Writing instrument

Abstract

A writing instrument 1 includes: a cylindrical inner cylinder 20 having a first opening end part 29; and a cylindrical rear shaft 10 that has a second opening end part 18 and that can couple with the inner cylinder 20 by means of the first opening end part 29 being inserted into the second opening end part 18. The opening edge or the area near the opening edge of the first opening end part 29 is provided with at least one thin section 30 formed so as to be thinner than portions other than the opening edge or the area near the opening edge.

Description

writing implements

[0001] The present invention relates to a writing instrument.

[0002] A writing instrument having an inner tube as a first cylindrical member and a rear barrel as a second cylindrical member is known (Patent Document 1). In the writing instrument described in Patent Document 1, the front end of the inner tube, which is the first open end, is inserted into the rear end of the rear barrel, which is the second open end, so that the inner tube and the rear barrel are fitted together. Specifically, in the fitted state, a recessed portion provided on the outer surface near the front end of the inner tube and a protruding portion provided on the inner surface of the rear barrel are engaged in the direction in which the inner tube is pulled out.

[0003] Japanese Patent Application Laid-Open No. 2021-30669

[0004] During assembly, when the front end of the inner tube is inserted into the rear end of the rear axle, the front end of the inner tube elastically deforms as it passes over the convex portion of the rear axle. The greater the force required to elastically deform the front end of the inner tube, i.e., the greater the amount of elastic deformation, the more difficult it becomes to assemble, i.e., fit, the inner tube and rear axle. If the height of the convex portion of the rear axle is reduced to reduce the amount of elastic deformation so that assembly can be performed with less force, this weakens the engagement with the concave portion of the inner tube, making it easier for the inner tube and rear axle to come loose.

[0005] On the other hand, if the depth of the recess in the inner cylinder and the height of the protrusion in the rear axle are increased to make it more difficult for the inner cylinder and rear axle to come apart, the amount of elastic deformation increases, requiring more force for assembly. Furthermore, the front end of the inner cylinder is circular and has a uniform thickness all around, making it less susceptible to elastic deformation. However, stress tends to concentrate, particularly in the front edge where the recess is formed, and there is a risk of breakage, such as cracking, due to elastic deformation.

[0006] While Patent Document 1 describes a fitting between a convex portion of the rear barrel and a concave portion of the inner barrel, the same applies to a writing instrument in which, for example, a first annular convex portion is formed on the outer surface of a first cylindrical member inserted inside, and a plurality of second convex portions arranged circumferentially are formed on the inner surface of a second cylindrical member. That is, in such a writing instrument, the first convex portion and the second convex portion fit together by climbing over each other, but even in this case, there is a risk that the front edge of the first cylindrical member will be damaged due to elastic deformation.

[0007] An object of the present invention is to provide a writing implement that is easy to assemble, has sufficient fitting strength, and is durable.

[0008] According to one aspect of the present invention, there is provided a writing instrument having a first tubular member with a first opening end, and a second tubular member with a second opening end, the first opening end being inserted into the second opening end so as to be able to engage with the first tubular member, and at least one thin-walled portion is provided at or near the opening edge of the first opening end, which is thinner than other portions at or near the opening edge.

[0009] The at least one thin portion may have at least two thin portions, and each of the at least two thin portions may be equally spaced around the central axis of the first tubular member. A boundary between the at least one thin portion and the other portion may be formed in a stepped shape. The first tubular member may be an inner tube, the second tubular member may be a barrel or a rear axle into which the inner tube is inserted from its rear end, a bulge portion may be formed at the rear end of the inner tube, a front end surface of the bulge portion may abut against the rear end surface of the barrel or the rear axle, the inner tube may have a clip, at least one first engaging portion may be provided on an inner surface of the barrel or the rear axle at a position rotated by a predetermined angle around the central axis with respect to the clip in a fitted state, and a second engaging portion engageable with the first engaging portion may be provided on an outer surface of the inner tube. A guide protrusion may be provided on an outer surface of the first cylindrical member, and the second cylindrical member may be provided with a groove or notch that extends from the second open end toward the interior of the second cylindrical member and receives the guide protrusion to guide insertion of the first cylindrical member.The writing instrument may further include a writing body, a spring that urges the writing body backward, an outer cam provided on the inner surface of the first cylindrical member or the second cylindrical member, a cylindrical operating member, a rotor that has an insertion portion that can be inserted into the front end opening of the operating member and is urged backward via the writing body by the spring, and is configured to cooperate with the outer cam by operation of the operating member, and an urging means provided between the writing body and the rotor, wherein the urging means is configured to tilt a central axis of the rotor with respect to a central axis of the first cylindrical member or the second cylindrical member. The biasing means may be a biasing surface provided on the front end surface of the rotor and inclined with respect to a plane perpendicular to the central axis of the rotor, or a biasing protrusion provided on the front end surface of the rotor.

[0010] According to the aspects of the present invention, the common effect of providing a writing implement that is easy to assemble, has sufficient fitting force, and is durable is achieved.

