Interdental brushes

Abstract

An interdental brush (100) includes a handle portion (13) and a cleaning portion (12), wherein: the cleaning portion (12) includes a shaft portion extending from the handle portion (13), and at least two projecting pieces projecting from the circumferential surface of the shaft portion; the shaft portion includes a synthetic resin (A) having a weight-average molecular weight not less than 250,000, and a synthetic resin (B) having a weight-average molecular weight of more than 250,000 and not more than 450,000; and at least one of the synthetic resin (A) and the synthetic resin (B) includes a synthetic resin having a long-chain branched structure.

Description

[Technical Field]

[0001] The present invention relates to an interdental brush. This application claims priority based on Japanese Patent Application No. 2020-214568, filed on December 24, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] Interdental brushes are used as auxiliary cleaning tools for cleaning between teeth, which is difficult to manufacture with toothbrushes. Interdental brushes are classified into those with a metal wire shaft and those with a synthetic resin shaft. Interdental brushes with a metal wire shaft have good interdental cleaning power and a good cleaning sensation for the user. Interdental brushes with a synthetic resin shaft feel better against the teeth or gums than those with a metal wire shaft.

[0003] When the shaft is made of synthetic resin, a reinforcing material is blended into the synthetic resin to ensure the buckling strength of the shaft (for example, Patent Documents 1 and 2). Increasing the buckling strength of the shaft makes it easier to insert between teeth (high insertability). However, blending a reinforcing material into the synthetic resin makes the shaft more likely to break during use (low shaft breaking strength). For this reason, synthetic resin shafts have the problem of low durability.

[0004] To address this issue, the invention of Patent Document 3 forms the shaft from a composite material containing synthetic resin, low-hardness resin that is less hard than the synthetic resin, and a reinforcing material. According to the invention of Patent Document 3, by blending the low-hardness resin, the shaft breakage strength is improved. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-108998 [Patent Document 2] Japanese Patent Application Publication No. 2019-111287 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-109018 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional techniques have not been able to sufficiently increase shaft breaking strength, and durability has not yet been satisfactory. SUMMARY OF THE INVENTION An object of the present invention is to provide an interdental brush that has both buckling strength and shaft breakage strength, and is excellent in ease of insertion and durability, despite having a shaft made of synthetic resin. [Means for solving the problem]

[0007] The present invention has the following aspects. <1> It has a handle portion and a cleaning portion, The cleaning part has a shaft part extending from the handle part and two or more protruding pieces protruding from a peripheral surface of the shaft part, The shaft portion contains a synthetic resin (A) having a weight-average molecular weight of 250,000 or less and a synthetic resin (B) having a weight-average molecular weight of more than 250,000 and 450,000 or less, An interdental brush, wherein at least one of the synthetic resin (A) and the synthetic resin (B) contains a synthetic resin having a long-chain branched structure. <2> The content of the synthetic resin having a long chain branched structure is 10 to 80% by mass with respect to the total mass of the synthetic resin constituting the shaft portion. <1> 10. An interdental brush as described in <3> the synthetic resin (B) contains the synthetic resin having a long chain branched structure, The content of the synthetic resin having a structure with long chain branches in the synthetic resin (B) is 5 to 60% by mass based on the total mass of the synthetic resin constituting the shaft portion. <1> or <2> 10. An interdental brush as described in <4> The shaft portion further contains a fibrous reinforcing material, and the content of the fibrous reinforcing material is 3 to 30 parts by mass per 100 parts by mass of the total mass of the synthetic resin constituting the shaft portion. <1> ~ <3> 10. An interdental brush according to any one of the preceding items. <5> The synthetic resin (B) includes a synthetic resin having no long chain branched structure, a mass ratio in the shaft portion expressed as (mass of the synthetic resin having a structure with long chain branches) / (mass of the synthetic resin not having a structure with long chain branches, in the synthetic resin (B)) of 0.1 to 16; <1> ~ <4> 10. An interdental brush according to any one of the preceding items. <6> The synthetic resin (A) includes a synthetic resin having no long chain branched structure, a mass ratio in the shaft portion expressed as (mass of the synthetic resin having a structure with long chain branches) / (mass of the synthetic resin not having a structure with long chain branches, in the synthetic resin (A)) of 0.2 to 7; <1> ~ <5> 10. An interdental brush according to any one of the preceding items. <7> The weight average molecular weight of the synthetic resin (A) is 150,000 to 250,000. <1> ~ <6> 10. An interdental brush according to any one of the preceding items. <8> The weight average molecular weight of the synthetic resin (B) is more than 250,000 and not more than 400,000. <1> ~ <7> 10. An interdental brush according to any one of the preceding items. <9> The synthetic resin (B) includes the synthetic resin having a long chain branched structure. <1> ~ <8> 10. An interdental brush according to any one of the preceding items. <10> Both the synthetic resin (A) and the synthetic resin (B) contain the synthetic resin having a long chain branched structure. <1> ~ <9> 10. An interdental brush according to any one of the preceding items. <11> The difference in weight average molecular weight between the synthetic resin (B) and the synthetic resin (A) is 100,000 or more. <1> ~ <10> 10. An interdental brush according to any one of the preceding items. <12> In the shaft portion, the mass ratio of the content of the synthetic resin (B) to the content of the synthetic resin (A) is 1 or more. <1> ~ <11> 10. An interdental brush according to any one of the preceding items. <13> The blending amount of the synthetic resin (B) in the shaft portion is 1.25 to 9 times the total mass of the other synthetic resins. <1> ~ <12> 10. An interdental brush according to any one of the preceding items.

