JP4839689B2 - Silver ultrafine particle production method, silver powder, and silver ultrafine particle dispersion - Google Patents

Description

  The present invention relates to a method for producing silver ultrafine particles, a silver powder, and a silver ultrafine particle dispersion, and more particularly to a method for producing silver ultrafine particles having excellent stability, a silver powder, and a silver ultrafine particle dispersion having good dispersion stability.

  Metal ultrafine particles having a particle size of 100 nm or less, particularly several nanometers to several tens of nanometers, are used as catalysts, adsorbents, and absorbents utilizing high surface activity. In addition, films, pastes, paints, or inks are dispersed in liquid dispersion media such as solvents and resins. Conductive patterns such as electrodes and wiring of various electronic circuits and semiconductor elements, transparent conductive films, and antistatics It is also used as a material for forming a conductive film such as a film, an electromagnetic wave shielding film, a color filter, and a functional film. In particular, such nanometer-sized metal fine particles (nanoparticles) sinter at a much lower temperature than micrometer-sized metal powders that are usually used as conductive fillers in thick film conductor pastes. By conducting heat treatment at a low temperature of about 300 ° C., a conductive film having high conductivity can be obtained. Further, since the particles are fine, a thin and fine conductor pattern can be formed. For this reason, application in the electronics field is expected. Furthermore, it is considered suitable as a conductive filler for ink-jet ink used for forming a conductor pattern by ink-jet printing. It can also be used as an additive for ordinary thick film conductor pastes, that is, a conductivity improver, a sintering accelerator and the like. Furthermore, the use as an antibacterial agent and a pharmaceutical is important.

  In these applications, particularly when used as a film-forming material or supported on a carrier, the ultrafine metal particles are required to exist in a stable state that is uniform and highly dispersed in a dispersion medium. The Furthermore, it is desired that long-term storage is possible in the state of a dispersion or powder.

  Conventionally, as a method for producing such ultrafine particles of metal, an inert gas evaporation method in which ultrafine particles are obtained by evaporating and cooling the metal in a vacuum in the presence of some inert gas, metal salt, etc. There is a gas phase method such as a gas phase chemical reaction method in which the vapor of the gas is reduced. In addition, a sol-gel method by hydrolysis of metal alkoxide and a liquid phase method represented by a method in which a metal salt is reduced with hydrogen gas or a reducing agent in a liquid phase to obtain a colloidal particle dispersion are also well known.

  Among these methods, the vapor phase method has limitations on the raw materials to be applied, requires special equipment for heating, etc., is expensive, and produces a small amount of ultrafine particles obtained at a time, making it suitable for mass production. Not.

  In this respect, the liquid phase method has few problems with raw materials and equipment, but the sol-gel method, for example, has a high production cost and it is difficult to obtain stable fine particles having a particle size of several nm. In addition, ultrafine particles obtained by liquid phase reduction generally have low crystallinity and tend to aggregate. For this reason, various studies have been made such as selection of a reducing agent, optimization of reaction conditions, and the presence of a protective colloid during reduction. However, generally, since it is necessary to perform the reaction in a dilute solution system in order to prevent aggregation, the efficiency is low and the cost is high.

  Among the liquid phase methods, a polyol method in which metal oxides and salts are heated in a polyol (polyhydric alcohol) in the presence or absence of a protective agent and reduced to obtain a metal fine powder is monodispersed. It is attracting attention as a method that can produce ultrafine metal particles having a uniform shape close to the above. (For example, see Non-Patent Document 1, Patent Document 1, and Patent Document 2.)

  For example, Non-Patent Document 1 discloses that an aqueous silver nitrate solution is heated and reduced using ethylene glycol in the presence of polyvinylpyrrolidone to obtain monodispersed ultrafine silver particles having a particle size of about 10 to 30 nm. Patent Document 1 discloses that a metal salt is dissolved in a polyol and heated to 100 to 250 ° C. to generate a stable metal powder of 10 nm or less. Patent Document 2 discloses a dispersant (stable, such as polyvinylpyrrolidone). It describes that ultrafine particles of 1 to 300 nm are produced by wet reduction using a polyol in the presence or absence of an agent, and used as a conductor paste. The polyol used in these polyol methods is specifically a liquid aliphatic glycol or a polyether of a corresponding glycol, such as ethylene glycol, propylene glycol, polyethylene glycol, etc., but usually ethylene glycol is used.

