JP2014029845A - Method for producing conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a conductive paste containing metal nickel fine particles in a highly dispersed state.SOLUTION: The method for producing a conductive paste comprises the steps of: A) preparing metal nickel fine particles coated with a primary amine; and B) mixing the metal nickel fine particles, an organic solvent, a nonaqueous polymer dispersant having a secondary or tertiary amino group, and an organic binder to obtain a conductive paste containing them. In the step B, at least part of the primary amine is substituted with the nonaqueous polymer dispersant on the surface of the metal nickel fine particles, thereby coating the metal nickel fine particles with the nonaqueous polymer dispersant.

Description

  The present invention relates to a method for producing a conductive paste, and more particularly to a method for producing a conductive paste that can be suitably used for forming an internal electrode of a multilayer ceramic capacitor (MLCC), for example.

  Since the metal fine particles have physical and chemical characteristics different from those of bulk metals, various materials such as electrode materials such as conductive pastes and transparent conductive films, high-density recording materials, catalyst materials, and ink-jet ink materials are used. It is used for industrial materials. In recent years, with the downsizing and thinning of electronic devices, fine metal particles have been made finer to about several tens to several hundreds of nanometers. For example, with the miniaturization of electronic devices, the multilayer ceramic capacitor electrodes are becoming thinner and more multilayered, and metal fine particles such as nickel fine particles are used as the material for the electrode layers.

  As described above, the metal fine particles used for industrial materials are required to have a particle diameter as small as, for example, less than 150 nm, a uniform particle diameter, and excellent dispersibility. However, with the progress of micronization, there is a problem that the metal microparticles easily aggregate due to an increase in surface energy.

  As a dispersant used for dispersing metal fine particles, for example, an anionic dispersant (for example, Patent Document 1) containing a fatty acid containing polyvalent carboxylic acid, an unsaturated fatty acid, or the like, or a polymeric ionic dispersant (for example, a patent) Document 2), phosphate ester compounds (for example, Patent Document 3) and the like are known. Although these dispersants can achieve a certain degree of dispersion effect, with the progress of micronization, it is not possible to sufficiently suppress aggregation of metal fine particles of about several tens to several hundreds of nanometers. It is. Accordingly, there is a demand for a dispersant exhibiting high dispersibility corresponding to further micronization of metal fine particles.

It is known that metal fine particles can be obtained by solid phase reaction or liquid phase reaction. Taking metallic nickel fine particles as an example, solid phase reactions include chemical vapor deposition of nickel chloride and thermal decomposition of nickel formate salt. In the liquid phase reaction, a nickel salt such as nickel chloride is directly reduced with a strong reducing agent such as sodium borohydride, a reducing agent such as hydrazine is added in the presence of NaOH, and the precursor [Ni (H ₂ NNH _{2 2} ] Method of thermal decomposition after forming SO ₄ · 2H ₂ O, Method of hydrothermal synthesis by putting nickel complex such as nickel chloride and nickel complex containing organic ligand into pressure vessel with solvent, nickel formate Examples thereof include a method of adding a reducing agent such as a primary amine to a salt or nickel acetate salt and irradiating with microwaves.

  Conventionally, when manufacturing a paste for internal electrodes such as a multilayer ceramic capacitor from metallic nickel fine particles obtained by solid phase reaction, metallic nickel fine particles are kneaded in a vehicle, and a cationic dispersant, nonionic at a predetermined timing. A nickel paste was prepared by adding and dispersing a dispersant such as a system dispersant or an amphoteric ion system. However, since this production method includes agglomerated nickel particles, coating with a dispersant is performed in the agglomerated state, and a sufficient dispersion effect cannot be obtained. In addition, a method has also been proposed in which nickel powder is pulverized using a jet mill or a high-pressure homogenizer, and an organic solvent and a saturated fatty acid are added and dispersed in the organic solvent (Patent Document 4). However, the present situation is that aggregation caused by micronization cannot be suppressed.

  Regarding the technique of the liquid phase reaction, a technique of obtaining metallic nickel fine particles by mixing a nickel precursor, an organic amine and a reducing agent and then heating is disclosed (Patent Document 5). According to this technique, it is said that the control of the size and shape of the metallic nickel fine particles is easy. The reason is not clear, but it is mentioned that the dispersibility in an organic solvent is excellent by coating metal nickel fine particles with an organic amine. However, when a strong reducing agent is used in this production method, it is difficult to control the reaction, and metallic nickel fine particles having a highly excellent dispersibility are not always suitably obtained. On the other hand, when a reducing agent having a weak reducing power is used, it is necessary to heat to high temperature in order to reduce nickel metal having a negative oxidation-reduction potential, and accordingly, reaction control is required.

