Method for producing conductive particles and conductive powder

Abstract

To provide a conductive particle capable of effectively breaking through an oxide film of an electrode by forming stably fixed projections on a conductive layer of the conductive particle to prevent the detachment of the projections.SOLUTION: Provided is a method for producing a conductive particle, including: a first step of mixing core material particles and an electroless nickel plating bath containing a nickel salt, a reducing agent, and a complexing agent to prepare a slurry containing primary plated particles in which a nickel initial thin film layer is formed on surfaces of the core material particles; and a second step of continuously adding an aqueous solution containing the nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the slurry obtained in the first step, stopping the addition for a time period of 10 minutes or more and 120 minutes or less to hold the slurry, and continuously adding again the aqueous solution containing the nickel salt, the aqueous solution containing the reducing agent, and the aqueous solution containing the alkali to the slurry to perform an electroless plating treatment on the primary plated particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing conductive particles and a conductive powder containing the conductive particles. [Background technology]

[0002] Conductive particles used as the conductive material in anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes generally have a conductive layer made of metal formed on the surface of a core particle. In recent years, the miniaturization and refinement of electronic devices has led to the need for fine-pitch connections between electrode terminals, and electrical connections between electrodes and wiring are achieved through the conductive layer of the conductive particles.

[0003] The conductive layer of these conductive particles is often a coating formed on the surface of core particles by electroless plating with a metal such as nickel, and various innovations have been made to achieve the desired properties. Patent Document 1, for example, discloses conductive particles having a protrusion structure on the surface, which are formed by electroless plating with amino resin microparticles on the surface of a base particle. Patent Document 1 describes that excellent adhesion between the surface of the base particle and the amino resin microparticles prevents the protrusions of the resulting conductive particles from detaching, thereby achieving both good conductivity and connection reliability. Patent Document 2 also discloses conductive particles having protrusions formed on the surface, which are formed by electroless plating resin particles composed of a spherical portion and a peripheral portion having multiple protrusions formed on the surface, the spherical portion and the peripheral portion having different compositions. Patent Document 3 also discloses conductive particles having protrusions formed on the surface, similar to Patent Document 2, which are formed by electroless plating resin particles composed of a peripheral portion having multiple protrusions on the surface and a spherical portion surrounded by the peripheral portion. Both of these documents describe that connection reliability can be ensured by suppressing protrusion detachment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-150802 [Patent Document 2] International Publication No. WO2015 / 141716 Brochure [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-85959 Summary of the Invention [Problem to be solved by the invention]

[0005] The purpose of forming protrusions on the conductive layer of conductive particles is mainly to break through the oxide film present on the electrode surface with the protrusions, which leads to lower connection resistance and improved connection reliability when connecting electrodes. However, all of the conductive particles described in the above patent documents have a conductive layer formed on a core resin particle with protrusions, so although the protrusions are difficult to detach, there is room for improvement in connection reliability and connection resistance. That is, in order to break through the oxide film of the electrode, it is desirable for the protrusions to have high strength, but if the inside of the protrusion is resin, sufficient strength cannot be obtained, making it difficult to break through the oxide film. Furthermore, because a thin conductive layer is formed on the protrusion-shaped portion made of resin, the resistance tends to be higher than that of protrusions made only of metal.

[0006] On the other hand, conductive particles having protrusions made only of metal have the advantage of having higher protrusion strength and lower resistance than the conductive particles described in the above patent documents, but because the protrusions are formed in a form that protrudes directly from the conductive layer, there is a problem that the protrusions are easily detached from the conductive layer due to external impact. In other words, if protrusions that are stably fixed to the conductive layer can be formed, it will be possible to provide conductive particles that are excellent in connection reliability and connection resistance.

[0007] Therefore, an object of the present invention is to provide conductive particles that can effectively break through the oxide film of an electrode by forming protrusions that are stably fixed to the conductive layer of the conductive particles, thereby preventing the protrusions from detaching. [Means for solving the problem]

[0008] As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have found that the protrusions can be stably fixed to the conductive layer by sufficiently capturing the autolysis products that form the nuclei of the protrusions and are generated in the electroless nickel plating bath on the surface of the core material particles. They have also found that in order to sufficiently capture the autolysis products on the surface of the core material particles, it is sufficient to stop the formation of the plating film at an early stage, wait until a sufficient amount of the autolysis products has been captured on the surface of the core material particles, and then resume the formation of the plating film, thereby completing the present invention.

[0009] That is, the present invention provides a method for producing conductive particles, which comprises: a first step of mixing core particles with an electroless nickel plating bath containing a nickel salt, a reducing agent, and a complexing agent to prepare a slurry containing primary plated particles in which an initial thin nickel layer is formed on the surface of the core particles; and a second step of successively adding an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the slurry obtained in the first step, then stopping the addition after a period of 10 minutes to 120 minutes to hold the slurry, and again successively adding an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the slurry to perform an electroless plating treatment on the primary plated particles.

[0010] The present invention also provides a conductive powder consisting of conductive particles having protrusions on the particle surface, in which when 0.05 g of the conductive powder is placed in a 150 mm diameter SUS cylindrical container and the conductive powder is ground by rotating a 2 kg SUS cylindrical weight 20 times, the number of detached protrusions per 100 conductive particles is 5 or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to form protrusions that are stably fixed to a conductive layer, and therefore it is possible to provide conductive particles that have low connection resistance and excellent connection reliability, a method for producing the same, and a conductive powder made of the conductive particles. [Brief explanation of the drawings]

[0012] [Figure 1]1 is an SEM image of the conductive particles obtained in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] A preferred embodiment of the method for producing conductive particles of the present invention will be described below. The method for producing conductive particles of the present invention comprises a first step of mixing core particles with an electroless nickel plating bath containing a nickel salt, a reducing agent, and a complexing agent to prepare a slurry containing primary plated particles in which an initial thin nickel layer is formed on the surface of the core particles; and a second step of successively adding an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the slurry obtained in the first step, then stopping the addition for a period of 10 minutes to 120 minutes to hold the slurry, and again successively adding an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali to the slurry to perform an electroless plating treatment on the primary plated particles.

[0014] The core particles can be inorganic or organic, as long as they are particulate. Examples of inorganic core particles include metal particles such as gold, silver, copper, nickel, palladium, and solder; alloys; glass; ceramics; silica; metal or non-metal oxides (including hydrates); metal silicates including aluminosilicates; metal carbides; metal nitrides; metal carbonates; metal sulfates; metal phosphates; metal sulfides; metal acid salts; metal halides; and carbon. Examples of organic core particles include thermoplastic resins such as natural fibers, natural resins, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomers, and polyester; and thermosetting resins such as alkyd resins, phenolic resins, urea resins, benzoguanamine resins, melamine resins, xylene resins, silicone resins, epoxy resins, and diallyl phthalate resins. These may be used alone or in combination.

[0015] The core particles may be composed of both inorganic and organic materials instead of the aforementioned inorganic and organic materials. When the core particles are composed of both inorganic and organic materials, the inorganic and organic materials may be present in the core particles in a core-shell configuration, such as a configuration having an inorganic core and an inorganic shell covering the surface of the core, or a core made of an organic material and an inorganic shell covering the surface of the core. Other examples include blend configurations in which inorganic and organic materials are mixed or randomly fused within a single core particle.

[0016] The core particles are preferably composed of an organic material or a material consisting of both inorganic and organic materials, and more preferably composed of a material consisting of both inorganic and organic materials. The inorganic material is preferably glass, ceramic, silica, metal or non-metal oxides (including hydrated oxides), metal silicates including aluminosilicates, metal carbides, metal nitrides, metal carbonates, metal sulfates, metal phosphates, metal sulfides, metal acid salts, metal halides, and carbon. The organic material is preferably natural fiber, natural resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylate, polyacrylonitrile, polyacetal, ionomer, polyester, or other thermoplastic resin. Using a core material made of such a material can improve the dispersion stability of the particles and also provide appropriate elasticity and improve conductivity during electrical connection of electronic circuits.

[0017] When an organic substance is used as the core particles, it is preferable that the organic substance does not have a glass transition temperature or that the glass transition temperature is higher than 100° C., because the shape of the core particles is easily maintained and the shape of the core particles is easily maintained in the process of forming a metal coating. The glass transition temperature can be determined, for example, as the intersection point of the tangent to the original baseline and the inflection point in the baseline shift portion of a DSC curve obtained by differential scanning calorimetry (DSC).

[0018] When an organic substance is used as the core particle, if the organic substance is a highly crosslinked resin, almost no baseline shift is observed even when the glass transition temperature is measured up to 200°C using the above method. In this specification, such particles are also referred to as particles that do not have a glass transition temperature, and such core particles may be used in the present invention. Specific examples of core particle materials that do not have a glass transition temperature can be obtained by copolymerizing the monomers that make up the organic substance exemplified above with a crosslinkable monomer. Examples of crosslinkable monomers include tetramethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, ethylene oxide di(meth)acrylate, tetraethylene oxide (meth)acrylate, 1,6-hexane di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, trimeterolpropane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, tetramethylolmethane tri(meth)acrylate, Examples include polyfunctional (meth)acrylates such as tetramethylolmethane tetra(meth)acrylate, tetramethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol di(meth)acrylate, and glycerol tridi(meth)acrylate, polyfunctional vinyl monomers such as divinylbenzene and divinyltoluene, silane-containing monomers such as vinyltrimethoxysilane, trimethoxysilylstyrene, and γ-(meth)acryloxypropyltrimethoxysilane, and monomers such as triallyl isocyanurate, diallyl phthalate, diallyl acrylamide, and diallyl ether. Core particles made of such hard organic materials are widely used, particularly in the field of COG (chip on glass).

