JP2015004123A - Production method of silver particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of silver particles, by which the particle diameter can be standardized while the size can be controlled within a range of ten and several of nanometers to one hundred and several tens of nanometers.SOLUTION: The present invention relates to a production method of silver particles by mixing a thermally decomposable silver compound and an amine to produce a silver-amine complex that is a precursor, and then heating a reaction system including the precursor, in which the moisture content in the reaction system before heating is 30-100 pts.wt. based on 100 pts.wt. of the silver compound. According to the present invention, it is possible to control the particle diameter and produce uniform silver particles.

Description

  The present invention relates to a method for producing silver particles. Specifically, the present invention relates to a method for producing silver particles having a uniform particle size while controlling the size in producing silver particles having a particle size in the range of several tens of nanometers to one hundred and several tens of nanometers.

  Silver (Ag) is a kind of noble metal that has long been known for use as a decorative product, but has excellent conductivity, light reflectivity, and unique properties such as catalytic action and antibacterial action. Therefore, the metal is expected to be used for various industrial applications such as electrodes / wiring materials, reflective film materials, catalysts, and antibacterial materials. As a utilization form of silver for these various uses, there is one in which silver particles are dispersed and suspended in an appropriate solvent. For example, this metal paste is formed by pasting silver particles into electrodes / wiring formation, adhesives / bonding materials, conductive adhesives / conductive bonding materials, and heat conductive materials of wiring boards mounted on electronic components such as semiconductor devices. The desired electrode, wiring, joint, and pattern can be formed by applying and baking.

  A generally known method for producing silver particles is a liquid phase reduction method. In the method for producing silver particles by the liquid phase reduction method, a silver compound as a precursor is dissolved in a solvent, and silver is precipitated by adding a reducing agent thereto. At this time, in order to prevent the precipitated silver particles from aggregating and coarsening, it is usual to add a compound called a protective agent. The protective agent binds to the silver particles that have been reduced and deposited, and suppresses the silver particles from contacting each other, thereby preventing aggregation of the silver particles.

  The method for producing silver particles by the liquid phase reduction method can produce silver particles efficiently by adjusting the concentration of the silver compound in the solvent, the type and amount of the reducing agent, and further selecting an appropriate protective agent. . However, silver particles produced by the liquid phase reduction method tend to be usually as large as several μm or more, and the particle size distribution tends to vary due to the concentration gradient of the reactants in the solvent.

Then, the thermal decomposition method of a silver complex is reported as a manufacturing method of the silver particle replaced with a liquid phase reduction method (patent document 1). This method basically utilizes the characteristics of a silver compound having thermal decomposability such as silver oxalate (Ag ₂ C ₂ 0 ₄ ). In this method, a complex is formed by such a silver compound and an organic compound that serves as a protective agent, and this is heated as a precursor to obtain silver particles. In Patent Document 1, an amine is added to silver oxalate as a protective agent to form a silver-amine complex, which is heated to a predetermined temperature, and silver particles are produced by thermal decomposition. According to this thermal decomposition method, extremely fine silver fine particles of several nm to several tens of nm can be produced, and silver fine particles having a relatively uniform particle diameter can be produced.

JP 2010-265543 A

  As described above, the field of use of silver particles tends to expand. Therefore, not only silver fine particles having a fine particle size of 10 nm or less, but also medium or larger sizes (for example, about several tens of nm) depending on applications. Silver particles are required. In order to meet this demand, a production method capable of controlling the size of the silver particles obtained according to the purpose of use is required. However, the conventional method for producing silver particles described above is insufficient from the viewpoint of particle size control. In the liquid phase reduction method, only large silver particles of about several μm can be produced. On the other hand, the thermal decomposition method is a production method for fine silver particles of several nm to several tens of nm.

  And in order to expand the range of future use of silver particles, in addition to being able to cope with a variety of average particle sizes that differ depending on the application, it is required that the particle size of the silver particles to be produced also has little variation. The In this regard, the silver particles obtained by the thermal decomposition method have a certain particle size, but as described above, the particle size suitable for production was a minute size depending on the type of silver compound. For this reason, when silver particles having a large particle size (for example, a particle size of several tens of nanometers or more) are produced by a thermal decomposition method, it is difficult to obtain a uniform particle size. For example, when a silver oxalate amine complex is used as the silver compound, although silver particles having a relatively uniform particle size can be obtained with respect to the size of about tens of nanometers, larger silver particles such as tens of nanometers can be obtained. When manufactured, the particle size distribution tends to vary.