[0008] <14> A method for manufacturing an interdental brush having a handle portion and a cleaning portion, the cleaning portion having a shaft portion extending from the handle portion and two or more protruding pieces protruding from a peripheral surface of the shaft portion, forming the shaft portion from a resin composition containing a synthetic resin (A) having a weight-average molecular weight of 250,000 or less and a synthetic resin (B) having a weight-average molecular weight of more than 250,000 and 450,000 or less; A method for producing an interdental brush, wherein at least one of the synthetic resin (A) and the synthetic resin (B) in the resin composition contains a synthetic resin having a long-chain branched structure. <15> the content of the synthetic resin having a long chain branched structure is 10 to 80% by mass relative to the total mass of the resin composition; <14> A method for manufacturing the interdental brush described in claim 1. <16> the synthetic resin (B) contains the synthetic resin having a structure with long chain branches, and the content of the synthetic resin having a structure with long chain branches in the synthetic resin (B) is 50 to 95% by mass with respect to the total mass of the resin composition; <14> or <15> A method for manufacturing the interdental brush described in claim 1. <17> The resin composition further comprises a fibrous reinforcing material, The synthetic resin (B) is blended into the resin composition as a reinforcing material-containing composition containing a fibrous reinforcing material. <14> ~ <16> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <18> The content of the fibrous reinforcing material is 3 to 30 parts by mass per 100 parts by mass of the total mass of the resin composition. <17> A method for manufacturing the interdental brush described in claim 1. <19> The synthetic resin (B) includes a synthetic resin having no long chain branched structure, In the resin composition, a mass ratio expressed as (mass of the synthetic resin having a structure with long chain branches) / (mass of the synthetic resin not having a structure with long chain branches, among the synthetic resin (B)) is 0.1 to 16. <14> ~ <18> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <20> The synthetic resin (A) includes a synthetic resin having no long chain branched structure, In the resin composition, a mass ratio expressed as (mass of the synthetic resin having a structure with long chain branches) / (mass of the synthetic resin not having a structure with long chain branches, among the synthetic resin (A)) is 0.2 to 7. <14> ~ <19> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <21> The weight average molecular weight of the synthetic resin (A) is 150,000 to 250,000. <14> ~ <20> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <22> The weight average molecular weight of the synthetic resin (B) is more than 250,000 and not more than 400,000. <14> ~ <21> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <23> The synthetic resin (B) includes the synthetic resin having a long chain branched structure. <14> ~ <22> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <24> Both the synthetic resin (A) and the synthetic resin (B) contain the synthetic resin having a long chain branched structure. <14> ~ <23> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <25> The difference in weight average molecular weight between the synthetic resin (B) and the synthetic resin (A) is 100,000 or more. <14> ~ <24> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <26> In the resin composition, the mass ratio of the content of the synthetic resin (B) to the content of the synthetic resin (A) is 1 or more. <14> ~ <25> 1. A method for manufacturing an interdental brush according to any one of the preceding claims. <27> The blending amount of the synthetic resin (B) in the resin composition is 1.25 to 9 times by mass the total mass of the other synthetic resins. <26> A method for manufacturing the interdental brush described in claim 1. [Effects of the Invention]

[0009] The interdental brush of the present invention has a shaft formed from synthetic resin, and has both buckling strength and shaft breaking strength, and is excellent in ease of insertion and durability. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view of an interdental brush according to an embodiment of the present invention. [Figure 2] FIG. 2 is a vertical cross-sectional view of the cleaning part of the interdental brush according to the embodiment of the present invention. [Figure 3] FIG. 10 is a vertical cross-sectional view of a cleaning part of an interdental brush according to another embodiment of the present invention. [Figure 4] FIG. 10 is a side view of an interdental brush according to another embodiment of the present invention. [Figure 5] FIG. 10 is a side view of an interdental brush according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Interdental brush) An interdental brush according to one embodiment of the present invention will now be described. In the drawings below, the dimensions of some components may be shown on different scales to make them easier to see.

[0012] Fig. 1 is a perspective view of an interdental brush 100 according to one embodiment. Fig. 2 is a cross-sectional view of the cleaning part 12 of the interdental brush 100 taken along the axis thereof.

[0013] The interdental brush 100 of FIG. 1 comprises a cleaning part 12 having a brush part 11 that is inserted into the gaps (interdental spaces) between adjacent teeth to clean the spaces between the teeth, and a handle part 13 that serves as a handle during use. The cleaning part 12 protrudes from the handle part 13. The brush part 11 is the part that is inserted between the teeth and is provided with a predetermined length in the axial direction. One axial end of the cleaning part 12 is connected to the handle part 13 almost perpendicularly, and the interdental brush 100 is an interdental brush 100 that is generally L-shaped overall (a so-called L-shaped interdental brush). The interdental brush 100 of this embodiment is manufactured by insert molding, and the cleaning part 12 and the handle part 13 are joined together to form an integrated structure.

[0014] 2, the cleaning part 12 has a shaft part 14 and a soft resin member 15 that covers at least a portion of the shaft part 14. The shaft part 14 has an overall cylindrical shape and is tapered toward the tip.

[0015] The shaft portion 14 has a first portion R1 and a second portion R2 that are aligned in the axial direction in this order from the tip 12a side of the cleaning part 12. The soft resin member 15 covers the entire axial area of the first portion R1 of the shaft portion 14. That is, in this embodiment, the first portion R1 of the shaft portion 14 is covered with the soft resin member 15, whereas the soft resin member 15 is not provided on the second portion R2.

[0016] The cleaning part 12 has a brush part 11 that is inserted between the teeth. The brush part 11 is made of a soft resin member 15 that covers the first portion R1 of the shaft part 14. Two or more flexible protruding pieces 11A are formed on the soft resin member 15. That is, the cleaning part 12 has the shaft part 14 and two or more protruding pieces 11A that protrude from the circumferential surface of the shaft part 14. The protruding pieces 11A form a protruding piece row with two or more protruding pieces 11A lined up from the front end 12a to the rear end 12b of the cleaning part 12, and the two or more protruding piece rows are arranged around the axis of the cleaning part 12.

[0017] The arrangement density of the protruding pieces 11A is, for example, 100 pieces / cm 2 ~600 pieces / cm 2 The arrangement density of the protruding pieces 11A is the value obtained by dividing the number of the protruding pieces 11A by the area of the region where the protruding pieces 11A are formed.

[0018] The height of the protruding piece 11A (the length from the base end to the tip end of the protruding piece) is appropriately determined within the range of, for example, 0.3 to 5 mm.

[0019] The rear end 12b side of the cleaning part 12 forms an insert part 16 that is connected to the handle part 13. The insert part 16 is a part that is inserted into the handle part 13. In this embodiment, when the cleaning part 12 is attached to the handle part 13, the insert part 16 is inserted into the insertion hole part 13a of the handle part 13 (FIG. 1), and the end edge part 15b of the soft resin member 15 and the second part R2 exposed from the soft resin member 15 are covered by the handle part 13.

[0020] The insert portion 16 is provided with a plurality of grooves 17 for improving the weldability with the handle portion 13 during insert molding. The grooves 17 are formed in an area 143 of the shaft portion 14 that constitutes the insert portion 16 and that is exposed from the soft resin member 15. At least two grooves 17 are formed around the axis of the shaft portion 14, and in this embodiment, four grooves 17 are formed. However, the number of grooves 17 may be five or more, or may be 0 to 1.

[0021] The handle portion 13 has a gripping portion 13A having a length in one direction, an extending portion 13B extending from one end of the gripping portion 13A, a holding portion 13C extending in a direction almost perpendicular to the end of the extending portion 13B opposite the gripping portion 13A, and a curved portion 13D formed at the connection between the holding portion 13C and the gripping portion 13A.

[0022] The grip portion 13A is cylindrical and extends in one direction for a predetermined length. Since the grip portion 13A is the part that the user grips, it has a length approximately equal to the width of the user's hand and a diameter that is easy to grip. In this embodiment, the grip portion 13A is cylindrical, but is not limited to this and can be appropriately modified to have a polygonal prism shape, etc.

[0023] An uneven anti-slip portion 13E is formed in a predetermined region including at least the central portion in the extension direction of the grip portion 13A of the handle portion 13. The anti-slip portion 13E is formed around the entire axis of the grip portion 13A. The formation area and uneven shape of the anti-slip portion 13E can be changed as appropriate.

[0024] Extension portion 13B extends at a slight incline in a direction intersecting the extension direction of grip portion 13A, and is gradually tapered from the grip portion 13A side toward holding portion 13C. The cross-sectional shape of extension portion 13B is not particularly limited.

