JP5975440B2 - Method for producing coated silver fine particles and coated silver fine particles produced by the production method - Google Patents

Description

  The present invention relates to a method for producing silver fine particles coated with a protective film containing an alkylamine, and a coated silver fine particle produced by the method.

Silver fine particles are known to be capable of forming a silver coating by sintering at a relatively low temperature in addition to the high electrical conductivity and oxidation stability characteristic of metallic silver, as well as the light reflectance in the visible region. Taking advantage of these characteristics, the use of silver fine particles as conductive ink and paste is expected as a wiring material in printed electronics, which is a next-generation process technology for producing electronic wiring and devices through simple printing and coating processes. Has been.
Silver ions exhibit extremely strong bactericidal properties against bacteria and the like, and it is expected that a high amount of bactericidal power can be obtained with a small amount of silver by using silver fine particles having a large specific surface area. In addition, taking advantage of unique optical properties, the use of silver fine particles as a material for pigments and reflectors has been studied.

  The silver fine particles can be produced by various methods. From the viewpoint of adding characteristics such as prevention of aggregation of the produced silver fine particles and improvement in dispersibility in a solvent, various kinds of silver fine particles are produced on the particle surface simultaneously with the production of the silver fine particles. A method of manufacturing as coated silver fine particles in which a protective film is formed is common. As a method for producing such coated silver fine particles, a method in which a compound containing silver is reduced with a reducing agent in an environment in which a compound containing silver and an organic molecule serving as a protective film coexist is common. For example, Patent Document 1 describes a technique for producing coated silver fine particles by dropping a silver nitrate-amine complex onto ascorbic acid or the like as a reducing agent to reduce silver nitrate. Patent Document 2 describes a technique for producing silver particles coated with an organic protective agent by heating and reducing a silver salt such as silver nitrate in the presence of an organic protective agent and a reducing auxiliary agent. .

  On the other hand, as described above, according to the method using a reduction reaction between a plurality of components of a compound containing silver and a reducing agent, silver particles are not necessarily uniformly distributed due to a minute fluctuation in the mixing ratio of each component. There was a problem that the resulting silver fine particles were not formed and were not uniform. In addition, in terms of mitigating fluctuations in the mixing ratio and prevention of coarsening of silver fine particles, it is effective to dilute the silver-containing compound and the reducing agent in a large amount of solvent. There are disadvantages in terms of cost and silver yield.

  In contrast to these technologies, the inventors of the present application apply alkylamine to a compound containing silver such as silver oxalate to form a complex compound, and then heat and thermally decompose the generated complex compound. Therefore, a technology for obtaining coated silver fine particles (amine complex thermal decomposition method) is being developed (see, for example, Patent Document 3). According to the amine complex decomposition method, as the reaction when producing silver fine particles, a reaction in which an amine complex as one component is thermally decomposed into a plurality of components is used. Therefore, silver fine particles having uniform characteristics are easily obtained, and generally no organic solvent is required, and silver fine particles can be obtained without a solvent.

JP 2009-144197 A JP 2007-39718 A JP 2010-265543 A

On the other hand, in the production of silver fine particles by the amine complex decomposition method, as described above, it is required to form a complex compound by previously depositing an alkylamine on a compound containing silver such as silver oxalate. In this regard, when using only alkylamine that can form a relatively stable film as a coating molecule for the coated silver fine particles to be produced, it is difficult to form a complex compound, or it takes a long time to form a complex compound There are many. For this reason, it is effective to use an auxiliary agent that promotes the formation of a compound containing silver and a complex compound containing alkylamine.
In the above-mentioned Patent Document 3, by using a more polar alkyldiamine together with an alkylamine, a compound containing silver and a complex compound containing alkylamine are quickly generated regardless of the type of alkylamine, and good coated silver fine particles Is obtained.
However, since alkyldiamines and the like used mainly for the formation of complex compounds are also included in the coating of the coated silver fine particles to be produced, it will affect various properties of the coated silver fine particles. It is expected that there may be cases where it is desirable to substitute with other components.

  Accordingly, the present invention provides a novel production method different from the conventional method for producing coated silver fine particles by a so-called amine complex decomposition method, and an object thereof is to provide coated silver fine particles produced by the method. .

  In order to solve the above problems, the present inventors have intensively studied a method for producing coated silver fine particles coated with a protective film containing an alkylamine, and as a result, a silver compound that can be decomposed by heating to produce metallic silver, When a complex compound is formed by mixing with an alkylamine, the formation of the complex compound is promoted by adding an alcohol compound that is soluble in water, and the complex compound is made efficient regardless of the type of alkylamine. We found that it can be generated well.

  That is, in the method for producing coated silver fine particles of the present invention, a silver compound that can be decomposed by heating to form metallic silver, an alkylamine, and at least one alcohol compound that is soluble in water are mixed. A first step of producing a complex compound containing the silver compound and an alkylamine, and a second step of thermally decomposing the complex compound to produce silver fine particles coated with a protective film containing an alkylamine, It is characterized by including. The complex formation step may include other auxiliary agents that do not affect the formation of the complex compound.

At least one of the alcohol compounds preferably has a solubility of 0.3 g / L or more at 20 ° C. in water. Further, it is more preferable that at least one of the alcohol compounds has a boiling point of 70 ° C. or higher.
In a preferred embodiment of the present invention, at least one of the alcohol compounds includes a polyhydric alcohol. In one preferable embodiment of the present invention, in the first step, a fatty acid can be further mixed, and in another embodiment, water can be further mixed. The silver compound is preferably composed mainly of silver oxalate.

  In a different aspect of the present invention, coated silver fine particles produced by any one of the above methods are provided. In still another aspect, a coated silver fine particle dispersion in which the coated silver fine particles are dispersed in a dispersion medium is provided.

  According to the method of the present invention, coated silver fine particles coated with a protective film containing an alkylamine are promoted by promoting the formation of a complex compound containing a silver compound capable of being decomposed by heating to form metallic silver and an alkylamine. The manufacturing method can be made more efficient and the manufacturing cost can be reduced. Furthermore, the method of the present invention is extremely useful in practice because the type of alkylamine used as a protective film can be selected and optimized in accordance with the use of the obtained coated silver fine particles. For example, when used as an ink, dispersibility in a solvent can be improved by including a long-chain alkylamine or a fatty acid. Moreover, in order to improve the sinterability at low temperatures, the content of medium-short chain alkylamines can be increased.

It is a transmission scanning electron microscope (STEM) image or a transmission electron microscope (TEM) image of the silver fine particles obtained in Examples 1 to 8. It is a transmission scanning electron microscope (STEM) image or a transmission electron microscope (TEM) image of the silver fine particles obtained in Examples 9 to 15.

