Ballpoint pen tip, ballpoint pen refill, and ballpoint pen

Abstract

To restrain a ballpoint pen tip from coming off a tip holder.SOLUTION: A ballpoint pen tip 40 comprises a ball 42, and a tip body 50 for holding the ball 42. The tip body 50 has a ball embracing chamber 52 for embracing the ball 42. The ball embracing chamber 52 includes a ball retainer seat 56 that is subject to writing pressure from the ball 42 during writing. A nitrided layer 70 is formed on an outer peripheral surface 65 of a back end 67 of the tip body 50 and the ball retainer seat 56.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Conventionally, a technique of nitriding the surface of a ball pen tip has been known. Patent Document 1 discloses a ball pen tip that has been nitrided in the manufacturing process. In the technique disclosed in Patent Document 1, a metal thin tube is nitrided, and then, cutting is performed on the inner surface of the tip portion of the nitrided metal thin tube to form a ball holding chamber, a ball pedestal, an ink guiding hole, and the like. Finally, a caulking process is performed in which a ball is inserted into the ball holding chamber and the peripheral edge portion at the tip of the ball holding chamber is pressed inward and bent. By going through such steps, there is an advantage that burrs are suppressed from occurring during cutting and the caulking process can be performed stably.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The ball pen tip is held by a tip holder. For example, the ball pen tip is held by the tip holder when the rear end portion of the ball pen tip is inserted forward into a hole formed in the front end portion of the tip holder. At this time, if the fitting force between the rear end portion of the ball pen tip and the tip holder is insufficient, the ball pen tip may come off from the tip holder.

[0005] The present invention has been made in consideration of such points, and an object thereof is to suppress the ball pen tip from coming off from the tip holder.

Means for Solving the Problem

[0006] The ball pen tip of this embodiment is [1] a ball pen tip comprising a ball and a tip body for holding the ball, wherein the tip body has a ball holding chamber for holding the ball, the ball holding chamber includes a ball receiving seat for receiving the writing pressure from the ball during writing, and a nitride layer is formed on the outer peripheral surface of the rear end portion of the tip body and on the ball receiving seat.

[0007] The ball pen tip of this embodiment is [2] the ball pen tip according to [1], wherein the thickness of the nitride layer of the ball receiving seat is smaller than the thickness of the nitride layer of the outer peripheral surface of the rear end portion.

[0008] The ball pen tip of this embodiment is [3] wherein the tip body further has a caulking portion for preventing the ball from coming out of the ball holding chamber, and the ball pen tip according to [1] or [2], wherein the thickness of the nitride layer of the front end surface of the caulking portion is larger than the thickness of the nitride layer of the outer peripheral surface of the rear end portion.

[0009] The ball pen refill of this embodiment is [4] a ball pen refill comprising the ball pen tip according to any one of [1] to [3] and an ink containing cylinder for containing ink.

[0010] The ball pen of this embodiment is [5] a ball pen comprising the ball pen refill according to [4].

Advantages of the Invention

[0011] According to the present invention, it is possible to suppress the ball pen tip from coming off the tip holder.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings attached to this specification, for the convenience of illustration and easy understanding, the scale, the aspect ratio in the vertical and horizontal directions, etc. are appropriately changed and exaggerated from those of the actual object.

[0014] Also, with regard to terms used in this specification for specifying shapes, geometric conditions, and their degrees, such as terms like "parallel", "orthogonal", "identical", etc., and values of lengths and angles, etc., they shall not be restricted to strict meanings, and shall be interpreted to include ranges that can be expected to have similar functions.

[0015] In this specification, the direction in which the central axis A of the ballpoint pen 10 extends (the longitudinal direction, the vertical direction in the longitudinal sectional view) is defined as the axial direction da, the direction orthogonal to the central axis A is defined as the radial direction, and the direction along the circumference around the central axis A is defined as the circumferential direction. Also, along the axial direction da, when writing, the side closer to the writing surface such as paper is defined as the front, and the side spaced apart from the writing surface is defined as the rear. That is, the pen tip side is the front, and the side opposite to the pen tip is the rear.

[0016] FIG. 1 is a view for explaining an embodiment of the present invention, and is a sectional view showing an example of the ballpoint pen 10. In the present embodiment, an example in which the ballpoint pen 10 is a so-called side knock type ballpoint pen will be described, but the ballpoint pen 10 is not limited thereto. The ballpoint pen 10 includes a barrel 20, a ballpoint pen refill 30 incorporated in the barrel 20, a projecting and retracting mechanism 12 for causing the tip of the ballpoint pen refill 30 to project and retract from the barrel 20, a friction member 14 for frictionally contacting the writing, and a clip 16.

