JP5975441B2 - 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 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. Yes. Taking advantage of these characteristics, silver fine particles are used as conductive ink and paste, and it 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. Yes.
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 generated uniformly due to minute fluctuations in the mixing ratio of each component. However, there was a problem that the obtained silver fine particles 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 was a problem that caused 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 technique for obtaining coated silver fine particles (“amine complex thermal decomposition method” or more simply “amine complex 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. It is difficult for non-uniformity to occur due to fluctuations in silver and it is easy to obtain silver fine particles having uniform characteristics. Moreover, generally an organic solvent etc. are not required and silver fine particles can be obtained even without 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 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 alkyl diamines and the like used mainly for the formation of complex compounds are also included in the coated silver fine particle coating, various properties of the coated silver fine particles will be affected. It is expected that there may be cases where it is desirable to substitute with other components.

  Therefore, 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 an alkylamine, a compound containing multiple bonds of carbon atoms and heteroatoms in the molecule and / or a compound containing multiple bonds between multiple heteroatoms in the molecule It has been found that the addition of the complex compound promotes the formation of the complex compound, and the complex compound can be efficiently produced in a short time.

  That is, the method for producing coated silver fine particles of the present invention comprises (1) a silver compound that can be decomposed by heating to produce metallic silver, (2) an alkylamine, and (3) a carbon atom and a heteroatom in the molecule. And a compound containing at least one of multiple bonds of heteroatoms or multiple bonds of heteroatoms to produce a complex compound containing the silver compound and alkylamine, and thermally decomposing the complex compound And a second step of producing silver fine particles coated with a protective film containing an alkylamine. The hetero atom is preferably an oxygen atom or a nitrogen atom, and is preferably a compound containing one or both of these. Further, the number of carbon atoms contained in the compound is more preferably 14 or less.

  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.

It is a transmission scanning electron microscope (STEM) image of a typical covering silver fine particle manufactured by the method of the present invention, or a scanning electron microscope (SEM) image. (A) Example 1, (b) Example 2, (c) Example 9, (d) Example 10, (e) Example 12 and (f) Coated silver fine particles produced by the method of Example 13 This is a STEM or SEM image. It is a transmission scanning electron microscope (STEM) image of a typical covering silver fine particle manufactured by the method of the present invention, or a scanning electron microscope (SEM) image. (G) Example 15, (h) Example 22, (i) Example 18, (j) Example 19, (k) Example 20 and (l) Coated silver fine particles produced by the method of Example 21 This is a STEM or SEM image. It is a transmission scanning electron microscope (STEM) image of the typical covering silver fine particle manufactured by the method of this invention. (M) STEM of coated silver fine particles produced by the method of Example 3. It is an electron microscope image (SEM image) which shows the surface structure of the film | membrane after sintering of the covering silver fine particle obtained by the method of Example 12. FIG.

  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. . In such an amine complex decomposition method, atomic metal silver is generated by a decomposition reaction of a silver amine complex that is a single kind of molecule, so that it is possible to generate atomic metal silver uniformly in the reaction system. Compared to the case where silver atoms are generated by reaction between a plurality of components, the reaction non-uniformity due to the composition fluctuation of the components constituting the reaction is suppressed, and a large amount of coated silver fine particles are produced especially on an industrial scale. This is advantageous when manufacturing.

  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 coated fine silver particles having an excellent 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 fine coated silver particles that 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, when a complex compound such as a complex compound is formed by mixing a solid silver compound and an alkylamine, carbon atoms and oxygen, nitrogen, sulfur, phosphorus in the molecule are formed. It has been clarified that the formation of a complex compound of a silver compound and an alkylamine proceeds smoothly by interposing a compound molecule containing multiple bonds with such heteroatoms or multiple heteroatoms.
The reason why the formation of the complex compound is promoted by such a compound is not necessarily clear, but in the case of heteroatoms such as oxygen and nitrogen bonded to carbon by multiple bonds, the unshared electron pair is exposed and is due to a single bond. It is known that it exhibits a strong polarity compared to the above, and this is considered to increase the tendency to form coordinate bonds with silver atoms in the silver compound. Even when multiple bonds between the same or different heteroatoms exist, the unshared electron pair of each atom is activated, and as a result, there is a tendency to form a coordinate bond with the silver atom in the silver compound. As a strong result, it is surmised that the solid silver compound is crushed to promote the formation of a complex compound with an alkylamine.

  In addition, for complex compounds formed by interposing compound molecules having multiple bonds, in the subsequent heating and decomposing step, it is shorter than complex compounds formed by mixing only silver compounds and alkylamines. Tend to complete the disassembly. 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 complex compounds formed in the presence of compound molecules having multiple bonds are forming macroscopic complex compounds as well as forming microscopically favorable complex compounds. .

Furthermore, in the coated silver fine particles produced according to the present invention, the properties such as the average particle size of the silver fine particles, the dispersibility in the solvent, and the sintering depending on the type of compound molecules added during the formation of the complex compound. It has been clarified that there is a significant difference in residual resistance at the time of contact. Therefore, the compound molecules used as the additive component are present in the coating portion of the complex compound to be produced and the coated silver fine particles, thereby affecting the production process of the coated silver fine particles and various kinds of the produced coated silver fine particles. It is presumed that this property is given.
Hereinafter, the method for producing coated silver fine particles according to the present invention and the coated silver fine particles produced by the production method will be specifically described.

