Method for manufacturing writing ball and writing ball obtained thereby

Abstract

The invention relates to a method for manufacturing a writing ball and the writing ball obtained by the method. A method for manufacturing a writing ball includes: a ball forming step of forming a ball including at least a first hard component including a first metal, a second hard component including a second metal, and a binding component; a surface treatment step for performing a mechanical roughening treatment after performing smooth surface finishing on the formed sphere to form a smooth surface; and an etching step for etching the surface-treated sphere using a solution in which the second hard component is dissolved but the first hard component is not dissolved, and performing the mechanical roughening treatment so as to obtain an amount of depression from the smooth surface that is greater than an amount of depression from the smooth surface through the etching step.

Description

[0001] This application is a divisional application of the invention patent application with application number 202280078126.3, application date November 17, 2022 and invention name "Writing ball, manufacturing method of writing ball and ballpoint pen with writing ball". Technical Field

[0002] The present invention relates to a writing ball attached to a ballpoint pen tip, a method for manufacturing the writing ball, and a ballpoint pen equipped with the writing ball. Background Art

[0003] A writing ball, rotatably attached to a ball holder of a ballpoint pen tip, rotates while contacting a paper surface, supplying ink to the paper surface for writing. Ideally, such a writing ball should have a property that the writing feel does not deteriorate even after long-term use. To address this, a writing ball has been proposed that contains at least tungsten carbide and cobalt as a binding component, wherein the ratio of nickel atoms to cobalt atoms within a depth of 1 μm from the ball surface is 0.01% by weight or more and 0.3% by weight or less (see, for example, Patent Document 1).

[0004] In the writing ball disclosed in Patent Document 1, by setting the ratio of nickel atoms to cobalt to 0.01% by weight and below 0.3% by weight, the elution of cobalt, a binding component, is prevented, and the resulting shedding of tungsten carbide is suppressed. This prevents an increase in the surface roughness of the writing ball, thereby maintaining a good writing feel over a long period of time.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-254609 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] Generally speaking, when the surface concavo-convex of the writing ball is increased, the ink load becomes good and the ink outflow is stable, but the problem of increased wear of the ball seat of the ballpoint pen tip occurs. On the other hand, when the concavo-convex of the ball surface is reduced, the wear of the ball seat decreases, but the ink load becomes poor and the ink outflow is unstable. Moreover, when the concavo-convex of the ball surface is small, sometimes seizure occurs. In the writing ball recorded in patent document 1, although the increase of the surface roughness of the writing ball can be suppressed, it is difficult to take into account both the suppression of the wear of the ball seat and the stabilization of the ink outflow.

[0010] Therefore, the object of the present invention is to solve the above-mentioned problems and provide a writing ball that can suppress the wear of the ball seat of a ballpoint pen tip and obtain stable ink flow, a manufacturing method of the writing ball, and a ballpoint pen equipped with the writing ball.

[0011] Solutions for solving problems

[0012] A writing roller ball according to one embodiment of the present invention,

[0013] The sphere comprises at least a first hard component, a second hard component and a bonding component, wherein the first hard component comprises a first metal, the second hard component comprises a second metal,

[0014] The writing ball has: a first outer surface, which is the outermost surface of the sphere where the first hard component is exposed; and a recessed portion, the recessed portion having a second outer surface where the second hard component is exposed and recessed inward from the first outer surface as a bottom surface, and the first outer surface has a smooth surface.

[0015] A method for producing a writing ball according to one embodiment of the present invention includes the following steps:

[0016] a sphere forming step of forming a sphere comprising at least a first hard component, a second hard component, and a bonding component, wherein the first hard component comprises a first metal and the second hard component comprises a second metal;

[0017] a surface treatment step of performing surface treatment on the formed sphere; and

[0018] The etching step uses a solution that dissolves the second hard component but does not dissolve the first hard component to etch the surface-treated sphere.

[0019] A ballpoint pen according to one embodiment of the present invention comprises:

[0020] The writing ball is rotatably attached to the ballpoint pen head of the ball base in a manner that the writing ball is in contact with the ball base.

[0021] Effects of the Invention

[0022] As described above, the present invention can provide a writing ball that can suppress wear of the ball seat of a ballpoint pen tip and achieve stable ink flow, a method for manufacturing the writing ball, and a ballpoint pen equipped with the writing ball. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1A This is a flowchart showing the flow of a method for producing a writing ball according to an embodiment of the present invention, and is a diagram showing a case where only smooth surface finishing is performed as a surface treatment step.

