Insulating fine particles and coated particles

Abstract

To provide: insulating fine particles that can further improve conduction reliability and insulation properties; and coated particles using the same.SOLUTION: Provided are insulating fine particles, each of which has an asymmetric structure comprising a crosslinked polymer fine particle and a polymer having sites to which metals can coordinate and which has inorganic metal salts coordinated to the sites to which metals can coordinate. The insulating fine particles can be produced by the steps of: impregnating crosslinked polymer fine particles with a monomer component containing a monomer having a site to which a metal can coordinate; polymerizing the monomer to obtain fine particles, each of which has an asymmetric structure comprising a crosslinked polymer fine particle and a polymer having sites to which metals can coordinate; and making an inorganic metal salt coordinate to the sites of the fine particles to which metals can coordinate.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] Conductive particles, in which a metal film such as nickel or gold is formed on the surface of core material 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 to be used in the conductive materials mentioned above. When using such small-particle conductive particles, the amount of conductive particles in the conductive material 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 unintended directions.

[0003] To solve the aforementioned problem, conductive particles coated with an insulating layer have been proposed, in which the surface of conductive particles is coated with an insulating material to prevent contact between the metal films of the conductive particles. With such coated particles, the insulating fine particles of the insulating layer usually melt, deform, or peel off when the coated particles are thermocompressed between electrodes, exposing the metal surface of the conductive particles and thereby enabling conductivity between the electrodes. Techniques are known to improve properties such as conductivity reliability by examining the constituent components of the insulating fine particles.

[0004] While resin microparticles such as styrene resin and acrylic resin, or inorganic microparticles such as silica and alumina are used as insulating microparticles, organic-inorganic composite microparticles, which combine organic and inorganic materials, are also being investigated with the aim of improving properties such as insulating properties and solvent resistance (see, for example, Patent Documents 1 to 5).

[0005] While coated conductive particles using insulating microparticles disclosed in Patent Documents 1 to 5 possess excellent insulating properties, they suffer from poor conductivity reliability because they shift from the electrodes due to mechanical forces during thermocompression bonding. To solve this problem, Patent Document 6 proposes insulating microparticles made of a block copolymer having hydrophobic and hydrophilic regions, in which an inorganic compound is supported on the hydrophilic region of mottled particles having hydrophobic and hydrophilic regions on their surface. It is believed that the inorganic compound supported on the hydrophilic region of the insulating microparticles successfully penetrates the electrodes, making it easier for the conductive particles to be fixed to the electrodes, thereby obtaining coated particles with excellent conductivity reliability and insulating properties. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Special Publication No. 2007-537570 [Patent Document 2] International Publication No. 2012 / 002508 Brochure [Patent Document 3] Japanese Patent Publication No. 2015-187984 [Patent Document 4] Japanese Patent Publication No. 2011-65750 [Patent Document 5] Japanese Patent Publication No. 2013-108026 [Patent Document 6] Japanese Patent Publication No. 2022-41178 [Overview of the project] [Problems that the invention aims to solve]

[0007] As mentioned above, when electrodes are heat-compressed together, the insulating fine particles of the insulating layer melt, deform, or peel off, exposing the metal surface of the conductive particles, thereby enabling conductivity between the electrodes. However, even with conductive particles that have an insulating layer, this phenomenon, i.e., a short circuit, can occur between adjacent conductive particles. Through our research, we have found that this is because the insulating layer cannot withstand the mechanical force during heat-compression bonding and is destroyed, exposing the metal surface of the conductive particles.

[0008] Therefore, the object of the present invention is to solve the above-mentioned problems and provide insulating fine particles and coated particles using the same that can further improve conductivity reliability and insulation properties. [Means for solving the problem]

[0009] The present inventors conducted intensive research to solve the aforementioned problems and found that by using a polymer having a metal-coordinating site as a constituent material for insulating fine particles, and by coordinating an inorganic metal salt to the metal-coordinating site, an insulating layer with increased mechanical strength compared to conventional materials can be formed. Furthermore, they discovered that by forming an insulating layer using such insulating fine particles, it is possible to immobilize them onto electrodes, resulting in coated particles with superior insulating properties as well as excellent conductivity reliability, thus completing the present invention.

[0010] In other words, the present invention provides insulating fine particles having an asymmetric structure composed of crosslinked polymer fine particles and a polymer having a site to which a metal can coordinate (hereinafter referred to as "polymer A"), wherein an inorganic metal salt is coordinated to the site to which the metal can coordinate.

[0011] Furthermore, the present invention provides coated particles comprising conductive particles having a metal film formed on the surface of a core material, and an insulating layer covering the conductive particles, wherein the insulating layer contains the insulating fine particles.

[0012] Furthermore, the present invention provides a method for producing insulating fine particles, which comprises a step of impregnating crosslinked polymer fine particles with a monomer component (hereinafter referred to as "monomer component A") containing a monomer having a site where a metal can be coordinated, a step of polymerizing the monomer component to obtain fine particles having an asymmetric structure composed of crosslinked polymer fine particles and a polymer having a site where a metal can be coordinated (hereinafter referred to as "asymmetric fine particles"), and a step of coordinating an inorganic metal salt to the site where the metal of the asymmetric fine particles can be coordinated.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide coated particles excellent in conduction reliability and insulation.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an embodiment of the coated particles. [Figure 2] FIG. 2 is a schematic view showing an embodiment of the insulating fine particles. [Figure 3] FIGS. 3(a) and (b) are schematic cross-sectional views showing an embodiment of the coated particles. [Figure 4] FIG. 4 is a SEM photograph of the asymmetric fine particles obtained in Example 1. [Figure 5] FIG. 5 is a TEM photograph of the asymmetric fine particles obtained in Example 1. [Figure 6] FIG. 6 is an FT-IR spectrum of the asymmetric fine particles obtained in Example 1. [Figure 7] FIG. 7 is a SEM photograph of the insulating fine particles obtained in Example 1. [Figure 8] FIG. 8 is a TEM photograph of the insulating fine particles obtained in Example 1.

Embodiments for Carrying Out the Invention

[0015] The insulating fine particles of the present invention and coated particles using them will be described below based on preferred embodiments. As shown in Figure 1, the coated particle 1 comprises conductive particles 5 having a conductive surface and an insulating layer 6 covering the conductive particles 5. The conductive particle 5 is a particle having a metal film formed on the surface of a core material, and its surface is conductive.

[0016] The insulating layer 6 covers the surface of the conductive particles 5. In the coated particles 1 shown in Figure 1, the insulating layer 6 is arranged on the surface of the metal film 3, covering the surface of the conductive particles 5.

[0017] The insulating layer 6 contains insulating fine particles of the present invention. An example of insulating fine particles is shown in Figure 2. The insulating fine particles 7 have an asymmetric structure composed of crosslinked polymer fine particles 7a and polymer A 7b, with an inorganic metal salt 7c coordinated to the metal-coordinating portion of polymer A 7b. An asymmetric structure refers to a structure in which crosslinked polymer fine particles and polymer A are composited, and which has a surface where the crosslinked polymer fine particles are exposed and a surface where polymer A is exposed. By coordinating the inorganic metal salt to the insulating fine particles, it is possible to form an insulating layer with increased mechanical strength compared to conventional materials. Even if a strong dispersion force is applied to the coated particles, the insulating layer is less likely to be destroyed, and physical penetration into the electrode occurs during pressurized connection, allowing conductive particles to be fixed to the electrode, thereby improving insulation and conductivity reliability.

[0018] From the viewpoint of achieving excellent balance between insulation and conductivity reliability in the desired direction, the average particle size of the insulating fine particles is preferably 50 nm to 3000 nm, and more preferably 80 nm to 2000 nm. Similarly, from the same viewpoint, the average particle size of the conductive particles is preferably 0.1 μm to 50 μm, and more preferably 0.5 μm to 30 μm.