[0019] There are no particular limitations on the shape of the core particles. Generally, the core particles are spherical. However, the core particles may have shapes other than spherical, such as fibrous, hollow, plate-like, or needle-like, and may have a large number of protrusions on their surfaces or may be amorphous. In the present invention, spherical core particles are preferred because they have excellent filling properties and are easy to coat with metal.

[0020] The conductive layer formed on the surface of the core particle is made of a conductive metal. Examples of metals constituting the conductive layer include gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, germanium, aluminum, chromium, palladium, tungsten, molybdenum, calcium, magnesium, rhodium, sodium, iridium, beryllium, ruthenium, potassium, cadmium, osmium, lithium, rubidium, gallium, thallium, tantalum, cesium, thorium, strontium, polonium, zirconium, barium, and manganese, as well as metal compounds such as ITO and solder. Among these, gold, silver, copper, nickel, palladium, rhodium, and solder are preferred due to their low electrical resistance, and nickel, gold, nickel alloys, and gold alloys are particularly preferred. The metal may be used alone or in combination with two or more.

[0021] The conductive layer may have a single layer structure or a laminated structure consisting of multiple layers. In the case of a laminated structure consisting of multiple layers, the outermost layer is preferably at least one selected from nickel, gold, silver, copper, palladium, a nickel alloy, a gold alloy, a silver alloy, a copper alloy, and a palladium alloy.

[0022] The conductive layer does not have to cover the entire surface of the core particle, but may cover only a portion of it. When only a portion of the surface of the core particle is covered, the covered portion may be continuous, or may be discontinuous, for example, in the form of islands.

[0023] The thickness of the conductive layer is preferably 0.1 nm or more and 2000 nm or less, and more preferably 1 nm or more and 1500 nm or less. When the thickness of the conductive layer is within the above range, the conductive particle has excellent electrical properties. In the present invention, the thickness of the conductive layer can be measured by cutting the particle to be measured into two pieces and observing the cross-section of the cut surface with a scanning electron microscope (SEM).

[0024] The average particle diameter of the conductive particles is preferably 0.1 μm or more and 50 μm or less, more preferably 1 μm or more and 30 μm or less. When the average particle diameter of the conductive particles is within the above range, it is easy to ensure conduction between the opposing electrodes without causing a short circuit in a direction different from that between the opposing electrodes. In the present invention, the average particle diameter of the conductive particles is a value measured by SEM observation. Specifically, the average particle diameter of the conductive particles is measured by the method described in the Examples. The particle diameter is the diameter of a circular conductive particle image. When the conductive particles are not spherical, the particle diameter refers to the longest length (maximum length) of the line segments crossing the conductive particle image.

[0025] The core particles preferably have a surface capable of capturing precious metal ions or are surface-modified to have such ability. The precious metal ions are preferably palladium or silver ions. Having the ability to capture precious metal ions means being able to capture precious metal ions as chelates or salts. For example, when amino groups, imino groups, amide groups, imide groups, cyano groups, hydroxyl groups, nitrile groups, carboxyl groups, etc. are present on the surface of the core particles, the surface of the core particles has the ability to capture precious metal ions. When the surface is modified to have the ability to capture precious metal ions, for example, the method described in JP-A-61-64882 can be used.

[0026] Such core particles are used to support precious metals on their surfaces. Specifically, the core particles are dispersed in a dilute acidic aqueous solution of a precious metal salt such as palladium chloride or silver nitrate. This allows precious metal ions to be captured on the particle surface. The concentration of the precious metal salt is 1 / m of the surface area of ​​the particle. 21x10 -7 ~1×10 -2 A molar range is sufficient. The core particles with the captured precious metal ions are separated from the system and washed with water. The core particles are then suspended in water, and a reducing agent is added to reduce the precious metal ions. Examples of reducing agents that can be used include sodium hypophosphite, sodium borohydride, potassium borohydride, dimethylamine borane, hydrazine, and formalin.

[0027] Before capturing precious metal ions on the surface of the core particles, the particles may be subjected to a sensitization treatment to adsorb tin ions onto the surface of the particles. To adsorb tin ions onto the surface of the particles, for example, the surface-modified core particles may be placed in an aqueous solution of stannous chloride and stirred for a predetermined period of time.

[0028] The core particles thus pretreated are then subjected to a process for forming a conductive layer having protrusions, which comprises the following first and second steps. The first step is to mix core particles with an electroless nickel plating bath containing a nickel salt, a reducing agent, and a complexing agent to prepare a slurry containing primary plated particles with an initial nickel thin film layer formed on the surface of the core particles. In this first step, autolysis of the plating bath occurs simultaneously with the formation of the initial nickel thin film layer on the core particles. This autolysis occurs near the core particles, so that the autolysis products are captured on the surface of the core particles during the formation of the initial nickel thin film layer, thereby generating nuclei for microprojections, and simultaneously forming the initial nickel thin film layer. The microprojections grow from the generated nuclei.

[0029] In the first step, the above-described primary plated particles are thoroughly dispersed in water, preferably in the range of 0.1 to 500 g / L, more preferably 1 to 300 g / L, to prepare an aqueous slurry. The dispersion operation can be carried out using normal stirring, high-speed stirring, or a shear dispersion device such as a colloid mill or homogenizer. Ultrasound may also be used in the dispersion operation. If necessary, a dispersant such as a surfactant may be added during the dispersion operation.

[0030] Examples of the dispersant include nonionic surfactants, zwitterionic surfactants, and / or water-soluble polymers. Examples of nonionic surfactants include polyoxyalkylene ether surfactants such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. Examples of zwitterionic surfactants include betaine surfactants such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethyl acetate betaine, and alkyldimethylamino acetate betaine. Examples of water-soluble polymers include polyvinyl alcohol, polyvinylpyrrolidinone, and hydroxyethyl cellulose. These dispersants can be used alone or in combination. The amount of dispersant used varies depending on the type, but is preferably 0.5 to 30 g / L relative to the volume of the electroless nickel plating bath. In particular, a dispersant used in an amount of 1 to 10 g / L relative to the volume of the electroless nickel plating bath is preferred from the viewpoint of further improving the adhesion of the conductive layer.

[0031] The nickel salt may be, for example, nickel chloride, nickel sulfate, or nickel acetate, and its concentration is preferably in the range of 0.1 to 50 g / L. The reducing agent may be, for example, the same as those used for reducing the precious metal ions described above, and is selected based on the constituent materials of the target base coating. When a phosphorus compound, such as sodium hypophosphite, is used as the reducing agent, its concentration is preferably in the range of 0.1 to 50 g / L.

[0032] Examples of the complexing agent include compounds that have a complexing effect on nickel ions, such as carboxylic acid salts (e.g., citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, gluconic acid, or their alkali metal salts or ammonium salts), amino acids (e.g., glycine), amines (e.g., ethylenediamine, alkylamine), other ammonium salts, EDTA, pyrophosphate, or its salts. These can be used alone or in combination. The concentration is preferably 1 to 100 g / L, more preferably 5 to 50 g / L. The preferred pH of the electroless nickel plating bath at this stage is 3 to 14. The electroless nickel plating reaction begins immediately upon addition of the aqueous slurry of core particles and is accompanied by the generation of hydrogen gas. The first step is completed when the generation of hydrogen gas is completely stopped. In this manner, a slurry containing primary plated particles is obtained, in which an initial nickel thin film layer is formed on the surface of the core particles.

[0033] Next, in the second step, an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali are successively added to the slurry obtained in the first step, and then the addition is stopped for a period of 10 minutes to 120 minutes to hold the slurry, and an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali are successively added to the slurry again to perform an electroless plating treatment on the primary plated particles. In the second step, these aqueous solutions are each simultaneously and successively added to the slurry obtained in the first step.

[0034] In the second step of the present invention, the aqueous solution containing a nickel salt, the aqueous solution containing a reducing agent, and the aqueous solution containing an alkali are intermittently added to the slurry obtained in the first step. Specifically, from the viewpoint of stably fixing the protrusions to the conductive layer, it is preferable to add each of the aqueous solutions in two or more batches, with a holding period during which the addition is stopped. The inventors believe that this is because, during the holding period without adding each of the aqueous solutions to the slurry, the autolyzed products that form the nuclei of the protrusions are sufficiently and stably captured on the surfaces of the core particles, and therefore the protrusions formed thereafter are also stably fixed on the conductive layer.

