Aqueous ink composition for writing tool and writing tool formed by housing the same

Abstract

To provide an aqueous ink composition for writing tools, which achieves dryness of handwriting and ink discharge stability at high degree, can form handwriting excellent in dryness, and can form clear handwriting and, a writing tool housing the ink composition.SOLUTION: An aqueous ink composition contained in a writing tool is equipped with a pen nib having a slit extending backward from the pen point at the front edge, wherein the ink composition for writing tool includes a coloring agent, a specific polyoxyethylene aryl ether, a specific phosphate ester, and water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink composition for a writing instrument and a writing instrument containing the same. [Background technology]

[0002] Conventionally, inks that use water as the primary solvent (water-based inks) have been widely used due to their low odor and high safety. Compared to inks that use volatile organic solvents as the primary solvent (oil-based inks), water-based inks do not penetrate the paper surface as quickly, which can result in poor drying of handwriting. Touching the wet handwriting immediately after writing often stains the paper surface around the handwriting, fingers, etc. For this reason, in the field of water-based inks, studies have been conducted to improve the drying of handwriting (see, for example, Patent Document 1). Patent Document 1 discloses a water-based ink containing an organic solvent selected from a specific polyhydric alcohol and glycol ethers. This ink has improved paper wettability due to the specific organic solvent, resulting in good ink penetration into the paper, and is said to be able to produce handwriting that dries quickly. However, this ink has a tendency for the colorant to penetrate the paper surface along with the vehicle, which can cause handwriting to show through.

[0003] To solve these problems, the present applicant has disclosed an aqueous ink composition containing a specific polyoxyethylene aryl ether and having a specific contact angle with writing paper A conforming to the old JIS P3201 (see, for example, Patent Document 2). This ink composition is capable of forming handwriting that is excellent in drying properties and also forms clear handwriting with reduced strike-through. However, depending on the writing instrument to which this ink composition is applied, although the handwriting drying properties are excellent, the ink ejection stability may be insufficient, and there is room for improvement in achieving a high level of both handwriting drying properties and ink ejection stability. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-193688 [Patent Document 2] International Publication No. 2023 / 095614 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made based on the background art as described above, and aims to provide a water-based ink composition for a writing instrument that can achieve both high levels of drying properties of handwriting and high ink ejection stability, and a writing instrument containing this ink composition. [Means for solving the problem]

[0006] The present invention provides an aqueous ink composition for a writing instrument, which is to be contained in a writing instrument having a pen tip with a slit extending rearward from a pen point at the front end, and which comprises a colorant, a polyoxyethylene aryl ether, a phosphate ester, and water, wherein the polyoxyethylene aryl ether is one or more compounds selected from the group consisting of compounds represented by the following general formula (I-1) or (I-2), and the phosphate ester is a compound represented by the following general formula (II): [ka] (In the formula, n1 is 0 or 1, n2 and n3 each independently represent a number from 1 to 50; If n1 is 1, R 11 is a divalent hydrocarbon group, R 12 , R 13 , R 14 , and R 15 are each independently a hydrogen atom or a C1-C3 alkyl group. [ka] (In the formula, R21 is C 10 ~C 20 is an aliphatic hydrocarbon group of the formula l is a number equal to or greater than 5, and m is a number equal to or greater than 0, n is 1 or 2. The polyoxyethylene aryl ether is one or more compounds selected from the group consisting of compounds represented by the following general formula (I-3) and (I-4). [ka] (In the formula, n4 and n5 are each independently a number from 1 to 50. Further, the polyoxyethylene aryl ether has an HLB value of 10 to 17, and the content (P1) of the polyoxyethylene aryl ether and the content (P2) of the phosphate ester relative to the total mass of the ink composition satisfy the following formula (1): 3≦P1 / P2≦80 (1) Furthermore, the present invention is directed to a writing instrument containing the ink composition. Further, the requirements are that part or all of the nib is made of gold-plated stainless steel or a gold alloy, and that the ink supply mechanism is provided with a pen core having a comb groove for temporarily storing ink, an ink flow passage, and an air passage. [Effects of the Invention]

[0007] The present invention provides a water-based ink composition for a writing instrument that satisfies both high levels of drying properties of handwriting and ink ejection stability, and is capable of forming handwriting that is excellent in drying properties and clear handwriting, and a writing instrument containing this ink composition. DETAILED DESCRIPTION OF THE INVENTION

[0008] The aqueous ink composition for a writing instrument according to the present invention (hereinafter sometimes referred to as "ink composition" or "ink") comprises a colorant, a polyoxyethylene aryl ether, a phosphate ester, and water. Each component constituting the ink composition according to the present invention will be described below.

[0009] The ink composition according to the present invention contains a colorant. As the colorant, dyes, pigments, and resin particles that are soluble or dispersible in an aqueous medium can all be used, that is, the colorant may contain at least one selected from the group consisting of dyes, pigments, and resin particles.

[0010] Examples of dyes include acid dyes, basic dyes, direct dyes, reactive dyes, vat dyes, sulfur dyes, alloy dyes, cationic dyes, and disperse dyes. Examples of pigments include inorganic pigments, organic pigments, luster pigments, fluorescent pigments, phosphorescent pigments, etc. Furthermore, water-dispersed pigments can also be used, which are pigments that have been finely and stably dispersed in an aqueous medium in advance using at least one of a surfactant and a resin.

[0011] If necessary, a pigment dispersant can be used, such as anionic or nonionic surfactants, anionic polymers such as polyacrylic acid and styrene-acrylic acid, and nonionic polymers such as PVP and PVA.

[0012] Pigments according to the present invention also include self-dispersed pigments. A self-dispersing pigment is a pigment that can be dispersed in an aqueous medium without using a dispersant such as a resin or a surfactant. By subjecting the pigment to physical or chemical treatment to form hydrophilic functional groups on the pigment surface, it becomes possible to disperse the pigment in an aqueous medium without using a dispersant. Examples of pigments that can be used include carbon black, benzimidazoline pigments, condensed azo pigments, isoindolinone pigments, quinophthalone pigments, quinacridone pigments, phthalocyanine pigments, and aluminum.

