KR20040081215A - Method for making super-fine metal particle solution with high concentration - Google Patents

Abstract

PURPOSE: A method for preparing a high concentrated ultrafine metal particle solution in which uniform metal particles having ultra-fine particle size of 100 nm or less are dispersed by effectively controlling agglomeration and growth of particles in the metal particle production process. CONSTITUTION: In a method for producing metal particles by adding reducing agent to a metal salt aqueous solution, the method for preparing a high concentrated ultrafine metal particle solution comprises the process of producing ultrafine metal particles by adding the reducing agent to the polymer-metal salt complex after forming polymer-metal salt complex by adding a polymer electrolyte to the metal salt aqueous solution, wherein the metal salt is nitrate, sulfate, carbonate or chloride of metal ions selected from silver (Ag), nickel (Ni), copper (Cu), gold (Au), cobalt (Co) and palladium (Pd), wherein the reducing agent is NaBH4, LiAlBH4, hydrazine, hydrazine hydrate, formaldehyde or a mixture thereof, wherein 0.2 to 2 equivalents of the reducing agent are used for 1 equivalent of the metal salt, wherein the polymer electrolyte is dissolved thus dissociated into water since dissociating group exists in polymer chains of the polymer electrolyte, wherein the polymer electrolyte is selected from a polymer material to which a dissociating group selected from polyacrylic acid, polymethacrylic acid, polystyrene sulfonate, lignin sulfonate and salts thereof is bonded, and a copolymer of the dissociating group bonded polymer material and other aqueous polymer without dissociating group, wherein 0.1 to 30 weight parts of the polymer electrolyte are used for 1 weight part of the metal salt, and wherein the produced metal particles are ultrafine powder having particle size of 100 nm or less.

Description

Method for making super-fine metal particle solution with high concentration

The present invention relates to a method for producing a high concentration ultrafine metal particle solution, and more particularly, to form a polymer-metal salt complex by adding a polymer electrolyte to an aqueous metal salt solution, and then treating the same with a reducing agent to prevent aggregation or sedimentation of the produced metal particles. Therefore, the present invention relates to a method for producing a highly concentrated ultrafine metal particle solution which can be used for the production of catalysts and small alloys for the chemical industry, and for the production of conductive pastes for forming internal electrodes of multilayer ceramic capacitors, having a small and uniform ultrafine size of 100 nm or less. .

The metal powder may be directly used as a catalyst for the chemical industry, or may be used to prepare a small alloy such as Ni-Cr, W-Ag or the like, or to prepare a conductive paste. Conductive pastes using metal powders are prepared by mixing various organic materials (resin, solvent, thixotropic agent, dispersant, plasticizer, etc.) with conductive metal powders such as silver, gold, copper and nickel. It is used to form internal circuits of ceramic electronic components such as ceramic capacitors. Particularly, for the purpose of miniaturization and thinning of electronic components, the particle size of the metal powder, which is a conductive component, needs to be adjusted as small as possible.

Problems in using the metal powder for such industrial purposes are the particle size, dispersibility, pulverization, and mixing properties of the metal powder. For example, when used as a catalyst for the chemical industry, the particle size should be as small as possible, and when used in the production of small alloys, mechanical compatibility with other metals or ceramic powders is important. Dispersibility and mixing with the resin are important.

The metal powder may be prepared by a chemical method, a physical method, or a mechanical method. Among the production methods, the chemical production method is most commonly applied, and the chemical production method consists of adding a base such as sodium hydroxide to an aqueous solution of a soluble metal salt to make it basic, and then reducing it to formaldehyde (formalin) or hydrazine. .

As a metal powder manufacturing method by a chemical method, the typical method is the silver (Ag) powder manufacturing method. In a conventional chemical silver (Ag) powder manufacturing method, a base is added to an aqueous solution of a soluble silver salt to generate silver hydroxide or silver oxide, and a reducing agent such as formaldehyde or hydrazine is added thereto to prepare silver (Ag) powder. At this time, the silver (Ag) particles produced are relatively large and have a non-uniform size distribution with a size of 1 to 10 μm. In addition, when the reduction reaction in the aqueous solution is agglomerated easily produced silver (Ag) particles, this has been mainly used for the purpose of controlling the aggregation and overgrowth of metal particles.

