TW201719678A - Nickel powder and nickel paste - Google Patents

Abstract

Provided are a nickel powder and a nickel paste which are suitable as inner electrode materials for MLCCs and have excellent binder removability and improved wettability and dispersibility with and in low-polar solvents. A spherical nickel powder in which the number average particle diameter D of primary particles is 1 [mu]m or less. The spherical nickel powder has a sodium concentration of 0.001% by mass or less, a calcium concentration of 0.001% by mass or less and a carbon concentration of 0.05 to 2.0% by mass inclusive, has an infrared absorption peak at 1600 cm-1 as measured with a Fourier transform infrared spectrometer, can exert metallic luster when formed into a pasty form by kneading together with dihydroterpinylacetate, and has a rate of decrease in a carbon concentration of 50% or more when treated with heat at 300 DEG C under an inert atmosphere.

Description

Nickel powder and nickel paste

The present invention relates to a nickel powder suitable for use in a conductive paste used for electronic parts and the like, and more particularly to a nickel powder suitable for use as a conductive paste for internal electrode use of a laminated ceramic capacitor.

A multilayer ceramic capacitor (hereinafter referred to as "MLCC") is an electronic component in which a dielectric body and a conductor are alternately overlapped, and is used in an electronic device such as a smart phone and a tablet terminal device.

Generally, MLCC is manufactured as follows. In other words, a dielectric paste in which a ceramic powder such as barium titanate or the like is mixed with an organic binder is formed into a sheet shape to form a dielectric green sheet. On the other hand, the metal fine powder for the internal electrode and the ceramic for controlling the sintering behavior (hereinafter referred to as "common material") are mixed with an organic compound such as an organic solvent or an organic binder to form an internal electrode paste. It is printed on a dielectric green plate and dried. After the dielectric layer coated with the electrode layer is laminated, it is heated and pressurized to form a layered body, which is processed into a target shape. Next, in order to remove the organic component such as the organic binder, the laminate is subjected to heat treatment in a weak oxidizing gas atmosphere (hereinafter referred to as "debonding treatment"), and then, at 1300 ° C in a reducing gas atmosphere. The left and right temperatures are fired. Finally, the external electrode is plated on the outside of the laminate. Get the MLCC on it.

In recent years, with the miniaturization and high performance of electronic equipment, MLCC has also been developed toward miniaturization and large capacity, and thin film formation of internal electrode layers is required. A metal fine powder for internal electrodes having a particle diameter of several tens nm to several hundreds nm. In the past, although precious metals such as palladium were used, the use of cheaper nickel such as nickel was increasing.

In the internal electrode of the MLCC, nickel powder is used, and a spherical nickel fine powder having an average particle diameter of 1.0 μm or less and high crystallinity can be synthesized with excellent productivity by, for example, a gas phase reaction method in which nickel chloride gas is brought into contact with hydrogen gas.

On the other hand, in order to thin the internal electrode, when the nickel powder is reduced in particle diameter, the nickel powder tends to aggregate in the liquid phase and in the gas phase due to an increase in the specific surface area of the nickel powder. When the nickel powder aggregates in the internal electrode paste, the capacity of the MLCC is lowered due to short-circuiting and delamination, which is a problem. Here, the short circuit refers to a structural defect in which the internal electrode layer loses flatness due to coarse particles or agglomerated nickel powder, and the uneven portion of the internal electrode layer penetrates the dielectric layer. Further, the delamination is caused by insufficient aggregation of the nickel powder by the agglomerated nickel powder, and the heat shrinkage behavior of the internal electrode layer and the dielectric layer is inconsistent, and the internal electrode layer and the dielectric are formed at the time of firing. Structural defects in which the body layer is peeled off. Therefore, in order to produce an MLCC having a small structural defect and a small/large capacity, nickel powder having good dispersibility in the internal electrode paste is required.

In order to improve the dispersibility of the nickel powder in the internal electrode paste, it is important to improve the wettability to the low polarity solvent. The following formula 1 is called the formula of WASHBURN and is a theoretical formula for the dispersion speed of particles into a solvent. Wherein v is a dispersion speed, η is a solvent viscosity, L is a pore length, r is a pore radius, γ _L is a surface tension of a solvent, θ is a contact angle, and ΔP is a dispersion pressure. As shown in this formula, the dispersion speed is determined by the sum of wettability (item 1) and dispersion pressure (item 2). That is, on the other hand, it is shown that if each particle and the solvent are applied with a high dispersion pressure, it can be dispersed, and on the other hand, if the wettability is high, even if the dispersion pressure becomes low, it can be dispersed.

Regarding the synthesis of nickel nanoparticles having an average particle diameter of primary particles of 1 μm or less and excellent dispersibility in a paste, for example, a method for producing nickel nanoparticles having a nickel carboxylate and a primary amine is proposed. a first step of the mixture; heating the mixture to obtain a second step of producing a mis-formed reaction solution of nickel complex; and irradiating the mis-action reaction liquid with microwaves and heating at a temperature of 200 ° C or higher to obtain nickel nanoparticles In the third step of the particle slurry, in the third step, heating is performed in a state in which a polyvalent carboxylic acid having a valence of 3 or more is present (for example, refer to JP-A-2011-214143 publication) ).

