Brush bristle material

Abstract

To provide a brush bristle material capable of efficiently transmitting stress to a target part even with a small force.SOLUTION: A brush bristle material is composed of a resin composition with a sea phase and an island phase that extend in a fiber axial direction, and has: an equal cross section part having a constant fiber diameter and a cross sectional shape in the fiber axial direction; and a tapered part that extends from at least one end of the equal cross section part and reduces a fiber diameter. In the cross section orthogonal to the fiber axis, when the center of the fiber is an original point and an outer periphery of the fiber is 100% position, the island phase exists only within a range from 10% to 90% in a radial direction, and at least a part of the surface formed by the island phase appearing to the tapered part forms a recess in the direction that goes to the center of the fiber from the tapered surface formed by the sea phase.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to brush bristle materials having locally arranged recesses on a tapered portion. [Background technology]

[0002] Monofilaments made of polyester resins have excellent mechanical properties and are therefore widely used in a range of applications from consumer goods to industrial uses.

[0003] In a brush using the above-described brush bristle material, for example, a toothbrush, it is desirable that the bristle tips have a good balance of tooth cleaning effect, a soft feel that does not damage the object being cleaned, and a massaging effect on the gums, etc., and further that the bristle tips have good scraping ability for removing dirt and plaque during cleaning.

[0004] However, if the brush bristles are made of monofilament of a single material all the way to the tip, it may be difficult to meet these requirements. That is, if the brush bristles are made of monofilament of a single material all the way to the tip, thickening the brush bristles will make the brush more flexible, improving the cleaning effect on the flat surfaces of the teeth and the massaging effect on the gums, etc., but it will be difficult for the bristles to penetrate narrow spaces such as the gingival sulcus, making it difficult to obtain the ability to scrape off dirt and plaque, and the bristles will be too harsh on the gums, making them more likely to cause scratches. Conversely, simply thinning the brush bristles will improve the cleaning effect on narrow spaces such as the gingival sulcus, but will weaken the bristles along their entire length, reducing the massaging effect on the gums, etc., and reducing the durability of the bristles themselves.

[0005] Regarding the above, for patients with advanced periodontal disease, in particular, it is essential to keep the oral cavity clean to prevent the condition from worsening, so it is desirable to use a toothbrush with strong bristles that provides excellent cleaning performance. However, since using a toothbrush with strong bristles can further damage weakened gums, there is a need for a toothbrush that is less irritating and has excellent cleaning performance.

[0006] Brushes for cleaning and washing in other fields present generally similar problems.

[0007] As a countermeasure against the above, techniques have been proposed, such as those disclosed in Patent Documents 1 and 2, in which unevenness is provided on the surface of the yarn, thereby enabling high cleaning performance with less force.

[0008] In toothbrushes with unevenness on the entire filament surface, as in Patent Document 1, the unevenness easily comes into contact with the gums during brushing, causing damage to the gums. In toothbrushes with unevenness only on the tapered portion, as in Patent Document 2, the surface friction at the tip of the filament increases, improving cleaning performance, but it also makes it difficult to penetrate gaps such as the gingival sulcus, causing the unevenness to come into contact with the gums during brushing and causing damage. Furthermore, the tip of the filament with unevenness on the surface is more likely to be brittle than a monofilament made of a single material, which also presents the problem of reduced wear resistance and breakage resistance. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 4807760 [Patent Document 2] Patent Publication No. 2021-065272 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to solve the above problems and provide brush bristle material that can efficiently transmit stress to targeted areas with little force when brushing, something that was not possible with conventional technology, thereby maintaining high cleaning ability and low irritation even with little force, and further having excellent wear resistance and breakage resistance at the tip. [Means for solving the problem]

