JP7781653B2 - writing implements - Google Patents

Description

The present invention relates to a writing instrument that is excellent at suppressing evaporation of water and the like from ink without impairing writing performance, even in environments with severe temperature changes or temperature gradients.

It has been known for some time that aqueous ink compositions for writing instruments such as marking pens contain polyhydric alcohols such as ethylene glycol and propylene glycol to inhibit evaporation of solvents in the ink and to prevent the pen tip from drying out.

For example, an ink composition for non-penetrating surfaces is known which contains ethylene glycol, and further contains propylene glycol and/or diethylene glycol, with the glycols contained in the ink composition in an amount of 4.0 to 12.0 wt %, a resin emulsion in which the resin solid content is 20 to 45 wt %, a pigment, and an aqueous solvent (see, for example, Patent Document 1).
However, this ink composition provides ink that has properties that ensure that handwriting is sufficiently water-resistant, warm water-resistant, and scratch-resistant even when written on the surface of glass or ceramic, and that allows handwriting to remain satisfactorily even after the glass product or ceramic is washed repeatedly. Therefore, the problem and technical concept (configuration and its effects) of the invention are different from those of the aqueous ink composition for writing instruments of the present invention, which is excellent in inhibiting evaporation of water and the like from the ink without impairing writing performance even in environments with severe temperature changes and temperature gradients.

On the other hand, conventionally, as a device for preventing water evaporation and condensation from a writing instrument, for example, a device for preventing water evaporation and condensation from a writing instrument is known, which is characterized in that, in a writing instrument having an ink tube containing water-based ink in the barrel, a liquid absorbent having continuous pores is attached to the barrel, and the liquid absorbent is made to absorb a saturated aqueous solution of salt that gives a relative humidity of 75 to 95% in a sealed atmosphere at room temperature (see, for example, Patent Document 2).
However, the device for preventing water evaporation and condensation of a writing instrument in Patent Document 2 prevents water evaporation and condensation by attaching a liquid absorbent with specific physical properties and continuous pores inside the barrel, and discloses a technology similar to that of the present invention.However, the present invention aims to suppress evaporation and suppress or prevent condensation, etc., from the perspective of ink composition, physical properties, etc., and the present invention and Patent Document 2 above have different technical concepts.

On the other hand, in recent years, some writing instruments have been known to use caps made of transparent materials with large internal volumes in order to show the pen tip. However, this type of writing instrument can have a problem in that condensation accumulates inside the cap in environments with temperature changes or temperature gradients, making it look unattractive.
In the past, the general approach to preventing condensation inside the cap was to reduce the internal volume of the cap and use an opaque material (so that it was not noticeable), but for writing instruments that use a cap made of a transparent material to reveal the pen tip, which has a window that allows the writing direction to be seen, it was currently difficult to make the cap out of an opaque material.In particular, with writing instruments that use ink that uses oil-soluble dyes, water-soluble dyes, or pigments as coloring materials, the coloring of condensation can be noticeable, so measures were needed.

JP 2017-71665 A (Claims, Tables 1 and 2, etc.) Utility Model Registration No. 61-40551 (Scope of Claims, Figure 1, etc.)

The present invention seeks to resolve the above-mentioned problems and current state of the prior art by providing an aqueous ink composition for writing instruments that is excellent at suppressing evaporation of water and other components in the ink without impairing writing performance, even in environments with severe temperature changes and temperature gradients; a writing instrument equipped with this aqueous ink composition; and a writing instrument equipped with this aqueous ink composition, even in a writing instrument equipped with a cap made of a transparent material, which, by incorporating the aqueous ink composition, does not cause condensation inside the cap, does not impair appearance, and allows the shape of the nib and the color of the aqueous ink to be visible through the cap, thereby providing a writing instrument with high quality and commercial value.

In light of the above-mentioned problems and other issues, the inventors conducted extensive research and discovered that by containing at least a colorant and water and setting the ink properties within specific ranges, it is possible to obtain the above-mentioned aqueous ink composition for a writing instrument, as well as a writing instrument, and thus completed the present invention.

That is, the aqueous ink composition for a writing instrument of the present invention is characterized by containing at least a coloring material and water, and the molar fraction of water in the ink is 0.96 (96%) or less.
The aqueous ink composition for a writing instrument preferably contains a water-soluble low-molecular-weight compound selected from Group A below.
Group A: ethylene glycol, propylene glycol, diethylene glycol, glycerin, amines, trimethylglycine, pentaerythritol, trimethylolpropane, trimethylolethane The writing instrument of the present invention is characterized by being equipped with an aqueous ink composition for a writing instrument having the above-mentioned composition.
It is preferable that the writing instrument comprises at least a barrel containing an aqueous ink composition for a writing instrument, a pen tip provided at the tip side of the barrel and capable of ejecting the aqueous ink composition for a writing instrument, and a cap made of a transparent material that is removably attached to the pen tip side of the barrel.
The pen tip preferably has a window through which the writing direction can be visually confirmed.

According to the present invention, even in environments with severe temperature changes and temperature gradients, a writing instrument equipped with a cap made of the transparent material of the present invention does not lose its writing performance , does not develop condensation inside the cap, and does not lose its appearance.Furthermore, the shape of the nib and the color tone of the water-based ink can be seen through the cap, so a writing instrument with high quality and commercial value is provided.
The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

1A and 1B are drawings showing an example (first embodiment) of an embodiment of a writing instrument having a cap formed of a transparent material of the present invention, in which (a) is a plan view, (b) is a front view, and (c) is a vertical cross-sectional view from the front. 2A and 2B are enlarged perspective views of the pen tip of the writing instrument of FIG. 1, where FIG. 2A is an enlarged perspective view of the pen tip as seen from one direction, and FIG. 2B is an enlarged perspective view of the pen tip as seen from a direction expanded 180° from FIG. 1A and 1B are drawings showing another example (second embodiment) of an embodiment of a writing instrument having a cap formed of a transparent material of the present invention, in which (a) is a plan view, (b) is a front view, and (c) is a vertical cross-sectional view from the front. 4A is an enlarged perspective view of the pen tip of the writing instrument of FIG. 3, where FIG. 4A is an enlarged perspective view of the pen tip as seen from one direction, and FIG. 4B is an enlarged perspective view of the pen tip as seen from a direction expanded 180° from FIG. 4A. 1A and 1B are drawings showing another example (third embodiment) of an embodiment of a writing instrument having a cap formed of a transparent material of the present invention, where (a) is a central longitudinal cross-sectional view and (b) is a central transverse cross-sectional view. 6A and 6B are diagrams showing an example of the writing implement of FIG. 5 with the cap removed, in which FIG. 6A is a perspective view seen from the front side, and FIG. 6B is a perspective view seen from the rear side. 6A to 6D are diagrams showing an example of the state in which the cap body of the writing instrument of FIG. 5 is attached, in which (a) is a front view, (b) is a plan view, (c) is a left side view, and (d) is a right side view.