(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 is advantageous in that it has a high silver content and is usually easily decomposed at a low temperature of 200 ° C. or lower, and oxalate ions are removed as carbon dioxide during the decomposition, so that metallic silver is obtained, so that impurities hardly remain. It is. 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 shall mean 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. It is preferably an amine RNH ₂ or an alkylamine RR′NH which is a secondary amino group. In the present specification, R and R ′ each independently represent a hydrocarbon group, and these hydrocarbon groups may contain a hetero atom such as an oxygen atom, a nitrogen atom, a sulfur atom or a silicon atom. . 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), Alkyl monoamines such as hexadecylamine (330 ° C.), oleylamine (349 ° C.), and octadecylamine (232 ° C. (32 mmHg)) are practical in terms of easy availability, but are not limited thereto. For other long-chain / medium-chain alkyl monoamines having a number of 6 or more, In response it can be used. Moreover, even if it will be a solid state at room temperature, if it liquefies by mixing with other components, such as the following additional component, it can be used in this invention.

  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 respect to 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, butylamine (78 ° C), diethylamine (55 ° C), propylamine (48 ° C). ), Isopropylamine (34 ° C.), ethylamine (17 ° C.), dimethylamine (7 ° C.) and the like are commercially available and are 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 alkyl amines, complex compounds formed by mixing alkyl amines constituting the coating of the produced silver fine particles with silver compounds, It is also possible to replace the alkylamine contained in the coating of the complex compound or the coated silver fine particles by mixing another type of alkylamine or the like with the coated silver fine particles. 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.

(Additional components for complex formation)
In the present invention, when forming a complex compound of a silver compound and an alkylamine, a silver compound is formed by interposing a compound containing multiple bonds of carbon atoms and heteroatoms, or multiple bonds of heteroatoms in the molecule. It has been clarified that the formation of complex compounds of alkylamines proceeds smoothly. In other words, when a compound containing the predetermined multiple bond is present, in the silver compound in the solid state, molecules or ions containing silver as the silver compound aggregate to form crystals, and particularly, long chain / medium chain Coordination to silver atoms by alkylamines and the like does not proceed well, but when the compound is mixed with alkylamines, coordination bonds to silver compounds by alkylamines and the like progress. It became clear by this invention that a complex compound produces | generates efficiently. Such an effect is considered to be due to the fact that the compound efficiently disintegrates crystals of the silver compound and the like, and the frequency with which the alkylamine or the like contacts the silver compound is increased. In order to further enhance such effects, the compound containing the predetermined multiple bond is preferably a solvent excellent in compatibility with alkylamine.

  The compound used in the present invention may be a compound containing multiple bonds of carbon atoms and heteroatoms or multiple bonds of heteroatoms in the molecule. In such compounds, the distribution of electrons related to the bonds belonging to the heteroatoms that form multiple bonds is biased by the multiple bonds, and the unshared electron pairs of the heteroatoms tend to be exposed. It is known that activity for reactions involving electron pairs tends to improve. In the present invention, the specific reason why the formation of the complex compound is promoted by interposing the compound having the predetermined multiple bond when forming the complex compound of the silver compound and the alkylamine is not clear. It is speculated that the inclusion of a hetero atom having an active unshared electron pair as described above is related to the promotion of the formation of a complex compound.

  More specifically, as the compound used in the present invention, a carbonyl compound or isocyanate compound containing a double bond of carbon and oxygen, an oxime compound containing a multiple bond of carbon and nitrogen, a Schiff base compound or a nitrile compound And nitro compounds and nitroso compounds containing multiple bonds of oxygen and nitrogen, and azo compounds, diazo compounds and azides containing multiple bonds of nitrogen atoms. A complex compound of a silver compound and an alkylamine can also be promoted by a compound containing a multiple bond related to sulfur, phosphorus or the like as a hetero atom. However, for example, in the production of silver fine particles used to form conductive wiring, since the sulfur atoms and phosphorus atoms tend to be adversely affected, the use of the produced silver fine particles It is desirable to consider use accordingly.

  In addition, for the compounds used in the present invention, the action of promoting the formation of complex compounds tends to decrease as the number of carbons contained in the compound and the number of carbons contained in each functional group in the compound increase. Is observed. The effect of the number of carbons on the action of promoting the formation of complex compounds varies depending on the basic structure of the compound. For example, in a compound having one multiple bond, the number of carbons contained in the compound generally exceeds 14. There is a tendency for the effect of promoting the formation of complex compounds to decrease. On the other hand, when the number of carbon atoms contained in the compound is 7 or less, generally a remarkable effect of promoting the formation of complex compounds is observed.

Taking advantage of such characteristics, as a preferred embodiment of the present invention, the complex compound can be obtained by interposing such a compound when producing coated silver fine particles mainly using a long-chain / medium-chain alkylamine. Generation can be assisted and promoted.
In addition, since the compound containing a predetermined multiple bond used in the present invention is also included in the complex compound to be produced and the coated portion of the coated silver fine particles obtained by pyrolyzing it, various compounds are used in the present invention. Various functions can be added to the produced coated silver fine particles by appropriately selecting and using them. For this reason, even when a short-chain alkylamine or alkyldiamine is present, the compound can be interposed as a means for imparting predetermined characteristics to the coated silver fine particles to be produced, together with the aid of complex compound formation.