[0025] In interdental brush 100, when the direction in which holding portion 13C of extension portion 13B is formed is defined as front surface 100a and the direction opposite holding portion 13C is defined as back surface 100b, extension portion 13B is tilted more toward back surface 100b on the holding portion 13C side than on the gripping portion 13A side, thereby forming curved portion 13D between extension portion 13B and gripping portion 13A. The presence of curved portion 13D in the middle of handle portion 13 makes it easier to insert brush portion 11 of cleaning part 12 into gaps between teeth, and improves operability of cleaning part 12 when interdental brush 100 is inserted into the oral cavity.

[0026] <Cleaning Department> <Shaft> The thickness of the shaft portion 14 is not particularly limited, as long as it is thick enough to allow the cleaning portion 12 to be inserted between teeth. The thickness of the shaft portion 14 is preferably, for example, 0.2 to 1.7 mm, and more preferably 0.3 to 0.9 mm. When the cross section of the shaft portion 14 is a perfect circle, the thickness of the shaft portion 14 is the diameter of the cross section. When the cross section of the shaft portion 14 is a polygon or an ellipse, the thickness of the shaft portion 14 is the diameter of the smallest encompassing circle of the cross section. The thickness of the shaft portion 14 is measured at its thickest point. Usually, the thickness of the shaft portion 14 is measured at the base end of the shaft portion 14 (at the boundary with the holding portion 13C).

[0027] The length of the shaft portion 14 is, for example, preferably 10 to 35 mm, and more preferably 10 to 15 mm.

[0028] The shaft 14 is made of synthetic resin. Examples of synthetic resins include polyolefin, polyester, polystyrene, and polyacetal. Examples of polyolefins include polypropylene (PP) and polyethylene (PE). Examples of polyesters include polytrimethylene terephthalate (PTT), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polycyclohexylene dimethylene terephthalate (PCT). Among these, the synthetic resin constituting the shaft portion 14 is preferably polyolefin or polyester, more preferably PP or PBT, and even more preferably PP.

[0029] The flexural modulus (JIS K7203) of the material of the shaft portion 14 is, for example, preferably 500 to 6000 MPa, more preferably 1000 to 6000 MPa, and even more preferably 2500 to 6000 MPa.

[0030] The synthetic resin constituting the shaft portion 14 includes a synthetic resin (A) having a weight-average molecular weight of 250,000 or less, and a synthetic resin (B) having a weight-average molecular weight of more than 250,000 and 450,000 or less.

[0031] [Synthetic resin (A): low molecular weight resin] The synthetic resin (A) is a synthetic resin having a weight average molecular weight of 250,000 or less. By including the synthetic resin (A) in the shaft portion 14, durability can be improved. The weight-average molecular weight of the synthetic resin (A) is preferably 250,000 or less, more preferably 220,000 or less, and even more preferably 200,000 or less. The weight-average molecular weight of the synthetic resin (A) is preferably 150,000 or more. The weight-average molecular weight of the synthetic resin (A) is preferably 150,000 to 250,000, more preferably 150,000 to 220,000, and even more preferably 150,000 to 200,000. If the weight-average molecular weight of the synthetic resin (A) is not less than the above lower limit, the rigidity of the shaft portion 14 can be increased, thereby further improving the insertability. If the weight-average molecular weight of the synthetic resin (A) is not more than the above upper limit, the toughness of the shaft portion 14 can be increased, thereby further improving the durability. The weight-average molecular weight of a synthetic resin is a value measured by a known method such as gel permeation chromatography (GPC). For example, the weight-average molecular weight of a synthetic resin can be determined by GPC using polystyrene (PS) as a standard substance.

[0032] The flexural modulus (JIS K7203) of the synthetic resin (A) is, for example, preferably 100 to 500 MPa, more preferably 200 to 400 MPa, and even more preferably 300 to 400 MPa. If the flexural modulus is equal to or greater than the above lower limit, the rigidity of the shaft portion 14 can be increased, thereby further improving the insertability. If the flexural modulus is equal to or less than the above upper limit, the toughness of the shaft portion 14 can be increased, thereby further improving the durability.

[0033] As the synthetic resin (A), a general-purpose synthetic resin can be used. The synthetic resin (A) is preferably polyolefin or polyester, more preferably PP or PBT, and even more preferably PP. If the synthetic resin (A) is one of these resins, the buckling strength and shaft bending strength of the shaft portion 14 can be further increased.

[0034] The content of synthetic resin (A) is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, relative to the total mass of the synthetic resins constituting the shaft portion 14. The content of synthetic resin (A) is preferably 50% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 12% by mass or less, relative to the total mass of the synthetic resins constituting the shaft portion 14. The content of synthetic resin (A) is preferably 3 to 50% by mass, more preferably 5 to 20% by mass, even more preferably 8 to 15% by mass, and particularly preferably 8 to 12% by mass, relative to the total mass of the synthetic resins constituting the shaft portion 14. When the content of synthetic resin (A) is equal to or greater than the above-mentioned lower limit, the toughness of the shaft portion 14 can be further increased, thereby improving durability. When the content of synthetic resin (A) is equal to or less than the above-mentioned upper limit, the rigidity of the shaft portion 14 can be further increased, thereby improving insertion ease.

[0035] [Synthetic resin (B): High molecular weight resin] The synthetic resin (B) has a weight average molecular weight of more than 250,000 and not more than 450,000. By including the synthetic resin (B), the shaft portion 14 has increased rigidity, improving insertability. The weight-average molecular weight of synthetic resin (B) is greater than 250,000, preferably greater than 280,000, and more preferably greater than 300,000. The weight-average molecular weight of synthetic resin (B) is equal to or less than 450,000, and preferably equal to or less than 400,000. The weight-average molecular weight of synthetic resin (B) is greater than 250,000 but equal to or less than 450,000, preferably greater than 250,000 but equal to or less than 400,000, more preferably greater than 280,000 but equal to or less than 400,000, and even more preferably greater than 300,000 but equal to or less than 400,000. If the weight-average molecular weight of synthetic resin (B) is equal to or greater than the lower limit, the rigidity of shaft portion 14 can be increased, thereby further improving insertion ease. If the weight-average molecular weight of synthetic resin (B) is equal to or less than the upper limit, the toughness of shaft portion 14 can be increased, thereby further improving durability. The difference in weight average molecular weight between synthetic resin (B) and synthetic resin (A) (BA molecular weight difference) is preferably 100,000 or more, more preferably 110,000 or more, and even more preferably 120,000 or more. The BA molecular weight difference is preferably 220,000 or less, and more preferably 150,000 or less. The BA molecular weight difference is preferably 100,000 or more, more preferably 110,000 to 220,000, and even more preferably 120,000 to 150,000. If the BA molecular weight difference is at least the above lower limit, the rigidity of the shaft portion can be increased, and the insertability can be further improved. If the BA molecular weight difference is at most the above upper limit, the toughness of the shaft portion can be increased, and the durability can be further improved.

