JP2011076938A - Conductive particulate, and manufacturing method of conductive particulate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive particulate superior in adhesion of a conductive layer, and to provide a manufacturing method of the conductive particulate. <P>SOLUTION: The conductive particulate has a conductive layer on the surface of a composite particulate, and the conductive particulate has a base material particulate and a plurality of resin particulates adhered on the surface of the base material particulate, and is obtained by hetero aggregation of the base material particulate and the resin particulates. The base material particulate has an average particulate size of 0.5-500 μm and the resin particulate has an average particulate size of 1-100 nm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to conductive fine particles having excellent adhesion of a conductive layer. The present invention also relates to a method for producing the conductive fine particles.

Conductive fine particles having a conductive layer on the surface of the base fine particles may be used for mounting anisotropic conductive materials such as anisotropic conductive films and anisotropic conductive pastes, ball grid array (BGA) mounting solder balls and the like. Widely used as a connecting material. Such conductive fine particles are usually produced by forming a conductive layer on the surface of the substrate fine particles by electroless plating or by further performing electroplating after electroless plating.

However, when using substrate fine particles made of organic substances such as resin, it is difficult to form a strong chemical bond between the substrate fine particles and the conductive layer, and the adhesion of the conductive layer cannot be obtained sufficiently. is there. If the adhesion of the conductive layer is low, when the electrodes such as circuit boards facing each other are connected using conductive fine particles, the conductive layer is caused by stress derived from pressure, heat, etc. required for connection. It becomes easy to break, resulting in poor conduction between electrodes and disconnection.

In order to improve the adhesion of the conductive layer, for example, it has been studied to roughen the surface of the substrate fine particles by attaching fine particles. By roughening the surface, an anchor effect is generated between the surface of the substrate fine particles and the conductive layer, and the adhesion of the conductive layer is improved as compared with the case where the surface is smooth.
As conductive fine particles having a roughened surface, for example, the present inventors have disclosed conductive fine particles obtained by performing metal plating on the surface of non-conductive fine particles having protrusions on the surface. As a method of obtaining non-conductive fine particles having protrusions on the surface, for example, a method of attaching child particles to the surface using conventional fine particles as mother particles is cited.

In addition, the present inventors applied metal plating to the surface of the composite fine particles in which the resin fine particles smaller than the substrate fine particles are bonded to the surface of the substrate fine particles as conductive fine particles having a low connection resistance value and excellent conductive reliability. Compressive elastic modulus (10% K value) when the conductive fine particles are subjected to 10% compression deformation, and 5000 to 8500 N / mm ² and compression when 30% compression deformation is performed. Patent Document 2 discloses conductive fine particles having an elastic modulus (30% K value) of 1500 to 3000 N / mm ² .

However, the average particle diameter of the child particles used in the example of Patent Document 1 is 1.2 μm, the average particle diameter of the resin fine particles used in the example of Patent Document 2 is 0.3 μm, and the surface is Since the average particle size of the fine particles used for the protrusions for roughening is relatively large, in these conductive fine particles, stress concentrates on the protrusions during drying and crushing, and the conductive layer is peeled off instead. There is. In addition, when attaching fine particles with a small average particle diameter, the conventional method using mechanical collision using a hybridizer or the like makes the adhesion of the fine particles non-uniform, and it is difficult to obtain a conductive layer having sufficient adhesion. is there.

JP-A-4-36902 JP 2006-107881 A

An object of this invention is to provide the electroconductive fine particle excellent in the adhesiveness of a conductive layer. Another object of the present invention is to provide a method for producing the conductive fine particles.

The present invention is a conductive fine particle having a conductive layer on the surface of a composite fine particle, the composite fine particle has a base particle and a plurality of resin fine particles attached to the surface of the base particle, and Obtained by hetero-aggregating the substrate fine particles and the resin fine particles, the substrate fine particles have an average particle diameter of 0.5 to 500 μm, and the resin fine particles have an average particle diameter of 1 to 100 nm. Conductive fine particles.
The present invention is described in detail below.

The inventors of the present invention are composite fine particles having base fine particles and a plurality of resin fine particles attached to the surface of the base fine particles, wherein the base fine particles have a predetermined average particle diameter, and the resin fine particles Has found that composite fine particles having a predetermined small average particle diameter can be produced by heteroaggregation. The present inventors have found that conductive fine particles having excellent adhesion of the conductive layer can be obtained by forming a conductive layer on the surface of such composite fine particles, and have completed the present invention.

