Notebook products

Abstract

To provide a writing instrument product which does not cause dew condensation in a cap and does not impair the appearance of the writing instrument to which the cap made of a transparent material is attached.SOLUTION: The wiring instrument is a writing instrument A at least including a barrel 10 containing a water-based ink composition for writing instruments, a pen tip 20 provided on the tip side of the barrel 10 and capable of ejecting water-based ink, and a cap 60 made of transparent material detachably attached to the pen tip 20 side of the barrel 10. As shown by the following formula (I), a difference between internal temperature of the writing instrument (x°C) and dew point temperature (y°C) in the product in that state is 1°C or more. x°C- y°C≥1°C...(I).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a writing instrument product in which condensation does not occur inside a writing instrument product such as a cap.

Background Art

[0002] Conventionally, in marking pen type writing instruments and the like, in recent years, in some cases, in order to show the pen tip, a cap made of a transparent material and having a large internal volume is known to be used. In this type of writing instrument, in an environment with temperature changes or a temperature gradient, condensation liquid may accumulate inside the cap, resulting in a problem of poor appearance. This problem has been an inherent problem in writing instruments having a pen tip with a large writing part and using a transparent cap or the like.

[0003] Conventionally, in order to suppress condensation inside the cap, it has been common to reduce the internal volume of the cap and use an opaque material (not conspicuous). However, in order to show a pen tip having a window part through which the writing direction can be visually recognized, in particular, in writing instruments using a cap made of a transparent material, it has been difficult to configure the cap with an opaque material at present. In particular, in writing instruments equipped with ink using oil-soluble dyes, water-soluble dyes, or pigments as coloring materials, the coloring of the condensation liquid may be remarkable, and countermeasures have been necessary. Also, even with an opaque cap, the problem of condensation liquid accumulating inside the cap is also a problem to be solved.

[0004] On the other hand, conventionally, as a moisture evaporation prevention and condensation prevention device for a writing instrument, for example, in a writing instrument incorporating an ink cylinder containing aqueous ink in a shaft cylinder, a liquid absorbent having continuous pores is mounted in the shaft cylinder, and the liquid absorbent is impregnated with a saturated aqueous solution of a salt that gives a relative humidity of 75 to 95% in a sealed atmosphere at room temperature. A moisture evaporation prevention and condensation prevention device for a writing instrument is known (see, for example, Patent Document 1).

[0005] Furthermore, in order to provide a writing instrument that uses components such as a cap made of a transparent material, yet does not lose its appearance due to fading or browning of the handwriting formed by the writing instrument from the beginning, and allows the shape of the pen tip and the color tone and remaining amount of ink inside the writing instrument to be visible, the present invention provides an ink containing a colorant selected from (a) an electron-donating organic compound, (b) an electron-accepting compound, (c) a reversible thermochromic material consisting of a reaction medium that determines the temperature at which the color reaction of the components of (a) and (b) occurs, a photochromic organic material, a dye, and a fluorescent pigment; an ink reservoir containing the ink; a barrel containing the ink reservoir inside; a pen tip from which the ink can be dispensed; and a holder for holding the pen tip. A writing instrument comprising a body and a cap made of a transparent material that is detachably attached to the pen tip side of the barrel, wherein the cap contains an ultraviolet absorber or a transparent ultraviolet shielding agent, or a light-stabilizing layer containing an ultraviolet absorber or a transparent ultraviolet shielding agent is provided on the surface of the cap. It is also known that the cap contains a light-stabilizing agent or the light-stabilizing layer contains a light-stabilizing agent, the holder is made of a transparent material, the holder contains an ultraviolet absorber or a transparent ultraviolet shielding agent, or a light-stabilizing layer containing an ultraviolet absorber or a transparent ultraviolet shielding agent is provided on the surface of the holder (see, for example, Patent Document 2).

[0006] The writing instrument moisture evaporation prevention and condensation prevention device described in Patent Document 1 above prevents moisture evaporation and condensation by installing a liquid absorbent with specific physical properties having continuous pores inside the barrel, and discloses a related technology to the present invention. However, the present invention aims to suppress or prevent condensation, etc., in terms of ink composition and physical properties, and therefore the technical concept of the present invention differs from that of Patent Document 1. Furthermore, the writing instrument described in Patent Document 2 above, in order to visually confirm the shape of the pen tip and the color and amount of ink remaining in the writing instrument, incorporates an ultraviolet absorber or a transparent ultraviolet shielding agent into the cap or holder, or forms a light-stable layer on the surface of the cap or holder. Thus, it differs from the present invention in terms of the problem to be addressed and the technical concept. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Utility Model Publication No. 61-40551 (Claims for Utility Model Registration, Figure 1, etc.) [Patent Document 2] Japanese Patent Publication No. 2020-29672 (Claims, Figures 1-6, etc.) [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In view of the problems and current status of the prior art described above, the present invention aims to solve these problems and provide a writing instrument product that does not produce condensation inside the cap or other writing instrument product. In particular, even if the writing instrument product uses a cap or other writing instrument product made of a transparent material, condensation does not occur inside the cap or other writing instrument product, the appearance is not impaired, and the shape of the pen tip and the color tone of the water-based ink can be seen through the cap, thereby providing a writing instrument product with high writing instrument quality and commercial value. [Means for solving the problem]

[0009] In view of the above-mentioned conventional problems, the present inventors conducted diligent research and, as a result, found that a writing instrument product comprising at least a barrel containing an aqueous ink composition for writing instruments, a pen tip provided at the tip end of the barrel from which the aqueous ink composition for writing instruments can be dispensed, and a cap made of a transparent material that is detachably attached to the pen tip end of the barrel, can be obtained by making the difference between the internal temperature of the product (x°C) and the dew point temperature inside the product in that state (y°C) greater than or equal to a predetermined value, thereby completing the present invention.

[0010] In other words, the writing instrument product of the present invention comprises at least a barrel containing an aqueous ink composition for writing instruments, a pen tip provided on the tip side of the barrel from which the aqueous ink composition for writing instruments can be dispensed, and a cap made of a transparent material that is detachably attached to the pen tip side of the barrel, characterized in that the difference between the internal temperature of the product (x°C) and the dew point temperature inside the product in that state (y°C) is 1°C or more, as shown by the following formula (I). x℃ - y℃ ≥ 1℃ ………(I) Preferably, the dew point temperature (y°C) is obtained by calculating the water vapor pressure from the internal temperature and relative humidity of the product, and then calculating the temperature at which that water vapor pressure becomes the saturated water vapor pressure. It is preferable that the internal temperature (x°C) of the product is 27°C or higher, and the dew point temperature is 1°C or higher. When the internal temperature of the product (x°C) is 27°C, it is preferable that the dew point temperature is 26°C or lower. Preferably, the pen tip has a window that allows the writing direction to be seen. [Effects of the Invention]

[0011] According to the present invention, a writing instrument product is provided in which condensation does not occur inside the writing instrument product, such as the cap. In particular, even with a writing instrument product using a cap made of a transparent material, condensation does not occur inside the writing instrument product, such as the cap, and the appearance is not impaired. Furthermore, the shape of the pen tip and the color tone of the water-based ink can be seen through the cap, thus providing a writing instrument product with high writing instrument quality and commercial value. The object and effect of the present invention are recognized and obtained, in particular, by using the components and combinations indicated in the claims. Both the general description above and the detailed description below are illustrative and descriptive, and do not limit the present invention as described in the claims. [Brief explanation of the drawing]

