JP2015206088A - Plate-like silver nanoparticle production method and plate-like silver nanoparticle-containing composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a plate-like silver nanoparticle having a high-aspect ratio and a large particle size.SOLUTION: A method of producing plate-like silver nanoparticles provided by the present invention comprises reducing silver ions in an aqueous solution containing at least a compound A represented by the general formula (1) in the figure. (In the formula, Rand Rare each independently selected from the group consisting of a hydrogen atom and alkyl groups having 4 or less carbon atoms. The alkyl groups include those with substituents.)

Description

  The present invention relates to a method for producing tabular silver nanoparticles and a composition containing tabular silver nanoparticles.

  Silver electrodes are used as conductors for electrodes such as electronic parts and solar cells. In such an electrode, conduction is achieved by contact of silver nanoparticles. In addition, attempts have been made to use flat silver nanoparticles that can easily have a large contact area in order to further improve conductivity. Patent document 1 is mentioned as a technical document regarding this kind of tabular silver nanoparticle. Patent Document 1 discloses tabular silver nanoparticles having a particle diameter of 20 nm to 140 nm and an aspect ratio of 1 to 4.5.

JP 2009-144188 A

  In recent years, higher conductivity has been required for electrodes of electronic components and the like. For this reason, the tabular silver nanoparticle with a larger particle diameter is calculated | required. In addition, with the improvement in performance and miniaturization of electronic parts and the like, fine lines (thinning) of electrodes are required. In order to achieve fine line formation, it is advantageous to use tabular silver nanoparticles having a small thickness and a large aspect ratio.

  Accordingly, an object of the present invention is to provide a method for producing tabular silver nanoparticles having a high aspect ratio and a large particle diameter. Another object is to provide a composition containing such tabular silver nanoparticles.

  The present inventor has found that tabular silver nanoparticles having a high aspect ratio and a large particle diameter can be obtained by reducing silver ions in an aqueous solution containing a specific compound, and the present invention has been completed. .

  That is, according to this specification, a method for producing tabular silver nanoparticles is provided. This production method is characterized in that silver ions are reduced in an aqueous solution containing at least compound A represented by the following general formula (1).

Here, in the formula, R ¹ and R ² are each independently selected from the group consisting of a hydrogen atom and an alkyl group having 4 or less carbon atoms. The alkyl group includes those having a substituent.

  Thus, by reducing silver ions in an aqueous solution containing a formamide compound having a hydrogen atom or an alkyl group on a nitrogen atom, tabular silver nanoparticles having a high aspect ratio and a large particle diameter can be formed.

  As a preferred example of the compound A represented by the general formula (1), at least one selected from the group consisting of formamide, N, N-dimethylformamide, N, N-diethylformamide and N, N-dipropylformamide Compounds. According to the compound A having such a structure, the effect of increasing the particle diameter of the tabular silver nanoparticles can be more effectively exhibited.

  In a preferred embodiment of the method for producing tabular silver nanoparticles disclosed herein, the volume ratio of the compound A and water in the aqueous solution is in the range of 1:30 to 1: 20000. When the volume ratio of the compound A and water is within such a range, it is easier to form tabular silver nanoparticles having a high aspect ratio and a large particle diameter. In a preferred embodiment, the volume ratio of the compound A and water in the aqueous solution is in the range of 1:30 to 1: 500. According to such a configuration, the particle diameter and aspect ratio of the tabular silver nanoparticles can be further increased.

  The present invention also provides a composition containing tabular silver nanoparticles as another aspect. In the tabular silver nanoparticle-containing composition, the average particle diameter of the tabular silver nanoparticles in the composition is 100 nm to 2000 nm, and the average aspect ratio is 5 to 30.

