Coated particles and conductive materials containing them

Abstract

To provide a coated particle that excels in adhesion and conduction reliability between an insulation particle and a conductive particle, and a conductive material including the same.SOLUTION: A coated particle includes a conductive particle having a metal film formed on a core particle, with the conductive particle coated with an insulation particle. In the insulation particle, a coat (1) is applied onto a silica particle with oxide and / or hydroxide of a metal (M), and an additional coat (2) is applied onto the coat (1) with fatty acid or a derivative thereof.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to coated particles in which conductive particles are coated with an insulating layer, and to conductive materials containing the same. [Background technology]

[0002] Conductive particles, in which metals such as nickel or gold are formed on the surface of resin particles, are used as conductive materials such as conductive adhesives, anisotropic conductive films, and anisotropic conductive adhesives. In recent years, with the increasing miniaturization of electronic devices, the circuit width and pitch of electronic circuits have become smaller and smaller. Consequently, there is a demand for conductive particles with smaller particle sizes for use in conductive adhesives, anisotropic conductive films, and anisotropic conductive adhesives. When using conductive particles with such small particle sizes, the amount of conductive particles must be increased to improve connectivity. However, increasing the amount of conductive particles can lead to short circuits due to conduction in unintended directions, i.e., conduction in directions different from those between opposing electrodes, making it difficult to obtain insulation in that direction. To solve this problem, insulating coated conductive particles are used, in which the surface of the conductive particles is coated with an insulating material to prevent contact between the metal layers of the conductive particles.

[0003] For example, Patent Document 1 describes coated particles having a core made of a conductive metal, the core being partially modified with organic particles made of an organic compound containing a functional group that binds to the metal, and that the organic compound has a positive or negative charge.

[0004] In Patent Document 2, coated particles similar to those in Patent Document 1 are described. The document states that the coated particles form a single-layer coating layer by chemically bonding insulating fine particles to particles having a surface made of conductive metal via a functional group having bonding property to the metal. The document also states that by thermocompression bonding such coated particles between electrodes, the insulating fine particles melt, deform or peel off, thereby exposing the metal surface of the metal-coated particles, enabling conduction between the electrodes and obtaining connectivity. In Patent Documents 1 and 2, ammonium group and sulfonium group are exemplified as the functional groups.

[0005] In Patent Document 3, after applying insulating resin fine particles containing a hetero element or a functional group having a bonding force with a metal on the surface of metal-coated particles and then heating the same, anisotropic insulating conductive particles having an insulating layer without a particle shape on the surface of the metal-coated particles can be obtained.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the case of conductive particles coated with insulating particles, improvement in the adhesion between the insulating particles and the conductive particles has been an issue. The adhesion between the insulating particles and the conductive particles is important for achieving conduction between opposing electrodes while obtaining insulation in a direction different from that of the opposing electrodes (hereinafter, also simply referred to as connection reliability). Therefore, further development of coated particles having excellent adhesion between the insulating particles and the conductive particles has been desired.

[0008] Therefore, an object of the present invention is to provide coated particles having excellent adhesion between insulating particles and conductive particles and electrical communication reliability, and a conductive material containing the same.

Means for Solving the Problems

[0009] As a result of intensive studies in view of the above circumstances, the inventors of the present invention found that when silica particles directly coated with a fatty acid or its derivative were used as insulating particles, the coating layer of the fatty acid or its derivative was easily peeled off by the load of a slight external force. On the other hand, when silica particles pretreated with a metal oxide such as aluminum or / and hydroxide were coated with a fatty acid or its derivative on the surface thereof and used as insulating particles, peeling of the coating layer of the fatty acid or its derivative from the particle surface of the conductive particles was suppressed even under the load of a slight external force. Conventionally, in order to obtain coated particles having excellent adhesion between insulating particles and conductive particles, the coating treatment has been performed using a solvent by a wet method. In contrast, when the insulating particles used in the present invention are used, even if the coating treatment of the insulating particles on the conductive particles is performed by a dry method, those having excellent adhesion between the insulating particles and the conductive particles can be obtained. Further, it has been found that the coated particles are also excellent in electrical communication reliability, and the present invention has been completed.

[0010] That is, a first invention provided by the present invention is a coated particle in which the surface of a conductive particle having a metal film formed on the surface of a core material particle is coated with an insulating particle, wherein the insulating particle is obtained by coating (1) the surface of silica particles with an oxide or / and hydroxide of a metal (M), and further coating (2) the surface of the coating (1) with a fatty acid or its derivative.

[0011] Further, a second invention provided by the present invention is a conductive material containing the coated particle of the first invention and an insulating resin.

Effect of the Invention

[0012] According to the present invention, the coating process of insulating particles onto conductive particles can be performed in a dry manner, and coated particles can be provided that exhibit excellent adhesion between insulating particles and conductive particles, as well as excellent conductivity reliability. [Modes for carrying out the invention]

[0013] The present invention will be described below based on preferred embodiments. The coated particles of this embodiment are coated particles in which the surface of conductive particles, on which a metal film is formed on the surface of core material particles, is coated with insulating particles, wherein the insulating particles are characterized in that the surface of silica particles is coated (1) with a metal (M) oxide and / or hydroxide, and the surface of the coating (1) is further coated (2) with a fatty acid or a derivative thereof.

[0014] (Conductive particles) As conductive particles, known ones conventionally used in conductive adhesives, anisotropic conductive films, and anisotropic conductive adhesives can be used.

[0015] The core material particles in conductive particles can be inorganic or organic without any particular restrictions. Examples of inorganic core material particles include metal particles such as gold, silver, copper, nickel, palladium, and solder; alloys; glass; ceramics; silica; metal or nonmetal oxides (including hydrated ones); metal silicates including aluminosilicates; metal carbides; metal nitrides; metal carbonates; metal sulfates; metal phosphates; metal sulfides; metal salts; metal halides; and carbon. Examples of organic core material particles include natural fibers, natural resins, thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylic acid esters, polyacrylonitrile, polyacetal, ionomer, and polyester; alkyd resins; phenolic resins; urea resins; benzoguanamine resins; melamine resins; xylene resins; silicone resins; epoxy resins; and diallyl phthalate resins. These may be used individually or in combination of two or more. Composite materials of organic and inorganic materials can also be used. Examples include styrene-silica composite resins, acrylic-silica composite resins, crosslinked alkoxylyl polymer-acrylic resins, polyorganosiloxane-silica, and styrene-acrylate-silica composite resins. Among these, core material particles made of resin or composite materials of organic and inorganic materials are preferred because they have a lower specific gravity and are less prone to settling compared to core material particles made of metal, they have excellent dispersion stability, and the elasticity of the resin makes it easier to maintain electrical connections. Furthermore, the composite material of organic and inorganic materials may have a core-shell structure.