[0024] Figure 1B This is a flowchart showing the flow of a method for manufacturing a writing ball according to an embodiment of the present invention, and is a diagram showing a case where a second surface treatment step as a mechanical roughening treatment is performed after a first surface treatment step as a smooth surface finishing step.

[0025] Figure 2 These are diagrams showing the uneven state of the surface of the writing ball according to the first embodiment of the present invention.

[0026] Figure 3 This is a microscope photograph (SEM) showing the surface of an example corresponding to the first embodiment.

[0027] Figure 4 It is a diagram showing the uneven state of the surface of a writing ball according to a second embodiment of the present invention.

[0028] Figure 5 This is a microscope photograph (SEM) showing the surface of an example corresponding to the second embodiment.

[0029] Figure 6 This is a microscope photograph (SEM) showing the surface of a comparative example.

[0030] Figure 7A This is a diagram showing the uneven state of the surface of the writing ball according to the first embodiment.

[0031] Figure 7B It is a diagram showing the uneven state of the surface of the writing ball according to the second embodiment.

[0032] Figure 7C It is a diagram showing the uneven state of the surface of the writing ball according to the third embodiment. DETAILED DESCRIPTION

[0033] Next, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0034] (Description of the Manufacturing Method of the Writing Ball According to the Embodiment of the Present Invention)

[0035] First, refer to Figure 1A and Figure 1B Next, a method for producing a writing ball according to an embodiment of the present invention will be described. Figure 1A and Figure 1B : is a flowchart showing the process of a method for manufacturing a writing ball according to an embodiment of the present invention. Figure 1A Indicates the case where only smooth surface finishing is performed as a surface treatment process. Figure 1BThis indicates the case where a second surface treatment step as a mechanical roughening treatment is performed after a first surface treatment step as a smooth surface finishing step. Figure 1A and Figure 1B same.

[0036] <Spheroid Formation Process>

[0037] First, a sphere forming process is performed to form a sphere serving as a matrix of a writing ball. The sphere comprises at least a first hard component, a second hard component, and a bonding component, wherein the first hard component comprises a first metal and the second hard component comprises a second metal. Examples of the first metal include titanium (Ti), and examples of the first hard component include titanium carbide (TiC). Examples of the second metal include tungsten (W), and examples of the second hard component include tungsten carbide (WC). Examples of the bonding component include nickel (Ni). Furthermore, in order to improve corrosion resistance, chromium (Cr) is preferably included.

[0038] By mixing and sintering the powders of the aforementioned metal components, a hard sphere serving as the base material for the writing ball can be formed. Predetermined amounts of TiC powder, WC powder, Ni powder, and Cr powder can be mixed and formed using non-pressure sintering methods such as thermal plasma sintering, microwave sintering, and millimeter wave sintering; or pressure sintering methods such as hot pressing, spark plasma sintering, ultrahigh pressure sintering, hot isostatic pressing, and high-pressure gas reaction sintering.

[0039] Examples of powder addition include approximately 8 to 15 wt% TiC powder, 80 to 88 wt% WC powder, 2 to 5 wt% Ni powder, and 2 wt% Cr powder. Thus, when the weight of the tungsten carbide (WC) component is approximately 10 times the weight of the titanium carbide (TiC) component, the volumes of the tungsten carbide (WC) and titanium carbide (TiC) components are similar. By sintering this powder mixture, a WC-TiC-Cr-Ni superhard sphere is obtained.

[0040] Surface treatment process

[0041] Next, a surface treatment step is performed to treat the surface of the spheres formed in the sphere forming step. Figure 1A The case where only smooth surface finishing is performed is shown and Figure 1B The figure shows a case where a first surface treatment step of smooth surface finishing is performed and then a second surface treatment step of mechanical roughening is performed.

[0042] [Smooth surface finishing]

[0043] During the surface treatment process, for example, the sphere can be polished to a smooth surface by grinding with relatively small diamond powder. However, this is not limiting and any other known method can be used for smooth surface finishing. This smooth surface finishing reliably makes the outermost surface of the sphere smooth. In a writing ball formed from this sphere, the smooth surface effectively reduces wear on the ball seat.