[0011] The present invention has the following configuration. [1] A brush bristle material made of a resin composition having a sea phase and an island phase extending in the fiber axis direction, the brush bristle material having a shape with a uniform cross-sectional portion having a constant fiber diameter and cross-sectional shape in the fiber axis direction and a tapered portion extending from at least one end of the uniform cross-sectional portion and in which the fiber diameter gradually decreases, in a cross section perpendicular to the fiber axis, when the center of the fiber is taken as the origin and the outer periphery of the fiber is taken as the 100% position, the island phases are present only in a range of 10% to 90% in the radial direction, and at least a portion of the surface formed by the island phases exposed in the tapered portion forms a recess in a direction toward the center of the fiber relative to the tapered surface formed by the sea phase. [2] The brush bristle material according to [1], wherein, when the fiber center is taken as the origin and the outer periphery of the fiber is taken as the 100% position, the island phase occupies 5% to 100% of the cross-sectional area perpendicular to the fiber axis within a range of 10% to 90% in the radial direction. [3] The taper length is 3 mm or more and 20 mm or less, and the island phase exposed in the taper section has an area of ​​1 μm 2 More than 300μm 2 The brush bristle material according to [1] or [2] above, having the following recesses, and the center-to-center distance between any two adjacent recesses is 20 μm or less. [4] The brush bristle material according to any one of [1] to [3], wherein the depth of the recesses from the tapered surface formed by the sea phase toward the center of the fiber axis to the bottom of the recesses is 0.5 μm or more and 30 μm or less. [5] The brush bristle material according to any one of [1] to [4] above, wherein the arithmetic mean roughness Ra of the yarn surface within a range of 50 to 100 μm from the yarn tip is 3.0 μm or less. [Effects of the Invention]

[0012] The brush bristles of the present invention are suitable for toothbrushes, paintbrushes, cosmetic brushes, and industrial brushes. When used as a toothbrush, they allow for efficient cleaning of narrow spaces such as gingival sulci with little force, and when used as a paintbrush, cosmetic brush, or industrial brush, they ensure high liquid and powder absorption only at the tip of the brush, eliminating the need for excessive liquid or powder, allowing for efficient work. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing an example of a cross section of a uniform cross section portion of a brush bristle material according to the present invention. [Figure 2] 1 is a schematic diagram showing an example of a cross section and a side surface of brush bristles according to Examples 1 to 6. FIG. [Figure 3] 1 is a schematic diagram showing an example of a cross section and a side surface of brush bristles of Comparative Examples 1 to 6. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below.

[0015] The brush bristle material of the present invention is made of a resin composition having a sea phase and island phases extending in the fiber axis direction, and has a shape having a uniform cross-sectional portion with a constant fiber diameter and cross-sectional shape in the fiber axis direction, and a tapered portion extending from at least one end of the uniform cross-sectional portion and in which the fiber diameter gradually decreases.In a cross section perpendicular to the fiber axis, when the center of the fiber is taken as the origin and the outer periphery of the fiber is taken as the 100% position, the island phases are present only in a range of 10% to 90% in the radial direction, and at least a portion of the surface formed by the island phases exposed in the tapered portion forms a recess in a direction toward the center of the fiber relative to the tapered surface formed by the sea phase.

[0016] Here, the sea phase and the island phase extending in the fiber axis direction means that in a cross section perpendicular to the fiber axis, the sea phase and the island phase are at the same position like a candy cane, but extend in the fiber axis direction.