Non-Patent Document 2 discloses that palladium acetate is reduced at 80 ° C. and 120 ° C. using high molecular weight polyethylene glycols having a molecular weight of 2000 and 4000, and without using other additives such as a dispersant. ) To produce a clear solution. However, these prior arts do not disclose reduction of silver salts with polyethylene glycol.
Japanese Patent Laid-Open No. 11-246901 Japanese Patent Laid-Open No. 2001-166761 J Matel Chem 7 (2) 293 (97) Elhsissen et.al Journal of Molecular Catalysis A: Chemical, 229, 7-12 (2005) C. Luo, Y. Zhang, and Y. Wang

  However, since ethylene glycol usually used in the above-described polyol method is volatile, there are concerns about environmental pollution and influence on the human body during the production of ultrafine silver particles. In addition, low molecular weight polyols have low reactivity at low temperatures, so in practice it is necessary to react at a high temperature close to the boiling point, for example, ethylene glycol at 180 to 190 ° C, but a large amount of polyol vapor is generated, which is a safety problem. Occurs. For this reason, a reflux apparatus etc. are needed and it is not suitable for mass production. When the reaction temperature is lowered, the reaction time for reduction becomes longer, the productivity is lowered, and it is easy to agglomerate to form a metal lump. In addition, in order to obtain highly dispersed ultrafine particles by preventing aggregation, it is necessary to react at a low silver salt concentration or to use a large amount of polyvinylpyrrolidone or the like, which is inefficient and high in cost. There is also a problem.

  In the method using the high molecular weight polyol described in Non-Patent Document 2, the obtained ultrafine palladium particles are dispersed in polyethylene glycol and are difficult to isolate. In addition, in this method, when silver is used instead of palladium, although silver ultrafine particles are generated, they are not stable, and aggregation progresses with time, and also occurs during separation and recovery. Highly dispersible silver ultrafine particles and silver ultrafine particle dispersion liquids with uniform properties cannot be obtained. That is, in this reaction, the high molecular weight polyethylene glycol acts as a reducing agent and a surface protective agent, but it is considered that the nano-level stabilizing action is insufficient for the ultrafine silver particles.

  On the other hand, for the colloidal dispersion obtained by the liquid phase reduction method including the polyol method, either use the obtained reaction solution as it is or collect the produced ultrafine particles once, and use this as a solvent or resin. Although it is used after being redispersed, it generally has the following problems.

(1) When collecting the powder generated in the liquid phase, if nanometer-sized extremely fine particles are monodispersed, solid-liquid separation from the reaction solution is difficult, and centrifugal separation is required for collection. Therefore, special operations such as the above are required, resulting in an increase in process and cost.
(2) Since the powder obtained by collection has high surface activity, it is difficult to handle. In particular, particles are fused to each other during a drying process or storage, and an aggregate is easily formed. It is difficult to re-disperse the ultrafine particles once aggregated in a resin or solvent.
(3) It is difficult to keep the ultrafine particle dispersion stable for a long period of time while maintaining high dispersibility. For this reason, conventionally, it was difficult to store at room temperature, and means such as ordinary frozen storage were required.

The present invention has been made in view of the above problems, and efficiently produces ultrafine silver particles at a relatively low temperature, preferably at a low temperature of 100 ° C. or less, and at a relatively high silver salt / polyol concentration. Providing a method, and thereby providing ultrafine silver particles (silver powder) having an average particle size of 1 nm to 100 nm, especially several nm to several tens of nm, a narrow particle size distribution and excellent storage stability At the same time, it is an object to produce such ultrafine silver particles at an inexpensive and industrial scale.
Further, as a further object of the present invention, in the process of producing ultrafine silver particles, separation and recovery from the reaction solution is easy, and excellent redispersion in a dispersion medium such as a resin or a solvent is achieved. The object is to provide silver ultrafine particles (silver powder) as obtained, and in particular to provide a silver ultrafine particle dispersion that is excellent in dispersion stability and can be stored for a long period of time even at room temperature.

In order to solve the above-mentioned problem, the invention according to claim 1 is a method for producing silver ultrafine particles,
By heating a mixed solution in which a silver salt , polyethylene glycol having an average molecular weight of 400 to 20,000, and a stabilizer are mixed and reducing the silver salt, ultrafine silver particles are generated in the mixed solution . It is characterized by that.

Invention of Claim 2 is a manufacturing method of the silver ultrafine particle of Claim 1,
The polyethylene glycol has an average molecular weight of 600 to 6,000.

Invention of Claim 3 is a manufacturing method of the silver ultrafine particle of Claim 1 or Claim 2, Comprising:
The ultrafine silver particles are produced in the presence of a base.

Invention of Claim 4 is a manufacturing method of the silver ultrafine particle as described in any one of Claims 1-3, Comprising:
The stabilizer is at least one selected from saturated or unsaturated linear fatty acids having 8 to 30 carbon atoms, salts of these fatty acids, and acid amides of these fatty acids.

The invention according to claim 5 is a silver powder,
The silver ultrafine particles obtained by the production method according to any one of claims 1 to 4 are collected from the reaction solution and then dried to obtain a silver having an average particle diameter of 1 to 100 nm. It consists of ultrafine particles.

The invention according to claim 6 is a silver powder,
It is a powder obtained by recovering the silver ultrafine particles obtained by the production method according to claim 4 from the reaction solution and then drying, and has an average particle diameter of 1 to 3 on the surface of the rod on which the stabilizer is self-assembled. It is characterized by comprising nanocomposite particles in which ultrafine silver particles of 100 nm are attached in a monodispersed state.