Embodiments of the present invention are described in detail below. However, please note that the technical scope of the present invention is not limited to the embodiments detailed below, but extends to the inventions set forth in the claims and their equivalents. Furthermore, the present invention can be implemented based on the content disclosed in this specification and common general technical knowledge in the relevant field (including design matters and obvious matters).

<Water-based ink composition for writing instruments>
The aqueous ink composition for a writing instrument of the present invention is characterized by containing at least a coloring material and water, and the molar fraction of water in the ink is 0.96 (96%) or less.

<Water mole fraction>
In the present invention, an aqueous ink composition for a writing instrument is used, in which the molar fraction of water is 0.96 (96%) or less. The evaporation of water contained in the ink and the molar fraction will be explained below.
When aqueous ink is placed in an environment of a certain temperature and humidity, the evaporation of the water contained in the ink does not proceed until all the water in the ink is gone; there is a correlation between the humidity and the end point of evaporation.
If the saturated water vapor pressure at a certain temperature is P (Pa), the partial pressure of water in the atmosphere is expressed by P x W/100 (Pa) where W (%) is the molar fraction of water (i.e., relative humidity). On the other hand, the frequency of evaporation of water molecules is roughly proportional to the molar fraction C (%) of water in the ink, so the amount of evaporated water is proportional to the molar fraction of water.

In the present invention, the "molar fraction of water" refers to the molar fraction of water in the water and water -soluble compounds with a molecular weight of 300 or less contained in the ink.
When an ink contains n (n≧0) water-soluble compounds other than water that have a molecular weight of 300 or less, in addition to water, the molar fraction of water can be calculated using the following formula (I), where the n water-soluble compounds are water-soluble compounds 1, 2, 3, ..., n, and the molecular weight of water is 18. In formula (1), _MW1 , _MW2 , _MW3 , ..., MWn respectively represent the molecular weights of water-soluble compounds 1, 2, 3, ..., n that have a molecular weight of 300 or less contained in the ink. Furthermore, Cw represents the content (% by mass) of water in the ink, and _C1 , _C2 , _C3 , ..., Cn respectively represent the content (% by mass) of water-soluble compounds 1, 2, 3, ..., n that have a molecular weight of 300 or less in the ink. Note that when an ink does not contain any water-soluble compounds other than water, the molar fraction of water in the ink is 100%.

The "molar fraction of water" in the present invention is a value calculated for water and water -soluble compounds having a "molecular weight of 300 or less."
The reason why compounds with a "molecular weight of 300 or less" are used as the target compounds for calculating the molar fraction of water is that compounds with a molecular weight sufficiently larger than that of water do not substantially affect the molar fraction of water at the normal content in an aqueous ink composition for writing instruments. Pigments, resins, surfactants, and other compounds typically used in aqueous ink compositions for writing instruments have much larger molecular weights than water, and therefore do not need to be considered because their molar numbers are extremely small at normal content levels in aqueous ink compositions for writing instruments. Furthermore, considering compounds that are soluble in water in an aqueous ink composition for writing instruments and whose content is 1.0% by mass or more is sufficient to substantially realize the effects of the present invention. Compounds that meet the above definition can essentially include water-soluble solvents (including water- soluble compounds and solid substances) as described below.

In the present invention, as will be described later, the effects of the present invention can be achieved by using an aqueous ink composition for a writing instrument in which the molar fraction of water is 0.96 (96%) or less, more preferably a water molar fraction of 0.75 (75%) or more and 0.96 (96%) or less, and particularly preferably a water molar fraction of 0.85 (85%) or more and 0.91 (91%) or less.
Inks with a water mole fraction greater than 0.96 (96%) will cause condensation to form inside the cap when the product is heated.

<Colorant>
Usable coloring materials include those used for writing instruments, such as dyes that dissolve or disperse in water, conventionally known inorganic and organic pigments such as titanium oxide, colored resin microparticles or dispersions thereof (including resin particle pigments containing pigments, pseudo-pigments in which resin emulsions are colored with dyes, white plastic pigments, hollow resin pigments (particles) and the like), pigments in which a silica or mica base is coated with a multilayer surface layer of iron oxide or titanium oxide or the like, thermochromic pigments, photochromic pigments, and composite pigments of these can be used.
Examples of dyes include fluorescent dyes, water-soluble dyes, and oil-soluble dyes.

Fluorescent dyes that can be used are not particularly limited as long as they have good color development, but examples include Basic Yellow 1, Basic Yellow 40, Basic Red 1, Basic Red 1:1, Basic Red 13, Basic Violet 1, Basic Violet 7, Basic Violet 10, Basic Violet 11:1, Basic Orange 22, Basic Blue 7, Basic Green 1, Acid Yellow 3, Acid Yellow 7, Acid Red 52, Acid Red 77, Acid Red 87, Acid Red 92, Acid Blue 9, Disperse Yellow 121, Disperse Yellow 82, Disperse Yellow 83, Disperse Orange 11, Disperse Red 58, Disperse Blue 7, Direct Yellow 85, Direct Orange 8, Direct Red 9, Direct Blue 22, Direct Green 6, Solvent Yellow 44, Solvent Red 49, Solvent Blue 5, and Solvent Green 7. Among the fluorescent dyes listed above, azomethine, xanthene, and triphenylmethane fluorescent dyes are particularly preferred in terms of color development and ink stability. Specifically, particularly preferred fluorescent dyes include azomethine fluorescent dyes such as Basic Yellow 1 and Basic Yellow 40, xanthene fluorescent dyes such as Basic Red 1:1 and Basic Violet 11:1, and triphenylmethane fluorescent dyes such as Basic Violet 1. These dyes may be used alone or in combination of two or more.

Examples of colored resin microparticles or dispersions thereof include a dispersion of colored resin microparticles in water, which are composed of at least a carboxyl group-containing vinyl monomer (A) having a solubility in water of 10% by mass or less as an acidic functional group, an ester monomer (B) of acrylic acid or methacrylic acid with a linear or cyclic alcohol having 2 to 18 carbon atoms, and a basic dye or oil-soluble dye; and a dispersion of colored resin microparticles in water, which are composed of cyclohexyl (meth)acrylate monomer and a basic dye or oil-soluble dye, wherein the content of the cyclohexyl (meth)acrylate monomer is 30% by mass or more, based on the total polymer components constituting the colored resin microparticles, and the content of the basic dye or oil-soluble dye is 15% by mass or more, based on the total polymer components constituting the colored resin microparticles.

Examples of thermochromic pigments include those produced by microencapsulating a thermochromic composition containing at least a leuco dye that functions as a color former, a color developer that is a component capable of causing the leuco dye to develop color, and a color change temperature regulator that can control the color change temperature during color development of the leuco dye and the color developer, so that the resulting microencapsulated particles have a predetermined average particle size (for example, 0.1 to 10 μm).
Examples of photochromic pigments include photochromic particles composed of at least one selected from photochromic dyes (compounds), fluorescent dyes, and the like, and a resin such as a terpene phenol resin; and photochromic pigments produced by microencapsulating a photochromic composition containing at least one selected from photochromic dyes (compounds), fluorescent dyes, and the like, an organic solvent, and additives such as an antioxidant, a light stabilizer, and a sensitizer, so as to have a predetermined average particle size (for example, 0.1 to 10 μm).
In the present invention (including examples), the "average particle size" is a D50 value calculated on a volume basis with a refractive index of 1.81 using a particle size distribution analyzer HR9320-X100 (manufactured by Nikkiso Co., Ltd.).

