JP6363002B2 - Conductive fine particles - Google Patents

Description

  The present invention relates to conductive fine particles, and particularly relates to conductive fine particles having low electrical resistance and good conductivity.

  2. Description of the Related Art Conventionally, in assembling electronic devices, a connection method using an anisotropic conductive material has been adopted to make electrical connection between a large number of opposing electrodes and wirings. An anisotropic conductive material is a material in which conductive fine particles are dispersed in a binder resin or the like. For example, anisotropic conductive film (ACF), anisotropic conductive paste (ACP), anisotropic conductive ink, anisotropic conductive There are sheets. As the conductive fine particles used for this anisotropic conductive material, those obtained by coating the surface of resin particles as a substrate with a conductive metal layer in addition to metal particles are used. Conductive fine particles composed of resin particles and a metal layer are electrically connected between electrodes and wirings by a conductive metal layer formed on the surface.

  As such conductive fine particles, for example, Patent Document 1 includes a plurality of nickel layers whose main component is nickel, in which a nickel layer containing phosphorus is an inner peripheral side and a nickel layer not containing phosphorus is an outer peripheral side. Conductive fine particles having a conductive layer on the outer periphery of the base fine particles are disclosed. Further, Patent Document 2 discloses conductive fine particles having a metal coating layer containing nickel as a main component and containing boron and phosphorus on the surface of resin fine particles.

Japanese Patent No. 5368611 Japanese Patent No. 4052832

  The technology of Patent Document 2 provides the conductive fine particles with the advantages of each alloy layer, such as excellent adhesion and flexibility to the resin particles of the nickel-phosphorus alloy and high conductivity of the nickel-boron alloy. It is the purpose. However, the conductivity decreases as the content of components other than nickel such as phosphorus and boron increases. In addition, since the alloy layer is inferior in flexibility to the pure nickel layer, there is a problem that the alloy layer breaks when a paste containing conductive particles is inserted between the electrodes and brought into pressure contact.

  The technique of Patent Document 1 uses a nickel layer that has a nickel layer on the outer side to lower the electrical resistance, and also has a nickel layer containing phosphorus with relatively good flexibility on the inner side. Since the flexibility is further improved as compared with Patent Document 2, peeling and damage of the nickel layer on the outer peripheral side are suppressed even when a compressive load is applied to the conductive fine particles, and the nickel layer inherently has low electrical resistance. Can be maintained. However, the conductive fine particles used for electrical connection between the electrodes are also required to have a hardness that can penetrate into the oxide layer on the electrode surface, and the technique of Patent Document 1 is further applied to the surface of the soft nickel-phosphorus layer. Since the soft nickel layer is provided, the hardness of the conductive metal layer is relatively low, the biting into the electrode may be insufficient, and the conductivity may be lowered.

  The present invention has been made paying attention to the above-described circumstances, and its purpose is to prevent the conductive metal layer from cracking during pressure connection when the surface is made of a pure nickel layer and the electrical resistance is lowered. An object of the present invention is to provide conductive fine particles that can not only prevent but also improve the biting into the electrode oxide layer, and an anisotropic conductive material using the conductive fine particles.

The conductive fine particles of the present invention that have solved the above problems have base particles and a conductive metal layer that covers the surface of the base particles,
The conductive metal layer is characterized in that it has a boron-containing nickel layer and a pure nickel layer in this order on the substrate particles.

The boron content in the boron-containing nickel layer is preferably 0.1% by mass or more and 5.0% by mass or less. Further, the base particle is obtained by polymerizing a monomer composition in which the ratio of the crosslinkable monomer in all monomers constituting the base particle is 1% by mass or more and 100% by mass or less. It is preferable that
The present invention also includes an anisotropic conductive material containing the conductive fine particles.

  The conductive fine particles of the present invention having a boron-containing nickel layer and a pure nickel layer in this order on the substrate particle as a conductive metal layer covering the surface of the substrate particle have low surface resistance and are pressurized. As a result of being able to ensure the bite into the electrode while suppressing cracking and peeling of the conductive metal layer at the time of connection, it has low electrical resistance and high conductivity. Therefore, the conductive fine particles of the present invention are extremely useful for anisotropic conductive materials such as anisotropic conductive films, anisotropic conductive pastes, anisotropic conductive adhesives, and anisotropic conductive inks.

FIG. 1 is a schematic cross-sectional view showing an embodiment of the conductive fine particles of the present invention. FIG. 2 is a scanning electron microscope (SEM) image of a cross section of the conductive fine particles produced in Example 1. 3 is a scanning electron microscope (SEM) image of a cross section of the conductive fine particles produced in Comparative Example 1. FIG.

1. Conductive fine particles The conductive fine particles of the present invention have substrate particles and a conductive metal layer covering the surface of the substrate particles, and the conductive metal layer is formed on the substrate particles with boron-containing nickel. It has the characteristic in having a layer and a pure nickel layer in this order.

  As a result of intensive studies to solve the above problems, the inventors of the present invention not only contributes to improving the conductivity by lowering the surface resistance of the particles by forming a pure nickel layer on the upper layer, It has been found that the pure nickel layer also has a function of highly preventing cracking of the lower metal layer. That is, Patent Document 2 teaches that while a nickel layer is formed on the upper side, the lower layer also needs to be a Ni-P layer in order to ensure flexibility for compression followability. If the upper layer is a pure nickel layer, the inventors prevent cracking even if the lower layer is not made as flexible as Ni-P (specifically, even if it is a boron-containing nickel layer). I found what I could do. And it discovered that the hardness of an electroconductive metal layer can be raised by making a lower layer into a hard boron containing nickel layer, and the biting property to an electrode oxidation layer can be improved, and completed this invention. According to such a layer structure, in the conductive fine particles having the conductive metal layer mainly composed of nickel, the mechanical and electrical characteristics inherent to nickel can be utilized to the maximum, the electric resistance is low, and the high conductivity. Conductive fine particles can be obtained.

  That is, when a conductive metal layer having a laminated structure in which the boron-containing nickel layer is the lower layer and the pure nickel layer is the upper layer is formed on the surface of the substrate particles, the surface resistance is reduced and the conductive metal layer is As a result of ensuring the bite into the electrode while suppressing the peeling, it was possible to provide conductive fine particles reflecting the electrical characteristics of nickel such as low electrical resistance and high conductivity.

1-1. Conductive metal layer The conductive metal layer in the present invention is a layer having a laminated structure that covers the surface of the substrate particles, and has a boron-containing nickel layer on the substrate particle side and a pure nickel layer on the surface side.
The conductive metal layer of the present invention may have a metal or alloy layer (preferably a gold layer) other than the boron-containing nickel layer and the pure nickel layer, and the metal or alloy layer (other metal layer) is It is preferably formed on the surface of the pure nickel layer, but preferably has no other metal layer. Nickel is inexpensive and readily available and can be easily plated. Therefore, it is possible to provide the conductive fine particles of the present invention at low cost by forming a conductive metal layer with a metal layer mainly composed of nickel. . Further, since the pure metal layer has a lower electrical resistance than the alloy layer, high conductivity can be realized by making the outermost surface of the conductive fine particles a pure nickel layer.
The thickness of the conductive metal layer is preferably 0.01 μm or more, more preferably 0.02 μm or more, further preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less, Preferably it is 0.3 micrometer or less.
First, the boron-containing nickel layer will be described.

1-1-1. Boron-containing nickel layer The boron-containing nickel layer contains nickel and boron as essential constituent elements. Specifically, the metal layer is preferably a metal layer mainly composed of nickel, and the metal layer preferably contains a nickel-boron alloy, and other elements may be added as necessary within a range not impairing the effects of the present invention. It can be included. By providing a boron-containing nickel layer between the base particle and the pure nickel layer, for example, when forming the pure nickel layer by an electroless plating method, it is possible to suppress aggregation of conductive fine particles, resulting in a resistance value. Can also be suppressed. Further, since the resistance value of the boron-containing nickel layer is lower than that in the case where the nickel layer contains phosphorus, even if the boron-containing nickel layer is exposed on the surface of the conductive fine particles, the resistance does not easily increase and stable electrical connection is achieved. There is also an advantage that it is easy to maintain.

  The content (purity) of nickel constituting the boron-containing nickel layer is, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more in the boron-containing nickel layer. The higher the nickel content (purity), the better the conductivity of the conductive fine particles. However, if the nickel content (purity) is too high, aggregated particles tend to be generated when the boron-containing nickel layer is formed. Therefore, the nickel content (purity) is preferably less than 99.5% by mass. More preferably, it is 99 mass% or less, More preferably, it is 98.5 mass% or less, More preferably, it is 98 mass% or less.

  The boron content of the boron-containing nickel layer according to the present invention is preferably 0.1% by mass or more in the boron-containing nickel layer. If the boron content is too low, the base material particles may aggregate when forming the boron-containing nickel layer, and the dispersibility of the conductive fine particles may decrease. On the other hand, if the boron content increases, the boron-containing nickel layer Since the hardness of the electrode can be increased, the biting into the electrode can be improved. Therefore, the boron content is more preferably 0.5% by mass or more, further preferably 1% by mass or more, and particularly preferably 2% by mass or more. Moreover, it is preferable that content of boron is 5.0 mass% or less. Since the content of nickel increases as the boron content in the boron-containing nickel layer decreases, the conductivity of the conductive fine particles can be improved. Therefore, the boron content is more preferably 4.5% by mass or less, and further preferably 4% by mass or less.

