Aqueous ink composition for ballpoints and ballpoint incorporating the same

Abstract

To provide an aqueous ink composition for ballpoints that satisfies dry-up resistance even for a shear-thinning aqueous ink applicable to simply structured writing instruments, while capable of exhibiting a smooth writing sensation with superior lubrication over a long duration, and a ballpoint incorporating the same.SOLUTION: The present invention provides an aqueous ink composition for ballpoints that contains a colorant, water, and a polyhydroxy fatty acid amide compound represented by the general formula (1), and a ballpoint 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, C10-C18 acyl group].SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous ink composition for a ballpoint pen. More particularly, the present invention relates to an aqueous ink composition for a ballpoint pen which is excellent in resistance to drying up at the pen tip and in lubricating performance, and a ballpoint pen incorporating the same. [Background technology]

[0002] 2. Description of the Related Art Water-based ballpoint pen ink compositions containing a shear thinning agent such as xanthan gum or diutan gum have been disclosed (see, for example, Patent Documents 1 and 2). This type of ink is highly viscous when left to stand without shear stress, and is stably held within the mechanism. During writing, the high shear force of the ball rotating at high speed reduces the viscosity of the ink near the ball, and as a result, the ink is discharged from the gap between the ball and the ball container and transferred to the paper. The ink transferred to the paper is released from the shear force and becomes highly viscous again, which does not cause bleeding of handwriting, a drawback of conventional water-based ink compositions. In addition, the ink does not leak due to the shear thinning property, and does not require a flow rate adjustment member (a temporary ink retention member such as a comb-shaped member) to adjust the ink flow rate, so that a writing instrument with a simple structure can be obtained, and it has many other advantages and is widely used. However, in the above-mentioned water-based inks, the shear thinning agent can inhibit the resistance to drying up, and therefore leaving the pen tip exposed to air for a long period of time can cause problems such as smudges at the beginning of writing or the inability to write.

[0003] In view of this, there have been proposals to improve the dry-up resistance by adding wetting agents such as water-soluble organic solvents, polyhydric alcohols, urea, and derivatives thereof (see, for example, Patent Document 3). However, inks containing the above-mentioned wetting agents often have insufficient drying prevention effects or increase the ink viscosity, which makes them prone to writing defects such as skipped lines and smudges, etc. For example, when urea is added in an increased amount to obtain the desired effect, water evaporates from the pen tip, the concentration of the water-soluble organic solvent increases, and solids precipitate on the pen tip, causing a so-called blooming phenomenon, which results in poor appearance and poor writing feel, resulting in smudges, etc. Furthermore, urea and its derivatives generate ammonia through decomposition, which increases the pH of the ink and promotes pigment aggregation, thereby worsening the writing feel, and so no satisfactory water-based ink composition could be obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 59-74175 [Patent Document 2] JP 2005-68363 A [Patent Document 3] Japanese Patent Application Publication No. 8-127746 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides an aqueous ink composition for a ballpoint pen, which has shear thinning properties that can be applied to a writing instrument of a simple structure, and which satisfies dry-up resistance requirements and can provide a smooth writing feel with excellent lubrication performance over a long period of time, and a ballpoint pen having the same built in. [Means for solving the problem]

[0006] The water-based ink composition for ballpoint pens 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, R1 is C 1 ~C 4 Alkyl or hydroxy substituted C 1 ~C 4 is an alkyl group, R 2 CO is linear or branched, saturated or unsaturated C 10 ~C 18 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, palmitic acid, oleic acid, linoleic acid or stearic acid. Further, the polyhydroxy fatty acid amide compound contains lauroyl methyl glucamide, myristoyl methyl glucamide, or a mixture thereof, and the compound of general formula (1) is contained in the aqueous ink in an amount of 0.1 to 20% by mass. Further, the colorant is a pigment, and the pigment 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 for controlling the color-forming reaction of (a) and (b) is encapsulated in a microcapsule. A further feature is a ballpoint pen incorporating the water-based ink composition for ballpoint pens. Effect of the Invention