The conductive fine particles of the present invention have composite fine particles having substrate fine particles and a plurality of resin fine particles attached to the surface of the substrate fine particles.
The lower limit of the average particle diameter of the substrate fine particles is 0.5 μm, and the upper limit is 500 μm. When the average particle diameter of the above-mentioned substrate fine particles is less than 0.5 μm, the substrate fine particles are likely to aggregate, and when using conductive particles in which a conductive layer is formed on the surface of the aggregated substrate fine particles, Easy to short circuit. When the average particle diameter of the base material fine particles exceeds 500 μm, it exceeds the range suitable for connection between electrodes such as a circuit board. The preferable lower limit of the average particle diameter of the substrate fine particles is 1 μm, and the preferable upper limit is 400 μm.
The average particle size of the above-mentioned substrate fine particles is obtained by measuring the particle sizes of 50 randomly selected substrate fine particles using an optical microscope or an electron microscope and arithmetically averaging the measured particle sizes. .

The coefficient of variation of the average particle diameter of the substrate fine particles is not particularly limited, but is preferably 10% or less. If the coefficient of variation exceeds 10%, the connection reliability of the conductive fine particles may be lowered. The above coefficient of variation is a numerical value obtained by dividing the standard deviation obtained from the particle size distribution by the average particle size and expressed as a percentage (%).

The substrate fine particles are not particularly limited, and examples thereof include organic resin fine particles, inorganic fine particles, and organic-inorganic hybrid fine particles. Among these, organic resin fine particles are preferable.

The organic resin fine particles are not particularly limited as long as they have fine compression properties, and may be crosslinked resin fine particles or non-crosslinked resin fine particles. Among these, crosslinked resin fine particles are preferable.
The monomer constituting the crosslinked resin fine particles is not particularly limited as long as it contains a crosslinkable monomer, and may be only a crosslinkable monomer, or may contain a non-crosslinkable monomer in addition to the crosslinkable monomer. .
Examples of the crosslinkable monomer include divinylbenzene and its derivatives, conjugated dienes such as butadiene and isoprene, polyfunctional (meta) such as polytetramethylene glycol di (meth) acrylate and 1,6-hexanediol di (meth) acrylate. ) Acrylates and the like. Here, (meth) acrylate means methacrylate or acrylate. The said crosslinkable monomer may be used independently and 2 or more types may be used together.

Examples of the non-crosslinkable monomer include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, and chloromethylstyrene, unsaturated nitriles such as vinyl chloride and acrylonitrile, and isobutyl (meth) acrylate. And monofunctional (meth) acrylates such as isooctyl (meth) acrylate. The said non-crosslinkable monomer may be used independently and 2 or more types may be used together.

The method for obtaining the organic resin fine particles is not particularly limited, and examples thereof include a method using a polymerization method such as suspension polymerization, seed polymerization, dispersion polymerization, dispersion seed polymerization, and emulsion polymerization.

The inorganic fine particles are not particularly limited, and examples thereof include fine particles composed of metal oxides such as silica and alumina.
The organic-inorganic hybrid fine particles are not particularly limited, and examples thereof include hybrid fine particles containing an acrylic polymer in an organosiloxane skeleton.

When the substrate fine particles are organic resin fine particles, the preferred lower limit of the 10% K value of the organic resin fine particles is 1000 MPa, and the preferred upper limit is 15000 MPa. When the 10% K value is less than 1000 MPa, the organic resin fine particles may be destroyed when the organic resin fine particles are compressed and deformed. When the 10% K value exceeds 15000 MPa, the conductive fine particles may damage the electrode. The more preferable lower limit of the 10% K value is 2000 MPa, and the more preferable upper limit is 10,000 MPa.

