Spherical alumina particles, their manufacturing method, and resin composition

Abstract

The present invention provides a resin composition obtained by mixing with a resin that exhibits spherical alumina particles with low dielectric tangent. It also provides spherical alumina particles containing more than 90% by mass of a crystalline phase of α-alumina, wherein the half-width of the (113) peak of α-alumina observed by X-ray diffraction is less than 0.124° and the average particle size is 0.5 to 40 μm.

Description

Technical Field

[0001] This invention relates to spherical alumina particles, methods for manufacturing the same, and resin compositions. Prior Technology

[0002] In recent years, with the increase in information communication volume in the communications field, high-frequency band applications have become widespread in electronic devices and communication equipment. Materials used in high-frequency band devices require low dielectric constant and low dielectric tangent. Furthermore, the miniaturization and high integration of related electronic materials and components are increasingly demanding improved heat dissipation.

[0003] Regarding high-frequency ceramic materials, alumina (Al₂O₃) has a quality factor (Qf) of approximately 680,000 (the product of the reciprocal of the dielectric tangent and the measured frequency) and a thermal conductivity of 30 W / m·K, making it a promising material for fillers with low dielectric tangent and good heat dissipation. Furthermore, to facilitate incorporation into resins, the closer the filler shape is to spherical shape, the better. Spherical alumina particles can be easily synthesized (e.g., Patent Document 1) and have been used in many applications. Therefore, its widespread use in high-frequency dielectric devices is also anticipated.

[0004] However, because the crystallinity of spherical alumina particles decreases during their synthesis, and the adsorbed moisture and functional groups on their surface increase, the dielectric tangent of resin compositions filled with spherical alumina particles sometimes becomes insufficient. For example, Patent Document 2 describes that surface treatment of alumina particles can reduce the dielectric tangent. However, even so, it is still insufficient in terms of dielectric tangent, and the effect when filled into resin, or the effect in the Extra High Frequency domain, is not described.

[0005] On the other hand, Patent Document 3 describes heat treatment of alumina particles to improve the α-oxidation rate. Furthermore, Patent Document 4 describes drying alumina powder to reduce its moisture content. [Previous Technical Documents] [Patent Literature]

[0006] [Patent Document 1] Japanese Patent No. 4361997 [Patent Document 2] Japanese Patent No. 6603777 [Patent Document 3] Japanese Patent No. 6755116 [Patent Document 4] Japanese Patent Application Publication No. 2015-193704 Summary of the Invention

[0007] [The problem that the invention aims to solve]

[0008] The object of the present invention is to provide a resin composition obtained by mixing with a resin that exhibits low dielectric tangent spherical alumina particles, a method for manufacturing the same, and the resin composition thereof. [Methods for solving problems]

[0009] The present invention includes the following embodiments.

[0010] [1] A spherical alumina particle containing more than 90% by mass of α-alumina crystalline phase, The half-width at half-maximum (WHM) of the (113) peak of α-alumina, as observed by X-ray diffraction, is less than 0.124°. The average particle size is 0.5~40μm.

[0011] [2] Spherical alumina particles as in [1], wherein the average sphericality of the spherical alumina particles is 0.90 or higher.

[0012] [3] Spherical alumina particles such as [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.

[0013] [4] The spherical alumina particles in any of [1] to [3] are surface treated with a surface treatment agent.

[0014] [5] The dielectric tangent of a polyethylene / alumina composite sheet made by incorporating 30% by volume of the spherical alumina particles into polyethylene resin, as measured by the resonator method at 30-40 GHz, does not reach 4.0 × 10⁻⁴.

[0015] [6] A method for manufacturing spherical alumina particles, which is the method for manufacturing spherical alumina particles as described in any one of [1] to [5], includes the following steps: Raw alumina particles with an average particle size of 0.5~40μm and an average roundness of 0.90 or higher are heated at 1350~1700℃.

[0016] [7] A resin composition comprising spherical alumina particles as described in any one of [1] to [5], and a resin.

[0017] [8] The resin composition as in [7], wherein the content of spherical alumina particles in the resin composition is 2 to 90% by mass.

[0018] [9] A resin composition as in [7] or [8], wherein the resin is selected from at least one of the group consisting of hydrocarbon elastomers, polyphenylene ethers and aromatic polyene resins.

[0019]

[10] Any of the resin compositions in [7] to [9] is a resin composition for high frequency substrates. [Effects of the Invention]

[0020] The present invention provides a resin composition system obtained by mixing with a resin exhibiting spherical alumina particles with low dielectric tangent, a method for manufacturing the same, and the resin composition thereof. Simple Explanation of the Diagram

[0021] [Figure 1] is a diagram showing the X-ray diffraction pattern of the spherical alumina particles of Example 1. Implementation

[0022] The following describes embodiments of the present invention. However, the present invention is not limited to these embodiments.

[0023] [Spherical alumina particles] The spherical alumina particles of this embodiment contain 90% by mass or more of the crystalline phase of α-alumina. Here, the half-width of the (113) peak of α-alumina observed by X-ray diffraction of the spherical alumina particles is less than 0.124°. Furthermore, the average particle size of the spherical alumina particles is 0.5 to 40 μm.

