Ballpoint pen tip, ballpoint pen refill, and ballpoint pen

Abstract

A ballpoint pen tip (40) comprises a ball (42) and a tip body (50) that holds the ball (42). The tip body (50) has a ball holding chamber (52) that holds the ball (42) and a crimping part (60) that prevents the ball (42) from coming out of the ball holding chamber (52). The ball holding chamber (52) includes a ball receiving base (56) that receives writing pressure from the ball (42) during writing. The outer peripheral surface (65) of the tip body (50) and the ball receiving base (56) have a nitride layer (70) formed thereon, and a thickness (T3) of the nitride layer (70) on the front end surface (63) of the crimping part (60) is greater than a thickness (T4) of the nitride layer (70) on the ball receiving base (56).

Description

Ballpoint pen tips, ballpoint pen refills and ballpoint pens

[0001] The present invention relates to a ballpoint pen tip, a ballpoint pen refill, and a ballpoint pen.

[0002] Conventionally, a technique for nitriding the surface of a ballpoint pen tip has been known. JPH02-160597A discloses a ballpoint pen tip that has been nitrided during its manufacturing process. In the technique disclosed in JPH02-160597A, a metal capillary tube is nitrided, and then the inner surface of the tip of the nitrided metal capillary tube is cut to form a ball holding chamber, a ball seat, an ink guide hole, and the like. Finally, a ball is inserted into the ball holding chamber, and a crimping process is performed in which the peripheral edge of the tip of the ball holding chamber is pressed inward and bent. This process has the advantage of suppressing the generation of burrs during cutting, allowing for stable crimping.

[0003] The ball holding chamber is configured to allow the ball to move slightly axially within the ball holding chamber. The ball holding chamber includes a ball receiving seat located behind the ball. In this case, when writing, the ball moves backward due to writing pressure, and the ball receiving seat receives writing pressure from the ball. If the ball rotates while in contact with the ball receiving seat during writing, the ball receiving seat may wear. When the ball receiving seat wears, the amount of retraction of the ball during writing gradually increases. This increases the gap between the ball and the crimped portion during writing, increasing the amount of ink ejected and resulting in thicker handwriting.

[0004] Furthermore, when writing, the tip of the crimped portion may come into contact with the writing surface, such as paper. In this case, repeated writing may cause the tip of the crimped portion to wear. When the tip of the crimped portion wears, the strength of the crimped portion decreases, and there is a risk that the crimped portion will deform when a large force is applied to the crimped portion due to a collision with another object, for example.

[0005] The present invention has been made in consideration of these points, and has as its object to suppress wear of the ball receiving seat and suppress a decrease in strength of the tip of the crimped portion.

[0006] The ballpoint pen tip of this embodiment is: [1] A ballpoint pen tip comprising a ball and a tip body that holds the ball, wherein the tip body has a ball holding chamber that holds the ball and a crimped portion that prevents the ball from escaping from the ball holding chamber, the ball holding chamber includes a ball receiving seat that receives writing pressure from the ball when writing, a nitride layer is formed on the outer peripheral surface of the tip body and the ball receiving seat, and the thickness of the nitride layer on the front end surface of the crimped portion is greater than the thickness of the nitride layer on the ball receiving seat.

[0007] The ballpoint pen tip of this embodiment is the ballpoint pen tip described in [1], wherein [2] the thickness of the nitride layer on the front end surface is greater than the thickness of the nitride layer on the outer surface of the tip body in the region from the rear end of the crimped portion to 0.2 mm rearward.

[0008] The ballpoint pen tip of this embodiment is a ballpoint pen tip described in [1] or [2], in which [3] the thickness of the nitride layer on the inner surface of the ball holding chamber is smaller than the thickness of the nitride layer on the outer surface of the tip body in the region from the rear end of the crimped portion to 0.2 mm rearward.

[0009] The ballpoint pen tip of this embodiment is a ballpoint pen tip according to any one of [1] to [3], wherein [4] the thickness of the nitride layer of the ball receiving seat is smaller than the thickness of the nitride layer on the inner surface of the ball holding chamber.

[0010] The ballpoint pen refill of this embodiment is a ballpoint pen refill comprising: [5] the ballpoint pen tip according to any one of [1] to [4]; and an ink reservoir tube for accommodating ink.

[0011] The ballpoint pen of this embodiment is a ballpoint pen equipped with the ballpoint pen refill described in [6] [5].

[0012] According to the present invention, it is possible to suppress wear of the ball receiving seat and also suppress a decrease in strength of the tip of the crimped portion.

