Writing instrument

Abstract

To provide a fitting structure of a flexible member capable of reliably preventing the flexible member from coming off and facilitating the fitting operation of the flexible member.SOLUTION: A writing instrument comprises a tube (shaft tube or cap) having a fitting hole opening upward in the axial direction, and a flexible member inserted into the fitting hole. Multiple inward protrusions divided in the circumferential direction are formed on the inner peripheral surface of the fitting hole. Multiple grooves extend in the axial direction between the respective inward protrusions. Multiple outward protrusions divided in the circumferential direction are formed on the outer peripheral surface of the flexible member. The outward protrusions can pass through the grooves from above in the axial direction toward below in the axial direction, but are prevented from passing through the grooves from below in the axial direction toward above in the axial direction due to the inward protrusions.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a writing instrument including a cylindrical body (for example, a shaft cylinder or a cap) having a mounting hole opening axially upward, and a soft member inserted into the mounting hole.

Background Art

[0002] Patent Document 1 discloses a structure in which an eraser (an example of a soft member) is attached to a pencil cap (an example of a cylindrical body).

[0003] However, in the attachment structure of Patent Document 1, there is a risk that the eraser may fall out of the attachment hole when the elasticity of the eraser decreases over time, and a large pushing force is required when press-fitting the eraser into the attachment hole, making the attachment work not easy.

[0004] Patent Document 2 discloses a mounting structure of a soft member in which, as shown in FIG. 26, a mounting hole 102 opening axially upward is provided at the upper end of a cylindrical body 101 of a writing instrument, and the soft member 103 is inserted into the mounting hole 102. An inward protrusion 121 is formed on the inner peripheral surface of the mounting hole 102, an outward protrusion 151 is formed on the outer peripheral surface of the soft member 103, and the outward protrusion 151 straddles the inward protrusion 121 from above to below.

[0005] According to the attachment structure of Patent Document 2, even when the elasticity of the soft member 103 decreases over time, the soft member 103 is unlikely to fall out of the attachment hole 102 due to the strong engagement between the outward protrusion 151 and the inward protrusion 121.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0007] However, also in the attachment structure of Patent Document 2, when the soft member 103 is press-fitted into the attachment hole 102, the outward protrusion 151 needs to overcome the inward protrusion 121 from above to below. For this reason, a large pushing force is required and the attachment work is not easy.

[0008] The present invention has been made based on the above background, and an object thereof is to provide an attachment structure for a soft member that enables reliable prevention of the soft member from falling off and facilitates the attachment work of the soft member.

Means for Solving the Problems

[0009] The present invention is a writing instrument including a cylindrical body (shaft cylinder or cap) having an attachment hole opening axially upward, and a soft member inserted into the attachment hole, wherein on the inner peripheral surface of the attachment hole, a plurality of inward protrusions divided in the circumferential direction are formed, between the plurality of inward protrusions, a plurality of grooves extend in the axial direction, on the outer peripheral surface of the soft member, a plurality of outward protrusions divided in the circumferential direction are formed, and the plurality of outward protrusions can pass through the plurality of grooves from the axial upper direction to the axial lower direction, while being inhibited from passing by the plurality of inward protrusions from the axial lower direction to the axial upper direction.

[0010] According to the present invention, since the plurality of outward protrusions can pass through the plurality of grooves from the axial upper direction to the axial lower direction, the attachment work of the soft member is easy, while since the passage is inhibited by the plurality of inward protrusions from the axial lower direction to the axial upper direction, a reliable effect of preventing the soft member from falling off can be achieved.

[0011] It is preferable that each of the plurality of outward protrusions is formed in a tapered shape downward in the axial direction in the circumferential direction at the end portion on the lower side in the axial direction.

[0012] According to this feature, the plurality of outward protrusions can more easily pass through the plurality of grooves from the axial upper direction to the axial lower direction.

