JP7215934B2 - Mechanical pencil unit and retractable writing instrument - Google Patents

Description

The present invention relates to a mechanical pencil unit constituting a refill for a mechanical pencil, a mechanical pencil, etc., and a retractable writing instrument equipped with the mechanical pencil unit.

Conventionally, in relation to this type of invention, for example, in Patent Document 1, there is disclosed a lead core feeding mechanism for feeding out a lead core clamped by the chuck by inserting and removing a chuck in the shaft cylinder from a clutch ring in the shaft cylinder, A mechanical pencil is disclosed that includes a lead guide tube that is fixed to the front end of a barrel and projects forward through a lead lead fed from a lead lead feeding mechanism.
Further, Patent Document 2 discloses a holding cylinder, a holder that is inserted through a front end opening of the holding cylinder, protrudes forward from the front end of the holding cylinder, and is supported so as to move back and forth with respect to the holding cylinder, and a lead core. a lead core feeding mechanism that is inserted into the core breaker and fed toward the holder; a movement direction changing mechanism that advances and tilts the holder relative to the holding cylinder and the lead core by a radial force applied from the lead core to the holder; A mechanical pencil unit is disclosed that includes a holder biasing member that biases the holder backward with respect to the holding cylinder. If this mechanical pencil unit is accommodated in the barrel, a retractable writing instrument can be easily constructed.
According to this retractable writing instrument, the mechanical pencil unit is advanced by a predetermined operation, and in a state in which the holder at the front end of the mechanical pencil unit protrudes from the front end opening of the barrel, the lead core protruding from the holder has a diameter. When a directional force is applied, the holder advances relative to the holding cylinder and the lead core, so that the lead core can be covered and protected by the holder.

Japanese Patent Application Laid-Open No. 2001-180181 JP 2017-159580 A

By the way, according to the above-mentioned conventional mechanical pencil, when excessive writing pressure is applied to the lead in the normal writing posture with the barrel inclined, the lead bends in the range between the lead guide tube and the chuck, causing the lead to bend. The core may be damaged.
In particular, in the conventional technology described in Patent Document 2, the holder advances and tilts slightly due to the force component in the radial direction, which increases the possibility of damaging the lead core.

In view of such problems, the present invention comprises the following configurations.
In a mechanical pencil unit having a lead lead feeding mechanism for drawing out a lead lead held between the chuck by inserting and removing a chuck from a clutch ring, a clutch receiver is provided on the rear side of the clutch ring, and the clutch ring is connected to the clutch. A mechanical pencil unit, characterized in that it is provided so as to be tilted in contact with the front end of a receiver.

Since the present invention is configured as described above, it is possible to prevent the lead core from being damaged due to bending of the lead core.

1 is a longitudinal sectional view showing an example of a mechanical pencil unit according to the present invention; FIG. The relationship between the clutch ring and the clutch receiver in the same mechanical pencil unit is shown in (a) and (b), respectively, and is an end view of one side of the cut portion along the center line. Note that hatching is omitted. It is an internal structure diagram showing an example of a writing instrument equipped with the same mechanical pencil unit. It is a vertical cross-sectional view showing the operation of the same mechanical pencil unit, (a) shows the state in which the holder is in the initial position, (b) shows the state in which the holder has advanced to the lead core protection position. In addition, hatching indicates a portion that has moved from the previous state. FIG. 4 is an enlarged vertical cross-sectional view of a main part showing the action of the clutch ring when a radial force is applied to the lead core; Note that hatching is omitted. Other examples of the clutch ring and clutch receiver are shown in (a) and (b), respectively, which are end views of one side of the cut along the centerline. Other examples of the clutch ring and clutch receiver are shown in (a) and (b), respectively, which are end views of one side of the cut along the centerline. Other examples of clutch rings and clutch receivers are shown in (a), (b) and (c), respectively, which are end views of one side of the cut along the centerline. Other examples of the clutch ring and clutch receiver are shown in (a) and (b), respectively, which are end views of one side of the cut along the centerline.

The present embodiment discloses the following features.
A first feature is that in a mechanical pencil unit having a lead lead feeding mechanism for inserting and removing a chuck from a clutch ring to feed a lead lead sandwiched between the chucks, a clutch receiver is provided on the rear side of the clutch ring, A clutch ring is provided so as to contact and tilt the front end of the clutch receiver (see FIGS. 1, 2, and 4 to 9).
The term "mechanical pencil unit" used herein includes mechanical pencil refills used in multifunctional retractable writing instruments, general mechanical pencils having a lead lead-out mechanism directly in the barrel, and the like.