[0036] The flexural modulus (JIS K7203) of the synthetic resin (B) is, for example, preferably 3500 to 6500 MPa, more preferably 4500 to 6500 MPa, and even more preferably 5500 to 6500 MPa. If the flexural modulus is equal to or greater than the above lower limit, the rigidity of the shaft portion 14 can be increased, thereby further improving the insertability. If the flexural modulus is equal to or less than the above upper limit, the toughness of the shaft portion 14 can be increased, thereby further improving the durability.

[0037] The synthetic resin (B) is preferably polyolefin or polyester, more preferably PP or PBT, and even more preferably PP. If the synthetic resin (B) is one of these resins, the buckling strength and shaft bending strength of the shaft portion 14 can be further increased. The synthetic resin (B) and the synthetic resin (A) may be resins of the same type or different types. That is, when the synthetic resin (A) is PP, the synthetic resin (B) may be polyolefin (i.e., the same type) or PP (i.e., the same type), or may be polyester, polystyrene, polyamide, etc. (i.e., a different type), or polyolefin or polyester other than PP (i.e., a different type). From the viewpoint of improving the compatibility between the synthetic resin (B) and the synthetic resin (A), the synthetic resin (B) and the synthetic resin (A) are preferably of the same type, more preferably the same type.

[0038] The content of synthetic resin (B) is preferably 5% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more, relative to the total mass of the synthetic resins constituting the shaft portion 14. The content of synthetic resin (B) is preferably 80% by mass or less, relative to the total mass of the synthetic resins constituting the shaft portion 14. The content of synthetic resin (B) is preferably 5 to 80% by mass, more preferably 30 to 80% by mass, and even more preferably 50 to 80% by mass, relative to the total mass of the synthetic resins constituting the shaft portion 14. If the content of synthetic resin (B) is equal to or greater than the above lower limit, the rigidity of the shaft portion 14 can be increased, thereby improving the ease of insertion. If the content of synthetic resin (B) is equal to or less than the above upper limit, the toughness of the shaft portion 14 can be increased, thereby improving the durability.

[0039] In shaft portion 14, the B / A mass ratio, which is the mass ratio of the content of synthetic resin (B) to the content of synthetic resin (A), is preferably 1 or more, more preferably 5 or more, and even more preferably 7 or more. The B / A mass ratio is preferably 9 or less. The B / A mass ratio is preferably 1 or more, more preferably 5 to 9, and even more preferably 7 to 9. If the B / A mass ratio is equal to or greater than the above-mentioned lower limit, the rigidity of shaft portion 14 can be increased, further improving the ease of insertion. If the B / A mass ratio is less than the above-mentioned lower limit, the toughness of shaft portion 14 can be increased, further improving durability.

[0040] [Synthetic resin with long-chain branching structure] At least one of the synthetic resins (A) and (B) constituting the shaft portion 14 has a long-chain branched structure. By including a synthetic resin having a long-chain branched structure (hereinafter sometimes referred to as a "long-chain branched resin") in the synthetic resin constituting the shaft portion 14, both insertability and durability can be achieved, and the insertability and durability can be further improved. As used herein, a "long-chain branched structure" refers to a structure having branched chains with 6 or more carbon atoms. The number of carbon atoms in the long-chain branched structure is 6 or more, preferably 6 to 72, more preferably 12 to 60, and even more preferably 12 to 48. A synthetic resin having a long-chain branched structure possesses both rigidity and toughness. Specifically, the entanglement of the branched chains provides rigidity, contributing to improved insertion. Furthermore, the entanglement of the branched chains loosens appropriately even with repeated use, ensuring toughness and reducing the risk of intermolecular cracks occurring when a load is applied, contributing to improved durability. The branching index g' can be used as an indicator of the degree of branching. The branching index g' is given by the ratio of the intrinsic viscosity [η]br of the long-chain branched resin to the intrinsic viscosity [η]lin of a linear polymer having the same molecular weight (i.e., [η]br / [η]lin). A long-chain branched structure can be considered to exist when g'<1. The definition of the branching index g' is described, for example, in "Developments in Polymer Characterization-4" (J.V. Dawkins ed., Applied Science Publishers, 1983), and is an index known to those skilled in the art. The branching index g' of PP is preferably 0.30 or more and less than 1.00 when the absolute molecular weight Mabs determined by light scattering is 1,000,000. A synthetic resin having a structure with long chain branches can be obtained, for example, by the manufacturing method described in Japanese Patent Application Laid-Open No. 2017-2229. Examples of synthetic resins having a structure with long chain branches include WAYMAX (registered trademark) MFX6 (manufactured by Japan Polypropylene Corporation).

[0041] The weight-average molecular weight of the long-chain branched resin is preferably 200,000 or more, more preferably 250,000 or more, and even more preferably 280,000 or more. The weight-average molecular weight of the long-chain branched resin is preferably 400,000 or less. The weight-average molecular weight of the long-chain branched resin is preferably 200,000 or more, more preferably 200,000 to 400,000, even more preferably 250,000 to 400,000, and particularly preferably 280,000 to 400,000. That is, the long-chain branched resin is more preferably part or all of synthetic resin (B), which is a synthetic resin having a weight-average molecular weight of more than 250,000 and not more than 450,000. When the weight-average molecular weight of the long-chain branched resin is not less than the above-mentioned lower limit, the rigidity of the shaft portion 14 can be increased, further improving the insertability. When the weight-average molecular weight of the long-chain branched resin is not more than the above-mentioned upper limit, the toughness of the shaft portion 14 can be increased, further improving the durability.

[0042] The ratio (long-chain branch / A molecular weight ratio) expressed as [weight average molecular weight of long-chain branched resin] / [weight average molecular weight of synthetic resin (A)] is preferably greater than 1, more preferably 1.4 or greater, and even more preferably 1.6 or greater. If the long-chain branch / A molecular weight ratio is equal to or greater than the above-mentioned lower limit, the rigidity of the shaft portion can be increased, and the insertability can be further improved. The upper limit of the long-chain branch / A molecular weight ratio is preferably substantially 3.0, for example.

[0043] The flexural modulus (JIS K7203) of the long-chain branched resin is, for example, preferably 1500 to 3000 MPa, more preferably 1800 to 2500, and even more preferably 2000 to 2500. If the flexural modulus is equal to or greater than the above lower limit, the rigidity of shaft portion 14 can be increased, further improving insertion ease. If the flexural modulus is equal to or less than the above upper limit, the toughness of shaft portion 14 can be increased, further improving durability.

[0044] The long-chain branched resin is preferably polyolefin or polyester, more preferably PP or PBT, and even more preferably PP. If the long-chain branched resin is one of these resins, the buckling strength and shaft bending strength of the shaft portion 14 can be further increased. The long-chain branched resin and the synthetic resin (A) may be resins of the same type or different types. That is, when the synthetic resin (A) is PP, the long-chain branched resin may be polyolefin (i.e., the same type) or PP (i.e., the same type), or may be polyester, polystyrene, polyamide, etc. (i.e., a different type), or polyolefin or polyester other than PP (i.e., a different type). From the viewpoint of improving the compatibility between the long-chain branched resin and the synthetic resin (A), the long-chain branched resin and the synthetic resin (A) are preferably of the same type, more preferably the same type.