  In this specification, the tabular silver nanoparticles are tabular silver nanoparticles having two main surfaces (the widest surface of the particles). For example, the main surfaces are substantially triangular and substantially rectangular. , A substantially pentagonal shape, a substantially hexagonal shape, a substantially heptagonal shape, or a substantially octagonal shape. The “average particle diameter” for such tabular silver nanoparticles is the minimum distance between two opposing sides in the main surface of the plurality of tabular particles contained in the composition (in the case where the main surface is an odd polygonal shape). An average value of a minimum distance between one vertex and one side facing the one vertex. Further, the “average thickness” for tabular silver nanoparticles is the thickness of a plurality of tabular grains contained in the composition (the minimum distance between two main surfaces and the tabular grains were viewed from the side. The average value of the thickness (see FIG. 5). The “average aspect ratio” for tabular silver nanoparticles refers to the average value of the particle diameter / thickness of a plurality of tabular grains contained in the composition. That is, the average particle diameter, the average thickness, and the average aspect ratio here are values indicating the average particle shape of the tabular silver nanoparticles. As a specific procedure, for example, using a scanning electron microscope (SEM), a predetermined number (for example, at least 100 (preferably 200 to 300) tabular grains randomly extracted) contained in the composition. The particle diameter and thickness of each tabular grain are obtained, and the value obtained by dividing the grain diameter of each tabular grain by the thickness is calculated as the grain diameter / thickness ratio (aspect ratio) of each tabular grain. The average particle diameter, average thickness, and average aspect ratio can be obtained by arithmetically averaging the particle diameter, thickness, and aspect ratio of the predetermined number of tabular grains.

  In a preferred embodiment of the tabular silver nanoparticle-containing composition disclosed herein, the average particle size of the tabular silver nanoparticles in the composition is as large as 100 nm to 2000 nm (preferably 500 nm to 2000 nm), and The average aspect ratio is 5 to 30 (preferably 15 to 30), which is larger than the conventional one. Such tabular silver nanoparticles having a high aspect ratio and a large particle diameter can form a suitable conductive network in the electrode, and can easily realize a fine line of the electrode. Therefore, it can be suitably used for electrodes and circuits in various fields.

  In a preferred embodiment of the tabular silver nanoparticle-containing composition disclosed herein, the average thickness of the tabular silver nanoparticles in the composition is 20 nm to 100 nm. Such thin tabular silver nanoparticles can contribute to fine line formation of electrodes.

  In a preferred embodiment disclosed herein, the composition further contains spherical silver nanoparticles. By using a combination of spherical silver nanoparticles and tabular silver nanoparticles, a more suitable conductive network can be formed in the electrode. In addition, further fine lines of the electrode can be realized.

  In a preferred embodiment disclosed herein, the average particle size of the spherical silver nanoparticles in the composition is 30 nm to 300 nm. According to such spherical silver nanoparticles, the above-described effects can be better exhibited.

  In a preferred embodiment disclosed herein, the content of tabular silver nanoparticles in the composition is 30% by number or more (preferably 50% by number or more, more preferably 90% by number or more). The effect mentioned above can be more exhibited as it is in the range of content of such flat silver nanoparticles.

2 is an FE-SEM image of silver nanoparticles according to Example 1. FIG. 3 is an FE-SEM image of silver nanoparticles according to Example 2. FIG. 4 is an FE-SEM image of silver nanoparticles according to Example 3. FIG. 6 is an FE-SEM image of silver nanoparticles according to Example 4. 6 is an FE-SEM image of silver nanoparticles according to Example 4.

  Hereinafter, preferred embodiments of the present invention will be described. In addition, matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention (for example, a method for producing a starting material) are design matters of a person skilled in the art based on conventional techniques in the field. Can be grasped as. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  A method for producing tabular silver nanoparticles disclosed herein (hereinafter referred to as “manufacturing method” as appropriate) will be described. The production method disclosed herein is characterized in that silver ions are reduced in an aqueous solution containing at least the compound A represented by the following general formula (1).

<Compound A>
Here, in the formula, R ¹ and R ² are each independently selected from the group consisting of a hydrogen atom and an alkyl group having 4 or less carbon atoms.