[0024] It is speculated that the crystalline α-alumina content of the spherical alumina particles in this embodiment is as high as 90% by mass or more, and the half-width of the (113) peak of α-alumina observed by X-ray diffraction is less than 0.124°. In addition, the crystallite size of α-alumina is large, so a low dielectric tangent can be achieved. Furthermore, it is speculated that because the average particle size of the spherical alumina particles in this embodiment is 0.5~40 μm, the spherical alumina particles are easy to incorporate into the resin, and a sufficiently low dielectric tangent can be achieved when mixed with the resin. In addition, the "spherical" in "spherical alumina particles" refers to an average sphericity of 0.80 or more as measured by the method described later.

[0025] The spherical alumina particles of this embodiment contain at least 90% by mass of α-alumina crystalline phase. If the content of the α-alumina crystalline phase is less than 90% by mass, the dielectric tangent will be higher. An α-alumina crystalline phase content of 93% by mass or more is ideal, 95% by mass or more is more ideal, and 98% by mass or more is even more ideal. Furthermore, the α-alumina crystalline phase content can also be 100% by mass.

[0026] Furthermore, the content of the crystalline phase of α-alumina was determined by powder X-ray diffraction. The measuring apparatus used was a sample-level multi-object X-ray diffraction apparatus (RIGAL, trade name: RINT-Ultima IV). The measurement was performed under the following conditions: X-ray source: CuKα, tube voltage: 40 kV, tube current: 40 mA, scanning speed: 10.0° / min, 2θ scanning range: 10°~80°. The content of the crystalline phase of α-alumina was calculated by the ratio (A) of the total peak area (012), (104), and (113) of α-alumina observed during X-ray diffraction of the measured sample to the total peak area (B) of the (012), (104), and (113) of α-alumina observed during X-ray diffraction of a standard α-alumina sample prepared by NIST ((A / B)*100).

[0027] The spherical alumina particles of this embodiment may contain 90% or more of the α-alumina crystalline phase, or other crystalline phases besides α-alumina. Examples of such other crystalline phases include θ-alumina and γ-alumina. However, considering the viewpoint of increasing the content of the α-alumina crystalline phase, a low content of the aforementioned other crystalline phases is preferable; less than 10% by mass is preferable, less than 5% by mass is even more preferable, and less than 2% by mass is even more preferable. Furthermore, it is preferable that the spherical alumina particles of this embodiment do not contain any of the aforementioned other crystalline phases.

[0028] The half-width at half-maximum (WHM) of the (113) peak of α-alumina observed by X-ray diffraction of the spherical alumina particles in this embodiment is 0.124° or less. If the WHM exceeds 0.124°, the crystallinity of α-alumina decreases and the dielectric tangent increases. A WHM of 0.122° or less is ideal, and 0.120° or less is even more ideal. Furthermore, the narrower the WHM, the better the crystallinity of α-alumina, so a narrower WHM is more ideal. In addition, the WHM was measured by powder X-ray diffraction of the test sample using the same method as the method used to determine the content of the crystalline phase of α-alumina.

[0029] The spherical alumina particles of 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 greater than 40 μm, the spherical alumina particles become difficult to incorporate into the resin. An average particle size of 0.8 to 30 μm is more ideal, and 1 to 18 μm is even more ideal. Furthermore, the average particle size was measured using a laser diffraction particle size distribution measuring device. Specifically, the measurement can be performed using the method described later.

[0030] In this embodiment, an average spherical spherical alumina particle spherical shape of 0.90 or higher is desirable. By achieving an average spherical ...

[0031] In this embodiment, considering the reduction of dielectric tangent and the reliability of electronic materials, the total Li, Na, and K content of the spherical alumina particles should ideally be less than 500 ppm by mass, less than 250 ppm by mass, and less than 150 ppm by mass, based on the total mass of the spherical alumina particles. Ideally, the spherical alumina particles should be free of Li, Na, and K. Furthermore, the Li, Na, and K contents can be determined using the methods described later. Also, considering the reduction of dielectric tangent and the reliability of electronic materials, the content of impurities such as Fe or anions such as Cl- and Br- in the spherical alumina particles should be as low as possible.

[0032] In this embodiment, it is preferable to surface treat the spherical alumina particles with a surface treatment agent. Surface treatment with a surface treatment agent can potentially increase the incorporation amount (filler content) in the resin and further reduce the dielectric tangent. For example, coupling agents can be used as surface treatment agents. Examples of coupling agents include silane coupling agents, titanate coupling agents, and aluminate coupling agents. Specifically, examples include hexamethyldisilazane (HMDS), vinyltrimethoxysilane, and 7-octenyltrimethoxysilane. One or more of these surface treatment agents can be used. The amount of surface treatment agent is not particularly limited; for example, the amount of surface treatment agent relative to 100 parts by mass of spherical alumina particles can be 0.01 to 5 parts by mass. In addition, when spherical alumina particles are surface treated with a surface treatment agent, the content of the crystalline phase of α-alumina, the half width of the (113) peak of α-alumina, the average particle size, the average roundness, and the contents of Li, Na and K are measured for the surface-treated spherical alumina particles.

