Ballpoint pen refill

Abstract

To provide a ballpoint pen refill capable of maintaining a good handwriting state, in order to solve the problem that, when fine particles are interposed between a writing ball and a ball seat, the fine particles are driven into the ball seat, changing the surface condition of the ball seat and making it difficult for the writing ball to rotate, which may cause so-called line skipping.SOLUTION: In the present invention, a ball seat has a projected area of 0.018 mm2 or more and 0.030 mm2 or less when viewed from the axial front, a portion of a writing ball protrudes from a front end opening and is rotatably held between the front end opening and an inward protruding portion, a pressing member presses the writing ball forward, an ink composition for a ballpoint pen containing at least fine particles is directly stored in an ink storage portion, the fine particles have a central particle diameter of 0.20 μm or more and 0.46 μm or less, and the content of the fine particles in the ink composition for a ballpoint pen is 0.003 wt.% or more and 0.09 wt.% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ballpoint pen refill. [Background technology]

[0002] Conventionally, inventions have been disclosed in which fine particles are contained in an ink composition for a ballpoint pen for various purposes. Specifically, fine particles contained in an ink composition interposed between a writing ball and a ball seat roll between the writing ball and the ball seat, and the writing ball rotates while in contact with the ball seat, suppressing wear of the ball seat due to friction. In addition, Patent Document 1 discloses an invention of an ink for a ballpoint pen containing 0.002 to 2% by weight of fine particles with an average particle diameter of less than 0.1 μm for the purpose of suppressing wear of the ball seat and improving the outflow and stability over time of the ink in a fine-writing ballpoint pen with a ball diameter of 0.4 mm or less. A ballpoint pen is used by contacting and releasing the pen tip against the writing surface. When writing, the writing ball recedes due to the writing pressure and approaches and contacts the ball seat. In this case, if fine particles are interposed between the writing ball and the ball seat, the fine particles are driven into the ball seat, increasing the surface hardness of the ball seat and suppressing wear. Examples of the types of fine particles include alumina, titanium oxide, and silica. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2007-518838 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if fine particles are repeatedly fired into the ball seat, the particles will become dense and accumulate, worsening the surface condition of the ball seat and making it difficult for the writing ball to rotate, which can result in areas where the ink in the writing mark is not transferred to the writing surface, which is known as skipped lines.

[0005] An object of the present invention is to provide a ballpoint pen refill capable of maintaining good handwriting formation. [Means for solving the problem]

[0006] The present invention relates to a ballpoint pen refill comprising at least a ballpoint pen tip and an ink reservoir arranged behind the ballpoint pen tip, the ballpoint pen tip comprising at least a ball holder, a writing ball and a pressing member, the ball holder being formed with at least a front end opening, an ink flow hole, an inward protruding portion protruding from an inner wall surface forming the ink flow hole, and a ball receiving seat on a front side wall of the inward protruding portion, the ball receiving seat having a projected area of ​​0.018 mm2 as viewed from the axial front. 2 More than 0.030mm 2 a portion of the writing ball protruding from the front end opening and rotatably held between the front end opening and the inward protruding portion; The pressing member presses the writing ball forward, and the ink storage section directly stores an ink composition for a ballpoint pen containing at least fine particles, the fine particles having a central particle diameter of 0.20 μm or more and 0.46 μm or less, and the content of the fine particles in the ink composition for a ballpoint pen is 0.003% by weight or more and 0.09% by weight or less. Effect of the Invention

[0007] The ballpoint pen refill according to the present invention contains fine particles in the ink composition for ballpoint pens, which can suppress wear of the ball holder between the writing ball and the ball seat. The fine particles have a median particle diameter of 0.20 μm or more and 0.46 μm or less, a content of 0.003% by weight or more and 0.09% by weight or less, and a projected area of ​​the ball seat as viewed from the axial front is 0.018 mm 2More than 0.030mm 2 By doing as described below, even if the writing ball that has advanced moves back against the pressing member due to the writing pressure during writing, fine particles present between the writing ball and the ball seat are less likely to be driven into the ball seat, the surface condition of the ball seat is less likely to change, and good handwriting formation conditions can be maintained. [Brief description of the drawings]

[0008] [Figure 1] Vertical cross-sectional view of ballpoint pen refill 1 [Diagram 2] Vertical cross-sectional view of ballpoint pen tip 2 [Diagram 3] Enlarged view of part A in Figure 2 [Figure 4] A cross-sectional view of the ballpoint pen tip 2 taken along the line BB' as viewed from the axial front. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the applicator according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiment, and various modifications can be made without departing from the gist of the present invention. *Regarding claim 1.

