Copper powder

Abstract

To provide a copper powder that can replace benzotriazole with a simplified process that has a low environmental impact and high productivity.SOLUTION: The copper powder of the present invention contains 0.5 pt.wt. or more of hydroxy acid per 100 pts.wt. of copper or copper alloy. The hydroxy acid preferably contains a racemic mixture, and is preferably tartaric acid or malic acid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to copper-based powders that are suitably used as raw material powders for various applications such as powder metallurgy, additive manufacturing, conductive materials, coating / printing, and catalysts, and to powders that are less likely to discolor due to oxidation in an environment containing oxygen represented by air.

Background Art

[0002] Copper is widely used as a conductive material and a heat dissipation material because of its excellent electrical conductivity and thermal conductivity.

[0003] In addition, copper is a relatively soft metal and has excellent compatibility with iron and the like, so it is also used as a bearing or a sliding material.

[0004] Moreover, copper has excellent corrosion resistance and has a beautiful reddish-brown color that other metal materials do not exhibit, so it is also widely used for coating / printing applications.

[0005] Furthermore, copper may function as a catalyst and may also be used in the chemical industry field.

[0006] In the above applications, a method using powder as a raw material may be advantageous as represented by the powder metallurgy method, and various copper-based powders produced by an atomization method, an electrolysis method, a reduction method, or a pulverization method are used in large quantities.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Copper is a more precious metal than other common metals such as iron and aluminum. Basically, it is a metal with excellent oxidation resistance and corrosion resistance. However, when stored in an oxygen-containing environment for a long time, it may discolor depending on the conditions. In particular, powders with a large specific surface area will turn blackish in a relatively short time.

[0009] This is mainly considered to be due to the reaction of the copper particle surface with oxygen to form cuprous oxide or copper oxide. If it is treated in a reducing atmosphere containing hydrogen, it can be easily reduced and return to its original color.

[0010] Also, depending on the application, even if it discolors, there may be no problem in use as the characteristics of copper-based powders. However, since discoloration can be easily judged visually, discolored copper-based powders are regarded as having undergone deterioration over time, which becomes a major quality problem such as being the subject of a claim.

[0011] Against this background, there has long been a demand for copper-based powders that are less likely to discolor due to oxidation in an oxygen-containing environment.

[0012] As represented by Patent Document 1, benzotriazole is generally used as a so-called rust inhibitor for preventing the oxidation of copper, not limited to powders, and is widely used.

[0013] Benzotriazole is an excellent rust inhibitor and has been known for a long time and has sufficient usage records. However, in powder metallurgy applications, if an excessive amount is treated, sintering defects may occur, and when used by mixing with various resins and solvents such as conductive pastes, there is a problem that it reacts with those mixtures and causes defects.

[0014] In applications for conductive materials, silver-coated copper powder is widely known as in Patent Document 2.

[0015] This thinly coats silver on the surface of copper particles by a plating method, which improves oxidation resistance, stabilizes conductivity, and has the effect of reducing the amount of expensive silver used compared to silver powder.

[0016] However, although the usage amount is small, since it is coated with expensive silver, the raw material cost is high. In addition to the complicated plating process, a large amount of plating waste liquid containing chelate is generated, so there is a problem of a large environmental load.

[0017] In order to solve the above problems, the inventors of the present invention have intensively conducted experiments on a treatment method for copper-based powders that can replace benzotriazole, have a simple process, a small environmental load, and high productivity. As a result, if it is a copper-based powder containing 0.5 parts by weight or more of a hydroxy acid that is highly safe and has a low environmental load and is used in food additives and the like, it has excellent oxidation resistance and is less likely to cause discoloration. They have obtained remarkable findings and solved the above technical problems.

Means for Solving the Problems

[0018] The present invention is a copper-based powder containing 0.5 parts by weight or more of a hydroxy acid with respect to 100 parts by weight of copper or a copper alloy.

[0019] Moreover, the present invention is the above copper-based powder containing a racemate as the hydroxy acid.

[0020] Moreover, the present invention is the above copper-based powder containing tartaric acid or malic acid as the hydroxy acid.