As an example of a carbonyl compound as a compound that is used in the present invention in the formation of a complex compound of a silver compound and an alkylamine, a ketone compound can be mentioned.
Ketone compounds have the formula (I):

Wherein R ¹ and R ² are each an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an alkylamino group, a hydroxylamino group, or an aryl group optionally having a substituent ( Aromatic monovalent mono- or polycarbocyclic groups, preferably phenyl groups or naphthyl groups). R ¹ and R ² may be combined to form a ring. In particular, the alkyl group in the present invention is a saturated aliphatic group consisting of a branched or straight chain of 1 to 10 carbon atoms (C _1-10 ), preferably 1 to 6 carbon atoms (C _1-6 ). A hydrocarbon group, preferably a group such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, isobutyl, t-butyl, n-pentyl, 3-methylbutyl, n-hexyl, 2-ethylbutyl, etc. Selected. The alkyl group may be partially substituted with a halogen in some cases.

In the present invention, the alkenyl group and alkynyl group each have 2 to 10 carbon atoms (C _2-10 ) having 1 carbon-carbon double bond or triple bond as an unsaturated bond, preferably 2 Vinyl, ethynyl, 1-propenyl, 2-propenyl, 1-propynyl, 2-propynyl or 2-butenyl, which are unsubstituted or substituted hydrocarbon chain groups consisting of ˜6 carbon atoms (C _2-6 ) (Crotyl), 2-butynyl and the like are preferably used. In addition, hydrocarbon chain groups containing two or more unsaturated bonds (double bonds or triple bonds), alkoxy groups, alkylamino groups, etc. are also those having a lower carbon number of about 6 or less. Preferably used.

  Non-limiting examples of such ketone compounds include acetone, methyl ethyl ketone, acetylacetone, 2-butanone, 3-pentanone, 4-heptanone, 4-methyl-3-penten-2-one (mesityl oxide), 4 -Methyl-2-pentanone, diacetyl, pinacholine, 2,4-dimethylpentanone, 2,6-dimethyl-3-heptanone, isoamylmethylketone, 3-methyl-2-butanone, 5-methyl-heptanone, 4-methyl Aliphatic ketones such as 2-pentanone, ethynyl isopropyl ketone, 2-octanone, cyclopentanone, cyclohexanone, 2-cyclohexenone, isophorone, dicyclohexyl ketone, and the like, and acetophenone, benzophenone, 4-phenyl -2-butanone, isobutyrofe Emissions, benzal acetone, and aromatic ketones such as propiophenone.

  Further, as ketone compounds, methyl acetoacetate, ethyl acetoacetate, dimethyl acetylsuccinate, α-acetyl-γ-butyrolactone, acetoacetate, methyl pyruvate, pyruvate, N, N-dimethylacetoacetamide, acetoacetanilide, Examples thereof include keto acid compounds containing an oxygen atom such as N-acetoacetylmorpholine.

Moreover, as an example of the carbonyl compound used in the production of the complex compound in the present invention, an aldehyde compound represented by the formula (II) in which one hydrogen atom is bonded to the carbonyl carbon can be exemplified.
Formula (II):

Here, R ¹ may be a hydrogen atom as defined above. Non-limiting examples of aldehyde compounds suitable for use in the method of the present invention include propionaldehyde, n-butyraldehyde, isobutyraldehyde, n-pentylaldehyde, 2-methylbutyraldehyde, n-hexylaldehyde, 2 -Methylpentanal, n-heptylaldehyde, 2-hexenal, n-octylaldehyde, benzaldehyde, cuminaldehyde, anisaldehyde, chlorobenzaldehyde, cinnamaldehyde, crotonaldehyde, isobutyraldehyde, butyraldehyde, pyruvaldehyde, terephthalaldehyde, tolualdehyde , Ethynyl phenyl ketone, furfural, or a mixture of any two or more thereof. Particularly preferred aldehyde compounds are those having 3 to 14 carbon atoms. An aliphatic or aromatic aldehyde, more preferably, the number of carbon atoms is an aliphatic aldehyde 3-7.

By forming a complex compound of a silver compound and an alkylamine via a ketone compound or an aldehyde compound, it is observed that the formation of the complex compound is completed in a very short time, typically 10 minutes or less. . It is also observed that the complex compound formed in the presence of a ketone compound or an aldehyde compound is thermally decomposed in a short time to produce fine coated silver fine particles having an average particle diameter of about 10 nm. The silver compound used in the present invention is generally activated by the formation of a good complex compound, the structure of the silver compound becomes unstable, and it tends to rapidly decompose even at temperatures below the original thermal decomposition temperature. It is inferred that a complex compound that is microscopically good is produced by the intervention of a ketone compound or an aldehyde compound.
Furthermore, coated silver fine particles produced by thermal decomposition of complex compounds formed in the presence of ketone compounds and aldehyde compounds generally tend to disperse in organic solvents at a high rate. This is effective when dispersed in a solvent to form ink.

As an example of a carbonyl compound as a compound used in the present invention in the formation of a complex compound of a silver compound and an alkylamine, the compound of formula (III):

The ester compound shown by these can be mentioned. The ester compound in this specification means a carboxylic acid ester represented by the formula (III), wherein R ¹ and R ² are as defined above. Non-limiting examples of ester compounds suitable for use in the method of the present invention include ethyl acetate, propylene carbonate, ethyl and methyl benzoate, ethyl p-methoxybenzoate, methyl p-ethoxybenzoate, ethyl p-ethoxybenzoate. , Ethyl acrylate, methyl methacrylate, ethyl acetate, ethyl p-chlorobenzoate, hexyl p-aminobenzoate, isopropyl naphthalate, n-amyl toluate, ethyl cyclohexanoate, and propyl pivalate.