  Other elements that can be contained in the boron-containing nickel layer are not particularly limited. For example, magnesium, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, copper, zinc, germanium, molybdenum, ruthenium, rhodium Metal elements such as palladium, silver, indium, tin, antimony, tungsten, platinum, gold, lead, and bismuth, and non-metallic elements such as carbon, silicon, and phosphorus. Among these metal or nonmetal elements, titanium, chromium, cobalt, copper, molybdenum, tin, tungsten, and phosphorus are more preferable. The content of other metal elements is preferably less than 20% by mass in the boron-containing nickel layer, more preferably 15% by mass or less, still more preferably 10% by mass or less, still more preferably 1% by mass or less, and particularly preferably. It is 0.1 mass% or less. In addition, the inner metal element of these other elements is an element to be contained in another metal layer (for example, a mode in which the surface of the pure nickel layer is plated with gold or the like) formed on the surface of the boron-containing nickel layer. Can also be used.

  The boron-containing nickel layer preferably has a granular structure. The granular structure may be spherical, spheroid, confetti or the like. The granular structure preferably has a major axis of 1 nm or more and 100 nm or less. More preferably, it is 3 nm or more, More preferably, it is 5 nm or more, It is more preferable that it is 50 nm or less, More preferably, it is 30 nm or less. The major axis of the granular structure in the present invention means a value measured by the method described in the examples.

  The thickness of the boron-containing nickel layer is preferably 0.005 μm or more, more preferably 0.01 μm or more, further preferably 0.03 μm or more, preferably 0.50 μm or less, more preferably 0.3 μm or less, Preferably it is 0.15 μm or less. If the thickness of the boron-containing nickel layer is within the above range, an appropriate hardness can be imparted to the conductive fine particles without impairing conductivity, and boron content when forming a pure nickel layer to be described later Aggregation of nickel layer-coated particles can also be suppressed.

1-1-2. Pure Nickel Layer In the present invention, the pure nickel layer means a layer composed of nickel and inevitable impurities, and substantially does not contain boron or phosphorus. Forming the pure nickel layer is effective not only for reducing the surface resistance of the conductive particles, but also prevents cracking even if the boron-containing nickel layer as the lower layer has low flexibility.

  Examples of the inevitable impurities include impurities derived from the manufacturing process of conductive metal layers such as nitrogen, carbon, sulfur, lead, and bismuth, and additives for plating solutions. In addition, in equipment for forming a pure nickel layer according to the present invention, nickel-boron plating or nickel-phosphorus plating may be applied, and these other components for plating are also mixed into the pure nickel layer as inevitable impurities. There is. Although the content of inevitable impurities is preferably as small as possible, the boron content in the pure nickel layer is preferably less than 0.1% by mass, for example, more preferably 0.05% by mass or less, and still more preferably 0.01% by mass. The phosphorus content is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and still more preferably 0.01% by mass or less. The inevitable impurities preferably have a total content including boron and phosphorus of 0.5% by mass or less, more preferably 0.2% by mass or less, and further preferably 0.1% by mass or less. It is. Of course, an embodiment in which impurities such as nitrogen, carbon, sulfur, lead, and bismuth are not contained in the pure nickel layer is the most preferable embodiment.

  The purity of nickel in the pure nickel layer is, for example, 99.5% by mass or more, preferably 99.8% by mass or more, and more preferably 100% by mass. The higher the nickel content, the better the conductivity of the conductive fine particles. The content of each element contained in the pure nickel layer can be measured by, for example, ICP emission analysis.

  The pure nickel layer may have a needle-like structure on its surface. The acicular structure is formed when nickel purity is high and the layer contains almost no components other than nickel (for example, components other than nickel in the pure nickel layer are 0.5 mass% or less). The needle-like structure includes a needle-like structure with both ends in the length direction sharp, and a structure such as a cone or a polygonal pyramid with only one end in the length direction being sharp.

  The length of the acicular structure is preferably 10 nm or more and 500 nm or less. More preferably, it is 25 nm or more, More preferably, it is 50 nm or more, It is more preferable that it is 400 nm or less, More preferably, it is 300 nm or less. The acicular structure preferably has an aspect ratio (longitudinal direction / width direction) of 0.1 to 5. More preferably, it is 0.5-4, More preferably, it is 1-3. When the pure nickel layer has such a needle-like structure on its surface, it is preferable because the penetration property of the conductive fine particles into the counterpart electrode is further improved. In addition, the length of the longitudinal direction and the width direction of the said acicular structure means the length measured by the method as described in an Example. The acicular structure is generated by using a hydrazine-based reducing agent as a reducing agent when a pure nickel layer is formed by an electroless plating method.

  The pure nickel layer may have the same structure on the surface and inside, or may have a different structure. The pure nickel layer according to the present invention preferably has a granular structure inside. The granular structure may be spherical, spheroid, confetti or the like. The granular structure preferably has a major axis of 1 nm or more and 1000 nm or less. More preferably, it is 10 nm or more, More preferably, it is 20 nm or more, It is more preferable that it is 800 nm or less, More preferably, it is 500 nm or less. As described above, since the boron-containing nickel layer has a granular structure, the presence of the granular structure inside the pure nickel layer makes it difficult for separation to occur at the interface between the boron-containing nickel layer and the pure nickel layer. This is preferable because the impact resistance of the conductive metal layer is improved and the conductivity is hardly lowered. The major axis of the granular structure in the present invention means a value measured by the method described in the examples.

  The surface of the pure nickel layer refers to a region of 10% from the outermost layer when the thickness of the pure nickel layer is 100% when the outermost layer of conductive fine particles is a pure nickel layer, or the conductive fine particles are pure. When having another metal layer on the nickel layer, it means a region of 10% from the interface between the other metal layer and the pure nickel layer toward the base particle side, while the inside of the pure nickel layer is In the pure nickel layer, it refers to a region from the substrate particle side to 90% (the thickness of the pure nickel layer is 100%).

The thickness of the pure nickel layer is preferably 0.005 μm or more, more preferably 0.01 μm or more, still more preferably 0.03 μm or more, and preferably 0.50 μm or less, more preferably 0.8. It is 3 μm or less, more preferably 0.15 μm or less. When the thickness of the layer of pure nickel is within the above range, stable electrical connection can be maintained when the conductive fine particles are used as the anisotropic conductive material. Further, a continuous pure nickel layer can be formed while suppressing aggregation of particles during the formation of the pure nickel layer.
The surface of the pure nickel layer may be subjected to a surface treatment, for example, a surface treatment with a corrosion inhibitor can be performed.

  The ratio of the thickness of the boron-containing nickel layer to the pure nickel layer (boron-containing nickel layer: pure nickel layer) is, for example, preferably 1:99 to 99: 1, more preferably 5:95 to 95: 5. And more preferably 10:90 to 90:10. As the thickness of the pure nickel layer is larger, aggregation tends to occur due to abnormal deposition of plating. On the other hand, if the thickness is too thin, the conductivity of each particle may be non-uniform. Generation | occurrence | production of the said malfunction can be suppressed by making the ratio of the thickness of a boron containing nickel layer and a pure nickel layer into the said range.

1-1-3. Other Metal Layer The conductive fine particles of the present invention may have another metal layer as a component constituting the conductive metal layer in addition to the pure nickel layer and the boron-containing nickel layer. Thereby, the physical properties derived from other metals can be imparted to the conductive fine particles. Examples of other metals include copper, palladium, silver, tin, and gold. Such another metal layer is preferably provided as the outermost layer of the conductive metal layer (that is, the outermost surface of the conductive fine particles) or as the innermost layer of the conductive metal layer (that is, the surface of the base particle).

  The thickness of the other metal layer is preferably 0.001 μm or more, more preferably 0.01 μm or more, further preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less, and still more preferably 0.1 μm or less. By setting the thickness of the other metal layer within the above range, it is possible to impart characteristics derived from the other metal to the conductive fine particles while suppressing an increase in manufacturing cost. Note that the conductive fine particles of the present invention having the above-described structure have low electrical resistance and good conductivity, and therefore may not have another metal layer, and therefore the thickness of the other metal layer is 0 μm. Is preferred.

  The ratio of the thickness (total) of the boron-containing nickel layer and the pure nickel layer to the thickness of the conductive metal layer (boron-containing nickel layer and pure nickel layer / conductive metal layer) is, for example, 0.5 or more Preferably, it is 0.7 or more, more preferably 0.8 or more. The larger the ratio (boron-containing nickel layer and pure nickel layer / conductive metal layer), the more the characteristics inherent in nickel can be utilized while suppressing an increase in manufacturing cost. The upper limit of the ratio is 1.

  The method for measuring the thickness of the conductive metal layer, that is, the thickness (total) of the boron-containing nickel layer, the pure nickel layer, and other optional metal layers is not particularly limited, and various known methods can be employed. it can. For example, a method in which the value obtained by dividing the difference between the number average particle size of the conductive fine particles and the number average particle size of the base particles by 2 is the thickness of the conductive metal layer; the conductive fine particles are cut along the diameter; A method of measuring the thickness of the conductive metal layer by observing the cross section with an electron microscope or the like; the thickness of the conductive metal layer by dissolving the conductive metal layer and analyzing the dissolved metal concentration with an ICP emission analyzer A method for determining the thickness; analyzing the cross section of the conductive fine particles by SEM-EDS (scanning electron microscope / energy dispersive X-ray spectroscopy) or TEM-EDS (transmission electron microscope / energy dispersive X-ray spectroscopy) A method of determining the thickness of each layer by observing the distribution state of elements such as Ni, B, and the like.

1-2. Base Particles The base particles in the present invention are preferably resin particles containing a resin component. By using resin particles, conductive fine particles having excellent elastic deformation characteristics can be obtained. The resin particles are not limited to resin particles composed only of organic materials, but may be resin particles composed of organic-inorganic composite materials.

