High purity metallic tin

Abstract

[Problem] To provide a high purity tin product which does not contain undesired carbon impurities. [Solution] In the provided high purity metallic tin product, an angular end part formed by a surface and another surface is chamfered.

Description

High-purity metallic tin

[0001] The present invention relates to high-purity metallic tin.

[0002] Products of high-purity metals, such as products of high-purity tin, are shipped in vacuum packaging to prevent oxidation and contamination. As the film for vacuum packaging, an aluminum vapor-deposited polyethylene film or the like is used.

[0003] The products shipped in vacuum packaging are used after opening the packaging. After opening the vacuum packaging, etching equipment is required to perform cleaning operations such as etching, and when the exposure time in the atmosphere becomes long due to these operations, oxidation of the products progresses. Therefore, products of high-purity metals, such as products of high-purity tin, are shipped in a manner that they can be used immediately after opening the vacuum packaging. And, for example, they are immediately melted and used for subsequent precision processing.

[0004] Patent Document 1 describes a technique related to a packaged high-purity target. When a high-purity target is packaged using a polyethylene bag manufactured by molding using clean air with an air cleanliness of class 6 or less, it is said that the taken-out target can achieve stability at the start of use in sputtering and long-life characteristics.

[0005] Patent Document 2 discloses a technique related to packaged high-purity tin. By using a fluorocarbon resin sheet on the surface of the packaging material that contacts the high-purity tin, a technique for reducing carbon impurities mixed into the molten liquid obtained by heating and melting the product of high-purity tin is disclosed.

[0006] JP-A-2001-240959, Patent No. 6850786

[0007] The present inventor has been promoting the reduction of impurities in high-purity tin. However, even when the high purity is advanced, when the shipped product of high-purity tin is heated and melted, carbon impurities are often mixed into the molten liquid, causing the formation of undesirable particles.

[0008] Therefore, an object of the present invention is to provide a high-purity tin product that does not contain undesirable carbon impurities.

[0009] The inventors have diligently studied and attempted to further purify high-purity tin in order to solve the above problems, but it was impossible to avoid some degree of carbon impurity contamination. However, by completely changing the perspective of research and development, when the surface of high-purity tin was observed with an electron microscope just before heating and melting, it was discovered that there were foreign substances that could not be seen with the naked eye, and analysis of the components revealed that they contained carbon. Furthermore, it was discovered that when high-purity tin was vacuum-packed with a fluorocarbon resin sheet interposed between the polyethylene sheet and the tin, the amount of carbon deposits in the high-purity tin product after opening the package was drastically reduced, leading to the technology described in Patent Document 2.

[0010] The technology described in Patent Document 2 is excellent, but the present inventor has been diligently conducting research and development to further improve this technology. As disclosed in Patent Document 2, high-purity tin products are usually provided as cylindrical metallic tin. In this cylindrical metallic tin, the surface of the cylindrical portion is formed as a continuous curved surface, but at the boundary between the upper surface (circular surface) and the surface of the cylindrical portion, and at the boundary between the lower surface (circular surface) and the surface of the cylindrical portion, if the cylindrical shape is maintained, protruding portions with right-angle cross-sections will be created. That is, in the cross-section obtained by cutting the cylinder with a plane parallel to the height direction of the cylinder, the line segment corresponding to the upper or lower surface of the cylinder and the line segment corresponding to the side surface of the cylinder intersect at a right angle.

[0011] Such right-angled protrusions were expected to become sharp contact points with the packaging material when cylindrical high-purity tin products were packaged with packaging material. If vacuum packaging were performed as is, it was foreseen that these would inevitably scrape the inner surface of the packaging material, potentially causing the generation of undesirable carbon impurities. Therefore, prior to the present invention, the inventors developed an improved product in which the right-angled ends were processed to have a rounded end shape with a curved cross-section.

[0012] The inventors have diligently conducted research and development to further reduce the inclusion of unwanted carbon impurities in this improved product. Surprisingly, they discovered that the inclusion of unwanted carbon impurities could be further reduced by giving the ends of the cylindrical high-purity tin product the shape described later, thus arriving at the present invention.

[0013] Therefore, the present invention includes (1) the following: (1) A high-purity metallic tin product in which the angular ends formed by two faces are chamfered.

[0014] According to the present invention, a high-purity tin product can be obtained in which the adhesion of foreign substances, including carbon impurities, to the edges is suppressed.