[0021] Moreover, the copper-based powder of the present invention is also a mixed powder of a copper powder or a copper alloy powder and a hydroxy acid powder, and is obtained by mixing the hydroxy acid powder with the copper powder or the copper alloy powder. At this time, examples of the copper alloy powder include binary copper alloys such as Cu-Au, Cu-Ag, Cu-Al, Cu-B, Cu-Be, Cu-Bi, Cu-Ce, Cu-Co, Cu-Cr, Cu-Fe, Cu-In, Cu-La, Cu-Li, Cu-Mg, Cu-Mn, Cu-Mo, Cu-Nb, Cu-Nd, Cu-Ni, Cu-P, Cu-Pb, Cu-Si, Cu-Sm, Cu-Sn, Cu-Ta, Cu-Ti, Cu-V, Cu-W, Cu-Y, Cu-Zn, Cu-Zr, etc., and ternary copper alloys such as Cu-Cr-Ag, Cu-Cr-Si, Cu-Cr-Zr, Cu-Co-Si, Cu-Fe-Mn, Cu-Fe-P, Cu-Fe-Zn, Cu-Ni-Si, Cu-Sn-Bi, Cu-Sn-Ni, Cu-Sn-P, Cu-Sn-Pb, Cu-Sn-Zn, Cu-Zn-Ni, etc.

[0022] The copper-based powder of the present invention contains 0.5 parts by weight or more of hydroxy acid with respect to 100 parts by weight of copper or copper alloy, so it has excellent oxidation resistance, is less likely to cause discoloration due to oxidation in the air, and has excellent stability in terms of quality.

[0023] In addition, when the copper-based powder in the present invention contains the racemic form of the above hydroxy acid, it further has excellent oxidation resistance and becomes a copper-based powder that is more stable in terms of quality.

[0024] In addition, when the copper-based powder in the present invention contains tartaric acid or malic acid as the above hydroxy acid, it further has excellent oxidation resistance and becomes a copper-based powder that is more stable in terms of quality.

Embodiments for Carrying Out the Invention

[0025] As the hydroxy acid in the present invention, aliphatic hydroxy acids having 9 or less carbon atoms, preferably 2 to 9 carbon atoms, or aromatic hydroxy acids can be used. Such hydroxy acids include optically active hydroxy acids, for example, lactic acid (C3H6O3), malic acid (C4H6O5), tartaric acid (C4H6O6), isocitric acid (C6H8O7), mevalonic acid (C6H 12 O4), leucic acid (C6H 13 NO3), shikimic acid (C7H10 O5), caffeic acid (C7H 12 O6), etc., and hydroxy acids without optical activity, such as glycolic acid (C2H4O3), tartronic acid (C3H4O5), citric acid (C6H8O7), salicylic acid (C7H6O3), gallic acid (C7H6O5), mandelic acid (C8H8O3), vanillic acid (C8H8O4), coumaric acid (C9H8O3), caffeic acid (C9H8O4), melilotate (C9H 10 O3), phloretic acid (C9H 10 O3), syringic acid (C9H 10 O5), etc. are mentioned, and tartaric acid and malic acid are preferred.

[0026] The hydroxy acid used in producing the copper-based powder of the present invention is a solid or a liquid at normal temperature.

[0027] Among these, solid hydroxy acids, particularly powdered hydroxy acids, exhibit effects only by being sufficiently mixed with copper powder or copper alloy powder, and are easy to handle. Therefore, the treatment process becomes simple and is suitable.

[0028] Examples of hydroxy acids that are easily available as powders include tartaric acid, malic acid, citric acid, etc.

[0029] Some hydroxy acids have optical isomers, namely the D-form and the L-form, and there are some racemic forms (DL-forms) that are mixtures of the D-form and the L-form and are commercially available.

[0030] Although the mechanism has not been fully elucidated, as confirmed by the inventors through various experiments, it has been found that the copper-based powder using the racemic form is superior in oxidation resistance to the D-form or the L-form alone. Examples of hydroxy acids for which the racemic form is easily available include tartaric acid and malic acid.

[0031] The hydroxy acid in the present invention may be a single hydroxy acid or may contain a plurality of hydroxy acids.

