toothbrush

Abstract

To provide a toothbrush capable of performing refined brush operation without damaging gripping performance of a handle part in the toothbrush equipped with a head part composed of a thin bristle planting base.SOLUTION: A toothbrush includes a head part 1 having a bristle planting base where bristle bundles 10 are planted, a neck part 2, and a handle part 3, in which the head part 1 is a thin head having the bristle planting base 11 whose thickness is 4 mm or less, the handle part 3 has a finger rest part 31 swelling in a radial direction at a position on an end side near the neck part, and a center of gravity of the whole toothbrush including the bristle bundles 10 is weight-distributed so that it is located in a prescribed area including the finger rest part 31 nearer on an end side than a center 32 an axial direction of the handle part 3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a toothbrush having a thin head portion.

Background Art

[0002] Conventionally, there has been provided a toothbrush having a thin head portion with a plate thickness of the bristle base being 4 mm or less (see, for example, Patent Document 1). According to such a toothbrush with a thin head portion, the operability in the oral cavity is enhanced, the head reaches even to fine parts of the back teeth, and it becomes possible to more surely and firmly brush the entire oral cavity including the back teeth. However, a toothbrush having a head portion composed of a thin bristle base usually tends to have a neck portion continuous with the proximal end of the head portion also formed in a thin shape corresponding to the head portion. Therefore, such a toothbrush with a thin head has a problem that its center of gravity tends to be biased toward the proximal end side of the handle portion, and the operability of the toothbrush tends to deteriorate.

[0003] That is, at least the tip side portion of the neck portion is inserted into the oral cavity together with the head portion, and thus tends to be formed in a thin shape, whereas the handle portion needs to have a thickness of a certain value or more so as to obtain stable gripping property. For this reason, the center of gravity of the toothbrush inevitably lies on the proximal end side of the handle portion, and when brushing teeth in a state of gripping the tip side portion of the handle portion close to the neck portion by a pen grip method of holding a pencil with the thumb, index finger, and middle finger, the head portion side is not stable. Thus, in a toothbrush having a thin head, although it should be excellent in insertability into narrow back teeth and make a delicate brushing operation possible, there is a problem that the operability deteriorates due to the influence of the center of gravity of the toothbrush.

[0004] Conventionally, toothbrushes have been known that, in order to provide a gentle and comfortable feel to the teeth and gums while easily suppressing over-brushing, include a head portion with a bristle surface located at the tip end along the long axis, a handle portion (gripping portion) located at the base end of the head portion, and a neck portion located between the bristle surface and the handle portion, wherein the handle portion is composed of a hard portion made of hard synthetic resin and a soft portion made of elastomer covering at least a part of the hard portion (see, for example, Patent Document 2). In this way, when the handle portion of a toothbrush is composed of a hard portion made of hard synthetic resin and a soft portion made of elastomer covering the hard portion, it is possible to some extent to suppress the bias of the toothbrush's center of gravity toward the base end of the handle portion because the elastomer constituting the soft portion has a lower specific gravity than the hard synthetic resin constituting the hard portion. However, there is a problem that using an elastomer or the like, which is more expensive than hard synthetic resin, as the coating layer of the handle increases the manufacturing cost of the toothbrush. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-16495 [Patent Document 2] Japanese Patent Publication No. 2021-7471 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Therefore, in view of the above circumstances, the present invention aims to provide an inexpensive toothbrush that has a head made of a thin bristle base, which allows for fine brushing without impairing the grip of the handle. [Means for solving the problem]

[0007] The toothbrush according to the present invention encompasses the following inventions.

[0008] (1) A toothbrush comprising a head portion having a bristle base on which a bundle of bristles is planted, a neck portion and a handle portion, wherein the head portion is a thin head having a bristle base with a thickness of 4 mm or less, the handle portion has a radially bulging finger rest portion at the tip end near the neck portion, and the weight distribution is such that the center of gravity of the entire toothbrush, including the bundle of bristles, is located within a predetermined area including the finger rest portion at the tip end, rather than the axial center of the handle portion.

