Method for producing conductive composite particles, conductive composite particles, and adhesive film for circuit connection

Abstract

One aspect of the present disclosure resides in a method for producing conductive composite particles each including a resin particle and a conductive fine particle contained in the resin particle, the method comprising: a step for preparing a resin-containing solution including the conductive fine particles, a resin for forming the resin particles, and an organic solvent compatible with an aqueous solvent; a step for preparing an emulsion in which droplets of the resin-containing solution are dispersed in the aqueous solution by emulsification using pores; and a step of inducing a polymerization reaction and / or a crosslinking reaction in the droplets of the resin-containing solution to form conductive composite particles.

Description

[Technical field]

[0001] The present disclosure relates to a method for producing conductive composite particles, the present disclosure also relates to conductive composite particles, and the present disclosure also relates to an adhesive film for circuit connection that includes the conductive composite particles. [Background technology]

[0002] There are two typical methods for mounting LCD driver ICs on LCD glass panels: COG (Chip-on-Glass) mounting and COF (Chip-on-Flex) mounting. In COG mounting, the LCD driver IC is directly bonded to the glass panel using an anisotropic conductive adhesive containing conductive particles. On the other hand, in COF mounting, the LCD driver IC is bonded to a flexible tape with metal wiring, and then these are bonded to the glass panel using an anisotropic conductive adhesive containing conductive particles.

[0003] The conductive particles used in anisotropic conductive adhesives are mainly conductive composite particles in which a metal layer is formed on the surface of a resin particle.

[0004] Patent Document 1 discloses composite particles comprising resin particles and a plurality of tin-doped indium oxide particles embedded in the resin particles and having an average particle size smaller than half the particle size of the resin particles. Patent Document 1 describes that the composite particles have a structure in which ITO (indium tin oxide) particles are embedded in the resin particles, and therefore can prevent damage and corrosion of the conductive layer that may occur in the composite particles, and can be used in transparent conductive materials that require transparency. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-216294 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, in the field of electronic devices such as liquid crystal displays, personal computers, tablet PCs, and smartphones, the high definition and narrow area of electrode circuits have been progressing, and miniaturization of conductive particles has been demanded. Also in the technology of Patent Document 1, further improvement in conductivity is demanded from the viewpoint of miniaturization. Therefore, a new technology capable of improving the conductivity of conductive composite particles is desired.

[0007] Here, as a method for improving conductivity, it is conceivable to contain conductive fine particles at a high concentration in resin particles serving as the core of the conductive composite particles. That is, by containing conductive fine particles at a high concentration in the resin particles, conduction can be achieved with the conductive fine particles contained inside, and it is considered that the conductivity can be improved. However, when attempting to produce conductive fine particles containing conductive fine particles at a high concentration in resin particles by a conventional preparation method, problems such as precipitation of particles due to the weight of the conductive fine particles and aggregation of resin particles occur, making production difficult. In particular, when attempting to reduce the particle size of the conductive composite particles, such problems occur remarkably.

[0008] Therefore, one object of the present disclosure is to provide a method capable of manufacturing conductive composite particles containing conductive fine particles at a high concentration.

Means for Solving the Problems

[0009] One aspect of the present disclosure is as follows.

[0010] A method for manufacturing conductive composite particles including resin particles and conductive fine particles contained in the resin particles, preparing a resin-containing solution including conductive fine particles, a resin for forming the resin particles, and an organic solvent having compatibility with an aqueous solvent; preparing an emulsion in which droplets of the resin-containing solution are dispersed in an aqueous solution by emulsification using pores; causing a polymerization reaction and / or a crosslinking reaction in the droplets of the resin-containing solution to form conductive composite particles; A method for producing conductive composite particles, comprising:

[0011] Conductive composite particles comprising resin particles and conductive fine particles contained in the resin particles, wherein the content of the conductive fine particles in the conductive composite particles is 40% or more.

[0012] An adhesive film for circuit connection comprising the conductive composite particles and a binder resin. [Effects of the Invention]

[0013] The present disclosure can provide a method for producing conductive composite particles containing conductive fine particles at a high concentration. [Brief description of the drawings]

[0014]

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Mode for Carrying Out the Invention

[0015] One aspect of the present embodiment is a method for manufacturing conductive composite particles including resin particles and conductive fine particles contained in the resin particles, the method including: preparing a resin-containing solution including the conductive fine particles, a resin for forming the resin particles, and an organic solvent having compatibility with an aqueous solvent; preparing an emulsion in which droplets of the resin-containing solution are dispersed in the aqueous solution by emulsification using pores; and causing a polymerization reaction and / or a crosslinking reaction to occur in the droplets of the resin-containing solution to form the conductive composite particles.

[0016] According to the configuration of the present embodiment, it is possible to provide a method capable of manufacturing conductive composite particles containing conductive fine particles at a high concentration.

[0017] Also, one aspect of the present embodiment is a conductive composite particle including resin particles and conductive fine particles contained in the resin particles, wherein the content rate of the conductive fine particles in the conductive composite particle is 40% or more.

[0018] With the configuration of the present embodiment, conductive composite particles having excellent conductivity can be provided. Therefore, even when the conductive composite particles are miniaturized, sufficient conductivity can be maintained, and the electrical communication reliability of the adhesive film for circuit connection can be ensured.

[0019] Hereinafter, the present embodiment will be described in detail.

[0020] [Manufacturing Method of Conductive Composite Particles] The manufacturing method according to the present embodiment relates to a method for manufacturing conductive composite particles including resin particles and conductive fine particles contained in the resin particles.

[0021] FIG. 1 shows a cross-sectional view showing a configuration example of the conductive composite particles obtained in the present embodiment. As shown in FIG. 1, the conductive composite particles 10 include resin particles 101 and a plurality of conductive fine particles 102 contained in the resin particles 101.