[0019] The average particle diameter mentioned above is the average value of the particle diameters obtained when 200 particles of the target particle were measured using a scanning electron microscope. If the target particle is not spherical in the scanning electron microscope image, the particle diameter refers to the longest length (maximum length) of the line segment that crosses the two-dimensional projection image of the particle. In this embodiment, the thickness of the insulating layer can be considered to be the average particle diameter of the insulating fine particles with the largest average particle diameter among the insulating fine particles.

[0020] The crosslinked polymer fine particles constituting the insulating fine particles of the present invention consist of a crosslinked polymer obtained by polymerizing a monomer component containing a non-crosslinkable monomer and a crosslinkable monomer. There are no particular restrictions on their shape; they may be spherical or have other shapes. Examples of shapes other than spherical include fibrous, hollow, plate-like, or needle-like forms. However, the crosslinked polymer fine particles are preferably spherical in terms of their adhesion to conductive particles and ease of synthesis.

[0021] Examples of non-crosslinkable monomers constituting the crosslinked polymer fine particles include styrene, nucleate-substituted styrenes such as o-,m- or p-methylstyrene, dimethylstyrene, ethylstyrene, and chlorostyrene; styrene derivatives such as α-methylstyrene, α-chlorostyrene, and β-chlorostyrene; olefin monomers such as ethylene and propylene; esters of acrylic acid or methacrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, and phenyl (meth)acrylate; and vinyl acetate.

[0022] 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, trimethylolpropane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, and tetramethylolmethane tri(meth)acrylate. Examples include polyfunctional (meth)acrylates such as tetramethylolmethanetetra(meth)acrylate, tetramethylolpropanetetra(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 triallyl isocyanurate, diallyl phthalate, diallyl acrylamide, and diallyl ether.

[0023] As the monomer component of the crosslinked polymer, styrene-based monomers are preferred because they readily form spherical particles and exhibit excellent adhesion to the surface of conductive particles, and styrene and divinylbenzene are more preferred.

[0024] The proportion of crosslinkable monomers in the monomer components of the aforementioned crosslinked polymer is preferably 1 to 30 mol%, and more preferably 3 to 25 mol%, from the viewpoint of ease of synthesis and mechanical properties.

[0025] The crosslinked polymer fine particles preferably have a charged functional group, and more preferably consist of a crosslinked polymer obtained using a monomer having a charged functional group. Having a charged functional group improves the adhesion of the resulting insulating fine particles to conductive particles, and also makes it easier for the coordinated metal salt to be located on the outermost surface of the coated particles, thus providing a greater effect in fixing the conductive particles to the electrode.

[0026] Examples of charged functional groups include onium-based functional groups such as phosphonium groups, ammonium groups, and sulfonium groups. Of these, ammonium groups or phosphonium groups are more preferable, and phosphonium groups are even more preferable, from the viewpoint of improving adhesion to conductive particles and forming coated particles that combine high levels of insulation and conductivity reliability.

[0027] The onium-based functional group is preferably represented by the following general formula (1).

[0028] [ka] (In the formula, X is a phosphorus atom, a nitrogen atom, or a sulfur atom; R may be the same or different, and is a hydrogen atom, a linear, branched, or cyclic alkyl group, or an aryl group. n is 1 when X is a nitrogen atom or a phosphorus atom, and 0 when X is a sulfur atom. * represents a bond.)

[0029] Examples of counter anions in onium-based functional groups include halide ions. An example of a halide ion is Cl - F - , Br - , I - These are some examples.

[0030] In formula (1), the linear alkyl group represented by R can be, for example, a linear alkyl group having 1 to 20 carbon atoms, specifically including methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, and the like.

[0031] In formula (1), the branched alkyl group represented by R can be, for example, a branched alkyl group having 3 to 8 carbon atoms, specifically including isopropyl group, isobutyl group, s-butyl group, t-butyl group, isopentyl group, s-pentyl group, t-pentyl group, isohexyl group, s-hexyl group, t-hexyl group, ethylhexyl group, and the like.

[0032] In formula (1), examples of cyclic alkyl groups represented by R include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclooctadecyl groups.

[0033] In formula (1), examples of the aryl group represented by R include the phenyl group, benzyl group, tolyl group, and o-xylyl group.

[0034] 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), it is even more preferable for R to be a linear alkyl group. This configuration of the onium-based functional group enhances the adhesion between insulating fine particles and conductive particles, ensuring insulation, and further improves conductivity reliability during thermocompression bonding.

[0035] From the viewpoint of facilitating the acquisition of monomers and the preparation of crosslinked polymer microparticles, the crosslinked polymer constituting the crosslinked polymer microparticles preferably has a structural unit represented by the following general formula (2) or general formula (3).

[0036] [Chemical formula] (In the formula, X, R and n have the same meanings as in the general formula (1). m is an integer of 0 or more and 5 or less. An - represents a monovalent anion.)

[0037] [Chemical formula] (In the formula, X, R and n have the same meanings as in the general formula (1). An - represents 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.)

[0038] As examples of R in the general formula (2) and the general formula (3), the description of the functional group of R in the general formula (1) described above is appropriately applicable. The ionic group may be bonded to any of the para-position, ortho-position, and meta-position with respect to the CH group of the benzene ring in the general formula (2), and is preferably bonded to the para-position. In the general formula (2) and the general formula (3), the monovalent An - is preferably a halide ion. Examples of the halide ion include Cl - , F - , Br - , I - .

[0039] Also, 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.

[0040] The crosslinked polymer having an charged functional group is preferably composed of a component derived from a monomer having an onium-based functional group and an ethylenically unsaturated bond.

[0041] Examples of monomers having an onium-based functional group and an ethylenically unsaturated bond include ammonium group-containing monomers such as N,N,N-trimethyl-N-2-methacryloyloxyethylammonium chloride; monomers having a sulfonium group such as phenyldimethylsulfonium methylsulfate methacrylate; and monomers having a phosphonium group such as 4-(vinylbenzyl)triethylphosphonium chloride, 4-(vinylbenzyl)trimethylphosphonium chloride, 4-(vinylbenzyl)tributylphosphonium chloride, 4-(vinylbenzyl)trioctylphosphonium chloride, 4-(vinylbenzyl)triphenylphosphonium chloride, 2-(methacroyloxyethyl)trimethylphosphonium chloride, 2-(methacroyloxyethyl)triethylphosphonium chloride, 2-(methacroyloxyethyl)tributylphosphonium chloride, 2-(methacroyloxyethyl)trioctylphosphonium chloride, and 2-(methacroyloxyethyl)triphenylphosphonium chloride. These non-crosslinkable monomers may be used individually or in combination of two or more.

[0042] In crosslinked polymers, the proportion of monomers containing charged functional groups is preferably 0.01 mol% to 20 mol%, and more preferably 0.02 mol% to 10 mol%. A high proportion of monomer components containing charged functional groups is undesirable because it makes it difficult to form spherical particles.

[0043] Crosslinked polymer fine particles can be easily produced by known methods such as suspension polymerization and emulsion polymerization using the above-mentioned monomers.

[0044] Polymer A in the insulating fine particles of the present invention is a polymer having a site to which a metal can coordinate. Examples of sites to which a metal can coordinate include functional groups having lone pairs of electrons, such as hydroxyl groups, carboxyl groups, carbonyl groups, amino groups, imino groups, cyanate groups, isocyanate groups, phosphino groups, and thiol groups, or β-diketone structures, enamine structures, and β-ketoiminate structures. Of these, the site to which an inorganic metal salt can coordinate is preferably a β-diketone structure because it can be easily coordinated.

[0045] Polymer A is preferably composed of components derived from monomers having metal-coordinating sites, and examples of such monomers include monomers that have metal-coordinating sites and also have ethylenically unsaturated bonds.

