Toothbrush

Abstract

To provide a toothbrush that can effectively prevent the occurrence of the over-brushing state, allows bristle bundles to follow the intended areas such as the dentition and interdental spaces even when brushing in the Fones method or the rolling method and can maintain the excellent cleaning performance.SOLUTION: There is provided a toothbrush in which a handle portion 3 includes a core material 4 made of a first hard resin integrally molded with a neck portion 2, and a coating material 5 made of a second hard resin having low adhesion properties relative to the first hard resin, the core material 4 includes a core material body and a movable portion 7 provided on the tip-side of the core material body, the tip-side portion of the coating material 5 has a pair of left and right branched arms 52, a through groove is formed between the arms 52, a connecting portion 53 that restricts the oscillating displacement of the movable portion 7 is spanned between the tips on the ventral side of the arms 52, and the volume of the movable portion 7 is 200 mm3 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a toothbrush including a head portion in which tufts are implanted, a neck portion connected to the head portion, and a handle portion serving as a grip.

Background Art

[0002] Conventionally, as shown in Patent Document 1, for example, in order to suppress overbrushing, a head portion having a tuft implantation surface provided on the tip side in the major axis direction, a gripping portion (handle portion) disposed on the rear end side of the head portion, a neck portion disposed between the tuft implantation surface and the gripping portion, a hard portion disposed on the rear end side of the tuft implantation surface and formed of a hard resin, and a soft portion formed of a soft resin and covering at least a part of the hard portion are included. A toothbrush is known that includes a deformable portion that deforms by an external force in a first direction orthogonal to the tuft implantation surface and in which the hard portion sandwiches and compresses the soft portion in the major axis direction.

[0003] The toothbrush described in this cited Document 1 allows the user to perceive that it is in an overbrushing state according to deformation. On the other hand, the gripability of the toothbrush is reduced, which may hinder the brushing operation. Further, since the hard portion is covered with a soft resin made of an expensive elastomer or the like, there is a problem that the manufacturing cost of the toothbrush is high. Furthermore, due to repeated deformation of the deformable portion, there is a possibility that the hard portion and the soft portion may peel off due to the difference in rigidity between them.

[0004] On the other hand, the present inventor has already proposed a toothbrush including a head portion in which tufts are implanted, a neck portion connected to the head portion, and a handle portion serving as a grip, the handle portion including a core material made of a first hard resin integrally formed with the neck portion, and a covering material formed to cover the core material with a second hard resin having a property of low adhesion to the first hard resin. The core material has a core body embedded in the covering material and a movable portion provided on the tip end side thereof that swings and displaces in a direction opposite to the protruding direction of the tufts in response to a brushing pressure acting in a direction orthogonal to the tuft implantation surface of the head portion. A space portion for allowing the swinging displacement of the movable portion is provided in the tip end side portion of the covering material (Patent Document 2).

[0005] According to the toothbrush of Patent Document 2, when the user brushes their teeth, the movable part provided on the tip side of the core material body made of the second hard resin can be swing-displaced within the space part of the coating material without deforming the coating material made of the second hard resin. Therefore, the user of the toothbrush can appropriately bring the tuft of bristles of the head part into contact with the teeth while holding the coating material of the handle part, and can swing-displace the movable part of the core material according to the brushing pressure. Therefore, it is possible to effectively clean the teeth by preventing the problem of deterioration of grip like the toothbrush of Patent Document 1 and preventing an excessive brushing pressure from acting.

[0006] By the way, the toothbrush of Patent Document 2 has a problem that, especially when polishing by the Fonseca method or the rolling method in which the toothbrush is actively moved in the width direction for cleaning, the tuft of bristles does not follow the target location such as the tooth row or the interdental space, and the cleaning performance may deteriorate.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, in view of the above situation, the problem to be solved by the present invention is to effectively prevent the occurrence of overbrushing, and also to make the tuft of bristles follow the target locations such as the tooth row and the interdental space even when polishing by the Fonseca method or the rolling method, and to provide a toothbrush that can maintain good cleaning performance.