These coloring materials can be used either alone or in combination of two or more (hereinafter simply referred to as "at least one").
The (total) (solid content) of these coloring materials is preferably 0.1 to 40% by mass, and more preferably 1 to 30% by mass, based on the total amount of the aqueous ink.
By setting the content of this coloring material to 0.1% by mass or more, sufficient line density can be obtained, while by setting it to 40% by mass or less, an increase in viscosity can be suppressed and the fluidity of the ink can be improved, which is preferable.

In the present invention, in order to efficiently adjust the molar fraction of water to 0.96 (96%) or less without deteriorating writing performance and to further enhance the effects of the present invention, it is preferable that the aqueous ink composition for a writing instrument contains at least one water-soluble low-molecular-weight compound selected from the following Group A:
Group A: ethylene glycol, propylene glycol, diethylene glycol, glycerin, amines, trimethylglycine, pentaerythritol, trimethylolpropane, trimethylolethane. Examples of amines include triethanolamine and aminomethylpropane.
Particularly preferably, propylene glycol, ethylene glycol, glycerin, and trimethylglycine are used.
The (total) content of these water-soluble low-molecular-weight compounds of Group A is not particularly limited as long as the molar fraction of water in the ink composition is 0.96 (96%) or less.
It is about 15 to 50 mass %.

<Other ingredients>
The aqueous ink of this embodiment contains the above-mentioned colorant, water (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.) as a solvent as the remainder, and a water-soluble low-molecular-weight compound. In addition, as long as the aqueous ink composition for a writing instrument has a water molar fraction of water of 0.96 (96%) or less, it may contain various components commonly used in aqueous inks, such as dispersants, surfactants, viscosity adjusters, fixing resins, rust inhibitors, preservatives or antibacterial agents, and pH adjusters, as necessary, within the range in which the effects of the present invention are achieved.

The dispersant and adhesive resin that can be used may contain a water-soluble resin. For example, at least one type can be selected from water-soluble resins such as acrylic resins, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, and urethane resins, as well as resin emulsions such as acrylic emulsions, vinyl acetate emulsions, urethane emulsions, and polyolefin emulsions.

The surfactant that can be used is not particularly limited, but at least one surfactant selected from the group consisting of fluorine-based surfactants, acetylene glycol-based surfactants, and silicone-based surfactants can be used.

Viscosity adjusters that can be used include natural polymers such as polysaccharides and synthetic polymers. Examples of polysaccharides that can be used include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, welan gum, succinoglycan, diutan gum, and dextran, as well as cellulose derivatives such as methylcellulose, ethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose, and starch glycolic acid and its salts. Examples of synthetic polymers that can be used include polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, polyethylene oxide, vinyl acetate-polyvinylpyrrolidone copolymer, styrene-acrylic acid copolymer and its salts, and isobutylene-maleic anhydride copolymer and its salts.

Usable antiseptics or antibacterial agents include phenol, sodium omadine, sodium benzoate, benzisothiazoline, benzimidazole compounds, etc. Usable rust inhibitors include benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, saponins, etc.
Examples of pH adjusters that can be used include amine compounds such as triethanolamine, diethanolamine, monoethanolamine, dimethylethanolamine, morpholine, and triethylamine; ammonia; and alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide.

The aqueous ink composition for a writing instrument of the present invention can be prepared by combining at least the above-mentioned colorant, water, the water-soluble low-molecular-weight compound selected from Group A above, and other components in an appropriate amount depending on the intended use of the writing instrument ink (for use in a marking pen, etc.), and mixing the components in suitable amounts using a stirrer such as a homomixer, homogenizer, or disper, and then, if necessary, removing coarse particles from the ink composition by filtration or centrifugation, thereby obtaining an aqueous ink composition for a writing instrument having a water molar fraction of 0.96 (96%) or less.
Furthermore, the pH (25°C) of the aqueous ink composition for a writing instrument is preferably adjusted to 5 to 10 using a pH adjuster or the like, from the viewpoints of usability, safety, the stability of the ink itself, and compatibility with the ink container, and more preferably 6 to 9.5.

The aqueous ink composition for writing instruments of the present invention, configured in this manner, contains at least a colorant and water, and by setting the water molar fraction in the ink to 0.96 (96%) or less, condensation inside the cap can be suppressed. This results in an aqueous ink composition for writing instruments that is excellent at suppressing evaporation of water and other components from the ink without impairing writing performance, even in environments with severe temperature changes and temperature gradients (this point will be further described in detail in the examples, etc., below).

<Writing instruments>
The writing instrument of the present invention is equipped with an aqueous ink composition for a writing instrument having the above-described characteristics, and is therefore capable of suppressing evaporation of the water content of the ink without impairing writing performance, even in environments with severe temperature changes or temperature gradients.
As a writing instrument, for example, it is mounted on a ballpoint pen, marking pen, or the like having a pen tip portion such as a ballpoint tip, fiber tip, felt tip, plastic tip, fiber core, or porous core.

In this invention, a "marking pen" refers to a pen that has a mechanism for supplying ink stored in an ink reservoir to a resin writing part by capillary action, and includes pens referred to as "sign pens." Also, a "ballpoint pen" refers to a pen that has a mechanism for causing ink stored in an ink reservoir to seep out by the rotation of a ball provided in the writing part.
For a ballpoint pen, the aqueous ink composition for a writing instrument having the above-described composition is contained in a ballpoint pen ink container (refill) equipped with a ball having a diameter of 0.18 to 2.0 mm, and an ink follower is added. The ink follower is a liquid that is incompatible with the aqueous ink composition for a writing instrument having the above-described characteristics contained in the ink container and has a lower specific gravity than the aqueous ink composition, such as polybutene, silicone oil, or mineral oil.
The structure of the ballpoint pen, marking pen, etc. is not particularly limited, and may be, for example, a direct ink type ballpoint pen or marking pen having a collector structure (ink retention mechanism) in which the barrel itself serves as an ink container and is filled with the aqueous ink composition for a writing instrument having the above-described structure.

<Writing Instrument of Preferred Embodiment: Figures 1 and 2>
As shown in Figures 1(a) to 1(c), the writing instrument of this embodiment is a writing instrument A comprising at least a barrel 10 in which an aqueous ink composition for a writing instrument having the above-mentioned characteristics is housed via an ink occlusion body 15, a nib 20 provided on the tip side of the barrel 10 and capable of ejecting the aqueous ink composition for a writing instrument, and a cap 60 made of a transparent material and removably attached to the nib 20 side of the barrel 10, wherein the aqueous ink composition for a writing instrument contains at least the above-mentioned colorant and water, and the molar fraction of water in the ink is 0.96 (96%) or less.
The aqueous ink composition for a writing instrument used is the above-mentioned aqueous ink composition for a writing instrument in which the molar fraction of water in the ink is 0.96 (96%) or less, and therefore a detailed description thereof will be omitted.

