JPWO2019017467A1 - Copper powder, method of manufacturing stereolithography product using the same, and stereolithography product of copper - Google Patents

Abstract

[Problem] To provide a copper powder having a composition equivalent to that of pure copper and capable of obtaining a dense stereolithography product of copper. [Solution] A copper powder having an average particle diameter D50 of primary particles of 1 μm or more and 100 μm or less, wherein the primary particles have a light absorbing layer containing a copper oxide on a surface thereof, and oxygen is contained in the entire copper powder. The copper powder has a content of 0.05% by mass or more and 2.2% by mass or less and a reflectance at a wavelength of 1070 nm of 60% or less.

Description

  The present invention relates to copper powder, and more particularly to copper powder used in a metal stereolithography method for obtaining a three-dimensional shaped object by irradiation with energy rays such as laser light.

  A 3D printer, which is capable of easily forming a 3D object, a so-called 3D printer, is becoming popular. Among the methods of manufacturing a modeled object using such a three-dimensional modeling apparatus, the metal optical modeling method is known as a method of obtaining a metal modeled object. In metal stereolithography, the surface of a layer made of metal powder is irradiated with an energy ray such as a high-energy laser to sinter or melt and solidify the metal powder particles, and a layer of several tens of microns is laminated. It is a method of obtaining a three-dimensional modeled object by repeatedly joining them. Practical application is progressing in the method using some metal species as a raw material, and the metal stereolithography method using metal powder such as Co-Cr alloy, titanium alloy, maraging steel, stainless steel, nickel-base superalloy as a raw material is The obtained molded products have high processing accuracy and high degree of perfection as products, and are being put to practical use. However, in the present metal stereolithography methods, usable metal species are limited, and the obtained metal products are limited to a certain range.

  The main reason for this is the problem of light absorption of the metal powder used as the raw material. That is, the metal stereolithography method utilizes the fact that the metal powder particles are sintered or melted and solidified when the metal powder absorbs energy rays such as laser light and is heated. Therefore, the metal powder used as a raw material needs to be capable of efficiently absorbing light energy. The wavelengths of general-purpose lasers used in metal stereolithography are in the near-infrared or far-infrared region, and metals with low light absorption in the laser wavelength range (for example, aluminum, gold, silver, copper, etc.) Cannot efficiently receive a sufficient amount of heat from the laser light or the like with which the surface layer portion is irradiated, so that the sintered density of the obtained metal photolithography product becomes low. Moreover, even if a metal with high thermal conductivity absorbs the energy rays of laser light as heat, it radiates heat in a short time before sufficient sintering and melting/solidification are performed, so dense metal stereolithography It is difficult to get things. Further, the relatively high melting point of copper, which is about 1084° C., is another factor that makes sintering difficult. Therefore, although copper is a metal having high thermal conductivity and electrical conductivity and excellent workability, it has not been used in metal stereolithography.

  Further, when the metal powder having a small average particle diameter is used, the packing density of the layer made of the metal powder can be increased, and thus a dense metal stereolithography product can be easily obtained. However, in the case of a metal powder having a particularly small average particle diameter, the fluidity of the metal powder is significantly reduced due to agglomeration, so that when a layer made of metal powder is formed by squeezing, a layer made of metal powder having a uniform thickness Is difficult to obtain. Here, squeegeeing, in the metal stereolithography method, a blade, a spatula, a roller, etc. are applied to the surface of the layer made of the supplied metal powder to move it, and the surface of the layer made of the metal powder is made smooth and surplus metal powder. Is to remove.

  With respect to the above problems, Patent Document 1 proposes to apply a copper alloy powder in which chromium and silicon are added to copper to a metal stereolithography method. Further, Patent Document 2 proposes that graphite powder is added to the metal powder to increase the absorption of laser light and reduce the occurrence of microcracks. Patent Document 3 proposes that a metal powder having excellent laser absorption can be obtained by roughening the surface of a metal powder such as a copper alloy and then further performing a process such as sputtering.

JP, 2016-211062, A JP, 2008-81840, A International Publication No. 2018/062527

  However, when other materials are added to the copper powder to form a copper alloy powder, the original properties of copper of the obtained shaped product, for example, electrical conductivity, thermal conductivity, workability, and metal color equivalent to pure copper are impaired. Often. Therefore, in order to improve the light absorption of the copper powder, for example, if the content of other materials is increased, the original characteristics of copper are impaired in the obtained stereolithography product, and a composition equivalent to the target pure copper is obtained. It means that a molded article equipped with is not obtained.

  Therefore, an object of the present invention is to provide a copper powder having a composition equivalent to that of pure copper and capable of obtaining a densely patterned stereolithography product.

  The inventors of the present invention provide pure copper by reducing the reflectance of copper particles by providing a light absorbing layer containing a specific amount of copper oxide on the surface of copper particles (primary particles) constituting copper powder. It was found that a dense stereolithography product can be obtained while having the same composition. The present invention is based on such findings. In the present specification, “copper particles” mean primary particles of pure copper, and “copper powder” means aggregates of a plurality of copper particles including secondary particles of copper particles.

