JP4573138B2 - Method for producing silver-containing powder, silver-containing powder and dispersion thereof - Google Patents

Description

  The present invention relates to a powder containing silver nanoparticles having an average particle diameter of 2 to 50 nm and a dispersion of the powder. Specifically, in the presence of a specific compound, the reduction reaction, concentration, The present invention relates to a silver-containing powder that is stable in a solid state, obtained by passing through a drying step, a dispersion obtained by redispersing it in a solvent, and a method for producing the same.

  In order to develop highly integrated, highly functional, small, and thin information devices, it is necessary to develop semiconductor microfabrication technology and at the same time have highly reliable mounting technology that supports the microfabrication. The component technology of the mounting technology includes the production of fine metal particles and the fine wiring / connection technology using the paste as a paste. The combination with printing technology such as inkjet has been attracting attention. Technology development is underway (for example, see Patent Document 1).

  In general, metal fine particles are produced by grasping the chemical / physical behavior of molecules or atoms based on a so-called top-down pulverization technique (see, for example, Patent Documents 2 and 3) and bottom-up. There is a method for controlling the structure by controlling the thickness (for example, see Patent Documents 4 to 6), and it is difficult to uniformly pulverize the particle diameter to the nanometer order by the top-down method. The up method is attracting attention.

  Metal nanoparticles whose particle size has been reduced to nano-sizes have increased surface energy, resulting in a melting point drop on the surface of the particles. As a result, metal nanoparticles tend to fuse with each other, resulting in poor storage stability. It has been known. Accordingly, many metal nanoparticles are provided which are coated with a protective agent or the like for preventing the fusion and dispersed in a colloidal form in a dispersion solvent.

  In contrast, dried (solid) metal nanoparticles can be easily incorporated into liquid compositions and solid mixtures in various applications, so that the colloidal form of metal nanoparticles protected with a protective agent is used. The application range is wider than that of the dispersion, and it is considered industrially advantageous in terms of transportation and storage. For example, when the dispersion solvent is distilled off from a dispersion that has been stably dispersed in a dispersion solvent and evaporated to obtain a powder (solid) containing metal nanoparticles, it exists on the surface of the adjacent powder. It is not practical because it cannot be stably stored due to adhesion between protective agents to be protected or fusion of metal nanoparticles from a location that is not sufficiently protected.

  Further, in the technique already provided by the present inventors in Patent Document 6 and the like, the metal used as a raw material when isolating a dispersion composed of metal nanoparticles obtained by reduction of metal ions and a polymer compound is used. A dialysis method is used to remove counter ions and the like generated from the compound, but this method is not suitable for industrial implementation in terms of production cycle and cost. In addition, the metal content in the powder obtained by dialysis and drying, as described in the Examples of Patent Document 6 and the like, is less than 92% by mass, and is not suitable for use as a conductive material. It was necessary to process.

  As a method for producing metal fine particles, for example, a method of drying a metal fine particle-containing liquid obtained by reducing metal ions in the presence of an alkali-soluble polymer by a freeze-drying method is provided (see, for example, Patent Document 7). . In this method, since it is necessary to completely dissolve the alkali-soluble polymer, a large amount of an alkaline aqueous solution having a pH of about 12 is required. Therefore, in order to obtain a certain amount of metal-containing powder, the alkaline aqueous solution used is used. The wastewater treatment has a high environmental impact and is not suitable as an industrial production method. Further, the metal content in the metal-containing powder obtained in the example of Patent Document 7 is as low as less than 90% by mass, and when used as a conductive material such as a conductive paste, Since there are many solids other than the metal in a body, it is thought that the process at high temperature is required for electroconductivity expression. Further, the stability in Patent Document 7 is the solid state (powder) from the viewpoint of the dispersion stability when redispersed in an organic solvent immediately after obtaining the powder and the storage stability over time of the redispersed liquid. ) Does not guarantee storage stability.

Further, there is also provided a method of obtaining metal fine particles in a solid powder state by removing excess dispersant and the like from a dispersion of metal fine particles and drying (see, for example, Patent Document 8), but the method is complicated. In addition, the redispersible solvent is limited, and there is a great limitation in application.
JP 2004-74267 A JP 2007-265801 A JP 2007-254845 A JP 11-319538 A JP 2006-257484 A JP 2008-37884 A JP 2007-86777 A International Publication No. 2005/037465 Pamphlet

  In view of the above circumstances, the problem to be solved by the present invention is that the silver-containing powder contains silver nanoparticles having an average particle diameter of 2 to 50 nm in an amount of 95% by mass or more, and has excellent storage stability and excellent reproducibility. A silver-containing powder in a dry state having dispersibility, a dispersion of a silver-containing powder that can be fused at low temperature obtained by redispersing it in various solvents, and a method for producing them that is excellent in industrial productivity Is to provide.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a segment that contributes to the development of high dispersibility and a segment that can immobilize metal fine particles or reduce metal ions. In addition, after reducing the silver compound in the presence of a compound having at least two kinds of segments, a silver-containing powder having a small average particle diameter and a high silver content can be obtained by passing through a concentration and drying step. The obtained silver-containing powder is excellent in storage stability in a solid state, can be easily redispersed in various solvents, and a dispersion having excellent stability can be obtained without using other dispersants. When the obtained dispersion was applied, it was found that high conductivity could be expressed by fusion at low temperature, and the present invention was completed.

That is, the present invention
(1) Compound (X) obtained by bonding polyethylene glycol (b) having a number average molecular weight of 500 to 5,000 to an amino group in polyethyleneimine (a) having a number average molecular weight of 500 to 50,000, or
A compound in which polyethylene glycol (b) having a number average molecular weight of 500 to 5,000 and an epoxy resin (c) are bonded to an amino group in polyethyleneimine (a) having a number average molecular weight of 500 to 50,000. Reducing the silver compound to silver nanoparticles (Z) in an aqueous medium in the presence of (Y);
(2) A step of adding an organic solvent to the mixture of the compound (X) or the compound (Y) obtained in (1), the silver nanoparticles (Z), and the aqueous medium, and then concentrating the mixture,
(3) A method for producing a silver-containing powder characterized by having a step of drying the concentrate obtained in (2), and silver nanoparticles having an average particle diameter of 2 to 50 nm obtained by the production method The silver containing powder which contains 95 mass% or more is provided.

  Furthermore, this invention provides the dispersion liquid of the silver containing powder obtained by re-dispersing the said silver containing powder in various solvents, and the electrically conductive paste using this.

  When the silver-containing powder obtained in the present invention is reduced to silver nanoparticles due to the reducing ability of the polyethyleneimine chain in the polymer compound used, the coordination bond force, electrostatic interaction, etc., It is a dry powder having a certain size obtained by coordination of a polymer compound on the surface of the silver nanoparticles, and is excellent in storage stability. Moreover, this silver-containing powder is excellent in redispersibility in water and various organic solvents, and a dispersion can be easily prepared without using other compounds such as a dispersant. Therefore, according to various uses of the metal material and the conductive material, the powder can be used for blending as it is or after it is prepared into a dispersion.