[0044] [Mechanical roughening treatment]

[0045] In the second surface treatment step, performed after the first surface treatment step (smooth surface finishing), the sphere can be mechanically roughened, for example, by grinding with diamond powder having a particle size larger than that of the smooth surface finish. However, this is not limiting and mechanical roughening can be performed using any other known method. This mechanical roughening process can form a roughened surface on the outermost surface of the sphere. In a writing ball formed from this sphere, the roughened surface prevents seizure of the ball seat and increases friction with the paper surface, making the ball easier to rotate and improving writing performance.

[0046] It should be noted that the mechanical roughening treatment does not treat the entire smooth surface to become a rough surface, but rather treats the surface to have a mixture of smooth and rough areas, such as numerous scar-like recessed portions distributed on the surface.

[0047] Etching process

[0048] Next, an etching step is performed on the surface-treated spheres. A solution that dissolves the second hard component but not the first hard component is used for etching. For example, if the first hard component is titanium carbide (TiC) and the second hard component is tungsten carbide (WC), etching can be performed using an alkaline solution that dissolves only the tungsten carbide (WC) but not the titanium carbide (TiC).

[0049] As an alkaline solution used for etching, an alkaline solution such as Murakami's reagent can be exemplified. Through this etching step, the writing ball according to the embodiment of the present invention is formed.

[0050] The rough surface formed on the surface of titanium carbide (TiC) remains as it is, while the rough surface formed on the surface of tungsten carbide (WC) becomes a deeper rough surface through the etching process.

[0051] As described above, by using an etching process that dissolves the second hard component but not the first hard component, the second hard component can be dissolved while maintaining the outermost surface of the sphere exposed by the first hard component, forming a recessed portion recessed from the outermost surface. This exposed outermost surface of the first hard component can suppress wear and seizure of the ball seat of the ballpoint pen tip to which the writing ball is attached. Furthermore, since ink can be retained in the recessed portion, ink flow is stabilized, which also helps lubricate the ball seat. Consequently, a writing ball with excellent writing performance and a prolonged lifespan of the ball seat can be reliably manufactured.

[0052] It should be noted that, in the above method, the etching step is performed after the surface treatment step, but the present invention is not limited thereto. Conversely, the surface treatment step may also be performed after the etching step.

[0053] (Writing Roller Ball According to the First Embodiment of the Present Invention)

[0054] Next, refer to Figure 2 and Figure 3 The writing ball according to the first embodiment manufactured by the above-mentioned manufacturing method will be described. Figure 2 These are diagrams showing the uneven state of the surface of the writing ball according to the first embodiment of the present invention. Figure 2 This figure is drawn based on a microscopic photograph of a cross section of a writing ball, and the concave and convex portions are highlighted. Figure 3 This is a microscope photograph (SEM / magnification 10000 times) showing the surface of an example corresponding to the first embodiment. Figure 1A The manufacturing method shown corresponds to a writing ball manufactured by performing only smooth surface finishing in the surface treatment step.

[0055] like Figure 2 As shown, the writing ball 10A of the first embodiment has: a first outer surface 2A, which is the outermost surface of the sphere where the first hard component is exposed; and a recess 6A, which has a second outer surface 4A as the bottom surface where the second hard component is exposed and is recessed inward from the first outer surface 2A.

[0056] exist Figure 2In the embodiment, the first outer surface 2A of the outermost surface that has been smoothed has an arithmetic mean height Sa (ISO25178) of less than 10 nm, preferably a surface roughness of less than 5 nm. In addition, by an etching process, a recess 6A is formed with a maximum height Sz (measured by NewView manufactured by Zygo Corporation based on ISO25178) that is recessed inwardly within a range of 5 nm to 0.5 μm. As an example of the width dimension of the recess 6A, an example of 0.1 μm to 10 μm can be shown. The second outer surface 4A constituting the bottom surface of the recess 6A is recessed inwardly from the first outer surface 2A by a range of 5 nm to 0.5 μm.

[0057] exist Figure 3 In the microscope photograph, the darker portion represents the first outer surface 2A, the outermost surface, and the whiter portion represents the inwardly recessed second outer surface 4A. As described above, in the writing ball 10A of this embodiment, the volumes of the titanium carbide (TiC) and tungsten carbide (WC) components are approximately equal. Therefore, the first outer surface 2A, where titanium carbide (TiC) is exposed as the first hard component, and the second outer surface 4A, where tungsten carbide (WC) is exposed as the second hard component, are roughly evenly distributed. During sintering to form the sphere that serves as the base material for the writing ball 10A, the TiC powder, WC powder, and Ni powder, a binder component, are uniformly mixed. Consequently, the recesses 6A, with the second outer surface 4A as the bottom, are uniformly distributed throughout the entire outermost surface formed by the first outer surface 2A.

