Thin-film copper powder and conductive paste containing the thin-film copper powder

Abstract

This invention provides a flake-shaped copper powder with low apparent density and strong horizontal orientation in the coating film. Therefore, conductive pastes using this flake-shaped copper powder as a conductive filler have more contact points with each other, allowing for the formation of a conductive network even with a low filler ratio through low-temperature calcination at around 300°C, resulting in a highly conductive paste. The flake-shaped copper powder, as measured by a laser diffraction particle size distribution measuring device, has a median particle size (D50) of 0.3 μm or more and 35 μm or less, an apparent density (AD) of 0.1 g / cm³ or more and 1.8 g / cm³ or less, and exhibits strong horizontal orientation in the coating film.

Description

Technical Field

[0001] This invention relates to a flake-shaped copper powder suitable for use as a conductive filler in conductive pastes. More specifically, it relates to a flake-shaped copper powder with low apparent density and a strong horizontal orientation in the coating film. Therefore, conductive pastes using this flake-shaped copper powder as a conductive filler have more contact points with each other in the coating film. Thus, even with a low ratio of conductive filler, a conductive network can be formed by low-temperature calcination at around 300°C, resulting in a conductive paste exhibiting high conductivity. Prior Technology

[0002] With the increasing demand for electronic components, conductive paste used to form conductive circuits has attracted much attention.

[0003] As a conductive filler in conductive paste, copper powder, which has excellent conductivity and is inexpensive, is mostly used.

[0004] In order for conductive paste to exhibit high conductivity, the shape of copper powder is important. Compared with spheres, flakes have more contact points between the copper powders, which is advantageous in forming a conductive network.

[0005] If it is thin-film copper powder, it can easily exhibit high conductivity even at a low content, making it suitable as a conductive filler for conductive pastes used in conductive circuits on flexible substrates.

[0006] In addition, conductive paste using flake copper powder as conductive filler can form a conductive network even when calcined at a lower temperature, thus contributing to the reduction of CO2 emissions.

[0007] In addition, as electronic components become more high-performance, uniform coating and substrate concealment are required. Conductive pastes with thin-film copper powder as conductive filler can also help achieve uniform coating and high substrate concealment.

[0008] Therefore, in order to produce thin-film copper powder suitable for conductive fillers in conductive pastes, research and development is being carried out focusing on particle size distribution, average particle size, and other parameters.

[0009] However, the currently popular flake copper powder is a thin sheet of copper powder with thick powder particles or a near-spherical shape. Therefore, there are problems such as weak horizontal orientation of the flake copper powder in the coating film and few contact points between the flake copper powder particles.

[0010] In addition, when the copper powder is thick or nearly spherical, it is difficult to form a conductive network in a conductive paste with a low ratio of conductive fillers, and it is difficult to calcine at a low temperature of around 300°C, thus resulting in a problem of difficulty in exhibiting high conductivity.

[0011] Therefore, it is desirable to develop a thin sheet of copper powder that can be used to make a conductive paste that exhibits high conductivity even when the ratio of conductive filler is low and the powder is calcined at a low temperature of around 300°C to form a conductive network. Existing technical documents Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2005-200734 Patent Document 2: Japanese Patent Application Publication No. 2005-314755 Patent Document 3: Japanese Patent Application Publication No. 2017-025393 Summary of the Invention

[0013] The problem that the invention aims to solve Patent document 1 describes a sheet-like copper powder for use as a conductive filler in a conductive paste that focuses on the thickness or aspect ratio, particle size distribution, etc.

[0014] However, the conductive paste described in Patent Document 1 is baked at a high temperature of 840°C, but there is no record of whether it can exhibit high conductivity when baked at a low temperature of around 300°C.

[0015] Patent document 2 describes a thin sheet of copper powder used as a conductive filler for a conductive paste that focuses on the aspect ratio or crystallite diameter, P content, etc.

[0016] However, there are no records related to the roasting temperature.

[0017] Patent document 3 describes a sheet-like copper powder for conductive paste that focuses on the aspect ratio distribution or C content of the powder.

[0018] However, there is no record of high conductivity being observed when calcined at a high temperature of approximately 845°C, but when calcined at a low temperature of around 300°C.