[0013] Fig. 1 is a diagram for explaining one embodiment of the present invention, and is a vertical cross-sectional view showing an example of a ballpoint pen incorporating a ballpoint pen refill having a ballpoint pen tip. Fig. 2 is a vertical cross-sectional view showing the ballpoint pen tip. Fig. 3 is a vertical cross-sectional view showing an enlarged view of the tip of the ballpoint pen tip. Fig. 4 is a diagram showing an enlarged view of the part marked IV in Fig. 3. Fig. 5 is a diagram showing an example of a method for manufacturing a ballpoint pen tip. Fig. 6 is a diagram showing an example of a method for manufacturing a ballpoint pen tip. Fig. 7 is a diagram showing an example of a method for manufacturing a ballpoint pen tip.

[0014] An embodiment of the present invention will now be described with reference to the drawings. In the drawings attached to this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of ease of illustration and understanding.

[0015] Furthermore, terms used in this specification that specify shapes, geometric conditions, and their degrees, such as "parallel," "orthogonal," and "identical," as well as values ​​of lengths and angles, are not to be construed as being bound by strict meanings, but rather as including a range within which similar functions can be expected.

[0016] In this specification, the direction in which the central axis A of the ballpoint pen 10 extends (longitudinal direction, up and down direction in a longitudinal cross section) is referred to as the axial direction da, the direction perpendicular to the central axis A is referred to as the radial direction, and the direction along the circumference around the central axis A is referred to as the circumferential direction. Also, along the axial direction da, the side that comes close to the surface to be written on, such as paper, when writing is referred to as the front, and the side that is away from the surface to be written on is referred to as the rear. In other words, the pen tip side is the front, and the side opposite the pen tip is the rear.

[0017] 1 is a diagram illustrating one embodiment of the present invention, and is a cross-sectional view showing an example of a ballpoint pen 10. In this embodiment, an example will be described in which the ballpoint pen 10 is a so-called side-knock type ballpoint pen, but the ballpoint pen 10 is not limited to this. The ballpoint pen 10 includes a barrel 20, a ballpoint pen refill 30 incorporated in the barrel 20, a retraction mechanism 12 for causing the tip of the ballpoint pen refill 30 to protrude and retract from the barrel 20, a friction member 14 for rubbing handwriting, and a clip 16.

[0018] The barrel tube 20 includes a front barrel 21, a rear barrel 25 connected to the front barrel 21, a rear end cap 28 attached to the rear end of the rear barrel 25, and a grip member 29 disposed around the outer surface of the front barrel 21. The front barrel 21 has an opening 22 at its front end through which the tip of the ballpoint pen tip 40 of the ballpoint pen refill 30 can be inserted and removed, a first engagement portion 23 on the inner surface of the front region, and a male thread portion 24 on the outer surface of the rear region. The rear barrel 25 has a female thread portion 26 on the inner surface of the front region. The front barrel 21 and the rear barrel 25 are joined together by threading the male thread portion 24 of the front barrel 21 with the female thread portion 26 of the rear barrel 25. The rear end cap 28 is fitted onto the rear end of the rear barrel 25. The grip member 29 is intended to be held with the user's fingers when writing with the ballpoint pen 10. The front axle 21, the rear axle 25 and the rear end cap 28 are made of, for example, resin, and the grip member 29 is made of, for example, rubber, elastomer or the like.

[0019] In this embodiment, the clip 16 functions as an operating part that is operated by the user when knocking. The barrel 20 is provided with a slide hole 27 that extends in the axial direction da and penetrates the wall of the barrel 20. The slide hole 27 is provided across the rear region of the rear barrel 25 and the front end of the rear end cap 28. In the illustrated example, the clip 16 extends from inside the barrel 20 to outside the barrel 20 through the slide hole 27. The range of movement of the clip 16 in the axial direction da can be defined by the front and rear ends of the slide hole 27.

[0020] The ballpoint pen refill 30 is housed retractably within the barrel 20. The ballpoint pen refill 30 includes an ink reservoir 32 that contains ink, a tip holder 34 disposed in front of the ink reservoir 32, and a ballpoint pen tip 40 disposed in front of the tip holder 34. In the example shown in FIG. 1 , the rear end of the tip holder 34 is inserted into the front end of the ink reservoir 32, and the rear end of the ballpoint pen tip 40 is inserted into the front end of the tip holder 34. The ballpoint pen refill 30 has a second engagement portion 36 provided on the outer surface of the front region. In the example shown, the second engagement portion 36 is provided on the outer surface of the tip holder 34. When the ballpoint pen refill 30 is assembled, the second engagement portion 36 of the ballpoint pen refill 30 is located rearward of the first engagement portion 23 of the front barrel 21, and a coil spring 18 is disposed in a compressed state between the first engagement portion 23 and the second engagement portion 36. As a result, the coil spring 18 biases the ballpoint pen refill 30 rearward.

