Writing instrument for paper diapers

Abstract

To provide a new writing instrument suitable for writing on paper diapers.SOLUTION: A writing instrument for paper diaper has an ink reservoir, a pen tip chip, and a spring, and the pen tip chip has a chip body and a valve body. The valve body has a spherical shape with a diameter of 0.8 mm or more and 1.2 mm or less, and is located in an accommodation space and partially exposed from a tip opening. The spring presses the valve body toward the tip opening side. A first pressing force, which is a pressing force of the spring in a state where the valve body blocks the tip opening, is 2.9×10-2 N or more and 1.5×10-1 N or less. The value obtained by subtracting the first pressing force from a second pressing force, which is a pressing force of the spring in a state where the valve body is in contact with a seat portion, is 6.9×10-3 N or less. The amount of ink flowing out during continuous writing is 100 mg or more and 200 mg or less per 10 m.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a writing instrument for paper diapers.

Background Art

[0002] Paper diapers used for infants and the like are widely spread. Paper diapers can be disposable and have a good texture. Also, it is easy to put on and take off for the user (wearer). Therefore, in childcare facilities that take care of infants, paper diapers are exclusively used.

[0003] Fig. 9 shows the structure of a general paper diaper. The paper diaper 100 shown in Fig. 9 has a waterproof outer skin material 101 and a water-permeable inner skin material 102 that touches the user's skin, and an absorbent material 103 is built in between them. The absorbent material 103 is, for example, a laminated material of water supply paper, cotton-like pulp, a high molecular absorbent, etc.

[0004] By the way, since paper diapers used in childcare facilities are usually brought by parents or guardians, childcare facilities handle paper diapers for multiple people. Therefore, parents or guardians are often required to pre-scribe their infant's name on the brought paper diapers. Here, the current situation is that parents or guardians are writing their infant's name etc. on paper diapers with existing writing instruments such as markers and ballpoint pens.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the outer skin material 101 of the disposable diaper 100 is often a non-woven fabric, which is formed by solidifying fibers into a sheet shape. Therefore, in the conventional writing instruments, the pen tip is likely to get caught on the outer skin material 101, making it difficult to write. For example, in a felt-tip pen, the pen tip is a fiber bundle, and when writing, the pen tip may get caught in the fibers of the outer skin material 101, making it difficult to write. In a marker, the pen tip is a resin or a sintered body, and since it is hard, the pen tip is likely to get caught on the outer skin material 101 when writing, making it difficult to write.

[0007] The same is true for ballpoint pens. The pen tip is likely to get caught on the outer skin material 101, making it difficult to write. That is, in a normal ballpoint pen, generally the diameter of the ball is 0.6 mm or less. On the other hand, the outer skin material 101 of the disposable diaper 100 is often a non-woven fabric as described above, which is formed by solidifying fibers into a sheet shape. Therefore, when using a conventional ballpoint pen, the ball is sandwiched between the fibers of the non-woven fabric, making it difficult to move the ballpoint pen.

[0008] Also, as a form of ballpoint pen, there is one in which a spring is built into the ballpoint pen, and the ball is pressed against the tip opening side by the spring. In a ballpoint pen with this structure, similar to the marker described above, it is necessary to push the ball against the spring. However, when the ball is pressed against the disposable diaper 100, the surface of the disposable diaper 100 is dented, making it difficult for the ball to move. Therefore, it becomes difficult to write smoothly.

[0009] An object of the present invention is to develop a new writing instrument suitable for writing on disposable diapers.

Means for Solving the Problems

[0010] A mode for solving the above problems is a writing instrument for disposable diapers having an ink storage section for storing ink, a pen tip chip connected to the ink storage section, and a spring. The pen tip chip has a chip body and a valve body. The chip body includes a storage space for storing the valve body, a tip opening, and an ink guide hole. The tip opening is on the tip side of the storage space and communicates the inside and outside of the storage space. The ink guide hole has an opening at the tip side on the inner surface of the rear end side of the storage space and communicates the inside and outside of the storage space. There is a seat portion in the storage space centered on the opening of the ink guide hole. The valve body is spherical with a diameter of 0.8 mm or more and 1.2 mm or less. The valve body is in the storage space and a part of it is exposed from the tip opening. The spring presses the valve body toward the tip opening side, and a first pressing force, which is the pressing force of the spring when the valve body blocks the tip opening, is 2.9×10 -2 N or more and 1.5×10 -1 N or less. The value obtained by subtracting the first pressing force from the second pressing force, which is the pressing force of the spring when the valve body abuts against the seat portion, is 6.9×10 -3 N or less. The writing instrument for disposable diapers is characterized in that the ink outflow amount during continuous writing is 100 mg or more and 200 mg or less per 10 m.

