Water-based ink composition for ballpoint pen and ballpoint pen containing the same

Abstract

To provide a water-based ink composition for a ballpoint pen, which is excellent in dry-up resistance and can form clear handwriting, and to provide a ballpoint pen containing the ink composition.SOLUTION: An aqueous ink composition for a ballpoint pen, comprising: a colorant; an alkyl polyglucoside having a C8 to C14 aliphatic-hydrocarbon group; a shear-thinning agent; and water. The colorant contains a reversible thermochromic microcapsule pigment containing a reversible thermochromic composition comprising at least (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium for determining the temperature at which the color development reaction of the components (a) and (b) occurs.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Conventionally, inks that use water as the primary solvent (water-based inks) have been widely used due to their low odor and high safety. When a writing instrument containing water-based ink is left in the atmosphere with the writing tip exposed, water evaporates from the writing tip, causing the writing tip to dry out (so-called drying up). This can lead to poor writing results such as blurring during writing due to a decrease in ink discharge. Therefore, studies have been conducted to improve the dry-up resistance of the writing tip by incorporating additives into the ink composition (see, for example, Patent Documents 1 and 2). Patent Document 1 discloses a water-based ink composition for ballpoint pens that contains a specific thickening resin and a sugar alcohol. Patent Document 2 discloses a water-based ink composition for ballpoint pens that contains a specific ester compound. Although the ink composition described above has a certain effect of suppressing drying at the writing tip, it is difficult to maintain the dry-up resistance over a long period of time, and the dry-up resistance is still insufficient. Furthermore, when a large amount of the above additives is blended to fully exhibit the dry-up resistance, the viscosity of the ink increases, which can cause poor writing.

[0003] In addition, a writing instrument (reversible thermochromic ballpoint pen) containing a reversible thermochromic aqueous ink composition has been proposed, which can produce handwriting that can alternately store and retain the pre- and post-color change states within a certain temperature range, such as room temperature. This writing instrument contains a reversible thermochromic microencapsulated pigment as a colorant in the ink composition. Because the reversible thermochromic microencapsulated pigment contains the reversible thermochromic composition, which is the colorant, encapsulated in microcapsules, it tends to be difficult to achieve high handwriting density compared to other writing instruments in which the colorant is not encapsulated in microcapsules. While increasing the content of the microencapsulated pigment in the ink composition can increase handwriting density, increasing the content can easily cause drying at the writing tip, resulting in poor writing results. Since reversible thermochromic microencapsulated pigments are relatively unique and different from general colorants, it has been difficult to fully demonstrate dry-up resistance even when additives applied to general ink compositions such as those disclosed in the above-mentioned references 1 and 2 are used in reversible thermochromic water-based ink compositions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 08-23917 [Patent Document 2] JP 2001-226621 Public Relations Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made based on the background art as described above, and aims to provide a water-based ink composition for a ballpoint pen that has excellent resistance to dry-up at the writing tip and exhibits good ink ejection performance, and a ballpoint pen containing this ink composition. [Means for solving the problem]

[0006] The present invention relates to a colorant and a C8 to C 14The present invention also provides an aqueous ink composition for a ballpoint pen, comprising an alkyl polyglucoside having an aliphatic hydrocarbon group, a shear thinning agent, and water. The colorant comprises a reversible thermochromic microcapsule pigment encapsulating a reversible thermochromic composition comprising at least (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color-forming reaction of components (a) and (b) occurs. The content of the alkyl polyglucoside relative to the total mass of the ink composition is in the range of 0.01 to 5% by mass. The shear thinning index in an environment of 20°C is in the range of 0.2 to 0.6. The shear thinning agent is xanthan gum or succinoglycan. The present invention also provides a ballpoint pen containing the ink composition. [Effects of the Invention]

[0007] The present invention can provide a water-based ink composition for ballpoint pens that has excellent resistance to drying up and can produce clear handwriting, and a ballpoint pen containing this ink composition. DETAILED DESCRIPTION OF THE INVENTION

[0008] The water-based ink composition for a ballpoint pen according to the present invention (hereinafter sometimes referred to as "ink composition" or "ink") comprises a colorant and a C8 to C 14 The composition comprises an alkyl polyglucoside having an aliphatic hydrocarbon group, a shear thinning agent, and water. Each component constituting the ink composition according to the present invention will be described below.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0044] The content of the colorant relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.5 to 20 mass%, more preferably 1 to 15 mass%, and even more preferably 3 to 10 mass%. If the content exceeds 20 mass%, the ink discharge performance of a writing instrument containing the ink composition is likely to deteriorate, and writing defects such as blurring and skipped lines are likely to occur. On the other hand, if the content is less than 0.5 mass%, it becomes difficult to obtain a writing density suitable for a ballpoint pen.

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

[0046] The ink composition according to the present invention is 14The alkyl polyglucoside according to the present invention has the effect of preventing ink components such as colorants from aggregating and adhering to the ball surface when water in the ink evaporates from the writing tip, and preventing the shear thinning agent described below from forming a strong dried film. In other words, the ink composition can have excellent resistance to drying up at the writing tip and good ink ejection performance.