[0058] from Figure 2 、 Figure 3 As can be seen, the outermost first outer surface 2A, surrounded by the recess 6A with the second outer surface 4A as its bottom, has a width measured in micrometers, providing a sufficiently smooth surface in contact with the ball seat. This effectively prevents wear and galling of the ball seat. Furthermore, the recess 6A with the second outer surface 4A as its bottom has a width and depth measured in micrometers, allowing it to hold a sufficient amount of ink.

[0059] Here, as a comparative example, a microscope photograph (SEM / magnification 10000 times) of the surface of a conventional WC-Co-Cr writing ball is shown. Figure 6 Even with etching, WC-Co-Cr writing balls only produce uniform surface roughness. Therefore, even with various etching and surface treatments, the size of the unevenness will only change. Therefore, increasing the surface roughness of a writing ball increases wear on the ball seat, while decreasing it can lead to poor ink retention.

[0060] As described above, the writing ball 10A of the first embodiment of the present invention is a sphere comprising at least a first hard component (TiC), a second hard component (WC), and a binding component (Ni), wherein the first hard component (TiC) comprises a first metal (Ti), and the second hard component (WC) comprises a second metal (W). The writing ball 10A has: a first outer surface 2A, which is the outermost surface of the sphere where the first hard component is exposed; and a recess 6A, the recess 6A having as its bottom a second outer surface 4A, which is recessed inward from the first outer surface 2A and where the second hard component is exposed.

[0061] The outermost first outer surface 2A suppresses wear and seizure of the ball seat of the ballpoint pen tip to which the writing ball 10A is attached. Furthermore, since ink is retained in the recess 6A, whose bottom is the second outer surface 4A, ink flow is stabilized, which also contributes to lubrication of the ball seat. Thus, a writing ball 10A is provided that suppresses wear of the ball seat and ensures stable ink flow.

[0062] In particular, when the first outer surface 2A is a smooth surface, wear and seizure of the ball seat can be more effectively suppressed.

[0063] When the first hard component is titanium carbide (TiC) and the second hard component is tungsten carbide (WC), for example, by etching with an alkaline solution, a first outer surface 2A as the outermost surface and a second outer surface 4A recessed inward from the outermost surface can be reliably formed.

[0064] Furthermore, since at least nickel (Ni) is contained as a bonding component, the first hard component (TiC) and the second hard component (WC) are firmly bonded together, and thus a high-strength writing ball 10A is obtained.

[0065] However, the bonding component is not limited to the above components, and for example, cobalt (Co) and the like can be exemplified.

[0066] (Writing Roller Ball According to Second Embodiment of the Present Invention)

[0067] Next, refer to Figure 4 and Figure 5 Next, a description will be given of the writing ball according to the second embodiment manufactured by the above-mentioned manufacturing method. Figure 4 It is a diagram showing the uneven state of the surface of a writing ball according to a second embodiment of the present invention. Figure 4 This figure is drawn based on a microscopic photograph of a cross section of a writing ball, with concavities and convexities highlighted. Figure 5 This is a microscope photograph (SEM / magnification 10000 times) showing the surface of an example corresponding to the second embodiment. Figure 1BThe manufacturing method shown corresponds to a writing ball manufactured by performing a first surface treatment step of smooth surface finishing and then performing a second surface treatment step of mechanical roughening.

[0068] like Figure 4 As shown, the writing ball 10B of the second embodiment also has: a first outer surface 2B, which is the outermost surface of the sphere where the first hard component (TiC) is exposed; and a recess 6B, with a second outer surface 4B exposed where the second hard component (WC) is recessed inward from the first outer surface 2B as the bottom surface.

[0069] exist Figure 4 In the first outer surface 2B, the outermost surface that has undergone the first and second surface treatment steps, a smooth surface 2B1 and a rough surface (hereinafter referred to as the "first rough surface") 2B2 are mixed. More specifically, the first outer surface 2B has a surface texture such that countless scar-like recessed portions (first rough surface) 2B2 are distributed on the smooth surface 2B1. The smooth surface 2B1 has a surface roughness with an arithmetic mean height Sa (ISO25178) of less than 10 nm, preferably less than 5 nm. The first rough surface 2B2 has a surface roughness with a maximum height Sz (measured using a NewView manufactured by Zygo Corporation based on ISO25178) of greater than 10 nm and less than 5 μm.