[0013] Moreover, each of the plurality of grooves preferably extends in the radial direction at the same height from the axial upper direction to the axial lower direction.

[0014] Also according to this feature, the plurality of outward protrusions can more easily pass through the plurality of grooves from the axial upper direction to the axial lower direction. In this case, regarding the shape seen in the circumferential direction, it may have the same width or be tapered toward the axial lower direction.

[0015] Alternatively, each of the plurality of grooves preferably extends in a tapered shape in the radial direction from the axial upper direction to the axial lower direction.

[0016] According to this feature, while maintaining the feature that the plurality of outward protrusions can more easily pass through the plurality of grooves from the axial upper direction to the axial lower direction, it is possible to make the plurality of outward protrusions and the plurality of grooves in a temporarily fitted state, so the stability in the so-called temporarily inserted state increases. In this case as well, regarding the shape seen in the circumferential direction, it may have the same width or be tapered toward the axial lower direction.

[0017] Moreover, the plurality of outward protrusions are preferably arranged evenly in the circumferential direction.

[0018] According to this feature, on the one hand, the circumferential alignment operation between the plurality of outward protrusions and the plurality of grooves is easy, and on the other hand, a more reliable effect of preventing the soft member from falling off can be achieved.

[0019] For example, the number of the plurality of outward protrusions is preferably 4, 6, or 8.

[0020] Also, although it is generally considered that the number of the plurality of grooves is designed to be equal to the number of the plurality of outward protrusions, it may be designed to be more than the number of the plurality of outward protrusions.

[0021] Further, the soft member preferably has a through-hole extending in the axial direction, and the through-hole is preferably located radially inward of the plurality of outward protrusions.

[0022] According to this feature, since the soft member can be easily elastically deformed radially inward, the plurality of outward protrusions can more easily pass through the plurality of grooves from the upper axial direction to the lower axial direction.

[0023] Also, in a state where the soft member is inserted into the mounting hole, it is preferable that the plurality of inward protrusions do not press against the outer peripheral surface of the soft member.

[0024] According to this feature, there is a low risk that the elasticity of the soft member will deteriorate over time, and the passage inhibition effect (drop prevention effect) from the lower axial direction to the upper axial direction can be reliably maintained.

Advantages of the Invention

[0025] According to the present invention, since the plurality of outward protrusions can pass through the plurality of grooves from the upper axial direction to the lower axial direction, the attachment operation of the soft member is easy. On the other hand, since the passage is inhibited by the plurality of inward protrusions from the lower axial direction to the upper axial direction, a reliable drop prevention effect of the soft member can be achieved.

Brief Description of the Drawings

[0026]

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Mode for Carrying Out the Invention

[0027] In this specification, "upper (upward in the axial direction)" refers to the side of the mounting hole in the cylindrical body and the side of the large-diameter portion in the soft member, and "lower (downward in the axial direction)" refers to the side opposite to the mounting hole in the cylindrical body and the side of the small-diameter portion in the soft member.

[0028] (Configuration of the First Embodiment) FIG. 1 is a perspective view showing a writing instrument 1 according to the first embodiment of the present invention, FIG. 2 is a longitudinal sectional view of the shaft cylinder 10 and the friction body 40 (an example of a soft member) of the writing instrument 1 in FIG. 1, FIG. 3 is an enlarged sectional view of part A in FIG. 2, and FIG. 4 is a schematic perspective view of FIG. 3.

[0029] Further, FIG. 5 is a side view of the friction body 40 according to the first embodiment of the present invention, FIG. 6a is a sectional view corresponding to FIG. 3 of the shaft cylinder 10 with the friction body 40 removed, FIG. 6b is a sectional view when the shaft cylinder in FIG. 6a is rotated 45° around the axis, and FIG. 7 is a perspective view of the vicinity of the mounting hole 20 of the shaft cylinder 10 according to the first embodiment of the present invention.