Figure 1(a) is a plan view of a writing instrument equipped with a cap formed from a transparent material of this embodiment, (b) is a front view thereof, and (c) is a front longitudinal cross-sectional view thereof. Figure 2 is an enlarged perspective view of the nib of the writing instrument of Figure 1, where (a) is an enlarged perspective view of the nib as seen from one direction, and (b) is an enlarged perspective view of the nib as seen from a direction expanded 180 degrees from (a).
1(a) to 1(c), the writing instrument A of this embodiment is loaded with water-based ink having the above-described characteristics, and is a twin-type writing instrument that includes a nib 20 that guides water-based ink supplied from an ink occlusion body 15 in a barrel (writing instrument body) 10 and has a window (visible portion) through which the writing direction can be visually confirmed, and also includes a rod-shaped polyacetal nib 50 on the opposite side of the nib 20. Attached to both sides of the writing instrument body 10 are a cap 60 having a clip portion 60a made of a transparent material that protects the detachable nib 20, and a cap 70 made of a transparent material that protects the nib 50.

The barrel 10 is made of, for example, a thermoplastic resin, a thermosetting resin, or the like, and is a cylindrical body that houses an ink absorbing body 15 impregnated with the water-based ink having the above-mentioned characteristics. One end, which is on the right side in the drawing, is a holding portion 11 having a fitting portion for fastening, by fitting, a holder 55 that holds a fine-point, rod-shaped nib 50, and the other end, which is on the left side, is fitted with a tip barrel 16 to which is fastened a nib 20 having a viewing portion that serves as a window through which the writing direction can be seen.
The barrel 10 is formed into a cylindrical shape using a resin such as polypropylene, and functions as the main body (shaft) of the writing instrument. The barrel 10 is formed to be opaque or transparent (and translucent), but either may be adopted from the viewpoint of appearance and practicality.

The ink occlusion body 15 is impregnated with an aqueous ink composition for writing instruments with the above-mentioned characteristics, and includes, for example, fiber bundles made of one or a combination of two or more types of natural fibers, animal hair fibers, polyacetal resins, acrylic resins, polyester resins, polyamide resins, polyurethane resins, polyolefin resins, polyvinyl resins, polycarbonate resins, polyether resins, polyphenylene resins, etc.; processed fiber bundles such as felt; and porous bodies such as sponges, resin particles, and sintered bodies. This ink occlusion body 15 is contained within the barrel 10, which forms the main body of the writing instrument.

2(a) and 2(b), the pen tip 20 is composed of at least a writing lead 30 having a writing portion 25 and a holder 40 having a visible portion. The writing lead 30 having the writing portion 25 is attached to the holder 40 (described later) by adhesive, welding, fitting, or the like.
The writing core 30 has a writing portion 25 that is inclined (knife-cut) to make writing easier, and thin plate bodies (sheet bodies) 31, 31 extending from both ends of the writing portion 25, all of which are connected together and have an external shape that is approximately U-shaped (including C-shaped), with the cross section of the thin plate bodies 31, 31 being rectangular.

The writing core 30 is not particularly limited as long as it efficiently guides (supplies) the water-based ink with the above-mentioned vapor pressure characteristics stored in the barrel 10 to the writing portion 25 via the thin plates 31, 31. Examples include materials made from fabrics such as nonwoven fabrics, woven fabrics, or knitted fabrics, or liquid-permeable materials such as liquid-permeable foams and sintered bodies. The writing core 30, including the writing portion 25, can be made from a single material, but it can also be made by combining multiple materials, such as by laminating them, or by connecting or joining the writing portion 25 and the parts other than the writing portion 25 together using separate members.

The shape and thickness of the writing lead 30 having the writing portion 25 are determined based on factors such as the manner of attachment to the holder 40, the shape of the writing portion 25, maximizing the area of the visible portion 43, and efficiently flowing (supplying) ink to the writing portion. Preferably, the width and length correspond to the width and circumferential lengths of the attachment surface of the holder 40 (described below) to which the thin plate members 31, 31 of the writing lead 30 are attached, respectively, and are set to lengths suitable for efficiently flowing ink to the writing portion 25. Furthermore, the thickness of the thin plate members 31, 31 of the writing lead 30 other than the writing portion 25 is preferably 0.3 to 3.0 mm, and most preferably 0.5 to 1.0 mm, in order to maximize the area of the visible portion 43.

In this embodiment, the writing part 25 is integral with the thin plate members 31, 31 of the writing lead 30, and is inclined (knife-cut) to facilitate writing, with the inclination being appropriately set according to ease of use for writing, etc. The writing part 25 also has a wide line width, preferably 1 mm or more, and more preferably 2 mm or more.
The writing lead 30 including the writing portion 25 of this embodiment is integrally formed from a sintered lead made by sintering plastic powder.

In the above embodiment, the writing portion 25 of the writing lead 30 and the thin plate members 31, 31 are integrally formed from the same material, but the writing portion 25 and the thin plate members 31, 31 may be formed from separate members and connected, joined, or abutted together. The writing portion 25 may be formed, for example, from a porous material having air holes, such as a sponge, sintered body, fiber bundle, foam, spongy body, felt, or porous body. Porous materials that can be used include, for example, natural fibers, animal hair fibers, polyacetal resins, polyethylene resins, acrylic resins, polyester resins, polyamide resins, polyurethane resins, polyolefin resins, polyvinyl resins, polycarbonate resins, polyether resins, and polyphenylene resins. Specifically, the writing portion 25 can be made from a sintered body of various plastic powders, and the thin plates 31, 31 can be made from a fabric such as nonwoven fabric, woven fabric, or knitted fabric, or a liquid-permeable material such as a liquid-permeable foam.

The holder 40 fixes the writing portion 25 and thin plate bodies 31, 31 of the writing lead 30 and is fixed to the tip opening of the tip shaft 16 of the writing instrument body 10, and has a visible portion (visible portion) 43 that allows the writing direction to be visually confirmed.
In addition, the portion of the holder 40 (thin plate-like body 31, 31) that abuts against the side of the holder 40 of the writing core 30 has a rectangular cross-section, and the outer edge of the visible portion 43, which forms the front end of the holder 40, is formed into an inclined refractive surface 43a, 43a.
By making the portion of the writing core 30 that abuts against the side of the holder 40 rectangular in cross section, the width of the visible portion 43 relative to the cross-sectional area can be increased, and by making the outer peripheral edge of the visible portion 43 of the holder 40 into inclined refractive surfaces 43a, 43a, the rectangular cross section can be made to appear thinner, and the area of the visible portion 43 can be made to appear even wider than before.