[0015] Figure 1A is an explanatory diagram illustrating the cross-section of the end with a C-chamfer. Figure 1B is a scanning electron microscope (SEM) image of the surface near the boundary between the curved side surface and the C-chamfer of the observed cylindrical tin metal. Figure 1C is an EDX (energy-dispersive X-ray spectroscopy) image of C Kα1_2 observed in the same field of view as Figure 1B. Figure 1D is an EDX (energy-dispersive X-ray spectroscopy) image of F Kα1_2 observed in the same field of view as Figure 1B. Figure 2A is an explanatory diagram illustrating the cross-section of the end with a R-chamfer. Figure 2B is a scanning electron microscope (SEM) image of the surface near the boundary between the curved side surface and the R-chamfer of the observed cylindrical tin metal. Figure 2C is an EDX (energy-dispersive X-ray spectroscopy) image of C Kα1_2 observed in the same field of view as Figure 2B. Figure 2D is an EDX (energy-dispersive X-ray spectroscopy) image of F Kα1_2 observed in the same field of view as Figure 2B.

[0016] 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.

[0017] [High-purity metallic tin product of the present invention] As disclosed in Patent Document 2, when high-purity tin products are vacuum-packed, a fluorocarbon resin sheet is interposed between the polyethylene sheet and the tin, resulting in a significantly reduced amount of carbon deposits in the high-purity tin product when the packaging is opened.

[0018] As is intuitively obvious, when high-purity tin products are processed into any of the common shapes such as cylinders, cubes, or rectangular prisms, angular ends are produced at the boundaries between the planes or curved surfaces that make up these shapes, where the cross-section of the intersecting planes is typically at an angle close to a right angle.

[0019] Immediately after processing into each shape, protruding processing marks called burrs often remain near these angular ends. As is readily apparent, when such metal burrs come into contact with fluorocarbon resin sheets, they can scrape off the surface of the fluorocarbon resin sheet, potentially leading to the generation of new carbon impurities.

[0020] Thus, prior to the present invention, the inventors developed an improved product in which the angular ends were processed to have a rounded end shape with a curved cross-section, in order to remove unwanted burrs that occurred immediately after processing into each shape.

[0021] This process of rounding the angular ends so that the cross-section becomes a curved surface is called round chamfering (R chamfering), and the inventors have long considered it a desirable process for removing burrs from the metal at the angular ends.

[0022] This is because it is believed that there is no other process that rounds the cross-section more carefully than round chamfering (R-chamfering).

[0023] If a process like a C-chamfer is performed instead of an R-chamfer, even if the angle of intersection between the faces is greater than a right angle, new angular ends will be generated, resulting in an increase in angular ends compared to the state before processing, thus creating a worse condition.

[0024] Chamfering is a process where the corner end is cut off at an angle. Because chamfering only involves cutting the corner end at an angle, it eliminates the need for the careful rounding of the cross-section required for round chamfering (R chamfering), making it a very simple process and thus offering the advantage of saving labor.

[0025] However, prioritizing the need to minimize the adhesion of carbon impurities and other contaminants to the edges of high-purity tin products, the inventors have long preferred the R-chamfering method, which involves carefully rounding the cross-section and is more labor-saving than the C-chamfering method.

[0026] However, the inventors re-examined the processing of the angular ends of high-purity tin products by conducting comparative experiments described later in the examples. They discovered that, instead of the time-consuming and careful R-chamfering process to round the cross-section, performing C-chamfering, which had previously been considered to have only the advantage of saving labor, actually suppressed the adhesion of carbon impurities and other contaminants to high-purity tin products, leading to the present invention.

[0027] Thus, the present invention relates to a high-purity metallic tin product, wherein the angular end is chamfered (C-chamfered).

[0028] [Shape of high-purity tin metal products] The present invention relates to high-purity tin metal products in which the angular ends are chamfered. Therefore, the effects of the present invention can be achieved as long as the shape of the high-purity tin metal product has a chamfered angular end.

[0029] Such shapes, before chamfering, can include, for example, cylindrical, prismatic, cubic, or rectangular prism shapes.

[0030] A typical example of a cylindrical shape is a cylinder in which the top and bottom circles have the same radius. Furthermore, a cylindrical shape can be a roughly cylindrical shape in which the top and bottom circles have different radii. Further, a cylindrical shape can be a roughly cylindrical shape in which the top and bottom circles are not perfect circles but elliptical. And further, a cylindrical shape can be a roughly conical shape in which the top and bottom circles have different radii, and the top circle is practically a point in size.

[0031] In a cylindrical shape, the top surface and the curved side surface intersect at the maximum angle at the cross-section containing the cylinder's central axis. This angle is, for example, a right angle. Therefore, the end surface having this right-angle intersection is defined as a corner end. In this invention, this corner end is chamfered. The cylinder's central axis is the axis connecting the center of the top surface and the center of the bottom surface. The angle at which the surfaces intersect at the cross-section refers to the angle at which the line segments originating from each surface intersect at the cross-section.

