JP2019065094A - Dielectric composite material - Google Patents

Abstract

To provide a dielectric composite material which has a high dielectric constant, a low dielectric loss, and a high breakdown strength.SOLUTION: A dielectric composite material has a matrix formed of a resin, and filler particles dispersed in the matrix. The filler particles are formed of a perovskite type compound, a half-value width of an X-ray diffraction peak on 111 plane is 0.20° or less, a ratio (c/a axial ratio) of a length of a c-axis to a length of an a-axis determined by powder X-ray diffraction is 1.006 or more, and an equal number (n) of Rosin-Rammler distribution function is 2.3 or more. A coefficient of variation of a distance between particles of the filler particles dispersed in the matrix is 0.9 or less.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a dielectric composite material, and more particularly to a dielectric composite material having a material structure in which filler particles made of an inorganic compound are uniformly dispersed in a resin matrix.

  Organic materials are widely used as a kind of capacitors and circuit boards which are passive elements of electronic devices. One of the important characteristics required for this application is the high relative dielectric constant (high dielectric constant). Since the capacitance of the material increases in proportion to the relative dielectric constant, a high dielectric constant capacitor can easily obtain a large capacitance, which is advantageous for downsizing of parts. However, organic materials generally have low dielectric constants. Therefore, in order to increase the dielectric constant of organic materials, a composite material in which an inorganic filler having a high dielectric constant is filled in the organic material, that is, a composite material having the combined advantages of both organic and inorganic materials has been widely proposed. There is.

For example, Patent Document 1 discloses a dielectric material in which 10 vol% of magnesium oxide fine particles (average particle diameter: 0.2 μm, half width of (200) peak: about 0.1 °) are dispersed in a thermoplastic resin. Resin compositions are disclosed.
In the same document,
(A) In a dielectric device used in a high frequency band, the use of a material having a high dielectric constant extremely reduces the design dimension of the dielectric device, and transmission delay causes a problem in high-speed processing of a signal. Point, and
(B) When magnesium oxide fine particles having good crystallinity are used, the relative dielectric constant ε and the quality factor index Qf of the resin composition for dielectrics decrease,
Is described.

Patent Document 2 discloses a composite magnetic material in which a carbonyl reduced iron powder is dispersed in a PC / ABS resin which is not a dielectric composition but is an insulating material.
In the document, it is possible to use a small-sized, high-bandwidth, high-efficiency in high frequency by blending an approximately spherical iron powder having an average particle diameter D of 50% of 0.1 to 3 μm into a relatively low loss insulating material It is stated that the antenna can be realized.

Patent Document 3 discloses a method of manufacturing a dielectric ceramic powder in which firing and crushing of a raw material composition are repeated twice or more.
In the same document,
(A) A point that a dielectric ceramic powder having a specific surface area of 9 m ² / cm ³ or less and a lattice strain of 0.2 or less is obtained by such a method;
(B) It is described that such dielectric ceramic powder can ensure the fluidity of a mixture with a resin even when it is composed of irregularly shaped particles by a pulverization method.

Patent Document 4 discloses a polymer composite piezoelectric body in which piezoelectric particles having a predetermined particle size distribution are dispersed in a matrix that is not a dielectric composition but is made of a polymer material.
In the same document,
(A) In order to obtain high transmission efficiency of vibrational energy, it is preferable that the particle size of the piezoelectric particles is large, but the large piezoelectric particles alone can not sufficiently increase the packing density of the piezoelectric particles. ,as well as,
(B) When large piezoelectric particles and small piezoelectric particles are mixed in the composite piezoelectric material, the large piezoelectric particles realize good vibration energy transfer efficiency, and the small piezoelectric particles are large piezoelectric particles. It is described that the packing density of the piezoelectric particles is increased by entering the gap.

The capacitance density (F / mm ³ ) of the capacitor is represented by ε _r · ε ₀ / d ² (ε _r : permittivity in vacuum (constant), ε ₀ : relative permittivity, d: thickness). Therefore, in order to reduce the size of the capacitor with the same capacitance, it is necessary to increase the relative permittivity of the material or to reduce the thickness of the capacitor.
On the other hand, the capacitor generates heat due to Joule heat generated due to a delay from the AC electric field and the phase angle (90 degrees) of the current during use. A tangent to a phase angle (δ) indicating this delay is evaluated as a dielectric tangent (tan δ). Therefore, in order to suppress heat generation, the dielectric loss tangent of the capacitor needs to be low.