[0019] The inventors have addressed the technical challenge of producing conductive fillers that enable conductive pastes with low conductive filler ratios to exhibit high conductivity through low-temperature calcination at around 300°C. Through repeated large-scale trials and experiments, they achieved the following results, realizing the aforementioned technical challenge: A flake-like copper powder is provided, wherein the median particle size (D50) measured by a laser diffraction particle size distribution measuring device is 0.3 μm or more and 35 μm or less, and the apparent density (AD) is 0.1 g / cm³ or more and 1.8 g / cm³ or less. The dispersion paste obtained by dispersing 20% ​​by weight of the flake-like copper powder in 80% by weight of a transparent organic solvent-based paint containing 10% by weight or more and 15% by weight of a resin soluble in an organic solvent is prepared according to JIS (K). The concealment rate measured by the concealment rate determination method specified in 5101-4:2004, calculated by (Equation 1) 『(1-ΔL / ΔL0)×100 (ΔL0=the difference between the brightness L value of the black part and the brightness L value of the white part of the concealment rate test paper, ΔL=the difference between the brightness L value of the black part and the brightness L value of the white part of the concealment rate test paper coated with dispersant paste)』, is 90% or higher. Based on this thin-film copper powder, the apparent density is low, and it is strongly oriented in the horizontal direction in the coating film. Therefore, the conductive paste with this thin-film copper powder as the conductive filler has more contact points between the conductive fillers in the coating film. Therefore, even the conductive paste with a low ratio of conductive filler can form a conductive network by low-temperature calcination at about 300°C, and become a conductive paste with high conductivity. Technical solutions for solving the problem

[0020] The aforementioned technical problem can be solved by the following invention.

[0021] This invention provides a flake-shaped copper powder, wherein the median particle size (D50) measured by a laser diffraction particle size distribution measuring device is 0.3 μm or more and 35 μm or less, and the apparent density (AD) is 0.1 g / cm3 or more and 1.8 g / cm3 or less. The dispersion paste obtained by dispersing 20% ​​by weight of the flake-shaped copper powder in 80% by weight of a transparent organic solvent-based paint containing 10% by weight or more and 15% by weight of a resin soluble in an organic solvent has a concealment rate of 90% or more as calculated by the following (Formula 1) according to the concealment rate determination method specified in JIS (K 5101-4:2004). (Equation 1) (1-ΔL / ΔL0)×100 ΔL = the difference between the luminance L value of the black area and the luminance L value of the white area of ​​the concealment test paper coated with dispersant paste. ΔL0 = the difference between the luminance L value of the black area and the luminance L value of the white area on the concealment rate test strip.

[0022] In addition, the present invention provides a conductive paste, wherein it contains the aforementioned flake-shaped copper powder.

[0023] Furthermore, in this invention, according to the conductive paste, the conductive paste is a conductive paste prepared by dispersing 100 parts by weight of flake copper powder in 44 parts by weight and less than 100 parts by weight of varnish. Invention Effects

[0024] The flake-shaped copper powder of the present invention is flake-shaped copper powder with a median particle size (D50) of 0.3 μm or more and 35 μm or less, and an apparent density (AD) of 0.1 g / cm3 or more and 1.8 g / cm3 or less, thus forming a shape in which the flake-shaped copper powders can easily form contact points with each other.

[0025] Furthermore, since the concealment rate is over 90% and the coating is strongly oriented horizontally, the conductive paste using the flake copper powder of the present invention as a conductive filler has more contact points with each other. Therefore, even with a low ratio of conductive filler, a conductive network can be formed by low-temperature calcination at around 300°C, exhibiting high conductivity.

[0026] Therefore, the conductive paste using the flake copper powder of the present invention as a conductive filler can be applied to circuit formation or the mounting of electronic components as conductive materials. Simple Explanation of the Diagram

[0027] Figure 1 is a scanning electron microscope (SEM) image (19,000x) highlighting the sheet-like copper powder of Example 1 and the shape of the powder. Figure 2 is a scanning electron microscope (SEM) image (19,000x) highlighting the thin sheet-like copper powder of Comparative Example 1 and the shape of the powder. Implementation

[0028] (Thin flakes of copper powder) The flake-shaped copper powder of the present invention is a flake-shaped copper powder with low apparent density and strong horizontal orientation in the coating film.

