JP2019035110A - Method for controlling a particle size of a silver particle - Google Patents

Abstract

To provide a method for controlling a particle size of a silver particle capable of adjusting a particle size of a silver particle to a desired size at an inexpensive price.SOLUTION: A method for controlling a particle size of a silver particle includes a reaction process that causes a silver ion to react with fatty acid at a reaction temperature, in which adjustments are made for a ratio of the silver ion in molar concentration and the fatty acid in molar concentration and/or the time for which the reaction temperature is maintained.SELECTED DRAWING: None

Description

  The present invention relates to a method for controlling the particle size of silver particles.

  Silver is known to have excellent electrical conductivity and chemical stability, as well as catalytic function and antibacterial properties, and is expected to be applied in various fields such as industrial and medical fields. Material. Therefore, conventionally, development of technology for producing silver particles has been advanced.

  As a method for producing silver particles, for example, Patent Document 1 discloses a solution containing silver ions and halides (eg, chloride, bromide, iodide) in the presence of colloidal particles (eg, silicon oxide). A method for producing silver halide fine particles by mixing with a solution containing the above ions is disclosed. Non-Patent Document 2 discloses a method for producing silver particles employing triethylamine as a solvent.

  In recent years, silver particles having different particle sizes have been reported to have different electrical, optical, chemical and biological properties, resulting in different behavior. For example, in Non-Patent Document 1, when the particle diameter of silver particles is nanometer size, the antibacterial activity of silver particles is improved, and when the particle diameter of silver particles is nanometer size, It has been reported that the toxicity is much lower than the same amount of silver salt compound. Therefore, it is very important to freely adjust the particle diameter of the silver particles.

  Under such circumstances, development of a method for controlling the particle size of silver particles is currently underway. For example, Patent Document 2 discloses a method of controlling the particle diameter of silver particles using thiol.

JP 2007-161649 A (released on June 28, 2007) International Publication 2014/163126 Pamphlet (October 9, 2014)

G. A. Martinez-Castanon et al., Journal of Nanoparticle Research, 10, 1343, 2008 Yamamoto T and Nakamoto M. Novel preparation of monodispersed silver nanoparticles via amine adducts derived from insoluble silver myristate in tertiary alkylamine.J. Mater. Chem., 13, 2064-2065, 2003

  However, the conventional technique for controlling the particle diameter of silver particles described in Patent Document 2 can adjust the particle diameter of silver particles to a desired size, but it is expensive material (more specifically, thiol). ) Must be used.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a method for controlling the particle size of silver particles, which can adjust the particle size of silver particles to a desired size at low cost. There is.

  In order to solve the above-mentioned problems, the inventors have intensively studied. As a result, in the reaction step of reacting silver ions and fatty acids at the reaction temperature, the adjustment of the ratio between the molar concentration of the silver ions and the molar concentration of the fatty acids, and In addition, by adjusting the time for maintaining the reaction temperature, the particle size of the silver particles can be adjusted to a desired size, and the particle size of the silver particles can be reduced at a low cost by using inexpensive fatty acids. The inventors have found that it can be adjusted to a desired size, and have come up with the present invention. That is, the present invention includes the inventions described in [1] to [5] below.

[1] A method of controlling the particle size of silver particles produced by aggregating silver ions,
Including a reaction step of reacting silver ions and fatty acids at the reaction temperature,
In the reaction step, the particle diameter of the silver particles is controlled by performing at least one selected from the following (1) and (2):
(1) adjusting the ratio between the molar concentration of the silver ions and the molar concentration of the fatty acid;
(2) The time for maintaining the reaction temperature is adjusted.

  [2] The method for controlling the particle diameter of silver particles according to [1], including a silver ion generation step of generating the silver ions by reacting a silver ion donor and a reducing agent before the reaction step. .

  [3] The method further comprises a distillation step of maintaining the mixture of the silver ion donor and the reducing agent at a temperature of 100 ° C. or higher and lower than the reaction temperature after the silver ion generation step. [2] A method for controlling the particle diameter of the silver particles according to the above.

  [4] The method according to any one of [1] to [3], further comprising a washing step of washing the reaction product obtained in the reaction step using an organic solvent after the reaction step. A method for controlling the particle diameter of the silver particles according to the above.

  [5] The silver particles according to [2] or [3], wherein the carbon number of the hydrocarbon group of the fatty acid is the same as the carbon number of the hydrocarbon group of the reducing agent Diameter control method.

  According to one embodiment of the present invention, there is an effect that the particle diameter of silver particles can be adjusted to a desired size at low cost.