[0012] [Figure 1]A drawing showing an example of an embodiment of the writing instrument product of the present invention (First Embodiment), where (a) is a plan view, (b) is a front view, and (c) is a longitudinal sectional view taken from the front. [Figure 2] An enlarged perspective view of the pen tip of the writing instrument product in FIG. 1, where (a) is an enlarged perspective view of the pen tip seen from one direction, and (b) is an enlarged perspective view of the pen tip seen from the direction 180° unfolded from (a). [Figure 3] A drawing showing another example of an embodiment of the writing instrument product of the present invention (Second Embodiment), where (a) is a plan view, (b) is a front view, and (c) is a longitudinal sectional view taken from the front. [Figure 4] An enlarged perspective view of the pen tip of the writing instrument product in FIG. 3, where (a) is an enlarged perspective view of the pen tip seen from one direction, and (b) is an enlarged perspective view of the pen tip seen from the direction 180° unfolded from (a). [Figure 5] A drawing showing another example of an embodiment of the writing instrument product of the present invention (Third Embodiment), where (a) is a central longitudinal sectional view and (b) is a central cross-sectional view. [Figure 6] A drawing showing an example of the state where the cap of the writing instrument product in FIG. 5 is removed, where (a) is a perspective view seen from the front side and (b) is a perspective view seen from the rear side. [Figure 7] A drawing showing an example of the state where the cap of the writing instrument product in FIG. 5 is attached, where (a) is a front view, (b) is a plan view, (c) is a left side view, and (d) is a right side view.

Mode for Carrying Out the Invention

[0013] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. However, note that the technical scope of the present invention is not limited to the embodiments detailed below, and extends to the invention described in the claims and its equivalents. Also, the present invention can be implemented based on the content disclosed in this specification and the common technical knowledge in the art (including design matters and self-evident matters).

[0014] <Writing Instrument Product of the First Embodiment: FIGS. 1 to 2> As shown in FIGS. 1(a) to 1(c), the writing instrument product of this embodiment includes at least a shaft cylinder 10 in which aqueous ink is incorporated via an ink storage body 15, a pen tip 20 provided on the tip side of the shaft cylinder 10 and capable of discharging the aqueous ink, and a product 60 composed of a cap formed of a transparent material detachably attached to the pen tip 20 side of the shaft cylinder 10. The writing instrument A is characterized in that, as shown by the following formula (I), the difference between the temperature (x ° C) inside the product and the dew point temperature (y ° C) inside the product in that state is 1 ° C or more. x ° C - y ° C ≥ 1 ° C ………(I)

[0015] In the above formula (I), the dew point temperature (y ° C) refers to the temperature at which condensation occurs when the gas is cooled, and can be directly measured with a dew point thermometer. In this embodiment, however, it is obtained by calculating the water vapor pressure (partial pressure of water vapor in moist air) from the temperature inside the product and the relative humidity, and then calculating the temperature at which this water vapor pressure is the saturated water vapor pressure. Specifically, the dew point temperature (y ° C) is obtained by the following formula. The water vapor pressure Px inside the product at the temperature (x ° C) inside the product is (saturated water vapor pressure at x ° C: Pmax) × [mole fraction of water: (N)]. Here, in the present invention, the “temperature (x ° C) inside the product” refers to the temperature of the space inside the cap. Also, the saturated water vapor pressure Pmax at x ° C is obtained as the saturated water vapor pressure at the temperature specified by the formula of August et al. Based on the parameter values of Tetens (1930) approximately. The saturated water vapor pressure (Pmax) is 6.111×10 t [t = (7.5 × x ° C) / (x ° C + 237.3)]

[0016] On the other hand, the water mole fraction: N is determined as follows. When the aqueous ink mounted on the writing instrument product is placed in an environment of a certain temperature and humidity, the evaporation of the water contained in the ink does not proceed until the water in the ink disappears, and there is a correlation between the humidity and the end point of evaporation. If the saturated water vapor pressure at a certain temperature is Pa, the partial pressure of water in the atmosphere is expressed as P × W / 100 (Pa), where W (%) is the mole fraction of water (i.e., relative humidity). On the other hand, the rate of evaporation of water molecules is approximately proportional to the mole fraction C (%) of water in the ink, so the amount of water evaporated is proportional to the mole fraction of water.

[0017] In this invention, "mole fraction of water: N" refers to the mole fraction of water in the water-soluble compounds (including water) with a molecular weight of 300 or less contained in the ink. When ink contains water along with n water-soluble compounds other than water, with a molecular weight of 300 or less (n≧0), the mole fraction of water can be calculated by the following formula (I), where the n water-soluble compounds are denoted as water-soluble compound 1, 2, 3, ..., n, and the molecular weight of water is 18. In formula (1) below, MW1, MW2, MW3, ..., MWn represent the molecular weights of water-soluble compounds 1, 2, 3, ..., n, each containing a molecular weight of 300 or less. Cw represents the water content (mass%) in the ink, and C1, C2, C3, ..., C n Each of these values ​​represents the content (mass%) of water-soluble compounds 1, 2, 3, ..., n, with a molecular weight of 300 or less, in the ink. Note that if the ink contains no water-soluble compounds with a molecular weight of 300 or less other than water, the mole fraction of water in that ink is 100%.

[0018] [ka]

[0019] In this invention, the "molescalation of water" is a value calculated for water-soluble compounds (including water) with a molecular weight of 300 or less. The reason why compounds with a molecular weight of 300 or less are used as the compounds to calculate the mole fraction of water is that compounds with a molecular weight sufficiently larger than water do not substantially affect the mole fraction of water at their usual content in aqueous ink compositions for writing instruments. Pigments, resins, surfactants, etc., which are usually included in the formulation of aqueous ink compositions for writing instruments, have molecular weights far larger than water, and their mole counts are extremely small at their usual content in aqueous ink compositions for writing instruments, so they do not need to be considered. Furthermore, considering compounds that dissolve in water in aqueous ink compositions for writing instruments and have a content of 1.0% by mass or more is substantially sufficient to realize the effects of the present invention. As described above, the water vapor pressure Px inside the product is given by (saturated water vapor pressure at x°C: Pmax) × [moles of water: (N)]. The temperature at which this water vapor pressure Px equals the saturated vapor pressure is the dew point temperature (y°C). Therefore, y℃ = [237.3 * Log10(6.11 / Px)] / [(Log10(Px / 6.11) - 7.5)], and the dew point temperature is calculated.

[0020] Based on the above, the internal temperature of the product (x°C) and the dew point temperature inside the product in that state (y°C) can be calculated. If the difference between this internal temperature (x°C) and the dew point temperature inside the product in that state (y°C) is 1°C or more, as shown in equation (I) above, then a writing instrument will be obtained in which no condensation occurs inside the writing instrument, such as in the cap. In particular, even with writing instruments that use caps made of transparent materials, condensation does not occur inside the writing product such as the cap, the appearance is not compromised, and the shape of the pen tip and the color tone of the water-based ink can be seen through the cap, resulting in writing instruments with high quality and commercial value. If the difference between the internal temperature of the product (x°C) and the dew point temperature inside the product in that state (y°C) does not satisfy formula (I) above, that is, if it is less than 1°C, condensation is likely to occur inside the writing instrument product such as the cap, and the effects of the present invention cannot be achieved. Preferably, the internal temperature (x°C) of the product is 27°C or higher, and the dew point temperature is 1°C or higher. Furthermore, when the internal temperature (x°C) of the product is 27°C, it is preferable that the dew point temperature is 26°C or lower. The reason why the internal temperature (x°C) is set at 27°C is that this is the temperature of the space inside the cap when it is placed on a typical hot carpet for one hour. Also, the internal temperature (x°C) of the product is usually around 20-25°C.