  The silver-containing powder dispersion obtained in the present invention is a silver nanoparticle obtained by a silver ion reduction reaction due to the function of the aforementioned polyethyleneimine chain in the compound covering the silver nanoparticles in the powder. The particles are stably held, and the hydrophilic segment and the hydrophobic segment in the compound express a good balance between the affinity with various media and the strong repulsive force due to the interaction between the segments. Excellent storage stability.

  In addition, the silver-containing powder obtained in the present invention is composed of nanometer-sized silver nanoparticles and an organic compound, has a certain structure, and has a high silver content. Etc. can be suitably used. Furthermore, it has the characteristics as nanometer-sized fine particles of metal such as large specific surface area, high surface energy, plasmon absorption, etc., and has various chemical, electrical, and magnetic performances, and has a wide variety Applications to fields such as catalysts, electronic materials, magnetic materials, optical materials, various sensors, color materials, medical examination applications, and the like are possible. In addition, the method for producing the silver-containing powder and the dispersion thereof of the present invention is based on the reduction reaction of silver ions under mild conditions, and is excellent in reproducibility, and the post-treatment method can be performed with general-purpose equipment. It is highly advantageous as an industrial production method.

The method for producing silver nanoparticle powder of the present invention is as follows: (1) Polyethylene glycol (b) having a number average molecular weight of 500 to 5,000 in the amino group in polyethyleneimine (a) having a number average molecular weight of 500 to 50,000 Or a compound (X) formed by binding, or
A compound in which polyethylene glycol (b) having a number average molecular weight of 500 to 5,000 and an epoxy resin (c) are bonded to an amino group in polyethyleneimine (a) having a number average molecular weight of 500 to 50,000. Reducing the silver compound to silver nanoparticles (Z) in an aqueous medium in the presence of (Y);
(2) A step of adding an organic solvent to the mixture of the compound (X) or the compound (Y) obtained in (1), the silver nanoparticles (Z), and the aqueous medium, and then concentrating the mixture,
(3) A step of drying the concentrate obtained in (2).

  The silver nanoparticle in the present invention means that the particle diameter observed in a transmission electron micrograph is on the order of nanometers, and the shape does not need to be a perfect sphere. Moreover, the number average molecular weight of each segment which comprises a compound (X) or a compound (Y) is a polystyrene conversion value measured by gel permeation chromatography (GPC).

  In the polyethyleneimine chain (a) constituting the compound (X) and the compound (Y) used in the present invention, the ethyleneimine unit in the chain can be coordinated with silver and its ions, and further reduction of silver ions Is a polymer chain that stabilizes and holds silver nanoparticles (Z). The structure has an ethyleneimine unit as the main repeating unit, and may be linear or branched, and may be either a commercial product or a synthetic product.

  The size of the silver-containing powder obtained in the present invention is not limited to the molecular weight of the compound (X) or compound (Y) used or the molecular weight of the polyethyleneimine (a), but constitutes the compound (X) or compound (Y). In the case of each component to be processed, that is, polyethylenemin (a), hydrophilic segment (b) described later, compound (Y), the structure and composition ratio of epoxy resin (c) described later, and the kind of silver used as a raw material Also affected by. In order to increase the content of silver nanoparticles (Z) in the silver-containing powder, it is preferable to use a branched polyethyleneimine chain.

  A commercially available branched polyethyleneimine is branched by a tertiary amine and can be used as a raw material for the compound (X) or the compound (Y) used in the present invention. From the viewpoint of obtaining a silver-containing powder having a preferable particle diameter, which can provide a silver-containing powder having excellent storage stability and a dispersion thereof, the degree of branching is expressed as a molar ratio of (tertiary amine) / (all amines). When it shows, it is preferable that it is a branching degree of the range of (1-49) / (100), and the range of a more preferable branching degree is (15-40) / in view of an industrial manufacture surface, availability, etc. (100).

  If the average molecular weight of the polyethyleneimine (a) portion is too low, the retention ability of the silver nanoparticles (Z) by the compound (X) or the compound (Y) tends to be lowered, and the storage stability becomes insufficient. If it is too high, the silver-containing powder tends to become enormous and the storage stability of the dispersion may be hindered. Therefore, the storage stability of the obtained silver-containing powder and its dispersion is more excellent, and the number average molecular weight is from the viewpoint of increasing the content of silver nanoparticles (Z) in the powder. Is in the range of 500 to 50,000, preferably in the range of 1,000 to 40,000, and most preferably in the range of 1,800 to 30,000.

  When the molecular weight of polyethylene glycol (b) is dispersed in a hydrophilic organic solvent, the dispersion stability may be deteriorated if the molecular weight is too low, and the dispersion may be aggregated if the molecular weight is too high. Further, in the silver-containing powder, it is necessary to balance the storage stability without aggregation in the solid state and the increase in the silver content, so that the number average molecular weight of the polyethylene glycol (b) portion. Is 500 to 5,000, more preferably 1,000 to 3,000.

  Polyethylene glycol (b) may generally be a commercial product or a synthetic product. Further, it may be a copolymer with other hydrophilic polymer. Examples of the hydrophilic polymer that can be used at this time include polyvinyl alcohol, polyacrylamide, polyisopropylacrylamide, and polyvinylpyrrolidone. From the viewpoint of increasing the silver content in the resulting silver-containing powder, even when a copolymer is used, the overall molecular weight is preferably in the range of 500 to 5,000.

  In the compound (Y) used in the present invention, an epoxy resin (c) is further bonded as a hydrophobic segment. By incorporating a structure derived from the epoxy resin (c) into the compound (Y), when the compound (Y) is redispersed in water or a hydrophilic solvent, a strong associative force within the molecule or between the molecules. By forming a micelle core, a stable micelle can be formed, and silver nanoparticles (Z) can be taken therein to obtain a stable dispersion. Further, when redispersed in a hydrophobic organic solvent, it has a high affinity with the solvent, so that the dispersion stability can be improved.

  The epoxy resin (c) can be used without particular limitation as long as it is generally commercially available or can be synthesized. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, naphthalene type tetrafunctional epoxy resin, tetramethylbiphenyl type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, Bisphenol A novolac type epoxy resin, triphenylmethane type epoxy resin, tetraphenylethane type epoxy resin, dicyclopentadiene-phenol addition reaction type epoxy resin, phenol aralkyl type epoxy resin, naphthol novolak type epoxy resin, naphthol aralkyl type epoxy resin, Naphthol-phenol co-condensed novolak epoxy resin, Naphthol-cresol co-condensed novolac epoxy resin, Aromatic hydrocarbon form Aldehyde resin modified phenol resin type epoxy resin, a biphenyl novolak type epoxy resin, a xanthene type epoxy resins described in JP-2003-201333, may be used alone, or may be a mixture of two or more. Among these, when using the obtained silver-containing powder or dispersion thereof as a conductive paste, it is preferable to use a bisphenol A type epoxy resin from the viewpoint of excellent adhesion to a substrate, etc., and a hydrophilic organic solvent It is preferable to use a trifunctional or higher functional epoxy resin such as a naphthalene type tetrafunctional epoxy resin from the viewpoint of obtaining a dispersion of a silver-containing powder having a strong associative force and excellent dispersion stability and storage stability. In addition, these epoxy resins may be used as the raw material of the compound (Y) as they are, and further may be those modified in various ways according to the structure of the target compound (Y). For example, a part of the epoxy group in the epoxy resin (c) can be ring-opened in advance with a compound having an aromatic ring having an interaction with a metal to obtain a more stable silver-containing powder.

