Ball-point pen tip

Abstract

To solve the problem that when the thick part at the rear end of the ball holder is deformed so as to be tilted inward by plastic deformation or the like, in the thickness of the front side of the ball holder, which is thinner due to the presence of the relatively large intermediate ball, deformation, such as buckle, occurs, and this narrows the ink flow path between the intermediate ball, the rear of the internal protrusion where the intermediate ball is disposed, and the wall surface of the ink flow hole, thereby impeding ink flow and impeding the rotation of the intermediate ball, resulting in smudged writing lines and a poor writing feel.SOLUTION: The gist of the present invention is a ball-point pen tip in which an intermediate ball has a diameter of 70% or more of the diameter of the writing ball, is rotatably disposed within the ink flow hole at the rear of the inward protrusion, and comes into contact with the writing ball by being pressed forward by a pressing member, and the pressing member is prevented from coming out by contacting the inner wall surface of the rear-end tilting portion, and the thickness of the ball holder is such that thickness A within the axial range in which the intermediate ball can exist is greater than thickness B of the rear-end tilting portion.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a ballpoint pen tip comprising a writing ball, a ball holder that rotatably holds the writing ball with a portion of the writing ball protruding from a tip opening, and an intermediate ball that biases the writing ball from behind. [Background technology]

[0002] In recent years, there has been a trend toward ballpoint pens that require little force to write with and offer a light, smooth writing feel, and as a result, inks with high permeability have become commonplace, with inks having low viscosity and surfactants added, etc. As a result, ink is prone to seeping out and leaking from the tiny gap between the front edge of the ball holder tip opening and the writing ball.To prevent this, ballpoint pen tips are known that have a structure in which a pressing member such as a coil spring located behind the writing ball biases the writing ball forward, pressing the writing ball against the inner surface of the front edge of the tip opening when not writing, thereby providing a seal.

[0003] Furthermore, as a means of improving the rotational stability of the writing ball and providing a better writing feel while providing more reliable sealing than ballpoint pen tips that directly press the writing ball with a coil spring, a ballpoint pen tip (Patent Document 1) is known in which an inward protrusion is formed to restrict the backward movement of the writing ball, a relatively large intermediate ball is placed behind the inward protrusion, and the intermediate ball is urged forward by a pressing member to abut against the rear surface of the writing ball.

[0004] [Patent Document 1] Patent Publication No. 2021-130280 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the pressing member that biases the intermediate ball is fixed inside the ball holder by broaching the rear end to create multiple convex cutting pieces that prevent the repulsive member from slipping out at the rear, but cutting processes such as broaching produce tiny metal shavings that can remain inside the ball holder and cause various problems.For this reason, one method of preventing the pressing member from slipping out is to use plastic deformation to tilt the thick part at the rear end of the ball holder inward, reducing its diameter.

[0006] However, when the thick rear end portion of the ball holder is deformed inward by plastic deformation as described above, the stress spreads to the entire ball holder, and deformation such as buckling occurs particularly at the front end of the ball holder, where the thickness has become thin due to the presence of the relatively large intermediate ball.This narrows the ink flow path between the intermediate ball, the rear of the internal protrusion where the intermediate ball is located, and the wall surface of the ink flow hole, which can impede ink flow or the rotation of the intermediate ball, resulting in smeared writing lines and a poor writing feel. [Means for solving the problem]

[0007] The present invention provides a ballpoint pen tip comprising at least a ball holder, a writing ball, an intermediate ball, and a pressing member, wherein the ball holder is formed with at least a front-end opening, an ink flow hole, an inward protrusion protruding from the inner wall surface that forms the ink flow hole, and a rear-end retracting portion; a portion of the writing ball protrudes from the front-end opening and is rotatably held between the front-end opening and the inward protrusion; the intermediate ball has a diameter that is 70% or more of the diameter of the writing ball and is rotatably disposed within the ink flow hole behind the inward protrusion; and the intermediate ball comes into contact with the writing ball by being pressed forward by the pressing member; the pressing member is prevented from coming out by contacting the inner wall surface of the rear-end retracting portion; and the ball holder has a thickness A within an axial range in which the intermediate ball can exist that is greater than a thickness B of the rear-end retracting portion. [Effects of the Invention]

