JP6759084B2 - Barium titanate fine particles and their dispersion and method for producing barium titanate fine particles - Google Patents

Description

The present invention relates to barium titanate fine particles, a dispersion containing the barium titanate fine particles, and a method for producing the barium titanate fine particles.

Barium titanate (BaTIO ₃ ) is an artificial mineral having a tetragonal perovskite crystal structure at room temperature, and is used in various technical fields as an electronic material because it exhibits a high relative permittivity. When a dielectric article is produced from this barium titanate, generally, a slurry (dispersion) in which fine particles of barium titanate are dispersed in a dispersion medium is prepared, and a target article is produced from this slurry. ing. With the progress of miniaturization and high quality of electronic parts and the like, barium titanate fine particles are also required to have a particle size as small as possible and good dispersibility. Further, when barium titanate is used for optical applications, higher homogeneity of individual particles is required as compared with the case of producing, for example, a dielectric article. As a conventional technique for producing barium titanate fine particles on the order of nanometers, for example, Patent Documents 1 to 4 can be mentioned.

Japanese Patent No. 5604735 JP-A-2010-064938 Japanese Unexamined Patent Publication No. 2014-144899 Japanese Patent No. 5112979

In Patent Document 1, barium titanate fine particles are produced by a hydrothermal synthesis method. Barium titanate fine particles obtained by a liquid phase method such as a hydrothermal synthesis method have relatively high crystallinity, but the finer the particle size, the higher the cohesiveness. Therefore, there is a problem that it is extremely difficult to prepare a slurry by powdering barium titanate fine particles and then dispersing them in a dispersion medium.
Further, in Patent Document 2, barium titanate fine particles are produced by the sol-gel method. According to the sol-gel method, it is difficult to obtain highly crystalline barium titanate fine particles. Further, when the obtained barium titanate fine particles are subjected to a heat treatment for increasing the crystallinity, there is a problem that grain growth is unavoidable and fine powder cannot be obtained. In addition, the sol-gel method has a drawback that the manufacturing cost is high because the manufacturing process is complicated and the manufacturing conditions are relatively difficult to control.

On the other hand, in the presence of an organic compound, barium titanate fine particles are produced at a relatively low temperature, and the surface of the fine particles is coated with the organic compound to enhance the redispersibility in the dispersion medium after powdering. It has been proposed (eg, Patent Documents 3 and 4).
As the barium titanate fine particles obtained in Patent Document 3, although a powder made of barium titanate fine particles having relatively good dispersibility can be obtained, it is difficult to finely adjust the amount of the organic compound coating. As a result, the organic compound coating becomes relatively excessive, and when powdered, the organic compound coating may be crosslinked or particles having a small coating amount may agglomerate to form an agglomerate. Therefore, the presence of agglomerates is also recognized in the slurry prepared thereafter, and it is required that a slurry having even higher uniformity can be prepared depending on the application.

Further, in Patent Document 4, an organic compound such as sodium oleate is used together with a titanium source and a barium source, and hydrothermal treatment is performed at a temperature of 300 ° C. or higher to produce barium titanate, which suppresses aggregation and has excellent dispersibility. are doing. However, Patent Document 4 has a drawback that only barium titanate fine particles having a diameter of more than 100 nm can be actually produced. Further, there is a problem that the organic compound coating amount is relatively large and cannot be used in applications where it is necessary to keep the content of impurities low.

The present invention has been made in view of the above points, and an object of the present invention is to provide barium titanate fine particles which are fine powders and have good dispersibility in a dispersion medium. From another point of view, it is an object of the present invention to provide a dispersion in which such barium titanate fine particles are dispersed, and a method for producing the barium titanate fine particles.

The present inventors have so far proposed barium titanate fine particles that are fine on the order of nanometers, are homogeneous, and have suppressed adhesion and cohesive force between particles (see Patent Document 3). The barium titanate fine particles are homogenically and isotropically titanium while suppressing the aggregation of the barium titanate fine particles by producing barium titanate by a heating and reflux method and coating it with a film made of a polyvinyl-based polymer compound. The barium titanate fine particles are produced. However, as described above, the barium titanate fine particles have good dispersibility during particle preparation because they are covered with a film, but the dispersibility of the particles after being powdered or stored (hereinafter referred to as redispersibility). There was a point to be improved that it was low for.).
As a result of intensive studies to satisfy these points, the present inventors have found that the coating amount can be adjusted with high accuracy by hydrothermally treating the barium titanate fine particles obtained as described above. .. Further, they have found that the redispersibility of the barium titanate fine particles becomes extremely good by adjusting the amount of the coating film, and have completed the present invention.

That is, the barium titanate fine particles disclosed herein include core particles mainly composed of barium titanate and a coating portion containing a polyvinyl compound provided on at least a part of the surface of the core particles. The proportion of the coated portion of the barium titanate fine particles is 6% by mass or more and 10% by mass or less, the average particle size based on the dynamic light scattering method is 20 nm or more and 250 nm or less, and the spectrum obtained by FTIR analysis. in a wave number 1450 cm ^-1 intensity I ₁₄₅₀ of the absorption peak in the vicinity of, the wave number 1550 cm ^-1 absorption peak of the intensity I ₁₅₅₀ of the proximity, the intensity ratio of (I ₁₄₅₀ / I ₁₅₅₀₎ is characterized by greater than 8.

According to such a configuration, barium titanate fine particles having core particles made of barium titanate having a fine average particle diameter but good crystallinity are provided. Further, these fine particles are derived from the amount of the coating portion provided on the surface of the core portion and the _three CH groups that increase when the C = O bond of the polyvinyl-based polymer compound is decomposed in the FTIR spectrum of the coating portion. an absorption peak at a wavenumber of 1450 cm ^-1 vicinity, for example the absorption peak in the vicinity of wave number 1550 cm ^-1 derived from NH bond, and the intensity ratio of, is controlled to be a predetermined value. As a result, barium titanate fine particles having good redispersibility in the dispersion medium are realized.

In a preferred embodiment of the barium titanate microparticles disclosed herein, the coating comprises a degradation product derived from polyvinylpyrrolidone. According to such a configuration, aggregation of core particles made of barium titanate can be suitably suppressed, which is preferable.

In a preferred embodiment of the barium titanate fine particles as disclosed herein, in the spectrum obtained by the FTIR analysis, the wave number 1450 cm ^-1 intensity I ₁₄₅₀ of the absorption peak in the vicinity, the intensity of the absorption peak at a wavenumber of 1650 cm ^-1 vicinity I ₁₆₅₀ And the intensity ratio (I ₁₄₅₀ / I ₁₆₅₀ ) is 2 or more and 7 or less. Since the peak near 1650 cm ^-1 is derived from the C = O bond of the polyvinyl-based polymer compound, according to such a configuration, the state of the coating portion of the barium titanate fine particles can be determined from the degree of decomposition of the polyvinyl-based polymer compound. It can be evaluated directly and appropriately.

In a preferred embodiment of the barium titanate fine particles disclosed herein, the average particle size based on electron microscope observation is 10 nm or more and 200 nm or less. According to such a configuration, for example, barium titanate fine particles suitable for manufacturing applications of electronic parts and optical parts are provided.

As described above, the barium titanate fine particles disclosed herein are realized as having good redispersibility in a dispersion medium while being in a powder state on the order of nanometers. Therefore, in another aspect, the technique disclosed herein also provides a dispersion in which the above-mentioned barium titanate fine particles are dispersed in a dispersion medium by utilizing the features of the barium titanate fine particles. The dispersion medium can include at least one selected from the group consisting of water, ethanol, terpineol, 2-propanol, 1-methoxy-2-propanol and ethylene glycol. This provides, for example, a dispersion suitable for manufacturing a dielectric device such as a multilayer ceramic capacitor (MLCC), a semiconductor element such as a temperature sensor and a heating element, and the like. Further, a dispersion that can be suitably used for manufacturing optical components such as an antireflection film and a light collecting material using barium titanate fine particles as a high refractive material is provided.

