Ball-point pen tip, ball-point pen refill, and ball-point pen

Abstract

To restrain a ball retainer seat from wearing out, and suppress a decrease in strength of a tip of a swaged part.SOLUTION: A ball-point pen tip 40 comprises a ball 42, and a tip body 50 for holding the ball 42. In the ball-point pen tip 40, the tip body 50 has a ball embracing chamber 52 for embracing the ball 42, and a swaged part 60 for hindering the ball 42 from coming off the ball embracing chamber 52. 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 the tip body 50 and the ball retainer seat 56. The thickness T3 of the nitrided layer 70 of a front end surface 63 of the swaged part 60 is greater than the thickness T4 of the nitrided layer 70 of the ball retainer seat 56.SELECTED DRAWING: Figure 3

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 tube is nitrided, and then, cutting is performed on the inner surface of the tip portion of the nitrided metal tube to form a ball holding chamber, a ball pedestal, an ink guiding hole, and the like. Finally, a ball is inserted into the ball holding chamber, and caulking is performed by pressing the peripheral edge portion of the tip of the ball holding chamber inward to bend it. By going through such steps, there is an advantage that burrs are suppressed from being generated during cutting, and caulking 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 holding chamber is configured such that the ball can move slightly in the axial direction within the ball holding chamber. The ball holding chamber includes a ball receiving seat located behind the ball. In this case, during writing, the ball moves backward due to the writing pressure, and the ball receiving seat receives the writing pressure from the ball. If the ball rotates while in contact with the ball receiving seat during writing, the ball receiving seat can be worn. When the ball receiving seat is worn, the backward movement amount of the ball during writing gradually increases. As a result, the gap between the ball and the caulked portion during writing increases, and the ink discharge amount increases, so that the formed handwriting becomes thick.

[0005] Also, during writing, the tip of the caulking portion can come into contact with the writing surface such as paper. In this case, repeated writing can cause the tip of the caulking portion to wear. When the tip of the caulking portion wears, the strength of the caulking portion decreases, and when a large force acts on the caulking portion due to a collision with another object or the like, the caulking portion may be deformed.

[0006] The present invention has been made in consideration of such points, and an object thereof is to suppress wear of the ball receiving seat and to suppress a decrease in the strength of the tip of the caulking portion.

Means for Solving the Problems

[0007] The ball pen tip of the present embodiment is [1] A ball pen tip including 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 caulking portion that prevents the ball from coming out of the ball holding chamber, The ball holding chamber includes a ball receiving seat that receives the writing pressure from the ball during writing, A nitride layer is formed on the outer peripheral surface of the tip body and the ball receiving seat, The thickness of the nitride layer on the front end surface of the caulking portion is greater than the thickness of the nitride layer on the ball receiving seat, which is a ball pen tip.

[0008] The ball pen tip of the present embodiment is [2] The thickness of the nitride layer on the front end surface is greater than the thickness of the nitride layer on the outer peripheral surface of the tip body in a region from the rear end of the caulking portion to 0.2 mm rearward, which is the ball pen tip according to [1].

[0009] The ball pen tip of the present embodiment is [3] The thickness of the nitrided layer on the inner surface of the ball holding chamber is smaller than the thickness of the nitrided layer on the outer peripheral surface of the chip body in the region from the rear end of the caulked portion to 0.2 mm rearward, the ballpoint pen chip according to [1] or [2].

[0010] The ballpoint pen chip of the present embodiment is [4] The thickness of the nitrided layer of the ball seat is smaller than the thickness of the nitrided layer of the inner surface of the ball holding chamber, the ballpoint pen chip according to any one of [1] to [3].

[0011] The ballpoint pen refill of the present embodiment is [5] [1] to [4] any one of the ballpoint pen chips described above, and An ink storage cylinder for storing ink, a ballpoint pen refill provided with.

[0012] The ballpoint pen of the present embodiment is [6] A ballpoint pen provided with the ballpoint pen refill according to [5].

Advantages of the Invention

[0013] According to the present invention, it is possible to suppress wear of the ball seat and suppress a decrease in the strength of the tip of the caulked portion.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0015] 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.

[0016] In addition, with regard to terms used in this specification that specify shapes, geometric conditions, and their degrees, such as terms like "parallel", "orthogonal", "identical", etc., and values of lengths and angles, etc., they are not bound by a strict meaning and are to be interpreted to include a range where similar functions can be expected.

