Replaceable toothbrushes and replacement brushes

Abstract

To provide a replaceable toothbrush capable of securing strength while having a slim brush part.SOLUTION: A replaceable toothbrush has a handle part 11 with a shaft part 17 projecting outwardly in a longitudinal direction X and formed in one end part on a replaceable brush part 12 side in the longitudinal direction X. The replaceable brush part 12 has, along the longitudinal direction X, a head part 13 having a bristle planting base 15, and a neck part 14 connected to the head part 13. The neck part 14 has an inserted part 19 into which the shaft part 17 is inserted in an end part on the opposite side of the head part 13. A thickness of the neck part 14 gradually reduces from the inserted part 19 in the longitudinal direction X toward the head part 13. A dimension ratio of a minimum thickness T2 of the neck part 14 to a diameter D1 on the tip side of the shaft part 17 is 1:1.3-1:1.5, a diameter D2 of the base end part of the shaft part 17 is 5.5 mm or more, and the diameter D2 is 2.5 times or less of the minimum thickness T2 of the neck part 14.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a replaceable toothbrush including a handle portion and a replaceable brush portion detachably attached to the tip side of the handle portion along the longitudinal direction.

Background Art

[0002] Since a replaceable toothbrush can discard only the consumed brush portion and replace only the brush portion with a new one, the amount of waste can be reduced compared to a toothbrush in which the brush portion and the handle portion are integrally formed. As the above-described replaceable toothbrush, for example, in Patent Document 1, there are a fitting portion on the handle neck side and a fitted portion on the tufted portion side that fits into it, and the fitting portion has a plurality of fitting units each including an engaging convex portion whose cross-section perpendicular to the axis is a polygon similar to each other and an engaging concave portion continuous thereto. A toothbrush is disclosed. This toothbrush is a replaceable toothbrush characterized in that fitting is completed when a plurality of engaged convex portions of the fitted portion simultaneously overcome a plurality of engaging convex portions of the fitting portion.

[0003] Further, in Patent Document 2, there are provided a brush main body portion and a replacement brush detachably attached to the tip side of the brush main body portion, and a shaft portion extending in the long axis direction from the tip of the handle portion constituting the brush main body portion is inserted into a groove-shaped shaft insertion portion formed in the mounting portion of the replacement brush from an opening on the outer peripheral surface side of the mounting portion into the shaft insertion portion. A replaceable toothbrush is disclosed. In this replaceable toothbrush, at least a part of the shaft portion in the shaft insertion portion is shielded by a shielding portion when the replacement brush is attached to the brush main body portion and when the replacement brush is attached to the brush main body portion, as viewed from the opening on the outer peripheral surface side of the mounting portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] While replaceable toothbrushes are preferable to have a slender brush head for ease of use and to reduce the amount of resin used, making the brush head slender presents a problem: it becomes more prone to breakage when stress is concentrated during use. However, the replaceable toothbrushes described in Patent Documents 1 and 2 had room for improvement in terms of ensuring strength while maintaining a slim profile.

[0006] Therefore, the object of the present invention is to provide a replaceable toothbrush that has a slender brush head while ensuring strength. [Means for solving the problem]

[0007] The present invention relates to a replaceable toothbrush comprising a handle portion and a replaceable brush portion detachably attached to the tip of the handle portion, along the longitudinal direction. In one embodiment, it is preferable that the handle portion has a shaft portion formed at one end on the side of the replaceable brush portion in the longitudinal direction, which protrudes outward in the longitudinal direction. In one embodiment, the replacement brush portion preferably has a head portion having a bristle base and a neck portion connected to the head portion along the longitudinal direction, wherein the neck portion has an insertion portion formed at the end opposite to the head portion into which the shaft portion is inserted. In one embodiment, it is preferable that the thickness of the neck portion gradually decreases from the insertion portion in the longitudinal direction toward the head portion. In one embodiment, it is preferable that the dimensional ratio between the minimum thickness of the neck portion and the diameter of the tip portion of the shaft portion is 1:1.3 to 1:1.5. In one embodiment, it is preferable that the diameter of the base end of the shaft portion is 5.5 mm or more, and that this diameter is 2.5 times or less the minimum thickness of the neck portion.

[0008] Furthermore, the present invention relates to a replacement brush used in the aforementioned replaceable toothbrush, and comprising the aforementioned replaceable brush portion. [Effects of the Invention]

[0009] According to the replaceable toothbrush and replacement brush of the present invention, the strength of the brush portion can be ensured even though the brush portion is slender. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a perspective view showing one embodiment of the replaceable toothbrush according to the present invention. [Figure 2] Figure 2 is an exploded perspective view of the replaceable toothbrush shown in Figure 1. [Figure 3] Figure 3(a) is a side view of the replaceable toothbrush shown in Figure 2, and Figure 3(b) is a top view of the replaceable toothbrush shown in Figure 2. [Figure 4] Figure 4(a) is a side view enlarged of the replacement brush section shown in Figure 1, and Figures 4(b) to (e) are cross-sectional views of BB, CC, DD, and EE, respectively, in Figure 4(a). [Figure 5] Figure 5 is an exploded perspective view of the part of the replaceable toothbrush shown in Figure 1 where the handle is attached to the replaceable brush head. [Figure 6] Figure 6(a) is a cross-sectional view of AA in Figure 3(b), and Figure 6(b) is a view equivalent to Figure 6(a) in the fitted state. [Figure 7] Figure 7(a) is a cross-sectional view of the FF section of Figure 6(a), and Figure 7(b) is a cross-sectional view of the GG section of Figure 6(b). [Figure 8] Figure 8 is a diagram corresponding to Figure 6(a) in another embodiment of the replaceable toothbrush according to the present invention. [Figure 9] Figure 9 shows the stress distribution diagrams obtained from simulations performed in the examples and comparative examples. [Modes for carrying out the invention]

[0011] Hereinafter, the detachable toothbrush of the present invention will be described based on its preferred embodiments with reference to the drawings. FIGS. 1 to 8 show a detachable toothbrush 10 according to an embodiment of the present invention. As shown in FIG. 1, the detachable toothbrush 10 of the present embodiment includes a handle portion 11 and a replaceable brush portion 12 that is detachably attached to the tip side of the handle portion 11.