Means for Solving the Problems

[0009] In view of such a situation, the present inventor has conducted intensive studies. As a result, especially after the movable part starts to move, the movable part moves not only in the direction perpendicular to the pressing direction of the brushing pressure (toothbrush width direction) by the gap of the through groove, but depending on the movement, it inhibits the original deflection of the head part and the neck part, and it has been found that the followability of the tuft deteriorates. Furthermore, in order to maintain the followability, it is important to set the volume of the movable part to 200 mm 3 or more, and the present invention has been completed based on this finding.

[0010] That is, the present invention includes the following inventions. (1) A toothbrush comprising a head part in which tufts are implanted, a neck part connected to the head part, and a handle part serving as a grip. The handle part includes a core material made of a first rigid resin integrally formed with the neck part, and a coating material formed to cover the core material with a second rigid resin having a property of low adhesion to the first rigid resin. The core material has a core body embedded in the coating material, and a movable part provided on the tip side thereof, which bends and swings in the reverse direction of the protruding direction of the tuft in response to the brushing pressure acting in a direction perpendicular to the tuft implantation surface of the head part. The tip side portion of the coating material has a pair of branched arms, and a through groove is formed between the arms to penetrate the coating material from the back side to the front side to allow the swinging displacement of the movable part. A connecting part that is formed to cover the movable part and restricts the swinging displacement of the movable part is provided between the front end portions on the front side of the arms. The volume of the movable part is 200 mm 3 or more.

[0011] (2) The toothbrush according to (1), wherein the neck part has a narrow-width part with a width of 5 mm or less near the head part.

[0012] (3) The toothbrush according to (2), wherein the thickness of the narrow-width part of the neck part is 5 mm or less.

[0013] (4) The area including the facing area where at least the connecting portion of the outer peripheral surface on the ventral side of the movable portion is covered and formed is composed of a pair of flat inclined surfaces that are inclined inward from the positions of the widest left and right skirts and extend linearly toward the ventral side for a predetermined length, and a convex curved surface that is substantially arc-shaped in cross-section connecting the extending ends thereof, and is characterized in that it is composed of a surface that is substantially arch-shaped in cross-section as described in (1).

Advantages of the Invention

[0014] According to the toothbrush of the present invention configured as described above, it is possible to effectively prevent the occurrence of overbrushing, and during cleaning, the tuft can be made to follow the targeted locations such as the tooth row and the interdental spaces, and good cleanability can be maintained.

Brief Description of the Drawings

[0015]

Figure 1

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Figure 16

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0017] As shown in FIGS. 1 to 3, the toothbrush H according to the present invention includes a head portion 1 in which a tuft 10 is implanted, a substantially rod-shaped neck portion 2 continuously provided on the proximal end side of the head portion 1, and a handle portion 3 serving as a grip continuously provided on the proximal end side of the neck portion 2. The head portion 1 is integrally formed of a hard synthetic resin such as polypropylene resin, polyethylene terephthalate resin, polyacetal resin, polybutylene terephthalate resin, or polyamide resin together with the neck portion 2. The handle portion 3 is composed of a core portion 4 integrally formed with the neck portion 11 and a covering material 5 formed separately covering the core material 4.

[0018] The head portion 1 has a substantially flat hair implanting table 11 from which the tuft 10 protrudes, and the thickness T1 of the hair implanting table 11 is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.5 mm or less. This makes it easy for the head portion to reach the deep part (rear teeth) of a narrow gap in the oral cavity. The lower limit value is preferably 2.0 mm or more, and more preferably 2.5 mm or more. If it is thinner than 2.0 mm, the strength cannot be maintained.

