Water-based ink composition for writing instruments and writing instruments using the same

Abstract

To provide an ink composition for a writing instrument excellent in handwriting-drying property, capable of obtaining a good handwriting suppressed in bleeding and permeation of ink, and further capable of obtaining excellent anti-dripping performance when using a writing instrument with a pen core, and a writing instrument.SOLUTION: The aqueous ink composition for a writing instrument according to the present invention is provided with a pen core having a comb groove for temporarily storing ink, an ink flow passage, and an air passage including: water; a coloring agent; a surface active agent having an acetylene bond in a structure thereof; and a specific organic solvent where the surface tension at 20°C of the ink composition is 30-60 mN / m.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to an aqueous ink composition for writing instruments and a writing instrument using the same. [Background technology]

[0002] Traditionally, water-based inks tend to have poor drying properties compared to oil-based inks due to the slower evaporation rate of the solvent. This means that it takes time for the ink to dry completely, and if the writing surface is touched while the ink is still wet, it can smudge or the writing itself can become dirty. Therefore, the issue of ink drying properties is a significant challenge. To address these issues, ink compositions have been proposed that improve the ink's penetration into the paper surface using various additives. (For example, Patent Document 1.)

[0003] However, while such ink compositions tend to improve the drying properties of the ink, their increased penetration into paper often resulted in smudges or show-through, making it difficult to achieve good handwriting. Furthermore, when such ink compositions were used in writing instruments that guided ink to the pen tip via capillary action through a pen nib with comb grooves and air passages, problems arose with ink retention between the comb grooves of the pen nib. When the pen tip was held vertically downwards, even when not writing, changes in atmospheric pressure and temperature could cause the ink to overflow, and shocks and vibrations could also cause ink to leak, potentially creating a new problem of ink blotting. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 8-170041 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to solve the above-mentioned problems and to provide an aqueous ink composition for a writing instrument equipped with a pen nib that has excellent drying properties, resistance to bleeding and show-through, and resistance to ink smudging. [Means for solving the problem]

[0006] To solve the above problems, the present invention "1. An aqueous ink composition for a writing instrument comprising water, a colorant, an organic solvent, and a surfactant having an acetylene bond in its structure, and comprising a pen nib having comb grooves for temporarily storing ink, an ink flow passage, and an air passage, The aforementioned organic solvent is an organic solvent represented by the following formula (i): [ka] (In the formula, R A is a linear or branched alkyl group having 1 to 4 carbon atoms, and R B A water-based ink composition for writing instruments, wherein L is a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms, L is an ethylene group (-CH2-CH2-) or trimethylene group (-CH2-CH2-CH2-) which may be substituted with a methyl group, and x is an integer from 1 to 5, and the surface tension of the ink composition at 20°C is 30 mN / m to 60 mN / m. 2. The aqueous ink composition for writing instruments according to paragraph 1, wherein the surfactant having an acetylene bond in its structure is a surfactant to which ethylene oxide has been added. 3. The aqueous ink composition for writing instruments according to paragraph 2, wherein the number of moles of ethylene oxide added to the surfactant having an acetylene bond in its structure is 2 to 40. 4. The aqueous ink composition for writing instruments according to any one of the first to third paragraphs, wherein the content ratio of the surfactant having an acetylene bond in its structure to the organic solvent is 0.001 to 0.1 by mass. 5. The aqueous ink composition for writing instruments according to any one of paragraphs 1 to 4, wherein the coloring agent is a dye. 6. A writing instrument characterized by containing the aqueous ink composition for writing instruments described in any one of paragraphs 1 to 5. 7. The writing instrument described in paragraph 6, wherein the writing instrument is a fountain pen. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an aqueous ink composition for writing instruments that dries quickly, suppresses bleeding and show-through of the resulting ink, and, when used in a writing instrument equipped with a pen tip, prevents ink from overflowing or leaking due to changes in atmospheric pressure or temperature, thereby providing excellent ink drying properties, resistance to bleeding and show-through, and resistance to ink blotting. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described in detail below. In this specification, unless otherwise specified, "parts," "%," and "ratio" used to indicate formulations are based on mass, and the content refers to the mass percentage of the constituent components based on the mass of the ink composition.