  The invention described in claim 7 is a silver ultrafine particle dispersion obtained by redispersing the silver powder obtained in claim 5 or 6 in a dispersion medium.

  In the present invention, when a silver salt is reduced with high molecular weight polyethylene glycol, the presence of a stabilizer causes the ultrafine particles of uniform particle size to be precipitated, and the precipitated ultrafine silver particles are chemisorbed to the stabilizer. It is the feature that it keeps stable by making it. That is, it is considered that the aggregation of silver ultrafine particles is suppressed by the high molecular weight polyethylene glycol and the stabilizer, so that the particle size becomes uniform and is stably held by the stabilizer. Thus, highly dispersible silver ultrafine particles having an average particle diameter of 1 nm to 100 nm, especially several nm to several tens of nm and having a uniform particle diameter are obtained.

  Further, the silver salt reduction reaction proceeds rapidly even at a relatively low temperature. For this reason, silver ultrafine particles can be produced at a lower reaction temperature and in a shorter time compared with the case of reducing with a low molecular weight polyol such as conventional ethylene glycol. For this reason, there is no danger due to the sudden boiling or rapid reaction of the polyol, and there is no reduction due to evaporation, which is efficient. Moreover, since non-volatile polyethylene glycol is used, it is safe and does not require a reflux device. For this reason, the cost can be significantly reduced, and production on an industrial scale becomes possible.

  The method of the present invention is efficient because it does not require a reaction in a dilute solution system because aggregation is unlikely to occur even when the concentration of the raw silver salt is high. In addition, since a dispersion having a high silver concentration can be obtained, it can be preferably used as a conductive filler or additive for various conductive compositions, and can be supported on a catalyst carrier or the like at a high density. Useful.

  The produced silver ultrafine particles can be easily collected as a powder. The collected powder has excellent storage stability and is easy to handle. The powder can be easily redispersed in a dispersion medium such as a solvent or a resin.

  The dispersion of the ultrafine silver particles of the present invention has excellent storage stability and can be stored for a long time in a highly dispersed state even at room temperature.

  Particularly, polyethylene glycol having an average molecular weight of 600 to 6,000 is preferable because it is easy to handle and has high reactivity.

  Further, by selecting a saturated or unsaturated linear fatty acid having 8 to 30 carbon atoms in total, a salt thereof, and an acid amide thereof (hereinafter sometimes referred to as “fatty acids”) as a stabilizer, more excellent characteristics are obtained. Silver ultrafine particles that are easy to handle and collect can be generated. When these stabilizers are used, silver ultrafine particles / fatty acid self-assembled composite particles having a structure in which monodispersed silver ultrafine particles are attached to the surface of the stabilizer are formed. It does not require special separation means such as separation, and can be easily filtered and collected using a hollow fiber or the like. The composite obtained by the collection hardly aggregates among silver ultrafine particles, is easy to handle, and is extremely excellent in redispersibility.

  Further, by carrying out the reduction reaction in the presence of a base such as ammonia, the reaction can be started and advanced quickly, and silver ultrafine particles can be generated in a short time.

Hereinafter, the method for producing silver ultrafine particles according to the present invention, the silver ultrafine particles produced by the production method, the silver powder using the same, and the silver ultrafine particle dispersion will be described in detail.
First, compounds used in the method for producing silver ultrafine particles will be described.

(Silver salt)
The salt (silver salt) used as a raw material for the silver ultrafine particles used in the present invention is not particularly limited, and examples thereof include inorganic acid salts such as nitrates, carbonates and sulfates, organic acid salts such as acetates and oxalates, Examples thereof include halides such as chlorides, oxides, hydroxides, and complex compounds such as ammonium complexes. Particularly preferred are silver nitrate and silver ammonium complex.
In addition, the alloy fine particle of these metals and silver, or composite metal fine particles can also be manufactured by dissolving the salt of metals other than silver in polyethylene glycol with silver salt. Although there is no restriction | limiting in particular as metals other than silver, For example, gold | metal | money, platinum, palladium, rhodium, ruthenium, copper, nickel, aluminum etc. are mentioned. As these metal salts, similarly to silver, various inorganic acid salts, organic acid salts, halides, oxides, hydroxides, complex compounds and the like are used.

(Polyethylene glycol)
The polyethylene glycol used in the present invention acts as a reaction solvent and a reducing agent, but at the same time protects the ultrafine silver particles that are precipitated, prevents aggregation of primary particles, and can also suppress aggregation due to high viscosity. is there. Polyethylene glycol having a high degree of polymerization having an average molecular weight of 400 to 20,000 is used. If the average molecular weight is less than 400, the reaction is slow and the aggregation proceeds, so that stable ultrafine particles cannot be obtained. On the other hand, when the average molecular weight is increased, the viscosity and melting point are increased, so that it becomes difficult to react at low temperatures or the risk of bumping is difficult to handle, so the average molecular weight exceeds 20,000. Things are not practical.
In particular, those having an average molecular weight of 600 to 6,000 are preferred because they are easy to handle, have high reactivity, and easily obtain highly dispersible ultrafine particles. Polyethylene glycols having different molecular weights may be used as a mixture of two or more.