  Hereinafter, the method for producing coated silver fine particles according to the present invention and the coated silver fine particles produced by the method according to the present invention will be described. As described in Patent Document 3, a complex compound mainly composed of a silver compound such as silver oxalate containing silver and an alkylamine is heated under predetermined conditions, and oxalate ions contained in the complex compound, etc. It is known that silver fine particles protected by an alkylamine protective film can be produced by generating atomic silver by decomposing the silver compound of this compound and aggregating it in the presence of alkylamine. . Such a production method is called an amine complex decomposition method, and atomic metal silver is generated by the decomposition reaction of a silver amine complex that is a single kind of molecule, so that atomic metal silver is uniformly generated in the reaction system. Compared with the case where silver atoms are generated by reaction between a plurality of components, reaction non-uniformity due to fluctuations in the composition of the components constituting the reaction is suppressed, and a large amount of coating is produced particularly on an industrial scale. This is advantageous when silver fine particles are produced.

  In the amine complex decomposition method, an alkylamine molecule is coordinated to the silver atom to be generated, and the movement of the silver atom during aggregation is controlled by the action of the alkylamine molecule coordinated to the silver atom. Inferred. As a result, even when the production is carried out in an environment where silver atoms are present at a high density, it is possible to produce silver fine particles that hardly cause excessive aggregation or the like and have a narrow particle size distribution. In addition, many alkylamine molecules also have relatively weak coordination bonds on the surface of the silver fine particles to be produced, and these form a dense protective film on the surface of the silver fine particles. It becomes possible to produce excellent silver fine particles having a clean surface. In addition, since the alkylamine molecules forming the film can be easily desorbed by heating or the like, silver fine particles that can be sintered at a very low temperature can be produced.

  As described above, the silver amine complex decomposition method has an advantage as a universal method for producing coated fine silver particles that are very fine and can be sintered at a low temperature. On the other hand, when producing silver fine particles by the amine complex decomposition method, the reaction in which the silver compound as the raw material and the alkylamine form a complex compound causes the alkylamine to coordinate with the silver atom in the silver compound. It is presumed that the free energy change at the time of formation progresses as a driving force. However, since the free energy change related to the formation of the coordination bond is not necessarily large, the formation of the complex compound does not always progress smoothly. Have. In addition, a solid silver compound is often used as a supply source of silver atoms, and the place where the formation reaction of a complex compound with an alkylamine or the like occurs is limited to the solid-liquid interface between the two, so the driving force is weak. In order to complete the formation reaction of complex compounds and the like, generally a long mixing process is required. Furthermore, depending on the choice of silver compound or alkylamine, there is a problem that complex compounds of both cannot be formed satisfactorily.

  As one means for solving this problem, in Patent Document 3 previously disclosed by the present inventor, a medium-short chain having a higher polarity than a medium-short chain alkyl monoamine having a boiling point of 100 ° C. to 250 ° C. It was shown that by using an alkyldiamine intervening, a complex compound can be synthesized without solvent, at a low temperature and in a short time, and by using this complex compound, coated silver fine particles that can be sintered at a low temperature can be produced. The coated silver fine particles produced by this method can be sintered near room temperature, which is a very low silver sintering temperature, and can be dispersed at a high concentration in an organic solvent. By using it as ink in a state dispersed in a medium, it is very useful in various applications such that a good conductive film can be formed on a plastic substrate having low heat resistance.

On the other hand, when the present inventors have made various studies, an alcohol compound having a certain degree of polarity is interposed when a complex compound such as a complex compound is produced by mixing a solid silver compound and an amine. Thus, it was revealed that the formation of a complex compound of a silver compound and an alkylamine proceeds smoothly. This is thought to be because in the environment where silver compound and alkylamine coexist, an alcohol compound having a certain degree of polarity intervenes to promote and assist the reaction of forming a complex compound between the two. .
In the present invention, the alcohol compound means one in which at least one hydrogen atom contained in the hydrocarbon is replaced with a hydroxy group (—OH), and the position and number of the hydrogen atoms to be substituted are not limited. To do. In the present invention, among these alcohol compounds, one having a certain degree of polarity is used.

Although it is generally difficult to quantitatively determine the polarity strength of an alcohol compound, semi-quantitative evaluation of the polarity strength of various alcohol compounds is performed based on the solubility in water (H ₂ O) as a polar solvent. Is possible. In other words, a strongly polar alcohol compound has a high solubility in water, and a tendency that the solubility decreases as the polarity decreases is observed.
In the present invention, various alcohol compounds were examined for various relations between the effect of promoting the formation of complex compounds between silver compounds and alkylamines and the solubility of the alcohol compounds in water. In the alcohol compound having the formula, a certain effect was observed in promoting the formation of a complex compound between the silver compound and the alkylamine. On the other hand, it has been clarified that alcohol compounds that are not soluble in water do not have a significant effect on promoting the formation of the complex compounds.

  Specifically, even when octanol, which is said to have a solubility in water of approximately 0.3 g / L (20 ° C.), was interposed, an effect of promoting the complex formation between the silver compound and the alkylamine was observed. . Furthermore, in alcohol compounds having a solubility in water of approximately 10 g / L or more, there is a tendency that the formation time of the complex compound between the silver compound and the alkylamine is significantly shortened, and the alcohol having a solubility of 30 g / L or more. In the compound, there was a tendency that the formation time of the complex compound was greatly shortened. Moreover, in the alcohol compound which shows the solubility of 70-80 g / L or more with respect to water, regardless of the magnitude of the solubility, depending on the individual structure such as the number of OH groups contained, between the silver compound and the alkylamine There was a tendency to determine the complex compound formation time. Here, the solubility with respect to water generally indicates the maximum mass of a solute that can be dissolved in 1 L of water at room temperature in g. The room temperature referred to above is 20 ° C. to 25 ° C., preferably 20 ° C.

  In addition, in the step of heating and decomposing the complex compound generated above, the complex compound generated in the presence of the alcohol compound is decomposed in a shorter time than the complex compound generated without any alcohol compound. There was a tendency to complete. A silver compound formed with a complex compound with an alkylamine generally tends to cause thermal decomposition at a temperature lower than the original thermal decomposition temperature. This is considered to be because the structure of the silver compound becomes unstable and activated when the alkylamine generates a coordination bond or the like with respect to the silver compound. From this point of view, it can be inferred that the complex compound formed in the presence of the alcohol compound is accompanied by the formation of a complex compound that is microscopically favorable along with the formation of the macro complex compound.

