JP2015151558A - Nickel fine particle slurry, metal fine particle and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for improving sintering resistance by increasing a crystallite diameter of metal fine particles, while suppressing aggregation or fusion of particles and carbonization of metal.SOLUTION: A nickel fine particle slurry contains: (A) nickel fine particles that have an average particle size (L) by a scanning electron microscope observation in the range of 20 to 200 nm, a coefficient of variation of particle size (standard deviation/average particle size) of 0.2 or less, a crystallite diameter (L) calculated by a Scherrer method of 15 nm or more, and a ratio of the crystallite diameter to the average particle size (L/L) of 0.15 or more; (B) a dispersant; and (C) a solvent having a boiling point of 100°C or more. A method for producing metal fine particles having a crystallite diameter, which is 1.3 times or more of a crystallite diameter before heating, includes: preparing raw material metal fine particles having an average particle size in the range of 20 to 200 nm; and heating the raw material metal fine particles by irradiating the raw material metal fine particles in a dispersed state in a liquid phase with laser beams.

Description

  The present invention relates to a nickel fine particle slurry, metal fine particles, and a method for producing the same, which can be suitably used as a material such as a conductive paste for forming an internal electrode of a multilayer ceramic capacitor (MLCC), for example.

  The MLCC is obtained by alternately laminating and pressing ceramic dielectrics and internal electrodes and then sintering and integrating them. The metal fine particles for internal electrodes used in MLCC are in the direction of miniaturization in order to reduce the size and increase the capacity of MLCC. Therefore, it is desired to use metal fine particles having a sharp particle size distribution with no coarse particles and a particle size of 200 nm or less. However, the metal fine particles have a high surface energy by being miniaturized, tend to be easily melted at a low temperature, and the sintering resistance is lowered. For example, when nickel fine particles are used as the internal electrode material, the sintering temperature of nickel fine particles is as low as several hundred degrees Celsius compared to the sintering temperature of ceramic dielectrics exceeding 1,000 ° C. The behavior such as volume change due to expansion / contraction is different, which may cause delamination or cracks.

  The nickel fine particles can be produced by a vapor phase method such as a thermal CVD (chemical vapor deposition) method or a plasma CVD method. However, in the vapor phase method, a technique for classifying fine metal particles having different particle diameters and an average particle diameter of 100 nm or less is not completed. Further, the accuracy of classification is not satisfactory, and coarse particles exceeding 200 nm cannot be completely removed. Therefore, defects due to short-circuit between electrode layers due to coarse particles are a problem.

  On the other hand, the metal fine particles synthesized by the liquid phase method have a narrower particle size distribution than those synthesized by the gas phase method, and thus are suitable for the use of the internal electrode material. However, since the liquid phase method has a lower thermal history than the gas phase method, the crystallite diameter is smaller than that of the gas phase method and tends to be sintered at a lower temperature. There is a concern that such behavior leads to delamination between the dielectric layer and the internal electrode layer in the MLCC manufacturing process, and may cause a product defect. Therefore, for metal fine particles synthesized by the liquid phase method, improvement in sinterability at low temperatures is desired.

  As one method for improving the sintering resistance of metal fine particles (particularly nickel fine particles), heat treatment (annealing, annealing) may be performed to increase the crystallite diameter. However, when heat treatment is performed at a high temperature in an organic solvent, the problem arises that the metal fine particles cause aggregation or fusion depending on the surface state of the metal fine particles, and the organic solvent is decomposed due to the catalytic action of the metal fine particles themselves. There is a problem that the carbon content of the solid solution dissolves in the metal fine particles and carbonizes, and the crystal structure of the metal fine particles changes from fcc to hcp. Therefore, the present inventors, as a method of increasing the crystallite diameter of the metal fine particles, in the aromatic nonpolar organic solvent having a boiling point of 200 ° C. or higher, the raw material metal fine particles in the range of an average particle diameter of 20 to 120 nm, A method of heating at a temperature in the range of 200 ° C. to 320 ° C. has been proposed (Patent Document 1). According to this method, the crystallite diameter of the metal fine particles can be increased by 3 to 300% compared to the raw metal fine particles before the heat treatment.

Moreover, the present inventors satisfy the relationship of the average particle diameter (L ₁ ), crystallite diameter (L ₂ ), and oxygen content (Mo) of the nickel fine particles of Mo × L ₁ / L ₂ ≦ 9. In this case, the inventors have found that the sintering resistance is improved, and filed a patent application first (Japanese Patent Application No. 2013-061308). Furthermore, the inventors set the ratio of the carbon element content (Mc) to the oxygen content (Mo) in the nickel fine particles (Mc / Mo) within the range of 0.1 to 0.8, thereby preventing the sintering. The patent application has been filed first (Japanese Patent Application No. 2013-048851).

JP2013-87308A (Claims etc.)

  An object of the present invention is to improve the sintering resistance by increasing the crystallite size of the metal fine particles while suppressing the aggregation, fusion and metal carbonization of the particles.

The nickel fine particle slurry of the present invention comprises the following components (A) to (C);
(A) Crystal calculated by the Scherrer method with an average particle diameter (L ₁ ) in the range of 20 to 200 nm observed with a scanning electron microscope, a coefficient of variation (standard deviation / average particle diameter) of 0.2 or less. Nickel fine particles having a child diameter (L ₂ ) of 15 nm or more and a ratio of the crystallite diameter to the average particle diameter (L ₂ / L ₁ ) of 0.15 or more,
(B) a dispersant, and (C) a solvent having a boiling point of 100 ° C. or higher,
Containing.

  In the nickel fine particle slurry of the present invention, the B component may be an anionic surfactant, and the C component may be water.

  In the nickel fine particle slurry of the present invention, the B component may be a non-aqueous polymer dispersant having a secondary or tertiary amino group, and the C component is an organic solvent having a boiling point of 100 ° C. or higher. Also good.

In the nickel fine particle slurry of the present invention, the oxygen content (Mo) of the nickel fine particles may be within a range of 0.3 to 3.0% by mass, and the Mo, L ₁ and L ₂ are Mo × L. The relationship of ₁ / L ₂ ≦ 9 may be satisfied.

  The nickel fine particle slurry of the present invention may have a carbon element content of the nickel fine particles in a range of 0.3 to 2.5% by mass, and the carbon element content relative to the oxygen content (Mo) in the nickel fine particles. The ratio (Mc / Mo) of the amount (Mc) may be in the range of 0.1 to 0.8.

The method for producing metal fine particles of the present invention includes a first step of preparing raw metal fine particles having an average particle diameter in the range of 20 to 200 nm by observation with a scanning electron microscope,
The raw metal fine particles are heated by irradiating laser light in a state dispersed in the liquid phase, and the crystallite diameter calculated by the Scherrer method is 1.3 of the crystallite diameter of the raw metal fine particles before heating. A second step of producing metal fine particles that are twice or more,
May be provided.

  In the method for producing metal fine particles of the present invention, the coefficient of variation (standard deviation / average particle size) of the particle diameter of the raw metal fine particles may be 0.2 or less.

  In the method for producing fine metal particles of the present invention, the average particle size of the fine metal particles after the second step may be less than 1.1 times the average particle size of the raw metal fine particles.

  In the method for producing metal fine particles of the present invention, the wavelength of the laser beam may be in the range of 200 to 800 nm.

  In the method for producing metal fine particles of the present invention, the laser beam irradiation may be pulsed irradiation.

  In the method for producing fine metal particles of the present invention, the liquid phase may be water or an organic solvent having a boiling point of 100 ° C. or higher. In this case, the liquid phase in the second step may be water and an anionic surfactant may be blended as a dispersing agent, or the liquid phase in the second step may be an organic solvent having a boiling point of 100 ° C. or higher. Further, a non-aqueous polymer dispersant having a secondary or tertiary amino group may be blended as a dispersant.

  In the method for producing fine metal particles of the present invention, the raw metal fine particles may be obtained by a wet reduction method.

  In the method for producing fine metal particles of the present invention, the raw metal fine particles may be raw nickel fine particles.

In the method for producing fine metal particles of the present invention, the raw material nickel fine particles are prepared in the following steps A and B;
A) Complexation reaction liquid production | generation process which heats the mixture containing nickel carboxylate and primary amine to the temperature within the range of 100 to 165 degreeC, and obtains a complexation reaction liquid,
as well as,
B) A raw material for heating the complexing reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexing reaction liquid to obtain a slurry of raw material nickel fine particles coated with a primary amine Nickel fine particle slurry generation process,
It may be prepared by performing a process including:

  The metal fine particles of the present invention are produced by any one of the above methods.