  Therefore, the present invention provides a method for producing silver particles, the size of which can be controlled within the range of tens of nanometers to hundreds of tens of nanometers, with the silver particles having a uniform particle size.

  As a method for solving the above-mentioned problems, the present inventors have first studied based on a method for producing silver particles by a pyrolysis method. As described above, the thermal decomposition method can produce silver particles having a relatively uniform particle size, and it is considered that the particle size adjustment is easier than the liquid phase reduction method.

  Here, the present inventors considered the generation mechanism of silver particles by the thermal decomposition method with reference to the general Lamer rule, which is the precipitation mechanism of monodisperse fine particles in a closed solution system, as follows. Here, a case where silver particles are produced by thermally decomposing a silver oxalate complex coordinated with hexylamine is taken as an example. When the hexylamine coordination-silver oxalate complex is heated at a constant heating rate, silver “nucleation” starts at 80 to 90 ° C., that is, slightly lower than the decomposition temperature of the complex (about 110 ° C.). And when heating is continued and it raises to the decomposition temperature vicinity (90 degreeC-110 degreeC), decomposition | disassembly of a complex advances on the surface of the produced | generated nucleus, and "nuclear growth" is carried out. And silver particle produces | generates by the nucleation and growth by heating to this decomposition temperature.

  In consideration of such a silver particle generation mechanism, the particle diameter of the generated silver particles is considered to change depending on the heating rate. That is, it is considered that silver particles having a small particle size are generated by increasing the heating rate, and silver particles having a large particle size are generated when the heating rate is low. However, when the heating rate is adjusted, the above-mentioned tendency is observed as a whole, but it is not easy to obtain uniform silver particles having no variation in particle size distribution. The inventors of the present invention have conceived the present invention in which the heating of the silver-amine complex is uniformly advanced in consideration of the temperature difference in the reaction system in the heating step as one of the causes of the variation in the particle size.

  That is, the present invention is a method for producing silver particles by mixing a silver compound having heat decomposability and an amine to produce a precursor silver-amine complex and heating the reaction system containing the precursor. And before the said heating, the water content of a reaction system is related with the manufacturing method of the silver particle which is 30-100 weight part with respect to 100 weight part of said silver compounds.

  The present invention is based on a method for producing silver particles by thermal decomposition, and allows a predetermined range of moisture to be present in the reaction system in the heating stage of the silver-amine complex. The water in the reaction system acts as a so-called buffering agent in the heating step for decomposing the complex so that the heating can proceed uniformly. In other words, by actively interposing water and acting as a heat buffer in the reaction system, the temperature difference in the reaction system during heating is reduced, and the nucleation and growth of silver particles proceed uniformly. It becomes easy to do.

  The water content of the reaction system needs to be in the range of 30 to 100 parts by weight with respect to 100 parts by weight of the silver compound. A preferable range of the water content is 30 to 95 parts by weight, and a more preferable range is 30 to 80 parts by weight. When the amount of water is small (less than 30 parts by weight), the particle size of the obtained silver particles is limited to a very small particle size, and silver particles having a targeted particle size cannot be produced. On the other hand, when the amount of water is large (exceeding 100 parts by weight), the particle size of silver particles tends to vary.

  The water content of the reaction system is the water content immediately before the heating step, and it is necessary to consider the amount of water added to the reaction system so far. As will be described later, the silver compound may be used in a wet state to which water has been added in advance, but the amount of water added in advance is also included in the amount of water. For this reason, when only the amount added in advance to the silver compound or the homogenizing agent falls within the specified range of the water content, it can be heated as it is without separately adjusting the water content of the reaction system. On the other hand, if the amount added in advance is less than the lower limit (30 parts by weight) of the water content, it is necessary to adjust the amount of water, such as adding water separately. The timing of adding water may be before the heating step, and may be added at any stage before formation of the silver-amine complex or after formation of the complex.

  In the manufacturing method of this invention demonstrated above, the silver-amine complex which is a precursor of silver particle shall have thermal decomposability. As the raw material, a thermally decomposable silver compound is used, and silver oxalate, silver nitrate, silver acetate, silver carbonate, silver oxide, silver nitrite, silver benzoate, silver cyanate, silver citrate, silver lactate, etc. are applied it can.