[0021] <Water-based ink> The aqueous ink used in this embodiment is not particularly limited as long as it satisfies the above formula (I), but preferably contains at least a colorant and water. <Colorants> Examples of colorants that can be used include those used for writing instruments, such as dyes that dissolve or disperse in water, conventionally known inorganic and organic pigments such as titanium dioxide, colored resin fine particles or dispersions thereof [including resin particle pigments containing pigments, pseudo-pigments obtained by coloring resin emulsions with dyes, white plastic pigments, hollow resin pigments (particles), etc.], pigments with silica or mica as a base material and a multi-layer coating of iron oxide or titanium dioxide on the surface, thermochromic pigments, photochromic pigments, etc., and composite pigments thereof can be used. Examples of dyes include fluorescent dyes, water-soluble dyes, and oil-soluble dyes.

[0022] There are no particular limitations on the fluorescent dyes that can be used, 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, Basic Yellow 7, Acid Red 52, Acid Red 77, Acid Red 87, Acid Red 92, Acid Blue 9, Disperse Yellow 121, Acid Yellow 82, Acid 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, Solvent Green 7, etc. In particular, from the standpoint of color development and ink stability, azomethine-based, xanthene-based, and triphenylmethane-based fluorescent dyes are preferably used among the above fluorescent dyes. Specifically, preferred fluorescent dyes include Basic Yellow 1 and Basic Yellow 40 as azomethine-based fluorescent dyes, Basic Red 1:1 and Basic Violet 11:1 as xanthene-based fluorescent dyes, and Basic Violet 1 as a triphenylmethane-based fluorescent dye. These dyes may be used individually or in combination of two or more.

[0023] Examples of oil-soluble dyes that can be used include CISolvent Black 7, 123, CISolvent Blue 2, 25, 55, 70, CISolvent Red 8, 49, 100, CISolvent Violet 8, 21, CISolvent Green 3, CISolvent Yellow 21, 44, 61, and CISolvent Orange 37.

[0024] Examples of water-soluble dyes that can be used include acid dyes, basic dyes, direct dyes, and food colorings. For example, CI Acid Black 1, 2, 24, 26, 31, 52, 107, 109, 110, 119, 154, CI Acid Yellow 1, 7, 17, 19, 23, 25, 29, 38, 42, 49, 61, 72, 78, 110, 127, 1 35, 141, 142, CI Acid Red 8, 9, 14, 18, 26, 27, 35, 37, 51, 52, 57, 82, 83, 87, 92, 94, 111, 129, 131, 138, 186, 249, 254, 265, 276, CI Acid Acid dyes such as CI Acid Violet 15, 17, 49, CI Acid Blue 1, 7, 9, 15, 22, 23, 25, 40, 41, 43, 62, 78, 83, 90, 93, 100, 103, 104, 112, 113, 158, CI Acid Green 3, 9, 16, 25, 27, CI Acid Orange 56, etc., basic dyes such as Malachite Green (CI 42000), Victoria Blue FB (CI 44045), Methyl Violet FN (CI 42535), Rhodamine F4G (CI 45160), Rhodamine 6GCP (CI 45160), Examples include direct dyes such as CI Direct Black 17, 19, 22, 32, 38, 51, and 71; CI Direct Yellow 4, 26, 44, and 50; CI Direct Red 1, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, and 227; CI Direct Blue 1, 15, 41, 71, 86, 87, 106, 108, and 199; and food colorings such as CI Food Yellow 3.

[0025] Examples of inorganic pigments include azo lakes, insoluble azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perinone pigments, and nitroso pigments. More specifically, inorganic pigments such as carbon black, titanium black, zinc oxide, red iron oxide, aluminum, chromium oxide, iron black, cobalt blue, iron oxide yellow, viridian, zinc sulfide, lithopone, cadmium yellow, vermilion, cadmium red, lead yellow, molybdide orange, zinc chromate, strontium chromate, white carbon, clay, talc, ultramarine, precipitated barium sulfate, barite powder, calcium carbonate, lead white, navy blue, navy blue, manganese violet, aluminum powder, brass powder, and CI Examples of organic pigments include CI Pigment Blue 15, CI Pigment Blue 17, CI Pigment Blue 27, CI Pigment Red 5, CI Pigment Red 22, CI Pigment Red 38, CI Pigment Blue 48, CI Pigment Blue 49, CI Pigment Red 53, CI Pigment Red 57, CI Pigment Red 81, CI Pigment Red 104, CI Pigment Red 146, CI Pigment Red 245, CI Pigment Yellow 1, CI Pigment Yellow 3, CI Pigment Yellow 12, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Yellow 34, CI Pigment Yellow 55, CI Pigment Yellow 7, CI Pigment Yellow 16, CI Pigment Yellow 5, CI Pigment Yellow 13, CI Pigment Yellow 16, CI Pigment Yellow 17, CI Pigment Yellow 19, CI Pigment Yellow 23, CI Pigment Yellow 50, CI Pigment Yellow 7, CI Pigment Green 7, and other organic pigments.

[0026] Examples of colored resin microparticles or their dispersions include a dispersion of colored resin microparticles in which colored resin microparticles are dispersed in water, comprising 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 and a linear or cyclic alcohol having 2 to 18 carbon atoms, and a basic dye or an oil-soluble dye; and a dispersion of colored resin microparticles in which colored resin microparticles are dispersed in water, comprising (meth)acrylic acid cyclohexyl monomer and a basic dye or an oil-soluble dye, wherein the content of the (meth)acrylic acid cyclohexyl monomer is 30% by mass or more relative to 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 relative to the total polymer components.

[0027] Examples of thermochromic pigments include those produced by microencapsulating a thermochromic composition containing at least a leuco dye that functions as a color developer, a developer that is a component capable of causing the leuco dye to develop color, and a color change temperature adjuster that can control the color change temperature in the color development of the leuco dye and the developer, so that the composition has 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, etc., and a resin such as a terpene phenol resin, or photochromic pigments produced by microencapsulating a photochromic composition containing at least one selected from photochromic dyes (compounds), fluorescent dyes, etc., an organic solvent, and additives such as antioxidants, light stabilizers, and sensitizers, to a predetermined average particle size (e.g., 0.1 to 10 μm). In this invention (including the examples), the "average particle diameter" is the D50 value calculated using a particle diameter distribution analyzer HR9320-X100 (manufactured by Nikkiso Co., Ltd.) with a refractive index of 1.81 and based on volume.

[0028] These colorants can be used individually or in combination of two or more (hereinafter simply referred to as "at least one"). The total solid content of these colorants is preferably 0.1 to 40% by mass, and more preferably 1 to 30% by mass, relative to the total amount of water-based ink. By setting the content of this colorant to 0.1% by mass or more, sufficient line density can be obtained, while setting it to 40% by mass or less is preferable because it suppresses viscosity increase and improves ink fluidity.