[0010] 1 is a vertical cross-sectional view of a ballpoint pen refill 1 according to the present invention, and FIG. 2 is a vertical cross-sectional view of a ballpoint pen tip 2. The ballpoint pen refill 1 is composed of at least the ballpoint pen tip 2 and an ink reservoir 3.

[0011] The ballpoint pen tip 2 is composed of at least a ball holder 4, a writing ball 5, and a spring 6 as a pressing member. The ballpoint pen tip 2 is a member for discharging ink supplied from an ink reservoir 3 arranged behind the ballpoint pen tip 2 onto a writing surface. Inside the ball holder 4, the writing ball 5 and the spring 6 are arranged.

[0012] Fig. 3 is an enlarged view of part A in Fig. 2, and Fig. 4 is a cross-sectional view taken along line BB' as viewed from the axial front of ballpoint pen tip 2. Note that writing ball 5 and spring 6 are omitted from Fig. 4. Ball holder 4 is a hollow member penetrating in the axial direction. Ball holder 4 is formed with at least a front end opening 7, an ink flow hole 8, an inward protruding portion 9 protruding from the inner wall surface that forms ink flow hole 8, and a ball seat 9a on the front side wall of inward protruding portion 9.

[0013] The material of the ball holder 4 may be, for example, stainless steel, nickel silver, or copper alloy such as brass. Considering the abrasion resistance against the writing ball 5 during writing and the corrosion resistance against the ballpoint pen ink composition L, stainless steel is preferred, and austenitic stainless steel SUS304 and ferritic stainless steel SUS430 are preferably used. In addition, in order to have good processability and to suppress unintended dents and deformation, it is preferable to set the Vickers hardness (HV) to 150 or more and 300 or less. In order to improve machinability, one or more so-called "free-cutting components" such as sulfur and lead may be added. In consideration of the natural environment, it is preferable to use lead in place of bismuth, which can impart the same level of processability.

[0014] The inner diameter of front end opening 7 is formed to be smaller than the diameter of writing ball 5. The inner edge of front end opening 7 restricts the forward movement of writing ball 5, preventing writing ball 5 from slipping out in the forward direction.

[0015] The inward protrusions 9 are formed to protrude radially inward from the inner wall surface that forms the ink flow hole 8 of the ball holder 4. The inward protrusions 9 are a plurality of protruding pieces spaced at equal intervals in the circumferential direction. The ink composition L for a ballpoint pen can flow through the arrow grooves 10 that are the gaps between the protruding pieces.

[0016] A ball seat 9a is formed in the front of the side wall of the inward protruding portion 9. The ball seat 9a is the surface that comes into contact with the writing ball 5 that recedes due to writing pressure when writing. The ball seat 9a is formed by deforming the inward protruding portion 9 by pressing the writing ball 5 against the inward protruding portion 9. A flat portion 9b, which will be described later, is present in the front of the side wall of the inward protruding portion 9, and by pressing the writing ball 5 against part of the flat portion 9b, a curved surface with approximately the same curvature as the writing ball 5 is transferred to the flat portion 9b, forming the ball seat 9a. The ball seat 9a is formed on all of the protruding pieces of the inward protruding portion 9.

[0017] The ball seat 9a has a projected area of ​​0.018 mm2 as viewed from the axial front. 2 More than 0.030mm 2 The projected area of ​​ball seat 9a as viewed from the axial front is calculated as the sum of the projected areas of the surfaces that function as ball seat 9a and are formed on each protruding piece of inward protruding portion 9. The projected area of ​​ball seat 9a as viewed from the axial front can be adjusted by appropriately changing the inner diameter of ink flow hole 8, the width of arrow groove 10, the number of arrow grooves 10, and the outer diameter of ball seat 9a.

[0018] The projected area as viewed from the axial front of ball seat 9a can be determined by forming ball seat 9a, inserting a small-diameter metallic rod-shaped member into the rear end of ballpoint pen tip 2, pressing writing ball 5 to remove it, obtaining a measurement sample in which ball seat 9a can be confirmed, placing it vertically with the front part facing up so that ball seat 9a can be confirmed using a Keyence Corporation VHX-6000 microscope (VH-ZST lens), and photographing a radial and horizontal front view of the ballpoint pen tip from the front to the rear at 200x magnification, and using the image measurement function to determine the projected area as viewed from the axial front of ball seat 9a from the photographed image.