[0017] In this specification, the direction in which the central axis A of the ball pen 10 extends (the longitudinal direction, the up - down direction in the longitudinal sectional view) is defined as the axial direction da, the direction orthogonal to the central axis A is the radial direction, and the direction along the circumference around the central axis A is the circumferential direction. Also, along the axial direction da, when writing, the side closer to the writing surface such as the paper surface is defined as the front, and the side separated 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.

[0018] FIG. 1 is a diagram for explaining an embodiment of the present invention, and is a sectional view showing an example of a ball pen 10. In this embodiment, an example in which the ball pen 10 is a so - called side - knock type ball pen will be described, but the ball pen 10 is not limited to this. The ball pen 10 includes a shaft cylinder 20, a ball pen refill 30 incorporated in the shaft cylinder 20, an ejecting mechanism 12 for making the tip of the ball pen refill 30 protrude from and retract into the shaft cylinder 20, a friction member 14 for rubbing the writing trace, and a clip 16.

[0019] The shaft cylinder 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 is provided at the front end with an opening 22 through which the tip of the ball pen tip 40 of the ball pen refill 30 can protrude 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. The front shaft 21 and the rear shaft 25 are coupled to each other by screwing the male screw portion 24 of the front shaft 21 and the female screw portion 26 of the rear shaft 25. 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 ball 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.

[0020] In the present embodiment, the clip 16 functions as an operation portion operated by the user at the time of knocking. The shaft cylinder 20 is provided with a slide hole 27 extending in the axial direction da and penetrating the wall portion of the shaft cylinder 20. The slide hole 27 is provided across the rear region of the rear shaft 25 and the front end portion 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 moving 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.

[0021] The ballpoint pen refill 30 is accommodated in the shaft cylinder 20 so as to be retractable. The ballpoint pen refill 30 includes an ink storage cylinder 32 for storing 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 the example shown in FIG. 1, the rear end portion of the tip holder 34 is inserted into the front end portion of the ink storage cylinder 32, and the rear end portion of the ballpoint pen tip 40 is inserted into the front end portion of the tip holder 34. The ballpoint pen refill 30 has a second engaging portion 36 provided on the outer surface of the front region. In the illustrated example, the second engaging portion 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 portion 36 of the ballpoint pen refill 30 is located behind the first engaging portion 23 of the front shaft 21, and a coil spring 18 is disposed in a compressed state between the first engaging portion 23 and the second engaging portion 36. Thereby, the coil spring 18 biases the ballpoint pen refill 30 rearward.

[0022] 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 a 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 a decolored state to a colored state by cooling can be used.

[0023] The friction member 14 of the present embodiment is a member for frictionally rubbing the handwriting with ink. When the ink is thermochromic ink, the friction member 14 can be a friction member having a function of rubbing the surface to be written, 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. Further, when the ink does not have thermochromic properties, the friction member 14 may be, for example, a member that scrapes off the handwriting by rubbing the surface to be written, such as paper, on which the handwriting is formed, such as eraser rubber.

[0024] The projecting and retracting mechanism 12 is a mechanism for alternately switching the ballpoint pen 10 between a knocked state in which the tip of the ballpoint pen tip 40 projects from the opening 22 of the front shaft 21 and a non-knocked 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 knocked state. In the non-knocked 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 projects 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 projects forward from the opening 22. When the user presses and slides the clip 16 forward with a finger again, 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 projecting and retracting operations 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.

[0025] With reference to FIGS. 2 to 4, the ballpoint pen tip 40 will be further described. FIG. 2 is a longitudinal sectional view showing the ballpoint pen tip 40. FIG. 3 is a longitudinal sectional view showing an enlarged tip of the ballpoint pen tip 40. FIG. 4 is an enlarged view showing the portion marked IV in FIG. 3.

[0026] 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, by moving the ball 42 on the writing surface such as paper while the user presses the ball 42 against the writing surface, the ball 42 rotates on the writing surface. Thereby, the ink attached to the ball 42 is transferred to the writing surface. Then, a handwriting 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.

[0027] The tip body 50 has a ball holding chamber 52, an ink flow hole 58, and a caulking portion 60. The ball holding chamber 52 has a function of holding the ball 42 and a function of holding the 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 referred to as the central axis A.

