JP7501834B1 - Tin metal for making tin balls - Google Patents

Abstract

[Problem] To provide a method for producing tin spheres with a high yield rate and a diameter of more than about 1 mm and high sphericity. [Solution] Metallic tin having a surface tension of 490×10-3 Nm-1 or more at a temperature of 1,000 K and 390×10-3 Nm-1 or more at a temperature of 1,300 K, as measured by an electromagnetic levitation method. [Selected Figure] Figure 2

Description

The present invention relates to metallic tin for the production of tin balls.

Manufacturing metal balls on an industrial scale is an extremely important basic technology. Therefore, industrial-scale manufacturing technologies for metal balls have been developed.

A common method for manufacturing metal balls is to use mechanical processing such as pressing and polishing. However, because this involves mechanical processing, it is a method suitable for hard metal materials such as high carbon chromium bearing steel and stainless steel. On the other hand, soft metal materials such as tin, lead and their alloys (solder) are not suitable for mechanical processing such as polishing, so metal balls are manufactured by casting.

A classic example of the production of metal balls using soft metal materials is the method of producing shotgun pellets. This method involves dropping molten lead from a high place (e.g., 50m or more) and collecting it in a water tank, and it is a large-scale method that requires the construction of a tower for production. Naturally, there is a large variation in the lead balls obtained, and it is not a method intended to control purity or sphericity.

Patent document 1 (JP Patent Publication 11-221662 A) discloses a technique for producing solder balls by dropping molten solder into soybean oil. However, patent document 1 does not mention the size, sphericity, or purity of the resulting solder balls, and discloses a classic technique that simply requires obtaining solder in a ball-shaped form.

Patent document 2 (JP Patent Publication 54-085171) discloses that metal spheres are obtained by spraying molten solder alloy metal from a nozzle into silicone oil while rotating a rotating plate with cutting holes. However, the size of the obtained metal spheres is 1 mm in diameter, and no technology is disclosed for obtaining metal spheres larger than this size.

Patent Document 3 (JP Patent Publication 55-158875) discloses that iron balls are obtained by dropping droplets of molten iron into water. However, with this technology, the crack rate rises sharply when the diameter of the iron ball exceeds 1 mm; for example, the crack rate reaches 70% when the diameter is 8 mm. Furthermore, there is no mention of the sphericity or purity of the obtained iron balls.

Patent Document 4 (JP Patent Publication 2001-226705 A) discloses a technique for producing microscopic metal spheres with a diameter of about 400 μm by ejecting molten solder into a chamber filled with nitrogen gas mixed with hydrogen gas while vibrating the molten solder with a piezoelectric element. The microscopic metal spheres obtained by this technique are small, with a diameter of about 400 μm, and there is a large variation in the diameter and sphericity.

Patent Document 5 (JP Patent Publication 50-17363 A) discloses a technique for producing copper particles by passing molten copper through a stainless steel mesh and dripping it into OF oil. However, Patent Document 5 does not mention the purity or sphericity of the obtained copper particles, and a magnified photograph of Patent Document 5 shows that there is a very large variation in size and sphericity.

Patent Document 6 (JP Patent Publication 60-114508 A) discloses a technique for obtaining alloy grains by dropping droplets of molten Co-W alloy, Ni-B alloy, and Cu-B alloy from a nozzle into cooling oil. However, Patent Document 6 does not mention the purity, size, or sphericity of the obtained alloy grains, and only evaluates them as "good" based on their weight and distribution.

Patent document 7 (JP Patent Publication 2000-8104) discloses a technique for producing spherical metal particles by dripping molten solder metal from a nozzle into engine oil or edible oil while vibrating it with a stainless steel shaft. However, the average particle size of the particles obtained with Patent document 7 is approximately 0.30 mm to 0.76 mm, which is a technique that results in an average particle size of 1 mm or less.

Thus, when melting soft metals such as tin to form particles, there has been no suitable technology to obtain particles with an average particle diameter of more than 1 mm and excellent spherical shape accuracy (sphericity), and such a technology is needed.

Non-Patent Documents 1 and 2 disclose the Rayleigh formula (see Non-Patent Document 1) and the Cummings & Blackburn correction formula (see Non-Patent Document 2), which are useful for calculating the surface tension from the frequency applied to a droplet of a molten metal sample and the sample mass.

Japanese Patent Application Laid-Open No. 11-221662 Japanese Patent Application Laid-Open Publication No. 54-085171 JP 55-158875 A JP 2001-226705 A JP 50-17363 A JP 60-114508 A JP 2000-8104 A

Lord Rayleigh, "On the Capillary Phenomena of Jets", Proceedings of the Royal Society of London, pp. 71-97, 1879. D. L. Cummings, D. A. Blackburn, "Oscillations of magnetically levated aspherical droplets", J. Fluid Mech., vol. 224, pp. 395-416, 1991.