[0019] The writing ball 5 partially protrudes from the front end opening 7 and is rotatably held between the front end opening 7 and the inward protruding portion 9. The writing ball 5 can be one having a diameter of 0.18 mm or more and 2.00 mm or less, and preferably has a general size of 0.30 mm or more and 1.00 mm or less. The smaller the diameter of the writing ball 5, the greater the pressure applied to the ball seat 9a during writing, making it easier for fine particles to be driven into the ball seat 9a. In addition, the ratio of the particle diameter of the fine particles to the projected area of ​​the ball seat 9a becomes larger, so the rate at which the surface of the ball seat changes when the fine particles are driven into the ball seat 9a becomes larger, resulting in a large impact. In particular, excellent effects can be obtained with a ballpoint pen having a small diameter of the writing ball 5 of 0.4 mm or less.

[0020] The material of the writing ball 5 can be appropriately selected from, for example, cemented carbide mainly composed of tungsten carbide, metals such as stainless steel, aluminum, and steel, ceramics such as silicon carbide, silicon nitride, titanium nitride, chromium carbide, alumina, and zirconia, resin materials such as polyethylene resin, polypropylene resin, polyacetal resin, and polyamide resin, and glass.

[0021] The spring 6 as a pressing member presses the writing ball 5 forward. The spring 6 is inserted from the rear of the ball holder 4. The spring 6 is placed inside the ball holder 4 in a state where its entire length is compressed. The front end of the spring 6 is in contact with the writing ball 5. The rear end of the spring 6 is in contact with the inner wall surface of the retaining portion 11 formed by the entire circumference of the rear end of the ball holder 4 being tilted radially inward. The spring 6 constantly presses the writing ball 5 forward by the restoring force caused by compression. The writing ball 5 pressed by the spring 6 is pressed against the inner edge forming the front end opening 7 of the ball holder 4, thereby blocking the flow path of the ballpoint pen ink composition L when not writing, and preventing ink leakage. The method of preventing the spring 6 from falling out is not limited to the above, and since the spring 6 can be fixed by creating a portion in the rear hole of the ball holder 4 whose inscribed circle diameter is smaller than the outer diameter of the spring 6, it may be formed by a method of forming a cutting piece by gouging out the inner wall surface of the rear end of the ball holder 4 by broaching, or by a method of creating a recess in the side wall portion of the ball holder 5 by punching or the like to form a convex portion on the inner wall surface. Alternatively, the method of preventing the spring 6 from falling out can be appropriately selected, such as using a separate member connected to the rear end of the ballpoint pen tip.

[0022] Examples of materials that can be used for the spring 6 include stainless steel wire such as SUS304, hard steel wire, piano wire, and resins such as polycarbonate and polyether ether ketone. Also, springs 6 whose surfaces are subjected to a surface coating treatment such as nickel plating can be used.

[0023] The ink reservoir 3 is a hollow cylindrical member that penetrates in the axial direction. The ink reservoir 3 can be manufactured by any method, such as extrusion molding or injection molding, using polyethylene resin, polyester resin, polypropylene resin, or the like. In addition to the ink composition L for a ballpoint pen, an ink backflow prevention body M, such as a high-viscosity fluid or a solid mobile plug, can also be disposed inside the ink reservoir 3 so as to contact the rear end interface of the ink composition L for a ballpoint pen.

[0024] A ballpoint pen ink composition L containing at least fine particles is directly stored in the ink storage section 3. By containing fine particles in the ballpoint pen ink composition L, the fine particles rotate between the writing ball 5 and the ball seat 9a, and wear of the ball seat 9a and therefore of the ball holder 4 can be suppressed.

[0025] As the fine particles, for example, alumina, titanium oxide, silica, silicon carbide, tungsten carbide, etc. can be appropriately used.

[0026] Examples of alumina particles that can be used include high-purity alumina AKP-50 (median particle size 0.20 μm), AKP-30 (median particle size 0.30 μm), AKP-20 (median particle size 0.46 μm), and AA-03 (median particle size 0.44 μm) manufactured by Sumitomo Chemical Co., Ltd., WA#30000 (median particle size 0.35 μm) and WA#20000 (median particle size 0.45 μm) manufactured by Fujimi Incorporated Co., Ltd., and alumina powder AP03 (median particle size 0.3 μm) manufactured by Harzok Japan Co., Ltd. These aluminas may be used alone or in combination of two or more types.