The 10% K value is obtained by using a micro compression tester (for example, “PCT-200” manufactured by Shimadzu Corporation), and using a smooth indenter end face of a diamond cylinder having a diameter of 50 μm and a compression speed of 2.6 mN. The compression displacement (mm) when compressed under the conditions of 10 g / second and a maximum test load of 10 g is measured, and is obtained by the following formula (1).
K value ^{(N / mm 2) = (} 3 / √2) · F · S -3/2 · R -1/2 (1)
F: Load value at 10% compression deformation of organic resin fine particles (N)
S: Compression displacement (mm) in 10% compression deformation of organic resin fine particles
R: Radius of organic resin fine particles (mm)

The shape of the substrate fine particles is not particularly limited, and examples thereof include a spherical shape and an elliptical spherical shape. Of these, spherical is preferable.

A plurality of resin fine particles are attached to the surface of the substrate fine particles.
The average particle diameter of the resin fine particles has a lower limit of 1 nm and an upper limit of 100 nm. When the average particle diameter of the resin fine particles is less than 1 nm, the anchor effect by roughening the surface is lowered, and the adhesion of the conductive layer of the conductive fine particles is lowered. When the average particle diameter of the resin fine particles exceeds 100 nm, stress concentrates on the resin fine particles during drying and pulverization of the conductive fine particles, and the adhesion of the conductive layer of the conductive fine particles decreases. The preferable lower limit of the average particle diameter of the resin fine particles is 10 nm, and the preferable upper limit is 80 nm.
In addition, the average particle diameter of the resin fine particles is obtained by measuring the particle diameters of 50 resin fine particles randomly selected using an optical microscope or an electron microscope, and arithmetically averaging the measured particle diameters.

The coefficient of variation of the average particle diameter of the resin fine particles is not particularly limited, but is preferably 10% or less. If the coefficient of variation exceeds 10%, the connection reliability of the conductive fine particles may be lowered. The above coefficient of variation is a numerical value obtained by dividing the standard deviation obtained from the particle size distribution by the average particle size and expressed as a percentage (%).

The ratio of the resin fine particles adhering to the surface of the substrate fine particles and covering the surface of the substrate fine particles (hereinafter also referred to as surface coverage) has a preferred lower limit of 5% and a preferred upper limit of 90%. When the surface coverage of the resin fine particles is less than 5%, the anchor effect due to the roughening of the surface is lowered, and the adhesion of the conductive fine particles to the conductive layer may be lowered. When the surface coverage of the resin fine particles exceeds 90%, the surface of the substrate fine particles is covered with the resin fine particles, and the resin fine particles are connected at the time of connection using the conductive fine particles as an anisotropic conductive material. The protrusion due to contact with the electrode may not be in a good connection state. A more preferable lower limit of the surface coverage of the resin fine particles is 10%, and a more preferable upper limit is 60%.

The surface coverage of the resin fine particles is given by the ratio of the sum of the projected areas of the resin fine particles to the surface area of the substrate fine particles. Specifically, the surface coverage of the resin fine particles is obtained by the following formula (2) by counting the number of protrusions due to the resin fine particles for 50 randomly selected conductive fine particles.
Surface coverage (%) = (πr ² × N / 4πR ² ) × 100 (2)
N: Number of protrusions due to adhering resin particles r: Average radius of adhering resin particles R: Average radius of substrate particles The surface coverage of the resin particles is, for example, the resin added to the substrate particles It can be easily controlled by changing the amount of fine particles.

The resin fine particles are not particularly limited as long as they are resin fine particles having appropriate compression characteristics, and may be crosslinked resin fine particles or non-crosslinked resin fine particles.
The monomer constituting the crosslinked resin fine particles is not particularly limited as long as it contains a crosslinkable monomer, and may be only a crosslinkable monomer, or may contain a non-crosslinkable monomer in addition to the crosslinkable monomer. . Examples of the crosslinkable monomer include crosslinkable monomers similar to the crosslinkable monomer constituting the substrate fine particles.
The monomer constituting the non-crosslinked resin fine particles is not particularly limited as long as it is a non-crosslinkable monomer, and examples thereof include the same non-crosslinkable monomer as the non-crosslinkable monomer constituting the substrate fine particles.

The method for obtaining the resin fine particles is not particularly limited, and examples thereof include a method using a polymerization method such as suspension polymerization, seed polymerization, dispersion polymerization, dispersion seed polymerization, and emulsion polymerization.

The shape of the resin fine particles is not particularly limited, and examples thereof include a spherical shape and an elliptical spherical shape. Of these, spherical is preferable.

