TWI487581B - Low carbon copper particles and methods for producing the same - Google Patents

Description

Low carbon copper particle and manufacturing method thereof

The present invention relates to a low carbon copper particle having an extremely low carbon content. The low carbon copper particles of the present invention are particularly suitable for use as a raw material for a copper paste, for example, for circuit formation of a printed wiring board or electrical conduction of an external electrode of a ceramic capacitor.

Conventionally, as a method of forming an electrode or a circuit of an electronic component or the like, it is known that a conductive paste obtained by dispersing a copper powder as a conductive material in a paste is printed on a substrate, and then the paste is baked and cured to form a circuit. The method.

For example, when a conductive paste is used for conducting the external electrodes of the ceramic capacitor, a conductive paste is applied onto the external electrodes, and then a debonding agent is heated by heating, and then copper particles are sintered. In this case, when the amount of carbon contained in the copper particles is too large, a gas containing carbon is generated by baking, and cracks may be generated in the conductor due to the gas, or the conductor may be peeled off from the substrate.

The method for producing copper particles which are raw materials for the conductive paste is roughly classified into a dry method represented by an atomization method and a wet method using reduction of copper ions in water, and if a dry method is used, there is an advantage that it is difficult to mix carbon in copper particles. . However, in the dry method, there is a limit in the production of copper particles having a small particle size. On the other hand, according to the wet method, there is an advantage that micron-sized micro-sized copper particles can be easily produced, but on the other hand, there is a tendency that a large amount of carbon derived from a dispersing agent or a reducing agent existing in the reaction system is mixed.

As one of the above-mentioned production methods, the present applicant has previously proposed a method for producing a copper powder by mixing an alkali hydroxide with an aqueous solution of a copper salt having a cupric ion to form copper oxide, and adding copper oxide by adding a reducing sugar. Reduction to cuprous oxide, reduction of cuprous oxide by addition of a lanthanide-based reducing agent, thereby producing copper metal, and pre-injecting a compounding agent in a copper salt aqueous solution, and mixing is equivalent to 1.10 to 1.60 in terms of reaction equivalent. The alkali hydroxide is subjected to a ripening reaction to form black copper oxide (see Patent Document 1). In this method, since reducing sugar is used as a reducing agent, carbon derived therefrom may be mixed into the copper particles.

Therefore, the present applicant has previously proposed a method for producing copper particles using a phosphoric acid compound instead of a dispersant containing an organic compound used in the production of copper particles by a wet method (see Patent Document 2). The method for producing copper particles using a phosphoric acid compound is also described in, for example, Patent Document 3.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-342621

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2009-74152

[Patent Document 3] US5801318A

According to the method described in Patent Document 2, copper particles having a small carbon content can be obtained. However, in this method, in order to improve the dispersibility of the obtained copper particles and to uniformize the particle diameter, it is washed in the middle of the step to adjust the pH of the reaction system. The pH adjustment is an operation necessary for improving dispersibility or obtaining copper particles having a uniform particle diameter, but correspondingly, the number of work steps is increased, which is not advantageous in terms of productivity. Further, even if the above pH adjustment is carried out, the dispersibility is not yet satisfactory.

In the method described in Patent Document 3, since a large amount of phosphoric acid is used to control the reaction, the amount of phosphorus contained in the obtained copper particles tends to increase. Copper particles containing a large amount of phosphorus sometimes have an adverse effect on the conductivity, and the amount of phosphorus in the waste liquid also increases, which is not preferable in terms of environmental load.

Accordingly, an object of the present invention is to provide a low carbon copper particle having further improved various characteristics compared to the copper particles of the prior art described above.

The present invention solves the above problems by providing low carbon copper particles characterized by having a carbon content of less than 0.01% by weight, containing phosphorus of 100 to 1000 ppm, and accumulating by laser diffraction scattering particle size distribution measurement. volume cumulative particle diameter D 90 at a volume capacity of _90%, and 50 vol% cumulative volume of the volume cumulative particle diameter D ₅₀ of the ratio D ₉₀ / D ₅₀ of 1.3 to 2.5, and measured by image analysis of the primary particles The average particle diameter D is 0.1 to 4 μm.

Further, the present invention provides a method for producing low carbon copper particles as a preferred method for producing the above low carbon copper particles, which is characterized by being included in the absence of a carbon-containing chemical species (excluding carbon-containing copper compounds) a method for producing low carbon copper particles by adding a reducing agent to an aqueous solution containing a water-soluble copper compound to carry out a reduction step of copper, and in the presence of a salt which does not contribute to the reduction reaction, in the presence of 11 to 15 mol/L, Copper particles are formed by reduction.

According to the present invention, it is possible to provide a copper particle which has a reduced carbon content and which is fine particles and has a uniform particle size distribution.

Hereinafter, the present invention will be described based on preferred embodiments thereof. One of the characteristics of the copper particles of the present invention is that the carbon content is reduced. The carbon content in the copper particles of the present invention is an extremely small amount of less than 0.01% by weight, preferably 0.005% by weight or less, more preferably 0.003% by weight or less. The carbon content was determined by measurement using a combustion-infrared absorption method in a gas stream, that is, EMIA-320V, which is a carbon analyzer manufactured by Horiba, Ltd. Specifically, a 0.5 g sample was added to the crucible, and a combustion improver (tungsten metal 1.5 g + tin metal 0.3 g) was further added, and the crucible was placed in the apparatus to measure.