  Further, the molecular weight of the epoxy resin (c) is not particularly limited, but when redispersed in a hydrophilic organic solvent, the dispersion stability is deteriorated if it is too low, and the micelles are aggregated if it is too high. In the case of dispersing in a hydrophobic organic solvent, if it is too low, the dispersibility of micelles is poor, and if it is too high, the affinity with the solvent cannot be maintained. From these viewpoints and the point that the silver content in the solid content of the silver-containing powder can be easily increased, the number average molecular weight of the epoxy resin (c) is usually preferably 100 to 200,000, In particular, it is preferably 300 to 100,000.

  Although it does not specifically limit as a manufacturing method of compound (X) and compound (Y) used by this invention, The thing by the following method is preferable from the point which can synthesize | combine a compound as designed easily.

  As described above, a commercially available or synthesized polyethyleneimine (a) can be suitably used. First, the case where a branched polyethyleneimine chain is used will be described.

  Since the terminal of the branched polyethyleneimine is a primary amine, the terminal of polyethylene glycol (b) can be used in the present invention by pre-modifying and reacting with a functional group that reacts with the primary amine. Compound (X) can be synthesized. The functional group that reacts with the primary amine is not particularly limited. For example, aldehyde group, carboxy group, isocyanate group, tosyl group, epoxy group, glycidyl group, isothiocyanate group, halogen, acid chloride, sulfonic acid Examples include chloride. Among them, a carboxy group, an isocyanate group, a tosyl group, an epoxy group, and a glycidyl group are advantageous in terms of production methods such as reactivity and ease of handling, and are preferable functional groups.

  In addition, the functional group may not be a functional group that directly reacts with the primary amine, but may be any functional group that can be reacted with the primary amine by various treatments. For example, polyethylene glycol having a hydroxy group may be used. For example, it may be reacted with a polyethyleneimine chain by a technique such as glycidylation. Furthermore, after performing the process which converts the primary amine of a branched polyethyleneimine chain | strand into the other functional group which can react with the polyethylene glycol which has a functional group, these are made to react and synthesize | combine a compound (X). Is also possible.

  When the polyethyleneimine chain (a) is a linear polyethyleneimine chain, a polymer compound is obtained by first synthesizing a polyacylated ethyleneimine chain by living polymerization, and subsequently introducing polyethylene glycol. Examples include a method of hydrolyzing an ethyleneimine chain to form a linear polyethyleneimine chain.

  In addition, the synthesis method for the compound (Y) used in the present invention has already been provided by the present inventor in Patent Document 6, Japanese Patent Application Laid-Open No. 2006-213877, Japanese Patent No. 4026662, Japanese Patent No. 4026664, and the like. You can refer to it.

  The molar ratio (a) :( b) of the polymer constituting the chain of each component of polyethyleneimine (a) and polyethylene glycol (b) in compound (X) and compound (Y) used in the present invention is particularly limited. Although it is not a thing, from the point which is excellent in the storage stability of the obtained silver containing powder, the dispersion stability of the dispersion liquid, and storage stability, Usually in the range of (a) :( b) = 1: 1-100. In particular, it is preferable to design such that the ratio is 1: 1 to 30.

  Moreover, when using a compound (Y), the molar ratio (a) :( b) :( c) of the polymer which comprises the chain | strand of each component of a polyethyleneimine (a), polyethyleneglycol (b), and an epoxy resin (c) Is not particularly limited, but is usually (a) :( b) :( c) from the viewpoint of excellent storage stability of the resulting silver-containing powder, dispersion stability of the dispersion, and storage stability. = 1: 1 to 100: 1 to 100, and it is particularly preferable that the design is 1: 1 to 30: 1 to 30.

  The compound (X) and the compound (Y) used in the present invention include polyethylene glycol (b), or further an epoxy resin, separately from the polyethyleneimine (a) capable of stably presenting silver nanoparticles (Z). It has a structure derived from (c). As described above, the polyethylene glycol (b) portion exhibits a high affinity with the solvent in the hydrophilic organic solvent, and the epoxy resin (c) portion exhibits a strong associating force in the hydrophilic organic solvent. Furthermore, when the epoxy resin (c) has an aromatic ring, it is considered that the π electrons of the aromatic ring interact with silver to further contribute to stabilizing the silver-containing powder. .

  Further, the polyethylene glycol (b) -derived structural portion present in the compound (X) and the compound (Y) is once concentrated in a subsequent purification step, and then reconstituted in water or a mixed solvent of water and a hydrophilic organic solvent. When dispersed, the compound (X) or the compound (Y) and the silver nanoparticles (Z) are considered to contribute to efficient rearrangement. That is, since the polyethylene glycol (b) -derived structure is unevenly distributed to the solvent side during redispersion, all of the polyethyleneimine (a) -derived structures in the compound are involved in the stable retention of the silver nanoparticles (Z). This will stabilize the silver nanoparticles (X) with the minimum necessary compound (X) or compound (Y), and the silver content in the resulting silver-containing powder will be reduced. It can be inferred that it can be increased. Therefore, it is considered that the silver-containing powder obtained in this manner is in a state where the outermost surface is covered with a structure derived from polyethylene glycol (b), and a dispersion is prepared by redispersing the powder. In this case, it is considered that this is a factor that facilitates the most dispersion and has excellent stability without using a new dispersant.

  The first step in the production method of the present invention is a step of dissolving or dispersing the aforementioned compound (X) or compound (Y) in an aqueous medium, that is, water or a mixed solvent of water and a hydrophilic organic solvent. In the case of polyethyleneimine (a), polyethylene glycol (b), and further compound (Y), the solubility and dispersibility in aqueous media differ depending on the combination of epoxy resin (c), but it dissolves uniformly. Or it is necessary to disperse. The hydrophilic organic solvent that can be used here may be any one that can be mixed at least 5 parts by mass with respect to 100 parts by mass of water at 25 to 35 ° C. to obtain a uniform mixed solvent. , Ethanol, isopropyl alcohol, n-propyl alcohol, tetrahydrofuran, dioxane, acetone, methyl ethyl ketone, dimethylacetamide, dimethylformamide, ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, diethylene glycol Glycerin, dimethylsulfone oxide, dioxirane, N-methylpyrrolidone, dimethylimidazolidinone, sulfo Can be exemplified emissions etc., may be used individually or as a mixture of two or more. Various ionic liquids may be used.

  As the use ratio of the compound (X) or the compound (Y) and the aqueous medium, the silver content of the silver-containing powder obtained from the viewpoint of easy handling and ease of silver ion reduction reaction. From the viewpoint of improvement, the concentration of the compound (X) or the compound (Y) is preferably 1 to 20% by mass, and more preferably 2 to 15% by mass. At this time, when the solubility / dispersibility of compound (X) or compound (Y) is insufficient, for example, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate Solubility and dispersibility can be adjusted by using a mixed solvent in combination. In order to dissolve or disperse the compound (X) or the compound (Y), usually, the compound (X) or the compound (Y) may be left standing or stirred at room temperature, and may be subjected to ultrasonic treatment, heat treatment or the like as necessary. Further, when the familiarity with the aqueous medium is low due to the crystallinity of the compound (X) or the compound (Y), for example, the compound (X) or the compound (Y) is dissolved or swollen with a small amount of a good solvent. Thereafter, it may be dispersed in a target aqueous medium. At this time, it is more effective to perform ultrasonic treatment or heat treatment.