  Also, a step of producing a mixed solution by adding a reducing agent, a dispersant, and a nickel salt to the polyol solution, a step of stirring and heating the mixed solution, and a step of reacting the mixed solution to produce metallic nickel fine particles And a method for producing metal nickel fine particles containing the same (Patent Document 6). In this case, although the reducing agent uses a strong reducing agent as described above, it is said that metallic nickel fine particles having a uniform particle size and excellent dispersibility can be obtained without agglomeration. As the dispersant, a cationic surfactant, an anionic surfactant, a cellulose derivative and the like are described.

JP 2001-066951 A JP 2010-135180 A JP 1998-092226 A JP 2006-183066 A JP 2010-037647 A JP 2009-024254 A

  For example, if the metal nickel fine particles used in forming the MLCC internal electrode have a large amount of agglomerated particles, the surface of the electrode layer is uneven, making it difficult to make the electrode layer thinner and multilayered. Cause deterioration of the mechanical characteristics. Therefore, as a conductive paste used for forming an electrode layer such as MLCC, it is required to use a paste in which most metallic nickel fine particles are in a highly dispersed state close to single particles.

  Accordingly, an object of the present invention is to provide a method for producing a conductive paste containing metallic nickel fine particles in a highly dispersed state.

The method for producing a conductive paste of the present invention includes the following steps A and B;
A) preparing metal nickel fine particles coated with a primary amine,
B) By mixing the metallic nickel fine particles, an organic solvent (hereinafter sometimes referred to as “first organic solvent”), a non-aqueous polymer dispersant having a secondary or tertiary amino group, and an organic binder. And a step of obtaining a conductive paste containing these. Here, in the step B, at least a part of the primary amine is replaced with the non-aqueous polymer dispersant on the surface of the metal nickel fine particles, and the metal nickel fine particles are coated with the non-aqueous polymer dispersant.

  In the method for producing a conductive paste of the present invention, the primary amine that coats the surface of the metal nickel fine particles may be an aliphatic primary amine.

  In the method for producing a conductive paste of the present invention, the metal nickel fine particles in the step A may be in a state of a slurry composition of the first organic solvent.

In the method for producing a conductive paste according to the present invention, the metal nickel fine particles coated with the primary amine are subjected to the following steps I and II;
I) a step of heating a mixture of nickel carboxylate and primary amine to a temperature in the range of 100 ° C. to 165 ° C. to obtain a complexing reaction solution;
II) A step of heating the complexing reaction solution to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexing reaction solution to obtain metallic nickel fine particles coated with a primary amine. ,
It may be prepared by a method comprising

  In the method for producing a conductive paste of the present invention, the metal nickel fine particles may be partially coated with elemental sulfur or a sulfur-containing compound in addition to the primary amine.

  The non-aqueous polymer dispersant having a secondary or tertiary amino group used in the method for producing a conductive paste of the present invention can be easily substituted with at least a part of a primary amine on the surface of metallic nickel fine particles. Since it has a strong aggregation inhibiting action on nickel fine particles, an excellent dispersion effect can be expected even with a small amount. Therefore, according to the method for producing a conductive paste of the present invention, for example, even for fine metallic nickel fine particles having a particle diameter of 150 nm or less, aggregation is suppressed and sharp metallic nickel fine particles with a single particle dispersed are obtained. A conductive paste containing can be obtained. When the conductive paste produced by the method of the present invention is used to form an internal electrode such as MLCC, for example, it is possible to prevent the occurrence of irregularities on the surface of the electrode layer (interface with the dielectric layer) and to flatten it, The electrode layer can be easily thinned and multilayered, and electrical reliability can be improved.

The manufacturing method of the conductive paste according to the present embodiment includes the following steps A and B;
A) preparing metal nickel fine particles coated with a primary amine,
B) A step of obtaining a conductive paste containing these by mixing the metal nickel fine particles, the first organic solvent, a non-aqueous polymer dispersant having a secondary or tertiary amino group, and an organic binder. I have. In Step B, at least a part of the primary amine is replaced with the non-aqueous polymer dispersant on the surface of the metal nickel fine particles, and the metal nickel fine particles are coated with the non-aqueous polymer dispersant.

Process A:
In this step, metallic nickel fine particles coated with a primary amine are prepared.

[Metallic nickel fine particles coated with primary amine]
The metal nickel fine particles coated with the primary amine can be produced by a known method. For example, a method of mixing metal nickel fine particles obtained by a gas phase method or a liquid phase method with a primary amine, a method of heating after mixing a nickel salt and a primary amine, which are precursors of metal nickel fine particles, and the like. Can be mentioned.

Since the gas phase method tends to be expensive to produce compared to the liquid phase method, it is advantageous to apply the liquid phase method. Among the liquid phase methods, as a method for easily producing metal nickel fine particles having a narrow particle size distribution in a short time, the following steps I and II;
I) a step of heating a mixture of nickel carboxylate and primary amine to a temperature in the range of 100 ° C. to 165 ° C. to obtain a complexing reaction solution;
II) A step of heating the complexing reaction solution to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexing reaction solution to obtain metallic nickel fine particles coated with a primary amine. Are preferably provided. Here, in the step II, it is preferable to obtain the metal nickel fine particles in the state of a slurry of an organic solvent (hereinafter sometimes referred to as “second organic solvent”).

