Toothbrush

Abstract

To provide a toothbrush in which a core material part and a coating body reliably move relatively with a prescribed force, and a method for manufacturing the same.SOLUTION: A coating body 6 includes: a coating part 7 coating a core material part 5; and a projection 8 having a surplus space S1 at a base end of the coating part which projects to a base end side further from the base end of the core material part 5 and inside which the core material part does not exit. A step part 62 with a base end part of the core material part 5 projecting from the coating part 7 just for a prescribed quantity is provided along a boundary part between the base end part facing the surplus space of the core material part 5 and the coating part 7. The core material part and the coating body are configured to be separate from each other when a force beyond the prescribed force is applied, and to allow a relative movement to the surplus space side.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a toothbrush having a head portion in which tufts are implanted, a neck portion connected to the proximal end side of the head portion, and a handle portion serving as a grip connected to the proximal end side of the neck portion, and particularly relates to a toothbrush capable of alleviating an impact when hitting the throat.

Background Art

[0002] As this type of toothbrush, conventionally, a toothbrush for infants has been proposed in which a buffer portion formed of a thermoplastic elastomer is provided on the proximal end side of the handle portion to alleviate the impact when hitting the throat (see, for example, Patent Document 1). However, since the conventional one alleviates the impact by bending of the material of the elastomer, if the elastomer is too hard, the alleviating effect when hitting the throat is low, and if it is too soft, the operability and cleanability during normal operation are significantly reduced, making it difficult to achieve both, and there are problems that the material is expensive and molding is difficult.

[0003] On the other hand, the present inventor has already proposed a toothbrush in which a handle portion is constituted by a core member portion made of a first rigid resin integrally formed with a neck portion and a covering body formed so as to cover the core member portion with a second rigid resin having a low adhesion property to the first rigid resin, the outer surface of the covering body functions as a gripping portion, a protruding portion having a surplus space where the core member portion does not exist is provided at the proximal end portion of the covering body, and engaging protrusions or engaged portions that engage with each other and inhibit the core member portion from relatively moving to the proximal end side of the covering body are provided on the core member portion and the covering body, and the engaging protrusions and the engaged portions are configured such that when a force exceeding a predetermined force acts, the engaging state is released by being separated from each other or the engaging protrusion breaking, and relative movement is allowed (Patent Document 2).

[0004] According to such a toothbrush, it is possible to easily achieve both the shock mitigation effect and the operability and cleanability during normal use as compared with those made of elastomer, without the need to use expensive specific elastomers, and since the range of material selection is relatively wide, cost reduction is possible. Furthermore, there is an advantage that it can be easily and efficiently manufactured by two-color molding or the like instead of assembling a plurality of parts.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when actually molding a toothbrush having the structure described in Patent Document 2 using a mold, it was found that the force at the time when the core material part and the covering body start relative movement varies, and in the worst case, the two may not move relative to each other. Therefore, when earnestly examining the factors, the following situations were observed. When the covering body is secondarily molded by inserting the core material part, the core material part cannot be supported by a pin or the like in the thickness direction for relative movement, and depending on the conditions (injection pressure and temperature of the second hard resin), the core material part, which is the primary molded product, may warp and its end may bite into the covering body, which is the secondary molded product. And it was considered that the occurrence of such a situation during molding is a factor that prevents the core material part and the covering body from starting relative movement with a predetermined force.

[0007] Therefore, in view of the above situation, what the present invention aims to solve is to provide a toothbrush and a method for manufacturing the same in which the core material part and the covering body can surely move relative to each other with a predetermined force.

Means for Solving the Problems

[0008] In view of such circumstances, the present inventor has conducted intensive studies and, as a result, configured the covering body to include a covering portion that covers the core material portion and a protruding portion that has a surplus space at its proximal end where the core material portion does not exist. By providing a stepped portion in a form in which the proximal end portion of the core material portion protrudes by a predetermined amount from the covering portion along the boundary portion between the proximal end portion facing the surplus space of the core material portion and the covering portion, even when the core material portion is warped, the end portion of the core material portion bites into the covering body and gets caught, preventing relative movement of the core material portion toward the proximal end side. Further, by opening and providing an injection gate of a secondary mold for molding the covering body in the space forming the protruding portion and injecting a second hard resin from this injection gate to mold the covering body, it has also been found that warping of the core material portion can be suppressed and relative movement of the core material portion toward the proximal end side can be suppressed by the end portion of the core material portion biting into the covering body. Based on the above findings, the present inventor has completed the present invention.

[0009] That is, the present invention includes the following inventions. (1) A toothbrush comprising a head portion in which tufts are implanted, a neck portion connected to the proximal end side of the head portion, and a handle portion serving as a grip connected to the proximal end side of the neck portion, wherein the handle portion has a core material portion made of a first hard resin integrally formed with the neck portion and a covering body formed to cover the core material portion with a second hard resin having a property of low adhesion to the first hard resin, and the outer surface of the covering body functions as a gripping portion. The covering body includes a covering portion that covers the core material portion and a protruding portion that protrudes further toward the proximal end side than the proximal end of the core material portion at the proximal end of the covering portion and has a surplus space inside where the core material portion does not exist. A stepped portion is provided along the boundary portion between the proximal end portion of the core material portion facing the surplus space and the covering portion in a form in which the proximal end portion of the core material portion protrudes by a predetermined amount from the covering portion. The core material portion and the covering body are configured to separate from each other and allow relative movement toward the surplus space side when a force exceeding a predetermined force acts. (2) The toothbrush according to item (1) above, wherein an extending portion that extends into the surplus space without contacting the covering portion is provided further on the proximal side than the stepped portion at the proximal end portion of the core material portion. (3) The core material portion and the covering body are provided with an engaging protrusion or an engaged portion that engage with each other to inhibit relative movement of the core material portion toward the surplus space inside the protruding portion of the covering body. The engaging protrusion and the engaged portion are configured such that when a force exceeding a predetermined force acts, the engaging state is disengaged by the engaging protrusion and the engaged portion moving apart from each other or the engaging protrusion breaking, and relative movement toward the surplus space side is allowed. The toothbrush according to item (1) or (2) above.

[0010] (4) A toothbrush comprising a head portion in which tufts are implanted, a neck portion connected to the proximal end side of the head portion, and a handle portion serving as a grip connected to the proximal end side of the neck portion, wherein the handle portion includes a core material portion made of a first hard resin integrally formed with the neck portion, and a covering body formed to cover the core material portion with a second hard resin having a property of low adhesion to the first hard resin, and the outer surface of the covering body functions as a gripping portion. The covering body includes a covering portion that covers the core material portion, and a protruding portion that protrudes further on the proximal side than the proximal end of the core material portion at the proximal end of the covering portion and has a surplus space in which the core material portion does not exist inside. A method for manufacturing a toothbrush, wherein the core material portion and the covering body are configured to move apart from each other when a force exceeding a predetermined force acts, allowing relative movement toward the surplus space side. A stepped convex portion for forming a stepped portion in a form in which the proximal end portion of the core material portion protrudes by a predetermined amount more than the covering portion is provided along the boundary portion between the proximal end portion of the core material portion facing the surplus space of the core material portion inserted into the secondary mold and the covering portion formed by the secondary mold in the secondary mold for molding the covering portion. A method for manufacturing a toothbrush, wherein the covering portion that forms the stepped portion with the proximal end portion of the core material portion is molded by injecting the second hard resin into the secondary mold. (5) In the toothbrush, an extension portion is further provided on the base end side of the stepped portion of the base end portion of the core material portion, extending into the surplus space without contacting the covering portion. A support portion for supporting the extension portion of the core material portion is provided on the secondary mold. When the core material portion is mounted on the secondary mold, the tip position of the extension portion is aligned with the support portion for mounting. The manufacturing method of the toothbrush according to item (4) above.

