Thermochromic writing implements

Abstract

To solve the problem that writing becomes impossible due to ink leakage from the pen tip or dry-up when the pen tip is stored with the axis inclined in a pen stand, etc. with the pen tip projecting downward at the store front, etc.SOLUTION: In a ballpoint pen having an elastic body installed in a non-extractable manner so as to always press the ball at the tip end directly or via a movable member, P is 150% or more of M between the ball pressing force P (N) in the pen tip and the total weight M(N) of the ballpoint pen including refills. That is, by making the pressing load on the writing ball larger than the weight of the pen, the weight of the ballpoint pen prohibits open of the ball valve even when the barrel is inclined, so ink leakage and dry-up when not in use can be prevented.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermochromic writing instrument equipped with a ballpoint pen having a so-called ball valve mechanism in which a writing ball is constantly pressed by an elastic body so as to come into close contact with the inner surface of the caulking at the tip end side of the tip. [Background technology]

[0002] Conventional ballpoint pen-type writing instruments include so-called oil-based ballpoint pens, which contain high-viscosity (approximately 10,000 cp) ink primarily made of higher alcohol solvents directly in the ink reservoir; so-called water-based ballpoint pens, which contain low-viscosity ink primarily made of water in a fiber core called a wadding; and gel ballpoint pens, which have shear-thinning properties. However, with all types of ink, problems have been identified when ballpoint pens are stored without writing (not observed when writing). Specifically, when retractable ballpoint pens are stored with the nib protruding downward without being retracted, or when cap-type ballpoint pens are stored in a pen stand with the nib protruding downward without the cap, problems such as the ball valve at the nib opening and causing ink to leak or the nib drying out and becoming unable to write have been discovered, creating a need for further improvement. Therefore, in order to solve the above problems, it has become common technical knowledge among those skilled in the art to prevent ink leakage from the pen tip by making the load of the ball valve at the pen tip higher than the axial load of the writing instrument, as in Patent Document 1 and Patent Document 2, or to prevent ink stains by using a padding member, as in Patent Document 3. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2005-231033 [Patent Document 2] Patent Publication No. 2014-8629 [Patent Document 3] Patent Publication No. 2010-213912 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when multiple writing instruments are stacked on top of each other, or when they are propped up in a holder after being tested in a store, the shaft is not stored with the shaft in a vertical position, but is tilted at an angle of θ = 10 to 45° as shown in Figure 13, and the leaked ink may leak and solidify, interfering with the rotation of the ball and resulting in poor writing.

[0005] Therefore, the present invention aims to improve so-called ballpoint pens, in which the ball that serves as the writing part is loosely fitted inside the pen tip so that it cannot be prevented from falling out, with the pen tip protruding from the tip, and to solve the problem of ink leaking from the pen tip and drying up, making it impossible to write, when the pen is stored with the shaft tilted in a pen stand or the like with the pen tip protruding downward. [Means for solving the problem]

[0006] As a result of diligent development by the inventors, the following inventions have been realized. The present invention is a thermochromic writing instrument that contains a refill within a barrel, the refill comprising an ink reservoir tube containing thermochromic ink, and a ballpoint pen tip that is provided at the tip of the ink reservoir tube and has a rotatable writing ball loosely fitted therein, the writing ball being restricted in its forward and backward movement by a crimp at the tip end and by a receiving seat at the rear end, the ballpoint pen tip having an ink hole inside for directing thermochromic ink from the rear end, the ballpoint pen tip having a channel groove formed of multiple grooves that connect the receiving seat and the ink hole, and a biasing part of a resilient member that is installed so as to constantly press against the ball at the tip, either directly or via a movable member in between, and that consumes 200 mg or more of ink when writing 100 m at a writing load of 40 g and a speed of 1 m per minute, wherein P satisfies 150% or more of the writing ball pressing force P (N) exerted by the biasing part and the total weight M (N) of the writing instrument including the refill.

[0007] The ballpoint pen tip is a retractable thermochromic writing instrument that has a coil spring inside the barrel that urges the refill rearward, and an operating part that is provided at the rear of the barrel and is located behind the refill and interlocks with the refill, and that is set in a writing position by pushing or rotating the operating part forward to cause the refill to protrude from the tip of the barrel, and the ballpoint pen tip has a writing ball and a holder that holds the writing ball at its tip, and a crimped part that holds the writing ball is provided at the tip of the holder, and the internal space of the holder contains a crimped part provided at the tip of the holder. The holder has a ball house into which the writing ball is inserted, a back hole extending from the rear end of the holder toward the front end to the vicinity of the ball house, and an ink guide hole connecting the back hole and the ball house. The ball house has a cylindrical surface that is approximately parallel to the axis, a conical bottom surface that is continuous with the cylindrical surface and narrows toward the rear, and a ball seat on the bottom surface of which the curved surface of the writing ball is transferred. Ink grooves, which are radial grooves drilled from the ball house side toward the rear, are formed at multiple locations evenly spaced around the ink guide hole. A spring member is inserted into the back hole to urge the writing ball toward the tip, and the tip portion of the spring member is formed as a spring member that extends linearly toward the tip and passes through the ink guide hole to abut against the rear end of the writing ball and urge it; the maximum volume of ink contained in the refill is 0.5 ml or more; the sphericity of the writing ball is 1.0 μm or less; the average particle diameter of the pigment used in the ink is 0.3 μm to 2.5 μm; the diameter of the writing ball is H; and the writing ball protrudes from the tip of the holder. Let J be the distance that the writing ball extends, K be the clearance that is the amount by which the writing ball can move in the holder in the axial direction of the ballpoint pen tip, L be the inner diameter of the cylindrical surface of the ball house, A be the inner diameter of the ink guide hole, F be the outermost diameter of the ball seat, G be the wire diameter of the urging portion, and C be the diameter of the circumscribed circle of the ink groove. Then, the clearance is (0.05×H)≦K≦(0.1×H), and the writing ball is held in the crimped portion so that (J+K)<(0.4×H), and the inner diameter of the cylindrical surface of the ball house is L≧(H×1.05) and F<(0.The ink guide hole is formed so that A≦(0.6×H), the wire diameter of the urging part is formed so that (0.2×A)≦G≦(0.6×A), and the diameter of the circumscribed circle of the ink groove is formed so that C>H.

