Method for producing tin flake powder and tin flake powder

Abstract

To provide a method for producing tin flake powder that can suppress variations in length in the direction perpendicular to the thickness, and to provide tin flake powder. [Solution] The method for producing tin flake powder comprises a preparation step of preparing tin foil made of tin or a tin alloy, and an ultrasonic irradiation step of irradiating the tin foil 1 with ultrasonic waves using a liquid medium to break the tin foil 1. The thickness of the tin foil 1 is less than 10 μm.

Description

Technical Field

[0001] The present invention relates to a method for producing tin flake powder and tin flake powder.

Background Art

[0002] Conventionally, metal powders have been used in a wide range of applications such as pigments, metal pastes, solder materials, and conductive materials.

[0003] As a method for producing such metal powders, for example, a method for producing wire-shaped metal fine particles including a step of disposing a metal mass having crystal orientation in a solvent and irradiating the metal mass with ultrasonic waves using the solvent as a medium to obtain wire-shaped metal fine particles has been proposed (see, for example, Patent Document 1). Specifically, in Patent Document 1, wire-shaped metal fine particles are produced by irradiating a copper foil (thickness 18 μm) with ultrasonic waves (see, for example, Example 1 of Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, metal powders may exhibit different physical properties depending on their shape. Therefore, in a method for producing metal powders, if there is a large variation in the shape of the metal powders, there is a problem that the quality of the products obtained using the metal powders deteriorates.

[0006] The present invention provides a method for producing tin flake powder capable of suppressing variation in the length extending in a direction orthogonal to the thickness, and tin flake powder.

Means for Solving the Problems

[0007] The present invention [1] is a method for producing tin flake powder, comprising a preparation step of preparing a tin foil made of tin or a tin alloy, and an ultrasonic irradiation step of irradiating the tin foil with ultrasonic waves using a liquid medium to break the tin foil, wherein the thickness of the tin foil is less than 10 μm.

[0008] The present invention [2] includes a method for producing tin flake powder as described in [1] above, wherein the liquid comprises a first liquid, and in the ultrasonic irradiation step, the tin foil is immersed in the first liquid, and the viscosity (at 25°C) of the first liquid is 1 mPa·s or more and 20 mPa·s or less.

[0009] The present invention [3] includes a method for producing tin flake powder according to [1] or [2] above, wherein the frequency of the ultrasound in the ultrasonic irradiation step is 200 kHz or less.

[0010] The present invention [4] includes a method for producing tin flake powder according to any one of the above [1] to [3], further comprising an embrittlement treatment step of applying an embrittlement treatment to the tin foil after the preparation step and before the ultrasonic irradiation step.

[0011] The present invention [5] includes a method for producing tin flake powder according to any one of the above [1] to [4], wherein the ultrasonic irradiation step is performed multiple times.

[0012] The present invention [6] is a tin flake powder made of tin or a tin alloy, wherein, in a cross-section of the tin flake powder observed by an optical microscope, the average of the maximum length extending in a direction perpendicular to the thickness of the tin flake powder is 20.00 μm or less, and the standard deviation of the maximum length is 10.00 or less.

[0013] The present invention [7] includes the tin flake powder described in [6] above, wherein the average major axis of the tin flake powder is 30.00 μm or less, the average thickness of the tin flake powder is 0.20 μm or more and 10.00 μm or less, the coefficient of variation of the thickness of the tin flake powder is 0.50 or less, and the average ratio of the maximum length to the thickness of the tin flake powder (maximum length / thickness) is 2.00 or more. [Effects of the Invention]

[0014] In the present invention's method for producing tin flake powder, the tin foil is made of tin or a tin alloy, and the thickness of the tin foil is less than 10 μm. In this method, the tin foil is fractured by irradiating it with ultrasonic waves using a liquid medium. Therefore, it is possible to produce tin flake powder with suppressed variation in length in the direction perpendicular to the thickness.

[0015] The tin flake powder of the present invention is made of tin or a tin alloy, and the standard deviation of the maximum length extending in the direction perpendicular to the thickness of the tin flake powder is 10.00 or less. Therefore, variations in the length extending in the direction perpendicular to the thickness of the tin flake powder can be suppressed. [Brief explanation of the drawing]

[0016] [Figure 1] Figures 1A to 1C show one embodiment of the method for producing tin flake powder according to the present invention. Figure 1A shows the preparation step for preparing tin foil. Figure 1B shows the ultrasonic irradiation apparatus in the ultrasonic irradiation step. Figure 1C shows the ultrasonic irradiation step in which the tin foil is fractured by irradiating the tin foil with ultrasonic waves using a liquid medium. [Figure 2] Figures 2A to 2C are explanatory diagrams of the manufacturing method for tin flake powder. Figure 2A is an explanatory diagram of the process when ultrasonic waves using a liquid medium are irradiated onto tin foil with a thickness of less than 10 μm. Figure 2B is an explanatory diagram when ultrasonic waves using a liquid medium are irradiated onto tin foil with a thickness of 10 μm or more. Figure 2C is an explanatory diagram when ultrasonic waves using a liquid medium are irradiated onto copper foil (thickness 18 μm). [Figure 3]Figure 3 shows the SEM photograph of the tin flake powder of Example 1. [Figure 4] Figure 4 shows the SEM photograph of the tin flake powder of Example 2. [Figure 5] Figure 5 shows the SEM photograph of the tin flake powder of Example 3. [Figure 6] Figure 6 shows the SEM photograph of the tin flake powder of Example 4. [Figure 7] Figure 7 shows the SEM photograph of the tin flake powder of Example 5. [Figure 8] Figure 8 shows the SEM photograph of the tin flake powder of Example 6. [Figure 9] Figure 9 shows the SEM photograph of the tin flake powder of Example 7.