Surfactants can be classified into anionic, cationic, zwitterionic and nonionic systems depending on the electrical properties of their ends.

The soaps we commonly use are representative of anionic surfactants. Taking soap as an example, the principle of dispersing the particles in the aqueous solution is briefly described as follows. Surfactants called "soaps" are generally composed of fatty acid sodium salts having a C12 to C18 carbon chain. The following formula (1) briefly shows the structure of a surfactant (soap), consisting of a hydrophobic group (hydrophilic group) and a charged hydrophilic group of a long carbon chain, when the metal ions are dissolved in water to surround the metal ions It forms the name 'micelle'.

In addition, among the surfactants, there are nonionic surfactants which exhibit surfactant activity without any ionization in aqueous solution. Although nonionic surfactants are not ionized in aqueous solution, hydrophilic and hydrophobic groups are present in their functional groups, and thus, they are widely used because they exhibit strong and stable surfactant effects in hard water and brine.

Using this principle, when preparing metal powders by reducing metal ions in a metal salt solution with a suitable reducing agent, a surfactant is adsorbed on the surface of the metal particles to be reduced by adding an appropriate surfactant, thereby further suppressing the growth of particles. By making it possible to produce a fine metal particles. Many researches have been conducted on the preparation of metal powders using surfactants, and Korean Patent Publication Nos. 2002-0022168 (Anisotropic Nanoparticles and Synthesis Methods thereof) and 2001-0070070 (Methods for Preparing Metal Colloids). And various inventions such as metal colloid prepared by the method, 2000-0012423 (manufacturing method of fine metal particles in aqueous surfactant solution), 2000-0011546 (method of producing nanoparticles of transition metal) Has been made public.

However, in the method of manufacturing the fine metal powder using the surfactant as described above, the smaller the size of the metal particles to be prepared, the exponentially increasing the amount of the surfactant to be used to prevent the growth and aggregation of the particles. Therefore, there is a disadvantage in that the concentration of the metal powder can not be more than a predetermined concentration simply by using a surfactant.

Therefore, the present inventors studied to find a new method for producing ultra-fine metal particles at high concentration, and as a result, a polymer electrolyte was effectively used for the purpose of effectively controlling the aggregation and growth of the metal particles produced in the aqueous metal salt solution. The use of the present invention has completed the present invention.

Accordingly, the present invention provides a method for producing a highly concentrated ultrafine metal particle solution containing metal particles that are small and uniform in size to ultrafine sizes of 100 nm or less by effectively controlling the aggregation and growth of particles in the metal particle production process. The purpose is.

1 is a transmission electron microscope (TEM) photograph of silver (Ag) powder prepared according to Example 7.

The present invention provides a method for producing metal particles by adding a reducing agent to an aqueous metal salt solution, after adding a polymer electrolyte to the aqueous metal salt solution to form a polymer-metal salt complex, and then adding a reducing agent to the high concentration ultrafine metal particle solution. The manufacturing method is characterized by the above-mentioned.

Referring to the present invention in more detail as follows.

In the conventional method for preparing a metal particle solution by adding a reducing agent to an aqueous metal salt solution, a surfactant is used as a material to control the aggregation and growth of the metal particles generated as a result of the reduction reaction, but the size of the metal particles produced In order to reduce the amount of exponentially a large amount of surfactant must be added and there is a limit to the generation of fine particles less than 300 nm even if the excess surfactant is added. However, in the present invention, the polymer electrolyte is selected as a material for controlling the aggregation and growth of the metal particles, which has the greatest technical feature. Thus, the particle aggregation and growth can be effectively controlled even by the addition of a small amount of the polymer electrolyte. It is possible to prepare a metal particle solution containing a high concentration of small and uniform metal particles with an ultra fine size of less than 100 nm.

