JP6568656B2 - Silver powder and method for producing the same - Google Patents

Description

  The present invention relates to silver powder and a method for producing the same.

  Silver is widely used as an electrode material in the electrical and electronic field due to its inherent high electrical conductivity and oxidation stability. In particular, recently, with the development of printed electronics technology for directly forming a circuit of a desired form, an industry relating to conductive silver paste in which silver is pulverized and processed into a paste or ink has been developed. Conductive silver paste that uses silver powder is not only used for traditional conductive electrodes such as through-holes, die bonding, and chip components, but also for various uses such as PDP, front and rear electrodes of solar cells, and touch screens. Besides, the usage is increasing.

  Conventionally, in the production of silver powder, a wet reduction process in which a silver ammine complex aqueous solution is produced with an aqueous silver nitrate solution and aqueous ammonia and an organic reducing agent is added thereto has been employed. Recently, these silver powders are mainly used for forming electrodes or circuits of chip parts, plasma display panels and the like.

  In the conventional silver powder and its manufacturing method, it was not easy to increase the crystallite diameter of the silver powder. Even if there is a separate method for increasing the crystallite diameter, it has caused other problems such as an increased content of residual organic matter.

JP 2001-107101 A

  An object of the present invention is to provide a silver powder having a large crystallite diameter and a low content of residual organic matter in order to solve such problems.

  Another object of the present invention is to provide a method for producing silver powder that can simultaneously improve the crystallite size and the residual organic matter content by a simple method.

  The present invention provides a silver salt comprising a reaction solution preparation step (S21) for preparing a reaction solution containing silver ions, a reducing agent and a phosphate compound, and a precipitation step (S22) for obtaining a silver powder by reacting the reaction solution. A method for producing a silver powder including a reduction step (S2) is provided.

  The phosphoric acid compound is selected from at least one of hypophosphite (phosphinate), phosphite (phosphonate), phosphate and polyphosphate, The phosphoric acid compound is a pyrophosphate.

  Further, the silver ion is in the form of a silver complex salt obtained by adding ammonia to silver nitrate.

  The reducing agent is selected from at least one of hydroquinone, ascorbic acid, alkanolamine, hydrazine and formalin.

  In addition, the phosphoric acid compound is included in a range of 0.01 to 1.0 part by weight with respect to 100 parts by weight of silver ions.

  The reaction solution preparation step (S21) is obtained by adding an aqueous solution containing a reducing agent to an aqueous solution or slurry containing the silver ions and the phosphate compound.

  In the present invention, the organic substance content is 1.0% by weight or less, the crystallite diameter is in the range of 250 to 600%, and the phosphorus (P) content is in the range of 0.002 to 0.03% by weight. Provide a silver powder that is within.

  In the silver powder and the method for producing the same according to the present invention, by adding a phosphoric acid compound, the content of residual organic matter can be greatly reduced, and the crystallite diameter can be increased.

  Prior to describing the present invention in detail, the terminology used herein is for the purpose of describing particular embodiments only and is intended to be limited only by the scope of the appended claims. It should be understood that it is not intended to limit the scope. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

  Throughout this specification and the claims, unless otherwise stated, the term “comprise”, “comprises”, “comprising” is meant to include the stated article, step or group of things, and step. And not intended to exclude any certain other thing, step or group of things or group of steps.

  On the other hand, the various embodiments of the present invention may be combined with any other embodiment, unless expressly indicated to the contrary. In particular, any feature indicated as preferred or advantageous may be combined with any other feature or feature indicated as preferred or advantageous. Hereinafter, embodiments of the present invention and effects thereof will be described with reference to the accompanying drawings.

  The method for producing silver powder according to an embodiment of the present invention includes a silver salt production step (S1), a silver salt reduction step (S2), a purification step (S3) such as filtration and washing, and a surface treatment step (S4). Comprising. The method for producing silver powder according to the present invention necessarily includes a silver salt reduction step (S2), and the other steps can be omitted.

1. Silver salt production stage (S1)
In the silver salt production step (S1) according to an embodiment of the present invention, the silver salt (Sg ⁺ ) containing silver ions (Ag ⁺ ) is obtained by acid-treating ingots, grains, and granulated silver (silver, Ag) A silver salt solution can be directly produced through this step to produce a silver powder, but a commercially available silver nitrate, silver salt complex or silver intermediate solution is used. Later steps can be performed.

2. Silver salt reduction stage (S2)
The silver salt reduction step (S2) according to an embodiment of the present invention includes a reaction solution preparation step (S21) of preparing a reaction solution containing silver ions, a reducing agent and a phosphate compound, and a silver solution by reacting the reaction solution. A precipitation step (S22) for obtaining a powder is included.

