JP7730415B2 - Spherical calcium titanate powder and resin composition using same - Google Patents

Description

The present invention relates to spherical calcium titanate powder and a resin composition using the same.

In recent years, with the increase in the volume of information communication in the field of communications, the use of high-frequency band signals has become widespread in electronic devices, communication devices, and the like. However, the application of high-frequency band signals to such devices has also caused a problem of increased transmission loss of circuit signals. In particular, materials with lower dielectric loss tangents are required for ceramic fillers used in AiPs (Antenna in Package: AiP) for RF (Radio Frequency: RF) modules, and the like.
Furthermore, as related electronic materials and components become more highly functional, further miniaturization of antenna devices is also required. Communication devices can be further miniaturized by increasing the relative dielectric constant of the antenna material incorporated therein. Therefore, ceramic fillers used in AiPs for RF modules and the like are required to have a high dielectric constant and a low dielectric loss tangent (see, for example, Patent Document 1).

Perovskite complex oxides are complex oxides mainly represented by the formula _ABO3 , such as barium titanate and strontium titanate. Powders of such perovskite complex oxides have a relatively high dielectric constant, and are therefore expected to be used as ceramic fillers that can be applied to next-generation electronic devices. Of these, titanium-based complex oxides are used as electronic materials because they exhibit excellent electrical properties such as dielectricity, pyroelectricity, and piezoelectricity. Patent Document 2 describes calcium titanate powder with high crystallinity and excellent electrical properties, and a method for producing the same.

Because ceramic fillers are often used by filling them into resins, it is desirable for their shape to be as spherical as possible in order to improve their fillability and dispersibility in the resin, thereby stabilizing their dielectric properties, as well as to improve processability and workability. The particles that make up the calcium titanate powder in Patent Document 2 are square pillars or similar in shape, and no powder containing spherical calcium titanate particles has been studied.

Patent Documents 3 and 4 propose powders made of spherical perovskite-type composite oxide particles with a specific specific surface area and average particle size, but the examples only examine barium titanate-based powders; calcium titanate powders are not considered. Furthermore, the particles described in Patent Documents 3 and 4 have a roughly spherical shape with significant surface irregularities, making them difficult to pack densely into resins. Furthermore, powders made of particles with such shapes have the problem of excessively high viscosity when made into a resin composition, reducing processability and workability.

Japanese Patent Application Laid-Open No. 2021-27386 JP 2011-116645 A JP 2013-155071 A JP 2013-155072 A Patent No. 4155750 Japanese Patent Application Laid-Open No. 2012-246203

The present invention aims to provide a spherical calcium titanate powder that is easy to process and work even when highly filled in resin, and that can achieve a high dielectric constant and low dielectric tangent and can be used as a ceramic filler for high-frequency band devices, as well as a resin composition using the same.

As a result of extensive research, the present inventors have discovered that, as long as the powder is spherical calcium titanate powder having an average circularity of 0.80 or more and a shear viscosity measured under specific conditions of 3,000 Pa s or less, processability and workability are not adversely affected even when the powder is highly filled into a resin, and furthermore, a high dielectric constant and a low dielectric dissipation factor can be simultaneously achieved, leading to the completion of the present invention.
That is, the present invention has the following aspects.
[1] A spherical calcium titanate powder having an average circularity of 0.80 or more and a shear viscosity measured under the following conditions of 3,000 Pa·s or less.
<Shear viscosity measurement conditions>
A resin composition consisting of 60% by volume of bisphenol A liquid epoxy resin (epoxy equivalent: 184 to 194) and 40% by volume of spherical calcium titanate powder is measured for viscosity using a rheometer at a shear rate of 0.11/s, a circular flat plate shape (10 mm diameter), a sample thickness of 1 mm, and a temperature of 25±1°C.
[2] The spherical calcium titanate powder according to [1], having an average particle diameter (D50) of 1 to 100 μm.
[3] The spherical calcium titanate powder according to [1] or [2], which has a specific surface area of 0.1 to 1.5 ^{m 2} /g.
[4] The spherical calcium titanate powder according to any one of [1] to [3], wherein the full width at half maximum (FWHM) of the X-ray diffraction peak at 2θ of 32° to 34° is 0.150° to 0.175°.
[5] The spherical calcium titanate powder according to any one of [1] to [4], wherein the shear viscosity is 1,500 Pa·s or less.
[6] The spherical calcium titanate powder according to any one of [1] to [5], which is for use in resin filling.
[7] A resin composition comprising the spherical calcium titanate powder according to any one of [1] to [6] and at least one resin selected from thermoplastic resins and thermosetting resins.