In the case where a surface treatment agent containing an organic compound is applied to the surface of the copper particles in the subsequent step, the carbon content is measured after the surface treatment agent is removed. It is known that a surface treatment agent containing an organic compound generally disappears from the surface of the copper particles by heating at 200 ° C to 300 ° C. Therefore, in the present invention, copper particles after heating at 400 ° C for 30 minutes in an atmospheric environment are determined by the above method. Carbon content.

When the amount of carbon contained in the copper particles of the present invention is less than 0.01% by weight, the conductive paste produced using the copper particles as a raw material is hard to be produced on the conductor when the conductor formed by the use of the conductive paste is used for firing. Crack, or a problem of peeling from the substrate. The reason for this is that the amount of carbon contained in the copper particles is reduced, so that the amount of gas generated by carbon is reduced. Specific means for reducing the amount of carbon contained in the copper particles will be described below.

It is not clear in which state the carbon contained in the copper particles of the present invention exists, and it is presumed that it exists, for example, in the state of an organic compound or a carbonate. However, the state in which carbon exists is not critical in the present invention.

The copper particles of the present invention also have the characteristics of uniform particle size. That is, it also has a characteristic that the particle size distribution is steep. The degree of particle size distribution of the copper particles of the present invention can be obtained by a volumetric cumulative particle diameter D ₉₀ at a cumulative volume of 90% by volume and a volume accumulation at a cumulative volume of 50% by volume as measured by a laser diffraction scattering particle size distribution measurement method. The ratio of the particle diameter D _{50 is represented} by D ₉₀ /D ₅₀ . In the copper particles of the present invention, the value of D ₉₀ /D ₅₀ is from 1.3 to 2.5, preferably from 1.35 to 2.4, and further preferably from 1.4 to 2.0. By setting the value of D ₉₀ /D ₅₀ within this range, it is possible to form a highly filled and dense film when the paste film is formed, and it is also advantageous in that the film thickness can be easily controlled.

The above-mentioned D ₉₀ and D _{50 are} not the particle diameter of the primary particles of the copper particles, but the aggregation diameter of the secondary particles in which the primary particles are agglomerated, and the copper particles of the present invention are also characterized by a low degree of aggregation of the primary particles. That is, it also has the characteristics of good dispersibility. In order to suppress aggregation of primary particles, for example, in the wet reduction method of copper, a conventional method has hitherto been to obtain a dispersant in a solution. However, the dispersant is usually an organic compound containing carbon, so carbon is mixed into the obtained copper particles by using a dispersant. On the other hand, although the copper particles of the present invention have a reduced carbon content as described above, the dispersibility is still high. That is, the copper particles of the present invention simultaneously satisfy two characteristics which have hitherto been incompatible with low carbon content and high dispersibility.

The degree of aggregation of primary particles can be obtained by a laser diffraction scattering particle size distribution measurement, and the volume cumulative particle diameter D ₅₀ at a cumulative volume of 50% by volume, and the average particle diameter of primary particles measured by image analysis. The ratio D is expressed as D ₅₀ /D. The closer the value is to 1, the smaller the degree of aggregation of the primary particles. However, generally, the smaller the particle size of the agglomerated particles, the more severe the degree, and conversely, as the particle size becomes larger, agglomeration becomes less likely to occur. For example, when the average particle diameter D of the primary particles is several hundred μm, the value of D ₅₀ /D may be close to 1 even if no special treatment is performed, but when the average particle diameter D of the primary particles is on the order of submicron. It is not easy to make the value of D ₅₀ /D close to 1. That is, the value of D ₅₀ /D indicating the degree of aggregation is a function of the average particle diameter D of the primary particles, and even if only the value of D ₅₀ /D is expressed, the technical meaning is shallow. Therefore, the inventors of the present invention conducted various studies on the relationship between the average particle diameter D of the primary particles and the value of D ₅₀ /D, and found that D ₅₀ /D was set to y, and the average particle diameter of the primary particles was used. When D is set to x, copper particles satisfying y and x satisfying the following formula (1) are advantageous in terms of improvement in performance of the conductive paste.

[Number 1]

The copper particles satisfying the relationship of the above formula (1) can form a smooth film especially when a paste film is formed. Further, it is preferable because it has an advantageous effect of forming a film having a high filling property and being dense.

The average particle diameter D measured by image analysis described above can be obtained by directly observing the copper particles by using a scanning electron microscope (SEM, Scanning Electron Microscope) to a magnification of 5000 times to 20,000 times. The SEM image was used to measure the maximum cross-sectional length of each copper particle (the number of measured samples was 10 or more), and the average number of samples was measured.

In addition to the low degree of aggregation of the primary particles, the copper particles of the present invention also have the characteristics of being fine particles. As described above, the smaller the particle size of the agglomerates of the particles, the more serious the degree. On the other hand, although the copper particles of the present invention are fine particles, the aggregation of the primary particles is low as described above. That is, the copper particles of the present invention simultaneously satisfy two characteristics which are incompatible with the small particle diameter and the high dispersibility.