[0008] The viscosity of the thermochromic ink was 20 to 300 mPa·s at a shear rate of 3.84 (1 / S) measured at 20°C using an E-type rotational viscometer.

[0009] Furthermore, the position of the operating part from the tip of the barrel to the rear end of the operating part is constant before and after the writing element appears and disappears.

[0010] In addition, an operating portion is provided that protrudes from the rear end of the barrel, and the operating portion is a friction portion that can easily change color with thermochromic ink, and the surface of the friction portion is formed with uneven portions. [Effects of the Invention]

[0011] This invention makes it possible to avoid ink leakage from the pen tip or ink drying up, which makes it impossible to write, when the pen is stored with the shaft tilted in a pen stand or the like with the pen tip protruding downward. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an overall view of a writing instrument showing an embodiment of the present invention. [Figure 2] 1 is a front cross-sectional view of a refill housed in a writing instrument showing an embodiment of the present invention. [Figure 3] 1 is a component diagram of a ballpoint pen tip, which is a writing part of a writing instrument showing an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of the tip portion of the holder. [Figure 5] FIG. 2 is a cross-sectional view of FIG. 4 . [Figure 6] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Figure 7]FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 4. [Figure 8] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Figure 9] 7 shows a ballpoint pen tip according to another embodiment in accordance with the cross-sectional view of FIG. 6. [Figure 10] 1 is a partial cross-sectional view showing the state of the holder and the resilient member of the ballpoint pen tip according to the present invention, with the writing ball omitted. [Figure 11] FIG. 4 is a front cross-sectional view of the tip of the ballpoint pen tip of FIG. 3. [Figure 12] FIG. 12 is a cross-sectional view of FIG. [Figure 13] 1 is an overall view showing a tilted state of a writing implement according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Corresponding components will be designated by the same reference numerals throughout the drawings. The writing portion side will be referred to as the front end or front, and the other end side will be referred to as the rear end or rear.

[0014] FIG. 1 shows a writing instrument 1 according to an embodiment of the present invention. An operating unit 3 protrudes rearward from the rear end of a barrel 2, and a ballpoint pen refill 5 housed inside the barrel 2 can be extended or retracted from a tip member 4 at the front of the barrel by operating the operating unit 3. A clip 6 is fixed to the side of the barrel 2, allowing the ballpoint pen refill 5 to be clipped between the barrel 2 and a pocket or piece of paper. The operating unit 3 can be pushed forward in the axial direction or rotated radially to extend or retract the ballpoint pen refill 5 from the tip surface of the tip member 4. The distance from the rear end surface of the operating unit 3 to the tip surface of the barrel 2 or the tip surface of the tip member 4 is constant regardless of whether the ballpoint pen refill 5 is extended or retracted. Apart from the tip of the ballpoint pen refill 5 protruding from the barrel 2 or the tip member 4 in the writing state, the writing instrument remains the same in both the writing state and the storage state, and the writing instrument's appearance is not impaired. A coil spring (not shown) is housed inside the barrel 2, and is configured to urge the ballpoint pen refill rearward.

[0015] The operating unit 3 has an uneven surface 7 formed thereon to prevent slipping during operation. The uneven surface 7 is made up of protrusions, grooves, or a combination of protrusions and grooves. The uneven surface 7 may also be matte.

[0016] The operation unit 3 can function as a friction unit when the ballpoint pen refill 5 contains thermochromic ink. It is formed to wear moderately so as not to damage the paper surface or blur the printed characters. Specifically, it is preferable that the Taber abrasion amount is 10 mg or more using the abrasion wheel CS-17 of the Taber abrasion tester under the abrasion test (ASTM D1044) specified in JIS K7204, a load of 9.8 N, and an environment of 1000 rpm. If the friction member has a Taber abrasion amount of less than 10 mg, the paper surface will be damaged and the printed characters will be blurred when the handwriting discolors due to friction.

[0017] The operation unit 3 may be formed from a rubber elastic material such as a thermosetting rubber, such as silicone rubber, nitrile rubber, ethylene propylene rubber, or ethylene propylene diene rubber, or a thermoplastic elastomer, such as a styrene-based elastomer, an olefin-based elastomer, or a polyester-based elastomer, a mixture of two or more rubber elastic materials, or a mixture of a rubber elastic material and a synthetic resin, configured to have a Taber abrasion volume of 10 mg or more. Furthermore, the operation unit 3 may be formed from a mixture of polypropylene resin and a styrene-based thermoplastic elastomer, or a mixture of polypropylene resin and an olefin-based thermoplastic elastomer, configured to have a Taber abrasion volume of 10 mg or more.

[0018] Furthermore, to adjust the Taber abrasion to 10 mg or more, alkylsulfonic acid phenyl ester, cyclohexanedicarboxylic acid ester, or phthalic acid plasticizer may be added to the material of the operation unit 3 to make it more flexible. By including alkylsulfonic acid phenyl ester, cyclohexanedicarboxylic acid ester, methacrylic acid ester, acrylic acid ester, acetyl tributyl citrate, adipic acid polyester, acetyl tributyl citrate, sebacate diester, diethylene glycol dibenzoate, or a phthalic acid plasticizer in the operation unit 3, the operation unit 3 becomes more susceptible to wear, making it possible to erase handwriting without damaging the paper surface or blurring printed characters. The operation unit 3 can also be used as a touch pen or stylus pen.

[0019] Furthermore, it is desirable that the operation part 3 has a durometer D hardness specified in JIS K6203 of 30 or more. This ensures a predetermined hardness, enabling a more stable scraping operation.

[0020] Additionally, antioxidants such as amines, phenols, imidazoles, phosphorus compounds, or thioureas may be added.

[0021] Examples of amines include phenyl-α-naphthylamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, p,p'-dioctyldiphenylamine, p,p'-dicumyldiphenylamine, N,N'-di-2-naphthyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

[0022] Examples of phenols include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methylphenol, styrenated methylphenol, 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), 2,5-di-tert-butylhydroquinone, and 2,5-di-tert-amylhydroquinone.