  Heating of the complexing reaction solution by microwave irradiation enables uniform heating in the reaction solution and can directly apply energy 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) occur simultaneously in the entire solution. Narrow monodisperse particles can be easily produced in a short time. In particular, it is suitable for producing metallic nickel fine particles having an average particle diameter in the range of 20 to 150 nm.

The kind of nickel salt is not particularly limited, and examples thereof include nickel hydroxide, nickel chloride, nickel nitrate, nickel sulfate, nickel carbonate, nickel carboxylate, Ni (acac) ₂ (β-diketonato complex), and nickel stearate. However, among these, it is advantageous to use nickel carboxylate having a relatively low dissociation temperature (decomposition temperature) in the reduction process.

  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. Even if it is a primary organic amine that is solid at room temperature, there is no particular problem as long as it is liquid by heating 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 metal nickel fine particles produced, for example, by adjusting the length of the carbon chain. From the viewpoint of controlling the particle diameter of the metal nickel fine particles, the aliphatic primary amine is preferably selected from those having about 6 to 20 carbon atoms. The larger the number of carbons, the smaller the particle diameter of the obtained metal nickel fine particles. Examples of such amines include octylamine, trioctylamine, dioctylamine, hexadecylamine, dodecylamine, tetradecylamine, stearylamine, oleylamine, myristylamine, and laurylamine.

  The primary amine is preferably liquid at room temperature from the viewpoint of ease of processing operation in the washing step of separating the solid component of the metal nickel fine particles produced after the reduction reaction and the solvent or unreacted primary amine. Further, the primary amine is preferably one having a boiling point higher than the reduction temperature from the viewpoint of easy reaction control when the nickel complex is reduced to obtain metallic nickel fine particles. The amount of the primary amine is preferably 2 mol or more, more preferably 2.2 mol or more, relative to 1 mol of the nickel salt. When the amount of the primary amine is less than 2 mol, it is difficult to control the particle diameter of the obtained metal nickel fine particles, 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.

  The primary amine can cause the reaction to proceed as the second organic solvent, but in order to proceed the reaction in a homogeneous solution more efficiently, as the second organic solvent, an organic different from the primary amine can be used. A solvent may be newly added. 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.

  Although the complex formation reaction can proceed even at room temperature, in order to perform a sufficient and more efficient complex formation reaction, for example, the reaction is performed by heating within a range of 100 ° C. to 165 ° C. This heating can be appropriately set from the viewpoint of separating from the subsequent heat reduction process by microwave irradiation of the nickel complex (or nickel ions) and completing the complex formation reaction. 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.

  In step II, the complexing reaction solution obtained by the complexation reaction between the nickel salt and the primary amine is heated by microwave irradiation to reduce the nickel ions in the complexing reaction solution, thereby forming the second metal nickel fine particles. A slurry of the organic solvent is obtained. The temperature for heating by microwave irradiation is preferably 170 ° C. or higher, more preferably 180 ° C. or higher, from the viewpoint of suppressing variation in the shape of the obtained metal 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.

  In order to generate metallic nickel fine particles having a uniform particle size, the heating temperature of the complexing reaction liquid generation step is adjusted within a specific range, and is surely lower than the heating temperature by microwave irradiation. Easily produce particles with a uniform particle size and shape. For example, if the heating temperature is too high in the complexing reaction solution generation process, the formation of nickel complex and the reduction reaction to nickel (zero valence) proceed simultaneously, and different types of metal are generated. There is a possibility that generation of fine particles may be difficult. In addition, if the heating temperature by microwave irradiation is too low, the reduction reaction rate to nickel (zero valence) becomes slow and the generation of nuclei is reduced, so that not only the particles become larger but also the size of the particles becomes uneven, This is also not preferable from the viewpoint of the yield of nickel fine particles.

  Further, as long as the surface of the metallic nickel fine particles is covered with a primary amine, there is no particular problem even if the surface of the metallic nickel fine particles is partially covered with a sulfur element or a sulfur-containing compound. The presence of elemental sulfur on the surface of the metal nickel fine particles reduces the surface activity of the metal nickel fine particles and suppresses the catalytic action, thereby improving the sintering resistance when used, for example, as a material for internal electrodes of a multilayer ceramic capacitor. This is more preferable.

  The metal nickel fine particles used in the present embodiment contain 50 parts by mass or more of nickel element with respect to 100 parts by mass of the metal nickel fine particles. The content of nickel may be appropriately selected according to the purpose of use, but the amount of nickel element is preferably 70 parts by mass or more, more preferably 90 parts by mass or more with respect to 100 parts by mass of metal nickel fine particles. It is preferable. Examples of metals other than nickel include base metals such as titanium, cobalt, copper, chromium, manganese, iron, zirconium, tin, tungsten, molybdenum, vanadium, gold, silver, platinum, palladium, iridium, osmium, ruthenium, Noble metals such as rhodium and rhenium can be mentioned, and these metal elements may be contained alone or in combination of two or more, and contain elements other than metal elements such as hydrogen, carbon, nitrogen and sulfur. Or an alloy thereof. Furthermore, the metal nickel fine particles may be composed of a single metal nickel fine particle, or may be a mixture of two or more kinds of metal nickel fine particles.

