Friction body unit and thermochromic writing instrument

Abstract

A friction body unit 3 comprises a friction body 5 and a holding unit 4. The friction body 5 is configured so as to be able to generate frictional heat for thermally discoloring the writing made with thermochromic ink. The holding unit 4 holds the friction body 5 and is configured to be able to be attached to and detached from a shaft tube 2 or a cap of a thermochromic writing utensil. The holding unit 4 has a cylindrical side wall that forms an inner space 41 that at least opens downward. The side wall has formed therein at least one ventilation hole 44 that connects to the inner space 41, allowing for the passage of air between the ventilation hole 44, the inner space 41, and the downward opening.

Description

Friction unit and thermochromic writing implement

[0001] The present invention relates to a friction body unit that is configured to be detachable from a thermochromic writing instrument, and to a thermochromic writing instrument equipped with the same.

[0002] A thermochromic writing instrument comprises thermochromic ink and a friction body. The friction body is made of an elastic material. Frictional heat is generated by rubbing the thermochromic ink mark written on paper with the friction body. This frictional heat causes the thermochromic ink mark to thermally discolor. The friction body wears out with repeated use. Therefore, the applicant proposes a friction body unit that can be attached and detached to a thermochromic writing instrument. The friction body unit makes it possible to easily replace a worn friction body with a new friction body.

[0003] For example, Figure 6 of Japanese Patent Application Laid-Open No. 2013-188922 discloses a conventional friction body unit proposed by the present applicant. The friction body unit includes a holding portion 4 and a friction body 5. Three grooves 4CA extending in the vertical direction are formed in a side wall 4C of the holding portion 4. The lower end of each groove 4CA is continuous with a through-hole 4CB. The through-hole 4CB penetrates a lower end 4D of the side wall 4C in the vertical direction. Even if a child accidentally swallows the friction body unit, the grooves 4CA and the through-holes 4CB allow air to circulate.

[0004] JP 2013-188922 A

[0005] In recent years, there has been a trend toward more beautifully designed writing instruments in order to improve the quality of life for consumers. Today, a wide variety of new writing instrument designs are being introduced to the market one after another. Meanwhile, all components that make up a writing instrument have a structure that achieves some function. It is desirable that the structure that achieves this function does not restrict the degree of freedom in the design of the writing instrument.

[0006] However, in the conventional friction body unit described above, there was a problem in that the plurality of through holes 4CB for circulating air limited the degree of freedom in the design of the holding part 4. That is, the plurality of through holes 4CB was configured to penetrate the lower end 4D of the side wall 4C of the holding part 4 in the vertical direction. In order to provide the plurality of through holes 4CB, the outer diameter of the lower end 4D of the side wall 4C had to be increased, which limited the degree of freedom in the design of the holding part 4. The limited degree of freedom in the design of the holding part 4 means that the degree of freedom in the design of the friction body unit and the thermochromic writing instrument is also limited.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a friction unit that can improve design freedom by having a structure that allows sufficient air to circulate without increasing the outer diameter of the side wall of the holding part, and a thermochromic writing instrument equipped with the same.

[0008] (1) In order to achieve the above object, the friction body unit of the present invention comprises a friction body and a holding part, the friction body being configured to be capable of generating frictional heat for thermally discoloring handwriting of thermochromic ink, and the holding part being configured to hold the friction body and be attachable to or detachable from the barrel or cap of a thermochromic writing instrument, characterized in that the holding part has a cylindrical side wall that forms an internal space that opens at least downward, and the side wall is formed with at least one air hole that communicates with the internal space, allowing air to circulate between the air hole, the internal space, and the downward opening.

[0009] In the friction body unit of (1) above, an air flow path connecting the inside and outside of the holding part is formed by the ventilation hole, the internal space, and the opening at the bottom of the internal space. This air flow path ensures an airway for the child to breathe even if the child accidentally swallows the friction body unit. In particular, by using the internal space and the opening at the bottom as the air flow path, sufficient air circulation is possible. Since this air flow path is formed from the outer surface of the side wall of the holding part to the inside, it does not limit the degree of freedom in designing the holding part. Therefore, according to the present invention, the degree of freedom in designing the friction body unit and the thermochromic writing instrument is improved.

[0010] (2) Preferably, in the friction body unit of (1) above, the cylindrical side wall of the holding portion includes a portion with a large outer diameter and a portion with a small outer diameter, and the air vent has a first opening formed on the outer surface of the side wall and a second opening formed on the inner surface of the side wall, and at least the first opening is located above the maximum outer diameter portion of the side wall.

[0011] In the frictional body unit (2) above, the first opening of the air vent is located in a portion of the cylindrical side wall of the holding part that has a smaller outer diameter than the maximum outer diameter portion. This means that if a child accidentally swallows the frictional body unit, the maximum outer diameter portion of the side wall of the holding part comes into contact with the child's tracheal wall, while the portion of the side wall with a smaller outer diameter than the maximum outer diameter portion does not come into contact with the child's tracheal wall. As a result, the first opening of the air vent is not blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0012] In the present invention, the term "outer diameter" refers to the diameter of a horizontal cross section of the side wall when the side wall of the holding part is cylindrical, and refers to the diameter of a circle circumscribing the horizontal cross section of the side wall when the side wall of the holding part is tubular other than cylindrical. Furthermore, the term "maximum outer diameter portion" refers to the portion where the diameter of a circle circumscribing the horizontal cross section of the side wall is maximum, assuming that the side wall of the holding part is tubular other than cylindrical.

[0013] (3) Preferably, in the friction body unit of (2) above, a tapered portion having an outer diameter that decreases from bottom to top is provided on at least a portion of the cylindrical side wall of the holding portion, and the first opening of the air hole is formed in the tapered portion.

[0014] In the friction body unit of (3) above, the first opening of the air vent is formed in a tapered portion whose outer diameter decreases from bottom to top. As a result, if a child accidentally swallows the friction body unit, the maximum outer diameter portion of the side wall of the holding part comes into contact with the child's tracheal wall, while the portion with an outer diameter smaller than the maximum outer diameter portion does not come into contact with the child's tracheal wall. As a result, the first opening of the air vent is not blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0015] (4) Preferably, in the friction body unit of (3) above, the cylindrical side wall of the holding portion includes a first tapered portion located above the maximum outer diameter portion and a second tapered portion located above the first tapered portion, the outer diameter of the first tapered portion decreases upward from the upper end of the maximum outer diameter portion, the outer diameter of the second tapered portion decreases upward from the upper end of the first tapered portion, the inclination angle of the second tapered portion is larger than the inclination angle of the first tapered portion, and the first opening of the air hole is formed in the second tapered portion.

[0016] The side wall of the holding portion of the friction body unit (4) above includes a maximum outer diameter portion, a first tapered portion, and a second tapered portion. The second tapered portion has an outer diameter smaller than that of the first tapered portion and an inclination angle larger than that of the first tapered portion. The first opening of the air vent is formed in the second tapered portion. As a result, if a child accidentally swallows the friction body unit, even if the friction body unit tilts and the first tapered portion comes into contact with the child's tracheal wall, the second tapered portion will not come into contact with the child's tracheal wall. As a result, the first opening of the air vent will not be blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0017] (5) Preferably, in the friction body unit of (3) above, the outer diameter of the portion of the cylindrical side wall of the holding portion above the upper end of the second opening of the air hole is equal to or smaller than the outer diameter of the upper end of the second opening.

[0018] The outer diameter of the side wall of the retaining portion of the friction body unit described above in (5) above is equal to or smaller than the outer diameter of the upper end of the second opening of the air vent. This prevents the upper end of the second opening of the air vent from coming into contact with the child's tracheal wall if the child accidentally swallows the friction body unit. This results in a larger gap being formed between the upper end of the second opening of the air vent and the child's tracheal wall, ensuring an airway for the child to breathe. Furthermore, because the outer diameter of the upper end of the second opening of the air vent is equal to or smaller than the outer diameter of the upper end of the second opening, the outer shape of the retaining portion can be injection molded using a single, undivided mold, eliminating the need for a slide core to form the air vent. This reduces the cost of injection molding the retaining portion.

[0019] (6) Preferably, in the friction body unit of any of (2) to (5) above, an annular outward protrusion is provided on the outer surface of the lower side of the friction body, an annular inward protrusion is provided on the inner surface of the cylindrical side wall of the holding part, the side wall opens downward and upward, at least the second opening of the air hole is located below the inward protrusion, the outward protrusion and the inward protrusion are engaged with each other when the lower side of the friction body is inserted into the internal space from the upper opening of the side wall, and a gap is formed between the outer surface of the outward protrusion and the inner surface of the side wall when the outward protrusion and the inward protrusion are engaged with each other, and the gap communicates with the air hole.