[0009] (2) The toothbrush according to (1), wherein the handle portion is configured such that its width gradually decreases from the finger rest portion toward the axial center, and the rate of decrease in the width between the finger rest portion and the axial center is 10 to 40%.

[0010] (3) The toothbrush according to (1) or (2), wherein the center of gravity is located at a distance of 50-70% of the total length of the toothbrush from the tip of the head toward the axial base end.

[0011] (4) The toothbrush according to any one of (1) to 3), wherein the finger rest portion is formed such that its thickness and width are approximately the same.

[0012] (5) The toothbrush according to any one of (1) to (4), wherein a long, flat surface extending along the entire axial length is formed on the back side of the handle portion.

[0013] (6) The toothbrush according to any one of (1) to (5), wherein the handle portion is a molded product formed mainly from a hard synthetic resin material.

[0014] (7) The toothbrush according to any one of (1) to (6), wherein the neck portion is a slender neck with a thickness and width dimension of 5.5 mm or less on the tip side of its axial center. [Effects of the Invention]

[0015] As described above, the toothbrush of the present invention has a finger rest portion that bulges radially at the tip of the handle portion near the neck portion, and the weight distribution is such that the center of gravity of the entire toothbrush is located within a predetermined area including the finger rest portion at the tip, rather than the axial center of the handle portion. Therefore, when brushing teeth while holding the finger rest portion with the thumb, index finger, and middle finger in a pen grip, the base end of the handle portion does not wobble, the bristles of the head portion can be properly brought into contact with the teeth, and the fine operability that is a characteristic of thin-head toothbrushes can be maintained without deterioration.

[0016] Furthermore, by reducing the width dimension between the finger rest and the axial center by 10-40%, the center of gravity of the entire toothbrush can be positioned at the finger rest, which is often located near the center of the toothbrush's overall length, or at a preferred position slightly closer to the base end, without worsening the grip of the handle. This effectively prevents the base end of the handle from wobbling and worsening operability when brushing teeth, which can occur due to the toothbrush's center of gravity being biased towards the base end of the handle.

[0017] In particular, when the center of gravity of the entire toothbrush is positioned at a distance of 50-70% of the total length of the toothbrush from the tip of the head towards the axial base, it is possible to effectively prevent the toothbrush from wobbling by making it difficult to firmly grip the finger rest because the center of gravity of the entire toothbrush is located towards the tip of the finger rest, and also prevent the base of the handle from wobbling because the center of gravity of the entire toothbrush is located towards the axial base.

[0018] Furthermore, if the thickness and width of the finger rest are formed to be approximately the same, it is possible to properly grip the handle in either the pen grip or palm grip position, which has the advantage of allowing for precise operation of the head and resulting in excellent cleaning performance.

[0019] In addition, if a long, flat surface extending over the entire axial length is provided on the back side of the handle portion, the gripping force when gripping the handle portion can be effectively improved, and when placing the back of the toothbrush on a table or the like, there are advantages such as obtaining a stable placement state.

[0020] In addition, if the handle portion is mainly formed using a hard synthetic resin material, it is possible to effectively prevent the base end side of the handle portion from wobbling and the operability from deteriorating when brushing teeth while gripping by the pen grip method, and it is possible to manufacture a toothbrush at a low cost.

[0021] In addition, if the neck portion is configured as a thin-type neck with a thickness and width of 5.5 mm or less on the tip side rather than the axial center of the neck portion, it is possible to achieve design unity by forming the neck portion with a small diameter corresponding to the thin head, and by positioning the center of gravity of the entire toothbrush including the tuft of bristles within a predetermined region including the finger rest portion on the tip side rather than the axial center of the handle portion, when brushing teeth while gripping the finger rest portion by the pen grip method, it is possible to effectively prevent the base end side of the handle portion from wobbling and the operability from deteriorating, and there is an advantage that the tuft of bristles of the head portion can be properly abutted against the teeth.