[0047] Alkyl polyglucosides are nonionic surfactants in which a reducing sugar and a higher alcohol are bonded via a glycosidic bond, and are represented by the following general formula (I-1). (X) n -OR (I-1) (In the formula, X is a residue derived from a reducing sugar, R is C8~C 14 is an aliphatic hydrocarbon group of the formula n is an integer greater than or equal to 1.) Alkyl polyglucosides are nonionic surfactants derived from natural sources that have a sugar skeleton, and the compounds themselves are considered to be safer than conventional nonionic surfactants derived from petrochemical sources. In other words, ink compositions containing alkyl polyglucosides are safe and have a low environmental impact.

[0048] In the general formula (I-1), X is a residue derived from a reducing sugar, and the reducing sugar may be not only a monosaccharide but also a disaccharide or higher sugar. Examples of reducing sugars include monosaccharides such as glucose, fructose, galactose, xylose, and mannose, and disaccharides or higher sugars such as maltose, sucrose, lactose, lactulose, cellobiose, gentianose, and raffinose. Among these, the reducing sugar is preferably glucose from the viewpoints of stability in the ink composition and easy availability, that is, alkyl polyglucosides represented by the following general formula (I-2) are preferred. (C6H 10 O5) n -OR (I-2) (In the formula, R is C8~C 14 is an aliphatic hydrocarbon group of the formula n is an integer greater than or equal to 1.)

[0049] In the above general formulas (I-1) and (I-2), R is a C8 to C 14 It is an aliphatic hydrocarbon group having a structure of C8 to C6, and includes saturated aliphatic hydrocarbon groups (alkyl groups) and unsaturated aliphatic hydrocarbon groups. 14 Examples of the aliphatic hydrocarbon group include a capryl group, a decyl group, a lauryl group, and a myristyl group. The alkyl polyglucoside according to the present invention may be a mixture of alkyl polyglucosides having different aliphatic hydrocarbon groups. Examples of such alkyl polyglucosides include C8 to C 14 Alkyl polyglucosides, C8-C 10 Alkyl polyglucoside, C 12 ~C 14 Examples include alkyl polyglucosides. The ink composition according to the present invention has excellent adhesion to a surface printed with toner (hereinafter, sometimes referred to as a "toner-printed surface") (i.e., the ink adheres well to the toner-printed surface), and therefore can form good handwriting without writing defects on the toner-printed surface. 12 ~C 14 Since alkyl polyglucosides are likely to exhibit the above effects, C 12 ~C 14 It is also suitable to use alkyl polyglucosides.

[0050] Alkyl polyglucosides, which are nonionic surfactants, adsorb to the surface of pigments and function as dispersants for the pigments, and therefore, it is suitable for the ink composition of the present invention to use pigments (including microencapsulated pigments) as colorants.

[0051] The glycosidic bond between the reducing sugar and the higher alcohol in the alkyl polyglucoside, and the glycosidic bond between the reducing sugars, may be either an α-bond or a β-bond, and one or more alkyl polyglucosides may be used in combination.

[0052] The alkyl polyglucosides according to the present invention are available, for example, from the Simulsol series manufactured by SEPPIC and the Glucopon series manufactured by BASF.

[0053] The content of alkyl polyglucosides relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01 to 5 mass%, more preferably 0.05 to 3 mass%, and even more preferably 0.1 to 2 mass%. By having the content within the above range, it becomes easy to improve the dry-up resistance of the writing tip.

[0054] The ink composition according to the present invention contains a shear thinning agent. Ink compositions using shear-thinning agents have high viscosity and are difficult to flow when left at rest or under low stress, but easily reduce in viscosity when external stress is applied. Such ink compositions are generally called gel inks and are used in writing instruments (ballpoint pens) equipped with ballpoint pen tips. Gel inks have high viscosity when left at rest without shear stress, so they are stably held within the ballpoint pen. During writing, the high shear stress generated by the high-speed rotation of the ball reduces the viscosity of the ink near the ball, resulting in the ink being ejected from the gap between the ball and the ball holder and adhering to the surface being written on. Gel ink also suppresses aggregation and / or sedimentation of colorants (especially pigments containing microencapsulated pigments or resin particles) and bleeding of handwriting, allowing for the creation of good handwriting. Furthermore, ballpoint pens containing gel ink prevent ink leakage from the gap between the ball and tip when not in use, and can prevent ink separation and backflow when the pen is left with the writing tip facing upward. When writing, this facilitates good ink ejection stability from the pen tip.

[0055] Examples of shear thinning agents include water-soluble polysaccharides, polymers having a molecular weight of 100,000 to 150,000 and mainly composed of alkyl esters of methacrylic acid, crosslinked poly-N-vinylcarboxylic acid amides, benzylidene sorbitol and its derivatives, benzylidene xylitol and its derivatives, alkali-thickening acrylic resins, crosslinkable acrylic acid polymers, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, and metal or amine salts of dialkyl sulfosuccinic acid. Among these, water-soluble polysaccharides are preferred because they can easily prevent the shear-thinning agent from precipitating when the water in the ink evaporates from the writing tip. This is thought to be because the sugar skeleton of alkyl polyglucosides is a hydrophilic group that easily interacts with the hydroxyl groups of water-soluble polysaccharides.