[0017] The barrel 20 includes a front shaft 21, a rear shaft 25 connected to the front shaft 21, a rear end cap 28 attached to the rear end portion of the rear shaft 25, and a grip member 29 disposed to surround the outer surface of the front shaft 21. The front shaft 21 has an opening 22 provided at the front end through which the tip of the ballpoint pen tip 40 of the ballpoint pen refill 30 can project and retract, a first engaging portion 23 provided on the inner surface of the front region, and a male screw portion 24 provided on the outer surface of the rear region. The rear shaft 25 has a female screw portion 26 provided on the inner surface of the front region. By screwing the male screw portion 24 of the front shaft 21 and the female screw portion 26 of the rear shaft 25, the front shaft 21 and the rear shaft 25 are coupled to each other. The rear end cap 28 is fitted to the rear end portion of the rear shaft 25. The grip member 29 is intended to be grasped by a finger when the user writes with the ballpoint pen 10. The front shaft 21, the rear shaft 25, and the rear end cap 28 are formed of, for example, resin, and the grip member 29 is formed of, for example, rubber, elastomer, or the like.

[0018] In this embodiment, the clip 16 functions as an operation part operated by the user during knocking. The shaft cylinder 20 is provided with a slide hole 27 that extends in the axial direction da and penetrates the wall part of the shaft cylinder 20. The slide hole 27 is provided across the rear region of the rear shaft 25 and the front end part of the rear end cap 28. In the illustrated example, the clip 16 extends from inside the shaft cylinder 20 to outside the shaft cylinder 20 through the slide hole 27. The movement range of the clip 16 in the axial direction da can be defined by the front end and the rear end of the slide hole 27.

[0019] The ballpoint pen refill 30 is accommodated in the shaft cylinder 20 so as to be able to project and retract. The ballpoint pen refill 30 includes an ink storage cylinder 32 that stores ink, a tip holder 34 disposed in front of the ink storage cylinder 32, and a ballpoint pen tip 40 disposed in front of the tip holder 34. In this embodiment, the rear end part of the tip holder 34 is inserted into the front end part of the ink storage cylinder 32, and the rear end part 67 of the ballpoint pen tip 40 is inserted into the front hole part 38 of the tip holder 34 (see FIG. 2). The ballpoint pen refill 30 has a second engaging part 36 provided on the outer surface of the front region. In the illustrated example, the second engaging part 36 is provided on the outer surface of the tip holder 34. In a state where the ballpoint pen refill 30 is assembled, the second engaging part 36 of the ballpoint pen refill 30 is located behind the first engaging part 23 of the front shaft 21, and a coil spring 18 is disposed in a compressed state between the first engaging part 23 and the second engaging part 36. Thereby, the coil spring 18 biases the ballpoint pen refill 30 rearward.

[0020] As the ink, ink that can be used for a ballpoint pen can be used without particular limitation. As an example, thermochromic ink can be used as the ink. The thermochromic ink may be reversible thermochromic ink. As the reversible thermochromic ink, for example, a heat-decoloring type reversible thermochromic ink that changes from a colored state to a decolored state by heating and changes from the decolored state to the colored state by cooling can be used.

[0021] The friction member 14 of this embodiment is a member for rubbing the handwriting made with ink. When the ink is thermochromic ink, the friction member 14 can be a friction member having a function of rubbing the writing surface such as paper on which the handwriting is formed and heating the ink forming the handwriting by frictional heat. In this case, the friction member 14 can be formed of, for example, an elastic material. The friction member 14 can be fixed to the rear end cap 28 by press-fitting, engagement, screwing, fitting, adhesion, two-color molding, or the like. Also, when the ink does not have thermochromic properties, the friction member 14 can be, for example, a member for scraping off the handwriting by rubbing the writing surface such as paper on which the handwriting is formed, such as eraser rubber.

[0022] The projecting and retracting 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 shaft 21 and a non-knock state in which the tip of the ballpoint pen tip 40 retracts into the opening 22. In FIG. 1, the ballpoint pen 10 is shown in the knock state. In the non-knock state, due to the elastic force of the coil spring 18, the ballpoint pen refill 30 is biased rearward, and thereby, the tip of the ballpoint pen tip 40 retracts from the opening 22. When the user presses and slides the clip 16 forward with a finger, the ballpoint pen refill 30 moves forward, and the tip of the ballpoint pen tip 40 protrudes forward from the opening 22. Even when the user releases the finger from the clip 16, the ballpoint pen refill 30 maintains the state in which the tip of the ballpoint pen tip 40 protrudes forward from the opening 22. When the user presses and slides the clip 16 forward again with a finger, the ballpoint pen refill 30 moves forward by a minute distance. When the user releases the finger from the clip 16 or relaxes the forward pressing force on the clip 16, due to the elastic force of the coil spring 18, the ballpoint pen refill 30 is biased rearward, and the tip of the ballpoint pen tip 40 retracts from the opening 22. Since the projecting and retracting mechanism 12 for realizing such a projecting and retracting operation is well-known, a detailed description thereof is omitted. As an example, as the projecting and retracting mechanism 12, it is possible to use the projecting and retracting mechanism disclosed in Japanese Patent Application Laid-Open No. 2012-6315.