[0009] <Water-based ink composition for writing instruments> The aqueous ink composition for writing instruments according to the present invention (hereinafter sometimes referred to as "ink composition") is an ink composition used in a writing instrument equipped with a pen nib, characterized by the combined use of water, a colorant, a surfactant having an acetylene bond in its structure, and a specific organic solvent, and by setting the surface tension of the ink to a specific value. In other words, by combining specific components and further setting the surface tension of the ink composition to a specific value, the ink composition of the present invention can obtain excellent ink drying properties, resistance to bleeding and show-through, and resistance to ink smudging. This leads to the following conclusion: By combining a surfactant having an acetylene bond in its structure with a specific organic solvent, the permeability of the ink composition to the paper surface can be dramatically improved. Therefore, it is presumed that the ink composition can quickly penetrate before showing capillary spread on the paper surface, the handwriting dries quickly, and bleeding and strike-through are suppressed. Further, by combining a surfactant having an acetylene bond in its structure with a specific organic solvent and setting the surface tension of the ink composition to a specific value, while dramatically improving the permeability to the paper surface as described above, the wettability to the pen core can be properly maintained. For this reason, both the ink inflow property and the ink storage property between the comb grooves of the pen core can be improved. Therefore, even when the internal pressure of the ink storage body changes, excess ink can smoothly flow into and be held in the pen core, so that the function of the pen core can be fully exerted, and it is presumed that dripping from the pen tip can be sufficiently suppressed. Therefore, the ink composition of the present invention can fully satisfy all of the handwriting drying property, the bleeding and strike-through resistance, and the anti-dripping property. Hereinafter, the constituent components in the ink composition will be described in detail.

[0010] <Surfactant having an acetylene bond in its structure> The ink composition of the present invention comprises a surfactant having an acetylene bond in its structure. The surfactant having an acetylene bond in its structure can improve the permeability of the ink composition to the paper surface. Further, by combining it with a specific organic solvent described later, this permeability can be further improved. In the present invention, by combining a surfactant having an acetylene bond in its structure with a specific organic solvent and further setting the surface tension of the ink to a specific value, while increasing the permeability of the ink composition to the paper, it is possible to properly maintain the wettability of the pen core. Therefore, the ink composition of the present invention is excellent in all of the handwriting drying property, the bleeding and strike-through resistance, and further the anti-dripping property.

[0011] As the surfactant having an acetylene bond in the structure used in the present invention, there is no particular limitation as long as it is a surfactant having an acetylene bond in the structure. For example, acetylene glycol-based surfactants and acetylene alcohol-based surfactants can be mentioned.

[0012] As the surfactant having an acetylene bond in the structure used in the present invention, it is preferable to use a surfactant having an acetylene bond to which ethylene oxide is added and having at least one ethylene oxide group in the structure. Since such a surfactant has excellent stability in the ink, the effects brought by the surfactant can be maintained for a long time. Furthermore, considering a further improvement in the penetrability of the ink composition by a combination with an organic solvent described later, the number of moles of ethylene oxide added to the surfactant having an acetylene bond to which ethylene oxide is added in the structure is preferably 2 to 40, more preferably 5 to 20, and even more preferably 8 to 15.

[0013] Also, considering the stability of the ink composition over time and a further improvement in the penetrability of the ink composition with respect to the paper surface, the HLB value of the surfactant having an acetylene bond in the structure is preferably 10 to 16, and more preferably 12 to 16. Here, the HLB value of the surfactant used in the present invention is a value for evaluating the hydrophilicity of a compound proposed by Griffin, and refers to a value calculated by the following general formula (ii). HLB value = 20 × (mass percentage of hydrophilic group) = 20 × (total sum of formula weights of hydrophilic groups / molecular weight of surfactant) ··· (ii)

[0014] Moreover, it is preferable that the surfactant having an acetylene bond in the structure used in the present invention has a certain foaming property and excellent defoaming property. By using such a surfactant having a specific acetylene bond in the structure together with an organic solvent described later, excellent handwriting drying property, bleeding resistance and strike-through resistance, and ink droplet resistance can be more easily obtained. Specifically, a 0.1% aqueous solution of a surfactant is used as the test solution. 20 ml of this test solution is taken into a 100 ml graduated cylinder and shaken up and down for 1 minute at 180 reciprocations / minute (shaking amplitude 40 mm). When the bubble heights immediately after and after 5 minutes are A mm and B mm, respectively, it is preferable to use a surfactant such that A ≥ 5 and AB (difference between A and B) ≥ 5. The reason is unclear, but I speculate the following: By using a surfactant with a certain foaming property, it is possible to maintain the surface tension of the ink composition above a certain value when it is stationary, and to suppress the increase in surface tension of the ink when movement occurs, thereby preventing deterioration of the wettability of the paper surface and writing instrument components such as the pen nib. Therefore, even when the ink is applied to the paper, the good penetration improved by the synergistic effect with the organic solvent is sufficiently maintained, and the ink can quickly penetrate the paper surface, improving the drying speed of the ink and the resistance to bleeding and show-through. Furthermore, even when the internal pressure of the ink reservoir changes, the appropriate wettability to the pen nib is maintained, so the ink can flow smoothly into and be retained between the comb grooves, making it easier for the pen nib to function properly. In addition, since the surfactant also has excellent anti-foaming properties, foam is less likely to remain in the ink. Therefore, although residual foam can sometimes hinder the flow of ink into the comb grooves of the pen nib, this can be suppressed. Thus, it is presumed that the resistance to ink blotting can also be improved. Based on the above, among surfactants containing acetylene bonds in their structure, using a surfactant that has characteristic acetylene bonds in its structure that possess the foaming and defoaming properties described above is effective because it can obtain better ink drying properties and resistance to ink smudging. Considering the improvement of the above effects, it is more preferable that A > 10, and even more preferable that A > 15. Furthermore, in terms of the difference between A and B, it is more preferable that AB > 10, and even more preferable that AB > 12. Also, it is preferable that B < 5.