(A) It is a figure which shows the FT-IR spectrum of the silver particle of Example 5, (B) oleylamine, and (C) oleic acid. 6 is a diagram showing a TG spectrum of silver particles of Example 5. FIG. (A) And (b) is a figure which shows the image and particle size distribution which were obtained with the transmission electron microscope (TEM) of the silver particle of Example 1, respectively. (C) And (d) is a figure which shows the image and particle size distribution which were obtained with the transmission electron microscope (TEM) of the silver particle of Example 2, respectively. (E) And (f) is a figure which shows the image and particle size distribution which were obtained with the transmission electron microscope (TEM) of the silver particle of Example 3, respectively. (G) is a figure which shows the average particle diameter of the silver particle of Examples 1-3. (A) And (b) is a figure which shows the image and particle size distribution which were obtained with the transmission electron microscope (TEM) of the silver particle of Example 5, respectively. (C) And (d) is a figure which shows the image and particle size distribution which were obtained with the transmission electron microscope (TEM) of the silver particle of Example 6, respectively. (E) And (f) is a figure which shows the image and particle size distribution which were obtained with the transmission electron microscope (TEM) of the silver particle of Example 8, respectively. (G) is a figure which shows the average particle diameter of the silver particle of Example 5, 6, and 8. FIG. (A) is a figure which shows the image obtained with the transmission electron microscope (TEM) of the silver particle of the comparative example 2, (b) is the transmission electron microscope (TEM) of the silver particle of the comparative example 3. It is a figure which shows the image obtained by.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to this, and can be implemented in a mode in which various modifications are made within the described range. Moreover, all the academic literatures and patent literatures described in this specification are incorporated herein by reference. Unless otherwise specified in this specification, “A to B” indicating a numerical range means “A or more and B or less”.

[Method for controlling particle diameter of silver particles]
The method for controlling the particle size of silver particles according to an embodiment of the present invention is a method for controlling the particle size of silver particles produced by aggregating silver ions. Although the outline of the formation process of silver particle is shown below, it is an example to the last and this invention is not limited to this.

  In the method for controlling the particle diameter of silver particles according to an embodiment of the present invention, silver ions and fatty acids are reacted at a predetermined reaction temperature in the reaction step. When the reaction temperature is set to a predetermined level, heat is added to silver ions and fatty acids, so that the reaction between silver ions and fatty acids proceeds. Through the reaction step, silver particles are formed in which fatty acids are bonded to at least a part of the surface of the particles formed by aggregation of silver ions.

  In one embodiment of the present invention, before the reaction step, silver ions may be generated by reacting a silver ion donor and a reducing agent in a silver ion generation step. Later, by-products generated by the silver ion generation step may be distilled off by a distillation step, and silver particles may be separated, dried and / or purified by a washing step after the reaction step. The silver ion generation step, the distillation step, and the washing step are not essential for the present invention.

  In the method for controlling the particle size of silver particles according to an embodiment of the present invention, at least one of the above-described reaction step, silver ion generation step, distillation step, and washing step is performed in an inert gas. It is more preferable that all of the above-described reaction step, silver ion generation step, distillation step, and washing step are performed in an inert gas. The inert gas can be selected from, for example, nitrogen, argon, helium and carbon dioxide. If it is the said structure, there exists an advantageous effect that the silver oxide production | generation by the silver produced | generated by reduction | restoration can be suppressed can be suppressed.

  In the method for controlling the particle size of silver particles according to an embodiment of the present invention, it is preferable that the reaction is performed by heating the raw material while stirring at least in the reaction step. The heating can be performed from the outside of the reaction vessel using an oil bath and a heater. An oil bath is desirable for uniformly heating the reaction vessel. Since it is preferable that heating temperature satisfy | fills specific conditions in each process, this is mentioned later. The heating temperature can be controlled by the temperature of the reaction vessel wall. In some cases, the temperature may be controlled by the temperature of the oil bath and the heater. If it is the said structure, there exists an advantageous effect that a condensation reaction with a fatty acid and an amine can be suppressed and a reduction reaction can be advanced gently.

  Below, the control method of the particle diameter of the silver particle which concerns on one Embodiment of this invention is demonstrated still in detail.

[Reaction process]
The method for controlling the particle size of silver particles according to an embodiment of the present invention includes a reaction step in which silver ions and a fatty acid are reacted at a reaction temperature. In the reaction step, the method is selected from the following (1) and (2) Control the particle size of the silver particles by doing at least one of the following:
(1) adjusting the ratio between the molar concentration of the silver ions and the molar concentration of the fatty acid;
(2) The time for maintaining the reaction temperature is adjusted.