However, the nickel powder treated with the polycarboxylic acid as exemplified in the above literature improves the dispersibility in a low-polarity solvent, but does not mention at all about the wettability to a low-polarity solvent. Therefore, in the case where a weak dispersion treatment is applied, it is not clear whether or not there is excellent dispersibility.

Further, the nickel powder treated with the polyvalent carboxylic acid mentioned in the above document has a high carbon content. As the metal powder used for the internal electrode of the MLCC, it is necessary to remove the organic matter in the step of removing the binder, and to use the metal powder having a high carbon content and containing an organic substance having a high decomposition temperature, the removal of the binder can not completely remove the organic matter, and the subsequent removal is performed. In the burning step, the residual The organic matter will become a gas, and as a result, it may become a cause of structural defects.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a nickel powder and a nickel paste which are suitable as an internal electrode material of MLCC and which have excellent adhesiveness and improved wettability and dispersibility for a low-polarity solvent.

The nickel powder of the present invention has a spherical nickel powder having a number average particle diameter D of 1 μm or less, and has a sodium concentration of 0.001% by mass or less, a calcium concentration of 0.001% by mass or less, and a carbon concentration of 0.05% by mass or more. 2.0% by mass or less, when measured by a Fourier transform infrared spectrophotometer, it has an absorption peak of infrared absorption at 1600 cm ^-1 , and when it is mixed with dihydroterpene alcohol acetate to form a paste, it exhibits metallic luster, and in an inert environment, 300 When the heat treatment is performed at ° C, the carbon concentration reduction rate is 50% or more.

According to the nickel powder of the present invention, the impurities which are a problem in the production process of the MLCC are reduced, and the wettability and dispersibility to the low-polarity solvent can be improved. Therefore, when the conductive paste for MLCC is used, the aggregated particles can be suppressed. It is also preferable to remove the binder in the manufacturing step of the MLCC. Thereby, it is possible to contribute to the manufacture of MLCC with less short circuit and delamination.

Fig. 1 is an infrared absorption spectrum of nickel powders obtained in Examples 1 to 4 and Comparative Examples 1 to 3.

[Formation of the Invention]

[nickel powder]

The nickel powder of the present invention contains nickel powder produced by various production methods and nickel alloy powder containing nickel as a main component. Nickel alloy powder is an alloy powder obtained by adding chromium, niobium, boron, phosphorus, a rare earth element, or a noble metal element to nickel in order to impart oxidation resistance and the like.

The nickel powder of the present invention has a number average particle diameter of 1.0 μm or less. More preferably, the number average particle diameter is 0.4 μm or less. The lower limit of the number average particle diameter of the nickel powder of the present invention is not particularly limited, and is preferably 0.01 μm or more from the viewpoint of the production cost and use of the usual nickel powder.

Further, the ratio (d/D) of the number average particle diameter D of the nickel powder of the present invention to the crystallite diameter d is preferably 0.40 or more. The crystallite diameter d of the present invention is obtained by X-ray diffraction measurement of the (111) plane, and is calculated by Xie Le's formula (Formula 2). Where K is the Xerox constant, λ is the measured X-ray wavelength, β is the half value width, and θ is the diffraction angle. By having a high d/D value, there is good sinterability in the manufacturing step of the MLCC.

The number average particle diameter of the nickel powder of the present invention is a photograph of primary particles of nickel powder taken by a scanning electron microscope, and the particle size of 500 or more particles is measured from the photograph using the image analysis software, and the particle size distribution of the obtained nickel powder is obtained. Calculate the number average particle size. At this time, the particle diameter is the diameter of the smallest circle surrounding the particles.

The nickel powder of the present invention has a spherical shape. The spherical shape of the present invention means that the aspect ratio is 1.2 or less and the circularity coefficient is 0.675 or more. The aspect ratio is the ratio of the major axis to the minor axis of the smallest ellipse surrounding the particle. The roundness coefficient is such that the area of the smallest ellipse surrounding the particle is S and the circumference is set to L. 4πS/(L×L) to define the value. When the shape of the nickel is spherical, the filling rate is increased and the flatness is improved during the internal electrode processing of the MLCC, and cracking and delamination can be suppressed.

The nickel powder of the present invention has a sodium concentration of 0.001% by mass or less and a calcium concentration of 0.001% by mass or less. Since sodium and calcium have problems such as reacting with a dielectric material of MLCC and lowering the capacity of MLCC, it is desirable not to contain it. The presence or absence of sodium and calcium can be confirmed by, for example, inductively coupled plasma mass analysis.

The nickel powder of the present invention has an absorption peak of infrared light absorption at 1600 cm ^-1 when measured by a Fourier transform infrared spectrophotometer, and the carbon concentration is 0.05% by mass or more and 2.0% by mass or less. Within this range, nickel powder excellent in debonding property and wettability to a low-polarity solvent can be obtained. More preferably, the carbon concentration is 0.1% by mass or more and 1.0% by mass or less, and more preferably 0.2% by mass or more and 0.8% by mass or less.

The nickel powder having an absorption peak of infrared absorption at 1600 cm ^-1 when measured by a Fourier transform infrared spectrophotometer can be achieved by coating the surface of the nickel powder with a carboxylic acid.