  Furthermore, a capacitor used under high voltage, such as an inverter circuit of an electric vehicle, is required to have high dielectric breakdown strength that can withstand high electrolytic drive. Therefore, in addition to the high dielectric constant and the low dielectric loss tangent, the capacitor used in the inverter circuit is required to have an even higher dielectric breakdown strength.

  In general, the relative dielectric constant and the dielectric loss tangent, and the relative dielectric constant and the dielectric breakdown strength are in a contradictory relationship, respectively. Therefore, when the relative dielectric constant of the material decreases, the dielectric loss is likely to be reduced, and the dielectric breakdown strength is also likely to be improved. However, in that case, the capacity of the capacitor decreases in the same volume, and the physique becomes large. In general, it is necessary to treat the dielectric loss tangent evaluated by a weak alternating electric field and the dielectric breakdown strength which is a high voltage phenomenon as different physical properties. So far, in composite materials, the requirements for achieving high dielectric constant, low dielectric loss, and high dielectric breakdown strength have not always been clear.

  On the other hand, when focusing on fillers, paraelectric materials (for example, magnesium oxide) tend to exhibit low dielectric loss tangent because they have symmetry in the crystal structure. However, the relative dielectric constant is low because the magnitude of polarization also tends to be small. Therefore, using a paraelectric filler makes it easy to obtain a composite material having a low dielectric loss tangent, but the relative dielectric constant also tends to be low.

On the other hand, a ferroelectric exhibits a high relative dielectric constant but tends to simultaneously exhibit a large dielectric loss. For example, BaTiO ₃ is known as a ferroelectric filler, and various studies have been made on the influence of the particle diameter and crystallinity of BaTiO ₃ on dielectric properties. However, all of these studies are for a sintered body, and the dielectric properties of BaTiO ₃ as a powder are not clear. Therefore, the requirements as a filler are not clear.

JP, 2014-024916, A JP, 2011-096923, A Unexamined-Japanese-Patent No. 2005-306662 JP, 2015-192120, A

H. HSIANG et al., J. Mater. Sci., 36, 3809-3815 (2001) B. Fan et al., Appl. Phys. Lett., 100, 012903 (2012) Y. Mao et al., J. Appl. Phys., 108, 01402 (2010)

  The problem to be solved by the present invention is to provide a dielectric composite material having a high dielectric constant, a low dielectric loss, and a high dielectric breakdown strength.

In order to solve the above-mentioned subject, a dielectric composite material concerning the present invention makes it a summary to have the following composition.
(1) The dielectric composite material is
A matrix made of resin,
And filler particles dispersed in the matrix.
(2) The filler particles are
Consists of perovskite type compounds,
The half width of the X-ray diffraction peak of plane 111 is 0.20 ° or less,
The ratio of the c-axis length to the a-axis length (c / a-axis ratio) determined from powder X-ray diffraction is 1.006 or more, and
The equal number (n) of the Rosin-Rammler distribution function is 2.3 or more.
(3) The variation coefficient of the interparticle distance of the filler particles dispersed in the matrix is 0.9 or less.

  The perovskite compound is a ferroelectric. The smaller half width of the 111 plane peak of the perovskite compound means smaller fluctuation of the crystal structure, that is, smaller dielectric loss tangent. In addition, the large c / a axis ratio of the perovskite compound means that the polarization is large, that is, the relative dielectric constant is high. Furthermore, the fact that the even number is large indicates that the variation in the particle size of the filler particles is small.

  In the case of producing a dielectric composite material using filler particles having such a high relative dielectric constant, a small dielectric loss tangent, and a small variation in particle diameter, optimization of the production conditions results in the formation of filler particles in the resin. The variation coefficient of interparticle distance (variation of interparticle distance) is reduced. As a result, the non-uniformity of the electric field distribution in the composite material is reduced, and high breakdown strength can be maintained. That is, the dielectric composite material according to the present invention can increase the relative dielectric constant while maintaining high dielectric breakdown strength while suppressing the increase in dielectric loss tangent as compared with the conventional one. Therefore, if this is applied to, for example, a capacitor, the capacitor can be effectively miniaturized.