[0035] In the second step of the present invention, when the aqueous solution containing a nickel salt, the aqueous solution containing a reducing agent, and the aqueous solution containing an alkali are first continuously added to the slurry obtained in the first step, the addition time is preferably 25 minutes or more, particularly 30 minutes to 90 minutes, from the viewpoint of stably fixing protrusion nuclei composed of decomposition products on the particle surfaces. Here, "continuously" refers to the continuous addition of each of the aqueous solutions. The addition of each of the aqueous solutions may be carried out at a constant rate or may be carried out at varying rates. However, from the viewpoint of stable protrusion formation and ease of process control, addition at a constant rate is preferred. The addition rate of each of the aqueous solutions depends on the reaction scale, but in the case of a 5-L scale reaction vessel, for example, it is preferably 0.01 to 10 mL / min, particularly 0.1 to 5 mL / min, for each. The amount of each of the aqueous solutions added is preferably 1 to 10% by volume relative to the slurry.

[0036] The time for which the addition of each aqueous solution to the slurry is stopped and the slurry is held is from 10 minutes to 120 minutes, preferably from 15 minutes to 100 minutes. The holding may be performed by leaving the slurry to stand or while stirring, but holding while stirring is preferred from the viewpoints of stably capturing the autolysates on the surfaces of the core particles and suppressing particle aggregation to form a uniform conductive layer.

[0037] While the addition of each aqueous solution to the slurry is stopped and maintained, metal nanoparticles may be added to serve as nuclei for protrusions. The metal nanoparticles may be added directly to the slurry, or a metal nanoparticle slurry in which metal nanoparticles are dispersed in water may be added to the slurry. In the present invention, adding a metal nanoparticle slurry to the slurry is preferable from the viewpoint of operability and dispersibility of the metal nanoparticles. The concentration of the metal nanoparticles in the metal nanoparticle slurry is preferably 0.1% by mass or more and 70% by mass or less, particularly preferably 1% by mass or more and 65% by mass or less, from the viewpoint of dispersibility of the metal nanoparticles. Furthermore, the amount of the metal nanoparticle slurry added to the slurry is preferably 0.01 parts by mass or more and 5 parts by mass or less, particularly preferably 0.10 parts by mass or more and 3 parts by mass or less, per part by volume of the slurry. A concentration within this range allows for stable adhesion of the metal nanoparticles to the core particles. Note that, in the quantitative ratio between the metal nanoparticle slurry and the slurry, "volume parts" refers to the amount per liter, and "mass parts" refers to the amount per gram. Furthermore, the temperature of the slurry when the metal nanoparticles are added is preferably 40° C. to 90° C. By maintaining the temperature in this range, the metal nanoparticles can be stably attached onto the core particles.

[0038] The metal of the metal nanoparticles is not particularly limited, but examples thereof include gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, germanium, aluminum, chromium, palladium, tungsten, molybdenum, calcium, magnesium, rhodium, sodium, iridium, beryllium, ruthenium, potassium, cadmium, osmium, lithium, rubidium, gallium, thallium, tantalum, cesium, thorium, strontium, polonium, zirconium, barium, and manganese. Among these, metals selected from gold, silver, copper, nickel, palladium, rhodium, and solder are preferred because of their low electrical resistance, and nickel is particularly preferred.

[0039] The shape of the metal nanoparticles is not particularly limited, and may be spherical, fibrous, plate-like, or core-like, or may be amorphous. The core material may be formed of metal nanoparticles alone, or may be formed of a particle mass, an aggregate of multiple particles, an amorphous mass, or the like.

[0040] The average particle size of the metal nanoparticles is preferably 1 nm or more and 900 nm or less, more preferably 50 nm or more and 200 nm or less. When the average particle size of the core material is in this range, the connection resistance between electrodes can be effectively reduced.

[0041] In the second step of the present invention, when the initial addition of the aqueous solution containing a nickel salt, the aqueous solution containing a reducing agent, and the aqueous solution containing an alkali to the slurry obtained in the first step is stopped and maintained, and then the aqueous solutions are successively added again, the addition time is preferably 40 minutes or more, particularly 50 minutes or more and 100 minutes or less, from the viewpoint of suppressing particle aggregation due to rapid plating film growth, etc.

[0042] The amount of each of the aqueous solution containing a nickel salt, the aqueous solution containing a reducing agent, and the aqueous solution containing an alkali added to the slurry after the retention is preferably 5 to 20% by volume relative to the slurry. The addition of each of the aqueous solutions may be carried out at a constant rate or may be carried out at a variable rate, but from the viewpoint of stable protrusion formation and ease of process control, addition at a constant rate is preferred. The addition rate of each of the aqueous solutions depends on the reaction scale, but in the case of a 5-L scale reaction vessel, for example, is preferably 0.01 to 10 mL / min, particularly 0.1 to 5 mL / min, for each.

[0043] In the second step, from the viewpoint of forming a dense film, it is preferable to add an aqueous solution containing a nickel salt and a mixed aqueous solution containing a reducing agent and an alkali separately to the slurry obtained in the first step.

[0044] The concentration of the nickel salt in the aqueous solution containing the nickel salt is preferably 10 to 1000 g / L, particularly 50 to 500 g / L. When a phosphorus compound is used as the reducing agent, the concentration of the reducing agent in the aqueous solution containing the reducing agent is preferably 100 to 1000 g / L, particularly 100 to 800 g / L. When a boron compound is used as the reducing agent, the concentration is preferably 5 to 200 g / L, particularly 10 to 100 g / L. When hydrazine or a derivative thereof is used as the reducing agent, the concentration is preferably 5 to 200 g / L, particularly 10 to 100 g / L. The concentration of the alkali in the aqueous solution containing the alkali is preferably 5 to 500 g / L, particularly 10 to 200 g / L.

[0045] The conductive particles obtained by the manufacturing method of the present invention have protrusions on their surfaces. That is, the protrusions are present on the outer surface of the conductive layer. The height of the protrusions is preferably 20 nm to 1,000 nm, more preferably 50 nm to 800 nm. The number of protrusions depends on the particle size of the conductive particles, but it is advantageous to have 1 to 20,000 protrusions per conductive particle, more preferably 5 to 5,000 protrusions per conductive particle, in order to further improve the conductivity of the conductive particles. The length of the base of the protrusions is preferably 5 nm to 1,000 nm, more preferably 10 nm to 800 nm. The length of the base of the protrusions refers to the length along the surface of the conductive particle at the location where the protrusions are formed when the cross section of the particle is observed with an SEM, and the height of the protrusions refers to the shortest distance from the base of the protrusion to the apex of the protrusion. Note that if a single protrusion has multiple apexes, the highest apex is used as the height of that protrusion. The length of the base of the protrusions and the height of the protrusions are the arithmetic mean values ​​measured for 20 different particles observed with an electron microscope.

[0046] The conductive particles obtained by the above-described method are preferably heat-treated under a vacuum of 1000 Pa or less, preferably 0.01 to 900 Pa, and particularly 0.01 to 500 Pa, at a temperature of 200 to 600°C, preferably 250 to 500°C, and particularly 300 to 450°C. Heating the conductive particles while maintaining such a vacuum promotes crystallization of the metal in the conductive layer, thereby reducing electrical resistance and improving electrical conductivity. Note that the degree of vacuum in the present invention is an absolute pressure, i.e., a value when an absolute vacuum is defined as 0.

[0047] The heat treatment time is preferably 0.1 to 10 hours, and more preferably 0.5 to 5 hours. By adopting this treatment time, increases in production costs can be suppressed, and denaturation of the core particles and conductive layer due to thermal history can be suppressed, minimizing the impact on quality. This heat treatment time is the time from when the target treatment temperature is reached to when the heat treatment is completed.

[0048] The heat treatment may be carried out while the conductive particles are left standing, or while stirring. When the heat treatment is carried out while the conductive particles are left standing, it is preferable that the conductive particles are left standing at a thickness of 0.1 mm to 100 mm. By leaving the conductive particles standing at this thickness, the heat treatment of the conductive layer is carried out successfully, and the manufacturing cost can be reduced.

[0049] The heat treatment is carried out after evacuating the container containing the conductive particles, either in a stationary state or with stirring. At this time, the gas phase of the container containing the conductive particles may be replaced with an inert gas such as nitrogen before evacuating, or the container may be evacuated as is. The heat treatment may be carried out multiple times as necessary.

[0050] The heat treatment is preferably carried out by reaching a vacuum of 1000 Pa or less, preferably 0.01 to 900 Pa, and particularly preferably 0.01 to 500 Pa, at room temperature, maintaining the pressure for 5 to 60 minutes, and more preferably 10 to 50 minutes, and then raising the temperature to the treatment temperature. This operation can prevent oxidation of the conductive layer due to oxygen and moisture in the heated atmosphere or the conductive particles, thereby reducing the connection resistance.

[0051] After the heat treatment, it is preferable to release the vacuum after lowering the temperature to 50°C or less, or even 40°C or less, while maintaining the vacuum level. The reason for this is that if the vacuum is released at the temperature immediately after the heat treatment, the presence of oxygen or moisture in the atmosphere may promote oxidation of the conductive layer, resulting in a risk of increased connection resistance. Furthermore, from the perspective of production costs, the vacuum may be released in normal air, but from the perspective of preventing oxidation of the conductive layer, it is more preferable to release the vacuum by purging with an inert gas such as nitrogen, argon, or helium, or a non-oxidizing gas such as a hydrogen-nitrogen mixed gas.

