JP2007138249A - Method for producing silver grain, silver grain-containing composition containing the obtained silver grain and its use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily produce plate-shaped silver grains using silver ions, a low molecular dispersant and a reducing agent. <P>SOLUTION: In the method for producing a silver grain mainly having a plate-like shape, a silver salt and a low molecular dispersant are added to water to prepare an aqueous solution of the silver salt and the low molecule based dispersant; a prescribed ratio of reducing agent is added to the aqueous solution so as to prepare a mixed solution; the mixed solution is kept still at 20 to 40°C to bring silver ions in the mixed solution into reduction reaction; wherein the additive ratio of the silver salt, the low molecular dispersant and the reducing agent is 1: (0.1 to 100): (0.001 to 100) by molar ratios. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a method for easily producing plate-like silver particles having a nano-order particle size having a selective absorption function for a specific wavelength of visible light or near-infrared light, and silver particles containing the obtained silver particles The present invention relates to a composition and its use.

Noble metal colloids hardly change chemically and constitute so-called nanoparticles having a particle size of about several nanometers to several tens of nanometers. In addition, it is expected to be applied to various uses, including the use as a colorant for paints and resin compositions, by developing colors specific to each colloid.
As a method for producing such colored metal particles, for example, a nanoprism forming method is disclosed in which a silver crystal is formed by exposing a suspension of amorphous silver particles to a light source having a wavelength of less than 700 nm (for example, , See Patent Document 1). By this method, a plate-like silver single crystal is formed. Also, BSPP (Bis (p-sulfonatophenyl) phenylphosphine dehydrate dipotassium salt) is dropped into a spherical silver colloid synthesized by reducing silver ions with sodium borohydride in an aqueous solution in which trisodium citrate and silver nitrate are dissolved. A method of synthesizing silver nanoprisms by irradiating the aqueous solution with a fluorescent lamp is disclosed (for example, see Non-Patent Document 1). In addition, silver colloid synthesized by reducing silver ions with sodium borohydride in an aqueous solution in which trisodium citrate and BSPP are dissolved is irradiated with visible light with two wavelengths selected by a filter. There is a method for controlling the absorption wavelength of the silver nanoprism. Further, it is known that plasmon absorption shifts to the longer wavelength side as the length of the side of the silver nanoprism becomes longer (for example, see Non-Patent Document 2). In addition, a silver colloid synthesized by reducing silver ions with sodium borohydride in an aqueous solution in which trisodium citrate and BSPP or PVP are dissolved is combined with visible light of one wavelength selected by fluorescent lamp → filter. There is a method of controlling the absorption wavelength of the silver nanoplate by irradiating (see Non-Patent Document 3, for example).

  In addition, paints have been developed that improve the colorability of the paint and the stability of the solution by utilizing a resonance absorption phenomenon called plasmon absorption that occurs when the metal fine particles are irradiated with light (for example, Patent Documents 2 and 3). reference.). In Patent Document 2, a noble metal or copper compound is dissolved in a solvent, and after adding a high molecular weight pigment dispersant, it is reduced to the noble metal or copper so that it has high chroma and has sufficient coloration properties. A method for producing a colloidal solution of noble metal or copper that does not aggregate when added to a resin is disclosed. According to this Patent Document 2, the color development due to the noble metal colloid is caused by the plasma vibration of electrons and is due to a color development mechanism called plasmon absorption. The color development due to plasmon absorption is caused by free electrons in the metal being shaken by the photoelectric field, This is because charges appear on the particle surface and nonlinear polarization occurs. In Patent Document 3, by reducing the noble metal or copper ions in the aqueous phase, generation of the noble metal or copper and interphase transfer of the noble metal or copper from the aqueous phase to the organic solvent phase immiscible with water are produced. In other words, a production method for obtaining colloidal particles of stable noble metal or copper in an organic solvent phase is disclosed. The noble metal or copper colloid obtained by the method disclosed in Patent Document 3 is stable and exists in a high concentration, and is described as being dark and highly saturated, and suitable as a colorant.