[0013] The pigments according to the present invention also include microencapsulated pigments. Microcapsule pigments are pigments in which a core substance is encapsulated in a wall film formed from a wall film-forming material. By encapsulating the core substance in a microcapsule, it is isolated and protected from the external environment, which can improve the water resistance and light resistance of the core substance.

[0014] The core substance may be a coloring composition comprising a coloring material and a medium, such as a dye or pigment dissolved or dispersed in an aqueous or oily medium. The dyes or pigments that can be used are those described above.

[0015] Examples of aqueous media include tap water, ion-exchanged water, ultrafiltered water, distilled water, and the like. Examples of oily media include esters such as monobasic acid esters, dibasic acid monoesters, dibasic acid diesters, partial or complete esters of polyhydric alcohols, aromatic hydrocarbons such as alkylbenzenes and alkylnaphthalenes, higher alcohols, ketones, and ethers. The aqueous medium or oily medium can be used alone or in combination of two or more kinds.

[0016] As the coloring composition, a photochromic material that changes color depending on the presence or absence of light irradiation can also be used. This color change may be reversible or irreversible, but a reversible photochromic material is preferred because it can repeatedly exhibit color changes depending on the presence or absence of light irradiation. An example of a photochromic material used as a coloring composition is a coloring composition in which a photochromic compound as a coloring material is dissolved in an oligomer as a medium, i.e., a reversible photochromic composition comprising at least a photochromic compound and an oligomer. By encapsulating the reversible photochromic composition in microcapsules, a reversible photochromic microcapsule pigment can be formed.

[0017] Examples of photochromic compounds include conventionally known spirooxazine derivatives, spiropyran derivatives, naphthopyran derivatives, etc. that develop color when irradiated with sunlight, ultraviolet light, or blue light with a peak emission wavelength in the range of 400 to 495 nm, and lose color when the irradiation is stopped. For example, compounds described in JP 2021-120493 A and WO 2020 / 137469 A can be cited. Furthermore, a photochromic compound having optical memory properties (color memory photochromism) can also be used. Examples of such photochromic compounds include diarylethene derivatives, such as those described in JP-A-2021-120493.

[0018] Examples of the oligomer include styrene-based oligomers, acrylic-based oligomers, terpene-based oligomers, and terpene-phenol-based oligomers. By dissolving the photochromic compound in various oligomers, it is possible to improve both the light resistance and the color density, and further to adjust the color change sensitivity. The oligomers can be used alone or in combination of two or more.

[0019] The coloring composition may be a thermochromic material that changes color with temperature. This color change may be reversible or irreversible, but a reversible thermochromic material is preferred because it can repeatedly change color with temperature changes. Examples of thermochromic materials used as coloring compositions include coloring compositions comprising at least (i) an electron-donating organic color-forming compound as a coloring material and (ii) an electron-accepting compound as a medium. Further examples include coloring compositions comprising at least a homogeneous solution of component (i) as a coloring material, component (ii) as a medium, and (iii) a reaction medium that determines the temperature at which the color reaction between components (i) and (ii) occurs, i.e., reversible thermochromic compositions comprising at least (i) an electron-donating organic color-forming compound, (ii) an electron-accepting compound, and (iii) a reaction medium that determines the temperature at which the color reaction between components (i) and (ii) occurs. Reversible thermochromic microcapsule pigments can be formed by encapsulating the reversible thermochromic composition in microcapsules.

[0020] Examples of reversible thermochromic compositions that can be used include heat-discolorable reversible thermochromic compositions with a relatively small hysteresis width (ΔH) (ΔH = 1 to 7°C), as described in Japanese Patent Publication Nos. 51-44706, 51-44707, and 1-29398. These reversible thermochromic compositions change color around a specific temperature (color change point), exhibiting a colorless state in a temperature range above the high-side color change point and a colored state in a temperature range below the low-side color change point. Only one of these two states exists at room temperature, and the other state is maintained while the heat or cold required to manifest that state is applied, but returns to the state it exhibits at room temperature when the heat or cold application is removed. The reversible thermochromic composition may also be a heat-discolorable reversible thermochromic composition having a large hysteresis width (ΔH = 8 to 80°C), as described in JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936, JP-A-2005-1369, etc. This reversible thermochromic composition exhibits color memory in a specific temperature range (between the color development onset temperature t2 and the color loss onset temperature t3 (a temperature range where two phases are essentially maintained)) where the shape of the curve plotting the change in color density with temperature is significantly different when the temperature is increased from below the color loss temperature range than when the temperature is decreased from above the color loss temperature range. The term "heat-discolorable" means that the color disappears when heated and develops color when cooled.

[0021] When the reversible thermochromic composition having the above-mentioned color memory property is applied to the present invention, the reversible thermochromic composition can effectively function to maintain the color it exhibits under normal conditions (the temperature range in everyday life) by specifying the complete color development temperature t1 as a temperature that can only be obtained in a freezer or in a cold region, and the complete decolorization temperature t4 as a temperature range that can be obtained from frictional heat generated by a friction body or a familiar heating body such as a hair dryer, and specifying the ΔH value as 40 to 100°C. The temperature that can only be obtained in a freezer or in a cold region is -50 to 0°C, preferably -40 to -5°C, and more preferably -30 to -10°C. The temperature obtainable from a familiar heating device such as a hair dryer is in the range of 50 to 95°C, preferably 50 to 90°C, and more preferably 60 to 80°C.

[0022] As the reversible thermochromic composition, a reversible thermochromic composition of the heat-coloring type using a gallic acid ester, as described in JP-B No. 51-44706 and JP-A No. 2003-253149, can also be used. The term "thermal coloring type" means that the color develops when heated and disappears when cooled.

[0023] The reversible thermochromic composition is a compatible solution containing the above components (A), (B), and (C) as essential components. The proportions of each component depend on the concentration, discoloration temperature, discoloration form, and type of each component, but the component ratios that generally provide the desired properties are 1 part of component (A) to 0.1 to 100, preferably 0.1 to 50, more preferably 0.5 to 20, of component (B), and 1 to 800, preferably 5 to 200, more preferably 5 to 100, and even more preferably 10 to 100, of component (C) (all of the above proportions are in parts by mass).