[0012] The detachable toothbrush 10 has a shape that is long in one direction and has a longitudinal direction X and a width direction Y orthogonal thereto. In the detachable toothbrush 10 of the present embodiment, the longitudinal direction X is a direction along the extending direction of the detachable toothbrush 10. Also, the direction orthogonal to both the longitudinal direction X and the width direction Y is referred to as the "vertical direction Z". In the present embodiment, the longitudinal direction X coincides with the extending direction of the handle portion 11 and the extending direction of the replaceable brush portion 12, respectively. The vertical direction Z coincides with the thickness direction of the bristle base 15 and the normal direction to the bristle surface 15a.

[0013] The replaceable brush portion 12 has a head portion 13 having a bristle base 15 and a neck portion 14 connected to the head portion 13 along the longitudinal direction X. The bristle base 15 in the head portion 13 has a pair of flat main surfaces, and implanting holes 16 for implanting a plurality of tufts of bristles 18 are formed in one of the main surfaces 15a (see FIGS. 1 and 2). The main surface 15a in which the implanting holes 16 are formed is hereinafter referred to as the "bristle surface 15a". The pair of flat main surfaces in the bristle base 15 face each other in the vertical direction Z. In a plan view seen from above, the plurality of implanting holes 16 are arranged, for example, in an annular shape or a staggered shape. A plurality of tufts of bristles 18 formed by bundling a plurality of bristles are implanted in the plurality of implanting holes 16 (see FIGS. 1 and 2).

[0014] In this specification, the side where the tufts of bristles 18 of the detachable toothbrush 10 are present, that is, the bristle surface 15a side, is referred to as "above", and the side opposite to the bristle surface 15a is referred to as "below".

[0015] The head portion 13 is a flat, plate-like section, and in a plan view from above, it has a roughly elliptical shape. The neck portion 14 is a rod-like section that extends from the head portion 13 toward the handle portion 11 in the longitudinal direction X, and its width and thickness gradually increase toward the handle portion 11. The head portion 13 and the neck portion 14 are connected in the longitudinal direction X. In the replacement brush portion 12 of this embodiment, the position where the width is narrowest in the longitudinal direction X is defined as the boundary BL between the head portion 13 and the neck portion 14 [see Figure 3(b)]. Unless otherwise specified in this specification, "width" refers to the length in the width direction Y, and "thickness" refers to the length in the vertical direction Z.

[0016] The neck portion 14 has an insertion portion 19 formed at the end opposite to the head portion 13 in the longitudinal direction X, into which the shaft portion 17 is inserted. The insertion portion 19 is a recess formed at the end of the neck portion 14 on the handle portion 11 side in the longitudinal direction X, and has an opening on the handle portion 11 side. The insertion portion 19 has an internal space (recess) corresponding to the three-dimensional shape of the shaft portion 17. When the handle portion 11 is attached to the replacement brush portion 12 (hereinafter also referred to as the "attached state"), the entire length of the shaft portion 17 in the longitudinal direction X is inserted into the insertion portion 19, and the outer circumferential surface of the shaft portion 17 and the inner circumferential surface of the insertion portion 19 are in close contact. This suppresses rattling between the replacement brush portion 12 and the handle portion 11, and maintains a more stable attached state.

[0017] The thickness of the neck portion 14 is minimum at the end on the boundary BL side with the head portion 13 and maximum at the insertion portion 19, which is furthest from the head portion 13. When an external force is applied to the head portion 13 from the vertical Z direction, the neck portion 14 is more flexible from the boundary BL side end to the insertion portion 19, making breakage of the replacement brush portion 12 less likely.

[0018] The handle portion 11 is the part that the user holds when brushing their teeth with the replaceable toothbrush 10. The handle portion 11 is a roughly cylindrical rod-shaped member that extends in the longitudinal direction X. From the viewpoint of facilitating the brushing operation with the replaceable toothbrush 10, the handle portion 11 of this embodiment has a shape that is gently curved upward when viewed from the width direction Y, as shown in Figure 3(a). This makes it easier to grip the handle portion 11. The handle portion 11 of this embodiment has a roughly rectangular shape when viewed from above in a plan view [see Figure 3(b)].

[0019] The handle portion 11 has a shaft portion 17 formed at one end on the side of the replaceable brush portion 12 in the longitudinal direction X, which protrudes outward in the longitudinal direction X. The shaft portion 17 protrudes from the end face portion 11a of the handle portion 11 facing the replaceable brush portion 12, along the same longitudinal direction X toward the replaceable brush portion 12. The shaft portion 17 of this embodiment is substantially frustoconical in shape and has a solid structure. More specifically, the tip of the shaft portion 17 in the longitudinal direction X is cylindrical, and the portion closer to the base end than the tip is frustoconical in shape, with the diameter expanding toward the handle portion 11. The replaceable toothbrush 10 is attached to the handle portion 11 by inserting the shaft portion 17 into the insertion portion 19 of the replaceable brush portion 12, which will be described later. In this attached state, the replaceable toothbrush 10 comprises the replaceable brush portion 12 and the handle portion 11 along the longitudinal direction X.

[0020] In this embodiment, the diameter D1 of the tip of the shaft portion 17 [see Figure 3(b)] is greater than the minimum thickness T2 of the neck portion 14 [see Figure 3(a)] (D1 > T2). More specifically, the dimensional ratio (hereinafter also simply referred to as "dimensional ratio A") between the minimum thickness T2 of the neck portion 14 and the diameter D1 at the tip of the shaft portion 17 is 1:1.3 to 1:1.5, preferably 1:1.3 to 1:1.45, and more preferably 1:1.35 to 1:1.45.

[0021] The diameter D2 at the base end of the shaft portion 17 [see Figure 3(b)] is greater than the minimum thickness T2 of the neck portion 14 [see Figure 3(a)] (D2 > T2). More specifically, the diameter D2 at the base end of the shaft portion 17 [see Figure 3(b)] is 2.5 times or less the minimum thickness T2 of the neck portion 14 [see Figure 3(a)], preferably 1.5 times or more, more preferably 1.6 times or more, also preferably 2.2 times or less, more preferably 2.0 times or less, also preferably 1.5 times or more and 2.5 times or less, more preferably 1.6 times or more and 2.2 times or less. Hereinafter, this ratio of the diameter D2 to the minimum thickness T2 will also be simply referred to as "diameter ratio B".