  There is no restriction | limiting in particular in the particle diameter of metal nickel fine particle, According to the use purpose, it selects from the range of 1-200 nm, for example. In particular, for example, metallic nickel fine particles having a particle diameter of 150 nm or less are preferable, and metallic nickel fine particles having a particle diameter of 100 nm or less are more preferable. From another viewpoint, the average particle diameter of the metallic nickel fine particles is preferably in the range of 10 to 150 nm, more preferably in the range of 20 to 120 nm.

In addition to the above steps I and II, the following step III;
III) A step of isolating the metal nickel fine particles coated with the primary amine from the slurry,
May be provided.

  In Step III, the slurry obtained by heating by microwave irradiation is, for example, statically separated, and after removing the supernatant liquid, washed with an appropriate solvent and dried to coat with a primary amine. Thus obtained metallic nickel fine particles are obtained.

  As described above, metallic nickel fine particles coated with a primary amine can be produced.

Process B:
In the step B, the metal nickel fine particles coated with the primary amine obtained in the step A are converted into the first organic solvent, a non-aqueous polymer dispersant having a secondary or tertiary amino group (hereinafter referred to as “non- It is abbreviated as “aqueous polymer dispersant”) and an organic binder to obtain a conductive paste containing them. In Step B, at least a part of the primary amine is replaced with the non-aqueous polymer dispersant on the surface of the metal nickel fine particles, and the metal nickel fine particles are coated with the non-aqueous polymer dispersant. At this time, the prepared metallic nickel fine particles coated with the primary amine may be in an isolated state, in a slurry state with the first organic solvent, or with microwave irradiation of the reaction liquid In the state of the organic solvent slurry in which the second organic solvent is replaced with the first organic solvent following the reduction reaction by the above, or the state of the slurry in which the metal nickel fine particles are dispersed again in the first organic solvent It may be. When the second organic solvent is a primary amine, it can be used as it is as the first organic solvent.

  The first organic solvent has good affinity with the non-aqueous polymer dispersant, and the non-aqueous polymer dispersant promotes the substitution reaction with the primary amine immobilized on the surface of the metal nickel fine particles. Use what has. Examples thereof include organic solvents that are immiscible with water. Specific examples thereof include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene, hexane, heptane, decane, octane, heptane, cyclohexane, and methylcyclohexane. , Aliphatic hydrocarbons such as ethylcyclohexane, esters such as ethyl acetate, butyl acetate, dihydroterpinyl acetate, isobornyl acetate, isobornyl proquinate, isobornyl butyrate, isobornyl isobutyrate, α- Examples include long-chain alcohols such as terpineol and butyl carbitol, and esters of long-chain alcohols and carboxylic acids. If the non-aqueous polymer dispersant does not aggregate, in addition to the above organic solvents, some organic solvents miscible with water, for example, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone are also used. Is possible. In addition, as the first organic solvent, for example, when a hydrophilic alcohol having 3 or less carbon atoms is used alone as it is, it is not preferable because the non-aqueous polymer dispersant is aggregated. It is possible to lower the polarity to such an extent that aggregation does not occur.

  The first organic solvent is a hydrocarbon organic solvent, a higher alcohol having 6 or more carbon atoms, an ester from the viewpoint of improving the affinity with the non-aqueous polymer dispersant or the solubility of the non-aqueous polymer dispersant. Of these, organic solvents and ketone organic solvents are preferred.

  The non-aqueous polymer dispersant used in the present embodiment is a polymer compound having high affinity with a low polarity solvent in the main skeleton and having a low polarity group, and further having an 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.

  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 metal nickel fine particles, It is considered that at least a part of the primary amine can be easily substituted on the surface, and the metal nickel fine particles can be coated. Since this non-aqueous polymer dispersant has a strong aggregation suppressing action on metallic nickel fine particles, an excellent dispersion effect can be expected even in a small amount. On the other hand, when the primary amine is not present on the surface of the nickel metal fine particles, even if a non-aqueous polymer dispersant is added, coating by substitution with the primary amine is unlikely to occur, and strong aggregation suppressing action and excellent dispersion effect Cannot be obtained. 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. Further, 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 spotted on the surface of the metallic nickel fine particles. It is thought that it is fixed permanently.

  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 15 mgKOH / g or less, more preferably 10 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), and the like are available.

  The addition amount of the non-aqueous polymer dispersant used in the present embodiment is in the range of 0.01 to 20 parts by mass, preferably in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the metallic nickel fine particles. Good. 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.