[0030] Referring to FIG. 5, the friction body 40 has a shape that is symmetric about the axis (excluding the outward protrusions 47 described later), and from the upper side in the axial direction, it has a large-diameter portion 41 (maximum diameter 6.4 mm, length 5.0 mm), a fitting portion 42 (diameter 5.0 to 5.6 mm, length 0.5 to 1.5 mm), a tapered portion 43 (maximum diameter 4.5 to 5.0 mm, length 5.5 mm, minimum diameter 3.5 to 4.5 mm), a passing portion 44 (diameter 3.5 to 4.5 mm, length 3.5 to 4.2 mm), and a tip portion 45 (length 0.5 to 1.5 mm, minimum diameter 3.2 to 3.5 mm). By the lower end of the large-diameter portion 41 of the friction body 40 abutting against the upper end of the shaft cylinder 10, the friction body 40 is prevented from dropping downward in the axial direction.

[0031] And in the passing portion 44, four outward protrusions 47 in the shape of shogi pieces (symmetric in the circumferential direction) divided in the circumferential direction are formed by resin molding. It is preferable that the friction body 40 and the outward protrusions 47 are molded from the same material. The four outward protrusions 47 are evenly arranged in the circumferential direction.

[0032] The size of each outward protrusion 47 is such that the radius at the circumferential center line is 2.2 to 2.5 mm (see also FIGS. 10 and 11), the circumferential width of the base is 1.0 to 2.4 mm, the circumferential width between the bent shoulders is 0.8 to 2.0 mm, and the length from the base to the apex is 1.2 to 3.2 mm.

[0033] In addition, the friction body 40 has an inner hole 48 extending in the axial direction, and the inner hole 48 is located radially inward of the four outward protrusions 47.

[0034] On the other hand, referring to FIGS. 6a, 6b, and 7, the mounting hole 20 of the shaft cylinder 10 has, from the upper side in the axial direction, a fitting hole 22 (diameter 5.7 mm, length 0.5 to 1.5 mm), a first tapered hole 23 (maximum diameter 5.7 mm, length 1.5 to 2.5 mm, minimum diameter 4.4 to 5.6 mm), a second tapered hole 24 (maximum diameter 4.4 to 5.6 mm, length 3.5 to 4.5 mm, minimum diameter 4.2 to 5.4 mm), and an inward flange portion 25 (thickness 0.5 to 1.2 mm, inner diameter 4.0 to 4.5 mm) (an example of an inward protrusion).

[0035] And mainly in the second tapered hole 24 and the inward flange portion 25, four grooves 27 (parallel to the axial direction in this embodiment) are formed which are circumferentially divided. The four grooves 27 are evenly arranged in the circumferential direction. Note that the shaft cylinder 10 including the grooves 27 is formed by resin molding (for example, polycarbonate).

[0036] The size of each groove 27 is such that the radius at the circumferential center line is 2.2 to 2.8 mm (see also FIGS. 10 and 11), the circumferential width is 0.6 to 2.0 mm, and the length is about 4.0 to 5.0 mm.

[0037] (Operation of the First Embodiment) FIG. 8 is a schematic view showing a temporary insertion state of the friction body 40 in the first embodiment, FIG. 9 is a longitudinal sectional view of FIG. 8, FIG. 10 is a sectional view taken along line B - B of FIG. 9, and FIG. 11 is a sectional view taken along line C - C of FIG. 9.

[0038] As shown in FIGS. 8 to 11, with the four outward protrusions 47 and the four grooves 27 aligned in the circumferential direction, the friction body 40 is inserted into the mounting hole 20, resulting in a temporarily inserted state. When the four outward protrusions 47 completely pass through the four grooves 27, the fitting state shown in FIGS. 3 and 4 is reached.