Also, a slurry containing a silver salt ammine complex and a heavy metal salt ammine complex that functions as a crystallizing agent during the reduction reaction, and a solution containing a reducing agent potassium sulfite and gelatin as a protective colloid are mixed at a time. Then, a method of producing hexagonal plate-like crystal silver fine particles having a primary particle size of 5 to 10 μm by reducing the silver salt ammine complex and recovering the produced silver particles is known (for example, (See Patent Document 4). Further, there is known a silver fine particle which is a substantially plate-like particle having two main surfaces, the particle having a thickness of 50 nm or less and a major axis of 5000 nm or less (for example, see Patent Document 5). .) In the method disclosed in Patent Document 5, silver fine particles are produced by stirring a solution obtained by dissolving at least a polymer compound, a reducing agent, and a silver salt at a temperature of 25 ° C. or higher and 60 ° C. or lower. . Furthermore, a coating for forming a metal thin film characterized by containing plate-like metal fine particles having a thickness of 50 nm or less and a major axis of 5000 nm or less is known (for example, see Patent Document 6). According to Patent Document 6, for example, the plate-like fine metal particles are prepared by adding citric acid to an aqueous solution containing silver nitrate or chloroplatinic acid, and adjusting the ratio of metal ions to citric acid or the concentration of metal ions in the aqueous solution. Thus, it can be manufactured by controlling the thickness and the major axis of the metal fine particles, and then heating and reducing.
US Patent Application Publication No. 2003/0136223 (claim 1, Fig. 7) JP-A-11-80647 (Claim 7, paragraph [0004], paragraph [0012]) JP 11-319538 A (Claim 1, paragraph [0081]) JP-A-11-106806 (Claim 2, paragraph [0004]) JP-A-2005-105376 (Claims 1 and 5) JP 2005-15647 A (Claim 1, paragraph [0019]) R.Jin et al, SCIENCE, Vol.294, 30 november 2001, p.1901-1903 R.Jin et al, Letter to Nature, Vol.425, 2 october 2003, p.487-490 A. Callegari et al, NANO LETTERS, Vol.3, No.11, 2003, p.1565-1568

  In the production of the silver prism and silver plate described in Patent Document 1 and Non-Patent Documents 1 to 3, the first step of reducing silver ions to a spherical silver colloid and the silver colloid reduced in the first step with light. A multi-step manufacturing process was required, such as a second step of irradiation to change the shape into a silver prism or silver plate. Moreover, since the specific wavelength light is irradiated for a long time when the shape is changed, it is not suitable for mass production. Furthermore, there is a problem that a high molecular weight dispersant is adsorbed on the surface of the obtained silver fine particles, and it is difficult to modify another chemical substance on the silver surface.

  Further, in the methods shown in Patent Document 2 and Patent Document 3, since a spherical noble metal colloid is used as a colorant and plate-shaped fine particles are not used as a colorant, variations in coloring cannot be obtained. . Further, the noble metal or copper colloid disclosed in Patent Document 2 has a problem that it is difficult to modify another chemical substance on the silver surface because the high molecular weight pigment dispersant functions as a protective colloid. In the method for producing silver fine particles shown in Patent Document 4 and Patent Document 5, since a polymer compound is used as a dispersant, the polymer compound is adsorbed on the obtained silver fine particles, and another chemical substance is used. There was a problem that it was difficult to modify the silver surface. Further, in the method for producing plate-like metal fine particles disclosed in Patent Document 6, it is necessary to carry out heat reduction after controlling the thickness and the major axis of the metal fine particles, which makes the production process complicated.

  An object of the present invention is to provide a method for easily producing plate-like silver particles using silver ions, a low molecular weight dispersant, and a reducing agent, a silver particle-containing composition containing the obtained silver particles, and use thereof. There is to do.

The invention according to claim 1 prepares an aqueous solution of a silver salt and a low molecular weight dispersant by adding a silver salt and a low molecular weight dispersant to water, and adds a reducing agent to the aqueous solution at a predetermined ratio to prepare a mixed solution. A method of producing silver particles mainly having a plate shape by preparing and allowing the mixed solution to stand at 20 to 40 ° C. to cause reduction reaction of silver ions in the mixed solution. Silver particles characterized in that the addition ratio of the dispersing agent and the reducing agent is a molar ratio of silver salt: low molecular weight dispersant: reducing agent = 1: (0.1-100) :( 0.001-100) It is a manufacturing method.
The invention according to claim 2 is the invention according to claim 1, wherein the low molecular dispersant is one or more organic acids selected from the group consisting of citric acid, malic acid, tartaric acid and succinic acid. Or the manufacturing method which is its salt.
The invention according to claim 3 is the method according to claim 1, wherein the reducing agent is a compound of either one or both of dimethylamine borane and hydrazine.
The invention according to claim 4 is the manufacturing method according to claim 1, wherein the obtained plate-like silver particles have a particle diameter of 10 to 1000 nm.