[0027] Examples of titanium oxide particles that can be used include titanium oxide JR-301 (median particle size 0.30 μm), JR-403 (median particle size 0.25 μm), JR-405 (median particle size 0.21 μm), JR-605 (median particle size 0.25 μm), and JR-800 (median particle size 0.27 μm) manufactured by Teika Corporation, titanium oxide CR-50 (median particle size 0.25 μm) and CR-Super70 (median particle size 0.25 μm) manufactured by Ishihara Sangyo Kaisha, Ltd., titanium oxide KRONOS KR-380N (median particle size 0.30 μm), TITANIX JR-800 (median particle size 0.27 μm) manufactured by Titan Kogyo Co., Ltd., and Ti-Pure R-900 (median particle size 0.41 μm) manufactured by DuPont Japan Limited. These titanium oxide particles may be used alone or in combination of two or more.

[0028] As the silica particles, for example, colloidal silica Snowtex MP-2040 (median particle size 0.20 μm) and MP-4540M (median particle size 0.45 μm) manufactured by Nissan Chemical Co., Ltd. can be appropriately used. These silica particles may be used alone or in combination of two or more kinds.

[0029] The median particle diameter of the microparticles is 0.20 μm or more and 0.46 μm or less. The median particle diameter of the microparticles is the diameter at which the larger powder and the smaller powder are equal in amount when the powder is divided into two at a certain particle diameter, and is also called the median diameter, median diameter, d50, etc. The median particle diameter of the microparticles can be measured, for example, by adding ethanol to the target microparticles and dispersing them with ultrasonic waves for 20 minutes using a dynamic light scattering particle size distribution analyzer (NanotracWave2-EX150) manufactured by Microtrack Bell Co., Ltd.

[0030] The content of the fine particles in the ink composition L for ballpoint pens is 0.003% by weight or more and 0.09% by weight or less. By containing 0.003% by weight or more and 0.09% by weight or less of fine particles having a median particle diameter of 0.20 μm or more and 0.46 μm or less with respect to the total amount of the ink composition L for ballpoint pens, even if the writing ball 5 that has advanced during writing is retracted against the spring 6, which is a pressing member, by the writing pressure, the fine particles present between the writing ball 5 and the ball seat 9a have a projected area of ​​0.018 mm2 as viewed from the front in the axial direction. 2 More than 0.030mm 2 The writing ball 5 and the ball seat 9a are not easily driven into a ball seat 9a of a size smaller than 1 mm. Since the surfaces of the writing ball 5 and the ball seat 9a are not perfect mirror surfaces but have roughness with some unevenness, it is presumed that the fine particles with such a central particle size and blending amount rotate between the writing ball 5 and the ball seat 9a and exert a wear suppression effect, but when subjected to pressure such as being driven into the ball seat 9a by the writing ball 5, they enter minute recesses or are pushed out into other spaces, making it difficult for the phenomenon of being driven into the ball seat 9a and becoming unable to rotate to occur. Therefore, the surface condition of the ball seat 9a is unlikely to change, skipped lines are unlikely to occur, and good handwriting formation can be maintained.

[0031] The spring load of the spring 6 that presses the writing ball 5 forward is preferably 0.05 N or more and 0.15 N or less. Using a spring with a spring load of 0.05 N or more and 0.15 N or less provides a load that can prevent ink leakage when not writing, but is weak enough that the writing ball 5 is unlikely to separate from the ball seat 9a even if the writing pressure decreases slightly when writing. In other words, fine particles that exist between the writing ball 5 and the ball seat 9a at that time are less likely to be struck into the ball seat 9a repeatedly due to changes in writing pressure, and good handwriting formation and writing feel can be maintained.

[0032] The amount of axial movement D of the writing ball 5 is preferably 0.010 mm or more and 0.025 mm or less. The amount of axial movement of the writing ball 5 can be adjusted by the amount of processing when the front end opening 7 of the ball holder 4 is crimped inward to prevent the writing ball 5 from falling out and the amount of pressing when forming the ball seat 9a.