On the other hand, the type of alcohol compound intervened in the formation of the complex compound of silver compound and alkylamine tended to affect the thermal decomposition process of the complex compound. That is, the thermal decomposition reaction of the complex compound is preferably carried out at a temperature as low as possible, usually about 70 to 150 ° C., from the viewpoint of preventing evaporation of the alkylamine used. However, when an alcohol compound having a relatively low boiling point is used, there is a tendency that remarkable evaporation occurs even in the temperature range, and a tendency that the formation reaction of the coated silver fine particles becomes unstable is observed. This was considered to be due to the latent heat absorption accompanying the evaporation of the alcohol compound and the dissociation of some complex compounds into silver compounds. Such a phenomenon is particularly a concern as an unstable factor in industrial mass synthesis. Since such a tendency is observed particularly in methanol, ethanol, etc., if necessary, the unnecessary alcohol compound is removed in advance after the formation of the complex compound, or after the substitution with another alcohol compound, alkylamine, etc. It is preferable to perform decomposition. It is also effective to reduce the vapor pressure by mixing other alcohol compounds or water with methanol.
On the other hand, when an alcohol compound having a relatively high boiling point is used, it remains in the reaction system stably even in the step of thermal decomposition of the complex compound, which is preferable in terms of stable formation of coated silver fine particles. On the other hand, in the case of an alkyl alcohol having one OH group, an alcohol compound having a high boiling point due to its large molecular weight generally has a low solubility in water and tends to reduce the formation promotion effect of a complex compound. A tendency to exist off is observed.
In consideration of the above, alcohol compounds particularly preferably used in the present invention include glycol having two OH groups in one molecule and glycerin having three OH groups.

  Further, the present invention has revealed that the particle diameter of the produced coated silver fine particles can be changed by interposing various alcohol compounds during the formation of the complex compound between the silver compound and the alkylamine. The reason why the particle diameter of the coated silver fine particles changes depending on the type of alcohol compound to be intervened is not clear, but the degree of coarsening prevention action by alkylamine in the process of aggregation of silver atoms generated by thermal decomposition of the complex compound is It is presumed to change depending on the type.

Further, as shown in the results of the following examples, it becomes clear that, for example, the conductivity after sintering of the obtained coated silver fine particles varies depending on the type of alcohol compound used in the present invention. ing. This is considered to indicate that, in addition to the particle diameter of the coated silver fine particles, the structure of the coated portion changes when the alcohol compound is contained in the coated portion, depending on the type of the alcohol compound.
Hereinafter, a method for producing coated silver fine particles according to the present invention will be described in detail.

(Silver compound that can be decomposed by heating to produce metallic silver)
As a silver raw material used for producing the coated silver fine particles, among silver-containing compounds, a silver compound that is easily decomposed by heating to generate atomic silver is preferably used. Examples of such a silver compound include silver chloride, silver nitrate, silver carbonate, and the like in addition to silver carboxylate in which a silver atom is combined with a carboxylic acid such as formic acid, acetic acid, oxalic acid, malonic acid, benzoic acid, and phthalic acid. Among these, silver oxalate is preferably used from the viewpoints of easily producing metallic silver by decomposition and hardly generating impurities other than silver. Silver oxalate has a high silver content and is usually easily decomposed at a low temperature of about 200 ° C. In addition, since oxalate ions are removed as carbon dioxide during decomposition, metal silver is obtained, so that impurities hardly remain. Is advantageous. As the silver oxalate used in the method of the present invention, for example, commercially available silver oxalate can be used. Moreover, you may use the silver compound which substituted the oxalate ion of silver oxalate by 1 or more types of 20 mol% or less of carbonate ion, nitrate ion, and oxide ion. In particular, silver oxalate in which 20 mol% or less of the oxalate ions are substituted with carbonate ions has improved thermal stability. However, when the substitution amount exceeds 20 mol%, the complex compound formed using the oxalate ions is thermally decomposed. It may be difficult.

(Alkylamine)
When the coated silver fine particles are to be produced by the amine complex decomposition method, as the amine to be used, an alkyl monoamine, an alkyldiamine or the like in which an amino group is bonded to a part of the alkyl group is desirably used. In this specification, an alkylamine includes an alkyl monoamine in which one amino group is bonded to an alkyl group, and an alkyl diamine in which two amino groups are bonded to an alkyl group. Moreover, when distinguishing both, it describes as alkyl monoamine and alkyldiamine, respectively.
In the production method according to the present invention, an alkyl monoamine is mainly used as the alkyl amine, but an alkyl diamine can be appropriately mixed and used depending on the characteristics required for the coated silver fine particles to be produced.

The alkylamine that can be used in the method of the present invention is an alkylamine in which the amino group contained in the amine moiety is a primary amino group in order to be able to form a coordinate bond via an amino group to the surface of the silver fine particles. An amine RNH ₂ or alkylamine R ¹ R ² NH which is a secondary amino group is preferred. In the present specification, R, R ¹ and R ² each independently represent a hydrocarbon group, and these hydrocarbon groups contain a hetero atom such as an oxygen atom, a nitrogen atom, a sulfur atom or a silicon atom. May be. By including a primary or secondary amino group, a complex bond between the amine moiety and the metal compound can be formed by generating a coordinate bond to the metal atom by the unshared electron pair of the nitrogen atom in the amino group, Thereby, an alkylamine film can be formed on the metal fine particles. On the other hand, when a tertiary amino group is included, the free space around the nitrogen atom in the amino group is generally narrow, which is undesirable in that it is difficult to form a coordinate bond to a metal atom. It is also possible to use the coated silver fine particles produced by the method depending on the application.

  In alkylamines and the like, generally, as the molecular weight of an alkyl group increases and becomes a long chain, the vapor pressure tends to decrease and the boiling point tends to increase. On the other hand, when the alkyl group has a small molecular weight and a short chain, the vapor pressure is high and the polarity tends to be strong. In addition, alkyldiamines having two amino groups in one molecule tend to be more polar than alkylmonoamines having one amino group in one molecule. According to the method of the present invention, these arbitrary alkylamines can be used, and those alkyl groups containing 2 to 5 carbon atoms are short-chained, and those having 6 to 12 carbon atoms are medium-chained. Those having 13 or more carbon atoms are defined as long chains, and their characteristics will be described below.

  Long- and medium-chain alkyl monoamines generally have low vapor pressures and are unlikely to evaporate, and because they have a high affinity with organic solvents, these alkyl monoamines and amine mixtures containing them can be used. The coating of the coated fine silver particles to be produced also contains long-chain / medium-chain alkyl monoamines at a predetermined ratio, which improves storage stability and improves dispersibility in nonpolar organic solvents. it can. In this regard, for example, when the coated silver fine particles to be produced are dispersed in an appropriate organic solvent and used as an ink or the like, the coating portion of the coated silver fine particles contains a long-chain / medium-chain alkyl monoamine. Is desirable.