  In the method for controlling the particle diameter of silver particles according to an embodiment of the present invention, the particle diameter of silver particles can be controlled by adjusting the ratio between the molar concentration of silver ions and the molar concentration of fatty acids.

  The ratio (X / Y) between the molar concentration of silver ions (X) and the molar concentration of fatty acids (Y) can be, for example, 1 / 0.1 ≧ X / Y ≧ 1/50, 1 / 0.25 ≧ X / Y ≧ 1/25, and more preferably 1 / 0.25 ≧ X / Y ≧ 1/5. If X / Y is in the above range, silver particles having a stable shape can be formed without causing fusion of silver particles and formation of metallic silver.

  When the molar concentration of the fatty acid is relatively large with respect to the molar concentration of the silver ions, the particle diameter of the silver particles becomes smaller than when the molar concentration of the silver ions and the molar concentration of the fatty acid are equal. This is presumably because the fatty acid surrounds the surface of the silver particle and the growth of the silver particle is suppressed by the fatty acid becoming dense on the surface of the silver particle. On the other hand, when the molar concentration of fatty acid is relatively small with respect to the molar concentration of silver ions, the particle diameter of silver particles becomes larger than when the molar concentration of silver ions and the molar concentration of fatty acid are equal. This is presumably because the fatty acid on the surface of the silver particles becomes sparse and the growth of the silver particles is promoted.

  Therefore, in the above (1), in order to reduce the particle diameter of the silver particles, the molar concentration of the fatty acid may be adjusted to be relatively large with respect to the molar concentration of silver ions. In order to increase the particle diameter, the fatty acid molar concentration may be adjusted to be relatively small relative to the silver ion molar concentration.

  The fatty acid may be a saturated fatty acid or an unsaturated fatty acid, and may be linear or branched.

  The fatty acid preferably has a hydrocarbon group having 3 to 30 carbon atoms, more preferably 5 to 25 carbon atoms, and still more preferably 15 to 20 carbon atoms. The longer the hydrocarbon group of the fatty acid, the smaller the average particle size of the silver particles produced.

  Examples of saturated fatty acids include butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid (capric acid), undecanoic acid, dodecanoic acid (lauric acid), tridecanoic acid, tetradecanoic acid (myristic acid), Pentadecanoic acid, hexadecanoic acid (palmitic acid), heptadecanoic acid (margaric acid), octadecanoic acid (stearic acid), nonadecanoic acid (tuberculostearic acid), icosanoic acid (arachidic acid), docosanoic acid (behenic acid), tetradocosanoic acid ( Lignoceric acid), hexadocosanoic acid (serotic acid), octadocosanoic acid (montanic acid, melicic acid) and the like can be mentioned.

  Examples of unsaturated fatty acids include butenoic acid (for example, crotonic acid and isocrotonic acid), pentenoic acid, hexenoic acid, heptenoic acid, octenoic acid, nonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid (for example, lauroleic acid), tridecenoic acid, Tetradecenoic acid (eg myristoleic acid, myristoleic acid), pentadecenoic acid, hexadecenoic acid (eg palmitoyl acid), octadecenoic acid (eg oleic acid, vaccenic acid), octadecadienoic acid (eg linoleic acid), octadecatrienoic acid (For example, linolenic acid, elestearic acid), icosadienoic acid, icosatrienoic acid, icosatetraenoic acid (arachidonic acid), tetradocosanoic acid (for example, nervonic acid), and the like.

  In the method for controlling the particle size of silver particles according to an embodiment of the present invention, the particle size of silver particles can be controlled by adjusting the time for maintaining the particle size at a predetermined reaction temperature. Adjustment of the reaction time also changes the amount of heat applied to the reacting molecules (silver ions and fatty acids). Therefore, it is considered that when the reaction time is extended, the amount of heat applied to the molecule is increased, and the formation of silver particles is promoted.

  Therefore, in the above (2), in order to reduce the particle diameter of the silver particles, the time for maintaining the reaction temperature may be adjusted to be short, or in order to increase the particle diameter of the silver particles, You may adjust so that the time maintained in reaction time may become long.

  The reaction temperature may be determined as appropriate depending on the amount of silver ions and fatty acids, the type of fatty acid, etc., as long as it can provide the amount of heat necessary for the reaction of silver ions and fatty acids. For example, the temperature may be 120 ° C or higher, 150 ° C or higher, 180 ° C or higher, 200 ° C or higher, 220 ° C or higher, or 250 ° C or higher.

  The time for maintaining the reaction temperature (hereinafter also referred to as reaction time) is preferably 15 minutes or more and 240 minutes or less, more preferably 20 minutes or more and 90 minutes or less, and further preferably 25 minutes or more and 60 minutes or less. . A reaction time within the above range is preferable because silver particles having a stable shape can be formed without causing fusion between silver particles and formation of metallic silver.