[0039] Even in this state, since the circumferential width (1.5 mm) of the bottom edge of each outward protrusion 47 is larger than the circumferential width (1.0 mm) of each groove 27, when passing through the groove 27, the outward protrusion 47 is compressed in the circumferential direction and elastically deformed. However, after passing through the groove 27, the outward protrusion 47 is released from the compression and returns to its original shape, and the bottom surface of the outward protrusion 47 and the inward flange portion 25 of the shaft cylinder 10 are in surface contact. Thereby, the effect of preventing the friction body 40 from falling off can be achieved. FIG. 12 is a cross-sectional view taken along line F-F of FIG. 3.

[0040] However, as shown in FIG. 13, if the friction body 40 is rotated 45° in the circumferential direction, the entire bottom edge of each outward protrusion 47 is blocked from passing by the inward flange portion 25, so that the effect of preventing the friction body 40 from falling off can be further improved. FIG. 14 is a cross-sectional view taken along line G-G of FIG. 13.

[0041] (Effect of the First Embodiment) According to the writing instrument 1 of the first embodiment as described above, since the four outward protrusions 47 can pass through the four grooves 27 from the axial upper direction to the axial lower direction, the mounting operation of the friction body 40 is easy. On the other hand, since the passage is blocked by the inward flange portion 25 from the axial lower direction to the axial upper direction, a reliable effect of preventing the friction body 40 from falling off can be achieved. Also, since there are a plurality of outward protrusions 47, a design with a reduced (suppressed) press-fitting force is possible.

[0042] Also, in the present embodiment, each of the four outward protrusions 47 is formed in the shape of a shogi piece, that is, at the end on the lower side in the axial direction, it is formed to taper downward in the axial direction (with respect to the circumferential width). Due to this feature, the insertability of the four outward protrusions 47 into the corresponding grooves 27 is improved, and the four grooves 27 can be more easily passed from the axial upper direction to the axial lower direction.

[0043] In addition, in the present embodiment, each of the four grooves 27 extends linearly in the axial direction. Due to this feature, the four outward protrusions 47 can more easily pass through the four grooves 27 from the upper axial direction to the lower axial direction.

[0044] Also, in the present embodiment, the four outward protrusions 47 are evenly arranged in the circumferential direction. Due to this feature, while the circumferential alignment operation between the four outward protrusions 47 and the four grooves 27 is easy, a more reliable effect of preventing the friction body 40 from falling off can be achieved.

[0045] In addition, in the present embodiment, the friction body 40 has an inner hole 48 extending in the axial direction, and the inner hole 48 is located radially inward of the four outward protrusions 47. Due to this feature, since the friction body 40 can be easily elastically deformed radially inward, the four outward protrusions 47 can more easily pass through the four grooves 27 from the upper axial direction to the lower axial direction.

[0046] Also, in the present embodiment, in the state where the friction body 40 is inserted into the mounting hole 20 (see FIGS. 4 and 13), the inward flange portion 25 does not press against the outer peripheral surface of the friction body 40. Due to this feature, there is a low risk that the elasticity of the friction body 40 will decrease over time, and the effect of inhibiting passage (effect of inhibiting falling off) from the lower axial direction to the upper axial direction can be reliably maintained.

[0047] (Configuration of the Second Embodiment) FIG. 15 is a cross-sectional view corresponding to FIG. 6a of the shaft cylinder of the second embodiment of the present invention, and FIG. 16 is a cross-sectional view corresponding to FIG. 3 of the second embodiment of the present invention.

[0048] The friction body 40 of the present embodiment is the same as the friction body 40 of the first embodiment (see FIG. 5).

[0049] Furthermore, the mounting hole 20 of the shaft cylinder 10 is the same as the mounting hole 20 of the first embodiment (see FIGS. 6a and 7), except that the four grooves 27' are formed of inclined surfaces as viewed in a side cross-section (see FIGS. 15 and 16) (a radially tapered aspect).