Further, the technique disclosed herein also provides the above-mentioned method for producing barium titanate fine particles. In this production method, nanoparticles comprising the core particles mainly composed of barium titanate and an organic film containing a polyvinyl-based polymer compound provided on at least a part of the surface of the core particles are prepared. This includes obtaining the barium titanate fine particles by reducing the amount of the organic film by subjecting the nanoparticles to hydrothermal treatment. With such a configuration, the amount of the organic film contained in the nanoparticles can be appropriately controlled, and barium titanate fine particles having even better dispersibility can be obtained.

It is a flow chart which shows the outline of the manufacturing method of the known nanoparticle. It is a flow chart which shows the outline of the manufacturing method of the barium titanate fine particles which concerns on one Embodiment. It is a figure which illustrated the FTIR spectrum of polyvinylpyrrolidone. It is a figure which illustrated the FTIR-ATR spectrum (2000-1000cm ^-1 ) of the barium titanate fine particle and PVP of each example. (A) and (b) are diagrams illustrating the FTIR-ATR spectrum (4000 to 2500 cm ^-1 ) of barium titanate fine particles and PVP of each example. It is a graph which shows the thermogravimetric analysis result of the barium titanate fine particles of Example 1, Comparative Examples 1, 3 and 5. It is sectional drawing which schematically explains the structure of the multilayer ceramic capacitor formed by using the barium titanate fine particles which concerns on one Embodiment.

Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than those specifically mentioned in the present specification (for example, the properties of barium titanate fine particles and the form of the dispersion medium) and necessary for carrying out the present invention (for example, obtaining raw materials and the like). The preparation method, general matters concerning the production of a dielectric element from barium titanate fine particles and a dispersion medium, etc.) can be grasped as design matters of those skilled in the art based on the prior art in the art. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the art. In this specification, the notation "A to B" indicating the range means A or more and B or less. Further, in the present specification, the dispersion is a state in which barium titanate fine particles as dispersoids are dispersed in an arbitrary dispersion medium, and includes those called pastes, slurries, inks, suspensions and the like. ..

The barium titanate fine particles disclosed herein include core particles substantially made of barium titanate and a coating portion containing a polyvinyl-based polymer compound provided on at least a part of the surface of the core particles.
The main part of the barium titanate fine particles is composed of core particles. The core particles consist substantially of barium titanate. Here, "substantially" means that unavoidable impurities and trace amounts of other components (for example, components contained in the coating portion) are allowed to be mixed, and the content of barium titanate is generally titanium. It is not particularly limited as long as it can be determined that it is composed of barium acid. Typically, it means that 95% by mass or more (preferably 98% by mass or more, for example, 99% by mass or more) of the core particles is barium titanate.

In addition, barium titanate is a metal composite oxide having a perovskite-type structure having a composition represented by the general formula: BaTIO ₃ . This barium titanate has an element ratio Ba / Ti of barium (Ba) and titanium (Ti) of 0.9 or more (preferably 0.95 or more) and 1.1 or less as long as the object of the present invention is not impaired. It may be changed to about (preferably 1.05 or less). However, from the viewpoint of maintaining a stable crystal structure, Ba / Ti is preferably "1" or close to "1". Further, the number of oxygen bonded to each atom of barium and titanium may deviate from "3".

Further, the Ba site and Ti site in the general formula may be substituted with other elements. Such a substitution element can be appropriately determined depending on the use of the samarium titanate fine particles and the like, and for example, an alkaline earth metal element such as calcium (Ca) and samarium (Sr), lanthanum (La) and neodymium (Nd). ), Samarium (Sm), Europium (Er), Disprosium (Dy) and other lanthanoid elements, Itria (Y), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co) , Nickel (Ni), Hafnium (Hf), Tantal (Ta), Tungsten (W), Zirconium (Zr), Niob (Nb), Molybdenum (Mo) and other transition metal elements, Ruthenium (Ru), Rodium (Rh) , Palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt) and other noble metal elements, tin (Sn), lead (Pb), bismuth (Bi) and other typical metal elements, selenium (Se), It may be an element such as germanium (Ge), tellurium (Te), antimony (Sb) and the like. These substituents can typically function as dopants. The ratio of the substituent is not particularly limited, but may be, for example, 0.002 atomic% or more and 0.05 atomic% or less.

The average particle size of the core particles is substantially the same as the average particle size of the barium titanate fine particles. Although the average particle size is not strictly limited, it can be typically about 10 nm or more, preferably 30 nm or more, for example 40 nm or more, from the viewpoint of handling and the like. Further, for example, if the average particle size is about 500 nm or less, the particle size can be controlled for production, but from the viewpoint that a finer particle size is required, about It may be 200 nm or less, preferably 150 nm or less, for example 120 nm or less. However, since the average particle size of the barium titanate fine particles can be adjusted by the production method, it may be out of the above-mentioned preferable range, and can be set to a desired size according to the intended use or the like. The average particle size can be adjusted by controlling, for example, the amount of the organic substance added to form the coating, the composition of the solvent, the temperature and pH of the raw material mixture in the manufacturing process, and the like.

Further, the "average particle size" of the powder of barium titanate fine particles referred to here is 100 selected in a plurality of (for example, 2 or more) observation fields or observation images observed by an observation means such as an electron microscope. It is defined as the arithmetic average value of the equivalent circle diameter of one or more particles. In the present specification, the average particle size specified by observation with a scanning electron microscope (SEM) is adopted. Hereinafter, it is also referred to as SEM average particle size and the like. The average particle size is clearly distinguished from the average particle size of barium titanate fine particles described later by the DLS method. As can be seen from this, the barium titanate fine particles are typically provided in the form of powder as an aggregate of a plurality of particles.

The above core particles have a coating portion containing a polyvinyl-based polymer compound on at least a part of a substantially spherical surface. The coating portion having the characteristics described below may be attached to a part of the core particles or may cover the entire coating portion. It is preferable that the coating portion is mainly composed of a polyvinyl-based polymer compound from the viewpoint that the adhesive force and cohesive force between the core particles can be suitably suppressed. Polyvinyl-based polymer compound, a homopolymer of a monomer having a vinyl group _(-CH 2 = CH-), or a copolymer of two or more monomers including a monomer having a vinyl group _(-CH 2 = CH-) , Those modified products, modified products, etc. are the main components. Here, "mainly" means that 50% by mass or more of the total mass of the coating portion is a polyvinyl-based polymer compound, and 70% by mass or more (preferably 80% by mass or more) is a polyvinyl-based polymer compound. It is a molecular compound.

Monomers having a vinyl group include N-vinyl-2-pyrrolidone, acrylonitrile, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, benzyl methacrylate, divinylbenzene, styrene, α-methylstyrene, vinyl chloride, vinyl acetate, and foot. Examples include vinylidene compound. Specific examples of the polyvinyl-based polymer compound include polymers having N-vinyl cyclic lactam units such as polyvinylpyrrolidone (PVP), polyacrylonitrile, and N-vinyl-ε-caprolactam, polystyrene, polyvinyl chloride, and polyvinyl acetate. , Polyvinyl alcohol, polyvinylidene fluoride, etc., and among them, polyvinylpyrrolidone is a preferable example. Since it is not preferable to overcoat the core particles with the coating portion, at least a part of them can be decomposed to make the coating amount substantially uniform. As a result, this coating may contain a chemical structure corresponding to a decomposition product obtained by decomposing a polyvinyl polymer compound. In the barium titanate fine particles disclosed herein, in order to more clearly identify the structure, the coating portion contains a polyvinyl-based polymer compound capable of forming an NH bond by decomposition. Is preferable. For example, it may be preferable that the coating portion contains at least a decomposition product of a polyvinyl-based polymer compound.

