JP6442240B2 - Silver-coated particles and method for producing the same - Google Patents

Description

  The present invention relates to silver-coated particles contained as a conductive filler in a conductive paste, an anisotropic conductive material, or the like, and a method for producing the same. More specifically, the present invention relates to a silver-coated particle that is excellent in conductivity and suitable for forming an electrode or the like with a fine line width and a method for producing the same.

  For example, a conductive paste is widely used for forming a semiconductor element such as a solar cell panel or a liquid crystal display, an electronic device (such as an electrode or an electric wiring) included in an electronic device or an electronic display device, and the like. The conductive paste contains a conductive filler made of metal particles as a conductive material. This conductive filler is mixed with other components such as resin and solvent as a binder component to prepare a paste. Is done. In order to form an electrode or the like using a conductive paste, first, the conductive paste is applied to the surface of a substrate or the like by a coating method such as a screen printing method or an offset printing method to form a printing pattern. Next, an electrode or the like is formed by drying or baking the formed printed pattern at a desired temperature. Such a method for forming an electrode or the like using a conductive paste is excellent in terms of cost and the like because it does not require a large amount of equipment as in a sputtering method performed in a vacuum, for example.

  An anisotropic conductive material such as an anisotropic conductive adhesive or an anisotropic conductive film is generally used as a material for electrically connecting electrodes, electrical wiring, and the like included in an electronic device. The anisotropic conductive material or the like also contains a conductive filler as a conductive material, like the conductive paste.

  In recent years, the movement toward thinner and lighter electronic devices has been remarkable, and in these fields, further improvement in conductivity and improvement in reliability in fine wiring and the like are required. In order to meet such requirements, conductive fillers contained in conductive pastes and anisotropic conductive materials are required to be further improved in resistance and miniaturization.

  In general, silver or the like is widely used as the conductive filler used in the conductive paste because of its low resistance and excellent oxidation resistance (see, for example, Patent Document 1). The silver powder disclosed in Patent Document 2 is said to have very excellent low-temperature sintering characteristics by attaching fine silver particles to the surface of silver powder.

  In addition, the conductive filler used in the anisotropic conductive material has a method of crushing when a load is applied when connecting wires or connecting a metal bump and a wire, or a recovery rate when the load is removed. In view of the above, fine particles or the like in which a metal such as gold-nickel is coated on the surface of particles made of ceramics or resin are generally used (see, for example, Patent Document 2). The fine particles include resin particles such as acrylic resin and styrene resin as base fine particles (mother particles), a base metal layer formed on the surface of the base fine particles, a conductive layer formed on the surface of the base metal layer, Have When the particle size distribution is measured using a sheath flow electric resistance type particle size distribution meter, the ratio of the conductive fine particles having a particle size of 1.26 times or more of the average particle size is 8% or less, and the particles are It is said that a highly reliable conductive connection can be made with few connected particles bonded together. The fine particles are manufactured by a method of performing electroless plating while applying ultrasonic waves to the liquid.

  Further, silver-coated sphere particles are disclosed in which silver is coated on a resin surface such as an acrylic resin via a tin adsorption layer (see, for example, Patent Document 3). In the silver-coated spherical resin shown in Patent Document 3 and the like, a resin having a specific gravity lower than that of silver is used, and the surface thereof is coated with silver. It is supposed to be obtained. In addition, compared to a conductive paste using silver powder as a conductive filler, since the amount of silver used is high, the production cost is excellent. Further, since the silver-coated spherical particles have a structure in which the surface of the mother particle having elasticity such as an acrylic resin is coated with a metal, the silver-coated spherical particles are also suitably used as a conductive filler used in an anisotropic conductive material. be able to. Furthermore, silver has the lowest resistance at room temperature among all single metals, and is lower in cost than gold, which is currently mainly used as a conductive filler for anisotropic conductive materials. An anisotropic conductive material excellent in terms of production cost can be manufactured.

  On the other hand, in the case of silver-coated particles having such a coating structure, for example, there are many points to be improved that do not exist in a single silver particle, such as problems related to adhesion between the mother particle and the silver coating layer. (For example, refer to Patent Document 4).

JP 2005-146408 (Claim 1, paragraph [0012]) Japanese Patent No. 5406544 (claims 4, 5, paragraphs [0009] to [0011], paragraph [0014], paragraph [0021]) International Publication No. 2012/023566 (Claim 1, Claim 9, Paragraph [0010]) JP 2010-229556 A (Claim 1, paragraph [0021])

  In the silver-coated spherical resin shown in the above-mentioned conventional patent document 3, if the crystallite diameter of the silver coating layer covering the mother particle surface is small, the silver crystals covering the mother particle surface are abnormally precipitated in a lump when the silver coating layer is formed However, since a dense film cannot be obtained and adhesion is lowered, the crystallite diameter of silver is controlled to a relatively large diameter. Further, when silver crystals are abnormally precipitated in a lump shape, coating unevenness occurs, and an uncoated portion may be generated, resulting in a decrease in conductivity. For this reason, it is difficult to coat the entire resin surface with a small amount of silver, resulting in a problem that the production cost increases.