The entire holder 40 configured in this manner is made of a hard material, such as a hard material with visibility, such as glass or a resin without rubber elasticity. Examples of resins without rubber elasticity that allow visibility include PP, PE, PET, PEN, nylon (including amorphous nylon in addition to common nylons such as nylon 6 and nylon 12), acrylic, polymethylpentene, polystyrene, and ABS. By molding the holder 40 from a material with a visible light transmittance of 50% or more, characters written in the writing direction can be effectively seen through the visible portion 43. Note that only the visible portion 43 (including the inclined refractive surfaces 43a, 43a) may be made of a visible material. Visible light transmittance (transmittance) can be determined by measuring reflectance using a multi-light source spectrophotometer (MSC-5N, manufactured by Suga Test Instruments Co., Ltd.).

The holder 40 may be made of one of the above materials, or two or more of them to further improve durability and visibility, and can be molded using various molding methods such as injection molding and blow molding.

The thin plate bodies 31, 31 of the writing lead 30 are fixed to the mounting surface of the U-shaped holding groove of this holding body 40 by adhesive bonding, welding, etc., and are fixed to the writing part 25.
In this embodiment, in order to maximize the viewing area of the viewing portion 43, the thickness of the thin plate bodies 31, 31 is thinner than the thickness of the writing portion 25, and it is desirable that the width of the ink guide portion be less than 90% of the width of the viewing portion 43 of the holder 40, and more preferably 50 to 80%.

As shown in Figures 1(a) to (c), the pen tip 50 is a fine-point rod-shaped pen tip with a circular cross section. The rear end (ink occlusion body side) of the pen tip 50 is inserted into the ink occlusion body 15, and aqueous ink having the above-mentioned vapor pressure characteristics of the ink occlusion body is supplied to the pen tip 50 by capillary force.
The pen tip 50 is made of a porous material, such as a parallel fiber bundle made of one or a combination of two or more types of natural fibers, animal hair fibers, polyacetal resin, polyethylene resin, acrylic resin, polyester resin, polyamide resin, polyurethane resin, polyolefin resin, polyvinyl resin, polycarbonate resin, polyether resin, polyphenylene resin, etc.; a fiber core made by processing fiber bundles such as felt or resin-processing these fiber bundles; or a porous body (sintered core) made by sintering plastic powder such as thermoplastic resins such as polyolefin resin, acrylic resin, polyester resin, polyamide resin, polyurethane resin, etc.

Preferred pen tips 50 include fiber bundle tips, fiber tips, sintered tips, felt tips, sponge tips, and inorganic porous tips, with fiber tips being particularly preferred in terms of deformation moldability and productivity. The porosity, size, hardness, and other properties of the pen tip 50 vary depending on the type of ink and writing implement, and a porosity of 30 to 60%, for example, is preferred. In the present invention, "porosity" is calculated as follows: First, a writing tip with a known mass and apparent volume is immersed in water, and after sufficient water absorption, the mass is measured after removal from the water. The volume of water absorbed into the writing tip is calculated from the measured mass. The volume of water is considered to be the same as the pore volume of the writing tip, and the porosity is calculated using the following formula:
Porosity (unit: %) = (volume of water) / (apparent volume of pen tip 50) × 100

In this embodiment, as shown in Figures 1(a) to (c), a cap 60 having a clip 60a made of a transparent material and removably attached by fitting to the outer periphery of one of the barrel tubes 10 on the pen tip 20 side and the outer periphery of the other barrel tube 10 on the pen tip 50 side is attached, and a cap 70 having an inner cap 70a is attached.
The caps 60 and 70 are made of, for example, a transparent (visible) material, such as glass, a resin without rubber elasticity, etc. Examples of transparent (visible) resin without rubber elasticity include PP, PE, PET, PEN, nylon (including amorphous nylon in addition to common nylons such as nylon 6 and nylon 12), acrylic, polymethylpentene, polystyrene, ABS, and other materials with a visible light transmittance of 50% or more, which allows the pen nibs 20 and 50 to be seen (visually recognized) through the caps 60 and 70 from the outside.

The caps 60 and 70 may be entirely made of a transparent (visible) material, or only part of them may be made of a transparent material, as long as the pen tip 20, 50 and the ink color can be seen (visually recognized). Furthermore, if the aqueous ink of this embodiment is a thermochromic ink, a thermoplastic elastomer with a pencil line erasability (erasure rate) of less than 70% as specified in JIS S 6050-2002 is formed on the top of the cap 60. This creates a friction body that easily generates frictional heat and has low wear when rubbed, thereby reducing the generation of eraser dust during friction and preventing stains on the surrounding area.

In writing instrument A configured in this manner, an ink occlusion body 15 containing water-based ink with the above-described characteristics is inserted and held within the writing instrument body 10, and the nib 20 configured as described above is attached to the tip end via the tip barrel 16 by sequentially fitting or the like. The holder 55 to which the nib 50 is attached is then attached to the other end by fitting, thereby easily creating a twin-type writing instrument A. The water-based ink with the above-described vapor pressure characteristics occluded in the ink occlusion body 15 is efficiently supplied to the writing section 25 and the nib 50 by capillary force in the nib 20 via the thin plates 31, 31 of the writing core 30, and is then used for writing.

Even in the marking pen-type writing instrument A of this embodiment, a cap 60 (including cap 70, hereinafter) made of a transparent material and with a large internal volume is used to reveal the nib 20. Even in environments with temperature changes or temperature gradients, such as in direct sunlight, near a heating vent, near a heat source such as a PC, or accidentally placed on an electric carpet, the water-based ink composition used has a water molar fraction of 0.96 (96%) or less, so condensation does not occur inside the cap 60 and the appearance is not impaired. Furthermore, the shape of the nib 20, 50 and the color of the water-based ink (e.g., yellow, pink, etc.) can be seen through the caps 60, 70, resulting in a writing instrument with high quality and commercial value (this point will be further described in the examples below).

Furthermore, in this writing instrument A, the nib 50 is the same as a conventional general-purpose nib, so to explain the function of the nib 20, as shown in Figures 1 and 2, the nib 20 has a viewing area (window) 43 that allows the writing direction to be visually confirmed, and the water-based ink with the above-mentioned vapor pressure characteristics of the ink occlusion body 15 reaches the writing area 25 by the capillary force of the thin plates 31, 31 of the writing core 30 and is used for writing. When writing, looking at the viewing side through the viewing area (window) 43 makes it easier to align the start position of the stroke and also allows you to stop exactly where you want to stop the stroke, preventing over-stroking or overdrawing.