  The non-aqueous polymer dispersant used in the present embodiment can be used alone or in combination of two or more. Moreover, it can also be used in combination with the dispersing agent which consists of another compound in the range which does not impair the effect of invention.

  Examples of the organic binder used in the present embodiment include cellulose resins such as methyl cellulose, ethyl cellulose, nitrocellulose, cellulose acetate, and cellulose propionate, methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth) acrylate. Acrylic esters such as alkyd resins, polyvinyl alcohol, and the like can be used. Further, the organic binder may be used in a state where an organic solvent such as ethanol or butanol (hereinafter sometimes referred to as “third organic solvent”) is added, and is dissolved in the above-mentioned first organic solvent. May be used. In addition, the addition amount of the organic binder can be appropriately adjusted according to the leveling property and sagging viscosity characteristic of the target conductive paste.

  In this step B, the method for preparing the conductive paste containing the metallic nickel fine particles coated with the primary amine, the first organic solvent, the non-aqueous polymer dispersant and the organic binder is not particularly limited, and is publicly known. Similar to the production of the conductive paste, the conductive paste can be prepared by mixing the components and then performing a treatment such as stirring and kneading. Here, it will be as follows if the preferable example of the order which mixes each component is given. First, a non-aqueous polymer dispersant is applied to a slurry of metallic nickel fine particles coated with a primary amine and a first organic solvent. The application method of the non-aqueous polymer dispersant to the slurry is not particularly limited. For example, a) a method of adding a predetermined amount of the non-aqueous polymer dispersant to the slurry, b) a high-pressure homogenizer, an ultrasonic homogenizer, a bead mill Using a disperser such as a disperser, the nickel metal fine particles coated with the primary amine are mechanically pulverized in a slurry state, and a predetermined amount of non-aqueous polymer dispersant is added before or after the pulverization. There are various methods such as a method of adding and dispersing. By applying the non-aqueous polymer dispersant in the slurry state in this way, the primary amine in which the secondary or tertiary amino group of the non-aqueous polymer dispersant is immobilized on the surface of the metallic nickel fine particles. The nickel metal fine particles can be coated with a non-aqueous polymer dispersant. Next, a conductive paste can be produced by adding a predetermined amount of an organic binder (may be in a state dissolved in a first or third organic solvent) to the slurry and performing mixing, kneading and the like.

  Although the conductive paste can be obtained as described above, a plasticizer, a lubricant, a dispersant, an antistatic agent, an antigelling agent, and the like may be added as long as the effects of the present invention are not impaired.

  As described above, by performing Step A and Step B, a conductive paste containing metal nickel fine particles coated with a non-aqueous polymer dispersant having a strong aggregation suppressing action can be obtained. This conductive paste is an aggregate of metal nickel fine particles having a sharp particle size distribution in which aggregation is suppressed and single particles are dispersed, for example, even for fine metal nickel fine particles having a particle size of 150 nm or less. It can be suitably used as a conductive paste for forming internal electrodes. That is, when the conductive paste produced by the method of the present invention is used for forming an internal electrode such as MLCC, the surface of the electrode layer (interface with the dielectric layer) can be prevented from being uneven and flattened. Therefore, the electrode layer can be easily thinned and multilayered, and the electrical reliability can be improved.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In the following examples, various measurements and evaluations are as follows unless otherwise specified.

[Measurement of average particle size]
The average particle size was measured by taking a photograph of the sample with an SEM (scanning electron microscope), randomly extracting 200 samples from the sample, obtaining each particle size, and calculating the average particle size. 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.

[Evaluation of surface roughness of conductive paste]
Two pieces of slide glass S1112 (76 mm × 26 mm × t1.1 mm) manufactured by Matsunami Glass Industry Co., Ltd. were wiped off with absorbent cotton moistened with acetone and dried. 0.05 g of conductive paste is weighed in the center of one slide glass, sandwiched between the other slide glass, and then printed while being pressed to the extent that it does not protrude from the side, and the slide glass is slid in the parallel direction. As a result, a smooth coating surface can be obtained. After the coating film was dried at 60 ° C. for 3 hours, the arithmetic average roughness Ra and the ten-point average roughness Rz were measured with a fine shape measuring apparatus, Kosaka Laboratory ET-200.

  The dispersants and their abbreviations used for producing the conductive paste are as follows.

