Ballpoint pen

Abstract

To provide a ballpoint pen in which there is no risk of a coating resin being significantly damaged in an assembly process and a core pin of the molding die on the inner surface of the front end portion of the shaft cylinder has sufficient durability, even if burrs occur at a rear end corner of a front end hole of a shaft cylinder.SOLUTION: A ballpoint pen refill 6 is housed inside a shaft cylinder 2 so as to be movable in the front-rear direction, and a front end portion of a chip body 7 of the ballpoint pen refill 6 can be retracted from a front end hole 31 of the shaft cylinder 2, a ball 74 is rotatably held at the front end of the chip body 7, a coating resin 11 is fixed to the outer surface of the front end portion of the chip body 7, at least the front end of the barrel 2 is composed of an injection molded product made of synthetic resin, and a rearward step portion 33 is formed at the rear end of the front end hole 31, and a radial length D of a step portion 33 is in a range of 0.1 mm to 0.3 mm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a ballpoint pen.

Background Art

[0002] In this type of ballpoint pen, Patent Document 1 relates to a ballpoint pen having a ballpoint pen body that protrudes and retracts from the tip of a shaft cylinder, and a rubber-like packing is attached to the tip of the ballpoint pen body. For the purpose of preventing the rubber-like packing from coming into contact with and coming off from the tip opening of the shaft body during the inspection of the protruding and retracting operation of the ballpoint pen body, a configuration in which a polygonal portion is formed on the inner surface near the protruding and retracting opening of the shaft cylinder, or a configuration in which a chamfering process is performed on the inner surface of the tip of the protruding and retracting opening of the shaft cylinder is disclosed.

[0003] Further, Patent Document 2 discloses a retractable writing instrument in which a writing instrument refill is housed inside a shaft cylinder, a tip port through which the pen tip of the writing instrument refill can protrude and retract is provided at the tip of the shaft cylinder, and the tip of the shaft cylinder is configured by at least injection molding of synthetic resin. A configuration is disclosed in which a concave portion is provided in a part of the opening end portion of the inner peripheral surface of the tip port, an injection molding gate portion is provided in the concave portion, and a support portion for supporting the outer peripheral surface of the writing instrument refill is provided in a portion of the inner peripheral surface of the tip port excluding the concave portion at the opening end portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the assembly process of inserting the ball pen body (corresponding to the ball pen refill of the present application) into the shaft body (corresponding to the shaft cylinder of the present application) composed of a front shaft and a rear shaft against the backward biasing of the elastic member (corresponding to the elastic body of the present application) in the ball pen of Patent Document 1, when the ball pen body is temporarily inserted into the front shaft or the rear shaft and then the front shaft and the rear shaft are connected, if the tip of the ball pen body (corresponding to the tip body of the present application) deviates greatly from the axis of the shaft body, the rubber-like packing (corresponding to the coating resin of the present application) strongly collides with the rear end corner of the entrance / exit port (corresponding to the front end hole of the present application), the rubber-like packing is severely damaged, and the sealing function of the front end portion of the tip body by the rubber-like packing may be lost. In particular, as the outer diameter of the ball at the pen tip increases, the outer diameter of the rubber-like packing also increases, and in the assembly process, the rubber-like packing is likely to strongly collide with the rear end corner of the entrance / exit port and be damaged.

[0006] In the retractable writing instrument of Patent Document 2, since the gate portion is provided at the opening end of the tip port (corresponding to the front end hole of the present application), the core pin of the mold forming the inner surface of the tip end portion of the shaft cylinder is composed of a fixed-side core pin forming the inner surface of the tip port and a movable-side core pin forming the inner surface behind the tip port, and the end portion of the movable-side core pin is slidably combined with the end portion of the fixed-side core pin having the gate portion. Therefore, there is a possibility that burrs may be generated at the rear end corner of the tip port after molding. If burrs are generated at the rear end corner of the tip port and the coating resin is fixed to the front end portion of the pen tip (ball pen tip) of the writing instrument refill, in the above assembly process, if the pen tip of the writing instrument refill deviates from the axis of the shaft cylinder, the coating resin may be severely damaged when it strongly collides with the rear end corner.

[0007] The present invention aims to solve the above-mentioned conventional problems, and even if burrs are generated at the rear end corner of the front end hole of the shaft cylinder, there is no possibility that the coating resin is severely damaged in the assembly process, and further provides a ball pen in which the core pin of the mold for forming the inner surface of the front end portion of the shaft cylinder obtains sufficient durability. In the present invention, "front" refers to the ball side of the tip body, and "rear" refers to the opposite side.