  After preparing a solution or dispersion of compound (X) or compound (Y), a silver compound is mixed. At this time, from the viewpoint of increasing the silver content in the obtained silver-containing powder, compound (X) or It is preferable to use it so that it may become 400-9900 mass parts as silver with respect to 100 mass parts of compounds (Y). Furthermore, it is preferable to mix so that it may become 2-80 mass% as a non volatile matter from a viewpoint which improves productivity by reducing the usage-amount of an aqueous medium, and can control a reductive reaction easily. More preferably, it is used so that it may become 900-9900 mass parts as silver and 3-50 mass% as a non volatile matter with respect to 100 mass parts of compound (X) or compound (Y).

  At this time, as a silver compound that can be used, any silver compound (Z) can be obtained by a reduction reaction. For example, silver nitrate, silver oxide, silver acetate, silver fluoride, silver acetylacetonate, benzoic acid Silver oxide, silver carbonate, silver citrate, silver hexafluorophosphate, silver lactate, silver nitrite, silver pentafluoropropionate, silver perchlorate, silver sulfate, silver chloride, silver bromide, silver iodide, silver sulfite, Examples thereof include silver tetrafluoroborate, silver p-toluenesulfonate, and silver trifluoroacetate. From the viewpoint of easy handling and industrial availability, it is preferable to use silver nitrate or silver oxide.

  In the step, the method of mixing the silver compound with the aqueous medium in which the compound (X) or the compound (Y) is dissolved or dispersed is not particularly limited, and the compound (X) or the compound (Y ) May be a method in which a silver compound is added to a medium in which the solution is dissolved or dispersed, or vice versa, or a method in which mixing is performed while simultaneously charging in another container. A mixing method such as stirring is not particularly limited.

  At this time, in order to accelerate the reduction reaction, it may be heated to about 30 to 70 ° C. as necessary, or a reducing agent may be used in combination.

  The reducing agent is not particularly limited. For example, hydrogen, hydrogenation can be performed because the reduction reaction can be easily controlled and can be easily removed from the reaction system in a subsequent purification step. Boron compounds such as sodium boron and ammonium borohydride, alcohols such as methanol, ethanol, propanol, isopropyl alcohol, ethylene glycol and propylene glycol, aldehydes such as formaldehyde, acetaldehyde and propionaldehyde, ascorbic acid, citric acid and citric acid It is preferable to use acids such as sodium and hydrazines such as hydrazine and hydrazine carbonate. Among these, sodium borohydride, ascorbic acid, sodium citrate and the like are more preferable from the viewpoint of industrial availability and handling.

  The addition amount of the reducing agent is not particularly limited as long as it is an amount necessary for reducing silver ions, and the upper limit is not particularly specified, but it is 10 mol times or less of silver ions. Is preferable, and it is more preferable that it is 2 mol times or less.

  Moreover, the addition method of a reducing agent is not limited, For example, a reducing agent can be dissolved and disperse | distributed and mixed as it is in aqueous solution or another solvent. Further, the order in which the reducing agent is added is not limited, and even when the reducing agent is added to the solution or dispersion of the compound (X) or the compound (Y) in advance, the reduction is performed simultaneously with the mixing of the silver compound. An agent may be added, and further, a method of mixing a reducing agent after several hours have elapsed after mixing a solution or dispersion of compound (X) or compound (Y) with a silver compound. .

  In particular, when using a raw material that does not dissolve or hardly dissolves in an aqueous medium such as silver oxide or silver chloride, a complexing agent may be used in combination. Examples of the complexing agent include propylamine, butylamine, diethylamine, dipropylamine, triethylamine, ammonia, ethylenediamine, N, N, N ′, N′-tetramethylethylenediamine, 1,3-diaminopropane, N, N , N ′, N′-tetramethyl-1,3-diaminopropane, triethylenetetramine, methylaminoethanol, dimethylaminoethanol, ethanolamine, diethanolamine, methyldiethanolamine, propanolamine, butanolamine, dimethylaminopropanol and the like. .

  The amount of the complexing agent added is not particularly limited as long as it is sufficient to be coordinated with silver oxide or the like to form a complex, and the upper limit is not particularly specified. It is preferable that it is 20 mole times or less. The method for adding the complexing agent is not limited. For example, the complexing agent can be mixed as it is or dissolved or dispersed in an aqueous solution or other solvent.

  The time required for the reduction reaction in step (1) varies depending on the presence or absence of a reducing agent and the type of compound (X) or compound (Y) used, but is usually 0.5 to 48 hours, from the viewpoint of industrial production. It is preferable to prepare for 0.5 to 24 hours. Examples of the preparation method include a method depending on the heating temperature, the amount of reducing agent and complexing agent added, and the timing thereof.

  Subsequent to step (1), concentration after adding an organic solvent, which is step (2), is not particularly limited, and any of dialysis, centrifugation, precipitation, etc. May be used or may be used simultaneously. Although it does not specifically limit as an organic solvent which can be used at this time, The point which can shorten the time which a concentration process takes, The point which can recycle this organic solvent, The mixture obtained by process (1) and From the viewpoint of easy mixing, it is preferable to use an organic solvent having a boiling point of 120 ° C. or lower, preferably 100 ° C. or lower, and it is particularly preferable to use a mixed solvent of a hydrophilic organic solvent and a hydrophobic organic solvent. The amount used is not particularly limited, but it is preferable to mix the mixture obtained in the step (1) in an amount of 1.5 to 5 times, preferably 2 to 3 times. Further, as a concentration method, it is preferable to use a centrifugal separation method from the viewpoint of excellent industrial productivity. In this centrifugal concentration step, in addition to a part of the medium used in step (1), the purpose is to remove reducing agents and complexing agents added as necessary, counter ions of silver ions, etc. It is. Therefore, it is preferable to use a concentration method according to the raw material used in step (1), and the non-volatile content is concentrated to 30% by mass or more, preferably 50% by mass or more.

  After centrifugal concentration, in order to remove the aqueous medium, vacuum drying or freeze drying is performed. In particular, lyophilization is preferred because a silver-containing powder having a high silver content can be easily obtained.

  When drying under reduced pressure, the temperature is preferably 40 ° C. or lower, particularly preferably 30 ° C. or lower. Therefore, it is necessary to adjust the degree of vacuum so that the dispersion medium can be sufficiently removed at this temperature.

  Freeze-drying involves freezing the slurry or solid silver-containing powder and allowing it to evaporate the aqueous medium by leaving it under reduced pressure. It is. This will be described in order.

  First, a preliminary freezing operation. The actual operation is performed by cooling the slurry-like or solid silver-containing powder. The cooling temperature may be any temperature as long as the silver-containing powder is frozen. For example, temperatures of 0 ° C. or lower and −90 ° C. or higher can be preferably used. Even if the temperature is lower than this, it does not affect the properties of the silver-containing powder obtained only by using extra energy, and if the temperature is higher than this, it can be actually frozen. Can not. The time for freezing is not particularly limited as long as it is a time required for freezing, but it is generally 30 minutes to 6 hours.