Copper powder according to the present invention,
A copper powder having an average particle diameter D50 of primary particles of 1 μm or more and 100 μm or less,
The primary particles have a light absorbing layer containing copper oxide on the surface,
The oxygen content relative to the entire copper powder is 0.05% by mass or more and 2.2% by mass or less,
The reflectance at a wavelength of 1070 nm is 60% or less.

  According to the present invention, on the surface of the copper particles constituting the copper powder, the light absorption layer containing copper oxide is provided so that the oxygen content relative to the entire copper powder is not more than a certain amount, and the reflectance of the copper particles is reduced. As a result, a copper powder having a composition equivalent to that of pure copper and capable of obtaining a dense stereolithography product can be realized.

The schematic diagram for explaining the ventilation test mode of a powder fluidity analyzer. Explanatory drawing for calculating|requiring a total energy value. The schematic diagram for explaining the shear test mode of a powder fluidity analyzer. Explanatory drawing for calculating a Cohesion value. The optical microscope photograph (25 times) of the cross-section of the stereolithography object of Example 3. The optical microscope photograph (25 times) of the cross section of the stereolithography thing of the comparative example 1.

The copper powder of the present invention has an average particle diameter D50 of the primary particles of 1 μm or more and 100 μm or less, and the primary particles constituting the copper powder have a light absorbing layer containing a copper oxide on the surface, and the copper powder with respect to the entire copper powder is The oxygen content is 0.05 mass% or more and 2.2 mass% or less. In the present invention, the primary particles constituting the copper powder have on their surface a light absorbing layer containing a copper oxide such that the oxygen content with respect to the entire copper powder is a certain amount or less, so that the copper powder at a wavelength of 1070 nm is obtained. Can have a reflectance of 60% or less. In this way, by using the treated copper powder in which the light absorption rate of the raw material copper powder is improved, it is possible to obtain a dense molded article having a composition equivalent to that of pure copper.
That is, with copper, the light absorption rate of a flat copper plate is about several percent in the wavelength range (1030 nm or more and 1070 nm or less) of general Yb fiber laser light used in metal stereolithography, It is a metal that is difficult to absorb. In addition, since the thermal conductivity is very high as compared with titanium, iron, nickel, etc., it is not easy to heat by irradiation with laser light as it is. Therefore, as in the present invention, a copper oxide layer having an oxygen content within a specific range with respect to the entire copper powder is used as a light absorbing layer such that the reflectance of the copper powder at a wavelength of 1070 nm is 60% or less. In this case, it is possible to obtain a dense stereolithography product having a composition equivalent to that of pure copper.

  In the present specification, the “average particle diameter D50” means the volume cumulative particle diameter D50 value at a cumulative volume of 50% by volume measured by a laser diffraction/scattering particle size distribution measuring method or the like. In addition, "reflectance" means the spectral reflectance measured using a spectrophotometer equipped with an integrating sphere unit, and total reflection on the measured surface (copper powder) measured for light of a specific wavelength. It means a ratio calculated based on the amount of total reflection light in a specific wavelength region of a standard reflection plate (for example, barium sulfate standard reflection plate) having a known spectral reflectance based on the amount of light. Generally used copper powder has a reflectance of about 70% to 80% at a wavelength of 1070 nm. In the present invention, a light absorbing layer containing copper oxide is provided on the surface of the copper particles so that the reflectance is 60% or less. Hereinafter, the copper powder of the present invention will be described in detail.

  As the copper powder before forming the light absorption layer, any copper powder having an average particle diameter D50 of primary particles of 1 μm or more and 100 μm or less can be used without particular limitation. For example, copper powder can be obtained by wet-reducing a copper compound such as copper acetate or copper sulfate using various reducing agents such as hydrazine. Also, copper powder can be obtained by an atomizing method using molten copper.

  The shape of the copper particles is not particularly limited, but when used in metal stereolithography, from the viewpoint of forming a copper powder layer having a high packing density of powder by squeezing, it has a shape close to a sphere. Preferably. Therefore, it is preferable to use the copper powder obtained by the atomization method. Examples of the atomizing method include a gas atomizing method and a water atomizing method, and the gas atomizing method is preferable if the copper particles are made more spherical.

  The copper powder obtained as described above can be classified as necessary in order to make the sizes of the copper particles uniform. This classification can be easily carried out by separating coarse powder and fine powder from the obtained copper powder using an appropriate classifier so that the target average particle diameter is obtained.

  The copper powder obtained as described above has an average primary particle diameter D50 of 1 μm or more and 100 μm or less. By using a copper powder having an average particle diameter of the primary particles in the above range, it is possible to form a copper powder layer having a high packing density when manufacturing a stereolithography product, and a molded product after sintering the copper powder. The sintered density of can also be increased. In recent years, metal stereolithography tends to require finer stereolithography, and in order to ensure the fluidity of copper powder, the average particle diameter of the copper particles used is 8 μm or more and 50 μm or less. The thickness is preferably 10 μm or more and 50 μm or less, more preferably 15 μm or more and 50 μm or less.