[0017] The brush bristle material of the present invention has a uniform cross-sectional portion with a constant fiber diameter and cross-sectional shape in the fiber axis direction and a tapered portion extending from at least one end of the uniform cross-sectional portion and gradually decreasing in fiber diameter. The uniform cross-sectional portion is a portion with a constant fiber diameter and cross-sectional shape in the fiber axis direction that is not tapered. A uniform fiber diameter and cross-sectional shape refers to a portion in which the fiber diameter and cross-sectional shape do not change substantially in the longitudinal direction. The term "substantially unchanged" refers to a portion in which, when the cross sections are stacked to minimize the deviation, the largest deviation in the outline is within ±1% of the cross-sectional diameter (diameter in the case of a circle, or major axis in the case of a non-circular section). While there are no particular limitations on the tapered shape, a sharper tip facilitates insertion into the gingival sulcus and improves cleaning performance in finer areas. The tapered length is preferably 3 mm or more and 20 mm or less. The presence of island phases in the cross section can be confirmed at any position within the uniform cross-sectional portion, but for ease of confirmation, it is usually confirmed at the center of the uniform cross-sectional portion in the fiber axis direction in the form obtained. Furthermore, the range of 10% to 90% in the radial direction is determined by taking the center of the fiber as the origin and the outer periphery of the fiber as the 100% position. However, in the case of modified cross-section yarns, the outer periphery defined as the 100% position is considered to be the inscribed circle with the largest diameter. If the island phases are located closer to the center of the yarn than the above 10% range in the radial direction, the ability to clean narrow areas such as gingival sulci is improved, but the tip becomes brittle and prone to wear and breakage. Furthermore, if the island phases are located farther from the center of the yarn than the above 90% range in the radial direction, the durability of the tip is improved, but the recesses are more likely to come into contact with the gums, causing gum damage. Therefore, the region in which the island phases are located needs to be limited to a range of 10% to 90% in the radial direction from the fiber center, more preferably a range of 10% to 85% inclusive, even more preferably a range of 10% to 80% inclusive, and particularly preferably a range of 10% to 70% inclusive.

[0018] Furthermore, in the brush bristle material of the present invention, when the fiber center is taken as the origin, the proportion of the cross-sectional area perpendicular to the fiber axis that is occupied by the island phases within a range of 10% to 90% in the radial direction may be 5% to 100%, more preferably 5% to 95%, even more preferably 7% to 90%, and particularly preferably 7% to 85%. If the proportion of the island phases is below the above range, irritation to the gums and the like will be reduced, but improvement in cleaning ability in fine details will not be expected, and the performance will be no different from that of brush bristle material with a general tapered shape.

[0019] Furthermore, the brush bristle material of the present invention has a tapered portion at one or both ends, and at least a portion of the surface formed by the island phase exposed at the tapered portion forms a recess that is closer to the fiber center than the tapered surface formed by the sea phase.

[0020] In the island phase exposed in the tapered section, the area of ​​the recessed portion within the island phase is 1 μm 2 More than 300μm 2 Preferably, it is less than 1 μm 2 More than 280μm 2 Less than 1 μm is more preferable. 2 More than 250μm 2 It is more preferable if it is less than 5 μm. 2 More than 250μm 2 It is particularly preferable that the area is less than 1 / 2 of the area indicated by the arrows. Here, there are cases where the outer edge of the recess cannot be visually recognized as a clear outline. In such cases, the tapered surface formed by the sea phase is assumed to be in the 0° direction, and the outer edge of the recess is defined as the line connecting the points where the tangent to the curved surface transitioning to the recess is 1°. If the area of ​​the recess is below the above range, the plaque scraping performance may be reduced, and further, plaque captured in the recess may become difficult to detach, which may lead to concerns about the proliferation of bacteria. If the area of ​​the recess is above the above range, plaque captured in the recess may be more easily detached, but the plaque scraping performance may be reduced.

[0021] The island phase that appears in the tapered section has an area of ​​1 μm 2 More than 300μm 2The island phase has the following recesses, and the shortest distance between the outer edges of any two adjacent recesses present in the island phase is preferably 30 μm or less, more preferably 25 μm or less, and particularly preferably 20 μm or less. If the shortest distance between the outer edges of two adjacent recesses exceeds the above range, the density of the recesses present in the island phase will be low, and the plaque scraping performance may be reduced.

[0022] Furthermore, the depth of the recesses from the tapered surface formed by the sea phase toward the center of the fiber axis to the bottom of the recesses is preferably 0.5 μm to 30 μm, more preferably 0.5 μm to 28 μm, even more preferably 1 μm to 28 μm, and particularly preferably 1 μm to 25 μm. If the depth to the bottom of the recesses is below the above range, scraped plaque may not be captured, and cleaning performance may not be ensured. If the depth exceeds the above range, the captured plaque may not be easily released from the recesses, resulting in poor cleaning performance and possible bacterial growth. Here, the depth to the bottom of the recesses is defined as the longest distance, starting from the tapered surface formed by the sea phase and a plane including the outer edge of the recess, perpendicular to the fiber axis direction.