[0029] <Other ingredients> The aqueous ink of this embodiment contains the above-mentioned colorant and, as a remainder, water as a solvent (tap water, purified water, distilled water, ion-exchanged water, pure water, etc.). In addition, to the extent that the effects of the present invention are achieved, it may optionally contain various components commonly used in aqueous inks, such as dispersants, surfactants, glycols, glycol ethers, hydrophilic polyhydric alcohols, water-soluble betaines, viscosity modifiers, fixing resins, rust inhibitors, preservatives or antibacterial agents, pH adjusters, etc.

[0030] The dispersant and fixing resin that can be used may contain a water-soluble resin. For example, at least one 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.

[0031] While not particularly limited, the surfactants that can be used may include at least one surfactant selected from fluorine-based surfactants, acetylene glycol-based surfactants, and silicone-based surfactants. Examples of glycols and glycol ethers that can be used include glycols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, neopentyl glycol, 1,3-octylene glycol, hexylene glycol, tripropylene glycol, thiodiethylene glycol, and glycerin, as well as glycol ethers such as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether. These can be used individually or in combination of two or more types. Examples of hydrophilic polyhydric alcohols that can be used include pentaerythritol, trimethylolethane, and trimethylolpropane. Water-soluble betaines (amphoteric compounds) are compounds that have non-adjacent positive and negative charges within the same molecule, and the molecule as a whole has no charge. The positively charged site is preferably a quaternary ammonium cation. Such betaines are not particularly limited, but examples include trimethylglycine, γ-butyrobetaine, fomarin, trigonelline, carnitine, homoserine betaine, valinebetaine, lysine betaine, ornithine betaine, alanine betaine, stachydrine, and glutamate betaine. Among these, trimethylglycine, γ-butyrobetaine, and carnitine are preferred, with trimethylglycine being more preferred. Using such water-soluble betaines tends to further improve the effects of the present invention. Note that water-soluble betaines may be used individually or in combination of two or more types.

[0032] Natural polymers such as polysaccharides and synthetic polymers can be used as viscosity modifiers. Examples of polysaccharides include gum arabic, tragacanth gum, guar gum, locust bean gum, alginic acid, carrageenan, gelatin, xanthan gum, and Gellan gum, succinoglycans, dieutan gum, dextran, and cellulose derivatives such as methylcellulose, ethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose, as well as starch glycolic acid and its salts can be used. As synthetic polymers, for example, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylic acid and its salts, polyethylene oxide, vinyl acetate-polyvinylpyrrolidone copolymer, styrene-acrylic acid copolymer and its salts, isobutylene maleic anhydride copolymer and its salts can be used.

[0033] Suitable preservatives or antibacterial agents include phenol, sodium omazine, sodium benzoate, benzoisothiazoline, and benzimidazole compounds. Suitable rust inhibitors include benzotriazole, toltriazole, dicyclohexylammonium nitride, and saponins. Suitable pH adjusters include amine compounds such as triethanolamine, diethanolamine, monoethanolamine, dimethylethanolamine, morpholine, and triethylamine, ammonia, or alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0034] In this embodiment, the aqueous ink may have a composition containing at least the above-mentioned colorant and water. In preferred embodiments, in addition to the glycols mentioned above, it can be prepared by suitably combining polyhydric alcohols (pentaerythritol, trimethylolethane, trimethylolpropane) and water-soluble betaines (amphoteric compounds) such as trimethylglycine (type, amount, etc.).

[0035] The aqueous ink of this embodiment is obtained by appropriately combining the above-mentioned colorants, water, and other components according to the application of the ink for writing instruments (such as for marking pens), and by combining them in suitable proportions (including the preferred embodiment described above), and by stirring and mixing them with an agitator such as a homomixer, homogenizer, or disper, and further removing coarse particles from the ink composition by filtration or centrifugation as necessary. Furthermore, the pH (at 25°C) of the aqueous ink in this embodiment is preferably adjusted to 5-10 using a pH adjuster or the like, and more preferably to 6-9.5, from the viewpoint of usability, safety, stability of the ink itself, and compatibility with the ink container.

[0036] <Writing instrument product of the first embodiment: Specific configuration> Figure 1(a) is a plan view of the writing instrument product of this embodiment, (b) is a front view thereof, and (c) is a front-view longitudinal section thereof. Figure 2 is an enlarged perspective view of the pen tip of the writing instrument product of Figure 1, where (a) is an enlarged perspective view of the pen tip seen from one direction, and (b) is an enlarged perspective view of the pen tip seen from the direction 180° expanded from (a). The writing instrument product A of this embodiment is equipped with water-based ink of the above composition, and as shown in Figures 1(a) to (c), it is a twin-type writing instrument that has a pen tip 20 having a window (visibility part) that guides the water-based ink supplied from the ink absorber 15 of the barrel (writing instrument body) 10 and allows the writing direction to be seen, and also has a rod-shaped polyacetal pen tip 50 on the opposite side of the pen tip 20. Furthermore, on both sides of the writing instrument body 10 are attached a cap 60 having a clip part 60a made of a transparent material that protects the detachable pen tip 20, and a cap 70 made of a transparent material that protects the pen tip 50.

[0037] The barrel 10 is made of, for example, a thermoplastic resin, a thermosetting resin, etc., and consists of a cylindrical body that houses an ink-absorbing body 15 impregnated with the above-mentioned water-based ink. In the drawing, the right end has a holding part 11 with a fitting part for fixing a holder 55 that holds a fine-point rod-shaped pen tip 50, and the other end, the left end, has a front barrel 16 attached to which a pen tip 20 is fixed, which has a viewing part that serves as a window for visually checking the writing direction. The barrel 10 is formed into a cylindrical shape using a resin such as polypropylene, and functions as the body (barrel) of the writing instrument. The barrel 10 is molded to be opaque or transparent (and semi-transparent), and either can be used from an appearance or practical standpoint.

[0038] The ink-absorbing body 15 is impregnated with aqueous ink of the above composition and includes, for example, fiber bundles made from one or more combinations of natural fibers, animal hair fibers, polyacetal resins, acrylic resins, polyester resins, polyamide resins, polyurethane resins, polyolefin resins, polyvinyl resins, polycarbonate resins, polyether resins, and polyphenylene resins, processed fiber bundles such as felt, and porous bodies such as sponges, resin particles, and sintered bodies. This ink-absorbing body 15 is housed and held within the barrel 10, which forms the body of the writing instrument.

[0039] As shown in Figures 2(a) and (b), the pen tip 20 is composed of a writing lead 30 having at least a writing portion 25 and a holder 40 having a viewing portion. The writing lead 30 having the writing portion 25 is attached to the holder 40, which will be described later, by adhesive, welding, fitting, etc. The writing lead 30 has a writing section 25 that is inclined (knife-cut) to provide a comfortable writing angle, and thin plate bodies (sheet bodies) 31, 31 extending from both ends of the writing section 25, which are integrally connected, and its outer shape is formed in a roughly U-shape (including a U-shape), with the cross-sections of the thin plate bodies 31, 31 being rectangular. The writing lead 30 is not particularly limited as long as it efficiently guides (supplies) the aqueous ink with the above-mentioned vapor pressure characteristics, which is absorbed into the barrel 10, to the writing section 25 via the thin plates 31, 31. Examples include fabrics such as nonwoven fabrics, woven fabrics or knitted fabrics, or materials that have liquid permeability such as liquid permeable foams or sintered bodies. The writing lead 30, including the writing section 25, can be made from one type of material, but it can also be made by combining multiple materials, such as by laminating them, or by connecting or joining the writing section 25 and the parts other than the writing section 25 with other components.