The excellent binder removal property in the present invention means that the carbon concentration reduction rate at the time of heat treatment at 300 ° C in an inert atmosphere is 50% or more. Specifically, about 2 g of the sample was placed on an alumina plate, and placed in a graphite tube type gas environment electric furnace (SUPERYAMA Co., Ltd., SUPER BURN SLT2035D), and argon gas was circulated in the furnace at 1.0 L/min. Heat treatment at a temperature of 2 ° C / min, a maximum temperature of 300 ° C, and a holding time of 1 h at the highest temperature, and a reduction rate of carbon concentration before and after heat treatment ((1 - carbon concentration before heat treatment / after heat treatment) The carbon concentration) × 100%) is 50% or more.

Further, in the present invention, when it is kneaded with dihydroterpene alcohol acetate to give a metallic luster, it is an index which has excellent wettability to a low-polarity solvent. The low-polarity solvent means a solvent having an HLB of 5 or less, and examples thereof include hexane, benzene, toluene, terpineol, dihydroterpineol, and dihydroterpineol acetate.

In the method of evaluating the wettability of the low-polarity solvent, specifically, 1 g of the sample was applied to a glass plate, and dihydroterpineol acetate (manufactured by NIPPON TERPENE CHEMICALS Inc., purity 95) was dropped by a dropper. %, HLB = 4.4), and thoroughly kneaded with a palette knife to obtain the amount of dihydroterpineol acetate required to be in a paste form, and the obtained paste was spread with a palette knife. Observe the surface. The higher the wettability of the nickel powder to the low-polarity solvent, the less the amount of dihydroterpineol acetate required to be in a paste form, and the resulting paste exhibits a metallic luster. The amount of dihydroterpineol acetate to be added to the paste was 10 drops or less and exhibited metallic luster, that is, it was evaluated to have excellent wettability to a low-polarity solvent.

A preferred aspect of the nickel powder of the present invention is coated with a monocarboxylic acid having a hydrophilic-lipophilic balance (HLB) of 11 or less and a decomposition temperature of 300 ° C or less. In the nickel powder of the present invention, from the viewpoint of excellent binder removal property, excellent wettability to a low-polarity solvent, and excellent dispersibility, it is preferred that the carboxylic acid is 1 or more HLB. 11 or less, more preferably one or more carboxylic acids having an HLB of 3.5 or more and 11 or less. The molecular structure of the monocarboxylic acid may be either linear or cyclic. The monocarboxylic acid having an HLB of 11 or less may, for example, be at least one selected from the group consisting of Metacarboxylic acid: butyric acid (HLB=10.2), valeric acid (HLB=8.8), hexanoic acid (HLB=7.7), heptanoic acid (HLB=6.9), octanoic acid (HLB=6.2), tannic acid (HLB=5.7) , citric acid (HLB = 5.2), benzoic acid (HLB = 7.4), p-toluic acid (HLB = 6.6). When considering workability, citric acid and benzoic acid are preferred.

Further, the nickel powder of the present invention may contain 0.01% by mass to 5.0% by mass of sulfur. By allowing the sulfur concentration to be in this range, the sintering behavior can be improved. The sulfur concentration in the nickel powder is preferably from 0.01% by mass to 1.0% by mass, more preferably from 0.02% by mass to 0.2% by mass. Particularly preferred is the surface of nickel which is coated with sulfur or a sulfate group.

[Method of manufacturing nickel powder]

The nickel powder of the present invention can be produced by a known method such as a vapor phase method or a liquid phase method. In particular, it can be easily controlled by a vapor phase reduction method in which nickel chloride gas is brought into contact with a reducing gas to produce a nickel powder, or a spray pyrolysis method in which a thermally decomposable nickel compound is sprayed and thermally decomposed. The particle diameter of the metal fine powder is more preferable from the viewpoint of efficiently producing spherical particles. In particular, a gas phase reduction method in which nickel chloride gas is brought into contact with a reducing gas is preferred from the viewpoint of finely controlling the particle diameter of the nickel powder generated and further preventing the generation of coarse particles.

In the vapor phase reduction method, a gas of vaporized nickel chloride is allowed to react with a reducing gas such as hydrogen. In this case, solid nickel chloride may also be heated to evaporate to produce nickel chloride gas. However, considering the oxidation of nickel chloride or preventing moisture absorption and energy efficiency, the chlorine gas is brought into contact with the metal nickel and the nickel chloride gas is continuously generated, and the nickel chloride gas is directly supplied to the reduction step, and then Connected with reducing gas In the touch, it is advantageous to continuously reduce the nickel chloride gas to produce a nickel fine powder. The vapor phase reduction method can obtain a nickel powder having a ratio (d/D) of a number average particle diameter D to a crystallite diameter d of 0.40 or more in a high yield.

In the case of a method for producing an alloy powder containing nickel as a main component, examples of the metal chloride gas other than the nickel chloride gas include ruthenium (III) chloride gas and ruthenium (IV) tetrachloride gas. , formoxane gas, copper (I) gas, copper (II) chloride gas, silver chloride gas, molybdenum(III) chloride gas, molybdenum chloride (V) gas, iron (II) chloride gas, Iron (III) chloride gas, chromium (III) chloride gas, chromium (VI) chloride gas, tungsten (II) chloride gas, tungsten (III) chloride gas, tungsten (IV) chloride gas, chlorination Tungsten (V) gas, tungsten (VI) chloride gas, cerium (III) chloride gas, cerium (V) chloride gas, cobalt chloride gas, cerium (III) chloride gas, cerium (IV) chloride gas , ruthenium chloride (V) gas, diborane gas, phosphine gas, and the like, and a mixed gas thereof.