Brief Description of the Drawings

[0022] [Figure 1] A plan view of the toothbrush according to a representative embodiment of the present invention as viewed from the ventral side. [Figure 2] Similarly, a side view of the toothbrush. [Figure 3] A cross-sectional view taken along line A-A of FIG. 1. [Figure 4] A cross-sectional view taken along line B-B of FIG.​​​​​​​​​​​​​​Cross-sectional view of the FF line in Figure 1. [Figure 10] Cross-sectional view of line GG in Figure 1. [Modes for carrying out the invention]

[0023] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] As shown in Figures 1 and 2, the toothbrush of the present invention comprises a head portion 1 on which a bundle of bristles 10 is planted, a substantially rod-shaped neck portion 2 connected to the base end of the head portion 1, and a handle portion 3 which serves as a grip, connected to the base end of the neck portion 2.

[0025] The head portion 1 is formed as a thin head having a substantially flat bristle base 11 with a thickness t of 4 mm or less, and multiple bristle bundles 10 are implanted on the bristle surface 12 located on the ventral side of the bristle base 11. The bristle base 11 and the neck portion 2 of the head portion 1 are formed from a first hard synthetic resin, such as polyethylene terephthalate (PET), which has a relatively high heat resistance temperature (melting point). This first hard synthetic resin is not limited to polyethylene terephthalate, but can also be polybutylene terephthalate (PBT), 6-nylon, 6,6-nylon, etc. Furthermore, in order to improve the design of the toothbrush, it is preferable that the first hard synthetic resin is colored to a predetermined color.

[0026] The bristle bundles 10 may be implanted by driving them into the implantation holes formed in the bristle base 11 along with flat wires, or they may be erected using fusion or in-mold methods without using flat wires. The material of each filament constituting the bristle bundle 10 is not particularly limited; it may be artificial hair made of resin materials such as nylon, polyester, or polyolefin, or natural hair such as pig bristles. In addition, known shapes can be widely adopted for the cross-sectional shape and size. The number and arrangement of the bristle bundles 10 are also not particularly limited.

[0027] Toothbrushes with the thin head described above offer improved maneuverability within the oral cavity, allowing the head 1 to reach even the smallest areas of the molars, enabling more thorough and effective cleaning of the entire oral cavity, including the molars, with less force. Furthermore, by reducing the thickness of the bristle base 11 to 4 mm or less, the contact of the bristle base 11 with the oral cavity is reduced, and it also appears thinner and slimmer than it actually is, offering the advantage of less resistance when inserting it into the molars.

[0028] The neck portion 2 has a tip-side neck portion 21 formed in a portion closer to the tip than its axial center 20, for example, in a range of about 10 mm to 20 mm from the tip of the neck portion 2, an intermediate neck portion 22 located on the base end side, and a base-side neck portion 23 located between the intermediate neck portion 22 and the handle portion 3.

[0029] As shown in Figure 3, the cross-sectional shape of the neck portion 21 near the tip is formed as a roughly rectangular shape, having a front surface 24 and a rear surface 25 parallel to the flocked surface 12 of the head portion 1, and left and right side surfaces 26 and 27 perpendicular to the flocked surface 12. This roughly rectangular shape is a concept that includes a roughly rectangular or roughly square shape with arc-shaped chamfered portions at the corners. Furthermore, the neck portion 21 near the tip is formed as a slender neck with a thickness t consisting of the distance between the front surface 24 located on the upper side of Figure 3 and the rear surface 25 located on the lower side of the figure, and a width dimension w consisting of the distance between the left and right side surfaces 26 and 27 of the neck portion 2, both of which are 5.5 mm or less.