[0016] When organic materials are used as core material particles, it is preferable that they have no glass transition temperature or that their glass transition temperature is above 100°C, as this makes it easier to maintain the shape of the core material particles in the anisotropic conductive connection process and in the process of forming a metal film. Furthermore, if the core material particles have a glass transition temperature, it is preferable that the glass transition temperature is 200°C or lower, as this makes it easier for the conductive particles to soften in the anisotropic conductive connection, increasing the contact area and thus facilitating conductivity. From this viewpoint, if the core material particles have a glass transition temperature, it is more preferable that the glass transition temperature is between 100°C and 180°C, and particularly preferable that it is between 100°C and 160°C.

[0017] When an organic material is used as the core particle, if the organic material is a highly crosslinked resin, the glass transition temperature is hardly observable even when measured up to 200°C using the method described in the examples below. In this specification, such particles are also referred to as particles without a glass transition temperature, and such core particles may be used in the present invention. A specific example of such a core particle material without a glass transition temperature can be obtained by copolymerizing the monomer constituting the organic material exemplified above with a crosslinkable monomer. 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, trimethylolpropane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, tetramethylolpropane tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Examples include polyfunctional (meth)acrylates such as rilate, 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 material particles made of such hard organic materials are particularly frequently used in the COG (Chip on Glass) field.

[0018] There are no particular restrictions on the shape of the core material particles. Generally, the core material particles are spherical. However, the core material particles may have shapes other than spherical, for example, fibrous, hollow, plate-like, or needle-like, and may have numerous protrusions on their surface or be irregular in shape. In the present invention, spherical core material particles are preferred because they have excellent filling properties and are easy to coat metal with.

[0019] The particle size distribution of a powder composed of core material particles, measured by the aforementioned method, has a range. Generally, the range of particle size distribution of a powder is expressed by the coefficient of variation shown in the following equation (1). Coefficient of variation (%) = (Standard deviation / Average particle size) × 100 (1) A large coefficient of variation indicates a broad distribution, while a small coefficient of variation indicates a sharp particle size distribution. In this invention, it is preferable to use core material particles with a coefficient of variation of 30% or less, particularly 20% or less, and especially 10% or less. This is because, when the conductive particles of this invention are used as conductive particles in an anisotropic conductive film, there is an advantage in that the effective contribution ratio to the connection increases.

[0020] Furthermore, while there are no particular restrictions on other physical properties of the core material particles, if the core material particles are resin particles, the value of K, as defined by the following formula (2), must be 100 N / mm² at 20°C. 2 ~100,000 N / mm 2Preferably, the material is within a certain range, and the recovery rate after 10% compression deformation is in the range of 1% to 100% at 20°C. Satisfying these physical properties allows sufficient contact between electrodes without damaging them when they are pressed together. K value (N / mm 2 ) = (3 / √2) × F × S -3 / 2 ×R -1 / 2 ...(2) [Here, F and S in formula (2) are the load value (N) and compression displacement (mm), respectively, at 10% compression deformation of the microsphere when measured using a micro-compression testing machine MCTM-500 (manufactured by Shimadzu Corporation), and R is the radius (mm) of the microsphere.]

[0021] The shape of the conductive particles is not particularly limited, although it depends on the shape of the core material particles. For example, they may be fibrous, hollow, plate-shaped, or needle-shaped, but spherical ones are preferred in terms of excellent filling properties and connectivity.

[0022] Furthermore, the conductive particles may have a smooth surface. Alternatively, the conductive particles may have multiple protrusions projecting from their surface. It is preferable that these protrusions are a continuum made of the same material as the metal film, as this further improves conductivity. More specifically, it is preferable that the metal film has a flat portion and a plurality of protrusions projecting from the flat portion and forming a continuum from the flat portion, and that the flat portion and the protrusions are made of the same material. "Continuum" means that the protrusions and flat portion of the metal film are formed in a single process, and that there are no parts between the flat portion and the protrusions of the metal film that would impair the sense of unity, such as seams. However, with respect to the protrusions, it is permissible that the protrusions are composed of a particle continuum in which a plurality of particles made of the material constituting the metal film are linked in a row, and that grain boundaries are observed between the particles. Therefore, for example, if core particles for protrusion formation, such as metals, metal oxides, non-metallic inorganic materials like graphite, or conductive polymers, are attached to the surface of core material particles, and protrusions are formed using these core particles as a starting point for growth, the flat portion and the protrusions are not formed in a single process, and thus are not included in the continuum as defined in the present invention. However, it should be noted that conductive particles having protrusions formed by attaching such core particles to core material particles and using these core particles as a starting point for growth are also within the scope of the present invention.

[0023] If the conductive particles have protrusions with the above-described configuration, when the electrodes are connected, the protrusions can penetrate the oxide film formed on the electrode surface, thereby reducing the connection resistance.

[0024] The protrusions preferably have a height H of 20 nm or more on average, and more preferably 50 nm or more. The number of protrusions depends on the particle size of the conductive particles, but it is preferable that there are 1 to 20,000, and more preferably 5 to 5,000, protrusions per particle, from the viewpoint of further improving the conductivity of the conductive particles. The aspect ratio of the protrusions is preferably 0.5 or more, and more preferably 1 or more. A larger aspect ratio of the protrusions is advantageous because it allows them to easily penetrate the oxide film mentioned above. Furthermore, when an anisotropic conductive film is formed using conductive particles, a larger aspect ratio of the protrusions is thought to increase the resin excludability, thus increasing conductivity. The aspect ratio is defined as the ratio of the height H of the protrusion to the length D of the base of the protrusion, i.e., H / D.

[0025] As described above, the aspect ratio of the protrusions is as described above, the length D of the base of the conductive particle protrusion is preferably 5 to 500 nm, particularly 10 to 400 nm, and the height H of the protrusion is preferably 5 to 500 nm, particularly 10 to 400 nm.

[0026] The metal film on conductive particles is conductive, and its constituent metals include, for example, metals or alloys thereof such as gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, antimony, bismuth, germanium, aluminum, chromium, palladium, tungsten, and molybdenum, as well as metal compounds such as ITO and solder. Among these, gold, silver, copper, nickel, palladium, or solder are preferred because they have low resistance, and in particular, nickel, palladium, gold, nickel alloys, palladium alloys, or gold alloys are preferably used because they have high bonding properties with insulating particles. One or more metals can be used in combination in the conductive particles. Nickel alloys also include nickel-phosphorus, nickel-boron, and nickel-boron-phosphorus, and palladium alloys also include palladium-phosphorus and palladium-boron.

