Aqueous ink composition for writing instrument and writing instrument incorporating the same

Abstract

To provide an aqueous ink composition for writing instruments with high practicality capable of obtaining clear fluorescent handwriting high in color development at the time of ultraviolet beam irradiation, without generating inconveniences such as deposition and strike through, by making a specific oil-soluble fluorescent material applicable as a colorant of an aqueous ink, and provide writing instruments incorporating the same.SOLUTION: An aqueous ink composition for writing instruments containing water as a main solvent, luminescent compounds represented by general formula (1), ethers with an SP value of 10 to 11.5, and polyoxyethylene polyoxypropylene alkyl ethers, as well as writing instruments incorporating the same.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous ink composition for a writing instrument and a writing instrument. The present invention further relates to an aqueous ink composition for a writing instrument that emits light when irradiated with ultraviolet light, and a writing instrument incorporating the same. [Background technology]

[0002] Special inks for writing instruments have been known that incorporate fluorescent substances into the ink to produce handwriting that is invisible under normal visible light but glows when exposed to ultraviolet light, and writing instruments with high security effects have been disclosed that eliminate the risk of others peek-a-boost at highly confidential information such as a PIN number when written on paper (see, for example, Patent Document 1). The fluorescent pigment used in the ink composition does not have high color development, so it is necessary to add a large amount when using it for the above-mentioned purpose. In addition, it has poor fixability to the paper surface, so it is necessary to add a larger amount of resin than that of a normal writing instrument. As a result, the solid content in the ink becomes excessive, which makes the pen tip prone to dry up, and furthermore, it has poor stability over time.

[0003] In response to this, an ink composition has been disclosed that uses a fluorescent material that has high color development even with the addition of a small amount and produces handwriting with a vivid fluorescent color when irradiated with ultraviolet light (see, for example, Patent Document 2). Although the fluorescent material has poor solubility in water, it has high color development properties as a compound and is highly soluble in alcohol-based organic solvents. Therefore, when applied to oil-based inks, it exhibits excellent printing performance with a high security effect in industrial applications such as inkjet and printing inks where ink is ejected in a fixed amount. However, when the oil-based ink is applied to a writing instrument for handwriting, which has various writing speeds and pressures depending on the user, the ink excessively strikes through to the paper surface, which is not practical. Therefore, there has been a demand for development of a water-based ink using the fluorescent material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-322402 A [Patent Document 2] JP 2007-277404 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is the result of extensive research into the development of water-based inks using the fluorescent material described in Patent Document 2 as a colorant, and aims to provide a highly practical water-based ink composition for writing instruments that produces handwriting in a vivid fluorescent color with high color development when exposed to ultraviolet light, without causing problems such as precipitation or strike-through, and a writing instrument incorporating the same. [Means for solving the problem]

[0006] The aqueous ink composition for a writing instrument of the present invention comprises water as a main solvent, a compound represented by the following general formula (1), an ether having an SP value of 10 to 11.5, and a polyoxyethylene polyoxypropylene alkyl ether. [ka] [In formula (1), R is a perfluoroalkyl group having 2 to 20 carbon atoms, and L1 and L2 are the same or different and each is a sulfoxide having an aryl group or an alkyl group having a substituent or no substituent.] Further, the polyoxyethylene polyoxypropylene alkyl ether has an HLB value in the range of 10 to 15, and is a compound represented by the following general formula (2). HO-(C2H4O) m (C3H6O) n -R1···(2) [In formula (2), R1 is an aliphatic hydrocarbon group having 4 to 24 carbon atoms, m is the average number of moles of ethylene oxide added and is a number from 3 to 45, and n is the average number of moles of propylene oxide added and is a number from 1 to 33.] Further, the polyoxyethylene polyoxypropylene alkyl ether is added in an amount 1 to 30 times the amount of the compound represented by general formula (1) in the water-based ink, and the amount of the ether in the water-based ink is in the range of 1 to 30% by mass. Further, the present invention requires that the pigment contains a colorant that is discolored by frictional heat, and that the colorant is a microencapsulated pigment in which a reversible thermochromic composition comprising (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that controls the color-forming reaction of (a) and (b) is encapsulated in a microcapsule. A further feature is a writing instrument incorporating any one of the above-described water-based ink compositions for writing instruments. Effect of the Invention

