Composite particles and conductive particles, method for producing conductive particles, and conductive adhesive

Abstract

To provide: a composite particle excellent in dispersion stability, excellent in compatibility with a catalytic solution and electroless plating solution and capable of forming a uniform conductive layer; conductive particles excellent in conductivity and long term connection stability; a method for manufacturing the same; and a conductive adhesive including the conductive particles.SOLUTION: A conductive particle includes: a core particle formed of a material containing polymer; a composite particle bonded onto a surface of the core particle to be in an indivisible state and including fine fibers containing cellulose nanofiber; and a conductive layer covering the fine fibers on the surface of the composite particle and including at least a metal element. 10%-displacement strength in a compression test of the composite particles is 5 MPa or more. The conductive layer comprises a material including at least one metal element of gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, antimony, bismuth, germanium, aluminum, chromium, palladium, tungsten and molybdenum.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to composite particles, conductive particles, a method for producing conductive particles, and a conductive adhesive. [Background technology]

[0002] Conductive particles used as conductive materials in anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes are generally known to have a conductive layer made of metal formed on the surface of core particles, and this conductive layer provides electrical connection between electrodes and wiring. When electrodes are pressure-connected using the conductive particles, the conductive particles have a hardness that can withstand heat and pressure, and the core material and conductive layer have high adhesion, which reduces connection resistance and increases connection reliability.

[0003] Meanwhile, in recent years, there have been active attempts to use chitin and / or chitosan, which make up the cellulose fibers in wood and the shells of crustaceans such as crabs, as new materials by micronizing them so that at least one side of their structure is on the order of nanometers.

[0004] For example, Patent Document 1 discloses that wood cellulose can be repeatedly mechanically processed using a blender or grinder to obtain pulverized cellulose, i.e., cellulose nanofibers (hereinafter also referred to as CNF). It has been reported that the CNF obtained by this method has a minor axis diameter of 10 to 50 nm and a major axis diameter ranging from 1 μm to 10 mm. This CNF is one-fifth the weight of steel and boasts five times the strength, and can be used for 250 m. 2 / g, it is expected to be used as a filler for reinforcing resins and as an adsorbent.

[0005] In addition, active efforts are being made to produce CNF by chemically treating the cellulose fibers in wood to facilitate their pulverization, followed by low-energy mechanical processing using a household mixer. While the chemical treatment method is not particularly limited, a preferred method is to introduce anionic functional groups into the cellulose fibers to facilitate pulverization. The introduction of anionic functional groups into the cellulose fibers facilitates the penetration of solvents into the cellulose microfibril structure due to the osmotic effect, significantly reducing the energy required to pulverize the cellulose raw material.

[0006] The method for introducing the anionic functional group is not particularly limited, but for example, Non-Patent Document 1 discloses a method in which the surface of cellulose fine fibers is selectively phosphorylated using a phosphoric acid esterification treatment.

[0007] Patent Document 2 discloses a method for carboxymethylating cellulose by reacting it with monochloroacetic acid or sodium monochloroacetate in a highly concentrated alkaline aqueous solution. Alternatively, carboxy groups may be introduced into cellulose by directly reacting it with a carboxylic anhydride compound such as maleic acid or phthalic acid that has been gasified in an autoclave.

[0008] A method for selectively oxidizing the surface of cellulose microfibers using the relatively stable N-oxyl compound 2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO) as a catalyst has also been reported (see, for example, Patent Document 3). The oxidation reaction using TEMPO as a catalyst (TEMPO oxidation reaction) allows for environmentally friendly chemical modification that proceeds in an aqueous system at room temperature and normal pressure. When applied to cellulose in wood, the reaction does not proceed inside the crystals, and only the alcoholic primary carbons in the cellulose molecular chains on the crystal surface can be selectively converted to carboxyl groups.

[0009] The osmotic pressure effect associated with the ionization of carboxyl groups selectively introduced to the crystal surface by TEMPO oxidation makes it possible to obtain cellulose single nanofibers (hereinafter also referred to as CSNF, TEMPO-oxidized cellulose nanofibers, or TEMPO-oxidized CNF) in which individual cellulose microfibril units are dispersed in a solvent. CSNF exhibits high dispersion stability due to the carboxyl groups on the surface. Wood-derived CSNF obtained from wood by the TEMPO oxidation reaction has a structure with a high aspect ratio, with a minor axis diameter of approximately 3 nm and a major axis diameter ranging from several tens of nanometers to several micrometers, and its aqueous dispersion and molded product have been reported to have high transparency. Patent Document 4 also reports that a laminated film obtained by coating and drying a CSNF dispersion has gas barrier properties.

[0010] Furthermore, studies are being conducted to impart further functionality to CNF or CSNF. For example, further functionality can be imparted by utilizing the carboxy groups on the surface of CSNF. Patent Document 5 discloses a composite (metal nanoparticle-supported CSNF) in which metal nanoparticles are supported on CSNF by reducing and precipitating the metal while metal ions are adsorbed on the carboxy groups on the surface of CSNF. Patent Document 5 also discloses an example of using metal nanoparticle-supported CSNF as a catalyst, reporting that catalytic activity is improved by making it possible to stabilize the dispersion of metal nanoparticles in a state with a high specific surface area.

[0011] Patent Document 6 discloses that chitin nanofibers can be obtained by crushing chitin and / or chitosan extracted from crab shells, etc., into ultrafine fibers. Chitin nanofibers are a recyclable resource that has antibacterial and biodegradable properties, and are expected to be used as an additive to foods and cosmetics, as reinforcing fibers for films, as an agricultural resource, and for medical purposes.

[0012] Because chitin and / or chitosan are tightly bound to each other by strong hydrogen bonds, it is not easy to prepare completely individual nanofibers from chitin and / or chitosan. According to the chitin nanofibers and production method thereof described in Patent Document 6, a dispersion containing individually separated chitin nanofibers can be obtained through a simple process.

[0013] As such, various studies are being conducted on the development of high-performance components that impart new functionality to fine fibers derived from natural materials, including cellulose nanofibers and chitin nanofibers.

[0014] However, in order to put these fine fibers into practical use, a problem remains in that the solids concentration of the resulting fine fiber dispersion is low, at around 0.1 to 5%. For example, when attempting to transport the fine fiber dispersion, it is equivalent to transporting a large amount of solvent, which leads to a rise in transportation costs and significantly impairs business viability.

[0015] However, simply removing the solvent from the fine fiber dispersion by heat drying or other methods will cause the fine fibers to aggregate and keratinize, or form a film, making it difficult to effectively utilize the high specific surface area of ​​the fine fibers and making it difficult to achieve stable functionality.Furthermore, because the solid concentration of the fine fibers is low, the process of removing the solvent by drying itself requires a great deal of energy, which is also a factor that impairs commercial viability.

[0016] As such, handling fine fibers such as cellulose nanofibers and chitin nanofibers in the form of a dispersion liquid is itself a cause of loss of commercial viability. Therefore, there is a strong demand for composite particles in which fine fibers are bonded to the surface of particles, which have a new handling method that can effectively utilize the high specific surface area of ​​the fine fibers and which are easy to wash and separate from the solvent. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-216021 [Patent Document 2] International Publication No. 2014 / 088072 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-001728 [Patent Document 4] International Publication No. 2013 / 042654 [Patent Document 5] International Publication No. 2010 / 095574 [Patent Document 6] Japanese Patent Application Laid-Open No. 2010-180309 [Non-patent literature]

[0018] [Non-Patent Document 1] Noguchi Y, Homma I, Matsubara Y. Complete nanofibrillation of cellulose prepared by phosphorylation. Cellulose. 2017;24:1295.10.1007 / s10570-017-1191-3 Summary of the Invention [Problem to be solved by the invention]

[0019] Therefore, an object of the present invention is to provide composite particles that have good dispersion stability, good affinity with catalyst solutions and electroless plating solutions, and are capable of forming a uniform conductive layer. Another object of the present invention is to provide conductive particles that have excellent conductivity and good long-term connection stability, a method for producing the same, and a conductive adhesive containing the conductive particles. [Means for solving the problem]

[0020] In order to solve the above problems, the first, second and third aspects of the present invention have the following configurations.

[0021] [First Aspect] Composite particles having core particles formed of a material containing a polymer, fine fibers containing cellulose nanofibers bonded to the surface of the core particles in an inseparable state, and a conductive layer covering the fine fibers on the surface of the composite particles and containing at least a metal element, wherein the composite particles have a 10% displacement strength of 5 MPa or more in a compression test, and the conductive layer is made of gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, or titanium. , Ge Conductive particles made of a material containing at least one metal element selected from the group consisting of ruthenium, aluminum, chromium, palladium, tungsten, and molybdenum.

[0022] [Second Aspect] A method for producing conductive particles, comprising: a step of defibrating a cellulose raw material in a solvent to obtain a fine fiber dispersion in which fine fibers including cellulose nanofibers are dispersed; a step of dispersing droplets containing core particle precursors in the fine fiber dispersion to coat the surfaces of the droplets with the fine fibers; a step of solidifying the core particle precursors inside the droplets to obtain a dispersion of composite particles in which the surfaces of the core particles are coated with the fine fibers; and a step of forming a conductive layer on the fine fibers on the surfaces of the composite particles in the dispersion of the composite particles by electroless plating.

[0023] [Third Aspect] A conductive adhesive comprising the conductive particles of the first embodiment and an adhesive resin. [Effects of the Invention]

[0024] According to the present invention, composite particles having good dispersion stability, good affinity with catalyst solutions and electroless plating solutions, and capable of forming a uniform conductive layer can be provided. Furthermore, conductive particles having excellent conductivity and good long-term connection stability, a method for producing the same, and a conductive adhesive containing the conductive particles can be provided. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram showing a conductive particle according to one embodiment of the present invention; [Figure 2] 3A to 3C are diagrams illustrating a method for producing conductive particles according to an embodiment. [Figure 3] Graph showing the results of measuring the spectral transmission spectrum of the aqueous dispersion of cellulose nanofibers obtained in Example 1. [Figure 4] Graph showing the results of steady-state viscoelasticity measurement using a rheometer on the aqueous dispersion of cellulose nanofibers obtained in Example 1. [Figure 5] FIG. 2 is a diagram (SEM image) showing the results of observing the composite particles obtained in Example 1 with a scanning electron microscope (SEM). [Figure 6] FIG. 2 is a diagram (SEM image) showing the results of observing the composite particles obtained in Example 1 at high magnification using a scanning electron microscope (SEM). DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a conductive particle according to one embodiment of the present invention. FIG. 2 is a diagram illustrating a method for producing a conductive particle according to an embodiment. However, in the drawings described below, corresponding parts are given the same reference numerals, and explanations of overlapping parts will be omitted as appropriate. Furthermore, this embodiment is merely an example of a configuration for embodying the technical idea of ​​the present invention, and the material, shape, structure, arrangement, dimensions, etc. of each part are not specified as described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims.

[0027] As shown in the right diagram of Fig. 1, the conductive particle 1 of this embodiment comprises a core particle 2 formed of a material containing a polymer, fine fibers 3 inseparably bonded to the surface of the core particle 2, and a conductive layer 4 containing a conductive material. The fine fibers 3 include cellulose nanofibers. The fine fibers 3 may also include fibers other than cellulose nanofibers, such as chitin nanofibers.

[0028] In this embodiment, it is preferable that the fine fibers 3 form a coating layer 30 that covers the surface of the core particle 2 .

[0029] The method for producing the conductive particle 1 is not particularly limited, and any known method can be used. For example, a particle (hereinafter referred to as composite particle 10) having a core particle 2 formed of a material containing a polymer and fine fibers 3 bonded to the surface of the core particle 2 in an inseparable state can be produced using a chemical preparation method or a physicochemical preparation method (left diagram in Figure 1), and then a conductive layer 4 is formed to produce the conductive particle 1 (right diagram in Figure 1).

[0030] Chemical preparation methods include polymerization granulation methods (emulsion polymerization, suspension polymerization, seed polymerization, radiation polymerization, etc.) in which particles are formed from polymerizable monomers during the polymerization process, while physicochemical preparation methods include dispersion granulation methods (spray drying, in-liquid hardening, solvent evaporation, phase separation, solvent dispersion cooling, etc.) in which particles are formed from microdroplets of a polymer solution.

[0031] A known method can be used to form the conductive layer 4 containing a conductive material on the surface of the composite particle 10. For example, the conductive layer 4 can be formed by a dry method such as a vapor deposition method, a sputtering method, a mechanochemical method, or a hybridization treatment, a wet method such as an electrolytic plating method or an electroless plating method, or a combination of these.

[0032] For example, by forming an O / W Pickering emulsion using the fine fibers 3 and solidifying the core particle precursor inside the droplets to produce fine fiber-coated particles in which the surfaces of the core particles 2 are coated with the fine fibers 3, it is possible to obtain composite particles in which the core particles 2 and the fine fibers 3 are bonded to each other in an inseparable state. The use of the fine fibers 3 allows stable droplets to be formed without the use of additives such as surfactants, and therefore spherical composite particles 10 with a narrow particle size distribution can be obtained.

[0033] The fine fibers 3 present on the surface of the composite particle 10 are hydrophilic, have a large specific surface area, and have good dispersibility, making the surface of the composite particle 10 hydrophilic, allowing conductive materials such as metal ions to efficiently adsorb to the surface of the composite particle 10 and forming a conductive layer 4 with good conductivity. In addition, fine irregularities are formed on the surface of the composite particle 10, resulting in good adhesion between the conductive layer 4 and the fine fibers 3. Furthermore, the conductive layer 4 is formed on the surface of the fine fibers 3, which are highly crystalline, have high strength, do not have a glass transition point (Tg), and have good dimensional stability even when heated. This makes it possible to obtain a conductive adhesive that has good electrical conductivity and can be used stably for a long period of time, and that can electrically connect opposing wiring patterns by thermocompression bonding.

[0034] The core particle precursor may be any material that can be solidified to form the core particle 2, such as a polymerizable monomer, a molten polymer, or a dissolved polymer. The method for solidifying the core particle precursor is not particularly limited, and the core particle precursor can be solidified by methods such as polymerizing a polymerizable monomer, solidifying a molten polymer, or removing the solvent from a dissolved polymer.

[0035] Furthermore, the conductive particles 1 of this embodiment can be dispersed in an adhesive resin and used as a conductive adhesive. Electronic components can be obtained using this conductive adhesive. The conductive adhesive can be used as an anisotropic conductive adhesive that is placed between two substrates on which conductive base materials are formed and bonds the conductive base materials together by heating and pressurizing, thereby providing electrical conductivity. The anisotropic conductive adhesive contains the conductive particles 1 and an adhesive resin. The adhesive resin is not particularly limited as long as it is insulating and can be used as an adhesive. For example, thermoplastic, thermosetting, or ultraviolet-curable resins or monomers can be used as the adhesive resin.

[0036] The conductive particles 1 of this embodiment can be produced by the production method shown in Fig. 2. The production method shown in Fig. 2 corresponds to the production method of the second embodiment described above, and includes a first step, a second step, a third step, and a fourth step.

[0037] The first step, as shown in FIG. 2(a), is to defibrate a cellulose raw material in a hydrophilic solvent 7 to obtain a dispersion of fine fibers 3 containing cellulose nanofibers. The second step, as shown in FIG. 2(b), is to disperse droplets 6 containing core particle precursors in the dispersion of fine fibers 3, thereby coating the surfaces of the droplets 6 with the fine fibers 3. The third step, as shown in FIG. 2(c), is to solidify the core particle precursors inside the droplets 6 to obtain a dispersion of composite particles 10 in which the surfaces of core particles 2 are coated with fine fibers 3. The fourth step, as shown in FIG. 2(d), is to coat the fine fibers 3 on the surfaces of the composite particles 10 in the dispersion of the composite particles 10 with a conductive layer 4 made of a conductive material by electroless plating. This step yields conductive particles 1 (particles in which the surfaces of core particles 2 are coated with fine fibers 3, and the conductive layer 4 is formed on the surfaces of the fine fibers 3). The dispersion shown in FIG. 2(d) can then be purified by filtration or centrifugation to separate the conductive particles 1.