[0027] The metal film may have a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, it is particularly preferable, from the viewpoint of reducing connection resistance, that the underlayer be nickel or a nickel alloy, and the outermost layer be nickel, palladium, gold, a nickel alloy, a palladium alloy, or a gold alloy, when the metal film is formed by electroless plating.

[0028] Furthermore, the thickness of the metal film on the surface of the core material particles is preferably 0.001 μm to 2 μm, and particularly preferably 0.005 to 1 μm.

[0029] Methods for forming a metal film on the surface of core material particles include dry methods using vapor deposition, sputtering, mechanochemical methods, hybridization, etc., and wet methods using electrolytic plating, electroless plating, etc. While these methods can be combined to form a metal film on the surface of core material particles, conductive particles with a metal film formed on their surface by electroless plating are preferred because they can uniformly and densely coat the particle surface.

[0030] The average particle diameter of the conductive particles is preferably 0.1 μm to 50 μm, more preferably 1 μm to 30 μm. Having the average particle diameter of the conductive particles within this range makes it easier to ensure conductivity between the counter electrodes without generating short circuits in directions different from those between the counter electrodes. In this invention, the average particle diameter of the conductive particles is the average value of particle diameters measured using a scanning electron microscope (SEM). If the conductive particles are spherical in the scanning electron microscope image, the particle diameter measured using the SEM is the diameter of the circular conductive particle image. If the insulating particles are not spherical, the particle diameter measured using the SEM is the largest length (maximum length) of the line segments crossing the image of the conductive particles.

[0031] Specifically, the average particle size of the conductive particles is measured by the method described in the examples.

[0032] Furthermore, conductive particles that contain fewer eluting impurity ions such as alkali metal ions, halogen ions, and organic acid ions are preferable from the viewpoint of suppressing corrosion of electrodes and other components.

[0033] (Insulating particles) The insulating particles used in the present invention are silica particles whose surface is coated (1) with a metal (M) oxide and / or hydroxide, and whose surface is further coated (2) with a fatty acid or a derivative thereof.

[0034] Examples of silica particles that can be used include those produced by particle growth from sodium silicate or activated silica solution, those produced using organosilicon compounds as raw materials, vapor-phase silica, precipitated silica, and the like.

[0035] The preferred physical properties of silica particles are that their average particle diameter, determined by dynamic light scattering, is 5 to 500 nm, preferably 10 to 300 nm. Having an average particle diameter within this range allows insulating particles to be uniformly dispersed and adsorbed onto the surface of conductive particles.

[0036] The coating (1) is an oxide or hydroxide of a metal (M). Examples of metal (M) include one or more of the following: aluminum, zinc, calcium, magnesium, strontium, barium, titanium, zirconium, tin, iron, and copper. Among these, aluminum is preferred as metal (M) because it has good affinity with silica particles and fatty acids and their derivatives, and can adhere the fatty acid and its derivative coating (2) more firmly to the surface of the coating (1).

[0037] The amount of metal (M) oxide and / or hydroxide coating on the silica particles is 1 to 40% by mass, preferably 5 to 25% by mass, in terms of metal (M) oxide relative to the silica particles, from the viewpoint of suppressing peeling of the fatty acid and its derivative coating layer. The reason for this is that if the amount of metal (M) oxide and / or hydroxide coating on the silica particles is less than 1% by mass, the silica particles tend not to be sufficiently coated with metal (M) oxide and / or hydroxide. Also, if it is greater than 40% by mass, the effect of coating with metal (M) oxide and / or hydroxide saturates, and excess metal (M) oxide and / or hydroxide is undesirable as it becomes an impurity for the coated particles of the present invention.

[0038] The fatty acid further coating the silica particle surface coated with a metal (M) oxide and / or hydroxide (1) is preferably a saturated or unsaturated linear or branched mono or polycarboxylic acid, more preferably a saturated or unsaturated linear or branched monocarboxylic acid, and even more preferably a saturated or unsaturated linear monocarboxylic acid. The fatty acid preferably has 7 or more carbon atoms. The derivative refers to a salt or amide of the fatty acid.

[0039] The fatty acids or derivatives used in the present invention preferably have 7 to 23 carbon atoms, and more preferably 10 to 20 carbon atoms. Examples of such fatty acids or derivatives 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; or metal salts or amides thereof. Examples of metal salts of fatty acids include alkali metals, alkaline earth metals, transition metals such as Zr, Cr, Mn, Fe, Co, Ni, Cu, and Ag, and salts of other metals other than transition metals such as Al and Zn, and are preferably polyvalent metal salts such as Al, Zn, W, and V. Depending on the valency of the metal, the fatty acid metal salt may be mono-form, di-form, tri-form, tetra-form, etc. Any combination of these is also acceptable for the fatty acid metal salt.

[0040] The amount of fatty acid or its derivative coating is preferably 0.05% to 30% by mass, more preferably 0.1% to 10% by mass, and even more preferably 0.2% to 5.0% by mass, relative to the silica particles. This range of coating amount enhances the adhesion of insulating particles to conductive particles.

[0041] The insulating particles according to the present invention can be easily manufactured, for example, by performing the following first and second steps. Step 1: A step of coating the surface of silica particles with a metal (M) oxide and / or hydroxide (1). Second step: A step in which the surface of silica particles obtained in the first step is coated (1) with a metal (M) oxide and / or hydroxide, and then the surface of the particles is further coated (2) with a fatty acid or a derivative thereof.

[0042] The first step is to coat the surface of the silica particles with a metal (M) oxide and / or hydroxide (1). For example, the first step involves adding a water-soluble metal (M)-containing compound to a silica dispersion obtained by dispersing silica particles in an aqueous solvent, and then adding an alkaline agent (1) to hydrolyze the water-soluble metal (M)-containing compound, thereby coating the surface of the silica particles with a metal (M) oxide and / or hydroxide (1).

[0043] Examples of water-soluble metal (M)-containing compounds used in the first step include metal (M) halides, sulfates, acetates, nitrates, and the like. Examples of the alkaline agent (1) for the first step include at least one selected from inorganic alkaline agents such as ammonia gas, ammonia water, caustic soda, caustic potash, NaHCO3, Na2CO3, K2CO3, KHCO3, Ca(OH)2, or organic alkaline agents such as ethanolamine.

[0044] The hydrolysis reaction of a water-soluble metal (M)-containing compound involves adjusting the pH of the reaction solution to 5.0 or higher, preferably 5.5 to 9, and carrying out the reaction and aging at a temperature of 15 to 95°C, preferably 50 to 90°C, to deposit fine hydroxides of the metal (M) onto the surface of silica particles. After the hydrolysis reaction of a water-soluble metal (M)-containing compound is complete, silica particles can be obtained in which the surface of the particles is coated with a metal (M) oxide and / or hydroxide (1) by washing, drying, etc., as necessary.