[0023] In the brush bristle material of the present invention, the method for forming the recesses is not particularly limited, and for example, the recesses can be formed by incorporating particulate additives such as various inorganic particles, various metal particles, and crosslinked polymer particles into the island phases, decomposing the island phases by hydrolysis using an alkaline aqueous solution, and releasing the additives. Another method is to distribute the same components as the sea phase with a reduced degree of crystalline orientation in the island phases, and locally increase the surface roughness of the island phases by alkaline hydrolysis, thereby forming the recesses.

[0024] The arithmetic mean roughness Ra of the tapered surface in the range from 50 μm to 100 μm from the thread tip is preferably 3.0 μm or less, more preferably 2.8 μm or less, even more preferably 2.5 μm or less, and particularly preferably 2.3 μm or less. The surface of the thread tip is preferably as smooth as possible to more smoothly penetrate narrow spaces such as the gingival sulcus. If the arithmetic mean roughness Ra of the surface of the sea phase exceeds the above range, the surface friction of the thread tip increases, making it difficult to slide, making it difficult to penetrate narrow spaces such as the gingival sulcus, and this may prevent the purpose of the present invention, which is to efficiently clean narrow spaces with little force, from being achieved.

[0025] The material of the brush bristle material of the present invention is not particularly limited, but for example, polyester resin, polyamide resin, thermoplastic elastomer, etc. are commonly used.

[0026] Here, the polyester resin referred to in the present invention is not particularly limited, but examples include polyethylene terephthalate, polybutylene terephthalate (hereinafter referred to as PBT), polyethylene naphthalate, polypropylene terephthalate, polymethylene naphthalate, polybutylene naphthalate, and polypropylene naphthalate, and among these, PBT is particularly preferred because it has sufficient physical properties as a brush bristle material and is ideal for post-processing such as tapering.

[0027] The processing for forming the tapered shape is not particularly limited, but hydrolysis treatment using an alkaline aqueous solution is preferred in order to stabilize the tip shape and obtain the shape described above.

[0028] Furthermore, the polyester resin may contain other dicarboxylic acid components and diol components as copolymerization components, provided that the object of the present invention is not impaired. For example, dicarboxylic acid components include terephthalic acid, isophthalic acid, phthalic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, benzophenonedicarboxylic acid, phenylindanedicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid. For example, diol components include aliphatic glycols such as ethylene glycol, propylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, decamethylene glycol, neopentylene glycol, cyclohexanediol, and cyclohexanedimethanol, o-xylylene glycol, p-xylylene glycol, m-xylylene glycol, 1,4-bis(2-hydroxyethoxy)benzene, 1,4-bis(2 -hydroxyethoxyethoxy)benzene, 4,4'-bis(2-hydroxyethoxy)biphenyl, 4,4'-bis(2-hydroxyethoxyethoxy)biphenyl, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, 2,2-bis[4-(2-hydroxyethoxyethoxy)phenyl]propane, 1,3-bis(2-hydroxyethoxy)benzene, 1,3-bis(2-hydroxyethoxyethoxy)benzene, 1,2-bis(2-hydroxyethoxy)benzene, 1,2-bis( Examples include aromatic glycols such as 4,4'-bis(2-hydroxyethoxyethoxy)benzene, 4,4'-bis(2-hydroxyethoxy)diphenyl sulfone, and 4,4'-bis(2-hydroxyethoxyethoxy)diphenyl sulfone, and diphenols such as hydroquinone, 2,2-bis(4-hydroxyphenyl)propane, resorcinol, catechol, dihydroxynaphthalene, dihydroxybiphenyl, and dihydroxydiphenyl sulfone, and two or more of these can be selected and used as appropriate.

[0029] Furthermore, the brush bristle material of the present invention can contain particles such as various inorganic particles, various metal particles, and crosslinked polymer particles, as well as known antioxidants, light resistance agents, weather resistance agents, ion exchange agents, color inhibitors, antistatic agents, various colorants, waxes, silicone oils, various surfactants, and various reinforcing fibers, depending on the purpose, as long as the effects of the invention are not impaired.