[0038] That is, in the production method, the O / W Pickering emulsion is stabilized by the adsorption of fine fibers 3 onto the interfaces of droplets 6 containing core particle precursors dispersed in a hydrophilic solvent 7. Then, while maintaining this stabilized state, the core particle precursors inside the emulsion are solidified to obtain fine fiber-coated particles (composite particles 10) in which the surfaces of core particles 2 are coated with fine fibers 3. Thereafter, a conductive layer 4 made of a conductive material is formed on the fine fibers 3 on the surfaces of the composite particles 10, thereby obtaining conductive particles 1. The production method will be described in detail later.

[0039] The term "inseparable" here means that the core particles 2 and the fine fibers 3 do not separate, and the coating state of the core particles 2 with the fine fibers 3 is maintained, even after repeated purification and washing operations such as centrifuging a dispersion containing the composite particles 10 to remove the supernatant and then redispersing the composite particles 10 by adding a solvent, or after repeated washing operations with a solvent by filtration and washing using a membrane filter. The coating state can be confirmed by observing the surface of the conductive particles 1 with a scanning electron microscope. The bonding mechanism between the fine fibers 3 and the core particles 2 in the composite particles 10 is not clear, but it is presumed that the composite particles 10 use an O / W emulsion stabilized by the fine fibers 3 as a template, and solidify the core particle precursor in a state where the fine fibers 3 come into contact with the core particle precursor inside the emulsion droplets 6, thereby physically immobilizing the fine fibers 3 on the surface of the core particles 2, ultimately resulting in an inseparable state between the core particles 2 and the fine fibers 3. Here, the O / W type emulsion is also called an oil-in-water type, in which water is the continuous phase and oil is dispersed as oil droplets (oil particles) therein.

[0040] Although not particularly limited, when conductive particles 1 are produced using an O / W emulsion stabilized by fine fibers 3 as a template, the O / W emulsion is stabilized, and therefore spherical composite particles 10 derived from the O / W emulsion and conductive particles 1 can be obtained. Specifically, it is preferable that a coating layer 30 made of fine fibers 3 is formed on the surface of a spherical core particle 2 with a relatively uniform thickness.

[0041] The particle sizes of the composite particles 10 and the conductive particles 1 can be confirmed by observation under an optical microscope. The average particle size can be calculated by measuring at 100 random locations and averaging the particle diameters. The average particle size is not particularly limited, but is preferably 0.1 μm to 1000 μm, more preferably 0.5 μm to 50 μm, and even more preferably 1 μm to 30 μm. If the average particle size is smaller than 0.1 μm, electrical continuity between opposing electrodes will be lost, and if the average particle size is larger than 1000 μm, short circuits may occur between adjacent electrodes.

[0042] The composite particles 10 and conductive particles 1 of this embodiment are preferably spherical, particularly true spheres. A stable O / W Pickering emulsion is formed by the fine fibers 3, thereby enabling the production of spherical composite particles 10 and conductive particles 1. A true sphericity suppresses aggregation and improves dispersibility in adhesive resins. The index of sphericity of the composite particles 10 and conductive particles 1 can be evaluated from the circularity measured by an image analysis particle size distribution analyzer. The average circularity of the composite particles 10 and conductive particles 1 is preferably 0.6 or more, more preferably 0.7 or more, and even more preferably 0.9 or more. If the circularity is less than 0.6, it becomes difficult to achieve a smooth feel when used. The average circularity (average circularity) can be calculated as the average circularity of 1,000 or more particles measured by an image analysis particle size distribution analyzer. The average circularity can be used as the index of sphericity. When the area of ​​a composite particle on an image is S and the perimeter is L, the circularity can be calculated as "circularity = 4πS / L" 2 It can be calculated using the formula: "The closer the circularity is to 1, the higher the sphericity.

[0043] The composite particles 10 and the conductive particles 1 have high strength due to the presence of the fine fibers 3, which are rigid fibers. Although not particularly limited, if they are crushed in a compression test, it is preferable that the average value of the crushing strength is 200 MPa or more. They do not necessarily have to be crushed in a compression test. The crushing strength may be measured by a crushing test based on JIS R 1639-5:2007 (Fine ceramics - Measurement of granule characteristics - Part 5: Single granule crushing strength).

[0044] The crushing strength can be evaluated, for example, as follows. A 20 μm flat compression terminal was used in the MCT-510 micro-compression tester, and particles were scattered on the sample stage, followed by a crushing test. The test can be performed under conditions of a maximum test force of 19.6 mN and a loading speed of 0.2231 mN / s. N=10 tests were performed, and the average value of the crushing strength was calculated. The following formula was used to calculate the crushing strength.

[0045] The crushing strength is "σ = α × P / (π d 2) where σ is the crushing strength (Pa), α is the coefficient, P is the crushing test force (N), and d is the particle size of the composite particle 1 (m). For α, the value "2.8" at the position where the value is maximum can be used.

[0046] Furthermore, the composite particles 10 and the conductive particles 1 have an average 10% displacement strength of 5 MPa or more, preferably 10 MPa or more, more preferably 20 MPa or more, and even more preferably 50 MPa or more, in a compression test. The 10% displacement strength refers to the strength at which the particle is displaced (compressed) by 10% of its diameter. The compression test is basically performed according to JIS Z 8844:2019 (Method for measuring the breaking strength and deformation strength of microparticles). The 10% displacement strength can be determined by using the same formula as for the crushing strength in a crushing test, where the strength at which the particle is displaced (compressed) by 10% of its diameter (10% displacement strength) is measured. The test can be performed using a microcompression tester MCT-510 with a 20 μm flat compression terminal, with the particles scattered on the sample stage, under conditions of a maximum test force of 19.6 mN and a loading speed of 0.2231 mN / s. The test is performed with N=10 to determine the average 10% displacement strength.

[0047] From the viewpoint of dispersion stability and ease of forming the conductive layer 4, it is preferable that the fine fibers 3 form a coating layer 30 on the surface of the core particle 2. The coating layer 30 preferably covers the entire surface of the core particle 2, but does not necessarily have to cover the entire surface. The thickness of the coating layer 30 composed of the fine fibers 3 is not particularly limited, but is preferably 0.1 nm to 1000 nm. It is more preferably 0.5 nm to 500 nm, and even more preferably 1.0 nm to 200 nm. If the thickness of the coating layer 30 is thinner than 0.1 nm, a stable Pickering emulsion cannot be formed, the particle size tends to vary, and it becomes difficult to form the conductive layer 4. The average thickness of the coating layer 30 can be calculated by cutting the composite particle 10 or the conductive particle 1 fixed with an embedding resin with a microtome, observing it with a scanning electron microscope, randomly measuring the thickness of the coating layer 30 at 100 points on the cross-sectional image of the conductive particle 1 in the image, and averaging the measured values.

[0048] Furthermore, it is preferable that the conductive particles 1 are uniformly coated with a coating layer 30 of a relatively uniform thickness. A uniform thickness of the coating layer 30 improves dispersion stability and facilitates the formation of the conductive layer 4. Specifically, the coefficient of variation of the thickness value of the coating layer 30 described above is preferably 0.5 or less, and more preferably 0.4 or less.

[0049] The fine fibers 3 in this embodiment include cellulose nanofibers. Cellulose nanofibers are fibers made of cellulose or cellulose derivatives and have a number-average minor axis diameter of 1 nm or more and 1000 nm or less. Cellulose nanofibers (CNF) are safe and biodegradable fine fibers 3 that can be obtained by grinding cellulose raw materials obtained from wood or the like into ultrafine fibers. The presence of the fine fibers 3 on the surface of the core particle 2 makes the surface of the composite particle 10 hydrophilic, improving its affinity with metal ions and allowing the conductive layer 4 to be formed efficiently. Furthermore, fine irregularities are formed on the surface of the composite particle 10, improving adhesion between the composite particle 10 and the conductive layer 4.

[0050] The fine fibers 3 preferably have ionic functional groups on the crystal surfaces of the fibers. The ionic functional groups function as a dispersion stabilizer, suppressing aggregation of the composite particles 10 and efficiently obtaining a uniform conductive layer 4. The conductive layer 4 is easily formed by using the ionic functional groups as starting points. The type of ionic functional group is not particularly limited, but an anionic functional group is preferable. Fine fibers 3 having an anionic functional group can bond cationic materials such as metal ions by ionic bonding, making it easier to form a conductive layer 4. Metal ions are coordinated to the anionic functional groups of the fine fibers 3 and are reduced and precipitated, allowing metal fine particles to be efficiently supported, and the conductive layer 4 can be formed from these as starting points. The anionic functional group is not particularly limited, but examples thereof include a carboxy group, a phosphate group, and a sulfo group. Among these, the carboxy group and the phosphate group are preferred, and the carboxy group is preferred because of its ease of selective introduction onto the surface of cellulose crystals.

[0051] Among these, it is preferable to use cellulose single nanofibers (hereinafter referred to as CSNF, TEMPO-oxidized cellulose nanofibers, or TEMPO-oxidized CNF) in which carboxy groups have been selectively introduced onto the crystal surface by TEMPO oxidation. Because the OH group at the C6 position on the crystal surface of TEMPO-oxidized CNF is selectively oxidized, the distance between carboxy groups is constant, enabling uniform adsorption of metal ions and the formation of a uniform conductive layer 4.

[0052] The content of the ionic functional group is preferably 0.1 mmol or more and 5.0 mmol or less per 1 g of dry weight of the fine fiber raw material and / or fine fibers 3. If it is less than 0.1 mmol, the dispersion stability of the composite particles 10 may deteriorate, making it difficult to form the conductive layer 4. If it exceeds 5.0 mmol, it may be impossible to maintain a rigid fiber structure, and the strength of the conductive particles 1 may decrease.

[0053] The amount of ionic functional groups present on the surface of the composite particles 10 is preferably 0.01 μmol to 100.0 μmol per 1 g of composite particles 10 (dry weight). It is more preferably 0.05 μmol to 50.0 μmol. If the amount of ionic functional groups is less than 0.01 μmol, the composite particles 10 may not have a uniform particle size distribution, or the dispersibility of the composite particles 10 may be poor. Furthermore, the conductive layer 4 may not be formed efficiently. The amount of ionic functional groups present on the surface of the composite particles 10 can be measured by conductometric titration.

[0054] Furthermore, the fine fibers 3 preferably have a fibrous shape derived from a microfibril structure. Specifically, the fine fibers 3 are fibrous, and preferably have a number-average minor axis diameter of 1 nm to 1000 nm, a number-average major axis diameter of 50 nm or more, and the number-average major axis diameter is at least five times the number-average minor axis diameter. If the number-average minor axis diameter exceeds 1000 nm, the unevenness of the fine fibers 3 in the composite particles 10 increases, and the adhesion when forming the conductive layer 4 may be poor. If the number-average minor axis diameter is less than 1 nm, a rigid fibrous structure cannot be obtained, and the strength of the composite particles 10 and the conductive particles 1 may be reduced. If the number-average major axis diameter is less than five times the number-average minor axis diameter, it becomes difficult to adequately control the size and shape of the conductive particles 1.

[0055] From the viewpoint of the strength of the conductive particles 1 of the composite particle 10 and dimensional stability during heating, the crystal structure of the cellulose nanofibers of the fine fibers 3 is preferably cellulose type I, and the crystallinity is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. A high crystallinity maintains the strength of the fine fibers 3 and dimensional stability during heating, thereby improving the conductivity and long-term stability of the conductive particles 1 after thermocompression bonding.

[0056] In this embodiment, the fine fibers 3 cover the surfaces of the core particles 2, thereby producing composite particles 10 that have small particle size variations, are spherical, and have good dispersibility. Furthermore, the hydrophilic nature of the fine fibers 3 provides good affinity with metal ions, allowing for efficient formation of a uniform conductive layer 4. The coating of the fine fibers 3 forms fine irregularities on the surface of the composite particles 10, resulting in good adhesion between the conductive layer 4 and the fine fibers 3. Furthermore, the high crystallinity of the fine fibers 3 provides high strength and no glass transition point. Therefore, the resulting conductive particles 1 and conductive adhesive exhibit high dimensional stability upon heating, good conductivity during thermocompression bonding, and long-term stable usability. In particular, the fine fibers 3 having ionic functional groups have good dispersion stability, allowing the conductive layer 4 to be formed starting from the ionic functional groups, allowing for efficient formation of a uniform conductive layer 4.

[0057] In the conductive particle 1 of this embodiment, the conductive layer 4 and the fine fibers 3 are in an "inseparable" state. The "inseparable" state of the fine fibers 3 and the conductive layer 4 means that the fine fibers 3 and the conductive layer 4 do not separate even after a procedure in which a dispersion containing the conductive particles 1 is centrifuged to remove the supernatant, and then a solvent is added to redisperse the conductive particles 1 to purify and wash the particles, or after repeated washing with a solvent by filtration and washing using a membrane filter.

[0058] The conductive layer 4 can be made of a known conductive material that exhibits conductivity. The conductive material is not particularly limited, but examples of the conductive material that constitutes the conductive layer 4 include metal elements. The metal elements are not particularly limited, but examples include metals such as gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, antimony, bismuth, germanium, aluminum, chromium, palladium, tungsten, and molybdenum, as well as alloys thereof. Among these, it is preferable to contain any of rubidium (Ru), iron (Fe), cobalt (Co), rhodium (Rh), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), and zinc (Zn). The conductive layer 4 may contain a single element or multiple elements. It may also contain components other than metals. For example, metal compounds such as ITO and solder can be used. Among these, from the viewpoint of electrical conductivity, it is preferable to include one or more metals or metal compounds selected from nickel (Ni), palladium (Pd), silver (Ag), and gold (Au), but is not particularly limited to these.

[0059] The metal elements constituting the conductive layer 4 can be analyzed by known methods, such as X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, atomic absorption spectrophotometer, and high-frequency inductively coupled plasma atomic emission spectroscopy.

[0060] The conductive layer 4 may have a single layer structure or a laminated structure consisting of multiple layers. From the viewpoint of conductivity, the conductive layer 4 preferably covers the entire surface of the composite particle 10, but does not necessarily have to cover the entire surface. The average thickness of the conductive layer 4 is not particularly limited, but is preferably 0.05 nm to 3000 nm, more preferably 0.5 nm to 2000 nm, and even more preferably 1 nm to 1000 nm. If the average thickness of the conductive layer 4 is thinner than 0.05 nm, the conductivity may be insufficient.

[0061] The average thickness of the conductive layer 4 can be calculated by cutting the conductive particle 1, which has been fixed in an embedding resin, with a microtome, observing the cut surface with a scanning electron microscope, measuring the thickness of the conductive layer 4 at 100 random points on the cross-sectional image of the conductive particle 1, and taking the average value. The conductive particle 1 may have many protrusions on its surface, but if it does have protrusions, the thickness of the protrusions is not included in the measurement.

[0062] When the composite particle 10 of the present invention is used, the conductive layer 4 of the conductive particle 1 can be formed to have a relatively uniform thickness. A uniform thickness of the conductive layer 4 improves dispersion stability, making it possible to impart stable conductivity. Specifically, the coefficient of variation of the thickness value of the conductive layer 4 described above is preferably 0.5 or less, and more preferably 0.4 or less.