As a second feature, a holder through which the lead core fed out from the lead core feeding mechanism is inserted, a holding cylinder that supports the holder by protruding from a front end opening, and a force component in the radial direction applied to the holder causes the above-mentioned and a motion direction changing mechanism for advancing and tilting the holder facing the holding cylinder (see FIGS. 1 and 4).

As a third feature, the clutch ring is provided with an annular inclined surface on the rear end side of the outer circumference thereof, the diameter of which gradually decreases toward the rear (see FIGS. 2 and 6).

As a fourth feature, the clutch ring is provided with an annular inclined surface on the rear end side of the inner periphery thereof, the diameter of which gradually increases toward the rear (see FIG. 6).

As a fifth feature, the clutch receiver is provided with an annular inclined surface that expands in diameter toward the front on the front end side of the inner periphery thereof (see FIG. 7).

As a sixth feature, the clutch receiver is provided with a projection that partially contacts the rear end of the clutch ring (see FIG. 8).

As a seventh feature, the protrusion is provided with an annular inclined surface on the front end side of the outer circumference thereof, the diameter of which gradually decreases toward the front (see FIG. 8).

As an eighth feature, the annular inclined surface is formed in a convex curved surface (see FIGS. 2(b), 6(b), 8(c), 9(a) and 9(b)).

As a ninth feature, in a half cross-sectional view, the radial dimension of the annular inclined surface is set larger than the radial dimension of the contact portion between the clutch ring and the clutch receiver (see FIG. 2).

As a tenth feature, the clutch ring is provided with an annular inclined surface that gradually expands in diameter toward the rear on the rear end side of the inner circumference, and the clutch receiver is provided with a projection that contacts the annular inclined surface. (See FIG. 9).

As an eleventh feature, the annular inclined surface is formed flat, and the projection is formed in a convex curved surface that makes line contact with the annular inclined surface (see FIG. 9A).

As a twelfth feature, the annular inclined surface is formed in a concave curved surface, and the projection is formed in a convex curved surface that makes surface contact with the annular inclined surface (see FIG. 9B).

The thirteenth feature is that the retractable writing instrument is provided with the mechanical pencil unit (see FIG. 3).

<First Embodiment>
Next, specific embodiments having the above characteristics will be described in detail with reference to the drawings. In this specification, the axial direction means the direction in which the center line of the holding cylinder 10 extends. Further, "front" means one side in the axial direction and the direction in which the lead core is drawn out. Also, "rear" means the side opposite to the one side.

Mechanical pencil unit 1 shown in FIG. a holder 20 through which the lead core x is inserted; a holding cylinder 10 that projects and supports the holder 20 from the front end opening; and a motion direction changing mechanism M2 that tilts while moving forward to the lead core protection position.

Here, the initial position is a position in which an excessive radial force is not applied to the holder 20 (see FIG. 4(a)). At this initial position, the holder 20 is in contact with the front end opening of the holding cylinder 10 over substantially the entire circumference of the cam slope 21a.
The lead core protection position is a state in which the holder 20 moves forward relative to the holding cylinder 10 due to an excessive radial force component and covers the tip side of the lead core x (see FIG. 4(b)). position.

The holding tube 10 includes a first tube portion 11, a second tube portion 12 concentrically connected to the rear end side of the first tube portion 11, and a rear end side of the second tube portion 12. It is integrally provided with a third cylindrical portion 13 concentrically connected to the body, and is configured in a long cylindrical shape. These first to third cylindrical portions 11, 12, 13 can be partly or wholly integrated.

Each of the first to third tubular portions 11, 12, 13 is made of a hard material such as metal.
The first cylindrical portion 11 internally includes a holder 20 that can move forward and backward, and a holder biasing member 23 that biases the holder 20 rearward, thereby forming a movement direction changing mechanism M2.
The second cylindrical portion 12 and the third cylindrical portion 13 internally include a core breaker 30, a chuck 40, a clutch ring 41, a clutch receiver 42, and the like, which are made of an elastic material, and constitute a lead core feeding mechanism M1. In FIG. 1, reference numeral 12a denotes a stepped portion that restricts the forward movement of the clutch ring 41, and reference numeral 12b denotes a stepped portion that receives the front end portion of the clutch receiver .