[0022] The content rate of the conductive fine particles in the conductive composite particles may be 40% by mass or more. When the content rate is 40% by mass or more, the conductive fine particles are present at a high concentration in the conductive composite particles, and the conductive fine particles can contact each other to efficiently establish conduction. The content rate of the conductive fine particles in the conductive composite particles may be 45% by mass or more, or may be 50% by mass or more. Also, the content rate of the conductive fine particles in the conductive composite particles may be 80% by mass or less, may be 70% by mass or less, or may be 60% by mass or less. Note that the content rate in the present embodiment can be obtained by measuring the mass concentration of the elements constituting the conductive fine particles from quantitative analysis by SEM-EDX.

[0023] [Resin-Containing Solution Preparation Step] The manufacturing method according to the present embodiment may include a step of preparing a resin-containing solution including conductive fine particles, a resin for forming the resin particles, and an organic solvent having compatibility with an aqueous solvent.

[0024] The conductive fine particles are fine particles having conductivity. Examples of the conductive fine particles include metal fine particles. The metal fine particles are particles composed of a metal. The metal fine particles preferably contain at least one metal selected from gold, silver, copper, platinum, zinc, iron, palladium, nickel, tin, chromium, titanium, aluminum, cobalt, germanium, cadmium, and alloys thereof. The metal fine particles may be used alone or in combination of two or more.

[0025] From the viewpoint of easily exhibiting good conductivity of the conductive composite particles, the average particle diameter of the conductive fine particles may be 10 nm or more and 500 nm or less, may be 20 nm or more and 300 nm or less, or may be 30 nm or more and 100 nm or less. Further, the average particle diameter of the conductive fine particles may be 1 / 10 or less, 1 / 50 or less, or 1 / 100 or less of the average particle diameter of the conductive composite particles. The average particle diameter (D 50 ) of the conductive fine particles can be calculated, for example, based on the volume-based particle size distribution measured using a laser diffraction particle size distribution measuring device.

[0026] The resin particles can be composed of, for example, a polyvinyl-based resin, a polyimide-based resin, a polyamide-based resin, a polyamideimide-based resin, a phenol-based resin, an epoxy-based resin, or a mixture thereof. Among these, a polyvinyl-based resin is preferably used. The polyvinyl-based resin is preferably a polyacrylic-based resin, a polyolefin-based resin, or a polystyrene-based resin. These may be used alone or in combination of two or more. The resin for constituting the resin particles, that is, the resin added to the resin-containing solution to constitute the resin particles, may be a resin compound in monomer form or a polymer in polymerized form (also referred to as a base polymer).

[0027] Polyacrylic resins can be obtained, for example, by polymerization of (meth)acrylic monomers. Examples of (meth)acrylic monomers include acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, dodecyl acrylate, stearyl acrylate, 2-ethylhexyl acrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, and diethylaminoethyl methacrylate. These monomers may be used alone or in combination of two or more. The polyacrylic resin may also be a copolymer obtained by copolymerization of a (meth)acrylic monomer with another monomer. Examples of other monomers include olefin-based monomers such as ethylene, propylene, isobutylene, and butadiene; glycol esters of (meth)acrylic acid such as ethylene glycol mono(meth)acrylate and polyethylene glycol mono(meth)acrylate; alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl esters such as vinyl acetate and vinyl butyrate; N-alkyl-substituted (meth)acrylamides such as N-methylacrylamide, N-ethylacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide; nitriles such as acrylonitrile and methacrylonitrile; polyfunctional monomers such as alkanediol di(meth)acrylate, divinylbenzene, ethylene glycol di(meth)acrylate, and trimethylolpropane triacrylate; and styrene-based monomers such as styrene, p-methylstyrene, p-chlorostyrene, chloromethylstyrene, and α-methylstyrene. These other monomers may be used alone or in combination of two or more.

[0028] Polyolefin resins can be obtained, for example, by polymerization of olefin monomers (such as alkenes). Examples of olefin monomers include ethylene, propylene, isobutylene, or butadiene, etc. These olefin monomers may be used alone or in combination of two or more. The polyolefin resin may also be a copolymer obtained by copolymerization of an olefin monomer and another monomer. Examples of other monomers include glycol esters of (meth)acrylic acid such as ethylene glycol mono(meth)acrylate and polyethylene glycol mono(meth)acrylate; alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl esters such as vinyl acetate and vinyl butyrate; N-alkyl substituted (meth)acrylamides such as N-methylacrylamide, N-ethylacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide; nitriles such as acrylonitrile and methacrylonitrile; polyfunctional monomers such as alkanediol di(meth)acrylate, divinylbenzene, ethylene glycol di(meth)acrylate, and trimethylolpropane triacrylate; (meth)acrylic monomers such as acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, dodecyl acrylate, stearyl acrylate, 2-ethylhexyl acrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, and diethylaminoethyl methacrylate; styrene monomers such as styrene, p-methylstyrene, p-chlorostyrene, chloromethylstyrene, and α-methylstyrene. These other monomers may be used alone or in combination of two or more.

[0029] The polystyrene resin can be obtained, for example, by polymerization of styrene monomers. Examples of the styrene monomers include styrene, p-methylstyrene, p-chlorostyrene, chloromethylstyrene, or α-methylstyrene. The styrene monomers may be used alone or in combination of two or more. The polystyrene resin may be a copolymer obtained by copolymerization of a styrene monomer and another monomer. Examples of the other monomers include olefin monomers such as ethylene, propylene, isobutylene or butadiene; glycol esters of (meth)acrylic acid such as ethylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate; alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether; vinyl esters such as vinyl acetate, vinyl butyrate; N-alkyl substituted (meth)acrylamides such as N-methylacrylamide, N-ethylacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide; nitriles such as acrylonitrile, methacrylonitrile; polyfunctional monomers such as alkanediol di(meth)acrylate, divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane triacrylate; (meth)acrylic monomers such as acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, dodecyl acrylate, stearyl acrylate, 2-ethylhexyl acrylate, tetrahydrofurfuryl acrylate, diethylaminoethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, diethylaminoethyl methacrylate. These other monomers may be used alone or in combination of two or more.