[0007] The present invention provides a highly practical aqueous ink composition for writing instruments and a writing instrument, which can obtain a vivid fluorescent mark with high color development when irradiated with ultraviolet light without problems such as precipitation in the aqueous ink or strike-through when written on paper, by stably forming an aqueous ink from a fluorescent material with high ultraviolet color development, which is disclosed in Patent Document 2 and has high solubility in alcohol-based organic solvents but poor solubility in water. Furthermore, by using the composition in combination with a colorant that fades when heated, it is possible to form a mark with a high security effect, which is invisible under normal conditions but makes it possible to confirm that the mark was formed by irradiating ultraviolet light after heating and decolorizing the mark. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The inventors have found that the compound represented by the general formula (1), which dissolves in alcohol-based solvents but does not dissolve directly in aqueous media, can be dissolved and stabilized for a long period of time even in an aqueous ink mainly composed of water, by using it in combination with an ether exhibiting a specific SP value and a polyoxyethylene polyoxypropylene alkyl ether. As a result, the ink can be applied as a versatile aqueous ink that is less susceptible to problems such as strike-through when written on paper, and that exhibits a vivid coloring effect when irradiated with ultraviolet light, which could not be achieved with conventional similar materials.

[0009] The light-emitting compound represented by the general formula (1) is such that R in the formula is a perfluoroalkyl group having 2 to 20 carbon atoms, and L1 and L2 are the same or different and each is a sulfoxide having a substituted or unsubstituted aryl group or alkyl group. More preferably, R is a linear perfluoroalkyl group having 2 to 10 carbon atoms, and L1 and L2 are sulfoxides having a branched or linear alkyl group or a phenyl group having 1 to 10 carbon atoms.

[0010] In formula (1), R is a perfluoroalkyl group having 2 to 20 carbon atoms, specifically, a C2F5- group, an n-C3F7- group, an i-C3F7- group, an n-C4F9- group, an i-C4F9- group, a sec-C4F9- group, an n-C5F 11 -Group, neo-C5F 11 - group, n-C6F 13 - group, n-C7F 15 - group, n-C8F 17 - group, 2-C8F 17 - group, n-C9F 19 - group, n-C 10 F 21 - group, n-C 12 F 25 - group, n-C 18 F 37 Of these, a linear perfluoroalkyl group having 2 to 10 carbon atoms is preferred.

[0011] In formula (1), L1 and L2 are the same or different and each is a sulfoxide having an aryl group or an alkyl group, which may or may not have a substituent. Examples of the aryl group include a phenyl group, a naphthyl group, and an anthranyl group. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a sec-butyl group, an n-pentyl group, a neo-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a 2-ethylhexyl group, an n-decyl group, a lauryl group, and a stearyl group. Examples of the substituent on the aryl group or alkyl group include halogen groups such as F, Cl, Br, and I; a nitro group; a cyano group; lower alkyl groups such as a methyl group, an ethyl group, a propyl group, and a butyl group; lower alkoxy groups such as a methoxy group, an ethoxy group, a propoxy group, and a butoxy group; aryl groups such as a phenyl group and a naphthyl group; and aralkyl groups such as a benzyl group, an α,α-dimethylbenzyl group, and a phenethyl group.

[0012] Specific examples include dimethyl sulfoxide, diethyl sulfoxide, dibutyl sulfoxide, dioctyl sulfoxide, diphenyl sulfoxide, bis(1-chlorophenyl) sulfoxide, ditolyl sulfoxide, bis(3-methoxyphenyl) sulfoxide, methyl ethyl sulfoxide, methyl butyl sulfoxide, ethyl butyl sulfoxide, methyl octyl sulfoxide, butyl octyl sulfoxide, methyl phenyl sulfoxide, and ethyl phenyl sulfoxide.

[0013] The luminescent compound of formula (1) can be practically used by adding it to the aqueous ink composition in an amount of 0.1 to 5% by mass, preferably 0.5 to 3% by mass.

[0014] In the present invention, in order to dissolve the compound of the general formula (1) in an aqueous medium, ethers having an SP value of 10 to 11.5 are used, such as triethylene glycol monobutyl ether (SP value 10.2), propylene glycol monomethyl ether (SP value 10.2), diethylene glycol monobutyl ether (SP value 10.5), hexylene glycol (SP value 10.5), propylene glycol-n-propyl ether (SP value 10.7), diethylene glycol monomethyl ether (SP value 10.7), tetraethylene glycol monobutyl ether (SP value 10.9), triethylene glycol monomethyl ether (SP value 11.2), phenyl glycol (SP value 11.5), polyoxyethylene benzyl ether (SP value 11.5), etc. are used. In addition, the SP value defined in this specification means the solubility parameter (δ) of ethers, and the value calculated by the Fedors' estimation method is adopted. Specifically, based on Fedors, Polym. Eng. Sci., 14(2), pp147-154 (1974), referring to Δei and Δvi related to the structure of the solvent, the formula δ=(ΣΔei / ΣΔvi) 1 / 2 Calculate the solubility parameter of ethers (unit: cal / cm 3 ) 1 / 2 ).