[0020] In the friction body unit of (6) above, the annular outward protrusion and the annular inward protrusion are engaged with each other over a 360-degree range, so that the underside of the friction body is firmly held in the internal space of the holding part. Furthermore, when the outward protrusion and the annular inward protrusion are engaged with each other, a gap is formed between the outer surface of the outward protrusion and the internal surface of the side wall. This gap communicates with the air vent, so that an air flow path communicating between the inside and outside of the holding part is maintained.

[0021] (7) Preferably, in the friction body unit of any one of (1) to (6) above, a plurality of recesses are formed along the lower end of the cylindrical side wall of the holding portion.

[0022] In the friction body unit (7) above, a plurality of recesses are formed along the lower end of the cylindrical side wall of the holding part. First, the plurality of recesses are used to maintain the orientation of the holding part in an automated assembly process of the friction body unit. That is, the plurality of recesses are engaged with a plurality of protrusions formed on a jig. This limits the movement and rotation of the holding part, making it possible to easily assemble the friction body to the holding part.

[0023] Second, the multiple recesses prevent the holder from being tightly attached to the barrel or cap of the thermochromic writing instrument. That is, the friction body unit is attached to the barrel or cap of the thermochromic writing instrument. At this time, the lower end of the side wall of the holder is in surface contact with the barrel or cap. If the surface contact pressure is high and the contact area is large, the lower end of the side wall of the holder may be tightly attached to the barrel or cap, making it impossible to remove the friction body unit by hand. The multiple recesses reduce the area of ​​the lower end of the side wall of the holder, making it easier to remove the friction body unit by hand.

[0024] In addition, the multiple recesses receive foreign matter such as dust and dirt that is interposed between the lower end of the side wall of the holder and the barrel or cap, preventing the foreign matter from interfering with the attachment of the friction body unit. Furthermore, multiple protrusions may be formed on the barrel or cap of the thermochromic writing instrument. When the friction body unit is attached to the barrel or cap of the thermochromic writing instrument, the multiple recesses engage with the multiple protrusions, restricting the rotation of the holder. When the friction body unit is configured to be screwed onto the barrel or cap, the friction body unit will not be unintentionally separated from the barrel or cap.

[0025] (8) In order to achieve the above object, the thermochromic writing instrument of the present invention is a thermochromic writing instrument equipped with a friction body unit of any one of (1) to (7) above, characterized in that a first connecting portion is provided on the barrel or cap of the thermochromic writing instrument, and a second connecting portion configured to be detachable from the first connecting portion is provided on the friction body unit.

[0026] In the thermochromic writing instrument of (8) above, the friction body unit can be freely designed according to the design of the barrel or cap. For example, by matching the outer diameter of the holding part of the friction body unit with the outer diameter of the barrel or cap, the appearance of the friction body unit can be integrated with the outer diameter of the barrel or cap. In particular, the friction body units of (1) to (7) above are not limited to having a large outer diameter of the holding part in order to ensure air circulation. Therefore, if the outer diameter of the barrel or cap is small, the outer diameter of the holding part can be made small. The friction body unit makes it possible to design the entire thermochromic writing instrument with a slim appearance.

[0027] (9) In order to achieve the above object, the thermochromic writing instrument of the present invention is a thermochromic writing instrument equipped with the friction body unit of (6) above, characterized in that a first connecting portion is provided on the barrel or cap of the thermochromic writing instrument, the friction body unit is provided with a second connecting portion configured to be detachable from the first connecting portion, and when the second connecting portion is connected to the first connecting portion, the first connecting portion is located in the gap formed between the outer surface of the outward protrusion and the inner surface of the side wall.

[0028] In the thermochromic writing instrument of (8) above, the gap formed in the internal space of the friction body unit of (6) above can be effectively utilized. That is, a gap constituting part of the air passage is formed in the internal space of the holding part of the friction body unit of (6) above. Here, the air passage of the friction body unit functions when a child accidentally swallows the friction body unit detached from the thermochromic writing instrument. On the other hand, when the friction body unit is attached to the thermochromic writing instrument, the air passage of the friction body unit does not function at all. Therefore, in the thermochromic writing instrument of (8) above, the first connecting part of the thermochromic writing instrument is accommodated in the gap constituting part of the air passage of the friction body unit, and this gap is effectively utilized.

[0029] The friction body unit of the present invention has a structure that allows sufficient air to circulate without increasing the outer diameter of the side wall of the holding part, thereby improving design freedom. Furthermore, the thermochromic writing instrument of the present invention allows the entire thermochromic writing instrument, including the friction body unit, to be designed with a unified appearance. In particular, it becomes possible to design the entire thermochromic writing instrument with a slim appearance.

[0030] 11 is a front view of a thermochromic writing instrument equipped with a friction body unit according to a first embodiment of the present invention. FIG. 1 is a cross-sectional view showing a portion including the friction body unit and barrel in FIG. 1. FIG. 2 is a cross-sectional view showing the friction body unit and barrel in a disassembled state. FIG. 3 is a front view of the friction body unit. FIG. 4 is a right side view of the friction body unit. FIG. 5 is a perspective view of the friction body unit. FIG. 6 is a perspective view showing an air vent in the friction body unit. FIG. 7 is a plan view of the friction body unit. FIG. 8 is a cross-sectional view taken along B-B in FIG. 4. FIG. 10 is a front view of a thermochromic writing instrument equipped with a friction body unit according to a second embodiment of the present invention. FIG. 11 is a cross-sectional view showing the friction body unit and barrel in a disassembled state. FIG. 12 is a front view of a thermochromic writing instrument equipped with a friction body unit according to a third embodiment of the present invention. FIG. 13 is a cross-sectional view showing a portion including the friction body unit and barrel in FIG. 14. FIG. 14 is a cross-sectional view showing the friction body unit and barrel in a disassembled state. FIG. 15 is a front view of the friction body unit. FIG. 16 is a left side view of the friction body unit. FIG. 17 is a perspective view of the friction body unit. FIG. 18 is a perspective view showing an air vent in the friction body unit. Fig. 16 is a plan view showing a friction body unit. Fig. 17 is a cross-sectional view taken along the line BB in Fig. 16. Fig. 18 is a perspective view showing a friction body unit according to a fourth embodiment of the present invention.

[0031] Hereinafter, embodiments of the friction body unit and thermochromic writing instrument of the present invention will be described with reference to the drawings. In the following description, the direction of the pen tip of the thermochromic writing instrument 1 shown in Figures 1, 10, and 13 is defined as "down" and the direction of the friction body 5 is defined as "up."

[0032] First Embodiment First, a friction body unit and a thermochromic writing implement according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 9. FIG.

[0033] As shown in FIG. 1 , the thermochromic writing instrument 1 of the first embodiment is, for example, a retractable thermochromic writing instrument, and a refill (not shown) is housed inside the barrel 2 so that it can move up and down. Thermochromic ink is housed inside the refill. A nib capable of discharging thermochromic ink is provided at the tip of the refill. The thermochromic writing instrument 1 is equipped with a nib extension / retraction mechanism. By sliding the clip 2d downward, the nib protrudes from the lower end of the barrel 2, or the nib is retracted into the barrel 2. FIG. 1 shows the state in which the nib is retracted inside the barrel 2. In this nib-retracted state, by sliding the clip body 2d downward, the nib protrudes from the lower end of the barrel 2. In this nib-retracted state, by sliding the clip body 2d downward, the nib is retracted into the barrel 2.

[0034] Meanwhile, a friction body unit 3 is attached to the upper end of the barrel 2. The friction body unit 3 is composed of a holding portion 4 and a friction body 5. Frictional heat is generated by rubbing the thermochromic ink markings on the paper surface with the friction body 5. This frictional heat can thermally discolor the thermochromic ink markings.

[0035] The thermochromic writing instrument of the present invention is not limited to a retractable type. For example, the thermochromic writing instrument of the present invention may be a cap-type thermochromic writing instrument in which the pen tip protruding from the lower end of the barrel is covered with a cap. In this case, the friction body unit 3 is attached to the end of the cap or the upper end of the barrel. Here, the end of the cap means the end opposite to the opening into which the lower end of the barrel is inserted. The barrel and cap of the cap-type thermochromic writing instrument are made of synthetic resin or metal.

[0036] Refill: The refill is configured by crimping the pen tip onto the opening at the bottom of the ink reservoir. The inside of the ink reservoir is filled with thermochromic ink and a follower. The follower is filled at the top of the thermochromic ink inside the ink reservoir and descends as the thermochromic ink is consumed. The follower is made of, for example, a high-viscosity fluid. A tail plug is attached to the opening at the top of the ink reservoir. The tail plug has a through hole to allow air to circulate between the inside and outside of the ink reservoir.