[0024] Examples of the wall film forming material, that is, the resin constituting the wall film, include urea resin, urethane resin, urea-urethane resin, epoxy resin, melamine resin, benzoguanamine resin, and isocyanate resin.

[0025] The microencapsulated pigment may also contain various additives such as antioxidants, ultraviolet absorbers, infrared absorbers, dissolution aids, preservatives, and antifungal agents, as long as they do not affect the functions of the pigment.

[0026] The microencapsulated pigment can be produced by a microencapsulation method, such as a conventionally known isocyanate-based interfacial polymerization method, a melamine-formalin-based or other in situ polymerization method, a liquid curing coating method, a phase separation method from an aqueous solution, a phase separation method from an organic solvent, a melt-dispersion cooling method, an air suspension coating method, or a spray drying method, and the method can be appropriately selected depending on the application. Furthermore, depending on the purpose, a secondary resin film may be provided on the surface of the microcapsule pigment to impart durability or to modify the surface properties for practical use.

[0027] The reversible thermochromic microcapsule pigment or reversible photochromic microcapsule pigment preferably has a core substance:wall membrane mass ratio of 7:1 to 1:1, and by having the core substance:wall membrane mass ratio within the above range, it is possible to prevent a decrease in color density and vividness during color development. A core substance:wall membrane mass ratio of 6:1 to 1:1 is more preferable.

[0028] The reversible thermochromic microencapsulated pigment or the reversible photochromic microencapsulated pigment can also be made into a microencapsulated pigment that exhibits color change behavior from a first color to a second color by incorporating a non-color-changing colorant such as a general dye or pigment into the microcapsules.

[0029] The resin particles include resin particles containing at least one of the above-mentioned dyes, pigments, thermochromic materials, and photochromic materials.

[0030] Examples of resin particles containing a dye include colored resin particles in which a dye is homogeneously dissolved or dispersed in resin particles, and colored resin particles in which a dye is dyed onto resin particles.

[0031] Examples of resin particles containing a pigment include colored resin particles in which the pigment is uniformly dispersed in the resin particles, colored resin particles in which the surfaces of the resin particles are coated with the pigment, etc. Here, the pigment may be surface-treated by various conventionally known methods in order to improve its dispersibility and adsorption to the resin that constitutes the resin particles.

[0032] Examples of resin particles containing a thermochromic material or a photochromic material include colored resin particles in which a reversible thermochromic composition is uniformly dispersed in the resin particles (hereinafter sometimes referred to as "reversible thermochromic resin particles"), and colored resin particles in which a reversible photochromic composition is uniformly dispersed in the resin particles (hereinafter sometimes referred to as "reversible photochromic resin particles").

[0033] The resin constituting the resin particles is not particularly limited as long as it is a thermoplastic resin or a thermosetting resin, and examples thereof include thermoplastic resins such as polystyrene, acrylic resin, polyester, polyvinyl chloride, polybutadiene, polymethyl methacrylate, acrylic-urethane copolymer resin, polyethylene, polypropylene, polyacrylonitrile, polyacetal, ethylene-propylene copolymer resin, ethylene-vinyl acetate copolymer resin, styrene-acrylic copolymer resin, styrene-butadiene copolymer resin, styrene-acrylonitrile copolymer resin, and acrylonitrile-butadiene copolymer resin; Thermosetting resins such as epoxy resin, epoxy acrylate resin, xylene resin, toluene resin, guanamine resin, benzoguanamine resin, melamine resin, urethane resin, phenol resin, alkyd resin, polyamide, polyimide, polyamide ester, urea resin, silicone resin, and unsaturated polyester can be exemplified respectively.

[0034] The resin particles according to the present invention include solid resin particles with no voids inside the particles, and hollow resin particles with voids inside the particles.

[0035] The resin particles can be produced by a pulverization method, a spray drying method, or a polymerization method in which polymerization is carried out in an aqueous or oily medium in the presence of at least one of a dye, a pigment, a thermochromic material, and a photochromic material, such as a suspension polymerization method, a suspension polycondensation method, a dispersion polymerization method, or an emulsion polymerization method.

[0036] The shape of the resin particles is not particularly limited, and resin particles having a spherical shape such as a perfect sphere, an oval sphere, or an approximately spherical shape, a polygonal shape, a flat shape, etc. Among these, spherical resin particles are preferred.

[0037] Reversible thermochromic resin particles or reversible photochromic resin particles can also be made into resin particles that exhibit color change behavior from a first color to a second color by blending a non-color-changing colorant such as a general dye or pigment into the resin particles.

[0038] The reversible thermochromic composition or reversible photochromic composition is preferably encapsulated in a microcapsule and used as a microencapsulated pigment, because encapsulation in a microcapsule makes it possible to form a chemically or physically stable pigment, and furthermore, the reversible thermochromic composition or reversible photochromic composition can maintain the same composition and exhibit the same effects under various use conditions.

[0039] The colorants according to the present invention can be used singly or in combination of two or more.

[0040] When the colorant is a reversible thermochromic microencapsulated pigment or a reversible photochromic microencapsulated pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, the average particle size of these colorants is not particularly limited, but is preferably in the range of 0.01 to 5 μm, more preferably 0.1 to 3 μm, and even more preferably 0.5 to 3 μm. If the average particle size of the colorant exceeds 5 μm, it becomes difficult to obtain good ink ejection properties when used in a writing instrument. On the other hand, if the average particle size is less than 0.01 μm, it becomes difficult to achieve high-density color development.

[0041] The average particle diameter was measured by determining the particle region using image analysis particle size distribution measurement software (manufactured by Mountec Co., Ltd., product name: MacView), calculating the diameter equivalent to a circle with a projected area (Heywood diameter) from the area of the particle region, and measuring the average particle diameter of particles equivalent to a sphere with the same volume using this value.

[0042] Furthermore, if the particle size of all or the majority of particles exceeds 0.2 μm, it is also possible to measure the average particle size of particles equivalent to an equal-volume sphere by the Coulter method using a particle size distribution analyzer (product name: Multisizer 4e, manufactured by Beckman Coulter, Inc.).