[0063] The method for forming the conductive layer 4 on the fine fibers 3 is not particularly limited. For example, as shown in FIG. 2, an O / W Pickering emulsion having droplets 6 containing core particle precursors is prepared using the fine fibers 3, and the core particle precursors inside the emulsion droplets 6 are solidified to produce particles (composite particles 10) coated with the fine fibers 3. The conductive particles 1 are then formed on the surfaces of the composite particles 10, thereby producing the conductive particles 1. The conductive particles 1 are purified, if necessary, by filtration or centrifugation. The method for forming the conductive layer 4 on the composite particles 10 is not particularly limited. The conductive layer 4 can be formed by dry methods such as vapor deposition, sputtering, mechanochemical methods, and hybridization treatments; wet methods such as electroplating and electroless plating; or a combination of these. Among these, forming the conductive layer 4 by electroless plating is preferred because it allows for the formation of a conductive layer 4 with a uniform thickness and high density. The method for forming the conductive layer 4 by electroless plating is not particularly limited, but may involve contacting the fine fibers 3 with metal ions derived from a metal salt to adsorb the metal ions onto the surface of the fine fibers 3, and then contacting the fine fibers with an electroless plating solution to form the conductive layer 4 by electroless plating on the surface of the composite particle 10. This allows the formation of a uniform conductive layer 4 with good adhesion to the surface of the composite particle 10 with good productivity.

[0064] The core particle 2 contains at least one type of polymer. The polymer may be a known polymer, or may be a polymer obtained by polymerizing a polymerizable monomer using a known method. Examples of polymers include acrylic polymers, epoxy polymers, polyester polymers, amino polymers, silicone polymers, fluorine-based polymers, and urethane-isocyanate polymers. The hardness of the conductive particle 1 can be adjusted by the type of polymer. The composite particle 10 and conductive particle 1 of this embodiment contain fine fibers 3 that are strong and highly dimensionally stable. Therefore, even when a polymer with a low Tg of 150°C or less or a highly flexible polymer with a 10% displacement strength of 20 MPa or less is used in polymer microparticles in which the fine fibers 3 are not coated, the shape is unlikely to collapse. Therefore, opposing wiring patterns can be electrically connected by thermocompression bonding, resulting in good electrical conductivity.

[0065] Although not particularly limited, the polymer is preferably a biodegradable polymer. Biodegradability refers to a polymer that decomposes and disappears in the global environment, such as in soil or seawater, and / or a polymer that decomposes and disappears in the living body. Generally, polymers are decomposed in soil or seawater by enzymes possessed by microorganisms, whereas in the living body, they are decomposed by physicochemical hydrolysis without the need for enzymes. Polymer decomposition occurs when the polymer becomes lower molecular weight or water-soluble and loses its form. Although not particularly limited, polymer decomposition occurs by hydrolysis of the main chain, side chain, or crosslinking point, or oxidative decomposition of the main chain. Biodegradable polymers include natural polymers derived from nature and synthetic polymers.

[0066] Examples of natural polymers include plant-produced polysaccharides (cellulose, starch, alginic acid, etc.), animal-produced polysaccharides (chitin, chitosan, hyaluronic acid, etc.), proteins (collagen, gelatin, albumin, etc.), and microbial-produced polyesters (poly(3-hydroxyalkanoates)) and polysaccharides (hyaluronic acid, etc.). Examples of synthetic polymers include aliphatic polyesters, polyols, and polycarbonates. Examples of fatty acid polyesters include glycol-dicarboxylic acid polycondensation systems (polyethylene succinate, polybutylene succinate, etc.), polylactides (polyglycolic acid, polylactic acid, etc.), polylactones (β-caprolactone, ε-caprolactone, etc.), and others (polybutylene terephthalate adipate, etc.). Examples of polyols include polyvinyl alcohol. Examples of polycarbonates include polyester carbonate. Other biodegradable synthetic polymers include polyacid anhydrides, polycyanoacrylates, polyorthoesters, and polyphosphazenes.

[0067] In addition to the polymer, the core particle 2 may contain other components such as functional components. Examples include colorants, oil absorbents, light blocking agents (e.g., UV absorbers, UV scattering agents), antibacterial agents, antioxidants, antiperspirants, antifoaming agents, antistatic agents, binders, bleaching agents, chelating agents, deodorizing ingredients, fragrances, perfumes, anti-dandruff active substances, emollients, insect repellents, preservatives, natural extracts, cosmetic ingredients, pH adjusters, vitamins, amino acids, hormones, oil-based ingredients such as fats and oils and waxes, surfactants, and inorganic particles (e.g., titanium oxide, silica, clay). The functional component may be in the form of a solid, gas, or liquid. The content of the functional component in the conductive particle 1 is not particularly limited, but is preferably within a range that allows the conductive particle 1 to stably maintain its shape. The content of the functional component is preferably 0.001 to 80 parts by mass per 100 parts by mass of the conductive particle 1.

[0068] <About the manufacturing method of conductive particles> As described above, the conductive particles 1 of the embodiment can be produced by the production method shown in FIG.

[0069] The conductive particles 1 obtained by the manufacturing method according to the present embodiment described above are obtained as a dispersion. Further, by removing the solvent, they are obtained as a dry solid. The method for removing the solvent is not particularly limited, and for example, excess water can be removed by centrifugation or filtration, followed by heat drying in an oven to obtain a dry solid (FIG. 2(e)). In this case, the obtained dry solid does not form aggregates, but is obtained as a fine, smooth powder. The composite particles 10 have good dispersibility because their surfaces are covered with fine fibers 3, and the presence of the fine fibers 3 creates fine irregularities on the surfaces of the conductive particles 1, which makes them less likely to aggregate together and provides good dispersibility in adhesive resins.

[0070] The dry powder of conductive particles 1 is a dry solid that contains almost no solvent and is redispersible in a solvent, specifically, the solid content can be 80% or more, even 90% or more, or even 95% or more. Because the solvent can be almost completely removed, favorable effects can be obtained from the viewpoints of reducing transportation costs, preventing spoilage, increasing the additive rate, and improving compatibility with plating solutions and adhesive resins.

[0071] Each step will be described in detail below. As described above, the method for producing the conductive particles 1 of the present invention includes the first step, the second step, the third step, and the fourth step.

[0072] (1st step) The first step is a step of defibrating a fine fiber raw material in a solvent to obtain a dispersion of fine fibers 3. The fine fiber raw material is a cellulose raw material that is the raw material for cellulose nanofibers.

[0073] First, various fine fiber raw materials are dispersed in a solvent to form a suspension. The concentration of the fine fiber raw materials in the suspension is preferably 0.1% or more and less than 10%. If it is less than 0.1%, the amount of solvent will be excessive, which will impair productivity, and it is not preferable. If it is 10% or more, the suspension will rapidly thicken as the fine fiber raw materials are defibrated, making uniform defibration processing difficult, which is also not preferable. In the following, unless otherwise specified, "%" indicates mass % (w / w%).

[0074] The solvent used to prepare the suspension is preferably a hydrophilic solvent 7. There are no particular limitations on the hydrophilic solvent 7, but water; alcohols such as methanol, ethanol, and isopropanol; cyclic ethers such as tetrahydrofuran, or a mixture thereof are preferred.

[0075] Preferably, the hydrophilic solvent 7 contains 50% or more of water. If the proportion of water in the suspension is 50% or less, dispersion of the fine fibers 3 is hindered in the step of obtaining a fine fiber dispersion by defibrating the fine fiber raw material in the solvent, which will be described later. In addition, the solvent contained other than water is preferably the hydrophilic solvent described above.

[0076] If necessary, the pH of the suspension may be adjusted to improve the dispersibility of the fine fiber raw material and the resulting fine fibers 3. Examples of alkaline aqueous solutions used for adjusting the pH include organic alkalis such as sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, and benzyltrimethylammonium hydroxide aqueous solution. A sodium hydroxide aqueous solution is preferred from the standpoint of cost, etc.

[0077] The suspension is then subjected to a physical defibration treatment to refine the fine fiber raw material. The physical defibration treatment method is not particularly limited, but examples include mechanical treatments such as those using a high-pressure homogenizer, ultra-high-pressure homogenizer, ball mill, roll mill, cutter mill, planetary mill, jet mill, attritor, grinder, juicer mixer, homomixer, ultrasonic homogenizer, nanogenizer, and underwater head-on collision. By performing such physical defibration treatment, the cellulose in the suspension of the cellulose raw material in the hydrophilic solvent 7 is refined, resulting in a dispersion of cellulose refined to the nanometer order of at least one side of the structure. Furthermore, the number-average minor axis diameter and number-average major axis diameter of the resulting fine fibers 3 can be adjusted by adjusting the time and number of times of the physical defibration treatment.

[0078] As described above, a dispersion (fine fiber dispersion) of fine fibers 3 is obtained, the structure of which has been refined to such an extent that at least one side is on the order of nanometers. The obtained dispersion can be used as it is or after being diluted, concentrated, or the like, as a stabilizer for O / W emulsions, which will be described later.

[0079] Furthermore, the dispersion of fine fibers 3 may contain other components in addition to cellulose and the component used for pH adjustment, as needed, as long as the effects of this embodiment are not impaired. The other components are not particularly limited and can be appropriately selected from known additives depending on the intended use of the conductive particles 1. Specific examples of such other components include organometallic compounds such as alkoxysilanes or their hydrolysates, inorganic layered compounds, inorganic acicular minerals, antifoaming agents, inorganic particles, organic particles, lubricants, antioxidants, antistatic agents, UV absorbers, stabilizers, magnetic materials, alignment promoters, plasticizers, crosslinking agents, pharmaceuticals, pesticides, fragrances, adhesives, enzymes, colorants, deodorizers, metals, metal oxides, inorganic oxides, preservatives, antibacterial agents, natural extracts, and surfactants.

[0080] Typically, the fine fibers 3 have a fibrous shape derived from a microfibril structure. Therefore, the fine fibers 3 used in the manufacturing method of this embodiment preferably have a fibrous shape within the range shown below. That is, the shape of the fine fibers 3 is preferably fibrous. Furthermore, the number-average minor axis diameter of the fibrous fine fibers 3 may be 1 nm or more and 1000 nm or less, preferably 2 nm or more and 500 nm or less. Here, if the number-average minor axis diameter is less than 1 nm, a highly crystalline, rigid fine fiber 3 fibrous structure cannot be obtained, making it difficult to stabilize the emulsion and form the composite particles 10 by, for example, a polymerization reaction using the emulsion as a template or solidification of the polymer. Furthermore, it becomes difficult to obtain composite particles 10 and conductive particles 1 with sufficient hardness. On the other hand, if the diameter exceeds 1000 nm, the size becomes too large to stabilize the emulsion, making it difficult to control the size and shape of the resulting composite particles 10 and conductive particles 1. Furthermore, the number-average major axis diameter is not particularly limited, but is preferably at least five times the number-average minor axis diameter. If the number average major axis diameter is less than five times the number average minor axis diameter, it is not possible to sufficiently control the size and shape of the conductive particles 1, which is undesirable.

[0081] The number average minor axis diameter of the fine fibers 3 is determined by measuring the minor axis diameters (minimum diameters) of 100 fibers by observation with a transmission electron microscope and an atomic force microscope, and averaging the measured values. On the other hand, the number average major axis diameter of the fine fibers 3 is determined by measuring the major axis diameters (maximum diameters) of 100 fibers by observation with a transmission electron microscope and an atomic force microscope, and averaging the measured values.

[0082] The type and crystalline structure of cellulose that can be used as the cellulose raw material are not particularly limited. Specifically, as raw materials consisting of cellulose type I crystals, for example, in addition to wood-based natural cellulose, non-wood-based natural celluloses such as cotton linter, bamboo, hemp, bagasse, kenaf, bacterial cellulose, sea squirt cellulose, and valonia cellulose can be used. Furthermore, regenerated celluloses, such as rayon fiber and cupra fiber, consisting of cellulose type II crystals can also be used. Due to the ease of material procurement, wood-based natural cellulose is preferred as the raw material. The wood-based natural cellulose is not particularly limited, and those commonly used in the production of cellulose nanofibers, such as softwood pulp, hardwood pulp, and recycled paper pulp, can be used. Softwood pulp is preferred due to its ease of purification and micronization.

[0083] Furthermore, it is preferable that the fine fiber raw material be chemically modified. More specifically, it is preferable that ionic functional groups be introduced onto the crystal surfaces of the fine fiber raw material. This is because the introduction of ionic functional groups onto the crystal surfaces of the fine fiber raw material makes it easier for the solvent to penetrate between the crystals of the fine fiber raw material due to the osmotic pressure effect, facilitating the micronization of the fine fiber raw material. In addition, emulsion stability can be improved, and composite particles 10 with good dispersibility and uniform particle size can be produced. Furthermore, by adsorbing metal ions via the ionic functional groups of the fine fibers 3 present on the surface of the composite particles 10, it becomes easier to form an electroless plating film on the composite particles 10.

[0084] The type of ionic functional group introduced to the crystal surface of the fine fiber raw material is not particularly limited. For example, the presence of an anionic functional group allows metal ions to be coordinated to the fine fibers 3 by ionic bonding, making it easier to form a conductive layer 4 by electroless plating, and a uniform conductive layer 4 can be formed. The type of anionic functional group and the method of introduction are not particularly limited, but a carboxy group or a phosphate group is preferred. In the case of cellulose, a carboxy group is preferred because it can be easily introduced selectively to the cellulose crystal surface.

[0085] The method for introducing carboxyl groups into the cellulose crystal surface is not particularly limited. Specifically, for example, carboxymethylation can be performed by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a highly concentrated alkaline aqueous solution. Alternatively, carboxyl groups can be introduced by directly reacting cellulose with gasified carboxylic anhydrides, such as maleic acid or phthalic acid, in an autoclave. Furthermore, a method using a co-oxidant in the presence of an N-oxyl compound, such as TEMPO, which has high selectivity for the oxidation of alcoholic primary carbons while maintaining the structure as much as possible under relatively mild aqueous conditions, can also be used. Oxidation using an N-oxyl compound is more preferred for selectivity of the carboxyl group introduction site and reduced environmental impact. In the method using a co-oxidant in the presence of an N-oxyl compound, the hydroxyl group at the C6 position on the crystal surface is selectively oxidized, resulting in an ordered distribution of carboxyl groups. This allows for uniform adsorption of metal ions, resulting in the formation of a uniform conductive layer 4.

[0086] Examples of N-oxyl compounds include TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy radical), 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, and 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl. Among these, TEMPO, which has high reactivity, is preferred. The amount of the N-oxyl compound used is not particularly limited and may be the amount used as a catalyst. It is usually 0.01% by mass or more and 5.0% by mass or less of the solid content of the wood-based natural cellulose to be oxidized.

[0087] An example of an oxidation method using an N-oxyl compound is a method in which wood-based natural cellulose is dispersed in water and oxidized in the presence of an N-oxyl compound. In this case, it is preferable to use a co-oxidizing agent together with the N-oxyl compound. In this case, the N-oxyl compound is sequentially oxidized by the co-oxidizing agent in the reaction system to produce an oxoammonium salt, and the cellulose is oxidized by the oxoammonium salt. This oxidation treatment allows the oxidation reaction to proceed smoothly even under mild conditions, improving the efficiency of introducing carboxyl groups. Mild conditions for the oxidation treatment make it easier to maintain the crystalline structure of cellulose.

[0088] Any oxidizing agent can be used as the co-oxidizing agent as long as it can promote the oxidation reaction, including halogens, hypohalous acids, halous acids, perhalogen acids, or their salts, halogen oxides, nitrogen oxides, and peroxides. Sodium hypochlorite is preferred due to its availability and reactivity. The amount of the co-oxidizing agent used is not particularly limited, and may be any amount that can promote the oxidation reaction. Typically, the amount is about 1 to 200% by mass based on the solid content of the wood-based natural cellulose to be oxidized.