The nickel fine particle slurry of the present invention is in a state where the nickel fine particles of the component (A) are uniformly dispersed in the solvent of the component (C) by the dispersant of the component (B). As a material, it can be used suitably. Particularly, the nickel fine particles of the component (A) have an average particle diameter (L ₁ ) in the range of 20 to 200 nm, a CV value of 0.2 or less, and a crystallite diameter (L ₂ ) of 15 nm or more. And the ratio of the average particle diameter (L ₂ / L ₁ ) is 0.15 or more, it is excellent in sintering resistance and can be preferably used, for example, as a material for internal electrodes of a multilayer ceramic capacitor.

  Moreover, according to the method for producing metal fine particles of the present invention, metal fine particles having a large crystallite and excellent sintering resistance can be produced by laser irradiation while preventing carbonization of the metal fine particles. That is, according to the method of the present invention, although the average particle diameter of the obtained metal fine particles is almost the same as before laser irradiation (less than 1.1 times), the crystal particles are crystallized compared to the raw metal fine particles before laser irradiation. Since the core diameter is 1.3 times larger, the sintering temperature is higher than that of the raw metal fine particles, and the sintering resistance is improved. Accordingly, the metal fine particles obtained by the method of the present invention can be suitably used, for example, as a material for an internal electrode of a multilayer ceramic capacitor.

It is a figure which shows the structure of a nickel complex, (a) shows a bidentate coordination, (b) shows a monodentate coordination, (c) shows the state which the carboxylate ion coordinated to the outer sphere, respectively. 2 is a drawing schematically illustrating changes in crystallite diameter of nickel fine particles due to heat treatment.

[Nickel fine particle slurry]
The nickel fine particle slurry of the present embodiment has the following components (A) to (C);
(A) Average particle diameter (L ₁ ) by scanning electron microscope observation is in the range of 20 to 200 nm, coefficient of variation of particle diameter (standard deviation / average particle diameter; CV value) is 0.2 or less, calculated by Scherrer method A fine nickel particle having a crystallite diameter (L ₂ ) of 15 nm or more and a ratio of crystallite diameter to average particle diameter (L ₂ / L ₁ ) of 0.15 or more,
(B) a dispersant,
And (C) a solvent having a boiling point of 100 ° C. or higher,
Containing.

(A) Component: Nickel fine particles In the present embodiment, the nickel fine particles contain a nickel element. The content of nickel element may be appropriately selected according to the purpose of use, but the amount of nickel element is preferably 90 parts by mass or more, more preferably 95 parts by mass or more with respect to 100 parts by mass of nickel fine particles. It is good. Examples of metals other than nickel include titanium, cobalt, copper, chromium, manganese, iron, aluminum, sodium, potassium, magnesium, zirconium, tin, tungsten, molybdenum, vanadium, barium, calcium, strontium, silicon, aluminum, and phosphorus. Base metals such as gold, silver, platinum, palladium, iridium, osmium, ruthenium, rhodium, rhenium, neodymium, niobium, holonium, dysprodium, yttrium and the like, and rare earth metals. These may be contained alone or in combination of two or more, may contain elements other than metal elements such as hydrogen, carbon, nitrogen, sulfur and boron, and may be alloys thereof. .

The nickel fine particles according to the present embodiment have an average particle diameter (L ₁ ) by scanning electron microscope observation in the range of 20 to 200 nm, preferably in the range of 40 to 150 nm. From another viewpoint, the average particle diameter (L ₁ ) by BET measurement is in the range of 20 to 200 nm, preferably in the range of 40 to 150 nm. If the average particle diameter (L ₁ ) of the nickel fine particles is below the above lower limit value, the nickel fine particles easily aggregate and melt by heating at the time of debinding, and it becomes easy to take in oxygen. Change will be greater. On the other hand, when the average particle diameter (L ₁ ) of the nickel fine particles exceeds the above upper limit value, the distribution width of the smallest and largest diameter particles becomes large, and when the nickel fine particles are used for an MLCC electrode, Prone to short-circuit failure due to the presence of.

  The nickel fine particles according to the present embodiment preferably have a CV value of 0.2 or less. By setting the CV value to 0.2 or less, it is easy to obtain the surface smoothness of the dried coating film after applying the paste.

The nickel fine particles according to the present embodiment have a crystallite diameter (L ₂ ) calculated by the Scherrer method of 15 nm or more. Since the crystallite diameter (L ₂ ) is preferably as large as possible, the upper limit is not limited, and may be the same as the particle diameter, for example. As for the nickel fine particles, the absolute value of the melting point greatly decreases as the average particle diameter (L ₁ ) decreases due to the melting point drop due to the quantum effect. Accordingly, the sintering temperature of the nickel fine particles becomes lower as the average particle diameter (L ₁ ) becomes smaller, but by increasing the ratio of the crystallite diameter (L ₂ ) to the average particle diameter (L ₁ ), the sintering temperature Can be high. Therefore, in the nickel fine particles according to the present embodiment, the ratio L ₂ / L ₁ of the crystallite diameter (L ₂ ) to the average particle diameter (L ₁ ) is 0.15 or more. When this ratio L ₂ / L ₁ is less than 0.15, the effect of increasing the sintering temperature cannot be sufficiently obtained.

Further, the nickel fine particles according to the present embodiment preferably contain an oxygen element. The content (Mo) of the oxygen element in the nickel fine particles is preferably in the range of 0.3 to 3.0% by mass, and more preferably in the range of 0.5 to 2.8% by mass. The oxygen element content (Mo) can be confirmed by elemental analysis of nickel fine particles. When the oxygen element content (Mo) is less than 0.3% by mass, the effect of suppressing the surface activity of the nickel fine particles tends to be small, and when it exceeds 3.0% by mass, the volume changes during sintering. Tends to occur and oxide diffusion tends to occur. The oxygen element is considered to be derived from the amount of oxygen contained in the oxide film on the surface of the nickel fine particles. This is, as the thickness of the oxide coating of nickel particles, whereas little significant difference regardless of the magnitude of the average particle diameter (L _1), the average particle size of the nickel particles (L ₁₎ is reduced, It is inferred from the tendency that the oxygen element content (Mo) tends to be high. That is, the smaller the average particle diameter (L ₁ ) of the nickel fine particles, the larger the total surface area (the total surface area of all the nickel fine particles), so that the oxygen element content (Mo) in the entire nickel fine particles is relatively This is thought to be due to growth.

The nickel fine particles according to the present embodiment have a content of oxygen element (Mo, unit: mass%) in consideration of the relative relationship between the content of oxygen element (Mo) and the average particle diameter (L ₁ ). The average particle diameter (L ₁ , unit; nm) and crystallite diameter (L ₂ , unit; mass%) preferably have a relationship of Mo × L ₁ / L ₂ ≦ 9 (unit: mass%), preferably 2 ≦ More preferably, Mo × L ₁ / L ₂ ≦ 9. By making it within such a range, the fusion of particles can be suppressed during sintering, and shrinkage at a low temperature can be prevented. When Mo × L ₁ / L ₂ is larger than 9, the sintering temperature becomes low, and excellent sintering resistance cannot be obtained. As described above, the nickel fine particles according to the present embodiment control the oxygen content (Mo) in consideration of the balance between the average particle diameter (L ₁ ) and the crystallite diameter (L ₂ ), so that at the time of debinding In addition to suppressing the oxidation of the nickel fine particles, the fusion of the particles is prevented, and the shrinkage at a low temperature is prevented.

  Moreover, the nickel fine particles of the present embodiment contain a carbon element. The carbon element content (Mc) of the nickel fine particles is preferably in the range of 0.3 to 2.5% by mass, more preferably in the range of 0.5 to 2.0% by mass with respect to the nickel fine particles. The carbon element content (Mc) can be confirmed by elemental analysis of nickel fine particles. The carbon element is derived from an organic compound present on the surface of the nickel fine particles, but a part of the carbon element may be present inside the nickel fine particles. The carbon element present on the surface of the nickel fine particles suppresses aggregation of the nickel fine particles, contributes to improvement in dispersibility, and promotes reduction of the oxygen element contained in the nickel fine particles. Therefore, when the carbon element content (Mc) is less than 0.3% by mass, the nickel fine particles are likely to be aggregated. However, if the carbon element content (Mc) exceeds 2.5% by mass, carbonization occurs during sintering to form residual charcoal, which causes gas expansion by gasification.