[0028] 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 at the rear portion of the ball holding chamber 52. In 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 in 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.

[0029] 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. 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.

[0030] 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.

[0031] In this embodiment, a nitride layer 70 is formed at least on the outer peripheral surface 65 of the chip body 50 and the ball receiving seat 56 of the ball holding chamber 52. Further, 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 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.

[0032] 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, and the like. From this perspective, the ball 42 may be formed of a material such as tungsten carbide, silicon carbide, silicon nitride, alumina, zirconia, and the like.

[0033] As the nitriding treatment, gas nitriding treatment, gas soft nitriding treatment, salt bath soft nitriding treatment, etc. can be used. For example, a 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.

[0034] 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 larger the thickness of the nitride layer 70, the harder the surface on which the nitride layer 70 is formed.

[0035] 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. If the 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.

[0036] 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. If the ball 42 rotates while in contact with the ball seat 56 during writing, the ball seat 56 may wear. When the ball seat 56 wears, 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 increases, and the ink discharge amount increases, so that the formed handwriting becomes thicker.

[0037] To solve this problem, in the present embodiment, a nitrided 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, the wear of the ball seat 56 is suppressed, and it is possible to suppress a change in the amount of backward movement of the ball 42 during writing. Therefore, the ink ejection amount during writing is stabilized, and writing can be continued with the same stroke width even when writing is repeated.

[0038] In the present embodiment, the thickness T1 of the nitrided layer 70 on the inner surface 53 of the ball holding chamber 52 is smaller than the thickness T2 of the nitrided layer 70 on the outer peripheral surface 65 of the chip body 50. The thickness T2 of the nitrided layer 70 on the outer peripheral surface 65 is measured in a region R from the rear end 62 of the caulking portion 60 to 0.2 mm rearward. Therefore, the thickness T1 of the nitrided layer 70 on the inner surface 53 of the ball holding chamber 52 is smaller than the thickness T2 of the nitrided 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. Also, the thickness T1 of the nitrided 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 nitrided layer 70 on the side surface 54 of the ball holding chamber 52 is smaller than the thickness T2 of the nitrided 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.

[0039] By forming the nitrided layer 70 on the inner surface 53 of the ball holding chamber 52, it is possible to suppress wear of the inner surface 53. In particular, by forming the nitrided layer 70 on the inner surface 61 in the caulking portion 60, it is possible to suppress wear of the inner surface 61 of the caulking portion 60. Thereby, it is possible to suppress the ball 42 from coming out of the ball holding chamber 52. Also, 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, it is possible to effectively suppress damage such as scratches on the ball 42.

[0040] The caulking portion 60 can come into contact with a writing surface such as paper when writing with the ballpoint pen 10. Therefore, with repeated writing, the tip of the caulking portion 60 may wear out. When the tip of the caulking portion 60 wears out, the strength of the caulking portion 60 decreases, and when a large force acts on the caulking portion 60 due to a collision with another object or the like, the caulking portion 60 may deform.

[0041] To solve this problem, in the present embodiment, the thickness T3 of the nitride layer 70 on the front end face 63 of the caulking portion 60 is larger 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 face 63 of the caulking portion 60 has a sufficient thickness T3, it is possible to suppress wear of the tip of the caulking portion 60 by repeated writing. Therefore, it becomes possible to maintain the strength of the caulking portion 60, and it is possible to suppress deformation of the caulking portion 60 when a large force acts on the caulking portion 60 due to a collision with another object or the like.

[0042] Further, when the nitride layer 70 on the front end face 63 of the caulking 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 caulking portion 60. In this case, even when writing is repeated, it is possible to suppress wear of the inner surface 61 of the caulking portion 60 due to friction with the ball 42. Thereby, it is possible to suppress the ball 42 from coming out of the ball holding chamber 52.