[0037] Thermochromic ink Thermochromic ink has the property of changing color when heated or cooled. The thermochromic ink's thermochromic changes include a change from colored to colorless, a change from colorless to colored, and a change from a first color to a second color.

[0038] The thermochromic ink is preferably a reversible thermochromic ink that can return to the state before and after the thermochromic change. Reversible thermochromic inks include types such as heat-discoloring type, color memory retention type, and heat-coloring type. Heat-discoloring type reversible thermochromic ink changes from colored to colorless upon heating. Color memory retention type reversible thermochromic ink reversibly changes to a colored or colorless state at a predetermined temperature and retains the changed state within a specific temperature range. Heat-coloring type thermochromic ink changes from colorless to colored upon heating and returns from the colored to colorless state upon cooling. For example, if the thermochromic writing instrument is a single-type thermochromic writing instrument with one refill, any one type of thermochromic ink is used alone. Furthermore, when the thermochromic writing instrument is a multiple-type thermochromic writing instrument equipped with two or more refills, two or more types of thermochromic inks can be used in combination.

[0039] The reversible thermochromic ink preferably contains a reversible thermochromic pigment in which a reversible thermochromic composition is encapsulated in microcapsules as the coloring material. The reversible thermochromic composition contains at least an electron-donating color-forming organic compound, an electron-accepting compound, and a reaction medium. The temperature at which the color reaction between the electron-donating color-forming organic compound and the electron-accepting compound occurs is determined by the reaction medium.

[0040] - Pen tip The pen tip is composed of, for example, a metal ballpoint pen tip. A hole is provided at the bottom end of the ballpoint pen tip, which serves as an outlet for the thermochromic ink. The ball is rotatably held on the inner surface of the edge of this hole. The ballpoint pen tip is press-fitted into the opening at the bottom end of the ink reservoir tube of the refill. Alternatively, the ballpoint pen tip is press-fitted into the opening at the bottom end of the ink reservoir tube of the refill via a synthetic resin pen tip holder. The pen tip holder holds the outer surface of the upper part of the ballpoint pen tip. A coil spring is housed inside the pen tip, which presses the ball against the bottom end of the pen tip. A rod portion is provided at the bottom end of the coil spring. The bottom end of this rod portion contacts the ball. The biasing force of the coil spring presses the ball tightly into the hole at the bottom end of the ballpoint pen tip. This prevents ink from leaking from the pen tip and ink from evaporating when not writing.

[0041] ・Barrel As shown in Figure 1, the barrel 2 of the thermochromic writing instrument 1 is composed of a lower barrel 2a, a central barrel 2b, and an upper barrel 2c. The majority of the lower barrel 2a is composed of a cylindrical section. A tapered section whose outer diameter decreases from top to bottom is provided at the lower end of the cylindrical section. The cylindrical section of the lower barrel 2a is used as the grip of the thermochromic writing instrument 1. An opening is provided at the tip of the tapered section of the lower barrel 2a. The nib of the refill protrudes and retracts from the opening at the tip of the tapered section. The central barrel 2b is composed only of a long cylindrical section. The lower end of the central barrel 2b is connected to the upper end of the lower barrel 2a by screwing or press-fitting. The upper barrel 2c is composed only of a short cylindrical section. The lower end of the upper barrel 2c is connected to the upper end of the central barrel 2b by screwing or press-fitting. The lower barrel 2a, central barrel 2b, and upper barrel 2c are formed from, for example, a synthetic resin such as polycarbonate, or a metal.

[0042] 2 and 3, a substantially cylindrical first coupling portion 21 that protrudes upward is provided at the upper end of the upper shaft 2c. A male thread 22 is provided on the outer surface of the first coupling portion 21. A second coupling portion 42 that is provided on the holding portion 4 of the friction body unit 3, which will be described later, is screwed into the first coupling portion 21. Note that the coupling between the first coupling portion 21 and the second coupling portion 42 is not limited to screwing, and may be changed to a coupling structure such as fitting, press-fitting, or engagement.

[0043] The outer diameter of the first coupling portion 21 is smaller than the outer diameter of the upper end of the upper shaft 2 c. As a result, an annular step portion 23 is formed at the upper end of the upper shaft 2 c. The lower end of the holding portion 4 of the friction body unit 3, which will be described later, comes into surface contact with this annular step portion 23.

[0044] Friction body unit Figures 2 to 9 show the friction body unit 3 of the first embodiment. As shown in Figure 3, the friction body unit 3 is composed of a holding portion 4 and a friction body 5. The friction body unit 3 is attached to the upper shaft 2c of the barrel 2 described above. The height of the friction body unit 3 is, for example, 14.0 mm.

[0045] 3 to 8, the friction body 5 is attached to an upper portion 47 of the holding portion 4. The holding portion 4 is formed of, for example, a synthetic resin such as polycarbonate or a metal. The height of the holding portion 4 is, for example, 8.0 mm.

[0046] As shown in Fig. 3, the retaining portion 4 has a cylindrical side wall that forms an internal space 41 that is open upward and downward. A second connecting portion 42 is provided on the lower side of the retaining portion 4. An internal thread 43 is provided on the internal surface of the second connecting portion 42. This internal thread 43 is threadedly engaged with the external thread 22 of the first connecting portion 21 of the barrel 2. Note that the connection between the first connecting portion 21 and the second connecting portion 42 is not limited to threaded engagement, and may be changed to a connecting structure such as fitting, press-fitting, or engagement.

[0047] The friction body 5 is attached to the upper part 47 of the holding part 4. An annular inward protrusion 45 is provided on the inner surface of the upper part 47. Meanwhile, an annular outward protrusion 54 is provided on the outer surface of the lower part of the friction body 5. When the lower side of the friction body 5 is inserted into the upper part 47 of the holding part 4, the inward protrusion 45 and the outward protrusion 54 are engaged with each other. Note that the connection between the holding part 4 and the friction body 5 is not limited to the engagement between the inward protrusion 45 and the outward protrusion 54, but may be by fitting, press-fitting, engagement, screwing, bonding, two-color molding, or the like.

[0048] The annular inward protrusion 45 has a tapered inclined surface whose inner diameter decreases from top to bottom, and an annular lower surface. The inclined surface of the inward protrusion 45 guides the lower side of the friction body 5 inserted into the upper part 47 of the holding part 4 downward into the internal space 41. This allows the outward protrusion 54 to be smoothly engaged with the inward protrusion 45, making it easy to assemble the friction body unit 3.

[0049] As shown in Figures 3, 4, and 8, two air vents 44 are formed in the holding part 4. The two air vents 44 are arranged symmetrically on the cylindrical side wall of the holding part 4 and communicate with the internal space 41 of the holding part 4. The air vents 44 function as an air flow path for a child to breathe if the child accidentally swallows the friction body unit 3. In addition, the first opening 44a (see Figure 7) of the air vent 44 formed on the outer surface of the holding part 4 functions as a non-slip surface for fingers gripping the friction body unit 3. This makes it easy to attach and detach the friction body unit 3 to and from the barrel 2.

[0050] 5, three tapered portions 4b, 4c, and 4d with different inclination angles α, β, and γ are provided on the outer surface of the holding portion 4. By making the inclination angles α, β, and γ of the three tapered portions 4b, 4c, and 4d all less than 45°, the side wall of the holding portion 4 can be easily gripped with fingers at any position. This makes it easy to attach and detach the friction body unit 3 to and from the barrel 2. Note that the outer surface of the side wall of the holding portion 4, excluding the air vent 44, may be formed with an anti-slip feature such as a recessed groove or knurling.

[0051] As shown in FIGS. 3 and 7 , the vent hole 44 has a first opening 44a formed on the outer surface of the side wall of the holding portion 4 and a second opening 44b formed on the inner surface of the side wall of the holding portion 4. The entire vent hole 44 is located above the second connecting portion 42, and the second opening 44b of the vent hole 44 is located below the inward protrusion 45. With this configuration, the vent hole 44 penetrates the side wall of the holding portion 4 without interfering with the second connecting portion 42 and the inward protrusion 45. In other words, the functions of the second connecting portion 42 and the inward protrusion 45 are not impaired by the vent hole 44 penetrating the side wall of the holding portion 4. As a result, the second connecting portion 42 can be securely screwed onto the first connecting portion 21, and the inward protrusion 45 can be securely engaged with the outward protrusion 54.