In the compound A, the substituents R ¹ and R ² on the nitrogen atom may be a hydrogen atom or an alkyl group having 1 to 4 (preferably 1 to 3, typically 1 or 2) carbon atoms. The alkyl group may be linear or branched. R ¹ and R ² may be the same or different. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, and a butyl group. In addition, the propyl group here is a concept including an n-propyl group and an isopropyl group. The butyl group is a concept including n-butyl group, isobutyl group, sec-butyl group and tert-butyl group. In addition to the alkyl group having no substituent, the alkyl group here may include an alkyl group in which one or more hydrogen atoms are substituted with a substituent (for example, a halogen group, a hydroxy group, etc.). . One kind of such compound A may be used alone, or two or more kinds may be used in combination.

  By reducing silver ions with an aqueous solution containing such a compound A (typically functioning as a reducing agent), tabular silver nanoparticles having a high aspect ratio and a large particle diameter can be formed.

Preferable examples of the compound A include those in which R ¹ and R ² are the same alkyl group. For example, it is preferable that R ¹ and R ² are the same alkyl group having 1 to 4 carbon atoms (preferably 1 to 3, typically 1 or 2). Specific examples of such compound A include N, N-dimethylformamide, N, N-diethylformamide, N, N-dipropylformamide, N, N-dibutylformamide; and the like. Of these, use of N, N-dimethylformamide and N, N-diethylformamide is preferable, and use of N, N-dimethylformamide is particularly preferable.

Other examples of the compound A include formamide in which R ¹ and R ² are both hydrogen atoms.

Other examples of the compound A include those in which R ¹ and R ² are different from each other. For example, it is preferable that ^one of R ¹ and R ² is a hydrogen atom, and the other is an alkyl group having 1 to 4 carbon atoms (preferably 1 to 3, typically 1 or 2). Specific examples of such compound (A) include N-methylformamide, N-ethylformamide, N-propylformamide, N-butylformamide; and the like.

Other examples of the compound A include those in which R ¹ and R ² are different alkyl groups. For example, it is preferable that ^one of R ¹ and R ² is an alkyl group having 2 to 4 carbon atoms and the other is a methyl group. Specific examples of such compound A include N, N-ethylmethylformamide, N, N-methylpropylformamide, N, N-butylmethylformamide; and the like.

  Although it does not specifically limit, the usage-amount of the compound A can be made into the quantity from which the volume ratio of the compound A and water in the said aqueous solution exists in the range of 1: 30-1: 20,000. From the viewpoint of increasing the particle diameter and aspect ratio of the tabular silver nanoparticles, the volume ratio of Compound A and water is preferably 1:30 to 1: 5000, and 1:30 to 1: 500. Is more preferable, and 1:30 to 1:50 (for example, 1:45) is particularly preferable. Such a volume ratio between the compound A and water is also preferable from the viewpoint of the yield of tabular silver nanoparticles.

<Polymer>
The aqueous solution used in the method for producing tabular silver nanoparticles disclosed herein may further contain a water-soluble polymer. Such a polymer may have, for example, an amino group, a thiol group, a sulfide group, an amino acid or a derivative thereof, a peptide bond, a heterocyclic structure, a vinyl structure and the like in the molecule. Preferable examples of the polymer disclosed herein include, for example, a polymer containing a nitrogen atom, a vinyl alcohol polymer, and the like.
Examples of the polymer containing a nitrogen atom include a polymer having a nitrogen atom in a side chain functional group (pendant group). Examples of the polymer having a nitrogen atom in the pendant group include a polymer containing an N-vinyl type monomer unit. For example, a homopolymer of N-vinyl pyrrolidone (polyvinyl pyrrolidone (PVP)) and a copolymer may be employed.
The vinyl alcohol-based polymer is typically a polymer (PVA) containing vinyl alcohol units as the main repeating unit. In PVA, the types of repeating units other than vinyl alcohol units are not particularly limited, and may be one or more selected from, for example, vinyl acetate units, vinyl propionate units, vinyl hexanoate units, and the like. All repeating units may consist essentially of vinyl alcohol units.
Other examples of polymers that can be included in the aqueous solution disclosed herein include cellulose derivatives such as methylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, and polyalkylenes. Examples include amines and partial alkyl esters of polyacrylic acid.