  Further, in the copper powder according to the present invention, the volume cumulative particle diameter D90 of primary particles is preferably 10 μm or more. When a stereolithography product is manufactured using copper powder by a stereolithography method, by using copper powder having an average particle diameter D50 of primary particles of 1 μm or more and 100 μm or less and a volume cumulative particle diameter D90 of 10 μm or more In the squeegeeing process, it becomes easy to form a copper powder layer having a uniform thickness. Further, the copper powder according to the present invention is also preferable in that the volume cumulative particle diameter D10 of the primary particles is 5 μm or more and 40 μm or less from the viewpoint of suppressing the excessive reaction during the blackening treatment and ensuring the fluidity of the powder. The volume cumulative particle diameter D90 of the primary particles means a volume cumulative particle diameter D90 value at a cumulative volume of 90% by volume measured by a laser diffraction/scattering particle size distribution measuring method or the like, and is defined as the volume cumulative particle diameter D10 of the primary particles. Means a volume cumulative particle diameter D10 value in a cumulative volume of 10% by volume measured by a laser diffraction/scattering particle size distribution measuring method or the like.

  In the present invention, the aspect ratio of the primary particles of the copper powder is preferably 2 or less. By using such a copper powder having a nearly spherical shape, it becomes easy to form a copper powder layer having a uniform thickness in the above-mentioned squeezing step. Note that the aspect ratio is to observe the copper powder using, for example, a scanning electron microscope, and measure the major axis and minor axis of each particle for 100 particles by an SEM image with a magnification of 1,000 times or 3,000 times. Then, the value obtained by dividing the major axis by the minor axis is averaged.

  Next, a method for forming the light absorbing layer containing copper oxide on the surface of the above-mentioned copper particles will be described. In one embodiment of the present invention, a light absorbing layer containing copper oxide is provided on the surface of the copper particles obtained as described above. The inventors of the present invention provide a light absorbing layer containing copper oxide on the surface of copper particles so that the oxygen content with respect to the entire copper powder is 0.05% by mass or more and 2.2% by mass or less. It was found that the reflectance of the copper powder at a wavelength of 1070 nm can be set to 60% or less, and as a result, a dense stereolithography product having a composition equivalent to that of pure copper can be obtained. Further, on the surface of the copper particles, by providing a light absorption layer containing a copper oxide such that the oxygen content relative to the entire copper powder is within the above range, the light absorption layer improves the fluidity of the copper powder. It also turned out to be possible.

  That is, although the copper particles have a high reflectance of 70 to 80% at a wavelength of 1070 nm when pure copper is used as described above, the light absorbing property is increased by providing a light absorbing layer containing a copper oxide on the surface of the copper particles, and the wavelength is increased. The reflectance at 1070 nm can be set to 60% or less. When the oxygen content is less than 0.05 mass% with respect to the entire copper powder, the reflectance at a wavelength of 1070 nm cannot be 60% or less, and a dense stereolithography object cannot be obtained, while 2.2. When the content is more than mass%, the proportion of copper oxide in the copper powder becomes high, so that it becomes difficult to exhibit the characteristics originally possessed by metallic copper (such as high electrical conductivity and thermal conductivity), which is not preferable. The oxygen content of the entire copper powder can be calculated by oxygen gas analysis or the like. A preferable range of the oxygen content relative to the entire copper powder is 0.08 mass% or more and 2.2 mass% or less, and a more preferable range is 0.1 mass% or more and 2.0 mass% or less. The reflectance of the entire copper powder at a wavelength of 1070 nm depends on the oxygen content relative to the entire copper powder, but is 10% or more from the viewpoint of not impairing the original properties of pure copper, and 35% from the ease of heating of the copper powder. The following is preferable.

In the copper powder according to the present invention, the value obtained by dividing the oxygen content (mass %) with respect to the entire copper powder by the BET specific surface area (m ² /g) of the copper powder is 4.0 mass%·g/m ² or less. Is more preferable, 1.0% by mass/g/m ² or more and 4.0% by mass/g/m ² or less is particularly preferable, and 1.5% by mass/g/m ² or more and 3.5% by mass is particularly preferable.・G/m ² or less. If the value obtained by dividing the oxygen content by the BET specific surface area of the copper powder is too large, the reflectance at the wavelength of 1070 nm of the copper powder is reduced and the light absorptivity is improved, so that a dense stereolithography product of copper can be obtained. It tends to be difficult to obtain a stereolithography product having a composition equivalent to that of pure copper. That is, the present inventors have found that the value obtained by dividing the oxygen content of the copper powder by the BET specific surface area is one index for obtaining a stereolithography object having a composition equivalent to that of pure copper and dense copper. Is found. The BET specific surface area can be measured by the BET one-point method using, for example, BELSORP-MR6 manufactured by Microtrac Bell.