[0008] The present invention reduces the thickness of the portion that is bent down and deformed to prevent the pressing member from falling out of the ball holder, relative to the radial thickness formed by the internal protrusion and the tip outer peripheral surface located radially from the wall surface of the ink flow hole in the area where the intermediate ball is located.This means that when the bent-down process is performed to form the anti-fall-out portion of the pressing member at the rear end of the ball holder, deformation such as buckling of the thick portion in the area where the intermediate ball is located is less likely to occur, and the ink flow space between the intermediate ball, the rear of the internal protrusion where the intermediate ball is located, and the wall surface of the ink flow hole can be stably maintained, so that the flow of ink is not hindered and the rotation of the intermediate ball is not hindered, thereby providing a ballpoint pen tip with abundant ink ejection and a good writing feel. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a longitudinal cross-sectional view of the ballpoint pen tip of the present invention. [Figure 2] Enlarged view of part D in Figure 1 (enlarged view of the front end) [Figure 3] Enlarged view of part E in Figure 1 (enlarged view of the rear end) [Figure 4] Overall view before tilting [Figure 5] Figure corresponding to part F in Figure 4 during tilting processing [Figure 6] Enlarged view of part D in Figure 1 (enlarged view of the front end) [Figure 7] Modified examples of the shape of the rear end tilted portion 6 DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the ballpoint pen tip of the present invention will be described with reference to the drawings as appropriate. The present invention is not limited to the embodiment, and various modifications can be made without departing from the gist of the present invention.

[0011] Fig. 1 is a longitudinal cross-sectional view showing an example of a ballpoint pen tip of the present invention. Ballpoint pen tip 1 comprises ball holder 2, writing ball 3 as a writing member, intermediate ball 4, and coil spring 5 as a pressing member. Coil spring 5 is inserted from the rear of ball holder 2 and pressed in so as to compress its entire length and prevent it from coming out. The restoring force from this compression urges intermediate ball 4 forward, which in turn urges writing ball 3 forward via intermediate ball 4. The thick portion of the rear end of ball holder 2 is tilted radially inward to reduce its diameter, forming rear end tilted portion 6, which prevents coil spring 5 from coming out of ball holder 2.

[0012] The ball holder 2 can be made of stainless steel or copper alloys such as nickel silver or brass. Among these, stainless steel is preferred in terms of abrasion resistance during writing and corrosion resistance against ink, with austenitic stainless steel SUS304 and ferritic stainless steel SUS430 being preferred. Furthermore, to ensure good processability and to prevent deformation such as dents and abrasion at the tip of the ball holder, the Vickers hardness (HV) is preferably 150 or more and 300 or less.

[0013] Materials that can be used for the writing ball 3 and the intermediate ball 4 include cemented carbide alloys primarily 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. However, cemented carbide and ceramics are preferred for the writing ball 3 in consideration of wettability with ink, corrosion resistance, sliding properties with the intermediate ball 4, and abrasion resistance. The intermediate ball 4 may be made of either the same material as the writing ball 3 or a different material. However, it is preferable to use a combination of high-hardness materials, such as cemented carbide alloys primarily composed of tungsten carbide. Furthermore, from the perspective of suppressing adhesive wear, it is more preferable to use a combination of materials with low mutual solubility, such as silicon carbide or chromium carbide, for the intermediate ball 4, rather than the same material as the writing ball 3.

[0014] The writing ball 3 can have a diameter of 0.18 mm to 2.0 mm, but a diameter in the range of 0.3 mm to 1.0 mm, as used in general ballpoint pens, is preferred. The size of the intermediate ball 4 is not particularly limited, but by making it 70% or more of the diameter of the writing ball 3, the friction between the writing ball 3 and the intermediate ball 4 generated by the rotation of the writing ball 3 generates a large rotational torque on the intermediate ball 4, making it easier to obtain a force that exceeds the frictional resistance caused by contact between the intermediate ball 4 and the coil spring 5. Therefore, when the writing ball 3 begins to rotate, such as at the start of writing, the intermediate ball 4 rotates easily with the writing ball 3, and is less likely to cause rotational resistance to the writing ball 3, resulting in a light writing feel. Furthermore, the diameter of the intermediate ball 4 is more preferably 80% or more of the diameter of the writing ball 3, and even more preferably 100% or more.