[0011] In the writing instrument for disposable diapers of this mode, the valve body is spherical, and the valve body is directly pressed against the surface of the disposable diaper for writing. Here, if the diameter of the valve body is too small, it will be caught by the fibers of the skin material (non-woven fabric) of the disposable diaper. On the other hand, if the diameter of the valve body is too large, it is difficult to write characters and the characters will be blurred. However, since the valve body adopted in this mode has a diameter of 0.8 mm or more, it is not easily caught by the non-woven fabric constituting the surface of the disposable diaper. Also, since the valve body adopted in this mode has a diameter of 1.2 mm or less, it is easy to write characters.

[0012] Also, in the writing instrument for disposable diapers of this mode, there is a valve body at the tip opening of the pen tip chip, and the valve body blocks the tip opening. Also, the valve body is pressed toward the tip opening side by a spring. In the writing instrument for disposable diapers of this embodiment, the tip opening is opened by pressing the valve body against the surface of the disposable diaper to discharge the ink. As described above, although the disposable diaper is soft, in the writing instrument for disposable diapers of this embodiment, since the pressing force of the spring (first pressing force) in the state where the tip opening is blocked is weak, the disposable diaper is less likely to be dented when the valve body is pressed, and it is easy to write. In addition, in the writing instrument for disposable diapers of this embodiment, the difference between the pressing force of the spring (first pressing force) in the state where the valve body blocks the tip opening and the pressing force of the spring (second pressing force) in the state where the valve body abuts on the seat portion is small. Therefore, even with a fluffy disposable diaper, it is easy to write. That is, in a normal ballpoint pen with a spring, the ball is pressed against the seat during writing, and even if there is a large difference between the first pressing force and the second pressing force, there is no inconvenience. On the other hand, in the case of a writing instrument for disposable diapers, writing may be performed in an intermediate state where the valve body does not contact the seat portion, and if the change in the pressing force is large, it is difficult to write. In contrast, in the writing instrument for disposable diapers of this embodiment, the difference between the pressing force of the spring (first pressing force) in the state where the valve body blocks the tip opening and the pressing force of the spring (second pressing force) in the state where the valve body abuts on the seat portion is small. Therefore, it is easy to write on the disposable diaper.

Effect of the Invention

[0013] According to the present invention, a writing instrument suitable for writing on disposable diapers can be provided.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described. Note that, for ease of understanding of the invention, in each drawing, the sizes, thicknesses, etc. of each member are drawn with some exaggeration and do not necessarily match the actual sizes, ratios, etc.

[0016] First, the constituent members and structure of the writing instrument 50 for disposable diapers will be roughly described. The writing instrument 50 for disposable diapers shown in Fig. 1 is composed of a core member 1, a main body portion 51 for housing the core member 1, and a cap 52.

[0017] As shown in FIGS. 2 and 3, the core member 1 has an ink storage portion 2, a tip plug 3, a pen tip 5, and a spring 6. The ink storage portion 2 is an elongated tube with a hollow interior. The ink storage portion 2 is filled with ink 7. Further, an ink follower 8 is provided at the rear end inside the ink storage portion 2.

[0018] The tip plug 3 is a member for connecting the pen tip 5 to the ink storage portion 2, and its outer shape is a member with a conical shape on the tip side. The interior of the tip plug 3 is hollow, and a communication hole 10 for conducting the ink 7 from the ink storage portion 2 to the pen tip 5 is provided. Inside the tip plug 3, a stepped portion 11 is provided as shown in FIG. 3.

[0019] The pen tip 5 has a tip body 13 and a valve body 15.

[0020] The outer shape of the tip body 13 is such that the outer shape on the tip side is substantially conical, and the outer shape on the rear end side is substantially cylindrical. Inside the tip body 13, a valve body accommodation space 16 and an ink conduction hole 17 are provided. The ink conduction hole 17 has an opening at the tip side on the inner surface of the rear end side of the valve body accommodation space 16 and communicates the inside and outside of the valve body accommodation space 16. Further, a tip opening 18 is provided at the tip of the valve body accommodation space 16. The tip opening 18 is located on the tip side of the valve body accommodation space 16 and communicates the inside and outside of the valve body accommodation space 16. In the valve body accommodation space 16, there is a seat portion 22 centered on the opening 20 of the ink conduction hole 17.