The polymer electrolyte used for the purpose of controlling the aggregation and growth of the metal particles produced by the present invention is a conventional polymer electrolyte having dissociation groups in the polymer chain and dissociated in water to dissociate. Dissociation groups present in the polymer chain, for example, carboxyl carbonate group (-COO ^-), sulfonate group (-SO ₃ ^-), sulfate group (-OSO ₃ ^-), phosphate groups (-OPO ₃ ^-), and phosphorus phosphonate group (-PO ₃ ^-) it can be included and the like. Specific examples of the polymer electrolyte that can be applied to the present invention may be polyacrylic acid, polymethacrylic acid, polystyrene sulfonic acid, lignin sulfonic acid or salts thereof. In addition, as the polymer electrolyte, a copolymer copolymerized with the above dissociated group and another water-soluble polymer having no dissociation group, for example, polyethylene, polyacrylamide, polyethylene glycol, or the like may be used. And the counter ion to combine with the dissociation group of the polymer electrolyte to form a salt may include a metal cation such as sodium, ammonium cation, amine cation and the like.

As a representative example of the polymer electrolyte to be used in the present invention, the structure of the ammonium polymethacrylate salt is represented by the following Chemical Formula 2.

Comparing the surfactant of Formula 1 and the polymer electrolyte of the present invention, which have been conventionally used in general, there are the following differences. First, both the polymer electrolyte and the surfactant are composed of carbon chains, but the surfactant is composed of tens or fewer carbon chains, whereas the polymer electrolyte is composed of thousands of tens or tens of thousands of long carbon chains. Second, the surfactant has only one end of the long chain that exhibits hydrophilicity, so that only one metal ion can be substituted per molecule, whereas the polymer electrolyte has numerous charge-bearing parts throughout the carbon chain. There is a difference in that. Therefore, as shown in the following Chemical Formula 3, each structural unit of the polymer electrolyte is substituted with metal ions to be reduced, thereby inhibiting particle growth from the reduction of ions. Thus, smaller particles can be produced as compared with using a general surfactant. In addition, since the polymer electrolyte has a myriad of functional groups capable of substituting metal ions in one electrolyte, it is possible to effectively control the aggregation and growth of particles even when using a very small amount compared to a general surfactant.

The method for producing a high concentration ultrafine metal particle solution according to the present invention is as follows. First, a soluble metal salt is added to distilled water to prepare an aqueous metal salt solution. Then, the polymer electrolyte is added to the metal salt aqueous solution and stirred to form a polymer-metal salt complex. Then, a reducing agent is added to the polymer-metal salt complex-containing solution to reduce metal ions to obtain a metal particle solution.

Looking at each component used in the manufacturing method of the present invention described above is as follows.

The metal salt is dissolved in water such as nitrate, sulfate, carbonate or chloride of a metal ion selected from silver (Ag), nickel (Ni), copper (Cu), gold (Au), cobalt (Co) and palladium (Pd). When the soluble metal salt is used, specifically, silver nitrate (AgNO ₃ ), nickel nitrate (Ni (NO ₃ ) ₂ ), or the like can be used.

As the reducing agent, NaBH ₄ , LiAlBH ₄ , hydrazine, hydrazine hydrate, formaldehyde, or the like may be used. The reducing agent is used in 0.2 to 2 equivalents to 1 equivalent of the metal salt to be reduced, if the amount of the reducing agent is less than 0.2 equivalents may have a problem that the metal salt is not 100% reduced, if used in excess of 2 equivalents It is undesirable because it is wasted.

As the polymer electrolyte, the above-mentioned ones may be used, and may vary depending on the degree of polymerization of the polymer, but in general, it is preferable to add 0.1 to 30 parts by weight based on 1 part by weight of the metal salt. If the amount of the polymer electrolyte used is less than 0.1 parts by weight, the fixing effect of the metal ions is remarkably inferior, and the metal ions are freely present in the solution, causing agglomeration during the reduction process. When the amount is exceeded, there is a problem that the solution gels due to a decrease in solubility.

According to the production method of the present invention as described above, it is possible to produce a uniform metal particles of ultra-fine size of 100 nm or less, and to prepare a high concentration solution of 1% by weight or more, as well as a low concentration solution even in the concentration of the metal particle solution You may. In addition, the high concentration metal particle solution prepared by the method of the present invention did not easily aggregate or settle even after being left for a long time, and it was confirmed that some precipitated aggregated particles could be easily redispersed by ultrasonic treatment.

The present invention as described above will be described in more detail based on the following examples, but the present invention is not limited to the examples.

Examples 1-4

Next, the metal particle solution was prepared by the content shown in Table 1 and the preparation method as follows.