[0052] 5 to 7, the first opening 44a of the vent hole 44 is formed on an inclined surface whose outer diameter decreases from bottom to top of the second tapered portion 4c. Therefore, a diameter difference A shown in FIG. 4 is generated between the upper and lower ends of the first opening 44a of the vent hole 44. This diameter difference A allows the interior of the vent hole 44 to expand from the second opening 44b to the first opening 44a. As a result, even if a child accidentally swallows the friction body unit 3, a sufficient amount of air can be obtained from the vent hole 44. The diameter difference A shown in FIG. 4 is preferably 0.5 mm or more.

[0053] 5 and 6, the outer surface of the holding portion 4 is composed of a maximum outer diameter portion 4a, a first tapered portion 4b, a second tapered portion 4c, a third tapered portion 4d, and a chamfered portion 4e. The first tapered portion 4b is located on the maximum outer diameter portion 4a. The second tapered portion 4c is located on the first tapered portion 4b. The third tapered portion 4d is located on the second tapered portion 4c. The chamfered portion 4e is located on the third tapered portion 4d. It is also possible to eliminate the outer surface of the maximum outer diameter portion 4a and have the lower end of the first tapered portion 4b serve as the maximum outer diameter portion 4a.

[0054] The outer diameters of the first tapered portion 4b, the second tapered portion 4c, and the third tapered portion 4d all decrease from bottom to top. Of the three tapered portions 4b, 4c, and 4d, the outer diameter of the first tapered portion 4b, which is the lowest, is preferably reduced by 10% to 30%. For example, the outer diameter of the lower end of the first tapered portion 4b (which is the same as the upper end of the maximum outer diameter portion 4a) is 10.0 mm, and the outer diameter of the upper end of the first tapered portion 4b is 8.6 mm.

[0055] The outer diameter of the lower end of the second tapered portion 4c is 8.6 mm, and the outer diameter of the upper end of the second tapered portion 4c is 7.0 mm. The inclination angle β of the second tapered portion 4c is greater than the inclination angle α of the first tapered portion 4b (α<β). To make the holding portion 4 easier to hold, the inclination angle γ of the third tapered portion 4d is preferably smaller than the inclination angle β of the second tapered portion 4c (γ<β). The air vent 44 is formed in the second tapered portion 4c. For example, α = 23°, β = 43°, and γ = 20°. Note that the first tapered portion 4b, the second tapered portion 4c, and the third tapered portion 4d may have a very small inclination angle, such as a draft angle to facilitate removal of the molded product from the mold. Furthermore, the edges that form the boundaries between the three tapered portions 4b, 4c, and 4d may be chamfered.

[0056] 9 shows the central angles θ1 and θ2 of the first openings 44a of the two ventilation holes 44. The central angles θ1 and θ2 of the first openings 44a are the angles formed by two imaginary lines connecting the two outermost ends of the first openings 44a and the center point of the holding portion 4. The sum θ of the central angles θ1 and θ2 of the first openings 44a (θ = θ1 + θ2) is preferably in the range of 90° to 180°, and more preferably in the range of 90° to 150°. This is because if the sum θ is less than 90°, sufficient ventilation cannot be achieved, and if the sum θ exceeds 180° (more preferably 150°), sufficient strength of the holding portion 4 cannot be achieved.

[0057] 5 shows the height C of the second opening 44b of the ventilation hole 44. The height C of the second opening 44b is preferably 0.5 mm or more. This is because if the height C of the second opening 44b is 0.5 mm or more, a sufficient amount of ventilation can be obtained in the event that a child accidentally swallows the friction body unit 3.

[0058] Friction Body As shown in FIG. 3 , the friction body 5 is configured by integrally forming a bullet-shaped friction portion 51 and a substantially cylindrical attachment portion 52. An inner hole extending in the axial direction is formed at the center of the friction body 5. As a result, the inside of the friction portion 5 is hollow except for the upper end portion of the friction portion 51. The outer surface of the upper end portion of the friction portion 51 is a convex curved surface. The horizontal cross section of the friction portion 51 is circular. The outer diameter of the friction portion 51 is larger than the outer diameter of the attachment portion 52. As a result, an annular step 53 is formed at the boundary between the friction portion 51 and the attachment portion 52.

[0059] The above-mentioned annular outward protrusion 54 is integrally formed on the outer surface of the attachment portion 52 of the friction body 5. The outward protrusion 54 has an annular upper surface and an inclined surface whose outer diameter decreases from top to bottom. When the attachment portion 52 of the friction body 5 is inserted into the upper portion 47 of the holding portion 4, the inclined surface of the outward protrusion 54 is guided by the inclined surface of the above-mentioned inward protrusion 45. As a result, the outward protrusion 54 smoothly passes over the inward protrusion 45 and is engaged with the inward protrusion 45. At this time, the step portion 53 of the friction body 5 abuts against the upper end of the holding portion 4.

[0060] The annular upper surface of the outward protrusion 54 abuts against the annular lower surface of the inward protrusion 45, so that the friction body 5 does not easily come off from the upper part 47 of the holding part 4. Note that the connection between the holding part 4 and the friction body 5 is not limited to the engagement between the inward protrusion 45 and the outward protrusion 54, but may be by fitting, press-fitting, engagement, screwing, bonding, two-color molding, or the like.

[0061] It is preferable that the outer diameter of the frictional portion 51 decreases from bottom to top. It is also preferable that the maximum outer diameter of the frictional portion 51 is smaller than the outer diameter of the upper end of the holding portion 4. With this configuration, it is possible to prevent the frictional body 5 from falling off the holding portion 4, and it is also possible to ensure an air flow path in the event that a child accidentally swallows the frictional body unit 3.

[0062] The friction body 5 is made of an elastic material. Examples of elastic materials that can be used include synthetic resins with rubber elasticity, such as silicone resin, SBS resin (styrene-butadiene-styrene copolymer), and SEBS resin (styrene-ethylene-butylene-styrene copolymer). Frictional heat is generated when the friction part 51 rubs against the thermochromic ink written on the paper. This frictional heat causes the thermochromic ink to thermally discolor.

[0063] 2 and 3, the friction unit 3 can be attached to and detached from the upper shaft 2c of the thermochromic writing instrument 1. As shown in Fig. 2, when the friction unit 3 is attached to the upper shaft 2c, the lower end of the holding portion 4 abuts against the step portion 23 of the upper shaft 2c.

[0064] As shown in Fig. 3, an expanded diameter portion 24 that fits the outer shape of the outward protrusion 54 is provided above the inner surface of the first coupling portion 21. The expanded diameter portion 24 has an inclined surface whose inner diameter increases from bottom to top. As shown in Fig. 2, when the friction body unit 3 is attached to the upper shaft 2c, the expanded diameter portion 24 does not come into contact with the outer surface of the outward protrusion 54.

[0065] The enlarged diameter portion 24 may be configured to come into contact with the outer surface of the outward protrusion 54. When the outer surface of the outward protrusion 54 comes into contact with the enlarged diameter portion 24, rattling of the friction body 5 is suppressed.

[0066] In the first embodiment, when the friction body unit 3 is attached to the upper shaft 2c, the upper end of the first connecting portion 21 is configured to be located above the lower end of the second opening 44b of the air vent 44. With this configuration, it is possible to visually check through the air vent 44 whether the friction body unit 3 is completely attached to the upper shaft 2c. It is preferable that the retaining portion 4 and the first connecting portion 21 are different colors. This makes it easy to determine whether the friction body unit 3 is completely attached to the upper shaft 2c.

[0067] Furthermore, since the upper end of the first connecting portion 21 is positioned higher than the lower end of the second opening 44b of the ventilation hole 44, dust and dirt are prevented from entering the inside of the friction body unit 3 through the ventilation hole 44, and the friction body unit 3 can be kept clean.

[0068] Effects and Benefits In the friction body unit 3 of the first embodiment described above, the air vent 44, the internal space 41, and the opening at the bottom of the internal space 41 form an air passage that connects the inside and outside of the holding part 4. This air passage ensures an airway for the child to breathe even if the child accidentally swallows the friction body unit 3. In particular, by using the internal space 41 and the opening at the bottom as the air passage, sufficient air circulation is possible. Since this air passage is formed from the outer surface of the side wall of the holding part 4 to the inside, it does not limit the degree of freedom in the design of the holding part 4. Therefore, the configuration of the first embodiment improves the degree of freedom in the design of the friction body unit 3 and the thermochromic writing instrument 1.