[0030] The resin-containing solution may further contain a crosslinking agent for crosslinking the base polymer. The crosslinking agent is not particularly limited, and known crosslinking agents can be appropriately used. Examples of the crosslinking agent include compounds having at least two unsaturated bonds (e.g., vinyl groups). Such compounds include, for example, divinylbenzene, divinylnaphthalene, divinyl ether, divinyl sulfone, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, or polypropylene glycol dimethacrylate. The crosslinking agent may be used alone or in combination of two or more.

[0031] The resin-containing solution can contain a reaction initiator for a polymerization reaction and / or a crosslinking reaction, if necessary. The reaction initiator is not particularly limited and can be appropriately selected and used according to the resin and crosslinking agent contained in the resin-containing solution. From the viewpoint of ease of operation of the reaction, the reaction initiator may have thermal responsiveness or light responsiveness. Also, the reaction initiator is preferably added to the resin-containing solution, but is not particularly limited thereto, and may be added to the aqueous solution, or may be added to both the resin-containing solution and the aqueous solution. Generally, many reaction initiators can be used for both polymerization reactions and crosslinking reactions. Examples of the reaction initiator include organic peroxides such as benzoyl peroxide, lauroyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butylperoxy-2-ethylhexanoate, di-t-butyl peroxide; and azo compounds such as 2,2'-azobisisobutyronitrile, 1,1'-azobiscyclohexanecarbonitrile, 2,2'-azobis(2,4-dimethylvaleronitrile). The reaction initiator may be used alone or in combination of two or more.

[0032] From the viewpoint of uniformly dispersing the conductive fine particles in the resin-containing solution, the resin-containing solution may contain a dispersant having a function of dispersing the conductive fine particles in an organic solvent. Uniform dispersion in the resin-containing solution leads to uniform dispersion in the conductive composite particles, and as a result, the conductivity of the conductive composite particles can be improved. As the dispersant, for example, commercially available dispersants can be appropriately used. Examples of the dispersant include Esleem (registered trademark, NOF Corporation), Megafac (registered trademark, DIC Corporation), Marialim (registered trademark, NOF Corporation), or Polyflow (registered trademark, Kyoeisha Chemical Co., Ltd.). The dispersant may be used alone or in combination of two or more.

[0033] As the organic solvent, any solvent can be used without particular limitation as long as it is compatible with the aqueous solvent and can dissolve the resin to be used. The organic solvent can be appropriately selected in consideration of its compatibility with the resin and aqueous solvent to be used. Examples of the organic solvent include tetrahydrofuran (THF), methyl ethyl ketone (MEK), acetone, methanol, ethanol, n-propanol, isopropanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), or a mixture thereof. Among them, ethanol, n-propanol, isopropanol, acetone, or THF is preferable. The organic solvent may be used alone or in combination of two or more.

[0034] (Emulsification step) Next, the production method according to the present embodiment may include a step of preparing an emulsion in which droplets of the resin-containing solution are dispersed in the aqueous solution by emulsification using pores. Specifically, the resin-containing solution may be discharged into the aqueous solution through the pores to prepare an emulsion.

[0035] Examples of the emulsification method using pores include, but are not particularly limited to, a membrane emulsification method using a porous membrane or a microchannel emulsification method. The membrane emulsification method using a porous membrane (SPG membrane emulsification method) is an emulsification method in which the oil phase is pressurized and dispersed in the aqueous phase through the pores of a porous membrane (for example, a Shirasu Porous Glass [SPG] membrane). Using this method, an emulsion having a uniform particle size can be obtained. The microchannel emulsification method is an emulsification method in which a large number of flat groove type microchannel arrays or through-hole type microchannel arrays are used, the oil phase is pressurized, and the oil phase is dispersed in the aqueous phase through the pores of the microchannels. The membrane emulsification method and the microchannel emulsification method can produce emulsion droplets with a smaller particle size distribution compared to other emulsification methods. Generally, it is said that the particle size of the emulsion droplets produced by the membrane emulsification method is about three times the pore diameter of the filter pores, and the particle size can be adjusted by changing the pore diameter.

[0036] Examples of the aqueous solvent include water or a mixed medium of water and a water-soluble solvent (e.g., lower alcohol).

[0037] The aqueous solution may contain a surfactant or a dispersion stabilizer in order to stably form droplets.

[0038] Examples of the surfactant include anionic surfactants, cationic surfactants, nonionic surfactants, or zwitterionic surfactants. Examples of the anionic surfactant include fatty acid oils such as sodium oleate and castor oil potassium, alkyl sulfate esters such as sodium lauryl sulfate and ammonium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, alkylnaphthalene sulfonates, alkane sulfonates, dialkyl sulfosuccinates such as sodium dioctyl sulfosuccinate, alkenyl succinates (dipotassium salts), alkyl phosphate esters, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phenyl ether sulfate esters, polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene alkyl sulfate esters, and triethanol dodecyl sulfate. Examples of the cationic surfactant include alkylamine salts such as laurylamine acetate and stearylamine acetate, and quaternary ammonium salts such as lauryl trimethyl ammonium chloride. Examples of the nonionic surfactant include hydrocarbon-based nonionic surfactants such as polyethylene glycol alkyl ethers, polyethylene glycol alkyl aryl ethers, polyethylene glycol esters, polyethylene glycol sorbitan esters, polyalkylene glycol alkyl amines or amides, polyether-modified silicone-based nonionic surfactants such as polyethylene oxide adducts of silicone and polypropylene oxide adducts, and fluorine-based nonionic surfactants such as perfluoroalkyl glycols. Examples of the zwitterionic surfactant include hydrocarbon surfactants such as lauryl dimethylamine oxide, phosphate ester-based surfactants, and phosphite ester-based surfactants. Among the above surfactants, anionic surfactants are preferred from the viewpoint of dispersion stability during the reaction. The surfactant may be used alone or in combination of two or more.