[0050] The size of each groove 27' is such that the radius at the circumferential center line at the open end on the upper side in the axial direction is 2.2 to 2.8 mm (see also FIGS. 18 and 19), and the radius at the circumferential center line at the connection end with the inward flange portion 25 on the lower side in the axial direction is 2.1 to 2.75 mm (see also FIGS. 18 and 19), that is, it is formed of a surface inclined at 0.5 to 2° as viewed in a side cross-section (see FIGS. 15 to 17). Further, the circumferential width of each groove 27' is 0.6 to 2.0 mm, and the axial length is about 4.0 to 5.0 mm.

[0051] (Operation of the Second Embodiment) FIG. 17 is a longitudinal sectional view showing a temporarily inserted state of the friction body 40 in the second embodiment, FIG. 18 is a sectional view taken along line D-D of FIG. 17, and FIG. 19 is a sectional view taken along line E-E of FIG. 17.

[0052] As shown in FIGS. 17 to 19, with the four outward protrusions 47 and the four grooves 27' aligned in the circumferential direction, the friction body 40 is inserted into the mounting hole 20, resulting in a temporarily inserted state. When the four outward protrusions 47 completely pass through the four grooves 27', the fitting state shown in FIG. 16 is reached.

[0053] In the second embodiment, since the four grooves 27' are formed of inclined surfaces as viewed in a side cross-section (see FIGS. 15 and 16) (a radially tapered aspect), while maintaining the feature that the four outward protrusions 47 can more easily pass through the four grooves 27' from the upper side in the axial direction to the lower side in the axial direction, the four outward protrusions 47 and the four grooves 27' can be in a temporarily fitted state during the intermediate stage of the passage. As a result, the stability in the so-called temporarily inserted state is increased.

[0054] Also in the second embodiment, since the circumferential width (1.5 mm) of the base of each outward protrusion 47 is larger than the circumferential width (1.0 mm) of each groove 27', the effect of preventing the friction body 40 from falling off can be achieved even in the state of Fig. 16 (see Fig. 12). Independently of the circumferential width of each outward protrusion 47 and the circumferential width of each groove 27, their radial height (depth) can also be freely set. For example, the maximum height (depth) in the radial direction of the groove 27 may be set to 2.66 mm and the minimum height (depth) may be set to 2.4 mm (tapering shape), and the radial height of the outward protrusion 47 may be set to 2.5 mm. By making the radial height of the outward protrusion 47 larger than the minimum height (depth) in the radial direction of the groove 27, it is possible to more reliably prevent falling off.

[0055] However, if the friction body 40 is rotated 45° in the circumferential direction, since the entire base of each outward protrusion 47 is blocked from passing by the inward flange portion 25, the effect of preventing the friction body 40 from falling off can be further improved (see Fig. 14).

[0056] (Effect of the second embodiment) Also with the writing instrument of the second embodiment as described above, the four outward protrusions 47 can pass through the four grooves 27' from the axial upper side to the axial lower side, making the attachment operation of the friction body 40 easy. On the other hand, from the axial lower side to the axial upper side, the passage is blocked by the inward flange portion 25, so that a reliable effect of preventing the friction body 40 from falling off can be achieved.

[0057] Also in this embodiment, each of the four outward protrusions 47 is formed in the shape of a shogi piece, that is, at the end on the lower side in the axial direction, it is formed to taper downward in the axial direction (with respect to the circumferential width). Due to this feature, the four outward protrusions 47 can more easily pass through the four grooves 27' from the axial upper side to the axial lower side.

[0058] In addition, in the present embodiment, since the four grooves 27' are formed by inclined surfaces as viewed in the side cross-section (see FIGS. 15 and 16) (a tapered shape in the radial direction), while maintaining the feature that the four outward protrusions 47 can more easily pass through the four grooves 27' from the axial upper direction to the axial lower direction, the four outward protrusions 47 and the four grooves 27' can be in a temporarily fitted state during the passage. As a result, the stability in the so-called temporarily inserted state is increased, and for example, when a station responsible for the temporary insertion operation and a station responsible for the press-fitting operation are independently prepared, the possibility of the friction body 40 falling between the two stations can be significantly reduced.