  On the other hand, when the silver crystallite covering the surface of the mother particle is large, adjacent silver-coated spherical resins are cross-linked and aggregated in a chain by the silver covering the surface of the mother particle, and the silver is formed by cross-linking and aggregation. Since the secondary particles of the coated spherical resin are enlarged, there is a problem that it is difficult to obtain silver-coated particles having a small particle size suitable for fine printing.

  Moreover, in the method of performing electroless plating while applying ultrasonic waves to the liquid as in Patent Document 2, it is necessary to use a throwing-type ultrasonic apparatus to irradiate the liquid with ultrasonic waves. For this reason, when performing electroless plating, the ultrasonic device is also covered with metal, which makes it difficult to perform maintenance and increases the cost.

  An object of the present invention is to provide a silver-coated particle that is excellent in conductivity and suitable for forming an electrode or the like with a fine line width, and that can also be used for an anisotropic conductive material, and a method for producing the same. There is to do.

A first aspect of the present invention is a silver-coated particle having a structure in which the surface of the mother particle is coated with silver, wherein the crystallite diameter of silver covering the mother particle is 12.5 to 17.9 nm, and the aqueous solution a dispersed particle diameter D ₅₀ 0.9~10μm silver-coated particles in the medium state, and are the volume resistivity measured by the state 1.0 × 10 ^-3 Ω · cm or less with a pressure of 100 kPa, the The mother particles are characterized by comprising a resin, a metal (however, excluding copper) or a metal oxide .

The second aspect of the present invention is an invention based on the first aspect, the primary particle size of more dispersed particle diameter D ₅₀ and the ratio of the primary particle diameter D _P of the mother particle (dispersed particle diameter D ₅₀ / base particle D _P ) is 1.1 to 3.0.

According to a third aspect of the present invention, in the method for producing silver-coated particles having a structure in which the surface of the mother particles is coated with silver, the mother particles are obtained by electroless plating using a dispersant containing a polycarboxylate. Including a step of reducing and precipitating silver on the surface of the material, the amount of polycarboxylate added is 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the mother particles, and the crystallite diameter of silver covering the mother particles Is 12.5 to 17.9 nm, the dispersed particle diameter D ₅₀ of the silver-coated particles in the aqueous solution is 0.9 to 10 μm, and the volume resistivity measured under a pressure of 100 kPa is 1.0. This is a method for producing silver-coated particles having a size of × 10 ⁻³ Ω · cm or less.
The 4th viewpoint of this invention is invention based on the 3rd viewpoint, Comprising: The said mother particle is a manufacturing method of the silver covering particle which consists of resin, a metal, or a metal oxide.

Since the silver-coated particles of the first aspect of the present invention have a very small crystallite diameter of 12.5 to 17.9 nm covering the base particles, cross-linking aggregation due to silver between adjacent silver-coated particles is suppressed. And the dispersed particle diameter D ₅₀ in the aqueous solution shows a very small value. In addition, although the crystallite diameter of silver is very small, silver crystals covering one base particle are dispersed along the surface to be coated uniformly without abnormal precipitation on the surface of the base particle. By covering in the state, the silver coating layer coats the surface of the mother particles uniformly and with a high coverage. Therefore, good conduction is obtained between the silver-coated particles, and the silver coating layer covering the surface of the mother particles becomes a dense film with excellent adhesion. As a result, the silver-coated particles can be made finer, and in order to develop high conductivity, if the silver-coated particles are used as a conductive filler contained in a conductive paste, an anisotropic conductive material, etc. In addition, an electrode or an electric wiring having excellent conductivity can be formed, and high continuity can be ensured.

Silver-coated particles of the second aspect of the present invention, the ratio of the primary particle diameter D _P of the dispersed particle diameter D ₅₀ and the primary particle (primary particle diameter D _P of the dispersion particle diameter D ₅₀ / mother particle) is 1.1 3.0 is shown. In other words, although the silver-coated particles have a small amount of silver covering one mother particle, the entire surface of the mother particle is efficiently coated with a very thin silver coating layer. Therefore, since the amount of high-cost silver used is reduced without impairing conductivity, production costs can be significantly reduced.