[0052] The conductive powder of the present invention is a conductive powder consisting of conductive particles having protrusions on their particle surfaces, and when 0.05 g of the conductive powder is placed in a 150 mm diameter SUS cylindrical container and crushed by rotating a 2 kg SUS cylindrical weight 20 times, the number of detached protrusions per 100 conductive particles is 5 or less. The conductive particles are obtained by the above-mentioned method of producing conductive particles of the present invention.

[0053] The number of detached protrusions per 100 conductive particles when conductive powder is ground can be measured using the following method. First, the ground conductive powder is mixed with an organic solvent and an epoxy resin to form a film having a thickness of 1 to 200 μm, preferably 10 to 150 μm. The resulting film is observed under an optical microscope at 1000x magnification, and the number of conductive particles and detached protrusions within the field of view are counted to calculate the number of detached protrusions per 100 conductive particles.

[0054] The organic solvent is not particularly limited as long as it is compatible with the epoxy resin, but examples include one or a mixture of two or more of acetone, ethyl ether, xylene, methyl acetate, ethyl acetate, toluene, methanol, isopropyl alcohol, 1-butanol, and methyl ethyl ketone. When kneading the conductive powder with the organic solvent and epoxy resin, it is preferable to use 10 to 40 parts by mass of the organic solvent per 1 part by mass of the conductive powder, and 10 to 50 parts by mass of the epoxy resin per 1 part by mass of the conductive powder. The kneading method is not particularly limited, and examples include a method in which the conductive powder and the organic solvent are mixed and then kneaded with the epoxy resin, a method in which the organic solvent and the epoxy resin are mixed and then kneaded with the conductive powder, and a method in which the conductive powder and the epoxy resin are mixed and then kneaded with the organic solvent.

[0055] When the conductive particles obtained by the manufacturing method of the present invention are used as a conductive filler in a conductive adhesive as described below, their surfaces can be further coated with an insulating resin to prevent short circuits between the conductive particles. The insulating resin coating is formed so that the surface of the conductive particles is not exposed as much as possible when no pressure is applied, and so that it is broken by the heat and pressure applied when bonding two electrodes with the conductive adhesive, exposing at least the protrusions on the surface of the conductive particles. The thickness of the insulating resin can be approximately 0.1 to 0.5 μm. The insulating resin may cover the entire surface of the conductive particles, or only a portion of the surface of the conductive particles.

[0056] A wide variety of insulating resins known in the art can be used, including, for example, resins made of organic polymers such as phenolic resin, urea resin, melamine resin, allyl resin, furan resin, polyester resin, epoxy resin, silicone resin, polyamide-imide resin, polyimide resin, polyurethane resin, fluororesin, polyolefin resin (e.g., polyethylene, polypropylene, polybutylene), polyalkyl(meth)acrylate resin, poly(meth)acrylic acid resin, polystyrene resin, acrylonitrile-styrene-butadiene resin, vinyl resin, polyamide resin, polycarbonate resin, polyacetal resin, ionomer resin, polyethersulfone resin, polyphenyloxide resin, polysulfone resin, polyvinylidene fluoride resin, ethyl cellulose resin, and cellulose acetate resin.

[0057] Methods for forming an insulating coating layer on the surface of conductive particles include chemical methods such as coacervation, interfacial polymerization, in situ polymerization, and liquid curing coating; physico-mechanical methods such as spray drying, air suspension coating, vacuum deposition coating, dry blending, hybridization, electrostatic coalescence, melting dispersion cooling, and inorganic encapsulation; and physico-chemical methods such as interfacial precipitation.

[0058] The organic polymer constituting the insulating resin may contain a compound containing an ionic group in the polymer structure as a monomer component, provided that the organic polymer is non-conductive. The compound containing an ionic group may be a crosslinkable monomer or a non-crosslinkable monomer. In other words, it is preferable that the organic polymer is formed using a compound in which at least one of the crosslinkable monomer and the non-crosslinkable monomer has an ionic group. The "monomer component" refers to a structure derived from a monomer in the organic polymer, and is a component derived from the monomer. By subjecting the monomer to polymerization, an organic polymer containing the monomer component as a constituent unit is formed.

[0059] The ionic group is preferably present at the interface of the organic polymer that constitutes the insulating resin. Furthermore, the ionic group is preferably chemically bonded to a monomer component that constitutes the organic polymer. Whether or not the ionic group is present at the interface of the organic polymer can be determined by determining whether or not the insulating resin is attached to the surface of the conductive particle by scanning electron microscope observation when an insulating resin containing an organic polymer having an ionic group is formed on the surface of the conductive particle.

[0060] Examples of the ionic group include onium-based functional groups such as a phosphonium group, an ammonium group, a sulfonium group, etc. Among these, from the viewpoint of increasing the adhesion between the conductive particle and the insulating resin and forming conductive particles that combine high levels of insulation and conduction reliability, an ammonium group or a phosphonium group is preferred, and a phosphonium group is more preferred.

[0061] The onium functional group is preferably one represented by the following general formula (1).

[0062] [ka] (In the formula, X represents a phosphorus atom, a nitrogen atom, or a sulfur atom; R may be the same or different and represents a hydrogen atom, a linear, branched, or cyclic alkyl group, or an aryl group; n is 1 when X represents a nitrogen atom or a phosphorus atom, and is 0 when X represents a sulfur atom; * represents a bond.)

[0063] Counterions for the ionic groups include, for example, halide ions. Examples of halide ions include Cl. - , F - , Br - , I - Examples include:

[0064] In formula (1), examples of the linear alkyl group represented by R include linear alkyl groups having 1 to 20 carbon atoms, and specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, and an n-icosyl group.

[0065] In formula (1), examples of the branched alkyl group represented by R include branched alkyl groups having 3 to 8 carbon atoms, and specific examples include an isopropyl group, an isobutyl group, an s-butyl group, a t-butyl group, an isopentyl group, an s-pentyl group, a t-pentyl group, an isohexyl group, an s-hexyl group, a t-hexyl group, and an ethylhexyl group.

[0066] In formula (1), examples of the cyclic alkyl group represented by R include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclooctadecyl.

[0067] In formula (1), examples of the aryl group represented by R include a phenyl group, a benzyl group, a tolyl group, and an o-xylyl group.

[0068] In general formula (1), R is preferably an alkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms, and even more preferably an alkyl group having 1 to 8 carbon atoms. Furthermore, in general formula (1), R is more preferably a linear alkyl group. Such a configuration of the onium functional group improves the adhesion between the insulating resin and the conductive particles, ensuring insulation, and further improving the reliability of conduction during thermocompression bonding.

[0069] From the viewpoint of facilitating the acquisition of monomers and the synthesis of polymers, as well as increasing the production efficiency of insulating resins, it is preferable that the organic polymer having an ionic group that constitutes the insulating resin has a constituent unit represented by the following general formula (2) or general formula (3).

[0070] [ka] (In the formula, X, R, and n are defined as in the general formula (1). m is an integer of 0 to 5. An - indicates a monovalent anion.)

[0071] [ka] (In the formula, X, R, and n are the same as those in the general formula (1). - indicates a monovalent anion. m 1 is an integer of 1 or more and 5 or less. R5 is a hydrogen atom or a methyl group.

[0072] As examples of R in formula (2) and formula (3), the explanation of the functional group of R in general formula (1) above is applied as appropriate. The ionic group may be bonded to the para-position, ortho-position, or meta-position relative to the CH group of the benzene ring in formula (2), and is preferably bonded to the para-position. In formula (2) and formula (3), monovalent An - Suitable examples of the halide ions include Cl. - , F - , Br - , I - Examples include:

[0073] In the general formula (2), m is preferably an integer of 0 or more and 2 or less, more preferably 0 or 1, and particularly preferably 1. In the general formula (3), m 1 is preferably 1 or more and 3 or less, more preferably 1 or 2, and most preferably 2.

[0074] The organic polymer having an ionic group preferably contains a monomer component having, for example, an onium-based functional group and an ethylenically unsaturated bond. From the viewpoint of facilitating the availability of the monomer and the synthesis of the polymer and improving the production efficiency of the insulating resin, the organic polymer having an ionic group also preferably contains a non-crosslinkable monomer component.

[0075] Examples of non-crosslinkable monomers having an onium functional group and an ethylenically unsaturated bond include ammonium group-containing monomers such as N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropylacrylamide, and N,N,N-trimethyl-N-2-methacryloyloxyethyl ammonium chloride; sulfonium group-containing monomers such as phenyl methacrylate dimethylsulfonium methyl sulfate; 4-(vinylbenzyl)triethylphosphonium chloride, 4-(vinylbenzyl)trimethylphosphonium chloride, and 4-(vinylbenzyl)tributyl Examples of suitable monomers include phosphonium chloride, 4-(vinylbenzyl)trioctylphosphonium chloride, 4-(vinylbenzyl)triphenylphosphonium chloride, 2-(methacryloyloxyethyl)trimethylphosphonium chloride, 2-(methacryloyloxyethyl)triethylphosphonium chloride, 2-(methacryloyloxyethyl)tributylphosphonium chloride, 2-(methacryloyloxyethyl)trioctylphosphonium chloride, and 2-(methacryloyloxyethyl)triphenylphosphonium chloride. The organic polymer having an ionic group may contain two or more non-crosslinkable monomer components.