[0070] Then, the etching step forms recesses 6B recessed inward with a maximum height Sz (measured by NewView manufactured by Zygo Corporation in accordance with ISO 25178) ranging from 5 nm to 0.5 μm. The width of each recess 6B may be approximately 0.1 μm to 10 μm.

[0071] The second outer surface 4B constituting the bottom surface of the recess 6B has: a non-convex-concave surface 4B1, which is formed by recessing the smooth surface formed in the first surface treatment process and the second surface treatment process through an etching process; and a rough surface (hereinafter referred to as the "second rough portion") 4B2, which is formed by further recessing the recess of the rough surface formed in the first surface treatment process and the second surface treatment process through an etching process.

[0072] like Figure 4 As shown, if the amount of depression of the non-concave-convex surface 4B1 relative to the smooth surface 2B1 of the first outer surface 2B is set to D1, it is 5 nm or more and 0.5 μm or less. On the other hand, if the amount of depression of the first rough surface 2B2 relative to the smooth surface 2B1 of the first outer surface 2B is set to D2, it is 10 nm or more and 5 μm or less.

[0073] Therefore, there is a relationship of D1<D2.

[0074] Thus, after the etching process, a rough surface will remain on the bottom surface of the recessed portion 6B, thereby increasing the amount of ink retained on the second outer surface 4B. Furthermore, the etching solution dissolves the second rough surface portion 4B2, which is more deeply recessed, thereby further retaining the second outer surface 4B.

[0075] exist Figure 5 In the microscope photograph of FIG, the dark portion represents first outer surface 2B, which is the outermost surface, and the white portion represents second outer surface 4B, which is recessed inward. Similarly to the above, recesses 6B, each having second outer surface 4B as its bottom, are uniformly distributed throughout the entire outermost surface formed by first outer surface 2B.

[0076] Depend on Figure 4 、 Figure 5 As can be seen, the outermost first outer surface 2B, enclosed by the recess 6B with the second outer surface 4B as its bottom, has a width dimension measured in micrometers. Therefore, the roughness of the first outer surface 2B prevents wear and seizure of the ball seat and increases friction with the paper surface, facilitating ball rotation and improving writing performance. Furthermore, the recess 6B with the second outer surface 4B as its bottom has a width and depth measured in micrometers, allowing it to hold a sufficient amount of ink.

[0077] As described above, the writing ball 10B of the second embodiment is also a sphere containing at least a first hard component (TiC), a second hard component (WC), and a binding component (Ni), wherein the first hard component (TiC) contains a first metal (Ti), and the second hard component (WC) contains a second metal (W). The writing ball 10B has: a first outer surface 2B, which is the outermost surface of the sphere where the first hard component is exposed; and a recessed portion 6B, the bottom surface of which is a second outer surface 4B recessed inward from the first outer surface 2B where the second hard component is exposed.

[0078] In the second embodiment, as in the first embodiment described above, the outermost first outer surface 2B suppresses wear of the ball seat of the ballpoint pen tip to which the writing ball 10B is attached. Furthermore, the second outer surface 4B retains ink in the recess, thereby stabilizing ink flow and contributing to lubrication of the ball seat and preventing galling. Thus, a writing ball 10B is provided that suppresses wear of the ball seat and provides stable ink flow.

[0079] In particular, when the first outer surface 2B further includes the first rough surface portion 2B2, wear and seizure of the ball seat are suppressed, and friction with the paper surface is increased, so that the ball easily rotates and writing performance can be improved.

[0080] (Distribution of concave portions)

[0081] In the above embodiment, the volumes of the titanium carbide (TiC) and tungsten carbide (WC) components of the writing balls 10A and 10B are approximately equal, and the outermost surface formed by the first outer surfaces 2A and 2B and the recesses 6A and 6B with the second outer surfaces 4A and 4B as their bottom surfaces are approximately equal. However, the distribution of the outermost surface formed by the first outer surfaces 2A and 2B and the recesses 6A and 6B with the second outer surfaces 4A and 4B as their bottom surfaces may be modified depending on the properties of the ink and the intended use. An example of modifying the distribution of the recesses 6A and 6B is described below.