Specifically, the average particle diameter D of the primary particles of the copper particles of the present invention is 0.1 to 4 μm. By setting the average particle diameter D of the primary particles within the range, it is possible to form an advantageous effect of forming a conductive film having a thin film thickness and a narrow pitch. The average particle diameter D of the primary particles of the copper particles of the present invention is preferably from 0.13 to 3 μm, more preferably from 0.15 to 2 μm, from the viewpoint of making the advantageous effect more conspicuous.

The shape of the copper particles of the present invention is not particularly limited, and may be, for example, various shapes such as a spherical shape, a polyhedral shape, a spindle shape, a flat shape, and an amorphous shape. The copper particles obtained by the preferred method for producing copper particles described below are usually formed in a slightly spherical shape having a non-curved portion in one of the surfaces (see FIG. 2 below). For example, one portion formed on the surface has a flat portion and has a slightly spherical shape with ridges or corners at the end portion of the flat portion. The above shape is significantly different from the shape of spherical copper particles having a smooth curved surface, for example, which is produced by an atomization method. The slightly spherical copper particles having a non-curved portion formed on one surface of the surface have lower filling properties than the particles of the sphere, and have higher filling properties than the flaky particles, so the paste containing the copper particles is used. In the case where a conductive film is formed, the conductive film has an advantage of exhibiting sufficient conductivity and excellent degassing property. It is advantageous in that it is difficult to cause cracks on the conductive film, etc., because it is excellent in degassing property.

The low carbon copper particles of the present invention contain phosphorus. The oxidation resistance of the low carbon copper particles can be improved by containing phosphorus. However, since a large amount of phosphorus is one of the causes of a decrease in conductivity of the copper particles, the phosphorus content in the low carbon copper particles of the present invention must be 100 to 1000 ppm, preferably 130 to 800 ppm, and more preferably 150. ~500 ppm. Further, ppm means the parts per million by weight. Further, the low carbon copper particles of the present invention preferably contain substantially no elements other than copper and phosphorus. The term "substantially not contained" is intended to exclude the intentional addition of the element, for example, to allow trace elements which are inevitably mixed in the manufacturing process of the product, or the presence of trace elements which are inevitably left to be removed by purification.

In order to contain phosphorus in the low carbon copper particles of the present invention, for example, a phosphorus-containing compound may be added to the following production method. Further, the phosphorus content in the low carbon copper particles of the present invention can be determined, for example, by measurement by ICP (Inductively Coupled Plasma). In the low carbon copper particles of the present invention, phosphorus is preferably present in the state of an oxide, for example, in the state of H ₃ PO ₄ or Na ₄ P ₂ O ₇ . Whether or not phosphorus is present in the form of an oxide can be confirmed by X-ray photoelectron spectroscopy (XPS, X-ray photoelectron spectroscopy) or X-ray Diffraction (XRD). Further, it is preferred that phosphorus is present in a state in which it is not chemically bonded to copper. When phosphorus is contained in the copper particles in a state of being chemically bonded to copper, it sometimes has an adverse effect on conductivity. Whether or not phosphorus is chemically bonded to copper can be confirmed by XPS or XRD.

Next, a preferred method of producing the flat copper particles of the present invention will be described. In the present production method, a reducing agent is added to an aqueous liquid containing a copper compound to carry out reduction of copper. In this method, all steps are carried out from the beginning to the end thereof in the absence of a carbonaceous chemical species (except for copper-containing copper compounds such as copper acetate or copper formate). Examples of the carbon-containing chemical species include various organic compounds (for example, hydrocarbons, alcohols, aldehydes, carboxylic acids, esters, ethers, ketones, organic decanes, amino acids, etc.), and carbon-containing ionic species (for example, carboxylate ions or carbonates). Ions, etc., carbon materials (such as black lead or graphite).

In the present production method, an aqueous liquid containing a divalent copper compound (hereinafter also referred to as "copper-containing liquid") is first prepared. As the copper compound, for example, a water-soluble copper compound such as copper sulfate, copper nitrate or a hydrate thereof can be used. Further, copper acetate can also be used as the copper compound. Copper acetate is a carbon-containing compound, but the carbon derived from copper acetate is a trace amount, so that carbon derived from copper acetate is not contained in a large amount in the target copper particles. Among these copper compounds, copper sulfate pentahydrate and copper nitrate have high water solubility, can increase the concentration of copper in an aqueous solution, and can easily obtain copper particles having a high uniformity of particle size, and thus can be preferably used.

The copper-containing liquid phase is preferably contained in an amount of 2.0 parts by weight to 4.0 parts by weight, more preferably 3.0 parts by weight to 3.8 parts by weight, based on 100 parts by weight of the water. It is preferable to contain a copper compound in a ratio of this range, since synthesis with excellent productivity can be achieved.

The copper-containing liquid can be prepared by dissolving or dispersing a divalent copper compound in water. As a method of dissolving the copper compound, for example, a method in which water is stirred and a copper compound is added thereto and stirred is mentioned. The liquid temperature at the time of preparation of the copper-containing liquid is preferably from 40 ° C to 90 ° C, and more preferably from 50 ° C to 80 ° C from the viewpoint of obtaining copper particles having a uniform particle diameter.