  By interposing an ester compound in which an oxygen atom is bonded to carbonyl carbon, it is possible to shorten the time for forming a complex compound and to produce coated silver fine particles having excellent sinterability. On the other hand, when compared with a ketone compound or an aldehyde compound in which an alkyl group or hydrogen is bonded to the carbonyl carbon, there is a tendency that it takes time to form a complex compound when an ester compound is used. This is presumably because the activity of the carbonyl oxygen decreases due to the bonding of the oxygen atom to the carbonyl carbon.

An example of a carbonyl compound as a compound that is used in the formation of a complex compound of a silver compound and an alkylamine in the present invention is an amide compound in which a nitrogen atom is bonded to a carbonyl carbon. Is the formula (IV):

The carboxylic acid amide compound shown by these is mentioned. In the formula (IV), R ¹ , R ² and R ³ may be a hydrogen atom and an amino group in addition to those defined above for R ¹ and R ² , respectively. R ¹ and R ² , R ¹ and R ³ , and R ² and R ³ may be combined to form a ring, and at least one of ammonia, primary amine, and secondary amine And cyclic lactam compounds obtained by dehydration condensation of carboxylic acid and linear carboxylic acid amide compounds. Examples of the linear carboxylic acid amide compound include formamide, acetamide, dimethylformamide, diethylformamide, N-methylformamide, N-ethylformamide, N- (2-hydroxyethyl) formamide, dimethylacetamide, and the like. The cyclic lactam compounds include 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-propylpyrrolidone, 5-methyl-2-pyrrolidone, 5-ethyl-2-pyrrolidone, 5-propyl-2- Examples include pyrrolidone and γ-butyrocaprolactam.

In the formula (IV), a carbamide compound in which R ³ is an amino group or an alkylamino group can be used. The carbamide compounds include, but are not limited to, urea, uric acid, tetramethylcarbamide and dimethylimidazolidinone, and can be used in the present invention. Other examples include imide compounds in which two carbonyl groups are bonded to primary amine or ammonia. By interposing an amide compound in which a nitrogen atom is bonded to carbonyl carbon, it is possible to shorten the complex compound formation time and to produce coated silver fine particles suitable for use as a paste agent. In particular, by using coated silver fine particles produced by using urea (carbamide compounds) or 2-pyrrolidone (lactam compounds), a paste agent having a very low resistance drop after printing and having a low residual resistance is obtained. It becomes possible.

  Furthermore, by using an isocyanate compound (RN—C═O) having a double bond between a carbon atom and a nitrogen atom together with a double bond between a carbon atom and an oxygen atom in one molecule, the reaction time can be shortened. A complex compound of a silver compound and an alkylamine can be formed. Isocyanate compounds preferably used in the method of the present invention include methyl isocyanate, butyl isocyanate, hexyl isocyanate, 4-chlorophenyl isocyanate, phenyl isocyanate, cyclohexyl isocyanate, hexamethylene diisocyanate, octadecyl isocyanate. Although it is included, it is not limited to these, It can be used. A cyanate compound (R—O—C≡N), which is an analog of an isocyanate compound, can be used in the same manner.

Examples of the compound containing multiple bonds of carbon and nitrogen that can be used in the present invention include oxime compounds and nitrile compounds.
An oxime compound is an organic compound having a structure represented by the general formula (> C═N—OH), a ketoxime in which two organic groups are bonded to a carbon atom that forms a double bond with nitrogen, and An aldoxime in which one organic group is replaced with hydrogen is typically mentioned.
Suitable oxime compounds for use in the method of the present invention include isobutyl methyl ketoxime, dimethylglyoxime, cyclohexanone oxime, methyl ethyl ketoxime, acetoxime, acetaldehyde oxime and the like. Furthermore, a Schiff base in which the hydroxyl group (OH) of> C = N—OH is substituted with an organic group can be used.

  The nitrile compound is a compound in which an alkyl group or the like is bonded to a cyano group (—CN) composed of a carbon atom and a nitrogen atom, and for example, acetonitrile, butyronitrile, acrylonitrile, benzonitrile and the like can be preferably used. Since a triple bond exists between the carbon atom forming the cyano group and the nitrogen atom, it is considered that this exposes the non-co-electron pair possessed by the nitrogen atom and exhibits high activity. Further, as a similar compound, an isonitrile compound having an isocyano group (—NC) can be used. Examples of the isonitrile compound include cyclohexyl isonitrile and benzyl isonitrile.

In the present invention, as a compound intervening in the formation of a complex compound of a silver compound and an alkylamine, in addition to the above compound containing a multiple bond between a carbon atom and an oxygen atom or nitrogen atom which is a heteroatom, a heteroatom A compound containing a moiety having a multiple bond between them can be used effectively.
Examples of compounds having multiple bonds between heteroatoms include nitro compounds and nitroso compounds containing multiple bonds between oxygen and nitrogen atoms. A nitro compound is a compound in which an alkyl group or the like is bonded to a nitro group (—NO ₂ ), and a nitroso compound is an organic compound in which an alkyl group or the like is bonded to a nitroso group (—NO). As such a compound containing a multiple bond between an oxygen atom and a nitrogen atom, nitromethane, nitroethane, nitrobenzene, nitrosobenzene and the like can be preferably used.