[0082] <Adjustment of particle size>

[0083] In the writing balls 10A and 10B of the above-described embodiment, the distribution of recesses 6A and 6B formed during the etching process can be adjusted by adjusting the particle sizes of titanium carbide (TiC) as the first hard component and tungsten carbide (WC) as the second hard component. Basically, increasing the particle size of titanium carbide (TiC) as the first hard component increases the proportion of the outermost surface formed by first outer surfaces 2A and 2B, while increasing the particle size of tungsten carbide (WC) as the second hard component increases the proportion of recesses 6A and 6B whose bottom surfaces are located on second outer surfaces 4A and 4B.

[0084] To achieve both reduced wear of the ball seat and stable ink flow, it is preferable to adjust the particle sizes of titanium carbide (TiC), the first hard component, and tungsten carbide (WC), the second hard component, so that the volume ratio of titanium carbide (TiC) to tungsten carbide (WC) falls within a range of 3:7 to 7:3. This achieves a balanced distribution of recesses 6A and 6B. In particular, varying the particle size of tungsten carbide (WC), the second hard component, effectively alters the distribution of the recesses, enabling the provision of a writing ball suited to the intended application.

[0085] <First to Third Examples>

[0086] Next, the writing balls of the first to third embodiments, which were actually produced by varying the particle size of tungsten carbide (WC) as the second hard component, will be described. Figure 7A 1 is a diagram showing the concavo-convex state of the surface of the writing ball of the first embodiment. Figure 7B 1 is a diagram showing the concavo-convex state of the surface of the writing ball of the second embodiment. Figure 7C It is a diagram showing the uneven state of the surface of the writing ball according to the third embodiment.

[0087] The writing balls 10A, 10C, and 10D of the first, second, and third embodiments are all made of the above-mentioned Figure 1A Specifically, first, a powder of titanium carbide (TiC) as a first hard component, a powder of tungsten carbide (WC) as a second hard component, and Ni powder and Cr powder as binder components are mixed and sintered to form a superhard sphere serving as the base material for the writing ball.

[0088] The same powder of titanium carbide (TiC) as the first hard component was used in Examples 1 to 3. Meanwhile, powders of tungsten carbide (WC) as the second hard component had different particle sizes in Examples 1 to 3.

[0089] In the first embodiment, tungsten carbide (WC) powder with a particle size dA of 1 μm to 2 μm was used. In the second embodiment, tungsten carbide (WC) powder with a particle size dC of 0.5 μm to 1 μm, which is smaller (approximately half) than that of the first embodiment, was used. In the third embodiment, powder with a particle size of 2 μm to 4 μm, which is larger (approximately twice) than that of the first embodiment, was used. It should be noted that the same Ni powder and Cr powder, which serve as the binder components, were used in the first through third embodiments.

[0090] Next, a surface treatment step is performed to smooth the surface of the sphere formed in the sphere forming step.

[0091] Next, the surface-treated spheres are etched with an alkaline solution. This etching process dissolves tungsten carbide (WC), the second hard component, while leaving the outermost surface of the sphere exposed, while maintaining titanium carbide (TiC), the first hard component. This forms a recessed portion recessed from the outermost surface.

[0092] Therefore, if Figure 7A As shown, a writing ball 10A of the first embodiment is obtained, which has a first outer surface 2A as the outermost surface of the sphere where the first hard component is exposed, and a second outer surface 4A where the second hard component is exposed and is recessed inward from the first outer surface 2A as the bottom surface. Figure 7A The writing ball 10A of the first embodiment shown is Figure 2 The writing ball 10A of the first embodiment shown above is substantially the same.

[0093] In addition, if Figure 7BAs shown, a writing ball 10C of the second embodiment is obtained, which has a first outer surface 2C as the outermost surface of the sphere where the first hard component is exposed, and a second outer surface 4C where the second hard component is exposed and is recessed inward from the first outer surface 2C as the bottom surface. Figure 7C As shown, a writing ball 10D of the third embodiment is obtained, which has a first outer surface 2D as the outermost surface of the sphere where the first hard component is exposed, and a recess 6D with a second outer surface 4D, where the second hard component is exposed and is recessed inward from the first outer surface 2D, as the bottom surface.

[0094] In the spherical body forming process, titanium carbide (TiC) powder, tungsten carbide (WC) powder, and Ni powder and Cr powder as binding components are uniformly mixed and then sintered. Therefore, titanium carbide (TiC) particles, Ni particles, and Cr particles are basically present between adjacent tungsten carbide (WC) particles. Therefore, it is believed that the recesses 6A, 6C, and 6D formed by dissolving the tungsten carbide (WC) particles by the etching solution have width dimensions LA, LC, and LD corresponding to the particle sizes dA, dC, and dD of the tungsten carbide (WC) particles, respectively.

