Brush bristle material

Abstract

To provide a brush bristle material capable of high efficient carrier of chemical components into a detailed part.SOLUTION: A brush bristle material is composed of a resin composition with a sea phase and an island phase extending in a fiber axial direction, and has: 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 an equal cross section part and reduces the fiber diameter. In a cross section orthogonal to a fiber axis, when a center of the fiber is an original point and an outer periphery of the equal cross section part of the fiber is a 100% position, the island phase exists only within a range from 10% to 90% of the radial direction, and a distance between a point nearest to the fiber center of the island phase and a farthest point is between 5.0 μm and 100 μm. In the tapered part, the island phase is more recessed across the whole region than 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] Brushes using the above-mentioned brush bristle materials, such as toothbrushes, are desired to have a good balance of tooth cleaning effect with the bristles, a soft feel that does not damage the object being cleaned, and a massaging effect on the gums, etc. Furthermore, by using them in combination with toothpaste that has effects such as strengthening tooth structure, preventing tooth decay, and preventing tartar deposition, a healthier oral environment can be maintained.

[0004] However, to fully utilize the effectiveness of toothpaste, it is necessary to deliver medicinal ingredients to the target area, and it can be difficult to meet this requirement if the brush bristles are made of monofilament of a single material all the way to the tip.

[0005] If the brush is made of a single monofilament material right down to the tip, thickening the bristles makes it difficult to deliver medicinal ingredients to narrow areas such as the gingival sulcus, and the brush is too harsh on the gums, making it more likely to cause damage.

[0006] Furthermore, in the case of brushes made from monofilament of a single material right down to the tip, simply making the bristles thinner will allow the bristles to penetrate into narrow spaces such as the gingival sulcus, but has the disadvantage that it will be difficult for highly viscous medicinal ingredients to reach deep into the brush.

[0007] Regarding the above, for example, patients with periodontal disease, especially those with advanced symptoms, need to apply medicinal ingredients to the affected area to prevent the condition from worsening, so it is desirable to brush the same area multiple times to deliver the medicinal ingredients to the affected area. However, since brushing more frequently can further damage weakened gums, there is a need for toothbrushes that can efficiently deliver the medicinal ingredients in toothpaste.

[0008] Brushes for cleaning and washing in other fields present generally similar problems.

[0009] As a countermeasure against the above, it is possible to load medicinal ingredients into the recesses by providing irregularities on the surface of the floss. However, because the recesses are shallow, more frequent brushing is required to deliver a sufficient amount of medicinal ingredients to the desired location. Furthermore, toothbrushes with irregularities on the entire surface of the floss, as in Patent Document 1, also have irregularities in the areas that come into contact with the gums, which can cause the irregular surface to come into contact with the gums during brushing and injure the gums. Furthermore, if irregularities are provided only on the tapered portion, as in Patent Document 2, penetration into gaps is reduced, which naturally results in brushing with greater force, causing gum injury. Furthermore, providing irregularities on the tip of the tapered portion, as in Patent Documents 1 and 2, also presents the problem of reduced abrasion resistance and breakage resistance. [Prior art documents] [Patent documents]

[0010] [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]

[0011] The present invention aims to solve the above problems and provide brush bristle materials that can efficiently deliver medicinal ingredients to the desired location during brushing and minimize irritation to the gums, something that was not possible with conventional technology. Furthermore, it is possible to minimize the deterioration of the wear resistance and breakage resistance of the tip portion and the deterioration of the bristle implantability. [Means for solving the problem]

[0012] The present invention has the following configuration. [1] A brush bristle material having a shape including 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 having a gradually decreasing fiber diameter, the shape being made of a resin composition having a sea phase and an island phase extending in the fiber axis direction, 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 uniform cross section 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 the distance between the closest point to the fiber center and the farthest point of the island phases is 5.0 μm to 100 μm, In the tapered section, the island phase is recessed over the entire area from the tapered surface formed by the sea phase. Bristles for brushes. [2] The brush bristle material according to [1], wherein the island phase occupies 1% to 100% of the area of ​​the cross section perpendicular to the fiber axis. [3] The brush bristle material according to [1] or [2], wherein the taper length is 3 mm or more and 20 mm or less, and the arithmetic mean roughness Ra of the tapered surface in the range of 50 to 100 μm from the tip of the thread is 3.0 μm or less. [Effects of the Invention]

[0013] The brush bristles of the present invention are suitable for toothbrushes, paint brushes, cosmetic brushes, and industrial brushes. When used as a toothbrush, they enable efficient delivery of medicinal ingredients, and when used as a paint brush, cosmetic brush, or industrial brush, they ensure high liquid and powder absorption only at the tip of the brush, allowing for efficient work. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing an example of a cross-sectional shape of a brush bristle material according to the present invention. [Figure 2] 1 is a schematic diagram showing an example of the cross-sectional and side surface configurations of brush bristles according to Examples 1 to 6. FIG. [Figure 3] 1 is a schematic diagram showing an example of the cross-sectional and side surface configurations of brush bristles of Comparative Examples 1 to 6. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below.