[0045] The second step is to further coat (2) the surface of silica particles (hereinafter sometimes referred to as "silica particles having coating (1)") obtained in the first step with a metal (M) oxide and / or hydroxide (1) with a fatty acid or a derivative thereof.

[0046] The coating treatment of fatty acids or their derivatives in the second step can be carried out by a wet or dry method.

[0047] When coating with a fatty acid or its derivative is performed by a wet method, for example, (a) silica particles having the coating (1) are added to a dispersion containing the fatty acid or its derivative at a desired concentration to form a slurry, and the slurry is spray-dried or the slurry is subjected to solid-liquid separation and the resulting solid is dried; (b) a salt of the fatty acid or its derivative is added to a dispersion containing silica particles having the coating (1), and then an alkaline agent (2) is added to hydrolyze the salt of the fatty acid or its derivative, thereby further coating (2) the surface of the silica particles having the coating (1) with the fatty acid or its derivative.

[0048] Examples of fatty acid or its derivative salts used in the coating method described in (b) above include sodium salts, calcium salts, potassium salts, aluminum salts, barium salts, magnesium salts, ammonium salts, and the like of the aforementioned fatty acid or its derivative. Examples of the alkaline agent (2) used in the coating method described in (b) above include at least one selected from inorganic alkaline agents such as ammonia gas, ammonia water, caustic soda, caustic potash, NaHCO3, Na2CO3, K2CO3, KHCO3, Ca(OH)2, or organic alkaline agents such as ethanolamine.

[0049] The hydrolysis reaction of fatty acids or their derivatives can be carried out by adjusting the pH of the reaction solution to 5.0 or higher, preferably 5.5 to 9, and performing the reaction and aging at a temperature of 15 to 95°C, preferably 50 to 90°C, to deposit fatty acids on the surface of silica particles having a coating (1).

[0050] When coating with fatty acids or their derivatives is performed by a dry method, for example, silica particles having the coating (1) and solid fatty acids or their derivatives can be mixed using a mixing device such as a ball mill, bead mill, Henschel mixer, or pneumatic grinder, or silica particles having the coating (1) can be mixed with a diluted solution obtained by diluting the fatty acids or their derivatives with a solvent, and then heat-treated as necessary to obtain silica particles whose surfaces are further coated (2) with fatty acids or their derivatives.

[0051] Furthermore, insulating particles in which the surface of silica particles having a coating (1) used in the present invention is further coated (2) with a fatty acid or its derivative can be heat-treated after the second step. The heat treatment temperature is preferably 70 to 230°C, more preferably 100 to 210°C, and the heat treatment time is preferably 10 minutes or more, more preferably 20 minutes to 10 hours. The atmosphere during the heat treatment may be a vacuum, an inert gas atmosphere, or an atmospheric atmosphere. By applying heat treatment, the fatty acid or its derivative of the coating component becomes denser, eliminating unevenness in the coating and resulting in a uniform fatty acid or its derivative coating layer. When heat treatment is performed, it is preferable from the viewpoint of obtaining a uniform fatty acid or its derivative coating layer that the heat treatment temperature is above the melting point of the fatty acid or its derivative and below the decomposition point of the fatty acid or its derivative.

[0052] (Coated particles) The method for coating the particle surface of the conductive particles with the insulating particles can be carried out wet or dry, but from the viewpoint of simplifying the operation, it is preferable to carry it out dry.

[0053] In the dry process, the product is prepared using mechanical means that apply strong shear force. Equipment that can be used in the dry process includes high-speed mixers, super mixers, turbosphere mixers, Eilich mixers, Henschel mixers, hybridization systems, Nauter mixers, ribbon blenders, jet mills, cosmoizers, bead mills, ball mills, and air-jet pulverizers.

[0054] Furthermore, in addition to the method of performing the second step described above, the coated particles of the present invention can also be produced by putting silica particles having the coating (1), conductive particles, and solid fatty acids or their derivatives together into the apparatus used in the dry method and performing a mixing treatment, as described in method (A) below.

[0055] Furthermore, in the present invention, by further heat-treating the coated particles obtained above, insulating particles can be firmly attached to the surface of conductive particles. The heat treatment temperature is preferably 70 to 230°C, more preferably 100 to 210°C, and the heat treatment time is preferably 30 minutes or more, more preferably 1 to 10 hours. The atmosphere during the heat treatment may be either a vacuum or an inert gas atmosphere. By applying the heat treatment, the fatty acids or their derivatives of the coating component become denser in structure, and at the same time, the fatty acids or their derivatives themselves further enhance their binder function, thereby allowing the insulating particles to adhere firmly to the surface of the conductive particles.

[0056] In the present invention, the coated particles have an insulating particle coverage of 30% or more, preferably 30 to 100%, and particularly preferably 30 to 80%, which is preferable from the viewpoint of achieving excellent electrical reliability when the upper and lower electrodes are electrically connected using the coated particles.

[0057] The coverage rate was calculated by counting the number of insulating particles n attached to the conductive particles using a scanning electron microscope (SEM), and then using the following formula. The coverage rate used for evaluation is the average value of 20 coated particles. Coverage rate (%) = (n / N) × 100 N: The number of insulating particles when insulating particles are arranged in close-packed formation on the surface of conductive particles. N=4π(R+r) 2 / 2√3r 2 (R: radius of conductive particles (nm), r: radius of insulating particles (nm))

[0058] Furthermore, the coated particles according to the present invention can be those in which the conductive particles have been surface-treated with a hydrophobic agent. When a hydrophobic agent is present on the surface of the conductive particles, it exhibits excellent affinity with insulating particles, and the coating rate of the insulating particles can be further increased. Examples of the hydrophobic agents include benzotriazole compounds, titanate coupling agents, higher fatty acids and their derivatives (2), phosphate esters, and phosphite esters. These can be used alone or in combination of two or more as needed.

[0059] In this case, the insulating particles may be attached to the surface of the conductive particles via a hydrophobic agent present on the surface of the conductive particles, or they may be attached directly to the surface of the conductive particles without a hydrophobic agent, or a mixture of 1) and 2) may be present.

[0060] The benzotriazole compound is preferably one represented by the following general formula (4). [ka] (In the formula, A1 and A2 represent the same or different alkyl group, aryl group, halogen atom, hydroxyl group, amino group, or carboxyl group, and p1 and q1 represent the same or different integers from 0 to 2.) In the general formula (4) above, A1 and A2 represent an alkyl group, an aryl group, a halogen atom, a hydroxyl group, an amino group, or a carboxyl group. Preferred alkyl groups include those with 1 to 5 carbon atoms, such as methyl, ethyl, propyl, and butyl groups. Preferred aryl groups include phenyl, tolyl, xyl, and naphthyl groups. Examples of halogen atoms include chlorine, bromine, and iodine. In the general formula (4) above, p1 and q1 represent the same or different integers from 0 to 2. Furthermore, A1 and A2 may be the same group or different groups.