A basic compound is added to the copper-containing liquid obtained in the above manner to form copper oxide (CuO). Examples of the basic compound used herein include hydroxides of alkali metals such as sodium hydroxide or potassium hydroxide, and ammonia. These basic compounds may be used singly or in combination of two or more. The generated copper oxide is suspended in the solution in the form of fine solid particles.

As a method of adding a basic compound to a copper-containing liquid, for example, a method in which a copper-containing liquid is stirred and an aqueous solution of a basic compound is added thereto is stirred. The liquid temperature at this time is preferably from 40 ° C to 90 ° C, and more preferably from 50 ° C to 80 ° C. When the liquid temperature is within this range, copper particles having a high uniformity of particle diameters in which primary particles are less aggregated are easily obtained, which is preferable. When two or more combinations are used as the basic compound, these may be added at the same time, or may be added in order.

The amount of the basic compound added to the copper-containing liquid is preferably 0.7 to 2.0 mol, more preferably 0.75 to 1.8 mol, based on the copper 1 molar. When the amount of the basic compound added is within this range, copper particles having a high uniformity in particle diameter can be easily obtained, which is preferable.

It is preferred to continue the stirring of the solution by adding a basic compound to the copper-containing liquid to form a copper oxide. The ripening is preferably carried out for 10 minutes to 60 minutes, and more preferably for 20 minutes to 40 minutes. It is preferable to form copper oxide sufficiently by aging to easily obtain copper particles having high uniformity in particle size.

After the copper oxide is formed in this manner, the first reduction step is carried out. In the present reduction step, a reducing agent is added while stirring the solution, thereby reducing the copper oxide contained in the solution to cuprous oxide (Cu ₂ O). Therefore, the reducing agent used in the present reduction step has a function of reducing copper oxide to cuprous oxide. As the reducing agent, for example, hydrazine can be used.

In the present reduction step, it is preferable to add 0.1 mol to 3 mol of the reducing agent with respect to the copper 1 mol contained in the solution, and it is preferable to add 0.3 mol to 1.5 mol. When the amount of the reducing agent added is within this range, the reduction reaction of copper oxide to cuprous oxide can be sufficiently performed. As a result, it is preferable that the target copper particles are less likely to agglomerate the primary particles.

Preferably, the copper oxide is reduced to form cuprous oxide by the reduction step, and the solution is further stirred for ripening. The ripening is preferably carried out for 10 minutes to 60 minutes, and more preferably for 20 minutes to 40 minutes. It is preferred that the copper particles are sufficiently formed by aging to make the target copper particles less likely to agglomerate the primary particles.

After the completion of the first reduction step, the second reduction step is followed. In the present reduction step, copper oxide particles are formed by reducing the cuprous oxide contained in the solution to copper by adding a reducing agent while stirring the solution. Therefore, the reducing agent used in the present reduction step has a function of reducing cuprous oxide to copper. As the reducing agent, for example, hydrazine can be used.

In the second reduction step, it is preferable to add 0.3 mol to 3 mol of the reducing agent to the copper 1 mol contained in the solution, and it is preferable to add 0.31 mol to 2 mol. By setting the amount of the reducing agent to be within this range, the target copper particles can be smoothly obtained.

As a result of research by the inventors of the present invention, it has been found that the formation of copper particles in the second reduction step causes the reaction system to contain a large amount of water-soluble salt which does not contribute to the reduction reaction, and the copper particles having a uniform particle diameter are smoothly obtained. advantageous. In order to unify the particle size of the copper particles, it is important to suppress the pH value of the solution when the copper particles are formed as much as possible, and by allowing the solution to contain a large amount of salt, the salt acts as a buffer to suppress the pH change. . From this point of view, it is preferred to set the concentration of the salt present in the solution to 11 to 15 mol/L, and more preferably to 11.5 to 14 mol/L, when the copper particles are formed.

As the salt which does not contribute to the reduction reaction, the cation and anion which are generated by ionization in water can be exemplified as those which do not contribute to the formation of copper oxide from copper oxide. Examples of the cation include sodium ions, potassium ions, protons, and the like. Examples of the anion include a sulfate ion, a nitrate ion, a chloride ion, an ammonium ion, and a hydroxide ion. Specific examples of the salt containing the combination of the cation and the anion include NaNO ₃ , NaCl, Na ₂ SO ₄ and the like.

The water-soluble salt is preferably present in the solution before the start of the second reduction step. In order to achieve the object, (A) may be supplied to the second reduction step without separating the cuprous oxide from the solution after the first reduction step, and the water-soluble portion may be after the first reduction step or before the second reduction step. The salt is added to the solution in such a manner that its concentration becomes 11 to 15 mol/L. As another method, (B) after the first reduction step, the cuprous oxide is separated from the solution and washed, and the like, the prepared cuprous oxide is contained and the water-soluble salt is contained in an amount of 11 to 15 mol/L. The slurry is supplied to the second reduction step.

The amount of the various compounds added for carrying out the production method is such that the concentration of the water-soluble salt in the solution satisfies the above range at the end of the first reduction step. In the above case, the second reduction step can be continued without using an additional water-soluble salt.