Means for Solving the Problems

[0008] According to the first invention of the present application, a ball pen refill is accommodated inside a shaft cylinder so as to be movable in the front-rear direction, the front end portion of the tip body of the ball pen refill can protrude and retract from the front end hole of the shaft cylinder, a ball is rotatably held at the front end portion of the tip body, a coating resin is fixed to the outer surface of the front end portion of the tip body, at least the front end portion of the shaft cylinder is formed of an injection molded body of synthetic resin, a rearward step portion is formed at the rear end of the front end hole, and the radial length of the step portion is in the range of 0.1 mm to 0.3 mm.

[0009] According to the first invention, since the radial length of the step portion is in the range of 0.1 mm to 0.3 mm (preferably in the range of 0.15 mm to 0.25 mm), burrs are generated at the rear end corner portion of the front end hole of the shaft cylinder, and moreover, in the assembly process of inserting the ball pen refill into the shaft cylinder, even if the tip body of the ball pen refill deviates from the axis of the shaft cylinder, it is possible to avoid the vicinity of the center of the coating resin from strongly colliding with the rear end corner portion of the front end hole, and there is no risk of significant damage to the coating resin. Furthermore, the core pin of the molding die for the inner surface of the front end portion of the shaft cylinder can obtain sufficient durability. If the radial length of the step portion is less than 0.1 mm, since the core pin of the molding die for the inner surface of the front end portion of the shaft cylinder has a thin portion, sufficient durability of the core pin cannot be obtained. If the radial length of the step portion is greater than 0.3 mm, in the assembly process, if the tip body of the ball pen refill deviates from the axis of the shaft cylinder, the vicinity of the center of the coating resin may strongly collide with the rear end corner portion of the front end hole, and there is a risk of significant damage to the coating resin.

[0010] The second invention of the present application is the ballpoint pen of the first invention, wherein the front end portion of the chip body is formed of a straight cylindrical metal cylinder, an inward front edge portion is formed at the front end of the chip body, and a plurality of recessed portions are circumferentially and dispersedly arranged on the outer surface of the front end portion of the chip body behind the front edge portion, and a plurality of inward protruding portions corresponding to the recessed portions are circumferentially and dispersedly arranged on the inner surface of the front end portion of the chip body behind the front edge portion. A ball is rotatably held between the front edge portion and the inward protruding portion, the coating resin is fixed so as to cover the ball, the front edge portion and the recessed portion, and the radial length of the step portion is smaller than the maximum radial wall thickness of the coating resin excluding the recessed portion.

[0011] According to the ballpoint pen of the second invention, the coating resin is firmly fixed to the outer surface of the chip body. In the assembly process, even when the chip body of the ballpoint pen refill deviates from the axis of the shaft cylinder, the vicinity of the axis of the coating resin strongly collides with the rear end corner portion of the front end hole (that is, the coating resin is strongly clamped in the axial direction between the rear end corner portion of the front end hole and the outer surface of the chip body), which can be avoided, and more reliably, damage to the coating resin can be prevented. That is, in the assembly process, even when the chip body of the ballpoint pen refill deviates from the axis of the shaft cylinder, since a space is formed behind the coating resin, the maximum outer diameter portion in the radial direction away from the axis of the coating resin lightly contacts the rear end corner portion of the front end hole, rather than strongly clamping the coating resin in the axial direction between the rear end corner portion of the front end hole and the outer surface of the chip body, so there is no risk of significant damage to the coating resin.

[0012] The third invention of the present application is the ballpoint pen of the first or second invention, wherein an elastic body locking portion is formed on the inner surface of the front end portion of the shaft cylinder behind the step portion, the elastic body locking portion can lock an elastic body that biases the ballpoint pen refill backward, and an annular guide surface that gradually reduces in diameter toward the front is formed on the inner surface of the front end portion of the shaft cylinder in front of the elastic body locking portion and behind the step portion.

[0013] According to the ballpoint pen of the third invention, in the assembly process, even when the tip body of the ballpoint pen refill deviates from the axis of the barrel, the coating resin smoothly contacts the guide surface, and it is possible to avoid the coating resin from colliding with the rear end corner of the front end hole, and more reliably prevent damage to the coating resin. In the present invention, the guide surface may have a shape in which the diameter gradually decreases toward the front, and examples thereof include a convex curved surface and a conical inner surface.

[0014] The fourth invention of the present application is the ballpoint pen of the third invention, when a virtual line in contact with the rear end corner of the front end hole and the guide surface is drawn, when the axial length from the contact point where the virtual line contacts the guide surface to the rear end corner is L and the radial length of the step portion is D, the value of L / D (the ratio of L to D) is in the range of 2 to 4.