[0046] Examples of monomers having a site to which a metal can coordinate and having an ethylenically unsaturated bond include acrylic acid, methacrylic acid, 3-acetylpropionic acid, 5-hexenoic acid, 8-nonenic acid, 9-decenoic acid, 10-undecenoic acid, 2-isocyanatoethyl methacrylate, 2-isocyanatoethyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl methacrylate, acrylamide, methacrylamide, 4-aminostyrene, aryl acetoacetate, diethyl allylmalonate, and 2-(acetoacetyloxy)ethyl methacrylate.

[0047] In polymer A, the proportion of monomers having sites to which metals can coordinate is preferably 0.1 to 10% by mass, and more preferably 1 to 5% by mass, from the standpoint of being able to easily adjust the amount of inorganic metal salt to be coordinated.

[0048] The insulating fine particles of the present invention can be manufactured by a method comprising: step 1 impregnating crosslinked polymer fine particles with a monomer component (monomer component A) containing a monomer having a site to which a metal can coordinate; step 2 polymerizing the monomer component A to obtain asymmetric fine particles composed of crosslinked polymer fine particles and polymer A; and step 3 coordinating an inorganic metal salt to the site to which a metal can coordinate of the fine particles.

[0049] In step 1, a method for impregnating the crosslinked polymer microparticles with monomer component A is to prepare a dispersion by dispersing the crosslinked polymer microparticles in a dispersion medium such as water, and then add monomer component A to this dispersion to allow the crosslinked polymer microparticles to absorb the monomer component.

[0050] In the above method, it is preferable to add a secondary particle formation inhibitor such as sodium nitrate, lithium nitrate, ammonium nitrate, or sodium nitrite to the dispersion in order to prevent the crosslinked polymer fine particles from agglomerating.

[0051] Furthermore, by adding surfactants such as sodium lauryl sulfate, ammonium lauryl sulfate, sodium sulfonate, polyoxyethylene alkyl ether, glyceryl stearate, PEG-25 stearate, glyceryl oleate, sucrose laurate, sucrose palmitate, sucrose stearate, hexadecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and dodecyltrimethylammonium bromide, monomer component A is more easily absorbed by cross-linked polymer microparticles.

[0052] The polymerization of monomer component A in step 2 can be carried out according to a conventional method using a known polymerization initiator. However, in step 1, a polymerization initiator, such as 2,2'-azobis(isobutyronitrile), can also be added to allow both monomer component A and the polymerization initiator to be absorbed into the crosslinked polymer fine particles, and then the dispersion can be heated to initiate polymerization.

[0053] By polymerizing crosslinked polymer microparticles while they are impregnated with monomer component A, the crosslinked polymer microparticles and polymer A become complex, and the monomer component A, which also has hydrophilic groups, localizes near the surface of the crosslinked polymer microparticles, which have been given hydrophilicity by onium-based functional groups, and polymerization proceeds, thus producing asymmetric microparticles composed of crosslinked polymer microparticles and polymer A.

[0054] One method for coordinating the inorganic metal salt in step 3 is to add the desired inorganic metal salt to a dispersion of the asymmetric fine particles obtained in step 2, thereby coordinating it to the site on polymer A where the metal can coordinate. Another method involves adding a raw material capable of forming a desired inorganic metal salt to a dispersion containing the asymmetric fine particles obtained in step 2, thereby precipitating the inorganic metal salt at the sites on polymer A where the metal can coordinate. For example, when coordinating a metal phosphate salt, the metal salt and phosphate salt can be added to the dispersion to generate the metal phosphate salt and coordinate it to the sites on polymer A where the metal can coordinate.

[0055] The particle size distribution of insulating fine particles obtained in the manner described above has a range. Generally, the range of particle size distribution of a powder is expressed by the coefficient of variation (CV) shown in the following calculation formula (I). CV(%)=(standard deviation / average particle diameter)×100...(I) A large CV indicates a wide particle size distribution, while a small CV indicates a sharp particle size distribution. The insulating fine particles of the present invention preferably have a CV of 0.1% to 20%, more preferably 0.5% to 19%. Having a CV within this range has the advantage of allowing for a uniform thickness of the insulating layer containing the insulating fine particles in the coating particles described later.

[0056] The coated particles of the present invention comprise conductive particles having a metal film formed on the surface of a core material, and an insulating layer coating the conductive particles, wherein the insulating layer contains the insulating fine particles of the present invention as described above.

[0057] The core material can be composed of inorganic and organic materials without particular limitations. The shape of the core material is not particularly limited, but it is preferably granular. Examples of granular core material shapes include spherical, fibrous, hollow, plate-like, needle-like, and irregular shapes. Of these, a spherical shape is preferred from the viewpoint of efficient particle filling and metal film formation on the core material. The core material may have multiple protrusions on its surface. In the following description, unless otherwise specified, embodiments using granular core material (core material particles) will be described.

[0058] Examples of inorganic materials used as core materials include metals such as gold, silver, copper, nickel, and palladium, or alloys thereof; metal compounds such as solder; glass; ceramics; silica; anhydrous or hydrated oxides of metals or nonmetals; metal silicates including aluminosilicates; metal carbides; metal nitrides; metal carbonates; metal sulfates; metal phosphates; metal sulfides; metal salts; metal halides; and carbon. These may be used individually or in combination of two or more.

[0059] Examples of organic materials used as core materials include natural fibers, natural resins, thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, polybutene, polyamide, polyacrylic acid ester, polyacrylonitrile, polyacetal, ionomer, polyester, acrylic resin, and methacrylic resin, and thermosetting resins such as alkyd resin, phenolic resin, urea resin, benzoguanamine resin, melamine resin, xylene resin, silicone resin, epoxy resin, and diallyl phthalate resin. These may be used individually or in combination of two or more types.

[0060] The core material may be composed of either inorganic or organic materials as described above, or alternatively, of a material composed of both inorganic and organic materials. When the core material 2 is composed of a material composed of both inorganic and organic materials, examples of the arrangement of inorganic and organic materials in the core material 2 include a core-shell type configuration, such as a configuration comprising a core made of inorganic material and a shell made of organic material covering the surface of the core, or a configuration comprising a core made of organic material and a shell made of inorganic material covering the surface of the core. In addition to these, examples of a blend type configuration include one in which inorganic and organic materials are mixed or randomly fused within the particles of a single core material 2.

[0061] In particular, the core material is preferably composed mainly of an organic material, more preferably a resin, and even more preferably a thermoplastic resin. By using a core material made of such a material, the dispersion stability between particles can be improved, and appropriate elasticity can be exhibited during the electrical connection of electronic circuits to improve conductivity. Furthermore, by using inorganic materials such as metal particles, ceramics, and silica as minor components, heat resistance can also be improved.

[0062] When using organic materials as core materials, 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. 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 to achieve conductivity in anisotropic conductive connections by making it easier for the conductive particles to soften and increasing the contact area. 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. The glass transition temperature can be measured by the method described in the examples below.

[0063] When organic matter is used as core material particles, if the organic matter 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. A specific example of such core material particle material without a glass transition temperature can be obtained by copolymerizing the monomer constituting the organic matter exemplified above with a crosslinkable monomer.

[0064] From a similar viewpoint, if the core material has a glass transition temperature, the difference between the glass transition temperature of the insulating layer and the glass transition temperature of the core material is preferably 160°C or less, more preferably 120°C or less, and particularly preferably 100°C or less. Furthermore, the difference between the glass transition temperature of the insulating layer and the glass transition temperature of the core material is preferably 5°C or more, and more preferably 10°C or more.