The composite fine particles can be obtained by hetero-aggregating the substrate fine particles and the resin fine particles. In general, heteroaggregation means that at least two kinds of fine particles having different properties are aggregated by van der Waals force or electrostatic interaction.
By using the hetero-aggregation, even when resin fine particles having a relatively small average particle diameter in the above range are adhered, the resin fine particles adhere uniformly to the surface of the substrate fine particles without overlapping, and the conductive layer Conductive fine particles having excellent adhesion can be obtained. Further, when the heteroaggregation is used, a chemical reaction between the substrate fine particles and the resin fine particles occurs quickly and reliably due to the solvent effect. On the other hand, when the resin fine particles are attached to the surface of the substrate fine particles by a dry method such as a conventional high-speed stirrer or a hybridizer, the adhesion of the resin fine particles becomes uneven. Loads such as frictional heat are likely to be applied. Further, if the resin fine particles are harder than the substrate fine particles, the substrate fine particles may be damaged. If the resin fine particles are softer than the substrate fine particles, collision with the substrate fine particles, frictional heat, etc. The resin fine particles may be deformed.

As a method of heteroaggregating the base material fine particles and the resin fine particles, for example, after adding the slurry containing the resin fine particles to a slurry obtained by adding the base material fine particles to ion-exchanged water, for example, an electrolyte Examples thereof include a method of adding an aqueous solution and the like, a method of changing pH by adding an acid or a base, and the like.
The kind of said electrolyte is not specifically limited, For example, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, sodium carbonate, sodium hydrogencarbonate, sodium nitrate, sodium nitrite, sodium sulfate etc. are mentioned.

When hetero-aggregating the substrate fine particles and the resin fine particles, the mixing ratio of the substrate fine particles and the resin fine particles is not particularly limited, and is appropriately set according to the target surface coverage of the resin particles. The

The conductive fine particles of the present invention have a conductive layer on the surface of the composite fine particles. The conductive layer may be a single layer or may have a plurality of layers.
Examples of the conductive layer include metal layers containing gold, silver, copper, platinum, palladium, nickel, rhodium, ruthenium, cobalt, tin, and the like. When the conductive layer has a plurality of layers, the outermost layer is preferably a gold layer, and more preferably a nickel layer or a palladium layer. Since the outermost layer is a gold layer, the connection resistance value between the electrodes is lowered. Moreover, the said outermost layer is a nickel layer or a palladium layer, The said conductive layer becomes hard and electroconductivity improves.

The conductive layer may be a low melting point metal layer made of tin or an alloy of tin and another metal. The said alloy is not specifically limited, For example, a tin-copper alloy, a tin-silver alloy, a tin-bismuth alloy, a tin-zinc alloy, a tin-indium alloy etc. are mentioned. Among these, a tin-silver alloy is preferable because the melting point of the low melting point metal layer to be formed can be lowered.

Furthermore, in order to improve the bonding strength between the low-melting-point metal layer and the electrode, the low-melting-point metal layer includes nickel, antimony, aluminum, iron, gold, titanium, phosphorus, germanium, tellurium, gallium, cobalt, manganese, A metal such as chromium, molybdenum, palladium, or indium may be contained. Especially, since it is excellent in the effect which improves the joining strength of the said low melting metal layer and an electrode, it is preferable to contain nickel, antimony, and aluminum in the said low melting metal layer.
The content of the metal in the total of metals contained in the low melting point metal layer is not particularly limited, but a preferred lower limit is 0.0001% by weight and a preferred upper limit is 2% by weight. When the content of the metal is less than 0.0001% by weight, the bonding strength between the low melting point metal layer and the electrode may not be sufficiently obtained. If the metal content exceeds 2% by weight, the melting point of the conductive fine particles may change.
Note that the conductive layer may have either one of the metal layer or the low-melting-point metal layer, or may have both.

The method for forming the conductive layer is not particularly limited, and examples thereof include a metal vapor deposition method and an electroless plating method. Of these, the electroless plating method is preferable because the conductive layer can be easily formed on the surface of the composite fine particles.
For example, when electroless nickel plating is performed by the above electroless plating method, for example, an electroless nickel plating solution composed of sodium hypophosphite as a reducing agent is bathed and heated according to a predetermined method. A method of immersing the composite fine particles provided with a catalyst and depositing a nickel layer by a reduction reaction of Ni ²⁺ + H ₂ PO ² + + H ₂ O → Ni + H ₂ PO ³ + 2H ⁺ is used.

