JP6914999B2 - Surface treatment copper powder - Google Patents

Description

The present invention relates to surface-treated copper powder.

Copper powder paste has come to be used as an electronic material. The copper powder paste is, for example, printed or applied to a base material and then fired in a reducing atmosphere to be used for forming wiring, forming electrodes, and the like. As the electrode layer used becomes thinner and the pitch of wiring becomes narrower, the copper powder of the paste material is required to be made finer.

Fine (eg, submicron-sized) metal powders begin to sinter at temperatures well below the melting point of elemental metals. Copper powder is attracting particular attention from the viewpoint of cost and migration.

In order for the copper powder paste to form high quality wiring and electrodes, it has been conventionally considered that the oxidation of the copper powder must be prevented as much as possible. However, in recent years, assuming that it is mainly used for firing in a reducing atmosphere, copper having excellent properties is obtained by positively forming an oxide layer on the surface of copper powder and controlling this formation. Attempts have been made to obtain powdered pastes.

Patent Document 1 discloses a technique for positively forming a uniform copper oxide layer on the surface of copper powder particles, thereby lowering the sintering temperature of the copper powder.

Patent Document 2 discloses a technique for heating and oxidizing a metal powder.

Patent Document 3 discloses a technique of adhering fatty acids to a metal powder to protect the copper oxide layer with fatty acids.

Patent Document 4 discloses a technique using copper powder having ^{a tap density value of 5.1 g / cm 3} or more in order to improve the printing characteristics of the copper powder paste.

Patent Document 5 discloses a method for producing copper powder by a disproportionation method.

Patent Document 6 discloses a method for producing copper powder by a chemical reduction method.

Japanese Unexamined Patent Publication No. 2011-094236 Japanese Unexamined Patent Publication No. 2003-105402 Japanese Unexamined Patent Publication No. 2013-136840 JP-A-2007-332391 Japanese Patent No. 6297018 Japanese Patent No. 4164009

According to the study of the present inventor, the metal powder produced by the techniques disclosed in Patent Document 1 and Patent Document 2 becomes difficult to crush the metal powder required after being oxidized by heating, and the metal powder agglomerates. There was a great risk that it would end up being a patent.

Further, according to the study of the present inventor, the metal powder produced by the technique disclosed in Patent Document 3 is one in which the metal powder is agglomerated due to the agglomeration of the metal powder being promoted by the fatty acids used. There was a great risk that it would become.

Then, according to the study of the present inventor, when the metal powder to which the oxide layer is imparted is aggregated to form an agglomerate, the metal powder agglomerate is calcined in a relatively low temperature reducing atmosphere. In that case, it was found that the inside of the agglomerate may not be sufficiently reduced, and as a result, a portion where the sintering is insufficient is generated and the specific resistance of the sintered body is increased. .. Furthermore, it was found that when the metal powder agglomerates were mixed, the coating film roughness became rough due to this. When a paste containing such a metal powder agglomerate is fired and used as a wiring material, problems such as an increase in transmission loss at high frequencies are expected.

Therefore, there has been a demand for a copper powder having an oxide layer on the surface of the copper powder, which solves the above-mentioned problems associated with the formation of the oxide layer. Therefore, an object of the present invention is that the surface roughness of the coating film of the paste is reduced when the paste is made of copper powder, and the specific resistance of the paste sintered body when sintered at a relatively low temperature is reduced. It is an object of the present invention to provide a copper powder having an oxide layer on the surface of the copper powder.

As a result of diligent research, the present inventor has found that the above object can be achieved by using copper powder, which will be described later, and has arrived at the present invention.

Therefore, the present invention includes the following (1).
(1)
A surface-treated copper powder having an oxide layer on its surface.
The thickness of the oxide layer determined from the photoelectron intensity ratio of O1s, C1s, and Cu2p3 in the XPS spectrum is 2 to 20 nm.
Surface-treated copper powder having a bulk density of 3 m ² g ^-1 or less.

According to the present invention, it is possible to obtain a copper powder having an oxide layer on the surface of the copper powder. Can be reduced, and the specific resistance of the sintered body of the coating film of this paste can be reduced.