[0032] Examples of prismatic shapes include rod-like shapes called timbers. Another example of a prismatic shape is a prismatic shape where the polygons on the top and bottom surfaces are of the same size. A third example of a prismatic shape is a roughly prism-like shape where the polygons on the top and bottom surfaces are of different sizes. Finally, a third example of a prismatic shape is a roughly polygonal pyramidal shape where the polygons on the top and bottom surfaces are of different sizes, and the polygon on the top surface is practically a point.

[0033] The polygons forming the top and bottom surfaces of the prism can be, for example, triangles, quadrilaterals, pentagons, hexagons, heptagons, octagons, nonagons, decagons, eleven-sided polygons, or dodecagons. By increasing the number of sides, the shape can be made closer to a cylindrical form. These polygons can be regular polygons or non-regular polygons.

[0034] In a prism shape, the polygonal face on the top and the quadrilateral face on the side intersect at a cross-section perpendicular to the side of interest, which includes the central axis of the prism. This cross-section is perpendicular to the side of interest, and the angle of intersection between the faces is maximized, for example, a right angle. Therefore, the end where the faces intersect to form this right angle is called a corner end. In this invention, this corner end is chamfered. The central axis of the prism is the axis connecting the center of the polygon on the top surface and the center of the polygon on the bottom surface of the prism. The center of the polygon means the centroid of the polygon, and in the case of a polygon with a geometric center, it means the geometric center. The angle of intersection between faces on the cross-section refers to the angle of intersection of the line segments that originate from each face and are generated on the cross-section.

[0035] Furthermore, in the case of a prismatic shape, the angle at which the two rectangular faces intersect is maximized at a cross-section perpendicular to these two faces. The angle at which the faces intersect can be, for example, 60 degrees, 90 degrees, or an angle corresponding to the polygonal shape of the top and bottom faces. Thus, the end where the intersecting faces form these angles exists as a corner end. In the present invention, this corner end can also be chamfered. The angle at which the faces intersect at the cross-section refers to the angle at which the line segments originating from each face intersect at the cross-section.

[0036] Even in the shapes of cubes and rectangular prisms, when faces intersect, the ends where these faces intersect exist as angular ends. In this invention, these angular ends can be given a chamfered shape.

[0037] [Chamfering] Chamfering generally refers to rounding off the corners of a material after machining. Typically, C-chamfering refers to the process of rounding off these corners at a 45-degree angle, but the present invention is not limited to this.

[0038] In a preferred embodiment, the C-chamfering process of the present invention can be performed by processing the corner end using a plane whose normal is a straight line whose angle of intersection between two faces is equal to the angle of the normals of the two intersecting faces at the corner end, where the corner end is perpendicular to the two faces of the corner end, and the corner end is processed using this plane as the C-plane.

[0039] The angle at which the faces intersect in the above-mentioned cross-section is equal to the angle at which the line segments originating from each face intersect in the cross-section. Therefore, in the C-chamfering process of the present invention, at the corner end, in the cross-section perpendicular to the two faces of the corner end, for example, there are two line segments originating from the two intersecting faces and arising in the cross-section, there are two perpendicular lines perpendicular to each of these two line segments, there is a straight line that has the same angle with both of these perpendicular lines, there is a plane normal to this straight line, and the corner end can be processed by using this plane as the C-plane.

[0040] Furthermore, in the case of a cylindrical shape, a cross-section perpendicular to the two faces of a corner-shaped end is a cross-section that includes the central axis of the cylinder. Also, in the case of a prismatic shape, a cross-section perpendicular to the two faces of a corner-shaped end is a cross-section that includes the central axis of the prismatic column and is perpendicular to the side of interest, for the corner-shaped end formed by the polygonal face on the top and the quadrilateral face on the side.

[0041] Alternatively, in a preferred embodiment of the present invention, the C-chamfering process can be performed on the corner end by using a plane as the C-plane, which is normalized to a straight line whose angle with the normals of the two intersecting surfaces is equal to, for example, within 15 degrees, preferably within 10 degrees, preferably within 5 degrees, preferably within 4 degrees, preferably within 3 degrees, preferably within 2 degrees, and preferably within 1 degree, at the cutting surface where the angle between the surfaces is greatest at the corner end.

[0042] In a preferred embodiment, in the chamfering process of the present invention, at the angular end portion, on the cut surface where the angle of intersection of the surfaces is maximized, for one of the intersecting surfaces, the distance from the tip of the angular end portion before the chamfering process to the end portion of the C chamfered surface after the chamfering process is, for example, in the range of 0.1 to 5 mm, preferably in the range of 0.3 to 3 mm. By doing so, the angular end portion can be processed and chamfered. Similarly, for the other intersecting surface, by setting the distance from the tip of the angular end portion before the chamfering process to the end portion of the C chamfered surface after the chamfering process within the above range, the angular end portion can be processed and chamfered.