[0039] The dispersant is not particularly limited, and examples thereof include polyvinyl alcohol, polycarboxylic acid, celluloses (hydroxyethyl cellulose, carboxymethyl cellulose, etc.), and polyvinyl pyrrolidone. Inorganic water-soluble polymer compounds such as sodium tripolyphosphate can also be used in combination. Among these, polyvinyl alcohol or polyvinyl pyrrolidone is preferred.

[0040] As described above, the aqueous solution may contain a reaction initiator for the polymerization reaction and / or crosslinking reaction, if necessary.

[0041] (Conductive composite particle formation step) Next, the manufacturing method according to the present embodiment may include a step of causing a polymerization reaction and / or crosslinking reaction to occur in the droplets of the resin-containing solution to form conductive composite particles.

[0042] The reaction temperature can be appropriately selected according to the types of the added resin and reaction initiator. The reaction temperature may be 30 to 110°C, or may be 50 to 100°C. After the reaction is completed, the aqueous solution can be removed from the reaction solution by centrifugation, if necessary. Further, the obtained conductive composite particles can be washed with water or a solvent, etc., if necessary, and then dried.

[0043] Note that the manufacturing method according to the present embodiment may include a step of promoting the elution of the organic solvent into the aqueous solution by heating before causing the polymerization reaction and / or crosslinking reaction to occur. By eluting the organic solvent into the aqueous solution, the particle size of the resin particles can be reduced.

[0044] Through the above steps, conductive composite particles containing conductive fine particles at a high concentration can be efficiently produced.

[0045] Possible methods for producing conductive composite particles other than the production method according to the present embodiment include, for example, emulsifying a resin solution containing conductive microparticles using an emulsifier such as a homogenizer or ultrasonic processor. However, when attempting to produce conductive composite particles containing a high concentration of conductive microparticles using such conventional methods, problems such as particle precipitation due to the weight of the conductive microparticles and aggregation of the resin particles arise. These problems become particularly pronounced when attempting to reduce the particle size of the conductive composite particles. Furthermore, because the shear force applied to the resin solution is not uniform, the particle size distribution of the produced conductive composite particles tends to be very large.

[0046] Also, in the manufacturing method according to the present embodiment, as the resin added to the resin-containing solution, it is preferable to use a base polymer, that is, a polymer after polymerization. By using the base polymer as the resin, conductive composite particles containing conductive fine particles at a high concentration can be produced with a smaller particle size. The reason will be explained below. For example, as a method of producing resin particles by the membrane emulsification method, J. Appl. Polymer Sci., Vol. 51, No. 1, pp. 1-11 (1994) reports a method of membrane emulsifying and polymerizing a resin solution containing a monomer. The particle size of the emulsion droplets before polymerization produced by this method is generally about three times the filter pore diameter, and the particle size of the resin particles obtained after polymerization is almost the same as the particle size of the emulsion droplets before polymerization. Therefore, in order to produce resin particles with a small particle size using a monomer as a material, it is necessary to use a filter with a small pore diameter. However, it is difficult to produce a filter with a small pore diameter, and the pressure resistance generated when flowing the monomer through the pores increases. Therefore, in the method of membrane emulsifying a monomer, it may be difficult to produce minute resin particles. On the other hand, in the manufacturing method according to the present embodiment, when a base polymer is used as the resin added to the resin-containing solution, after membrane emulsification, the organic solvent contained in the emulsion droplets elutes into the aqueous solution. Note that this elution can be promoted by heating. And with this elution, the polymer in the emulsion droplets aggregates and forms particles, so that resin particles smaller than the pore diameter of the filter can be produced. Also, since small resin particles can be formed without using a filter with a small pore diameter, there is an advantage that clogging by fine particles is less likely to occur when emulsifying the resin-containing solution. Furthermore, there is also an advantage that the particle size of the resin particles can be controlled by adjusting not only the pore diameter of the filter but also the concentration of the resin. Also, as described above, a microchannel may be used for emulsifying the resin-containing solution. Emulsification using a microchannel has the characteristic of being able to produce emulsion droplets with a very uniform particle size. However, since the fine flow path of the microchannel is used, the flow path is likely to be blocked by the material and the product. Therefore, when a resin-containing solution in which a base polymer is dissolved in an organic solvent is used as a material, resin particles smaller than the flow path width of the microchannel can be produced.Therefore, there is an advantage that clogging of the flow path is unlikely to occur. For the above reasons, it is preferable to use a base polymer, i.e., a polymer after polymerization, as the resin to be added to the resin-containing solution. As described above, examples of the base polymer include polyvinyl resins, polyimide resins, polyamide resins, polyamideimide resins, phenolic resins, epoxy resins, and mixtures thereof. Of these, it is preferable that the base polymer is a polyvinyl resin. Preferred examples of the polyvinyl resin include polyacrylic resins, polyolefin resins, polystyrene resins, and mixtures thereof. One type of base polymer may be used alone, or two or more types may be used in combination.

[0047] In one embodiment, the resin-containing solution may contain the base polymer as a resin and a crosslinking agent for crosslinking the base polymer. By including the crosslinking agent, the base polymer can be crosslinked to obtain conductive composite particles with appropriate strength and hardness. The crosslinking agent is not particularly limited, and examples thereof include the above-mentioned compounds having at least two unsaturated bonds (e.g., vinyl groups).

[0048] [Conductive composite particles] A cross-sectional view showing an example of the configuration of a conductive composite particle according to this embodiment is shown in Fig. 1. As shown in Fig. 1, a conductive composite particle 10 includes a resin particle 101 and a plurality of conductive fine particles 102 contained in the resin particle 101.

[0049] The content of the conductive fine particles in the conductive composite particles may be 40 mass% or more, and may be within the above-mentioned range. In this embodiment, the content can be calculated from the results of measuring the weight concentration of the elements constituting the conductive fine particles by quantitative analysis using SEM-EDX.