[0019] On the hair implanting surface 12, a plurality of bottomed hair implanting holes 13 having a substantially circular cross-section are formed. The opening diameter, depth, number, arrangement form, etc. of the hair implanting holes 13 are not limited in any way in this example. The hair bundle 10 may be implanted by driving it into the hair implanting holes 13 of the hair implanting surface 12 together with a flat wire, or the hair bundle 10 may be erected by a fusion method or an in-mold method without using a flat wire. The material of each filament constituting the hair bundle 10 is not particularly limited, and it may be artificial hair made of a resin material such as nylon, polyester, or polyolefin, or natural hair such as pig hair. In addition, known forms can be widely adopted for the cross-sectional shape, cross-sectional size, etc.

[0020] The neck portion 2 is configured to have a tapered structure in which the width in the front-back and left-right directions gradually narrows toward the tip side. In particular, the portion on the tip side of the central position 2c has a thin-type neck with a thickness in the front-back direction and a width in the left-right direction both being 5 mm or less, more preferably 4.5 mm or less, and even more preferably 4 mm or less. Thereby, when brushing teeth, the head portion 1 can reach the narrow part of the back teeth, and the cleaning property of the back teeth can be improved.

[0021] The narrow-width portion 2n, which is the portion where the left-right width of the neck portion 2 is the narrowest. In this example, the boundary portion with the head portion 1 is also the portion where the front-back thickness is the smallest, but its cross-sectional shape is set to be substantially quadrangular in a cross-sectional view as shown in FIG. 5(a). Here, the substantially quadrangular shape includes a concept including a substantially rectangular or substantially square shape provided with an arcuate chamfered portion at the corner. By configuring the narrow-width portion 2n of the neck portion 2 to have such a substantially quadrangular cross-sectional shape, it is possible to effectively suppress the head portion 1 from greatly wobbling left and right or the tip of the neck portion 2 from being greatly twisted during toothbrushing, and the operability of the toothbrush can be maintained in a good state.

[0022] That is, when the cross-sectional shape is formed into a substantially rectangular shape, deflection corresponding to the load transmitted from the head portion 1 is likely to occur in the front-rear and left-right directions and less likely to occur in the diagonal direction. Therefore, it is possible to prevent deflection from occurring in a direction contrary to the user's intention and maintain good operability. Moreover, a greater torsional rigidity can be obtained compared to a cross-sectional shape that is a perfect circle. As a result, it is effectively suppressed that large torsion occurs in this portion according to the rotational moment M transmitted from the head portion 1, and it is possible to prevent deterioration of the operation feeling caused by the head portion 1 wobbling. Such a portion with a substantially rectangular cross-sectional shape is preferably set over the entire narrow range up to the central position 2c of the above-described neck portion 2.

[0023] Also, a more preferable shape of the portion with a substantially rectangular cross-section when viewed in cross-section is formed into a vertically long substantially rectangular shape. Thereby, the left-right width can be made relatively small, so that the design of the thin neck can be maintained, and the bending rigidity in the front-rear thickness direction can be made relatively large, preventing the neck portion 2 from bending greatly in the front-rear direction when brushing teeth, and good cleanability can be maintained. In this example, as shown in FIGS. 5(a) and 5(b), the entire narrow region from the tip to the central position of the neck portion 2 is configured to have this vertically long substantially rectangular cross-sectional shape. Also, in this example, the narrow region has a straight shape in which each dimension of the above-described vertically long substantially rectangular shape is also the same (constant). The ratio (T2 / W2) of the front-rear thickness T2 to the left-right width W2 is preferably set to 1.01 to 1.50.

[0024] As shown in FIGS. 1 to 3, the handle portion 3 is provided with a bent portion 8 that is more bendable than adjacent portions (the base end portion of the neck portion 2 adjacent to the tip side and the portion of the handle portion 3 adjacent to the base end side) at the tip portion continuous with the neck portion 2. The bent portion 8 is composed of a rod-shaped movable portion 7 whose left-right width and front-rear thickness connected to the base end of the neck portion 2 are smaller than those of other portions of the handle portion 3, and a restricting portion 50 that is located around the movable portion 7 and restricts the bending movement of the movable portion 7 and supports the movable portion 7.