[0089] In addition, at least one compound selected from the group consisting of bromides and iodides may be used in combination with the N-oxyl compound and co-oxidizing agent. This allows the oxidation reaction to proceed smoothly and improves the efficiency of introducing carboxy groups. Sodium bromide or lithium bromide is preferred as such a compound, with sodium bromide being more preferred in terms of cost and stability. The amount of the compound used is not particularly limited and may be any amount that can promote the oxidation reaction. It is usually about 1 to 50% by mass based on the solid content of the wood-based natural cellulose to be oxidized.

[0090] The reaction temperature for the oxidation reaction is preferably 4°C to 80°C, and more preferably 10°C to 70°C. If the temperature is below 4°C, the reactivity of the reagent decreases and the reaction time becomes longer. If the temperature exceeds 80°C, side reactions are promoted, the sample becomes low-molecular-weight, and the fiber structure of the highly crystalline, rigid cellulose nanofiber collapses, making it impossible to use as a stabilizer for O / W emulsions.

[0091] The reaction time for the oxidation treatment can be appropriately set in consideration of the reaction temperature, the desired amount of carboxyl groups, etc., and is not particularly limited, but is usually from 10 minutes to 5 hours.

[0092] The pH of the reaction system during the oxidation reaction is not particularly limited, but is preferably 9 or more and 11 or less. A pH of 9 or more allows the reaction to proceed efficiently. A pH of more than 11 may cause side reactions to proceed, which may accelerate the decomposition of the sample. Furthermore, in the oxidation treatment, as the oxidation progresses, carboxyl groups are generated, causing the pH in the system to decrease. Therefore, it is preferable to maintain the pH of the reaction system at 9 or more and 11 or less during the oxidation treatment. One method for maintaining the pH of the reaction system at 9 or more and 11 or less is to add an alkaline aqueous solution as the pH decreases.

[0093] Examples of the alkaline aqueous solution include organic alkalis such as aqueous sodium hydroxide solution, aqueous lithium hydroxide solution, aqueous potassium hydroxide solution, aqueous ammonia solution, aqueous tetramethylammonium hydroxide solution, aqueous tetraethylammonium hydroxide solution, aqueous tetrabutylammonium hydroxide solution, and aqueous benzyltrimethylammonium hydroxide solution. In terms of cost, aqueous sodium hydroxide solution is preferred.

[0094] The oxidation reaction with an N-oxyl compound can be terminated by adding an alcohol to the reaction system. At this time, it is preferable to maintain the pH of the reaction system within the above range. As the alcohol to be added, low-molecular-weight alcohols such as methanol, ethanol, and propanol are preferred in order to quickly terminate the reaction, and ethanol is particularly preferred in view of the safety of by-products generated by the reaction.

[0095] The reaction solution after the oxidation treatment may be subjected to the micronization step as is, but it is preferable to recover the anion-modified cellulose contained in the reaction solution and wash it with a washing solution to remove catalysts such as N-oxyl compounds, impurities, etc. The anion-modified cellulose can be recovered by known methods such as filtration using a glass filter or a nylon mesh with a pore size of 20 μm. Methods for recovering the cellulose after the anion-modification treatment include, for example, a method in which the anionic functional groups remain as salts, a method in which an acid is added to the reaction solution to adjust the system to an acidic state and then the cellulose is filtered, and a method in which an organic solvent is added to cause coagulation and then the cellulose is filtered.

[0096] In a method for filtering the anion-modified groups while they are still in the form of salts, the washing liquid used for washing the anion-modified cellulose is preferably pure water. In this case, cationic substances in the alkaline aqueous solution used for adjusting the pH bind as counter ions to at least a portion of the anionic groups of the anion-modified cellulose into which anionic functional groups have been introduced.

[0097] As a method of adjusting the reaction mixture to an acidic state by adding an acid and then filtering, washing with an acidic solution such as hydrochloric acid can be used. For example, if the anionic functional group is a carboxyl group, washing can be performed using an acidic solution, converting the carboxyl group to COOH (acid form) and washing the cationic substance, followed by adding a new aqueous alkaline solution to neutralize. In this case, adding an alkali different from the alkali used to adjust the pH of the TEMPO oxidation reaction can replace the counterion cationic substance. The alkali used for neutralization can be an aqueous solution of sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, or an organic onium compound / amine.

[0098] Preferably, at least a portion of the anion-modified cellulose after washing has a cationic substance bonded thereto as a counter ion (counter cation) to the anionic functional group. The cationic substance is not particularly limited, but examples include metal ions of alkali metals such as sodium ions, potassium ions, and lithium ions, alkaline earth metals such as magnesium ions and calcium ions, organic onium cations, and amines. From the viewpoint of the dispersion stability of the anion-modified cellulose, fine fibers 3, and composite particles 10, metal ions of alkali metals such as sodium ions, potassium ions, and lithium ions, organic onium cations, and amines are preferred. By defibrating oxidized cellulose to which cationic substances such as alkali metal or alkaline earth metal ions, organic onium cations, or amines are bonded as counter cations, fine fibers 3 can be obtained to have alkali metal or alkaline earth metal ions, organic onium cations, or amines bonded as counter cations.

[0099] In particular, fine fibers 3 bound to organic onium cations or amines as counter cations have high emulsion stability and can form stable O / W Pickering emulsions regardless of the type of core particle precursor, enabling composite particles 10 with uniform particle sizes to be obtained in high yields with a variety of core resins. The ionized state of an organic onium compound is referred to as an organic onium ion or organic onium cation. The term "amine" used here refers to a compound that is partially or completely ionized and contains an ammonium ion. Hereinafter, either an organic onium compound or amine, or an organic onium cation or ammonium ion, will also be referred to as "organic onium compound / amine" or "organic onium cation (or organic onium ion) / ammonium ion," respectively.

[0100] From the viewpoint of emulsion stability, the average binding amount of organic onium ions / ammonium ions in the anion-modified cellulose or the fine fibers 3 is preferably 0.02 mmol / g or more, more preferably 0.2 mmol / g or more, and preferably 3 mmol / g or less, more preferably 2.5 mmol / g or less, and even more preferably 2 mmol / g or less, per cellulose. Any two or more types of organic onium ions / ammonium ions may be bound to the fine fibers 3 simultaneously. In this case, the average binding amount of organic onium ions / ammonium ions is preferably such that the total amount of the introduced modifying groups falls within the above-mentioned range. The average binding amount of organic onium ions / ammonium ions (mmol / g) can be measured by known methods. For example, it can be calculated by titration, IR measurement, or the like.

[0101] When the surface of the fine fibers 3 has been partially hydrophobized by bonding with organic onium ions / ammonium ions, the contact angle of the film produced using the fine fibers 3 with water is not particularly limited, but it is preferable that the contact angle be 45° or more, and more preferably 50° or more. The contact angle is measured by pouring a 0.5% aqueous dispersion of the fine fibers 3 into a 5 cm x 5 cm container, drying the film at a temperature of 30°C and a humidity of 80%, and then drying the film under a nitrogen atmosphere. Then, 2 μl of pure water is dropped onto the film using a contact angle meter (PCA-1, manufactured by Kyowa Interface Science Co., Ltd.) to measure the contact angle.

[0102] A cationic substance other than an organic onium ion / ammonium ion may be bonded as a counter ion to the anionic functional group of the anion-modified cellulose or the fine fibers 3. The cationic substance is not particularly limited, but examples thereof include metal ions such as alkali metals such as sodium ions, potassium ions, and lithium ions, and alkaline earth metals such as magnesium ions and calcium ions. From the viewpoint of dispersion stability of the anion-modified cellulose, the fine fibers 3, and the composite particles 10, metal ions of alkali metals such as sodium ions, potassium ions, and lithium ions are preferred.

[0103] The binding equivalent of the cationic substance other than organic onium ions / ammonium ions is preferably 0.02 mmol / g or more, more preferably 0.2 mmol / g or more, per cellulose, from the viewpoint of the dispersion stability and emulsion stability of the anion-modified cellulose and the fine fibers 3. It is also preferably 3 mmol / g or less, more preferably 2.5 mmol / g or less, and even more preferably 2 mmol / g or less. Any two or more types of cationic substances may be simultaneously introduced into the anion-modified cellulose and the fine fibers 3. The average binding amount (mmol / g) of the cationic substance can be measured by a known method. For example, in the case of metal ions, methods such as EPMA using an electron beam microanalyzer, X-ray fluorescence analysis, and elemental analysis by ICP emission spectrometry can be used.

[0104] The organic onium compound in this embodiment has a cation structure represented by structural formula (1).

[0105] [ka]

[0106] In structural formula (1), M is a nitrogen atom, phosphorus atom, or sulfur atom, and R1, R2, R3, and R4 are a hydrogen atom, a hydrocarbon group, or a hydrocarbon group containing a heteroatom. For example, when M is a nitrogen atom and R1, R2, R3, and R4 are all hydrogen atoms, the organic onium compound is ammonia. When three of R1, R2, R3, and R4 are hydrogen atoms, the organic onium compound is a primary amine; when two are hydrogen atoms, the organic onium compound is a secondary amine; when one is hydrogen atoms, the organic onium compound is a tertiary amine; and when none are hydrogen atoms, the organic onium compound is a quaternary amine. All of these organic onium compounds are within the scope of this embodiment. Examples of hydrocarbon groups containing a heteroatom include alkyl groups, alkylene groups, oxyalkylene groups, aralkyl groups, aryl groups, and aromatic groups. R1, R2, R3, and R4 may form a ring.

[0107] In structural formula (1), M is a nitrogen atom, and examples of the quaternary ammonium compound include tetraethylammonium hydroxide (TEAH), tetraethylammonium chloride, tetrabutylammonium hydroxide (TBAH), tetrabutylammonium chloride, didecyldimethylammonium chloride, lauryltrimethylammonium chloride, dilauryldimethylchloride, stearyltrimethylammonium chloride, distearyldimethylammonium chloride, cetyltrimethylammonium chloride, alkylbenzyldimethylammonium chloride, and coconut amine. Didecyldimethylammonium chloride, cetyltrimethylammonium chloride, and alkylbenzyldimethylammonium chloride are particularly preferred because they can impart antibacterial properties.

[0108] In structural formula (1), examples of the quaternary phosphonium compound in which M is a phosphorus atom include phosphoniums such as tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, tetrabutylphosphonium hydroxide, benzyltrimethylphosphonium hydroxide, benzyltriethylphosphonium hydroxide, and hexadecyltrimethylphosphonium hydroxide.

[0109] In this embodiment, the primary amine, secondary amine, and tertiary amine have the structures shown in the following structural formulas (2), (3), and (4), respectively. When these amines are ionized to form ammonium ions with a cationic structure, the structures become (2)', (3)', and (4)', respectively.

[0110] [ka]

[0111] In the above structural formulas (2) to (4'), R1 to R6 are either a hydrocarbon group or a hydrocarbon group containing a hetero atom.

[0112] Examples of primary amines, secondary amines, and tertiary amines include methylamine, ethylamine, propylamine, butylamine, n-octylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, hexylamine, 2-ethylhexylamine, dihexylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, trioctylamine, trihexylamine, dioctylamine, dodecylamine, stearylamine, and oleylamine. Examples of amino-modified silicone compounds include polyetheramines, polyethylene glycol amines (PEG-NH2), and amines having an ethylene oxide / propylene oxide (EO / PO) copolymerization moiety.

[0113] When the resulting anion-modified cellulose is subjected to a defibration treatment, fine fibers 3 having anionic functional groups are obtained. When the TEMPO-oxidized cellulose (oxidized cellulose) obtained by TEMPO oxidation is subjected to a defibration treatment, TEMPO-oxidized cellulose nanofibers (TEMPO-oxidized CNF, also known as cellulose single nanofibers or CSNF) with a uniform fiber width of approximately 3 nm are obtained. When CSNF is used as the raw material for the cellulose nanofibers of the composite particles 10 and the conductive particles 1, the particle size of the resulting O / W emulsion tends to be uniform due to its uniform structure.

[0114] As described above, the CSNF used in this embodiment can be obtained by a process of oxidizing a cellulose raw material and a process of micronizing and dispersing the cellulose. The content of carboxy groups introduced into the CSNF is preferably 0.1 mmol / g to 5.0 mmol / g, more preferably 0.5 mmol / g to 2.0 mmol / g. If the amount of carboxy groups is less than 0.1 mmol / g, the solvent does not penetrate between the cellulose microfibrils due to the osmotic effect, making it difficult to micronize and uniformly disperse the cellulose. Furthermore, if the amount of carboxy groups exceeds 5.0 mmol / g, the cellulose microfibrils are depolymerized due to side reactions associated with the chemical treatment, preventing the formation of a highly crystalline, rigid cellulose nanofiber fiber structure. This makes it difficult to use the CSNF as a stabilizer for O / W emulsions.

[0115] (2nd process) The second step is a step in which the surfaces of the droplets 6 containing the core particle precursors in the dispersion of the fine fibers 3 obtained in the first step are coated with the fine fibers 3 to stabilize the emulsion.

[0116] Specifically, this is a step in which the core particle precursor-containing liquid is dispersed as droplets 6 in the dispersion of fine fibers 3 obtained in the first step, thereby covering the surfaces of the droplets 6 with the fine fibers 3, thereby producing an O / W type emulsion stabilized by the fine fibers 3. The O / W type emulsion stabilized by the fine fibers 3 is called an emulsion liquid.

[0117] The method for producing an O / W emulsion is not particularly limited, and can be a general emulsification process, such as various homogenizer processes or mechanical stirring processes, and specific examples include mechanical processes using a high-pressure homogenizer, an ultra-high-pressure homogenizer, a universal homogenizer, a ball mill, a roll mill, a cutter mill, a planetary mill, a jet mill, an attritor, a grinder, a juicer mixer, a homomixer, an ultrasonic homogenizer, a nanogenizer, underwater head-on collision, a paint shaker, etc. Furthermore, a combination of multiple mechanical processes can be used.

[0118] For example, when using an ultrasonic homogenizer, a core particle precursor-containing liquid is added to a dispersion of fine fibers 3 to form a mixed solvent, and the tip of the ultrasonic homogenizer is inserted into the mixed solvent to perform ultrasonic treatment. The treatment conditions for the ultrasonic homogenizer are not particularly limited, but for example, a frequency of 20 kHz or more and an output of 10 W / cm are common. 2 The above is the general procedure. There is no particular limitation on the processing time, but it is usually about 10 seconds to 1 hour.

[0119] The ultrasonic treatment described above causes droplets 6 containing core particle precursors to disperse in the dispersion of fine fibers 3, promoting emulsification. Furthermore, the fine fibers 3 selectively adsorb to the liquid / liquid interface between the droplets 6 and the fine fiber dispersion, thereby coating the droplets 6 with the fine fibers 3 and forming a stable structure as an O / W emulsion. Such emulsions stabilized by the adsorption of solid matter at the liquid / liquid interface are academically known as "Pickering emulsions." As mentioned above, the mechanism by which Pickering emulsions are formed by fine fibers 3 is unclear. However, cellulose exhibits amphiphilic properties due to its molecular structure, which has hydrophilic sites derived from hydroxyl groups and hydrophobic sites derived from hydrocarbon groups. It is therefore thought that cellulose adsorbs to the liquid / liquid interface between the hydrophobic monomer and the hydrophilic solvent due to its amphiphilic properties.

[0120] The O / W emulsion structure can be confirmed by observation under an optical microscope. The particle size of the O / W emulsion is not particularly limited, but the average particle size is preferably 0.1 μm or more and 1000 μm or less. The average particle size can be calculated by measuring the diameter of 100 randomly selected emulsion particles and taking the average value.