[0050] As shown in FIG. 2, the conductive composite particle according to this embodiment may include a conductive layer 105 as the outermost layer. FIG. 2 is a schematic cross-sectional view showing a conductive composite particle 11 including a conductive layer 105 on a resin particle 101 as the outermost layer. The conductive layer 105 cooperates with the conductive fine particles 102 present in the resin particle 101 to further improve the conductivity of the conductive composite particle. Furthermore, since the strength of the conductive composite particle can be improved, damage to the conductive composite particle due to pressure during compression bonding can be suppressed. Even if the conductive layer breaks, the conductive layer portions separated by the break are electrically connected via the conductive fine particles in the resin particle, so that a decrease in conductivity is unlikely to occur. The conductive layer may be a single layer or two or more layers.

[0051] The conductive layer is preferably a metal layer containing a metal, and examples of the metal constituting the metal layer include, but are not limited to, gold, silver, copper, platinum, zinc, iron, tin, aluminum, cobalt, indium, palladium, nickel, chromium, titanium, antimony, bismuth, germanium, cadmium, and alloys thereof.

[0052] The method for forming the conductive layer is not particularly limited, and examples thereof include electroless plating, electroplating, physical vapor deposition, and a method for applying a paste containing metal powder to the surface of resin particles. Examples of physical vapor deposition include vacuum deposition, ion plating, and ion sputtering. Electroless plating is preferred as the method for forming the conductive layer.

[0053] From the viewpoint of miniaturization, the thickness of the conductive layer may be 10 nm or more and 300 nm or less, or 50 nm or more and 200 nm or less. The thickness of the conductive layer can be determined, for example, by observing the cross section of the conductive composite particle using a transmission electron microscope (TEM).

[0054] The average particle size of the conductive composite particles may be 0.1 μm or more and 20 μm or less, may be 0.5 μm or more and 10 μm or less, or may be 1.0 μm or more and 5.0 μm or less from the viewpoint of miniaturization.

[0055] The CV value of the particle size (diameter) of the conductive composite particles may be 15% or less, may be 10% or less, may be 7% or less, or may be 5% or less. By the CV value of the conductive composite particles being 15% or less, the electrical connection reliability can be made higher. In the present specification, the CV value (coefficient of variation) of the particle size means the ratio of the standard deviation of the particle size to the average value of the particle size expressed as a percentage.

[0056] [Adhesive Film for Circuit Connection] The adhesive film for circuit connection according to the present embodiment contains the above conductive composite particles and a binder resin. FIG. 3 is a schematic cross-sectional view showing a configuration example of the adhesive film for circuit connection according to the present embodiment. The adhesive film for circuit connection 40 includes a binder resin 20 having insulating properties and conductive composite particles 10 uniformly dispersed in the binder resin 20.

[0057] As the binder resin, for example, a thermosetting resin composition containing a thermosetting resin, a curing agent, or a film-forming polymer or the like can be used.

[0058] The thermosetting resin is not particularly limited, but from the viewpoint of heat resistance, it is preferable to use an epoxy resin. As the epoxy resin, various epoxy compounds having two or more glycidyl groups in the molecule can be used. For example, bisphenol type epoxy resins, novolac type epoxy resins, naphthalene type epoxy resins, biphenyl type epoxy resins, alicyclic type epoxy resins, glycidylamine compounds, glycidyl ether compounds, and glycidyl ester compounds can be mentioned. The thermosetting resin may be used alone or in combination of two or more.

[0059] As the epoxy resin, impurity ions (Na + , Cl- When using high-purity products with hydrolyzable chlorine and the like reduced to 300 ppm or less, it becomes easier to prevent electromigration.

[0060] The curing agent is not particularly limited. For example, a latent curing agent can be used. Examples of the latent curing agent include imidazole compounds, hydrazide compounds, boron trifluoride-amine complexes, sulfonium salts, amine imides, salts of polyamines, and dicyandiamide.

[0061] The film-forming polymer is not particularly limited as long as it can contribute to the film shape of the adhesive film for circuit connection. Examples of the film-forming polymer include thermoplastic resins such as phenoxy resins, polyester resins, or polyamide resins.

[0062] To the binder resin, butadiene rubber, acrylic rubber, styrene-butadiene rubber, or silicone rubber can be mixed to reduce the stress after adhesion or improve the adhesiveness.

[0063] An inorganic filler can also be compounded into the binder resin. As the inorganic filler, for example, a filler made of silica, magnesia, bentonite, smectite, alumina, or boron nitride can be used.

[0064] In addition, in the binder resin, instead of the thermosetting resin and the curing agent, a photocurable resin composition containing a radically polymerizable resin and a photoinitiator such as an organic peroxide may be used.

[0065] The adhesive film for circuit connection can be produced, for example, as follows. First, a thermosetting resin composition containing an epoxy resin, an acrylic rubber, a latent curing agent, and a film-forming polymer is dissolved or dispersed in an organic solvent as necessary to be liquefied, and a composition for forming a binder resin is prepared. Next, conductive composite particles are dispersed in the composition for forming a binder resin to produce a liquid adhesive composition for circuit connection. The organic solvent may be an organic solvent that can dissolve the resin component and has a boiling point of 50 to 150 °C at normal pressure. Examples of such an organic solvent include toluene, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, propyl acetate, butyl acetate, and the like.

[0066] The liquid adhesive composition for circuit connection can be used as it is for connecting circuit members, but it is preferably formed into a film and used. The adhesive film for circuit connection can be produced by applying the liquid adhesive composition for circuit connection onto a release film, removing the organic solvent at a temperature below the activation temperature of the curing agent, and then peeling it from the release film. In this case, the adhesive film for circuit connection can also be referred to as a layer provided on the release film and containing the conductive composite particles and a binder resin for dispersing the conductive composite particles (i.e., a binder resin layer containing the conductive composite particles). As the release film, a resin film such as a fluororesin film, a polyethylene terephthalate film, or a polyolefin film is preferably used. The adhesive film for circuit connection is convenient from the viewpoint of handleability.