Embodiments for Carrying Out the Invention

[0017] Referring to FIGS. 1A to 1C, an embodiment of the method for manufacturing the tin flake powder of the present invention will be described.

[0018] The method for manufacturing the tin flake powder includes a preparation step of preparing a tin foil 1, a embrittlement treatment step of subjecting the tin foil 1 to an embrittlement treatment, and an ultrasonic irradiation step of irradiating the tin foil 1 with ultrasonic waves using a liquid (specifically, a first liquid 2 and a second liquid 3) as a medium to break the tin foil 1.

[0019] <Preparation Step> In the preparation step, as shown in FIG. 1A, a tin foil 1 is prepared.

[0020] The tin foil 1 has a sheet shape.

[0021] The thickness of the tin foil 1 is less than 10 μm, preferably 5 μm or less, more preferably 3 μm or less, still more preferably 2 μm or less, and, for example, 0.5 μm or more.

[0022] If the thickness of the tin foil 1 is below the above upper limit, as will be explained in more detail later, flake-shaped tin flake powder 20 can be manufactured from the tin foil 1. As a result, variations in the length extending in the direction perpendicular to the thickness of the tin flake powder 20 can be suppressed.

[0023] On the other hand, if the thickness of the tin foil 1 exceeds the above upper limit, it becomes impossible to manufacture the tin flake powder 20, as will be explained in more detail later. As a result, variations cannot be suppressed in the length extending in the direction perpendicular to the thickness of the tin flake powder 20.

[0024] Tin foil is made of tin or a tin alloy.

[0025] Examples of tin alloys include tin-bismuth alloy (Sn-Bi), tin-silver-copper alloy (Sn-Ag-Cu), tin-antimony alloy (Sn-Sb), and tin-silver alloy (Sn-Ag).

[0026] In tin alloys, the tin content is, for example, 40% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and also, for example, 99% by mass or less.

[0027] <Embrittlement Treatment Process> In the embrittlement treatment process, the tin foil 1 is subjected to an embrittlement treatment.

[0028] Specifically, in the embrittlement treatment process, stress is applied to the tin foil 1. More specifically, first, the tin foil 1 is heated to a high temperature (for example, 40°C to 100°C), and then cooled to a low temperature (for example, -210°C to -150°C) using liquid nitrogen, for example. This creates a temperature gradient on the tin foil 1, generating stress (thermal stress) in the tin foil 1. Then, by irradiating the stressed (thermal stressed) tin foil 1 with ultrasound in the ultrasonic irradiation process described later, it is possible to produce even finer tin flake powder 20 (specifically, with a shorter maximum length extending in the direction perpendicular to the thickness (described later)).

[0029] Furthermore, the embrittlement treatment process can be performed multiple times. Specifically, the number of times the embrittlement treatment process is performed is, for example, 1 to 20 times, preferably 5 to 15 times, and more preferably 7 to 12 times.

[0030] <Ultrasonic irradiation process> In the ultrasonic irradiation process, the tin foil 1 is fractured by irradiating it with ultrasound using liquids (first liquid 2 and second liquid 3) as a medium.

[0031] The ultrasonic irradiation process is carried out using an ultrasonic irradiation device 10. The ultrasonic irradiation device 10 will be described in detail below with reference to Figure 1B.

[0032] The ultrasonic irradiation device 10 comprises a first tank 11, a second tank 12 that houses the first tank 11, and an ultrasonic transducer 13.

[0033] The first tank 11 is a container with a smaller volume than the second tank 12. The first tank 11 is, for example, a glass container. The first liquid 2 and the tin foil 1 are contained in the first tank 11.

[0034] The tin foil 1 is immersed in the first liquid 2. The first liquid 2 is the medium that comes into contact with the tin foil 1. The first liquid 2 is not particularly limited as long as it is a medium that propagates ultrasound. Examples of the first liquid 2 include water, alcohol, ketone, ether, alicyclic hydrocarbon, aromatic hydrocarbon, and aromatic hydrocarbon. Preferably, the first liquid 2 is an alcohol, from the viewpoint of adjusting the viscosity of the first liquid 2 (at 25°C), which will be described later.

[0035] Examples of alcohols include monohydric alcohols and dihydric alcohols.

[0036] Examples of monohydric alcohols include monohydric alcohols having 1 to 12 carbon atoms. Examples of monohydric alcohols having 1 to 12 carbon atoms include methanol, ethanol, propanol, isopropanol (2-propanol), n-butanol, isobutanol, s-butanol, t-butanol, 2-ethylhexyl alcohol, and lauryl alcohol. Preferably, monohydric alcohols have 1 to 4 carbon atoms. More preferably, monohydric alcohols include ethanol and isopropanol (2-propanol).