[0015] The coil spring 5 can be made of stainless steel wire such as SUS304, hard steel wire, piano wire, or resin such as polycarbonate or polyether ether ketone. To prevent corrosion and leaching into ink, nickel-plated coil springs can also be used. From the viewpoint of lubrication for the rotation of the intermediate ball 4, nickel-plated coil springs are preferred.

[0016] If the pressure load of the coil spring 5 that biases the intermediate ball 4 forward is too small, the sealing caused by the pressure between the writing ball 3 and the front end opening of the ball holder 2 will become unstable, which may lead to ink seeping or leakage.If the pressure load is too strong, the contact load between the writing ball 3 and the intermediate ball 4 will become large, which will promote wear of the intermediate ball due to rotation and make the writing feel heavy.Therefore, it is preferable that the pressure load be between 0.03 (N) and 0.40 (N).

[0017] Next, the front end of the ballpoint pen tip 1 will be described in detail using FIG. 2, which is an enlarged view of portion D in FIG. 1. Note that the diagonal hatching lines indicating a cross section have been omitted from FIG. 2. The ball holder 2 has a front end opening 7 formed at its front side, and an ink flow hole 8 formed from the front end opening 7 toward the rear. Furthermore, inward protrusions 9 are formed protruding at equal intervals circumferentially from the inner wall surface of the ink flow hole 8. The writing ball 3 partially protrudes from the front end opening 7, and the internal protrusions 9 restrict rearward movement, thereby rotatably holding the writing ball 3 within the ink flow hole 8. Furthermore, an intermediate ball 4 is rotatably disposed in the ink flow hole 8 behind the inward protrusions 9 so as to abut against the writing ball 3. A coil spring 5 is disposed behind the intermediate ball 4 so as to contact and bias the intermediate ball 4.

[0018] The inner edge of the front-end opening 7 is pressed against the writing ball 3 during the crimping process, resulting in a mirror finish that replicates the curved surface of the writing ball 3. When writing, the writing ball 3 is forced forward and comes into close contact with the mirror-finished surface around its circumference, preventing ink leakage and air inflow. However, if an ink that is difficult to leak is used or if more abundant ink is desired, the front-end opening 7 may be formed without being pressed against the writing ball 3. Furthermore, by firmly pressing the writing ball 3 against the inward protrusion 9, a ball receiving seat 10 with roughly the same curvature as the writing ball 3 is formed. However, this may not be formed if it is desired to ensure sufficient ink circulation space around the writing ball 3.

[0019] Next, we will explain the thickness A of the ball holder 2 within the axial range in which the intermediate ball 4 can exist. As shown by the horizontally hatched area in Figure 2, thickness A is the radial thickness of the ball holder 2 corresponding to the range in which the intermediate ball 4 exists, and we have defined all thicknesses corresponding to the axial range from the front end to the rear end of the intermediate ball 4 as thickness A. As described above, in the present invention, the intermediate ball 4 is relatively large, at 70% or more compared to the writing ball 3, to achieve a light writing feel, and therefore the ink flow hole 8 in which the intermediate ball 4 exists is formed large. Therefore, thickness A of the ball holder 2 corresponding to the range in which the intermediate ball 4 exists is naturally thin, and if a tilting process is performed to reduce the diameter of the rear end of the ball holder 2 in order to prevent the coil spring 5 from slipping out of the ball holder 2, the resulting stress will cause buckling or deformation in the thinner portion of thickness A.