[0022] The diameter D1 of the tip of the shaft portion 17 (see Figure 3(b)) is 4.0 mm or more, preferably 4.2 mm or more, more preferably 4.5 mm or more, also preferably 5.2 mm or less, more preferably 5.0 mm or less, also preferably 4.0 mm or more and 5.2 mm or less, more preferably 4.2 mm or more and 5.0 mm or less, and even more preferably 4.5 mm or more and 5.0 mm or less. The tip of the shaft portion 17 is within a range of 6.0 mm from the end edge of the shaft portion 17 on the replacement brush portion 12 side toward the handle portion 11 side in the longitudinal direction X, and the maximum diameter in this range is defined as the diameter D1 of the tip. The diameter D2 of the base end of the shaft portion 17 (see Figure 3(b)) is 5.5 mm or more, preferably 6.0 mm or more, preferably 7.5 mm or less, more preferably 7.0 mm or less, and also preferably 5.5 mm or more and 7.5 mm or less, more preferably 6.0 mm or more and 7.0 mm or less. The base end of the shaft portion 17 is within a range of 3.0 mm from the end edge of the shaft portion 17 on the handle portion 11 side toward the replacement brush portion 12 side in the longitudinal direction X, and the maximum diameter in this range is defined as the diameter D2 of the base end. The difference between the diameter D1 at the tip and the diameter D2 at the base of the shaft portion 17 is preferably 0.3 mm to 3.5 mm, more preferably 1.5 mm to 2.5 mm.

[0023] In the replaced toothbrush 10 when installed, the replaceable brush portion 12 is supported by the handle portion 11 in a cantilevered manner. When brushing teeth with this replaced toothbrush 10, the tip of the bristle bundle 18 is in contact with the tooth surface, and the surface is brushed. At this time, the head portion 13 of the replaced toothbrush 10 is susceptible to external forces acting in the direction normal to the bristle surface 15a, that is, external forces acting in the vertical direction Z. When an external force acts on the head portion 13 from the vertical direction Z, this external force is transmitted to the neck portion 14 and the connection portion between the neck portion 14 and the handle portion 11 (inserted portion 19 and shaft portion 17), which can cause bending stress to concentrate in the inserted portion 19 and shaft portion 17. In the replaceable toothbrush 10 of this embodiment, the thickness of the neck portion 14 gradually decreases from the insertion portion 19 in the longitudinal direction X toward the head portion 13, making the boundary BL side of the neck portion 14 more prone to bending in one direction in the vertical direction Z. For example, when an external force is applied to the head portion 13, the neck portion 14 becomes more prone to bending in the direction of the external force. Furthermore, the inventors have found that by setting the aforementioned dimensional ratio A(T2:D1) to 1:1.3 to 1:1.5, the diameter D2 at the base end of the shaft portion 17 to 5.5 mm or more, and the diameter magnification B(D2 / T2) to 2.5 times or less, the strength of the replaceable toothbrush 10 can be ensured while making the replaceable brush portion 12 slender. This effect is thought to be due to the distribution of bending stress when an external force along the vertical Z direction acts on the head portion 13, causing it to flex from the end on the boundary BL side between the head portion 13 and the neck portion 14 to the insertion portion 19 of the neck portion 14. As a result, damage to the replaceable brush portion 12 at the boundary BL is suppressed, and the replaceable brush portion 12 becomes less likely to break. In addition, the mounting state of the shaft portion 17 to the insertion portion 19 is stably maintained. Such a slender replaceable brush portion 12 can also improve operability and design while reducing the amount of resin used in the neck portion 14.

[0024] As shown in Figures 4(b) to 4(e), the cross-sectional shape of the neck portion 14 in this embodiment gradually expands along the width direction Y from the end on the boundary BL side to the insertion portion 19. The cross-sectional shape of this neck portion 14 has a horizontal shape that is long in the width direction Y at the end on the boundary BL side, but as it approaches the insertion portion 19, it continuously changes to a vertical shape that is long in the vertical direction Z. In other words, the second moment of area of ​​the neck portion 14 in this embodiment gradually increases from the end on the boundary BL side to the insertion portion 19 in the longitudinal direction X. As a result, the bending stress is more easily distributed in the neck portion 14 in this embodiment from the end on the boundary BL side to the insertion portion 19, and it becomes less likely to break when an external force is applied to the head portion 13 from the vertical direction Z.

[0025] From the viewpoint of making it easier to distribute bending stress and from the viewpoint of maintaining a more stable state in which the shaft portion 17 is inserted into the inserted portion 19, it is preferable that the cross-sectional shape of the neck portion 14 along the width direction Y has an inverted aspect ratio between the boundary BL and the inserted portion 19. From the same viewpoint as above, it is preferable that the cross-sectional shape of the neck portion 14 along the width direction Y has a ratio (vertical / horizontal) of the length in the vertical direction Z (vertical / horizontal) to the length in the width direction Y (horizontal length) within the following range. The cross-section at the boundary BL side end of the neck portion 14 has a ratio (vertical / horizontal) of the vertical length Z to the horizontal length Y, which is preferably 0.80 or more and 1.00 or less, more preferably 0.85 or more and 0.90 or less. The cross-section of the neck portion 14 at the insertion portion 19 has a ratio (vertical / horizontal) of the length in the vertical direction Z (vertical length) to the length in the width direction Y (horizontal length), which is preferably 0.90 or more and 1.10 or less, and more preferably 0.95 or more and 1.00 or less.

[0026] From the viewpoint of further suppressing breakage of the replacement brush portion 12, the dimensions of the neck portion 14 are preferably within the following range. The difference between the maximum thickness T1 (see Figure 3(a)) and the minimum thickness T2 (see Figure 3(a)) of the neck portion 14 (T1-T2) is preferably 5.5 mm or more and 9.0 mm or less, more preferably 6.0 mm or more and 7.0 mm or less. The minimum thickness T2 of the neck portion 14 [see Figure 3(a)] is preferably 3.0 mm or more and 5.0 mm or less, more preferably 3.5 mm or more and 4.0 mm or less. The maximum thickness T1 of the neck portion 14 [see Figure 3(a)] is preferably 8.0 mm or more and 12.0 mm or less, more preferably 9.0 mm or more and 11.0 mm or less. The maximum thickness T1 of the neck portion 14 is the thickness including the insertion portion 19 if the portion having the maximum thickness T1 has an insertion portion 19.

[0027] The thickness of the neck portion 14 gradually increases from the boundary BL in the longitudinal direction X toward the handle portion 11. From the viewpoint of making the replaceable brush portion 12 more flexible and further suppressing breakage of the replaceable brush portion 12, the thickness increase per 10 mm in the longitudinal direction X of the neck portion 14 is preferably 1.10 mm / 10 mm or more and 1.25 mm / 10 mm or less, more preferably 1.15 mm / 10 mm or more and 1.20 mm / 10 mm or less. The thickness increase per 10 mm in the longitudinal direction X is the amount of change in the thickness of the neck portion 14 that increases from the boundary BL in the longitudinal direction X toward the handle portion 11.