[0043] Furthermore, the volumetric particle size and average particle size may be measured using a calibrated laser diffraction / scattering particle size distribution analyzer (manufactured by HORIBA, Ltd., product name: LA-960V2) based on values measured using the above-mentioned software or a measuring device using the Coulter method.

[0044] The content of the colorant relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.5 to 15 mass%, more preferably 1 to 10 mass%, and even more preferably 1 to 5 mass%. If the content exceeds 15 mass%, the ink discharge performance of a writing instrument containing the ink composition is likely to deteriorate, and writing defects such as smearing and skipped lines are likely to occur. On the other hand, if the content is less than 0.5 mass%, it becomes difficult to obtain a writing density suitable for the writing instrument.

[0045] When the colorant is a reversible thermochromic microencapsulated pigment or a reversible photochromic microencapsulated pigment, or a reversible thermochromic resin particle or a reversible photochromic resin particle, the content of the colorant relative to the total mass of the ink composition is preferably 5 to 40% by mass, more preferably 10 to 40% by mass, and even more preferably 10 to 30% by mass. If the content exceeds 40% by mass, the ink discharge performance of a writing instrument containing the ink composition decreases, and writing defects such as blurring and skipped lines are likely to occur. On the other hand, if the content is less than 5% by mass, it is difficult to achieve the color change and writing density suitable for a writing instrument, and it is difficult to fully fulfill the color change function.

[0046] The ink composition according to the present invention contains a polyoxyethylene aryl ether selected from compounds represented by the following general formula (I-1) or (I-2). [ka] (In the formula, n1 is 0 or 1, n2 and n3 are each independently a number from 1 to 50; If n1 is 1, R 11 is a divalent hydrocarbon group, R12 , R 13 , R 14 , and R 15 are each independently a hydrogen atom or a C1-C3 alkyl group. If n1 is 0, R 11 is a single bond. When n1 is 1, R 11 is preferably a divalent aliphatic hydrocarbon group.

[0047] The polyoxyethylene aryl ether of the present invention can form clear handwriting by increasing the permeability of the vehicle to the paper surface, improving the drying properties of the handwriting, and suppressing the penetration of the colorant into the paper surface and causing strike-through of the handwriting. The vehicle is a composition consisting of the components of the ink composition excluding the colorant component.

[0048] From the viewpoints of increasing the dissolution stability of the polyoxyethylene aryl ether and suppressing strike-through while improving the drying properties of handwriting, the polyoxyethylene aryl ether according to the present invention is preferably a compound represented by the following general formula (I-3) or (I-4): [ka] (In the formula, n4 and n5 are each independently a number from 1 to 50.

[0049] From the viewpoint of increasing the solubility in the ink to improve the stability of the ink while also being able to form handwriting that is excellent in drying properties, it is preferable that the polyoxyethylene aryl ether has an HLB value of 10 to 17. The HLB value is a value based on the Griffin method and is calculated using the following formula. The HLB value according to the Griffin method is in the range of 0 to 20, with a larger value indicating a more hydrophilic compound. HLB value = 20 × (mass % of hydrophilic groups) = 20 × (sum of formula weights of hydrophilic groups / molecular weight of surfactant)

[0050] The polyoxyethylene aryl ethers can be used alone or in combination of two or more.

[0051] The content of polyoxyethylene aryl ether (hereinafter sometimes referred to as "P1") relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.1 to 10 mass%, more preferably 0.5 to 7 mass%, and even more preferably 1 to 5 mass%. When the content is within the above range, it becomes easy to suppress bleed-through of handwriting while improving the drying properties of handwriting.

[0052] The ink composition according to the present invention contains a phosphoric acid ester represented by the following general formula (II). [ka] (In the formula, R 21 is C 10 ~C 20 is an aliphatic hydrocarbon group of the formula l is a number greater than or equal to 5, and m is a number greater than or equal to 0, n is 1 or 2.)

[0053] In the above general formula (II), "CH2CH2O" is an ethylene oxide group, and "CH2CH(CH3)O" is a propylene oxide group, and the ethylene oxide group and the propylene oxide group may each form a block or be arranged randomly.

[0054] In the above general formula (II), "l" is the number of moles of ethylene oxide added, and "m" is the number of moles of propylene oxide added, where l is a number of 5 or more (l≧5) and m is a number of 0 or more (m≧0). Preferably, l is a number from 5 to 35 and m is a number from 0 to 10, and more preferably, l is a number from 5 to 30 and m is a number from 0 to 5. "n" is 1 or 2, and when n is 1, the phosphate ester of the above general formula (II) is a phosphate diester. When n is 2, the phosphate ester of the above general formula (II) is a phosphate monoester. The phosphate ester according to the present invention may be a mixture of a phosphate monoester and a phosphate diester.

[0055] In the above general formula (II), R 21 is C 10 ~C 20 C is an aliphatic hydrocarbon group, and includes saturated aliphatic hydrocarbon groups (alkyl groups) and unsaturated aliphatic hydrocarbon groups. 10 ~C 20 Examples of the aliphatic hydrocarbon group include a decyl group, a lauryl group, a myristyl group, a cetyl group, a stearyl group, and an oleyl group. The phosphate ester according to the present invention is R 21 The phosphate ester may be a mixture of phosphate esters having different aliphatic hydrocarbon groups. Examples of such phosphate esters include polyoxyethylene alkyl (12-15) ether phosphate ester, polyoxyethylene oleyl cetyl ether phosphate ester, etc. R 21 Preferred examples of the alkyl group include a lauryl group, a cetyl group, and an oleyl group.

[0056] The phosphoric acid ester according to the present invention may be neutralized with a base, for example, an alkali metal salt such as a sodium salt or a potassium salt, an ammonium salt, or an amine salt.

[0057] The phosphate esters can be used alone or in combination of two or more.

[0058] The phosphate ester according to the present invention can be obtained, for example, from the Emulgen series manufactured by Kao Corporation, the NIKKOL series manufactured by Nikko Chemicals Co., Ltd., the Phosphanol series manufactured by Toho Chemical Industry Co., Ltd., and the Plysurf series manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.