[0065] Examples of methods for measuring the glass transition temperature include the following: Using a differential scanning calorimeter "STAR SYSTEM" (METTLER TOLEDO), 0.04 to 0.06 g of the sample was heated to 200°C and then cooled to 25°C at a rate of 5°C / min. The sample was then heated again at a rate of 5°C / min and the heat quantity was measured. When a peak was observed, the temperature of that peak was defined as the glass transition temperature. When no peak was observed but a step was observed, the temperature at the intersection of the tangent line showing the maximum slope of the curve at the step and the extension of the baseline on the high-temperature side of the step was defined as the glass transition temperature.

[0066] Examples of conductive materials used in metal coatings to exhibit conductivity on the surface of conductive particles include metals such as gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, germanium, aluminum, chromium, palladium, tungsten, and molybdenum, or their alloys, as well as metal compounds such as ITO and solder. These materials can be used individually or in combination of two or more.

[0067] From the viewpoint of lowering electrical resistance during conduction while improving adhesion with the insulating layer described later, the metal film is preferably composed of at least one conductive material selected from gold, silver, copper, nickel, palladium, and solder, and more preferably contains at least one conductive material selected from nickel, palladium, gold, nickel alloys, and palladium alloys.

[0068] The shape of the conductive particles is not particularly limited, although it depends on the shape of the core material particles. Examples of conductive particle shapes include spherical, fibrous, hollow, plate-like, needle-like, and irregular shapes. Of these, from the viewpoint of achieving excellent filling and connectivity, it is preferable that the particles be spherical or have protrusions on their surface. When the conductive particles have protrusions on their surface, it is preferable that they have multiple protrusions on their surface, and it is even more preferable that the surface of a sphere has multiple protrusions. When the conductive particles have multiple protrusions, these protrusions may be formed by core material particles having multiple protrusions, or the core material particles may not have protrusions, and the metal coating may have multiple protrusions.

[0069] If conductive particles have protrusions on their surface, the height of the protrusions is preferably 20 nm to 500 nm, and more preferably 50 nm to 400 nm. The number of protrusions depends on the particle size of the conductive particles, but it is advantageous for further improving the conductivity of the conductive particles if there are preferably 1 to 20,000 protrusions per conductive particle, and more preferably 5 to 5,000 protrusions. The length of the base of the protrusions is preferably 5 nm to 500 nm, and more preferably 10 nm to 400 nm. The length of the base of the protrusions refers to the length along the surface of the conductive particle at the site where the protrusion is formed, measured using an electron microscope image of the cross-section of the particle, and the height of the protrusions refers to the shortest distance from the base of the protrusion to the apex of the protrusion. If a single protrusion has multiple apexes, the height of the highest apex is taken 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.

[0070] When a metal film is formed on the core material, the thickness of the metal film is preferably 0.001 μm to 2 μm, and more preferably 0.01 μm to 1.5 μm. If the metal film has a laminated structure consisting of multiple layers, the total thickness of the laminated structure of the metal film should be within the above range. Furthermore, if the conductive particles have protrusions as described later, the height of the protrusions shall not be included in the thickness of the metal film as referred to here. The thickness of the metal film can be measured, for example, by cutting the coated particle to be measured in two and observing the cross-section of the cut surface with a scanning electron microscope (SEM).

[0071] The insulating layer covers the surface of the conductive particles. In Figure 1, the coated particle 1 has an insulating layer 6 on the surface of the metal film 3, which covers the surface of the conductive particle 5.

[0072] The insulating layer contains the insulating fine particles of the present invention as described above. The coordination of inorganic metal salts to these insulating fine particles allows for physical penetration into the electrode during pressurized connection, thereby fixing the conductive particles to the electrode and improving both insulating properties and conductivity reliability.

[0073] The insulating layer may continuously and evenly cover the entire surface of the conductive particles, or it may cover only a portion of the surface of the conductive particles. In the former case, the entire surface of the metal film of the conductive particles is completely covered by the insulating layer, so that the surface of the conductive particles is not exposed. In the latter case, the conductive particles consist of a portion whose surface is made up of at least one of the underlying core material and metal film, and a portion made up of the insulating layer. When the insulating layer covers only a portion of the surface of the conductive particles, the covered portion may be continuous, discontinuous in an island-like pattern, or a combination of these.

[0074] In detail, the forms of forming the insulating layer in the coated particles include, for example, the forms shown in (i) and (ii) below. (i) As shown in Figure 3(a), insulating fine particles 7, in which an inorganic metal salt 7c is coordinated to polymer A7b, are arranged in layers on the surface of conductive particles 5. (ii) As shown in Figure 3(b), a layered insulating layer 6 consisting of an insulating material 8 and insulating fine particles 7 is arranged on the surface of the conductive particles 5.

[0075] As shown in Figure 3(b), when the insulating layer 6 is layered, the insulating material 8 can be melted or dissolved in a solvent to a state of high fluidity, and can have the property of coating the surface of the conductive particles 5 in a film-like manner. Examples include styrene-based and acrylic-based thermoplastic resins. Furthermore, the insulating layer 6 may be continuous, discontinuous in an island-like pattern, or a combination of these.

[0076] The method for producing coated particles is described below. First, conductive particles with a metal film formed on the surface of a core material are prepared. Methods for forming the metal film on the surface of the core material include, for example, dry methods using vapor deposition, sputtering, mechanochemical methods, hybridization, etc., and wet methods using electroplating, electroless plating, etc. These methods can be used individually or in combination. Alternatively, commercially available conductive particles may be used.

[0077] Next, the insulating fine particles and conductive particles are mixed to obtain coated particles having an insulating layer made of insulating fine particles on the surface of the conductive particles. For example, insulating fine particles and conductive particles can be mixed to form coated particles having an insulating layer containing insulating fine particles on the surface of the conductive particles.

[0078] Mixing insulating fine particles and conductive particles is preferable when adding these particles to a dispersion medium to form a dispersion. Examples of dispersion mediums include water, organic solvents, and mixtures thereof, with water, ethanol, or a mixture of ethanol and water being preferred.

[0079] The dispersion preferably contains an inorganic salt, an organic salt, or an organic acid, as this makes it easier to obtain coated particles with a coating rate of a certain level or higher for the insulating layer. As the inorganic salt, organic salt, or organic acid, those that dissociate anions are preferably used. As an anion, Cl- F - , Br - , I - SO4 2- CO3 2- NO3 - COO - RCOO - (R is an organic group) etc. are preferred as inorganic salts. For example, NaCl, KCl, LiCl, MgCl2, BaCl2, NaF, KF, LiF, MgF2, BaF2, NaBr, KBr, LiBr, MgBr2, BaBr2, NaI, KI, LiI, MgI2, BaI2, Na2SO4, K2SO4, Li2SO4, MgSO4, Na2CO3, NaHCO3, K2CO3, KHCO3, Li2CO3, LiHCO3, MgCO3, NaNO3, KNO3, LiNO3, MgNO3, BaNO3, etc. can be used as organic salts. Sodium oxalate, sodium acetate, sodium citrate, sodium tartrate, etc. can be used as organic acids. Amino acids such as glycine, succinic acid, oxalic acid, acetic acid, citric acid, tartaric acid, malonic acid, fumaric acid, maleic acid, etc. can be used as organic acids.

[0080] The preferred concentrations of inorganic salts, organic salts, and organic acids vary depending on the desired coverage area of ​​the insulating fine particles on the conductive particle surface area. However, a concentration of, for example, 0.1 mmol / L to 100 mmol / L in the dispersion after mixing the conductive particles is preferred because it provides a suitable coverage rate and makes it easier to obtain coated particles with a single layer of insulating fine particles. From this viewpoint, the concentrations of inorganic salts, organic salts, and organic acids in the dispersion are particularly preferred to be 1.0 mmol / L to 80 mmol / L.