[Silver ion production process]
The method for controlling the particle size of silver particles according to an embodiment of the present invention includes a silver ion generation step of generating silver ions by reacting a silver ion donor and a reducing agent before the reaction step. May be included. In the silver ion generation step, silver ions are generated by reducing the silver ion donor with a reducing agent. The reducing agent also promotes deprotonation of oleic acid (in other words, ionization of oleic acid) in the reaction step.

  The silver ion donor is not particularly limited, and for example, a silver salt may be used as an ion source. Examples of the silver salt include silver oxide (I), silver oxide (II), silver acetate, silver nitrate, silver acetylacetonate, silver benzoate, silver bromate, silver bromide, silver carbonate, silver chloride, silver citrate, Silver fluoride, silver iodate, silver iodide, silver lactate, silver nitrite, silver perchlorate, silver phosphate, silver sulfate, silver sulfide, silver trifluoroacetate, silver sulfide and the like can be used. Among these, only 1 type may be used and 2 or more types may be used together.

  Examples of the solvent for mixing the silver ion donor and the reducing agent include water, an organic solvent (for example, toluene), or a mixture of water and an organic solvent (for example, toluene). It is not limited to.

  The reducing agent only needs to be reducible with respect to the silver ion donor and promote deprotonation of oleic acid, and examples thereof include amines.

  The amine may be any of primary amine, secondary amine, and tertiary amine, but primary amine is preferable because primary amine is more reducible than secondary amine and tertiary amine. . A secondary amine and / or a tertiary amine may be used in combination as long as the effect of the primary amine is not impaired.

  The primary amine preferably has a hydrocarbon group having 3 to 30 carbon atoms, such as n-propylamine, isopropylamine, n-butylamine, sec-butylamine, tert-butylamine, isobutylamine, n-pentyl. Amine, neopentylamine, isopentylamine, n-hexylamine, n-octylamine, n-decylamine, n-undecylamine, n-dodecylamine, n-tridecylamine, n-tetradecylamine, n-penta Decylamine, n-hexadecylamine, n-heptadecylamine, n-octadecylamine, n-nonadecylamine, n-eicosylamine, n-heneicosylamine, n-docosylamine, n-tricosylamine, n-tetracosylamine Luamine, n-pentacosylamine aliphatic amines having a saturated hydrocarbon group such as n-hexacosylamine, n-heptacosylamine, n-octacosylamine, n-nonacosylamine, n-triacontylamine; fats having an unsaturated hydrocarbon group such as oleylamine Group amines and the like.

  When the reducing agent has a hydrocarbon group, the hydrocarbon group preferably has the same carbon number as the hydrocarbon group of the fatty acid. That is, for example, when the fatty acid is stearic acid, the reducing agent is preferably stearylamine. For example, when the fatty acid is oleic acid, the reducing agent is preferably oleylamine. If the carbon number of the hydrocarbon group possessed by the reducing agent is the same as the carbon number of the hydrocarbon group possessed by the fatty acid, it is preferable because the compatibility of the reducing agent with an organic solvent is high in the washing step described later. In addition, it is preferable that the reducing agent and the fatty acid have similar properties because the reaction conditions (heating temperature and heating time) in the reaction step and the silver ion generation step can be easily set.

  In the silver ion generation step, the reducing agent acts as a catalyst by heating, and reduction from the silver ion donor to silver ions occurs. The heating temperature in the silver ion generation step can be appropriately selected according to the type of the reducing agent, but is preferably at least higher than the melting point of the reducing agent. It is preferable that the heating temperature in the silver ion generation step is equal to or higher than the melting point of the reducing agent because the remaining amount of the silver ion donor is small and the silver ion generation efficiency is good.

[Distillation step]
In the method for controlling the particle size of silver particles according to an embodiment of the present invention, after the silver ion generation step, the mixture of the silver ion donor and the reducing agent is maintained at a temperature of 100 ° C. or higher and lower than the reaction temperature. You may have the distillation process to do. In the distillation step, by-products such as water in the reaction between the silver ion donor and the reducing agent can be removed by evaporation at a temperature equal to or higher than the boiling point of the by-products. By performing the distillation step, it is preferable because a by-product can be removed and the recovery efficiency of the reaction product can be increased.

  The lower limit value of the temperature maintained in the distillation step may be determined as appropriate in consideration of the boiling point of the by-product such as water, as long as the by-product can be distilled off. For example, when the by-product is water, the boiling point of water under atmospheric pressure is 100 ° C., and therefore, it is preferable to perform the reaction at 100 ° C. or higher.

