JP4197151B2 - Two-layer coated copper powder, method for producing the two-layer coated copper powder, and conductive paste using the two-layer coated copper powder - Google Patents

Description

  The invention according to the present application is a two-layer coated copper powder having a first inorganic coat layer and a second inorganic coat layer on the surface of a copper powder particle as a core, a method for producing the two-layer coated copper powder, and two The present invention relates to a conductive paste using layer-coated copper powder. It is an object of the present invention to provide copper powder that is particularly suitable for low-temperature fired ceramic materials.

  Conventionally, copper powder has been widely used as a raw material for conductive pastes and a conductor for forming low-temperature fired ceramic substrates. Conductive pastes have been used to easily form conductors in a wide range of areas, from experimental use to electronic industry applications. For example, for sample preparation of electron microscopes, formation of conductor circuits for printed wiring boards, formation of interlayer conductive conductors as an alternative to through holes for obtaining interlayer conduction of multilayer printed wiring boards, formation of electrodes for ceramic capacitors, low-temperature fired ceramic substrates Etc. have been used. The copper powder used in these products is processed into a conductive paste, and when a conductor such as the above-mentioned product is formed, it has good oxidation resistance that enables a low electrical resistance of the conductor, and sintering. Therefore, there has been a demand for good heat shrinkage performance that minimizes the dimensional change.

Conventional technology regarding oxidation resistance: In order to improve the oxidation resistance of copper powder, surface-treated copper powder in which an organic coating (organic coating layer) is formed on the surface of the copper powder has been used. A typical example is the copper powder shown in Patent Document 1, and surface treatments using various fatty acids as surface treating agents have been performed in order to prevent oxidation of the particle surface. When this surface-treated copper powder is compared with copper powder that has not been surface-treated, the surface-treated copper powder is less prone to surface oxidation, and the metal oxide content when the conductor is formed by sintering is reduced. It has been known that it is possible to obtain a low-resistance conductor having excellent electrical conductivity.

Conventional technology related to heat-shrinkage performance: Conventionally, in order to improve the heat-shrinkage performance of copper powder, two methods have been considered effective. One is the control of the crystallite diameter of the copper powder as disclosed in Patent Document 2 filed before the present invention, and the other is the inorganic coating on the surface of the copper powder powder disclosed in Patent Document 3. is there. The thermal shrinkage performance is particularly problematic in low-temperature fired ceramic applications in which a conductive shape is used to draw a conductor shape on a green sheet and fired simultaneously at a temperature of 900 ° C. or higher.

  First, the control of the crystallite size will be described. In general, the production of copper powder can be broadly classified and classified into a dry production method and a wet production method. The latter wet manufacturing method can be said to be a method of manufacturing by directly depositing copper powder from a solution containing a target metal element. On the other hand, it can be said that the former dry production method includes not only a pulverization method using a completely mechanical method but also an atomization method using a molten metal.

  As a feature of the copper powder obtained by these methods, the copper powder obtained by the former dry production method has a crystallite diameter in the range of 40 to 50 nm, which is relatively large. It has the advantage of being excellent in oxidation resistance and heat shrinkage resistance. On the other hand, the copper powder produced by the wet production method generally has a crystallite diameter of 35 nm or less and is smaller than the copper powder obtained by the dry production method, and has oxidation resistance and heat shrinkage resistance during firing. It has the disadvantage of being inferior. The heat shrinkability is generally said to be greatly influenced by the size of the crystallite. The larger the crystallite diameter, the smaller the shrinkage when heated at a high temperature, and the better the heat shrinkability. As long as these things are considered, it is considered that all problems can be solved by using copper powder produced by a dry production method. However, the difference in heat shrinkage between the powder obtained by the actual dry manufacturing method and the powder obtained by the wet manufacturing method is not very large, and the powder obtained by any of the manufacturing methods is It has a sintering characteristic that sintering at a low temperature occurs quickly.

  On the other hand, the inorganic coating on the surface of the copper powder grain means that a high-temperature heat resistance is imparted to the coating layer in the outer shell by forming a thick metal oxide layer with excellent heat resistance on the surface of the copper powder grain. In addition, heat shrinkage is ensured by preventing heat deformation of the outer shell shape.

JP-A-2-218762 Japanese Patent Application No. 2003-183688 US Pat. No. 5,126,915

  However, it is very difficult for copper powder to have both oxidation resistance and heat shrinkage resistance, and the following disadvantages exist in the various copper powders described above.

Problems of oxidation-treated surface-treated copper powder: From those skilled in the art of producing a conductive paste using surface-treated copper powder, the surface-treated copper powder surface-treated with fatty acids is processed into a conductive paste. There was an opinion that the paste viscosity was not so stable that there was no problem in process control. That is, the conductive paste manufactured using the surface-treated copper powder treated with fatty acid has a high initial paste viscosity, and the paste viscosity may change over time and thicken. Long-term storage is difficult, and quality control of copper paste and the like used for manufacturing electronic parts and the management spent on quality maintenance are complicated, which has been an obstacle to the expansion of their use.

Problems with copper powder with heat shrinkability : As a characteristic of the powder obtained by the dry production method, which is said to be excellent in heat shrinkability, there is a defect that the particle size distribution is broad and it is difficult to produce fine powder with high accuracy. To do. In recent years, the requirements for the finishing accuracy of the surface of low-temperature fired ceramics have become more and more severe, and copper powder having a sharp particle size distribution with a volume cumulative particle size D ₅₀ value of 10 μm or less by laser diffraction scattering type particle size distribution measurement method. Thus, the demand for copper powder having excellent dispersibility becomes remarkable, and the powder obtained by the dry production method does not meet this requirement.