[0029] The median particle size (hereinafter referred to as "D50") of the flake-shaped copper powder of the present invention, as determined by a laser diffraction particle size distribution device, is preferably 0.3 μm to 35 μm, more preferably 0.5 μm to 30 μm, and even more preferably 0.7 μm to 30 μm.

[0030] When D50 is greater than 35μm, there are a certain number of coarse particles, which may prevent the formation of circuits through printing.

[0031] In addition, when D50 is greater than 35 μm, the calcined film is difficult to densify, and therefore high conductivity may not be obtained.

[0032] On the other hand, thin-film copper powder with a D50 of less than 0.3 μm is difficult to produce by mechanical pulverization.

[0033] This is because the particles produced by crushing may aggregate with each other.

[0034] In addition, in the laser diffraction particle size distribution determination method, the sphere equivalent diameter is determined by analyzing the intensity of the scattered light generated when a laser is irradiated onto particles dispersed in a solvent, and the particle size distribution of the volume reference is determined.

[0035] The apparent density (hereinafter referred to as "AD") of the flake copper powder of the present invention is preferably 0.1 g / cm3 to 1.8 g / cm3, more preferably 0.1 g / cm3 to 1.5 g / cm3.

[0036] The particle shape of thin, flake-like copper powder with low AD becomes irregular. This is because the lower the AD, the more voids there are between the copper powder particles.

[0037] As shown in Figure 1, the flake-shaped copper powder of the present invention has a shape with multiple indentations (like a serrated saw blade) on the edge of the powder particles without rounded corners, thus indicating an increase in the contact points between the flake-shaped copper powder particles in the coating.

[0038] Therefore, a lower AD is better, but it is difficult to produce thin flake copper powder with an AD of less than 0.1 g / cm3.

[0039] When AD exceeds 1.8 g / cm3, as shown in Figure 2, the powder particles have rounded corners, so the contact points between the thin-film copper powders become fewer. If it is a conductive paste with a low ratio of conductive filler, it is difficult to form a conductive network at a low temperature of around 300℃, and high conductivity may not be obtained.

[0040] AD can be measured according to JIS Z2504:2020.

[0041] The thin-film copper powder of the present invention can be produced by mechanically pulverizing copper powder from raw materials.

[0042] There are no particular restrictions on the copper powder used as raw material; copper powder produced by various methods such as atomization, reduction, and electrolysis can be used.

[0043] The pulverization method can be either dry pulverization or wet pulverization, but dry pulverization is preferred if post-pulverization processing is taken into account.

[0044] There are no particular restrictions on the type of crusher; examples include ball mills, vibratory mills, and pulverizers.

[0045] To prevent copper powder from agglomerating and to promote crushing during the crushing process, a lubricant can also be used.

[0046] There are no particular restrictions on lubricants, but examples include saturated fatty acids such as stearic acid, palmitic acid, myristic acid, and lauric acid, or unsaturated fatty acids such as oleic acid, ethanol, and graphite.

[0047] The thin-film copper powder of the present invention may also contain unavoidable impurities during the manufacturing process.

[0048] (Concealment rate) The flake-shaped copper powder of the present invention is strongly oriented in the horizontal direction in the coating film.

[0049] When thin-film copper powder is oriented in various directions, it may not achieve sufficient contact points in the coating.

[0050] The horizontal orientation of flake copper powder in a coating film can be determined by the masking rate specified in JIS (K5101-4:2004).

[0051] When the thin-film copper powder in the coating has a strong orientation in the horizontal direction and is neatly arranged without gaps, the concealment rate becomes higher.

[0052] In the determination of the concealment rate of the present invention, a dispersion paste obtained by dispersing 20% ​​by weight of the thin-film copper powder in 80% by weight of a transparent organic solvent-based paint was used.

[0053] The resin component dissolved in the transparent organic solvent-based paint is preferably 10% by weight or more and 15% by weight or less.

[0054] Examples of transparent organic solvent-based paints include nitrocellulose varnish (SELVA (registered trademark) 26 / resin content 10%~15% by weight / manufactured by Kansai Paint Co., Ltd.).

