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

Abstract

To provide an aqueous ink composition for writing instruments that can impart dry-up resistance without limiting the structure or form of ink-incorporated writing instruments, while capable of maintaining excellent writing performance over a long duration, and a writing instrument incorporating the same.SOLUTION: The present invention provides an aqueous ink composition for writing instruments that contains a colorant, water, and a polyhydroxy fatty acid amide compound represented by the general formula (1), and a writing instrument incorporating the same [where R1 is a C1-C4 alkyl group or a hydroxy-substituted C1-C4 alkyl group, and R2CO is a linear or branched, saturated or unsaturated, C8-C22 acyl group].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 having excellent resistance to drying up of the pen tip and a writing instrument incorporating the same. [Background technology]

[0002] Conventionally, if the pen tip is left exposed for a long period of time with the cap removed, the moisture near the pen tip will evaporate, causing the resin and colorant in the ink to dry out and harden, which can result in smudged handwriting or poor writing performance. In order to solve the above problems, the addition of various compounds has been considered; for example, a technique of adding a mixture of polyvinyl alcohol and diglyceryl borate or sulfonic acid-modified polyvinyl alcohol has been disclosed (see, for example, Patent Documents 1 and 2).

[0003] In the aqueous ink composition of the cited document, the ink viscosity is increased significantly by the addition of each compound, and the ink improves the resistance to drying up of the pen tip when the ink is incorporated in a ballpoint pen refill. Therefore, when the ink is applied to ballpoint pens of other structures (such as those in which the ink is directly stored inside the barrel and an ink flow rate adjusting member made of a comb groove or fiber bundle is interposed, or those in which the ink occluding body made of a fiber bundle is impregnated with the ink) or marking pens, the ink is not discharged and writing is not possible, making the ink composition less practical for application to writing instruments in general. Furthermore, when applied to refillable ballpoint pens, if the blended amount is increased to obtain a sufficient effect, the ink viscosity becomes too high, resulting in defects such as smearing and line cracking in handwriting. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-117786 A [Patent Document 2] JP 2017-155161 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides an aqueous ink composition for a writing instrument that can impart dry-up resistance and maintain good writing performance for a long period of time without causing the problems of the conventional techniques described above and without limiting the structure or shape of the writing instrument that contains the ink, and a writing instrument that contains the same. [Means for solving the problem]

[0006] The aqueous ink composition for a writing instrument of the present invention comprises a colorant, water, and a polyhydroxy fatty acid amide compound represented by the following general formula (1). [ka] [In the formula, R 1 is a C1-C4 alkyl group or a hydroxy-substituted C1-C4 alkyl group, R 2 CO is linear or branched, saturated or unsaturated, C8-C 22 It is an acyl group. Furthermore, the R 1 is a methyl group and R is an acyl group. 2 The requirement is that the CO is derived from capric acid, lauric acid, myristic acid, oleic acid, linoleic acid, palmitic acid or stearic acid. It is a further requirement that the polyhydroxy fatty acid amide comprises caproyl methyl glucamide, lauroyl methyl glucamide, cocoyl methyl glucamide, myristoyl methyl glucamide, or a mixture thereof. Further, the polyhydroxy fatty acid amide compound is contained in the aqueous ink in an amount ranging from 0.1 to 10% by mass. 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 aqueous ink composition for writing instruments of the present invention contains a polyhydroxy fatty acid amide compound represented by the general formula (1), and thus can improve the dry-up resistance at the pen tip without causing an increase in the ink viscosity associated with the addition of the compound. Therefore, the composition can be applied to all writing instruments without limiting the structure or form, and can provide a writing instrument that can maintain good writing performance for a long period of time without causing blurring or line cracking in handwriting. In addition, the composition can impart lubricating properties, and when applied to a ballpoint pen, it can suppress seat wear during writing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The polyhydroxy fatty acid amide compound represented by the general formula (1) is classified as a nonionic surfactant, and R 1 is a C1-C4 alkyl group or a hydroxy-substituted C1-C4 alkyl group, R 2 CO is linear or branched, saturated or unsaturated, C8-C 22 It is an acyl group. By adding it to water-based ink, it is possible to suppress the drying-up that occurs when the tip of the writing instrument is exposed to the air for a long time. In particular, since the ink viscosity is not likely to increase due to the addition, it can be widely used without limiting the structure or shape of the writing instrument in which the ink is built, and good writing is possible without the blurring or line cracking that occurs with high-viscosity ink. R 2 In CO, the above C8 to C 22 Acyl groups are applicable, but C8 to C 18 is particularly preferred since it is the most effective. The compound is preferably R 1 is a methyl group and R is an acyl group. 2 The CO is derived from capric acid, lauric acid, myristic acid, oleic acid, linoleic acid, palmitic acid or stearic acid. In another preferred embodiment, R 1 is a methyl group and R is an acyl group. 2 CO is derived from coconut oil.