Preferably, the cuprous oxide is reduced to copper by the second reduction step, and the solution is further stirred to be aged. The ripening is preferably carried out for 20 minutes to 120 minutes, and more preferably for 40 minutes to 90 minutes. It is preferred that the target copper particles are less likely to be agglomerated by primary particles by aging.

In the above production method, a phosphorus compound is added in any step so that the target low carbon copper particles contain phosphorus. By making the low carbon copper particles contain phosphorus, the oxidation resistance of the particles can be improved. Further, by adding a phosphorus compound in the step, aggregation of primary particles can be suppressed, and copper particles having good dispersibility can be obtained.

The addition time of the phosphorus compound may be, for example, any one of the following times or two or more times: (i) before adding a basic compound to the copper-containing liquid, (ii) adding a basic compound to the copper-containing liquid, or Thereafter, before the first reduction step, (iii) while adding the reducing agent in the first reduction step or after and before the second reduction step, (iv) adding the reducing agent to the second reduction step, or Thereafter. In particular, it is preferable to add a phosphorus compound to the time of (i) or both of (i) and (iii) for the prevention of aggregation of primary particles.

As the phosphorus compound, a compound which can form a phosphate ion such as a orthophosphate ion, a pyrophosphate ion or a metaphosphate ion in the presence of water is preferably used. Examples of the phosphorus compound include orthophosphoric acid; polyphosphoric acid such as pyrophosphoric acid and tripolyphosphoric acid; metaphosphoric acid such as trimetaphosphoric acid; orthophosphate such as sodium orthophosphate and potassium orthophosphate; and sodium pyrophosphate and potassium pyrophosphate. Phosphate; metaphosphate such as sodium trimetaphosphate and potassium trimetaphosphate. Among these phosphorus compounds, if pyrophosphate, tripolyphosphate or orthophosphate is used, aggregation prevention of primary particles is more effective.

The total amount of the phosphorus compound added in the production method is expressed by the amount converted into P (phosphorus), and is preferably 0.1 millimolar to 100 millimolar, and more preferably 0.2 millimeter, relative to the copper 1 molar. Ears ~50 millimoles. When the amount of the phosphorus compound added is within this range, the conductivity of the target low carbon copper particles can be prevented, and aggregation of the primary particles can be effectively prevented, which is preferable.

The copper particles produced by the above method are reacted in the absence of the carbon-containing chemical species (excluding the carbon-containing copper compound) from the beginning to the end of the step, so that in principle, no carbon is contained at all, or even if carbon is contained, The amount is also reduced to a very low level. Further, the particle diameter is uniform, and aggregation of primary particles is suppressed. Even if the copper particles contain carbon, the carbon is inevitably mixed into the copper particles. In the present production method, the operation of intentionally causing carbon in the copper particles is not performed.

The target low carbon copper particles can be obtained by the above method. The low carbon copper particles obtained in this manner are preferably used, for example, as a raw material for a conductive paste. The conductive paste contains metal particles, an organic vehicle, and a glass frit containing the low carbon copper particles of the present invention. The organic vehicle contains a resin component and a solvent. Examples of the resin component include an acrylic resin, an epoxy resin, ethyl cellulose, and carboxyethyl cellulose. Examples of the solvent include terpene-based solvents such as terpineol and dihydroterpineol, and ether solvents such as ethyl carbitol and butyl carbitol. Examples of the glass frit include borosilicate glass, bismuth boron bismuth glass, and zinc borosilicate glass. The proportion of the metal powder in the conductive paste is preferably set to 36 to 97.5 wt%. The proportion of the glass frit is preferably set to 1.5 to 14% by weight. The ratio of the organic vehicle is preferably from 1 to 50% by weight. As the metal particles in the conductive paste, only the low carbon copper particles of the present invention may be used, or the low carbon copper particles and other shapes of copper particles such as flat sheets may be used in combination. By combining the low carbon copper particles of the present invention with copper particles of other shapes, it is easy to precisely adjust the viscosity of the paste.

The conductive paste obtained in this manner can be preferably used for circuit formation of a printed wiring board, electrical conduction securing of an external electrode of a ceramic capacitor, and the like, and EMI (Electro Magnetic Interference) countermeasure.

[Examples]

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the invention is not limited by the embodiment. As long as there is no special provision, "%" means "% by weight".

[Example 1]

(1) Preparation of copper-containing aqueous solution

Copper sulfate pentahydrate was added to 6.5 L of pure water at 65 ° C so that the copper concentration became the value shown in Table 1, and the mixture was stirred. Further, sodium pyrophosphate was further added thereto, and stirring was continued for 30 minutes in this state to obtain a copper-containing aqueous solution. The amount of sodium pyrophosphate added was set to the amount shown in Table 1 with respect to copper 1 molar.

(2) Formation of copper oxide

Two kinds of basic compounds shown in Table 1 were simultaneously added to the aqueous solution while stirring the aqueous solution to form copper oxide in the solution. Stirring was then continued for 30 minutes. The amount of the basic compound added was set to the amount shown in Table 1 with respect to the copper 1 molar.

(3) Reduction of copper oxide to cuprous oxide

Then, hydrazine and ammonia water are added to carry out the first reduction reaction, and the copper oxide is reduced to cuprous oxide. Stirring was then continued for 30 minutes. The amount of hydrazine and ammonia added was set to the amount shown in Table 1 with respect to copper 1 molar. The concentration of the water-soluble salt (salt which does not contribute to the reduction reaction) in the solution at this time is shown in Table 1.