[0061] Preferable specific compounds of the benzotriazole-based compound represented by the general formula (4) include, for example, benzotriazole, 4-methylbenzotriazole, 5-methylbenzotriazole, 4-ethylbenzotriazole, 5-ethylbenzotriazole, 4,5-dimethylbenzotriazole, 4,6-dimethylbenzotriazole, 5,6-dimethylbenzotriazole, 4,5-diethylbenzotriazole, 4,6-diethylbenzotriazole, 5,6-diethylbenzotriazole, 4-phenylbenzotriazole, 5-phenylbenzotriazole, 4-chlorobenzotriazole, 5-chlorobenzotriazole, 4-carboxybenzotriazole, 5-carboxybenzotriazole, 4,5-dicarboxybenzotriazole, 4,6-dicarboxybenzotriazole, and the like.

[0062] Examples of the titanate coupling agent include those represented by the following formula (i) or formula (ii). (B 1 O)Ti(OB 2 )(OB 3 )(OB 4 ) (i) (In the formula, B 1 is an alkyl group, and B 2 to B 4 are each a group selected from an alkyl group, a group in which a methylene group other than the terminal in the alkyl group is substituted with an oxygen atom, an alkenyl group, a group in which a methylene group other than the terminal in the alkenyl group is substituted with an oxygen atom, an alkanoyl group, a dialkyl pyrophosphate group, and an alkylbenzene sulfonyl group. However, any one or more of B 2 to B 4 is an alkanoyl group, a dialkyl pyrophosphate group, or an alkylbenzene sulfonyl group. B 1 and B 2 may together form a ring.)

[0063] (B 5 O)Ti(OB 6 )(OB 7 )(OB 8 )·[P(OB 9)2OH]2(ii) (In the formula, B 5 ~B 8 These are, respectively, an alkyl group, a group in which a methylene group other than the terminal in an alkyl group is substituted with an oxygen atom, an alkenyl group, or a group in which a methylene group other than the terminal in an alkenyl group is substituted with an oxygen atom. 9 (It is an alkyl group.) In equation (i) mentioned above, B 1 ~B 4 Two or three of the groups may be identical, B 1 ~B 4 It is also possible that all of them are different. In the compound represented by formula (ii), B 5 ~B 8 Two or three of the groups may be identical, B 5 ~B 8 It is acceptable for all of them to be different. There are two B 9 These may be the same or different. In the compound represented by formula (i), the preferred number of alkanoyl groups, dialkylpyrophosphate groups, or alkylbenzenesulfonyl groups is 1 to 3, more preferably 2 to 3, and particularly preferably 3.

[0064] Examples of alkyl groups listed above include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, 2-methylbutyl group, 1-methylbutyl group, n-hexyl group, isohexyl group, 3-methylpentyl group, 2-methylpentyl group, 1-methylpentyl group, heptyl group, octyl group, isooctyl group, 2-ethylhexyl group, 3,7-dimethyloctyl group, nonyl group, decyl group, undecyl group, dodecyl group, lauryl group, tetradecyl group, hexadecyl group, octadecyl group (including stearyl group), nonadecyl group, eicosyl group, triacontyl group, and tetracontyl group. Examples of alkenyl groups include groups obtained by changing one or more carbon-carbon single bonds of the above alkyl groups to carbon-carbon double bonds.

[0065] Groups in which methylene groups other than the terminal ones in an alkyl group are substituted with oxygen atoms are not alkoxy groups, but rather groups in which the methylene groups within the alkyl group are interrupted by oxygen atoms. The same applies to groups in which methylene groups other than the terminal ones in an alkenyl group are substituted with oxygen atoms.

[0066] B 1 ~B 4 B 5 ~B 8 The alkyl group represented by , the group in which a methylene group other than the terminal in the alkyl group is substituted with an oxygen atom, the alkenyl group, and the group in which a methylene group other than the terminal in the alkenyl group is substituted with an oxygen atom, preferably has 3 to 40 carbon atoms, and more preferably 3 to 32. 2 ~B 4 The alkanoyl group represented by is preferably one with 2 to 40 carbon atoms. 2 ~B 4 The alkyl group of the dialkylpyrophosphate group represented by is preferably one having 3 to 40 carbon atoms. 2 ~B 4 The alkyl group of the alkylbenzenesulfonyl group represented by is preferably one with 3 to 40 carbon atoms. 9 The alkyl group represented by is preferably one having 3 to 40 carbon atoms.

[0067] B 1 and B 2 Examples of rings formed by these elements together include rings in which -CH2-CH2- or -CH2-COO- are formed with the oxygen and titanium atoms in formula (i).

[0068] Each group represented by formula (i) or formula (ii) above may be substituted with a substituent. Examples of substituents include halogen atoms, epoxy groups, amino groups, vinyl groups, acrylic groups, isocyanate groups, and mercapto groups.

[0069] Specific examples of titanate-based coupling agents used in the present invention include isopropyltriisostearoyl titanate, isopropyltridodecylbenzenesulfonyl titanate, isopropyltris(dioctyl pyrophosphate) titanate, tetraisopropyl(dioctyl phosphite) titanate, tetraisopropylbis(dioctyl phosphite) titanate, tetraoctylbis(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, which can be used one or more of these. These titanate-based coupling agents are commercially available, for example, from Ajinomoto Fine Techno Co., Ltd.

[0070] The higher fatty acid or its derivative (2) is preferably a saturated or unsaturated linear or branched mono or polycarboxylic acid, more preferably a saturated or unsaturated linear or branched monocarboxylic acid, and even more preferably a saturated or unsaturated linear monocarboxylic acid. The higher fatty acid preferably has 7 or more carbon atoms. The derivative refers to a salt or amide of the higher fatty acid.

[0071] The higher fatty acid or its derivative (2) used in the present invention preferably has 7 to 23 carbon atoms, and more preferably 10 to 20 carbon atoms. Examples of such higher fatty acids or their derivatives 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; or metal salts or amides thereof. Examples of metal salts of higher fatty acids include alkali metals, alkaline earth metals, transition metals such as Zr, Cr, Mn, Fe, Co, Ni, Cu, and Ag, and salts of other metals other than transition metals such as Al and Zn, and are preferably polyvalent metal salts such as Al, Zn, W, and V. Depending on the valency of the metal, the higher fatty acid metal salt may be mono-form, di-form, tri-form, tetra-form, etc. The higher fatty acid metal salt may be any combination of these.

[0072] As phosphate esters and phosphite esters, those having an alkyl group with 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.