[0055] The concealment rate was determined using the aforementioned dispersant paste, following the procedure specified in JIS (K5101-4:2004), by printing the concealment rate onto concealment rate test paper using a bar coater (#18).

[0056] Examples of printing methods include: dripping paint onto the front of the printing bar, pressing both ends with uniform force to the whole bar, pulling it to the front at a constant speed without rotating the bar, and printing manually; and automatically printing using a benchtop test coating machine (e.g., K Control Coater / RK Print-Coat Instruments).

[0057] Regarding the concealment rate, the difference between the brightness L value of the black part and the brightness L value of the white part of the concealment rate test paper with white and black parts is set as ΔL0, and the difference between the brightness L value of the black part and the brightness L value of the white part of the concealment rate test paper coated with dispersant paste is set as ΔL. When ΔL is equal to ΔL0, it is set to 0%, and when there is no difference (ΔL=0), it is set to 100%. The calculation is performed using the following (Equation 1).

[0058] (Equation 1) (1-ΔL / ΔL0)×100

[0059] The concealment rate of the dispersing paste is preferably 90% or more, more preferably 93% or more, and even more preferably 98% or more.

[0060] If the dispersion paste contains flake copper powder with a hiding rate of less than 90%, there will be many gaps on the coating surface and few contact points between the flake copper powders. Therefore, if it is used as a conductive filler in a conductive paste, high conductivity may not be achieved.

[0061] (Conductive paste) The conductive paste using the flake copper powder of the present invention as a conductive filler can be prepared by dispersing the flake copper powder into a varnish using a mixer or metal scraper.

[0062] There are no particular limitations on varnishes; examples include varnishes made by dissolving acrylic resins, polyester resins, or polyvinyl butyral resins in solvents.

[0063] Examples of solvents for dissolving the resin include γ-butyrolactone (γ-BL), butyl carbitol acetate, butyl cellosolve, and terpineol.

[0064] There are no particular restrictions on the proportion of flake copper powder in the conductive paste.

[0065] The ratio of flaky copper powder in conductive paste can be calculated by dividing the weight of the flaky copper powder by the total weight of the flaky copper powder and the weight of the resin contained in the varnish.

[0066] This is because the solvent components in the varnish decompose and volatilize due to baking, but the resin and metal components remain.

[0067] In a varnish containing 25% by weight of resin, it is preferable to disperse 100 parts by weight of flake copper powder in 44 to 100 parts by weight of the varnish.

[0068] The conductive paste of the present invention is applied to a substrate and dried to form a coating film, and then calcined to form a calcined film.

[0069] There are no particular restrictions on the drying method; for example, drying it by leaving it in the atmosphere at 60°C for 10 minutes is shown.

[0070] There are no particular restrictions on the calcination method; examples include the heating reduction method using a reducing atmosphere and the light sintering method using a xenon lamp.

[0071] The preferred roasting temperature is 250℃~300℃, and more preferably 275℃~300℃.

[0072] The volume resistivity of the calcined film can be calculated by measuring the film thickness and linewidth using a surface roughness measuring instrument after the resistance value is calculated by a resistance value measuring instrument. Example

[0073] The present invention will be described in more detail with examples and comparative examples shown, but the present invention is not limited thereto.

[0074] (Thin flakes of copper powder) 10 kg to 20 kg of steel balls with a diameter of 1.6 mm to 6.4 mm were added to 1 kg to 2 kg of spherical copper powder (D50: 2 μm to 150 μm) prepared by atomization or reduction. Stearic acid was used as a lubricant, and the mixture was pulverized at a speed of 40 rpm to 70 rpm for 5 hours to 400 hours to obtain the thin-film copper powders of the examples and comparative examples.

[0075] (Determination of D50 and AD) The median particle size (D50: μm) of each sheet of copper powder in the examples and comparative examples was determined using a laser diffraction particle size distribution measuring device (SALD-2300 / manufactured by Shimadzu Corporation). The apparent density (AD: g / cm3) was determined using a funnel with an aperture of 5.0 mm according to JIS Z2504.

[0076] (Concealment rate) Each of the examples and comparative examples was prepared by mixing 20% ​​by weight and 80% by weight of nitrocellulose varnish (SELVA (registered trademark) 26 / resin content ratio 10% to 15% by weight / manufactured by Kansai Paint Co., Ltd.) with a paint conditioner.