  Examples of such long and medium chain alkyl monoamines include dipropylamine (107 ° C), dibutylamine (159 ° C), hexylamine (131 ° C), cyclohexylamine (134 ° C), heptylamine (155 ° C). ), 3-butoxypropylamine (170 ° C), octylamine (176 ° C), nonylamine (201 ° C), decylamine (217 ° C), 3-aminopropyltriethoxysilane (217 ° C), dodecylamine (248 ° C), Alkylmonoamines such as hexadecylamine (330 ° C), oleylamine (349 ° C), octadecylamine (232 ° C (at 32 mmHg)) are practical in terms of easy availability, but are not limited thereto. For other long and medium chain alkyl monoamines having 6 or more carbon atoms, It can be used depending on.

  On the other hand, generally, as the alkyl chain of the alkyl monoamine becomes longer, the tendency of forming a complex compound with the silver compound tends to decrease, and when a long-chain alkyl monoamine having about 18 carbon atoms is used It is also observed that the formation of complex compounds is not completed by long-term mixing. In addition, when a medium-chain alkyl monoamine is used, a complex compound can generally be formed by mixing with a silver compound for a long period of time.

On the other hand, when an alkyl diamine or a short-chain alkyl monoamine having 5 or less carbon atoms is used, a complex compound with a silver compound can be formed relatively easily. Therefore, when it is intended to produce coated silver fine particles by the amine complex decomposition method, it is also possible to use such alkyl diamines or alkyl amines mainly composed of short-chain alkyl monoamines having 5 or less carbon atoms. It is.
Furthermore, by using such an alkyl diamine or a short-chain alkyl monoamine having 5 or less carbon atoms in a predetermined ratio with a long-chain / medium-chain alkyl monoamine, a coated silver that takes advantage of both advantages Fine particles can be produced. In other words, by using a mixture containing an alkylamine in which both are mixed at an appropriate ratio, a complex compound with a silver compound is formed well, and it has excellent storage stability and can be dispersed in a nonpolar organic solvent. Silver fine particles can be produced.

  Such short-chain alkyl monoamines include amylamine (boiling point 104 ° C.), 2-ethoxyethylamine (105 ° C.), 4-methoxybutylamine, diisopropylamine (84 ° C.), butylamine (78 ° C.), diethylamine (55 ° C.). ), Propylamine (48 ° C.), isopropylamine (34 ° C.), ethylamine (17 ° C.), dimethylamine (7 ° C.) and the like are industrially available and desirably used.

  The alkyl diamine has a boiling point of 100 ° C. or higher considering the thermal decomposition temperature of the complex compound, and has a boiling point of 250 ° C. or lower considering the low-temperature sinterability of the obtained coated silver fine particles. It is considered. For example, ethylenediamine (118 ° C), N, N-dimethylethylenediamine (105 ° C), N, N'-dimethylethylenediamine (119 ° C), N, N-diethylethylenediamine (146 ° C), N, N'-diethylethylenediamine ( 153 ° C.), 1,3-propanediamine (140 ° C.), 2,2-dimethyl-1,3-propanediamine (153 ° C.), N, N-dimethyl-1,3-diaminopropane (136 ° C.), N , N′-dimethyl-1,3-diaminopropane (145 ° C.), N, N-diethyl-1,3-diaminopropane (171 ° C.), 1,4-diaminobutane (159 ° C.), 1,5-diamino 2-methylpentane (193 ° C.), 1,6-diaminohexane (204 ° C.), N, N′-dimethyl-1,6-diaminohexane (228 ° C.) , 1,7-diaminoheptane (224 ° C.), 1,8-but-diamino octane (225 ° C.), and the like, but is not limited thereto.

  In addition, when producing coated silver fine particles by an amine complex decomposition method using various alkylamines, the alkylamine constituting the coating of the produced silver fine particles is mixed with a silver compound to form a complex compound, In addition to producing the coated silver fine particles by thermally decomposing the complex compound, the complex compound and the coated silver fine particles are mixed by mixing another kind of alkylamine or the like with the complex compound or the coated silver fine particles once formed. It is also possible to replace the alkylamine contained in the coating. Such a technique is effective when, for example, coated silver fine particles containing an alkylamine that is difficult to form a complex compound in the coated portion are produced.

(Alcohol compound)
The present invention is characterized in that an alcohol compound having a certain degree of polarity is interposed when a complex compound such as a silver compound and an alkylamine is produced. It is desirable that the alcohol compound used in such an application has a solubility in water (H ₂ O) typically at room temperature. Alcohol compounds exhibiting solubility in water have a certain polarity, and the use of such alcohol compounds can promote the formation of silver compounds and complex compounds such as alkylamines. Although the specific action of such an alcohol compound is not clear, in a solid-state silver compound, molecules containing silver as the silver compound are agglomerated by forming crystals or the like. Coordination to silver atoms by alkylamines etc. does not proceed well, but when a polar alcohol compound is present, the alkylamine is used to break up the silver compound crystals etc. It is considered that the coordination by etc. progresses efficiently.
In addition, since the alcohol compound used in this way is also included in the complex compound to be formed and the coated part of the coated silver fine particles obtained by pyrolyzing it, various alcohol compounds are appropriately selected in the present invention. By using these, various functions can be added to the coated silver fine particles to be produced.
Taking advantage of such characteristics of a predetermined alcohol compound, as a preferred embodiment of the present invention, such an alcohol compound is intervened in the production of coated silver fine particles mainly using long-chain / medium-chain alkylamine. This can assist / promote the formation of complex compounds. Even in the presence of short-chain alkylamines or alkyldiamines, various alcohol compounds can be interposed as means for imparting predetermined characteristics to the coated silver fine particles to be produced, together with the aid of complex compound formation.

  Examples of the alcohol compound exhibiting solubility in water include linear alkyl alcohols having one OH group, from methanol having 1 carbon atom to octanol having 8 carbon atoms. On the other hand, when the number of carbon atoms is 9 or more, it does not substantially dissolve in water, and even if such an alcohol compound is interposed during the formation of the complex compound, the formation promoting effect of the complex compound is not observed. In addition to alkyl alcohols, phenols or those obtained by substituting hydrogen atoms of appropriate hydrocarbons having an ether bond in the molecule with OH groups can be used.