First, silver nitrate was dissolved in distilled water using a soluble metal salt, and then a polymer electrolyte (ammonium polymethacrylate salt, Darvan-C) was dispersed and stirred for 1 hour to form a polymer-silver nitrate complex in which silver ions were substituted in the polymer electrolyte functional group. Separately, a reducing agent solution was prepared by dissolving an equivalent amount of NaBH ₄ required to reduce the silver nitrate in distilled water. The silver-Ag ions were reduced by slowly dropwise adding the reducing agent solution prepared above while strongly stirring the solution containing the polymer-silver nitrate. After the reduction, the solution appeared dark black, and when diluted, the solution became light yellow. The metal particle solution containing the silver particles prepared as described above was analyzed by a particle size analyzer and a transmission electron microscope (TEM), and the results are shown in Table 1 below.

division Metal salt solution Reducing agent solution Metal particle solution Distilled water (g) AgNO ₃ (g) Polyelectrolyte (g) Distilled water (g) NaBH ₄ (g) Ag particle size (nm) Ag concentration (% by weight) ⁽¹⁾ Concentration Ratio ⁽²⁾ Example 1 79.86 0.04 0.10 24.99 0.01 12.8 0.024 One Example 2 78.60 0.40 1.00 24.91 0.09 19.7 0.242 10 Example 3 73.00 2.00 5.00 24.55 0.45 32.8 1.210 50 Example 4 66.00 4.00 10.00 24.10 0.90 31.0 2.419 100 (One) (2) Concentration ratio: Means the concentration ratio when the concentration of the metal particle solution of Example 1 is set to one.

As shown in Table 1, according to the present invention, it is possible to prepare uniform metal particles of ultra fine size of 100 nm or less, and to prepare a low concentration solution as well as a high concentration solution of 1% by weight or more even in the concentration of the metal particle solution. In addition, even if the concentration of the metal particle solution is concentrated to 100 times the reference concentration of the metal particles was confirmed that the maximum size of only 32.8 nm.

Example 5

The metal particle solution was prepared by changing the amount of the polymer electrolyte (polyammonium methacrylate salt, Darvan-C) and fixing the metal salt concentration in Example 4 as shown in Table 2 below.

The prepared metal particle solution containing silver (Ag) particles was analyzed by particle size analyzer and transmission electron microscope (TEM), and the results are shown in Table 2 below.

division Metal salt solution Reducing agent solution Metal particle solution Distilled water (g) AgNO ₃ (g) Polymer electrolyte (g) Distilled water (g) NaBH ₄ (g) Ag particle size (nm) Ag concentration (% by weight) ⁽¹⁾ Concentration Ratio ⁽²⁾ Example 4 66.00 4.00 10.00 24.10 0.9 31.0 2.419 100 Example 5 46.00 30.00 29.8

As shown in Table 2, it was confirmed that the silver (Ag) particles produced in Example 5 to which the polymer electrolyte was added in excess are fine as in Example 4.

Examples 6-8

In Example 1, the metal particle solution was prepared while changing the concentration of the metal particle solution to 5 to 20% by weight. The prepared metal particle solution containing silver (Ag) particles was analyzed by particle size analyzer and transmission electron microscope (TEM), and the results are shown in Table 3 below. It was confirmed that silver (Ag) particles having a size of 20 to 50 nm were prepared even at an ultra high concentration of 20 wt%. As a representative example, a transmission electron microscope (TEM) photograph of the solution prepared in Example 7 is shown in FIG. 1.

division Metal salt solution Reducing agent solution Metal particle solution Distilled water (g) AgNO ₃ (g) Polymer electrolyte (g) Distilled water (g) Hydrazine (g) NaBH ₄ (g) Ag particle size (nm) Ag concentration (% by weight) ⁽¹⁾ Concentration Ratio ⁽²⁾ Example 6 47.89 7.87 20.0 20.0 0.0 2.0 40 5.0 200 Example 7 43.29 15.75 33.0 10.0 5.0 4.0 20-50 10.0 400 Example 8 16.50 31.50 33.0 5.0 10.0 8.0 20-50 20.0 800

