JP6903538B2 - Dielectric composite - Google Patents

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 inside a resin base material.

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

For example, Patent Document 1 describes for a dielectric in which 10 vol% magnesium oxide fine particles (average particle size: 0.2 μm, half-value width of (200) peak: about 0.1 °) are dispersed in a thermoplastic resin. The resin composition is disclosed.
In the same document,
(A) When a material having a high relative permittivity is used in a dielectric device used in a high frequency band, the design dimensions of the dielectric device become extremely small, and transmission delay hinders high-speed signal processing. Points and
(B) When magnesium oxide fine particles having good crystallinity are used, the relative permittivity ε and the quality coefficient index Qf of the resin composition for a dielectric material are lowered.
Is described.

Patent Document 2 discloses a composite magnetic material in which carbonyl-reduced iron powder is dispersed in a PC / ABS-based resin, which is an insulating material, although it is not a dielectric composition.
In the same document, by blending substantially spherical iron powder having an average particle diameter D of 50% of 0.1 to 3 μm into a relatively low-loss insulating material, a small size that can be used in a wide band and with high efficiency at high frequencies. The points that can realize an antenna are described.

Patent Document 3 discloses a method for producing a dielectric ceramic powder in which the raw material composition is repeatedly fired and pulverized twice or more.
In the same document,
(A) By such a method, ^{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 can be obtained.
(B) It is described that such a dielectric ceramic powder can secure the fluidity of a mixture with a resin even when it is composed of amorphous particles produced by a pulverization method.

Patent Document 4 discloses a polymer composite piezoelectric material in which piezoelectric particles having a predetermined particle size distribution are dispersed in a matrix made of a polymer material, although it is not a dielectric composition.
In the same document,
(A) In order to obtain high vibration energy transmission efficiency, it is preferable that the particle size of the piezoelectric particles is large, but the packing density of the piezoelectric particles cannot be sufficiently increased only with the large piezoelectric particles. ,as well as,
(B) When large piezoelectric particles and small piezoelectric particles are mixed in the composite piezoelectric particle, good vibration energy transmission efficiency is realized by the large piezoelectric particles, and the small piezoelectric particles are the 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 : vacuum permittivity (constant), ε ₀ : relative permittivity, d: thickness). Therefore, in order to reduce the physique of a capacitor with the same capacitance, it is necessary to increase the relative permittivity of the material or reduce the thickness of the capacitor.
On the other hand, the capacitor generates heat due to Joule heat generated by the delay from the phase angle (90 degrees) of the AC electric field and the current during use. The tangent with respect to the phase angle (δ) indicating this delay is evaluated as the dielectric loss tangent (tan δ). Therefore, in order to suppress heat generation, it is necessary that the dielectric loss tangent of the capacitor is low.

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

In general, the relative permittivity and the dielectric loss tangent, and the relative permittivity and the dielectric breakdown strength are in a contradictory relationship, respectively. Therefore, when the relative permittivity of the material is reduced, the dielectric loss is likely to be reduced and the dielectric breakdown strength is likely to be improved. However, in that case, since the capacity of the capacitor decreases with the same volume, the physique becomes large. Further, in general, the dielectric loss tangent evaluated by a weak AC electric field and the dielectric breakdown strength, which is a high voltage phenomenon, need to be treated as different physical characteristics. Until now, in composite materials, the requirements for parallelizing high relative permittivity, low dielectric loss, and high dielectric breakdown strength have not always been clear.

On the other hand, focusing on the filler, an isoelectric material (for example, magnesium oxide) tends to show a low dielectric loss tangent because it has symmetry in its crystal structure. However, since the magnitude of polarization tends to be small, the relative permittivity is low. Therefore, when a normal dielectric filler is used, it is easy to obtain a composite material having a low dielectric loss tangent, but the relative permittivity is also likely to be low.

Ferroelectrics, on the other hand, exhibit a high relative permittivity, but at the same time tend to exhibit a large dielectric loss. As a ferroelectric filler, for example, BaTiO ₃ is known, and various studies have been made on the influence of the particle size and crystallinity of _{BaTiO 3 on the dielectric properties.} However, all of these studies are for sintered bodies, and there are many unclear points about the dielectric properties _{of BaTiO 3 as a powder.} Therefore, the requirements as a filler are not clear.