In the light absorption layer containing copper oxide formed as described above, the copper oxide contains CuO and Cu ₂ O. The proportions of CuO and Cu ₂ O in the copper oxide can be measured by XPS analysis. Specifically, the peak of Cu _2p2/3 measured by X-ray photoelectron spectroscopy is waveform-separated into the peaks of CuO and Cu and Cu ₂ O, and from the respective peak area ratios, the total is 100%. calculating the ratio of CuO and Cu ₂ O. The proportion of CuO is preferably 20% or more and 99% or less. When the proportion of CuO is within the above range, the frictional force is reduced due to the fine irregularities on the surface of the light absorption layer, and the fluidity of the copper powder is increased.

  Further, in the present invention, by forming a light absorbing layer made of copper oxide on the surface of the copper particles, it is possible to make the copper powder less likely to change with time. That is, it is known that metallic copper is extremely easily oxidized by air and moisture, and the physical properties of powder are likely to change during storage. Even when the same lot of metallic copper powder is used, the characteristics of the copper powder change with time due to storage, and thus there is a possibility that a stereolithographic product having desired physical properties cannot be obtained. In order to suppress this, by providing a light absorbing layer made of copper oxide or the like on the surface of the metal copper powder, it is possible to control the progress of the oxidation reaction with the atmosphere and moisture, and as a result, more stable stereolithography You can get things.

  As a method for forming the light absorption layer containing copper oxide, a known method can be adopted. For example, a method of oxidizing copper powder in an oxygen atmosphere, a solution containing Fe or Cu ions, a solution containing halogen ions such as chloride ions, a method of oxidizing the copper surface by immersing in a solution such as hydrogen peroxide, or A method of treating with a halogen gas is known. From the viewpoint of homogeneity of the light absorption layer to be formed and ease of controlling the layer thickness, a mixed aqueous solution of hypochlorite and sodium hydroxide, a mixed aqueous solution of chlorite and sodium hydroxide, and peroxodisulfate. It is preferable to select a method of forming a layer (light absorbing layer) made of copper oxide on the surface of copper powder using a mixed aqueous solution of sodium hydroxide and sodium hydroxide. Specifically, by immersing the copper powder in a mixed aqueous solution of hypochlorite and sodium hydroxide or a mixed aqueous solution of chlorite and sodium hydroxide, a layer made of copper oxide is formed on the surface of the copper powder. Can be formed.

The average thickness of the light absorbing layer containing copper oxide is preferably 20 nm or more and 1300 nm or less, and more preferably 30 nm or more and 1000 nm or less. However, the thickness of the light absorbing layer containing the copper oxide having the average thickness within the above range is preferably 30% or less of the average particle diameter D50 of the copper powder primary particles to be used, and 10% or less. Is more preferable. The average thickness of the light absorbing layer containing copper oxide can be adjusted by the concentration of the solution and the processing conditions (time, temperature). When the average thickness of the light absorbing layer containing copper oxide exceeds 1300 nm, or when it exceeds 30% of the average particle diameter D50 of the copper powder primary particles, the light absorbing property of the copper powder increases, but aggregates of primary particles are formed. It is easily formed, and thus the fluidity of the copper powder is reduced. In addition, since the proportion of oxygen in the entire copper powder increases, it becomes difficult for the obtained stereolithography product to exhibit various characteristics originally possessed by metallic copper (such as high electrical conductivity and thermal conductivity). In the present specification, the average thickness of the light absorption layer can be evaluated by a depth direction analysis in which an X-ray photoelectron spectroscopy (XPS) method and ion etching are used in combination, and specifically, it is based on JIS K 0146. It means the SiO ₂ equivalent depth measured by the method.

  The copper powder of the present invention is pure copper and has an average particle diameter D50 of primary particles (copper particles) of 1 μm or more and 100 μm or less. Since the light absorption layer containing the copper oxide as described above is formed on the surface of the copper powder, the laser light of the three-dimensional modeling apparatus can be efficiently absorbed, and as a result, it has the same composition as pure copper. In addition, it is possible to obtain a dense stereolithography product. Further, in the present invention, since the fluidity of the copper powder is improved by forming a light absorbing layer containing the above-described copper oxide on the surface of the copper particles, squeegeeing at the time of producing a molded article becomes easy. A layer made of copper powder having a uniform distribution in the thickness direction can be prepared. The copper powder of the present invention can have a fluidity of 5 seconds/50 g or more and 30 seconds/50 g or less in order to make it more suitable for metal stereolithography. In addition, in this specification, a fluidity means the value measured based on JISZ2502.