  In the reaction liquid preparation step (S21) according to one embodiment of the present invention, first, a reaction liquid containing silver ions, a reducing agent and a phosphate compound is prepared. Although not limited, the reaction solution may be obtained by preparing an aqueous solution or slurry containing silver ions and a phosphoric acid compound and then adding an aqueous solution containing a reducing agent. While stirring the aqueous solution or slurry containing silver ions and the phosphate compound, the aqueous solution containing the reducing agent can be slowly added dropwise or added together. Addition at once is preferable because the reduction reaction is completed at once in a short time, so that aggregation of particles can be prevented and dispersibility can be improved.

  The silver ions are not limited as long as they are in the form of silver cations. For example, it can be silver nitrate, a silver salt complex or a silver intermediate. The silver salt complex can be produced by adding ammonia water, ammonium salt, chelate compound or the like to silver nitrate or the like. The silver intermediate can be produced by adding sodium hydroxide, sodium chloride, sodium carbonate or the like to silver nitrate or the like. The concentration of silver ions is not limited, but is preferably in the range of 6 g / L to 20 g / L. When it is less than the above range, it is inferior in economic efficiency, and when it exceeds the above range, aggregation of powder is caused.

  In order to produce silver powder having an appropriate particle size and spherical shape, it is preferable to use an ammine complex obtained by adding aqueous ammonia to an aqueous silver nitrate solution.

  The reducing agent is not limited, but may be one or more selected from the group consisting of ascorbic acid, alkanolamine, hydroquinone, hydrazine and formalin. Of these, hydroquinone can be preferably selected. The reducing agent is preferably used in an amount of 1/2 to 2/3 equivalent of silver. When the reducing agent is used at less than 1/2 equivalent of silver ions, all the silver ions may not be reduced. When the reducing agent is used at more than 2/3 equivalents of silver ions, it contains an organic substance. The amount may increase and become a problem.

  By adding a phosphoric acid compound to the reaction solution, the inventor performs a reaction in which phosphorus acts as a seed and grows silver, so that the content of residual organic matter can be reduced. It is presumed that the crystallite diameter can be increased periodically. This is supported by experimental examples described later.

The phosphoric acid compound is not limited, but at least one of hypophosphite (phosphinate), phosphite (phosphonate), phosphate and polyphosphate can be selected. Hypophosphite (phosphinate) includes metal salts of phosphinate (hypophosphite) and hypophosphorous acid (H ₃ PO ₂ ). For example, sodium hypophosphite (NaPH ₂ O ₂ ), calcium hypophosphite (Ca (PH ₂ O ₂ ) ₂ ), ammonium iron hypophosphite and the like can be mentioned. Phosphites (phosphonates) include the salt form of phosphonic acid (phosphorous acid) (H ₃ PO ₃ ) and can be salts of ammonium sodium potassium and calcium. Examples of the phosphate include a salt form of phosphoric acid (H ₃ PO ₄ ), and may be a salt of ammonium sodium potassium and calcium. All or part of the hydrogen can be replaced with a salt. That is, it can be a monobasic, dibasic or tribasic (ie, containing 1, 2 or 3 metal atoms) salt. Examples of sodium salts include sodium dihydrogen orthophosphate [monobasic phosphate (NaH ₂ PO ₄ )], disodium monohydrogen orthophosphate [dibasic phosphate (Na ₂ HPO ₄ )], and And trisodium phosphate [tribasic phosphate (Na ₃ PO ₄ )]. Examples of the polyphosphate include pyrophosphate (diphosphate), which is a salt form of pyrophosphate (H ₄ P ₂ O ₇ ), and metaphosphate (here, metaphosphate (HPO ₃ ) _n ) N is preferably in the range of 2 to 10), and examples thereof include polyphosphate having a high degree of polymerization. These can be ammonium sodium potassium and calcium salts. However, it should be a water availability salt.

  Among these, pyrophosphate and phosphoric acid are preferable because they are excellent in the effect of reducing the content of organic substances and the effect of increasing the crystallite diameter, and particularly preferably in the form of a sodium salt.

  Although content of a phosphoric acid compound is not restrict | limited, It is good to add within the range of 0.01-1 weight part with respect to 100 weight part of silver ions. If the amount is less than 0.01 parts by weight, the effect of increasing the crystallite diameter is negligible. If the amount exceeds 1 part by weight, the increase in the crystallite diameter decreases.