[0021] As the ink, any ink that can be used for a ballpoint pen can be used without any particular limitation. As an example, a thermochromic ink can be used as the ink. The thermochromic ink may be a reversible thermochromic ink. As an example of the reversible thermochromic ink, a heat-discoloring type reversible thermochromic ink that changes from a colored state to a colorless state when heated and changes from the colorless state back to a colored state when cooled can be used.

[0022] The friction member 14 of this embodiment is a member for rubbing the ink marks. If the ink is thermochromic, the friction member 14 may be a friction member that rubs against a writing surface, such as paper, on which handwriting has been formed, thereby heating the ink that forms the handwriting by frictional heat. In this case, the friction member 14 may be formed, for example, from an elastic material. The friction member 14 may be fixed to the rear end cap 28 by press-fitting, engagement, screwing, fitting, adhesive, two-color molding, or the like. Alternatively, if the ink is not thermochromic, the friction member 14 may be, for example, a member that scrapes off the handwriting by rubbing against the writing surface, such as paper, on which handwriting has been formed. This may be a sand eraser, for example.

[0023] The retraction mechanism 12 is a mechanism for alternately switching the ballpoint pen 10 between a knock state in which the tip of the ballpoint pen tip 40 protrudes from the opening 22 of the front barrel 21 and a non-knock state in which the tip of the ballpoint pen tip 40 retracts from the opening 22. FIG. 1 shows the ballpoint pen 10 in the knock state. In the non-knock state, the elastic force of the coil spring 18 urges the ballpoint pen refill 30 rearward, causing the tip of the ballpoint pen tip 40 to retract from the opening 22. When a user pushes and slides the clip 16 forward with their finger, the ballpoint pen refill 30 moves forward, causing the tip of the ballpoint pen tip 40 to protrude forward from the opening 22. Even when the user releases their finger from the clip 16, the ballpoint pen refill 30 maintains a state in which the tip of the ballpoint pen tip 40 protrudes forward from the opening 22. When the user again pushes and slides the clip 16 forward with his / her finger, the ballpoint pen refill 30 moves forward by a small distance. When the user releases his / her finger from the clip 16 or releases the forward pressure on the clip 16, the resilient force of the coil spring 18 urges the ballpoint pen refill 30 rearward, and the tip of the ballpoint pen tip 40 retracts from the opening 22. The retraction mechanism 12 that realizes such a retraction operation is well known, so a detailed description will be omitted. As an example, the retraction mechanism disclosed in Japanese Patent Application Laid-Open No. 2012-6315 can be used as the retraction mechanism 12.

[0024] The ballpoint pen tip 40 will be further described with reference to Figures 2 to 4. Figure 2 is a vertical cross-sectional view showing the ballpoint pen tip 40. Figure 3 is a vertical cross-sectional view showing an enlarged view of the tip of the ballpoint pen tip 40. Figure 4 is an enlarged view of the portion marked IV in Figure 3.

[0025] The ballpoint pen tip 40 includes a ball 42 and a tip body 50 that holds the ball 42. The diameter of the ball 42 may be greater than 0 mm and less than 2.0 mm. The diameter of the ball 42 may be greater than 0.2 mm and less than 1.6 mm. The diameter of the ball 42 may be greater than 0.4 mm and less than 1.0 mm. The tip body 50 functions to guide the ink contained in the ink reservoir 32 to the ball 42. When writing, the user presses the ball 42 against a writing surface, such as paper, and moves it across the writing surface, causing the ball 42 to rotate on the writing surface. This causes the ink adhering to the ball 42 to be transferred to the writing surface. The transferred ink then forms a handwriting on the writing surface. Note that the ink transferred to the writing surface may also penetrate into the writing surface.

[0026] The tip body 50 has a ball holding chamber 52, an ink flow hole 58, and a crimped portion 60. The ball holding chamber 52 has the function of holding the ball 42, as well as the function of retaining ink within the ball holding chamber 52 and adhering the ink to the ball 42. The ball holding chamber 52 is composed of a hole formed from the front end of the tip body 50 toward the rear. The ball holding chamber 52 is configured to allow the ball 42 to move slightly in the axial direction within the ball holding chamber 52. The inner surface 53 of the ball holding chamber 52 includes a side surface 54 and a ball receiving seat 56. The central axis of the tip body 50 coincides with the central axis A of the ballpoint pen 10. Therefore, in this specification, the central axis of the tip body 50 is sometimes referred to as the central axis A.