[0043] As the means for chamfering, known means can be used. For example, the means described later in the examples can be used.

[0044] [Purity of High-Purity Metallic Tin Products] Since the high-purity metallic tin products of the present invention are achieved by pursuing the suppression of the adhesion of carbon impurities, the high purity referred to in the present invention can be defined as having a high purity to a certain extent that is valuable for pursuing the suppression of the adhesion of carbon impurities. Such high purity of metallic tin can be, for example, 2N (99% by mass) or more, 3N (99.9% by mass) or more, 4N (99.99% by mass) or more, 5N (99.999% by mass) or more, 6N (99.9999% by mass) or more.

[0045] [Vacuum Package of High-Purity Metallic Tin Products] The present invention also relates to a vacuum package of high-purity metallic tin products in which the adhesion of carbon impurities is minimized by chamfering the angular end portions.

[0046] In a preferred embodiment, the vacuum package of high-purity metallic tin products can be vacuum-packed with a fluorocarbon resin sheet interposed between the vacuum-packing film and the metallic tin during vacuum packing.

[0047] The vacuum-packed high-purity tin metal product of the present invention can be used immediately after opening the vacuum packaging without the need for cleaning or other treatments. For example, the vacuum-packed high-purity tin metal product according to the present invention can be used as molten metal in ultrafine processing equipment such as LSIs. This molten metal has extremely reduced carbon impurities, suppressing the formation of unwanted particles and preventing clogging of fine flow channels.

[0048] [Process of covering with a fluorocarbon resin sheet] In a preferred embodiment, the vacuum-packed high-purity metallic tin product of the present invention may be vacuum-packed with a fluorocarbon resin sheet interposed between the vacuum packaging film and the metallic tin. Prior to vacuum packaging, a process of covering with a fluorocarbon resin sheet is performed in order to interpose the fluorocarbon resin sheet. When covering with the fluorocarbon resin sheet, at least a portion of the chamfered corner edge of the high-purity metallic tin product is covered with the fluorocarbon resin sheet.

[0049] In a preferred embodiment, the high-purity tin metal product can be covered not only with respect to at least a portion of the chamfered corner edges, but also with respect to the portion of the high-purity tin metal product that is not chamfered corner edges. In a preferred embodiment, the entire surface of the high-purity tin metal product may be covered. To effectively cover the product while maintaining workability, at least a portion of the surface to be covered is selected, depending on the shape of the high-purity tin metal product, from the surface that will be strongly pressed with the vacuum packaging film during vacuum packaging. For example, if the high-purity tin metal product is cylindrical, the surface of the curved side of the cylindrical high-purity tin metal product and the chamfered corner edges located at the ends of this side surface are covered with a fluorocarbon resin sheet. In this case, the top and / or bottom surfaces of the cylindrical high-purity tin metal product may be further covered as desired, resulting in the entire surface of the cylindrical high-purity tin metal product being covered.

[0050] [Fluorocarbon Resin Sheet] In a preferred embodiment, as the fluorocarbon resin sheet, for example, polytetrafluoroethylene (PTFE) sheet, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (4,6-fluorinated), tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride (2-fluorinated), polychlorotrifluoroethylene (3-fluorinated), chlorotrifluoroethylene-ethylene copolymer sheet, etc. are used. Preferably, as the polytetrafluoroethylene (PTFE) sheet, Teflon® sheet manufactured by DuPont or Nafuron® sheet manufactured by Nichias Corporation are used. In a preferred embodiment, the thickness of the fluorocarbon resin sheet can be, for example, in the range of 0.01 to 6.0 mm, 0.05 to 5.0 mm, preferably in the range of 0.02 to 4.0 mm or 0.05 to 3.0 mm. By defining the range in this manner, it is possible to achieve both the rigidity necessary to reduce carbon deposits and the flexibility necessary to prevent the vacuum packaging film from tearing during vacuum packaging.

[0051] [Vacuum Packaging Film] As for vacuum packaging films, conventional vacuum packaging films used for vacuum packaging of high-purity metals can be used without particular limitations. Examples of vacuum packaging films used in this way include films with reduced oxygen permeability (oxygen barrier films) and films with reduced water vapor permeability (water vapor barrier films). Examples of such vacuum packaging films include highly flexible resin films and laminated films provided by vapor deposition or the like. Examples of resin films used in such laminated films include polyethylene films, nylon films, and PET films. Examples of metals used in the metal layer provided by vapor deposition or the like include Al (aluminum) and Sn, and examples of metal oxides used in the metal oxide layer include Al ２ O ３ (Aluminum oxide), SiO ２Silicon oxide can be used as an example. Preferably, Al-deposited polyethylene film or Sn-deposited polyethylene film can be used. As a film for vacuum packaging, a laminated film can be used which is further laminated on such a film. For example, a laminated film can be made in which polyethylene film, nylon film, or PET film is further laminated on the surface of a metal layer and a metal oxide layer. Alternatively, depending on the desire for reliable protection during transport or to further enhance water vapor barrier properties, multiple films (laminated films) can be appropriately stacked and vacuum packaged.