Among the silver compounds, silver oxalate (Ag ₂ C ₂ O ₄ ) or silver carbonate (Ag ₂ CO ₃ ) is particularly preferable. Silver oxalate and silver carbonate can be decomposed at a relatively low temperature without requiring a reducing agent to produce silver particles. Further, since carbon dioxide generated by the decomposition is released as a gas, no impurities remain in the solution. Since silver oxalate is an explosive powdery solid, water or an organic solvent (alcohol, alkane, alkene, alkyne, ketone, ether, ester, carboxylic acid, fatty acid, aromatic, amine, It is preferable to use a mixture obtained by mixing amide, nitrile, etc.) as a dispersion solvent and making it wet. By making it wet, explosiveness is remarkably lowered and handling becomes easy. At this time, what mixed 10-200 weight part dispersion | distribution solvent with respect to 100 weight part of silver oxalates is preferable. However, as described above, since the present invention strictly regulates the amount of water in the reaction system, the mixing of water needs to be within a range not exceeding the specified amount.

  And as for the amine made to react with a silver compound, it is preferable that the total of carbon number of a hydrocarbon group is 4-10, and 4-8 are especially preferable. Thus, the preferable range for the total number of carbon atoms of the hydrocarbon group is defined by the silver particles produced by changing the stability and decomposition temperature of the silver-amine complex formed by the amine coordinated to the silver compound. This is because the particle size of the material is changed. When an amine having a total carbon number of less than 4 is applied, the resulting silver particles have a particle size of several tens of nanometers to several μm, and variations in particle size distribution tend to increase. When an amine having a total number of carbon atoms exceeding 10 is applied, the silver-amine complex is hardly thermally decomposed during synthesis, and many unreacted substances other than silver particles are likely to remain.

As the number of amino groups in the amine, (mono) amine having one amino group or diamine having two amino groups can be applied. An amine having one hydrocarbon group bonded to an amino group, that is, a primary amine (RNH ₂ ) is preferable. In the diamine having two amino groups, at least one amino group is preferably a primary amine. Tertiary amines tend not to form complexes with silver compounds. The hydrocarbon group bonded to the amino group is preferably a straight chain or branched chain hydrocarbon that does not contain a cyclic structure, and particularly preferably a saturated hydrocarbon that does not contain an unsaturated hydrocarbon.

Specific examples of preferred amines in the present invention include the following.

  As described above, since the decomposition temperature of the silver-amine complex varies depending on the type of amine (total number of carbon atoms of the hydrocarbon group), in the present invention, the particle size of silver particles is controlled by selecting the type of amine. Can do. According to the configuration of the present invention, for example, when hexylamine is applied, silver particles having a particle diameter of 50 to 190 nm can be produced. Further, when octylamine is applied, finer silver particles can be formed than when hexylamine is applied, and silver particles having a particle diameter of 15 to 50 nm can be produced. Moreover, the amine made to react with a silver compound in this invention can apply 2 or more types. By applying two or more kinds of amines, intermediate stability complexes are formed for the respective amines, and silver particles having a particle size corresponding to the complex can be produced. For example, when hexylamine and octylamine are used in the same amount, silver particles having an intermediate particle size can be produced with respect to the particle size range in which both can be produced.

The mixing ratio of the silver compound and the amine is the ratio of the number of moles of amino groups (mol _NH2 ) to the number of moles of silver ions (Ag ⁺ ) of the silver compound (mol _{Ag +} ) (mol _NH2 / mol _{Ag +} ). The above is preferable. If the amine is insufficient, unreacted silver compounds may remain, and sufficient silver particles cannot be produced, and the particle size distribution of the silver particles varies. On the other hand, the upper limit of the amine addition amount is not particularly limited, but is preferably 6 or less in consideration of the purity of the obtained silver particles.

The reaction system in the present invention only needs to be composed of a silver-amine complex and an appropriate range of moisture, and silver particles having a uniform particle diameter can be produced without other additives. However, the addition of an additive that further stabilizes the complex is not excluded. Examples of the additive applicable in the present invention include oleic acid, myristic acid, palmitoleic acid, linoleic acid and the like. These additives, silver ions (Ag ⁺⁾ number of moles of _{(mol Ag +)} moles of additives to the ratio of (mol _Additives) (mol _additive / _{mol Ag +),} and 0.01 to 0.1 It is preferable to do this.

  The reaction system confirms that the water content is in an appropriate range, and then heats to precipitate silver particles. The heating temperature is preferably equal to or higher than the decomposition temperature of the silver-amine complex. As described above, the decomposition temperature of the silver-amine complex varies depending on the type of amine coordinated to the silver compound. When the amine suitable for the present invention shown above is applied, the decomposition temperature is 90 to 130 ° C.