Examples 9-16

In Example 1, the concentration of the metal salt was fixed to 10 wt%, and the metal particle solution was prepared while changing the type of the counterion of the polymer electrolyte and the structure of the main chain of the polymer electrolyte. The prepared metal particle solution containing silver (Ag) particles was analyzed by particle size analyzer and transmission electron microscope (TEM), and the results are shown in Table 4 below. It was confirmed that the silver particles having a size of 20 to 200 nm were prepared even at an ultra high concentration of 20 wt%, and that the nanoparticles were synthesized regardless of the structure of the polymer electrolyte and the type of the counter ion.

division Metal salt solution Reducing agent solution Metal particle solution Distilled water (g) AgNO ₃ (g) Polymer electrolyte (g) Distilled water (g) Hydrazine (g) NaBH ₄ (g) Ag particle size (nm) Ag concentration (% by weight) ⁽¹⁾ Concentration Ratio ⁽²⁾ Example 7 43.29 15.75 33.0 10.0 5.0 4.0 20-50 10.0 400 Example 9 56.11 15.75 16.14 5.0 0.0 2.0 20-50 10.0 400 Example 10 57.50 15.75 14.75 5.0 5.0 4.0 20-50 10.0 400 Example 11 57.50 15.75 14.75 5.0 10.0 4.0 20-50 10.0 400 Example 12 57.50 15.75 14.75 5.0 10.0 4.0 20-100 10.0 400 Example 13 57.50 15.75 14.75 5.0 10.0 4.0 20-100 10.0 400 Example 14 57.50 15.75 14.75 5.0 10.0 4.0 20-100 10.0 400 Example 15 57.50 15.75 14.75 5.0 10.0 4.0 20-100 10.0 400 Example 16 57.50 15.75 14.75 5.0 10.0 4.0 20-100 10.0 400 Example 7 Use of Polymer Electrolyte of Ammonium Polymethacrylate Example 9 Use of Polymer Electrolyte of Sodium Polyacrylic Acid Example 10 Use of Polymer Electrolyte of Polyacrylic Acid Amine Salt Polymer electrolyte of sodium sulfonate salt Example 13 Polymer electrolyte of sodium lignin sulfonate salt Example 14 Polymer electrolyte of polyethylene-methacrylate sodium salt copolymer Example 15 Polymer electrolyte of polyethylene-vinylacetate-methacrylic acid copolymer Example 16 Use of Polyelectrolyte of Polyethylene-Methylacrylate-Acrylic Acid Copolymer

Comparative Examples 1 to 8

A metal particle solution was prepared in the same manner as in Examples 1 to 4, except that Tween 20 and Triton X-100, which were nonionic surfactants, were used instead of the polymer electrolyte as a dispersant. It was.

The prepared metal particle solution containing silver (Ag) particles was analyzed by particle size analyzer and transmission electron microscope (TEM), and the results are shown in Table 5 below.

division Metal salt solution Reducing agent solution Metal particle solution Distilled water (g) AgNO ₃ (g) Twin 20 (g) Triton X-100 (g) Distilled water (g) NaBH ₄ (g) Ag particle size (nm) Ag concentration (% by weight) ⁽¹⁾ Concentration Ratio ⁽²⁾ Comparative Example 1 79.86 0.04 0.10 - 24.99 0.01 31.4 0.024 One Comparative Example 2 78.60 0.40 1.00 - 24.91 0.09 37.3 0.242 10 Comparative Example 3 73.00 2.00 5.00 - 24.55 0.45 102.2 1.210 50 Comparative Example 4 66.00 4.00 10.00 - 24.10 0.90 Cohesion 2.419 100 Comparative Example 5 79.86 0.04 - 0.10 24.99 0.01 19.5 0.024 One Comparative Example 6 78.60 0.40 - 1.00 24.91 0.09 Cohesion 0.242 10 Comparative Example 7 73.00 2.00 - 5.00 24.55 0.45 Cohesion 1.210 50 Comparative Example 8 66.00 4.00 - 10.00 24.10 0.90 Cohesion 2.419 100

As shown in Table 5, in Comparative Examples 1, 2, and 5 in which the concentration of the metal particle solution is maintained at a relatively low concentration (concentration ratio 1 or 10), the metal particle size was small, but the silver (Ag) content was low and economical. This is undesirable because it lacks. In addition, when the silver (Ag) content is adjusted to a high concentration, the particles become too large or aggregate and settle, and thus it is confirmed that the use of a general surfactant as in the comparative example makes it impossible to prepare a high concentration metal particle solution.