[0030] Furthermore, the cross-sectional shape of the cross section perpendicular to the fiber axis of the synthetic fibers used in the brush bristles of the present invention is not particularly limited, and may be any shape, such as a circle or an irregular cross section other than a circle, such as a triangle (1 in Figure 1), a square (2 in Figure 1), a hexagon (3 in Figure 1), or a star (4 in Figure 1). For example, in paint brushes and cosmetic brushes, a specific cross-sectional shape can be used to achieve the desired feel, as well as improve liquid and powder absorption, resulting in an excellent usability.

[0031] The brush bristles of the present invention have the above-mentioned properties and are therefore suitable for use at least in part in brushes, such as toothbrushes, tongue brushes, interdental brushes, cosmetic brushes, facial brushes, and paint brushes, and are also suitable for industrial applications such as application brushes and liquid crystal cleaning brushes.

[0032] The brush bristle material of the present invention can be efficiently produced by the melt spinning method described below. When melting the resin, ordinary conditions using an extruder-type spinning machine can be used, and the melt temperature should be set in the range of 150 to 230°C. To ensure the melt extrudability of the polymer while suppressing loss of strength due to thermal degradation, it is even more preferable to set the melt temperature 10 to 50°C higher than the melting point. The extruder extrusion pressure can be set to 2 to 30 MPa, the nozzle hole diameter to 0.1 to 20 mm, and the spinning speed to 0.3 to 100 m / min. Appropriate conditions can be selected depending on the thickness and cross-sectional shape of the monofilament to be used as the desired brush bristle material.

[0033] The melt-spun monofilament passes through a short gas zone and is then cooled in a cooling bath, where a liquid inert to the polymer, usually water, is used as the cooling medium. The cooling temperature should be 10 to 50°C lower than the crystallization temperature of the polymer.

[0034] The cooled and solidified monofilament is then sent to the drawing section. The preferred atmosphere (bath) for drawing and heat setting is a heated heat medium bath such as water or polyethylene glycol, a hot gas bath, or a steam bath. The drawing process must be carried out in multiple stages, and a total draw ratio of 4.5 to 5.5 times or more is generally sufficient to obtain high-strength monofilaments. The resulting monofilaments are then bundled and fixed with a fixture such as tape, and cut to a length appropriate for the intended use to produce brush bristle materials.

[0035] The processing for forming the tapered shape is not particularly limited, but hydrolysis treatment using an alkaline aqueous solution is preferred in order to stabilize the tip shape. [Example]

[0036] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Each item in the examples was measured by the following method. Note that, for measurements where the number of evaluations (n) is not specified, the evaluation was performed with n=1.

[0037] (1) Microscopic observation ·Equal cross section Diameter and minimum / maximum distance from center point to island phase: Five threads were randomly selected from the brush bristle material. Each thread was sliced ​​with a cutter at the center point in the length direction in a direction perpendicular to the fiber axis to a thickness of approximately 0.5 mm to form a cross section. The cross section was photographed at 50x magnification using a KEYENCE VK-X1100 laser microscope, and the minimum / maximum distance from the center point in the fiber axis direction to the island phase for each diameter and equal cross section was measured using the length measurement tool in the analysis application, and the average value was calculated. Island phase ratio: Five threads were randomly selected from the brush bristle material. Each thread was sliced ​​at its longitudinal center in a direction perpendicular to the fiber axis with a cutter to a thickness of approximately 0.5 mm to form a cross section. The cross section was photographed at 50x magnification using a KEYENCE VK-X1100 laser microscope, and the total area and island phase area within a range of 10% to 90% in the radial direction from the center point were measured using the area measurement tool in the analysis application. The island phase ratio was then calculated and its average value was obtained. Tapered section Depression area: For each of five strands randomly selected from the brush bristles, images of 10 depressions were taken at 150x magnification using a KEYENCE VK-X1100 laser microscope, and the area was measured using the area measurement tool in the analysis application, after which the average value was calculated. Depth of recess: For each of five strands randomly selected from the brush bristles, images of 10 recesses were taken at 150x magnification using a KEYENCE VK-X1100 laser microscope, and the maximum depth of the recesses was measured using the line roughness measurement tool in the analysis application, and the average value was calculated.