Dispersant (1): Polyurethane polymer dispersant (manufactured by Nippon Lubrizol, trade name: Solsperse 76500, mixture of polyurethane-polyoxyethylene block copolymer containing secondary amino group and tertiary amino group, effective Ingredient: 50%, polar: low, insoluble in water, amine value as active ingredient: 15 mg KOH / g, acid value as active ingredient: 0 mg KOH / g)
Dispersant (2): Polyester polymer dispersant (manufactured by Nippon Lubrizol Corporation, trade name: Solsperse 13940, mixture of polyester graft copolymer containing secondary amino group and tertiary amino group, active ingredient; 40% Low, insoluble in water, amine value as active ingredient; 93 mgKOH / g, acid value as active ingredient; 0 mgKOH / g)
Dispersant (3): Polyester polymer dispersant (manufactured by Nippon Lubrizol, trade name; Solsperse 13240, mixture of polyester graft copolymer containing secondary amino group and tertiary amino group, active ingredient; 40% Low, insoluble in water, amine value as active ingredient; 93 mgKOH / g, acid value as active ingredient; 0 mgKOH / g)
Dispersant (4): Polyurethane polymer dispersant (manufactured by Big Chemie Japan, trade name: BYK163, mixture of polyurethane block copolymer containing secondary amino group, active ingredient: 45%, polarity: low, (Insoluble in water, amine value as active ingredient; 10 mg KOH / g, acid value as active ingredient; 0 mg KOH / g, weight average molecular weight; 20,000 to 30,000)
Dispersant (5): Polyurethane-polyester polymer dispersant (manufactured by Big Chemie Japan, trade name: BYK2155, mixture of polyurethane-polyester block copolymer containing tertiary amino groups, active ingredient;> 99% Low to medium, insoluble in water, amine value; 48 mg KOH / g, acid value; 0 mg KOH / g, weight average molecular weight; 20,000)
Dispersant (6): Basic polyurethane polymer dispersant (manufactured by Big Chemie Japan, trade name; BYK2164, mixture of polyurethane block copolymer containing secondary amino group and tertiary amino group, active ingredient; 66%, polar; low, insoluble in water, amine value as active ingredient; 14 mg KOH / g, acid value as active ingredient; 0 mg KOH / g, weight average molecular weight; 20,000 to 30,000)
Dispersant (7): Cationic polymer dispersant (trade name; Hypermer KD-1, a hydrocarbon-based graft copolymer having a polyamine as a main chain, polarity: medium, insoluble in water)
Dispersant (8): Cationic polymer dispersant (trade name; Hypermer KD-2, hydrocarbon graft copolymer having polyamine as the main chain, polarity: high, soluble in water)
Dispersant (9): Anionic polymer dispersant (trade name; Hypermer KD-9, hydrocarbon graft copolymer having polycarboxylic acid as the main chain, polar: medium, insoluble in water)
Dispersant (10): Polyester polymer dispersant (manufactured by Enomoto Kasei Co., Ltd., trade name: HIPLAAD ED216, mixture of polyamines containing secondary and tertiary amino groups and high molecular weight carboxylic acid, active ingredient: 75%, polar Low, insoluble in water, amine value as active ingredient; 40 mg KOH / g, acid value as active ingredient; 15 mg KOH / g, weight average molecular weight; 10,000 to 20,000)

(Synthesis Example 1)
18.5 g of nickel formate dihydrate was added to 125.9 g of laurylamine and heated at 120 ° C. for 10 minutes under a nitrogen flow to dissolve nickel formate to obtain a complexing reaction solution. Next, 83.9 g of laurylamine was further added to the complexing reaction solution, and the mixture was heated at 180 ° C. for 10 minutes using a microwave to obtain a metal nickel fine particle slurry 1a ′.

  The obtained metallic nickel fine particle slurry 1a 'was allowed to stand and separated, and the supernatant was removed, followed by washing with a mixed solvent having a volume ratio of methanol to toluene of 1: 4. Then, the metal nickel fine particle 1a which the primary amine coat | covered was obtained by drying with the vacuum dryer maintained at 60 degreeC for 6 hours. The average particle diameter of the metallic nickel fine particles 1a thus obtained was 100 nm, and as a result of elemental analysis, C: 0.9, N; 0.06, O; 1.4 (unit: mass%) It was.

(Synthesis Example 2)
0.070 g of dodecanethiol is added to 100 g of the metal nickel fine particle slurry 1a ′ obtained in Synthesis Example 1 (adjusted to a solid content concentration of 2.5 wt%), and again irradiated with microwaves to 250 By heating at 0 ° C. for 5 minutes, a metal nickel fine particle slurry 2a ′ coated with primary amine and sulfur element was obtained.

  The obtained metal nickel fine particle slurry 2a 'was separated and allowed to stand and separated, and the supernatant was removed, followed by washing with a mixed solvent of methanol and toluene in a volume ratio of 1: 4. Then, the nickel metal microparticles | fine-particles 2a which the primary amine and the sulfur element coat | covered were obtained by drying with the vacuum dryer maintained at 60 degreeC for 6 hours. The average particle diameter of the metallic nickel fine particles 2a thus obtained is 100 nm. As a result of elemental analysis, C: 0.6, N: 0.05, O: 1.4, S: 0.4 (unit Was mass%).