[0009] Specifically, preferred polyhydroxy fatty acid amides include, for example, caproyl methyl glucamide, lauroyl methyl glucamide, cocoyl methyl glucamide, myristoyl methyl glucamide, or mixtures thereof, and more preferably, lauroyl methyl glucamide, myristoyl methyl glucamide, caproyl methyl glucamide, or mixtures thereof.

[0010] Further, the ink composition of the present invention contains short chain fatty acids, particularly C1-C4-, C6-, C8-, C 10 -acyl groups.

[0011] Examples of commercially available polyhydroxy fatty acid amide compounds suitable for use in the present invention include Clariant lauroyl / myristoyl methyl glucamide (GLUCOTAIN Flex and GLUCOTAIN Clean), cocoyl methyl glucamide (GLUCOTAIN Care), capryloyl / caproyl methyl glucamide (GLUCOTAIN Clear), capryloyl / caproyl methyl glucamide lauroyl / myristoyl methyl glucamide (GLUCOTAIN Plus), sunflower fatty acid methyl glucamide (GLUCOTAIN Sence) and mixtures thereof.

[0012] The ink composition of the present invention contains a polyhydroxy fatty acid amide compound in an amount of 0.1 to 10 mass %, more preferably 0.1 to 8 mass %, and even more preferably 0.1 to 5 mass %, based on the total mass of the ink. Within the above range, the dry-up resistance is particularly effectively exhibited. Furthermore, when applied to ballpoint pens, it is possible to impart lubricating properties in addition to dry-up resistance, resulting in a ballpoint pen that can produce excellent handwriting with a smooth writing feel for a long period of time without the addition of a lubricant, which is generally added separately.

[0013] 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. As the dye, an acid dye, a basic dye, a direct dye, etc. can be used. Acid dyes include Naphthol Green B (CI 10020), Naphthol Yellow S (CI 10316), Acid Yellow 9 (CI 13015), Metanil Yellow (CI 13065), Orange I (CI 14600), Ponceau SX (CI 14700), Orange II (CI 15510), Sunset Yellow FCF (CI 15985), New Coccine (CI 16255), and First Acid Maze. (CI17200), Acid Fast Red 3G (CI18050), Fast Light Yellow 3G (CI18820), Tartrazine (CI19140), Resorcinol Brown (CI20170), Acid Blue 29 (CI20460), Naphthol Blue Black (CI20470), Acid Orange 56 (CI22895), Acid Yellow 42 (CI22910), Guinea Green B (CI42085), First Green FCF (CI42053), Brilliant Blue FCF (CI42090), Acid Violet 6B (CI42640), Acid Blue 1 (CI42045), Brilliant Blue G (CI42655), Brilliant Blue P-1 (CI42735), Water Blue (CI42755), Eriogreen B (CI44025), Acid Red (CI 45100), Violamin R (CI 45190), Uranine (CI 45350), Eosin (CI 45380), Phloxine B (CI 45410), Erythrosine (CI 45430), Nigrosine (CI 50420), Pyranine Conc (CI 59040), Alizarin Purple (CI 60730), Alizarin Cyanine Green F (CI 61570), Indigo Carmine (CI 73015), etc. are used. 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.