[0025] The handle portion 3 is, more specifically, as shown in FIG. 4, an axially-shaped core material 4 integrally formed with the head portion 1 and the neck portion 2 by the same rigid resin (the first rigid resin) as the rigid resin for forming the head portion 1 and the neck portion 2, and a rigid resin having a property of low adhesion to the first rigid resin, that is, a property (low welding property) of being separated from each other after molding without mixing with the first rigid resin during molding, and a coating material 5 that covers the core material 4.

[0026] For example, a crystallized resin made of polyacetal resin (POM), polyamide resin (PA), polybutylene terephthalate (PBT), or polypropylene resin (PP), etc. has a property of low adhesion (low welding) to each other when the other party is a crystallized resin (except for PP to PP) or a non-crystallized resin. Therefore, if either one of the first rigid resin constituting the core material 4 and the second rigid resin constituting the coating material 5 is a crystallized resin such as polyacetal resin (POM), and the other is a non-crystallized resin made of, for example, acrylonitrile-butadiene-styrene resin (ABS), polycarbonate (PC), or acrylic resin (PMMA), etc., the first rigid resin and the second rigid resin will not mix during molding, and the core material 4 and the coating material 5 will be separated from each other after molding.

[0027] When both the first rigid resin and the second rigid resin are crystallized resins, it is possible to prevent the core material 4 and the coating material 5 from fusing with each other in principle. For example, if either one of the first rigid resin constituting the core material 4 and the second rigid resin constituting the coating material 5 is a crystallized resin such as polyacetal resin (POM), and the other is a crystallized resin made of polyacetal resin (POM), polyamide resin (PA), or polypropylene resin (PP), etc., it is possible to prevent the first rigid resin and the second rigid resin from mixing during molding and keep the core material 4 and the coating material 5 separated from each other after molding. However, among the crystallized resins, polypropylene resins (PP) have high adhesion to each other, so those in which both the first rigid resin and the second rigid resin are polypropylene resins (PP) are excluded.

[0028] And as shown in FIG. 4, the core material 4 is composed of a substantially rod-shaped core material body 6 embedded in the coating material 5, and a movable portion 7 provided on the tip end side of the core material body 6 and configured to form the above-described bent portion 8 that bends and swings in the dorsal direction, which is the direction opposite to the protruding direction of the hair bundle 10, according to the brushing pressure.

[0029] As shown in the enlarged view in FIG. 7, the movable portion 7 is formed in a vertically long substantially oval shape in which the thickness in the front-rear direction from the back to the abdomen is larger than the left-right width in the lateral direction in cross-section. Further, the outer peripheral surface is composed of a pair of flat inclined surfaces 71, 71 that are inclined inward from the position of the widest hem, in this example, the central position 70 in the front-rear direction, toward the abdomen and the back, respectively, and linearly extend for a predetermined length L in the abdominal or dorsal direction, and a convex curved surface 72 that is substantially arc-shaped in cross-section connecting the extending ends thereof, forming a cross-sectionally substantially arch-shaped surface. The inclination angle θ of each inclined surface 71 of the pair of inclined surfaces 71 on the abdomen side and the back side is 3 degrees or more, and the length of each inclined surface 71 is preferably 1 mm or more and 2 mm or less.

[0030] In this example, the movable portion 7 has a uniform cross-sectional shape over the length direction, but is not limited thereto. For example, it is also possible to gradually change the cross-sectional shape of the movable portion 7. However, when the movable portion 7 has a uniform cross-sectional shape in the length direction, etc., including the holding portion by the connecting portion 53 and the region exposed in the through groove 52, a pair of flat inclined surfaces 71, 71 as described above and a convex curved surface 72 that is substantially arc-shaped in cross-section connecting the extending ends thereof are provided on the abdomen side of the movable portion 7, forming a cross-sectionally substantially arch-shaped surface. In this case, there is an advantage that the toothbrush formed in the molding space of the molding die can be easily taken out.