  In the heating process of this reaction system, the heating rate affects the particle size of the silver particles to be precipitated. That is, in the present invention, the particle size of the silver particles can be prepared by two systems, that is, the type of amine that forms a silver-amine complex (amine that reacts with the silver compound) and the heating rate of the heating step. By these two means, silver particles having a targeted particle diameter can be produced within an average particle diameter of 10 to 200 nm. When the particle size is 10 to 100 nm, it is particularly easy to obtain silver particles having a uniform particle size, and when the particle size is 15 to 50 nm, the particle size is more likely to be uniform. In addition, it is preferable to adjust the heating rate in a heating process in the range of 2-50 degrees C / min to said decomposition temperature. Further, temperature control at 5 ° C./min or more is easy.

  Silver particles precipitate through the heating step. With respect to this reaction system, silver particles can be taken out through appropriate washing and solid-liquid separation. In some cases, the silver particles may be fixed to each other, but this can be easily crushed and separated. The recovered silver particles can be stored and used in ink, paste, slurry, or dried powder dispersed in an appropriate solvent.

  According to the production method of the present invention described above, the size of the silver particles can be easily controlled. Further, the obtained silver particles are uniform in size.

The figure explaining the silver particle manufacturing process in this embodiment. Test No. 1 of the first embodiment. The SEM photograph of 1-4 silver particles. Test No. 1 of the first embodiment. SEM photographs of silver particles 5 and 6. Test No. 1 of the first embodiment. The SEM photograph of 7-11 silver particles. Test No. 1 of the first embodiment. SEM photograph of 14 silver particles. Test No. 1 of the first embodiment. SEM photographs of 15 and 16 silver particles. Test No. 1 of the first embodiment. The SEM photograph of 17-21 silver particles. The particle size distribution figure of the silver particle of Test No.6,10,11 of 1st Embodiment. Test No. 2 of the second embodiment. SEM photograph of 22 silver particles.

  Hereinafter, preferred embodiments of the present invention will be described. In the present embodiment, silver particles were produced while changing various conditions along the process of FIG. 1, and their properties were evaluated.

In this embodiment, 1.5 g of silver oxalate (Ag ₂ C ₂ O ₄ ) (silver ion (Ag ⁺ ) 9.9 mmol) or 1.38 g of silver carbonate (Ag ₂ CO ₃ ) as a thermally decomposable silver compound ( Silver ion (Ag +) 10 mmol) was used. As for silver oxalate, there were prepared a case where it was used in a dry state and a wet state by adding 0.3 g of water (20 parts by weight with respect to 100 parts by weight of silver oxalate). To this silver compound, the amine shown in the following table was added to produce a silver-amine complex. The silver compound and amine were mixed at room temperature and kneaded until a white cream was formed. When oleic acid was used as an additive, it was added to the silver-amine complex produced above.

  Water was added to the reaction system produced above as necessary to keep the water content within a predetermined range. Specifically, when the water content in the reaction system was 20 parts by weight, the following heating was performed without adding water separately if the raw material was wet silver oxalate (20 parts by weight of water). When the water content of the reaction system was 47 parts by weight using the same raw material, water was added to adjust the water content.

  And the reaction system was heated from room temperature, the silver-amine complex was decomposed | disassembled, and silver particle was deposited. The heating temperature at this time assumed 110 degreeC as a decomposition temperature of a complex, and made this the ultimate temperature. The heating rate was 10 ° C./min.

  In this heating process, generation of carbon dioxide was confirmed from around the decomposition temperature. Heating was continued until the generation of carbon dioxide stopped to obtain a liquid in which silver particles were suspended. After precipitation of silver particles, methanol was added to the reaction solution for washing, and this was centrifuged. This washing and centrifugation were performed twice.

About the collect | recovered silver particle, the particle size (average particle diameter) and particle size distribution were examined. In this evaluation, first, SEM observation and photography were performed on the silver particles, the particle size of the silver particles in the image was measured (about 100 to 200 particles), and the average value was calculated. Furthermore, as a relative variation index of the particle size distribution, a coefficient of variation (CV) is obtained from the following formula, and when the coefficient of variation is 30% or less, “pass: ○”, and when it exceeds 30% and 40% or less, “fail: Δ ”, More than 40% was defined as“ defect: x ”. FIG. 8 shows a particle size distribution diagram.
Coefficient of variation (%) = (standard deviation / average particle size) × 100

  The evaluation results of the silver particles produced in this embodiment are shown in Table 2 together with the production conditions. For the sample whose particle size distribution diagram is shown in FIG. 8, the standard deviation and the calculated coefficient of variation are also shown (Table 3).