[0014] Examples of pigments that can be used 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 the like. Examples of such pigments include CI Pigment Blue 15:3B (product name: SS Blue GLL, pigment content 22%, manufactured by Sanyo Pigment Co., Ltd.), CI Pigment Red 146 (product name: SSPink 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.). As the fluorescent pigment, there can be used a fluorescent pigment in the form of fine particles of synthetic resin in which various fluorescent dyes are solid-dissolved in a resin matrix. Other examples include pearl pigments, gold and silver metallic pigments, phosphorescent pigments, white pigments such as titanium dioxide, metal powders such as aluminum, thermochromic compositions, photochromic compositions, and capsule pigments in which fragrances and the like are directly or microencapsulated.

[0015] As the thermochromic composition, a reversible thermochromic composition consisting of (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 is suitable, and the composition is encapsulated in microcapsules and used as a reversible thermochromic microcapsule pigment. 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) of 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., which discolors around a certain temperature (discoloration point), exhibits 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 of the two states, only one specific state 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 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 by frictional heat from a friction body or a familiar heating body such as a hair dryer, i.e., 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).

[0016] The colorants can be used alone or in a suitable mixture of two or more kinds, and are used in an amount of 1 to 35% by mass, preferably 2 to 30% by mass, in the ink composition. In the composition using the above-mentioned colorants that are dispersed in water, the composition is more effective because the composition is prone to dry up when the water evaporates. Therefore, the addition of a polyhydroxy fatty acid amide compound to the pigment-based water-based ink composition is the most effective means.

[0017] The ink composition according to the present invention comprises water. The water 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 35 to 95 mass %, more preferably 40 to 90 mass %.

[0018] In addition to the above-mentioned essential components, the ink composition according to the present invention can contain optional components within a range that does not impair the effects of the present invention.

[0019] For example, conventional water-soluble organic solvents that are compatible with water can 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, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, 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 60% by mass, preferably 5 to 35% by mass, in the ink composition.

[0020] Furthermore, a water-soluble resin may be added to impart adhesion and viscosity to the paper surface. Examples of the water-soluble resin include alkyd resin, acrylic resin, styrene-maleic acid copolymer, cellulose derivative, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. The water-soluble resin can be used alone or in combination of two or more kinds, and is used in the range of 1 to 30 mass % in the ink composition.

[0021] In addition, if necessary, rust inhibitors such as benzotriazole, tolyltriazole, 2,5-dimercapto-1,3,4-thiadiazole, and saponin, preservatives or antifungals such as phenol, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine; Wetting agents such as urea, nonionic surfactants, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysates, and sodium pyrophosphate; In addition, defoamers, dispersants, specific gravity adjusters, etc. may be used. Furthermore, air bubbles can be removed chemically by adding ascorbic acids, erythorbic acids, α-tocopherol, catechins, synthetic polyphenols, kojic acid, alkylhydroxylamines, oxime derivatives, α-glucosylrutin, α-lipoic acid, phosphonates, phosphinates, sulfites, sulfoxylates, dithionites, thiosulfates, thiourea dioxide, or the like. 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. Furthermore, a lubricant can be added in combination. For example, metal soap, polyalkylene glycol fatty acid ester, ethylene oxide addition type cationic surfactant, phosphate ester type surfactant, β-alanine type surfactant, N-acylamino acid, N-acylmethyltaurine, 2,5-dimercapto-1,3,4-thiadiazole, its salt or oligomer, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensation product of N-acyl-L-glutamic acid and L-lysine or its salt can be used.