The holder 20 includes a holder main body 21 having a cam slope 21a, and a cylindrical receiver connected to the rear side of the holder main body 21 to receive the rear end of a holder biasing member 23 (a compression coil spring in the illustrated example). It is integrally formed with the portion 22 and is supported so as to be able to advance and retreat with respect to the holding cylinder 10 .

The holder main body 21 is a substantially cylindrical member that is inserted into the first cylindrical portion 11 and protrudes forward from the front end opening of the first cylindrical portion 11 . An annular cam slant surface 21 a is provided along the entire periphery of the holder main body 21 so as to be in sliding contact with the front end opening of the first cylindrical portion 11 .

The cam slope 21a is formed in the shape of a conical surface that expands in diameter toward the front. The cam slope 21a advances the holder 20 relative to the holding cylinder 10 by a radial force component applied to the holder 20. As shown in FIG.

The motion direction conversion mechanism M2 is composed of the first cylindrical portion 11, the cam slope 21a of the holder 20, the holder biasing member 23 that biases the holder 20 backward, and the like. This movement direction conversion mechanism M2 is such that when an excessive radial force is applied to the holder 20 via the lead core x, the force component in the radial direction causes the cam slope 21a to move toward the front end opening of the first cylindrical portion 11. and slide the holder 20 forward from the initial position (see FIG. 4(a)) to a predetermined lead core protection position (see FIG. 4(b)). The holder 20 is slightly tilted as it advances.
It is possible to apply the structure of Patent Document 1 to the basic structure of the lead core feeding mechanism M1.

Further, the lead lead feeding mechanism M1 includes a lead breaker 30 held on the front end side in the second cylindrical portion 12, a chuck 40 that advances and retreats behind the lead breaker 30, and a chuck 40 that A clutch ring 41 that fits in an annular shape, a substantially cylindrical clutch receiver 42 that receives the clutch ring 41 from the rear side, a support member 43 that supports the rear end side of the chuck 40, and is connected to the rear end side of the support member 43. It is provided with a guide tube portion 44 for guiding the advance and retreat of the lead tank portion 60, and first to third urging members 51 to 53. As shown in FIG.
The lead lead feeding mechanism M1 feeds out the lead x clamped by the chuck 40 by forward and backward movement transmitted from the lead tank section 60. As shown in FIG. The lead feeding mechanism M1 retracts the chuck 40 and the like together with the lead x when a backward urging force stronger than a preset writing pressure is applied to the lead x clamped by the chuck 40 . These basic operations are substantially the same as the invention of Patent Document 1.

The core breaker 30 is made of an elastic material such as elastomer resin or synthetic rubber and has a substantially cylindrical shape. They are fitted so that they cannot advance or retreat (see FIGS. 1 and 4). The core breaker 30 is loosely pressed against the outer peripheral surface of the lead core x to be inserted.

The chuck 40 is made of an elastically flexible hard material (for example, synthetic resin, metal, etc.), and the inner diameter side surface of the chuck 40 clamps and releases the lead core x.

The clutch ring 41 is a substantially cylindrical member with a gap secured between it and the inner peripheral surface of the second cylindrical portion 12 , and is tiltable with its rear end in contact with the front end of the clutch receiver 42 .
The clutch ring 41 is annularly fitted to the chuck 40 from the rear side, holds the lead core in a sandwiched state, and is engaged with the stepped portion 12 a in the second tubular portion 12 when the clutch ring 41 moves forward together with the chuck 40 . It is removed from the chuck 40 rearward to release the above-mentioned lead core clamping state. The annular rear end of the clutch ring 41 abuts against the front end surface of the clutch receiver 42 when the clutch ring 41 is retracted.

A flat annular inclined surface 41a whose diameter gradually decreases toward the rear is formed on the rear end side of the outer circumference of the clutch ring 41 (see FIG. 2).

The annular inclined surface 41a is provided at the intersection of the outer diameter surface of the clutch ring 41 and the rear end surface.
As exemplified in FIG. 2( a ), in a half cross-sectional view, the radial dimension a of the annular inclined surface 41 a is set larger than the radial dimension b of the contact portion between the clutch ring 41 and the clutch receiver 42 .
With this configuration, contact resistance between the clutch ring 41 and the clutch receiver 42 can be reduced, and flexible movement (for example, tilting, radial movement, etc.) of the clutch ring 41 can be facilitated.

The annular inclined surface 41a on the rear end side of the clutch ring 41 may be replaced with a convexly curved annular inclined surface 41a' like the clutch ring 41' in FIG. 2(b).