In an alcohol compound, strong polarity develops as the number of OH groups contained in one molecule increases, and in the present invention, glycols containing two OH groups and glycerin containing three OH groups are also present. Pentaerythritol containing 4 OH groups is preferably used.
Examples of such alcohol compounds include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, allyl alcohol, benzyl alcohol, pinacol, propylene glycol, menthol, catechol, hydroquinone, salicyl alcohol, pentaerythritol, sucrose, Examples thereof include glucose, xylitol, methoxyethanol, triethylene glycol monomethyl ether, pentaerythritol, and the like, and polyethylene glycols including ethylene glycol, triethylene glycol, tetraethylene glycol, and pentaethylene glycol.
Depending on the application of the coated silver fine particles to be produced, 2,2′-thiodiethanol, 3-thiopheneethanol, 2-thiopheneethanol, 3-thiophenemethanol, 2-thiophenemethanol, an alcohol compound containing a sulfur atom, Examples include α-thioglycerol and 2- (methylthio) ethanol. Moreover, dimethyl (hydroxymethyl) phosphonate, dimethyl (2-hydroxyethyl) phosphonate, etc. can be used as an alcohol compound containing a phosphorus atom. Furthermore, alcohol compounds such as 2- (trimethylsilyl) ethanol, 2- (trimethylsilyl) -1-propanol, and triethylsilanol containing silicon atoms can be used.

In addition, since some of the alcohol compounds used for the formation of complex compounds are contained in the reaction medium when the complex compounds and complex compounds are thermally decomposed, the complex compounds are used when the alcohol compound used has a high vapor pressure. When the coated silver fine particles are produced by heating, the alcohol compound evaporates and desorbs, making the production process of the coated silver fine particles unstable and reducing the yield of silver atoms recovered as coated silver fine particles. Arise.
Since the formation of coated silver fine particles by thermal decomposition of a complex compound is usually performed in the range of about 70 to 150 ° C., the alcohol compound used in the present invention is preferably one having a low vapor pressure in the temperature range. The In particular, when the production of coated silver fine particles under atmospheric pressure is taken into consideration, the influence of the vapor pressure of the alcohol compound tends to be large. Specifically, when the coated silver fine particles are produced through the intervention of methanol or the like having a low boiling point, there is a tendency that variations in characteristics among batches and a decrease in silver yield are likely to occur. For this reason, it is preferable that the alcohol compound used has a boiling point of 70 ° C. or higher, more preferably a boiling point of 80 ° C. or higher.

  It is also effective to reduce the vapor pressure of each alcohol compound by using a mixture of a plurality of alcohol compounds from the viewpoint of suppressing the evaporation of the alcohol compound during the complex compound formation reaction. It is also effective in terms of reducing vapor pressure to mix and use an appropriate amount of a substance having solubility in alcohol compounds to be used such as water, ketones and aldehydes.

The amount of the alcohol compound used in the method of the present invention is preferably about 5 mol% to 500 mol% with respect to the alkylamine used in the formation of the complex compound. When the amount of the alcohol compound used is 5 mol% or less with respect to the alkylamine, there is a tendency that the complex compound formation promoting action is not sufficient. On the other hand, when the amount of the alcohol compound used is 500 mol% or more with respect to the alkylamine, the activity of the alkylamine tends to be reduced and the formation of the complex compound tends to be inhibited.
In particular, when the amount of the alcohol compound used is about 10 mol% to 300 mol% with respect to the alkylamine, the formation of the complex compound is favorably promoted and a good complex compound can be produced. . Further, when the proportion of the alcohol compound is increased within this range, the formation time of the complex compound is generally shortened, and the proportion of the alcohol compound contained in the complex compound is increased, so that the coated silver generated by the thermal decomposition of the complex compound. As the particle diameter of the fine particles increases, the dispersibility of the resulting coated silver fine particles in a polar solvent can be improved. On the other hand, by decreasing the proportion of the alcohol compound, the alcohol compound contained in the complex compound or the coating of the coated silver fine particles is decreased, and a tendency to obtain coated silver fine particles having a fine and dense coating is observed.

  Most typically, the amount of the alcohol compound is preferably about 25 mol% to 100 mol% with respect to the alkylamine, but the type and proportion of the alcohol compound to be specifically used are the coated silver fine particles to be produced. It is preferable to adjust appropriately according to the characteristics required for the above.

In the present invention, when an alcohol compound is used in the formation of a complex compound of a silver compound and an alkylamine, the silver compound is added to a mixture in which the alkylamine and the alcohol compound are mixed in advance, and the alcohol compound is mixed with the silver compound. Then, after crushing or the like, an alkylamine may be added to form a complex compound, or a complex compound may be formed by adding an alcohol compound to a mixture of a silver compound and an alkylamine.
Furthermore, for the purpose of increasing the yield of coated silver fine particles or improving uniformity, a complex compound is formed by adding an alcohol compound to a mixture obtained by mixing a silver compound and an alkylamine to form a complex compound. You may process about the silver compound which has not completed reaction.

(Dispersion medium)
The coated silver fine particles produced by the method according to the present invention are mainly selected according to the use of alkylamine, depending on the application used, for example, polar solvents such as alcohol and ester solvents, and nonpolar such as octane. It can be used as a dispersion liquid dispersed at a high concentration in an appropriate organic solvent such as a solvent or a mixed solvent thereof. Moreover, it can be set as a paste-form composition. By using the coated silver fine particles produced by the method according to the present invention as a dispersion or paste, it can be preferably used as a material for forming a silver wiring particularly at a low temperature.
The organic solvent used in the case of dispersing the coated silver fine particles produced by the method according to the present invention to form a dispersion is one that hardly causes the elimination of alkylamines and the like contained in the protective film of the coated silver fine particles. Preferably used.

  Further, in order to improve the dispersibility of the coated silver fine particles in the dispersion medium, for example, a fatty acid such as oleic acid may be mixed with an alkylamine when forming a complex compound. The used oleic acid and the like is contained in the coating of the produced coated silver fine particles, and is particularly effective for improving dispersibility in a nonpolar solvent. In particular, it is effective to add an appropriate fatty acid when an amine mixture having a small average molecular weight of alkylamine is used, for example, by containing a large proportion of short-chain alkylamine. However, when an excessive amount of fatty acid is used, the desorption temperature of the protective film from the coated metal fine particles tends to increase, so the amount added is 5 mol with respect to the silver atoms contained in the reaction system. % Or less is desirable.

(Complex compound production process)
Formation of a complex compound of a silver compound and an alkylamine is generally performed by mixing a predetermined amount of an alkylamine with a powdery silver compound. In the present invention, the formation of a complex compound is promoted by interposing a predetermined alcohol compound in the reaction system. As a method of interposing the alcohol compound in the reaction system, a silver compound may be added to a mixture of an alkylamine and an alcohol compound prepared in advance, or the silver compound is mainly crushed by mixing the alcohol compound with the silver compound. Then, an appropriate method can be used such as adding an alkylamine to form a complex compound of a silver compound and an alkylamine.