[0069] In the frictional body unit 3 of the first embodiment, the first opening 44a of the air vent 44 is located in a portion of the cylindrical side wall of the holding part 4 that has a smaller outer diameter than the maximum outer diameter part 4a. As a result, if a child accidentally swallows the frictional body unit 3, the maximum outer diameter part 4a of the side wall of the holding part 4 comes into contact with the child's tracheal wall, while the portion of the side wall with a smaller outer diameter than the maximum outer diameter part 4a does not come into contact with the child's tracheal wall. As a result, the first opening 44a of the air vent 44 is not blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0070] In the friction body unit 3 of the first embodiment, the first opening 44a of the air vent 44 is formed in the second tapered portion 4c whose outer diameter decreases from bottom to top. As a result, if a child accidentally swallows the friction body unit 3, the maximum outer diameter portion 4a of the side wall of the holding part 4 comes into contact with the child's tracheal wall, while the portion with an outer diameter smaller than the maximum outer diameter portion 4a does not come into contact with the child's tracheal wall. As a result, the first opening 44a of the air vent 44 is not blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0071] The side wall of the holding portion 4 of the friction body unit 3 in the first embodiment includes a maximum outer diameter portion 4a, a first tapered portion 4b, and a second tapered portion 4c. The second tapered portion 4c has an outer diameter smaller than that of the first tapered portion 4b and an inclination angle β larger than the inclination angle α of the first tapered portion 4b. The first opening 44a of the air vent 44 is formed in the second tapered portion 4c. As a result, even if a child accidentally swallows the friction body unit 3 and the friction body unit 3 tilts, causing the first tapered portion 4b to come into contact with the child's tracheal wall, the second tapered portion 4c will not come into contact with the child's tracheal wall. As a result, the first opening 44a of the air vent 44 will not be blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0072] In the thermochromic writing instrument 1 of the first embodiment, the annular outward protrusion 54 and the annular inward protrusion 45 are engaged with each other over a 360-degree range, thereby firmly holding the attachment portion 52 of the friction body 5 in the internal space 41 of the holding portion 4. Furthermore, when the annular outward protrusion 54 and the annular inward protrusion 45 are engaged with each other, a gap is formed between the outer surface of the outward protrusion 54 and the inner surface of the holding portion 4. This gap communicates with the ventilation hole 44, thereby maintaining an air flow path connecting the inside and outside of the holding portion 4.

[0073] Furthermore, the air flow path of the friction body unit 3 functions when a child accidentally swallows the friction body unit 3 that has been removed from the thermochromic writing instrument 1. On the other hand, the air flow path of the friction body unit 3 does not function when the friction body unit 3 is attached to the thermochromic writing instrument 1. Therefore, in the first embodiment, the first connecting portion 21 of the thermochromic writing instrument 1 is accommodated in a gap that constitutes part of the air flow path of the friction body unit 3, and this gap can be effectively utilized.

[0074] Second Embodiment Next, a friction body unit and a thermochromic writing implement according to a second embodiment of the present invention will be described with reference to FIGS.

[0075] 11 and 12, the friction body unit 3 and thermochromic writing instrument 1 of the second embodiment differ from the first embodiment in that a female thread 22 is provided in the first connecting portion 21 of the upper shaft 2c, and a male thread 43 is provided in the second connecting portion 42 of the holder 4. In the friction body unit 3 and thermochromic writing instrument 1 of the second embodiment described below, detailed description of the same configuration as in the first embodiment will be omitted.

[0076] - Barrel As shown in Figure 10, the barrel 2 of the thermochromic writing instrument 1 is composed of a lower barrel 2a, a central barrel 2b, and an upper barrel 2c. Most of the lower barrel 2a is composed of a cylindrical section. A tapered section whose outer diameter decreases from top to bottom is provided at the lower end of the cylindrical section. The cylindrical section of the lower barrel 2a is used as the grip of the thermochromic writing instrument 1. An opening is provided at the tip of the tapered section of the lower barrel 2a. The nib of the refill protrudes and retracts from the opening at the tip of the tapered section. The central barrel 2b is composed only of a long cylindrical section. The lower end of the central barrel 2b is connected to the upper end of the lower barrel 2a by screwing or press-fitting. The upper barrel 2c is composed only of a short cylindrical section. The lower end of the upper barrel 2c is connected to the upper end of the central barrel 2b by screwing or press-fitting. The lower shaft 2a, the center shaft 2b, and the upper shaft 2c are made of, for example, a synthetic resin such as polycarbonate or a metal.

[0077] 11 and 12 , a first coupling portion 21 is provided at the upper end of the cylindrical upper shaft 2c. A female thread 22 is provided on the inner surface of the first coupling portion 21. A second coupling portion 42 provided on the holding portion 4 of the friction body unit 3 is screwed into the first coupling portion 21. Note that the coupling between the first coupling portion 21 and the second coupling portion 42 is not limited to screwing, and may be changed to a coupling structure such as fitting, press-fitting, or engagement.

[0078] 11 and 12, the friction body unit 3 is composed of a holding portion 4 and a friction body 5. The friction body unit 3 is attached to the upper shaft 2c of the barrel 2. The height of the friction body unit 3 is, for example, 14.0 mm.

[0079] Holding Part The friction body 5 is attached to an upper part 47 of the holding part 4. The holding part 4 is made of, for example, a synthetic resin such as polycarbonate or a metal. The height of the holding part 4 is, for example, 8.0 mm.

[0080] 12 , the retaining portion 4 has a cylindrical side wall that forms an internal space 41 that is open upward and downward. A substantially cylindrical second connecting portion 42 that protrudes downward is provided on the lower side of the retaining portion 4. A male thread 43 is provided on the outer surface of the second connecting portion 42. This male thread 43 is threadedly engaged with the female thread 22 of the first connecting portion 21 of the barrel 2. Note that the connection between the first connecting portion 21 and the second connecting portion 42 is not limited to threaded engagement, and may be changed to a connecting structure such as fitting, press-fitting, or engagement.

[0081] The outer diameter of the second connecting portion 42 is smaller than the maximum outer diameter of the retaining portion 4. As a result, an annular step 46 is formed at the boundary between the maximum outer diameter portion 4a of the retaining portion 4 and the second connecting portion 42. This annular step 46 comes into surface contact with the upper end of the upper shaft 2c of the barrel 2 described above.

[0082] Two ventilation holes 44 are formed in the holding part 4. The two ventilation holes 44 are arranged symmetrically on the cylindrical side wall of the holding part 4 and communicate with the internal space 41 of the holding part 4. The ventilation holes 44 function as an air passage for a child to breathe if the child accidentally swallows the friction body unit 3. Furthermore, a first opening 44a (see FIG. 7) of the ventilation hole 44 formed on the outer surface of the holding part 4 functions as a non-slip surface for fingers gripping the friction body unit 3. This makes it easy to attach and detach the friction body unit 3 to and from the barrel 2. Note that a non-slip surface such as a recessed groove or knurling may be formed on the outer surface of the side wall of the holding part 4 excluding the ventilation holes 44.

[0083] The entire vent hole 44 is located above the second coupling portion 42, and the second opening 44b (see FIG. 7) of the vent hole 44 is located below the inward protrusion 45. With this configuration, the vent hole 44 penetrates the side wall of the holder 4 without interfering with the second coupling portion 42 and the inward protrusion 45. In other words, the functions of the second coupling portion 42 and the inward protrusion 45 are not hindered by the vent hole 44 penetrating the side wall of the holder 4. As a result, the second coupling portion 42 can be securely screwed onto the first coupling portion 21, and the inward protrusion 45 can be securely engaged with the outward protrusion 54.

[0084] 12, the outer surface of the holding portion 4 is composed of a maximum outer diameter portion 4a, a first tapered portion 4b, a second tapered portion 4c, a third tapered portion 4d, and a chamfered portion 4e. The first tapered portion 4b is located above the maximum outer diameter portion 4a. The second tapered portion 4c is located above the first tapered portion 4b. The third tapered portion 4d is located above the second tapered portion 4c. The chamfered portion 4e is located above the third tapered portion 4d. In the second embodiment, the lower end of the first tapered portion 4b is the maximum outer diameter portion 4a, and the maximum outer diameter portion 4a does not have an outer surface.

[0085] The outer diameters of the first tapered portion 4b, the second tapered portion 4c, and the third tapered portion 4d all decrease from bottom to top. Of the three tapered portions 4b, 4c, and 4d, the outer diameter of the first tapered portion 4b, which is the lowest, is preferably reduced by 10% to 30%. For example, the outer diameter of the lower end of the first tapered portion 4b (same as the maximum outer diameter portion 4a) is 10.0 mm, and the outer diameter of the upper end of the first tapered portion 4b is 8.8 mm.

[0086] The outer diameter of the lower end of the second tapered portion 4c is 8.8 mm, and the outer diameter of the upper end of the second tapered portion 4c is 6.8 mm. The inclination angle β of the second tapered portion 4c is larger than the inclination angle α of the first tapered portion 4b (α<β). To make the holding portion 4 easier to hold, the inclination angle γ of the third tapered portion 4d is preferably smaller than the inclination angle β of the second tapered portion 4c (γ<β). The air vent 44 is formed in the second tapered portion 4c. For example, α=40°, β=58°, and γ=20°.