[0067] The adhesive film for circuit connection in the above embodiment may be an anisotropic conductive adhesive film or a conductive adhesive film having no anisotropic conductivity.

[0068] [Connection structure] The connection structure of circuit members according to this embodiment includes a first circuit member with a first circuit electrode formed on the main surface of a first circuit board, a second circuit member with a second circuit electrode formed on the main surface of a second circuit board, and a connection portion interposed between the first circuit member and the second circuit member. The second circuit member is arranged such that the second circuit electrode faces the first circuit electrode. The connection portion contains conductive composite particles according to this embodiment.

[0069] FIGS. 4A and 4B are schematic cross-sectional views showing a method for manufacturing a connection structure of circuit members using an adhesive film for circuit connection according to this embodiment.

[0070] First, as shown in FIG. 4A, a first circuit board 4 with a first circuit electrode 5 formed thereon and a second circuit board 6 with a second circuit electrode 7 formed thereon are prepared, and an adhesive film 40 for circuit connection is disposed therebetween. At this time, the positions are adjusted so that the first circuit electrode 5 and the second circuit electrode 7 face each other. Then, the first circuit board 4 and the second circuit board 6 are laminated while being pressure-heated in the direction in which the first circuit electrode 5 and the second circuit electrode 7 face each other to obtain a connection structure 42 shown in FIG. 4B. The connection structure 42 is electrically connected by a cured product of the adhesive film 40 for circuit connection.

[0071] Examples of the first circuit board 4 and the second circuit board 6 include a glass substrate, a tape substrate such as polyimide, a bare chip such as a driver IC, and a rigid package substrate.

Example

[0072] Hereinafter, this embodiment will be specifically described by way of examples. However, this embodiment is not limited to the following examples.

[0073] [Example 1: Preparation of Conductive Composite Particles E1] (Step a: Preparation of a Suspension of Conductive Fine Particles) Nickel fine particles (manufactured by EM Japan Co., Ltd., average particle size: 40 nm) and a dispersant (Esreem® C-2093I, manufactured by NOF Corporation) were added to tetrahydrofuran, an organic solvent compatible with water, and mixed using a bead mill (trade name: MSC-50, manufactured by Nippon Coke and Engineering Co., Ltd.) using zirconia particles (φ0.015 mm) to obtain a suspension. Note that because the particle size of the nickel fine particles is very small, adding them to an organic solvent of nickel fine particles without a dispersant will result in the formation of aggregates several tens of μm in size. Therefore, in Example 1, in order to prevent aggregation of the nickel fine particles and to achieve good dispersion, the dispersant was added, and further, a strong dispersion treatment using a bead mill was performed.

[0074] The content of the nickel fine particles in the suspension was 20 mass %. The content of the dispersant was 2 parts by mass relative to 100 parts by mass of the nickel fine particles. Mixing using a bead mill was carried out for 60 minutes.

[0075] (Step b: Preparation of fine particle-containing resin solution) Polystyrene (trade name: Polystyrene (MW800-5,000), manufactured by Polysciences Co., Ltd.), divinylbenzene, and benzoyl peroxide were added to the suspension of conductive particles prepared in step a and stirred to prepare a resin solution containing fine particles. Divinylbenzene functions as a crosslinking agent for polystyrene, and benzoyl peroxide functions as a polymerization initiator. The solution was stirred for 15 minutes using an ultrasonic cleaner.

[0076] The content of polystyrene in the resin solution containing fine particles was 10% by mass, the content of divinylbenzene in the resin solution containing fine particles was 3% by mass, and the content of benzoyl peroxide in the resin solution containing fine particles was 0.04% by mass.

[0077] (Step c: Preparation of aqueous solution) Polyvinyl alcohol was added to pure water and stirred to prepare an aqueous solution. Polyvinyl alcohol acts as a dispersion stabilizer, stabilizing the emulsion. The solution was stirred for 15 minutes using a magnetic stirrer.

[0078] The content in the aqueous solution of polyvinyl alcohol was 1%.

[0079] (Step d: Emulsification of the fine particle-containing resin solution) Using the membrane emulsification system 12 described in FIG. 5, the fine particle-containing resin solution prepared in Step b was emulsified. Hereinafter, the method will be described with reference to FIGS. 5 to 8.

[0080] FIG. 5 is a schematic diagram for explaining the configuration of the membrane emulsification system 12. The membrane emulsification system 12 includes a syringe 110 that holds the fine particle-containing resin solution 15, a liquid feeding pump (not shown), an aqueous solution holding container 111 that holds the aqueous solution 16, a filter 112 having pores and held in the aqueous solution holding container 111, a connecting tube 113 that connects the syringe 110 and the filter 112, a stirring device 114 disposed at the bottom of the aqueous solution holding container 111 for generating a flow in the aqueous solution 16, and a heater 115 for heating the aqueous solution 16. The fine particle-containing resin solution 15 contained in the syringe 110 is fed into the filter 112 through the connecting tube 113 by the liquid feeding pump. The filter 112 has innumerable pores on its surface, and the fine particle-containing resin solution 15 is ejected from these pores into the aqueous solution 16 in the aqueous solution holding container 111 to form an emulsion. The emulsion is of the water-in-oil type.

[0081] Specifically, in this example, a syringe pump (flow rate: 15 mL / h) was used as the liquid feeding pump, a PTFE tube was used as the connecting tube 113, a porous glass membrane (pore diameter: 3 to 10 μm) was used as the filter, and an overhead stirrer (rotation speed: 500 rpm) was used as the stirring device 114. The feeding amount of the fine particle-containing resin solution 15 was 10 mL, and the aqueous solution was 300 mL.