[0015] According to the ballpoint pen of the fourth invention, in the assembly process, damage to the coating resin can be further prevented, and the core pin of the mold for forming the inner surface of the front end of the barrel can obtain sufficient durability. If the value of L / D is less than 2, the axial distance between the guide surface and the step portion becomes excessively short, and the effect of avoiding the coating resin from contacting the rear end corner of the front end hole may be reduced. If the value of L / D is greater than 4, since the core pin of the mold for forming the inner surface of the front end of the barrel has a thin part, the durability of the core pin may be reduced.

[0016] The fifth invention of the present application is the ballpoint pen of any one of the first to fourth inventions, characterized in that the maximum outer diameter in the radial direction of the coating resin is in the range of 70% to 95% of the inner diameter of the front end hole. According to the ballpoint pen of the fifth invention, a ballpoint pen having a ball with a relatively large outer diameter that exhibits the above effect can be obtained. In the present invention, the ball has an outer diameter of 0.5 mm to 1.0 mm (preferably 0.7 mm to 1.0 mm).

[0017] The sixth invention of the present application is such that a ball pen refill is accommodated inside a shaft cylinder so as to be movable in the front-rear direction, the front end of the tip body of the ball pen refill can protrude and retract from the front end hole of the shaft cylinder, a ball is rotatably held at the front end of the tip body, a coating resin is fixed to the outer surface of the front end of the tip body, at least the front end of the shaft cylinder is formed of an injection molded body of synthetic resin, a rearward step portion is formed at the rear end of the front end hole, the front end of the tip body is formed of a straight cylindrical metal barrel, an inward front edge portion is formed at the front end of the tip body, a plurality of recessed portions are circumferentially and dispersedly arranged on the outer surface of the front end of the tip body behind the front edge portion, and a plurality of inward protruding portions corresponding to the recessed portions are circumferentially and dispersedly arranged on the inner surface of the front end of the tip body behind the front edge portion. The ball is rotatably held between the front edge portion and the inward protruding portion, the coating resin is fixed so as to cover the ball, the front edge portion and the recessed portion, and the radial length of the step portion is smaller than the maximum wall thickness in the radial direction of the coating resin excluding the recessed portion. It is a ball pen characterized by this.

[0018] According to the ball pen of the sixth invention, the coating resin is firmly fixed to the outer surface of the tip body. Also, in the assembly process, even when the tip body of the ball pen refill deviates from the axis of the shaft cylinder, it is possible to avoid the situation where the vicinity of the axis of the coating resin strongly collides with the rear end corner of the front end hole (that is, strongly sandwiching the coating resin in the axial direction between the rear end corner of the front end hole and the outer surface of the tip body), and it is possible to surely prevent damage to the coating resin. That is, in the assembly process, even when the tip body of the ball pen refill deviates from the axis of the shaft cylinder, since a space is formed behind the coating resin, the maximum outer diameter portion in the radial direction away from the axis of the coating resin lightly contacts the rear end corner of the front end hole, rather than strongly sandwiching the coating resin in the axial direction between the rear end corner of the front end hole and the outer surface of the tip body. Therefore, there is no risk of significant damage to the coating resin.

[0019] The seventh invention of the present application is the ballpoint pen of the sixth invention, wherein an elastic body locking portion is formed on the inner surface of the front end portion of the shaft cylinder behind the step portion, and the elastic body locking portion can lock an elastic body that biases the ballpoint pen refill backward. An annular guide surface that gradually decreases in diameter toward the front is formed on the inner surface of the front end portion of the shaft cylinder in front of the elastic body locking portion and behind the step portion.

[0020] According to the ballpoint pen of the seventh invention, in the assembly process, even when the tip body of the ballpoint pen refill deviates from the axis of the shaft cylinder, the coating resin can smoothly contact the guide surface, and it is possible to avoid the coating resin from colliding with the rear end corner portion of the front end hole, and more reliably prevent damage to the coating resin.

[0021] The eighth invention of the present application is the ballpoint pen of the seventh invention. When a virtual line that contacts the rear end corner portion of the front end hole and the guide surface is drawn, when the axial length from the contact point where the virtual line contacts the guide surface to the rear end corner portion is L and the radial length of the step portion is D, the value of L / D (the ratio of L to D) is in the range of 2 to 4.

[0022] According to the ballpoint pen of the eighth invention, in the assembly process, damage to the coating resin can be further prevented, and the core pin of the molding die for the inner surface of the front end portion of the shaft cylinder can obtain sufficient durability. If the value of L / D is less than 2, the axial distance between the guide surface and the step portion becomes excessively short, and the effect of avoiding the contact of the coating resin with the rear end corner portion of the front end hole may be reduced. If the value of L / D is greater than 4, the core pin of the molding die for the inner surface of the front end portion of the shaft cylinder has an excessively thin portion, so the durability of the core pin may be reduced.