[0121] In the O / W emulsion structure, the thickness of the coating layer 30 (fine fiber layer) formed on the surface of the droplets 6 is not particularly limited, but is preferably 3 nm or more and 1000 nm or less. Although not particularly limited, the particle size in the emulsion structure is approximately the same as the particle size of the composite particles 10 obtained in the third step. The thickness of the coating layer 30 can be measured using, for example, a cryo-TEM.

[0122] The weight ratio of the dispersion of fine fibers 3 to the core particle precursor that can be used in the second step is not particularly limited, but it is preferable that the amount of core particle precursor is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of fine fibers 3. If the amount of core particle precursor is 1 part by mass or less, the yield of composite particles 10 decreases, which is not preferable, and if the amount exceeds 50 parts by mass, it becomes difficult to uniformly coat the droplets 6 with the fine fibers 3, making particle size control difficult and also making it difficult to form the conductive layer 4, which is not preferable.

[0123] The core particle precursor-containing liquid may contain a core particle precursor and may form an O / W emulsion, and is preferably hydrophobic to stably form the O / W emulsion. The core particle precursor is a precursor that solidifies through a chemical or physicochemical change to form core particles 2. The core particle precursor is not particularly limited as long as it can stably form droplets 6. Examples of the core particle precursor that can be used include a polymerizable compound, a molten polymer, and a dissolved polymer.

[0124] Polymerizable compounds that can be used as core particle precursors in the second step include polymerizable monomers (monomers), polymerizable oligomers (oligomers), and polymerizable polymers. The polymerizable monomer is a polymer monomer that has a polymerizable functional group in its structure, is liquid at room temperature, is incompatible with water, and can form a polymer (high molecular weight polymer) through a polymerization reaction. The polymerizable monomer has at least one polymerizable functional group. A polymerizable monomer having one polymerizable functional group is also called a monofunctional monomer. A polymerizable monomer having two or more polymerizable functional groups is also called a polyfunctional monomer. The type of polymerizable monomer is not particularly limited, but examples include (meth)acrylic monomers and vinyl monomers. It is also possible to use polymerizable monomers having a cyclic ether structure such as an epoxy group or an oxetane structure (e.g., ε-caprolactone). The term "(meth)acrylate" includes both "acrylate" and "methacrylate."

[0125] Examples of monofunctional (meth)acrylic monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isobornyl (meth)acrylate. acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphate (meth)acrylate, ethylene oxide-modified phosphate (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide-modified phenoxy (meth)acrylate, propylene oxide-modified propylene oxide Phenoxy (meth)acrylate, nonylphenol (meth)acrylate, ethylene oxide modified nonylphenol (meth)acrylate, propylene oxide modified nonylphenol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl diethyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate,Examples of the mono(meth)acrylate include adamantane derivative mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from 2-adamantane and adamantanediol.

[0126] Examples of bifunctional (meth)acrylic monomers include di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and hydroxypivalic acid neopentyl glycol di(meth)acrylate.

[0127] Examples of the tri- or higher functional (meth)acrylic monomer include tri(meth)acrylates such as trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris(2-hydroxyethylisocyanurate tri(meth)acrylate, glycerin tri(meth)acrylate, and trifunctional (meth)acrylate compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate. and polyfunctional (meth)acrylate compounds having three or more functional groups such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate, as well as polyfunctional (meth)acrylate compounds in which a portion of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.

[0128] Preferred monofunctional vinyl monomers are liquids that are incompatible with water at room temperature, such as vinyl ethers, vinyl esters, aromatic vinyls, and especially styrene and styrene monomers. Among the monofunctional vinyl monomers, examples of the (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, alkyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, diethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, heptafluorodecyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and tricyclodecanyl (meth)acrylate. Furthermore, examples of monofunctional aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, isopropenyltoluene, isobutyltoluene, tert-butylstyrene, vinylnaphthalene, vinylbiphenyl, and 1,1-diphenylethylene.

[0129] The polyfunctional vinyl monomer may be a polyfunctional group having an unsaturated bond such as divinylbenzene, etc. A liquid that is incompatible with water at room temperature is preferred. Specific examples of polyfunctional vinyl monomers include: (1) divinyls such as divinylbenzene, 1,2,4-trivinylbenzene, and 1,3,5-trivinylbenzene; (2) dimethacrylates such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexamethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, and 2,2-bis(4-methacryloxydiethoxyphenyl)propane; (3) trimethacrylates such as trimethylolpropane trimethacrylate and triethylolethane trimethacrylate; (4) ethylene glycol diacrylate, diethylene glycol dimethacrylate, and 2,2-bis(4-methacryloxydiethoxyphenyl)propane; (4) diacrylates such as trimethylolpropane triacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, 1,3-dipropylene glycol diacrylate, 1,4-dibutylene glycol diacrylate, 1,6-hexylene glycol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, 2,2-bis(4-acryloxypropoxyphenyl)propane, and 2,2-bis(4-acryloxydiethoxyphenyl)propane; (5) triacrylates such as trimethylolpropane triacrylate and triethylolethane triacrylate; (6) tetraacrylates such as tetramethylolmethane tetraacrylate; and (7) others, such as tetramethylene bis(ethyl fumarate), hexamethylene bis(acrylamide), triallyl cyanurate, and triallyl isocyanurate.Specific examples of functional styrene-based monomers include divinylbenzene, trivinylbenzene, divinyltoluene, divinylnaphthalene, divinylxylene, divinylbiphenyl, bis(vinylphenyl)methane, bis(vinylphenyl)ethane, bis(vinylphenyl)propane, and bis(vinylphenyl)butane.

[0130] In addition to these, polymerizable polymers and polymerizable oligomers having at least one polymerizable functional group can also be used. Examples of polymerizable polymers that can be used include polyether resins, polyester resins, polyurethane resins, epoxy resins, alkyd resins, spiroacetal resins, polybutadiene resins, and polythiolpolyene resins, and the material is not particularly limited.

[0131] The above polymerizable monomers may be used alone or in combination of two or more kinds.

[0132] A polymerization initiator may be added to the polymerizable monomer. Typical polymerization initiators include radical initiators such as organic peroxides and azo polymerization initiators.

[0133] Examples of organic peroxides include peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxycarbonates, and peroxyesters.

[0134] Examples of azo polymerization initiators include ADVN and AIBN. For example, 2,2-azobis(isobutyronitrile) (AIBN), 2,2-azobis(2-methylbutyronitrile) (AMBN), 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1-azobis(1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2-azobisisobutyrate (MAIB), 4,4-azobis(4-cyanovaleric acid) (ACVA), 1,1-azobis(1-acetoxy-1-phenylethane), 2,2-azobis(2-methylbutyronitrile), 2,2-azobis(4- methoxy-2,4-dimethylvaleronitrile), 2,2-azobis(2-methylamidinopropane) dihydrochloride, 2,2-azobis[2-(2-imidazolin-2-yl)propane], 2,2-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2-azobis(2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2-azobis(N-butyl-2-methylpropionamide), 2,2-azobis(N-cyclohexyl-2-methylpropionamide), and the like.

[0135] If a core particle precursor-containing liquid containing a polymerizable monomer and a polymerization initiator is used in the second step, the polymerization initiator will be contained in the droplets 6 of the O / W emulsion in the third step described below, which will facilitate the polymerization reaction when polymerizing the monomer inside the emulsion droplets 6 in the third step described below.

[0136] The weight ratio of the polymerizable monomer to the polymerization initiator that can be used in the second step is not particularly limited, but it is usually preferable that the amount of the polymerization initiator is 0.1 part by mass or more per 100 parts by mass of the polymerizable monomer. If the amount of the polymerizable monomer is less than 0.1 part by mass, the polymerization reaction does not proceed sufficiently, which is undesirable because it reduces the yield of the composite particles 10 and further the conductive particles 1.

[0137] The core particle precursor-containing liquid may contain a solvent. Although not particularly limited, it is preferable to use an organic solvent to stabilize the emulsion in the second step. Examples of solvents that can be used include toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), isophorone, cellosolve acetate, isophorone, Solvesso 100, trichlene, hexane, chloroform, dichloromethane, dichloroethane, isooctane, and nonane.

[0138] The weight ratio of the polymerizable monomer to the solvent that can be used in the second step is not particularly limited, but it is preferable that the solvent is 80 parts by mass or less per 100 parts by mass of the polymerizable monomer.

[0139] The polymer used to obtain the dissolved polymer that can be used as the core particle precursor in the second step is not particularly limited, but preferably is poorly soluble in the hydrophilic solvent 7. If the polymer dissolves in the hydrophilic solvent 7, a stable emulsion cannot be formed. Examples of polymers that can be used to obtain the dissolved polymer include: cellulose acetate derivatives such as cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate; polysaccharides such as chitin and chitosan; polylactic acids such as polylactic acid and copolymers of lactic acid and other hydroxycarboxylic acids; dibasic acid polyesters such as polybutylene succinate, polyethylene succinate, and polybutylene adipate; polycaprolactones such as polycaprolactone and copolymers of caprolactone and hydroxycarboxylic acids; polyhydroxybutyrates such as polyhydroxybutyrate and copolymers of polyhydroxybutyrate and hydroxycarboxylic acids; aliphatic polyesters such as polyhydroxybutyric acid and copolymers of polyhydroxybutyric acid and other hydroxycarboxylic acids; polyamino acids, polyester polycarbonates, natural resins such as rosin, etc. These can be used alone or in combination of two or more.

[0140] A dissolved polymer can be obtained by dissolving the polymer in a solvent that dissolves the polymer. It is preferable to use a solvent that has low compatibility with the dispersion of the fine fibers 3 as the solvent for dissolving the polymer. If the solubility in the hydrophilic solvent 7 is high, the solvent will easily dissolve from the droplet 6 phase into the hydrophilic solvent 7 phase, making emulsification difficult. Furthermore, it is preferable for the solvent to have a boiling point of 90°C or less. If the boiling point is higher than 90°C, when the solvent inside the droplets 6 is evaporated to solidify the core particle precursor in the subsequent third step, the hydrophilic solvent 7 of the dispersion of the fine fibers 3 will evaporate before the solvent inside the droplets 6, making it difficult to obtain the composite particles 10. Specific examples of solvents that can be used include benzene, toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), isophorone, cellosolve acetate, isophorone, Solvesso 100, trichlene, hexane, chloroform, dichloromethane, dichloroethane, isooctane, and nonane.

[0141] The weight ratio of the polymer to be dissolved to the solvent is not particularly limited as long as it can dissolve the polymer. Preferably, the weight of the solvent is 0.005 parts by mass or more and 100 parts by mass or less, more preferably 0.1 parts by mass or more and 80 parts by mass or less, per 100 parts by mass of the polymer.

[0142] A method for obtaining a molten polymer that can be used as a core particle precursor in the second step is, for example, to melt a polymer that is solid at room temperature to form a liquid. Preferably, the molten polymer is mechanically treated with an ultrasonic homogenizer or the like as described above, and then added to a dispersion of fine fibers 3 heated to a temperature at which the polymer can be maintained in a molten state, thereby stabilizing the molten polymer droplets in the dispersion as an O / W emulsion.

[0143] The molten polymer preferably has low solubility in the hydrophilic solvent 7 of the fine fibers 3. If the solubility in the hydrophilic solvent 7 is high, the polymer will easily dissolve from the molten polymer droplet 6 phase into the hydrophilic solvent 7 phase, making emulsification difficult. In addition, the melting point of the molten polymer is preferably 90°C or lower. If the melting point is higher than 90°C, the water in the dispersion of the fine fibers 3 will evaporate, making emulsification difficult.

[0144] Specific examples of polymers used for the molten polymer include pentaerythritol tetrastearate, pentaerythritol distearate, pentaerythritol tristearate, stearyl stearate, batyl stearate, stearyl stearate, myristyl myristate, cetyl palmitate, ethylene glycol distearate, behenyl alcohol, microcrystalline wax, paraffin wax, hydrocarbon wax, fatty acid alkyl ester, polyol fatty acid ester, mixture of fatty acid ester and wax, fatty acid ester Mixture, glycerin monopalmitate ( / stearic acid monoglyceride), glycerin mono-distearate ( / glycerin stearate), glycerin monoacetomonostearate ( / glycerin fatty acid ester), succinic acid fatty acid monoglyceride ( / glycerin fatty acid ester), saturated citric acid fatty acid monoglyceride, sorbitan monostearate, sorbitan fatty acid ester, sorbitan tribehenate, propylene glycol monobehenate ( / propylene glycol fatty acid ester), stearic acid pentaerythritol polymer of adipic acid ester, pentaerythritol tetrastearate, dipentaerythritol hexastearate, stearyl citrate, pentaerythritol fatty acid ester, glycerin fatty acid ester, ultra-light color rosin, rosin-containing diol, ultra-light color rosin metal salt, hydrogenated petroleum resin, rosin ester, hydrogenated rosin ester, special rosin ester, novolac, crystalline poly-α-olefin, polyalkylene glycol, polyalkylene glycol ester, polyoxyalkylene ether, polylactic acid, copolymers of lactic acid with other hydroxycarboxylic acids and other polylactic acids; poly Examples of materials that can be used include dibasic acid polyesters such as butylene succinate, polyethylene succinate, and polybutylene adipate; polycaprolactones such as polycaprolactone and a copolymer of caprolactone and a hydroxycarboxylic acid; polyhydroxybutyrates such as polyhydroxybutyrate and a copolymer of polyhydroxybutyrate and a hydroxycarboxylic acid; aliphatic polyesters such as polyhydroxybutyric acid and a copolymer of polyhydroxybutyric acid and another hydroxycarboxylic acid; polyamino acids; polyester polycarbonates; and natural resins such as rosin.

[0145] The droplets 6 may also contain functional components other than the polymerization initiator. Specific examples include colorants, oil absorbents, light-blocking agents (e.g., UV absorbers, UV scattering agents), antibacterial agents, antioxidants, antiperspirants, antifoaming agents, antistatic agents, binders, bleaching agents, chelating agents, deodorizers, air fresheners, fragrances, anti-dandruff active substances, emollients, insect repellents, preservatives, natural extracts, cosmetic ingredients, pH adjusters, vitamins, amino acids, hormones, oil-based ingredients such as fats and oils and waxes, surfactants, inorganic particles (e.g., titanium oxide, silica, clay), enzymes, etc. When the polymerizable compound already contains functional components other than the polymerization initiator, the functional components can be incorporated into the core particles 2 when the composite particles 10 are formed, enabling the core particles 2 to exhibit functions according to their intended use.

[0146] It is preferable that the functional component is easily dissolved or dispersed in the droplets 6, but is difficult to dissolve or disperse in the hydrophilic solvent 7. By dissolving or dispersing the functional component in the droplets 6, the functional component can be easily encapsulated in the droplets 6 of the emulsion when an O / W emulsion is formed, and composite particles 10 encapsulating the functional component can be efficiently obtained. In addition, the amount of the encapsulated functional component can be increased.

[0147] Furthermore, it is also possible to form droplets 6 using a combination of a polymerizable compound and a dissolved polymer or a molten polymer as the core particle precursor, and then emulsify the droplets 6. Furthermore, when a biodegradable polymer (resin) is selected as the polymer type for the core particle 2 of the composite particle 10, the resulting composite particle 10 will be composed of core particles 2 made of a biodegradable polymer and fine fibers 3, and therefore it is possible to provide composite particles 10 made of a biodegradable material that are highly environmentally friendly.

[0148] (3rd step) This is a step in which the core particle precursor inside the droplets 6 is solidified to obtain a dispersion of composite particles 10 in which the surfaces of core particles 2 are covered with fine fibers 3.