[0031] The volume of the movable portion 7 is set to be 200 mm 3 or more. When the volume of the movable portion 7 is less than 200 mm 3 the movable portion 7 cannot withstand the lateral force, and the movable portion 7 bends in the opposite direction before the neck portion 2 extends and follows the unevenness of the teeth, so that the neck portion 2 cannot extend, and the original followability of the neck portion 2 cannot be exhibited. Also, the left - right width W3 of the movable part 7 is preferably set to 2.5 - 5.0 mm. Also, the front - rear thickness TR3 of the movable part 7 is preferably set to 3.0 - 6.0 mm.

[0032] On the other hand, as can be seen from FIGS. 6, 8, and 9, the tip - side portion of the covering material 5 has a pair of arms 51, 51 branched to the left and right. A through - groove 52 is formed between the arms 51, 51 to allow the covering material 5 to penetrate from the back side to the front side and permit the rocking displacement of the movable part 7. Also, a connecting part 53 that holds the ventral part of the movable part 7 is provided between the ventral - side tip parts of the arms 51, 51. These arms 51, 51 and the connecting part 53 constitute the restricting part 50 that restricts and supports the bending operation of the movable part 7.

[0033] As shown in FIG. 6(a), the connecting part 53 has a recessed hole 59 having inclined surfaces 57, 57 and a concave surface 58 corresponding to the inclined surfaces 71, 71 and the convex surface 72 of the movable part 7. By fitting and holding the ventral part of the movable part 7 in the recessed hole 59 of the connecting part 53, the rocking displacement of the movable part 7 to the ventral side, the lateral deviation in which the movable part 7 is displaced in the left - right lateral direction, and the torsion in which the movable part 7 rotates about the axis center are respectively restricted.

[0034] When the movable part 7 undergoes rocking displacement, the movable part 7 can be smoothly rocked without rubbing against the recessed hole 59 of the connecting part 53. Moreover, since a convex surface 72 having a substantially arc - shaped cross - section when viewed in cross - section connecting the extending ends of the inclined surfaces 71, 71 is provided on the movable part 7, when the bent state of the movable part 7d is released and it returns to its original shape, the peripheral surface of the movable part 7 does not catch on the recessed hole 59 of the connecting part 53, and the ventral part of the movable part 7 can be neatly accommodated in the recessed hole 59.

[0035] Next, a method for manufacturing the toothbrush H will be described. First, as shown in FIG. 10, with the first split mold 81 and the second split mold 82 of the first molding die 8 clamped, the above-described first hard resin such as polyacetal resin (POM) is injected into the molding space 80 of the first molding die 8 from the injection gate 83, whereby, as shown in FIG. 3, a primary molded product 11 in which the head portion 1, the neck portion 2, and the core material 4 of the handle portion 3 are integrally connected is molded.

[0036] Next, after opening the first molding die 8 and taking out the primary molded product 11, as shown in FIG. 11, with the primary molded product 11 set in the second molding die 9 having the installation space for the primary molded product 11 and the molding space 90 for the coating material 5, the first split mold (movable mold) 91 and the second split mold (fixed mold) 92 are clamped. Then, as shown in FIG. 12, the above-described second hard resin is injected into the molding space 90 of the second molding die 9 from the injection gate 93 formed in the first split mold 91 or the like to mold the coating material 5. In this way, a toothbrush H is manufactured in which the core material 4 of the primary molded product 11 made of the first hard resin is covered with the coating material 5 made of the second hard resin.

[0037] As shown in FIG. 7, when the movable portion 7 provided in the core material 4 of the toothbrush H has a vertically long shape in which the thickness T3 in the front-rear direction from the back to the belly is larger than the lateral width W3 in a cross-sectional view, by sufficiently ensuring the rigidity of the movable portion 7 in the acting direction (front-rear direction) of the brushing pressure and suppressing the lateral width W3 to be small, it is possible to prevent the gripping property of the toothbrush H from deteriorating due to the width dimension of the corresponding through groove 52 becoming excessively large.