[0023] With reference to FIGS. 2 to 5, the ball pen tip 40 will be further described. FIG. 2 is a longitudinal sectional view showing the ball pen tip 40 and the tip holder 34. FIG. 3 is a longitudinal sectional view showing an enlarged tip end portion of the ball pen tip 40. FIG. 4 is an enlarged view showing the portion marked IV in FIG. 3. FIG. 5 is a longitudinal sectional view showing an enlarged connection portion between the ball pen tip 40 and the tip holder 34.

[0024] The tip holder 34 includes an ink flow hole 35, an inner flange portion 37, and a front hole portion 38. The ink flow hole 35 is located between the ink storage cylinder 32 and the ball pen tip 40 and communicates the ink storage cylinder 32 and the ball pen tip 40. The ink flow hole 35 extends along the axial direction da. The tip holder 34 functions as a flow path for ink from the ink storage cylinder 32 to the ball pen tip 40. The central axis of the ink flow hole 35 coincides with the central axis A of the ball pen 10.

[0025] The inner flange portion 37 is a protruding portion that protrudes inward from the inner peripheral surface of the tip holder 34. In the example shown in FIGS. 2 and 5, the inner flange portion 37 extends annularly along the circumferential direction. A through hole extending in the axial direction da is formed inside the inner flange portion 37. This through hole constitutes a part of the ink flow hole 35.

[0026] The front hole portion 38 accommodates a rear end portion 67 of a chip body 50 (to be described later) of the ball pen tip 40 and has a function of holding the ball pen tip 40. The front hole portion 38 is located in front of the inner flange portion 37. The front hole portion 38 opens at the front end of the tip holder 34 and extends linearly along the axial direction da.

[0027] 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 exceed 0 mm and be 2.0 mm or less. The diameter of the ball 42 may be 0.2 mm or more and 1.6 mm or less. The diameter of the ball 42 may be 0.4 mm or more and 1.0 mm or less. The tip body 50 has a function of guiding the ink accommodated in the ink storage cylinder 32 to the ball 42. When writing, as the user moves the ball 42 on the writing surface such as paper while pressing the ball 42 against the writing surface, the ball 42 rotates on the writing surface. Thereby, the ink adhering to the ball 42 is transferred to the writing surface. Then, a writing trace is formed on the writing surface by the transferred ink. Note that the ink transferred to the writing surface may penetrate into the writing surface.

[0028] The tip body 50 has a ball holding chamber 52, an ink flow hole 58, a caulking portion 60, and a rear end portion 67. The ball holding chamber 52 has a function of holding the ball 42 and also has a function of holding ink in the ball holding chamber 52 and attaching the ink to the ball 42. The ball holding chamber 52 is composed of a hole formed from the front end to the rear of the tip body 50. The ball holding chamber 52 is configured such that the ball 42 can 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 may also be denoted as the central axis A.

[0029] 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 caulking portion 60. The central axis of the side surface 54 may coincide with the central axis A. The ball seat 56 is located in the rear portion of the ball holding chamber 52. Inside the ball holding chamber 52, the ball 42 is slightly movable in the front-rear direction. The ball seat 56 is a surface that the ball 42 contacts when the ball 42 is located at the most rearward position inside the ball holding chamber 52. The ball seat 56 receives the writing pressure from the ball 42 when writing with the ballpoint pen 10. The ball seat 56 may have a complementary shape to a part of the outer surface of the ball 42. That is, the ball seat 56 may have a shape that constitutes a part of a spherical surface.

[0030] The ink flow hole 58 is located between the ball holding chamber 52 and the tip holder 34 and communicates the ball holding chamber 52 and the tip holder 34. In particular, the rear end portion of the ink flow hole 58 communicates with the ink flow hole 35 of 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.

[0031] The caulking portion 60 is a portion provided by deforming inward (toward the central axis A side) at the tip of the tip body 50. The caulking portion 60 has a function of preventing the ball 42 from coming out of the ball holding chamber 52. The caulking portion 60 is formed by caulking the tip of the tip body 50 so as to deform inward (toward the central axis A side) after the ball 42 is disposed in the ball holding chamber 52. Thereby, the ball 42 is held in the ball holding chamber 52.