According to the studies by the inventors, when the core particles do not have a coating portion or when the coating amount is not sufficient, agglomeration of the core particles is unavoidable due to the size effect. On the other hand, when the core particles are covered with an excessive amount of the coating portion, or when the amount of the coating portion covering the surface of the core particles is uneven, the barium titanate fine particles are crosslinked by the coating portion. A situation could occur in which agglomerates were formed. In particular, with barium titanate fine particles produced by the reflux method, it is difficult to precisely control the coating amount, and even seemingly homogeneous barium titanate fine particles may have a plurality of particles bonded to each other. In such a case, even if the powdered barium titanate fine particles are to be redispersed in the dispersion medium, it is difficult for the barium titanate fine particles to be uniformly dispersed in the dispersion medium in a monodispersed state. On the other hand, by appropriately treating the coating portion on the surface of the barium titanate fine particles, a part of the coating portion is decomposed and removed to adjust the coating amount, and the unevenness of the coating portion is reduced. It was found that the cross-linking between the barium titanate fine particles can be remarkably suppressed, and the redispersibility in the dispersion medium can be remarkably enhanced. Although the details are unknown, it is considered that the cross-linking between the coating portions is preferably suppressed by disturbing the chemical structure of the polyvinyl-based polymer compound constituting the coating portion by decomposition. The barium titanate fine particles disclosed herein have been completed based on such findings.

Such a coating portion can be confirmed by examining at least whether or not the chemical structure of the organic compound constituting the coating portion contains a structure corresponding to the polyvinyl polymer compound and its decomposition product. .. There are various methods for identifying the chemical structure of such an organic substance, but in the present specification, Fourier Transform Infrared Spectroscopy (FTIR) is a widely used method capable of relatively high-precision analysis. Qualitative analysis is adopted. In addition, since the organic substance to be measured exists only on the surface of the core particles, such analysis obtains the absorption spectrum of the sample surface by measuring the light totally reflected on the sample surface. Attenuated Total Reflection : ATR) It is preferable to carry out by the measurement method.

As an example, a is PVP Preferred examples of the polyvinyl-based polymer compounds, the general _{formula: (C 6 H 9 NO)} n; has a composition represented by, as shown in the following formula, 5-membered cyclic lactam structure and It is a polymer compound having a polymerized structure of N-vinyl-2-pyrrolidone (CH ₂ CHNC ₃ H ₃ CO) having a vinyl group.

Then, as shown in the FTIR absorption spectrum of PVP in FIG. 2, for example, in the polyvinyl-based polymer compound, an absorption band derived from the molecular structure and assigned to the following predetermined wave number as described below is observed. For example, derived from the linear backbone of the polyvinyl-based polymer ^{compound, 2980cm -1, 2916cm -1,} absorption peaks are observed near 2882cm ^-1. Also, due to the 5-membered ring structure of PVP, absorption peaks are observed near 2949 cm ^-1 and 2916 cm ^-1 .
Wave number 2980 cm ^-1 near: linear CH ₂ reverse target expansion and contraction vibration Wave number 2916 cm ^-1 near: Linear CH ₂ target expansion and contraction vibration Wave number 2882 cm ^-1 near: linear CH expansion and contraction vibration Wave number 2949 cm ^-1 near: annular CH ₂ reverse target expansion and contraction Vibration wave number 2916 cm ^-1 vicinity: Circular CH ₂ Target expansion and contraction vibration

Also, the degradation product of PVP comprises ₃ CH groups due to, for example, the opening of the 5-membered ring lactam structure of PVP, the C = O bond and the degradation of the CC skeleton. obtain. Also, the degradation product of PVP may comprise an NH bond due to the broken bond between nitrogen (N) and carbon (C). Therefore, it can be confirmed that there is a chemical structure corresponding to the decomposition product of PVP by confirming the spectrum caused by these _three CH groups and NH bonds in the spectrum obtained by FTIR analysis. At the same time, by confirming the spectrum caused by the C = O bond and the C—N bond caused by PVP, it can be determined that a part of PVP is decomposed to form a decomposition product. it can.

From this point of view, the barium titanate fine particles disclosed herein have, for example, an absorption peak derived from _three CH groups in the vicinity of a wave number of 1450 cm- ¹ in the FTIR spectrum by the ATR method (hereinafter referred to as FTIR-ATR spectrum). and has an absorption peak derived from NH bond near the wave number 1550 cm ^-1, and has an absorption peak derived from C = O bonds in the vicinity of 1650 cm ^-1.
Then, since it is preferable to polyvinyl polymer compound is sufficiently decomposed, and the intensity I ₁₄₅₀ of the absorption peak of 1450 cm ^-1 vicinity, the ratio of the intensity I ₁₆₅₀ of the absorption peak of 1650 cm ^-1 vicinity (I ₁₄₅₀ / I ₁₆₅₀ ) is not particularly limited as long as it is larger than 1, but the ratio is preferably 2 or more, more preferably 2.5 or more, further preferably 2.9 or more, and 3 The above is particularly preferable. Since the number of CH ₃ groups increases significantly as the decomposition of the polyvinyl polymer compound progresses, the upper limit of these peak intensity ratios (I ₁₄₅₀ / I ₁₆₅₀ ) is not particularly limited, but the dispersibility during the synthesis of barium titanate fine particles is not particularly limited. From the viewpoint that the above can be ensured, it may be a preferable embodiment that the polyvinyl-based polymer compound is present to some extent. Therefore, the peak intensity ratio (I ₁₄₅₀ / I ₁₆₅₀ ) can be, for example, 10 or less, more preferably 7 or less, and 5 or less.

Similarly, the intensity I ₁₄₅₀ of the absorption peak of 1450 cm ^-1 vicinity, 1550 cm ratio between ^-1 intensity I ₁₅₅₀ of the absorption peak in the vicinity (I ₁₄₅₀ / I ₁₅₅₀₎ is strictly not limited, PVP some It is preferable that the mixture is sufficiently decomposed leaving the above. From this, the ratio of ₃ CH groups to the NH bond (I ₁₄₅₀ / I ₁₅₅₀ ) is preferably 8 or more (more than 8), and more preferably 8.05 or more. The upper limit of the peak intensity ratio (I ₁₄₅₀ / I ₁₅₅₀ ) is not particularly limited, but can be, for example, 11 or less, more preferably 10 or less.

In most of the barium titanate fine particles disclosed herein, the coating portion containing the polyvinyl-based polymer compound cannot be clearly confirmed by observation with an electron microscope such as SEM. In this respect, it can be reliably distinguished from the barium titanate nanoparticles disclosed in the prior art of the present inventors (Patent Document 3). Then, the amount of the coated portion attached can be confirmed from, for example, the weight loss rate (%) by thermogravimetric analysis. That is, the content of the coating portion adhering to the barium titanate fine particles can be expected to be improved by providing even a very small amount, but 6 mass is required to ensure good redispersibility. % Or more, more preferably 7% by mass or more, and particularly preferably 8% by mass or more. Further, excessive adhesion of the coating portion is not preferable because even if the chemical structure thereof is decomposed, the barium titanate fine particles are likely to be crosslinked. Therefore, the content of the covering portion can be 10% by mass or less (for example, less than 10% by mass), more preferably 9.5% by mass or less, and particularly preferably 9% by mass or less.

As described above, such barium titanate fine particles have a chemical structure corresponding to a decomposition product of a polyvinyl-based polymer compound in the coating portion. Further, by partially decomposing the covering portion, the amount of the covering portion is adjusted to a predetermined range, and cross-linking with each other is suppressed. As a result, the dispersibility when dispersed in a dispersion medium from the powder state is remarkably improved. Such dispersibility is evaluated, for example, by using the average particle size based on the Dynamic light scattering (DLS) method as an index for evaluating the aggregated state of barium titanate fine particles in the dispersion medium. Can be done. In the DLS method, it is possible to estimate the mean diameter of particles whose size dispersed in a liquid is mainly in the submicron to nanometer region, and to measure the spread of the particle size distribution. Therefore, the average particle size of the barium titanate fine particles in the dispersion in which the barium titanate fine particles are dispersed in the dispersion medium based on the DLS method is the same as or closer to the average particle size based on the electron microscope observation in the above powder state. Assuming that the aggregation of the barium titanate fine particles is suppressed, it can be judged that the dispersibility is good.
The average particle size based on the DLS method can be measured according to JIS Z 8828: 2013.