  Therefore, from the viewpoint of making fine particles, it is considered desirable to satisfy these requirements by using copper powder having a fine particle size and a sharp particle size distribution obtained by a wet manufacturing method. However, the copper powder obtained by the wet method has a small crystallite diameter, and when trying to increase the crystallite diameter to a level that can improve the heat shrinkage resistance, the copper powder is heated to form a granule. It is necessary to grow the grain size inside. Therefore, it is considered that the copper powder obtained by the wet method may be heated. Therefore, considering that the copper powder obtained by the wet method is heated, when heating is performed in a normal copper powder state, the surface of the copper powder is oxidized, and an oxide film is formed on the surface. The agglomerated state will proceed, and the dispersibility of the powder will be significantly impaired. If such a powder is used for the production of a low-temperature fired ceramic, the resulting low-temperature fired ceramic has a rough surface. Therefore, by simply heating ordinary copper powder, it is possible to provide copper powder having a sharp particle size distribution and a small particle size, as well as ensuring the dispersibility of the particles and at the same time having excellent oxidation resistance and heat shrinkage resistance. It becomes difficult.

  As is clear from what has been described above, in the market, copper powder satisfying two points has been required. i) It is a fine powder that can lower the paste viscosity when processed into a conductive paste and that can effectively suppress the change in paste viscosity over time. ii) Even if it is a fine copper powder, it is a powder excellent in the oxidation resistance in the temperature range which can be sintered, and the heat shrinkable property which delays the shrinkage start at the time of sintering.

  Therefore, as a result of earnest research, the inventors of the present invention have increased the viscosity of the conductive paste by forming a two-layer coated copper powder in which the surface of the copper powder is coated with an organic coat layer and a thin inorganic oxide coat layer. It was conceived that it was possible to obtain a powder excellent in heat resistance shrinkage with good oxidation resistance and small shrinkage during sintering by suppressing the change with time. The present invention will be described below.

A. Two-layer coated copper powder: The basic configuration of the two-layer coated copper powder according to the present invention is “two layers comprising a two-layer inorganic coating layer on the surface of copper powder particles used as a core material used in the production of a conductive paste. It is a coated copper powder, and the powder particle surface of the copper powder that is the core material is composed of either one of copper oxide or cuprous oxide or two of them, and the converted mass thickness is 3 of the double-layer coated copper powder mass. A first inorganic coat layer having a mass% to 20 mass% is provided, and any one or two of silicon oxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium oxide, and zinc oxide are provided on the outer shell of the first inorganic coat layer. “A two-layer coated copper powder comprising a second inorganic coating layer composed of an inorganic oxide and composed of seeds or more”.

  The thickness of the second inorganic coat layer referred to here is the first feature in that the thickness is extremely thinner than that of the inorganic oxide layer disclosed in Patent Document 3. In order to form this thin second inorganic coat layer, the first inorganic coat layer is first present, and it is necessary to form the second inorganic coat layer on the outer shell. In this way, the first inorganic coat layer is present, and further, the second inorganic coat layer is formed, so that the second inorganic coat layer is thinly and uniformly attached to the surface of the particle, and for the first time, the oxidation resistance and the heat shrink resistance are simultaneously improved. It can be improved.

(First inorganic coating layer)
First, the first inorganic coat layer located on the surface of the copper powder powder as the core material will be described. The first inorganic coat layer serves as an auxiliary layer for forming the second inorganic coat layer thinly, but the first inorganic coat layer alone is a layer that directly contributes to heat shrinkage resistance. There is no. However, since the first inorganic coating layer is a layer formed by atmospheric oxidation or chemical treatment by heating, it is considered that the first inorganic coating layer is more uniformly formed on the surface of the copper powder particles that are the core material than the second inorganic coating layer. It is done. Therefore, when the copper powder is heated, if the second inorganic coating layer cannot prevent the diffusion of oxygen into the core material, the first inorganic coating layer serves as a barrier that prevents the growth of an excess oxide film. It plays a role. The fact that no excess oxide film is formed in this way means that it is possible to effectively prevent an increase in electrical resistance of the conductor obtained by sintering, and to ensure good electrical conductivity of the formed conductor. Is an indispensable element.

  In the first inorganic coating layer, it is preferable to use a composite compound composed of any one of copper oxide and cuprous oxide, or two of these. It is because it is excellent in adhesiveness with the second inorganic coat layer formed on the outer shell of the first inorganic coat layer and does not become a significant inhibiting component of electrical conductivity. Here, “two types” may include a plurality of components among the above components depending on the method of forming the first inorganic coating layer, and as long as the inventors confirm, This is because the same effect as when used is exhibited.

It is difficult to physically indicate the thickness of the first inorganic coat layer as a gauge thickness as a copper powder that is an aggregate of fine powder particles. Accordingly, the inventors of the present invention decided to express the thickness of the first inorganic coat layer as a converted mass thickness. The reduced mass thickness, the proportion of first inorganic coating layer in a two layer coating copper powder mass, the oxygen content of the copper powder immediately after formation of a first inorganic coating layer was measured, the cuprous oxide It is assumed that it is captured by mass% when converted. Strictly speaking, when considering the converted mass thickness, it is necessary to consider the particle size of the copper powder. As the quality of the copper powder is constant, if present copper powder and the particle size diameter is small and a large copper powder, larger in specific surface area of the former, the surface coating of the particulate with the same amount of inorganic This is because the inorganic coating layer of the former copper powder becomes thinner if performed.