[0081] In a dispersion containing insulating fine particles and conductive particles, the conductive particles are preferably present in an amount of 100 ppm to 100,000 ppm by mass, and more preferably in an amount of 500 ppm to 80,000 ppm. The insulating fine particles are preferably present in an amount of 10 ppm to 50,000 ppm by mass, and more preferably in an amount of 250 ppm to 30,000 ppm.

[0082] From the viewpoint of obtaining coated particles of consistent quality, the temperature of the dispersion is preferably 20°C to 100°C, and more preferably 40°C to 100°C, when the insulating fine particles and conductive particles are mixed. In particular, when the glass transition temperature of the polymer having the lowest glass transition temperature is Tg(°C), the temperature of the dispersion is preferably Tg-30°C to Tg+30°C. Within this range, the insulating fine particles can easily adhere to the surface of the conductive particles while maintaining their shape. In particular, the affinity between the insulating fine particles and the conductive particles can be further increased, making it possible to produce coated particles with a sufficiently high coverage rate.

[0083] The dispersion time in the dispersion is preferably 0.1 hours to 24 hours to allow sufficient adhesion between the insulating fine particles and the conductive particles. During this time, it is preferable to stir the dispersion. After this, if necessary, the solid components of the dispersion are washed and dried to obtain coated particles in which insulating fine particles are attached to the surface of the conductive particles. The coated particles obtained in this way have an insulating layer formed on the surface of the conductive particles, with multiple insulating fine particles attached to it.

[0084] When forming a layered insulating layer as shown in Figure 3(b), first, insulating fine particles and fine particles made of an insulating material are used to produce coated particles in which multiple of these particles adhere to the surface of conductive particles. Then, by treating these coated particles with an organic solvent or by heat treatment, the fine particles made of the insulating material are made highly fluid, and an insulating layer can be formed that coats the surface of the conductive particles in a film-like manner together with the insulating fine particles. By forming the insulating layer in a film-like manner, the adhesion between the insulating layer and the conductive particles can be increased, resulting in higher insulation performance.

[0085] Coating particles in which insulating fine particles and fine particles made of insulating material adhere to the surface of conductive particles can be coated with a film-like layer on the surface of conductive particles by adding an organic solvent to the dispersion, which can make the fine particles made of insulating material fluid. When melting the fine particles made of insulating material, tetrahydrofuran, toluene, methyl ethyl ketone, N-methyl-2-pyrrolidone, and N,N-dimethylformamide can be used as the organic solvent. The amount of organic solvent to be added is preferably 1 to 100 parts by mass, and more preferably 5 to 50 parts by mass, per 1 part by mass of coated particles in the dispersion, in order to easily form a uniform film without the insulating fine particles and fine particles made of insulating material falling off. The addition temperature is preferably 10°C to 100°C, and more preferably 20°C to 80°C, in order to easily form a uniform film without the insulating fine particles and fine particles made of insulating material falling off. The time to allow the film to form after addition is preferably 0.1 hours to 24 hours, in order to form a uniform film. In this way, a layered insulating layer, as shown in Figure 3(b), can be suitably formed.

[0086] Methods for heating the coated particles include heating a dispersion after attaching insulating fine particles and fine particles made of insulating material to the surface of conductive particles, heating the obtained coated particles again in a solvent such as water, and heating them in the solvent, and heating the obtained coated particles in a gas phase such as an inert gas. The heating temperature is preferably between Tg+1°C and Tg+60°C, more preferably between Tg+5°C and Tg+50°C, and most preferably above Tg+15°C, where Tg (°C) is the glass transition temperature of the insulating material, in order to easily form a uniform film without the insulating fine particles and fine particles made of insulating material falling off. The heating time is preferably between 0.1 hours and 24 hours, in order to easily form a uniform film. Furthermore, when heating the coated particles in the gas phase, the pressure conditions can be atmospheric pressure, reduced pressure, or increased pressure. In this way, a layered insulating layer as shown in Figure 3(b) can be suitably formed.

[0087] Coated particles, in which the surface of conductive particles is covered with a layered insulating layer, may undergo annealing treatment to further stabilize the insulating layer. Methods for annealing include heating the coated particles in a gas phase such as an inert gas. The heating temperature is preferably between Tg+1°C and Tg+60°C, and more preferably between Tg+5°C and Tg+50°C, where Tg (°C) is the glass transition temperature of the insulating material. The heating atmosphere is not particularly limited and can be carried out under atmospheric pressure, reduced pressure, or increased pressure in an inert gas atmosphere such as nitrogen or argon, or an oxidizing atmosphere such as air.

[0088] The coated particles obtained as described above have an insulating layer coordinated with an inorganic metal salt, resulting in an insulating layer with increased mechanical strength compared to conventional materials. Even if a strong dispersion force is applied to the coated particles, the insulating layer is less likely to be destroyed. Furthermore, when the coated particles are heat-pressed between electrodes, the inorganic metal salt makes them easier to fix to the electrodes, thus improving conductivity reliability. The coated particles of the present invention are suitably used as conductive materials such as conductive adhesives, anisotropic conductive films, and anisotropic conductive adhesives. These conductive materials contain the coated particles of the present invention and insulating resins such as epoxy resins and acrylic resins, preferably as a mixture of these. The conductive material may further contain a resin curing agent or an organic solvent as needed. [Examples]

[0089] The present invention will be described below with reference to examples. However, the scope of the present invention is not limited to these examples.

[0090] [Example 1] [Manufacturing of crosslinked polymer microparticles and asymmetric microparticles] 100 mL of pure water was added to a 200 mL four-necked flask fitted with a condenser and stirring blades. Then, 27.8 mmol of styrene monomer (St, manufactured by Kanto Chemical Co., Ltd.), 2.2 mmol of divinylbenzene (DVB-960, manufactured by Nippon Steel Chemical & Material Co., Ltd.), 0.03 mmol of 4-(vinylbenzyl)triethylphosphonium chloride (VBTEPC, manufactured by Nippon Chemical Industrial Co., Ltd.), and 2.7 mg of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Tokyo Chemical Industry Co., Ltd.) as a polymerization initiator were added. Nitrogen was aerated for 15 minutes to remove dissolved oxygen, and then the temperature was raised to 60°C and maintained for 6 hours to allow the polymerization reaction to proceed. After cooling in an ice bath, the solid particulate matter was settled using a centrifuge, the supernatant was removed, and the mixture was washed with pure water. The obtained cross-linked polymer microparticles had a particle size of 260-280 nm and a CV of 3.9%. Next, 0.25 g of the cross-linked polymer microparticles and 50 mL of pure water were added to a 100 mL four-necked flask equipped with a condenser and stirring blades. Then, 11.7 mmol of styrene monomer (St, manufactured by Kanto Chemical Co., Ltd.), 0.15 mmol of 2-(acetoacetyloxy)ethyl methacrylate (AAEM, manufactured by Tokyo Chemical Industries, Ltd.), and 40 mg of 2,2'-azobis(isobutyronitrile) (AIBN, manufactured by Tokyo Chemical Industries, Ltd.) were added as polymerization initiators. Furthermore, 100 mg of sodium nitrate (NaNO3, manufactured by Kanto Chemical Co., Ltd.) was added as an inhibitor of secondary particle formation in the aqueous phase, and 7.5 mg of hexadecyltrimethylammonium bromide (CTAB, manufactured by Tokyo Chemical Industries, Ltd.) was added as a monomer absorption aid. The cross-linked polymer microparticles were stirred at room temperature for 24 hours to absorb styrene monomer, 2-(acetoacetyloxy)ethyl methacrylate, and 2,2'-azobis(isobutyronitrile). Then, nitrogen was passed through for 15 minutes to remove dissolved oxygen, and the temperature was raised to 80°C and maintained for 24 hours to allow the polymerization reaction to proceed. After cooling in an ice bath, the solid components of the microparticles were settled using a centrifuge, the supernatant was removed, and the mixture was washed with pure water to obtain asymmetric microparticles. SEM images of the obtained asymmetric microparticles are shown in Figure 4, and TEM images are shown in Figure 5. Figure 6 shows the results of measurements of the obtained asymmetric microparticles using a Fourier transform infrared spectrophotometer (JASCO Corporation, FT / IR-6600). The shape was confirmed by SEM and TEM images, as well as the FT-IR spectrum from 1720 to 1750 cm⁻¹. -1 Since C=O stretching vibrations originating from carbonyl groups were observed nearby, it was confirmed that the obtained asymmetric nanoparticles were composed of crosslinked polymer nanoparticles and polymers having a β-diketone structure derived from AAEM.