[0076] In the organic polymer constituting the insulating resin, ionic groups may be bonded to all of the monomer components, or ionic groups may be bonded to a portion of all the structural units of the organic polymer. When ionic groups are bonded to a portion of all the structural units of the organic polymer, the proportion of the monomer components to which ionic groups are bonded is preferably 0.01 mol% to 99 mol%, more preferably 0.02 mol% to 95 mol%. Here, the number of monomer components in the organic polymer is calculated by counting a structure derived from one ethylenically unsaturated bond as one structural unit of the monomer. When ionic groups are contained in both crosslinkable and non-crosslinkable monomers, the proportion of the monomer components is the total amount.

[0077] The insulating resin coating may be in the form of a layer of insulating fine particles or a continuous insulating film.

[0078] When the insulating resin is made of insulating fine particles, by thermocompression bonding conductive particles coated with the insulating fine particles between electrodes, the insulating fine particles melt, deform, peel off, or move on the conductive particle surface, exposing the metal surface of the conductive particle in the thermocompression-bonded portion, thereby enabling conduction between the electrodes and obtaining connectivity. Meanwhile, the surface portion of the conductive particle facing in a direction other than the thermocompression bonding direction is generally maintained in a state where the conductive particle surface is covered with the insulating fine particles, so that conduction in a direction other than the thermocompression bonding direction is prevented.

[0079] The insulating fine particles, containing the ionic groups on their surfaces, easily adhere to the conductive particles, thereby ensuring a sufficient proportion of the conductive particle surfaces covered with the insulating fine particles and effectively preventing the insulating fine particles from peeling off from the conductive particles, etc. Therefore, the insulating fine particles are more likely to exhibit a short-circuit prevention effect in a direction different from that between the opposing electrodes, and improved insulation in that direction can be expected.

[0080] The shape of the insulating fine particles is not particularly limited and may be spherical or may be a shape other than spherical. Examples of shapes other than spherical include fibrous, hollow, plate-like, and needle-like. The insulating fine particles may also have a large number of protrusions on their surface or may be amorphous. Spherical insulating fine particles are preferred in terms of adhesion to conductive particles and ease of synthesis.

[0081] The average particle diameter (D) of the insulating fine particles is preferably 10 nm or more and 3,000 nm or less, more preferably 15 nm or more and 2,000 nm or less. When the average particle diameter of the insulating fine particles is within the above range, the obtained coated particles do not cause a short circuit in a direction different from that between the opposing electrodes, and it is easy to ensure conductivity between the opposing electrodes. In the present invention, the average particle diameter of the insulating fine particles is a value measured by observation using a scanning electron microscope, and specifically, it is measured by the method described in the examples below.

[0082] The particle size distribution of insulating fine particles measured by the above-mentioned method has a certain range. Generally, the range of the particle size distribution of a powder is expressed by the coefficient of variation (hereinafter also referred to as "CV") shown in the following calculation formula (1). CV(%)=(standard deviation / average particle diameter)×100...(1) A large CV indicates a wide particle size distribution, while a small CV indicates a sharp particle size distribution. The coated particles of this embodiment preferably use insulating fine particles with a CV of 0.1% or more and 20% or less, more preferably 0.5% or more and 15% or less, and most preferably 1% or more and 10% or less. A CV within this range has the advantage of allowing the thickness of the coating layer of insulating fine particles to be uniform.

[0083] Furthermore, the insulating resin may be a continuous film made of a polymer and having ionic groups, instead of the insulating fine particles. When the insulating resin is a continuous film having ionic groups, thermocompression bonding of the conductive particles between electrodes melts, deforms, or peels the continuous film, exposing the metal surface of the conductive particles, thereby enabling conduction between the electrodes and achieving connectivity. In particular, thermocompression bonding of the conductive particles between electrodes often results in the continuous film being torn, exposing the metal surface. Meanwhile, the surface portions of the conductive particles facing in a direction different from the thermocompression bonding direction generally maintain the state of coating the conductive particles with the continuous film, preventing conduction in directions other than the thermocompression bonding direction. It is preferable that the continuous film also has ionic groups on its surface.

[0084] The thickness of the continuous film is preferably 10 nm or more from the viewpoint of improving insulation in a direction different from that between the opposing electrodes, and is preferably 3,000 nm or less from the viewpoint of facilitating electrical conduction between the opposing electrodes. From this viewpoint, the thickness of the continuous film is preferably 10 nm or more and 3,000 nm or less, and more preferably 15 nm or more and 2,000 nm or less.

[0085] As with insulating fine particles, in the continuous coating, the ionic group is preferably part of the chemical structure of the substance that constitutes the continuous coating. In the continuous coating, the ionic group is preferably contained in at least one structure of the structural unit of the polymer that constitutes the continuous coating. The ionic group is preferably chemically bonded to the polymer that constitutes the continuous coating, more preferably bonded to a side chain of the polymer.

[0086] When the insulating resin is a continuous film, it is preferable that the continuous film be obtained by coating conductive particles with insulating fine particles having ionic groups on their surfaces and then heating the insulating fine particles. Alternatively, it is preferable that the continuous film be obtained by dissolving the insulating fine particles in an organic solvent. As described above, insulating fine particles having ionic groups tend to adhere to conductive particles, which ensures a sufficient proportion of the insulating fine particles on the conductive particle surface and makes it easier to prevent the insulating fine particles from peeling off from the conductive particles. Therefore, the continuous film obtained by heating or dissolving the insulating fine particles that coat the conductive particles can have a uniform thickness and a high proportion of the insulating fine particles on the conductive particle surface.

[0087] The conductive particles according to the manufacturing method of the present invention may be treated with a surface treatment agent in order to enhance the affinity with the insulating resin and improve adhesion. Examples of the surface treatment agent include benzotriazole compounds, titanium compounds, higher fatty acids or derivatives thereof, phosphate esters, phosphites, etc. These may be used alone or in combination as needed.

[0088] The surface treatment agent may or may not be chemically bonded to the metal on the surface of the conductive particle. The surface treatment agent is sufficient as long as it is present on the surface of the conductive particle, and in this case, it may be present on the entire surface of the conductive particle or only on a part of the surface.

[0089] Examples of the triazole-based compounds include compounds having a nitrogen-containing heterocyclic structure having three nitrogen atoms in a five-membered ring.

[0090] The triazole compounds include compounds having a triazole monocyclic structure that is not condensed with other rings, as well as compounds having a ring structure in which a triazole ring is condensed with other rings, such as a benzene ring or a naphthalene ring.

[0091] Among these, compounds having a ring structure in which a triazole ring is fused with another ring are preferred because of their excellent adhesion to insulating resins, and benzotriazole-based compounds, which are compounds having a structure in which a triazole ring is fused with a benzene ring, are particularly preferred. Benzotriazole compounds include those represented by the following general formula (I).

[0092] [ka] (In the formula, R 11 is a negative charge, a hydrogen atom, an alkali metal, an optionally substituted alkyl group, an amino group, a formyl group, a hydroxyl group, an alkoxy group, a sulfonic acid group, or a silyl group, and R 12 , R 13 , R 14 and R 15 are each independently a hydrogen atom, a halogen atom, an optionally substituted alkyl group, a carboxyl group, a hydroxyl group, or a nitro group.