[0095] The particle size dC of the tungsten carbide (WC) particles of the second embodiment is approximately half the particle size dA of the tungsten carbide (WC) particles of the first embodiment. Therefore, the width dimension LC of the recess 6C of the second embodiment is approximately half the width dimension LA of the recess 6A of the first embodiment. Furthermore, the particle size dD of the tungsten carbide (WC) particles of the third embodiment is approximately twice the particle size dA of the tungsten carbide (WC) particles of the first embodiment. Therefore, the width dimension LD of the recess 6D of the third embodiment is approximately twice the width dimension LA of the recess 6A of the first embodiment.

[0096] As described above, in the first embodiment, the outermost smooth surface, first outer surface 2A, effectively prevents wear and seizure of the ball seat of the ballpoint pen tip to which the writing ball 10A is attached. Furthermore, ink is retained in recess 6A, whose bottom is located on second outer surface 4A. This stabilizes the flow of ink and contributes to lubrication of the ball seat.

[0097] In the second embodiment, a finer concavo-convex shape can be obtained compared to the first embodiment, so the smooth surface serving as the first outer surface 2C is more finely continuous. This provides a writing ball 10C that can slide stably against random movement.

[0098] In the third embodiment, a rougher concavoconvex shape can be obtained compared to the first embodiment, so the intervals between the smooth surfaces of the first outer surface 2D are wider. This provides a writing ball 10D that improves writing performance by exerting a peak effect to bite the paper surface.

[0099] Thus, the recesses 6A, 6C, 6D have width dimensions LA, LC, LD corresponding to the particle sizes dA, dC, dD of the particles constituting the second hard component (tungsten carbide (WC)), thereby providing writing balls 10A, 10C, 10D having performance suitable for their intended use.

[0100] As described above, a sphere forming step is performed to form a sphere containing at least a first hard component (titanium carbide (TiC)), a second hard component (tungsten carbide (WC)), and a binding component (Ni, Cr); a surface treatment step is performed to treat the surface of the formed sphere; and an etching step is performed to etch the surface-treated sphere using a solution that dissolves the second hard component but does not dissolve the first hard component. Writing balls 10A, 10C, and 10D according to first to third embodiments are prototyped, wherein the first hard component (titanium carbide (TiC)) contains a first metal and the second hard component (tungsten carbide (WC)) contains a second metal.

[0101] At this time, the manufactured writing balls 10A, 10C, and 10D have a first outer surface 2A, 2C, and 2D as the outermost surface of the sphere, where the first hard component (titanium carbide (TiC)) is exposed, and a recess 6A, 6C, and 6D with a second outer surface 4A, 4C, and 4D exposed as the second hard component (tungsten carbide (WC)) and recessed inward from the first outer surface 2A, 2C, and 2D as the bottom surface. By making the particle sizes dA, dC, and dD of the particles constituting the second hard component (tungsten carbide (WC)) used in the sphere forming process different, the width dimensions LA, LC, and LD of the recess 6A, 6C, and 6D of the manufactured writing balls 10A, 10C, and 10D can be made different.

[0102] By making the particle sizes dA, dC, and dD of the particles constituting the second hard component (tungsten carbide (WC)) different, writing balls 10A, 10C, and 10D having recesses 6A, 6C, and 6D with width dimensions LA, LC, and LD that exhibit performance appropriate to the application can be reliably manufactured.

[0103] It should be noted that the particle sizes of the particles constituting the first hard component and the particles constituting the second hard component are not limited to the values ​​described above, and particles of any other particle size can be used. In addition, in the above description, only a smooth surface finishing treatment is performed as a surface treatment step, but the same effects can be achieved by further performing a mechanical roughening treatment.

[0104] As described above, by adjusting the particle sizes of the first hard component (TiC) and the second hard component (WC), the distribution of the areas retaining the outermost surfaces 2A and 2B of the writing balls 10A and 10B and the recesses 6A and 6B can be reliably adjusted. This allows for the reliable manufacture of writing balls 10A and 10B having desired properties.

[0105] <Adjustment of the Ratio of the First Hard Component to the Second Hard Component>

[0106] As described above, when the weight of the tungsten carbide (WC) component is about 10 times the weight of the titanium carbide (TiC) component, the volumes of the tungsten carbide (WC) component and the titanium carbide (TiC) component become close to each other. Figure 3 and Figure 5 The state distribution shown.