[0028] From the viewpoint of further stabilizing the mounting state of the shaft portion 17 to the insertion portion 19, the replaceable toothbrush 10 is preferably within the following dimensions. The length L11 of the shaft portion 17 in the longitudinal direction X is preferably 10% to 30%, more preferably 15% to 20%, of the length L12 of the replaceable brush portion 12 in the longitudinal direction X. The length L11 of the shaft portion 17 in the longitudinal direction X is preferably 15% to 50%, more preferably 20% to 30%, of the length L14 of the neck portion 14 in the longitudinal direction X. The length L11 of the shaft portion 17 in the longitudinal direction X is preferably 7.5 mm or more and 25.0 mm or less, more preferably 10.0 mm or more and 15.0 mm or less. The length L12 of the replacement brush portion 12 in the longitudinal direction X is preferably 60 mm to 95 mm, and more preferably 70 mm to 80 mm. The length L14 of the neck portion in the longitudinal direction X is preferably 25 mm to 70 mm, more preferably 35 mm to 65 mm, and even more preferably 45 mm to 55 mm. Here, the length L14 of the neck portion 14 is the distance from the insertion portion 19 to the boundary BL in the longitudinal direction X [see Figure 3(a)].

[0029] As shown in Figure 5, the replaceable toothbrush 10 of this embodiment has a shaft portion 17 with a positioning projection 20 at its base end and an outer annular engagement portion 21 extending circumferentially from the outer circumferential surface of the base end. The positioning projection 20 of this embodiment protrudes radially outward from the outer circumferential surface on the base end side of the shaft portion 17, and the radial position of the outer surface of the positioning projection 20 and the outer circumferential surface of the handle portion 11 are approximately the same. The end of the positioning projection 20 on the handle portion 11 side in the longitudinal direction X is inserted into the handle portion 11 (see Figure 5). In this embodiment, the positioning projection 20 has an oval shape when viewed from above in plan view. However, the plan view shape of the positioning projection 20 is not limited to this and can be any shape. Furthermore, it is preferable that the positioning projection 20 is located on the bristle surface 15a side in the circumferential direction of the shaft portion 17 when it is attached. By being located on the bristle surface 15a side, the attached state can be made more stable and the unintentional detachment can be further suppressed. In this embodiment, the outer annular engagement portion 21 is positioned spaced apart from the end face portion 11a of the handle portion 11 towards the replaceable brush portion 12 in the longitudinal direction X. It is preferable that the positioning projection portion 20 and the outer annular engagement portion 21 overlap in the longitudinal direction X, as shown in Figure 5. In this case, the outer annular engagement portion 21 is continuous in the circumferential direction of the base end of the shaft portion 17 via the positioning projection portion 20.

[0030] The insertion portion 19 of this embodiment has a positioning notch 22 at the end on the insertion side into which the shaft portion 17 is inserted, and an inner annular engagement portion 23 extending circumferentially on the inner circumferential surface of the end. The positioning notch 22 is a portion of the opening periphery that forms the insertion port that is cut out toward the head portion 13. In this embodiment, the inner annular engagement portion 23 is positioned spaced apart from the end on the insertion opening 19a side toward the head portion 13 in the longitudinal direction X. Preferably, the inner annular engagement portion 23 and the positioning notch portion 22 overlap in the longitudinal direction X. In this case, the inner annular engagement portion 23 is continuous with the insertion portion 19 in the circumferential direction via the positioning notch portion 22.

[0031] In this embodiment, when the replaceable toothbrush 10 is installed with the shaft portion 17 inserted into the insertion portion 19, the outer annular engaging portion 21 and the inner annular engaging portion 23 engage with each other, and the positioning projection 20 fits into the positioning notch 22. As a result, the outer annular engaging portion 21 and the inner annular engaging portion 23 engage the replaceable brush portion 12 and the handle portion 11 in the circumferential direction, and the positioning projection 20, which is fitted in the longitudinal direction X, restricts the movement of the replaceable brush portion 12 in the longitudinal direction X and the positioning notch 22. As a result, the installed state can be made more stable, and the accidental detachment of the replaceable brush portion 12 from the handle portion 11 can be further suppressed.

[0032] In a plan view, the notch shape of the positioning notch 22 corresponds to the plan view shape of the end of the positioning projection 20 on the replacement brush portion 12 side in the longitudinal direction X, and these are substantially the same shape. When the replacement brush portion 12 is attached to the handle portion 11, the positioning projection 20 is made capable of engaging with the positioning notch 22. This allows for more accurate alignment of the circumferential position when attaching the replacement brush portion 12 to the handle portion 11, and also makes it possible to match the direction of curvature of the handle portion 11 in a side view with the circumferential orientation of the bristle surface 15a. As a result, the operability when brushing with the replaceable toothbrush 10 can be further improved.

[0033] In this embodiment, the distance from the end of the inner annular engagement portion 23 to the insertion opening 19a side is equal to the distance from the outer annular engagement portion 21 to the end face portion 11a of the handle portion 11. As a result, when installed, the insertion opening 19a of the replacement brush portion 12 comes into contact with the end face portion 11a of the handle portion 11, thereby stabilizing the installed state.

[0034] As shown in Figures 5 and 6(b), the replaceable toothbrush 10 of this embodiment has an outer annular engaging portion 21 which is an annular rib 21a, and an inner annular engaging portion 23 which is an annular groove 23a that can engage with the annular rib. The annular rib 21a is a substantially annular protrusion that projects radially outward from the outer circumferential surface of the base end of the shaft portion 17. The annular groove 23a is a substantially annular recess formed on the inner circumferential surface of the insertion portion 19. The cross-sectional shape of the outer annular engagement portion 21 and the inner annular engagement portion 23 along the longitudinal direction X is, for example, a semicircular shape, a U-shape, or a V-shape, but is not limited to these. From the viewpoint of achieving both stability in the mounting state of the replacement brush section 12 and the handle section 11, and ease of attachment and detachment of the replacement brush section 12, the width of the annular rib 21a and the annular groove 23a is preferably 0.1 mm or more and 2.0 mm or less, more preferably 0.3 mm or more and 1.0 mm or less. The respective widths of the annular rib 21a and the annular groove 23a are the lengths in the direction perpendicular to the extending direction of these ribs and grooves. From the same viewpoint as described above, the height of the annular rib 21a and the depth of the annular groove 23a are preferably 0.05 mm or more and 0.50 mm or less, and more preferably 0.15 mm or more and 0.30 mm or less.

