Material Co., Ltd. Aromatic polyene resins also include aromatic polyene polymer resins whose main structural unit is the above-mentioned aromatic polyene monomer.

[0050] When preparing the resin composition according to this embodiment, the spherical alumina particles or mixed powder according to this embodiment and the resin described above can be crosslinked and cured using a crosslinking agent or curing agent. Examples of crosslinking agents include various maleimides, bismaleimides, maleic anhydride, glycidyl (meth)acrylate, triallyl isocyanurate, tri(meth)acrylic isocyanurate, and trimethylolpropane tri(meth)acrylate. These crosslinking agents may be used alone or in combination. Maleimides and bismaleimides are described, for example, in International Publication No. 2016 / 114287 and are commercially available from Daiwa Chemical Industry Co., Ltd. These maleimide group-containing compounds may be used as polyaminobismaleimide compounds from the viewpoints of solubility in organic solvents, high-frequency characteristics, high adhesion to conductors, and prepreg moldability. Polyaminobismaleimide compounds can be obtained, for example, by subjecting a compound having two maleimide groups at its terminals to a Michael addition reaction with an aromatic diamine compound having two primary amino groups in its molecule. To achieve high crosslinking efficiency with a small amount of addition, it is preferable to use a crosslinking agent having a multifunctional group (e.g., bifunctional or higher), such as bismaleimides, triallyl isocyanurate (TAIC), or trimethylolpropane tri(meth)acrylate. When a crosslinking agent is used, the amount of the crosslinking agent is preferably 0.1 to 30 parts by mass, more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the resin.

[0051] The curing agent can be a known curing agent that can be used for the polymerization or curing of aromatic polyenes or aromatic vinyl compounds. Examples of such curing agents include radical polymerization initiators, cationic polymerization initiators, and anionic polymerization initiators, with radical polymerization initiators being preferred. Organic peroxides and azo-based polymerization initiators are more preferred, and can be freely selected depending on the application and conditions. Commercially available organic peroxides are available from, for example, NOF Corporation, Wako Pure Chemical Industries, Ltd., and Tokyo Chemical Industry Co., Ltd., and examples are listed in the catalogs posted on the websites of these companies. Known photopolymerization initiators that utilize light, ultraviolet light, or radiation can also be used as a curing agent. Examples of photopolymerization initiators include photoradical polymerization initiators, photocationic polymerization initiators, and photoanionic polymerization initiators. Commercially available photopolymerization initiators are available from, for example, Tokyo Chemical Industry Co., Ltd. Furthermore, curing using radiation or electron beams themselves is also possible. Crosslinking and curing by thermal polymerization of the raw materials contained therein can also be performed without the use of a curing agent. When a curing agent is used, there are no particular restrictions on the amount of curing agent used, but 0.01 to 10 parts by mass per 100 parts by mass of the resin is preferred. When using a curing agent such as a peroxide or azo-based polymerization initiator, the curing treatment can be carried out at an appropriate temperature and time, taking into account its half-life. In this case, the conditions can be determined according to the curing agent, but a temperature range of approximately 50°C to 180°C is appropriate.

[0052] When the spherical alumina particles or mixed powder according to this embodiment are used as a material for a high-frequency substrate or an insulating material, the various resins, crosslinking agents, curing agents, etc. that are used are described in, for example, the following patent documents: JP-A-8-208856, JP-A-2017-75270, JP-A-2009-167268, JP-A-2011-68713, JP-A-2018-131519, JP-A-2016-534549, JP-A-2017-57352, WO2016 / 175325 International Publication Pamphlet, and WO2016 / 175326 International Publication Pamphlet. [Example]

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0054] [Example 1] 50 g of raw alumina particles 1 (manufactured by Denka, product name: DAW-05, average particle diameter: 5.1 μm, average circularity: 0.95) were placed in an alumina crucible and heat-treated in an air atmosphere at an electric furnace temperature of 1400°C for 4 hours. After the heat treatment, the mixture was naturally cooled until the furnace temperature reached 200°C or less, and the powder was recovered and crushed in a mortar to obtain spherical alumina particles.