[0033] If the amount of axial movement of the writing ball 5 is 0.010 mm or more and 0.025 mm or less, when writing is not being performed and the writing ball 5 is separated from the ball seat 9a by the spring 6, which is a pressing member, the thickness of the ink composition L for ballpoint pens interposed between the writing ball 5 and the ball seat 9a can be made appropriate, and it is presumed that this can prevent the fine particles in the ink composition L for ballpoint pens from getting too far between the writing ball 5 and the ball seat 9a. Therefore, the fine particles are less likely to be driven into the ball seat 9a, and good handwriting formation and writing feel can be maintained.

[0034] It is preferable that the opening angle α, which is the apex angle of a virtual cone whose generating line is a line segment along the flat surface portion 9b at the front of the side wall of the inward protruding portion 9, is 90° or more and 120° or less. The flat surface portion 9b is a plane that is connected to the ball seat 9a at the front of the side wall of the inward protruding portion 9. In this embodiment, the flat surface portion 9b is located radially outward from the ball seat 9a. If the opening angle α is in an angle range of 90° or more and 120° or less, which is not too open, the shape change of the ball seat 9a due to so-called springback that occurs when the writing ball 5 is struck against the inward protruding portion 9 to form the ball seat 9a with approximately the same curvature as the curvature of the ball is reduced, and it is presumed that the curvature of the curved surface formed on the surface of the ball seat 9a is closer to the curvature of the writing ball 5. Therefore, even if the writing ball 5 that has advanced moves back against the spring 6, which is a pressing member, due to the writing pressure during writing, the ball seat 9a can disperse the pressure received from the writing ball 5, making it difficult for fine particles to be driven into the ball seat 9a, and good handwriting formation and writing feel can be maintained.

[0035] The opening angle α, which is the apex angle of a virtual cone whose generating line is a line segment along the flat portion 9b at the front of the side wall of the inward protrusion 9, can be calculated by inserting a small-diameter metallic rod-shaped member into the rear end of the ballpoint pen tip 2, pressing the writing ball 5 to remove the writing ball 5, and measuring the shape of the flat portion 9b of the front side wall of the inward protrusion located radially outward from the ball seat using a device for measuring surface shape such as a laser microscope (VK-X3100) manufactured by Keyence Corporation, and then calculating the opening angle α, which is the apex angle of a virtual cone whose generating line is a line segment along the flat portion 9b.

[0036] The opening angle α is the apex angle of a virtual cone whose generating line is a line segment along the flat surface 9b before the ball seat 9a is formed. It can be adjusted by adjusting the angle of the cutting tool tip when forming the flat surface 9b so that a virtual cone is formed when the line segment along the flat surface 9b is taken as the generating line. EXAMPLES

[0037] Examples and comparative examples according to the present invention will be described below, but the descriptions thereof are not intended to limit the technical scope of the present invention in any way.

[0038] The ballpoint pens of the examples and comparative examples were prepared using the ballpoint pen tip and the ballpoint pen ink composition shown in Table 1. The ballpoint pen tip (material of ballpoint pen holder: stainless steel, material of writing ball: carbide) was connected to an ink holder, and the ink holder was filled with the ballpoint pen ink composition to prepare a ballpoint pen refill. The ballpoint pen refill was attached to a ballpoint pen barrel (product name: Calme, product code: BXA105, manufactured by Pentel Co., Ltd.), and the results of the measurements and evaluations described below are also shown in Table 1.

[0039] [Table 1]