[0059] Also, in the present embodiment, the four outward protrusions 47 are evenly arranged in the circumferential direction. Due to this feature, on the one hand, the circumferential alignment work between the four outward protrusions 47 and the four grooves 27' is easy, and on the other hand, a more reliable effect of preventing the friction body 40 from falling off can be achieved.

[0060] Also, in the present embodiment, the friction body 40 has an inner hole 48 extending in the axial direction, and the inner hole 48 is located radially inward of the four outward protrusions 47. Due to this feature, the friction body 40 can be easily elastically deformed radially inward, so that the four outward protrusions 47 can more easily pass through the four grooves 27' from the axial upper direction to the axial lower direction.

[0061] Also, in the present embodiment, when the friction body 40 is inserted into the mounting hole 20 (see FIG. 16), the inner flange portion 25 does not press against the outer peripheral surface of the friction body 40. Due to this feature, the possibility of the elasticity of the friction body 40 decreasing over time is low, and the passage inhibition effect (falling-off inhibition effect) from the axial lower direction to the axial upper direction can be reliably maintained.

[0062] (Modification of the shape of the outward protrusion 47) In the above-described first and second embodiments, the shape of the outward protrusion 47 was in the shape of a shogi piece, but it is not limited thereto, and modifications as shown in FIGS. 20 to 25 can also be adopted.

[0063] In the example shown in FIG. 20, the opposing side edges are in a pentagonal shape parallel to the axial direction.

[0064] In the example shown in FIG. 21, the upper side in the axial direction has the same rectangular shape as the example in FIG. 20, and the lower side in the axial direction is rounded into a semi-circular shape.

[0065] In the example shown in FIG. 22, the lower side in the axial direction is an isosceles triangle shape with an acute angle.

[0066] In the example shown in FIG. 23, the upper side in the axial direction has substantially the same shape as the example in FIG. 22, and the tip of the lower side in the axial direction is rounded.

[0067] In the example shown in FIG. 24, it is a shape in which an isosceles trapezoid shape with a narrow lower side in the axial direction is connected above an isosceles triangle shape with an acute angle on the lower side in the axial direction.

[0068] In the example shown in FIG. 25, the upper side in the axial direction has substantially the same shape as the example in FIG. 24, and the tip of the lower side in the axial direction is rounded.

[0069] As shown in each of the above examples, regarding the shape of the outward protrusion 47 of the friction body 40, it is preferable that the upper end surface (the right end side surface in FIGS. 20 to 25) is flat (flat), and acute angle portions (edges) are formed at both circumferential ends of the upper end surface. Such a shape is suitable for more reliably preventing the friction body 40 from falling off.

[0070] Also, the radially outer surface of the outward protrusion 47 of the friction body 40 may be formed as a flat surface or as a cylindrical surface concentric with the shaft cylinder 10.

[0071] On the other hand, regarding the shape of the inward flange portion 25, it is preferable that the lower end surface is flat (flat), and an acute angle portion (edge) is formed at the inner diameter side end of the lower end surface. Such a shape is suitable for more reliably preventing the friction body 40 from falling off.

[0072] (Supplementary) Regarding the use of the friction member 40, for example, there is a conceivable use of rubbing a thermochromic image or handwriting formed by thermochromic ink on a writing surface, and making the thermochromic image or handwriting thermochromic with the frictional heat generated at that time.

[0073] When the shaft cylinder 10 is a cylindrical body with a hollow interior, it can be used in a thermochromic writing instrument. When used in a thermochromic writing instrument, the shaft cylinder 10 is a shaft cylinder for a thermochromic writing instrument that houses thermochromic ink inside and has a pen tip through which the thermochromic ink can be discharged. Further, such a thermochromic writing instrument may include a cap attached to the pen tip side of the shaft cylinder 10.