[0030] In this embodiment, the cross-sectional shape of the neck portion 21 near the tip is formed as a vertically elongated, approximately rectangular shape, with a thickness t greater than the width dimension w. Furthermore, the neck portion 21 near the tip has a straight shape throughout its entire axial range, with a cross-sectional shape that is the same as an approximately rectangular shape with rounded corners, and the dimensions are also the same.

[0031] As shown in Figure 4, the intermediate neck portion 22 has a cross-sectional shape that is roughly rectangular with each side curving outward and rounded corners, and widens towards the base end in both plan and side views. The ratio t / w of the vertical dimension (thickness t) in the front-to-back direction and the horizontal dimension (width w) in the left-to-right direction of the cross-section is configured to be constant along the axial direction. Specifically, the cross-sectional shape of the tip surface of the intermediate neck portion 22 is formed as a vertically elongated, roughly rectangular shape having the same shape and dimensions as the tip-side neck portion 21 (see Figure 3). Furthermore, while the ratio t / w of the thickness t and width w of the intermediate neck portion 22 is maintained constant, the intermediate neck portion 22 has a tapered plan and side view shape in which the thickness t and width w gradually increase from the tip side to the base end.

[0032] As shown in Figure 5, the cross-sectional shape of the tip portion 23a of the base-end neck portion 23 is a roughly rectangular shape that is close to a vertically elongated ellipse, with a thickness t greater than the width w. On the other hand, as shown in Figure 6, the cross-sectional shape of the base portion 23b of the base-end neck portion 23 is a roughly elliptical shape that is horizontally elongated, with a width w greater than the thickness t. Furthermore, the base-end neck portion 23 has a flared shape (trumpet shape) where the diameter increases towards the base end, and the rate of increase is greater towards the base end. Although not shown in the figure, the cross-sectional shape of the portion located between the tip portion 23a and the base portion 23b of the base-end neck portion 23 is roughly circular.

[0033] As shown in Figures 1 and 2, the handle portion 3 has a core material 4 formed integrally with the neck portion 2, and a covering material 5 formed to cover the core material 4. The core material 4 is made of the same material as the bristle base 11 and neck portion 2 of the head portion 1, that is, a saturated polyester resin with a high heat resistance temperature, and is formed integrally with the bristle base 11 and neck portion 2 by a first hard synthetic resin colored to a predetermined color. Furthermore, as shown in Figure 7, the core material 4 has a rod-shaped portion 41 embedded in the covering material 5, cylindrical protrusions 42 and 43 protruding from the front (ventral) side of the rod-shaped portion 41, and a circular plate-shaped portion 44 provided at the base end of the rod-shaped portion 41.

[0034] The cross-sectional shape of the rod-shaped portion 41a (see Figure 8), located at the tip of the core material 4, that is, near the base of the neck portion 2, is formed to be approximately square. On the other hand, the cross-sectional shape of the rod-shaped portion 41b (see Figure 9), located in the middle of the length of the core material 4, is formed to be approximately circular. Furthermore, the cross-sectional shape of the rod-shaped portion 41c (see Figure 10), located at the base end of the core material 4, is formed to be approximately square. The radial dimension of the rod-shaped portion 41b, located in the middle of the length of the core material 4, is formed to be slightly smaller than the radial dimension of the rod-shaped portion 41a, located at the tip of the core material 4, and the radial dimension of the rod-shaped portion 41c, located at the base end of the core material 4.

[0035] The covering material 5 is made of a second rigid synthetic resin with a lower heat resistance temperature than the first rigid synthetic resin that constitutes the core material 4, such as polycarbonate (PC), acrylonitrile butadiene styrene (ABS), acrylonitrile styrene copolymer (AS resin), polystyrene (PS), polyethylene (PE), or polypropylene (PP), and is also made of a light-transmitting material. "Light-transmitting" means that visible light can be transmitted. Furthermore, even if a small amount of a substance that does not transmit visible light (e.g., glitter, pigment, etc.) is mixed into the resin, it is considered transparent if it can transmit visible light. As for the transparent synthetic resin, it is particularly preferable to use a resin in which the value measured by the test method of JIS K 7105 is 80% or more.