[0032] The rear end portion 67 is a portion intended to be inserted into the front hole portion 38 of the chip holder 34. In the example shown in FIGS. 2 and 5, a stepped portion 68 is formed on the outer peripheral surface 65 of the chip body 50. In the illustrated example, the rear end portion 67 is a portion behind the stepped portion 68. Note that the present invention is not limited to this, and the chip body 50 may not have the stepped portion 68. In that case, the portion of the chip body 50 that is inserted into the front hole portion 38 of the chip holder 34 is the rear end portion 67. In the present embodiment, the outer diameter of the rear end portion 67 is slightly larger than the inner diameter of the front hole portion 38. Therefore, the rear end portion 67 is press-fitted into the front hole portion 38, and the rear end portion 67 and the front hole portion 38 are fitted together. In a state where the rear end portion 67 and the front hole portion 38 are fitted together, the frictional force acting between the outer peripheral surface 65 of the rear end portion 67 and the inner peripheral surface of the front hole portion 38 suppresses the ball pen tip 40 from coming out of the chip holder 34.

[0033] In the present embodiment, a nitride layer 70 is formed on at least the outer peripheral surface 65 of the rear end portion 67 of the chip body 50 and the ball receiving seat 56. Also, in the present embodiment, a nitride layer 70 is formed on the inner surface 53 of the ball holding chamber 52. The nitride layer 70 is formed by a nitriding treatment that diffuses nitrogen atoms from the surface of the chip body 50 into the chip body 50 to form a compound containing metal atoms and nitrogen atoms that constitute the chip body 50. Examples of metals that can form a nitride layer by bonding with nitrogen include chromium (Cr), aluminum (Al), molybdenum (Mo), titanium (Ti), vanadium (V), and the like. Therefore, the chip body 50 is preferably formed of a metal material containing at least one of chromium, aluminum, molybdenum, titanium, and vanadium. As such a metal material, for example, stainless steel may be used.

[0034] In this embodiment, as will be described later, the nitriding treatment is performed after the ball 42 is assembled to the chip body 50. However, in this nitriding treatment step, it is preferable that a nitride layer 70 is not formed on the surface of the ball 42. Therefore, the ball 42 is preferably made of a material that does not contain any of chromium, aluminum, molybdenum, titanium, and vanadium, a material with an extremely low content of chromium, aluminum, molybdenum, titanium, and vanadium, or a material containing chromium, aluminum, molybdenum, titanium, and vanadium in a stable state. Examples of chromium, aluminum, molybdenum, titanium, and vanadium in a stable state include chromium carbide, vanadium carbide, alumina, etc. From such a viewpoint, the ball 42 may be formed of a material such as tungsten carbide, silicon carbide, silicon nitride, alumina, zirconia, or the like.

[0035] As the nitriding treatment, gas nitriding treatment, gas soft nitriding treatment, salt bath soft nitriding treatment, or the like can be used. For example, the nitride layer 70 may be formed by gas nitriding treatment. The gas nitriding treatment can be performed, for example, by bringing ammonia gas into contact with the surface of the chip body 50 heated to about 400°C to 600°C. Since the nitriding treatment can be performed at a lower temperature compared to other heat treatments such as quenching, deformation of the chip body 50 during the treatment is suppressed.

[0036] By performing the nitriding treatment, the hardness of the surface of the chip body 50 is improved. Therefore, the wear resistance of the surface of the chip 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. That is, the greater the thickness of the nitride layer 70, the harder the surface on which the nitride layer 70 is formed.

[0037] The outer peripheral surface 65 of the chip body 50 may come into contact with other members during manufacturing or during the use of the ballpoint pen 10. When a nitride layer 70 is formed on the outer peripheral surface 65, the wear resistance of the outer peripheral surface 65 is improved. Therefore, when the outer peripheral surface 65 comes into contact with other members during the manufacturing of the chip body 50 or during the use of the ballpoint pen 10, it is possible to suppress the occurrence of scratches or wear on the outer peripheral surface 65.

[0038] As described above, the ball holding chamber 52 is configured such that the ball 42 can move slightly in the axial direction within the ball holding chamber 52. In this case, during writing, the ball 42 moves backward due to the writing pressure, and the ball seat 56 receives the writing pressure from the ball 42. When the ball 42 rotates while in contact with the ball seat 56 during writing, the ball seat 56 can be worn. When the ball seat 56 is worn, the backward movement amount of the ball 42 during writing gradually increases. As a result, the gap between the ball 42 and the caulking portion 60 during writing becomes larger, and the amount of ink discharged increases, resulting in a thicker writing trace.

[0039] To solve this problem, in the present embodiment, a nitride layer 70 is formed on the ball seat 56. Thereby, the hardness of the ball seat 56 is improved. Therefore, the wear resistance of the ball seat 56 can be improved. Thereby, wear of the ball seat 56 is suppressed, and it is possible to suppress a change in the backward movement amount of the ball 42 during writing. Therefore, the amount of ink discharged during writing is stabilized, and writing can be continued with the same writing trace width even when writing is repeated.