[0007] According to the present invention, even if the aqueous ink has shear thinning properties, the pen tip has excellent dry-up resistance and lubrication properties without the addition of unnecessary additives, resulting in an aqueous ink composition for ballpoint pens that can produce good handwriting over a long period of time, and a ballpoint pen incorporating the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The polyhydroxy fatty acid amide compound represented by the general formula (1) has a high affinity with aqueous inks due to its structure, and can impart shear thinning properties to aqueous media. Furthermore, it can form a coating with moisture retention at points exposed to the outside air, such as the tip of a pen. Shear thinning agents such as gums and water-soluble polymers that have traditionally been added to inks tend to form a very strong dry film when the water evaporates from the pen tip, and as a result, writing problems are likely to occur if the writing part is left exposed to the outside air for a long period of time. However, in the configuration of the present invention, the polyhydroxy fatty acid amide compound forms a coating with moisture-retaining properties to cover the pen tip, thereby preventing the formation of a strong coating such as the dry film described above and is thought to impart dry-up resistance.

[0009] The polyhydroxy fatty acid amide compound represented by the general formula (1) is classified as a nonionic surfactant, and R 1 is C 1 ~C 4 Alkyl or hydroxy substituted C 1 ~C 4 is an alkyl group, R 2 CO is linear or branched, saturated or unsaturated C 10 ~C 18 It is an acyl group, and when added to water-based ink, it gels the ink like a general-purpose shear thinning agent, thereby thinning the ink's physical properties by shear. It also imparts moisture retention, forming a moisturizing coating on the pen tip and other points that come into contact with the outside air, thereby preventing the pen tip from drying out when exposed to the air for long periods of time. R 2 In CO, the above-mentioned C 10 ~C 18 Acyl groups are applicable, but more preferably C 12 ~C 16 The ones with C are highly effective. 12 ~C 14 are particularly preferred. 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, palmitic acid, oleic acid, linoleic acid or stearic acid. In another preferred embodiment, R 1 is a methyl group and R is an acyl group. 2CO is derived from coconut oil.

[0010] 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.

[0011] Furthermore, the ink composition of the present invention contains a short chain fatty acid, particularly C 1 ~C 4 -, C 6 -, C 8 -, C 10 -acyl groups.

[0012] Examples of commercially available polyhydroxy fatty acid amide compounds suitable for use in the present invention include lauroyl / myristoyl methyl glucamide (GLUCOTAIN Flex and GLUCOTAIN Clean), cocoyl methyl glucamide (GLUCOTAIN Care), and mixtures thereof, available from Clariant.

[0013] The polyhydroxy fatty acid amide compound can be added in an amount of 0.1 to 20 mass % of the total ink composition. In particular, when the shear thinning property is to be imparted solely to the ink composition, the polyhydroxy fatty acid amide compound is preferably added in an amount of 1 to 20 mass % of the total ink composition. When used alone, it is difficult to impart sufficient shear thinning properties at less than 1% by mass, and since no change in the ink properties is observed even if more than 20% by mass is added, there is no need to add more than this.

[0014] 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.

[0015] 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 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.

[0016] The thermochromic composition is preferably 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, 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).

[0017] 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 particular, since the ink viscosity needs to be increased in order for the pigment to maintain a dispersed state in the ink for a long period of time, while conventional shear thinning agents tend to cause problems such as blurred handwriting due to high viscosity, the composition of the present invention is useful because it can stabilize the dispersion of the pigment without causing the above problems. Furthermore, the reversible thermochromic microencapsulated pigment is particularly useful because it can maintain a dispersed state for a long period of time without causing aggregation, etc.

[0018] Furthermore, if necessary, conventional water-soluble organic solvents that are compatible with water can be used, specifically, ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene 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, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, etc. The water-soluble organic solvents can be used alone or in combination of two or more kinds, and are used in the range of 2 to 60% by mass, preferably 5 to 35% by mass.

[0019] Furthermore, a water-soluble resin can 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, and is used in the range of 1 to 30% by mass in the ink composition.