  Examples of the organic material constituting the resin particles include polyolefins such as polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene, polyisobutylene, and polybutadiene; vinyl heavy resins such as styrene resins, acrylic resins, and styrene-acrylic resins. Polyesters such as polyethylene terephthalate and polyethylene naphthalate; polycarbonates; polyamides; polyimides; phenol formaldehyde resins; melamine formaldehyde resins; melamine benzoguanamine formaldehyde resins; Examples of the organic / inorganic composite material include a silicone resin and a material containing the organic material and a polysiloxane skeleton (for example, a material in which a polysiloxane skeleton and a vinyl polymer are combined). The material which comprises these resin particles may be used independently, and 2 or more types may be used together.

  Among the materials constituting the resin particles, those containing a vinyl polymer and / or a polysiloxane skeleton are preferable. A material containing a vinyl polymer has an organic skeleton formed by polymerizing vinyl groups, and is excellent in elastic deformation during pressure connection. In particular, a vinyl polymer containing divinylbenzene as a polymerization component has little decrease in particle strength after coating with a conductive metal. In addition, the material containing the polysiloxane skeleton has excellent contact pressure with respect to the connected body during pressure connection. In particular, a material in which a polysiloxane skeleton and a vinyl polymer are combined is preferable because it is excellent in elastic deformability and contact pressure, and the connection reliability of the obtained conductive fine particles becomes more excellent.

  The vinyl polymer can be formed by polymerizing a vinyl monomer (vinyl group-containing monomer) (radical polymerization). This vinyl monomer is composed of a vinyl crosslinkable monomer and a vinyl noncrosslinkable. Divided into monomers. The polysiloxane skeleton can be formed by using a silane monomer, and the silane monomer is divided into a silane crosslinkable monomer and a silane noncrosslinkable monomer.

  The “vinyl group” includes not only a carbon-carbon double bond but also a functional group such as (meth) acryloxy group, allyl group, isopropenyl group, vinylphenyl group, isopropenylphenyl group, and polymerizable carbon- Substituents composed of carbon double bonds are also included. In this specification, “(meth) acryloxy group”, “(meth) acrylate” and “(meth) acryl” are “acryloxy group and / or methacryloxy group”, “acrylate and / or methacrylate” and “acryl and / Or methacryl ".

  The ratio of the crosslinkable monomer (for example, the total of the vinyl-based crosslinkable monomer and the silane-based crosslinkable monomer) in the total monomers constituting the resin particles is preferably 1% by mass or more, more preferably. Is 5% by mass or more, more preferably 10% by mass or more. When the ratio of the crosslinkable monomer is within the above range, solvent resistance can be imparted to the obtained conductive fine particles, and for example, when used for ACF formation, swelling and deformation of particles due to the influence of the solvent can be prevented. it can. On the other hand, the upper limit of the ratio of the crosslinkable monomer is not particularly limited, but is preferably 100% by mass or less, more preferably 90% by mass or less, still more preferably 80% by mass or less, and further preferably 70% by mass or less. is there. Moreover, if the usage-amount of a crosslinkable monomer exists in the said range, even after forming the electroconductive metal layer which concerns on this invention, favorable electrode biting property can be ensured.

  When the resin particles are made of an organic-inorganic composite material containing a vinyl polymer and a polysiloxane skeleton, the amount of the vinyl monomer used is preferably 1 part by mass or more with respect to 100 parts by mass of the silane monomer, More preferably, it is 5 mass parts or more, More preferably, it is 10 mass parts or more, 5000 mass parts or less are preferable, More preferably, it is 4000 mass parts or less, More preferably, it is 3000 mass parts or less.

  The vinyl-based crosslinkable monomer has a vinyl group and can form a crosslinked structure, and specifically, a monomer (monomer having two or more vinyl groups in one molecule). (1)), or having one vinyl group and a binding functional group other than a vinyl group in one molecule (a protic hydrogen-containing group such as a carboxyl group or a hydroxy group, or a terminal functional group such as an alkoxy group). A monomer (monomer (2)) is mentioned. However, in order to form a crosslinked structure with the monomer (2), it is necessary to have a counterpart monomer capable of reacting (binding) with the binding functional group of the monomer (2).

  Examples of the monomer (1) (monomer having two or more vinyl groups in one molecule) among the vinyl-based crosslinkable monomers include, for example, allyl (meth) acrylate such as allyl (meth) acrylate. ) Acrylates; alkanediol di (meth) acrylate (for example, ethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9- Nonanediol di (meth) acrylate, 1,10-decanediol di (meth) acrylate, 1,3-butylene di (meth) acrylate, etc.), polyalkylene glycol di (meth) acrylate (for example, diethylene glycol di (meth) acrylate, Triethylene glycol di (meth) acrylate, decaethylene glycol di ( ) Acrylate, pentadecaethylene glycol di (meth) acrylate, pentacontahector ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate Di (meth) acrylates such as trimethylolpropane tri (meth) acrylate; tetra (meth) acrylates such as pentaerythritol tetra (meth) acrylate; dipentaerythritol hexa (meth) ) Hexa (meth) acrylates such as acrylates; aromatic hydrocarbon-based crosslinking agents such as divinylbenzene, divinylnaphthalene, and derivatives thereof (preferably divinylbenzene Ren-based polyfunctional monomer); N, N-divinyl aniline, divinyl ether, divinyl sulfide, hetero atom-containing crosslinking agents such as divinyl sulfonic acid; and the like. Among these, (meth) acrylates (polyfunctional (meth) acrylate) having two or more (meth) acryloyl groups in one molecule and aromatic hydrocarbon crosslinking agents (especially styrene polyfunctional monomers) are included. preferable. Among the (meth) acrylates having two or more (meth) acryloyl groups in one molecule, (meth) acrylates having three or more (meth) acryloyl groups in one molecule are particularly preferable. Among these, acrylates having 3 or more acryloyl groups in one molecule are preferable. Among the styrenic polyfunctional monomers, monomers having two vinyl groups in one molecule such as divinylbenzene are preferable. A monomer (1) may be used independently and may use 2 or more types together.

  Among the vinyl-based crosslinkable monomers, the monomer (2) (monomer having one vinyl group and a binding functional group other than vinyl group in one molecule) is, for example, (meth) Monomers having a carboxyl group such as acrylic acid; hydroxy group-containing (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and 2-hydroxybutyl (meth) acrylate, p -Monomers having hydroxy groups such as hydroxy group-containing styrenes such as hydroxystyrene; alkoxy groups such as 2-methoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-butoxyethyl (meth) acrylate Contains (meth) acrylates and alkoxy groups such as alkoxystyrenes such as p-methoxystyrene That monomer; and the like. A monomer (2) may be used independently and may use 2 or more types together.

  The vinyl-based non-crosslinkable monomer is a monomer having one vinyl group in one molecule (monomer (3)) or the monomer in the case where there is no counterpart monomer (2) (monomer having one vinyl group and a binding functional group other than vinyl group in one molecule).

  Among the vinyl non-crosslinkable monomers, the monomer (3) (monomer having one vinyl group in one molecule) includes (meth) acrylate monofunctional monomers and styrene monofunctional monomers. Monomers are included. Examples of the (meth) acrylate monofunctional monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and pentyl (meth) acrylate. , Hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, 2-ethylhexyl (meth) acrylate Alkyl (meth) acrylates such as: cyclopropyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cyclooctyl (meth) acrylate, cyclo Cycloalkyl (meth) acrylates such as ndecyl (meth) acrylate, cyclododecyl (meth) acrylate, isobornyl (meth) acrylate, 4-t-butylcyclohexyl (meth) acrylate; phenyl (meth) acrylate, benzyl (meth) acrylate And aromatic ring-containing (meth) acrylates such as tolyl (meth) acrylate and phenethyl (meth) acrylate, and alkyl (meth) acrylates such as methyl (meth) acrylate are preferred. Styrene monofunctional monomers include styrene; alkyl styrenes such as o-methyl styrene, m-methyl styrene, p-methyl styrene, α-methyl styrene, pt-butyl styrene, o-chlorostyrene, m-chloro. Examples include halogen group-containing styrenes such as styrene and p-chlorostyrene, and styrene is preferred. A monomer (3) may be used independently and may use 2 or more types together.

  The vinyl monomer preferably includes at least the vinyl crosslinkable monomer (1). Among them, the vinyl crosslinkable monomer (1) and the vinyl noncrosslinkable monomer ( 3) (in particular, a copolymer of the monomer (1) and the monomer (3)) is preferable. Specifically, an embodiment containing a styrene monofunctional monomer as a constituent component, an embodiment containing a styrene monofunctional monomer and a monomer having two or more (meth) acryloyl groups in one molecule, a styrene monofunctional An embodiment containing a monomer and a styrenic polyfunctional monomer is preferred. Among these, an embodiment including a styrene monofunctional monomer and a styrene polyfunctional monomer is preferable.

  The polysiloxane skeleton is formed by hydrolyzing a silane monomer and generating a siloxane bond by a condensation reaction. In particular, when a silane crosslinkable monomer is used as a silane monomer, a crosslinked structure is formed. Can do. Examples of the crosslinked structure formed by the silane-based crosslinking monomer include those that crosslink an organic polymer skeleton (for example, a vinyl polymer skeleton) and an organic polymer skeleton (first form); a polysiloxane skeleton; One that crosslinks a polysiloxane skeleton (second form); one that crosslinks an organic polymer skeleton and a polysiloxane skeleton (third form).