It is appropriate that the molecular weight of the polymer is approximately 0.5 × 10 ⁵ or more, preferably 1 × 10 ⁵ or more, more preferably 1.5 × 10 ⁵ or more, and further preferably 2 ×. 10 ⁵ or more. In a preferred embodiment, the molecular weight of the polymer may be 2.5 × 10 ⁵ or more, for example, 3 × 10 ⁵ or more. The molecular weight of the polymer is typically 10 × 10 ⁵ or less, preferably 8 × 10 ⁵ or less, and more preferably 5 × 10 ⁵ or less. In addition, as a molecular weight of a polymer, the mass average molecular weight (Mw) calculated | required by GPC is employable.

  The content of the polymer in the aqueous solution is not particularly limited and can be, for example, 0.01% by mass or more. The preferable content is 0.05% by mass or more, and more preferably 0.1% by mass or more. Moreover, it is preferable to make the said content into 1 mass% or less, and it is more preferable to set it as 0.5 mass% or less.

<Silver ion>
The aqueous solution used in the method for producing flat silver nanoparticles disclosed herein further contains silver ions. The silver ion contained in the aqueous solution can be suitably contained in the aqueous solution by, for example, dissolving various salts or complexes of silver. Examples of such salts include nitrates, sulfides, sulfates, hydroxides, halides such as chlorides, bromides, and iodides, and potassium composite oxides, ammonium composite oxides, sodium composite oxides, and the like. A composite oxide of the above can be used. In particular, the use of nitrate is preferable from the viewpoint of facilitating production. As the complex, an ammine complex, a cyano complex, a halogeno complex, a hydroxy complex, or the like can be used. The content of the silver salt or silver complex contained in the aqueous solution is not particularly limited. The content of the silver salt or silver complex is usually in the range of 0.01% by mass to 1% by mass (preferably 0.05% by mass to 0.5% by mass), from the viewpoint of easy production. Is preferable.

  In the manufacturing method disclosed here, in addition to the above-described materials, various additives may be used as subcomponents as necessary. Examples of such additives include surfactants, antioxidants, viscosity modifiers, pH adjusters, preservatives, and the like.

  Next, each process of the manufacturing method disclosed here will be described. In the production method disclosed herein, an aqueous solution is prepared by adding the above-described compound A, polymer and silver salt to water (typically distilled water or deionized water). The order in which compound A, polymer and silver salt are added to water is not particularly limited. Preferably, compound A, silver salt, and polymer are added to water in this order. After adding these materials to water, the mixture may be stirred using a stirrer, for example, at a rotational speed of 100 rpm to 1000 rpm (preferably 300 rpm to 600 rpm) for about 10 minutes to 60 minutes (preferably 20 minutes to 40 minutes). . Thereby, the aqueous solution in which the compound A, the polymer, and the silver salt are uniformly dispersed can be prepared. As water to be used, water substantially free of metal ions (typically distilled water or deionized water) is suitable. By using water substantially free of metal ions, tabular silver nanoparticles can be efficiently formed.

  After preparing an aqueous solution containing compound A, polymer and silver salt in this way, the aqueous solution is then heated. The heating temperature is not particularly limited as long as it is a temperature range in which silver ions in the aqueous solution react. For example, the heating temperature is suitably about 120 ° C. to 180 ° C., preferably 140 ° C. to 160 ° C. The heating time is not particularly limited as long as the silver ions in the aqueous solution are sufficiently reacted. For example, the heating time is suitably about 10 hours to 50 hours, preferably 15 hours to 25 hours.

  Thus, by heating the aqueous solution containing Compound A to reduce silver ions, tabular silver nanoparticles can be produced.