[0016] 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 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: (i) 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 uniform cross-sectional portion 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 the distance between the points closest to the fiber center and the farthest points on the island phases is 5.0 μm to 100 μm; and (ii) in the tapered portion, the island phases are recessed over the entire area from the tapered surface formed by the sea phase.

[0017] 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.

[0018] 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 overlapped 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 penetration into the gingival sulcus and improves the delivery of medicinal ingredients to detailed 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 radial range of 10% to 90% 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% radial range, the ability to carry medicinal ingredients to narrow areas such as the gingival sulcus is improved, but the tip becomes brittle and wears and breaks. Furthermore, if the island phases are located farther from the center of the yarn than the above 90% radial range, the tip durability is improved, but the island phases are more likely to come into contact with the gums, causing damage. Therefore, the region in which the island phases are located needs to be limited to a radial range of 10% to 90% from the center of the fiber, more preferably a range of 10% to 85%; even more preferably a range of 10% to 80%; and particularly preferably a range of 10% to 70%.

[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] 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 island phases within a range of 10% to 90% in the radial direction is preferably 1% to 100%, more preferably 1% to 95%, even more preferably 3% to 90%, and particularly preferably 5% to 85%. If the proportion of the island phases is below the above range, although irritation to the gums and the like can be reduced, the improvement in the ability to carry medicinal ingredients to fine details may be insufficient, and the performance may be no different from that of brush bristle material with a general tapered shape.

[0021] As described above, in the present invention, the island phases are (i) present in a cross section perpendicular to the fiber axis only in a range of 10% to 90% in the radial direction, when the center of the fiber is taken as the origin and the outer periphery of the fiber is taken as the 100% position, and in addition, the distance between the closest and furthest points of the island phases is 5.0 μm to 100 μm, and (ii) in the tapered portion, the island phases are recessed over the entire area from the tapered surface formed by the sea phase. In the present invention, the distance between the closest and furthest points of the island phases to the fiber center is sometimes referred to as the depth of the island phase. The depth of the island phase is 5.0 μm to 100 μm, preferably 5.0 μm to 90 μm, more preferably 5.0 μm to 80 μm, and even more preferably 5.0 μm to 70 μm. If the island depth is less than 5.0 μm, the medicinal ingredients cannot be captured, and no improvement in carrier properties can be expected.Also, if the island depth is more than 100 μm, the captured medicinal ingredients tend to remain in the recesses when the toothbrush is washed after brushing, making it easier for bacteria to grow.

[0022] In the brush bristle material of the present invention, the arithmetic mean roughness Ra of the tapered surface in the range from the tip of the thread to 50 to 100 μm should be 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 3.0 μm, it will be difficult to penetrate narrow spaces such as the gingival sulcus, and it may not be possible to efficiently carry medicinal ingredients into narrow spaces with little force, which is the purpose of the present invention.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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, by using a specific cross-sectional shape, the desired liquid and powder absorption capacity can be further improved, resulting in an excellent feel when used.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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, a hot gas bath, or a steam bath. The drawing process must be carried out in multiple stages, and a total draw ratio of typically 4.5 to 5.5 times or more is likely to produce 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.

[0033] 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]

[0034] 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 specifically stated, the evaluation was performed with n=1. (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 with a cutter 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 total area and island phase area within a range of 10% to 90% of the radius from the center point were measured using the area measurement tool in the analysis application. The island phase ratio was then calculated and the average value was obtained. Tapered section Depression state of island phases: Five strands randomly selected from the brush bristle material were observed in the fiber axis direction at 50x magnification using a KEYENCE VK-X1100 laser microscope, and it was confirmed that the entire island phase was depressed. Island depth: Five strands randomly selected from the brush bristle material were observed in the fiber axis direction at 50x magnification using a KEYENCE VK-X1100 laser microscope, and the distance between the point closest to the fiber center and the point farthest from the center of each island was measured, and the average value was calculated. (2) Arithmetic mean roughness Ra For each of five strands 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 50μm to 100μm from the tip of the thread at the tapered portion was measured using the line roughness measurement tool in the analysis application, and the average value was calculated. (3) Liquid carrier property evaluation Five toothbrushes (n=5) were prepared for each level, each with different bristle materials. A drop of artificial plaque (manufactured by Nissin) was placed on the toothbrush, and a straight line was drawn at a speed of 10 mm / sec with a load of 30 g until no artificial plaque was left on the copy paper. Liquid carrier properties were evaluated by comparing the average distance. (4) Usability evaluation Twenty subjects were asked to brush their teeth using Weltec's Concool Gel Coat F and evaluate three items on a scale of 1 to 5: (A) whether they felt that the medicinal ingredients had reached the tooth surface, (B) whether they felt that the medicinal ingredients had reached the gingival sulcus, and (C) whether they felt pain in the gums. For items (A) and (B), the closer to 5 is the more "reached," and the closer to 1 is the more "not reached." For item (C), the closer to 5 is the more "no pain felt," and the closer to 1 is the more "pain felt." After the test, the average score for each item was calculated to evaluate the usability.