[0015] Furthermore, it is preferable that the cloud point of a surfactant having an acetylene bond in its structure be 40°C or higher. This is because when the cloud point of the surfactant is 40°C or higher, its solubility in water is stable, making separation from water less likely and allowing the surfactant's effect to be fully obtained.

[0016] Furthermore, it is preferable to use an acetylene glycol-based surfactant as the surfactant having an acetylene bond in its structure for use in the present invention. This is because acetylene alcohol-based surfactants tend to be highly volatile, and using an acetylene glycol-based surfactant makes it easier to obtain good resistance to drying up while also achieving excellent ink drying properties.

[0017] The content of surfactants having an acetylene bond in their structure is preferably 0.001% by mass or more and 1% by mass or less, based on the total mass of the ink composition. If it is 0.001% by mass or more, the penetration into the paper surface can be improved and the drying of the writing can be improved. On the other hand, if it is 1% by mass or less, an extreme decrease in surface tension can be suppressed, the wettability to the pen tip can be properly maintained, excellent resistance to ink blotting can be obtained, and furthermore, the surfactant can be more easily stably present in the ink, improving the ink's stability over time. To further improve the drying properties of the handwriting, a concentration of 0.003% by mass or more is more preferable, and 0.005% by mass or more is even more preferable. Furthermore, considering further improvements in resistance to dripping and stability over time, it is more preferable that the amount be 0.3% by mass or less, even more preferable that it be 0.1% by mass or less, particularly preferable that it be 0.05% by mass or less, and most preferable that it be 0.03% by mass or less. Furthermore, surfactants containing an acetylene bond in their structure can be used individually or as a mixture of two or more.

[0018] <Specific organic solvents> The specific organic solvent used in the present invention is represented by the organic solvent shown in the following formula (i). [ka] In the formula, R A is a linear or branched alkyl group having 1 to 4 carbon atoms, and R B x is either a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms, L is an ethylene group (-CH2-CH2-) or trimethylene group (-CH2-CH2-CH2-), which may be substituted with a methyl group, and x is an integer from 1 to 5.

[0019] As described above, the present invention dramatically improves the penetration of an ink composition into the paper surface by combining a surfactant having an acetylene bond in its structure with a specific organic solvent as shown in formula (i). As a result, the ink composition can penetrate the paper surface quickly before it spreads due to capillary action, the writing dries quickly, and bleeding and show-through are suppressed. Furthermore, by combining a surfactant having an acetylene bond in its structure with a specific organic solvent, and by setting the surface tension of the ink to a specific value, it becomes possible to maintain the proper wettability of the pen tip while increasing the penetration of the ink composition into the paper. As a result, excellent resistance to ink smudging can also be obtained.

[0020] Considering the improvement of the above effects, preferably, R in formula (i) A However, it is a methyl group or an ethyl group, and R B is an organic solvent in which R in formula (i) is either a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms, L is an ethylene group (-CH2-CH2-) or a trimethylene group (-CH2-CH2-CH2-), and x is an integer from 1 to 5, more preferably R A However, it is a methyl group and R B L is an organic solvent that is either a hydroxyl group or a methoxy group, L is an ethylene group (-CH2-CH2-) or a trimethylene group (-CH2-CH2-CH2-), and x is an integer between 2 and 4.

[0021] In addition, the density of the organic solvent represented by formula (i) at 20°C is preferably 0.80 g / cm 3 ~1.05 g / cm 3 more preferably 0.90 g / cm 3 ~1.02 g / cm 3 even more preferably 0.95 g / cm 3 ~0.98 g / cm 3 If the density is within the above numerical range, it can exist stably in the ink, and a synergistic effect with the surfactant having an acetylene bond in its structure is easily obtained.

[0022] In addition, the surface tension of the organic solvent represented by formula (i) is preferably 25 mN / m to 40 mN / m, more preferably 25 mN / m to 35 mN / m, and particularly preferably 26 mN / m to 30 mN / m in a 25°C environment.

[0023] Specific examples of the organic solvent represented by formula (i) include diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monobutyl ether, and the like. Among them, considering the improvement of permeability due to the synergistic effect with the surfactant having an acetylene bond in its structure and the further improvement of the drying property of the handwriting, dipropylene glycol monomethyl ether and tetraethylene glycol dimethyl ether are preferred, and it is particularly preferred to use dipropylene glycol monomethyl ether.