[0027] The side surface 54 may be a cylindrical surface having a central axis extending in the axial direction da. The side surface 54 also includes the inner surface 61 of the crimping portion 60. The central axis of the side surface 54 may coincide with the central axis A. The ball receiving seat 56 is located in the rear portion of the ball holding chamber 52. Within the ball holding chamber 52, the ball 42 is slightly movable in the front-to-rear direction. The ball receiving seat 56 is the surface with which the ball 42 contacts when the ball 42 is located at its rearmost position within the ball holding chamber 52. The ball receiving seat 56 receives writing pressure from the ball 42 when writing with the ballpoint pen 10. The ball receiving seat 56 may have a shape complementary to a portion of the outer surface of the ball 42. In other words, the ball receiving seat 56 may have a shape that forms a portion of a spherical surface.

[0028] The ink flow hole 58 is located between the ball holding chamber 52 and the tip holder 34, and connects the ball holding chamber 52 and the tip holder 34. The ink flow hole 58 extends linearly along the axial direction da. The ink flow hole 58 functions as a flow path for ink from the tip holder 34 to the ball holding chamber 52. The central axis of the ink flow hole 58 coincides with the central axis A of the tip body 50.

[0029] The crimping portion 60 is a portion provided at the tip of the tip body 50 that is deformed inward (toward the central axis A). The crimping portion 60 has the function of preventing the ball 42 from escaping from the ball holding chamber 52. The crimping portion 60 is formed by crimping the tip of the tip body 50 so that it is deformed inward (toward the central axis A) after the ball 42 is placed in the ball holding chamber 52. This causes the ball 42 to be held in the ball holding chamber 52.

[0030] In this embodiment, a nitride layer 70 is formed at least on the outer peripheral surface 65 of the tip body 50 and the ball seat 56 of the ball holding chamber 52. In this embodiment, a nitride layer 70 is also formed on the inner surface 53 of the ball holding chamber 52. The nitride layer 70 is formed by a nitriding process in which nitrogen atoms are diffused from the surface of the tip body 50 into the tip body 50 to form a compound containing nitrogen atoms and metal atoms constituting the tip body 50. Metals that can bond with nitrogen to form a nitride layer include chromium (Cr), aluminum (Al), molybdenum (Mo), titanium (Ti), and vanadium (V). Therefore, the tip body 50 is preferably formed from a metallic material containing at least one of chromium, aluminum, molybdenum, titanium, and vanadium. Stainless steel, for example, may be used as such a metallic material.

[0031] In this embodiment, as described below, the nitriding treatment is performed after the ball 42 is assembled to the chip body 50. However, it is preferable that the nitride layer 70 not be formed on the surface of the ball 42 during this nitriding treatment. Therefore, the ball 42 is preferably made of a material that does not contain any of chromium, aluminum, molybdenum, titanium, or vanadium, a material with extremely low contents of chromium, aluminum, molybdenum, titanium, or vanadium, or a material that contains chromium, aluminum, molybdenum, titanium, or vanadium in a stable state. Examples of stable chromium, aluminum, molybdenum, titanium, and vanadium include chromium carbide, vanadium carbide, and alumina. From this perspective, the ball 42 may be made of a material such as tungsten carbide, silicon carbide, silicon nitride, alumina, or zirconia.

[0032] As the nitriding treatment, gas nitriding treatment, gas soft nitriding treatment, salt bath soft nitriding treatment, etc. can be used. For example, the nitride layer 70 may be formed by gas nitriding treatment. Gas nitriding treatment can be performed, for example, by bringing ammonia gas into contact with the surface of the tip body 50 heated to about 400°C to 600°C. Since nitriding treatment can be performed at a lower temperature than other heat treatments such as quenching, deformation of the tip body 50 during treatment is suppressed.

[0033] Nitriding treatment improves the hardness of the surface of the tip body 50. Therefore, the wear resistance of the surface of the tip body 50 can be improved. Here, there is a positive correlation between the thickness of the nitride layer 70 and the hardness of the surface on which the nitride layer 70 is formed. In other words, the thicker the nitride layer 70, the harder the surface on which the nitride layer 70 is formed.