Therefore, the present inventors consider that the two-layer coated copper powder is used for conductor formation, and considering the particle size, the value of the cumulative volume particle size D ₅₀ by the laser diffraction scattering particle size distribution measurement method is 0. Based on the case of 1 μm to 10 μm. In such a case, the converted mass thickness of the first inorganic coat layer is preferably in the range of 3% by mass to 20% by mass of the two-layer coated copper powder.

  When the coating amount is less than 3% by mass, the function of the second inorganic coating layer as a binder layer is not achieved, and the second inorganic coating layer cannot be formed uniformly by a mechanochemical method. Furthermore, in order to further stabilize the formation state of the second inorganic coat layer, it is preferably 5% by mass or more. On the other hand, even if the thickness exceeds 20% by mass, the effect of further improving the uniform throwing power of the second inorganic coating layer cannot be obtained. However, 15% by mass can be regarded as a realistic upper limit. This is because the effect of improving the uniform throwing power of the second inorganic coating layer between 15% by mass and 20% by mass is only slightly increased.

(Second inorganic coating layer)
Next, the second inorganic coat layer provided on the first inorganic coat layer will be described. When the inorganic oxide coating layer was formed by the method disclosed in Patent Document 3, it became thick and had to be completely coated with powder particles. On the other hand, the two-layer coated copper powder of the present invention provides a first inorganic coat layer in advance on the surface of the powder and forms a thin second inorganic coat layer with excellent adhesion on the first inorganic coat layer. The second inorganic coat layer is preferably formed by employing a mechanochemical manufacturing method described later. The second inorganic coat layer may be completely coated on the surface of the powder particles, but it is preferable that the second inorganic coat layer is in a discontinuous adhesion state in which the first inorganic coat layer is partially exposed.

  In the second inorganic coating layer, one or more of silicon oxide, aluminum oxide, magnesium oxide, zirconium oxide, and zinc oxide are used. Among these, it is preferable to use any one of silicon oxide, aluminum oxide, and magnesium oxide. Silicon oxide, aluminum oxide, and magnesium oxide are easily fixed uniformly on the surface of the copper powder particles. At the same time, considering that the firing temperature of the low-temperature fired ceramic is generally 900 ° C. or higher, it functions as one that most effectively prevents aggregation of the copper powder as the core material.

The thickness of the second inorganic material coating layer, as in the first inorganic material coating layer, expressed as reduced mass thickness, reduced mass thickness of the second inorganic material coating layer, 0 bilayer coated copper powder. It is preferable that it exists in the range of 1 mass%-10 mass%.

When the converted mass thickness is less than 0.1% by mass, it does not play the role of preventing the progress of aggregation of the powder particles by heating at the firing level of the low-temperature fired ceramic. On the other hand, in the case of the converted mass thickness exceeding 10% by mass , it is considered that it is caused by the production method described below, but the dispersibility of the obtained two-layer coated copper powder is deteriorated. . By forming the uniform and thin second inorganic coating layer in this way, the two-layer coated copper powder according to the present invention can minimize the deterioration of the electrical conductivity of the powder itself. It is. Furthermore, in order to eliminate the manufacturing variation described below and further stabilize the heat-resistant shrinkage obtained, the converted mass thickness of the second inorganic coating layer is in the range of 0.2% by mass to 5% by mass. It is more preferable to do this.

  By adopting the two-layer coated copper powder having the structure as described above, the heat treatment performed later can be easily performed, and the crystallite diameter can be adjusted. That is, even if the crystallite diameter is adjusted by heating, the change in the particle shape is minimized by the presence of the second inorganic coat layer in the outer shell, and the first inorganic coat layer is heated. Oxygen that sometimes diffuses and penetrates into the powder grains is blocked, and unnecessary growth of the oxide layer on the surface of the copper powder as the core material is prevented. As a result, even if heating to adjust the crystallite size is performed, the aggregation of powder particles is effectively prevented and the dispersibility as a powder property is not significantly deteriorated. It can be done.

  At this time, the crystallite diameter of the copper powder particles as the core material is preferably 50 nm or more. This crystallite diameter of 50 nm or more is equal to or larger than the crystallite diameter of the copper powder obtained by the dry manufacturing method, and the copper powder obtained by the wet method can be provided without heat treatment. There is no crystallite size value. Further, when the value of the crystallite diameter is 50 nm or more, the heat shrinkage resistance is suddenly improved.

B. Production method of two-layer coated copper powder: The production of the two-layer coated copper powder according to the present invention involves forming a first inorganic coat layer on the surface of the copper powder particles, and then forming a second on the surface of the first inorganic coat layer. By sequentially forming the inorganic coating layer. Moreover, the adjustment process of a crystallite diameter is added as needed. Hereinafter, each process will be described in detail.

(Formation process of 1st inorganic substance coating layer)
Using a heat treatment or a wet chemical treatment in the air atmosphere, the powder particle surface of the copper powder of the core material is composed of either one of copper oxide or cuprous oxide or two of these, and the converted mass thickness is two layers. A 1st inorganic substance coating layer which is 3 mass%-20 mass% of coat copper powder mass is formed. The formation of the first inorganic coat layer is performed by modifying the powder particle surface of the copper powder as the core material, and can be roughly divided into two methods. One is a method in which copper powder as a core material is heated and oxidized in an air atmosphere to form a copper oxide layer on the surface of the copper powder particles (hereinafter, simply referred to as “heating method”). And the other is that a layer made of any one of copper oxide and cuprous oxide or a composite compound of these two types is formed on the surface of copper powder particles as a core material using wet chemical treatment. (Hereinafter simply referred to as “chemical method”).