[0015] The ethers can be added in an amount of 1 to 30% by mass, preferably 1.5 to 15% by mass, in the aqueous ink composition. If the amount is less than 1% by mass, it is difficult to obtain the desired effect, and if the amount exceeds 30% by mass, no further effect can be obtained, so there is no need to add any more than this.

[0016] Polyoxyethylene polyoxypropylene alkyl ether exerts the effect of solubilizing the compound of general formula (1) in an aqueous medium, and by using it in combination with the above-mentioned ethers, it is possible to impart dissolution stability over time. As the polyoxyethylene polyoxypropylene alkyl ether, a compound represented by the following general formula (2) is used. HO-(C2H4O) m (C3H6O) n -R1···(2) [In formula (2), R1 is an aliphatic hydrocarbon group having 4 to 24 carbon atoms, m is the average number of moles of ethylene oxide added and is a number from 3 to 45, and n is the average number of moles of propylene oxide added and is a number from 1 to 33.] Examples of commercially available polyoxyethylene polyoxypropylene alkyl ethers include the Newpol 50HB series manufactured by Sanyo Chemical Industries, Ltd., the Adekanol BPE series manufactured by ADEKA Corporation, the NIKKOL PBC series manufactured by Nikko Chemicals Co., Ltd., the EMALEX DAPE series manufactured by Nippon Emulsion Co., Ltd., as well as the Brownon DC series, SRP series, and Finesurf NDB series manufactured by Aoki Oil & Fat Industries Co., Ltd. The polyoxyethylene polyoxypropylene alkyl ether contained in the aqueous ink composition according to the embodiment of the present invention may be one type or two or more types.

[0017] The HLB value of the polyoxyethylene polyoxypropylene alkyl ether is preferably 10 or more and less than 15. This allows particularly stable solubility to be obtained. The HLB value is a value that indicates the balance between hydrophobicity and hydrophilicity of a dispersant, etc., and generally, the larger the value, the more hydrophilic the dispersant is, and the smaller the value, the more hydrophobic the dispersant is. In an embodiment of the present invention, the HLB value is determined by the Griffin method, and specifically, is determined as shown in the following formula (3). HLB value = 20 × (sum of formula weights of hydrophilic parts) / (molecular weight) (3)

[0018] The polyoxyethylene polyoxypropylene alkyl ether can be added in an amount of 0.1 to 15% by mass, preferably 0.5 to 10% by mass, in the ink composition. If the amount is less than 0.1% by mass, it is difficult to obtain the desired effect, and if the amount exceeds 15% by mass, no further effect can be obtained, so there is no need to add more than this. Furthermore, it is preferable that polyoxyethylene polyoxypropylene alkyl ether is added in an amount of 1 to 30 times by mass relative to the amount of the compound represented by general formula (1). In the above-mentioned range of the blending ratio, the conditions are particularly favorable for suppressing the precipitation of the light-emitting compound, and more stable solubility can be obtained over a long period of time.

[0019] In the present invention, by using the luminescent compound represented by the general formula (1) as a colorant, colorless handwriting can be seen as clearly luminescent when irradiated with ultraviolet light. However, by using a small amount of a general-purpose colorant in combination, the handwriting can also be seen as being visible when written. As the colorant, any dye or pigment that is soluble or dispersible in an aqueous medium can be used, and specific examples thereof are given below. The dyes that can be used include acid dyes, basic dyes, and direct dyes. Examples of acid dyes that can be used include New Coccine (CI 16255), Tartrazine (CI 19140), Acid Blue Black 10B (CI 20470), Guinea Green (CI 42085), Brilliant Blue FCF (CI 42090), Acid Violet 6B (CI 42640), Soluble Blue (CI 42755), Naphthalene Green (CI 44025), Eosin (CI 45380), Phloxine (CI 45410), Erythrosine (CI 45430), Nigrosine (CI 50420), and Acid Flavin (CI 56205). Examples of basic dyes that can be used include chrysoidine (CI11270), methyl violet FN (CI42535), crystal violet (CI42555), malachite green (CI42000), Victoria blue FB (CI44045), rhodamine B (CI45170), acridine orange NS (CI46005), and methylene blue B (CI52015). Direct dyes include Congo Red (CI 22120), Direct Sky Blue 5B (CI 24400), Violet BB (CI 27905), Direct Deep Black EX (CI 30235), Kayalas Black G Conc (CI 35225), Direct Fast Black G (CI 35255), Phthalocyanine Blue (CI 74180), etc.