The flow characteristics of the copper powder can be evaluated by using a powder fluidity analyzer, for example, a powder rheometer (FT4, manufactured by freeman technology). Although the powder fluidity analyzer has several measurement modes, two types of tests, a ventilation test mode and a shear test mode, can be performed to evaluate the dynamic fluidity evaluation of copper powder. In the aeration test mode, as shown in FIG. 1, the powder is ventilated from below in the vertical direction at a predetermined flow rate, and the blade (rotary blade) spirals in the powder from the height of H1 to the height of H2. The dynamic fluidity can be measured by using the rotational torque and the vertical load measured by moving while rotating. The measurement conditions are shown below.
Blade diameter: 23.5 mm
Blade tip speed: 100 mm/s
Container volume: 25 ml (inner diameter 25 mm)
Blade entry angle: -5°

In an aeration test using a powder fluidity analyzer, the total energy value when not aerated is E ₁ (mJ), the total energy value when aerated at 4 mm/s is E ₂ (mJ), primary particles of copper powder When the average particle diameter D50 of is D (mm), the following formula:
F=E ₂ /E ₁ ·1/D
The fluidity parameter F represented by is preferably 0.05 mm ⁻¹ or more and 10 mm ⁻¹ or less, and more preferably 0.5 mm ⁻¹ or more and 8 mm ⁻¹ or less.

The total energy value is obtained as an integrated area when the vertical load and the rotational torque are plotted according to the moving distance as shown in FIG. Generally, the following formula is used as an index relating to the adhesion and cohesiveness of powder:
AR=E ₁ /E ₂
(E ₁ and E ₂ in the formula are the same as defined above)
The ventilation index AR (Aeration Ratio) represented by is known. This indicates that the smaller the ventilation index AR, the weaker the adhesion and cohesiveness of the powder. It is also known that the fluidity energy decreases as the gas velocity passing through the powder increases, but this is because the influence of the decrease in frictional resistance due to the decrease in contact points between particles is greater. The inventors of the present invention have found that as the average particle size of copper particles increases, the number of contact points per same volume decreases, and as a result, the ventilation index AR also decreases even with copper powder having the same adhesion and cohesiveness. I found that there is a tendency. Then, by normalizing the ventilation index AR with the average particle diameter of the copper particles, it was found that the adhesion and cohesiveness of the copper powder can be evaluated even if the copper particles have different average particle diameters. Obtained. The above-mentioned fluidity parameter F is obtained by dividing the reciprocal of the ventilation index AR by the average particle diameter D50 of the copper powder primary particles, and is considered to be an index when evaluating the adhesion and cohesiveness of the copper powder.

In the copper powder in which the average particle diameter D50 of the copper particles as the primary particles is in the range of 1 μm or more and 100 μm or less, the fluidity parameter F exceeds 10 mm ⁻¹ , but the copper oxide as described above on the surface of the copper particles. It is considered that the fluidity parameter F is reduced to 10 mm ⁻¹ or less by providing the light absorption layer containing Although the reason for this is not clear, it is presumed that the frictional force is reduced due to the presence of fine irregularities formed on the surface of the light absorption layer. The air flow rate when measuring E ₂ is not particularly limited, but is set to 4 mm/s here.

In the shear test mode, as shown in FIG. 3, a shear jig held at a predetermined vertical stress is pressed against the powder to measure the shear stress when the stress is applied in the rotation direction. The measurement conditions are shown below.
Shearing jig diameter: 23.5mm
Shear rate: 18°/min
Volume of container: 10 ml (inner diameter 25 mm)
Vertical load: 1.00kPa, 1.25kPa, 1.50kPa, 1.75kPa, 2.00kPa

  The shear stress when the vertical stress is 0 kPa measured in a shear test mode using a powder fluidity analyzer is preferably 0.01 kPa or more and 0.3 kPa or less, and 0.05 kPa or more and 0.25 kPa or less. Is preferred. Here, the shear stress means a stress when the powder reaches a yield stress and starts to flow when a stress is applied to the powder in a rotating direction under a constant vertical stress. The shear stress when the vertical stress is 0 kPa can be obtained as an adhesive force between particles, and this adhesive force is called a Cohesion value. The Cohesion value is obtained by plotting the shear stress measured under each normal stress and extrapolating it, as shown in FIG. In metal stereolithography, it is required to squeege the powder more uniformly and stably in order to obtain a high-quality molded object. To achieve this, the adhesive force between the powder particles is required. Weak and easy to flow is important. That is, by using a copper powder having a Cohesion value measured using a powder fluidity analyzer within the shear stress range, squeegeeing in metal stereolithography can be easily performed. As a result, a molded article having a higher density and a more precise shape can be obtained.