Furthermore, the pen tip 20 guides ink from the ink occlusion body 15 to the writing part 25 via the thin plates 31, 31 of the writing lead 30, which are thinner than the thickness of the writing part 25 and have a good flow-through property. Furthermore, since these thin plates 31, 31 are made of a sheet-like porous material, they have good ink flow-through properties, do not need to be designed to be thick, and the visible part 43 is not obstructed. Furthermore, by making the portion of the writing lead 30 that abuts the side of the holder 40 rectangular in cross section, the width of the visible part 43 relative to the cross-sectional area can be increased, and the outer periphery of the visible part 43 of the holder 40 can be adjusted. By making the edges into sloping refractive surfaces 43a, 43a, the rectangular cross section appears thinner, so that when a right-handed person writes from left to right, they can draw lines with the writing part 25 while visually checking the writing direction with the visual part 43.In addition, the effective area of the visual part relative to the entire pen tip is maximized, and the thin plate bodies 31, 31 with the above-mentioned characteristics efficiently supply ink to the integrally constructed writing part 25, resulting in good ink outflow, resulting in a writing instrument that maximizes the effective area of the visual part 43 without compromising ink outflow.

<Writing instrument of second embodiment: Overall configuration: FIGS. 3 and 4>
As shown in Figure 3, the writing instrument of this second embodiment is characterized by being a writing instrument comprising at least a barrel 10 in which an aqueous ink composition for a writing instrument, in which the molar fraction of water in the ink having the above-mentioned characteristics is 0.96 (96%) or less, is contained via an ink occlusion body 15, a nib 20 capable of ejecting aqueous ink and provided on the tip side of the barrel 10, and a cap 60 made of a transparent material and removably attached to the nib 20 side of the barrel 10.

<Writing Instrument of Second Embodiment: Specific Configuration>
Figure 3(a) is a plan view of a writing instrument having a cap made of a transparent material according to the second embodiment, (b) is a front view thereof, and (c) is a longitudinal cross-sectional view thereof viewed from the front. Figure 4 is an enlarged perspective view of the nib of the writing instrument of Figure 1, where (a) is an enlarged perspective view of the nib as viewed from one direction, and (b) is an enlarged perspective view of the nib as viewed from a direction expanded 180° from (a).
As shown in Figure 3, the writing instrument of this embodiment is a writing instrument B that includes at least a barrel 10 in which an aqueous ink composition for a writing instrument, the water content of which is 0.96 (96%) or less, is contained in an ink occlusion body 15; a nib 20 that is provided at the tip of the barrel 10 and is capable of ejecting the aqueous ink; and a cap 60 made of a transparent material that is removably attached to the nib 20 side of the barrel 10, wherein the aqueous ink contains at least a colorant and water, and the water content of the ink is 0.96 (96%) or less.
In the second embodiment below, when the writing instrument has the same configuration and function as the writing instrument A of the first embodiment, the same reference numerals are used in the drawings and the description thereof will be omitted.

The writing instrument B of the second embodiment uses a writing lead 30 with a U-shaped outer shape as in the above embodiment, but the second embodiment differs in that a writing lead 35 with an L-shaped outer shape is attached to a holder 40, as shown in Figures 3 and 4.
The writing portion 36 of the writing lead 35 of the second embodiment has the same shape as the writing portion of the above embodiment, and is inclined (knife-cut) to make writing easier. In the writing lead 35, a thin plate body 37 is integrally connected to the end side of the writing portion 36, and the outer shape is formed in an L-shape, and the cross section of the thin plate body 37 is rectangular.
As shown in Figure 4, the holder 40 secures the writing portion 36 and thin plate body 37 of the writing lead 35 and is fixed to the tip opening of the front barrel 16 of the writing instrument body 10. In the embodiment of Figure 1, mounting surfaces for attaching the thin plate bodies 31, 31 were formed on the top and bottom, but in this embodiment, since the outer shape is L-shaped, the holder 40 is attached only to the bottom side.

Even in the writing instrument B of this second embodiment, a cap 60 made of a transparent material with a large internal volume is used to allow the nib 20 to be seen. Even in environments with temperature changes or temperature gradients, such as in direct sunlight, near a heating vent, near a heat source such as a PC, or accidentally placed on an electric carpet, the aqueous ink composition used has a water molar fraction of 0.96 (96%) or less, so condensation does not occur inside the cap 60 and the appearance is not impaired. Furthermore, the shape of the nib 20, 50 and the color of the aqueous ink (e.g., yellow, pink, etc.) can be seen through the caps 60, 70, resulting in a writing instrument with high quality and commercial value (this point will be further described in the examples below).

In addition, in this second embodiment of writing instrument B, the writing lead 35 has an L-shaped outer shape, and therefore, unlike the U-shaped outer shape of Figure 1, the thin plate body 31 is not attached to the upper surface of the visible portion 43, so there is no obstruction and the area of the visible portion can be increased accordingly.Furthermore, by making the portion of the writing lead 35 that abuts the side of the holder 40 rectangular in cross section, the width of the visible portion 43 relative to the cross-sectional area on the bottom side can be increased.Furthermore, by making the outer peripheral edge of the visible portion 43 of the holder 40 into inclined refractive surfaces 43a, 43a, the rectangular cross section can be made to appear thinner, making the area of the visible portion 43 appear even larger than in Figure 1.

The pen tip 20 of this second embodiment is attached in the same manner as the writing implement of Figure 1 and has a viewing portion (window portion) 43 that allows the writing direction to be viewed, and the water-based ink in the ink occlusion body 15 reaches the writing portion 35 by the capillary force of the writing core 36 and is used for writing. When writing, looking at the viewing side through the viewing portion (window portion) 43 makes it easier to align the start position of the stroke and also allows the stroke to be stopped exactly where you want it to end, preventing over-stroking or overdrawing.
In the second embodiment, the pen tip 20 guides the water-based ink from the ink occlusion body 15 to the writing part 36 via a thin plate 37 of the writing lead 35 that is thinner than the thickness of the writing part 35 and has a tendency to flow out. Furthermore, this thin plate 37 is made of a material that has a better ink supplying ability than the embodiment of FIG. 1, so the ink flow is good, there is no need to design it thick, and the visible part 43 is not obstructed. Furthermore, by making the part of the writing lead 35 that abuts against the side of the holder 40 rectangular in cross section, the width of the visible part 43 relative to the cross-sectional area can be increased, and the width of the holder 40 can be reduced. By making the outer edge of the visible portion 43 into inclined refractive surfaces 43a, 43a, the rectangular cross section can be made to appear thinner, so that when a right-handed person writes from left to right, they can draw lines with the writing portion 36 while viewing the writing direction with the visible portion 43.Furthermore, in addition to maximizing the effective area of the visible portion relative to the entire pen tip, the thin plate body 37 with the above-mentioned characteristics allows ink to be efficiently supplied to the integrally constructed writing portion 36, so that the ink outflow properties are also good, and a writing instrument can be obtained that can maximize the effective area of the visible portion 43 more than the embodiment of Figure 1 without impairing the outflow properties of ink.

<Writing instrument of third embodiment: Overall configuration: FIGS. 5 to 7>
The writing instrument C of this third embodiment is a marking pen type writing instrument, and comprises at least a barrel 80 containing aqueous ink, a nib 90 capable of ejecting aqueous ink and provided at the tip side of the barrel 80, and a cap 65 formed of a transparent material and removably attached to the nib 90 side of the barrel 80, wherein the aqueous ink is an aqueous ink composition for writing instruments in which the molar fraction of water in the ink is 0.96 (96%) or less.