[0020] Examples of the pigment include inorganic pigments such as carbon black and ultramarine, organic pigments such as copper phthalocyanine blue and benzidine yellow, and water-dispersed pigment products that have been finely and stably dispersed in an aqueous medium using a surfactant or resin. Examples of the pigment include CI Pigment Blue 15:3B (product name: Sandye Super Blue GLL, pigment content 24%, manufactured by Sanyo Pigment Co., Ltd.), CI Pigment Red 146 (product name: Sandye Super Pink FBL, pigment content 21.5%, manufactured by Sanyo Pigment Co., Ltd.), CI Pigment Yellow 81 (product name: TC Yellow FG, pigment content approximately 30%, manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd.), and CI Pigment Red 220 / 166 (product name: TC Red FG, pigment content approximately 35%, manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd.). Examples of the resin for dispersing the pigment include polyamide resin, polyurethane resin, polyester resin, epoxy resin, melamine resin, phenol resin, silicone resin, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polystyrene, acrylic acid resin, maleic acid resin, gum arabic, cellulose, dextran, casein, and derivatives thereof, and copolymers of the above-mentioned resins. Also usable are white pigments such as titanium oxide, metal powders such as aluminum, natural mica, synthetic mica, alumina, and pearl pigments in which the surface of a core substance selected from glass pieces is covered with a metal oxide such as titanium dioxide, and cholesteric liquid crystal type luster pigments.

[0021] Furthermore, as a colorant that changes color due to frictional heat, a thermochromic pigment such as a microcapsule pigment (heat-discolorable pigment) containing a thermochromic composition or a microcapsule pigment containing a dye or pigment together with a thermochromic composition can be used. When the heat-discolorable pigment is used in combination, the handwriting made by the pigment is visible when writing, and after the handwriting is heated and erased, the handwriting that emits light clearly can be visible when irradiated with ultraviolet light, making it possible to configure a writing instrument with high security effects and unexpectedness.

[0022] The thermochromic composition constituting the heat-discolorable pigment is preferably a reversible thermochromic composition comprising (i) an electron-donating color-forming organic compound, (ii) an electron-accepting compound, and (iii) a reaction medium that determines the temperature at which the color-forming reaction between the two occurs, and is applied as a reversible thermochromic microcapsule pigment by encapsulating it in microcapsules. As the reversible thermochromic composition, there can be used a heat-discoloring type microcapsule pigment in which a reversible thermochromic composition having a relatively small hysteresis width (ΔH=1 to 7° C.) is encapsulated in a microcapsule, the reversible thermochromic composition being described in JP-B-51-44706, JP-B-51-44707, JP-B-1-29398, etc., and discoloring around a predetermined temperature (discoloration point), exhibiting a discolored state in a temperature range above the high-temperature discoloration point and a colored state in a temperature range below the low-temperature discoloration point, and only one of the two states exists in the room temperature range, and the other state is maintained while the heat or cold required to express that state is applied, but returns to the state exhibited in the room temperature range when the application of the heat or cold is removed. Further, there are those exhibiting relatively large hysteresis characteristics (ΔH=8 to 50° C.) as described in JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, JP-A-8-39936, etc., and those exhibiting large hysteresis characteristics as described in JP-A-2006-137886, JP-A-2006-188660, JP-A-2008-45062, JP-A-2008-280523, etc. In other words, the shape of the curve plotting the change in color density due to temperature change will change color along a path that is significantly different when the temperature is increased from a lower temperature side than the color change temperature range than when the temperature is decreased from a higher temperature side than the color change temperature range, and the colored state in a low temperature range below the complete color development temperature, or the decolored state in a high temperature range above the complete decolorization temperature, can also be applied to heat-discolorable microcapsule pigments that encapsulate a reversible thermochromic composition that has color memory properties in a specific temperature range. Specifically, the reversible thermochromic composition having color memory has a complete color-developing temperature that is a temperature that can only be obtained in a freezer or in a cold region, i.e., -50 to 0°C, preferably -40 to -5°C, more preferably -30 to -10°C, and a complete decolorization temperature that is a temperature obtained from frictional heat produced by a friction body or a familiar heating body such as a hair dryer, i.e., a range of 50 to 95°C, preferably 50 to 90°C, more preferably 60 to 80°C, and a ΔH value of 40 to 100°C, thereby allowing the composition to effectively function in maintaining the color that it exhibits under normal conditions (daily living temperature range).