  As the former heating method, a method of heating at a high temperature in an air atmosphere or a method of heating at a high temperature in an inert gas replacement atmosphere in which oxygen is slowly leaked is employed. There are no particular restrictions on the conditions of the heating method and the like, and a simpler method for controlling the thickness of the first inorganic coat layer described above may be arbitrarily employed.

  As for the latter chemical method, if the solution is a solution that uniformly forms copper oxide, cuprous oxide, or a composite compound thereof on the surface of the copper powder particles, a method in which the copper powder is put into the solution and reacted is adopted. There is no limitation regarding the method. However, chemical methods may contain extra components that become impurities that increase electrical resistance, and extreme care should be taken when selecting chemicals.

(Formation process of 2nd inorganic substance coating layer)
The second inorganic coat layer is formed by the following method. That is, the inorganic oxide layer is formed by fixing the inorganic oxide on the outer shell of the first inorganic coating layer. The inorganic oxide layer can be formed by either a wet coating method or a dry coating method. With respect to the wet coating method, there is no particular limitation on the method, and the inorganic oxide layer can be formed according to a conventional method, and the adhesion of the inorganic oxide coating layer to the powder particle surface is improved. On the other hand, from the viewpoint of control of the component balance of the inorganic oxide layer, from the viewpoint of control of the component balance of the inorganic oxide layer is the preferred to fixed by Mekanokemika Le technique is a dry coating method.

Here, a method for fixing the inorganic oxide constituting the second inorganic coat layer to the surface of the copper powder particles by a mechanochemical method will be described. The mechanochemical method is to stir and mix the copper powder forming the first inorganic coat layer and the inorganic oxide powder constituting the second inorganic coat layer, using a ball mill type media, etc. The inorganic oxide is fixed to the surface of the copper powder particles on which the first inorganic coating layer is formed, and the copper powder particles and the inorganic oxide powder particles on which the first inorganic coating layer is formed. Any device capable of mixing and colliding is sufficient, and no special equipment is required. As the inorganic oxide powder used at this time, a powder having a specific surface area of 50 m ² / g or more is preferably used. This specific surface area depends mainly on the particle diameter of the inorganic oxide powder, and it can be said that the particle diameter decreases as the specific surface area increases.

The shell of the thus first inorganic coating layer, by forming the inorganic oxide coating layer with Mekanokemika Le technique improves the adhesion of the hard, brittle supposed inorganic oxides would otherwise thin uniform A second inorganic coating layer made of an inorganic oxide having a thickness can be formed. When the formation of the second inorganic coat layer is completed, the form of the two-layer coated copper powder according to the present invention is temporarily provided.

(Process for adjusting crystallite diameter)
When the copper powder used as the core material has a small crystallite diameter, the two-layer coated copper powder obtained by the above-described process is subjected to a heat treatment for the purpose of adjusting the crystallite diameter, The crystallite diameter of the powder is preferably 50 nm or more. This heat treatment is performed under the following conditions. This heat treatment is to promote so-called recrystallization and increase the crystallite diameter. However, this heat treatment should not change the quality of the first inorganic coat layer and the second inorganic coat layer or promote the aggregation of the powder particles of the two-layer coated copper powder.

  Considering these, it is desirable to perform the heat treatment in an inert gas atmosphere at 500 ° C. to 1000 ° C. Heating at a temperature of less than 500 ° C. makes it difficult to recrystallize the copper powder crystals obtained by the wet manufacturing method. On the other hand, when heating at a temperature exceeding 1000 ° C., even if the first inorganic coat layer and the second inorganic coat layer are present, the aggregation of the two-layer coated copper powder proceeds, and the powder particles themselves It will soften and the shape of the powder will deteriorate. In order to prevent unintended oxidation of the core material itself, it is preferable to employ an inert gas atmosphere as the heating atmosphere.

By adopting the production method as described above, it is possible to prevent the agglomeration of the two-layer coated copper powder, and “the average particle diameter D ₅₀ by the laser diffraction scattering type particle size distribution measuring method and the standard deviation of the particle size distribution”. The variation coefficient CV value represented by the relational expression SD / D ₅₀ with respect to SD can be prevented from deteriorating. The “standard deviation SD” is a standard deviation obtained from the particle size distribution of the powder obtained as a result of measurement using the laser diffraction / scattering particle size distribution measurement method. The smaller the value of this CV value, the smaller the CV value. This means that the particle diameters of the particles are uniform, the dispersibility is excellent, and there is no large variation.

  The two-layer coated copper powder according to the present invention comprises a first inorganic coat layer and a second inorganic coat, and the presence of the first inorganic coat layer on the powder particle surface of the copper powder serving as the core material, The adhesion of the second inorganic coating layer made of an inorganic oxide is improved, and the second inorganic coating layer is formed as a thin inorganic layer. This two-layer coated copper powder simultaneously has good oxidation resistance and good heat shrinkage performance. Moreover, the viscosity reduction of the electrically conductive paste manufactured using the two-layer coat copper powder concerning this invention can also be achieved. Moreover, the manufacturing method of the two-layer coated copper powder adopted in the present invention is excellent in the production stability of the two-layer coated copper powder, and is optimal for supplying the two-layer coated copper powder with little variation in product quality.