[0033] Regarding the spherical alumina particles of this embodiment, it is ideal for the polyethylene / alumina composite sheet made by incorporating 30% by volume of the aforementioned spherical alumina particles into polyethylene resin to have a dielectric tangent of less than 4.0 × 10⁻⁴, less than 3.6 × 10⁻⁴, and even more ideal to have a dielectric tangent of less than 3.2 × 10⁻⁴, measured in the resonator method at 30-40 GHz. By ensuring that the dielectric tangent is less than 4.0 × 10⁻⁴, the resin composition containing the aforementioned spherical alumina particles exhibits a low dielectric tangent, making it suitable as a filler, for example, in resin compositions used as fillers in high-frequency substrates. The dielectric characteristics at 30-40 GHz can be measured, for example, using a 36 GHz cavity resonator, a 40 GHz split-type cylinder resonator, or a balanced circular plate resonator. Considering the need for high accuracy, it is more ideal to measure using a 36 GHz cavity resonator or a 40 GHz split-type cylinder resonator. Furthermore, the aforementioned dielectric tangent can be measured using the method described later.

[0034] Regarding the spherical alumina particles of this embodiment, it is preferable that the thermal conductivity of the epoxy resin / alumina composite sheet formed by incorporating 40% by volume of the aforementioned spherical alumina particles into the epoxy resin is 1.1 W / m·K or higher, more preferably 1.2 W / m·K or higher, and even more preferably 1.3 W / m·K or higher. By achieving a thermal conductivity of 1.1 W / m·K or higher, the resin composition containing the aforementioned spherical alumina particles exhibits high thermal conductivity (heat dissipation), making it suitable as a filler, for example, in resin compositions used as fillings in high-frequency substrates. Furthermore, the aforementioned thermal conductivity can be measured using the method described later.

[0035] The spherical alumina particles of this embodiment are useful as fillers in resin compositions requiring low dielectric tangents because the resulting resin composition exhibits a low dielectric tangent after mixing with the resin. For example, they are suitable as fillers in resin compositions used in high-frequency substrates.

[0036] [Manufacturing Method of Spherical Alumina Particles] The method for manufacturing spherical alumina particles according to this embodiment includes the following steps: heating raw alumina particles with an average particle size of 0.5 to 40 μm and an average sphericity of 0.90 or higher at a temperature of 1350 to 1700°C (hereinafter also referred to as the heating step). In addition to the heating step described above, the method of this embodiment may also include other steps. By means of the method of this embodiment, the spherical alumina particles of this embodiment can be manufactured easily and efficiently.

[0037] (Heating step) In this step, raw alumina particles with an average particle size of 0.5~40μm and an average sphericity of 0.90 or higher are heated at 1350~1700℃. The raw alumina particles are not particularly limited to amorphous, α-phase, δ-phase, γ-phase, or other crystalline systems, and the preparation method is not particularly limited; spherical alumina produced by the powder melting method is preferred. The powder melting method refers to the method of introducing non-spherical alumina, aluminum hydroxide, boehmite, etc., into a high-temperature field above their melting point, such as a flame, plasma, electric furnace, or gas furnace, and spheroidizing them. Furthermore, since the particle size of the spherical alumina particles obtained through the heating step reflects the particle size of the raw alumina particles, an average particle size of 0.5–40 μm and an average sphericity of 0.90 or higher are ideal for the raw alumina particles. An average particle size of 0.8–30 μm and an average sphericity of 0.93 or higher are even more ideal, and an average particle size of 1–18 μm and an average sphericity of 0.95 or higher are even more desirable. In addition, the average particle size and average sphericity of the raw alumina particles are measured in the same manner as those of the spherical alumina particles.

[0038] Regarding the heating device for heating alumina particles, there are no particular limitations as long as the device can perform high-temperature heating; examples include electric furnaces, rotary kilns, and pusher furnaces. The heating environment is not particularly limited; examples include atmospheric conditions, N₂, Ar, and vacuum. A heating temperature of 1350–1700℃ is ideal, 1400–1600℃ is more ideal, and 1400–1550℃ is even more ideal. By heating the temperature above 1350℃, the content of the crystalline phase of α-alumina increases, and the crystallinity of α-alumina is improved, thus achieving a lower dielectric tangent. Furthermore, by heating the temperature below 1700℃, the formation of agglomerates due to particle fusion can be suppressed, making it ideal for use as a filler mixed with resin. While the heating time is also related to the heating temperature, 1–24 hours is ideal, 2–20 hours is more ideal, and 2–12 hours is even more ideal. By heating for more than 1 hour, the content of the crystalline phase of α-alumina increases, and the crystallinity of α-alumina is also improved, thus achieving a lower dielectric tangent. Furthermore, by heating for less than 24 hours, productivity can be improved.

[0039] The spherical alumina particles obtained after heating may sometimes form aggregates of multiple particles. These aggregates can be used as spherical alumina particles themselves, or they can be broken down and used as spherical alumina particles as needed. The method for breaking down the aggregates is not particularly limited; examples include using an agate mortar and pestle, ball milling, vibratory grinding, jet milling, and wet jet milling. Breakdown can be carried out using dry methods, or it can be done using a wet method by mixing with liquids such as water or alcohol. In wet methods, drying after breaking down yields spherical alumina particles. The drying method is not particularly limited; examples include heat drying, vacuum drying, freeze drying, and supercritical carbon dioxide drying.

[0040] (Other steps) The method for manufacturing spherical alumina particles according to this embodiment may, in addition to the heating step described above, include a grading step for obtaining a desired average particle size of the spherical alumina particles, a surface treatment step for surface treatment using a surface treatment agent such as a coupling agent, a washing step for reducing impurities, and other steps. The type and amount of surface treatment agent used in the above surface treatment step may be the same as those described above.