[0032] As the hydroxy acid in the present invention, hydrates mainly composed of hydroxy acids such as gallic acid monohydrate and citric acid monohydrate may be used. However, since it may be a factor promoting oxidation, the amount of water of hydration in the hydrate is preferably 10% by weight or less.

[0033] In the present invention, the method for producing the copper powder or copper alloy powder to be mixed with the hydroxy acid is not particularly limited.

[0034] In the present invention, as the method for producing the copper powder or copper alloy powder, various copper powders or copper alloy powders produced by general methods such as the atomization method using water or gas as the spraying medium, the centrifugal atomization method typified by the rotating disk method and the plasma rotating electrode method, the electrolysis method, the pulverization method, the dry reduction method, and the wet reduction method can be used.

[0035] The particle size and particle shape of the copper powder or copper alloy powder are not limited either. However, the finer the particle size and the more deviated from the spherical shape, the larger the specific surface area, so it is desirable to increase the amount of hydroxy acid.

[0036] Also, if the particle size of the copper powder or copper alloy powder is too fine, in addition to an increase in the required amount of hydroxy acid, it becomes difficult to mix uniformly. Therefore, those having an average particle diameter (D50) of 0.1 μm or more are preferred, and 1 μm or more is more preferred. Here, the average particle diameter (D50) refers to the cumulative 50% particle diameter (D50) based on volume, and is measured using a commercially available laser diffraction particle size distribution measuring device.

[0037] In addition, as the copper powder or copper alloy powder used when producing the copper-based powder of the present invention, those having an average particle diameter (D50) of 100 μm or less are generally used for powder metallurgy, and those of 10 μm or less are generally used for electronic materials, depending on the intended use.

[0038] The copper powder or copper alloy powder mentioned here generally has a purity that circulates as a copper powder or copper alloy powder, and may contain unavoidable impurities of 1% by weight or less.

[0039] The use of the copper-based powder of the present invention is not limited.

[0040] As described above, copper-based powders are used in various industries, but discoloration due to oxidation is regarded as one type of deterioration over time and is not welcomed in any field.

[0041] The hydroxy acid contained in the copper-based powder of the present invention is generally highly safe and has a low environmental impact. Therefore, there are low barriers to its use in any field and it is easily accepted.

[0042] The method for producing the copper-based powder of the present invention is not particularly limited, but from the viewpoint of simplicity of the treatment process as described above, it is preferably carried out by mixing.

[0043] In the present invention, the mixing method is not particularly limited, but from the viewpoint of being able to perform mass production and being able to directly use commercially available equipment, a rocking mixer is preferable.

[0044] When using a rocking mixer, for the purpose of allowing mixing to proceed in a short time, media such as balls may be added simultaneously, or a stirrer may be inserted into the capsule.

[0045] Also, when the processing amount is large, it is more practical to use a double-cone type or V-type blender rather than a rocking mixer. In the present invention, in addition to the above treatment method, the hydroxy acid may be dissolved in a solvent in which the hydroxy acid is soluble, mixed with the powder, and then dried if necessary. The copper-based powder of the present invention obtained by such treatment has a structure in which the hydroxy acid adheres to the periphery of the copper powder or copper alloy powder.

[0046] The amount of the hydroxy acid contained in the copper-based powder of the present invention is 0.5 parts by weight or more, preferably 0.7 parts by weight or more, more preferably 1.0 parts by weight or more with respect to 100 parts by weight of copper.

[0047] If the amount of hydroxy acid is less than 0.5 parts by weight, sufficient oxidation resistance cannot be obtained due to insufficient amount, and discoloration may occur.

[0048] On the other hand, even if the treatment is carried out with the amount of hydroxy acid exceeding 10.0 parts by weight, the effect on oxidation resistance reaches a plateau, which not only causes an increase in cost but also may impair other properties of copper-based powder such as sinterability. The amount of hydroxy acid in the present invention is 0.5 to 10.0 parts by weight, preferably 0.5 to 5.0 parts by weight, more preferably 0.7 to 4.0 parts by weight, and particularly preferably 1.0 to 3.0 parts by weight with respect to 100 parts by weight of copper.