[0021] As shown in FIGS. 3 and 4, the valve body accommodation space 16 has a side wall surface 21 with a cylindrical inner shape, a seat portion forming surface 25 and a connection surface 23 located on the rear end side of the side wall surface 21. The connection surface 23 is a surface that connects the side wall surface 21 and the seat portion forming surface 25. As shown in FIG. 4, the shape of the connection surface 23 is the side surface shape of a truncated cone with the apex on the tip side. Therefore, an annular groove 30 is provided between the side wall surface 21 and the seat portion 22. Further, on the central side of the seat portion 22, there is a bulging portion 31 that bulges toward the ink conduction hole 17 side. Around the ink guide hole 17, as shown in Fig. 4(c), radial slits 38 are provided. The slit 38 is what is called a groove. The slit 38 is connected to the valve body accommodation space 16 side, and the ink 7 can enter the slit 38 from the ink guide hole 17 and flow out to the valve body accommodation space 16 side. That is, at the opening end of the ink guide hole 17 on the valve body accommodation space 16 side, there is a seat portion 22 that supports the valve body 15, and the valve body 15 contacts the seat portion 22. However, since there is a slit 38 in the seat portion 22, the opening end of the ink guide hole 17 is not completely blocked by the valve body 15.

[0022] The valve body 15 adopted in this embodiment is spherical. As shown in Figs. 3 and 4(a), a part of the valve body 15 is exposed from the tip opening 18 which is the opening of the valve body accommodation space 16. The valve body 15 is rotatably held within the valve body accommodation space 16. The material of the valve body 15 is SiC. However, the material of the valve body 15 is not particularly limited, and stainless steel, alumina sintered body, zirconia, WC, and other known materials can also be used.

[0023] As shown in Fig. 3, the spring 6 is a member for biasing the valve body 15 outward from the pen tip chip 5. The spring 6 is generally in a coiled shape wound spirally and has a biasing force. As shown in Fig. 3, the spring 6 is provided with tightly wound portions 33, 35 and a loosely wound portion 36. The loosely wound portion 36 is located between the tightly wound portions 33, 35. At the tip of the tightly wound portion 33 on the tip side, there is a small-diameter wound portion 40.

[0024] The rear end side of the tip plug 3 is fitted to the tip portion of the ink storage portion 2. Further, the rear end side of the pen tip chip 5 is fitted to the tip portion of the tip plug 3. The spring 6 is fixed between the tip plug 3 and the pen tip 5. Specifically, the spring 6 is disposed across the ink guide hole 17 of the tip body 13 of the pen tip 5 and the communication hole 10 of the tip plug 3. The rear end side of the spring 6 protrudes from the tip body 13 and abuts against and is locked to the stepped portion 11 of the communication hole 10 of the tip plug 3. On the other hand, the tip of the spring 6 reaches into the valve body accommodation space 16 through the ink guide hole 17 of the tip body 13 and abuts against the valve body 15.

[0025] The writing instrument 50 for disposable diapers has a core member 1 accommodated in a main body portion 51 and further has a cap 52 attached thereto. When in use, the cap 52 is removed and the main body portion 51 is held by hand.

[0026] In this embodiment, the valve body 15 is pressed by the spring 6 outward from the pen tip 5. Therefore, normally, the tip opening 18 of the pen tip 5 is forcibly sealed by the valve body 15, preventing leakage of the ink 7. That is, except during writing, the valve body 15 is pushed by the spring 6 to forcibly seal the tip opening 18. On the other hand, when writing with the writing instrument 50 for disposable diapers, the valve body 15 is pressed against the disposable diaper 100, the valve body 15 moves inward against the spring 6, and the valve body 15 moves away from the tip opening 18, creating a discharge gap between the tip opening 18 and the valve body 15. The ink 7 is discharged from between the tip opening 18 and the valve body 15. When the writing instrument 50 for disposable diapers is moved while being pressed against the disposable diaper 100, the valve body 15 rotates and a line is drawn.