  Moreover, it is preferable to freeze after adding water further to the concentrate obtained at the process (2) before freezing operation. Prior to newly adding water, a solvent other than water present in the concentrate can be easily removed by azeotropic distillation with water, and polyethylene in compound (X) or compound (Y) Silver nanoparticles (Z) by electrostatic interaction and hydrogen bonding between the imine (a) -derived structural part and the polyethylene glycol (b) -derived structural part, and the interaction between the silver nanoparticle (Z) and the ethyleneimine unit. Can be efficiently coated again, the storage stability of the powder after drying is improved, and good redispersibility is obtained when dispersed in solvents again, and the particle size of the silver-containing powder is improved. Effects such as homogenization and development of conductivity of a coating film obtained using the same can be obtained.

  The amount of water to be added is not particularly limited, but from the viewpoint of efficiently expressing the above-described effects and the balance of shortening the time required for the drying process, it is based on the weight of the solid content in the concentrate. Usually, it is 0.01-100 times amount, and it is preferable that it is the range of 0.1-10 times amount.

  Moreover, in order to control the speed of freeze-drying and the degree of freezing, it can also freeze-dry using an organic solvent together. Examples of organic solvents that can be used include alcohols such as methanol, ethanol, and propanol, polyols such as ethylene glycol, diethylene glycol, propylene glycol, trimethylolpropane, and glycerin, ketones such as acetone and methyl ethyl ketone, methyl acetate, Esters such as ethyl acetate, butyl acetate and ethyl formate, nitriles such as acetonitrile and propionitrile, ethers such as dimethoxyethane, dioxane and tetrahydrofuran, halogenated hydrocarbons such as methylene chloride and chloroform, dimethylformamide, Amides such as dimethylacetamide, cyclic esters such as ethylene carbonate, propylene carbonate, butyrolactone, propiolactone, etc. Sulfoxide, dimethyl imidazolidinone, N- methylpyrrolidone, hexamethylphosphoric triamide, and the like hexamethyl phosphorous acid triamide. Further, the amount of these solvents added is preferably in the range of 0.001 to 1 times the weight of the solid content in the concentrate.

  Next, an operation for reducing the pressure will be described. The decompression operation may be performed under reduced pressure obtained by using a normal commercially available lyophilizer, but specifically, it is usually 620 Pa or less and 100 Pa or less because of the necessity of sublimating the frozen water. It is preferable that the pressure be 40 Pa or less.

  In addition, when reducing the pressure, it is not always necessary to set the pressure reduction degree immediately, and a method of lowering the pressure reduction degree to a predetermined pressure degree after leaving it in a relatively high pressure state may be used in order to remove volatile substances.

  By passing through the steps of mixing, concentrating, redispersing and drying as necessary, the resulting silver-containing powder has excellent storage stability in a solid state and is redispersed in various solvents. And the average particle size can be reduced. Furthermore, since the silver content rate in a silver containing powder can be made high, it becomes possible to manufacture the silver containing powder which can be used suitably as an electrically conductive paste etc. with high efficiency.

  In general, metal fine particles in a size region of several tens of nm have characteristic optical absorption resulting from surface plasmon excitation, depending on the metal species. Therefore, by measuring the plasmon absorption of the silver-containing powder obtained in the present invention, it is confirmed that silver is present as nanometer-sized fine particles, that is, silver nanoparticles (Z) in the powder. Furthermore, it is possible to observe the shape, particle size, and the like in a TEM (transmission electron microscope) photograph of the film obtained by casting the dispersion.

  As described above, in the production method of the present invention, it is possible to carry out with a general-purpose equipment under mild conditions such as a spontaneous reduction reaction in an aqueous medium, a general-purpose concentration step, and if necessary water addition and drying. In addition, since the solvent to be used can be isolated and separated by a concentration or drying process, it can be reused and is excellent in industrial productivity. Further, since the obtained silver-containing powder can be re-dispersed in an arbitrary solvent, it is possible to design a product according to the intended use, and the utility is high.

  The silver-containing powder of the present invention has a compound (X) in which polyethylene glycol (b) is bonded to polyethylene imine (a), or polyethylene glycol (b) and epoxy resin (c) bonded to polyethylene imine (a). It contains the compound (Y) and silver nanoparticles (Z) having an average particle diameter of 2 to 50 nm, and the content of silver nanoparticles (Z) in the powder is 95% by mass or more. To do. Furthermore, the silver-containing powder dispersion of the present invention is obtained by redispersing the above-mentioned silver-containing powder in water or various organic solvents.

  Conventionally, water-based dispersions using silver-containing powders have been made with a silver content of up to about 90% in the solid content, but it is very difficult to produce those exceeding this at low cost. It was. For example, many random copolymers of a hydrophilic monomer and a monomer capable of coordinating to a metal are known. If an attempt is made to make a silver-containing powder using this, the coordination ability to silver It was difficult to achieve compatibility with hydrophilicity. As a result, it was only possible to obtain a dispersion using a large amount of polymer. Therefore, when using a polymer having a structure in which the role of coordinating ability to silver and the portion having hydrophilicity are shared, for example, when a (multi) block copolymer or graft copolymer is used In addition, it is necessary to add a low molecular complexing agent and a reducing agent to the system, and after adjusting the dispersion of the silver-containing powder having a good dispersion state, an excessive low molecular complexing agent, reducing agent, Furthermore, there is a problem that it becomes difficult to separate the reaction product of the complexing agent and the reducing agent from the silver-containing powder. In order to solve this, capital investment that is unsuitable for industrial production such as dialysis operation is required, or a complicated process as provided in Patent Document 8 or the like is required.

  In this application, after performing the reductive reaction of a silver compound using specific compound (X) or compound (Y), the said problem is solved by performing the above-mentioned concentration and drying process continuously. .

  In the silver-containing powder of the present invention and the dispersion obtained by using the same, it is essential that the silver content in the powder solid content is 95% by mass or more. It can also be made into mass% or more. By increasing the silver content, a low resistance value, which is an essential physical property of the conductive material, can be easily realized. In other words, it contains silver at such a high content and is excellent in stability, and it has been difficult to achieve with conventional silver fine particles and dispersions thereof, and conductive pastes using these, at low temperatures (~ The desired conductivity (low resistance value) can be expressed only by heating at 180 ° C.). Further, the silver-containing powder obtained in the present invention is preferable for use as a raw material for a conductive paste suitably used for the fine wiring and the like, as the average particle diameter of the silver-containing powder is smaller. Is characterized by the fact that the average value of the particle size of 100 particles randomly extracted from a photograph obtained by TEM observation is 2-50 nm, which is an unprecedented small size, and has an advantage. is there.

  Conventionally, a conductive paste has been difficult to obtain a desired conductive film unless heated to a high temperature, for example, 250 to 350 ° C. That is, by heating to a high temperature, the protective agent that has stabilized the metal fine particles is decomposed and a part thereof is removed, the content of components other than the metal in the film is reduced, and the metal fine particles are fused to make the conductivity. Is expressed. If the particle size of the metal fine particles is reduced, the temperature required for fusing can be lowered, but if the particle size is reduced to that extent, a large amount of protective agent is required to protect it. Therefore, the metal content in the solid content cannot be increased. That is, in the prior art, there is a trade-off relationship between increasing the metal content and reducing the particle size of the metal fine particles, and the present invention eliminates this trade-off.