The object of the present invention is therefore to provide a means for producing tin balls with a diameter and sphericity greater than about 1 millimeter in high yields.

As a result of extensive research, the inventors discovered that the above objectives can be achieved by the means described below, and thus arrived at the present invention.

In other words, while conventional technology has attempted to produce tin balls with a diameter of more than about 1 mm and high sphericity (accuracy of spherical shape) at a high yield rate by devising manufacturing processes, the present invention achieves this objective by using a specific tin for manufacturing tin balls.

Therefore, the present invention includes the following (1):
(1)
The surface tension measured by the electromagnetic levitation method is
At a temperature of 1,000K, it is 490×10 ⁻³ Nm ⁻¹ or more,
Metallic tin having a specific surface area of 390×10 ⁻³ Nm ⁻¹ or more at a temperature of 1,300K.

According to the present invention, it is possible to produce high-purity tin spheres with a diameter larger than about 1 mm and high sphericity with a high yield.

FIG. 1 is a schematic diagram of an apparatus for measuring the surface tension of molten tin metal. FIG. 2 is a graph showing the results of measuring the surface tension of molten metallic tin of high purity tin (sample 1) (Example) and high purity tin (sample 2) (Comparative Example). FIG. 3 is a schematic diagram of a tin ball manufacturing apparatus. Figure 4 shows the method for determining whether a tin ball is acceptable or not. Figure 5 shows the pass/fail result for the tin balls. FIG. 6A is a photograph showing the appearance of a tin ball produced in the example. FIG. 6B is a photograph showing the appearance of a tin ball produced in the comparative example. FIG. 7 is a photograph showing the appearance of a group of tin balls, which are spherical products remaining after visual sorting and rolling sorting in Example 1.

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

[Tin for making tin balls]
The metallic tin of the present invention is metallic tin for producing tin balls, and has a surface tension measured by an electromagnetic levitation method of 490×10 ⁻³ Nm ⁻¹ or more at a temperature of 1,000 K and 390×10 ⁻³ Nm ⁻¹ or more at a temperature of 1,300 K.

By using metallic tin for producing tin balls according to the present invention, it is possible to produce high-purity tin balls with diameters greater than about 1 millimeter and high sphericity in high yields.

When solidifying molten tin metal to obtain spherical particles, the principal force acting to form the particles is surface tension.

However, prior to the present invention, the relationship between the surface tension of molten metallic tin and particle formation had not been clarified as a specific technology. In other words, it had not been clarified what type of particle formation would occur when a specific value of the surface tension of molten metallic tin was given.

The reason for this is unclear, but one possible reason is that measuring the surface tension of molten tin metal is itself extremely difficult.

In other words, when trying to measure the surface tension of molten tin metal, the molten tin metal is usually placed on some kind of substrate before measurement, but the surface tension of the molten tin metal itself is affected by contact with the substrate, resulting in a non-negligible difference in the measured value.

However, in this invention, as shown in the examples described below, it was possible to measure the surface tension of molten tin metal by suspending the molten tin metal in midair without it coming into contact with any substrate material. By examining the relationship between the surface tension measured in this way and the particles formed, it was discovered that tin with a specific surface tension is particularly suitable for obtaining particles with an average particle diameter of more than 1 mm and excellent spherical shape accuracy (sphericity), and this led to the invention of the present application.

[Surface tension measured by electromagnetic levitation]
In a preferred embodiment, the metallic tin of the present invention has a surface tension, measured by an electromagnetic levitation method, at a temperature of 1,000 K of, for example, 490×10 ^-3 Nm ^-1 or more, preferably 495×10 ^-3 Nm ^-1 or more, more preferably 500×10 ^-3 Nm ^-1 or more, or 505×10 ^-3 Nm ^-1 or more, preferably 510×10 ^-3 Nm ^-1 or more, and at a temperature of 1,300 K of, for example, 390×10 ^-3 Nm ^-1 or more, preferably 395×10 ^-3 Nm ^-1 or more, more preferably 400×10 ^-3 Nm ^-1 or more, or 405×10 ^-3 Nm ^-1 or more, preferably 410×10 ^-3 Nm ^-1 or more.

Surface tension can be measured using the electromagnetic levitation method as described below in the examples.

In a preferred embodiment, the metallic tin of the present invention has a surface tension, measured by an electromagnetic levitation method, at a temperature of 1,000 K, in the range of, for example, 490×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ , preferably in the range of 495×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ , more preferably in the range of 500×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ , or in the range of 500×10 ⁻³ Nm ⁻¹ to 505×10 ⁻³ Nm ⁻¹ , or in the range of 490×10 ⁻³ Nm ⁻¹ to 505×10 ⁻³ Nm ⁻¹ , preferably in the range of 490×10 ⁻³ Nm ⁻¹ to 500×10 ⁻³ Nm ⁻¹ , more preferably in the range of 495×10 ⁻³ Nm ⁻¹ to 500×10 ⁻³ Nm ⁻¹ , or alternatively 490×10 ⁻³ Nm ⁻¹ to 495×10 ⁻³ Nm ⁻¹ .