[0022] Furthermore, a shear thinning agent can be added to the ink composition. Examples of such agents include water-soluble polysaccharides, polymers having a molecular weight of 100,000 to 150,000 that are primarily composed of alkyl esters of methacrylic acid, crosslinked poly-N-vinyl carboxylic acid amides, benzylidene sorbitol and derivatives thereof, benzylidene xylitol and derivatives thereof, alkali-thickening acrylic resins, 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, and the like. Examples of water-soluble polysaccharides include xanthan gum, welan gum, zeta sea gum, diutan gum, macrophomopsis 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, alkyl alginates, glucomannan, and carbohydrates having gelling ability extracted from seaweed, such as agar and carrageenan. The shear thinning agents may be used alone or in combination of two or more. In addition, the shear thinning property of ink refers to a rheological property in which the ink has a high viscosity and is difficult to flow when it is at rest or under low stress, but when the stress increases, the viscosity decreases and the ink exhibits good flowability. This liquid property is also known as thixotropy or pseudoplasticity.

[0023] The aqueous ink composition for writing instruments of the present invention is filled into capped or retractable writing instruments such as marking pens and ballpoint pens equipped with a fiber tip, felt tip, plastic tip, or ballpoint pen tip at the writing tip, and further, fountain pens.

[0024] 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.

[0025] 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 occlusion 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 adjustment member in the shape of a comb groove or an ink flow rate adjustment member 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 communicates with a tip having a ball attached to its tip, and further having an ink backflow prevention body in close contact with the end face of the ink.

[0026] 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. EXAMPLES

[0027] 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.

[0028] [Table 1]

[0029] The contents of the ingredients in the table are explained according to the note numbers. (1) Trade name: Phloxine (CI Acid Red 92), manufactured by Hodogaya Chemical Industry Co., Ltd. (2) Sanyo Pigment Co., Ltd., product name: Sandai Super Color Blue GLL (3) A microcapsule pigment encapsulating a reversible thermochromic composition consisting of 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluoran as component (A), 4.5 parts of 1,1-bis(4'-hydroxyphenyl)n-decane as component (B), 7.5 parts of 2,2-bis(4'-hydroxyphenyl)hexafluoropropane as component (B), and 50.0 parts of 4-benzyloxyphenylethyl caprate as component (C) (complete color development temperature (t1): -20°C, complete decolorization temperature (t4): 57°C, average particle size: 2.5 μm, color change from black to colorless). (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) Capryloyl / caproyl methyl glucamide, manufactured by Clariant, trade name: GLUCOTAIN Clear (50% aqueous solution) (6) Capryloyl / caproyl methyl glucamide, lauroyl / myristoyl methyl glucamide, Clariant, trade name: GLUCOTAIN Plus (50% aqueous solution) (7) Lauroyl / myristoyl methyl glucamide, Clariant, trade name: GLUCOTAIN Flex (35% aqueous solution) (8) Cocoyl methyl glucamide, Clariant, trade name: GLUCOTAIN Care (40% aqueous solution) (9) Mitsubishi Chemical Corporation, trade name: GOHSENOL GL-05 (10) Mitsubishi Chemical Corporation, trade name: Gohsenex L-3266 (11) Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf AL (12) Arcade Japan, product name: Proxel XL-2

[0030] Preparation of marking pen ink The raw materials were mixed in the amounts given in Examples 1 and 2 and Comparative Examples 1 and 2, stirred and dissolved at 20° C. for 1 hour, and then filtered to obtain marking pen ink compositions.

[0031] Making a marking pen The marking pen ink composition was impregnated into an ink occlusion body made of polyester sliver covered with a synthetic resin film, and the ink was housed in a barrel made of polypropylene resin. A resin-processed polyester fiber chip (bullet-shaped) was connected to the tip of the barrel via a holder, and a cap was attached to obtain a marking pen.

[0032] Preparation of ballpoint pen ink A The raw materials were mixed in the amounts shown in Examples 1 and 2 and Comparative Examples 1 and 2, and the mixture was stirred at 20° C. and 400 rpm in a disperser for 1 hour, and then filtered to obtain a ballpoint pen ink composition.

[0033] Making ballpoint pen A A pen core (comb-tooth-shaped ink reservoir) with a stainless steel tip holding a 0.7 mm diameter cemented carbide ball was fitted into the front (open side) of the barrel, resulting in a pen core-type writing instrument exterior with the rear (closed side) acting as the ink reservoir. The ink was then filled into the exterior and a cap was fitted to create ballpoint pen A.