[0038] The cross-sectional shape of the movable portion 7 is not limited to the above-described embodiment, and various modifications are possible. For example, it may be formed in an oval shape, a substantially rectangular shape, an elliptical shape, or a circular shape. Further, the cross-sectional shape of the movable portion 7 does not need to be uniform in the length direction. For example, the tip side of the movable portion 7 may be formed in a vertically long elliptical shape, the base end side of the movable portion 7 may be formed in a perfect circular shape, or the cross-sectional shape may be configured to gradually change.

[0039] The following describes the results of a strain test that reflects the movement of the neck portion when polishing by the Fones method for each sample of the toothbrush of the example and the comparative example.

[0040] , the shape and dimensions of the neck portion (Sample) Each sample of the toothbrush of the example and the comparative example is a toothbrush having the structures of FIGS. 1 to 9 described in the above embodiment. The shape and dimensions of the head portion, the arrangement and number of tufts, and the material of each part are all the same. However, regarding the configuration of the region from the narrow portion 2n at the tip of the neck portion to the central position 2c, only in Example 4, it has a relatively thick straight shape with a substantially square cross-sectional shape (5.5 mm × 5.5 mm) of equal length in the vertical and horizontal directions shown in FIGS. 15(a) and (b), and the other samples have a thin straight shape with a vertically long substantially rectangular cross-sectional shape (W2 is 3.6 mm, T2 is 4.1 mm) shown in FIGS. 5(a) and (b). The bent portion of the handle portion has a cross-sectional shape of all movable portions as shown in FIGS. 6 and 7, which is a vertically long oval shape and is inclined inward from the central position in the front-rear direction and extends linearly by a predetermined length L to the ventral side and the dorsal side with a pair of flat inclined surfaces and a convex curved surface that is substantially arc-shaped in cross-section connecting the extending ends. It is composed of a cross-sectionally substantially arch-shaped surface, and the cross-sectional shape has a straight bar-shaped structure that is continuous over the entire axial length. Its left-right width W3, front-rear thickness T3, and axial length L3 were set to different dimensions as shown in Table 1, respectively.

[0041] In any sample, the first hard resin is a PBT resin and the second hard resin is a PC resin. Also, in any sample, the axial length of the neck portion is 52.6 mm, and the arm portion 51 of the covering portion 5 is adjusted in length and width so that the gap t1 with the neck portion is about 1.2 mm and the gap t2 of the through groove 52 is about 0.8 mm, respectively, according to the dimensions of the movable portion 7 of each sample.

[0042]

Table 1

[0043] (Strain test) As shown in Fig. 13, a strain gauge G1 was attached to the left and right lateral sides in the horizontal direction of the neck portion of each sample (toothbrush), the handle portion was fixed to the driving device, and as shown in Figs. 14(a) and (b), the center of the tuft surface of the head portion 2 was positioned at the center c1 of the tooth surface of the upper left central incisor of the dental arch model Tm, and while maintaining a load of 200 gf such that the tuft bundle 10 perpendicularly hit near the center c1 of the tooth surface, the surface parallel to the tuft surface 12 was rotationally driven while maintaining the load, and the variation in the amount of strain was measured when rotationally driven in the movement method of the Fones method starting from the position of the tooth surface center c1 and rotating once in the order of (1) to (5) and returning to the position of the center c1. The value of the strain gauge G1 is positive when the neck portion extends and negative when it contracts. The measurement results are shown in the graph of Fig. 16.

[0044] As can be seen from the graph of Fig. 16, in Examples 1 to 4, when the toothbrush was moved in the directions of (1) to (3), the amount of strain was positive (in Example 4, it was positive until halfway through (3)). This indicates that when the toothbrushes of Examples 1 to 4 move to a position with a low tooth surface (a position far from the head portion), the neck portion and the head portion follow the curved wave surface, the head slides on the tooth surface, and the head moves while the neck portion extends. Therefore, when originally moved in the direction of (1), the neck portion should bend in the direction in which the strain gauge contracts, but the amount of strain is positive.