  The upper limit of the temperature maintained in the distillation step is preferably less than the reaction temperature. As described above, the reaction temperature can be appropriately determined depending on the type of fatty acid.

  What is necessary is just to determine suitably the time (time to maintain at predetermined | prescribed temperature) which performs a distillation process suitably according to the quantity of a by-product.

[Washing process]
The method for controlling the particle size of silver particles according to an embodiment of the present invention includes a washing step of washing the reaction product obtained in the reaction step using an organic solvent after the reaction step. Also good. In the washing step, by using an organic solvent for the reaction product, the reaction product can be crystallized, and the recovery efficiency of the reaction product can be increased.

  The organic solvent is not particularly limited and may be appropriately determined so that the reaction product can be crystallized. For example, aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, and tetradecane; alicyclic hydrocarbon solvents such as cyclohexane; aromatics such as toluene, xylene, mesitylene, etc. Hydrocarbon solvents; alcohol solvents such as methanol, ethanol, propanol, butanol and the like; ethers such as diethyl ether; acetonitrile and acetone. Among these, only 1 type may be used and 2 or more types may be used together.

  The amount of the organic solvent is not particularly limited, and may be appropriately determined so that the reaction product can be crystallized.

  The frequency | count of performing the said washing | cleaning process is not specifically limited, What is necessary is just to determine suitably according to the desired purity of a silver particle, and it may be 1 time and multiple times.

  After the washing step, silver particles can be obtained by filtering the crystallized reaction product. General filtration means include natural filtration, suction filtration, vacuum filtration, centrifugal dehydration, filter press and the like. The filtration is preferably suction filtration or centrifugal dehydration from the viewpoint of improving the filtration rate. The pore size of the filter used for the filtration may be appropriately determined according to the size of the silver particles. For example, a filter having a pore size of less than 20 μm can be used, and the pore size is preferably 0.05 to 2.0 μm. A filter is used.

[Silver particles]
The particle diameter can be set to a desired size by the method for controlling the particle diameter of silver particles according to an embodiment of the present invention. For example, the average particle diameter of silver particles may be 1000 nm or less, 100 nm or less, 50 nm or less, 30 nm or less, or 26 nm or less, It may be 10 nm or less, 7 nm or less, 5 nm or less, or 1 nm. Moreover, the lower limit of the average particle diameter of the silver particles is not particularly limited, but may be, for example, 1 nm, 0.5 nm, 0.1 nm, or 0.01 nm.

  The average particle diameter of the silver particles can be appropriately determined by a known method. For example, it can be determined by measuring the diameter of the particles observed under a microscope with a ruler and correcting the measured value with the observation magnification of the microscope. The average particle diameter of the silver particles can also be determined using, for example, a laser diffraction / scattering particle size distribution analyzer (product name: LMS-30, Seishin). The average particle diameter of the silver particles is intended to be the size of particles in which metallic silver is aggregated, and does not include the length of the fatty acid bonded to at least a part of the particle surface.

  In the silver particles, fatty acids are bonded to at least a part of the surface of the particles containing metallic silver. The ratio of the particle surface to which the fatty acid is bonded is not particularly limited. For example, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more of the particle surface. % Or more, 90% or more, or 100% may have a chemically modifying group bonded thereto. In addition, the ratio of the particle | grain surface which the fatty acid has couple | bonded can be determined with a well-known method suitably. For example, it can be determined by measuring the change in the weight of silver particles by thermogravimetric-differential thermal analysis (TG-DTA), but is not limited thereto.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples.

[1. Production of silver particles)
<Example 1>
(A) Synthesis Step First, three-necked experimental system used in the synthesis process such as the flask was _{N 2} purged _{(N 2} purge during synthesis at all times 0.05 L / min), silver acetate (silver acetate (I), Wako Pure Chemical 400 mg (2.40 mmol) manufactured by Kogyo Co., Ltd., catalog number 190-08112) and 50 mL of oleylamine (manufactured by Wako Pure Chemical Industries, Ltd., catalog number 320-27575) were added to the three-necked flask. The three-necked flask was placed in an oil bath, the temperature of the oil bath was 30 ° C., and the mixture was stirred for 12 hours at about 900 rpm using a stirrer to generate silver ions (silver ion generation step). In addition, the temperature of the oil bath at the time of producing | generating silver ion was set in view of the melting | fusing point of oleylamine being 18 degreeC under atmospheric pressure. Next, the temperature of the oil bath was raised to 110 ° C. and kept for 1 hour to distill off by-products (water and acetic acid) (distillation step). After distilling out the by-product, 339 mg (1.20 mmol) of oleic acid (manufactured by Wako Pure Chemical Industries, Ltd., catalog number 159-00246) was added, the temperature of the oil bath was raised to 240 ° C., and silver ions and oleic acid were added. The reaction with was started. The time from when the temperature in the oil bath reached 240 ° C. (that is, the reaction time) was 30 minutes (reaction process). In order to complete the reaction, the heater of the oil bath was turned off and the mixture was stirred and cooled at about 700 rpm until the temperature of the oil bath reached about 60 ° C. to obtain a reaction product. During the synthesis process, stirring was always performed using a stirrer.