  Examples of the silane-based crosslinkable monomer that can form the first form (crosslinking between organic polymers) include silane compounds having two or more vinyl groups such as dimethyldivinylsilane, methyltrivinylsilane, and tetravinylsilane. Can be mentioned. Examples of the silane crosslinkable monomer that can form the second form (crosslink between polysiloxanes) include tetrafunctional silane single monomers such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, and tetrabutoxysilane. Examples of the polymer include trifunctional silane monomers such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, and ethyltriethoxysilane. Examples of the silane-based crosslinkable monomer that can form the third form (crosslinking between organic polymer and polysiloxane) include 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3- (Meth) acryloyl such as acryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxyethoxypropyltrimethoxysilane Di- or trialkoxysilanes having a group; di- or trialkoxysilanes having a vinyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane; 3-glycidoxypropyltrimethoxysilane, 3 Di- or trialkoxysilanes having an epoxy group such as glycidoxypropyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane; 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, etc. Or a di- or trialkoxysilane having an amino group. These silane crosslinking monomers may be used alone or in combination of two or more.

  Examples of the silane-based non-crosslinkable monomer include bifunctional silane-based monomers such as dimethyldimethoxysilane and dialkylsilane such as dimethyldiethoxysilane; and trialkylsilanes such as trimethylmethoxysilane and trimethylethoxysilane. And monofunctional silane-based monomers. These silane non-crosslinkable monomers may be used alone or in combination of two or more.

  In particular, the polysiloxane skeleton is preferably a skeleton derived from a polymerizable polysiloxane having a radical-polymerizable carbon-carbon double bond (for example, a vinyl group such as a (meth) acryloyl group). That is, the polysiloxane skeleton is a silane crosslinkable monomer (preferably having a (meth) acryloyl group) capable of forming at least the third form (crosslinking between the organic polymer and the polysiloxane) as a constituent component. More preferably, it is a polysiloxane skeleton formed by hydrolysis and condensation of 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, vinyltrimethoxysilane).

  In addition, the composition ratio of each monomer constituting the resin particle is not particularly limited, and depends on characteristics (for example, hardness, recovery rate during compression, heat resistance, etc.) required for the base particle, What is necessary is just to set suitably.

  As the method for producing the resin particles, emulsion polymerization, suspension polymerization, dispersion polymerization, seed polymerization, sol-gel seed polymerization method and the like can be adopted, but seed polymerization and sol-gel seed polymerization method are preferable because the particle size distribution can be reduced. . The sol-gel seed polymerization method is an embodiment of seed polymerization, and particularly means that seed particles are synthesized by the sol-gel method. For example, the case where polysiloxane obtained by the hydrolysis condensation reaction of alkoxysilane is used as seed particles can be used. Therefore, the seed polymerization includes a case where the seed particles are made of an organic material and a case where the seed particles are made of a material in which an organic material and an inorganic material are combined (in the case of a sol-gel seed polymerization method). For example, in the case where the resin particles have a vinyl polymer skeleton and a polysiloxane skeleton, the production method thereof is to polymerize a crosslinkable silane monomer having a radical polymerizable group by hydrolysis and condensation reaction. After preparing the polysiloxane particles, a method of polymerizing the polymerizable polysiloxane particles by absorbing the vinyl monomer and the like is preferably employed.

  The substrate particles preferably have a hydrophilic surface. If the surface is hydrophilic, the wettability to the electroless plating solution described later is high, and a conductive metal layer can be uniformly formed on the surface of the substrate particles. Moreover, when the micro unevenness | corrugation is formed in the resin particle surface by the hydrophilization process, the effect that the adhesiveness of a base particle and an electroconductive metal layer improves further by the anchor effect of the unevenness | corrugation is also acquired.

  The substrate particles having a hydrophilic surface can be obtained by subjecting the above-described resin particles to a hydrophilic treatment. The method of the hydrophilization treatment is not particularly limited, and a conventionally known method can be adopted. For example, oxidizer such as chromic acid, chromic anhydride-sulfuric acid mixed solution, permanganic acid; hydrochloric acid, sulfuric acid, hydrofluoric acid, nitric acid, etc. A strong alkaline solution such as sodium hydroxide or potassium hydroxide; a method using various other commercially available hydrophilizing agents (etching agents), and gas phase treatment such as ozone gas treatment.

  The shape of the substrate particles (resin particles) is not particularly limited, and may be any of spherical, spheroid, scalloped, thin plate, needle, eyebrows, etc., and is preferably spherical. A true spherical shape is particularly preferable. Further, the properties of the surface of the substrate particles are not particularly limited, and may be smooth or may have protruding protrusions.

  The number average particle size of the substrate particles (resin particles) means an average particle size determined from a number-based particle size distribution, preferably 1.0 μm or more, more preferably 1.1 μm or more, and even more preferably 1. .2 μm or more, more preferably 1.3 μm or more, preferably 50 μm or less, more preferably 30 μm or less, still more preferably 25 μm or less, and even more preferably 20 μm or less. The coefficient of variation (CV value) of the particle size of the substrate particles is a value determined from the number-based particle size distribution, preferably 10.0% or less, more preferably 8.0% or less, and even more preferably 5 0.0% or less, more preferably 4.5% or less, and particularly preferably 4.0% or less. The number average particle diameter and the coefficient of variation of the particle diameter of the substrate particles can be measured by the same method as the number average particle diameter and the coefficient of variation of the conductive fine particles, and specifically, a method described later in Examples. Can be measured.

As described above, the conductive fine particles of the present invention include a boron-containing nickel layer having a relatively high hardness in the conductive metal layer, but the outermost layer is composed of a flexible pure nickel layer. Therefore, it is desirable that the base material particles have a specific hardness from the viewpoint of ensuring the bite into the electrode.
In addition, since the deformation amount at the time of pressure connection tends to decrease as the particle diameter of the base material particle decreases, from the viewpoint of suppressing the connection resistance value when the conductive fine particle is used, the particle diameter of the base material particle is There is a suitable hardness depending on For example, number average particle diameter of the base particles are of less than 10 [mu] m, the compression modulus when the diameter is displaced 20% (20% K value) is 1000 N / mm ² or more and 15000 N / mm ² or less Is preferred. More preferably 1500 N / mm ² or more and 12000N / mm ² or less, more preferably 2000N / mm ² or more and 10000 N / mm ² or less. On the other hand, if the number average particle size of the substrate particles is more than 10 [mu] m, the 20% K value is 500 N / mm ² or more, preferably 10000 N / mm ² or less. More preferably 750 N / mm ² or more and 9000 N / mm ² or less, more preferably 1000 N / mm ² or more and 8000 N / mm ² or less. When the 20% K value is in the above range, it is easy to ensure the biting into the electrode, and a good contact area with the electrode can be obtained. In addition, the conductive fine particles are likely to be moderately hard, and as a result, they are not easily deformed when dispersed in a binder resin or the like, and it is easy to ensure connection with electrodes and the like. On the other hand, as the 20% K value is smaller, the deformation is appropriately performed according to the compressive stress, and a sufficient contact area between the electrode and the conductive fine particles can be secured, so that an increase in the connection resistance value can be further suppressed.

  Specifically, the 20% K value is constant in the direction of the center of the particle using a circular plate indenter (material: diamond) having a diameter of 50 μm for one sample particle spread on the sample table (material: SKS flat plate). And a load speed of 2.65 mN / sec (0.27 gf / sec). Then, the compression load (N) and the amount of compression displacement (mm) when the particle is deformed until the particle diameter is displaced by 20% are measured, and the 20% K value is calculated based on the following formula. The 20% K value is preferably measured, for example, by measuring about 10 points for the same type of substrate particles (or conductive fine particles). The ambient temperature at the time of measurement is 25 ° C.

(In the formula, E is the compressive elastic modulus (N / mm ² ), F is the compressive load (N), S is the amount of compressive displacement (mm), and R is the radius (mm) of the sample particles)

1-3. Conductive fine particles The conductive fine particles of the present invention preferably have an average particle size (number average particle size) of 1.0 μm or more, more preferably 1.1 μm or more, and still more preferably obtained from a number-based particle size distribution. It is 1.2 μm or more, more preferably 1.3 μm or more, particularly preferably 1.4 μm or more, preferably 50 μm or less, more preferably 30 μm or less, still more preferably 25 μm or less, and still more preferably 20 μm or less. The conductive fine particles of the present invention preferably have a particle size variation coefficient (CV value) determined from the number-based particle size distribution of 10.0% or less, more preferably 8.0% or less, and even more preferably. Is 5.0% or less, more preferably 4.5% or less, and particularly preferably 4.0% or less. The “number average particle size” and the “particle size variation coefficient” in the present invention are precision particle size distribution measuring devices using the Coulter principle (for example, trade name “Coulter Multisizer III type”, manufactured by Beckman Coulter, Inc.). The value measured by The coefficient of variation of the particle diameter is a value calculated according to the following formula.
Variation coefficient of particle diameter (%) = 100 × (standard deviation of particle diameter / number-based average particle diameter)
Specifically, the number average particle diameter and variation coefficient of the conductive fine particles can be measured by, for example, a method described later in Examples.

Conductive fine particles of the present invention, the compression modulus when the diameter of the particles is displaced 20% (20% K value) is 1000 N / mm ² or more, it is preferable that 20000N / mm ² or less. When the 20% K value is in the above range, a good contact area with the electrode can be obtained. The 20% K value is more preferably 1500 N / mm ² or more, and still more preferably 2000 N / mm ² or more. When the 20% K value is in the above range, the conductive fine particles are reasonably hard, so that they are not easily deformed even when dispersed in a binder resin or the like, and it is easy to ensure a connection with an electrode or the like. Further, more preferably 18000N / mm ^2, more preferably not more than 15000 N / mm ^2. The smaller the 20% K value, the more moderately deforms according to the compressive stress, and the sufficient contact area between the electrode and the conductive fine particles can be secured, so that the increase in the connection resistance value can be further suppressed.