Japanese Unexamined Patent Publication No. 2014-024916 Japanese Unexamined Patent Publication No. 2011-09623 Japanese Unexamined Patent Publication No. 2005-306662 Japanese Unexamined Patent Publication No. 2015-192120

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, 014102 (2010)

An object to be solved by the present invention is to provide a dielectric composite material having a high relative permittivity, a low dielectric loss, and a high dielectric breakdown strength.

In order to solve the above problems, it is a gist that the dielectric composite material according to the present invention has the following constitution.
(1) The dielectric composite material is
A matrix made of resin and
It includes 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 on the 111th plane is 0.20 ° or less.
The ratio of the length of the c-axis to the length of the a-axis obtained from powder X-ray diffraction (c / a-axis ratio) is 1.006 or more, and
The equal number (n) of the rosin-ramler distribution function is 2.3 or more.
(3) The coefficient of variation of the interparticle distance of the filler particles dispersed in the matrix is 0.9 or less.

The perovskite compound is a ferroelectric substance. The small half-value width of the 111-plane peak of the perovskite compound indicates that the fluctuation of the crystal structure is small, that is, the dielectric loss tangent is small. Further, a large c / a axis ratio of the perovskite compound indicates a large polarization, that is, a high relative permittivity. Further, a large uniform number 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 a high relative permittivity, a small dielectric loss tangent, and a small variation in particle size, if the production conditions are optimized, the filler particles in the resin can be produced. The coefficient of variation of the inter-particle distance (variation of the inter-particle distance) becomes small. As a result, the non-uniformity of the electric field distribution in the composite material is reduced, and it is possible to maintain high dielectric breakdown strength. That is, the dielectric composite material according to the present invention can increase the relative permittivity while maintaining high dielectric breakdown strength while suppressing an increase in dielectric loss tangent as compared with the conventional one. Therefore, if this is applied to a capacitor, for example, the capacitor can be effectively miniaturized.

It is sectional drawing of the dielectric composite material which concerns on this invention. It is a process drawing of the manufacturing method of a dielectric composite material. It 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 equal number of filler particles, and the coefficient of variation of a 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 the dielectric composite material according to the present invention.
In FIG. 1, the dielectric composite material 10 is
Matrix 12 made of resin and
It includes filler particles 14 dispersed in the 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 is a resin having dielectric properties.
Examples of the resin constituting the matrix 12 include, for example.
(A) Thermosetting resins such as phenol resin, epoxy resin, melamine resin, urea resin, polyurethane, unsaturated polyester resin, and thermosetting polyimide.
(B) Thermoplastic resins such as polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polycarbonate, polyvinyl chloride, polyamide, acrylic resin, fluororesin, thermoplastic polyimide, polyvinylidene fluoride, etc.
and so on.

Any one of these thermosetting resins or thermoplastic resins may be used for the matrix 12, or two or more thermosetting resins or two or more thermoplastic resins may be used in combination. good. Further, one kind or two or more kinds of thermosetting resins may be used in combination with one kind or two or more kinds of thermoplastic resins.

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

[1.1.2. Relative permittivity]
The higher the relative permittivity of the resin constituting the matrix 12, the better. Generally, the relative permittivity of a resin is about 5 at the maximum, which is lower than that of a dielectric made of an inorganic compound. However, since the resin has a low relative permittivity, its dielectric loss tends to be low.

[1.2. Filler particles]
[1.2.1. composition]
In the present invention, the filler particles 14 are made of a perovskite compound. The perovskite compound is an inorganic compound whose chemical formula is represented by ABO ₃ (A and B are metal elements, respectively). Examples of the perovskite compound include
(A) A is composed of divalent elements such as Ba, Pb, Ca and Sr, and B is composed of tetravalent elements such as Ti, Zr, Sn and Hf.
(B) A is composed of monovalent elements such as Li, Na and K, and B is composed of pentavalent elements such as Nb and Ta.
(C) There are these solid solutions and the like.