(4) Reduction of cuprous oxide to copper particles

Then, sodium pyrophosphate is added to the solution, and further, hydrazine is added to carry out the second reduction reaction, and the cuprous oxide is reduced to copper. Stirring was continued for 1 hour and the reaction was terminated. The total amount of sodium pyrophosphate added and the amount of sodium pyrophosphate added before was set to be the amount shown in Table 1 with respect to copper 1 molar. The amount of ruthenium added was set to the amount shown in Table 1 with respect to copper 1 molar. After completion of the reaction, the obtained slurry was filtered using a Buchner funnel, followed by washing with pure water, followed by drying to obtain a target copper particle. The copper particles were observed by SEM. As a result, as shown in Fig. 2, it was confirmed that the copper particles had a slightly spherical shape in which a part of the surface had a non-curved surface portion.

[Embodiment 2]

The same operation as in Embodiment 1 was carried out before the step of (2). Among them, copper nitrate was used instead of copper sulfate as a copper compound. Then, hydrazine and ammonia water are added to carry out the first reduction reaction, and the copper oxide is reduced to cuprous oxide. Stirring was then continued for 30 minutes. The amount of hydrazine and ammonia added was set to the amount shown in Table 1 with respect to copper 1 molar. Then, the formed cuprous oxide was separated by filtration using a Buchner funnel, and washed with pure water. The washed cuprous oxide was reslurryed with pure water (the proportion of cuprous oxide was 70%), and the water-soluble salt shown in Table 1 was further added to have the concentration shown in the same table.

Then, sodium pyrophosphate is added to the solution, and further, hydrazine is added to carry out the second reduction reaction, and the cuprous oxide is reduced to copper. Stirring was continued for 1 hour and the reaction was terminated. The total amount of sodium pyrophosphate added and the amount of sodium pyrophosphate added before was set to be the amount shown in Table 1 with respect to copper 1 molar. The amount of ruthenium added was set to the amount shown in Table 1 with respect to copper 1 molar. After completion of the reaction, the obtained slurry was filtered using a Buchner funnel, followed by washing with pure water, followed by drying to obtain a target copper particle. When the copper particles were observed by SEM, it was confirmed that the copper particles had a slightly spherical shape having a non-curved portion on one of the surfaces.

[Example 3]

The same operation as in Embodiment 1 was carried out before the step of (2). Among them, an aqueous copper solution was prepared at 60 °C. Then, hydrazine and ammonia water are added to carry out the first reduction reaction, and the copper oxide is reduced to cuprous oxide. Stirring was then continued for 30 minutes. The amount of hydrazine and ammonia added was set to the amount shown in Table 1 with respect to copper 1 molar. Then, the water-soluble salt shown in Table 1 was added to the solution without separating the cuprous oxide from the solution. The amount of the water-soluble salt added is such that the total concentration of the water-soluble salt present in the solution is the value shown in Table 1.

Then, ruthenium is added to the solution to carry out the second reduction reaction, and the cuprous oxide is reduced to copper. Stirring was continued for 1 hour and the reaction was terminated. The amount of ruthenium added was set to the amount shown in Table 1 with respect to copper 1 molar. After completion of the reaction, the obtained slurry was filtered using a Buchner funnel, followed by washing with pure water, followed by drying to obtain a target copper particle. When the copper particles were observed by SEM, it was confirmed that the copper particles had a slightly spherical shape having a non-curved portion on one of the surfaces.

[Example 4 to Example 16]

Copper particles were obtained in the same manner as in Examples 1 to 3 except that the conditions shown in Table 1 were employed. When the obtained copper particles were observed by SEM, it was confirmed that the copper particles had a slightly spherical shape having a non-curved portion on one of the surfaces.

[Example 17]

In the present embodiment, copper acetate was used as the copper compound. Further, the conditions shown in Table 1 were employed. Copper particles were obtained in the same manner as in Examples 1 to 3 except for the above. When the obtained copper particles were observed by SEM, it was confirmed that the copper particles had a slightly spherical shape having a non-curved portion on one of the surfaces.

[Comparative Example 1]

Copper particles were produced in accordance with Example 1 described in Patent Document 2. First, 6000 g of copper sulfate was added to 6.5 L of pure water and stirred, and then the liquid temperature was maintained at 50 ° C, and water was further added so that the amount of the copper sulfate aqueous solution became 9 L, and the concentration was adjusted. To the copper sulfate aqueous solution, 2537 ml of an aqueous ammonia solution (concentration: 25%) was added for 30 minutes to carry out neutralization to obtain a copper salt compound slurry. Then, the copper salt compound slurry was allowed to stand for 30 minutes for ripening. The liquid temperature of the copper salt compound slurry was kept at 50 ° C until now, and the liquid temperature was adjusted to 45 ° C after the aging.