[0052] [Vacuum Packaging] Vacuum packaging using vacuum packaging film can be carried out by known means and under known conditions. Examples of usable vacuum packaging equipment include the Kashiwagi vacuum packaging machine (manufactured by NPC Corporation) and the GDP-400 (manufactured by Tamura Seal Co., Ltd.). In a preferred embodiment, vacuum packaging can be carried out under low particle conditions.

[0053] [Preferred Embodiments of the Invention] As a preferred embodiment of the present invention, the present invention includes the following: (1) A high-purity metallic tin product in which the angular ends formed by faces are chamfered. (2) The high-purity metallic tin product according to (1), wherein the overall shape of the high-purity metallic tin product before chamfering is cylindrical, prismatic, cubic, or rectangular parallelepiped, and the angular ends formed by faces are: the angular ends formed by the top surface and the curved side surface of a cylinder, and the angular ends formed by the bottom surface and the curved side surface of a cylinder; the angular ends formed by the top surface and the side surface of a prismatic shape, the angular ends formed by the bottom surface and the side surface of a prismatic shape, and the angular ends formed by the side surface and the adjacent side surface of a prismatic shape; the angular ends formed by a face of a cube and an adjacent face; or the angular ends formed by a face of a rectangular parallelepiped and an adjacent face.

[0054] (3) A high-purity metallic tin product according to any one of (1) to (2), wherein the corner end is chamfered by processing the corner end with a plane whose normal is a line whose angle is within 15 degrees from a line whose angle with the normals of the two intersecting faces is equal in a cross-section perpendicular to both faces of the two intersecting faces.

[0055] (4) A high-purity metallic tin product according to any one of (1) to (3), wherein the overall shape of the high-purity metallic tin product before chamfering is cylindrical, and the chamfer is defined as a plane whose normal is a line within 15 degrees from a line whose angle with the normals of two intersecting faces is equal in the cross-section including the central axis of the cylinder, or the overall shape of the high-purity metallic tin product before chamfering is prismatic, and the chamfer is defined as a plane whose normal is a line within 15 degrees from a line whose angle with the normals of two intersecting faces is equal in the cross-section including the central axis of the prismatic column and perpendicular to the side surface of the prismatic column, and the corner end is processed to perform the chamfering.

[0056] (5) A high-purity metallic tin product according to any one of (1) to (4), wherein, at the corner end, the corner end is processed by making the distance from the tip of the corner end before chamfering to the edge of the chamfered surface after chamfering within the range of 0.1 to 5 mm for one of the intersecting surfaces, and the corner end is processed by making the distance from the tip of the corner end before chamfering to the edge of the chamfered surface after chamfering within the range of 0.1 to 5 mm for the other intersecting surface.

[0057] (6) A vacuum-packed high-purity metallic tin product according to any one of (1) to (5), wherein at least a portion of the chamfered corner end of the high-purity metallic tin product is covered with a fluorocarbon resin sheet, and the high-purity metallic tin product, in which at least a portion of the chamfered corner end is covered with a fluorocarbon resin sheet, is vacuum-packed with a vacuum-packing film.

[0058] (7) The vacuum packaging of high-purity metallic tin products according to (6), wherein the fluorocarbon resin sheet is a polytetrafluoroethylene (PTFE) sheet. (8) The vacuum packaging of high-purity metallic tin products according to any one of (6) to (7), wherein the fluorocarbon resin sheet has a thickness of 0.05 to 5.0 mm.

[0059] (9) A vacuum-packed high-purity metallic tin product according to any one of (6) to (8), wherein a laminated film having a metal vapor deposition layer or a metal oxide vapor deposition layer is used as the vacuum packaging film, and the metal vapor deposition layer or metal oxide vapor deposition layer is vacuum-packed without contact with the high-purity metallic tin product.

[0060] The present invention will be described in detail below with reference to examples. The present invention is not limited to the examples illustrated below.

[0061] [Example 1] [Manufacturing of cylindrical tin metal and chamfering] As Example 1, cylindrical tin metal with chamfered ends was manufactured as follows.