FIG. 1 is a chart obtained by XPS analysis on the surface-treated copper powder according to Example 4. FIG. 2 is a graph showing the relationship between the sputtering depth and the atomic concentration of oxygen with respect to the surface-treated copper powder according to Example 4.

Hereinafter, the present invention will be described in detail with reference to embodiments. The present invention is not limited to the specific embodiments listed below.

[Surface-treated copper powder with an oxide layer on the surface of the copper powder]
The surface-treated copper powder according to the present invention is a surface-treated copper powder having an oxide layer on its surface, and the thickness of the oxide layer determined from the photoelectron intensity ratio of O1s, C1s, and Cu2p3 in the XPS spectrum is 2 to 20 nm. The bulk density of the surface-treated copper powder is 3 m ² g ^-1 or less.

By using such a surface-treated copper powder, it is possible to reduce the surface roughness of the coating film of the printed paste when the copper powder paste is used, and the coating film of this paste is baked. The body has a reduced specific resistance.

[Oxidized layer]
The surface-treated copper powder according to the present invention has an oxide layer on its surface. In a preferred embodiment, the oxide layer is a layer of an oxide of metallic copper, and cuprous oxide can be mentioned as a suitable oxide.

[Thickness of oxide layer]
The thickness of the oxide layer can be measured and calculated by means described later in the examples. That is, it can be obtained from the photoelectron intensity ratios of O1s, C1s, and Cu2p3 in the XPS spectrum based on the means described later in the examples. In a preferred embodiment, the thickness of the oxide layer measured by this means can be, for example, 2 to 20 nm, preferably 2.0 to 18.5 nm, or 5.0 to 23 nm. Alternatively, it can be 6.0 to 18.5 nm, or 2.0 to 9.0 nm.

In a preferred embodiment, the surface-treated copper powder according to the present invention is said to have a reduced surface roughness of a coating film obtained by this paste when a paste containing the surface-treated copper powder is prepared. At the same time, the specific resistance of the sintered body obtained by sintering the paste is extremely reduced. Although the reason for this is unknown, it is stated that the thickness of the oxide layer in the above range provides good dispersibility in the paste and at the same time realizes excellent sinterability. The inventor is considering. The excellent sinterability is such that the thickness of the oxide layer in the above range is sufficiently reduced at the time of sintering, and it behaves well as a sintering starting point between the surface-treated copper powders without causing a reduction defective portion. The present inventor considers that it is realized by this.

[Bulk density]
In a preferred embodiment, the copper powder according to the present invention has a tap density (bulk density) of, for example, 3 g / cm ³ or less, preferably 2.9 g / cm ³ or less, preferably 2.8 g / cm ³ or less. Can be. By making the tap density (bulk density) smaller than the above upper limit, the dispersibility of the copper powder in the paste can be improved. In a preferred embodiment, the tap density (bulk density) can be, for example, 1.0 g / cm ³ or more, preferably 1.7 g / cm ³ or more. In the present invention, it is sometimes referred to as low filling property to indicate that it has a reduced bulk density as described above.

The tap density can be measured by a known means, and specifically, can be measured by the means and conditions described later in the examples. That is, it can be measured using a powder tester PT-X manufactured by Hosokawa Micron Co., Ltd. Specifically, attach a guide to a 10 cc cup, put the powder in it, tap it 1000 times, remove the guide, scrape off the part that exceeds the volume of 10 cc, and weigh the powder in the container. It can be measured and the bulk density can be determined.

In a preferred embodiment, the surface-treated copper powder according to the present invention has a reduced surface roughness of the coating film obtained by the paste when a paste containing the surface-treated copper powder is prepared. There is. The reason for this is unknown, but the present inventor considers that it is related to the low tap density (bulk density). That is, the low bulk density (low filling property) promotes the penetration of the composition of the paste such as solvent and resin, and realizes good dispersibility, thereby realizing the uniformity of the coating film. The present inventor considers whether or not it is possible.

[Specific surface area]
In a preferred embodiment, the surface-treated copper powder according to the present invention has a BET specific surface area of, for example, 1.5 m ² g ^-1 or more, preferably 1.9 m ² g ^-1 or more and 50 m ² g ^-1 or less, and further. It is preferably 1.9 m ² g ^-1 or more and 20 m ² g ^-1 or less, and more preferably 1.9 m ² g ^-1 or more and 5.0 m ² g ^-1 or less. The BET specific surface area can be measured by a known means, and specifically, can be measured by the means and conditions described later in the examples.