[0027] Next, the characteristic configuration of the writing instrument 50 for disposable diapers of this embodiment will be described. The writing instrument 50 for disposable diapers of this embodiment has the following characteristic configuration. (1) The diameter of the valve body 15 is larger than that of a normal ballpoint pen. (2) The pressing force of the spring 6 that presses the valve body 15 is weak. (3) The amount of change in the force that presses the valve body 15 is small. (4) The amount of ink discharged is large.

[0028] (1) Diameter of the valve body 15 The diameter of the valve body 15 adopted in the disposable diaper writing instrument 50 of the present embodiment is 0.8 mm or more and 1.2 mm or less. In the disposable diaper writing instrument 50 of the present embodiment, since a ball larger than the ball of a normal ballpoint pen is used as the valve body and the writing ball, it is less likely to catch on the non-woven fabric constituting the surface of the disposable diaper and is easy to write. Also, since the diameter of the valve body 15 is 1.2 mm or less, the line during writing does not become excessively thick, and bleeding of the ink is less likely to occur, making it easy to write characters.

[0029] (2) Pressing force of the spring 6 The spring 6 adopted in the disposable diaper writing instrument 50 of the present embodiment has a pressing force (first pressing force) of the spring 6 in a state where the valve body 15 seals the tip opening 18 of the tip body 13 of 2.9×10 -2 N or more and 1.5×10 -1 N or less (3 gf or more and 15 gf or less). The first pressing force of the spring 6 is preferably 6.9×10 -2 N or more and 1.2×10 -1 N or less (7 gf or more and 12 gf or less), and more preferably 8.8×10 -2 N or more and 1.1×10 -1 N or less (9 gf or more and 11 gf or less).

[0030] The disposable diaper writing instrument 50 of the present embodiment has a tip opening 18 in the tip body 13 of the pen tip 5, and the valve body 15 seals the tip opening 18. Although the disposable diaper 100 is soft, in the disposable diaper writing instrument 50 of the present embodiment, since the pressing force (first pressing force) of the spring 6 in a state where the tip opening 18 is sealed is weak, the disposable diaper 10 is less likely to be indented when the valve body 15 is pressed against it, and it is easy to write. Conversely, the valve body 15 can be pushed and moved with a slight force so as not to dent the surface of the disposable diaper, and the ink can be discharged. Also, although the force is weak, since the valve body 15 is pressed against the tip opening 18 by the spring 6, the risk of ink leakage during non-use is low. Also, although the force is weak, since the valve body 15 seals the tip opening 18, the internal ink does not dry during non-use. According to the experiments of the present inventors, if the first pressing force of the spring 6 is 2.9×10 -2 N or more (3 gf or more), ink leakage during non-use is less likely. However, in some cases, it may take time for the valve body 15 to completely seal the tip opening 18 immediately after writing, and ink may leak immediately after writing. If the first pressing force of the spring 6 is 6.9×10 -2 N or more (7 gf or more), ink leakage immediately after writing is significantly reduced. If the first pressing force of the spring 6 is 8.8×10 -2 N or more (9 gf or more), ink leakage immediately after writing can be almost completely prevented. On the other hand, the indentation of the disposable diaper 10 is less as the pressing force of the spring 6 is weaker.

[0031] (3) Amount of change in the force pressing the valve body 15 The spring 6 employed in the writing instrument 50 for disposable diapers of the present embodiment is the difference (ΔF = F2 - F1) between the pressing force of the spring 6 (first pressing force: F1) in the state where the valve body 15 seals the tip opening 18 and the pressing force of the spring (second pressing force: F2) in the state where the valve body 15 is pushed in maximally and abuts against the seat portion 22, that is, the value obtained by subtracting the first pressing force from the second pressing force, which is 6.9×10 -3 N or less (0.7 gf or less). Fig. 5(a) shows the state where the valve body 15 seals the tip opening 18, and Fig. 5(b) shows the state where the valve body 15 is pushed in maximally and abuts against the seat portion 22. In the present embodiment, the movement amount L of the valve body 15 between the two is 0.08 mm to 0.12 mm, preferably 0.1 mm. The spring constant of the spring 6 is desirably 7.4×10 -3 N / mm or less (7.5 gf / mm or less).

[0032] In the writing instrument 50 for disposable diapers, there may be a case where writing is performed in an intermediate state where the valve body 15 is not in contact with the seat portion 22, and if the change in the pressing force is large, it is difficult to write. On the other hand, in the writing instrument 50 for disposable diapers of the present embodiment, since the difference between the pressing force of the spring (first pressing force) in the state where the valve body 15 seals the tip opening and the pressing force of the spring (second pressing force) in the state where the valve body 15 is in contact with the seat portion is small, it is easy to write on the disposable diaper 100.