  The content ratio of carbon element to oxygen element in the nickel fine particles of the present embodiment (carbon element content (Mc) / oxygen element content (Mo); hereinafter, may be referred to as “Mc / Mo ratio”). Within the range of 0.1 to 0.8, more preferably within the range of 0.1 to 0.5, and most preferably within the range of 0.25 to 0.5. If the Mc / Mo ratio is less than 0.1, the nickel fine particles tend to aggregate during the reduction, and the nickel fine particles shrink during the oxygen reduction, resulting in a decrease in sintering resistance. On the other hand, when the Mc / Mo ratio exceeds 0.8, carbonization occurs at the time of sintering to form residual carbon, which causes gas expansion by gasifying.

Component (B): Dispersant The component B dispersant in the nickel fine particle slurry according to the present embodiment is not particularly limited as long as it can uniformly disperse the nickel fine particles. Preferred examples include an anionic surfactant. A non-aqueous polymer dispersant or the like can be used.

(Anionic surfactant)
As the anionic surfactant, for example, a surfactant having a carboxylic acid, sulfonic acid, sulfate ester, phosphoric acid, phosphate ester structure can be used. Specific examples thereof include ammonium polycarboxylate and polyacrylic acid. Sodium salt, polyacrylic acid, polyacrylate ester, copolymers thereof, ammonium dodecylbenzenesulfonate, sodium dialkyl succinatesulfonate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene alkyl ether sulfate A salt, polyoxyalkylene alkyl ether phosphate, etc. can be used. These anionic surfactants can be used alone or in combination of two or more.

  When the anionic surfactant is a polymer, the weight average molecular weight is preferably 5000 or more, more preferably 10,000 or more. If the weight average molecular weight is less than 5000, the dispersibility may decrease.

  Examples of the anionic surfactant include SN Dispersant 5468 (trade name: manufactured by Sannobuco), New Coal 1020-SN (trade name: manufactured by Nippon Emulsifier Co., Ltd., Zephrym 3300B, Crodafos N3A, KD-4, KD-9 (trade name). : Commercially available from Kuroda Japan Co., Ltd.).

  The compounding amount of the anionic surfactant is within the range of 0.01 to 3.0 parts by mass, preferably within the range of 0.1 to 2.0 parts by mass with respect to 100 parts by mass of the nickel fine particles of component (A). Good. If the amount of the anionic surfactant is less than the above lower limit, the dispersibility tends to decrease. Even if the amount exceeds the upper limit, an improvement in dispersibility according to the amount of addition cannot be expected. Since the organic matter contained in is excessive, debinding during firing may be insufficient, or nickel may be carbonized during sintering.

(Non-aqueous polymer dispersant)
The non-aqueous polymer dispersant is a polymer compound having a low polarity group having a high affinity with a low polarity solvent in the main skeleton, and further having a secondary or tertiary amino group as a functional group. Examples of such a polymer compound include those having a molecular skeleton such as polyamide, polyallylamine, polyester, polyurethane, and polyoxyalkylene, and among these, polyurethane, polyoxyethylene are particularly preferable. Those having a molecular skeleton of the system are preferred. The molecular structure is linear, linear or comb, or a comb having a trident branch point in which a linear side chain is bonded to a linear main chain, or a block copolymer or graft copolymer. Although it may be a coalescence, it has one or more secondary or tertiary amino groups in the molecule. These non-aqueous polymer dispersants can be used alone or in combination of two or more.

  Since the secondary or tertiary amino group of the non-aqueous polymer dispersant used in the present embodiment can undergo a substitution reaction with the primary amine immobilized on the surface of the nickel fine particles, It is considered that at least a part of the primary amine can be easily substituted to coat the nickel fine particles. Since this non-aqueous polymer dispersant has a strong aggregation suppressing action on the nickel fine particles, an excellent dispersion effect can be expected even in a small amount. On the other hand, when primary amine is not present on the surface of the nickel fine particles, even if a non-aqueous polymer dispersant is added, coating due to substitution with primary amine is unlikely to occur, and strong aggregation suppressing action and excellent dispersion effect are obtained. I can't get it. The tertiary amino group contained in the non-aqueous polymer dispersant may be present as a quaternary ammonium ion with an alkyl group bonded to a part thereof. These amino groups are preferably included in the linear main chain in a comb shape or at the end of the linear main chain, and the individual amino groups present in these amino groups are scattered on the surface of the nickel fine particles. Is considered to be fixed.

  This means the number of mg of KOH equivalent to the amount of HCl required to neutralize 1 g of the solid content (or active ingredient excluding the solvent) of the non-aqueous polymer dispersant used in the present embodiment, JIS The amine value (or base value) measured by the method of K7237 is preferably in the range of 10 to 100 mgKOH / g from the viewpoint of improving dispersibility. In addition, it means the number of mg of KOH required to neutralize 1 g of the solid content (or active ingredient excluding the solvent) of the non-aqueous polymer dispersant used in the present embodiment, which is measured by the method of JIS K0070. From the viewpoint of improving dispersibility, the acid value is preferably 60 mgKOH / g or less, more preferably 40 mgKOH / g or less.

  The weight average molecular weight of the non-aqueous polymer dispersant used in the present embodiment is preferably in the range of 1,000 to 200,000, more preferably in the range of 5,000 to 100,000. When the weight average molecular weight is less than the above lower limit, dispersion stability may not be sufficient with respect to a low-polarity solvent, and when it exceeds the above upper limit, the viscosity may be too high and handling may be difficult.

  Examples of commercially available non-aqueous polymer dispersants that can be suitably used include Solsperse 11200 (trade name), Solsperse 13940 (trade name), Solsperse 13240 (trade name), and Big Chemie Japan, manufactured by Japan Lubrizol Corporation. DISPERBYK-161 (trade name), DISPERBYK-163 (trade name), DISPERBYK-2164 (trade name), DISPERBYK-2155 (trade name), ED-216 (trade name) manufactured by Enomoto Kasei Co., Ltd. -211 (product name).

  The addition amount of the non-aqueous polymer dispersant used in the present embodiment is within a range of 0.01 to 3.0 parts by mass, preferably 0.1 to 2 parts per 100 parts by mass of the nickel fine particles of component (A). Within the range of 0.0 part by mass is preferable. When the addition amount is less than the above lower limit, the dispersibility tends to decrease, and when it exceeds the upper limit, aggregation tends to occur.

Component (C): Solvent having a boiling point of 100 ° C. or higher Examples of the solvent having a boiling point of 100 ° C. or higher include water and organic solvents. When an anionic surfactant is used as the dispersant for the component B, it is preferable to use water as the solvent for the component C. When a non-aqueous polymer dispersant or the like is used as the B component dispersant, an organic solvent is preferably used as the C component solvent.

  Examples of the organic solvent include aromatic hydrocarbons, aliphatic hydrocarbons, long-chain alcohols, glycols, and esters having a boiling point of 100 ° C. or more among esters of long-chain alcohols and carboxylic acids. Can be mentioned. These can be suitably used as a solvent for metal ink and paste. Specific examples of such compounds include terpineol, dihydroterpineol, dihydroterpineol estate, butyl carbitol, butyl carbitol acetate, propylene glycol monomethyl ether, propylene glycol monophenyl ether, ethylene glycol, tetraethylene glycol, decane, tetradecane, etc. These may be used alone or in admixture of two or more.

  In the nickel fine particle slurry of the present embodiment, the nickel fine particles of the component (A) are uniformly dispersed in the solvent of the component (C) using, for example, ultrasonic waves in the presence of the dispersant of the component (B). Can be prepared.

In the nickel fine particle slurry of the present embodiment, the nickel fine particles of the component (A) are in a state of being uniformly dispersed in the solvent of the component (C) by the dispersant of the component (B). As a material, it can be used suitably. In particular, the nickel fine particle of component (A) is a crystal calculated by the Scherrer method, in which the average particle diameter (L ₁ ) by scanning electron microscope observation is in the range of 20 to 200 nm, the CV value of the particle diameter is 0.2 or less. Since the core diameter (L ₂ ) is 15 nm or more and the ratio of crystallite diameter to average particle diameter (L ₂ / L ₁ ) is 0.15 or more, it has excellent sintering resistance. For example, a multilayer ceramic capacitor It can be preferably used as a material for the internal electrode. In addition, the nickel fine particle slurry of the present embodiment can be made into a paste without impairing the dispersibility of the nickel fine particles of component (A) by directly adding a binder resin such as allyl resin, butyral resin, ethyl cellulose, or the like. Convenient.

[Production method of metal fine particles]
Next, a method for producing metal fine particles typified by nickel fine particles of the component (A) will be described. The method for producing metal fine particles of the present embodiment includes a first step of preparing raw metal fine particles having an average particle diameter in a range of 20 to 200 nm by observation with a scanning electron microscope, Metal fine particles heated by irradiating a laser beam in a dispersed state and having a crystallite diameter calculated by the Scherrer method of 1.3 times or more of the crystallite diameter of the raw metal fine particles before heating The 2nd process (laser irradiation process) which manufactures.