[0011] FIG. 1 is a longitudinal cross-sectional view of a writing instrument according to an embodiment of the present invention. FIG. 2 is a longitudinal cross-sectional view of the rear barrel. FIG. 3 is another longitudinal cross-sectional view of the rear barrel corresponding to line A-A in FIG. 2. FIG. 4 is a perspective view of the inner barrel. FIG. 5 is a longitudinal cross-sectional view of the inner barrel. FIG. 6 is another longitudinal cross-sectional view of the inner barrel corresponding to line B-B in FIG. 5. FIG. 7 is a horizontal cross-sectional view of the inner barrel corresponding to line C-C in FIG. 5. FIG. 8 is an exploded perspective view of the rear barrel and inner barrel. FIG. 9 is a longitudinal cross-sectional view of an assembled portion of the rear barrel and inner barrel. FIG. 10 is another longitudinal cross-sectional view of an assembled portion of the rear barrel and inner barrel corresponding to line D-D in FIG. 9. FIG. 11 is a longitudinal cross-sectional view of the rear half of a writing instrument according to another embodiment of the present invention in a non-writing state. FIG. 12 is a longitudinal cross-sectional view of the rear half of the writing instrument of FIG. 11 in a writing state. FIG. 13 is a perspective view of the inner barrel. FIG. 14 is a longitudinal cross-sectional view of the inner barrel. FIG. 15 is an exploded perspective view of the rear barrel and inner barrel. FIG. 16 is a perspective view of a rotor. FIG. 17 is a side view of the rotor.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Corresponding components throughout the drawings are designated by common reference numerals.

[0013] 1 is a vertical cross-sectional view of a writing instrument 1 according to an embodiment of the present invention. The writing instrument 1 is a ballpoint pen, which is a so-called knock-type writing instrument.

[0014] The writing instrument 1 comprises a barrel 2 equipped with a front barrel 3 and a rear barrel 10 that screws onto the outer peripheral surface of the rear end of the front barrel 3; an inner barrel 20 that fits onto the inner peripheral surface of the rear end of the barrel 2, i.e., the rear end of the rear barrel 10, and is equipped with a clip 21; a refill 4 that is a writing body disposed within the barrel 2 and has a writing portion 4a at one end; and a spring 5 that is an elastic member that biases the refill 4 rearward. In this embodiment, the refill 4 is a ballpoint pen refill. In this specification, in the axial direction of the writing instrument 1, the side of the writing portion 4a is defined as the "front" side, and the side opposite the writing portion 4a is defined as the "rear" side. The barrel 2 may also include the inner barrel 20.

[0015] A grip 3a is provided on the outer surface of the front barrel 3 by two-color molding to make it easier for the user to grip. The front barrel 3 is made of a semi-hard or hard resin material such as polypropylene or polycarbonate. The grip 3a is made of a material with rubber elasticity such as a thermoplastic elastomer or a soft resin material.

[0016] Grip 3a may extend forward beyond the front end of front barrel 3 and may be provided so as to cover the front end face of front barrel 3, as disclosed in JP 2013-52678 A, for example. This allows all users who hold grip 3a in different positions to enjoy a comfortable feel when using writing instrument 1. Furthermore, grip 3a may be provided on the outer peripheral surface of front barrel 3, extend rearward beyond flange 3b that engages the front end face of rear barrel 10, and have a convex portion that protrudes radially outward on the extended portion, as disclosed in JP 2014-46639 A, for example. This allows the convex portion to be compressed by the inner peripheral surface of rear barrel 10 when front barrel 3 and rear barrel 10 are threaded together, preventing loosening of the threaded engagement.

[0017] A known knock mechanism is disposed within the rear end of the inner tube 20. The knock mechanism includes a rotor 40 movably disposed within the inner tube 20 in the front-rear direction, and an operating member 7 that protrudes rearward from the rear end opening of the rear axle 10 and is disposed behind the rotor 40 and movable in the front-rear direction. The operating member 7 is a cylindrical member with a closed rear end, and a cam surface 7a is provided on its annular front end surface. The rotor 40 consists of an insertion portion 41 that is inserted into the front end opening of the operating member 7 and used for centering, and a main body portion 42 formed in front of the insertion portion 41. Four inner cams 43 extending in the front-rear direction are provided at equal intervals circumferentially on the outer peripheral surface of the main body portion 42. The annular rear end surface of the main body portion 42 is provided with a cam receiving surface 44 that cooperates with the cam surface 7a of the operating member 7. The rotor 40 and operating member 7 are biased rearward together with the refill 4 by a spring 5. That is, the rear end surface of the refill 4 is always in contact with the front end surface of the rotor 40. The rotor 40 is configured so that the cam surface 7a of the operating member 7 and the cam receiving surface 44 of the rotor 40 cooperate with each other to rotate in the circumferential direction.