[0023] Examples of imidazoles include 2-mercaptobenzimidazole, zinc salts of 2-mercaptobenzimidazole, and nickel dibutyldithiocarbamate.

[0024] In addition, phosphorus compounds such as tris(nonylated phenyl)phosphite, thioureas such as 1,3-bis(dimethylaminopropyl)-2-thiourea and tributylthiourea, and waxes for preventing ozone degradation may also be used.

[0025] The above antioxidants may be used alone or in combination of two or more, and among these, it is preferable to use N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.

[0026] The content of the antioxidant is preferably 0.1 to 5 parts by mass per 100 parts by mass of the polymer component. If the content of the antioxidant is less than 0.1 parts by mass, the anti-aging effect cannot be obtained. On the other hand, if the content of the antioxidant is more than 5 parts by mass, blooming occurs in the polymer composition. The content of the antioxidant is more preferably 0.3 to 4 parts by mass.

[0027] Additionally, the outer components of the writing instrument 1, such as the barrel 2, the operating element 3, the tip element 4, and the clip 6, can also contain an antibacterial agent. Primary materials used for the substrate containing the antibacterial agent of the present invention include synthetic resins such as styrene resin, acrylic resin, polyvinyl chloride, polyethylene, polypropylene, chlorosulfonated polyethylene, ABS resin, polycarbonate, polyamide, polyester, polyethylene terephthalate, polyacetal, phenolic resin, urea resin, natural rubber, and synthetic rubber, as well as paper, wood, and metal. Synthetic resins are typically used together with auxiliary agents such as colorants, fillers, stabilizers, and plasticizers. For example, resin materials that can be sterilized in an autoclave (120-130°C) include polyetherimides (PEI) such as "Ultem" manufactured by GE; polyethersulfones (PES) such as "Sumikaexcel" manufactured by Sumitomo Chemical, "Ultrason" manufactured by BASF, and "Radel" manufactured by AMOCO; polysulfones (PSF) such as "Udel" manufactured by AMOCO; polyetheretherketones (PEEK) such as "Victrex" manufactured by Victrex and "PEEK" manufactured by Mitsui Toatsu Co., Ltd.; and polyphenylene sulfide (PPS) such as "PPS" manufactured by Toray Industries, Inc.

[0028] Antibacterial agents usable in the present invention include imidazoles such as 2-(4-thiazolyl)benzimidazole, 2-benzimidazole carbamate methyl, 1-(butylcarbamoyl)2-benzimidazole carbamate methyl, 2-(methoxycarbonylamino)benzimidazole, and 2-(benzimidazole)carbamate methyl, 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, and 2-(4-thiocyanomethylthio)benzthiazole. , thiazoles such as 5-chloro-2-methyl-4-isothiazolin-3-one, iodine-based compounds such as 3-iodo-2-propargyl butylcarbamic acid, 4-chlorophenyl-3-iodopropargyl formal, diiodomethyl-p-tolylsulfone, and 3-ethoxycarbonyloxy-1-bromo-1,2-diiodo-1-propene, nitriles such as 2,3,5,6-tetrachloroisophthalonitrile and 5-chloro-2,4,6-trifluoroisophthalonitrile, and p-chloro-m-cre phenols such as 2,4,4'-trichloro-2'-hydroxydiphenyl ether, N-(fluorodichloromethylthio)phthalimide, N,N-dimethyl-N'-(dichlorofluoromethylthio)-N'-phenylsulfamide, N,N-dimethyl-N'-(dichlorofluoromethylthio)-N'-tolylsulfamide, N-(trichloromethylthio)phthalimide, tetrachloroethylthiotetrahydrophthalimide, N-trichloromethylthio-4-cyclohexene -1,2-dicarboximide and other haloalkylthiol systems, sodium 2-pyridinethiol-1-oxide, zinc 2-pyridinethiol-1-oxide, pyridine systems such as 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, triazine systems such as hexahydro-1,3,5-tris(2-hydroxyethyl)S-triazine and hexahydro-1,3,5-triethyl-S-triazine, 2-bromo-2-nitro-1,3-propanediol, 1,2-dibromo-2,Bromine systems such as 4-dicyanobutane; inorganic systems such as silver-zeolite, zinc-zeolite, silver-apatite, zirconium phosphate-silver, titania-silver, water-soluble glass-silver, calcium phosphate-silver, zeolite-copper, zeolite-zinc, zinc oxide, magnesium oxide, amorphous copper, sodium percarbonate, sodium hypochlorite, and barium metaborate; halodiallylurea systems such as trichlorcarban; guanidine systems such as chlorohexazine gluconate, chlorohexazine gluconate + cyclopirox olamine, and polyhexamethylenepyridine guanidine hydrochloride; fatty acid ester systems such as propyl glycol mono fatty acid esters and glycerin fatty acid esters; cellulose copper, copper crosslinked acrylonitrile-acrylic acid copolymers, metal oxide-coordinated aminosilicon polymers, and polymer-coordinated metal systems such as zinc-coordinated acrylic acid polymers. 0'-Oxybisphenoxyarsine, 8-Oxyquinoline copper, methylene histiocyanate, bis(dimethyldithiocarbamoyl)disulfide, 1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride, 3,5-dimethyltetrahydro-1,3,5-thiadiazine-2-thione, zinc dimethyldithiocarbamate, 4,4'-(2-ethyl-2-nitrotrimethylene)diamine Examples of suitable surfactants include fluoroquinone, levan-degrading enzymes, N-(2-hydroxypropyl)aminomethanol, 2-(methoxycarbonylamino)benzimidazole + 8-oxyquinoline copper, and 5-(chloro-2-methyl-4-isothiazolin-3-one + 1,2-benzisothiazolin-3-one. Commercially available products include Polyalpha BN, ZAG, AG, and DN (manufactured by Towa Chemical Co., Ltd.), and Amteclean Z MK-10, MK-2, MK-20, and MK-30 (manufactured by Matsushita Amtec Co., Ltd.). Also suitable are masterbatch products such as Daikiller PEM701, PEM702, PEM703, ABM501, and PSM401 (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and silver nanoparticles (Ion Flare, manufactured by Yachiyo Kogyo Co., Ltd., average particle size = 5 nm).