  The formation process of a complex compound of a silver compound and an alkylamine is, for example, a mixture by reaction utilizing the fact that crystals of the silver compound etc. are crushed and the generated complex compound generally exhibits a color corresponding to its constituent components. By detecting the end of the color change by appropriate spectroscopy or the like, the end point of the complex compound formation reaction can be detected. In addition, the complex compound formed by silver oxalate, which is mainly used in the following examples, is generally colorless (white), but even in this case, the formation of the complex compound is based on the change in form such as the viscosity of the mixed solution is changed. The state can be detected.

  In the present invention, it is not always necessary to complete the formation of the complex compound before the thermal decomposition heating of the complex compound, and the coated silver fine particles are generated by appropriately heating in the complex compound formation process. be able to. On the other hand, from the viewpoint of increasing the ratio of recovering silver atoms contained in the silver compound as coated silver fine particles or generating coated silver fine particles with uniform characteristics, it is preferable to perform thermal decomposition after the formation of a good complex compound. .

  Formation of the complex compound is preferably performed in a temperature range in which generation of a decomposition reaction of the silver compound and evaporation of the alkylamine or alcohol compound can be suppressed. Typically, the complex compound can be produced by stirring at around room temperature, but it is also possible to heat the complex compound in a range that does not cause the decomposition reaction of the silver compound in terms of promoting the formation of the complex compound. . Moreover, since the coordination reaction of the amine with respect to the silver compound is accompanied by heat generation, it is also preferable to carry out stirring while cooling to room temperature or lower as necessary in order to suppress the decomposition reaction of the silver compound.

  In the formation of a complex compound of a silver compound and an alkylamine, it is desirable that the total amount of alkylamine to be used is greater than or equal to the stoichiometric amount (equal mole) of silver atoms contained in the silver compound. If the total amount of alkylamine is less than the stoichiometric amount with the silver atom, a silver compound that does not become a complex compound is generated, so that enlargement or subsequent thermal decomposition does not occur during the formation of silver fine particles. This is not preferable because a silver compound remaining in the substrate is generated. Typically, silver fine particles having a uniform particle diameter can be stably obtained by mixing an alkylamine having a molar amount of 2 times or more of silver atoms when a complex compound is formed. Also, if the amine is 5 times the molar amount of silver atoms or more, the density of silver atoms in the reaction system is reduced, the final yield of metallic silver is reduced and the environmental load is increased. It is preferable that the amount is not more than 5 times the molar amount of silver atoms.

(Process for thermal decomposition of complex compounds)
The complex compound of the silver compound and amine mixture produced | generated by the above is heated, a silver compound contained in a complex compound is decomposed | disassembled, a silver atom is liberated, and these are aggregated, A silver microparticle is formed. In the process of producing coated silver fine particles by such an amine complex decomposition method, atomic silver is supplied by a thermal decomposition reaction of a single component (complex compound) produced in advance. In comparison, it is presumed that unevenness of reaction due to fluctuations in the concentration of each component and the like hardly occurs, and silver fine particles having a uniform particle diameter can be produced stably. For this reason, the production of silver fine particles by the amine complex decomposition method is considered to be advantageous particularly in a large-scale industrial production process in which it is difficult to uniformly mix a plurality of components involved in the reaction.

When a silver compound complexed by coordination of alkylamine is released by thermal decomposition etc. under appropriate conditions to release atomic silver, the alkylamine is released with respect to the released atomic silver. It is inferred that the molecule maintains a coordinate bond via the amino group. For this reason, when free atomic silver aggregates with each other to form an aggregate, an alkyl chain fixed by a coordinate bond of an amino group is present at a high density around the aggregate to form a film. As a result, the resulting silver fine particles are prevented from growing beyond a predetermined size. As a result, in the coated silver fine particles produced by the amine complex decomposition method, fine silver nanoparticles with a uniform particle diameter are stabilized. It is assumed that it can be manufactured.
On the other hand, in the present invention, when an alcohol compound is interposed during the formation of the complex compound, a part of the silver compound is expected to form a complex compound with the alcohol compound. For this reason, by using an alcohol compound that coordinates to the silver compound with a weaker binding strength than an alkylamine, etc., when the complex compound is thermally decomposed, a part of the alcohol compound is detached and only silver atoms aggregate. As a result, it is considered that the average particle diameter of the produced coated silver fine particles can be increased.

  In the silver amine complex decomposition method, since there is a mechanism for making the size of the silver fine particles generated constant as described above, the generation of coarse particles is suppressed even in the presence of metallic silver atoms at a high density. As a result, it is possible to produce fine particles with less solvent and collect them as silver fine particles compared to the conventional method in which fine particles are produced by maintaining the density of metallic silver atoms in the reaction system low by dilution with a solvent. It is also possible to maintain the yield of metallic silver atoms at a very high rate of 95% or more.

  Such coated silver fine particles are preferably produced by heating the complex compound produced as described above in a reaction medium containing an alkylamine. That is, after an excess alkylamine or alcohol compound is mixed with the silver compound to form a complex compound, the remaining alkylamine or the like may be heated as it is as a reaction medium. It is also possible to further mix them as a reaction medium. Moreover, after separating the complex compound from the mixture containing the complex compound by a method such as centrifugation, the coated metal fine particles are produced by heating in a state of being remixed with a reaction medium containing an appropriate alkylamine or the like, It is also possible to produce coated silver fine particles by substituting a part of alkylamine or the like forming a complex compound with another alkylamine.

  The temperature at which atomic silver is liberated from the complex compound varies depending on the type of complex compound to be used, but in general, it is preferably carried out in a temperature range immediately above the temperature at which the liberation of the atomic silver starts. On the other hand, when excessive heating is performed, the coordination bond of the alkylamine to the silver is likely to be released, so that the coating of the coated silver fine particles to be generated becomes unstable and coarse particles are likely to be generated. . Further, from the viewpoint of active evaporation of alkylamine or the like constituting the reaction medium, the temperature at which atomic silver is liberated from the complex compound is preferably as low as possible within the range in which atomic silver is liberated. Specifically, it is preferable to decompose the silver compound contained in the complex compound by heating to a temperature range of 70 to 150 ° C., more typically 80 to 120 ° C.

In producing the coated silver fine particles produced according to the present invention, silver oxalate is preferably used as the silver compound. Silver oxalate usually decomposes at about 200 ° C., and oxalate ions are removed as carbon dioxide, leaving metallic silver. On the other hand, by forming a complex compound using an amine mixture containing a predetermined amount of an alkylamine and an alcohol compound by the method according to the present invention, thermal decomposition of oxalate ions occurs at a temperature of about 100 ° C. to release metallic silver. Can be possible. Similar to the above, this temperature is desirably set to a low temperature within a range that causes thermal decomposition of oxalate ions. However, since the rate of thermal decomposition increases as the temperature rises, good silver fine particles can be obtained. The heating temperature can be appropriately increased within the range.
The coated silver fine particles produced as described above are stored and used after being separated from an alkylamine or the like as a reaction medium, and then mixed with an appropriate dispersion medium or the like according to the application.