  The contents of Table 2 will be described. First, the present invention is based on a thermal decomposition method in which silver particles are produced by thermal decomposition of a silver-amine complex, but requires a predetermined amount of water to coexist in the reaction system. Looking at the results regarding the water content of the reaction system (Test Nos. 1 to 4 and 7 to 11), when the water content is less than 30 parts by weight (Test Nos. 7 and 8), the size of the silver particles is silver. -To achieve the object of the present invention to obtain silver particles having a target particle size of about 10 to several tens of nanometers, limited to minute ones (average particle size less than 10 nm) depending on the type of amine complex. I can't. On the other hand, those having an appropriate water content (Test Nos. 1, 2, 6, and 9) can produce silver particles having a uniform particle size, and the effectiveness of the present invention can be confirmed. On the other hand, it is as above-mentioned that water is required, but it can confirm that the upper limit also exists (test No. 3, 4, 10, 11). In addition to making the particle size of the silver particles coarse, the amount of water becomes a factor of variation in the particle size.

  As an amine for producing a silver-amine complex, it was confirmed that silver particles having a uniform particle diameter can be produced using an amine having a total of 4 to 10 carbon atoms in an alkyl group. When a mixed amine of n-hexylamine and n-octylamine is used as the amine (Test No. 6, 12-14), the higher the mixing ratio of n-hexylamine, the larger the silver particle size is produced. (Test Nos. 6 and 14). When mixed amine is used, silver particles having an intermediate particle size can be produced. In this embodiment, since the heating rate up to the decomposition temperature is common, it can be confirmed that the particle size can be adjusted by selecting an amine. Further, the amount of amine mixed for producing a silver-amine complex (Test Nos. 5 and 6) is such that the ratio of the number of moles of amino groups to the number of moles of silver ions is 1.6 or more. Is obtained (Test No. 6).

  In addition, about the necessity of the oleic acid which is an additive (test No. 6, 15, 16), it can confirm that addition of additives, such as an oleic acid, is not essential. Oleic acid is thought to be effective in maintaining a suitable particle size distribution, but suitable silver particles can be produced without the addition of oleic acid.

Second Embodiment : As described above, the particle size of the silver particles varies depending on the amine for producing the silver-amine complex, but in the present invention, it is possible to cope with the heating rate of the reaction system as a means for adjusting the particle size. is there. Therefore, next, the above test No. The heating rate was changed about 6 and the silver particle was manufactured. In the first embodiment, the heating rate is 10 ° C./min, but here the heating rate is 2 ° C./min (Test No. 22). The evaluation results for the silver particles produced here are shown in Table 4.

  From Table 4, it can be seen that the particle size can be adjusted by changing the heating rate. By reducing the heating rate, the particle size of the silver particles tends to increase. As described above, in the present invention, it is possible to adjust the particle size of the silver particles to be manufactured from different approaches of selecting an amine and adjusting the heating rate. Even when the heating rate is adjusted in this way, a good particle size distribution will not be lost.

  As described above, according to the present invention, uniform silver particles can be produced while controlling the particle size. The present invention relates to silver particles used in various applications such as electrodes / wiring materials, adhesives / bonding materials, conductive adhesives / conductive bonding materials, thermal conductive materials, reflective film materials, catalysts, antibacterial materials, etc. High quality products can be manufactured.

Claims (6)

A method for producing silver particles by mixing a silver compound having thermal decomposability and an amine to produce a precursor silver-amine complex, and heating a reaction system containing the precursor,
Before the heating, the water content of the reaction system is 30 to 100 parts by weight with respect to 100 parts by weight of the silver compound.   The silver compound having thermal decomposability is any one of silver oxalate, silver nitrate, silver acetate, silver carbonate, silver oxide, silver nitrite, silver benzoate, silver cyanate, silver citrate, and silver lactate. The method for producing silver particles according to 1.   The method for producing silver particles according to claim 1 or 2, wherein the total number of carbon atoms in the amine is 4 to 10.   The method for producing silver particles according to claim 1, wherein the hydrocarbon group in the amine is composed of a chain saturated hydrocarbon.   The method for producing silver particles according to any one of claims 1 to 4, wherein the amine is added in a molar ratio of 1.6 times or more with respect to silver ions in the silver compound.   The method for producing silver particles according to any one of claims 1 to 5, wherein the heating temperature of the reaction system is not less than the decomposition temperature of the silver-amine complex.