[0038] (2) Arithmetic mean roughness Ra For each of five threads randomly selected from the brush bristle material, the tapered portion was photographed at 20x magnification using a KEYENCE VK-X1100 laser microscope, and the arithmetic mean roughness Ra of the thread surface in the range of 50 μm to 100 μm from the tip of the tapered portion was measured using the line roughness measurement tool in the analysis application, and the average value was calculated.

[0039] (3) Cleanability evaluation Five toothbrushes of each standard were prepared (n=5) using various brush bristle materials. The object to be cleaned was an acrylic plate with a grid of five 3mm deep, 1mm wide wedge-shaped grooves, each orthogonal to the other, with a mesh size of 1mm x 1mm. Artificial plaque (manufactured by Nissin) was applied to the sidewalls of the grooves and allowed to dry at room temperature for 10 minutes. After drying, the toothbrush was placed in a Trinity Lab TL201Tt static friction tester and slid across the grid at a load of 100g and a speed of 10mm / s. If the artificial plaque was not completely removed after 10 strokes, the test was stopped. The number of strokes required to completely remove the artificial plaque was counted (in 0.5 increments, with one stroke considered 0.5), and the average was compared to evaluate cleaning performance.

[0040] (4) Usability evaluation Thirty subjects brushed their teeth and were asked to rate three items on a scale of 1 to 5: (A) whether they felt that plaque had been removed from the surface of their teeth, (B) whether they felt that plaque had been removed from between their teeth, and (C) whether they felt pain in their gums. For items (A) and (B), the closer to 5, the more "removed," and the closer to 1, the more "not removed." For item (C), the closer to 5, the more "no pain" they felt, and the closer to 1, the more "pain" they felt. After the test, the average score for each item was calculated to evaluate the usability.

[0041] [Example 1] The island phase was a mixture of PBT pellets (Toray Industries, Inc.'s "Trecon (registered trademark)" 1200S) blended with 10% by mass of titanium oxide powder with an average particle size of 5 μm. The sea phase was also composed of PBT pellets (Toray Industries, Inc.'s "Trecon (registered trademark)" 1200S) fed into a composite melt spinning machine. The mixture was melt-kneaded in the melt spinning machine and then extruded from a sea-island composite spinneret. The resulting mixture was then cooled and solidified in a cooling bath, stretched, and heat-set to produce a monofilament with a 200 μm diameter sea-island composite structure, as shown in Figure 2(a). The monofilament had eight 20 μm diameter island phases, each 20 μm in diameter from the center of the cross section perpendicular to the fiber axis, evenly spaced over a minimum distance of 40 μm and a maximum distance of 60 μm. The monofilament was then alkali-treated to produce a brush bristle with a tapered tip angle of 15° and a maximum length of 8 mm.

[0042] [Example 2] A brush bristle material having a tapered shape with a tip angle of 20° and a taper length of 8 mm as shown in Figure 2(b) was obtained in the same manner as in Example 1, except that the cross-sectional shape of the uniform cross-section portion was a square with one side measuring 200 μm.

[0043] [Example 3] A brush bristle material having a tapered shape with a tip angle of 19° and a taper length of 7.5 mm as shown in Figure 2(c) was obtained in the same manner as in Example 1, except that the cross-sectional shape of the uniform cross-sectional portion was a star shape formed by rotating the cross-sectional shape of the uniform cross-sectional portion of Example 2 by 45° and overlapping it.

[0044] [Example 4] A brush bristle material having a tapered shape with a tip angle of 14° and a taper length of 8.5 mm as shown in Figure 2(d) was obtained in the same manner as in Example 1, except that the cross-sectional shape of the island phase was a triangle with one side measuring 17.3 μm.

[0045] [Example 5] A brush bristle material having a tapered shape with a tip angle of 14° and a taper length of 9 mm, as shown in Figure 2(e), was obtained in the same manner as in Example 1, except that the cross-sectional shape of the island phase was a square with one side measuring 20 μm.