[0045] The content of the long-chain branched resin is preferably 10% by mass or more relative to the total mass of the synthetic resin constituting the shaft portion 14. The content of the long-chain branched resin is preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less relative to the total mass of the synthetic resin constituting the shaft portion 14. The content of the long-chain branched resin is preferably 0 to 80% by mass, more preferably 10 to 50% by mass, and even more preferably 10 to 20% by mass relative to the total mass of the synthetic resin constituting the shaft portion 14. If the content of the long-chain branched resin is equal to or greater than the above-mentioned lower limit, the rigidity of the shaft portion 14 can be increased, thereby improving the insertability. If the content of the long-chain branched resin is equal to or less than the above-mentioned upper limit, the toughness of the shaft portion 14 can be increased, thereby improving the durability.

[0046] The content of the long-chain branched resin (hereinafter sometimes referred to as "low-molecular-weight long-chain branched resin") in synthetic resin (A) is preferably 40% by mass or less, more preferably 20% by mass or less, and may even be 0% by mass, when the content of synthetic resin (B) is 45% by mass or more, relative to the total mass of the synthetic resins constituting shaft portion 14. When the content of synthetic resin (B) is less than 45% by mass, the content of the low-molecular-weight long-chain branched resin is preferably 50% by mass or more, more preferably 60% by mass or more, relative to the total mass of the synthetic resins constituting shaft portion 14. When the content of the low-molecular-weight long-chain branched resin is equal to or greater than the above-mentioned lower limit, the durability of shaft portion 14 can be further improved. When the content of the low-molecular-weight long-chain branched resin is equal to or less than the above-mentioned upper limit, the insertability of shaft portion 14 can be further improved.

[0047] The content of the long-chain branched resin (hereinafter sometimes referred to as "high-molecular-weight long-chain branched resin") in the synthetic resin (B) is preferably 5 to 60 mass %, more preferably 10 to 40 mass %, and even more preferably 10 to 20 mass %, relative to the total mass of the synthetic resins constituting the shaft portion 14. If the content of the high-molecular-weight long-chain branched resin is equal to or greater than the above-mentioned lower limit, the insertability of the shaft portion 14 can be further improved. If the content of the high-molecular-weight long-chain branched resin is equal to or less than the above-mentioned upper limit, the durability of the shaft portion 14 can be further improved.

[0048] The mass of the long-chain branched resin contained in synthetic resin (B) relative to the mass of synthetic resin (A) (hereinafter sometimes referred to as the "long-chain branched / A mass ratio of B") is preferably 4 or less, more preferably 2 or less. The long-chain branched / A mass ratio of B is preferably 1 or more. The long-chain branched / A mass ratio of B is preferably 1 to 4, more preferably 1 to 2. When the long-chain branched / A mass ratio of B is equal to or less than the above upper limit, the durability of shaft portion 14 is further improved. When the long-chain branched / A mass ratio of B is equal to or more than the above lower limit, the insertability of shaft portion 14 is further improved.

[0049] The combined mass of synthetic resin (A) and synthetic resin (B) is preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass, of the total mass of the synthetic resins constituting shaft portion 14. If the combined mass of synthetic resin (A) and synthetic resin (B) is equal to or greater than the above lower limit, the insertability and durability of shaft portion 14 can be further improved.

[0050] When synthetic resin (A) and synthetic resin (B) are resins of the same type, the content of the different type of synthetic resin relative to the total mass of the synthetic resins constituting the shaft portion 14 is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 0 mass%. When synthetic resin (A) and synthetic resin (B) are the same type of resin, the content of the same but different synthetic resin relative to the total mass of the synthetic resin constituting the shaft portion 14 is preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 0 mass%.

[0051] The content of the synthetic resin (A) in the shaft portion 14 that does not have a long-chain branched structure (hereinafter sometimes referred to as "low-molecular-weight linear resin") is preferably 5% by mass or more, and more preferably 10% by mass or more, relative to the total mass of the synthetic resins constituting the shaft portion 14. The content of the low-molecular-weight linear resin is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, relative to the total mass of the synthetic resins constituting the shaft portion 14. The content of the low-molecular-weight linear resin is preferably 5 to 50% by mass, more preferably 5 to 30% by mass, and even more preferably 10 to 20% by mass, relative to the total mass of the synthetic resins constituting the shaft portion 14. When the content of the low-molecular-weight linear resin is equal to or greater than the above-mentioned lower limit, the toughness and durability of the shaft portion 14 can be further improved. When the content of the low-molecular-weight linear resin is equal to or less than the above-mentioned upper limit, the rigidity of the shaft portion 14 can be further improved, and the insertion ability can be further improved.

[0052] In the shaft portion 14, the mass ratio (mass of the synthetic resin having a long-chain branching structure) / (mass of the synthetic resin (A) that does not have a long-chain branching structure) (hereinafter sometimes referred to as the "long-chain branching resin / low-molecular-weight linear resin mass ratio") is preferably 0.2 or more, more preferably 0.5 or more, and even more preferably 1.0 or more. The long-chain branching resin / low-molecular-weight linear resin mass ratio is preferably 7.0 or less, more preferably 5.0 or less, and even more preferably 3.0 or less. The long-chain branching resin / low-molecular-weight linear resin mass ratio is preferably 0.2 to 7.0, more preferably 0.5 to 5.0, and even more preferably 1.0 to 3.0. When the long-chain branching resin / low-molecular-weight linear resin mass ratio is equal to or greater than the above-mentioned lower limit, the rigidity of the shaft portion 14 can be increased, thereby improving the insertability. When the long-chain branching resin / low-molecular-weight linear resin mass ratio is equal to or less than the above-mentioned upper limit, the toughness of the shaft portion 14 can be increased, thereby improving the durability.

[0053] In the shaft portion 14, the mass ratio (hereinafter sometimes referred to as the "long-chain branched resin / high-molecular-weight linear resin mass ratio") expressed as (mass of the synthetic resin having a long-chain branched structure) / (mass of the synthetic resin (B) that does not have a long-chain branched structure) is preferably 0.1 or more, and more preferably 0.2 or more. The long-chain branched resin / high-molecular-weight linear resin mass ratio is preferably 16 or less, more preferably 1.0 or less, and even more preferably 0.7 or less. The long-chain branched resin / high-molecular-weight linear resin mass ratio is preferably 0.1 to 16, more preferably 0.1 to 1.0, and even more preferably 0.2 to 0.7. When the long-chain branched resin / high-molecular-weight linear resin mass ratio is equal to or greater than the above-mentioned lower limit, the rigidity of the shaft portion 14 can be increased, thereby improving the insertability. When the long-chain branched resin / high-molecular-weight linear resin mass ratio is equal to or less than the above-mentioned upper limit, the toughness of the shaft portion 14 can be increased, thereby improving the durability.