(Coated silver fine particles)
An example of the coated silver fine particles produced by the method of the present invention is shown in FIG. 1 (FIGS. 1-1 and 1-2). FIG. 1 shows silver fine particles coated with a protective film containing an alkylamine mixture prepared by the method described in the following examples. The coated silver fine particles produced according to the present invention can adjust the particle size of the silver fine particles in a range of about 5 to 500 nm by selecting the type of alcohol compound to be used. By covering the particle surface with a protective film containing an alkylamine having a thickness of several nanometers, each silver fine particle can exist independently and stably as shown in FIG.

  The coated silver fine particles produced as described above are used in an appropriate mode depending on the characteristics and applications. For example, when coated silver fine particles are applied in a predetermined shape by an ink jet or the like to form a silver film by low-temperature sintering, the amine used as a reaction medium is replaced with a desired organic solvent, whereby the coated silver fine particles are converted into an organic solvent. It is desirable to store and use in a state in which the coating of the coated silver fine particles is difficult to be removed by using an ink-like dispersion liquid dispersed therein. The coated silver fine particles can be mixed with an appropriate terpin oil or the like and used as a paste. Further, in the case of coated silver fine particles provided with a film mainly composed of a relatively long chain alkylamine, the coated silver fine particles can be stored as a powdery product from which the amine as a reaction medium has been removed.

(Conducted by sintering)
On the other hand, by heating the coated silver fine particles produced according to the present invention to an appropriate temperature, the alkylamine forming the protective film is eliminated and the silver fine particles are brought into direct contact with each other, thereby forming a conductor. Conductors can be formed even at temperatures below about the above. This is thought to be because the alkylamine that forms the protective film is weakly bonded to the surface of the silver fine particles due to the coordination bond via the amino group, and the alkylamine can be removed relatively easily. It is done.

(Substrate for forming a film containing coated silver fine particles and film forming method)
There are no particular limitations on the material and shape of the substrate applied to form the conductor film using the ink or paste containing the alkylamine-coated silver fine particles produced by the method of the present invention. For example, thermoplastic resin, thermosetting A material made of a conductive resin, glass, paper, metal, silicon, ceramics, or the like can be used. Examples of the thermoplastic resin include polyethylene, polyethylene terephthalate, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene copolymer resin, acrylonitrile-styrene copolymer resin, polycarbonate, polyacetal, polybutylene terephthalate, polyphenylene oxide, polyamide, Polyphenylene sulfide, polysulfone, polyethersulfone, polyether-etherketone, polyarylate, aromatic polyester, aromatic polyamide, fluororesin, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetate, polyvinyl formal, polyvinyl butyral, polymethyl methacrylate And cellulose acetate.

Examples of the thermosetting resin include phenol resin, urea resin, xylene resin, urea resin, melamine resin, epoxy resin, silicon resin, diallyl phthalate resin, furan resin, aniline resin, acetone-formaldehyde resin, alkyd resin, and the like. Can be mentioned. The ceramic means inorganic compounds such as oxides, carbides, nitrides, borides and the like. For example, alumina (Al ₂ O ₃ ), silicon nitride (SiN), silicon carbide (SiC), aluminum nitride (AlN) ), Zirconium boride (ZrB ₂ ), and the like.

  The process of forming a predetermined film or the like on the substrate using an ink containing coated silver fine particles is not particularly limited as long as it is a method capable of forming a film with a desired thickness. Spray coating or the like can be used. In particular, in the process of forming a pattern serving as a wiring precursor on a substrate with a film containing coated silver fine particles, various conventional printing methods can be used. For example, a screen printing method, an inkjet printing method, an intaglio Printing, letterpress printing, lithographic printing, and the like can be used. Moreover, the use of the metal film obtained by making a film containing coated silver fine particles into a conductor is not limited to electrical wiring, and can be used for mirror surfaces for optical devices, various decorations, and the like.

The thickness of the film formed on the substrate by the ink or paste containing the coated silver fine particles can be appropriately set according to the purpose of the metal film obtained by making the conductor. For ordinary electrical wiring, etc., a film is formed with the ink so as to be a metal film of about 1 μm or less, and with the paste so as to be a metal film of about 1 to 50 μm, and is made into a conductor. Thus, good characteristics can be obtained.
In addition, by utilizing the fact that the coated silver fine particles according to the present invention have a very large specific surface area, by dispersing an appropriate amount in water, it can be used as a bactericidal agent exhibiting a strong bactericidal action with a small amount of silver fine particles. Is also effective.
Further, since the silver surface of the coated silver fine particles produced by the method according to the present invention is very clean and exhibits a specific plasmon, it is also effective to use it as a coloring material utilizing this.

[Examples 1 to 15]
The coated silver fine particles according to Examples 1 to 15 were produced by the following method. As the silver compound, silver oxalate synthesized from silver nitrate (Kanto Chemical, first grade) and oxalic acid dihydrate (Kanto Chemical, special grade) was used. In each Example, 20.0 mmol (2%) of the various alcohol compounds shown in Table 1 and n-hexylamine (Tokyo Kasei, special grade) as an alkylamine with respect to 5.00 mmol (1.519 g) of silver oxalate. .024 g) and 0.23 mmol (0.065 g) of oleic acid (Tokyo Kasei,> 85.0%), which is a fatty acid, was mixed for the purpose of enhancing the dispersibility of the coated silver fine particles to be produced in an organic solvent. , Each was stirred at room temperature. In addition, about Examples 1-12 and 14, 14 mmol equivalent of each alcohol compound was mixed. About solid alcohol compounds, such as a phenol, silver oxalate was mixed with what was previously melt | dissolved in n-hexylamine. For Example 13, 1.32 g of polyethylene glycol having an average molecular weight of about 300 was mixed. In Example 15, 8 mmol of ethylene glycol and 10 mmol of water were mixed.