[0023] The colorants can be used alone or in an appropriate mixture of two or more. When the colorant emits light when irradiated with ultraviolet light while leaving the initial mark, a small amount (for example, 0.3% by mass or less) is added. When the colorant emits light when irradiated with ultraviolet light after being discolored by frictional heat, the colorant is used in the range of 0.01 to 30% by mass in the ink composition.

[0024] In the present invention, the ink contains water as a main medium, and the water to be used is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water. The content of water relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 45 to 95 mass %, more preferably 50 to 90 mass %.

[0025] In addition, conventional water-soluble organic solvents that are compatible with water can also be used, such as ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, hexylene glycol, 1,3-butanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, 2-pyrrolidone, and N-methyl-2-pyrrolidone. The water-soluble organic solvents may be used alone or in combination of two or more kinds, and are used in an amount of 2 to 45% by mass, preferably 5 to 35% by mass, in the ink composition.

[0026] In addition, if necessary, inorganic salts such as sodium carbonate, sodium phosphate, sodium acetate, etc., pH adjusters such as organic basic compounds such as water-soluble amine compounds, rust inhibitors such as benzotriazole, tolyltriazole, saponin, etc., preservatives or antifungal agents such as carbolic acid, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, wetting agents such as urea, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysates, sodium pyrophosphate, etc., defoamers, and fluorine-based surfactants and nonionic surfactants which improve the penetration of the ink may be used. Furthermore, a lubricant can be added, and examples of the lubricant that can be used include metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-added cationic surfactants, phosphate ester surfactants, N-acyl amino acid surfactants, dicarboxylic acid surfactants, β-alanine surfactants, 2,5-dimercapto-1,3,4-thiadiazole, salts or oligomers thereof, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, and condensates of N-acyl-L-glutamic acid and L-lysine, and salts thereof. In addition, by adding a thickening inhibitor such as an oligomer of N-vinyl-2-pyrrolidone, an oligomer of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, or an oligomer of N-vinyl-ε-caprolactam, the functionality in the retractable form can be improved.

[0027] In addition, one or more water-soluble resins such as alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. may be added, as long as the drying resistance is not impaired. One or more wetting agents such as urea, nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysates, sodium pyrophosphate, etc. may also be added.

[0028] A shear thinning agent may also be added to the water-based ink composition. As the shear thinning agent, a substance that is soluble or dispersible in water is effective, and examples thereof include xanthan gum, welan gum, zeta sea gum, diutan gum, macrohomopsis gum, succinoglycan (average molecular weight: about 1 to 8 million), which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and derivatives thereof, hydroxyethyl cellulose, alginic acid alkyl esters, polymers having a molecular weight of 100,000 to 150,000 and containing an alkyl ester of methacrylic acid as the main component, glucomannan, carbohydrates having gelling ability extracted from seaweed such as agar and carrageenin, poly N-vinyl-carboxylic acid amide crosslinked products, benzylidene sorbitol and benzylidene xylitol or derivatives thereof, crosslinkable acrylic acid polymers, inorganic fine particles, nonionic surfactants having an HLB value of 8 to 12, metal salts and amine salts of dialkyl sulfosuccinic acid, etc. Furthermore, N-alkyl-2-pyrrolidone and an anionic surfactant may be added in combination to the ink composition. The shear thinning agent can be used in the ink composition in an amount of 0.1 to 20% by mass.

[0029] The aqueous ink composition for writing instruments of the present invention is filled into marking pens and ballpoint pens equipped with a fiber tip, felt tip, plastic tip, or ballpoint pen tip at the writing tip, as well as fountain pens (capped or retractable).