[0091] [Manufacturing of insulating microparticles coordinated with inorganic metal salts] Next, 25 mg of the asymmetric microparticles, 18.7 mg of calcium nitrate tetrahydrate (Ca(NO3)2·H2O, manufactured by Kanto Chemical Co., Ltd.), 3.1 mg of diammonium hydrogen phosphate ((NH4)2HPO4, manufactured by Kanto Chemical Co., Ltd.), and 10 mL of pure water were added to a 5 mL sample bottle. The pH was adjusted to 10 by adding aqueous ammonia, and the mixture was left at room temperature for 24 hours while stirring. Subsequently, the particles were separated by centrifugation and redispersed in pure water, and this process was repeated four times to purify the mixture and obtain insulating microparticles. The particle size of the obtained insulating microparticles was 260-280 nm, and the CV was 3.9%. SEM images of the obtained insulating microparticles are shown in Figure 7, and TEM images are shown in Figure 8. These images confirmed that the precipitated calcium phosphate was supported on the surface of the insulating microparticles.

[0092] [Manufacturing of coated particles] As a core material, spherical particles made of cross-linked acrylic resin (glass transition temperature: 120°C) were used, and conductive particles (Ni-plated particles; manufactured by Nippon Chemical Industrial Co., Ltd.) with an average particle diameter of 5.3 μm and a smooth surface were prepared, each having a nickel metal film with a thickness of 0.150 μm on the surface of the core material particles. 5.0 g of the Ni-plated particles were added to 100 mL of pure water and stirred to obtain a dispersion of Ni-plated particles. 10 mL of an aqueous solution of 1% by mass of benzotriazole was added to this dispersion and stirred for 5 minutes to perform surface treatment. After that, the dispersion was filtered through a membrane filter with a mesh opening of 2.0 μm to recover the Ni-plated particles having a benzotriazole layer on their surface. To the dispersion of these Ni-plated particles in 100 mL of pure water, the insulating fine particles obtained above and Na2SO4 were added, and the mixture was stirred at 40°C for 30 minutes. After adding insulating microparticles and Na2SO4, the solid content concentration of the insulating microparticles in the dispersion was 10,000 ppm by mass, and the concentration of Na2SO4 was 5 mmol / L. After removing the supernatant, solid-liquid separation was performed, and the washing operation with fresh pure water was repeated three times. The particles were then vacuum-dried at 50°C to obtain coated particles. The average particle size of the obtained coated particles was 5.4 μm.

[0093] [Example 2] [Manufacturing of crosslinked polymer microparticles and asymmetric microparticles] Crosslinked polymer fine particles and asymmetric fine particles were obtained using the same method as in Example 1. [Manufacturing of insulating microparticles coordinated with inorganic metal salts] Insulating fine particles were obtained using the same method as in Example 1.

[0094] [Manufacturing of non-crosslinked polymer microparticles] 100 mL of pure water was added to a 200 mL four-necked flask fitted with a condenser and stirring blades. Then, 30.0 mmol of styrene monomer (St, manufactured by Kanto Chemical Co., Ltd.), 5.3 mmol of n-butyl acrylate (nBA, manufactured by Kanto Chemical Co., Ltd.), 0.03 mmol of 4-(vinylbenzyl)triethylphosphonium chloride (VBTEPC, manufactured by Nippon Chemical Industrial Co., Ltd.), and 2.7 mg of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Tokyo Chemical Industry Co., Ltd.) as a polymerization initiator were added. Nitrogen was aerated for 15 minutes to remove dissolved oxygen, and then the temperature was raised to 60°C and maintained for 6 hours to allow the polymerization reaction to proceed. After cooling in an ice bath, the solid components of the fine particles were settled using a centrifuge, the supernatant was removed, and the mixture was washed with pure water. The average particle size of the obtained non-crosslinked polymer fine particles was 245 nm, and the CV was 3.6%.

[0095] [Manufacturing of coated particles] 5.0 g of Ni-plated particles having the same benzotriazole layer on their surface as used in Example 1 were dispersed in 100 mL of pure water. Insulating microparticles, non-crosslinked polymer microparticles, and Na2SO4 were added to the dispersion, and the mixture was stirred at 40°C for 30 minutes. After adding the insulating microparticles, non-crosslinked polymer microparticles, and Na2SO4, the solid content concentration of the insulating microparticles in the dispersion was 8,000 ppm by mass, the solid content concentration of the non-crosslinked polymer microparticles was 2,000 ppm by mass, and the concentration of Na2SO4 was 5 mmol / L. After removing the supernatant, the solid-liquid separation was performed, and the washing operation with fresh pure water was repeated three times to obtain washed particles. The washed particles were dispersed in 80 mL of pure water, and 20 mL of tetrahydrofuran was added to this dispersion. The mixture was stirred at room temperature for 6 hours. After stirring was complete, the solid matter was separated using a membrane filter with a mesh size of 2 μm and vacuum-dried at 50°C to obtain coated particles having an insulating layer formed by a composite of insulating fine particles and a polymer layer formed by the melting of non-crosslinked polymer fine particles into a film. The average particle size of the obtained coated particles was 5.4 μm.

[0096] [Example 3] In Example 2, [Production of Coated Particles], 5.0 g of washed particles were added to 100 mL of pure water to form a dispersion, and the dispersion was stirred at 95°C for 6 hours. After stirring, the solid matter was separated using a membrane filter with a mesh size of 2 μm, and the mixture was vacuum-dried at 50°C to obtain coated particles having an insulating layer formed by a composite of insulating fine particles and a polymer layer formed by the melting of non-crosslinked polymer fine particles into a film. The average particle size of the obtained coated particles was 5.4 μm.

[0097] [Example 4] In Example 1, the coated particles were manufactured in the same manner as in Example 1, except that the smooth-surfaced conductive particles were replaced with conductive particles having numerous protrusions with an average height of 0.1 μm (protruding Ni-plated particles; manufactured by Nippon Chemical Industrial Co., Ltd.). The average particle diameter of the coated particles was 5.4 μm.