[0043] As described above, when writing with the ballpoint pen 10, the ball seat 56 receives the writing pressure from the ball 42. Generally, the surface roughness of the nitrided layer 70 is greater than the surface roughness of the surface where the nitrided layer 70 is not formed. Therefore, when the thickness of the nitrided layer 70 of the ball seat 56 is large, when writing with the ballpoint pen 10, the rough surface of the nitrided layer 70 may interfere with the rotation of the ball 42. In this case, the smooth writing feel of the ballpoint pen 10 may be impaired. In the present embodiment, the thickness T4 of the nitrided layer 70 of the ball seat 56 is smaller than the thickness T3 of the nitrided layer 70 of the front end face 63 of the caulking portion 60. Further, in the present embodiment, the thickness T4 of the nitrided layer 70 of the ball seat 56 is smaller than the thickness T1 of the nitrided layer 70 of the inner surface 53 of the ball holding chamber 52. In particular, the thickness T4 of the nitrided layer 70 of the ball seat 56 is smaller than the thickness T1 of the nitrided layer 70 of the side surface 54 of the ball holding chamber 52. In this case, the surface roughness of the nitrided layer 70 in the ball seat 56 can be reduced. Thereby, when writing with the ballpoint pen 10, it is possible to suppress the surface of the nitrided layer 70 from interfering with the rotation of the ball 42. Therefore, it is possible to suppress the smooth writing feel of the ballpoint pen 10 from being impaired.

[0044] Further, in the present embodiment, the thickness T3 of the nitrided layer 70 of the front end face 63 of the caulking portion 60 is larger than the thickness T2 of the nitrided layer 70 of 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. In this case, the hardness of the front end face 63 of the caulking portion 60 is greater 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 writing surface and wearing.

[0045] The thicknesses T1 to T4 of the nitride layer 70 are all the thicknesses measured in the 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 Nitrided Layer Depth of Steel". When measuring the thicknesses T1 to T4 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 precisely polished, the cut surface is etched using a Marble reagent. At this time, only the portions other than the nitride layer 70 are etched, and the nitride layer 70 is not etched, so that the nitride layer 70 and the portions other than the nitride layer 70 can be visually distinguished 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. As the microscope, the lens and the video unit of the micro Vickers hardness tester HM-200 manufactured by Mitutoyo Corporation are used. Incidentally, when measuring the thicknesses T1 to T4 of the nitride layer 70, the thicknesses of the nitride layer 70 are 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 is taken as the thicknesses T1 to T4 of the nitride layer 70 at that portion.

[0046] Next, with reference to FIGS. 5 to 7, an example of the manufacturing method of the ball pen tip 40 of the present embodiment will be described.

[0047] First, as shown in FIG. 5, a chip body 50 is prepared. At this stage, the caulking portion 60 is not formed on the chip body 50. Next, as shown in FIG. 6, the ball 42 is inserted into the ball holding chamber 52 from the front. Then, as shown in FIG. 7, the tip portion of the chip body 50 is deformed inward (toward the central axis A side) to form the caulking portion 60.

[0048] After that, nitriding treatment is performed on the entire ball 42 and the chip body 50. The nitriding treatment can be performed, for example, 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. 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 combine with nitrogen atoms to form nitrides. As a result, a nitride-containing nitriding layer 70 is formed on the surface of the chip body 50. On the other hand, in the present embodiment, the ball 42 is 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. Such materials are, for example, tungsten carbide, silicon carbide, silicon nitride, alumina, and zirconia. In this case, even if the nitriding treatment is performed, a nitriding layer 70 is not formed on the surface of the ball 42.

[0049] 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 nitriding layer 70 formed on the inner surface of the chip body 50 becomes smaller compared to the thickness of the nitriding layer 70 formed on the outer peripheral surface 65 of the chip body 50. As a result, the thickness T1 of the nitriding layer 70 on the inner surface 53 of the ball holding chamber 52 is smaller than the thickness T2 of the nitriding layer 70 on the outer peripheral surface 65 of the chip body 50.

[0050] When deforming the tip of the chip body 50 to form the caulked portion 60, the thickness of the caulked portion 60 becomes thinner overall. In this case, when gas nitriding treatment is performed, nitrogen atoms enter the front end portion of the caulked 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 caulked portion 60 becomes larger than the thickness of the nitride layer 70 on the other outer peripheral surface 65. As a result, the thickness T3 of the nitride layer 70 on the front end surface 63 of the caulked portion 60 becomes larger than the thickness T4 of the nitride layer 70 on the ball seat 56. Also, the thickness T3 of the nitride layer 70 on the front end surface 63 of the caulked 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.

[0051] When performing gas nitriding treatment, by arranging the chip body 50 so that the ball 42 is in a horizontal or downward direction, a gap is generated between the ball 42 and the ball seat 56, and ammonia gas flows into this gap, so that a nitride layer 70 is also formed on the ball seat 56. When the ball 42 is pressed against the ball seat 56 during the gas nitriding treatment, ammonia gas does not flow into the gap 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 T3 of the nitride layer 70 on the front end surface 63 of the caulked portion 60. 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.