[0034] The outer peripheral surface 65 of the tip body 50 may come into contact with other components during manufacturing or use of the ballpoint pen 10. Forming the nitride layer 70 on the outer peripheral surface 65 improves the wear resistance of the outer peripheral surface 65. Therefore, when the outer peripheral surface 65 comes into contact with other components during manufacturing of the tip body 50 or use of the ballpoint pen 10, it is possible to prevent scratches or wear on the outer peripheral surface 65.

[0035] As described above, the ball holding chamber 52 is configured to allow the ball 42 to move slightly axially within the ball holding chamber 52. In this case, when writing, the ball 42 moves rearward due to writing pressure, and the ball receiving seat 56 receives writing pressure from the ball 42. If the ball 42 rotates while in contact with the ball receiving seat 56 during writing, the ball receiving seat 56 may wear. As the ball receiving seat 56 wears, the amount of retraction of the ball 42 during writing gradually increases. As a result, the gap between the ball 42 and the crimped portion 60 increases during writing, increasing the amount of ink ejected and resulting in thicker handwriting.

[0036] To solve this problem, in this embodiment, a nitride layer 70 is formed on the ball seat 56. This increases the hardness of the ball seat 56. Therefore, the wear resistance of the ball seat 56 can be improved. This reduces wear on the ball seat 56 and prevents changes in the amount of retraction of the ball 42 during writing. This stabilizes the amount of ink ejected during writing, allowing writing to be continued with the same handwriting width even when writing repeatedly.

[0037] In this embodiment, the thickness T1 of the nitride layer 70 on the inner surface 53 of the ball-holding chamber 52 is smaller than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the tip body 50. The thickness T2 of the nitride layer 70 on the outer peripheral surface 65 is measured in a region R extending 0.2 mm rearward from the rear end 62 of the crimping portion 60. Therefore, the thickness T1 of the nitride layer 70 on the inner surface 53 of the ball-holding chamber 52 is smaller than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the tip body 50 in the region R extending 0.2 mm rearward from the rear end 62 of the crimping portion 60. Furthermore, the thickness T1 of the nitride layer 70 on the inner surface 53 of the ball-holding chamber 52 is measured on the side surface 54 of the inner surface 53. Therefore, it can be said that the thickness T1 of the nitride layer 70 on the side surface 54 of the ball-holding chamber 52 is smaller than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the tip body 50 in the region R extending 0.2 mm rearward from the rear end 62 of the crimping portion 60.

[0038] Forming the nitride layer 70 on the inner surface 53 of the ball holding chamber 52 can suppress wear of the inner surface 53. In particular, forming the nitride layer 70 on the inner surface 61 of the crimped portion 60 can suppress wear of the inner surface 61 of the crimped portion 60. This can suppress the ball 42 from slipping out of the ball holding chamber 52. Furthermore, when the thicknesses T1 and T2 satisfy the above relationship, the hardness of the inner surface 53 of the ball holding chamber 52 is less than the hardness of the outer peripheral surface 65 of the tip body 50. In this case, it is possible to effectively suppress damage such as scratches to the ball 42 when the ball 42 and the inner surface 53 of the ball holding chamber 52 come into contact with each other.

[0039] The crimped portion 60 may come into contact with a surface to be written on, such as a piece of paper, when writing with the ballpoint pen 10. Therefore, repeated writing may cause wear at the tip of the crimped portion 60. When the tip of the crimped portion 60 wears, the strength of the crimped portion 60 decreases, and there is a risk that the crimped portion 60 may be deformed when a large force acts on the crimped portion 60 due to a collision with another object, for example.

[0040] To solve this problem, in this embodiment, the thickness T3 of the nitride layer 70 on the front end surface 63 of the crimped portion 60 is greater than the thickness T4 of the nitride layer 70 on the ball receiving seat 56. In this case, since the nitride layer 70 on the front end surface 63 of the crimped portion 60 has a sufficient thickness T3, it is possible to prevent the tip of the crimped portion 60 from wearing down due to repeated writing. This makes it possible to maintain the strength of the crimped portion 60 and to prevent deformation of the crimped portion 60 when a large force is applied to the crimped portion 60 due to a collision with another object, for example.

[0041] Furthermore, when the nitride layer 70 on the front end surface 63 of the crimped portion 60 has a sufficient thickness T3, a nitride layer 70 having a sufficient thickness is also formed on the inner surface 61 of the crimped portion 60. In this case, even when writing is repeated, it is possible to prevent the inner surface 61 of the crimped portion 60 from being worn down due to friction with the ball 42. This makes it possible to prevent the ball 42 from slipping out of the ball holding chamber 52.