The present invention provides spherical calcium titanate powder that is resistant to deterioration in processability and workability even when highly filled in resin, and that can be used as a ceramic filler for high-frequency band devices, achieving a high dielectric constant and low dielectric dissipation factor, as well as a resin composition using the same.

1 is a scanning electron microscope photograph showing one embodiment of a spherical calcium titanate powder according to the present embodiment. 1 is a scanning electron microscope photograph showing another aspect of the spherical calcium titanate powder according to the present embodiment.

One embodiment of the present invention will be described in detail below, but the present invention is not limited to the following embodiment. In this specification, the term "to" means "at least or equal to or less than." For example, "3 to 15" means at least 3 and at most 15. In addition, in this specification, "powder" means "an aggregate of multiple particles."

[Spherical calcium titanate powder]
The spherical calcium titanate powder according to this embodiment is characterized by having an average circularity of 0.80 or more and a shear viscosity measured under the following conditions of 3,000 Pa·s or less.
<Shear viscosity measurement conditions>
The viscosity of a resin composition consisting of 60% by volume of a bisphenol A liquid epoxy resin (epoxy equivalent: 184 to 194, for example, product name "JER828" manufactured by Mitsubishi Chemical Corporation) and 40% by volume of spherical calcium titanate powder is measured using a rheometer (for example, product name "MCR302" manufactured by Anton-Paar GmbH) at a shear rate of 0.11/s, a circular flat plate shape (10 mmφ), a sample thickness of 1 mm, and a temperature of 25±1°C.
The spherical calcium titanate powder according to this embodiment is less likely to deteriorate in processability and workability even when highly filled in a resin, and can simultaneously achieve a high dielectric constant and a low dielectric loss tangent.

The spherical calcium titanate powder according to this embodiment (hereinafter sometimes simply referred to as "powder") has an average circularity of 0.80 or more. The average circularity is the average value of the circularities calculated from the projected area (S) and projected perimeter (L) of the particles constituting the spherical calcium titanate powder using the following method. Powders having such an average circularity are composed of particles whose shape is closer to a perfect sphere, allowing for a high filling rate in resin. Furthermore, powders according to this embodiment having such an average circularity can achieve a high dielectric constant and a low dielectric loss tangent. In one embodiment, the average circularity of the powder may be 0.85 or more, or may be 0.90 or more.
<Average circularity>
The spherical calcium titanate powder is fixed with carbon tape and then coated with osmium. Then, the particles constituting the powder are photographed at a magnification of 500 to 50,000 times using a scanning electron microscope (e.g., JEOL Ltd., product name "JSM-7001F SHL"), and the projected area (S) and projected perimeter (L) of the particles are calculated using an image analyzer (e.g., Nippon Roper Co., Ltd., product name "Image-Pro Premier Ver. 9.3"), after which the circularity is calculated using the following formula (1). The circularity of any 200 particles is calculated, and the average value is taken as the average circularity of the spherical calcium titanate powder.
Circularity=4πS/ ^L2 (1)

FIG. 1 is an electron microscope photograph showing one embodiment of the powder according to this embodiment. As shown in FIG. 1, each particle of the powder according to this embodiment has a spherical shape that is close to a perfect sphere. Powders having such shapes do not reduce workability or processability even when highly packed in a resin. Even more surprisingly, the powder according to this embodiment has a very low shear viscosity of 3,000 Pa·s or less, measured by the above method. The powder according to this embodiment, which has these characteristics, can simultaneously achieve the high dielectric constant and low dielectric loss tangent required for ceramic fillers for high-frequency band devices, for example, GHz band devices.
Spherical calcium titanate powder having an average circularity of 0.80 or more can be easily achieved by spheroidizing calcium titanate powder by, for example, powder melting, atomizing, or spray drying.

The shear viscosity (hereinafter simply referred to as "shear viscosity") of the spherical calcium titanate powder according to this embodiment, measured using the method described above, is 3,000 Pa·s or less. Powder according to this embodiment, which has a shear viscosity of 3,000 Pa·s or less, can achieve a low dielectric tangent, due in part to the fact that it can reduce the interaction at the interface between the resin and the filler. Furthermore, powder according to this embodiment, which has such a shear viscosity, can provide a resin composition that is excellent in processability and workability.

The shear viscosity of the powder according to this embodiment is preferably 2,500 Pa·s or less, more preferably 1,500 Pa·s or less, and even more preferably 1,000 Pa·s or less. Powders with a shear viscosity of 3,000 Pa·s or less can be easily achieved, for example, by increasing the proportion of polycrystalline particles in the spherical calcium titanate powder or by preparing a powder with a relatively wide particle size distribution.