The invention according to claim 5 is a silver particle-containing composition comprising silver particles obtained by the production method according to any one of claims 1 to 4.
The invention which concerns on Claim 6 is a coating composition, a coating film, or a film formed using the silver particle containing composition of Claim 5.
The invention according to claim 7 is an optical filter, a wiring material, an electrode material, a catalyst, a colorant, a cosmetic, a near-infrared absorption containing silver particles obtained by the production method according to any one of claims 1 to 4. Agent, anti-counterfeiting ink, electromagnetic shielding material, surface-enhanced fluorescent sensor, biomarker, recording element, drug carrier for drug delivery system (DDS), biosensor, DNA chip, test drug or Raman enhancement Reagent.

  In the method for producing silver particles of the present invention, a silver salt and a low molecular weight dispersant are added to water to prepare an aqueous solution of a silver salt and a low molecular weight dispersant, and a reducing agent is added to the aqueous solution at a predetermined ratio. This is a method for producing silver particles mainly having a plate shape by preparing a mixed solution and allowing the mixed solution to stand at 20 to 40 ° C. to cause silver ions in the mixed solution to undergo a reduction reaction. The addition ratio of the molecular dispersant and the reducing agent is silver salt: low molecular dispersant: reducing agent = 1: (0.1-100) :( 0.001-100) in a molar ratio. . A silver salt, a low molecular weight dispersant and a reducing agent are added so that the molar ratio is within the above range to prepare a mixed solution, and this mixed solution is allowed to stand at 20 to 40 ° C. to obtain silver ions in the mixed solution. By carrying out the reduction reaction, plate-like silver particles having a predetermined particle diameter can be easily produced. In addition, by using one or more organic acids selected from the group consisting of citric acid, malic acid, tartaric acid and succinic acid or salts thereof as the low molecular weight dispersant, the plate-like silver particles are stably dispersed. An aqueous solution can be obtained and plate-like silver particles can be produced efficiently. By using one or both of dimethylamine borane and hydrazine as the reducing agent, plate-like silver particles can be obtained with good reproducibility.

Moreover, the silver particle obtained by the manufacturing method of this invention can be utilized as a silver particle containing composition. Moreover, silver particle containing composition by containing 1 type, or 2 or more types chosen from the group which consists of dye, a pigment, fluorescent substance, a metal oxide, a spherical metal particle, and a rod-shaped metal particle (metal nanorod) with silver particle It can be used as a thing. This silver particle containing composition can be utilized with various forms, such as a coating composition, a coating film, or a film.
Furthermore, the silver particles obtained by the production method of the present invention are optical filters, wiring materials, electrode materials, catalysts, colorants, cosmetics, near infrared absorbers, anti-counterfeiting inks, electromagnetic wave shielding materials, surface-enhanced fluorescent sensors, biomarkers. It can be widely used for a recording element, a drug holder for a drug delivery system, a biosensor, a DNA chip, a test agent, a Raman enhancement reagent, and the like.

Next, the best mode for carrying out the present invention will be described.
In the present invention, “plate-like silver particles” are substantially plate-like silver particles having two main surfaces. The main surface of the substantially plate-like silver particles is selected from shapes such as a substantially triangular shape, a substantially pentagonal shape, and a substantially hexagonal shape. This particle shape may contain a part of irregularly shaped particles with some missing corners and sides. The width of the two main surfaces of the silver particles is 40 nm or less, and the particle diameter that is the maximum length of the main surfaces of the particles is 10 to 1000 nm. The aspect ratio of the plate-like silver particles (the maximum length of the main surface of the plate-like silver particles / the width of the main surface) is 3 or more.

  In the method for producing silver particles of the present invention, a silver salt and a low molecular weight dispersant are added to water to prepare an aqueous solution of a silver salt and a low molecular weight dispersant, and a reducing agent is added to the aqueous solution at a predetermined ratio. This is a method for producing mainly silver particles having a plate shape by preparing a mixed solution and allowing the mixed solution to stand at 20 to 40 ° C. to cause a reduction reaction of silver ions in the mixed solution. The characteristic structure is that silver salt, low molecular weight dispersant and reducing agent are added in a molar ratio of silver salt: low molecular weight dispersant: reducing agent = 1: (0.1-100) :( 0.001 ~ 100). A silver salt, a low molecular weight dispersant and a reducing agent are added so that the molar ratio is within the above range to prepare a mixed solution, and this mixed solution is allowed to stand at 20 to 40 ° C. to obtain silver ions in the mixed solution. By carrying out the reduction reaction, plate-like silver particles having a predetermined particle diameter can be easily produced.

  Examples of the silver salt used include silver nitrate, silver sulfate, silver acetate and silver halide. Of these, silver nitrate is particularly preferred because of its high solubility in water. When preparing the mixed solution, the silver salt is preferably dissolved in water and added and mixed as an aqueous solution. Silver salts exist as silver ions and anions in aqueous solutions. The silver concentration in the production is suitably in the range of 10 to 100,000 μmol / L, particularly preferably in the range of 100 to 10,000 μmol / L. If the silver concentration is less than the lower limit, the production efficiency of the plate-like silver particles decreases, and if it exceeds the upper limit, uniform growth of the silver particles is hindered, and the shape reproducibility of the plate-like silver particles decreases.