[0020] The details of the rear end of the ballpoint pen tip 1 will be explained using Figure 3, which is an enlarged view of part E in Figure 1, and Figures 4 and 5, which are examples of rear end tilting processing that prevents the coil spring 5 from slipping out of the ball holder 2. Figure 4 is an overall view before tilting processing is performed, and Figure 5 is an enlarged view corresponding to part F in Figure 4 after tilting processing is performed. The ballpoint pen tip 1 is placed on the ballpoint pen tip stand 11 so as to support the tapered portion of the outer wall on the front end side. A reduced diameter portion 6a, which will later become the rear end tilting portion 6, is formed at the rear end of the ball holder 2, and the intermediate ball 4 and coil spring 5 have already been placed inside the ink flow hole 8. The coil spring 5 is not yet prevented from slipping out and is in an uncompressed state, protruding from the rear end of the ball holder 2. From this state, as shown in Figure 5, a tilting jig 12 with a conical inner tapered surface and a spring push pin 13 installed in the center of the tilting jig 12 is used to compress the coil spring 5 while pressing the inner tapered surface against the reduced diameter portion 6a, thereby tilting the coil spring 5 radially inward around the entire circumference and forming a rear end tilting portion 6, which prevents the coil spring 5 from coming loose.

[0021] In other words, thickness B of rear-end tilting portion 6 corresponds to the thickness of reduced-diameter portion 6a before tilting, and it can be said that the thicker thickness B is, the greater the processing stress caused by tilting is applied to the entire ball holder 2, which will have adverse effects such as buckling and deformation in the portion of thickness A of ball holder 2 where the thickness is thin and the strength is likely to be weak, so the relationship between thickness A and thickness B is important. Therefore, by making thickness A within the axial range in which intermediate ball 4 can exist greater than thickness B of rear-end tilting portion 6, buckling and deformation are less likely to occur in thickness A when processing is performed to form the retaining portion for coil spring 5 behind ball holder 2, and the ink flow space between intermediate ball 4 and ink flow hole 8 in which intermediate ball 4 is placed can be stably maintained, so that the flow of ink is not hindered and the rotation of intermediate ball 4 is not hindered, resulting in a ballpoint pen tip with abundant ink discharge and a good writing feel.

[0022] Furthermore, if the ink flow space between the intermediate ball 4 and the ink flow hole 8 is deformed, if the deformation is at the front side closer to the writing ball, it not only impedes ink flow but also leads to deformation of the inner protrusion 9 and the ball receiving seat 10, which can destabilize the contact between the writing ball 3 and the ball receiving seat 10, making the rotation of the writing ball unstable and resulting in a poor writing feel, resulting in more serious problems. Therefore, as shown in the horizontally hatched area in Figure 6, the thickness within the axial range from the maximum diameter of the intermediate ball 4 to the front hemisphere where it can exist is defined as thickness C, and by making thickness C 115% or more of the thickness B of the rear-end indentation 6, buckling and deformation of the inward protrusion 9 near the writing ball 3 and the front side of the ink flow hole 8 can be more firmly prevented, thereby ensuring a ballpoint pen tip with abundant ink discharge and a good writing feel. Note that the diagonal hatching lines indicating a cross-section have been omitted from Figure 6.

[0023] The method of forming the rear end leaning portion 6 is not limited to forming the rear end leaning portion 6 around the entire circumference as shown in Figures 4 and 5. For example, as shown in Figure 7, it is also possible to form the rear end leaning portion 6 by cutting out multiple locations around the circumference with a broach jig (not shown). However, the method of forming the rear end leaning portion 6 around the entire circumference as shown in Figures 4 and 5 makes it possible to evenly distribute the stress from the leaning process around the entire circumference of the ball holder 2, making it less likely that deformation or buckling will occur in the wall thickness A. Furthermore, by rotating the leaning jig 12 shown in Figures 4 and 5, stress can be applied evenly around the entire circumference, allowing for more stable leaning.