[0055] [Examples 2 and 3] Spherical alumina particles were prepared in the same manner as in Example 1, except that the heating temperature or heating time in the heat treatment was changed as shown in Table 1.

[0056] [Example 4] Spherical alumina particles were prepared in the same manner as in Example 1, except that raw alumina particles 2 (manufactured by Denka, trade name: DAW-15, average particle diameter: 15.2 μm, average circularity: 0.97) were used as the raw alumina particles and the heating temperature was changed as shown in Table 1.

[0057] [Example 5] To 100 parts by mass of the spherical alumina particles obtained in Example 1, 0.1 parts by mass of hexamethyldisilazane (HMDS) (Shin-Etsu Silicones, product name: SZ-31) was added as a surface treatment agent. The mixture was then mixed for 2 minutes at an acceleration of 60 G using a vibration mixer manufactured by Resodyn, and the mixed powder was dried for 24 hours in a vacuum dryer (under an environment of 120°C and less than 133 Pa). This produced surface-treated spherical alumina particles.

[0058] [Example 6] Surface-treated spherical alumina particles were prepared in the same manner as in Example 5, except that 1 part by mass of vinyltrimethoxysilane (manufactured by Shin-Etsu Silicones Co., Ltd., trade name: KBM-1003) was added as a surface treatment agent.

[0059] [Example 7] Spherical alumina particles were prepared in the same manner as in Example 1, except that raw alumina particles 3 (manufactured by Denka, trade name: DAW-0105, average particle diameter: 1.0 μm, average circularity: 0.96) were used as the raw alumina particles, and the heating time was changed as shown in Table 1.

[0060] [Example 8] Spherical alumina particles were prepared in the same manner as in Example 1, except that raw alumina particles 4 (manufactured by Denka, trade name: DAM-05, average particle diameter: 5.0 μm, average circularity: 0.95) were used as raw alumina particles.

[0061] [Example 9] When evaluating the dielectric constant and dielectric loss tangent of the resin composition containing the spherical alumina particles obtained in Example 1, which will be described later, the evaluation was carried out using polypropylene (manufactured by Sumitomo Seika Chemicals Co., Ltd., product name: Flowblen QB200) as the resin.

[0062] [Comparative Examples 1 to 3] Spherical alumina particles were prepared in the same manner as in Example 1, except that the heating temperature and / or heating time in the heat treatment was changed as shown in Table 2.

[0063] Comparative Example 4 Spherical alumina particles were prepared in the same manner as in Example 1, except that raw alumina particles 5 (manufactured by Denka, trade name: ASFP-20, average particle diameter: 0.3 μm, average circularity: 0.95) were used as the raw alumina particles and the heating temperature was changed as shown in Table 2.

[0064] Comparative Example 5 When evaluating the dielectric constant and dielectric loss tangent of the resin composition containing spherical alumina particles obtained in Comparative Example 2, which will be described later, the evaluation was carried out using polypropylene (manufactured by Sumitomo Seika Chemicals, product name: Flowblen QB200) as the resin.

[0065] The properties of the spherical alumina particles prepared in each of the Examples and Comparative Examples, and the raw alumina particles 1 to 5 themselves as Reference Examples 1 to 5, were evaluated by the following methods. The evaluation results are shown in Tables 1 to 3.

[0066] [Average circularity] Spherical alumina particles or raw alumina particles were fixed to a sample stage with carbon tape, then coated with osmium. Images were taken with a scanning electron microscope (JEOL Ltd., product name: JSM-7001F SHL) at a magnification of 500 to 50,000 times and a resolution of 1280 x 1024 pixels. Images were then imported into a personal computer. The projected area (S) and projected perimeter (L) of the particles were calculated using an image analyzer (Nippon Roper Co., Ltd., product name: Image-Pro Premier Ver. 9.3). The circularity was then calculated using the following formula (1): The circularity was calculated for 200 particles with a random projected area and a circle-equivalent diameter of 0.8 to 50 μm, and the average value was used as the average circularity. Circularity = 4πS / L 2 (1)

[0067] [density] 2.0 g of spherical alumina particles or raw alumina particles was placed in a measurement sample cell, and the density was measured by a gas (helium) substitution method using a dry density meter (Shimadzu Corporation, trade name: Accupyc II1340).