(Stabilizer)
The stabilizer used in the present invention, when present in the reaction solution, protects and stabilizes the produced silver ultrafine particles, suppresses and stabilizes grain growth and aggregation. In the absence of a stabilizer, a brown clear solution is obtained indicating the formation of silver ultrafine particles, but is unstable and causes aggregation during the reaction or over time.
The stabilizer may be, for example, a water-soluble polymer such as polyvinyl pyrrolidone, gelatin, gum arabic, or polyvinyl alcohol, but is particularly stable when a compound selected from the following stabilizers (1) to (3) is used. It is preferable because ultra-fine silver particles can be obtained which are easy to handle and can be easily separated and collected. These stabilizers may be used in combination of two or more.

(1) Saturated or unsaturated linear fatty acids having a total carbon number of 8 to 30: for example, octylic acid, nonanoic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, Saturated fatty acids such as stearic acid, nonadecanoic acid, arachidic acid and behenic acid, and unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid.
(2) Salts of saturated or unsaturated linear fatty acids having a total carbon number of 8 to 30: For example, alkali metal salts such as sodium stearate and ammonium stearate, and ammonium salts are preferred.
(3) Saturated or unsaturated linear fatty acid amide having a total carbon number of 8 to 30: nonanoic acid amide, capric acid amide, stearic acid amide and the like.

It is considered that the stabilizers (1) to (3) contribute to stabilization by forming a composite having a special structure with the precipitated silver fine particles.
For example, silver particles produced using silver nitrate, polyethylene glycol having an average molecular weight of 2,000, and stearic acid as a stabilizer were recovered from the reaction solution, washed with water and alcohol, and then dried. When the powder was observed with a transmission electron microscope, as shown in FIG. 1 (a), a dendritic material having a size of about several μm was formed, such as a collection of microrods regarded as organic materials. The main body of this dendritic material is a rod-shaped self-assembly of stabilizers via a long alkyl chain, and on its surface, a spherical silver superconductor having a particle size of about 10 to 20 nm is prepared. The fine particles were adhered in a state where there was no fusion (see FIG. 1B). This is due to the reaction between the stabilizer and silver ions, which partially produces silver stearate, which self-assembles due to hydrophobic interaction (intermolecular force) via the alkyl chain, and has a diameter of about several tens to 100 nm. It is considered that a rod having a length of about several μm was formed, and at the same time, ultrafine silver particles that were reduced and deposited adhered uniformly to the surface of the rod to form composite particles.

  In this way, nanocomposite particles in which ultrafine silver particles with an average particle diameter of 1 to 100 nm are attached in a monodispersed state on the surface of the rod on which the stabilizer is self-assembled can be easily separated and captured. In addition, the silver ultrafine particles are stable even though they are very small, and the silver ultrafine particles are not easily fused and aggregated during the drying process after collection and the subsequent storage process, and handling is easy. It is estimated that

  In addition, when the obtained composite is redispersed in a resin, a solvent, etc., the stabilizer itself acts as a dispersant, loosening the surface of the silver ultrafine particles with the stabilizer, Since it is dispersed as ultrafine particles of size, it is possible to disperse silver ultrafine particles satisfactorily in a state close to monodispersion. Therefore, by appropriately selecting a stabilizer according to the type of dispersion medium to be used, redispersibility and the like can be improved, and a silver ultrafine particle dispersion suitable for the purpose can be obtained.

  In addition, fatty acids having a side chain and fatty acids having a short chain length are unlikely to form such a complex, but the saturated or unsaturated medium chain to long chain having no side chain as described in (1) to (3) above. It has been experimentally confirmed that fatty acids, salts thereof, and acid amides easily form similar silver ultrafine particle / stabilizer composite particles. Of these, fatty acids having 9 to 20 carbon atoms, salts thereof, and acid amides are preferable, and nonanoic acid, lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and salts and acid amides thereof are relatively inexpensive. It is preferable because it is easily dissolved in polyethylene glycol and can easily form the complex.

  Next, the manufacturing method of the silver ultrafine particle which concerns on this invention using the said compound is demonstrated.

  First, a silver salt and a stabilizer are heated together with the polyethylene glycol, and the silver salt is reduced to produce silver ultrafine particles in polyethylene glycol. Here, the silver salt may be in a solid form such as powder or granule, but may be used as a solution such as an aqueous solution or an alcohol solution.

  Specifically, for example, a stabilizer is mixed and dissolved in polyethylene glycol. When polyethylene glycol is solid at room temperature, a mixture of polyethylene glycol and a stabilizer is heated and melted. Next, the silver salt is added and dissolved, and the mixture is heated and reacted for a predetermined time with stirring to reduce the silver salt to produce ultrafine silver particles. Alternatively, a stabilizer and a silver salt may be mixed with polyethylene glycol, melted with stirring, and reacted.