[0062] A commercially available block of metallic tin with a purity of 6N (99.9999% by mass, excluding carbon, nitrogen, oxygen, and hydrogen) was prepared. It was machined on a lathe into a cylindrical shape with a diameter of φ40 mm, a length of 100 mm, and a surface roughness of Ra 1.6 μm or less. After machining it into a cylindrical shape, the ends of the cylinder (the boundary between the top and bottom surfaces and the curved surfaces of the cylindrical side surfaces) were chamfered using the following procedure to obtain the cylindrical metallic tin of Example 1. C1 chamfering is a process in which a length of 1 mm is cut off from the tip of the angular end on two surfaces that intersect at a right angle, forming a new surface (C-surface) with a 45-degree angle to each surface.

[0063] The specific C1 chamfering process was carried out as follows: The workpiece was mounted in the chuck. It was confirmed that the workpiece was securely fixed. The chamfering tool was set in the tool post. It was confirmed that the chamfering tool had a 45-degree angle. Next, the spindle of the lathe was rotated. Then, the chamfering tool was pressed against the workpiece by manual feed and the chamfering was performed. The C1 chamfering was performed by cutting 1 mm in the X direction (2 mm in diameter) and 1 mm in the Z direction. Once the chamfering was complete, the workpiece was removed and the chamfered area was checked.

[0064] [Vacuum packaging and end observation of cylindrical metallic tin] The cylindrical metallic tin obtained in Example 1 as described above was wrapped in a 0.3 mm thick Nafuron sheet (manufactured by Nichias Corporation), and then sandwiched from above and below with two Al-deposited polyethylene films (manufactured by Dai Nippon Printing Co., Ltd., product name DNP Technopack) (Al deposition thickness 12 μm, polyethylene thickness 80 μm), with the polyethylene surfaces facing inward. The ends were then heat-sealed with a sealer to form a bag, and the bag opening was heat-sealed under a vacuum suction of approximately -64 kPa to perform vacuum packaging. A Kashiwagi-type vacuum packaging machine was used as the vacuum packaging device. After leaving the vacuum-packed product for 3 hours, it was opened, and the ends of the curved surface of the side of the cylindrical metallic tin, from the upper to the lower surface, were observed using SEM (scanning electron microscope) and EDX (energy-dispersive X-ray spectroscopy). The results are shown in Figures 1A to 1D.

[0065] Figure 1A is an explanatory diagram illustrating the cross-section of a chamfered end. As shown in Figure 1A, in the chamfered end, a length of 1 mm is cut off from the tip of the end before chamfering, on two faces that intersect at a right angle, and the newly generated chamfered surface is provided at a 45-degree angle to both faces. The horizontal line segment at the top of the figure in Figure 1A corresponds to the side surface of the cylinder, and the vertical line segment on the right side of the figure in Figure 1A corresponds to the bottom surface of the cylinder. The portion corresponding to the surface of the area enclosed by the circle in Figure 1A was observed using an SEM (scanning electron microscope) in Figure 1B.

[0066] Figure 1B is a scanning electron microscope (SEM) image of the surface near the boundary between the curved side surface and the C-plane of the observed cylindrical tin metal. The area observed in Figure 1B corresponds to the surface of the region enclosed by the circle in Figure 1A.

[0067] Figure 1C is an EDX (energy-dispersive X-ray spectroscopy) image of C Kα1_2 observed in the same field of view as Figure 1B. No carbon atoms were observed in the field of view.

[0068] Figure 1D is an EDX (energy-dispersive X-ray spectroscopy) image of F Kα1_2 observed in the same field of view as Figure 1B. No fluorine atoms were observed in the field of view.

[0069] [Evaluation of Observation Results] As shown in Figures 1B to 1D, observations using SEM (scanning electron microscope) and EDX (energy-dispersive X-ray spectroscopy) confirmed that there was no foreign matter containing carbon and fluorine adhering to the edges near the boundary with the C-plane on the side surface of the opened high-purity tin product in which the cylindrical metallic tin of Example 1 was vacuum-packed.

[0070] [Comparative Example 1] [Manufacturing of Cylindrical Metallic Tin and R-Chamfering] As Comparative Example 1, cylindrical metallic tin with R-chamfered ends was manufactured as follows. As in Example 1, a block of tin with a purity of 6N was prepared. As in Example 1, it was machined into a cylindrical shape using a lathe. After machining into a cylindrical shape, the ends of the cylinder (the boundary between the top and bottom surfaces and the cylindrical side surfaces) were R1 chamfered using the following procedure to obtain the cylindrical metallic tin of Comparative Example 1. R1 chamfering is a process in which the tip of the angular end is rounded for a length of 1 mm on two perpendicularly intersecting surfaces, so that the cross-section is one-quarter of the circumference of a circle with a radius of 1 mm, and a new surface (R surface) with a cross-section of one-quarter of a circle with a radius of 1 mm is formed from the end of one chamfered surface to the end of the other chamfered surface.