[Example 1-1]
10 g of the metal nickel fine particle slurry 1a ′ prepared in Synthesis Example 1 was statically separated, replaced with toluene, and then adjusted to a solid content concentration of 10 wt%. To this was added 0.05 g of dispersant (1) (0.03 g as an active ingredient), and the mixture was stirred for 15 minutes, then replaced with dihydroterpinyl acetate solvent while washing with dihydroterpinyl acetate, and the solid content concentration Was adjusted to 60 wt%. 1.67 g of the slurry composition A1 thus obtained was weighed in a mortar with 0.3 g of a cellulose-based binder (EC-100FTP manufactured by Nisshin Kasei Co., Ltd.), 0.17 g of dihydroterpinyl acetate. After mixing, kneading was performed at a gap of 10 μm using a 3-roll BR-100V manufactured by Imex Co., Ltd. to obtain a conductive paste A1. Table 1 shows the results of applying and drying the obtained conductive paste A1 on a slide glass and measuring the surface roughness.

[Example 1-2]
Except having used the dispersing agent (2) instead of the dispersing agent (1) in Example 1-1, it obtained slurry composition A2 similarly to Example 1-1, and obtained electrically conductive paste A2. It was. The results are shown in Table 1.

[Example 1-3]
A slurry composition A3 was obtained in the same manner as in Example 1-1 except that the dispersant (3) was used instead of the dispersant (1) in Example 1-1, and a conductive paste A3 was obtained. . The results are shown in Table 1.

[Example 1-4]
A slurry composition A4 was obtained in the same manner as in Example 1-1 except that the dispersant (4) was used instead of the dispersant (1) in Example 1-1, and a conductive paste A4 was obtained. . The results are shown in Table 1.

[Example 1-5]
A slurry composition A5 was obtained in the same manner as in Example 1-1 except that the dispersant (5) was used instead of the dispersant (1) in Example 1-1, and a conductive paste A5 was obtained. . The results are shown in Table 1.

[Example 1-6]
A slurry composition A6 was obtained in the same manner as in Example 1-1 except that the dispersant (6) was used instead of the dispersant (1) in Example 1-1, and a conductive paste A6 was obtained. . The results are shown in Table 1.

[Comparative Example 1-1]
A slurry composition A7 was obtained in the same manner as in Example 1-1 except that the dispersant (7) was used instead of the dispersant (1) in Example 1-1, and a conductive paste A7 was obtained. . The results are shown in Table 1.

[Comparative Example 1-2]
A slurry composition A8 was obtained in the same manner as in Example 1-1 except that the dispersant (8) was used instead of the dispersant (1) in Example 1-1, and a conductive paste A8 was obtained. . The results are shown in Table 1.

[Comparative Example 1-3]
Except having used the dispersing agent (9) instead of the dispersing agent (1) in Example 1-1, it carried out similarly to Example 1-1, and obtained slurry composition A9, and obtained electrically conductive paste A9. . The results are shown in Table 1.

[Comparative Example 1-4]
Except not having used the dispersing agent (1) in Example 1-1, it carried out similarly to Example 1-1, and obtained slurry composition A10, and obtained electrically conductive paste A10. The results are shown in Table 1.

  The above results are summarized in Table 1.

[Example 2-1]
10 g of the metal nickel fine particle slurry 2a ′ prepared in Synthesis Example 2 was statically separated and replaced with toluene, and then the solid content concentration was adjusted to 10 wt%. To this was added 0.05 g of dispersant (1) (0.03 g as an active ingredient), and the mixture was stirred for 15 minutes, then replaced with dihydroterpinyl acetate solvent while washing with dihydroterpinyl acetate, and the solid content concentration Was adjusted to 60 wt%. 1.67 g of the slurry composition B1 thus obtained was weighed in a mortar with 0.3 g of a cellulose binder (EC-100FTP manufactured by Nisshin Kasei Co., Ltd.), 0.17 g of dihydroterpinyl acetate. After mixing, kneading was performed at a gap of 10 μm using a 3-roll BR-100V manufactured by Imex Co., Ltd. to obtain a conductive paste B1. Table 2 shows the results of applying and drying the obtained conductive paste B1 on a slide glass and measuring the surface roughness.

[Example 2-2]
A slurry composition B2 was obtained in the same manner as in Example 2-1, except that the dispersant (2) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B2 was obtained. It was. The results are shown in Table 2.

[Example 2-3]
A slurry composition B3 was obtained in the same manner as in Example 2-1, except that the dispersant (3) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B3 was obtained. It was. The results are shown in Table 2.

[Example 2-4]
A slurry composition B4 was obtained in the same manner as in Example 2-1, except that the dispersant (4) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B4 was obtained. It was. The results are shown in Table 2.

[Example 2-5]
A slurry composition B5 was obtained in the same manner as in Example 2-1, except that the dispersant (5) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B5 was obtained. It was. The results are shown in Table 2.

[Example 2-6]
A slurry composition B6 was obtained in the same manner as in Example 2-1, except that the dispersant (6) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B6 was obtained. It was. The results are shown in Table 2.