[0024] The content of the organic solvent represented by formula (i) is preferably 0.1% by mass to 10% by mass, more preferably 0.5% by mass to 5% by mass, and even more preferably 1% by mass to 5% by mass based on the total mass of the ink composition. If the content of the organic solvent shown in formula (i) is within the above range, the synergistic effect with the surfactant having an acetylene bond in its structure greatly improves permeability while allowing the surface tension to be set within a specific range, and furthermore, the wettability of the pen tip can be appropriately maintained. As a result, the drying time of the writing, resistance to bleeding and show-through, and resistance to ink smudging can be improved in a well-balanced manner. Furthermore, the organic solvents represented by formula (i) can be used individually or as a mixture of two or more.

[0025] Furthermore, the ratio of a surfactant having an acetylene bond in its structure to an organic solvent as shown in formula (i) (surfactant having an acetylene bond in its structure / specific organic solvent) is preferably 0.001 to 0.1 by mass, more preferably 0.002 to 0.08, and even more preferably 0.002 to 0.01. Within the above numerical range, the synergistic effect of the two components can be effectively obtained, resulting in a well-balanced improvement of excellent ink drying properties, bleed-resistant properties, show-through resistance, and ink stain resistance.

[0026] <Coloring agent> Next, the colorants included in the ink composition of this embodiment will be described. The colorants used in the ink composition are not particularly limited and can be selected and used as appropriate, such as dyes and pigments.

[0027] Examples of dyes include various types such as acid dyes, basic dyes, reactive dyes, direct dyes, disperse dyes, and food colorings.

[0028] Examples of acid dyes include CI Acid Red 18, CI Acid Orange 10, CI Acid Yellow 3, CI Acid Yellow 7, CI Acid Yellow 23 (Tartrazine), CI Acid Yellow 42, CI Acid Green 3, CI Acid Green 16, CI Acid Blue 1, CI Acid Blue 9, CI Acid Blue 22, CI Acid Blue 90, CI Acid Blue 239, CI Acid Blue 248, CI Acid Violet 15, CI Acid Violet 49, CI Acid Black 1, CI Acid Black 2, CI Acid Red 52, CI Acid Red 289, CI Acid Red 388, CI Acid Red 87 (Eosin), CI Acid Red 92 ( Examples include Phloxine, CI Acid Red 97, CI Acid Red 51 (Erythrosine), CI Acid Red 94 (Rose Bengal), Acridine Red (CI 45000), Rhodamine 110, Rhodamine 123, Rhodamine 6G (CI Basic Red 1), Rhodamine 6G Extra, Rhodamine 116, Rhodamine B (CI 45170), Tetramethylrhodamine perchlorate, Rhodamine 3B, Rhodamine 19, Sulforhodamine, Pyronin G (CI 45005), Rhodamine S (CI 45050), Rhodamine G (CI 45150), Ethylrhodamine B (CI 45175), Rhodamine 4G (CI 45166), Rhodamine 3GO (CI 45215), Sulforhodamine G, etc.

[0029] Examples of basic dyes include CI Basic Orange 2, CI Basic Orange 14, CI Basic Green 4, CI Basic Blue 9, CI Basic Blue 26, CI Basic Violet 1, CI Basic Violet 3, CI Basic Violet 10, Chrysoidine (CI 11270), Methyl Violet FN (CI 42535), Crystal Violet (CI 42555), Malachite Green (CI 42000), Victoria Blue FB (CI 44045), Acridine Orange NS (CI 46005), and Methylene Blue B (CI 52015).

[0030] Examples of direct dyes include CI Direct Red 28, CI Direct Yellow 44, CI Direct Blue 86, CI Direct Blue 87, CI Direct Violet 51, and CI Direct Black 19.

[0031] Examples of food colorings include CI Food Yellow 3, CI Food Black 2, Congo Red (CI22120), Direct Sky Blue 5B (CI24400), Violet BB (CI27905), Direct Deep Black EX (CI30235), Kayaras Black G Concentrate (CI35225), Direct Fast Black G (CI35255), and Phthalocyanine Blue (CI74180).

[0032] Examples of pigments include inorganic, organic, and processed pigments. Specifically, examples of pigments include carbon black, aniline black, ultramarine, lead yellow, titanium dioxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, quinophthalone-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, aluminum pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, and complementary pigments. In addition, microcapsule pigments may be used as pigments. Microcapsule pigments are obtained by dispersing a pigment in a medium and then encapsulating or solid-solubilizing a colored body made of a resin wall-forming material within a known microencapsulation method. Furthermore, as pigments, colored resin particles in which the pigment is covered with a transparent or translucent resin, or colorless resin particles colored with a pigment or dye can also be used.