  The heating is desirably performed at a temperature of about 50 to 150 ° C. If it is lower than 50 ° C., the reaction is slow and the efficiency is poor. Heating may be performed at a temperature higher than 150 ° C. However, if the temperature is too high, there is a risk of bumping and the cost is increased. Preferably it is about 70-100 degreeC. Although the heating time depends on the type of polyethylene glycol and the heating temperature, it is usually about 1 to 120 minutes.

  Moreover, although the quantity of the silver salt with respect to polyethyleneglycol changes also with the kind of silver salt, the molecular weight of polyethyleneglycol, etc., it is desirable to set it as about 0.01-10 mol in metal conversion with respect to polyethyleneglycol 1L. When the concentration is lower than 0.01 mol / L, the production efficiency is poor. On the other hand, if the concentration is higher than 10 mol / L, the produced particles are likely to aggregate and it is difficult to obtain ultrafine particles. Preferably, it is the range of 0.05-5 mol / L.

  Moreover, although the addition amount of a stabilizer is suitably adjusted with the kind of stabilizer, the density | concentration of silver salt, etc., about 0.5 to 500 weight% is desirable with respect to the weight of metallic silver. More preferably, about 1.0 to 200% by weight is added.

  If the reaction solution is acidic, the silver salt reduction reaction tends not to start or to proceed easily. In this case, when a base such as ammonia or alkali hydroxide is added to the reaction solution, the reaction is promoted. Therefore, the silver salt reduction reaction is preferably carried out in the presence of a base. Further, the reduction reaction can be promptly caused by using a silver ammonium complex as the silver salt or by using an ammonium salt or alkali metal salt of a fatty acid as a stabilizer. In this case, it is not necessary to further add a base, but the reaction can be promoted by adding it. In addition, it is thought that formation of the said nanocomposite particle | grains of the said silver ultrafine particle / fatty acid will be accelerated | stimulated because it will become easy to produce | generate fatty acid silver when a base component exists in this way.

  Silver ultrafine particles obtained through such a reaction can be used as a dispersion without being separated from the reaction solution. In this case, if necessary, operations such as removal of polyethylene glycol and stabilizer, concentration, dilution, solvent substitution, etc. are performed, and the concentration, composition, viscosity characteristics, etc. of the dispersion are adjusted as appropriate. Further, it can be directly mixed as an additive with resin or ink.

  On the other hand, when the ultrafine silver particles obtained through the reduction reaction are recovered from the reaction solution, they are collected by filtration or separation using a normal filtration device or a centrifugal separator. In particular, when the above-mentioned silver ultrafine particles / fatty acid self-assembly complex is formed, solid-liquid separation is facilitated, and therefore, filtration and collection can be easily performed even using a hollow fiber or the like. The composite obtained by the collection hardly aggregates among silver ultrafine particles, is easy to handle, and is extremely excellent in redispersibility. If necessary, the polyethylene glycol may be removed by washing with water or the like prior to filtration and separation. In order to preserve the silver ultrafine particles in a stable state, it is desirable to leave at least a part of the stabilizer, but the excess stabilizer can be removed by washing with alcohol or the like. The collected ultrafine silver particles can be powdered by washing and drying as desired.

  And the particle | grains or dry powder (silver powder) obtained by collecting can be disperse | distributed to another dispersion medium, and can be used. There is no limitation on the dispersion medium, usually used water, solvents such as alcohol solvents, ketone solvents, ether solvents, ester solvents, terpene solvents, petroleum solvents, hydrocarbon solvents, thermoplastics Resins such as resins and thermosetting resins, and mixtures thereof are used. By using an appropriate dispersion medium according to the application, a paste-like, paint-like or ink-like dispersion having extremely excellent properties such as dispersibility, stability, and coatability can be obtained. If necessary, the viscosity characteristics may be adjusted by a resin, a plasticizer or the like, or other metal powders, glass powders, surfactants, and other additives usually used in this type of dispersion may be blended.

In order to form a conductive film using such a dispersion, the silver ultrafine particle dispersion is applied to a substrate by spin coating, dipping, screen printing, ink jet printing, transfer printing, and other various methods, and heated. To sinter silver ultrafine particles. Since the silver ultrafine particles obtained by the present invention are extremely easy to sinter, they are dense, highly conductive and fine even at a low temperature of 500 ° C. or lower, for example, about 100 to 300 ° C. A conductive film, a color filter, or the like can be formed. In addition, since it can be fired at a low temperature, it can be applied to substrates with low heat resistance such as glass, resin, ITO, etc., and at a low temperature comparable to the curing temperature of polymer-based conductor paste, it is a high-temperature fired type conductor paste. High electrical conductivity comparable to the above can be obtained.
The ultrafine silver particles can be added as a conductivity improver or a sintering accelerator to a thick film conductor paste using a normal conductive powder or a conductive adhesive. Further, when using the silver ultrafine particle dispersion of the present invention in which the silver ultrafine particles are dispersed in a dispersion medium, the ultrafine silver particles can be uniformly supported on the surface of a carrier such as ceramic, carbon, or organic polymer, It is also useful for the production of catalysts, adsorbents, absorbents, antibacterial agents, and pharmaceuticals.