[0045] In contrast, in Comparative Examples 1 and 2, the amount of strain is negative. In Comparative Example 1, since the movable portion is too slender and the volume is less than 200 mm 3 it can be seen that the movable portion easily bends to the side opposite to the direction of the brushing pressure, the neck portion cannot follow, the head portion stays near the center position of the tooth surface, and the amount of strain is zero to negative. Also, in Comparative Example 2, since the movable portion is short and too thick and the volume is also less than 200 mm 3 it can be seen that the movable portion is rigid, the neck portion bends to the side opposite to the direction of the brushing pressure, cannot follow the curved tooth surface, and similarly the head portion stays near the center position of the tooth surface, the strain gauge contracts, and the amount of strain is negative.

[0046] Also, when the toothbrush is moved in the directions of (4) to (5), the neck portion and the head portion are difficult to follow the wave surface that is curved so as to move to a high position (a position close to the head portion) on the tooth surface. However, in Examples 1 to 3, the head portion follows the tooth surface and moves while the neck portion extends. Therefore, the amount of strain is positive. In Example 4, the neck portion is thick and does not follow in the process of (4) to (5).

[0047] On the other hand, in Comparative Example 1, the movable portion is too slender and the volume is less than 200 mm 3 , so the movable portion easily bends to the side opposite to the direction of the brushing pressure, the neck portion cannot follow, the head portion stays near the upper position of the tooth surface, does not follow in the directions of (4) or (5), and it can be seen that the amount of strain is negative. Also, in Comparative Example 2, the movable portion is short and too thick, and the volume is likewise less than 200 mm 3 , so the movable portion is rigid, the neck portion bends to the side opposite to the direction of the brushing pressure, cannot follow the curved tooth surface, the head portion stays near the upper position of the tooth surface, does not follow in the directions of (4) or (5), and it can be seen that the amount of strain is negative.

Explanation of Reference Numerals

[0048] 1 Head portion 2 Neck portion 2n Narrow portion 3 Handle portion 4 Core material 5 Coating material 6 Core material body 7 Movable portion 8 First molding die 9 Second molding die 10 Tuft 11 Primary molded product 51 Arm portion 52 Through groove 53 Connecting portion 54 Tapered surface 55 Gap 56 Gap 80 Molding space 81 First split die 82 Second split mold 83 Injection gate 90 Molding space 91 First split mold 92 Second split mold 94 - 97 Ejector pins H Toothbrush

Claims

1. A toothbrush comprising a head portion in which tufts of bristles are implanted, a neck portion connected to the head portion, and a handle portion serving as a grip, wherein the handle portion has a core material made of a first rigid resin integrally formed with the neck portion, and a coating material formed to coat the core material with a second rigid resin having a property of low adhesion to the first rigid resin, the core material has a core body embedded in the coating material, and a movable portion provided on the tip end side thereof, which bends and swings in the reverse direction to the protruding direction of the tufts of bristles in response to a brushing pressure acting in a direction orthogonal to the implanting surface of the head portion, the tip end side portion of the coating material has a pair of arm portions branched left and right, and a through groove is formed between the arm portions to penetrate the coating material from the back side to the front side and allow the swinging displacement of the movable portion, a connecting portion is provided between the front end portions on the front side of the arm portions, which is formed to cover the movable portion and restricts the swinging displacement of the movable portion, The volume of the movable part is 200 mm ３ or more, and the toothbrush is characterized by this.

2. The neck portion has a narrow width portion with a width of 5 mm or less near the head portion. The toothbrush according to Claim 1.

3. The thickness of the narrow width portion of the neck portion is 5 mm or less. The toothbrush according to Claim 2.

4. The region including at least the facing region where the connecting portion is formed to cover the outer peripheral surface on the front side of the movable portion is composed of a pair of flat inclined surfaces that are inclined inward from the positions of the widest left and right skirts respectively and extend linearly toward the front side for a predetermined length, and a convex curved surface that is substantially arc-shaped in cross-section connecting the extending ends thereof, and is characterized by being a surface that is substantially arch-shaped in cross-section. The toothbrush according to Claim 1.

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