[0073] In the present invention, a higher fatty acid or its derivative (2) is particularly preferred as the hydrophobic agent because it has excellent affinity for insulating particles and is highly effective in increasing the coverage rate of insulating particles.

[0074] In the present invention, the hydrophobic agent may be present on the surface of the conductive particles, and may be present on the entire surface of the conductive particles or only on a part of the surface. Furthermore, the hydrophobic agent may form a layer that covers part or all of the surface of the conductive particles.

[0075] There are no particular limitations on the method for surface-treating the conductive particles with a hydrophobic agent, and known methods can be used. One example is a method of mixing the conductive particles and the hydrophobic agent in a solvent.

[0076] The solvent may be water or an organic solvent, or a mixed solvent of water and an organic solvent. Examples of organic solvents include toluene, methanol, ethanol, propanol, butanol, isobutyl alcohol, acetone, methyl ethyl ketone, tetrahydrofuran, acetonitrile, N-methylpyrrolidone, and dimethylformamide. In the dispersion obtained by adding conductive particles and a hydrophobic agent to the solvent, the concentration of the hydrophobic agent is 0.01 to 20% by mass. The concentration of conductive particles in this dispersion is 1 to 50% by mass.

[0077] By filtering the dispersion after processing and drying it if necessary, conductive particles having a hydrophobic agent on their surface can be obtained.

[0078] Furthermore, as a method for coating the particle surface of conductive particles treated with a hydrophobic agent with the insulating particles, a dry method similar to the method described above for coating the particle surface of conductive particles with the insulating particles can be used.

[0079] Furthermore, in the present invention, when a higher fatty acid or a derivative thereof (2) is used as a hydrophobic agent, the coated particles of the present invention may be produced by the following two methods. Method (A) is a method of putting silica particles having a coating (1), conductive particles, and the solid higher fatty acid or its derivative (2) together into the apparatus used in the dry method of the second step and performing a mixing process. Method (B) is a method in which, when dry mixing and coating the particle surface of the conductive particles with the insulating particles, a higher fatty acid or its derivative (2) is also added to the dry mixing apparatus in addition to the conductive particles and insulating particles, and the mixing process is carried out together.

[0080] According to method (A), silica particles having a coating (1) and conductive particles can be coated all at once with a higher fatty acid or its derivative (2). According to method (B), insulating particles can be attached all at once to the surface of the conductive particles and / or the conductive particles coated with the higher fatty acid or its derivative (2) while coating the particle surface of the conductive particles with the higher fatty acid or its derivative (2).

[0081] The coated particles of the present invention are suitably used, for example, in anisotropic conductive films (ACF), heat-seal connectors (HSC), and conductive materials for connecting electrodes of liquid crystal display panels to circuit boards of driving LSI chips, by taking advantage of the insulating properties between coated particles and the connectivity between opposing electrodes. In particular, they are suitably used as conductive fillers in conductive adhesives.

[0082] The conductive adhesive described above is preferably used as an anisotropic conductive adhesive that is placed between two substrates on which conductive substrates are formed, and adheres the conductive substrates to them by heating and pressing to establish electrical conductivity. This anisotropic conductive adhesive contains the conductive particles and adhesive resin of the present invention. The adhesive resin can be any resin that is insulating and is used as an adhesive resin, without any particular limitations. It may be either a thermoplastic resin or a thermosetting resin, and it is preferable that it exhibits adhesive properties upon heating. Examples of such adhesive resins include thermoplastic types, thermosetting types, and UV-curing types. There are also so-called semi-thermosetting types that exhibit properties intermediate between thermoplastic and thermosetting types, and composite types of thermosetting and UV-curing types. These adhesive resins can be appropriately selected according to the surface characteristics and usage of the circuit board or other object to be bonded. In particular, adhesive resins composed of thermosetting resins are preferred because they have excellent material strength after bonding.

[0083] Specifically, adhesive resins include those prepared as a main component from one or more selected materials from 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, or silicone resin. Among these, styrene-butadiene rubber and SEBS are preferred as thermoplastic resins due to their excellent reworkability. Epoxy resins are preferred as thermosetting resins. Of these, epoxy resin is the most preferred due to its advantages of high adhesive strength, excellent heat resistance and electrical insulation, as well as low melt viscosity and the ability to connect at low pressure.

[0084] As the epoxy resin mentioned above, any polyvalent epoxy resin having two or more epoxy groups in one molecule can be used, and commonly used epoxy resins are acceptable. Specific examples include novolac resins such as phenol novolac and cresol novolac; polyvalent 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 polyvalent carboxyl compounds such as adipic acid, phthalic acid, and isophthalic acid, which are reacted with epichlorohydrin or 2-methylepichlorohydrin to obtain glycidyl-type epoxy resins. Other examples include aliphatic and alicyclic epoxy resins such as dicyclopentadiene epoxy and butadiene dimer epoxy. These can be used individually or in combination of two or more.

[0085] Furthermore, from the viewpoint of preventing ion migration, it is preferable to use high-purity adhesive resins with reduced impurity ions (such as Na and Cl) and hydrolyzable chlorine as described above.

[0086] The amount of conductive particles used in an anisotropic conductive adhesive is typically 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, an increase in connection resistance and melt viscosity is suppressed, connection reliability is improved, and sufficient anisotropy of the connection can be ensured.

[0087] In addition to the conductive particles and adhesive resin described above, the anisotropic conductive adhesive may contain additives known in the art. The amount of these additives may also be within the range known in the art. Examples of other additives include tackifiers, reaction aids, epoxy resin curing agents, metal oxides, photoinitiators, sensitizers, curing agents, vulcanizing agents, degradation inhibitors, heat-resistant additives, thermal conductivity enhancers, softeners, colorants, various coupling agents, or metal deactivators.

[0088] Examples of tackifiers include rosin, rosin derivatives, terpene resins, terpene phenol resins, petroleum resins, coumarone-indene resins, styrene resins, isoprene resins, alkylphenol resins, and xylene resins. Examples of reactive additives, i.e., crosslinking agents, include polyols, isocyanates, melamine resins, urea resins, utropines, amines, acid anhydrides, and peroxides. As for epoxy resin curing agents, any agent having two or more active hydrogen atoms per minute can be used without particular limitations. 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 individually or in combination of two or more. Latent curing agents may also be used as needed. Examples of usable latent curing agents include imidazole-based, hydrazide-based, boron trifluoride-amine complexes, sulfonium salts, amineimides, polyamine salts, dicyandiamides, and modified versions thereof. These can be used individually or as a mixture of two or more.