[0071] The specific R1 chamfering process was carried out as follows: The workpiece was fixed in the lathe chuck. The origin was set to determine the reference position for machining. A form cutting tool and a profile cutting tool were used for the R1 chamfer. The tool was selected according to the dimensions and shape of the chamfer. The tool post was tilted to perform the R1 chamfer. The tool post had an angle scale, and the work was performed by tilting it according to the angle. The tool was brought closer to the workpiece to adjust the position of the chamfer. The rotation of the tool post was clamped, and machining was performed while feeding the tool. The tool was applied to the workpiece, and the R1 chamfer was performed. Care was taken to avoid producing burrs during machining. After the R1 chamfer was completed, finishing was performed. Burrs were removed to achieve a smooth finish. If any burrs remained after chamfering, they were removed appropriately.

[0072] [Vacuum packaging and end observation of cylindrical tin metal] The cylindrical tin metal of Comparative Example 1 obtained as described above was vacuum packaged in the same manner as in Example 1, then opened, and SEM / EDX observation was performed on the ends of the curved surface of the side of the cylindrical tin metal, from the upper to the lower surface. The results are shown in Figures 2A to 2D.

[0073] Figure 2A is an explanatory diagram illustrating the cross-section of an R-chamfered end. As shown in Figure 2A, the R1-chamfered end is cut off in such a way that a length of 1 mm from the tip of the end before R1 chamfering is rounded on two perpendicularly intersecting faces. The newly created R-face is set to be one-quarter of the circumference of a circle with a radius of 1 mm, starting from the end of one face and ending at the end of the other face. The horizontal line segment at the top of the figure in Figure 2A corresponds to the side surface of the cylinder, and the vertical line segment on the right side of the figure in Figure 2A corresponds to the bottom surface of the cylinder. The portion corresponding to the surface of the area enclosed by the circle in Figure 2A was observed using an SEM (scanning electron microscope) in Figure 2B.

[0074] Figure 2B is a scanning electron microscope (SEM) image of the surface near the boundary between the curved surface and the R-surface on the side of the observed cylindrical tin metal. The area observed in Figure 2B corresponds to the surface of the region enclosed by the circle in Figure 2A.

[0075] Figure 2C is an EDX (energy-dispersive X-ray spectroscopy) image of C Kα1_2 observed in the same field of view as Figure 2B. Near the center of the image in the horizontal direction, the presence of carbon atoms was observed as two rows of diagonal lines, or wide diagonal lines that appear as two rows, extending from the top to the bottom of the image. These diagonal lines coincided with the location of the stain-like diagonal lines observed in the SEM image of Figure 2B.

[0076] Figure 2D is an EDX (energy-dispersive X-ray spectroscopy) image of F Kα1_2 observed in the same field of view as Figure 2B. Near the center of the image in the horizontal direction, the presence of F (fluorine) atoms was observed as two rows of diagonal lines, or diagonal lines that appear to be two rows, extending from the top to the bottom of the image. The position of these diagonal lines coincided with the position of the diagonal lines observed in the image of Figure 2C.

[0077] [Evaluation of Observation Results] As shown in the image in Figure 2B, numerous vertical lines extending from the top to the bottom of the photograph are observed on the end of the opened high-purity tin sample of the cylindrical metallic tin of Comparative Example 1, which was vacuum-packed. These are vertical lines that appear to be caused by lathe machining and are thought to be continuous linear protrusions. Among these vertical lines, a deposit of a certain width that spreads like a stain along the vertical line is observed near the center of the photograph in the left-right direction. This appears to be near the top of each line if it were considered to be a continuous linear protrusion. Also, near the center of the photograph, a lump-shaped deposit with a different shape from the deposit along this vertical line is observed. Figure 2C is an EDX photograph of the same field of view as Figure 2B, and it is clearly observed that the deposit is a carbon-containing deposit. Figure 2D is also an EDX photograph of the same field of view as Figure 2B, and it is clearly observed that the deposit is a fluorine-containing deposit. Since the positions of the deposits in Figure 2C and Figure 2D coincide, it is thought that this stain-like deposit is a deposit containing carbon and fluorine.

[0078] [Summary of the evaluation of the observation results] The inventors investigated possible origins of the carbon and fluorine-containing deposits observed in Figures 2B, 2C, and 2D, and concluded that they are Nafuron sheets that were pressed onto the surface of the end of the cylindrical tin metal during vacuum packaging.