As described above, in the production method of the present invention, silver ultrafine particles can be efficiently produced at a relatively low temperature, desirably at a low temperature of 100 ° C. or less, and at a relatively high silver salt / polyol concentration. As a result, it is possible to obtain silver ultrafine particles and silver powder having an average particle size of 1 nm to 100 nm or less, particularly a narrow particle size distribution on the order of several nm to several tens of nm, and excellent storage stability. Etc. can be produced at low cost and on an industrial scale.
In addition, it is easy to separate and recover from the reaction solution, is excellent in redispersion in a dispersion medium such as a resin or a solvent, and can obtain silver ultrafine particles and silver powder that can obtain a highly dispersed dispersion. In particular, a silver ultrafine particle dispersion that is excellent in dispersion stability and can be stored for a long time even at room temperature can be obtained.

  Hereinafter, production and evaluation of silver ultrafine particles will be described as examples, but the present invention is not limited thereto.

[Example 1]
First, stearic acid was mixed with 1.0 L of polyethylene glycol (PEG 2000) having an average molecular weight of 2,000 so as to have a molar ratio of 20% with respect to silver ions, and dissolved at 80 ° C.
To this solution, 100 mL of a 1M aqueous solution of silver nitrate was mixed and dissolved by stirring at 80 ° C. for 10 minutes. Then, 10 mL of concentrated aqueous ammonia was added, and stirring was further continued for 30 minutes to cause a reduction reaction.
After completion of the reaction, a viscous brown slurry liquid was obtained and solidified upon cooling. This was washed with water and methanol to remove part of polyethylene glycol and fatty acids, solid-liquid separation was performed using a hollow fiber filter, and dried to obtain a powder. The following analysis and evaluation were performed about the powder which is the obtained product.

[Product]
The obtained powder was analyzed by an X-ray diffractometer (Rigaku Miniflex), and it was confirmed from the X-ray diffraction pattern that metallic silver was produced. In addition, by observation with a transmission electron microscope (TEM manufactured by JEOL Ltd.) and analysis by GCMS (GCMS system manufactured by Agilent), about 10 to 20 nm of stearic acid self-assembled into a rod shape having a length of 2 to 3 μm is formed. It was confirmed that a nanocomposite in which spherical silver ultrafine particles were adhered in a monodispersed state was formed. A TEM image is shown in FIG. 1 and the properties of the powder are shown in Table 1. In Table 1, regarding the properties of the powder, it was confirmed that silver ultrafine particles / stabilizer nanocomposite particles in which silver ultrafine particles were adhered in a monodispersed state on the surface of the stabilizer rod were confirmed. “Nanocomposite particles” are not formed, but nanocomposite particles are not formed, but those obtained with ultrafine silver particles are “ultrafine particles”. Described as “aggregates”.
[Stability]
In addition, as a test for examining the stability (stability test), the same item as the item examined in the above [Product] as the change over time after leaving the obtained powder in air at room temperature for one month. As a result, it was confirmed that no changes were observed in the properties of the silver particles, the TEM image, and the like. The results are shown in Table 1. In Table 1, “no change” is indicated for those in which no change with time is observed, and “aggregation” is indicated for those in which agglomeration is observed. Those that had already aggregated were described as “-(not implemented)”) without performing a stability test.
[Redispersibility]
Further, as a test for examining redispersibility (redispersibility test), 0.5 g of the obtained powder was added to 100 mL of butyl carbitol, and subjected to a dispersion treatment with ultrasonic waves for 2 minutes. Then, when the particle size distribution measurement (LB550 by Horiba, Ltd.) was performed with respect to the solution which performed the dispersion process, it confirmed that it was disperse | distributing favorable. When this solution was allowed to stand at room temperature for 1 week, no change was observed. The results are shown in Table 1. In Table 1, those in which the powder was well dispersed in the dispersion were described as “good”, and those in which the powder was not dispersed and aggregated were described as “aggregation”.