<Platform silver nanoparticles>
The tabular silver nanoparticles disclosed herein are produced by reducing silver ions in an aqueous solution containing Compound A. Therefore, the obtained tabular silver nanoparticles can have a high aspect ratio and a large particle diameter. Typically, the average particle diameter of the tabular silver nanoparticles is 100 nm or more (for example, 100 nm to 2000 nm), preferably 200 nm or more, more preferably 400 nm or more, still more preferably 500 nm or more, Preferably it is 1000 nm or more. In a preferred embodiment, the average particle size of the tabular silver nanoparticles is 1500 nm to 2000 nm. The average aspect ratio of the tabular silver nanoparticles is typically 5 or more (for example, 5 to 30), preferably 10 or more, more preferably 15 or more, and further preferably 20 or more. Yes, particularly preferably 25 or more (for example, 25 to 30).

  Preferred examples of the tabular silver nanoparticles disclosed herein are those having an average particle diameter of 200 nm or more and an average aspect ratio of 5 or more; an average particle diameter of 400 nm or more and an average aspect ratio of 10 The average particle size is 500 nm or more and the average aspect ratio is 15 or more; The average particle size is 1000 nm or more and the average aspect ratio is 20 or more; The average particle size is 1500 nm And those having an average aspect ratio of 25 or more. By having both the average particle diameter and the average aspect ratio within such a predetermined range, it is possible to obtain tabular silver nanoparticles capable of constructing a high-performance electrode that could not be obtained conventionally. Specifically, the flat silver nanoparticles having the above-described shape can form a suitable conductive network in the electrode, and can easily realize fine line formation of the electrode. Therefore, it can be suitably used for electrodes and circuits in various fields (for example, electronic parts of semiconductor products and solar cells).

  The average thickness of the tabular silver nanoparticles disclosed herein is typically 100 nm or less (for example, 20 nm to 100 nm), preferably 80 nm or less, more preferably 65 nm or less, and even more preferably It is 50 nm or less, and particularly preferably 30 nm or less (for example, 20 nm to 30 nm). Such thin tabular silver nanoparticles can contribute to fine line formation of electrodes.

  According to the production method disclosed herein, not only the flat silver nanoparticles described above but also spherical silver nanoparticles can be obtained. That is, the tabular silver nanoparticle-containing composition produced by the production method disclosed herein may contain spherical silver nanoparticles in addition to the above-described tabular silver nanoparticles.

  The average particle diameter of the spherical silver nanoparticles in the composition is typically 30 nm or more (for example, 30 nm to 300 nm), preferably 60 nm or more, more preferably 100 nm or more, and further preferably 150 nm. It is above, Especially preferably, it is 200 nm or more (for example, 200 nm-300 nm). A more suitable conductive network can be formed in the electrode by using a combination of the spherical silver nanoparticles having such an average particle diameter and the flat silver nanoparticles having the shape described above. In addition, further fine lines of the electrode can be realized. In addition, the average particle diameter of spherical silver nanoparticles shall be measured by the same method as tabular silver nanoparticles.

  Although not particularly limited, the content of the tabular silver nanoparticles in the composition is approximately 2% by number or more (typically 2% to 100%, for example, 2% to 98%). %), Preferably 7% by number or more, more preferably 30% by number or more, and still more preferably 60% by number or more. In a preferred embodiment, the content of tabular silver nanoparticles in the composition is 90% by number to 98% by number. The effect mentioned above can be more exhibited as it is in the range of content of such flat silver nanoparticles.

  Next, some test examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the test examples.

<Example 1>
An aqueous solution was prepared by mixing N, N-dimethylformamide (hereinafter referred to as “DMF”) with distilled water. Silver nitrate (AgNO ₃ ) and PVP (molecular weight 360000; product name K90; manufactured by Wako Pure Chemical Industries, Ltd.) are added to this aqueous solution so that the mass ratio of aqueous solution: silver nitrate: PVP is 900: 1: 1 and stirred. The mixture was stirred for 30 minutes at 400 rpm. Thereafter, the aqueous solution was transferred to a sealed container and heated at 150 ° C. for 20 hours to produce silver nanoparticles. In this example, the volume ratio of DMF to water was 1: 18000.