[0033] In particular, it is preferable to use dyes as colorants. Unlike pigments, dyes exist in a dissolved state in the ink, so they do not easily hinder the penetration-enhancing effect of surfactants and organic solvents, and excellent ink drying properties, as well as resistance to bleeding and show-through, can be easily obtained. Furthermore, in this invention, it is preferable to use two or more dyes, and even when various types of paper are used on the writing surface, it tends to produce excellent ink drying properties. The reason for this is not entirely clear, but it is speculated that by using different dyes in combination, slight differences in penetration into the paper surface are created, allowing the ink to penetrate the paper surface in an orderly manner, and as a result, the entire ink can penetrate the paper surface quickly. This tendency is particularly pronounced with black ink, and it is more effective to use three or more dyes of different colors than to use black dye alone. Moreover, it is even more effective to use at least one blue dye, one red dye, and one yellow dye.

[0034] <Water> The ink composition according to the present invention comprises water. There are no particular restrictions on the water used, and examples include tap water, deionized water, ultrafiltered water, or distilled water.

[0035] <Other additives> The ink composition of the present invention can contain any additives as necessary. The additives that can be used are described as follows.

[0036] <pH adjuster> The ink composition according to the present invention can contain a pH adjuster. Examples of the pH adjuster include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate, and sodium hydroxide; basic organic compounds such as alkanolamines such as sodium acetate, triethanolamine, and diethanolamine; lactic acid, citric acid, and the like. Considering the stability of the ink composition over time, it is preferable to use a basic organic compound, and further preferably an alkanolamine that is less likely to affect the permeability to the paper surface and the wettability of the pen core. These pH adjusters can also be used as a mixture of two or more types.

[0037] In addition, the pH value of the ink composition of the present invention is preferably 11 or less. This is because when the pH value is 11 or less, the effects of surfactants and organic solvents having an acetylene bond in the structure can be easily obtained sufficiently, and high stability over time can be easily obtained. Also, from the viewpoints of the stability of the ink composition over time and the prevention of corrosion of metal members in contact with the ink composition, the pH value is preferably 6 or more. Therefore, the pH value of the ink composition is more preferably 6 to 11, and even more preferably 7 to 10. In the present invention, the pH value indicates the value measured at 20°C using an HM-30R type pH meter.

[0038] <Antibacterial substance> The ink composition according to the present invention may contain an antimicrobial substance. Examples of antimicrobial substances include phenol, phenoxyethanol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, sodium 2-pyridinethiol-1-oxide, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, orthophenylphenol or its salts, and more preferably selected from the group consisting of phenoxyethanol, 1,2-benzisothiazolin-3-one (hereinafter sometimes referred to as BIT), 2-methyl-4-isothiazolin-3-one (hereinafter sometimes referred to as MIT), 2-n-octyl-4-isothiazolin-3-one (hereinafter sometimes referred to as OIT), and mixtures thereof.

[0039] <Rust Inhibitor> The ink composition according to the present invention may contain a rust inhibitor. Examples of rust inhibitors include benzotriazole and its derivatives, toltriazole, dicyclohexylammonium nitride, diisopropylammonium nitride, sodium thiosulfate, saponin, or dialkylthiourea.

[0040] <Chelating agent> The ink composition according to the present invention may contain a chelating agent. Examples of chelating agents include ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), glycol etherdiaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), hydroxyethyliminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), and their alkali metal salts, ammonium salts, or amine salts.

[0041] <Moisturizer> The ink composition according to the present invention may contain a humectant to an extent that does not impair the effect of drying the writing. Examples of humectants include polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin, urea, sorbitol, N,N,N-trialkyl amino acids, or hyaluronic acid derivatives.

[0042] Furthermore, lubricants such as phosphate ester surfactants and fatty acids, as well as various resins such as acrylic resins, urethane resins, styrene-butadiene resins, polyester resins, and vinyl acetate resins, can also be added to improve the ink's properties and functionality.

[0043] <Physical properties of ink compositions for writing instruments> The surface tension of the ink composition according to the present invention must be 30 mN / m to 60 mN / m at a temperature of 20°C. As described above, the present invention's ink composition is characterized by the combined use of a surfactant having an acetylene bond in its structure and a specific organic solvent, as well as setting the surface tension of the ink within a specific range. This dramatically improves penetration while maintaining proper wettability to the pen nib, thereby improving both ink inflow and ink retention between the comb grooves of the pen nib. As a result, it becomes possible to satisfy all requirements regarding ink drying speed, resistance to bleeding and show-through, and resistance to ink blotting. Considering the improvement of the above effects, a value of 40 mN / m to 60 mN / m is more preferable, and a value of 45 mN / m to 50 mN / m is even more preferable. The surface tension of the ink composition is determined by measuring it using a platinum plate and the vertical plate method at a temperature of 20°C using a surface tension meter manufactured by Kyowa Interface Science Co., Ltd.