As shown in FIGS. 5 to 7, the writing instrument C of the third embodiment includes a barrel 80, an ink storage body 85, a lead 95, a pen tip 90, and a cap body 65, which constitute the writing instrument body.
The barrel 80 is made of the same material as the barrel 10 of the first embodiment, and has a bottomed, cylindrical rear barrel 81 that houses an ink absorbing body 85 impregnated with water-based ink having the above-mentioned characteristics, and a front barrel 86 to which the nib 40 is fixed.
The rear barrel 81 is molded into a long, bottomed elliptical cylinder using a synthetic resin such as PP, and functions as the main body (barrel tube) of the writing instrument. As shown in Figures 5(a) and 5(b), the rear barrel 81 is provided with a retaining member 82 made of a retaining piece that holds the rear end of the ink occlusion body 85 inside the rear end. The entire rear barrel and the front barrel (described later) are molded opaque or transparent (and translucent), but either may be adopted from the perspective of appearance and practicality. The front barrel 86 is fixed to the opening on the nib side of the rear barrel 81 by fitting or the like.

The ink occlusion body 85 is made of the same material as the ink occlusion body 15 of the first embodiment.
The relay core 95 serves as a relay core for supplying the aqueous ink in the ink occlusion body 85 to an ink guide section 97 provided in the holder 96, which will be described later, and is a fiber bundle core obtained by processing a fiber bundle such as a fiber bundle or felt, similar to the ink occlusion bodies 15 and 85, or a hard sponge, a resin particle porous body made of a resin particle sintered body, or a sliver core having continuous pores (flow paths), and is not particularly limited in shape or structure as long as it can supply the aqueous ink having the above-mentioned vapor pressure characteristics or blending characteristics impregnated in the ink occlusion body 85 to the ink guide section 97 of the holder 96 via the relay core 95. Examples of the cross-sectional shape of the relay core 95 include a circle, an ellipse, a square, a rectangle, a trapezoid, a parallelogram, a diamond, a semi-cylindrical shape, and a crescent shape. In this embodiment, the cross-sectional shape is a circle.

The pen tip 90 includes a pen tip 98, which serves as the writing portion, and a holder 96 that holds the pen tip 98 and has an ink guide portion 97 for supplying ink to the writing portion.

The entire pen tip 90 configured in this manner or the holder 96 described below is made of a visible material, such as PP, PE, PET, PEN, nylon (including amorphous nylon in addition to common nylons such as nylon 6 and nylon 12), acrylic, polymethylpentene, polystyrene, ABS, etc., and is preferably made of a material with a visible light transmittance of 50% or more.
Furthermore, the entire pen tip 90 or the holder 96 described below can be made of one of the above materials, or two or more materials to further improve durability and visibility. If made of two or more materials, it is preferable that at least one of them is made of a material with a visible light transmittance of 50% or more, and it can be molded by various molding methods such as injection molding and blow molding.

Figures 6(a) and (b) are drawings showing an example of the writing instrument C of this embodiment with the cap removed, and Figures 7(a) to (d) are drawings showing an example of the writing instrument C with the cap attached.
In the writing instrument C of this embodiment, an ink absorbing body 85 containing ink and an intermediate core 95 are held within the rear barrel 81 that constitutes the barrel of the writing instrument, and the writing instrument C can be easily produced by sequentially attaching the pen tip 90 with the pen core 98 attached and the front barrel 86 by fitting or the like.
The cap 65 can be attached to and detached from the tip barrel 86 by fitting it, etc., and is composed of an inner cap portion 66 that protects the pen core 98 and a cylindrical outer cap portion 67, with a concave portion 68 formed on the surface of the outer cap portion 67 to improve design.
Like the cap of the first embodiment described above, this cap 65 is made of a transparent (visible) material and is molded from a material with a visible light transmittance of 50% or more, so that the pen tip 90 can be seen (visually recognized) through the cap 65 from the outside.

In the writing instrument C of this embodiment, which is configured in this manner, as in the first and second embodiments described above, condensation does not occur inside the cap 65, so the appearance is not marred, and the shape of the nib 90 and the color of the water-based ink (for example, the ink color is yellow, pink, etc.) can be seen through the cap 65, resulting in a writing instrument with high quality and commercial value.
Furthermore, the aqueous ink with the above-described characteristics can be continuously and efficiently supplied from the ink absorbing body 85 to the relay core 95, the ink guide section 97, and the pen core 98 by capillary action, thereby ensuring an appropriate ink flow rate and preventing smearing during writing, thereby providing a writing instrument that stabilizes the writing flow rate and allows the aqueous ink in the ink absorbing body 85 to be fully used up.
Furthermore, as described above, the pen tip 90 comprises a pen core 98 that serves as the writing portion, and a holder 96 that holds the pen core 98 and has at least one ink guide portion 97 for supplying ink to the writing portion. The pen tip 90 also has a relay core 95 for supplying the water-based ink contained in the ink occluder 85 to the ink guide portion 97 provided in the holder 96. Furthermore, the holder 96 is made of a visible material, so that the entire surface (entire surface) of the holder 96, except for the ink guide portion 97, serves as a visible portion that allows the writing direction to be visually confirmed. This allows the area ratio of the visible portion to be 40% or more of the nib protruding from the tip of the front barrel 86, and preferably the visible portion on the side of the nib holder 96 is also 40% or more.Furthermore, by forming the ink guide portion 97 in the longitudinal center of the holder 96 and suitably setting the widthwise length, diameter, cross-sectional area, etc. of the ink guide portion 97 within a preferred predetermined range, it is possible to provide sufficient visibility that allows characters written in the writing direction to be read reliably compared to conventional methods, and a writing instrument is provided that can be used until the end of the stroke.

In each of the writing instruments of the above-mentioned embodiments A to C, the ink occlusion body 15, 85 is described as occluding an aqueous ink composition for a writing instrument having the above-mentioned characteristics of a water molar fraction of 0.96 (96%) or less. However, since the writing instrument of the present invention is characterized by being equipped with an aqueous ink composition for a writing instrument having the above-mentioned characteristics, it may also be a direct ink type writing instrument, for example, a collector type writing instrument in which the aqueous ink is stored directly in the barrel and the aqueous ink is supplied to the writing part of the pen tip via an intermediate core.
Furthermore, in each of the writing instruments of the above embodiments A to C, a cap made of a transparent material is attached, and the writing instrument nib 20, 90 has a window portion through which the writing direction can be seen, but the shape and structure of the nib are not particularly limited as long as the cap is made of a transparent material.

Next, the aqueous ink composition for writing instruments and writing instruments of the present invention will be described in more detail using examples and comparative examples, but the present invention is not limited to the following examples, etc.