The average particle size (D50) of the spherical calcium titanate powder according to this embodiment is preferably 1 to 100 μm, more preferably 1 to 50 μm, and even more preferably 3 to 20 μm. In one embodiment, the average particle size (D50) of the spherical calcium titanate powder may be 3 to 100 μm, 20 to 100 μm, or 50 to 100 μm. In another embodiment, the average particle size (D50) may be 1 to 13 μm or 7 to 13 μm. An average particle size (D50) of 1 to 100 μm facilitates dispersion in resin, making it easier to incorporate the powder according to this embodiment into resin. This also facilitates the attainment of good and stable dielectric properties. The average particle size (D50) of the spherical calcium titanate powder refers to the particle size corresponding to the cumulative value of 50% in the volume-based cumulative particle size distribution measured using a laser diffraction particle size analyzer. The cumulative particle size distribution is expressed by a distribution curve with the particle diameter (μm) on the horizontal axis and the cumulative value (%) on the vertical axis.

Figure 2 is a scanning electron microscope photograph showing another aspect of the spherical calcium titanate powder according to this embodiment. As such, in one embodiment, fine particles may be attached to the surface of the powder. Powders containing such fine particles tend to improve the powder's handleability and to become powders with lower shear viscosity when blended with resins. Furthermore, when made into a resin composition, they tend to have better workability and processability.

The specific surface area of the spherical calcium titanate powder according to this embodiment is preferably 0.1 to 1.5 ^{m 2} /g, more preferably 0.2 to 1.4 ^{m 2} /g, and even more preferably 0.3 to 1.3 m ² /g. In one embodiment, the specific surface area of the spherical calcium titanate powder may be 0.5 to 1.4 ^{m 2} /g, or may be 0.6 to 1.4 m ² /g. A specific surface area of 1.5 m ² /g or less tends to result in a powder with a shear viscosity of 3,000 Pa·s or less, and a small dielectric loss tangent when used in a resin composition. Furthermore, a specific surface area of 0.1 m ² /g or more tends to result in a powder with good fillability and dispersibility in resin. The specific surface area of the spherical calcium titanate powder can be measured by the BET single-point method using a fully automatic specific surface area measuring device.

The calcium titanate constituting the powder of this embodiment is a composite oxide having a perovskite-type crystal structure represented by the general formula _ABO3 , which refers to _CaTiO3 in which A is occupied by Ca and B is occupied by Ti. The crystal structure of the powder can be determined by X-ray diffraction measurement. The full width at half maximum (FWHM) of the X-ray diffraction peak of the spherical calcium titanate powder according to this embodiment at 2θ of 32° to 34° is preferably 0.150° to 0.175°, more preferably 0.150° to 0.170°, even more preferably 0.155° to 0.170°, and particularly preferably 0.166° to 0.172°. The crystals of the spherical calcium titanate powder having the FWHM of 0.150° to 0.175° tend to be polycrystalline while maintaining a certain degree of crystallinity. Although the exact reason is unknown, the powder according to this embodiment has a high dielectric constant due to a certain degree of crystallinity, and is polycrystalline, so the particle surface is relatively smooth, and the interaction at the interface between the resin and the filler can be reduced, making it easy to achieve a low dielectric tangent. The half-width mentioned above can be measured under the following conditions.
<Method for measuring X-ray diffraction of spherical calcium titanate powder>
Using an XRD device (for example, Rigaku Corporation, product name "RINT-Ultima IV"), the X-ray diffraction peak of the spherical calcium titanate powder is measured under the following conditions. Then, using XRD analysis software (for example, Rigaku Corporation, product name "Comprehensive Powder X-ray Analysis Software PDXL2"), the half-value width at 2θ of 32° to 34° is calculated.
X-ray source: CuKα
Tube voltage: 40 kV
Tube current: 40mA
Scan speed: 4.0°/min
2θ scan range: 10° to 50°

The average particle density of the spherical calcium titanate powder according to this embodiment is preferably 3.8 to 4.3 g/ ^cm3 , and more preferably 4.0 to 4.3 g/ ^cm3 . When the average particle density is 3.8 to 4.3 g/ ^cm3 , the number of voids within the particles is reduced, which tends to result in a good dielectric constant. The average particle density of the spherical calcium titanate powder can be measured by the following method.
<Method for measuring average particle density>
5.0 g of spherical calcium titanate powder is placed in a measurement sample cell, and the average particle density is measured by a gas (helium) substitution method using a dry density meter (for example, product name "Accupyk II 1340" manufactured by Shimadzu Corporation).