[0023] The ninth invention of the present application is characterized in that, in the ballpoint pen of the sixth to eighth inventions, the maximum outer diameter in the radial direction of the coating resin is in the range of 70% to 95% of the inner diameter of the front end hole. According to the ballpoint pen of the ninth invention, a ballpoint pen having a relatively large outer diameter ball that exhibits the above effects can be obtained. In the present invention, a ball having an outer diameter of 0.5 mm to 1.0 mm (preferably 0.7 mm to 1.0 mm) is adopted.

Advantages of the Invention

[0024] Even if burrs occur at the rear end corner of the front end hole of the shaft cylinder in the ballpoint pen of the present invention, there is no risk of significant damage to the coating resin during the assembly process, and furthermore, the core pin of the mold for forming the inner surface of the front end of the shaft cylinder obtains sufficient durability.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0026] Embodiments of the present invention will be described with reference to the drawings. (See FIGS. 1 to 7) The ballpoint pen 1 of this embodiment comprises a barrel 2, a ballpoint pen refill 6 that is accommodated in the barrel 2 so as to be movable in the front-rear direction, and an elastic body 5 (e.g., a compression coil spring) that is accommodated in the barrel 2 and biases the ballpoint pen refill 6 rearward.

[0027] The barrel 2 is provided with a projecting and retracting mechanism. The projecting and retracting mechanism is a rear-end knock type knock mechanism that makes the ballpoint pen refill 6 in a pen tip retracted state (tip body retracted state) into a pen tip projecting state (tip body projecting state) by pressing forward an operation portion 41 that projects rearward from the rear end of the barrel 2. Further, the projecting and retracting mechanism employs a double knock type knock mechanism that makes the pen tip projecting state into the pen tip retracted state by pressing the operation portion 41 forward. Note that, as the projecting and retracting mechanism, in addition to the rear-end knock type, there are, for example, a side slide type in which an operation portion that projects radially outward from the side wall of the barrel 2 is slid forward, a side knock type in which an operation portion that projects radially outward from the side wall of the barrel 2 is pressed radially inward, a rotary type in which the rear portion and the front portion of the barrel 2 are relatively rotated, and the like.

[0028] ·Barrel The barrel 2 consists of a front shaft 3 and a rear shaft 4. The front shaft 3 and the rear shaft 4 are cylindrical bodies obtained by injection molding of a synthetic resin. Examples of the synthetic resin constituting the front shaft 3 and the rear shaft 4 include polycarbonate, polypropylene, and the like.

[0029] ·Front shaft The front shaft 3 is composed of a tapered front end portion 36, a gripping portion 37 integrally connected to the rear of the front end portion 36, and a connecting portion 38 integrally connected to the rear of the gripping portion 37. At the front end of the front shaft 3, a straight front end hole 31 through which the tip body 7 can protrude and retract is axially penetrated. The gripping portion 37 can also be integrally provided with an anti-slip layer made of an elastic material on its outer surface by two-color molding. Further, the gripping portion 37 can also be provided with an anti-slip layer made of an elastic material on its outer surface by attaching a separate member. A male thread portion is formed on the outer surface of the connecting portion 38. A recess 39 that opens radially inward and axially forward is formed on the inner peripheral surface of the front end hole 31. An injection gate portion 39a is located in the recess 39. The inner peripheral surface of the front end hole 31 has a circular cross-sectional shape in the portion excluding the recess 39.

[0030] At the rear end of the front end hole 31 of the front shaft 3, a rearward stepped portion 33 that is continuously provided radially outward from the rear end corner portion 32 of the front end hole 31 is integrally formed in an annular shape. The stepped portion 33 is composed of a plane substantially perpendicular to the axis. The radial length D of the stepped portion 33 is in the range of 0.1 mm to 0.3 mm, preferably in the range of 0.15 mm to 0.25 mm, and is set to, for example, 0.2 mm.