Examples of the reducing gas include hydrogen gas, hydrogen sulfide gas, ammonia gas, carbon monoxide gas, methane gas, and a mixed gas thereof. Particularly preferred are hydrogen, hydrogen sulfide gas, ammonia gas, and a mixture thereof.

In the production process of the nickel powder by the vapor phase reduction reaction, nickel atoms are generated at the moment when the nickel chloride gas comes into contact with the reducing gas, and the nickel atoms collide and aggregate, and the nickel particles are generated and grown. Then, the particle size of the produced nickel powder is determined in accordance with the conditions of the partial pressure of the nickel chloride gas in the reduction step and the temperature. According to the method for producing a nickel powder as described above, the amount of the nickel chloride gas supplied to the reduction step can be adjusted by controlling the amount of chlorine gas supplied in accordance with the amount of chlorine gas supplied. It can control the particle size of the produced nickel powder.

In addition, since nickel chloride gas is produced by the reaction of chlorine gas with a metal, unlike the method of generating nickel chloride gas by heating and evaporation of solid nickel chloride, not only the use of the carrier gas but also the production conditions can be reduced. A carrier gas is used. Therefore, in the gas phase reduction reaction, the production cost can be reduced by reducing the amount of the carrier gas used and reducing the heating energy associated therewith.

Further, by mixing an inert gas into the nickel chloride gas generated in the chlorination step, the partial pressure of the nickel chloride gas in the reduction step can be controlled. By controlling the supply amount of chlorine gas or the branching of the nickel chloride gas supplied to the reduction step, the particle size of the nickel powder can be controlled, the fluctuation of the particle diameter can be suppressed, and the particle diameter can be arbitrarily set.

For example, the nickel chloride of the starting material is a metallic nickel such as a granular, massive or plate-like material having a purity of 99.5% or more, which is first reacted with chlorine gas to generate nickel chloride gas. The temperature at this time is 800 ° C or more in order to sufficiently carry out the reaction, and the melting point of nickel is 1453 ° C or less. Considering the reaction speed and the durability of the chlorination furnace, it is practically preferably in the range of 900 ° C to 1100 ° C.

Next, this nickel chloride gas is directly supplied to a reduction step, and is brought into contact with a reducing gas such as hydrogen. At this time, the partial pressure of the nickel chloride gas can be controlled by diluting the nickel chloride gas with an inert gas such as argon or nitrogen. By controlling the partial pressure of the nickel chloride gas, it is possible to control the quality such as the particle size distribution of the metal powder generated in the reduction portion. The quality of the metal powder produced thereby can be arbitrarily set, and the quality can be stabilized. The temperature of the reduction reaction may be at least the temperature sufficient to complete the reaction, preferably less than the melting point of nickel, and 900 ° C in consideration of economy. 1100 ° C is practical.

After the nickel powder thus subjected to the reduction reaction is produced, the produced nickel powder is cooled. At the time of cooling, in order to prevent secondary particles from being generated by aggregation of primary particles of nickel generated, and to obtain nickel powder having a desired particle diameter, it is desirable to terminate the reduction reaction at 1000 ° C by blowing an inert gas such as nitrogen. Rapidly cool to about 400~800 °C. Then, the produced nickel powder is separated and recovered, for example, by a bag filter or the like.

In the method for producing nickel powder by the spray pyrolysis method, a thermally decomposable nickel compound is used as a raw material. Specifically, it may contain one or more of a nitrate, a sulfate, a basic nitrate, a basic sulfate, a chloride, an ammonium complex, a phosphate, a carboxylate, and an alkoxide. A solution containing the nickel compound is sprayed to form fine droplets. As the solvent at this time, water, ethanol, acetone, diethyl ether or the like is used. The spraying method is carried out by a spraying method such as an ultrasonic wave or a double jet nozzle. The fine droplets are produced in this manner, and then heated at a high temperature to thermally decompose the metal compound to produce nickel powder. The heating temperature at this time is preferably higher than the temperature at which the specific nickel compound used is thermally decomposed, and is preferably near the melting point of the metal.

In the method for producing a nickel powder by a liquid phase method, a nickel aqueous solution containing nickel sulfate, nickel chloride or a nickel complex is added to an alkali metal hydroxide such as sodium hydroxide to cause contact with nickel. The hydroxide is then reduced with a reducing agent such as hydrazine to obtain a metallic nickel powder. The metal nickel powder thus produced is pulverized as needed in order to obtain uniform particles.

The nickel powder obtained by the above method is preferably dispersed in a liquid phase for washing to remove residual raw materials. For example, will The nickel powder obtained by the above method is suspended in an aqueous solution of carbonic acid under specific conditions controlled by pH and temperature. By treating with an aqueous solution of carbonic acid, impurities such as chlorine adhering to the surface of the nickel powder are sufficiently removed, and the hydroxide and the particles present on the surface of the nickel powder are separated from each other by friction or the like. The formed fine particles are removed, and a uniform nickel oxide film can be formed on the surface. As a treatment method using an aqueous solution of carbonic acid, a method of mixing nickel powder with an aqueous solution of carbonic acid may be used, or carbon dioxide may be blown into a water slurry in which nickel powder is first washed with pure water, or an aqueous solution of carbonic acid may be added to nickel powder. It is treated with water slurry which has been washed first with pure water.