[0089] The aforementioned anisotropic conductive adhesive is manufactured using manufacturing equipment commonly used in the art. For example, conductive particles and an adhesive resin, along with a curing agent and various additives as needed, are blended and mixed in an organic solvent if the adhesive resin is a thermosetting resin, or melt-kneaded at a temperature above the softening point of the adhesive resin, preferably about 50 to 150°C, if the adhesive resin is a thermoplastic resin. The anisotropic conductive adhesive thus obtained may be applied by coating or in the form of a film. [Examples]

[0090] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0091] <Preparation of insulating particle samples> (Insulating particle 1) 100g of aqueous silica sol (SiO2: 22.7% by mass, water: 77.3% by mass) was heated to 85°C in a reaction vessel. Next, an aqueous solution of aluminum chloride was added to the silica particles to a concentration of 10% by mass in terms of Al2O3. After adjusting the pH to 5.5 with an aqueous solution of sodium hydroxide, the aluminum chloride was hydrolyzed while stirring for 30 minutes to obtain a slurry containing silica particles coated with aluminum hydroxide on the surface. Next, the slurry was filtered to obtain a filter cake, which was then dispersed again in 2 L of pure water. This process was repeated three times for washing. The washed cake was then dried to obtain silica particles coated with aluminum hydroxide on the surface. For the aqueous silica sol used, we selected a commercially available product with a particle size of 219 nm determined by dynamic light scattering. Fifty parts by mass of silica particles coated with aluminum hydroxide prepared above and 0.25 parts by mass of stearic acid (melting point 62°C to 72°C) were crushed and mixed in an air-jet pulverizer (Seishin Corporation, A-O Jet Mill). The mixture was then heat-treated at 100°C for 30 minutes to obtain silica particles coated with aluminum hydroxide on the surface, and then further coated with stearic acid. These were used as insulating particle samples. The conditions for the air-jet pulverizer were as follows: powder supply rate: 3g / min, pusher pressure: 0.6MPa, and jet pressure: 0.6MPa. (Insulating particles 2) An insulating particle sample was prepared in the same manner as insulating particle 1, except that an aqueous aluminum chloride solution was added to the silica particles to a concentration of 20% by mass in terms of Al2O3. (Insulating particles 3) 100g of aqueous silica sol (SiO2: 22.7% by mass, water: 77.3% by mass) was heated to 85°C in a reaction vessel. Next, an aqueous solution of aluminum chloride was added to the silica particles to a concentration of 10% by mass in terms of Al2O3. After adjusting the pH to 5.5 with an aqueous solution of sodium hydroxide, the aluminum chloride was hydrolyzed while stirring for 30 minutes to obtain a slurry containing silica particles coated with aluminum hydroxide on the surface. Next, the slurry was filtered to obtain a filter cake, which was then dispersed again in 2 L of pure water. This process was repeated three times for washing. The washed cake was then dried to obtain silica particles coated with aluminum hydroxide on the surface. For the aqueous silica sol used, we selected a commercially available product with a particle size of 219 nm determined by dynamic light scattering. Fifty parts by mass of silica particles coated with aluminum hydroxide prepared above and 0.25 parts by mass of zinc stearate (melting point 128°C to 140°C) were crushed and mixed in an air-jet mill (Seishin Corporation, A-O Jet Mill). The mixture was then heat-treated at 200°C for 30 minutes to obtain silica particles coated with aluminum hydroxide on the surface, and further coated with zinc stearate on the surface. These were used as insulating particle samples. The conditions for the air-jet pulverizer were as follows: powder supply rate: 3g / min, pusher pressure: 0.6MPa, and jet pressure: 0.6MPa. (Insulating particles 4) An insulating particle sample was prepared in the same manner as insulating particle 3, except that an aqueous aluminum chloride solution was added to the silica particles to a concentration of 20% by mass in terms of Al2O3. (Insulating particles 5) 100g of aqueous silica sol (SiO2: 22.7% by mass, water: 77.3% by mass) was placed in a reaction vessel, and while stirring, it was heated to a temperature that maintained a boiling state to remove the water and obtain silica particles. For the aqueous silica sol, we used one with a particle size of 219 nm, determined by a commercially available dynamic light scattering method. Fifty parts by mass of the silica particles prepared above and 0.25 parts by mass of stearic acid (melting point 62°C to 72°C) were crushed and mixed in an air-jet pulverizer (Seishin Corporation, A-O Jet Mill). The mixture was then heat-treated at 100°C for 30 minutes to obtain silica particles coated with stearic acid. These were used as insulating particle samples. The conditions for the air-jet pulverizer were as follows: powder supply rate: 3g / min, pusher pressure: 0.6MPa, and jet pressure: 0.6MPa. (Insulating particles 6) 100g of aqueous silica sol (SiO2: 22.7% by mass, water: 77.3% by mass) was placed in a reaction vessel, and while stirring, it was heated to a temperature that maintained a boiling state to remove the water and obtain silica particles. For the aqueous silica sol, we used one with a particle size of 219 nm, determined by a commercially available dynamic light scattering method. Fifty parts by mass of the silica particles prepared above and 0.25 parts by mass of zinc stearate (melting point 128°C to 140°C) were crushed and mixed in an air-jet pulverizer (Seishin Corporation, A-O Jet Mill). The mixture was then heat-treated at 100°C for 30 minutes to obtain silica particles coated with zinc stearate. These were used as insulating particle samples. The conditions for the air-jet pulverizer were as follows: powder supply rate: 3g / min, pusher pressure: 0.6MPa, and jet pressure: 0.6MPa. (Insulating particles 7) 100g of aqueous silica sol (SiO2: 22.7% by mass, water: 77.3% by mass) was heated to 85°C in a reaction vessel. Next, an aqueous solution of aluminum chloride was added to the silica particles to a concentration of 10% by mass in terms of Al2O3. After adjusting the pH to 5.5 with an aqueous solution of sodium hydroxide, the aluminum chloride was hydrolyzed while stirring for 30 minutes to obtain a slurry containing silica particles whose surfaces were coated with aluminum hydroxide. Next, the slurry was filtered to obtain a filter cake, which was then dispersed again in 2 L of pure water. This process was repeated three times for washing. The washed cake was then dried to obtain silica particles coated with aluminum hydroxide on the surface. These were used as the insulating particle sample.

[0092] [Table 1] Note) 1) The amount of aluminum hydroxide coating indicates the amount of Al2O3 coating relative to the silica particles. 2) The amount of fatty acid coating indicates the amount of fatty acid coating relative to the silica particles.

[0093] <Preparation of conductive particle samples> The following commercially available conductive particles were used. The average particle diameter of conductive particles was determined by randomly extracting 200 particles from scanning electron microscope (SEM) images (magnification 100,000x), measuring their particle diameters, and using the average value of these measurements.