In a preferred embodiment, the metallic tin of the present invention has a surface tension, measured by an electromagnetic levitation method, at a temperature of 1,300 K, in the range of, for example, 390×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ , preferably in the range of 395×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ , more preferably in the range of 400×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ , or in the range of 400×10 ⁻³ Nm ⁻¹ to 405×10 ⁻³ Nm ⁻¹ , or in the range of 390×10 ⁻³ Nm ⁻¹ to 405×10 ⁻³ Nm ⁻¹ , preferably in the range of 390×10 ⁻³ Nm ⁻¹ to 400×10 ⁻³ Nm ⁻¹ , more preferably in the range of 395×10 ⁻³ Nm ⁻¹ to 400×10 ⁻³ Nm ⁻¹ , or alternatively 390×10 ⁻³ Nm ⁻¹ to 395×10 ⁻³ Nm ⁻¹ .

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 490×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 390×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 495×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 395×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 500×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 400×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 490×10 ⁻³ Nm ⁻¹ to 505×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 390×10 ⁻³ Nm ⁻¹ to 405×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 490×10 ⁻³ Nm ⁻¹ to 500×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 390×10 ⁻³ Nm ⁻¹ to 400×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 495×10 ⁻³ Nm ⁻¹ to 500×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 395×10 ⁻³ Nm ⁻¹ to 400×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 490×10 ⁻³ Nm ⁻¹ to 495×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 390×10 ⁻³ Nm ⁻¹ to 395×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

In a preferred embodiment, the surface tension of the metallic tin of the present invention, measured by an electromagnetic levitation method, can be in the range of 500×10 ⁻³ Nm ⁻¹ to 505×10 ⁻³ Nm ⁻¹ at a temperature of 1,000 K, and in the range of 400×10 ⁻³ Nm ⁻¹ to 405×10 ⁻³ Nm ⁻¹ at a temperature of 1,300 K.

[Production of tin balls]
The metallic tin of the present invention can be heated and melted to form a molten tin metal, and this molten tin metal can be used to manufacture tin balls.

The means for heating and melting the metallic tin of the present invention to form a molten metallic tin can be any known means, for example, radiant heating or induction heating can be used to heat and melt the molten tin to prepare the molten metallic tin.

In a preferred embodiment, tin balls can be suitably manufactured by a method including the steps of dripping the molten tin metal of the present invention into a liquid cooling medium, and cooling the tin metal droplets as they fall through the liquid cooling medium to form solid tin balls.

In a preferred embodiment, the cooling liquid medium that can be used to drip the molten tin metal of the present invention can be any liquid that is stable at temperatures higher than the melting point of the tin metal. Examples of such cooling liquid medium include animal and vegetable oils, mineral oils, and synthetic oils, and preferably lubricating oils and silicone oils, and more preferably silicone oils.

In a preferred embodiment, the means for introducing the molten metal tin of the present invention into the liquid cooling medium is not particularly limited, and any known means can be used as long as it is dripping, for example, gravity dripping or power dripping, preferably natural dripping or pump discharge, and particularly preferably pump discharge.

In a preferred embodiment, the molten metal of the present invention is dropped into a liquid cooling medium, and then cooled as it falls through the liquid cooling medium to form a solid tin ball. The fall is by gravity, and it is preferable to set the height of the liquid cooling medium so that the molten metal can fall a distance sufficient to form a solid tin ball.

[Tin ball]
The tin spheres produced using the molten tin metal of the present invention have the above-mentioned surface tension as measured by the electromagnetic levitation method, and as a result, high-purity tin spheres with a diameter of more than about 1 millimeter and high sphericity are produced in a high yield.

In the present invention, the high sphericity of the manufactured tin balls means that, in the group of manufactured tin balls, the proportion of spherical products, as described below, is high, and at the same time, the proportion of spherical products with a diameter variation ratio of less than 0.04 is high.

[Spherical product ratio]
In a preferred embodiment, the tin balls produced using the molten tin metal of the present invention can have a spherical product percentage (%) calculated by the following formula in the group of solid tin balls formed, for example, of 80% or more, preferably 90% or more, and preferably 95% or more:
"Ratio of spherical products" = "Weight of spherical products (g)" / ("Weight of spherical products (g)" + "Weight of irregularly shaped products (g)") x 100%

In a preferred embodiment, the tin balls produced using the molten tin metal of the present invention have no particular upper limit on the percentage of spherical products (%) calculated by the above formula in the mass of solid tin balls formed, but it can be, for example, 100% or less, 99.5% or less, 99% or less, 98.5% or less, or 98% or less.