[Example 2]
In the production method of Example 1, instead of stearic acid, the same procedure was performed except that nonanoic acid was added as a fatty acid instead of stearic acid, and the obtained powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
As a result, even in the case of powders produced using nonanoic acid as a stabilizer, the ultrafine silver particles / stabilizer nanoparticle in which the ultrafine silver particles adhere to the surface of the rod of the stabilizer in a monodispersed state. Formation of composite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 3
In the production method of Example 1, instead of stearic acid, as a fatty acid in place of stearic acid, the same procedure was performed except that lauric acid was added, and the obtained powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
As a result, even in the case of a powder produced using lauric acid as a stabilizer, silver ultrafine particles / stabilizer nanoparticle in which silver ultrafine particles are attached in a monodispersed state on the surface of the rod of the stabilizer. Formation of composite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 4
In the production method of Example 1, instead of stearic acid, as a fatty acid in place of stearic acid, the same procedure was performed except that palmitic acid was added, and the obtained powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
As a result, even in the case of powders manufactured using palmitic acid as a stabilizer, silver ultrafine particles / stabilizer nanoparticle in which silver ultrafine particles are adhered in a monodispersed state on the surface of the rod of the stabilizer. Formation of composite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 5
In the production method of Example 1, instead of stearic acid, as a fatty acid in place of stearic acid, the same procedure was performed except that oleic acid was added, and the obtained powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
As a result, even in the case of a powder produced using oleic acid as a stabilizer, silver ultrafine particles / stabilizer nano particles in which silver ultrafine particles are adhered in a monodispersed state on the surface of the rod of the stabilizer. Formation of composite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 6
In the production method of Example 1, instead of stearic acid, the same procedure was performed except that linoleic acid was added as a fatty acid instead of stearic acid, and the obtained powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
As a result, even in the case of a powder produced using linoleic acid as a stabilizer, silver ultrafine particles / stabilizer nanoparticle in which silver ultrafine particles are adhered in a monodispersed state to the surface of the rod of the stabilizer. Formation of composite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 7
In the production method of Example 1, instead of stearic acid, as a fatty acid in place of stearic acid, it was performed in the same manner except that sodium stearate was added, and the obtained powder was evaluated in the same manner as in Example 1. . The results are shown in Table 1.
As a result, even in the case of a powder produced using sodium stearate as a stabilizer, silver ultrafine particles / stabilizer in which silver ultrafine particles are adhered in a monodispersed state on the surface of the rod of the stabilizer Formation of nanocomposite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 8
In the production method of Example 1, instead of stearic acid, as a fatty acid in place of stearic acid, the same procedure was performed except that stearamide was added, and the obtained powder was evaluated in the same manner as in Example 1. . The results are shown in Table 1.
As a result, even in the case of a powder produced using stearamide as a stabilizer, silver ultrafine particles / stabilizer in which silver ultrafine particles are adhered in a monodispersed state on the surface of the rod of the stabilizer Formation of nanocomposite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 9
The production method of Example 8 was carried out in the same manner as in Example 1 except that the stirring time was 60 minutes and no concentrated aqueous ammonia was added. Evaluation of the obtained powder was carried out in the same manner as in Example 1. The results are shown in Table 1.
As a result, although the reaction rate was slow compared to Example 8, even in the case of powder produced without adding concentrated aqueous ammonia, ultrafine silver particles adhered to the surface of the rod of the stabilizer in a monodispersed state. Production of ultrafine silver particles / stabilizer nanocomposite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 10
In the production method of Example 1, instead of silver nitrate, a silver salt instead of silver nitrate was added in the same manner except that a silver ammonium complex was added and no concentrated aqueous ammonia was added. Evaluation of the obtained powder was also performed. The same operation as in Example 1 was performed. The results are shown in Table 1.
As a result, even in the case of a powder produced using a silver ammonium complex as a silver salt, the silver ultrafine particles / stabilizer nanoparticle in which the silver ultrafine particles are adhered in a monodispersed state on the surface of the stabilizer rod. Formation of composite particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

Example 11
In the production method of Example 1, instead of stearic acid, polyvinylpyrrolidone was added as a stabilizer other than fatty acids so as to have a molar ratio of 27% with respect to silver ions, and the powder was replaced with solid-liquid separation. The obtained powder was evaluated in the same manner as in Example 1 except that it was separated by centrifugation. The results are shown in Table 1.
As a result, in the case of a powder produced using polyvinylpyrrolidone as a stabilizer, nanocomposite particles were not formed, but the formation of silver ultrafine particles was confirmed. In the stability test, no change was observed in the properties of the silver particles, the TEM image, and the like. Further, in the redispersibility test, it was well dispersed and, as in Example 1, it was confirmed that no change was observed in the dispersion even after standing for 1 week.

[Comparative Example 1]
In the production method of Example 1, the same procedure was performed except that stearic acid was not added as the fatty acids were not added, and the obtained powder was evaluated in the same manner as in Example 1. The results are shown in Table 1.
As a result, in the case of a powder produced without adding a stabilizer, nanocomposite particles were not formed, but the formation of ultrafine silver particles was confirmed. However, in the stability test, changes were observed in the properties of the silver particles, TEM images, etc., and aggregation of the silver particles was observed. Aggregation of silver particles was also observed in the redispersibility test.

[Comparative Example 2]
In the production method of Example 1, the same procedure as in Example 1 was performed except that propionic acid having 3 carbon atoms in total was added instead of stearic acid. The results are shown in Table 1.
As a result, in the case of a powder produced using propionic acid, silver particles were aggregated and silver ultrafine particles were not confirmed. Aggregation of silver particles was also observed in the redispersibility test.