[Comparative Example 2-1]
A slurry composition B7 was obtained in the same manner as in Example 2-1, except that the dispersant (7) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B7 was obtained. It was. The results are shown in Table 2.

[Comparative Example 2-2]
A slurry composition B8 was obtained in the same manner as in Example 2-1, except that the dispersant (8) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B8 was obtained. It was. The results are shown in Table 2.

[Comparative Example 2-3]
A slurry composition B9 was obtained in the same manner as in Example 2-1, except that the dispersant (9) was used instead of the dispersant (1) in Example 2-1, and a conductive paste B9 was obtained. It was. The results are shown in Table 2.

[Comparative Example 2-4]
Except not having used the dispersing agent (1) in Example 2-1, it carried out similarly to Example 2-1, and obtained slurry composition B10, and obtained electrically conductive paste B10. The results are shown in Table 2.

  As shown in Table 1 and Table 2, in Examples 1-1 to 1-6 and 2-1 to 2-6, the arithmetic average roughness Ra, which is an index of surface smoothness, is sufficiently small. In the comparative example, it was found that the arithmetic average roughness Ra is large, there are many aggregates, and the surface smoothness is inferior. Also, the ten-point average roughness Rz, which is an index of the maximum surface roughness due to coarse aggregates, was confirmed to be significantly smaller in Examples than in Comparative Examples, with few coarse aggregates, and good surface smoothness. It was done. In addition, although a result is abbreviate | omitted, in Example 2-1 to 2-6 using the metal nickel fine particle 2a which the primary amine and the sulfur element coat | covered, sintering resistance was improving.

(Comparative Example 3-1)
Aldrich nickel powder [average particle size: 90 nm, elemental analysis value: C: 0.08, N: less than detection limit value, O: 1.5 (unit: mass%)] slurry of toluene solvent (solid content The concentration of 10 wt% was adjusted, and 0.05 g (0.03 g as an active ingredient) of the dispersant (1) was added thereto. After stirring for 15 minutes, dihydroterpinyl acetate was washed with dihydroterpinyl acetate. Substitution with a solvent was performed, and the solid content concentration was adjusted to 60 wt%. To 1.67 g of the slurry composition thus obtained, 0.3 g of EC-100FTP manufactured by Nisshin Kasei Co., Ltd., 0.17 g of dihydroterpinyl acetate, and a mortar were weighed and mixed. Using a three-roll BR-100V manufactured by Co., Ltd., kneading was performed at a gap of 10 μm to obtain a conductive paste. The obtained conductive paste was applied to a slide glass and dried, and the surface roughness was measured. As a result, Ra = 0.54 and Rz = 0.602.

[Example 3]
After removing 60 g of the supernatant liquid 2a ′ of the metallic nickel fine particle slurry prepared in Synthesis Example 2, a solution of the dispersant (10) diluted with xylene so that the active ingredient of the dispersant is 10 wt%, It added so that the active ingredient of a dispersing agent might be 5 wt% with respect to nickel element, and it stirred at 40 degreeC for 1 hour. Then, after wash | cleaning using the mixed solution whose volume ratio of xylene and methanol is 4: 1, it substituted by dihydro terpinyl acetate, the slurry composition C1 was obtained, and the electrically conductive paste C1 was obtained. The obtained conductive paste C1 was applied onto a slide glass and dried, and the surface roughness was measured. As a result, Ra = 0.006 and Rz = 0.043.

  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.

Claims (5)

Next steps A and B;
A) preparing metal nickel fine particles coated with a primary amine,
B) A step of obtaining a conductive paste containing these by mixing the metal nickel fine particles, an organic solvent, a non-aqueous polymer dispersant having a secondary or tertiary amino group, and an organic binder,
With
In the step B, production of a conductive paste in which at least a part of the primary amine is replaced with the non-aqueous polymer dispersant on the surface of the metal nickel fine particles, and the metal nickel fine particles are coated with the non-aqueous polymer dispersant. Method.   The method for producing a conductive paste according to claim 1, wherein the primary amine covering the surface of the metal nickel fine particles is an aliphatic primary amine.   The method for producing a conductive paste according to claim 1 or 2, wherein the metal nickel fine particles in the step A are in a state of a slurry composition of the organic solvent. Metallic nickel fine particles coated with the primary amine are
Next steps I and II;
I) a step of heating a mixture of nickel carboxylate and primary amine to a temperature in the range of 100 ° C. to 165 ° C. to obtain a complexing reaction solution;
II) A step of heating the complexing reaction solution to a temperature of 170 ° C. or higher by microwave irradiation to reduce nickel ions in the complexing reaction solution to obtain metallic nickel fine particles coated with a primary amine. ,
The method for producing a conductive paste according to any one of claims 1 to 3, wherein the conductive paste is prepared by a method comprising:   The method for producing a conductive paste according to any one of claims 1 to 4, wherein the metallic nickel fine particles are partially coated with a sulfur element or a sulfur-containing compound in addition to the primary amine.