[0093] R in formula (I) 11 Examples of the alkali metal represented by R include lithium, sodium, and potassium. 11 The alkali metal represented by R in formula (I) is an alkali metal cation. 11 is an alkali metal, R 11 The bond between the nitrogen atom and the alkyl group may be an ionic bond. R in formula (I) 11 , R 12 , R 13 , R 14 and R 15 Examples of the alkyl group represented by the formula (I) include those having 1 to 20 carbon atoms, and particularly preferably those having 1 to 12 carbon atoms. The alkyl group may be substituted, and examples of the substituent include an amino group, an alkoxy group, a carboxyl group, a hydroxyl group, an aldehyde group, a nitro group, a sulfonic acid group, a quaternary ammonium group, a sulfonium group, a sulfonyl group, a phosphonium group, a cyano group, a fluoroalkyl group, a mercapto group, and a halogen atom. R 11The alkoxy group represented by the following formula is preferably an alkoxy group having 1 to 12 carbon atoms. Also, R 12 , R 13 , R 14 and R 15 The number of carbon atoms in the alkoxy group as a substituent of the alkyl group represented by formula (I) is preferably 1 to 12. 12 , R 13 , R 14 and R 15 Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0094] Specific triazole compounds include compounds having a triazole monocyclic structure such as 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, 5-mercapto-1H-1,2,3-triazole sodium, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, and 3-amino-5-mercapto-1,2,4-triazole, as well as compounds having a ring structure in which a triazole ring is condensed with another ring, such as benzotriazole, 1-methyl-1H-benzotriazole, 4-methyl-1H-benzotriazole, 5-methyl-1H-benzotriazole, 4-carboxy-1H-benzotriazole, 5-carboxy-1H-benzotriazole, 5-ethyl-1H-benzotriazole, and 5-propyl-1H-benzotriazo benzotriazole, 5,6-dimethyl-1H-benzotriazole, 1-aminobenzotriazole, 5-nitrobenzotriazole, 5-chlorobenzotriazole, 4,5,6,7-tetrabromobenzotriazole, 1-hydroxybenzotriazole, 1-(methoxymethyl)-1H-benzotriazole, 1H-benzotriazole-1-methanol, 1H-benzotriazole-1-carboxaldehyde, 1-(chloromethyl)-1H-benzotriazole, 1-hydroxy-6-(trifluoromethyl)benzotriazole, benzotriazole butyl ester, 4-carboxyl-1H-benzotriazole butyl ester, 4-carboxyl-1H-benzotriazole octyl ester, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol, tetrabutylphosphonium benzotriazolate, 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate, 1H-benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate, 1-(formamidomethyl)-1H-benzotriazole, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3- Oxide hexafluorophosphate, 1-[bis(dimethylamino)methylene]-1H-benzotriazolium 3-oxide tetrafluoroborate, (6-chloro-1H-benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis(tetramethylene)uronium hexafluorophosphate, O-(6-chlorobenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium Tetrafluoroborate, O-(6-chlorobenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(benzotriazol-1-yl)-N,N,N',N'-bis(pentamethylene)uronium hexafluorophosphate, 1-(trimethylsilyl)-1H-benzotriazole, 1-[2-(trimethylsilyl)ethoxycarbonyloxy]benzotriazole, 1-(trifluoromethanesulfonyl)-1H-benzotriazole, (trimethylsilyl)-1H-benzotriazole, trifluoroacetyl)benzotriazole, tris(1H-benzotriazol-1-yl)methane, 9-(1H-benzotriazol-1-ylmethyl)-9H-carbazole, [(1H-benzotriazol-1-yl)methyl]triphenylphosphonium chloride, 1-(isocyanomethyl)-1H-benzotriazole, 1-[(9H-fluoren-9-ylmethoxy)carbonyloxy]benzotriazole, 1,2,3-benzotriazole sodium salt, naphthotriazole, and the like.

[0095] As the titanium-based compound, for example, a compound having a structure represented by general formula (II) is particularly preferred because when present on the surface of a conductive particle, affinity between the insulating resin and the conductive particle can be easily obtained, and the compound is easily dispersed in a solvent, allowing the surface of the conductive particle to be uniformly treated.

[0096] [ka] (R 21 is a divalent or trivalent group, and R 22 is an aliphatic hydrocarbon group having from 2 to 30 carbon atoms, an aryl group having from 6 to 22 carbon atoms, or an arylalkyl group having from 7 to 23 carbon atoms, p and r are each an integer of from 1 to 3, satisfying p+r=4, q is an integer of 1 or 2, and R 21 is a divalent group, q is 1, and R 21 When R is a trivalent group, q is 2. When q is 2, multiple R 22 may be the same or different. * represents a bond.)

[0097] R 22 Examples of the aliphatic hydrocarbon group having 4 to 28 carbon atoms represented by the formula (I) include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosenyl, docosyl, etc. Examples of unsaturated aliphatic hydrocarbon groups include alkenyl groups such as dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, nonadecenyl, icosenyl, eicosenyl, henicosenyl, and docosenyl. Examples of the aryl group having 6 to 22 carbon atoms include a phenyl group, a tolyl group, a naphthyl group, and an anthryl group. Examples of the arylalkyl group having 7 to 23 carbon atoms include a benzyl group, a phenethyl group, and a naphthylmethyl group. As the hydrophobic group, a straight-chain or branched-chain aliphatic hydrocarbon group is particularly preferred, and a straight-chain aliphatic hydrocarbon group is particularly preferred. In order to enhance the affinity between the insulating resin and the conductive particles, the aliphatic hydrocarbon group as the hydrophobic group is more preferably one having 4 to 28 carbon atoms, and most preferably one having 6 to 24 carbon atoms.

[0098] R 21 Examples of the divalent group represented by the formula include -O-, -COO-, -OCO-, and -OSO2-. 21 Examples of the trivalent group represented by the formula include -P(OH)(O-)2, -OPO(OH)-OPO(O-)2, and the like.

[0099] In general formula (II), * represents a bond, which may be bonded to the metal coating of the conductive particle or to another group, etc. In this case, examples of the other group include hydrocarbon groups, and specific examples include alkyl groups having 1 to 12 carbon atoms.

[0100] The titanium-based compound having the structure represented by general formula (II) includes the titanium-based compound having the structure represented by general formula (II) 21 A compound having a structure in which R is a divalent group is preferred in terms of availability and the ability to process the conductive particles without impairing their conductive properties. 21 The structure in which is a divalent group is represented by the following general formula (III).

[0101] [ka] (R 21 is a group selected from -O-, -COO-, -OCO-, and -OSO2-; p, r, and R 22 has the same meaning as general formula (II).

[0102] In general formulas (II) and (III), r is preferably 2 or 3 from the viewpoint of improving the adhesion between the insulating resin and the conductive layer, and r is most preferably 3.

[0103] Specific examples of titanate-based coupling agents used in the present invention include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraisopropyl(dioctyl phosphite) titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctyl pyrophosphate)ethylene titanate, and the like, and these can be used alone or in combination of two or more. These titanate coupling agents are commercially available from, for example, Ajinomoto Fine-Techno Co., Ltd.

[0104] The higher fatty acid is preferably a saturated or unsaturated, straight-chain or branched-chain mono- or polycarboxylic acid, more preferably a saturated or unsaturated, straight-chain or branched-chain monocarboxylic acid, and even more preferably a saturated or unsaturated, straight-chain monocarboxylic acid. The fatty acid preferably has 7 or more carbon atoms. Furthermore, the derivative refers to a salt or amide of the fatty acid.

[0105] The higher fatty acid or derivative thereof used in the present invention preferably has 7 to 23 carbon atoms, more preferably 10 to 20 carbon atoms. Examples of such higher fatty acids or derivatives thereof include saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid; unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and arachidonic acid; and metal salts or amides thereof. Metal salts of higher fatty acids include salts of alkali metals, alkaline earth metals, transition metals such as Zr, Cr, Mn, Fe, Co, Ni, Cu, and Ag, and metals other than transition metals such as Al and Zn. Polyvalent metal salts such as Al, Zn, W, and V are preferred. Higher fatty acid metal salts may be mono-, di-, tri-, or tetra-forms depending on the valence of the metal. The higher fatty acid metal salt may also be any combination of these.

[0106] As the phosphate ester and phosphite ester, those having an alkyl group having 6 to 22 carbon atoms are preferably used. Examples of phosphate esters include hexyl phosphate, heptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, and monopentadecyl phosphate. Examples of phosphite esters include hexyl phosphite, heptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, and monopentadecyl phosphite.

[0107] In the present invention, the surface treatment agent is preferably a triazole-based compound or a titanium-based compound, in that it has excellent affinity with the insulating resin and is highly effective in increasing the coverage rate of the insulating resin, and in particular, benzotriazole, 4-carboxybenzotriazole, isopropyl triisostearoyl titanate, and tetraisopropyl (dioctyl phosphite) titanate are particularly preferred.

[0108] The conductive particles can be treated with a surface treatment agent by dispersing the conductive particles in a solution of the surface treatment agent and then filtering the dispersion. Before the treatment with the surface treatment agent, the conductive particles may have been treated with another treatment agent or may be untreated. The concentration of the surface treatment agent in the solution of the surface treatment agent (solution containing conductive particles) in which the conductive particles are dispersed can be 0.01% by mass or more and 10.0% by mass or less. Examples of solvents for the solution of the surface treatment agent include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, isopentyl alcohol, and cyclohexanol, ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone, and methyl-n-butyl ketone, esters such as methyl acetate and ethyl acetate, ethers such as diethyl ether and ethylene glycol monoethyl ether, normal hexane, cyclohexanone, toluene, 1,4-dioxane, N,N-dimethylformamide, and tetrahydrofuran. The dispersed and filtered surface-treated conductive particles are preferably dispersed again in a solvent to remove excess surface treatment agent.

[0109] The surface treatment of conductive particles with a surface treatment agent can be carried out by mixing the conductive particles, the surface treatment agent, and a solvent at room temperature. Alternatively, the conductive particles and the surface treatment agent may be mixed in a solvent and then heated to promote the reaction. The heating temperature can be, for example, 30°C or higher and 50°C or lower.

[0110] The conductive particles of the present invention have low connection resistance and excellent connection reliability, and are therefore suitable for use, for example, in anisotropic conductive films (ACFs), heat seal connectors (HSCs), and as conductive materials for connecting electrodes of liquid crystal display panels to circuit boards of driving LSI chips. Examples of such conductive materials include the conductive particles of the present invention used as they are, or materials prepared by dispersing the conductive particles of the present invention in a binder resin. Other forms of the conductive material are not particularly limited, and in addition to the above, examples include anisotropic conductive pastes, conductive adhesives, and anisotropic conductive inks.