[High molecular]
In a preferred embodiment, the surface-treated copper powder of the present invention is one or more selected from polysaccharides, natural rubbers, and high molecular weight proteins on the surface of the oxide layer, depending on the production method thereof. The polymer of the above may be attached, and the layer may be formed. As a suitable natural rubber, for example, gum arabic can be mentioned.

[Manufacturing of surface-treated copper powder]
In a preferred embodiment, the surface-treated copper powder of the present invention can be produced by the method described later in the examples. However, the method for producing the surface-treated copper powder of the present invention is not limited to the method described later in the examples. The "surface-treated copper powder" is a copper powder that has reached a surface-treated state, and specifically, is a copper powder that has been treated to provide specific matters according to the present invention.

In a preferred embodiment, in the surface-treated copper powder of the present invention, the copper powder produced by the wet method is repeatedly washed with water by decantation until the pH of the slurry is in the range of 4 to 9, and solid-liquid separation is performed. It can be produced by a method including a pH treatment step of contacting the obtained copper powder with an alkaline aqueous solution having a pH of 8 to 14.

[PH treatment step]
In a preferred embodiment, the pH treatment step is performed by contacting with an alkaline aqueous solution of the above pH. In a preferred embodiment, the contact can be performed, for example, by stirring the copper powder produced by the wet method in the aqueous solution. Stirring can be performed by, for example, known means, and the stirring time, which can be stirred using, for example, a homogenizer, a rotary blade, ultrasonic irradiation, a mixer, and a stirrer, is, for example, 5 minutes or more and 48 hours or less. It can be preferably 20 minutes or more and 36 hours or less, and more preferably 60 minutes or more and 24 hours or less. In a preferred embodiment, the temperature maintained during stirring can be, for example, 10 to 50 ° C, preferably 10 to 35 ° C. In a preferred embodiment, the contact can be performed, for example, by passing the above aqueous solution through a copper powder produced by a wet method. The contact with the alkaline aqueous solution may be performed once, for example, in a batch system, or may be performed a plurality of times. The copper powder after being brought into contact with the alkaline aqueous solution can be solid-liquid separated by a known means to obtain a cake. In a preferred embodiment, the copper powder after contact with the alkaline aqueous solution can be washed with pure water.

In a preferred embodiment, washing with pure water can be performed by known means, for example, by passing pure water through a cake obtained by solid-liquid separation.

In one aspect of the preferred embodiment, the pH treatment step can be performed after the above-mentioned polymer is attached to the copper powder. As a result, an oxide layer can be gently formed on the copper powder. In one preferred embodiment, the pH treatment step can be performed prior to adhering the macromolecules to the copper powder. As a result, an oxide layer can be formed on the copper powder in a short time.

[Alkaline aqueous solution]
In a preferred embodiment, the pH of the alkaline aqueous solution to be brought into contact with the copper powder produced by the wet method can be, for example, pH 8 to 14, pH 8 to 12, pH 10 to 13.5. As the alkaline aqueous solution adjusted to the above pH, for example, an aqueous solution of ammonia, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of an organic substance containing an amino group at the molecular terminal, or a mixed aqueous solution thereof can be used.

[Dry]
In a preferred embodiment, the pH treated copper powder is then dried. The drying can be carried out by a known means, for example, at 60 to 300 ° C., preferably 60 to 150 ° C., and can be dried in a nitrogen atmosphere or a vacuum atmosphere. The copper powder thus obtained is often obtained in the form of a dried cake.

[Crushing]
In a preferred embodiment, the pH-treated and then dried copper powder is then crushed. The crushing can be performed by a known means, for example, a pestle, a mortar, or a mixer can be used. According to the present invention, the secondary particles are sufficiently reduced by being sufficiently crushed by coarse crushing by such a simple means. However, the crushing means does not exclude the adoption of a more powerful crushing means, and mechanical crushing such as a Henschel mixer or jet mill crushing may be performed.

In a preferred embodiment, the crushed particles may be classified as a post-crushing treatment. The means that can be used for classification is not particularly limited, and known means can be used. Examples of such means include passing through a sieve, air flow classification, and wet classification. As a guideline for classification, for example, a guideline for passing through a sieve having an opening of 10 to 100 μm can be given.