[0094] (Conductive particle 1) Ni-plated particles (manufactured by Nippon Chemical Industrial Co., Ltd.) with an average particle diameter of 3 μm and a nickel coating of 0.125 μm thickness on the surface of spherical resin particles were prepared. The resin particles were made of crosslinkable acrylic resin and had a glass transition temperature of 120°C. The average particle diameter was determined by randomly selecting particles from scanning electron microscope (SEM) images (magnification: 100,000x), measuring their diameters, and then using the average value of those measurements.

[0095] (Conductive particle 2) Ni-plated particles (manufactured by Nippon Chemical Industrial Co., Ltd.) were prepared, with a nickel coating of 0.125 μm thickness and an average particle diameter of 3 μm, having 1,030 protrusions on the surface of spherical resin particles, an average height of 0.1 μm, an average base length of 0.197 μm, and an aspect ratio of 0.5. The resin particles were made of crosslinkable acrylic resin and had a glass transition temperature of 120°C. The average particle diameter was measured using the same method as for conductive particles 1.

[0096] {Examples 1-8 and Comparative Examples 1-4} Ten parts by weight of insulating particles and 100 parts by weight of conductive particles, as shown in Table 2, along with zirconia balls (particle size: 1 mm) with an apparent volume of 0.3 L, were placed in a cylindrical container (pot mill) with a volume of 0.7 L and an inner diameter of 0.09 m, sealed, and rotated at 100 rpm. The rotation speed at this time was calculated using the following formula (t), where a = 0.71. After processing for 60 minutes to ensure that the insulating particles uniformly adhered to the conductive particles, the zirconia balls and the resulting coated particles were separated. The resulting coated particles were used as the coated particle sample. N = a × 42.3 / √D ····(t) N: Rotational speed (rpm) D: Inner diameter of ball mill container (m) a: constant

[0097] (Evaluation of coverage) The difference in coating ratio when insulating particles were coated onto conductive particles was evaluated from the coated particles obtained in the examples and comparative examples. The results are shown in Table 2. The coating ratio was determined by the following method.

[0098] <Method for measuring coverage> The number of insulating particles N when insulating particles are arranged in close-packed formation on the surface of conductive particles was calculated using the following formula. N=4π(R+r) 2 / 2√3r 2 (R: radius of conductive particles (nm), r: radius of insulating particles (nm)) The number of insulating particles n attached to conductive particles was counted using SEM, and the coverage rate was calculated using the following formula. The results are shown in Table 1. Coverage rate (%) = (n / N) × 100 The coverage rate used for evaluation was the average value of 20 conductive particles.

[0099] (Evaluation of degree of closeness) One g of the coated particles obtained in the examples and comparative examples were added to 100 mL of pure water, and ultrasonic treatment was performed for 2 minutes using an ultrasonic device (VELVO-CLEAR, VS-D100) at an oscillation frequency of 24 kHz. The coating rate of the obtained coated particles was calculated using the same method as for evaluating the coating rate described above, and the degree of adhesion was calculated using the following formula to evaluate the adhesion, and the results are shown in Table 2. A higher degree of adhesion indicates less shedding of insulating particles due to ultrasonic treatment, and therefore indicates high adhesion between conductive particles and insulating particles. Adhesion (%) = (Coverage after ultrasonic treatment / Coverage before ultrasonic treatment) × 100

[0100] [Table 2]

[0101] {Examples 9-10 and Comparative Examples 5-6} The coated particles obtained in Examples 5 and 7 and Comparative Example 3 were subjected to heat treatment under the conditions shown in Table 3, and these were used as coated particle samples. The coating rate and adhesion were evaluated in the same manner as in Examples 1 to 8.

[0102] [Table 3]

[0103] {Examples 11-12} Four parts by weight of insulating particles, 100 parts by weight of conductive particles, and 0.05 parts by weight of fatty acid, as shown in Table 4, were placed in a cylindrical container (pot mill), and coated particles were prepared in the same manner as in Examples 1 to 8, and these were used as coated particle samples. The coating rate and adhesion were also evaluated in the same manner as in Examples 1 to 8.

[0104] [Table 4]

[0105] {Examples 13-14} The coated particles obtained in Examples 11 and 12 were heat-treated under the conditions shown in Table 5, and these were used as coated particle samples. The coating rate and adhesion were evaluated in the same manner as in Examples 1 to 8.

[0106] [Table 5]

[0107] <Evaluation of conductivity> An insulating adhesive was prepared by mixing 100 parts by mass of epoxy resin, 150 parts by mass of curing agent, and 70 parts by mass of toluene. This adhesive was then mixed with 15 parts by mass of the coated particle sample obtained in the example to obtain an insulating paste. This paste was applied to a silicone-treated polyester film using a bar coater, and the paste was then dried to form a thin film on the film. The resulting thin film was placed between a glass substrate with aluminum vapor deposition on its entire surface and a polyimide film substrate with copper patterns formed at a 50 μm pitch. Electrical connection was established by heat bonding (160°C, 200 N, 30 seconds). The conductivity of the coated particles was evaluated at room temperature (25°C, 50% RH) by measuring the conductivity resistance between these substrates. A lower resistance value indicates higher conductivity of the coated particles. The conductivity of the coated particles was evaluated as follows: particles with a resistance of less than 2Ω were classified as "very good" (indicated by "○" in Table 6), particles with a resistance of 2Ω or more but less than 5Ω were classified as "good" (indicated by "△" in Table 6), and particles with a resistance of 5Ω or more were classified as "poor" (indicated by "×" in Table 6). The results are shown in Table 6.

[0108] [Table 6]

Claims

1. Coated particles comprising conductive particles having a metal film formed on the surface of core material particles, wherein the surface of conductive particles is coated with insulating particles, the insulating particles being characterized in that the surface of silica particles is coated (1) with a metal (M) hydroxide, and the surface of the coating (1) is further coated (2) with a fatty acid or a derivative thereof.

2. The coated particles according to claim 1, characterized in that the core material particles are a resin or a composite material of organic and inorganic materials.

3. The coated particle according to claim 1 or 2, characterized in that the metal film is at least one film selected from nickel, palladium, gold, nickel alloy, palladium alloy, and gold alloy.

4. The coated particles according to claim 1 or 2, characterized in that the conductive particles have a plurality of protrusions on the metal film.

5. The coated particle according to claim 1 or 2, characterized in that the metal (M) is aluminum.

6. The coated particle according to claim 1 or 2, characterized in that the fatty acid or derivative thereof is a fatty acid or derivative thereof having 7 or more carbon atoms.

7. The coated particles according to claim 1 or 2, characterized in that the conductive particles are surface-treated with a hydrophobic agent.

8. The coated particle according to claim 7, characterized in that the hydrophobic agent is a higher fatty acid or a derivative thereof.

9. A conductive material comprising the coated particles and an insulating resin as described in claim 1.

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