[0036] As described above, by constructing the coating material 5 with a second hard synthetic resin that has light transmittance, the core material 4 of the handle part 3, which is colored in a predetermined color, can be seen through the coating material 5, thereby giving the toothbrush a unique design. Furthermore, by using a material with a lower heat resistance temperature than the first hard synthetic resin that makes up the core material 4 as the second hard synthetic resin that makes up the coating material 5, it is possible to prevent the core material 4, which is made of the first hard synthetic resin, from melting and becoming cloudy when the second hard synthetic resin is injected, thus preventing deterioration of appearance.

[0037] As shown in Figure 1, a radially bulging finger rest portion 31 is provided at the tip of the handle portion 3, that is, near the neck portion 2. At the tip of this finger rest portion 31, a tapered portion 30 is provided, which is configured such that the radial dimension gradually decreases toward the base end of the neck portion 2. In addition, a plurality of grooves 50 extending in the width direction are formed on the front side (ventral side) of the finger rest portion 31, which form a non-slip surface for the fingers and are configured to allow the user to clearly recognize the position of the finger rest portion 31.

[0038] The finger rest portion 31 and its base end portion are configured such that their width gradually decreases toward the axial center 32 of the handle portion 3. Furthermore, the portion closer to the base end than the axial center 32 is provided with an enlarged diameter portion 33 configured such that its width gradually increases toward the base end of the handle portion 3, and a terminal portion 34 configured such that its width gradually decreases toward the base end of the handle portion 3.

[0039] The reduction rate (W1-W2) / W1 between the finger rest portion 31 shown in Figure 8 and the axial center 32 of the handle portion 3 shown in Figure 9 is set to 10-40%. Specifically, if the maximum width W1 of the covering material 5 located at the tip of the finger rest portion 31 is, for example, 12 mm, then the minimum width W2 of the covering material 5 located at the axial center 32 of the handle portion 3 is formed within a range from 10.8 mm (10% reduction), which is 1.2 mm smaller than the width W1 of the finger rest portion 31, to 7.2 mm (40% reduction), which is 4.8 mm smaller than the width W1 of the finger rest portion 31.

[0040] As shown in Figure 8, the finger rest portion 31 of the handle portion 3 is formed such that its thickness T1 and width W1 are approximately the same. Furthermore, as shown in Figures 2 and 8 to 10, a long flat surface 35 is provided on the rear side (rear surface) of the handle portion 3, extending over approximately the entire axial length of the handle portion 3. On the other hand, the front surface on the ventral side of the handle portion 3, and both the left and right sides of the handle portion 3 are formed as curved surfaces with a predetermined curvature. The width W3 at the rear end of the enlarged diameter portion 33 (see Figure 10), specifically the width of the covering material 5 located near the rear end of the handle portion 3, is formed to be approximately the same as, or slightly smaller than, the width W1 of the finger rest portion 31 (see Figure 8).

[0041] A method for manufacturing a toothbrush having the above-described configuration is explained below. First, with a primary mold for molding a primary molded product (see Figure 7) in which the toothbrush head portion 1, neck portion 2, and the core material 4 of the handle portion 3 are integrally connected, a first hard synthetic resin is injected into the primary mold to form the primary molded product. Next, after opening the primary mold, with a secondary mold for molding a secondary molded product consisting of a covering material 5, a second hard synthetic resin is injected into the secondary mold to form the secondary molded product consisting of the covering material 5.

[0042] In this way, a toothbrush can be formed having a handle portion 3 in which a core material 4 formed from a first hard synthetic resin colored to a predetermined color is covered with a covering material 5 made of a transparent second hard synthetic resin. It should be noted that the handle portion 3 does not necessarily have to be composed of a core material 4 made of the first hard synthetic resin and a covering material 5 made of the second hard synthetic resin; for example, the head portion 1 and neck portion 2 and the entire handle portion 3 may be integrally formed from a single hard synthetic resin material.

