High-purity metallic tin

Abstract

We provide high-purity tin products that are free from unwanted carbon impurities. [Solution] A high-purity tin metal product in which the angular ends formed by the surfaces are chamfered.

Description

Technical Field

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

Background Art

[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 unpacked and used. After opening the vacuum packaging, etching equipment is required to perform cleaning operations such as etching. Also, if the exposure time in the atmosphere becomes long due to these operations, the 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 formed 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 and long-life characteristics at the start of use in sputtering.

[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.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] The inventors have been working to reduce impurities in high-purity tin. However, even with efforts to increase purity, when the shipped high-purity tin product is heated and melted, carbon impurities often become mixed into the molten liquid, causing the formation of undesirable particles.

[0008] Therefore, the object of the present invention is to provide a high-purity tin product that does not contain unwanted carbon impurities. [Means for solving the problem]

[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, they observed the surface of high-purity tin just before heating and melting with an electron microscope and found that there were foreign substances that could not be seen with the naked eye, and that analysis of these components revealed that they contained carbon. Furthermore, they found 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 tin metal product in which the angular ends formed by the surfaces are chamfered (C-chamfered). [Effects of the Invention]

[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. [Brief explanation of the drawing]

[0015] [Figure 1A] Figure 1A is an explanatory diagram illustrating a cross-section of a chamfered end portion. [Figure 1B] Figure 1B is a SEM (scanning electron microscope) image of the surface near the boundary between the curved surface of the side of the observed cylindrical metallic tin and the C surface. [Figure 1C] 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] 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] Figure 2A is an explanatory diagram illustrating a cross-section of a chamfered end portion. [Figure 2B] Figure 2B is a SEM (scanning electron microscope) image of the surface near the boundary between the curved surface of the side of the observed cylindrical metallic tin and the R surface. [Figure 2C] 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] 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.

Embodiments for Carrying Out the Invention

[0016] The present invention will be described in detail below by way of 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 a high-purity tin product is vacuum-packed with a fluorocarbon resin sheet interposed between a polyethylene sheet and tin, in the high-purity tin product with the package opened, carbon deposits are extremely reduced.

[0018] Although it is intuitively obvious, when the shape of a high-purity tin product is processed into any of the general shapes such as a cylindrical shape, a cube, or a rectangular parallelepiped, at the boundaries between the planes or between the curved surfaces and the planes that make up these shapes, angular end portions occur where the cross-section of the intersection of the surfaces is typically at an angle close to a right angle.

[0019] And immediately after processing into each shape, often, protruding processing traces called burrs remain in the vicinity of such angular end portions. As is obvious at first glance, when such metal burrs come into contact with a fluorocarbon resin sheet or the like, they may scrape off the surface of this fluorocarbon resin sheet and may cause the generation of new carbon impurities.

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

[0021] The process of rounding the angular end portions so that the cross-section is a curved surface is a process called round chamfer (R chamfer), and the inventor has long considered it to be a desirable process for removing the burrs of the metal at the angular end portions.

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

[0023] If a process such as C chamfer is performed instead of R chamfer, even if the angle of intersection of the surfaces is greater than a right angle, new angular end portions will be generated, and it is considered that the number of angular end portions will increase compared to the state before processing, creating a more deteriorated state.

[0024] Chamfering (C-chamfering) is a process that essentially involves cutting off the corner end at an angle. Because chamfering only requires cutting off the corner end at an angle, it eliminates the need for the careful rounding of the cross-section that is required for round chamfering (R-chamfering), making it a very simple process that can be completed with minimal effort and thus 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 with a C-chamfer.

[0028] [Shape of high-purity tin metal products] Since the present invention relates to a high-purity metallic tin product in which the angular end is chamfered, the effects of the present invention can be achieved as long as the shape of the high-purity metallic tin 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 of intersection in a cross-section containing the cylinder's central axis. This angle of intersection 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 of intersection between surfaces in a cross-section refers to the angle of intersection of line segments originating from each surface and occurring in 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 the 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 in the cross-section refers to the angle of intersection of the line segments that originate from each face and arise in 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 given a chamfered shape. 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] [C chamfering] Chamfering generally refers to rounding off the corners of a material after machining, and C-chamfering typically 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 an equal 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 corner-shaped ends formed by a polygonal face on the top and a 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, where the corner end is processed by using a plane whose normal is a straight line whose angle with the normals of the two intersecting faces 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, preferably within 1 degree, at the cutting surface where the angle between the faces is greatest.

[0042] In a preferred embodiment, the chamfering process of the present invention can be performed on a corner end by setting the distance from the tip of the corner end before chamfering to the edge of the chamfered surface after chamfering to, for example, 0.1 to 5 mm, preferably 0.3 to 3 mm, at the cross-section where the angle of intersection between two surfaces is maximum. Similarly, the other intersecting surface can be chamfered by setting the distance from the tip of the corner end before chamfering to the edge of the chamfered surface after chamfering to the above range.

[0043] Known methods can be used for chamfering, and for example, the methods described later in the examples can be used.