Among these, the perovskite compound is preferably BaTIO ₃ , or _{a solid solution of BaTIO 3} and the other perovskite compound. BaTiO ₃ or its solid solution has a higher relative permittivity than other perovskite compounds or other inorganic compounds, and is therefore suitable as an inorganic compound constituting the filler particles 14.

[1.2.2. Half width]
Generally, in a dielectric composite material, the larger the relative permittivity of the inorganic compound contained in the dielectric composite material, the higher the relative permittivity can be obtained by adding a small amount of the inorganic compound. Therefore, it is desirable that the relative permittivity of the inorganic compound is high. On the other hand, as the particle size of the inorganic compound becomes smaller, the ratio of the surface layer to the entire particles increases. Since the surface of the particle is in a higher energy state than the inside, the structural order is easily disturbed and the crystallinity is lowered. Therefore, the physical and chemical properties change from the original composition, the relative permittivity decreases on the particle surface, and the dielectric loss tangent tends to increase. Therefore, it is desirable that the crystallinity is high even if the particle size of the inorganic compound is small.

The degree of crystallinity can be evaluated by the half width of the X-ray diffraction peak on the 111th plane. Here, in the present invention, the "half width" means the full width at half maximum. In general, the smaller the full width at half maximum, the smaller the fluctuation of the crystal structure and the smaller the dielectric loss tangent.
In order to obtain a dielectric composite material having a small dielectric loss tangent, the filler particles 14 need to have a half width of the X-ray diffraction peak on the 111th surface of 0.20 ° or less. 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. In general, the larger the ratio of the c-axis length to the a-axis length (c / a-axis ratio), the larger the polarization and the higher the relative permittivity. This c / a axis ratio changes depending on the composition and crystallinity of the perovskite compound. The c / a axis ratio can be determined from powder X-ray diffraction.
In order to obtain a dielectric composite material having a high relative permittivity, the filler particles 14 need to have a c / a axis ratio of 1.006 or more obtained from powder X-ray diffraction. The c / a axis ratio is preferably 1.007 or more, more preferably 1.009 or more.

[12.4. 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 = 100exp (−bD ⁿ ) ・ ・ ・ (1)
However, R is the mass% of the particles on the integrated sieve, D is the particle size of the particles, b is a constant, and n is an equal number.

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

If the filler particles 14 are non-uniformly dispersed in the matrix 12, the non-uniformity 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 are uniformly dispersed in the matrix 12. However, if the particle size distribution of the filler particles 14 is broad, it becomes difficult to uniformly disperse the filler particles 14.
In order to obtain high dielectric breakdown strength, the equal number (n) in the rosin-ramler distribution function needs to be 2.3 or more. The equal number (n) is preferably 2.5 or more, more preferably 2.7 or more.

[1.2.5. Average particle size]
Generally, the smaller the average particle size of the filler particles 14, the higher the relative permittivity can be obtained by adding a small amount of the filler particles 14. In order to obtain such an effect, the average particle size 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, if the average particle size of the filler particles 14 becomes too small, it becomes difficult to obtain the highly crystalline filler particles 14, and the relative permittivity of the filler particles 14 also decreases. Therefore, it is difficult to obtain a high dielectric constant with the composite material when it is filled in the matrix 12. Further, since the cohesive force is also high, it becomes difficult to uniformly disperse in the matrix 12, and the dielectric breakdown strength is also lowered. Therefore, the average particle size 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 size" refers to the median value (D 50} ) of the particle size measured by the laser diffraction / scattering method.

[1.3. Characteristics of Dielectric Composites]
[13.1. Coefficient of variation]
The "coefficient of variation of the interparticle distance" means 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" means the closest distance between the filler particles. The method of calculating the closest distance will be described later. The small coefficient of variation of the inter-particle distance indicates 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 permittivity of the dielectric composite material 10. Generally, if the volume fraction of the filler particles 14 becomes too small, the relative permittivity 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, if the volume fraction of the filler particles 14 becomes too large, the moldability is lowered and pores are likely to be formed in the dielectric composite material 10. The pores in the dielectric composite material 10 cause a decrease in the relative permittivity. 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 manufactured 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 : vacuum dielectric constant). ε ₀ : Relative permittivity, d: Thickness). That is, the thinner the thickness of the dielectric composite material 10, the higher the capacitance density. 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, if the thickness of the dielectric composite material 10 becomes too thin, the probability that the filler particles 14 are connected to each other between the electrodes increases, and as a result, the dielectric breakdown strength tends to decrease. Therefore, the thickness is preferably 2 μm or more. The thickness is preferably 4 μm or more, more preferably 6 μm or more.