[0087] 11 and 12, the friction body unit 3 can be attached to and detached from the upper shaft 2c of the thermochromic writing instrument 1. As shown in Fig. 11, when the friction body unit 3 is attached to the upper shaft 2c, the step 46 of the holder 4 abuts against the upper end of the upper shaft 2c.

[0088] 12, the ventilation hole 44 of the second embodiment is formed in the side wall of the holding part 4 where the second connecting part 42 is not provided. As a result, the air flow path formed by the ventilation hole 44, the internal space 41, and the opening below the internal space 41 is not affected at all by the unevenness of the male thread 43, and air can circulate smoothly.

[0089] Effects and Benefits In the friction unit 3 of the second embodiment described above, the vent hole 44, the internal space 41, and the opening below the internal space 41 form an air passage that connects the inside and outside of the holding portion 4. This air passage ensures an airway for the child to breathe even if the child accidentally swallows the friction body unit 3. In particular, by using the internal space 41 and the opening below as the air passage, sufficient air circulation is possible. Because this air passage is formed from the outer surface of the side wall of the holding portion 4 to the inside, it does not limit the degree of freedom in designing the holding portion 4. Therefore, the configuration of the second embodiment improves the degree of freedom in designing the friction body unit 3 and the thermochromic writing instrument 1.

[0090] In the frictional body unit 3 of the second embodiment, the first opening 44a of the air vent 44 is located in a portion of the cylindrical side wall of the holding part 4 that has a smaller outer diameter than the maximum outer diameter part 4a. As a result, if a child accidentally swallows the frictional body unit 3, the maximum outer diameter part 4a of the side wall of the holding part 4 comes into contact with the child's tracheal wall, while the portion of the side wall with a smaller outer diameter than the maximum outer diameter part 4a does not come into contact with the child's tracheal wall. As a result, the first opening 44a of the air vent 44 is not blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0091] In the friction body unit 3 of the second embodiment, the first opening 44a of the air vent 44 is formed in the second tapered portion 4c whose outer diameter decreases from bottom to top. As a result, if a child accidentally swallows the friction body unit 3, the maximum outer diameter portion 4a of the side wall of the holding part 4 comes into contact with the tracheal wall of the child, while the portion with an outer diameter smaller than the maximum outer diameter portion 4a does not come into contact with the tracheal wall of the child. As a result, the first opening 44a of the air vent 44 is not blocked by the tracheal wall of the child, and an airway for the child to breathe is secured.

[0092] The side wall of the holding portion 4 of the friction body unit 3 of the second embodiment includes a maximum outer diameter portion 4a, a first tapered portion 4b, and a second tapered portion 4c. The second tapered portion 4c has an outer diameter smaller than that of the first tapered portion 4b and an inclination angle β larger than the inclination angle α of the first tapered portion 4b. The first opening 44a of the air vent 44 is formed in the second tapered portion 4c. As a result, if a child accidentally swallows the friction body unit 3, even if the friction body unit 3 tilts and the first tapered portion 4b comes into contact with the child's tracheal wall, the second tapered portion 4c will not come into contact with the child's tracheal wall. As a result, the first opening 44a of the air vent 44 will not be blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0093] Third Embodiment Next, a friction body unit and a thermochromic writing implement according to a third embodiment of the present invention will be described with reference to FIGS.

[0094] 14 and 15 , the friction body unit 3 and thermochromic writing instrument 1 of the third embodiment differ from those of the first and second embodiments in the configuration of the holding portion 4 of the friction body unit 3. In the friction body unit 3 and thermochromic writing instrument 1 of the third embodiment described below, detailed description of the same configuration as that of the first embodiment will be omitted.

[0095] - Barrel As shown in Figure 13, the barrel 2 of the thermochromic writing instrument 1 is composed of a lower barrel 2a, a central barrel 2b, and an upper barrel 2c. Most of the lower barrel 2a is composed of a cylindrical section. A tapered section whose outer diameter decreases from top to bottom is provided at the lower end of the cylindrical section. The cylindrical section of the lower barrel 2a is used as the grip of the thermochromic writing instrument 1. An opening is provided at the tip of the tapered section of the lower barrel 2a. The nib of the refill protrudes and retracts from the opening at the tip of the tapered section. The central barrel 2b is composed only of a long cylindrical section. The lower end of the central barrel 2b is connected to the upper end of the lower barrel 2a by screwing or press-fitting. The upper barrel 2c is composed only of a short cylindrical section. The lower end of the upper barrel 2c is connected to the upper end of the central barrel 2b by screwing or press-fitting. The lower shaft 2a, the center shaft 2b, and the upper shaft 2c are made of, for example, a synthetic resin such as polycarbonate or a metal.

[0096] 14 and 15 , a cylindrical first coupling portion 21 that protrudes upward is provided at the upper end of the upper shaft 2c. A male thread 22 is provided on the outer surface of the first coupling portion 21. A second coupling portion 42 that is provided on the holding portion 4 of the friction body unit 3 is screwed into the first coupling portion 21. Note that the coupling between the first coupling portion 21 and the second coupling portion 42 is not limited to screwing, and may be changed to a coupling structure such as fitting, press-fitting, or engagement.

[0097] The outer diameter of the first coupling portion 21 is smaller than the outer diameter of the upper end of the upper shaft 2 c. As a result, an annular step portion 23 is formed at the upper end of the upper shaft 2 c. The lower end of the holding portion 4 of the friction body unit 3 comes into surface contact with this annular step portion 23.

[0098] 14 to 21 show the friction body unit 3 of the third embodiment. As shown in Fig. 14, the friction body unit 3 is composed of a holding portion 4 and a friction body 5. The friction body unit 3 is attached to the upper shaft 2c of the barrel 2 described above. The height of the friction body unit 3 of the third embodiment is 15.0 mm.

[0099] 15 to 20, the friction body 5 is attached to an upper portion 47 of the holding portion 4. The holding portion 4 is formed of, for example, a synthetic resin such as polycarbonate or a metal. The total axial length of the holding portion 4 in the third embodiment is 9.0 mm.

[0100] 15 , the holding portion 4 has a cylindrical side wall that forms an internal space 41 that is open upward and downward. A second coupling portion 42 is provided on the lower side of the holding portion 4. An internal thread 43 is provided on the internal surface of the second coupling portion 42. This internal thread 43 is threadedly engaged with the external thread 22 of the first coupling portion 21 of the barrel 2. Note that the coupling between the first coupling portion 21 and the second coupling portion 42 is not limited to threaded engagement, and may be changed to a coupling structure such as fitting, press-fitting, or engagement.

[0101] The friction body 5 is attached to the upper part 47 of the holding part 4. An annular inward protrusion 45 is provided on the inner surface of the upper part 47. Meanwhile, an annular outward protrusion 54 is provided on the outer surface of the lower part of the friction body 5. When the lower side of the friction body 5 is inserted into the upper part 47 of the holding part 4, the inward protrusion 45 and the outward protrusion 54 are engaged with each other. Note that the connection between the holding part 4 and the friction body 5 is not limited to the engagement between the inward protrusion 45 and the outward protrusion 54, but may be by fitting, press-fitting, engagement, screwing, bonding, two-color molding, or the like.

[0102] The annular inward protrusion 45 has an inclined surface whose inner diameter decreases from top to bottom, and an annular lower surface. The inclined surface of the inward protrusion 45 guides the lower side of the friction body 5 inserted into the upper part 47 of the holding part 4 downward into the internal space 41. This allows the outward protrusion 54 to be smoothly engaged with the inward protrusion 45, making it easy to assemble the friction body unit 3.

[0103] 15 , 16 , and 20 , three air vents 44 are formed in the holding part 4. The three air vents 44 are arranged at equal intervals on the cylindrical side wall of the holding part 4 and communicate with the internal space 41 of the holding part 4. The air vents 44 function as air passages for a child to breathe if the child accidentally swallows the friction body unit 3. In addition, a first opening 44 a (see FIG. 19 ) of the air vent 44 formed on the outer surface of the holding part 4 functions as a non-slip surface for fingers gripping the friction body unit 3. This makes it easy to attach and detach the friction body unit 3 to and from the barrel 2.

[0104] 17, three tapered portions 4b, 4c, and 4d with different inclination angles α, β, and γ are provided on the outer surface of the holding portion 4. By making the inclination angles α, β, and γ of the three tapered portions 4b, 4c, and 4d all less than 45°, the side wall of the holding portion 4 can be easily gripped with fingers at any position. This makes it easy to attach and detach the friction body unit 3 to and from the barrel 2. Note that the outer surface of the side wall of the holding portion 4, excluding the air vent 44, may be formed with an anti-slip feature such as a recessed groove or a knurled portion.