The powder according to this embodiment may be surface-treated with a surface treatment agent. By treating the surface with a surface treatment agent, the powder according to this embodiment is likely to have better fillability into resin. Examples of surface treatment agents include silane coupling agents and aluminate coupling agents. These may be used alone or in combination of two or more. Of these, from the viewpoint of easily reducing polar functional groups on the particle surface, treatment with a silane coupling agent is preferred, and silazanes such as hexamethyldisilazane (HMDS) and silane coupling agents having a vinyl group such as vinyltrimethoxysilane are more preferred.
In one embodiment, by treating the powder with a treating agent having a hydrophobic functional group, such as vinylsilane or hexamethyldisilazane (HMDS), polar functional groups on the surface of the particles constituting the powder are easily reduced, making it easier to achieve a lower dielectric tangent. Whether the powder has been surface treated or not can be confirmed by analyzing the powder using, for example, IR, TG-DTA, mass spectrometry, or the like.

The spherical calcium titanate powder according to this embodiment may contain other components in addition to calcium titanate. Examples of other components include calcium carbonate and titanium oxide. These other components may be contained alone or in combination of two or more. If the powder according to this embodiment contains other components, the amount of these components is preferably 1% by mass or less, and more preferably 0.5% by mass or less, relative to the total mass of the powder. From the perspective of reducing the dielectric loss tangent, it is preferable that the powder according to this embodiment does not contain other components.

In one embodiment, the dielectric constant at 36 GHz of a resin sheet containing the spherical calcium titanate powder according to this embodiment, measured under the conditions described below, is preferably 30 or more, and more preferably 50 or more. The dielectric dissipation factor at 36 GHz measured on a similar resin sheet is preferably 2.5×10 ⁻³ or less, and more preferably 2.0×10 ⁻³ or less. The above-mentioned "dielectric constant" and "dielectric dissipation factor" refer to the filler-equivalent dielectric constant (εr _f ) and filler-equivalent dielectric dissipation factor (tan δ _f ) calculated from the following formulas (2) and (3).

log(εr _c )=V _f・log(εr _f )+(1−V _f )・log(εr _r ) (2)
tan δ _c = V _f・tan δ _f + (1−V _f )・tan δ _r (3)
In formulas (2) and (3), εr _c represents the dielectric constant of the resin composition, V _f represents the filler content (mass%), εr _r represents the dielectric constant of the polyethylene resin (density 0.92 g/cm ³ ), tanδ _c represents the dielectric tangent of the resin composition, and tanδ _r represents the dielectric tangent of the polyethylene resin.

As described above, the spherical calcium titanate powder of this embodiment can simultaneously achieve a dielectric constant and dielectric dissipation factor suitable for use in GHz-band devices. Ordinary calcium titanate powder has a high dielectric dissipation factor, making it difficult to apply to GHz-band devices. The inventors of the present application improved the dielectric properties by spheroidizing calcium titanate powder to improve its dispersibility and filling ability in resin. Surprisingly, they discovered that by adjusting the crystallinity and reducing the interaction at the resin/filler interface, they could achieve a low dielectric dissipation factor while maintaining a high level of dielectric constant.

[Method of manufacturing spherical calcium titanate powder]
The spherical calcium titanate powder according to this embodiment can be produced by a method including spheronizing a raw material calcium titanate powder (step (i)). Hereinafter, one embodiment of the method for producing spherical calcium titanate powder including step (i) will be described.

<Step (i)>
Step (i) is a step of spheroidizing the raw material calcium titanate powder, and step (i) is preferably performed by a powder melting method.
The calcium titanate powder as the raw material (hereinafter simply referred to as "raw material powder") preferably has an average particle size (D50) of 0.2 to 100 μm, more preferably 1 to 50 μm, from the viewpoints of the average particle size of the powder after spheroidization, ease of handling of the powder, and ease of feeding. The average circularity of the raw material powder is not particularly limited.

The method for preparing the raw material powder is not particularly limited. For example, a bulk powder of calcium titanate obtained by reacting titanium oxide (TiO ₂ ) with calcium carbonate (CaO) under high temperature conditions may be used as the raw material powder, or a calcium titanate powder prepared by a wet method may be used as the raw material powder. From the viewpoints of availability and economy, it is preferable to use a raw material powder prepared by a solid-phase method.

From the viewpoint of reducing the dielectric loss tangent and improving the reliability of the electronic material, the raw material powder preferably contains a small amount of impurities such as alkali metal elements such as Li, Na, and K, and metal elements such as Fe, and anions such as Cl ⁻ and Br ⁻ . Specifically, the total amount of these impurities and anions in the raw material powder is preferably 0.01 mass% or less.