[0149] The method for solidifying the core particle precursor is not particularly limited. When a polymerizable compound is used as the core particle precursor, the core particle precursor can be solidified by polymerizing the polymerizable compound, such as a polymerizable monomer. When a dissolved polymer is used as the core particle precursor, the polymer can be solidified by removing the solvent by diffusing the solvent inside the droplets 6 into a hydrophilic solvent 7 or by evaporating the solvent. When a molten polymer is used as the core particle precursor, the molten polymer can be solidified by cooling and solidifying it.

[0150] For example, the O / W emulsion prepared in the second step, in which droplets 6 containing a polymerizable monomer and a polymerization initiator as core particle precursors are coated with fine fibers 3 and stabilized, is heated while stirring to polymerize the polymerizable monomer and solidify the core particle precursors. The stirring method is not particularly limited, and known methods can be used, specifically, a disperser or a stirrer. Alternatively, only heat treatment without stirring may be performed.

[0151] The temperature conditions during heating can be set appropriately depending on the type of polymerizable monomer and the type of polymerization initiator, but a temperature of 20°C or higher and 150°C or lower is preferred. Temperatures below 20°C are undesirable because the polymerization reaction rate decreases, while temperatures above 150°C are undesirable because the fine fibers 3 may be denatured. The time required for the polymerization reaction can be set appropriately depending on the type of polymerizable monomer and the type of polymerization initiator, but is usually about 1 to 24 hours. The polymerization reaction may also be carried out by irradiation with ultraviolet light, which is a type of electromagnetic wave. In addition to electromagnetic waves, particle beams such as electron beams may also be used.

[0152] Specifically, the solvent (organic solvent) of the dissolved polymer can be evaporated and removed by heating and / or drying under reduced pressure. If the boiling point of the dissolved polymer solvent is lower than that of water, the solvent can be selectively removed. Although not particularly limited, the solvent can be efficiently removed by heating under reduced pressure. The heating temperature is preferably 20°C or higher and 100°C or lower, and the pressure is preferably 600mmHg or higher and 750mmHg or lower.

[0153] Specifically, the method for diffusing the solvent of the dissolved polymer involves adding a solvent or salt to the O / W emulsion to diffuse the solvent inside the droplets 6. As the solvent of the dissolved polymer, which has low solubility in the hydrophilic solvent 7, diffuses into the hydrophilic solvent 7 phase over time, the dissolved polymer precipitates and can be solidified as particles.

[0154] In order to solidify the molten polymer, a method is used in which the O / W emulsion liquid is cooled to solidify the molten polymer.

[0155] Through the above-described steps, composite particles 10 can be produced in which core particles 2 are coated with fine fibers 3. Immediately after the production of the composite particles 10, a large amount of water and free fine fibers 3 that do not contribute to the formation of the coating layer 30 are mixed in the dispersion of the composite particles 10. Therefore, in order to improve the efficiency of forming the conductive layer 4, it is preferable to recover and purify the composite particles 10. As a recovery and purification method, washing by centrifugation or filtration washing is preferable. Furthermore, residual solvent may be removed.

[0156] Known methods can be used for the washing method by centrifugation, and specifically, the composite particles 10 are precipitated by centrifugation, the supernatant is removed, and the composite particles 10 are redispersed in water or a water-methanol mixed solvent, and the procedure is repeated, and finally, the residual solvent is removed from the sediment obtained by centrifugation to recover the composite particles 10. Known methods can also be used for filtration and washing, and for example, suction filtration with water and methanol is repeated using a PTFE membrane filter with a pore size of 0.1 μm, and finally, the residual solvent is further removed from the paste remaining on the membrane filter to recover the composite particles 10.

[0157] If necessary, the composite particles 10 may be washed with an acidic solution such as hydrochloric acid. By washing with an acidic solution, the counter ions of the anionic functional groups can be washed away, converting them to an acid form. If the anionic functional group is a carboxyl group, for example, COO-Na+ can be substituted with COOH. By washing away the counter ions of the anionic functional groups, the particles can more easily adsorb metal ions to be introduced when forming the conductive layer 4.

[0158] The method for removing the residual solvent is not particularly limited, and can be carried out by air drying or heat drying in an oven. The dried solid material containing the composite particles 10 thus obtained is not in the form of a film or aggregates as described above, but is obtained as a fine-textured powder. Furthermore, the drying step may be carried out after carrying out the step of washing the composite particles 10 with an acidic solution as described above.

[0159] (4th step) The fourth step is a step of forming a conductive layer 4 on the fine fibers 3 on the surface of the composite particles 10 in a dispersion of the composite particles 10.

[0160] The method for forming the conductive layer 4 on the fine fibers 3 on the surface of the composite particle 10 is not particularly limited, and known methods can be used. For example, the conductive layer 4 can be formed by dry methods such as vapor deposition, sputtering, mechanochemical methods, and hybridization treatment, wet methods such as electrolytic plating and electroless plating, or a combination of these. The presence of the fine fibers 3 on the surface of the composite particle 10 imparts hydrophilicity to the composite particle 10 and further forms fine irregularities, making it easier to form the conductive layer 4. Furthermore, the core particle 2 and the fine fibers 3 are inseparable, and the adhesion between the fine fibers 3 and the conductive layer 4 is also good, resulting in excellent conductivity. In particular, the electroless plating method can be used to form a conductive layer 4 with fewer defects.

[0161] The following method can be used to form the conductive layer 4 by electroless plating. First, the composite particles 10 are brought into contact with an electroless plating decomposition catalyst solution (catalyst solution) containing metal ions and an acid, and the metal ions are adsorbed onto the fine fibers 3 on the surface of the composite particles 10 to provide a catalyst. Next, it is preferable to bring the catalyzed composite particles 10 into contact with an electroless plating solution containing a metal salt and a reducing agent to form the conductive layer 4 on the surface of the fine fibers 3 of the composite particles 10.

[0162] As described above, when forming the conductive layer 4 on the composite particle 10, it is preferable that anionic functional groups are previously introduced onto the crystal surfaces of the fine fibers 3. When the composite particle 10 having anionic functional groups is brought into contact with the electroless catalyst solution, the catalyst is efficiently imparted by adsorbing metal ions through ionic bonds, and the conductive layer 4 is easily formed on the fine fibers 3 on the surface of the composite particle 10.

[0163] The method for forming the conductive layer 4 on the composite particle 10 using fine fibers 3 having anionic functional groups as the fine fibers 3 is not particularly limited, but for example, there is a method that applies the following steps 4a and 4b. Step 4a) a catalyst imparting step of bringing at least one type of composite particle 10 into contact with a catalyst solution to impart a catalyst; Step 4b) A plating step of contacting the catalyst-applied composite particles 10 with an electroless plating solution to form a conductive layer 4. It has.

[0164] (Step 4a: Catalyst application step) In the method for forming the conductive layer 4 on the composite particles 10, in step 4a, at least one type of catalyst solution is brought into contact with at least one type of composite particles 10. Specifically, a dispersion of at least one type of composite particles 10 is prepared, and a plating catalyst solution containing metal ions and an acid is added to the composite particles 10 and stirred, thereby causing cationic metal ions to be adsorbed onto the anionic functional groups of the fine fibers 3 having anionic functional groups, thereby providing a catalyst.

[0165] The catalyst can be added by adding the composite particles 10 to a catalyst solution and stirring the mixture. After the catalyst is added using the catalyst solution, it is preferable to wash the particles by filtration or the like.

[0166] First, a dispersion of the composite particles 10 is prepared. The solid content concentration of the dispersion of the composite particles 10 is not particularly limited, but is preferably 0.1% by mass or more and 50% by mass or less, and more preferably 0.5% by mass or more and 20% by mass or less. If the solid content concentration of the composite particle dispersion is less than 0.01% by mass, the efficiency of forming the conductive layer 4 on the composite particles 10 decreases. On the other hand, if the solid content concentration of the dispersion of the composite particles 10 exceeds 50% by mass, it becomes difficult to form the conductive layer 4 uniformly.

[0167] The solvent for the catalyst solution is not particularly limited, and water is generally used. The temperature of the dispersion of the composite particles 10 is not particularly limited, but when water is used as the solvent, it is preferably 4°C or higher and 100°C or lower.

[0168] The metal ions may be, for example, palladium ions, silver ions, copper ions, and optionally tin ions, and a solution containing an acid such as hydrochloric acid. Specifically, it is preferable to use a metal salt such as palladium chloride (II), silver nitrate (I), or copper acetate (II). The solvent for the catalyst solution is not particularly limited, but water can be used. The acid is not particularly limited, but hydrochloric acid is preferably used.

[0169] The concentration of metal ions in the catalyst solution is not particularly limited, but is preferably 0.002 mmol / L or more and 100.0 mmol / L or less. In particular, when composite particles 10 having anionic functional groups are used, metal ions are coordinated to the anionic functional groups, so it is preferable to adjust the concentration of metal salts or metal ions to be equal to or greater than the amount of anionic functional groups. If the concentration of metal salts (concentration of metal ions) is lower than the amount of anionic functional groups in composite particles 10, the adsorption rate of metal ions will be low.

[0170] (Process 4b: Plating process) The metal fine particle-supported composite particles 10 obtained in step 4a are subjected to electroless plating to form a conductive layer 4. Specifically, the catalyzed composite particles 10 are brought into contact with an electroless plating solution containing a metal salt, a reducing agent, and a complexing agent, and the conductive layer 4 is formed by electroless plating.

[0171] The solvent for the electroless plating solution is not particularly limited, but water can be used. The pH of the electroless plating solution may be adjusted to improve the dispersibility of the composite particles 10. The pH of the electroless plating solution is preferably pH 2 or higher and pH 14 or lower. Examples of alkaline aqueous solutions used for pH adjustment include organic alkalis such as sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, and benzyltrimethylammonium hydroxide aqueous solution. A sodium hydroxide aqueous solution is preferred from the standpoint of cost, etc.

[0172] Metal salts that can be used include salts of Ru, Sn, Co, Rh, Ni, Pd, Pt, Cu, Ag, Au, and Zn, as well as chlorides, sulfides, iodides, fluorides, and bromides thereof. Examples of metal salts that can be used include silver nitrate, silver chloride, silver oxide, silver sulfate, silver acetate, silver nitrite, silver chlorate, chloroauric acid, sodium chloroaurate, potassium chloroaurate, platinum chloride, platinum oxide, copper chloride, copper acetate, nickel chloride, nickel sulfate, nickel acetate, palladium sulfate, palladium chloride, and tin chloride. These metal salts can be used alone or in combination. The concentration of the metal salt is not particularly limited, but is preferably 0.001 to 5.00 parts by weight, and more preferably 0.01 to 1.0 parts by weight, per 100 parts by weight of the electroless plating solution.

[0173] Examples of reducing agents include low-valent inorganic metal compounds, metal hydrides (metal hydrides), borohydrides, boranes, silanes, phosphites, hypophosphites, ascorbic acids, and oxalates, or their free acids, formaldehyde, hydrazine, and hydrazides. Commonly used reducing agents include sodium borohydride, dimethylamine borane, sodium citrate, ascorbic acid and alkali metal ascorbic acid salts, hydrazine, and formaldehyde. The concentration of the reducing agent is not particularly limited, but is preferably 0.5 to 30 parts by mass per 100 parts by mass of the electroless plating solution.

[0174] The complexing agent may be any known complexing agent, provided that it has a complexing effect on metal ions. Examples of the complexing agent include carboxylic acids and carboxylates such as citric acid, hydroxyacetic acid, tartaric acid, malic acid, lactic acid, and gluconic acid, as well as their alkali metal and ammonium salts; amino acids such as glycine; amino acids such as ethylenediamine and alkylamines; other ammonium salts; EDTA; pyrophosphoric acid; and pyrophosphate salts. These may be used alone or in combination. Among these, it is preferable to use fine fibers 3 having an anionic functional group such as a carboxylic acid or a carboxylate salt. By forming the conductive layer 4 in the fourth step without separating the free fine fibers 3 in the third step, the fine fibers 3 can be used directly as a complexing agent, thereby efficiently forming the conductive layer 4. The concentration of the complexing agent is not particularly limited, but is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5.0 parts by mass, based on 100 parts by mass of the electroless plating solution.

[0175] Since the surface of the composite particles 10 is covered with the fine fibers 3, the composite particles 10 have good dispersibility and do not require a dispersant when forming the conductive layer 4.

[0176] When a dispersant is used, known surfactants or polymers such as anionic surfactants, zwitterionic surfactants, and nonionic surfactants can be used. Cationic surfactants are not preferred because they may adsorb to the anionic functional groups of the fine fibers 3. Examples of zwitterionic surfactants include betaine-based surfactants such as alkyldimethyl acetate betaine, alkyldimethylcarboxymethyl acetate betaine, and alkyldimethylamino acetate betaine. Examples of nonionic surfactants include polyoxyalkylene ethers such as polyethylene glycol, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether. Examples of water-soluble polymers include polyvinyl alcohol, polyvinylpyrrolidinone, and hydroxyethyl cellulose. Dispersants can be used alone or in combination. The concentration of the dispersant is not particularly limited, but is preferably 0.05 to 5 parts by mass per 100 parts by mass of the electroless plating solution.

[0177] The electroless plating reaction begins when the composite particles 10 are added to the electroless plating solution and ends when hydrogen gas generation is no longer observed. If necessary, electroless plating can be performed by further adding electroless plating solution containing metal salts, reducing agents, etc., to adjust the film thickness. At this time, the composite particles 10 may be washed by filtration or the like before being added again to the electroless plating solution.

[0178] The method for forming the conductive layer 4 on the composite particle 10 by electroless plating is not limited to this method, but preferably includes the above-mentioned steps 4a and 4b, and other steps may be inserted between each step.

[0179] If necessary, protrusions made of at least a portion of a semiconductor or metal, a metal oxide thereof, or the like may be provided on the surface of the conductive layer 4. The semiconductor, metal, and oxide thereof used to form the protrusions are not particularly limited, but examples include metals such as gold, silver, copper, aluminum, iron, platinum, zinc, palladium, ruthenium, iridium, rhodium, osmium, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, metal salts, metal complexes, and alloys thereof, or oxides, double oxides, and silica.

[0180] If necessary, the electroless plating solution may be removed by washing the conductive particles 1 by filtration, centrifugation, etc. Furthermore, an insulating layer may be formed on the conductive particles 1 if necessary.

[0181] The dry powder of the conductive particles 1 of this embodiment can be mixed and dispersed in an adhesive resin such as an ultraviolet curable resin or a monomer to be used as a conductive adhesive. Electronic components can be obtained using this conductive adhesive.

[0182] The conductive adhesive of this embodiment can be used as an anisotropic conductive adhesive that is placed between two substrates each having a conductive base material formed thereon and adheres the conductive base material to establish electrical conductivity by applying heat and pressure. The anisotropic conductive adhesive includes conductive particles 1 and an adhesive resin. The adhesive resin is not particularly limited as long as it is insulating and can be used as an adhesive. For example, thermoplastic, thermosetting, or ultraviolet-curable resins or monomers can be used as the adhesive resin. For example, ethylene-vinyl acetate copolymer, carboxyl-modified ethylene-vinyl acetate copolymer, ethylene-isobutyl acrylate copolymer, polyamide, polyimide, polyester, polyvinyl ether, polyvinyl butyral, polyurethane, etc. can be used as the adhesive resin.

[0183] The method for dispersing the conductive particles 1 in the adhesive resin is not particularly limited, but the conductive particles 1 can be dispersed in advance in a solvent, then added to the adhesive resin, and stirred using a disperser or a stirrer to disperse the conductive particles 1. The addition rate of the conductive particles 1 is not particularly limited, but is preferably 0.1 parts by mass or more and 50 parts by mass or less, and more preferably 1 part by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the adhesive resin.