The characteristics of the barium titanate fine particles will be described in more detail below by showing a suitable method for producing the barium titanate fine particles disclosed herein. However, the method for producing barium titanate fine particles disclosed herein is not limited to the following aspects.

The method for producing the barium titanate fine particles disclosed herein is not particularly limited. For example, the barium titanate fine particles produced by the heating / reflux method described in Patent Document 3 (hereinafter referred to as barium titanate fine particles before hydrothermal treatment). Is referred to as "nanoparticles") as a starting material, and these nanoparticles are hydrothermally treated to adjust the shape and amount of the coating.

Since the method for producing nanoparticles is not the essence of the present invention, the description thereof will be simplified, but as shown in FIG. 1A, it essentially includes the following steps. For details on the production of nanoparticles by such a heating / reflux method, the disclosure of Patent Document 3 can be referred to.
(S10) Mixing a titanium source, a barium source, and a polyvinyl polymer compound in a solvent to prepare a raw material mixture (mixing step).
(S20) The raw material mixture is heated to reflux at a predetermined temperature to precipitate a precursor (heating / reflux step).
(S30) The raw material mixture after heating and reflux is cooled at a predetermined cooling rate to obtain nanoparticles (cooling step).
(S40) Recovery of precipitated nanoparticles (recovery step)

<S10; Mixing step>
First, at least a titanium (Ti) source, a barium (Ba) source, and a polyvinyl-based molecular compound are prepared as raw materials, and these raw materials are mixed in a predetermined solvent to prepare a raw material mixture. The amount ratio of the metal elements (Ti element and Ba element) contained in the mixed solution can be appropriately adjusted according to the characteristics of the nanoparticles as the target substance. When preparing the raw material mixture, all the raw materials may be put into the solvent at once, or these materials may be put into the solvent sequentially. In the flow chart shown in FIG. 1A, an example is shown in which a Ti source and a Ba source are first added to a solvent to uniformly disperse them, and then a polyvinyl polymer compound is mixed.

As the titanium source or barium source, salts of each metal (that is, Ti salt or Ba salt) can be preferably used. The anions in these metal salts can be appropriately selected so as to be soluble in the solvent used by the metal salts, and can be, for example, chloride ions, carbonate ions, hydroxide ions, sulfate ions, nitrate ions and the like. .. The anions of these metal salts may be the same or different from each other. The flow chart shown in FIG. 1A shows an example in which chloride salts of each metal (that is, titanium chloride and barium chloride) are used. The concentration of the raw material mixture can be, for example, about 0.2 mol / L to 2.2 mol / L in total of the metal elements (Ti and Ba in this case). As described above, when the Ba sites and Ti sites of barium titanate are replaced with other elements, the metal salts of the other elements can be added at a desired ratio based on stoichiometry. ..

As the polyvinyl-based polymer compound, one or more of the above-mentioned ones can be used without particular limitation. The flow chart shown in FIG. 1A shows an example of using polyvinylpyrrolidone (PVP). Although not particularly limited to the invention, such a polymer compound can act as a chelating agent in the heating / refluxing step described later. That is, the polymer compound can be coordinated to the surface of the precipitated precursor, which suppresses the growth of the precursor, so that fine (nanometer-sized) particles can be preferably obtained. In addition, since the surface of the obtained fine particles is thinly coated with a polymer compound, the adhesive force and cohesive force between the particles may be reduced as compared with the conventional case. Therefore, for example, even when it is stored in a powder state, it has an effect that aggregation is unlikely to occur.

The amount of the polyvinyl-based polymer compound added may be at least the stoichiometric amount required for chelate formation, and the proportion of the polymer compound in the total raw material mixture is preferably 5% by mass to 50% by mass. In other words, the molar ratio of the polymer compound to the metal elements (Ti and Ba) can usually be 0.01 times or more, preferably 0.01 to 1 times, for example, 0.015 times. More preferably, it is ~ 0.5 times.

The solvent (dispersion medium) for dispersing the raw materials can be used without particular limitation as long as the raw material compounds to be used (that is, a titanium source or barium source and a polyvinyl polymer compound) can be uniformly dispersed or dissolved. .. As such a solvent, water or a mixed solvent mainly composed of water can be used. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. As the organic solvent, for example, a solvent containing a functional group capable of producing an aldehyde by oxidation (for example, a hydroxyl group, a carbonyl group, an ether group) and having a relatively high boiling point can be preferably used. As a particularly preferable solvent, an organic solvent containing a hydroxyl group and having a boiling point of 100 ° C. or higher, such as ethylene glycol (boiling point 196 ° C.), is exemplified.

<S20; heating / refluxing step>
Next, the above-prepared raw material mixture is heated to reflux at a predetermined temperature, whereby a precursor is precipitated in the raw material mixture. In the flow chart shown in FIG. 1A, the heating / refluxing step (S20) includes a temperature adjusting step (S22) and a pH adjusting step (S24).
In the temperature adjusting step (S22), the temperature of the raw material mixture is adjusted within a predetermined range. The lower limit of the reflux temperature is not particularly limited because it may differ depending on the type of solvent used and the properties (for example, particle size and particle shape) of the nanoparticles to be produced. However, if it is too low, the reduction rate becomes slow, and a precursor having a shape in which only a predetermined direction is grown (for example, a flat plate shape) can be precipitated, which is not preferable. Therefore, in order to obtain homogeneous spherical nanoparticles, the temperature environment is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, and particularly preferably 80 ° C. or higher. The upper limit of the reflux temperature depends on the boiling point of the solvent used, but for example, for the purpose of forming a relatively homogeneous coating portion, it is preferably 100 ° C. or lower, more preferably 95 ° C. or lower, 90. ℃ or less is particularly preferable.

By setting the reaction mixture in the above temperature range, the reduction reaction can be promoted and a desired precursor can be obtained in a relatively short time. Further, at this time, since the polyvinyl-based polymer compound is coordinated on the surface of the precursor, the growth of the precursor is appropriately suppressed by this, and a fine powdery precursor can be preferably obtained. .. As shown in Examples described later, in the above temperature range, the reflux temperature and the average particle size of the nanoparticles are generally correlated, and the higher the reflux temperature, the larger the average particle size tends to be. This is because by setting the reflux temperature high, the reducing ability of the solvent is increased, and the thickness of the core portion made of barium titanate is substantially increased.

The size (average particle size) of the precursor precipitated in the heating / reflux step (S20) may depend on pH. Therefore, as shown in the flow chart of FIG. 1A, it is preferable to include the pH adjusting step (S24) after the temperature adjusting step (S22). The pH can be adjusted, for example, by adding an alkaline solution generally used for pH adjustment (for example, an aqueous ammonia solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, etc.) to the raw material mixture. The initial pH of the raw material mixture is adjusted to approximately 10 to 14 (typically 11 to 12, for example, around 11.5). Then, it is preferable to perform heating and reflux while maintaining this initial pH (that is, while sequentially supplying an alkaline aqueous solution into the raw material mixture as needed). The pH value in the present specification refers to a pH value based on a liquid temperature of 25 ° C.

The time for heating and refluxing (that is, the time for continuing the precipitation of the precursor) can be appropriately set according to the properties (typically, the particle size) of the target nanoparticles. Usually, it can be about 10 minutes to 120 minutes (preferably 30 minutes to 90 minutes). As a tendency, in order to obtain nanoparticles having a larger particle size, it is preferable to lengthen the holding time.