The clutch receiver 42 is a substantially cylindrical member in which the chuck 40 is loosely inserted in the center side thereof. It is in contact with the stepped portion 12b inside the cylindrical portion 12 (see FIG. 1).
An annular wall portion 42a for receiving the rear end portion of the clutch ring 41 is provided at the front end portion of the clutch receiver 42 (see FIG. 2).

The annular wall portion 42a is formed in a disc shape having a through hole on the center side. An annular inclined surface 42a1 whose diameter decreases toward the rear of the clutch ring 41 is provided on the front end side of the inner periphery of the annular wall portion 42a.
The annular inclined surface 42a1 is a convex curved surface, reduces the contact area between the clutch ring 41 and the clutch receiver 42, and reduces the resistance when the clutch ring 41 moves flexibly.

Further, the lead tank part 60 is configured in a substantially cylindrical shape with an open front end, and supplies the lead core x from the rear side to the lead lead feeding mechanism M1. The lead tank portion 60 includes a slide cylinder portion 61 engaged with the rear end side of the holding cylinder 10 so as to advance and retreat, and a cylindrical tank body portion 62 connected to the slide cylinder portion 61 and extending rearward. (see FIG. 1). The slide cylinder portion 61 and the tank main body portion 62 can be formed from an integral member.

Then, the mechanical pencil unit 1 having the above configuration is incorporated into a multifunctional retractable writing instrument A, as illustrated in FIG.
In the multi-function retractable writing instrument A, by selectively advancing a plurality of pieces a2 and a3, the front end writing part of the refill connected to the advanced pieces a2 (or a3) protrudes forward from the front end of the barrel a1. Let Said refill is, according to the illustrated example, a mechanical pencil unit 1 or a ballpoint pen refill 9 .
For example, a piece a2 having a clip a6 with an opening/closing function is operated to move forward against the biasing force of a coil spring a4, and the front end writing portion of a mechanical pencil unit 1 (refill) connected to this piece a2 moves toward the shaft tube a1. When the piece a2 protrudes forward from the front end opening of the shaft tube a1, the piece a2 is locked by the locking portion a5 provided in the shaft tube a1, and this projecting state is maintained.
When the clip a6 is advanced in this protruded state, the lead x is drawn out from the front end of the mechanical pencil unit 1. As shown in FIG.
For this multifunctional retractable writing instrument A, it is possible to apply the basic structure disclosed in, for example, Japanese Patent Application Laid-Open No. 2014-198439.

Next, the characteristic functions and effects of the mechanical pencil unit 1 and the multifunctional retractable writing instrument A configured as described above will be described in detail.

In the normal writing state shown in FIG. 4(a), the cam slope 21a of the holder 20 and the front end opening of the holding cylinder 10 are in contact over substantially the entire circumference, and the lead is inserted from the holding cylinder 10 to the holder 20. x is kept substantially linear. In this state, the lead x is in contact with the lead sliding contact portion 21 b of the holder 20 , the inner peripheral surface of the lead breaker 30 and the chuck 40 at three points.

Then, as shown in FIG. 4(b), when the lead x is strongly pressed against a writing surface p (for example, a paper surface) and an excessive radial force is applied to the lead x, The cam slope 21a is brought into sliding contact with the front end opening of the holding cylinder 10, so that the holder 20 moves forward relative to the lead core x and the holding cylinder 10. As shown in FIG.
During this forward movement, the holder 20 is slightly tilted as shown in FIG. 4(b). Therefore, the lead core x is curved and tilted in the front and back range from the lead core sliding contact portion 21b to the chuck 40 . Then, the inner peripheral surface side of the core breaker 30 is radially pressed by the lead core x and slightly elastically deformed.

In addition, the chuck 40 bends so as to follow the inclination of the lead core x, and along with this, the clutch ring 41 moves flexibly, such as tilting with respect to the axis and fine movement in the radial direction, while being in contact with the clutch receiver 42. (see Figure 5).

Therefore, it is possible to reduce the partial pressing force applied to the lead core x and prevent the lead core x from being broken.

<Second embodiment>
Next, another embodiment of the mechanical pencil unit according to the present invention will be described. Since the embodiments shown below are partially modified from the embodiments described above, mainly the modified parts will be described in detail, and parts that function in the same way will be denoted by the same reference numerals and duplicated. detailed description is omitted.