[0029] As a method for incorporating an antibacterial agent into the outer surface components of the writing implement of the present invention, metal and wood can be coated with a coating material containing an antibacterial agent, but it is preferable to mix the antibacterial agent into the above-mentioned synthetic resin and necessary auxiliary agents and mold it by injection molding, extrusion, etc. Furthermore, it is preferable to apply a so-called R-processing to the uneven parts and corners of the outer surface components, and to combine the components so that grooves, gaps, etc. do not occur.

[0030] When incorporating antibacterial agents into synthetic resins, the following methods can be used to enhance their effectiveness after molding: (1) Adding wax during molding or using a masterbatch in which wax and antibacterial agent are premixed. (2) Adding additives such as zinc stearate, magnesium stearate, or lithium stearate to improve dispersion of the antibacterial agent. For example, the antibacterial agent and zinc stearate are mixed, stirred, and dissolved in a ratio of 7:3 to 8:2. That is, the antibacterial agent is heated to 120 to 180°C and melted, and then a metal stearate is added. The resulting mixture of antibacterial agent and additive is added at 1 to 2% to a resin such as polyolefin, PVC, or ABS, and mixed in a kneader for approximately 10 minutes. (3) Adding a surfactant. (4) Adding a hydrophilic polymer. This method increases the antibacterial agent's effectiveness by moistening the surface of the molded product.

[0031] The amount of antibacterial agent contained in the components of the writing / applicating tool of the present invention varies depending on the type of antibacterial agent, the type of the component, and the type of material used, and is not particularly limited, but is usually contained in the component at 0.001 to 30%.

[0032] In addition, by adding an antibacterial agent to the ink in the ballpoint pen refill 5, it is possible to impart an antibacterial effect to handwriting as well.

[0033] As an antibacterial standard, it is preferable that the antibacterial activity value is 2.0 or higher when antibacterial processed products are tested based on JIS Z2801, which satisfies the guidelines set by the Antibacterial Products Council.

[0034] As shown in FIG. 2, the ballpoint pen refill 5 is formed by attaching a ballpoint pen tip 20, which serves as a writing part, to an ink reservoir 16 containing ink 18 via a coupling 17, thereby forming the ballpoint pen refill 15. The rear end of the ink 18 is filled with a grease-like ink follower 19 to prevent backflow from the tail end of the ink 18, and a float 19a with an equal specific gravity is housed within the ink follower 19 to enhance its followability. The ballpoint pen refill 5 is housed inside the barrel 2. In this embodiment, the writing instrument 1 including the ballpoint pen refill 5 weighs 25 g, and the spring pressure load at that time is 40 g. This prevents ink 18 from leaking from the ballpoint pen tip 20 even when the writing instrument 1 is stored at an angle with the ballpoint pen tip 20 protruding from the barrel 2.

[0035] The ink 18 is a thermochromic ink filled in the ink reservoir 16. Thermochromic ink maintains a predetermined color (first color) at room temperature (e.g., 25°C), changes to a different color (second color) when heated to a predetermined temperature (e.g., 65°C), and then returns to the original color (first color) when cooled to a predetermined temperature (e.g., -10°C). Generally, the second color may be colorless, and a line drawn in the first color (e.g., red) may be heated to become colorless. Therefore, the friction body 9 rubs against the paper surface on which the drawn line is drawn, generating frictional heat, thereby changing the drawn line to colorless. Naturally, the second color may be a color other than colorless. More specifically, the thermochromic microencapsulated pigment used as the coloring material for the thermochromic ink may be a microencapsulated thermochromic composition containing at least a leuco dye, a color developer, and a color-change temperature regulator. The reversible thermochromic microencapsulated pigment preferably has an average particle size in the range of 0.3 to 2.5 μm. The reversible thermochromic microencapsulated pigment is preferably blended in an amount of 4 to 30 wt % relative to the total amount of the ink composition. The average particle size was measured using a particle size measuring instrument N4Plus (manufactured by COULTER). The sample was diluted with water to reach the recommended concentration for N4Plus, and the measurement was performed at a temperature of 25°C. The ink viscosity at a shear rate of 3.84 (1 / S) measured with an E-type rotational viscometer at 20°C was 20 to 300 mPa·s. The volume of ink contained in the ink reservoir 16 was 0.5 ml or more.

[0036] The leuco dye that can be used is not particularly limited as long as it is an electron-donating dye that functions as a color former. Specifically, in order to obtain an ink with excellent color-developing properties, conventionally known dyes such as triphenylmethane, spiropyran, fluoran, diphenylmethane, rhodamine lactam, indolylphthalide, and leucoauramine can be used alone (one type) or in a mixture of two or more types (hereinafter simply referred to as "at least one type").

[0037] Specifically, 6-(dimethylamino)-3,3-bis[4-(dimethylamino)phenyl]-1(3H)-isobenzofuranone, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethylaminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthol, Thalide, 1,3-dimethyl-6-diethylaminofluoran, 2-chloro-3-methyl-6-dimethylaminofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-xylidinofluoran, 2-(2-chloroanilino)-6-dibutylaminofluoran, 3,6-dimethoxyfluoran, 3,6-di-n-butoxyfluoran Fluoran, 1,2-benz-6-diethylaminofluoran, 1,2-benz-6-dibutylaminofluoran, 1,2-benz-6-ethylisoamylaminofluoran, 2-methyl-6-(Np-tolyl-N-ethylamino)fluoran, 2-(N-phenyl-N-methylamino)-6-(Np-tolyl-N-ethylamino)fluoran, 2-(3'-trifluoromethylanilino)-6-diethylaminofluoran, 3-chloro-6-chloro- Examples of suitable leuco dyes include cyclohexylaminofluoran, 2-methyl-6-cyclohexylaminofluoran, 3-di(n-butyl)amino-6-methoxy-7-anilinofluoran, 3,6-bis(diphenylamino)fluoran, methyl-3',6'-bisdiphenylaminofluoran, chloro-3',6'-bisdiphenylaminofluoran, and 3-methoxy-4-dodecoxystyrinoquinoline, and at least one of these can be used. These leuco dyes have a lactone skeleton, a pyridine skeleton, a quinazoline skeleton, a bisquinazoline skeleton, or the like, and exhibit color development through ring-opening of these skeletons (rings). Preferably, a leuco dye that changes from colored to colorless upon heating is used.