  Hereinafter, the present invention will be described in more detail with reference to the present invention through an embodiment while comparing with a comparative example.

Production of copper powder: First, a method for producing copper powder used as a core material will be described. 4 kg of copper sulfate (pentahydrate) and 120 g of aminoacetic acid were dissolved in water to prepare an 8 L (liter) copper salt aqueous solution having a liquid temperature of 60 ° C. While stirring this aqueous solution, 5.75 kg (1.15 equivalents) of 25 wt% sodium hydroxide solution was quantitatively added over about 30 minutes, and stirring was performed at a liquid temperature of 60 ° C. for 60 minutes. The cupric oxide was produced by aging until the color was completely black. Thereafter, the mixture was allowed to stand for 30 minutes, 1.5 kg of glucose was added, and the cupric oxide was reduced to cuprous oxide by aging for 1 hour. Furthermore, 1 kg of hydrated hydrazine was quantitatively added over 5 minutes to reduce cuprous oxide to form metallic copper, thereby producing a copper powder slurry.

Then, the obtained copper powder slurry was filtered, sufficiently washed with pure water, filtered again, and dried in an inert gas to prevent excessive oxidation, thereby obtaining copper powder. The cumulative volume particle diameter _{D 50} of the laser diffraction scattering particle size distribution measurement method of a copper powder is 0.93 .mu.m, coefficient of variation CV value was 0.22, and the crystallite diameter 32.2Nm, converted to cuprous oxide The oxide coating amount was 2% by mass. And as a result of measuring a thermal expansion coefficient, shrinkage | contraction started from 600 degreeC vicinity, and the shrinkage | contraction rate in 900 degreeC was 13.0%.

  In addition, the measurement of the crystallite diameter in the present specification is obtained by calculating the average crystallite diameter using RINTKU V made by RIGaku and using the crystallite analysis software. The crystallite diameter in the present specification is the average crystal diameter. It is a child diameter. The shrinkage is measured by thermal expansion while heating the obtained powder in a predetermined atmosphere using a thermomechanical analyzer (TMA / SS6000 manufactured by Seiko Denshi Kogyo Co., Ltd.) at a heating rate of 10 ° C./min. The rate was continuously measured, and the thermal shrinkage rate when the ambient temperature was 900 ° C. was measured.

Formation of first inorganic coat layer: The formation of the first inorganic coat layer in this example is performed by using the copper powder obtained by the above-described method using a ball mill (using zirconia beads having a diameter of 0.65 mm as a medium). While preventing agglomeration of the powder particles, the heat treatment was performed in an air atmosphere by an oxidation heat treatment at 150 ° C. for 1 hour. Cumulative volume particle diameter D ₅₀ of the laser diffraction scattering particle size distribution measurement method of a copper powder to form a first inorganic coating layer is 0.99 .mu.m, coefficient of variation CV value was 0.25, and the crystallite diameter 33 The amount of oxide coating converted to 0.2 nm and cuprous oxide was 4% by mass. And as a result of measuring a thermal expansion coefficient, shrinkage | contraction started from 550 degreeC vicinity, and the shrinkage rate in 900 degreeC was 13.5%.

Formation of second inorganic coat layer: Then, 3 kg of copper powder on which this first inorganic coat layer was formed and 30 g of aluminum oxide powder (average particle size 10 nm) as an inorganic oxide were rotated at 6000 rpm using a hybridizer. Then, a mechanochemical fixing process for 5 minutes was performed to produce a two-layer coated copper powder having a second inorganic coating layer composed of aluminum oxide. The coating amount of aluminum oxide coated on the surface of the two-layer coated copper powder was 1% by mass. The cumulative volume particle diameter _{D 50} of the laser diffraction scattering particle size distribution measurement method of two-layer coated copper powder immediately after coating is 0.98 .mu.m, coefficient of variation CV value was 0.23, and the crystallite diameter 27.5nm Met. As a result of measuring the thermal expansion coefficient, the shrinkage rate at 900 ° C. was 3.6%. That is, when the core copper powder is subjected to mechanochemical processing, the crystallite diameter is smaller than that of the copper powder obtained by the original wet manufacturing method, but the second inorganic coat layer is the oxide coat layer. Therefore, the shrinkage rate at the time of thermal expansion was reduced, and the shrinkage rate was within the range required by the market.

Adjustment of crystallite diameter: Therefore, the two-layer coated copper powder obtained as described above is heated for 1 hour at each temperature of 500 ° C., 700 ° C., and 900 ° C. in a nitrogen gas atmosphere. Three types of two-layer coated copper powders were prepared. As a result, A) When the temperature of 500 ° C. is employed, the volume cumulative particle size D ₅₀ of the laser diffraction scattering particle size distribution measurement method of the two-layer coated copper powder after heating is 0.98 μm, and the crystallite diameter is 50.6 nm, coefficient of variation CV value is 0.24, B) Volume cumulative particle size of laser diffraction scattering type particle size distribution measurement method of double layer coated copper powder after heating when temperature of 700 ° C. is adopted D ₅₀ is 0.99 μm, the crystallite diameter is 58.4 nm, the coefficient of variation CV is 0.25, and C) of the two-layer coated copper powder after heating when a temperature of 900 ° C. is adopted cumulative volume particle diameter _{D 50} of the laser diffraction scattering particle size distribution measurement method is 1.00 .mu.m, crystallite size 66.8Nm, coefficient of variation CV value was 0.25.