It is a cross-sectional schematic diagram of the dielectric material composite material which concerns on this invention. It is process drawing of the manufacturing method of dielectric material composite material. 7 is an X-ray diffraction pattern (111 diffraction) of the BaTiO ₃ powder used in Comparative Example 2. It is a figure which shows the relationship between the equivalent number of filler particles, and the variation coefficient of the distance between particles.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Dielectric composite material]
FIG. 1 shows a schematic cross-sectional view of a dielectric composite material according to the present invention.
In FIG. 1, the dielectric composite material 10 is
A matrix 12 made of resin,
And filler particles 14 dispersed in a matrix 12.

[1.1. matrix]
[1.1.1. composition]
The matrix 12 is made of resin. In the present invention, the composition of the resin constituting the matrix 12 is not particularly limited as long as it has a dielectric property.
As resin which comprises the matrix 12, for example,
(A) thermosetting resin such as phenol resin, epoxy resin, melamine resin, urea resin, polyurethane, unsaturated polyester resin, thermosetting polyimide,
(B) Thermoplastic resins such as polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polycarbonate, polyvinyl chloride, polyamide, acrylic resin, fluorine resin, thermoplastic polyimide, polyvinylidene fluoride, etc.
and so on.

  Any one of these thermosetting resins or thermoplastic resins may be used as the matrix 12, or two or more thermosetting resins or two or more thermoplastic resins may be used in combination. good. Furthermore, one or more thermosetting resins may be used in combination with one or more thermoplastic resins.

  Among these, polyvinylidene fluoride or a copolymer thereof is preferable as the resin constituting the matrix 12. Polyvinylidene fluoride has a high relative dielectric constant as a resin. Therefore, when this is used as the matrix of the composite material, the relative dielectric constant of the entire composite material can be increased.

[1.1.2. Dielectric constant]
The higher the dielectric constant of the resin constituting the matrix 12, the better. In general, the dielectric constant of the resin is at most about 5 and is lower than the dielectric composed of an inorganic compound. However, since the resin has a low relative dielectric constant, its dielectric loss tends to show a low value.

[1.2. Filler particle]
[1.2.1. composition]
In the present invention, the filler particles 14 are made of a perovskite compound. The perovskite compound refers to an inorganic compound whose chemical formula is represented by ABO ₃ (A and B are each a metal element). As a perovskite compound, for example,
(A) A consisting of divalent elements such as Ba, Pb, Ca, Sr, and B consisting of tetravalent elements such as Ti, Zr, Sn, Hf, etc.
(B) A consisting of monovalent elements such as Li, Na and K, and B consisting of pentavalent elements such as Nb and Ta,
(C) There is such a solid solution.

Among these, the perovskite compound is preferably BaTiO ₃ or a solid solution of BaTiO ₃ and the other perovskite compounds. BaTiO ₃ or a solid solution thereof is preferable as the inorganic compound constituting the filler particle 14 because the dielectric constant is higher than that of the other perovskite compounds or the other inorganic compounds.

[1.2.2. Half width]
In general, in the dielectric composite material, the higher the relative dielectric constant of the inorganic compound contained in the dielectric composite material, the higher the relative dielectric constant can be obtained by the addition of a small amount of the inorganic compound. Therefore, it is desirable that the relative dielectric constant of the inorganic compound be high. On the other hand, as the particle diameter of the inorganic compound decreases, the ratio of the surface layer to the entire particle increases. Since the surface of the particle is in a higher energy state than the interior, the structural order is easily disturbed and the crystallinity is reduced. As a result, the physical and chemical properties change from those inherent in the composition, the relative dielectric constant decreases on the particle surface, and the dielectric loss tangent tends to increase. Therefore, it is desirable that the crystallinity be high even if the particle size of the inorganic compound is reduced.