<S30; Cooling process>
Then, the raw material mixture after heating and refluxing (for example, 50 ° C. to 100 ° C.) is cooled at a predetermined cooling rate. There is a general correlation between the cooling rate and the average particle size of the nanoparticles, and the higher the cooling rate, the smaller the average particle size tends to be. This is because the growth of particles is suppressed by quenching. Therefore, it is usually appropriate to rapidly cool the raw material mixture containing the precursor at a rate of about 0.2 ° C./s to 8 ° C./s, and it is generally 0.5 ° C./s to 2 ° C./s ( It is preferable to carry out at an average cooling rate (some errors are acceptable). By setting the cooling rate within the range, it is possible to preferably obtain nanoparticles having a substantially spherical shape and a uniform particle size. In addition, nanoparticles having good crystallinity can be obtained.

<S40; Recovery process>
Further, typically, the solvent is removed from the cooled raw material mixture, and the precipitated nanoparticles are recovered. Such a method is not particularly limited, but it is preferable to precipitate the nanoparticles with a centrifuge, remove the supernatant (solvent), and then dry the particles. Alternatively, it may be separated from the solvent by filtration, washed and dried. As a result, unreacted raw materials, side reaction products, and the like can be suitably removed, and highly pure nanoparticles can be prepared.

After preparing the nanoparticles in this way, as shown in the flow chart of FIG. 1B, the barium titanate fine particles disclosed herein can be produced according to the following steps.
(S50) Preparing a reaction solution by dispersing the prepared nanoparticles in a dispersion medium (solution preparation step).
(S60) Hydrothermally treating the raw material mixture at a predetermined temperature (hydrothermal treatment step).
(S70) Recovery of barium titanate fine particles from which at least a part of the coating portion has been decomposed and removed (recovery step)

<S50; Solution preparation step>
In order to subject the prepared nanoparticles to hydrothermal treatment, the nanoparticles are dispersed in a dispersion medium to prepare a reaction solution. As the dispersion medium, an aqueous dispersion medium containing at least water can be used. Further, the aqueous dispersion medium may be water, or may be a mixed solution containing a lower alcohol that can be uniformly mixed with water in addition to water. As the water, ion-exchanged water, pure water, distilled water and the like can be used. As the alcohol, a lower alcohol having 1 to 4 carbon atoms can be preferably used. Specific examples thereof include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol and the like.

When a mixed solution of water and alcohol is used, the mixing ratio of both is not particularly limited. Alcohol has the function of slightly slowing the progress of the hydrothermal reaction. Therefore, the proportion of alcohol can be changed according to the properties of the nanoparticles used. However, the inclusion of excess alcohol is not preferable because it inhibits the hydrothermal reaction. Therefore, the proportion of alcohol in the mixed solvent is, for example, preferably 70% by mass or less, more preferably 60% by mass or less, and particularly preferably 50% by mass or less.

The ratio of the nanoparticles to the entire reaction solution is not particularly limited, but from the viewpoint of accurately adjusting the decomposition amount of the coating portion, it can be, for example, 20% by mass or less, more preferably 10% by mass or less, and 5% by mass. % Or less is more preferable. From the viewpoint of efficiently decomposing the covering portion, for example, it can be 0.5% by mass or more, more preferably 1.0% by mass or more, and more preferably 1.5% by mass or more.

<S60; Hydrothermal treatment process>
Then, the reaction solution prepared as described above is subjected to hydrothermal treatment. The hydrothermal treatment is characterized in that, for example, an aqueous solution is heat-treated under a temperature range of 150 ° C. or higher and 240 ° C. or lower and a pressure condition of more than 1 atm. Such hydrothermal treatment may be carried out by using, for example, an apparatus capable of forming a high temperature and high pressure environment such as an autoclave.

The reaction temperature is preferably 150 ° C. or higher, more preferably 160 ° C. or higher, and particularly preferably 170 ° C. or higher, from the viewpoint of efficiently promoting the decomposition of the coating portion. On the other hand, if the reaction temperature is too high, the entire polyvinyl-based polymer compound constituting the coating portion is decomposed, which makes precise decomposition and removal difficult, which is not preferable. From this point of view, the upper limit temperature of hydrothermal synthesis is preferably 240 ° C. or lower, more preferably 235 ° C. or lower.

Further, it is important that the pressure at the time of reaction is set to a pressure condition higher than the atmospheric pressure (typically, it exceeds 1 atm, preferably 2 atm or more). Such a reaction environment can be realized by heating in an environment where the pressure can be adjusted, for example, by putting the above-mentioned raw material mixture in a closed container. The upper limit of the pressure during the reaction is not strictly defined, but can be, for example, about 45 atm or less, preferably about 35 atm or less, for example, about 4 to 30 atm. For example, it can be used as a rough guide to store the raw material mixture in a closed container at about 1/3 of the volume and heat it.

The time of the hydrothermal treatment is not particularly limited, and can be appropriately controlled according to the amount of the coating portion in the nanoparticles and the like. In general, the longer the hydrothermal treatment time, the larger the decomposition amount of the coating portion, and the shorter the hydroheat treatment time, the smaller the decomposition amount of the coating portion. The approximate time of the hydrothermal treatment can be, for example, 30 minutes or more, more preferably 1 hour or more, and for example, 2 hours or more. However, since it is more preferable to control the amount of the coating portion in the nanoparticles to some extent when preparing the nanoparticles, the hydrothermal treatment time is, for example, 12 hours or less, preferably 6 hours or less, for example, 3 hours. It is preferable to suppress it to the following. As a result, the coating portion of the nanoparticles can be appropriately decomposed and removed.

As described above, the decomposition of the coating part in the nanoparticles shows that the ratio of the coating part is 6% by mass or more and 10% by mass or less, and in the spectrum obtained by FTIR analysis, the absorption peak near the wave number of 1450 cm ^-1. It can be carried out with the intensity ratio (I ₁₄₅₀ / I ₁₅₅₀ ) of the intensity I ₁₄₅₀ and the intensity I ₁₅₅₀ of the absorption peak near ₁₅₅₀ cm ^-1 as a guide.

<S70; Recovery process>
Next, the solvent is removed from the above reaction solution, and barium titanate fine particles in which at least a part of the coating portion is decomposed are recovered. The recovery method is not particularly limited, but as described above, for example, the nanoparticles are precipitated by a centrifuge to remove the supernatant liquid (solvent), or separated from the solvent by filtration, and then washed and dried. Good. At this time, it is preferable to use a solvent of the same type as the solvent used for cleaning. Examples of the drying method include hot air drying device, low humidity air drying device, vacuum drying device, various infrared drying devices, electromagnetic induction drying device, microwave drying device, dry air and the like, and drying promoting means such as blowing air, decompression and heating. Can be used alone or in combination. The drying conditions (for example, the drying method and the required time) can be appropriately determined depending on the type of solvent and the amount of solvent. As a result, unreacted raw materials, side reaction products and the like can be suitably removed, and high-purity barium titanate fine particles can be obtained. Further, it is possible to obtain barium titanate fine particles having an average particle diameter of 20 nm or more and 250 nm or less based on the dynamic light scattering method and having excellent redispersibility.

The powder (fine particle group) of the barium titanate fine particles thus obtained has at least an organic substance derived from the decomposition product of the polyvinyl-based polymer compound on the surface of the barium titanate core particles. Therefore, for example, even when stored in a powder state, aggregation is unlikely to occur. Further, although the details are not clear, at least a part of the polyvinyl polymer compound is decomposed, and the amount and form thereof are controlled. Therefore, when this powder is dispersed in the dispersion medium again, the dispersion medium Among them, barium titanate fine particles have a special effect of being dispersed with extremely good dispersibility. This can be a new finding that has never been known.