[0056] Examples of water-soluble polysaccharides include xanthan gum, welan gum, zeta sea gum, diutan gum, macrophomopsis gum, succinoglycan (for example, succinoglycan (average molecular weight of 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, alginic acid alkyl esters, glucomannan, agar, carrageenan, and other carbohydrates having gelling ability extracted from seaweed. Among these, xanthan gum or succinoglycan is preferred because it has a large effect of imparting shear thinning properties.

[0057] The shear thinning agents can be used alone or in combination of two or more.

[0058] The content of the shear thinning agent relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 0.01 to 1 mass%, more preferably 0.05 to 0.5 mass%, and even more preferably 0.1 to 0.5 mass%. By having the content within the above range, it becomes easy to maintain a high level of dry-up resistance while suppressing aggregation and / or sedimentation of the colorant.

[0059] The ink composition according to the present invention further comprises water. The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water. The content of water relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 30 to 90 mass %, more preferably 40 to 85 mass %.

[0060] The ink composition of the present invention may also contain various other additives as required. Examples of additives include water-soluble organic solvents, water-soluble resins, specific gravity adjusters, surfactants, pH adjusters, resin particles, rust inhibitors, wetting agents, viscosity adjusters, preservatives or antifungal agents, air bubble absorbers, antifoaming agents, antioxidants, ultraviolet absorbers, lubricants, etc. These additives can be selected from those conventionally used in water-based inks and used appropriately.

[0061] The ink composition of the present invention preferably uses a reversible thermochromic microcapsule pigment as the colorant. Thermochromic writing instruments containing ink compositions containing reversible thermochromic microencapsulated pigments have been known, and handwriting formed using these writing instruments can be decolorized by heating. Because the reversible thermochromic microencapsulated pigment contains a reversible thermochromic composition encapsulated in microcapsules, the density of handwriting formed using these writing instruments tends to be lower than that of handwriting formed using writing instruments that use general colorants. While increasing the content of the reversible thermochromic microencapsulated pigment is considered to increase the density of handwriting, increasing the content increases the solids content of the ink composition, which tends to make the microencapsulated pigment more likely to precipitate when the water in the ink evaporates. However, the ink composition of the present invention, even when the content of the reversible thermochromic microencapsulated pigment in the ink composition is high, exhibits excellent resistance to dry-up at the writing tip and good ink discharge stability, allowing for clear handwriting.

[0062] The thermochromic writing implement described above heats handwriting (hereinafter sometimes referred to as "initial handwriting") formed on paper to erase it, and then forms a new handwriting (hereinafter sometimes referred to as "overwritten handwriting") on the erased initial handwriting, thereby enabling easy correction of characters, etc. In other words, the overwritten handwriting is written over the erased initial handwriting. However, while the initial handwriting is formed by depositing ink on the paper surface, the overwritten handwriting is formed by further depositing ink on the ink containing the reversible thermochromic microencapsulated pigment that formed the initial handwriting. Therefore, the overwritten handwriting may be blurred or interrupted. However, the ink composition according to the present invention has excellent adhesion to handwriting formed with the ink containing the reversible thermochromic microencapsulated pigment (good ink adhesion), and therefore can form a good overwritten handwriting without writing defects on the erased initial handwriting. Hereinafter, the ease of forming an overwritten handwriting on the initial handwriting may be referred to as "overwriting performance." In other words, the ink composition according to the present invention, which uses a reversible thermochromic microencapsulated pigment as a colorant, exhibits excellent resistance to drying up even when the content of the microencapsulated pigment in the ink is high, and is also excellent in the ability to form overwritten handwriting on an initial handwriting (i.e., excellent overwriting performance). Therefore, it is also preferable that the ink composition according to the present invention contains a reversible thermochromic microencapsulated pigment as a colorant.

[0063] The method for producing the ink composition according to the present invention is not particularly limited, and any conventionally known method can be used. Specifically, the ink composition can be produced by stirring a mixture containing the above-mentioned components with a stirrer such as a propeller stirrer, a homodisper, or a homomixer, or by dispersing the mixture with a disperser such as a bead mill.

[0064] The viscosity of the ink composition according to the present invention is not particularly limited, but it is preferably measured at a rotation speed of 1 rpm (shear rate of 3.84 sec) in an environment of 20°C. -1When measured under the conditions of 100 rpm (shear rate 384 sec), the viscosity is preferably in the range of 50 to 2000 mPa·s, more preferably 100 to 1500 mPa·s, and even more preferably 150 to 1000 mPa·s. -1 When measured under the conditions of (1) to (5), the viscosity is preferably in the range of 1 to 200 mPa·s, more preferably 10 to 100 mPa·s, and even more preferably 20 to 50 mPa·s. By having the viscosity within the above range, the stability of the ink composition and the free flow of the ink within the mechanism of the ballpoint pen can be maintained at a high level. The viscosity was measured using a rheometer (manufactured by TA Instruments, product name: DHR-2) at a shear rate of 3.84 sec. under an environment of 20°C. -1 , 38.4sec -1 , or 384 seconds -1 The measurement can be performed under the following conditions.