(I) Washing step The reaction product after stirring and cooling is taken out into a 200 mL beaker, and 10 mL of toluene (Nacalai Tesque, catalog number 34122-15) and 140 mL of methanol (Nacalai Tesque, 21914-74) are added. Then, ultrasonic irradiation was performed for 1 hour while stirring at about 700 rpm using a stirrer. Thereafter, suction filtration was performed using a 45 mm diameter 0.1 μm PTFE membrane filter (product name: T010A047A, manufactured by Advantech) to purify the reaction product. This washing step (reagent addition, ultrasonic irradiation and suction filtration) was repeated a total of 4 times. After the fourth suction filtration, in order to wash away toluene, 100 mL of methanol was added, and ultrasonic irradiation was performed for 1 hour while stirring at about 600 rpm using a stirrer, and then a 45 mm diameter 0.1 μm PTFE membrane filter was removed. Using this, suction filtration was performed to purify the silver particles. The purified silver particles were air-dried at room temperature, and after confirming that methanol had completely evaporated, they were stored in a sample tube to obtain silver particles of Example 1.

<Examples 2 and 5>
Silver particles of Example 2 and Example 5 were produced in the same manner as Example 1 except that 678 mg (2.40 mmol) of oleic acid was used.

<Example 3>
Silver particles of Example 3 were produced in the same manner as Example 1 except that 1.36 g (4.80 mmol) of oleic acid was used.

<Example 4>
Silver particles of Example 4 were produced in the same manner as Example 1 except that 2.03 g (7.20 mmol) of oleic acid was used.

<Example 6>
Silver particles of Example 6 were produced in the same manner as Example 2 except that the heat retention time was 45 minutes.

<Example 7>
Silver particles of Example 7 were produced in the same manner as Example 6 except that 1.36 g (4.80 mmol) of oleic acid was used.

<Example 8>
Silver particles of Example 8 were produced in the same manner as Example 2 except that the heat retention time was 60 minutes.

<Comparative Example 1>
Silver particles of Comparative Example 1 were produced in the same manner as Example 1 except that the heat retention time was 45 minutes.

<Comparative example 2>
Silver particles of Comparative Example 2 were produced in the same manner as Comparative Example 1 except that 2.03 g (7.20 mmol) of oleic acid was used.

<Comparative Example 3>
Silver particles of Comparative Example 3 were produced in the same manner as Example 2 except that the heat retention time was 90 minutes.

[2. (Yield of silver particles)
Yield was measured about the silver particle of Examples 1-8 and the silver particle of Comparative Examples 1-3. The measurement results are shown in Table 1. In Table 1, “NA” means not measured, and “−” means that measurement was not possible.

  As shown in Table 1, in Examples 1 to 8, a sufficient yield of silver particles having a stable round shape was obtained. Comparing Examples 1 to 3, it can be seen that increasing the amount of oleic acid increased the yield.

  On the other hand, in Comparative Examples 1 and 3, the silver particles were fused together, and the shape was unstable. In Comparative Example 3, it was confirmed that a silver substance adhered to the inside of the flask after the reaction time exceeded 70 minutes. This is considered that the silver particles once formed were further reduced and metal silver was precipitated. In Comparative Example 2, the shape became unstable and the particle size was not stable.

[3. (Evaluation of silver particles by Fourier transform infrared spectrophotometer)
Evaluation of functional groups present on the surface of silver particles of Example 5 using a Fourier Transform Infrared Spectroscopy (FT-IR) (product name: Spectrum 65, manufactured by PerkinElmer Japan Co., Ltd.) Went.

  The FT-IR spectrum measurement of oleylamine and oleic acid (hereinafter also referred to as reaction reagent) was carried out by the total reflection measurement method (ATR) because oleylamine and oleic acid are liquid at room temperature. Moreover, since the silver particle was solid at normal temperature, the FT-IR spectrum measurement of the silver particle was implemented by transmission type FT-IR. In ATR, the background was air, and several drops of the reaction reagent were spotted on the FT-IR sample stage. In the transmission type FT-IR, the background is potassium bromide (manufactured by Wako Pure Chemical Industries, Ltd., catalog number 169-16271, hereinafter also referred to as KBr), 3 mg of silver particles are diluted with 300 mg of KBr, 20 mg of which is Then, pressurization was performed at 50 MPa for 60 seconds using a hydraulic pump, and an IR sample was prepared and measured.