  The compressive fracture deformation ratio (displacement of particle diameter at the time of fracture) of the conductive fine particles of the present invention is not particularly limited, but is generally 30% or more, and the higher the deformation ratio, the more conductive the conductive metal layer becomes the connection resistance value. In view of notably affecting the above, it is preferably 40% or more, more preferably 50% or more, still more preferably 53% or more, and particularly preferably 55% or more. The upper limit of the compression fracture deformation rate is not particularly limited, but is generally 80% or less, and more preferably 75% or less.

  The conductive fine particles of the present invention have good dispersibility in binder resins such as epoxy resins, acrylic resins and urethane resins.

2. Production Method of Conductive Fine Particles The conductive fine particles of the present invention can be produced by first forming a boron-containing nickel layer and then forming a pure nickel layer on the surface of the substrate particles by electroless plating. According to the electroless plating method, a conductive metal layer can be easily formed without requiring a large-scale apparatus, and the conductive fine particles of the present invention can be obtained efficiently.
Hereinafter, the electroless plating method will be described.

2-1. Catalytic Step First, the base particles subjected to electroless plating are subjected to a catalytic treatment. In this catalyzing treatment, after precious metal ions are captured on the surface of the base material particles, they are reduced and supported on the surface of the base material particles. As the noble metal ion, a divalent palladium ion is preferable. In addition, as the base particles to be subjected to the catalyst treatment, the above-described base particles having a hydrophilic surface are preferable. When the substrate particles themselves do not have the ability to capture noble metal ions, it is also preferable to perform a surface modification treatment before the catalytic conversion. The surface modification treatment can be performed by bringing the substrate particles into contact with water or an organic solvent in which the surface treatment agent is dissolved. As the surface treatment agent, for example, cationic surfactants such as amine salts and quaternary ammonium salts are preferably used.

As the catalyst treatment method, for example, a solution containing palladium chloride and tin chloride is used as a catalyst reagent, and the catalyst particles are adsorbed on the surface of the substrate particles by immersing the substrate particles in the solution. Contains a method (catalyst-accelerator method) for depositing palladium on the surface of the substrate particles by reducing the palladium ions with an acid solution such as hydrochloric acid or an alkali solution such as sodium hydroxide, or tin ions (Sn ²⁺ ). A method in which palladium is deposited on the surface of the substrate particle by contacting the solution with the substrate particle to adsorb tin ions on the surface of the substrate particle and then immersing the solution in a solution containing palladium ions (Pd ²⁺ ) ( Sensitizing-activating method) and the like.

2-2. Electroless Plating Step In the electroless plating step, a conductive metal layer is formed on the surface of the catalyst base material particles on which the palladium catalyst is adsorbed by the catalyst treatment. Specifically, a boron-containing nickel plating layer containing nickel and boron can be formed by performing an electroless plating reaction using an electroless plating solution containing a nickel salt and a boron-based reducing agent. The layer can be formed by performing an electroless plating reaction using an electroless plating solution having a nickel salt and hydrazine or a hydrazine derivative as a reducing agent.

  The electroless plating process may be repeated as necessary. By repeating the electroless plating process using electroless plating solutions of different metal types, the surface of the substrate particles is coated with several layers of different metals. it can. As described above, the conductive metal layer according to the present invention has a boron-containing nickel plating layer containing nickel and boron and a pure nickel plating layer in this order from the substrate particle side. The conductive metal layer according to the present invention is obtained by sequentially performing the electroless plating step (first step) to be formed and the electroless plating step (second step) for forming the pure nickel plating layer. Hereinafter, the boron-containing nickel layer forming step (first step) and the pure nickel plating layer forming step (second step) will be described in this order.

2-2-1. Boron-containing nickel layer formation process (first process)
In carrying out the boron-containing nickel layer forming step (first step), first, the catalyzed base particles are sufficiently dispersed in water to prepare an aqueous slurry of the catalyzed base particles. In order to form a uniform conductive metal layer, it is preferable to sufficiently disperse the catalyzed base material particles in an aqueous medium to be plated. In order to improve the dispersibility of the base particles, it is preferable to add a dispersant such as a surfactant. As this dispersant, perfluoroalkyltrimethylammonium salt, perfluoroalkylsulfonate, perfluoroalkyl phosphate ester. It is preferable to use a fluorosurfactant such as perfluoroalkyl carboxylate, perfluoroalkyl ammonium iodide, and perfluoroalkylamine oxide. In addition to this, conventionally known dispersing means such as a normal stirring apparatus, a high speed stirring apparatus, a shearing dispersion apparatus such as a colloid mill or a homogenizer may be employed as the dispersing means for the catalyzed base particles. Ultrasound may be used in combination.

Next, an electroless plating solution containing a nickel salt and a boron-based reducing agent is added to the aqueous slurry of the catalyzed substrate particles prepared above (first step).
Examples of the nickel salt contained in the electroless plating solution include nickel chloride, nickel sulfate, nickel acetate and the like. There may be only one kind of nickel salt, or two or more kinds. The concentration of the nickel salt in the electroless plating solution may be appropriately determined in consideration of the size (surface area) of the base particles so that a conductive metal layer having a desired thickness is formed.

  The boron reducing agent contained in the electroless plating solution in the first step is not particularly limited as long as it contains boron, but amine borane compounds such as dimethylamine borane and trimethylamine borane are preferable, and dimethylamine borane is particularly preferable. The amount of the boron-based reducing agent used is preferably 1 part by mass or more, more preferably 5 parts by mass or more, still more preferably 7 parts by mass or more, and 20 parts by mass or less with respect to 100 parts by mass of the nickel salt. Preferably, it is 15 parts by mass or less, more preferably 13 parts by mass or less. When the content of the boron-based reducing agent is in the above range, the activity of the plating reaction is appropriate.

  The electroless plating solution preferably contains a complexing agent. Examples of the complexing agent include dicarboxylic acid-based complexing agents, and examples of the dicarboxylic acid-based complexing agent include dicarboxylic acid and salts of dicarboxylic acid. The dicarboxylic acid means a compound having two carboxy groups in one molecule, and may have a functional group other than a carboxy group such as a hydroxy group.

  The dicarboxylic acid is preferably a dicarboxylic acid having 2 to 6 carbon atoms, for example, a dicarboxylic acid having 2 carbon atoms such as oxalic acid; a dicarboxylic acid having 3 carbon atoms such as malonic acid; a carbon number such as succinic acid, malic acid or tartaric acid. 4 dicarboxylic acids; dicarboxylic acids having 5 carbon atoms such as glutaric acid and hydroxyglutaric acid; and dicarboxylic acids having 6 carbon atoms such as adipic acid, hydroxyadipic acid and tetrahydroxyadipic acid. Moreover, alkali metal salts and ammonium salts can be used as salts of these dicarboxylic acids. Examples of the alkali metal salt include lithium salt, sodium salt, potassium salt, and sodium potassium salt. As the dicarboxylic acid complexing agent, it is preferable to use one kind alone. Among them, as the dicarboxylic acid complexing agent, a C 3-5 dicarboxylic acid and an alkali metal salt thereof are more preferable, a C 3-4 dicarboxylic acid and an alkali metal salt thereof are more preferable, and a carbon number 3-4. More preferred are alkali metal salts of dicarboxylic acids.

  The amount of the complexing agent used is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, further preferably 90 parts by mass or more, with respect to 100 parts by mass of the nickel salt used in the first electroless plating step. 300 mass parts or less are preferable, More preferably, it is 250 mass parts or less, More preferably, it is 200 mass parts or less.

  In addition, the electroless plating solution may contain various additives. As this additive, a stabilizer etc. are mentioned, for example. The stabilizer has an action of suppressing the self-decomposition reaction of the electroless plating solution and stabilizes the electroless plating reaction. When various additives are included, the total content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and still more preferably 3 parts by mass or less with respect to 100 parts by mass of the nickel salt. is there. Moreover, although a minimum is not specifically limited, For example, it is 0.1 mass part or more, Preferably it may be 1 mass part or more.

  The electroless plating solution is preferably added (dropped) gradually to the aqueous slurry. The dropping rate of the electroless plating solution may be adjusted as appropriate, but the addition amount of the nickel salt is preferably 5 parts by mass / min or more, more preferably 10 parts by mass / min with respect to 100 parts by mass of the base particles. It is min or more, more preferably 15 parts by mass / min or more, preferably 35 parts by mass / min or less, more preferably 30 parts by mass / min or less, and further preferably 25 parts by mass / min or less.

  The liquid temperature when the electroless plating solution is dropped into the aqueous slurry may be adjusted as appropriate, but the liquid temperature is preferably 50 ° C. or higher and lower than 100 ° C. The pH of the electroless plating solution is not limited, but is preferably 4 or more and 8 or less, more preferably 5 or more and 7 or less. The pH of the electroless plating solution can be adjusted by appropriately adding an alkaline aqueous solution such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, or aqueous ammonia, or an acidic aqueous solution such as sulfuric acid or hydrochloric acid.

  When the electroless plating solution is added to the aqueous slurry of the catalyst base material particles, the electroless plating reaction starts immediately. Since the electroless plating reaction is accompanied by the generation of hydrogen gas, the electroless plating reaction in the first step may be completed when hydrogen gas generation is no longer recognized.

2-2-2. Pure nickel layer formation process (second process)
After completion of the boron-containing nickel plating layer forming step (first step), a second electroless plating step (pure nickel layer forming step) may be performed subsequently, or a boron-containing nickel plating layer is formed from within the reaction system. Take out the base material particles (boron-containing nickel layer coated particles), wash and dry as necessary, then prepare an aqueous slurry of boron-containing nickel layer coated particles and perform the second electroless plating step May be.