In a preferred embodiment, the tin balls produced using the molten tin metal of the present invention have a spherical product percentage (%) calculated by the above formula in the mass of solid tin balls formed, which can be, for example, in the range of 80% to 100%, preferably in the range of 80% to 99.5%, preferably in the range of 80% to 99%, preferably in the range of 80% to 98.5%, preferably in the range of 80% to 98%, for example, in the range of 90% to 100%, preferably in the range of 90% to 99.5%, preferably in the range of 90% to 99%, preferably in the range of 90% to 98.5%, preferably in the range of 90% to 98%, for example, in the range of 95% to 100%, preferably in the range of 95% to 99.5%, preferably in the range of 95% to 99%, preferably in the range of 95% to 98.5%, preferably in the range of 95% to 98%.

In the present invention, the selection of spherical and irregularly shaped tin balls can be carried out by the means disclosed in the examples described below.

When manufacturing a large number of balls, it is useful to measure the weight of a group of tin balls to control the quality, and the spherical product ratio described above is a suitable indicator for such quality control.

[Diameter variation ratio]
In a preferred embodiment, the tin spheres produced using the molten tin metal of the present invention can have a ratio of spherical products having a diameter variation ratio of less than 0.04 calculated by the following formula in a group of spherical products obtained from a group of solid tin spheres formed, for example, 50% or more, preferably 55% or more, and preferably 60% or more:
"Diameter variation ratio" = "Diameter variation (mm) measured in accordance with the provisions of JIS B1509:2009" / "Average diameter (mm)"

In a preferred embodiment, the tin balls produced using the molten tin metal of the present invention have no particular upper limit on the percentage (%) of spherical products in the group of solid tin balls formed that have a diameter variation ratio calculated by the above formula of less than 0.04, but it can be, for example, 100% or less, 99% or less, 98% or less, 97% or less, 96% or less, 95% or less, 90% or less, 85% or less, 80% or less, or 75% or less.

In a preferred embodiment, the tin balls produced using the molten tin metal of the present invention have a ratio of spherical products having a diameter variation ratio of less than 0.04 calculated by the following formula in a group of spherical products obtained from a group of solid tin balls formed, which can be, for example, in the range of 50% to 100%, preferably in the range of 50% to 99%, preferably in the range of 50% to 95%, preferably in the range of 50% to 90%, preferably in the range of 50% to 85%, preferably in the range of 50% to 80%, preferably in the range of 50% to 75%, and can be, for example, in the range of 5 ... It can be in the range of 0%, preferably in the range of 55% to 99%, preferably in the range of 55% to 95%, preferably in the range of 55% to 90%, preferably in the range of 55% to 85%, preferably in the range of 55% to 80%, preferably in the range of 55% to 75%, for example in the range of 60% to 100%, preferably in the range of 60% to 99%, preferably in the range of 60% to 95%, preferably in the range of 60% to 90%, preferably in the range of 60% to 85%, preferably in the range of 60% to 80%, preferably in the range of 60% to 75%.

The diameter variation (mm) and average diameter (mm) of the tin balls in this invention can be measured according to the provisions of JIS B1509:2009 by the means disclosed in the examples described below.

[diameter]
In a preferred embodiment, the diameter of the tin balls produced using the molten metal of the present invention can be greater than about 1 millimeter. The diameter of the tin balls can be determined by calculating the average diameter of each of 10 tin balls taken from a group of tin balls, and averaging the average diameters of the individual tin balls, i.e., the average diameter value, can be in the range of, for example, 1 mm to 5 mm, preferably 1.5 mm to 4.5 mm, and preferably 2 mm to 4 mm.