[0038] The color developer that can be used is a component capable of causing the leuco dye to develop color, and examples thereof include phenolic resin compounds, salicylic acid metal chlorides, salicylic acid resin metal salt compounds, solid acid compounds, etc. Specific examples include o-cresol, tertiary butyl catechol, nonylphenol, n-octylphenol, n-dodecylphenol, n-stearylphenol, p-chlorophenol, p-bromophenol, o-phenylphenol, hexafluorobisphenol, n-butyl p-hydroxybenzoate, n-octyl p-hydroxybenzoate, resorcinol, dodecyl gallate, 2,2-bis(4'-hydroxyphenyl)propane, 4,4-dihydroxydiphenyl sulfone, 2-bis(4'-hydroxyphenyl)ethane, 2,2-bis(4'-hydroxy-3-methylphenyl)propane, bis(4-hydroxyphenyl)sulfide, 1-phenyl-2-bis( 4'-hydroxyphenyl)ethane, 2-bis(4'-hydroxyphenyl)-3-methylbutane, 2-bis(4'-hydroxyphenyl)-2-methylpropane, 2-bis(4'-hydroxyphenyl)n-hexane, 2-bis(4'-hydroxyphenyl)n-heptane, 2-bis(4'-hydroxyphenyl)n-octane, 2-bis(4'-hydroxyphenyl)n-nonane, 2-bis(4'-hydroxyphenyl)n-decane, 2-bis(4' 2,2-bis(4'-hydroxyphenyl)n-dodecane, 2,2-bis(4'-hydroxyphenyl)butane, 2,2-bis(4'-hydroxyphenyl)ethyl propionate, 2,2-bis(4'-hydroxyphenyl)-4-methylpentane, 2,2-bis(4'-hydroxyphenyl)hexafluoropropane, 2,2-bis(4'-hydroxyphenyl)n-heptane, 2,2-bis(4'-hydroxyphenyl)n-nonane, and the like may be mentioned.

[0039] The amount of the developer used may be selected arbitrarily depending on the desired color density and is not particularly limited, but it is usually preferable to select it within the range of about 0.1 to 100 parts by mass per 1 part by mass of the leuco dye.

[0040] The color-change temperature regulator is a substance that controls the color-change temperature during color development of the leuco dye and the color developer, and any conventionally known substance can be used, such as alcohols, esters, ketones, ethers, acid amides, azomethines, fatty acids, and hydrocarbons.

[0041] Specific examples include at least one of bis(4-hydroxyphenyl)phenylmethane dicaprylate (C7H5), bis(4-hydroxyphenyl)phenylmethane dilaurate (C2H23), bis(4-hydroxyphenyl)phenylmethane dimyristate (C13H27), bis(4-hydroxyphenyl)phenylethane dimyristate (C13H27), bis(4-hydroxyphenyl)phenylmethane dipalmitate (C5H30), bis(4-hydroxyphenyl)phenylmethane dibehenate (C21H43), and bis(4-hydroxyphenyl)phenylethylhexylidene dimyristate (C13H27).

[0042] The viscosity of the ink containing the shear thinning agent is preferably 20 to 300 mPa·s at a shear rate of 3.84 (1 / S) as measured at 20°C using an E-type rotational viscometer, and the shear thinning index is preferably 0.1 to 0.9. By achieving the above-mentioned viscosity range and shear thinning index, ink leakage and backflow can be further prevented. The shear thinning index (n) is a value calculated by applying the shear stress value (T) and shear rate value (j) to the empirical formula T = Kjn (K is a non-Newtonian viscosity coefficient) obtained from rheological measurements using a viscometer.

[0043] 3 shows the ballpoint pen tip 20, which is the writing part according to this embodiment. The ballpoint pen tip 20 is composed of a holder 21, a writing ball 35 held at the tip of the holder 21, and a resilient member 40 housed inside the holder 21.

[0044] The holder 21 is formed by cutting a cylindrical material made of stainless steel. As shown in Fig. 3(A), the tip portion thereof is cut into a substantially conical shape with a tapered end to form a tapered portion 22. On the other hand, the rear end portion is formed as an inserted portion 24 with a reduced outer diameter. This portion is inserted into a joint 17 described later. Further, the tip portion of the writing ball 35 held inside the tapered portion 22 is exposed from the tip edge, and the mouth of the tapered portion 22 is pressed inward to form a caulked portion 23 with a reduced diameter. The internal space of the holder 21 includes a ball house 26 into which the writing ball 35 is inserted inside the tapered portion 22, a back hole 28 provided from the rear end of the holder 21 in the tip direction to the vicinity of the ball house 26, and an ink guiding hole 30 connecting the back hole 28 and the ball house 26. A plurality of ink grooves 31, which are grooves penetrating the ink guiding hole 30 radially from the ball house 26 side to the tip portion 29 of the back hole 28, are formed at a plurality of locations equally distributed around the ink guiding hole 30. An elastic member 40 for urging the writing ball 35 in the tip direction is inserted into the back hole 28. The tip portion of the elastic member 40 is formed into a straight rod shape and extends in the tip direction, and is formed as an urging portion 41 that contacts the rear end of the writing ball 35 through the ink guiding hole 30 and urges it. An inward convex portion 32 that protrudes inward is formed at a position where it contacts the rear end of each ink groove 31 in the tip portion 29 of the back hole 28. When the inner diameter of the ink guiding hole 30 is A, the inner diameter of the tip portion 29 of the back hole 28 is B, the diameter of the circumscribed circle of the ink groove 31 is C, and the diameter of the inscribed circle of the inward convex portion 32 is D, the relationship A < B < C and D < B is satisfied. The inward convex portion 32 is formed using a deformed portion generated when forming the ink groove 31, and the urging portion 41 is abutted against the inward convex portion 32 so as not to contact the ink groove 31.