[0059] The phosphate ester of the present invention, when used in combination with the polyoxyethylene aryl ether, can enhance the wettability of the ink on impermeable surfaces such as metals, synthetic resins, rubber, etc., and can facilitate the supply of ink to the pen tip, thereby improving ink ejection stability. In other words, the ink composition of the present invention can achieve a high degree of both good drying properties of the handwriting and good ink ejection stability. Furthermore, the ink composition of the present invention can maintain good wettability even in writing instruments with narrow ink flow paths leading to the pen tip, such as fountain pens with pen cores described below, and can therefore improve the ink ejection stability of such writing instruments.

[0060] From the viewpoint of ink jetting stability of the writing implement, the phosphate ester according to the present invention is preferably R 21 C 12 ~C 18 where l is a number from 5 to 35 and m is a number from 0 to 10. More preferably, R 21 is a lauryl group, a cetyl group, or an oleyl group; l is a number from 5 to 30; and m is a number from 0 to 5.

[0061] The content of the phosphate ester (hereinafter sometimes referred to as "P2") relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01 to 1 mass%, more preferably 0.03 to 0.5 mass%, and even more preferably 0.05 to 0.3 mass%. By having the content within the above range, it becomes easier to achieve good ink ejection stability.

[0062] In the ink composition according to the present invention, it is preferable that the ratio (P1 / P2) of the content of polyoxyethylene aryl ether (P1) to the content of phosphate ester (P2) satisfies the following formula (1). 3≦P1 / P2≦80 (1) With regard to P1 / P2, it is more preferable that it satisfies 5≦P1 / P2≦45, and even more preferable that it satisfies 15≦P1 / P2≦40. When P1 / P2 is within the above range, the affinity between the polyoxyethylene aryl ether and the phosphate ester is improved, making it easier to achieve a high level of both drying properties of the handwriting and ink ejection stability.

[0063] The ink composition according to the present invention further comprises water. The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water.

[0064] The ink composition according to the present invention may contain an organic solvent that is compatible with water (a water-soluble organic solvent). Examples of organic solvents include aliphatic monohydric alcohols having a total of 3 to 8 carbon atoms and having at least one of an alkyl group and an oxyalkyl group on the side chain, such as ethanol, 1-propanol, butanol, glycerin, sorbitol, 2-ethylhexanol, and 3-methoxy-3-methylbutanol; branched aliphatic dihydric alcohols having a total of 5 to 12 carbon atoms and having an alkyl group with 1 or 2 carbon atoms on the side chain, such as hexylene glycol (2-methyl-2,4-pentanediol) and 2-methyl-1,3-pentanediol; dialkylene glycols such as diethylene glycol and dipropylene glycol, thiodiethylene glycol, ethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-hexanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether. alkylene glycol monoalkyl ethers such as diethylene glycol ethyl ether, ethylene glycol isopropyl ether, ethylene glycol monobutyl ether, ethylene glycol-2-ethylhexyl ether, propylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol-2-ethylhexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, and tetraethylene glycol dimethyl ether; alkylene glycol dialkyl ethers such as diethylene glycol ethyl methyl ether and triethylene glycol butyl methyl ether; ethylene glycol monomethyl ether acetate, 2-pyrrolidone, and N-methyl-2-pyrrolidone.

[0065] The content of the organic solvent relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.1 to 30 mass %.

[0066] Among the above organic solvents, aliphatic monohydric alcohols having a total of 3 to 8 carbon atoms and having at least one of an alkyl group and an oxyalkyl group in their side chains, branched dihydric alcohols having a total of 5 to 12 carbon atoms and having an alkyl group with 1 or 2 carbon atoms in their side chains, dialkylene glycols, alkylene glycol monoalkyl ethers, and alkylene glycol dialkyl ethers can suppress strike-through of handwriting while improving the permeability of the vehicle to the paper surface and improving the drying properties of handwriting. Considering the formation of handwriting with suppressed strike-through and good drying properties, preferred organic solvents are aliphatic monohydric alcohols having a total of 3 to 8 carbon atoms and having at least one of an alkyl group and an oxyalkyl group in their side chains, branched dihydric alcohols having a total of 5 to 12 carbon atoms and having an alkyl group with 1 or 2 carbon atoms in their side chains, and dialkylene glycols.

[0067] The content of the organic solvent relative to the total mass of the ink composition is preferably in the range of 0.5 to 15 mass%, more preferably 1 to 10 mass%. When the content is within the above range, it becomes easy to form clear handwriting with excellent drying properties and reduced strike-through.

[0068] The organic solvents can be used alone or in combination of two or more.

[0069] The ink composition of the present invention may also contain various other additives as required. Examples of additives include water-soluble resins, specific gravity adjusters, surfactants, pH adjusters, resin particles, rust inhibitors, wetting agents, viscosity adjusters, preservatives or antifungal agents, air bubble absorbers, antifoaming agents, antioxidants, ultraviolet absorbers, etc. These additives can be selected from those conventionally used in water-based inks and used appropriately.

[0070] The method for producing the ink composition according to the present invention is not particularly limited, and any conventionally known method can be used. Specifically, the ink composition can be produced by stirring a mixture containing the above-mentioned components with a stirrer such as a propeller stirrer, a homodisper, or a homomixer, or by dispersing the mixture with a disperser such as a bead mill.

[0071] The viscosity of the ink composition according to the present invention is not particularly limited, but is preferably 1 to 5 mPa·s, and more preferably 1 to 3 mPa·s, in an environment of 20° C. By having a viscosity within the above range, it becomes easy to improve the ink dischargeability even in writing instruments with narrow ink flow paths leading to the pen tip, such as fountain pens with pen cores described below, while also improving the ink's paper penetration and achieving excellent writing drying properties. The viscosity was measured using an EL-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., product name: RE-80L, cone-type rotor: standard type (1°34' x R24)) by placing the ink composition in an environment of 20°C.