  An FE-SEM (field-emission scanning electron microscope) image of the obtained silver nanoparticles is shown in FIG. As shown in FIG. 1, in this example, a mixture of tabular silver nanoparticles and spherical silver nanoparticles was obtained. Properties (yield, average particle diameter, average thickness, average aspect ratio) of the obtained tabular silver nanoparticles and properties (yield, average particle diameter) of the spherical silver nanoparticles are shown in the corresponding columns of Table 1.

<Example 2>
Silver nanoparticles were produced under the same conditions as in Example 1 except that the volume ratio of DMF to water was changed to 1: 4500. An FE-SEM image of the obtained silver nanoparticles is shown in FIG. As shown in FIG. 2, in this example, a mixture of tabular silver nanoparticles and spherical silver nanoparticles was obtained. Properties of the obtained tabular silver nanoparticles and spherical silver nanoparticles are shown in the corresponding columns of Table 1.

<Example 3>
Silver nanoparticles were produced under the same conditions as in Example 1 except that the volume ratio of DMF to water was changed to 1: 450. An FE-SEM image of the obtained silver nanoparticles is shown in FIG. As shown in FIG. 3, in this example, a mixture of tabular silver nanoparticles and spherical silver nanoparticles was obtained. Properties of the obtained tabular silver nanoparticles and spherical silver nanoparticles are shown in the corresponding columns of Table 1.

<Example 4>
Silver nanoparticles were produced under the same conditions as in Example 1 except that the volume ratio of DMF to water was changed to 1:45. FE-SEM images of the obtained silver nanoparticles are shown in FIGS. 4 and 5. As shown in FIGS. 4 and 5, in this example, a mixture of tabular silver nanoparticles and spherical silver nanoparticles was obtained. Properties of the obtained tabular silver nanoparticles and spherical silver nanoparticles are shown in the corresponding columns of Table 1.

  As shown in FIGS. 1 to 5 and Table 1, according to Examples 1 to 4 in which silver ions were reduced in an aqueous solution containing DMF, the average particle diameter was 100 nm to 2000 nm, and the average aspect ratio was 5 to 5. 30 tabular silver nanoparticles were obtained. Particularly, the tabular silver nanoparticles of Examples 3 and 4 have a large average particle diameter of 500 nm or more and a large average aspect ratio of 18 or more. Such tabular silver nanoparticles having a high aspect ratio and a large particle diameter can be suitably used for electrodes and circuits in various fields.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

Claims (11)

A method for producing tabular silver nanoparticles, comprising reducing silver ions in an aqueous solution containing at least a compound A represented by the following general formula (1).
(In the formula, R ¹ and R ² are each independently selected from the group consisting of a hydrogen atom and an alkyl group having 4 or less carbon atoms. The alkyl group includes those having a substituent.)   The aqueous solution contains at least one selected from the group consisting of formamide, N, N-dimethylformamide, N, N-diethylformamide, and N, N-dipropylformamide as the compound A. Production method.   The production method according to claim 1 or 2, wherein the volume ratio of the compound A and water in the aqueous solution is in the range of 1:30 to 1: 20000.   The manufacturing method as described in any one of Claims 1-3 whose volume ratio of the said compound A and water in the said aqueous solution exists in the range of 1: 30-1: 500. A composition containing tabular silver nanoparticles,
The tabular silver nanoparticle containing composition whose average particle diameter of the tabular silver nanoparticle in the said composition is 100 nm-2000 nm, and whose average aspect-ratio is 5-30.   The composition according to claim 5, wherein the average particle diameter of the tabular silver nanoparticles in the composition is 500 nm to 2000 nm, and the average aspect ratio is 15 to 30.   The composition according to claim 5 or 6, wherein the average thickness of the tabular silver nanoparticles in the composition is 20 nm to 100 nm.   The composition according to any one of claims 5 to 7, further comprising spherical silver nanoparticles.   The composition of Claim 8 whose average particle diameter of the spherical silver nanoparticle in the said composition is 30 nm-300 nm.   The composition according to any one of claims 5 to 9, wherein the content of the tabular silver nanoparticles in the composition is 30% by number or more. The composition according to any one of claims 5 to 10, wherein the content of the tabular silver nanoparticles in the composition is 90% by number or more.