As described above, step (i) is preferably a step of spheroidizing the raw material powder by a powder melting method. The powder melting method is a method of spheroidizing the raw material powder by introducing it into a high-temperature condition above the melting point, such as a flame, plasma, electric furnace, or gas furnace, and methods such as those described in Patent Documents 5 and _{6 can be used. The melting atmosphere is not particularly limited, but from the viewpoint of easily preventing reduction of the raw material powder, it is desirable to perform spheroidization in an environment with a high oxygen partial pressure. For example, spheroidization can be performed in a flame using LPG/O2} gas. Furthermore, when introducing the raw material powder, the powder may be dispersed in water, alcohol, or the like and introduced in the form of a slurry.

The above-mentioned spheroidization process can produce spherical calcium titanate powder with an average circularity of 0.80 or more.

<Step (ii)>
The production method according to this embodiment may include a step (ii) of heat-treating the spheroidized calcium titanate powder after the step (i). However, from the viewpoint of making it easier to obtain a spherical calcium titanate powder having a lower shear viscosity, it is preferable not to carry out the step (ii).
When step (ii) is carried out, the heating temperature is preferably 1250°C or lower, more preferably 1150°C or lower, and even more preferably 600 to 1000°C. Heat-treating the spherical calcium titanate powder at such a heating temperature makes it possible to adjust the crystallinity and reduce the amount of impurities. As a result, when the powder is filled into a resin, it becomes easier to control the dielectric constant and dielectric loss tangent while ensuring high reliability. Note that, from the viewpoint of easily adjusting the shear viscosity of the final powder to 3,000 Pa s or lower, it is desirable that the heating temperature in step (ii) does not exceed 1250°C.
As the heating device, for example, an electric furnace or a gas furnace can be used. Step (ii) is preferably carried out in the atmosphere. The heating time is preferably 1 to 24 hours, more preferably 1 to 12 hours. If the heating time is 1 to 24 hours, productivity tends to be good.

The powder according to this embodiment can be prepared by a manufacturing method including the aforementioned step (i) (or, if necessary, a manufacturing method including steps (i) and (ii)). After step (i) or step (ii), the powder obtained may be in the form of aggregates. Therefore, a crushing process may be performed, if necessary. The crushing method is not particularly limited as long as it produces a powder with an average circularity of 0.80 or greater. For example, crushing methods using an agate mortar, ball mill, vibration mill, jet mill, wet jet mill, etc. can be used. Crushing may be performed dry, or wet by mixing with a liquid such as water or alcohol. Wet crushing can produce spherical calcium titanate powder by drying after crushing. Furthermore, the drying method is not particularly limited, but examples include heat drying, vacuum drying, freeze drying, and supercritical carbon dioxide drying.

The production method according to this embodiment may also include a step of classifying the spherical calcium titanate powder to obtain a spherical calcium titanate powder having a desired average particle size (D50). Examples of classification methods include classification using a sieve, as well as liquid cyclone and air classification.
Furthermore, the method may include a step of surface-treating the spherical calcium titanate powder with a surface treatment agent, a washing step for reducing impurities (such as the above-mentioned anions) in the spherical calcium titanate powder, and the like.

In one embodiment, the powder according to this embodiment may be blended or mixed with other spherical calcium titanate powders having different specific surface areas or average particle sizes, or other inorganic metal powders, or inorganic oxide powders, to form a mixed powder. By forming a mixed powder, it is possible to more easily adjust the dielectric constant, dielectric loss tangent, thermal expansion coefficient, thermal conductivity, filling rate, etc. when blended into a resin material.

[Application]
The spherical calcium titanate powder according to this embodiment can simultaneously achieve a high dielectric constant and a low dielectric loss tangent when filled in a resin, and can therefore be suitably used as a filler for resins.

[Resin composition]
The resin composition according to this embodiment contains the spherical calcium titanate powder and at least one resin selected from thermoplastic resins and thermosetting resins.
The content of the spherical calcium titanate powder in the resin composition is not particularly limited and can be adjusted appropriately depending on the purpose. The spherical calcium titanate powder according to this embodiment does not deteriorate in processability or workability even when highly loaded in a resin, so the amount of powder blended in the resin composition can be adjusted to obtain the desired dielectric properties. For example, when used as a substrate material for high-frequency bands or as an insulating material, the powder may be blended in an amount ranging from 1 to 80% by mass, more preferably from 10 to 70% by mass, based on the total mass of the resin composition.