[0045] The holder 21 refers to the "main body portion of the ballpoint pen tip 20 excluding the writing ball 35," and can be formed, for example, by cutting a cylindrical metal material such as stainless steel. The tapered portion at the tip end of the holder 21 is called the "tapered portion 22." For example, if the holder 21 is formed from a cylindrical metal material, the tapered portion 22 is formed by cutting. The "tip end" here refers to the side of the writing tip of the ballpoint pen tip 20, and the opposite side is the "rear end." There are no particular limitations on the rear end of the holder 21, but it can be cut to reduce its outer diameter to form a portion that is inserted directly into the ink reservoir 16 or a portion that is inserted into a fitting 17 or the like that is interposed between the ink reservoir 16 and the ink reservoir 16.

[0046] Ball house 26 refers to the space formed in the portion from the tip side that contacts the inner circumference of tapered portion 22, into which writing ball 35 is inserted. When holder 21 is formed from a cylindrical metal material, ball house 26 is formed by cutting from the tip. Writing ball 35 inserted into ball house 26 is held in place by "crimped portion 23," which narrows the diameter of the tip edge of tapered portion 22 inward, to prevent it from falling out. From the standpoints of ink flowability and writing ball retention, it is desirable that the inner diameter L of the inner cylindrical surface of ball house 26 be 1.05 times or more the diameter H of writing ball 35, more preferably 1.10 times or more but less than 1.15 times.

[0047] Back hole 28 is a central hole that extends from the rear end of holder 21 to a position close to but not reaching ball house 26, and is formed by cutting when holder 21 is made of a cylindrical metal material. It is also desirable that back hole 28 have an inner diameter that gradually decreases from the rear end of holder 21 toward ball house 26.

[0048] The ink guide hole 30 is a central hole that connects the back hole 28 and the ball house 26 and has a smaller diameter than the back hole 28 .

[0049] The ink grooves 31 are multiple axial grooves evenly spaced about the ink guide hole 30. When the holder 21 is formed from a metal column, the ink grooves 31 are formed by cutting from the bottom surface 27 of the ball house 26 using a broaching tool. The ink grooves 31 extend all the way to the tip 29 of the back hole 28. This allows ink guided to the tip of the back hole 28 to reach the ball house 26 via the ink grooves 31 and the ink guide hole 30. For stable processing, the diameter C of the circumscribing circle of the ink groove 31 is preferably smaller than the inner diameter of the ball house 26. Furthermore, the diameter C of the circumscribing circle of the ink groove 31 is preferably larger than the diameter of the writing ball 35. This prevents the bottom surface 27 of the ball house 26 from wearing down due to the long rotation of the writing ball 35 during writing, which could lead to the writing ball 35 clogging the ink groove 31. This also contributes to stable ink outflow.

[0050] The resilient member 40 is preferably a coil spring that minimizes clogging of the ink guide hole 30. However, other components, such as a rubber rod or damper, are also suitable as long as they constantly press the writing ball 35 forward when stationary. In a knock-type ballpoint pen, where the writing tip is constantly exposed to the air, the resilient member 40 is a necessary component to prevent ink from dripping when the writing tip is left facing downwards. Of course, using such a resilient member 40 in a cap-type ballpoint pen, where the writing tip is sealed by replacing the cap when not in use, is not a problem, since the pen may be stored upside down without the cap replaced. Furthermore, when using shear-thinning ink, using the resilient member 40, particularly a coil spring, allows the internal movement of the coil spring during writing to easily generate shear force in the ink, improving ink flow.

[0051] The biasing portion 41 formed at the tip of the resilient member 40 penetrates from the back hole 28 through the ink guide hole 30 and abuts against the rear end of the writing ball 35 located inside the ball house 26. The elasticity of the resilient member 40 constantly biases the writing ball 35 toward the tip. The biasing portion 41 is formed in a straight rod shape. The wire diameter G of the biasing portion is preferably 20% to 60% of the inner diameter A of the ink guide hole.

[0052] The inward convex portion 32 is a protrusion formed to protrude inward at a position that contacts the tip portion 29 of the back hole 28 and the rear end of the ink groove 31. Because the inward convex portion 32 is provided to correspond to each of the multiple ink grooves 31, it is equally spaced about the axis, just like the ink grooves 31. The inner circumferential surface of the inward convex portion 32 is finished, as necessary, by cutting or other processing so as to have an inner diameter D that is smaller than the inner diameter B of the tip portion 29 of the back hole 28. That is, the ink groove 31 in the portion of the ink guide hole 30 where the fluid resistance is greatest before the ink reaches the writing ball 35 has a through structure. The inner diameter B of the tip portion 29 of the back hole 28 is set smaller than the diameter C of the circumscribing circle of the ink groove 31 and larger than the inner diameter A of the ink guide hole 30. Furthermore, the ink groove 31 is machined up to the tip portion 29 of the back hole 28. The inward convex portion 32 is formed by a deformed portion that occurs when cutting the ink groove 31, for example, a metal portion that is cut and pushed toward the rear end of the ink groove 31 during the process. With the above configuration, if the tip of the urging portion 41 of the elastic member 40 tilts toward the ink groove 31, it will come into contact with the inner circumferential surface of the inward convex portion 32 before reaching the ink groove 31. Further movement toward the ink groove 31 is then prevented. This prevents the elastic member 40 from getting stuck in the ink groove 31, even if the width of the ink groove 31 is designed to be larger than the diameter of the urging portion 41 of the elastic member 40, and improves the outflow of ink with high static viscosity.

[0053] There are no particular restrictions on the size of the writing ball 35 as long as it is in the form of a ballpoint pen tip 20, but a particularly significant effect is achieved with a relatively large ball diameter of 0.9 mm or more. Regarding the number of ink grooves 31, two or more will not pose any problems with ink outflow, but three wide, evenly spaced grooves are particularly desirable.