  In the precipitation step (S22) according to an embodiment of the present invention, the reaction solution is reacted to obtain silver powder. The reaction solution should be stirred. On the other hand, in the embodiment of the present invention, in order to improve the dispersibility of silver particles and prevent aggregation, it is not excluded from the scope of the right that the reactant contains a dispersant. Examples of the dispersant include fatty acids, fatty acid salts, surfactants, organic metals, chelating agents, and protective colloids.

  However, when the dispersant is included, the content of residual organic matter may increase and become a problem. Preferably, it is necessary to control the particle size of the silver powder, the content of residual organic matter, and the crystallite size without adding a dispersant.

3. Purification stage (S3)
In the purification step (S3) according to an embodiment of the present invention, after completing the silver particle precipitation reaction through the silver salt reduction step (S2), the silver powder dispersed in the aqueous solution or slurry is filtered or the like. Separating and washing (S31). More specifically, after the silver particles in the silver powder dispersion are settled, the supernatant of the dispersion is discarded and filtered using a centrifuge, and the filter medium is washed with pure water. The cleaning process is performed by completely removing the cleaning water from which the powder has been cleaned. Therefore, the water content is reduced to less than 10%. Optionally, before the filtration, it is also possible to add the above dispersant to the reaction completion solution to prevent aggregation of the silver powder.

  In addition, the purification step (S3) according to an embodiment of the present invention may further include a drying and crushing step (S34) after washing.

4). Surface treatment stage (S4)
The surface treatment step (S4) according to an embodiment of the present invention is a step of hydrophobizing the hydrophilic surface of the silver powder and may be selectively performed. More specifically, after the moisture content of the wet cake obtained after filtration is adjusted to less than 10%, a surface treatment agent is added for the surface treatment of the silver powder, and the moisture content is increased from 70% to It can be adjusted to 85%. Thereafter, silver powder can be obtained through drying and crushing processes. The surface treatment is sufficiently performed only when the powder is well dispersed when the surface treatment is performed on the silver powder. If the water content is low, the dispersion efficiency is poor. Therefore, the surface treatment should be performed with a certain water content.

  After the reaction is completed, the silver powder is separated using filtration or the like and is subjected to a washing process. Optionally, before the filtration, it is also possible to add the above dispersant to the reaction completion solution to prevent aggregation of the silver powder. Alternatively, after adjusting the moisture content of the wet cake obtained after filtration to less than 10%, a surface treatment agent is added for the surface treatment of the silver powder, and the moisture content is adjusted to 70% to 85%. be able to. Thereafter, silver powder can be obtained through drying and crushing processes.

  The silver powder produced according to an embodiment of the present invention has an organic content of 1.0% by weight or less, a crystallite diameter in the range of 250 to 600%, and a phosphorus (P) content of 0.002. It is in the range of wt% to 0.03 wt%. By containing phosphorus in the above range, it is possible to obtain a silver powder having a large crystallite size while reducing the content of organic matter. The particle size of the silver powder is not limited, but is preferably in the range of 0.5 to 3.0 μm.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments of the present invention can be modified in various other forms and should not be construed to limit the scope of the present invention. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

Examples and Experimental Examples <Example 1>
A first aqueous solution was prepared by adding 128 g of silver nitrate, 175 g of ammonia (concentration 25%) and 0.02 g of sodium pyrophosphate to 730 g of pure water at room temperature, stirring and dissolving. On the other hand, 20 g of hydroquinone was added to 1000 g of pure water at room temperature, stirred and dissolved to prepare a second aqueous solution (see Table 1).

  Next, the first aqueous solution was stirred, the second aqueous solution was added to the first aqueous solution, and the mixture was further stirred for 5 minutes after the addition was completed to grow particles in the mixed solution. Thereafter, the stirring is stopped, and the particles in the mixed solution are allowed to settle. Then, the supernatant of the mixed solution is discarded, the mixed solution is filtered using a centrifuge, the filter medium is washed with pure water, dried, and silver powder. Got.

  With respect to the obtained silver powder, SEM size, crystallite diameter, and organic content were measured by the following methods. The results are shown in Table 2.

  (SEM size): Using a scanning electron microscope manufactured by JEOL, the diameter of each of 100 powders was measured, and then the average value was obtained.

  (Crystallite diameter): Powder X-ray diffraction was performed using an X-ray diffractometer X'pert manufactured by PANalytical, and Scherrer equation was calculated from the diffraction angle peak position and half width of the obtained [111] plane. ) Was used to determine the crystallite size.

  (Content of organic substance): Using TG / DTA EXART6600 manufactured by Seiko Instruments Inc., TGA analysis was performed in the air at a temperature rising rate of 10 ° C / min in the range from room temperature to 500 ° C. The content was measured.