[0040] The components of the inks used in the examples and comparative examples are shown below in detail. Pigment (1): Printex35 (carbon black, manufactured by Evonik Japan Co., Ltd.) Pigment (2): FUJI FAST RED 8800 (CI Pigment Red 254, manufactured by Fuji Pigment Co., Ltd.) Pigment (3): DCC Blue A3R (CI Pigment Blue 60, manufactured by Dominion Color Corporation) Dye (1): VALIFAST VIOLET 1731 (Acid Violet 17 (triarylmethane acid dye) and onium salt of methine basic dye, manufactured by Orient Chemical Industries Co., Ltd.) Dye (2): OIL BLUE 613 (a mixture of CISolvent Blue 5 (triarylmethane dye) and rosin-modified resin, manufactured by Orient Chemical Industry Co., Ltd.) Dye (3): Aizen Spilon Yellow C-GNH New (yellow oil dye, manufactured by Hodogaya Chemical Industry Co., Ltd.) Dye (4): Aizen Spilon Red C-GH (a mixture of CI Basic Red 1:1 and an acidic substance, manufactured by Hodogaya Chemical Industry Co., Ltd.) Dye (5): VALIFAST YELLOW 1108 (disazo dye, manufactured by Orient Chemical Industries Co., Ltd.) Dye (6): VALIFAST BLUE 1631 (Basic Blue 7 (triarylmethane dye) and onium salt of colorless acid radical, manufactured by Orient Chemical Industry Co., Ltd.) Organic solvent (1): Ethylene glycol isopropyl ether Organic solvent (2): Ethylene glycol monophenyl ether Organic solvent (3): Diethylene glycol monomethyl ether Resin (1): S-LEC B BL-1 (polyvinyl butyral, manufactured by Sekisui Chemical Co., Ltd.) Resin (2): S-LEC B BH-3 (polyvinyl butyral, manufactured by Sekisui Chemical Co., Ltd.) Resin (3): PVP K-90 (Polyvinylpyrrolidone, manufactured by Ashland Japan Co., Ltd.) Resin (4): TEGO VariPlus SK (polyol resin, manufactured by Evonik Industries, Ltd.) Phosphate ester (1): Phosphanol LB-400 (polyoxyethylene alkyl ether phosphate, manufactured by Toho Chemical Industry Co., Ltd.) Organic amine (1): Triisopropanolamine Surfactant (1): DOWSIL L-7002 (polyether modified silicone oil, manufactured by Dow Toray Co., Ltd.) Surfactant (2): Nikkol HCO-10 (POE hydrogenated castor oil, manufactured by Nikko Chemicals Co., Ltd.) Surfactant (3): Uniol D-2000 (polypropylene glycol, manufactured by NOF Corporation) Surfactant (4): NIKKOL BL-9EX (polyoxyethylene lauryl ether, manufactured by Nikko Chemicals Co., Ltd.) Microparticles (1): AKP-3000 (alumina, median particle size 0.70 μm, manufactured by Sumitomo Chemical Co., Ltd.) Microparticles (2): AKP-20 (alumina, median particle size 0.46 μm, manufactured by Sumitomo Chemical Co., Ltd.) Microparticles (3): AKP-50 (alumina, median particle size 0.20 μm, manufactured by Sumitomo Chemical Co., Ltd.) Microparticles (4): AP01 (alumina, central particle size 0.10 μm, manufactured by Harzok Japan Co., Ltd.) Microparticles (5): JR-800 (titanium oxide, median particle size 0.27 μm, manufactured by Teika Corporation) Microparticles (6): MP-4540M (colloidal silica, median particle size 0.45 μm, manufactured by Nissan Chemical Industries, Ltd.)

[0041] Of the above components, the entire amount of organic solvent (3) and the entire amount of resin (1) were stirred, mixed and dissolved at 70°C, and then cooled to room temperature, after which the entire amount of pigment (1) was added, and the mixture was passed 10 times using a Dyno Mill (beads mill, manufactured by Shinmaru Enterprises Co., Ltd.) using zirconia beads with a diameter of 0.3 mm to obtain a pigment paste. Next, the remaining materials were added to this paste, and the mixture was stirred at 70°C for 3 hours to obtain an oil-based ink composition for ballpoint pens.

[0042] Ink is manufactured by mixing the dispersed pigment with other ingredients, such as a viscosity adjusting resin, a solvent, a lubricant, etc., and dissolving and mixing the mixture in a stirrer such as a homogenizer until it becomes uniform. In some cases, however, there is no problem in further dispersing the mixed ink in a disperser, or filtering or centrifuging the resulting ink to remove coarse particles and insoluble components.

[0043] (Evaluation method) A handwriting test was conducted in which participants hand-wrote "Dates of the National Diet" on writing paper (each character was approximately 1 cm square, 400 characters were written per sheet of writing paper), and 50 sheets were written. The handwriting in the handwriting test was visually evaluated, and the writing feel was evaluated sensorily. The evaluation was performed according to the following criteria. Handwriting evaluation A: Even on the 50th sheet of writing paper, there are no skipped lines and the handwriting is clear. B: Even on the 50th sheet of writing paper, there are almost no skipped lines and the handwriting is clear. C: From the 30th sheet onwards, lines are continually skipped and the handwriting is unclear. D: From the 10th sheet onwards, lines are continually skipped and the handwriting is unclear. Writing feel evaluation A: Even on the 50th sheet of writing paper, the writing feel is still very smooth. B: The writing feel changes slightly as you write, but the smooth writing feel is maintained even on the 50th sheet of writing paper. C: The resistance increases with writing, and the writing feel becomes slightly worse after the 30th sheet of writing paper. D: The resistance increases with writing, and the writing feel clearly worsens after the 10th sheet of writing paper.