[0011] (6) A toothbrush comprising a head portion where the tufts are implanted, a neck portion connected to the base end side of the head portion, and a handle portion serving as a grip connected to the base end side of the neck portion. The handle portion has a core material portion made of a first hard resin integrally formed with the neck portion, and a covering formed to cover the core material portion with a second hard resin having a property of low adhesion to the first hard resin. The outer surface of the covering functions as a gripping portion. The covering has a covering portion that covers the core material portion, and a protruding portion at the base end of the covering portion that protrudes further toward the base end side than the base end of the core material portion and has a surplus space where the core material portion does not exist inside. A manufacturing method of a toothbrush in which the core material portion and the covering are configured to separate from each other and allow relative movement to the surplus space side when a force exceeding a predetermined force acts. The injection gate of the secondary mold for molding the covering is provided to open into the space for forming the protruding portion. A manufacturing method of a toothbrush, characterized by injecting the second hard resin from the injection gate to mold the covering. (7) In the toothbrush, an engaging protrusion or an engaged portion that engages with each other to inhibit the core material portion from relatively moving to the surplus space side inside the protruding portion of the covering is provided on the core material portion and the covering. The engaging protrusion and the engaged portion are configured to disengage from each other when a force exceeding a predetermined force acts, thereby allowing relative movement to the surplus space side. A pair of protrusions that form the cut-out portion of the engaging protrusion having a cut-out shape formed in the covering portion are provided at a predetermined position on the inner surface of the secondary mold, on the side opposite to the opening position of the injection gate with respect to the axis. The method for manufacturing a toothbrush according to the preceding paragraph (6), wherein with the core material portion supported by the protrusions, the second hard resin is injected from the injection gate to form a covering portion having the engaging protrusion.

Effect of the Invention

[0012] In the toothbrush according to the present invention thus constituted, the core material portion and the covering body can surely move relative to each other with a predetermined force.

[0013] That is, by providing a predetermined step portion along the boundary portion between the base end portion facing the surplus space of the core material portion and the covering portion, even when the core material portion is warped, the end portion thereof is prevented from biting into the covering body. This is because in addition to being able to fix the base end portion of the core material portion in the secondary mold so as to suppress the influence of warping in order to provide the step portion, even when fixed in this way, since there is no support pin in the intermediate portion in the axial direction of the core material portion, a slight warping occurs, resulting in warping due to residual stress after demolding. Even if the vicinity of the base end portion of the core material portion is warped, at the step portion, the base end portion of the core material portion protrudes to the base end side from the covering portion, so that the tip of the base end portion of the core material portion is prevented from biting into the covering body. As a result, the end portion of the core material portion is prevented from being caught by the covering body and the relative movement of the core material portion toward the base end side is prevented, and the core material portion and the covering body can surely move relative to each other with a predetermined force.

[0014] Further, when an extending portion that does not contact the covering portion and extends into the surplus space is provided on the more base end side than the step portion at the base end portion of the core material portion, a support portion for supporting the extending portion can be provided in the secondary mold. Therefore, when mounting the core material portion in the secondary mold, the tip position of the extending portion can be aligned with the support portion of the secondary mold for mounting. Therefore, a desired step portion can be surely formed in the toothbrush.

[0015] Further, the core member portion and the covering body are provided with an engaging protrusion or an engaged portion that engage with each other to prevent the core member portion from relatively moving toward the surplus space side inside the protruding portion of the covering body. When a force exceeding a predetermined force acts on the engaging protrusion and the engaged portion, the engaging state is released by the engaging protrusion and the engaged portion being separated from each other or the engaging protrusion being broken, and the relative movement toward the surplus space side is allowed. By releasing the engaging state between the engaging protrusion and the engaged portion, the core member portion and the covering body serving as the gripping portion are relatively moved in the axial direction to mitigate the impact. Therefore, it is easy to set the force at which the engagement is released in the structural design of the engaging protrusion and the engaged portion to a predetermined value as intended. Accordingly, it is possible to easily achieve both the impact mitigation effect and the operability and cleanability during normal use.

[0016] In addition, the manufacturing method of the toothbrush according to the present invention as described above can easily manufacture a toothbrush in which the core member portion and the covering body can surely relatively move with a predetermined force.

[0017] That is, in the first manufacturing method, a step convex portion for forming a step portion in which the base end portion of the core member portion protrudes by a predetermined amount more than the covering portion is provided along the boundary portion between the base end portion of the core member portion facing the surplus space of the core member portion inserted into the secondary mold and the covering portion formed by the secondary mold in the secondary mold for molding the covering portion of the toothbrush according to the present invention. Therefore, it is possible to easily form a desired step portion between the base end portion of the core member portion and the covering portion with the second hard resin injected into the secondary mold. Therefore, even when the core member portion is warped, it is possible to prevent the end portion thereof from biting into the covering body, and it is possible to easily manufacture a toothbrush in which the core member portion and the covering body can surely relatively move with a predetermined force.

[0018] In addition, in the first manufacturing method, when an extending portion is provided in the toothbrush according to the present invention, a supporting portion for supporting the extending portion is provided in the secondary mold. Since the position of the core member portion can be simply and surely determined by this supporting portion, it is possible to more surely and easily manufacture a toothbrush provided with a desired step portion. In addition, due to molding shrinkage or the like, the dimensions in the length direction of the core member may vary, or misalignment may occur on the base end side of the core member within the secondary mold. In such a case, an unintentional space is formed between the outer surface of the core member and the inner surface of the secondary mold, and the relative movement between the core member and the covering body may be hindered by the second hard resin filled in the space. However, by providing a predetermined extension portion on the core member and attaching the extension portion to the support portion of the secondary mold, the core member can be securely attached to the secondary mold at a predetermined position, misalignment can be prevented, the formation of such an unintentional space can be prevented, and the relative movement between the core member and the covering body can be realized more reliably.

[0019] In addition, in the second manufacturing method, when manufacturing a toothbrush having a predetermined core member and a predetermined covering body having a covering portion and a protruding portion having a surplus space, and configured to allow relative movement to the surplus space when a force exceeding a predetermined force acts on the core member and the covering body, an injection gate of a secondary mold for molding the covering body is provided to open into the space for forming the protruding portion, and by injecting a second hard resin from the injection gate to mold the covering body, the injection pressure can be controlled at the protruding portion, and the load on the core member can be reduced. Therefore, warping of the core member can be suppressed, the end portion thereof can be prevented from biting into the covering body, and a toothbrush in which the core member and the covering body can reliably move relative to each other with a predetermined force can be easily manufactured.

[0020] Also, in the second manufacturing method, in the toothbrush, a predetermined engaging protrusion or engaged portion is provided on the core material portion and the covering body, and when a force exceeding a predetermined force acts on these, the engaging state between them is disengaged and configured to allow relative movement toward the surplus space side. In such a case, a pair of protrusions for forming the cut-out portion of the engaging protrusion having a cut-out shape formed on the covering portion are provided at the opening position of the injection gate on the inner surface of the secondary mold and a predetermined position on the opposite side with respect to the axis. When injecting the second hard resin from the injection gate, the core material portion can be supported by the protrusions, so that warping of the core material portion can be more reliably suppressed. Further, since a cut-out-shaped engaging protrusion is formed on the back side of the covering portion on the side opposite to the side where the tufts are implanted, the design property of the front side of the covering portion that is often visually observed by the user is good.