[0044] Furthermore, the ink composition according to the present invention preferably has a relatively low viscosity. By reducing the viscosity of the ink composition, the permeability of the ink composition can be improved, and the drying properties of the ink can be further enhanced. For this reason, it is preferable that the ink viscosity measured using a Type B rotational viscometer at a rotational speed of 60 rpm and 20°C be 50 mPa·s or less, more preferably 10 mPa·s or less, and particularly preferably 2 mPa·s or less. Viscosity can be measured using a Type B rotational viscometer (Model: BLII, Rotor: BL adapter, manufactured by Toki Sangyo Co., Ltd.). Furthermore, by using an ink with reduced viscosity and surface tension within the aforementioned range, the pen nib functions more effectively, resulting in excellent ink discharge performance along with superior resistance to ink blotting.

[0045] <Method for manufacturing ink composition> The ink composition according to the present invention can be manufactured by any conventionally known method. Specifically, it can be manufactured by blending the required amounts of each component and mixing them using various stirrers such as magnetic stirrers, propeller stirrers, homogenizer stirrers, homodispersers, homomixers, and planetary stirrers, as well as various dispersers such as bead mills.

[0046] <Writing implements> The present invention is for use in writing instruments equipped with a pen nib. The pen nib has comb grooves for temporarily storing ink, an ink flow passage, and an air passage. When the internal pressure of the ink reservoir changes, this pen nib functions as an ink supply mechanism in which excess ink flows into and is retained between the comb grooves of the pen nib, thereby suppressing ink leakage and overflow from the pen tip, and further adjusting the ink discharge performance to produce a good writing line. Pen nibs often have complex shapes due to the functions described above, and are generally molded from resin. However, depending on the type of resin used and the additives such as mold lubricants used during molding, hydrophobicity may increase, leading to problems with wettability with the ink composition. However, the ink composition of the present invention can maintain good wettability even in such pen nibs, and in this respect as well, the ink composition of the present invention is useful.

[0047] Furthermore, the structure of a writing instrument filled with the aqueous ink composition for writing instruments of the present invention is not particularly limited, as long as it has a pen tip having comb grooves for temporarily storing ink, an ink flow passage, and an air passage. For example, conventional, general-purpose materials can be used, including marking pens (sign pens) with fiber tips, felt tips, and plastic tips, ballpoint pens with ballpoint pen tips, and various other writing instruments such as fountain pens.

[0048] Examples of materials used for the nibs of writing instruments include metals such as cemented carbide, stainless steel, gold, and iridium, as well as ceramics such as silicon carbide, for ballpoint pens and fountain pens, and synthetic resins such as polyester, nylon, polyurethane, polyethylene, polypropylene, and acrylic for marking pens (sign pens).

[0049] The ink composition according to the present invention exhibits good wettability to metals such as stainless steel, gold-plated stainless steel, 14k gold, 18k gold, and 22k gold, resulting in excellent ink discharge from the pen tip and producing a good writing line. For this reason, it can be suitably used in writing instruments having a metal pen tip.

[0050] Furthermore, fountain pens tend to dispense a larger amount of ink from the nib compared to other writing instruments. This often leads to problems with the drying time of the resulting writing. As described above, the ink composition of the present invention has excellent penetration into paper and therefore possesses excellent writing drying properties. For this reason, using the ink composition of the present invention in a fountain pen is suitable and effective.

[0051] Furthermore, a writing instrument that can use the ink composition according to the present invention may have a configuration in which the ink composition is directly filled, or it may have an ink reservoir that can be filled with the ink composition.

[0052] Examples of ink storage containers include cartridge-type containers that can be detachably replaced on the writing instrument body or pen nib and are pre-filled with ink composition or ink, and ink-filling type containers equipped with an ink-filling mechanism that allows ink composition or ink to be filled from an ink container such as an ink bottle.

[0053] The ink filling mechanism may be directly installed within the writing instrument body, or it may be detachably attached to the writing instrument body or nib, like a converter.

[0054] Furthermore, writing instruments that can use the ink composition of the present invention include capped writing instruments equipped with a cap that covers the pen tip, and retractable writing instruments equipped with a knock mechanism, a rotating mechanism, or a sliding mechanism that allows the pen tip to be stored inside the barrel. Because the ink composition of the present invention has excellent resistance to ink blotting, it can be suitably used in retractable writing instruments, which are prone to problems such as ink leakage. [Examples]

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0056] <Example 1> The following raw materials were mixed by propeller stirring to obtain the ink composition of Example 1. • Surfactants containing an acetylene bond in their structure: 0.01% by mass (Acetylene glycol-based surfactant A: Acetylene glycol-based surfactant with ethylene oxide added) • Diethylene glycol monomethyl ether: 4.0% by mass • Coloring agent: 10.0% by mass (black dye) Triethanolamine: 1.0% by mass • 1,2-Benzisothiazolin-3-one (BIT): 0.05% by mass ·Water: remainder

[0057] Furthermore, the surface tension of the ink composition was measured using a surface tension meter (at 20°C, using a platinum plate and the vertical plate method, manufactured by Kyowa Interface Science Co., Ltd., model: DY-200) and was found to be 48 mN / m.