[0065] The ink composition according to the present invention preferably has a shear thinning index (n) in the following formula (II) in a 20°C environment in the range of 0.2 to 0.6, more preferably 0.3 to 0.5. S=αD n (II) (In the formula, S is the shear stress (dyn / cm 2 =0.1 Pa), D is the shear rate (sec -1 ) and n is the shear thinning index α is the viscosity coefficient.) The shear thinning index was measured by placing the ink composition in a 20°C environment using a rheometer (manufactured by TA Instruments, product name: DHR-2) and measuring a shear thinning rate of 3.84 sec. -1 , 38.4sec -1 , and 384sec -1 and the shear stresses obtained from those shear rates, to the above formula (II). By having the shear thinning index within the above range, aggregation and / or sedimentation of the colorant is suppressed, and the ink is ejected without accumulating in the gap between the ball and the ball container during writing, making it easier to create clear handwriting.

[0066] The surface tension of the ink composition according to the present invention is not particularly limited, but is preferably in the range of 20 to 50 mN / m, and more preferably 25 to 40 mN / m, in an environment of 20° C. If the surface tension is within the above range, bleeding of written lines and strike-through onto the paper surface can be easily suppressed, and the wettability of the ink to the paper surface can be improved. The surface tension can be measured using a surface tension measuring instrument (manufactured by Kyowa Interface Science Co., Ltd., product name: DY-300) by placing the ink composition in an environment of 20°C and using a vertical plate method using a platinum plate.

[0067] The ink composition according to the present invention is particularly useful as an aqueous ink composition for ballpoint pens, since it contains a shear thinning agent. The structure and shape of the ballpoint pen itself are not particularly limited, and the ink composition may be housed in, for example, a ballpoint pen refill or ballpoint pen equipped with a ballpoint pen tip and an ink filling mechanism.

[0068] A ballpoint pen tip consists of a tip body and a ball attached to the front end of the tip body. Examples of ballpoint pen tips include a tip formed by deforming a metal pipe tip body near the tip end by pressing the ball inward from the outer surface in a ball-holding portion, a tip formed by cutting a metal tip body with a drill or the like to hold the ball, a tip with a resin ball receiving seat provided inside a metal or plastic tip body, and a tip in which the ball held by the tip is biased forward by a spring.

[0069] The material of the tip body and the ball is not particularly limited, and examples include cemented carbide (super hard), stainless steel, ruby, ceramic, resin, rubber, etc. Furthermore, the ball can be subjected to a surface treatment such as a DLC coating.

[0070] The diameter of the ball is generally 0.1 to 3 mm, with 0.1 to 2 mm, 0.2 to 2 mm, 0.2 to 1.5 mm, 0.2 to 1.2 mm, 0.2 to 1 mm, and 0.28 to 1 mm being preferred in that order. The ballpoint pen tip may be configured so that a resilient member that resiliently urges the rear end of the ball forward is disposed within the tip, and the ball is pressed against the inner edge of the tip tip to create a tight contact state when not writing, and the ball is retracted by writing pressure when writing, allowing ink to flow out, thereby preventing ink leakage when not in use. The resilient member may be, for example, a thin metal wire spring, a spring with a straight portion (rod portion) at one end, or a linear plastic processed body, and is configured to be pressable with a resilient force of 5 to 40 g. Generally, ballpoint pens equipped with small diameter balls have a small amount of ink on the ball surface, which means that moisture easily evaporates from the ball surface, causing solid matter such as colorants to precipitate and resulting in poor writing. However, the ink composition of the present invention has excellent resistance to drying up, making it less likely to result in poor writing, and is particularly suitable for use in ballpoint pens equipped with balls having a diameter of 0.2 to 0.5 mm.

[0071] The ink filling mechanism is not particularly limited, and may be, for example, an ink reservoir that can be filled with ink. The ink reservoir may be a molded body made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body. To prevent the ink from being denatured by oxygen, a molded body made of a resin with low oxygen permeability may also be used. Examples of resins with low oxygen permeability include ethylene-vinyl alcohol copolymer, polyvinylidene chloride, acrylonitrile resin, and polyester. The ink reservoir may have a single layer structure or a multi-layer structure.

[0072] A ballpoint pen refill (hereinafter sometimes referred to as "refill") can be formed by connecting a ballpoint pen tip to an ink reservoir directly or via a connecting member and directly filling the ink reservoir with ink. A ballpoint pen can be formed by storing this refill in a barrel.

[0073] The ink reservoir is filled with an ink backflow preventer at the rear end thereof, which may be a liquid stopper or a solid stopper. The liquid plug is made of a non-volatile liquid and / or a hardly-volatile liquid, such as petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or co-oligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, fatty acid-modified silicone oil, etc. The non-volatile liquid and / or the hardly-volatile liquid can be used alone or in combination of two or more kinds. Examples of solid plugs include solid plugs made of polyethylene, polypropylene, polymethylpentene, and the like. As the ink backflow preventer, a solid plug and the above-mentioned liquid plug can be used in combination.

[0074] It is preferable to add a thickener to the non-volatile liquid and / or the hardly-volatile liquid to thicken it to a suitable viscosity. Examples of thickeners include clay-based thickeners such as silica with a hydrophobic surface treatment, fine particle silica with a methylated surface treatment, aluminum silicate, swellable mica, and hydrophobically treated bentonite and montmorillonite; fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate; dextrin-based compounds such as tribenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, and fatty acid dextrins; and cellulose-based compounds.