  As described above, the silver-containing powder of the present invention has a small average particle diameter and a high silver content, but particularly when used as a raw material for forming a conductive film using a conductive paste or the like. The melting point determined by differential scanning calorimetry is preferably 100 to 250 ° C, particularly preferably 100 to 200 ° C. By having a melting point in this temperature range, it can be applied to a glass substrate or a plastic substrate, which has conventionally been difficult to form a conductive film on because of its low heat resistance.

  Even if the silver-containing powder of the present invention is composed of one silver nanoparticle (Z) and one compound (X) or compound (Y), a plurality of silver nanoparticles (Z), Alternatively, a plurality of compounds (X) and a compound (Y) may be included.

In the silver-containing powder of the present invention, the powder is aggregated in a dry state and does not float. For example, when using air collected in the workplace of the silver-containing powder of the present invention performs the airborne dust measurement, or less far less 0.005 mg / m ³ than 3 mg / m ³ is an environmental management OEL scattering It has a feature that does not. This is because the silver-containing powder in which the ethyleneimine unit in the polyethyleneimine (a) in the compound (X) or compound (Y) used in the present invention is adjacent to the silver nanoparticles (Z) while being coordinated. Compound (X) or Compound (Y) which forms hydrogen bonds with compound (X) or Compound (Y) in the body efficiently and at a high density and is coordinated to silver nanoparticles (Z). It is considered that the powder is agglomerated in the dry state of the silver-containing powder due to the interaction by van der Waals force between them, which is several tens of microns when the powder is observed by TEM. It is clear from the fact that it is larger, and it is thought that airborne dust has been reduced.

  The silver-containing powder obtained in the present invention can be redispersed in various solvents to obtain the dispersion of the present invention. The concentration at this time is not particularly limited, and the concentration of the silver-containing powder in the dispersion is preferably 10 to 70% by mass, and particularly preferably 20 to 60% by mass. The concentration of the silver-containing powder in the dispersion can be adjusted according to the form of the application field in which the dispersion is used. In addition, although the solvent which can be used at this time is not specifically limited, For example, water, methanol, ethanol, isopropyl alcohol, n-propyl alcohol, tetrahydrofuran, dioxane, acetone, methyl ethyl ketone, dimethylacetamide, dimethylformamide, ethylene glycol, Propylene glycol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, diethylene glycol, glycerin, dimethyl sulfone oxide, dioxirane, N-methylpyrrolidone, dimethylimidazolidinone, sulfolane, etc. However, a mixture of two or more types may be used. Among them, the redispersion solvent is preferably a solvent made of a compound having a hydroxy group from the viewpoint that uniform dispersibility can be easily obtained. The redispersion method is not particularly limited, and the solid silver-containing powder can be added while stirring the solvent, or the solvent can be added to the solid silver-containing powder.

  When redispersed in a hydrophobic organic solvent, it is preferably a silver-containing powder obtained by using the compound (Y), and the epoxy resin (c) -derived structural portion in the compound (Y) is a powder. It is presumed that the silver-containing powder is stabilized in the solvent by rearrangement on the outermost surface. Therefore, the redispersion step may take a little longer than when water, a hydrophilic organic solvent, or a mixed solvent thereof is used. For this reason, in order to raise productivity more, it is preferable to make a density | concentration into 20-60 mass%, and it is preferable to use together dispersion techniques, such as an ultrasonic treatment, besides simple stirring.

  The use of the silver-containing powder and dispersion thereof of the present invention is not limited in any way, and various conductive compositions, adhesive compositions, etc., and also the special coloration derived from silver nanoparticles are used. It can be added to and mixed with compositions in various fields such as coating compositions.

  Among these, in particular, it can be suitably used as a conductive paste. A typical method of use is a method of processing on a base material by casting, spin coater, bar coater, applicator, various printing machines, printers, dispensers, etc. on various base materials selected according to the purpose. , A method of creating a molded product on a substrate, such as a processing method by dipping into a dispersion of a silver-containing powder or a composition containing the same, a method using a flow gun or a flow coater, spraying, etc. Method, brush coating, puff coating, roller coating, etc., a method of sandwiching a plurality of same or different substrates, a method of forming a thick film structure or a thick structure by repeating these methods, a combination of different substances A method of creating a molded product on a substrate, such as a method of forming a laminated structure by repeating the above-described method, A method of removing various molded products formed from a substrate to obtain a molded product, a method of sandwiching between a substrate and other materials, a method of coating a part or all of other materials on the substrate, Examples thereof include a method of coating a part or all of the same or different materials, various molds according to purposes, and a method of processing using a mold.

  It is also possible to suitably perform treatments such as dehydration, solvent removal, drying, heating, ultraviolet irradiation, electron beam irradiation, etc. according to various purposes in the aforementioned pre-process, various steps, post-process, etc. These processing methods can be used without any particular limitation.

  The form obtained by the above processing method is not particularly limited. In particular, as an example of the form of the workpiece obtained by the representative example described above, a coating film, a coating film, a coating, a bonded product, a laminate, a sealing material, a film, a sheet, a board, a fibrous molded product, Examples thereof include tube-shaped molded products, three-dimensional molded products, gel-shaped molded products, and solid sol-shaped molded products.

  When used as the conductive paste, it can be mixed with other components selected according to the purpose, and the other components are not particularly limited. For example, for electronic materials, various conductive components, components that improve affinity and adhesion with electronic materials, etc., components that smooth the surface or control irregularities, and solvents having various boiling points Viscosity modifiers, and various additives suitable for various purposes.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “%” represents “mass%”.

Synthesis Example 1 [Synthesis Example of Compound (X-1)]
Under a nitrogen atmosphere, 9.6 g of p-toluenesulfonic acid chloride was added to a mixed solution of 20.0 g (10.0 mmol) of methoxypolyethylene glycol [Mn = 2,000], 8.0 g (100.0 mmol) of pyridine and 20 ml of chloroform ( A chloroform (30 ml) solution containing 50.0 mmol) was added dropwise for 30 minutes with ice-cooling and stirring. After completion of dropping, the mixture was further stirred at a bath temperature of 40 ° C. for 4 hours. After completion of the reaction, 50 ml of chloroform was added to dilute the reaction solution. Subsequently, after sequentially washing with 100 ml of 5% hydrochloric acid aqueous solution, 100 ml of saturated aqueous sodium hydrogen carbonate solution and 100 ml of saturated saline solution, it was dried over magnesium sulfate, filtered and concentrated under reduced pressure. The obtained solid was washed several times with hexane, filtered, and dried under reduced pressure at 80 ° C. to obtain 22.0 g of a tosylated product.