[0044] [Purity of high-purity metallic tin products] The high-purity metallic tin products of the present invention are achieved by pursuing the suppression of carbon impurity adhesion. Therefore, the high purity referred to in the present invention can be defined as a level of purity that is worth pursuing the suppression of carbon impurity adhesion. Examples of such high-purity metallic tin include purities of 2N (99% by mass) or higher, 3N (99.9% by mass) or higher, 4N (99.99% by mass) or higher, 5N (99.999% by mass) or higher, and 6N (99.9999% by mass) or higher.

[0045] [Vacuum-packed high-purity tin metal products] This invention also relates to vacuum packaging of high-purity metallic tin products, in which the adhesion of carbon impurities is minimized by chamfering the angular ends.

[0046] In a preferred embodiment, the vacuum-packed high-purity metallic tin product may be vacuum-packed with a fluorocarbon resin sheet interposed between the vacuum packaging film and the metallic tin.

[0047] The vacuum-packed high-purity metallic tin 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 metallic tin product according to the present invention can be used as molten metal in ultra-fine 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 step of covering with a fluorocarbon resin sheet is performed to interpose the fluorocarbon resin sheet. In this covering with the fluorocarbon resin sheet, at least a portion of the chamfered corner edges 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 these side surfaces 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, the fluorocarbon resin sheet can be, 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), or chlorotrifluoroethylene-ethylene copolymer sheet. Preferably, as the polytetrafluoroethylene (PTFE) sheet, Teflon® sheet manufactured by DuPont or Nafuron® sheet manufactured by Nichias Corporation is 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 setting the thickness within this range, it is possible to achieve both rigidity to reduce carbon deposits and flexibility to prevent the vacuum packaging film from tearing during vacuum packaging.

[0051] [Vacuum packaging film] As the vacuum packaging film, any vacuum packaging film conventionally used for vacuum packaging of high-purity metals can be used without particular limitation. 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 Al2O3 (aluminum oxide) and SiO2 (silicon oxide). Preferably, Al-deposited polyethylene films and Sn-deposited polyethylene films can be used. As the vacuum packaging film, a laminated film further laminated on such a film can be used, for example, a laminated film in which polyethylene film, nylon film, or PET film is further laminated on the surface of the metal layer and metal oxide layer. Alternatively, to ensure reliable protection during transport or to further enhance water vapor barrier properties, multiple films (laminated films) can be layered as needed and vacuum-packed.

[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 present invention] In preferred embodiments, the present invention includes (1) and the following: (1) A high-purity tin metal product in which the angular ends formed by the surfaces are chamfered (C-chamfered). (2) The overall shape of the high-purity tin metal product before chamfering is cylindrical, prismatic, cubic, or rectangular. The angular end formed by two faces is The angular end formed by the cylindrical top surface and the curved side surface, and the angular end formed by the cylindrical bottom surface and the curved side surface; Angular end formed by the top surface and side surface of a prismatic shape, an angled end formed by the bottom surface and side surface of a prismatic shape, and an angled end formed by a side surface of a prismatic shape and an adjacent side surface; The angular end formed between a face of a cube and an adjacent face; or, The high-purity metallic tin product described in (1), which is a corner-shaped end formed by a face of a rectangular parallelepiped and an adjacent face.

[0054] (3) The high-purity metallic tin product described in (1), wherein 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 of the two intersecting faces.

[0055] (4) The overall shape of the high-purity tin metal product before chamfering is cylindrical. In a cross-section containing the central axis of a cylinder, the plane whose normal is a line within 15 degrees of the normal to a line that makes equal angles with the normals of two intersecting faces is defined as the C-plane, or Or, The overall shape of the high-purity tin metal product before chamfering is a rectangular prism shape. The high-purity metallic tin product according to (1), wherein the cross-section includes the central axis of the prism, and in the cross-section perpendicular to the side surface of the prism, the plane whose normal is a line whose angle is within 15 degrees from a line whose angle with the normals of two intersecting faces is equal is defined as the C-plane, and the angular end is processed to achieve a C-chamfer.

[0056] (5) At the angular end, in a cross-section perpendicular to both of the two intersecting faces, For one of the intersecting surfaces, 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 a range of 0.1 to 5 mm. The high-purity metallic tin product described in (1) is obtained by processing the corner end of the other intersecting surface, such that the distance from the tip of the corner end before chamfering to the end of the chamfered surface after chamfering is in the range of 0.1 to 5 mm.

[0057] (6) A vacuum-packed high-purity metallic tin product as described in any of (1) to (5), At least a portion of the chamfered corner edge of a high-purity metallic tin product is covered with a fluorocarbon resin sheet. A vacuum-packed high-purity metallic tin product, in which at least a portion of the chamfered corner ends is covered with a fluorocarbon resin sheet, is vacuum-packed with a vacuum packaging 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) A vacuum-packed high-purity metallic tin product according to (6), wherein the fluorocarbon resin sheet has a thickness of 0.05 to 5.0 mm.

[0059] (9) The vacuum-packed high-purity metallic tin product according to (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. [Examples]

[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 process] As Example 1, a cylindrical tin metal with chamfered corners was manufactured as follows.