[0042] As described above, the ball receiving seat 56 receives writing pressure from the ball 42 when writing with the ballpoint pen 10. Generally, the surface roughness of the nitride layer 70 is greater than the roughness of a surface without the nitride layer 70. Therefore, if the nitride layer 70 of the ball receiving seat 56 is thick, the rough surface of the nitride layer 70 may hinder the rotation of the ball 42 when writing with the ballpoint pen 10. In this case, the smooth writing feel of the ballpoint pen 10 may be impaired. In this embodiment, the thickness T4 of the nitride layer 70 of the ball receiving seat 56 is smaller than the thickness T3 of the nitride layer 70 of the front end surface 63 of the crimping portion 60. Also, in this embodiment, the thickness T4 of the nitride layer 70 of the ball receiving seat 56 is smaller than the thickness T1 of the nitride layer 70 of the inner surface 53 of the ball holding chamber 52. In particular, the thickness T4 of the nitride layer 70 of the ball receiving seat 56 is smaller than the thickness T1 of the nitride layer 70 of the side surface 54 of the ball holding chamber 52. In this case, the surface roughness of the nitride layer 70 in the ball receiving seat 56 can be reduced. This prevents the surface of the nitride layer 70 from interfering with the rotation of the ball 42 when writing with the ballpoint pen 10. Therefore, the smooth writing feel of the ballpoint pen 10 is prevented from being impaired.

[0043] Furthermore, in this embodiment, the thickness T3 of the nitride layer 70 on the front end surface 63 of the crimped portion 60 is greater than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the tip body 50 in the region R extending 0.2 mm rearward from the rear end 62 of the crimped portion 60. In this case, the hardness of the front end surface 63 of the crimped portion 60 is greater than the hardness of the outer peripheral surface 65 in the region R. This improves the wear resistance of the crimped portion 60, thereby preventing the crimped portion 60 from coming into contact with the writing surface and wearing down.

[0044] The thicknesses T1 to T4 of the nitride layer 70 are all measured in a direction perpendicular to the surface of the nitride layer 70. The thicknesses T1 to T4 of the nitride layer 70 are measured in accordance with JIS G0562:1993, "Method for Measuring the Depth of Nitride Layers in Steel." To measure the thicknesses T1 to T4 of the nitride layer 70, the ballpoint pen tip 40 to be measured is first cut along a plane including the central axis A. After precision polishing the cut surface, the cut surface is etched using Marble reagent. Since only the portions other than the nitride layer 70 are etched and the nitride layer 70 itself is not etched, the nitride layer 70 and the portions other than the nitride layer 70 are visually distinguishable from each other. Therefore, the thickness of the nitride layer 70 at each portion can be measured by observing the cut surface with a microscope. The microscope used was the lens and video unit of a Mitutoyo Corporation Micro Vickers Hardness Tester HM-200. When measuring the thicknesses T1 to T4 of the nitride layer 70, the thickness of the nitride layer 70 is measured at five points that are sufficiently spaced apart from each other so as to reflect the overall thickness of the area being measured, and the arithmetic mean value is used as the thickness T1 to T4 of the nitride layer 70 at that area.

[0045] Next, an example of a method for manufacturing the ballpoint pen tip 40 of this embodiment will be described with reference to FIGS.

[0046] First, as shown in Fig. 5, the tip body 50 is prepared. At this stage, the crimped portion 60 is not formed on the tip body 50. Next, as shown in Fig. 6, the ball 42 is inserted from the front into the ball holding chamber 52. Thereafter, as shown in Fig. 7, the tip of the tip body 50 is deformed inward (toward the central axis A) to form the crimped portion 60.

[0047] The ball 42 and the entire tip body 50 are then subjected to a nitriding treatment. The nitriding treatment can be performed, for example, by gas nitriding. The gas nitriding treatment can be performed, for example, by contacting ammonia gas with the surface of the tip body 50 heated to approximately 400°C to 600°C. In this embodiment, the tip body 50 is formed of a metal material containing at least one of chromium, aluminum, molybdenum, titanium, and vanadium. Such a metal material is, for example, stainless steel. By performing the nitriding treatment, nitrogen atoms diffuse from the surface of the tip body 50 into the tip body 50, and atoms of chromium, aluminum, molybdenum, titanium, or vanadium contained in the tip body 50 bond with nitrogen atoms to form nitrides on the surface of the tip body 50. As a result, a nitride layer 70 containing nitrides is formed on the surface of the tip body 50. On the other hand, in this embodiment, ball 42 is formed from a material that does not contain any of chromium, aluminum, molybdenum, titanium, or vanadium, a material with an extremely low content of chromium, aluminum, molybdenum, titanium, or vanadium, or a material that contains chromium, aluminum, molybdenum, titanium, or vanadium in a stable state. Examples of such materials include tungsten carbide, silicon carbide, silicon nitride, alumina, and zirconia. In this case, even if nitriding treatment is performed, nitride layer 70 is not formed on the surface of ball 42.