  In the silver-coated particles according to the third aspect of the present invention, the mother particles are made of resin, metal or metal oxide. For example, by using resin particles or the like having a cost lower than that of silver for the mother particles, it is possible to reduce the amount of silver used at a high cost and to suppress the production cost. In addition, by using resin particles having a specific gravity smaller than that of silver for the mother particles, it is possible to prepare a paste having excellent print pattern shape retention, such as prevention of deformation of the print pattern due to the self-weight of the conductive filler.

  The manufacturing method of the 4th viewpoint of this invention is the manufacturing method of the silver coating particle which has the structure where the surface of the mother particle was coat | covered with silver, By the electroless-plating method using the dispersing agent containing polycarboxylate And a step of reducing and precipitating silver on the surface of the mother particles, and controlling the amount of polycarboxylate added to a desired ratio. As a result, fine silver-coated particles with small cross-linking aggregation between the silver-coated particles and a small particle diameter, the mother particle surface being coated with a silver coating layer at a high coverage, and silver-coated particles having excellent conductivity Can be obtained. Thereby, for example, an excellent conductive paste or anisotropic conductive material that does not cause a problem such as a short circuit when a fine electrode or electric wiring is formed can be manufactured.

It is a photograph figure when the silver coating particle obtained in Example 1 is observed with a scanning electron microscope. It is a photograph figure when the silver coating particle obtained by the comparative example 1 is observed with a scanning electron microscope. It is a photograph figure when the silver coating particle obtained in the comparative example 4 is observed with a scanning electron microscope.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings.

  The silver-coated particle of the present invention is a silver-coated particle used as a conductive filler contained in a conductive paste or the like, and has a structure in which the surface of the mother particle is coated with silver. In addition, the structure in which the tin adsorption layer etc. were previously provided in the mother particle surface before coat | covering silver may be sufficient. The shape of the silver-coated particles is not limited to a sphere, but may be a flat shape or a rod shape, but is preferably a sphere. The reason is that uniform conductive connection between the wirings cannot be ensured unless the spherical particles have a uniform particle diameter. Also, in the conductive paste, the spherical shape has an advantage that the volume filling rate of the conductive filler can be easily calculated. Note that the spherical shape is not limited to a perfect sphere, and includes a shape close to a spherical shape such as an ellipse, a shape having a slight unevenness on the surface, and the like.

  The crystallite diameter of silver covering the mother particles is in the range of 12.5 to 17.9 nm. The reason for limiting the crystallite diameter of silver covering the mother particles to the above range is that if the crystallite diameter is controlled to be less than the lower limit value, silver crystals are abnormally precipitated in a lump on the mother particle surface, and the silver coating layer is formed. It is not formed into a dense film, and the adhesion of silver to the resin is lowered. Furthermore, it is because agglomerated crystals tend to grow and it is difficult to keep a crystallite diameter of less than 12.5 nm. That is, at present, it is difficult to obtain silver-coated particles having a crystallite diameter of less than the lower limit value even according to the present invention. On the other hand, when the upper limit is exceeded, aggregation occurs between the silver covering the surface of one base particle and the silver covering the surface of another adjacent base particle, and the size of one silver-covered particle This is because the chain is enlarged in a chain and does not become the desired fine particles. Among these, it is preferable that the crystallite diameter of silver which coat | covers a mother particle is 15-17 nm. In the present specification, the crystallite diameter of silver covering the mother particles is a value calculated using an X-ray diffractometer (model name: RINT2000, manufactured by Rigaku Corporation) and the Debye-Scherrer equation.

In this silver-coated particle, the crystallite diameter of the silver covering the mother particle is controlled within a desired range, so that the above-described cross-linking and aggregation of the silver-coated particles with the silver is suppressed, thereby having a desired particle diameter. Thus, the silver-coated particles are suitable for forming electrodes and the like with a fine line width. Specifically, the dispersed particle diameter D ₅₀ of the silver-coated particles in the aqueous solution is 0.9 to 10 μm. The dispersion particle diameter D ₅₀ is limited to the range described above, when the particle diameter becomes smaller, further aggregation between the particles, consisting for easily enlarged, the dispersion particle diameter D ₅₀ of less than 1.0 .mu.m, and suitable conductive material This is because silver-coated particles are difficult to obtain at present. On the other hand, when the upper limit is exceeded, it becomes difficult to form electrodes and the like by fine printing. In addition, in this specification, the said aqueous solution means the solution which added dispersing agents, such as sodium hexametaphosphate, in the ratio of 0.5 mass% to water. Further, the dispersed particle size D ₅₀ of the silver-coated particles, silver-coated particles in the aqueous solution is added at a ratio of 0.1 mass% were dispersed by ultrasonic irradiation, and stirred at a rotational speed 100~500rpm For the particles in the state, the median value D ₅₀ at the volume-based particle diameter measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Shimadzu Corporation, model name: SALD-200VER) is used.