The method of containing sulfur in the nickel powder of the present invention is not particularly limited, and for example, the following method can be employed.

(1) A method of adding a sulfur-containing gas to the above reduction reaction

(2) Method for contacting nickel powder with sulfur-containing gas

(3) Method for dry mixing nickel powder with solid sulfur compound

(4) A method of adding a sulfur-containing compound solution to a slurry obtained by dispersing nickel powder in a liquid phase

(5) A method of blowing a sulfur-containing gas into a slurry obtained by dispersing nickel powder in a liquid phase

In particular, from the viewpoint of precisely controlling the sulfur content and the viewpoint of uniformly adding sulfur, the methods (1) and (4) are preferred. The sulfur-containing gas used in the methods (1), (2), and (5) is not particularly limited, and may be sulfur vapor, sulfur dioxide gas, hydrogen sulfide gas, or the like, and is a gas gas at a temperature of the reduction step. Use as it is or diluted. Among them, from the viewpoint of easily controlling the flow rate at a normal temperature as a gas, it is possible to mix impurities. From the standpoint of low energy, sulfur dioxide gas and hydrogen sulfide gas are advantageous.

After the aforementioned washing step and the vulcanization step, the nickel powder slurry is dried. The drying method is not particularly limited, and a known method can be used. Specific examples include air drying in a dry state in contact with a high-temperature gas, heat drying, vacuum drying, and the like. Among them, the air flow drying is preferable because the sulfur-containing layer is not damaged by collision of particles.

Next, the obtained nickel powder is immersed in a solution containing the above-mentioned monocarboxylic acid having a hydrophilic-lipophilic balance (HLB) of 11 or less, and then stirred.

A solvent containing a solution of a monocarboxylic acid having a hydrophilic-lipophilic balance (HLB) of 11 or less can be selected from a solvent selected from at least one of pure water, ethanol or industrial alcohol or a mixture thereof. In particular, from the viewpoint of easiness of dispersion of nickel powder and economy, it is desirable to use pure water. The monocarboxylic acid having a hydrophilic-lipophilic balance (HLB) of 11 or less is the same as the above monocarboxylic acid.

In this case, the amount of the above monocarboxylic acid dissolved in the solvent depends on the particle diameter of the nickel powder to be added and the desired dispersibility, and in the case of the nickel powder having a number average particle diameter of about 100 nm, it is preferred. It is 0.1 to 10% by mass, preferably 0.2 to 2% by mass, based on the nickel powder. This range is preferable because the effect of improving the wettability and dispersibility of the low-polarity solvent of the nickel powder and the reduction of the carbon concentration after drying can be sufficiently obtained.

Further, the amount of the solvent is preferably adjusted to a concentration of the nickel powder of 20 to 50% by mass from the viewpoint of easiness of dispersion and economy.

When stirring, it is preferred to use a wet disperser to make the solvent The nickel particles are sufficiently dispersed, and stirred at a temperature of more than 0 ° C and less than 70 ° C for 1 minute to 10 hours, preferably 30 minutes to 1 hour. Then, the nickel powder slurry is dried to obtain the nickel powder of the present invention.

The drying method is the same as the drying step after the washing step or after the washing step and the vulcanization step. The drying step is not particularly limited, and a known method can be used. Specific examples include air drying in a dry state in contact with a high-temperature gas, heat drying, vacuum drying, and the like. Among them, the airflow drying is preferred because the sulfur-containing layer is not damaged by collision of particles. Further, a pulverization treatment by a jet mill may be added as needed.

Then, the nickel powder of the present invention can be, for example, a solvent such as terpineol, an organic binder such as ethyl cellulose, a dispersant, and an unfired powder of a ceramic to be coated, and then a three-roller. A well-known method of mixing is to easily manufacture a high-performance nickel paste. Examples of the solvent include ethanol, acetone, propanol, ethyl acetate, butyl acetate, diethyl ether, petroleum ether, mineral spirits, and other paraffinic hydrocarbon solvents, or butyl carbitol, terpineol, and Acetic acid such as hydroquinone alcohol, butyl carbitol acetate, dihydroterpineol acetate, dihydrocarvyl acetate, celery acetate, rosin acetate, and acetal acetate An ester-based or propionate-based solvent such as dihydroterpineol propionate, dihydrocarvyl propionate or isodecyl propionate, or celecoxib such as celecoxib or dingsailusu. Aromatic, diethyl phthalate, etc. Further, as the organic binder, a resin binder is preferable, and examples thereof include ethyl cellulose, polyvinyl acetal, acrylic resin, and acid alcohol resin.

As the dispersing agent, a well-known appropriate agent can be used, for example. A vinyl polymer, a polyvalent carboxylic acid amine salt, a polyvalent carboxylic acid system, or the like can be used.

[Examples]

The present invention will be further illustrated by the following examples and comparative examples, but this is merely illustrative and not restrictive.

The sample preparation conditions of the examples and the comparative examples are summarized in Table 1.

The evaluation method is as follows.