[0184] As a method for bonding electronic components using a conductive adhesive containing conductive particles 1, a known method can be used. For example, the conductive adhesive of this embodiment can be applied to the surface of a transparent substrate on which an electrode has been formed using a coating device such as a slit coater, roll coater, spin coater, screen printing method, metal mask printing method, dispenser, or jet dispenser, and the electronic component can be bonded by placing the electronic component on the transparent substrate so that a portion of the electronic component is positioned above the electrode and irradiating ultraviolet-visible light from the transparent substrate side.

[0185] (Effect of conductive particles 1) The conductive particles 1 of this embodiment solve the problem of excess solvent in the fine fibers 3 containing cellulose nanofibers, and provide composite particles 1 having a new type of fine fibers 3 that can be produced by a simple method. In other words, the conductive particles 1 can be handled as a dry solid that does not form aggregates.

[0186] According to the first and second aspects of the present invention, it is possible to provide composite particles 10 coated with fine fibers that are highly safe, highly crystalline, strong, good dispersibility, highly hydrophilic, and have a large specific surface area. By coating the fine fibers 3, the hydrophilicity, specific surface area, and dispersibility are increased, and metal ions are easily adsorbed onto the surface of the composite particles 10, so that it is possible to provide conductive particles 1 having a conductive layer 4 formed thereon efficiently and uniformly with a high density.

[0187] Furthermore, the fine fibers 3 are hydrophilic and form fine irregularities on the surface of the composite particle 10, resulting in good adhesion between the conductive layer 4 and the fine fibers 3. The presence of highly crystalline fine fibers 3 that do not have a glass transition point (Tg) and the formation of a uniform conductive layer 4 on their surfaces makes it possible to provide conductive particles and a conductive adhesive that have good electrical conductivity and can electrically connect opposing wiring patterns by thermocompression bonding, and that can be used stably for a long period of time.

[0188] According to the production method of the second aspect of the present invention, the conductive particles of the first aspect of the present invention can be produced.

[0189] Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to the present embodiment, and design modifications and the like are also included within the scope of the present invention. Furthermore, the components shown in the above-described embodiments can be appropriately combined to form a configuration. For example, the core particle 2 may contain other components in addition to the polymer and functional component. [Example]

[0190] The present invention will be described in detail below based on examples, but the technical scope of the present invention is not limited to these examples. In each example below, "%" indicates mass % (w / w%) unless otherwise specified.

[0191] Example 1 (Step 1: Step of obtaining cellulose nanofiber dispersion) (TEMPO oxidation of wood cellulose) 70 g of softwood kraft pulp was suspended in 3500 g of distilled water, and a solution of 0.7 g of TEMPO and 7 g of sodium bromide dissolved in 350 g of distilled water was added. The suspension was then cooled to 20 °C. 450 g of a 2 mol / L, 1.15 g / mL aqueous solution of sodium hypochlorite was added dropwise to initiate the oxidation reaction. The temperature of the system was maintained at 20 °C, and the pH was maintained at 10 by adding 0.5 N aqueous sodium hydroxide to counteract any decline in pH during the reaction. When the total amount of sodium hydroxide added relative to the weight of cellulose reached 3.0 mmol / g, approximately 100 mL of ethanol was added to terminate the reaction, yielding oxidized pulp (oxidized cellulose). (Washing oxidized cellulose) Thereafter, filtration and washing with distilled water was repeated using a glass filter to recover oxidized pulp (oxidized cellulose).

[0192] (Measurement of carboxyl group content of oxidized cellulose) The oxidized pulp and reoxidized pulp obtained by the TEMPO oxidation were weighed out in an amount of 0.1 g by solid weight, dispersed in water at a concentration of 1%, and hydrochloric acid was added to adjust the pH to 2.5. The amount of carboxyl groups (mmol / g) was then determined by conductometric titration using a 0.5 M aqueous solution of sodium hydroxide.

[0193] (Oxidized cellulose defibration treatment) 0.5 g of the oxidized cellulose obtained by the TEMPO oxidation described above was dispersed in distilled water to a volume of 100 g with an aqueous solution of sodium hydroxide (NaOH) as an alkali, in an amount equivalent to the amount of carboxyl groups. This suspension was then pulverized in a juicer mixer for 30 minutes to obtain a 0.5% aqueous dispersion of cellulose nanofibers. (Evaluation of cellulose nanofibers)

[0194] The carboxyl group content, crystallinity, number-average major axis diameter, light transmittance, and rheology of the obtained oxidized cellulose and cellulose nanofibers were measured and calculated as follows. The evaluation results of the obtained cellulose nanofibers are shown in Table 1, Figures 3 and 4.

[0195] (Measurement of Carboxy Group Amount) The amount of carboxyl groups in oxidized cellulose before dispersion treatment was calculated using the following method. 0.2 g of oxidized cellulose (equivalent to a dry weight) was placed in a beaker and 80 mL of ion-exchanged water was added. 5 mL of 0.01 mol / L aqueous sodium chloride solution was added, and while stirring, 0.1 mol / L hydrochloric acid was added to adjust the overall pH to 2.8. Using an automatic titrator (product name: AUT-701, manufactured by DKK-TOA Corporation), 0.1 mol / L aqueous sodium hydroxide solution was injected at a rate of 0.05 mL per 30 seconds. The conductivity and pH were measured every 30 seconds, and measurements were continued until the pH reached 11. The titration amount of sodium hydroxide was determined from the resulting conductivity curve, and the carboxyl group content was calculated.

[0196] (Calculation of crystallinity) The crystallinity of TEMPO-oxidized cellulose was calculated. The X-ray diffraction pattern of TEMPO-oxidized cellulose was measured using a horizontal sample multipurpose X-ray diffractometer (product name: Ultima III, manufactured by Rigaku) ​​at an X-ray output of 40 kV and 40 mA in the range of 5°≦2θ≦35°. Since the obtained X-ray diffraction pattern is derived from the cellulose type I crystal structure, the crystallinity of TEMPO-oxidized cellulose was calculated using the following formula (2) according to the method shown below. Crystallinity (%)=[(I22.6-I18.5) / I22.6]×100...(2) Here, I22.6 indicates the diffraction intensity of the lattice plane (002 plane) (diffraction angle 2θ=22.6°) in X-ray diffraction, and I18.5 indicates the diffraction intensity of the amorphous portion (diffraction angle 2θ=18.5°).

[0197] (Calculation of the number average diameter of the long axis of cellulose nanofibers) The number-average diameter of the long axis of cellulose nanofibers was calculated using an atomic force microscope. First, a cellulose nanofiber aqueous dispersion was diluted to 0.001% and 20 μL of the dispersion was cast onto a mica plate and air-dried. After drying, the shape of the cellulose nanofibers was observed in DFM mode using an atomic force microscope (product name: AFM5400L, manufactured by Hitachi High-Technologies Corporation). The number-average diameter of the long axis of the cellulose nanofibers was calculated by measuring the long axis diameter (maximum diameter) of 100 fibers from the image observed using the atomic force microscope and averaging the results.

[0198] (Measurement of light transmittance of cellulose nanofiber aqueous dispersion) The light transmittance was measured for a 0.5% by mass aqueous dispersion of cellulose nanofibers. Water was placed in one side of a quartz sample cell as a reference, and the cellulose nanofiber aqueous dispersion was placed in the other side, taking care not to introduce air bubbles. The light transmittance was measured at wavelengths from 220 nm to 800 nm at an optical path length of 1 cm using a spectrophotometer (product name: NRS-1000, manufactured by JASCO Corporation). The measurement results are shown in Figure 3.

[0199] (Rheology measurement) The rheology of a 0.5% by mass dispersion of cellulose nanofiber was measured using a rheometer (product name: AR2000ex, manufactured by TA Instruments) with a cone plate at an inclination angle of 1°. The temperature of the measurement section was adjusted to 25°C, and the rheology was measured at 0.01 s. -1 From the 1000s -1 The shear viscosity of the cellulose nanofiber dispersion was measured, and the results are shown in Figure 4. As is clear from Figure 4, the cellulose nanofiber dispersion exhibited thixotropy.

[0200] The results are shown in Table 1. Regarding the rheology measurement, the results of steady-state viscoelasticity measurement using a rheometer are shown in Figure 4. -1 and 100s -1 The shear viscosity at this time is shown in Table 1.

[0201] [Table 1]

[0202] As is clear from Figure 3, the cellulose nanofiber aqueous dispersion exhibited high transparency in the visible light region. Furthermore, the number-average minor axis diameter of the cellulose nanofibers (TEMPO-oxidized CNF) contained in the cellulose nanofiber aqueous dispersion was 3 nm, and the number-average major axis diameter was 831 nm. Furthermore, as is clear from Figure 4, the cellulose nanofiber dispersion exhibited thixotropy.

[0203] (Second step: Step of preparing an O / W emulsion) Next, 1 g of the polymerization initiator 2,2-azobis-2,4-dimethylvaleronitrile (hereinafter referred to as ADVN) was dissolved in 10 g of the polymerizable monomer divinylbenzene (hereinafter referred to as DVB). When the entire amount of the prepared polymerizable monomer mixture was added to 40 g of the cellulose nanofiber dispersion, the polymerizable monomer mixture and the cellulose nanofiber dispersion each separated into two phases.

[0204] Next, the shaft of an ultrasonic homogenizer was inserted into the liquid surface of the upper phase of the mixture that had separated into two phases, and ultrasonic homogenization was performed for 3 minutes at a frequency of 24 kHz and an output of 400 W. The appearance of the mixture after ultrasonic homogenization was a cloudy emulsion. When a drop of the mixture was placed on a slide glass, sealed with a cover glass, and observed under an optical microscope, countless emulsion droplets of about several μm in size were generated, and it was confirmed that the dispersion was stabilized as an O / W emulsion.

[0205] (Third step: solidifying the core particle precursor) The O / W emulsion dispersion was placed in a water bath at 70°C and stirred with a stirrer for 8 hours to carry out the polymerization reaction. After 8 hours of treatment, the dispersion was cooled to room temperature. There was no change in the appearance of the dispersion before and after the polymerization reaction.

[0206] (Washing and drying process) The resulting dispersion was centrifuged at 75,000 g for 5 minutes to obtain a precipitate. The supernatant was removed by decantation to collect the precipitate, which was then washed twice with pure water and twice with methanol using a PTFE membrane filter with a pore size of 0.1 μm.

[0207] The purified and recovered material was redispersed at a concentration of 1%, and the particle size was evaluated using a particle size analyzer (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.). The purified and recovered material was then air-dried and further vacuum-dried at room temperature (25°C) for 24 hours, yielding a fine-textured white dry powder (composite particles).

[0208] (Shape observation using a scanning electron microscope) The obtained dried powder was observed with a scanning electron microscope (SEM). The SEM image is shown in Figure 5. It was confirmed that the polymerization reaction was carried out using the O / W emulsion droplets as a template, resulting in the formation of countless spherical particles derived from the shape of the emulsion droplets. Furthermore, it was confirmed that their surfaces were uniformly coated with cellulose nanofibers several nanometers wide. Despite repeated filtration and washing, the particle surfaces were uniformly coated with cellulose nanofibers, indicating that the core particles and cellulose nanofibers were bonded and inseparable.

[0209] (Evaluation of dispersibility) The dried powder was added to pure water at a concentration of 1% by mass and redispersed by stirring with a stirrer for 24 hours. The powder redispersed easily, with no visible aggregation. Furthermore, when the particle size was evaluated using a particle size analyzer, the average particle size was found to be similar to that before drying, and the particle size analyzer data showed no signals indicating aggregation. These results demonstrate that, despite the surface of composite particle 10 being coated with cellulose nanofibers, it can be obtained as a powder without forming a film upon drying, and that it also has good redispersibility.

[0210] (4th step: conductive layer 4 formation step)

[0211] (Step 4a: Catalyst application step) The composite particles 10 obtained through the first, second, and third steps, and the washing and drying steps were dispersed at 1% in an electroless plating catalyst solution containing 0.1 g / L of palladium chloride and 1 ml / L of concentrated hydrochloric acid, and the dispersion was stirred with a stirrer at 25° C. for 1 hour to apply the catalyst. At this time, the particles were dispersed in the catalyst solution without agglomeration.

[0212] (Cleaning process) The mixture was washed four times with pure water using a PTFE membrane filter with a pore size of 0.1 μm.

[0213] (Step 4b: Conductive layer 4 formation step) An electroless nickel plating solution (nickel sulfate 25 g / L, sodium hypophosphite 20 g / L, sodium acetate 10 g / L, sodium citrate 10 g / L) was heated to 70°C, and the composite particles 10 to which the catalyst had been applied in step 4a were immersed to react, and the particles were then recovered.

[0214] <Example 2> Conductive particles 1 were produced under the same conditions as in Example 1, except that in the first step, a carboxymethylated CNF dispersion obtained by performing a carboxymethylation (hereinafter also referred to as CM) treatment according to Patent Document 2, cited as a prior art document, was used instead of TEMPO oxidation. The crystallinity of the carboxylated CNF was over 50%.

[0215] Example 3 Conductive particles 1 were produced under the same conditions as in Example 1, except that in the first step, a phosphated CNF dispersion obtained by performing a phosphate esterification treatment according to Non-Patent Document 1, cited as a prior art document, was used instead of TEMPO oxidation. The crystallinity of the phosphated CNF was 50% or more.

[0216] <Examples 4 to 7> The oxidized pulp obtained by TEMPO oxidation in the first step was added to a hydrogen chloride aqueous solution adjusted to pH 2, dehydrated, and then washed with water for the first acid treatment. Next, the pulp was added to a hydrogen chloride aqueous solution adjusted to pH 3, dehydrated, and then washed with water for the second acid treatment. After that, washing and dehydration were repeated to obtain refined oxidized pulp.

[0217] After the TEMPO oxidation reaction, the oxidized pulp (before acid treatment) was washed with distilled water, and the oxidized pulp (after acid treatment) was acid-treated with a hydrogen chloride aqueous solution and then washed with water. The oxidized pulp was sandwiched between glass slides and dried at 70°C for 3 hours. FT-IR measurements were performed using the ATR method (JASCO Corporation, FT / IR-6300). The oxidized pulp after acid treatment had a peak at 1720 cm originating from the COOH group. -1 While a peak around 1600 cm attributable to COO- was observed before acid treatment, -1 The peak around this point disappears. From the above, it was confirmed that the COO- groups (Na type) of the oxidized pulp were completely replaced by COOH groups (H type) through acid treatment.

[0218] Water was added to the oxidized pulp to prepare a suspension with a solids concentration of 5%, and 1.0 equivalent of tetrabutylammonium hydroxide (TBAH) was added as an alkaline species relative to the carboxyl groups of the oxidized pulp. The mixture was stirred for 1 hour using a stirrer, yielding oxidized pulp with tetrabutylammonium (TBA) ions introduced by counterion substitution.

[0219] In the second step, the following monomers and oligomers were used as core particle precursors instead of divinylbenzene (DVB). Otherwise, conductive particles 1 according to Examples 4 to 7 were produced using the same procedures as in Example 1. Example 4 Monofunctional Acrylate Isobornyl Methacrylate (IB-X) Example 5 Monofunctional Acrylate Isobornyl Acrylate (IB-XA) Example 6 Monofunctional vinyl monomer p-methylstyrene (p-MeSt) Example 7 Difunctional Urethane Acrylate Oligomer (UA4200)

[0220] Example 8 (Step 1: Step of obtaining cellulose nanofiber dispersion) A cellulose nanofiber dispersion was obtained under the same conditions as in Example 4.

[0221] (Second step: Step of preparing an O / W emulsion) Next, 10 g of poly-ε-caprolactone (PCL, manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 200 g of ethyl acetate to prepare a dissolved polymer.