[0041] [Resin Composition] The resin composition of this embodiment includes the spherical alumina particles of this embodiment and a resin. Because the resin composition of this embodiment contains the spherical alumina particles of this embodiment, it exhibits a low dielectric tangent. Furthermore, because the resin composition containing the spherical alumina particles of this embodiment has low viscosity, it has excellent flowability and formability.

[0042] Regarding the aforementioned resins, there is no particular limitation; examples include polyethylene, polypropylene, epoxy resin, polysiloxane resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamide-imide, polyetherimide, etc., polyesters such as polybutylene terephthalate and polyethylene terephthalate, polyphenylene sulfide, fully aromatic polyester, polyurethane, liquid crystal polymers, polyether sulfide, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, etc. One of these resins may be used, or two or more may be used in combination.

[0043] The content of spherical alumina particles in the above-mentioned resin composition is appropriately selected based on the target dielectric tangent and other physical properties. A content of 2-90% by mass is relatively ideal, 10-80% by mass is more ideal, and 10-70% by mass is even more ideal. The resin content in the above-mentioned resin composition is relatively ideal at 10-98% by mass, more ideal at 30-90% by mass, and even more ideal at 30-70% by mass.

[0044] Alternatively, other powders with different specific surface area, average particle size, and composition from the spherical alumina particles of this embodiment can be mixed with the resin to obtain a mixed powder, thereby preparing a resin composition. By mixing the mixed powder with the resin, the dielectric constant, dielectric tangent, coefficient of thermal expansion, thermal conductivity, and filling rate of the resin composition can be more easily adjusted.

[0045] The optimal dielectric tangent of the resin composition of this embodiment varies depending on the type of resin, the amount of admixture, and the presence or absence of additives. However, when 30% by volume is added to low-dielectric-tangent resins such as polytetrafluoroethylene, polyethylene, and polypropylene, a dielectric tangent measured in the resonator method at 30-40 GHz is less than 4.0 × 10⁻⁴, less than 3.6 × 10⁻⁴ is more ideal, and less than 3.2 × 10⁻⁴ is even more ideal. The optimal thermal conductivity of the resin composition of this embodiment varies depending on the type of resin, the amount of admixture, and the presence or absence of additives. However, for example, when 40% by volume is added to epoxy resin, a thermal conductivity of 1.1 W / m·K or higher is more ideal, 1.2 W / m·K or higher is more ideal, and 1.3 W / m·K or higher is even more ideal. Furthermore, the dielectric tangent and thermal conductivity of the above-mentioned resin composition are values ​​measured by the methods described later.

[0046] The resin composition of this embodiment exhibits a low dielectric tangent, making it particularly useful as a resin composition for high-frequency substrates. Examples of high-frequency substrates include fluoropolymer substrates, PPE substrates, and ceramic substrates. When using the resin composition of this embodiment as a material or insulating material for such high-frequency substrates, a low-dielectric resin can be used as the resin constituting the resin composition. Examples of low-dielectric resins include hydrocarbon elastomers, polyphenylene ethers, and aromatic polyene resins, with hydrocarbon elastomers or polyphenylene ethers being more ideal. One or more of these resins can be used. The spherical alumina particles of this embodiment can also be incorporated into these resins, and then the resins can be cross-linked and cured as needed. The mass ratio of spherical alumina particles or the above-mentioned mixed powder to these resins (spherical alumina particles or the above-mentioned mixed powder: resin) is arbitrary, but can be, for example, 5:95 to 80:20, or 5:95 to 70:30.

[0047] Examples of hydrocarbon-based elastomers include ethylene-based elastomers, propylene-based elastomers, conjugated diene polymers, block copolymers or random copolymers of aromatic vinyl compounds-conjugated diene compounds, and their hydrides (hydrogenated products). Examples of ethylene-based elastomers include ethylene-octene copolymers, ethylene-1-hexene copolymers, and other ethylene-α-olefin copolymers, EPR, EPDM, etc. Examples of propylene-based elastomers include heterostructured polypropylene, low stereoregularity polypropylene, and propylene-1-butene copolymers, etc. Examples of conjugated diene polymers include polybutadiene, 1,2-polybutadiene, etc. Examples of aromatic vinyl compound-conjugated diene block copolymers or random copolymers, and their hydrides (hydrogenated products), include SBS, SIS, SEBS, SEPS, SEEPS, SEEBS, etc.

[0048] These hydrocarbon-based elastomers can be used individually or in combination. Among these, conjugated diene polymers are more ideal for hydrocarbon-based elastomers, with 1,2-polybutadiene being even more desirable. 1,2-Polybutadiene is commercially available not only in the form of products from companies such as JSR Corporation, but also in liquid polybutadiene from Nippon Soda Corporation, under the product names B-1000, 2000, and 3000. Furthermore, commercially available examples of copolymers containing the 1,2-polybutadiene structure that are ideally suited for use include "Ricon100" from Total Cray Valley. A molecular weight average of 1000 or higher for the number of hydrocarbon elastomers is ideal, and 10,000 or higher is even more desirable.