[0040] The shape and thickness of the writing tip 30 having the writing section 25 are determined based on the mounting method to the holder 40, the shape of the writing section 25, maximizing the viewing area of ​​the viewing section 43, and efficiently supplying ink to the writing section. Preferably, the width and length are the width and circumferential lengths of the mounting surface and circumferential length of the holder 40, which will be described later, to which the thin plate bodies 31, 31 of the writing tip 30 are fixed, and lengths suitable for efficiently supplying ink to the writing section 25 are set accordingly. Furthermore, the thickness of the thin plate bodies 31, 31 other than the writing section 25 of the writing tip 30 is preferably 0.3 to 3.0 mm, and most preferably 0.5 to 1.0 mm, based on the point of maximizing the viewing area of ​​the viewing section 43.

[0041] In this embodiment, the writing section 25 is integrally formed with the thin plate bodies 31, 31 of the writing lead 30, and is inclined (knife-cut) to provide a comfortable writing angle. This inclination and other characteristics are set as appropriate to suit the ease of use for writing. Furthermore, the writing section 25 has a thick line width, preferably 1 mm or more, and more preferably 2 mm or more. The writing tip 30, including the writing section 25 of this embodiment, is integrally constructed from a sintered core made by sintering plastic powder.

[0042] In the above embodiment, the writing portion 25 of the writing lead 30 and the thin plates 31, 31 are integrally constructed from the same material. However, the writing portion 25 and the thin plates 31, 31 may be constructed from separate components and connected, joined, or abutted together. The writing portion 25 may be made of, for example, a porous material having pores. Specifically, examples include sponges, sintered bodies, fiber bundles, foams, sponges, felts, and porous materials. Materials used to form the porous body 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 may be made from a sintered body obtained by sintering various plastic powders, and the thin plates 31, 31 may be made from, for example, nonwoven fabrics, woven or knitted fabrics, or permeable materials such as permeable foams.

[0043] 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 front shaft 16 of the writing instrument body 10, and has a viewing portion (visible part) 43 that allows the writing direction to be seen. Furthermore, the holder 40 has a rectangular cross-section for the portion (thin plate-like body 31, 31) of the writing lead 30 that comes into contact with the side surface of the holder 40, and the outer edge of the visible portion 43, which is the front end of the holder 40, is formed as an inclined bending surface 43a, 43a. By making the portion of the writing lead 30 that contacts the side surface of the holder 40 rectangular in cross-section, the width of the visible portion 43 relative to the cross-sectional area can be increased. Furthermore, by making the outer edges of the visible portion 43 of the holder 40 inclined bending surfaces 43a, 43a, the rectangular cross-section can be made to appear thinner, making the area of ​​the visible portion 43 appear even wider than before.

[0044] The entire holder 40, as constructed in this manner, is made of a hard material, such as a hard material that is visible, such as glass or a resin that does not have rubber elasticity. As a resin that does not have rubber elasticity and is visible, for example, by molding it from a material with a visible light transmittance of 50% or more, 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, or ABS, the characters written in the writing direction can be effectively seen on the viewing part 43. Alternatively, only the viewing part 43 (including the inclined refractive surfaces 43a, 43a) may be made of a material that is visible. The visible light transmittance (transmittance) can be determined by measuring the reflectance with a multi-light source spectrophotometer [Suga Test Instruments Co., Ltd., (MSC-5N)]. Furthermore, the holder 40 may be constructed using one of the above materials, or two or more materials for further improvements in durability, visibility, etc., and can be molded by various molding methods such as injection molding and blow molding.

[0045] The thin plates 31, 31 of the writing lead 30 are fixed to the mounting surface of the U-shaped retaining groove of the holder 40 by adhesive bonding, welding, etc., and are fixed to the writing section 25. In this embodiment, in order to maximize the viewing area of ​​the viewing area 43, the thickness of the thin plate bodies 31, 31 is thinner than the thickness of the writing area 25, and it is desirable that the width of the ink guidance area be less than 90% of the width of the viewing area 43 of the holder 40, and more preferably 50-80%.

[0046] 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 of the pen tip 50 (the side facing the ink reservoir) is inserted into the ink reservoir 15, and the aqueous ink of the ink reservoir, which has the aforementioned ink composition, is supplied to the pen tip 50 by capillary action. This pen tip 50 is made of a porous material, such as natural fibers, animal hair fibers, polyacetal resin, polyethylene resin, acrylic resin, and polyester resin. It consists of a parallel fiber bundle made of one or more types of resins such as polyamide resin, polyurethane resin, polyolefin resin, polyvinyl resin, polycarbonate resin, polyether resin, and polyphenylene resin, 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 resin such as polyolefin resin, acrylic resin, polyester resin, polyamide resin, and polyurethane resin. Preferred pen tip 50 includes fiber bundle cores, fiber cores, sintered cores, felt cores, sponge cores, and inorganic porous cores, with fiber cores being particularly preferred from the viewpoint of deformation moldability and productivity. Furthermore, the porosity, size, hardness, etc. of the pen tip 50 used will vary depending on the type of ink, the type of writing instrument, etc., and for example, a porosity of 30 to 60% is preferred. In the present invention, "porosity" is calculated as follows. First, a writing lead having a known mass and apparent volume is immersed in water and, after being thoroughly soaked in water, the mass is measured when it is removed from the water. From the measured mass, the volume of water soaked into the writing lead is derived. Assuming that this volume of water is the same as the pore volume of the writing lead, the porosity is calculated from the following formula. Porosity (unit: %) = (volume of water) / (apparent volume of pen tip 50) × 100

[0047] In this embodiment, as shown in Figures 1(a) to (c), a cap 60 having a clip 60a made of a transparent material is attached to the outer circumference of one pen tip 20 side and the outer circumference of the other pen tip 50 side of the barrel 10 by fitting, and a cap 70 having an inner cap 70a is attached. These caps 60 and 70 are made of a transparent (visible) material, such as glass or a resin that does not have rubber elasticity. The transparent (visible) resin that does not have rubber elasticity is made from a material with a visible light transmittance of 50% or more, such as PP, PE, PET, PEN, nylon (including amorphous nylon in addition to common nylons like nylon 6 and nylon 12), acrylic, polymethylpentene, polystyrene, or ABS, and is formed by molding. This allows the pen tips 20 and 50 to be seen (visible) from the outside through the respective caps 60 and 70. Furthermore, while the entire caps 60 and 70 are formed from a transparent (visible) material, it is also acceptable to use a material that allows the pen tips 20 and 50 to be seen (visualized) and the ink color to be seen (confirmed), even if only a part of the caps 60 and 70 is made of such a material. In addition, if the water-based ink with the above characteristics in this embodiment is a thermochromic ink, a thermoplastic elastomer with an erasing ability (erasing rate) of less than 70% of pencil lines 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 through rubbing and has low wear, thereby reducing the generation of eraser residue during friction and preventing staining of the surrounding area.