[Preferred embodiment of the present invention]
As a preferred embodiment, the present invention includes the following (1) and the following:
(1)
The surface tension measured by the electromagnetic levitation method is
At a temperature of 1,000K, it is 490×10 ⁻³ Nm ⁻¹ or more,
Metallic tin having a specific surface area of 390×10 ⁻³ Nm ⁻¹ or more at a temperature of 1,300K.
(2)
The surface tension measured by the electromagnetic levitation method is
At a temperature of 1,000K, it is in the range of 490×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ ,
The tin metal according to (1), having a specific resistance in the range of 390×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ at a temperature of 1,300K.
(3)
The metallic tin described in (1) above, which is metallic tin for manufacturing tin balls.
(4)
A method for producing tin balls using the molten metal tin described in (1).
(5)
A method for producing tin balls, comprising the steps of:
A step of dropping the molten metal of tin described in (1) into a liquid medium for cooling;
a step in which the droplets of metallic tin are cooled as they fall through a liquid cooling medium to form solid tin spheres;
A method for producing a tin ball, comprising:
(6)
The manufacturing method according to (5), wherein the percentage of spherical products (%) calculated by the following formula in the group of solid tin balls formed is 80% or more:
"Ratio of spherical products" = "Weight of spherical products (g)" / ("Weight of spherical products (g)" + "Weight of irregularly shaped products (g)") x 100%
(7)
The manufacturing method according to (5), wherein in a group of spherical products obtained from the group of solid tin spheres formed, the ratio of spherical products having a diameter variation ratio of less than 0.04 calculated by the following formula is 50% or more:
"Diameter variation ratio" = "Diameter variation (mm) measured in accordance with the provisions of JIS B1509:2009" / "Average diameter (mm)"
(8)
The manufacturing method described in (5) above, wherein the diameter of the tin ball is in the range of 1 mm to 5 mm.

The present invention will be described in detail below with reference to examples. The present invention is not limited to the examples illustrated below.

[Example 1: Production of high purity tin (sample 1)]
[casting]
1.7 kg of raw tin (purity 99.999 wt%) was heated to 300°C or higher and melted in a graphite crucible. After removing the floating slag, the mixture was poured into a graphite mold to obtain two plates measuring approximately 10 mm in thickness, 70 mm in width, and 150 mm in height.

[Electrolytic dissolution]
A sheet of raw tin was used as the anode and placed in the electrolytic cell facing a titanium plate (width 70 mm, height 150 mm) as the cathode. The cathode plate was placed in a cathode box with an anion exchange membrane attached to the surface facing the anode. A sulfuric acid aqueous solution with a concentration of 9N was placed in the cathode box, which was connected to an outer container by a tube pump so that the sulfuric acid aqueous solution was circulated. Dilute sulfuric acid with a concentration of 0.5N was placed outside the cathode box and in the electrolytic cell. After that, the raw tin cast into a plate shape was connected to the positive pole of the rectifier, and the titanium plate was connected to the negative pole of the rectifier with electrical wiring.

Electrolysis was carried out at a current density of ² A/dm2 to obtain 3 L of tin sulfate solution with a tin concentration of 90 g/L.

5 g/L of strontium carbonate was added to the obtained tin sulfate solution and stirred for 1 hour, and the precipitated solids were filtered and removed. 5 g/L of hydroquinone and 5 g/L of Brownon N-514 manufactured by Aoki Oil Industries Co., Ltd. were added to the obtained filtrate as a surfactant, and the mixture was stirred and dissolved to obtain 2.8 L of tin sulfate electrolyte.

[Electrowinning]
The tin sulfate electrolyte obtained above was diluted with pure water to a tin concentration of 20 g/L and placed in the anode side of the electrolytic cell to prepare the anode side electrolyte (anolyte). The tin sulfate electrolyte was placed in the cathode side of the electrolytic cell without dilution to prepare the cathode side electrolyte (catholyte). The electrolytic cell was charged with the raw tin cast into the plate shape described above as the anode, and a titanium plate of the same size as the above was placed in the cathode.
The positive pole of a rectifier was connected to the raw tin, and the negative pole of the rectifier was connected to the titanium plate, and electrolysis was performed at a current density of 1.5 A/dm ^2. The above procedure was repeated while switching between anolyte and catholyte, to obtain approximately 600 g of plate-shaped electrolytic tin.

[Vacuum casting]
The obtained electrolytic tin was thoroughly washed and dried, then placed in a graphite crucible and heated in the air to remove the slag, and cooled and solidified. It was then placed in a vacuum melting furnace, heated to 1,000°C, held there for 16 hours, and then cooled and solidified to obtain a high-purity tin ingot.

[Cutting and cleaning]
The surface of the high purity tin ingot was cut and removed, leaving only the healthy part inside.

Small pieces were machined off from the remaining healthy high-purity tin, which was then washed with acid and pure water.

In this way, high purity tin (sample 1) was obtained. Impurity analysis of the obtained high purity tin (sample 1) was performed using GD-MS. The results of the obtained impurity analysis are shown in Table 1 below. Unless otherwise specified in Table 1, the units of values are wtppm.

[Example 2: Production of high purity tin (sample 2)]
The high purity tin (sample 2) used in the comparative example was produced as follows.
Electrolysis was performed in the same manner as for the high purity tin (sample 1) produced in Example 1, to obtain plate-shaped electrolytic tin. Next, the obtained electrolytic tin was thoroughly washed and dried, and then placed in a graphite crucible and heated in the air to remove the slag, and then cooled and solidified. The surface of the obtained tin lump was cut and removed, and only the healthy part inside was used. Small pieces were cut out of the tin that was left with only the healthy part by machining, and were washed with acid and pure water to be used as high purity tin (sample 2).