  Examples of the low molecular weight dispersant used include one or more organic acids selected from the group consisting of citric acid, malic acid, tartaric acid, and succinic acid, or salts thereof. By using the above kind of low molecular weight dispersant, an aqueous solution in which silver particles are stably dispersed without aggregation can be obtained, and silver particles can be produced efficiently. The low molecular weight dispersant is mixed with water to make an aqueous solution in which the low molecular weight dispersant is dissolved, and then the aqueous solution in which the low molecular weight dispersant is dissolved and the aqueous solution in which the silver salt is dissolved are mixed to form a silver salt and a low molecular weight dispersant. It is preferable to prepare an aqueous solution of a molecular dispersant. The low molecular weight dispersant is added so that the molar ratio with the silver salt falls within the range of silver salt: low molecular weight dispersant = 1: (0.1 to 100). For example, it adds so that it may become a molar ratio of 0.1-100 micromol with respect to 1 micromol of silver. The concentration of the low molecular weight dispersant during production is suitably in the range of 1 to 10000000 μmol / L, more preferably in the range of 10 to 1000000 μmol / L. If the concentration of the low molecular weight dispersant is less than the lower limit, the reduction reaction of silver ions proceeds rapidly, so that not only plate-like silver particles are difficult to produce, but also the dispersion stability of the silver particles deteriorates and agglomerates. It becomes easy to do. When the concentration of the low molecular weight dispersant exceeds the upper limit, the production rate of spherical silver particles increases and the production amount of plate-like silver particles decreases. Therefore, the malfunction which raises the cost which manufactures plate-like silver particle arises.

  As a reducing agent to be used, either one or both of dimethylamine borane and hydrazine may be mentioned. When adding the reducing agent, it is preferable to add the reducing agent while stirring the aqueous solution of the prepared silver salt and low molecular weight dispersant so that the concentration of the reducing agent is not locally biased. The reducing agent is added so that the molar ratio with the silver salt falls within the range of silver salt: reducing agent = 1: (0.001 to 100). The reducing agent is preferably added at an appropriate ratio as follows depending on the type used.

Dimethylamine borane is mixed with water to obtain an aqueous solution having an arbitrary concentration, and then an aqueous solution in which dimethylamine borane is dissolved is mixed with an aqueous solution of a silver salt and a low molecular weight dispersant to prepare a mixed solution. The addition amount when dimethylamine borane is used as the reducing agent is preferably silver salt: reducing agent = 1: (0.1 to 100) in molar ratio. When the addition amount of the reducing agent with respect to the silver salt is less than the above ratio, the reduction reaction of silver ions in the mixed solution becomes insufficient, and the yield of the plate-like silver particles is deteriorated. Moreover, when there are more addition amounts of a reducing agent than the said ratio, a reductive reaction will advance rapidly, many spherical silver particles will generate | occur | produce, and the production amount of plate-like silver particles will decrease.
Hydrazine is mixed with an undiluted solution or water to obtain an aqueous solution having an arbitrary concentration, and then a mixed solution is prepared by mixing an aqueous solution of hydrazine undiluted solution or hydrazine with an aqueous solution of a silver salt and a low molecular weight dispersant. The addition amount when hydrazine is used as the reducing agent is preferably silver salt: hydrazine = 1: (0.1 to 10) in molar ratio. If the amount of hydrazine added to the silver salt is less than the above ratio, the reduction of silver ions in the mixed solution will be insufficient, and the yield of plate-like silver particles will deteriorate. On the other hand, when the amount of hydrazine added is larger than the above ratio, the reduction reaction proceeds rapidly, a large amount of spherical silver particles are generated, and the amount of plate-like silver particles produced is reduced.

After preparing a mixed solution by adding a reducing agent to an aqueous solution of a silver salt and a low molecular weight dispersant, this mixed solution is allowed to stand at 20 to 40 ° C. for 1 to 120 hours to reduce silver ions in the mixed solution. By making it react, the silver particle whose shape is mainly plate-like is obtained. The mixture is preferably left under light shielding conditions.
Furthermore, in the manufacturing method of this invention, you may add various additives as needed other than the said silver salt, a low molecular weight dispersing agent, and a reducing agent. Specific examples include leveling agents, antifoaming agents, slip agents, preservatives, and the like.