[0024] Next, examples and comparative examples will be described. In the example shown in Figure 1, for two types of diameters of writing ball 3, 0.8 (mm) and 1.0 (mm), ballpoint pen tips 1 were produced with various dimensions, with A representing the thickness of the thinnest part of ball holder 2 corresponding to the axial range from the front end to the rear end of intermediate ball 4, C representing the thickness of the thinnest part within the axial range from the maximum diameter part of intermediate ball 4 where the front hemisphere can exist, and B representing the thickness of the rear end tilted part of ball holder 2. Each of the ballpoint pen tips 1 thus fabricated was then attached to a commercially available gel ink ballpoint pen (manufactured by Pentel Co., Ltd., product code BL17-A). The ink tank was filled with the test ink shown below, and the pen tip was positioned so that centrifugal force would act toward the pen tip. The ink was then centrifuged in a centrifuge (Kokusan Centrifugal Machine Co., Ltd., tabletop centrifuge H-103N) to remove any unnecessary air from the refill. Test ballpoint pen samples were then prepared and subjected to the following tests. The results are shown in Table 1. The diameter of the intermediate ball 4 was 0.8 mm, regardless of whether the diameter of the writing ball 3 was 0.8 mm or 1.0 mm. The compression load of the coil spring 5 was 0.20 N.

[0025] (Test ink) Water Black #256L (14% aqueous solution of black dye, Orient Chemical Industry Co., Ltd.) ) 35.0 parts by weight Water Yellow #1 (CI Acid Yellow 23, Orient Chemical Industry Co., Ltd.) ) 1.2 parts by weight Ethylene glycol 6.0 parts by weight Glycerin 8.0 parts by weight Thiodiglycol 8.0 parts by weight Sarcosinate OHV (N-oleoyl sarcosine, manufactured by Nikko Chemicals Co., Ltd.) 3.0 parts by weight Benzotriazole 0.5 parts by weight Proxel GXL (20% dipropylene glycol solution of 1,2-benzisothiazolin-3-one, manufactured by Avecia Co., Ltd.) 0.2 parts by weight Potassium hydroquinone sulfonate 0.3 parts by weight BC-5.5 (Polyoxyethylene cetyl ether, HLB 11.5, Nikko Chemicals Co., Ltd.) ) 1.0 parts by weight AKP-50 (fine particle alumina, average particle size 0.2 μm, manufactured by Sumitomo Chemical Co., Ltd.) 0.05 parts by weight Sodium hydroxide 0.3 parts by weight Kelzan AR (xanthan gum, manufactured by Sansho Co., Ltd.) 0.4 parts by weight Ion-exchanged water 36.05 parts by weight Of the above ingredients, the entire amount of Kelzan AR was added to 5 parts by weight of water while stirring and stirred for 1 hour to obtain an aqueous solution of Kelzan AR. The remaining ingredients were then mixed and stirred for 1 hour to dissolve uniformly, after which the aqueous solution of Kelzan AR was added and stirred for a further 2 hours to obtain a black test ink. The viscosity of the test ink was measured using an ELD-type viscometer (Tokimec Co., Ltd.) with an ST-type rotor at a temperature of 25°C and a shear rate of 100 s-1, and was found to be 200 mPa·s. The pH value of the test ink was 8.7, and was measured using a compact pH meter B-212 (Horiba, Ltd.).

[0026] (Test 1: Visual handwriting evaluation) Each ballpoint pen sample was spirally written for 100 m using a writing tester under the conditions of a writing angle of 70°, a writing load of 0.98 (N), and a writing speed of 7 (cm / sec), and the handwriting was visually inspected and evaluated based on the following criteria. ◎ and ○ are judged as good products, and △ and × are judged as bad products. ◎: No smudges, and the handwriting is clean throughout. ○: There are occasional smudges, but the handwriting is generally clean. △: Blurring occurs in multiple places. ×: Blurring occurs periodically or throughout the image.