[0054] It is preferable that the synthetic resin (B) has a long-chain branched structure in the shaft portion 14. When the synthetic resin (B) has a long-chain branched structure, it is possible to further achieve both ease of insertion and durability, and the ease of insertion and durability can be further improved. Both the synthetic resin (A) and the synthetic resin (B) may have a long-chain branched structure in the shaft portion 14. When both the synthetic resin (A) and the synthetic resin (B) have a long-chain branched structure, the rigidity of the shaft portion 14 can be further increased, and the insertability can be further improved.

[0055] [Reinforcement material] The shaft portion 14 may further include a reinforcing material, which increases the rigidity of the shaft portion 14 and improves insertion ease.

[0056] Examples of the reinforcing material include fibrous reinforcing materials and non-fibrous reinforcing materials. Examples of the non-fibrous reinforcing material include needle-shaped reinforcing materials, plate-shaped reinforcing materials, and granular reinforcing materials. Among these, fibrous reinforcing materials are preferred. Use of fibrous reinforcing materials can further increase the rigidity of the shaft portion 14 and improve insertability.

[0057] Examples of fibrous reinforcing materials include glass fibers, aramid fibers, carbon fibers, cellulose fibers, and nanocellulose fibers. When contained in the shaft portion 14, the length of the fibrous reinforcing material is, for example, preferably 100 to 1000 μm, and more preferably 300 to 900 μm. The length of the fibrous reinforcing material can be measured, for example, using an X-ray CT device. The thickness of the fibrous reinforcing material is, for example, preferably 5 to 60 μm, more preferably 20 to 50 μm. The thickness of the fibrous reinforcing material can be measured, for example, using an X-ray CT device.

[0058] The content of the reinforcing material in the shaft portion 14 is determined appropriately taking into consideration the type of reinforcing material, etc. If the reinforcing material is a fibrous reinforcing material, the content of the reinforcing material in the shaft portion 14 is preferably 3 to 30 parts by mass, more preferably 13 to 30 parts by mass, even more preferably 15 to 30 parts by mass, and particularly preferably 18 to 24 parts by mass, per 100 parts by mass of the synthetic resin constituting the shaft portion 14. If the content of the reinforcing material is equal to or greater than the above-mentioned lower limit, the rigidity of the shaft portion 14 can be further increased, thereby improving the insertability. If the content of the reinforcing material is equal to or less than the above-mentioned upper limit, the toughness of the shaft portion 14 can be further increased, thereby improving the durability.

[0059] [others] The shaft 14 may contain optional components (optional shaft components) other than the synthetic resin (A), the synthetic resin (B), and the reinforcing material. Examples of optional shaft components include pigments, talc, wollastonite, and elastomers. The content of the optional component in the shaft portion is, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the synthetic resin that constitutes the shaft portion 14. Shank 14 may contain a synthetic resin (optional synthetic resin) other than synthetic resin (A) and synthetic resin (B). Examples of optional synthetic resins include synthetic resins with a weight-average molecular weight higher than synthetic resin (B) and synthetic resins with a weight-average molecular weight lower than synthetic resin (A). The content of optional synthetic resin is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially none, relative to the total mass of the synthetic resins constituting shaft 14. If the content of optional synthetic resin is equal to or less than the above upper limit, the insertability and durability of shaft 14 can be further improved.

[0060] <Soft resin components> [Soft resin] Examples of the material (soft resin) of the soft resin member 15 include known elastomer resins such as polyolefin elastomers, styrene elastomers, polyester elastomers, etc. One type of soft resin may be used, or two or more types may be used. The Shore A hardness of the soft resin is preferably A90 or less, and more preferably A30 to A80.

[0061] [others] The soft resin member 15 may contain optional components other than the soft resin (optional components of the soft resin member), such as a pigment, a flow improver, and a foaming agent. The content of the optional component of the soft resin member is, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the soft resin that constitutes the soft resin member 15.

[0062] <Handle section> The handle portion 13 is made of a so-called hard resin. Examples of the hard resin material include polyolefin, polyester, polystyrene, polyacetal, and the like, similar to the synthetic resin that makes up the shaft portion 14. Among these, polyolefin and polyester are preferred as the hard resin that makes up the handle portion 13, with PP and PBT being more preferred, and PP being even more preferred. The synthetic resin that forms the handle portion 13 may be the same as the synthetic resin that forms the shaft portion 14, or may be different.

[0063] The flexural modulus (JIS K7203) of the hard resin constituting the handle portion 13 is, for example, preferably 800 to 2000 MPa, more preferably 800 to 1500 MPa, and even more preferably 800 to 1000 MPa. If the flexural modulus is equal to or greater than the above lower limit, the strength of the handle portion 13 can be further increased. If the flexural modulus is equal to or less than the above upper limit, the handle portion 13 is provided with appropriate flexibility, and the operability of the interdental brush 100 can be further improved.

[0064] The handle portion 13 may include a reinforcement material. The handle portion 13 may contain optional components (optional handle portion components) other than the hard resin and reinforcing material. The optional handle portion components include the same components as the optional shaft portion components. The content of the optional handle portion components is the same as the content of the optional shaft portion components.

[0065] (Interdental brush manufacturing method) Next, a method for manufacturing the interdental brush 100 will be described below. Here, a method for manufacturing the cleaning part 12 will be described in detail. The cleaning part 12 is manufactured by, for example, so-called two-color molding.

[0066] Synthetic resin (A), synthetic resin (B), and, if necessary, a reinforcing material and optional components of the shaft portion are melt-kneaded to form a resin composition (hereinafter sometimes referred to as "shank portion resin composition") (kneading step). When a reinforcing material is blended into the shaft portion resin composition, synthetic resin (B) is preferably blended into the shaft portion resin composition as a reinforcing material-containing composition in which the reinforcing material has been kneaded in advance. By subjecting the reinforcing material-containing composition to the kneading step, the reinforcing material is more uniformly dispersed in the shaft portion resin composition. The reinforcement-containing composition may be supplied, for example, as pellets.

[0067] When a reinforcing material-containing composition is used, the blending amount of synthetic resin (B) is preferably 1.25 to 9 times by mass, more preferably 3 to 8 times by mass, and even more preferably 3 to 7 times by mass, the total mass of other synthetic resins (synthetic resins contained in the shaft resin composition excluding synthetic resin (B)). If the blending ratio of synthetic resin (B) constituting the reinforcing material-containing composition is equal to or greater than the above lower limit, the insertion property can be further improved. If the blending ratio of synthetic resin (B) constituting the reinforcing material-containing composition is equal to or less than the above upper limit, the durability can be further improved.

[0068] Next, the stem resin composition is injected into a primary mold in which a cavity in the shape of the stem 14 is formed, to obtain the stem 14 (primary molding step). The obtained shaft portion 14 is placed in a secondary mold, and a soft resin material containing a soft resin is injected to cover the first part R1 of the shaft portion 14 with a soft resin member 15, thereby obtaining a cleaning portion 12 in which a protruding piece 11A is formed on the circumferential surface of the shaft portion 14 (secondary molding process). In the secondary molding step, a soft resin material is injected from the tip side of the shaft portion 14.