[0048] In the writing instrument A configured in this way, an ink-absorbing body 15 containing the above-mentioned aqueous ink is inserted and held inside the writing instrument body 10, the pen tip 20 of the above configuration is sequentially fitted and fixed to the front end via the front shaft 16, and the holder 55 to which the pen tip 50 is fixed is fitted and fixed to the other end, thereby easily creating a twin-type writing instrument A. The aqueous ink with the above-mentioned vapor pressure characteristics absorbed in the ink-absorbing body 15 is efficiently supplied by capillary action to the writing section 25 and the pen tip 50 via the thin plates 31, 31 of the writing core 30 at the pen tip 20, and used for writing.

[0049] In the marking pen type writing instrument A of this embodiment, a cap 60 (including cap 70, hereinafter the same) made of a transparent material with a large internal volume is used to expose the pen tip 20. Even in environments with temperature changes or temperature gradients, such as in a place exposed to direct sunlight, near a heating vent, near a heat source such as a PC, or when mistakenly placed on an electric carpet, the difference between the internal temperature of the product such as the cap (x°C) and the dew point temperature inside the product in that state (y°C) will be 1°C or more, as shown by the above formula (I). Therefore, a writing instrument can be obtained in which condensation does not occur inside the writing instrument product such as the cap. In particular, even with a writing instrument using a cap made of a transparent material, condensation does not occur inside the writing product such as the cap, the appearance is not impaired, and the shape of the pen tip and the color tone of the water-based ink can be seen through the cap, resulting in a writing instrument with high quality and commercial value (this point will be described in more detail in the embodiments described later).

[0050] Furthermore, in this writing instrument A, the pen tip 50 is the same as that of a conventional general-purpose pen tip. To explain the function of the pen tip 20, as shown in Figures 1 and 2, the pen tip 20 has a viewing section (window) 43 that allows the writing direction to be visually confirmed. The water-based ink of the ink storage body 15, with the aforementioned vapor pressure characteristics, reaches the writing section 25 by the capillary force of the thin plates 31, 31 of the writing core 30 and is used for writing. When writing, by looking at the viewing side through the viewing section (window) 43, it becomes easier to align the starting position of the stroke, and it is possible to stop precisely at the desired end of the stroke, preventing over-strokes and smudging.

[0051] Furthermore, the pen tip 20 guides ink from the ink storage body 15 to the writing section 25 via thin, flowable plates 31, 31 of the writing lead 30, which are thinner than the thickness of the writing section 25. Since these thin plates 31, 31 are made of sheet-like porous material, the ink flow is good, there is no need to design it to be thick, the visibility area 43 is not obstructed, and by making the part of the writing lead 30 that contacts the side surface of the holder 40 rectangular in cross-section, the width of the visibility area 43 relative to the cross-sectional area can be increased, and the outer circumference of the visibility area 43 of the holder 40 By making the edges into inclined bending surfaces 43a, 43a, the rectangular cross-section can be made to appear thinner. This allows right-handed users to draw lines with the writing section 25 while visually confirming the writing direction with the viewing section 43 when writing from left to right. Furthermore, in addition to maximizing the effective area of ​​the viewing section relative to the entire pen tip, ink is efficiently supplied to the writing section 25, which is integrally constructed by the thin plates 31, 31 with the above characteristics. As a result, the ink flow is also good, and a writing instrument is obtained that achieves maximization of the effective area of ​​the viewing section 43 without compromising ink flow.

[0052] <Writing instrument of the second embodiment: Overall configuration: Figures 3-4> The writing instrument of this second embodiment, as shown in Figure 3, is a writing instrument B comprising at least a barrel 10 in which aqueous ink is contained via an ink absorber 15, a pen tip 20 provided on the tip side of the barrel 10 from which aqueous ink can be dispensed, and a cap 60 made of a transparent material that is detachably attached to the pen tip 20 side of the barrel 10, and can be calculated in the same way as the first embodiment, and is characterized in that the difference between the internal temperature of the product (x°C) and the dew point temperature inside the product in that state (y°C) is 1°C or more, as shown by formula (I) above.

[0053] <Specific configuration of the writing instrument in the second embodiment> Figure 3(a) is a plan view of the writing instrument of the second embodiment, (b) is a front view thereof, and (c) is a front-view longitudinal section thereof. Figure 4 is an enlarged perspective view of the pen tip of the writing instrument of Figure 1, where (a) is an enlarged perspective view of the pen tip seen from one direction, and (b) is an enlarged perspective view of the pen tip seen from the direction of (a) rotated 180°. As shown in Figure 3, the writing instrument of this embodiment comprises at least a barrel 10 in which aqueous ink having the above-mentioned composition is contained in an ink reservoir 15, a pen tip 20 provided on the tip side of the barrel 10 from which aqueous ink can be dispensed, and a cap 60 made of a transparent material that is detachably attached to the pen tip 20 side of the barrel 10. In addition, if the writing instrument has the same configuration and function as the writing instrument A of the first embodiment described above, the same reference numerals will be used in the drawings, etc., and their descriptions will be omitted in the following second embodiment.

[0054] The writing instrument B of the second embodiment uses a writing lead 30 with a U-shaped outer shape, but the second embodiment differs in that, as shown in Figures 3 and 4, a writing lead 35 with an L-shaped outer shape is attached to the holder 40. The writing portion 36 of the writing lead 35 in the second embodiment has the same shape as the writing portion of the above embodiment, and is inclined (knife-cut) to provide an angle that is easy to write with. In the writing lead 35, a thin plate body 37 is integrally attached from the end side of the writing portion 36, and its outer shape is formed in an L shape, with a rectangular cross-section of the thin plate body 37. As shown in Figure 4, the holder 40 fixes the writing portion 36 and the thin plate body 37 of the writing lead 35 and is fixed to the tip opening of the front shaft 16 of the writing instrument body 10. In the embodiment shown in 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, it is attached only to the bottom side of the holder 40.

[0055] 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 expose the pen tip 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 when mistakenly placed on an electric carpet, the difference between the internal temperature of the cap and other parts of the product (x°C) and the dew point temperature inside the product in that state (y°C) will be 1°C or more, as shown by formula (I) above. Therefore, a writing instrument can be obtained in which condensation does not occur inside the writing instrument product such as the cap. In particular, even with a writing instrument using a cap made of a transparent material, condensation does not occur inside the writing instrument product such as the cap, the appearance is not impaired, and the shape of the pen tip and the color tone of the water-based ink can be seen through the cap, resulting in a writing instrument with high quality and commercial value (this point will be described in more detail in the examples described later).

[0056] Furthermore, in this second embodiment of the writing instrument B, since the writing lead 35 has an L-shape, the structure does not require the thin plate 31 to be attached to the upper surface of the viewing area 43, unlike the U-shaped structure in Figure 1. Therefore, there is nothing obstructing the view, and the area of ​​the viewing area can be enlarged. In addition, by making the portion of the writing lead 35 that contacts the side surface of the holder 40 rectangular in cross-section, the width of the viewing area 43 relative to the cross-sectional area on the bottom side can be increased. Moreover, by making the outer edges of the viewing area 43 of the holder 40 inclined bending surfaces 43a, 43a, the rectangular cross-section can be made to appear thinner, and the area of ​​the viewing area 43 can be made to appear even wider than in Figure 1.

[0057] The pen tip 20 of this second embodiment is attached in the same way as the writing instrument in Figure 1, and has a viewing section (window) 43 that allows the writing direction to be seen. The water-based ink in the ink storage body 15 reaches the writing section 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 section (window) 43 makes it easier to align the starting position of the stroke, and also allows the user to stop precisely at the desired end of the stroke, preventing over-strokes and smudging.