In the second step, an electroless plating solution containing a nickel salt and a hydrazine reducing agent is added to the reaction solution after the first step or an aqueous slurry of substrate particles having the boron-containing nickel plating layer prepared above. Do.
As the nickel salt contained in the electroless plating solution according to the second step, the same nickel salt as in the first step can be used. The concentration of the nickel salt in the electroless plating solution is also appropriately determined in consideration of the size (surface area) of the base particles and boron-containing nickel layer-coated particles so that a pure nickel layer having a desired thickness is formed. do it.

As the reducing agent contained in the electroless plating solution in the second step, a hydrazine-based reducing agent can be used. Examples of the hydrazine reducing agent include hydrazine derivatives such as hydrazine (hydrazine monohydrate), hydrazine hydrochloride, hydrazinium sulfate, dimethyl hydrazine, acetohydrazide, carbohydrazide and the like. Among these, hydrazine, hydrazine hydrochloride, and hydrazinium sulfate are preferable because impurities derived from the reducing agent hardly remain in the pure nickel plating layer. In addition, a hydrazine type reducing agent may be used individually by 1 type, and may mix and use 2 or more types suitably.
The amount of the hydrazine-based reducing agent used is preferably 1 part by mass or more, more preferably 5 parts by mass or more, further preferably 10 parts by mass or more, and 2500 parts by mass with respect to 100 parts by mass of the nickel salt used in the second step. Part or less, more preferably 2000 parts by weight or less, still more preferably 1500 parts by weight or less. If the content of the hydrazine-based reducing agent is in the above range, it is preferable because the reaction can be easily controlled.

  The electroless plating solution used in the second step may contain a complexing agent and various additives (for example, a stabilizer) in the same manner as the electroless plating solution in the first step. Any of those used for the electroless plating solution in the first step can be used, and the amount used can be within the same range as the electroless plating solution in the first step.

  Also in the second step, it is preferable to gradually add (drop) the electroless plating solution to the aqueous slurry. The dropping rate of the electroless plating solution may be adjusted as appropriate, but the addition amount of the nickel salt is preferably 0.1 parts by mass / min or more, more preferably, 0.1 parts by mass or more with respect to 100 parts by mass of the base particles. 5 parts by mass / min or more, more preferably 1.0 parts by mass / min or more, preferably 20 parts by mass / min or less, more preferably 10 parts by mass / min or less, still more preferably 5 parts by mass / min. It is below min.

  The liquid temperature when the electroless plating solution is dropped into the aqueous slurry may be appropriately adjusted, but the liquid temperature is preferably 70 ° C. or higher and lower than 100 ° C. The pH of the electroless plating solution is not limited, but is preferably 9 or more and 14 or less, more preferably 10 or more and 13 or less. The pH of the electroless plating solution can be adjusted by appropriately adding an alkaline aqueous solution such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, or aqueous ammonia, or an acidic aqueous solution such as sulfuric acid or hydrochloric acid.

  When the electroless plating solution of the second step is added to the aqueous slurry of boron-containing nickel layer-coated particles, the electroless plating reaction starts. Since the electroless plating reaction in the second step involves generation of nitrogen gas, it may be terminated when gas generation is no longer recognized. After completion of the electroless plating reaction (formation of a pure nickel layer; second step), substrate particles (pure nickel-coated particles) in which a pure nickel plating layer is formed on the boron-containing nickel plating layer are taken out from the reaction system, Conductive fine particles can be obtained by washing and drying as necessary.

  The electroless plating process may be repeated as necessary. For example, by repeating the electroless plating process using electroless plating solutions having different metal types, the surface of the substrate particles can be coated with several layers of different kinds of metals. For example, by adding pure nickel-coated particles obtained through the first and second steps to an electroless gold plating solution and performing gold displacement plating, the outermost layer is covered with a gold layer, and pure nickel is coated on the inside. Conductive fine particles having a layer and a boron-containing nickel layer are obtained.

3. Insulating coating conductive fine particles, etc. The conductive fine particles of the present invention may be provided with an insulating resin layer on at least a part of the surface. That is, an embodiment in which an insulating resin layer is further formed on the surface of the conductive metal layer (insulating coated conductive fine particles) may be used. When the insulating resin layer is further laminated on the conductive metal layer on the surface in this way, it is possible to prevent the lateral conduction that is likely to occur when a high-density circuit is formed or when a terminal is connected.
Further, the conductive fine particles of the present invention can be subjected to a surface treatment with a silane coupling agent, an organic compound or the like as necessary within a range not impairing the effects of the present invention.

4). Anisotropic Conductive Material The conductive fine particles of the present invention can be preferably used for an anisotropic conductive material. Examples of the anisotropic conductive material include those in which the conductive fine particles are dispersed in a binder resin. The form of the anisotropic conductive material is not particularly limited, and examples thereof include various forms such as an anisotropic conductive film, an anisotropic conductive paste, an anisotropic conductive adhesive, and an anisotropic conductive ink. By providing these anisotropic conductive materials between opposing substrates or between electrode terminals, good electrical connection can be achieved. The anisotropic conductive material using the conductive fine particles of the present invention includes a conductive material for a liquid crystal display element (conductive spacer and composition thereof).

  The binder resin is not particularly limited as long as it is an insulating resin. For example, thermoplastic resins such as acrylic resins, ethylene-vinyl acetate resins, styrene-butadiene block copolymers; monomers and oligomers having a glycidyl group; Examples thereof include a curable resin composition that is cured by a reaction with a curing agent such as isocyanate; a curable resin composition that is cured by light or heat; The anisotropic conductive material can be obtained by dispersing conductive fine particles in the binder resin to obtain a desired form. For example, the binder resin and the conductive fine particles are used separately to try to connect them. You may connect by making electroconductive fine particles exist with binder resin between the base material to perform or between electrode terminals.

  In the anisotropic conductive material containing the conductive fine particles of the present invention, the content of the conductive fine particles may be appropriately determined depending on the application, but for example, with respect to the total amount (100% by volume) of the anisotropic conductive material. Is preferably 1% by volume or more, more preferably 2% by volume or more, further preferably 5% by volume or more, preferably 50% by volume or less, more preferably 30% by volume or less, and still more preferably 20% by volume or less. . If the content of the conductive fine particles is too small, it may be difficult to obtain sufficient electrical continuity. On the other hand, if the content of the conductive fine particles is too large, the conductive fine particles are in contact with each other, and anisotropy is caused. The function as a conductive material may be difficult to be exhibited.

  Regarding the film thickness in the anisotropic conductive material referred to in the present invention, the coating thickness of the paste or adhesive, the print thickness, etc., consider the particle size of the conductive fine particles to be used and the specifications of the electrode to be connected. In addition, it is preferable that the conductive fine particles are sandwiched between the electrodes to be connected and that the gap between the bonding substrates on which the electrodes to be connected are formed is sufficiently filled with the binder resin layer.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention. In the following, “part” means “part by mass” and “%” means “mass%” unless otherwise specified.
For each conductive fine particle obtained in each example or comparative example, various analyzes and conductivity evaluations were performed by the following methods.

<Number average particle diameter of base particles and conductive fine particles, coefficient of variation (CV value)>
Particle size analyzer (Beckman Coulter "Coulter Multisizer III")
The particle diameter of 30000 particles was measured to determine the number-based average particle diameter and the standard deviation of the particle diameter, and the number-based CV value (variation coefficient) was calculated according to the following formula. Particle variation coefficient (%) = 100 × (standard deviation of particle diameter / number-based average particle diameter)
In the measurement of the base particles and conductive fine particles, a surfactant (“Hitenol (registered trademark) N-08” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to 0.005 parts by mass of the base particles or conductive fine particles. A dispersion obtained by adding 20 parts by mass of a 1% by weight aqueous solution and subjecting it to ultrasonic dispersion for 10 minutes was used as a measurement sample.

<Measurement of 20% K value of substrate particles>
Using a micro-compression tester (“MCT-W500” manufactured by Shimadzu Corporation) at room temperature (25 ° C.), one sample particle dispersed on the sample table was used as a “standard surface” using a circular flat plate indenter with a diameter of 50 μm. A load was applied at a constant loading rate (2.65 mN / sec) toward the center of the particles in the “detection” mode. Then, the load (mN) when the compression displacement became 20% of the particle diameter was measured, and a 20% K value was calculated from the obtained compression load, particle compression displacement, and particle diameter. In addition, the measurement was performed on 10 different particles for each sample, and the average value was used as the measurement value.

<Measurement of thickness of conductive metal layer>
Using a field emission transmission electron microscope (TEM-EDS, “JEM-2100F” manufactured by JEOL Ltd.), measure the cross-section of the conductive fine particles in a thin section with a microtome, and use the boron content or nickel content as a guide. The thicknesses of the pure nickel layer (boron content less than 0.1% by mass) and the boron-containing nickel layer (boron content of 0.1% by mass or more) were measured.

<Measuring method of acicular structure and granular structure>
Using a field emission transmission electron microscope (TEM-EDS, “JEM-2100F” manufactured by JEOL Ltd.), a cross-section of the conductive fine particles made into a thin slice with a microtome was photographed at a magnification of 10,000 times or more to obtain conductivity. In the surface area of the fine particles, the direction of the line segment connecting the midpoint of the base particle side end (base part) of one needle-like structure and the end part (top part) on the conductive metal layer surface side is a needle shape The length of the structure (longitudinal direction), and when a straight line orthogonal to the above line segment is drawn, the width (width direction) is the maximum length of the straight line cut by the outline of the needle-like structure. ).
On the other hand, in the granular structure, conductive fine particles are taken in an agate bowl and ground to expose the cross section of the conductive metal layer, and a field emission scanning electron microscope (FE-SEM, “S-4800” manufactured by Hitachi, Ltd.). ) (100,000 times).