[0105] 15 and 19 , the vent hole 44 has a first opening 44a formed on the outer surface of the side wall of the holding portion 4 and a second opening 44b formed on the inner surface of the side wall of the holding portion 4. The entire vent hole 44 is located above the second connecting portion 42, and the second opening 44b of the vent hole 44 is located below the inward protrusion 45. With this configuration, the vent hole 44 penetrates the side wall of the holding portion 4 without interfering with the second connecting portion 42 and the inward protrusion 45. In other words, the functions of the second connecting portion 42 and the inward protrusion 45 are not impaired by the vent hole 44 penetrating the side wall of the holding portion 4. As a result, the second connecting portion 42 can be securely screwed onto the first connecting portion 21, and the inward protrusion 45 can be securely engaged with the outward protrusion 54.

[0106] 16 and 19, the first opening 44a of the ventilation hole 44 is formed on an inclined surface whose outer diameter decreases from bottom to top of the second tapered portion 4c. Therefore, a diameter difference A shown in FIG. 16 is generated between the upper and lower ends of the first opening 44a of the ventilation hole 44. The interior of the ventilation hole 44 can be expanded from the second opening 44b to the first opening 44a. This allows a sufficient amount of air to be obtained from the ventilation hole 44 even if a child accidentally swallows the friction body unit 3. The diameter difference A shown in FIG. 16 is preferably 0.5 mm or more.

[0107] 17 and 18, the outer surface of the holding portion 4 is composed of a maximum outer diameter portion 4a, a first tapered portion 4b, a second tapered portion 4c, a third tapered portion 4d, and two chamfered portions 4e. The first tapered portion 4b is located on the maximum outer diameter portion 4a. The first chamfered portion 4e is formed between the first tapered portion 4b and the second tapered portion 4c. The second tapered portion 4c is located on the chamfered portion 4e. The third tapered portion 4d is located on the second tapered portion 4c. The second chamfered portion 4e is formed on the third tapered portion 4d. In the third embodiment, the lower end of the first tapered portion 4b is the maximum outer diameter portion 4a, and the maximum outer diameter portion 4a does not have an outer surface.

[0108] The outer diameters of the first tapered portion 4b, the second tapered portion 4c, and the third tapered portion 4d all decrease from bottom to top. In the third embodiment, the outer diameter of the lower end of the first tapered portion 4b (same as the maximum outer diameter portion 4a) is 10.2 mm, and the outer diameter of the upper end of the first tapered portion 4b is 10.0 mm.

[0109] The outer diameter of the lower end of the second tapered portion 4c is 9.7 mm, and the outer diameter of the upper end of the second tapered portion 4c is 6.8 mm. The inclination angle β of the second tapered portion 4c is greater than the inclination angle α of the first tapered portion 4b (α<β). To make the holding portion 4 easier to hold, the inclination angle γ of the third tapered portion 4d is preferably smaller than the inclination angle β of the second tapered portion 4c (γ<β). The air vent 44 is formed in the second tapered portion 4c. For example, α = 3.2°, β = 44°, and γ = 11°. Note that the first tapered portion 4b, the second tapered portion 4c, and the third tapered portion 4d may have a very small inclination angle, such as a draft angle to facilitate removal of the molded product from the mold. The boundary edge between the second tapered portion 4c and the third tapered portion 4d may be chamfered.

[0110] 21 shows the central angles θ1, θ2, and θ3 of the first openings 44a of the three ventilation holes 44. The central angles θ1, θ2, and θ3 of the first openings 44a are the angles formed by two imaginary lines connecting the two outermost ends of the first openings 44a and the center point of the holding portion 4. The sum θ of the central angles θ1, θ2, and θ3 of the first openings 44a (θ = θ1 + θ2 + θ3) is preferably in the range of 90° to 180°, and more preferably in the range of 90° to 150°. This is because if the sum θ is less than 90°, sufficient ventilation cannot be achieved, and if the sum θ exceeds 180° (more preferably 150°), sufficient strength of the holding portion 4 cannot be achieved.

[0111] 17 shows the height C of the second opening 44b of the ventilation hole 44. The height C of the second opening 44b is preferably 0.5 mm or more. This is because if the height C of the second opening 44b is 0.5 mm or more, a sufficient amount of ventilation can be obtained in the event that a child accidentally swallows the friction body unit 3.

[0112] As shown in Figures 15 and 18, in the third embodiment, a sidewall portion 4f extending from the upper end of the first opening 44a of the air vent 44 to the upper end of the second opening 44b has a constant outer diameter. The outer diameter of the sidewall portion 4f is the same as the outer diameter of the upper end of the first opening 44a. Due to this sidewall portion 4f, the outer diameter of the portion of the sidewall of the holding part 4 above the upper end of the second opening 44b of the air vent 44 is equal to or smaller than the outer diameter of the upper end of the second opening 44b. This prevents the portion of the air vent above the upper end of the second opening from coming into contact with the child's tracheal wall if the friction body unit is accidentally swallowed by a child. As a result, a larger gap is formed between the portion of the air vent above the upper end of the second opening and the child's tracheal wall, ensuring an airway for the child to breathe.

[0113] Furthermore, the outer diameter of the portion of the vent hole 44 above the upper end of the second opening 44b is equal to or smaller than the outer diameter of the upper end of the second opening 44b, which means that there will be no undercut in the vent hole 44 when the outer shape of the holder 4 is molded using a mold. This allows the outer shape of the holder 4 to be injection molded using a single, undivided mold, eliminating the need for a slide core to form the vent hole 44. As a result, the cost of injection molding the holder 4 is reduced.

[0114] 14 and 15, the friction body unit 3 can be attached to and detached from the upper shaft 2c of the thermochromic writing instrument 1. As shown in Fig. 14, when the friction body unit 3 is attached to the upper shaft 2c, the lower end of the holder 4 abuts against the step 23 of the upper shaft 2c. As in the second embodiment described above, the upper shaft 2c of the third embodiment may be provided with a female thread 22 and the holder 4 may be provided with a male thread 43.

[0115] Effects and Benefits In the friction body unit 3 of the third embodiment described above, the vent hole 44, the internal space 41, and the opening at the bottom of the internal space 41 form an air flow path that connects the inside and outside of the holding part 4. This air flow path ensures an airway for the child to breathe even if the child accidentally swallows the friction body unit 3. In particular, by using the internal space 41 and the opening at the bottom as the air flow path, sufficient air circulation is possible. Since this air flow path is formed from the outer surface of the side wall of the holding part 4 to the inside, it does not limit the degree of freedom in the design of the holding part 4. Therefore, according to the configuration of the first embodiment, the degree of freedom in the design of the friction body unit 3 and the thermochromic writing instrument 1 is improved.

[0116] In the frictional body unit 3 of the third embodiment, the first opening 44a of the air vent 44 is located in a portion of the cylindrical side wall of the holding part 4 that has a smaller outer diameter than the maximum outer diameter part 4a. As a result, if a child accidentally swallows the frictional body unit 3, the maximum outer diameter part 4a of the side wall of the holding part 4 comes into contact with the child's tracheal wall, while the portion of the side wall with a smaller outer diameter than the maximum outer diameter part 4a does not come into contact with the child's tracheal wall. As a result, the first opening 44a of the air vent 44 is not blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0117] In the friction body unit 3 of the third embodiment, the first opening 44a of the air vent 44 is formed in the second tapered portion 4c whose outer diameter decreases from bottom to top. As a result, when a child accidentally swallows the friction body unit 3, the maximum outer diameter portion 4a of the side wall of the holding part 4 comes into contact with the tracheal wall of the child, while the portion with an outer diameter smaller than the maximum outer diameter portion 4a does not come into contact with the tracheal wall of the child. As a result, the first opening 44a of the air vent 44 is not blocked by the tracheal wall of the child, and an airway for the child to breathe is secured.

[0118] The side wall of the holding portion 4 of the friction body unit 3 of the third embodiment includes a maximum outer diameter portion 4a, a first tapered portion 4b, and a second tapered portion 4c. The second tapered portion 4c has an outer diameter smaller than that of the first tapered portion 4b and an inclination angle β larger than the inclination angle α of the first tapered portion 4b. The first opening 44a of the air vent 44 is formed in the second tapered portion 4c. As a result, even if a child accidentally swallows the friction body unit 3 and the friction body unit 3 tilts, causing the first tapered portion 4b to come into contact with the child's tracheal wall, the second tapered portion 4c will not come into contact with the child's tracheal wall. As a result, the first opening 44a of the air vent 44 will not be blocked by the child's tracheal wall, and an airway for the child to breathe is secured.