<First step: Step of preparing raw metal fine particles>
In the first step, raw material metal fine particles having an average particle diameter in the range of 20 to 200 nm by observation with a scanning electron microscope are prepared. Examples of the metal species constituting the raw metal fine particles (metal fine particles used as the raw material to be irradiated with laser) include Co, Fe, Ni, Cu, Ag, Au, Pt, Pd, Ru, In, and alloys thereof. Etc. Among these, magnetic metals such as Co, Fe, Ni, and alloys thereof are preferable. As the raw material metal fine particles, nickel fine particles are most preferable. As the nickel fine particles, those similar to the component (A) described above can be used.

  The average particle size of the raw metal fine particles is within the range of 20 to 200 nm in terms of the average particle size by observation with a scanning electron microscope, for example, considering use for a conductive paste for forming an internal electrode of a multilayer ceramic capacitor (MLCC). , 40 to 150 nm is preferable. In particular, since the raw metal fine particles having an average particle diameter of 100 nm or less have a low sintering resistance from the beginning, the effect of improving the sintering resistance by the method of the present invention can be greatly obtained. The particle size distribution of the raw metal fine particles is preferably as narrow as possible, and the CV value is preferably 0.2 or less, for example. The method for preparing such raw material metal fine particles is not particularly limited, and for example, those prepared by a liquid phase method, a gas phase method or the like can be used. This is preferable because the distribution is narrow. In addition, raw metal fine particles prepared by the liquid phase method tend to sinter more easily than raw metal fine particles prepared by the gas phase method, and therefore, the sintering resistance is improved by the method of the present invention. The effect is greatly obtained.

  In the method for producing raw metal fine particles by the liquid phase method, a solution in which at least one metal salt is dissolved or dispersed in a solvent is used. For example, the raw metal fine particles are obtained by heat reduction, hydrothermal synthesis, reduction with a reducing agent, or the like. Can be obtained. Although the kind of metal salt is not specifically limited, The kind of metal salt can be selected according to the kind of metal which comprises the raw material fine metal particle obtained. Examples of the metal salt include hydroxide, halide, nitrate, sulfate, carbonate, carboxylate, β-diketonate and the like. Among these, it is advantageous to use a carboxylate having a relatively low dissociation temperature (decomposition temperature) in the reduction step, but the crystallinity in the obtained raw metal fine particles is low, that is, the crystallites in the obtained raw metal fine particles are low. Since it is small, it is easy to obtain the effects of the present invention.

  Hereinafter, the case where the raw metal fine particles are raw nickel fine particles will be described as an example, and a method for producing raw metal fine particles by a wet reduction method will be described.

Production of the raw material nickel fine particles by the wet reduction method includes the following steps A and B;
A) Complexation reaction liquid production | generation process which heats the mixture containing nickel carboxylate and primary amine to the temperature within the range of 100 to 165 degreeC, and obtains a complexation reaction liquid,
as well as,
B) A raw material for heating the complexing reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexing reaction liquid to obtain a slurry of raw material nickel fine particles coated with a primary amine Nickel fine particle slurry generation process,
Can be included.

Step A) Complexation reaction solution generation step:
(Nickel carboxylate)
The nickel carboxylate (nickel salt of carboxylic acid) is not limited to the type of carboxylic acid. For example, the carboxyl group may be a monocarboxylic acid having one carboxyl group, or a carboxylic acid having two or more carboxyl groups. It may be. Moreover, acyclic carboxylic acid may be sufficient and cyclic carboxylic acid may be sufficient. As such nickel carboxylate, nickel acyclic monocarboxylate can be preferably used, and among nickel acyclic monocarboxylate, nickel formate, nickel acetate, nickel propionate, nickel oxalate, benzoic acid It is more preferable to use nickel or the like. By using these nickel acyclic monocarboxylates, for example, the resulting raw material nickel fine particles are suppressed from variation in shape and are easily formed in a uniform shape. The nickel carboxylate may be an anhydride or a hydrate.

In addition, it is possible to use inorganic salts such as nickel chloride, nickel nitrate, nickel sulfate, nickel carbonate, nickel hydroxide instead of nickel carboxylate, but in the case of inorganic salts, dissociation (decomposition) is high temperature. In the process of reducing the dissociated nickel ions (or nickel complex), heating at a higher temperature is required, which is not preferable. It is also possible to use nickel salts composed of organic ligands such as Ni (acac) ₂ (β-diketonato complex) and nickel stearate, but using these nickel salts increases the raw material cost. It is not preferable.

(Primary amine)
The primary amine can form a complex with nickel ions, and effectively exhibits a reducing ability for nickel complexes (or nickel ions). On the other hand, secondary amines have great steric hindrance and may hinder the good formation of nickel complexes. Since tertiary amines do not have the ability to reduce nickel ions, none can be used alone. When these are used, they may be used in combination as long as they do not hinder the shape of the raw material nickel fine particles to be produced. The primary amine is not particularly limited as long as it can form a complex with nickel ions, and can be a solid or liquid at room temperature. Here, room temperature means 20 ° C. ± 15 ° C. The primary amine that is liquid at room temperature also functions as an organic solvent for forming the nickel complex. In addition, even if it is a primary amine solid at normal temperature, there is no particular problem as long as it is liquid by heating at 100 ° C. or higher, or can be dissolved using an organic solvent.

  The primary amine may be an aromatic primary amine, but an aliphatic primary amine is preferred from the viewpoint of easy nickel complex formation in the reaction solution. The aliphatic primary amine can control the particle diameter of the raw material nickel fine particles produced, for example, by adjusting the length of the carbon chain, and in particular, the raw material nickel fine particles having an average particle diameter in the range of 20 nm to 100 nm. This is advantageous in the case of manufacturing. From the viewpoint of controlling the particle diameter of the raw material nickel fine particles, the aliphatic primary amine is preferably selected from those having about 6 to 20 carbon atoms. The larger the number of carbon atoms, the smaller the particle diameter of the raw material nickel fine particles obtained. Examples of such amines include octylamine, trioctylamine, dioctylamine, hexadecylamine, dodecylamine, tetradecylamine, stearylamine, oleylamine, myristylamine, and laurylamine. For example, oleylamine exists in a liquid state under the temperature conditions in the raw material nickel fine particle production process, and therefore the reaction can proceed efficiently in a homogeneous solution.

Since the primary amine functions as a surface modifier during the production of the raw material nickel fine particles, secondary aggregation can be suppressed even after removal of the primary amine. In addition, the primary amine is liquid at room temperature from the viewpoint of ease of processing operation in the washing process for separating the solid component of the raw material nickel fine particles generated after the reduction reaction and the solvent or the unreacted primary amine. preferable. Further, the primary amine is preferably one having a boiling point higher than the reduction temperature from the viewpoint of ease of reaction control when the nickel complex is reduced to obtain raw material nickel fine particles. That is, the aliphatic primary amine preferably has a boiling point of 180 ° C. or higher, more preferably 200 ° C. or higher, and preferably has 9 or more carbon atoms. Here, for example, the boiling point of C ₉ H ₂₁ N (nonylamine) of an aliphatic amine having 9 carbon atoms is 201 ° C. The amount of primary amine is preferably 2 mol or more, more preferably 2.2 mol or more, and more preferably 4 mol or more with respect to 1 mol of nickel. When the amount of the primary amine is less than 2 mol, it is difficult to control the particle diameter of the raw material nickel fine particles to be obtained, and the particle diameter tends to vary. The upper limit of the amount of primary amine is not particularly limited, but is preferably 20 mol or less from the viewpoint of productivity, for example.

(Organic solvent)
In step A, an organic solvent different from the primary amine may be newly added in order to allow the reaction in the homogeneous solution to proceed more efficiently. When an organic solvent is used, the organic solvent may be mixed simultaneously with the nickel carboxylate and the primary amine. However, when the organic solvent is added after first mixing the nickel carboxylate and the primary amine to form a complex, It is more preferable because it efficiently coordinates to a nickel atom. The organic solvent that can be used is not particularly limited as long as it does not inhibit the complex formation between the primary amine and the nickel ion. For example, the organic solvent having 4 to 30 carbon atoms, 7 to 30 carbon atoms, and the like. A saturated or unsaturated hydrocarbon organic solvent, an alcohol organic solvent having 8 to 18 carbon atoms, or the like can be used. Moreover, from the viewpoint of enabling use even under heating conditions by microwave irradiation, it is preferable to select an organic solvent having a boiling point of 170 ° C. or higher, more preferably in the range of 200 to 300 ° C. It is better to choose one. Specific examples of such an organic solvent include tetraethylene glycol and n-octyl ether.