[0044] In the ballpoint pens of Examples 1 to 18, the projected area of ​​the ball seat 9a as viewed from the axial front is 0.018 mm 2 More than 0.030mm 2 The median particle diameter of the fine particles is 0.20 μm or more and 0.46 μm or less, and the content of the fine particles in the ink composition for the ballpoint pen is 0.003% by weight or more and 0.09% by weight or less. Therefore, compared with the ballpoint pens of Comparative Examples 1 to 6, the fine particles are less likely to be driven into the ball seat 9a, so the surface state of the ball seat is less likely to change, and good handwriting formation state can be maintained.

[0045] In particular, in the ballpoint pens of Examples 2 to 18, the spring load of spring 6 is 0.05 N or more and 0.15 N or less, so that the fine particles present between writing ball 5 and ball seat 9a are less susceptible to being repeatedly struck into ball seat 9a due to changes in writing pressure during writing, thereby enabling good handwriting formation and writing feel to be maintained.

[0046] In particular, in the ballpoint pens of Examples 3 to 18, the axial movement amount of the writing ball 5 is 0.010 mm or more and 0.025 mm or less. Therefore, when the writing ball 5 is separated from the ball seat 9a by the spring 6 during non-writing, the thickness of the ballpoint pen ink composition L interposed between the writing ball 5 and the ball seat 9a can be made appropriate, and it is presumed that this can prevent the fine particles in the ballpoint pen ink composition L from getting too far between the writing ball 5 and the ball seat 9a. As a result, the fine particles are less likely to be driven into the ball seat 9a, and good handwriting formation and writing feel can be maintained.

[0047] In particular, in the ballpoint pens of Examples 4 to 18, the opening angle α, which is the apex angle of a virtual cone whose generating line is a line segment along the flat portion 9b in front of the side wall of the inward protruding portion 9, is 90° or more and 120° or less, so that it is presumed that the shape change of the ball seat 9a due to so-called spring back that occurs when the writing ball 5 is struck against the inward protruding portion 9 to form a ball seat 9a with approximately the same curvature as the curvature of the ball is reduced, and the curvature of the curved surface formed on the surface of the ball seat 9a becomes closer to the curvature of the writing ball 5. Therefore, even if the writing ball 5 that has advanced during writing is moved back against the spring 6, which is a pressing member, by the writing pressure, the pressure that the ball seat 9a receives from the writing ball 5 can be dispersed, so that fine particles are less likely to be driven into the ball seat 9a, and a good handwriting formation state and writing feel can be maintained.

[0048] In Comparative Example 1, the median particle diameter of the microparticles exceeds 0.46 μm, so that the microparticles are easily driven into the ball seat 9a. Also, when the microparticles are driven into the ball seat 9a, the ratio of the particle diameter of the microparticles to that of the ball seat 9a is large, so that the surface condition of the ball seat 9a is easily changed, resulting in skipped lines and a deterioration in the writing feel.

[0049] In Comparative Example 2, the microparticles had a central particle diameter of less than 0.20 μm, so the microparticles easily penetrated the unevenness present on the surfaces of the writing ball 5 and ball seat 9a, and the wear-inhibiting effect of the microparticles on the ball seat 9a was not fully exerted, resulting in a deterioration in the writing feel as writing was performed.

[0050] In Comparative Example 3, the content of microparticles in the ballpoint pen ink composition L was less than 0.003% by weight, so it is presumed that the microparticles were not able to effectively suppress wear on the ball seat 9a, and the writing feel deteriorated as writing progressed.

[0051] In Comparative Example 4, the content of microparticles in the ink composition L for ballpoint pen exceeds 0.09% by weight, and therefore the proportion of microparticles in the ink composition is large. It is therefore presumed that the microparticles are easily driven into the ball seat 9a, causing the surface condition of the ball seat 9a to change, resulting in skipped lines and a deterioration in the writing feel.

[0052] In Comparative Example 5, the projected area of ​​the ball seat 9a as viewed from the axial front is 0.018 mm 2 Since the projected area of ​​the ball seat 9a is less than 0.018 mm, the pressure that the ball seat 9a receives during writing is large, and fine particles are easily driven into the ball seat 9a. 2 Compared to ball seat 9a with the above projected area, the rate at which the surface condition of ball seat 9a changes when the same number of microparticles are shot into ball seat 9a is greater, and it is presumed that this changes the friction between writing ball 5 and ball seat 9a from what was designed, making it difficult for writing ball 5 to rotate, resulting in skipped lines and a worsening writing feel.