Examples of other compounds having multiple bonds between heteroatoms include azo compounds, diazo compounds, and azides containing multiple bonds between nitrogen atoms. An azo compound is an azo group (—N═N—) in which an alkyl group, a phenyl group, or the like is bonded, and a diazo compound is a diazo group (—N ₂ ), in which an alkyl group, a phenyl group, or the like is bonded. is there. An azide is a compound in which an alkyl group, a phenyl group, or the like is bonded to an azide group (—N ₃ ), and examples thereof include methyl azide, ethyl azide, and diphenyl phosphate azide.

  The compound containing a predetermined multiple bond as described above can be appropriately selected and used according to the type of alkylamine to be used, characteristics expected of the coated silver fine particles to be produced, and the like. In addition, it is possible to use a combination of a plurality of compounds, and it is possible to combine not only the reaction time for complex formation, but also the type of alkylamine and the silver yield and the dispersibility of the coated silver fine particles. is there.

  As shown in the examples below, depending on the functional group and structure contained in the compound containing a predetermined multiple bond used in the present invention, the degree to promote the formation of a complex compound of a silver compound and an alkylamine is generated. Although there is a difference in the properties of the complex compound and the coated silver fine particles, generally, as the molecular weight increases, the formation promoting action of the complex compound of the silver compound and the alkylamine tends to decrease. For this reason, as the carbonyl compound, oxime compound, nitrile compound, etc., a compound having 14 or less carbon atoms in each compound is preferable, a compound having 10 or less carbon atoms is more preferable, and still more preferable. Is a compound having 6 to 8 carbon atoms, and most preferably a compound having 7 or less carbon atoms.

On the other hand, some of the compounds used to form complex compounds are contained in the complex compound and the reaction medium used when thermally decomposing the complex compounds, so if the vapor pressure of the compound used is high, the complex compound is heated. Thus, when the coated silver fine particles are produced, the compound evaporates and desorbs, thereby destabilizing the production process of the coated silver fine particles and causing a problem of reducing the yield of silver atoms recovered as the coated silver fine particles.
Since the production 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 compound added at the time of formation of the complex compound in the present invention has a vapor pressure in the temperature range. Low ones are preferably used. For this reason, it is preferable to use a compound having a boiling point of 70 ° C. or higher, more preferably a boiling point of 80 ° C. or higher.

  For example, when acetone having a low boiling point or the like is used, it tends to evaporate during mixing with the silver compound or the decomposition process of the complex compound tends to become unstable. Therefore, when using a compound having a low boiling point, the vapor pressure is suppressed by combining with other ketone compounds, aldehyde compounds, carboxylic acid amide compounds or esters such as acetylacetone, propionaldehyde or propylene carbonate. Are preferably used.

  The amount of the compound containing a predetermined multiple bond used in the present invention is 5 mol% to 500 mol% with respect to the alkylamine as long as it can form a uniform mixture with the alkylamine used in the formation of the complex compound. It is preferable to set the degree. When the amount of the compound used is 5 mol% or less with respect to the alkylamine, the effect of promoting the formation of complex compounds tends to be insufficient. On the other hand, when the amount of the compound used is 500 mol% or more with respect to the alkylamine, the activity of the alkylamine tends to decrease, and the formation of complex compounds tends to be inhibited. Typically, when the amount of the compound used is about 10 mol% to 300 mol% with respect to the alkylamine, the formation of a complex compound can be promoted well, and a good complex compound can be produced. It becomes possible. On the other hand, it is preferable that the amount of the compound is about 25 mol% to 100 mol% with respect to the alkylamine from the viewpoint of achieving both the production efficiency of the complex compound and the properties of the coated portion of the coated silver fine particles. It is preferable that the type and use ratio of the compound used in the above are appropriately adjusted according to the characteristics required for the coated silver fine particles to be produced.

In the present invention, when a compound containing a predetermined multiple bond 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 compound are mixed in advance. The compound may be mixed and crushed to add an alkylamine to form a complex compound, or a complex compound may be formed by adding the compound to a mixture of a silver compound and an alkylamine. Good.
Furthermore, for the purpose of increasing the yield of coated silver fine particles or improving uniformity, the compound is added to the mixture in which the complex compound is formed by mixing the silver compound and the alkylamine, thereby generating a complex compound. You may perform the process about the silver compound which has not completed reaction.

(Dispersant)
The coated silver fine particles produced as described above have a high concentration in an appropriate organic solvent such as an alcohol solvent such as butanol, a nonpolar solvent such as octane, or a mixed solvent thereof, depending on the selection of the alkylamine used. It can be stably dispersed and can be used as an ink by being dispersed in an organic solvent according to the purpose of use. As the organic solvent to be used, an organic solvent that does not cause detachment of alkylamine or the like contained in the protective film of the coated silver fine particles and evaporates relatively quickly when the dispersion is applied is preferably used. As a dispersant for improving the dispersibility of the coated silver fine particles to be produced in the dispersion medium, for example, a fatty acid such as oleic acid may be mixed with the amine mixture and used. 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 with respect to the metallic silver atoms contained in the reaction system. It is desirable to make it mol% or less.