[0075] By using the barrel itself as the ink filling mechanism, filling ink directly into the barrel, and attaching a ballpoint pen tip to the front end of the barrel, it is possible to form a ballpoint pen equipped with a ballpoint pen tip and an ink filling mechanism.

[0076] If the ink filled in the ink filling mechanism has a low viscosity, a ballpoint pen equipped with a ballpoint pen tip and an ink filling mechanism may further include an ink supply mechanism for supplying the ink filled in the ink filling mechanism to the pen tip.

[0077] The ink supply mechanism is not particularly limited, and examples include: (1) a mechanism that has an ink guide core made of a fiber bundle or the like as an ink flow rate regulator and supplies ink to the pen tip through this; (2) a mechanism that has a comb-shaped ink flow rate regulator and supplies ink to the pen tip through this; and (3) a mechanism that supplies ink to the pen tip through a pen core consisting of multiple disks arranged in parallel with comb-shaped intervals, with slit-shaped ink guide grooves running axially through the disks and wider air vent grooves than the grooves, and an ink guide core arranged in the axis center to guide ink from the ink filling mechanism to the pen tip.

[0078] There are no particular restrictions on the material of the pen core, as long as it is a synthetic resin that can be injection molded into a structure in which multiple discs are arranged in a comb-like groove pattern. Acrylonitrile-butadiene-styrene copolymer (ABS resin) is preferably used because it has high moldability and is easy to obtain pen core performance.

[0079] Specific examples of the configuration of a ballpoint pen containing an ink composition according to an embodiment of the present invention include: (1) a ballpoint pen having an ink reservoir filled with ink within a barrel, to which a ballpoint pen tip is connected either directly or via a connecting member, and in which an ink backflow prevention body is filled at the end face of the ink; (2) a ballpoint pen in which ink is directly filled within the barrel and which is provided with a mechanism for supplying ink to the pen tip via a comb-shaped ink flow regulator or an ink guide core made of a fiber bundle or the like as an ink flow regulator; and (3) a ballpoint pen in which ink is directly filled within the barrel and which is provided with a mechanism for supplying ink to the pen tip via the above-mentioned pen core.

[0080] When a pigment (including a microencapsulated pigment) is used as the colorant, a stirring body such as a stirring ball for stirring the ink may be incorporated into the barrel or ink reservoir filled with the ink to facilitate redispersion of the pigment. Examples of the shape of the stirring body include a spherical body and a rod-like body. The material of the stirring body is not particularly limited, and examples thereof include metal, ceramic, resin, and glass.

[0081] The ink filling mechanism of the ballpoint pen according to the present invention may be a cartridge type that uses an ink cartridge that is detachably replaceable from the ballpoint pen body and is pre-filled with ink. In this case, after the ink in the ink cartridge of the ballpoint pen is used up, the ballpoint pen can be used again by replacing it with a new ink cartridge. The ink cartridge can be one that doubles as the barrel that constitutes the ballpoint pen when connected to the ballpoint pen body, or one that covers and protects the barrel (rear barrel) after being connected to the ballpoint pen body. In the latter case, the ink cartridge can be connected to the ballpoint pen body, or it can be one that is housed in the barrel in a disconnected state so that the ballpoint pen user can connect the ink cartridge in the barrel when using the ballpoint pen and start using it.

[0082] The ballpoint pen according to the present invention is provided with a cap that is attached to cover the pen tip (writing tip), making it a cap-type ballpoint pen, which can prevent the writing tip from being contaminated or damaged. In addition, a retractable ballpoint pen can be provided with a retraction mechanism that allows the writing tip to protrude and retract from the barrel, thereby preventing the writing tip from being contaminated or damaged. Since the pen tip of a retractable ballpoint pen is always exposed to the outside air, the ink composition of the present invention is particularly effective.

[0083] Any retractable ballpoint pen can be used as long as the writing tip is housed within the barrel and the writing tip protrudes from within the barrel when the retractable mechanism is activated. Examples of retraction mechanisms include: (1) a side-slide retraction mechanism in which an operating part (clip) that can move back and forth in the radial direction protrudes radially outward from the rear side wall of the barrel, and the writing tip is retracted from the front end opening of the barrel by sliding the operating part forward; (2) a rear-end knock retraction mechanism in which the operating part at the rear end of the barrel is pressed forward to cause the writing tip to retract from the front end opening of the barrel; (3) a side-knock retraction mechanism in which the operating part that protrudes from the outer surface of the barrel side wall is pressed radially inward to cause the writing tip to retract from the front end opening of the barrel; and (4) a rotational (twist) retraction mechanism in which the operating part at the rear of the barrel is rotated to cause the writing tip to retract from the front end opening of the barrel.

[0084] The form of the ballpoint pen is not limited to the above-mentioned configuration, and may be a composite ballpoint pen (double-ended, retractable tip, etc.). Examples of composite ballpoint pens include (1) ballpoint pens equipped with tips of different shapes, (2) ballpoint pens equipped with tips that dispense inks of different tones or hues, and (3) ballpoint pens equipped with tips of different shapes, each of which dispenses ink of a different color tone or hues.