(1) Primary particle size

The sample was observed by a field emission scanning electron microscope (S-4700, manufactured by Hitachi High-Technologies Co., Ltd.), and a secondary electron image in which the particles occupied the entire surface of the field of view was imaged at an appropriate magnification. Then, image analysis was performed on 500 or more particles, and the particle size distribution was calculated from the diameter of the smallest circle surrounding the particles. Further, the shape of the particles was evaluated from the average aspect ratio and the average circularity coefficient.

(2) crystallite diameter

X-ray diffraction measuring device (manufactured by PANalytycal, X'pert-MPD/PRO-MPD divergence slit 0.5°, no light-receiving slit), using CuKα line (wavelength λ=1.5418Å), tube voltage 45kV, tube current 40 mA, step angle 0.02 °, scanning speed 0.04 ° / s, the diffraction angle 2θ = 43.5 ~ 45.5 ° X-ray diffraction measurements were taken. The peak position θ corresponding to the (111 plane) near 44.5° was analyzed by the attached analysis software (X'pert High Score) and the half value width B was measured. The Xiele constant K=0.9 was calculated using Xie Le's formula. diameter.

(3) Impurity concentration

After dissolving 0.1 g of the sample with hydrofluoric acid and nitric acid, a solution of the internal standard element was added to carry out constant volume. Then, it was introduced into an inductively coupled plasma mass spectrometer (SPQ9700, manufactured by SII Nanotechnology Inc.) to quantify the sodium concentration and the calcium concentration.

(4) Adsorption state of organic matter

The infrared absorption spectrum was measured by a Fourier transform infrared spectrophotometer (Nicolet 6700, manufactured by Thermo Fisher Scientific Inc.), and the baseline was analyzed with an attached analysis software to analyze the adsorption state of the organic substance on the surface of the nickel powder.

(5) Carbon concentration

0.5 g of the sample was placed in an alumina crucible and burned in a high-frequency furnace oxygen stream. At this time, the carbon dioxide generated from the carbon in the sample was analyzed by a carbon/sulfur analyzer (manufactured by Horiba, Ltd., EMIA-520SP) to calculate the carbon concentration.

(6) Remove the binder

About 2 g of the sample was placed on an alumina plate, and placed in a graphite tube type gas environment electric furnace (SUPERYAMA Co., Ltd., SUPER BURN SLT2035D), and argon gas was circulated in the furnace at 1.0 L/min, and the temperature was raised and lowered. The carbon concentration was measured by the above method at a heat treatment of 2 ° C / min, a maximum temperature of 300 ° C, and a holding time of the highest temperature for 1 h. By comparison The binder concentration was evaluated to be higher than the carbon concentration before and after the heat treatment. The carbon concentration reduction rate by the heat treatment ((1-carbon concentration before heat treatment/carbon concentration after heat treatment) × 100%) is preferably (○) if it is 50% or more, and is not evaluated if it is less than 50%. Good (×).

(7) Wettability to low polarity solvents

1 g of the sample was placed on a glass plate, and dihydroterpineol acetate (manufactured by NIPPON TERPENE CHEMICALS Inc., purity: 95%, HLB = 4.4) was dropped by a dropper, and kneaded thoroughly with a palette knife. At this time, the amount of dihydroterpineol acetate required to be in a paste form was determined. Then, the obtained paste was spread with a palette knife to observe the surface. The higher the wettability of the nickel powder to the low-polarity solvent, the less the amount of dihydroterpineol acetate required to form a paste, and the resulting paste exhibits metallic luster. In the case where the amount of the dihydroterpineol acetate to be in the form of a paste is 10 drops or less and the metallic luster is present, it is evaluated as good (○), and the dihydroterpineol acetic acid is formed into a paste. When the amount of the drop of the ester exceeded 10 drops and the metallic luster was not observed, it was evaluated as not good (x).

(8) Dispersion in paste

0.2 g of the sample was weighed in a beaker, and 20 ml of dihydroterpineol acetate was added thereto, and then subjected to dispersion treatment for 5 minutes in an ultrasonic cleaning tank (USK-1A, manufactured by AS ONE Co., Ltd.). On the other hand, a flow tank of a laser diffraction type wet particle size distribution measuring machine (BE-MAN, manufactured by BECKMAN COULTER Co., Ltd.) was filled with dihydroterpineol acetate. After the dispersion treatment of the sample, the sample was taken in an appropriate amount in a dropper, and introduced into a laser diffraction type particle size distribution measuring machine to measure the particle size distribution. The particle size distribution thus obtained showed a grain ratio as observed by an electron microscope. The particle size distribution of the sub-particles is also a large value, but this is to determine the particle size distribution of the aggregates in which the particles are agglomerated in the dihydroterpene alcohol acetate. The particle size distributions D25, D50, and D75 mean the particle diameters obtained by accumulating the volume frequency of 25%, 50%, and 75%, respectively. The better the dispersibility of the sample in the paste, the smaller the particle size of the aggregate becomes. When D75 is 2.30 μm or less, the evaluation is good (○), and when it exceeds 2.30, it is evaluated as not good (×).