The results of the impurity analysis of high purity tin (sample 2) are shown in Table 2 below. In Table 2, unless otherwise specified, the units of values are wtppm.

[Example 3: Measurement of surface tension of high purity tin (sample 1)]
[Surface tension measuring device]
The surface tension of the resulting high purity tin (sample 1) was measured.
FIG. 1 is an explanatory diagram showing an outline of a measuring device used for measuring surface tension.

The measuring device shown in FIG. 1 is equipped with a sealed quartz chamber 4, and is structured so that gas can be introduced into the quartz chamber 4 through a gas inlet pipe 7 and exhausted through a gas exhaust pipe 8. Inside the quartz chamber 4, a sample holder 5 is provided for holding a sample. The sample holder 5 is structured so that a sample of tin 1 can be placed on it and held in a position where it can be inductively heated by a coil 2, and at the same time, it is structured so that the sample (tin 1) inductively heated by the coil 2 can be melted and floated and simultaneously pulled down. The measuring device is equipped with a high-frequency power source capable of supplying a high-frequency current to the coil outside the quartz chamber 4. An observation window 6 for observing the inside of the quartz chamber 4 is provided at the top of the quartz chamber 4, and high-speed photography of the inside can be performed through this observation window 6 with a camera 9.

[Procedure for measuring surface tension]
Using the measuring device shown in FIG. 1, the surface tension of high purity tin was measured as follows.

High-purity tin (sample 1) was cut into 420-480 mg square pieces (each side approximately 5 mm) and harvested.

The surface of the collected rectangular tin sample was etched with a 3 vol. % hydrochloric acid solution using an ultrasonic cleaner, and then further washed with acetone.

The tin sample was placed in a quartz glass holder in the electromagnetic levitation chamber.

After evacuating the inside of the measurement system (10 ⁻⁷ atm), atmospheric gas (argon-helium) was introduced from the top at 2 L/min. The oxygen partial pressure of the atmospheric gas (argon-helium) was set to 1×10 ⁻⁷ atm (volume concentration: 0.1 vol. ppm).

A high-frequency alternating current was passed through the electromagnetic levitation coil, and the sample was heated while being electromagnetically levitated. In order to separate the sample from the holder before the sample melted, the sample holder was pulled down at the same time that heating began.

The temperature was measured using two monochromatic radiation thermometers with different wavelengths.
Wavelength 1: 1.64 μm
Wavelength 2: 1.4 μm

At the chamber inlet, the atmospheric oxygen partial pressure of the introduced gas was measured using a zirconia-type oxygen sensor operated at 1,008 K.

The surface vibration behavior of the droplet after the sample melted was recorded from above with a high-speed camera (500 FPS, 8192 images (16.384 seconds)).

Immediately after recording, helium gas was sprayed onto the top of the sample at 20 L/min to rapidly cool and solidify it.

The sample mass was measured using an electronic balance.

The droplet projection images were analyzed to determine the movement of the droplet's center of gravity, radius, and area, and the m=0, m=±1, and m=±2 frequencies of the l=2 mode and the m=0, m=±1 frequencies of the l=1 mode were identified.

From the obtained frequency and sample mass, the surface tension was calculated using Rayleigh's formula (see Non-Patent Document 1) and the correction formula of Cummings & Blackburn (see Non-Patent Document 2).

[Surface tension measurement results]
The results of the surface tension measurements thus obtained are shown in FIG.

[Example 4: Measurement of surface tension of high purity tin (sample 2)]
The surface tension of high purity tin (sample 2) was measured in the same manner as that of high purity tin (sample 1) measured in Example 3. The results of the measured surface tension are summarized in FIG.

[Evaluation of surface tension measurement results]
2, the surface tension of Sample 1, an example of the present invention, was 500 (490-510) x ^10-3 Nm ^-1 or more at a temperature of 1,000 K and 400 (390-410) x ^10-3 Nm ^-1 or more at a temperature of 1,300 K, whereas the surface tension of Sample 2, a comparative example, was similarly measured and found to be 440-460 x ^10-3 Nm ^-1 or more at a temperature of 1,000 K and 330-350 x ^10-3 Nm ^-1 or more at a temperature of 1,300 K. From these results, it was found that there is a negative correlation between temperature and surface tension in this sample, and that the surface tension of Sample 1, an example of the present invention, is higher than that of Sample 2, a comparative example.

[Example 5: Production of tin balls (Examples 1 to 3)]
[Tin ball manufacturing equipment]
The obtained high purity tin (sample 1) was used to manufacture tin balls.
FIG. 3 is an explanatory diagram showing an outline of the manufacturing apparatus used to manufacture the tin balls.