[0072] The surface tension of the ink composition according to the present invention is not particularly limited, but is preferably 40 to 50 mN / m in an environment of 20° C. When the surface tension is within the above range, the ink has good paper penetration and it is easy to suppress strike-through and bleeding of handwriting. The surface tension was measured using a surface tension measuring instrument (manufactured by Kyowa Interface Science Co., Ltd., product name: DY-300) by placing the ink composition in an environment of 20°C using a vertical plate method using a platinum plate.

[0073] The ink composition of the present invention is used by being contained in a writing implement having a pen tip with a slit extending rearward from a pen point at the front end. The writing implement is not particularly limited in structure or shape as long as it has the above-mentioned pen tip, and an example is a writing implement that has the above-mentioned pen tip and an ink filling mechanism.

[0074] Examples of nibs (tips) include those in the form of fountain pens, which have a pen point, which is the front end that comes into contact with the paper when writing, a slit extending a predetermined length rearward from the pen point, and a hole located approximately in the center of the nib. The pen tip may be made of a metal plate cut into a tapered shape and then bent or curved, or made of resin molded into a pen tip shape.

[0075] Examples of materials for the pen tip include metals such as cemented carbide, stainless steel, gold-plated stainless steel, gold alloys such as 14K gold, 18K gold, and 22K gold, pure gold, and iridium. The ink composition of the present invention has good wettability with respect to gold-plated stainless steel or gold alloys, and therefore is excellent in ink discharge stability from a pen tip made of the above material, enabling the formation of good handwriting. Therefore, the ink composition is suitably used for writing instruments having a pen tip made entirely or partially of gold-plated stainless steel or gold alloys.

[0076] The ink filling mechanism is not particularly limited, and may be, for example, an ink reservoir that can be filled with ink. The ink reservoir may be a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body. Furthermore, a writing instrument can be formed by using the barrel of the writing instrument itself as an ink filling mechanism, filling the barrel with ink directly, and attaching a pen tip to the front end of the barrel.

[0077] The ink refilling mechanism is detachably replaceable from the writing instrument body and may be a cartridge type that uses an ink cartridge pre-filled with ink. In this case, after the ink in the ink cartridge of the writing instrument is used up, the writing instrument can be used again by replacing it with a new ink cartridge. The ink cartridge may be one that doubles as the barrel that constitutes the writing instrument when connected to the writing instrument body, or one that covers and protects the barrel (rear barrel) after being connected to the writing instrument body. In the latter case, the ink cartridge may be connected to the writing instrument body, or it may be housed in the barrel in a disconnected state so that the user of the writing instrument can connect the ink cartridge in the barrel when using it and start using it.

[0078] The ink filling mechanism may be an ink suction type having a suction mechanism that can fill ink from an ink bottle or the like that contains ink. The suction mechanism may be either one that is directly provided on the writing instrument body, or one that is detachably attached to the writing instrument body like a converter.

[0079] If the ink filling mechanism is configured to be able to directly fill the ink and the colorant contains a pigment, the barrel or ink reservoir into which the ink is filled may have a built-in agitator such as a stirring ball for stirring the ink to facilitate re-dispersion of the pigment. Examples of the shape of the agitator include a spherical body and a rod-like body. The material of the agitator is not particularly limited, and examples thereof include metal, ceramic, resin, and glass.

[0080] A writing instrument equipped with a pen tip and an ink filling mechanism may further include an ink supply mechanism, which is interposed between the pen tip and the ink filling mechanism and serves to supply the ink filled in the ink filling mechanism to the pen tip.

[0081] The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow regulator and supplies ink to the pen tip through this; (2) a mechanism that has a comb-shaped ink flow regulator and supplies ink to the pen tip through this; (3) a mechanism in which a number of disks are arranged in parallel with comb-shaped intervals, and have slit-shaped ink guide grooves that run vertically through the disks in the axial direction and wider ventilation grooves than these grooves, and an ink guide core is arranged at the axial center to guide ink from the ink filling mechanism to the pen tip; (4) a mechanism that has a porous body with continuous pores that can be impregnated with ink as an ink flow regulator and supplies ink to the pen tip through this; and (5) a mechanism that has an ink flow regulator with a valve mechanism and supplies ink to the pen tip by opening the valve.

[0082] An example of a comb-shaped ink flow rate regulator is one having comb grooves for temporarily storing ink, ink flow passages, and air passages, which is a so-called pen core. When the internal pressure of the ink filling mechanism changes, excess ink flows into the comb grooves of the pen tip and is retained there, preventing ink leakage and overflow from the pen tip and also adjusting the ink ejection properties, resulting in a good handwriting. Pen cores often have complex shapes to achieve the above-mentioned effects, and are generally molded from resin. However, the type of resin used and the additives used during molding can increase the hydrophobicity of the pen core, resulting in insufficient wettability with ink. Furthermore, the narrow ink flow path leading to the pen tip can sometimes cause problems with ink ejection stability. However, the ink composition of the present invention can maintain good wettability even with such pen cores, thereby improving the ink ejection stability of writing instruments. The pen core may have a conventionally known double pen core structure consisting of an outer core and an inner core.

[0083] The writing implement according to the present invention is provided with a cap that is attached to cover the pen tip (writing tip), making it a cap-type writing implement, which can prevent the writing tip from being contaminated or damaged. Furthermore, a retractable writing implement can be provided with a retractable mechanism that allows the writing tip to protrude and retract from the barrel, thereby preventing the writing tip from becoming contaminated or damaged.

[0084] Any retractable writing implement can be used as long as the writing tip is housed within a barrel and the writing tip protrudes from within the barrel when a retractable mechanism is activated. Examples of retraction mechanisms include: (1) a side-slide retraction mechanism in which an operating part (clip) that can move back and forth in the radial direction protrudes radially outward from the rear side wall of the barrel, and the writing tip is retracted from the front end opening of the barrel by sliding the operating part forward; (2) a rear-end knock retraction mechanism in which the operating part at the rear end of the barrel is pressed forward to cause the writing tip to retract from the front end opening of the barrel; (3) a side-knock retraction mechanism in which the operating part that protrudes from the outer surface of the barrel side wall is pressed radially inward to cause the writing tip to retract from the front end opening of the barrel; and (4) a rotational (twist) retraction mechanism in which the operating part at the rear of the barrel is rotated to cause the writing tip to retract from the front end opening of the barrel. The retractable writing instrument may have a lid provided in front of the barrel, and the lid can be opened and closed by operating the retraction mechanism. With a writing instrument of this structure, when the lid is closed, it is possible to prevent the writing tip from drying out and dust from entering the barrel, and by operating the retraction mechanism, the writing tip can press the lid open, allowing the writing tip to protrude from the barrel and ready for writing. The retractable mechanism may be a combination of the above-mentioned retractable mechanisms, such as a retractable mechanism in which the writing tip is protruded from inside the barrel by pressing forward an operating part (knock part) provided at the rear end of the barrel, and the writing tip is stored inside the barrel by rotating an operating part (knob part) at the rear of the barrel.