[0040] 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 chip body 50. The thickness T2 of the nitride layer 70 on the outer peripheral surface 65 is measured in the region R from the rear end 62 of the caulking portion 60 to 0.2 mm rearward. 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 chip body 50 in the region R from the rear end 62 of the caulking portion 60 to 0.2 mm rearward. Further, 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 also 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 chip body 50 in the region R from the rear end 62 of the caulking portion 60 to 0.2 mm rearward.

[0041] By forming the nitride layer 70 on the inner surface 53 of the ball holding chamber 52, wear of the inner surface 53 can be suppressed. In particular, by forming the nitride layer 70 on the inner surface 61 in the caulking portion 60, wear of the inner surface 61 of the caulking portion 60 can be suppressed. Thereby, the ball 42 can be prevented from coming out of the ball holding chamber 52. Further, when the thickness T1 and the thickness T2 satisfy the above relationship, the hardness of the inner surface 53 of the ball holding chamber 52 becomes smaller than the hardness of the outer peripheral surface 65 of the chip body 50. In this case, when the ball 42 and the inner surface 53 of the ball holding chamber 52 come into contact with each other, damage such as scratches on the ball 42 can be effectively suppressed.

[0042] The caulking portion 60 can come into contact with a surface to be written on such as a sheet of paper when writing with the ballpoint pen 10. Therefore, there is a possibility that the caulking portion 60 will wear out by repeating writing. In the present embodiment, the thickness T3 of the nitride layer 70 on the front end surface 63 of the caulking portion 60 is larger than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the tip body 50 in the region R from the rear end 62 of the caulking portion 60 to 0.2 mm rearward. In this case, the hardness of the front end surface 63 of the caulking portion 60 becomes larger than the hardness of the outer peripheral surface 65 in the region R. Therefore, the wear resistance of the caulking portion 60 can be improved. Thereby, it is possible to suppress the caulking portion 60 from coming into contact with the surface to be written on and wearing out.

[0043] As described above, in a state where the rear end portion 67 of the tip body 50 and the front hole portion 38 of the tip holder 34 are fitted, the frictional force acting between the outer peripheral surface 65 of the rear end portion 67 and the inner peripheral surface of the front hole portion 38 suppresses the ballpoint pen tip 40 from coming out of the tip holder 34. However, if this frictional force is insufficient, there is a possibility that the ballpoint pen tip 40 will come out of the tip holder 34. Therefore, it is desirable to sufficiently ensure the frictional force acting between the outer peripheral surface 65 of the rear end portion 67 and the inner peripheral surface of the front hole portion 38.

[0044] In the present embodiment, a nitride layer 70 is formed on the outer peripheral surface 65 of the rear end portion 67 of the tip body 50. The roughness of the surface on which the nitride layer 70 is formed by nitriding treatment becomes larger than the roughness of the surface before the nitride layer 70 is formed. In the present embodiment, this property of the nitride layer 70 is utilized to improve the frictional force acting between the outer peripheral surface 65 of the rear end portion 67 and the inner peripheral surface of the front hole portion 38.

[0045] In the present embodiment, since the nitride layer 70 is formed on the outer peripheral surface 65 of the rear end portion 67 of the tip body 50, the roughness of the outer peripheral surface 65 becomes relatively large. Thereby, the frictional force acting between the outer peripheral surface 65 of the rear end portion 67 and the inner peripheral surface of the front hole portion 38 becomes large. Therefore, it is possible to effectively suppress the ballpoint pen tip 40 from coming out of the tip holder 34.

[0046] In addition, since the nitride layer 70 is formed on the outer peripheral surface 65 of the rear end portion 67 of the chip body 50, the strength of the rear end portion 67 is increased. Therefore, it becomes possible to reduce the thickness of the rear end portion 67 along the radial direction. Thereby, the inner diameter of the rear end portion 67 can be increased without changing the outer diameter of the rear end portion 67. In this case, the cross-sectional area of the ink flow hole 58 of the chip body 50 is increased. Therefore, the flow rate of the ink passing through the ink flow hole 58 can be increased, and it is possible to suppress the occurrence of blurring in the handwriting during writing.

[0047] The arithmetic mean height Sa of the outer peripheral surface 65 of the rear end portion 67 is preferably 0.06 μm or more and 0.3 μm or less. Since the arithmetic mean height Sa of the outer peripheral surface 65 of the rear end portion 67 is 0.06 μm or more, the roughness of the outer peripheral surface 65 becomes sufficiently large, and the frictional force acting between the outer peripheral surface 65 of the rear end portion 67 and the inner peripheral surface of the front hole portion 38 can be sufficiently ensured. Further, since the arithmetic mean height Sa of the outer peripheral surface 65 of the rear end portion 67 is 0.3 μm or less, when assembling the ballpoint pen refill 30, the ballpoint pen tip 40 can be smoothly inserted into the front hole portion 38 of the tip holder 34. The arithmetic mean height Sa of the outer peripheral surface 65 of the rear end portion 67 is more preferably 0.08 μm or more and 0.2 μm or less.