  FIG. 1 shows FT-IR spectra of (A) silver particles of Example 5, (B) oleylamine and (C) oleic acid.

In the FT-IR spectrum, infrared absorption at 3008 cm ⁻¹ is due to (= CH) stretching vibration, and a plurality of infrared absorptions at 2956 to 2851 cm ⁻¹ are due to (CH) stretching vibration. Infrared absorption at 1464 cm ⁻¹ and 1412 cm ⁻¹ is due to (CH ₂ ) bending vibration. These infrared absorptions are observed in the FT-IR spectrum of oleic acid and are derived from the alkyl chain that oleic acid has. On the other hand, infrared absorption that does not coincide with the absorption behavior in the reaction reagent was also observed. In the FT-IR spectrum of oleic acid, infrared absorption of (C═O) symmetrical stretching vibration derived from a carboxyl group was observed at 1708 cm ⁻¹ . On the other hand, in the FT-IR spectrum of the silver particles, infrared absorption due to the carboxyl group disappeared, and infrared absorption due to (COO ⁻ ) stretching vibration (symmetric and asymmetric) was observed at 1560 cm ⁻¹ and 1399 cm ⁻¹ . This is presumed that the free carboxyl group has disappeared due to the interaction between the carboxyl group and silver ions.

[4. (Thermogravimetric measurement of silver particles)
The organic matter content of the silver particles of Example 5 was evaluated by TG (Thermo Gravimetry). The TG spectrum was measured using a thermogravimetric instrument (product name: TGA-50, manufactured by Shimadzu Corporation) under measurement conditions of an N ₂ gas flow of 50 mL / min and a heating rate of 10 ° C./min. In addition, the average particle diameter of the silver particles measured this time was 6.6 ± 1.1 nm calculated from an image taken with a transmission electron microscope.

  FIG. 2 shows the TG spectrum of the silver particles of Example 5. As shown in FIG. 2, the silver particles of Example 5 showed a two-stage weight change. The first stage weight change began at about 190 ° C. and the weight decreased by about 4.2%. The second stage weight change began at about 250 ° C. and the weight decreased by about 12.3%. Since the boiling point of oleic acid at 100 Pa is 195 ° C., it is presumed that the weight change in the first step is derived from the decomposition of oleic acid bonded to the surface of particles in which metallic silver is aggregated. In addition, the weight change in the second stage is presumed to be caused by the decomposition of oleic acid that has entered the particles in which metallic silver is aggregated by strongly interacting with silver ions. From this, the produced silver particles have a quasi-bilayer structure of a layer in which metallic silver is aggregated (that is, particles in which metallic silver is aggregated) and an oleic acid layer (that is, oleic acid bonded to the surface of the particles). It is thought that it forms. Further, it is considered that the silver particles are composed of about 4.2% by weight of oleic acid bonded to the particle surface, about 12.3% by weight of oleic acid entering the particle, and about 83.5% by weight of metallic silver. .

[5. Observation of silver particle morphology by transmission electron microscope (TEM) and calculation of average particle diameter]
Silver particles were photographed using a transmission electron microscope (manufactured by Hitachi High-Technologies Corporation) to observe the morphology of the silver particles (hereinafter, an image obtained with a transmission electron microscope (TEM) was measured with a TEM). Also called an image). The acceleration voltage was 100 kV. Further, 100 silver particles were selected from the photographed TEM image, the particle diameter was measured, and the average particle diameter of the silver particles was calculated from the measured value. Table 1 shows the average particle diameters of the silver particles of Examples 1 to 8 and the silver particles of Comparative Examples 1 to 3.

  3 (a) and FIG. 3 (b) show the TEM image and particle size distribution of the silver particles of Example 1, respectively. 3 (c) and FIG. 3 (d) show the TEM image and particle size distribution of the silver particles of Example 2, respectively. FIG. 3 (e) and FIG. 3 (f) show the TEM image and particle size distribution of the silver particles of Example 3, respectively.

  3A, 3C, and 3E, it can be seen that the silver particles of Examples 1 to 3 are substantially round without being fused, and the shape is stable. 3B, 3D, and 3F, it can be seen that the silver particles of Examples 1 to 3 have one peak in the vicinity of the average particle size.