[0027] (Test 2: Written resistance test) Using a static and dynamic friction tester (Tribo-master Type TL201Sa; Trinity Lab Co., Ltd.), test ballpoint pen samples were written on paper specified in JIS S 6061 with a pressure of 0.98 N, a writing angle of 70°, and a linear movement of 15 cm at a speed of 7 cm / sec. The load applied to the ballpoint pen body in the direction of writing movement due to the paper's movement was measured using a load cell, and this was used as the writing resistance. Measurements were conducted for 2.5 seconds, during which 500 data points were obtained. The 100 data points at the beginning and end of each period, when writing speed was unstable, were subtracted, and the average of the approximately 300 data points was used as the test result. Three ballpoint pen samples were prepared for each test level. The average values ​​of the three samples are listed in the table and evaluated based on the following criteria. In addition, ◎ and ○ are judged as non-defective products, and △ and × are judged as defective products. ◎: 0.10 (N) or less, very light writing feel. ◯: Greater than 0.10 (N) and smaller than 0.13 (N), light writing feel. △: 0.13 (N) or more, less than 0.17 (N), giving a slightly heavy writing feel. ×: 0.17 (N) or more, the writing feel is heavy.

[0028] [Table 1]

[0029] As shown in Table 1, Examples 1 to 9 have a larger wall thickness A relative to wall thickness B, thereby providing ballpoint pens that produce beautiful handwriting. Among these, Examples 1 to 5 have a larger wall thickness A relative to wall thickness B than Examples 6 to 9, resulting in no smearing and a cleaner handwriting. Furthermore, while Examples 8 and 9 also provide a light writing feel, Examples 1 to 7 have a wall thickness C of 115% or more relative to wall thickness B, which reduces the initial writing resistance and provides a lighter writing feel than Examples 8 and 9. Furthermore, Examples 1 to 5 have a wall thickness C greater than 115% relative to wall thickness B, which further reduces the initial writing resistance and provides a lighter writing feel.

[0030] In Comparative Examples 1 and 2, thickness A and thickness B were formed equal, so the stress generated during the tilting process slightly affected the area around thickness A, deforming ink flow holes 8 and resulting in insufficient ink flow, resulting in smeared handwriting. In Comparative Examples 3 to 6, thickness B was larger than thickness A, and thickness C was also less than 115% of thickness B. This resulted in deformation of not only the ink flow holes 8 around thickness A but also the inward protrusion 9 near the front end and the ball seat 10 formed there. This reduced the rotational stability of the writing ball 3, significantly increased writing resistance, and worsened the writing feel. In Comparative Examples 7 and 8, thickness A was formed thinner than thickness B, but thickness B was formed to be at least 115% of thickness C. This resulted in smeared handwriting, but low writing resistance, and a good writing feel. In other words, even if the thickness falls within the range of intermediate ball 4, the quality will be affected differently depending on whether the thinner part is at the front end or the rear end. By making thickness A thicker than thickness B and thickness C 115% or more of thickness B, it can be said that a high-quality ballpoint pen with a light writing feel and beautiful handwriting can be provided. [Explanation of symbols]

[0031] 1 ballpoint pen tip 2 ball holders 3 Writing ball 4 Medium Ball 5 coil springs 6 Rear end tilt section 6a Reduced diameter part 7 Front end opening 8 Ink flow hole 9 Inward protrusion 10 Ball seat 11 Ballpoint pen tip holder 12 Tipping jig 13 Spring push pin

Claims

1. A ballpoint pen tip including at least a ball holder, a writing ball, an intermediate 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 rear end inclined portion, a portion of the writing ball protruding from the front end opening and rotatably supported between the front end opening and the inward protruding portion; the intermediate ball has a diameter that is 70% or more of the diameter of the writing ball, is rotatably disposed within the ink flow hole at the rear of the inward protruding portion, and comes into contact with the writing ball by being pressed forward by the pressing member, and the pressing member comes into contact with an inner wall surface of the rear end tilting portion to prevent it from coming out; A ballpoint pen tip in which a thickness A of the ball holder within an axial range in which the intermediate ball can exist is greater than a thickness B of the rear end inclined portion.

2. 2. The ballpoint pen tip according to claim 1, wherein a thickness C of said intermediate ball within an axial range in which said front hemisphere can exist from the maximum diameter portion thereof is 115% or more of a thickness B of said rear end inclined portion.

3. 3. The method for manufacturing a ballpoint pen tip according to claim 1, wherein the rear end inclined portion is formed by pressing a pressing tool having a conical surface against the rear end of the ball holder to invert the entire circumference.

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