Experimental Example

In order to determine the stability of the prepared metal particle solution, each of the metal particle solutions prepared in Examples 3 to 7 and Comparative Examples 3 to 6 was checked for agglomeration while standing at room temperature for a long time, and the results are shown in Table 6 below. Indicated.

division Surfactants Ag concentration (%) Right after 1 day past 5 days 10 days past Example 3 PMMA Ammonium Salt 1.2 ◎ ◎ ◎ ◎ Example 4 PMMA Ammonium Salt 2.4 ◎ ◎ ◎ ◎ Example 6 PMMA Ammonium Salt 5.0 ◎ ◎ ◎ ○ Example 7 PMMA Ammonium Salt 10.0 ◎ ◎ ◎ ○ Comparative Example 3 Tw 20 1.2 ◎ ○ △ × Comparative Example 4 Tw 20 2.4 ○ ○ △ × Comparative Example 6 Triton X-100 0.24 × × × × ◎; Very good, ○; Good, Δ; Instability, ×; Cohesion

As shown in Table 6, the high concentration metal particle solution prepared by the method of the present invention did not easily aggregate or settle even after being left for a long time and some precipitated aggregated particles could be easily redispersed by ultrasonic treatment, but the interface All of the metal particle solutions using the activator were found to be unstable solutions that did not exceed 1 day, resulting in the formation of aggregated particles.

As described above, in the present invention, the polymer electrolyte is added to the aqueous solution in which the metal salt is dissolved to form a polymer-metal salt complex, thereby controlling the growth and aggregation of particles in the reduction process of the metal ions, thereby providing a uniform metal having an ultra fine size of 100 nm or less. The particles can be prepared in high concentration solutions.

Therefore, the metal particles produced by the production method according to the present invention are useful for preparing catalysts and small alloys for the chemical industry and for preparing conductive pastes for forming internal electrodes of multilayer ceramic capacitors.

Claims (10)

In the method for producing metal particles by adding a reducing agent to the aqueous metal salt solution, After the polymer electrolyte is added to the aqueous metal salt solution to form a polymer-metal salt complex, a reducing agent is added thereto to produce ultra fine metal particles. The metal salt of claim 1, wherein the metal salt is nitrate, sulfate, carbonate or chloride of a metal ion selected from silver (Ag), nickel (Ni), copper (Cu), gold (Au), cobalt (Co), and palladium (Pd). Method for producing a high concentration ultrafine metal particle solution, characterized in that. The method of claim 1, wherein the reducing agent is selected from NaBH ₄ , LiAlBH ₄ , hydrazine, hydrazine hydrate, and formaldehyde or mixed. The method for producing a highly concentrated ultrafine metal particle solution according to claim 1, wherein the reducing agent is used in an amount of 0.2 to 2 equivalents based on 1 equivalent of the metal salt. The method of claim 1, wherein the polymer electrolyte has a dissociation group in the polymer chain and is dissolved in water to dissociate. The method of claim 5, wherein the dissociation group (解離基) carbonate is carboxy group (-COO ^-), sulfonate group (-SO ₃ ^-), sulfate group (-OSO ₃ ^-), phosphate groups (-OPO ₃ ^-) and a phosphonate group (-PO ₃ ^-) a high concentration of the second method of producing metal fine particle solution, wherein is selected from the. The polymer electrolyte of claim 1, wherein the polymer electrolyte is a polymer material having a dissociation group selected from polyacrylic acid, polymethacrylic acid polystyrenesulfonic acid, lignin sulfonic acid, and salts thereof, or a polymer material having no dissociation group bonded thereto. Method for producing a high concentration ultrafine metal particle solution, characterized in that selected from copolymers of other water-soluble polymers. 8. The highly concentrated ultrafine metal particles according to claim 1, 5 or 7, wherein a counter ion which combines with a dissociation group of the polymer electrolyte to form a salt is selected from alkali metal cations, ammonium cations and amine cations. Method of preparation of the solution. The method of claim 1, wherein the polymer electrolyte is used in an amount of 0.1 to 30 parts by weight based on 1 part by weight of the metal salt. The method of claim 1, wherein the produced metal particles are 100 nm or less ultra fine powder.