[0077] For the preparation of the dispersion paste, a bar coater #18 is used. After the coating is dripped in front of the bar, the two ends are pressed down in a way that applies uniform force to the whole, and the bar is pulled in front at a constant speed without rotating, and printed onto the coating paper for the concealment test (ΔL0=79.23).

[0078] Using a colorimeter (SE6000 / manufactured by Nippon Denshoku Kogyo Co., Ltd.), the luminance L value of the black part and the luminance L value of the white part of the opacity test paper and the opacity test paper printed with dispersant paste were measured, and the opacity was calculated by the above (Equation 1).

[0079] (Conductive paste) 100 parts by weight of each of the sheet-like copper powders in the examples and comparative examples, and 44 or 100 parts by weight of varnish containing 25% by weight of a resin composed of polyvinyl butyral resin (S-LEC (registered trademark) / manufactured by Sekisui Chemicals Co., Ltd.) and γ-BL (manufactured by Mitsubishi Chemical Co., Ltd.) were mixed with a calciner to prepare conductive pastes with 90% by weight and 80% by weight of sheet-like copper powder, respectively.

[0080] Using the prepared conductive paste, a coating with a line width of 4 mm and a film thickness of 50 μm was formed on a glass substrate using a metal scraper.

[0081] The formed coating film is dried in the atmosphere at 60°C for 10 minutes to obtain a dried coating film.

[0082] The dried coating was baked at 300°C for 60 minutes under a nitrogen atmosphere to prepare a baked film.

[0083] For the calcined film, the resistance was measured using a resistance meter (RM3545 / manufactured by Hioki Electric Co., Ltd.) with an inter-electrode distance of 40 mm, and the film thickness and linewidth were measured using a surface roughness meter (SE500A / manufactured by Kosaka Research Institute Co., Ltd.) to calculate the volume resistivity.

[0084] The results are shown in Table 1.

[0085] [Table 1]

[0086] As can be seen from Table 1, the conductive paste containing the flake copper powder of the present invention, even when the proportion of calcined flake copper powder is 80% by weight, has a low volume resistivity and can achieve high conductivity.

[0087] For the flake-shaped copper powders of Example 1 and Comparative Example 1, scanning electron microscope (SEM) images (19,000x) were taken, and the shapes were compared (Figures 1 and 2).

[0088] It can be seen that in the flake copper powder of the embodiment, the edge of the particle has a shape with multiple indentations facing the interior of the powder. In contrast, in the flake copper powder of the comparative example, the edge of the particle has rounded corners. Industrial availability

[0089] The flake-shaped copper powder of the present invention has a low apparent density and is strongly oriented horizontally in the coating film. Therefore, the conductive paste using this flake-shaped copper powder as a conductive filler has more contact points between the conductive fillers in the coating film. Thus, even if the ratio of conductive filler is low, a conductive network can be formed by low-temperature calcination at around 300°C, resulting in a conductive paste with high conductivity. Therefore, this invention is highly industrially applicable.

[0090] (none)

Claims

1. A thin-film copper powder, wherein the median particle size (D50) measured by a laser diffraction particle size distribution measuring device is ≥0.3μm and ≤35μm, and the apparent density (AD) is ≥0.1g / cm³ and ≤1.8g / cm³, wherein, The concealment rate of the dispersion paste obtained by dispersing 20% ​​by weight of the thin-film copper powder in 80% by weight of a transparent organic solvent-based paint containing 10% to 15% by weight of a resin soluble in an organic solvent is 90% or more, calculated by the concealment rate determination method specified in JIS (K 5101-4:2004) using the following formula (1): (Formula 1) (1-ΔL / ΔL0)×100 ΔL = the difference between the brightness L value of the black part and the brightness L value of the white part of the concealment rate test paper coated with the dispersion paste ΔL0 = the difference between the brightness L value of the black part and the brightness L value of the white part of the concealment rate test paper.

2. A conductive paste comprising flake-shaped copper powder as claimed in claim 1.

3. The conductive paste as described in claim 2, wherein, The conductive paste is made by dispersing 100 parts by weight of thin-film copper powder in 44 parts by weight and less than 100 parts by weight of varnish.

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