[0018] The knocking operation is performed by pressing the operating member 7 forward against the biasing force of the spring 5. As the operating member 7 moves due to the knocking operation, the rotor 40 and the refill 4 are pressed and move forward within the inner tube 20. Next, when the force applied to the operating member 7 is released, the rotor 40 rotates around the central axis, and the rear end face of the inner cam 43 formed on the outer circumferential surface of the rotor 40 engages with the front end face of the outer cam 9 formed on the inner circumferential surface of the inner tube 20. This causes the writing instrument 1 to maintain a writing state in which the writing part 4a protrudes from the tip of the barrel 2. When the knocking operation is performed while the writing instrument 1 is in the writing state, the rotor 40 and the refill 4 are pressed and move forward within the inner tube 20 as the operating member 7 moves, and the engagement between the rear end face of the inner cam 43 of the rotor 40 and the front end face of the outer cam 9 of the inner tube 20 is released. Next, when the force applied to the operating member 7 is released, the rotor 40 rotates around the central axis, and the refill 4 moves rearward due to the biasing force of the spring 5. This puts the writing instrument 1 into a non-writing state (FIG. 1) in which the writing part 4a is retracted into the barrel 2. In other words, the rotor is configured to cooperate with the external cam.

[0019] The refill 4 may be a writing instrument other than a ballpoint pen, such as a marking pen, a touch pen, or an eraser. Furthermore, part or all of the operating member 7 may serve as an erasing unit for erasing handwriting made with the writing instrument 1. The refill 4 may contain thermochromic ink containing a thermochromic coloring material. In this case, the writing instrument 1 is a thermochromic writing instrument, and the handwriting made with the writing instrument 1 can be thermochromic due to the frictional heat generated when rubbed with a friction body acting as an erasing member.

[0020] Here, thermochromic ink refers to ink that maintains a predetermined color (first color) at room temperature (e.g., 25°C), changes to a different color (second color) when heated to a predetermined temperature (e.g., 60°C), and then returns to the original color (first color) when cooled to a predetermined temperature (e.g., -5°C). In a writing instrument using thermochromic ink, the second color is colorless, and "erasing" refers to heating a line drawn in the first color (e.g., red) to make it colorless. Therefore, a frictional body rubs against the writing surface on which the line was drawn, generating frictional heat, thereby changing the drawn line to colorless, i.e., erasing it. Naturally, the second color may be a color other than colorless.

[0021] FIG. 2 is a longitudinal cross-sectional view of the rear body 10, and FIG. 3 is another longitudinal cross-sectional view of the rear body 10 corresponding to line AA in FIG.

[0022] The rear axle 10 is a cylindrical member. The rear end surface 10a of the rear axle 10 is formed as a slope inclined at approximately 45 degrees with respect to the central axis. The rear end surface 10a is not strictly a slope, but is formed as a slightly convex curved surface. A small diameter portion 11 with a smaller inner diameter than the inner surface in the front part is formed on the inner surface rearward of the center in the axial direction of the rear axle 10.

[0023] A substantially rectangular first guide groove 12 extending forward from the rear end face 10a is formed on the inner surface of the rear axle 10. The first guide groove 12 is formed in the most forward portion of the sloped rear end face 10a. The first guide groove 12 may be a notch extending forward from the rear end face 10a of the rear axle 10. Furthermore, two substantially rectangular second guide grooves 13 extending forward from the rear end face 10a are formed on the inner surface of the rear axle 10. Each of the two second guide grooves 13 is positioned approximately 90 degrees rotated around the central axis of the rear axle 10 relative to the first guide groove 12. The two second guide grooves 13 face each other. A first engagement portion 14, which is a groove shallower than the remaining portion of the second guide groove 13, is formed in the front end portion of the interior of the second guide groove 13. In other words, the first engagement portion 14 is a protrusion provided inside the second guide groove 13.

[0024] Two protrusions 15 are formed on the inner surface of the rear axle 10, extending rearward from the front edge of the small diameter portion 11. The protrusions 15 protrude at a uniform height from the inner surface of the rear axle 10. Each of the two protrusions 15 is positioned at a position rotated approximately 90 degrees around the central axis of the rear axle 10 with respect to the first guide groove 12. The two protrusions 15 face each other. Therefore, each of the two protrusions 15 is aligned axially with the corresponding second guide groove 13. An inclined surface 16 is provided at the rear end of the protrusions 15. A forward-facing locking surface 17 is formed on the front end surface of the protrusions 15.

[0025] Figure 4 is a perspective view of the inner tube 20, Figure 5 is a longitudinal cross-sectional view of the inner tube 20, Figure 6 is another longitudinal cross-sectional view of the inner tube 20 corresponding to line B-B in Figure 5, and Figure 7 is a transverse cross-sectional view of the inner tube 20 corresponding to line C-C in Figure 5.