Examples

[0049] Examples of the present invention are shown below, but the present invention is not limited thereto.

[0050] <Raw material powder> As the raw material powder of the copper-based powder in Examples and Comparative Examples, atomized copper powder (Cu-HWQ 5μm manufactured by Fukuda Metal Foil & Powder Co., Ltd.) with an average particle size (D50) of 5.2μm measured by the laser diffraction / scattering method was used.

[0051] <Mixing treatment> A mixed powder obtained by adding a predetermined amount of treatment agent to 300 g of atomized copper powder was mixed with a rocking mixer (RM1.2 / 10(S)HD / MC manufactured by Aichi Electric Co., Ltd.) at a rotation speed of 20 rpm for 60 minutes to produce a copper-based powder.

[0052] (Example 1) To 100 parts by weight of copper powder produced by the atomization method, 1.0 part by weight of D-tartaric acid (manufactured by Kanto Chemical Co., Inc., purity 99.0% or more) composed of hydroxy acid mainly composed of D-form was added and mixed with a rocking mixer.

[0053] (Example 2) To 100 parts by weight of copper powder produced by the atomization method, 1.0 part by weight of L-tartaric acid (manufactured by Kanto Chemical Co., Inc., purity 99.0% or more) composed of hydroxy acid mainly composed of L-form was added and mixed with a rocking mixer.

[0054] (Example 3) To 100 parts by weight of copper powder produced by the atomizing method, 0.5 part by weight of DL-tartaric acid (manufactured by Kanto Chemical Co., Inc., purity 99.0% or more) composed mainly of a racemic body of hydroxy acid was added and mixed with a rocking mixer.

[0055] (Example 4) To 100 parts by weight of copper powder produced by the atomizing method, 1.0 part by weight of DL-tartaric acid was added and mixed with a rocking mixer.

[0056] (Example 5) To 100 parts by weight of copper powder produced by the atomizing method, 2.0 parts by weight of DL-tartaric acid was added and mixed with a rocking mixer.

[0057] (Example 6) To 100 parts by weight of copper powder produced by the atomizing method, 5.0 parts by weight of DL-tartaric acid was added and mixed with a rocking mixer.

[0058] (Example 7) To 100 parts by weight of copper powder produced by the atomizing method, 1.0 part by weight of D-malic acid (manufactured by Kanto Chemical Co., Inc., purity 97.0% or more) composed mainly of the D-form of hydroxy acid was added and mixed with a rocking mixer.

[0059] (Example 8) To 100 parts by weight of copper powder produced by the atomizing method, 1.0 part by weight of L-malic acid (manufactured by Kanto Chemical Co., Inc., purity 98.0% or more) composed mainly of the L-form of hydroxy acid was added and mixed with a rocking mixer.

[0060] (Example 9) To 100 parts by weight of copper powder produced by the atomizing method, 1.0 part by weight of DL-malic acid (manufactured by Kanto Chemical Co., Inc., purity 98.0% or more) composed mainly of a racemic body of hydroxy acid was added and mixed with a rocking mixer.

[0061] (Example 10) To 100 parts by weight of copper powder produced by the atomization method, 2.0 parts by weight of DL-malic acid was added and mixed with a rocking mixer.

[0062] (Example 11) To 100 parts by weight of copper powder produced by the atomization method, 5.0 parts by weight of DL-malic acid was added and mixed with a rocking mixer.

[0063] (Example 12) To 100 parts by weight of copper powder produced by the atomization method, 1.0 part by weight of gallic acid monohydrate (purity 98% or more, manufactured by Fujifilm Wako Pure Chemical Corporation) consisting of hydroxy acid (0.96 part by weight as gallic acid which is a hydroxy acid) was added and mixed with a rocking mixer.

[0064] (Example 13) To 100 parts by weight of copper powder produced by the atomization method, 0.5 part by weight each of gallic acid monohydrate and DL-tartaric acid (0.48 part by weight as gallic acid which is a hydroxy acid for gallic acid monohydrate) was added and mixed with a rocking mixer.

[0065] (Comparative Example 1) Only copper powder produced by the atomization method was used.