[0222] When the entire amount of dissolved polymer was added to 500 g of a 0.5 mass % cellulose nanofiber dispersion, the dissolved polymer and the cellulose nanofiber dispersion each separated into two phases.

[0223] Next, the upper liquid surface of the mixed liquid in the two-phase separated state was subjected to ultrasonic homogenization using an ultrasonic homogenizer in the same manner as in the second step of Example 1. An optical microscope confirmed that countless emulsion droplets of about 1 to several tens of μm were produced, and that the emulsion was dispersed and stabilized as an O / W emulsion.

[0224] (Third step: solidifying the core particle precursor) The O / W emulsion was dried under reduced pressure of 700 mgHg at 40°C for 3 hours to completely volatilize the ethyl acetate. There was no change in the appearance of the dispersion before and after the ethyl acetate was evaporated.

[0225] The obtained dispersion was separated and purified under the same conditions as in Example 1 to obtain spherical composite particles 10 having a particle size of about 1 to several tens of μm. The collected material was dried under the same conditions as in Example 1 to obtain a white, fine-textured dry powder.

[0226] (4th step: conductive layer 4 formation step) Conductive particles 1 were obtained under the same conditions as in the fourth step of Example 1.

[0227] <Example 1-2> Conductive particles 1 were produced under the same conditions as in Example 1, except that in step 4b, a mixture of electroless copper plating solution (copper sulfate 10 g / L, formalin 20 ml / L, sodium hydroxide 10 g / L, EDTA4Na 25 g / L) was used instead of the electroless nickel plating solution.

[0228] <Examples 1-3> Conductive particles 1 were produced under the same conditions as in Example 1, except that tin chloride was used instead of nickel sulfate in step 4b.

[0229] <Comparative Example 1> The experiment was carried out under the same conditions as in Example 1, except that pure water was used instead of the TEMPO-oxidized CNF dispersion.

[0230] <Comparative Example 2> The experiment was carried out under the same conditions as in Example 1, except that an aqueous polyvinyl alcohol (PVA) solution was used instead of the TEMPO-oxidized CNF dispersion.

[0231] <Comparative Example 3> The experiment was carried out under the same conditions as in Example 1, except that an aqueous solution of carboxymethyl cellulose (hereinafter also referred to as CMC) was used instead of the TEMPO-oxidized CNF dispersion.

[0232] <Comparative Example 4> The experiment was carried out under the same conditions as in Example 4, except that a CMC aqueous dispersion was used instead of the TEMPO-oxidized CNF dispersion.

[0233] <Comparative Example 5> The experiment was carried out under the same conditions as in Example 5, except that a CMC aqueous dispersion was used instead of the TEMPO-oxidized CNF dispersion.

[0234] <Comparative Example 6> The experiment was carried out under the same conditions as in Example 6, except that a CMC aqueous dispersion was used instead of the TEMPO-oxidized CNF dispersion.

[0235] <Comparative Example 7> The experiment was carried out under the same conditions as in Example 7, except that a CMC aqueous dispersion was used instead of the TEMPO-oxidized CNF dispersion.

[0236] <Comparative Example 8> The experiment was carried out under the same conditions as in Example 8, except that a CMC aqueous dispersion was used instead of the TEMPO-oxidized CNF dispersion.

[0237] <Comparative Example 9> Various evaluations were carried out in the same manner as in Example 1 for a dry powder mixture (conventional polymer particles) of commercially available styrene-divinylbenzene copolymer microbeads (particle diameter 4.5 μm, Techno Chemical) and spherical silver microparticles (particle diameter 10 nm, Sigma-Aldrich).

[0238] <Evaluation method>

[0239] (Evaluation of whether composite particles can be generated) Whether composite particles were formed or not was judged by observing the shape using a scanning electron microscope. The obtained dry powder was observed using a scanning electron microscope. Whether composite particles were formed or not was judged according to the following criteria. ○: Spherical particles were obtained, the maximum particle diameter was 1000 μm or less, and the surface of the particles was coated with cellulose nanofibers. ×: Does not meet the above criteria.

[0240] (Evaluation of dispersibility) The dry powder was added to pure water at a concentration of 1% by mass, stirred with a stirrer for 24 hours to disperse it, and visually inspected for the presence of agglomerations. ◯: No aggregates were visually observed. ×: Aggregates were visually observed. It was judged as such.

[0241] (Crushing strength evaluation) Using a 20μm flat compression terminal in a micro-compression testing machine MCT-510, particles were scattered on the sample stage, and a compression test was carried out with N=10 under the conditions of a maximum test force of 19.6mN and a loading speed of 0.2231mN / s, and the average value of the crushing strength was calculated. The following formula was used to calculate the crushing strength. Crushing strength σ = α × P / (π d 2 ) where: σ: Crushing strength (Pa) α: coefficient P: Crushing test force (N) d: particle diameter (m) is. In addition, the value "2.8" was adopted as the position where the value of α is maximum. The evaluation was carried out according to the following criteria. ◯: The crushing strength was 200 MPa or more. ×: The crushing strength was less than 200 MPa, or the sample did not crush. It was judged as such.

[0242] (10% displacement strength evaluation) Using a 20μm flat compression terminal in the MCT-510 microcompression tester, particles were scattered on the sample stage and compression tests were performed under conditions of a maximum test force of 19.6mN and a loading rate of 0.2231mN / s. Tests were performed with N=10, and the average value of the 10% displacement strength was calculated. The 10% displacement strength was calculated using the same formula as for the crushing test, and is the strength at the point where the particle size has been displaced by 10%. ○: 10% displacement strength was 5 MPa or more. ×: 10% displacement strength was lower than 5 MPa. It was judged as such.

[0243] (Affinity with catalyst liquid) The dry powder was dispersed at 1% in an electroless plating catalyst solution containing 0.1 g / L palladium chloride and 1 ml / L concentrated hydrochloric acid, and the dispersion was stirred at 25°C for 1 hour using a stirrer, and the presence of agglomeration was confirmed visually. ◯: No aggregates were visually observed. ×: Aggregates were visually observed. It was judged as such.

[0244] (Uniformity of conductive layer) The average thickness of the conductive layer was determined by cutting the particles, which had been fixed in an embedding resin, with a microtome and observing them under a scanning electron microscope. The thickness of the conductive layer in the cross-sectional image of the particle in the image was measured at 100 random points on the image, and the coefficient of variation was calculated from the standard deviation and average value using the formula "coefficient of variation = standard deviation / average value". ○: The coefficient of variation was 0.4 or less. ×: Greater than 0.4. It was judged as such.

[0245] (Evaluation of conductivity) An insulating adhesive containing 100 parts by weight of epoxy resin JER828 (Mitsubishi Chemical), 30 parts by weight of curing agent Amicure PN23J (Ajinomoto Fine-Techno Co., Ltd.), and 70 parts by weight of toluene was mixed with 15 parts by weight of the particles obtained in the Examples and Comparative Examples to obtain a conductive adhesive. This paste was applied to a silicone-treated polyester film using a bar coater, and then the paste was dried to form a thin film on the film. The resulting thin-film-formed film was placed between a glass substrate entirely coated with aluminum and a polyimide film substrate with a 50 μm-pitch copper pattern to establish an electrical connection. The conductivity of the particles was evaluated at room temperature (25°C, 50% RH) by measuring the conduction resistance between the substrates. A lower resistance value indicates higher particle conductivity. ○: The resistance value was 2Ω or less. ×: Resistance value exceeded 2Ω.

[0246] (Evaluation of connection reliability) The samples used in the conductivity evaluation were subjected to an environment of 121°C, 100% humidity, and 2 atmospheres for 10 hours, after which the connection resistance was evaluated at room temperature (25°C, 50% RH) in the same manner as in the conductivity evaluation. The lower the resistance value, the higher the particle's connection reliability. ○: The resistance value was 10Ω or less. ×: Resistance value exceeded 10Ω. It was judged as such.

[0247] The sample preparation conditions for the above examples and comparative examples are summarized in Table 2. Table 2 shows the stabilizer, counter ions for the carboxyl groups of the cellulose nanofibers, core particle precursors that constitute core particles 2, and metal salts used to adsorb metal ions. The stabilizer column indicates cellulose nanofibers or emulsion stabilizers used in place of cellulose nanofibers.

[0248] [Table 2]

[0249] The evaluation results of the examples and comparative examples are summarized in the following Table 3. Note that the particle production feasibility, dispersibility, 10% displacement strength, and crushing strength in Examples 1-2 and 1-3 are the same as those in Example 1. [Table 3]

[0250] As shown in Examples 1 to 8 in Table 3, it was confirmed that composite particles 10 could be produced in which core particles 2 containing polymers of various monomers or biodegradable polymers were coated with fine fibers 3, regardless of the type of fine fibers (TEMPO-oxidized CNF, carboxymethylated CNF, phosphate-esterified CNF). All of these composite particles 10 had a uniform particle size and a spherical shape. Furthermore, regardless of the type of fine fibers 3 or core particles 2, they had good affinity with catalyst solutions and electroless plating solutions, allowing the formation of a uniform conductive layer 4. Furthermore, regardless of the core particles 2, even when core particles 2 made of highly flexible polymers or polymers with low Tg were used, the presence of fine fibers 3 ensured good affinity with catalyst solutions and electroless plating solutions, allowing the production of conductive particles 1 with excellent conductivity and connection stability.

[0251] In Examples 1-2 and 1-3, the presence of the fine fibers 3 enabled the formation of a uniform conductive layer 4 regardless of the type of metal. In addition, the conductive layer 4 had good affinity with the catalyst solution and the electroless plating solution, and exhibited excellent conductivity and connection stability.

[0252] The conductive particles 1 obtained in Examples 1 to 8, 1-2, and 1-3 could be filtered and washed, and had good redispersibility even after drying.

[0253] On the other hand, in Comparative Examples 1 to 8, no spherical composite particles coated with fine fibers 3 and having a maximum particle size of 1000 μm or less were obtained.

[0254] In Comparative Example 1, spherical composite particles could not be obtained, and irregular lumps exceeding 1000 μm were formed, so that 10% displacement strength evaluation and crushing strength evaluation could not be performed. An attempt was made to form a conductive layer, but the affinity between the fine fibers 3 and the catalyst solution or electroless plating solution was not good, so a uniform conductive layer 4 could not be formed, and the conductivity and connection stability were not good.

[0255] In Comparative Examples 2 to 8, particle size variation was large under all conditions in which PVA or CMC was used as the stabilizer, but spherical particles were not obtained. Due to the strength characteristics of the core particles 2 themselves, Comparative Examples 2, 3, 6, and 8 had sufficient 10% displacement strength and crushing strength, but poor affinity with the catalyst solution or electroless plating solution meant that a uniform conductive layer could not be formed, and the conductivity and connection stability were poor. In Comparative Examples 4, 5, and 7, strength was insufficient and affinity with the catalyst solution or electroless plating solution was poor, so a uniform conductive layer 4 could not be formed, and the conductivity and connection stability were poor.

[0256] Comparative Example 9 showed sufficient strength in the 10% displacement strength evaluation and crushing strength evaluation. However, since the particle dispersibility was not good and the affinity with the plating solution was not good, a uniform conductive layer 4 could not be formed, and the conductivity and connection stability were not good.

[0257] The composite particle 10 of the present invention solves the problem of excess solvent in cellulose nanofibers and provides conductive particles 1 having a new type of fine fibers 3 that can be produced by a simple method. Cellulose nanofibers are composed of cellulose, a biodegradable polymer. Therefore, by also constructing the core particle 2 from a material containing a biodegradable polymer, it is possible to provide composite particles 10 that reduce the burden on the environment and solve the microplastic problem.

[0258] Furthermore, by using the fine fibers 3, stable droplets can be formed without using additives such as surfactants, and therefore spherical composite particles 10 with a narrow particle size distribution can be obtained.

[0259] The fine fibers 3 present on the surface of the composite particle 10 are hydrophilic, have a large specific surface area, and have good dispersibility, so that conductive materials such as metal ions can be efficiently adsorbed onto the surface of the composite particle 10, forming a conductive layer 4 with good conductivity.

[0260] Furthermore, the fine fibers 3 are highly crystalline, have high strength, and do not have a glass transition point. Therefore, regardless of the type of core particles 2, the conductive layer 4 is formed on the surface of the fine fibers 3, which have good dimensional stability even when heated. As a result, it is possible to obtain a conductive adhesive such as an anisotropic conductive adhesive that exhibits good electrical conductivity when heated and pressed and can be used stably for a long period of time, and electronic components using the same. [Explanation of symbols]

[0261] 1. Conductive particles 2. Core particles 3. Fine fibers 4 Conductive layer 6 droplets 7 Hydrophilic solvent 10 Composite particles

Claims

1. A composite particle having a core particle formed of a material containing a polymer and fine fibers containing cellulose nanofibers bonded to the surface of the core particle and inseparably connected thereto; a conductive layer that covers the fine fibers on the surface of the composite particle and contains at least a metal element, The composite particles have a 10% displacement strength of 5 MPa or more in a compression test; Conductive particles, wherein the conductive layer is made of a material containing at least one metal element selected from the group consisting of gold, platinum, silver, copper, iron, zinc, nickel, tin, lead, antimony, bismuth, cobalt, indium, titanium, germanium, aluminum, chromium, palladium, tungsten, and molybdenum.

2. The composite particle according to claim 1 , wherein the composite particle has a crushing strength of 200 MPa or more.

3. The conductive particle according to claim 1 or 2, wherein the conductive layer has a thickness of 0.05 nm or more and 3000 nm or less.

4. The conductive particle according to claim 1 , wherein the cellulose nanofiber has an ionic functional group.

5. The conductive particle according to claim 1 , wherein the polymer includes at least an acrylic polymer, an epoxy polymer, a polyester polymer, an amino polymer, a silicone polymer, a fluorine polymer, or a urethane-isocyanate polymer.

6. The conductive particle according to claim 1 , wherein the polymer comprises a biodegradable polymer.

7. a step of defibrating a cellulose raw material in a solvent to obtain a fine fiber dispersion in which fine fibers including cellulose nanofibers are dispersed; a step of dispersing droplets containing core particle precursors in the fine fiber dispersion and coating the surfaces of the droplets with the fine fibers; solidifying the core particle precursors inside the droplets to obtain a dispersion of composite particles in which the surfaces of core particles are coated with the fine fibers; and forming a conductive layer on the fine fibers on the surfaces of the composite particles by electroless plating in a dispersion of the composite particles.

8. forming a conductive layer on the fine fibers on the surfaces of the composite particles by electroless plating in a dispersion of the composite particles, a catalyst imparting step of imparting a catalyst by bringing the composite particles into contact with a catalyst solution; The method for producing conductive particles according to claim 7 , further comprising a plating step of contacting the composite particles to which the catalyst has been applied in the catalyst application step with an electroless plating solution to form a conductive layer.

9. The method for producing conductive particles according to claim 7 or 8, wherein the core particle precursor is any one of a polymerizable compound, a dissolved polymer, and a molten polymer.

10. the catalytic solution contains at least metal ions selected from palladium ions, silver ions, copper ions, and tin ions; The electroless plating solution may contain silver nitrate, silver chloride, silver oxide, silver sulfate, silver acetate, silver nitrite, silver chlorate, chloroauric acid, sodium chloroaurate, potassium chloroaurate, platinum chloride, platinum oxide, salt 9. The method for producing conductive particles according to claim 8, wherein the metal salt is selected from copper chloride, copper acetate, nickel chloride, nickel sulfate, nickel acetate, palladium sulfate, palladium chloride, and tin chloride.

11. A conductive adhesive comprising the conductive particles according to claim 1 and an adhesive resin.

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