[0068] [Average particle size] The average particle size was measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, product name: LS 13 320). 3 0.1 g of pure water and 0.1 g of spherical alumina particles or raw alumina particles were placed in a container and dispersed for 1 minute using an ultrasonic homogenizer (BRANSON, product name: SFX250). The dispersed powder dispersion was added dropwise to a laser diffraction particle size analyzer using a dropper, and measurements were taken 30 seconds after the specified amount was added. The particle size distribution was calculated from the light intensity distribution data of the diffracted / scattered light by the particles detected by the sensor in the laser diffraction particle size analyzer. The average particle size was calculated by multiplying the measured particle size value by the relative particle amount (difference %) and dividing the result by the total relative particle amount (100%). Note that % here means volume %.

[0069] [Measurement of α-alumina crystalline phase content and half-width of (113) peak] Identification of the α-alumina crystalline phase contained in the spherical alumina particles and raw alumina particles, as well as measurement of the α-alumina crystalline phase content and the half-width of the (113) peak, were performed by powder X-ray diffraction measurement. A horizontal sample multipurpose X-ray diffractometer (Rigaku Corporation, product name: RINT-Ultima IV) was used as the measurement device. The measurement was performed under the following conditions: X-ray source: CuKα, tube voltage: 40 kV, tube current: 40 mA, scan rate: 10.0° / min, 2θ scan range: 10° to 80°. For reference, the X-ray diffraction pattern of the spherical alumina particles prepared in Example 1 is shown in Figure 1. The content of α-alumina crystalline phase was calculated from the ratio (A / B)*100 of the sum of the peak areas (A) of α-alumina (012), (104), and (113) observed when the measurement sample was subjected to X-ray diffraction analysis to the sum of the peak areas (B) of α-alumina (012), (104), and (113) observed when the NIST α-alumina standard sample for X-ray diffraction was subjected to X-ray diffraction analysis. The half-width of the α-alumina (113) peak was also calculated.

[0070] [Measurement of Li, Na and K contents] The Li, Na, and K contents were measured by inductively coupled plasma atomic emission spectrometry. An ICP atomic emission spectrometry analyzer (manufactured by SPECTRO, product name: CIROS-120) was used as the analytical device. 0.1 g of spherical alumina particles and raw alumina particles were weighed into a platinum crucible, and measurement solutions were prepared by pressure acid decomposition at 200°C using hydrofluoric acid and sulfuric acid, and measurements were then performed. Note that the Li, Na, and K contents in Tables 1 to 3 indicate the total contents of Li, Na, and K.

[0071] [Thermal conductivity of resin composition] The resin composition was prepared as follows: 25.6 parts by mass of bisphenol A liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, product name: JER828) and 6.4 parts by mass of 4,4'-diaminophenylmethane (manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed while melting at 95°C. Spherical alumina particles or raw alumina particles were added to this mixture at a loading of 40% by volume (density: 3.7 g / cm). 3The mixture was added so that the total weight was 66 parts by mass (66 parts by mass in the case of 100%) and mixed using a planetary mixer (Thinky Corporation, product name: Awatori Rentaro AR-250, rotation speed: 2000 rpm). The resulting mixture was poured into a silicone mold (2 cm square x 6 mm thick) preheated to 80°C and press-cured using a vacuum heating press (Imoto Manufacturing Co., Ltd., product name: IMC-1674-A) at 80°C for 1 hour at 3 MPa, 150°C for 1 hour at 5 MPa, and 200°C for 0.5 hours at 7 MPa to obtain a resin composition. The thermal conductivity of the resin composition was calculated by multiplying the thermal diffusivity, specific gravity, and specific heat. The thermal diffusivity was measured by a laser flash method using a cured sample cut into a 10 mm wide x 10 mm wide x 1 mm thick sample. A xenon flash analyzer (NETZSCH, product name: LFA447 NanoFlash) was used as the measurement device. The specific gravity was determined using the Archimedes method. The specific heat was measured using a differential scanning calorimeter (TA Instruments, product name: Q2000) in a nitrogen atmosphere by heating from room temperature to 200°C at a rate of 10°C / min.