<Measurement of resistance value 1 (paste method)>
10 parts by mass of conductive fine particles, 100 parts by mass of an epoxy resin (“JER828” manufactured by Mitsubishi Chemical Corporation) as a binder resin, 2 parts by mass of a curing agent (“Sun Aid (registered trademark) SI-150” manufactured by Sanshin Chemical Co., Ltd.) and The mixture to which 100 parts by mass of toluene was added was stirred and dispersed at 300 rpm for 10 minutes using a stirrer equipped with two stainless steel stirring blades to prepare an anisotropic conductive paste.

  The obtained anisotropic conductive paste was applied to a glass substrate having an ITO wiring for resistance measurement with a bar coater, dried (thickness: 20 μm), and further sandwiched between glass substrates formed with an aluminum pattern (line width 300 μm), While thermocompression bonding under pressure bonding conditions of 5 MPa and 170 ° C., a connection structure was obtained by curing the binder resin. The resistance value (Ω) between the electrodes of the obtained connection structure was measured by a four-terminal method. A resistance value of 0.03Ω or less was ○ (good), and a resistance value of more than 0.03Ω was × (defective) ).

<Measurement of resistance value 2 (micro compression method)>
Using conductive fine particles as sample particles, the resistance value (Ω) was measured at room temperature (25 ° C.) using a micro compression tester (“MCT-W200” manufactured by Shimadzu Corporation; attached to a resistance measurement kit). Specifically, a sample particle spread on the sample stage is measured by applying a load at a constant load speed (2.6 mN / sec) toward the center of the particle using a circular plate indenter having a diameter of 50 μm. went. Measurement was performed 10 times, and the average value of the resistance value at the time of 40% compression deformation of the particle diameter was obtained. The resistance value of 5Ω or less was evaluated as ○ (good), and the resistance value exceeding 5Ω was evaluated as × (bad). .

<Nickel, boron, phosphorus content>
The content of nickel, boron and phosphorus in each nickel layer is measured by a field emission type transmission electron microscope (TEM-EDS, “JEM-2100F” manufactured by JEOL Ltd.) using a microtome to make the cross section of the conductive fine particles into a thin slice. It was measured.

(Manufacture of substrate particles)
Production Example 1
In a four-necked flask equipped with a condenser, a thermometer, and a dripping port, 1800 parts by mass of ion-exchanged water, 450 parts by mass of methanol and 24 parts by mass of 25% by mass ammonia water were added, and then from the dripping port with stirring. A mixed liquid of 100 parts by mass of methacryloxypropyltrimethoxysilane (“KBM-503” manufactured by Shin-Etsu Silicone Co., Ltd.) and 150 parts by mass of methanol is added to conduct hydrolysis and condensation reaction of 3-methacryloxypropyltrimethoxysilane, An emulsion of polysiloxane particles having methacryloyl groups (polymerizable polysiloxane particles) as seed particles was prepared. The number average particle diameter of the polysiloxane particles was 1.46 μm.

  Subsequently, 10 parts by mass of a 20% by mass aqueous solution of polyoxyethylene styrenated phenyl ether sulfate ammonium salt (“HITENOL (registered trademark) NF-08” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier is added to 400 parts by mass of ion-exchange water. 440 parts by mass of styrene and 60 parts by mass of divinylbenzene (“DVB960” manufactured by Nippon Steel Chemical Co., Ltd .; 96% by mass of divinylbenzene) as monomer components, and 2,2′-azobis (2, 4-dimethylvaleronitrile) (“V-65” manufactured by Wako Pure Chemical Industries, Ltd.) (4.8 parts by mass) was added and emulsified and dispersed to prepare an emulsion of monomer components. After stirring this emulsion for 2 hours, it was added to the emulsion of the polysiloxane particles and further stirred. One hour after the addition of the emulsified liquid, the mixed liquid was sampled and observed with a microscope. As a result, it was confirmed that the polysiloxane particles, which are seed particles, absorbed the monomer and enlarged.

Next, 96 parts by mass of a 20% by mass aqueous solution of the same polyoxyethylene styrenated phenyl ether sulfate ammonium salt and 500 parts by mass of ion-exchanged water are added to the obtained mixed liquid, and 65 ° C. in a nitrogen atmosphere. After the temperature was raised to 65 ° C., the monomer component was radically polymerized by holding at 65 ° C. for 2 hours. Then, the emulsion after radical polymerization was subjected to solid-liquid separation, and the obtained cake was washed with ion-exchanged water and methanol, and then dried at 80 ° C. for 4 hours in a nitrogen atmosphere to obtain polymer particles. The polymer particles were subjected to an etching treatment with sodium hydroxide or the like for hydrophilization, and the obtained particles were used as substrate particles (1). The number average particle diameter of the substrate particles (1) was 3.02 μm, and the coefficient of variation (CV value) of the number-based particle diameter was 3.5%. Further, the 20% K value of the substrate particles (1) was 3297 N / mm ² .

Production Example 2
In the production of the polysiloxane of Production Example 1, in place of 100 parts by mass of 3-methacryloxypropyltrimethoxysilane, 59.3 parts by mass of 3-methacryloxypropyltrimethoxysilane and 40.7 parts by mass of vinyltrimethoxysilane (KBM1003) Polysiloxane particles having a number average particle diameter of 1.40 μm were obtained in the same manner as in Production Example 1 except that the parts were used.

Next, as an emulsion of the monomer component, instead of 440 parts by mass of styrene and 60 parts by mass of divinylbenzene used in Production Example 1, 500 parts by mass of divinylbenzene were used, and after washing with methanol, 320 under a nitrogen atmosphere. Substrate particles (2) were obtained in the same manner as in Production Example 1 except that the heat treatment was carried out at 1 ° C. for 1 hour. The number average particle diameter of the substrate particles (2) was 3.04 μm, and the coefficient of variation (CV value) in the number-based particle diameter was 2.8%. Further, the 20% K value of the substrate particles (2) was 8493 N / mm ² .

Production Example 3
In a four-necked flask equipped with a condenser, a thermometer, and a dripping port, 2080 parts by mass of ion-exchanged water, 520 parts by mass of methanol, 26 parts by mass of 25% aqueous ammonia, and ammonium polyoxyethylene styrenated phenyl ether sulfate After mixing 50 parts by mass of a 20% aqueous solution and dispersing 100 parts by mass of the base particles (1), 3-methacryloxypropyltrimethyl as a monomer component for shell 1 (silane monomer for shell) was added here. 10 parts by mass of methoxysilane was added and stirred for 2 hours to prepare a core particle dispersion.

  In a different flask, 0.9 part by mass of a 20% aqueous solution of polyoxyethylene styrenated phenyl ether sulfate ammonium salt was dissolved in 100 parts by mass of ion-exchanged water. 10 parts by mass of DVB (divinylbenzene, “DVB960” manufactured by Nippon Steel Chemical Co., Ltd.) as a polymer, and 2,2′-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., “V -65 ") A solution in which 0.5 part by mass was dissolved was added and emulsified and dispersed to prepare an emulsion of the monomer component 2 for shell.

The resulting emulsion of monomer component 2 for shell was added to the core particle dispersion and stirred for 1 hour, and then the reaction solution was heated to 65 ° C. and held for 2 hours in a nitrogen atmosphere. Radical polymerization was performed. The emulsion after radical polymerization was subjected to solid-liquid separation, and the obtained cake was washed with ion-exchanged water and methanol, and then vacuum-dried at 80 ° C. for 4 hours to obtain base particles (3). The number average particle diameter of the substrate particles (3) was 3.10 μm, and the coefficient of variation (CV value) in number-based particle diameter was 3.8%. Further, the 20% K value of the substrate particles (3) was 3262 N / mm ² . In the SEM image obtained by imaging the cross section of the base particle (3) with a scanning electron microscope (SEM, magnification of 10,000 times or more), the surface of the base particle (3) has an average height of 50 nm and a convex surface having an equivalent circle diameter of 125 nm. Department was confirmed.

  Here, in the SEM image, the average height connects two points (both ends of the bottom of the convex section) where the boundary of the convex portion and the boundary of the spherical portion present on the peripheral portion of the base particle (3) intersect. The length of the ellipse segment (distance between the two points where the boundary of the convex part and the boundary of the spherical part intersect) is defined as the equivalent circle average diameter of the bottom surface, and the vertical distance from the line segment to the highest part of the convex part Measured as height. The height and base diameter of 50 convex portions were measured and averaged to determine the average height and average base diameter of the base particles (3).

Example 1
The base particles (1) produced in Production Example 1 were directly subjected to electroless plating to produce conductive fine particles. Specifically, 21 g of the base particle (1) was treated with a cationic surfactant (commercially available product) to modify the surface of the base particle. Next, after washing with water, the obtained particles were immersed in an aqueous solution consisting of 100 mg / L of palladium chloride, 10 g / L of tin chloride and 100 mL / L of concentrated hydrochloric acid, filtered and washed with water, and then treated with 10% by mass hydrochloric acid. Then, the palladium catalyst was supported on the surface of the base material particles.

  Next, the obtained catalyzed substrate particles were washed with water and then added to pure water containing a cationic surfactant (commercially available product) to prepare a slurry. The slurry was put into 2000 mL of pure water heated to 70 ° C. and stirred to prepare a catalyst base material particle dispersion. Next, while stirring the obtained catalyst base particle dispersion, 200 mL of electroless nickel plating solution (1-1) prepared with the following composition was added to the catalyst base particle dispersion at 160 mL / min. It was dripped at the dripping speed of.