[0030] When loading ink into a marking pen, the structure and shape of the marking pen itself are not particularly limited, and examples of marking pens include a structure in which a marking pen tip (bullet type, chisel type, brush pen type, etc.) such as a fiber tip, felt tip, or plastic tip is attached to the writing tip, and ink is impregnated into an ink occlusion body made of a fiber bundle contained inside the barrel to supply ink to the writing tip; a structure in which ink is directly contained inside the barrel and a predetermined amount of ink is supplied to the writing tip through the intermediation of a comb-shaped ink flow rate adjustment member or an ink flow rate adjustment member made of a fiber bundle; and a structure in which ink is directly contained inside the barrel and a valve mechanism supplies a predetermined amount of ink to the writing tip. In addition to a pen with one pen tip, it may be a double-ended pen with pen tips of different thicknesses and shapes on both ends of the barrel. In the double-ended pen, one end may be a ballpoint pen.

[0031] When filling a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited, and examples include a structure in which ink is impregnated into an ink absorbing body made of a fiber bundle contained inside the barrel and ink is supplied to the writing tip, a structure in which ink is directly contained inside the barrel and an ink flow rate regulator in the shape of a comb groove or made of a fiber bundle is interposed, and a ballpoint pen having an ink reservoir tube filled with the ink composition inside the barrel, which ink reservoir tube is connected to a tip having a ball attached to its tip, and further having an ink backflow preventer in close contact with the end face of the ink.

[0032] The ink backflow preventive material may be either liquid or solid. Examples of the liquid ink backflow preventive material include non-volatile media such as polybutene and silicone oil. If desired, silica, aluminum silicate, etc. may be added to the media. As the solid ink backflow preventive material, a resin molded product can be mentioned. The liquid and solid ink backflow preventive materials can be used in combination.

[0033] The aqueous ink composition for writing instruments of the present invention is prepared by adding a compound represented by general formula (1), an ether having an SP value of 10 to 11.5, a polyoxyethylene polyoxypropylene alkyl ether, and various additives as necessary to an aqueous medium, and further heating and stirring as necessary to dissolve and disperse the mixture. The aqueous ink composition for writing instruments of the present invention is filled into writing instruments in the form of marking pens such as felt-tip pens, felt-tip pens, and brush pens, ballpoint pens, fountain pens, and the like for use. EXAMPLES

[0034] Examples will be described below, but the present invention is not limited to these examples. The compositions of the water-based inks for writing instruments of the Examples and Comparative Examples are shown in Table 1. The numerical values ​​of the compositions in the table indicate parts by mass.

[0035] [Table 1]

[0036] The contents of the ingredients in the table are explained according to the note numbers. (1) In the general formula (1), R: C2F5, L1: O=S(Me)2, L2: O=S(Me)2 (2) In the general formula (1), R: C2F5, L1: O=S(Bu)2, L2: O=S(Bu)2 (3) In the general formula (1), R: n-C3F7, L1: O=S(Me)2, L2: O=S(Bu)2 (4) A microcapsule pigment encapsulating a reversible thermochromic composition consisting of 1.0 parts of 3,6-bis(diphenylamino)fluoran as component (A), 3.0 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane and 5.0 parts of 2,2-bis(4'-hydroxyphenyl)-hexafluoropropane as components (B), and 50.0 parts of 4-benzyloxyphenylethyl caprate as component (C) (complete color development temperature (t1): -20°C, complete decolorization temperature (t4): 55°C, average particle size: 1.8 μm, color change from blue to colorless). (5) Polyoxyethylene benzyl ether, manufactured by Aoki Oil Co., Ltd., trade name: BA-2 [SP value (Fedors estimate): 11.5] (6) Diethylene glycol monobutyl ether, manufactured by Archroma Japan Co., Ltd., trade name: Liocol BC [SP value (Fedors estimated): 10.5] (7) Tetraethylene glycol monobutyl ether, manufactured by Kyowa Hakko Chemical Co., Ltd., trade name: Butycenol 40 [SP value (Fedors estimate): 10.9] (8) Propylene glycol-n-propyl ether, manufactured by Dow Corporation, trade name: Dowanol PnP [SP value (Fedors estimate): 10.7] (9) Polyoxyethylene benzyl ether, manufactured by Aoki Oil Co., Ltd., trade name: BA-1 [SP value (Fedors estimate): 12] (10) Polyoxyethylene polyoxypropylene alkyl ether (HLB: 10.5) ···INCI name: PPG4-ceteth-10 (11) Polyoxyethylene polyoxypropylene alkyl ether (HLB: 13) ···INCI name: PPG6-decyltetradeceth-30 (12) Polyoxyethylene polyoxypropylene alkyl ether (HLB: 15) ···INCI name: PPG2-DECETH-30 (13) Phosphate ester surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf AL (14) Arcade Japan, product name: Proxel XL-2

[0037] Adjustment of writing instrument ink The raw materials were mixed in the amounts described in the Examples and Comparative Examples, and the mixture was stirred and dissolved in a disperser at 25° C. for 1 hour to obtain a water-based ink composition.