[0098] [Example 5] [Manufacturing of crosslinked polymer microparticles and asymmetric microparticles] 100 mL of pure water was added to a 200 mL four-necked flask fitted with a condenser and stirring blades. Then, 27.8 mmol of styrene monomer (St, manufactured by Kanto Chemical Co., Ltd.), 2.2 mmol of divinylbenzene (DVB-960, manufactured by Nippon Steel Chemical & Material Co., Ltd.), 0.03 mmol of 4-(vinylbenzyl)triethylammonium chloride (VBTEPC, manufactured by Nippon Chemical Industrial Co., Ltd.), and 2.7 mg of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Tokyo Chemical Industry Co., Ltd.) as a polymerization initiator were added. Nitrogen was aerated for 15 minutes to remove dissolved oxygen, and then the temperature was raised to 60°C and maintained for 6 hours to allow the polymerization reaction to proceed. After cooling in an ice bath, the solid particulate matter was settled using a centrifuge, the supernatant was removed, and the mixture was washed with pure water. The obtained cross-linked polymer microparticles had a particle size of 260-280 nm and a CV of 3.9%. Next, 0.25 g of the cross-linked polymer microparticles and 50 mL of pure water were added to a 100 mL four-necked flask equipped with a condenser and stirring blades. Then, 11.7 mmol of styrene monomer (St, manufactured by Kanto Chemical Co., Ltd.), 0.15 mmol of 2-(acetoacetyloxy)ethyl methacrylate (AAEM, manufactured by Tokyo Chemical Industries, Ltd.), and 40 mg of 2,2'-azobis(isobutyronitrile) (AIBN, manufactured by Tokyo Chemical Industries, Ltd.) were added as polymerization initiators. Furthermore, 100 mg of sodium nitrate (NaNO3, manufactured by Kanto Chemical Co., Ltd.) was added as an inhibitor of secondary particle formation in the aqueous phase, and 7.5 mg of hexadecyltrimethylammonium bromide (CTAB, manufactured by Tokyo Chemical Industries, Ltd.) was added as a monomer absorption aid. The crosslinked polymer microparticles were stirred at room temperature for 24 hours to absorb styrene monomer, 2-(acetoacetyloxy)ethyl methacrylate, and 2,2'-azobis(isobutyronitrile). Then, nitrogen was passed through for 15 minutes to remove dissolved oxygen, and the temperature was raised to 80°C and maintained for 24 hours to allow the polymerization reaction to proceed. After cooling in an ice bath, the solid components of the microparticles were settled using a centrifuge, the supernatant was removed, and the mixture was washed with pure water to obtain asymmetric microparticles.

[0099] [Manufacturing of insulating microparticles coordinated with inorganic metal salts] Next, 25 mg of the asymmetric microparticles, 18.7 mg of calcium nitrate tetrahydrate (Ca(NO3)2·H2O, manufactured by Kanto Chemical Co., Ltd.), 3.1 mg of diammonium hydrogen phosphate ((NH4)2HPO4, manufactured by Kanto Chemical Co., Ltd.), and 10 mL of pure water were added to a 5 mL sample bottle. The pH was adjusted to 10 by adding aqueous ammonia, and the mixture was left at room temperature for 24 hours while stirring. Subsequently, the particles were separated by centrifugation and redispersed in pure water, and this process was repeated four times to purify the mixture and obtain insulating microparticles. The particle size of the obtained insulating microparticles was 260-280 nm, and the CV was 3.9%.

[0100] [Manufacturing of coated particles] As a core material, spherical particles made of cross-linked acrylic resin (glass transition temperature: 120°C) were used, and conductive particles (Ni-plated particles; manufactured by Nippon Chemical Industrial Co., Ltd.) with an average particle diameter of 5.3 μm and a smooth surface were prepared, each having a nickel metal film with a thickness of 0.150 μm on the surface of the core material particles. 5.0 g of the Ni-plated particles were added to 100 mL of pure water and stirred to obtain a dispersion of Ni-plated particles. 10 mL of an aqueous solution of 1% by mass of benzotriazole was added to this dispersion and stirred for 5 minutes to perform surface treatment. After that, the dispersion was filtered through a membrane filter with a mesh opening of 2.0 μm to recover the Ni-plated particles having a benzotriazole layer on their surface. To the dispersion of these Ni-plated particles in 100 mL of pure water, the insulating fine particles obtained above and Na2SO4 were added, and the mixture was stirred at 40°C for 30 minutes. After adding insulating microparticles and Na2SO4, the solid content concentration of the insulating microparticles in the dispersion was 10,000 ppm by mass, and the concentration of Na2SO4 was 5 mmol / L. After removing the supernatant, solid-liquid separation was performed, and the washing operation with fresh pure water was repeated three times. The particles were then vacuum-dried at 50°C to obtain coated particles. The average particle size of the obtained coated particles was 5.4 μm.

[0101] [Example 6] [Manufacturing of crosslinked polymer microparticles and asymmetric microparticles] Crosslinked polymer fine particles and asymmetric fine particles were obtained using the same method as in Example 5. [Manufacturing of insulating microparticles coordinated with inorganic metal salts] Insulating fine particles were obtained using the same method as in Example 5.

[0102] [Manufacturing of non-crosslinked polymer microparticles] 100 mL of pure water was added to a 200 mL four-necked flask fitted with a condenser and stirring blades. Then, 30.0 mmol of styrene monomer (St, manufactured by Kanto Chemical Co., Ltd.), 5.3 mmol of n-butyl acrylate (nBA, manufactured by Kanto Chemical Co., Ltd.), 0.03 mmol of 4-(vinylbenzyl)triethylammonium chloride (VBTEPC, manufactured by Nippon Chemical Industrial Co., Ltd.), and 2.7 mg of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Tokyo Chemical Industry Co., Ltd.) as a polymerization initiator were added. Nitrogen was aerated for 15 minutes to remove dissolved oxygen, and then the temperature was raised to 60°C and maintained for 6 hours to allow the polymerization reaction to proceed. After cooling in an ice bath, the solid particulate matter was settled using a centrifuge, the supernatant was removed, and the mixture was washed with pure water. The average particle size of the obtained non-crosslinked polymer fine particles was 245 nm, and the CV was 3.6%.

[0103] [Manufacturing of coated particles] 5.0 g of Ni-plated particles having the same benzotriazole layer on their surface as used in Example 5 were dispersed in 100 mL of pure water. Insulating microparticles, non-crosslinked polymer microparticles, and Na2SO4 were added to the dispersion, and the mixture was stirred at 40°C for 30 minutes. After adding the insulating microparticles, non-crosslinked polymer microparticles, and Na2SO4, the solid content concentration of the insulating microparticles in the dispersion was 8,000 ppm by mass, the solid content concentration of the non-crosslinked polymer microparticles was 2,000 ppm by mass, and the concentration of Na2SO4 was 5 mmol / L. After removing the supernatant, the solid-liquid separation was performed, and the washing operation with fresh pure water was repeated three times to obtain washed particles. The washed particles were dispersed in 80 mL of pure water, and 20 mL of tetrahydrofuran was added to this dispersion. The mixture was stirred at room temperature for 6 hours. After stirring was complete, the solid matter was separated using a membrane filter with a mesh size of 2 μm and vacuum-dried at 50°C to obtain coated particles having an insulating layer formed by a composite of insulating fine particles and a polymer layer formed by the melting of non-crosslinked polymer fine particles into a film. The average particle size of the obtained coated particles was 5.4 μm.

[0104] [Example 7] In Example 6, [Production of Coated Particles], 5.0 g of washed particles were added to 100 mL of pure water to form a dispersion, and the dispersion was stirred at 95°C for 6 hours. After stirring, the solid matter was separated using a membrane filter with a mesh size of 2 μm, and the mixture was vacuum-dried at 50°C to obtain coated particles having an insulating layer formed by a composite of insulating fine particles and a polymer layer formed by the melting of non-crosslinked polymer fine particles into a film. The average particle size of the obtained coated particles was 5.4 μm.

[0105] [Example 8] In Example 5, during the [Production of Coated Particles], the coated particles were produced in the same manner as in Example 5, except that the smooth-surfaced conductive particles were replaced with conductive particles having numerous protrusions with an average height of 0.1 μm (Ni-plated particles with protrusions; manufactured by Nippon Chemical Industrial Co., Ltd.). The average particle diameter of the coated particles was 5.4 nm.

[0106] [Comparative Example 1] In Example 1, coated particles were obtained using the same method as in Example 1, except that the crosslinked polymer fine particles having phosphonium groups obtained in [Production of Crosslinked Polymer Fine Particles and Asymmetric Fine Particles] were used as insulating fine particles to coat Ni-plated particles. The average particle size of the coated particles was 5.4 μm.