[0053] In Comparative Example 6, the projected area of ​​the ball seat 9a as viewed from the axial front is 0.030 mm 2 It is presumed that because this exceeds the limit, the contact area between the writing ball 5 and the ball seat 9a becomes too large, increasing the frictional resistance, which becomes greater than the frictional resistance between the writing ball 5 and the paper surface, impeding the rotation of the writing ball 5, causing skipped lines, and deteriorating the writing feel.

[0054] In Comparative Examples 1 to 6, the spring load exceeds 0.15 N, and therefore when the writing pressure is slightly reduced during writing, the forward pressing force of the spring on the writing ball 5 is likely to be excessive. When the writing pressure is slightly reduced, the writing ball 5 is separated from the ball seat 9a by the forward pressing force of the spring, and the ink composition gets between the writing ball 5 and the ball seat 9a. When the writing pressure again exceeds the forward pressing force of the spring, the writing ball 5 comes into contact with the ball seat 9a, and this action of fine particles being shot into the ball seat 9a is repeated, which is presumably why the surface condition of the ball seat 9a changes, causing skipped lines and a worsening writing feel.

[0055] In Comparative Examples 1 to 4 and 6, the amount of movement of the writing ball 5 in the axial direction exceeds 0.025 mm, so that when the writing ball 5 is separated from the ball seat 9a by the spring 6, which is a pressing member, many fine particles are present due to the thickness of the ink composition L for ballpoint pens interposed between the writing ball 5 and the ball seat 9a, and the fine particles are easily driven into the ball seat 9a. Furthermore, since the opening angle α, which is the apex angle of a virtual cone whose generatrix is ​​a line segment along the flat surface portion 9b in front of the side wall of the inward protruding portion 9, exceeds 120°, the springback that occurs when the ball seat 9a is formed becomes large, so that the curvature of the curved surface formed on the surface of the ball seat 9a and the curvature of the writing ball 5 become large, and the pressure received from the writing ball 5 cannot be received by the entire ball seat 9a, and the pressure is concentrated on a part of the ball seat 9a, so that the fine particles are easily driven into the ball seat 9a. As a result, it is presumed that the surface condition of the ball seat 9a changes, line skipping occurs, and the writing feel deteriorates. [Explanation of symbols]

[0056] 1 ballpoint pen refill 2 Ballpoint pen tip 3 Ink storage unit 4 Ball holder 5 Writing ball 6. Spring 7 Front end opening 8 Ink flow hole 9 Inward protrusion 9a Ball seat 9b Plane part 10 Arrowhead 11 Stopper D Axial movement of the writing ball L Ballpoint pen ink composition M Ink backflow prevention body α Opening angle

Claims

1. A ballpoint pen refill including at least a ballpoint pen tip and an ink reservoir disposed behind the ballpoint pen tip, The ballpoint pen tip is at least composed of a ball holder, a writing ball, and a pressing member, The ball holder is formed with at least a front end opening, an ink flow hole, an inward protruding portion protruding from an inner wall surface that defines the ink flow hole, and a ball seat in front of a side wall of the inward protruding portion; The ball seat has a projected area of ​​0.018 mm2 as viewed from the axial front. ２ More than 0.030 mm ２ is as follows: a writing ball having a portion protruding from the front end opening and rotatably supported between the front end opening and the inward protruding portion; The pressing member presses the writing ball forward, The ink reservoir directly contains an ink composition for a ballpoint pen, the ink composition containing at least fine particles; The median particle diameter of the fine particles is 0.20 μm or more and 0.46 μm or less, and the content of the fine particles in the ink composition for a ballpoint pen is 0.003% by weight or more and 0.09% by weight or less. Ballpoint pen refills.

2. The pressing member is a spring having a spring load of 0.05 N or more and 0.15 N or less. The ballpoint pen refill according to claim 1.

3. The amount of movement of the writing ball in the axial direction is 0.010 mm or more and 0.025 mm or less. The ballpoint pen refill according to claim 2.

4. an opening angle, which is the apex angle of a virtual cone whose generating line is a line segment along the flat portion at the front of the side wall of the inward protrusion, is 90° or more and 120° or less; The ballpoint pen refill according to claim 3.

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