(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 compound containing a predetermined multiple bond in the reaction system. As a method of interposing the compound in the reaction system, a silver compound may be added to a mixture of the alkylamine and the compound prepared in advance, or the compound is mainly mixed with the silver compound to crush 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. In addition, water, various alcohols, organic solvents, and the like can be further mixed and used in the reaction system for generating the complex compound without departing from the spirit of the present invention.

  The formation process of the complex compound of the silver compound and the alkylamine is, for example, based on the reaction by utilizing the fact that the complex compound to be formed generally exhibits a color corresponding to its constituent components while the crystal of the silver compound is crushed. By detecting the end of the color change of the mixture 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 alkylamine or the like 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 alkylamine with respect to a silver compound is accompanied by heat_generation | fever, in order to suppress the decomposition reaction etc. of a silver compound, it is also preferable to cool and stir as needed.

  In the formation of a complex compound of a silver compound and an alkylamine or the like, it is desirable that the total amount of alkylamine used is greater than the stoichiometric amount with the metal silver atoms contained in the silver compound. If the total amount of alkylamine is less than the stoichiometric amount with the metallic silver atom, a silver compound that does not become a complex compound is generated, so that subsequent enlargement of silver fine particles may occur or thermal decomposition may occur. This is not preferable because a silver compound remaining without being generated 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. In addition, when the alkylamine is more than 5 times the molar amount of silver atoms, the density of silver atoms in the reaction system decreases, the final yield of metal silver recovery decreases and the environmental load increases. The amount is preferably not more than 5 times the molar amount of silver atoms.

(Process for thermal decomposition of complex compounds)
The silver compound produced | generated by the above and the complex compound of alkylamine etc. are heated, the metal silver atom in a silver compound is liberated, and these silver aggregate, and thereby silver fine particles are formed. In the process of producing coated silver fine particles by such a silver amine complex decomposition method, atomic silver is supplied by the thermal decomposition reaction of a single component (complex compound) produced in advance. Compared to the above, it is presumed that unevenness of reaction due to fluctuations in the concentration of each component and the like is less likely to occur, 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.

In addition, when atomic silver is liberated by subjecting a silver compound complexed by coordination of alkylamine to heat decomposition under appropriate conditions, etc., It is presumed that the alkylamine molecule maintains the coordination 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 generated 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 fine particles having a uniform particle diameter are stably formed. It is assumed that it can be manufactured.
On the other hand, according to the method of the present invention, it is also possible to control the size and particle size distribution of the silver fine particles to be generated by selecting the kind of compound having a predetermined multiple bond. Although this mechanism is not necessarily clear, there is a possibility that the strength of the coordinate bond with the silver atom is affected by the interaction of the compound with an alkylamine which is a protective molecule.

  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 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 the like 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, and an appropriate alkylamine or the like may be added as necessary. Further, it can be mixed to make a reaction medium. Further, after separating the complex compound from the mixture containing the complex compound by a method such as centrifugation, a part of the amine that forms the complex compound is mixed with another reaction medium containing an appropriate alkylamine by other mixing. It is also possible to produce coated silver fine particles by substituting with amines.

  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, a complex compound using an amine mixture containing a predetermined amount of an alkylamine and a compound containing a predetermined multiple bond by the method according to the present invention causes thermal decomposition of oxalate ions at a temperature of about 100 ° C. Thus, metallic silver can be released. 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. FIG. 1 shows silver fine particles coated with a protective film containing an alkylamine produced by the method described in the following examples. In the coated silver fine particles, the particle size of the silver fine particles is about 5 to 500 nm, and the particle size can be adjusted by selecting the kind of the compound containing a predetermined multiple bond 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 the photograph.

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.
Further, as shown in the following examples, in the coated silver fine particles obtained by thermally decomposing a complex compound formed by interposing a compound containing a predetermined multiple bond by the method of the present invention, the kind of compound to be used Depending on the above, characteristics as coated silver fine particles such as dispersibility in an organic solvent and the like and residual resistance after firing change. This is presumed to suggest that the compound used or its derivative is included in the coated portion of the coated silver fine particles together with the alkylamine.

(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 or the like forming the protective film is weakly bonded to the surface of the silver fine particles by the coordinate bond via the amino group and can be removed relatively easily by heating. 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 step of forming a predetermined film or the like on the substrate using 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, and a general spin coat, bar coat or spray Application or the like can be used. In particular, the process of forming a pattern serving as a wiring precursor on a substrate with a film containing coated silver fine particles can use various conventional printing methods, such as screen printing, inkjet printing, 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, in a color material using this, a solar cell, etc., a photoelectric conversion efficiency enhancer It is also effective to use as

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the method for producing coated silver fine particles according to the present invention, but the present invention is not limited to the following examples.

[Examples 1 to 25]
The coated silver fine particles according to Examples 1 to 25 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 each of the compounds described in Table 1 and n-hexylamine (Tokyo Kasei, special grade) as an alkylamine was added to 5.00 mmol (1.519 g) of silver oxalate. , 2, 4-25], or n-octylamine (Tokyo Kasei, special grade) for 20.0 mmol [Example 3] and for the purpose of enhancing the dispersibility of the coated silver fine particles to be produced in an organic solvent, Oleic acid (Tokyo Kasei,> 85.0%), 0.065 g (0.23 mmol), which is a fatty acid, was mixed and stirred at room temperature. Moreover, as a comparative example, only silver oxalate, n-hexylamine and oleic acid in the same amount as above were mixed and stirred at room temperature. In addition, about Examples 1-21, 10 mmol equivalent of each compound was mixed. About Examples 22-25, 5 mmol each was mixed and used about 2 types of compounds.