[0026] The inner tube 20 is a cylindrical member. The inner surface of the rear end of the inner tube 20 is formed with the aforementioned outer cam 9, which is made up of multiple protrusions extending in the front-to-rear direction. A bulge 22 that protrudes radially outward is formed on the outer surface of the rear end of the inner tube 20. The outer surface of the bulge 22 is formed to be, for example, flush with, the outer peripheral surface of the rear axle 10 so as to be integrated with the outer peripheral surface of the rear axle 10 when the inner tube 20 is fitted to the rear axle 10. The front end surface of the bulge 22 is formed with a fitting surface 22a that fits with the rear end surface 10a of the rear axle 10 when the inner tube 20 is fitted to the rear axle 10. Therefore, the fitting surface 22a is formed in a concave curved shape that is complementary to the rear end surface 10a of the rear axle 10. A clip 21 is integrally formed on the bulge 22. The clip 21 is formed so as to be positioned at the rearmost portion of the sloped rear end surface 10a of the rear axle 10 when the inner tube 20 is fitted to the rear axle 10. A rear end recess 22b is provided on the rear end surface of the inner cylinder 20 near the base of the clip 21 so as to be adjacent to and connected to the opening through which the operating member 7 projects. A bottom surface 22c of the rear end recess 22b is formed to be approximately flat.

[0027] A substantially rectangular guide protrusion 23 is formed on the outer surface of the inner tube 20 at the center in the axial direction. The guide protrusion 23 is provided on the opposite side of the clip 21 with respect to the central axis of the inner tube 20. The circumferential width of the guide protrusion 23 is slightly smaller than the width of the first guide groove 12 of the rear axle 10. Two substantially rectangular second engagement portions 24 are formed on the outer surface of the inner tube 20 closer to the rear of the guide protrusion 23. The two second engagement portions 24 are substantially rectangular protrusions. Each of the two second engagement portions 24 is positioned approximately 90 degrees rotated around the central axis of the inner tube 20 with respect to the guide protrusion 23. The two second engagement portions 24 face each other. The circumferential width of the second engagement portions 24 is slightly smaller than the width of the second guide groove 13 of the rear axle 10.

[0028] Two rectangular recesses 25 are formed on the front outer surface of the inner tube 20. The recesses 25 are recesses of a uniform depth from the outer surface of the inner tube 20. Each of the two recesses 25 is positioned at a position rotated approximately 90 degrees around the central axis of the inner tube 20 relative to the clip 21. The two recesses 25 face each other. Therefore, each of the two recesses 25 is aligned axially with the corresponding second engagement portion 24. A substantially U-shaped U-hole 26 is formed in the rectangular recess 25. The U-hole 26 consists of a through hole along the rear edge and two through holes extending forward from each end of the through hole. An elastic deformation portion 27 is defined within the recess 25 by the U-hole 26. The elastic deformation portion 27 has a cantilever shape extending rearward within the recess 25. A substantially spherical protrusion 28 protruding radially outward is formed on the outer surface of the elastic deformation portion 27.

[0029] The outer surface of the inner tube 20 near the first open end 29 at the front is formed with an annular surface 29a that is smaller in diameter than the other portions. The inner surface near the first open end 29 is formed with a slope 29b that slopes forward. The inner surface of the first open end 29 is formed with two thin-walled portions 30 that extend rearward from the front end face of the inner tube 20. The thin-walled portions 30 are recessed and thinner than the other portions of the first open end 29, including the slope 29b. The boundaries of the thin-walled portions 30 with the other portions of the inner tube 20 are stepped ( FIG. 7 ). Each of the two thin-walled portions 30 is aligned radially with respect to the clip 21. In other words, each of the two thin-walled portions 30 is positioned approximately 90 degrees rotated around the central axis of the inner tube 20 relative to the two recesses 25. The two thin-walled portions 30 face each other.

[0030] Assembly of the rear axle 10 and inner cylinder 20 will be described with reference to Figures 8 to 10. Figure 8 is an exploded perspective view of the rear axle 10 and inner cylinder 20, Figure 9 is a longitudinal cross-sectional view of the assembled portion of the rear axle 10 and inner cylinder 20, and Figure 10 is another longitudinal cross-sectional view of the assembled portion of the rear axle 10 and inner cylinder 20 corresponding to line D-D in Figure 9.

[0031] The first open end 29 of the inner cylinder 20 is inserted into the rear second open end 18 of the rear axle 10. At this time, the inner cylinder 20 is aligned around the central axis so that the guide protrusion 23 of the inner cylinder 20 enters the first guide groove 12 of the rear axle 10. As the insertion of the first open end 29 continues with the guide protrusion 23 entered into the first guide groove 12, each of the two second engagement portions 24 of the inner cylinder 20 then enters the corresponding second guide groove 13 of the rear axle 10.