[0079] From a common-sense perspective, cylindrical tin metal with rounded edges is less likely to damage the pressed sheet. Conversely, cylindrical tin metal with chamfered edges is more likely to damage the pressed sheet.

[0080] However, contrary to expectations based on such common technical knowledge, in reality, cylindrical tin metal with chamfered ends (C-chamfered) resulted in less material being removed from the crimping sheet than those with rounded ends (R-chamfered).

[0081] The reason for this result is unclear, but in actual manufacturing, it is difficult to process the end of the curved side surface of a cylinder into a continuous, smooth curve. Rather, the cross-section ends up being a polygon with countless angles. Therefore, the inventors consider that it would have been more appropriate in actual manufacturing to process the end into a shape with as few angles as possible, but not as sharp as a right angle, rather than processing it in this way.

[0082] According to the present invention, high-purity tin products can be obtained that are free from foreign substances, including undesirable carbon impurities. This invention is industrially useful.

Claims

1. A high-purity tin metal product in which the angular ends formed by the faces are chamfered (C-chamfered).

2. The high-purity metallic tin product according to claim 1, wherein the overall shape of the high-purity metallic tin product before chamfering is cylindrical, prismatic, cubic, or rectangular parallelepiped, and the angular ends formed by faces are: the angular ends formed by the top surface and the curved side surface of a cylinder, and the angular ends formed by the bottom surface and the curved side surface of a cylinder; the angular ends formed by the top surface and the side surface of a prismatic shape, the angular ends formed by the bottom surface and the side surface of a prismatic shape, and the angular ends formed by the side surface of a prismatic shape and the adjacent side surface; the angular ends formed by a face of a cube and an adjacent face; or the angular ends formed by a face of a rectangular parallelepiped and an adjacent face.

3. The high-purity metallic tin product according to claim 1, wherein at the corner end, the corner end is chamfered by processing the corner end with a plane whose normal is a line within 15 degrees from a line whose angle with the normals of the two intersecting faces is equal in a cross-section perpendicular to both faces, and the corner end is chamfered.

4. The high-purity metallic tin product according to claim 1, wherein the overall shape of the high-purity metallic tin product before chamfering is cylindrical, and the chamfering is performed by processing the corner end of the high-purity metallic tin product according to claim 1, wherein chamfering is performed by processing the corner end of the high-purity metallic tin product according to claim 1, wherein the chamfering is performed by processing the corner end of the high-purity metallic tin product according to claim 1, where the chamfering is performed by processing the overall shape of the high-purity metallic tin product before chamfering is cylindrical, and the chamfering is performed by processing the corner end of the high-purity metallic tin product according to claim 1, where the chamfering is performed by processing the overall shape of the high-purity metallic tin product before chamfering is cylindrical, and the chamfering is performed by processing the corner end of the high-purity metallic tin product according to claim 1, in which case the chamfering is performed by processing the overall shape of the high-purity metallic tin product before chamfering is cylindrical, and the chamfering is performed by processing the corner end of the high-purity metallic tin product according to claim 1, in which case the chamfering is performed by processing the overall shape of the high-purity metallic tin product before chamfering is cylindrical, and the chamfering is performed by processing the corner end of the high-purity metallic tin product according to claim 1, in which case the chamfering is performed 5. A high-purity metallic tin product according to claim 1, wherein, at the corner end, in a cross-section perpendicular to both faces of the two intersecting faces, the corner end is processed by setting the distance from the tip of the corner end before chamfering to the edge of the chamfered surface after chamfering to be in the range of 0.1 to 5 mm for one of the intersecting faces, and the corner end is processed by setting the distance from the tip of the corner end before chamfering to the edge of the chamfered surface after chamfering to be in the range of 0.1 to 5 mm for the other intersecting face.

6. A vacuum-packed high-purity metallic tin product according to any one of claims 1 to 5, wherein at least a portion of the chamfered corner end of the high-purity metallic tin product is covered with a fluorocarbon resin sheet, and the high-purity metallic tin product, in which at least a portion of the chamfered corner end is covered with a fluorocarbon resin sheet, is vacuum-packed with a vacuum-packing film.

7. The vacuum packaging of high-purity metallic tin products according to claim 6, wherein the fluorocarbon resin sheet is a polytetrafluoroethylene (PTFE) sheet.

8. The vacuum packaging of high-purity metallic tin products according to claim 6, wherein the fluorocarbon resin sheet has a thickness of 0.05 to 5.0 mm.

9. The vacuum-packed high-purity metallic tin product according to claim 6, wherein a laminated film having a metal vapor deposition layer or a metal oxide vapor deposition layer is used as the vacuum packaging film, and the metal vapor deposition layer or metal oxide vapor deposition layer is vacuum-packed without contact with the high-purity metallic tin product.

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