[0033] (4) Ink discharge amount In the writing instrument 50 for disposable diapers of the present embodiment, the ink outflow amount during continuous writing is 100 mg or more and 200 mg or less per 10 m. The ink outflow amount during continuous writing can be evaluated by measuring the ink outflow amount (mg) when continuously writing 10 m on high-quality paper under the conditions of a load of 100 g, a writing angle of 65 degrees, a writing speed of 7 cm / second, a temperature of 23 °C, and a humidity of 50%. The ink outflow amount of the writing instrument 50 for disposable diapers during continuous writing is larger than the ink outflow amount of a normal ballpoint pen.

Example

[0034] 1. Relationship between snag and ball diameter (1) Microscopic observation of the surface of the disposable diaper The surface of a commercially available disposable diaper (product name: Moony, manufactured by Unicharm Corporation) was observed with a microscope (Fig. 6). In Fig. 6, circles with diameters of 0.5 mm, 0.6 mm, 0.8 mm, and 1.0 mm are added (indicated as φ05, φ06, φ08, and φ10, respectively). That is, on the surface of the disposable diaper, the fibers of the non-woven fabric are entangled disorderly, and it was considered that this entanglement state strongly affects the snag of the ball.

[0035] (2) Microscopic observation of the state during writing In order to examine the relationship between the snag on the surface of the disposable diaper and the diameter of the ball (ball diameter), a simulated writing instrument equipped with a ball having a diameter of 0.6 mm, 0.8 mm, or 1.0 mm was produced. Simulating writing, the surface of the disposable diaper was rubbed with each writing instrument, and the state at that time was observed with a microscope. The results are shown in FIGS. 7(a) to 7(c). That is, when the ball diameter was 0.6 mm, the tip pierced into the gaps between the fibers of the nonwoven fabric, and the snag during writing was remarkable (FIG. 7(a)). On the other hand, when the ball diameter was 0.8 mm, the snag of the tip was reduced (FIG. 7(b)), and when the ball diameter was 1.0 mm, there was almost no snag (FIG. 7(c)).

[0036] 2. Relationship between spring load and ink leakage (1) Preparation of ink composition An ink composition having the following composition was prepared (unit: part by mass). · Nigrosine dye: 11 · Oleic acid: 7 · Alkylphenol resin: 4 · Maleic acid resin: 6 · Sucrose benzoate: 2 · Propylene glycol monomethyl ether: 53.5 · Ethyl alcohol: 10 · Propylene glycol n-butyl ether: 6 · Silicon-based surfactant: 0.5

[0037] The viscosity (20 ° C., 20 rpm, ELD type viscometer 1 ° 34 ′ cone) of the prepared ink composition was 15 mPa·s, and the surface tension was 22.5 mN / m.

[0038] (2) Production of writing instruments with different spring loads Six types of writing instruments (ball pens) with different spring loads (the pressing force of the spring when the ball seals the tip opening. First pressing force) were produced using a 0.8 mm diameter ball and the above ink composition. As the spring load, 3.8 gf (Experimental Example 2), 5.5 gf (Experimental Example 3), 7.5 gf (Experimental Example 4), 10.0 gf (Experimental Example 5), 12.5 gf (Experimental Example 6), and 20 gf (Experimental Example 7) were selected. Separately, a similar writing instrument without a spring (Experimental Example 1) was also produced. The movement amount L of the ball (Fig. 5) was set to 0.1 mm. At this time, the second pressing force (the pressing force of the spring when the ball is in contact with the seat) for each writing instrument was 3.99 gf (Experimental Example 2), 5.77 gf (Experimental Example 3), 7.88 gf (Experimental Example 4), 10.51 gf (Experimental Example 5), 13.14 (Experimental Example 6), and 21.04 gf (Experimental Example 7). The first pressing force (F1), second pressing force (F2), the difference between the first and second pressing forces (ΔF = F2 - F1), and the ratio (%) of the above difference to the first pressing force (P = ΔF / F1 × 100) for each writing instrument are shown in Table 1.