A method for obtaining a copper stereolithography product using the above-described copper powder will be described. First, copper powder is supplied to the modeling stage, and the powder surface is squeezed using a squeegee blade to form a copper powder layer having a predetermined thickness (step 1). Note that particularly squeegee in the present invention, a blade or a spatula on the surface of the layer made of metal powder supplied in the metal stereolithography, moved by moving the roller, etc., smooth the surface of the layer made of metal powder, surplus Is to remove the metal powder. Then, a light beam such as a laser beam is applied to an arbitrary position above the copper powder layer. This irradiation position can be determined from a tomographic plan view created based on the three-dimensional CAD data of the article to be modeled. The plurality of copper particles at the positions irradiated with the light beam are sintered or melted and solidified to form the first layer (step 2). Then, the position of the modeling stage is moved by a depth corresponding to the thickness of the first layer (step 3). By repeating these steps 1 to 3, a second layer, a third layer and a plurality of layers are sequentially laminated on the first layer to manufacture a stereolithography object made of copper. An infrared laser is generally mounted as a light beam in such a metal stereolithography apparatus, and a solid-state laser having a wavelength band including infrared rays having a wavelength of 1064 nm, a fiber laser having a wavelength band of 950 nm or more and 1900 nm or less, 10 A CO ₂ laser or the like having a wavelength band of 0.6 μm is used. Rare earth elements such as Yb (1030 nm or more and 1070 nm or less), Nd (about 950 nm), Tm (about 1900 nm), Er (about 1550 nm) are generally used as an amplification medium for the glass core of the fiber laser. Since the copper powder of the present invention has a reflectance of 60% or less at a wavelength of 1070 nm, it is preferable to use a Yb-doped fiber laser having a center wavelength of 1070 nm. The laser irradiation mode may be either single mode or multi-mode, although there are differences in beam quality and focusing property. Further, the above-described modeling method is merely an example in which the optical modeling method is used, and the present invention is not limited to this.

  The stereolithography product obtained from the copper powder as described above is dense. Therefore, it is possible to obtain an optical molding product made of copper having high mechanical strength. For example, it is possible to obtain a stereolithographic object made of copper having a Vickers hardness (Hv) measured according to JIS Z 2244 of 80 Hv or more and 300 Hv or less. Even when the copper particles are provided with a light absorption layer containing copper oxide, it has a composition equivalent to that of pure copper because the proportion of copper oxide in the entire stereolithography product made of copper is very small. The stereolithography object can have the original characteristics of metallic copper (such as high electrical conductivity and thermal conductivity). Specifically, by using the copper powder of the present invention, a dense stereolithography product having a composition equivalent to that of pure copper having an oxygen content of 0.05% by mass or more and 2.2% by mass or less and made of copper Can be obtained. Although the stereolithography of the present invention does not exclude inclusion of materials other than copper powder, the purity of copper in the stereolithography is preferably 97.8% by mass or more, and 98.5% by mass. % Or more, and more preferably 99.0 mass% or more.

  Next, embodiments of the present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

<Preparation of copper powder>
The following three types of copper powder manufactured by the gas atomizing method were prepared.
Copper powder 1: MA-C15, manufactured by Mitsui Mining & Smelting Co., Ltd. (average particle size of primary particles D50: 15 μm, D90: 25 μm)
Copper powder 2: MA-CHS, manufactured by Mitsui Mining & Smelting Co., Ltd. (average particle size of primary particles D50: 33 μm, D90: 53 μm)
Copper powder 3: MA-CNS, manufactured by Mitsui Mining & Smelting Co., Ltd. (average particle size of primary particles D50: 64 μm, D90: 86 μm)

<Formation of light absorption layer>
Sodium chlorite (BO-200A, manufactured by MacDermid Performance Solutions Japan Co., Ltd.) is 40% by volume, and sodium hydroxide (BO-200B, manufactured by MacDermid Performance Solutions Japan Co., Ltd.) is 15% by volume. A mixed solution containing 4% by volume of an inorganic salt (BO-200C, manufactured by MacDermid Performance Solutions Japan Co., Ltd.) and 41% by volume of pure water was prepared. All of the prepared copper powders 1 to 3 were immersed in a mixed solution prepared so that the concentration became 0.25 kg/L, and physical stirring was performed using a stirring blade. The treatment conditions were the temperature and time shown in Table 1. After stirring, the mixed solution was filtered to separate the copper powder, and the copper powder that had been sufficiently washed with water was left at room temperature for 12 hours, and then dried at 140° C. in a nitrogen atmosphere to form a light absorbing layer. Copper powders of Examples 1 to 8 and Comparative Examples 1 to 5 (hereinafter referred to as treated copper powders) were obtained.
Of these treated copper powders, the treated copper powder of Comparative Example 5 was treated under the same conditions as the copper powder of Example 13 described in WO2018/062527, When the copper powder is treated under the same conditions as the copper powder of Example 13 described in International Publication No. 2018/062527, the copper powder reacts violently with the treatment liquid, and foaming remarkably causes roughening treatment. Therefore, the treatment conditions were changed to conditions in which an aqueous solution containing 20 g/L of sulfuric acid and 10 g/L of hydrogen peroxide was kept at 30° C. and immersed for 5 minutes. However, since it is considered that this change in the roughening treatment conditions has almost no effect on the amount of oxidation of the copper powder surface or the reaction of the blackening treatment, the copper powder of Example 13 described in International Publication No. 2018/062527 is disclosed. It can be considered that the roughening treatment is equivalent to. Further, the light absorption layer formation after the roughening treatment was performed by the two-step dipping treatment in the same manner as in Example 13 described in International Publication No. 2018/062527 to produce treated copper powder.