[0035] As shown in Figure 5, the replaceable toothbrush 10 of this embodiment has a positioning projection 20 that protrudes radially outward from the outer circumferential surface of the handle portion 11, and also has a curved portion 20a on the tip side of the shaft portion 17. With this configuration, when attaching the replaceable brush portion 12 to the handle portion 11, it becomes easier to insert the positioning projection 20 into the positioning notch 22, making the fitting of the two parts easier. From the viewpoint of facilitating the fitting of the positioning projection 20 and the positioning notch 22, the height h of the positioning projection 20 (see Figure 6(b)) is preferably 0.8 mm or more and 4.0 mm or less, more preferably 1.0 mm or more and 3.0 mm or less. The height h of the positioning projection 20 is the height of the radial outward projection from the outer circumferential surface of the shaft portion 17. If the outer diameter of the base end of the shaft portion 17 changes as described later, the minimum value of the length in the direction normal to the outer circumferential surface of the shaft portion 17 is set as the height h of the positioning projection 20. Since the positioning projection 20 has a curved surface portion 20a on the tip side of the shaft portion 17, the positioning projection 20 can be smoothly fitted into the positioning notch portion 22. From the viewpoint of further improving this effect, the radius of curvature of the curved surface portion 20a in plan view is preferably 0.5 mm or more and 3.0 mm or less, more preferably 1.0 mm or more and 2.0 mm or less.

[0036] As shown in Figures 5 and 6(b), the shaft portion 17 of this embodiment has a straight portion 17a with a constant outer diameter at the tip end in the longitudinal direction X, and a tapered portion 17b located closer to the base end than the straight portion 17a, with the outer diameter gradually increasing toward the base end. This makes it easier to insert the shaft portion 17 into the insertion portion 19, and further prevents the insertion portion 19 from falling out of the shaft portion 17. From the viewpoint of achieving a better balance between ease of insertion of the shaft portion 17 into the insertion portion 19 and the effect of preventing the insertion portion 19 from falling out of the shaft portion 17, the taper angle of the tapered portion 17b is preferably 1° or more and 6° or less, more preferably 2° or more and 4° or less. The taper angle of the tapered portion 17b is the angle of inclination of the outer edge (contour) of the tapered portion 17b with respect to the central axis of the shaft portion 17 in a plan view.

[0037] As shown in Figures 6(a), 7(a), and 7(b), the insertable portion 19 of this embodiment has, in the mounted state in which the shaft portion 17 is inserted into the insertable portion 19, an inner insertable portion 19b where the straight portion 17a is located, and an insertion-side insertable portion 19e whose inner diameter gradually widens toward the handle portion 11. The inner circumferential surface of the insertion-side insertable portion 19e corresponds to the outer circumferential surface of the tapered portion 17b. Multiple press-fit ribs 19c are formed on the inner circumferential surface of the inner insertion portion 19b along the longitudinal direction X (see Figure 6(a)). In the replaced toothbrush 10 of this embodiment, when the straight portion 17a is inserted into the inner insertion portion 19b, the press-fit ribs 19c are crushed. This increases the frictional force between the straight portion 17a and the press-fit ribs 19c, making it possible to maintain the fitted state more stably. In this embodiment, four press-fit ribs 19c are formed at equal intervals in the circumferential direction (see Figures 7(a) and 7(b)). From the viewpoint of generating an appropriate frictional force between the straight section 17a and the press-fit rib 19c, it is preferable that the dimensions of the straight section 17a and the press-fit rib 19c are within the following ranges. The total length of the straight portion 17a in the longitudinal direction X is preferably 2.0 mm or more and 8.0 mm or less, more preferably 4.0 mm or more and 6.0 mm or less. The number of press-fit ribs 19c is preferably 2 to 6, more preferably 3 to 5. The length of the press-fit rib 19c in the longitudinal direction X is preferably 1.0 mm or more and 8.0 mm or less, more preferably 4.0 mm or more and 6.0 mm or less. The width of the press-fit rib 19c is preferably 0.5 mm or more and 3.0 mm or less, more preferably 1.0 mm or more and 2.0 mm or less. The width of the press-fit rib 19c is the length in the direction perpendicular to the extension direction of the press-fit rib 19c. The height of the press-fit rib 19c is preferably 0.02 mm or more and 0.2 mm or less, more preferably 0.04 mm or more and 0.1 mm or less. The height of the press-fit rib 19c is the height of the protrusion from the inner circumferential surface of the inner insertion portion 19b.

[0038] In this embodiment, a recessed portion 19d for gripping with the fingers is formed on the outer circumferential surface of the insertion portion 19. The recessed portion 19d in this embodiment is formed on the outer circumferential surface of the insertion portion 19 and is an elliptical recess having a major axis extending from the front to the back surface where the positioning notch 22 of the insertion portion 19 is located. That is, in a side view, the recessed portion 19d has an elliptical shape. This elliptical recessed portion 19d is formed on each side of the insertion portion 19 and is symmetrical with respect to the central axis of the neck portion 14 in a plan view. When using the replaceable toothbrush 10 of this embodiment, the replaceable brush part 12 can be grasped by pinching the recessed portion 19d with the thumb and index finger. This further improves the ease of attaching and detaching the replaceable brush part 12. From the viewpoint of further improving this effect, the depth of the recessed portion 19d is preferably 0.5 mm or more and 2.0 mm or less, more preferably 0.8 mm or more and 1.5 mm or less.

[0039] The thickness of the bristle base 15 is preferably 2.0 mm to 4.0 mm, more preferably 2.5 mm to 3.5 mm. With this configuration, breakage at the head portion 13 is further suppressed, and a thinner head portion 13 can be made, thereby reducing the amount of resin used and improving operability.