[0082] FIG. 6A is a conceptual diagram showing the state of the fine particle-containing resin solution 15 before emulsification. Further, FIG. 6B is a conceptual diagram showing the state of the fine particle-containing resin solution 15 during or after emulsification. The fine particle-containing resin solution 15 before emulsification contains a polymer 150, an organic solvent 151, a crosslinking agent 152, fine particles 153, a dispersant, and a reaction initiator. In this example, as described above, polystyrene was used as the polymer 150, tetrahydrofuran was used as the organic solvent 151, divinylbenzene was used as the crosslinking agent 152, nickel fine particles were used as the fine particles 153, and benzoyl peroxide was used as the reaction initiator.

[0083] When the fine particle-containing resin solution 15 passes through the pores of the filter 112, it is sheared and emulsified when released from the filter 112 into the liquid phase. In this example, the emulsion droplets formed by emulsification are referred to as fine particle-containing emulsified particles. The fine particle-containing emulsified particles 170 contain a polymer 150, a crosslinking agent 152, fine particles 153, a dispersant, and a reaction initiator in the organic solvent 151.

[0084] (Step e: Elution of the organic solvent from the fine particle-containing emulsified particles) FIG. 7A is a conceptual diagram showing the state in which the organic solvent 151 elutes from the fine particle-containing emulsified particles 170 to become fine particle-containing resin particles 171.

[0085] Since the organic solvent 151 contained in the fine particle-containing emulsified particles 170 is compatible with water, the organic solvent 151 elutes from the fine particle-containing emulsified particles 170 into the aqueous solution 16. Since the polymer 150 is insoluble in the aqueous solution 16, it aggregates in the fine particle-containing emulsified particles 170 as the organic solvent 151 elutes. The aggregated particles are referred to as fine particle-containing resin particles in this example.

[0086] In step e, as shown in FIG. 7B, the aqueous solution 16 was heated at 50° C. for 30 minutes by the heater 115 to promote the elution of the organic solvent 151.

[0087] (Step f: Crosslinking polymerization of the polymer in the fine particle-containing resin particles) FIG. 8A is a conceptual diagram showing how the polymer 150 in the fine particle-containing resin particles 171 is crosslinked by the crosslinking agent 152.

[0088] In step f, as shown in FIG. 8B, the aqueous solution 16 was heated at 70° C. for 8 hours by the heater 115. By heating the aqueous solution 16 to 70° C. with the heater 115, radicals are generated from benzoyl peroxide which is a polymerization initiator, and the polymer 150 in the fine particle-containing resin particles 171 is crosslinked by the crosslinking agent 152.

[0089] Through the above steps, the conductive composite particles E1 were produced.

[0090] [Example 2: Production of Conductive Composite Particles E2] The conductive composite particles E2 were produced in the same manner as in Example 1, except that the amounts of nickel fine particles and polystyrene were adjusted so that the content in the suspension of nickel fine particles was 10% by mass and the content in the fine particle-containing resin solution of polystyrene was 3% by mass.

[0091] [Example 3: Production of Conductive Composite Particles E3] The conductive composite particles E3 were produced in the same manner as in Example 1, except that the amounts of nickel fine particles and polystyrene were adjusted so that the content in the suspension of nickel fine particles was 10% by mass and the content in the fine particle-containing resin solution of polystyrene was 1% by mass.

[0092] [Example 4: Production of Conductive Composite Particles E4] The conductive composite particles E4 were produced in the same manner as in Example 1, except that the amounts of nickel fine particles and polystyrene were adjusted so that the content in the suspension of nickel fine particles was 10% by mass and the content in the fine particle-containing resin solution of polystyrene was 0.3% by mass.

[0093] [Evaluation: SEM Photograph, EDX Spectrum] Figure 9A is a photograph taken by a Scanning Electron Microscope (SEM) showing the conductive composite particles E3 produced in Example 3. Figure 9B is an EDX spectrum obtained by Energy Dispersive X-ray spectroscopy (EDX). The SEM is SU6600 manufactured by Hitachi High-Tech Corporation, and the EDX is QUANTAX200 manufactured by BRUKER. From the SEM photograph and the EDX spectrum shown in Figures 9A and 9B, it was confirmed that conductive composite particles containing nickel fine particles at a high concentration were successfully produced.

[0094] [Evaluation: Average particle size of conductive composite particles] From the SEM photographs of the produced conductive composite particles E1 to E4, the average particle size of each was measured. The particle size of each conductive composite particle was obtained by converting it to the diameter of a circle corresponding to the area of each conductive composite particle. The equivalent circle diameter was measured for 50 conductive composite particles, and the average value was taken as the average particle size of the conductive composite particles. The results are shown in Table 1.

[0095] [Evaluation: Content rate of conductive fine particles] For the produced conductive composite particles E1 to E4, EDX spectra were measured by the above-mentioned EDX, and using the software built into the EDX apparatus, the content rate of nickel fine particles was calculated from the EDX spectrum. The results are shown in Table 1.

[0096] In addition to the average particle size of the conductive composite particles and the content rate of nickel fine particles, Table 1 also shows the content in the suspension of nickel fine particles and the content in the fine particle-containing resin solution of polystyrene.

[0097]

Table 1

[0098] The upper limit value and / or lower limit value of the numerical range described in this specification can each be arbitrarily combined to define a preferred range. For example, the upper limit value and lower limit value of the numerical range can be arbitrarily combined to define a preferred range, the upper limit values of the numerical range can be arbitrarily combined to define a preferred range, and the lower limit values of the numerical range can also be arbitrarily combined to define a preferred range.

[0099] The claims following this described disclosure are expressly incorporated in this specification in this described disclosure, and each claim is independent as an individual embodiment. This disclosure includes all those obtained by replacing the independent claims with their dependent claims. Further, additional embodiments derived from the independent claims and the subsequent dependent claims are also expressly incorporated in this described specification.

[0100] Those skilled in the art can use the above description to make the most of this disclosure. The claims and embodiments disclosed in this specification are merely illustrative and exemplary and should not be construed as limiting the scope of this disclosure in any way. With the aid of this disclosure, changes can be made to the details of the above embodiments without departing from the basic principles of this disclosure. In other words, various modifications and improvements to the embodiments specifically disclosed in the above specification are within the scope of this disclosure.