[0049] Regarding polyphenylene ether (PPE), commercially available and known PPE can be used. The number-average molecular weight of PPE is arbitrary, but considering the processability of the blend, a number-average molecular weight of 10,000 or less is ideal, and 5,000 or less is even more ideal. A number-average molecular weight of 500 or more is also ideal. Furthermore, when adding PPE for the purpose of hardening the blend, it is ideal for the molecular ends to be modified, and / or for each molecule to have multiple functional groups. Examples of functional groups include allyl, vinyl, and epoxy groups. Furthermore, free radical polymerizable functional groups are ideal, and vinyl groups are even more ideal. For vinyl groups, (meth)acrylate and aromatic vinyl groups are ideal. Finally, difunctional PPE with free radical polymerizable functional groups modified at both ends of the molecular chain is even more ideal. For this type of polyphenylene ether, commercially available products include Noryl (trademark) SA9000 from SABIC Corporation and difunctional polyphenylene ether oligomer (OPE-2St) manufactured by Mitsubishi Gas Chemical Corporation.

[0050] Aromatic polyene resins include divinylbenzene reactive multibranched copolymers (PDVs). Such PDVs are described, for example, in the literature "Synthesis of Multifunctional Aromatic Vinyl Copolymers and Development of Novel IPN-Type Low Dielectric Loss Materials Using Them" (Masanori Kawabe, Journal of the Institute of Electrical Installations, p. 125, Vol. 12 No. 2 (2009)). Commercially available products include PDVs manufactured by Nippon Steel & Sumitomo Metal Chemicals Co., Ltd. Furthermore, aromatic polyene resins include aromatic polyene polymer resins that use the aforementioned aromatic polyene monomers as the main constituent units.

[0051] When preparing the resin composition of this embodiment, a crosslinking material and a curing agent can also be used together with the spherical alumina particles or mixed powder of this embodiment and the aforementioned resin to crosslink and cure the resin. Examples of such crosslinking materials include various maleimides, bismaleimides, maleic anhydride, glycidyl methacrylate, triallyl isocyanurate, tri(meth)acrylate isocyanurate, and trimethylolpropane tri(meth)acrylate. One or more of these can be used together. Maleimides and bismaleimides are, for example, described in International Publication No. 2016 / 114287, and are commercially available, for example, from Daiwa Chemical Industries, Ltd. Considering factors such as solubility in organic solvents, high-frequency characteristics, high adhesion to conductors, and moldability of prepregs, polyamine-based bismaleimide compounds are preferred among these maleimide-containing compounds. Polyamine-based bismaleimide compounds can be obtained, for example, by performing a MacCard addition reaction between a compound with two maleimide groups at the end and an aromatic diamine compound with two primary amine groups in its molecule. When attempting to achieve high crosslinking efficiency with minimal addition, it is ideal to use crosslinking materials with more than two functional groups, such as bismaleimides, triallyl isocyanurate (TAIC), and trimethylolpropane tri(meth)acrylate. When using crosslinking materials, an amount of 0.1 to 30 parts by weight relative to 100 parts by weight of the aforementioned resin is ideal, and 0.1 to 10 parts by weight is even more ideal.

[0052] Regarding the aforementioned curing agents, known curing agents that can be used in the polymerization or curing of aromatic polyenes and aromatic vinyl compounds can be used. Examples of such curing agents include free radical polymerization initiators, cationic polymerization initiators, and anionic polymerization initiators, but free radical polymerization initiators are preferred. Organic peroxide-based (peroxide) polymerization initiators and azo-based polymerization initiators are even more desirable, and can be freely selected according to the application and conditions. For example, commercially available organic peroxides are available from companies such as Nippon Oil, Wako Pure Chemicals, and Tokyo Chemical Industries, as listed in their respective catalogs on their websites. Alternatively, known photopolymerization initiators utilizing light, ultraviolet light, or radiation can also be used as curing agents. Examples of photopolymerization initiators include photoradioactive free radical polymerization initiators, photocationic polymerization initiators, and photoanionic polymerization initiators. These photopolymerization initiators are available commercially from companies such as Tokyo Chemical Industries. Curing can then be achieved using radiation or electron beams themselves. Alternatively, crosslinking and curing can be achieved through thermal polymerization of the raw materials without a hardener. When using a hardener, the amount used is not particularly limited, but 0.01 to 10 parts by weight relative to 100 parts by weight of the aforementioned resin is ideal. When using peroxide-based or azo-based polymerization initiators, their half-life should be considered to determine the appropriate temperature and time for curing. The conditions in this case are arbitrary depending on the hardener used, but a temperature range of approximately 50°C to 180°C is generally suitable.

[0053] When the spherical alumina particles or mixed powders of this embodiment are used as materials for high-frequency substrates or as insulating materials, the various resins, crosslinking materials, hardeners, etc. used are described in, for example, the following patent documents: Japanese Patent Application Publication No. Hei 8-208856, Japanese Patent Application Publication No. 2017-75270, Japanese Patent Application Publication No. 2009-167268, Japanese Patent Application Publication No. 2011-68713, Japanese Patent Application Publication No. 2018-131519, Japanese Patent Application Publication No. 2016-534549, Japanese Patent Application Publication No. 2017-57352, International Publication No. WO2016 / 175325, and International Publication No. WO2016 / 175326. [Example]

[0054] The present invention will now be described in more detail with reference to embodiments, but the present invention is not limited to the embodiments.

[0055] [Example 1] 50g of raw alumina particles 1 (manufactured by DENKA, trade name: DAW-05, average particle size: 5.1μm, average sphericity: 0.95) were loaded into an alumina crucible as raw alumina particles and heated in an electric furnace at 1400℃ for 4 hours under atmospheric conditions. After heating treatment, the mixture was allowed to cool naturally until the furnace temperature dropped below 200℃. The powder was then collected and crushed in a mortar to obtain spherical alumina particles.