[Copper powder paste]
In a preferred embodiment, the surface-treated copper powder of the present invention can be suitably used as an aspect of a copper powder paste containing this copper powder. The copper powder paste can be prepared, for example, by kneading surface-treated copper powder with a binder resin and an organic solvent.

In a preferred embodiment, the binder resin used for the paste is not particularly limited as long as it is a binder resin having a Tg of 50 to 200 ° C. Since the copper fine particles are fired in a non-oxidizing atmosphere or a reducing atmosphere, a binder resin having a low thermal decomposition temperature is preferable as the binder resin. Suitable binder resins include, for example, cellulose-based resins, acrylic resins, methacrylic resins, acrylic methacrylic copolymer resins butyral resins, and rosins. As the binder resin, an acrylic resin, a methacrylic resin, an acrylic methacrylic copolymer resin or a rosin is particularly preferable. In particular, when TG measurement (thermogravimetric measurement) is performed in a nitrogen atmosphere, a binder resin having a weight loss of 30% or more at 250 to 350 ° C. can be preferably used. The copper fine particles obtained in the present invention can be made into a paste together with only an organic solvent, but even when a binder resin is added to the paste, copper is copper even when fired at a temperature at which the binder resin does not completely decompose and burn. It is characterized by the progress of sintering between fine particles. When it is desired to obtain a thick coating film with a paste, it is possible to form a thick film without impairing printability by increasing the amount of the binder resin.

[Surface roughness Ra of paste coating film]
In a preferred embodiment, after printing the copper powder paste containing the surface-treated copper powder of the present invention, the surface roughness Ra of the dried coating film is, for example, in the range of 0.01 to 0.4 μm, preferably 0. It can be in the range of 01 to 0.3 μm, preferably in the range of 0.04 to 0.2 μm, preferably in the range of 0.04 to 0.15 μm, preferably in the range of 0.04 to 0.10 μm. The surface roughness Ra of the dry coating film can be measured by a known means, and specifically, can be measured by the means and conditions described later in the examples. The sintered body formed by sintering such a coating film can be suitably used as an electrode layer, a conductive layer, or the like in an electronic circuit or an electronic component.

[Sintered body]
In a preferred embodiment, the copper powder paste containing the surface-treated copper powder of the present invention can be printed or coated, and then sintered to obtain a sintered body. In a preferred embodiment, the obtained sintered body has a smooth surface and at the same time has excellent specific resistance. The smooth surface is considered to suggest that the copper powder is uniformly filled (dispersed) in the coating film, which promotes sintering between the powders and realizes low resistivity. The inventor thinks that he did.

In a preferred embodiment, the sintering for preparing the sintered body can be carried out under known conditions, for example, at a temperature in the range of 200 to 1000 ° C. under a reducing atmosphere, 0.1 to 10 It can be sintered by heating for hours.

[Specific resistance of sintered body]
In a preferred embodiment, the sintered body of the coating film of the copper powder paste containing the surface-treated copper powder of the present invention has excellent specific resistance. The specific resistance can be measured by the means described later in the examples. In a preferred embodiment, the resistivity value can be, for example, 15 μΩcm or less, preferably 14 μΩcm or less, for example, in the range of 2-12 μΩcm, preferably in the range of 5-14 μΩcm.

The reason why the resistivity of the sintered body of the coating film of the copper powder paste containing the surface-treated copper powder of the present invention is reduced in this way is unknown, but the oxide layer of the surface-treated copper powder When the thickness is in the above range, it is sufficiently reduced at the time of sintering, no poor reduction portion is generated, and it behaves well as a sintering starting point between the surface-treated copper powders, so that an excellent ratio as a whole is obtained. The present inventor considers that it has become a resistance.

[Copper powder produced by the wet method]
In a preferred embodiment, the copper powder subjected to the pH treatment step is a copper powder produced by a wet method. The wet method includes, for example, a so-called disproportionation method and a so-called chemical reduction method.