[0037] Examples of dihydric alcohols include dihydric alcohols having 1 to 12 carbon atoms. Examples of dihydric alcohols having 1 to 12 carbon atoms include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Preferably, dihydric alcohols have 1 to 4 carbon atoms. More preferably, ethylene glycol is used as the dihydric alcohol.

[0038] The first liquid 2 can be used alone or in combination of two or more types. Preferably, from the viewpoint of adjusting the viscosity of the liquid (25°C) described later, monohydric alcohols and dihydric alcohols are used in combination as the first liquid 2.

[0039] The viscosity of the first liquid 2 (at 25°C) is, for example, 1 mPa·s to 20 mPa·s, preferably 5 mPa·s to 15 mPa·s.

[0040] More specifically, the viscosity (at 25°C) of the first liquid 2 is, for example, 1 mPa·s or more, preferably 5 mPa·s or more, and for example, 20 mPa·s or less, preferably 15 mPa·s or less.

[0041] If the viscosity of the first liquid 2 (at 25°C) is above the lower limit and below the upper limit, ultrasonic waves can be reliably transmitted to the tin foil 1. As a result, it is possible to produce tin flake powder 20 that is even finer (specifically, with a shorter maximum length (described later) in the direction perpendicular to the thickness).

[0042] The method for measuring the viscosity (at 25°C) of the first liquid 2 will be described in detail in the examples below.

[0043] The temperature of the first liquid 2 is, for example, 5°C to 25°C, preferably 8°C to 15°C.

[0044] The second tank 12 is a container with a larger volume than the first tank 11. The second tank 12 is, for example, a glass container. The first tank 11, the second liquid 3, and the ultrasonic transducer 13 are housed in the second tank 12.

[0045] The second liquid 3 is not particularly limited as long as it is a medium that propagates ultrasonic waves. The second liquid 3 is a medium that propagates ultrasonic waves to the first liquid 2 without coming into contact with the tin foil 1. Examples of the second liquid 3 include the liquids exemplified in the first liquid 2. Water is preferably the second liquid 3.

[0046] The viscosity (at 25°C) of the second liquid 3 is not particularly limited. For example, the viscosity (at 25°C) of the second liquid 3 is 0.1 mPa·s to 20 mPa·s, preferably 0.5 mPa·s to 5 mPa·s.

[0047] The temperature of the second liquid 3 is, for example, 5°C to 25°C, preferably 8°C to 15°C.

[0048] The ultrasonic transducer 13 is not particularly limited as long as it can generate the ultrasonic frequencies described later. In Figure 1B, an ultrasonic transducer housed in the second chamber 12 (for example, an immersion type transducer) is selected as the ultrasonic transducer 13, but the ultrasonic transducer 13 is not limited to this, and for example, a flange type transducer (a flange type transducer placed at the bottom outside the second chamber 12) can also be selected as the ultrasonic transducer 13.

[0049] Then, in order to irradiate the tin foil 1 with ultrasound using liquids (first liquid 2 and second liquid 3) as a medium, first, the first liquid 2 and the tin foil 1 are added to the first tank 11, and the tin foil 1 is immersed in the first liquid 2. As a result, the first liquid 2 and the tin foil 1 are contained in the first tank 11.

[0050] Next, the first tank 11, the second liquid 3, and the ultrasonic transducer 13 are added to the second tank 12. This brings the first tank 11, the second liquid 3, and the ultrasonic transducer 13 to the second tank 12. The amount of the second liquid 3 is not particularly limited, as long as it is an amount sufficient for the ultrasonic waves to propagate in the order of second liquid 3, the partition wall of the first tank 11, and the first liquid 2.

[0051] Next, ultrasonic waves are generated by the vibration of the ultrasonic transducer 13.

[0052] The ultrasonic irradiation conditions include a frequency of, for example, 10kHz to 200kHz, preferably 20kHz to 180kHz, more preferably 30kHz to 150kHz, even more preferably 40kHz to 130kHz, particularly preferably 60kHz to 120kHz, and most preferably 80kHz to 110kHz.

[0053] More specifically, the frequency is, for example, 10 kHz or higher, preferably 20 kHz or higher, more preferably 30 kHz or higher, even more preferably 40 kHz or higher, particularly preferably 60 kHz or higher, most preferably 80 kHz or higher, and also, for example, 200 kHz or lower, preferably 180 kHz or lower, more preferably 150 kHz or lower, even more preferably 130 kHz or lower, particularly preferably 120 kHz or lower, most preferably 110 kHz or lower.

[0054] If the frequency is above the lower limit mentioned above, it is possible to suppress the excessive size of the shock waves (described later) generated by ultrasonic cavitation. As a result, it is possible to suppress the excessive shortening of the maximum length (described later) extending in the direction perpendicular to the thickness of the tin flake powder 20.

[0055] Furthermore, if the frequency is below the above upper limit, it is possible to suppress the excessive reduction of the shock wave (described later) generated by ultrasonic cavitation. This ensures that the tin foil 1 is reliably fractured. As a result, the maximum length (described later) extending in the direction perpendicular to the thickness of the tin flake powder 20 can be shortened, and variations in the length extending in the direction perpendicular to the thickness of the tin flake powder 20 can be suppressed.

[0056] Furthermore, the ultrasonic irradiation conditions include an output power of, for example, 30W to 600W, preferably 50W to 550W, more preferably 70W to 500W, even more preferably 90W to 450W, and most preferably 100W to 400W.