The embodiment shown in FIG. 6(a) is obtained by replacing the clutch ring 41 with a clutch ring 71 in the mechanical pencil unit 1 described above. The clutch ring 71 is obtained by adding a flat annular inclined surface 41b that gradually increases in diameter toward the rear on the rear end side of the inner circumference of the clutch ring 41 (FIG. 2(a)).

The flat annular inclined surfaces 41a and 41b on the rear end side of the clutch ring 71 are formed into convexly curved annular inclined surfaces 41a' and 41b', respectively, like the clutch ring 71' shown in FIG. 6(b). may be replaced.

According to the embodiment shown in FIGS. 6(a) and 6(b), the contact area between the clutch ring 71 (or 71') and the clutch receiver 42 is reduced, and the clutch ring 71 (or 71') can be moved more flexibly. , the damage to the lead core x can be reduced.

<Third embodiment>
The embodiment shown in FIG. 7(a) is obtained by replacing the clutch ring 41 with a clutch ring 41'' and replacing the clutch receiver 42 with a clutch receiver 72 in the mechanical pencil unit 1 described above.

The clutch ring 41'' is obtained by omitting the annular inclined surface 41a from the clutch ring 41. The symbol c in FIG. 7 denotes a general chamfered portion c having a relatively small area.

The clutch receiver 72 has an annular wall portion 72a on its front end side, and a flat annular inclined surface 72a1 whose diameter increases forward is formed on the inner peripheral front end side of this annular wall portion 72a.

The flat annular inclined surface 72a1 of the clutch receiver 72 may be replaced with a convex curved annular inclined surface 72a1' like the clutch receiver 72' shown in FIG. 7(b).

According to the embodiments shown in FIGS. 7(a) and 7(b), the contact area between the clutch ring 41'' and the clutch receiver 72 (or 72') is small, so that the clutch ring 41'' can be flexibly moved to Damage to the core x can be reduced.

<Fourth Embodiment>
8(a) is the mechanical pencil unit 1 in which the clutch ring 41 is replaced with the clutch ring 41'' and the clutch receiver 42 is replaced with the clutch receiver 73. FIG.

The clutch receiver 73 has an annular wall portion 73a on its front end side. The front end surface of the annular wall portion 73a is provided with a protrusion 73a1 that partially contacts the rear end portion of the clutch ring 41''.

The protrusion 73a1 is a protrusion whose cross-sectional area gradually decreases toward the front, and is in annular contact with the rear end portion of the clutch ring 41″. , an annular inclined surface 73a11 whose diameter gradually decreases toward the front is provided.

The protrusion 73a1 may be replaced with a protrusion 73a2 like a clutch receiver 73' shown in FIG. 8(b), or replaced with a protrusion 73a3 like a clutch receiver 73'' shown in FIG. 8(c). It is possible to

The protrusion 73a2 is an annular protrusion that contacts the rear end portion of the clutch ring 41'', and has an annular inclined surface 73a21 on its outer peripheral side that gradually decreases in diameter toward the front. It has an annular inclined surface 73a22 that gradually expands in diameter toward (see FIG. 8(b)).

The protrusion 73a3 is an annular protrusion that contacts the rear end portion of the clutch ring 41'', and is formed in a semicircular cross section as shown in FIG. 8(c).

According to the embodiments shown in FIGS. 8(a), (b), and (c), the contact area between the clutch ring 41'' and the clutch receiver 73 (73' or 73'') is small, so that the clutch ring 41'' can be made flexible. can be moved to effectively reduce the damage to the lead core x.
<Fifth Embodiment>
9(a) and 9(b), respectively, in the mechanical pencil unit 1, the clutch ring 41 is replaced with clutch rings 74, 74' and the clutch receiver 42 is replaced with clutch receivers 75, 75'. It is a thing.

The clutch ring 74 is formed in a substantially cylindrical shape, and has a flat annular inclined surface 74a on the rear end side of its inner circumference, the diameter of which gradually increases toward the rear (see FIG. 9A).

The clutch receiver 75 has an annular wall portion 75a on its front end side, and a projection 75a1 that protrudes forward and contacts the annular inclined surface 74a on the front end surface of the annular wall portion 75a.
The protrusion 75a1 is formed in a convex curved shape so that the portion on the outer diameter side thereof is in line contact with the flat annular inclined surface 74a (see FIG. 9A).

Further, the clutch ring 74' is formed in a substantially cylindrical shape, and has, on the rear end side of the inner circumference thereof, a concave curved annular inclined surface 74a' whose diameter gradually increases toward the rear (Fig. 9(b)). reference).