[0058] In the second embodiment, the pen tip 20 guides the aqueous ink from the ink storage body 15 to the writing section 36 via a thin plate 37 of the writing lead 35 that is thinner than the thickness of the writing section 35 and has good ink flowability. Furthermore, since this thin plate 37 is made of a material that has better ink supply capacity than the embodiment in Figure 1, the ink flowability is good, there is no need to design it to be thick, the visibility section 43 is not obstructed, and by making the part of the writing lead 35 that contacts the side surface of the holder 40 rectangular in cross-section, the width of the visibility section 43 relative to the cross-sectional area can be increased, and the holder 40 By making the outer edges of the viewing portion 43 inclined bending surfaces 43a, 43a, the rectangular cross-section can be made to appear thinner. This allows right-handed users to visually confirm the writing direction with the viewing portion 43 while drawing lines with the writing portion 36 when writing from left to right. Furthermore, in addition to maximizing the effective area of ​​the viewing portion relative to the entire pen tip, ink is efficiently supplied to the writing portion 36, which is integrally constructed by the thin plate body 37 with the above characteristics. As a result, the ink flow is also good, and a writing instrument can be obtained that achieves a greater maximization of the effective area of ​​the viewing portion 43 than the embodiment in Figure 1 without compromising ink flow.

[0059] <Writing instrument of the third embodiment: Overall configuration: Figures 5-7> The writing instrument C of this third embodiment is a marking pen type writing instrument, comprising at least a barrel 80 containing water-based ink, a pen tip 90 provided on the tip side of the barrel 80 from which water-based ink can be dispensed, and a cap 65 made of a transparent material that is detachably attached to the pen tip 90 side of the barrel 80, and can be calculated in the same way as in the first embodiment, and is characterized in that the difference between the internal temperature of the product (x°C) and the dew point temperature inside the product in that state (y°C) is 1°C or more, as shown by formula (I) above.

[0060] As shown in Figures 5 to 7, the writing instrument C of this third embodiment comprises a barrel 80, an ink reservoir 85, a lead refill 95, a pen tip 90, and a cap 65 that constitute the main body of the writing instrument. The barrel 80 is made of the same material as the barrel 10 of the first embodiment described above, and has a bottomed cylindrical rear barrel 81 that houses an ink-absorbing body 85 impregnated with the above-described water-based ink, and a front barrel 86 to which the pen tip 40 is fixed. The rear barrel 81 is molded into a long, bottomed oval cylinder using a synthetic resin such as PP, and functions as the body (barrel) of the writing instrument. As shown in Figures 5(a) and (b), the rear barrel 81 is provided with a retaining member 82 inside the rear end, which consists of a retaining piece that holds the rear end of the ink storage body 85. The entire rear barrel and the front barrel, which will be described later, are molded to be opaque or transparent (and semi-transparent), but either can be adopted from the viewpoint of appearance and practicality. In addition, the front barrel 86 is fixed to the opening on the pen tip side of the rear barrel 81 by fitting or the like.

[0061] The ink absorber 85 is made of the same material as the ink absorber 15 in the first embodiment described above. The relay core 95 is a core body for supplying the aqueous ink from the ink absorber 85 to the ink guide section 97 provided in the holder 96, which will be described later. Similar to the ink absorbers 15 and 85, it can be a fiber bundle core made by processing fiber bundles such as fiber bundles or felt, or a resin particle porous body made of hard sponge, resin particle sintered body, etc., or a sliver core having continuous pores (flow channels). Its shape and structure are not particularly limited as long as it can supply the aqueous ink with the above-mentioned vapor pressure characteristics or formulation characteristics impregnated in the ink absorber 85 to the ink guide section 97 of the holder 96 via the relay core 95. Examples of cross-sectional shapes of this relay core 95 include circles, ellipses, squares, rectangles, trapezoids, parallelograms, rhombuses, semi-circular shapes, and crescent shapes, and in this embodiment, the cross-sectional shape is circular. The pen tip 90 comprises a pen nib 98 which serves as the writing section, and a holder 96 which holds the pen nib 98 and has an ink guide section 97 for supplying ink to the writing section.

[0062] The entire pen tip 90 or the holder 96 described later, configured in this way, is made of a material that has visibility, 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 later can be made from one of the above materials, or from two or more materials for further improvements in durability and visibility. When made from two or more materials, it is preferable that at least one of them is made from 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.

[0063] Figures 6(a) and 6(b) show examples of the writing instrument C of this embodiment with the cap removed, while Figures 7(a) to 7(d) show examples of the writing instrument with the cap attached. In this embodiment of the writing instrument C, an ink-absorbing body 85 containing ink and a connecting core 95 are held within the rear shaft 81 that constitutes the barrel of the writing instrument. The pen tip 90 with the pen feed 98 attached and the front shaft 86 are then attached sequentially by fitting or other means, allowing the writing instrument C to be easily manufactured. The cap 65 is detachably attached to the front barrel 86 by fitting or the like, and consists of an inner cap portion 66 that protects the pen nib 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 its design. Similar to the cap of the first embodiment described above, this cap 65 is made of a transparent (visible) material with a visible light transmittance of 50% or more, and is constructed by molding from such a material, so that the pen tip 90 can be seen (visually observed) from the outside through the cap 65.

[0064] In the writing instrument C of this embodiment, even if the cap differs in structure and shape from those of the first and second embodiments, as shown by formula (I) above, if the difference between the internal temperature of the cap (x°C) and the dew point temperature inside the product in that state (y°C) is 1°C or more, condensation will not occur inside the cap 65, just as in the first and second embodiments, the appearance will not be compromised, and the shape of the pen tip 90 and the color tone 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, since the water-based ink with the above characteristics can be continuously and efficiently supplied from the ink-absorbing body 85 to the relay core 95, ink guide section 97, and pen tip 98 by capillary action, an appropriate ink flow rate is ensured, preventing skipping during writing, and a writing instrument is obtained that provides stable writing flow and allows for the full utilization of the water-based ink in the ink-absorbing body 85. Furthermore, as described above, the pen tip 90 comprises a pen nib 98 which forms the writing section, and a holder 96 which holds the pen nib 98 and has at least one ink guide section 97 for supplying ink to the writing section. It also has a relay core 95 for supplying the aqueous ink contained in the ink absorber 85 to the ink guide section 97 provided on the holder 96, and since the holder 96 is made of a visible material, the entire surface (the whole) of the holder 96 other than the ink guide section 97 becomes a visible section from which the writing direction can be seen. By making the area ratio of the visible portion 40% or more of the pen tip protruding from the tip of the front barrel 86, preferably the visible portion on the side of the pen tip holder 96 is also 40% or more, and further, by forming the ink guide portion 97 in the longitudinal center of the holder 96 and suitably setting the length, diameter, cross-sectional area, etc. in the width direction of the ink guide portion 97 to a preferred predetermined range, it is possible to provide sufficient visibility that allows the characters written in the writing direction to be read reliably, more so than in conventional writing, and to provide a writing instrument that can be used until the end of writing.