  According to the production method of the present invention, plate-like silver particles having a particle diameter of 10 to 1000 nm can be obtained in a dispersed state in an aqueous solution. The particle size of the obtained plate-like silver particles can be adjusted according to the type and amount of the low molecular dispersant used and the type and amount of the reducing agent. For example, the addition of a low molecular weight dispersant or a reducing agent in a small amount tends to increase the particle diameter of the resulting silver particles, and it can be obtained by adding a large amount of a low molecular weight dispersant or a reducing agent. The particle diameter of silver particles tends to be small. According to the method for producing silver particles of the present invention, silver particles having various shapes such as spherical silver particles and polyhedral silver particles are obtained as by-product particles together with plate-like silver particles. The production amount of the by-product particles can be increased or decreased by adjusting the type and addition amount of the reducing agent to be used. For example, by reducing the amount of reducing agent added, the amount of by-product particles tends to decrease, and by increasing the amount of reducing agent added, the amount of by-product particles tends to increase. is there.

  The silver particle containing composition of this invention contains the silver particle obtained by the said manufacturing method, It is characterized by the above-mentioned. Although the silver particle obtained by the said manufacturing method is obtained in the state disperse | distributed in aqueous solution, it can disperse | distribute stably also in non-aqueous solvents other than water by surface-treating this silver particle. By subjecting the silver particles to surface treatment with a non-aqueous dispersant having a side chain having an affinity for the non-aqueous solvent, a dispersion in which the silver particles are well dispersed in the non-aqueous solvent can be obtained. As the non-aqueous dispersant, those containing nitrogen atoms or sulfur atoms having high adsorptivity to silver particles are preferable. Examples of the dispersant containing a nitrogen atom include hexylamine, octylamine, decylamine, and dodecylamine. Examples of the dispersant containing a sulfur atom include butanethiol, hexanethiol, octanethiol, decanethiol, and dodecanethiol. Such a non-aqueous solvent dispersion of silver particles can be used as a raw material for the silver particle-containing composition. For example, a coating composition containing a binder such as a resin and a dispersion medium together with silver particles can be obtained.

  The aqueous dispersion of silver particles obtained by the production method of the present invention contains the low molecular weight dispersant used in the production, and the silver particles are recovered in a state containing the low molecular weight dispersant. When used in applications such as conductive materials, the low molecular dispersant exhibits an insulating action, so that high conductivity tends not to be obtained. Therefore, after the silver particles are produced, it is preferable to reduce or remove the low molecular weight dispersant contained in the aqueous dispersion. A low molecular weight dispersant reduced to 50 parts by weight or less, preferably 15 parts by weight or less with respect to 100 parts by weight of silver particles is suitable as the conductive material, and the proportion of the low molecular weight dispersant is more than that. High electrical conductivity cannot be obtained, which is not practical. Examples of the method for reducing or removing the low molecular weight dispersant from the aqueous dispersion of the silver particles produced include a precipitation method by aggregation and a centrifugal separation method. The sedimentation method by agglomeration is, for example, adding a pH adjusting agent or an electrolyte to the silver particle aqueous dispersion at a predetermined ratio to reduce the dispersion stability of the silver particles, and lightly agglomerate and settle the silver particles to form a supernatant. This is a method of removing the remaining low molecular weight dispersant. In this method, since the low molecular weight dispersant is not completely removed from the silver particle aqueous dispersion, it can be redispersed. Centrifugation is a method in which silver particles are precipitated by applying centrifugal force to an aqueous dispersion of silver particles, and the low molecular weight dispersant remaining in the supernatant is removed. By combining these methods, the low molecular weight dispersant can be efficiently reduced or removed. For example, by adding sodium hydroxide as a pH adjuster to a silver particle aqueous dispersion manufactured using trisodium citrate as a low molecular weight dispersant, the dispersion stability of the silver particles is reduced. At the same time as removing trisodium citrate depositing and remaining in the supernatant liquid by lightly aggregating each other and then centrifuging to accelerate the sedimentation speed of the agglomerates and allowing the silver particles to settle in a short time The silver particles can be concentrated.

  Since the silver particles obtained by the production method of the present invention contain not only plate-like silver particles but also by-product particles such as spherical silver particles, coating is performed using a silver particle-containing composition containing these silver particles. When a film (wiring) is formed, there is an advantage that the contact probability between particles is higher than that of silver particles having only a spherical shape or silver particles having only a plate shape, and the specific resistance value is lowered in the case of conductive use. .

  Since the silver particles obtained by the production method of the present invention are produced using a low molecular weight dispersant, an appropriate dispersant selected according to the use can be further added to the silver particle aqueous dispersion. Surface modification to silver particles can be easily performed. For example, in the case of conductive use, if a dispersant that volatilizes when heated is added, low temperature sintering becomes possible and a conductive paste with improved dispersion stability can be obtained. As such a dispersant, it is preferable to use a low molecular compound having an amino group, a thiol group, or a carboxyl group.