[0085] A preferred writing instrument according to the present invention is a fountain pen having a slit extending rearward from the pen point at the front end, a fountain pen-shaped nib made of gold-plated stainless steel or a gold alloy, an ink filling mechanism, and a pen core as an ink supply mechanism. In such a writing instrument (fountain pen), the ink composition of the present invention moves smoothly through the ink flow path from the ink filling mechanism to the pen tip, and the ink filled in the ink filling mechanism is stably supplied to the pen tip. Since the ink flow rate can be appropriately adjusted, the writing instrument has excellent ink ejection stability and can produce clear handwriting. Furthermore, since the handwriting produced has excellent drying properties, the writing instrument can achieve a high degree of both handwriting drying properties and ink ejection stability. The ink composition of the present invention is suitable for use in a writing instrument having the above-described configuration.

[0086] When the pigment contains a reversible thermochromic microencapsulated pigment, handwriting formed on a surface using a writing implement containing the ink can be discolored by rubbing with a finger or by using a heating or cooling tool.

[0087] Examples of heating tools include an electrically heated discoloring tool equipped with a resistance heating element such as a PTC element, a heat discoloring tool filled with a medium such as hot water, a heat discoloring tool using steam or laser light, and the application of a hair dryer. However, friction members and friction bodies are preferred because they can change color in a simple manner. Examples of cooling devices include electrically operated thermochromic devices using a Peltier element, thermochromic devices filled with a refrigerant such as cold water or ice chips, refrigerants, refrigerators, freezers, and the like.

[0088] As the friction member and friction body, elastic bodies such as elastomers and plastic foams that are highly elastic and can generate appropriate friction and frictional heat when rubbed are preferred, but plastic molded bodies, stone, wood, metal, fabric, etc. can also be used. Note that while a general eraser used to erase pencil marks may be used to rub the marks, eraser dust is generated during rubbing, and therefore the above-mentioned friction member and friction body that generate almost no eraser dust are preferably used.

[0089] Examples of materials for the friction member and friction body include silicone resin, styrene-ethylene-butadiene-styrene block copolymer (SEBS resin), etc. Silicone resin tends to adhere to areas that have been erased by rubbing, and handwriting tends to be repelled when writing is repeated, so SEBS resin is more preferably used.

[0090] The friction member or friction body may be a separate component of any shape from the writing instrument, but by providing it on the writing instrument, the writing instrument can be made more portable. Also, a writing instrument set can be obtained by combining a writing instrument with a separate friction member or friction body of any shape from the writing instrument.

[0091] In the case of a writing instrument with a cap, the location where the friction member or friction body is provided is not particularly limited. For example, the cap itself may be formed from a friction member, the barrel itself may be formed from a friction member, or if a clip is provided, the clip itself may be formed from a friction member, or the friction member or friction body may be provided at the tip (top) of the cap or the rear end of the barrel (the part where the writing tip is not provided), etc.

[0092] In the case of a writing instrument equipped with a retractable mechanism, the location where the friction member or friction body is provided is not particularly limited. For example, the barrel itself may be formed from a friction member, and if a clip is further provided, the clip itself may be formed from a friction member, or the friction member or friction body may be provided near the front end of the barrel, the rear end of the barrel (the part where the writing tip is not provided), or in the knock portion. [Example]

[0093] Examples are shown below. Unless otherwise specified, "parts" in the examples refer to "parts by mass."

[0094] Example 1 Preparation of ink composition 10 parts of a black dye (manufactured by Orient Chemical Industries Co., Ltd., product name: Water Black 191-L (solid content: 15%)), 4 parts of polyoxyethylene β-naphthyl ether (n4=10 in general formula (I-3)) (HLB value: 15.0), and 4 parts of polyoxyethylene oleyl ether phosphate (R 21 =C 18 H 35 An ink composition was prepared by mixing 0.1 parts of ethanolamine (1 = 7, m = 0), 0.2 parts of triethanolamine, 5 parts of diethylene glycol, 0.1 parts of a preservative (manufactured by Arcsada Japan Co., Ltd., product name: Proxel XL-2(S)), and 80.6 parts of water. The content of polyoxyethylene aryl ether (P1) relative to the total mass of the ink composition was 4, the content of phosphate ester (P2) was 0.1, and the ratio of P1 to P2 (P1 / P2) was 40.

[0095] Making writing implements The ink composition of Example 1 was filled into the ink cartridge of a fountain pen (product name: Custom 74, manufactured by Pilot Corporation) which was equipped with a 14-karat gold fountain pen-shaped nib (writing width: F) having a slit extending rearward from the pen point at the front end, a polyethylene ink cartridge as an ink filling mechanism, and a pen core having a comb groove for temporarily storing ink, an ink flow passage, and an air passage as an ink supply mechanism, with the ink filling mechanism and nib being joined via the ink supply mechanism.A writing instrument (fountain pen) was prepared by attaching a cap. The writing implement was placed with the pen tip facing downwards, and the filled ink was allowed to flow up to the pen tip, making it ready for writing.

[0096] The ink compositions of Examples 2 to 8 and Comparative Examples 1 to 5 were prepared in the same manner as in Example 1, except that the types and amounts of the ingredients added were changed to those shown in Table 1 below. P1, P2, and P1 / P2 in each ink composition are as shown in Table 1. The writing instruments of Examples 2 to 8 and Comparative Examples 1 to 5 were produced in the same manner as in Example 1.