As a method for applying the catalyst, for example, the composite fine particles may be subjected to alkali degreasing, acid neutralization, sensitizing in a tin dichloride (SnCl ₂ ) solution, and activation in a palladium dichloride (PdCl ₂ ) solution. And a method of performing an electroless plating pretreatment step.
Sensitizing is a process of adsorbing Sn ²⁺ ions on the surface of a non-conductive substance, and activating is a reaction of Sn ²⁺ + Pd ²⁺ → Sn ⁴⁺ + Pd ^{0 on the} surface of a non-conductive substance. In this process, palladium is used as a catalyst core for electroless plating.

Although the thickness of the said conductive layer is not specifically limited, A preferable minimum is 0.02 micrometer and a preferable upper limit is 5 micrometers. When the thickness of the conductive layer is less than 0.02 μm, the conductive fine particles may be thin and the conductive layer may not have sufficient conductivity. If the thickness of the conductive layer exceeds 5 μm, the conductive layer may be easily peeled off because the non-conductive substance constituting the composite fine particles and the metal constituting the conductive layer have different coefficients of thermal expansion. .
The thickness of the conductive layer is a thickness obtained by observing and measuring a cross section of ten randomly selected conductive fine particles with a scanning microscope (SEM) and arithmetically averaging the measured values.

By forming such a conductive layer on the surface of the composite fine particles, the conductive fine particles of the present invention can be obtained.
In the method for producing conductive fine particles of the present invention, the base fine particles and a plurality of resin fine particles attached to the surface of the base fine particles are obtained by heteroaggregating the base fine particles and the resin fine particles. A method for producing conductive fine particles comprising a step of obtaining composite fine particles and a step of forming a conductive layer on the surface of the composite fine particles is also one aspect of the present invention.

Examples of the use of the conductive fine particles of the present invention include mounting of anisotropic conductive materials such as plating base particles, anisotropic conductive films, and anisotropic conductive paste, and solder balls for mounting Ball Grid Array (BGA). Connection materials and the like.
Since the conductive fine particles of the present invention are excellent in adhesion of the conductive layer, for example, the conductive fine particles are excellent in connection reliability when connecting electrodes such as circuit boards facing each other using the conductive fine particles, and are necessary for connection. Even if stress derived from the applied pressure, heat, or the like occurs, poor conduction between electrodes, disconnection, or the like can be suppressed.

According to the present invention, it is possible to provide conductive fine particles having excellent adhesion of the conductive layer. Moreover, according to this invention, the manufacturing method of this electroconductive fine particle can be provided.

The embodiments of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
(Preparation of substrate fine particles)
5 g of styrene particles (average particle size of 0.75 μm) as seed particles, 500 g of ion-exchanged water and 100 g of a 5 wt% polyvinyl alcohol aqueous solution are mixed and dispersed by applying ultrasonic waves, and then the mixture is separable. It put into the flask and stirred uniformly. Next, an emulsion prepared from 128 g of polytetramethylene glycol diacrylate and 32 g of divinylbenzene, 12 g of an oil-soluble polymerization initiator, 9 g of cetyltrimethylammonium bromide, 118 g of ethanol, and 1035 g of ion-exchanged water as monomers is separated. In addition to the bull flask, the mixture was stirred for 12 hours to allow the seed particles to absorb the monomer. Thereafter, 500 g of a 5% by weight aqueous polyvinyl alcohol solution was added to the separable flask, nitrogen gas was introduced, and the mixture was reacted in an autoclave at 130 ° C. for 9 hours to form a group consisting of crosslinked resin fine particles having an average particle size of 4.0 μm. Material fine particles were obtained.

(Preparation of resin fine particles)
1 g of an anionic emulsifier (Daiichi Kogyo Seiyaku Co., Ltd., Aqualon HS-10) was mixed and dissolved in 900 g of ion-exchanged water, and the temperature was raised to 70 ° C. while stirring. After adding 2 g of potassium persulfate as a radical polymerization initiator, a monomer mixture composed of 80 g of methyl methacrylate, 18 g of ethylene glycol dimethacrylate and 3 g of methacrylic acid was added dropwise at a rate of 1 g / min to initiate the reaction. After completion of the monomer dropping, the mixture was further aged at 70 ° C. for 1 hour to obtain resin fine particles composed of crosslinked resin fine particles having an average particle diameter of 18 nm.