¹ H-NMR (manufactured by JEOL Ltd., AL300,300MHz) of the product obtained measurement results are shown below.
¹ H-NMR (CDCl ₃ ) measurement result:
δ (ppm): 7.82 (d), 7.28 (d), 3.74-3.54 (bs), 3.41 (s), 2.40 (s)

  2.0.0 g (0.8 mmol) of 5.39 g (2.5 mmol) of a methoxypolyethylene glycol compound having a p-toluenesulfonyloxy group at the terminal synthesized above and branched polyethyleneimine (manufactured by Aldrich, molecular weight 25,000) Then, 0.07 g of potassium carbonate and 100 ml of N, N-dimethylacetamide were stirred at 100 ° C. for 6 hours under a nitrogen atmosphere. To the resulting reaction mixture, 300 ml of a mixed solution of ethyl acetate and hexane (V / V = 1/2) was added, and after vigorous stirring at room temperature, the solid product was filtered. The solid was repeatedly washed twice with 100 ml of a mixed solution of ethyl acetate and hexane (V / V = 1/2) and then dried under reduced pressure to give a compound in which polyethylene glycol was bound to branched polyethyleneimine (X- 24.4g of 1) solid was obtained.

¹ H-NMR (manufactured by JEOL Ltd., AL300,300MHz) of the product obtained measurement results are shown below.
¹ H-NMR (CDCl ₃ ) measurement result:
δ (ppm): 3.50 (s), 3.05 to 2.20 (m)

Synthesis Example 2 [Synthesis Example of Compound (Y-1)]
Bisphenol A type epoxy resin EPICLON AM-040-P (manufactured by DIC Industrial Co., Ltd., epoxy equivalent 933) 18.7 g (20 m equivalent), 4-phenylphenol 1.28 g (7.5 mmol), 65% ethyltriphenylphosphonium acetate An ethanol solution (0.26 ml, 0.12 mol%) and N, N-dimethylacetamide (50 ml) were reacted at 120 ° C. for 6 hours in a nitrogen atmosphere. After standing to cool, it was dropped into 150 ml of water, and the resulting precipitate was washed twice with methanol and then dried under reduced pressure at 60 ° C. to obtain a monofunctional epoxy resin. The yield of the obtained product was 19.6 g, and the yield was 98%.

The measurement results of ¹ H-NMR (manufactured by JEOL Ltd., AL300, 300 MHz) of the obtained monofunctional epoxy resin are shown below.
¹ H-NMR (CDCl ₃ ) measurement result:
δ (ppm): 7.55 to 6.75 (m), 4.40 to 3.90 (m), 3.33 (m), 2.89 (m), 2.73 (m), 1. 62 (s)

  A solution of the monofunctional epoxy resin obtained above (3.0 g, 1.5 mmol) and acetone (50 ml) in the compound (X-1) 14.4 g (0.48 mmol) obtained in Synthesis Example 1, methanol 60 ml The solution was added and stirred at 60 ° C. for 2 hours under a nitrogen atmosphere. After completion of the reaction, the solvent was removed to obtain a compound (Y-1) in which polyethylene glycol and an epoxy resin were bonded to branched polyethyleneimine.

Example 1
10.0 g of silver oxide was added to 138.8 g of an aqueous solution using 0.592 g of the compound (X-1) obtained in Synthesis Example 1, and the mixture was stirred at 25 ° C. for 30 minutes. Subsequently, when 46.0 g of dimethylethanolamine was gradually added with stirring, the reaction solution turned black-red and slightly exothermic, but was left as it was and stirred at 25 ° C. for 30 minutes. Thereafter, 15.2 g of a 10% ascorbic acid aqueous solution was gradually added with stirring. While maintaining the temperature, stirring was continued for another 20 hours to obtain a black-red dispersion.

  The obtained dispersion was sampled, and a peak of a plasmon absorption spectrum was observed at 400 nm by measurement of a visible absorption spectrum of a 10-fold diluted solution (manufactured by Hitachi, Ltd., UV-3500), and production of silver nanoparticles was confirmed. In addition, spherical silver nanoparticles were confirmed by TEM measurement (JEM-2200FS, manufactured by JEOL Ltd.). And as a result of measuring silver content in solid, using TG-DTA (SII nanotechnology Co., Ltd. make, TG / DTA6300), 97.2% was shown.

  A mixed solvent of 200 ml of isopropyl alcohol and 200 ml of hexane was added to the dispersion obtained after completion of the reaction and stirred for 2 minutes, followed by centrifugal concentration at 3000 rpm for 5 minutes. After removing the supernatant, a mixed solvent of 50 ml of isopropyl alcohol and 50 ml of hexane was added to the precipitate and stirred for 2 minutes, followed by centrifugal concentration at 3000 rpm for 5 minutes. After removing the supernatant, 20 g of water was further added to the precipitate, followed by stirring for 2 minutes, and the organic solvent was removed under reduced pressure. Further, 10 g of water was added and stirred and dispersed, and then the dispersion was left to stand overnight in a −40 ° C. freezer and frozen for 24 hours using a freeze dryer (FDU-2200 manufactured by Tokyo Rika Kikai Co., Ltd.). Treatment gave 9.1 g of a flake-like mass with a grey-green metallic luster. The obtained silver-containing powder (solid) was observed by an optical microscope (Olympus fluorescence microscope BX60, manufactured by Olympus Optical Co., Ltd.), and was confirmed to be an aggregate of several tens of microns. The silver content in the powder was 97.4% by mass measured using TG-DTA (TG / DTA6300, manufactured by SII Nanotechnology Co., Ltd.), and the silver nanoparticles that can be observed with a transmission electron micrograph When 100 particles were randomly extracted and the average value thereof was determined, the average particle size was 16.8 nm, and the melting point determined by differential scanning calorimetry (SII Nanotechnology, DSC7200) was 140. It was -170 degreeC.

Also, the work of transferring about 60 g of the obtained silver-containing powder to another container is carried out, air in the workplace is collected, and floating dust is collected using a light scattering digital dust meter (M-3423, manufactured by Rex Corporation). Measurement was measured. The result is 0.005 mg / m ³ or less, and it is considered that there is almost no suspended dust in the atmosphere of the workplace. Further, it was confirmed that the above property values did not change even after the silver-containing powder of the child was allowed to stand at room temperature (25 ° C.) for 3 months.

  The silver-containing powder obtained above is re-dispersed by stirring in pure water for 3 hours to prepare a dispersion having a solid content of 20%, and spin coated at 700 rpm on a slide glass for 30 seconds using a spin coater. And made a thin film. This was heated on a hot plate at 180 ° C. for 30 minutes, the volume resistivity of the film was measured with “low resistivity meter Loresta EP” manufactured by Mitsubishi Chemical Corporation, and the thickness of the film was measured with a laser confocal microscope. The corrected value was 5.4 μΩ · cm.

  The silver-containing powder obtained above was redispersed by stirring for 3 hours using ethanol, isopropyl alcohol, a mixed solvent of ethanol and water, etc. in addition to pure water, to prepare a dispersion. The following table shows the evaluation results of the dispersion stability and storage stability of various dispersions.

Dispersion stability: The dispersion was allowed to stand in a refrigerator at 5 ° C. for 3 days, and then layer separation and dispersion state retention were visually observed.
Storage stability: After storing the dispersion in a refrigerator at 5 ° C. for 3 months, the average particle diameter obtained from a transmission electron micrograph of silver nanoparticles and the shape of the transmission electron micrograph are compared.