[0043] As described above, in a toothbrush equipped with a thin head having a bristle base 11 with a thickness of 4 mm or less, by reducing the width of the handle portion 3 so that the width gradually decreases from the finger rest portion 31 toward the axial center 32 of the handle portion 3, it is possible to effectively prevent the center of gravity of the entire toothbrush from being significantly biased toward the base end of the handle portion 3. Therefore, when brushing teeth while holding the finger rest portion 31 provided on the tip side of the handle portion 3 with the thumb, index finger, and middle finger in a pen grip, it is possible to effectively prevent the base end of the handle portion 3 from wobbling and worsening the operability, and it is possible to properly contact the bristle bundle 10 of the head portion 1 with the teeth.

[0044] In the above embodiment, the weight distribution is such that the center of gravity of the entire toothbrush is located within a predetermined area including the finger rest portion 31, by making the reduction in width between the finger rest portion 31 and the reduced diameter portion located at the axial center 32 of the handle portion 3 10% or more. For example, the center of gravity of the entire toothbrush is positioned either near the center of the entire length of the toothbrush, at the finger rest portion 31, or slightly towards the base end, preferably 50-70% of the total length of the toothbrush, away from the tip of the head portion 1 towards the axial base end. This effectively prevents the base end of the handle portion 3 from wobbling and worsening operability when brushing teeth, which can occur when the center of gravity of the toothbrush is biased towards the base end of the handle portion 3.

[0045] In a toothbrush equipped with a thin head, in order to position the center of gravity of the entire toothbrush within a predetermined area including the finger rest 31 located towards the tip of the axial center of the handle 3, it is desirable to maximize the reduction in width between the finger rest 31 and the axial center 32 of the handle 3. However, if the reduction in width becomes excessively large, when gripping the handle 3 using the palm grip method, the gripability of the handle 3 may deteriorate due to the large difference in thickness between the finger rest 31 where the thumb and index finger are located and the axial center 32 of the handle 3 where the middle and ring fingers are located. Therefore, it is desirable to configure the toothbrush so that the center of gravity of the entire toothbrush is positioned within a predetermined area including the finger rest 31 located towards the tip of the axial center of the handle 3 by setting the reduction in width between the finger rest 31 and the axial center 32 of the handle 3 within the range of 10 to 40%.

[0046] Furthermore, instead of the above embodiment in which the width dimension of the handle portion 3 is configured to gradually decrease from the finger rest portion 31 toward the axial center of the handle portion 3, it is also possible to gradually decrease both the width dimension and the thickness of the handle portion 3 toward the axial center of the handle portion 3. However, in this case, due to the reduction in thickness at the axial center 32 of the handle portion 3, the gripability when holding the handle portion 3 with a palm grip will worsen, and the appearance of the handle portion 3 will inevitably become weaker. Therefore, it is desirable to distribute the weight so that the center of gravity of the entire toothbrush is located within a predetermined area including the finger rest portion 31, by mainly changing only the width dimension of the handle portion 3 without significantly changing the thickness of the handle portion 3.

[0047] Furthermore, by using a resin material with a higher specific gravity for the finger rest portion 31 of the handle portion 3 compared to the resin material for the handle portion 3 located behind it, it is possible to distribute the weight so that the center of gravity of the entire toothbrush is located within a predetermined area including the finger rest portion 31 on the tip side of the axial center 32 of the handle portion 3, without significantly changing the width dimensions of the handle portion 3. However, in this case, it is necessary to use different materials for the finger rest portion 31 of the handle portion 3 and the part located behind it, which has the disadvantage of increasing manufacturing costs. In particular, if an elastomer with a low specific gravity is used to lighten the handle portion 3, the material cost itself is expensive, so it is unavoidable that the manufacturing cost of the toothbrush will be even higher. Therefore, as shown in the above embodiment, it is desirable to keep the manufacturing cost of the toothbrush low by molding the handle portion 3 mainly using a hard synthetic resin material.