[Examples 1 to 8 and Comparative Examples 1 and 2]
According to the formulations shown in Table 1 below, aqueous ink compositions for writing instruments were prepared by conventional methods.
The molar fraction (%) of water in the aqueous ink composition for writing instruments in Table 1 is a value calculated based on the above formula (I) assuming that the molecular weights of water, glycerin, ethylene glycol, and trimethylglycine are 18.0, 92.1, 62.1, and 117.1, respectively.
Furthermore, the evaporation suppression of each of the resulting aqueous ink compositions for writing instruments was evaluated by the following evaluation method.
Furthermore, each of the resulting aqueous ink compositions for writing instruments was loaded onto a writing instrument having the following configuration. Using each of the resulting writing instruments, the presence or absence of condensation and writing performance were evaluated using the following evaluation methods. The results are shown in Table 1 below.

(Configuration of writing implement)
The pen tip and writing implement used were configured as shown below and conforming to Figures 1 and 2. The dimensions and physical properties of the pen tip, holder, etc. used were as shown below.

(Configuration of pen tip 20)
Made of acrylic resin, visible light transmittance 85% (reflectance was measured using a multi-light source spectrophotometer (MSC-5N) manufactured by Suga Test Instruments Co., Ltd., and the measured value was used as the visible light transmittance).
Size of the viewing portion (window portion) 43 (square): 9 mm x 8 mm x 5 mm x 4 mm
Width of visible part: 3.0 mm
Writing lead 30: Thin plate members 31, 31: polyethylene sintered lead, width: 2 mm, length: 20 mm, thickness: 0.5 mm, Writing part 25: polyethylene sintered lead, porosity: 50%, 4 x 3 x 6 mm, thickness = 3 mm, length: 5.5 mm

Ink occlusion body 15: PET fiber bundle, porosity 85%, φ6×77 mm
Writing instrument body 10, caps 60, 70: Made of polypropylene (PP) Pen tip 50: Polyester fiber bundle core, porosity 60%, φ2.0 x 40.0 mm
Cap 60: Made of polypropylene (PP), transmittance: 70%
Cap 70: Made of polypropylene (PP), transmittance: 60%

(Method for evaluating the presence or absence of condensation)
Each of the resulting writing implements was left on a heated carpet (at about 32°C) for 9 hours, and the presence or absence of condensation was evaluated according to the following evaluation criteria.
Evaluation criteria:
◎: No condensation.
○: A little cloudy.
△: Mostly cloudy.
△△: droplets are generated.
×: Liquid is accumulated.

(Writing performance evaluation method)
Each of the resulting writing implements was used to write 25 cm on PPC paper at a normal speed, and the writing performance was evaluated according to the following evaluation criteria.
Evaluation criteria:
○: No abnormality in the written lines.
△: Some parts are scratched.
×: Almost completely scratched.

As is clear from the results in Table 1 above, the aqueous ink compositions for writing instruments in Examples 1 to 8, which fall within the scope of the present invention, and the writing instruments incorporating these aqueous ink compositions, were confirmed to be superior in suppressing evaporation of water and other components from the ink, without impairing writing performance, even in environments with severe temperature changes and temperature gradients, compared to Comparative Examples 1 and 2, which fall outside the scope of the present invention. Furthermore, with writing instruments within the scope of the present invention, even those equipped with caps made of transparent materials, writing performance is not impaired, condensation does not occur inside the cap, and appearance is not impaired. Furthermore, the shape of the nib and the color of the aqueous ink can be seen through the cap, confirming that a writing instrument with high quality and commercial value can be obtained.

Furthermore, each of the writing instruments in Examples 1 to 8 conforms to Figures 1 and 2, and guides ink from the ink occlusion body 15 to the writing part 25 using thin plate bodies 31, 31 that are thinner than the thickness of the writing part 25 and have good flow properties. Furthermore, the U-shaped writing core 30 including the writing part 25 and thin plate bodies 31, 31 is composed of a polyethylene sintered core with the above-mentioned configuration, so that the capillary force relative to the porosity is strong, and the thickness can be made extremely thin, resulting in good ink flow properties. There is no need to design the ink guide part to be thick, and the visibility part 43 is not obstructed. Furthermore, by making the cross-sectional shape of the portion of the writing core 30 that abuts against the side of the holder 40 rectangular, the cross-sectional shape The width of the visible portion 43 relative to the area can be increased, and by making the outer edge of the visible portion 43 of the holder 40 into an inclined refractive surface 43a, 43a, the rectangular cross section appears thinner. This allows a right-handed person writing from left to right to draw lines with the writing portion 25 while visually checking the writing direction using the visible portion 43. Furthermore, by maximizing the effective area of the visible portion relative to the entire pen tip, and efficiently supplying ink to the integrally constructed writing portion 25 using the thin plate bodies 31, 31 with the above-mentioned characteristics, ink flow is also excellent. It was confirmed that a writing instrument can be obtained that maximizes the effective area of the visible portion 43 without compromising ink flow. It was also confirmed that writing can be performed without smearing even after being dropped from a height of 1 meter.

The resulting aqueous ink composition for writing instruments can be suitably used in writing instruments such as felt-tip pens and marking pens.

10 barrel 20 nib 25 writing part 30 writing lead 40 holder 43 visual part 60 cap

Claims (4)

a writing instrument comprising at least a barrel containing an aqueous ink composition for a writing instrument; a nib provided on the tip side of the barrel from which the aqueous ink composition for a writing instrument can be ejected; and a cap made of a transparent material detachably attached to the nib side of the barrel, wherein the aqueous ink composition for a writing instrument contains at least a colorant, at least one water-soluble compound selected from the group A below having a molecular weight of 300 or less, and water, and wherein the molar fraction of water relative to the water-soluble compound from group A having a molecular weight of 300 or less and the water in the ink is 0.78 (78%) to 0.96 (96%) (however, this does not apply to aqueous ink compositions for writing instruments containing at least a colorant, trimethylglycine, pentaerythritol, 10% by mass or less of a water-soluble organic solvent, and water. This does not apply to aqueous ink compositions for writing instruments containing at least a colorant, trimethylglycine, pentaerythritol, 10% by mass or less of a water-soluble organic solvent, and water. Furthermore, this does not apply to aqueous ink compositions for writing instruments having a water molar fraction of 0.82, 0.86, 0.87, or 0.96) .
Group A: ethylene glycol, propylene glycol, diethylene glycol, glycerin, triethanolamine, aminomethylpropane, trimethylglycine, pentaerythritol, trimethylolpropane, trimethylolethane 2. The writing instrument according to claim 1, wherein the content of the water- soluble compound of Group A having a molecular weight of 300 or less in the aqueous ink composition for a writing instrument is 15 to 50% by mass relative to the total amount of the aqueous ink composition. The writing instrument according to claim 1 or 2, characterized in that the water molar fraction of the aqueous ink composition for a writing instrument is 0.85 (85%) or more and 0.91 (91%) or less. A writing instrument as described in claim 1 or 2, characterized in that the pen tip has a window that allows the writing direction to be visually confirmed.