In any of Examples 1 to 25 and Comparative Example, the mixed solution containing silver oxalate was changed to a viscous solution during stirring, and stirring was performed at the time when it was recognized that the change was apparently finished. finished. Table 1 shows the time during which the stirring was performed when each compound was added as the complex compound formation time.
When an infrared absorption spectrum of the white viscous material obtained above was measured by the diamond ATR method (Nicolet 6700 FT-IR spectrometer), the C = O stretching in the oxalate ion was observed when any compound was added. It is observed that the peak wave number of absorption derived from vibration shifts to the higher wave number side, and the line width (half width) of the absorption band is about half that of the raw material silver oxalate. This is because, as described above, silver oxalate and alkylamine etc. are mixed and stirred, so that alkylamine and the like produce coordinate bonds while maintaining the skeleton of silver oxalate. This shows that the electronic state of the has changed.

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 silver fine particles exhibiting blue or green luster are suspended in a mixture containing an alkylamine by stirring until the carbon dioxide generation proceeds with heating and stirring until carbon dioxide generation is completed. A liquid was obtained. In Examples using a compound having a high vapor pressure, the high vapor pressure component was removed by an evaporator at 30 ° C. before heating to 110 ° C. Table 1 shows the time until the generation of carbon dioxide is completed when each compound is added as the decomposition time of the complex compound.
Next, 10 mL of methanol (Kanto Kagaku, first grade) was added to this suspension and stirred, and then silver fine particles were precipitated and separated by centrifugation (2600 G), and 10 mL of methanol was added again to the separated silver fine particles, By stirring and centrifuging, silver fine particles were precipitated and separated to obtain paste-like coated silver fine particles.

(Evaluation of silver yield)
The obtained coated silver fine particles are heated in a thermogravimetric analyzer (Shimadzu TGA-50) to completely remove the coated portion of the coated silver fine particles, whereby the metallic silver contained in each coated silver fine particle The weight of was measured. As a result, it was shown that 95% or more of silver atoms contained in the silver oxalate used as a raw material were recovered as coated silver fine particles for the coated silver fine particles produced under any conditions.

(Evaluation of particle diameter of coated silver fine particles)
The coated silver fine particles produced in Examples 1 to 25 and Comparative Example 1 were dispersed in octane, and the dispersion was dropped onto a collodion film (copper mesh grid, for transmission electron microscope), washed with methanol, and then transmitted and scanned. The results of (STEM) or scanning electron microscope (SEM) observation (JEOL JSM-7600F thermal field emission scanning electron microscope) are shown in FIG. Table 2 shows the particle diameter estimated from the observed STEM image or SEM image.

(Evaluation of dispersibility in solvent)
The dispersibility of each coated silver fine particle obtained above in a solvent was evaluated as follows. That is, 3 mL of a mixed solvent (volume ratio 1: 4) of butanol (Kanto Chemical Co., Ltd.) and octane (Gordo) was added to the total amount of each paste-like coated silver fine particle obtained above, and the mixture was further centrifuged. Separation was performed to precipitate and remove particulate components having poor dispersibility to obtain a saturated dispersion, and the dispersibility in the solvent was evaluated by evaluating the amount of silver fine particles therein. The amount of the mixed solvent is an amount corresponding to the amount that can be dispersed in the coated silver fine particles having the most excellent dispersibility.

As a result of the above evaluation, it was shown that the dispersibility of the produced coated silver fine particles in the mixed solvent varies depending on the kind of the compound added at the time of complex formation of silver oxalate and alkylamine. In other words, almost all of the coated silver fine particles having excellent dispersibility were independently dispersed in the mixed solvent, and a dispersion having a deep yellow-orange color as a whole was obtained. On the other hand, depending on the type of the added component, the degree of coloration of the solvent was low and a clear precipitate was observed.
Of the dispersions obtained above, those that showed relatively good dispersibility were heated in a thermogravimetric analyzer (Shimadzu TGA-50) after removing the precipitate, and mixed with the mixed solvent. By completely removing the coated portion of the silver fine particles, the weight of the metallic silver contained in the dispersion was measured, and the weight ratio of silver fine particles in each dispersion (saturated dispersion amount, expressed as wt%) was obtained. The results are shown in Table 1. As shown in Table 1, in the dispersion in which almost all of the coated silver fine particles were dispersed, it was shown that the silver fine particles were dispersed at a high ratio of 30% by weight or more in the dispersion.

(Sinterability evaluation)
The sinterability of each coated silver fine particle obtained above was evaluated as follows. In other words, according to the above evaluation of dispersibility, for coated silver fine particles that can be dispersed in a mixed solvent at a ratio of approximately 15% by weight or more of silver fine particles, the sinterability using a saturated dispersion liquid in the mixed solvent as ink. Was evaluated. For coated silver fine particles for which a high-concentration dispersion cannot be obtained, the terpine dispersant Tersolve THA-70 (Nippon Terpine Chemical Co., Ltd.) is used instead of the above mixed solvent so that the weight ratio of the silver fine particles is about 65% by weight. Co., Ltd.) 0.5 mL was added and stirred to make a paste containing silver fine particles, and the sinterability was evaluated.