[0069] The handle portion 13 is manufactured by injection molding, etc. The insert portion 16 of the cleaning part 12 is inserted into the insertion hole 13a formed in the holding part 13C of the obtained handle portion 13, thereby obtaining the interdental brush 100. In this embodiment, the shaft portion 14 and the handle portion 13 are molded separately, but the present invention is not limited to this, and the shaft portion 14 and the handle portion 13 may be molded integrally in the primary molding process.

[0070] As described above, the interdental brush of this embodiment contains synthetic resin (A) and synthetic resin (B), and at least one of synthetic resin (A) and synthetic resin (B) contains a synthetic resin with a long-chain branched structure. Therefore, due to the properties of each synthetic resin, the brush has both buckling strength and shaft breaking strength, improving insertion ease and durability. In addition, the interdental brush of this embodiment has a reinforcing material in the shaft, which further improves ease of insertion.

[0071] The cleaning part may be in a form other than the cleaning part 12 shown in Figure 2. The cleaning part may be, for example, a cleaning part 212 as shown in Figure 3. Figure 3 is a cross-sectional view taken along the axis of the cleaning part 212 of the interdental brush.

[0072] As shown in FIG. 3, the cleaning part 212 has a shaft part 214 and a soft resin member 215 that covers at least a portion of the shaft part 214. The shaft part 214 has a first part R1 and a second part R2 that are aligned in the axial direction from the tip 212a of the cleaning part 212. The second part R2 has a cylindrical shape that gradually increases in diameter from the rear end 212b of the cleaning part 212. The cleaning part 212 has an expanded diameter part 218 that increases in diameter with a step, following the second part R2. The cleaning part 212 has a tapered shape that narrows toward the tip 212a of the cleaning part 212, following the expanded diameter part 218. The base end of the first part R1 is bulged, and the edge part 215b of the soft resin member 215 is located at the boundary with the second part R2. Cleaning unit 212 differs from cleaning unit 12 in that it has expanded diameter section 218. By having expanded diameter section 218, cleaning unit 212 stops the insertion between the teeth at expanded diameter section 218 even if the interdental brush is accidentally pushed hard in the axial direction with brush section 211 inserted between the teeth, which makes it easier to prevent the interdental brush from damaging the inside of the oral cavity. In addition, by having the expanded diameter portion 218, the cleaning portion 212 can prevent the brush portion 211 from shifting within the mold when the cleaning portion 212 is insert-molded into the handle portion.

[0073] The soft resin member 215 covers the entire axial area of the first portion R1 of the shaft portion 214. That is, in this embodiment, the first portion R1 of the shaft portion 214 is covered with the soft resin member 215, whereas the soft resin member 215 is not provided on the second portion R2.

[0074] The cleaning part 212 has a brush part 211 that is inserted between the teeth. The brush part 211 is made of a soft resin member 215 that covers the first portion R1 of the shaft part 214. Two or more flexible protruding pieces 211A are formed on the soft resin member 215. That is, the cleaning part 212 has the shaft part 214 and two or more protruding pieces 211A that protrude from the circumferential surface of the shaft part 214. The protruding pieces 211A are arranged in a row from the front end 212a to the rear end 212b of the cleaning part 212, and the two or more protruding piece rows are arranged around the axis of the cleaning part 212.

[0075] The arrangement density of the protruding pieces 211A is the same as the arrangement density of the protruding pieces 11A. The arrangement density of the protruding pieces 211A is a value obtained by dividing the number of the protruding pieces 211A by the area of the region where the protruding pieces 211A are formed.

[0076] The height of the protruding piece 211A (the length from the base end to the tip of the protruding piece) is the same as the height of the protruding piece 11A.

[0077] The rear end 212b of the cleaning part 212 forms an insert part 216 that is connected to the handle part. The insert part 216 is the part that is inserted into the handle part. In this embodiment, when the cleaning part 212 is attached to the handle part, the insert part 216 is inserted into the insertion hole of the handle part and stops at the edge part 215b of the soft resin member 215 and the expanded diameter part 218.

[0078] The thickness of the shaft 214 is the same as the thickness of the shaft 14 . The length of the shank 214 is similar to the length of the shank 14 . The flexural modulus of the material of shaft 214 is similar to the flexural modulus of the material of shaft 14 . The synthetic resin that constitutes the shaft portion 214 is the same as the synthetic resin that constitutes the shaft portion 14 . The material of the soft resin member 215 is the same as the material of the soft resin member 15 .

[0079] The interdental brush of this embodiment can be manufactured in the same manner as the interdental brush 100. The cleaning part 212 is manufactured in the same manner as the cleaning part 12, and the insert part 216 of the cleaning part 212 is inserted into the insertion hole 13a formed in the holding part 13C of the handle part 13 to obtain the interdental brush 200.

[0080] In the above embodiment, a so-called L-shaped interdental brush has been described as an example, but the present invention is not limited to this. For example, the present invention may be applied to so-called I-shaped interdental brushes, curved interdental brushes, and approximately S-shaped interdental brushes. I-shaped interdental brushes have a handle portion that extends in one direction and a cleaning portion that extends forward from the tip of the handle portion, with the handle portion and cleaning portion being aligned in an approximately straight line. Typically, in I-shaped interdental brushes, the handle portion and the shaft portion are integrally formed (primary molding), and the brush portion is formed by coating part or all of the shaft portion of this primary molded body with a soft resin composition (secondary molding).

[0081] Figure 4 is a side view of an interdental brush according to another embodiment. As shown in Figure 4, curved interdental brush 300 has a curved handle portion 313 and a cleaning portion 312 that extends forward from the tip of handle portion 313. In curved interdental brush 300, handle portion 313 and cleaning portion 312 are not arranged in a substantially straight line, but are instead arc-shaped.

[0082] Figure 5 is a side view of an interdental brush according to another embodiment. As shown in Figure 5, the approximately S-shaped interdental brush 400 has a handle portion 413 that curves downward and then upward, and a cleaning portion 412 that extends forward from the tip of the handle portion 413. In the approximately S-shaped interdental brush 400, the handle portion 413 and the cleaning portion 412 are not aligned in an approximately straight line, but are formed in an approximately S shape.

[0083] Typically, in such curved interdental brushes and approximately S-shaped interdental brushes, the handle portion and the shaft portion are formed as a single unit (primary molding), and then part or all of the shaft portion of this primary molded body is coated with a soft resin composition to form the brush portion (secondary molding). By applying the present invention to I-shaped interdental brushes, curved interdental brushes, and approximately S-shaped interdental brushes, the ease of insertion and durability of the interdental brushes can be improved. [Example]

[0084] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description.

[0085] (Raw materials used) <Synthetic resin (A)> A-1: Polypropylene with a long-chain branched structure. Branching index g'=0.8, weight-average molecular weight 200,000. A-2: Linear polypropylene. Branching index g'≧1, weight average molecular weight 250,000. A-3: Linear polypropylene. Branching index g'≧1, weight average molecular weight 200,000. A-4: Linear polypropylene. Branching index g'≧1, weight average molecular weight 180,000.