  (G) of FIG. 3 is a figure which shows the average particle diameter of the silver particle of Example 1, Example 2, and Example 3. FIG. From FIG. 3 (g), it can be seen that by adjusting the molar ratio of silver acetate and oleic acid, it is possible to control the particle size of silver particles in the range of an average particle size of about 4 to 10 nm. From Example 1, when the addition amount of oleic acid is relatively increased with respect to the addition amount of silver acetate, compared with the case where the addition amount of silver acetate and the addition amount of fatty acid are equal, It turns out that a particle diameter becomes small. Silver particles are prepared by silver acetate being reduced by oleylamine and protected by oleic acid, but the larger the amount of oleic acid, the faster the particles are protected, so it is assumed that the particle size of the silver particles has decreased. The Further, from Example 3, when the addition amount of oleic acid is relatively small with respect to the addition amount of silver acetate, the addition amount of silver acetate and the addition amount of fatty acid is compared with the case where the addition amount of silver acetate is equal. It can be seen that the particle diameter of the particles increases. This is presumably because the formation of silver particles is promoted because the amount of oleic acid protecting the surface of the silver particles is small.

  On the other hand, as shown in FIG. 5A, when the molar ratio of silver acetate to oleic acid was set to 1: 3 or more in Comparative Example 2, the shape of the silver particles became unstable and the particle diameter was not stable. This is presumed to be because the formation of silver particles is inhibited by excessive addition of oleic acid, and floating silver ions are generated without forming particles.

  4 (a) and 4 (b) show the TEM image and particle size distribution of the silver particles of Example 5, respectively. FIG. 4C and FIG. 4D show the TEM image and the particle size distribution of the silver particles of Example 6, respectively. FIG. 4E and FIG. 4F show the TEM image and the particle size distribution of the silver particles of Example 8, respectively.

  4 (a), (c) and (e), substantially circular silver particles having a stable shape were obtained without fusing in Example 5, Example 6 and Example 8. I understand. 4B, 4D, and 4F, it can be seen that the particle diameters of the silver particles of Example 5, Example 6, and Example 8 have one peak near the average particle diameter. .

  (G) of FIG. 4 is a figure which shows the average particle diameter of the silver particle of Example 5, Example 6, and Example 8. FIG. From FIG. 4 (g), it can be seen that the particle size of the silver particles can be controlled in the range of the average particle size of about 6 to 9 nm by adjusting the reaction time. Moreover, it turns out that the particle diameter of a silver particle becomes large as reaction time becomes long in order of Example 5, Example 6, and Example 8. FIG. This is presumed that the reduction reaction and particle formation are promoted because the amount of heat applied to the molecule increases when the reaction time is extended, as the reduction reaction is promoted when the reaction temperature is raised.

  On the other hand, as shown in FIG. 5 (b), when the reaction time was 90 minutes in Comparative Example 3, the silver particles were observed to be elliptical rather than round and unstable in shape due to the fusion of the silver particles. It was done.

  As described above, by using the method for controlling the particle diameter of silver particles according to an embodiment of the present invention, the particle diameter of silver particles can be set to a desired size with a simple apparatus without using a large-scale apparatus. It turns out that it can be adjusted. Moreover, although the synthesis period was as short as 3 days, 200 mg yield of silver particles could be obtained.

  The present invention can be used for antibacterial, sterilization or sterilization of medical devices and the like. More specifically, the present invention can be used as a coating agent for medical devices and the like.

Claims (5)

A method of controlling the particle size of silver particles produced by aggregating silver ions,
Including a reaction step of reacting silver ions and fatty acids at the reaction temperature,
In the reaction step, the particle diameter of the silver particles is controlled by performing at least one selected from the following (1) and (2):
(1) adjusting the ratio between the molar concentration of the silver ions and the molar concentration of the fatty acid;
(2) The time for maintaining the reaction temperature is adjusted.   The method for controlling the particle diameter of silver particles according to claim 1, comprising a silver ion generation step of generating the silver ions by reacting a silver ion donor and a reducing agent before the reaction step.   3. The method according to claim 2, further comprising a distillation step of maintaining the mixture of the silver ion donor and the reducing agent at a temperature of 100 ° C. or higher and lower than the reaction temperature after the silver ion generation step. A method for controlling the particle size of silver particles.   The silver particles according to any one of claims 1 to 3, further comprising a washing step of washing the reaction product obtained in the reaction step using an organic solvent after the reaction step. Control method of particle diameter.   The method for controlling the particle size of silver particles according to claim 2 or 3, wherein the carbon number of the hydrocarbon group of the fatty acid is the same as the carbon number of the hydrocarbon group of the reducing agent.