[0048] The arithmetic mean height Sa is measured in accordance with ISO 25178. In the present embodiment, the arithmetic mean height Sa is measured using a white interferometer NewView8000 manufactured by Zygo Corporation. When measuring the arithmetic mean height Sa, in order to reflect the roughness of the entire surface to be measured, the arithmetic mean height Sa is measured at five points that are sufficiently separated from each other, and the added average value is taken as the arithmetic mean height Sa on the surface.

[0049] As described above, when writing with the ballpoint pen 10, the ball receiving seat 56 receives the writing pressure from the ball 42. When the thickness of the nitride layer 70 of the ball receiving seat 56 is large, the rough surface of the nitride layer 70 may prevent 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 the present embodiment, the thickness T4 of the nitride layer 70 of the ball receiving seat 56 is smaller than the thickness T5 of the nitride layer 70 of the outer peripheral surface 65 of the rear end portion 67 of the chip body 50. In this case, the surface roughness of the nitride layer 70 in the ball receiving seat 56 can be reduced. Thereby, when writing with the ballpoint pen 10, it is possible to suppress the surface of the nitride layer 70 from preventing the rotation of the ball 42. Therefore, it is possible to suppress the smooth writing feel of the ballpoint pen 10 from being impaired.

[0050] Note that the thickness T4 of the nitride layer 70 of the ball receiving seat 56 may be smaller than the thickness T1 of the nitride layer 70 of the inner surface 53 of the ball holding chamber 52. Also by this, when writing with the ballpoint pen 10, it is possible to suppress the surface of the nitride layer 70 from preventing the rotation of the ball 42. Therefore, it is possible to suppress the smooth writing feel of the ballpoint pen 10 from being impaired.

[0051] In the present embodiment, the thickness T6 of the nitride layer 70 of the inner peripheral surface of the ink flow hole 58 of the chip body 50 is smaller than the thickness T5 of the nitride layer 70 of the outer peripheral surface 65 of the rear end portion 67. In this case, the roughness of the inner peripheral surface of the ink flow hole 58 becomes smaller than the roughness of the outer peripheral surface 65 of the rear end portion 67. In this case, it is possible to suppress the ink flow in the ink flow hole 58 from being hindered. Therefore, it is possible to sufficiently secure the flow rate of the ink passing through the ink flow hole 58 and suppress the occurrence of streaks in the handwriting during writing.

[0052] In addition, in the present embodiment, the thickness T3 of the nitride layer 70 on the front end face 63 of the caulking portion 60 is greater than the thickness T5 of the nitride layer 70 on the outer peripheral face 65 of the rear end portion 67. In this case, the hardness of the front end face 63 of the caulking portion 60 becomes greater than the hardness of the outer peripheral face 65 of the rear end portion 67. Therefore, the wear resistance of the caulking portion 60 can be improved. Thereby, it is possible to suppress the caulking portion 60 from coming into contact with the writing surface and wearing out.

[0053] The thicknesses T1 to T6 of the nitride layer 70 are all thicknesses measured in a direction perpendicular to the surface of the nitride layer 70. The thicknesses T1 to T6 of the nitride layer 70 are measured in accordance with JIS G0562:1993 "Method for Measuring Nitrided Layer Depth of Steel". When measuring the thicknesses T1 to T6 of the nitride layer 70, first, the ball pen tip 40 to be measured is cut along a plane including the central axis A. After the cut surface is polished precisely, the cut surface is etched using a Marble reagent. At this time, only the portion other than the nitride layer 70 is etched, and the nitride layer 70 is not etched, so that the nitride layer 70 and the portion other than the nitride layer 70 can be visually distinguished from each other. Therefore, by observing the cut surface with a microscope, the thickness of the nitride layer 70 in each portion can be measured. As the microscope, the lens and the video unit of the micro Vickers hardness tester HM-200 manufactured by Mitutoyo Corporation are used. When measuring the thicknesses T1 to T6 of the nitride layer 70, the thickness of the nitride layer 70 is measured at five points that are sufficiently separated from each other so as to reflect the entire thickness of the portion to be measured, and the arithmetic mean value thereof is taken as the thicknesses T1 to T6 of the nitride layer 70 at that portion.

[0054] Next, with reference to FIGS. 6 to 8, an example of the manufacturing method of the ball pen tip 40 of the present embodiment will be described.