A divalent nickel ion is known as a ligand-substituted active species, and the ligand of the complex to be formed may easily change in complex formation by ligand exchange depending on temperature and concentration. For example, in the step of obtaining a reaction solution by heat-treating a mixture of nickel carboxylate and primary amine, considering steric hindrance such as the carbon chain length of the amine used, for example, carboxylate ions (R ₁ COO as shown in FIG. 1) , R ₂ COO) may be coordinated by either bidentate coordination (a) or monodentate coordination (b), and when the amine concentration is in large excess, carboxylate ions are present in the outer sphere. There are at least three possibilities of (c). In order to obtain a homogeneous solution at the target reaction temperature (reduction temperature), at least one of the ligands of A, B, C, D, E, and F must be coordinated with a primary amine. There is. In order to take this state, it is necessary that the primary amine is excessively present in the reaction solution, and it is preferable that at least 2 mol per 1 mol of nickel ions is present, and 2.2 mol or more exist. It is more preferable that 4 mol or more is present.

  Although this complex formation reaction can proceed even at room temperature, the reaction is carried out by heating to a temperature in the range of 100 ° C. to 165 ° C. in order to perform a sufficient and more efficient complex formation reaction. This heating is particularly advantageous when nickel carboxylate hydrate such as nickel formate dihydrate or nickel acetate tetrahydrate is used as nickel carboxylate. The heating temperature is preferably a temperature exceeding 100 ° C., more preferably a temperature of 105 ° C. or more, so that the ligand substitution reaction between the coordinating water coordinated with nickel carboxylate and the primary amine is efficient. The water molecule as the complex ligand can be dissociated, and the water can be discharged out of the system, so that the complex can be formed efficiently. For example, nickel formate dihydrate has a complex structure in which two coordination waters and two formate ions as bidentate ligands exist at room temperature. In order to efficiently form a complex by substituting a ligand for a primary amine, it is preferable to dissociate the water molecule as the complex ligand by heating at a temperature higher than 100 ° C. In addition, the heat treatment in the complex formation reaction between nickel carboxylate and primary amine is surely separated from the subsequent heat reduction process by microwave irradiation of the nickel complex (or nickel ion) to complete the complex formation reaction. In view of the above, the temperature is set to the upper limit temperature or lower, preferably 160 ° C. or lower, more preferably 150 ° C. or lower.

  The heating time can be appropriately determined according to the heating temperature and the content of each raw material, but is preferably 10 minutes or more from the viewpoint of completing the complex formation reaction. There is no upper limit on the heating time, but heat treatment for a long time is useless from the viewpoint of saving energy consumption and process time. The heating method is not particularly limited, and may be heating by a heat medium such as an oil bath or heating by microwave irradiation.

  The complex formation reaction between nickel carboxylate and primary amine can be confirmed by a change in the color of the solution when a solution obtained by mixing nickel carboxylate and primary amine in an organic solvent is heated. . In addition, this complex formation reaction is carried out by measuring the absorption maximum wavelength of the absorption spectrum observed in the wavelength region of 300 nm to 750 nm using, for example, an ultraviolet / visible absorption spectrum measuring apparatus, and measuring the maximum absorption wavelength of the raw material (for example, nickel formate). In dihydrate, the maximum absorption wavelength is 710 nm, and in nickel acetate tetrahydrate, the maximum absorption wavelength is 710 nm.) The shift of the complexing reaction solution (the maximum absorption wavelength shifts to 600 nm) is observed. Can be confirmed.

  After the complex formation between nickel carboxylate and primary amine is performed, the resulting reaction solution is heated by microwave irradiation to reduce the nickel ions of the nickel complex as described below. At the same time, the carboxylate ions coordinated to the base metal are decomposed, and finally, nickel fine particles containing nickel having an oxidation number of 0 are produced. In general, nickel carboxylate is hardly soluble under conditions other than using water as a solvent, and a solution containing nickel carboxylate needs to be a homogeneous reaction solution as a pre-stage of the heat reduction reaction by microwave irradiation. On the other hand, the primary amine used in the present embodiment is liquid under the operating temperature conditions, and is considered to be liquefied by coordination with nickel ions to form a homogeneous reaction solution.

Process B) Raw material nickel fine particle slurry production process:
In this step, the complexing reaction solution obtained by the complexation reaction between nickel carboxylate and primary amine is heated to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexing reaction solution. To obtain a raw material nickel fine particle slurry coated with a primary amine. The temperature for heating by microwave irradiation is preferably 180 ° C. or higher, more preferably 200 ° C. or higher, from the viewpoint of suppressing variation in the shape of the obtained raw material nickel fine particles. The upper limit of the heating temperature is not particularly limited, but is preferably set to 270 ° C. or less, for example, from the viewpoint of efficiently performing the treatment. In addition, the use wavelength of a microwave is not specifically limited, For example, it is 2.45 GHz. The heating temperature can be appropriately adjusted depending on, for example, the type of nickel carboxylate and the use of an additive that promotes the nucleation of the raw material nickel fine particles.

  In this step, since microwaves penetrate into the reaction solution, uniform heating is performed, and energy can be directly applied to the medium, so that rapid heating can be performed. As a result, the entire reaction solution can be made uniform at a desired temperature, and the processes of reduction, nucleation, and nucleation of the nickel complex (or nickel ions) can occur simultaneously in the entire solution. Narrow monodisperse particles can be easily produced in a short time.

  In order to generate the raw material nickel fine particles having a uniform particle size, the nickel complex is uniformly and sufficiently generated in the complexing reaction liquid generating step (step in which the nickel complex is generated) in step A, and this step In the raw material nickel fine particle slurry generation step of B, it is necessary to simultaneously generate and grow nickel (zero-valent) nuclei generated by reduction of the nickel complex (or nickel ions). That is, by adjusting the heating temperature of the complexing reaction liquid generation step within the above specific range and ensuring that it is lower than the heating temperature by the microwave in the raw material nickel fine particle slurry generation step, Easy to produce ordered particles. For example, if the heating temperature is too high in the complexing reaction liquid generation process, the formation of a nickel complex and the reduction reaction to nickel (zero valence) proceed at the same time to generate different types of metal species. It may be difficult to produce particles having a uniform particle shape. Moreover, if the heating temperature in the raw material nickel fine particle slurry generation process is too low, the reduction reaction rate to nickel (zero valence) is slowed and the generation of nuclei is reduced, so that not only the particles are enlarged, but also the yield of the raw material nickel fine particles is reduced. It is not preferable also from a point.

  The raw material nickel fine particle slurry obtained by heating by microwave irradiation is, for example, left and separated, and after removing the supernatant liquid, the raw material nickel fine particles are obtained by washing with an appropriate solvent and drying. In the raw material nickel fine particle slurry generating step, the organic solvent described above may be added as necessary. As described above, the primary amine used for the complex formation reaction is preferably used as it is as the organic solvent.

  As described above, raw material nickel fine particles having an average particle diameter in the range of 20 to 200 nm can be prepared. Raw metal fine particles other than nickel can also be produced according to the above method.

<Second step: laser irradiation step>
In the second step, heating is performed by irradiating a laser beam in a state where raw metal fine particles typified by raw nickel fine particles are dispersed in a liquid phase. As the laser, for example, an ultraviolet laser, a visible light laser, an infrared laser, or the like can be used. In particular, an ultraviolet laser and a visible light laser having a laser beam wavelength in the range of 200 to 800 nm are preferable. For example, as the ultraviolet laser, it is preferable to use an excimer laser that is pulsed laser light. The excimer laser can select ultraviolet light having a wavelength of 400 nm or less from ArF, KrF, XeCl, XeF, F ₂ or the like. As the visible light laser, for example, a helium neon laser, an argon ion laser, a semiconductor laser, or the like can be used. Further, the wavelength of the laser beam may be appropriately selected depending on the elements constituting the raw metal fine particles, the particle diameter, etc., but the solvent is not easily absorbed (not easily heated) and the raw metal fine particles are easily absorbed (easily heated). Therefore, an ultraviolet laser can be preferably used as the laser for irradiation.

The conditions for laser irradiation are preferably determined in consideration of the behavior of the raw metal fine particles during laser irradiation, and may be continuous irradiation or pulse irradiation. The intensity of the laser is preferably set so that the temperature is equal to or lower than the melting temperature of the raw metal fine particles. For example, in the case of an ultraviolet pulse laser, the intensity per pulse is preferably ²⁰ to 120 mJ / cm ² , for example. When the intensity per pulse exceeds 120 mJ / cm ² , the metal fine particles after irradiation may cause aggregation. Moreover, when the intensity | strength per pulse is 20 mJ / cm < ² > or less, the growth of a crystallite becomes inadequate and it does not contribute to the improvement of sintering temperature in many cases.