[0031] A resilient body locking portion 34 is integrally formed in an annular shape behind the stepped portion 33 on the inner surface of the front shaft 3. The front end of a resilient body 5 that biases the ballpoint pen refill 6 rearward is locked to the resilient body locking portion 34. An annular guide surface 35 is integrally formed on the inner surface of the front shaft 3 in front of the resilient body locking portion 34 and behind the stepped portion 33. The guide surface 35 is composed of a convex curved surface whose diameter gradually decreases toward the front. When a virtual line is drawn in contact with the rear end corner portion 32 of the front end hole 31 and the guide surface 35 (convex curved surface), the axial length L from the contact point where the virtual line contacts the guide surface 35 to the rear end corner portion 32 is set to, for example, 0.6 mm. When the radial length D of the stepped portion 33 is 0.2 mm, the value of L / D (the ratio of L to D) is 3 and is in the range of 2 to 4. Incidentally, the guide surface 35 may also be a conical inner surface in addition to the convex curved surface.

[0032] · Rear shaft The rear shaft 4 has a male threaded portion formed on the inner surface of the opening at the front end. The male threaded portion of the connecting portion 38 of the front shaft 3 can be screwed into the male threaded portion. A clip 42 is formed on the outer surface of the side wall at the rear end of the rear shaft 4. An operating portion 41 protrudes rearward from the rear end of the rear shaft 4.

[0033] ·Ballpoint pen refill The ballpoint pen refill 6 consists of a tip body 7 (pen tip), a tip holder 8 to which the rear part of the tip body 7 is press-fitted and fixed, and an ink storage cylinder 10 to which the rear end portion of the tip holder 8 is press-fitted and fixed.

[0034] The tip body 7 is made of a straight cylindrical thin tube made of metal (for example, austenitic stainless steel such as SUS304 or SUS321). At the front end of the tip body 7, a ball 74 is rotatably held. At the front end of the tip body 7, an annular inward front edge portion 71 is formed by inward pressing deformation. On the outer surface of the side wall of the front end portion of the tip body 7 behind the front edge portion 71, a plurality (for example, 3 or 4) of conical recessed portions 73 are formed at equal intervals in the circumferential direction by inward pressing deformation. At the same time, on the inner surface of the side wall of the front end portion of the tip body 7 behind the front edge portion 71, a plurality (for example, 3 or 4) of inward protruding portions 72 (i.e., ball seats) are formed at equal intervals in the circumferential direction by inward pressing deformation corresponding to the recessed portions 73. The ball 74 is rotatably held between the front edge portion 71 and the inward protruding portion 72. The ball 74 has, for example, an outer diameter of 1.0 mm. In addition, in the present invention, in addition to this, it may be a type in which a ball holding portion (ball seat) is formed by cutting at the front end portion of the metal cylindrical body of the tip body 7. Also, in the present invention, it is a type in which a ball holding portion (ball seat) is formed by cutting at the front end portion of the metal cylindrical body of the tip body 7, and the tip body 7 has a conical outer surface behind the front edge portion, and a coating resin 11 is fixed to the conical outer surface behind the front edge portion.

[0035] ·Coating resin The coating resin 11 is composed of a mixture of a thermoplastic resin, a tacky resin, and a wax. By heating and melting the mixture and adhering and solidifying it to the front end of the chip body 7, the coating resin 11 can be fixed to the front end of the chip body 7. The coating resin 11 is fixed to the front end portion of the chip body 7 so as to circumferentially cover the outer surface of the ball 74 protruding from the front end of the chip body 7 and the straight cylindrical outer surface of the region from the front edge portion 71 to the rear of the recessed portion 73, thereby preventing the solvent component in the ink from volatilizing from the pen tip. Incidentally, examples of the thermoplastic resin include ethylene-vinyl acetate copolymer, polyethylene, polyacetal, polyester, polycarbonate, polyamide, polyvinyl ether, and the like. Examples of the tacky resin include terpene resin, coumarone resin, phenol resin, ester gum, and gum rosin. Examples of the wax include paraffin wax, microcrystalline wax, carnauba wax, polyethylene wax, natural wax, fatty acid wax, and the like.

[0036] · Maximum wall thickness of the coating resin In the case of the ball 74 having an outer diameter of 0.5 mm, the maximum wall thickness T in the radial direction of the coating resin 11 is specifically 0.35 mm. In the case of the ball 74 having an outer diameter of 0.7 mm, the maximum wall thickness T in the radial direction of the coating resin 11 is specifically 0.45 mm. In the case of the ball 74 having an outer diameter of 1.0 mm, the maximum wall thickness T in the radial direction of the coating resin 11 is specifically 0.55 mm. The length D in the radial direction of the stepped portion 33 is specifically 0.2 mm, and the length D in the radial direction of the stepped portion 33 is smaller than the maximum wall thickness T in the radial direction of the coating resin 11 regardless of which ball 74 with an outer diameter of 0.5 mm, 0.7 mm, or 1.0 mm is adopted. Incidentally, in the present invention, the maximum wall thickness T of the coating resin 11 is the radial distance between the outer surface of the chip body 7 excluding the recessed portion 73 and the topmost portion in the radial direction of the coating resin 11.