[0065] In the writing instruments A to C of the first embodiment described above, a type was described in which the ink storage bodies 15 and 85 absorb the aqueous ink having the vapor pressure characteristics of the first embodiment. However, a direct-ink type writing instrument may also be used, such as a collector type writing instrument in which aqueous ink is directly contained in the barrel and supplied to the writing part of the pen tip via an intermediate core, as long as it is a cap made of a transparent material that can be detachably attached to the pen tip side of the barrel. Furthermore, in each of the above embodiments A to C, the pen tips 20 and 90 had windows that allowed the writing direction to be seen. However, the shape and structure of the pen tip and cap are not particularly limited, as long as they are equipped with a cap that can be detachably attached to the pen tip side of the barrel. [Examples]

[0066] [Examples 1-9 and Comparative Examples 1-2] Each aqueous ink composition for writing instruments was prepared by conventional methods according to the formulation shown in Table 1 below. Furthermore, each of the obtained aqueous ink compositions for writing instruments was incorporated into writing instruments with the following configuration. Using each of the obtained writing instruments, the presence or absence of condensation and writing performance were evaluated according to the evaluation methods described below. These results are shown in Table 1 below.

[0067] (Writing instrument components) The following configuration and the nib and writing instrument conforming to Figures 1 and 2 were used. The dimensions and physical properties of the nib, holder, etc., are as shown below.

[0068] (20-piece pen nib configuration) Made of acrylic resin, with a visible light transmittance of 85%. [Reflectance was measured using a multi-light source spectrophotometer (MSC-5N) manufactured by Suga Test Instruments Co., Ltd., and the visible light transmittance was determined from this.] Dimensions of the viewing area (window) 43 (square): 9mm x 8mm x 5mm x 4mm Width of the visible area: 3.0 mm Writing core 30: Thin plate body 31, 31 composition: Polyethylene sintered core, width direction length: 2 mm, length direction length: 20 mm, thickness: 0.5 mm; Writing part 25: Polyethylene sintered core, porosity: 50%, 4 x 3 x 6 mm, thickness = 3 mm, length direction length = 5.5 mm

[0069] Ink absorbent 15: PET fiber bundle, 85% porosity, φ6 × 77 mm Writing instrument body 10, caps 60, 70: Made of polypropylene (PP) Pen tip 50: Polyester fiber bundle core, 60% porosity, φ2.0 × 40.0 mm Cap 60: Made of polypropylene (PP), light transmission: 70% Cap 70: Made of polypropylene (PP), light transmission: 60%

[0070] The internal temperature of Cap 60 was set to 27°C, and the internal water vapor pressure Px was calculated from the saturated water vapor pressure Pmax and the mole fraction of water (N) at 27°C. The dew point temperature (y°C) at which this water vapor pressure Px equals the saturated water vapor pressure was calculated using the formula described above. The difference between the internal temperature of the product (27°C) and the dew point temperature (y°C) at that state was determined. Table 1 below lists the saturated water vapor pressure Pmax, the mole fraction of water (N), the internal water vapor pressure Px, the dew point temperature (y°C), and the difference between the internal temperature of the product (27°C) and the dew point temperature (y°C) at that state for each example and comparative example.

[0071] (Method for evaluating the presence or absence of condensation) Using each of the obtained writing instruments, they were left on a heated carpet (product internal temperature: 32°C, etc.) for 9 hours, and the presence or absence of condensation was evaluated according to the following evaluation criteria. Evaluation criteria: ◎: No condensation. ○: It's a little cloudy. △: Mostly cloudy. △△: Droplets are forming. ×: Liquid has accumulated.

[0072] (Method for evaluating writing performance) Using each of the obtained writing instruments, a 25cm straight line was written on PPC paper, and the writing performance was evaluated according to the following evaluation criteria. Evaluation criteria: ○: No abnormalities in the writing lines. △: Partially faded. ×: Almost completely faded.

[0073] [Table 1]

[0074] As is clear from the results in Table 1 above, each of the writing instruments in Examples 1 to 9, which fall within the scope of the present invention, compared to Comparative Examples 1 and 2, which fall outside the scope of the present invention, does not impair writing performance, does not cause condensation inside the cap, does not impair appearance, and furthermore, the shape of the pen tip and the color tone of the water-based ink can be seen through the cap, thus confirming that a writing instrument with high quality and commercial value can be obtained. Furthermore, in Example 9, a writing instrument was created using an opaque material for the cap, and evaluated in the same manner as in the above example (with an internal product temperature of 30°C). It was confirmed that the writing performance was not significantly impaired, and no condensation occurred inside the cap.

[0075] Furthermore, each writing instrument in Examples 1 to 9 conforms to Figures 1 to 2, and guides ink from the ink-absorbing body 15 to the writing body 25 with thin, flowable plates 31, 31 that are thinner than the thickness of the writing body 25. The writing core 30, which has a U-shaped outer shape including the writing body 25 and the thin plates 31, 31, is made of a polyethylene sintered core with the above configuration, so the capillary force relative to the porosity is high, and its thickness can be made extremely thin, resulting in good ink flowability, there is no need to design the ink guidance part to be thick, the visibility part 43 is not obstructed, and by making the part of the writing core 30 that contacts the side surface of the holder 40 a rectangular cross-section, The width of the visible portion 43 relative to the surface area can be widened, and by making the outer edges of the visible portion 43 of the holder 40 into inclined bending surfaces 43a, 43a, the rectangular cross-section can be made to appear thinner. This allows right-handed users to draw lines with the writing portion 25 while visually confirming the writing direction with the visible portion 43 when writing from left to right. In addition, the effective area of ​​the visible portion relative to the entire pen tip is maximized, and ink is efficiently supplied to the writing portion 25, which is integrally constructed by the thin plates 31, 31 with the above characteristics. As a result, the ink flow is also good, and it has been confirmed that a writing instrument can be obtained that maximizes the effective area of ​​the visible portion 43 without impairing the ink flow. Furthermore, it was confirmed that writing can be performed without skipping even after being dropped from a height of 1m. [Industrial applicability]

[0076] It can be used effectively with writing instruments of the type known as felt-tip pens or marking pens. [Explanation of Symbols]

[0077] 10 shaft cylinder 20 nibs 25 Writing section 30 writing lead 40 Holder 43 Visibility section 60 caps

Claims

[Claim 1] A writing instrument product comprising at least a barrel containing a water-soluble ink composition for writing instruments, a pen tip provided on the tip side of the barrel from which the water-soluble ink composition for writing instruments can be dispensed, and a cap made of a transparent material that is detachably attached to the pen tip side of the barrel, wherein the water-soluble ink composition for writing instruments contains at least a colorant, a water-soluble compound with a molecular weight of 300 or less, and water, and the water-soluble compound contains ethylene glycol and glycerin at a concentration of 20% by mass or more relative to the total amount of the ink composition, and has a molecular weight of 300 A writing instrument product characterized in that the mole fraction of water calculated for the following water-soluble compounds and water is 0.83 to 0.88, and the difference between the temperature inside the cap (x°C), which is the internal temperature of the product, and the dew point temperature inside the cap (y°C), which is obtained by calculating the water vapor pressure from the temperature inside the cap (x°C) and relative humidity, and then calculating the temperature at which that water vapor pressure becomes the saturated water vapor pressure, is 1°C or more, and this temperature difference (x°C - y°C) is such that when the temperature inside the cap (x°C) is 27°C, the dew point temperature (y°C) is 26°C or less. x℃-y℃≧1℃……(I)

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