[0119] In the friction body unit 3 of the third embodiment, the outer diameter of the portion of the vent hole 44 above the upper end of the second opening 44b is equal to or smaller than the outer diameter of the upper end of the second opening 44b. Therefore, when the outer shape of the holder 4 is molded using a mold, there is no undercut in the vent hole 44. This allows the outer shape of the holder 4 to be injection molded using a single, undivided mold, eliminating the need for a slide core to form the vent hole 44. As a result, the cost of injection molding the holder 4 is reduced.

[0120] In the thermochromic writing instrument 1 of the third embodiment, the annular outward protrusion 54 and the annular inward protrusion 45 are engaged with each other over a 360-degree range, thereby firmly holding the attachment portion 52 of the friction body 5 in the internal space 41 of the holding portion 4. Furthermore, when the annular outward protrusion 54 and the annular inward protrusion 45 are engaged with each other, a gap is formed between the outer surface of the outward protrusion 54 and the inner surface of the holding portion 4. This gap communicates with the ventilation hole 44, thereby maintaining an air flow path connecting the inside and outside of the holding portion 4.

[0121] Furthermore, the air flow path of the friction body unit 3 functions when a child accidentally swallows the friction body unit 3 that has been removed from the thermochromic writing instrument 1. On the other hand, the air flow path of the friction body unit 3 does not function when the friction body unit 3 is attached to the thermochromic writing instrument 1. Therefore, in the third embodiment, the first connecting portion 21 of the thermochromic writing instrument 1 is accommodated in a gap that constitutes part of the air flow path of the friction body unit 3, and this gap can be effectively utilized.

[0122] Fourth Embodiment Next, a friction body unit and a thermochromic writing implement according to a fourth embodiment of the present invention will be described with reference to FIG.

[0123] As shown in Fig. 22, the friction body unit 3 of the fourth embodiment has a plurality of recesses 48 formed along the lower end of the cylindrical side wall of the holding portion 4. The plurality of recesses 48 are formed on the inner surface at the lower end of the holding portion 4. As a result, the lower end of the holding portion 4 has a shape in which a plurality of recesses 48 and protrusions 49 are alternately arranged in succession. The plurality of recesses 48 and protrusions 49 may also be formed on the outer surface at the lower end of the holding portion 4. In the fourth embodiment, the configuration other than the recesses 48 and protrusions 49 is the same as that of the friction body unit 3 and thermochromic writing instrument 1 shown in Figs. 13 to 21.

[0124] First, the recesses 48 are used to maintain the posture of the holding part 4 in the automated assembly process of the friction body unit 3. That is, the recesses 48 are engaged with the protrusions formed on a jig (not shown). This restricts the movement and rotation of the holding part 4, making it possible to easily assemble the friction body 5 to the holding part 4.

[0125] Second, the multiple recesses 48 prevent the holder 4 from being tightly attached to the barrel 2 of the thermochromic writing instrument 1. That is, the friction body unit 3 is attached to the first connecting portion 21 of the upper shaft 2c shown in FIG. 15. At this time, the lower end of the side wall of the holder 4 comes into surface contact with the annular step portion 23 of the upper shaft 2c. If the surface contact pressure is high and the contact area is large, the lower end of the side wall of the holder 3 may be tightly attached to the step portion 23 of the upper shaft 2c, making it impossible to remove the friction body unit 3 by hand. The multiple recesses 48 reduce the area of ​​the lower end of the side wall of the holder 4, making it easier to remove the friction body unit 3 by hand.

[0126] Additionally, the multiple recesses 48 receive foreign matter such as dust and dirt interposed between the lower end of the side wall of the holder 4 and the step 23 of the upper shaft 2c, preventing the foreign matter from interfering with the attachment of the friction body unit 3. Furthermore, multiple protrusions (not shown) may be formed on the step 23 of the upper shaft 2c. When the friction body unit 3 is attached to the upper shaft 2c, the multiple recesses 48 engage with the multiple protrusions formed on the step 23, restricting rotation of the holder 4. This maintains the threaded engagement between the first coupling portion 21 and the second coupling portion 42 shown in FIG. 14, preventing the friction body unit 3 from being unintentionally separated from the upper shaft 2c.

[0127] <Others> The friction body unit and thermochromic writing instrument of the present invention are not limited to the configurations of the first to fourth embodiments described above. For example, the friction body unit is not limited to retractable thermochromic writing instruments, but can also be applied to capped thermochromic writing instruments. In this case, the friction body unit is attached to the end of the cap opposite the opening. Furthermore, the thermochromic writing instrument to which the friction body unit is applied is not limited to ballpoint pens. The friction body unit can be applied to thermochromic writing instruments other than ballpoint pens, such as pencils or markers.

[0128] REFERENCE SIGNS LIST 1 Thermochromic writing implement 2 Barrel 2a Lower barrel 2b Center barrel 2c Upper barrel 2d Clip 21 First connecting portion 22 Male thread, female thread 23 Step portion 24 Enlarged diameter portion 3 Friction body unit 4 Holding portion 41 Internal space 42 Second connecting portion 43 Female thread, male thread 44 Ventilation hole 44a First opening 44b Second opening 45 Inward protrusion 46 Step portion 47 Upper portion 48 Recessed portion 49 Protruding portion 4a Maximum outer diameter portion 4b First tapered portion 4c Second tapered portion 4d Third tapered portion 4e Chamfered portion 4f Side wall portion 5 Friction body 51 Friction portion 52 Mounting portion 53 Step portion 54 Outward protrusion

Claims

1. A friction body unit comprising a friction body and a holding part, wherein the friction body is configured to be capable of generating frictional heat for thermally discoloring handwriting of thermochromic ink, and the holding part is configured to hold the friction body and be attachable to or detachable from the barrel or cap of a thermochromic writing instrument, wherein the holding part has a cylindrical side wall that forms an internal space that opens at least downward, and the side wall is formed with at least one air hole that communicates with the internal space, allowing air to circulate between the air hole, the internal space, and the lower opening.

2. A friction body unit as described in claim 1, wherein the cylindrical side wall of the holding part includes a portion with a large outer diameter and a portion with a small outer diameter, and the air vent has a first opening formed on the outer surface of the side wall and a second opening formed on the inner surface of the side wall, and at least the first opening is located above the maximum outer diameter part of the side wall.

3. A friction body unit as described in claim 2, wherein at least a portion of the cylindrical side wall of the holding part is provided with a tapered section whose outer diameter decreases from bottom to top, and the first opening of the air hole is formed in the tapered section.

4. A friction body unit as described in claim 3, wherein the cylindrical side wall of the holding part includes a first tapered part located above the maximum outer diameter part and a second tapered part located above the first tapered part, the outer diameter of the first tapered part decreases upward from the upper end of the maximum outer diameter part, the outer diameter of the second tapered part decreases upward from the upper end of the first tapered part, the inclination angle of the second tapered part is larger than the inclination angle of the first tapered part, and the first opening of the air hole is formed in the second tapered part.

5. The friction body unit according to claim 3, wherein the outer diameter of the portion of the cylindrical side wall of the holding portion above the upper end of the second opening of the vent hole is equal to or smaller than the outer diameter of the upper end of the second opening.

6. A friction body unit according to any one of claims 2 to 5, wherein an annular outward protrusion is provided on the outer surface of the lower side of said friction body, an annular inward protrusion is provided on the inner surface of the cylindrical side wall of said holding part, and said side wall opens downward and upward, at least the second opening of said air hole is located below said inward protrusion, said outward protrusion and said inward protrusion are engaged with each other when the lower side of said friction body is inserted into said internal space from said upper opening of said side wall, and a gap is formed between the outer surface of said outward protrusion and the inner surface of said side wall when said outward protrusion and said inward protrusion are engaged with each other, and said gap communicates with said air hole.

7. A friction body unit according to any one of claims 1 to 6, wherein a plurality of recesses are formed along the lower end of the cylindrical side wall of said holding portion.

8. A thermochromic writing instrument equipped with a friction body unit as set forth in any one of claims 1 to 7, characterized in that a first connecting portion is provided on the barrel or cap of the thermochromic writing instrument, and a second connecting portion configured to be detachable from the first connecting portion is provided on the friction body unit.

9. A thermochromic writing instrument equipped with the friction body unit described in claim 6, wherein a first connecting portion is provided on the barrel or cap of the thermochromic writing instrument, and a second connecting portion configured to be detachable from the first connecting portion is provided on the friction body unit, and when the second connecting portion is connected to the first connecting portion, the first connecting portion is located in the gap formed between the outer surface of the outward protrusion and the inner surface of the side wall.