[0086] <Synthetic resin (B)> B-1: Polypropylene with a long-chain branched structure. Branching index g'=0.9, weight-average molecular weight 400,000. B-2: Polypropylene with a long-chain branched structure. Branching index g'=0.9, weight-average molecular weight 300,000. B-3: Polypropylene with a long-chain branched structure. Branching index g'=0.9, weight-average molecular weight 350,000. B-4: Polypropylene with a long-chain branched structure. Branching index g'=0.8, weight-average molecular weight 400,000. B-5: Polypropylene with a long-chain branched structure. Branching index g'=0.8, weight-average molecular weight 300,000. B-6: Linear polypropylene. Branching index g'≧1, weight average molecular weight 380,000. B-7: Linear polypropylene. Branching index g'≧1, weight average molecular weight 330,000. B-8: Linear polypropylene. Branching index g'≧1, weight average molecular weight 310,000. B-9: Linear polypropylene. Weight average molecular weight: 270,000.

[0087] <Synthetic Resin (B')> Comparison product of Synthetic Resin (B) B'-1: Polypropylene with a long-chain branched structure. Branching index g' = 0.9, weight-average molecular weight 500,000.

[0088] <Reinforcement material> Fibre reinforcement: glass fibre. When contained in the shaft, the fibre length is 500μm and the fibre thickness is 45μm.

[0089] (Evaluation method) <Insertion> Ten monitors evaluated the interdental insertion ability of each interdental brush when cleaning between teeth using the following criteria. The average scores of the ten monitors were calculated, and an average score of 4.5 or more was assigned an "A," an average score of 4.0 to less than 4.5 was assigned a "B," an average score of 3.0 to less than 4.0 was assigned a "C," an average score of 2.0 to less than 3.0 was assigned a "D," and an average score of less than 2.0 was assigned an "E."

[0090] <Evaluation Criteria> 5 points: Excellent interdental insertion. 4 points: "Interdental insertion" is somewhat good. 3 points: "Interdental insertion" is neutral. 2 points: "Interdental insertion" is somewhat poor. 1 point: "Interdental insertion" is very poor.

[0091] <Durability> Ten monitors cleaned between their teeth with each interdental brush for seven days, and evaluated the durability of the brush shaft based on the percentage of monitors who broke the brush after seven days, using the following criteria: Average scores of the ten monitors were calculated, with an average score of 4.5 or more given an "A," an average score of 4.0 to less than 4.5 given a "B," an average score of 3.0 to less than 4.0 given a "C," an average score of 2.0 to less than 3.0 given a "D," and an average score of less than 2.0 given an "E."

[0092] <Evaluation Criteria> 5 points: The maximum deviation between the axis of the cleaning part before use and the axis of the cleaning part after 7 days of use is 0.5 mm or less. 4 points: The maximum deviation between the axis of the cleaning part before use and the axis of the cleaning part after 7 days of use is more than 0.5 mm and less than 1.0 mm. 3 points: The maximum deviation between the axis of the cleaning part before use and the axis of the cleaning part after 7 days of use is more than 1.0 mm and less than 2.0 mm. 2 points: The maximum deviation between the axis of the cleaning part before use and the axis of the cleaning part after 7 days of use is more than 2.0 mm and less than 3.0 mm. 1 point: The maximum deviation between the axis of the cleaning part before use and the axis of the cleaning part after 7 days of use is more than 3.0 mm.

[0093] (Examples 1 to 6, Comparative Examples 1 to 6) According to the compositions in Tables 1 and 3, synthetic resins (A) and (B) and a fibrous reinforcing material were melt-kneaded to form a shaft resin composition, which was then injection-molded to form the shaft. The resulting shaft was coated with a styrene-based elastomer to form a cleaning part. The resulting cleaning part was attached to a separately molded handle to obtain the interdental brush of each example. The interdental brush of each example was the same as the interdental brush 100 in Figure 1. The handle of the resulting interdental brush had a thickness (at its thickest point) of 7 mm, a shaft thickness of 0.6 to 1 mm, and a shaft length of 12 mm. The interdental brushes of each example were evaluated for ease of insertion and durability, and the results are shown in the table.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] [Table 4]

[0098] As shown in Tables 2 and 4, Examples 1 to 6 to which the present invention was applied were rated "C" to "A" for insertability and "C" to "A" for durability. In Comparative Example 1, in which the synthetic resin constituting the shaft portion did not have a long chain branched structure, the durability was rated "E." In Comparative Example 2, in which neither the synthetic resin (A) nor the synthetic resin (B) had a long chain branched structure, the durability was rated "E". In Comparative Example 3, in which the synthetic resin constituting the shaft portion did not have a long chain branched structure, the insertability was rated "E". Comparative Example 4, which did not contain synthetic resin (A), was rated "D" for both insertability and durability. Comparative Examples 5 and 6, which did not contain synthetic resin (B), were rated "E" for insertability. From these results, it was confirmed that by applying the present invention, both insertability and durability can be achieved. [Explanation of symbols]

[0099] 11A protruding piece 12 Cleaning Department 14 Shaft 13 Handle 100 interdental brushes

Claims

1. It has a handle portion and a cleaning portion, The cleaning part has a shaft part extending from the handle part and two or more protruding pieces protruding from a peripheral surface of the shaft part, the shaft portion comprises a synthetic resin (A) having a weight-average molecular weight of 250,000 or less and a synthetic resin (B) having a weight-average molecular weight of more than 250,000 and 450,000 or less, At least one of the synthetic resin (A) and the synthetic resin (B) contains a synthetic resin having a long-chain branched structure.

2. 2. The interdental brush according to claim 1, wherein the content of said synthetic resin having a long chain branched structure is 10 to 80% by mass relative to the total mass of said synthetic resin constituting said shaft portion.

3. 3. The interdental brush according to claim 1, wherein the synthetic resin (B) contains a synthetic resin having a structure with long chain branches, and the content of the synthetic resin having a structure with long chain branches in the synthetic resin (B) is 5 to 60% by mass relative to the total mass of the synthetic resin constituting the shaft portion.

4. An interdental brush according to any one of claims 1 to 3, wherein the shaft further comprises a fibrous reinforcing material, and the content of the fibrous reinforcing material is 3 to 30 parts by mass per 100 parts by mass of the total mass of the synthetic resin constituting the shaft.

5. The synthetic resin (B) includes a synthetic resin having no long chain branched structure, The interdental brush according to any one of claims 1 to 4, wherein the mass ratio in the shaft, expressed as (mass of the synthetic resin having a structure with long chain branches) / (mass of the synthetic resin (B) that does not have a structure with long chain branches), is 0.1 to 16.

6. The synthetic resin (A) includes a synthetic resin having no long chain branched structure, The interdental brush according to any one of claims 1 to 5, wherein the mass ratio in the shaft, expressed as (mass of the synthetic resin having a structure with long chain branches) / (mass of the synthetic resin in the synthetic resin (A) that does not have a structure with long chain branches), is 0.2 to 7.0.

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