Example 2
When 23.0 g of dimethylethanolamine was gradually added to 77.0 g of an aqueous solution using 0.263 g of the compound (Y) obtained in Synthesis Example 2, a little heat was generated. Subsequently, when the reaction temperature was changed to 45 ° C. and gradually added to 5.0 g of silver nitrate, the reaction solution turned black-red. Thereafter, the reaction temperature was set to 50 ° C. and stirred for 4.5 hours to complete the reaction, and a black-red dispersion was obtained.

  The obtained dispersion was sampled, and a peak of a plasmon absorption spectrum was observed at around 400 nm by measuring a visible absorption spectrum of a 10-fold diluted solution, thereby confirming the formation of silver nanoparticles. In addition, spherical silver nanoparticles were confirmed by TEM measurement. Moreover, as a result of measuring the silver content in solid using TG-DTA, 96.6% was shown.

  A mixed solvent of 100 ml of isopropyl alcohol and 100 ml of hexane was added to the dispersion liquid after completion of the reaction obtained above and stirred for 2 minutes, followed by centrifugal concentration at 3000 rpm for 5 minutes. After removing the supernatant, a mixed solvent of 25 ml of isopropyl alcohol and 25 ml of hexane was added to the precipitate and stirred for 2 minutes, followed by centrifugal concentration at 3000 rpm for 5 minutes. After removing the supernatant, 10 g of water was added to the precipitate and stirred for 2 minutes to remove the organic solvent under reduced pressure. After further adding 5 g of water to this and stirring and dispersing it, it was left to stand overnight in a -40 ° C. freezer and frozen, and this was treated with a freeze dryer (FDU-2200, manufactured by Tokyo Rika Kikai Co., Ltd.) for 12 hours. Thus, 3.1 g of a flake-like lump having a grayish green metallic luster was obtained. This was re-dispersed in pure water to prepare a dispersion having a solid content of 30%, and spin coated on a slide glass at 700 rpm for 30 seconds using a spin coater to form a thin film. When this was heated on a hot plate at 180 ° C. for 30 minutes and the resistivity was measured, it was 3.7 μΩ · cm.

  The silver-containing powder obtained above was redispersed by stirring for 3 hours using ethanol, isopropyl alcohol, a mixed solvent of ethanol and water, etc. in addition to pure water, to prepare a dispersion. The following table shows the evaluation results of the dispersion stability and storage stability of various dispersions.

Comparative Example 1
A silver-containing powder was obtained in the same manner as in Example 1 except that 0.474 g of branched polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., SP-200) was used instead of compound (X-1). While stirring was continued while maintaining the reaction temperature, precipitation occurred with the reaction time, and a dispersion of silver nanoparticles could not be obtained. The precipitate had a metallic luster, was not dispersed in water or a polar solvent, and plasmon absorption peculiar to silver nanoparticles was not observed.

Comparative Example 2
A silver-containing powder was obtained in the same manner as in Example 2 except that 0.210 g of branched polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., SP-200) was used instead of the compound (Y-1). While stirring was continued while maintaining the reaction temperature, precipitation occurred with the reaction time, and a dispersion of silver nanoparticles could not be obtained. The precipitate had a metallic luster, was not dispersed in water or a polar solvent, and plasmon absorption peculiar to silver nanoparticles was not observed.

Comparative Example 3
The dispersion obtained in step (1) of Example 1 was immediately subjected to a freeze-drying step without going through a centrifugal concentration step using an organic solvent. Because of the large amount of water, it took about 10 days to freeze-dry, but it became a clay-like mass instead of a dry powder. The obtained clay-like silver-containing solid was stirred and redispersed in distilled water for 3 hours in the same manner as in Example 1 to prepare a dispersion having a solid content of 20%. A thin film was formed by spin coating at 700 rpm for 30 seconds, but it did not become a thin film with good film forming properties. When this was heated on a hot plate at 180 ° C. for 30 minutes and the volume resistivity of the film was measured with “Low resistivity meter Loresta EP” manufactured by Mitsubishi Chemical Corporation, it was overrange (OL measurement impossible). It was.

Comparative Example 4
The black-red dispersion obtained from the step (1) of Example 2 was immediately subjected to a freeze-drying step without going through a centrifugal concentration step using an organic solvent. Because of the large amount of water, it took about 5 days to freeze-dry, but it became a highly viscous mass instead of a dry powder. Using the obtained highly viscous lump containing silver-containing solid material, stirring in distilled water for 3 hours and redispersing in the same manner as in Example 2 to prepare a dispersion with a solid content of 30%, using a spin coater to slide glass A thin film was formed by spin coating at 700 rpm for 30 seconds, but it did not become a thin film with good film forming properties. When this was heated on a hot plate at 180 ° C. for 30 minutes and the volume resistivity of the film was measured with “Low resistivity meter Loresta EP” manufactured by Mitsubishi Chemical Corporation, it was overrange (OL measurement impossible). It was.

Comparative Example 5
In order to remove nitrate ions in the black-red dispersion obtained in the step (1) of Example 2, 100 g of the obtained dispersion was placed in a dialysis tube (RVDF 500,000, manufactured by Spectra). The water exchange was repeated 3 times for about 16 hours in 5 L of water. Subsequently, centrifugation was repeated twice using the dialysate (8000 rpm, 5 minutes) to obtain a paste-like silver-containing powder concentrated to a solid content of 50%. The treatment time took about 55 hours in total compared to about 1 hour or less in Example 2, and the amount of waste liquid generated in the post-treatment process was 30 times or more that in Example 2. From these facts, it is clear that the production method of the present invention is a method for producing a silver-containing powder that is easy in the post-treatment process and industrially highly practical.

2 is a TEM image of the silver-containing powder obtained in Example 1. FIG. 2 is a photograph of the silver-containing powder obtained in Example 1. 2 is an optical micrograph of the silver-containing powder obtained in Example 1. 2 is a photograph of an aqueous dispersion of silver-containing powder obtained in Example 1. 3 is a TEM image of the silver-containing powder obtained in Example 2. 2 is a photograph of the silver-containing powder obtained in Example 2. 2 is a photograph of an aqueous dispersion of silver-containing powder obtained in Example 2.

Claims (2)

(1) Compound (X) obtained by bonding polyethylene glycol (b) having a number average molecular weight of 500 to 5,000 to an amino group in polyethyleneimine (a) having a number average molecular weight of 500 to 50,000, or
A compound in which polyethylene glycol (b) having a number average molecular weight of 500 to 5,000 and an epoxy resin (c) are bonded to an amino group in polyethyleneimine (a) having a number average molecular weight of 500 to 50,000. A step of reducing the silver compound to silver nanoparticles (Z) having an average particle diameter of 2 to 50 nm in an aqueous medium in the presence of (Y);
(2) The mixture of the compound (X) or the compound (Y) obtained in (1), the silver nanoparticles (Z) having an average particle diameter of 2 to 50 nm, and the aqueous medium has a boiling point of 120 ° C. or lower. A method for producing a silver-containing powder comprising: adding an organic solvent, concentrating, and then adding water (3) and drying the product obtained in (2). The method for producing a silver-containing powder according to claim 1, wherein the drying step (3) is freeze-drying.

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