[0085] When the colorant contains a reversible thermochromic microencapsulated pigment, handwriting formed on a surface using a ballpoint pen containing the ink can be discolored by rubbing with a finger or by using a heating or cooling tool.

[0086] Examples of heating tools include an electrically heated discoloring tool equipped with a resistance heating element such as a PTC element, a heat discoloring tool filled with a medium such as hot water, a heat discoloring tool using steam or laser light, and the application of a hair dryer. However, friction members and friction bodies are preferred because they can change color in a simple manner. Examples of cooling devices include electrically operated thermochromic devices using a Peltier element, thermochromic devices filled with a refrigerant such as cold water or ice chips, refrigerants, refrigerators, freezers, and the like.

[0087] As the friction member and friction body, elastic bodies such as elastomers and plastic foams that are highly elastic and can generate appropriate friction and frictional heat when rubbed are preferred, but plastic molded bodies, stone, wood, metal, fabric, etc. can also be used. Note that while a general eraser used to erase pencil marks may be used to rub the marks, eraser dust is generated during rubbing, and therefore the above-mentioned friction member and friction body that generate almost no eraser dust are preferably used.

[0088] Examples of materials for the friction member and friction body include silicone resin, styrene-ethylene-butadiene-styrene block copolymer (SEBS resin), etc. Silicone resin tends to adhere to areas that have been erased by rubbing, and handwriting tends to be repelled when writing is repeated, so SEBS resin is more preferably used.

[0089] The friction member or friction body may be a separate component of any shape from the ballpoint pen, but by providing it in the ballpoint pen, the ballpoint pen can be made more portable. Also, a ballpoint pen set can be obtained by combining a ballpoint pen with a separate friction member or friction body of any shape.

[0090] In the case of a ballpoint pen with a cap, the location where the friction member or friction body is provided is not particularly limited; for example, the cap itself may be formed from a friction member, the barrel itself may be formed from a friction member, or if a clip is provided, the clip itself may be formed from a friction member, or the friction member or friction body may be provided at the tip (top) of the cap or the rear end of the barrel (the part where the writing tip is not provided), etc.

[0091] In the case of a ballpoint pen equipped with a retractable mechanism, the location where the friction member or friction body is provided is not particularly limited; for example, the barrel itself may be formed from a friction member, and if a clip is further provided, the clip itself may be formed from a friction member, or the friction member or friction body may be provided near the front end of the barrel, the rear end of the barrel (the part where the writing tip is not provided), or at the knock portion. [Example]

[0092] Examples are shown below. Unless otherwise specified, "parts" in the examples refer to "parts by mass."

[0093] Example 1 Preparation of ink composition 25 parts of black pigment dispersion (Fuji Pigment Co., Ltd., product name: Fuji SP Black 8922 (solid content: 20%)) and C8-C 10 An ink composition was prepared by mixing 0.1 parts of alkyl polyglucoside (manufactured by BASF Japan Ltd., product name: Glucopon 225DK), 0.25 parts of a shear thinning agent (succinoglycan) (manufactured by Sansho Co., Ltd., product name: Rheozan), 10 parts of diethylene glycol, 2 parts of dextrin (manufactured by Sanwa Starch Industry Co., Ltd., product name: Sandec 70), 1.5 parts of triethanolamine, 1 part of a phosphate ester surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Plysurf AL), 0.2 parts of a preservative (manufactured by Arcsada Japan Co., Ltd., product name: Proxel XL-2(S)), and 59.95 parts of water.

[0094] Making writing implements The ink composition of Example 1 was filled into a polypropylene ink reservoir by suction, and then connected to a ballpoint pen tip having a 0.5 mm diameter cemented carbide (superhard) ball at its tip via a resin holder. Next, a viscoelastic ink backflow preventive (liquid plug) mainly composed of polybutene was filled into the rear end of the ink reservoir, and a tail plug was fitted to the rear of the pipe. The ink was then degassed by centrifugation to obtain a ballpoint pen refill. Next, the refill was incorporated into a barrel to prepare a writing instrument (retractable ballpoint pen). In the above-mentioned ballpoint pen, the tip provided in the ballpoint pen refill is stored in the barrel while being exposed to the outside air, and a rear-end knock-type protruding / retracting mechanism is provided in which the tip protrudes from the front end opening of the barrel by pressing forward an operating part provided at the rear end of the barrel.

[0095] The ink compositions of Example 2 and Comparative Example 1 were prepared in the same manner as in Example 1, except that the types and amounts of the ingredients were changed to those shown in Table 1 below. The writing implements of Example 2 and Comparative Example 1 were produced in the same manner as Example 1.

[0096] Example 3 Preparation of ink composition 16 parts of reversible thermochromic microcapsule pigment A (previously cooled to -20°C or below to develop a blue color), C 12 ~C 14 An ink composition was prepared by mixing 2 parts of alkyl polyglucoside (manufactured by BASF Japan Ltd., product name: Glucopon 600 CS UP), 0.3 parts of a shear thinning agent (xanthan gum) (manufactured by Sansho Co., Ltd., product name: Kelzan), 2 parts of dextrin (manufactured by Sanwa Starch Industry Co., Ltd., product name: Sandec 70), 0.2 parts of triethanolamine, 0.2 parts of a preservative (manufactured by Arcsada Japan Co., Ltd., product name: Proxel XL-2(S)), and 79.3 parts of water.