[0048] Furthermore, instead of the above embodiment in which the weight distribution is such that the center of gravity of the entire toothbrush is located at a point 50-70% of the total length of the toothbrush, away from the tip of the head portion 1 towards the axial base end, it is also possible to position the center of gravity of the entire toothbrush closer to the tip than this range. However, if the center of gravity of the entire toothbrush is located at a position less than 50% of the total length of the toothbrush, the center of gravity of the entire toothbrush will be located closer to the tip than the finger rest portion 31, requiring a firm grip on the finger rest portion 31 to prevent the tip of the toothbrush from wobbling, which can lead to hand fatigue and other problems. On the other hand, if the center of gravity of the entire toothbrush is located at a position greater than 70% of the total length of the toothbrush, when brushing teeth while holding the tip of the handle portion 3, which is close to the neck portion 2, using a pen grip method, the base end of the handle portion 3 tends to wobble, making it difficult to properly contact the tips of the bristle bundles 10 provided on the head portion 1 with the teeth. Therefore, as shown in the above-described embodiment, it is preferable to position the center of gravity of the entire toothbrush at a distance of 50-70% of the total length of the toothbrush, axially from the tip of the head portion 1 toward the base end.

[0049] Furthermore, as shown in Figure 8, when the thickness T1 and width W1 of the finger rest portion 31 are configured to be approximately the same, it is possible to properly grip the handle portion 3 in either the pen grip method or the palm grip method, which has the advantage of allowing for accurate operation of the head portion 1 and resulting in excellent cleaning performance.

[0050] Furthermore, as shown in Figures 8 to 10, by providing a long, flat surface 35 extending along its entire axial length on the back side of the handle portion 3, the gripping force when holding the handle portion 3 can be effectively improved. Moreover, there are advantages such as being able to achieve a stable resting position when the back side (flat surface 35) of the toothbrush is placed on a table or the like.

[0051] In the above-described embodiment, the present invention is applied to a toothbrush in which the neck portion 2 connected to the base end of the head portion 1 is formed as a slender neck with a thickness t and width w of 5.5 mm or less on the tip side of its axial center 20. With this configuration, while the design can be unified by forming the neck portion 2 in a slender diameter to match the thin head, the center of gravity of the toothbrush tends to be biased toward the base end of the handle portion 3. Therefore, in a toothbrush with a slender neck, it is more preferable to configure the width dimension of the handle portion 3 so that the width dimension gradually decreases from the finger rest portion 31 toward the axial center 32 of the handle portion 3, thereby positioning the center of gravity of the entire toothbrush, including the bristles, within a predetermined area including the finger rest portion 31 on the tip side of the axial center 32 of the handle portion 3.

[0052] Although embodiments of the present invention have been described above, the present invention is not limited in any way to these examples, and can be implemented in various forms without departing from the spirit of the invention.

[0053] The following describes the results of an analysis of the relationship between the width dimension of the handle portion 3 and the center of gravity of the entire toothbrush in a toothbrush with a thin head. [Examples]

[0054] The toothbrush material and dimensions are as follows: • Material: PBT (Polybutylene Terephthalate) • Hair strand arrangement: 4 rows • Maximum thickness of hair bundle holder: 3mm • Maximum width of the gripping part: 12mm • Minimum width of the gripping part: 9mm • Reduction in the width of the gripping section: 25% • Toothbrush length: 180mm • Toothbrush weight: 12.58g • Distance from the tip of the club head to the center of gravity: 113.4 mm • Ratio of toothbrush length to distance to center of gravity: 63% • Weight of the toothbrush near its center of gravity (10mm along the axial length): 1.86g • Ratio of weight near the center of gravity to the total weight of the toothbrush: 14.8%