[0054] Next, with reference to FIGS. 3 through 10, the manufacturing process for the ballpoint pen tip 20 according to the present invention will be described. First, the tip end of a stainless steel cylindrical material is tapered to form the tapered portion 22. Next, the outer diameter near the rear end of the holder 21 is reduced to form the insertion portion 24 (FIG. 3(A)). Then, from the rear end of the holder 21 to the middle of the tapered portion 22, the back hole 28 is drilled while reducing the diameter in several stages (FIGS. 3(B) and 4). Next, an ink guide hole 30 is drilled from the tip of the holder 21 to the back hole 28, and then a ball house 26 is drilled again from the tip using a drill with a diameter slightly larger than the outer diameter of the writing ball 35 (FIG. 4). Next, an ink groove 31 is formed around the ink guide hole 30 from the bottom surface 27 of the ball house 26 using a broaching tool (FIGS. 5 and 10). As shown in FIG. 5, which is a cross section taken along line II of FIG. 4, and FIG. 6, which is a cross section taken along line II-II of FIG. 4, three ink grooves 31 are provided radially and equidistantly around the ink guide hole 30. The ink grooves 31 penetrate all the way to the tip 29 of the back hole 28 (FIG. 4). When the ink grooves 31 are formed, the pressed portion is pushed toward the rear end, causing the inner periphery of the portion that bulges inward. This is then smoothly machined with a drill to form an inward protrusion 32 (FIG. 4). As shown in FIG. 5 and FIG. 7, which is a cross section taken along line III-III of FIG. 4, the inward protrusion 32 can be seen toward the rear end of the ink groove 31 when viewed from the front end. Furthermore, as shown in FIG. 8, which is a cross section taken along line IV-IV of FIG. 4, the inward protrusion 32 is formed to protrude inward from the tip 29 of the back hole 28.

[0055] Here, let the inner diameter of the ink guiding hole 30 be A, the inner diameter of the tip portion 29 of the back hole 28 be B, the diameter of the circumscribed circle of the ink groove 31 be C, and the inner diameter of the inner peripheral surface of the inner convex portion 32 be D. As shown in FIGS. 5 and 7, D < A < C, and as shown in FIG. 8, D < B. Further, in FIGS. 7 and 8, it can be seen that A < B and B < C by comparison with D of the same size. Therefore, from these figures, A < B < C and D < B. Note that the fact that A > D as shown in FIG. 7 is just an example, and for example, A < D can also be set as in another embodiment shown in FIG. 9. However, if the dimensional difference between A and D is too large, ink outflow becomes difficult, so the relationship of A ≒ D is desirable.

[0056] A writing ball 35 made of cemented carbide is then inserted into the ball house 26, and the tip of the tapered portion 22 is then pressed inward with a crimping tool to form the crimped portion 23 (FIGS. 3A, 3B, and 11). By ensuring that the sphericity of the writing ball is 1.0 μm or less, the ball's rotation can be stabilized, resulting in a comfortable writing experience. The sphericity is measured using a sphericity measuring device (ROUNDTEST RA-2000, manufactured by Mitutoyo Corporation). The writing ball 35 is also formed with a maximum ball surface roughness Ra of 10 nm. This is because if the surface roughness Ra of the writing ball 30 exceeds 10 nm, the seat wear will be severe during writing, reducing the amount of ink flow as the writing distance increases. In the worst case, ink flow will stop, making writing impossible. The surface roughness Ra was measured using a non-contact surface profiler (Zygo NewView 7200) under the following conditions: lens magnification: 50x, evaluation length: 100 μm, Gaussian filter: 25 μm. All other parameters conform to JIS B0601 (Product Geometric Characteristics Specifications - Surface Texture). A spring 40 formed from a coil spring is inserted into the back hole 28. The tip of the spring 40 is formed into a straight rod-like shape and is referred to as the biasing portion 41. The tip of the biasing portion 41 passes through the ink guide hole 30 and contacts the rear end of the writing ball 35, constantly pressing it toward the tip. A portion of the rear end of the holder 21 is crimped inward, forming the fixing portion 25 that prevents the spring 40 from falling off (Figure 3(B)).

[0057] 10, in this ballpoint pen tip 20, when the biasing portion 41 at the tip of the elastic member 40 becomes eccentric toward the ink groove 31, it abuts against the inward convex portion 32 and does not come into contact with the ink groove 31. Therefore, even if the width of the ink groove 31 is designed to be larger than the diameter of the biasing portion 41, the biasing portion 41 will not get stuck in the ink groove 31.

[0058] FIG. 11 is a front cross-sectional view of the tip of ballpoint pen tip 20. The diameter of writing ball 35 is 0.5 mm or more, preferably 0.9 to 1.2 mm. Furthermore, if the diameter of writing ball 35 is H, the writing ball protrusion dimension, which is the distance by which writing ball 35 protrudes from the tip of holder 21 as shown in FIG. 12, is J, and the clearance, which is the amount by which writing ball 35 can move in the axial direction of ballpoint pen tip 20 within holder 21, is K, then the clearance is (0.05×H)≦K≦(0.1×H), and writing ball 35 is held in holder 21 so that the relationship (J+K)<(0.4×H) holds. Furthermore, the outer diameter of crimped portion 23 is chamfered to reduce frictional resistance when writing at an angle.

[0059] Figure 12 is a detailed enlarged front view of the tip of the ballpoint pen tip, cut along section II in Figure 11. Ball house 26 has cylindrical surface 26b that is approximately parallel to the axis, bottom surface 27 that is a conical surface that is continuous with cylindrical surface 26b and tapers rearward, and ball seat 27c, on which the curved surface of writing ball 35 is transferred, as shown in Figure 4. Here, as shown in Figure 4, if the inner diameter of cylindrical surface 26b of ball house 26 is L, the inner diameter of ink guide hole 30 is A, and the outermost diameter of the ball seat is F, ball house 26 is formed so that L ≥ (diameter H of writing ball × 1.05) and F < (0.65 × H). Furthermore, the ink guide hole 30 is formed so that its inner diameter A is 60% or less of the diameter H of the writing ball, and ink grooves 31, which are grooves that radiate from the ball house 26 side toward the back hole 28, are formed at three equally spaced locations around the periphery of the ink guide hole 30. Furthermore, by making the diameter C of the circumscribing circle of the ink grooves 31 larger than the diameter H of the writing ball 35, a stable writing flow rate can be maintained even if the ball seat 27c wears and the diameter increases.