[0058] <Examples 2-13, Comparative Examples 1-2> By changing the types and amounts of raw materials, ink compositions for Examples 2-13 and Comparative Examples 1-2 were obtained. The compositions of the prepared ink compositions are shown in the table. Furthermore, the surface tension of the obtained ink compositions in the examples and comparative examples was measured using a surface tension meter, similar to the ink composition in Example 1. The results are shown in the table.

[0059] Furthermore, the raw materials used in the examples and comparative examples are as follows. The explanation will follow the note numbers in the table.

[0060] (1) Product name: Olfin E1010, manufactured by Nisshin Chemical Industry Co., Ltd., acetylene glycol-based surfactant with added ethylene oxide, number of moles of EO added: 10, HLB: 13-14, cloud point: 42℃, foaming properties: immediately after (A) 17ml, after 5 minutes (B) 2ml, active ingredient 100% (2) Product name: Orphine Exp. 4200, manufactured by Nisshin Chemical Industry Co., Ltd., acetylene glycol-based surfactant, HLB: 10-13, foaming properties: immediately after (A) 3 ml, after 5 minutes (B) 0 ml, active ingredient 75% (3) Density: 1.019g / cm3 , Surface tension: 34.3mN / m (4) Density: 0.943g / cm 3 , Surface tension: 28.1mN / m (5) Density: 0.955g / cm 3 , Surface tension: 27.9mN / m (6) Density: 1.049g / cm 3 , Surface tension: 36.4mN / m (7) Density: 0.984g / cm 3 , Surface tension: 30.0mN / m (8) Density: 1.011g / cm 3 , Surface tension: 31.8mN / m (10) Water Black 191-L, manufactured by Orient Chemical Industry Co., Ltd., aqueous solution containing 15% coloring agent. (11) Water Blue 9, manufactured by Orient Chemical Industries, Ltd. (CI Acid Blue 9) (12) Water Blue 105, manufactured by Orient Chemical Industry Co., Ltd., (CI Acid Blue 90) (13) Edible red 106 (14) Food yellow 5 (15) Spilon Yellow WS-1, manufactured by Hodogaya Chemical Co., Ltd., (CI Acid Yellow 23)

[0061] Furthermore, the viscosity of the ink composition obtained in Example 4 was measured using a B-type rotational viscometer (model: BLII, rotor: BL adapter, manufactured by Toki Sangyo Co., Ltd., sample volume: 20 ml), and the viscosity at 20°C and a rotational speed of 60 rpm was 1.3 mPa·s. In addition, the surface tension of the ink composition was measured using a surface tension meter (at 20°C, platinum plate, vertical plate method, manufactured by Kyowa Interface Science Co., Ltd., model: DY-200), and was found to be 46 mN / m. Furthermore, the pH of the aqueous ink composition was measured at 20°C using an IM-40S pH meter (manufactured by Toa DKK Co., Ltd.), and the result was a pH of 9.5.

[0062] [Table 1]

[0063]

Table 2

[0064] <Test and Evaluation> The obtained ink compositions of the examples and comparative examples were evaluated by the following method.

[0065] <Writing Drying Property> The ink compositions of the examples and comparative examples were injected into a resin ink reservoir (ink capacity 0.9 ml) from its opening by 0.3 ml. This ink reservoir was equipped with a nib of width M made of gold-plated stainless steel and a pen core having a comb groove for temporarily storing ink, an ink flow path, and an air passage, and was attached to a knock-type fountain pen (manufactured by Pilot Corporation, trade name: Capless (width M)). This writing instrument was used as the test writing instrument. The test writing instrument was placed with the nib facing downwards, and the filled ink composition was allowed to flow to the nib to make it in a writable state. In that state, the character "永" (the size of the character was approximately 1 cm in both vertical and horizontal directions) was written on a writing test paper (commercially available Campus Notebook A ruled (manufactured by Kokuyo Co., Ltd.)), and when it was rubbed with tissue paper at each elapsed time, if the periphery of the handwriting was not soiled and good handwriting was obtained, it was regarded that the handwriting was dried, and the writing drying property was evaluated according to the following criteria. The evaluation criteria for the writing drying property are shown below. Also, the evaluation results were shown in a table.

[0066] Evaluation Criteria for Writing Drying Property ◎◎: The handwriting dried in less than 3 seconds of writing. ◎: The handwriting dried in 3 seconds or more and less than 5 seconds of writing. ○: The handwriting dried in 5 seconds or more and less than 10 seconds of writing. ×: The handwriting dried in 10 seconds or more and less than 20 seconds of writing.