[Comparative Example 3]
In the manufacturing method of Example 1, it carried out similarly except adding valeric acid with a total carbon number of 5 instead of stearic acid, and the evaluation about the obtained powder was also performed similarly to Example 1. The results are shown in Table 1.
As a result, even in the case of a powder produced using valeric acid, silver particles were aggregated and silver ultrafine particles were not confirmed. Aggregation of silver particles was also observed in the redispersibility test.

[Comparative Example 4]
In the manufacturing method of Example 1, it carried out similarly except adding neodecanoic acid which is tertiary fatty acid instead of stearic acid, and the evaluation about the obtained powder was also performed similarly to Example 1. The results are shown in Table 1.
As a result, even in the case of a powder produced using neodecanoic acid, silver particles were aggregated and silver ultrafine particles were not confirmed. Aggregation of silver particles was also observed in the redispersibility test.

Example 12
In the production method of Example 1, instead of PEG 2000, polyethylene glycol (PEG 600) having an average molecular weight of 600 was used, and stearic acid was used as a stabilizer. After adding concentrated ammonia water, when 20 minutes passed, 20 mL of water was added to terminate the reaction. At this time, it was examined whether or not silver ultrafine particles were generated, and it was confirmed that silver ultrafine particles / stabilizer nanocomposite particles were generated.

Example 13
In the production method of Example 12, it was carried out in the same manner except that polyethylene glycol (PEG 1000) having an average molecular weight of 1000 was used instead of PEG 600, and as in Example 12, it was examined whether or not silver ultrafine particles were produced. Formation of ultrafine silver particles / stabilizer nanocomposite particles was confirmed.

Example 14
In the production method of Example 12, instead of PEG600, it was carried out in the same manner except that polyethylene glycol having an average molecular weight of 4000 (PEG4000) was used, and as in Example 12, it was examined whether or not silver ultrafine particles were produced. Formation of ultrafine silver particles / stabilizer nanocomposite particles was confirmed.

[Comparative Example 5]
In the production method of Example 12, the reaction was carried out in the same manner as in Example 12 using ethylene glycol instead of PEG 600 and using stearic acid as a stabilizer. After adding concentrated aqueous ammonia, there was almost no reaction even after 20 minutes. When heating was continued, silver ions were reduced, but agglomerated and a stable dispersion of ultrafine silver particles could not be obtained.

[Comparative Example 6]
In the production method of Example 12, instead of PEG 600, polyethylene glycol (PEG 300) having an average molecular weight of 300 was used, and stearic acid was used as a stabilizer, and the reaction was performed in the same manner as in Example 12. As in Comparative Example 5, the reaction hardly occurred even after 20 minutes had passed after the addition of concentrated aqueous ammonia. When heating was continued, silver ions were reduced, but agglomerated and a stable dispersion of ultrafine silver particles could not be obtained.

Example 15
Stearic acid was mixed with 1.0 L of PEG2000 at a molar ratio of 20% with respect to silver ions, and dissolved at 80 ° C. This solution was mixed with 500 mL of a 3M aqueous solution of silver nitrate, stirred and dispersed at 80 ° C. for 10 minutes, and then allowed to cool to room temperature. After 50 mL of concentrated aqueous ammonia was added and stirred for 10 minutes to disperse, stirring was continued at 80 ° C. for 20 minutes to obtain a viscous brown slurry liquid. After cooling, it was washed with water and methanol, and solid-liquid separation was performed using a hollow fiber filter to obtain the same silver ultrafine particles / stabilizer nanocomposite particles as in Example 1.

2 is a TEM image of silver ultrafine particles / stabilizer nanocomposite particles obtained in Example 1. FIG.

Claims (7)

By heating a mixed solution in which a silver salt , polyethylene glycol having an average molecular weight of 400 to 20,000, and a stabilizer are mixed and reducing the silver salt, ultrafine silver particles are generated in the mixed solution . A method for producing ultrafine silver particles.   The method for producing ultrafine silver particles according to claim 1, wherein the polyethylene glycol has an average molecular weight of 600 to 6,000.   The method for producing silver ultrafine particles according to claim 1 or 2, wherein the silver ultrafine particles are produced in the presence of a base.   The stabilizer is at least one selected from saturated or unsaturated linear fatty acids having a total carbon number of 8 to 30, a salt of these fatty acids, and an acid amide of these fatty acids. The method for producing ultrafine silver particles according to any one of claims 3 to 4.   The silver ultrafine particles obtained by the production method according to any one of claims 1 to 4 are collected from the reaction solution and then dried to obtain a silver having an average particle diameter of 1 to 100 nm. A silver powder comprising ultrafine particles.   It is a powder obtained by recovering the silver ultrafine particles obtained by the production method according to claim 4 from the reaction solution and then drying, and has an average particle diameter of 1 to 3 on the surface of the rod on which the stabilizer is self-assembled. A silver powder comprising nanocomposite particles to which 100 nm silver ultrafine particles are adhered in a monodispersed state.   A silver ultrafine particle dispersion obtained by redispersing the silver powder obtained in claim 5 or 6 in a dispersion medium.