[0055] First, as shown in FIG. 6, prepare the chip body 50. At this stage, the caulking portion 60 is not formed on the chip body 50. Next, as shown in FIG. 7, insert the ball 42 into the ball holding chamber 52 from the front. Then, as shown in FIG. 8, deform the tip of the chip body 50 inward (toward the central axis A) to form the caulking portion 60.

[0056] After that, perform nitriding treatment on the entire ball 42 and the chip body 50. The nitriding treatment can be performed, for example, by gas nitriding. The gas nitriding treatment can be performed, for example, by bringing ammonia gas into contact with the surface of the chip body 50 heated to about 400°C to 600°C. In the present embodiment, the chip 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 chip body 50 into the chip body 50, and on the surface of the chip body 50, atoms of chromium, aluminum, molybdenum, titanium, or vanadium contained in the chip body 50 and nitrogen atoms are combined to form nitrides. As a result, a nitride-containing nitride layer 70 is formed on the surface of the chip body 50. On the other hand, in the present embodiment, the ball 42 is formed of a material that does not contain any of chromium, aluminum, molybdenum, titanium, and vanadium, a material having an extremely low content of chromium, aluminum, molybdenum, titanium, and vanadium, or a material containing chromium, aluminum, molybdenum, titanium, and vanadium in a stable state. Such materials are, for example, tungsten carbide, silicon carbide, silicon nitride, alumina, and zirconia. In this case, even if the nitriding treatment is performed, no nitride layer 70 is formed on the surface of the ball 42.

[0057] When the ball 42 is assembled to the chip body 50, the gas flow rate passing through the inside of the chip body 50 decreases. That is, by performing the gas nitriding treatment with the ball 42 assembled to the chip body 50, the inflow amount of ammonia gas into the inside of the chip body 50 is suppressed. As a result, the thickness of the nitride layer 70 formed on the inner surface of the chip body 50 becomes smaller than the thickness of the nitride layer 70 formed on the outer peripheral surface 65 of the chip body 50. Consequently, the thickness T6 of the nitride layer 70 on the inner peripheral surface of the ink flow hole 58 becomes smaller than the thickness T5 of the nitride layer 70 on the outer peripheral surface 65 of the rear end portion 67. Also, the thickness T1 of the nitride layer 70 on the inner surface 53 of the ball holding chamber 52 becomes smaller than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the chip body 50.

[0058] When deforming the tip of the chip body 50 to form the caulking portion 60, the thickness of the caulking portion 60 becomes thinner as a whole. In this case, when the gas nitriding treatment is performed, nitrogen atoms enter the front end portion of the caulking portion 60 from three directions: the outer side in the radial direction, the inner side in the radial direction, and the front. Therefore, the thickness of the nitride layer 70 at the front end portion of the caulking portion 60 becomes larger than the thickness of the nitride layer 70 on the other outer peripheral surfaces 65. As a result, the thickness T3 of the nitride layer 70 on the front end surface 63 of the caulking portion 60 becomes larger than the thickness T2 of the nitride layer 70 on the outer peripheral surface 65 of the chip body 50 in the region R.

[0059] When performing gas nitriding treatment, by arranging the chip body 50 so that the ball 42 faces horizontally or downward, a gap is generated between the ball 42 and the ball seat 56, and ammonia gas flows into this gap, whereby a nitride layer 70 is also formed on the ball seat 56. If the ball 42 is pressed against the ball seat 56 during the gas nitriding treatment, ammonia gas does not flow into the space between the ball 42 and the ball seat 56, and further formation of the nitride layer 70 is suppressed. Thereby, the thickness of the nitride layer 70 on the ball seat 56 can be controlled. That is, the thickness T4 of the nitride layer 70 on the ball seat 56 can be made smaller than the thickness T5 of the nitride layer 70 on the outer peripheral surface 65 of the rear end portion 67. Also, 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.

[0060] The ballpoint pen tip 40 of the present embodiment is a ballpoint pen tip including a ball 42 and a chip body 50 that holds the ball 42. The chip body 50 has a ball holding chamber 52 that holds the ball 42. The ball holding chamber 52 includes a ball seat 56 that receives the writing pressure from the ball 42 during writing, and a nitride layer 70 is formed on the outer peripheral surface 65 of the rear end portion 67 of the chip body 50 and on the ball seat 56.

[0061] The ballpoint pen refill 30 of the present embodiment includes the above-described ballpoint pen tip 40 and an ink storage cylinder 32 that stores ink.

[0062] The ballpoint pen 10 of the present embodiment includes the above-described ballpoint pen refill 30.