[0097] [Table 1]

[0098] The materials in Table 1 are as follows: (1) Orient Chemical Industries Co., Ltd., Product Name: Water Black 191-L (Solid content: 15%) (2) Daiwa Chemical Industry Co., Ltd., Product Name: Eosin (3) Polyoxyethylene β-naphthyl ether [n4=10 in general formula (I-3)] (HLB value: 15.0) (4) Polyoxyethylene p-cumylphenyl ether [n5=8 in general formula (I-4)] (HLB value: 12.6) (5) Polyoxyethylene p-cumylphenyl ether [n5=25 in general formula (I-4)] (HLB value: 17.7) (6) Polyoxyethylene styrenated phenyl ether [manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Noigen EA-177] (HLB value: 15.6) (7) Polyoxyethylene oleyl ether phosphate ester (in general formula (II), R 21 =C 18 H 35 , l=7, m=0) (8) Polyoxyethylene polyoxypropylene cetyl ether phosphate ester (in general formula (II), R 21 =C 16 H 33 , l=10, m=5) (9) Polyoxyethylene lauryl ether phosphate ester (in general formula (II), R 21 =C 12 H 25 , l=20, m=0) (10) Polyoxyethylene oleyl ether phosphate ester [wherein R 21 =C 18 H 35 , l=3, m=0) (11) Polyoxyethylene lauryl ether phosphate ester [wherein R 21 =C 12 H25 , l = 4, m = 0 (12) Manufactured by Ark Thera Japan Co., Ltd., Product Name: Proxel XL-2(S)

[0099] [Viscosity Measurement] For the ink compositions of Examples 1 to 8 and Comparative Examples 1 to 5, using an EL type rotational viscometer [manufactured by Toki Sangyo Co., Ltd., Product Name: RE-80L, Cone type rotor: Standard type (1°34′×R24)], the viscosity was measured at room temperature (20°C) under the condition of a rotational speed of 50 rpm. The measurement results are as shown in Table 1.

[0100] [Surface Tension Measurement] For the ink compositions of Examples 1 to 8 and Comparative Examples 1 to 5, using an automatic surface tension meter [manufactured by Kyowa Interface Science Co., Ltd., Product Name: DY-300], the surface tension was measured at room temperature (20°C) by the vertical plate method using a platinum plate. The measurement results are as shown in Table 1.

[0101] [Evaluation of Writing Drying Property] The caps of each writing instrument prepared in Examples 1 to 8 and Comparative Examples 1 to 5 were removed, and at room temperature (20°C), the character "永" was handwritten on A4-sized test paper (vertically). After a certain time from the writing, the character "永" was erased, and it was visually confirmed whether the ink spread around the writing. Based on the time until the writing dried, the writing drying property was evaluated according to the following criteria. The evaluation results are as shown in Table 2 below, and evaluations "A" and "B" were regarded as passing. For the test paper, writing paper A conforming to the former JIS P3201 was used. A: When the writing was erased 3 seconds after writing, no trace of the ink spreading around the writing was confirmed. B: When the writing was erased 3 seconds after writing, the ink spread around the writing, but when the writing was erased 5 seconds after writing, no trace of the ink spreading around the writing was confirmed. C: Even after 5 seconds had passed since writing, when the writing was erased, a trace of the ink spreading around the writing was confirmed.

[0102] [Evaluation of Ink Discharge Stability] The caps were removed from each of the writing instruments prepared in Examples 1 to 8 and Comparative Examples 1 to 5, and a 15 cm straight line was handwritten parallel to the short edge of an A4-sized test paper (portrait orientation) at room temperature (20°C). The resulting handwriting was visually inspected, and the ink discharge stability was evaluated according to the following criteria. The evaluation results are shown in Table 2 below, with ratings of "A" and "B" being considered acceptable. Writing paper A conforming to the old JIS P3201 was used as the test paper. A: There was no fading or skipping of lines in the handwriting, and good handwriting with consistent density and line width was obtained. B: There was some smearing or skipping of lines in the handwriting, but it was at a level that would not cause any problems in practical use. C: There were many smudges and missing lines in the handwriting, or it was impossible to write.

[0103] [Table 2]

Claims

1. The aqueous ink composition for a writing instrument is to be contained in a writing instrument having a pen tip with a slit extending rearward from a pen point at the front end, the aqueous ink composition comprising a colorant, a polyoxyethylene aryl ether, a phosphate ester, and water, wherein the polyoxyethylene aryl ether is one or more compounds selected from the group consisting of compounds represented by the following general formula (I-1) or (I-2), and the phosphate ester is a compound represented by the following general formula (II): 【Chemical 1】 (In the formula, n1 is 0 or 1, n2 and n3 each independently represent a number from 1 to 50; When n1 is 1, R １１ is a divalent hydrocarbon group, R １２ , R １３ , R １４ , and R １５ are each independently a hydrogen atom or C １ ~C ３ is an alkyl group represented by the formula: 【Chemistry 2】 (In the formula, R ２１ is C １０ ~C ２０ is an aliphatic hydrocarbon group of the formula l is a number equal to or greater than 5, and m is a number equal to or greater than 0; n is 1 or 2.

2. 2. The ink composition according to claim 1, wherein the polyoxyethylene aryl ether is at least one compound selected from the group consisting of compounds represented by the following general formula (I-3) and (I-4): 【Chemistry 3】 (In the formula, n4 and n5 are each independently a number from 1 to 50.

3. 3. The ink composition according to claim 1, wherein the polyoxyethylene aryl ether has an HLB value of 10 to 17.

4. The content of the polyoxyethylene aryl ether (P １ ) and the content of the phosphate ester (P ２ 4. The ink composition according to claim 1, wherein the following formula (1) is satisfied: 3≦P １ / P ２ ≦80 (1)

5. A writing implement containing the ink composition according to any one of claims 1 to 4.

6. 6. The writing implement according to claim 5, wherein a part or all of the nib is made of gold-plated stainless steel or a gold alloy.

7. 7. A writing implement according to claim 5 or 6, further comprising, as the ink supply mechanism, a pen core having a comb groove for temporarily storing ink, an ink flow passage, and an air passage.

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