[0060] Figure 13 shows the writing instrument according to an embodiment of the present invention in a state where it is inclined at an angle θ. By adopting a configuration in which the writing ball pressing force P (N) by the biasing portion satisfies 150% or more of M, where M is the total weight (N) of the writing instrument including the refill, it is possible to avoid the inability to write due to ink leakage or drying up from the ball pen tip 20, which is the pen tip, even in the inclined state. And for the writing instrument of this embodiment, the total weight M of the writing instrument is 0.157 N (16 g), and the writing ball pressing force P is 0.245 N (25 g). Also, when a metal member is used to make the total weight M of the writing instrument 0.245 N (25 g) or more in order to obtain a high-class feeling or the like for the shaft cylinder, a more remarkable effect can be exerted by setting the writing ball pressing force P to 0.39 N (40 g) or more accordingly. Further, the ink amount of the ball pen refill 5 is at least 0.5 ml or more, so that a writing distance of 100 m or more can be obtained. Also, when the writing speed is 1.0 m / min and the writing load is 40 g, when the outer diameter of the writing ball 35 is 0.5 to 0.7 mm, the ink consumption for 100 m is preferably 200 to 400 mg, and when it is 0.9 to 1.2 mm, it is 500 to 1000 mg. If the ink consumption is small with respect to the ball diameter H, the handwriting is thin and difficult to see, and if it is large, the handwriting is difficult to dry and there is a risk of soiling the hand with the handwriting after writing. In particular, when the ball diameter is 0.9 mm to 1.2 mm, a smooth writing feeling can be obtained, which is suitable. The ink consumption is measured using a measuring instrument conforming to JIS S 6061 and under writing conditions, except for the aforementioned writing conditions.

[0061] Furthermore, in the case of a retractable writing instrument in which a relational expression: (15 × H × H) < P < (60 × H × H) holds between the diameter H (mm) of the writing ball and the writing ball pressing force P (N) by the biasing portion, and the ball pen refill 5 is configured to be biased rearward of the shaft cylinder by a coil spring, by adopting a configuration in which a relational expression: 50·M < S < (50 × M + 20 × P) is satisfied among the writing ball pressing force P (N) by the biasing portion, the pressing force S (N) of the return spring, and the total weight M (N) of the writing instrument, it is suitable for ensuring high-level performance such as ball skipping, scratching during a strong impact, and the balance of writing performance.

Explanation of Reference Numerals

[0062] 1 writing implements 2 shaft cylinder 3 Control section 4 Tip member 5 ballpoint pen refills 6 clips 7 Uneven part 16 Ink reservoir tube 17 Joints 18 Ink 19 Ink Follower 19a Float 20 Ballpoint Pen Tips 21 Holder 22 Tapered section 23 Crimping part 24 Inserted part 25 Fixed part 26 Ball House 26b Cylindrical surface of ball house 27 bottom 27c Ball seat 28 Back hole 29 Tip of back hole 30 Ink guide hole 31 Ink groove 32 Inner convex part 33 Cylindrical Surface 35 Writing Ball 40 Elastic member 41 energizing portion A Inner diameter of ink guide hole B Inside diameter of tip of back hole C Diameter of the circumscribed circle of the ink groove (outer diameter of the ink groove on the ball house side) D Diameter of the inscribed circle of the inner convex part F Outer diameter of ball seat G Wire diameter of the energizing part H Diameter of writing ball J The distance the writing ball projects from the tip of the holder. K Clearance L: Inner diameter of the cylindrical surface of the ball house M Total weight of writing implement P: Writing ball pressing force by the biasing part S Return spring pressure

Claims

1. The refill is housed in a barrel, and the refill comprises an ink reservoir tube containing thermochromic ink, a ballpoint pen tip provided at the tip of the ink reservoir tube, a writing ball loosely fitted in a rotatable manner and restricted in its forward and backward movement by a crimp at the tip end and by a receiving seat at the rear end, and an ink hole inside for leading out the thermochromic ink from the rear end, the ballpoint pen tip having a channel groove formed by a plurality of grooves communicating with the receiving seat and the ink hole, and a biasing part of a resilient member installed so as to constantly press the ball at the tip directly or via a movable member, and a writing load of 40 g. A thermochromic writing instrument that consumes 200 mg or more of ink when writing 100 m at a speed of 1 m per minute, is configured such that P (N) of the writing ball pressing force by the urging part and M (N) of the total weight of the writing instrument including the refill are equal to or greater than 150% of M, the surface of the barrel contains an antibacterial agent, and is provided with an operating part that protrudes from the rear end of the barrel and allows the refill to be operated to extend and retract from the front end of the barrel, the operating part is a friction part that can discolor the thermochromic ink, and the friction part has added thereto an antioxidant that is 0.1 to 5 parts by mass per 100 parts by mass of polymer components.

2. The ballpoint pen tip comprises a writing ball having a diameter of 0.9 to 1.2 mm and a holder that holds the writing ball at its tip, and the tip of the holder is provided with a crimped portion that holds the writing ball. The internal space of the holder is formed with a ball house that is provided at the tip of the holder and into which the writing ball is inserted, a back hole that is provided from the rear end of the holder toward the tip to the vicinity of the ball house, and an ink guide hole that connects the back hole to the ball house. The ball house has a cylindrical surface that is approximately parallel to the axis, a conical bottom surface that is continuous with the cylindrical surface and tapers rearward, and a ball receiving seat on the bottom surface of which the curved surface of the writing ball is transferred. The diameter of the writing ball is H, and the distance that the writing ball projects from the tip of the holder is I.

2. The thermochromic writing instrument of claim 1, wherein the clearance is (0.05 × H)≦K≦(0.1 × H), the writing ball is held in the crimped portion so that (J+K)<(0.4 × H), the inner diameter of the cylindrical surface of the ball house is formed so that L≧(H × 1.05) and F<(0.65 × H), the ink guide hole is formed so that A≦(0.6 × H), and the diameter of the circumscribing circle of the ink groove is formed so that C>H, where J is the ball projection dimension, K is the clearance that is the amount by which the writing ball can move within the holder in the axial direction of the ballpoint pen tip, L is the inner diameter of the cylindrical surface of the ball house, A is the inner diameter of the ink guide hole, F is the outermost diameter of the ball seat, G is the wire diameter of the biasing portion, and C is the diameter of the circumscribing circle of the ink groove.

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