In a preferred embodiment, as a method for producing copper powder by the disproportionation method, for example, the method disclosed in Patent Document 5 (Patent No. 6297018) can be used. In a preferred embodiment, as a method for producing copper powder by the disproportionation method, for example, a step of adding cuprous oxide to an aqueous solvent containing an additive of arabic rubber to prepare a slurry, and adding dilute sulfuric acid to the slurry. A production method including a step of adding all at once within 5 seconds to carry out a disproportionation reaction can be mentioned. In a preferred embodiment, the slurry can be kept at room temperature (20 to 25 ° C.) or lower, and dilute sulfuric acid similarly kept at room temperature or lower can be added to carry out a disproportionation reaction. In a preferred embodiment, the slurry can be kept at 7 ° C. or lower, and dilute sulfuric acid similarly kept at 7 ° C. or lower can be added to carry out a disproportionation reaction. In a preferred embodiment, the dilute sulfuric acid can be added so as to have a pH of 2.5 or less, preferably pH 2.0 or less, and more preferably pH 1.5 or less. In a preferred embodiment, the addition of dilute sulfuric acid to the slurry should be within 5 minutes, preferably within 1 minute, more preferably within 30 seconds, even more preferably within 10 seconds, even more preferably within 5 seconds. , Can be added. In a preferred embodiment, the disproportionation reaction can be completed in 10 minutes. In a preferred embodiment, the concentration of gum arabic in the slurry can be 0.229 to 1.143 g / L. As the cuprous oxide, cuprous oxide used by a known method, preferably cuprous oxide particles, can be used, and the particle size and the like of the cuprous oxide particles are copper powder produced by the disproportionation reaction. Since it is not directly related to the particle size and the like of the particles, coarse-grained cuprous oxide particles can be used. The principle of this disproportionation reaction is as follows:
Cu ₂ O + H ₂ SO ₄ → Cu ↓ + Cu _{SO 4} + H ₂ O

The copper powder thus obtained may be subjected to the above-mentioned pH treatment step in the form of a slurry after being washed, or may be subjected to the above-mentioned pH treatment step in the form of once dried copper powder. ..

In a preferred embodiment, as a method for producing copper powder by a chemical reduction method, for example, the method disclosed in Patent Document 6 (Patent No. 4164009) can be used. In a preferred embodiment, as a method for producing copper powder by a chemical reduction method, for example, after adding 2 g of Arabic rubber to 2900 mL of pure water, 125 g of copper sulfate is added and stirred to obtain 80% hydrazine monohydrate. 360 mL was added, the temperature was raised from room temperature to 60 ° C. over 3 hours after the addition of hydrazine monohydrate, and copper oxide was reacted over another 3 hours. It can be filtered with (1), then washed with pure water and methanol, and further dried to obtain copper powder. The dried copper powder thus obtained may be subjected to the above-mentioned pH treatment step, or may be subjected to the above-mentioned pH treatment step in the form of a slurry.

[Preferable embodiment]
The present invention includes the following (1) embodiments.
(1)
A surface-treated copper powder having an oxide layer on its surface.
The thickness of the oxide layer determined from the photoelectron intensity ratio of O1s, C1s, and Cu2p3 in the XPS spectrum is 2 to 20 nm.
Surface-treated copper powder having a bulk density of 3 m ² g ^-1 or less.
(2)
The surface-treated copper powder according to (1), wherein the oxide layer is a layer containing cuprous oxide.
(3)
The surface-treated copper powder according to any one of (1) to (2), wherein the surface of metallic copper is coated with a layer of cuprous oxide.
(4)
The surface-treated copper powder according to any one of (1) to (3), which has a specific surface area of 1.5 m ² g ^{-1 or more.}

Therefore, the present invention includes the above-mentioned surface-treated copper powder, and includes low-fillable treated copper powder, low-fillable copper powder, and low-fillable surface-treated copper powder.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples.