(Example 1)

After the gas phase reaction method in which nickel chloride and hydrogen are reacted, it is washed in pure water and an aqueous solution of carbonic acid, dried, and pulverized to prepare nickel powder. The nickel powder was evaluated by an electron microscope, and as a result, it was confirmed that the number average particle diameter D was 110 nm, the average aspect ratio was 0.85, and the average circularity coefficient was 1.09. Further, from the results of the X-ray diffraction measurement, the crystallite diameter d was 54.7 nm, and the ratio d/D of the number average particle diameter to the crystallite diameter was 0.50. The impurity concentration is such that the sodium concentration is less than 0.001% by mass and the calcium concentration is less than 0.001% by mass.

The benzoic acid (manufactured by Kanto Chemical Co., Ltd., special grade, HLB=7.4) was weighed in a flask so that the concentration of the nickel powder was 0.25 mass%, and pure water was added to the above nickel powder to a stirrer at 100 rpm x 30 min. After stirring, it was dissolved and adjusted to a nickel powder dispersion. Then, while allowing nitrogen gas to flow through the gap of the flask at about 100 ml/min, the bottom of the flask was heated to 100 ° C in an oil bath to volatilize the water. After cooling to room temperature, nickel powder was recovered and sieved through a 250 μm nylon mesh as a sample.

The obtained sample was evaluated for the adsorption state of the organic substance, the carbon concentration/debinding agent property, the wettability to the low-polarity solvent, and the dispersibility in the paste. The analysis results of the adsorption state of organic substances are shown in Fig. 1, carbon concentration The evaluation results of the removal of the binder property, the wettability to the low-polarity solvent, and the dispersibility in the paste are shown in Table 2.

(Example 2)

A sample was prepared and evaluated in the same manner as in Example 1 except that the amount of benzoic acid was changed to 0.5% by mass. The analysis results of the adsorption state of the organic substance are shown in Fig. 1, and the results of evaluation of the carbon concentration, the binder removal property, the wettability to the low-polarity solvent, and the dispersibility in the paste are shown in Table 2.

(Example 3)

A sample was prepared and evaluated in the same manner as in Example 1 except that the amount of benzoic acid was changed to 1% by mass. The analysis results of the adsorption state of the organic substance are shown in Fig. 1, and the results of evaluation of the carbon concentration, the binder removal property, the wettability to the low-polarity solvent, and the dispersibility in the paste are shown in Table 2.

(Example 4)

In addition to the change of benzoic acid to n-decanoic acid (manufactured by Kanto Chemical Co., Ltd., deer grade 1, HLB = 5.2) 1% by mass, pure water was changed to ethanol, and the heating temperature of the oil bath was changed to 80 ° C, and Example 1 The sample was prepared in the same manner and evaluated. The analysis results of the adsorption state of the organic substance are shown in Fig. 1, and the results of evaluation of the carbon concentration, the binder removal property, the wettability to the low-polarity solvent, and the dispersibility in the paste are shown in Table 2.

(Comparative Example 1)

A sample was prepared and evaluated in the same manner as in Example 1 except that the benzoic acid of Example 1 was changed to 1% by mass of acetic acid (manufactured by Kanto Chemical Co., Ltd., special grade, HLB = 15.0). The analysis results of the adsorption state of the organic substance are shown in Fig. 1, and the results of evaluation of the carbon concentration, the binder removal property, the wettability to the low-polarity solvent, and the dispersibility in the paste are shown in Table 2.

(Comparative Example 2)

A sample was prepared and evaluated in the same manner as in Example 4 except that the n-decanoic acid of Example 4 was changed to a commercially available polycarboxylic acid-based dispersant (manufactured by Croda Japan KK, Hypermer KD-9, HLB<9). The analysis results of the adsorption state of the organic substance are shown in Fig. 1, and the results of evaluation of the carbon concentration, the binder removal property, the wettability to the low-polarity solvent, and the dispersibility in the paste are shown in Table 2.

(Comparative Example 3)

The same evaluation as in Example 1 was carried out for the nickel powder to which the organic substance prepared in Example 1 was not added. The analysis results of the adsorption state of the organic substance are shown in Fig. 1, and the results of evaluation of the carbon concentration, the binder removal property, the wettability to the low-polarity solvent, and the dispersibility in the paste are shown in Table 2.

As a result of measuring the infrared absorption spectrum, Examples 1 to 4 and Comparative Examples 1 and 2 in which organic substances were added showed that the infrared absorption spectrum was changed as compared with Comparative Example 3 in which no organic substance was added.

In Examples 1 to 3, there are in the vicinity of 1600cm ^-1 attributable to the C = O of carboxylic acid anions of the asymmetric stretching absorption peak attributable to carboxylate anion has the symmetric stretching of the C = O absorption peak near 1400cm ^-1, Further, in the vicinity of 750 and 700 cm ^-1 , there is an absorption peak of C=C stretching vibration attributed to the aromatic 1 substituent, and it is understood that benzoic acid is adsorbed on nickel.

In Example 4, there are in the vicinity of 1600cm ^-1 attributable to the C = O of carboxylic acid anions of the asymmetric stretching absorption peak attributable to carboxylate anion has the symmetric stretching of the C = O absorption peak near 1400cm ^-1, 2950 There is an absorption peak derived from the stretching vibration of the hydrocarbon chain -CH ₂ - in the vicinity of 2850 cm ^-1 , and it is understood that n-decanoic acid is adsorbed on nickel.