The clutch receiver 75' has an annular wall portion 75a on its front end side, and has a projection 75a1' on the front end surface of the annular wall portion 75a, which protrudes forward and contacts the annular inclined surface 74a'.
The protrusion 75a1' has a convexly curved portion on the outer diameter side thereof, and is in surface contact with the concavely curved annular inclined surface 74a' (see FIG. 9B).

According to each aspect shown in FIGS. 9(a) and 9(b), the contact between the annular inclined surface 74a (or 74a') and the protrusion 75a1 (or 75a1') causes the front end side of the clutch ring 74 (or 74') to move. , the lead core x can be oscillated so as to follow the tilting motion of the lead core x, and damage to the lead core x can be effectively reduced.

<Other Modifications>
In the above embodiments, the radial dimension a is set larger than the radial dimension b only in the example shown in FIG. 2, but in the other examples shown in FIGS. can be set larger than the radial dimension of the contact portion between the clutch ring and the clutch receiver to facilitate flexible movement of the clutch ring.

In addition, the present invention is not limited to the embodiments described above, and can be changed as appropriate without changing the gist of the present invention.

1: Mechanical Pencil Unit 10: Holding Cylinder 20: Holder 40: Chuck 41, 41', 41'', 71, 71', 74, 74': Clutch Ring 42, 72, 72', 73, 73', 73'', 75, 75': Clutch receiver 41a, 41b, 72a1, 74a: Annular inclined surface (flat surface)
41a', 41b', 42a1, 72a1', 74a': annular inclined surface (curved surface)
73a1, 73a2: Protrusions (flat surfaces)
73a3, 75a1, 75a1': Protrusions (curved surfaces)
x: Lead A: Multifunctional retractable writing instrument M1: Lead feeding mechanism M2: Movement direction changing mechanism

Claims (13)

A mechanical pencil unit equipped with a lead lead feeding mechanism that feeds out a lead lead sandwiched between the chuck by inserting and removing the chuck from the clutch ring,
A clutch receiver is provided on the rear side of the clutch ring,
A mechanical pencil unit, wherein the clutch ring is provided so as to be in contact with a front end portion of the clutch receiver and tilt. A holder through which the lead core fed from the lead core feeding mechanism is inserted; a holding cylinder that projects and supports the holder from a front end opening; 2. The mechanical pencil unit according to claim 1, further comprising a movement direction changing mechanism for advancing and tilting the holder. 3. The mechanical pencil unit according to claim 1, wherein the clutch ring is provided with an annular slanted surface gradually decreasing in diameter toward the rear on the rear end side of the outer periphery thereof. The mechanical pencil unit according to any one of claims 1 to 3, wherein the clutch ring is provided with an annular inclined surface gradually increasing in diameter toward the rear on the rear end side of the inner periphery thereof. The mechanical pencil unit according to any one of claims 1 to 4, wherein the clutch receiver is provided with an annular inclined surface that expands in diameter toward the front on the front end side of the inner periphery thereof. 3. The mechanical pencil unit according to claim 1, wherein the clutch receiver is provided with a projection that partially contacts the rear end of the clutch ring. 7. The mechanical pencil unit according to claim 6, wherein the projection has an annular inclined surface on the front end side of the outer periphery thereof, the diameter of which gradually decreases toward the front. The mechanical pencil unit according to any one of claims 3 to 5 and 7, wherein the annular inclined surface is formed in a convex curved surface. Claims 3 to 5, 7 and 8, wherein the radial dimension of the annular inclined surface is set larger than the radial dimension of the contact portion between the clutch ring and the clutch receiver in a half cross-sectional view. The mechanical pencil unit according to any one of items 1 to 3. The clutch ring is provided with an annular inclined surface that gradually expands in diameter toward the rear on the rear end side of the inner periphery thereof,
3. The mechanical pencil unit according to claim 1, wherein the clutch receiver is provided with a projection that contacts the annular inclined surface. 11. The mechanical pencil unit according to claim 10, wherein said annular inclined surface is formed in a flat shape, and said protrusion is formed in a convex curved surface that makes line contact with said annular inclined surface. 11. The mechanical pencil unit according to claim 10, wherein the annular inclined surface is formed in a concave curved surface, and the protrusion is formed in a convex curved surface that makes surface contact with the annular inclined surface. A retractable writing instrument comprising the mechanical pencil unit according to any one of claims 1 to 12.

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