[0056] [Examples 2 and 3] The heating temperature or heating time in the heat treatment was changed as shown in Table 1. Otherwise, spherical alumina particles were prepared in the same manner as in Example 1.

[0057] [Example 4] Using raw material alumina particles 2 (manufactured by DENKA Corporation, trade name: DAW-15, average particle size: 15.2 μm, average sphericity: 0.97) as raw material alumina particles, and changing the heating temperature as shown in Table 1, spherical alumina particles were prepared in the same manner as in Example 1.

[0058] [Example 5] Relative to 100 parts by weight of the spherical alumina particles obtained in Example 1, 0.1 parts by weight of hexamethyldisilazane (HMDS) (manufactured by Shin-Etsu Polysiloxane Co., Ltd., trade name: SZ-31) was added as a surface treatment agent. Then, the mixture was mixed at an acceleration of 60G for 2 minutes using a vibratory mixer manufactured by Resodyn, and subsequently dried in a vacuum powder dryer (120°C, below 133 Pa) for 24 hours. This yielded surface-treated spherical alumina particles.

[0059] [Example 6] One part by weight of vinyltrimethoxysilane (manufactured by Shin-Etsu Polysiloxane Co., Ltd., trade name: KBM-1003) was added as a surface treatment agent, and otherwise, spherical alumina particles after surface treatment were prepared in the same manner as in Example 5.

[0060] [Example 7] Using raw material alumina particles 3 (manufactured by DENKA Corporation, trade name: DAW-0105, average particle size: 1.0 μm, average sphericity: 0.96) as raw material alumina particles, and varying the heating time as shown in Table 1, spherical alumina particles were prepared in the same manner as in Example 1.

[0061] [Example 8] Raw material alumina particles 4 (manufactured by DENKA Corporation, trade name: DAM-05, average particle size: 5.0 μm, average sphericity: 0.95) were used as raw material alumina particles. Otherwise, spherical alumina particles were prepared in the same manner as in Example 1.

[0062] [Example 9] In the evaluation of the dielectric constant and dielectric tangent of the resin composition containing the spherical alumina particles obtained in Example 1, polypropylene (manufactured by Sumitomo Seika Co., Ltd., trade name: FLOBLEN QB200) was used as the resin.

[0063] [Comparative Examples 1-3] The heating temperature and / or heating time in the heat treatment were changed as shown in Table 2. Otherwise, spherical alumina particles were prepared in the same manner as in Example 1.

[0064] [Comparative Example 4] Using raw material alumina particles 5 (manufactured by DENKA, trade name: ASFP-20, average particle size: 0.3 μm, average sphericity: 0.95) as raw material alumina particles, and changing the heating temperature as shown in Table 2, spherical alumina particles were prepared in the same manner as in Example 1.

[0065] [Comparative Example 5] In the evaluation of the dielectric constant and dielectric tangent of the resin composition containing the spherical alumina particles obtained in Comparative Example 2, polypropylene (manufactured by Sumitomo Seika Co., Ltd., trade name: FLOBLEN QB200) was used as the resin.

[0066] The various characteristics of the spherical alumina particles prepared in each example and comparative example, as well as the raw material alumina particles 1-5 used as reference examples 1-5, were evaluated using the following methods. The evaluation results are shown in Tables 1-3.

[0067] [Average roundness] After fixing spherical alumina particles or raw alumina particles onto the sample stage with carbon tape, osmium coating is applied. Then, images obtained by scanning electron microscopy (JEM Co., Ltd., trade name: JSM-7001F SHL) at a magnification of 500 to 50,000 times and a resolution of 1280 × 1024 pixels are read into a personal computer. The projected area (S) and projected perimeter (L) of the particles are calculated using an image analysis device (NIPPON ROPER Co., Ltd., trade name: Image-Pro Premier Ver. 9.3), and the roundness is calculated using the following formula (1). The roundness is calculated for 200 particles with an equivalent circle diameter of 0.8 to 50 μm obtained in this manner, and the average value is taken as the average roundness. Circularity = 4πS / L 2(1)

[0068] [density] 2.0 g of spherical alumina particles or raw alumina particles were loaded into the sample cell for testing, and the density was determined by gas (helium) displacement method using a dry densitometer (Shimadzu Corporation, trade name: AccuPycII1340).

[0069] [Average Particle Size] The average particle size was determined using a laser diffraction particle size distribution measuring device (Beckman Coulter, trade name: LS 13 320). 50 cm³ of pure water and 0.1 g of spherical alumina particles or raw alumina particles were placed in a glass beaker and dispersed using an ultrasonic homogenizer (BRANSON, trade name: SFX250) for 1 minute. The dispersion of the powder was then added dropwise to the laser diffraction particle size distribution measuring device, and the measurement was performed 30 seconds after the predetermined amount was added. The particle size distribution was calculated based on the intensity distribution of diffracted / scattered light obtained from the particle detection by the sensor in the laser diffraction particle size distribution measuring device. The average particle size was obtained by multiplying the measured particle size value by the relative particle mass (difference %), and then dividing by the total relative particle mass (100%). Note that the % here refers to volume.