Further, when the mother particle is coated with silver, if the crystallite diameter of silver is small, the silver crystal covering one mother particle is likely to be abnormally precipitated in a lump shape. When this abnormal precipitation occurs, a part of the surface of the mother particle is not coated with silver, and the coverage is reduced, so that good conductivity cannot be obtained, or a dense silver film cannot be obtained, and the mother particle There is a tendency that the adhesiveness of silver with respect to is poor. On the other hand, in the silver-coated particles of the present invention, although the crystallite diameter of the silver covering the mother particles is very small as described above, the above-described aggregation is suppressed, and the silver-coated layer has a uniform surface of the mother particles, and Covers with high coverage. In addition, since the silver coating layer covering the surface of the mother particles becomes a dense film having excellent adhesion to the mother particles, good conduction can be obtained between the silver coated particles. Specifically, the volume resistivity measured in a state where a pressure of 100 kPa is applied shows a value of 1.0 × 10 ⁻³ Ω · cm or less. This makes it possible to form electrodes and the like by fine printing and to exhibit excellent conductivity. When the covering ratio is reduced and the volume resistivity exceeds 1.0 × 10 ⁻³ Ω · cm, the resistance value is too high and is not suitable for a conductive material. Among these, the volume resistivity is preferably 5.0 × 10 ⁻⁴ Ω · cm or less.

Further, it is preferable that the ratio of the primary particle diameter D _P of the dispersed particle diameter D ₅₀ and the primary particle (primary particle diameter D _P of the dispersion particle diameter D ₅₀ / mother particle) is 1.1 to 3.0. When the value of D ₅₀ / D _P is less than the lower limit value, there may be a problem that the covering rate or the like is lowered and the volume resistivity is increased. On the other hand, if the upper limit value is exceeded, the dispersed particle diameter D ₅₀ becomes large, which makes it unsuitable as a material for forming fine electrodes or electrical wiring, and may cause poor dispersion during paste preparation. Of these, the value of D ₅₀ / D _P is particularly preferably 1.1 to 2.0. The primary particle diameter D _{P of the} mother particles refers to the average value of the diameters of 1000 particles calculated by the method described later.

  The material of the mother particles constituting the silver-coated particles is not particularly limited, and examples thereof include particles made of resin, metal, or metal oxide. As the resin particles, one or more selected from the group consisting of acrylic, phenol, polystyrene, silicone, melamine, epoxy, polyamide and PTFE (polytetrafluoroethylene) for reasons such as chemical resistance and heat resistance. Is mentioned. Since resin particles have a lower specific gravity than metal particles or the like, the specific gravity of silver-coated particles can be reduced by using resin particles as mother particles. Therefore, if this silver-coated particle is used as a conductive filler contained in a conductive paste or the like, it is possible to prevent deformation of the printed pattern (paste after printing) due to its own weight. That is, it is excellent in that it is easy to prepare a conductive paste having excellent printed pattern shape retention. Examples of the metal particles include metal particles that are lower in redox potential than silver and include particles of copper, nickel, iron, aluminum, zinc, tin, cobalt, indium, vanadium, or lead. Examples of the metal oxide particles include particles of silica, alumina, copper oxide, iron oxide, titanium oxide, and the like.

The base particles, primary particle diameter D _P is preferably used spherical particles 0.3～9.5Myuemu. This is because easily obtained silver-coated particles with a desired specific gravity, the desired dispersed particle size D _50. The spherical shape here is not limited to a perfect sphere. The primary particle diameter D _P of the mother particle is 1000 particles with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, model name: SU-1500) at a magnification of 5000 times by software (product name: PC SEM). This is the average value calculated by measuring the diameter. Furthermore, when using a spherical thing, it is preferable to use the thing with the variation coefficient of a particle size, Preferably it is 7% or less, More preferably, it is 5% or less, and the particle size is uniform. The coefficient of variation (CV value, unit:%) of the base particle is a value obtained from the primary particle diameter D _P of the above 1000 base particles by the formula: [(standard deviation / primary particle diameter D _P ) × 100]. Say.

  When resin particles and metal oxide particles are used for the mother particles, a tin adsorption layer can be provided on the surface of the mother particles before coating with silver by a pretreatment described later. Generally, when electroless plating is performed on the surface of a nonconductor such as an organic material or an inorganic material, it is necessary to perform a catalyst treatment on the surface of the nonconductor in advance. As a pretreatment, this catalyst treatment is carried out and a tin adsorption layer is provided on the surface of the mother particles, whereby silver (silver coating layer) having the following characteristics is formed by an electroless plating method described later. The tin adsorption layer is formed by adhering divalent ions of tin in the tin compound used in the pretreatment to the surface of the mother particle.