[0063] According to such a ballpoint pen tip 40, ballpoint pen refill 30, and ballpoint pen 10, since the nitride layer 70 is formed on the ball receiving seat 56, the hardness of the ball receiving seat 56 is improved. Therefore, the wear resistance of the ball receiving seat 56 can be improved. Thereby, the wear of the ball receiving seat 56 is suppressed, and it is possible to suppress a change in the amount of retreat of the ball 42 during writing. Therefore, the ink discharge amount during writing is stabilized, and writing can be continued with the same handwriting width even when writing is repeated.

[0064] Also, according to such a ballpoint pen tip 40, ballpoint pen refill 30, and ballpoint pen 10, since the nitride layer 70 is formed on the outer peripheral surface 65 of the rear end portion 67 of the tip body 50, the roughness of the outer peripheral surface 65 becomes relatively large. Thereby, the frictional force acting between the outer peripheral surface 65 of the rear end portion 67 and the inner peripheral surface of the front hole portion 38 becomes large. Therefore, it is possible to effectively suppress the ballpoint pen tip 40 from coming out of the tip holder 34.

[0065] Also, since the nitride layer 70 is formed on the outer peripheral surface 65 of the rear end portion 67 of the tip body 50, the strength of the rear end portion 67 becomes large. Therefore, it becomes possible to reduce the thickness of the rear end portion 67 along the radial direction. Thereby, the inner diameter of the rear end portion 67 can be increased without changing the outer diameter of the rear end portion 67. In this case, the cross-sectional area of the ink flow hole 58 of the tip body 50 becomes large. Therefore, it is possible to increase the flow rate of the ink passing through the ink flow hole 58 and suppress the occurrence of streaks in the handwriting during writing.

[0066] In the ballpoint pen tip 40 of the present embodiment, the thickness T4 of the nitride layer 70 of the ball receiving seat 56 is smaller than the thickness T5 of the nitride layer 70 of the outer peripheral surface 65 of the rear end portion 67.

[0067] According to such a ballpoint pen tip 40, the roughness of the surface of the nitride layer 70 in the ball receiving seat 56 can be reduced. Thereby, when writing with the ballpoint pen 10, it is possible to suppress the surface of the nitride layer 70 from interfering with the rotation of the ball 42. Therefore, it is possible to suppress the smooth writing feeling of the ballpoint pen 10 from being impaired.

[0068] In the ballpoint pen tip 40 of the present embodiment, the chip body 50 further has a caulking portion 60 that prevents the ball 42 from coming out of the ball holding chamber 52, and the thickness T3 of the nitride layer 70 on the front end surface 63 of the caulking portion 60 is larger than the thickness T5 of the nitride layer 70 on the outer peripheral surface 65 of the rear end portion 67.

[0069] According to such a ballpoint pen tip 40, the hardness of the front end surface 63 of the caulking portion 60 is greater than the hardness of the outer peripheral surface 65 of the rear end portion 67. Therefore, the wear resistance of the caulking portion 60 can be improved. Thereby, it is possible to suppress the caulking portion 60 from contacting and wearing against the writing surface.

Explanation of Reference Numerals

[0070] 10 Ballpoint pen 12 Protrusion and retraction mechanism 14 Friction member 16 Clip 18 Coil spring 20 Shaft cylinder 21 Front shaft 22 Opening 23 First engaging portion 24 Male screw portion 25 Rear shaft 26 Female screw portion 27 Slide hole 28 Rear end cap 29 Grip member 30 Ballpoint pen refill 32 Ink storage cylinder 34 Tip holder 35 Ink flow hole 36 Second engaging portion 37 Inner flange portion 38 Front hole portion 40 ball pen tip 42 ball 50 tip body 52 ball holding chamber 53 inner surface 54 side surface 56 ball seat 58 ink flow hole 60 caulked part 61 inner surface 62 rear end 63 front end face 65 outer peripheral surface 67 rear end part 68 stepped part 70 nitride layer A central axis A R region da axial direction da

Claims

1. A ballpoint pen tip comprising a ball and a tip body for holding the ball, wherein the tip body has a ball holding chamber for holding the ball, the ball holding chamber includes a ball receiving seat for receiving the writing pressure from the ball during writing, and a nitride layer is formed on the outer peripheral surface of the rear end portion of the tip body and on the ball receiving seat. A ballpoint pen tip.

2. 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 outer peripheral surface of the rear end portion.

3. The tip body further has a caulking portion for preventing the ball from coming out of the ball holding chamber, and the thickness of the nitride layer on the front end face of the caulking portion is larger than the thickness of the nitride layer on the outer peripheral surface of the rear end portion. The ballpoint pen tip according to claim 1.

4. A ballpoint pen refill comprising the ballpoint pen tip according to any one of claims 1 to 3, and an ink storage cylinder for storing ink.

5. A ballpoint pen comprising the ballpoint pen refill according to claim 4.

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