  The laser irradiation time is preferably determined in consideration of the average particle diameter of the raw material metal fine particles, the intensity of the laser beam, and the like, and can be, for example, in the range of 3 to 30 minutes.

  The laser irradiation in the second step can be performed in a state where the raw material metal fine particles are dispersed in the liquid phase. Here, the liquid phase is preferably composed of water or an organic solvent having a boiling point of 100 ° C. or higher. Laser irradiation is a raw metal fine particle slurry in which the liquid phase is water and an anionic surfactant is blended as a dispersant, or an organic solvent having a boiling point of 100 ° C. or higher, and 2 as a dispersant. It is preferable to carry out in the state of the raw material metal fine particle slurry in which a non-aqueous polymer dispersant having a tertiary or tertiary amino group is blended, and contains the raw metal fine particles, the above-mentioned (B) component and (C) component. Most preferably, it is carried out in the state of a metal fine particle slurry. By performing laser irradiation in a state where the raw metal fine particles are dispersed in water or an organic solvent having a boiling point of 100 ° C. or higher, crystallites can be grown while preventing fusion of the metal fine particles, and surface water can be grown. By changing an oxide (such as nickel hydroxide) to an oxide (such as nickel oxide), aggregation of metal fine particles can be suppressed.

By laser irradiation, the crystallite diameter of the metal fine particles can be increased to 1.3 times or more, preferably 1.5 to 10 times the crystallite diameter of the raw metal fine particles before irradiation. Here, the crystallite diameter of the metal fine particles after laser irradiation is, for example, 15 nm or more, and there is no limit on the upper limit, and it may be, for example, the same as the particle diameter. The crystallite diameter can be calculated by the Scherrer equation. Further, the ratio L ₂ / L ₁ of the crystallite diameter (L ₂ ) to the average particle diameter (L ₁ ) can be set to 0.15 or more by laser irradiation. The sintering temperature of the metal fine particles decreases as the average particle diameter (L ₁ ) decreases, but the sintering temperature can be reduced by increasing the ratio of the crystallite diameter (L ₂ ) to the average particle diameter (L ₁ ). Can be high.

  In addition, the average particle diameter of the fine metal particles after the second step by observation with a scanning electron microscope is less than 1.1 times the average particle diameter of the raw metal fine particles. For example, when the average particle diameter of the raw metal fine particles is in the range of 20 to 200 nm and the CV value of the particle diameter is 0.2 or less, the average particle diameter of the metal fine particles after laser irradiation is less than 22 nm at the maximum. It is within the range of less than 220 nm, preferably within the range of 20 to 200 nm, and the CV value of the particle diameter is 0.2 or less. As described above, in the method according to the present embodiment, only the crystallite diameter can be increased by changing the average particle diameter of the metal fine particles with laser irradiation.

  The manufacturing method of the metal fine particle of this Embodiment can be made into a series of processes including the 1st process of preparing the raw material metal microparticle containing the said process A and B, and the 2nd process of performing laser irradiation. .

  As described above, metal fine particles having large crystallites and excellent sintering resistance can be produced. Although the average particle diameter of the obtained metal fine particles is almost the same as that before laser irradiation (less than 1.1 times), the crystallite diameter is 1.3 times or more larger than the raw metal fine particles before laser irradiation. It has become. Therefore, for example, in the case of nickel fine particles, the sintering temperature is 50 ° C. or higher (preferably 100 ° C. or higher) higher than the raw material nickel fine particles, and the sintering resistance is improved. Accordingly, the metal fine particles obtained by the method of the present invention can be suitably used, for example, as a material for an internal electrode of a multilayer ceramic capacitor.

<Action>
Next, the action of the method of the present invention will be described by taking nickel fine particles as an example. The raw material nickel fine particles synthesized by the liquid phase method by microwave irradiation including the steps A and B have an advantage that the particle size distribution is very narrow within an average particle size range of 20 to 200 nm. However, in the raw material nickel fine particles, the crystallite size calculated by the Scherrer equation by XRD measurement is as small as 5 to 25 nm, and a hydroxide film of 2 to 6 nm is formed on the particle surface. Therefore, in the measurement by thermomechanical analysis (TMA), the 5% heat shrinkage temperature in an H ₂ / N ₂ atmosphere is 250 to 350 ° C., and nickel fine particles (crystallites) having the same particle diameter obtained by the vapor phase method are used. The size is 20 to 200 nm, and the surface of the nickel fine particles is about 100 ° C. lower than the oxide film of 1 to 2 nm. As described above, the reason why the sintering resistance of the raw material nickel fine particles synthesized by the liquid phase method by microwave irradiation is lower than that by the vapor phase method is that the crystallite is small and the hydroxide film This is probably because a dehydration reaction occurs at a high temperature due to the presence, the surface hydroxyl groups condense, and the particles themselves shrink.

Therefore, in the present embodiment, the raw material nickel fine particles are heated by laser irradiation in a uniformly dispersed slurry state. The process of changing from raw nickel fine particles to nickel fine particles by this laser irradiation is schematically shown in FIG. FIG. 2A shows a cross-sectional structure of the raw material nickel fine particles 10. The raw material nickel fine particles 10 synthesized by the liquid phase method by microwave irradiation are configured as an aggregate of a plurality of crystallites 10a, and countless hydroxides are attached to the surface. FIG. 2B shows a cross-sectional structure of the nickel fine particles 100 obtained by heating the raw material nickel fine particles 10 by laser irradiation. The nickel fine particle 100 is an aggregate of a plurality of crystallites 10a. The nickel fine particles 100 obtained by performing laser irradiation heating on the raw material nickel fine particles 10 synthesized by microwave irradiation by a liquid phase method and having hydroxyl groups on the surface thereof have the surface hydroxyl groups removed. Such a change in the surface state of the particles is not observed by external heating such as a normal oil bath or mantle heater. For example, when external heating is performed on a slurry containing water as a solvent, the water temperature during the treatment reaches only 100 ° C., and the nickel fine particle surface has a wave number of 3600 to 3700 cm ⁻ in an infrared absorption spectrum by a diffuse reflection method. ^The nickel hydroxide film remains to the extent that an absorption peak at ¹ (peak derived from hydroxide) is detected. Therefore, the dispersibility of the nickel fine particles is reduced by the easily agglomerated hydroxide film, and the crystallite growth hardly occurs, so that the sintering resistance is not improved. On the other hand, in laser irradiation, the laser light is hardly absorbed by water and is efficiently absorbed by the raw material nickel fine particles, so that the heating temperature of the raw material nickel fine particles 10 instantaneously rises to several hundred degrees, and by the diffuse reflection method. Nickel hydroxide can be reduced to such an extent that an absorption peak (peak derived from hydroxide) at a wave number of 3600 to 3700 cm ⁻¹ in the infrared absorption spectrum is not detected. In addition, the laser irradiation causes the temperature rise of the nickel fine particles, and there is a concern that the solvent may volatilize due to the heat transfer to the solvent caused by this. From the viewpoint of suppressing this, the laser irradiation is a pulse irradiation. Is preferred.

Further, by locally heating the raw material nickel fine particles 10 dispersed in the liquid phase by laser irradiation, the crystallites 10a constituting the raw material nickel fine particles 10 are grown with large thermal energy, and the size of the crystallites 10a is increased. can do. In Figure 2, it shows a particle size of crystallite 10a constituting the raw material nickel particles 10 before laser irradiation d _2, the particle size of the crystallites 10a constituting the nickel particles 100 after laser irradiation in L _2. This relationship is L ₂ > d ₂ , preferably L ₂ ≧ 1.3 × d ₂ (in FIG. 2, the difference between L ₂ and d ₂ is exaggerated). By increasing the crystallite size in this way, an effect of increasing the sintering temperature of the nickel fine particles 100 can be obtained.

  As described above, in the method for producing metal fine particles of the present embodiment, the crystallites constituting the raw metal fine particles are effective by performing heat treatment by laser irradiation on the raw metal fine particles in the range of an average particle diameter of 20 to 200 nm. Therefore, metal fine particles having a high sintering temperature can be obtained. Thus, metal fine particles having an average particle diameter in the range of 20 to 200 nm and a high sintering temperature can be suitably used, for example, as a material for internal electrodes of a multilayer ceramic capacitor.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples. In the examples of the present invention, various measurements and evaluations are as follows unless otherwise specified.