[0032] As the first open end 29 continues to be inserted further, it reaches the protrusion 15 of the rear axle 10. Here, the outer diameter of the first open end 29 of the inner cylinder 20, i.e., the outer diameter of the annular surface 29a, is slightly larger than the diameter of the inscribed circle of the two opposing protrusions 15 of the rear axle 10. Therefore, when the inner cylinder 20 is pressed against the rear axle 10, the first open end 29 elastically deforms as it climbs over the inclined surface 16 provided at the rear end of the protrusion 15. This allows the first open end 29 of the inner cylinder 20 to be further inserted into the rear axle 10. Finally, the protrusion 15 of the rear axle 10 is accommodated in the recess 25 of the inner cylinder 20, and the two second engagement portions 24 of the inner cylinder 20 radially coincide and engage with the corresponding first engagement portions 14 of the rear axle 10 within the second guide groove 13, completing the assembly of the rear axle 10 and inner cylinder 20, i.e., fitting.

[0033] When the rear axle 10 and inner tube 20 are assembled, even if a force acts on the inner tube 20 to pull it out of the rear axle 10, as shown in FIG. 10 , the locking surface 17 of the protrusion 15 of the rear axle 10 locks with the front step 25a of the recess 25 of the inner tube 20, preventing the inner tube 20 from coming off the rear axle 10. Furthermore, the protrusion 28 of the elastically deforming portion 27 abuts against the surface of the protrusion 15 of the rear axle 10, elastically deforming the elastically deforming portion 27 so that it curves radially inward. Therefore, the rear end edge 27a of the inner surface of the elastically deforming portion 27 protrudes radially inward inside the inner tube 20. As a result, for example, when replacing the refill 4, the rotor 40, which is located at the rear inside the inner tube 20, locks with the rear end edge 27a of the inner surface of the elastically deforming portion 27, preventing the rotor 40 from falling off.

[0034] When the first open end 29 elastically deforms, the thin-walled portion 30 is more susceptible to elastic deformation because its thinness reduces its rigidity compared to other portions. In other words, if the open end were uniform in thickness around its entire circumference, the circular cross-sectional shape of the open end would also make it less susceptible to elastic deformation. Therefore, an inner barrel 20 having a first open end 29 with a thin-walled portion 30 can be assembled with less force than an identical inner barrel and rear barrel 10, except that the open end does not have a thin-walled portion, while maintaining sufficient mating force between the rear barrel 10 and the inner barrel 20. Furthermore, the elastic deformation of the thin-walled portion 30 absorbs and relieves stress at and near the first open end 29, improving the durability of the inner barrel 20. In short, the writing instrument 1 achieves easy assembly, sufficient mating force, and durability.

[0035] The thin-walled portion 30 described above is formed as a recess on the inner surface of the first open end 29 of the inner tube 20, but may also be formed as a recess on the outer surface of the first open end 29. The boundary between the thin-walled portion 30 and other portions of the inner tube 20 is formed as a step, but the thin-walled portion 30 may be formed so that it is smoothly and continuously connected to other portions of the inner tube 20. At least one thin-walled portion 30 may be provided, and three or more thin-walled portions 30 may be provided. When at least two thin-walled portions 30 are provided, they are preferably arranged at equal intervals around the central axis of the inner tube 20, but they do not have to be arranged at equal intervals. It is sufficient that the thin-walled portion 30 is provided at least on the opening edge of the first open end 29 or near the opening edge.

[0036] The thin-walled portions 30 are preferably provided in positions where elastic deformation is likely to be greater. For example, in the inner cylinder 20, the pair of recesses 25 and the pair of thin-walled portions 30 are located at positions rotated approximately 90 degrees around the central axis of the inner cylinder 20. When assembling the rear axle 10 and the inner cylinder 20, when the portion of the first open end 29 of the inner cylinder 20 corresponding to the recesses 25 rides over the protrusion 15 of the rear axle 10, that portion elastically deforms radially inward. On the other hand, the portion of the first open end 29 rotated approximately 90 degrees around the central axis of the inner cylinder 20 from that portion has the largest radius of curvature and therefore the largest stress. Because the thin-walled portions 30 are provided in this portion of the inner cylinder 20 where stress is greatest, stress is absorbed by elastic deformation, preventing damage to the first open end 29, etc. In short, the shape (e.g., width in the circumferential direction, length extending in the axial direction, depth from the inner surface of the inner tube 20, etc.) and number of the thin-walled portion 30 can be appropriately configured depending on the shape, form, or number of the mating parts.

[0037] When the assembly of the rear axle 10 and the inner tube 20 is complete, as described above, each of the two second engagement portions 24 of the inner tube 20 is engaged with the corresponding first engagement portion 14 in the second guide groove 13. The engagement of the first engagement portion 14 and the second engagement portion 24 prevents the inner tube 20 from coming off the rear axle 10 when the clip 21 is used. In other words, when an item is gripped by the clip 21, the clip 21 is expanded with the connection portion with the bulge portion 22 as a fulcrum. At this time, the force expanding the clip 21 acts on the rear end surface 10a of the rear axle 10 via the bulge portion 22, and a force is applied to the inner tube 20 to pull it rearward from the rear axle 10, just like using a bottle opener to remove a cork. However, since the two second engagement portions 24 of the inner tube 20 are engaged with the first engagement portions 14 within the second guide groove 13, as part of the force acting based on the principle of leverage, the inner tube 20 is restricted from swinging relative to the rear axle 10, preventing the inner tube 20 from coming off the rear axle 10.