[0067] <Bleeding Resistance and Ink Smear Resistance> The ink compositions of the examples and comparative examples were each injected with 0.3 ml from the opening into a resin ink reservoir (ink capacity: 0.9 ml). This ink reservoir was attached to a knock-type fountain pen (manufactured by Pilot Corporation, trade name: Capless (character width M)) having a gold-plated stainless steel pen tip with a character width M, and a pen core having a comb groove for temporarily storing ink, an ink flow path, and an air path. This writing instrument was used as the test writing instrument. The test writing instrument was placed with the pen tip facing downward, and the filled ink composition was allowed to flow to the pen tip to make it in a writable state. In that state, the character "永" (character size: approximately 1 cm in both vertical and horizontal directions) was written on test writing paper (commercially available Campus Notebook A ruled (manufactured by Kokuyo Co., Ltd.)). The bleeding resistance and bleeding-through resistance were evaluated according to the following criteria based on the state of the obtained handwriting. The evaluation criteria for bleeding resistance and bleeding-through resistance are shown below. Also, the evaluation results are shown in a table.

[0068] Evaluation Criteria for Bleeding Resistance ○: Almost no bleeding is observed. △: A slight bleeding is observed, but there is no problem in practical use. ×: Bleeding is recognized.

[0069] Evaluation Criteria for Bleeding-through Resistance ○: Almost no bleeding-through is observed. △: A slight bleeding-through is observed, but there is no problem in practical use. ×: Bleeding-through is recognized.

[0070] <Resistance to Ink Spillage> 0.3 ml each of the ink compositions of the examples and comparative examples was injected into a resin ink reservoir (ink capacity 0.9 ml) through its opening. This ink reservoir was then mounted in a retractable fountain pen (manufactured by Pilot Corporation, product name: Capless (nib width M)) which had a gold-plated stainless steel nib with a medium-width nib and a nib with a comb groove for temporary ink storage, an ink flow passage, and an air passage. This writing instrument was used as the test writing instrument. The test writing instrument was placed with the nib facing downwards and left undisturbed in a vacuum desiccator. In this state, the pressure inside the desiccator was reduced to -70 mmHg relative to atmospheric pressure over 5 minutes. Subsequently, the test writing instruments were left in the desiccator for another 5 minutes while maintaining a reduced pressure of -70 mmHg relative to atmospheric pressure. The presence or absence of ink leakage (dubbing) from the pen tip of the test writing instruments was checked during both the reduced pressure and the maintenance of the reduced pressure state, and the resistance to ink dripping was evaluated according to the following criteria. The evaluation criteria for ink dripping resistance are shown below. The evaluation results are also shown in the table.

[0071] Evaluation criteria for resistance to dripping. ○: No ink dripping occurred from the pen tip. ×: Ink may drip from the pen tip.

[0072] Furthermore, the ink drying properties of the ink compositions of Example 4 and Example 13 were re-evaluated using the same method as in the above evaluation of ink drying properties, except that commercially available fountain pen paper (manufactured by Pilot Corporation) was used for the test paper. It was confirmed that the ink composition of Example 13 dried faster than the ink composition of Example 4.

[0073] From the above, it was found that an ink composition comprising a surfactant having an acetylene bond in its structure, a specific organic solvent, water, and a colorant, wherein the surface tension of the ink composition at 20°C is 30 mN / m to 60 mN / m, is excellent as an ink composition for writing instruments equipped with a pen tip, exhibiting superior drying properties, resistance to bleeding and show-through, and resistance to ink blotting.

Claims

1. A water-based ink composition for fountain pens comprising water, a coloring agent, a surfactant having an acetylene bond in its structure, and an organic solvent, and comprising a pen nib having comb grooves for temporarily storing ink, an ink flow passage, and an air passage, The aforementioned organic solvent is an organic solvent represented by the following formula (i): 【Chemistry 1】 (In the formula, R Ａ is a linear or branched alkyl group having 1 to 4 carbon atoms, and R Ｂ is a hydroxyl group or an alkoxy group having 1 to 3 carbon atoms, and L may be substituted with a methyl group, or an ethylene group (-CH ２ -CH ２ -) or trimethylene group (-CH ２ -CH ２ -CH ２ -) and x is an integer from 1 to 5. The surface tension of the ink composition at 20°C is 30 mN / m to 60 mN / m. A water-based ink composition for fountain pens, wherein the ratio of the surfactant having an acetylene bond in its structure to the organic solvent is 0.001 to 0.08 by mass.

2. The aqueous ink composition for fountain pens according to claim 1, wherein the surfactant having an acetylene bond in its structure is a surfactant to which ethylene oxide has been added.

3. The aqueous ink composition for fountain pens according to claim 2, wherein the number of ethylene oxide addition moles of the surfactant having an acetylene bond in its structure is 2 to 40.

4. The aqueous ink composition for fountain pens according to any one of claims 1 to 3, wherein the coloring agent is a dye.

5. A fountain pen characterized by containing the aqueous ink composition for fountain pens described in any one of claims 1 to 4.

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