[0040] The materials used to form each part of the replaceable toothbrush 10 in the above-described embodiment will now be explained. The handle portion 11 and the replacement brush portion 12 that make up the replaceable toothbrush 10 can be formed using synthetic resins such as polypropylene (PP), polyacetal (POM), polystyrene (PS), polyethylene terephthalate (PET), acrylonitrile, butadiene, polybutylene terephthalate (PBT), and styrene copolymer. The materials used to form the handle portion 11 and the replacement brush portion 12 may be the same or different. In a replaceable toothbrush 10, the replaceable brush head 12 is replaceable, while the handle 11 is used continuously. Therefore, each time the replaceable brush head 12 is attached, the shaft 17 of the handle 11 and its vicinity tend to wear down. From the viewpoint of using the handle 11 for a longer period of time, it is preferable that the material of the handle 11 of the replaceable toothbrush 10 is harder than the material of the replaceable brush head 12. From the same viewpoint as above, the difference in bending modulus (JIS 7171) between the replacement brush section 12 and the handle section 11 is preferably 300 MPa or more and 2500 MPa or less, more preferably 1000 MPa or more and 1500 MPa or less. The bending modulus of the handle portion 11 is preferably 1000 MPa or more and 3500 MPa or less, more preferably 1300 MPa or more and 2600 MPa or less. The flexural modulus of the replacement brush section 12 is preferably 800 MPa to 3000 MPa, more preferably 1300 MPa to 2600 MPa. The flexural modulus of the materials of the replacement brush section 12 and the handle section 11 is measured by the following method.

[0041] [Method for measuring the flexural modulus] Cut out 100g portions from either the replacement brush section 12 or the handle section 11. These 100g portions may be taken from multiple replacement toothbrushes 10 of the same type. Next, supply the mixture to a kneader and melt-knead it at 30rpm at 180°C for 5 minutes. For this kneader, use a Laboplast Mill 28-125 model (both manufactured by Toyo Seiki Seisakusho Co., Ltd.) equipped with a Roller Mixer R-60. Then, supply the melt-kneaded mixture to a press machine (Labo Press P2-30T, Toyo Seiki Seisakusho Co., Ltd.) fitted with a 4.0mm thick spacer, and press at 180°C and 200kg / cm². 2 Then, heat-press for 5 minutes at 20°C, 5 kg / cm². 2 The material is then cooled and pressed for one minute to produce a measuring piece with a thickness of 4.0 mm. Each measuring piece is cut out individually, measuring 10.0 mm in width and 80.0 mm in length. Next, the flexural modulus is measured using a Tensilon test machine (RTC-1150A, manufactured by Orientec Co., Ltd.) in accordance with JIS K7171 (Plastics - Test methods for bending properties).

[0042] Examples of materials for the handle portion 11 include polypropylene (PP), glycol-modified polyethylene terephthalate (PETG), and polybutylene terephthalate (PBT). Examples of materials for the replacement brush portion 12 include polypropylene, polyethylene, polyethylene terephthalate (PET), polyacetal (POM), acrylonitrile, butadiene, and styrene copolymers. A preferred combination of materials for the handle portion 11 and the replacement brush portion 12 is a combination in which the handle portion 11 is made of polybutylene terephthalate (PBT) and the replacement brush portion 12 is made of polypropylene. The replacement brush section 12 and the handle section 11 of this embodiment are molded products, obtained by the injection molding method using synthetic resin as described above.

[0043] In this embodiment, a bundle of bristles 18, each consisting of a number of bristles corresponding to the cross-sectional area of ​​a bristle implantation hole 16, is inserted and fixed into each of the multiple bristle implantation holes 16. The bristles constituting each bristle bundle 18 are preferably made of synthetic resin. Any known synthetic resin used for bristles can be used without particular limitation as the synthetic resin forming the bristles. Examples include polyamides such as nylon (registered trademark) and nylon 6, polyesters such as polybutylene terephthalate, and polyolefins, with polybutylene terephthalate being preferred.

[0044] The diameter of the bristle is, for example, 75 to 250 μm, preferably 100 to 220 μm, and more preferably 140 to 200 μm. If the bristle is a tapered bristle, the diameter of the bristle is the diameter of the portion excluding the tapered portion. The tapered portion of a tapered bristle can be easily created by sharpening the tip of the bristle by polishing it using a known polishing device, or by sharpening the tip of the bristle by immersing it in a known dissolving solvent to a predetermined depth. Preferably, the tapered bristle is created by processing the tip of the bristle by immersing it in a dissolving solvent. The length of the tapered portion in a tapered bristle is preferably 1 to 10 mm, and more preferably 3 to 8 mm.

[0045] Various known bristle implantation methods can be used for implanting bristle bundles 18 into multiple bristle implantation holes 16. For example, (1) a method of folding the bristle bundle 18 in half with a flat wire and inserting it, (2) a method of heating one end of the bristle bundle 18 to form a molten mass, and then injecting molten resin into a mold in which the molten mass is placed to injection form the bristle base 15, or (3) a method of obtaining a bristle base 15 (replacement brush part 12) with bristle bundles 18 implanted by going through an insertion step of inserting the bristle bundle 18 into the bristle implantation holes 16 (through holes) of a bristle base, a heat processing step of heating one end of the bristle bundle 18 protruding from the bristle implantation holes 16 to form a molten mass, and a coating step of covering the molten mass.

[0046] The method for implanting the bristle bundles 18 is preferably a fusion bristle implantation method including the methods described in (2) and (3) above, in which a molten mass is formed at one end of the bristle bundle, and more preferably the method described in (3) above. This is preferable from the viewpoint of improving ease of brushing molars, maneuverability, and appearance, as the bristle bundles can be efficiently implanted into relatively small diameter implantation holes and the thickness of the implantation base can be reduced. Specific examples of the method described in (3) above include the methods described in Japanese Patent Publication No. 9-182632 and Japanese Patent Publication No. 2003-310353. In the method described in Japanese Patent Publication No. 2003-310353, one end of the bristle bundle is heated with a non-contact heat source such as a laser beam to form a molten mass, and the molten mass is fused to the opening periphery of the implantation hole.

[0047] The filling rate of the hair bundles 18 into the hair implantation holes 16 is preferably 0.6 to 0.85%, and more preferably 0.65 to 0.85%. The filling rate is the "total cross-sectional area of ​​the bristle / cross-sectional area of ​​the hair implantation holes". If the bristle is a tapered bristle, the filling rate is the "total cross-sectional area of ​​the portion excluding the tapered portion / cross-sectional area of ​​the hair implantation holes".

[0048] The hair bundles 18 implanted in the hair implantation holes 16 preferably have a height (hair length) from the hair implantation surface 15a of the hair implantation base 15 to the tip of the bristle, which is, for example, 7 to 16 mm as the average height for each hair bundle 18.