[0037] · Maximum outer diameter of the coating resin In the case of the ball 74 with an outer diameter of 0.5 mm, the maximum outer diameter A in the radial direction of the coating resin 11 is specifically 1.45 mm. In the case of the ball 74 with an outer diameter of 0.7 mm, the maximum outer diameter A in the radial direction of the coating resin 11 is specifically 1.9 mm. In the case of the ball 74 with an outer diameter of 1.0 mm, the maximum outer diameter A in the radial direction of the coating resin 11 is specifically 2.25 mm. The inner diameter B of the front end hole 31 is specifically 2.53 mm. In the case of the ball 74 with an outer diameter of 0.5 mm, the maximum outer diameter A in the radial direction of the coating resin 11 is 57% of the inner diameter B of the front end hole 31. In the case of the ball 74 with an outer diameter of 0.7 mm, the maximum outer diameter A in the radial direction of the coating resin 11 is 75% of the inner diameter B of the front end hole 31. In the case of the ball 74 with an outer diameter of 1.0 mm, the maximum outer diameter A in the radial direction of the coating resin 11 is 89% of the inner diameter B of the front end hole 31.

[0038] · Chip Holder The chip holder 8 is a cylindrical body obtained by injection molding of a synthetic resin (for example, polypropylene, polyacetal, etc.). The chip holder 8 includes a front portion 81 to which the chip body 7 is attached, a flange portion 82 that abuts against the front end of the ink storage cylinder 10, and a rear portion 83 that is press-fitted and fixed to the front end opening of the ink storage cylinder 10. Inside the chip holder 8, a mounting hole 84 into which the chip body 7 is press-fitted and fixed and an ink flow hole 85 that communicates with the rear of the mounting hole 84 are formed. A plurality of axially extending ribs 86 are formed on the outer peripheral surface of the front portion 81 of the chip holder 8, and in the state where the pen tip protrudes, the ribs 86 are supported by the inner surface of the front end hole 31 excluding the recess 39. In the state where the pen tip protrudes, an air passage is formed between the ribs 86 and the inner surface of the front end hole 31, and air can be taken into the rear end of the ball pen refill 6 in the shaft cylinder 2 in the state where the pen tip protrudes.

[0039] In the ink flow hole 85 and the chip body 7, a spring 9 composed of a straight rod portion 91 and a coil portion 92 connected to the rear of the rod portion 91 is inserted and arranged. The rod portion 91 of the spring 9 biases the ball 74 forward, and when not writing, the ball 74 is in annular close contact with the inner surface of the front edge portion 71. The rear end portion of the spring 9 bulges in the radial direction, and it is locked to the locking projection 85a on the inner surface of the ink flow hole 85.

[0040] · Ink storage cylinder The ink storage cylinder 10 is a cylindrical body with both ends open, and is obtained by extrusion molding of a synthetic resin (for example, polypropylene). A chip holder 8 having a chip body 7 is press-fitted and fixed to the front end opening of the ink storage cylinder 10. A tail plug (not shown) with a vent hole penetrating therethrough is press-fitted and fixed to the rear end opening of the ink storage cylinder 10. Inside the ink storage cylinder 10, ink 10a and a grease-like follower 10b arranged at the rear end of the ink 10a and advancing as the ink is consumed are filled.

[0041] · Mold Fig. 7 shows a mold for molding the front end portion 36 of the front shaft 3. The mold includes a cavity 12, a fixed-side core pin 13, and a movable-side core pin 14. The fixed-side core pin 13 is fixed to the cavity 12 and forms the front end hole 31 of the front shaft 3. The movable-side core pin 14 has an insertion hole 14a at its front end into which the rear end portion of the fixed-side core pin 13 is inserted, and when the mold is opened and closed, the rear end portion of the fixed-side core pin 13 slides in the inner surface of the insertion hole 14a of the movable-side core pin 14 in the front-rear direction. The front end portion of the movable-side core pin 14 is thinner than the portion of the movable-side core pin 14, but since the step portion 33 is in the range of 0.mm to 0.3 mm (preferably 0.15 mm to 0.25 mm), the movable-side core pin 14 of the mold obtains sufficient durability.