[0097] Making writing implements The ink composition of Example 3 was filled by suction into an ink reservoir made of a polypropylene pipe, and then connected to a ballpoint pen tip having a 0.5 mm diameter carbide ball at its tip via a resin holder. Next, a viscoelastic ink backflow preventive (liquid stopper) mainly composed of polybutene was filled into the rear end of the ink reservoir, and a tail plug was fitted to the rear of the pipe. The ink was then degassed by centrifugation to obtain a ballpoint pen refill. Next, the refill was incorporated into a barrel to prepare a writing instrument (retractable ballpoint pen). The ballpoint pen has a tip attached to a ballpoint pen refill housed in a barrel exposed to the outside air, and the tip protrudes from the front opening of the barrel by operating a clip-shaped slide mechanism attached to the rear side wall of the barrel. The rear end of the barrel is fitted with SEBS resin as a friction member.

[0098] The ink compositions of Examples 4 to 5 and Comparative Examples 2 to 3 were prepared in the same manner as in Example 3, except that the types and amounts of the ingredients were changed to those shown in Table 1 below. The writing instruments of Examples 4 and 5 and Comparative Examples 2 and 3 were produced in the same manner as in Example 3.

[0099] [Table 1]

[0100] The materials in Table 1 are as follows: (1) Fuji Pigment Co., Ltd., Product Name: Fuji SP Black 8922 (Solid content: 20%) (2) Fuji Pigment Co., Ltd., product name: Fuji SP Blue 6455 (solid content: 27.5%) (3) Cooled to -20°C or below to turn blue (4) Cooled to -20°C or below to turn black (5) C8~C 10 Alkyl polyglucoside (manufactured by BASF Japan Ltd., product name: Glucopon 225DK) (in general formula (I-2), R is C8-C10 is an aliphatic hydrocarbon group of the formula: (6) C8~C 14 Alkyl polyglucoside (manufactured by BASF Japan Ltd., product name: Glucopon 425 N / HN) (in general formula (I-2), R is C8-C 14 is an aliphatic hydrocarbon group of the formula: (7) C 12 ~C 14 Alkyl polyglucoside (BASF Japan Ltd., product name: Glucopon 600 CS UP) (in general formula (I-2), R is C 12 ~C 14 is an aliphatic hydrocarbon group of the formula: (8) Heptyl polyglucoside (manufactured by SEPPIC, product name: Simulsol SL 7G) [In general formula (I-2), R is a C7 aliphatic hydrocarbon group.] (9) Succinoglycan [manufactured by Sansho Co., Ltd., product name: Leozan] (10) Xanthan gum (manufactured by Sansho Co., Ltd., product name: Kelzan) (11) Sanwa Starch Industry Co., Ltd., Product Name: Sandec 70 (12) Daiichi Kogyo Seiyaku Co., Ltd., product name: Plysurf AL (13) Arcsada Japan Co., Ltd., Product Name: Proxel XL-2(S)

[0101] The above-mentioned reversible thermochromic microcapsule pigment was prepared as follows. Preparation of reversible thermochromic microcapsule pigment A A reversible thermochromic composition consisting of 2 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindol-3-yl) as component (A), 8 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as component (B), and 50 parts of 4-benzyloxyphenylethyl caprate as component (C) was added to a mixed solution consisting of 35 parts of an aromatic isocyanate prepolymer as a wall material and 40 parts of a cosolvent, and then emulsified and dispersed in an 8% aqueous polyvinyl alcohol solution. After heating and stirring, 2.5 parts of a water-soluble aliphatic modified amine was added and further stirring was continued to prepare a microcapsule dispersion. From the above microcapsule dispersion, a reversible thermochromic microcapsule pigment A with an average particle size of 2.3 μm was obtained by centrifugation. The reversible thermochromic microcapsule pigment A had a complete color development temperature t1 of -20°C and a complete decolorization temperature t4 of 60°C, and reversibly changed from blue to colorless with temperature change.

[0102] Preparation of reversible thermochromic microcapsule pigment B A reversible thermochromic composition consisting of 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluoran (A), 4.5 parts of 1,1-bis(4-hydroxyphenyl)n-decane (B), 7.5 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane (C), and 50 parts of 4-benzyloxyphenylethyl caprate (D) was added to a mixed solution consisting of 35 parts of an aromatic isocyanate prepolymer and 40 parts of a cosolvent (W), followed by emulsification and dispersion in an 8% aqueous polyvinyl alcohol solution. After heating and stirring, 2.5 parts of a water-soluble aliphatic modified amine was added and further stirring was continued to prepare a microcapsule dispersion. From the microcapsule dispersion, a reversible thermochromic microcapsule pigment B with an average particle size of 1.9 μm was obtained by centrifugation. The reversible thermochromic microcapsule pigment B had a complete color development temperature t1 of -20°C and a complete decolorization temperature t4 of 59°C, and reversibly changed from black to colorless with temperature change.