The degree of crystallinity can be evaluated by the half value width of the X-ray diffraction peak of the 111 plane. Here, in the present invention, “half width” refers to the full width at half maximum. Generally, the smaller the half width, the smaller the fluctuation of the crystal structure and the smaller the dielectric loss tangent.
In order to obtain a dielectric composite material with a small dielectric loss tangent, it is necessary for the filler particles 14 to have a half width of 0.21 ° or less of the X-ray diffraction peak on the 111 plane. The half width is preferably 0.18 ° or less, more preferably 0.16 ° or less.

[1.2.3. c / a axis ratio]
The perovskite compound has a tetragonal or orthorhombic crystal structure at room temperature, and the length of the c-axis is longer than the length of the a-axis. Generally, as the ratio of the c-axis length to the a-axis length (c / a-axis ratio) increases, the polarization increases and the relative dielectric constant increases. The c / a axis ratio changes depending on the composition, crystallinity and the like of the perovskite compound. The c / a axial ratio can be determined from powder X-ray diffraction.
In order to obtain a dielectric composite material having a high relative dielectric constant, it is necessary for the filler particles 14 to have a c / a axial ratio determined from powder X-ray diffraction of 1.006 or more. The c / a axial ratio is preferably 1.007 or more, more preferably 1.009 or more.

[1.2.4. Equal number]
In general, the particle size distribution of particles is often expressed by the formula of Rosin-Rammler represented by the following formula (1).
R = 100 exp (-bD ⁿ ) (1)
However, R is the mass% of particles on the integrated screen, D is the particle size of the particles, b is a constant, and n is an even number.

  When the horizontal axis (x axis) is log D and the vertical axis (y axis) is log (log (100 / R)), the measured values of particle diameter D and mass R (%) of particles on integrated screen are plotted, From equation (1), log D and log (log (100 / R)) have a linear relationship, and the even number (n) indicates the slope of the straight line. A large equivalent number (n) indicates that the particle size distribution is sharp. Also, the constant b can be obtained from y intercept (= −n · log b).

If the filler particles 14 are unevenly dispersed in the matrix 12, the inhomogeneity of the electric field distribution in the dielectric composite material 10 becomes large, and the dielectric breakdown strength decreases. In order to obtain high dielectric breakdown strength, it is preferable that the filler particles 14 be uniformly dispersed in the matrix 12. However, if the particle size distribution of the filler particles 14 is broad, uniform dispersion of the filler particles 14 becomes difficult.
In order to obtain high dielectric breakdown strength, the equal number (n) in the Rosin-Rammler distribution function needs to be 2.3 or more. The equivalent number (n) is preferably 2.5 or more, more preferably 2.7 or more.

[1.2.5. Average particle size]
In general, the smaller the average particle size of the filler particles 14 is, the higher the relative dielectric constant can be obtained by the addition of a small amount of filler particles 14. In order to obtain such an effect, the average particle diameter of the filler particles 14 is preferably 500 nm or less. The average particle size is preferably 400 nm or less, more preferably 300 nm or less.

On the other hand, when the average particle diameter of the filler particles 14 becomes too small, it becomes difficult to obtain the highly crystalline filler particles 14, and the relative dielectric constant of the filler particles 14 also decreases. Therefore, when filling in the matrix 12, it becomes difficult to obtain a high dielectric constant in the composite material. In addition, since the cohesion force also becomes high, it becomes difficult to disperse uniformly in the matrix 12, and the dielectric breakdown strength also decreases. Therefore, the average particle diameter of the filler particles 14 is preferably 5 nm or more. The average particle size is preferably 10 nm or more, more preferably 15 nm or more.
Here, the "average particle diameter" refers to the median value (D ₅₀ ) of the particle diameter measured by the laser diffraction scattering method.