[0057] More specifically, the output is, for example, 30W or more, preferably 50W or more, more preferably 70W or more, even more preferably 90W or more, particularly preferably 100W or more, and also, for example, 600W or less, preferably 550W or less, more preferably 500W or less, even more preferably 450W or less, particularly preferably 400W or less.

[0058] If the output is above the lower limit mentioned above, it is possible to suppress the excessive reduction of the shock wave (described later) generated by ultrasonic cavitation. This ensures that the tin foil 1 is reliably fractured. As a result, the maximum length (described later) extending in the direction perpendicular to the thickness of the tin flake powder 20 can be shortened, and variations in the length extending in the direction perpendicular to the thickness of the tin flake powder 20 can be suppressed.

[0059] Furthermore, if the value is above the lower limit mentioned above, it is possible to suppress the excessive size of the shock waves (described later) generated by ultrasonic cavitation. As a result, it is possible to suppress the excessive shortening of the maximum length (described later) extending in the direction perpendicular to the thickness of the tin flake powder 20. In addition, it is possible to suppress the decrease in viscosity of the first liquid 2 due to heat generation.

[0060] Furthermore, the ultrasonic irradiation conditions include an irradiation time of, for example, 1 to 72 hours, preferably 12 to 36 hours, and more preferably 18 to 30 hours.

[0061] The ultrasonic waves generated from the ultrasonic transducer 13 propagate in the following order: second liquid 3, partition wall of first tank 11, and first liquid 2 (if the ultrasonic transducer 13 is a flange-type transducer, the waves propagate in the following order: partition wall of second tank 12, second liquid 3, partition wall of first tank 11, and first liquid 2).

[0062] Next, ultrasonic cavitation occurs in the first liquid 2. The shock waves generated by this ultrasonic cavitation break the tin foil 1. Specifically, as shown in the enlarged view of Figure 1C, the tin foil 1 is broken in the thickness direction, and the broken tin foil 1 is similarly broken in the thickness direction. As this breaking occurs sequentially, the surface of the broken tin foil 1 is scraped away. This produces tin flake powder 20.

[0063] <Tin flake powder> The tin flake powder 20 has a flake shape (flattened or scaly shape). Specifically, tin flake powder 20 having a flake shape is tin flake powder 20 in which the ratio of the maximum length of the tin flake powder 20 to the thickness of the tin flake powder 20 (described later) is 2.00 or more, and the average of the area ratio of the top surface area of ​​the tin flake powder 20 to the cross-sectional area of ​​the tin flake powder 20 (top surface area / cross-sectional area) (described later) is 2.00 or more.

[0064] The average major axis of the tin flake powder 20 is, for example, 5.00 μm to 30.00 μm, preferably 10.00 μm to 20.00 μm.

[0065] More specifically, the average major diameter of the tin flake powder 20 is, from the viewpoint of handling, for example, 5.00 μm or more, preferably 10.00 μm or more, and for example, 30.00 μm or less, preferably 20.00 μm or less.

[0066] If the average major diameter of the tin flake powder 20 is less than or equal to the above upper limit, bridging can be suppressed even if the distance (pitch) of electrodes arranged in the planar direction is short when the tin flake powder 20 is used in the manufacture of the laminate described later.

[0067] The method for measuring the average major diameter of the tin flake powder 20 will be described in detail in the examples described later.

[0068] The standard deviation of the major axis of the tin flake powder 20 is, for example, 15 or less, preferably 5 or less.

[0069] If the standard deviation of the major axis of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0070] The method for calculating the standard deviation of the major axis of the tin flake powder 20 will be described in detail in the examples described later.

[0071] The coefficient of variation (standard deviation / mean major axis) of the major axis of the tin flake powder 20 is, for example, 1 or less, preferably 0.5 or less.

[0072] If the coefficient of variation of the major axis of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0073] The average minor diameter of the tin flake powder 20 is, for example, 3.00 μm to 25.00 μm, preferably 5.00 μm to 15.00 μm.

[0074] More specifically, the average short diameter of the tin flake powder 20 is, from the viewpoint of handling, for example, 3.00 μm or more, preferably 5.00 μm or more, and for example, 25.00 μm or less, preferably 15.00 μm or less.

[0075] If the average minor diameter of the tin flake powder 20 is less than or equal to the above upper limit, bridging can be suppressed even if the distance (pitch) between electrodes arranged in the planar direction is short when the tin flake powder 20 is used in the manufacture of the laminate described later.

[0076] The method for measuring the average minor diameter of the tin flake powder 20 will be described in detail in the examples described later.

[0077] The standard deviation of the minor axis of the tin flake powder 20 is, for example, 12 or less, preferably 5 or less.

[0078] If the standard deviation of the minor axis of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0079] The method for calculating the standard deviation of the minor axis of the tin flake powder 20 will be described in detail in the examples described later.

[0080] The coefficient of variation (standard deviation / mean minor axis) of the minor axis of the tin flake powder 20 is, for example, 1 or less, preferably 0.5 or less.

[0081] If the coefficient of variation of the minor axis of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0082] The average surface area (major axis × minor axis) of the tin flake powder 20 is, for example, 20 μm. 2 ~600μm 2 Preferably, 100 μm 2 ~400μm 2 That is the case.