[0062] Commercially available solid tin with a purity of 6N (99.9999% by mass, excluding carbon, nitrogen, oxygen, and hydrogen) was prepared. The object 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 the material 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. I confirmed that the workpiece was securely fixed. The chamfering tool was set in the tool post. I confirmed that the chamfering tool had a 45-degree angle. Next, the spindle of the lathe was rotated. Next, the chamfering tool was pressed against the workpiece by hand to perform the chamfering. The C1 chamfer was created 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-edge observation of cylindrical tin metal] The cylindrical tin metal obtained in Example 1 was wrapped in a 0.3 mm thick Nafuron sheet (manufactured by Nichias Corporation), and then sandwiched between 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) from above and below, with the polyethylene surfaces facing inward. The ends were then heat-sealed with a sealer to form a bag, and after wrapping, the opening of the bag 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 cylindrical tin metal, from the top to the bottom, 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 created 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 area corresponding to the surface of the region 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 contamination of foreign matter containing carbon and fluorine at the edges near the boundary with the C-plane on the side surface of the opened high-purity tin sample in which the cylindrical metallic tin of Example 1 was vacuum-packed.

[0070] [Comparative Example 1] [Manufacturing of cylindrical tin metal and R-chamfering process] As Comparative Example 1, a cylindrical tin metal with rounded edges was manufactured as follows. As in Example 1, a block of tin with a purity of 6N was prepared. Similar to Example 1, the cylinder was machined using a lathe. After machining the material into a cylindrical shape, the ends of the cylinder (the boundary between the top and bottom surfaces and the cylindrical side surfaces) were chamfered with an R1 chamfer 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 becomes one-quarter of the circumference of a circle with a radius of 1 mm. This process forms a new surface (R surface) with a cross-section of one-quarter of a circle with a radius of 1 mm 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 secured to the lathe chuck. The origin point was set, and the reference position for machining was determined. For the R1 chamfer, a full-form cutting tool and a contour cutting tool were used. The selection of the tool was made according to the dimensions and shape of the chamfer. The tool post was tilted to perform the R1 chamfer. The tool post had angle markings, and the work was performed by tilting it according to the angle. I moved the cutting tool closer to the workpiece and adjusted the chamfer position. I clamped the rotation of the tool post and performed the machining while feeding the cutting tool. The cutting tool was applied to the workpiece, and a radius of R1 chamfer was performed. Care was taken to avoid creating burrs during the machining process. After the R1 chamfering was completed, the finishing touches were applied. Burrs were removed, resulting in a smooth finish. If burrs remained after chamfering, they were properly removed.

[0072] [Vacuum packaging and end-edge observation of cylindrical tin metal] The cylindrical metallic tin of Comparative Example 1, obtained as described above, was vacuum-packed 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 metallic tin, extending to the upper and lower surfaces. 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 1 mm of 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, from top to bottom, two rows of diagonal lines, or wide diagonal lines that appear as two rows, were observed, indicating the presence of carbon atoms. 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, from top to bottom, two rows of diagonal lines, or diagonal lines that appear as two rows, were observed, indicating the presence of fluorine (F) atoms. 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 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 is observed spreading along the vertical line like a stain. This appears to be near the top of each vertical line if it were considered to be a continuous linear protrusion. Also, near the center of the photograph, a lumpy deposit with a different shape from the deposit along the 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 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 pressed onto the surface of the ends of 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 these predictions based on 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. [Industrial applicability]

[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 surfaces are chamfered (C-chamfered).

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

3. The high-purity metallic tin product according to claim 1, wherein 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 of the two intersecting faces, and the corner end is chamfered.

4. The overall shape of the high-purity tin metal product before chamfering is cylindrical. In a cross-section containing the central axis of a cylinder, the plane whose normal is a line within 15 degrees of the normal to a line that makes equal angles with the normals of two intersecting faces is defined as the C-plane, or Or, The overall shape of the high-purity tin metal product before chamfering is a rectangular prism shape. The high-purity metallic tin product according to claim 1, wherein the cross-section of the prism includes the central axis of the prism, and in the cross-section perpendicular to the side surface of the prism, the plane whose normal is a line whose angle is within 15 degrees from a line whose angle with the normals of two intersecting faces is equal is defined as the C-plane, and the angular end is processed to achieve a C-chamfer.

5. At the angular end, in a cross-section perpendicular to both of the two intersecting faces, For one of the intersecting surfaces, the corner end is processed by setting the distance from the tip of the corner end before chamfering to the end of the chamfered surface after chamfering to a range of 0.1 to 5 mm. The high-purity metallic tin product according to claim 1, wherein the corner end is chamfered by processing the other intersecting surface such that the distance from the tip of the corner end before chamfering to the end of the chamfered surface after chamfering is in the range of 0.1 to 5 mm.

6. A vacuum-packed high-purity metallic tin product according to any one of claims 1 to 5, At least a portion of the chamfered corner edge of a high-purity tin metal product is covered with a fluorocarbon resin sheet. A vacuum-packed high-purity metallic tin product, in which at least a portion of the chamfered corner ends is covered with a fluorocarbon resin sheet, is vacuum-packed with a vacuum packaging 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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