As can be seen from the above, the barium titanate fine particles disclosed herein are provided as having excellent dispersibility in a dispersion medium even after being once powdered. Therefore, the technique disclosed herein also provides a dispersion obtained by dispersing the barium titanate fine particles in a dispersion medium. The dispersion medium in such a dispersion is not particularly limited. For example, ion-exchanged water, distilled water, water such as pure water, ethanol, 2-propanol, 1-methoxy-2-propanol, terpineol, ethylene glycol, diethylene glycol, toluene, xylene, mineral spirit, butyl cellosolve acetate, butyl carbitol acetate. , Butyl carbitol and the like may be an organic solvent.

Binders and various additives (for example, surfactants, defoamers, plasticizers, thickeners, antioxidants, dispersants, polymerization inhibitors, etc.) are appropriately added to the dispersion as needed. can do. As the binder, a binder that can be evaporated and removed (degreased) by a binder removal treatment (typically, a heat treatment at 20 ° C. to 500 ° C. in an oxidizing atmosphere) at the time of manufacturing the target dielectric device is preferably used. Can be done. Specifically, for example, ethyl cellulose, hydroxyethyl cellulose, polybutyl methacrylate, polymethyl methacrylate, polyethyl methacrylate, polyvinyl alcohol, polyvinyl bratil and the like can be used.
The proportion of the nanoparticles in the entire paste-like composition is not particularly limited, but may be, for example, 30% by mass to 70% by mass (preferably 40% by mass to 60% by mass).

As described above, this dispersion can be provided, for example, as having a CV value of 50% or less in the particle size distribution of the dispersoid barium titanate fine particles based on the DLC method. Therefore, it can be a dispersion in which fine barium titanate fine particles on the order of nanometers are highly dispersed. Therefore, by using such a dispersion, for example, a thinner and more homogeneous dielectric layer made of barium titanate can be stably formed. Therefore, this dispersion can be suitably used for manufacturing, for example, a multilayer ceramic capacitor as shown in FIG.

FIG. 6 is a cross-sectional view schematically showing the multilayer ceramic capacitor 1. The multilayer ceramic capacitor 1 is an electronic component in which a dielectric layer (ceramic layer) 12 formed by using the barium titanate fine particles and an internal electrode layer 22 formed on the dielectric layer 12 are alternately laminated. It includes a main body 10 and an external electrode 20 provided on the outside of the electronic component main body 10. The monolithic ceramic capacitor 1 can be typically manufactured by the following procedure. That is, first, a dispersion containing barium titanate fine particles is supplied in the form of a carrier sheet (which may be coating, molding, etc.) to form a green sheet made of a dielectric material. Then, an electrode paste for forming an internal electrode is supplied (including printing and transfer) on the green sheet in a predetermined electrode pattern. A plurality of such green sheets with an electrode pattern (for example, 100 or more) are produced, and these are laminated and crimped to produce unfired laminated chips. Next, the laminated chips are dried and fired under predetermined heating conditions (maximum firing temperature is approximately 1000 ° C. to 1400 ° C.) for a predetermined time (for example, about 10 minutes to 2 hours for maintaining the maximum firing temperature). .. As a result, the green sheet is fired to form the dielectric layer 12, and the electrode paste is fired to form the internal electrode layer 22. Then, the electronic component main body 10 of the multilayer ceramic capacitor 1 in which the internal electrode layer 22 is sandwiched between the plurality of dielectric layers 12 is manufactured. After that, the external electrode 20 is formed by applying a paste-like composition for forming an external electrode to a desired portion of the electronic component main body 10 and firing the composition. In this way, the monolithic ceramic capacitor 1 can be manufactured. Since the process for constructing the multilayer ceramic capacitor 1 described above does not particularly characterize the present invention, detailed description thereof is omitted.

Here, the barium titanate fine particles (and core particles) used for forming the dielectric layer 12 are fine on the nanometer order and have preferable properties as a high-dielectric material. Further, the dispersibility of the barium titanate fine particles in the dispersion (which may be a slurry) in which the barium titanate fine particles are dispersed in the dispersion medium can be extremely good. Therefore, the green sheet made of a dielectric material and the dielectric layer 12 which is a fired product thereof can be produced as a thin, dense and homogeneous material. As a result, it is possible to reduce the thickness of the dielectric layer 12 and, by extension, reduce the size and quality of the multilayer ceramic capacitor 1.

Examples of the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

(Comparative Example 1)
First, titanium chloride (TiCl ₄ ) as a Ti source and barium chloride (BaCl ₂ ) as a Ba source were weighed so as to have a molar ratio of Ti element: Ba element = 1: 2. In addition, polyvinylpyrrolidone (PVP) was weighed so as to have a mass ratio of 2.1 times that of barium titanate (BaTIO ₃ ) theoretically obtained from the Ti source and the Ba source. Then, these titanium chloride, barium chloride and PVP were added to water as a solvent and stirred to prepare a raw material solution (S10). Next, an alkaline aqueous solution was added to this raw material solution to adjust the pH of the raw material solution to 10 to 14 alkaline. Then, this raw material solution was placed in a reflux device and refluxed at a reflux temperature of 80 ° C. for about 1 hour to precipitate a precursor (S20). The mixed solution thus obtained was cooled to room temperature (25 ° C.) (S30), the precursor was filtered and recovered, washed with ion-exchanged water, and then vacuum dried at 65 ° C. Powdery nanoparticles were obtained. These nanoparticles were used as a sample of Comparative Example 1.

(Examples 1 and 2, Comparative Examples 2 and 3)
Next, the nanoparticles obtained above (sample of Comparative Example 1) were added to the dispersion medium shown in Table 1 below to prepare a liquid sample, and then the liquid sample was placed in an autoclave reaction vessel and placed in an autoclave. Barium titanate fine particles were obtained by autoclaving under the treatment conditions shown in Table 1. The obtained barium titanate fine particles were collected by filtration, washed with ion-exchanged water, and vacuum dried at 65 ° C. to form a powder to prepare samples for each example. The mixing ratio of water and ethanol in Example 1 was 50:50 as water: ethanol in terms of volume ratio.

(Comparative Example 4)
In Comparative Example 1, the Ti source and the Ba source were set to have a molar ratio of Ti element: Ba element = 1: 1, and PVP was set to have a mass ratio of 8.6 times that of barium titanate. In the same manner as in Comparative Example 1, powdery nanoparticles were obtained. These nanoparticles were used as a sample of Comparative Example 4.

(Example 3)
Next, the nanoparticles (sample of Comparative Example 4) are added to the dispersion medium shown in Table 1 below to prepare a liquid sample, and then the liquid sample is placed in a reaction vessel for autoclave and shown in Table 1 by autoclave. Barium titanate fine particles were obtained by autoclaving under the treatment conditions. The obtained barium titanate fine particles were collected by filtration, washed with ion-exchanged water, and vacuum dried at 65 ° C. to form a powder to prepare a sample of Example 3.

(Comparative Example 5)
Commercially available barium titanate fine particles (manufactured by Sigma-Aldrich, barium titanate (IV), particle size; <100 nm (BET)) were prepared and used as a sample of Comparative Example 5. The barium titanate fine particles do not have a coating with an organic substance.

[Average particle size by SEM]
The obtained samples of each example were observed with a scanning electron microscope (JSM-6490LA manufactured by JEOL Ltd.), and the average particle diameter was calculated from the arithmetic mean of the equivalent circle diameters measured for 100 or more particles. Calculated. The results are shown in the "SEM" column of "Average particle size" in Table 1.

[Average particle size by DLS]
The average particle size of each of the obtained samples was measured by a dynamic light scattering method (DLS method). That is, the average particle size of the barium titanate fine particles was determined in the state of a dispersion in which the powder of the barium titanate fine particles was dispersed in distilled water. The particle size distribution was measured using a dynamic light scattering photometer (DLS7000 manufactured by Otsuka Electronics Co., Ltd.), and the average particle size was calculated by the cumulant analysis method. In the measurement, the viscosity of the dispersion at 23 ° C. was measured with a rheometer, and this value was used as the viscosity of the solvent. The measurement was performed for each sample in each of 5 batches (5 times), and the average value is shown in the column of "Average particle size (DLS)" in Table 1. As the viscosity and refractive index of water as a dispersion medium, viscosity: 0.8902 and refractive index: 1.3313 were used.