[Example 1]
[Adjustment of copper powder cake]
3.9 kg of copper sulfate pentahydrate and 8.8 L of pure water were placed in a 30 L container, and the mixture was stirred at 200 rpm with a rotary blade while being heated to 70 ° C. in a water bath to prepare a copper sulfate aqueous solution. 28% aqueous ammonia was added thereto until the pH of the aqueous solution reached 8.5. While further stirring ^{, 100 g of 80 gL -1} aqueous gum arabic solution was added, then 6 L of 25% hydrazine aqueous solution was ^{added at a rate of 1} Lmin -1, and the mixture was stirred for 1 hour after the completion of the dropping. The supernatant liquid generated by allowing to stand was discarded, 10 L of pure water was added thereto, and the mixture was stirred at 300 rpm for 10 minutes. In the same manner, the supernatant liquid generated by standing still was discarded, 10 L of pure water was added thereto, dilute sulfuric acid was added so that the pH became 7.0 ± 0.2, and the mixture was stirred at 300 rpm for 10 minutes. This slurry was solid-liquid separated by suction filtration, and 10 L of pure water was further applied to the cake remaining on the filter paper for suction filtration.

[Treatment after preparation of copper powder cake]
1100 g (wet mass) of the recovered copper powder cake was put into 2 L of aqueous ammonia prepared to pH 8 and stirred. Stirring was performed at 30 ° C. for 1 hour. Then, solid-liquid separation was performed by suction filtration to obtain a pH-treated copper powder cake. The obtained cake was washed with pure water so that the pH of the pure water after filtration was less than 8 as a guide.
The washed copper powder cake was dried at 100 ° C. in a nitrogen atmosphere to obtain a pH-treated copper powder dried cake.
The obtained dried cake was crushed with a milk stick and a mortar and passed through a sieve having a mesh size of 37 μm to obtain copper powder to be used for a paste described later.

[Examples 2 to 5, Comparative Examples 1 and 4]
As Examples 2 to 5 and Comparative Examples 1 and 4, the pH value and the treatment time were changed to prepare a copper powder cake in the same manner as in Example 1. The obtained copper powder cake was put into ammonia water adjusted to each predetermined pH, stirred at 30 ° C. for each predetermined time, and the pH-treated copper powder was dried in the same manner as in Example 1. I got a cake. Then, in the same manner as in Example 1, copper powder to be used for the paste described later was obtained. However, in each Example and Comparative Example, each pH value of the adjusted ammonia and each stirring time at 30 ° C. were changed from Example 1 to the values shown in Table 1 for the treatment. The pH values and treatment times in each Example and Comparative Example are summarized in Table 1.

[Example 6]
In the procedure for milling in Example 1, the same operation as in Example 1 was carried out except that the concentration of the gum arabic aqueous solution was 20 gL ^-1 and the addition rate of hydrazine was 0.5 Lmin ^-1.

[Comparative Example 2]
In the procedure of Example 1, the copper powder cake recovered after suction filtration after milling, pickling, and washing with water was dried at 100 ° C. in a nitrogen atmosphere to obtain a dried cake.
The dried cake was crushed with a pestle and a mortar and passed through a sieve having a mesh size of 37 μm to obtain copper powder.
The obtained copper powder was heat-treated on a hot plate at 200 ° C. for 2 hours in accordance with the conditions described in Patent Document 2 (Japanese Unexamined Patent Publication No. 2003-105402). As a result, a copper powder having an oxide film formed on its surface was obtained.
The obtained copper powder was crushed by a milk stick and a mortar and did not pass through a sieve having a mesh size of 37 μm. Therefore, the copper powder was passed through a sieve having a mesh size of 88 μm to obtain copper powder to be used for a paste described later.

[Comparative Example 3]
In the procedure of Example 1, the copper powder cake recovered after suction filtration after milling, pickling, and washing was dispersed in 5 L of an alkaline aqueous solution adjusted to pH 8 with caustic soda, and stirred with a rotary blade. 5 g of oleic acid was added thereto, and the mixture was stirred for 1 hour. The cake was collected by suction filtration, and the recovered cake was air-dried at room temperature of 25 ° C. until the moisture content fell below 1% with an infrared moisture meter to obtain a dried cake.
The obtained dried cake was crushed with a milk stick and a mortar, and since it did not pass through a sieve having a mesh size of 37 μm, it was passed through a sieve having a mesh size of 105 μm to obtain copper powder to be used for a paste described later.