  The electroless nickel plating solution (1-1) is prepared so as to be nickel sulfate 30 g / L, sodium succinate 50 g / L, ammonium chloride 30 g / L, and dimethylamine borane 3.4 g / L. The electroless nickel plating solution (1-1) subjected to dropping was adjusted to pH 6.0 and heated to 70 ° C. After completion of the dropwise addition of the electroless nickel plating solution (1-1), stirring was continued for 60 minutes to complete the reaction.

Next, the resulting electroless plating particles were filtered and washed with water, and then pure water was added to prepare a slurry. The slurry was poured into 1000 mL of pure water heated to 80 ° C. and stirred to prepare a boron-containing nickel layer-coated particle dispersion.
To the boron-containing nickel layer-coated particle dispersion, 2000 mL of electroless nickel plating solution (1-2) prepared in the following composition was dropped at a dropping rate of 120 mL / min.

  The electroless nickel plating solution (1-2) was prepared so that it might become nickel chloride 2.6g / L, sodium tartrate 5.6g / L, and hydrazine 32g / L. In addition, the electroless nickel plating solution (1-2) used for dripping was adjusted to pH 10.0, and was heated at 90 degreeC.

  After completion of dropping of the electroless nickel plating solution, stirring was continued for 60 minutes to complete the reaction. Thereafter, the generated electroless plating particles were filtered, washed with water, and dried to obtain conductive fine particles (1). The thickness of the boron-containing nickel layer of the conductive fine particles (1) was 0.037 μm, and the thickness of the pure nickel layer was 0.037 μm. The nickel content of the boron-containing nickel layer is 97.0% by mass, the boron content is 3.0% by mass, and the nickel content of the pure nickel layer is 100% by mass and does not contain boron or phosphorus. It was. Table 1 shows the analysis and evaluation results of the conductive fine particles (1).

Examples 2-3
In the same manner as in Example 1 except that instead of the base material particle (1), the base material particle (2) (Example 2) and the base material particle (3) (Example 3) were used, the conductivity was improved. Fine particles (2) and (3) were obtained. The thickness of the boron-containing nickel layer of the conductive fine particles (2) is 0.037 μm, the thickness of the pure nickel layer is 0.037 μm, and the thickness of the boron-containing nickel plating layer of the conductive fine particles (3) is 0.00. The thickness of 037 μm and the pure nickel layer was 0.037 μm. The nickel content of the boron-containing nickel layer of the conductive fine particles (2) is 97.1% by mass, the boron content is 2.9% by mass, the nickel content of the pure nickel layer is 100% by mass, and boron and phosphorus are contained. The nickel content of the boron-containing nickel layer of the conductive fine particles (3) is 97.0% by mass, the boron content is 3.0% by mass, and the nickel content of the pure nickel layer is 100% by mass. % Was free of boron and phosphorus. Table 1 shows the analysis and evaluation results of the conductive fine particles (2) and (3).

Comparative Example 1
In the same manner as in Example 1, a palladium catalyst is supported on the surface of the base particle (1), and the resulting catalyzed base particle is washed with water, and then contains a cationic surfactant (same as in Example 1). In addition to pure water, a slurry was prepared. The slurry was put into 2000 mL of pure water heated to 50 ° C. and stirred to prepare a catalyzed substrate particle dispersion. Next, while stirring the resulting catalyzed base particle dispersion, 300 mL of electroless nickel plating solution (1) prepared with the following composition was dropped into the catalyzed base particle dispersion at 160 mL / min. It was dripped at a speed.

The electroless nickel plating solution (2-1) was prepared so as to be nickel sulfate 20 g / L, sodium citrate 30 g / L, ammonium chloride 30 g / L, and sodium hypophosphite 15 g / L. The electroless nickel plating solution (2-1) used for the dropping was adjusted to pH 9.0 and heated to 50 ° C.
After completion of the dropwise addition of the electroless nickel plating solution (2-1), stirring was continued for 60 minutes to complete the reaction. The generated electroless plating particles were filtered and washed with water, and then pure water was added to prepare a slurry. The slurry was poured into 1000 mL of pure water heated to 90 ° C. and stirred to prepare a phosphorus-containing nickel layer-coated particle dispersion.
Next, 2000 mL of electroless nickel plating solution (2) prepared with the following composition was dropped into the phosphorus-containing nickel layer coated particle dispersion at a dropping rate of 120 mL / min.

  The electroless nickel plating solution (2-2) was prepared so that it might become nickel chloride 2.6g / L, sodium tartrate 5.6g / L, and hydrazine 32g / L. In addition, the electroless nickel plating solution (2-2) used for dripping was adjusted to pH 10.0, and was heated at 90 degreeC.

After completion of dropping of the electroless nickel plating solution, stirring was continued for 60 minutes to complete the reaction. Thereafter, the generated electroless plating particles were filtered, washed with water, and dried to obtain conductive fine particles (4). The thickness of the phosphorus-containing nickel layer of this conductive fine particle (4) was 0.037 μm, and the thickness of the pure nickel layer was 0.037 μm. Further, the nickel content of the phosphorus-containing nickel layer is 96.0% by mass, the phosphorus content is 4.0% by mass, and the nickel content of the pure nickel layer is 100% by mass and does not contain boron or phosphorus. It was.
Table 1 shows the analysis and evaluation results of the conductive fine particles (4).

Comparative Example 2
In the same manner as in Example 1, a palladium catalyst is supported on the surface of the base particle (1), and the resulting catalyzed base particle is washed with water, and then contains a cationic surfactant (same as in Example 1). In addition to pure water, a slurry was prepared. The slurry was put into 1000 mL of pure water heated to 90 ° C. and stirred to prepare a catalyzed substrate particle dispersion. To the catalyst base particle dispersion, 4000 mL of electroless nickel plating solution (3-2) prepared with the following composition was added dropwise at a dropping rate of 120 mL / min.

  The electroless nickel plating solution (3-2) was prepared so that it might become nickel chloride 2.6g / L, sodium tartrate 5.6g / L, and hydrazine 32g / L. The electroless nickel plating solution (3-2) subjected to dropping was adjusted to pH 10.0 and heated to 90 ° C.

After completion of dropping of the electroless nickel plating solution, stirring was continued for 60 minutes to complete the reaction. Thereafter, the generated electroless plating particles were filtered, washed with water, and dried to obtain conductive fine particles (5). The thickness of the pure nickel layer of the conductive fine particles (5) was 0.075 μm, and the nickel content of the pure nickel layer was 100% by mass and did not contain boron or phosphorus. The conductive fine particles (5) were extremely aggregated, and it was difficult to take out the conductive fine particles individually.
Table 1 shows the analysis and evaluation results of the conductive fine particles (5).

  From Table 1, the conductive fine particles of Examples 1 to 3 having a boron-containing nickel layer and a pure nickel layer in this order on the base particle as the conductive metal layer have low resistance values 1 and 2 and are stable. It can be seen that it has electrical connectivity. This is because the conductive fine particles of Examples 1 to 3 have a pure nickel layer as the outermost layer, so that cracking of the conductive metal layer is prevented even when a compressive load is applied, and the characteristics derived from the pure nickel layer ( This is considered to be due to the fact that the low electrical resistance) is maintained and that the boron-containing nickel layer as the underlayer improves the biting into the electrode oxide layer. Further, as shown in FIG. 2, a needle-like structure can be confirmed on the surface of the pure nickel layer of Example 1, and it is considered that the needle-like structure also contributes to the biting property to the electrode oxide layer.

  On the other hand, since the conductive fine particles of Comparative Example 1 are a phosphorus-containing nickel layer with a soft underlayer, the conductive fine particles do not sufficiently penetrate into the electrode oxide layer when a compressive load is applied, and the resistance value is increased. Conceivable. Further, as shown in FIG. 3, in the conductive fine particles of Comparative Example 1, the interface where the phosphorus-containing nickel layer and the pure nickel layer are in contact with each other can be clearly confirmed. That is, in Comparative Example 1, the homogeneity of the entire conductive metal layer is lowered, and the continuity between the phosphorus-containing nickel layer and the pure nickel layer is not obtained, which also affects the increase in resistance value. Inferred. The conductive fine particles of Comparative Example 2 had a good resistance value 2 (micro compression method) because the outermost layer was a pure nickel layer, but the resistance value 1 (paste method) was higher than that of Examples 1-3. Showed a high value. This is presumably because the conductive fine particles aggregated even in the cured resin and sufficient electrical conduction was not obtained.

  The conductive fine particle of the present invention has a boron-containing nickel layer and a pure nickel layer in this order on the substrate particle as a conductive metal layer covering the surface of the substrate particle. Since the outermost layer is composed of a pure nickel layer, it has low electrical resistance and high conductivity. Therefore, the conductive fine particles of the present invention are extremely useful for anisotropic conductive materials such as anisotropic conductive films, anisotropic conductive pastes, anisotropic conductive adhesives, and anisotropic conductive inks.

1. Base particle 1. 2. boron-containing nickel layer Pure nickel layer

Claims (4)

Having substrate particles and a conductive metal layer covering the surface of the substrate particles;
Conductive fine particles, wherein the conductive metal layer has a boron-containing nickel layer and a pure nickel layer in this order on a base particle.   The conductive fine particles according to claim 1, wherein the boron content in the boron-containing nickel layer is 0.1 mass% or more and 5.0 mass% or less.   The base particle is obtained by polymerizing a monomer composition in which the proportion of the crosslinkable monomer in the total monomer constituting the base particle is 1% by mass or more and 100% by mass or less. The conductive fine particles according to claim 1 or 2.   An anisotropic conductive material comprising the conductive fine particles according to claim 1.