  The silver particles obtained by the production method of the present invention can be used as a silver particle-containing composition in which a surface treatment is performed with an appropriate dispersant and a dispersion medium and a binder are added thereto. As the binder, various resins that are normally transmissive for visible light to near infrared light, which are used for paints and moldings, can be used without any particular limitation. For example, acrylic resins, polyester resins, alkyd resins, urethane resins, silicone resins, fluororesins, epoxy resins, polycarbonate resins, polyvinyl chloride resins, polyvinyl alcohol, and other organic resins, radical polymerizable oligomers and monomers (if necessary Typical examples include a sol-gel solution using an alkoxysilane as a resin skeleton.

  In the silver particle-containing composition, as the solvent to be blended as necessary, a solvent in which the binder is dissolved or stably dispersed may be appropriately selected. Specifically, in addition to water, alcohols such as methanol, ethanol, propanol, hexanol, ethylene glycol and α-terpineol, glycols such as ethylene glycol, hydrocarbons such as decane and turpentine oil, and aromatics such as xylene and toluene Typical examples include hydrocarbons, cycloaliphatic hydrocarbons such as cyclohexane, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, ethers such as ethylene glycol monobutyl ether, and mixtures thereof. It is mentioned as a thing. The solvent is not limited to those listed above, and conventionally known solvents can be used as long as the binder is dissolved or stably dispersed.

  In the silver particle-containing composition, the content of silver particles is suitably 0.1 to 10,000 parts by weight with respect to 100 parts by weight of the binder, preferably 550 with respect to 100 parts by weight of the binder for conductive use. ~ 9900 parts by weight are preferred. If the amount of silver particles added is less than the lower limit, the influence of the insulating effect by the binder becomes large, and it is difficult to obtain high conductive properties. On the other hand, when the addition amount of silver particles exceeds the upper limit value, aggregation of silver particles tends to occur, so that storage stability is lowered.

  The silver particle-containing composition of the present invention is one or two selected from the group consisting of a dye, a pigment, a phosphor, a metal oxide, a spherical metal particle, and a rod-shaped metal particle (metal nanorod) depending on the purpose. The above may be further added. Moreover, you may add a leveling agent, an antifoamer, and other various additives as needed.

  The silver particle containing composition of this invention can be used with various forms, such as a coating composition, a coating film, a film, or a board | plate material, and can obtain the base material which has the coating film formed with this composition. For example, an electromagnetic wave shielding filter can be formed by directly applying or printing on a base material to be shielded from electromagnetic waves. Further, the composition of the present invention may be formed into a film shape, a plate shape, or the like, and the formed composition may be laminated on a base material to be shielded against electromagnetic waves, or the base material may be surrounded. In addition, a laminate is formed by laminating a formation such as the above-described coating film or film formed by the composition of the present invention on a substrate, and the laminate is further laminated or enclosed as a substrate for shielding electromagnetic waves as an electromagnetic wave shielding filter. May be used. In each of the above usage forms, the thickness of the filter is suitably about 0.01 μm to 1 mm, and preferably 0.1 μm to 200 μm in view of cost, light transmittance, and the like. What has a coating film, a film, a board | plate material, etc. which were formed with the silver particle containing composition of this invention as a filter layer can be used as a base material and a filter excellent in electrical conductivity, such as a wiring and an electromagnetic wave shielding filter, for example.

  Since the silver particles obtained by the production method of the present invention have high heat resistance, weather resistance, chemical resistance, and specific wavelength absorption ability, optical filters, colorants, cosmetics, near infrared absorbers, anti-counterfeit inks, surface It is suitable as a material for sensitizers for enhanced fluorescence sensors, biomarkers, drug holders for DDS, biosensors, DNA chips, test agents, Raman enhancement reagents, and the like. Moreover, since silver shows high electroconductivity, it can be used as a wiring material, an electrode material, and an electromagnetic wave shielding material. In addition, it can be used as a recording element based on shape anisotropy. Furthermore, since the particles have a large surface area, they are suitable as materials for providing a field for catalytic reaction. In applications where the target substance is adsorbed on the surface of silver particles, such as a catalyst or a Raman enhancing reagent, it is preferable to use the low molecular weight dispersant used in the production after reducing it as much as possible.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
First, 6000 μl (60 μmol) of a 10 mM silver nitrate aqueous solution as an aqueous solution in which a silver salt is dissolved, 1000 μl (100 μmol) of a 100 mM trisodium citrate aqueous solution as an aqueous solution in which a low molecular weight dispersant is dissolved, and an aqueous solution in which a reducing agent is dissolved. As a sample, 2500 μl (100 μmol) of a 40 mM dimethylamine borane aqueous solution was prepared. Next, an aqueous solution in which a low molecular weight dispersant was dissolved was added to 50 ml of water to dilute, and an aqueous solution in which a silver salt was dissolved was further added to prepare an aqueous solution of a silver salt and a low molecular weight dispersant. Next, an aqueous solution in which a reducing agent is dissolved in an aqueous solution of a silver salt and a low molecular weight dispersant is added with stirring to prepare a mixed solution. After stirring for 10 minutes, the mixed solution is subjected to light shielding conditions under 30 conditions. Silver particles were produced by storing for 48 hours in a state of standing at ℃. The obtained silver particles contained plate-like silver particles having a particle diameter of 10 to 50 nm. In addition to the plate-like silver particles, various shaped silver particles such as spherical silver particles and polyhedral silver particles were formed as by-product particles.