[0107] [Comparative Example 2] In Example 1, the crosslinked polymer fine particles having phosphonium groups obtained in [Production of Crosslinked Polymer Fine Particles and Asymmetrical Fine Particles] and the non-crosslinked polymer fine particles having phosphonium groups obtained in Example 2, were used as insulating fine particles and coated with Ni-plated particles to obtain coated particles. 5.0 g of these coated particles were placed in 80 mL of pure water and dispersed. 20 mL of tetrahydrofuran was added to this dispersion and stirred at room temperature for 6 hours. After stirring, the solid matter was separated using a membrane filter with a mesh size of 2 μm and vacuum-dried at 50°C to obtain coated particles having an insulating layer formed by a composite of insulating fine particles consisting of crosslinked polymer fine particles having phosphonium groups and a polymer layer formed by the melting of non-crosslinked polymer fine particles into a film. The average particle size of the obtained coated particles was 5.4 μm.

[0108] [Comparative Example 3] In Example 1, coated particles were obtained using the same method as in Example 1, except that the crosslinked polymer fine particles having phosphonium groups obtained in [Production of Crosslinked Polymer Fine Particles and Asymmetric Fine Particles] were used as insulating fine particles as is, and the smooth conductive particles used in [Production of Coated Particles] were replaced with conductive particles having numerous protrusions with an average height of 0.1 μm (Ni-plated particles with protrusions; manufactured by Nippon Chemical Industrial Co., Ltd.). The average particle diameter of the coated particles was 5.4 nm.

[0109] [Comparative Example 4] In Example 5, coated particles were obtained using the same method as in Example 5, except that the ammonium group-containing crosslinked polymer fine particles obtained in [Production of Crosslinked Polymer Fine Particles and Asymmetric Fine Particles] were used directly as insulating fine particles to coat Ni-plated particles. The average particle size of the coated particles was 5.4 μm.

[0110] [Comparative Example 5] In Example 5 [Production of Crosslinked Polymer Microparticles and Asymmetrical Microparticles], crosslinked polymer microparticles having ammonium groups were obtained, and in Example 6 [Production of Non-Crosslinked Polymer Microparticles], non-crosslinked polymer microparticles having ammonium groups were obtained. These were then coated onto Ni-plated particles as insulating microparticles to obtain coated particles. 5.0 g of these coated particles were placed in 80 mL of pure water and dispersed. 20 mL of tetrahydrofuran was added to this dispersion, and the mixture was stirred at room temperature for 6 hours. After stirring, the solid matter was separated using a membrane filter with a mesh size of 2 μm, and the mixture was vacuum-dried at 50°C to obtain coated particles having an insulating layer formed by a composite of insulating microparticles consisting of crosslinked polymer microparticles having ammonium groups and a polymer layer formed by the melting of non-crosslinked polymer microparticles into a film. The average particle size of the obtained coated particles was 5.4 μm.

[0111] [Comparative Example 6] In Example 5, coated particles were obtained using the same method as in Example 5, except that the ammonium group-containing crosslinked polymer fine particles obtained in [Production of Crosslinked Polymer Fine Particles and Asymmetric Fine Particles] were used as insulating fine particles, and the smooth-surfaced conductive particles used in [Production of Coated Particles] were replaced with conductive particles having numerous protrusions with an average height of 0.1 μm (protruding Ni-plated particles; manufactured by Nippon Chemical Industrial Co., Ltd.). The average particle diameter of the coated particles was 5.4 nm.

[0112] [Evaluation of coverage rate] The coverage rate of the coated particles obtained in the examples and comparative examples was calculated by the following method. Specifically, the backscattered electron composition (COMPO) image of the coated particles from the SEM images was imported into an automated image analysis system (Nireco Corporation, Luzex® AP), and the coverage rate of the coated particles was calculated for 20 coated particles in the COMPO image. A higher coverage rate indicates a denser insulating layer. The results are shown in Table 1.

[0113] [Evaluation of conductivity and insulation properties] The conductivity and insulation properties of the coated particles of the examples and comparative examples were evaluated using the following method.

[0114] [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 coated particles obtained in the examples and comparative examples 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, and an electrical connection was made. 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 the symbol "○" in Table 1), particles with a resistance of 2Ω or more but less than 5Ω were classified as "good" (indicated by the symbol "△" in Table 1), and particles with a resistance of 5Ω or more were classified as "poor" (indicated by the symbol "×" in Table 1). The results are shown in Table 1.

[0115] [Evaluation of insulating properties] Using a microcompression tester MCTM-500 (manufactured by Shimadzu Corporation), 20 coated particles were tested. The coated particles of the examples and comparative examples were compressed at a loading speed of 0.5 mN / sec, and the insulating properties of the coated particles were evaluated by measuring the compression displacement until a resistance value was detected. A larger compression displacement before a resistance value was detected indicates higher insulating properties of the coated particles. For the insulating properties of the coated particles, an arithmetic mean of the compression displacement before a resistance value was detected of 10% or more was classified as "very good" (indicated by the symbol "○" in Table 1), an arithmetic mean of the compression displacement between 3% and 10% was classified as "good" (indicated by the symbol "△" in Table 1), and an arithmetic mean of the compression displacement of 3% or less was classified as "poor" (indicated by the symbol "×" in Table 1). The results are shown in Table 1.

[0116] [Table 1]

[0117] As shown in Table 1, the coated particles using the insulating particles of the present invention have a high mechanical strength in the insulating layer and are easily fixed to the electrodes by the inorganic metal salt, thus exhibiting excellent insulating properties as well as excellent conductivity reliability. [Explanation of symbols]

[0118] 1. Coated particles 2 Core material 3 Metal coating 5. Conductive particles 6. Insulating layer 7. Insulating particles 7a Crosslinked polymer fine particles 7b Polymer A 7c Inorganic metal salts 8. Insulating materials

Claims

1. Insulating microparticles having an asymmetric structure composed of crosslinked polymer microparticles and a polymer having a site to which a metal can coordinate, wherein an inorganic metal salt is coordinated to the site to which the metal can coordinate.

2. The insulating fine particles according to claim 1, wherein the crosslinked polymer fine particles have a charged functional group.

3. The insulating fine particles according to claim 2, wherein the charged functional group is an ammonium group or a phosphonium group.

4. The insulating fine particles according to claim 1, wherein the site to which the metal can coordinate is a β-diketone structure.

5. The insulating fine particles according to claim 1, wherein the inorganic metal salt is at least one metal phosphate selected from alkali metal phosphates and alkaline earth metal phosphates.

6. The device comprises conductive particles with a metal film formed on the surface of a core material, and an insulating layer covering the conductive particles. Coating particles wherein the insulating layer contains insulating fine particles according to any one of claims 1 to 5.

7. The coated particle according to claim 6, wherein the insulating layer is in the form of a film.

8. The coated particle according to claim 6, wherein the metal constituting the metal film is at least one selected from nickel, palladium, gold, nickel alloy, palladium alloy, and gold alloy.

9. A process of impregnating crosslinked polymer fine particles with a monomer component containing a monomer having a site to which a metal can coordinate, A step of polymerizing the monomer component to obtain fine particles having an asymmetric structure composed of crosslinked polymer fine particles and a polymer having a site to which a metal can coordinate, and A step of coordinating an inorganic metal salt to a site in the fine particles where metal can coordinate, A method for producing insulating fine particles consisting of [the specified material].

10. The inorganic metal salt is at least one metal phosphate salt selected from alkali metal phosphates and alkaline earth metal phosphates. The method for producing insulating fine particles according to claim 9, wherein the step of coordinating the inorganic metal salt is a step of reacting a metal salt and a phosphate in the presence of the fine particles to produce the metal phosphate salt and coordinating the metal phosphate salt to a site on the fine particles where the metal can coordinate.

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