[0042] The ballpoint pen 1 of the present embodiment has a ballpoint pen refill 6 housed inside a barrel 2 so as to be movable in the front-rear direction, and a front end portion of a tip body 7 of the ballpoint pen refill 6 is configured to be able to protrude and retract from a front end hole 31 of the barrel 2. A ball 74 is rotatably held at the front end portion of the tip body 7, a coating resin 11 is fixed to the outer surface of the front end portion of the tip body 7, and at least the front end portion of the barrel 2 is formed of an injection molded body of synthetic resin. A rearward step portion 33 is formed at the rear end of the front end hole 31, and a radial length D of the step portion 33 is in a range of 0.1 mm to 0.3 mm (preferably in a range of 0.15 mm to 0.25 mm). Thereby, burrs are generated at a rear end corner portion 32 of the front end hole 31 of the barrel 2. Moreover, even when the tip body 7 of the ballpoint pen refill 6 deviates from the axis of the barrel 2 in the assembly process of inserting the ballpoint pen refill 6 into the barrel 2, it is possible to avoid the vicinity of the center of the coating resin 11 from strongly colliding with the rear end corner portion 32 of the front end hole 31, and there is no risk of significant damage to the coating resin 11. Further, a core pin of a molding die for the inner surface of the front end portion of the barrel 2 can obtain sufficient durability.

[0043] The ballpoint pen 1 of this embodiment has a front end portion of the chip body 7 formed of a straight cylindrical metal tube body. An inward front edge portion 71 is formed at the front end of the chip body 7. A plurality of recessed portions 73 are circumferentially and dispersedly arranged on the outer surface of the front end portion of the chip body 7 behind the front edge portion 71, and a plurality of inward protruding portions 72 corresponding to the recessed portions 73 are circumferentially and dispersedly arranged on the inner surface of the front end portion of the chip body 7 behind the front edge portion 71. A ball 74 is rotatably held between the front edge portion 71 and the inward protruding portion 72. The coating resin 11 is fixed so as to cover the ball 74, the front edge portion 71, and the recessed portions 73. The radial length D of the stepped portion 33 is smaller than the maximum radial wall thickness T of the coating resin 11 excluding the recessed portions 73. Thereby, the coating resin 11 is firmly fixed to the outer surface of the chip body 7. Also, in the assembling process, even when the chip body 7 of the ballpoint pen refill 6 deviates from the axis of the shaft cylinder 2, it is possible to avoid the vicinity of the axis of the coating resin 11 strongly colliding with the rear end corner portion 32 of the front end hole 31 (that is, strongly clamping the coating resin 11 in the axial direction between the rear end corner portion 32 of the front end hole 31 and the outer surface of the chip body 7), and more reliably prevent damage to the coating resin 11.

[0044] In the ballpoint pen 1 of this embodiment, an elastic body locking portion 34 is formed on the inner surface of the front end portion of the shaft cylinder 2. The elastic body locking portion 34 can lock an elastic body 5 that biases the ballpoint pen refill 6 rearward. An annular guide surface 35 that gradually decreases in diameter toward the front is formed on the inner surface of the front end portion of the shaft cylinder 2 in front of the elastic body locking portion 34 and behind the stepped portion 33. Thereby, in the assembling process, even when the chip body 7 of the ballpoint pen refill 6 deviates from the axis of the shaft cylinder 2, the coating resin 11 can smoothly contact the guide surface 35, and it is possible to avoid the coating resin 11 colliding with the rear end corner portion 32 of the front end hole 31, and more reliably prevent damage to the coating resin 11.

[0045] When a virtual line that contacts the rear end corner 32 of the front end hole 31 and the guide surface 35 is drawn for the ballpoint pen 1 of the present embodiment, when the axial length from the contact point where the virtual line contacts the guide surface 35 to the rear end corner 32 is L and the radial length of the step portion 33 is D, the value of L / D is in the range of 2 to 4. Thereby, in the assembly process, damage to the coating resin 11 can be further prevented, and the core pin of the molding die for the inner surface of the front end portion of the shaft cylinder 2 can obtain sufficient durability.

[0046] The ballpoint pen 1 of the present embodiment has a ball 74 with a relatively large outer diameter that exhibits the above effects because the maximum outer diameter A in the radial direction of the coating resin 11 is in the range of 70% to 95% of the inner diameter B of the front end hole 31.