[Measurement of oxide layer thickness]
The copper powder used in the pastes obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was spread on the sample container so that the bottom surface could not be seen, and the copper powder layer spread by hand press was smoothed to obtain an ULVAC FI. XPS analysis was performed under the following conditions using PHI 5000 Versa Probe II manufactured by PHI Co., Ltd. This result was analyzed as described later, and the thickness of the oxide layer existing on the surface of the dried copper powder was determined.
Ultimate vacuum: 8.2 x 10 ^-8 Pa
Excitation source: Monochromatic AlKα
Output: 24.9W
X-ray beam diameter: 100 μmφ
Incident angle: 90 degrees Extraction angle: 45 degrees With neutralizing gun Sputtering conditions:
Ion species: Ar +
Acceleration voltage: 2kV
Rate: 3.6 nm / min (SiO ₂ conversion)

FIG. 1 shows a chart obtained by XPS analysis on the copper powder used in the paste obtained in Example 4. The horizontal axis is the binding energy (eV), and the vertical axis is the photoelectron intensity.
First, in the chart of FIG. 1, attention was paid to the photoelectron spectrum of Cu 2p of 930 eV to 960 eV. _{Since a peak caused by Cu 2} O was observed instead of a peak caused by Cu O, it was found that a layer of oxide was present on the surface of the copper powder, that the oxide was Cu ₂ O, and that the oxide was Cu 2 O. Judged.

Similarly, it was confirmed that a layer containing _{Cu 2} O was also present on the surfaces of the copper powders of Examples 1 to 3, 5 and 6 and Comparative Examples 1 to 4.
FIG. 2 shows the concentration profile in the depth direction of the oxygen concentration (atomic concentration%) with respect to the copper powder of Example 4. The horizontal axis is the sputtering depth (nm), and the vertical axis is the oxygen concentration (atomic concentration%).
More specifically, for each depth position, the photoelectron intensity ratio of O1s, C1s, and Cu2p3 in the XPS spectrum (ratio of the photoelectron intensity of O1s to the total photoelectron intensity of these three) was calculated as the oxygen concentration.
The depth position where the calculated slope of the oxygen concentration exceeds -1 is defined as the boundary position between the copper layer and the oxide layer, that is, the thickness of the oxide layer.

As an example, a method for calculating the specific thickness of the oxide layer of the copper powder of Example 4 shown in FIG. 2 will be described.
First, the plots excluding the data on the outermost layer (equivalent to a sputter depth of 0 nm) are subjected to a power approximation (the least squares method is applied as linear regression after logarithmic conversion of each plot data), and the slope of the tangent line of the approximation curve is -1. The position exceeding the above was determined to be the thickness of the oxide layer.
Assuming that y is the oxygen concentration and x is the sputter depth, the power approximation gives y = 34.857 × x ^ (−0.407). Since the slope at each point was −0.407 × 34.857 × x ^ (-1.407), it was 6.8 nm that the slope exceeded -1.

While the particle size obtained from the BET specific surface area, which will be described later, is about 0.2 μm, the X-ray irradiation area (analysis area) is 100 μmφ, so the information obtained by XPS is more than one particle. It is reasonable to see it as the overall information across the particles. Then, information in the depth direction can be obtained by sputtering the entire powder spread in the sample container. First, the copper oxide of the particles existing on the uppermost surface of the container is sputtered, and as the sputter depth approaches the bottom surface of the container, the metallic copper of the particles is exposed and the metallic copper is sputtered. However, even if the copper oxide on the upper surface of the particle is scraped off to expose the metallic copper, the copper oxide on the side surface of the particle is still exposed. At the same time, the copper oxide on the upper surface of the particles other than the particles is also sputtered, so that the metallic copper and the copper oxide are continuously detected at the same time as a whole. As a result, copper oxide is not undetectable, and only metallic copper is not detected. Therefore, it is determined that the position of the spatter depth where the slope of the logarithmic graph is "-1" as described above is the position where the contribution of the movement in the depth direction to the decrease of the oxygen concentration is sufficiently small. This position is defined as corresponding to the boundary position between the copper oxide layer and the metallic copper layer.

[Measurement of bulk density]
The tap densities of the dried copper powders obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were measured under the following conditions.
The measurement was carried out using Powder Tester PT-X manufactured by Hosokawa Micron Co., Ltd. Attach a guide to a 10cc cup, put the powder in it, tap it 1000 times, remove the guide, scrape off the part that exceeds the volume of 10cc, weigh the powder in the container, and tap it. The density (bulk density) was determined.