  From this result, the crystallite diameter is the same as the copper powder obtained by the dry manufacturing method when temperatures of 500 ° C. and 700 ° C. are adopted, and when heated at a temperature of 900 ° C., the dry crystal type is obtained. It can be seen that a crystallite size larger than the copper powder obtained by the production method is obtained. Moreover, even if it heats at any temperature, it turns out that it has not deteriorated greatly seeing from the CV value of the copper powder before forming a 2nd inorganic substance coating layer.

Evaluation of heat resistance characteristics: Further, the thermal expansion coefficient was measured by the same method as described above using three types of two-layer coated copper powder. As a result, the shrinkage rate at 900 ° C. was A) heating at 500 ° C. When the temperature is adopted, the shrinkage rate of the two-layer coated copper powder after heating is 2.5%. B) When the heating temperature of 700 ° C. is adopted, the shrinkage rate of the two-layer coated copper powder after heating is 2 0.0%, C) When the heating temperature of 900 ° C. is adopted, the shrinkage rate of the two-layer coated copper powder after heating is 1.8%, and the shrinkage rate within 5% seems to be all ideal. It was settled.

Evaluation of specific resistance of the film : The specific resistance of the film was measured by adding 20 g of powder used for measurement into 20 g of a solution of 95 wt% terpineol C and 5 wt% ethyl cellulose, kneading with a three roll, and then an alumina substrate. Was screen-printed and dried at a temperature of 80 ° C. for 1 hour. Then, after hold | maintaining at 300 degreeC for 1 hour in nitrogen substitution atmosphere containing 1 wt% of hydrogen, it baked at 950 degreeC for 1 hour. Thereafter, the obtained fired film was returned to room temperature, and the film resistance was measured. As a result, 1.9 × 10 ⁻⁶ Ω · cm when the core copper powder before coating was used, and 2 when the two-layer coated copper powder obtained in this example before heat treatment was used. .6 × 10 ⁻⁶ Ω · cm, when two-layer coated copper powder after heating at 500 ° C. is used 2.4 × 10 ⁻⁶ Ω · cm, two-layer coated copper after heating at 700 ° C. When the powder was used, it was 2.3 × 10 ⁻⁶ Ω · cm, and when the two-layer coated copper powder after heating at 900 ° C. was used, it was 2.1 × 10 ⁻⁶ Ω · cm. From this result, it is clear that even when two inorganic coating layers are provided, the specific resistance of the film does not change greatly, and the specific resistance of the film is reduced by heating the two-layer coated copper powder. It is.

Paste viscosity evaluation: Further, the inventors of the present invention produced a terpineol-based conductive paste using the two-layer coated copper powder (immediately after the formation of the second inorganic coating layer) obtained as described above. The terpineol-based conductive paste produced here was obtained by kneading these two-layer coated copper powders with a composition of 88 parts by mass and binder of 12 parts by mass. As the binder at this time, a binder having a composition of 93 parts by mass of terpineol and 7 parts by mass of ethyl cellulose was used. When the viscosity of this terpineol-based conductive paste is measured, it is 450 Pa · s.

  In this example, the method for forming the first inorganic coating layer of Example 1 was changed to a chemical method, and other two-layer coated copper powder was produced in the same manner as in Example 1. Therefore, the description regarding the production of the copper powder is omitted, and the description will be made from the formation of the first inorganic coat layer.

Formation of the first inorganic coating layer: For the formation of the first inorganic coating layer, 1 kg of the copper powder used for the core material in Example 1 was dispersed in 3 liters of pure water to form a copper powder slurry, and the powder was stirred. While preventing agglomeration of particles, 10 g / l concentration of hydrogen peroxide solution is added over 1 hour, and the powder of copper powder is modified to a first inorganic coating layer composed of copper oxide and cuprous oxide, The copper powder provided with the 1st inorganic substance coating layer was obtained by washing with water and drying. Cumulative volume particle diameter D ₅₀ of the laser diffraction scattering particle size distribution measurement method of a copper powder to form a first organic coating layer is 0.99 .mu.m, coefficient of variation CV value was 0.26, and the crystallite diameter 33 The amount of oxide coating converted to 0.2 nm and cuprous oxide was 4.5% by mass. And as a result of measuring a thermal expansion coefficient, shrinkage | contraction started from 530 degreeC vicinity, and the shrinkage rate in 900 degreeC was 13.9%.

Formation of second inorganic coat layer: Then, 3 kg of copper powder on which this first inorganic coat layer was formed and 30 g of aluminum oxide powder (average particle size 10 nm) as an inorganic oxide were rotated at 6000 rpm using a hybridizer. Then, a mechanochemical fixing process for 5 minutes was performed to produce a two-layer coated copper powder having a second inorganic coating layer composed of aluminum oxide. The coating amount of aluminum oxide coated on the surface of the two-layer coated copper powder was 1% by mass. The cumulative volume particle diameter _{D 50} of the laser diffraction scattering particle size distribution measurement method of two-layer coated copper powder immediately after coating is 0.98 .mu.m, coefficient of variation CV value was 0.24, and the crystallite diameter 27.8nm Met. As a result of measuring the thermal expansion coefficient, the shrinkage rate at 900 ° C. was 3.8%.