[0046] [Example 6] In a cross section perpendicular to the fiber axis of the uniform cross section portion, with the fiber center as the origin, 10% to 90% of the radial range was entirely formed of island phases, and a brush bristle material with a tapered tip angle of 15° and a taper length of 8 mm was obtained in the same manner as in Example 1, as shown in Figure 2(f).

[0047] [Comparative Example 1] A brush bristle material having a tapered tip angle of 14° and a taper length of 8.5 mm, as shown in Figure 3(g), was obtained in the same manner as in Example 1, except that 24 islands, each 5 μm in diameter from the center point of the cross section perpendicular to the fiber axis of the uniform cross section, were arranged at equal intervals with a shortest distance of 92.5 μm and a longest distance of 97.5 μm.

[0048] Comparative Example 2 A mixture of PBT pellets blended with 10% by mass of titanium oxide powder with an average particle size of 5 μm to form the sea phase, and PBT pellets as the island phase were fed into a composite melt spinning machine. In a cross section perpendicular to the fiber axis, with the fiber center as the origin, 90% or less of the radial range was entirely formed by the island phase, and the same method as in Example 1 was used to obtain a brush bristle material with a tapered shape with a tip angle of 16° and a taper length of 7.5 mm, as shown in Figure 3(h).

[0049] Comparative Example 3 A brush bristle material having a tapered tip angle of 13° and a taper length of 9 mm, as shown in Figure 3(i), was obtained in the same manner as in Example 1, except that eight islands, each 5 μm in diameter from the center point of the cross section perpendicular to the fiber axis of the uniform cross section, were arranged at equal intervals with a shortest distance of 2.5 μm and a longest distance of 7.5 μm.

[0050] Comparative Example 4 In a cross section perpendicular to the fiber axis of the uniform cross section portion, when the fiber center is taken as the origin and the outer periphery of the fiber is taken as the 100% position, a brush bristle material having a tapered shape with a tip angle of 12° and a taper length of 9.5 mm as shown in Figure 3(j) was obtained in the same manner as in Example 1, except that less than 10% of the range in the radial direction was entirely formed of island phases.

[0051] Comparative Example 5 A brush bristle material having a tapered shape with a tip angle of 15° and a taper length of 8 mm as shown in Figure 3(k) was obtained in the same manner as in Example 1, except that 10% by mass of titanium oxide powder with an average particle size of 20 μm was blended with PBT pellets to form an island phase.

[0052] Comparative Example 6 A mixture of PBT pellets as the main component and 10% by mass of titanium oxide powder with an average particle size of 5 μm was fed into a melt spinning machine, melted and kneaded inside the melt spinning machine, and then the molten material was extruded through a die. It was then cooled and solidified in a cooling bath, stretched, and heat-set to produce monofilaments with a diameter of 200 μm. These were then alkali-treated to form a tapered tip with a 12° angle and a 10 mm taper, yielding the brush bristle material shown in Figure 3(l).

[0053] Comparative Example 7 PBT pellets were fed into a melt spinning machine, melted and kneaded in the melt spinning machine, and then extruded from a die. The extruded material was then cooled and solidified in a cooling bath, stretched, and heat-set to produce monofilaments with a diameter of 200 μm. These monofilaments were then alkali-treated to produce brush bristle materials with a tapered tip angle of 15° and a taper length of 8 mm.

[0054] Table 1 shows the evaluation results of the brush bristles obtained in the above Examples and Comparative Examples.

[0055] [Table 1]

[0056] As is clear from the results shown in Table 1, in the brush bristles of the present invention (Examples 1 to 6), in a cross section perpendicular to the fiber axis, when the fiber center is taken as the origin, island phases having recesses are present only in a range of 10% to 90% in the radial direction. This means that dirt in gaps can be efficiently removed with a small number of strokes. Furthermore, a usability test showed that the brush bristles are less likely to cause pain when used, demonstrating that they possess unique functions.