[FTIR measurement]
The obtained barium titanate fine particles were subjected to FTIR measurement to estimate the structure (qualitative analysis) of the organic matter adhering to the surface. The measurement was carried out by a Fourier transform near-infrared spectroscopic analyzer (Frontier IR, manufactured by PerkinElmer) by the ATR method in the range of wave numbers 4000 to 2500 cm- ¹ and 2000 to 1000 cm- ¹ . The measurement resolution in FTIR measurement was 4 cm ^-1 , the scan speed was 0.2 cm ^-1 / S, and the number of integrations was 4.
3 and 4 show measurement spectra for each example sample and PVP (single substance). Spectrum of 1450 cm ^-1 vicinity of FTIR spectra derived from -CH ₃ group, the spectrum of 1550 cm ^-1 vicinity derived from NH bond, spectrum of 1650 cm ^-1 vicinity from C = O bonds. The intensity I ₁₄₅₀ of the absorption peak of 1450 cm ^-1 vicinity of each spectrum, calculated peak intensity ratio of the intensity I ₁₆₅₀ of the absorption peak of 1650 cm ^-1 vicinity of (I ₁₄₅₀ / I _1650), "FTIR peak ratio of Table 1 It is shown in the column of "I ₁₄₅₀ / I ₁₆₅₀ ". Further, the intensity I ₁₄₅₀ of the absorption peak of 1450 cm ^-1 vicinity of each spectrum, calculated peak intensity ratio of the intensity I ₁₅₅₀ of the absorption peak of 1550 cm ^-1 vicinity of (I ₁₄₅₀ / I _1550), Table 1, "FTIR It is shown in the column of "Peak ratio I ₁₄₅₀ / I ₁₅₅₀ ". In the calculation of the peak intensity ratio, the peak intensity of both wave numbers was set to the height from the baseline connecting the measurement points of 1800 cm ^{- 1} and 1100 cm- ¹ .

[Measurement of organic matter]
The amount of organic matter adhering to the surface of the barium titanate fine particles was measured by performing thermogravimetric analysis on the samples of each example. For the measurement, a differential thermal balance (manufactured by Rigaku Co., Ltd., TG-DTA) was used, and the measurement was performed in the range from room temperature (25 ° C.) to 800 ° C. The obtained weight loss rate is shown in the "Weight loss amount" column of Table 1. For reference, TG curves for Example 1, Comparative Examples 1, 3, and 5 are shown in FIG.

[Evaluation]
First, from the FTIR-ATR spectrum of 4000 to 2500 cm ^-1 in FIGS. 4 (a) and 4 (b), the spectra of other examples excluding Comparative Example 5 consisting only of barium titanate include polyvinyl-based polymer compounds (here, in this case). An absorption spectrum derived from the chemical structure of PVP) was observed, and it was confirmed that the surface of the core particles made of barium titanate was provided with a coating portion of a polyvinyl polymer compound.

The sample of Comparative Example 1 is nanoparticles prepared by a heating / reflux method, and is barium titanate fine particles whose surface is covered with a PVP coating portion. In the sample of Comparative Example 1, it was confirmed that the average particle size by SEM was as small as 65 nm, and barium titanate fine particles having the same particle size were obtained. In SEM observation, it was confirmed that the surface of the core particles made of barium titanate was covered with PVP. Furthermore, it was also confirmed that a plurality of barium titanate fine particles were bonded and crosslinked by PVP to form secondary particles. The thermogravimetric reduction rate of the sample of Comparative Example 1 was 12%, and it was confirmed that a relatively large amount of PVP covered the surface of the core particles. Since I ₁₄₅₀ / I ₁₆₅₀ and I ₁₄₅₀ / I ₁₅₅₀ of the sample of Comparative Example 1 are both relatively small at 1.51 and 4.55, they are derived from the C = O bond characteristic of PVP near 1650 cm ^-1. is relatively large peaks, C = a O bond peaks of 1450 cm ^-1 vicinity from CH ₃ group which is formed by the decomposition of, it can be seen that the peak of 1550 cm ^-1 vicinity derived from NH bond is relatively small .. That is, in the sample of Comparative Example 1, it was confirmed that PVP remained on the surface of the core particles without being substantially decomposed. It was confirmed that the average particle size of the sample of Comparative Example 1 by DLS was coarsened to 260 nm, some particles formed agglomerates in the dispersion medium, and there was room for improvement in redispersibility. ..

On the other hand, Example 1 is an example in which the sample of Comparative Example 1 was hydrothermally treated to obtain barium titanate fine particles. The hydrothermal treatment of Example 1 was carried out in a dispersion medium consisting of a mixed solution of water and alcohol. FTIR spectra of the samples of Example 1, 1650 cm ^-1 peak in the vicinity is greatly reduced, strong peak of 1550 cm ^-1 vicinity derived from the peak and NH bonds of 1450 cm ^-1 vicinity from CH ₃ group is instead As a result, the values of I ₁₄₅₀ / I ₁₆₅₀ and I ₁₄₅₀ / I ₁₅₅₀ were both increased to 2.92 (about 1.9 times) and 9.60 (about 2.1 times) as compared with Comparative Example 1. I found out that It was also confirmed that the thermogravimetric reduction rate was 8%, and the amount of PVP in the covering portion was reduced as compared with Comparative Example 1. From these results, it can be seen that in the sample of Example 1, a part of PVP of the coating portion was decomposed by hydrothermal treatment, and a decomposition product of PVP was present. Then, it was found that the average particle size of the sample of Example 1 by DLS was relatively small at 210 nm, and the redispersibility of the barium titanate fine particles was improved as compared with Comparative Example 1. For this reason, in the barium titanate fine particles disclosed herein, excess PVP may be removed by decomposing and removing a part of the PVP coating portion provided on the surface of the core particles made of barium titanate. It was confirmed that the coating unevenness was eliminated and good redispersibility was exhibited.

Example 2 is an example in which the dispersion medium in the hydrothermal treatment is only water. In Example 2, I ₁₄₅₀ / I ₁₆₅₀ is larger, I ₁₄₅₀ / I ₁₅₅₀ is smaller, and the amount of thermogravimetric reduction is slightly increased to 9% as compared with Example 1. That is, it can be seen that the decomposition of PVP in the coating portion by hydrothermal treatment is progressing mildly as compared with Example 1. However, as compared with Comparative Example 1, I ₁₄₅₀ / I ₁₆₅₀ was 3.35, which was about 2.2 times, and I ₁₄₅₀ / I ₁₅₅₀ was 8.08, which was about 1.8 times, and the decomposition of PVP proceeded sufficiently. It can be confirmed that As a result, it was found that the average particle size of the barium titanate fine particles of Example 2 by DLS was slightly increased to 250 nm, and although the redispersibility of the barium titanate fine particles was good, it was slightly lower than that of Example 1. .. From this, it was found that the decomposition state of the PVP coating portion of the barium titanate fine particles disclosed herein is changed depending on the dispersion medium used for the hydrothermal treatment. The dispersion medium may contain water, but it has been found that the decomposition of PVP can be promoted by containing alcohol together with water as in Example 1.