[Average particle diameter of nickel fine particles]
For the average particle size, a sample photograph was taken with an SEM (scanning electron microscope), 200 samples were randomly extracted from the sample, and the average particle size (area average diameter) and standard deviation were obtained. Specifically, the area of each of the extracted fine particles was obtained, and the average particle size of the primary particles was determined based on the particle size when converted to a true sphere. The CV value (coefficient of variation) was calculated by (standard deviation) / (average particle diameter). In addition, it shows that a particle diameter is so uniform that a CV value is small.

[Crystal diameter of nickel fine particles]
From the powder X-ray diffraction (XRD) result, the calculation was performed according to Scherrer's equation.

[5% heat shrink temperature]
A sample is put into a 5Φ × 2 mm cylindrical molding machine, and a molded body obtained by press molding is produced, and measured by a thermomechanical analyzer (TMA) in an atmosphere of nitrogen gas (containing 3% hydrogen gas). The temperature of 5% heat shrinkage was taken as 5% heat shrinkage temperature.

[Evaluation of dispersion stability of slurry]
For evaluating the dispersion stability of the slurry, the slurry placed in the centrifuge tube is centrifuged at 300 rpm using a particle size distribution / dispersion stability analyzer (trade name; LUMiSizer, manufactured by LUM). In the centrifugal field, particles settle and a supernatant is formed. When the increase in transmitted light of the slurry is continuously measured with the formation of the supernatant liquid and the numerical value is large, the aggregated particles are large and the sedimentation rate is high, that is, the dispersion stability is poor. The amount of change in the amount of transmitted light of the slurry of Comparative Example 2 was set to 1.00. Based on this, the case of 1.00 or less was determined as “good”, and the case of exceeding 1.00 was determined as “not possible”.

[Example 1]
<Dissolution process>
To 120.0 g (480 mmol) of nickel acetate tetrahydrate, 690 g (2.58 mol) of oleylamine was added, and nickel acetate was dissolved in oleylamine by heating at 140 ° C. for 20 minutes under a nitrogen flow.

<Reduction process>
Next, the solution was irradiated with microwaves and heated to 250 ° C., and the temperature was maintained for 5 minutes to obtain a nickel fine particle slurry 1 ′.

<Washing and drying process>
The nickel fine particle slurry 1 ′ was allowed to stand and separated, and the supernatant liquid was removed, followed by washing with toluene and methanol three times, followed by drying for 6 hours in a vacuum dryer maintained at 70 ° C. to obtain nickel fine particles 1 ′ (average Particle diameter d ₁ ; 140 nm, CV value; 0.17, crystallite diameter d ₂ ; 17 nm, d ₂ / d ₁ ; 0.12).

<Distributed processing>
100 g of water was put into a test tube with respect to 1 g of nickel fine particles 1 ′, and was subjected to dispersion treatment with an ultrasonic homogenizer for 3 minutes. Further, Dispersant 1 (anionic surfactant, manufactured by San Nobco, trade name: SN Dispersant 5468, active ingredient: 40.5% ammonium polycarboxylate) is used as an active ingredient for nickel fine particles 1 ′ in an amount of 0.5. % Was added and dispersed again with an ultrasonic homogenizer for 1 minute.

<Laser irradiation treatment>
The dispersion-treated slurry was irradiated with a non-condensing laser having a wavelength of 355 nm at 66 mJ / cm ² per pulse for 10 minutes to obtain slurry 1.

<Analysis of nickel fine particles>
The slurry 1 was centrifuged, dried at 60 ° C. under vacuum (one day and night), and nickel fine particles 1 obtained by pulverization in an agate mortar were obtained. The characteristics of the obtained nickel fine particles 1 are as follows.

1) Elemental analysis of nickel fine particles 1; C; 0.52, O; 1.43, N; 0.08 (unit: mass%). Mc / Mo ratio = 0.36.
2) Average particle diameter L 1 of nickel fine particles ₁ ; 140 nm, CV value: 0.17, crystallite diameter L ₂ ; 35 nm (L ₂ / L ₁ = 0.25, Mo × L ₁ / L ₂ = 5.72) , L ₂ / d ₂ = 2.1).
3) 5% heat shrink temperature; 420 ° C.
4) Dispersion stability: Good 5) Absorption peak (peak derived from hydroxide) at wave number 3600-3700 cm ⁻¹ in infrared absorption spectrum by diffuse reflection method: None

[Example 2]
In the same manner as in Example 1, nickel fine particles 2 ′ (average particle diameter d ₁ ; 140 nm, CV value; 0.17, crystallite diameter d ₂ : 17 nm, d ₂ / d ₁ ; 0.12) were obtained.

  Instead of water in Example 1, DHT (dihydroterpineol, boiling point: 200 to 220 ° C.) was used, and instead of dispersant 1, dispersant 2 (polyester polymer dispersant, manufactured by Enomoto Kasei Co., Ltd., Product name: HIPLAAD ED216, active ingredient: 75% polyamine containing secondary and tertiary amino groups and a mixture of high molecular weight carboxylic acids, polar; low, insoluble in water, amine value as active ingredient; 40 mg KOH / g, Dispersion treatment was performed in the same manner as in Example 1 except that an acid value as an active ingredient; 15 mg KOH / g, weight average molecular weight; 10,000 to 20,000) was used.

  In the same manner as in Example 1, the dispersion-treated slurry was irradiated with a laser to obtain slurry 2 and nickel fine particles 2 were obtained. The characteristics of the obtained nickel fine particles 2 are as follows.

1) Elemental analysis of nickel fine particles 2; C; 0.43, O; 1.41, N; 0.06 (unit: mass%). Mc / Mo ratio = 0.30.
2) Average particle diameter L ₁ of nickel fine particles 2; 140 nm, CV value: 0.17, crystallite diameter L ₂ ; 37 nm (L ₂ / L ₁ = 0.26, Mo × L ₁ / L ₂ = 5.34) , L ₂ / d ₂ = 2.2).
3) 5% heat shrink temperature; 450 ° C
4) Dispersion stability: Good 5) Absorption peak (peak derived from hydroxide) at wave number 3600-3700 cm ⁻¹ in infrared absorption spectrum by diffuse reflection method: None

[Example 3]
In Example 1, nickel fine particles 3 ′ (average particle diameter d ₁ ; 45 nm, CV value; 0.17, crystals) were obtained in the same manner as in Example 1 except that nickel acetate tetrahydrate was changed to 20.0 g (80 mmol). Child diameter d ₂ ; 12 nm, d ₂ / d ₁ ; 0.27).

  Instead of water in Example 1, terpineol (boiling point: 217 ° C.) was used, and in place of Dispersant 1, Dispersant 3 (polyester polymer dispersant, manufactured by Nippon Lubrizol Corporation, trade name: Solsperse 13240 , Active ingredient: 40% of a mixture of polyester-based graft copolymer containing secondary amino group and tertiary amino group, polar: low, insoluble in water, amine value as active ingredient; 93 mgKOH / g, as active ingredient The dispersion treatment was performed in the same manner as in Example 1 except that the acid value of 0 mgKOH / g) was used.

  In the same manner as in Example 1, the dispersion-treated slurry was irradiated with laser to obtain slurry 3, and nickel fine particles 3 were obtained. The characteristics of the obtained nickel fine particles 3 are as follows.

1) Elemental analysis of nickel fine particles 3; C; 1.95, O; 2.62, N; 0.18 (unit: mass%). Mc / Mo ratio = 0.74.
2) Average particle diameter L ₁ of nickel fine particles 3; 45 nm, CV value; 0.17, crystallite diameter L ₂ ; 18 nm (L ₂ / L ₁ = 0.40, Mo × L ₁ / L ₂ = 6.55) , L ₂ / d ₂ = 1.5).
3) 5% heat shrink temperature: 360 ° C
4) Dispersion stability: Good 5) Absorption peak (peak derived from hydroxide) at wave number 3600-3700 cm ⁻¹ in infrared absorption spectrum by diffuse reflection method: None

Comparative Example 1
After obtaining nickel fine particles (average particle diameter d ₁ ; 140 nm, CV value; 0.17, crystallite diameter d ₂ : 17 nm, d ₂ / d ₁ ; 0.12) in the same manner as in Example 1, 1 g 100 g of DHT with respect to the nickel fine particles was put in a test tube, and dispersed with an ultrasonic homogenizer for 3 minutes.

  The obtained slurry was centrifuged, vacuum dried at 60 ° C. (one day and night), and nickel fine particles obtained by pulverization in an agate mortar were obtained. The characteristics of the obtained nickel fine particles are as follows.