  Subsequently, a method for producing the silver-coated particles of the present invention will be described. First, when resin particles and metal oxide particles are used for the mother particles, the mother particles are pretreated with an aqueous solution of a tin compound (a step of forming a tin adsorption layer). Next, electroless silver plating is performed on the mother particles using a reducing agent (a step of forming a silver coating layer).

  In the pretreatment, for example, mother particles are added to an aqueous solution of a tin compound and stirred. Then, the mother particles are filtered and washed with water. Although stirring time is suitably determined by the temperature of the following aqueous solution of a tin compound and the content of the tin compound, it is preferably 0.5 to 24 hours.

  The temperature of the aqueous solution of the tin compound is 20 to 45 ° C, preferably 27 to 35 ° C. When the temperature of the aqueous solution of the tin compound is less than 20 ° C., the activity of the aqueous solution is lowered due to the temperature decrease, and the tin compound does not sufficiently adhere to the mother particles. On the other hand, when the temperature of the aqueous solution of the tin compound is higher than 45 ° C., the tin compound is oxidized, so that the aqueous solution becomes unstable and the tin compound does not sufficiently adhere to the mother particles. By carrying out this pretreatment with an aqueous solution at 20 to 45 ° C., silver crystals having an appropriate crystallite diameter can be precipitated. For this reason, the silver plating layer (silver coating layer) excellent in adhesiveness and denseness can be formed.

Examples of the tin compound used in the pretreatment include stannous chloride, stannous fluoride, stannous bromide, stannous iodide, and the like. When stannous chloride is used, the content of stannous chloride contained in the tin compound aqueous solution is preferably in the range of ^{30 to} 100 g / dm ³ . If the content of stannous chloride is 30 g / dm ³ or more, it is easy to form a uniform tin adsorption layer. Moreover, it is easy to suppress the amount of inevitable impurities in stannous chloride as the content of stannous chloride is 100 g / dm ³ or less. Note that stannous chloride can be contained in an aqueous solution of a tin compound until saturation.

It is preferable that the aqueous solution of a tin compound contains 0.5-2 cm < ³ > of hydrochloric acid with respect to 1 g of stannous chloride. When the amount of hydrochloric acid is 0.5 cm ³ or more, the solubility of stannous chloride can be improved and the hydrolysis of tin can be suppressed. When the amount of hydrochloric acid is 2 cm ³ or less, the pH of the aqueous solution of tin compound does not become too low, and tin can be efficiently adsorbed to the mother particles.

  The electroless plating method is a so-called wet plating method which is a chemical plating method based on the reducing power of a reducing agent. For example, (1) a complexing agent is added together with a dispersing agent while adding mother particles to a solvent such as water. A method of adding a reducing agent or the like and stirring to prepare a slurry, and then dropping a silver salt aqueous solution, and (2) adding a mother particle to a solvent such as water and stirring the silver salt together with the dispersing agent and complexing A method in which a slurry is prepared by adding a stirring agent and the like and then adding a reducing agent aqueous solution, and (3) adding a mother particle to a solvent such as water and stirring the complexing agent, a reducing agent, etc. together with the dispersing agent And stirring to prepare a slurry, and then adding a silver salt, preferably maintaining the temperature at 5 to 30 ° C., and further dropping a caustic aqueous solution such as an aqueous sodium hydroxide solution to adjust the pH to preferably 10. The method of adjusting to 0 or more is mentioned, whichever one But it may be applied. In addition, in the method of said (1)-(3), it does not specifically limit about the procedure at the time of preparing the said slurry, For example, a dispersing agent, a reducing agent, etc. are added to solvents, such as water, and a dispersing agent etc. are included. After preparing the aqueous solution in advance, it may be adjusted by the procedure of adding the mother particles at the end. Moreover, when preparing the said slurry, you may add sodium hydroxide etc. for pH adjustment.