[0034] Preparation of ballpoint pen ink B The raw materials except for the thickener were mixed in the amounts shown in Examples 3 to 6 and Comparative Examples 3 to 6, and stirred at 400 rpm in a disperser at 20°C for 1 hour. The thickener was then added and stirred for an additional hour to obtain a ballpoint pen ink composition.

[0035] Preparation of ink backflow preventer 1.5 parts of fatty acid amide as a thickener was added to 98.5 parts of polybutene as a base oil, and then the mixture was kneaded with a three-roll mill to obtain an ink backflow preventive material.

[0036] Preparation of ballpoint pen B Each of the ink compositions was filled into a ballpoint pen refill having a stainless steel tip holding a 0.4 mm diameter cemented carbide ball fitted into one end of a transparent polypropylene pipe, and the ink backflow prevention body was placed at the rear end of the pipe. The ballpoint pen refill was then inserted into the barrel and a cap was attached to produce ballpoint pen B.

[0037] The following tests were carried out using each of the ink compositions and writing implements obtained. For ballpoint pen samples, abrasion tests and writing tests were also carried out. Cap-off test (checking dry-up resistance) After confirming that each writing instrument was writable, the pen tip was exposed to the air and left lying flat in a 20°C environment for 7 days, after which 12 spiral circles were handwritten in three consecutive lines on JIS P3201 writing paper A at room temperature. The condition of the handwriting was then visually confirmed. Ink Stability Test Each ink was sealed in a container and left in a thermostatic chamber at 50°C for 30 days, and then allowed to cool to room temperature, after which the state of the ink was visually inspected. Abrasion Test For each ballpoint pen that was confirmed to be writable, the amount of wear of the ball seat (the amount the ball sinks with the pen tip facing upwards) was measured using an automatic writing tester after 1,000 m of continuous writing of a spiral circle on JIS P3201 writing paper A was performed. The tester was used under the conditions of a writing load of 100 g, a writing angle of 70°, and a writing speed of 4 m / min. The measured values ​​were the average values ​​of five pens each. Written exam After each ballpoint pen was confirmed to be capable of writing, it was left in an environment of 50°C for 30 days, after which 12 spiral circles were handwritten in succession on JIS P3201 writing paper A. The results of each test are shown below.

[0038] [Table 2]

[0039] The test results were evaluated as follows: Cap-off test ○: No smearing occurred, or recovery occurred within one line of writing. ×: Not recovered within 3 lines of writing or unable to write. Ink Stability Test ○: No change from before the test. ×: Separation, precipitation or aggregation of layers was observed. Written exam A: Good handwriting was obtained. ×: Line cracks or fading were observed in the handwriting.

Claims

1. An aqueous ink composition for a writing instrument comprising a colorant, water, and a polyhydroxy fatty acid amide compound represented by the following general formula (1): 【Chemistry 1】 [In the formula, R １ is C １ ~C ４ Alkyl or hydroxy substituted C １ ~C ４ is an alkyl group, R ２ CO is a linear or branched, saturated or unsaturated C ８ ~C ２２ It is an acyl group.

2. The R １ is a methyl group, and R is an acyl group. ２ 2. The aqueous ink composition for writing instruments according to claim 1, wherein CO is derived from capric acid, lauric acid, myristic acid, oleic acid, linoleic acid, palmitic acid or stearic acid.

3. 3. The aqueous ink composition for a writing instrument according to claim 1 or 2, wherein the polyhydroxy fatty acid amide compound comprises caproyl methyl glucamide, lauroyl methyl glucamide, cocoyl methyl glucamide, myristoyl methyl glucamide or a mixture thereof.

4. 4. The aqueous ink composition for writing instruments according to claim 1, wherein the polyhydroxy fatty acid amide compound is present in an amount of 0.1 to 10% by mass in the aqueous ink.

5. A writing instrument incorporating the water-based ink composition for writing instruments according to any one of claims 1 to 4.

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