[0048] With the ball 42 assembled to the tip body 50, the gas flow rate passing through the interior of the tip body 50 is reduced. That is, by performing the gas nitriding process with the ball 42 assembled to the tip body 50, the amount of ammonia gas flowing into the interior of the tip body 50 is suppressed. As a result, the thickness of the nitride layer 70 formed on the inner surface of the tip body 50 is smaller than the thickness of the nitride layer 70 formed on the outer peripheral surface 65 of the tip body 50. As a result, the thickness T1 of the nitride layer 70 on the inner surface 53 of the ball holding chamber 52 is smaller than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the tip body 50.

[0049] When the tip of the tip body 50 is deformed to form the crimped portion 60, the thickness of the crimped portion 60 becomes thinner overall. In this case, when gas nitriding is performed, nitrogen atoms enter the front end of the crimped portion 60 from three directions: the radially outer side, the radially inner side, and the front side. Therefore, the thickness of the nitride layer 70 at the front end of the crimped portion 60 becomes greater than the thickness of the nitride layer 70 on the remaining outer peripheral surface 65. As a result, the thickness T3 of the nitride layer 70 on the front end surface 63 of the crimped portion 60 becomes greater than the thickness T4 of the nitride layer 70 on the ball seat 56. Furthermore, the thickness T3 of the nitride layer 70 on the front end surface 63 of the crimped portion 60 becomes greater than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the tip body 50 in region R.

[0050] During the gas nitriding process, by positioning the chip body 50 so that the ball 42 faces sideways or downward, a gap is created between the ball 42 and the ball seat 56. Ammonia gas flows into this gap, forming a nitride layer 70 on the ball seat 56. Pressing the ball 42 against the ball seat 56 during the gas nitriding process prevents ammonia gas from flowing between the ball 42 and the ball seat 56, preventing further formation of the nitride layer 70. This allows the thickness of the nitride layer 70 on the ball seat 56 to be controlled. Specifically, the thickness T4 of the nitride layer 70 on the ball seat 56 can be made smaller than the thickness T3 of the nitride layer 70 on the front end surface 63 of the crimping portion 60. Furthermore, the thickness T4 of the nitride layer 70 on the ball seat 56 can be made smaller than the thickness T1 of the nitride layer 70 on the inner surface 53 of the ball-holding chamber 52.

[0051] The ballpoint pen tip 40 of this embodiment is a ballpoint pen tip 40 comprising a ball 42 and a tip body 50 that holds the ball 42, wherein the tip body 50 has a ball holding chamber 52 that holds the ball 42 and a crimping portion 60 that prevents the ball 42 from escaping from the ball holding chamber 52, the ball holding chamber 52 including a ball receiving seat 56 that receives the writing pressure from the ball 42 when writing, and a nitride layer 70 is formed on the outer peripheral surface 65 of the tip body 50 and the ball receiving seat 56, and the thickness T3 of the nitride layer 70 on the front end surface 63 of the crimping portion 60 is greater than the thickness T4 of the nitride layer 70 on the ball receiving seat 56.

[0052] The ballpoint pen refill 30 of this embodiment includes the ballpoint pen tip 40 described above and an ink reservoir tube 32 that contains ink.

[0053] The ballpoint pen 10 of this embodiment includes the ballpoint pen refill 30 described above.

[0054] According to the ballpoint pen tip 40, ballpoint pen refill 30, and ballpoint pen 10, the nitride layer 70 is formed on the ball receiving seat 56, thereby improving the hardness of the ball receiving seat 56. This improves the wear resistance of the ball receiving seat 56. This reduces wear on the ball receiving seat 56 and prevents changes in the amount of retraction of the ball 42 during writing. This stabilizes the amount of ink ejected during writing, allowing writing to be continued with the same writing width even when writing repeatedly.

[0055] Furthermore, in the ballpoint pen tip 40, ballpoint pen refill 30, and ballpoint pen 10, the thickness T3 of the nitride layer 70 on the front end surface 63 of the crimped portion 60 is greater than the thickness T4 of the nitride layer 70 on the ball receiving seat 56, so that the nitride layer 70 on the front end surface 63 of the crimped portion 60 has a sufficient thickness T3. This makes it possible to prevent the tip of the crimped portion 60 from wearing down due to repeated writing. This makes it possible to maintain the strength of the crimped portion 60, and to prevent the crimped portion 60 from deforming when a large force acts on the crimped portion 60 due to a collision with another object, for example.