The properties of the copper powders 1 to 3 and the treated copper powders obtained as described above were measured as follows.
(1) Reflectivity The reflectivity of the copper powders 1 to 3 and each of the treated copper powders was measured by using a spectrophotometer (U-4100, manufactured by Hitachi High-Technologies Corporation) to fill a concave holder with copper powder and then use quartz. The sample was sealed with a cover glass, and the wavelength was set to 1070 nm, and measurement was performed by an integrating sphere method.

(2) Aspect ratio The copper powders 1 to 3 and the treated copper powders are observed with a scanning electron microscope (XL-30FEG, manufactured by Japan FEI Co., Ltd.), and the SEM image at a magnification of 1,000 times or 3,000 times gives particles. The major axis and minor axis of each particle were measured for 100 particles, and the average value of the values obtained by dividing the major axis by the minor axis was calculated to obtain the aspect ratio.

(3) Oxygen content Copper powders 1 to 3 and each treated copper powder, and the oxygen content (mass %) of a model manufactured using these powders were measured by an oxygen analyzer (EMGA-820ST, Horiba Seisakusho). It was measured by heating and melting in a He atmosphere.

(4) BET Specific Surface Area The BET specific surface areas of the copper powders 1 to 3 and each of the treated copper powders were measured by the BET one-point method using BELSORP-MR6 manufactured by Microtrac Bell.

(5) Oxidation resistance In order to evaluate the oxidation resistance of the treated copper powder, a storage test was performed under normal temperature and normal humidity environment using the copper powder 2 and the treated copper powder treated with the copper powder 2. The test was carried out under the environment of an average room temperature of 22° C. (range 20.5 to 24.5° C.) and an average humidity of 55% (range 26 to 74%) for 20 days by placing copper powder or each treated copper powder on an evaporation dish. After storage, the oxygen content (mass %) was measured using an oxygen analyzer in the same manner as above. Oxidation resistance was evaluated by the rate of increase expressed as a percentage obtained by dividing the difference in oxygen content before and after storage by the oxygen content before storage. The lower the increase rate, the higher the oxidation resistance.

(6) Thickness of light absorption layer A monochrome Al-Kα excitation source was used by using a depth direction analyzer (Quantum 2000, manufactured by ULVAC-PHI Co., Ltd.) that uses both X-ray photoelectron spectroscopy (XPS) method and ion etching. Line (hν = 1486.7 eV), the angle between the detector and the sample stage was 45 degrees, and MultiPak 9.0 made by ULVAC-PHI was used as analysis software, and the thickness of the light absorption layer according to JIS K 0146. Was measured. More specifically, XPS analysis is performed while performing ion etching at a rate of 7.7 nm/min (SiO ₂ conversion), and a CuLMM line peak derived from metallic copper and copper oxide (a peak appearing at 540 eV or more and 610 eV or less). Each peak was separated using an internal standard sample. That is, the CuLMM main peak (570 eV or more and 571 eV or less) derived from the oxide and the CuLMM main peak (568 eV or more and 569 eV or less) derived from the metal are separated (background mode: Shirley), and the signal intensity of the CuLMM derived from the oxide is 50%. The etching depth at the position was defined as the average thickness of the light absorption layer. In addition, the main peak of Cu2p _2/3 of XPS (peak appearing at 930 eV or more and 940 eV or less) of CuO (933.0 eV or more and 937.0 eV or less) and Cu and Cu ₂ O (930.0 eV or more and 933.0 eV or less) Waveforms were separated into peaks (background mode: Shirley), and the ratio (%) of CuO and Cu ₂ O was calculated from the respective peak area ratios.

(7) Fluidity The Cohesion value was measured in a shear stress measurement mode using a powder rheometer (FT4, manufactured by freeman technology). The measuring method is as described above. In addition, in the ventilation test mode, the total energy value E ₁ (mJ) without ventilation and the total energy value E ₂ (mJ) with ventilation at 4 mm/s were measured. From the obtained values of E ₁ and E ₂ and the average particle diameter D of the copper powder, a fluidity parameter F represented by F=E ₂ /E ₁ ·1/D was calculated.
Furthermore, using a fluidity meter (Tsutsui Rikagaku Kikai Co., Ltd.), 50 g of each powder was placed in a funnel, and the fluidity (second) of the powder was measured by a method according to JIS Z 2502. It was The measurement results of (1) to (5) above are as shown in Table 1. As shown in Table 1, the treated copper powder used in Example 6 and the copper powder used in Comparative Examples 1 and 2 had a catch when falling from the funnel at the time of fluidity measurement, All of the powder (copper powder or treated copper powder) charged in (1) was not dropped (note that all of the powder was not dropped is indicated by "X" in Table 1).
(8) Powder Coverage To evaluate the squeezing performance of copper powder, a spoonful of copper powder was placed on a smooth glass substrate, and a glass was applied using an applicator (Baker type applicator manufactured by Nippon Cedar Service Co., Ltd.). The gap between the substrate and the applicator was set to 100 μm, and the cylindrical applicator was manually moved by 15 cm to spread the copper powder on the glass substrate. The shape of the copper powder spread on the glass substrate was photographed and binarized to measure the area of the copper powder spread. The area ratio (%) of the spread copper powder to the entire imaging area was calculated, and the powder spread degree was evaluated according to the following evaluation criteria.
A: 95% or more O: 90% or more and less than 95% B: 80% or more and less than 90% X: less than 80% The evaluation results are shown in Table 1 below.