[0038] Creation of writing implements Of the obtained water-based ink compositions, in Examples 1 to 3 and 5 and Comparative Examples 1 to 4 and 6, 1.5 g was filled into a commercially available marking pen exterior (Pilot Corporation; SW-VSP) to obtain water-based marking pens. In Examples 4 and 6 and Comparative Example 5, 1 g of the composition was filled into a commercially available marking pen exterior (SFL-15LM, manufactured by Pilot Corporation) to obtain a water-based marking pen.

[0039] The following tests were carried out using the resulting ink compositions and writing implements. Solubility Test 10 g of each ink was sealed in a 20 cc screw cap bottle and allowed to stand for 5 minutes, after which the state of the ink was visually inspected. Written exam Using each of the obtained writing implements, spiral circles were written by hand continuously on JIS P3201 writing paper A, and then the state of the handwriting was visually confirmed when ultraviolet light was irradiated using a Panasonic "FL4BLB black light blue fluorescent lamp (maximum wavelength: 352 nm)." Note that in Examples 4 and 6 and Comparative Example 5, the handwriting was rubbed off with a styrene-based elastomer immediately after writing and then irradiated with ultraviolet light to confirm the state. The results of each test are shown below.

[0040] [Table 2]

[0041] The symbols in the table are evaluated as follows: Solubility Test ○: No remaining insoluble matter was observed. ×: Insoluble matter thought to be a luminescent compound was observed. Written exam ◯: Good handwriting was obtained, and clear light emission was observed when the handwriting was irradiated with ultraviolet light. ×: Blurred or skipped lines were observed in the handwriting, and sufficient light emission was not confirmed when the handwriting was irradiated with ultraviolet light, or writing was impossible.

Claims

1. The aqueous ink composition for a writing instrument comprises water as a main solvent, a compound represented by the following general formula (1), an ether having an SP value of 10 to 11.5, and a polyoxyethylene polyoxypropylene alkyl ether: 【Chemistry 1】 [In formula (1), R is a perfluoroalkyl group having 2 to 20 carbon atoms, L １ , L ２ are the same or different and each is a sulfoxide having a substituted or unsubstituted aryl or alkyl group.

2. 2. The water-based ink composition for writing instruments according to claim 1, wherein the HLB value of said polyoxyethylene polyoxypropylene alkyl ether is in the range of 10 to 15.

3. 3. The aqueous ink composition for a writing instrument according to claim 1, wherein the polyoxyethylene polyoxypropylene alkyl ether is a compound represented by the following general formula (2): H-O-(C ２ H ４ O) ｍ (C ３ H ６ O) ｎ -R １ ・・・(2) [In formula (2), R １ is an aliphatic hydrocarbon group having 4 to 24 carbon atoms, m is the average number of moles of ethylene oxide added and is a number from 3 to 45, and n is the average number of moles of propylene oxide added and is a number from 1 to 33.

4. The aqueous ink composition for a writing instrument according to any one of claims 1 to 3, wherein the polyoxyethylene polyoxypropylene alkyl ether is added in an amount of 1 to 30 times by mass relative to the amount of the compound represented by general formula (1) in the aqueous ink.

5. 2. The aqueous ink composition for writing instruments according to claim 1, wherein the content of the ether is in the range of 1 to 30% by mass in the aqueous ink.

6. 6. The water-based ink composition for a writing instrument according to claim 1, further comprising a colorant which is discolored by frictional heat.

7. 7. The aqueous ink composition for writing instruments according to claim 6, wherein the colorant is a microencapsulated pigment having a reversible thermochromic composition encapsulated in a microcapsule, the reversible thermochromic composition comprising (a) an electron-donating organic color-forming compound, (b) an electron-accepting compound, and (c) a reaction medium for controlling the color-forming reactions of (a) and (b).

8. A writing instrument incorporating the water-based ink composition for writing instruments according to any one of claims 1 to 7.

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