<Resin>
The resin composition according to the present embodiment contains at least one resin selected from thermoplastic resins and thermosetting resins. More specifically, examples thereof include polyethylene resins; polypropylene resins; epoxy resins; silicone resins; phenolic resins; melamine resins; urea resins; unsaturated polyester resins; fluororesins; polyamide-based resins such as polyimide resins, polyamideimide resins, and polyetherimide resins; polyester-based resins such as polybutylene terephthalate resins and polyethylene terephthalate resins; polyphenylene sulfide resins; wholly aromatic polyester resins; polysulfone resins; liquid crystal polymer resins; polyethersulfone resins; polycarbonate resins; maleimide-modified resins; ABS resins; AAS (acrylonitrile-acrylic rubber-styrene) resins; AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins; hydrocarbon-based elastomer resins; polyphenylene ether resins; and aromatic polyene-based resins. These may be used alone or in combination of two or more.

The resin composition of this embodiment may contain curing agents, curing accelerators, release agents, coupling agents, colorants, flame retardants, ion capture agents, etc., as long as the effects of the present invention are not impaired.

<Method of producing resin composition>
The method for producing the resin composition is not particularly limited, and the resin composition can be produced by stirring, dissolving, mixing, and dispersing predetermined amounts of each material. The apparatus for mixing, stirring, dispersing, etc., of these mixtures is not particularly limited, and examples that can be used include a mortar and pestle machine equipped with a stirring and heating device, a three-roll mill, a ball mill, a planetary mixer, etc. These apparatuses may also be used in appropriate combination.

As described above, the resin composition containing the spherical calcium titanate powder according to this embodiment can achieve a high dielectric constant and a low dielectric loss tangent. Furthermore, the resin composition containing the spherical calcium titanate powder according to this embodiment has low viscosity, making it easy to process and work with.

The present invention will be explained in detail below using examples, but the present invention is not limited to the following description.

[Example 1]
A raw material powder (calcium titanate powder; manufactured by Kyoritsu Material Co., Ltd., product name "CT-03", average circularity of aggregates 0.75, average particle diameter (D50) 4 μm, specific surface area 1.9 m ² /g) was spheroidized by a powder fusion method to obtain spherical calcium titanate powder. The average circularity, shear viscosity, average particle diameter (D50), specific surface area, and half-width of the X-ray diffraction peak of the obtained spherical calcium titanate powder were measured under the following conditions. The results are shown in Table 1.

<Method for measuring average circularity>
Spherical calcium titanate powder was fixed to a sample stage with carbon tape and then osmium-coated. Images were then taken with a scanning electron microscope (manufactured by JEOL Ltd., product name "JSM-7001F SHL") at a magnification of 500 to 50,000 times and a resolution of 1280 x 1024 pixels, and imported into a personal computer. The images were analyzed using an image analyzer (manufactured by Nippon Roper Co., Ltd., product name "Image-Pro Premier Ver. 9.3") to calculate the projected area (S) and projected perimeter (L) of the particles constituting the powder, and then the circularity was calculated using the following formula (1). The circularity was calculated for 200 randomly selected particles, and the average value was used as the average circularity of the powder.
Circularity=4πS/ ^L2 (1)

<Method for measuring shear viscosity>
The viscosity of a resin composition consisting of 60% by volume of bisphenol A liquid epoxy resin (epoxy equivalent: 184 to 194, manufactured by Mitsubishi Chemical Corporation, product name "JER828") and 40% by volume of spherical calcium titanate powder was measured using a rheometer (manufactured by Anton-Paar, product name "MCR302") at a shear rate of 0.11/s, plate shape: circular flat plate (10 mmφ), sample thickness: 1 mm, and temperature: 25±1°C.

<Method for measuring average particle size (D50)>
The average particle size was measured using a laser diffraction particle size analyzer (manufactured by Beckman Coulter, trade name "LS 13 320"). First, 50 ^cm3 of pure water and 0.1 g of spherical calcium titanate powder were placed in a glass beaker and dispersed for 1 minute using an ultrasonic homogenizer (manufactured by Branson, trade name: SFX250). The dispersed spherical calcium titanate powder dispersion was added dropwise to the laser diffraction particle size analyzer using a dropper, and measurements were performed 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 of the spherical calcium titanate powder detected by a sensor in the laser diffraction particle size analyzer. The average particle size was calculated from the particle size corresponding to a cumulative value of 50% in the volume-based cumulative particle size distribution of the particle size being measured.

<Method for measuring specific surface area>
A measurement cell was filled with 2 g of spherical calcium titanate powder (1 g of the raw material calcium titanate powder "CT-03" alone), and the specific surface area was measured using a Macsorb HM model-1201 fully automatic specific surface area diameter measuring device (BET one-point method) manufactured by Mountainech. The degassing conditions before measurement were 200°C and 10 minutes. Nitrogen was used as the adsorption gas.