In the present invention, when a silver coating layer is formed by reducing and depositing silver on the surface of the mother particle by an electroless plating method, a predetermined dispersant is used at a predetermined ratio, so that The crystallite diameter is controlled in the above-mentioned range of 12.5 to 17.9 nm. The crystallite diameter of silver covering the surface of the mother particle can be reduced by adjusting the temperature conditions in the electroless plating or the above-mentioned pretreatment conditions, but the crystallite diameter is reduced by these methods. Then, as described above, silver crystallites covering one base particle are abnormally precipitated in a lump shape on the surface of the base particle, and it becomes difficult to form a dense and excellent silver coating layer with high coverage. . In the present invention, a polycarboxylate is used as the dispersant, and the amount added is 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the base particles. Here, the mother particle refers to a mother particle before pretreatment. The addition amount of the polycarboxylate is limited to the above range because if the addition amount of the polycarboxylate is less than the lower limit, the crystallite diameter is not sufficiently reduced, and the surface of one base particle is coated. having a silver are, crosslinking occurs agglomeration between the silver coating the other adjacent surface of the base particles, the desired dispersion particle diameter D ₅₀ size of each of the silver-coated particles are chained to bloat This is because silver-coated particles cannot be obtained. When the upper limit is exceeded, the polycarboxylate inhibits the plating reaction, and the adhesion of the silver coating layer to the mother particles decreases, so that the mother particles are not sufficiently covered with silver, and the desired volume resistivity is obtained. This is because there is a problem that it cannot be performed. Among these, it is preferable to make the addition amount of polycarboxylate into the ratio used as 0.2-1.0 mass part with respect to 100 mass parts of mother particles. Suitable polycarboxylates include ammonium polycarboxylate, sodium polycarboxylate, polyacrylic acid, ammonium polyacrylate, sodium polyacrylate, ammonium salt of polycarboxylic acid copolymer, polycarboxylic acid copolymer Examples thereof include sodium salts, dicarboxylic acid polymer sodium salts, and dicarboxylic acid copolymer salts.

  As the silver salt, silver nitrate or silver dissolved in nitric acid can be used. As the complexing agent, salts such as ammonia, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, nitrotriacetic acid, triethylenetetraamminehexaacetic acid, sodium thiosulfate or iodide salt can be used. As the reducing agent, formalin, glucose, Rochelle salt (sodium potassium tartrate), hydrazine and its derivatives, hydroquinone, L-ascorbic acid, formic acid, or the like can be used. As the reducing agent, formaldehyde is preferable because of its strong reducing power, a mixture of two or more reducing agents containing at least formaldehyde is more preferable, and a mixture of reducing agent containing formaldehyde and glucose is most preferable.

  Through the above steps, the silver-coated particles of the present invention are obtained. The silver-coated particles can be used as a conductive filler in conductive pastes, anisotropic conductive materials, and the like that are used when forming electrical wirings and electrodes by a printing method. The conductive paste can be prepared using a resin component, a curing agent, a solvent and the like in addition to the conductive filler. With the conductive paste using the silver-coated particles of the present invention as a conductive filler, it is possible to form fine electric wires or electrodes having excellent conductivity.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, 20 g of stannous chloride and 15 cm ³ of hydrochloric acid having a concentration of 35% were diluted to 1 dm ³ with water using a 1 dm ³ volumetric flask and kept at 30 ° C. To this aqueous solution, a 2.0μm primary particle diameter D _P as mother particles, and by adding the acrylic resin 50g spherical a 2.1% coefficient of variation of particle size, and stirred for 1 hour, then, acrylic The resin was filtered off and washed with water for pretreatment.

Next, a silver coating layer was formed by electroless plating on the acrylic resin surface on which the tin coating layer was formed by the pretreatment. Specifically, first, 40 g of ethylenediaminetetraacetate as a complexing agent, 20.0 g of sodium hydroxide as a pH adjusting agent, and 15 ml of formalin (formaldehyde concentration 37% by mass) as a reducing agent are added to 2 dm ³ of water. Ammonium polycarboxylate (ie, 0.25 g) in an amount of 0.5 parts by mass with respect to 100 parts by mass of the acrylic resin before pretreatment is added as a dispersant, and these are dissolved to form a complexing agent, a reducing agent. An aqueous solution containing an agent, a dispersant and the like was prepared. Next, a slurry was prepared by immersing the pretreated acrylic resin in this aqueous solution.

  Next, 30 g of silver nitrate, 35 ml of 25% ammonia water, and 50 ml of water were mixed to prepare an aqueous solution containing silver nitrate, and the aqueous solution containing silver nitrate was added dropwise while stirring the slurry. Further, a sodium hydroxide aqueous solution was dropped into the slurry after dropping the silver nitrate-containing aqueous solution to adjust the pH to 12, and silver was deposited on the resin surface by stirring while maintaining the temperature at 325 ° C. Then, washing | cleaning and filtration were performed, and it was finally dried at the temperature of 80 degreeC, and the silver coating particle shown in the following Table 1 was obtained.

<Example 2>
The mother particles, a primary particle diameter D _P is 1.0 .mu.m, and except that the coefficient of variation of particle diameter was changed to spherical silica particles is 2.2% in the same manner as in Example 1, the following table Silver-coated particles shown in 1 were obtained.

<Example 3>
The mother particles, a primary particle diameter D _P is 1.2 [mu] m, and the coefficient of variation of particle diameter was changed to copper particles spherical is 3.8% silver-coated on the surface of the base particles without pretreatment Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 1 except that the layer was formed.