[0021] Note that the above-described first and second manufacturing methods can be arbitrarily combined to further exhibit the effects based on each manufacturing method.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

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Figure 6

Figure 7

Figure 8

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Figure 11

Figure 12

Figure 13

Figure 14

MODE FOR CARRYING OUT THE INVENTION

[0023] Hereinafter, a toothbrush according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0024] As shown in FIGS. 1 and 2, a toothbrush 1 according to an embodiment of the present invention includes a head portion 2 in which a tuft 20 is implanted, a substantially rod-shaped neck portion 3 connected to the proximal end side (rear end portion) of the head portion 2, and a handle portion 4 serving as a grip connected to the proximal end side (rear end portion) of the neck portion 3. The handle portion 4 includes a core material portion 5 integrally formed with the neck portion 3 from a first hard resin, and a coating 6 formed to cover the core material portion 5 with a hard resin having a low welding property with respect to the first hard resin, that is, a property of separating from each other after molding without mixing with the first hard resin during molding. The outer surface of the coating 6 functions as a grip portion.

[0025] As the first hard resin constituting the core material portion 5 and the second hard resin constituting the coating 6, those having low weldability with each other are selected. As an index in this case, the crystallinity of the resin can be adopted. For example, crystalline resins such as polyacetal resin (POM), polyamide resin (PA), polybutylene terephthalate (PBT), and polypropylene resin (PP) have low weldability with each other when the other is a crystalline resin (except for the combination of PP), or acrylonitrile-butadiene-styrene resin (ABS), polycarbonate (PC), polymethyl methacrylate resin (PMMA), etc. in the case of non-crystalline resins.

[0026] Therefore, by making either one of the first hard resin constituting the core material portion 5 and the second hard resin constituting the coating 6 a crystalline resin and the other a crystalline resin (except for the combination of PP) or a non-crystalline resin, the first hard resin and the second cured resin do not mix during molding, and the core material portion 5 and the coating 6 can be separated from each other after molding. It is preferable to use a crystalline resin as the first hard resin.

[0027] Since polypropylene resin (PP) has high weldability, it is usually difficult to make both the first and second hard resins PP even if it is a crystalline resin. When one of the first and second hard resins is PP, the other may be a crystalline resin or a non-crystalline resin other than PP.

[0028] As the second curable resin constituting the covering 6, a transparent material may be used. This "transparent" means that visible light can be transmitted. Also, a resin in which a small amount of a substance that does not transmit visible light (for example, lame, pigment, etc.) is mixed is considered transparent as long as it can transmit visible light. As the transparent synthetic resin, in particular, it is preferable to use a resin having a value of 80% or more measured by the test method of JIS K7105. If the covering 6 is constituted by the second curable resin made of such a transparent material, the pattern provided on the outer peripheral surface of the core material portion 5 can be visually recognized through the covering 6, thereby improving the designability of the toothbrush.

[0029] As shown in FIGS. 1 to 4, the covering 6 includes a covering portion 7 that covers the core material portion 5, and a protruding portion 8 that protrudes from the proximal end 7a of the covering portion 7 to a more proximal side than the proximal end 5a of the core material portion 5. The protruding portion 8 has a surplus space S1 in which the core material portion 5 does not exist inside.

[0030] As shown in FIGS. 2 and 5, along the boundary portion 61 between the covering 6 and the desired proximal end portion 51 of the surplus space S1 of the core material portion 5, a stepped portion 62 is provided in a form in which the proximal end portion 51 of the core material portion 5 protrudes by a predetermined amount more than the covering portion 7. Further, along the boundary portion 61, a proximal end surface 74 of the surplus space S1 is provided at the proximal end 7a of the covering portion 7, so as to separate the peripheral edge of the proximal end 5a of the core material portion 5 or the peripheral surface of the proximal end portion 51 from the inner peripheral surface of the protruding portion 8. In the present embodiment, as shown in FIG. 5, the stepped portion 62 is continuously provided along the boundary portion 61 excluding a part on the front side where the tuft 20 is implanted. However, considering the warping direction of the core material portion 5 (primary molded product) during secondary molding or the molding shrinkage and molding error of the core material portion 5, etc., the stepped portion 62 may be formed at necessary positions of the boundary portion 61. Also, as shown in FIG. 5, the proximal end surface 74 is continuously provided along the boundary portion 61 excluding a part on the front side (the continuous portion between the core material portion 5 and the extending portion 9) so as to surround the proximal end periphery of the core material portion 5. However, considering various conditions during secondary molding, the formation position of the stepped portion 62, etc., it may be provided so as to extend over the entire circumference of the periphery of the proximal end 7a of the covering portion 7, or may be provided on a part of the periphery of the proximal end 7a.

[0031] The position where the stepped portion 62 is formed is preferably on the same side as the opening position of the injection gate of the secondary mold in the secondary molding because the core member 5 is likely to bend toward the side opposite to the axis. This is because the influence of the warping of the core member 5 can be suppressed. However, if the influence of the warping of the core member 5 can be suppressed by other means, it is not necessary to provide the stepped portion 62 on the same side as the opening position of the gate. For example, the stepped portion 62 may be provided on the whole or a part of the range that can be confirmed when viewed from the front side of the back side of the core member 5.

[0032] In the embodiment shown in FIGS. 1 to 5, an extending portion 9 is provided on the more proximal side than the stepped portion 62 of the proximal end portion 51 of the core member 5, extending into the surplus space S1 without contacting the covering portion 7. Further, the extending portion 9 is provided so as to be continuous with the proximal end portion 51 of the core member 5 so as to be in surface contact with the protruding portion 8 of the covering body 6 in a part of the front side. Therefore, the stepped portion 62 is not formed in the continuous portion with the core member 5.

[0033] On the other hand, in another modification, it is of course possible not to provide the extending portion 9 on the proximal end portion 51 of the core member 5 or to provide the extending portion 9 so as not to contact the protruding portion 8. In this case, the stepped portion 62 may be provided along the whole of the boundary portion 61 between the covering body 6 and the proximal end 5a facing the surplus space S1 of the core member 5. Alternatively, the stepped portion 62 may be provided only at necessary locations in consideration of the warping direction etc. of the core member 5 (primary molded product). The same applies to the base end surface 74 provided so as to face the surplus space S1 at the base end 7a of the covering portion 7.

[0034] In the embodiments shown in FIGS. 1 to 5, the front surface of the extending portion 9 is in surface contact with the inner surface facing the surplus space S1 of the protruding portion 8 of the covering body 6. That is, on the inner peripheral surface of the protruding portion 8, a stepped portion 75 having an inner peripheral surface corresponding to the shape of the front surface of the extending portion 9 that continuously extends from the base end surface 74 toward the base end side is formed. And at the boundary portion of the stepped portion 75 of the protruding portion 8 and the base end portion 91 of the extending portion 9 at the base end portion 91, a space S2 where both do not contact along this boundary portion is provided. By this space S2, the base end portion 91 of the extending portion 9 can be prevented from biting into the protruding portion 8. That is, the portion forming this space S2 can perform the same function as the above-described stepped portion 62. However, when the influence such as warping of the core material portion 5 is suppressed by the presence of the above-described stepped portion 62, this space S2 is not necessarily required.