<Method for measuring X-ray diffraction of spherical calcium titanate powder>
The X-ray diffraction peaks of the spherical calcium titanate powder were measured under the following conditions using an XRD device (Rigaku Corporation, product name "RINT-Ultima IV"): Then, the half-width at 2θ of 32° to 34° was calculated using XRD analysis software (Rigaku Corporation, product name "Comprehensive Powder X-ray Analysis Software PDXL2").
X-ray source: CuKα
Tube voltage: 40 kV
Tube current: 40mA
Scan speed: 4.0°/min
2θ scan range: 10° to 50°

Next, resin compositions containing spherical calcium titanate powder were prepared with varying filling rates as follows, and the viscosity of each resin composition was measured to evaluate workability and processability.
<Evaluation of workability and processability of resin composition>
Resin composition 1 was prepared, consisting of 40% by volume of spherical calcium titanate powder and 60% by volume of bisphenol A liquid epoxy resin (epoxy equivalent: 184-194, manufactured by Mitsubishi Chemical Corporation, product name "JER828"), and its viscosity was measured under the same conditions as those for the shear viscosity measurement described above. Next, resin composition 2 was prepared by changing the filling rate of the spherical calcium titanate powder to 30% by volume, and its viscosity was measured under the same conditions. Based on the viscosities of resin compositions 1 and 2, the workability and processability were evaluated according to the following evaluation criteria. The results are shown in Table 1.
(Evaluation criteria)
Excellent: The difference in viscosity between resin compositions 1 and 2 was 500 Pa·s or less.
Good: The difference in viscosity between resin compositions 1 and 2 was more than 500 Pa·s and 3000 Pa·s or less.
Pass: The difference in viscosity between resin compositions 1 and 2 was more than 3000 Pa·s and 5000 Pa·s or less.
Unacceptable: The difference in viscosity between resin compositions 1 and 2 exceeded 5,000 Pa·s.

The dielectric constant and dielectric loss tangent of the resin composition containing the spherical calcium titanate powder were measured under the following conditions to determine the filler-equivalent dielectric constant and dielectric loss.
<Evaluation of dielectric properties (dielectric constant and dielectric loss tangent)>
Spherical calcium titanate powder and polyethylene resin powder (manufactured by Sumitomo Seika Chemicals Co., Ltd., trade name "Flothane (registered trademark) UF-20S") were weighed so that the loading of the spherical calcium titanate powder was 20% by volume, and mixed using a vibration mixer (manufactured by Resodyn) at an acceleration of 60 G for a processing time of 2 minutes to obtain a resin composition. The obtained resin composition was placed in a metal frame with a diameter of 3 cm in an amount to give a thickness of approximately 0.3 mm, and sheeted using a nanoimprinting device (manufactured by SCIVAX, trade name: X-300) under conditions of 140°C, 5 minutes, and 30,000 N. The obtained sheet was cut into a size of 1.5 cm x 1.5 cm to obtain an evaluation sample.
Next, a 36 GHz cavity resonator (manufactured by Samtec Co., Ltd.) was connected to a vector network analyzer (manufactured by Keysight Technologies, product name "85107"), and the evaluation sample was placed so as to cover a 10 mm diameter hole in the cavity resonator, and the resonance frequency (f0) and unloaded Q value (Qu) were measured. The evaluation sample was rotated 60 degrees for each measurement, and the same measurement was repeated five times. The average values of the obtained f0 and Qu were used as the measured values, and the dielectric constant (εr _f ) and dielectric loss tangent (tan δ _f ) were calculated using the following equations (2) and (3) using analysis software (manufactured by Samtec Co., Ltd.). The measurement was performed under conditions of a measurement temperature of 20°C and a humidity of 60% RH. The obtained dielectric constant and dielectric loss tangent values were evaluated according to the following evaluation criteria. The results are shown in Table 1.
log(εr _c )=V _f・log(εr _f )+(1−V _f )・log(εr _r ) (2)
tan δ _c = V _f・tan δ _f + (1−V _f )・tan δ _r (3)
In formulas (2) and (3), εr _c represents the dielectric constant of the resin composition, V _f represents the filler content (mass%), εr _r represents the dielectric constant of the polyethylene resin (density 0.92 g/cm ³ ), tanδ _c represents the dielectric tangent of the resin composition, and tanδ _r represents the dielectric tangent of the polyethylene resin.
(Evaluation criteria)
<Dielectric constant>
3 points: Dielectric constant is 50 or more.
2 points: Dielectric constant is 30 or more and less than 50.
1 point: Dielectric constant is 20 or more and less than 30.
0 points: Dielectric constant is less than 20.
<Dielectric loss tangent>
3 points: Dielectric tangent is 2.0×10 ⁻³ or less.
2 points: Dielectric loss tangent is greater than 2.0×10 ⁻³ and is 3.0×10 ⁻³ or less.
1 point: Dielectric tangent is greater than 3.0 × 10 ^-3 and less than or equal to 5.0 × 10 ^-3 .
0 point: Dielectric tangent is 5.0×10 ⁻³ or more.
<Overall rating>
The scores of the dielectric constant and the dielectric loss tangent were totaled, and the dielectric properties were evaluated according to the following criteria.
Excellent: The dielectric constant and dielectric loss tangent both score 3 points (total score 6 points).
Good: Either the dielectric constant or the dielectric loss tangent is 3 points, and the other is 2 points (total score is 5 points).
Pass: The dielectric constant and dielectric loss tangent both receive a score of 2 (total score is 4).
Unacceptable: The score for either the dielectric constant or the dielectric loss tangent is less than 2 points (total score is 4 points or less).