The evaluation of sinterability is carried out by applying each dispersion and each paste to a polyester film substrate (OHP sheet) by spin coating in the case of each dispersion (ink) and by barcode in the case of paste. After baking at 20 ° C. for 3 hours or 20 hours, the sheet resistance of the silver coating formed by baking the coated silver fine particles was measured by the four probe method (Kyowa Riken K-705RS). Moreover, the film thickness of each silver film was measured with the film thickness meter, and the volume resistance of the silver film obtained by baking for 20 hours was calculated | required using the value.
Table 2 shows the sheet resistance, volume resistance, and average film thickness measured above for the coated silver fine particles produced in Examples 1 to 25 and Comparative Example.

  As shown in Tables 1 and 2, ketone compounds (Examples 1 to 8) and aldehydes contained in the carbonyl compound when a complex compound of silver oxalate and n-hexylamine or n-octylamine is formed. When the compounds (Examples 9 to 11) are added, both the complex compound formation time and the decomposition time thereof are remarkably shortened, and the average particle diameter of the coated silver fine particles is as small as about 10 nm. The produced coated silver fine particles were dispersible at high density in the mixed solvent used.

On the other hand, when a compound having an amide moiety in the molecule (Examples 12 to 15) among the carbonyl compounds is added, it takes a longer time to generate and decompose the complex compound than the ketones and aldehydes. In addition, there was a tendency to obtain coated silver fine particles suitable for use as a paste in terms of dispersibility in a mixed solvent.
When urea (Example 12) or 2-pyrrolidone (Example 15), which is a kind of compound having an amide moiety, is used, the average particle size is relatively large as the particle size distribution of the coated silver fine particles to be produced. A mixture of small particles (about 10 to 20 nm) and relatively large particles (about 30 to 100 nm) was obtained ((e) and (g) in FIG. 1). When a paste containing these coated silver fine particles was applied to the substrate, it was revealed that the electrical resistance rapidly decreased and the residual resistance after firing for a long time was also low. In FIG. 2, the electron microscope image (SEM image) which shows the surface of a silver film after sintering the covering silver fine particle obtained in Example 12 is shown.

  Such a phenomenon does not depend on the particle diameter of the coated silver fine particles, and the coating thickness is constant with the length of the alkylamine molecule. Therefore, the coated silver fine particles having a relatively large particle diameter have a volume ratio of the coated portion. It seems to be related to becoming smaller. Compared with the case where the average particle size is uniformly small by mixing the particles having a relatively large particle size with a mixture of particles having a relatively small particle size at a predetermined ratio and filling the gaps between the particles. Therefore, it is considered that the fact that the diffusion distance of silver atoms for causing bonding between grains does not change greatly also contributes to a decrease in resistance value.

On the other hand, when dimethylacetamide or the like, which is a kind of compound having an amide moiety, is used (Examples 13 and 14), there is a tendency that fine cracks are generated in the silver coating produced by baking at 100 ° C. The value was difficult to evaluate.
Further, in the ester compounds (Examples 16 and 17) among the carbonyl compounds, it tends to take time for the formation of complex compounds as compared with other carbonyl compounds. It is possible to obtain good coated silver fine particles, such as low residual resistance in the silver coating applied.
Furthermore, a compound group having multiple bonds between carbon atoms and nitrogen atoms (Examples 19 and 20), a compound group having multiple bonds between heteroatoms (Example 21), and between a carbon atom and an oxygen atom in one molecule The compound having a double bond between a carbon atom and a nitrogen atom together with the double bond (Example 18) also shortens the formation time of a complex compound of silver oxalate and an alkylamine, resulting in a high yield of good coated silver fine particles. Can be manufactured at a rate.
Furthermore, also in the case where a plurality of additive compounds exhibiting the effect of promoting the formation of complex compounds are used (Examples 22 to 25), the effect of shortening the formation time of complex compounds is seen, and good coated silver fine particles are produced. Can be manufactured.

Claims (9)

(1) a silver compound that can be decomposed by heating to produce metallic silver;
(2) alkylamine,
(3) a compound containing in the molecule at least one of multiple bonds of carbon atoms and heteroatoms, or multiple bonds of heteroatoms;
To produce a complex compound containing the silver compound and alkylamine,
And a second step of producing silver fine particles coated with a protective film containing alkylamine by thermally decomposing the complex compound, and producing a coated silver fine particle.   The method according to claim 1, wherein the heteroatom is at least one of an oxygen atom and a nitrogen atom.   The number of carbon atoms contained in the compound containing at least one of a multiple bond of carbon atoms and heteroatoms, or a multiple bond of heteroatoms in the molecule is 14 or less. The method described.   In the first step, at least one compound selected from the group consisting of a carbonyl compound, an oxime compound, a nitrile compound, an isonitrile compound, an isocyanate and a cyanate compound, containing a multiple bond of a carbon atom and a hetero atom in the molecule is used. The method according to claim 1, wherein the method is performed.   The first step is performed using at least one compound selected from the group consisting of an azo compound, a nitro compound, a nitroso compound and an azide, and containing a multiple bond of heteroatoms in the molecule. The method as described in any one of Claims 1-3.   The method as described in any one of Claims 1-5 in which the said silver compound has silver oxalate as a main component.   Coated silver fine particles produced by the method according to any one of claims 1 to 6.   A coated silver fine particle dispersion comprising the coated silver fine particles according to claim 7 dispersed in an organic solvent.   A coated silver fine particle-containing paste comprising the coated silver fine particles according to claim 7.