[0035] When the extending portion 9 is provided, in addition to facilitating the alignment of the core material portion 5 (primary molded product) in the secondary mold, the core material portion 5 can be more reliably supported in the secondary mold via the extending portion 9, so it is also effective in suppressing warping of the core material portion 5.

[0036] As shown in FIGS. 2 to 4 and FIG. 6, the core material portion 5 and the covering body 6 are provided with an engaging protrusion 4a or an engaged portion 4b that engage with each other and inhibit the core material portion 5 from relatively moving toward the base end side of the covering body 6. In the present embodiment, the engaging protrusion 4a or the engaged portion 4b has a structure in which they are separated from each other and the concavo-convex engagement is released. In the embodiments shown in FIGS. 1 to 4 and FIG. 6, as the engaged portion 4b, one recess is formed in the outer peripheral portion near the base end of the core material portion 5, and as the engaging protrusion 4a, the engaging piece 72 having a notch shape formed of the inner remaining portion obtained by cutting out the peripheral wall of the base end portion of the covering portion 7 in a substantially U shape is formed at the tip of the protruding piece 71 formed on the covering body 6.

[0037] When a force exceeding a predetermined force acts, such as when the user inserts the toothbrush too deep into the mouth and hits the throat, as shown in FIG. 6(b), the engaging piece 72 of the covering 6 bends and deforms outward, and the protruding piece 71 (engaging protrusion 4a) separates from the concave portion 52 (engaged portion 4b) of the core member 5, releasing the engaged state. The main body side including the core member 5 moves relative to the surplus space S1 on the proximal end side of the covering 6 held by the user's hand, and the impact force can be mitigated. After use, the main body side including the core member 5 is moved relative to the distal end side of the covering 6. The concave groove portion 52 and the protruding piece 71 are engaged with each other in a concave-convex manner, and the bent and deformed engaging piece 72 returns to its original state, enabling reuse. That is, since the engaged state and the disengaged state between the protruding piece 71 and the concave groove portion 52 can be repeatedly formed, repeated use is possible. In the embodiment shown in FIGS. 1 to 4, since the cross-sectional shape perpendicular to the axial direction of the core member 5 has a substantially square shape, the core member 5 is prevented from relatively rotating with the central axis in the axial direction of the covering portion 7 as the rotation axis. Therefore, alignment between the protruding piece 71 and the concave groove portion 52 can be achieved only by moving them relative to each other in the axial direction after use, and the engaged state and the disengaged state can be easily and repeatedly formed.

[0038] Also, as will be described later, in order to form the engaging piece 72 at the proximal end portion of the covering portion 7, a substantially U-shaped through groove 73 is provided in the peripheral wall. A protrusion corresponding to this shape is provided on the secondary mold, and the proximal end portion 51 of the core member 5 is supported by this protrusion, suppressing warping of the core member 5 (primary molded product) during secondary molding (see FIG. 9). That is, forming the engaging piece 72 of such a form at a predetermined position of the covering portion 7 has the significance of suppressing warping during secondary molding of the core member 5 while controlling relative movement between the core member 5 and the covering 6.

[0039] As the engaging protrusion 4a, in addition to the protruding piece 71 formed on the covering 6 being provided at the tip of the engaging piece 72 having a notch shape formed by cutting out the peripheral wall of the covering portion 7 in a substantially U shape, as shown in FIG. 7, as the engaging protrusion 4a, the engaging piece 72 formed on the covering 6 may be provided with a protruding piece 71 at the tip of the engaging piece 72 having a notch shape formed between a pair of through grooves 73 along the axial direction released to the base end surface of the covering portion 7.

[0040] The engaging projection 4a and the engaged portion 4b may have a structure in which the engaging projection 4a breaks and the concave-convex engagement is released, in addition to the structure in which the concave-convex engagement is released by being separated from each other in this way. For example, in the modified example shown in FIG. 8, as the engaged portion 4b, two concave portions 52 are formed at angular positions symmetric about the axis on the outer peripheral portion near the proximal end of the core member portion 5, and at two positions corresponding to the concave portions 52 on the inner peripheral wall of the covering body 6, the engaging projection 4a is formed as a projecting piece 71 in a state of being in concave-convex engagement (concave-convex fitting) with the concave portion 52.

[0041] And in such a structure, in the normal use state shown in FIG. 8(a), when a force exceeding a predetermined force such as thrusting the throat acts, as shown in FIG. 8(b), the projecting piece 71 (engaging projection 4a) of the core member portion 5 breaks, and the engagement state with the concave portion 52 (engaged portion 4b) is released, and the main body side including the core member portion 5 relatively moves to the surplus space S1 side inside the projecting portion 8 of the covering body 6 being held, and is designed to be able to relieve the impact force. The reference numeral 710 indicates a broken piece obtained by breaking of the projecting piece 71.

[0042] In the modified example of the present invention, the core member portion 5 and the covering body 6 may not be provided with the engaging projection or the engaged portion as described above. For example, by adjusting the sliding characteristics between the contact surfaces of the core member portion 5 and the covering portion 7 of the covering body 6 according to the types and molding conditions of the first hard resin and the second hard resin described above, the magnitude of the force for starting the relative movement between the core member portion 5 and the covering body 6 can be adjusted.

[0043] FIG. 6(b) shows that when the proximal end portion 1a of the toothbrush 1 (covering body 6) is thrusted against the floor, wall, etc., the main body side relatively moves toward the proximal end side by the axial length of the surplus space S1, and the impact can be absorbed by shortening the overall length of the toothbrush. In the present embodiment, the projecting portion 8 of the covering body 6 is projected only from a predetermined range of a part of the entire circumference of the proximal end edge of the covering portion 7. Therefore, when the proximal end portion 1a of the toothbrush is thrusted against the floor or the like due to a fall or the like, the central axis of the main body side is likely to incline, and the tip of the toothbrush is likely to face in a direction different from the direction of the throat such as the cheek in the oral cavity, so that the throat-thrusting prevention effect is further improved.

[0044] The magnitude of the force at which the core material portion 5 and the covering 6 start relative movement is, for example, in the case of a toothbrush targeted at infants and children (elementary school students), effectively set in consideration of the values in a report created by a local government or the like. In a report created by a certain local government, for various commercially available toothbrushes, using a drop tester, applying a load comparable to that of an infant's head to the toothbrush, the average value of the load value when piercing into chicken breast meat has been measured at the fall speeds corresponding to each of the standing and sitting positions. As a result, it has been reported that in the case of 1-year-old children, it was 323.60 N to 705.06 N in the standing position and 224.69 N to 518 N in the sitting position. Therefore, adopting a force that does not interfere with brushing at approximately the lowest value or below of such measurement results, setting it as the magnitude of the force at which the core material portion 5 and the covering 6 start relative movement, and adopting the structure of the engaging protrusion 4a and the engaged portion 4b, or selecting the first and second hard resins may be appropriate.