[Examples 2 to 4 and Comparative Example 1]
The calcium titanate powder was subjected to a spheroidizing process under the manufacturing conditions shown in Table 1, followed by a heat treatment under the conditions shown in Table 1. The average circularity, shear viscosity, average particle diameter (D50), specific surface area, and half-width of each spherical calcium titanate powder were measured using the same method as in Example 1. Resin compositions were also prepared under the same conditions as in Example 1, and their workability, processability, and dielectric properties were evaluated. The results are shown in Table 1.

Reference Example 1 in Table 1 shows the evaluation results of the raw material calcium titanate powder. The raw material powder of Reference Example 1 had a low average circularity and a large specific surface area, resulting in a high shear viscosity and poor workability and processability. Furthermore, the dielectric dissipation factor was also high, failing to achieve a high dielectric constant and low dielectric dissipation factor. In contrast, the spherical calcium titanate powders of Examples 1 to 4, which satisfy the configuration of the present invention, were able to produce resin compositions with high dielectric constants and low dielectric dissipation factors. Even when the powder was heavily loaded into the resin, the viscosity did not become too high, resulting in excellent workability and processability. On the other hand, Comparative Example 1, which did not satisfy the configuration of the present invention, had a high shear viscosity due to a low average circularity, resulting in poor workability and processability. Furthermore, the dielectric dissipation factor was also high, failing to achieve a high dielectric constant and low dielectric dissipation factor. These results confirm that the spherical calcium titanate powder of the present invention can simultaneously achieve a high dielectric constant and a low dielectric dissipation factor when loaded into a resin material. Furthermore, it was confirmed that even when heavily loaded into the resin, workability and processability are not significantly reduced.

The spherical calcium titanate powder according to this embodiment does not deteriorate in processability or workability even when highly filled in a resin. Furthermore, a resin composition containing the spherical calcium titanate powder according to this embodiment can simultaneously achieve a high dielectric constant and a low dielectric loss tangent. Therefore, the spherical calcium titanate powder according to this embodiment and a resin composition using the same can be used as a ceramic filler for high-frequency devices.

Claims (6)

A spherical calcium titanate powder having an average circularity of 0.80 or more,
The shear viscosity measured under the following conditions is 3,000 Pa s or less,
A spherical calcium titanate powder having a specific surface area of 0.1 to 1.5 m ² /g.
<Shear viscosity measurement conditions>
The viscosity of a resin composition consisting of 60% by volume of bisphenol A liquid epoxy resin (epoxy equivalent: 184 to 194) and 40% by volume of spherical calcium titanate powder is measured using a rheometer at a shear rate of 0.11/s, a plate shape of a circular flat plate: 10 mm diameter, a sample thickness of 1 mm, and a temperature of 25±1°C. The spherical calcium titanate powder according to claim 1, having an average particle diameter (D50) of 1 to 100 μm. The spherical calcium titanate powder according to claim 1 or 2, wherein the full width at half maximum (FWHM) of the X-ray diffraction peak at 2θ of 32° to 34° is 0.150° to 0.175°. The spherical calcium titanate powder according to claim 1 or 2, wherein the shear viscosity is 1,500 Pa·s or less. The spherical calcium titanate powder according to claim 1 or 2, which is for use in resin filling. A resin composition comprising the spherical calcium titanate powder according to claim 1 or 2 and at least one resin selected from thermoplastic resins and thermosetting resins.