[1.3. Properties of dielectric composites]
[1.3.1. Coefficient of variation]
The “coefficient of variation of interparticle distance” refers to a value (= σ / L _m ) obtained by dividing the standard deviation (σ) of the interparticle distance by the arithmetic mean (L _m ) of the interparticle distance. In the present invention, the "inter-particle distance" refers to the closest contact distance between filler particles. The method of calculating the closest distance will be described later. The small variation coefficient of the inter-particle distance means that the variation of the inter-particle distance is small (that is, the filler particles 14 are uniformly dispersed). As described above, the coefficient of variation affects the dielectric breakdown strength of the dielectric composite material 10.
In order to obtain high dielectric breakdown strength, the coefficient of variation needs to be 0.9 or less. The coefficient of variation is preferably 0.8 or less, more preferably 0.7 or less.

[1.3.2. Volume fraction]
The volume fraction (filling amount) of the filler particles 14 affects the relative dielectric constant of the dielectric composite material 10. In general, when the volume fraction of the filler particles 14 becomes too small, the dielectric constant of the dielectric composite material 10 decreases. Therefore, the volume fraction of the filler particles 14 is preferably 2 vol% or more. The volume fraction is preferably 5 vol% or more, more preferably 10 vol% or more.

  On the other hand, when the volume fraction of the filler particles 14 is too large, the formability is reduced and pores are easily generated in the dielectric composite material 10. Pores in the dielectric composite material 10 cause the relative dielectric constant to decrease. Therefore, the volume fraction of the filler particles 14 is preferably 50 vol% or less. The volume fraction is preferably 45 vol% or less, more preferably 40 vol% or less.

[1.3.3. Thickness]
When a capacitor is produced using the dielectric composite material 10 according to the present invention, the capacitance density (F / mm ³ ) of the capacitor is ε _r · ε ₀ / d ² (ε _r : permittivity (constant) of vacuum, ε _{0 is a} relative dielectric constant, d is a thickness). That is, as the thickness of the dielectric composite material 10 decreases, the capacitance density increases. In order to obtain such an effect, the thickness of the dielectric composite material 10 is preferably 50 μm or less. The thickness is preferably 30 μm or less, more preferably 10 μm or less.
On the other hand, when the thickness of the dielectric composite material 10 is too thin, the probability that the filler particles 14 are connected between the electrodes becomes high, and as a result, the dielectric breakdown strength tends to be small. Therefore, the thickness is preferably 2 μm or more. The thickness is preferably 4 μm or more, more preferably 6 μm or more.

[1.3.4. Dielectric property]
As described above, when the half width of the filler particle 14, c / a axis ratio, coefficient of variation, uniform number, and the like are optimized, the dielectric composite material has high dielectric constant, low dielectric loss, and high dielectric breakdown strength. 10 is obtained. Specifically, when these parameters are optimized,
(A) The relative dielectric constant is greater than 15 at a frequency of 10 kHz,
(B) The dielectric loss tangent tan δ is 0.02 or less at a frequency of 10 kHz, and
(C) A dielectric composite material 10 having a dielectric breakdown strength of greater than 150 V / μm is obtained.

[1.4. electrode]
When the dielectric composite material 10 is used as a capacitor, the dielectric composite material 10 is formed into a thin film, and electrodes 16 and 18 are formed on the upper and lower surfaces of the thin film, respectively. The shape, material, and the like of the electrodes 16 and 18 are not particularly limited, and an optimal one can be selected according to the purpose.

[2. Method of manufacturing dielectric composite material]
The dielectric composite material according to the present invention is
(A) Mix resin and filler particles to make a slurry,
(B) The slurry is applied onto a substrate to form a coating of a predetermined thickness,
(C) It can manufacture by drying a coating film.

[2.1. Mixing process]
First, resin and filler particles are mixed to obtain a slurry (mixing step). Specifically, a resin and a solvent are mixed and melted to prepare a resin varnish. Next, a predetermined amount of filler particles is added to the resin varnish, and these are thoroughly mixed.
The solvent may be any one that can melt the resin. Examples of the solvent include N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone, dimethylacetamide, dimethylsulfoxide, trimethyl phosphate, tetrahydrofuran, methyl ethyl ketone and the like. The amount of the solvent may be such an amount that the filler particles are uniformly dispersed, and a slurry having a coatable viscosity can be prepared. The mixing method and the mixing conditions are not particularly limited, and an optimum one can be selected according to the purpose.