[13.4. Dielectric properties]
As described above, when the half-price width, c / a axis ratio, coefficient of variation, equal number, etc. of the filler particles 14 are optimized, a dielectric composite material having a high relative permittivity, a low dielectric loss, and a high dielectric breakdown strength. 10 is obtained. Specifically, optimizing these parameters
(A) The relative permittivity 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 greater than 150 V / μm can be 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 shapes, materials, and the like of the electrodes 16 and 18 are not particularly limited, and the optimum one can be selected according to the purpose.

[2. Manufacturing method of dielectric composite material]
The dielectric composite material according to the present invention is
(A) The resin and filler particles are mixed to form a slurry.
(B) The slurry is coated on the base material to form a coating film having a predetermined thickness.
(C) It can be produced by drying the coating film.

[2.1. Mixing process]
First, the resin and the filler particles are mixed to obtain a slurry (mixing step). Specifically, the resin and the solvent are mixed and melted to prepare a resin varnish. Next, a predetermined amount of filler particles are added to the resin varnish, and these are thoroughly mixed.
The solvent may be any solvent capable of melting the resin. Examples of the solvent include N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone, dimethylacetamide, dimethyl sulfoxide, trimethyl phosphate, tetrahydrofuran, methyl ethyl ketone and the like. The amount of the solvent may be an amount as long as the filler particles are uniformly dispersed and a slurry having a viscosity sufficient for coating can be produced. The mixing method and mixing conditions are not particularly limited, and the optimum mixing method can be selected according to the intended purpose.

[2.2. Coating process]
Next, the slurry is applied onto the substrate to obtain a coating film (coating step). The type of base material 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 film on the substrate is dried (drying step). As a result, the solvent is volatilized from the coating film, and the dielectric composite material according to the present invention is obtained. The drying method and drying conditions are not particularly limited, and the optimum conditions can be selected according to the purpose. After drying, the dielectric composite is stripped from the substrate.

[3. Action]
The perovskite compound is a ferroelectric substance. The small half-value width of the 111-plane peak of the perovskite compound indicates that the fluctuation of the crystal structure is small, that is, the dielectric loss tangent is small. Further, a large c / a axis ratio of the perovskite compound indicates a large polarization, that is, a high relative permittivity. Further, a large uniform number 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 a high relative permittivity, a small dielectric loss tangent, and a small variation in particle size, if the production conditions are optimized, the filler particles in the resin can be produced. The coefficient of variation of the inter-particle distance (variation of the inter-particle distance) becomes small. As a result, the non-uniformity of the electric field distribution in the composite material is reduced, and it is possible to maintain high dielectric breakdown strength. That is, the dielectric composite material according to the present invention can increase the relative permittivity while maintaining high dielectric breakdown strength while suppressing an increase in dielectric loss tangent as compared with the conventional one. Therefore, if this is applied to a capacitor, for example, the capacitor can be effectively miniaturized.

(Examples 1 to 5, Comparative Examples 1 to 7)
[1. Preparation of sample]
FIG. 2 shows a process diagram of a method for manufacturing a dielectric composite material. Pelleted polyvinylidene fluoride (PVDF) and N, N-dimethylformamide (DMF) were mixed and melted to prepare a PVDF / DMF varnish. The filler particles were weighed so that the filling amount in the final composite material was 20 vol%, and mixed with PVD / DMF varnish to prepare a slurry. _{As the filler particles, various BaTIO 3} particles having different average particle size, equal number, half width, and / or c / a axis ratio were used.