[0083] For more details, the average surface area of ​​the tin flake powder 20 is, for example, 20 μm, from the standpoint of ease of handling. 2 Preferably, 100 μm 2 In addition, for example, 600 μm 2 Preferably, 400 μm 2 The following applies:

[0084] If the average surface area of ​​the tin flake powder 20 is less than or equal to the above upper limit, bridging can be suppressed even if the distance (pitch) between electrodes arranged in the planar direction is short when the tin flake powder 20 is used in the manufacture of the laminate described later.

[0085] The average aspect ratio (major axis / minor axis) of the tin flake powder 20 is, for example, 1.0 to 4.0, preferably 1.1 to 2.0.

[0086] More specifically, the average aspect ratio of the tin flake powder 20 is, from the viewpoint of handling, for example, 1.0 or more, preferably 1.1 or more, and 4.0 or less, preferably 2.0 or less.

[0087] If the average aspect ratio of the tin flake powder 20 is less than or equal to the above upper limit, then when the tin flake powder 20 is used in the manufacture of the laminate described later, bridging can be suppressed even if the distance (pitch) of the electrodes arranged in the planar direction is short.

[0088] The average thickness of the tin flake powder 20 is, for example, 0.20 μm to 10.00 μm, preferably 0.30 μm to 5.00 μm, more preferably 0.40 μm to 2.00 μm, even more preferably 0.50 μm to 1.10 μm, particularly preferably 0.60 μm to 1.00 μm, most preferably 0.70 μm to 0.95 μm, even more preferably 0.80 μm to 0.93 μm, and even more preferably 0.85 μm to 0.92 μm.

[0089] More specifically, the average thickness of the tin flake powder 20 is, from the viewpoint of ease of handling, for example, 0.20 μm or more, preferably 0.30 μm or more, more preferably 0.40 μm or more, even more preferably 0.50 μm or more, particularly preferably 0.60 μm or more, most preferably 0.70 μm or more, even more preferably 0.80 μm or more, and even more preferably 0.85 μm or more. Furthermore, from the viewpoint of reducing the height of the laminate described later, it is, for example, 10.00 μm or less, preferably 5.00 μm or less, more preferably 2.00 μm or less, even more preferably 1.10 μm or less, particularly preferably 1.00 μm or less, most preferably 0.95 μm or less, even more preferably 0.93 μm or less, and even more preferably 0.92 μm or less.

[0090] The average thickness of the tin flake powder 20 can be measured from the cross-section of the tin flake powder 20 observed with an optical microscope. Further details will be provided in the examples described later.

[0091] The standard deviation of the thickness of the tin flake powder 20 is, for example, 0.40 or less, preferably 0.35 or less, and more preferably 0.30 or less.

[0092] If the standard deviation of the thickness of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0093] The method for calculating the standard deviation of the thickness of the tin flake powder 20 will be described in detail in the examples described later.

[0094] The coefficient of variation (standard deviation / average thickness) of the thickness of the tin flake powder 20 is, for example, 0.50 or less, preferably 0.40 or less, more preferably 0.35 or less, and even more preferably 0.33 or less.

[0095] If the coefficient of variation of the thickness of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0096] The average maximum length of the tin flake powder 20 extending in a direction perpendicular to its thickness is 20.00 μm or less. More specifically, the average length of the tin flake powder 20 is, for example, 1.00 μm to 20.00 μm, preferably 5.00 μm to 15.00 μm, more preferably 6.00 μm to 10.00 μm, even more preferably 7.00 μm to 9.00 μm, particularly preferably 7.50 μm to 8.00 μm, and most preferably 7.60 μm to 7.80 μm.

[0097] More specifically, the average maximum length of the tin flake powder 20 is, from the viewpoint of handling, for example, 1.00 μm or more, preferably 5.00 μm or more, more preferably 6.00 μm or more, even more preferably 7.00 μm or more, particularly preferably 7.50 μm or more, most preferably 7.60 μm or more, and also 20.00 μm or less, preferably 15.00 μm or less, more preferably 10.00 μm or less, even more preferably 9.00 μm, particularly preferably 8.00 μm, most preferably 7.80 μm or less.

[0098] If the average of the maximum lengths of the tin flake powder 20 is less than or equal to the above upper limit, then when the tin flake powder 20 is used in the manufacture of the laminate described later, bridging can be suppressed even if the distance (pitch) of the electrodes arranged in the planar direction is short.

[0099] The average of the maximum length can be measured from the cross-section of the tin flake powder 20 observed with an optical microscope. Further details will be provided in the examples described later.

[0100] The standard deviation of the maximum length of the tin flake powder 20 is 10.00 or less, preferably 8.00 or less, more preferably 5.00 or less, even more preferably 4.00 or less, particularly preferably 3.50 or less, and most preferably 3.00 or less.

[0101] If the standard deviation of the maximum length of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0102] The coefficient of variation (standard deviation / mean of maximum length) of the maximum length of the tin flake powder 20 is, for example, 1.00 or less, preferably 0.50 or less, more preferably 0.45 or less, and even more preferably 0.40 or less.

[0103] If the coefficient of variation of the maximum length of the tin flake powder 20 is below the above upper limit, the deterioration of the quality of the product obtained using the tin flake powder 20 can be suppressed.