[0101] (Appendix 1) A method for producing conductive composite particles including resin particles and conductive fine particles contained in the resin particles, a step of preparing a resin-containing solution including conductive fine particles, a resin for forming the resin particles, and an organic solvent having compatibility with an aqueous solvent; a step of preparing an emulsion in which droplets of the resin-containing solution are dispersed in an aqueous solution by emulsification using pores; a step of causing a polymerization reaction and / or a crosslinking reaction to occur in the droplets of the resin-containing solution to form conductive composite particles; A method for producing conductive composite particles, comprising: (Appendix 2) Attachment 1: The method for producing conductive composite particles according to claim 1, wherein the content of the conductive fine particles in the conductive composite particles is 40 mass % or more. (Appendix 3) 3. The method for producing conductive composite particles according to claim 1 or 2, wherein the conductive composite particles have an average particle size of 0.1 μm or more and 20 μm or less. (Appendix 4) 4. The method for producing conductive composite particles according to any one of claims 1 to 3, wherein the conductive fine particles include metal fine particles. (Appendix 5) 5. The method for producing conductive composite particles according to any one of claims 1 to 4, wherein the resin contains a base polymer. (Appendix 6) 6. The method for producing conductive composite particles according to claim 5, wherein the base polymer comprises at least one selected from the group consisting of polyacrylic resins, polyolefin resins, and polystyrene resins. (Appendix 7) 7. The method for producing conductive composite particles according to claim 5 or 6, wherein the resin-containing solution contains a crosslinking agent for crosslinking the base polymer. (Appendix 8) A method for producing conductive composite particles described in any of Appendices 1 to 7, which includes a step of promoting the dissolution of an organic solvent into an aqueous solution by heating before causing a polymerization reaction and / or a crosslinking reaction in droplets of a resin-containing solution. (Appendix 9) 9. The method for producing conductive composite particles according to any one of appendices 1 to 8, wherein the resin-containing solution or the aqueous solution contains a reaction initiator for a polymerization reaction and / or a crosslinking reaction. (Appendix 10) 10. The method for producing conductive composite particles according to any one of appendixes 1 to 9, wherein the resin-containing solution contains a dispersant for dispersing the conductive fine particles in the organic solvent. (Appendix 11) 11. A method for producing conductive composite particles according to any one of claims 1 to 10, wherein the resin-containing solution is released into an aqueous solution through pores to prepare an emulsion. (Appendix 12) A conductive composite particle comprising resin particles and conductive fine particles contained in the resin particles, wherein the content of the conductive fine particles in the conductive composite particle is 40% by mass or more. (Appendix 13) The conductive composite particle according to Appendix 12, wherein the average particle diameter of the conductive composite particle is 0.1 μm or more and 20 μm or less. (Appendix 14) The conductive composite particle according to Appendix 12 or 13, wherein the resin particles contain at least one selected from the group consisting of polyacrylic resins, polyolefin resins, and polystyrene resins. (Appendix 15) An adhesive film for circuit connection, comprising the conductive composite particle according to any one of Appendices 12 to 14 and a binder resin.

Explanation of symbols

[0102] 4: First circuit board 5: First circuit electrode 6: Second circuit board 7: Second circuit electrode 10: Conductive composite particle 11: Conductive composite particle 12: Membrane emulsification system 15: Fine particle-containing resin solution 16: Aqueous solution 20: Binder resin 40: Adhesive film for circuit connection 42: Connection structure 101: Resin particles 102: Conductive fine particles 105: Conductive layer 110: Syringe 111: Aqueous solution holding container 112: Filter 113: Connecting tube 114: Stirring tool 115: Heater 150: Polymer 151: Organic solvent 152: Crosslinking agent 153: Fine particles 170: Fine particle-containing emulsion particles 171: Resin particles containing fine particles

Claims

1. A method for producing conductive composite particles comprising resin particles and conductive fine particles contained in the resin particles, the method comprising: preparing a resin-containing solution containing the conductive fine particles, a resin for forming the resin particles, and an organic solvent compatible with an aqueous solvent; preparing an emulsion in which droplets of the resin-containing solution are dispersed in an aqueous solution by emulsification using pores; causing a polymerization reaction and / or a crosslinking reaction to occur in the droplets of the resin-containing solution to form conductive composite particles.

2. The method for producing conductive composite particles according to claim 1, wherein the content of the conductive fine particles in the conductive composite particles is 40% by mass or more.

3. The method for producing conductive composite particles according to claim 1 or 2, wherein the average particle diameter of the conductive composite particles is 0.1 μm or more and 20 μm or less.

4. The method for producing conductive composite particles according to any one of claims 1 to 3, wherein the conductive fine particles include metal fine particles.

5. The method for producing conductive composite particles according to any one of claims 1 to 4, wherein the resin includes a base polymer.

6. The method for producing conductive composite particles according to claim 5, wherein the base polymer includes at least one selected from the group consisting of polyacrylic resins, polyolefin resins, and polystyrene resins.

7. The method for producing conductive composite particles according to claim 5 or 6, wherein the resin-containing solution includes a crosslinking agent for crosslinking the base polymer.

8. The method for producing conductive composite particles according to any one of claims 1 to 7, further comprising a step of promoting elution of the organic solvent into the aqueous solution by heating before causing a polymerization reaction and / or a crosslinking reaction to occur in the droplets of the resin-containing solution.

9. The method for producing conductive composite particles according to any one of claims 1 to 8, wherein the resin-containing solution or the aqueous solution includes a reaction initiator for the polymerization reaction and / or the crosslinking reaction.

10. The method for producing conductive composite particles according to any one of claims 1 to 9, wherein the resin-containing solution includes a dispersant for dispersing the conductive fine particles in the organic solvent.

11. The method for producing conductive composite particles according to any one of claims 1 to 10, wherein the resin-containing solution is discharged into the aqueous solution through pores to prepare an emulsion.

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