[0038] In the above-described embodiment, the second guide groove 13 of the rear axle 10 and the first engagement portion 14 formed therein, and the second engagement portion 24 of the inner tube 20 are arranged opposite each other, i.e., at positions rotated approximately 90 degrees around the central axis relative to the clip 21, but they may also be arranged at positions rotated within a range of 45 degrees to 135 degrees with the clip 21 as the reference.

[0039] The first engagement portion 14 of the rear axle 10 and the second engagement portion 24 of the inner cylinder 20 may be configured in any manner as long as they engage when the rear axle 10 and the inner cylinder 20 are fitted together and disengagement due to the expansion of the clip 21 is prevented. For example, an axially extending key groove may be formed on the inner surface of the rear axle, and an axially extending key protrusion corresponding to the key groove may be formed on the outer surface of the inner cylinder. When the rear axle and the inner cylinder are fitted together, the key protrusion may be received in the key groove, thereby restricting the inner cylinder from swinging relative to the rear axle when the clip is in use.

[0040] In the above-described embodiment, the assembly of the inner tube of the writing instrument is described as the first cylindrical member and the barrel, i.e., the rear barrel, as the second cylindrical member. However, the above-described configuration may also be applied to the assembly of two other cylindrical members in a writing instrument. For example, the above-described configuration may also be applied to the assembly of a front barrel and a rear barrel. Furthermore, the above-described configuration may also be applied to writing instruments other than knock-type writing instruments, such as cap-type writing instruments.

[0041] In the above-described embodiment, the recessed portion provided on the first tubular member and the protruding portion provided on the second tubular member are fitted together. However, the above configuration may also be applied to a configuration in which, for example, a first annular protruding portion provided on the outer surface of the first tubular member inserted inside is fitted together with a plurality of second protruding portions provided circumferentially on the inner surface of the second tubular member. The above configuration may also be applied to a configuration in which one or both of the first and second tubular members do not have protruding portions or recessed portions, or both. In other words, the above configuration may be applied to any configuration of a writing instrument having a tubular first tubular member with a first open end and a tubular second tubular member with a second open end, the first open end of which is inserted into the second open end and can be fitted together with the first tubular member.

[0042] The surface of the barrel 2, excluding the grip 3a, i.e., the surface of the rear barrel 10 and the inner barrel 20, is textured, or "matt-finished," to prevent scratches and achieve a matte finish. The arithmetic mean roughness (Ra) of the matt finish is preferably in the range of 5 μm to 50 μm. If the value is less than 5 μm, the surface resembles a mirror, making scratches more noticeable. On the other hand, if the value is greater than 50 μm, demolding during resin molding becomes difficult. Furthermore, in order to achieve good design, particularly a matte finish, an arithmetic mean roughness (Ra) in the range of 10 μm to 25 μm is even more preferable. The matt finish can be achieved by subjecting the mold surface to etching, sandblasting, or polishing other than a mirror finish. Alternatively, a matt finish can be achieved by leaving the mold component surface unpolished after electrical discharge machining. The arithmetic mean roughness (Ra) of the matte finish refers to the arithmetic mean roughness (Ra) defined in JIS B0601:2013, and the surface roughness is measured using a Mitutoyo SJ-301. Note that by replacing the grip 3a of the front body 3 with the same material and surface roughness as the rear body 10, it is possible to obtain a design that gives a sense of unity to the entire body of the barrel 2.

[0043] 11 to 17, a writing instrument 100 according to another embodiment of the present invention that provides the same effects as the above-described embodiment will be described. As mentioned above, corresponding components are given the same reference numerals, and therefore, a description of these components will be omitted.

[0044] FIG. 11 is a longitudinal cross-sectional view of the rear half of a writing instrument 100 according to another embodiment of the present invention in a non-writing state, and FIG. 12 is a longitudinal cross-sectional view of the rear half of the writing instrument 100 of FIG. 11 in a writing state. The writing instrument 100 differs from the writing instrument 1 described above only in the shapes of the inner tube 120 and the rotor 140; the shapes of the other components are the same. In the non-writing state shown in FIG. 11 , the rear end surface of the inner cam 43 of the rotor 140 and the front end surface of the outer cam 9 of the inner tube 20 are not engaged, so the rotor 140 moves back together with the refill 4. In the writing state shown in FIG. 12 , the rear end surface of the inner cam 43 of the rotor 140 and the front end surface of the outer cam 9 of the inner tube 20 are engaged, so the rotor 140 moves forward together with the refill 4, and the writing part 4a protrudes from the tip of the barrel 2.