[0111] Examples of the binder resin include thermoplastic resins and thermosetting resins, etc. Examples of the thermoplastic resin include acrylic resin, styrene resin, ethylene-vinyl acetate resin, and styrene-butadiene block copolymer, and examples of the thermosetting resin include epoxy resin, phenol resin, urea resin, polyester resin, urethane resin, and polyimide resin.

[0112] In addition to the conductive particles and binder resin of the present invention, the conductive material may contain, as necessary, a tackifier, a reactivity aid, an epoxy resin curing agent, a metal oxide, a photoinitiator, a sensitizer, a curing agent, a vulcanizing agent, an anti-degradation agent, a heat-resistant additive, a thermal conductivity improver, a softener, a colorant, various coupling agents, or a metal deactivator.

[0113] In the conductive material, the amount of conductive particles used may be determined appropriately depending on the application. From the viewpoint of easily achieving electrical conduction without the conductive particles coming into contact with each other, the amount of conductive particles used is preferably, for example, 0.01 parts by mass or more and 50 parts by mass or less, particularly 0.03 parts by mass or more and 40 parts by mass or less, per 100 parts by mass of the conductive material.

[0114] The conductive particles of the present invention are particularly suitable for use as a conductive filler for a conductive adhesive, among the above-mentioned forms of conductive materials.

[0115] The conductive adhesive is preferably used as an anisotropic conductive adhesive that is placed between two substrates each having a conductive base material and adheres the conductive base material to establish electrical conductivity by heating and pressurizing. This anisotropic conductive adhesive contains the conductive particles of the present invention and an adhesive resin. Any adhesive resin can be used without particular limitations as long as it is insulating and suitable for use as an adhesive resin. Either a thermoplastic or thermosetting resin may be used, and those that exhibit adhesive properties upon heating are preferred. Examples of such adhesive resins include thermoplastic, thermosetting, and UV-curable types. Other examples include semi-thermosetting types that exhibit intermediate properties between thermoplastic and thermosetting types, and hybrid types that combine thermosetting and UV-curable types. These adhesive resins can be selected appropriately depending on the surface characteristics and usage of the circuit board or other substrate to be adhered. In particular, adhesive resins containing a thermosetting resin are preferred due to their excellent material strength after adhesion.

[0116] Specific examples of adhesive resins include those prepared using one or a combination of two or more resins selected from the group consisting of ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral, polyurethane, SBS block copolymer, carboxyl-modified SBS copolymer, SIS copolymer, SEBS copolymer, maleic acid-modified SEBS copolymer, polybutadiene rubber, chloroprene rubber, carboxyl-modified chloroprene rubber, styrene-butadiene rubber, isobutylene-isoprene copolymer, acrylonitrile-butadiene rubber (hereinafter referred to as NBR), carboxyl-modified NBR, amine-modified NBR, epoxy resin, epoxy ester resin, acrylic resin, phenolic resin, and silicone resin as the main component. Among these, thermoplastic resins such as styrene-butadiene rubber and SEBS are preferred due to their excellent reworkability. As a thermosetting resin, epoxy resin is preferred. Of these, epoxy resin is most preferred because it has the advantages of high adhesive strength, excellent heat resistance and electrical insulation, and also low melt viscosity, allowing connection at low pressure.

[0117] The epoxy resin may be any commonly used polyhydric epoxy resin having two or more epoxy groups per molecule. Specific examples include novolak resins such as phenol novolak and cresol novolak; polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, resorcinol, and bishydroxydiphenyl ether; polyhydric alcohols such as ethylene glycol, neopentyl glycol, glycerin, trimethylolpropane, and polypropylene glycol; polyamino compounds such as ethylenediamine, triethylenetetramine, and aniline; and polycarboxylic compounds such as adipic acid, phthalic acid, and isophthalic acid, reacted with epichlorohydrin or 2-methylepichlorohydrin. Other examples include aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxide and butadiene dimer diepoxide. These may be used alone or in combination.

[0118] It is preferable to use high-purity adhesive resins with reduced impurity ions (Na, Cl, etc.) and hydrolyzable chlorine as the various adhesive resins mentioned above, from the viewpoint of preventing ion migration.

[0119] The amount of conductive particles used in the anisotropic conductive adhesive is usually 0.1 to 30 parts by mass, preferably 0.5 to 25 parts by mass, and more preferably 1 to 20 parts by mass, per 100 parts by mass of the adhesive resin component. By keeping the amount of conductive particles within this range, increases in connection resistance and melt viscosity are suppressed, connection reliability is improved, and sufficient anisotropy of the connection can be ensured.

[0120] In addition to the conductive particles and adhesive resin described above, the anisotropic conductive adhesive may contain additives known in the art. The amounts of these additives may be within the ranges known in the art. Examples of other additives include tackifiers, reactivity aids, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, anti-degradants, heat-resistant additives, thermal conductivity improvers, softeners, colorants, various coupling agents, and metal deactivators.

[0121] Examples of tackifiers include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene-based resins, isoprene-based resins, alkylphenol resins, and xylene resins. Examples of reactive auxiliaries, i.e., crosslinking agents, include polyols, isocyanates, melamine resins, urea resins, utropines, amines, acid anhydrides, and peroxides. Any epoxy resin curing agent having two or more active hydrogen atoms per molecule can be used without particular limitation. Specific examples include polyamino compounds such as diethylenetriamine, triethylenetetramine, metaphenylenediamine, dicyandiamide, and polyamidoamine; organic acid anhydrides such as phthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and pyromellitic anhydride; and novolac resins such as phenol novolac and cresol novolac. These can be used alone or in combination. A latent curing agent may also be used if necessary. Usable latent curing agents include, for example, imidazoles, hydrazides, boron trifluoride-amine complexes, sulfonium salts, amine imides, polyamine salts, dicyandiamide, and modified products thereof. These can be used alone or in combination of two or more.

[0122] The anisotropic conductive adhesive is manufactured using a manufacturing device commonly used in the art. For example, it is manufactured by blending conductive particles, an adhesive resin, and optionally a curing agent and various additives, and mixing them in an organic solvent if the adhesive resin is a thermosetting resin, or by melt-kneading them at a temperature above the softening point of the adhesive resin, specifically preferably about 50 to 130°C, more preferably about 60 to 110°C, if the adhesive resin is a thermoplastic resin. The anisotropic conductive adhesive thus obtained may be applied as a coating or in the form of a film.

[0123] The connection structure according to the present invention is obtained by connecting two circuit boards together using the conductive particles according to the present invention or the conductive material according to the present invention. Examples of the form of the connection structure include a connection structure between a flexible printed circuit board and a glass substrate, a connection structure between a semiconductor chip and a flexible printed circuit board, and a connection structure between a semiconductor chip and a glass substrate. [Example]

[0124] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. The properties in the examples were measured by the following methods. (1) Average particle size 200 particles were randomly extracted from a scanning electron microscope (SEM) photograph of the object to be measured, and the particle diameters were measured at a magnification of 10,000 times, and the arithmetic mean value was taken as the average particle diameter. (2) Thickness of the conductive layer The conductive particles were cut into two pieces, and the cross sections of the cut pieces were observed and measured using a scanning electron microscope (SEM).