[0039]

Table 1

[0040] (3) Evaluation of diaper writing performance and ink leakage Using each writing instrument, "10-round writing" of continuously drawing a circle (〇) 10 times on white paper notepaper was carried out, and the presence or absence of ink leakage from the pen tip when not writing was examined (pen tip ink leakage test). Also, using each writing instrument, writing was done on a paper diaper, and the presence or absence of interruption of the handwriting was examined (diaper writing performance test). As the paper diapers, the product names "Moony" (Unicharm Corporation), "MamyPoko" (Unicharm Corporation), "Pampers" (Procter & Gamble Company), "Merries" (Kao Corporation), "Genki!" (Prince Nippon Paper Crecia Co., Ltd.), and "Goon" (Daio Paper Corporation) were used. 10 samples of each writing instrument were prepared and used for each test.

[0041] The results of the ink leakage test are shown in Table 2. The results of the diaper writing test are shown in Figure 8. In the numerical values (fractions) in Table 2, the denominator indicates the number of times of writing with a round pen, and the numerator indicates the number of times of ink leakage. For example, "1 / 20" indicates that writing with a round pen was performed 20 times, and ink leakage occurred once among them. The leakage rate is the ratio (%) of the total number of times of ink leakage to the total number of test times. Table 2 also shows the spring load (3.8 to 20 gf) of each writing instrument.

[0042]

Table 2

[0043] As shown in Table 2, ink leakage from the pen tip was well suppressed in the range where the spring load was 3.8 gf or more (leakage rate: 0 to 5.8%). In particular, the effect of suppressing ink leakage from the pen tip was remarkable in the range where the spring load was 7.5 gf or more (leakage rate: 0%). On the other hand, when there was no spring, ink leakage from the pen tip occurred frequently (leakage rate: 17%).

[0044] As shown in Figure 8, good writing performance was obtained in the range where the spring load was 12.5 gf or less (evaluations A, B). Particularly good writing performance was obtained in the range where the spring load was 10.0 gf or less (evaluation A). On the other hand, when the spring load was 20 gf, breaks in the handwriting occurred frequently (evaluation C).

[0045] (4) Ink outflow amount during continuous writing For each writing instrument, the ink outflow amount during continuous writing was measured. Specifically, under the conditions of a load of 100 g, a writing angle of 65 degrees, a writing speed of 7 cm / second, a temperature of 23 °C, and a humidity of 50%, continuous writing of 10 rounds with a circumference of 10 cm was performed on high-quality paper (manufactured by Kishu Paper Co., Ltd.) for a total of 10 m of writing. As a result, for all writing instruments, the ink outflow amount was in the range of 100 mg to 200 mg / 10 m.

[0046] From the above, the spring load (F1) is 3.8 gf to 12.5 gf (3.7×10 -2 N to 1.2×10 -1in the range of (N), and by setting the difference in pressing force (ΔF) to 0.64 gf or less (6.3×10 -3 N or less), it was possible to provide a writing instrument for disposable diapers that is excellent in both suppressing ink leakage from the pen tip and having a disposable diaper writing property.

Explanation of Signs

[0047] 1 Core member 2 Ink storage part 5 Pen tip 6 Spring 7 Ink 13 Tip body 15 Valve body 16 Valve body accommodation space (accommodation space) 17 Ink guide hole 18 Tip opening 22 Seat part 50 Writing instrument for disposable diapers 100 Disposable diaper

Claims

【Claim 1】 An ink writing instrument for diapers having an ink storage section storing ink, a pen tip chip connected to the ink storage section, and a spring, The pen tip chip has a chip body and a valve body. The chip body includes a storage space for accommodating the valve body, a tip opening, and an ink guiding hole. The tip opening is on the tip side of the storage space and communicates the inside and outside of the storage space. The ink guiding hole has its tip side opening on the inner surface of the rear end side of the storage space and communicates the inside and outside of the storage space. There is a seat portion centered on the opening of the ink guiding hole in the storage space. The valve body is spherical with a diameter of 0.8 mm or more and 1.2 mm or less. The valve body is in the storage space and a part of it is exposed from the tip opening. The spring presses the valve body toward the tip opening side. A first pressing force, which is the pressing force of the spring when the valve body seals the tip opening, is 2.9×10 －２ N or more and 1.5×10 －１ N or less. A value obtained by subtracting the first pressing force from a second pressing force, which is the pressing force of the spring when the valve body abuts against the seat portion, is 6.9×10 －３ N or less. A diaper writing instrument characterized in that an ink outflow amount during continuous writing is 100 mg or more and 200 mg or less per 10 m.

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