[2.2. Coating process]
Next, the slurry is coated on a substrate to obtain a coating (coating step). The type of substrate and the coating method are not particularly limited as long as a uniform coating film can be formed.

[2.3. Drying process]
Next, the coating on the substrate is dried (drying step). Thereby, the solvent is volatilized from the coating film, and the dielectric composite material according to the present invention is obtained. The drying method and the drying conditions are not particularly limited, and optimum conditions can be selected according to the purpose. After drying, the dielectric composite is peeled from the substrate.

[3. Action]
The perovskite compound is a ferroelectric. The smaller half width of the 111 plane peak of the perovskite compound means smaller fluctuation of the crystal structure, that is, smaller dielectric loss tangent. In addition, the large c / a axis ratio of the perovskite compound means that the polarization is large, that is, the relative dielectric constant is high. Furthermore, the fact that the even number is large indicates that the variation in the particle size of the filler particles is small.

  In the case of producing a dielectric composite material using filler particles having such a high relative dielectric constant, a small dielectric loss tangent, and a small variation in particle diameter, optimization of the production conditions results in the formation of filler particles in the resin. The variation coefficient of interparticle distance (variation of interparticle distance) is reduced. As a result, the non-uniformity of the electric field distribution in the composite material is reduced, and high breakdown strength can be maintained. That is, the dielectric composite material according to the present invention can increase the relative dielectric constant while maintaining high dielectric breakdown strength while suppressing the increase in dielectric loss tangent as compared with the conventional one. Therefore, if this is applied to, for example, a capacitor, the capacitor can be effectively miniaturized.

(Examples 1 to 5, Comparative Examples 1 to 7)
[1. Preparation of sample]
FIG. 2 shows a flow chart of a method of manufacturing a dielectric composite material. A PVDF / DMF varnish was prepared by mixing and melting pelletized polyvinylidene fluoride (PVDF) and N, N-dimethylformamide (DMF). The filler particles were weighed so that the final composite material had a loading of 20 vol%, and mixed with a PVD / DMF varnish to prepare a slurry. As the filler particles, various BaTiO ₃ particles having different average particle diameter, equal number, half width and / or c / a axial ratio were used.

  Next, the slurry was applied onto the substrate to obtain a coating having a thickness of 250 μm. Further, the coating was dried at 200 ° C. for 1 hour to obtain a film-like dielectric composite material. After peeling the film from the substrate, electrodes were formed on both sides to obtain a test piece for electrical property evaluation (see FIG. 1).

[2. Test method]
[2.1. Dielectric and insulating properties]
The relative permittivity and the dielectric loss tangent were measured by an impedance analyzer (Keysight, HP4194A). The direct current dielectric breakdown strength was evaluated in the insulating oil by an ultra-high voltage withstand voltage tester (Measurement Technology Laboratory, 7474). All evaluations were performed at room temperature.

[2.2. Filler particle half width and c / a axis ratio]
The half width and c / a axis ratio were measured using an X-ray diffractometer (RINT-TTR, manufactured by Rigaku Corporation). With an X-ray tube Cu, a tube voltage of 50 kV, a tube current of 300 mA, and a step size of 0.01 °, measurement was made at 2θ = 10 ° to 90 °. The half value width of 111 diffraction was calculated from the peak corresponding to 111 diffraction of BaTiO ₃ appearing near the diffraction angle of 38.8 °.
In addition, based on the crystal structure of tetragonal BaTiO ₃ reported in the database, the lattice constant of each filler particle was refined by the method of least squares. The c / a axis ratio was calculated from the length of the a axis and the length of the c axis obtained. As an example, FIG. 3 shows an X-ray diffraction pattern (111 diffraction) of the BaTiO ₃ powder used in Comparative Example 2.

[2.3. Equal number of filler particles]
The uniform number of filler particles was determined using equation (1).