[0049] The present invention is not limited to the embodiments described above and can be modified as appropriate. Furthermore, the configurations of the embodiments described above may be combined. For example, as shown in Figure 8, the replaceable toothbrush 10 according to the present invention may have an inner annular engaging portion 23 which is an annular rib 23b, and an outer annular engaging portion 21 which is an annular groove 21b that can engage with the annular rib 23b. In this case, the annular rib 23b is a substantially annular protrusion that projects inward from the inner circumferential surface of the insertion portion 19. The annular groove 21b is a substantially annular recess formed on the outer circumferential surface of the base end of the shaft portion 17. As a result, even if the annular rib 23b on the replaceable brush portion 12 side wears out, the replaceable brush portion 12 itself can be replaced, so that the mounting state between the replaceable brush portion 12 and the handle portion 11 can be maintained in good condition even after long-term use of the handle portion 11.

[0050] Furthermore, in the replaceable toothbrush 10 according to the present invention, the material of the handle portion 11 may have the same hardness as the material of the replaceable brush portion. In this case, the material of the handle portion 11 may be the same as the material of the replaceable brush portion.

[0051] Furthermore, the present invention includes a replacement brush used in the aforementioned replaceable toothbrush. The replacement brush consists of a replacement brush part 12 that is attached to the handle part 11 of the replaceable toothbrush 10. With the aforementioned replacement brush, the strength of the replacement brush section 12 can be made slender, similar to the replacement toothbrush 10, while maintaining the strength of the replacement toothbrush 10. Furthermore, such a slender replacement brush can reduce the amount of resin used in the neck section 14 while also improving operability and design. [Examples]

[0052] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples.

[0053] [Evaluation of Izod impact test using simulation] To evaluate the strength of the neck portion 14 of the replaceable toothbrush 10, a simulation of the Izod impact test was performed. The Izod impact test measures the toughness (strength) of a test object by measuring the amount of kinetic energy absorbed when a pendulum hammer strikes the object. Toughness represents the degree of resistance of a material to brittle fracture. The evaluation models used in the Izod impact test simulation were 3D models created using the dimensional data of Example 1 and Comparative Examples 1-3. The physical properties of these 3D models were set based on the stress-strain diagram of polybutylene terephthalate (PBT) (see the stress-strain diagram of NOVADURAN® from Mitsubishi Chemical Corporation URL: https: / / www.mcc-polymers.com / cms / wp-content / themes / mcg / assets / pdf / product / novaduran / physicality.pdf#page=5). The Abaqus / Explicit damage and fracture analysis model was used for the Izod impact test simulation. In the simulation of the Izod impact test, the pendulum hammer (hereinafter also simply referred to as "hammer") is 10 3 mm 3 A cubic rigid body was set up. The Izod impact test using a hammer was performed by simulating the movement of the hammer horizontally impacting the bristle surface 15a (replaceable brush part 12) from the back, with the tip of the bristle surface 15a of the replaceable toothbrush 10 facing vertically upward and the handle part 11 completely fixed. In this simulation, the kinetic energy of the hammer just before impact with the head part 13 was set to 2.75 J. Impact tests were conducted using the aforementioned simulation, and areas in the replacement brush section 12 that showed deformation (strain) were colored according to the von Mises stress. Areas where the von Mises stress was higher than the material property value of PBT were identified as damaged areas. If there were no damaged areas, it was evaluated as "none," and if there was one or more damaged areas, it was evaluated as "present."

[0054] [Example 1] In Example 1, a 3D model of a replaceable toothbrush having the same configuration as the replaceable toothbrush of the embodiment shown in Figures 1 to 7 described above was created. Specifically, the material used to form the replaceable brush portion 12 and the handle portion 11 was polybutylene terephthalate, and the dimensions were set to those shown in Table 1 below. The thickness of the bristle base 15 was set to 3.1 mm, and the outer diameter of the end of the handle portion 11 on the replaceable brush portion 12 side was set to 9.5 mm. The insertion portion 19 was set to have a rear insertion portion 19b and an insertion port insertion portion 19e, and the shaft portion 17 was set to have a straight portion 17a and a tapered portion 17b. The inner circumferential surface of the rear insertion portion 19b corresponds to the outer circumferential surface of the straight portion 17a, and the inner circumferential surface of the insertion port insertion portion 19e corresponds to the outer circumferential surface of the tapered portion 17b. A 3D model of a replaceable toothbrush was created using the above settings, and the aforementioned Izod impact test evaluation was performed through simulation. The results are shown in Table 1.

[0055] [Examples 2 and 3] In Examples 2 and 3, the Izod impact test evaluation described above was simulated using different forming materials for replaceable toothbrushes. The dimensions were set to be the same as in Example 1. In Example 2, polyoxymethylene (POM) was used as the forming material for a replaceable toothbrush, and the physical properties of the 3D model were set accordingly. These physical properties of the 3D model were set based on the physical properties listed in the catalog for Duracon® POM M270-44 manufactured by Polyplastics Co., Ltd. (https: / / www.polyplastics.com / Gidb / GradeListSelectGradeAction.do?id=1773). In Example 3, polypropylene (PP) was used as the forming material for a replaceable toothbrush, and the physical properties of the 3D model were set accordingly. These physical properties of the 3D model were set based on the physical properties listed in the catalog of Novatec® PP manufactured by Nippon Polypropylene Co., Ltd. (https: / / www.pochem.co.jp / jpp / product / novatec-pp / novatec-pp_bussei.pdf).

[0056] [Comparative Examples 1-3] Except for the dimensions set as shown in Table 1 below, the Izod impact test evaluation simulation was performed in the same manner as in Example 1. The results are shown in Table 1.

[0057] In Examples 1-3 and Comparative Examples 1-3, a slender neck portion 14 with a minimum thickness of 3.8 mm or less was set. In the Izod impact test simulations for each Example 1 and Comparative Examples 1-3, the deformation of the replacement brush portion 12 due to the hammer impact can be shown in video. Figure 9 shows still images captured from the video. In the simulation for Comparative Example 1, the replacement brush portion 12 bent due to the hammer impact, and the inserted portion 19 detached from the shaft portion 17. In the simulations for Comparative Examples 2 and 3, the replacement brush portion 12 bent due to the hammer impact, and then, due to the recoil, bent significantly in the opposite direction to the hammer impact. In Comparative Examples 2 and 3, the mounted state with the shaft portion 17 inserted into the inserted portion 19 was maintained. In the simulations of Examples 1 to 3, the replacement brush section 12 bent upon impact with the hammer, and then bent again in the opposite direction of the hammer impact due to the recoil, but this recoil was smaller than that of Comparative Examples 2 and 3. Furthermore, in the simulations of Examples 1 to 3, the mounted state in which the shaft section 17 was inserted into the insertion section 19 was maintained.