1) Elemental analysis of nickel fine particles; C; 0.48, O; 1.24, N; 0.06 (unit: mass%). Mc / Mo ratio = 0.39.
2) Average particle diameter L ₁ of nickel fine particles: 140 nm, CV value: 0.17, crystallite diameter L ₂ : 17 nm (L ₂ / L ₁ = 0.12, Mo × L ₁ / L ₂ = 10.21, _{L 2 / d 2 = 1.0)} .
3) 5% heat shrinkage temperature: 310 ° C
4) Dispersion stability: Impossible 5) Absorption peak at a wave number of 3600 to 3700 cm ⁻¹ (peak derived from hydroxide) in an infrared absorption spectrum by a diffuse reflection method: None

Comparative Example 2
Nickel fine particles were prepared in the same manner as in Example 1 except that the dispersion-treated slurry in Example 1 was heated and refluxed at 100 ° C. for 10 minutes using a mantle heater instead of being laser-irradiated. Obtained. The characteristics of the obtained nickel fine particles are as follows.

1) Elemental analysis of nickel fine particles; C; 0.66, O; 1.32, N; 0.06 (unit: mass%). Mc / Mo ratio = 0.50.
2) Average particle diameter L ₁ of nickel fine particles: 140 nm, CV value: 0.17, crystallite diameter L ₂ ; 18 nm (L ₂ / L ₁ = 0.13, Mo × L ₁ / L ₂ = 10.27, _{L 2 / d 2 = 1.1)} .
3) 5% heat shrink temperature; 320 ° C
4) Dispersion stability: Good 5) Absorption peak at a wave number of 3600-3700 cm ⁻¹ (peak derived from hydroxide) in infrared absorption spectrum by diffuse reflection method: Existence

Comparative Example 3
Using a known method of adding hydrazine hydrate as a reducing agent to an aqueous nickel chloride solution and then adding sodium hydroxide, nickel fine particles (average particle diameter d ₁ ; 135 nm, CV value; 0.23, Crystallite diameter d ₂ ; 15 nm, d ₂ / d ₁ ; 0.11) was obtained.

  100 g of DHT was put into a test tube with respect to 1 g of nickel fine particles, and subjected to a dispersion treatment for 3 minutes with an ultrasonic homogenizer.

  The obtained slurry was centrifuged, vacuum dried at 60 ° C. (one day and night), and nickel fine particles obtained by pulverization in an agate mortar were obtained. The characteristics of the obtained nickel fine particles are as follows.

1) Elemental analysis of nickel fine particles; C; 0.07, O; 1.12, N <0.01 (unit: mass%). Mc / Mo ratio = 0.06.
2) Average particle diameter L ₁ of nickel fine particles: 135 nm, CV value: 0.23, crystallite diameter L ₂ : 15 nm (L ₂ / L ₁ = 0.11, Mo × L ₁ / L ₂ = 10.008, _{L 2 / d 2 = 1.0)} .
3) 5% heat shrink temperature; 305 ° C
4) Dispersion stability: Impossible 5) Absorption peak at wave number 3600-3700 cm ⁻¹ (peak derived from hydroxide) in infrared absorption spectrum by diffuse reflection method: Existence

Comparative Example 4
In the same manner as in Example 3, nickel fine particles (average particle diameter d ₁ ; 45 nm, CV value; 0.17, crystallite diameter d ₂ : 12 nm, d ₂ / d ₁ ; 0.27) were obtained.

  Nickel fine particles were obtained in the same manner as in Example 3 except that the dispersant 3 in Example 3 was not used and laser irradiation was not performed. The characteristics of the obtained nickel fine particles are as follows.

1) Elemental analysis of nickel fine particles; C; 1.75, O; 2.53, N; 0.08 (unit: mass%). Mc / Mo ratio = 0.69.
2) Average particle diameter L ₁ of nickel fine particles: 45 nm, CV value: 0.17, crystallite diameter L ₂ : 12 nm (L ₂ / L ₁ = 0.27, Mo × L ₁ / L ₂ = 9.49, _{L 2 / d 2 = 1.0)} .
3) 5% heat shrink temperature; 245 ° C
4) Dispersion stability: Impossible 5) Absorption peak at a wave number of 3600 to 3700 cm ⁻¹ (peak derived from hydroxide) in an infrared absorption spectrum by a diffuse reflection method: None

  The above results are summarized in Table 1 and Table 2.

  From Table 1 and Table 2, in Examples 1-3 which performed laser irradiation in the state of the slurry which disperse | distributed raw material nickel fine particles in a liquid phase, it is 5% heat | fever compared with Comparative Examples 1-4 which do not perform laser irradiation. It was confirmed that the shrinkage temperature was high and the sintering resistance was excellent.

As mentioned above, although embodiment of this invention was described in detail for the purpose of illustration, this invention is not restrict | limited to the said embodiment, A various deformation | transformation is possible.

  10 ... Raw material nickel fine particles, 10a ... Crystallite, 100 ... Nickel fine particles

Claims (17)

The following components (A) to (C);
(A) Crystal calculated by the Scherrer method with an average particle diameter (L ₁ ) in the range of 20 to 200 nm observed with a scanning electron microscope, a coefficient of variation (standard deviation / average particle diameter) of 0.2 or less. Nickel fine particles having a child diameter (L ₂ ) of 15 nm or more and a ratio of the crystallite diameter to the average particle diameter (L ₂ / L ₁ ) of 0.15 or more,
(B) a dispersant, and (C) a solvent having a boiling point of 100 ° C. or higher,
Nickel fine particle slurry containing   The nickel fine particle slurry according to claim 1, wherein the B component is an anionic surfactant and the C component is water.   The nickel fine particle slurry according to claim 1, wherein the component B is a non-aqueous polymer dispersant having a secondary or tertiary amino group, and the component C is an organic solvent having a boiling point of 100 ° C or higher. The oxygen content (Mo) of the nickel fine particles is in the range of 0.3 to 3.0% by mass, and the Mo, L ₁ and L ₂ satisfy the relationship of Mo × L ₁ / L ₂ ≦ 9. The nickel fine particle slurry according to any one of claims 1 to 3.   The content of carbon element in the nickel fine particles is in the range of 0.3 to 2.5% by mass, and the ratio of the carbon element content (Mc) to the oxygen content (Mo) in the nickel fine particles (Mc / Mo ) Is in the range of 0.1 to 0.8, the nickel fine particle slurry according to any one of claims 1 to 4. A first step of preparing raw metal fine particles having an average particle diameter in the range of 20 to 200 nm by observation with a scanning electron microscope;
The raw metal fine particles are heated by irradiating laser light in a state dispersed in the liquid phase, and the crystallite diameter calculated by the Scherrer method is 1.3 of the crystallite diameter of the raw metal fine particles before heating. A second step of producing metal fine particles that are twice or more,
A method for producing metal fine particles.   The method for producing metal fine particles according to claim 6, wherein a variation coefficient (standard deviation / average particle diameter) of the particle diameter of the raw metal fine particles is 0.2 or less.   The method for producing metal fine particles according to claim 6 or 7, wherein an average particle size of the metal fine particles after the second step is less than 1.1 times the average particle size of the raw metal fine particles.   The method for producing fine metal particles according to any one of claims 6 to 8, wherein the wavelength of the laser beam is in a range of 200 to 800 nm.   The method for producing fine metal particles according to any one of claims 6 to 9, wherein the laser beam irradiation is pulse irradiation.   The method for producing fine metal particles according to any one of claims 6 to 10, wherein the liquid phase is water or an organic solvent having a boiling point of 100 ° C or higher.   The method for producing fine metal particles according to claim 11, wherein the liquid phase in the second step is water and an anionic surfactant is blended as a dispersant.   The liquid phase in the second step is an organic solvent having a boiling point of 100 ° C or higher, and a non-aqueous polymer dispersant having a secondary or tertiary amino group is blended as a dispersant. A method for producing fine metal particles.   The method for producing metal fine particles according to any one of claims 6 to 13, wherein the raw metal fine particles are obtained by a wet reduction method.   The method for producing metal fine particles according to claim 14, wherein the raw metal fine particles are raw material nickel fine particles. The raw material nickel fine particles are the following steps A and B;
A) Complexation reaction liquid production | generation process which heats the mixture containing nickel carboxylate and primary amine to the temperature within the range of 100 to 165 degreeC, and obtains a complexation reaction liquid,
as well as,
B) A raw material for heating the complexing reaction liquid to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexing reaction liquid to obtain a slurry of raw material nickel fine particles coated with a primary amine Nickel fine particle slurry generation process,
The method for producing metal fine particles according to claim 15, which is prepared by performing a process including:   Metal fine particles produced by the method according to any one of claims 6 to 16.

Images