[0045] In this embodiment, the overall length of the toothbrush 1, particularly the overall length of the main body including the head portion 2, the neck portion 3, and the core material portion 5, can be appropriately determined according to the age of the user, etc. However, for infants and children who are highly likely to have a risk of choking, it is necessary to ensure a length that allows these children to hold and brush their back teeth. The length from these viewpoints can be effectively determined based on reports by, for example, countries, local governments, pediatric dental societies, etc. According to these reports, for example, in the case of a 3-year-old child, the length that can reach the back teeth is preferably such that when using a choking prevention checker (opening diameter 39 mm, depth from the edge 51 mm), it does not protrude from the choking prevention checker, that is, a length similar to the depth from its edge (51 mm) is adopted. Also, the size of the child's hand is preferably determined considering the hand width that serves as a standard for the length of the handle portion 4 that becomes the grip of the toothbrush 1. For example, the average value of the hand width of a 7-year-old child is said to be 56.5 mm (Japanese anthropometric data, 1997). Thus, it is preferable to set the overall length of the toothbrush 1 such that the length that allows the child to hold and brush the back teeth is the sum of the depth from the edge of the choking prevention checker and the hand width of the child. The length of the handle portion 4 that becomes the grip of the toothbrush 1 is determined by the core material portion 5. However, even if the length of the core material portion 5 corresponds to the hand width of the child, depending on the conditions, warping of the core material portion 5 may occur during secondary molding. Therefore, the present invention, which can suppress the influence of the warping of this core material portion 5 and enable the choking prevention mechanism configured to allow relative movement between the core material portion 5 and the covering body 6 when necessary to function properly, is particularly effective as a toothbrush capable of preventing choking in children.

[0046] In this embodiment, at least a part of the boundary surface between the core material portion 5 and the covering body 6 is an inclined surface whose peripheral length increases toward the proximal end side. Thereby, when using for normal toothbrushing, etc., the covering body 6 is prevented from coming off toward the proximal end side.

[0047] In the embodiments shown in FIGS. 1 to 4, at least the cross-section orthogonal to the axial direction of the core member portion 5 has a substantially square shape along the axial direction, and the four corners have a predetermined R shape (see FIG. 12). At the base end portion 51 of the core member portion 5, the Rs at the two corners on the back side are small and the Rs at the two corners on the front side are large. On the tip side from the base end portion 51, the four corners have an R shape with substantially equal size with the size of the R on the front side of the base end portion 51. And, on the back side of the base end side 51, a portion that is substantially flat is formed. On the other hand, in the modified examples shown in FIGS. 13 and 14, at least the core member portion 5 has a substantially circular cross-section over the entire axial length. By making the cross-section substantially circular in this way, the area between the outer surface of the core member portion 5 and the inner surface of the covering portion 7 facing this is minimized, and in particular, the frictional force when the two are in surface contact can be reduced. Therefore, it becomes easier to adjust the magnitude of the stress at which the core member portion 5 and the covering body 6 start relative movement to the surplus space side.

[0048] Also in the modified examples shown in FIGS. 13 and 14, similar to the embodiments shown in FIGS. 1 to 4, the core member portion 5 and the covering body 6 are provided with an engaging protrusion 4a or an engaged portion 4b that engage with each other and inhibit the core member portion 5 from relatively moving to the base end side of the covering body 6. Also in the modified examples shown in FIGS. 13 and 14, as the engaged portion 4b, one recess is formed in the outer peripheral portion near the base end of the core member portion 5, and as the engaging protrusion 4a, a protruding piece 71 formed on the covering body 6 is formed at the tip of an engaging piece 72 having a notch shape formed by the remaining inner portion of a through groove 73 that cuts out the peripheral wall of the base end portion of the covering portion 7 in a substantially U shape. However, in this modified example, since the cross-section of the core member portion 5 is substantially circular, as shown in FIG. 14(b), the inner surface side of the engaging piece 72 has a curved surface corresponding to the shape of the core member portion 5. However, from the viewpoint of making it easier to adjust the force for releasing the engagement between the two, in the portion where the engaging piece 72 is formed, a plane may be formed along the axial direction on the outer peripheral surface of the core member portion 5 so that the inner surface side of the engaging piece 72 becomes a plane. In particular, in the vicinity of the portion continuous with the peripheral wall on the tip side of the engaging piece 72, it is preferable that the outer surface of the core member portion 5 and the inner surface of the corresponding engaging piece 72 are planes.

[0049] In the embodiments shown in FIGS. 1 to 4, the stepped portion 62 and the base end surface 74 are continuously provided along the boundary portion 61 excluding a part on the front side. However, in the modified examples shown in FIGS. 13 and 14, the stepped portion 62 is provided only in the semi-circular arc portion on the front side of the boundary portion 61, that is, the portion visible in a plan view from the front side. Further, in the embodiments shown in FIGS. 1 to 4, a space S2 is provided between the outer peripheral surface of the extending portion 9 of the core material portion 5 and the inner peripheral surface of the protruding portion 8. However, in the modified examples shown in FIGS. 13 and 14, the space S2 is not provided. In the secondary mold used at the time of secondary molding, due to the formation of the protrusion 68 for forming the substantially U-shaped through groove 73, the support portion 65 for supporting the extending portion 9, the stepped convex portion 66 for forming the stepped portion 62, etc., it is possible to suppress the influence of the warpage of the core material portion 5.

[0050] The modified examples shown in FIGS. 13 and 14 have the same configuration as the embodiments shown in FIGS. 1 to 4 except for the above points, and for the description of the configuration, reference is made to the description of the configuration with corresponding reference numerals in the drawings.

[0051] Next, a method for manufacturing a toothbrush according to an embodiment of the present invention will be described with reference to the accompanying drawings. First, a method for manufacturing a toothbrush of the representative embodiment shown in FIGS. 1 to 4 (hereinafter, may be referred to as "Manufacturing Example 1") will be described.

[0052] First, with the primary mold for molding a primary molded product in which the core material portion 5 of the head portion 2, the neck portion 3, and the handle portion 4 of the toothbrush are integrally connected being clamped, for example, a first hard resin made of the above-described crystallization resin is filled into this primary mold to mold the primary molded product. The primary mold can employ an efficient upper and lower split structure mold.

[0053] The injection gate of the primary mold is preferably provided to open at a position other than the position that comes into contact with the covering body 6, that is, at a position other than the position corresponding to the outer peripheral surface of the core material portion 5. When the extension portion 9 is provided to protrude from the proximal end 5a of the core material portion 5, it is preferable to provide the injection gate to open at a position other than the position corresponding to the contact surface with the protruding portion 8 of the extension portion 9. If the injection gate is provided to open at a position corresponding to the portion that comes into contact with the covering body 6, for example, the gate mark formed in the case of defective gate cut treatment protrudes outside the outer peripheral surface of the core material portion 5, and the gate mark may bite into the covering body 6 during secondary molding and prevent the relative movement between the core material portion 5 and the covering body 6. Also, the position of the ejector pin for demolding the primary molded product from the primary mold provided as necessary is preferably provided at a position other than the position that becomes the portion in contact with the covering body 6 as described above. When demolding using the ejector pin, if the ejector pin pushes the primary molded product immediately after molding, Pushing mark is formed, so that during secondary molding, the covering body 6 is formed to bite into the Pushing mark of the primary molded product, which may prevent the relative movement between the core material portion 5 and the covering body 6.