Then, water was added so that the copper concentration of the copper salt compound slurry became 2.0 mol/L, and the amount of liquid was adjusted. The copper salt compound slurry was maintained at a pH of 6.3 and a liquid temperature of 50 ° C, and 459 ml of hydrazine monohydrate and 591 ml of an aqueous ammonia solution (concentration: 25%) were continuously added thereto over 30 minutes to prepare a cuprous oxide slurry. Material (first reduction treatment). Then, the reduction reaction was carried out completely, and stirring was continued for further 30 minutes.

Thereafter, in order to perform repulping washing, pure water was added to the cuprous oxide slurry, and the amount of the liquid was adjusted to 18 L, and then allowed to stand to precipitate the cuprous oxide particles, and the supernatant was allowed to stand still after repeated standing. The operation of 14 L was removed until the pH reached 4.7. Then, 8 L of warm pure water was added to make the total liquid amount to 12 L, the liquid temperature was maintained at 45 ° C, and the copper concentration was adjusted to 2.0 mol/L, and this was made into a washed cuprous oxide slurry. The concentration of the water-soluble salt at this time was 11.7 mol/L.

3.02 g of ammonium hypophosphite was added to the washed cuprous oxide slurry after the copper concentration adjustment, and the mixture was stirred for 5 minutes.

Water was again added so that the copper concentration of the washed cuprous oxide slurry became 2.0 mol/L, and the amount of liquid was adjusted. To the washed cuprous oxide slurry, 1200 g of hydrazine monohydrate was added over 30 minutes. Then, the mixture was further stirred for 15 minutes, and the reduction reaction was completely carried out to reduce the precipitation of copper particles (second reduction treatment). When the obtained copper particles were observed by SEM, it was confirmed that the copper particles had a slightly spherical shape having a non-curved portion on one of the surfaces.

[Comparative Example 2]

This comparative example is an example corresponding to Embodiment 6 of Patent Document 3 (US Pat. No. 5,801,318 A), which is hereby incorporated by reference. Copper sulfate pentahydrate was added and dissolved by stirring 30 ° C of pure water at 170 rpm to prepare a 0.63 mol/L copper sulfate aqueous solution. Sodium pyrophosphate decahydrate was added to the solution. The amount added was set to 1 mol with respect to copper 1 mol, and sodium pyrophosphate was 95.1 mmol. A copper ammonia stray solution was prepared by adding 25% ammonia water to the solution. The amount of ammonia added was set to be 1.56 moles with respect to copper 1 mol. The concentration of the water-soluble salt at this time was 1.8 mol/L. An anhydrous hydrazine is added to the copper ammonia counterion solution. The amount of niobium added was set to 1 mol relative to copper, and the amount of niobium was 3.9 m. Then, the solution was heated to 80 ° C, and the temperature was maintained for 2 hours to obtain copper particles.

[Comparative Example 3]

The present comparative example corresponds to an example of the embodiment of the patent document 1 (Japanese Patent Laid-Open No. 2003-342621), which is hereby incorporated by reference. Copper sulfate pentahydrate and glycine acid were dissolved in a state of stirring at 60 ° C in pure water at 170 rpm to prepare a 2 mol/L copper sulfate aqueous solution. The amount of glycine added was set to be 1 mol with respect to copper 1 mol, and glycine acid was 0.1 mol. While stirring the aqueous solution, a 25% aqueous sodium hydroxide solution was quantitatively added over a period of about 5 minutes, and the mixture was stirred at a liquid temperature of 60 ° C for 60 minutes to be matured until the liquid color completely became black to form copper oxide. The amount of sodium hydroxide added was set to 1.77 moles of copper relative to copper. Thereafter, it was allowed to stand for 30 minutes, glucose was added, and it was aged for 1 hour, thereby reducing copper oxide to cuprous oxide. The amount of glucose added was set to be 1 part by mole with respect to copper 1 mol. Further, anhydrous cerium was quantitatively added over 5 minutes to reduce cuprous oxide, thereby forming metallic copper to obtain copper particles. The amount of ruthenium added was set to be 1.95 moles relative to copper 1 mole.

[Evaluation]

The amount of carbon contained in the copper particles obtained in the examples and the comparative examples was measured by the carbon analysis described above, and the amount of phosphorus was measured by ICP emission analysis. Further, D ₉₀ and D ₅₀ of the copper particles obtained in the examples and the comparative examples were measured using a Microtrac HRA manufactured by Nikkiso Co., Ltd. Further, the average particle diameter D of the primary particles was measured by the above method. Drawn from the measurement results of D and D ₅₀ are formed by the relationship ₅₀ / D and D of the D 1 shown in FIG. Also shown in the same figure is a curve according to the above formula (1). Further, with respect to the copper particles obtained in the examples and the comparative examples, a slurry was prepared by the following method, and the surface roughness of the film made of the slurry was measured. These results are shown in Table 2 below.

[Determination of Surface Roughness of Film Made of Slurry]

The copper particles obtained in the examples and the comparative examples and a solvent (a mixture of 95 g of terpineol and 5 g of ethyl cellulose) were mixed at a weight ratio of 1:1 to form a slurry. The slurry was rotated at 2000 rpm for 45 seconds using a mixer (Thinky Co., Ltd., ARE-250) to perform preliminary kneading. Then, the slurry was further kneaded by a three-roll mill (AIMEX Co., Ltd., Model RMZ-1). The gap between the rolls was set to 5 μm. The slurry obtained in this manner was applied onto a glass substrate using a 30 μm applicator (YOSHIMITSU SEIKI Co., Ltd., Model YR-1) to form a coating film. The coating film was dried at 80 ° C for 5 minutes. The surface roughness Ra and Rmax of the film obtained in this manner were measured using a surface roughness shape measuring instrument (Tokyo Precision Co., Ltd., Surfcom 130A).