The manufacturing apparatus shown in FIG. 3 is equipped with a melting vessel 14 for melting and storing tin, which is the raw material used to manufacture tin balls. The tin in the melting vessel 14 is heated by a heater 15 and is in a molten state. The melting vessel 14 is sealed, and when the silicon oil stored in the silicon oil vessel 17 is introduced by a pump 19 through a silicon oil delivery pipe 18, the molten tin in the melting vessel 14 is dripped through the tin delivery pipe 16 into the silicon oil filled in the granulation vessel 12 by the pressure. A heater 13 is provided at the top of the granulation vessel 12, and the molten tin is maintained in a molten state at the top of the granulation vessel 12. The space in the manufacturing apparatus is filled with argon gas, not air, to suppress oxidation of the molten tin. The molten tin droplets introduced through the tin delivery tube 16 and dropped into the silicone oil filled in the granulation vessel 12 first become spherical as they freely fall through the silicone oil filled in the granulation vessel 12, then cool and solidify, becoming tin spheres 11 that accumulate at the bottom of the granulation vessel 12.

[Procedure for manufacturing tin balls]
Using high purity tin (sample 1), tin balls were manufactured as follows.

2,000 g of small pieces of high-purity tin (sample 1) that had been acid-washed and water-washed were placed in the melting vessel of a quartz tin ball manufacturing device. Meanwhile, the granulation vessel was filled with silicone oil. The lids of the melting vessel and granulation vessel were closed, and high-purity argon gas was allowed to flow at a flow rate of 1 L/min until the oxygen concentration inside the granulation vessel fell to 0.1 vol% or less.

The melting vessel and the top of the granulation vessel were heated with an external heater.

When the high-purity tin in the melting vessel had melted, the pump was started and the molten tin was discharged from the melting vessel into the granulating vessel, where it dripped and fell freely. During this free-fall process, the molten tin became spherical due to surface tension. As the lower part of the granulating vessel was not heated, the molten tin solidified and piled up while remaining spherical.

After the discharge was completed, the discharge pump and heater were turned off, and after cooling, the flow of argon gas was stopped and the tin ball was removed.

The removed tin ball was washed with toluene to remove the silicone oil, and then washed with dilute hydrochloric acid.

The tin balls were sorted according to their shape and size.

The above procedure was repeated three times to produce tin balls, resulting in Examples 1 to 3.

[Example 6: Production of tin balls (Comparative Examples 1 to 3)]
In the manufacture of the tin balls of the comparative examples, the above-mentioned high purity tin (sample 2) was used as the raw material instead of the high purity tin (sample 1). The manufacture of the tin balls was repeated three times using the same equipment and procedures as in Example 5 to manufacture the tin balls of Comparative Examples 1 to 3.

Example 7: Evaluation of tin balls
[Procedure for evaluating tin balls]
The groups of six tin balls obtained in Examples 1 to 3 and Comparative Examples 1 to 3 had tin ball diameters in the range of 3.2 to 3.6 mm.

These tin balls were evaluated according to the following procedure. Figure 4 shows an explanatory diagram of the procedure for evaluating the tin balls.

[Visual sorting]
We visually removed any that were extremely large, extremely small, or misshapen.

[Rolling sorting]
They were then rolled over a metal angle bent at 90° to remove any that would not roll.

[Sorting of spherical and irregularly shaped products]
After visual sorting and rolling sorting, the remaining products were classified as spherical products. After visual sorting and rolling sorting, the products removed were classified as irregularly shaped products.

[Spherical product ratio]
The percentage of spherical products was calculated from the weight of the spherical products and the weight of the irregularly shaped products according to the following formula.
"Ratio of spherical products" = "Weight of spherical products" / ("Weight of spherical products" + "Weight of irregularly shaped products") x 100%

[Diameter variation ratio]
Ten balls were randomly taken from the spherical products, and 10 measurements were taken for each ball while changing the measurement points using a micrometer instead of a measurement plane and a probe perpendicular to the measurement plane, with reference to the provisions of JIS B1509:2009, and the diameter variation was calculated using the 10 measured values. In the present invention, the arithmetic mean value of the 10 measured values for each ball was taken as the average diameter value of each ball, and the diameter variation ratio was calculated as the ratio of the diameter variation to the average diameter value.

[Tin ball evaluation results]
The calculation results of the ratio of spherical products obtained for the tin ball populations in Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in FIG.

As shown in Figure 5, the percentage of spherical products in Examples 1 to 3 was greater than 80%, whereas the percentage of spherical products in Comparative Examples 1 to 3 was less than 80%. This shows that the samples in the Examples are more suitable for producing spherical products.

The appearance of the spherical and irregularly shaped products obtained from the tin ball clusters of Examples 1 to 3 is shown as an example in Figure 6A. The appearance of the spherical and irregularly shaped products obtained from the tin ball clusters of Comparative Examples 1 to 3 is shown as an example in Figure 6B.