Adjustment of crystallite diameter: Thus, three types of two-layer coated copper powders having the crystallite diameter adjusted in the same manner as in Example 1 were obtained from the two-layer coated copper powder obtained as described above. As a result, A) When adopting a temperature of 500 ° C., the volume cumulative particle diameter D ₅₀ of the laser diffraction scattering type particle size distribution measurement method of the two-layer coated copper powder after heating is 0.99 μm, and the crystallite diameter is 50.5 nm, coefficient of variation CV value is 0.24, and B) Volume cumulative particle diameter of laser diffraction scattering type particle size distribution measurement method of double-layer coated copper powder after heating when temperature of 700 ° C. is adopted D ₅₀ is 1.00 μm, the crystallite diameter is 57.6 nm, the coefficient of variation CV is 0.25, and C) of the two-layer coated copper powder after heating when a temperature of 900 ° C. is adopted. cumulative volume particle diameter _{D 50} of the laser diffraction scattering particle size distribution measurement method is 1.01Myuemu, crystallite size 63.4Nm, coefficient of variation CV value was 0.26.

  From this result, the crystallite diameter is the same as the copper powder obtained by the dry manufacturing method when temperatures of 500 ° C. and 700 ° C. are adopted, and when heated at a temperature of 900 ° C., the dry crystal type is obtained. It can be seen that a crystallite size larger than the copper powder obtained by the production method is obtained. Moreover, even if it heats at any temperature, it turns out that it has not deteriorated greatly seeing from the CV value of the copper powder before forming a 2nd inorganic substance coating layer.

Evaluation of heat resistance characteristics: Further, the thermal expansion coefficient was measured by the same method as described above using three types of two-layer coated copper powder. As a result, the shrinkage rate at 900 ° C. was A) heating at 500 ° C. When the temperature is adopted, the shrinkage rate of the two-layer coated copper powder after heating is 2.6%. B) When the heating temperature of 700 ° C. is adopted, the shrinkage rate of the two-layer coated copper powder after heating is 2 .2%, C) When the heating temperature of 900 ° C. is adopted, the shrinkage rate of the two-layer coated copper powder after heating is 1.9%, and the shrinkage rate within 5% seems to be all ideal. It was settled.

Evaluation of specific resistance of film : The specific resistance of the film was measured in the same manner as in Example 1. As a result, 1.9 × 10 ⁻⁶ Ω · cm when the core copper powder before coating was used, and 2 when the two-layer coated copper powder obtained in this example before heat treatment was used. .7 × 10 ⁻⁶ Ω · cm, when two-layer coated copper powder after heating at 500 ° C. is used 2.6 × 10 ⁻⁶ Ω · cm, two-layer coated copper after heating at 700 ° C. When powder was used, it was 2.5 × 10 ⁻⁶ Ω · cm, and when double-layer coated copper powder after heating at 900 ° C. was used, it was 2.2 × 10 ⁻⁶ Ω · cm. From this result, it is clear that even when two inorganic coating layers are provided, the specific resistance of the film does not change greatly, and the specific resistance of the film is reduced by heating the two-layer coated copper powder. It is.

Paste viscosity evaluation: Further, similarly to Example 1, a terpineol-based conductive paste was produced using the two-layer coated copper powder (immediately after the formation of the second inorganic coating layer) obtained as described above. The viscosity of this terpineol-based conductive paste is measured to be 460 Pa · s.

Comparative Example 1

In this comparative example, 500 g of the same copper powder as used in Example 1 was dispersed in 2 liters of pure water to form a copper slurry, and the bath temperature was 60 ° C. To this, 40 ml of a 0.4 g / ml NaAl (OH) ₄ aqueous solution was added over 1 hour with stirring. During this addition, a 20 wt% aqueous hydrochloric acid solution was used to maintain the solution pH at 8. Thereafter, stirring was continued for 30 minutes, followed by filtration, washing and drying to obtain a surface-treated copper powder.

The surface treatment volume cumulative particle diameter _{D 50} of the laser diffraction scattering particle size distribution measurement method of a copper powder is 1.50 .mu.m, coefficient of variation CV value was 0.52, and the crystallite diameter was 32.0 nm. As a result of measuring the thermal expansion coefficient, the shrinkage rate at 900 ° C. was 3.2%.

The specific resistance of the film was measured in the same manner as in Example 1. As a result, when the surface-treated copper powder obtained in the present example was used, it was 3.5 × 10 ⁻⁵ Ω · cm, and a value different in order from the above example was obtained. Furthermore, similarly to Example 1, a terpineol-based conductive paste was produced using the surface-treated copper powder obtained as described above. The viscosity of this terpineol-based conductive paste is 750 Pa · s.

Comparative Example 2

  In this comparative example, the same copper powder as used in Example 1 was used, and the first inorganic coat layer was not formed, and the same as the formation of the second inorganic coat layer of Example 1 on the powder particle surface of the copper powder. In this way, only the second inorganic coating layer was formed to obtain an inorganic oxide-coated copper powder.

This inorganic oxide-coated copper powder had a volume cumulative particle size D ₅₀ of 0.98 μm, a coefficient of variation CV of 0.27, and a crystallite size of 27.5 nm. It was. As a result of measuring the thermal expansion coefficient, the shrinkage rate at 900 ° C. was 4.5%.

The specific resistance of the film was measured in the same manner as in Example 1. As a result, when the inorganic oxide-coated copper powder obtained in this comparative example is used, it is 6.6 × 10 ⁻⁶ Ω · cm, which is a relatively higher resistance than the above-described example. Judging from this result, it is considered that the shrinkage rate at 900 ° C. is increased because the adhesion of the inorganic oxide coating layer is poor. Furthermore, similarly to Example 1, a terpineol-based conductive paste was produced using the surface-treated copper powder obtained as described above. The viscosity of this terpineol-based conductive paste is 780 Pa · s.