[0054] In the primary mold used for molding the embodiment having the extension portion 9 shown in FIGS. 1 to 4, the injection gate and the ejector pin are provided on the back side, which is the side opposite to the front side that comes into contact with the protruding portion 8 of the covering body 6 of the extension portion 9. The reference numeral 92 in FIGS. 2 and 4 is For example, when there is a problem such as a defective gate cut process, a gate mark is formed protruding outside the outer peripheral surface of the core material portion 5, and in order to prevent contact with a finger the formed recess and is also the position pushed by the ejector pin . In this way, by providing the extension portion 9 having a portion that does not come into contact with the protruding portion 8 of the covering body 6, opening the gate at a position corresponding to the portion, and providing the ejector pin, it is possible to surely perform alignment during secondary molding. In addition, even if a gate cut defect occurs or an ejector pin is provided, secondary molding can be performed so that the relative movement between the core material portion 5 and the covering body 6 is surely possible, and the production efficiency can be improved. Also, the extension portion 9 is formed at the proximal end portion of the primary molded product, and the mold release property is good by pushing with the ejector pin at the end portion of the primary molded product having the long axis direction, and the production efficiency can be improved also in this respect.

[0055] Next, after opening the first mold, with the second mold for molding the secondary molded product made of the covering body 6 in a closed state, the above-described second hard resin made of a cured resin having low adhesion properties with respect to the first hard resin is injected into this second mold to mold the secondary molded product. Here, as the second mold, in addition to the upper and lower split molds, a slide mold provided with a slide core that can be retracted in the axial direction to form all or part of the surplus space S1 at the base end as needed can be used.

[0056] Hereinafter, the state in which the primary molded product is attached to the second mold and the second mold is closed will be described with reference to the drawings.

[0057] As shown in FIGS. 9 and 10, the primary molded product is attached to the second mold 63 such that the core material portion 5 of the primary molded product is positioned within the cavity 64 of the second mold 63. The primary molded product is supported and fixed in its entirety at least at the base end portion of the neck portion 3 on the tip side by the second mold 63. Also, on the base end side thereof, the base end portion 51 and the extension portion 9 of the core material portion 5 are mainly supported from the back side. The space around the core material portion 5 is a cavity 64 for molding the covering body 6 which is the secondary molded product, and the core material portion 5 of the primary molded product is supported only at substantially both end portions in the axial direction. That is, although no support pins for supporting the core material portion 5 are provided between both ends of the core material portion 5, by adopting the structure of the second mold 63 described later, warping or displacement of the core material portion 5 can be suppressed and prevented.

[0058] In Production Example 1, an injection gate 82 is provided on the front side of the second mold 63 on the side where the hair bundle 20 of the primary molded product is implanted. Further, this injection gate 82 is provided to open into the space for forming the protrusion 8 at the position where the protrusion 8 of the covering body 6 is formed, particularly at a position on the base end side of the base end of the primary molded product in the axial direction. Thereby, the resin pressure filled around the core material portion 5 is likely to be uniform, and warping and displacement of the core material portion 5 can be further suppressed. However, when providing the step protrusion 66 described later on the second mold 63, the opening position of the injection gate is not particularly limited in the axial direction.

[0059] The secondary mold 63 is provided with a step projection 66 for forming a step portion 62 that protrudes by a predetermined amount from the covering portion 7 formed by the secondary mold 63. The step projection 66 is formed over the entire circumference of the base end portion 51 of the core material portion 5 except for the portion where the extending portion 9 is provided on the front side of the base end portion 51 of the core material portion 5. In this case, since the base end portion 51 of the core material portion 5 can be supported from the front side, even when the core material portion 5 is warped, the warp of this base end portion 51 can be suppressed. Further, by fitting the base end portion 51 of the core material portion 5 in accordance with the step projection 66, the position of the primary molded product in the secondary mold 63 can be determined. Note that the base end surface 74 is formed on the covering portion 7 by the portion of the step projection 66 facing the tip side of the primary molded product.

[0060] In the toothbrush 1 according to the embodiment shown in FIGS. 1 to 4, since the extending portion 9 is provided on the base end side of the core material portion 5, the secondary mold 63 is provided with a support portion 65 for supporting the extending portion 9. The support portion 65 is formed in the secondary mold 63 as a recess that is opened toward the tip side and the front side of the primary molded product, supports the extending portion 9 from the back side of the primary molded product, and can be attached to the secondary mold 63 with the tip position of the base end side of the extending portion 9 aligned. The presence of this support portion 65 enables more reliable alignment of the primary molded product in the secondary mold 63 than in the case where the step projection 66 is provided. Further, even when the core material portion 5 is likely to warp toward the back side due to the resin filled from the injection gate 82 provided on the front side, such as when the injection gate is opened at the position where the core material portion 5 is present, since the extending portion 9 can be supported from the back side, the influence of the warp of the core material portion 5 near the base end of the core material portion 5 can be more reliably suppressed.

[0061] Further, at the boundary portion at the base end of the stepped portion 75 of the protruding portion 8 and the base end portion of the extending portion 9, since a space S2 where they do not contact each other is provided along this boundary portion, a stepped convex portion 67 for forming this space S2 is provided along the periphery of the front end portion of the inner surface on the base end side of the support portion 65. This stepped convex portion 67 further ensures alignment within the secondary mold 63 and can more reliably suppress the influence of the warping of the core member portion 5. However, as described above, when there is no influence of the warping of the core member portion 5 due to the presence of the support portion 65 or the stepped convex portion 66, the stepped convex portion 67 in the support portion 65 may not be provided. In this case, the base end surface of the stepped portion 75 and the base end surface of the extending portion 9 are formed to be on the same plane.

[0062] In the secondary mold 63 of the present embodiment, in addition to the upper and lower two-part molds 63a and 63b on the front side and the back side, a stepped convex portion 66 that fits with the base end portion 51 of the core member portion 5 and a stepped convex portion 67 that fits with the base end portion 91 of the extending portion 9 are formed on the front side of the core member portion 5. Therefore, in a predetermined range including this portion, it is necessary to provide the slide core mold 63c so as to be retractable in the axial direction.

[0063] In the toothbrush 1 according to the embodiment shown in FIGS. 1 to 4, the core member portion 5 and the covering 6 are provided with an engaging protrusion 4a and an engaged portion 4b that are spaced apart from each other and can be disengaged from the engaged state. The protruding piece 71 formed on the covering 6 is formed at the tip of an engaging piece 72 having a notch shape that is composed of the inner remaining portion of a through groove 73 formed by cutting out the peripheral wall of the base end portion of the covering portion 7 in a substantially U-shape. Therefore, a protrusion 68 for forming the through groove 73 is formed in the secondary mold. The protrusion 68 has a shape corresponding to the substantially U-shaped through groove 73 and has a pair of protrusions 68 extending in the axial direction of the primary molded product. Further, these pair of protrusions 68 are continuous at the base ends on the base end side to form a substantially U-shaped protrusion 68. When the toothbrush 1 has the protruding piece 71 of the modified example shown in FIG. 7, a pair of protrusions that extend continuously from the stepped convex portion 66 of the secondary mold 63 to the tip side in the axial direction of the primary molded product (inside the cavity 64) are formed.

[0064] When the protruding piece 71 is formed on the covering part 7 of the toothbrush 1 shown in FIGS. 1 to 4 and the engaging protrusion 4a is formed at the base end thereof, the back side of the base end part 51 of the core material part 5 of the primary molded product has a flat surface. may be Yes. in this case Also, the shape of the portion of the protrusion 68 that contacts the core material part 5 is also a flat surface of the same height. become Thus, it is possible to form the protruding piece 71 of a predetermined shape on the covering body 6 without complicating the structure of the mold. In the case of the modified example shown in FIGS. 13 and 14, the back side of the core material part 5 has a curved surface of a cylinder extending in the axial direction, and from the viewpoint of stable support of the core material part 5, it is preferable that the shape of the portion of the protrusion 68 of the secondary mold 63 that contacts the core material part 5 is a curved surface corresponding to the curved surface of the core material part 5.