[Measurement of specific surface area]
The BET specific surface area of the dried copper powders obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was measured using BELSORP-miniII (Microtrac Bell) in accordance with JIS Z8830: 2013. More specifically, the specific surface area was measured after degassing the copper powder in vacuum at 200 ° C. for 5 hours.

[Measurement of angle of repose]
The angle of repose of the dried copper powder obtained in Examples 1 to 6 and Comparative Examples 1 to 4 was measured using Powder Tester PT-X of Hosokawa Micron Co., Ltd. in accordance with JIS R9301-2-2: 1999. More specifically, after passing the copper powder through a 710 μm sieve, 100 g of the copper powder was dropped. The mountain formed by this was photographed from the side, and the internal angle of the bottom of the mountain was calculated as the angle of repose.

[Surface roughness Ra of paste coating film]
Weigh dihydroterpineol and acrylic resin vehicle (solid content 35%, balance dihydroterpineol, reciprocal chemical KFA-2000) so that the ratio of dihydroterpineol: acrylic resin (solid content) is 14: 1, and use a rotation / revolution mixer for 5 Stir for minutes. The dried copper powders obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were mixed so that the ratio of the agitated product to the agitated product was 85: 1 (weight ratio), and the mixture was further stirred with a rotation / revolution mixer for 5 minutes. The obtained mixture was passed through three rolls having a roll diameter of 80 mm and a gap between rolls of 5 μm for 5 passes to obtain a paste. All three rolls are alumina rolls. The obtained paste was coated on a slide glass at a moving speed of 5 cm / sec using an applicator with a 25 μm gap, and dried at 120 ° C. for 10 minutes. Ra in the coating direction of the obtained coating film was measured with a stylus type roughness meter according to JIS B 0601-2001, and calculated by averaging 5 points.

[Measurement of resistivity]
The paste prepared for the measurement of the surface roughness Ra is placed on a slide glass using a screen plate (stainless steel mesh, wire diameter 18 μm, gauze thickness 38 μm, opening 33 μm, aperture ratio 42%), width 5 mm, length. Three 20 mm lines were printed. A calcined product was obtained by firing in 3 vol% hydrogen (residual nitrogen) at 250 ° C., which is much lower than the melting point of copper, for 30 minutes. The resistance of the obtained fired body was measured by Lorester GX, the thickness of the fired body was calculated by a three-dimensional measuring device, and the specific resistance of the fired body was obtained from the resistance value, the cross-sectional area of the fired body, and the length of the fired body.

[result]
The results of the above measurements for Examples 1 to 6 and Comparative Examples 1 to 4 are summarized in Table 1.

As shown in Table 1, the surface-treated copper powder according to the embodiment of the present invention has a reduced surface roughness of a coating film printed as a copper powder paste, and at the same time, this coating film is fired. The specific resistance of the fired body was reduced. The reduction of surface roughness is a guideline for expressing the small amount of metal powder agglomerates contained in the coating film, which is more than a simple guideline for smoothness, and is also a guideline for expressing the small number of voids inside the coating film. Therefore, the present inventor considers that it expresses not only the low resistivity of the fired body of the coating film but also the excellent high frequency characteristics.

The present invention provides a surface-treated copper powder that can be suitably used for a copper powder paste. The present invention is an industrially useful invention.

Claims (4)

A surface-treated copper powder having an oxide layer on its surface.
The thickness of the oxide layer determined from the photoelectron intensity ratios of O1s, C1s, and Cu2p3 in the XPS spectrum is 2.5 to 9 nm .
For surface-treated copper powder , attach a guide to a 10 cc cup, put the powder in it, tap it 1000 times, remove the guide, scrape off the part that exceeds the volume of 10 cc, and put the powder in the container. A surface-treated copper powder having a bulk density of 2.9 g / cm ³ or less, obtained by measuring the weight. The surface-treated copper powder according to claim 1, wherein the oxide layer is a layer containing cuprous oxide. The surface-treated copper powder according to any one of claims 1 and 2, wherein the surface of metallic copper is coated with a layer of cuprous oxide. The surface-treated copper powder according to any one of claims 1 to 3, wherein the specific surface area is 1.5 m ² g ^{-1 or more.}

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