[0047] The ballpoint pen 1 of this embodiment has a ballpoint pen refill 6 housed inside a shaft cylinder 2 so as to be movable in the front-rear direction. The front end portion of the tip body 7 of the ballpoint pen refill 6 is configured to be able to protrude and retract from the front end hole 31 of the shaft cylinder 2. At least the front end portion of the shaft cylinder 2 is formed of an injection molded body of synthetic resin. A ball 74 is rotatably held at the front end portion of the tip body 7. A coating resin 11 is fixed to the outer surface of the front end portion of the tip body 7. A rearward step portion 33 is formed at the rear end of the front end hole 31. The front end portion of the tip body 7 is formed of a straight cylindrical metal cylinder. An inward front edge portion 71 is formed at the front end of the tip body 7. A plurality of recessed portions 73 are circumferentially and dispersedly arranged on the outer surface of the front end portion of the tip body 7 behind the front edge portion 71, and a plurality of inward protruding portions 72 corresponding to the recessed portions 73 are circumferentially and dispersedly arranged on the inner surface of the front end portion of the tip body 7 behind the front edge portion 71. The ball 74 is rotatably held between the front edge portion 71 and the inward protruding portion 72. The coating resin 11 is fixed so as to cover the ball 74, the front edge portion 71, and the recessed portions 73. The radial length D of the step portion 33 is smaller than the maximum radial wall thickness T of the coating resin 11 excluding the recessed portions 73. Thereby, the coating resin 11 is firmly fixed to the outer surface of the tip body 7. Also, in the assembly process, even when the tip body 7 of the ballpoint pen refill 6 is displaced from the axis of the shaft cylinder 2, it is possible to avoid the vicinity of the axis of the coating resin 11 strongly colliding with the rear end corner portion 32 of the front end hole 31 (that is, strongly sandwiching the coating resin 11 in the axial direction between the rear end corner portion 32 of the front end hole 31 and the outer surface of the tip body 7), and it is possible to surely prevent damage to the coating resin 11.

Explanation of Signs

[0048] 1 Ballpoint pen 2 Shaft cylinder 3 Front shaft 31 Front end hole 32 Rear end corner portion 33 Step portion 34 Elastic body locking portion 35 Guide surface 36 Front end portion 37 Gripping portion 38 Connecting portion 39 Recessed portion 39a Gate section 4 Rear axle 41 Operating section 42 Clip 5 Elastic body 6 Ball pen refill 7 Chip body 71 Front edge 72 Inner protruding portion (ball receiving seat) 73 Depression 74 Ball 8 Chip holder 81 Front part 82 Flange 83 Rear part 84 Mounting hole 85 Ink flow hole 85a Locking projection 86 Rib 9 Spring 91 Rod part 92 Coil part 10 Ink storage cylinder 10a Ink 10b Follower 11 Coating resin D Radial length of the step portion T Maximum radial wall thickness of the coating resin L Axial length from the contact point where the virtual line touches the guide surface to the rear end corner A Maximum outer diameter of the coating resin in the radial direction B Inner diameter of the front end hole 12 Cavity 13 Fixed side core pin 14 Movable side core pin 14a Insertion hole

Claims

1. A ball pen refill is accommodated inside a shaft cylinder so as to be movable in the front-rear direction, and a front end portion of a tip body of the ball pen refill is configured to be able to project and retract from a front end hole of the shaft cylinder. A ball is rotatably held at the front end portion of the tip body, a coating resin is fixed to an outer surface of the front end portion of the tip body, at least a front end portion of the shaft cylinder is formed of an injection molded body of synthetic resin, a rearward step portion is formed at a rear end of the front end hole, and a radial length of the step portion is 0.1 mm or more. An elastic body locking portion is formed on an inner surface of a front end portion of the shaft cylinder behind the step portion. The elastic body locking portion is capable of locking an elastic body that biases the ball pen refill rearward. An annular guide surface that gradually decreases in diameter toward the front is formed on an inner surface of a front end portion of the shaft cylinder in front of the elastic body locking portion and behind the step portion. The front end portion of the tip body is formed of a straight cylindrical metal barrel. An inward front edge portion is formed at the front end of the tip body. A plurality of recessed portions are circumferentially and dispersedly arranged on an outer surface of the front end portion of the tip body behind the front edge portion, and a plurality of inward protruding portions corresponding to the recessed portions are circumferentially and dispersedly arranged on an inner surface of the front end portion of the tip body behind the front edge portion. The ball is rotatably held between the front edge portion and the inward protruding portions, and the coating resin is fixed so as to cover the ball, the front edge portion, and the recessed portions. A ball pen, characterized in that a radial length of the step portion is smaller than a maximum radial wall thickness of the coating resin excluding the recessed portions.

2. When a virtual line contacting the rear end corner portion of the front end hole and the guide surface is drawn, when an axial length from a contact point where the virtual line contacts the guide surface to the rear end corner portion is L, and a radial length of the step portion is D, The ball pen according to claim 1, wherein a value of L / D is in a range of 2 to 4.

3. The ball pen according to claim 1 or 2, wherein a maximum outer diameter in the radial direction of the coating resin is in a range of 70% to 95% of an inner diameter of the front end hole.

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