[0104] The average ratio of the maximum length of the tin flake powder 20 to the thickness of the tin flake powder 20 (maximum length / thickness) is 2.00 or greater. More specifically, the average ratio of the maximum length of the tin flake powder 20 to the thickness of the tin flake powder 20 (maximum length / thickness) is, for example, 2.00 to 20.00, preferably 5.00 to 15.00, more preferably 6.00 to 10.00, even more preferably 7.00 to 9.00, and particularly preferably 8.00 to 8.80.

[0105] More specifically, the average ratio of the maximum length of the tin flake powder 20 to the thickness of the tin flake powder 20 (maximum length / thickness) is, from the viewpoint of handling, 2.00 or more, preferably 5.00 or more, more preferably 6.00 or more, even more preferably 7.00 or more, and particularly preferably 8.00 or more. Also, from the viewpoint of handling, for example, 20.00 or less, preferably 15.00 or less, more preferably 10.00 or less, even more preferably 9.00 or less, and particularly preferably 8.80 or less.

[0106] The average product of the thickness of the tin flake powder 20 and the maximum length of the tin flake powder 20 (thickness × maximum length, hereinafter sometimes referred to as cross-sectional area) is, for example, 2.00 to 20.00, preferably 3.00 to 15.00, more preferably 4.00 to 10.00, even more preferably 5.00 to 9.00, particularly preferably 6.00 to 8.00, and most preferably 6.50 to 7.00.

[0107] More specifically, the average cross-sectional area of ​​the tin flake powder 20 is, for example, 2.00 or more, preferably 3.00 or more, more preferably 4.00 or more, even more preferably 5.00 or more, particularly preferably 6.00 or more, most preferably 6.50 or more, or, for example, 20.00 or less, preferably 15.00 or less, more preferably 10.00 or less, even more preferably 9.00 or less, particularly preferably 8.00 or less, most preferably 7.00 or less.

[0108] The average ratio of the surface area of ​​the tin flake powder 20 to the cross-sectional area (surface area / cross-sectional area) is 2.00 or greater. More specifically, the average ratio of the surface area of ​​the tin flake powder 20 to the cross-sectional area (surface area / cross-sectional area) is, for example, 2.00 to 30.00, preferably 10.00 to 20.00.

[0109] More specifically, the average ratio of the surface area of ​​the tin flake powder 20 to the cross-sectional area of ​​the tin flake powder 20 (surface area / cross-sectional area) is, from the viewpoint of ease of handling, 2.00 or more, preferably 10.00 or more, and, from the viewpoint of ease of handling, for example, 30.00 or less, preferably 20.00 or less.

[0110] The tin flake powder 20 produced by this manufacturing method exhibits suppressed variation in length in the direction perpendicular to the thickness of the tin flake powder 20. Therefore, it is suitable for a wide range of applications, such as pigments, metal pastes, soldering materials (for example, soldering materials used to connect electrodes when manufacturing a laminate by connecting substrates having multiple electrodes arranged in the planar direction so that the electrodes face each other), and conductive materials. Furthermore, it is possible to suppress a decrease in the quality of products obtained using the tin flake powder 20.

[0111] <Effects and Effects> In the method for producing tin flake powder, the tin foil 1 is made of tin or a tin alloy, and the thickness of the tin foil 1 is less than 10 μm. In this method, the tin foil 1 is fractured by irradiating it with ultrasonic waves using liquids (first liquid 2 and second liquid 3) as a medium. As a result, it is possible to produce tin flake powder 20 with suppressed variation in length in the direction perpendicular to the thickness of the tin flake powder 20.

[0112] More specifically, in this method, the thickness of the tin foil 1 is less than 10 μm. When ultrasonic waves using liquids (first liquid 2 and second liquid 3) as a medium are irradiated onto the tin foil 1, as shown in Figure 2A, the tin foil 1 breaks from the middle of its major axis, and the broken pieces of tin foil 1 also break from the middle of their major axis. As such breakages occur sequentially, tin flake powder 20 is produced. Therefore, it is possible to produce tin flake powder 20 with suppressed variation in length in the direction perpendicular to the thickness of the tin flake powder 20.

[0113] On the other hand, as shown in Figure 2B, when the thickness of the tin foil 1 is 10 μm or more, if ultrasonic waves using liquids (first liquid 2 and second liquid 3) as a medium are irradiated onto the tin foil 1, the surface of the tin foil 1 is cut without the tin foil 1 breaking due to its thickness. Since there is variation in the degree of cutting, in such cases it is not possible to manufacture tin flake powder 20 with suppressed variation in the length extending in a direction perpendicular to the thickness of the tin flake powder 20.

[0114] Furthermore, the manner in which metals are fractured when irradiated with ultrasound depends on the type of metal. In this method, since the tin foil 1 is made of tin or a tin alloy, it is presumed that the above-described fracture will occur from the viewpoint of hardness. In other words, as long as the thickness is less than 10 μm, the above-described fracture will not occur regardless of the type of metal foil. That is, by using tin foil 1 which is less than 10 μm thick and made of tin or a tin alloy, the above-described fracture can be achieved, and as a result, tin flake powder 20 with suppressed variation in length in the direction perpendicular to the thickness of the tin flake powder 20 can be manufactured.