[0020] In addition, a conventionally known shear thinning agent can be added in combination with the polyhydroxy fatty acid amide compound. In this case, as described above, sufficient shear thinning can be obtained even if the amount of the polyhydroxy fatty acid amide compound added is reduced, and it is also possible to impart dry-up resistance and lubricity. As the shear thinning agent, for example, 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 consisting mainly of alkyl esters of methacrylic acid, 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.

[0021] 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, defoamers, fluorine-based surfactants and nonionic surfactants that improve the permeability of the ink may be used. Other wetting agents such as sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysate, urea, sodium pyrophosphate, etc. may also be used in combination. 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 addition type cationic activators, phosphate ester-based activators, dicarboxylic acid type surfactants, β-alanine type surfactants, 2,5-dimercapto-1,3,4-thiadiazole, its salts and oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, and condensates of N-acyl-L-glutamic acid and L-lysine, and its salts. Air bubbles can also 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, and 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.

[0022] The water-based ink composition is filled into a ballpoint pen having a ballpoint tip attached to the writing end. The structure and shape of the ballpoint pen itself are not particularly limited, and conventional general-purpose ones can be used. For example, there is a ballpoint pen having an ink reservoir tube filled with an ink composition inside a barrel, the ink reservoir tube communicating with a tip having a ball attached to the tip, and further having an ink backflow prevention body in close contact with the end face of the ink to prevent backflow.

[0023] To explain the ballpoint pen tip in more detail, a tip in which a ball is held in a ball-holding portion formed by deforming the vicinity of the tip of a metal pipe by pressing inward from the outer surface, or a tip in which a ball is held in a ball-holding portion formed by cutting a metal material with a drill or the like, or a tip formed by cutting a metal pipe or metal material, in which the ball held in the tip is urged forward by a spring body, etc., can be applied. The balls may be made of cemented carbide, stainless steel, ruby, ceramics, etc., and are preferably in the range of diameter 0.1 mm to 2.0 mm.

[0024] The ink reservoir tube for containing the water-based ink composition is preferably made of a molded article made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, etc., in terms of low evaporation of the ink and productivity. In addition, by using a transparent, colored transparent, or translucent molded article as the ink reservoir tube, the ink color, remaining amount of ink, etc. can be confirmed. The ink reservoir may be connected to the tip directly or through a connecting member. Furthermore, the ink reservoir may be in the form of a refill, with the refill accommodated within a barrel, or the barrel itself with a tip attached to the end may serve as the ink reservoir, with ink being filled directly into the barrel.

[0025] Furthermore, an ink backflow prevention body (liquid plug) is filled at the rear end of the ink composition filled in the ink reservoir tube. The ink backflow preventive may be either liquid or solid, and examples of the liquid ink backflow preventive include non-volatile media such as polybutene, α-olefin co-oligomer, silicone oil, refined mineral oil, etc., and if desired, silica, aluminum silicate, swellable mica, fatty acid amide, etc. may be added to the media. Examples of the solid ink backflow preventive include resin molded products. The liquid and solid ink backflow preventives may be used in combination.

[0026] The ballpoint pen may be of either a cap type or a retractable type, and as a retractable ballpoint pen, any structure in which the writing tip provided on the ballpoint pen refill is stored within the barrel (outer barrel) while being exposed to the outside air, and the writing tip protrudes from the barrel opening upon activation of the retractable mechanism can be used. The method of operating the retractable mechanism includes a knock type, a rotation type, a slide type, and the like. The knock type can be exemplified by a configuration in which a knock portion is provided at the rear end or side of the barrel, and pressing the knock portion causes the writing tip of the ballpoint pen refill to protrude and retract from the opening at the front end of the barrel, or a configuration in which pressing a clip portion provided on the barrel causes the writing tip of the ballpoint pen refill to protrude and retract from the opening at the front end of the barrel. The rotating type can be exemplified by a configuration having a rotating part at the rear of the barrel, and by rotating the rotating part, the writing tip of the ballpoint pen refill appears and disappears from the opening at the front end of the barrel. The sliding type can be exemplified by a configuration having a sliding portion on the side of the barrel, and by operating the sliding portion, the writing tip of the ballpoint pen refill can be made to appear and disappear from the front end opening of the barrel, or a configuration in which a clip portion provided on the barrel is slid to cause the writing tip of the ballpoint pen refill to appear and disappear from the front end opening of the barrel. The retractable ballpoint pen may be a composite type retractable ballpoint pen (refill replaceable type) that accommodates a plurality of ballpoint pen refills in the barrel. 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 ballpoint pens of the Examples and Comparative Examples are shown in the following table. Note that the numerical values ​​of the compositions in the table indicate parts by weight.