[0056] Furthermore, when the nitride layer 70 on the front end surface 63 of the crimped portion 60 has a sufficient thickness T3, a nitride layer 70 having a sufficient thickness is also formed on the inner surface 61 of the crimped portion 60. In this case, even when writing is repeated, it is possible to prevent the inner surface 61 of the crimped portion 60 from being worn down due to friction with the ball 42. This makes it possible to prevent the ball 42 from slipping out of the ball holding chamber 52.

[0057] In the ballpoint pen tip 40 of this embodiment, the thickness T3 of the nitride layer 70 on the front end surface 63 is greater than the thickness of the nitride layer 70 on the outer surface 65 of the tip body 50 in the region R extending from the rear end 62 of the crimped portion 60 to 0.2 mm rearward.

[0058] According to this ballpoint pen tip 40, the hardness of the front end surface 63 of the crimped portion 60 is greater than the hardness of the outer peripheral surface 65 in the region R. This improves the wear resistance of the crimped portion 60. This makes it possible to prevent the crimped portion 60 from coming into contact with the writing surface and becoming worn.

[0059] In the ballpoint pen tip 40 of this embodiment, the thickness T1 of the nitride layer 70 on the inner surface 53 of the ball holding chamber 52 is smaller than the thickness T2 of the nitride layer 70 on the outer surface 65 of the tip body 50 in the region R extending 0.2 mm rearward from the rear end 62 of the crimping portion 60.

[0060] In this ballpoint pen tip 40, the nitride layer 70 is formed on the inner surface 53 of the ball holding chamber 52, thereby suppressing wear of the inner surface 53. In particular, the nitride layer 70 is formed on the inner surface 61 of the crimped portion 60, thereby suppressing wear of the inner surface 61 of the crimped portion 60. This prevents the ball 42 from slipping out of the ball holding chamber 52. Furthermore, when the thicknesses T1 and T2 satisfy the above relationship, the hardness of the inner surface 53 of the ball holding chamber 52 is less than the hardness of the outer peripheral surface 65 of the tip body 50. In this case, damage such as scratches to the ball 42 can be effectively suppressed when the ball 42 and the inner surface 53 of the ball holding chamber 52 come into contact with each other.

[0061] In the ballpoint pen tip 40 of this embodiment, the thickness T4 of the nitride layer 70 of the ball receiving seat 56 is smaller than the thickness T1 of the nitride layer 70 of the inner surface 53 of the ball holding chamber 52.

[0062] According to this ballpoint pen tip 40, the surface roughness of the nitride layer 70 in the ball receiving seat 56 can be reduced. This prevents the surface of the nitride layer 70 from interfering with the rotation of the ball 42 when writing with the ballpoint pen 10. This prevents the smooth writing feel of the ballpoint pen 10 from being impaired.

Claims

1. A ballpoint pen tip comprising a ball and a chip body for holding the ball, wherein the chip body has a ball holding chamber for holding the ball and a caulking portion for preventing the ball from coming out of the ball holding chamber, the ball holding chamber includes a ball receiving seat for receiving the writing pressure from the ball during writing, a nitride layer is formed on the outer peripheral surface of the chip body and the ball receiving seat, and the thickness of the nitride layer on the front end surface of the caulking portion is larger than the thickness of the nitride layer on the ball receiving seat.

2. The ballpoint pen tip according to claim 1, wherein the thickness of the nitride layer on the front end surface is larger than the thickness of the nitride layer on the outer peripheral surface of the chip body in a region from the rear end of the caulking portion to 0.2 mm rearward.

3. The ballpoint pen tip according to claim 1, wherein the thickness of the nitride layer on the inner surface of the ball holding chamber is smaller than the thickness of the nitride layer on the outer peripheral surface of the chip body in a region from the rear end of the caulking portion to 0.2 mm rearward.

4. The ballpoint pen tip according to claim 1, wherein the thickness of the nitride layer on the ball receiving seat is smaller than the thickness of the nitride layer on the inner surface of the ball holding chamber.

5. A ballpoint pen refill comprising the ballpoint pen tip according to any one of claims 1 to 4 and an ink storage cylinder for storing ink.

6. A ballpoint pen comprising the ballpoint pen refill according to claim 5.

Images