<Example 2>
Silver particles were produced under the same conditions as in Example 1 except that 25 μl (50 μmol) of a 10% strength by weight hydrazine aqueous solution was used as the aqueous solution in which the reducing agent was dissolved. The obtained silver particles contained plate-like silver particles having a particle diameter of 10 to 50 nm. In addition to the plate-like silver particles, various shaped silver particles such as spherical silver particles and polyhedral silver particles were formed as by-product particles.
<Example 3>
Example 1 except that 1000 μl (100 μmol) of 100 mM citric acid was used as the aqueous solution in which the low molecular weight dispersant was dissolved, and 25000 μl (1000 μl) of dimethylamine borane at 40 mM concentration was used as the aqueous solution in which the reducing agent was dissolved. Silver particles were produced under the conditions. The obtained silver particles contained plate-like silver particles having a particle size of 30 to 60 nm. In addition to the plate-like silver particles, various shaped silver particles such as spherical silver particles and polyhedral silver particles were formed as by-product particles.

<Example 4>
Silver particles were produced under the same conditions as in Example 3 except that 1000 μl (100 μmol) of 100 mM malic acid was used as an aqueous solution in which a low molecular weight dispersant was dissolved. The obtained silver particles contained plate-like silver particles having a particle size of 30 to 60 nm. In addition to the plate-like silver particles, various shaped silver particles such as spherical silver particles and polyhedral silver particles were formed as by-product particles.
<Example 5>
Silver particles were produced under the same conditions as in Example 3 except that 1000 μl (100 μmol) of tartaric acid having a concentration of 100 mM was used as the aqueous solution in which the low molecular dispersant was dissolved. The obtained silver particles contained plate-like silver particles having a particle size of 30 to 60 nm. In addition to the plate-like silver particles, various shaped silver particles such as spherical silver particles and polyhedral silver particles were formed as by-product particles.
<Example 6>
Silver particles were produced under the same conditions as in Example 3, except that 1000 μl (100 μmol) of succinic acid having a concentration of 100 mM was used as the aqueous solution in which the low molecular dispersant was dissolved. The obtained silver particles contained plate-like silver particles having a particle size of 30 to 60 nm. In addition to the plate-like silver particles, various shaped silver particles such as spherical silver particles and polyhedral silver particles were formed as by-product particles.

<Comparative Example 1>
Silver particles were produced under the same conditions as in Example 1, except that 5000 μl (5000 μmol) of trisodium citrate having a concentration of 1000 mM was used as the aqueous solution in which the low molecular weight dispersant was dissolved. In the obtained silver particles, spherical silver particles having a particle diameter of 10 to 30 nm were formed, and no plate-like silver particles were present.
<Comparative example 2>
Silver particles were produced under the same conditions as in Example 1 except that trisodium citrate, which is a low molecular weight dispersant, was not added. Since the obtained silver particles did not contain a low molecular weight dispersant, they aggregated and a massive sediment was observed.

<Comparison test 1>
The production conditions of the silver particles in Examples 1 to 6 and Comparative Examples 1 and 2 are shown in Table 1 below. Moreover, the silver particle obtained in Example 3 image | photographed by TEM to the photograph of the silver particle obtained in Example 2 image | photographed with the transmission electron microscope (TEM) in FIG. 1 (a) and FIG.1 (b). These photographs are shown in FIG. 2 (a) and FIG. 2 (b), respectively. FIGS. 1B and 2B are partially enlarged views of FIGS. 1A and 2A. Moreover, the silver particle aqueous dispersion obtained in Examples 1 to 3 and Comparative Example 1 was diluted with water at a predetermined ratio to prepare a diluted solution, and a spectrophotometer (V-570; (Manufactured by JASCO Corporation) was used to measure the wavelength absorption characteristics at 300 to 800 nm. The results are shown in FIGS.