[0058] [Table 1]

[0059] As shown in Table 1, no damage occurred in the replaceable toothbrushes of Examples 1 to 3, whereas damage occurred in the replaceable toothbrushes of Comparative Examples 1 to 3. More specifically, in Comparative Examples 1 to 3, damage occurred on the outer surface of the shaft of the handle or in the vicinity of the shaft. When damage occurs on the outer surface of the shaft or in the vicinity of the shaft, it becomes difficult to fit the shaft into the insertion part, making repeated use of the handle 11 difficult.

[0060] [Izod Impact Test Evaluation] An Izod impact test was conducted using an actual replaceable toothbrush as the test specimen. The test method was carried out in accordance with "JIS K 7110:1999 Test method for Izod impact strength of plastics". Specifically, the replaceable toothbrush of Comparative Example 4 was supported in a cantilevered manner so that the head part was vertically upward, and a hammer swung in a pendulum-like motion struck the back surface of the bristle surface of the replaceable toothbrush. At this time, the potential energy before the hammer was swung down was 2.75 [J], the pendulum length was 0.335 m, and the weight of the pendulum was 13.94 N. The result was evaluated as "None" if there were no damaged areas, and as "Damaged" if there was one or more damaged areas. Examples 4, Comparative Examples 4 and 5 shown below were used as replaceable toothbrushes for the test specimens.

[0061] [Example 4] A replaceable toothbrush having the same dimensions as in Example 1 was manufactured by injection molding. Polybutylene terephthalate was used as the material for forming the replaceable brush portion 12 and the handle portion 11.

[0062] [Comparative Examples 4 and 5] A replaceable toothbrush was manufactured in the same manner as in Example 2, except that the dimensions were set as shown in Table 2 below.

[0063] [Table 2]

[0064] In Comparative Examples 4 and 5, the replaceable toothbrushes, upon impact with a hammer during the Izod test, did not exhibit neck flexion, but the connection between the insertion part and the shaft broke. In contrast, in Example 4, even upon hammer impact, the attachment between the insertion part and the shaft of the replaceable toothbrush remained intact, and no damage occurred to the replaceable brush part 12 or the handle part 11. The results above demonstrate that the replaceable toothbrush of the present invention can ensure strength while having a slender replaceable brush head. [Explanation of symbols]

[0065] 10 replaceable toothbrushes 11 Handle section 12 Replacement brush section 13 Head section 14. Neck section 15. Hair implantation stand 15a Hair implantation surface 16 Hair transplant holes 17. Shaft section 17a Straight section 17b Tapered section 18 strands of hair 19 Inserted part 20 Positioning projection 21 Outer annular engagement portion 22 Positioning notch 23 Inner annular engagement portion X Longitudinal direction Y width direction Z vertical direction

Claims

1. A replaceable toothbrush comprising a handle portion and a replaceable brush portion detachably attached to the tip of the handle portion, along its longitudinal direction, The handle portion has a shaft portion formed at one end on the side of the replaceable brush portion in the longitudinal direction, which protrudes outward in the longitudinal direction. The replacement brush section comprises a head section having a bristle base and a neck section connected to the head section, along the longitudinal direction, and the neck section has an insertion section formed at the end opposite to the head section into which the shaft section is inserted. The thickness of the neck portion gradually decreases from the insertion portion in the longitudinal direction toward the head portion. The dimensional ratio between the minimum thickness of the neck portion and the diameter of the tip portion of the shaft portion is 1:1.3 to 1:1.

5. The diameter of the base end of the shaft portion is 5.5 mm or more, and the diameter is 2.5 times or less the minimum thickness of the neck portion. The cross-sectional shape of the neck portion has a horizontally elongated shape at the end on the boundary side with the head portion, which is longer in the width direction perpendicular to the longitudinal direction, but as it approaches the insertion portion, it continuously changes to a vertically elongated shape which is longer in the vertical direction, coinciding with the normal direction of the bristled surface of the bristled base. The shaft portion has a straight section with a constant outer diameter at the tip end in the longitudinal direction, and a tapered section located closer to the base end than the straight section, with the outer diameter gradually increasing toward the base end, in a replaceable toothbrush.

2. The replaceable toothbrush according to claim 1, wherein the thickness of the bristle base is 2.0 mm or more and 4.0 mm or less.

3. The shaft portion has a positioning projection at its base end and an outer annular engaging portion extending circumferentially on the outer surface of the base end. The positioning projection and the outer annular engagement portion overlap in their longitudinal positions. The portion to be inserted has a positioning notch at the end on the insertion side into which the shaft portion is inserted, and an inner annular engaging portion extending in the circumferential direction on the inner circumferential surface of the end portion. The positioning notch is such that a portion of the opening periphery forming the insertion port is cut out toward the head portion. The inner annular engagement portion and the positioning notch portion overlap in their longitudinal positions. The replaceable toothbrush according to claim 1, wherein, in the installed state in which the shaft portion is inserted into the insertion portion, the outer annular engaging portion and the inner annular engaging portion engage with each other, and the positioning projection fits into the positioning notch.

4. The replaceable toothbrush according to claim 3, wherein the outer annular engaging portion is an annular rib, and the inner annular engaging portion is an annular groove that can engage with the annular rib.

5. The replaceable toothbrush according to claim 3, wherein the inner annular engaging portion is an annular rib, and the outer annular engaging portion is an annular groove that can engage with the annular rib.

6. The replaceable toothbrush according to claim 4 or 5, wherein the material of the handle portion is harder than the material of the replaceable brush portion.

7. The positioning projection protrudes radially outward from the outer circumferential surface of the handle portion and has a curved surface on the tip side of the shaft portion, as described in any one of claims 3 to 5.

8. The replaceable toothbrush according to claim 1 or 2, wherein a recess for gripping with fingers is formed on the outer circumferential surface of the insertion portion.

9. The shaft portion has a straight section with a constant outer diameter at the tip end in the longitudinal direction, and a tapered section located closer to the base end than the straight section, with the outer diameter gradually increasing toward the base end. The insertion portion has a rear insertion portion where the straight portion is located when the shaft portion is inserted into the insertion portion, and a plurality of press-fit ribs are formed on the inner circumferential surface of the rear insertion portion along the longitudinal direction. The replaceable toothbrush according to claim 1 or 2, wherein, in the above-mentioned mounting state, the straight portion is press-fitted into the inner insertion portion, thereby crushing the press-fit rib.

10. A replacement brush used in the replaceable toothbrush described in claim 1 or 2, and comprising the replacement brush portion.

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