Comparative Example 3

In this comparative example, 1 kg of the copper powder similar to that used in Example 1 was used to make a copper powder slurry in 3 liters of pure water, and 500 g / l of hydrogen peroxide solution was added for 1 hour while stirring. It added, synthesize | combined oxidation treatment copper powder, washed with water, dried, and obtained the oxidation treatment copper powder whose oxide coat amount when converted into cuprous oxide was 25 mass%. Cumulative volume particle diameter _{D 50} of the laser diffraction scattering particle size distribution measuring method of the oxidation-treated copper powder is 1.95Myuemu, coefficient of variation CV value was 0.45, and the crystallite diameter was 31.1nm. And as a result of measuring a thermal expansion coefficient, shrinkage | contraction started from 500 degreeC, and the shrinkage | contraction rate in 900 degreeC was 15.9%.

And 3 kg of this oxidized copper powder and 30 g of aluminum oxide, which is an inorganic oxide, were mechanochemically processed at a rotational speed of 6000 rpm using a hybridizer to obtain aluminum oxide-coated copper powder. Then, the cumulative volume particle diameter _{D 50} of the laser diffraction scattering particle size distribution measuring method of the aluminum oxide coated copper powder is 1.08 .mu.m, coefficient of variation CV value was 0.30, and the crystallite diameter in the 24.6nm there were. As a result of measuring the thermal expansion coefficient, the shrinkage rate at 900 ° C. was 5.1%.

The specific resistance of the film was measured in the same manner as in Example 1. As a result, when the inorganic oxide-coated copper powder obtained in this comparative example is used, it is 7.5 × 10 ⁻⁶ Ω · cm, which is a relatively higher resistance than the above-described example. Furthermore, similarly to Example 1, a terpineol-based conductive paste was produced using the surface-treated copper powder obtained as described above. The viscosity of this terpineol-based conductive paste is measured to be 880 Pa · s.

  The two-layer coated copper powder according to the present invention is an oxidation resistance and heat shrinkage when subjected to high temperature heating while maintaining uniform fineness and excellent dispersibility, which are advantages of the copper powder obtained by the wet manufacturing method. At the same time with excellent quality. By using this two-layer coated copper powder, it is possible to improve the dimensional stability of a sintered body containing copper powder such as a low-temperature fired ceramic, and it is possible to dramatically improve the product yield. In addition, the two-layer coated copper powder can be heated at high temperature without agglomerating the copper powder of the core material, so that it is easy to adjust the crystallite diameter of the copper powder of the core material. It becomes possible to adopt.

  Moreover, since the two-layer coated copper powder according to the present invention includes the first inorganic coating layer on the powder particle surface of the copper powder that is the core material, the second inorganic coating layer provided on the outer shell is unprecedented. Since the thickness can be reduced, it is possible to minimize the deterioration of the electrical conductive characteristics.

Claims (6)

It is a two-layer coated copper powder comprising a two-layer inorganic coating layer on the surface of copper powder particles used as a core material for the production of a conductive paste ,
The powder particle surface of the copper powder, which is the core material, is composed of either one of copper oxide and cuprous oxide, or two of these, and the converted mass thickness is 3% to 20% by mass of the mass of the two-layer coated copper powder. A first inorganic coating layer,
On the outer shell of the first inorganic coat layer, a second inorganic coat layer made of an inorganic oxide composed of one or more of silicon oxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium oxide, and zinc oxide is provided. A two-layer coated copper powder characterized by comprising. The two-layer coated copper powder according to claim 1, wherein the converted mass thickness of the second inorganic coat layer is 0.1 mass% to 10 mass% of the mass of the two-layer coated copper powder. The double-layer coated copper powder according to claim 1 or 2, wherein the crystallite diameter of the copper powder particles as the core material is 50 nm or more. It is a manufacturing method of the two-layer coat | court copper powder in any one of Claims 1-3, Comprising: The following A) 1st inorganic substance coat layer formation process and B) 2nd inorganic substance coat layer formation process are provided. A method for producing a two-layer coated copper powder, wherein
A) Using heat treatment or wet chemical treatment in an air atmosphere, the surface of the copper powder of the core material is composed of either one of copper oxide or cuprous oxide or two of them, and the equivalent mass thickness is A 1st inorganic substance coat layer which is 3 mass%-20 mass% of double layer coat copper powder mass is formed.
B) Further, a second inorganic coat layer made of an inorganic oxide is formed on the outer shell on which the first inorganic layer is formed. It is a manufacturing method of the two-layer coated copper powder of Claim 4, Comprising: A) 1st inorganic substance coat layer formation process shown below, B) 2nd inorganic substance coat layer formation process, C) Crystallite diameter adjustment process shown below A method for producing a two-layer coated copper powder, comprising:
A) Using heat treatment or wet chemical treatment in an air atmosphere, the surface of the copper powder of the core material is composed of either one of copper oxide or cuprous oxide or two of them, and the equivalent mass thickness is A 1st inorganic substance coat layer which is 3 mass%-20 mass% of double layer coat copper powder mass is formed.
B) Further, a second inorganic coat layer made of an inorganic oxide is formed on the outer shell on which the first inorganic layer is formed.
C) The copper powder having the first inorganic coat layer and the second inorganic coat layer formed as described above is heat-treated in an inert gas atmosphere at 500 ° C. to 1000 ° C. so that the crystallite diameter of the copper powder is 50 nm or more. Adjust so that The electroconductive paste manufactured using the two-layer coat | court copper powder in any one of Claims 1-3 .