[0052] The ball pen tip 40 of this embodiment is a ball pen tip 40 including 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 caulking portion 60 that prevents the ball 42 from coming out of the ball holding chamber 52. The ball holding chamber 52 includes a ball receiving seat 56 that receives the writing pressure from the ball 42 during writing. A nitride layer 70 is formed on the outer peripheral surface 65 of the tip body 50 and the ball receiving seat 56. The thickness T3 of the nitride layer 70 on the front end surface 63 of the caulking portion 60 is larger than the thickness T4 of the nitride layer 70 on the ball receiving seat 56.

[0053] The ball pen refill 30 of this embodiment includes the above-described ball pen tip 40 and an ink storage cylinder 32 that stores ink.

[0054] The ball pen 10 of this embodiment includes the above-described ball pen refill 30.

[0055] According to such a ball pen tip 40, ball pen refill 30, and ball 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, 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 amount of ink discharged during writing is stabilized, and writing can be continued with the same handwriting width even when writing is repeated.

[0056] Further, according to such a ball pen tip 40, ball pen refill 30, and ball pen 10, since the thickness T3 of the nitride layer 70 on the front end surface 63 of the caulking portion 60 is larger than the thickness T4 of the nitride layer 70 on the ball receiving seat 56, the nitride layer 70 on the front end surface 63 of the caulking portion 60 has a sufficient thickness T3. Thereby, it is possible to suppress wear of the tip of the caulking portion 60 by repeating writing. Therefore, it becomes possible to maintain the strength of the caulking portion 60, and it is possible to suppress deformation of the caulking portion 60 when a large force acts on the caulking portion 60 due to a collision with another object or the like.

[0057] Further, when the nitride layer 70 on the front end face 63 of the caulking 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 caulking portion 60. In this case, even when writing is repeated, it is possible to suppress wear of the inner surface 61 of the caulking portion 60 due to friction with the ball 42. Thereby, it is possible to suppress the ball 42 from coming out of the ball holding chamber 52.

[0058] In the ball pen tip 40 of the present embodiment, the thickness T3 of the nitride layer 70 on the front end face 63 is larger than the thickness 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.

[0059] According to such a ball pen tip 40, the hardness of the front end face 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 contacting and wearing against the writing surface.

[0060] In the ball pen tip 40 of the present 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 in the region R from the rear end 62 of the caulking portion 60 to 0.2 mm rearward.

[0061] According to such a ballpoint pen tip 40, since the nitride layer 70 is formed on the inner surface 53 of the ball holding chamber 52, it is possible to suppress wear of the inner surface 53. In particular, since the nitride layer 70 is formed on the inner surface 61 in the caulked portion 60, wear of the inner surface 61 of the caulked portion 60 can be suppressed. Thereby, it is possible to suppress the ball 42 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 tip 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, it is possible to effectively suppress damage such as scratches on the ball 42.

[0062] 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 T1 of the nitride layer 70 of the inner surface 53 of the ball holding chamber 52.

[0063] According to such a ballpoint pen tip 40, it is possible to reduce the surface roughness of the nitride layer 70 in the ball receiving seat 56. Thereby, when writing with the ballpoint pen 10, it is possible to suppress the surface of the nitride layer 70 from hindering the rotation of the ball 42. Therefore, it is possible to suppress the smooth writing feeling of the ballpoint pen 10 from being impaired.

Explanation of Reference Numerals

[0064] 10 Ballpoint pen 12 Retracting 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 Chip holder 36 Second engaging part 40 Ballpoint pen tip 42 Ball 50 Chip body 52 Ball holding chamber 53 Inner surface 54 Side surface 56 Ball receiving seat 58 Ink flow hole 60 Caulking part 61 Inner surface 62 Rear end 63 Front end face 65 Outer peripheral surface 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 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 pen pressure from the ball during writing, a nitride layer is formed on the outer peripheral surface of the tip body and the ball receiving seat, a ballpoint pen tip in which the thickness of the nitride layer on the front end surface of the caulking portion is greater 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 greater than the thickness of the nitride layer on the outer peripheral surface of the tip 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 tip 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 containing cylinder for containing ink.

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

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