[0070] [Determination of the crystalline phase content of α-alumina and the half-width of the (113) peak] The identification of the α-alumina crystalline phase contained in the spherical alumina particles and raw alumina particles, as well as the determination of the α-alumina crystalline phase content and the half-width of the (113) peak, were performed by powder X-ray diffraction. The measuring apparatus used was a sample-level multi-object X-ray diffraction device (Rigaku Corporation, trade name: RINT-Ultima IV). The measurements were performed under the following conditions: X-ray source: CuKα, tube voltage: 40 kV, tube current: 40 mA, scanning speed: 10.0° / min, 2θ scanning range: 10°~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 the crystalline phase of α-alumina was calculated by the ratio (A) of the total peak area (012), (104), and (113) of α-alumina observed during X-ray diffraction measurement of the test sample to the total peak area (B) of the same phase observed during X-ray diffraction measurement of the NIST-prepared standard α-alumina sample (012), (104), and (113) (A / B)*100. Furthermore, the half-width of the (113) peak of α-alumina was calculated.

[0071] [Determination of Li, Na and K content] The determination of Li, Na, and K contents was performed using inductively coupled plasma optical emission spectrometry (ICP-OES). The analytical apparatus used was an ICP-OES spectrometer (SPECTRO, trade name: CIROS-120). Spherical alumina particles and 0.1 g of raw alumina particles were weighed into a platinum crucible, and the test solution was prepared by pressurized acid decomposition using hydrofluoric acid and sulfuric acid at 200°C. The Li, Na, and K contents listed in Tables 1-3 represent the total Li, Na, and K contents.

[0072] [Thermal conductivity of resin components] The resin composition was prepared as follows: 25.6 parts by weight of bisphenol A type liquid epoxy resin (manufactured by Mitsubishi Chemical Corporation, trade name: JER828) and 6.4 parts by weight of 4,4'-diaminobenzylmethane (manufactured by Tokyo Chemical Co., Ltd.) were melted at 95°C and mixed simultaneously. Spherical alumina particles or raw alumina particles were added to this mixture at a filler content of 40% by volume (66 parts by weight when the density is 3.7 g / cm³), and the mixture was stirred using a planetary mixer (THINKY Corporation, trade name: Rentaro AR-250 degassing mixer, speed 2000 rpm). The obtained mixture was poured into a polysilicon mold (2cm square × 6mm thick) preheated to 80°C, and hardened by pressure heating in the following order: 80°C / 1 hour / 3MPa, 150°C / 1 hour / 5MPa, and 200°C / 0.5 hours / 7MPa, 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 determined by processing the hardened sample into a 10mm wide × 10mm × 1mm thick sample and then using the laser flash method. The measuring apparatus was a xenon flash analyzer (NETZSCH, LFA447 NanoFlash). The specific gravity was determined using the Archimedes method. The specific heat coefficient was determined using a differential scanning calorimeter (TA Instruments, trade name: Q2000) under nitrogen atmosphere by heating from room temperature to 200°C at a heating rate of 10°C / min.

[0073] [Dielectricity and dielectric tangent of the resin composition] To ensure that the filling amount of spherical alumina particles or raw alumina particles was 30% by volume, spherical alumina particles or raw alumina particles, polyethylene powder (manufactured by Sumitomo Seika Co., Ltd., trade name: FLO-THENE UF-20S; Examples 1-8, Comparative Examples 1-4, Reference Examples 1-5) or polypropylene powder (manufactured by Sumitomo Seika Co., Ltd., trade name: FLOBLENQB200; Example 9 only, Comparative Example 5) were measured and mixed using a vibratory mixer manufactured by Resodyn Co., Ltd. (acceleration 60G, processing time 2min). The obtained mixed powder was measured in predetermined volume portions (to make the thickness approximately 0.3mm) and placed in a metal frame with a diameter of 3cm. The sample was sheeted using a nanoimprint apparatus (manufactured by SCIVAX Co., Ltd., trade name: X-300) at 140°C, 5 minutes, and 30000N for polyethylene, and at 190°C, 5 minutes, and 30000N for polypropylene to prepare evaluation samples. The thickness of the sheet material used for evaluation is 0.3 mm. If it can be mounted on the measuring instrument, the shape and size will not affect the evaluation results, but it should be 1.5 cm square.

[0074] The dielectric constant and dielectric tangent were determined using the following method. A 36 GHz cavity resonator (manufactured by SAMTECH) was connected to a vector network analyzer (trade name: 85107, manufactured by Keysight Technologies). An evaluation sample (1.5 cm square, 0.3 mm thick) was placed in a 10 mm diameter hole in the resonator, and the resonant frequency (f0) and unloaded Q value (Qu) were measured. The evaluation sample was rotated during each measurement, and this process was repeated five times. The average of the obtained f0 and Qu values ​​was calculated as the measured values. The dielectric constant was calculated from f0 using analysis software (manufactured by SAMTECH), and the dielectric tangent (tanδc) was calculated from Qu. The measurement temperature was 20°C, and the humidity was 60%RH. Additionally, the dielectric constant of polyethylene sheeted under the same conditions without filler was 2.3, and the dielectric tangent was 2.6 × 10⁻⁴.