[0035] [Example 1] PET pellets (Mitsui PET® J055, manufactured by Mitsui Chemicals) as the island phase and PBT pellets (Toraycon® 1200S, manufactured by Toray Industries, Inc.) as the sea phase were fed into a composite melt spinning machine, melt-kneaded in the melt spinning machine, and then the molten material was 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 cross-section, as shown in Figure 2(a), in which eight 20 μm diameter island phases were arranged at equal intervals of 40 μm and 60 μm, with the island phases measuring 20 μm in diameter from the center of the cross section perpendicular to the fiber axis. This monofilament was then alkali-treated to produce a brush bristle material with a tapered tip angle of 15° and a taper length of 8.5 mm.

[0036] [Example 2] A brush bristle material having a tapered shape with a tip angle of 21° 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.

[0037] [Example 3] 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(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.

[0038] [Example 4] A brush bristle material having a tapered shape with a tip angle of 13° and a taper length of 8 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.

[0039] [Example 5] A brush bristle material having a tapered shape with a tip angle of 15° and a taper length of 7.5 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.

[0040] [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).

[0041] [Comparative Example 1] A brush bristle material having a tapered tip angle of 15° and a taper length of 8 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.

[0042] Comparative Example 2 A brush bristle material having a tapered tip angle of 14° and a taper length of 9 mm, as shown in Figure 3(h), 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.

[0043] Comparative Example 3 In a cross section perpendicular to the fiber axis of the uniform cross section, 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 with a tip angle of 15° and a taper length of 8 mm as shown in Figure 3(i) 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.

[0044] Comparative Example 4 The 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 8.5 mm.

[0045] Table 1 shows the evaluation results of the brush bristles obtained in the above Examples and Comparative Examples.

[0046] [Table 1]

[0047] As is clear from the results shown in Table 1, in the brush bristle materials of the present invention (Examples 1 to 6), when the fiber center is taken as the origin in a cross section perpendicular to the fiber axis, the island phases are present only in a range of 10% to 90% in the radial direction, so that they can carry a large amount of liquid.Furthermore, a usability test showed that the brush bristle materials of the present invention have unique functions, as they are less likely to cause pain when used as a brush.

[0048] [Table 2]

[0049] In a cross section perpendicular to the fiber axis, with the fiber center as the origin, the brush bristle material (Comparative Example 1) had 24 islands arranged at equal intervals over a range of 91% or more in the radial direction. Although it was able to carry liquid efficiently in the liquid carrying evaluation, the evaluation score for the feeling that the medicinal ingredients had reached the gingival sulcus was lower in the usability survey.

[0050] In contrast, in a cross section perpendicular to the fiber axis, with the fiber center as the origin, a brush bristle material (Comparative Example 2) in which eight islands were arranged at equal intervals within an area of ​​less than 10% of the radius was able to carry liquid efficiently, but in a usability test, it tended to cause pain when using the brush.

[0051] In contrast, in a cross section perpendicular to the fiber axis, when the fiber center is taken as the origin, the brush bristle material (Comparative Example 3), in which less than 10% of the radial area is entirely formed of island phases, was able to carry liquid very efficiently, but in a usability survey, it was most likely to cause pain when using the brush.

[0052] The brush bristle material having no recesses (Comparative Example 4) had the lowest liquid carrying ability in the liquid carrying ability evaluation. [Industrial Applicability]

[0053] According to the present invention, brush bristle material can be obtained that has high liquid and powder absorption properties and is also capable of minimizing irritation to the human body, making it applicable to all types of brushes and particularly suitable for toothbrushes, paint brushes, cosmetic brushes, and industrial brushes.When used as a toothbrush, it becomes possible to efficiently carry more of the medicinal ingredients contained in toothpaste to narrow spaces such as the gingival sulcus, and when used as a paint brush, cosmetic brush, or industrial brush, it is possible to ensure high liquid and powder absorption properties only at the tip of the brush, allowing for efficient work. [Explanation of symbols]

[0054] 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~i Sea-island composite fiber (comparison example)

Claims

1. A brush bristle material is made of a resin composition having a sea phase and an island phase 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 having a gradually decreasing fiber diameter, 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 uniform cross section 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 the distance between the closest point to the fiber center and the farthest point of the island phases is 5.0 μm to 100 μm, In the tapered section, the island phase is recessed over the entire area from the tapered surface formed by the sea phase. Bristles for brushes.

2. 2. The brush bristle material according to claim 1, wherein the island phases occupy 1% to 100% of the area of ​​a cross section perpendicular to the fiber axis.

3. 3. The brush bristle material according to claim 1, wherein the taper length is 3 mm or more and 20 mm or less, and the arithmetic mean roughness Ra of the tapered surface in the range of 50 to 100 μm from the tip of the bristle is 3.0 μm or less.

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