[0107] Here, the distribution of recesses 6A and 6B formed by the etching process can be adjusted by adjusting the weight ratio of titanium carbide (TiC) as the first hard component and tungsten carbide (WC) as the second hard component. Basically, increasing the weight ratio of titanium carbide (TiC) as the first hard component increases the proportion of the outermost surface formed by first outer surfaces 2A and 2B, while increasing the weight ratio of tungsten carbide (WC) as the second hard component increases the proportion of recesses 6A and 6B formed by second outer surfaces 4A and 4B.

[0108] To achieve both ball seat wear reduction and ink outflow stabilization, the weight of tungsten carbide (WC), the second hard component, is preferably controlled within a range of 7 to 13 times the weight of titanium carbide (TiC), the first hard component. By maintaining this range, the volume ratio of titanium carbide (TiC) to tungsten carbide (WC) falls within a range of 3:7 to 7:3, resulting in a balanced distribution of recesses 6A and 6B.

[0109] By adjusting the weight ratio of the first hard component (TiC) to the second hard component (WC), the distribution of the areas retaining the outermost surfaces 2A and 2B and the recesses 6A and 6B of the writing balls 10A and 10B can be reliably adjusted. This allows for the reliable manufacture of writing balls 10A and 10B having desired characteristics.

[0110] (Ballpoint Pen Equipped with the Writing Ball of the Present Embodiment)

[0111] The writing balls 10A and 10B of the embodiment described above are rotatably attached to the ball seat of the ballpoint pen tip. By providing a ballpoint pen tip with such writing balls 10A and 10B attached, a ballpoint pen with excellent writing performance and high reliability, with minimal wear and seizure of the ball seat, can be provided.

[0112] The writing balls 10A and 10B of the present embodiment can be applied to ballpoint pen tips using various inks including oil-based ink, water-based ink, and gel ink.

[0113] While the embodiments of the present invention have been described, the disclosure may be varied in structural details, and combinations and changes in order of elements in the embodiments may be implemented without departing from the scope and spirit of the claimed invention.

[0114] Description of reference numerals:

[0115] 2A, 2B, 2C, 2D: first outer surface;

[0116] 2B1: smooth surface;

[0117] 2B2: first rough face;

[0118] 4A, 4B, 4C, 4D: second outer surface;

[0119] 4B1: non-convex and concave surface;

[0120] 4B2: second rough face;

[0121] 6A, 6B, 6C, 6D: concave parts;

[0122] 10A, 10B, 10C, 10D: Writing balls.

Claims

1. A method for manufacturing a writing ball, comprising the following steps: The sphere forming step forms a sphere comprising at least a first hard component, a second hard component and a bonding component, wherein: The first hard component comprises a first metal, and the second hard component comprises a second metal; a surface treatment step of mechanically roughening the sphere after smooth surface finishing to form a smooth surface; as well as an etching step, wherein a solution that dissolves the second hard component but does not dissolve the first hard component is used to etch the surface-treated sphere. The mechanical roughening treatment is performed to obtain a recess amount from the smooth surface that is larger than a recess amount from the smooth surface obtained by the etching step.

2. The method for producing a writing ball according to claim 1, wherein: The manufactured writing ball has a first outer surface, which is the outermost surface of the sphere where the first hard component is exposed; and a recessed portion, the recessed portion having a second outer surface, where the second hard component is exposed and recessed inward from the first outer surface, as a bottom surface. By varying the particle diameters of the particles constituting the second hard component used in the spherical body forming step, the width dimensions of the recesses of the produced writing balls can be varied.

3. The method for producing a writing ball according to claim 2, wherein: The width of the concave portion is 0.1 to 10 μm.

4. The method for producing a writing ball according to any one of claims 1 to 3, wherein: The particle sizes of the first hard component and the second hard component are adjusted so that the volume ratio of the first hard component to the second hard component is in the range of 3:7 to 7:3, thereby adjusting the distribution of the recesses formed by the etching step.

5. A writing ball obtained by the method for producing a writing ball according to any one of claims 1 to 3, wherein: The first hard component is titanium carbide, ie, TiC, and the second hard component is tungsten carbide, ie, WC.

6. The writing roller ball according to claim 5, wherein: At least nickel is contained as the bonding component.

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