[0075] [Table 1] unit Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Types of raw alumina particles - DAW-05 DAW-05 DAW-05 DAW-15 DAW-05 DAW-05 DAW-0105 DAM-05 DAW-05 Heating temperature ℃ 1400 1500 1400 1450 1400 1400 1400 1400 1400 Heating time h 4 4 16 4 4 4 2 4 4 Surface treatment - - - - - HMDS Vinyltrimethoxysilane - - - Average roundness - 0.95 0.91 0.94 0.93 0.92 0.93 0.97 0.96 0.95 density g / cm 3 3.9 4.0 3.9 4.0 3.9 3.9 3.9 3.9 3.9 Average particle size μm 6.0 6.0 6.0 18.0 5.7 5.7 1.2 5.4 6.0 α-alumina crystalline phase content quality% 98 100 99 100 98 98 99 98 98 The half-width at half-maximum of the (113) peak of α-alumina ° 0.119 0.117 0.120 0.115 0.118 0.118 0.121 0.119 0.119 Li, Na and K content mass ppm 260 220 220 140 260 250 290 520 260 Thermal conductivity of resin components W / m･K 1.2 1.2 1.3 1.3 1.3 1.3 1.2 1.2 1.2 Dielectricity of resin components - 3.6 3.6 3.5 3.6 3.6 3.5 3.6 3.6 3.6 Dielectric tangent of resin composition - 3.0×10⁻⁴ 2.8×10⁻⁴ 3.0×10⁻⁴ 2.8×10⁻⁴ 3.0×10⁻⁴ 2.9×10⁻⁴ 3.4×10⁻⁴ 3.2×10⁻⁴ 2.9×10⁻⁴

[0076] [Table 2] unit Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Types of raw alumina particles - DAW-05 DAW-05 DAW-05 ASFP-20 DAW-05 Heating temperature ℃ 1300 1200 1300 1300 1200 Heating time h 4 4 twenty four 4 4 Surface treatment - - - - - - Average roundness - 0.95 0.95 0.93 0.72 0.95 density g / cm 3 3.8 3.8 3.9 3.8 3.8 Average particle size μm 5.2 5.3 5.7 2.8 5.3 α-alumina crystalline phase content quality% 76 53 94 98 53 The half-width at half-maximum of the (113) peak of α-alumina ° 0.127 0.129 0.126 0.158 0.129 Li, Na and K content mass ppm 420 500 390 Under 10 500 Thermal conductivity of resin components W / m･K 1.0 1.0 1.1 0.93 1.0 Dielectricity of resin components - 3.6 3.5 3.6 3.6 3.5 Dielectric tangent of resin composition - 4.5×10⁻⁴ 5.6×10⁻⁴ 4.2×10⁻⁴ 8.3×10⁻⁴ 5.2×10⁻⁴

[0077] [Table 3] unit Reference Example 1 See Example 2 See Example 3 See Example 4 See Example 5 Types of raw alumina particles - DAW-05 DAW-15 DAW-0105 DAM-05 ASFP-20 Average roundness - 0.95 0.97 0.96 0.95 0.95 density g / cm 3 3.7 3.8 3.7 3.7 3.7 Average particle size μm 5.1 15.2 1.0 5.0 0.3 α-alumina crystalline phase content quality% 38 64 twenty two 35 0 The half-width at half-maximum of the (113) peak of α-alumina ° 0.127 0.125 0.130 0.128 - Thermal conductivity of resin components W / m･K 0.92 0.97 0.88 0.90 0.84 Dielectricity of resin components - 3.5 3.6 3.5 3.5 3.4 Dielectric tangent of resin composition - 7.0×10⁻⁴ 5.2×10⁻⁴ 7.8×10⁻³ 6.5×10⁻³ 2.4×10⁻³

[0078] none

Claims

1. A spherical alumina particle containing more than 90% by mass of α-alumina crystalline phase, wherein the half-width of the (113) peak of α-alumina observed by X-ray diffraction under the conditions of X-ray source: CuKα, tube voltage: 40kV, tube current: 40mA, scanning speed: 10.0° / min, and 2θ scanning range: 10°~80° is less than 0.124°, and the average particle size is 18~40μm, and the total content of Li, Na and K in the spherical alumina particle, based on the total mass of the spherical alumina particle, is less than 500 ppm by mass.

2. Spherical alumina particles as described in claim 1, wherein, The average sphericality of the alumina particles is above 0.

90.

3. The spherical alumina particles in request item 1 or 2 are surface-treated with a surface treatment agent.

4. Spherical alumina particles as requested in item 1 or 2, wherein, The dielectric tangent of a polyethylene / alumina composite sheet made by incorporating 30% by volume of the spherical alumina particles into polyethylene resin did not reach 4.0 × 10⁻⁴ when measured in a resonator method at 30–40 GHz.

5. A method for manufacturing spherical alumina particles, which is the method for manufacturing spherical alumina particles according to any one of claims 1 to 4, comprising the following steps: heating raw alumina particles with an average particle size of 15.2 to 40 μm and an average sphericity of 0.90 or higher at a temperature of 1350 to 1700°C.

6. A resin composition comprising spherical alumina particles as claimed in any one of claims 1 to 4, and a resin.

7. The resin composition as claimed in claim 6, wherein, The content of spherical alumina particles in the resin composition is 2-90% by mass.

8. The resin composition as claimed in item 6 or 7, wherein, The resin is selected from at least one of the group consisting of hydrocarbon elastomers, polyphenylene ethers, and aromatic polyene resins.

9. The resin composition in claim 6 or 7 is a resin composition for high-frequency substrates.

Images