When the mixed solution was stirred, silver oxalate was dissolved and changed to a viscous white solution as a whole. Stirring was terminated when the change was observed to be apparently finished. A white viscous material obtained by mixing and stirring ethylene glycol and silver oxalate for 70 minutes at room temperature (system containing no oleic acid in Example 12) was subjected to infrared absorption by the diamond ATR method (Nicolet 6700 FT-IR spectrometer). When the spectrum was measured, the peak wave number of the C═O stretching vibration of the oxalate ion portion was shifted from 1562 in the case of the raw material silver oxalate to 1568 cm ⁻¹ . Also, the line width (half-value width) of the absorption band derived from the C = O stretching vibration was about half that of the raw material silver oxalate, and became sharper. This indicates that the alkylamine and alcohol act on (bond to) the silver oxalate to change its structure and electronic state. In the white viscous material, an infrared absorption spectrum derived from n-hexylamine and ethylene glycol is observed at the same time, and it is clear that the balance is a mixture of an alkylamine and an alcohol compound.

  The liquid mixture containing the complex compound obtained above was transferred to an aluminum block heating stirrer (Koike Seimitsu Seisakusho) and heated and stirred at a temperature setting of 110 ° C. Suspension in which fine particles exhibiting blue or green luster are suspended in a mixture containing alkylamine by stirring until the carbon dioxide generation proceeds with heating and stirring is completed. Got. In addition, about Example 1, the excess methanol was removed at 30 degreeC with the evaporator before heating to 110 degreeC.

Next, in order to replace the dispersion medium of this suspension, 10 mL of methanol (Kanto Kagaku, first grade) is added and stirred, and then the coated silver fine particles are precipitated and separated by centrifugation (2600 G). To the fine particles, 10 mL of methanol was added again, and stirring and centrifugation were performed to precipitate and separate the coated silver fine particles. The coated silver fine particles were mixed with 0.5 mL of a terpine dispersant Tersolve THA-70 (Nippon Terpine Chemical Co., Ltd.) and stirred to obtain a paste containing the coated silver fine particles.
The coated silver fine particles separated above are heated in a thermogravimetric analyzer (Shimadzu TGA-50) to completely remove the coated portion, thereby measuring the weight of metallic silver contained in each coated silver fine particle, The ratio with respect to the weight of the silver atom contained in the silver oxalate used in the manufacture was calculated | required, respectively. As a result, it was shown that 90% by weight or more of silver atoms were recovered as coated silver fine particles when any alcohol compound was used. Further, the silver content of the prepared paste was about 70% by weight.

[Evaluation result 1]
For the coated silver fine particles produced in Examples 1 to 15, the complex compound decomposes at the time required for the production of the complex compound at room temperature and the temperature setting of 110 ° C. to produce silver fine particles. Table 1 shows the time required to do this.

  As shown in Table 1, the alcohol compound or the like having solubility in water used in the Examples is interposed in the formation of a complex compound of silver oxalate and n-hexylamine, so that no alcohol compound or the like is used. Compared to the case (Comparative Example), the formation of complex compounds was promoted. In addition, in hexanol (6 carbon atoms) and octanol (8 carbon atoms), a part of silver oxalate remained even after 200 minutes of stirring, but in both cases, the amount of silver oxalate remaining is small compared to the comparative example. Was observed. In all cases, it was observed that the silver oxalate remaining in the process of heating the mixture for decomposition of the complex compound was crushed and disappeared.

  Moreover, in any Example, it was guessed that the time required for decomposition | disassembly of a complex compound was shortened compared with the comparative example, and silver oxalate was activated as a result of the production | generation of a complex compound being accelerated | stimulated. In particular, in Examples 12 to 15 using an alcohol compound having a plurality of OH, it was inferred that the complex compound was formed well because the complex compound formation time and the thermal decomposition time thereof were shortened.

[Evaluation result 2]
The coated silver fine particle paste produced in Examples 1 to 15 was diluted with octane, dropped onto a collodion film (copper mesh grid, for transmission electron microscope), washed with methanol, and observed with a scanning transmission electron microscope (STEM). (JEOL JSM-7600F Thermal Field Emission Scanning Electron Microscope) or Amorphous Carbon Support Film (Copper Mesh Grid, for Transmission Electron Microscope) and observed by Transmission Electron Microscope (TEM) (JEOL JEM-2100F Field Emission Electron The result of performing a microscope is shown in FIG. Table 2 shows the particle diameters estimated from the STEM image or TEM image thus measured.
All of the coated silver fine particles produced in Examples 1 to 15 had an average particle diameter of about 8 to 40 nm, and each was observed to exhibit a sharp particle size distribution.

[Evaluation result 3]
It shows in Table 2 about the result of having evaluated the sinterability at the time of apply | coating to the board | substrate and sintering the paste of the covering silver fine particle manufactured in the said Examples 1-15. Each paste was applied to a polyester film substrate (OHP sheet) by bar coating and baked at 100 ° C. for 3 hours and 20 hours, and then the sheet resistance value of the resulting silver coating was measured by the four-probe method (Kyowa). (RIKEN K-705RS). In addition, the volume resistance was calculated from the sheet resistance value of the silver coating subjected to baking for 20 hours in consideration of the film thickness of the silver coating after baking.

  As shown in Table 2, it was observed that those in which a complex compound was generated using an alcohol compound had a lower residual resistance in the sintered silver film than the comparative example in which no alcohol compound was used. In Examples 5 to 8 and 11, since many cracks were generated in the silver coating obtained by sintering the coated silver fine particles, it was difficult to measure the macro resistance value.

Claims (11)

A silver compound that can be decomposed by heating to form metallic silver, an alkylamine, and at least one alcohol compound having solubility in water are mixed to form a complex compound containing the silver compound and the alkylamine. 1 process,
And a second step of producing silver fine particles coated with a protective film containing an alkylamine by thermally decomposing the complex compound.   The method for producing coated silver fine particles according to claim 1, wherein at least one of the alcohol compounds has a solubility of 0.3 g / L or more in water at 20 ° C.   The method for producing coated silver fine particles according to claim 1 or 2, wherein at least one of the alcohol compounds has a boiling point of 70 ° C or higher.   The method for producing coated silver fine particles according to any one of claims 1 to 3, wherein at least one of the alcohol compounds is a polyhydric alcohol.   In the said 1st process, a fatty acid is further mixed, The manufacturing method of the covering silver fine particle as described in any one of Claims 1-4 characterized by the above-mentioned.   In the said 1st process, water is further mixed, The manufacturing method of the covering silver fine particle as described in any one of Claims 1-5 characterized by the above-mentioned.   The said silver compound has silver oxalate as a main component, The manufacturing method of the covering silver fine particle as described in any one of Claims 1-6 characterized by the above-mentioned.   Coated silver fine particles produced by the method according to any one of claims 1 to 7.   The coated silver fine particles according to claim 8, wherein the average particle size of the silver fine particles is larger than 30 nm.   A coated silver fine particle dispersion, wherein the coated silver fine particles according to claim 8 or 9 are dispersed in a dispersion medium. A coated silver fine particle-containing paste comprising the coated silver fine particles according to claim 8 or 9.