<Manufacturing of stereolithography>
Each of the copper powder 2 and each treated copper powder was modeled using a metal stereolithography machine (LUMEX Avance-25, Matsuura Machinery Co., Ltd.). Using an S50C base plate (125×125×10 mm), under a flow of nitrogen gas, the energy density per unit volume by laser light is 160 J/mm ³ , the energy density per unit area is 8 J/mm ² , and the output is 320 W. The spot diameter was 0.2 mm, the stacking pitch was 0.05 mm, and the scanning pitch was 0.2 mm. Three stereolithography samples of copper having a length of 10 mm, a width of 10 mm, and a height of 1.8 mm were produced in a central horizontal row of the base plate at intervals of 20 mm.
The treated copper powder of Comparative Example 4 in Table 1 had a strong cohesive property and formed into a large lump, and the treated copper powder of a size suitable for modeling could not be collected. As a result, it was not possible to form a desired sintered layer, and thus it was not possible to obtain a stereolithography product by the metal stereolithography machine.

<Characteristic evaluation of stereolithography>
As an evaluation of the denseness of the obtained stereolithography of copper, an optical microscope (25 times) was used to observe a central 900 μm×120 μm region of the vertical cross section, and a sintered or melt-solidified portion (matrix area) and a pore portion (non-) were observed. The area occupancy (%) of the sintered or melt-solidified portion was calculated by dividing the sample into two regions (matrix region) and the average value of three samples for each of the examples and comparative examples. At the time of this measurement, a region where an alloy of iron and copper was formed was seen near the base plate, but this region was not included, and only the region having a luster peculiar to metallic copper was evaluated from the appearance. ..
The Vickers hardness (Hv) of the stereolithography product made of copper was measured according to JIS Z 2244. The measurement results were as shown in the table below. FIG. 5 shows a cross-sectional optical microscope photograph (25 times) of the stereolithographic object of Example 3, and FIG. 6 shows a cross-sectional optical microscope photograph (25 times) of the stereolithographic object of Comparative Example 1.

Claims (13)

A copper powder having an average particle diameter D50 of primary particles of 1 μm or more and 100 μm or less,
The primary particles have a light absorbing layer containing copper oxide on the surface,
The oxygen content relative to the entire copper powder is 0.05% by mass or more and 2.2% by mass or less,
Copper powder having a reflectance of 60% or less at a wavelength of 1070 nm.   The copper powder according to claim 1, wherein an aspect ratio of the primary particles is 2 or less. The value obtained by dividing the oxygen content (mass %) with respect to the entire copper powder by the BET specific surface area (m ² /g) of the copper powder is 4 mass%·g/m ² or less. The copper powder according to any one of 1. Using a powder flowability analyzer, the total energy value measured in the ventilation test mode without ventilation was E ₁ (mJ), and the total energy value with ventilation at 4 mm/s was E ₂ (mJ), copper powder. The average particle size D50 of the primary particles is D (mm),
Then, the following formula:
F=E ₂ /E ₁ ·1/D
The copper powder according to any one of claims 1 to 3, wherein the fluidity parameter F represented by is 10 (mm ^-1 ) or less. The copper powder according to claim 4, wherein the fluidity parameter F is 0.05 (mm ^-1 ) or more and 10 (mm ^-1 ) or less.   The copper according to any one of claims 1 to 5, wherein an average thickness of the light absorption layer is 20 nm or more and 1300 nm or less and is 30% or less of an average particle diameter D50 of the primary particles. powder.   The copper powder according to any one of claims 1 to 6, which has a fluidity of 5 seconds/50 g or more and 30 seconds/50 g or less measured in accordance with JIS Z 2502.   The copper powder according to any one of claims 1 to 7, wherein the average particle diameter D50 of the primary particles is 50 µm or less.   The copper powder according to any one of claims 1 to 8, wherein the average particle diameter D50 of the primary particles is 8 µm or more.   The copper powder according to any one of claims 1 to 9, wherein a volume cumulative particle diameter D90 of the primary particles is 10 µm or more.   A method for producing a stereolithographic object using copper, comprising a step of sintering or melting and solidifying the copper powder according to any one of claims 1 to 10 by laser light.   The method for producing a stereolithographic object using copper according to claim 11, wherein the laser light is a Yb-doped fiber laser.   A stereolithography object made of copper having an oxygen content of 0.05% by mass or more and 2.2% by mass or less and a Vickers hardness of 80 Hv or more and 300 Hv or less.