[0045] Figure 13 is a perspective view of the inner barrel 120, Figure 14 is a longitudinal cross-sectional view of the inner barrel 120, and Figure 15 is an exploded perspective view of the rear barrel 10 and the inner barrel 120. The inner barrel 120 differs from the inner barrel 20 of the writing instrument 1 in that it does not have an annular surface 29a formed on the outer surface near the first open end 29 at the front of the inner barrel 20, that it has a third engagement portion 31 in addition to the second engagement portion 24, and that it has a bottom surface 122c instead of the rear end recess 22b. Note that the inner barrel 120 may have the annular surface 29a.

[0046] The inner tube 120 has a rear-end recess 122b on its rear end surface near the base of the clip 21, adjacent to and connected to the opening through which the operating member 7 protrudes. The bottom surface 122c of the rear-end recess 122b protrudes rearward and is formed as a convex curved surface that slopes overall toward the opening. The inner tube 120 has the rear-end recess 122b and its bottom surface 122c is formed as a convex curved surface, resulting in a favorable design. Furthermore, the convex curved bottom surface 122c prevents the accumulation of dust and other particles, and even if dust and other particles do accumulate, they can be easily removed. The bottom surface 122c may not only be a convex curved surface, but may also be a flat slope that slopes toward the opening through which the operating member 7 protrudes.

[0047] A third engagement portion 31 is formed integrally with each second engagement portion 24 on the outer surface of the inner cylinder 120 behind each second engagement portion 24. The two third engagement portions 31 are trapezoidal protrusions whose rear portions are connected to the mating surface 22a. The circumferential width of each third engagement portion 31 is greater than the width of each second engagement portion 24. The height of each third engagement portion 31 is also less than the height of each second engagement portion 24. When assembling the rear body 10 and the inner cylinder 120, as described above, the second engagement portions 24 of the inner cylinder 120 radially coincide and engage with the corresponding first engagement portion 14 of the rear body 10 within the second guide groove 13. At this time, the circumferential width of each third engagement portion 31 is greater than the width of the second guide groove 13 of the rear body 10. Therefore, the portion of each third engagement portion 31 that is greater than the width of the second guide groove 13 engages with the inner surface of the rear body 10 near the second guide groove 13. As a result, when an article is gripped by the clip 21 as described above, rattle of the inner cylinder 120 relative to the rear body 10 can be more reliably prevented.

[0048] The third engagement portion 31 of the inner cylinder 120 may be located in any position and have any shape as long as it can fit into the inner surface of the rear body 10. Therefore, the third engagement portion 31 does not have to be aligned in the axial direction with the second engagement portion 24. There may be one third engagement portion 31 or three or more third engagement portions 31.

[0049] FIG. 16 is a perspective view of the rotor 140, and FIG. 17 is a side view of the rotor 140. The rotor 140 differs from the rotor 40 of the writing instrument 1 only in the shape of its front end surface. Therefore, the rotor 140 consists of an insertion portion 41, which is inserted into the front-end opening of the operating member 7 and used for centering, and a main body portion 42 formed in front of the insertion portion 41. Four inner cams 43 extending in the front-rear direction are provided at equal intervals around the circumference on the outer circumferential surface of the main body portion 42. The annular rear end surface of the main body portion 42 is provided with a cam receiving surface 44 that cooperates with the cam surface 7a of the operating member 7. Furthermore, the annular front end surface of the rotor 140 is provided with an urging surface 145, which is a flat surface inclined with respect to a plane perpendicular to the central axis of the rotor 140. An urging protrusion 146 is provided at the rearmost portion of the inclined urging surface 145. The biasing projection 146 has a flat, sloped side surface 146a provided closer to the central axis and a flat tip surface 146b provided at the tip of the biasing projection 146. The outer surface of the biasing projection 146 opposite the central axis is provided flush with the main body 42. The biasing surface 145 has an air vent groove 147 provided in the same line passing through the central axis. The air vent groove 147 prevents the interior of the refill 4 from being sealed between the front end surface of the rotor 140 and the refill 4.

[0050] The biasing surface 145 and the biasing projection 146 constitute a biasing means that biases the rotor 140 to tilt relative to the central axis of the writing instrument 100. This will be described with reference to FIGS.

[0051] When the writing instrument 100 is in a non-writing state, as shown in FIG. 11 , the operating member 7 is biased rearward by the spring 5 via the refill 4 and the rotor 140. Therefore, rattle of the operating member 7 is minimal or nonexistent. On the other hand, when the writing instrument 100 is in a writing state, as shown in FIG. 12 , the rear end surface of the inner cam 43 of the rotor 40 is engaged with the front end surface of the outer cam 9 of the inner barrel 120, so the biasing force of the refill 4 is not transmitted to the operating member 7. Therefore, if the operating member 7 is not fixed, rattle may occur only between the positions shown in FIG. 11 and FIG. 12 . In other words, since a writing action typically involves continuous up-and-down movement of the writing instrument, if the operating member is not fixed, the operating member may rattle up and down in response to the writing action. Rattle of the operating member generates noise or vibration that is unpleasant to the user.