[0125] Example 1 (1) Pretreatment Spherical styrene-acrylate-silica composite resin particles with an average particle size of 3.0 μm were used as core particles. 9 g of these particles were added to 200 mL of a conditioner solution (Rohm and Haas Electronic Materials' "Cleaner Conditioner 231") while stirring. The concentration of the conditioner solution was 40 mL / L. The solution was then stirred at 60°C for 30 minutes with ultrasonic waves to modify the surface of the core particles and disperse them. The solution was filtered, and the core particles were repulped and washed once to form a 200 mL slurry. 0.1 g of stannous chloride was added to the slurry. The mixture was stirred at room temperature for 5 minutes to sensitize the core particles, adsorbing tin ions onto their surfaces. The solution was then filtered, and the core particles were repulped and washed once to form a 200 mL slurry, which was then maintained at 60°C. 1.5 mL of a 0.11 mol / L palladium chloride solution was then added to the slurry. The core particles were activated by stirring at 60°C for 5 minutes, and the palladium ions were captured on their surfaces. The aqueous solution was then filtered, and the core particles were repulped and washed with hot water once to form a 100 mL slurry. 10 mL of a 0.5 g / L dimethylamine borane solution was added, and the mixture was stirred for 2 minutes while applying ultrasound to obtain a slurry of pretreated core particles. (2) Preparation of plating bath Three liters of an electroless nickel-phosphorus plating bath was prepared from an aqueous solution containing 5 g / L of sodium tartrate, 2 g / L of nickel sulfate hexahydrate, 10 g / L of trisodium citrate, 0.1 g / L of sodium hypophosphite, and 2 g / L of polyethylene glycol, and the temperature was raised to 70°C. (3) First step The slurry of the pretreated core particles was added to this electroless plating bath and stirred for 5 minutes, after which it was confirmed that the hydrogen bubbling had stopped. (4)Second process To this slurry, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added by metering pumps at an addition rate of 1.0 mL / min for 45 minutes. After the addition was complete, the slurry was maintained with stirring for 30 minutes. After 30 minutes had elapsed, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution of 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added again separately and continuously by metering pumps at an addition rate of 1.0 mL / min for 74 minutes. (5) Post-processing The resulting electroless plating solution was stirred for 5 minutes while maintaining the temperature at 70°C. The solution was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain conductive particles having an electroless nickel-phosphorus plating layer formed as a conductive layer on the surface of the core particles. The resulting conductive particles had an average particle size of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0126] Example 2 The same operations as in Example 1 were carried out up to the first step (3) to prepare a slurry. (4)Second process To the obtained slurry, a 224 g / L aqueous nickel sulfate solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added by metering pumps at an addition rate of 1.0 mL / min for 45 minutes. After the addition was complete, the slurry was maintained with stirring for 60 minutes. After 60 minutes had elapsed, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution of 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added again separately and continuously by metering pumps at an addition rate of 1.0 mL / min for 74 minutes. (5) Post-processing Conductive particles were obtained by carrying out the same procedure as in Example 1, in which an electroless nickel-phosphorus plating layer was formed as a conductive layer on the surface of core particles. The resulting conductive particles had an average particle diameter of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0127] Example 3 The same operations as in Example 1 were carried out up to the first step (3) to prepare a slurry. (4)Second process To the obtained slurry, a 224 g / L aqueous nickel sulfate solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added by metering pumps at an addition rate of 1.0 mL / min for 45 minutes. After the addition was complete, the slurry was maintained with stirring for 90 minutes. After 90 minutes had elapsed, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution of 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added again separately and continuously by metering pumps at an addition rate of 1.0 mL / min for 74 minutes. (5) Post-processing Conductive particles were obtained by carrying out the same procedure as in Example 1, in which an electroless nickel-phosphorus plating layer was formed as a conductive layer on the surface of core particles. The resulting conductive particles had an average particle diameter of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0128] Example 4 The same operations as in Example 1 were carried out up to the first step (3) to prepare a slurry. (4)Second process To the obtained slurry, a 224 g / L aqueous nickel sulfate solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added by metering pumps at an addition rate of 1.0 mL / min for 80 minutes. After the addition was complete, the slurry was maintained with stirring for 30 minutes. After 30 minutes had elapsed, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution of 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added again separately and continuously by metering pumps at an addition rate of 1.0 mL / min for 45 minutes. (5) Post-processing Conductive particles were obtained by carrying out the same procedure as in Example 1, in which an electroless nickel-phosphorus plating layer was formed as a conductive layer on the surface of core particles. The resulting conductive particles had an average particle diameter of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0129] Example 5 The same operations as in Example 1 were carried out up to the first step (3) to prepare a slurry. (4)Second process To the obtained slurry, a 224 g / L aqueous nickel sulfate solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added by metering pumps at an addition rate of 1.0 mL / min for 45 minutes. After the addition was completed, 20 g of a nickel nanoparticle slurry prepared by dispersing 7 g of nickel nanoparticles (manufactured by Mitsui Mining & Smelting Co., Ltd.) having an average particle size of 90 nm in water was added, and the slurry was maintained for 60 minutes while stirring. After 60 minutes had elapsed, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution of 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added again separately and continuously by metering pumps at an addition rate of 1.0 mL / min for 74 minutes. (5) Post-processing Conductive particles were obtained by carrying out the same procedure as in Example 1, in which an electroless nickel-phosphorus plating layer was formed as a conductive layer on the surface of core particles. The resulting conductive particles had an average particle diameter of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0130] Comparative Example 1 The same operations were carried out as in Example 1 up to step (3) 1. Next, a 224 g / L aqueous nickel sulfate solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added to the obtained slurry by metering pumps at an addition rate of 1.0 mL / min for 119 minutes, and electroless plating was initiated. After adding the entire nickel sulfate aqueous solution and the mixed aqueous solution of sodium hypophosphite and sodium hydroxide, stirring was continued for 5 minutes while maintaining the temperature at 70°C. The solution was then filtered, and the filtrate was washed three times and then dried in a vacuum dryer at 110°C to obtain conductive particles in which an electroless nickel-phosphorus plating layer was formed as a conductive layer on the surface of the core particles. The obtained conductive particles had an average particle size of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0131] Comparative Example 2 In Example 1, the same operations were carried out up to the first step (3) to prepare a slurry. (4)Second process To the obtained slurry, a 224 g / L aqueous nickel sulfate solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added by metering pumps at an addition rate of 1.0 mL / min for 45 minutes. After the addition was complete, the slurry was maintained under stirring for 5 minutes. After 5 minutes had elapsed, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution of 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added again separately and continuously by the metering pumps at an addition rate of 1.0 mL / min for 74 minutes. (5) Post-processing Conductive particles were obtained by carrying out the same procedure as in Example 1, in which an electroless nickel-phosphorus plating layer was formed as a conductive layer on the surface of core particles. The resulting conductive particles had an average particle diameter of 3.2 μm, a conductive layer thickness of 100 nm, and protrusions.

[0132] Comparative Example 3 In Example 1, the same operations were carried out up to the first step (3) to prepare a slurry. (4)Second process To the obtained slurry, a 224 g / L aqueous nickel sulfate solution and a mixed aqueous solution containing 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were separately and continuously added by metering pumps at an addition rate of 1.0 mL / min for 45 minutes. After the addition was complete, the slurry was maintained with stirring for 180 minutes. After 180 minutes, a 224 g / L aqueous solution of nickel sulfate and a mixed aqueous solution of 210 g / L sodium hypophosphite and 80 g / L sodium hydroxide were added separately and continuously by metering pumps at a rate of 1.0 mL / min for 74 minutes. However, the nickel layer dissolved, and no conductive particles were obtained.

[0133] (Evaluation of protrusion detachment) 0.05 g of conductive powder consisting of the conductive particles obtained in the Examples and Comparative Examples was placed in a 150 mm diameter SUS cylindrical container, and a 2 kg SUS cylindrical weight was inserted. The cylindrical weight was rotated 20 times to grind the conductive particles in the container, creating a measurement sample. This measurement sample was uniformly mixed with toluene and epoxy resin, and then thinly spread to a uniform thickness to form a film. The obtained film was observed in 10 fields using an optical microscope at 1000x magnification, and the number of detached protrusions per 100 conductive particles was calculated and evaluated according to the following criteria. ◯: The number of detached protrusions per 100 conductive particles is 5 or less. ×: The number of detached protrusions per 100 conductive particles is more than 5.

[0134] [Table 1]

[0135] As is clear from the results of the Examples and Comparative Examples, the conductive particles obtained in the Examples had a small number of detached protrusions, and it was found that the protrusions were stably fixed to the conductive layer.

Claims

1. A first step of mixing core particles with an electroless nickel plating bath containing a nickel salt, a reducing agent, and a complexing agent to prepare a slurry containing primary plated particles having an initial nickel thin film layer formed on the surface of the core particles; a second step in which an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali are successively added to the slurry obtained in the first step, the additions are stopped, the slurry is maintained for a time period of 10 minutes to 120 minutes, and an aqueous solution containing a nickel salt, an aqueous solution containing a reducing agent, and an aqueous solution containing an alkali are successively added again to the slurry to perform an electroless plating treatment on the primary plated particles; A method for producing conductive particles having the above structure.

2. 2. The method for producing conductive particles according to claim 1, wherein the addition time when the aqueous solution containing a nickel salt, the aqueous solution containing a reducing agent, and the aqueous solution containing an alkali are first successively added to the slurry obtained in the first step is 25 minutes or more.

3. 3. The method for producing conductive particles according to claim 1, wherein the addition time when the aqueous solution containing a nickel salt, the aqueous solution containing a reducing agent, and the aqueous solution containing an alkali are successively added again after the slurry is held in the second step is 40 minutes or more.

4. 3. The method for producing conductive particles according to claim 1, wherein in the second step, the aqueous solution containing the nickel salt and the mixed aqueous solution containing the reducing agent and alkali are added separately to the slurry of the first step.

5. 3. The method for producing conductive particles according to claim 1 or 2, wherein in the second step, the addition of the aqueous solution containing a nickel salt, the aqueous solution containing a reducing agent, and the aqueous solution containing an alkali is stopped and the metal nanoparticles are added while the slurry is maintained.

6. A conductive powder comprising conductive particles having a nickel plating layer with protrusions formed on the surface of a core particle, When 0.05 g of the conductive powder is placed in a 150 mm diameter SUS cylindrical container and crushed by rotating a 2 kg SUS cylindrical weight 20 times, the number of detached protrusions per 100 conductive particles is 5 or less.

7. A conductive powder as described in claim 6, wherein the nickel plating layer is an electroless nickel plating layer.

8. 8. The conductive powder according to claim 6, wherein the protrusions have microprotrusions formed as cores from autolysis products of the electroless nickel plating bath.

9. 8. The conductive powder according to claim 6, wherein the protrusions have metal nanoparticles as cores.

10. The conductive powder according to claim 9, wherein the metal of the metal nanoparticles is nickel.

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