[0057] [Table 2]

[0058] In contrast, as is clear from the results shown in Table 2, in a cross section perpendicular to the fiber axis, when the fiber center is taken as the origin, the brush bristles (Comparative Example 1) in which island phases having recesses are arranged over a range of 91% or more in the radial direction showed that the recesses did not reach the dirt in the grooves in the cleaning performance evaluation, and the brush bristles were unable to efficiently remove the dirt. In a cross section perpendicular to the fiber axis, when the fiber center is taken as the origin, the brush bristles (Comparative Example 2) in which sea phases having recesses are arranged over the entire range of more than 90% in the radial direction showed excellent tooth surface cleaning ability but tended to cause gum pain. In a cross section perpendicular to the fiber axis, when the fiber center is taken as the origin, the brush bristles (Comparative Example 3) in which island phases having recesses with a diameter of 5 μm are arranged over less than 10% in the radial direction showed reduced gum pain but did not improve cleaning ability. In a cross section perpendicular to the fiber axis, with the fiber center taken as the origin, the brush bristle material (Comparative Example 4) in which islands with recesses were arranged over an area of ​​less than 10% in the radial direction made it difficult for the tip of the thread to enter the gingival sulcus, which tended to worsen pain in the gums. 2 The brush bristles exceeding this (Comparative Example 5) showed good initial cleaning performance in the cleaning performance evaluation, but dirt became clogged in the recesses, making it impossible to improve cleaning performance. The brush bristles having recesses all over the brush bristles (Example 6) were excellent in cleaning performance but tended to cause pain in the gums. The brush bristles without recesses (Comparative Example 7) were less likely to cause pain in the gums, but had poor cleaning efficiency. [Industrial Applicability]

[0059] The present invention allows for efficient transmission of stress to targeted areas with minimal force, making it suitable for use in a variety of brushes, particularly toothbrushes, paintbrushes, cosmetic brushes, and industrial brushes. For example, when used as a toothbrush, it allows for efficient cleaning of narrow spaces such as tooth grooves with minimal force, while also minimizing excessive irritation to the gums. Furthermore, when used as a paintbrush, cosmetic brush, or industrial brush, it ensures high liquid and powder absorption only at the tip of the brush, eliminating the need for excessive liquid or powder, allowing for efficient work. [Explanation of symbols]

[0060] A Tapered section B Equal cross section 1~4 Variations in the shape of equal cross-section parts 5 Sea phase 6 Island Phase a-f Sea-island composite fibers (Examples) g~l Sea-island composite fiber (comparison example)

Claims

1. A brush bristle material is made of a resin composition having a sea phase and island phases extending in the fiber axis direction, and has a shape having a uniform cross-sectional portion having a constant fiber diameter and cross-sectional shape in the fiber axis direction, and a tapered portion extending from at least one end of the uniform cross-sectional portion and in which the fiber diameter gradually decreases, wherein, in a cross section perpendicular to the fiber axis, when the center of the fiber is taken as the origin and the outer periphery of the fiber is taken as the 100% position, the island phases are present only in a range of 10% to 90% in the radial direction, and at least a portion of the surface formed by the island phases exposed in the tapered portion forms a recess in a direction toward the center of the fiber relative to the tapered surface formed by the sea phase.

2. 2. The brush bristle material according to claim 1, wherein, when the center of the fiber is taken as the origin and the outer periphery of the fiber is taken as the 100% position, the island phases occupy 5% to 100% of the area of ​​a cross section perpendicular to the fiber axis within a range of 10% to 90% in the radial direction.

3. The taper length is 3 mm or more and 20 mm or less, and the island phase exposed in the taper portion has an area of ​​1 μm ２ 300 μm or more ２ 3. The brush bristle material according to claim 1, wherein the bristle material has the following recesses:

4. 3. The brush bristle material according to claim 1, wherein the depth of the recesses from the tapered surface formed by the sea phase toward the center of the fiber axis to the bottom of the recesses is 0.5 μm or more and 30 μm or less.

5. 3. The brush bristle material according to claim 1, wherein the arithmetic mean roughness Ra of the yarn surface within a range of 50 to 100 μm from the yarn tip is 3.0 μm or less.

Images