[0115] Furthermore, in Example 1 of Patent Document 1, wire-shaped metal nanoparticles 30 are manufactured by irradiating a copper foil (thickness 18 μm) with ultrasonic waves. Specifically, as shown in Figure 2C, first, when ultrasonic waves are irradiated onto a copper foil 32 consisting of a plurality of copper crystal grains 31, crushing progresses on the surface of the copper foil 32, and the copper foil 32 is pulverized. Then, when ultrasonic waves are irradiated onto the pulverized copper foil 32 again, the copper crystal grains 31 move along the interface 33 of the crystal planes of the plurality of copper crystal grains 31 in the copper foil 32. This produces wire-shaped metal nanoparticles 30. In such a case, the major axis of the wire-shaped metal nanoparticles 30 depends on the degree to which the copper foil 32 is pulverized and the amount of movement of the copper crystal grains 31 along the interface 33, so there is a large variation in the length extending in the direction perpendicular to the thickness of the tin flake powder 20.

[0116] On the other hand, in this method, as shown in Figure 2A, the tin foil 1 is broken from the middle of its major axis, and the broken tin foil 1 is similarly broken from the middle of its major axis. As such breaking occurs sequentially, tin flake powder 20 is produced. Therefore, variations in the length extending in the direction perpendicular to the thickness of the tin flake powder 20 can be suppressed.

[0117] <Variation> In the modified examples, components and processes similar to those in the first embodiment are given the same reference numerals, and their detailed descriptions are omitted. Furthermore, the modified examples can achieve the same effects and advantages as the first embodiment, unless otherwise specified. Moreover, the first embodiment and the modified examples can be combined as appropriate.

[0118] In the above description, the method for producing tin flake powder includes an embrittlement treatment step after the preparation step and before the ultrasonic irradiation step, but the embrittlement treatment step is not required. Preferably, from the viewpoint of producing tin flake powder 20 that is even finer (specifically, with a smaller maximum length), the method for producing tin flake powder includes an embrittlement treatment step.

[0119] In the above explanation, the number of tin foils 1 to be prepared in the preparation step is one. However, from the viewpoint of improving production efficiency, multiple tin foils 1 may be prepared in the preparation step, and the embrittlement treatment step and ultrasonic irradiation step may be performed on multiple tin foils 1. The number of tin foils 1 may be, for example, one or more, preferably five or more, and for example, 50 or less.

[0120] In the explanation above, the ultrasonic irradiation process is performed once, but it is also possible to perform the ultrasonic irradiation process multiple times.

[0121] When the ultrasonic irradiation process is performed multiple times, it is preferable to adjust the ultrasonic irradiation conditions so that the shock wave generated by the current ultrasonic cavitation is smaller than the shock wave generated by the previous ultrasonic cavitation.

[0122] Specifically, the frequency in the current ultrasonic irradiation process is set higher than the frequency in the previous ultrasonic irradiation process, and / or the output power in the current ultrasonic irradiation process is set lower than the output power in the previous ultrasonic irradiation process.

[0123] This allows the tin foil 1 to be significantly fractured by a relatively strong shock wave in the previous ultrasonic irradiation process, and then the fractured tin foil 1 to be further fractured by a relatively weaker shock wave in the current ultrasonic irradiation process. As a result, the tin flake powder 20 can be manufactured in a shorter time.

[0124] The number of ultrasonic irradiation steps is, for example, 1 to 10 times, preferably 2 to 5 times.

[0125] In the explanation above, ultrasound is irradiated using the first liquid 2 and the second liquid 3 as the medium, but it is also possible to irradiate with ultrasound using only the first liquid 2 as the medium. [Examples]

[0126] Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples. Unless otherwise specified, "parts" and "%" are based on mass. Furthermore, specific numerical values ​​such as blending ratios (content), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than") of the blending ratios (content), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0127] <Details of ingredients> The trade names and abbreviations of the components used in each example are described in detail below. 2-PtOH: Isopropanol (2-propanol) EtOH: Ethanol EG: Ethylene glycol

[0128] <Manufacturing of tin flake powder> Example 1 [Preparation process] I prepared tin foil (127mm x 127mm, 1.3μm thick, manufactured by Narika Co., Ltd.).

[0129] [Ultrasonic irradiation process] An ultrasonic irradiation apparatus 10, as shown in Figure 1B, was prepared. A conical flask was used as the first tank 11. A glass water tank was used as the second tank 12. An ultrasonic transducer 13, product name "WF1973", manufactured by WAVE FACTORY, was used. The tin foil 1 was the tin foil prepared in the above preparation step. 2-PtOH was used as the first liquid 2. Water was used as the second liquid 3.

[0130] The first liquid 2 and tin foil 1 were added to the first tank 11, and the tin foil 1 was immersed in the first liquid 2. As a result, the first liquid 2 and tin foil 1 were contained in the first tank 11.

[0131] Next, the first tank 11, the second liquid 3, and the ultrasonic transducer 13 were added to the second tank 12. As a result, the first tank 11, the second liquid 3, and the ultrasonic transducer 13 were contained within the second tank 12.