As is clear from the results shown in Table 2, the copper particles obtained in the respective examples had a low carbon content, a sharp particle size distribution, and were fine particles. Further, it was found that the surface properties of the film formed by using the copper particles obtained in the respective examples were good. On the other hand, it is understood that the copper particles obtained in Comparative Example 1 have a low carbon content, but they are less dispersible and agglomerate than the copper particles of the examples. As a result, it was found that the surface properties of the film were not good.

Further, although not shown in the table, the copper particles obtained in the examples and the comparative examples were subjected to measurement of TG-MS in a helium atmosphere containing 50 ppm of oxygen (temperature up rate 100 ° C/min), and each of the results In the copper particles of the examples, no peak was observed in the temperature range of 0 to 1000 ° C. On the other hand, the copper particles of Comparative Example 3 observed peaks derived from the contained carbon at around 800 ° C.

Further, although not shown in the table, the state of phosphorus contained in the copper particles obtained in the examples was investigated by XPS, and it was confirmed that the phosphorus was present in the form of an oxide, and the phosphorus was not chemically bonded to copper. The status exists.

Unlike the above measurement and evaluation, the volume resistivity of the copper particles obtained in Example 10 and Comparative Example 2 having the same particle diameter was measured by the following method. As a result, the volume resistivity of the copper particles of Example 10 was a lower value of 5.1 × 10 ^-2 Ω ‧ cm, whereas the volume resistivity of the copper particles of Comparative Example 2 was 3.8 × 10 ¹ Ω · cm Higher value. The reason why the volume resistivity of the copper particles of Comparative Example 2 is high is that a large amount (0.2%) of phosphorus is contained.

[Volume resistance value]

The powder resistance value was measured using a powder resistance measuring system (Mitsubishi Chemical, PD-41) and a resistivity meter (Mitsubishi Chemical, MCP-T600). 15 g of the sample was placed in the probe cylinder, and the probe unit was placed in the PD-41. The resistance value at a pressure of 1000 f/kg applied by a hydraulic jack was measured using an MCP-T600. The volume resistance value was calculated from the measured resistance value and the sample thickness.

Fig. 1 is a graph in which the relationship between (D ₅₀ /D) and D of the copper particles obtained in the examples is plotted.

2 is a scanning electron microscope image of the copper particles obtained in Example 1.

(no component symbol description)

Claims (8)

A low carbon copper particle characterized by having a carbon content of less than 0.01% by weight, containing 100 to 1000 ppm of phosphorus, and a volume cumulative particle diameter of 90% by volume of a cumulative volume measured by a laser diffraction scattering particle size distribution measurement method D _90, 50 with the cumulative volume of the volume capacity of the% cumulative particle diameter D ₅₀ of the ratio of D ₉₀ / D ₅₀ of 1.3 to 2.5, and is measured by the image analysis of the primary particle average particle diameter D of 0.1 ~ 4μm, Wherein the ratio (D ₅₀ /D) of the volume cumulative particle diameter D _{50 at the} cumulative volume of 50% by volume to the average particle diameter D of the primary particles determined by image analysis is y, the average particle diameter of the primary particles When D is set to x, y and x satisfy the following formula (1), The low carbon copper particle of claim 1, wherein the phosphorus is present in the form of an oxide. The low carbon copper particle of claim 1, which has a slightly spherical shape having a non-curved portion on one of the surfaces. A method for producing low carbon copper particles, which is characterized in that it is included in the absence of a carbon-containing chemical species (excluding a carbon-containing copper compound), and a reducing agent is added to an aqueous liquid containing a copper compound for copper reduction The method for producing low carbon copper particles in the reduction step, and forming copper particles by reduction in the presence of a salt which does not contribute to the reduction reaction in the presence of 11 to 15 mol/L. The method of claim 4, comprising adding a basic compound to the aqueous liquid containing the copper compound to form copper oxide, and reducing the generated copper oxide to cuprous oxide in the first reduction step, followed by the second reduction In the step, copper oxide is reduced to form copper particles, and in the second reduction step, copper particles are formed by reduction in the presence of a salt which does not contribute to the reduction reaction in the range of 11 to 15 mol/L. The manufacturing method of claim 5, wherein after the first reduction step, the cuprous oxide is not separated from the solution and supplied to the second reduction step, and after the first reduction step and before the second reduction step, the addition does not contribute to the reduction. The salt of the reaction forms copper particles by reduction under the condition that the total concentration of the salt which does not contribute to the reduction reaction is 11 to 15 mol/L. The method of claim 5, wherein after the first reduction step, the cuprous oxide is separated from the solution to prepare a slurry comprising the separated cuprous oxide and containing a salt which does not contribute to the reduction reaction, 11 to 15 mol/L, The prepared slurry is supplied to the second reduction step, and copper particles are produced by reduction. A conductive paste characterized by containing low carbon copper particles as claimed in claim 1.