As is clear from FIGS. 1A, 1B, 2A, and 2B, both plate-like silver particles and spherical silver particles are dispersed in the aqueous dispersion. Existed in a state.
As is clear from FIG. 4, the silver particles of Comparative Example 1 were observed to have sharp absorption at a wavelength near 400 nm. Absorption around 400 nm indicates absorption by spherical silver particles. On the other hand, as is clear from FIG. 3, in the silver particles of Examples 1 to 3, absorption was observed not only at a wavelength near 400 nm but also at a longer wavelength side near 400 nm. Plasmon absorption on the longer wavelength side from around 400 nm indicates that absorption according to the length of the side of the plate is obtained. This confirms that the silver particles obtained in Examples 1 to 3 contain both spherical silver particles and plate-like silver particles. Moreover, in Examples 1-3, since there was a difference in the plasmon absorption wavelength on the long wavelength side from around 400 nm, it was found that plate-like silver particles having different sizes were produced depending on the production conditions.

<Example 7>
First, the silver particle aqueous dispersion produced in Example 2 was centrifuged at 12000 rpm, and the supernatant in the dispersion was removed to obtain a 2% by weight silver particle concentrated aqueous dispersion. Next, 0.5 g of a dispersion liquid concentrated in 1.0 g of a 6% by weight aqueous polyvinyl alcohol solution was added to form a paint. Next, this paint was applied to the surface of the glass plate using a bar coater, and the applied glass plate was dried at 60 ° C. for 30 minutes to form a coating film on the surface of the glass plate. The obtained coating film was red and absorbed a wavelength of about 550 nm.
<Example 8>
First, the silver particle aqueous dispersion produced in Example 2 was centrifuged at 12000 rpm, and the supernatant in the dispersion was removed to obtain a 2% by weight silver particle concentrated aqueous dispersion. Next, 0.5 g of ethylene glycol was added to 1.0 g of the concentrated dispersion to form a paste. Next, this paste was applied to the glass plate surface using a bar coater, and the applied glass plate was dried at 250 ° C. for 30 minutes to form a coating film on the glass plate surface. When the resistivity value of the obtained coating film was measured by a resistivity meter (Loresta GP; manufactured by Mitsubishi Chemical Corporation) using a four-end needle method, a high conductivity of 8 × 10 ⁻⁶ Ω · cm was obtained. This is presumably because the silver particles forming the coating film contain not only plate-like silver particles but also by-product particles such as spherical silver particles, and the contact probability between the particles is increased.

The transmission electron microscope photograph figure of the silver particle obtained in Example 2. FIG. The transmission electron micrograph figure of the silver particle obtained in Example 3. FIG. The specific wavelength absorption characteristic figure of the silver particle in Examples 1-3. The specific wavelength absorption characteristic figure of the silver particle in the comparative example 1.

Claims (7)

A silver salt and a low molecular weight dispersant are added to water to prepare an aqueous solution of a silver salt and a low molecular weight dispersant, a reducing agent is added to the aqueous solution at a predetermined ratio to prepare a mixed solution, and the mixed solution is It is a method of producing silver particles mainly having a plate shape by allowing the silver ions in the mixed solution to undergo a reduction reaction by standing at 20 to 40 ° C.,
The silver salt, the low molecular weight dispersant, and the reducing agent are added at a molar ratio of silver salt: low molecular weight dispersant: reducing agent = 1: (0.1-100) :( 0.001-100). A method for producing silver particles.   The production method according to claim 1, wherein the low molecular weight dispersant is one or more organic acids selected from the group consisting of citric acid, malic acid, tartaric acid and succinic acid, or a salt thereof.   The production method according to claim 1, wherein the reducing agent is one or both of dimethylamine borane and hydrazine.   The production method according to claim 1, wherein the obtained plate-like silver particles have a particle size of 10 to 1000 nm.   A silver particle-containing composition comprising silver particles obtained by the production method according to any one of claims 1 to 4.   The coating composition, coating film, or film formed using the silver particle containing composition of Claim 5.   An optical filter, a wiring material, an electrode material, a catalyst, a colorant, a cosmetic, a near-infrared absorber, an anti-counterfeit ink, an electromagnetic wave shield containing silver particles obtained by the production method according to any one of claims 1 to 4. Materials, surface-enhanced fluorescent sensors, biomarkers, recording elements, drug carriers for drug delivery systems, biosensors, DNA chips, test drugs, or Raman-enhancing reagents.