[0065] As described above, with the primary molded product mounted on the secondary mold 63 and the secondary mold 63 clamped, a desired second hard resin is filled from the injection gate 82 using an injection molding machine to mold the covering body 6. Since the molten resin filled from the injection gate 82 flows gradually from the base end side to the tip side from the core material part 5 and is filled into the cavity 64 on the outer periphery of the core material part 5, a resin pressure is evenly applied to the core material part 5 and warping is suppressed. Also, at this time, since the tip part of the base end part 51 of the core material part 5 is fitted into the portion where the step protrusion 66 for forming the step part 62 is formed, displacement and warping of the base end part 51 of the core material part 5 due to the flowing molten resin are suppressed, and in particular, the presence of the step protrusion 66 on the front side prevents the core material part 5 from biting into the covering body 6, which is a secondary molded product, due to warping not only during molding but also after demolding.

[0066] In the present embodiment, the extending part 5 on the base end side of the core material part 5 is supported and positioned more reliably by the support part 65. As a result, displacement and warping of the base end part 51 of the core material part 5 are more reliably suppressed and prevented by the flow of the molten resin during molding. Furthermore, the base end part 51 of the core material part 5 is supported by the protrusion 68 for forming the protruding piece 71 having the engaging protrusion 4a (71). As a result, displacement and warping of the base end part 51 of the core material part 5 are even more reliably suppressed and prevented.

[0067] The molding conditions can be appropriately determined according to the properties of the second hard resin and the like.

[0068] By demolding after cooling, a secondary molded product having a coating 6 formed so as to cover the core material portion 5 is obtained. In the present embodiment, at a position corresponding to the injection gate 82 of the secondary mold 63 in a recess 81 is formed on the outer surface of the protruding portion 8 of the coating 6. By making the gate mark present in the recess, it becomes less conspicuous, and the design property on the front side is good.

[0069] In this way, a toothbrush including a head portion 2 in which the tuft 20 is implanted, a neck portion 3 connected to the head portion 2, and a handle portion 4 serving as a handle, and a core material portion 5 made of a first hard resin integrally formed with the neck portion 3, and a coating 6 made of a second hard resin having a low welding property with respect to the first hard resin can be easily and inexpensively manufactured by two-color molding.

[0070] Next, a manufacturing method of a modified example of the toothbrush 1 according to the representative embodiment shown in FIGS. 1 to 4 (hereinafter, may be referred to as "Manufacturing Example 2") will be described. In the toothbrush of this modified example, as the position for forming the stepped portion (corresponding to reference numeral 62 of the toothbrush 1), the stepped portion is provided only in the visible range in the front view on the back side of the core member portion 5. The space S2 is not provided at the base end portion 91 of the extending portion 9, and the base end surface of the base end portion 91 and the stepped portion (corresponding to reference numeral 75 of the toothbrush 1) are on the same plane. Although it is different from the representative embodiment shown in FIGS. 1 to 4, other configurations are the same. When the stepped portion (62) is provided at such a position, when resin is injected from the injection gate provided on the front side of the primary molded product, the stepped portion (62) is provided on the same side as the direction in which the core member portion 5 warps. Therefore, it is considered that the effect of suppressing the warping of the core member portion 5 by the stepped portion (62) cannot be expected much. However, due to the position of the injection gate 82 of the secondary mold, the support portion 65 that supports the extending portion 9, and the pair of protrusions 68 for providing the protruding piece 71 on the back side of the primary molded product, the resin pressure during filling is uniformly applied to the core member portion 5, so that the warping of the core member portion 5 during molding and after demolding is suppressed. At the base end portion 51 of the core member portion 5, displacement and warping are prevented by the resin pressure to be filled. Therefore, even when the stepped portion 62 is formed only at the above-mentioned predetermined position, the biting of the secondary molded product, which is the covering body 6, due to the warping of the core member portion 5 is prevented.

[0071] In Manufacturing Example 2, since the same primary molded product as in the case of Manufacturing Example 1 can be used, the description thereof is omitted. Next, in the same manner as in Manufacturing Example 1, the secondary mold for molding the secondary molded product made of the covering body 6 is brought into a clamped state. Hereinafter, in the state where the primary molded product is attached to the secondary mold and the secondary mold is clamped, the parts different from those in Manufacturing Example 1 will be described with reference to FIGS. 11 and 12.

[0072] As shown in Fig. 11, on the inner surface of the proximal end side of the support portion 65 of the secondary mold 63 that supports the extending portion 9 of the primary molded product, there is no step convex portion 67 for forming the space S2 existing in the secondary mold 63 used in Production Example 1, and it has a uniform flat surface. Further, as shown in Figs. 11(b) and 12(a), different from the secondary mold 63 used in Production Example 1, a step convex portion 66 for forming a step portion (62) formed along the boundary portion between the core material portion 5 and the coating portion 7 is formed in a shape that can form the step portion (62) only in the range visible by front view from the back side of the core material portion 5. By providing the step convex portion 66 with such a shape, it is possible to support the proximal end portion 51 of the core material portion 5 during resin filling and suppress and prevent displacement. Further, the substantially C-shaped surface of the step convex portion 66 facing the cavity 64 in the axial direction of the core material portion 5 forms the base end surface (74) of the coating portion (7). Providing the extending portion 9 is effective in suppressing and preventing displacement. Further, the structure of the secondary mold 63 is divided into upper and lower two parts (reference numerals 63a and 63b in Figs. 11 and 12), and there is no need to provide the slide core mold 63c as in the case of Production Example 1, which contributes to improving productivity without complicating the mold structure. In this modification, the step convex portion 66 has an inclined structure in which the protruding length on the tip side decreases from the back side to the front side, but it is not limited to this. For example, in the modifications shown in Figs. 13 and 14, it may not be inclined in this way, and may have a stepped structure in which the protruding length is the same from the back side to the front side and the step convex portion 66 is not provided at a position where the step portion (62) is not provided. Further, as shown in Figs. 11 and 12(b), similar to the case of Production Example 1, a substantially U-shaped protrusion 63 for supporting the proximal end portion 51 is formed on the back side of the core material portion 5.

[0073] As described above, with the primary molded product mounted on the secondary mold 63 and the secondary mold 63 clamped, a desired second hard resin is filled from the injection gate 82 using an injection molding machine to form the covering body 6. Since the molten resin filled from the injection gate 82 gradually flows from the base end side to the tip end side from the core material portion 5 and is filled into the cavity 64 on the outer periphery of the core material portion 5, a resin pressure is evenly applied to the core material portion 5 and warping is suppressed. Also, at this time, since the tip portion of the base end portion 51 of the core material portion 5 is fitted into the portion where the step projection 66 for forming the step portion 62 is formed, displacement of the base end portion 51 of the core material portion 5 due to the flowing molten resin is suppressed. Further, the extending portion 5 on the base end side of the core material portion 5 is surely supported and positioned by the support portion 65. As a result, displacement and warping of the base end portion 51 of the core material portion 5 are surely suppressed and prevented by the flow of the molten resin during molding. Furthermore, it is further supported by a substantially U-shaped projection 68 for forming an engaging piece 72 having an engaging projection 4a (projection piece 71) at the base end portion 51 of the core material portion 5. As a result, displacement and warping of the base end portion 51 of the core material portion 5 are more surely suppressed and prevented. That is, in Production Example 2, the resin pressure is controlled by the opening position of the injection gate, and warping and displacement of the base end portion 51 of the core material portion 5 are prevented by the support portion 65 of the secondary mold 63 and the substantially U-shaped projection 68 including a pair of projections extending in the axial direction, so that biting of the secondary molded product, the covering body 6, due to warping of the core material portion 5 after molding and demolding is prevented.