[0055] In Example 1, it was confirmed that by reducing the width dimension of the handle portion 3 by 25%, the center of gravity of the toothbrush was positioned near the finger rest portion 31, specifically 113.4 mm away from the tip of the head portion towards the base end. [Examples]

[0056] • Material: PBT (Polybutylene Terephthalate) • Hair strand arrangement: 4 rows • Maximum thickness of hair bundle holder: 3mm • Maximum width of the gripping part: 12mm • Minimum width of the gripping section: 7.2 mm • Reduction in the width of the gripping section: 40% • Toothbrush length: 180mm • Toothbrush weight: 10.0g • Distance from the tip of the club head to the center of gravity: 97.9 mm • Ratio of toothbrush length to distance to center of gravity: 54.4% • Weight of the toothbrush near its center of gravity (10mm along the axial length): 1.42g • Ratio of weight near the center of gravity to the total weight of the toothbrush: 14.2% In Example 2, by reducing the width of the handle portion 3 by 40%, it was confirmed that the center of gravity of the toothbrush was positioned 97.9 mm further towards the tip than in Example 1, specifically from the tip to the base of the head portion. Comparative Example

[0057] • Material: PBT (Polybutylene Terephthalate) • Hair strand arrangement: 4 rows • Maximum thickness of hair bundle holder: 3mm • Maximum width of the gripping part: 12mm • Minimum width of the gripping section: 11.4 mm • Reduction in the width of the gripping section: 5% • Toothbrush length: 180mm • Toothbrush weight: 14.78g • Distance from the tip of the club head to the center of gravity: 117.38 mm • Ratio of toothbrush length to distance to center of gravity: 65.2% • Weight of the toothbrush near its center of gravity (10mm along the axial length): 2.33g • Ratio of weight near the center of gravity to the total weight of the toothbrush: 15.7%

[0058] The comparative example described above was configured with a 5% reduction in the width dimension of the handle portion 3, while other conditions were the same as in Examples 1 and 2. In this comparative example, it was confirmed that the center of gravity of the entire toothbrush was located at a position significantly further towards the base end than in Examples 1 and 2, specifically at a position 117.38 mm away from the tip of the head portion towards the base end. [Explanation of symbols]

[0059] 1. Head section 2. Knack section 3. Handle section 4 Core material 5 Covering material 10 strands of hair 11. Hair implantation stand 12 Hair transplant surface 20 Axial center of the neck 21. Neck section near the tip 22. Intermediate neck section 23. Neck section near the base 24 Front of the neck 25 Rear of the neck 26, 27 Both left and right sides of the neck 30 Tapered section 31 Finger rest area 32 Axial center of the handle 33 Expanded diameter part 34 Terminal section 35 Flat surface

Claims

1. A toothbrush comprising a head portion having a bristle base on which bristle bundles are implanted, a neck portion and a handle portion, The head portion is a thin head having a bristle base with a thickness of 4 mm or less. The handle portion has a finger rest portion that bulges radially at the tip end near the neck portion, The weight distribution is such that the center of gravity of the entire toothbrush, including the bristle bundle, is located within a predetermined area including the finger rest portion, which is closer to the tip than the axial center of the handle portion. The handle portion is configured such that its width gradually decreases from the finger rest portion toward the axial center, and the rate of decrease in the width between the finger rest portion and the axial center is 10 to 40%. A toothbrush in which the neck portion is a slender neck with a thickness and width of 5.5 mm or less on the tip side than the axial center.

2. The center of gravity is located at a position 50-70% of the total length of the toothbrush, axially from the tip of the head towards the base end. The toothbrush according to claim 1.

3. The aforementioned finger rest portion is formed such that its thickness and width are approximately the same. The toothbrush according to claim 1.

4. On the back side of the handle portion, a long, flat surface is formed that extends along its entire axial length. The toothbrush according to claim 1.

5. The handle portion is a molded product mainly made from a hard synthetic resin material. The toothbrush according to claim 1.

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