<Example 4>
Silver coated particles shown in Table 1 below were obtained in the same manner as in Example 1 except that sodium polycarboxylate was used as a dispersant instead of ammonium polycarboxylate.

<Example 5>
The silver shown in Table 1 below is the same as in Example 1 except that the amount of ammonium polycarboxylate added is changed to an amount of 0.05 parts by mass with respect to 100 parts by mass of the acrylic resin before pretreatment. Coated particles were obtained.

<Example 6>
The silver shown in Table 1 below is the same as in Example 1 except that the amount of ammonium polycarboxylate added is changed to 2.0 parts by mass with respect to 100 parts by mass of the acrylic resin before pretreatment. Coated particles were obtained.

<Example 7>
The mother particles, a primary particle diameter D _P is 0.3 [mu] m, and except that the coefficient of variation of particle diameter was changed to spherical acrylic resin which is a 12.0 percent in the same manner as in Example 1, the following table Silver-coated particles shown in 1 were obtained.

<Example 8>
The mother particles, a primary particle diameter D _P is 5.0 .mu.m, and was changed to spherical acrylic resin is 2.4% coefficient of variation of particle diameter in the same manner as in Example 1, the following table Silver-coated particles shown in 1 were obtained.

<Example 9>
The mother particles, a primary particle diameter D _P is 9.5 .mu.m, and was changed to spherical acrylic resin is 2.2% coefficient of variation of particle diameter in the same manner as in Example 1, the following table Silver-coated particles shown in 1 were obtained.

<Comparative Example 1>
Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 1 except that ammonium polycarboxylate as a dispersant was not used.

<Comparative Example 2>
Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 2 except that ammonium polycarboxylate as a dispersant was not used.

<Comparative Example 3>
Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 3 except that ammonium polycarboxylate as a dispersant was not used.

<Comparative example 4>
Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 1 except that gelatin was used as a dispersant instead of ammonium polycarboxylate.

<Comparative Example 5>
The silver shown in Table 1 below is the same as in Example 1 except that the amount of ammonium polycarboxylate added is changed to an amount of 0.03 parts by mass with respect to 100 parts by mass of the acrylic resin before pretreatment. Coated particles were obtained.

<Comparative Example 6>
The silver shown in Table 1 below is the same as Example 1 except that the amount of ammonium polycarboxylate added is changed to 2.1 parts by mass with respect to 100 parts by mass of the acrylic resin before pretreatment. Coated particles were obtained.

<Comparative Example 7>
Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 7 except that ammonium polycarboxylate as a dispersant was not used.

<Comparative Example 8>
Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 8 except that ammonium polycarboxylate as a dispersant was not used.

<Comparative Example 9>
Silver-coated particles shown in Table 1 below were obtained in the same manner as in Example 9 except that ammonium polycarboxylate as a dispersant was not used.

<Comparison test and evaluation>
For the silver-coated particles obtained in Examples 1 to 9 and Comparative Examples 1 to 9, the crystallite diameter of silver (silver coating layer), the dispersed particle diameter D ₅₀ of the silver-coated particles, and the volume resistivity were measured. The appearance of the particles was evaluated. These results are shown in Table 1 below. Moreover, the photograph figure when the silver coating particle obtained in Example 1 and Comparative Examples 1 and 4 was observed with the scanning electron microscope (Hitachi High-Technologies Corporation model name: SU-1500) is respectively shown in FIGS. As shown in FIG.

  (i) Crystallite size: Calculated using an X-ray diffractometer (Rigaku Corporation model name: RINT2000) and Debye-Scherrer equation.

(ii) Dispersed particle diameter D ₅₀ : 20 ml of an aqueous solution prepared by adding 0.5% by mass of sodium hexametaphosphate to water was prepared. To this aqueous solution, silver-coated particles were added at a ratio of 0.1% by mass and then sufficiently dispersed by ultrasonic irradiation. Thereafter, the aqueous solution in which the silver-coated particles are dispersed is stirred at a rotation speed of 500 rpm, and the silver-coated particles in the stirred state are subjected to laser diffraction scattering type particle size distribution analyzer (manufactured by Shimadzu Corporation, model name: SALD-200V). ER) was used to measure the median value D ₅₀ at the volume-based particle size. Further, the value of D ₅₀ / D _P was calculated from the measured value of the dispersed particle diameter D _{50 and} the value of the primary particle diameter D _P of the mother particles.