[0074] By demolding after cooling, a secondary molded product having a covering body 6 formed so as to cover the core material portion 5 as in the case of Production Example 1 is obtained.

[0075] By adopting the manufacturing method as described above, a toothbrush 1 including a head portion 2 in which the hair bundle 20 is implanted, a neck portion 3 connected to the head portion 2, and a handle portion 4 serving as a handle, the toothbrush 1 having a core material portion 5 made of a first hard resin integrally formed with the neck portion 3 and a covering body 6 made of a second hard resin having a low welding property with respect to the first hard resin is easily and more inexpensively manufactured.

[0076] By using the toothbrush as described above, the user can firmly brush the back teeth by bringing the bristle tufts 20 of the head portion 2 into contact with the teeth while stably gripping the covering body 6 located on the outer peripheral portion of the handle portion 4. Further, even when the base end of the covering body 6 comes into contact with a desk, a floor, etc. for some reason during toothbrush use and the tip portion of the toothbrush jabs into the throat or the inner wall of the mouth, when a force exceeding a predetermined force acts, the core member portion 5 and the covering body 6 surely move relative to each other, so that the impact can be surely mitigated. Thus, the toothbrush of the present invention can surely brush the back teeth and at the same time can surely mitigate the impact when jabbing into the throat or the like, and is suitable as a toothbrush to be used, for example, when a child brushes his / her teeth by himself / herself.

[0077] As described above, the embodiments of the present invention have been explained. However, the present invention is not limited to such examples at all, and it goes without saying that the present invention can be implemented in various forms without departing from the gist of the present invention.

Explanation of Reference Numerals

[0078] 1 Toothbrush 1a Base end portion 2 Head portion 3 Neck portion 4 Handle portion 4a Engaging protrusion 4b Engaged portion 5 Core member portion 5a Base end 6 Covering body 7 Covering portion 7a Base end 8 Protrusion 9 Extension portion 20 Bristle tufts 51 Base end portion 52 Recess 61 Boundary portion 62 Step portion 63 Secondary mold 63a Front-side split mold 63b Back-side split mold 63c Slide core mold 64 Cavity 65 Support portion 66, 67 Step protrusions 68 protrusions 71 tabs 72 engaging pieces 73 through grooves 74 base end faces 75 stepped portions 81 recesses 82 injection gates 91 base end portions 92 recesses S1 surplus spaces S2 spaces

Claims

1. A toothbrush comprising a head portion in which tufts are implanted, a neck portion connected to the proximal end side of the head portion, and a handle portion serving as a grip connected to the proximal end side of the neck portion, wherein the handle portion includes a core member portion made of a first rigid resin integrally formed with the neck portion, and a covering formed to cover the core member portion with a second rigid resin having a property of low adhesion to the first rigid resin, and an outer surface of the covering functions as a gripping portion, the covering includes a covering portion that covers the core member portion, and a protruding portion provided at the proximal end of the covering portion, protruding further toward the proximal end side than the proximal end of the core member portion and having a surplus space in which the core member portion does not exist inside, a stepped portion is provided along a boundary portion between the proximal end portion of the core member portion facing the surplus space and the covering portion, in a form in which the proximal end portion of the core member portion protrudes by a predetermined amount more than the covering portion, the core member portion and the covering are configured to separate from each other when a force exceeding a predetermined force acts, and allow relative movement toward the surplus space side.

2. The toothbrush according to claim 1, wherein an extending portion is provided on the proximal end side of the stepped portion of the proximal end portion of the core member portion, extending into the surplus space without contacting the covering portion.

3. The core member portion and the covering are provided with an engaging protrusion or an engaged portion that engage with each other to prevent the core member portion from relatively moving toward the surplus space side inside the protruding portion of the covering, the engaging protrusion and the engaged portion are configured to separate from each other or the engaging protrusion breaks when a force exceeding a predetermined force acts, disengaging the engaged state and allowing relative movement toward the surplus space side, according to claim 1 or 2.

4. A toothbrush comprising a head portion in which tufts are implanted, a neck portion connected to the proximal end side of the head portion, and a handle portion serving as a grip connected to the proximal end side of the neck portion, wherein the handle portion includes a core member portion made of a first rigid resin integrally formed with the neck portion, and a covering formed to cover the core member portion with a second rigid resin having a property of low adhesion to the first rigid resin, and an outer surface of the covering functions as a gripping portion, the covering includes a covering portion that covers the core member portion, and a protruding portion provided at the proximal end of the covering portion, protruding further toward the proximal end side than the proximal end of the core member portion and having a surplus space in which the core member portion does not exist inside, A method for manufacturing a toothbrush, wherein the core material part and the covering are configured to separate from each other when a force exceeding a predetermined force acts thereon, and to allow relative movement toward the surplus space side. On a secondary mold for forming the covering part, along the boundary between the base end part facing the surplus space of the core material part inserted into the secondary mold and the covering part formed by the secondary mold, a step projection is provided for forming a step part in which the base end part of the core material part protrudes by a predetermined amount more than the covering part. A method for manufacturing a toothbrush, wherein the covering part forming the step part between the base end part of the core material part is formed by injecting the second hard resin into the secondary mold.

5. In the toothbrush, an extending part extending into the surplus space without contacting the covering part is further provided on the base end side of the step part of the base end part of the core material part. On the secondary mold, a support part for supporting the extending part of the core material part is provided. The method for manufacturing a toothbrush according to claim 4, wherein when the core material part is mounted on the secondary mold, the tip position of the extending part is aligned with the support part and mounted.

6. A toothbrush comprising a head part in which tufts of bristles are implanted, a neck part connected to the base end side of the head part, and a handle part serving as a grip connected to the base end side of the neck part. The handle part has a core material part made of a first hard resin integrally formed with the neck part, and a covering formed by covering the core material part with a second hard resin having a property of low adhesion to the first hard resin. The outer surface of the covering functions as a gripping part. The covering has a covering part covering the core material part, and a protruding part provided at the base end of the covering part, protruding further toward the base end side than the base end of the core material part and having a surplus space where the core material part does not exist inside. A method for manufacturing a toothbrush, wherein the core material part and the covering are configured to separate from each other when a force exceeding a predetermined force acts thereon, and to allow relative movement toward the surplus space side. An injection gate of a secondary mold for forming the covering is provided to open into the space for forming the protruding part. A method for manufacturing a toothbrush, characterized in that the covering is formed by injecting the second hard resin from the injection gate.

7. In the toothbrush, the core member portion and the covering body are provided with an engaging protrusion or an engaged portion that engage with each other to inhibit the core member portion from relatively moving toward the surplus space side inside the protruding portion of the covering body. The engaging protrusion and the engaged portion are configured to disengage from each other when a force exceeding a predetermined force acts, thereby allowing relative movement toward the surplus space side. A pair of protrusions that form the cutout portion of the engaging protrusion having a cutout shape formed in the covering portion are provided at a predetermined position on the opposite side of the opening position of the injection gate on the inner surface of the secondary mold with respect to the axis. The method for manufacturing a toothbrush according to claim 6, wherein with the core member portion supported by the protrusions, the second hard resin is injected from the injection gate to form a covering portion having the engaging protrusion.

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