[2.4. Coefficient of variation]
After embedding the composite material in an epoxy resin, the cross section was processed with an argon beam and observed at 10,000 times with a scanning electron microscope (SEM: Hitachi High-Technologies, SU3500). Matrix and filler particles were binarized from light and dark of the observed image by image processing software for a plurality of visual fields. With respect to the detected filler particles, triangles having vertices of closest centroids to each other were formed for all particles in the image. The distance between particles was calculated from the distance between the centers of gravity which is one side of the formed triangle. The interparticle distance for a given two particles is
(Distance between particles) = (distance between centers of gravity)-(sum of equivalent circle radius of each particle)
Defined by
Here, the equivalent circle radius is the radius of the equivalent circle diameter, and the equivalent circle diameter is obtained from the area S of each of the detected particles by the equivalent circle diameter = √ (4 × S / π).
Determine the interparticle distance for all particles in the image, and change the interparticle distance variation coefficient by (interparticle distance variation coefficient) = (average deviation of interparticle distance) / (average interparticle distance)
Calculated from

[3. result]
[3.1. Powder characteristics and dielectric / insulation characteristics]
Table 1 shows the powder properties of the BaTiO ₃ filler, and the dielectric and insulating properties of the obtained composite material. The tan δ of the composite material was 0.02 or less when the c / a axial ratio of the BaTiO ₃ filler was 1.006 or more and the 111 half width was 0.20 ° or less. In addition, when the 111 half width of the BaTiO ₃ filler was 0.20 ° or less and the variation coefficient of the interparticle distance was 0.9 or less, the dielectric breakdown strength showed a value higher than 150 V / μm.

[3.2. Relationship between even number and coefficient of variation]
FIG. 4 is a graph in which the abscissa represents the reciprocal 1 / n of the equivalent number and the abscissa represents the variation coefficient of the distance between particles for Example 5, Comparative Example 6, and Comparative Example 7 having the same particle diameter. Show. As shown in FIG. 4, in order to reduce the variation coefficient of the interparticle distance, it is understood that reducing 1 / n (that is, narrowing the particle size distribution) is effective. That is, by dispersing the filler having a uniform number of 2.3 or more (the particle size distribution is narrow) in the resin, the variation coefficient of the distance between the filler particles (the variation of the distance between particles) in the composite material is 0 .9 or less and the dielectric breakdown strength is increased.
As apparent from the above, it has been found that the composite material according to the present invention has a high dielectric constant, a low dielectric loss, and a high dielectric breakdown strength, and effectively functions as a capacitor.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited at all to the said embodiment, A various change is possible within the range which does not deviate from the summary of this invention.

  The dielectric composite material according to the present invention can be used as a dielectric of a capacitor or a capacitor element.

10 dielectric composite 12 matrix 14 filler particles

Claims (8)

Dielectric composite material having the following configuration.
(1) The dielectric composite material is
A matrix made of resin,
And filler particles dispersed in the matrix.
(2) The filler particles are
Consists of perovskite type compounds,
The half width of the X-ray diffraction peak of plane 111 is 0.20 ° or less,
The ratio of the c-axis length to the a-axis length (c / a-axis ratio) determined from powder X-ray diffraction is 1.006 or more, and
The equal number (n) of the Rosin-Rammler distribution function is 2.3 or more.
(3) The variation coefficient of the interparticle distance of the filler particles dispersed in the matrix is 0.9 or less. The dielectric composite material according to claim 1, wherein the filler particle comprises BaTiO ₃ or a solid solution of the BaTiO ₃ and the other perovskite compound.   The dielectric composite material according to claim 1, wherein the resin is polyvinylidene fluoride or a copolymer thereof.   The dielectric composite material according to any one of claims 1 to 3, wherein an equal number (n) of the Rosin-Rammler distribution function is 2.5 or more. The relative permittivity is greater than 15 at a frequency of 10 kHz,
The dielectric loss tangent tan δ is 0.02 or less at a frequency of 10 kHz, and
The dielectric composite material according to any one of claims 1 to 4, wherein the dielectric breakdown strength is greater than 150 V / μm.   The dielectric composite material according to any one of claims 1 to 5, wherein an average particle diameter of the filler particles is 500 nm or less.   The dielectric composite material according to any one of claims 1 to 6, which has a thickness of 2 μm to 50 μm.   The dielectric composite material according to any one of claims 1 to 7, wherein a volume fraction (filling amount) of the filler particles is 2 vol% or more and 50 vol% or less.

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