[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) Tokai Carbon Co., Ltd., product name: Aqua Black 162 (3) Sanyo Pigment Co., Ltd., product name: Sandai Super Color Blue GLL (4) 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 and 7.5 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): 57°C, average particle size: 2.5μm, color change from black to colorless). (5) 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). (6) Lauroyl / myristoyl methyl glucamide, manufactured by Clariant, trade name: GLUCOTAIN Clean (60% aqueous solution) (7) Cocoyl methyl glucamide, Clariant, trade name: GLUCOTAIN Care (40% aqueous solution) (8) Sansho Co., Ltd., product name: KELZAN (9) Sansho Co., Ltd., product name: Leozan (10) Daiichi Kogyo Seiyaku Co., Ltd., trade name: Plysurf AL (11) Product name: Proxel XL-2, manufactured by Arcade Japan

[0030] Ink Preparation All ingredients except the thickener were added to water and mixed and stirred, after which the polyhydroxy fatty acid amide compound and thickener were added, and the mixture was stirred at 400 rpm in a disperser at 20°C for 1 hour and filtered to prepare each ink.

[0031] 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.

[0032] Making a ballpoint pen The ink compositions of the above examples and comparative examples were filled into ballpoint pen refills having a stainless steel tip holding a 0.4 mm diameter cemented carbide ball fitted into one end of a polypropylene pipe, and the above ink backflow prevention body was then placed at the rear end of the pipe. The ballpoint pen refill was then fitted into a barrel (capped) to prepare a sample ballpoint pen. The following tests were carried out using the sample ballpoint pens.

[0033] 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.

[0034] 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.

[0035] Written exam Each sample ballpoint pen that was confirmed to be writable was left lying flat in an environment of 50°C for 60 days, after which the writing feel and condition of the handwriting were visually checked when a spiral circle was handwritten continuously on JIS P3201 writing paper A. The results of said tests are shown in the table below.

[0036] [Table 2]

[0037] The test results were evaluated as follows: Cap-off test ○: No smearing occurred, or recovery occurred within one line of writing. △: One line was blurred, but recovered within three lines of writing. ×: Not recovered within 3 lines of writing or unable to write. Ink Stability Test ○: No abnormalities. ×: Separation, precipitation or aggregation of layers was observed. Written exam ○: Writing was smooth and good handwriting was obtained. △: Writing is possible smoothly, but there are some uneven spots in the handwriting, and writing causes significant wear on the seat, resulting in poor writing. ×: The writing feel is poor, there are many faint marks and skipped lines in the handwriting, and the seat is significantly worn down, making it impossible to write.

Claims

1. A water-based ink composition for a ballpoint pen, 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 １０ ~C １８ It is an acyl group.

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

3. 3. The water-based ink composition for ballpoint pens according to claim 1 or 2, wherein the polyhydroxy fatty acid amide compound comprises lauroyl methyl glucamide, myristoyl methyl glucamide, or a mixture thereof.

4. 4. The water-based ink composition for ballpoint pens according to claim 1, wherein the compound of general formula (1) is present in an amount of 0.1 to 20% by mass in the water-based ink.

5. 5. The water-based ink composition for a ballpoint pen according to claim 1, wherein the colorant is a pigment.

6. 6. The water-based ink composition for a ballpoint pen according to claim 1, wherein the pigment is a microencapsulated pigment having a reversible thermochromic composition encapsulated in a microcapsule, the reversible thermochromic composition comprising (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium for controlling the color-forming reaction of (a) and (b).

7. A ballpoint pen incorporating the water-based ink composition for ballpoint pens according to any one of claims 1 to 6.

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