[0132] Next, ultrasonic waves were generated by the vibration of the ultrasonic transducer 13 based on the ultrasonic irradiation conditions shown in Table 1. By irradiating the tin foil 1 with ultrasonic waves using liquids (first liquid 2 and second liquid 3) as a medium, the tin foil 1 was fractured, and tin flake powder 20 was produced.

[0133] Examples 2 to 5 Tin flake powder 20 was manufactured following the same procedure as in Example 1. However, the conditions in each step were changed according to Table 1.

[0134] Example 6 Tin flake powder 20 was manufactured following the same procedure as in Example 1. However, the conditions in each step were changed according to Table 1. In addition, after the preparation step and before the ultrasonic irradiation step, an embrittlement treatment step was performed.

[0135] [Embrittlement process] Place the tin foil in a plastic beaker and heat it on a 50°C hot plate. 100 mL of liquid nitrogen was added to a plastic beaker and cooled (dried). This procedure was repeated 10 times.

[0136] Example 7 Tin flake powder 20 was manufactured following the same procedure as in Example 1. However, the conditions in each step were changed according to Table 1. In addition, the ultrasonic irradiation process was performed twice.

[0137] <Rating> [Viscosity of the first and second liquids] The viscosity (at 25°C) of the first and second liquids was measured. Specifically, a Type B rotational viscometer (RE-85L) was used. The viscosity of EtOH and 2-PrOH was measured at a rotational speed of 100 rpm, while the viscosity of EG and a mixture of EG and EtOH was measured at a rotational speed of 20 rpm. The results are shown in Table 1.

[0138] [Observation of tin flake powder] SEM images of the tin flake powder from each example were measured using the following apparatus and conditions. The SEM images of Examples 1 to 7 are shown in Figures 3 to 9. SEM device: JEOL Ltd. (JEOL) JSM-7610F Measurement conditions: Acceleration voltage 5kV Observation magnification: 500x to 2000x

[0139] [Long axis and short axis] For each example of tin flake powder, the major and minor axes were measured. Specifically, binarization was performed on the SEM images. Next, the major and minor axes of the tin flake powder were calculated using ImageJ's Fit elipse (ellipse approximation). The aspect ratio (major axis / minor axis) was also calculated from the above major and minor axes. The upper area was taken from the Area value in ImageJ. The above operations were performed for 180 tin flake powders (or tin powders). Based on the results, the mean major axis, standard deviation of the major axis, coefficient of variation of the major axis, mean minor axis, standard deviation of the minor axis, coefficient of variation of the minor axis, mean upper area, and mean aspect ratio were calculated. The results are shown in Table 1.

[0140] [Thickness and maximum length] For each example, the thickness and maximum length of the tin flake powder were measured. Specifically, for each example, a sample for cross-sectional observation, allowing observation of the cross-sectional shape, was prepared using a freeze microtome, and optical microscope images were obtained.

[0141] Next, the optical microscope images were binarized. Then, the thickness of the tin flake powder and the maximum length extending in the direction perpendicular to the thickness were measured using ImageJ's Fit elipse (elliptic approximation). Furthermore, the ratio of the maximum length to the thickness and the cross-sectional area (thickness × maximum length) were calculated from the above thickness and maximum length.

[0142] The above procedure was performed on 196 tin flakes (or tin powder). Based on the results, the average thickness, standard deviation of thickness, coefficient of variation of thickness, average maximum length, standard deviation of maximum length, coefficient of variation of maximum length, average ratio of maximum length to thickness, and average cross-sectional area (thickness × maximum length) were calculated. The results are shown in Table 1.

[0143] [Table 1] [Explanation of Symbols]

[0144] 1 tin foil 2 1st liquid 20 Tin flake powder

Claims

1. A preparation process for preparing tin foil made of tin or a tin alloy, The system includes an ultrasonic irradiation step in which the tin foil is fractured by irradiating it with ultrasonic waves using a liquid medium, A method for producing tin flake powder, wherein the thickness of the tin foil is less than 10 μm.

2. The aforementioned liquid includes the first liquid, In the ultrasonic irradiation step, the tin foil is immersed in the first liquid. The method for producing tin flake powder according to claim 1, wherein the viscosity (at 25°C) of the first liquid is 1 mPa·s or more and 20 mPa·s or less.

3. The method for producing tin flake powder according to claim 1, wherein the frequency of the ultrasound in the ultrasonic irradiation step is 200 kHz or less.

4. A method for producing tin flake powder according to claim 1, further comprising an embrittlement treatment step of applying an embrittlement treatment to the tin foil after the preparation step and before the ultrasonic irradiation step.

5. A method for producing tin flake powder according to any one of claims 1 to 4, wherein the ultrasonic irradiation step is performed multiple times.

6. Tin flake powder made of tin or tin alloy, In the cross-section of the tin flake powder observed by an optical microscope, the average of the maximum length extending in the direction perpendicular to the thickness of the tin flake powder is 20.00 μm or less. Tin flake powder having a standard deviation of 10.00 or less for the maximum length.

7. The average of the major axis of the tin flake powder is 30.00 μm or less. The average thickness of the tin flake powder is 0.20 μm or more and 10.00 μm or less. The coefficient of variation of the thickness of the tin flake powder is 0.50 or less. The tin flake powder according to claim 6, wherein the average ratio of the maximum length to the thickness of the tin flake powder (maximum length / thickness) is 2.00 or more.

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