Comparative Example 2 is an example in which the dispersion medium in the hydrothermal treatment is only alcohol. In Comparative Example 2, compared with Example 1, I ₁₄₅₀ / I ₁₆₅₀ , I ₁₄₅₀ / I _1550, and the amount of thermogravimetric reduction were almost the same as in Comparative Example 1, and even if hydrothermal treatment was performed, the PVP of the covering portion was decomposed. Was found to have hardly progressed. Compared with Comparative Example 1, I ₁₄₅₀ / I ₁₆₅₀ was 1.52, which was about 1.0 times, and I ₁₄₅₀ / I ₁₅₅₀ was 4.10, which was about 0.9 times, indicating that the decomposition of PVP was not so advanced. Was confirmed. As a result, it was confirmed that the average particle size of the barium titanate fine particles of Comparative Example 2 by DLS was greatly increased to 390 nm, the barium titanate fine particles formed large agglomerates, and the redispersibility was lower than that of Comparative Example 1. It was. The reason why the redispersibility deteriorates due to the hydrothermal treatment is not clear, but it is expected that the PVP of the coating portion is not decomposed by the hydrothermal treatment using only alcohol as the dispersion medium, but the unevenness of the coating portion is increased. To. From this, it was confirmed that the dispersion medium in the hydrothermal treatment needs to contain water, and that the redispersibility of the barium titanate fine particles is improved by appropriately performing the hydrothermal treatment.

In Comparative Example 3, the hydroheat treatment time was extended to 24 hours as compared with Example 1. In the sample of Comparative Example 3, I ₁₄₅₀ / I ₁₆₅₀ and I ₁₄₅₀ / I ₁₅₅₀ were significantly larger than those of Example 1, and the amount of thermogravimetric loss was reduced to 5%. Compared with Comparative Example 1, it was confirmed that I ₁₄₅₀ / I ₁₆₅₀ was 14.98, which was about 9.9 times larger, and I ₁₄₅₀ / I ₁₅₅₀ was 11.30, which was about 2.5 times larger. That is, in Comparative Example 3, it can be seen that the decomposition of PVP in the coating portion by hydrothermal treatment is progressing more significantly than in Example 1. As a result, the average particle size of the barium titanate fine particles of Comparative Example 3 by DLS became unmeasurable due to the severe aggregation of the barium titanate fine particles. From this, it was found that the barium titanate fine particles disclosed herein are not preferable because even if the PVP is excessively decomposed and removed by hydrothermal treatment, the redispersibility is rather lowered. It was also confirmed that the degree of decomposition of PVP by hydrothermal treatment can be adjusted by the hydrothermal treatment time.

Comparative Example 4 is nanoparticles produced by heating and refluxing in the same manner as in Comparative Example 1, and the SEM average particle diameter is as large as 109 nm due to the difference in formulation. However, in this Comparative Example 4, the amount of thermogravimetric reduction was substantially the same as that of Comparative Example 1, but the results were that I ₁₄₅₀ / I ₁₆₅₀ and I ₁₄₅₀ / I ₁₅₅₀ were slightly reduced. That is, it is understood that the PVP coating is slightly less. The average particle size of the barium titanate fine particles of Comparative Example 4 by DLS is 216 nm, which is smaller than that of Comparative Example 1, but it cannot be said that it is sufficiently reduced. From this, it was confirmed that although the coating amount of PVP and its morphology slightly changed depending on the conditions at the time of reflux, it was not sufficient to make the redispersibility suitable.

Example 3 is an example in which only distilled water is used as the dispersion medium during the hydrothermal treatment in Comparative Example 4. That is, it is an example in which the SEM average particle size is as large as 109 nm as compared with Example 2 and hydrothermal treatment is performed with a material having good dispersibility. In this Example 3, there is no significant difference in I ₁₄₅₀ / I ₁₆₅₀ and I ₁₄₅₀ / I ₁₅₅₀ and the amount of thermogravimetric reduction as compared with Example 2. Compared with Comparative Example 4, I ₁₄₅₀ / I ₁₆₅₀ was 3.40, which was about 2.6 times, and I ₁₄₅₀ / I ₁₅₅₀ was 8.10, which was about 1.8 times, and the decomposition of PVP proceeded sufficiently. It can be confirmed that there is. It was found that the average particle size of the barium titanate fine particles of Example 3 by DLS was as small as 200 nm, and the redispersibility of the barium titanate fine particles was further improved as compared with Comparative Example 4. For this reason, in the barium titanate fine particles disclosed herein, excess PVP may be removed by decomposing and removing a part of the PVP coating portion provided on the surface of the core particles made of barium titanate. It was confirmed that the coating unevenness was eliminated and good redispersibility was exhibited.

Comparative Example 5 is a commercially available barium titanate fine particles, and although the SEM average particle diameter is 100 nm, which is close to that of Comparative Example 4, the surface treatment with an organic substance such as PVP has not been performed. As a result, the redispersibility in water was extremely poor, and the barium titanate fine particles were violently aggregated, making it impossible to measure the average particle size by DLS. From this, it can be seen that in order to redisperse the nanometer-sized barium titanate fine particles into the dispersion medium, it is necessary to perform some surface treatment on the barium titanate fine particles.

Therefore, when the FTIR-ATR spectra related to the barium titanate fine particles of each example were reconfirmed, as shown in FIG. 3, from the comparison of the spectra of Comparative Examples 1, 2, 4 and PVP, these were in the vicinity of 1650 cm ^-1 . It can be seen that the peak derived from the C = O bond characteristic of PVP is large. On the other hand, in Examples 1 to 3, the peak near 1650 cm ^-1 is low, and it can be confirmed that this peak is hardly observed in Comparative Examples 3 and 5. On the other hand, the peak near 1450 cm ^-1 derived from ₃ CH groups is larger in Examples 1 to 3 than in Comparative Examples 1, 2, 4 and PVP. Comparative Example 3, although it clearly confirmed the peak of 1450 cm ^-1 vicinity, it was found that the peak of 1650 cm ^-1 vicinity can not be confirmed substantially. These are consistent with the degree of decomposition of PVP, and it can be seen that the degree of decomposition of organic matter on the surface of the core particles can be well confirmed by these peaks. From the above, the barium titanate fine particles disclosed herein have a decomposition product obtained by decomposing PVP on the surface of the core particles made of barium titanate, and a coating derived from PVP. It was confirmed that good redispersibility can be provided by appropriately controlling the amount and state of the parts.

Although the present invention has been described above in terms of preferred embodiments, such a description is not a limitation, and of course, various modifications can be made.

Claims (6)

A core particle mainly composed of barium titanate and a coating portion containing a polyvinyl-based polymer compound provided on at least a part of the surface of the core particle are provided.
The proportion of the covering portion is 6% by mass or more and 10% by mass or less.
The average particle size based on the dynamic light scattering method is 20 nm or more and 250 nm or less.
In the spectrum obtained by FTIR analysis, greater than the wave number 1450 cm ^-1 intensity I ₁₄₅₀ of the absorption peak in the vicinity of, the wave number 1550 cm ^-1 absorption peak of the intensity I ₁₅₅₀ of the proximity, the intensity ratio of (I ₁₄₅₀ / I ₁₅₅₀₎ is 8 ,
Barium titanate fine particles. The barium titanate fine particles according to claim 1, wherein the coating portion contains a decomposition product derived from polyvinylpyrrolidone. In the spectrum obtained by FTIR analysis, the wavenumber 1450 cm ^-1 absorption peak of the intensity I ₁₄₅₀ of the vicinity, the wave number 1650 cm ^-1 intensity I ₁₆₅₀ of the absorption peak in the vicinity, the intensity ratio of (I ₁₄₅₀ / I ₁₆₅₀₎ is 2 to 7 The barium titanate fine particles according to claim 1 or 2, which are as follows. The barium titanate fine particles according to any one of claims 1 to 3, wherein the average particle size based on electron microscope observation is 10 nm or more and 200 nm or less. A barium titanate fine particle dispersion in which the barium titanate fine particles according to any one of claims 1 to 4 are dispersed in a dispersion medium. The method for producing barium titanate fine particles according to any one of claims 1 to 4.
To prepare nanoparticles comprising the core particles mainly composed of barium titanate and an organic film containing a polyvinyl-based polymer compound provided on at least a part of the surface of the core particles.
By subjecting the nanoparticles to hydrothermal treatment, the amount of the organic film is reduced to obtain the barium titanate fine particles.
A method for producing barium titanate fine particles, including.

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