  (iii) Volume resistivity: The silver coated particles were measured for the volume resistivity of the powder in a state where a pressure of 100 kPa was applied using a resistivity meter (model name: Loresta GP MCP manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

  (iv) Appearance: The appearance of the silver-coated particles was observed and evaluated with a scanning electron microscope (model name: SU-1500, manufactured by Hitachi High-Technologies Corporation). In Table 1, “A” indicates a case where the area occupied by silver is 80% or more with respect to 100% area of one silver-coated particle projected on the SEM image, and “B” indicates that silver occupies. The case where the area is 50% or more and less than 80% is shown, and “C” shows the case where the area occupied by silver is less than 50%.

As is clear from Table 1, when compared with Examples 1-9 and Comparative Examples 1-9, Comparative Examples 1 to 9 without using a polycarboxylate as a dispersant and having a crystallite diameter of silver exceeding 17.9 μm. In Example 3 and Comparative Examples 7-9, the same results as in Examples 1-9 were obtained in terms of volume resistivity and appearance evaluation. On the other hand, as shown in FIG. 2, in Comparative Example 1 and the like, cross-linking aggregation due to silver between adjacent silver-coated particles occurred, and the size of one silver-coated particle was enlarged in a chain, so that the dispersed particle diameter D ₅₀ Values and the like were larger than those in Examples 1 to 8. From this, it can be seen that Examples 1 to 8 are superior in terms of fine printing and the like. In Example 9, due to the use of those relatively large primary particle diameter D _P to the base particles, while indicating a large value is dispersed particle diameter D ₅₀ as compared to Comparative Example 1, evaluation of appearance In addition, since the value of D ₅₀ / D ₁₀ is a very small value of 1.1, there is little aggregation, and a high coverage is achieved with an extremely thin silver coating layer. Therefore, it is superior to Comparative Example 1 in terms of productivity.

In Comparative Example 4 using a dispersant other than polycarboxylate, cross-linking aggregation due to silver is somewhat suppressed, and the value of the dispersed particle diameter D ₅₀ is higher than that in Comparative Example 1 using no dispersant. Although the particle size is small, many particles whose surface of the mother particle is not covered with silver as shown in FIG. 3 are observed because the dispersing agent itself causes the formation of the silver coating layer. It was. Therefore, the silver coverage was significantly reduced, and the volume resistivity was very high compared to Examples 1-9.

Moreover, although the polycarboxylate was used as the dispersant, the amount used was less than the predetermined amount, and in Comparative Example 5 in which the crystallite diameter of silver slightly exceeded 17.9 μm, the aggregation was more than in Example 5. The degree of enlargement and the degree of enlargement increased, and “dispersed particle diameter D ₅₀ ” and “D ₅₀ / D _P ” showed high values. Moreover, although the polycarboxylic acid salt was used as a dispersing agent, in the comparative example 6 in which the usage-amount exceeds predetermined amount, the silver coating rate fell and the volume resistivity showed the high value.

  On the other hand, in Examples 1 to 9, as shown in FIG. 1, aggregation of silver-coated particles, coating unevenness, and the like were not observed, which was suitable for forming electrodes and the like by fine printing, and was excellent in conductivity. Silver-coated particles were obtained.

  The present invention is suitable for forming an electronic component (electrode or electrical wiring, etc.) or an anisotropic conductive material provided in a semiconductor element, electronic device, electronic display device, or the like, which requires formation with a fine line width. Available.

Claims (4)

In the silver-coated particle having a structure in which the surface of the mother particle is coated with silver,
The silver crystallite diameter covering the mother particles is 12.5 to 17.9 nm,
The dispersed particle diameter D ₅₀ of the silver-coated particles in the aqueous solution is 0.9 to 10 μm,
Volume resistivity measured while applying a pressure of 100kPa is Ri der 1.0 × 10 ^-3 Ω · cm or less,
Silver-coated particles , wherein the base particles are made of resin, metal (except copper) or metal oxide . Silver of the dispersed particle diameter D ₅₀ and is according to claim 1, which is a 1.1 to 3.0 (primary particle diameter D _P of the dispersion particle diameter D ₅₀ / base particles) the ratio of the primary particle diameter D _P of the mother particle Coated particles. In the method for producing silver-coated particles having a structure in which the surface of the mother particle is coated with silver,
Including a step of reducing and precipitating silver on the surface of the mother particles by an electroless plating method using a dispersant containing a polycarboxylate,
The addition amount of the polycarboxylate is 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the base particles,
The crystallite diameter of the silver covering the mother particles is 12.5 to 17.9 nm, the dispersed particle diameter D ₅₀ of the silver-coated particles in the aqueous solution is 0.9 to 10 μm, and the pressure is 100 kPa. A method for producing silver-coated particles, wherein the volume resistivity measured in the applied state is 1.0 × 10 ⁻³ Ω · cm or less. The method for producing silver-coated particles according to claim 3, wherein the mother particles are made of resin, metal, or metal oxide.