In Comparative Example 1, there are in the vicinity of 1600cm ^-1 of the absorption peak attributable to the antisymmetric stretching C = O of carboxylate anion, there is attributable to carboxylate anion, and the symmetric stretching of the C = O absorption peak near 1400cm ^-1, apparent Acetic acid is adsorbed on nickel.

To 2, 1700 to have assigned to the C = O stretching vibration of carboxylic acids, carboxylic acid have attributed to CO stretching vibration in the vicinity of 1200cm ^-1 Example Comparative near 1750cm ^-1, and at 2950cm ^-1, 2850cm ^-1 nearby The absorption peak of the stretching vibration attributed to the hydrocarbon chain -CH ₂ - was observed to be adsorbed on the nickel by the organic substance having a carboxyl group.

In Comparative Example 3, it was not observed in the Examples can be seen near 1400cm ^-1 attributable to a carboxylate anion of the symmetric stretching of the C = O absorption peaks and the vicinity of 1600cm ^-1 attributable to a carboxylic acid anions of C = O opposes the absorption peak of stretching.

Further, as a result of analysis of the carbon concentration, it was found that Examples 1 to 4 and Comparative Examples 1 and 3 had a lower carbon concentration than Comparative Example 2 in which a commercially available dispersant was added. Further, from the viewpoint of the reduction rate of the carbon concentration by the heat treatment, it is understood that Examples 1 to 4 and Comparative Example 1 are more preferable in the removal of the binder than Comparative Example 2 using a commercially available dispersant. In Examples 1 to 4 and Comparative Example 1, since the molecular weight and decomposition temperature of the added organic substance were low, it was considered that the removal of the binder property was better.

In the evaluation results of the wettability to the low-polarity solvent, Examples 1 to 4 in which the organic substance having a low HLB was added and Comparative Example 1 were compared with Comparative Example 1 in which acetic acid having a high HLB was added and Comparative Example 3 in which no organic substance was added. In Example 2, the amount of the solvent required for the paste to be formed was small, and since the obtained paste exhibited metallic luster, the wettability to the low-polarity solvent was further improved. It is considered that the wettability is improved by coating the nickel powder with an organic substance having a low HLB.

In the evaluation results of the dispersibility in the paste, in Comparative Example 1 in which acetic acid having a high HLB was added, and Comparative Example 3 in which no organic substance was added, Examples 1 to 4 and Comparative Example 2 in which an organic substance having a low HLB was added were added. The aggregate has a small particle size, and since D75 is less than 2.30 μm, the dispersibility in the paste is better. This is considered to be because, in Examples 1 to 4 and Comparative Example 2, since the wettability to the low-polarity solvent was improved, it was easy to disperse when a certain dispersing force was applied.

In Examples 1 to 4, since the organic substance to be added is a monocarboxylic acid having a decomposition temperature and a low molecular weight, the removal of the binder is more preferable. And because the added organic matter has a low HLB, it is wettable to low polarity solvents. Improved, the dispersion in the paste is also improved.

In Comparative Example 1, since the added organic substance is a monocarboxylic acid having a decomposition temperature and a low molecular weight, the removal of the binder is more preferable. However, since the HLB of the added organic substance is high, the wettability to the low-polarity solvent is insufficient, and as a result, the dispersibility in the paste is also insufficient.

In Comparative Example 2, since the added organic matter had a low HLB, the wettability to the low-polarity solvent and the dispersibility in the paste were improved. However, since the added organic substance is a polycarboxylic acid having a decomposition temperature and a high molecular weight, the removal of the binder property is inferior to the present invention.

In Comparative Example 3, since the carbon concentration was low because no organic matter was added, since the surface of the nickel powder was covered with hydrophilic nickel oxide, the wettability to the low-polarity solvent was low, and the dispersibility in the paste was poor.

According to the present invention, it is possible to provide a low decomposition temperature and a carbon concentration of the added organic substance, which is advantageous for removing the binder treatment, improving the wettability and dispersibility of the low-polarity solvent, and being suitable for the nickel powder and nickel produced by the MLCC. paste.

Claims (5)

A nickel powder which is a spherical nickel powder having a number average particle diameter D of primary particles of 1 μm or less, and has a sodium concentration of 0.001% by mass or less, a calcium concentration of 0.001% by mass or less, and a carbon concentration of 0.05% by mass or more. 2.0% by mass or less, when measured by a Fourier transform infrared spectrophotometer, it has an absorption peak of infrared absorption at 1600 cm ^-1 , and when it is kneaded with dihydroterpene alcohol acetate to give a paste, it exhibits metallic luster in an inert environment. When the heat treatment is performed at 300 ° C, the carbon concentration reduction rate is 50% or more. The nickel powder of claim 1 is coated with a monocarboxylic acid having a hydrophilic-lipophilic balance (HLB) of 11 or less and a decomposition temperature of 300 ° C or less. The nickel powder of claim 1 or 2 has a ratio (d/D) of the number average particle diameter D to the crystallite diameter d of 0.40 or more, wherein the crystallite diameter d is an X-ray diffraction measurement of the (111) plane. Calculated using Xie Le's formula (Formula 2), K is the Xie Le constant, λ is the X-ray wavelength, β is the half value width, and θ is the diffraction angle. The nickel powder according to any one of claims 1 to 3, which has an aspect ratio of 1.2 or less and a circularity coefficient of 0.675 or more. A nickel paste characterized by containing the nickel powder of any one of claims 1 to 4.