(Preparation of composite fine particles)
After adding 60 g of a slurry containing 5% by weight of the obtained resin fine particles to a slurry composed of 95 g of ion-exchanged water and 5 g of the obtained dry powder of base fine particles, 40 g of a 500 mM sodium chloride aqueous solution was added. Heteroaggregates were obtained. The obtained hetero-aggregate was centrifuged, washed with ion exchange water, and then dried to obtain composite fine particles. Table 1 shows the surface coverage (%) of the resin fine particles obtained for the obtained composite fine particles.

(Formation of conductive layer)
10 g of the obtained composite fine particles were subjected to alkali degreasing with an aqueous sodium hydroxide solution, acid neutralization, and sensitizing in a tin dichloride solution. Thereafter, an electroless plating pretreatment consisting of activation in a palladium dichloride solution was performed, and after filtering and washing, composite fine particles having palladium adhered to the particle surface were obtained. The obtained composite fine particles adhered with palladium were further diluted with 1200 mL of water, and after adding 4 mL of plating stabilizer, nickel sulfate 450 g / L, sodium hypophosphite 150 g / L, sodium citrate 116 g / L were added to this aqueous solution. Then, 120 mL of a mixed solution of 6 mL of plating stabilizer was added through an 8 metering pump. Thereafter, the mixture was stirred until the pH became stable, and it was confirmed that hydrogen bubbling stopped, and the first electroless plating step was performed.
Next, 650 mL of a mixed solution of 450 g / L of nickel sulfate, 150 g / L of sodium hypophosphite, 116 g / L of sodium citrate, and 35 ml of plating stabilizer was added through a metering pump. Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating late process was performed. Next, the plating solution was filtered, and the filtrate was washed with water, and then dried with a vacuum dryer at 80 ° C. to obtain nickel-plated conductive fine particles.

(Example 2)
(Preparation of substrate fine particles)
896 g of a 1% by weight aqueous polyvinyl alcohol solution and 4 g of cetyltrimethylammonium bromide were placed in a separable flask and stirred uniformly. Next, a mixed solution of 68 g of styrene and 30 g of divinylbenzene as a monomer and 2 g of an oil-soluble polymerization initiator is added to a separable flask, nitrogen gas is introduced, and the mixture is reacted at 130 ° C. for 9 hours in an autoclave. Got. The obtained resin particles were classified with a sieve to obtain substrate fine particles composed of crosslinked resin fine particles having an average particle diameter of 102 μm.

(Preparation of resin fine particles)
1 g of an anionic reaction emulsifier (Daiichi Kogyo Seiyaku Co., Ltd., Aqualon HS-10) was mixed and dissolved in 900 g of ion-exchanged water to obtain an aqueous emulsifier solution. A monomer mixture composed of 80 g of methyl methacrylate, 18 g of ethylene glycol dimethacrylate, and 3 g of methacrylic acid was added all at once to the above emulsifier aqueous solution and emulsified and mixed by stirring. The temperature was raised to 70 ° C. with stirring, and 2 g of potassium persulfate was added as a radical polymerization initiator to initiate the reaction. Aging was performed at 70 ° C. for 2 hours to obtain resin fine particles composed of crosslinked resin fine particles having an average particle diameter of 83 nm.

(Production of composite fine particles and formation of conductive layer)
Nickel-plated conductive fine particles were obtained in the same manner as in Example 1 except that the obtained base material fine particles and resin fine particles were used.

(Comparative Example 1)
(Preparation of substrate fine particles)
895 g of ion-exchanged water and 5 g of polyoxyethylene nonylphenyl ether were placed in a separable flask and stirred until uniform. Next, 68 g of methyl methacrylate and 30 g of diethylene glycol dimethacrylate as monomers, 2 g of an oil-soluble polymerization initiator, and 10 g of hexadecane were added to a separable flask, and emulsified and mixed by an ultrasonic emulsifier. Nitrogen gas was introduced, and reaction was performed in an autoclave at 70 ° C. for 4 hours to obtain resin particles. The obtained resin particles were classified with a sieve to obtain substrate fine particles composed of crosslinked resin fine particles having an average particle diameter of 0.32 μm.