As shown in Figures 6A and 6B, the spherical products had a shape very close to a sphere. Also, as shown in Figures 6A and 6B, irregularly shaped products were observed, including products with shapes that looked like multiple spheres were bonded together and products with shapes that looked like they had been deformed from a sphere. Although no numerical data is shown, in Examples 1 to 3, the majority of irregularly shaped products in which multiple spheres were bonded together were products in which two spheres were bonded together, whereas in Comparative Examples 1 to 3, many irregularly shaped products in which more than two spheres were bonded together were observed.

The results of measuring the average diameters obtained from the tin ball populations of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 3. In Table 3, No. is the number assigned to each individual tin ball taken out for measurement. Unless otherwise specified in Table 3, the units of values are mm.

As shown in Table 3, the diameter of the obtained tin balls (average of the average diameter values) was between 3 and 4 mm, making them sufficiently large spheres.

The results of the diameter variation ratio measurements obtained from the tin ball groups of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 4. In Table 4, No. is the number assigned to each individual tin ball taken out for measurement.

As shown in Table 4, in Examples 1 to 3, the proportion of samples with a diameter variation ratio of less than 0.04 accounted for 50% or more of the total. On the other hand, in Comparative Examples 1 to 3, the proportion of samples with a diameter variation ratio of less than 0.04 was less than 50% of the total. This shows that even when comparing spherical products, the sphericity of the samples in the Examples is higher than that of the Comparative Examples, indicating that the samples in the Examples are more suitable for manufacturing spherical products. Furthermore, when the average diameter variation ratios of the measured samples were taken, all of Examples 1 to 3 were less than 0.04, while all of Comparative Examples 1 to 3 were 0.04 or higher, which also suggests that the sphericity of the samples in the Examples was higher than that of the Comparative Examples.

Figure 7 shows a photograph of the appearance of a group of tin balls, which are spherical products that remained after visual sorting and rolling sorting in Example 1. By using the high-purity tin of the present invention, it was possible to efficiently produce a large number of high-quality spherical tin balls like those in Figure 7 at the same time.

[Relationship between surface tension and tin ball evaluation results]
The surface tension of the tin of the present invention, measured by the electromagnetic levitation method, was 492×10 ^-3 Nm ^-1 at a temperature of 1,000 K and 397×10 ^-3 Nm ^-1 at a temperature of 1,300 K. The proportion of spherical objects, excluding irregularly shaped objects, contained in the tin balls produced using this tin was high, at 96.9 to 97.5%.

On the other hand, the surface tension of tin, which has a lower surface tension than this, measured by electromagnetic levitation was 455 x 10 ^-3 Nm ^-1 at a temperature of 1,000 K and 365 x 10 ^-3 Nm ^-1 at a temperature of 1,300 K, and the proportion of spherical objects excluding irregularly shaped objects contained in tin balls produced using this tin was low at 70.1 to 75.9%.

According to the present invention, it is possible to produce tin balls with a large diameter and high sphericity with a high yield. This invention is an industrially useful invention.

Claims (5)

The surface tension measured by the electromagnetic levitation method is
At a temperature of 1,000K, it is 490×10 ⁻³ Nm ⁻¹ or more,
A method for producing tin balls having a diameter in the range of 1 mm to 5 mm using a molten metal of tin having a viscosity of 390×10 ⁻³ Nm ⁻¹ or more at a temperature of 1,300 K. The surface tension measured by the electromagnetic levitation method is
At a temperature of 1,000K, it is in the range of 490×10 ⁻³ Nm ⁻¹ to 510×10 ⁻³ Nm ⁻¹ ,
The method of claim 1, wherein the viscosity is in the range of 390×10 ⁻³ Nm ⁻¹ to 410×10 ⁻³ Nm ⁻¹ at a temperature of 1,300K. dripping the molten tin metal into a liquid cooling medium;
a step in which the droplets of metallic tin are cooled as they fall through a liquid cooling medium to form solid tin spheres;
The method of claim 1 , comprising: The manufacturing method according to claim 1 , wherein the percentage of spherical products (%) in the mass of solid tin balls formed is 80% or more, as calculated by the following formula:
"Ratio of spherical products" = "Weight of spherical products (g)" / ("Weight of spherical products (g)" + "Weight of irregularly shaped products (g)") x 100% The method according to claim 1, wherein in a group of spherical products obtained from the group of solid tin spheres formed, the ratio of spherical products having a diameter variation ratio of less than 0.04 calculated by the following formula is 50% or more:
"Diameter variation ratio" = "Diameter variation (mm) measured in accordance with the provisions of JIS B1509:2009" / "Average diameter (mm)"