<Example 2>
A first aqueous solution was prepared by adding 128 g of silver nitrate, 175 g of ammonia (concentration 25%), and 0.032 g of sodium pyrophosphate to 730 g of pure water at room temperature, stirring and dissolving. On the other hand, 20 g of hydroquinone was added to 1000 g of pure water at room temperature, stirred and dissolved to prepare a second aqueous solution (see Table 1).

  Next, the first aqueous solution was stirred, the second aqueous solution was added to the first aqueous solution, and the mixture was further stirred for 5 minutes after the addition was completed to grow particles in the mixed solution. Thereafter, the stirring is stopped, and the particles in the mixed solution are allowed to settle. Then, the supernatant of the mixed solution is discarded, the mixed solution is filtered using a centrifuge, the filter medium is washed with pure water, dried, and silver powder. Got.

  With respect to the obtained silver powder, SEM size, crystallite diameter, and organic content were measured by the following methods. The results are shown in Table 2.

<Example 3>
A first aqueous solution was prepared by adding and stirring 128 g of silver nitrate, 175 g of ammonia (concentration 25%), and 0.08 g of sodium phosphate in 730 g of pure water at room temperature. On the other hand, 20 g of hydroquinone was added to 1000 g of pure water at room temperature, stirred and dissolved to prepare a second aqueous solution (see Table 1).

  Next, the first aqueous solution was stirred, the second aqueous solution was added to the first aqueous solution, and the mixture was further stirred for 5 minutes after the addition was completed to grow particles in the mixed solution. Thereafter, the stirring is stopped, and the particles in the mixed solution are allowed to settle. Then, the supernatant of the mixed solution is discarded, the mixed solution is filtered using a centrifuge, the filter medium is washed with pure water, dried, and silver powder. Got.

  With respect to the obtained silver powder, SEM size, crystallite diameter, and organic content were measured by the following methods. The results are shown in Table 2.

<Comparative Example 1>
A first aqueous solution was prepared by adding 128 g of silver nitrate and 175 g of ammonia (concentration 25%) to 730 g of pure water at room temperature, stirring and dissolving. On the other hand, 20 g of hydroquinone was added to 1000 g of pure water at room temperature, stirred and dissolved to prepare a second aqueous solution (see Table 1).

  Next, the first aqueous solution was stirred, the second aqueous solution was added to the first aqueous solution, and the mixture was further stirred for 5 minutes after the addition was completed to grow particles in the mixed solution. Thereafter, the stirring is stopped, and the particles in the mixed solution are allowed to settle. Then, the supernatant of the mixed solution is discarded, the mixed solution is filtered using a centrifuge, the filter medium is washed with pure water, dried, and silver powder. Got.

  With respect to the obtained silver powder, SEM size, crystallite diameter, and organic content were measured by the following methods. The results are shown in Table 2.

  As shown in Table 2, it can be confirmed that when a phosphoric acid compound is added, the content of the organic substance is remarkably reduced and the crystallite diameter is greatly increased.

The embodiments of the present invention have been described above. However, this is merely an example, and various modifications and other equivalents will be made by those having ordinary knowledge in the technical field to which the present invention belongs. It will be appreciated that embodiments are possible. Accordingly, the true technical protection scope of the present invention should be determined by the claims set forth below.

Claims (6)

A silver salt reduction step (S2) including a reaction solution preparation step (S21) for preparing a reaction solution containing silver ions, a reducing agent and a phosphate compound, and a precipitation step (S22) for reacting the reaction solution to obtain silver powder. The reaction solution prepared in the reaction solution preparation step (S21) includes an aqueous solution or slurry containing the silver ions and a phosphate compound, and then an aqueous solution containing a reducing agent. The silver powder has a crystallite diameter in the range of 250 to 600% and a phosphorus (P) content of 0.002 to 0.00. A method for producing silver powder , which is within the range of 03% by weight . The method for producing silver powder according to claim 1, wherein the phosphoric acid compound is selected from at least one of hypophosphite, phosphite, phosphate and polyphosphate.     The method for producing silver powder according to claim 1, wherein the phosphoric acid compound is pyrophosphate.     The method for producing a silver powder according to claim 1, wherein the silver ions are in the form of a silver complex salt obtained by adding ammonia to silver nitrate.     The method for producing a silver powder according to claim 1, wherein the reducing agent is selected from at least one of hydroquinone, ascorbic acid, alkanolamine, hydrazine, and formalin.     2. The method for producing a silver powder according to claim 1, wherein the phosphoric acid compound is contained within a range of 0.01 to 1.0 part by weight with respect to 100 parts by weight of silver ions.