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

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

[2.2. Half width of filler particles and c / a axis ratio]
The full width at half maximum and the c / a axis ratio were measured using an X-ray diffractometer (RINT-TTR, manufactured by Rigaku Corporation). The X-ray tube was Cu, the tube voltage was 50 kV, the tube current was 300 mA, the step size was 0.01 °, and the measurement was performed at 2θ = 10 ° to 90 °. The full width at half maximum of 111 diffractions was calculated from the peak corresponding to 111 diffractions 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 least squares method. The c / a-axis ratio was calculated from the obtained a-axis length and c-axis length. 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 equal number of filler particles was determined using the formula (1).

[2.4. Coefficient of variation]
After embedding the composite material in epoxy resin, the cross section was processed with an argon beam and observed at 10,000 times using a scanning electron microscope (SEM: Hitachi High-Technologies Corporation, SU3500). The matrix and filler particles were binarized from the brightness of the observed image by image processing software for multiple fields of view. For the detected filler particles, a triangle whose apex is the center of gravity closest to each other was formed for all the particles in the image. The interparticle distance was calculated from the distance between the centers of gravity, which is one side of the formed triangle. The interparticle distance for two particles is
(Distance between particles) = (Distance between centers of gravity)-(Sum of equivalent radii of each particle)
Defined in.
Here, the circle-equivalent radius is the radius of the circle-equivalent diameter, and the circle-equivalent diameter is obtained from the detected area S of each particle by the circle-equivalent diameter = √ (4 × S / π).
Obtain the inter-particle distance for all particles in the image, and set the coefficient of variation of the inter-particle distance as (coefficient of variation of inter-particle distance) = (average deviation of inter-particle distance) / (average inter-particle 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 / insulating properties of the obtained composite material. When _{the c / a axis ratio of the BaTiO 3} filler was 1.006 or more and the 111 half width was 0.20 ° or less, the tan δ of the composite material was 0.02 or less. Further, when _{the 111 half width of the BaTiO 3} filler was 0.20 ° or less and the coefficient of variation 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 equal numbers and coefficient of variation]
FIG. 4 shows a graph of Example 5, Comparative Example 6 and Comparative Example 7 having the same particle size when the reciprocal 1 / n of an equal number is taken on the horizontal axis and the coefficient of variation of the interparticle distance is taken on the horizontal axis. Shown. As shown in FIG. 4, it can be seen that it is effective to reduce 1 / n (that is, narrow the particle size distribution) in order to reduce the coefficient of variation of the interparticle distance. That is, by dispersing the filler having an equal number of 2.3 or more (narrow particle size distribution) in the resin, the coefficient of variation of the interparticle distance of the filler particles in the composite material (variation of the interparticle distance) is 0. It becomes 9.9 or less, and the insulation breaking strength becomes high.
As is clear from the above, it has been found that the composite material according to the present invention has a high relative permittivity, a low dielectric loss, and a high dielectric breakdown strength, and effectively functions as a capacitor.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present 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 (2)

A dielectric composite material having the following configurations.
(1) The dielectric composite material is
A matrix made of resin and
It includes 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 on the 111th plane is 0.20 ° or less.
The ratio of the length of the c-axis to the length of the a-axis obtained from powder X-ray diffraction (c / a-axis ratio) is 1.006 or more .
Rosin-Rammler equal number of distribution function (n) is not less than 2.5, and,
The average particle size is 500 nm or less.
(3) The coefficient of variation of the interparticle distance of the filler particles dispersed in the matrix is 0.9 or less.
(4) The dielectric composite material has a volume fraction (filling amount) of the filler particles of 2 vol% or more and 50 vol% or less.
(5) The filler particles are composed of BaTiO ₃ or _{a solid solution of the BaTiO 3} and the other perovskite compound.
The resin is made of polyvinylidene fluoride or a copolymer thereof.
(6) The dielectric composite material is
Relative permittivity greater than 15 at a frequency of 10 kHz
Dissipation factor tan δ is 0.02 or less at a frequency of 10 kHz, and
Dielectric breakdown strength is greater than 150 V / μm. The dielectric composite material according to claim 1, wherein the thickness is 2 μm or more and 50 μm or less.

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