[0052] In the writing instrument 100 according to this embodiment, as shown in FIG. 12 in particular, the rear end surface of the refill 4, which is biased rearward by the spring 5, presses the biasing surface 145 of the rotor 140. The rear end surface of the refill 4 is a surface perpendicular to the central axis of the writing instrument 100, while the biasing surface 145 is a plane inclined relative to the plane perpendicular to the central axis of the rotor 140. Therefore, the biasing force of the spring 5 acts in a direction inclined relative to the central axis of the rotor 140 so that the entire surface of the biasing surface 145 and the entire surface of the rear end surface of the refill 4 come into contact. As a result, the central axis of the rotor 140 is inclined relative to the central axis of the writing instrument 100. Furthermore, at this time, the peripheral edge of the rear end surface of the refill 4 abuts against the biasing protrusion 146, specifically the side surface 146a, restricting radial movement of the rear end of the refill 4 along the biasing surface 145. As a result, the center axis of the refill 4 is aligned with the center axis of the writing instrument 100, and the rotor 140 can be tilted more reliably.

[0053] The inclined insertion portion 41 of the rotor 140 biases the operating member 7 into which the insertion portion 41 is inserted from the inside. That is, the operating member 7 is biased by the insertion portion 41 of the rotor 140 against the inner surface of the barrel 2, specifically against the inner surface of the opening of the inner barrel 120 from which the operating member 7 protrudes. Therefore, the operating member 7 is sandwiched and fixed between the insertion portion 41 of the rotor 140 and the inner surface of the barrel 2, preventing rattling of the operating member 7. As a result, it is possible to prevent noise or vibration from occurring during writing, improving the writing experience for the user.

[0054] Note that either the urging surface 145 or the urging protrusion 146 may be omitted. Furthermore, a configuration corresponding to the urging surface 145 and the urging protrusion 146 may be provided on the rear end surface of the refill 4. That is, as the urging means, a urging protrusion may be provided on the rear end surface of the refill 4, or a urging surface that is a flat surface inclined with respect to a plane perpendicular to the central axis of the refill 4 may be provided on the rear end surface of the refill 4. The urging means may be a separate member attached to the refill 4 or the rotor 140.

[0055] REFERENCE SIGNS LIST 1 Writing implement 2 Barrel 3 Front barrel 4 Refill 5 Spring 6 Rotor 7 Operating member 9 Outer cam 10 Rear barrel 11 Small diameter portion 12 First guide groove 13 Second guide groove 14 First engagement portion 15 Convex portion 16 Inclined surface 17 Locking surface 18 Second opening end 20 Inner barrel 21 Clip 22 Bulging portion 23 Guide projection 24 Second engagement portion 25 Concave portion 26 U-shaped hole 27 Elastic deformation portion 28 Projecting portion 29 First opening end 30 Thin portion

Claims

1. A writing instrument having a first tubular member with a first opening end, and a second tubular member with a second opening end, the first opening end being inserted into the second opening end so as to be able to fit into the first tubular member, wherein at least one thin-walled portion is provided at or near the opening edge of the first opening end, the thin-walled portion being thinner than other portions at or near the opening edge.

2. The writing implement according to claim 1, wherein said at least one thin portion has at least two thin portions, each of said at least two thin portions being equally spaced around the central axis of said first tubular member.

3. The writing implement according to claim 1 or 2, wherein the boundary between said at least one thin portion and said other portion is formed in a stepped shape.

4. A writing instrument as described in claim 1 or 2, wherein the first tubular member is an inner tube, the second tubular member is a barrel or rear barrel into which the inner tube is inserted from its rear end, a bulge is formed at the rear end of the inner tube, the front end surface of the bulge abuts the rear end surface of the barrel or rear barrel, the inner tube has a clip, at least one first engagement portion is provided on the inner surface of the barrel or rear barrel at a position rotated a predetermined angle around the central axis relative to the clip in an engaged state, and a second engagement portion capable of engaging with the first engagement portion is provided on the outer surface of the inner tube.

5. A writing instrument as described in claim 1 or 2, wherein a guide protrusion is provided on the outer surface of the first tubular member, and the second tubular member is provided with a groove or notch extending from the second opening end toward the inside of the second tubular member and receiving the guide protrusion to guide insertion of the first tubular member.

6. A writing instrument as described in claim 1 or 2, further comprising: a writing body; a spring for urging the writing body backward; an outer cam provided on the inner surface of the first cylindrical member or the second cylindrical member; a cylindrical operating member; a rotor having an insertion portion that can be inserted into the front end opening of the operating member and urged backward via the writing body by the spring, the rotor being configured to cooperate with the outer cam by operation of the operating member; and a biasing means provided between the writing body and the rotor, wherein the biasing means is configured to incline the central axis of the rotor with respect to the central axis of the first cylindrical member or the second cylindrical member.

7. A writing implement as described in claim 6, wherein the biasing means is a biasing surface provided on the front end face of the rotor and inclined with respect to a plane perpendicular to the central axis of the rotor, or a biasing protrusion provided on the front end face of the rotor.

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