[0074] The soft member is not limited to the friction member 40, and examples include an eraser and an input member of an input pen used for a portable information terminal. The friction member 40 is preferably integrally formed of a rubber elastic material (a material having rubber elasticity) such as synthetic rubber or elastomer. Examples of the rubber elastic material include silicone resin, SBS resin (styrene-butadiene-styrene copolymer), SEBS resin (styrene-ethylene-butylene-styrene copolymer), polyester resin, olefin resin, ethylene propylene diene rubber (EPDM), and the like. In particular, the rubber elastic material preferably consists of a low-wear elastic material that hardly generates wear debris during friction, rather than a high-wear elastic material (such as an eraser). Alternatively, the friction member 40 is obtained by injection molding of a thermoplastic elastomer (for example, a polyester-based elastomer or a styrene-based elastomer).

[0075] By providing a groove 27 in the shaft cylinder 10, the resin amount can be reduced compared to the existing shape (without a groove), which is advantageous in terms of the environment and cost. Also, by providing an outward protrusion 47 on the friction member 40, the resin amount can be reduced compared to the existing shape (the outward protrusion is annular), which is advantageous in terms of the environment and cost.

Explanation of Reference Numerals

[0076] 1 Writing instrument 10 Shaft cylinder 20 Mounting hole 22 Fitting hole 23 First tapered hole 24 Second tapered hole 25 Inner flange portion 27 Groove (parallel to the axial direction) 27’ Groove (tapered in the radial direction) 40 Friction body 41 Large-diameter portion 42 Fitting portion 43 Tapered portion 44 Passing portion 45 Tip portion 47 Outer protrusion 48 Inner hole 101 Cylindrical body 102 Mounting hole 103 Soft member 121 Inner protrusion 151 Outer protrusion

Claims

1. A writing instrument comprising a cylindrical body having a mounting hole opening upward in the axial direction, and a soft member inserted into the mounting hole, wherein a plurality of inward protrusions divided in the circumferential direction are formed on the inner peripheral surface of the mounting hole, a plurality of grooves extend in the axial direction between the plurality of inward protrusions, a plurality of outward protrusions divided in the circumferential direction are formed on the outer peripheral surface of the soft member, and the plurality of outward protrusions can pass through the plurality of grooves from the upper side in the axial direction to the lower side in the axial direction, while the passage from the lower side in the axial direction to the upper side in the axial direction is inhibited by the plurality of inward protrusions. The writing instrument is characterized by the above.

2. Each of the plurality of outward protrusions is formed to be tapered downward in the circumferential direction at the lower end portion on the axial direction lower side. The writing instrument according to claim 1, characterized by the above.

3. Each of the plurality of grooves extends with the same height in the radial direction from the upper side in the axial direction to the lower side in the axial direction. The writing instrument according to claim 1 or 2, characterized by the above.

4. Each of the plurality of grooves extends in a tapered shape in the radial direction from the upper side in the axial direction to the lower side in the axial direction. The writing instrument according to claim 1 or 2, characterized by the above.

5. The plurality of outward protrusions are evenly arranged in the circumferential direction. The writing instrument according to claim 1 or 2, characterized by the above.

6. The number of the plurality of outward protrusions is four. The writing instrument according to claim 5, characterized by the above.

7. The number of the plurality of grooves is equal to the number of the plurality of outward protrusions. The writing instrument according to claim 5, characterized by the above.

8. The number of the plurality of grooves is more than the number of the plurality of outward protrusions. The writing instrument according to claim 5, characterized by the above.

9. The soft member has an inner hole extending in the axial direction, and the inner hole is located radially inward of the plurality of outward protrusions. The writing instrument according to claim 1 or 2, characterized by the above.

10. In a state where the soft member is inserted into the mounting hole, the plurality of inward protrusions do not press against the outer peripheral surface of the soft member. The writing instrument according to claim 1 or 2, characterized by the above. ​ ​ ​

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