[0066] (Comparative Example 2) To 100 parts by weight of copper powder produced by the atomization method, 0.1 part by weight of DL-tartaric acid was added and mixed with a rocking mixer.

[0067] (Comparative Example 3) To 100 parts by weight of copper powder produced by the atomization method, 0.1 part by weight of DL-malic acid was added and mixed with a rocking mixer.

[0068] (Comparative Example 4) 100 parts by weight of copper powder produced by the atomizing method was mixed with 1.0 part by weight of stearic acid, a fatty acid (purity 99.0% or more, manufactured by Shin Nippon Rika Co., Ltd.) using a rocking mixer.

[0069] <Evaluation of Oxidation Resistance> 1 g of the copper-based powder was scattered on a slide glass and heated in a muffle furnace at 130 °C and 150 °C for 60 minutes in the air, and the difference in color before and after heating was confirmed and evaluated. Those in which no change in color occurred due to heat treatment (the same "reddish-brown" as the copper powder) were rated "○", those in which a change in color occurred due to heat treatment (including "brown" in which a little oxidation progressed and "color unevenness" in which oxidation progressed partially) were rated "△", and those in which a large change in color occurred (the same "black" as completely oxidized copper oxide) were rated "×".

[0070] The results of each example are shown in Table 1, and the results of each comparative example are shown in Table 2.

[0071]

Table 1

[0072]

Table 2

[0073] From Table 1 and Table 2, it was proved that the copper-based powder containing a predetermined amount of hydroxy acid of the present invention (Examples 1 to 13) is less likely to change in color compared to the copper-based powder that does not contain hydroxy acid (Comparative Example 1), the copper-based powder that contains less than the predetermined amount (Comparative Examples 2 and 3), and the copper-based powder that contains a higher fatty acid (Comparative Example 4), and has high oxidation resistance.

[0074] (Example 14) 1.0 part by weight of L-tartaric acid (manufactured by Kanto Chemical Co., Inc., purity 99.0% or higher) mainly composed of the L-form of hydroxy acid was dissolved in 20 parts by weight of water to prepare a solution. To this solution, 100 parts by weight of the copper powder produced by the atomizing method was added and mixed. Then, it was dried in a muffle furnace at 60 °C for 120 minutes to obtain a copper-based powder.

[0075] (Example 15) 1.0 part by weight of DL-tartaric acid (manufactured by Kanto Chemical Co., Inc., purity 99.0% or higher) mainly composed of the racemic form of hydroxy acid was dissolved in 20 parts by weight of water to prepare a solution. To this solution, 100 parts by weight of the copper powder produced by the atomizing method was added and mixed. Then, it was dried in a muffle furnace at 60 °C for 120 minutes to obtain a copper-based powder.

[0076] Regarding the copper-based powders obtained in Examples 14 and 15 above, the oxidation resistance was evaluated by the above-described oxidation resistance evaluation method. The results are shown in Table 3.

[0077]

Table 3

[0078] From Table 3, it was proved that the copper-based powder with a predetermined amount of hydroxy acid attached in the form of a solution is also a copper-based powder with high oxidation resistance, in which the color change due to heat treatment hardly occurs, similar to the copper-based powder obtained by mixing with powdery hydroxy acid.

Industrial Applicability

[0079] The copper-based powder of the present invention is a powder that is difficult to discolor due to oxidation in an environment containing oxygen as a raw material powder in various applications such as for powder metallurgy, additive manufacturing, conductive materials, coating / printing, and catalysts. Therefore, it can be stably used from a quality perspective in various applications, and it is a practical powder that can be expected to improve productivity because the process is simple and the environmental load is small.

Claims

Claim 1 A copper-based powder containing 0.5 parts by weight or more of a hydroxy acid with respect to 100 parts by weight of copper or a copper alloy. Claim 2 The copper-based powder according to Claim 1, containing a racemate as the hydroxy acid. Claim 3 The copper-based powder according to Claim 1, containing tartaric acid or malic acid as the hydroxy acid. Claim 4 The copper-based powder according to Claim 1, obtained by mixing copper powder or copper alloy powder and hydroxy acid powder.

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