[0103] [Viscosity measurement] The ink compositions of Examples 1 to 5 and Comparative Examples 1 to 3 were measured at a shear rate of 3.84 sec at room temperature (20°C) using a rheometer (manufactured by TA Instruments, product name: DHR-2). -1 , 38.4sec -1 , 384sec -1 The viscosity was measured under the following conditions. The measurement results are shown in Table 1.

[0104] [Calculation of shear thinning index] The ink compositions of Examples 1 to 5 and Comparative Examples 1 to 3 were measured at a shear rate of 3.84 sec at room temperature (20°C) using a rheometer (manufactured by TA Instruments, product name: DHR-2). -1 , 38.4sec -1 , and 384sec -1 The shear stress was measured under the following conditions. The shear rate and the shear stress obtained from each shear rate were applied to the above formula (II) to calculate the shear thinning index. The results are shown in Table 1.

[0105] [Surface tension measurement] The surface tension of the ink compositions of Examples 1 to 5 and Comparative Examples 1 to 3 was measured by the vertical plate method using a platinum plate at room temperature (20°C) using an automatic surface tensiometer (manufactured by Kyowa Interface Science Co., Ltd., product name: DY-300). The measurement results are shown in Table 1.

[0106] [Initial writing performance evaluation] Using the ballpoint pens prepared in Examples 1 to 5 and Comparative Examples 1 to 3, 12 elliptical circles (major axis 15 mm, minor axis 8 mm) per line were handwritten in a spiral pattern so that the circles touched each other, parallel to the short side of an A4-size test paper (portrait orientation) at room temperature (20°C). Note that the test paper used was writing paper A conforming to the old JIS P3201. When the handwriting obtained was visually inspected, it was found that none of the handwriting was blurred or broken, and was in good condition.

[0107] [Dry-up resistance evaluation] The ballpoint pens used in the initial writing performance evaluation were placed with the writing tip protruding (knock-on state) and placed horizontally in a thermostatic chamber set at 50°C and 30% relative humidity for 30 days. After 30 days, the pens were removed from the chamber and placed at room temperature (20°C). A line of 12 oval circles (approximately 15 mm long and 8 mm short) was handwritten in a spiral pattern, with the circles touching each other, parallel to the short edge of an A4-sized test paper (portrait orientation). The test paper used was writing paper A conforming to the old JIS P3201. The resulting handwriting was visually inspected and evaluated according to the following criteria: The evaluation results are shown in Table 2 below, with ratings of "A" and "B" being considered acceptable. A: The handwriting was free of smears or breaks, and good handwriting similar to the initial handwriting was obtained. B: Immediately after starting writing, some blurring or breaks were observed in the handwriting, but these were not observed by the end of writing, and were at a level that would not cause any problems in practical use. C: Compared to the initial handwriting, many faint or broken lines were observed in the handwriting, or it was impossible to write.

[0108] [Evaluation of writing performance on toner-printed surfaces] Using the ballpoint pens prepared in Examples 1 to 5 and Comparative Examples 1 to 3, the symbol "#" was handwritten on the toner-printed surface of A4-sized high-quality paper that had been solid-printed with toner in a room temperature (20°C) environment. The resulting handwriting was visually inspected and evaluated according to the following criteria: The evaluation results are shown in Table 2 below, with ratings of "A" and "B" being considered acceptable. A: The handwriting was not blurred or broken, and good handwriting was obtained. B: Some fading or breaks were observed in the handwriting, but this was at a level that would not cause any problems in practical use. C: Many smudges or breaks were found in the handwriting, or it was impossible to write.

[0109] [Overwrite performance evaluation] Using the ballpoint pens prepared in Examples 3 to 5 and Comparative Examples 2 and 3, a square measuring 1 cm on a side was drawn on a test paper at room temperature (20°C), and the inside of the square was filled in. Next, the square was rubbed with a friction member attached to the rear end of the ballpoint pen to erase the color, and the symbol "#" was written by hand on the erased square using the ballpoint pen. Note that writing paper A conforming to the old JIS P3201 was used as the test paper. The resulting handwriting was visually inspected and evaluated according to the following criteria: The evaluation results are shown in Table 2 below, with ratings of "A" and "B" being considered acceptable. A: The handwriting was not blurred or broken, and good handwriting was obtained. B: Some fading or breaks were observed in the handwriting, but this was at a level that would not cause any problems in practical use. C: Many smudges or breaks were found in the handwriting, or it was impossible to write.

[0110] [Table 2]

Claims

1. Colorant and C ８ ~C １４ The aqueous ink composition for a ballpoint pen comprises an alkyl polyglucoside having an aliphatic hydrocarbon group of the formula (I), a shear thinning agent, and water.

2. 2. The ink composition according to claim 1, wherein the colorant comprises a reversible thermochromic microcapsule pigment encapsulating a reversible thermochromic composition comprising at least (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color-forming reaction of components (a) and (b) occurs.

3. 3. The ink composition according to claim 1, wherein the content of the alkyl polyglucoside is in the range of 0.01 to 5% by mass relative to the total mass of the ink composition.

4. The ink composition according to any one of claims 1 to 3, which has a shear thinning index in the range of 0.2 to 0.6 in an environment at 20°C.

5. 5. The ink composition according to claim 1, wherein the shear thinning agent is xanthan gum or succinoglycan.

6. A ballpoint pen containing the ink composition according to any one of claims 1 to 5.

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