(Production of composite fine particles and formation of conductive layer)
An attempt was made to produce composite fine particles in the same manner as in Example 1 except that the obtained base fine particles were used. As a result, the base fine particles were aggregated and composite fine particles could not be obtained.

(Comparative Example 2)
(Preparation of substrate fine particles)
In the same manner as in Example 1, substrate fine particles having an average particle size of 4.0 μm were obtained.
(Preparation of resin fine particles)
1 g of an anionic reactive emulsifier (Daiichi Kogyo Seiyaku Co., Ltd., Aqualon HS-10) was mixed and dissolved in 400 g of ion-exchanged water to obtain an aqueous emulsifier solution. A monomer mixture composed of 80 g of methyl methacrylate and 20 g of ethylene glycol dimethacrylate was added all at once to the aqueous emulsifier solution, and an emulsified mixed solution was obtained by stirring. 500 g of ion-exchanged water was added to the separable flask, and the temperature was raised to 70 ° C. while stirring. As a radical polymerization initiator, 2 g of potassium persulfate and 10 g of the emulsified mixed solution were added to initiate the reaction. Subsequently, the remaining emulsified mixture was added dropwise at a rate of 5 g / min. After completion of dropping, the mixture was further aged at 70 ° C. for 1 hour to obtain resin fine particles composed of crosslinked resin fine particles having an average particle diameter of 250 nm.

(Production of composite fine particles and formation of conductive layer)
Nickel-plated conductive fine particles were obtained in the same manner as in Example 1 except that the obtained base material fine particles and resin fine particles were used.

(Comparative Example 3)
(Preparation of substrate fine particles)
In the same manner as in Example 1, substrate fine particles having an average particle size of 4.0 μm were obtained.
(Preparation of resin fine particles)
In the same manner as in Example 1, resin fine particles having an average particle diameter of 18 nm were obtained.
(Production of composite fine particles and formation of conductive layer)
10 g of the obtained dry powder of substrate fine particles and 10 g of the dry powder of resin fine particles were mixed and adhered by a hybridization system NHS-0 (manufactured by Nara Machinery Co., Ltd.) to obtain composite fine particles. Nickel-plated conductive fine particles were obtained in the same manner as in Example 1 except that the obtained composite fine particles were used.

(Evaluation)
The following evaluation was performed about the electroconductive fine particles obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Adhesiveness of conductive layer 1 g of the obtained conductive fine particles is dispersed in 10 mL of ion-exchanged water, and is irradiated with ultrasonic waves (50 ° C., 2 ° C. using an ultrasonic irradiation device (“USD-1R” manufactured by ASONE)). Time, 28 kHz). The conductive fine particles after irradiation are observed with a scanning electron microscope ("S-3000N" manufactured by Hitachi High-Technologies Corporation) at a magnification of 2000 times, and the conductive layer cracks in any 100 conductive fine particles. The number of fine particles was confirmed, and the adhesion of the conductive layer was evaluated according to the following criteria.
○ Less than 10 conductive particles in which cracking of conductive layer was confirmed Δ 10 or more and less than 50 conductive particles in which cracking of conductive layer was confirmed × 50 conductive particles in which cracking of conductive layer was confirmed more than

According to the present invention, it is possible to provide conductive fine particles having excellent adhesion of the conductive layer. Moreover, according to this invention, the manufacturing method of this electroconductive fine particle can be provided.

Claims (2)

Conductive fine particles having a conductive layer on the surface of the composite fine particles,
The composite fine particles are obtained by heteroaggregating the substrate fine particles and the resin fine particles, having base fine particles and a plurality of resin fine particles attached to the surface of the substrate fine particles,
The substrate fine particles have an average particle diameter of 0.5 to 500 μm,
The fine resin particles have an average particle diameter of 1 to 100 nm. A method for producing the conductive fine particles according to claim 1,
Obtaining a composite fine particle having the base fine particles and a plurality of resin fine particles attached to the surface of the base fine particles by heteroaggregating the base fine particles and the resin fine particles;
And a step of forming a conductive layer on the surface of the composite fine particles.