[0072] [Dielectric constant and dielectric loss tangent of resin composition] Spherical alumina particles or raw alumina particles and polyethylene powder (manufactured by Sumitomo Seika Chemicals, product name: Flothane UF-20S; Examples 1-8, Comparative Examples 1-4, and Reference Examples 1-5) or polypropylene powder (manufactured by Sumitomo Seika Chemicals, product name: Floblen QB200; Example 9 and Comparative Example 5 only) were weighed so that the loading of the spherical alumina particles or raw alumina particles was 30% by volume, and mixed using a Resodyn vibration mixer (acceleration 60 G, processing time 2 min). The resulting mixed powder was weighed to a predetermined volume (so that the thickness was approximately 0.3 mm), placed in a metal frame with a diameter of 3 cm, and sheeted using a nanoimprinting device (manufactured by SCIVAX, product name: X-300) under conditions of 140°C, 5 minutes, and 30,000 N for polyethylene, and 190°C, 5 minutes, and 30,000 N for polypropylene, to prepare evaluation samples. The evaluation sample sheets had a thickness of 0.3 mm. The shape and size do not affect the evaluation results as long as they can be mounted on the measuring instrument, but the size was 1.5 cm square.

[0073] The dielectric constant and dielectric loss tangent were measured using the following method. A 36 GHz cavity resonator (manufactured by SAMTECH) was connected to a vector network analyzer (product name: 85107, manufactured by Keysight Technologies), and an evaluation sample (1.5 cm square, 0.3 mm thick) was set so as to cover a 10 mm diameter hole in the resonator. The resonance frequency (f0) and unloaded Q value (Qu) were measured. The evaluation sample was rotated for each measurement, and the measurement was repeated five times in the same manner. The obtained f0 and Qu values ​​were averaged and used as the measured value. The dielectric constant was calculated from f0, and the dielectric loss tangent (tan δc) was calculated from Qu using analysis software (manufactured by SAMTECH). The measurement temperature was 20°C, and the humidity was 60% RH. When polyethylene was formed into a sheet under the same conditions without filling it with filler, the dielectric constant was 2.3 and the dielectric loss tangent was 2.6 × 10 -4 It was.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

Claims

1. Spherical alumina particles containing 90% by mass or more of an α-alumina crystal phase, The half-width of the (113) peak of α-alumina observed by X-ray diffraction is 0.124° or less, The average particle size is 0.5 to 40 μm, The spherical alumina particles have a total content of Li, Na and K of less than 500 ppm by mass based on the total mass of the spherical alumina particles.

2. 2. The spherical alumina particles according to claim 1, wherein the spherical alumina particles have an average circularity of 0.90 or more.

3. 3. The spherical alumina particles according to claim 1, which have been surface-treated with a surface treatment agent.

4. The dielectric loss tangent of a polyethylene / alumina composite sheet, in which 30% by volume of the spherical alumina particles are blended in polyethylene resin, measured by a resonator method in the range of 30 to 40 GHz is 4.0 × 10 －４ The spherical alumina particles according to any one of claims 1 to 3, wherein the average particle diameter is less than 1 / 2 mm.

5. A method for producing spherical alumina particles according to any one of claims 1 to 4, comprising: A method for producing spherical alumina particles, comprising the step of heating raw material alumina particles having an average particle diameter of 0.5 to 40 μm and an average circularity of 0.90 or more at 1350 to 1700°C.

6. A resin composition comprising the spherical alumina particles according to any one of claims 1 to 4 and a resin.

7. The resin composition according to claim 6, wherein the content of the spherical alumina particles in the resin composition is 2 to 90 mass%.

8. The resin composition according to claim 6 or 7, wherein the resin is at least one selected from the group consisting of a hydrocarbon-based elastomer, a polyphenylene ether, and an aromatic polyene-based resin.

9. The resin composition according to any one of claims 6 to 8, which is a resin composition for a high-frequency substrate.

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